DE19517168B4 - Device and method for controlling an internal combustion engine - Google Patents

Abstract

Control device for an internal combustion engine (1) with an exhaust gas purification catalytic converter (13), which is arranged in an exhaust line (14) of the internal combustion engine (1), the exhaust gas purification catalytic converter (13) being operable in such a way that it adsorbs nitrogen oxide when it enters the exhaust gas purification catalytic converter ( 13) inflowing exhaust gases have a lean air-fuel ratio and that it deoxidizes adsorbed nitric oxide when the oxygen concentration of the inflowing exhaust gases is reduced, characterized by
an adsorption state estimator (23, 32) including first nitrogen oxide discharge amount estimation means (33) for estimating a discharge amount of nitrogen oxide from the exhaust gas purifying catalyst (13), and the adsorption state estimation means (23,32) estimates a adsorption state of nitrogen oxide by the exhaust gas purification catalyst (13) ) is adsorbed based on the estimated discharge amount of nitrogen oxide from the exhaust gas purifying catalyst (13); and
combustion condition deteriorating means (23,36) for deteriorating a combustion condition in the internal combustion engine (1) according to the adsorbed state of the nitrogen oxide estimated by the adsorbed state estimating device (32) when the engine is in the lean burn condition.

Description

The invention relates to a device and a procedure for the control of an internal combustion engine with which the emission of Nitrogen oxide from an internal combustion engine can be suppressed into the atmosphere can.

It is a process for improvement fuel economy or other performance criteria an internal combustion engine is known in which the air-fuel ratio regulating a target value (e.g. 22) that is leaner than the theoretical air-fuel ratio (14.7) to thereby perform lean burn in the engine if the engine is in a predetermined drive state is driven. However, will Three way catalyst converter for uses the engine to which the aforementioned method is applied, can nitric oxide (NOx) during the lean burn is not enough be cleaned because the three-way catalyst converter in the lean Air fuel ratio range doesn't work at its full potential. Are in this regard Experiments carried out the emission of NOx also in the lean combustion engine reduce by using a so-called NOx catalyst, the NOx absorbed by the engine in an oxygen enriched Condition (oxidizing atmosphere) is released, and the adsorbed NOx in a hydrocarbon (HC) excess state deoxidized (reducing atmosphere).

The amount of NOx from the NOx catalyst can be absorbed, however, is limited. The engine becomes continuous driven in the lean-burn state, the catalyst is with NOx saturated. In this case, the largest part of NOx gas emitted by the engine is emitted into the atmosphere. To counteract this before or when the NOx catalyst with adsorbed NOx saturated is a transition to control the grease mixture, which determines the air-fuel ratio a theoretical relationship or controls a near value to thereby operate in theoretical relationship or to start the engine's fat-burning operation. The resulting Exhaust gas containing a lot of unburned gases is generated a reducing atmosphere for the Deoxidation of NOx around the catalyst.

In view of the point in time at which the lean-burn operation is switched over to the operation in the theoretical ratio or the fat-burning operation, a procedure is following JP 0005133260 AA (Patent Abstract of Japan), in which the elapsed time from the start of the lean fuel ratio control is measured and the transition to the rich air-fuel control is performed more intensely when a predetermined time has passed. In this method, the lean air-fuel ratio control is restarted after completion of the deoxidation of NOx that is adsorbed by the catalyst during the rich air-fuel ratio control. In this way, the lean burn and the rich burn are alternatively carried out to reduce the emission of NOx.

If the predetermined time from the start lean air-fuel ratio control has elapsed, however, after that in the aforementioned publication disclosed control always determines that the amount of adsorbed NOx the saturated Has reached value. At this moment, the lean burn condition reinforced changed to the rich combustion state. The improvement of Lean-burn fuel consumption cannot therefore be used in sufficient Ways can be achieved and fuel economy will be appropriate reduced. About that also varies at the time of changing the air-fuel ratio the engine torque and has a bad impact on the Motor operation. In a vehicle that uses the engine as its primary drive used can be a change of the engine torque a shock similar to one Cause acceleration shock, so that drive feeling deteriorates when the engine torque variation occurs frequently, during that Vehicle is running at a constant speed. It also increases the emission of HC when the air-fuel ratio is enriched. From the point of view of improving the driving experience and reducing the Emission of HC is therefore not preferable to increase the air-fuel ratio and frequently to change.

In international patent publication no. W093 / 08383 discloses a process for deoxidizing NOx, that of the exhaust gas purification device during the lean-burn drive of the Motors is adsorbed. In this process, the amount of adsorption of NOx from the exhaust gas purifying catalyst and the drive state in changes the rich combustion state when based on the Result of the estimate it is determined that the adsorption amount of NOx is the saturation amount has reached

In this procedure, in which the base of the estimated Adsorption amount of NOx is determined whether the catalyst with NOx saturated However, it is sometimes when the NOx adsorption properties of the Catalysts, which are attached to the individual engines, from each other deviate, sometimes impossible, correctly determine that the catalyst is saturated Has reached state.

It is an object of the present invention, an apparatus and a method for a combustion Providing an engine capable of determining an amount of nitrogen oxide that is emitted from an exhaust gas purification device, thereby positively and easily determining that the exhaust gas purification device has reached a saturated state where it is mixed with nitrogen oxide adsorbed thereby , is saturated without the need to directly determine an amount of nitrogen oxide adsorbed by the exhaust gas purifying device for determining the saturated state, and is able to operate the engine smoothly with low fuel consumption based on the results of the determination , and is able to reduce an amount of nitric oxide that is emitted into the atmosphere.

According to the first aspect of the present invention according to the entirety of the features of claim 1. is a control device for one Internal combustion engine created an exhaust gas purification catalyst having. which is arranged on an exhaust pipe of the engine, to reduce the emission of nitric oxide to the atmosphere, whereby the catalyst can be operated in such a way that it adsorbs nitrogen oxide, which is contained in the exhaust gases emitted by the engine when the engine is lean burn, and that Air-fuel ratio one fed to the engine Air-fuel mixture is leaner than the theoretical air-fuel ratio, and to deoxidize the adsorbed nitric oxide when the engine is in a fat burning state where the air-fuel ratio is the same is or richer than the theoretical air-fuel ratio.

The control device has one Adsorptionszustandsschätzeinrichtung to appreciate the adsorption state of the nitrogen oxide on the exhaust gas purification catalyst on; and a combustion deterioration device for Deterioration of the combustion state in the engine according to the adsorption state of nitric oxide from the adsorption state estimator estimated when the engine is lean burn.

The closest to the present invention are EP 0598917A1 and DE 433424A1 ,

In the present invention a donation size of nitric oxide estimated by an exhaust gas purification catalyst device and it is determined whether the estimated Dispensed amount of nitrogen oxide exceeds a predetermined amount or not. If it is determined that the release amount of nitrogen oxide exceeds a predetermined amount a combustion state of an internal combustion engine is deteriorated, when the machine is operating in a lean burn mode becomes.

According to this invention, the Release amount of nitrogen oxide, d. H. the amount of nitric oxide which is expelled from the exhaust gas purification catalyst direction, determined, and when the amount of nitrogen oxide released is not the predetermined Quantity is reached, the combustion of the machine is not deteriorated, So that the Softness in machine operation and fuel consumption are not is deteriorating. Can continue according to this Invention by worsening the combustion state of the machine while the lean burn unburned gases to the exhaust gas purifying catalyst device are supplied to thereby remove the nitrogen oxide which is on the exhaust gas purifying catalyst device is absorbed to deoxidize, and the amount of nitrogen oxide released can be suppressed by the machine itself.

The EP 0598917A1 discloses a control system for an internal combustion engine which is provided with a NOx absorbing agent disposed within an exhaust pipe of the engine and which absorbs NOx when the air / fuel ratio of exhaust gas flowing therein is lean and emits NOx which it has absorbed when there; Air / fuel ratio of exhaust gas flowing into it becomes rich. In the disclosed system, the amount of NOx absorbed in the NOx absorbent agent is estimated from the engine load and the number of revolutions of the engine, and when this estimated amount of NOx becomes the maximum NOx absorption capacity of the NOx absorbent agent, the air / fuel ratio of the exhaust gas flowing into the NOx absorbing agent is made rich.

The system, which in the EP0598917A1 discloses the amount of NOx that the NOx absorbent has absorbed, but fails to determine what amount of NOx is expelled from the NOx absorbent without being absorbed by the NOx absorbent.

On the other hand, the present determines Invention an amount of NOx emitted from the exhaust gas purifying catalyst device pushed out which is a NOx catalyst includes, d. H. an amount of NOx that is emitted into the atmosphere.

According to the system in the EP 0598917A1 an amount of NOx emitted from the NOx absorbent agent is not determined. This makes it impossible to suppress exactly one control for suppressing an amount of NOx discharged into the atmosphere up to a prescribed amount.

Even in the system in the EP 0598917A1 , an attempt to control an amount of NOx released into the atmosphere up to a prescribed amount based on the determined amount of NOx absorbed by the NOx absorbing agent will be made. However, in this case the request is made placed the system to perform control, the following requirement, e.g. B. is considered.

There is a relationship that the bigger a lot of absorbed NOx, the larger the ratio of one Amount of NOx released into the atmosphere to one Amount of NOx released from the machine. Thus, an engine operating state must be considered where a great Amount of NOx is emitted from the machine. In particular, the air / fuel ratio must be rich its (i.e., NOx reducing operation must be done) for release and reducing NOx derived from the NOx absorbent agent is absorbed before the amount of NOx absorbed becomes large. As a result, there is a high likelihood of unnecessary fat Operations carried out with the result of deteriorated fuel consumption. In contrast, according to the present Invention made a determination of the amount of nitric oxide, which is exhausted from the exhaust gas purifying catalyst device, and engine operation to deteriorate the combustion condition is not carried out in the machine until the amount of NOx, which in the atmosphere is released, exceeds a predetermined amount so that none Deterioration in the smooth running of the machine and fuel consumption is caused.

The DE 43 33 424 A1 discloses a technical teaching serving as a combustion temperature reducing device in which (i) EGR is recirculated to the intake side; or (ii) an oxygen retention filter is placed in one of the conduits and there is provided a combustion delay magnification device which delays the fuel injection timing to the top dead center and which overloads the inlet; or (iii) the swirl is increased to thereby reduce the NOx concentration without increasing the smoke concentration.

On the other hand, the DE 43 33 424 A1 providing an exhaust gas purification device disposed in the exhaust pipe and operable to absorb nitrogen oxide when an air-fuel ratio of the exhaust gas flowing therein is lean and to deoxidize adsorbed nitrogen oxide when an oxygen concentration of exhaust gas which flows in there decreases.

In addition, the DE 433424A1 no emission control device as defined in the claims of this application is available, and therefore fails to do so DE 43 33 424 A1 disclose the feature of this invention to estimate a discharge amount of nitrogen oxide from the exhaust gas purifying catalyst device and to determine whether the estimated discharge amount of nitrogen oxide exceeds a predetermined amount.

The DE 43 33 424 A1 fails to provide advantages of the present invention so that no deterioration in the smooth machine running and fuel consumption is caused because a determination is made of the amount of nitrogen oxide released from the exhaust gas purifying catalyst device and an engine operation to deteriorate a combustion state in the engine The machine is not operated until the amount of nitrogen oxide released into the atmosphere exceeds a predetermined amount.

According to a second aspect of Invention according to the entirety of the features of claim 3 is a Tax procedure for an internal combustion engine to reduce nitrogen oxide emissions into the atmosphere created by causing nitric oxide to enter the Exhaust gases are contained, which are emitted by the internal combustion engine are absorbed on the exhaust gas purification catalyst, which in the Exhaust pipe of the engine is arranged when the engine is in the lean-burn state is where the air-fuel ratio one fed to the engine Air-fuel mixture is leaner than the theoretical air-fuel ratio, and by the adsorbed nitrogen oxide by means of the exhaust gas purification catalyst is deoxidized when the engine is in the rich combustion state, where the air-fuel ratio is the same or richer than the theoretical air-fuel ratio.

The present control procedure comprises a first step, namely Estimate the adsorption state of the nitrogen oxide on the exhaust gas purification catalyst, and a second step, namely Deterioration of the combustion state in the internal combustion engine according to the adsorption state of the Nitrogen oxide, which is estimated in the first step when the engine is in Is lean burn condition.

The control device and that Control methods of the present invention offer the advantage that the The state of combustion in the engine can deteriorate if the absorbed amount of nitric oxide increases, causing unburned Gases are supplied to the exhaust gas purification catalyst to make nitrogen oxide to deoxidize, which is absorbed by the exhaust gas purification catalyst, and that the The amount of nitrogen oxide released by the engine itself is kept low can be. Unlike in the case where the drive state is increased from Lean burn state to theoretical ratio drive state or the rich combustion state is changed, the Output amount of nitrogen oxide from the engine can be reduced without that the Engine running softness and fuel economy deteriorated become.

The adsorption state estimation device of the control device preferably has an adsorption saturation determination device for determining whether the adsorption amount of nitrogen oxide on the exhaust gas purification catalytic converter is one Has reached a value that is equal to or close to the amount of saturation. Further, the combustion state deterioration means deteriorates the combustion state when the adsorption saturation determination means determines that the adsorption amount of nitrogen oxide on the exhaust gas purifying catalyst has reached the value that is equal to or near the saturation amount in the lean combustion state (claim 2).

In this preferred embodiment, if the exhaust gas purification catalyst with adsorbed nitrogen oxide saturated is, the amount of unburned gases can be increased by the combustion state in the engine deteriorates without the amount of fuel supplied elevated must become, while the internal combustion engine remains in the lean-burn state. This allows it, the adsorbed nitrogen oxide by hydrocarbon to reasonable Way to deoxidize and remove that in the unburned gases is included. The cleanability of the exhaust gas purification catalyst can therefore be restored and the emission of nitrogen oxide can be suppressed without the fuel economy and the driving feeling deteriorate.

The adsorption saturation determination device preferably has a nitrogen oxide delivery amount estimator for estimating the delivery amount of nitrogen oxide from the exhaust gas purification catalyst, or a Lean burn period measuring device for measuring the lean burn period, at which the lean burn condition continues, or a lean burn accumulator for accumulating of parts of load information on the internal combustion engine that is in the lean combustion state running, thereby an accumulated value on parts of the load information derive. Has the nitrogen oxide delivery amount by the nitrogen oxide delivery amount estimator estimated a predetermined value is exceeded, or has the lean burn period determined by the lean burn period meter is measured, has exceeded a predetermined value, or has the accumulated value on parts of the load information from the lean-burn accumulator is derived, exceeds a predetermined value, it is determined that the adsorption amount of nitrogen oxide on the exhaust gas purification catalytic converter reaches a value has the same or close to the saturation amount (claim 4).

According to these preferred embodiments may be the time when the amount of adsorption of nitrogen oxide the amount of saturation achieved correctly and simply according to the amount of nitrogen oxide released, the lean burn period or the accumulated value of parts of the load information on the engine to be determined in the lean-burn state is operated without the Amount of nitrogen oxide adsorbed on the exhaust gas purification catalyst must be derived directly.

Preferably, the (see claim 14) Combustion state deterioration means of the control device the combustion temperature of the air / fuel mixture supplied to the internal combustion engine according to the adsorption state of the nitrogen oxide from the adsorption state estimator estimated becomes. According to this preferred embodiment is the production of nitrogen oxide in a period during which the drive state from the lean combustion state to the theoretical one Ratio driving state or the fat burning state is completely changed by Lowering the combustion temperature of the air-fuel mixture can be suppressed.

The control device preferably has furthermore an acceleration determination device for determination on whether the internal combustion engine was in the acceleration drive is by the load information representing the load condition of the internal combustion engine indicates compared to an acceleration determination threshold becomes; an air-fuel ratio setting device to set the air-fuel ratio to a value that is the same or richer than the theoretical air-fuel ratio if the accelerator determines that the engine is in the accelerating drive state is; and a threshold changer to change the acceleration determination threshold value according to the adsorption state of the Nitric oxide from the adsorption state estimator estimated will (claim 15).

According to this preferred embodiment it is in a case where the combustion temperature is lowered and the engine output is reduced because the exhaust gas purifying catalyst is included adsorbed nitrogen oxide saturated is, more easily, the drive state from the lean-burn state to the theoretical ratio drive state or to change the rich combustion state in which the engine output is high, which makes it possible response to the acceleration drive request improve.

Preferably, the combustion condition deterioration means of the control device includes an ignition timing adjusting device for adjusting the ignition timing of the internal combustion engine, or an exhaust gas recirculation means for recirculating the exhaust gas from the internal combustion engine to the engine delivery system, or an air-fuel ratio setting means for adjusting the air-fuel ratio of an air-fuel mixture supplied to the engine. The combustion condition deteriorating means lowers the combustion temperature by retarding the ignition timing or by increasing the amount of recirculation on exhaust gases or by changing the air-fuel ratio towards the lean side. According to the preferred embodiments above, the combustion temperature of the air-fuel mixture can be adjusted in an appropriate and simple manner (see claims 23 and 24).

Preferably, the combustion condition deterioration device stops the deterioration of the combustion state for a predetermined period of time upright. According to this preferred embodiment the adsorbed nitrogen oxide can be deoxidized sufficiently by the deteriorated combustion state is maintained.

Preferably, the combustion condition deterioration device deteriorates the combustion condition in the internal combustion engine by causing an ignition failure is caused in the engine. According to this preferred embodiment can unburned gases are easily generated, making it allows will improve the deoxidation of the adsorbed nitric oxide.

The control method of the present invention comprises preferred embodiments that are similar to those of the aforementioned control device, and the like Deliver benefits.

The invention is described below the drawing for example closer explained. In this show:

1 1 shows a schematic view of a combustion control device according to an embodiment of the invention together with an engine,

2 a functional block diagram of the in l combustion control device shown,

3 a portion of a flowchart of the combustion control routine used by the in 2 shown electronic control unit is executed,

4 the remaining part of the flow chart of the combustion control routine that corresponds to the flow chart of 3 follows

5 part of a fluff chart in the 4 shown subroutine for calculating the NOx release amount Q _NT ,

6 the remaining part of the flow chart of the subroutine for calculating the NOx release amount Q _NT , which is the flow chart of 5 follows

7 2 shows a graphical representation of an exemplary diagram of the excess air ratio λ-estimated amount D _{N of} the concentration of the engine output NOx,

8th 2 shows a graphic representation of an exemplary diagram of the ignition timing correction coefficient K _Ig ,

9 a graphical illustration of an exemplary graph of the accumulated value SQ _{N (i + 1)} the amount of the engine output estimated NOx adsorption ratio K _NOX of the NOx catalyst,

10 2 shows a graphical representation of an exemplary diagram of the excess air ratio λ-estimated value K _{CAT of} the NOx purification ratio of a three-way catalytic converter,

11 6 is a flowchart of the misfire control routine executed in a combustion control method for an internal combustion engine according to a second embodiment of the present invention;

12 6 is a flowchart of the ignition control routine executed in a combustion control method for an internal combustion engine according to a third embodiment of the present invention;

13 1 is a functional block diagram of an electronic control unit of a combustion control device for an internal combustion engine according to a fourth embodiment of the present invention;

14 a flowchart of the air-fuel ratio control routine performed by the in 13 shown electronic control unit is executed,

15 the remaining part of the flowchart of the subroutine for calculating the estimated NOx release amount corresponding to the flowchart of 5 follows

16 a graphical representation of the changes in the amount Q _{NO of} the engine output NOx and the amount Q _{NT of} the catalyst output NOx over time,

17 an exemplary graphical representation of an EGR quantity diagram for the normal lean-burn engine, which is in the in the 3 and 4 combustion control routine shown is used, and

18 an exemplary graphical representation of an ignition timing diagram for the normal lean-burn engine used in the combustion control routine.

It now becomes a combustion control method and a device for an internal combustion engine according to various embodiments the invention described with reference to the accompanying drawings.

In 1 Reference numeral 1 denotes the car engine which is operated under the control of a combustion control device which will be described below. The engine, ie, for example, a six-cylinder in-line gasoline engine, has combustion chambers, a supply system, an ignition system and the like, which are designed for the lean combustion drive.

The motor 1 has feed openings 2 on that with a feed manifold 4 are connected in which fuel injectors 3 are provided for the corresponding cylinders. A supply line 9 that is connected to the intake manifold is with an air purifier 5 and a throttle valve 7 provided (more generally speaking, with an output operating device for adjusting the motor output). The throttle valve 7 is with the accelerator pedal 7a connected. An idle engine speed control valve 8th (ISC) is provided in a bypass line, which is the throttle valve 7 bridged. An exhaust manifold 11 is with exhaust ports 10 of the motor 1 connected. There is also a silencer (not shown) with the exhaust manifold 11 via an exhaust pipe 14 and an exhaust gas purifying catalyst 13 connected.

The exhaust gas purification catalyst 13 has a NOx catalyst 13a and a three-way catalyst converter 13b on that on the downstream side of the NOx catalyst 13a is arranged. The NOx catalyst 13a contains Pt (platinum) and an alkali precious earth metal such as lanthanum and cerium as a catalytic substance, and functions to adsorb NOx in the oxidizing atmosphere and deoxidize NOx in N ₂ (nitrogen) and the like in the reducing atmosphere containing HC. The three-way catalyst converter 13b works by oxidizing HC and CO (carbon monoxide) and deoxidizing NOx. The NOx deoxidation ability is maximum in or near the theoretical (stoichiometric) air-fuel ratio.

There is also a circulation line 26 for exhaust gas recirculation (EGR) between the exhaust manifold 11 and the feed manifold 4 connected so that part of the exhaust gases in the exhaust manifold 11 to the intake manifold 4 via the circulation line 26 returned and the combustion chamber 15 is fed when one in the line 26 arranged EGR valve 27 is open. When the exhaust gas is recirculated to the supply side in this manner, the combustion temperature is lowered to suppress the generation of NOx.

The motor 1 is also with a spark plug 16 to ignite a mixture of air and fuel provided by the supply opening 2 to the combustion chamber 5 is directed.

The combustion control device according to a first embodiment of the invention for controlling combustion in the engine 1 has an electronic control unit 23 (ECU) as the main component. The ECU 23 comprises an input / output device, a memory device (ROM, RAM, non-volatile RAM or the like) with a multiplicity of control programs stored therein, a central processing unit (CPU), a time counter and the like (these are not shown in the drawing). Various sensors used in 1 are shown with the input side of the ECU 23 connected.

In 1 denotes the reference symbol 6 an airflow sensor attached to the supply line 9 is attached and the supply air quantity A _f detected. A Karman vortex airflow sensor or the like is appropriately used as an airflow sensor 6 used. Furthermore, the reference symbol denotes 12 an air-fuel ratio sensor (linear air-fuel ratio sensor or the like) that is attached to the exhaust pipe 14 is arranged to detect the excess air ratio λ (more generally, an air-fuel ratio information variable); 18 denotes a crank angle sensor with an encoder that is connected to the camshaft of the engine 1 is connected and generates a crank angle _{synchronization} signal θ _CR ; and 19 denotes a throttle sensor for detecting the opening θ _{TH of} the throttle valve 7 , Furthermore, the reference symbol denotes 20 a water temperature sensor for detecting the engine cooling temperature T _W ; 21 denotes an atmospheric pressure sensor for detecting the atmospheric pressure P _a ; and 22 denotes a supply air temperature sensor for detecting the supply air temperature T _a . The engine speed N _e is determined by the ECU 23 calculated according to the time interval between the crank angle synchronization signals θ _CR by the crank angle sensor 18 to be delivered. The engine load L _e is calculated according to the engine revolution speed N _e or the throttle opening θ _TH by the throttle sensor 19 is detected.

The ECU 23 calculates the optimal values of the fuel injection amount, the ignition timing and the like based on parts of the information detected by various sensors. The ECU 23 drives the fuel injectors 23 and the ignition unit 24 according to the results of the calculation. These elements 3 and 24 are with the output side of the ECU 23 connected. The ignition unit 24 supplies a high voltage to the spark plug 16 of each cylinder in response to the command from the ECU 23 ,

The ECU 23 This embodiment has various functions from a functional point of view 2 are shown.

Specifically, the ECU 23 a drive state determination unit 30 to determine if the engine 1 is to be operated in the lean-burn state or the theoretical air-fuel ratio drive state (hereinafter referred to as the theoretical ratio drive state) in accordance with the engine speed N _e , the cooling temperature T _W , the engine load L _e and the presence / absence of the acceleration determination signal. The ECU also contains 23 an air-fuel ratio changing unit 31 to switch the air-fuel ratio of the engine 1 supplied air-fuel mixture between the lean air-fuel ratio and the theoretical air-fuel ratio according to the result of the determination of the drive state determination unit 30 , The ECU also has an adsorpti onssättigungsbestimmungseinheit 32 to determine whether the NOx catalyst 13a is saturated with NOx. The adsorption saturation determination unit 32 outputs a NOx reducing signal when it is determined that the NOx catalyst 13a is saturated with NOx. In a broad sense, the adsorption saturation determination unit estimates 32 the state of adsorption of NOx of the NOx catalyst 13a ,

The adsorption saturation determination unit 32 has a catalyst delivery NOx amount estimator (nitrogen oxide delivery amount estimator) 33 for deriving an estimated value Q _{NT of} the amount of NOx discharged from the NOx catalyst 13a from parts of the information which is detected by the corresponding sensors; and a comparator 34 to compare the estimated value Q _NT with the threshold value Q _NTO . The comparator 34 provides the NOx reducing signal to a flip-flop circuit 35 to be set if the estimated value Q _{NT is} greater than the threshold value Q _NTO . The flip-flop circuit 35 is reset when the theoretical air-fuel ratio is changed from the air-fuel ratio changing unit 31 is selected.

The ECU 23 has a combustion temperature lowering unit 36 to lower the combustion temperature in the engine 1 in the required manner. The temperature reduction unit 36 sets the EGR amount and the ignition timing in the engine 1 according to the presence / absence of the NOx reducing signal and increases the EGR amount and retards the ignition timing to lower the combustion temperature to reduce NOx. In a broad sense, the temperature lowering unit deteriorates 36 the state of combustion in the engine.

Furthermore, the ECU 23 an acceleration determination / threshold change unit 37 on. The threshold change unit 37 compares the valve opening speed of the throttle valve 7 with an acceleration determination threshold A _th . If the throttle valve opening speed exceeds the threshold value A _th , the threshold value change unit determines 37 that the acceleration drive request is issued and outputs an acceleration determination signal. In response to this signal, the drive state determination unit determines 30 that the engine 1 should be operated in the theoretical ratio drive state. The threshold A _th that of the threshold change unit 37 used for the determination takes a different value according to the presence or absence of the NOx reducing signal. That is, when the NOx reducing drive is applied in response to the NOx reducing signal, the threshold value A _th becomes small; this makes it easier to change the drive state from the lean-burn state to the theoretical ratio drive state. The operation of the combustion control device having the above configuration will now be explained.

Determines the drive state determination unit 30 that the engine is to run in the lean-burn state, the lean air-fuel ratio becomes from the air-fuel ratio changing unit 31 selected. In this case the throttle valve 7 and / or the ISC valve 8th opened to increase the amount of supply air, the fuel injection amount from the fuel injection valve 3 is kept substantially constant. It follows that an air-fuel mixture with an air-fuel ratio larger than the theoretical air-fuel ratio is the engine 1 is fed, causing the engine 1 is driven in the lean combustion state. During the lean-burn drive, there is a reducing atmosphere around the NOx catalyst 13a generated around so that NOx that is in the exhaust gases from the engine 1 is contained on the NOx catalyst 13a can be adsorbed.

However, in the lean-burn state, the estimated value Q _{NT of} the NOx discharge amount becomes from the NOx estimation unit 33 is estimated, and the estimated value Q _NT is compared with the threshold value Q _NTO from the comparator 34 compared. If the estimated value Q _{NT is} larger than the threshold value Q _NTO , it is determined that the NOx adsorbing ability of the NOx catalyst 13a has substantially reached the saturated state, and the NOx reducing signal is from the comparator 34 output. Thereupon, the EGR amount and the ignition timing from the temperature lowering unit 36 is set, which responds to the NOx reducing signal, and the NOx reducing drive is applied to deteriorate the combustion condition or the combustion in the engine 1 mitigate. As a result, the combustion temperature is lowered to reduce the amount of NOx discharged.

If the acceleration determination signal from the threshold value changing unit 37 to the drive state determination unit 30 is supplied, the drive state determining unit determines 30 further that the engine 1 is to be driven in the theoretical ratio driving state, and the theoretical air-fuel ratio is changed from the air-fuel ratio changing unit 31 selected. In this case, a theoretical or stoichiometric air-fuel mixture is added to the engine 1 fed so that the engine 1 in the theoretical ratio drive state is driven to the output of the engine 1 to increase. During the drive in the theoretical ratio contain those from the engine 1 exhaust gases emitted a larger amount of HC and CO than in the lean-burn state. There is therefore a reducing atmosphere around the NOx catalyst 13a witnessed to cause deoxidation (reduction) of the adsorbed NOx.

Furthermore, at the time of the NOx reducing drive the acceleration determination threshold set to a smaller value so that the change in the drive state in the theoretical ratio drive state is facilitated. It follows that the response of the acceleration drive request can be improved in the NOx-reduced drive, in which the Motor output reduced compared to the drive that is not reduced in NOx is.

Next is the operation of the Combustion control device explained in detail.

While driving the engine 1 becomes a crank angle synchronization signal θ _CR from the crank angle sensor 18 generated at every crank angle CA, for example at 120 °. Every time the crank angle synchronization signal θ _{CR of} the ECU 23 is entered as an interrupt signal, the combustion control routine included in the 3 and 4 is shown by the ECU 23 executed.

First, in step S10 from the drive state determination unit 30 the ECU 23 according to the engine speed N _e , the cooling temperature T _W , the engine load Le, and the presence / absence of the acceleration determination signal from the threshold value changing unit 37 determines whether the theoretical ratio drive condition applies. For example, the theoretical ratio driving condition is true when the engine speed N _e and the coolant temperature T _W is equal to or greater than the respective predetermined values and the engine load Le is equal to or smaller than a predetermined value. This condition also exists when the acceleration determination signal is generated.

If the theoretical ratio driving condition is not given and therefore the result of the determination in step S10 is "NO", the air-fuel ratio is changed by the air-fuel ratio changing unit 31 set to the lean air-fuel ratio (step S11). At the next step S12, a determination is made as to whether the value of a flag f (NR) is "1", thereby indicating the execution of the NOx reducing engine. Is the NOx catalyst 13a not yet saturated with adsorbed NOx, the result of the determination in step S12 becomes "NO", and control proceeds to step S14.

In step S14, the estimated value Q _{NT of} a discharge amount of NOx from the exhaust gas purification device 13 through the NOx estimation unit 33 calculated. For the calculation of the estimated value Q _NT , a subroutine is executed which uses a method ( 5 ) Of the votes for calculating the amount of NOx from the engine Q _NO 1 and a process ( 6 ) for calculating the estimated value Q _NT , which is based on the value Q _NO , which is in the calculation method of 5 was derived.

In step S60 of 5 according to the excess air ratio λ (more generally, the air-fuel ratio information variable), the estimated value D _{N of} the concentration of the engine output NOx (NOx output from the engine) is obtained from a graph ( 7 ), which is determined empirically and previously in the ECU 23 was saved. The excess air ratio λ is either that of the air-fuel ratio sensor 12 measured value or a target value set according to the motor drive condition. Furthermore, the estimated NOx concentration D _{N may be determined} according to the air-fuel ratio or the equivalent ratio (which is reciprocal to the excess air ratio) instead of the excess air ratio λ.

In the diagram of 7 the estimated value D _{N of} the concentration of the engine output NOx is set to have a maximum value when the excess air ratio λ is slightly larger than 1.0, that is, when the air-fuel ratio is slightly leaner than the theoretical air-fuel ratio. The estimated value D _N decreases substantially at a constant rate with a decrease in the excess air ratio λ in an area (lean air-fuel ratio range) where the excess air ratio λ is small, and decreases significantly at a constant rate with an increase in the excess air ratio λ in an area (rich air-fuel ratio range) where the excess air ratio λ is large.

When the readout of the estimated engine output NOx concentration D _N is completed, control proceeds to step S62. In step S62, a correction coefficient K _Ig for the ignition timing is obtained from a diagram of 8th taken. The correction coefficients K _Ig were previously in the ECU 23 saved. In the in 8th In the diagram shown, the correction coefficient K _{Ig is} set so that it takes a reference value 1.0 when the ignition timing is set at a predetermined value on the leading side, and decreases when the ignition timing is changed toward the delay side.

As will be described later, the correction coefficient K _{Ig is} used to correct the estimated value D _{N of} the concentration of the engine output NOx read in step S60. The correction is made to properly deduce the amount of engine output NOx from the fact that the combustion is weakened and the combustion temperature is lowered to decrease the amount of engine output NOx when the ignition timing is changed toward the retard side.

In step S62, various correction coefficients for the EGR amount, the supply air temperature, the humidity and the like can be calculated and used to correct the estimated value D _{N of} the concentration of the engine output NOx, which is extracted in step S60.

In the next step S64, supply air is supplied quantity Q _a for everyone. Cylinder, that is, a supply air amount Q _a from the previous measurement time (before the current measurement time by the crank angle 120 ° CA) to the current measurement time based on the detection value A _f from the air flow sensor 6 and the machine speed N _e . The influence of atmospheric pressure and the supply air temperature on the detection value A _{f of} the air flow sensor 6 switch off, the detection value A _f according to the detection signals P _a and T _a from the atmospheric pressure sensor 21 and the supply air temperature sensor 22 corrected. The supply air quantity Q _a can also depend on the motor speed N _e , the supply air pressure P _b ect. are derived, and the calculation method for this is not limiting.

In step S66, the amount Q _NO of NOx discharged from the engine is calculated for each detection of the crank angle synchronization signal θ _CR with the following equation (1) according to the estimated value D _{N of} the concentration of the engine discharge NOx, the supply air amount Q _a, and the correction coefficient K _Ig derived as described above. Q N0 = k 1 × K Ig x Q a × D N , ---(1) where k _{1 is} a correction coefficient related to the amount of EGR, humidity and the like other than the correction coefficient KIg.

After calculating the amount Q _{N0 of} the engine output NOx, control proceeds to step S68. At step 568, the accumulated value SQ _{N (i + 1) of} the amount Q _N0 of NOx discharged from the engine and the exhaust gas purifying catalyst 13 happened up to the present time, calculated by the following equation (2), the value expressing the integrated value ∫Q _N0 dt of the amount Q _N0 of NOx emitted by the engine up to the present time: ∫Q N0 dt = SQ N (i + 1) = SQ N (i) + Q N0 , --- (2) where ∫SQ _{N (i)} indicates an integrated or accumulated value calculated in the previous cycle of the control routine, and Q _N0 indicates the amount of engine output NOx calculated in step S66 in the current cycle of the control routine.

In the next step S70, an estimated value K _NOX is the adsorption of NOx on the NOx catalyst 13a when the engine output NOx the exhaust gas purifying catalyst 13 happens based on the accumulated value SQ _{N (i + 1) of} the amount of the engine output NOx derived in step S68. For this purpose, an estimated adsorption ratio K _NOX , which corresponds to the accumulated value SQ _{N (i + 1)} , is taken from the diagram of 9 taken from that previously in the ECU 23 was saved.

In the diagram of 9 the estimated adsorption ratio K _{NOX is} set to take a maximum value of 1.0 when the accumulated value SQ _{N (i + 1) is} "0" and gradually decreases to a predetermined value K _N1 (e.g., a value of 0, 1) with an increase in the accumulated value SQ _{N (i + 1)} . One in 9 curve shown accumulated value SQ _{N (i + 1)} -estimated adsorption ratio K _NOX is expressed by the following equation (3): K NOX = (1-K N1 ) × exp [(- k 2 ) × SQ N (i + 1 )] + K N1 , --- (3) where k _{2 is} a correction coefficient (constant).

The estimated adsorption ratio K _NOX can be derived by performing a calculation based on equation (3) instead of estimating the adsorption ratio K _NOX using the graph of 9 is carried out.

In the next step S72, the estimated value K _{CAT of} the ratio of the NOx purification by the three-way catalyst converter 13b of the exhaust gas purification catalyst 13 from the diagram of 10 taken on the basis of the excess air ratio λ. In view of the fact that the NOx purifying ability of the three-way catalyst converter 13b only in a narrow excess air ratio range where the excess air ratio λ is 1.0 or a near value thereof, the estimated cleaning ratio K _CAT according to the diagram of FIG 10 set such that it very quickly reaches a maximum value K _C2 (for example a value of 0.95) from a predetermined value K _C1 (for example a value of 0 to 0.1) when the excess air ratio λ increases from a value, which is slightly less than 1.0 up to a value of 1.0, increases and decreases very quickly from the maximum value K _C2 to the predetermined value K _C1 with a further increase in the excess air ratio λ. Since the excess air ratio λ during the lean-burn engine is a value (for example, 1.5) that is considerably larger than 1.0, the estimated cleaning ratio (K _CAT ) during the lean-burn engine becomes equal to the predetermined value K _C1 .

Instead of estimating the cleaning ratio K _CAT using the diagram of 10 The estimated cleaning ratio K _CAT can be easily derived by assuming that the cleaning ratio K _{CAT has} a value of 0 for the excess air ratio λ that falls within the narrow excess air ratio range (e.g. 0.95 ≤ λ ≤ 1.05) , 95, and that the cleaning ratio K _{CAT has} a value of "0" for the excess air ratio λ falling within a range (e.g., λ <0.95, 1.05 <λ) outside the narrow excess air ratio range.

In the next step S74, the NOx emission ratio calculated according to the equation (NOx discharge ratio = (1-K _NOX ) × (1-K _CAT )) based on the engine discharge NOx amount Q _N0 , the estimated value K _{NOX of} the adsorption ratio of NOx by the NOx catalyst 13a and the estimated value K _{CAT of} the NOx purification ratio by the three-way catalyst converter 13b , Furthermore, the estimated value Q _{NT of} the catalyst output NOx amount for each detection of the crank angle synchronization signal θ _CR is calculated by using the following equation (4), which is based on the NOx output ratio and the engine output NOx amount Q _N0 in step S66 is calculated. The estimated value Q _NT is substantially equal to the actually measured value of the amount of NOx released by the exhaust gas purification device 13 is released into the atmosphere. Q NT = Q N0 × {(1-K NOX ) × (1-K CAT )} --- (4)

Equation (4) indicates that if the adsorption of NOx by the NOx catalyst 13a is continued under such a condition that the purification ratio K _CAT by the three-way catalyst converter 13b has the predetermined value K _C1 , such as in the lean-burn state, the NOx cleanability of the exhaust gas purification device 13 is reduced and therefore the catalyst discharge NOx amount Q _NT increases, so that the NOx adsorption ratio K _{NOX is} reduced.

After the estimated catalyst discharge NOx amount Q _NT is calculated, control goes to step S16 3 further. The comparator determines in step S16 34 whether the estimated value Q _{NT of} the amount of catalyst discharge NOx derived as described above is larger than the predetermined threshold value Q _NT0 . For example, a legal limit of NOx emission is used as the basis for setting the threshold value Q _NT0 . If the result of the determination in step S16 is "NO", that is, if the NOx adsorption amount has not reached the saturated state, it is determined that the amount of NOx released into the atmosphere is equal to or less than the maximum allowable value , and control goes to step S40 4 further.

In step S40, the amount of recirculation electricity (hereinafter referred to as EGR amount) E _{gr of} the EGR gas in the normal lean-burn state is set. In detail, an EGR quantity E _{LN is} calculated as an EGR quantity Egr for the normal lean-burn combustion drive from an EGR quantity diagram ( 17 ) for the normal lean-burn engine, which was previously in the ECU 23 was stored according to the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture. In the EGR quantity diagram, the EGR quantity E _{LN is expressed} as a function of the engine speed Ne and the charging efficiency η _{v of} the air / fuel mixture (E _gr = E _LN (N _e , η _v ).

Unlike the NOx-reduced drive state or the theoretical ratio drive state, a large amount of EGR is not required in the normal lean-burn state. The EGR quantity E _LN in the diagram is therefore set smaller than the EGR quantities E _N0 , E _ST for the same N _e , η _v in the EGR setting diagram for the NOx-reduced drive state or the theoretical ratio drive state.

In the next step S42, an ignition timing θ _{LN is determined} from an ignition timing diagram ( 18 ) which was previously in the ECU 23 was stored for the normal lean-burn engine, as the ignition timing θ _Ig for the normal lean-burn engine according to the engine speed Ne and the charge efficiency η _{v of} the air-fuel mixture. In the diagram, the ignition timing θ _{LN is expressed} as a function of the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _LN (N _e , η _v )). Since the ignition timing needs to be advanced to improve the combustion efficiency at the time of the normal lean-burn engine, the ignition timing θ _LN in this ignition timing diagram becomes a value on the advanced side from the ignition timings θ _N0 , θ _ST for the same N _e , η _v for the NOx-reduced drive and the theoretical ratio drive.

After setting the ignition timing θ _Ig , control proceeds to step S44. In step S44, the acceleration determination threshold value A _{th is set} to a reference threshold value A ₀ , which is greater than the threshold value A _N0 for the NOx-reduced drive (A ₀ > A _N0 ). Therefore, during the normal lean burn drive, there is no shift to the theoretical ratio drive state without the throttle valve 7 is opened faster than in the NOx-reduced drive state. This is because the engine output is higher in the normal lean-burn state than in the NOx-reduced drive state, and it is therefore possible to consider a fairly substantial acceleration drive requirement even if the theoretical ratio drive is not performed. Another reason is to prevent the drive state from being changed frequently to the theoretical ratio drive state in order to avoid reducing the fuel consumption.

Next, control proceeds to step S36, in which the fuel amount is accurately calculated based on the supply air amount and the air-fuel ratio in a usual manner. After this, the execution of the combustion control routine in the current cycle is completed. A next crank angle synchronization signal θ _{CR of} the ECU 23 supplied, the combustion control routine is then again from the Started step S10.

If it is determined in step S10 that the theoretical ratio driving condition is not given, and if it is determined in step S16 that the estimated value Q _{NT of} the catalyst _discharge NOx amount has not reached the threshold value Q _NT0 , a sequence of the steps becomes S10, S11, S12, S14, S16, S40, S42, S44 and S36 performed repeatedly to operate the engine 1 in the normal lean-burn state. During this time, NOx is in the exhaust gases on the NOx catalytic converter 13a adsorbed.

Thereafter, if it is determined in step S16 that the estimated value Q _{NT of} the catalyst discharge NOx amount has exceeded the threshold value Q _NTO during the lean-burn drive and the result of the determination in step S16 therefore becomes "YES", it is determined that the NOx adsorbability of the NOx catalyst 13a is saturated. In this case, control proceeds to step S18. In step S18, the value of a flag f (NR) is set to "1", indicating that the NOx-reduced drive is being carried out.

Next, control goes to step S30 4 further. In step S30, according to the engine speed Ne and the charge efficiency η _{v of} the air-fuel mixture, an EGR amount E _N0 as an EGR amount E _gr for the NOx-reduced drive by the temperature lowering unit 36 of 1 taken from an EGR setting diagram (not shown) for the NOx-reduced drive. This diagram was determined empirically and in the ECU 23 saved.

In the diagram for the NOx-reduced drive, the EGR quantity E _{N0 is expressed} as a function of the engine speed Ne and the charge effectiveness η _{v of} the air / fuel mixture (E _gr = E _N0 (N _e , η _v )) and set to a value that is greater is the EGR quantity E _gr for the same N _e , η _v in the EGR setting diagram ( 17 ) for the normal lean-burn drive. The EGR amount E _gr that from the exhaust manifold 11 to the intake manifold 4 is circulated becomes larger than in the case of the normal lean-burn engine, thereby lowering the combustion temperature and reducing the NOx release amount.

After the EGR amount E _gr is set, control proceeds to step S32. In step S32, in accordance with the engine speed N _e and the charge effectiveness η _{v of} the air / fuel mixture, an ignition timing θ _N0 as the ignition timing θ _Ig for the NOx-reduced drive is read from an ignition timing diagram (not shown) for the NOx-reduced drive, this diagram being determined empirically and previously in the ECU 23 was saved.

In the ignition timing diagram (not shown) for the NOx-reduced drive, the ignition timing θ _{N0 is expressed} as a function of the engine speed Ne and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _N0 (N _e , η _v )) and up to a value the delay side from the ignition timing θ _Ig for the same N _e , η _v in the ignition timing diagram ( 18 ) set for the normal lean-burn drive. The time for the spark plug 16 therefore, the ignition of the air-fuel mixture is delayed so that the exhaust stroke is started before the combustion is completed. Therefore, the combustion temperature does not rise so high and the NOx release amount is reduced.

After setting the ignition timing θ _Ig , control proceeds to step S34. In step S34, according to an acceleration determination threshold setting diagram (not shown) for the NOx-reduced drive, the valve opening speed threshold (acceleration determination threshold) A _{th of} the throttle valve 7 to the NOx-reduced acceleration determination threshold value A _N0 by the threshold value change unit 38 changed. In this diagram, the threshold value A _N0 , which is expressed as a function of the vehicle speed, is set to a value that is smaller than the normal threshold value A ₀ . The transition from the lean-burn engine to the theoretical ratio engine is therefore carried out on the low throttle valve opening speed side. As a result, when an acceleration drive request is issued during the NOx-reduced drive, the engine output, which has been reduced by lowering the combustion efficiency by the NOx-reduced drive, is rapidly increased, thereby making the acceleration drive smooth.

After setting the acceleration determination threshold A _th , control proceeds to step S36. In step S36, the amount of fuel from the fuel injection valve 3 must be supplied, calculated in the usual manner based on the supply air amount and the air-fuel ratio according to a predetermined equation. The amount of fuel supplied during the NOx-reduced drive is kept at a constant value when the air-fuel ratio is kept at a predetermined value. On the other hand, if the air-fuel ratio is changed within the lean air-fuel ratio range to thereby lower the combustion temperature, the fuel supply amount is variably set according to the EGR amount E _N0 and the ignition timing θ _N0 .

When the calculation of the fuel supply amount is completed in step S36, the execution of the combustion control routine in the current cycle is completed. After that, when the next crank angle synchronization signal θ _{CR of} the ECU 23 is supplied, the combustion control routine is started again from step S10.

Since the flag f (NR) is already at "1" after the start of the NOx-reduced drive is set, a sequence of steps S10, S11, S12, S30, S32, S34 and S36 are repeatedly executed to reduce the NOx Drive, when it is determined in step S10 that the theoretical ratio driving condition is not given.

As described above, according to the engine combustion control of this embodiment, even when the catalyst _discharge NOx estimated amount Q _{NT reaches} the predetermined value Q _NT0 at which the NOx adsorption amount can be regarded as substantially saturated during the lean-burn drive, there is no possibility that the drive state is increasingly changed from the lean-burn drive to the theoretical ratio drive in order to deoxidize the adsorbed NOx. Rather, in the engine combustion control of this embodiment, when the NOx catalyst 13a is saturated, the NOx-reduced drive, in which the EGR amount is increased and the ignition timing is delayed, is exercised. As a result, the amount of NOx released into the atmosphere can always be kept at a value equal to or less than the constant value Q _NT0 without _causing a torque _variation due to the transition to the theoretical ratio driving state.

Further, since the acceleration determination threshold A _{th is set} to a small value in the NOx-reduced driving state so that the driving state tends to be changed to the theoretical ratio driving state, the NOx-reduced driving is usually not maintained for a long period of time , Therefore, a reduction in fuel economy caused by the NOx-reduced engine can be suppressed within an allowable range.

While the normal lean-burn drive or the lean-burn drive for NOx reduction Control proceeds to step S20 if it is determined in step S10 that the theoretical ratio drive condition is given and therefore the result of the determination in step S10 becomes "YES". In step S20 becomes the air-fuel ratio from the lean air-fuel ratio changed to the theoretical Luftkraftstoffver ratio, whereby the drive state from Lean combustion state is changed to the theoretical ratio drive state.

In the next step S22, the flag f (NR) is set to "0", which indicates that the NOx-reduced drive is not being applied. This is because the NOx-reduced drive is inhibited in the theoretical ratio drive state, as will be described later. Furthermore, in step S22, a time counter for counting the elapsed time from the moment at which the theoretical ratio drive starts is started. In the next step S24, it is checked by referring to the content of the time counter whether a predetermined time t _R (for example, 3 seconds) has elapsed from the start of the theoretical ratio drive. If the result of the determination in step S24 is "NO", control proceeds to step S50 4 further.

In step S50, in accordance with the engine speed Ne and the loading efficiency η _{v of} the air / fuel mixture, an EGR quantity E _{ST is} read out as EGR quantity E _gr for the theoretical ratio drive from the EGR quantity setting diagram (not shown) for the theoretical ratio drive, that previously in the ECU 23 was saved. In this diagram, the theoretical air-fuel ratio EGR amount E _{ST is expressed} as a function of the engine speed N _e and the charging efficiency η _{v of} the air-fuel mixture (E _gr = E _ST (N _e , η _v )), and is set to a value that is larger is the EGR quantity E _gr for the same N _e , η _v in the EGR quantity law diagram ( 17 ) for the normal lean-burn drive. The EGR amount E _gr in the theoretical ratio drive therefore becomes larger than the EGR amount in the normal lean-burn engine, which lowers the combustion temperature and reduces the NOx release amount.

After the EGR amount E _gr is set, control proceeds to step S52. In step S52, an ignition timing θ _ST as the ignition timing θ _Ig for the theoretical ratio drive is read out from an ignition timing diagram (not shown) for the theoretical ratio drive that was previously in the ECU 23 was stored according to the engine speed N _e and the charge effectiveness η _{v of} the air-fuel mixture. In the above diagram, the ignition timing θ _{ST is expressed} as a function of the engine speed N _e and the charge efficiency η _{v of} the air-fuel mixture (θ _Ig = θ _ST (N _e , η _v )) _, and to a value on the retard side from the ignition timing θ _Ig for that same N _e , η _v in the ignition timing diagram ( 18 ) for the normal lean-burn engine or the one for the NOx-reduced engine. Because the time for the spark plug 16 is delayed to ignite the air-fuel mixture, therefore, the exhaust stroke is started before the combustion is completely completed, whereby the NOx release amount is reduced. Furthermore, knocking in the theoretical ratio drive can also be prevented.

In the next step S44, the acceleration determination threshold value A _{th is reset} from the threshold value A _N0 for the NOx-reduced drive to the reference threshold value A ₀ , which is greater than the threshold value A _N0 . In the next step S36, the fuel quantity to be delivered is then calculated. After the fuel delivery amount is fully calculated in step S36, the execution of the combustion control routine in the current cycle is ended. A next crank angle synchronization signal θ _{CR of} the ECU 23 is supplied, the combustion control routine is then started again from step S10.

After the start of the theoretical ratio drive, a sequence of steps S10, S20, S22, S24, S50, S52, S44 and S36 is repeatedly executed to perform the theoretical ratio drive until the predetermined time t _{R has} passed. In the theoretical ratio drive, the exhaust gas contains a lot of HC, so that around the NOx catalyst 13a the reducing atmosphere is created. It follows from this that the NOx catalyst 13a absorbed NOx is reduced or deoxidized.

If the predetermined time t _{R has passed} from the start of the theoretical ratio drive, and therefore the result of the determination in step S24 becomes "YES", control proceeds to step S26. In step S26, it is determined that the reduction or deoxidation of the adsorbed NOx is sufficiently exerted, and the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to a value "0". Steps S50, S52, S44 and S36 are then carried out in succession.

In the next and the following The theoretical ratio drive is executed as long as control cycles the theoretical ratio drive condition given is. If the condition is not met, there will be a transition to the lean-burn drive.

Next is a combustion control process for one Internal combustion engine according to a second embodiment of the invention explained.

A combustion control device for performing the method of the second embodiment may be the same as the device of FIG 1 be constructed so that an explanation of the device is therefore unnecessary.

In this embodiment, every time a crank angle synchronization signal θ _{CR of} the ECU 23 as an interrupt signal while driving an engine 1 is fed, which in 11 shown combustion control (ignition failure control) routine from the ECU 23 carried out. The combustion control of this routine determines whether the combustion condition is to be deteriorated when the NOx adsorbability of the catalyst 13a Significantly reaches the saturation state during the lean-burn drive by igniting an air-fuel mixture that is in a predetermined cylinder of the engine 1 is initiated, is prevented at intervals of a predetermined cycle. This intermittently causes a misfire, which leads to the NOx catalyst 13a a reducing atmosphere is created by unburned HC contained in the unburned gases generated at that time, so that adsorbed NOx in the reducing atmosphere is reduced (deoxidized) and removed.

First, in step S110, an estimated value Q _{NT of} the catalyst discharge NOx amount from the ECU 23 calculated. As in the first embodiment, that shown in FIGS 5 and 6 shown subroutine performed. The subroutine has already been explained, so that no further explanation is necessary.

After the estimated catalyst discharge NOx amount Q _NT is calculated, control proceeds to step S112 11 further. In step S112 the comparator 34 the adsorption saturation determination unit 32 determines whether the estimated value Q _{NT of} the amount of catalyst discharge NOx calculated in the manner described above is larger than a predetermined threshold value Q _NT0 . When it is determined in step S112 that the amount of NOx adsorption has not reached the saturated state and therefore the result of the determination in step S112 becomes "NO", it is determined that the amount of NOx released into the atmosphere is the same or less than a maximum allowable value.

In this case, control proceeds to step S124, and the number N _mis of ignition failures (hereinafter referred to as ignition failure number Nmis) is set to "0". This is because the ignition failure control, which is described below, has not yet been started. The combustion control routine in the current cycle is then completed. A next crank angle synchronization signal θ _{CR of} the ECU 23 supplied, the ignition failure control routine is started again from step S110.

As described above, the normal engine drive is applied when it is determined in step S112 that the NOx catalyst 13a is not saturated with adsorbed NOx.

If it is determined in step S112 that the estimated value Q _{NT of} the NOx _{discharge amount} is larger than the threshold value Q _NT0 and therefore the result of the determination in step S112 is "YES", it is determined that the adsorbability of the NOx catalyst 13a has reached the saturated state. In this case, control proceeds to step S114. In step S114, a determination is made as to whether the number of times that the ignition failure control routine has been performed, that is, the number of times N that the crank angle synchronization signals θ _{CR has been} generated (hereinafter referred to as θ _CR generation number N) after the first time that the estimated NOx release amount Q _NT has exceeded the threshold or after the ignition inhibition for ignition failure, Q _{NT0 has reached} a predetermined number of times N ₀ (which is, for example, 50 and _hereinafter as a predetermined number N ₀ is referred to), which corresponds to a predetermined ignition failure period.

If it is determined in step S114 that the θ _CR generation number N is not the predetermined On number of times N has reached ₀ and therefore the result of the determination in step S114 becomes "NO", control proceeds to step S115, in which a value "1" is added to the θ _CR generation number N, and the combustion control routine is current The cycle is then completed.

If the result of the determination in step S112 is "NO", a sequence of steps S110, S112, S114 and S115 is carried out repeatedly. After that, the θ _CR generation number N reaches the predetermined number N ₀ , and the result of the determination in step S114 becomes "YES". In this case, it is determined that the ignition inhibition time has been reached, and control proceeds to step S116. In step S116, the ECU supplies 23 the spark plug 24 not with a voltage command, that of a spark plug 16 a predetermined cylinder (for example, the first cylinder). It follows that the ignition in this cylinder is inhibited, causing an ignition failure. The air-fuel mixture in the associated combustion chamber 15 is therefore not burned and is released as unburned gases from the exhaust opening 10 towards the NOx catalyst 13a issued. It follows that there is a reducing atmosphere around the NOx catalyst 13a is created by unburned HC contained in the unburned gases, and the adsorbed NOx is deoxidized in the reducing atmosphere.

In the next step S118, the θ _CR generation number N is reset to "1" and a value "1" is added to the ignition failure number Nmis. It is further determined in step S120 whether the ignition failure number Nmis exceeds a predetermined value N _mis0 . The predetermined value N _mis0 is set in advance to the number of ignition failures (for example 50) that can be considered sufficient that of the NOx catalyst 13a deoxidize adsorbed NOx. If the result of the determination in step S120 is "NO", it is therefore determined that that is on the NOx catalyst 13a adsorbed NOx is not completely oxidized, the combustion control routine in the present cycle is completed.

If the result of the determination in step S114 is "NO", the sequence of steps S110, S112, S114 and S115 is repeated. Thereafter, when the θ _CR generation number N has reached the predetermined number N ₀ and the result of the determination in step S114 becomes "YES", an intermittent ignition failure is caused (step S116).

As described above, the ignition failure drive or the ignition fault drive executed intermittently.

If the number of ignition failures N _mis caused by the intermittent ignition failure drive exceeds the predetermined value N _mis0 , the result of the determination in step S120 becomes "YES". In this case, it can be assumed that a period of time has passed that is necessary for the complete oxidation of the NOx catalyst 13a adsorbed NOx. It can therefore be assumed that the NOx is completely from the NOx catalyst 13a has been eliminated and the NOx adsorbability of the NOx catalyst 13a was recovered. Control therefore proceeds to step S122. In step S122, the accumulated value SQ _{N (i + 1) of} the engine discharge NOx amount is reset to "0", which value is used for the calculation of the estimated NOx discharge amount Q _NT in step S110.

As a result, the estimated NOx adsorption ratio K _{NOX is set} to 1.0 when the in the 5 and 6 shown subroutine is again executed in step S110 in the next ignition failure control routine execution cycle. Therefore, the estimated value Q _{NT of} the catalyst discharge NOx amount calculated in step S110 in the next ignition failure control routine execution cycle becomes "0". Therefore, the result of the determination in step S112 becomes "NO", control proceeds to step S124, and the ignition failure drive is ended.

In this embodiment, as described in detail above, each time the estimated value Q _{NT of} the catalyst _discharge NOx amount exceeds the threshold value Q _NT0 , the ignition associated with a predetermined cylinder _becomes one for a predetermined number of times at intervals predetermined cycle inhibited. It follows that unburned gases containing unburned HC intermittently the NOx catalyst 13a are supplied, whereby adsorbed NOx is deoxidized and the NOx adsorbability of the NOx catalyst 13a is restored in an appropriate manner. Furthermore, a stabilized lean-burn driving state of the engine can 1 be maintained.

In addition, it is not necessary to increase the amount of fuel which is supplied to supply the unburned HC. It occurs therefore no quick change in engine output due to an increase in the amount of fuel supplied and therefore no deterioration in the drive "feeling". Furthermore, fuel economy not decreased.

The engine is stopped during the intermittent ignition failure drive or the ignition failure drive 1 driven with the lean air-fuel ratio and the exhaust gases coming from the engine 1 emitted contain a large amount of oxygen. Unburned gases, which are caused by the ignition failure and are not used for the deoxidation of NOx, are therefore completely eliminated by the three-way catalytic converter 13b oxidized and are not released into the atmosphere.

A combustion control method for an internal combustion engine according to a third embodiment The invention is explained in the following.

The method of this embodiment has the feature that the air-fuel ratio is set to an air-fuel ratio (over-lean air-fuel ratio) that is leaner than the air-fuel ratio that corresponds to the combustion limit, thereby causing ignition failure. A combustion control device for performing the method of the third embodiment can be made in the same manner as the device of FIG 1 be constructed so that an explanation of this device is unnecessary.

In this embodiment, every time a crank angle synchronization signal θ _{CR of} the ECU 23 while an engine is running 1 is supplied, the combustion control (ignition failure control) routine, which in 12 is shown by the ECU 23 executed.

First, in step S130, the step S110 of 11 corresponds to that in the 5 and 6 Subroutine shown by the NOx estimation unit 33 is performed to calculate an estimated value Q _{NT of} the amount of catalyst discharge NOx. Then the comparator 34 the adsorption saturation determination unit 32 in step S132, which corresponds to step S112 of 11 determines whether the estimated value Q _{NT of} the catalyst _delivery NOx amount has exceeded a predetermined threshold value Q _NT0 .

If the result of the determination in step S132 is "NO", step S142, which corresponds to step S124 of 11 is executed to set the ignition failure number Nmis to "0", and the combustion control routine in the current cycle is ended.

On the other hand, if the result of the determination in step S132 is "YES", control proceeds to step S134, and the ignition failure drive becomes under the control of the ECU 23 started.

Specifically, in step S134, the air-fuel ratio of an air-fuel mixture supplied to a predetermined cylinder (for example, the first cylinder) is corrected according to the following equation (5) to set the air-fuel ratio to the leaner air-fuel ratio AF _T : AF T = AF 0 + D AF , --- (5) where AF _{0 is} a lean target air-fuel ratio during normal driving and D _{AF is} the target ratio correction value.

The over-lean air-fuel ratio AF _T has a value that is set on the lean side with respect to the air-fuel ratio that corresponds to the limit of combustion, and is set to a value that causes ignition failure with a predetermined probability (for example, 0.02) when the air-fuel mixture of the lean air-fuel ratio AF _T through the spark plug 16 is ignited. If the lean air-fuel ratio AF _{T is set} to an excessively large value, no combustion occurs at any time and the engine is driven 1 cannot be maintained, which causes a problem.

Therefore, in order to obtain the appropriate super-lean air-fuel ratio AF _T , the correction value DAF is determined empirically, so that the ignition failure is caused with a predetermined probability (frequency), for example to cause an ignition failure once every 50 ignitions.

If the lean air-fuel ratio AFT is set, it is under the control of the ECU 23 from the fuel injector 3 injected fuel amount reduced to a value corresponding to the lean air-fuel ratio AF _T. As a result, the ignition failure occurs with a predetermined probability. If the ignition failure has occurred, unburned gases are directed towards the NOx catalytic converter 13a emitted and that of the catalyst 13a adsorbed NOx is deoxidized and removed from unburned HC contained in the unburned gases.

Furthermore, in step S134, the EGR valve 27 opened by a predetermined angle. As a result, a predetermined amount of exhaust gases are directed toward the side of the supply port 2 circulates to reduce the amount of oxygen in the air-fuel mixture, thereby facilitating ignition failure.

In the next step S136, a value 0.02, which is equal to a predetermined probability of occurrence of the ignition failure, is added to the ignition failure number Nmis. Then, in the next step S138, which is the step S120 of 11 determines whether the number of ignition failures Nmis exceeds a predetermined value N _mis0 . The predetermined value N _mis0 is set to a value which is equal to the number of ignition failures (for example 50) at which the NOx catalyst 13a adsorbed NOx can be regarded as sufficiently deoxidized.

If the result of the determination in step S138 is "NO", it is determined that it is on the NOx catalyst 13a adsorbed NOx is not completely deoxidized, and the control routine in the current cycle is ended. Thereafter, if the ignition failure number _Nmis does not exceed the predetermined value N _mis0 , the ignition failure drive is continued.

On the other hand, if the ignition failure number Nmis has the predetermined value N _mis0 ( 50 ) and if the result of the determination in step S138 becomes "YES", it is determined that the period of the ignition failure drive is sufficiently long and therefore that on the NOx catalytic converter 13a adsorbed NOx is completely deoxidized. In this case the control closes Step S140 further. In step S140, the air-fuel ratio is set to the lean air-fuel ratio AF ₀ and the EGR valve 27 closed or returned to the normal opening position. Then, the accumulated value SQ _{N (i + 1) of} the engine discharge NOx amount used for the calculation of the estimated NOx discharge amount QNT in step S130 is reset to "0", and the control routine is ended in the current cycle.

Thus, when the accumulated value SQ _{N (i + 1) of} the engine discharge NOx amount is reset to "0", the estimated value Q _NT becomes the catalyst discharge NOx amount, which is determined in step S130 (corresponding to step S110) of the next failure routine execution cycle was calculated to "0" as in step S110 of 11 explained. The result of the determination in the next step S132 therefore becomes "NO". In this case, the ignition failure drive is ended and control proceeds to step S142, and the ignition failure number Nmis is reset to "0".

Therefore, each time the estimated value Q _{NT of} the catalyst _discharge NOx amount exceeds the threshold value Q _NT0 , the air-fuel ratio of the air-fuel mixture supplied to the predetermined cylinder is set to the over-lean air-fuel ratio AFT. As a result, the ignition failure occurs in a predetermined number at a predetermined frequency, so that unburned gases intermittently the NOx catalyst 13a are fed. Therefore, the NOx catalyst 13a adsorbed NOx completely deoxidized and removed, and the NOx adsorbability of the NOx catalyst 13a will be restored accordingly.

Furthermore, according to this embodiment, as in the case of the second embodiment, a sufficient amount of unburned gas can be the NOx catalyst 13a without increasing the amount of fuel supplied by performing the ignition failure drive in which the ignition failure is caused for a predetermined number of times at intervals of a predetermined cycle (at a predetermined frequency) for the predetermined cylinder. Hence the engine 1 are kept stably in the lean-burn drive state without causing a rapid change in engine output and the NOx adsorbability of the NOx catalyst 13a can be restored without deteriorating driving feel and fuel economy.

Furthermore, as in the case of the second embodiment, unburned gases generated from the ignition failure and which are not used for the deoxidation of NOx become entirely from the three-way catalyst converter 13b oxidized and not released into the atmosphere.

The following is a combustion control device for one Internal combustion engine according to one fourth embodiment of the invention explained.

The device of this embodiment is constructed essentially the same as the device of FIG 1 , so that an explanation for common components of both devices is unnecessary. In this embodiment, the EGR circulation line 26 and the EGR valve 27 , in the 1 shown are not required.

The ECU 23 this embodiment has various functions, in 13 components shown.

In detail, the ECU 23 an engine delivery NOx quantity estimator 130 for estimating the amount of NOx released from the engine 1 to the exhaust pipe 14 , The NOx estimation unit 130 has an engine output NOx concentration estimation unit 131 to estimate the concentration D _{N of} the NOx from the engine 1 to the exhaust pipe 14 is delivered according to the excess air ratio λ; a delay correction unit 132 for deriving a correction coefficient KIg, which is used to correct the estimated NOx concentration D _N according to the ignition timing; and a supply air amount calculation unit 133 to calculate the amount Q _a of supply air supplied to the engine 1 is fed. In the NOx estimation unit 130 becomes the product of the supply air quantity Q _a , the estimated NOx concentration D _N and the correction coefficient K _Ig by multipliers 200 is calculated as the estimated value Q _{NO of} the engine output NOx amount.

The ECU 23 also includes an adsorption ratio estimator 135 for deriving the estimated value K _{NOX of} the adsorption ratio of NOx by the NOx catalyst 13a according to the accumulated value SQ _{N (i + 1) of} the engine output NOx amount; a cleaning ratio estimator 136 for deriving the estimated value K _{CAT of} the purification ratio of NOx by the three-way catalyst converter 13b according to the excess oxygen ratio λ; a catalyst delivery NOx quantity estimator 137 for deriving the NOx discharge ratio based on the estimated NOx adsorption ratio K _NOX and the estimated NOx purification ratio K _CAT , and for deriving the product of the NOx discharge ratio and the estimated engine discharge NOx amount Q _N0 as the estimated catalyst discharge NOx -Quantity Q _NT ; and a comparator 138 to compare the estimated amount of catalyst _delivery NOx Q _NT with the threshold Q _NT0 . If the estimated _{discharge amount} Q _{NT is} larger than the threshold value Q _NT0 , a fat burning drive _signal from the comparator 138 output. When the fat burning drive signal is output for a predetermined period of time t _R , a reset signal becomes the adsorption ratio estimator 135 is output so that the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to "0".

The above combustion control The device is designed to change the driving state to the fat burning state when the NOx adsorbing ability of the NOx catalyst 13a is substantially saturated during the lean burn drive and maintains the fat burn drive for a predetermined period of time around the NOx catalyst 13a in a reducing atmosphere to increase the adsorbability of the NOx catalyst 13a regain. The fat-burning state contains a drive state in which the air-fuel ratio is feedback-controlled (regulated) essentially in relation to the theoretical air-fuel ratio.

Operation of the above combustion control device is explained below.

Every time the crank angle synchronization signal θ _{CR of} the ECU 23 while the engine is running 1 is fed, the in 14 shown combustion control routine executed.

First, it is determined in step S210 whether the lean-burn driving condition is given. For example, the lean burn drive condition is given when the following requirements and the like are satisfied at the same time: the engine 1 is operated in the warm-up state; the motor 1 is operated in a predetermined drive range determined by the engine speed Ne and the engine load; and the engine 1 is not operated in a drive state in which the motor should be accelerated or decelerated.

Is the result of the determination in Step S210 is "NO", that is, the lean-burn driving condition not fulfilled, Control proceeds to step S212 and the fat burning drive control is carried out.

On the other hand, if the lean-burn driving condition is satisfied and the result of the determination in step S210 is "YES", control proceeds to step S214 and the estimated value Q _{NT of} the NOx amount from the exhaust gas purifying catalyst device 13 delivered is derived. In step S214, the subroutine that executes the in 5 calculation method shown and a in 15 contains the calculation method shown. Since the calculation method of 5 has already been explained and most of the in 15 the calculation method shown in that 6 , the subroutine is briefly explained below.

In this subroutine, the estimated value of the engine output NOx concentration is taken from the graph of 7 (Step S60 from 5 ) according to the excess air ratio λ by the concentration estimation unit 131 , in the 13 is read out. Furthermore, the correction coefficient KIg from the diagram of 8th according to the ignition timing by the delay correction unit 132 of 13 (Step S62) read out. Next, the supply air amount Q _a for each cylinder according to the engine speed Ne and the detection value A _f from the air flow sensor 6 through the supply air amount calculation unit 133 of 13 (Step S64). Then, the engine output NOx amount Q _{N0 is determined} for each detection of the crank angle synchronization signal θ _CR by using the equation (1) according to the estimated NOx concentration D _N , the correction coefficient K _Ig, and the supply air amount Q _a by the NOx amount estimator 130 of 13 (Step S66).

After the calculation of the engine output NOx amount Q _N0 , control proceeds to step S367 15 further. In step S367, it is determined whether a predetermined time period t _R (for example, 3 seconds) has passed from the start of the combustion engine. During the lean-burn drive, the result of the determination in step S367 becomes "NO", and control proceeds to step S368, which goes to step S68 6 equivalent. In step S368, the accumulated value SQ _{N (i + 1) of} the engine output NOx amount Q _N0 is calculated using the equation (2).

In the next step S370, which corresponds to step S70 of 6 corresponds to, the estimated value K _{NOX of} the adsorption ratio of NOx, that of the NOx catalyst 13a at the time when the NOx discharged from the engine is the exhaust gas purifying catalyst device 13 happens, derived in accordance with the accumulated value SQ _{N (i + 1) of} the engine output NOx amount Q _N0 calculated in step S368. The diagram of 9 is used to estimate the adsorption ratio K _NOX . Alternatively, the calculation is performed using equation (3) or the following regression equation: K NOX (i + 1) = 1 - (1-K N1 ) × k 2 × {(1-α) × SQ N (i) + α × Q N (i) } where α is a constant.

In the next step S372, which corresponds to step S72 of 6 corresponds to, the estimated value K _{CAT of} the purification ratio of NOx by the three-way catalyst converter 13b from the diagram of 10 on the basis of the excess air ratio λ by the cleaning ratio estimation unit 136 of the 13 taken. Instead of estimating the cleaning ratio K _CAT using the diagram of 10 The cleaning ratio K _CAT can be determined briefly by determining whether the excess air ratio λ is within or outside a narrow excess air ratio range, as is the case with the first embodiment.

Further, in step S374, the step S74 of 6 corresponds to the NOx discharge ratio by the catalyst discharge NOx quantity estimation unit 137 of 13 based on the estimated value K _{NOX of} the adsorption ratio of NOx by the NOx catalyst 13a and the ge estimated K _CAT value of the NOx purification ratio by the three-way catalyst converter 13b calculated. Further, the estimated value Q _{NT of} the catalyst output NOx amount for each detection of the crank angle synchronization signal θ _{CR is} calculated according to the aforementioned equation (4) based on the NOx output ratio and the engine output NOx amount Q _N0 , which are performed in step S66 the engine output NOx quantity estimation unit 130 the 13 is calculated.

After calculating the estimated value Q _NT , control goes to step S216 14 further. In step S216, the comparator 138 of 13 determines whether the estimated value Q _{NT of} the catalyst _discharge NOx amount is larger than a predetermined threshold value Q _NT0 . If the result of the determination in step S216 is "NO", it is determined that the amount of NOx released into the atmosphere is equal to or less than a maximum allowable value, and control proceeds to step S218 to execute the lean-burn drive control.

On the other hand, if the result of the determination in step S216 is "YES", that is, if the catalyst discharge NOx amount Q _{NT is} larger than the predetermined threshold value Q _NT0 , the _{adsorbability of} the NOx catalyst becomes 13a considered saturated. In this case, control proceeds to step S212 to execute the fat burning drive control.

If a change is made from the lean burn engine to the fat burn engine when the NOx amount Q _NT becomes larger than the threshold value Q _NT0 , the amount of HC released by the engine 1 is released, larger than in the lean-burn state. The HC then reacts with NOx to that of the NOx catalyst 13a deoxidize adsorbed NOx. It follows that the amount of NOx released into the atmosphere is reduced and the NOx catalyst 13a can adsorb NOx again.

If it is determined in step S216 for the first time that the amount of NOx Q _{NT is} larger than the threshold value Q _NT0 and a change is made in the fat-burning drive control as described above, the time counter of the ECU becomes 23 started at this time to start counting the elapsed time from the start of the fat burning drive control.

As described above, if the NOx catalyst 13a is saturated with adsorbed NOx even if the lean burn drive condition is not satisfied, the fat burn drive is executed to deoxidize NOx. During this time, a sequence of steps S210, S214, S216 and S212 is carried out repeatedly. If the result of the determination in step S367 is that in FIGS 5 and 15 Subroutine "NO" shown and corresponding to step S214, ie, a predetermined time t _R does not pass after the start of the fat-burning drive control, the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is also updated in S368. It is therefore determined in step S216 that the catalyst discharge NOx amount Q _{NT is} still larger than the threshold value Q _NT0 . As a result, the fat-burning driving state is maintained for the predetermined time t _R so that the NOx is completely deoxidized.

If the predetermined time t _{R has passed} after the start of the fat burning drive control and the result of the determination in step S367 is "YES", control proceeds to step S376. In step S376, it is assumed that all of the NOx on the NOx catalyst 13a has been adsorbed, deoxidized, and a reset signal becomes the adsorption ratio estimation unit 135 of 13 is output, whereby the accumulated value SQ _{N (i + 1) of} the engine output NOx amount is reset to "0". As a result, the estimated value of the NOx adsorption ratio K _NOX derived in the next step S370 becomes 1.0, and the estimated value Q _{NT of} the catalyst discharge NOx amount calculated in step S374 becomes "0". In this case, control proceeds to step S218 to restart the lean burn drive control. This means that the fat burning drive control for deoxidizing NOx has ended.

Thereafter, when the estimated NOx adsorption ratio K _{NOX is decreased} again as the accumulated value SQ _{N (i + 1) of} the engine output NOx amount increases, the estimated value Q _{NT of} the catalyst output NOx amount increases again.

Will the drive state of the engine 1 Changes between the lean-burn state and the fat-burn state, the engine discharge NOx amount Q _N0 and the catalyst discharge NOx amount Q _{NT change} with the elapsed time as in FIG 16 shown. In 16 the one- _dot chain line indicates the engine output NOx amount Q _N0 , the solid line indicates the catalyst output NOx amount Q _NT , and the dashed area indicates the NOx adsorption amount or. Amount of cleaning by the exhaust gas purifying catalyst device 13 on.

As in 16 shown, the NOx purification amount is reduced by the exhaust gas purifying catalyst device 13 with the elapsed time during the lean-burn drive. Then, when the estimated value Q _{NT of} the catalyst _discharge NOx amount reaches the predetermined value Q _NT0 , when a time of, for example, t _{L1 has} elapsed from the start of the lean-burn engine, the engine drive state is changed from the lean-burn state (A) to the fat-burning state. Thereafter, the fat burning drive is maintained for the predetermined period of time t _R. During the fat burning drive all of the NOx catalyst 13a adsorbed NOx deoxidizes. If the predetermined time t _{R has passed} after the start of the fat-burning drive and the lean-burn state (B) has been set again, the NOx adsorption capacity of the NOx catalytic converter becomes 13a restored.

Further, since a change from the lean-burn state to the fat-burn state is made immediately after the catalyst discharge NOx amount Q _{NT reaches} the predetermined value Q _NT0 , the amount of NOx released into the atmosphere can always be equal to or less than the predetermined value Q _{NT0 be} pressed. As indicated, for example, by the time period t _{L1 of} the lean-burn combustion engine (A) and the time period t _L2 (≠ t _L1 ) of the lean-burn combustion engine (B), the time period t of the lean-burn combustion state is not always constant. That is, in the driving state in which the NOx discharge amount is small, the lean-burn drive is maintained for a relatively long period of time. The frequency of transition to the fat-burning engine is therefore small, making it possible to suppress deterioration in fuel economy and variation in torque. Further, in the case that the engine drive is carried out in such a manner that the engine drive range frequently changes between drive ranges with different target air-fuel ratios, a transition between the lean-burn engine and the rich-combustion engine is performed according to the drive state thus changed. Therefore, no problem arises even if the present invention is applied to such a motor drive.

For example, in the first embodiment the engine drive condition from the lean burn condition to the theoretical Ratio driving state changed where the air-fuel ratio is set to the theoretical air-fuel ratio, for example at the time of the accelerator drive or a heavy duty drive. Alternatively, a transition from the lean burn condition to the fat burn condition where that Air-fuel ratio is set smaller than the theoretical air-fuel ratio.

Furthermore, in the first embodiment, the determination as to whether the transition to the NOx-reduced drive should be made is made according to the result of a comparison of the estimated value Q _NT and the amount of catalyst discharge NOx (g / sec) with the threshold value Q _NT0 . However, the determination as to whether the transition to the NOx-reduced drive should be made can also be made according to the result of a comparison between an actually measured value or an estimated value that of the NOx catalyst 13a adsorbed amount of NOx and the saturated amount of adsorption, or according to the result of a determination associated with the release NOx concentration (PPM).

It is also possible to determine that the amount of adsorption of NOx by the NOx catalyst 13a has reached the saturated value, and perform the NOx-reduced drive when a predetermined period of time has passed from the start of the lean-burn drive. Preferably, the predetermined period of time is set so that the output NOx amount Q _NT does not exceed the predetermined value Q _NT0 .

Furthermore, the NOx-reduced drive the EGR amount increases and the ignition timing delayed to lower the combustion temperature. However, it is not necessary both processes simultaneously perform, and only one of these operations can be performed.

In the NOx discharge amount calculation subroutine the first embodiment are valued Values used, which are taken from different diagrams. It can however, actually measured values are used instead of the estimated values, the parts of the information correspond to that of different sensors is delivered.

Furthermore, in the first embodiment Acceleration determination (i.e., determining whether there is an acceleration drive request or does not exist) based on the opening speed of the Throttle valve performed. Alternatively, the acceleration determination can be based on a Feed information variables are performed, for example a variation in the supply air amount or a variation in the negative pressure of the supply air.

In the first embodiment, it is determined that the NOx catalyst 13a is saturated with adsorbed NOx when the catalyst _delivery NOx amount Q _N has exceeded the threshold value Q _NT0 . Instead, it is possible to include parts of the engine's load information (for example, amounts of fuel that the engine 1 to be accumulated) during the lean-burn drive, to derive the accumulated value therefrom and to determine that the NOx catalyst 13a is saturated with adsorbed NOx when the accumulated value exceeds a predetermined value. In this modification, the ECU 23 the lean burn accumulation through.

In the third embodiment, the air-fuel ratio is set to the super-lean air-fuel ratio AF _T and a predetermined amount of exhaust gases are recirculated by EGR to cause ignition failure. A sufficient effect can, however, only be achieved by setting the air-fuel ratio to the super-lean air-fuel ratio AF _T. Furthermore, an ignition failure can reasonably be caused simply by recirculating the exhaust gases from EGR. In this case, it is advantageous to recirculate the exhaust gases to a larger value.

In the second and third embodiments, the period during which the ignition failure drive is continued is set based on the number Nmis of ignition failures (ie, the accumulated number of generation of crank angle synchronization signals θ _CR ). However, considering the fact that the θ _CR signal generation number is proportional to the accumulated number of revolutions of the engine 1 , also possible to set the ignition failure occurrence period based on the accumulated number of engine revolutions derived from the θ _CR signal generation number by an engine revolution number detection device (e.g., the ECU 23 which with the crank angle sensor 18 cooperates to serve as an engine revolution number detector) is used. Further, the ignition failure drive can be maintained until a predetermined time has passed after the ignition failure control is started.

Further, in the second and third embodiments, the ignition failure is caused in a predetermined cylinder (for example, the first cylinder). However, the ignition failure can occur in a large number of cylinders and in particular also sequentially in all cylinders under the control of the ECU 23 caused.

Furthermore, in the second and third embodiments, it is determined that the NOx adsorption _{amount has} reached a saturated value when the NOx _{discharge amount} Q _{NT has reached} the threshold value Q _NT0 . Alternatively, it is possible to determine that the NOx adsorption amount has reached the saturated value when the elapsed time from the start of the lean-burn engine is that of the time counter in the ECU 23 is measured, has exceeded a predetermined time, or when the accumulated fuel injection amount during the lean-burn engine exceeds a predetermined value.

In the fourth embodiment, the air-fuel ratio is substantially set to the theoretical air-fuel ratio in the fat-burning drive control for deoxidizing adsorbed NOx. However, it is only necessary to have a reducing atmosphere around the NOx catalyst 13a to create around that contains HC. Therefore, the air-fuel ratio can be set to a value that is on the rich side in terms of the theoretical air-fuel ratio.

Further, in the fourth embodiment, the determination of whether a transition between the lean-burn engine and the fat-burn engine should be made is made according to the result of comparing the catalyst _discharge NOx amount Q _NT with the threshold value Q _NT0 . Alternatively, the need for a transition may be determined according to the result of a determination associated with the emission NOx concentration (PPM), etc. In each of the above embodiments, estimated values are used which are derived from various diagrams. However, actually measured values can also be used instead of the estimated values.

Furthermore, in each embodiment a six-cylinder in-line petrol engine used. The combustion control device however, the present invention can be applied to any type of internal combustion engine independently of the number of cylinders and type are applied. Furthermore, the feature of the first to fourth embodiments in the required Ways can be combined.

Claims (64)

Control device for an internal combustion engine ( 1 ) with an exhaust gas purification catalyst ( 13 ), which is in an exhaust pipe ( 14 ) of the internal combustion engine ( 1 ) is arranged, the exhaust gas purification catalyst ( 13 ) is operable in such a way that it adsorbs nitrogen oxide when the exhaust gas purification catalyst ( 13 ) incoming exhaust gases have a lean air-fuel ratio and that it deoxidizes adsorbed nitric oxide when the oxygen concentration of the incoming exhaust gases is reduced, characterized by an adsorption state estimator ( 23 . 32 ) which is a first nitrogen oxide delivery size estimator ( 33 ) to estimate a discharge amount of nitrogen oxide from the exhaust gas purifying catalyst ( 13 ) and the adsorption state estimator ( 23 . 32 ) estimates an adsorption state of nitrogen oxide by the exhaust gas purification catalyst ( 13 ) is adsorbed based on the estimated discharge amount of nitrogen oxide from the exhaust gas purifying catalyst ( 13 ); and a combustion deterioration device ( 23 . 36 ) to deteriorate a combustion state in the internal combustion engine ( 1 ) according to the adsorption state of the nitrogen oxide, which is from the adsorption state estimation device ( 32 ) was estimated when the engine was lean burn. A control device according to claim 1, wherein the adsorption state estimating means ( 23 . 32 ) an adsorption saturation determination device ( 32 ) to determine whether an amount (Q _NT ) of nitrogen oxide released from the exhaust gas purification catalyst ( 13a ) has been adsorbed, has reached a saturation range; and wherein the combustion condition deteriorating means ( 23 . 36 ) the combustion state of the internal combustion engine ( 1 ) worsened when the Adsorption saturation determination device ( 32 ) determines that the amount of nitrogen oxide released by the exhaust gas purification catalyst ( 13a ) has been adsorbed, has reached the saturation range in the lean combustion state. The control device according to claim 2, wherein the adsorption saturation determining means ( 32 ) determines that the amount of nitrogen oxide released by the exhaust gas purification catalyst ( 13 ) has reached the saturation range when the nitrogen oxide delivery amount (Q _NT ) by the nitrogen oxide delivery amount estimator ( 33 ); ( 130 . 135 . 136 . 137 ) is estimated to exceed a predetermined value (Q _NTO ). A control device according to claim 3, wherein the nitrogen oxide delivery amount estimation means ( 33 ); ( 130 . 135 . 136 . 137 ) a second nitrogen oxide delivery rate estimator ( 130 ) for estimating a quantity of nitrogen oxide (Q _NO ) released from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ), and an adsorption ratio estimator ( 135 ) to estimate an adsorption ratio (K _NOX ) of nitrogen oxide _generated by the exhaust gas purification catalyst ( 13a ) is adsorbed; and the first nitrogen oxide delivery amount estimator ( 33 ); ( 130 . 135 . 136 . 137 ) the amount (Q _NT ) of nitrogen oxide released from the exhaust gas purification catalyst ( 13a ) estimates the amount of nitrogen oxide delivered by the internal combustion engine (Q _NO ) ( 1 ) based on the second nitrogen oxide delivery rate estimator ( 130 ) and the adsorption ratio (K _NOX ) of the exhaust gas purification catalyst ( 13a ) adsorbed nitrogen oxide from the adsorption ratio estimator ( 135 ) is estimated. A control device according to claim 4, wherein the first nitrogen oxide delivery amount estimation means ( 130 . 135 . 136 . 137 ) a cleaning ratio estimator ( 136 ) for estimating a purification ratio (K _CAT ) of the nitrogen oxide which is generated by the exhaust gas purification catalytic converter ( 13b ) is cleaned; and the first nitrogen oxide delivery amount estimator ( 130 . 135 . 136 . 137 ) the amount (Q _NT ) of nitrogen oxide released from the exhaust gas purification catalyst ( 13 ) estimates the amount of nitrogen oxide delivered by the internal combustion engine (Q _NO ) ( 1 ) based on the second nitrogen oxide delivery rate estimator ( 130 ) is estimated, the adsorption ratio (K _NOX ) of the nitrogen oxide from the exhaust gas purification catalyst ( 13a ) which is adsorbed by the adsorption ratio estimator ( 135 ) and the purification ratio (K _CAT ) of the nitrogen oxide from the exhaust gas purification catalyst ( 13b ) which is cleaned by the cleaning ratio estimating device ( 136 ) is estimated. A control device according to claim 4, wherein the second nitrogen oxide delivery amount estimation means ( 130 ) the amount (Q _NO ) of nitrogen oxide released by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) based on the concentration (D _N ) of nitrogen oxide generated by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) and a supply information variable representing an amount (Qa) of supply air supplied to the internal combustion engine ( 1 ) is conducted. A control device according to claim 6, wherein the second nitrogen oxide delivery amount estimation means ( 130 ) estimates the concentration (D _N ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) that is based on an air-fuel ratio information variable (λ) that represents the air-fuel ratio of the air-fuel mixture that is sent to the internal combustion engine ( 1 ) is delivered. A control device according to claim 4, wherein the second nitrogen oxide delivery amount estimation means ( 130 ) the amount (Q _NO ) of nitrogen oxide released by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) corrected by the second nitrogen oxide delivery rate estimator ( 130 ) according to the ignition timing (θ _Ig ) of the internal combustion engine ( 1 ) is estimated. A control device according to claim 4, wherein the second nitrogen oxide delivery amount estimation means ( 130 ) the amount (Q _NO ) of nitrogen oxide released by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) corrected by the second nitrogen oxide delivery rate estimator ( 130 ) is estimated according to an amount of exhaust gases to the internal combustion engine ( 1 ) recirculated. A control device according to claim 4, wherein the adsorption ratio estimator ( 135 ) estimates the adsorption ratio (K _NOX ) of nitrogen oxide from the exhaust gas purification catalyst ( 13a ) is adsorbed, which is based on the total amount (∫Q _NO dt) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust gas purification catalyst ( 13 ) based on a period of time that begins when the lean burn condition starts and ends when the fat burn condition changes. The control device according to claim 2, wherein the adsorption saturation determining means ( 32 ) a lean burn period measuring device ( 23 ) for measuring a lean-burn period during which the internal combustion engine is operating in the lean-burn state; and the adsorption saturation determination device ( 32 ) determines that the amount of nitrogen oxide adsorbed by the exhaust gas purification catalyst has reached the saturation range when the lean-burn period by the lean-burn period meter ( 23 ) is measured, exceeds a predetermined value (t _R ). The control device according to claim 2, wherein the adsorption saturation determining means ( 32 ) a lean burn accumulator ( 23 ) for the accumulation of load information on the internal combustion engine ( 1 ) operated in the lean-burn state to thereby derive an accumulated value of the load information; and the adsorption saturation determination device ( 32 ) determines that the amount of nitrogen oxide released by the exhaust gas purification catalyst ( 13a ) has reached the saturation range when the accumulated value of the load information generated by the lean-burn drive accumulator ( 23 ) is derived, exceeds a predetermined value. The control device according to claim 12, wherein the load information includes an amount of fuel that the internal combustion engine ( 1 ) is supplied. A control device according to claim 1, wherein combustion condition deterioration means ( 36 ) lowers a combustion temperature of the air-fuel mixture, which leads to the internal combustion engine ( 1 ) is supplied according to the adsorption state of the nitrogen oxide, which is from the adsorption state estimator ( 32 ) is estimated. A control device according to claim 14, further comprising acceleration determining means ( 37 ) to determine whether the internal combustion engine ( 1 ) is in an acceleration drive state in which the load information indicating a load state of the internal combustion engine is compared with an acceleration determination threshold value (A _th ); an air-fuel ratio setting device ( 30 . 31 ) for setting the air-fuel ratio to a value equal to or richer than the theoretical air-fuel ratio when the acceleration determining means ( 37 ) determines that the internal combustion engine ( 1 ) is in the acceleration drive state; and a threshold changing device ( 37 ) for changing the acceleration determination threshold (A _th ) according to the adsorption state of the nitrogen oxide, which is determined by the adsorption state estimator ( 32 ) is estimated. The control device according to claim 15, wherein the adsorption state estimating means ( 23 . 32 ) an adsorption saturation determination device ( 32 ) to determine whether an amount of nitrogen oxide released from the exhaust gas purification catalyst ( 13a ) is adsorbed, has reached a saturation range; and the threshold changing device ( 37 ) changes the acceleration determination threshold (A _th ) in order for the acceleration determination device ( 37 ) to simplify the determination that the internal combustion engine ( 1 ) is in the acceleration drive state when the adsorption saturation determining means ( 32 ) determines that the amount of nitrogen oxide released by the exhaust gas purification catalyst ( 13a ) is adsorbed, has reached the saturation range. The control device according to claim 15, wherein the acceleration determining means ( 37 ) at least one operating state variable which represents an operating state of the internal combustion engine ( 1 ) is compared with the acceleration determination threshold (A _th ) to determine whether the engine ( 1 ) is in the acceleration drive state. A control device according to claim 17, wherein the acceleration determining means ( 37 ) determines whether the internal combustion engine ( 1 ) is in the acceleration drive state by an operating speed of an output operating device ( 7 ), which sets an output of the internal combustion engine, is compared with the acceleration determination threshold value (A _th ). A control device according to claim 17, wherein the acceleration determining means ( 37 ) determines whether the internal combustion engine ( 1 ) is in the acceleration drive state by an operating state variable, which actuates an accelerator pedal ( 7a ) with which the acceleration determination threshold value (A _th ) is compared. The control device according to claim 15, wherein the acceleration determining means ( 37 ) determines whether the internal combustion engine ( 1 ) is in the acceleration drive state by a supply information variable indicating a supply air state of the internal combustion engine ( 1 ) indicates to which the acceleration determination threshold value (A _th ) is compared. A control device according to claim 20, wherein the supply information variable indicates a change in an amount (Qa) of supply air supplied to the internal combustion engine ( 1 ) is supplied. A control device according to claim 20, in which The supply information variable indicates a change in the pressure of the supply air that is applied to the internal combustion engine ( 1 ) is supplied. The control device according to claim 14, wherein the combustion condition deteriorating means ( 36 ) an ignition timing device ( 24 ) for setting the ignition timing (θ _Ig ) of the internal combustion engine ( 1 ), and the combustion condition deteriorating means ( 36 ) lowers the combustion temperature by using the ignition timing ( 24 ) is instructed to retard the ignition timing (θ _Ig ). The control device according to claim 14, wherein the combustion condition deteriorating means ( 36 ) an exhaust gas recirculation device ( 26 . 27 ) for recirculating exhaust gases from the internal combustion engine ( 1 ) to a feed system ( 2 ) of the motor ( 1 ), and the combustion condition deteriorating means ( 36 ) lowers the combustion temperature by the exhaust gas recirculation device ( 26 . 27 ) is instructed to increase the recirculation amount of the exhaust gas. The control device according to claim 14, wherein the combustion condition deteriorating means ( 23 ) an air-fuel ratio setting device ( 323 . 138 ) for adjusting the air-fuel ratio of the air-fuel mixture that is to the internal combustion engine ( 1 ) and the combustion condition deterioration device ( 22 ) lowers the combustion temperature by using the air-fuel ratio setting device ( 323 . 138 ) is instructed to change the air-fuel ratio to a lean side. The control device according to claim 1, wherein the combustion condition deteriorating means ( 23 ) the deterioration of the combustion state of the internal combustion engine ( 1 ) for a predetermined period of time (t _R ). The control device according to claim 26, wherein the combustion condition deteriorating means ( 23 ) an accumulation device ( 18 . 23 ) has an accumulated number of revolutions of the internal combustion engine ( 1 ) at and after the start of the deterioration of the combustion state in the internal combustion engine ( 1 ) to derive; and the combustion deterioration device ( 23 ) the deterioration of the combustion state of the internal combustion engine ( 1 ) until the accumulated number of revolutions by the accumulator ( 18 . 23 ) is derived, a predetermined number of revolutions is reached. The control device according to claim 1, wherein the combustion condition deteriorating means ( 23 ) deteriorates the combustion state of the internal combustion engine 1 by an ignition failure (misfire) of the internal combustion engine ( 1 ) is caused. The control device according to claim 28, wherein the combustion condition deteriorating means ( 23 ) the ignition failure in the internal combustion engine ( 1 ) caused intermittently in which the ignition of the internal combustion engine ( 1 ) is inhibited intermittently. The control device according to claim 28, wherein the combustion condition deteriorating means ( 23 ) the ignition failure in the internal combustion engine ( 1 ) caused intermittently by the air-fuel ratio of the air-fuel mixture that the internal combustion engine ( 1 ) is set toward a lean air-fuel ratio (AF _T ) that is larger than an air-fuel ratio that corresponds to a combustion limit of the internal combustion engine 1 equivalent. The control device according to claim 28, wherein the combustion condition deteriorating means ( 23 ) an exhaust gas recirculation device ( 26 . 27 ) for recirculating exhaust gases from the internal combustion engine ( 1 ) to a feed system ( 2 ), and the combustion condition deteriorating means ( 23 ) the ignition failure in the internal combustion engine 1 caused by a predetermined amount of exhaust gases by means of the exhaust gas recirculation device ( 26 . 27 ) is recirculated. The control device according to claim 28, wherein the combustion condition deteriorating means ( 23 ) the ignition failure in part of a plurality of cylinders of the internal combustion engine ( 1 ) caused. Internal combustion engine control method for reducing the emission of nitrogen oxide into the atmosphere, wherein nitrogen oxide contained in exhaust gases generated by an internal combustion engine ( 1 ) is emitted by an exhaust gas purification catalyst ( 13 ) is adsorbed in the exhaust pipe ( 14 ) of the internal combustion engine ( 1 ) is arranged when the motor ( 1 ) is in a lean-burn state where the air-fuel ratio of an air-fuel mixture that the engine ( 1 ) is leaner than a theoretical air-fuel ratio, the adsorbed nitrogen oxide by means of the exhaust gas purification catalyst ( 13 ) is deoxidized when the internal combustion engine ( 1 ) is in a fat burning state where the air-fuel ratio is the same or richer than the theoretical air-fuel ratio, with the following steps: a) Estimating (S30, S32) an adsorption state of the nitrogen oxide generated by the exhaust gas purification catalyst ( 13 ) is adsorbed, wherein step a) a step a0) of estimating a discharge amount of nitrogen oxide from the exhaust gas purification catalyst ( 13 ) and estimating the adsorption state of nitrogen oxide adsorbed by the exhaust gas purifying catalyst based on the estimated discharge amount of nitrogen oxide from the exhaust gas purifying catalyst ( 13 ); and b) deterioration (S30, S32) of a combustion state of the internal combustion engine ( 1 ) according to the adsorption state of the nitrogen oxide estimated in step a) (S14) when the engine ( 1 ) is in the lean combustion state. The control method according to claim 33, wherein step a) (S14, S16) includes a step of a1), wherein it is determined (S16) whether an amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13 ) is adsorbed, has reached a saturation range; and step b) deterioration (S30, S32) of the combustion state of the internal combustion engine ( 1 ) includes when it is determined in step a) (S16) that the amount of nitrogen oxide is that from the exhaust gas purifying catalyst ( 13a ) is adsorbed, has reached the saturation range in the lean combustion state. The control method according to claim 34, wherein step a) (S14, S16) includes a step of a0)), wherein a discharge amount (Q _NT ) of nitrogen oxide from the exhaust gas purifying catalyst ( 13 ) is estimated (S14), and step a1) (S16) determines that the amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) has reached the saturation range when the estimated amount (N _NT ) of nitrogen oxide released from the exhaust gas _{purifying catalyst} exceeds a predetermined value (Q _NTO ). The control method according to claim 34, wherein step a0) (514, S16) includes the steps of: a01) estimating (S66) the amount of discharge (Q _NO ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ), a02) Estimating (S70) an adsorption ratio (K _NOX ) of the nitrogen oxide generated by the exhaust gas purifying catalyst ( 13a ) is adsorbed, and a03) estimating (S74) a discharge amount (Q _NT ) of nitrogen oxide from the exhaust gas purification catalyst ( 13 ), which is based on the estimated amount (Q _NO ) of nitrogen oxide generated by the internal combustion engine ( 1 ) and the estimated adsorption ratio (K _NOX ) of the nitrogen oxide generated by the exhaust gas purification catalyst ( 13a ) is adsorbed. The control method according to claim 36, wherein step a0) (S14) further comprises step a04), wherein a purification ratio (K _CAT ) of the nitrogen oxide estimated from the exhaust gas purifying catalyst ( 13b ) is cleaned, and step a03) (S74) the discharge amount (Q _NT ) of nitrogen oxide from the exhaust gas purifying catalyst ( 13 ) based on the estimated amount (Q _NO ) of nitrogen oxide generated by the internal combustion engine ( 1 ) is given, the estimated adsorption ratio (K _NOX ) of the nitrogen oxide, which is from the exhaust gas purification catalyst ( 13a ) and the estimated purification ratio (K _CAT ) of the nitrogen oxide generated by the exhaust gas purification catalyst ( 13b ) is cleaned. The control method according to claim 36, wherein step a01) (S14) estimates (S66) the amount of discharge (Q _NO ) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ), which is based on the concentration (D _N ) of the nitrogen oxide emitted by the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ), and a supply information variable representing an amount (Qa) of supply air that the engine ( 1 ) is supplied. The control method according to claim 38, wherein step a01) (S14) includes estimating (S60) the concentration (D _N ) of the nitrogen oxide released from the internal combustion engine ( 1 ) to the exhaust pipe ( 14 ) that is based on the air-fuel ratio information variable (λ) that represents the air-fuel ratio of the air-fuel mixture that the internal combustion engine ( 1 ) is supplied. The control method according to claim 36, wherein the step a0) (S14) further comprises a step a04) of correcting (S62) the estimated discharge amount (Q _NO ) of nitrogen oxide from the internal combustion engine ( 1 ) according to the ignition timing (θ _Ig ) of the internal combustion engine ( 1 ) contains. The control method according to claim 36, wherein the step a0) (S14) further comprises a step a04) of correcting the estimated discharge amount (Q _NO ) of nitrogen oxide from the internal combustion engine ( 1 ) according to an amount of exhaust gases that are supplied to the internal combustion engine ( 1 ) is recirculated there. The control method according to claim 36, wherein step a02) includes estimating the adsorption ratio (K _NOX ) of the nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) is adsorbed, which is based on a total amount (∫Q _NO dt) of nitrogen oxide from the internal combustion engine ( 1 ) to the exhaust gas purification catalyst ( 13 ) based on a period of time that begins at the start of the lean burn state and ends upon the change to the fat burn state. The control method according to claim 36, wherein step a) (S70) includes step a0) of measuring a lean-burn period during which the internal combustion engine ( 1 ) operates in the lean-burn state, and step a1) determines that the amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) has reached the saturation range when the measured lean-burn period exceeds a predetermined value (t _R ). The control method according to claim 34, wherein step a) (S14) comprises a step a0) of accumulating the load information of the internal combustion engine ( 1 ) driven during the lean-burn state, and step a1) determines that the amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) is adsorbed, has reached the saturation range when the load information thus accumulated exceeds a predetermined value. The control method according to claim 44, wherein the load information includes an amount of fuel that the internal combustion engine ( 1 ) is supplied. The control method according to claim 33, wherein the step b) (S30, S32) includes lowering a combustion temperature of the air-fuel mixture that the combustion engine ( 1 ) is supplied according to the adsorption state of the nitrogen oxide, which is estimated in step a) (S14). The control method of claim 46, further comprising: c) determining (S10) whether the internal combustion engine ( 1 ) is in an acceleration drive state by comparing the load information indicating a load state of the internal combustion engine with an acceleration determination threshold (A _th ); d) setting (S20) the air-fuel ratio to a value equal to or richer than the theoretical air-fuel ratio when step c) (S10) determines that the engine ( 1 ) is in an acceleration drive state; and e) changing (S34, S44) the acceleration determination threshold value in accordance with the adsorption state of the nitrogen oxide, which is estimated in step a) (S14). A control method according to claim 47, wherein step a) (S14, S16) includes determining (S16) whether the amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) is adsorbed, has reached the saturation range; and step e) (S34, S44) includes changing the acceleration determination threshold to make it easier to determine in step c) (S10) that the engine ( 1 ) is in the acceleration drive state when step a) (S16) determines that the amount of nitrogen oxide released from the exhaust gas purifying catalyst ( 13a ) is adsorbed, has reached the saturation range. The control method according to claim 47, wherein step c) (S10) includes determining whether the engine ( 1 ) is in the acceleration drive state by at least one operating state variable which represents an operating state of the internal combustion engine ( 1 ) with which the acceleration determination threshold value (A _th ) is compared. The control method according to claim 49, wherein step c) (S10) compares an operating speed of an output operating device ( 7 ) which have an output of the internal combustion engine ( 1 ) with which the acceleration determination threshold (A _th ) contains. The control method according to claim 49, wherein step c) (S10) includes making the determination whether the internal combustion engine ( 1 ) is in the acceleration drive state by the operating state variable, which is the actuation of an accelerator pedal ( 7a ) is compared with the acceleration determination value (A _th ). The control method according to claim 47, wherein step c) (S10) includes making the determination of whether the internal combustion engine ( 1 ) is in the acceleration drive state by the supply information variable indicating a supply air state of the internal combustion engine ( 1 ) indicates with which the acceleration determination threshold value is compared. The control method according to claim 52, wherein the supply information variable indicates a change in an amount (Qa) of supply air that is supplied to the internal combustion engine ( 1 ) is supplied. A control method according to claim 52, wherein the supply information variable indicates a change in the pressure of the supply air which is applied to the internal combustion engine ( 1 ) is supplied. The control method according to claim 46, wherein step b) (S30, S32) includes lowering the combustion temperature by (S32) the ignition timing (θ _Ig ) of the internal combustion engine ( 1 ) is delayed. The control method according to claim 46, wherein step b) (S30, S32) includes a step of lowering the combustion temperature by a recirculation amount of exhaust gases from the internal combustion engine ( 1 ) to a feed system ( 2 ) of the engine via an exhaust gas recirculation device ( 26 . 27 ) is increased. 46. The control method according to claim 46, wherein step b) (S130, S132, S134) includes lowering the combustion temperature by changing (S134) the air-fuel ratio of the air-fuel mixture containing the internal combustion engine ( 1 ) is fed to a lean side. The control method according to claim 33, wherein step b) maintaining (S24) deterioration of the combustion state of the internal combustion engine ( 1 ) for a predetermined period of time (t _R ). The control method of claim 58, wherein step b) includes the steps of: b1) deriving an accumulated number of revolutions of the internal combustion engine ( 1 ) at and after the start of the deterioration of the combustion state in the engine ( 1 ), and b2) maintaining the deterioration of the combustion state of the internal combustion engine ( 1 ) until the accumulated number of revolutions reaches a predetermined number of revolutions. The control method according to claim 33, wherein step b) deteriorating the combustion state of the internal combustion engine by causing an ignition failure (S116, S134) in the engine ( 1 ) contains. A control method according to claim 60, wherein step b) intermittently causing the ignition failure (S116) in the internal combustion engine ( 1 ) by intermittent inhibition of the ignition in the internal combustion engine ( 1 ) contains. A control method according to claim 60, wherein step b) intermittently causing the ignition failure in the internal combustion engine ( 1 ) contains, by the air-fuel ratio of the air-fuel mixture, which the internal combustion engine ( 1 ) is set to a lean air-fuel ratio (AFT) which is greater than an air-fuel ratio which corresponds to a combustion limit of the internal combustion engine ( 1 ) corresponds. A control method according to claim 60, wherein step b) causes the ignition failure in the internal combustion engine ( 1 ) by adding a predetermined amount of exhaust gases to a delivery system ( 2 ) of the internal combustion engine ( 1 ) via an exhaust gas recirculation device ( 26 . 27 ) is recirculated. The control method according to claim 60, wherein step b) causes the ignition failure in a part of a plurality of cylinders of the internal combustion engine ( 1 ) contains.