JPH09125938A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an engine for reducing the NOx concentration of exhaust gases liable to increase, due to the deterioration or the failure of a catalyst for purifying exhaust gases by computing a catalyst purification rate from the NOx concentration before and after the catalyst, and changing an engine operation mode on the basis of the purification rate. SOLUTION: NOx sensors 26 and 27 before and after a catalyst CAT are provided upstream and downstream of a catalyst device 25 laid on the intermediate part of an exhaust pipe 21, and output signals from the sensors 26 and 27 are sent to a control unit 15, together with signals from other various sensors or the like. A purification rate is, then, calculated from the values of NOx concentration before and after the catalyst CAT. Thereafter, judgement is made as to whether the purification concentration rate corresponds to a stoichiometric mixture or a lean condition, and in the case of the lean condition, the deterioration of a catalyst function is identified, when the purification rate is equal to or below the preset value. On the other hand, in the case of the stoichiometric mixture, the deterioration of the catalyst function is identified, when the purification rate is equal to or below the preset value. Then, determination is made as to whether in a lean or stoichiometric mixture mode operation is made, depending on a catalyst deterioration pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine control device, and more particularly to an engine control device that copes with an increase in emission of nitrogen oxides due to deterioration and damage of a catalyst.

[0002]

2. Description of the Related Art Conventionally, from the viewpoint of environmental protection, regulations have been made on each component of exhaust gas emitted from an engine of a vehicle in order to prevent air pollution. Various proposals have been made to efficiently purify the oil. For example, as a means for purifying nitrogen oxides (hereinafter referred to as NOx) in the exhaust gas, a catalyst device is provided in the exhaust pipe of the engine, or a part of the exhaust gas in the exhaust pipe is taken into an intake manifold. There is a case where an exhaust gas recirculation device (EGR device) that recirculates into the air is provided.

Accurate knowledge of the functions and operating states of each of the devices installed in the engine is important for efficient engine operation control and clearing the exhaust gas regulations, and engine control. It is also important in improving the accuracy of. As a means for detecting the function / operation state of each device (including deterioration or failure of the device), a NOx sensor is arranged in the exhaust pipe to detect the NOx concentration of exhaust gas and to know the function / operation state. Is being done. For example, as described in Japanese Utility Model Laid-Open No. 64-56554, a NOx sensor is installed in the exhaust pipe near the cylinder outlet of the engine, the NOx sensor detects the NOx concentration in the exhaust gas, and the engine operates. The reference NOx concentration predetermined by the state and the detection N
There is one that diagnoses a failure of the EGR device of the engine by comparing it with the Ox concentration.

[0004]

By the way, in the above-mentioned conventional diagnosis method, since the NOx concentration in front of the catalyst can be detected, an increase in the NOx concentration due to the EGR device is detected to detect the function / operation state of the EGR device. E of deterioration, breakdown, etc.
Although the GR device can be diagnosed, the catalyst device installed in the exhaust pipe downstream of the NOx sensor cannot be diagnosed. That is, as long as the NOx concentration before the catalyst device is within the predetermined range, the purification rate of the catalyst decreases,
There is a problem that the NOx concentration cannot be detected even if the NOx concentration in the final exhaust gas increases.

Further, the catalyst itself used in the catalyst device is
The purification rate varies depending on the operating state of the engine, that is, the difference in the air-fuel ratio, and the reduction in the purification rate due to its deterioration also varies depending on the air-fuel ratio. In order to operate with a low NOx concentration, it is necessary to control the operation based on the state of deterioration or damage of the catalyst itself.

The present invention has been made in view of such problems, and an object thereof is to increase the NOx concentration after the catalyst finally released into the atmosphere due to deterioration or damage of the catalyst. At this time, it is an object of the present invention to provide an engine control device that enables diagnosis of deterioration or failure of a catalyst, and enables engine control that reduces the NOx concentration of exhaust gas that increases due to deterioration or failure of the catalyst.

[0007]

[Means for Solving the Problems] To achieve the above object,
A control device for an internal combustion engine according to the present invention comprises a catalyst for purifying exhaust gas, a device for measuring nitrogen oxide concentrations in front and rear portions of the catalyst, and a catalyst diagnostic device, and the catalyst diagnostic device passes through the catalyst diagnostic device. It is characterized in that it comprises means for calculating the purification rate of the catalyst from the nitrogen oxide concentrations of the exhaust gas before and after the catalyst, and means for changing the operating state of the engine based on the purification rate.

In a more specific aspect, the means for changing the operating state of the engine is a means for changing the air-fuel ratio, ignition timing, fuel injection timing, or intake air flow rate, or a plurality of such means. And a means for changing the operating state of the engine, when the purification rate becomes a predetermined value or less during operation with lean air-fuel ratio, it is changed to stoichiometric. The means for calculating the purification rate calculates the purification rate during operation in stoichiometry and the purification rate during operation in lean, and when the purification rate in lean is below a predetermined value, the operation is performed in stoichiometry and even in stoichiometry. However, it is characterized by running lean when the purification rate becomes less than a predetermined value.

Further, the catalyst diagnosing device is provided with means for judging catalyst deterioration when the calculated purification rate is less than or equal to a predetermined value and storing information on the catalyst degradation, and the calculated purification rate is predetermined. It is characterized in that it is provided with means for turning on a warning lamp or displaying information on catalyst deterioration when it is determined that the value is less than or equal to a value.

The engine control device according to the present invention, which is constructed as described above, is arranged in front of and behind the catalyst when the NOx concentration after the catalyst finally released to the atmosphere increases due to deterioration or damage of the catalyst. A device for measuring the concentration of NOx of
By the means for calculating the purification rate of the catalyst from the NOx concentration before and after passing through the catalyst, the failure diagnosis of the catalyst can be performed depending on whether the purification rate of the monitored catalyst is larger or smaller than a predetermined value. . Further, when the purification rate of the catalyst becomes smaller than a predetermined value, NOx of exhaust gas from the engine
It is possible to perform control to change the operating state of the engine (lean or stoichiometric operation) so as to reduce the concentration.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an engine control device of the present invention will be described in detail below with reference to the drawings.
FIG. 1 shows the entire configuration of an engine and a control device for the engine according to the present embodiment.

Each cylinder of the engine 7 has a piston 7a,
A combustion chamber 7c composed of a cylinder 7b is arranged, and an intake pipe 8 and an exhaust pipe 21 are connected to the upper portion of the combustion chamber 7c. The air sucked into each cylinder of the engine 7 is taken in from an inlet portion 2 of an air cleaner 1 connected to the intake pipe 8, and an air flow meter 3 and a throttle valve accommodating a throttle valve for controlling the intake air flow rate are accommodated. Through body 5, collector 6
to go into. The intake air entering the collector 6 is transferred to the engine 7
Distributed to each intake pipe 8 connected to each cylinder 7b of
It is guided into the cylinder 7b.

Fuel such as gasoline is stored in the fuel tank 9
Is sucked and pressurized by the fuel pump 10, and then supplied to the fuel system in which the fuel damper 11, the fuel filter 12, the fuel injection valve (injector) 13, and the fuel pressure regulator 14 are piped. The fuel is regulated to a constant pressure by the fuel pressure regulator 14, and the injector 1 provided in the intake pipe 8 of each cylinder 7b.
3 is injected into the intake pipe 8. Here, the injection of fuel from the injector 13 may be a method of injecting into the intake pipe as shown in the figure, or a method of directly injecting into the cylinders 7c.

A control unit 15 is attached to the engine 7, which takes in detection signals from various sensors described later and controls the engine 7 based on the detection results. The air flow meter 3 detects the intake flow rate and outputs a detection signal to the control unit 15. A throttle sensor 18 for detecting the opening of the throttle valve is attached to the section of the throttle body 5, and the detection output is also input to the control unit 15.

The distributor 16 has a built-in crank angle sensor (not shown). The crank angle sensor is for detecting a reference angle signal REF indicating the rotational position of the crankshaft of the engine 7 and a rotational signal (rotation speed). Angle signal PO
S is detected, and the detection signal is detected by the control unit 15
Output to The ignition coil 17 ignites the ignition plug 23 via the distributor 16.

An A / F sensor 20 is arranged in the exhaust pipe 21, and a detection signal detected by the A / F sensor 20 is also input to the control unit 15. Here, the A / F sensor 20 is for detecting an actual operating air-fuel ratio, and may be of a type that outputs a linear output with respect to the detected air-fuel ratio, or if it is in a rich state with respect to a predetermined air-fuel ratio. Alternatively, it may be a type that detects whether it is in a thin state.

A water temperature sensor 22 is arranged in the cylinder 7b of the engine 7, and a detection signal of the water temperature sensor is input to the control unit 15. A catalyst device 25 is provided in the middle of the exhaust pipe 21,
Purifies CO, HC, NOx, etc. in the exhaust gas. The before-catalyst (CAT) NOx sensor 26 detects the NOx concentration discharged from the engine 7, and the after-catalyst (CAT) NOx sensor 27 detects the NOx concentration after being purified by the catalyst device.

Main parts of the control unit 15 are central processing units MPU, ROM, RA as shown in FIG.
M and an I / O LSI including an A / D converter, etc., and receives signals from the various sensors or the like for detecting the operating state of the engine 7 as an input and executes predetermined arithmetic processing, Various control signals calculated as the result of this calculation are output, and the injector 13 and the ignition coil 1 are output.
7, a predetermined control signal is output to the fuel pump 10, etc., and fuel supply amount control, ignition timing control, etc. are executed.

FIG. 3 shows the characteristics of the engine 7 with respect to the air-fuel ratio (set from stoichiometric to lean side) of the air-fuel mixture sucked into the engine 7 in the engine 7 and the apparatus for controlling the engine having the above-described configuration. As shown. That is, when the air-fuel ratio is made lean while keeping the torque and the engine rotation constant, the intake air amount increases, so the fuel consumption rate improves and the fuel consumption can be reduced. On the other hand, the NOx emission concentration decreases because the combustion temperature decreases when the air-fuel ratio becomes lean, and the combustion stability that can be quantitatively grasped by the torque fluctuation is that the ignitability of the air-fuel mixture becomes greater when the air-fuel ratio becomes lean. Since it worsens, it gradually deteriorates to a certain air-fuel ratio, and if it exceeds it, the ignitability is extremely lowered, and there is a tendency that it suddenly deteriorates.
As described above, the combustion stability and NOx emission concentration in the lean region largely depend on the air-fuel ratio. Therefore, in order to operate lean, when operating at an air-fuel ratio close to the combustion stability allowable limit,
It has good fuel economy and low NOx emissions. In the example of FIG. 3, the vicinity of the air-fuel ratio 24 is suitable for lean operation.

FIG. 4 shows the NOx concentration and NO with respect to the air-fuel ratio.
It shows the relationship of the purification rate of x catalyst. here,
The case where the catalyst (CAT) is normal is shown. The catalyst considered here is of a type that has a three-way function in stoichiometry and temporarily adsorbs NOx lean.

The NOx concentration 41 of the exhaust gas before the catalyst (CAT) increases from stoichiometric to around the air-fuel ratio 17,
When it becomes leaner than that, it tends to decrease. NO
The x purification rate shows a purification rate close to 100% at an air-fuel ratio richer than stoichiometry, but the oxygen becomes excessive as it becomes thinner than stoichiometry, so the purification rate drops to around 50%. Comparing the stoichiometric and lean (for example, air-fuel ratio 24) NOx concentrations, the NOx concentration at stoichiometry is 4A, which is higher than 4C at the time of lean, but at the NOx concentration 42 of the exhaust gas after the catalyst (CAT). Since the purification rate of stoichiometry is high, it is reversed, and stoichiometric concentration 4B is lower than lean concentration 4D.

Next, FIG. 5 shows that the catalyst (CA
T) Shows a case where the performance is deteriorated. Assuming a case where the NOx adsorption / purification performance deteriorates only when the catalyst (CAT) is in a lean operating state, the purification rate shows a value close to 100% in stoichiometry, but drops to nearly 0% in lean, so the catalyst ( If CAT) deteriorates in this way, it will eventually be released to the atmosphere unless it is operated in a stoichiometric NOx concentration of 5B, rather than in a lean NOx concentration of 5D after the catalyst (CAT). NO
There is a possibility that the x concentration becomes high and the exhaust gas regulation value is significantly exceeded.

Therefore, when deterioration of the catalyst (CAT) as shown in FIG. 5 is detected, it is necessary to perform control to switch to stoichiometric operation even during lean operation. A specific example of such control will be described later based on the flowchart of FIG. 7 and the timing chart of FIG. FIG. 6 illustrates a case where the performance of the catalyst (CAT) is deteriorated over the entire range from stoichiometric to lean.

In the example of FIG. 6, due to the physical loss of the catalyst (CAT), a bypass passage is formed from before the catalyst (CAT) to after the catalyst (CAT), and the purification rate is significantly improved regardless of whether it is stoichiometric or lean. It is assumed that the rate has dropped. As shown in FIG. 6, the purification rate drops from around stoichiometric to around 0% over the lean range, so when the catalyst (CAT) deteriorates in this way,
In order to reduce the NOx concentration finally released to the atmosphere as much as possible, it is better to operate lean with NOx concentration of 6D than to operate stoichiometric with NOx concentration of 6B after the catalyst (CAT).

Therefore, when deterioration of the catalyst (CAT) as shown in FIG. 6 is detected, it is necessary to perform control to switch to lean operation even during stoichiometric operation. A specific example will be described later based on the flowchart of FIG. 7 and the timing chart of FIG. FIG. 7 is a control flowchart of the engine control device of the present embodiment. First,
In step 701, a regular interrupt is applied to step 702.
Proceed to. In step 702, NO before the catalyst (CAT)
Take in the value of x concentration NOx-IN. Specifically, catalyst C
The signal from the NOx sensor 26 before AT is A / D converted to N
Converted to Ox concentration and imported. Next, at step 703, the value of NOx concentration NOx-OUT after the catalyst CAT is taken in, and the routine proceeds to step 704. In the step 704,
NOx concentration taken in NOx-IN and NOx-O
The purification rate η is calculated from UT.

The subsequent steps from step 705 to step 718 are the parts for diagnosing the deterioration of the respective catalysts during stoichiometry and lean. Step 705
Then, branching occurs when the air-fuel ratio is 15 or less, and stoichiometric and lean are separated here. If lean, step 7
When the purification rate η is equal to or less than the predetermined value η _L , it is determined that the performance of the catalyst is deteriorated, and the counter CNT is determined in step 708. L
Is incremented. Here, the counter is used so as not to be erroneously determined to be catalyst performance deterioration due to a momentary reduction in purification rate during transients and an apparent reduction in purification rate due to noise.
This is because the deterioration is determined only when the purification rate decreases for a certain period of time.

On the other hand, if it is judged at step 706 that the purification rate has not decreased, at step 709 the counter CNT is reached.
L is cleared to 0. Then, in step 712, the counter CNT If L is determined to be the predetermined number N _L or more, the process proceeds to step 714, and the flag L is set to 1 in step 714.
Then, it is determined that the performance of the catalyst is lean. Counter CNT If it is determined that _{L is} equal to or less than the predetermined number N _L , the process proceeds to step 715, and the flag L is set to 0 in step 715, and it is determined that the lean catalyst performance is normal.

Returning to step 705, the air-fuel ratio becomes 15
Below, the process when it is determined to be stoichiometric will be described. In step 707, if the purification rate η is equal to or less than the predetermined value η _S , it is determined that the catalyst performance is deteriorated, the process proceeds to step 710, and in step 710, the counter CNT is counted. Increment S. Here, the counter is used for the same reason as in the lean case.

On the other hand, in step 707, the purification rate is the predetermined value η.
_If it is determined that the value is not lower than _S , the process proceeds to step 711, and in step 711, the counter CNT S is cleared to 0. Then, in step 713, the counter CNT
If it is determined that S is equal to or greater than the predetermined number Ns, the process proceeds to step 716, and in step 716, the flag S is set to 1 and it is determined that the catalyst performance has deteriorated due to stoichiometry. Counter CN
T If S is equal to or less than the predetermined number N _S , the process proceeds to step 717, the flag S is set to 0, and it is determined that the catalyst performance in stoichiometry is normal.

During the following steps 718 to 723, it is determined whether to operate lean or stoichiometric according to the deterioration pattern of the catalyst. If the flag L is not 1 in step 718, the purification performance in lean is normal, so the routine proceeds to step 722, and in step 722 it is decided to operate in lean.

When it is determined in step 718 that the flag L is 1, it is determined that the lean purification performance has deteriorated, and the process proceeds to step 719. In step 719, the stoichiometric purification performance is further determined. . If the flag S = 1, the purification performance in stoichiometry is deteriorated and the failure pattern shown in FIG. 6 is obtained. Therefore, the process proceeds to step 720, and in step 720 it is decided to operate lean. On the other hand, if it is determined in step 719 that the flag S = 0, only the stoichiometric purification performance shown in FIG. 5 has a normal failure pattern, and therefore the process proceeds to step 721 and the step 7
At 21, he decided to drive in stoichiometry.

Finally, the process returns at step 723 to return to the processing contents before the interruption. The information of the flag L and the flag S in the above description is backed up in memory and stored even if the main power of the control unit 15 is turned off. Further, when the flag S or the flag L becomes 1, it is possible to turn on or display a warning lamp for informing the driver that the catalyst is out of order.

FIG. 8 is a timing chart when the above-described control processing is performed by the engine control device of the present embodiment. In FIG. 8, before the time T ₁ , the air-fuel ratio 24
Although those of operating at lean, the purification rate is deteriorated at the boundary of time T _1. At this point, whether the deterioration state of the catalyst is the deterioration pattern shown in FIG.
I do not know if it is the deterioration pattern shown in. At time T ₁ , since the purification rate η became lower than η _L , CNT The count-up of L is started, and at time T ₂ , it becomes N _L times, so that the flag L is set to 1 and the deterioration of the purification performance in lean is confirmed. At this time, the engine is operated by changing the air-fuel ratio from lean to stoichiometric. If the purification rate is lower and lower than η _S even after switching to stoiki, from time T ₃ to CNT S
Is started, and since it has become N _S times at time T ₄ , the flag S is set to 1 and the deterioration of the purification rate due to stoichiometry is determined. Since it was found that the catalyst deterioration pattern at this time point was the pattern shown in FIG. 6, the set air-fuel ratio was changed to lean to operate.

As described above, the engine control system according to the present embodiment can switch the control so as to minimize the amount of exhausted NOx depending on the deterioration pattern of the catalyst. It is also possible to inform the driver that the catalyst has deteriorated. Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various designs can be made without departing from the spirit of the invention described in the claims. Can be changed.

For example, the means for changing the operating state of the engine based on the calculation of the purification rate of the catalyst is not limited to the change in the operating state of the air-fuel ratio from stoichiometric to lean or lean to stoichiometric as in the above-mentioned specific example. Instead, it is possible to employ means for changing the ignition timing, the fuel injection timing, or the intake air flow rate as a parameter for lowering the NOx emission amount in the state of the catalyst at that time, and changing the operating state. The means to be performed is not limited to one of the specific examples, and may be a combination of the plurality of means.

[0036]

As can be understood from the above description, the engine control device of the present invention fails when the NOx concentration after the catalyst finally released to the atmosphere increases due to deterioration or damage of the catalyst. It is possible to prompt the repair or replacement of the catalyst by making a diagnosis and notifying the driver that the catalyst has deteriorated. Further, when the NOx concentration after the catalyst finally released to the atmosphere increases due to deterioration or damage of the catalyst, the catalyst is repaired or replaced by switching the control so as to reduce the NOx concentration discharged from the engine. NOx leading to air pollution until
The amount of emissions can be minimized.

[Brief description of the drawings]

FIG. 1 is an engine configuration diagram including an engine control device according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a configuration of a control unit of the engine control device of FIG. 1;

FIG. 3 is a diagram showing the relationship between the air-fuel ratio and the concentration of exhaust gas components.

FIG. 4 is a diagram showing an example of a relationship between a catalyst (normal) purification rate and an air-fuel ratio.

FIG. 5 is a diagram showing an example of the relationship between the air-fuel ratio and the purification rate of the catalyst (lean region deterioration).

FIG. 6 is a diagram showing an example of the relationship between the air-fuel ratio and the purification rate of the catalyst (whole area deterioration).

7 is a control flowchart of the engine control device of FIG.

8 is a control timing chart of the engine control device of FIG.

[Explanation of symbols]

7 ... Engine, 13 ... Injector, 15 ... Control unit, 25 ... Catalyst, 26 ... NOx sensor before CAT, 27 ... NOx sensor after CAT

Claims (6)

[Claims] 1. An engine control device comprising a catalyst for purifying exhaust gas, a device for measuring nitrogen oxide concentration of exhaust gas in front and rear parts of the catalyst, and a catalyst diagnostic device, wherein the catalyst diagnostic device is provided. The apparatus includes means for calculating a purification rate of the catalyst from nitrogen oxide concentrations of exhaust gas passing through the catalyst before and after the catalyst, and means for changing an operating state of the engine based on the purification rate. An engine control device characterized by the above. 2. The means for changing the operating state of the engine is a means for changing the air-fuel ratio, ignition timing, fuel injection timing, or intake air flow rate, or a combination of a plurality of these means. The engine control device according to claim 1. 3. The means for changing the operating state of the engine is to change to stoichiometric when the purification rate becomes a predetermined value or less during operation with the air-fuel ratio being lean. The engine control device described. 4. The means for calculating the purification rate of the catalyst calculates the purification rate during operation in stoichiometry and the purification rate during operation in lean, and the means for changing the operating state of the engine is in the lean. The engine control device according to claim 1, wherein when the purification rate is equal to or lower than a predetermined value, the operation is performed stoichiometrically, and when the purification rate is stoichiometric or lean, the operation is performed lean when the purification rate is equal to or lower than the predetermined value. 5. The catalyst diagnosing device comprises means for determining catalyst deterioration when the calculated purification rate is less than or equal to a predetermined value, and storing information on the catalyst deterioration. 1. The engine control device according to 1. 6. The catalyst diagnosing device comprises means for deciding that the catalyst has deteriorated when the calculated purification rate is less than or equal to a predetermined value and for turning on a warning lamp or for displaying information on the catalyst deterioration. The engine control device according to claim 1, wherein the engine control device is provided.