JPH07186785A - Controller for internal combustion engine with automatic transmission - Google Patents

Abstract

PURPOSE:To eliminate SOX poisoning of an NOX absorbent without using any auxiliary heating means such as a heater. CONSTITUTION:An NOX absorbent 18 is arranged in the exhaust passage 17 of an internal combustion engine 1, and NOX in exhausting is absorbed by the NOX absorbent by normally driving the engine with the lean air-fuel ratio. An electronic control circuit 30 estimates the amount of sulfur oxides(SOX) absorbed by the NOX absorbent on the basis of the engine driving state and drives the engine with the rich air-fuel ratio when the SOX absorbed amount becomes the specific value or more and also changes the speed change controlling characteristic of an automatic transmission 40, so as to enlarge the driving range at the low speed stage. Thereby, the exhaust temperature is raised, and the temperature of the NOX absorbent is increased to higher temperatures, and the NOX absorbent becomes the rich air-fuel ratio atmosphere, thereby the SOX absorbed by the NOX absorbent is discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a control apparatus for an internal combustion engine with an automatic transmission, air-fuel ratio of the exhaust gas flowing in detail absorbs NO _X in the exhaust gas when the lean, reduced exhaust oxygen concentration a control device for an internal combustion engine with an automatic transmission having an exhaust gas purification apparatus using the _the NO _X absorbent to release the absorbed NO _X when.

[0002]

2. Description of the Related Art NO when the air-fuel ratio of the exhaust gas is lean
_The applicant of the present application has already proposed an exhaust gas purification device equipped with a NO _x absorbent that absorbs _X and releases the absorbed NO _X when the oxygen concentration in the inflowing exhaust gas decreases. (See International Publication WO 93-7363).

[0003] In the apparatus, the majority of the place _the NO _X absorbent in the exhaust passage of the internal combustion engine performing lean air-fuel ratio operation in the operating region, the NO _X in the exhaust gas during the lean air-fuel ratio operation NO _X
Absorbed onto the absorbent, NO after _X absorbed in the air-fuel ratio of the engine by performing the operation is switched to the stoichiometric air-fuel ratio or rich air-fuel ratio, the NO _X to NO _X absorbed from the absorbent are released together to release the NO _X Unburned HC and C in the exhaust
A reducing component such as O is used for reduction purification.

[0004]

SUMMARY OF THE INVENTION An object of _the NO _X absorbent absorbs NO _X in the exhaust gas of a lean air-fuel ratio as described above, the oxygen concentration in the exhaust gas to release NO _X absorbed and reduced N
It acts to absorb and release O _X. The mechanism of this absorbing and releasing action will be described in detail later, but sulfur oxide (SO
_X ) exists, the NO _X absorbent absorbs SO _X in the exhaust gas by the same mechanism as that of absorbing NO _X. In general, fuel and lubricating oil of an engine contain sulfur, so SO _x exists together with NO _{x in} engine exhaust,
SO _X not NO _X only in the NO _X absorbent when placing _the NO _X absorbent in the engine exhaust passage as described above is absorbed.

However, NO_XSO absorbed by absorbent
_XForms stable sulphate, so normal NO_XAbsorbent
NO from_XRelease, reduction purification (hereinafter "NO_XAbsorbent
It is difficult to decompose and release under the condition of "regeneration")
O_XIt tends to accumulate in the absorbent. However,
NO_XSO in absorbent_XWhen the accumulated amount increases, NO_XSucking
NO of collecting agent _XThe absorption capacity decreases, and NO in exhaust gas
_XSince the removal of NO can not be absorbed sufficiently, NO in exhaust gas
_XOf so-called SO_XPoisoning occurs
There's a problem.

On the other hand, when the SO _X poisoning of the NO _X absorbent occurs by the exhaust air-fuel ratio to the rich while maintaining _the NO _X absorbent than during reproduction of the normal of the NO _X absorbent to a high temperature, The SO _X absorbed by the NO _X absorbent is released and S
It is known that O _X it is possible to eliminate the poisoning. However, in order to keep the _the NO _X absorbent to a high temperature, it is necessary to increase the engine exhaust temperature. For example, it is possible to raise the exhaust gas temperature to some extent by operating the engine at a rich air-fuel ratio or by retarding the ignition timing.
Since the exhaust gas temperature changes according to the operating conditions, the engine does not rise only enough exhaust temperature at the above-mentioned means are operated at a low speed, it is difficult to eliminate SO _X poisoning.
On the other hand, if the driver is forced to perform the operation while keeping the engine speed high when SO _X poisoning occurs, there is a problem that the driver's burden is increased.

[0007] Therefore, conventionally, in order to solve the SO _X poisoning, heater, an auxiliary heating means such as a burner, arranged in _the NO _X absorbent, the operating temperature of the NO _X absorbent when SO _X poisoning recovery operation It was required to keep high regardless of the conditions. However, it is not preferable to separately provide an auxiliary heating means such as a heater and a burner in the exhaust gas purification device because the device cost will increase. Further, there is a problem that the device becomes complicated and the mountability of the device deteriorates.

The present invention relates to an internal combustion engine with an automatic transmission, the above N
When mounting the exhaust gas purifying apparatus using the O _X absorbent, to provide a means making it possible to eliminate the heater, the SO _X poisoning of the NO _X absorbent without the use of auxiliary heating means such as a burner, Is intended.

[0009]

According to the present invention, when the air-fuel ratio of the exhaust gas, which is arranged in the exhaust passage of the internal combustion engine for a vehicle, is lean, the NO _x in the exhaust gas is absorbed and the oxygen concentration in the exhaust gas is reduced. A NO _x absorbent that releases the absorbed NO _x when it has dropped, an automatic transmission connected to the internal combustion engine, a shift control means that sets a shift speed of the automatic transmission according to a running state, In a control device for an internal combustion engine with an automatic transmission, comprising an air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine,
Estimating means for estimating the amount of sulfur oxides absorbed in the NO _x absorbent is provided, and the shift control means comprises the NO _x
The amount of the absorbed sulfur oxide absorbent to set the gear stage depending on the running state based on a predetermined first shift control characteristics in the case of less than the predetermined value, the absorbed sulfur oxides of the _the NO _X absorbent When the amount of the object is larger than a predetermined value, the shift speed is set according to the traveling state based on the second shift control characteristic in which the operating range on the low speed side is wider than the first shift control characteristic, air-fuel ratio control means when the amount of the absorbed sulfur oxide of _the NO _X absorbent is larger than the predetermined value, and controlling the rich side than the stoichiometric air-fuel ratio of the engine automatic A control device for an internal combustion engine with a transmission is provided.

[0010]

In normal operation, the shift control means sets the shift stage of the automatic transmission according to the traveling state based on the first shift control characteristic. On the other hand, when the amount of sulfur oxide absorbed by the NO _X absorbent increases and exceeds the predetermined value, the shift control means sets the shift stage of the automatic transmission based on the second shift control characteristic. The operating range on the low speed stage side is expanded. Further, at this time, the air-fuel ratio control means sets the engine air-fuel ratio to the rich air-fuel ratio at the same time, so that the engine can be operated at the rich air-fuel ratio and the opportunity to operate the engine at high speed increases, so that the overall Exhaust temperature rises. For this reason,
The NO _X absorbent is maintained in an atmosphere of high temperature and rich air-fuel ratio, and the absorbed sulfur oxide is released, so SO _X poisoning is eliminated.

When the amount of sulfur oxides in the NO _x absorbent decreases and SO _x poisoning is eliminated, the shift control means sets the shift speed again based on the first shift control characteristic. The air-fuel ratio control means sets the engine air-fuel ratio to the normal air-fuel ratio, and the engine operating state returns to normal.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall view of an internal combustion engine with an automatic transmission to which the present invention is applied. In FIG. 1, reference numeral 1 is an internal combustion engine such as a gasoline engine that performs lean air-fuel combustion, and 3 is an engine 1.
Of the engine, 6 is an intake port of the engine, and 8 is an exhaust port. Each intake port 6 is connected to a surge tank 10 via an intake branch pipe 9, and a fuel injection valve 11 for injecting fuel into each intake port 6 is arranged in each branch pipe 9.

Further, the surge tank 10 is connected to an air cleaner 13 via an intake passage 12, and a throttle valve 14 having an opening degree corresponding to an operation of an accelerator pedal (not shown) by a driver is provided in the intake passage 12. It is arranged. Also,
The surge tank 10 is provided with an intake pressure sensor 15 that generates an output voltage proportional to the absolute pressure in the surge tank 10.

On the other hand, the exhaust port 8 of the engine 1 is connected to an exhaust passage 17 via an exhaust manifold 16, and the exhaust passage 17 is connected to a casing 19 containing a NO _x absorbent 18 described later. Further, reference numeral 40 in FIG. 1 denotes an automatic transmission connected to an output shaft (not shown) of the engine 1. The automatic transmission 40 includes a torque converter 41.
And a transmission 42, and the output shaft of the transmission 42 is connected to the drive wheels of the vehicle via a differential gear (not shown).

The transmission 42 is of a known type having a planetary gear train and a friction element, and the control hydraulic pressure is switched to switch the engagement state of the friction elements (brake, clutch, etc.) to change each planetary gear train. Shifting operation is performed by fixing and connecting the elements. The torque converter 41 is of a known type including a pump directly connected to the engine output shaft and a turbine driven by the pump discharge fluid, and the turbine output shaft (hereinafter referred to as the converter output shaft) of the transmission 42. It is directly connected to the input shaft. The torque converter 41 has a known torque amplification action of amplifying the torque input from the engine output shaft and outputting it to the converter output shaft. Further, to the automatic transmission 40, a converter output shaft rotation speed sensor 22 that outputs a pulse signal having a frequency corresponding to the rotation speed of the converter output shaft, and a pulse signal having a frequency corresponding to the rotation speed of the output shaft of the transmission 42 are transmitted. Transmission output shaft rotation speed sensors 23 for outputting are respectively provided.

Reference numeral 30 in FIG. 1 is an electronic control circuit of the engine 1. The electronic control circuit 30 includes a ROM (read only memory) 32, a RAM (random access memory) 3
3, CPU (microprocessor) 34, input port 3
5. A digital computer having a known structure in which the output ports 36 are connected to each other by the bidirectional bus 31.
In addition to performing basic control of the engine such as fuel injection amount control of the engine 1 and ignition timing control, shift control means for performing a shift operation of the transmission 42 according to the running state, air-fuel ratio control means for controlling the engine air-fuel ratio, NO The function as each means described in claim 1 such as an estimation means for estimating the amount of SO _X absorbed by the _X absorbent is fulfilled.

For the above purpose, a voltage signal corresponding to the intake pressure from the intake pressure sensor 15 and a voltage signal representing the opening of the throttle valve 14 from the throttle opening sensor 20 are connected to the input port 35 of the control circuit 30. Further, the voltage signals representing the vehicle traveling speed from the vehicle speed sensor 24 are respectively supplied to the AD converters 3.
7, a pulse signal representing the engine speed from an engine speed sensor 21 provided in a distributor (not shown) of the engine, the converter output shaft speed sensor 22 and the transmission described above. Output shaft speed sensor 2
The pulse signals from 3 and 3 are input respectively.

The output port 36 of the control circuit 30 is
The fuel injection valve 11 is driven through the corresponding drive circuit 38.
Is connected to the ignition plug 4 to control the fuel injection from the fuel injection valve 11 and the ignition timing of the engine. The NO _x absorbent 18 contained in the casing 19 uses, for example, a carrier such as alumina, on which potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba or calcium Ca. At least one selected from such alkaline earths, lanthanum La, and rare earths such as yttrium Y and a noble metal such as platinum Pt are supported. This NO _X absorbent 18 is NO _X when the air-fuel ratio of the inflowing exhaust gas is lean.
That absorbs NO and releases NO _X when the oxygen concentration decreases
_It absorbs and releases _X.

Incidentally, the above-mentioned exhaust air-fuel ratio means here N
It means the ratio of the total amount of air and the total amount of fuel supplied to the exhaust passage on the upstream side of the O _X absorbent 18, the engine combustion chamber, the intake passage, and the like. Therefore, NO _X absorbent 1
When fuel or air is not supplied to the upstream exhaust passage 8 of No. 8, the exhaust air-fuel ratio becomes equal to the air-fuel ratio of the engine (air-fuel ratio in combustion in the engine combustion chamber).

In this embodiment, an engine that burns with a lean air-fuel ratio is used, so the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 18 absorbs NO _{X in} the exhaust. Further, when the air-fuel ratio of the engine is switched from the lean air-fuel ratio to the rich or stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases, the NO _X absorbent 18 releases the absorbed NO _X.

[0021] There are some points where the detailed mechanism of this absorption / release action is not clear. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, regarding this mechanism, platinum P on the carrier
A case of supporting t and barium Ba will be described as an example, but other precious metals, alkali metals, alkaline earth metals,
The same mechanism can be achieved by using rare earths.

That is, the inflow exhaust becomes considerably lean.
And the oxygen concentration in the exhaust gas increased significantly, as shown in Fig. 2 (A).
As these oxygen O₂Is O₂ ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, the NO in the exhaust gas is
This O on the surface of platinum Pt₂ ^-Or O^2-Reacts with N
O₂Becomes (2NO + O₂→ 2 NO₂ ). Then generated
NO₂Part of the inside of the absorbent while being oxidized on platinum Pt
While being absorbed by and bound to barium oxide BaO,
As shown in (A), nitrate ion NO₃ ^-Absorbent in the form of
Diffuse in. NO in this way_XIs NO_XAbsorbent 1
Absorbed in 8.

Therefore, NO ₂ is produced on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high, and NO ₂ is absorbed in the absorbent and nitrate ion NO ₃ unless the NO _X absorbing capacity of the absorbent is saturated. ^- is generated. Organization 1
When the air-fuel ratio of is switched to rich or stoichiometric air-fuel ratio,
The oxygen concentration in the inflowing exhaust gas decreases and the amount of NO ₂ produced decreases. Thus the reaction is reverse (NO ₃ ^- → NO ₂₎ proceeds, the nitrate ions NO in absorbent ₃ ^- are released from the absorbent in the form of NO _2. On the other hand, unburned HC,
When components such as CO are present, these components are oxidized by reacting with oxygen O ₂ ⁻ or O ^{2 −} on platinum Pt, and platinum Pt
It consumes oxygen above. Further, NO ₂ released from the NO _x absorbent 18 is reduced by reacting with HC and CO as shown in FIG. 2 (B). In this way, N on the surface of platinum Pt
When O ₂ is no longer present, NO ₂
Is released.

That is, HC and CO in the inflowing exhaust gas are first reacted with O ₂ ⁻ or O ²⁻ on platinum Pt immediately to be oxidized, and then O ₂ ⁻ or O ²⁻ on platinum Pt are consumed. If HC and CO still remain, the NO _X released from the absorbent by the HC and CO and the NO _X that flows in with the exhaust gas are reduced. In this embodiment, during normal lean-burn operation using the above together to absorb NO _X in the exhaust gas in the NO _X absorbent, short engine air when the absorbed amount of NO _X in _the NO _X absorbent is increased by switching the ratio to the rich or the stoichiometric air-fuel ratio is performed and reduction purification and release of the NO _X from _the NO _X absorbent. That is,
When the engine air-fuel ratio is switched to the rich or stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas sharply decreases, and the amounts of unburned HC and CO discharged from the engine greatly increase.
Therefore, by switching the engine air-fuel ratio to the rich or stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is reduced and the amount of unburned HC and CO is increased, so that N
The regeneration of the _Ox absorbent 18 will be performed.

Next, NO_XAbsorbent SO_XPoisoned mechanics
I will explain about. SO during exhaust_XContains ingredients
Then NO_XAbsorbent is NO above_XSame mechanism as absorption of
SO in the exhaust_XAbsorbs. That is, exhaust air-fuel
SO in the exhaust when the ratio is lean_X(Eg SO₂) Is
SO oxidized by platinum Pt₃ ^-, SO_Four ^-And then acid
BaSO combined with BaO_FourTo form. B
aSO _FourIs relatively stable, and the crystals become coarse.
Once produced, it is difficult to decompose and release due to rinsing. others
No_XBaSO in the absorbent_FourWhen the production of
NO_XThe amount of BaO that can be involved in the absorption of NO decreases_X
Absorbs less. This SO_XPrevent poisoning
NO in order to_XBaSO formed in the absorbent_FourTo
SO which is decomposed at high temperature and is generated by this₃
^-, SO_Four ^-Reduce the sulfate ion of NO, NO_XFrom absorbent
Need to be released. In the present invention, as described below,
Make the air-fuel ratio rich and change the automatic transmission 40
By changing the speed control characteristic to raise the engine exhaust temperature
Than SO_XThe poisoning has been eliminated.

Next, the air-fuel ratio control of the engine of this embodiment will be described. In this embodiment, the above-mentioned International Publication WO No. WO is used.
Air-fuel ratio control similar to that described in No. 93-7363 is performed. The air-fuel ratio control will be briefly described below. In the present embodiment, the fuel injection amount from the fuel injection valve 11,
That is, the valve opening time (fuel injection time) TAU of the fuel injection valve 11 at the time of fuel injection is set by the control circuit 30 to, for example, TA.
It is calculated as U = TP × K.

Here, TP represents the fuel injection time required to bring the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber to the stoichiometric air-fuel ratio, that is, the basic fuel injection time, which is detected by the intake pressure sensor 15. As a function of the absolute pressure PM in the surge tank 10 and the engine speed N obtained, it is obtained in advance by experiments or the like and stored in the ROM 32 of the control circuit 30 in the form of a numerical table as shown in FIG.

Further, K is a correction coefficient for controlling the engine air-fuel ratio, and when K = 1.0 is set, the engine air-fuel ratio becomes the theoretical air-fuel ratio. Further, if K> 1.0, the engine air-fuel ratio becomes smaller than the theoretical air-fuel ratio (that is, rich air-fuel ratio), and if K <1.0, the engine air-fuel ratio becomes larger than the theoretical air-fuel ratio (that is, lean air-fuel ratio). Becomes the fuel ratio). The value of the correction coefficient K is given as a function of the absolute pressure PM in the surge tank 10 and the engine speed N, for example, in the form shown in FIG. That is, as shown in FIG. 4, in the present embodiment, a region where the PM is relatively low (engine low / medium load operation region)
Then, the correction coefficient K is set to be smaller than 1.0, and the engine is operated at a lean air-fuel ratio. Further, in a region where PM is relatively high (engine high load operating region), the value of the correction coefficient K is 1.0, and the engine is operated at the stoichiometric air-fuel ratio. In addition, PM
In a high range (engine full load operation range), the value of the correction coefficient K is set to be larger than 1.0, and the engine is operated at the rich air-fuel ratio. In a vehicle engine or the like, a low-to-medium-load operation is usually most frequently performed, so these engines are operated at a lean air-fuel ratio for most of the period during operation.

[0029] As described above, NO NO _X absorbent engine absorbs NO _X in the exhaust gas when being operated at a lean air-fuel ratio, the engine is absorbed when being operated at a rich or stoichiometric air-fuel ratio _X To release. Therefore, if the operation of the rich or the stoichiometric air-fuel ratio is appropriately performed, NO _X absorption of the NO _X absorbent is not increased beyond a certain level, it is not necessary to perform special reproduction operation. However, when the engine operating conditions which may operated at a lean air-fuel ratio such that long-lasting, NO _X absorption of the NO _X absorbent increases,
There is a risk that the NO _x absorption capacity will be saturated.

[0030] Therefore, the electronic control circuit 30 in the present embodiment estimates the amount of NO _{X the} NO _X absorbent 18 is absorbed, when the estimated NO _X absorption amount becomes a predetermined amount or more, though the area of FIG. 4 not, short (e.g., time of about 0.5 to 1 second) driving the forcibly set to the engine a value of the correction coefficient K to 1.0 or rich or stoichiometric air-fuel ratio, of the NO _X absorbent NO _X absorbing capacity of the NO _X absorbent by performing reproduction operation is prevented from saturating.

In this embodiment, the electronic control circuit 30 controls the N _{x of} the NO _x absorbent 18 according to the operating condition of the engine at regular intervals.
By adding and subtracting the absorption amount counter representing the O _X absorption amount, the NO _X absorbent 1 is calculated from the value of this absorption amount counter.
The NO _x absorption amount of No. 8 is estimated. That is, when the engine is operated at a lean air-fuel ratio, the NO _X absorbent 18
Absorbs NO _{X in} the exhaust gas, and N of the NO _X absorbent 18 is absorbed.
O _X absorption amount is increased. NO at this time per unit time
It is considered that the amount of NO _X absorbed by the _X absorbent 18 is proportional to the amount of NO _X emitted from the engine per unit time. on the other hand,
The amount of NO _X discharged from the engine in a unit time is determined by the engine load condition, and increases as the engine load (engine intake pressure) increases and the engine speed increases, for example. Therefore, in this embodiment, the NO _X emission amount of the engine is obtained in advance as a function of the engine load and the rotational speed by actual measurement, and this NO _X is calculated.
The value obtained by multiplying the emission amount by a certain coefficient is NO per unit time
As NO _X absorption amount of _X absorbent, are stored in the form of a numerical table of the same format as FIG. 3 in ROM32 of the electronic control circuit 30. When the engine is operated with a lean air-fuel ratio, the electronic control circuit 30 calculates the NO _X absorption amount per unit time from the engine load (intake pressure) and the engine speed at regular time intervals using the above numerical table. Then, the value is added to the value of the NO _x absorption amount counter described above.

Further, when the engine is operating at a rich or stoichiometric air-fuel ratio, the NO _x absorbent 18 has absorbed the N
To release O _X, NO _X absorption of the NO _X absorbent 18 is reduced. Therefore, in the present embodiment, the electronic control circuit 30
When the engine is operated in a rich or stoichiometric air-fuel ratio, performs an operation of subtracting the constant value corresponding to the NO _X release amount per unit from the value of the NO _X absorption counter time at predetermined time intervals.

As a result, the above NO_XAbsorption amount counter
Is always NO_XAbsorbent 18 NO _XCorresponding to the amount absorbed
Since it becomes a value, NO_XNo from the value of the absorption counter_XSucking
NO of collecting agent 18_XIt is possible to estimate the absorption amount.
In addition, the electronic control circuit 30 uses the above-mentioned NO._XAbsorption amount
Is a predetermined value (for example, NO_XCan absorb the absorbent 18
Maximum NO_X70% of the amount)
If you get a certain time (for example, 0.5 seconds to 1 second
The engine air-fuel ratio is set to rich or stoichiometric.
Replace with NO_XRegenerate the absorbent 18, but after regeneration
The above NO_XThe value of the absorption counter is returned to zero.
It

Next, the shift operation of the automatic transmission of this embodiment will be described. In this embodiment, the shift operation of the automatic transmission 40 is performed based on the vehicle traveling speed and the throttle valve opening. That is, the electronic control circuit 30 inputs the vehicle traveling speed and the throttle valve opening from the vehicle speed sensor 24 and the throttle opening sensor 20, respectively, and selects the shift speed of the automatic transmission 40 based on these values to shift gears. Do the operation.

Further, in this embodiment, there are prepared two types of relationships (shift control characteristics) between the vehicle running speed for performing the above-described shift operation, the throttle valve opening, and the selected shift speed. As will be described later, the circuit 30 is configured to select either one of the shift control characteristics according to the amount of sulfur oxide (SO _X ) absorbed by the NO _X absorbent 18.

5 and 6 show examples of shift control characteristics used in this embodiment. FIGS. 5 and 6 show shift characteristics of an automatic transmission having an overdrive (OD) mechanism and three-speed transmission gears. In FIGS. 5 and 6, the vertical axis represents the throttle valve opening TA and the horizontal axis represents the vehicle traveling speed. Each SP is shown. Also,
In FIG. 6, a solid line shows a shift line from a low speed stage to a high speed stage (shift up), and a dotted line shows a shift line from a high speed stage to a low speed stage (shift down). (Note that in order to avoid complication, only the shift line at the time of upshift is shown in FIG. 6.) Here, FIG. 5 is selected when the SO _X absorption amount of the NO _X absorbent is small. 6 shows a shift control characteristic (first shift control characteristic). FIG. 6 shows a shift control characteristic (second shift control characteristic) selected for eliminating SO _X poisoning when the SO _X absorption amount of the NO _X absorbent is large. Control characteristics). As can be seen by comparing FIG. 5 and FIG. 6, in the second shift control characteristic (FIG. 6), the shift-up shift line of each shift speed is generally larger than that in the first shift control characteristic (FIG. 5). The vehicle is shifting to the right (the direction in which the vehicle travels at a higher speed), and the operating range at low speeds is expanding to the high-speed travel side. In addition, FIG.
Although not shown in the figure, in the second shift control characteristic, the shift-down shift line is similarly shifted to the high-speed running side,
The shift down is carried out earlier (on the high speed side), and the operating range at the low speed stage is expanded as in the case of the shift up.

Therefore, when the second speed change control characteristic is selected, the operating range in the low speed gear is expanded, so that the engine speed is generally high even under the same traveling speed condition, and the first speed change control is performed. Exhaust temperature will rise compared to the case of characteristics. Next, the SO _X poisoning elimination operation of the NO _X absorbent of the present embodiment will be described. In this embodiment, the electronic control circuit 3
0 is the same as the above-mentioned NO _x absorption estimation,
SO representing the amount of SO _X absorbed by the NO _X absorbent 18
Calculate the _X absorption counter. Further, when the value of the SO _X absorption amount counter exceeds a predetermined value, the NO _X absorbent 1
It is determined that SO _X poisoning of No. 8 has occurred, and the following SO _X poisoning elimination operation is performed.

That is, at the time of eliminating the poisoning, the electronic control circuit 30 sets the value of the air-fuel ratio correction coefficient K to a predetermined value K so that the engine air-fuel ratio becomes the rich air-fuel ratio regardless of the operating region of FIG.
_It is fixed at ₀ (K ₀ > 1.0). In addition, the electronic control circuit 3
At the same time, 0 controls the shift of the automatic transmission 40 based on the second shift control characteristic (FIG. 6). As a result, the engine as a whole operates on the high-speed rotation side, and the air-fuel ratio becomes rich, so the exhaust temperature rises. Therefore, the _the NO _X absorbent 18, SO _X is released from _the NO _X absorbent 18 will be evacuated of high temperature and rich air-fuel ratio flows, NO
_The amount of SO _X in the _X absorbent 18 is reduced.

Further, the electronic control circuit 30 is NO by the above.
_When it is determined that the SO _X amount in the _X absorbent 18 has decreased and SO _X poisoning has been eliminated, the normal control of the air-fuel ratio, which sets the value of the air-fuel ratio correction coefficient K based on the operating region of FIG. 4, is restored. At the same time, the shift operation of the automatic transmission 40 is controlled based on the first shift control characteristic (FIG. 5). FIG. 7 shows the above S
O _X is a flowchart showing a contamination-removing operation. This routine is executed by the electronic control circuit 30 at regular intervals.

In FIG. 7, steps 701 to 707 are performed.
Is NO_XSO absorbed in absorbent 18_XShows an estimate of quantity
Then, steps 713 to 721 are the above SO._XBased on quantity
SO _XThe poisoning elimination operation is shown. In Figure 7
When the engine starts, in step 701, the above-mentioned intake
From the pressure sensor 15 to the absolute pressure PM of the surge tank 10,
Also, the engine speed N is read from the speed sensor 21 respectively.
Get caught.

Next, at step 703, it is judged using the value of the air-fuel ratio correction coefficient K whether or not the engine is currently operating at the lean air-fuel ratio, and if the lean air-fuel ratio operation is being performed ( K <1.0) The routine proceeds to step 705, where the engine intake air amount Q is calculated, and at step 707 NO
_To the value of the counter S that represents the SO _X absorption amount of the _X absorbent 18,
A value obtained by multiplying the intake air amount Q by a constant α is added.

As described above, the NO _X absorbent 18 absorbs SO _X contained in the exhaust when the exhaust air-fuel ratio is lean, and absorbs SO _X when the exhaust temperature is high and the exhaust air-fuel ratio is rich. _{Emit X.} Further, the SO _X absorption amount of the NO _X absorbent 18 per unit time during lean air-fuel ratio operation is proportional to the SO _X generation amount of the engine. In addition, the SO
_The amount of _X generation is relatively small and proportional to the amount of fuel. Therefore, it may be considered that it is approximately proportional to the intake air amount of the engine.

Therefore, in the present embodiment, the intake air amount Q of the engine is previously obtained by actual measurement as a function of the engine load (intake pressure PM) and the rotational speed N, and RO of the electronic control circuit 30 is obtained.
When the engine is operated at a lean air-fuel ratio, it is stored in M32 in the form of a numerical table similar to that of FIG. 3, and in step 705, this relationship is used to calculate the intake air amount Q from the values of PM and N. Read out. Further, as described above, the SO _X absorption amount of the NO _X absorbent 18 per unit time is considered to be proportional to the engine intake air amount Q.
_{The X} absorption amount counter S is incremented by a value obtained by multiplying Q by a predetermined constant α. As a result, the value of the SO _X absorption amount counter increases according to the SO _X absorption amount of the NO _X absorbent 18 per unit time.

When the engine is operating at the stoichiometric air-fuel ratio or the rich air-fuel ratio at step 705 (K ≧ 1.
0), the routine proceeds to step 709, where it is determined whether the exhaust temperature T _EX is equal to or higher than the predetermined value T _0. If T _EX ≧ T ₀ , the routine proceeds to step 711, where the SO _X absorption counter S
The value of is decreased by a constant value β. Here, the predetermined value T ₀ of the exhaust gas temperature is the exhaust gas temperature required for the temperature of the NO _X absorbent 18 to reach the SO _X release temperature (for example, about 600 ° C.).

As described above, when the exhaust gas has a high temperature and a rich air-fuel ratio, the NO _X absorbent 18 releases the absorbed SO _X , but this release rate may be considered to be a substantially constant value. Therefore, in the present embodiment, the exhaust air-fuel ratio is rich (step 70
3) When the exhaust temperature is high (step 709), the value of the SO _X absorption amount counter is decreased by a constant value. As a result, the value of the SO _X absorption amount counter is the NO _X absorbent 1
It decreases according to the amount of SO _X released per unit time of 8.

In this embodiment, the exhaust temperature T _EX used in step 709 does not use an exhaust temperature sensor or the like,
It is calculated based on the operating condition of the engine. That is, the engine exhaust temperature is determined by the engine load state (intake pressure PM, rotational speed N) and the engine operating air-fuel ratio (air-fuel ratio correction coefficient K). Further, in this embodiment, the value of the air-fuel ratio (K) is as shown in FIG.
It is determined by the intake pressure PM and the rotation speed N using the relationship of In the present embodiment, the value of the exhaust temperature T _EX is obtained in advance as a function of the intake pressure PM and the rotation speed N by actual measurement or the like,
It is stored in the ROM 32 in the form of a numerical table similar to that of FIG. 3, and in step 709, the exhaust temperature T _EX is determined from this numerical table using the values of PM and N input in step 701.

It is also possible to actually provide an exhaust gas temperature sensor at the inlet of the NO _x absorbent to measure the exhaust gas temperature T _EX . Further, NO carriers temperature _X absorbent is provided a temperature sensor for detecting may be adapted to calculate the actual value of SO _X absorbed amount counter by _the NO _X absorbent temperature. On the other hand, if T _EX <T ₀ in step 709, that is, if the exhaust air-fuel ratio is rich but the exhaust temperature is lower than the SO _X release temperature, the value of the SO _X absorption counter S is not increased or decreased. This is because SO _x is not absorbed by the NO _x absorbent because the exhaust gas has a rich air-fuel ratio, and the SO _x from the NO _x absorbent is low because the exhaust temperature is low.
This is because no release occurs.

After the calculation of the SO _X absorption amount counter is completed as described above, the value of the flag F is set in steps 713 to 721 as described later. In the present embodiment, when the value of the flag F is set to 1, the electronic control circuit 30 fixes the air-fuel ratio correction coefficient K to a predetermined value K ₀ to keep the operating air-fuel ratio of the engine at the rich air-fuel ratio, and The shift operation of the automatic transmission is controlled based on the second shift control characteristic, and the SOx of the NO _x absorbent is
_X Perform poisoning elimination operation. Further, when the value of the flag F is set to 0, the electronic control circuit 30 sets the air-fuel ratio correction coefficient K based on the operating region of FIG. 4, and makes the shift operation of the automatic transmission the first shift control characteristic. Based on.

[0049] In the present embodiment, the value of the flag F is 1 when the SO _X absorbed amount S of the NO _X absorbent becomes ₁ or greater than a predetermined value S
Is set to 0 (steps 715 and 717), and is set to 0 when the SO _X absorption amount S decreases to a predetermined value S ₂ or less (steps 719 and 721). Here, S ₂ is set to a value larger than S ₁ , and the value of the flag F is set to have hysteresis. As a result, the amount of SO _X in the NO _X absorbent is controlled within a certain range, and frequent SO _X poisoning elimination operation is prevented.

According to this embodiment, the SO _X amount absorbed by the NO _X absorbent is estimated as described above, and when the SO _X amount increases, the engine air-fuel ratio is made rich and the low speed of the automatic transmission is reduced. By expanding the operating area on the stage side, N
O _X absorbent is maintained at a high temperature and rich atmosphere, SO _X
Poisoning is eliminated. In the embodiment described above, the shift control characteristic of the automatic transmission is set so that the shift line generally moves to the high speed running side during the SO _X poisoning elimination operation (FIG. 6). Even if the operation at the high speed stage (for example, the OD stage in FIG. 5) is prohibited and only the low speed stage is operated, the operating range at the low speed stage is also expanded. Therefore, the exhaust temperature should be raised as a whole. You can

In the above embodiment, the engine air-fuel ratio is set to the rich air-fuel ratio but the engine ignition timing is not changed. However, during the SO _X poisoning elimination operation, the ignition timing is added to the rich air-fuel ratio operation. By retarding the exhaust gas, it is possible to further raise the exhaust gas temperature and quickly eliminate SO _X poisoning. Further, as described above, when the shift control characteristics are switched so that the engine air-fuel ratio is kept rich and the operating range at the low speed stage is widened, the engine fuel consumption naturally increases, but the amount of SO _X to is very small, since the frequency of the SO _X poisoning recovery operation is performed is very small, in practice, an increase in operating costs due to the SO _X poisoning recovery operation is not a problem.

[0052]

According to the present invention, the amount of SO _X absorbed by the NO _X absorbent is estimated, and when the estimated amount of SO _X increases, the engine air-fuel ratio is set to the rich air-fuel ratio and
Since the shift control characteristics of the automatic transmission are switched so that the operating range on the low speed stage side is expanded, the NO _x absorbent can be kept in a high temperature and rich atmosphere, and auxiliary heating means such as a heater or burner must be used. Without NO _X absorbent S
The effect that O _X poisoning can be eliminated can be obtained.

[Brief description of drawings]

FIG. 1 is an overall view of an internal combustion engine with an automatic transmission showing an embodiment of the present invention.

[FIG. 2] NO _X used in the exhaust purification system of the embodiment of FIG. 1.
Absorbent is a diagram for explaining the absorbing and releasing action of NO _X.

FIG. 3 is a diagram showing a format of a numerical table used for determining a basic fuel injection amount.

FIG. 4 is a diagram showing a setting example of a fuel injection amount correction coefficient.

5 is a diagram showing a first shift control characteristic of the automatic transmission according to the embodiment of FIG.

6 is a diagram showing a second shift control characteristic of the automatic transmission according to the embodiment of FIG.

FIG. 7 is a flowchart illustrating SO _X poisoning elimination control of a NO _X absorbent.

[Explanation of symbols]

1 ... Internal combustion engine 17 ... Exhaust passage 18 ... NO _X absorbent 30 ... Electronic control circuit 40 ... Automatic transmission

Claims (1)

[Claims] 1. A disposed in an exhaust passage of an internal combustion engine for a vehicle, NO air-fuel ratio of the exhaust gas is the oxygen concentration in the absorbing evacuating the NO _X in the exhaust gas when the lean absorbed when reduced _X
A NO _x absorbent that releases NOx, an automatic transmission connected to the internal combustion engine, a shift control unit that sets a shift speed of the automatic transmission according to a running state, and an air-fuel ratio of the internal combustion engine is controlled. the control apparatus for an internal combustion engine with an automatic transmission having a air-fuel ratio control means comprises an estimation means for estimating the amount of the _the NO _X absorbent absorbs sulfur oxide in the shift control means, the NO _When the amount of sulfur oxide absorbed by the _X absorbent is less than or equal to a predetermined value, the gear stage is set according to the running state based on the predetermined first shift control characteristic, and the sulfur absorbed by the NO _X absorbent is set. When the amount of the oxide is larger than a predetermined value, the shift speed is set according to the traveling state based on the second shift control characteristic in which the operating range on the lower speed side is wider than the first shift control characteristic, The air-fuel ratio control means absorbs the NO _x absorbent. When the amount of sulfur oxide is larger than the predetermined value, the air-fuel ratio of the engine is controlled to be richer than the stoichiometric air-fuel ratio.