JP2022100067A - Control device for internal combustion engine - Google Patents

Abstract

To provide a control device for an internal combustion engine capable of suppressing deterioration of emissions while reducing the amount of ammonia discharged from the internal combustion engine to the outside of a vehicle.SOLUTION: In a control device for an internal combustion engine including: an exhaust emission control catalyst provided in an exhaust passage of the internal combustion engine and purifying exhaust gas passing through the exhaust passage; an EGR passage communicating between the exhaust passage and an intake passage of the internal combustion engine; and an EGR valve provided in the exhaust passage or the EGR passage and controlling the amount of exhaust gas passing through the exhaust passage, when an air-fuel ratio of exhaust gas discharged from the internal combustion engine has changed from a lean air-fuel ratio leaner than a theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air fuel ratio and when a temperature of the exhaust emission control catalyst is in a predetermined temperature range in which ammonia is easily generated in the exhaust emission control catalyst, an opening of the EGR valve is controlled so that the amount of exhaust gas passing through the EGR passage increases compared to when the temperature is outside the predetermined temperature range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a control device for an internal combustion engine that recirculates a part of exhaust gas flowing through the exhaust passage of the internal combustion engine to the intake passage.

As a technique for reducing the amount of harmful substances discharged from the internal combustion engine into the atmosphere, Patent Document 1 includes an exhaust gas recirculation device that recirculates a part of the exhaust gas flowing through the exhaust passage of the internal combustion engine to the intake passage. Techniques and techniques for providing an exhaust purification catalyst (hereinafter abbreviated as "catalyst") such as a three-way catalyst, an oxidation catalyst, or a NOx storage reduction catalyst in an exhaust passage of an internal combustion engine are described.

Japanese Unexamined Patent Publication No. 2008-255940

By the way, exhaust gas containing HC, CO and water flows into the exhaust purification catalyst. Then, it is known that hydrogen is generated in the exhaust gas purification catalyst by the catalytic action. Here, when NOx contained in the exhaust gas reacts with hydrogen, ammonia is generated, and the exhaust gas containing the ammonia flows out from the exhaust purification catalyst. It has also been found that the amount of ammonia produced increases or decreases depending on the temperature of the exhaust gas purification catalyst.

Ammonia generated by the exhaust purification catalyst passes through the exhaust passage and is discharged to the outside of the vehicle as it is, which deteriorates the emission. Therefore, it is difficult to discharge the ammonia to the outside of the vehicle, especially when the amount of ammonia generated is large. Control is required.

The present disclosure has been made in view of the above problems, and an object thereof is an internal combustion engine control device capable of suppressing deterioration of emissions while reducing the amount of ammonia discharged from the internal combustion engine to the outside of the vehicle. Is to provide.

The present disclosure has been made to solve the above-mentioned problems, and the gist thereof is as follows.

(1) An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine to purify the exhaust gas passing through the exhaust passage, an EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine, and an exhaust passage or an EGR passage. It is a control device of an internal combustion engine provided with an EGR valve for adjusting the amount of exhaust gas passing through the exhaust passage, and the control device has an air-fuel ratio of exhaust gas discharged from the internal combustion engine higher than the theoretical air-fuel ratio. When the lean air fuel ratio changes from a lean air fuel ratio to a rich air fuel ratio richer than the theoretical air fuel ratio, and the temperature of the exhaust purification catalyst is in a predetermined temperature range in which ammonia is likely to be generated in the exhaust purification catalyst, the exhaust gas is empty. When the fuel ratio changes from a lean air fuel ratio leaner than the theoretical air fuel ratio to a rich air fuel ratio richer than the theoretical air fuel ratio, and the amount of exhaust gas passing through the EGR passage increases compared to when it is outside the predetermined temperature range. An internal combustion engine control device that adjusts the opening of the EGR valve.

(2) The control device for an internal combustion engine according to (1) above, wherein the EGR passage communicates the exhaust passage on the downstream side of the exhaust purification catalyst with the intake passage of the internal combustion engine.

(3) The control device for an internal combustion engine according to (1) or (2) above, wherein the predetermined temperature range is 400 ° C. or higher and 650 ° C. or lower.

(4) The control device for an internal combustion engine according to any one of (1) to (3) above, wherein the exhaust gas purification catalyst is a three-way catalyst or a NOx storage reduction catalyst.

According to the present disclosure, there is provided a control device for an internal combustion engine capable of suppressing deterioration of emissions while reducing the amount of ammonia discharged from the internal combustion engine to the outside of the vehicle.

FIG. 1 is a diagram schematically showing an internal combustion engine in which the control device according to the present embodiment is used. FIG. 2 is a diagram schematically showing the reaction occurring in the exhaust gas purification catalyst. FIG. 3 is a diagram schematically showing the relationship between the temperature of the exhaust purification catalyst and the amount of ammonia produced when the exhaust gas flows into the exhaust purification catalyst. FIG. 4 is a flowchart showing a control routine of an internal combustion engine according to the present embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, similar components are given the same reference numbers.

<The present embodiment>
≪Explanation of the entire internal combustion engine≫
FIG. 1 is a diagram schematically showing an internal combustion engine in which the exhaust gas purification device according to the present embodiment is used. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a piston that reciprocates in the cylinder block 2, 4 is a cylinder head fixed on the cylinder block 2, and 5 is a piston 3 and a cylinder head 4. A combustion chamber formed between them, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, and 9 is an exhaust port. The intake valve 6 opens and closes the intake port 7, and the exhaust valve 8 opens and closes the exhaust port 9.

As shown in FIG. 1, the spark plug 10 is arranged in the central portion of the inner wall surface of the cylinder head 4, and the fuel injection valve 11 is arranged in the peripheral portion of the inner wall surface of the cylinder head 4. The spark plug 10 is configured to generate sparks in response to an ignition signal. Further, the fuel injection valve 11 injects a predetermined amount of fuel into the combustion chamber 5 in response to the injection signal. The fuel injection valve 11 may be arranged so as to inject fuel into the intake port 7. Further, in the present embodiment, gasoline having a theoretical air-fuel ratio of 14.6 is used as the fuel. However, in the internal combustion engine in which the control device of the present disclosure is used, a fuel other than gasoline or a mixed fuel with gasoline may be used.

The intake port 7 of each cylinder is connected to the surge tank 14 via the corresponding intake branch pipe 13, and the surge tank 14 is connected to the air cleaner 16 via the intake pipe 15. The intake port 7, the intake branch pipe 13, the surge tank 14, and the intake pipe 15 form an intake passage. Further, a throttle valve 18 driven by the throttle valve drive actuator 17 is arranged in the intake pipe 15. The throttle valve 18 can be rotated by the throttle valve drive actuator 17, so that the opening area of the intake passage can be changed.

On the other hand, the exhaust port 9 of each cylinder is connected to the exhaust manifold 19, and the exhaust manifold 19 is connected to the casing 21 containing the exhaust purification catalyst 20. A portion downstream of the casing 21 and a portion upstream of the intake port 7 are communicated with each other by a low-pressure EGR passage 23. The exhaust port 9, the exhaust manifold 19, the casing 21, the exhaust pipe 22, and the low-pressure EGR passage 23 form an exhaust passage through which exhaust gas flows. Further, an EGR valve 28 driven by an EGR valve drive actuator 27 is arranged in the low pressure EGR passage 23. The EGR valve 28 can be rotated by the EGR valve drive actuator 27 to change the opening area of the low pressure EGR passage 23. In a configuration in which a portion upstream of the casing 21 and a portion upstream of the intake port 7 are communicated with each other by a high-pressure EGR passage (not shown), the high-pressure EGR passage may be provided with an EGR valve 28. The low-pressure EGR passage 23 and the high-pressure EGR passage are collectively referred to as an EGR passage.

The electronic control unit (ECU) 31 is composed of a digital computer, and has a RAM (random access memory) 33, a ROM (read-only memory) 34, a CPU (microprocessor) 35, and inputs connected to each other via a bidirectional bus 32. It includes a port 36 and an output port 37.

An air flow meter 39 for detecting the flow rate of air flowing in the intake pipe 15 is arranged in the intake pipe 15, and the output of the air flow meter 39 is input to the input port 36 via the corresponding AD converter 38. Further, the exhaust manifold 19 is provided with an upstream air-fuel ratio sensor 40 that detects the air-fuel ratio of the exhaust gas flowing in the exhaust manifold 19 (that is, the exhaust gas flowing into the exhaust purification catalyst 20). In addition, a downstream air-fuel ratio sensor 41 that detects the air-fuel ratio of the exhaust gas flowing in the exhaust pipe 22 is arranged in the exhaust pipe 22. The outputs of the air-fuel ratio sensors 40 and 41 are also input to the input port 36 via the corresponding AD converter 38.

Further, the exhaust gas purification catalyst 20 is provided with a catalyst temperature sensor 46 for detecting the temperature of the exhaust gas purification catalyst 20. The temperature sensor 46 is input to the input port 36 via the corresponding AD converter 38. A heater (not shown) for raising the temperature of the exhaust gas purification catalyst 20 may be provided, and the catalyst temperature may be estimated from the amount of electricity supplied to the heater and the operating state of the internal combustion engine.

Further, a load sensor 43 that generates an output voltage proportional to the amount of depression of the accelerator pedal 42 is connected to the accelerator pedal 42, and the output voltage of the load sensor 43 is input to the input port 36 via the corresponding AD converter 38. To. For example, the crank angle sensor 44 generates an output pulse every time the crankshaft rotates by 15 degrees, and this output pulse is input to the input port 36. In the CPU 35, the engine speed is calculated from the output pulse of the crank angle sensor 44.

On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, the throttle valve drive actuator 17, and the EGR valve drive actuator 27 via the corresponding drive circuit 45. Therefore, the ECU 31 (control device) functions as a control device for controlling the operation of the spark plug 10, the fuel injection valve 11, the throttle valve drive actuator 17, and the EGR valve drive actuator 27.

In the present embodiment, the exhaust purification catalyst 20 is a three-way catalyst in which a catalyst noble metal having a catalytic action (for example, platinum (Pt), palladium (Pd), rhodium (Rh), etc.) is supported on a carrier made of ceramic. .. The three-way catalyst has a function of simultaneously purifying unburned HC, CO and NOx when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is maintained at the stoichiometric air-fuel ratio. The exhaust gas purification catalyst 20 may be a catalyst other than the three-way catalyst, such as a NOx storage reduction catalyst, as long as it supports a catalytic substance having a reducing action.

≪About ammonia production≫
Hereinafter, the principle of ammonia generation in the exhaust gas purification catalyst 20 will be described with reference to FIG. FIG. 2 is a diagram schematically showing the reaction that occurs in the exhaust purification catalyst 20 when the exhaust gas having a rich air-fuel ratio flows into the exhaust purification catalyst 20.

In order to promote the catalytic action of the exhaust gas purification catalyst 20, it is necessary to raise the temperature of the exhaust gas purification catalyst 20 to a temperature higher than the active temperature thereof. Specifically, the temperature of the exhaust gas purification catalyst 20 is set to 300 ° C. or higher and 700 ° C. or lower, preferably 400 ° C. or higher and 650 ° C. or lower.

In addition, in promoting the catalytic action of the exhaust purification catalyst 20, the air-fuel ratio of the exhaust gas discharged from the engine body 1 is leaner than the theoretical air-fuel ratio (hereinafter, also referred to as "lean air-fuel ratio"). The fuel injection amount from the fuel injection valve 11 is controlled so that the air-fuel ratio is richer than the theoretical air-fuel ratio (hereinafter, also referred to as "rich air-fuel ratio").

Here, the exhaust gas having a rich air-fuel ratio contains unburned HC and CO. In addition, since water is generated by the combustion of the air-fuel mixture in the combustion chamber 5, the exhaust gas contains water. Therefore, the exhaust gas containing unburned HC, CO, and water flows into the exhaust purification catalyst 20.

When the temperature of the exhaust purification catalyst 20 is from 300 ° C to 500 ° C, when the exhaust gas containing CO and water flows into the exhaust purification catalyst 20, it is represented by the following formula (1) due to the catalytic action of the exhaust purification catalyst 20. An aqueous gas shift reaction occurs in the exhaust gas purification catalyst 20.
CO + H2O → H2 + CO2 ... (1)

Further, when the temperature of the exhaust purification catalyst 20 is 500 ° C. or higher, when the exhaust gas containing unburned HC and water flows into the exhaust purification catalyst 20, the following formula (2) or formula is formed by the catalytic action of the exhaust purification catalyst 20. The steam reforming reaction as represented by (3) occurs in the exhaust gas purification catalyst 20.
CH4 + H2O → 3H2 + CO… (2)
C12H26 + 12H2O → 25H2 + 12CO ... (3)

Therefore, when the temperature of the exhaust purification catalyst 20 is equal to or higher than the active temperature (for example, 300 ° C.), when the exhaust gas having a rich air-fuel ratio flows into the exhaust purification catalyst 20, hydrogen is generated in the exhaust purification catalyst 20.

Further, even when the air-fuel ratio of the exhaust gas discharged from the engine main body 1 is the rich air-fuel ratio, NOx (mainly NO) is contained in the exhaust gas. When the temperature of the exhaust gas purification catalyst 20 is relatively high, the NO contained in the exhaust gas is represented by the following formula (4) in the exhaust gas purification catalyst 20 due to the catalytic action of the exhaust gas purification catalyst 20. It reacts with hydrogen to produce ammonia. Further, when the air-fuel ratio of the exhaust gas discharged from the engine body 1 changes to the rich air-fuel ratio via the lean air-fuel ratio caused by the fuel cut control, the catalyst warm-up control, and the intermittent operation control, the air-fuel ratio in the exhaust gas is changed. Since the NOx concentration becomes high and reacts with a large amount of hydrogen, a large amount of ammonia is produced. Such a reaction is particularly likely to occur when the temperature of the exhaust gas purification catalyst 20 is 400 ° C. to 650 ° C.
2NO + 5H2 → 2NH3 + 2H2O ... (4)

Therefore, when the temperature of the exhaust purification catalyst 20 is equal to or higher than the active temperature (particularly when the temperature is 400 ° C. to 650 ° C.), when the exhaust gas having a rich air fuel ratio flows into the exhaust gas purification catalyst 20, the exhaust gas purification catalyst 20 emits ammonia. Exhaust gas with a rich air-fuel ratio including the above will flow out.

Here, when the exhaust gas containing ammonia flows through the EGR passage, flows into the intake passage, and burns with oxygen in the combustion chamber, the reaction represented by the following formula (5) occurs in the combustion chamber.
2NH3 + 3 / 2O2 → N2 + 3H2O ... (5)

Therefore, the exhaust gas containing ammonia generated by the exhaust purification catalyst 20 flows through the EGR passage and flows into the intake passage, and the ammonia is burned in the combustion chamber, so that the ammonia generated by the exhaust purification catalyst 20 is used in the vehicle. It is possible to suppress the exhaust to the outside.

FIG. 3 shows the relationship between the temperature of the exhaust purification catalyst 20 and the amount of ammonia produced when the exhaust gas having a rich air-fuel ratio flows into the exhaust purification catalyst 20. The predetermined temperature zone in the figure is a temperature zone including Tmax ° C., which is the catalyst temperature when the amount of ammonia produced is the largest, and is a temperature zone in which ammonia is easily produced in the exhaust gas purification catalyst 20.

≪Specific control≫
Next, with reference to FIG. 4, specific control in the control of the internal combustion engine according to the present embodiment will be described. FIG. 4 is a flowchart showing a control routine of an internal combustion engine according to the present embodiment. The illustrated control routine is executed at regular time intervals.

First, in step S101, the control device 31 reads the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst 20 and the temperature of the exhaust purification catalyst 20. As the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst 20, a value output from the air-fuel ratio sensor 40 may be used, or the fuel injection amount from the fuel injection valve 11 and the intake air amount from the throttle valve may be used. It may be estimated based on the exhaust gas recirculation amount of the exhaust gas flowing in from the EGR valve 28. The temperature of the exhaust gas recirculation catalyst 20 may be a value output from the temperature sensor 46, or the fuel injection amount from the fuel injection valve 11, the intake air amount from the throttle valve, and the inflow from the EGR valve 28. It may be estimated based on the exhaust gas recirculation amount of the exhaust gas.

In step S102, it is determined whether or not the air-fuel ratio flowing into the exhaust gas purification catalyst 20 has changed from a lean air-fuel ratio than the theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air-fuel ratio. If it is determined in step S102 that the air-fuel ratio flowing into the exhaust gas purification catalyst 20 has not changed from a lean air-fuel ratio than the theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air-fuel ratio, the control routine is used. Is terminated. If it is determined in step S102 that the air-fuel ratio flowing into the exhaust gas purification catalyst 20 has changed from a lean air-fuel ratio than the theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air-fuel ratio, the step is taken. Proceed to S103.

In step S103, it is determined whether or not the temperature of the exhaust gas purification catalyst 20 is in a predetermined temperature range in which ammonia is likely to be generated by the exhaust gas purification catalyst 20. The predetermined temperature range in which ammonia is easily generated is a temperature range including Tmax ° C., which is the catalyst temperature when the amount of ammonia produced is maximum. Specifically, the temperature of the exhaust gas purification catalyst 20 is 400 ° C. or higher and 650 ° C. or lower. It is determined whether or not it is. When the operating state is such that ammonia is easily generated, the predetermined temperature zone may be widened. When the operating state is such that ammonia is difficult to be generated, the predetermined temperature zone may be narrowed.

In step S104, the control device 31 adjusts the opening degree of the EGR valve 28 so that the amount of exhaust gas passing through the EGR passage increases. Specifically, the operation of the drive actuator 27 of the EGR valve 28 is controlled, and the EGR valve 28 is controlled to the opening side so as to increase the opening area of the low pressure EGR passage 23. As a result, the amount of ammonia generated by the exhaust purification catalyst 20 passing through the exhaust passage and being discharged to the outside of the vehicle as it is is reduced, and deterioration of emissions can be suppressed. After adjusting the opening degree of the EGR valve 28 so that the amount of exhaust gas passing through the EGR passage is adjusted, when the temperature of the exhaust purification catalyst 20 changes to a temperature other than the predetermined temperature range, the exhaust gas passing through the EGR passage is used. The opening degree of the EGR valve 28 may be adjusted so that the amount of the EGR valve 28 is reduced. Specifically, the operation of the drive actuator 27 of the EGR valve 28 is controlled, and the EGR valve 28 is controlled to the closing side so as to reduce the opening area of the low pressure EGR passage 23.

Moreover, the present invention is not limited by the above-described embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above embodiment, and various modifications can be made.

1: Engine body 5: Combustion chamber 11: Fuel injection valve 20: Exhaust gas recirculation catalyst 27: EGR valve drive actuator 28: EGR valve 31: ECU (control device)
40,41: Air-fuel ratio sensor 46: Catalyst temperature sensor

Claims (4)

An exhaust purification catalyst provided in the exhaust passage of an internal combustion engine to purify the exhaust gas passing through the exhaust passage,
An EGR passage that connects the exhaust passage and the intake passage of the internal combustion engine,
An EGR valve provided in the exhaust passage or the EGR passage and adjusting the amount of exhaust gas passing through the exhaust passage, and an EGR valve.
It is a control device of an internal combustion engine equipped with
The control device is used when the air-fuel ratio of the exhaust gas discharged from the internal combustion engine changes from a lean air-fuel ratio leaner than the theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air-fuel ratio, and the exhaust purification catalyst. When the temperature is in a predetermined temperature range in which ammonia is likely to be generated in the exhaust purification catalyst, the air-fuel ratio of the exhaust gas changes from a lean air-fuel ratio leaner than the theoretical air-fuel ratio to a rich air-fuel ratio richer than the theoretical air-fuel ratio. A control device for an internal combustion engine that adjusts the opening degree of the EGR valve so that the amount of exhaust gas passing through the EGR passage is increased as compared with the case where the temperature is outside the predetermined temperature range. The control device for an internal combustion engine according to claim 1, wherein the EGR passage communicates the exhaust passage on the downstream side of the exhaust purification catalyst with the intake passage of the internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2, wherein the predetermined temperature range is 400 ° C. or higher and 650 ° C. or lower. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the exhaust gas purification catalyst is a three-way catalyst or a NOx storage reduction catalyst.

Images