JPH11247688A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine which allows compatibly establishing the prevention of thermal ill influence upon an exhaust gas recirculating mechanism, for example an EGR valve, and prevention of degradation of emission. SOLUTION: An engine 11 executes combustion on either of the combustion systems according to the present operating situation, i.e., homogenious combustion, homogenious lean combustion, weak stratified combustion, and stratified combustion. An electronic control unit(ECU) furnished at the engine 11 recirculates part of the exhaust gas from the engine 11 to the suction passage 32 via an EGR passage 42 during the execution of lean combustion such as the homogenious lean combustion, weak stratified combustion, or stratified combustion. When an EGR valve 43 installed on the way of EGR passage 42 gets a temperature over the heat resisting limit, the ECU controls the EGR valve 43 so that the amount of exhaust gas recirculated nullifies and performs a feedback control so that the air-fuel ratio of the mixture gas becomes the theoretical value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine that performs a lean burn while recirculating a part of exhaust gas to an intake system.

[0002]

2. Description of the Related Art In recent years, in internal combustion engines for automobiles,
In order to improve fuel efficiency, a device that performs lean combustion in which an air-fuel ratio greater than the stoichiometric air-fuel ratio is burned has been proposed and put into practical use. An example of an internal combustion engine that performs such lean combustion is described, for example, in Japanese Patent Application Laid-Open No. 8-189405.

[0003] In the internal combustion engine described in the publication,
In low load areas where high output is not required, lean combustion is performed to improve fuel efficiency, and in high load areas where high output is required, sufficient engine output is obtained by performing combustion at the stoichiometric air-fuel ratio. . By switching the combustion method of the internal combustion engine in this manner, it is possible to obtain sufficient engine output while improving fuel efficiency.

Further, the internal combustion engine employs an exhaust gas recirculation (EGR) mechanism for recirculating a part of exhaust gas to an intake system in order to reduce emission during lean combustion. The EGR mechanism includes an EGR passage that connects an exhaust passage and an intake passage of the engine, and an EGR valve for adjusting an exhaust flow area of the EGR passage.

When the internal combustion engine is performing lean combustion, the EGR valve is opened, and the exhaust gas is supplied to the intake passage via the EGR passage by the pressure in the exhaust passage. In this way, the exhaust gas of the internal combustion engine is recirculated to the intake system, so that the temperature in the combustion chamber decreases and the nitrogen oxides (N
Ox) is suppressed and emission is reduced.

[0006]

However, during lean combustion, if the exhaust pressure in the exhaust passage increases due to, for example, melting of a catalyst provided in the exhaust system of the internal combustion engine, the EGR amount becomes excessively large. There is a possibility that the temperature of the EGR valve becomes higher than the heat-resistant limit temperature due to the heat of the exhaust gas. Such E
It is conceivable to reduce the EGR amount by closing the GR valve in order to suppress a rise in the temperature of the GR valve. However, in this case, NOx increases and the emission deteriorates.

The present invention has been made in view of such circumstances, and has as its object to provide an internal combustion engine capable of preventing both adverse effects of heat on an exhaust gas recirculation mechanism such as an EGR valve and emission deterioration. An object of the present invention is to provide an engine control device.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an air-fuel ratio of an air-fuel mixture is detected from an exhaust purification catalyst provided in an exhaust system of an internal combustion engine and exhaust gas from the engine. Air-fuel ratio detecting means, and an exhaust gas recirculation mechanism for recirculating exhaust gas from the engine to the intake system, and a control device for an internal combustion engine that performs lean combustion when the operating state of the engine is in a lean combustion region. When the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than a predetermined high temperature, the exhaust gas recirculation mechanism is controlled to reduce the amount of exhaust gas recirculation, and mixing is performed based on a detection signal from the air-fuel ratio detection means. Control means is provided for performing feedback control of the air-fuel ratio of the gas to the stoichiometric air-fuel ratio.

According to this configuration, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than the predetermined high temperature, the amount of exhaust gas recirculation is reduced, and the temperature rise of the exhaust gas recirculation mechanism is suppressed. Further, at this time, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, and the exhaust gas is efficiently purified by the exhaust purification catalyst. Therefore, even if the exhaust gas recirculation amount is reduced, the emission does not deteriorate. Therefore, it is possible to achieve both the prevention of the adverse effect of the heat on the exhaust gas recirculation mechanism and the prevention of the deterioration of the emission of the internal combustion engine.

According to a second aspect of the present invention, in the first aspect of the present invention, when the state in which the temperature of the exhaust gas recirculation mechanism has become a predetermined high temperature or more has continued for a predetermined time or more, The control of the exhaust gas recirculation mechanism to reduce the amount of exhaust gas recirculation and the feedback control to the stoichiometric air-fuel ratio are performed.

According to the above construction, it is possible to accurately detect that the temperature of the exhaust gas recirculation mechanism has become higher than a predetermined high temperature, and to prevent unnecessary reduction of the exhaust gas recirculation amount. It is possible to prevent emission deterioration due to a large reduction in the amount of exhaust gas recirculation.

According to the third aspect of the present invention, the first or second aspect is provided.
In the invention described in the above, the exhaust gas recirculation mechanism comprises a passage for supplying exhaust gas to the intake system and a valve for adjusting an exhaust flow area of the passage, and a valve temperature detecting means for detecting a temperature of the valve. Further, the control means determines whether or not the temperature of the exhaust gas recirculation mechanism has become equal to or higher than a predetermined high temperature based on the valve temperature detected by the valve temperature detection means.

According to the above configuration, by adjusting the exhaust gas recirculation amount to the reduction side based on the valve temperature in the exhaust gas recirculation mechanism, it is possible to preferably prevent the valve from being adversely affected by thermal distortion or the like. Become like

According to a fourth aspect of the present invention, in the first aspect of the present invention, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than a predetermined high temperature, the control means controls the exhaust gas recirculation. The exhaust gas recirculation mechanism is controlled so that the circulation amount becomes “0”.

According to this configuration, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than a predetermined high temperature, the exhaust gas recirculation amount is set to "0" and the temperature rise of the exhaust gas recirculation mechanism is suitably suppressed.
An adverse effect on the exhaust gas recirculation mechanism due to heat is suitably prevented.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a first embodiment in which the present invention is applied to an in-line four-cylinder automobile gasoline engine will be described.
An embodiment will be described with reference to FIGS.

As shown in FIG. 1, the engine 11 has a total of four pistons 12 (only one is shown in FIG. 1) provided so as to be able to reciprocate in a cylinder block 11a. These pistons 12 are connected via a connecting rod 13 to a crankshaft 14 which is an output shaft. The reciprocating movement of the piston 12 is converted into rotation of the crankshaft 14 by the connecting rod 13.

A signal rotor 14a is attached to the crankshaft 14. This signal rotor 14
A plurality of protrusions 14b are provided at equal angles around the axis of the crankshaft 14 on the outer peripheral portion of a. A crank position sensor 14c is provided on the side of the signal rotor 14a. When the crankshaft 14 rotates and the projections 14b of the signal rotor 14a sequentially pass by the side of the crank position sensor 14c, the sensor 14c detects pulse-like detection corresponding to the passage of the projections 14b. A signal is output.

A cylinder head 15 is provided at the upper end of the cylinder block 11a, and a combustion chamber 16 is provided between the cylinder head 15 and the piston 12.
A pair of intake ports 17a and 17b provided in the cylinder head 15 and a pair of exhaust ports 18a and 18b are also connected to the combustion chamber 16 (one intake port 17b and one exhaust port in FIG. 1). 18b only).
These intake and exhaust ports 17a, 17b, 18a, 1
FIG. 2 shows a plane cross-sectional shape of 8b.

As shown in FIG.
Is a helical port extending in a curved manner, and the intake port 17b is a straight port extending in a straight line. When air passes through the intake port (helical port) 17a and is sucked into the combustion chamber 16, swirl is generated in the combustion chamber 16 in the direction indicated by the dashed arrow. The intake ports 17a and 17b and the exhaust ports 18a and 18b are provided with an intake valve 19 and an exhaust valve 20, respectively.

On the other hand, as shown in FIG. 1, an intake cam shaft 21 and an exhaust cam shaft 22 for opening and closing the intake valve 19 and the exhaust valve 20 are rotatably supported on the cylinder head 15. The intake and exhaust camshafts 21 and 22 are connected to the crankshaft 1 via a timing belt and gears (both not shown).
4 and the rotation of the crankshaft 14 is transmitted by the belt and the gears. Then, when the intake camshaft 21 rotates, the intake valve 19 is driven to open and close, so that the intake ports 17a and 17b and the combustion chamber 16 are communicated and shut off. Further, when the exhaust camshaft 22 rotates, the exhaust valve 20 is driven to open and close, and the exhaust ports 18a, 18b and the combustion chamber 16 are communicated and shut off.

In the cylinder head 15, a cam position sensor 21b for detecting a protrusion 21a provided on the outer peripheral surface of the intake camshaft 21 and outputting a detection signal is provided on a side of the intake camshaft 21. When the intake camshaft 21 rotates, the protrusion 21a of the shaft 21 passes by the side of the cam position sensor 21b. In this state, the cam position sensor 21b
Thus, the detection signal is output at predetermined intervals corresponding to the passage of the protrusion 21a.

The intake ports 17a and 17b and the exhaust ports 18a and 18b have an intake pipe 30 and an exhaust pipe 3 respectively.
1 is connected. The interior of the intake pipe 30 and the interior of the intake ports 17a and 17b constitute an intake passage 32, and the interior of the exhaust pipe 31 and the interior of the exhaust ports 18a and 18b constitute an exhaust passage 33.
It has become. In the middle of the exhaust passage 33, the engine 11
An exhaust gas purifying catalyst 33a for purifying the exhaust gas and an oxygen (O2) sensor 37 for outputting a signal corresponding to the oxygen concentration in the exhaust gas are provided. On the other hand, a throttle valve 23 is provided in an upstream portion of the intake passage 32. The opening of the throttle valve 23 is adjusted by driving the throttle motor 24. The opening of the throttle valve 23 is detected by a throttle position sensor 44.

The driving of the throttle motor 24 is controlled based on the amount of depression of an accelerator pedal 25 provided in the cabin of the automobile. That is, when the driver of the automobile depresses the accelerator pedal 25, the accelerator pedal 25
Is detected by the accelerator position sensor 26, and the drive of the throttle motor 24 is controlled based on the detection signal of the accelerator position sensor 26. This throttle motor 2
By adjusting the opening degree of the throttle valve 23 based on the drive control of No. 4, the air flow area of the intake passage 32 changes, and the amount of air taken into the combustion chamber 16 is adjusted.

In the intake passage 32, the throttle valve 2
A vacuum sensor 36 for detecting a pressure in the passage 32 is provided in a portion located downstream of the passage 3. Then, the vacuum sensor 36 outputs a detection signal corresponding to the detected pressure in the intake passage 32. In addition, a swirl control valve (SCV) 34 is provided in the intake passage 32 located downstream of the vacuum sensor 36 and communicating with the intake port (straight port) 17b. The SCV 34 is rotated by driving the swirl motor 35 to adjust the opening. Then, as the opening degree of the SCV 34 decreases, the amount of air passing through the intake port (helical port) 17a shown in FIG.
The swirl generated in the combustion chamber 16 increases.

As shown in FIG. 2, the cylinder head 15 is provided with a fuel injection valve 40 and a spark plug 41. Then, the fuel injected from the fuel injection valve 40 into the combustion chamber 16 is mixed with the air sucked into the combustion chamber 16 through the intake passage 32, so that the combustion chamber 1
A mixture of air and fuel is formed in 6. Further, the air-fuel mixture in the combustion chamber 16 is ignited by the ignition plug 41 and burns, and the air-fuel mixture after the combustion is sent to the exhaust passage 33 as exhaust gas and purified by the exhaust purification catalyst 33a. The ignition timing of the air-fuel mixture by the ignition plug 41 is adjusted by an igniter 41a provided above the ignition plug 41.

On the other hand, the throttle valve 2 in the intake passage 32
The downstream side of the third passage 3 communicates with the exhaust passage 33 via an exhaust gas recirculation (EGR) passage 42. This EGR passage 42
Is provided with an EGR valve 43 having a step motor 43a. Then, the EGR valve 43
The opening is adjusted by controlling the drive of the stepping motor 43a. By adjusting the opening degree of the EGR valve 43, the amount of exhaust gas recirculated to the intake passage 32 via the exhaust passage 33 is adjusted.

Here, the detailed structure of the EGR valve 43 will be described with reference to FIG. As shown in FIG.
The R valve 43 includes a housing 51 in which the EGR passage 42 is formed, and a case 53 attached to the housing 51 by bolts 52. EGR passage 4
In the middle of 2, there is provided a sheet 54 formed in a ring shape and attached to the inner peripheral surface of the passage 42. The valve body 55 comes into contact with the seat 54, and the flow of exhaust gas in the EGR passage 42 is prohibited by the contact between the valve body 55 and the seat 54. Further, the valve element 55 is attached to a distal end of a shaft 56 extending in the axial direction of the seat 54 formed in a ring shape. The base end of the shaft 56 penetrates the case 53 and is connected to a step motor 43 a attached to the case 53.

When the step motor 43a is driven, the shaft 56 moves in its own axial direction, and the valve body 55
Approaches or separates from the sheet 54. This valve element 55
The movement of the exhaust gas changes the area of exhaust gas flow between the seat 54 and the valve element 55, so that the amount of exhaust gas (EGR amount) passing through the EGR passage 42 is adjusted. EGR valve 4
3, the temperature of the housing 51, the seat 54 and the valve body 5
The temperature such as 5 increases as the EGR amount increases,
It decreases as the amount of R decreases. And the housing 5
1, a temperature sensor 57 for detecting the temperature of the seat 54 as the temperature of the EGR valve 43 is provided.

Next, the electrical configuration of the control device for the engine 11 in this embodiment will be described with reference to FIG. This control device controls fuel injection amount, fuel injection timing, SC
An electronic control unit (hereinafter referred to as “ECU”) for controlling the operating state of the engine 11 such as V opening control and EGR control
92). This ECU 92 has a ROM
93, CPU 94, RAM 95, and backup RAM
It is configured as a logical operation circuit having 96 or the like.

Here, the ROM 93 is a memory that stores various control programs and maps and the like that are referred to when executing the various control programs.
The arithmetic processing is executed based on various control programs and maps stored in the OM 93. The RAM 95 is a CPU
94 is a memory for temporarily storing the calculation result at 94, data input from each sensor, and the like.
Reference numeral 6 denotes a nonvolatile memory for storing data to be stored when the engine 11 is stopped. And ROM93, CP
The U 94, the RAM 95, and the backup RAM 96 are connected to each other via a bus 97, and are also connected to an external input circuit 98 and an external output circuit 99.

The external input circuit 98 is connected to the crank position sensor 14c, the cam position sensor 21b, the accelerator position sensor 26, the vacuum sensor 36, the oxygen sensor 37, the throttle position sensor 44, the temperature sensor 57, and the like. On the other hand, the external output circuit 9
9 includes a throttle motor 24 and a swirl motor 3
5, the fuel injection valve 40, the EGR valve 43, and the like are connected.

The ECU 92 configured as described above obtains the engine speed NE based on the detection signal from the crank position sensor 14c. Further, a fuel injection amount Q representing the load of the engine 11 is obtained based on the detection signal from the throttle position sensor 44 or the vacuum sensor 36 and the engine speed NE. The ECU 92 shown in FIG.
The combustion method of the engine 11 is determined from the engine speed NE and the fuel injection amount Q with reference to the map. This map includes a homogeneous combustion region A, a homogeneous lean combustion region B, a weak stratified combustion region C, and a stratified combustion region D. Then, depending on which of the regions A to D the engine speed NE and the fuel injection amount Q are located in, the combustion system of the engine 11 is switched to homogeneous combustion, homogeneous lean combustion, weak stratified combustion, and stratified combustion by the ECU 92, respectively. It is determined.

As is apparent from the above map, as the operating state of the engine 11 shifts to high rotation and high load, the combustion method of the engine 11 sequentially changes to stratified combustion, weakly stratified combustion, homogeneous lean combustion, and homogeneous combustion. Will be done. The reason for changing the combustion method in this way is to increase the engine output by lowering the air-fuel ratio of the air-fuel mixture during high-speed high-load operation where high power is required, and to increase the air-fuel ratio during low-speed low-load operation where high output is not required. This is to increase fuel efficiency to improve fuel economy.

When the combustion mode of the engine 11 is determined to be “homogeneous combustion”, the ECU 92
The amount of intake air is calculated based on the detection signal from. Then, the fuel injection amount Q is obtained from a known map based on the calculated intake air amount and the engine speed NE. EC
The U 92 controls the drive of the fuel injection valve 40 based on the fuel injection amount Q obtained in this way, and causes the fuel to be injected from the fuel injection valve 40 during the intake stroke of the engine 11. Also, ECU
92 corrects the fuel injection amount Q based on the detection signal from the oxygen sensor 37 and performs feedback control of the air-fuel ratio of the air-fuel mixture in the combustion chamber 16 to the stoichiometric air-fuel ratio. Furthermore, EC
The U92 controls the opening of the SCV 34 by controlling the drive of the swirl motor 35 so that the air-fuel mixture in the combustion chamber 16 becomes uniform by the swirl.

When the combustion method of the engine 11 is determined to be “homogeneous lean combustion”, the ECU 92 obtains the opening of the throttle valve 23 (throttle opening) based on the detection signal from the throttle position sensor 42. Then, the fuel injection amount Q is obtained from a known map based on the obtained throttle opening and the engine speed NE. EC
U92 controls the driving of the fuel injection valve 40 based on the fuel injection amount Q thus obtained, and controls the fuel injection valve 4 during the intake stroke.
Fuel is injected from 0 to make the air-fuel ratio of the air-fuel mixture larger than the stoichiometric air-fuel ratio (for example, 15 to 23). Furthermore, EC
The U92 controls the opening of the SCV 34 by controlling the drive of the swirl motor 35, and stably burns the air-fuel mixture having an air-fuel ratio larger than the stoichiometric air-fuel ratio by swirling.

When the combustion mode of the engine 11 is determined to be "weak stratified combustion", the ECU 92 obtains the fuel injection amount Q from the throttle opening and the engine speed NE in the same manner as described above. The ECU 92 controls the drive of the fuel injection valve 40 based on the fuel injection amount Q obtained in this manner to inject fuel during the intake stroke and the compression stroke of the engine 11 and to change the air-fuel ratio of the air-fuel mixture during “homogeneous lean combustion”. Is larger than the air-fuel ratio (for example, 20 to 23).

At the time of such "weak stratified combustion", the fuel injected and supplied during the intake stroke is evenly distributed to the air in the combustion chamber 16 by the swirl, and the fuel injected and supplied during the compression stroke is swirl and swirl. The gas is collected around the spark plug 41 by a depression 12 a provided in the head of the piston 12. The ECU 92 controls the drive of the swirl motor 35 to adjust the opening of the SCV 34 so that the swirl strength is suitable for the above-described fuel dispersion and aggregation. As described above, the fuel injection is performed in two stages, the intake stroke and the compression stroke, so that the air-fuel mixture is produced in a combustion mode (weak stratified combustion) intermediate between the above-mentioned "homogeneous lean combustion" and "stratified combustion" described later. Is performed, and the "weak stratified combustion" suppresses torque shock when switching between "homogeneous lean combustion" and "stratified combustion".

On the other hand, when the combustion mode of the engine 11 is determined to be "stratified combustion", the ECU 92 obtains the fuel injection amount Q from the throttle opening and the engine speed NE in the same manner as described above. The ECU 92 controls the driving of the fuel injection valve 40 based on the fuel injection amount Q obtained in this manner, injects fuel during the compression stroke of the engine 11, and sets the air-fuel ratio of the air-fuel mixture to be lower than the air-fuel ratio at the time of “weak stratified combustion”. Large values (for example, 25
５０50). Further, the ECU 92 controls the driving of the swirl motor 35 so as to generate swirl in the combustion chamber 16 to adjust the opening of the SCV 34,
The fuel injected and supplied by the swirl is collected around the spark plug 41. By collecting the fuel around the ignition plug 41 in this manner, even if the average air-fuel ratio of the entire air-fuel mixture in the combustion chamber 16 is larger than that during “weak stratified combustion”,
The fuel concentration of the air-fuel mixture around the plug 41 is increased, and good air-fuel mixture is ignited.

Next, a procedure for detecting that the temperature of the EGR valve 43 has exceeded the heat resistant limit temperature will be described with reference to FIG. FIG. 6 is a flowchart showing a temperature abnormality detection routine for detecting that the EGR valve 43 has reached or exceeded the heat-resistant limit temperature. This temperature abnormality detection routine is executed, for example, by an interrupt at predetermined time intervals through the ECU 92.

In the temperature abnormality detection routine, the ECU 9
2 is a process of step S101, in which the temperature sensor 57
It is determined whether or not the temperature of the EGR valve 43 is equal to or higher than the heat-resistant limit temperature (for example, 300 ° C.) based on the detection signal. When it is determined that the EGR valve 43 is at or above the heat resistant limit temperature, the process proceeds to step S102, and when it is determined that the EGR valve 43 is at or above the heat resistant limit temperature, step S10 is performed.
Proceed to 3. The ECU 92 adds "1" to the temperature abnormality counter Ct in the process of step S102, and resets the temperature abnormality counter Ct to "0" in the process of step S103.

Subsequently, the process proceeds to step S104, where the ECU 9
2 judges whether the temperature abnormality counter Ct is larger than a predetermined value A or not. The predetermined value A is determined by the EGR valve 4
3 corresponds to the duration after the temperature reaches the heat-resistant limit temperature, and the time during which the EGR valve 43 can reliably determine that the temperature is equal to or higher than the heat-resistant limit temperature (0.5 second in the present embodiment).
Is a value corresponding to. Therefore, “Ct> A” means that the state where the EGR valve 43 has reached the heat-resistant limit temperature or more has continued for 0.5 seconds or more.

If it is determined in step 104 that "Ct>A", the process proceeds to step S10.
Then, if it is determined that "Ct>A" is not satisfied, the process proceeds to step S106. The ECU 92 stores “1” in the predetermined area of the RAM 95 as the temperature abnormality flag F in the processing of step S105, and stores “0” in the predetermined area of the RAM 95 in the processing of step S106.
Thereafter, the ECU 92 once ends the temperature abnormality detection routine. By such a temperature abnormality detection routine, the temperature abnormality flag F is set to "1" or "0", so that it is possible to determine whether or not the EGR valve 43 is at or above the heat-resistant limit temperature.

Next, a combustion control procedure in the engine 11 will be described with reference to FIG. FIG. 8 shows the engine 1
4 is a flowchart illustrating a combustion control routine for performing the first combustion control. This combustion control routine is executed by the ECU 9
2 through, for example, a time interruption every predetermined time.

In the combustion control routine, the ECU 92
Determines whether the fuel injection amount Q is larger than the determination value QA as the process of step S201. This judgment value QA
As shown in the map of FIG. 5, on the boundary between the stratified combustion region D and the weakly stratified combustion region C, the engine speed NE
And changes in the fuel injection amount Q as shown in the figure.
If "Q>QA" is not satisfied in step S201, it is determined that the operation state of the engine 11 is in the stratified combustion region D, and the process proceeds to step S207. ECU
92 executes the above-described "stratified combustion" as the processing of step S207, and executes EG as the processing of subsequent step 208.
After executing R, the combustion control routine is temporarily ended.

In the process of step S208, E
The CU 92 calculates a map of the opening of the EGR valve 43 from the map of FIG. 7 based on the fuel injection amount Q and the engine speed NE. When the opening of the EGR valve 43 is calculated in this way, the ECU 92 controls the drive of the EGR valve 43 by another routine so that the opening corresponds to the calculated valve opening. By controlling the opening degree of the EGR valve 43, a part of the exhaust gas in the engine 11 is recirculated to the intake passage 32, thereby reducing the emission.

On the other hand, if it is determined in step S201 that "Q>QA", the process proceeds to step S202. The ECU 92 determines whether or not the fuel injection amount Q is larger than the determination value QB as the process of step S202. This determination value QB is, as shown in the map of FIG. 5, on the boundary between the weakly stratified combustion region C and the homogeneous lean combustion region B, with respect to changes in the engine speed NE and the fuel injection amount Q as shown in the figure. Transition to. If "Q>QB" is not satisfied in step S202, it is determined that the operation state of the engine 11 is in the weak stratified combustion region C, and the process proceeds to step S209. The ECU 92 executes the above-described “weak stratified combustion” as the processing of step S209, and executes the above-described step S210 as the processing of step S210.
After executing the EGR in the same manner as in the process of 208, the combustion control routine is temporarily terminated.

In the process of step S202, "Q
> QB ”, step S20
Proceed to 3. The ECU 92 determines whether or not the fuel injection amount Q is larger than the determination value QDJ as the process of step S203. As shown in the map of FIG. 5, the determination value QDJ changes as shown in the figure with respect to changes in the engine speed NE and the fuel injection amount Q on the boundary between the homogeneous lean combustion region B and the homogeneous combustion region A. I do. Then, the above step S20
3, if “Q> QDJ”, the engine 11
Is determined to be in the homogeneous combustion region A, and the routine proceeds to step S211. The ECU 92 executes the above-described “homogeneous combustion” as the process of step S211. Then E
The CU 92 controls the drive of the EGR valve 43 so that the opening degree of the EGR valve 43 becomes “0” as the process of step S212, and the amount of exhaust gas (EGR) passing through the EGR passage 42
Amount) to “0”. Thereafter, the ECU 92 once ends the combustion control routine.

On the other hand, if it is determined in step S203 that Q> QDJ is not satisfied, it is determined that the operating state of the engine 11 is in the homogeneous lean burn region B, and the routine proceeds to step S204. The ECU 92 sets “1” as the temperature abnormality flag F in the process of step S204.
Is stored in a predetermined area of the RAM 95, that is, whether or not the state in which the EGR valve 43 has exceeded the heat resistant limit temperature has continued for a predetermined time (0.5 seconds in the present embodiment).

If the result of step S204 is NO, the process proceeds to step S205. EC
The U92 executes the above-mentioned "homogeneous lean combustion" as the processing of step S205, executes EGR as the processing of the subsequent step S206, and then temporarily ends the combustion control routine. Also, in step S204, YE
If determined to be S, steps S211 and S2 described above are performed.
After sequentially executing the processes of No. 12, the combustion control routine is temporarily ended.

As described above, proceeding from step S204 to steps S211, S212 means that the exhaust gas purification catalyst 33a is melted and damaged during execution of "homogeneous lean combustion", so that the exhaust pressure in the exhaust passage 33 becomes excessively high. This occurs when the EGR amount becomes excessively large, and the state in which the exhaust valve 43 becomes higher than the heat resistant limit temperature due to exhaust heat continues for 0.5 seconds or more. Even if the temperature of the EGR valve 43 becomes equal to or higher than the heat-resistant limit temperature in this manner, the EGR valve 43 performs the processing in step S212.
Since the amount is set to “0” and the heating of the EGR valve 43 by the exhaust heat is suitably suppressed, the temperature of the EGR valve 43 is suitably suppressed to be equal to or lower than the heat-resistant limit temperature.

Further, even when the EGR amount is set to "0" as described above, the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio by executing "homogeneous combustion" in the process of step S211. The exhaust of the engine 11 is efficiently purified by the exhaust purification catalyst 33a. Therefore, deterioration of the emission caused by setting the EGR amount to “0” in order to prevent the heating of the EGR valve 43 is prevented.

According to this embodiment in which the processing described above is performed, the following effects can be obtained. (1) If the EGR valve 43 becomes higher than the heat-resistant limit temperature during “homogeneous lean combustion”, the EGR amount is set to “0” and the EGR
Since the heating of the valve 43 is suitably suppressed, it is possible to preferably prevent the occurrence of a problem such as the thermal distortion of the housing 51 or the like and the valve 43 not being fully closed. When the EGR amount is set to “0” as described above, the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio, so that the exhaust gas of the engine 11 is efficiently purified by the exhaust gas purification catalyst 33a. , The deterioration of emission caused by setting the EGR amount to “0” can be prevented. Therefore, it is possible to achieve both the prevention of the adverse effect of the heat on the EGR valve 43 and the prevention of the deterioration of the emission.

(2) In the temperature abnormality detection routine of FIG. 6, by executing the processing of step S104, the EGR
When the state where the temperature of the valve 43 has exceeded the heat-resistant limit temperature has continued for a predetermined time (0.5 second), the temperature abnormality flag F is set to “1”.
To determine that the temperature of the valve 43 has become equal to or higher than the heat-resistant limit temperature. Therefore, even when the temperature of the EGR valve 43 fluctuates near the heat resistant limit temperature, the
3 can be accurately determined to be equal to or higher than the heat-resistant limit temperature, thereby preventing the EGR amount from being unnecessarily set to “0”. In this way, it is prevented that the EGR amount is unnecessarily set to “0”, so that the unnecessary EGR amount =
It is possible to prevent "0" from leading to emission deterioration.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the second embodiment, the ECU
Only the combustion control routine executed through 92 differs from the first embodiment. That is, in the present embodiment, not only at the time of "homogeneous lean combustion", but also at the time of "weak stratified combustion" and "stratified combustion", when the state where the EGR valve 43 has reached the heat-resistant limit temperature or more has continued for a predetermined time. , The EGR amount is set to “0”, and the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio. Note that, in the present embodiment, only parts different from the first embodiment will be described, and detailed description of other parts that are the same as the first embodiment will be omitted.

FIG. 9 is a flowchart showing a combustion control routine according to this embodiment. This combustion control routine
For example, the processing is executed by the ECU 92 by interruption every predetermined time.

In this routine, the ECU 92 determines that the fuel injection amount Q is equal to the determination value QDJ in step S301.
It is determined whether the operating state of the engine 11 is in the homogeneous combustion region A or not. If “Q> QDJ” in the process of step S301, it is determined that the operating state of the engine 11 is in the homogeneous combustion region A, and the process proceeds to step S306. The ECU 92 executes "homogeneous combustion" as the process of step S306, stops the execution of EGR as the process of the subsequent step S307, and then temporarily ends the combustion control routine.

In the process of step S301,
If “Q> QDJ” is not satisfied, it is determined that the operating state of the engine 11 is in the homogeneous lean burn region B, the weak stratified burn region C, or the stratified burn region D, and the process proceeds to step S302.
The ECU 92 determines whether or not “1” is stored in the predetermined area of the RAM 95 as the temperature abnormality flag F in the process of step S302. Then, in step S302, if YES is determined, the process proceeds to step S306, and if NO is determined, the process proceeds to step S303. When the process proceeds to step S303 in this way, EGR is executed by the process of step S310 described later.

Further, proceeding from step S302 to step S306 is because the EGR valve 43 is activated due to the erosion of the catalyst 33a during the execution of "homogeneous lean combustion", "weak stratified combustion" or "stratified combustion". Occurs when the temperature exceeds the heat-resistant limit temperature. However, even if the EGR valve 43 becomes equal to or higher than the heat-resistant limit temperature in this way, step S307 is performed.
By setting the EGR amount to “0” in the processing of the above, the heating of the EGR valve 43 due to the exhaust heat is suppressed,
Is suppressed below the heat-resistant limit temperature. Further, even when the EGR amount is set to “0” as described above, step S3
By performing “homogeneous combustion” in the process 06, the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio, and the exhaust gas of the engine 11 is efficiently purified by the exhaust purification catalyst 33a. Therefore, deterioration of the emission caused by setting the EGR amount to “0” in order to prevent the heating of the EGR valve 43 is prevented.

On the other hand, if it is determined NO in step S302 and the process proceeds to step S303, the ECU 92 determines whether the fuel injection amount Q is larger than the determination value QA. If it is determined in step S303 that “Q> QA” is not satisfied, the operating state of the engine 11 is changed to the stratified combustion region D.
, And the process proceeds to step S308. ECU 9
2 executes “stratified combustion” as the process of step S308. Thereafter, the process proceeds to step S310.

In the process of step S303,
If it is determined that “Q> QA”, the process proceeds to step S304. The ECU 92 performs the process of step S304 as follows:
It is determined whether the fuel injection amount Q is larger than the determination value QB. Then, in the process of step S304, “Q>
If not QB ”, it is determined that the operating state of the engine 11 is in the weak stratified combustion region C, and the routine proceeds to step S309. The ECU 92 executes “weak stratified combustion” as the process of step S309. Thereafter, the process proceeds to step S310.

In the process of step S304,
If "Q>QB", it is determined that the operating state of the engine 11 is in the homogeneous lean burn region B, and step S30 is performed.
Go to 5. The ECU 92 executes “homogeneous lean combustion” as the process of step S305. Then, step S3
Go to 10. After performing various lean burns in the processing of steps S305, S308, and S309, step S310 is performed.
The ECU 92 executes EGR as the process of step S310, and then temporarily ends the combustion control routine.

According to this embodiment in which the processing described in detail above is performed, the following effects can be obtained in addition to the effects (1) and (2) shown in the first embodiment. (3) Not only when the EGR valve 43 is at or above the heat-resistant limit temperature during "homogeneous lean combustion", but also when the EGR valve 43 is at or above the heat-resistant limit temperature during "weak stratified combustion" and "stratified combustion". , The EGR amount is set to “0”, and the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio. Therefore, even when the EGR valve 43 becomes higher than the heat-resistant limit temperature not only during “homogeneous lean combustion” but also during “weak stratified combustion” and “stratified combustion”, it is possible to appropriately suppress the temperature rise of the EGR valve 43. And EG
Emission deterioration caused by R amount = “0” can be prevented.

The above embodiments can be modified, for example, as follows. In the above embodiments, for example, the temperature of the housing 51 or the exhaust gas temperature in the exhaust passage 32 may be detected as the valve temperature instead of detecting the temperature of the seat 54 in the EGR valve 43 as the valve temperature.

In each of the above embodiments, instead of directly detecting the temperature of the EGR valve 43, the temperature of the EGR valve 43 may be estimated based on a parameter that changes in accordance with the valve temperature. Such parameters include, for example, the exhaust pressure in the exhaust passage 32.

In the above embodiments, the EGR valve 43
Is determined to be above the heat-resistant limit temperature,
The EGR amount is set to "0", but instead of this, E
The GR amount may simply be reduced.

In the above embodiments, the EGR valve 43
Is determined to be equal to or higher than the heat-resistant limit temperature, and the EGR amount is set to “0” based on the determination result.
It does not need to be the heat-resistant limit temperature. When the valve temperature serving as the criterion is changed in this way, it is preferable that the valve temperature is set to a value slightly lower than the heat-resistant limit temperature of the EGR valve 43 to appropriately prevent thermal distortion and the like of the EGR valve 43.

In the above embodiments, the predetermined value A used in the process of step S104 in the temperature abnormality detection routine of FIG. 6 is fixed to a value corresponding to 0.5 second, but the value may be changed as appropriate. You may.

In the above embodiments, the step motor 4
Although the EGR valve 43 of the type opened and closed by 3a is illustrated, an E type of ELO valve opened and closed by an actuator driven by the intake negative pressure of the engine 11 is used instead.
A GR valve may be employed.

In the above embodiments, lean combustion such as "stratified combustion", "weak stratified combustion", and "homogeneous stratified combustion" is performed in addition to "homogeneous combustion", but the present invention is not limited to this. Not done. That is, instead of performing all of “stratified combustion”, “weak stratified combustion”, and “homogeneous stratified combustion”, any one or two of these lean combustion systems may be performed. Good.

Next, technical ideas other than the claims that can be grasped from the above embodiments are described below together with their effects. (1) A control method for an internal combustion engine that recirculates exhaust gas from an internal combustion engine to an intake system by an exhaust recirculation mechanism and performs lean combustion when the operating state of the engine is in a lean combustion region. A control method for an internal combustion engine, wherein when the temperature becomes higher than a predetermined high temperature, the amount of exhaust gas recirculation is reduced and the air-fuel ratio of the air-fuel mixture is feedback-controlled to a stoichiometric air-fuel ratio.

According to this method, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than the predetermined high temperature, the amount of exhaust gas recirculation is reduced, and the temperature rise of the exhaust gas recirculation mechanism is suppressed. Further, at this time, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, and the exhaust gas is efficiently purified by the exhaust purification catalyst. Therefore, even if the exhaust gas recirculation amount is reduced, the emission does not deteriorate.
Therefore, it is possible to achieve both the prevention of the adverse effect of the heat on the exhaust gas recirculation mechanism and the prevention of the deterioration of the emission of the internal combustion engine.

(2) A computer which records a control program of an internal combustion engine that recirculates exhaust gas of the internal combustion engine to an intake system by an exhaust gas recirculation mechanism and performs lean combustion when the operating state of the engine is in a lean combustion region. In a possible recording medium, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than a predetermined high temperature, the amount of exhaust gas recirculation is reduced, and the air-fuel ratio of the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio. A computer-readable storage medium storing a control program for an internal combustion engine.

According to the control program recorded on the recording medium, when the temperature of the exhaust gas recirculation mechanism becomes higher than a predetermined high temperature, the amount of exhaust gas recirculation is reduced, and the temperature rise of the exhaust gas recirculation mechanism is suppressed. . Further, at this time, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, and the exhaust gas is efficiently purified by the exhaust purification catalyst. Therefore, even if the exhaust gas recirculation amount is reduced, the emission does not deteriorate. Therefore, it is possible to achieve both the prevention of the adverse effect of the heat on the exhaust gas recirculation mechanism and the prevention of the deterioration of the emission of the internal combustion engine.

In the present specification, the lean combustion means not only "homogeneous lean combustion" but also combustion of an air-fuel mixture at an air-fuel ratio larger than the stoichiometric air-fuel ratio, such as "weak stratified combustion" or "stratified combustion". It shall include all methods.

[0076]

According to the first aspect of the present invention, when the temperature of the exhaust gas recirculation mechanism becomes higher than the predetermined high temperature, the amount of exhaust gas recirculation is reduced, and the temperature rise of the exhaust gas recirculation mechanism is suppressed.
Further, at this time, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, and the exhaust gas is efficiently purified by the exhaust purification catalyst. Therefore, even if the exhaust gas recirculation amount is reduced, the emission does not deteriorate. Therefore, it is possible to achieve both the prevention of the adverse effect of the heat on the exhaust gas recirculation mechanism and the prevention of the deterioration of the emission of the internal combustion engine.

According to the second aspect of the present invention, it is accurately detected that the temperature of the exhaust gas recirculation mechanism has become higher than the predetermined high temperature, thereby preventing unnecessary reduction of the exhaust gas recirculation amount. Therefore, it is possible to prevent the emission from being deteriorated due to the unnecessary reduction of the exhaust gas recirculation amount.

According to the third aspect of the present invention, by adjusting the exhaust gas recirculation amount to the reduction side based on the valve temperature in the exhaust gas recirculation mechanism, it is possible to preferably prevent the valve from being adversely affected by thermal distortion or the like. can do.

According to the fourth aspect of the present invention, when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than the predetermined high temperature, the exhaust gas recirculation amount is set to "0", and the temperature rise of the exhaust gas recirculation mechanism is suitably suppressed. Therefore, it is possible to appropriately prevent the heat from adversely affecting the exhaust gas recirculation mechanism.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an entire engine to which a control device according to a first embodiment is applied.

FIG. 2 is a sectional view of a cylinder head showing shapes of intake and exhaust ports in the engine.

FIG. 3 is an enlarged sectional view showing an EGR valve;

FIG. 4 is a block diagram showing an electrical configuration of the air-fuel ratio control device.

FIG. 5 is a map referred to when determining the combustion mode of the engine.

FIG. 6 is a flowchart showing a procedure for detecting that the temperature of the EGR valve is equal to or higher than a heat-resistant limit temperature.

FIG. 7 is a map referred to when calculating the opening degree of the EGR valve.

FIG. 8 is a flowchart illustrating a combustion control procedure according to the first embodiment.

FIG. 9 is a flowchart illustrating a combustion control procedure according to the second embodiment.

[Explanation of symbols]

11 ... engine, 31 ... exhaust pipe, 33 ... exhaust passage, 33
a: exhaust purification catalyst, 37: oxygen sensor, 40: fuel injection valve, 42: EGR passage, 43: EGR valve, 57: temperature sensor, 92: electronic control unit (ECU).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 43/00 301 F02D 43/00 301N F02M 25/07 550 F02M 25/07 550R 570 570A

Claims (4)

[Claims] An exhaust purification catalyst provided in an exhaust system of an internal combustion engine, air-fuel ratio detection means for detecting an air-fuel ratio of an air-fuel mixture from exhaust of the engine, and exhaust gas for recirculating exhaust of the engine to an intake system. A control device for an internal combustion engine that includes a recirculation mechanism and performs lean combustion when the operating state of the engine is in a lean combustion region; wherein when the temperature of the exhaust recirculation mechanism becomes equal to or higher than a predetermined high temperature, Control means for controlling the exhaust gas recirculation mechanism on the side of reducing the recirculation amount, and feedback control of the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio based on a detection signal from the air-fuel ratio detection means. A control device for an internal combustion engine. 2. The control device according to claim 1, wherein when the temperature of the exhaust gas recirculation mechanism is equal to or higher than a predetermined high temperature for a predetermined time or more, the control means controls the exhaust gas recirculation mechanism to reduce the exhaust gas recirculation amount. 2. The control device for an internal combustion engine according to claim 1, wherein feedback control to the stoichiometric air-fuel ratio is performed. 3. The control device for an internal combustion engine according to claim 1, wherein the exhaust gas recirculation mechanism includes a passage for supplying exhaust gas to the intake system and a valve for adjusting an exhaust flow area of the passage. And a valve temperature detecting means for detecting a temperature of the valve, wherein the control means determines whether the temperature of the exhaust gas recirculation mechanism has become equal to or higher than a predetermined high temperature based on the valve temperature detected by the valve temperature detecting means. A control device for an internal combustion engine, wherein the control device determines whether or not it is not. 4. The exhaust gas recirculation mechanism controls the exhaust gas recirculation mechanism so that when the temperature of the exhaust gas recirculation mechanism becomes equal to or higher than a predetermined high temperature, the exhaust gas recirculation amount becomes “0”. The control device for an internal combustion engine according to any one of claims 1 to 3.