JPH0417755A - Exhaust gas recirculation device of supercharged internal lean-burn engine - Google Patents

Abstract

PURPOSE:To rapidly realize switching from theoritical to lean air-fuel ratio wihtout reducing torque by controlling an exhaust gas recirculation control valve when supercharging pressure is detected as being increased so that the amount of reflow exhaust gas allowed to pass through an exhaust gas recirculating passage is increased. CONSTITUTION:When a lean air-fuel ratio control area identifying means D identifies the area where air-fuel ratio is to be set to the lean side, a supercharging pressure increasing means E increases supercharging pressure generated by a supercharger A. When the supercharging pressure detecting means F detects the supercharging pressure as being increased, an exhaust gas recirculation control means G controls an exhaust gas recirculation control valve C so that the amount of reflow exhaust gas allowed to pass through an exhaust gas recirculating passage B is increased. In the area of the shift from theoritical to lean air-fuel ratio, the exhaust gas is recirculated at the same time that the supercharging pressure is increased, whereby generation of nitrogen oxides is restrained while preventing torque from being reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an exhaust gas recirculation device in a supercharged lean-burn internal combustion engine.

[Prior art]

Japanese Patent Application No. 1-156685 proposes a method (hereinafter referred to as high-density supercharging) for internal combustion engines that use gasoline as fuel, to perform strong supercharging with a large turbocharger and increase air density to achieve lean combustion during high-load operation. lean burn). By performing high-density supercharging, the amount of fuel per unit volume is maintained even if the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, ensuring stable combustion while achieving lean combustion and reducing fuel consumption. Efficiency can be improved.

[Problem to be solved by the invention]

In the high-density supercharging lean burn system, the air-fuel ratio is set to the stoichiometric air-fuel ratio at low speeds and low loads, where the turbocharger does not provide sufficient supercharging effect, and at high speeds and high loads, the air-fuel ratio becomes lean. Set. When switching from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range, ideally the air-fuel ratio should be from the stoichiometric air-fuel ratio (14,5) to 19.
．． It is preferable to switch in steps such as 0. This is because at such an intermediate air-fuel ratio (for example, 16.0), the amount of nitrogen oxide components discharged from the exhaust gas increases. However, since the engine torque changes suddenly due to a stepwise change in the air-fuel ratio setting, the air-fuel ratio is actually set to be continuously changed from the stoichiometric air-fuel ratio to the target lean air-fuel ratio. Therefore, there is a problem that the amount of nitrogen oxide components discharged from the exhaust gas increases.

The object of the present invention is to quickly switch from a stoichiometric air-fuel ratio to a lean air-fuel ratio without reducing torque and without increasing the amount of nitrogen oxide component emissions.

[Means to solve the problem]

According to this invention, in FIG. 1, the air-fuel ratio is controlled to the lean side during operation when the supercharger A achieves the supercharging effect, and the exhaust gas recirculation passage B is connected to the exhaust gas recirculation passage B that connects the exhaust system and the intake system. In an internal combustion engine equipped with an exhaust gas recirculation control valve C, means for determining an operating range in which the air-fuel ratio should be controlled to the lean side;
means E for increasing supercharging pressure by the supercharger when it is determined that the lean air-fuel ratio control region is reached; and means F for detecting an increase in supercharging pressure;
and means G for controlling an exhaust gas recirculation control valve C so that the amount of recirculated exhaust gas passing through an exhaust gas recirculation passage B increases when an increase in boost pressure is detected. A waste recirculation device is provided.

[Effect]

When the lean air-fuel ratio control region determining means determines the region in which the air-fuel ratio should be set lean, the supercharging pressure increasing means E controls the turbocharger A.
Increase boost pressure due to

When the boost pressure detection means F detects that the boost pressure has increased, the exhaust gas recirculation control means G controls the exhaust gas recirculation control valve C so that the amount of recirculated exhaust gas passing through the exhaust gas recirculation passage B increases. control.

〔Example〕

FIG. 2 shows the entire high-density supercharged gasoline internal combustion engine of the present invention, where 1o is the engine body, the intake pipe 12
and the exhaust pipe 14 are connected. In the internal combustion engine of the embodiment, each intake boat 1o-1 is divided into two parts, one of which is equipped with a swirl control valve 10-2, and when the control valve 10-2 is closed, air is supplied only from the other part. The air-fuel mixture is introduced into the cylinder and forms a swirl within the cylinder, and when the force control valve 10-2 is opened, the air-fuel mixture is introduced from both portions of the intake port and the swirl is eliminated. The swirl is intended to improve the combustion of an air-fuel mixture that is leaner than the stoichiometric air-fuel ratio.

A large turbocharger 17 and a small turbocharger I8 are arranged in series. The large turbocharger 17 includes a compressor 20, a turbine 22, and a rotating shaft 24. The small turbocharger 18 is the compressor 2
6, a turbine 28, and a rotating shaft 25.

In the intake pipe 12, the compressor 20 of the large turbocharger 17 and the compressor 26 of the small turbocharger I8 are arranged in this order in the flow direction of intake air, and an intercooler 29 is arranged downstream thereof. In the exhaust pipe, the turbine 28 of the small turbocharger 18 and the turbine 22 of the large turbocharger 17 are arranged in this order in the flow direction of exhaust gas.

A first exhaust bypass passage 30 is connected to the exhaust pipe, bypassing the turbine of the large turbocharger 17, and a wastegate valve 32, which is a swing door type valve, is arranged in the first exhaust bypass passage 30.

Wastegate valve 32 is connected to a diaphragm actuator 34 whose diaphragm 34 a is connected to bypass valve 32 . Bypass valve 32 has spring 34b
Normally, the wastegate valve 32 is biased to close, but the positive pressure applied to the diaphragm 34a causes the wastegate valve 32 to open against the spring 34b.

A second exhaust bypass passage 36 is provided to bypass the turbine 28 of the small turbocharger 18, and an exhaust switching valve 38 as a butterfly valve is provided in the second bypass passage 36. The exhaust switching valve 38 is connected to its actuator 40, and the actuator 40 is configured as a two-stage diaphragm mechanism.

As will be described later, this actuator 40 closes the exhaust switching valve 38 until the large turbocharger 17 exerts its full supercharging capacity, and switches the exhaust switching valve 38 when the large turbocharger 17 reaches its full supercharging capacity. It has the property of causing the valve 38 to open rapidly. The actuator 40 is a diaphragm 40a.

40b and springs 40c and 40d, one diaphragm 40a is connected to the rod 4. The other diaphragm 40b is connected to a rod 40f. The step-like opening characteristic of the exhaust gas switching valve 38 can be obtained by applying supercharging pressure to the diaphragm 40a or by applying supercharging pressure to the diaphragm 40b. That is, when supercharging pressure is applied to the diaphragm 40b, the exhaust switching valve 38 is opened against the force of the spring 40c and the combined force of the spring 40d, so that the valve is opened slowly. When supercharging pressure acts on the diaphragm 40a, the exhaust switching valve 38 is opened against only the force of the spring 40c, so that the valve operation is quick during that time.

An intake bypass passage 44 that bypasses the compressor 26 of the small turbocharger 18 is provided, and an intake bypass valve 46 is disposed in the intake bypass passage 44. Switching valve 4
6 is connected to a diaphragm actuator 48, and the operation of the intake bypass valve 46 is controlled by the pressure applied to the diaphragm 48a. This intake bypass valve 46 is connected to the intake bypass passage 4 in the operating range of the small turbocharger 18 where the startup of the large turbocharger 17 is not completed.
4 is closed, but after that is completed, supercharging pressure acts on the diaphragm 48a from below, and the intake bypass valve 46 is opened.

The internal combustion engine is provided with an exhaust gas recirculation (EGR) device, which comprises an exhaust gas recirculation passage (EGR passage) 50 and an exhaust gas recirculation control valve (EGR valve) 52 on the EGR passage 50; The EGR valve 52 is a diaphragm 52a
and a valve body 52b, and the opening and closing of the valve body 52b is controlled according to the pressure applied to the diaphragm 52a. The EGR passage 50 is located at its upstream end (exhaust gas outlet).
50A is connected to the exhaust pipe 14 upstream of the turbine 28 of the small turbocharger 18, and is connected to the downstream end (exhaust gas inlet 5
0B) is connected to the intake pipe downstream of the intercooler 29.

A three-way solenoid valve (VSVI) 54 is provided for pressure control to the actuator 34 of the wastegate valve 32;
This solenoid valve 54 is switched between a position where atmospheric pressure is introduced into the diaphragm 34a and a position where supercharging pressure is introduced at a position 56 downstream of the small turbocharger 26 and upstream of the intercooler 29. When atmospheric pressure is introduced, the wastegate valve 32 is driven to close by the spring 34b, and when supercharging pressure is introduced, the wastegate valve 32 is driven to close against the spring 34b.
2 valve opening is performed.

A three-way solenoid valve (VSV2) 58 is provided to control the pressure on the diaphragm 40a of the actuator 40 of the exhaust switching valve 38. 60 and the position where supercharging pressure is introduced. Also,
The diaphragm 40b has a small turbocharger outlet 60.
pressure is constantly applied.

Two 30,000 solenoid valves 64,66 are provided for pressure control to the actuator 48 of the intake bypass valve 46. A three-way solenoid valve (VSV3) 64 is provided above the diaphragm 48a of the actuator 48 of the intake bypass valve 46 for pressure control;
The position is switched between a position where atmospheric pressure is introduced to the upper side of the compressor and a position where supercharging pressure from the compressor outlet 60 of the small turbocharger 18 is introduced. In addition, 3-way solenoid valve (VSV4) 66
is provided to control the pressure below the diaphragm 48a of the actuator 48 of the intake bypass valve 46, and this solenoid valve 66 is located at a position where the negative pressure of the negative pressure boat 68 downstream of the throttle valve I6 is introduced, and at a position where the negative pressure is introduced into the large turbocharger. The position is changed depending on the position at which the supercharging pressure is introduced at the outlet of the compressor 66.

Three-way solenoid valve (VSV5) 70 is provided to control the operation of the EGR valve 52, and this solenoid valve 70 is connected to the diaphragm 5.
The position is switched between a position where atmospheric pressure is introduced into 2a and a position where negative pressure from the negative pressure port 68 downstream of the throttle valve 16 is introduced. The electromagnetic valve 70 is driven by a pulse signal, and can be controlled to a desired EGR amount by controlling its duty ratio.

The solenoid valve 71 (VSV6) is provided to rapidly increase the supercharging pressure by closing the exhaust switching valve 38 when the air-fuel ratio is switched from the stoichiometric air-fuel ratio setting to the lean air-fuel ratio setting. This solenoid valve 71 is connected to the spring 4 of the diaphragm 40a.
The position where atmospheric pressure is introduced to the 0c side and the throttle valve 16
The position of the negative pressure boat 68 downstream of the negative pressure boat 68 is switched.

The control circuit 72 is a supercharging control vignetting system in the present invention, each solenoid valve 54 (VSVI), 58 (VSV
2), 64 (VSV3), 66 (VSV4), 7
0 (VSV5), 71 (VSV6) drive signals are generated. Further, in order to control the ignition timing, an ignition plug (not shown) is controlled via an igniter 74 and a distributor 76. The control circuit 72 is connected to various sensors in order to execute control according to the present invention. First, a first pressure sensor 78 is provided to detect the outlet pressure P1 of the compressor 20 of the large turbocharger 17, and a second pressure sensor 80 is provided to detect the outlet pressure P2 of the compressor 26 of the small turbocharger 18. provided. The air-fuel ratio sensor 82 generates a signal according to the air-fuel ratio.

Although not shown, a sensor for detecting the intake air amount Q to the engine and a crank angle sensor that generates a pulse signal every time the crankshaft rotates 30 degrees and 720 degrees are provided.

The operation of the control circuit 72 will be explained below with reference to flowcharts shown in FIGS. 3 to 6. FIG. 3 shows a supercharging control routine. In step 100, it is determined whether the intake air amount--engine speed ratio Q/NE is greater than a predetermined value X. This predetermined value X is a value of the intake air amount--engine rotation speed ratio that serves as a reference when switching the air-fuel ratio from the stoichiometric air-fuel ratio to the lean air-fuel ratio. The switching point from the stoichiometric air-fuel ratio to the lean air-fuel ratio may be based on the intake manifold pressure or other factors instead of switching based on the intake air amount-engine speed ratio as in the embodiment. When Q/NE ≦
The negative pressure of the negative pressure port 68 downstream of the diaphragm 40a
The diaphragm 40 is introduced into the spring 40c side of the
a moves to the left against the spring 40c, and the exhaust switching valve 38
is opened.

When it is determined in step 100 that Q/NE > X,
That is, if the air-fuel ratio should be controlled to the lean side, the process proceeds to step 104, where the solenoid valve 71 (VSV6) is turned off and the atmospheric pressure is applied to the spring 4 of the diaphragm 40a.
0c side, the diaphragm 40a is urged rightward against the spring 40c, and the exhaust gas switching valve 38 is urged to close. The reason why the exhaust switching valve 38 is controlled to switch from open to closed at the switching point from the stoichiometric air-fuel ratio setting to the lean air-fuel ratio setting is to rapidly increase the boost pressure and counteract the tendency for torque reduction due to the lean air-fuel ratio. .

In step 106, the intake air amount-engine speed ratio Q/
It is determined whether NE>Y. This predetermined value Y (>X)
detects an actual increase in supercharging pressure due to switching of the exhaust switching valve 38 from open to closed. When Q/NE≦Y, it is assumed that the supercharging pressure has not increased yet, and the process proceeds to step 108, where flag F is cleared. Due to F.0, dilution of the air-fuel ratio is prohibited by an air-fuel ratio control routine to be described later, and the air-fuel ratio is set to the stoichiometric air-fuel ratio.

Next, the process proceeds to step 110, where the EGR rate correction coefficient K.1.
It is set to 0. K is a coefficient that corrects the EGR rate to be as much as possible than the map value in the air-fuel ratio switching range from the stoichiometric air-fuel ratio to the lean air-fuel ratio, and by setting K=1.0, the EGR rate becomes the map value.

When it is determined in step 106 that Q/NE > Y, that is, when it is considered that the boost pressure has increased, the process proceeds to step 111.
Then, flag F is set. When F=1, leanening of the air-fuel ratio is permitted by an air-fuel ratio control routine to be described later. In step 112, an EGR rate correction coefficient K is calculated. The EGR rate correction coefficient is used to correct the EGR rate to be higher than the normal value when transitioning from the stoichiometric air-fuel ratio to the lean air-fuel ratio, and to suppress the emission of nitrogen oxide components that are often generated when the air-fuel ratio changes. It is. In step 114, it is determined whether the intake air amount-engine rotation speed ratio Q/NE is greater than a predetermined value Z. This predetermined value Z (>Y) becomes the threshold value of the upper limit boundary of the region in which the EGR rate is increased in the switching region from the stoichiometric air-fuel ratio to the lean air-fuel ratio. When Q/NE≦Z, step 110 is exited. Therefore, the EGR rate is increased. When Q/NE>Z, it is determined that the nitrogen oxide increase range in switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio has been passed, and the process proceeds to step 110, where the EGR rate correction coefficient is set to K.1.0, and the EGR rate is is considered to be the original map value.

The processing from step 120 onwards is a routine for switching from two-stage supercharging to one-stage supercharging. In the step tube 120, the compressor y outlet pressure P2 of the small turbocharger 18
>Compressor outlet pressure P of large turbocharger 17
It is determined whether or not 1 holds true. FIG. 7 shows the relationship between the engine speed NE and supercharging pressure (turbocharger outlet pressure) when the opening degree of the throttle valve 16 is fixed constant, and the rise of the small turbocharger outlet pressure P2 is the same as that of the large turbocharger. This is faster than the rise of charger outlet pressure P1. Therefore, in a state where the engine speed has not yet increased, P2>Pl holds true, and the process proceeds to step 122 and subsequent steps. Ste.

At step 122, the solenoid valve 54 (VSVI) is turned off, atmospheric pressure is introduced into the diaphragm 34a, and the spring 34b is turned off.
The wastegate valve 32 is closed. Solenoid valve 5B (
VSV2) is turned off. Therefore, atmospheric pressure acts on the diaphragm 40a of the actuator 40.

On the other hand, a small turbocharger 1 is attached to the diaphragm 40b.
Since the compressor outlet pressure of 8 is always introduced,
The operation of the exhaust switching valve 38 is controlled by the compressor outlet pressure of the small turbocharger 18 that opposes the spring force corresponding to the resultant force of the springs 40c and 40d.

That is, as long as the spring force is dominant over the supercharging pressure P2, the exhaust switching valve 38 remains fully closed, but until the rotation speed at which the supercharging pressure P2 reaches the predetermined value PSET (NET in FIG. 7) is reached. The exhaust switching valve 38 is kept fully closed, and P2=predetermined value P
When the exhaust switching valve 38 reaches the spring 4
The valve gradually starts to open against the closing biasing force which is the resultant force of 0c and 40d. Note that even if P2 < PI, if the intake air amount-engine speed ratio Q/NE≦X (Yes in step 100), the exhaust switching valve 38 is opened by introducing negative pressure to the diaphragm 40a, so the exhaust switching valve 38 is opened. The actual closure of 38 occurs after Q/NE>X (No at step 100). Regarding the operation of the intake bypass valve 46 at low engine speeds, in step 126 the solenoid valve 6
4 (VSV3) is turned on and the compressor outlet pressure P of the turbocharger 20 acts on the upper side of the diaphragm 48a, so the intake bypass valve 46 is closed. Also,
In step 128, the solenoid valve 66 (VSV4) is turned off, so the negative pressure from the negative pressure pump 67 is applied to the diaphragm 48.
a, the diaphragm 48a is pulled downward, increasing the closing force of the intake bypass valve 46 and ensuring its reliable closing.

In the acceleration state, the engine speed NE increases to NH3, and the rise of the compressor outlet pressure P of the large turbocharger 17 catches up with the compressor outlet pressure P2 of the small turbocharger I8, and when P2=P, the step starts from step 120. 130 steps forward, solenoid valve 5
4 (VSVI) is turned on, supercharging pressure from position 56 is introduced into the diaphragm 34a, and the wastegate valve 32 is urged in the opening direction against the spring 34b. In step 132, the solenoid valve 58 for operating the exhaust switching valve 38
(VSV2) is turned on. Therefore, diaphragm 4
Since the supercharging pressure acts on 0a, the spring 40d does not participate in the force to close the exhaust switching valve 38 that opposes the supercharging pressure, and only the weak biasing force of the spring 40c participates in the closing force. Therefore, the actuator 40 is connected to the exhaust switching valve 3.
8 to open the valve at once. In step 134, the solenoid valve 64 (VSV3) is turned off, so that atmospheric pressure acts on the upper side of the diaphragm 48a, and in step 136, the solenoid valve 66 (VSV4) is turned on, and the supercharging pressure is applied to the diaphragm 48a.
8b, the diaphragm 48a is pressed upward, and the intake bypass valve 46 is opened all at once.

FIG. 4 shows an exhaust gas recirculation control routine, and in step 140, it is determined whether or not the operating range is for exhaust gas recirculation. During high rotation and high load operation, EGR is stopped, and the process proceeds to step 142, where the solenoid valve 70 for driving the EGR valve 52 (
Duty ratio DUTY in drive signal of VSV5)
Set to 0. Therefore, the solenoid valve 70 (VSV5) is continuously turned off, and atmospheric pressure is introduced into the diaphragm 52a, so the EGR valve 52 is closed.

When the EGR region is determined in step 140, the process proceeds to step 44, where the duty ratio DUTY in the drive signal of the solenoid valve 70 (VSV5) corresponding to the EGR rate in the normal state is calculated from the map MAP. This map has a duty ratio DUTY value that corresponds to the optimum EGR rate according to the load at that time (for example, intake air amount - engine speed ratio Q/NE), and it is determined by interpolation to match the duty ratio DUTY to the current operating condition. Duty ratio D corresponding to the EGR rate
A calculation of IRTY is performed. In step 146, the duty ratio DUTY multiplied by the correction coefficient K is DUTY.
It is said that FIG. 9 schematically shows an EGR rate correction coefficient map for the rotational speed and air-fuel ratio A/F when the throttle valve opening is held constant. The line of K=1 is 2
This indicates the boundary area for EGR rate correction when switching from stage supercharging to first stage supercharging, and the correction coefficient is set to be large at the air-fuel ratio (AF = AF0) where nitrogen oxide emissions peak. ing. Further, as the rotational speed increases, the correction coefficient becomes smaller. Step 148 shows the output of the duty ratio signal, so that the solenoid valve 70 (VS
V5) is operated at that duty ratio, and the calculated EG
R rate can be obtained.

In FIG. 7, the EGR rate map set in step 144 (FIG. 4) is schematically shown by contour lines. Q/
The shaded area between NE=Y and Q/NE=Z is the intermediate air-fuel ratio area where the amount of nitrogen oxide emissions increases, and the EGR rate increases according to the map in Figure 9 by the EGR rate correction coefficient K. be done.

Figure 5 shows a fuel injection routine, in which the fuel injection timing for that cylinder is determined by the crank angle sensor at 30°CA, 7°C.
This is executed based on the 20' CA multiplied signal.

In step 150, the basic fuel injection amount Tp is calculated.

The basic fuel injection amount is a standard value that makes the air-fuel ratio the stoichiometric air-fuel ratio at that load and rotation speed. In step 152, it is determined whether the air-fuel ratio control flag F=1. When F.0, that is, when the air-fuel ratio should be controlled to the stoichiometric air-fuel ratio, the process proceeds from step 152 to step 154, where the air-fuel ratio correction coefficient KLEAN.1.0 and the feedback flag FB=1.
is set to KLEAN is a coefficient that corrects the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio, and KLEAN=1. By setting the air-fuel ratio to O, the air-fuel ratio is set to the stoichiometric air-fuel ratio. By setting the feedback flag FB=1, feedback control of the air-fuel ratio is executed. In step 156, the air-fuel ratio correction coefficient FAF is directly entered into FAF. F
AF is a coefficient that corrects the air-fuel ratio during feedback of the air-fuel ratio so that it becomes the stoichiometric air-fuel ratio.

When F=1, that is, when the air-fuel ratio should be controlled to a lean air-fuel ratio, the process proceeds from step 152 to step 158, where the air-fuel ratio correction coefficient KLEAN is calculated from the map. The air-fuel ratio is controlled to be as lean as possible in terms of fuel consumption rate, and there is a requirement to suppress the degree of leanness in terms of output, so it is set appropriately in harmony with these requirements. A well-known interpolation operation is performed to obtain a value of KLEAN suitable for the operating conditions. Step 16
At 0, the feedback correction coefficient FAF·1.0 is set. That is, during lean air-fuel ratio control, feedback control of the air-fuel ratio is not performed.

In step 162, the final fuel injection amount is TAU=Tp
Calculated by x KLEAN x FAF.

Step 164 shows the output of a fuel injection signal to the injector 15 so that the amount of fuel calculated in step 162 is injected.

FIG. 6 schematically shows the air-fuel ratio feedback control routine. In step 170, it is determined whether the feedback flag FB is 1. If FB=0, that is, when there is no feedback, the process proceeds to step 171, where FAFlo is set. When FB=1, that is, when performing air-fuel ratio feedback, the process proceeds from step 170 to step 172, and the air-fuel ratio sensor 8
A signal is input to step 2, and in step 174, it is determined from the signal of the air-fuel ratio sensor whether the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and if it is determined to be lean, the process proceeds to step 176, where the feedback correction coefficient FAF is increased. If it is determined to be on the rich side, the process proceeds to step 178 and the feedback correction coefficient is decreased.

FIG. 8 is a timing chart schematically explaining the operation of the embodiment of the present invention. (a) is the EGR rate, (b) is the nitrogen oxide (NOx) emission amount, (c) is the fuel amount Gf, (d)
indicates the operation of the exhaust switching valve 38, (E) indicates the intake air amount engine speed ratio Q/NE, and (G) indicates the air-fuel ratio A/F. Time t indicates the transition region from the stoichiometric air-fuel ratio to the lean air-fuel ratio. At the start timing (Yes in step 100 of FIG. 3), a signal for switching the exhaust switching valve 38 from open to closed is generated at the same time. An increase in the intake air amount engine speed ratio Q/NE is detected. Step 106 in Figure 3) t,
At this point, the EGR rate correction coefficient is set (step 112 in FIG. 3), the EGR rate (a) is rapidly increased, and the air-fuel ratio is gradually increased toward the target lean air-fuel ratio (step 112). E
By increasing the GR rate, it is possible to suppress the amount of nitrogen oxide component emissions in the air-fuel ratio transition region. (0)
The broken line indicates the NOx emission in the conventional case (when EGR is not increased).

At time t2, when the transition region has been passed, the increase in the EGR rate is stopped and the EGR rate returns to the map value (step 144 in FIG. 4) (A).

In the above embodiment, the EGR rate is controlled to be increased from the normal map value when transitioning from stoichiometric air-fuel ratio operation to lean air-fuel ratio operation, but in an engine that does not perform EGR as a normal control, the amount of nitrogen oxide component emissions increases. It is possible to perform control (control based only on k in the embodiment) such that EGR is performed only at the time of transition from the problematic stoichiometric air-fuel ratio operation to lean air-fuel ratio operation.

Further, the swirl control valve 10-2 is closed in an intermediate air-fuel ratio region where the EGR rate increases, thereby generating an intake swirl in the cylinder, thereby improving combustibility in the EGR rate increasing region.

〔effect〕

According to this invention, in the transition region from stoichiometric air-fuel ratio to lean air-fuel ratio operation, by increasing boost pressure and simultaneously recirculating exhaust gas, it is possible to suppress the generation of nitrogen oxides while suppressing a decrease in torque. be able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the functional configuration of the present invention. FIG. 2 is a diagram showing the configuration of an embodiment of the invention. 3 to 6 are flowcharts illustrating the operation of the control circuit. FIG. 7 is a graph showing changes in supercharging pressure with respect to engine speed. FIG. 8 is a timing diagram schematically explaining the operation of the control circuit. FIG. 9 is a diagram schematically explaining a map of EGR rate correction coefficients. 0... Engine body, 12... Intake pipe, 4... Exhaust pipe, 17... Large turbocharger, 8... Small turbocharger, 0... First exhaust bypass passage, 2... Waste Gate valve, 6... Second exhaust bypass passage, 8... Exhaust switching valve, 44... Intake bypass passage, 0
...EGR passage, 52...EGR valve, 58, 64.
66, 70-Solenoid valve (VSV), 80...pressure sensor. Figure 1 Figure Figure Figure Q, /NE Y,') Line Figure Figure Figure

Claims (1)

[Claims] In an internal combustion engine that controls the air-fuel ratio to a lean side during operation in which a supercharger achieves a supercharging effect, and is equipped with an exhaust gas recirculation control valve in an exhaust gas recirculation passage connecting an exhaust system and an intake system, means for determining an operating range in which the air-fuel ratio should be controlled to the lean side; means for increasing supercharging pressure by a supercharger when it is determined that the air-fuel ratio is in the lean air-fuel ratio control range; and means for detecting an increase in supercharging pressure. and means for controlling an exhaust gas recirculation control valve to increase the amount of recirculated exhaust gas passing through an exhaust gas recirculation passage when an increase in boost pressure is detected. Device.