JP2009191678A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of effectively utilizing exhaust heat for warming up an engine. <P>SOLUTION: Respective cylinders 2 have a first exhaust valve 30A for opening and closing a first exhaust passage 32 communicating with a turbine 24b, and a second exhaust valve 30B for opening and closing a second exhaust passage 34 communicating with the downstream side of the turbine 24b. The upstream side of the turbine 24b of the first exhaust passage 32 and an intake passage 18 are connected by an EGR passage 42. The midway of the EGR passage 42 and the second exhaust passage 34 are connected by a connecting passage 50. An EGR cooler 46 for exchanging heat between engine cooling water and exhaust gas is arranged in the EGR passage 42 upstream of a connecting position of the connecting passage 50. When the engine is cold, a part of the exhaust gas flowing in the first exhaust passage 32 is introduced to the second exhaust passage 34 by passing through the EGR passage 42 and the connecting passage 50. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine with a supercharger, and more particularly to control of EGR.

  A device (independent exhaust engine) including a first exhaust valve that opens and closes a first exhaust passage that leads to a turbine and a second exhaust valve that opens and closes a second exhaust passage that does not pass through the turbine is known for each cylinder. (For example, refer to Patent Document 1). According to the apparatus of Patent Document 1, the EGR passage to the intake system is connected between the turbine and the junction of the first exhaust passage and the second exhaust passage.

  In addition, an apparatus is known in which an exhaust passage communicating with a first exhaust valve and an exhaust passage communicating with a second exhaust valve are connected to each other and then led to a turbine (see, for example, Patent Document 2). . According to the apparatus of Patent Document 2, the EGR passage is connected to only one exhaust passage, and the control valve is provided in the exhaust passage downstream of the connection portion of the EGR passage. By controlling the control valve, the EGR can be reliably circulated.

JP-A-11-210449 JP 2002-30980 A

  By the way, normally, since the EGR valve is closed when the engine is cold, EGR is not performed. If it does so, exhaust gas will not be guide | induced to an EGR channel | path, but will just pass an exhaust system as it is. Therefore, conventionally, exhaust heat could not be effectively used for engine warm-up.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can effectively utilize exhaust heat for engine warm-up.

In order to achieve the above object, a first invention is a control device for an internal combustion engine with a supercharger,
A first exhaust valve that opens and closes a first exhaust passage leading to the turbine of the supercharger;
A second exhaust valve for opening and closing a second exhaust passage leading to the downstream of the turbine;
An EGR passage connecting the upstream of the turbine of the first exhaust passage and an intake passage of the internal combustion engine;
A communication passage connecting the middle of the EGR passage and the second exhaust passage;
An EGR cooler is provided in the EGR passage upstream of the position where the communication passage is connected, and performs heat exchange between the cooling water of the internal combustion engine and the exhaust gas flowing through the EGR passage. And

The second invention is the first invention, wherein
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve,
The control means opens the exhaust control valve when the engine is cold.

The third invention is the first invention, wherein
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve;
A supercharging pressure acquisition means for acquiring a supercharging pressure of the internal combustion engine;
The control means opens the exhaust control valve when the supercharging pressure is equal to or higher than a reference value.

Moreover, 4th invention is set in 1st invention,
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve;
An EGR catalyst provided in the EGR passage upstream of the position where the communication passage is connected;
The control means opens the exhaust control valve when the engine is cold or the air-fuel ratio is rich.

The fifth invention is the first invention, wherein
An exhaust control valve provided in the middle of the communication passage;
An EGR valve provided in the EGR passage downstream from the position where the communication passage is connected;
Control means for controlling the opening degree of the exhaust control valve and the EGR valve,
The control means controls the opening degree of the EGR valve after opening the exhaust control valve when the required EGR amount is equal to or less than a reference value.

The sixth invention is the first invention, wherein
An exhaust control valve provided in the middle of the communication passage;
An EGR valve provided in the EGR passage downstream from the position where the communication passage is connected;
Control means for controlling the opening degree of the exhaust control valve and the EGR valve,
The control means increases the opening of the exhaust control valve and reduces the opening of the EGR valve at the time of deceleration compared to before the deceleration.

  In the first invention, the EGR passage and the second exhaust passage are connected by the communication passage. The exhaust pressure upstream of the turbine in the first exhaust passage is higher than the exhaust pressure in the second exhaust passage. For this reason, a part of the exhaust gas flowing through the first exhaust passage can be recirculated not only to the intake passage but also to the second exhaust passage. According to the first invention, the exhaust gas taken out from the first exhaust passage can be caused to flow through the EGR cooler by flowing the exhaust gas through the EGR passage into the second exhaust passage. In the EGR cooler, heat exchange is performed between the engine cooling water and the exhaust gas. Thereby, exhaust heat can be effectively utilized for engine warm-up.

  In the second invention, the exhaust control valve provided in the middle of the communication passage is opened when the engine is cold. As a result, the exhaust gas can flow through the EGR cooler when the engine is cold. Therefore, the cooling water of the internal combustion engine can be warmed by the exhaust heat. Therefore, the warm-up property of the internal combustion engine can be improved. Thereby, exhaust emission characteristics can be improved.

  In the third invention, the exhaust control valve is opened when the supercharging pressure is equal to or higher than the reference value. Thereby, the amount of exhaust gas supplied to the turbine is reduced. As a result, the turbine speed and the supercharging pressure can be lowered. Therefore, since the supercharging pressure can be controlled by the exhaust control valve, it is possible to omit the wastegate valve that has been integrated with the conventional supercharger.

  In the fourth invention, the exhaust control valve is opened when the engine is cold and the air-fuel ratio is rich, where particulates are likely to occur. By purifying the particulates in the exhaust gas by the EGR catalyst, it is possible to reduce the particulate discharge amount. Furthermore, since the amount of exhaust gas guided to the second exhaust passage by bypassing the turbine increases, the warm-up performance of the catalyst can be improved and the exhaust emission characteristics can be improved.

  In the fifth invention, when the EGR request amount is equal to or less than the reference value, the opening degree of the EGR valve is controlled after the exhaust control valve is opened. When the exhaust control valve is opened, the differential pressure before and after the EGR valve is made smaller than when the exhaust control valve is closed. Thereby, the control amount of EGR with respect to the constant opening degree change of the EGR valve is reduced. In this state, since the opening degree control of the EGR valve is performed, a minute adjustment of the EGR amount can be performed. Therefore, according to the fifth aspect, EGR controllability can be improved.

  In the sixth aspect of the invention, at the time of deceleration, the opening degree of the exhaust control valve is increased and the opening degree of the EGR valve is reduced as compared to before the deceleration. Here, if the opening degree of the EGR valve is reduced during deceleration, the differential pressure before and after the EGR increases remarkably, so that the EGR amount increases transiently. However, since the differential pressure before and after EGR can be reduced by increasing the opening degree of the exhaust control valve as compared with before deceleration, a transient increase in the EGR amount during deceleration can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram showing a system configuration according to Embodiment 1 of the present invention. The system of the first embodiment is an independent exhaust engine system having a supercharger (turbocharger).

  The system shown in FIG. 1 includes an engine 1 having a plurality of cylinders 2. For example, an in-line four-cylinder diesel engine can be used as the engine 1. The pistons (not shown) of each cylinder 2 are connected to a common crankshaft 4 via a crank mechanism. A crank angle sensor 5 that detects a rotation angle (crank angle CA) of the crankshaft 4 is provided in the vicinity of the crankshaft 4. Further, the engine 1 is provided with a water temperature sensor 3 for detecting the cooling water temperature Tw.

  The engine 1 has an injector 6 corresponding to each cylinder 2. The injector 6 is configured to inject high pressure fuel directly into the cylinder 2. Each injector 6 is connected to a common delivery pipe 7. The delivery pipe 7 communicates with the fuel tank 9 via the fuel pump 8.

  The engine 1 has an intake port 10 corresponding to each cylinder 2. A plurality of intake valves 12 are provided in the intake port 10. Connected to the intake valve 12 is a variable valve mechanism 13 that can change the valve opening characteristics (opening / closing timing and lift amount) of the intake valve 12. As the variable valve mechanism 13, a known electromagnetically driven valve mechanism, a mechanical or hydraulic variable valve mechanism, or the like can be used.

  Each intake port 10 is connected to a common intake manifold 16. The intake manifold 16 is provided with a supercharging pressure sensor 17. The supercharging pressure sensor 17 is configured to measure the pressure of air (hereinafter referred to as “supercharging air”) supercharged by a compressor 24a, which will be described later, that is, a supercharging pressure PIM that is an intake system pressure. .

  An intake passage 18 is connected to the intake manifold 16. A throttle valve 20 is provided in the middle of the intake passage 18. The throttle valve 20 is an electronically controlled valve that is driven by a throttle motor 21. The throttle valve 20 is driven based on the accelerator opening AA detected by the accelerator opening sensor 23. A throttle opening sensor 22 that detects the throttle opening TA is provided in the vicinity of the throttle valve 20. An intercooler 25 for cooling the supercharged air is provided upstream of the throttle valve 20.

  A compressor 24 a of the supercharger 24 is provided upstream of the intercooler 25. The compressor 24a is connected to the turbine 24b via a connecting shaft (not shown). The turbine 24b is provided in a first exhaust passage 32 described later. As the turbine 24b is rotationally driven by the exhaust dynamic pressure (exhaust energy), the compressor 24a is rotationally driven. An air flow meter 26 is provided upstream of the compressor 24a. The air flow meter 26 is configured to detect an intake air amount Ga.

  The engine 1 has a first exhaust valve 30A and a second exhaust valve 30B corresponding to each cylinder 2. The first exhaust valve 30A opens and closes the first exhaust passage 32 that communicates with the turbine 24b. The turbine 24 b is configured to be rotationally driven by the exhaust dynamic pressure flowing through the first exhaust passage 32. The second exhaust valve 30B opens and closes the second exhaust passage 34 that does not communicate with the turbine 24b, that is, the second exhaust passage 34 that bypasses the turbine 24b.

  These exhaust valves 30A and 30B are connected to a variable valve mechanism 31 capable of changing the valve opening characteristics (opening / closing timing and lift amount) of the exhaust valves 30A and 30B. As the variable valve mechanism 31, similarly to the variable valve mechanism 13, a known electromagnetically driven valve mechanism, a mechanical or hydraulic variable valve mechanism, or the like can be used.

  An air-fuel ratio sensor 38 for detecting the exhaust air-fuel ratio is provided in the exhaust passage 36 downstream of the junction 35 between the first exhaust passage 32 and the second exhaust passage 34. An oxidation catalyst as a start-up catalyst 39 is provided downstream of the air-fuel ratio sensor 38. The oxidation catalyst 39 has a function of oxidizing HC and CO.

  A NOx catalyst 40 is provided downstream of the oxidation catalyst 39. The NOx catalyst 40 occludes NOx in the exhaust gas in an atmosphere where the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, in an atmosphere leaner than the stoichiometric air-fuel ratio, and in the atmosphere where the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio, In the following rich atmosphere, it has a function of reducing and purifying the stored NOx and reducing it. The NOx catalyst 40 also has a function of collecting particulates in the exhaust gas. The oxidation catalyst 39 and the NOx catalyst 40 may be housed in one container.

  One end of an EGR passage 42 is connected to the first exhaust passage 32 upstream of the turbine 24b. The other end of the EGR passage 42 is connected to the intake passage 18. In the present system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 18 through the EGR passage 42, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  An EGR catalyst 44 is provided in the middle of the EGR passage 42. An oxidation catalyst can be used as the EGR catalyst 44. An EGR cooler 46 is provided in the EGR passage 42 downstream of the EGR catalyst 44. The EGR cooler 46 is configured to cool the exhaust gas flowing through the EGR passage 42 with engine cooling water. In the EGR cooler 46, heat exchange between the exhaust gas and the engine coolant is performed.

  An EGR valve 48 that controls the flow rate of the EGR gas is provided in the EGR passage 42 downstream of the EGR cooler 46. The EGR valve 48 is provided in the EGR passage 42 near the intake passage 18. The EGR valve 48 has a stepping motor (not shown) as a drive source. When the EGR valve 48 is opened, a part of the exhaust gas is returned to the intake passage 18 through the EGR catalyst 44 and the EGR cooler 46. As the opening degree of the EGR valve 48 is increased, the amount of exhaust gas passing through the EGR passage 42 (that is, the external EGR amount or the external EGR rate) can be increased.

  One end of a communication passage 50 is connected to the EGR passage 42 between the EGR valve 48 and the EGR cooler 46. The other end of the communication passage 50 is connected to the second exhaust passage 34. An exhaust control valve 52 that controls the exhaust gas flow rate in the communication passage 50 is provided in the middle of the communication passage 50.

The system according to the first embodiment includes an ECU (Electronic Control Unit) 60 that is a control device. Connected to the input side of the ECU 60 are a water temperature sensor 3, a crank angle sensor 5, a supercharging pressure sensor 17, a throttle opening sensor 22, an accelerator opening sensor 23, an air flow meter 26, an air-fuel ratio sensor 38, and the like. Further, an injector 6, a fuel pump 8, variable valve mechanisms 13 and 31, a throttle motor 21, an EGR valve 48, an exhaust control valve 52, and the like are connected to the output side of the ECU 60.
The ECU 60 calculates the engine speed NE based on the crank angle CA. Further, the ECU 60 calculates the engine load (load factor) KL [%] based on the intake air amount Ga and the like. Further, the ECU 60 calculates the fuel injection amount Q from the injector 6 from the intake air amount Ga and the target air-fuel ratio. This fuel injection amount Q can be corrected by known feedback control or the like. The ECU 60 controls the operating state of the diesel engine 1 by operating each actuator according to a predetermined program based on signals from the sensors.

[Features of Embodiment 1]
In the above system, the EGR passage 42 is connected upstream of the turbine 24b. By taking out the EGR from the upstream side of the turbine 24b having a high exhaust pressure, a large amount of external EGR can be performed during supercharging.

  By the way, when the engine is in a cold state (hereinafter referred to as “when the engine is cold”), external EGR is not normally performed in order to ensure combustion stability. That is, since the EGR valve provided in the EGR passage is closed, the exhaust gas is not circulated to the intake passage. Then, the exhaust gas just passes through the exhaust system as it is. In this case, exhaust heat cannot be effectively utilized for engine warm-up.

Therefore, in the system of the first embodiment, the communication passage 50 that connects the EGR passage 42 downstream of the EGR cooler 46 and the second exhaust passage 34 is provided. An exhaust control valve 52 is provided in the middle of the communication passage 50.
When the engine is cold, the exhaust control valve 52 is opened. At this time, the exhaust pressure upstream of the turbine 24 b in the first exhaust passage 32 is higher than the exhaust pressure in the second exhaust passage 34. As a result, even when the EGR valve 48 is closed (that is, when the external EGR is not performed), a part of the exhaust gas in the first exhaust passage 32 is allowed to flow into the EGR passage 42, the communication passage 50, and the second passage. It will flow through the exhaust passage 34. Therefore, even when the external EGR is not performed, the exhaust gas passes through the EGR cooler 46. In the EGR cooler 46, heat exchange is performed between the exhaust gas and the engine coolant. For this reason, when the engine 1 is in a cold state, the engine coolant is warmed by the exhaust heat. As a result, warm-up of the engine 1 can be promoted, and fuel efficiency and exhaust emission characteristics can be improved.

[Specific Processing in Embodiment 1]
FIG. 2 is a flowchart showing a routine executed by ECU 60 in the first embodiment. This routine is started at predetermined intervals.

  According to the routine shown in FIG. 2, first, the coolant temperature Tw is acquired (step 100). In step 100, the coolant temperature Tw detected by the water temperature sensor 3 is read into the ECU 60. Next, it is determined whether or not the coolant temperature Tw acquired in step 100 is equal to or lower than a reference value Twth (step 102). In step 102, it is determined based on the coolant temperature Tw whether or not the engine is cold.

  If it is determined in step 102 that the coolant temperature Tw is equal to or lower than the reference value Twth, it is determined that the engine is cold. In this case, the exhaust control valve 52 is opened (step 104). As a result, part of the exhaust gas flowing through the first exhaust passage 32 flows into the second exhaust passage 34 via the EGR passage 42 and the communication passage 50. As a result, since the exhaust gas flows through the EGR cooler 46 provided in the EGR passage 42, the engine cooling water is warmed by the exhaust heat. After the processing of step 104, this routine is terminated.

  On the other hand, if it is determined in step 102 that the coolant temperature Tw is higher than the reference value Twth, it is determined that the exhaust gas does not need to flow through the communication passage 50 because the engine 1 has been warmed up. The That is, it is determined that there is no need to warm the engine coolant with exhaust heat. In this case, the exhaust control valve 52 is closed (step 106). Thereafter, this routine is terminated.

  As described above, in the first embodiment, the exhaust control valve 52 is opened when the engine is cold (that is, when the coolant temperature Tw is equal to or lower than the reference value Twth). Then, the first exhaust passage 32 and the second exhaust passage 34 communicate with each other via the EGR passage 42 and the communication passage 50. The exhaust pressure upstream of the turbine 24 b in the first exhaust passage 32 is higher than the exhaust pressure in the second exhaust passage 34. Therefore, a part of the exhaust gas flowing through the first exhaust passage 32 flows into the second exhaust passage 34 via the EGR passage 42 and the communication passage 50. As a result, the exhaust gas flows through the EGR cooler 46 provided in the EGR passage 42, so that the engine coolant can be warmed by the exhaust heat. Therefore, since the warm-up property of the engine 1 can be improved, the fuel efficiency and exhaust emission characteristics can be improved.

  By the way, in the first embodiment, the EGR catalyst 44 is provided upstream of the EGR cooler 46, but if the EGR passage 42 is upstream of the connection point 47 of the communication passage 50, the EGR catalyst 44 and EGR The installation position of the cooler 46 is arbitrary. For example, the EGR catalyst 44 may be provided on the downstream side of the EGR cooler 46.

  Moreover, although the case where this invention was applied to the diesel engine was demonstrated in this Embodiment 1, you may apply when the present invention is applied to a gasoline engine.

In the first embodiment, the supercharger 24 is the “supercharger” in the first invention, the turbine 24b is the “turbine” in the first invention, and the first exhaust passage 32 is the first invention. The first exhaust valve 30A is the “first exhaust valve” in the first invention, the second exhaust passage 34 is the “second exhaust passage” in the first invention, the second exhaust is The valve 30B corresponds to the “second exhaust valve” in the first invention.
In the first embodiment, the NOx catalyst 40 is the “catalyst” in the first invention, the EGR passage 42 is the “EGR passage” in the first invention, and the communication passage 50 is the “contact” in the first invention. In the “passage”, the EGR cooler 46 is the “EGR cooler” in the first invention, the exhaust control valve 52 is the “exhaust control valve” in the second to sixth inventions, and the EGR catalyst 44 is the “EGR in the fourth invention”. The EGR valve 48 corresponds to the “catalyst” and corresponds to the “EGR valve” in the fifth and sixth inventions, respectively.
In the first embodiment, the “control means” according to the second aspect of the present invention is realized by the ECU 60 executing the processing of steps 102 and 104.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. The system of the second embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 3 described later using the hardware configuration shown in FIG.

[Features of Embodiment 2]
In the first embodiment, the exhaust control valve 52 is opened when the engine is cold (during warming up), and the exhaust control valve 52 is closed after the engine 1 is warmed up.
By the way, in order to control the supercharging pressure, conventionally, a wastegate valve is integrally formed with the supercharger. By opening this wastegate valve, the turbine can be bypassed and exhausted. As a result, the turbine speed and the supercharging pressure can be lowered.

  In the second embodiment, the exhaust control valve 52 is opened when the supercharging pressure PIM becomes equal to or higher than the target value PIMtrg. Thereby, the amount of exhaust gas supplied to the second exhaust passage 34 via the EGR passage 42 and the communication passage 50, that is, the amount of exhaust gas bypassing the turbine 24b can be increased. Therefore, the amount of exhaust gas supplied to the turbine 24b can be reduced, and the turbine speed and the supercharging pressure can be lowered. Therefore, the supercharging pressure control can be performed by the exhaust control valve 52.

[Specific Processing in Second Embodiment]
FIG. 3 is a flowchart showing a routine executed by ECU 60 in the second embodiment. This routine is started at predetermined intervals.

  According to the routine shown in FIG. 3, similarly to the routine shown in FIG. 2, the coolant temperature Tw is acquired (step 100), and it is determined whether or not the acquired coolant temperature Tw is equal to or lower than the reference value Twth (step 102). ). When it is determined in step 102 that the coolant temperature Tw is equal to or lower than the reference value Twth, that is, when the engine is cold, the exhaust control valve 52 is opened (step 104). Thereafter, this routine is terminated.

  If it is determined in step 102 that the coolant temperature Tw is higher than the reference value Twth, the supercharging pressure PIM is acquired (step 107). In step 107, the boost pressure PIM detected by the boost pressure sensor 17 is read into the ECU 60. Then, it is determined whether or not the supercharging pressure PIM acquired in step 107 is higher than the target supercharging pressure PIMtrg (step 108). As the target boost pressure PIMtrg, a value calculated by a routine different from this routine is read. In this step 108, it is determined whether it is necessary to increase the amount of exhaust gas that bypasses the turbine 24b.

  If it is determined in step 108 that the boost pressure PIM is higher than the target boost pressure PIMtrg, it is determined that the amount of exhaust gas that bypasses the turbine 24b needs to be increased. In this case, the exhaust control valve 52 is opened (step 104). Thereafter, this routine is terminated.

  On the other hand, when it is determined in step 108 that the supercharging pressure PIM is equal to or lower than the target supercharging pressure PIMtrg, the exhaust control valve 52 is closed (step 110). Thereafter, this routine is terminated.

  As described above, in the second embodiment, the exhaust control valve 52 is opened when the supercharging pressure PIM is higher than the target supercharging pressure PIMtrg. As a result, the amount of exhaust gas supplied to the turbine 24b is reduced. As a result, the turbine speed (turbo speed) and the supercharging pressure PIM can be lowered. Since the supercharging pressure can be controlled using the exhaust control valve 52 in this way, the wastegate valve that has been configured integrally with the conventional supercharger can be omitted.

  In the second embodiment, the ECU 60 executes the processing of steps 102 and 104, so that the “control means” in the second invention executes the processing of steps 108 and 104, and the third invention. The “control means” in FIG.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. The system of the third embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 4 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 3]
When the engine is cold (for example, immediately after the engine is started, etc.), the mixing of the fuel and air is likely to occur in the cylinder, so that particulates are likely to occur. Further, when the engine is cold, there is a high possibility that the NOx catalyst 40 is not sufficiently warmed up. As a result, the amount of particulates discharged from the vehicle may increase.

  In addition, when the air-fuel ratio is rich where OT increase, rich spike, or the like is performed, the fuel becomes excessive with respect to the intake air. For this reason, particulates are likely to be generated due to insufficient oxygen during in-cylinder combustion. Further, when the air-fuel ratio is rich, the purification rate of the NOx catalyst 40 decreases. As a result, similarly to when the engine is cold, there is a high possibility that the amount of particulates discharged from the vehicle will increase.

  Thus, in the third embodiment, the exhaust control valve 52 is opened when the air-fuel ratio is rich or when the engine is cold. At this time, the exhaust pressure upstream of the turbine 24 b in the first exhaust passage 32 is higher than the exhaust pressure in the second exhaust passage 34. Thereby, even when the EGR valve 48 is closed, part of the exhaust gas in the first exhaust passage 32 flows through the EGR passage 42, the communication passage 50, and the second exhaust passage 34.

  Here, as shown in FIG. 1, an EGR catalyst 44 is provided in the EGR passage 42. The oxidation catalyst used as the EGR catalyst 44 has a particulate purification function to some extent. For this reason, when exhaust gas is actively introduced into the EGR catalyst 44 when the air-fuel ratio is rich or when the engine is cold such as immediately after the start of engine startup, the amount of particulate emissions from the vehicle can be reduced.

  An oxidation catalyst provided with a particulate purification function (for example, a trap function or a continuous purification function) may be used as the EGR catalyst 44. Thereby, since the particulate reduction effect by the EGR catalyst 44 increases, the particulate discharge amount from the vehicle can be further reduced.

[Specific Processing in Embodiment 3]
FIG. 4 is a flowchart showing a routine executed by the ECU 60 in the third embodiment. This routine is started at predetermined intervals.

  According to the routine shown in FIG. 4, first, the coolant temperature Tw and the air-fuel ratio A / F are acquired (step 101). In step 101, the coolant temperature Tw detected by the water temperature sensor 3 and the air-fuel ratio A / F detected by the air-fuel ratio sensor 38 are read into the ECU 60. The air-fuel ratio A / F may be estimated from the intake air amount Ga, the fuel injection amount Q, and the like.

  Next, similarly to the routine shown in FIG. 2, it is determined whether or not the coolant temperature Tw is equal to or lower than the reference value Twth (step 102). When it is determined in step 102 that the coolant temperature Tw is equal to or lower than the reference value Tw, that is, when the engine is cold, it is determined that there is a high possibility that the particulate discharge amount will increase. That is, it is determined that the exhaust gas needs to be actively guided to the EGR catalyst 44. Therefore, in this case, the exhaust control valve 52 is opened (step 104).

  On the other hand, if it is determined in step 102 that the coolant temperature Tw is higher than the reference value Twth, that is, after the engine warm-up is completed, the air-fuel ratio A / F obtained in step 101 is richer than the reference value. It is determined whether or not there is (step 103). Even when it is determined in step 103 that the air-fuel ratio A / F is rich, there is a high possibility that the particulate emission will increase as in the case of the cold engine, so the EGR catalyst 44 is positively affected. It is determined that exhaust gas needs to be led. Therefore, also in this case, the exhaust control valve 52 is opened (step 104). After the processing of step 104, this routine is terminated.

  If it is determined in step 103 that the air-fuel ratio A / F is not rich, that is, if the air-fuel ratio A / F is lean or stoichiometric, it is determined that there is a low possibility that the particulate discharge amount will increase. The In this case, the exhaust control valve 52 is closed (step 106). After the processing of step 106, this routine is finished.

  As described above, in the third embodiment, the exhaust control valve 52 is opened when the engine is cold and when the air-fuel ratio is rich, that is, when there is a high possibility that the particulate discharge amount will increase. Then, a part of the exhaust gas flowing through the first exhaust passage 32 flows into the second exhaust passage 34 via the EGR passage 42 and the communication passage 50. As a result, the exhaust gas flows through the EGR catalyst 44 provided in the EGR passage 42. The EGR catalyst 44 has a particulate purification performance. For this reason, the particulate discharge amount from the vehicle can be reduced when the air-fuel ratio is rich or when the engine is cold such as immediately after the start of the engine.

  In the third embodiment, the “control means” according to the fourth aspect of the present invention is realized by the ECU 60 executing the processing of steps 102, 103, and 104.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG. The system of the fourth embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 5 described later using the hardware configuration shown in FIG.

[Features of Embodiment 4]
In a state in which the exhaust control valve 52 is closed, the pressure upstream of the EGR valve 48 corresponds to the pressure of the first exhaust passage 32 upstream of the turbine 24b. The pressure downstream of the EGR valve 48 corresponds to the pressure in the intake passage 18, that is, the supercharging pressure PIM. When the differential pressure across the EGR valve 48 is large, the amount of change in EGR with respect to the amount of change in the constant opening of the EGR valve 48 becomes large.

  By the way, at a light load, the EGR request amount is small and the intake system pressure is generally small. For this reason, at such a light load, the differential pressure across the EGR valve 48 tends to increase. Then, there is a possibility that the EGR amount cannot be controlled in a systematic manner.

  Therefore, in the fourth embodiment, the differential pressure across the EGR valve 48 is reduced by opening the exhaust control valve 52 at a light load. Thereby, the variation | change_quantity of EGR with respect to the fixed opening amount variation | change_quantity of the EGR valve 48 can be made small. That is, the EGR adjustment amount per step of the EGR valve 48 can be reduced. Therefore, the EGR amount can be accurately controlled at light load.

  By the way, when the exhaust control valve 52 is opened, the amount of exhaust gas flowing through the EGR cooler 46 increases. Thereby, since the cooling capacity of the EGR cooler 46 is lowered, the temperature of the EGR gas is increased. When there is a high load, there is a problem of knocking, and thus the temperature rise of the EGR gas is not preferable. On the other hand, since the low temperature combustion is performed in the cylinder at a light load, it is preferable to introduce a high temperature EGR gas into the cylinder, and it is not preferable to introduce a low temperature EGR gas. Therefore, the temperature increase of the EGR gas at the time of light load is rather preferable from the viewpoint of combustion stability.

[Specific Processing in Embodiment 4]
FIG. 5 is a flowchart showing a routine executed by ECU 60 in the fourth embodiment. This routine is started at predetermined intervals.

  According to the routine shown in FIG. 5, first, the engine load KL is acquired (step 110). In step 110, for example, the engine load KL calculated from the intake air amount Ga or the like is read. Next, the required EGR amount is calculated based on the engine load KL acquired in step 110 (step 112). In step 112, for example, the EGR request amount is calculated with reference to a map in which the EGR request amount is defined in relation to the engine load KL. According to the map, the EGR request amount at light load is calculated to be smaller than the EGR request amount at high load.

  Next, it is determined whether or not the EGR request amount calculated in step 112 is equal to or less than a reference value (step 114). This reference value is a threshold value for determining whether or not the EGR request amount is a minute amount. If it is determined in step 114 that the required EGR amount is larger than the reference value, the exhaust control valve 52 is closed (step 118). Then, the EGR valve opening is calculated (step 120). After the processing of step 120, this routine is finished.

  On the other hand, if it is determined in step 114 that the required EGR amount is equal to or less than the reference value, the exhaust control valve 52 is opened (step 116). Thereby, the differential pressure before and after the EGR valve 48 can be reduced. Then, the EGR valve opening is calculated (step 120). In step 120, the EGR valve opening is calculated with reference to a map in which the EGR valve opening is defined in relation to the EGR required amount. At this time, since the differential pressure across the EGR valve 48 is reduced, the resolution of the EGR valve is reduced. Therefore, fine adjustment of the EGR amount can be performed with high accuracy.

  As described above, in the fourth embodiment, when it is determined that the EGR request amount is equal to or less than the reference value, the exhaust control valve 52 is opened. Then, since the pressure upstream of the EGR valve 48 becomes low, the differential pressure before and after the EGR valve 48 becomes smaller than when the exhaust control valve 52 is closed. In this state, since the opening degree of the EGR valve 48 is controlled, fine adjustment of EGR at light load can be performed with high accuracy.

  In the fourth embodiment, the “control means” according to the fifth aspect of the present invention is realized by the ECU 60 executing the processes of steps 114, 116, and 120.

Embodiment 5 FIG.
Next, a fifth embodiment of the present invention will be described with reference to FIG. The system of the fifth embodiment can use the hardware configuration shown in FIG.

[Features of Embodiment 5]
When the vehicle is decelerated during EGR, the engine load decreases rapidly. In this case, the EGR request amount also decreases rapidly. For this reason, it is necessary to rapidly reduce the amount of fresh air and reduce the amount of EGR.

Therefore, in the fifth embodiment, the control shown in FIG. 6 is performed during deceleration. FIG. 6 is a timing chart showing control at the time of deceleration in the fifth embodiment.
Specifically, FIG. 6A shows changes in engine load, FIG. 6B shows changes in EGR demand, FIG. 6C shows changes in EGR opening, and FIG. 6D shows exhaust control. The change of the opening degree of a valve is shown, respectively. Further, FIG. 6 (E) shows a change in intake system pressure, FIG. 6 (F) shows a change in differential pressure before and after the EGR valve, and FIG. 6 (G) shows a change in EGR flow rate.

  As shown in FIG. 6, at time t1, the engine load KL is high and EGR is being performed. When there is a deceleration request from time t2 to time t3, the engine load KL decreases rapidly, and the EGR request amount also decreases rapidly as the engine load KL changes.

  The responsiveness of the opening degree of the EGR valve 48 is low with respect to the sudden change in the engine load KL and the EGR request amount. As shown in FIG. 6C, the opening degree of the EGR valve 48 gradually decreases from time t2 to time t5. On the other hand, since the amount of fresh air is reduced as the engine load KL changes, the intake system pressure rapidly decreases as shown in FIG. 6 (E).

  Here, as a comparative example with respect to the fifth embodiment, it is assumed that the exhaust control valve 52 is kept closed as indicated by a broken line in FIG. 6D from time t2 to time t5. Then, as indicated by a broken line in FIG. 6E, the differential pressure before and after the EGR valve 48 increases rapidly. For this reason, as indicated by a broken line in FIG. 6G, the EGR flow rate increases transiently. Thereby, knocking may occur.

In the fifth embodiment, the transient increase in the EGR flow rate is avoided by controlling the opening degree of the exhaust control valve 52. Specifically, the opening degree of the exhaust control valve 52 is increased as compared with the time of high load, as shown in the solid line in FIG. That is, at the time of deceleration, the opening degree of the exhaust control valve 52 is made larger than before the deceleration.
As a result, the pressure upstream of the EGR valve 48 is reduced, so that the differential pressure across the EGR valve 48 can be reduced as shown by the solid line in FIG. As a result, as shown by a solid line in FIG. 6G, it is possible to prevent a transient increase in the EGR flow rate during deceleration.
Therefore, according to the fifth embodiment, knocking can be prevented from occurring by preventing a transient increase in the EGR flow rate resulting from an increase in the differential pressure across the EGR valve 48 during deceleration.

It is a figure which shows the system configuration | structure by Embodiment 1 of this invention. 5 is a flowchart showing a routine that is executed by the ECU 60 in the first embodiment of the present invention. In Embodiment 2 of this invention, it is a flowchart which shows the routine which ECU60 performs. In Embodiment 3 of this invention, it is a flowchart which shows the routine which ECU60 performs. In Embodiment 4 of this invention, it is a flowchart which shows the routine which ECU60 performs. In Embodiment 5 of this invention, it is a timing chart which shows the control at the time of deceleration.

Explanation of symbols

1 engine 18 intake passage 30A first exhaust valve 30B second exhaust valve 32 first exhaust passage 34 second exhaust passage 40 NOx catalyst 42 EGR passage 44 EGR catalyst 46 EGR cooler 48 EGR valve 50 communication passage 52 exhaust control valve 60 ECU

Claims (6)

A control device for an internal combustion engine with a supercharger,
A first exhaust valve that opens and closes a first exhaust passage leading to the turbine of the supercharger;
A second exhaust valve for opening and closing a second exhaust passage leading to the downstream of the turbine;
An EGR passage connecting the upstream of the turbine of the first exhaust passage and an intake passage of the internal combustion engine;
A communication passage connecting the middle of the EGR passage and the second exhaust passage;
An EGR cooler is provided in the EGR passage upstream from the position where the communication passage is connected, and performs heat exchange between the cooling water of the internal combustion engine and the exhaust gas flowing through the EGR passage. A control device for an internal combustion engine with a supercharger. The control apparatus for an internal combustion engine with a supercharger according to claim 1,
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve,
The control device for an internal combustion engine with a supercharger, wherein the control means opens the exhaust control valve when the engine is cold. The control apparatus for an internal combustion engine with a supercharger according to claim 1,
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve;
A supercharging pressure acquisition means for acquiring a supercharging pressure of the internal combustion engine;
The control device for an internal combustion engine with a supercharger, wherein the control means opens the exhaust control valve when the supercharging pressure is equal to or higher than a reference value. The control apparatus for an internal combustion engine with a supercharger according to claim 1,
An exhaust control valve provided in the middle of the communication passage;
Control means for controlling the opening of the exhaust control valve;
An EGR catalyst provided in the EGR passage upstream of the position where the communication passage is connected;
The control device for an internal combustion engine with a supercharger, wherein the control means opens the exhaust control valve when the engine is cold or when the air-fuel ratio is rich. The control apparatus for an internal combustion engine with a supercharger according to claim 1,
An exhaust control valve provided in the middle of the communication passage;
An EGR valve provided in the EGR passage downstream from the position where the communication passage is connected;
Control means for controlling the opening degree of the exhaust control valve and the EGR valve,
The control device for an internal combustion engine with a supercharger, wherein when the required EGR amount is equal to or less than a reference value, the opening degree of the EGR valve is controlled after the exhaust control valve is opened. . The control apparatus for an internal combustion engine with a supercharger according to claim 1,
An exhaust control valve provided in the middle of the communication passage;
An EGR valve provided in the EGR passage downstream from the position where the communication passage is connected;
Control means for controlling the opening degree of the exhaust control valve and the EGR valve,
The control device for an internal combustion engine with a supercharger, wherein the control means increases the opening degree of the exhaust control valve and reduces the opening degree of the EGR valve as compared to before the deceleration at the time of deceleration.

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