JP2014231821A - Controller for internal combustion engine equipped with supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller for an internal combustion engine equipped with a supercharger capable of discharging condensed water in a low-pressure EGR passage to an exhaust path while stabilizing combustion.SOLUTION: A controller comprises: an air bypass passage connecting an air intake passage downstream of a compressor to an air intake passage upstream thereof and bypassing the compressor; an air bypass valve provided in the air bypass passage; a low-pressure EGR passage connecting an exhaust passage downstream of a turbine to the air intake passage upstream of the compressor; and an EGR valve provided in the low-pressure EGR passage. During an operating state in which surging of the compressor should be suppressed, the air bypass valve is opened. In response to opening of the air bypass valve, the EGR valve is opened. Thereafter, in response to closing of the air bypass valve, the EGR valve is closed.

Description

  The present invention relates to a control device for an internal combustion engine with a supercharger.

  Conventionally, as disclosed in Patent Document 1, for example, an internal combustion engine with a supercharger having a low pressure EGR passage is known. The low pressure EGR passage is a passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor. A part of the exhaust is taken in as low pressure EGR gas from the exhaust passage downstream of the turbine and the low pressure EGR gas is supplied to the intake passage upstream of the compressor. Reflux.

In addition, the internal combustion engine of Patent Document 1 includes an exhaust throttle valve that adjusts the amount of exhaust gas that flows through the exhaust passage downstream of the location where the low-pressure EGR passage is connected, and the low-pressure EGR passage and exhaust throttle valve that are downstream of the EGR cooler. And a communication passage communicating with the exhaust passage downstream. In Patent Document 1, the exhaust throttle valve is closed to increase the pressure in the low-pressure EGR passage, thereby generating a differential pressure between the low-pressure EGR passage and the exhaust passage via the communication passage, and the low-pressure EGR passage. It is disclosed that the condensed water inside is discharged to the exhaust passage.
The applicant has recognized the following documents including the above-mentioned documents as related to the present invention.

JP 2008-002351 A JP 2007-198310 A JP-A-5-256213 JP-A-4-370324 JP-A-8-177597

  However, in the internal combustion engine of Patent Document 1, the change in the back pressure due to the closing operation of the exhaust throttle valve varies depending on the operating state, and it is difficult to obtain both a sufficient condensed water removal effect and stable combustion. Specifically, the back pressure largely depends on the air flow rate, but in the low flow rate operation region where the impact on combustion is relatively small due to the increase in back pressure, the increase in back pressure due to throttle of the exhaust throttle valve is small, and condensed water removal The effect is small. Further, in the high flow rate operation region, although the back pressure is greatly increased by restricting the exhaust throttle valve and the condensed water removal effect is large, there is a risk of deterioration in combustion or reduction in output performance. This is because when the back pressure increases, the residual gas in the cylinder increases, and in order to obtain the same boost pressure, it is necessary to increase the turbine front back pressure to increase the expansion ratio. This is because it cannot be raised more than a certain amount due to factors such as the astringency of closing.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine with a supercharger that can discharge condensed water in a low-pressure EGR passage to an exhaust passage while stabilizing combustion. The purpose is to provide.

In order to achieve the above object, a first invention is a control device for an internal combustion engine with a supercharger,
A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage;
An air bypass passage connecting the intake passage downstream of the compressor and the upstream intake passage, bypassing the compressor;
An air bypass valve provided in the air bypass passage;
A low pressure EGR passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor;
An EGR valve provided in the low pressure EGR passage;
Air bypass valve control means for opening the air bypass valve during an operating state in which surging of the compressor is to be suppressed;
EGR valve control means for opening the EGR valve in response to opening of the air bypass valve by the air bypass valve control means, and then closing the EGR valve in response to closing of the air bypass valve; It is characterized by providing.

The second invention is the first invention, wherein
The operating state in which the surging of the compressor should be suppressed is during engine deceleration in the supercharging region,
The EGR valve control means opens the EGR valve after the air bypass valve is opened by the air bypass valve control means, and then closes the EGR valve simultaneously with closing the air bypass valve; It is characterized by.

The third invention is the first or second invention, wherein
An EGR cooler disposed in the low pressure EGR passage upstream of the EGR valve is further provided.

According to the first or second invention, the condensed water in the low pressure EGR passage can be discharged to the exhaust passage while stabilizing the combustion.
In the present invention, the opening of the air bypass valve or the EGR valve is not only to fully open the valve opening, but also to be larger than the control target value of the valve opening that is predetermined according to the operating conditions. It also means. Further, the closing of the air bypass valve or the EGR valve not only means that the valve opening is fully closed, but also means that the valve opening is made smaller than the control target value determined in advance according to the operating conditions. To do.

  According to the third aspect, the condensed water in the EGR cooler can be discharged to the exhaust passage.

It is a conceptual block diagram for demonstrating the system configuration | structure which concerns on Embodiment 1 of this invention. 4 is a timing chart showing opening / closing timings of the air bypass valve 24 and the EGR valve 32 during deceleration in the first embodiment of the present invention. It is a schematic diagram for demonstrating the EGR gas behavior in the period A of FIG. It is a flowchart of the control routine which ECU50 performs in Embodiment 1 of this invention. It is a schematic diagram for demonstrating a problem when the closing timing of the EGR valve 32 is late. It is a schematic diagram for demonstrating a problem in case the closing timing of the EGR valve 32 is quick.

  Hereinafter, embodiments of the present invention will be described in detail 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.
[System Configuration of Embodiment 1]
FIG. 1 is a conceptual configuration diagram for explaining a system configuration according to Embodiment 1 of the present invention. The system shown in FIG. 1 includes an engine 10 as an internal combustion engine. The engine 10 is mounted on a vehicle or the like and is used as a power source. In FIG. 1, the engine 10 is shown as an in-line four-cylinder type, but the number and arrangement of the cylinders are not limited to this.

  An intake passage 12 and an exhaust passage 14 are connected to each cylinder of the engine 10. An air cleaner 16 is attached near the inlet of the intake passage 12. The system includes a supercharger 18. The supercharger 18 includes a compressor 18a and a turbine 18b. The compressor 18a and the turbine 18b are integrally connected by a connecting shaft. The compressor 18 a is provided in the intake passage 12 downstream of the air cleaner 16.

  An intercooler 20 for cooling the intake air compressed by the compressor 18a is provided in the intake passage 12 downstream of the compressor 18a.

  One end of an air bypass passage 22 is connected to the intake passage 12 between the compressor 18 a and the intercooler 20. The other end of the air bypass passage 22 is connected to the intake passage 12 between the air cleaner 16 and the compressor 18a. Thus, the air bypass passage 22 bypasses the compressor 18a. An air bypass valve (ABV) 24 that communicates with the air bypass passage 22 by opening the valve and blocks the air bypass passage 22 by closing the valve is disposed in the air bypass passage 22. The air bypass valve 24 is an electronically controlled valve that is opened and closed by an electric actuator, for example.

  A throttle 26 is disposed in the intake passage 12 downstream of the intercooler 20. The throttle 26 is an electronically controlled valve that is opened and closed by an electric actuator.

  A turbine 18 b is provided in the exhaust passage 14. The compressor 18a is rotationally driven by the energy of exhaust gas input to the turbine 18b.

  Moreover, the system of this embodiment is equipped with the low pressure loop (LPL: Law Pressure Loop) EGR system. One end of a low pressure EGR passage 28 is connected to the exhaust passage 14 downstream of the turbine 18b. The other end of the low pressure EGR passage 28 is connected to the intake passage 12 between the air cleaner 16 and the compressor 18a. In the example shown in FIG. 1, the other end of the low pressure EGR passage 28 is connected to the intake passage 12 upstream of the connection port between the air bypass passage 22 and the intake passage 12.

  An EGR cooler 30 is provided in the middle of the low pressure EGR passage 28. The low pressure EGR passage 28 downstream of the EGR cooler 30 is provided with an EGR valve (EGRV) 32 that communicates with the low pressure EGR passage 28 by opening the valve and shuts off the low pressure EGR passage 28 by closing the valve. The EGR valve 32 is an electronically controlled valve that is opened and closed by an electric actuator, and the flow rate can be controlled by controlling the opening degree.

  The system of this embodiment includes an ECU (Electronic Control Unit) 50. The input part of the ECU 50 includes a crank angle sensor 52 for detecting the crank position and the engine speed, an accelerator opening sensor 54 for detecting an accelerator opening corresponding to the operation amount of the accelerator pedal of the vehicle, and a compressor 18a. Various sensors for detecting the operating state of the engine 10 such as a pressure sensor 56 for detecting the intake pressure in the intake passage 12 between the throttle 26 and the throttle 26 are connected.

  In addition, the output unit of the ECU 50 includes the actuator of the air bypass valve 24, the actuator of the throttle 26, the actuator of the EGR valve 32, and the engine 10 such as a fuel injection valve (not shown) for supplying fuel into the cylinder. Various actuators for controlling the operation state are connected.

  The ECU 50 controls the operating state of the engine 10 by executing predetermined programs based on input information from various sensors and operating various actuators.

  In the system of the present embodiment including the supercharger 18, surging (intake pulsation) of the compressor 18a is a phenomenon that occurs when the throttle 26 is suddenly closed in a supercharged state (for example, during engine deceleration). When the throttle 26 is suddenly closed in a supercharged state, the intake air compressed by the compressor 18a is blocked by the throttle 26 and loses its place of travel, and the pressure in the intake passage 12 downstream of the compressor 18a increases more than necessary. The system of the present embodiment includes air bypass valve control means for opening the air bypass valve 24 during an operating state in which surging of the compressor 18a is to be suppressed (for example, during engine deceleration in the supercharging region). . As a result, the intake air is released into the intake passage 12 upstream of the compressor 18a via the air bypass passage 22.

  The low-pressure loop EGR system described above connects the exhaust passage 14 downstream of the turbine 18b and the intake passage 12 upstream of the compressor 18a, and a part of the low-pressure exhaust gas downstream of the turbine 18b is used as EGR gas. It recirculates to the intake system.

  In the low pressure loop EGR system, condensed water derived from the EGR gas cooled by the EGR cooler 30 is generated. If the condensed water flows into the intake passage 12, members such as the compressor 18a and the intercooler 20 may be corroded. Therefore, it is desired to suppress the inflow of condensed water into the intake passage 12.

[Characteristic Control in Embodiment 1]
Therefore, in the system according to the present embodiment, the EGR valve 32 is opened in response to the opening of the air bypass valve 24 by the above-described air bypass valve control means, and then the EGR valve is operated in response to the closing of the air bypass valve 24. 32 is closed. Preferably, after the air bypass valve 24 is opened, the opening degree of the EGR valve 32 is made higher than the current value, and then the EGR valve 32 is closed simultaneously with the closing of the air bypass valve 24. This characteristic control is executed in an operating state in which the pressure in the intake passage 12 downstream of the compressor 18a is higher than the pressure in the exhaust passage 14 downstream of the turbine 18b.

  FIG. 2 is a timing chart showing opening / closing timings of the air bypass valve 24 and the EGR valve 32 during deceleration. At time t1, the throttle opening 26 decreases as the accelerator opening decreases rapidly. At time t2, the EGR valve 32 is opened after the air bypass valve 24 is opened. Preferably, as shown in FIG. 3, the opening degree of the EGR valve 32 is set higher than the control target value of the valve opening degree determined in advance according to the operating conditions. Thereafter, at time t3, the EGR valve 32 is closed simultaneously with the closing of the air bypass valve 24.

  FIG. 3 is a schematic diagram for explaining the EGR gas behavior in the period A of FIG. 2 that is generated by the characteristic control of the first embodiment. 3, 5 and 6, the EGR cooler 30 is not shown in order to show the EGR gas behavior.

  When the EGR valve 32 is opened after the air bypass valve 24 is opened, a reverse flow of the EGR mixed gas as shown in the left diagram of FIG. 3 occurs. The pressure in the intake passage 12 downstream of the compressor 18a is higher than the pressure in the intake passage 12 upstream of the compressor 18a and the pressure in the exhaust passage 14 downstream of the turbine 18b. Due to this pressure difference, the EGR mixed gas compressed in the intake passage 12 downstream of the compressor 18a is returned into the intake passage 12 upstream of the compressor 18a, and further, a part of the EGR mixed gas returned into the intake passage 12 Flows back through the low-pressure EGR passage 28 through the opened EGR valve 32. As a result, the condensed water in the EGR cooler 30 can be discharged to the exhaust passage 14.

  Thereafter, the EGR valve 32 is closed simultaneously with the closing of the air bypass valve 24. As shown in the right diagram of FIG. 3, the EGR valve 32 is closed before the EGR mixed gas in the low pressure EGR passage 28 flows forward and is sucked into the intake air, thereby increasing the EGR concentration of the EGR mixed gas returning to the intake passage 12. Can be suppressed. Since EGR gas remaining in the intake passage 12 can be reduced, it is possible to reduce misfires at slow light loads, unstable combustion, and slack during reacceleration.

  As described above, according to the characteristic control of the first embodiment, the condensed water in the low-pressure EGR passage 28 (particularly, the EGR cooler 30) can be discharged to the exhaust passage while stabilizing the combustion.

  The ECU 50 outputs an instruction for controlling the opening degree of the EGR valve 32 according to the operating conditions. When the air bypass valve 24 is opened along with deceleration by the above-described air bypass valve control means in a state in which the EGR valve 32 is instructed to close, priority is given to the EGR valve 32 closing instruction. The EGR valve 32 is opened. Thereafter, the EGR valve 32 is closed according to the closing of the air bypass valve 24 (here, the valve closing operation according to the above-described valve closing instruction is completed). Although the valve closing operation is delayed with respect to the valve closing instruction of the EGR valve 32, according to this control, the EGR gas flows back into the low pressure EGR passage 28 as described above, so that the EGR gas flows into the intake passage 12. Can be prevented, and no harmful effects occur.

  As described above, the opening / closing timing of the air bypass valve 24 and the EGR valve 32 is important. As a comparison object with the present invention, a case where the closing timing of the EGR valve 32 is late (FIG. 5) and a case where the closing timing of the EGR valve 32 is early (FIG. 6) will be described.

FIG. 5 is a schematic diagram for explaining a problem when the closing timing of the EGR valve 32 is late.
As shown in the left diagram of FIG. 5, the EGR valve 32 is opened in response to the opening of the air bypass valve 24 due to deceleration, so that the EGR mixed gas causes the EGR valve 32 and the EGR cooler 30 to be moved by the pressure difference described above. The condensed water that has passed and adhered to the EGR cooler can be discharged to the exhaust passage 14.

  However, if the timing for closing the EGR valve 32 thereafter is late, as shown in the right diagram of FIG. 5, when the EGR gas returns to the intake air, the concentration of the EGR mixed gas that has returned to the intake upstream is increased. Combustibility may deteriorate and may lead to misfire.

FIG. 6 is a schematic diagram for explaining a problem when the closing timing of the EGR valve 32 is early.
As shown in FIG. 6, if the EGR valve 32 is closed immediately after deceleration, the concentration of the EGR gas is not increased, but conversely, there is no effect of decreasing the concentration, and the condensate in the EGR cooler 30 is removed from the exhaust passage. 14 can not be discharged.

  Next, the control routine of this embodiment will be described with reference to FIG. FIG. 4 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described operation. This routine is executed every predetermined cycle, at least during engine deceleration in the supercharging region. In FIG. 4, an explanation will be given by taking as an example the case of engine deceleration in a state where the EGR valve 32 is instructed to close.

  In the routine shown in FIG. 4, in step S100, the ECU 50 determines whether or not the engine is being decelerated in the supercharging region. For example, the determination can be made based on the operating region (engine speed, engine load), the rotation state of the compressor 18a, the amount of decrease in the accelerator opening when the accelerator is off, the amount of decrease in the throttle opening, the detected value of the pressure sensor 56, and the like. If it is determined that the engine is decelerating, the process proceeds to step S110.

  In step S110, the ECU 50 determines whether or not an instruction to close the EGR valve 32 is given. Specifically, the ECU 50 stores in advance a map or model that defines the relationship between the operating state and the opening degree of the EGR valve 32, and based on this, the opening degree of the EGR valve 32 corresponding to the operating state is determined. Instruct. When the valve closing instruction is given, the process proceeds to step S120.

  In step S120, the ECU 50 determines whether or not the air bypass valve 24 is open. Specifically, the determination can be made based on the instruction content to the air bypass valve 24 of the ECU 50 in the air bypass valve control means described above. In the case of a valve opening instruction, the process proceeds to step S130.

  In step S130, the ECU 50 opens the EGR valve 32. That is, the EGR valve 32 is opened prior to the instruction to close the EGR valve 32 in step S110. Preferably, the opening degree of the EGR valve 32 is set higher than the control target value of the valve opening degree determined in advance according to the operating conditions.

  Thereafter, in step S140, the ECU 50 causes the air bypass valve control means to close the air bypass valve 24 and simultaneously close the EGR valve 32 when the pressure downstream of the compressor 18a decreases.

  By the way, in the system of Embodiment 1 mentioned above, although the air bypass valve 24 is made into the electronic control type, it is not limited to this. For example, a diaphragm type may be used. In this case, the open / closed state of the air bypass valve 24 can be estimated using a map or model related to the operating region, the rotational state of the compressor 18a, the throttle opening, the detected value of the pressure sensor 56, and the like.

  The engine to which the present invention is applied is not limited to a spark ignition engine, and may be a compression self-ignition engine.

In the first embodiment described above, the supercharger 18 is the “supercharger” in the first invention, the air bypass passage 22 is the “air bypass passage” in the first invention, and the air bypass valve. 24 is the “air bypass valve” in the first invention, the low pressure EGR passage 28 is the low pressure EGR passage in the first invention, the EGR valve 32 is the “EGR valve” in the first invention, and the EGR cooler 30 Corresponds to the “EGR cooler” in the third invention.
Further, here, the ECU 50 executes the above-described air bypass valve control means, so that the “air bypass valve control means” in the first invention executes the processes of the above steps S120 to S140. Each of the “EGR valve control means” in the present invention is realized.

10 Engine 12 Intake passage 14 Exhaust passage 18, 18a, 18b Supercharger, compressor, turbine 22 Air bypass passage 24 Air bypass valve 26 Throttle 28 Low pressure EGR passage 30 EGR cooler 32 EGR valve 50 ECU

Claims (3)

A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage;
An air bypass passage connecting the intake passage downstream of the compressor and the upstream intake passage, bypassing the compressor;
An air bypass valve provided in the air bypass passage;
A low pressure EGR passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor;
An EGR valve provided in the low pressure EGR passage;
Air bypass valve control means for opening the air bypass valve during an operating state in which surging of the compressor is to be suppressed;
EGR valve control means for opening the EGR valve in response to opening of the air bypass valve by the air bypass valve control means, and then closing the EGR valve in response to closing of the air bypass valve; ,
A control device for an internal combustion engine with a supercharger. The operating state in which the surging of the compressor should be suppressed is during engine deceleration in the supercharging region,
The EGR valve control means opens the EGR valve after the air bypass valve is opened by the air bypass valve control means, and then closes the EGR valve simultaneously with closing the air bypass valve;
The control device for an internal combustion engine with a supercharger according to claim 1. An EGR cooler disposed in the low pressure EGR passage upstream of the EGR valve;
The control device for an internal combustion engine with a supercharger according to claim 1 or 2, further comprising:

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