JP2011241723A - Egr device of internal combustion engine with supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an effect of a twin-entry turbo while preventing a gap of an air-fuel ratio in some cylinders from affecting an EGR gas.SOLUTION: An engine 10 includes exhaust passages 22A, 22B connected to exhaust sides of two groups of cylinders, a twin-entry type supercharger 26, EGR passages 30A, 30B and a common EGR passage 30C, respectively, where the EGR passages 30A and 30B are equipped with check valves 38A and 38B. Therefore, exhaust gas pressure in one exhaust passage of the exhaust passages 22A, 22B is restricted from having an effect on the other exhaust passage through the EGR passages, and thus the effect of a twin-entry turbo is obtained. In addition, because exhaust gases from all the cylinders are used as the EGR gas, the gap of air-fuel ratio in some cylinders is prevented from having an effect on the EGR gas.

Description

  The present invention relates to an EGR device for an internal combustion engine with a supercharger, and more particularly to an EGR device for an internal combustion engine with a supercharger equipped with a twin entry turbo.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-38681), an EGR device for an internal combustion engine with a supercharger equipped with a twin entry type turbocharger (twin entry turbo) is known. It has been. In the prior art, for example, in a four-cylinder engine, a first exhaust passage connected to the exhaust ports of # 1 and # 4 cylinders and a second exhaust passage connected to the exhaust ports of # 2 and # 4 cylinders It is set as the structure which provides.

  The first and second exhaust passages are individually connected to two turbines of the twin entry turbo, and the exhaust gas flowing through these exhaust passages merges on the downstream side of each turbine. Thereby, in the twin entry turbo, it is possible to drive the turbine while preventing exhaust interference between the cylinders. In the prior art, for example, an EGR (Exhaust Gas Recirculation) passage is provided between the second exhaust passage and the intake passage, and the exhaust gas of the # 2 cylinder and # 4 cylinder is recirculated to the intake passage through this EGR passage. It is said.

JP 2008-38681 A Japanese Patent Laid-Open No. 10-238412

  In the prior art described above, only the exhaust gas of a specific cylinder is recirculated to the intake system as EGR gas. Therefore, in this specific cylinder, when an air-fuel ratio shift occurs due to deterioration of the fuel injection valve over time, rich or lean exhaust gas is recirculated to the intake system. For this reason, in the prior art, there is a problem that combustibility deteriorates when an air-fuel ratio shift occurs in some cylinders involved in EGR. As a solution to this problem, for example, an EGR passage may be connected to both exhaust passages to recirculate exhaust gases from all cylinders to the intake system. However, in this case, exhaust interference occurs between the two exhaust passages via the EGR passage, so that the effect of the twin entry turbo is impaired.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to prevent twin-entry while preventing an air-fuel ratio shift occurring in some cylinders from being reflected in EGR gas. An object of the present invention is to provide an EGR device for an internal combustion engine with a supercharger capable of exerting a turbo effect.

A first invention is an intake passage for sucking intake air into a plurality of cylinders of an internal combustion engine;
A first exhaust passage connected to an exhaust side of the first cylinder group among the first and second cylinder groups in which the plurality of cylinders are divided into two groups;
A second exhaust passage connected to the exhaust side of the second cylinder group;
A twin-entry supercharger that has first and second turbines provided separately in the first and second exhaust passages and a compressor provided in the intake passage, and supercharges intake air; ,
A first EGR passage connected to the first exhaust passage upstream of the first turbine and into which exhaust gas of the first cylinder group flows;
A second EGR passage connected to the second exhaust passage upstream of the second turbine and into which exhaust gas of the second cylinder group flows;
A common EGR passage that is connected between the downstream side of the first and second EGR passages and the intake passage and recirculates exhaust gases flowing through the EGR passages to the intake passage;
An EGR valve provided in the common EGR passage for adjusting a recirculation amount of exhaust gas;
First and second check valves that are individually provided in the first and second EGR passages and prevent exhaust gas from flowing back in the respective EGR passages;
It is characterized by providing.

The second invention is located between the first and second check valves and the EGR valve in the entire EGR passage including the first and second EGR passages and the common EGR passage. Pressure acquisition means for acquiring the pressure in the valve passage;
High pressure valve opening control means for opening the EGR valve when the pressure in the inter-valve passage becomes equal to or higher than a predetermined upper limit determination value while the EGR valve is closed.

  In a third aspect of the invention, when the EGR valve is opened from the closed state, the transient opening degree suppression is performed to suppress the transient opening degree immediately after the EGR valve is opened relative to the steady state opening degree. Means.

4th invention is located between the said 1st, 2nd non-return valve and the said EGR valve among the whole EGR path | routes which match | combined the said 1st, 2nd EGR path | route and the said common EGR path | route. Pressure acquisition means for acquiring the pressure in the valve passage;
When the EGR valve is opened from the closed state, the EGR valve is a means for suppressing the opening degree at the time of transition immediately after the EGR valve is opened relative to the opening degree at the steady state, and at least in the inter-valve passage And a transient opening suppression means for controlling the throttle opening amount during the transition based on the pressure.

  According to a fifth aspect of the invention, the transient opening suppression means is based on the pressure in the inter-valve passage and the target EGR rate, and an initial throttle amount of the transient opening and an attenuation amount of the throttle amount, And the throttle amount of the opening at the time of transition is gradually attenuated from the initial throttle amount at a speed corresponding to the attenuation amount.

  According to a sixth aspect of the invention, the pressure acquisition means estimates the pressure in the inter-valve passage based on an integrated value of the load and rotation speed of the internal combustion engine during the period when the EGR valve is closed. Yes.

  According to the first invention, in the first and second check valves, the exhaust pressure of one of the first and second exhaust passages acts on the other exhaust passage via the EGR passage. Can be regulated. Therefore, even when the EGR passage is connected between the first and second exhaust passages, it is possible to prevent the occurrence of exhaust interference between the cylinder groups and to stably exhibit the effect of the twin entry turbo. Since exhaust gas from all cylinders can be used as EGR gas, even if an air-fuel ratio shift occurs in some cylinders, the influence of the air-fuel ratio shift on the EGR gas can be suppressed. As a result, when the EGR control is executed, it is possible to maintain good combustibility without being affected by variations in the air-fuel ratio among the cylinders.

  According to the second invention, when the pressure (pipe pressure) in the valve passage becomes excessive due to the operation of the check valve, the EGR valve can be opened to release the pipe pressure. Therefore, durability of piping etc. which constitute the passage between valves can be improved.

  According to the third invention, immediately after the EGR valve is opened, the opening degree of the EGR valve can be appropriately reduced. As a result, an overshoot of the EGR amount that occurs immediately after the EGR valve is opened can be prevented, and misfires caused by this can be avoided.

  According to the fourth invention, immediately after the EGR valve is opened, the opening degree of the EGR valve can be appropriately reduced according to the high piping pressure during the transition. Thereby, an overshoot of the EGR amount that occurs immediately after the EGR valve is opened can be prevented, and misfires can be avoided. In addition, since the opening degree of the EGR valve can be feedback-controlled according to the piping pressure, the EGR amount can be stably adjusted to the target value immediately after the EGR valve is opened until the steady state is reached.

  According to the fifth invention, the transient opening suppression means calculates the initial throttle amount and the throttle amount attenuation of the transient opening based on the pressure in the valve passage and the target EGR rate. be able to. Then, the opening degree of the EGR valve can be gradually increased from the most narrowed state immediately after the opening to the opening degree at the steady state. Therefore, immediately after the EGR valve is opened, an overshoot of the EGR amount can be prevented, and the EGR amount can be stably adjusted to the target value immediately after the EGR valve is opened until the steady state is reached. it can.

  According to the sixth aspect, the pressure acquisition means can estimate the pressure in the inter-valve passage based on the integrated value of the load and the rotational speed of the internal combustion engine during the period when the EGR valve is closed. Thereby, since it is not necessary to use a pressure sensor etc., the structure of a system can be simplified.

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a timing chart which shows the operation | movement of control by Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a flowchart which shows the control performed by ECU. It is a timing chart which shows the operation | movement of control by Embodiment 3 of this invention. In Embodiment 3 of this invention, it is a flowchart which shows the control performed by ECU. It is a timing chart which shows the operation | movement of control by Embodiment 4 of this invention. In Embodiment 4 of this invention, it is a flowchart which shows the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes an engine 10 as an internal combustion engine, and the engine 10 is equipped with four cylinders from # 1 cylinder to # 4 cylinder. In the present embodiment, a four-cylinder engine is illustrated, but the present invention is not limited to four cylinders, and is applicable to an arbitrary number of cylinders of two or more.

  The engine 10 includes an intake passage 12 that sucks intake air into each cylinder. The intake passage 12 is provided with an air cleaner 14, an intercooler 16, a throttle valve 18, and the like. The throttle valve 18 is constituted by an electronically controlled valve, and adjusts the intake air amount based on the accelerator opening and the like. Further, the downstream side of the intake passage 12 is connected to an intake port of each cylinder via an intake manifold 20 constituting a part thereof.

  The engine 10 includes a first exhaust passage 22A connected to an exhaust port of a first cylinder group (for example, # 1 cylinder and # 4 cylinder), and a second cylinder group (for example, # 2 cylinder and # 4). A second exhaust passage 22B connected to the exhaust port of the three cylinders), and a common exhaust passage 22C in which these exhaust passages 22A and 22B merge on the downstream side. The two cylinder groups described above are configured by grouping cylinders that do not cause exhaust interference. The common exhaust passage 22C is provided with a catalyst 24 for purifying exhaust gas and the like.

  The engine 10 is equipped with a twin entry type turbocharger (twin entry turbo) 26. The supercharger 26 is connected to the first turbine 26A disposed downstream of the exhaust passage 22A, the second turbine 26B disposed downstream of the exhaust passage 22B, and the turbines 26A and 26B. And a compressor 26C. The turbines 26A and 26B are driven separately by the pressure of the exhaust gas flowing through the exhaust passages 22A and 22B. The compressor 26C is disposed in the intake passage 12, and supercharges intake air by being driven to rotate by the turbines 26A and 26B. Further, a waste gate valve (WGV) 28 is provided between the exhaust passages 22A and 22B and the common exhaust passage 22C to bypass the turbines 26A and 26B and to distribute the exhaust gas.

  Here, the effect of the twin entry turbo will be described. For example, in a single entry turbo operated by exhaust gas flowing through a single exhaust passage, exhaust pulsation generated in each cylinder is attenuated by exhaust interference between the cylinders. On the other hand, the twin entry turbo drives the two turbines 26A and 26B separately by the exhaust pressures of the two cylinder groups that are grouped so that the exhaust interference does not occur. Therefore, according to the twin entry turbo, it is possible to efficiently drive the turbines 26A and 26B by utilizing the large exhaust pulsation generated in the individual exhaust passages 22A (22B), and to reduce the turbo lag and increase the supercharging response. Can be increased.

  On the other hand, the engine 10 includes a first EGR passage 30A connected to the exhaust passage 22A on the upstream side of the turbine 26A, a second EGR passage 30B connected to the exhaust passage 22B on the upstream side of the turbine 26B, and these A common EGR passage 30C connected between the downstream side of the EGR passages 30A and 30B and the intake manifold 20 is provided. The common EGR passage 30C collectively returns the exhaust gas of the first cylinder group flowing into the EGR passage 30A and the exhaust gas of the second cylinder group flowing into the EGR passage 30B to the intake passage 12 together. In the common EGR passage 30C, an EGR catalyst 32 that purifies exhaust gas (EGR gas) recirculated to the intake passage 12, an EGR cooler 34 that cools the EGR gas, and a recirculation amount (EGR amount) of the EGR gas. An EGR valve 36 for adjustment is provided. In the following description, the entire EGR passage including the EGR passages 30 </ b> A and 30 </ b> B and the common EGR passage 30 </ b> C is referred to as an all EGR passage 30.

  First and second check valves 38A and 38B are provided in the EGR passages 30A and 30B, respectively. These check valves 38A, 38B allow the exhaust gas to flow from the upstream side (exhaust passage 22A, 22B side) to the downstream side (common EGR passage 30C side) in the EGR passages 30A, 30B, and the exhaust gas is downstream. The reverse flow from the side to the upstream side is restricted. Accordingly, the check valves 38A and 38B prevent the exhaust pressures of the first and second cylinder groups from interfering with each other in a state where the two exhaust passages 22A and 22B are connected via the all EGR passages 30. It is preventing. A portion surrounded by a dotted line in FIG. 1 among all the EGR passages 30 is an inter-valve passage 30D located between the check valves 38A and 38B and the EGR valve 36.

  The system of the present embodiment includes a sensor system including an air-fuel ratio sensor 40, a pressure sensor 42, and the like, and an ECU (Electronic Control Unit) 50 for controlling the operating state of the engine 10 and a vehicle on which the engine 10 is mounted. Yes. First, the sensor system will be described. The air-fuel ratio sensor 40 is provided in the common exhaust passage 22C at a position downstream of the supercharger 26 and upstream of the catalyst 24, and exhaust gases of all cylinders are mixed. The exhaust air-fuel ratio is detected at the position. The pressure sensor 42 detects the pressure in the inter-valve passage 30D and constitutes a pressure acquisition means.

  In addition to the sensors 40 and 42, the sensor system includes various sensors necessary for vehicle and engine control. For example, a crank angle sensor that detects the rotation of the crankshaft, an airflow sensor that detects the intake air amount, an intake pressure sensor that detects intake pressure (supercharging pressure), and a water temperature sensor that detects the temperature of engine cooling water And an accelerator opening sensor for detecting the accelerator opening. These sensors are connected to the input side of the ECU 50. On the other hand, to the output side of the ECU 50, various actuators including the throttle valve 18, the WGV 28, the EGR valve 36, the fuel injection valve of each cylinder, and the like are connected.

  The ECU 50 detects operation information of the engine using a sensor system, and performs operation control by driving each actuator based on the detection result. Specifically, the engine speed and the crank angle are detected based on the output of the crank angle sensor, and the intake air amount is detected by the air flow sensor. Then, the fuel injection amount is calculated based on the intake air amount, the engine speed, etc., the fuel injection timing is determined based on the crank angle, and the fuel injection valve is driven. Further, the ECU 50 executes generally known air-fuel ratio control and EGR control. In the air-fuel ratio control, the actual air-fuel ratio is controlled to the target air-fuel ratio based on the output of the air-fuel ratio sensor 40. This target air-fuel ratio is the air-fuel ratio at which the exhaust purification ability of the catalyst 24 and the EGR catalyst 32 is maximized. Set to area. In the EGR control, the EGR valve 36 is driven based on the operating state of the engine to appropriately control the EGR amount.

[Operation of Embodiment 1]
Next, the system operation of this embodiment will be described. During engine operation, exhaust gases are discharged from the first and second cylinder groups. Then, the exhaust gas of the first cylinder group flows through the exhaust passage 22A to drive the turbine 26A, and is then discharged to the outside from the common exhaust passage 22C. Further, the exhaust gas of the second cylinder group flows through the exhaust passage 22B, drives the turbine 26B, and is discharged to the outside from the common exhaust passage 22C. Accordingly, when the supercharger 26 is operated, the turbines 26A and 26B are separately driven by the exhaust pressures of the first and second cylinder groups, and the compressor 26C is efficiently driven using the exhaust pulsation of the individual cylinder groups. be able to.

  Further, when the supercharger 26 is in operation, the check valve 38 </ b> A restricts the exhaust pressure in the second exhaust passage 22 </ b> B from acting on the first exhaust passage 22 </ b> A via the entire EGR passage 30. Further, the check valve 38 </ b> B restricts the exhaust pressure in the first exhaust passage 22 </ b> A from acting on the second exhaust passage 22 </ b> B through the entire EGR passage 30. Therefore, even when all the EGR passages 30 are connected between the exhaust passages 22A and 22B, it is possible to prevent the occurrence of exhaust interference between the cylinder groups, and to stably exhibit the effect of the twin entry turbo. Can do.

  On the other hand, in an operating state suitable for EGR control, EGR control is executed by the ECU 50, and the opening degree of the EGR valve 36 is adjusted based on the operating state. When the EGR valve 36 is opened, part of the exhaust gas flowing through the exhaust passages 22A and 22B flows into the EGR passages 30A and 30B as EGR gas, and these EGR gases are collectively collected by the common EGR passage 30C. To reflux. Therefore, in this embodiment, the exhaust gas of all cylinders can be used as EGR gas without impairing the effect of the twin entry turbo. As a result, even if an air-fuel ratio shift occurs in some cylinders due to deterioration of the fuel injection valve over time, the influence of the air-fuel ratio shift on the EGR gas can be reduced.

  Therefore, when EGR control is executed, it is possible to maintain good combustibility without being affected by variations in the air-fuel ratio between cylinders. Further, according to the above configuration, even if there is air-fuel ratio variation between the cylinders, the entire exhaust gas controlled to the target air-fuel ratio by the air-fuel ratio control can be supplied to the EGR catalyst 32 as EGR gas. Therefore, the system using the single air-fuel ratio sensor 40 can stably operate both the catalyst 24 and the EGR catalyst 32. For example, another air-fuel ratio sensor is added upstream of the EGR catalyst 32. Since it is not necessary, the system can be simplified.

  Also, the check valve 38A and the check valve 38B transmit only the positive pressure of the exhaust pulsation acting in the EGR passages 30A and 30B to the common EGR passage 30C side with the exhaust gas flow direction as the positive direction, Pressure transmission can be cut off. Thereby, the peak pressure of the exhaust pulsation can be maintained on the common EGR passage 30C side. Therefore, the pressure of EGR gas can be increased by the check valve 38A and the check valve 38B, and the EGR amount can be increased.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment presupposes the configuration of the first embodiment (FIG. 1) and prevents the pressure in the EGR passage from becoming excessive by control, and is characterized by this point. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
In the configuration of the first embodiment, when the EGR valve 36 is closed, the pressure in the inter-valve passage 30D of all the EGR passages 30 is likely to increase. That is, as described above, the check valve 38A and the check valve 38B transmit only the positive pressure of the exhaust pulsation into the inter-valve passage 30D. Therefore, when the EGR valve 36 is closed, the inter-valve passage 30D. The pressure inside increases unilaterally. In particular, during the high load acceleration operation, the EGR control is stopped and the exhaust pressure becomes relatively high. Therefore, when this operation is continued, the check valve 38A and the check valve 38B act to operate the valve passage 30D. The internal pressure becomes excessive, and there is a problem in that the durability of the piping constituting the inter-valve passage 30D is lowered.

  For this reason, in the present embodiment, when the pressure in the inter-valve passage 30D becomes equal to or higher than the predetermined upper limit determination value Pmax while the EGR valve 36 is closed, even in the operation region where the EGR control is stopped, The EGR valve 36 is forcibly opened. Here, the upper limit determination value Pmax is set based on, for example, the pressure resistance of the pipes constituting the inter-valve passage 30D, and is stored in the ECU 50 in advance. Hereinafter, the control of the present embodiment will be described with reference to FIG. FIG. 2 is a timing chart showing a control operation according to the second embodiment of the present invention. In the following description including FIG. 2, the pressure in the inter-valve passage 30 </ b> D is sometimes expressed as piping pressure.

  As shown in FIG. 2, when the EGR valve 36 is fully closed to stop the EGR control, the piping pressure gradually increases. The ECU 50 detects the pipe pressure by the pressure sensor 42, and opens the EGR valve 36 when the pipe pressure becomes equal to or higher than the upper limit determination value Pmax. At this time, if it is an operating state where EGR control should be stopped, the opening degree of the EGR valve 36 is controlled to the minimum opening degree necessary for releasing the piping pressure. In addition, in a situation where it is desired to increase the engine torque as much as possible, for example, during high load acceleration operation, it may be desired to avoid a decrease in torque by opening the EGR valve 36 by the above control. In this case, when the EGR valve 36 is opened, control for compensating for a decrease in torque is executed. More specifically, for example, as shown in FIG. 2, the opening degree of the WGV 28 is decreased, and the torque is increased by increasing the supercharging pressure. As another method, the opening of the throttle valve 18 may be increased to increase the torque.

  As described above, according to this embodiment, when the pressure in the inter-valve passage 30D becomes excessive due to the action of the check valve 38A and the check valve 38B, the EGR valve 36 is opened to increase the pressure. I can escape. Therefore, in addition to the operational effects of the first embodiment, the durability of the piping or the like constituting the inter-valve passage 30D can be improved.

[Specific Processing for Realizing Embodiment 2]
FIG. 3 is a flowchart showing the control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the internal combustion engine. In the routine shown in FIG. 3, it is first determined whether or not the EGR valve 36 is closed. If this determination is not established, the control is terminated as it is (step 100). When the determination in step 100 is established, the inter-valve passage 30D is closed on the downstream side, so that the pipe pressure is acquired (detected) based on the output of the pressure sensor 42 (step 102). ).

  Then, it is determined whether or not the detected value of the piping pressure is equal to or higher than the upper limit determination value Pmax. If this determination is not satisfied, the control is terminated as it is (step 104). If the determination in step 104 is established, the piping pressure has increased excessively, so the EGR valve 36 is opened (step 106). Then, control for compensating for a decrease in torque due to opening of the EGR valve 36 is executed by decreasing the opening of the WGV 28 or increasing the opening of the throttle valve 18 (step 108).

  In the second embodiment, steps 104 and 106 in FIG. 3 show a specific example of the high-pressure valve opening control means in claim 2. In the first embodiment, the pressure sensor 42 is used as the pressure acquisition means. However, the present invention is not limited to this, and in step 102 in FIG. The pressure acquisition unit may be configured by this calculation process. A specific method for calculating the pressure in the inter-valve passage 30D will be described in the fourth embodiment.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. 4 and FIG. This embodiment is based on the configuration of the first embodiment (FIG. 1), and prevents the EGR amount from increasing during a transition immediately after the valve is opened when the EGR valve is opened from the closed state. This is a feature. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 3]
When the EGR valve 36 is closed, as described in the second embodiment, the pressure (pipe pressure) in the inter-valve passage 30D is relatively high due to the action of the check valve 38A and the check valve 38B. When resuming EGR control from this state, if the EGR valve 36 is opened from the fully closed position to the opening corresponding to the steady target EGR amount (target EGR rate) at once, the EGR amount is reduced by the high pipe pressure. There is a problem that it increases transiently (overshoot) and misfires occur.

  For this reason, in this Embodiment, it is set as the structure which performs the opening degree suppression control at the time of a transition. In the transient opening suppression control, when the EGR valve 36 is opened from the closed state, the transient opening immediately after the EGR valve 36 is opened is suppressed with respect to the steady opening. is there. The steady-state opening is an opening corresponding to the above-described steady-state target EGR amount and target EGR rate. Hereinafter, an example of the transient opening suppression control will be described with reference to FIG. FIG. 4 is a timing chart showing the control operation according to the third embodiment of the present invention.

  As shown in FIG. 4, when the EGR valve 36 is fully closed to stop the EGR control, the piping pressure gradually increases. In particular, during high load acceleration, the piping pressure tends to increase. Then, when the EGR valve is opened to restart the EGR control at a certain time, the EGR rate becomes excessive due to a transient increase in the EGR amount as in the comparative example indicated by the dotted line in FIG. . On the other hand, in the transient opening suppression control, as shown by the solid line in FIG. 4, the throttle opening amount during transient of the EGR valve 36 is controlled according to the pipe pressure.

  Specifically, immediately after the opening of the EGR valve 36, the pipe pressure is the highest, so the throttle amount (suppression amount) of the opening is set large, and the opening of the EGR valve 36 is set to the opening at the normal time. On the other hand, it is greatly reduced. Then, as the EGR valve 36 is opened, the throttle amount of the opening is gradually reduced according to the pipe pressure at each time point as the pipe pressure gradually decreases. As a result, the opening degree of the EGR valve 36 gradually approaches the opening degree at the steady state as the pipe pressure gradually approaches the steady state pressure, and is controlled to the opening degree at the steady state in the final steady state. .

  According to the above control, immediately after the EGR valve 36 is opened, the opening degree of the EGR valve 36 can be appropriately reduced according to the high piping pressure during the transition. As a result, as shown in FIG. 4, it is possible to prevent an overshoot of the EGR amount (EGR rate) that occurs immediately after the EGR valve 36 is opened, and to avoid misfires caused by this. Further, since the opening degree of the EGR valve 36 can be feedback-controlled according to the piping pressure, the EGR amount can be stably adjusted to the target value immediately after the EGR valve 36 is opened until the steady state is reached.

[Specific Processing for Realizing Embodiment 3]
FIG. 5 is a flowchart showing the control executed by the ECU in the third embodiment of the present invention. The routine shown in this figure is repeatedly executed during the operation of the internal combustion engine. In the routine shown in FIG. 5, it is first determined whether or not it is time to resume the EGR operation from the stopped state. If this determination is not established, the control is terminated as it is (step 200). If the determination in step 200 is established, the piping pressure is acquired based on the output of the pressure sensor 42 (step 202), and whether or not the piping pressure is a steady value (pressure value at the steady state). Determination is made (step 204). If this determination is established, the control is terminated as it is.

  On the other hand, if the determination in step 204 is not established, the opening degree of the EGR valve 36 is calculated based on the piping pressure, and the EGR valve 36 is opened based on the calculation result (step 206). Thereby, the opening degree of the EGR valve 36 is controlled (suppressed) based on the piping pressure. Then, returning to step 202, the pipe pressure after changing the opening of the EGR valve 36 is detected. Therefore, the processing of steps 202 to 206 is repeatedly executed until the piping pressure reaches a steady value. Finally, the determination in step 204 is established, and the opening degree of the EGR valve 36 is set to the opening degree at the steady state.

  In the third embodiment, the timing chart shown in FIG. 4 and step 206 shown in FIG. 5 show a specific example of the transient opening suppression means in claims 3 and 4. In the third embodiment, the transient opening suppression control has been described. However, in the present invention, the transient opening suppression control may be combined with the control during valve closing described in the second embodiment. .

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIGS. The present embodiment shows an example of the transient opening suppression control different from the third embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 4]
In the present embodiment, first, based on the pressure in the inter-valve passage 30D (pipe pressure) and the target EGR rate, the initial throttle amount of the EGR valve 36 during the transition and the attenuation amount of the throttle amount are calculated. calculate. The throttle amount of the opening at the time of transition is gradually attenuated from the initial throttle amount at a speed corresponding to the attenuation amount. Hereinafter, the transition opening degree suppression control described above will be described with reference to FIG. FIG. 6 is a timing chart showing a control operation according to the fourth embodiment of the present invention.

  In the present embodiment, as shown in FIG. 6, first, the piping pressure is estimated based on the integrated value of the engine load and the rotational speed during the period when the EGR valve 36 is closed. Next, based on the piping pressure and the target EGR rate, the initial throttle amount of the opening degree during the transition of the EGR valve 36 and the attenuation amount of the throttle amount are calculated. Here, the target EGR rate is a target value of the ratio between the EGR amount and the intake air amount, and is set based on the operating state of the engine by generally known EGR control.

  The initial throttle amount corresponds to the difference between the opening when the EGR valve 36 is opened and the opening at the steady state. Further, the amount of attenuation of the throttle amount is the speed at which the opening degree of the EGR valve 36 gradually increases from the opening degree at the time of opening to the opening degree at the steady state (the characteristic line of the opening shown in FIG. 6). It corresponds to (tilt). As a specific example of the initial throttling amount and attenuation amount setting method, the initial throttling amount is set to a larger value as the pipe pressure is higher and the target EGR rate is lower. On the other hand, the attenuation amount is set to a larger value as the initial aperture amount is larger and the target EGR rate is higher.

  After the EGR valve 36 is opened, the process for calculating the throttle amount based on the initial throttle amount and the attenuation amount is executed at a constant calculation cycle, and the throttle amount at each time point is calculated. Then, the target opening of the EGR valve 36 is calculated based on the calculation result of the throttle amount, and the actual opening is controlled to the target opening (EGR valve throttle control). As a result, the opening degree of the EGR valve 36 becomes the most throttled state immediately after opening the valve, and gradually increases toward the opening degree in the steady state as the pipe pressure gradually approaches the pressure in the steady state. In the final steady state, the opening is controlled to be steady.

  In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as those of the third embodiment. In particular, in the present embodiment, since the piping pressure is estimated based on the operating state during closing of the EGR valve 36, the pressure sensor 42 can be dispensed with and the configuration of the system can be simplified. .

[Specific processing for realizing Embodiment 4]
FIG. 7 is a flowchart showing the control executed by the ECU in the fourth embodiment of the present invention. The routine shown in this figure is repeatedly executed during the operation of the internal combustion engine. In the routine shown in FIG. 7, it is first determined whether or not it is time to resume the EGR operation from the stopped state. If this determination is not established, the control is terminated as it is (step 300). If the determination in step 300 is satisfied, as described above, the piping pressure is estimated based on the integrated value of the engine load and the rotational speed during the period when the EGR valve 36 is closed (step 302). . Then, based on the piping pressure and the target EGR rate, an initial throttle amount of the opening degree of the EGR valve 36 and an attenuation amount of the throttle amount are calculated (step 304).

  Next, the above-described EGR valve throttle control is executed based on the above-described initial throttle amount and attenuation amount, and the opening degree of the EGR valve 36 is controlled (step 306). Then, it is determined whether or not it is time to end the control, and the processes of steps 306 and 308 are repeatedly executed until this determination is satisfied (step 308). Specifically, in step 308, for example, it is determined whether or not the opening degree of the EGR valve 36 has reached a steady-state opening degree, or whether or not the piping pressure has reached a steady-state pressure. Finally, the determination in step 308 is established, and the opening degree of the EGR valve 36 is set to the steady-state opening degree.

  In the fourth embodiment, the timing chart shown in FIG. 6 and the steps 304 and 306 shown in FIG. 7 show specific examples of the transient opening suppression means in claims 3, 4, and 5. Further, in the fourth embodiment, the transient opening suppression control has been described. However, in the present invention, the transient opening suppression control may be combined with the control during valve closing described in the second embodiment. Furthermore, in the fourth embodiment, the pipe pressure is estimated. However, the present invention is not limited to this, and the pressure sensor 42 may be used to detect the pipe pressure in the control of the fourth embodiment.

  Further, the embodiment has been described by taking the four-cylinder engine 10 as an example. However, the present invention is not limited to this, and any multi-cylinder internal combustion engine can be applied to an internal combustion engine having three or less cylinders or five or more cylinders.

10 Engine (Internal combustion engine)
12 Intake passage 14 Air cleaner 16 Intercooler 18 Throttle valve 20 Intake manifold (intake passage)
22A, 22B First and second exhaust passages 22C Common exhaust passage 24 Catalyst 26 Superchargers 26A, 26B First and second turbines 26C Compressor 28 Wastegate valves 30A, 30B Common to first and second EGR passages 30C EGR passage 30D Intervalve passage 32 EGR catalyst 34 EGR cooler 36 EGR valves 38A, 38B First and second check valves 40 Air-fuel ratio sensor 42 Pressure sensor (pressure acquisition means)
50 ECU

Claims (6)

An intake passage for sucking intake air into a plurality of cylinders of the internal combustion engine;
A first exhaust passage connected to an exhaust side of the first cylinder group among the first and second cylinder groups in which the plurality of cylinders are divided into two groups;
A second exhaust passage connected to the exhaust side of the second cylinder group;
A twin-entry supercharger that has first and second turbines provided separately in the first and second exhaust passages and a compressor provided in the intake passage, and supercharges intake air; ,
A first EGR passage connected to the first exhaust passage upstream of the first turbine and into which exhaust gas of the first cylinder group flows;
A second EGR passage connected to the second exhaust passage upstream of the second turbine and into which exhaust gas of the second cylinder group flows;
A common EGR passage that is connected between the downstream side of the first and second EGR passages and the intake passage and recirculates exhaust gases flowing through the EGR passages to the intake passage;
An EGR valve provided in the common EGR passage for adjusting a recirculation amount of exhaust gas;
First and second check valves that are individually provided in the first and second EGR passages and prevent exhaust gas from flowing back in the respective EGR passages;
An EGR device for an internal combustion engine with a supercharger. The pressure in the inter-valve passage located between the first and second check valves and the EGR valve in the entire EGR passage including the first and second EGR passages and the common EGR passage. Pressure acquisition means for acquiring,
A high-pressure valve opening control means for opening the EGR valve when the pressure in the inter-valve passage becomes equal to or higher than a predetermined upper limit determination value while the EGR valve is closed;
The EGR device for an internal combustion engine with a supercharger according to claim 1.   When the EGR valve is opened from the closed state, a transient opening suppression means is provided that suppresses the transient opening immediately after the EGR valve is opened relative to the steady opening. Item 3. An EGR device for an internal combustion engine with a supercharger according to item 1 or 2. The pressure in the inter-valve passage located between the first and second check valves and the EGR valve in the entire EGR passage including the first and second EGR passages and the common EGR passage. Pressure acquisition means for acquiring,
When the EGR valve is opened from the closed state, the EGR valve is a means for suppressing the opening degree at the time of transition immediately after the EGR valve is opened relative to the opening degree at the steady state, and at least in the inter-valve passage A transient opening suppression means for controlling a throttle amount of the transient opening based on the pressure of
The EGR device for an internal combustion engine with a supercharger according to claim 1.   The transient opening suppression means calculates an initial throttle amount of the transient opening and an attenuation amount of the throttle amount based on the pressure in the inter-valve passage and the target EGR rate, 5. The EGR device for an internal combustion engine with a supercharger according to claim 4, wherein the throttle amount is gradually attenuated from the initial throttle amount at a speed corresponding to the attenuation amount.   The pressure acquisition means is configured to estimate a pressure in the inter-valve passage based on an integrated value of a load and a rotation speed of the internal combustion engine during a period in which the EGR valve is closed. An EGR device for an internal combustion engine with a turbocharger.

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