JP2009209887A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To switch to a recirculating flow of exhaust gas of using a low pressure EGR device from a recirculating flow of exhaust gas of using a high pressure EGR device, by properly restraining an extreme change in supercharging pressure. <P>SOLUTION: This control device of an internal combustion engine controls a system having a high pressure turbocharger, a low pressure turbocharger, the high pressure EGR device and the low pressure EGR device. Actually, a control means controls a speed for increasing the ratio occupied by an EGR gas quantity recirculated by the low pressure RGR device to the whole EGR gas quantity recirculated to an intake system, by controlling so that a change speed of the supercharging pressure becomes a predetermined value or less by making a feedback process, when switching to the recirculating flow of the EGR gas of using the low pressure EGR device from the recirculating flow of the EGR gas of using the high pressure EGR device. Thus, the extreme change in the supercharging pressure apt to be caused in switching can be properly restrained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that controls a system having a multistage turbocharger, a high-pressure EGR device, and a low-pressure EGR device.

  Conventionally, a system (multistage supercharging system) in which a high-pressure turbocharger and a low-pressure turbocharger having different capacities are arranged in series is known. For example, Patent Document 1 proposes a technique for switching a feedback region according to a performance difference between a high-pressure turbocharger and a low-pressure turbocharger in a multistage turbocharging system. In this technique, by performing feedback control in consideration of the EGR rate, the suction efficiency is improved over a wide operation range.

  In an internal combustion engine such as a diesel engine, an EGR device (exhaust gas recirculation device) that returns a part of exhaust gas from an exhaust passage to an intake passage is known. For example, an EGR device that recirculates exhaust gas from an exhaust passage upstream of the turbine of the turbocharger to an intake passage downstream of the compressor (hereinafter referred to as a “high pressure EGR device”), and a downstream of the turbocharged turbine. A technique using an EGR device that recirculates exhaust gas from an exhaust passage to an intake passage upstream of a compressor (hereinafter referred to as “low pressure EGR device”) has been proposed.

JP-A-2005-330811

  By the way, when switching from exhaust gas recirculation using the high pressure EGR device to exhaust gas recirculation using the low pressure EGR device in a system having the multistage turbocharger, the high pressure EGR device, and the low pressure EGR device as described above, It is conceivable that the following problems occur. When the switching is performed in the high-pressure turbocharger usage area, the amount of gas flowing into the turbine may increase suddenly. As a result, the turbocharger may choke, the supercharging pressure changes greatly, and drivability and EGR controllability may deteriorate. Note that Patent Document 1 described above does not describe a method for dealing with such a problem.

  The present invention has been made in order to solve the above-described problems, and appropriately suppresses an extreme change in the supercharging pressure, etc., thereby reducing the low pressure EGR device from the exhaust gas recirculation using the high pressure EGR device. An object of the present invention is to provide a control device for an internal combustion engine that can be switched to the recirculation of exhaust gas used.

  In one aspect of the present invention, a high pressure turbocharger in which a compressor is disposed in an intake passage and a turbine is disposed in an exhaust passage, and a compressor is disposed in an intake passage on the upstream side of the compressor of the high pressure turbocharger, and the high pressure turbo A low-pressure turbocharger in which a compressor is arranged in an exhaust passage downstream of the turbine of the charger, and an exhaust gas is circulated from an exhaust passage upstream of the turbine of the high-pressure turbocharger to an intake passage downstream of the compressor of the high-pressure turbocharger. A control apparatus for an internal combustion engine, comprising: a high-pressure EGR device to be recirculated; and a low-pressure EGR device to recirculate exhaust gas from an exhaust passage downstream of the low-pressure turbocharged turbine to an intake passage upstream of a compressor of the low-pressure turbocharger. EG using the high pressure EGR device When switching from gas recirculation to EGR gas recirculation using the low pressure EGR device, feedback control is performed so that the change rate of the supercharging pressure becomes a predetermined value or less, whereby the total amount of EGR gas recirculated to the intake system The control means which controls the speed | rate which increases the ratio which the amount of EGR gas recirculated by the said low pressure EGR apparatus accounts is increased.

  The control device for the internal combustion engine is preferably used to control a system having a high pressure turbocharger and a low pressure turbocharger, and a high pressure EGR device and a low pressure EGR device. Specifically, the control means performs feedback so that the change rate of the supercharging pressure becomes a predetermined value or less when switching from the recirculation of the EGR gas using the high pressure EGR device to the recirculation of the EGR gas using the low pressure EGR device. By controlling, the speed at which the ratio of the EGR gas amount recirculated by the low pressure EGR device to the total EGR gas amount recirculated to the intake system is increased is controlled. Thereby, it is possible to appropriately suppress an extreme change in the supercharging pressure that may occur at the time of switching. Therefore, it becomes possible to suppress deterioration of drivability and EGR controllability.

  In one aspect of the control apparatus for an internal combustion engine, the control means uses a feedback gain used for a valve that adjusts an EGR gas flow rate recirculated by the high-pressure EGR device when performing the feedback control at the time of switching. The feedback gain used for the valve when the EGR gas is recirculated using only the high-pressure EGR device. Thereby, the response speed of the valve in the high pressure EGR device can be increased during the switching. Therefore, the valve can be appropriately controlled based on the supercharging pressure, and switching can be performed while effectively suppressing an extreme change in the supercharging pressure.

  Preferably, in the control device for an internal combustion engine, the control means controls a speed at which the ratio is increased in a use range of the high-pressure turbocharger.

  In a preferred embodiment, the control means includes at least one of a valve for adjusting a flow rate of EGR gas recirculated by the high pressure EGR device and a valve for adjusting a flow rate of EGR gas recirculated by the low pressure EGR device. By controlling this, the speed at which the ratio is increased is controlled.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[overall structure]
FIG. 1 is a schematic diagram illustrating a configuration of a vehicle 100 to which the control device for an internal combustion engine according to the present embodiment is applied. In FIG. 1, solid line arrows indicate an example of gas flow, and broken line arrows indicate signal input and output.

  The vehicle 100 mainly includes a throttle valve 1a, 1b, an intake passage 2, a high pressure turbocharger 3, a low pressure turbocharger 4, an intercooler 5, an intake manifold 6, an internal combustion engine 7, and an exhaust manifold 8. The exhaust passage 9, the bypass passage 12, the bypass valve 13, the exhaust purification catalyst 14, the supercharging pressure sensor 19, the high pressure EGR device 20, the low pressure EGR device 21, and an ECU (Engine Control Unit) 50, Is provided.

  In the intake passage 2, in order from the upstream side, a throttle valve 1 a that adjusts the intake amount, a compressor 4 a of a low-pressure turbocharger 4 that supercharges intake air, a compressor 3 a of a high-pressure turbocharger 3 that supercharges intake air, and cools the intake air. An intercooler 5 and a throttle valve 1 a for adjusting the intake air amount are provided, and the intake passage 2 is connected to an intake manifold 6. The intake manifold 6 is provided with a supercharging pressure sensor 19 configured to be able to detect the supercharging pressure. The supercharging pressure sensor 19 supplies a detection signal S19 corresponding to the detected supercharging pressure to the ECU 50. The position where the supercharging pressure sensor 19 is provided is not limited to the position shown in FIG.

  The vehicle 100 uses the high-pressure turbocharger 3 and the low-pressure turbocharger 4 to perform supercharging by a multistage supercharging system (two-stage supercharging system). The high-pressure turbocharger 3 is configured as a small-capacity low-speed turbocharger with a large supercharging capacity in the low and medium speed range, and the low-pressure turbocharger 4 is a large-capacity high-speed with a large supercharging capacity in the medium and high speed range. It is configured as a type supercharger. Specifically, in the high-pressure turbocharger 3, a compressor 3 a is disposed in the intake passage 2, and a turbine 3 b is disposed in the exhaust passage 9. The low-pressure turbocharger 4 has a compressor 4a disposed in the intake passage 2 upstream of the compressor 3a of the high-pressure turbocharger 3, and a compressor 4b disposed in the exhaust passage 9 downstream of the turbine 3b of the high-pressure turbocharger 3. Yes. By arranging the high-pressure turbocharger 3 and the low-pressure turbocharger 4 in this way, the intake air supercharged by the high-pressure turbocharger 3 can be further supercharged by the low-pressure turbocharger 4. Basically, supercharging is performed mainly by the high pressure turbocharger 3 in the low and medium speed ranges, and supercharging is performed mainly by the low pressure turbocharger 4 in the medium and high speed ranges.

  The internal combustion engine 7 generates power by burning a mixture of intake air and fuel supplied from the intake passage 2 via the intake manifold 6. The internal combustion engine 7 is configured by, for example, a gasoline engine or a diesel engine. The internal combustion engine 7 discharges the exhaust gas generated by the combustion to the exhaust passage 9 via the exhaust manifold 8.

  In the exhaust passage 9, a turbine 3b of the high-pressure turbocharger 3, a turbine 4b of the low-pressure turbocharger 4, and an exhaust purification catalyst 14 configured to purify exhaust gas are provided in order from the upstream side. The exhaust purification catalyst 14 is configured by, for example, a DPF (Diesel Particulate Filter). A catalyst may be further provided on the exhaust passage 9 on the downstream side of the exhaust purification catalyst 14.

  The exhaust passage 9 is provided with a bypass passage 12 configured to allow the exhaust gas to flow by bypassing the turbine 3 b of the high-pressure turbocharger 3. Specifically, the bypass passage 12 connects the upstream side of the turbine 3b of the high-pressure turbocharger 3 and the downstream side of the turbine 3b. The bypass passage 12 is provided with a bypass valve 13 that can adjust the flow rate of the exhaust gas flowing through the bypass passage 12.

  Further, the vehicle 100 includes a high pressure EGR device 20 that recirculates exhaust gas from the exhaust passage 9 upstream of the turbine 3b of the high pressure turbocharger 3 to the intake passage 2 downstream of the compressor 3a of the high pressure turbocharger 3, and a low pressure turbocharger. And a low pressure EGR device 21 that recirculates the exhaust gas from the exhaust passage 9 downstream of the turbine 4 b to the intake passage 2 upstream of the compressor 4 a of the low pressure turbocharger 4. The high-pressure EGR device 20 can adjust the flow rate of the EGR gas that passes through the high-pressure EGR passage 10 that connects the upstream position of the turbine 3 b in the exhaust passage 9 and the downstream position of the compressor 3 a in the intake passage 2, and the high-pressure EGR passage 10. And a high pressure EGR valve 11. An EGR cooler that cools the EGR gas may be provided on the high-pressure EGR passage 10. On the other hand, the low pressure EGR device 21 includes a low pressure EGR passage 15 that connects a downstream position of the turbine 4b and the exhaust purification catalyst 14 in the exhaust passage 9 and an upstream position of the compressor 4a in the intake passage 2, and an EGR that passes through the low pressure EGR passage 15. An EGR cooler 16 that cools the gas and a low-pressure EGR valve 17 that can adjust the flow rate of the EGR gas that passes through the low-pressure EGR passage 15 are provided.

  The opening degree of the high pressure EGR valve 11 and the low pressure EGR valve 17 is controlled by control signals S11 and S17 supplied from the ECU 50, respectively. Specifically, the ECU 50 controls the high-pressure EGR valve 11 and the low-pressure EGR valve 17 to control the exhaust gas to recirculate to the intake system (EGR control). Specifically, the ECU 50 recirculates EGR gas using only the high-pressure EGR device 20 (hereinafter referred to as “high-pressure EGR mode”) or a mode recirculating EGR gas using only the low-pressure EGR device 21 (hereinafter referred to as “high-pressure EGR mode”). , And a mode in which the EGR gas is recirculated using both the high pressure EGR device 20 and the low pressure EGR device 21. For example, the high pressure EGR mode is set at a light load, and the low pressure EGR mode is set at a high load.

  The ECU 50 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown). The ECU 50 acquires detection signals from various sensors provided in the vehicle 100 and performs various controls on the components in the vehicle 100. Specifically, the ECU 50 functions as control means in the present invention. Details of the control performed by the ECU 50 will be described later.

[First Embodiment]
Next, control performed by the ECU 50 in the first embodiment of the present invention will be described. In the first embodiment, the ECU 50 performs control so that the high pressure EGR mode is switched to the low pressure EGR mode while appropriately suppressing an extreme change in the supercharging pressure. Specifically, at the time of the switching, the ECU 50 performs feedback control so that the change rate (change width) of the supercharging pressure becomes a predetermined value or less, thereby reducing the total EGR gas amount recirculated to the intake system. Control of the speed at which the ratio occupied by the amount of EGR gas recirculated by the EGR device 21 (hereinafter referred to as “low pressure EGR ratio”) is performed. Specifically, the ECU 50 performs such control by adjusting the opening degree of the high pressure EGR valve 11 and / or the low pressure EGR valve 17.

  The reason for performing such control is as follows. In the high pressure EGR mode, since EGR gas flows into the high pressure EGR passage 10, the amount of inflow gas to the turbines 3b and 4b (hereinafter simply referred to as “turbine inflow gas amount”) is only the amount of new air. On the other hand, in the low pressure EGR mode, the EGR gas also flows to the turbines 3b and 4b, so that the turbine inflow gas amount is a gas amount obtained by adding the fresh air amount and the EGR gas amount. Therefore, particularly when the high pressure turbocharger 3 is switched from the high pressure EGR mode to the low pressure EGR mode, the high pressure turbocharger 3 may choke (that is, the supercharging pressure changes greatly). This is considered to be due to the fact that the amount of turbine inflow gas significantly increased at the time of switching and that the high-pressure turbocharger 3 has no margin for the large exhaust flow rate. Thus, when the supercharging pressure changes greatly, it is considered that drivability deteriorates.

  Further, since the high-pressure turbocharger 3 has a relatively small turbine capacity, that is, a turbine passage area is relatively small, if the exhaust gas flow rate increases when switching from the high-pressure EGR mode to the low-pressure EGR mode as described above, It can be said that the pressure tends to increase. Since the amount of EGR gas recirculated by the high-pressure EGR device 20 is determined by the differential pressure between the intake pressure and the exhaust pressure and the opening degree of the high-pressure EGR valve 11, when the exhaust pressure rises in this way, the high-pressure EGR device 20 It is conceivable that the amount of EGR gas increases. Therefore, it is conceivable that EGR controllability deteriorates.

  Therefore, in the first embodiment, the ECU 50 changes the supercharging pressure change rate to a predetermined value or less when switching from the high pressure EGR mode to the low pressure EGR mode in order to appropriately prevent the occurrence of such a problem. In this way, the speed at which the low pressure EGR ratio is increased (hereinafter referred to as “low pressure EGR ratio increase speed”) is controlled while performing feedback control. Accordingly, it is possible to switch from the high pressure EGR mode to the low pressure EGR mode while appropriately suppressing an extreme change in the supercharging pressure.

  FIG. 2 shows an example of a result when the control according to the first embodiment is performed. For comparison, FIG. 2 also shows a result when control according to a comparative example is performed. Specifically, FIG. 2A shows time on the horizontal axis, the low-pressure EGR ratio and load on the vertical axis, and FIG. 2B shows time on the horizontal axis and excess time on the vertical axis. Supply pressure and load are shown. In FIGS. 2A and 2B, solid lines A11 and A12 indicate results when the control according to the first embodiment is performed, and broken lines A21 and A22 indicate when the control according to the comparative example is performed. Shows the results. As described above, in the control according to the first embodiment, the high pressure EGR mode is changed from the high pressure EGR mode to the low pressure EGR mode by controlling the increase rate of the low pressure EGR ratio while performing feedback so that the change rate of the supercharging pressure becomes a predetermined value or less. Is switched. On the other hand, the control according to the comparative example switches from the high pressure EGR mode to the low pressure EGR mode without considering the change rate of the supercharging pressure. It is assumed that switching from the high pressure EGR mode to the low pressure EGR mode is started at time t11. For example, the switching is started due to the load of the internal combustion engine 7 changing from a light load to a high load.

  As shown in FIG. 2B, the time change Δpim1 of the supercharging pressure when the control according to the first embodiment is performed is larger than the time change Δpim2 of the supercharging pressure when the control according to the comparative example is performed. I understand that it is small. That is, it can be said that when the control according to the first embodiment is performed, the change rate of the supercharging pressure is moderate as compared with the case where the control according to the comparative example is performed. Specifically, the time change Δpim1 in the first embodiment is a result of feeding back the supercharging pressure so that the change speed of the supercharging pressure becomes a predetermined value or less, and the time change Δpim2 in the comparative example is the feedback. This is due to the result that was not performed.

  When such control according to the first embodiment is performed, the change in the supercharging pressure is small as compared with the control according to the comparative example, as indicated by the broken line regions B1 and B2 in FIG. I understand that. Further, as shown in FIG. 2A, it can be seen that when the control according to the first embodiment is performed, the low-pressure EGR ratio is gradually changed as compared with the control according to the comparative example.

  FIG. 3 is a flowchart showing processing according to the first embodiment. This process is executed by the ECU 50. Further, this processing is executed when the load on the internal combustion engine 7 changes from a light load to a high load (for example, when an acceleration instruction is issued).

  First, in step S101, the ECU 50 starts switching from the high pressure EGR mode to the low pressure EGR mode. Specifically, the ECU 50 controls the opening degrees of the high pressure EGR valve 11 and the low pressure EGR valve 17 so that the low pressure EGR ratio increases. For example, the ECU 50 adjusts the opening degrees of the high pressure EGR valve 11 and the low pressure EGR valve 17 so that the low pressure EGR ratio increases at a preset speed (initial speed). Basically, the ECU 50 adjusts the opening degree so that the high-pressure EGR valve 11 is finally closed, and adjusts the opening degree so that the low-pressure EGR valve 17 is finally opened. Switching from the EGR mode to the low pressure EGR mode is performed. When the above process ends, the process proceeds to step S102. The ECU 50 can perform control to increase the low pressure EGR ratio while monitoring the low pressure EGR ratio. In this case, the ECU 50 directly acquires the low pressure EGR ratio from a sensor or the like, or calculates the low pressure EGR ratio from the air-fuel ratio, the intake air temperature, or the intake pressure.

  In step S102, the ECU 50 determines whether or not the change rate of the supercharging pressure exceeds a predetermined value. Specifically, the ECU 50 performs the determination based on the supercharging pressure (corresponding to the detection signal S19) acquired from the supercharging pressure sensor 19. Such a determination is performed in order to feed back the supercharging pressure so that the change speed of the supercharging pressure becomes a predetermined value or less. The predetermined value used for the determination is set to, for example, a change rate of the supercharging pressure that hardly deteriorates drivability and EGR controllability when switching from the high pressure EGR mode to the low pressure EGR mode.

  When the change rate of the supercharging pressure exceeds a predetermined value (step S102; Yes), the process proceeds to step S103. In step S103, the ECU 50 decreases the current low pressure EGR ratio increase rate. Specifically, the ECU 50 adjusts the opening degree of the high pressure EGR valve 11 and the low pressure EGR valve 17 to decrease the low pressure EGR ratio increase rate so that the change rate of the supercharging pressure becomes a predetermined value or less. When the above process ends, the process exits the flow. On the other hand, when the change rate of the supercharging pressure is equal to or lower than the predetermined value (step S102; No), the process exits the flow. In this case, the current low pressure EGR ratio increase rate is maintained.

  According to the first embodiment described above, it is possible to appropriately suppress an extreme change in the supercharging pressure that may occur when switching from the high pressure EGR mode to the low pressure EGR mode. Therefore, it is possible to effectively suppress deterioration of drivability and EGR controllability at the time of switching.

  In the above description, an example in which the low pressure EGR ratio increasing speed is controlled while feeding back the supercharging pressure changing speed to be equal to or lower than a predetermined value regardless of whether the high pressure turbocharger 3 is in use or not is shown. This control may be performed only when the high-pressure turbocharger 3 is in the use range (see FIG. 3).

  Moreover, although the example which detected the supercharging pressure by the supercharging pressure sensor 19 was shown above, you may estimate a supercharging pressure instead. That is, the supercharging pressure may be estimated based on the driving state of the vehicle 100 or the like.

[Second Embodiment]
Next, control performed by the ECU 50 in the second embodiment of the present invention will be described. Also in the second embodiment, as in the first embodiment described above, the ECU 50 controls the low pressure while performing feedback control so that the change rate of the supercharging pressure becomes a predetermined value or less when switching from the high pressure EGR mode to the low pressure EGR mode. Controls the rate of EGR ratio increase. However, in the second embodiment, the ECU 50 makes the feedback gain used for the high pressure EGR valve 11 during the feedback control at the time of switching larger than the feedback gain used for the high pressure EGR valve 11 when the high pressure EGR mode is set. To do. Specifically, the ECU 50 sets the feedback gain used for the high pressure EGR valve 11 to a large value so that the responsiveness of the high pressure EGR valve 11 is improved when switching from the high pressure EGR mode to the low pressure EGR mode.

  The reason for performing such control is as follows. Since the high-pressure turbocharger 3 has a relatively small turbine capacity, that is, has a relatively small turbine passage area, as described above, when the exhaust gas flow rate increases when switching from the high-pressure EGR mode to the low-pressure EGR mode, the exhaust pressure Can be said to be on the rise. Since the amount of EGR gas recirculated by the high pressure EGR device 20 is determined by the differential pressure between the intake pressure and the exhaust pressure and the opening degree of the high pressure EGR valve 11, when the exhaust pressure rises in this way, the high pressure EGR valve 11 It is considered that the sensitivity of the EGR gas amount with respect to the opening degree is increased. Therefore, in this case, it can be said that the controllability of the high pressure EGR valve 11 is deteriorated.

  Here, the relationship between the turbine flow rate (turbine inflow gas amount) and the exhaust pressure will be specifically described with reference to FIG. FIG. 4 is a diagram showing an example of the relationship between the turbine flow rate (horizontal axis) and the exhaust pressure (vertical axis). In FIG. 4, the solid line C <b> 1 shows a graph of the high pressure turbocharger 3, and the broken line C <b> 2 shows a graph of the low pressure turbocharger 4. In addition, these graphs have shown an example of the result obtained in the state which maintained the high pressure EGR valve 11 at the same opening degree.

  As shown by the arrow D in FIG. 4, it can be seen that when the high pressure EGR mode is switched to the low pressure EGR mode, the exhaust pressure in the high pressure turbocharger 3 greatly increases. Therefore, when the high pressure EGR valve 11 is set to the same opening, it is conceivable that the amount of EGR gas recirculated by the high pressure EGR device 20 increases. Therefore, in this case, it can be said that the EGR controllability deteriorates.

  As described above, in the second embodiment, in order to suppress such deterioration in controllability, the feedback gain used for the high pressure EGR valve 11 is changed according to the exhaust pressure when switching from the high pressure EGR mode to the low pressure EGR mode. to correct. Specifically, the ECU 50 corrects the feedback gain used for the high pressure EGR valve 11 at the time of the switching to a value larger than the feedback gain used when the high pressure EGR mode is set. Thereby, the response speed of the high pressure EGR valve 11 can be increased when switching from the high pressure EGR mode to the low pressure EGR mode.

  FIG. 5 is a flowchart showing processing according to the second embodiment. This process is executed by the ECU 50. Further, this processing is executed when the load on the internal combustion engine 7 changes from a light load to a high load (for example, when an acceleration instruction is issued).

  First, in step S201, the ECU 50 starts switching from the high pressure EGR mode to the low pressure EGR mode. Specifically, the ECU 50 controls the opening degrees of the high pressure EGR valve 11 and the low pressure EGR valve 17 so that the low pressure EGR ratio increases. For example, the ECU 50 adjusts the opening degrees of the high pressure EGR valve 11 and the low pressure EGR valve 17 so that the low pressure EGR ratio increases at a preset speed (initial speed). Basically, the ECU 50 adjusts the opening degree so that the high-pressure EGR valve 11 is finally closed, and adjusts the opening degree so that the low-pressure EGR valve 17 is finally opened. Switching from the EGR mode to the low pressure EGR mode is performed. When the above process ends, the process proceeds to step S202. The ECU 50 can perform control to increase the low pressure EGR ratio while monitoring the low pressure EGR ratio. In this case, the ECU 50 directly acquires the low pressure EGR ratio from a sensor or the like, or calculates the low pressure EGR ratio from the air-fuel ratio, the intake air temperature, or the intake pressure.

  In step S202, the ECU 50 determines whether or not the high-pressure turbocharger 3 is in the usage range. For example, the ECU 50 performs the determination based on the load of the internal combustion engine 7. If it is in the use range of the high-pressure turbocharger 3 (step S202; Yes), the process proceeds to step S203. On the other hand, if the high pressure turbocharger 3 is not used (step S202; No), the process exits the flow. In this case, the feedback gain used for the high pressure EGR valve 11 is not corrected.

  In step S203, the ECU 50 corrects the feedback gain used for the high pressure EGR valve 11. Specifically, the ECU 50 makes the feedback gain used for the high pressure EGR valve 11 at the time of switching larger than the feedback gain used when setting the high pressure EGR mode. Specifically, the feedback gain is corrected to a large value according to the exhaust pressure so that the response speed of the high pressure EGR valve 11 is increased. When the above process ends, the process exits the flow. Thereafter, as described above, the ECU 50 controls the low pressure EGR ratio increase speed while performing feedback so that the change speed of the supercharging pressure becomes a predetermined value or less. Specifically, the ECU 50 performs processing similar to the processing in steps S102 and S103 shown in FIG.

  According to the second embodiment described above, the response speed of the high pressure EGR valve 11 can be increased when switching from the high pressure EGR mode to the low pressure EGR mode. Therefore, the high-pressure EGR valve 11 can be appropriately controlled based on the supercharging pressure, and the switching can be performed while effectively suppressing an extreme change in the supercharging pressure.

  In the above, an example in which the feedback gain of the high pressure EGR valve 11 is corrected only when the high pressure turbocharger 3 is in use (see FIG. 5), but at the time of switching from the high pressure EGR mode to the low pressure EGR mode. The feedback gain of the high-pressure EGR valve 11 may be corrected regardless of whether the high-pressure turbocharger 3 is in use.

[Modification]
The present invention is not limited to application to a system having two turbochargers, that is, a high-pressure turbocharger 3 and a low-pressure turbocharger 4 (that is, a multistage turbocharging system). The present invention can be similarly applied to a system having only one small-capacity low-speed turbocharger with good response. Even in such a system, since the supercharging pressure may change suddenly when switching from the high pressure EGR mode to the low pressure EGR mode, such a problem is solved by performing the control according to the present invention as described above. Because it can be done.

1 is a schematic configuration diagram of a vehicle to which an internal combustion engine control device according to an embodiment is applied. An example of the result at the time of performing control concerning a 1st embodiment is shown. It is a flowchart which shows the process which concerns on 1st Embodiment. An example of the relationship between turbine flow volume and exhaust pressure is shown. It is a flowchart which shows the process which concerns on 2nd Embodiment.

Explanation of symbols

2 Intake passage 3 High pressure turbocharger 4 Low pressure turbocharger 7 Internal combustion engine 9 Exhaust passage 11 High pressure EGR valve 17 Low pressure EGR valve 19 Supercharging pressure sensor 20 High pressure EGR device 21 Low pressure EGR device 50 ECU
100 vehicles

Claims (4)

A high-pressure turbocharger in which a compressor is disposed in the intake passage and a turbine is disposed in the exhaust passage, and a compressor is disposed in the intake passage on the upstream side of the compressor of the high-pressure turbocharger, and the exhaust on the downstream side of the turbine in the high-pressure turbocharger A low-pressure turbocharger in which a compressor is disposed in a passage; a high-pressure EGR device that recirculates exhaust gas from an exhaust passage upstream of the turbine of the high-pressure turbocharger to an intake passage downstream of the compressor of the high-pressure turbocharger; A low-pressure EGR device that recirculates exhaust gas from an exhaust passage downstream of a turbocharged turbine to an intake passage upstream of a compressor of the low-pressure turbocharger,
By performing feedback control so that the change rate of the supercharging pressure becomes a predetermined value or less when switching from the recirculation of the EGR gas using the high pressure EGR device to the recirculation of the EGR gas using the low pressure EGR device, A control device for an internal combustion engine, comprising control means for controlling the speed at which the ratio of the EGR gas recirculated by the low-pressure EGR device to the total amount of EGR gas recirculated is increased.   When the feedback control is performed at the time of switching, the control means uses a feedback gain used for a valve for adjusting an EGR gas flow rate recirculated by the high-pressure EGR device, and uses EGR gas using only the high-pressure EGR device. The control device for an internal combustion engine according to claim 1, wherein the control device is set to be larger than a feedback gain used for the valve when the recirculation is performed.   The control device for an internal combustion engine according to claim 1 or 2, wherein the control means controls a speed at which the ratio is increased in a use range of the high-pressure turbocharger.   The control means controls at least one of a valve for adjusting the flow rate of EGR gas to be recirculated by the high pressure EGR device and a valve for adjusting the flow rate of EGR gas to be recirculated by the low pressure EGR device, The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein a speed for increasing the ratio is controlled.

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