JP2010242514A - Internal combustion engine control system - Google Patents

Abstract

A technique for suppressing the backflow of gas through an EGR passage in an internal combustion engine equipped with an EGR device is provided.
An EGR passage communicating an exhaust passage and an intake passage of an internal combustion engine, a throttle valve provided in an intake passage upstream of a connection portion of the EGR passage, and recirculation of exhaust gas through the EGR passage And there is a control request accompanied by a request to open the throttle valve to an opening greater than or equal to a predetermined opening under operating conditions where the engine load is equal to or less than the predetermined load, Control means for controlling the internal combustion engine so as to be in an operating state with a lighter load than the target engine load and a higher engine speed than the target engine speed.
[Selection] Figure 4

Description

  The present invention relates to a control system for an internal combustion engine.

  2. Description of the Related Art There is known an internal combustion engine that includes an EGR device that causes part of exhaust gas discharged from an internal combustion engine to flow into an intake passage via an EGR passage that connects the exhaust passage and the intake passage of the internal combustion engine.

  Patent Document 1 describes a technique for closing an EGR valve when an EGR gas flow rate is smaller than a predetermined threshold in an internal combustion engine including an EGR device and a supercharger.

  Patent Document 2 describes a technique for preventing a backflow of EGR gas by providing a check valve in the middle of the EGR passage.

  Patent Document 3 describes a technique in which a passage connecting an intake passage and an exhaust passage is provided, and the opening degree of a valve provided in the passage is changed in synchronization with a periodic change in intake pressure or exhaust pressure. Yes.

JP 2008-101498 A JP 2005-133605 A JP 2007-332925 A

  When the throttle valve is fully opened (WOT) or when it is suddenly opened to an opening close to it, such as during acceleration from a light load operation state where the exhaust pressure is low, the intake pressure suddenly rises and temporarily exceeds the exhaust pressure. May be higher. In an internal combustion engine equipped with an EGR device, when the exhaust gas is recirculated through the EGR passage, if the intake pressure becomes higher than the exhaust pressure in this way, the gas flows from the intake passage side to the exhaust passage side through the EGR passage. There is a possibility of backflow. When a backflow of gas occurs in the EGR passage in this way, the air in the intake passage flows into the exhaust passage via the EGR passage, the air-fuel ratio shifts, affecting the engine output and the exhaust performance, or the exhaust system catalyst. There is a risk that the lean gas will flow in excessively and the catalyst will deteriorate.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a technique for suppressing the backflow of gas through an EGR passage in an internal combustion engine equipped with an EGR device.

In order to solve the above problems, a control system for an internal combustion engine according to the present invention includes:
An EGR passage communicating the exhaust passage and the intake passage of the internal combustion engine;
A throttle valve provided in an intake passage upstream of the connection portion of the EGR passage;
A control request with a request to open the throttle valve to an opening greater than or equal to a predetermined opening under operating conditions in which exhaust gas is recirculated through the EGR passage and the engine load is less than or equal to a predetermined load Control means for controlling the internal combustion engine so that the operating state is lighter than the target engine load and higher than the target engine speed in the control request,
It is characterized by providing.

  Here, the “predetermined load” relating to the engine load and the “predetermined opening” relating to the throttle valve opening are the opening of the throttle valve when the throttle valve is opened to the opening from the operating condition of the engine load. This is a reference value of the engine load and the throttle valve opening for determining whether or not the intake pressure is higher than the exhaust pressure in the process of increasing the intake pressure and the exhaust pressure.

  When the throttle valve is opened to an opening greater than or equal to a predetermined opening under operating conditions where the engine load is less than or equal to the predetermined load, the intake pressure is greater than the exhaust pressure in the process of increasing the intake pressure and exhaust pressure associated with the opening of the throttle valve. It can be determined that a high state occurs. Therefore, if such opening of the throttle valve is performed under operating conditions in which exhaust gas is recirculated through the EGR passage, the EGR passage is opened when the intake pressure becomes higher than the exhaust pressure. There is a risk of backflow.

  According to the present invention, when there is a control request that may cause a backflow in the EGR passage, the load is lighter than the target engine load in the control request and higher than the target engine speed. Since the internal combustion engine is controlled so as to be in a number of operating states, the throttle valve can be prevented from being opened to an opening greater than a predetermined opening. Therefore, it is possible to suppress the occurrence of a state in which the intake pressure is higher than the exhaust pressure in the process of the pressure increase accompanying the opening of the throttle valve. As a result, it is possible to suppress the occurrence of backflow in the EGR passage. Even if the engine load is limited to a lighter load than the target in the control request, the engine speed is controlled to be higher than the target, so that the output of the internal combustion engine can be suppressed from being insufficient with respect to the required output.

  In the present invention, the control means controls the internal combustion engine so as to gradually increase the engine load from the light load operation state to the target engine load operation state than the target engine load in the control request. May be performed.

  Thereby, the opening degree of the throttle valve can be gradually increased. If the opening of the throttle valve is not increased rapidly, it is possible to suppress the intake pressure from becoming higher than the exhaust pressure. Therefore, it is possible to open the throttle valve to an opening greater than or equal to the predetermined opening while suppressing backflow in the EGR passage.

  In this case, as the engine load is gradually increased, the engine speed is gradually increased from the operating state at a higher speed than the target engine speed in the control request to the operating state at the target engine speed. The internal combustion engine may be controlled so as to lower the value. By doing so, it is possible to suppress the output of the internal combustion engine from being excessive or insufficient with respect to the required output.

  According to the present invention, in an internal combustion engine equipped with an EGR device, it is possible to suppress the backflow of gas through the EGR passage.

1 is a diagram schematically showing the configuration of an engine according to a first embodiment and its intake system and exhaust system. FIG. FIG. 6 is a diagram illustrating an operation region where EGR is performed in the engine according to the first embodiment and an operation region where the exhaust pressure is lower than the intake pressure during WOT control. (A) Time variation of throttle valve opening, (B) Time variation of engine speed, and (C) Time variation of intake pressure and exhaust pressure when engine control according to the first embodiment is performed. is there. 3 is a flowchart of engine control according to the first embodiment. It is the figure which showed typically the schematic structure of the hybrid system containing the engine which concerns on Example 2, its intake system and exhaust system, and an engine. FIG. 6 is a time chart showing (A) time change in throttle valve opening, (B) time change in engine speed, and (C) time change in intake pressure and exhaust pressure when engine control according to the second embodiment is performed. is there. 6 is a flowchart of engine control according to a second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the present embodiment are not intended to limit the technical scope of the invention only to those unless otherwise specified.

  An internal combustion engine control system according to Embodiment 1 of the present invention will be described.

  FIG. 1 is a conceptual diagram schematically showing a schematic configuration of an internal combustion engine to which an internal combustion engine control system according to this embodiment is applied, and its intake system and exhaust system.

  The engine 1 shown in FIG. 1 includes four cylinders 2, and each cylinder 2 communicates with an intake manifold 5 and an exhaust manifold 6.

  An intake passage 3 is connected to the intake manifold 5. An EGR passage 9 that connects the exhaust manifold 6 and the intake passage 3 is connected to the intake passage 3. The intake passage 3 upstream of the connection portion of the EGR passage 9 is provided with a throttle valve 23 that changes the flow passage area of the intake passage 3. The intake passage 3 upstream of the installation position of the throttle valve 23 is provided with an intercooler 11 that cools the intake air flowing through the intake passage 3. A supercharger compressor 7 is provided in the intake passage 3 upstream of the installation position of the intercooler 11. An air flow meter 25 for measuring the amount of intake air is provided in the intake passage 3 upstream of the installation position of the compressor 7.

  An exhaust passage 4 is connected to the exhaust manifold 6. The exhaust passage 4 is provided with the turbocharger turbine 8. An exhaust gas purification device 17 is provided in the exhaust passage 4 on the downstream side of the installation position of the turbine 8. The exhaust purification device 17 is a known filter such as a particulate filter that collects particulate matter in the exhaust, a NOx storage reduction catalyst that reduces and purifies NOx in the exhaust, or an oxidation catalyst that oxidizes CO or HC in the exhaust. The various exhaust purification catalysts are configured. The exhaust passage 4 is open to the atmosphere downstream of the exhaust purification device 17.

  The EGR passage 9 is provided with an EGR valve 10 that changes the flow area of the EGR passage 9. When the EGR valve 10 is opened, a part of the exhaust discharged from the cylinder 2 to the exhaust manifold 6 flows into the intake passage 3 via the EGR passage 9, and the mixed gas of fresh air and exhaust becomes the cylinder 2. Will be inhaled. The introduction of exhaust gas into the intake passage 3 via the EGR passage 9 is referred to as “exhaust gas recirculation (EGR)”. By performing EGR, the exhaust performance of the engine 1 is improved.

  The engine 1 is provided with an ECU 28 that is a computer that controls the operating state of the engine 1. In addition to the air flow meter 25 described above, the ECU 28 is electrically connected to a crank angle sensor 22 that measures the rotation angle of the crankshaft of the engine 1, an accelerator opening sensor 27 that measures the amount of depression of the accelerator pedal, and other various sensors. Then, measurement data obtained by these various sensors is input to the ECU 28. In addition to the throttle valve 23 and the EGR valve 10 described above, various devices are electrically connected to the ECU 28, and a signal for controlling the operation of these various devices is output from the ECU 28. The ECU 28 acquires the operation state and control request of the engine 1 based on measurement data input from various sensors, and controls the operation of various devices based on the acquired operation state.

  The operating conditions under which EGR is performed are defined by the load and rotation speed of the engine 1. In FIG. 2, the operating conditions under which EGR is performed are shown in a region defined by the load and the rotational speed.

  When the driver depresses the accelerator pedal, the depression amount is measured by the accelerator opening sensor 27, and control for increasing the opening of the throttle valve 23 according to the measured value is executed by the ECU. When the accelerator pedal is greatly depressed during sudden acceleration or the like, control is performed to fully open the throttle valve 23. Control for fully opening the throttle valve 23 is referred to as WOT (Wide Open Throttle) control. 2 represents the engine load of the engine 1 corresponding to the case where the throttle valve 23 is fully opened in the WOT control.

  When the opening degree of the throttle valve 23 is increased, the intake pressure and the exhaust pressure increase accordingly, but the exhaust pressure starts to increase later than the intake pressure. Therefore, when the opening degree of the throttle valve 23 is suddenly increased by WOT control under a light load operation condition where the exhaust pressure is low, the intake pressure rises sharply during a period in which the exhaust pressure rise is delayed. In some cases, the intake pressure is higher than the exhaust pressure.

  This will be described with reference to FIG. As shown in FIG. 3A, it is assumed that at time t1, the accelerator pedal is greatly depressed, a WOT control request is generated, and the opening degree of the throttle valve 23 is greatly increased from Dth1 to Dth2 (fully open) (indicated by a broken line). Show). Then, as shown in FIG. 3C, the intake pressure begins to rise from Pin1 immediately after time t1 when the opening of the throttle valve 23 is increased (indicated by a broken line. Pin1 is a light before the generation of the WOT control request. Intake pressure under load operation). On the other hand, the exhaust pressure does not increase until the timing t3 delayed from the time t1, and remains Pex1 (Pex1 is the exhaust pressure in the light load operation state before the generation of the WOT control request). Therefore, the intake pressure that suddenly increases as the throttle valve 23 significantly increases exceeds the exhaust pressure Pex1 at time t2. Then, a state in which the intake pressure is higher than the exhaust pressure occurs until time t4.

  In FIG. 2, the operating conditions in which the intake pressure may temporarily be higher than the exhaust pressure during execution of the WOT control are defined by the load and the rotational speed in the same manner as the operating conditions in which EGR is performed. Shown in area. The operating condition in which the intake pressure is higher than the exhaust pressure during WOT control is a relatively light load operating region. Hereinafter, this operation region is referred to as a “WOT pressure reversal region”.

  As shown in FIG. 2, the EGR region and the WOT pressure reversal region partially overlap each other. In FIG. 2, this overlapped area is indicated by hatching. When the opening degree of the throttle valve 23 is suddenly increased in response to the WOT control request under the operating conditions belonging to this overlapping region, the state where the intake pressure is higher than the exhaust pressure is the EGR valve 10 opened. Sometimes it happens. Then, there is a possibility that the gas flows backward through the EGR passage 9 from the intake passage 3 side to the exhaust manifold 6 side. When the air in the intake passage 3 flows backward through the EGR passage 9 and flows into the exhaust manifold 6, the air-fuel ratio shifts and good combustion cannot be performed, or the lean air-fuel ratio gas is not intended and the exhaust purification device 17. There is a risk that the catalyst may deteriorate due to flow into the catalyst. Hereinafter, the operation region (operation region indicated by hatching in FIG. 2) at the common part of the EGR region and the WOT pressure reversal region is referred to as a “WOT backflow generation region”.

In this embodiment, when there is a WOT control request in the operating condition S1 belonging to this WOT backflow generation region, as shown in FIG. 2, the target of the control of the engine 1 performed in response to the WOT control request is shown. As the operating state, the original target operating state S existing on the WOT line
An operation state S2 ′ in which 2 is corrected to a light load and high rotation side is set.

  Thereby, as shown in FIG. 3 (A), in the valve opening control of the throttle valve 23 performed in response to the WOT control request, the opening degree Dth2 when the control is performed with the operation state S2 on the WOT line as a target. The opening Dth2 ′ on the closing side can be set. As shown in FIG. 3C, the opening degree Dth2 ′ is an opening degree that does not cause a state where the intake pressure is higher than the exhaust pressure when the opening degree of the throttle valve 23 is increased from Dth1 to Dth2 ′. Can be determined. In this way, by restricting the opening degree of the throttle valve 23 to an opening degree at which the intake pressure is not higher than the exhaust pressure, it is possible to suppress the backflow in the EGR passage 9. Therefore, it is possible to avoid the above-described problems of air-fuel ratio deviation and catalyst deterioration.

  Further, as shown in FIG. 3B, the throttle valve 23 is opened as described above because the engine speed is controlled to the engine speed Ne2 ′ higher than the original target engine speed Ne2 for engine control corresponding to the WOT control request. It is also possible to prevent a situation in which the output of the engine 1 is insufficient with respect to the required output due to the restriction on the opening.

  The engine control in the present embodiment described above will be described based on the flowchart of FIG. The process represented by the flowchart of FIG. 4 is periodically executed by the ECU 28 during operation of the engine 1.

  In step S <b> 101, the ECU 28 acquires the operating state of the engine 1. In this embodiment, the engine load and engine speed of the engine 1 are calculated based on data input from the accelerator opening sensor 27 and the crank angle sensor 22.

  In step S102 and step S103, the ECU 28 determines whether or not the operating state of the engine 1 belongs to the WOT back flow generation region. First, in step S102, it is determined whether or not the operating state of the engine 1 acquired in step S101 belongs to the EGR region. If an affirmative determination is made in step S103, the operating state of the engine 1 acquired in step S101 is WOT. It is determined whether or not it belongs to the hour pressure reversal region. If an affirmative determination is made, the process proceeds to step S104. If a negative determination is made in step S102 or step S103, the ECU 28 exits the processing of this flowchart.

  In step S104, the ECU 28 determines whether or not there is a WOT control request. In this embodiment, when it is detected that the accelerator pedal depression amount measured by the accelerator opening sensor 27 exceeds a predetermined threshold, it is determined that there is a WOT control request. If an affirmative determination is made in step S104, the ECU 28 proceeds to the process of step S105, and if a negative determination is made, the process of this flowchart is exited.

  In step S105, the ECU 28 corrects the original target operating state in the engine control corresponding to the WOT control request (the operating state S2 existing on the WOT line in FIG. 2) to the light load and high rotation speed side, and performs the correction. The engine 1 is controlled with the later operation state S2 ′ as a target.

  The ECU 28 that executes the processing of the flowchart described above corresponds to the “control unit” in the present invention. In the present embodiment, the operating condition belonging to the “WOT backflow generation region” indicated by the diagonal lines in FIG. 2 is the “recirculation of exhaust gas through the EGR passage and the engine load is equal to or less than a predetermined load in the present invention. It corresponds to "a certain operating condition". Further, the WOT control request in this embodiment corresponds to the “control request accompanied by a request to open the throttle valve to an opening greater than or equal to a predetermined opening” in the present invention.

  The ECU 28 performs the processing shown in the above flow chart to suppress the air in the intake passage 3 from flowing backward through the EGR passage 9 even when there is a WOT control request during EGR. Is possible.

  Next, a second embodiment of the present invention will be described. In this embodiment, the control system for an internal combustion engine according to the present invention is applied to a hybrid system.

  FIG. 5 schematically shows a schematic configuration of the hybrid system according to the present embodiment. The difference from the internal combustion engine of the first embodiment shown in FIG. 1 is that motor generators MG1 and MG2, which are power sources other than the engine 1, and the output of the MG1 and the output of the engine 1 are integrated and transmitted to the drive wheels 51. The ECU 28 further includes a power split mechanism 50, and the ECU 28 further has a function of controlling the rotational speed and torque of the MG1 and MG2. In addition, although it has the same configuration as a general hybrid system such as a battery or an inverter, it is omitted here in order to avoid complexity. Further, the same components and elements as those of the first embodiment are designated by the same names and reference numerals as those of the first embodiment, and detailed description thereof is omitted.

  In such a hybrid system, the degree of freedom in controlling the engine speed of the engine 1 is high. Therefore, in this embodiment, when there is a WOT control request under the operating conditions belonging to the WOT backflow generation region, lighter load and higher rotation than the original target operating state (S2 in FIG. 2) existing on the WOT line. First, the engine 1 is controlled in the operation state (S2 ′ in FIG. 2), and the operation state is gradually changed from the operation state S2 ′ toward the original target operation state S2 on the WOT line. The engine 1 was controlled.

  Explaining based on FIG. 6, as shown in FIG. 6A, in the valve opening control of the throttle valve 23 performed in response to the WOT control request at time t1, the engine control is performed with the operation state S2 on the WOT line as a target. The opening degree of the throttle valve 23 is limited to the opening degree Dth2 ′ that is closer to the closing side than the target opening degree Dth2 when performing the operation, and the opening degree of the throttle valve 23 is gradually increased from the opening degree Dth2 ′ to the original target opening degree Dth2. I will let you.

  As a result, the intake pressure can be prevented from abruptly increasing. Therefore, as shown in FIG. 6C, the intake pressure is higher than the exhaust pressure in the process of increasing the pressure accompanying the valve opening control of the throttle valve 23. It can suppress that a state arises.

  Further, as shown in FIG. 6 (B), the engine speed is controlled to a rotation speed Ne2 ′ higher than the target rotation speed Ne2 when the engine control is performed with the operation state S2 on the WOT line as a target. The engine speed is gradually reduced from Ne2 ′ to the original target speed Ne2.

  Thereby, it is possible to suppress an excess or deficiency in the output of the engine 1 with respect to the requested engine output corresponding to the WOT control request.

  The engine control in the present embodiment described above will be described based on the flowchart of FIG. 7 is periodically executed by the ECU 28 during operation of the engine 1.

  In the flowchart of FIG. 7, the processing contents from step S101 to step S104 are the same as the flowchart described based on FIG. 4 in the first embodiment, and thus the description thereof is omitted here.

  In the flowchart of FIG. 7, when an affirmative determination is made in step S104 (that is, when it is determined that a WOT control request has occurred under operating conditions belonging to the WOT backflow generation region), the ECU 28 proceeds to the process of step S205. First, the engine 1 is controlled with the target operation state S2 ′ obtained by correcting the original target operation state S2 existing on the WOT line to a light load and high rotation side as a target, and the original target operation state from the operation state S2 ′. The engine 1 is controlled so as to gradually change the operating state toward S2. Specifically, as described in FIG. 6, the opening degree of the throttle valve 23 is gradually increased from the corrected target opening degree Dth2 ′ toward the original target opening degree Dth2, and the engine speed is increased. The corrected target rotational speed Ne2 ′ is gradually decreased toward the original target rotational speed Ne2.

  The ECU 28 that executes the processing of the flowchart described above corresponds to the “control unit” in the present invention.

  In this embodiment, when there is a WOT control request under the operating conditions belonging to the WOT backflow generation region, the operating state S2 is lighter and higher than the original target operating state S2 existing on the WOT line. In the above description, the engine control is first performed with 'as the target. However, the engine control is performed so that the operation state is gradually changed from the operation state before the generation of the WOT control request toward the original target operation state S2 on the WOT line. You can go.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in addition to fully opening the throttle valve in response to a WOT control request under operating conditions belonging to the WOT backflow generation region, when the throttle valve opening is suddenly increased, the intake pressure is temporarily higher than the exhaust pressure. Can be expensive. Therefore, the engine control according to the present invention is applied when there is a control request to increase the throttle valve opening to an opening having an opening difference that is greater than or equal to a predetermined reference value under operating conditions belonging to the EGR region. Also good. Here, the “reference value” is the difference in opening of the throttle valve before and after opening to determine whether or not the intake pressure is higher than the exhaust pressure in the process of pressure change accompanying the opening of the throttle valve. Is the reference value.

1 Engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Intake manifold 6 Exhaust manifold 7 Compressor 8 Turbine 9 EGR passage 10 EGR valve 11 Intercooler 17 Exhaust purification device 22 Crank angle sensor 23 Throttle valve 25 Air flow meter 27 Accelerator opening sensor 28 ECU
50 Power split mechanism 51 Drive wheel

Claims (2)

An EGR passage communicating the exhaust passage and the intake passage of the internal combustion engine;
A throttle valve provided in an intake passage upstream of the connection portion of the EGR passage;
A control request with a request to open the throttle valve to an opening greater than or equal to a predetermined opening under operating conditions in which exhaust gas is recirculated through the EGR passage and the engine load is less than or equal to a predetermined load Control means for controlling the internal combustion engine so that the operating state is lighter than the target engine load and higher than the target engine speed in the control request,
An internal combustion engine control system comprising: In claim 1,
The control means controls the internal combustion engine so as to gradually increase the engine load from a light load operation state to a target engine load operation state than the target engine load in the control request. A control system for an internal combustion engine.

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