JP2018091272A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a torque shock caused by a sudden change of an air-fuel ratio due to start and end of catalyst temperature raising control, and prevent misfire due to ignition timing retard control. A control device for an internal combustion engine includes an execution unit that executes a rich combustion in an arbitrary cylinder and a lean combustion in another cylinder to execute a catalyst temperature increase control for increasing a temperature of a catalyst, and a catalyst temperature increase control. Is started, the air-fuel ratio of each cylinder is gradually changed to the target air-fuel ratio at the time of executing the catalyst temperature raising control, and when the end request of the catalyst temperature raising control is issued, the air-fuel ratio of each cylinder is changed to the internal combustion engine. When the ignition timing retard request other than the purpose of suppressing knocking is made during the execution of the catalyst temperature raising control or during the gradual change, the gradual change processing unit that gradually changes to the target air-fuel ratio according to the operating state of A time shortening unit that shortens the time until the air-fuel ratio of each cylinder reaches the target air-fuel ratio according to the operating state of the internal combustion engine as compared to when there is no ignition timing retard request other than for the purpose of suppressing knocking. [Selection diagram] Figure 1

Description

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

  An engine exhaust system is provided with a catalyst for purifying exhaust gas. In order to effectively exhibit the exhaust gas purification ability of the catalyst, it is necessary to raise the catalyst temperature and raise the catalyst temperature to the activation temperature.

  In Patent Document 1, rich combustion in which an air-fuel ratio at the time of combustion in a cylinder is smaller than the stoichiometric air-fuel ratio in any cylinder among a plurality of cylinders is performed, and the air-fuel ratio at the time of combustion in a cylinder is stoichiometrically empty in other cylinders. Catalyst combustion is promoted by performing lean combustion larger than the fuel ratio and controlling the fuel injection amount in each cylinder so that the average of the air-fuel ratios of the plurality of cylinders becomes the stoichiometric air-fuel ratio.

JP 2012-57492 A

  In the catalyst temperature increase control in which rich combustion and lean combustion are executed in separate cylinders, the temperature increase effect increases as the ratio of increase in the air-fuel ratio from the theoretical air-fuel ratio (hereinafter referred to as dither amplitude) increases. However, when the dither amplitude is large, a torque shock may occur due to a rapid change in the air-fuel ratio at the start and end of the catalyst temperature increase control.

  On the other hand, the engine generated torque may be suppressed by retarding the ignition timing in order to reduce shock at the time of acceleration / deceleration of the vehicle or at the time of shifting or to speed up the shift change. At this time, if the catalyst temperature rise control is being performed, there is no ignition timing delay margin for misfire, particularly in a cylinder that performs lean combustion, so a slight ignition timing delay may cause misfire. The ignition timing retardation request is limited, and the engine generated torque may not be controlled as desired.

  Therefore, the control device for an internal combustion engine disclosed in the present specification is accompanied by a rapid change in the air-fuel ratio due to the start and end of catalyst temperature increase control in catalyst temperature increase control in which rich combustion and lean combustion are executed in separate cylinders. It is an object of the present invention to reduce torque shock and suppress the occurrence of misfire due to ignition timing retardation control.

  In order to solve such a problem, an internal combustion engine control device disclosed in the present specification has an air-fuel ratio at the time of combustion in a cylinder of any of the plurality of cylinders of the internal combustion engine smaller than the stoichiometric air-fuel ratio. Catalyst temperature increase control for increasing the temperature of a catalyst that purifies exhaust from the plurality of cylinders by executing rich combustion, performing lean combustion in which the air-fuel ratio during combustion in the cylinder is greater than the stoichiometric air-fuel ratio in other cylinders When the catalyst temperature raising control start request is made, the air-fuel ratio at the time of combustion of each cylinder is gradually changed until the target air-fuel ratio at the time of performing the catalyst temperature raising control is reached, and the catalyst When a request to end the temperature increase control is made, the air-fuel ratio at the time of combustion of each cylinder is gradually changed until the target air-fuel ratio according to the operating state of the internal combustion engine after the completion of the catalyst temperature increase control is reached. During the execution of the change processing unit and the catalyst temperature increase control, When the ignition timing retardation request other than the purpose of suppressing knocking is made during the gradual change, the air-fuel ratio at the time of combustion of each cylinder is set to the target air-fuel ratio according to the operating state of the internal combustion engine. A time shortening unit that shortens the time as compared with a case where there is no ignition timing retardation request other than the purpose of suppressing knocking.

  According to the control device for an internal combustion engine disclosed in the present specification, in catalyst temperature increase control in which rich combustion and lean combustion are performed in separate cylinders, accompanying a rapid change in the air-fuel ratio due to the start and end of catalyst temperature increase control Torque shock can be reduced and the occurrence of misfire due to ignition timing retardation control can be suppressed.

FIG. 1 is a schematic diagram illustrating a configuration of an engine system to which an internal combustion engine control apparatus according to an embodiment is applied. FIG. 2 is a flowchart illustrating an example of a return process from the catalyst temperature increase control executed by the ECU. FIG. 3 is a time chart showing an example of changes in the air-fuel ratio in the rich cylinder and the air-fuel ratio in the lean cylinder in the return processing from the catalyst temperature increase control.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of each part may not be shown so as to completely match the actual ones. In some cases, details are omitted in some drawings.

  First, an engine system to which a control device for an internal combustion engine according to an embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating a configuration of an engine system 1 to which an internal combustion engine control device according to an embodiment is applied.

  As shown in FIG. 1, the engine system 1 includes an internal combustion engine 20. The internal combustion engine 20 generates power by burning a mixture of fuel and air in a combustion chamber 23 formed in the cylinder block 21 and reciprocating a piston 24 in the combustion chamber 23. The internal combustion engine 20 is a vehicular multi-cylinder engine (only one cylinder is shown). In this embodiment, the internal combustion engine 20 is a four-cylinder engine including cylinders # 1 to # 4. Note that the number of cylinders included in the internal combustion engine 20 is not limited to this embodiment.

  The cylinder head of the internal combustion engine 20 is provided with an intake valve Vi for opening and closing an intake port and an exhaust valve Ve for opening and closing an exhaust port for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 27 for igniting the air-fuel mixture in the combustion chamber 23 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to the surge tank 18 via a branch pipe for each cylinder. An intake pipe 10 is connected to the upstream side of the surge tank 18, and an air cleaner 19 is provided at the upstream end of the intake pipe 10. An air flow meter 15 for detecting the intake air amount and an electronically controlled throttle valve 13 are incorporated in the intake pipe 10 in order from the upstream side.

  An injector 12 for injecting fuel into the intake port is installed at the intake port of each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 23 when the intake valve Vi is opened, compressed by the piston 24, and ignited and burned by the spark plug 27. It is done.

  On the other hand, the exhaust port of each cylinder is connected to the exhaust pipe 30 via a branch pipe for each cylinder. A catalyst 31 is provided in the exhaust pipe 30. An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 30. An air-fuel ratio sensor 33 for detecting the air-fuel ratio of the exhaust gas is installed on the upstream side of the catalyst 31. The air-fuel ratio sensor 33 is a so-called wide-area air-fuel ratio sensor, which can continuously detect an air-fuel ratio over a relatively wide range and outputs a signal having a value proportional to the air-fuel ratio.

  The engine system 1 includes an ECU (Electronic Control Unit) 50. The ECU 50 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage device. The ECU 50 performs various controls by executing a program stored in the ROM or the storage device. The ECU 50 is an example of an internal combustion engine control device that includes an execution unit, a gradual change processing unit, and a time shortening unit.

  The ECU 50 is electrically connected to the spark plug 27, the throttle valve 13, the injector 12, and the like. In addition, the ECU 50 does not show the air flow meter 15, the air-fuel ratio sensor 33, the crank angle sensor 25 that detects the crank angle of the internal combustion engine 20, the accelerator opening sensor that detects the accelerator opening, and other various sensors. It is electrically connected via an A / D converter or the like. The ECU 50 controls the ignition plug 27, the throttle valve 13, the injector 12 and the like so as to obtain a desired output based on the detection values of various sensors, etc., and performs ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  Further, the ECU 50 performs catalyst temperature increase control for increasing the temperature of the catalyst 31. Specifically, the ECU 50 sets an arbitrary cylinder among the four cylinders to a rich cylinder in which rich combustion in which the air-fuel ratio during combustion in the cylinder is smaller than the stoichiometric air-fuel ratio is executed. In addition, the ECU 50 sets the other cylinders as lean cylinders in which lean combustion is performed in which the air-fuel ratio during combustion in the cylinder is greater than the stoichiometric air-fuel ratio. Here, the purification capacity of the catalyst 31 becomes high when the air-fuel ratio of the exhaust gas flowing into the catalyst 31 is near the stoichiometric air-fuel ratio (stoichiometric, for example, 14.55). Therefore, the ECU 50 controls the fuel injection amount to each cylinder so that the rich combustion is executed in the rich cylinder, the lean combustion is executed in the lean cylinder, and the average of the air-fuel ratios of all the cylinders becomes the stoichiometric air-fuel ratio. . Specifically, the ECU 50 feedback-controls the fuel injection amount to each cylinder so that the air-fuel ratio detected by the air-fuel ratio sensor 33 matches the stoichiometric air-fuel ratio. Note that the air-fuel ratio of the exhaust gas flowing into the catalyst 31 may not coincide with the stoichiometric air-fuel ratio, and may be within a predetermined range including the stoichiometric air-fuel ratio.

  In addition, the ECU 50 executes a return process from the catalyst temperature increase control described above. FIG. 2 is a flowchart illustrating an example of the return process executed by the ECU 50. The process of FIG. 2 is executed when the catalyst temperature increase control is started.

  When the catalyst temperature increase control is started, the ECU 50 starts the catalyst temperature increase control start air-fuel ratio gradual change process for gradually changing the air-fuel ratio of each cylinder to the target air-fuel ratio at the time of catalyst temperature increase control (step S11). . For example, when the catalyst temperature increase control request is turned on at time t1 in FIG. 3, the ECU 50 starts the catalyst temperature increase control start air-fuel ratio gradual change process. As a result, as shown at times t1 to t2 in FIG. 3, the air-fuel ratios of the rich cylinder and the lean cylinder gradually change to the target air-fuel ratio at the time of catalyst temperature increase control. It is possible to suppress the occurrence of a torque shock accompanying a sudden change.

  Next, the ECU 50 determines whether or not there is an instantaneous ignition timing retardation request (step S13). The instantaneous ignition timing retardation request is an ignition timing retardation request other than the ignition timing retardation request for the purpose of suppressing knocking, for example, an ignition timing retardation request made to instantaneously reduce the torque. . Examples of the instantaneous ignition timing retardation request include an ignition timing retardation request for reducing shift shock and an ignition timing retardation request for suppressing torque before and after fuel cut.

  When there is no instantaneous ignition timing retardation request (step S13 / NO), the ECU 50 determines whether or not the air-fuel ratio of each cylinder has reached the target air-fuel ratio during the catalyst temperature increase control (step S15).

  When the air-fuel ratio of each cylinder has not reached the target air-fuel ratio at the time of catalyst temperature increase control (step S15 / NO), the process returns to step S13. On the other hand, when the air-fuel ratio of each cylinder reaches the target air-fuel ratio at the time of catalyst temperature increase control (step S15 / YES), the ECU 50 determines whether or not there is a request for retarding the instantaneous ignition timing (step S21).

  When there is no instantaneous ignition timing retardation request (step S21 / NO), the ECU 50 determines whether or not there is an end request for requesting the end of the catalyst temperature increase control (step S25). For example, as shown at time t2 in FIG. 3, the ECU 50 determines that an end request has been made when the catalyst temperature increase control request is turned off.

  When there is a request to end the catalyst temperature rise control (step S25 / YES), the ECU 50 sets the air-fuel ratio of each cylinder to the target sky set according to the operating state of the internal combustion engine 20 after the catalyst temperature rise control ends. An air-fuel ratio gradual change process at the end of catalyst temperature increase control for gradually changing to the fuel ratio is started (step S27). For example, when the catalyst temperature increase control request is turned OFF at time t2 in FIG. 3, the ECU 50 starts the air-fuel ratio gradual change process at the end of the catalyst temperature increase control. Then, the ECU 50 gradually changes the air-fuel ratio of each cylinder to the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20, as shown at times t2 to t3 in FIG.

  After the start of the catalyst temperature increase control end air-fuel ratio gradual change processing, the ECU 50 determines whether or not there is a request for retarding the instantaneous ignition timing (step S29). When there is no instantaneous ignition timing retardation request (step S29 / NO), the ECU 50 determines whether or not the air-fuel ratio of each cylinder has reached the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20 (step S33). ). In FIG. 3, for example, at time t3, the air-fuel ratio of each cylinder has reached the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20, so the determination in step S33 becomes YES at time t3.

  When the air-fuel ratio of each cylinder has not reached the target air-fuel ratio according to the operating state of the internal combustion engine 20 (step S33 / NO), the process returns to step S29, but the air-fuel ratio of each cylinder is the operation of the internal combustion engine 20. When the target air-fuel ratio corresponding to the state is reached (step S33 / YES), the ECU 50 ends the process of FIG. If there is no instantaneous ignition timing retardation request at the end of the catalyst temperature increase control, the air-fuel ratio of each cylinder gradually changes to the target air-fuel ratio corresponding to the internal combustion engine 20. It is possible to suppress the occurrence of a torque shock accompanying a change.

  On the other hand, after the start of the air-fuel ratio gradual change process at the end of catalyst temperature increase control in step S27, when there is an instantaneous ignition timing delay request (step S29 / YES), the ECU 50 performs the air-fuel ratio gradual change process at the end of catalyst temperature increase control. The operation is stopped, and the air-fuel ratio of each cylinder is set to the target air-fuel ratio according to the operating state of the internal combustion engine 20 (step S31). For example, it is assumed that the catalyst temperature increase control request is turned OFF at time t4 in FIG. 3, and thus the ECU 50 starts the air-fuel ratio gradual change process at the end of the catalyst temperature increase control (step S27). Here, as shown in FIG. 3, when the instantaneous ignition timing retardation request is turned on at time t5, the determination in step S29 is affirmed, and the ECU 50 stops the air-fuel ratio gradual change process at the end of the catalyst temperature increase control, The air-fuel ratio of each cylinder is set to a target air-fuel ratio corresponding to the operating state of the internal combustion engine 20 (step S31). Thereby, generation | occurrence | production of misfire can be suppressed.

  In addition, when there is no request | requirement of completion | finish of catalyst temperature rising control (step S25 / NO), it returns to step S21.

  When there is an instantaneous ignition timing retardation request (step S21 / YES) after the air-fuel ratio of each cylinder reaches the target air-fuel ratio at the time of catalyst temperature increase control (step S15 / YES), the ECU 50 causes the catalyst temperature increase control. The air-fuel ratio of each cylinder is set to the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20 without performing the ending air-fuel ratio gradual change process (step S23). For example, as shown at time t6 in FIG. 3, when the instantaneous ignition timing retardation request is turned ON, the ECU 50 does not perform the air-fuel ratio gradual change processing at the end of the catalyst temperature increase control, and sets the air-fuel ratio of each cylinder to the internal combustion engine. The target air-fuel ratio is set according to the operation state of 20. Thereby, generation | occurrence | production of misfire is suppressed.

  On the other hand, if there is an instantaneous ignition timing retardation request during the air-fuel ratio gradual change process at the start of the catalyst temperature increase control (step S13 / YES), the ECU 50 does not perform the air-fuel ratio gradual change process at the end of the catalyst temperature increase control. The air / fuel ratio of the cylinder is set to a target air / fuel ratio corresponding to the operating state of the internal combustion engine 20 (step S17). For example, as shown at time t7 in FIG. 3, when the instantaneous ignition timing retardation request is turned ON during the catalyst temperature increase control start air-fuel ratio gradual change process, the ECU 50 performs the catalyst temperature increase control end air-fuel ratio gradual change process. The air-fuel ratio of each cylinder is set to the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20 without performing the above. Thereby, generation | occurrence | production of misfire is suppressed.

  As described above in detail, the ECU 50 according to the present embodiment executes rich combustion in which the air-fuel ratio at the time of combustion in the cylinder is smaller than the stoichiometric air-fuel ratio in any cylinder among the plurality of cylinders of the internal combustion engine 20. Catalyst temperature increase control for increasing the temperature of the catalyst that purifies the exhaust gas from the plurality of cylinders by executing lean combustion in which the air-fuel ratio at the time of combustion in the cylinder is larger than the stoichiometric air-fuel ratio in the other cylinder, When a start request for temperature increase control is made, the air-fuel ratio at the time of combustion of each cylinder is gradually changed until it reaches the target air-fuel ratio at the time of catalyst temperature increase control execution, and when an end request for catalyst temperature increase control is made, The air-fuel ratio at the time of combustion of the cylinder is gradually changed until the target air-fuel ratio corresponding to the operating state of the internal combustion engine after the completion of the catalyst temperature increase control is reached, while the catalyst temperature increase control is being executed, or during the gradual change, Ignition timing retardation request other than the purpose of suppressing knocking is made If the time of the air-fuel ratio at the time of combustion in each cylinder until the target air-fuel ratio in accordance with the operating state of the internal combustion engine, is shorter than when there is no ignition timing delay request other than the purpose of knocking suppression. At the start and end of the catalyst temperature increase control, when there is no request for retarding the instantaneous ignition timing, the air-fuel ratio of each cylinder is the target air-fuel ratio at the time of catalyst temperature increase control or the target air-fuel ratio according to the operating state of the internal combustion engine 20 Therefore, torque shock associated with a sudden change in the air-fuel ratio can be suppressed. On the other hand, when there is a request for retarding the instantaneous ignition timing, the time until the air-fuel ratio of each cylinder is set to the target air-fuel ratio corresponding to the operating state of the internal combustion engine 20 is shorter than when there is no request for retarding the instantaneous ignition timing. Therefore, the occurrence of misfire can be suppressed.

  In the above embodiment, when the instantaneous ignition timing retardation request is made, the ECU 50 has set the target air-fuel ratio according to the operating state of the internal combustion engine 20 without performing the gradual change processing of the air-fuel ratio. When there is no instantaneous ignition timing retardation request for increasing the gradual change speed (increasing the gradient of gradual change) and setting the air-fuel ratio of each cylinder to the target air-fuel ratio according to the operating state of the internal combustion engine 20 May be shortened.

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention, and It is apparent from the above description that various other embodiments are possible within the scope.

1 engine system 20 internal combustion engine 31 catalyst 50 ECU (control device of internal combustion engine, execution unit, gradual change processing unit, time reduction unit)

Claims (1)

Of a plurality of cylinders of an internal combustion engine, rich combustion in which the air-fuel ratio at the time of combustion in the cylinder is smaller than the stoichiometric air-fuel ratio is executed in any cylinder, and the air-fuel ratio at the time of combustion in the cylinder is the stoichiometric air-fuel ratio in the other cylinders An execution unit for executing a catalyst temperature increase control for increasing the temperature of a catalyst for purifying exhaust gas from the plurality of cylinders, and performing lean combustion larger than
When a request to start the catalyst temperature increase control is made, the air-fuel ratio at the time of combustion of each cylinder is gradually changed until it reaches the target air-fuel ratio at the time of execution of the catalyst temperature increase control. A gradual change processing unit that gradually changes the air-fuel ratio at the time of combustion of each cylinder until it reaches a target air-fuel ratio according to the operating state of the internal combustion engine after the completion of the catalyst temperature increase control;
When an ignition timing retardation request other than the purpose of suppressing knocking is made during execution of the catalyst temperature increase control or during the gradual change, the air-fuel ratio at the time of combustion of each cylinder is set to the operating state of the internal combustion engine. A time shortening unit that shortens the time until the corresponding target air-fuel ratio is reached as compared with the case where there is no ignition timing retardation request other than the purpose of suppressing knocking;
A control device for an internal combustion engine.

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