JP6686863B2 - Control device for internal combustion engine - Google Patents

Description

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

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

  In Patent Document 1, in any of the plurality of cylinders, rich combustion is performed in which an in-cylinder combustion air-fuel ratio is smaller than the theoretical air-fuel ratio, and in other cylinders, in-cylinder combustion air-fuel ratio is the theoretical air-fuel ratio. By executing lean combustion that is larger than the fuel ratio and controlling the fuel injection amount in each cylinder so that the average of the air-fuel ratios of a plurality of cylinders becomes the theoretical air-fuel ratio, the catalyst temperature rise is promoted.

JP 2012-57492 A

  During execution of the catalyst temperature raising control in which rich combustion and lean combustion are performed in different cylinders, combustion control parameters such as the air-fuel ratio and ignition timing differ for each cylinder. For this reason, during the execution of the catalyst temperature raising control, there is a possibility that the engine rotation variation may differ from that in the case where the catalyst temperature raising control is not executed. Therefore, when the misfire is determined based on the amount of rotation fluctuation of the engine, the accuracy of the misfire determination may decrease due to the execution of the catalyst temperature increase control.

  Therefore, the control device for the internal combustion engine disclosed in the present specification is intended to suppress a decrease in the determination accuracy of the misfire determination due to the catalyst temperature increase control in which the rich combustion and the lean combustion are performed in different cylinders. It is an issue.

In order to solve such a problem, the control device for an internal combustion engine disclosed in the present specification has a plurality of cylinders of the internal combustion engine in which any cylinder has an air-fuel ratio smaller than the theoretical air-fuel ratio during combustion in the cylinder. A catalyst temperature raising control that causes rich combustion to be performed and lean combustion to be performed in another cylinder in which the air-fuel ratio at the time of combustion in the cylinder is greater than the theoretical air-fuel ratio to raise the temperature of the catalyst that purifies exhaust gas from the plurality of cylinders. An execution unit that executes the above, a fluctuation amount calculation unit that calculates a rotation fluctuation amount of the internal combustion engine, and a misfire determination unit that determines that a misfire has occurred when the rotation fluctuation amount is larger than a first threshold value. When the rotational fluctuation amount exceeds a second threshold value that is smaller than the first threshold value during execution of the catalyst temperature increase control, the air-fuel ratio in the cylinder that executes the rich combustion during the catalyst temperature increase control and the aforesaid Willingness to perform lean burning The difference between the air-fuel ratio, and a control unit to be smaller than the difference when the amount the rotational fluctuation is lower than the second threshold value, the second threshold value, due to the catalyst Atsushi Nobori control in, It is a threshold value that is set while the catalyst temperature increasing control is being executed so that the accuracy of the misfire determination does not decrease due to the rotation fluctuation amount becoming larger than when the catalyst temperature increasing control is not executed. .

  According to the control device for an internal combustion engine disclosed in the present specification, it is possible to suppress deterioration of the determination accuracy of misfire determination due to the catalyst temperature increase control that executes rich combustion and lean combustion in different cylinders. it can.

FIG. 1 is a schematic diagram showing a configuration of an engine system to which a control device for an internal combustion engine according to an embodiment is applied. FIG. 2 is a flowchart showing an example of the air-fuel ratio changing process 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 air-fuel ratio changing process.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of the respective parts may not be shown to be completely the same as the actual ones. In addition, in some drawings, details may be omitted.

  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 showing a configuration of an engine system 1 to which a control device for an internal combustion engine 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 burns a mixture of fuel and air inside a combustion chamber 23 formed in a cylinder block 21 and reciprocates a piston 24 in the combustion chamber 23 to generate power. The internal combustion engine 20 is a multi-cylinder engine for a vehicle (only one cylinder is shown), and in the present embodiment, it is a four-cylinder engine including cylinders # 1 to # 4. 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 that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a cam shaft (not shown). An ignition 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. The 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 in the intake port of each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. This air-fuel mixture is sucked into the combustion chamber 23 when the intake valve Vi is opened, compressed by the piston 24, and ignited by the ignition plug 27. To be

  On the other hand, the exhaust port of each cylinder is connected to the exhaust pipe 30 via a branch pipe for each cylinder. The exhaust pipe 30 is provided with a catalyst 31. 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 exhaust gas is installed on the upstream side of the catalyst 31. The air-fuel ratio sensor 33 is a so-called wide-range air-fuel ratio sensor, is capable of continuously detecting 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 CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, and the like. The ECU 50 executes various programs by executing programs stored in the ROM and the storage device. The ECU 50 is an example of a control device for an internal combustion engine that includes an execution unit, a fluctuation amount calculation unit, a misfire determination unit, and a control unit.

  The ignition plug 27, the throttle valve 13, the injector 12 and the like described above are electrically connected to the ECU 50. The ECU 50 is not shown with the air flow meter 15, the air-fuel ratio sensor 33, the crank angle sensor 25 for detecting the crank angle of the internal combustion engine 20, the accelerator opening sensor for detecting 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, and the ignition timing, the fuel injection amount, the fuel injection timing, and the throttle opening. Control degree etc.

  Further, the ECU 50 determines whether or not a misfire has occurred, based on the detection value of the crank angle sensor 25. More specifically, the ECU 50 first measures the time T required for the crankshaft to rotate by 30 ° CA starting from the compression top dead center in the combustion stroke of each cylinder. Then, the difference (= T-Ti) between this time T and the previously measured time (Ti) is calculated as the rotation fluctuation amount ΔT. Then, when the rotation variation amount ΔT is larger than the misfire determination threshold value which is an example of the first threshold value, it is determined that a misfire has occurred.

  Further, the ECU 50 executes catalyst temperature raising control for raising the temperature of the catalyst 31. Specifically, the ECU 50 sets any one of the four cylinders as a rich cylinder in which rich combustion is performed in which the air-fuel ratio during combustion is smaller than the stoichiometric air-fuel ratio. Further, the ECU 50 sets the other cylinders to lean cylinders in which lean combustion is performed in which the air-fuel ratio at the time of combustion in the cylinder is larger than the theoretical 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 such that the rich combustion is performed in the rich cylinder and the lean combustion is performed in the lean cylinder, and the average of the air-fuel ratios of all the cylinders becomes the theoretical 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 theoretical air-fuel ratio. The air-fuel ratio of the exhaust gas flowing into the catalyst 31 does not have to match the stoichiometric air-fuel ratio and may be within a predetermined range including the stoichiometric air-fuel ratio.

  Further, when the catalyst temperature raising control is started, the ECU 50 executes an air-fuel ratio changing process for changing the air-fuel ratios of the rich cylinder and the lean cylinder based on the rotation fluctuation amount ΔT of the internal combustion engine 20.

  FIG. 2 is a flowchart showing an example of the air-fuel ratio changing process executed by the ECU 50. The process of FIG. 2 is started when the catalyst temperature increase request is turned on.

  When the catalyst temperature increase request is turned on, the ECU 50 controls the fuel injection amount to each cylinder so that the air-fuel ratios of the rich cylinder and the lean cylinder become the target air-fuel ratio initial value that is predetermined for each of the rich cylinder and the lean cylinder. Yes (step S11). For example, in FIG. 3, when the catalyst temperature increase request is turned on at time t1, the ECU 50 controls the lean cylinder so that the air-fuel ratio of the lean cylinder becomes the lean cylinder target air-fuel ratio initial value larger than the theoretical air-fuel ratio. Control the fuel injection amount. Further, the ECU 50 controls the fuel injection amount into the rich cylinder so that the air-fuel ratio of the rich cylinder becomes the rich cylinder target air-fuel ratio initial value smaller than the theoretical air-fuel ratio.

  Next, the ECU 50 determines whether or not the rotation fluctuation amount ΔT of the internal combustion engine 20 is less than the catalyst temperature increase control determination threshold value that is smaller than the misfire determination threshold value (step S13). The catalyst temperature increase control determination threshold value is an example of a second threshold value.

  When the rotation variation amount ΔT is less than the catalyst temperature increase control determination threshold value (step S13 / YES), the ECU 50 continues the catalyst temperature increase control at the current air-fuel ratio (step S15). For example, at times t1 to t2 in FIG. 3, the rotation variation amount ΔT is less than the catalyst temperature increase control determination threshold value, so the ECU 50 performs the catalyst temperature increase control so that the air-fuel ratio of each cylinder becomes the target air-fuel ratio initial value. continue.

  On the other hand, when the rotation variation amount ΔT is equal to or more than the catalyst temperature increase control determination threshold value (step S13 / NO), the ECU 50 determines that the rotation variation amount ΔT is the difference between the rich-cylinder air-fuel ratio and the lean cylinder air-fuel ratio. It is made smaller than the difference when it is less than the catalyst temperature rise control determination threshold value (step S17). For example, it is assumed that the rotation fluctuation amount ΔT becomes equal to or larger than the catalyst temperature increase control determination threshold value at time t2 in FIG. In this case, the ECU 50 increases the fuel injection amount from the current fuel injection amount in the lean cylinder so that the combustion air-fuel ratio becomes smaller than the current air-fuel ratio, and in the rich cylinder, the combustion air-fuel ratio is currently increased. The fuel injection amount is reduced from the current fuel injection amount so as to be larger than the air-fuel ratio of. Thereby, the difference between the air-fuel ratio of the rich cylinder and the air-fuel ratio of the lean cylinder is smaller than the difference (for example, the difference between times t1 and t2) when the rotation variation amount ΔT is less than the catalyst temperature increase control determination threshold value. Become. By reducing the difference between the air-fuel ratio of the rich cylinder and the air-fuel ratio of the lean cylinder, the rotational fluctuation amount ΔT due to the catalyst temperature increase control is suppressed as shown after time t2 in FIG. It is possible to suppress a decrease in the accuracy of misfire determination due to. Further, it is possible to achieve the maximum catalyst temperature raising effect within a range that does not affect the determination accuracy of the misfire determination.

  After executing step S15 or step S17, the ECU 50 determines whether or not the catalyst temperature increase request is turned off (step S19). When the catalyst temperature increase request remains ON (step S19 / NO), the process returns to step S13. On the other hand, when the catalyst temperature increase request is turned off (step S19 / YES), the ECU 50 returns the target air-fuel ratio of each cylinder to the initial value (step S21), and ends the process of FIG.

  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 in-cylinder combustion is smaller than the theoretical air-fuel ratio in any of the plurality of cylinders of the internal combustion engine 20. Then, lean combustion is performed in the other cylinders in which the in-cylinder air-fuel ratio at the time of combustion is larger than the stoichiometric air-fuel ratio, and catalyst temperature raising control is performed to raise the temperature of the catalyst 31 that purifies exhaust gas from the plurality of cylinders. Further, the ECU 50 calculates the rotation variation amount ΔT of the internal combustion engine 20, and determines that the misfire has occurred when the rotation variation amount ΔT is larger than the misfire determination threshold value (first threshold value). Further, if the rotation variation amount ΔT exceeds the catalyst temperature increase control determination threshold value (second threshold value) smaller than the misfire determination threshold value during execution of the catalyst temperature increase control, the ECU 50 performs rich combustion during the catalyst temperature increase control. The difference between the air-fuel ratio in the rich cylinder that executes the above and the air-fuel ratio in the lean cylinder that executes the lean combustion is set to be smaller than the difference when the rotation fluctuation amount ΔT is less than the catalyst temperature increase control determination threshold value. As a result, the rotation variation amount ΔT due to the catalyst temperature increase control is suppressed, and thus it is possible to prevent the determination accuracy of the misfire determination from decreasing due to the catalyst temperature increase control. Further, it is possible to achieve the maximum catalyst temperature raising effect within a range that does not affect the determination accuracy of the misfire determination.

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

20 Internal Combustion Engine 31 Catalyst 50 ECU (Control Device for Internal Combustion Engine)

Claims (1)

Among multiple cylinders of an internal combustion engine, in any cylinder, the air-fuel ratio during combustion in the cylinder is smaller than the theoretical air-fuel ratio, and rich combustion is performed, and in other cylinders, the air-fuel ratio during combustion in the cylinder is the theoretical air-fuel ratio. An executing unit that executes a leaner combustion that is larger than the above, and executes a catalyst temperature raising control that raises the temperature of a catalyst that purifies exhaust gas from the plurality of cylinders;
A fluctuation amount calculation unit for calculating the rotation fluctuation amount of the internal combustion engine,
A misfire determination unit that determines that a misfire has occurred when the rotation fluctuation amount is larger than a first threshold value;
When the rotation variation amount exceeds a second threshold value that is smaller than the first threshold value during execution of the catalyst temperature increase control, the air-fuel ratio and the lean air-fuel ratio in the cylinder that executes the rich combustion during the catalyst temperature increase control A control unit that makes a difference from the air-fuel ratio in the cylinder that executes combustion smaller than the difference when the rotation fluctuation amount is less than the second threshold value;
Equipped with
The second threshold value is set so that the misfire determination accuracy does not decrease due to the rotation variation amount being larger than that in the case where the catalyst temperature raising control is not executed due to the catalyst temperature raising control. It is a threshold value that is set while the catalyst temperature raising control is being executed.
Control device for internal combustion engine.

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