JP2017150412A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a time necessary for raising a temperature of a catalyst while avoiding that combustion becomes instable, in catalyst temperature rise control accompanied by the gradual variation processing of an air-fuel ratio.SOLUTION: When starting catalyst temperature rise control, a control device of an internal combustion engine gradually changes an air-fuel ratio of each cylinder at a prescribed gradual change speed until the air-fuel ratio reaches a target air-fuel ratio. When the catalyst temperature rise control which is performed at a combination of a rich cylinder whose combustion deterioration index becomes smaller than a first threshold and a lean cylinder is performed once again in the same trip, the control device raises the gradual change speed more than the last gradual change time. When the catalyst temperature rise control at a combination of a rich cylinder whose combustion deterioration index becomes equal to or larger than the first threshold and smaller than a second threshold and the lean cylinder is performed once again in the same trip, the control device makes the gradual change speed coincide with the last gradual change speed. When the catalyst temperature rise control is performed at a combination of a rich cylinder whose deterioration index reaches the second threshold or larger and the lean cylinder once again in the same trip, the control device retards the gradual change speed more than the last gradual change speed.SELECTED DRAWING: Figure 3

Description

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

  It is a noble metal as an exhaust gas purification catalyst for simultaneously and efficiently purifying harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines such as automobiles. A three-way catalyst having platinum (Pt), palladium (Pd), and rhodium (Rh) as main active species (catalyst metal) is widely used.

  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.

  In Patent Document 2, when the rich cylinder that performs rich combustion is switched to the lean cylinder that performs lean combustion, or vice versa, the air-fuel ratio is gradually changed from the rich side to the lean side or vice versa at a predetermined gradual change rate. I am letting.

JP 2012-57492 A JP 2009-215924 A

  In catalyst temperature rise control in which rich combustion and lean combustion are executed in separate cylinders, when the air-fuel ratio is gradually changed, if the air-fuel ratio gradually changes, combustion at the target air-fuel ratio is started in each cylinder. Since the time required until the temperature of the catalyst is increased, the time required for raising the catalyst temperature can be shortened, but there is a risk that the combustion in each cylinder becomes temporarily unstable. On the other hand, if the gradual change rate of the air-fuel ratio is slowed, the time until the combustion at the target air-fuel ratio starts in each cylinder becomes longer. There is a possibility that the time required for raising the temperature of the catalyst may become longer.

  In view of this, the control device for an internal combustion engine disclosed in the present specification makes combustion unstable in each cylinder in catalyst temperature rise control in which rich combustion and lean combustion are executed in separate cylinders by gradually changing the air-fuel ratio. It is an object to reduce the period of temperature rise of the catalyst while avoiding the above.

  In order to solve such a problem, an internal combustion engine control device disclosed in the present specification includes a catalyst provided in an exhaust passage of the internal combustion engine, an operating state detection unit that detects an operating state of the internal combustion engine, A calculation unit that calculates a combustion deterioration index indicating whether or not the combustion state of the internal combustion engine has deteriorated based on the operation state of the internal combustion engine detected by the operation state detection unit, and any of a plurality of cylinders This cylinder is set to a rich cylinder that executes rich combustion in which the air-fuel ratio during combustion in the cylinder is smaller than the stoichiometric air-fuel ratio, and the other cylinders are set to lean combustion where the air-fuel ratio during combustion in the cylinder is greater than the stoichiometric air-fuel ratio A setting unit for setting the lean cylinder to perform the combustion, and the rich cylinder burns the rich cylinder, the lean cylinder burns the lean combustion, and the fuel to each cylinder is set so that the average of the air-fuel ratios of all the cylinders becomes the stoichiometric air-fuel ratio. And a controller that executes a catalyst temperature increase control for increasing the temperature of the catalyst by controlling an injection amount, and the controller performs the catalyst temperature increase control in any combination of the rich cylinder and the lean cylinder. When the engine is started, the air-fuel ratio of each cylinder is gradually changed at a predetermined gradual change rate until the air-fuel ratio of each cylinder reaches the respective target air-fuel ratio, and the rich engine whose combustion deterioration index becomes less than the first threshold value. When the catalyst temperature increase control in the combination of the cylinder and the lean cylinder is executed again in the same trip, the gradual change speed is set as the rich cylinder and the lean whose combustion deterioration index is less than the first threshold. The rich cylinder and the lean cylinder in which the catalyst temperature increase control in combination with the cylinder is faster than the gradual change speed at the time of the previous execution, and the combustion deterioration index is not less than the first threshold value and less than the second threshold value. When When the catalyst temperature increase control in combination is executed again in the same trip, the gradual change speed is determined based on the rich cylinder and the lean cylinder in which the combustion deterioration index is equal to or higher than the first threshold value and lower than the second threshold value. The catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder in the combination of the rich cylinder and the lean cylinder in which the combustion deterioration index is equal to or greater than a second threshold is set to be the same as the gradual change speed when the catalyst temperature increase control was previously performed. When the temperature control is executed again in the same trip, the gradual change speed is set to the previous time when the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder whose combustion deterioration index is equal to or greater than the second threshold is performed. Slower than the gradual change rate when executed.

  According to the control device for an internal combustion engine disclosed in the present specification, in the catalyst temperature increase control in which rich combustion and lean combustion are executed in separate cylinders by gradually changing the air-fuel ratio, combustion becomes unstable in each cylinder. It is possible to reduce the period of the temperature rise of the catalyst while avoiding this.

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 showing an example of catalyst temperature increase control executed by the ECU. FIG. 3 is a flowchart illustrating an example of a gradual change speed changing process executed by the ECU. FIG. 4 shows the relationship between the gradual change speed, the change in the air-fuel ratio of each cylinder, and the combustion deterioration index when there is no record of performing the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder. It is a time chart which shows an example. FIG. 5 shows the relationship between the gradual change speed, the change in the air-fuel ratio of each cylinder, and the combustion deterioration index when there is a track record of performing the catalyst temperature increase control in a combination of the rich cylinder and the lean cylinder. It is a time chart which shows an example.

  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 three-way 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 three-way 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 a calculation unit, a setting unit, and a control 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 crank angle sensor 25 is an example of an operation state detection unit that detects an operation state of the internal combustion engine 20. 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 executes catalyst temperature increase control for increasing the temperature of the three-way catalyst 31. FIG. 2 is a flowchart showing an example of catalyst temperature increase control executed by the ECU 50. The processing in FIG. 2 is executed at a predetermined calculation cycle (for example, every 0.1 to 0.3 ms).

  First, the ECU 50 determines whether or not the catalyst temperature increase request is ON (step S11). When the catalyst temperature increase request is OFF (step S11 / NO), the ECU 50 ends the process of FIG.

  On the other hand, when the catalyst temperature increase request is ON (step S11 / YES), the ECU 50 causes the rich cylinder that performs rich combustion in which the air-fuel ratio during combustion in the cylinder is smaller than the stoichiometric air-fuel ratio, and the air during combustion in the cylinder. A combination with a lean cylinder that performs lean combustion in which the fuel ratio is larger than the stoichiometric air-fuel ratio is set (step S13). For example, the ECU 50 sets an arbitrary cylinder (for example, cylinder # 1) among the four cylinders # 1 to # 4 as a rich cylinder and sets other cylinders (for example, cylinders # 2 to # 4) as lean cylinders. Set.

  Subsequently, the ECU 50 starts calculation and recording of the cycle-to-cycle variation and the inter-cylinder variation of the engine rotation speed based on the detection value of the crank angle sensor 25 (step S14). The cycle-to-cycle variation of the engine rotation speed and the cylinder-to-cylinder variation of the engine rotation speed are examples of a combustion deterioration index that indicates whether or not the combustion state of the internal combustion engine 20 has deteriorated. The cycle-to-cycle fluctuation of the engine rotation speed means a difference in engine rotation speed between cycles when a crank angle from 0 degree to 720 degrees is defined as one cycle. Further, the inter-cylinder fluctuation of the engine rotation speed means a difference in engine rotation speed between the cylinders in the combustion stroke. The ECU 50 records the calculated cycle-to-cycle variation of the engine speed and the variation between the cylinders in association with the combination of the lean cylinder and the rich cylinder.

  After step S14, the ECU 50 performs a gradual change process in which the air-fuel ratio of each cylinder is gradually changed at a predetermined gradual change speed to the respective target air-fuel ratio (step S15), and the air-fuel ratio of each cylinder is changed to the target air-fuel ratio. When the fuel ratio is reached, the operation at the target air-fuel ratio is continued (step S17). Here, the three-way catalyst 31 simultaneously purifies NOx, HC, and CO when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 31 is near the stoichiometric air-fuel ratio (stoichiometric, for example, 14.55). Therefore, the ECU 50 performs the rich combustion in the rich cylinder and the lean combustion in the lean cylinder during the processes of steps S15 and S17, so that the average of the air-fuel ratios of all the cylinders becomes the stoichiometric air-fuel ratio. The fuel injection amount to each cylinder is controlled. 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.

  Subsequently, the ECU 50 determines whether or not a predetermined number of cycles have been operated with the current combination of rich and lean cylinders (step S19).

  When the predetermined number of cycles is operated with the combination of the current rich cylinder and the lean cylinder (step S19 / YES), the ECU 50 changes the combination of the rich cylinder and the lean cylinder (step S21). For example, the ECU 50 sets an arbitrary cylinder (for example, cylinder # 2) among the four cylinders # 1 to # 4 as a rich cylinder, and sets other cylinders (for example, cylinders # 1, # 3, and # 4). Set to lean cylinder.

  When the combination of the rich cylinder and the lean cylinder is changed, the ECU 50 executes a gradual change process until the air-fuel ratio of each cylinder reaches the target air-fuel ratio (step S15), and then continues operation at the target air-fuel ratio. (Step S17).

  Incidentally, the ECU 50 determines whether or not the catalyst temperature increase request has been turned off (step S23) when the predetermined number of cycles has not been operated with the combination of the current rich cylinder and the lean cylinder (step S19 / NO). When the catalyst temperature increase request is not turned OFF (step S23 / NO), the process returns to step S17, and the operation is continued with the current combination of the rich cylinder and the lean cylinder.

  On the other hand, when the catalyst temperature increase request is turned OFF (step S23 / YES), the ECU 50 ends the calculation and recording of the cycle-to-cycle fluctuation and the cylinder-to-cylinder fluctuation of the engine rotation speed (step S25), and ends the process of FIG. To do.

  As described above, the ECU 50 according to the present embodiment performs the gradual change process (FIG. 2: Step S15) at the start of the catalyst temperature increase control and when the combination of the rich cylinder and the lean cylinder is changed during the catalyst temperature increase control. )I do. At this time, as described above, the slower the gradual change rate, the longer the time required to start combustion at the target air-fuel ratio in each cylinder, and the longer the time required for catalyst temperature rise. Further, if the gradual change rate is too fast, the combustion in each cylinder may be temporarily unstable.

  Therefore, the ECU 50 according to the present embodiment executes the following gradual change speed changing process at the start of the gradual change process (FIG. 2: step S15), thereby avoiding instability of combustion and preventing the cylinder from becoming unstable. The time required to raise the catalyst temperature is reduced by shortening the time until combustion is started at each target air-fuel ratio.

  FIG. 3 is a flowchart illustrating an example of the gradual change speed changing process executed by the ECU 50. The process of FIG. 3 is executed when the gradual change process is started, that is, when the catalyst temperature increase control is started, and when the combination of the rich cylinder and the lean cylinder is changed during the catalyst temperature increase control.

  First, the ECU 50 determines whether or not there is a track record of executing the catalyst temperature increase control with the combination of the currently set rich cylinder and lean cylinder within the same trip (step S51). In the present embodiment, one trip refers to a period from one start to stop of the engine.

  If there is no track record of executing the catalyst temperature increase control with the combination of the currently set rich cylinder and lean cylinder (step S51 / NO), the ECU 50 sets the gradual change speed to a predetermined default value ( Step S53). For example, it is assumed that the catalyst temperature increase request is turned ON at time t1 in FIG. 4, and the ECU 50 sets the cylinder # 1 as a rich cylinder and sets the cylinders # 2 to # 4 as lean cylinders. Here, when there is no track record of executing the catalyst temperature increase control in the same trip with the combination of the cylinder # 1 as the rich cylinder and the cylinders # 2 to # 4 as the lean cylinder, the ECU 50, as shown in FIG. The gradual change speed is set to the default value Vdef. Further, for example, it is assumed that the catalyst temperature increase request is turned ON at time t4 in FIG. 4, and the ECU 50 sets the cylinder # 2 as a rich cylinder and sets the cylinders # 1, # 3, and # 4 as lean cylinders. Here, when there is no track record of executing the catalyst temperature increase control in the same trip in a combination where the cylinder # 2 is a rich cylinder and the cylinders # 1, # 3, and # 4 are lean cylinders, the ECU 50 is shown in FIG. Thus, the gradual change speed is set to Vdef which is a default value. In the case of FIG. 4, since the gradual change speed is the same, when the cylinder # 1 is set as a rich cylinder, a period T1 (t2-t1) until each cylinder reaches the respective target air-fuel ratio, and the cylinder # 2 The period T2 (t5-t4) until each cylinder reaches its target air-fuel ratio when is set as a rich cylinder is the same.

  Returning to FIG. 3, when there is a track record of executing the catalyst temperature increase control with the currently set combination of the rich cylinder and the lean cylinder (step S51 / YES), the ECU 50 performs the previous catalyst temperature increase control with the combination. It is determined whether or not the cycle-to-cycle variation of the engine rotation speed when executed is less than the first cycle threshold, and whether the variation in the engine rotation speed is less than the first cylinder threshold (step S55). The first inter-cycle threshold and the first inter-cylinder threshold are examples of the first threshold, and are values that can be used to determine that the internal combustion engine 20 is operating safely.

  If the determination in step S55 is YES, the ECU 50 makes the gradual change speed faster than the gradual change speed when the previous catalyst temperature increase control was executed with the combination of the currently set rich cylinder and lean cylinder (step S55). S57).

  For example, when the catalyst temperature increase control is first executed in a combination where the cylinder # 1 is a rich cylinder and the cylinders # 2 to # 4 are lean cylinders, the engine speed varies between cycles as shown in FIG. It is assumed that it is less than the first threshold and the inter-cylinder variation of the engine speed is less than the first inter-cylinder threshold. Here, as shown in FIG. 5, it is assumed that the catalyst temperature increase request is turned ON at time t7 in the same trip, and the ECU 50 sets a combination in which cylinder # 1 is a rich cylinder and cylinders # 2 to # 4 are lean cylinders. . In this case, as shown in FIG. 5, the ECU 50 sets the gradual change speed to a gradual change speed V1 that is faster than the gradual change speed Vdef when the previous catalyst temperature increase control was executed. As a result, the period T3 (t8-t7) until the start of combustion at each target air-fuel ratio in each cylinder can be made shorter than the period T1 in FIG. can do.

  On the other hand, if the determination in step S55 is NO, the ECU 50 determines that the cycle-to-cycle variation in the engine speed when the catalyst temperature increase control was previously performed with the combination of the currently set rich cylinder and lean cylinder is the second cycle. It is determined whether it is less than the threshold value and the inter-cylinder variation of the engine rotation speed is less than the second inter-cylinder threshold value (step S56). Here, the second threshold value between cycles and the second threshold value between cylinders are examples of the second threshold value, and are values that can be determined that the internal combustion engine 20 is safely operated within an allowable range.

  If the determination in step S56 is YES, the ECU 50 sets the gradual change speed to be the same as the gradual change speed when the previous catalyst temperature increase control was executed with the combination of the currently set rich cylinder and lean cylinder (step S56). S59). A gradual change that minimizes the period until the start of combustion at the target air-fuel ratio in each cylinder within a range in which the previous gradual change speed can safely operate the internal combustion engine 20 in the combination of the current rich cylinder and lean cylinder. This is because it is a variable speed.

  On the other hand, if the determination in step S56 is NO, the ECU 50 makes the gradual change speed slower than the gradual change speed when the previous catalyst temperature increase control was executed with the combination of the rich cylinder and the lean cylinder that are currently set. (Step S61).

  For example, as shown in FIG. 4, when the catalyst temperature increase control is executed for the first time in a combination where the cylinder # 2 is a rich cylinder and the cylinders # 1, # 3, and # 4 are lean cylinders, the engine speed varies between cycles. Is greater than or equal to the second threshold value between cycles, and the inter-cylinder variation in engine speed is also greater than or equal to the second threshold value between cylinders. Here, as shown in FIG. 5, the catalyst temperature increase request is turned ON at time t9 in the same trip, and the ECU 50 has a combination in which cylinder # 2 is a rich cylinder and cylinders # 1, # 3, and # 4 are lean cylinders. Suppose that it is set. In this case, as shown in FIG. 5, the ECU 50 sets the gradual change rate to a gradual change rate V2 that is slower than the gradual change rate Vdef when the previous catalyst temperature increase control was executed. As a result, it is possible to avoid unstable combustion in each cylinder.

  After executing step S53, S57, S59, or S61, the ECU 50 stores the currently set combination of the rich cylinder and the lean cylinder and the gradually changing speed set in step S53, S57, S59, or S61. (Step S63), the gradual change process is executed at the gradual change speed (Step S65).

As described above in detail, the engine system 1 according to the present embodiment includes the three-way catalyst 31 provided in the exhaust pipe 30 of the internal combustion engine 20, and the crank angle sensor 25 that detects the crank angle of the internal combustion engine 20. Based on the crank angle detected by the crank angle sensor 25, the cycle fluctuation and the cylinder fluctuation of the engine rotation speed are calculated, and the air-fuel ratio at the time of combustion in any cylinder among the plurality of cylinders is theoretically calculated. The rich cylinder that performs rich combustion smaller than the air-fuel ratio is set, the other cylinders are set to lean cylinders that perform lean combustion in which the air-fuel ratio during combustion in the cylinder is greater than the stoichiometric air-fuel ratio, and the rich cylinders are rich The fuel is burned, the lean cylinders are lean burned, the fuel injection amount to each cylinder is controlled so that the average of the air-fuel ratios of all the cylinders becomes the stoichiometric air-fuel ratio, and the temperature of the three-way catalyst 31 is raised. Comprising the ECU50 to perform temperature increase control, the. When the ECU 50 starts the catalyst temperature increase control in any combination of the rich cylinder and the lean cylinder, the ECU 50 sets the air-fuel ratio of each cylinder to a predetermined level until the air-fuel ratio of each cylinder reaches the target air-fuel ratio. Change gradually at a gradual change rate. The ECU 50 has the same catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder in which the cycle-to-cycle fluctuation and the cylinder-to-cylinder fluctuation of the engine speed are less than the first threshold value between cycles and the first threshold value between cylinders, respectively. When it is executed again in the trip, the gradual change speed is made faster than the gradual change speed when the catalyst temperature increase control in the combination was executed last time. As a result, the period until the start of combustion at each target air-fuel ratio in each cylinder can be made shorter than in the previous control, so that the time required for catalyst temperature rise can be shortened. Further, the ECU 50 determines whether the engine rotation speed cycle-to-cycle variation and the cylinder-to-cylinder variation are more than the first threshold value between cycles and less than the second threshold value between cycles and between the first threshold value between cylinders and less than the second threshold value between cylinders. When the catalyst temperature increase control in combination with the cylinder is executed again in the same trip, the gradual change speed is made the same as the gradual change speed when the catalyst temperature increase control in the combination was executed last time. As a result, it is possible to minimize the period until the combustion at each target air-fuel ratio is started in each cylinder within a range where the internal combustion engine 20 can be safely operated. Further, the ECU 50 has a cycle-to-cycle variation in engine rotation speed that is greater than or equal to a second threshold value between cycles,
Alternatively, when the catalyst temperature increase control is executed again in the same trip in the combination of the rich cylinder and the lean cylinder in which the inter-cylinder fluctuation of the engine rotation speed is equal to or greater than the second threshold value between the cylinders, The catalyst temperature increase control at is made slower than the gradual change speed at the previous execution. As a result, it is possible to avoid unstable combustion in each cylinder.

  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.

  In the above-described embodiment, the ECU 50 determines the deterioration of combustion using the cycle-to-cycle variation of the engine speed and the cylinder-to-cylinder variation of the engine rotation speed. Combustion deterioration may be determined using either one of the fluctuations between the cylinders.

1 Engine system (control device for internal combustion engine)
20 Internal combustion engine 25 Crank angle sensor (operating state detector)
30 Exhaust pipe (exhaust passage)
50 ECU (setting unit, control unit, calculation unit)

Claims (1)

A catalyst provided in the exhaust passage of the internal combustion engine;
An operating state detector for detecting an operating state of the internal combustion engine;
A calculation unit that calculates a combustion deterioration index indicating whether or not the combustion state of the internal combustion engine is deteriorated based on the operation state of the internal combustion engine detected by the operation state detection unit;
Of the multiple cylinders, any cylinder is set to a rich cylinder that performs rich combustion in which the air-fuel ratio during combustion in the cylinder is smaller than the stoichiometric air-fuel ratio, and the other cylinders have theoretical air-fuel ratio during combustion in the cylinder A setting unit for setting a lean cylinder that performs lean combustion larger than the air-fuel ratio;
A catalyst for causing the rich cylinder to perform the rich combustion, causing the lean cylinder to perform the lean combustion, and controlling the fuel injection amount to each cylinder so that the average of the air-fuel ratios of all the cylinders becomes the stoichiometric air-fuel ratio, thereby raising the temperature of the catalyst. A control unit for executing temperature rise control;
With
The controller is
When the catalyst temperature increase control in any combination of the rich cylinder and the lean cylinder is started, the air-fuel ratio of each cylinder is changed to a predetermined gradual change rate until the air-fuel ratio of each cylinder becomes the respective target air-fuel ratio. Gradually change the
When the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder whose combustion deterioration index is less than the first threshold is executed again in the same trip, the gradually changing speed is set as the combustion deterioration index. Is made faster than the gradual change speed when the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder, which has become less than the first threshold, is executed last time,
When the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder whose combustion deterioration index is greater than or equal to the first threshold and less than the second threshold is executed again in the same trip, the gradual change speed is , The combustion deterioration index is the same as the gradual change speed at the time when the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder with the first threshold value or more and less than the second threshold value was previously executed,
When the catalyst temperature increase control in the combination of the rich cylinder and the lean cylinder in which the combustion deterioration index is equal to or greater than a second threshold is executed again in the same trip, the gradually changing speed is set to the combustion deterioration index. A control device for an internal combustion engine that makes the catalyst temperature increase control in a combination of the rich cylinder and the lean cylinder, for which is equal to or greater than a second threshold value, slower than a gradual change speed when it was previously executed.

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