JP7196391B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to an internal combustion engine control apparatus for controlling an internal combustion engine including an exhaust purification device for purifying exhaust gas emitted from a plurality of cylinders and a fuel injection valve provided for each of the plurality of cylinders.

For example, Patent Literature 1 describes a control device that corrects the injection amount in order to feedback-control the detection value of an air-fuel ratio sensor on the upstream side of an exhaust purification catalyst (exhaust purification device) to a target value. This control device performs dither control processing to make the air-fuel ratio of some cylinders richer than the stoichiometric air-fuel ratio and to make the air-fuel ratio of the remaining cylinders leaner than the stoichiometric air-fuel ratio when there is a request to raise the temperature of the exhaust purification device. to run.

JP 2016-169665 A

By the way, when the dither control is executed, the detected value of the air-fuel ratio sensor may fluctuate due to the dither control, which may deteriorate the controllability of the air-fuel ratio.

In order to solve the above problems, a control device for an internal combustion engine controls an internal combustion engine that includes an exhaust purification device that purifies exhaust gas emitted from a plurality of cylinders, and a fuel injection valve that is provided for each of the plurality of cylinders. Some of the plurality of cylinders are set as rich combustion cylinders in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and a cylinder other than the one of the plurality of cylinders is selected. , a dither control process for operating the fuel injection valve in order to create a lean combustion cylinder in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio; A feedback process for correcting the injection amount injected from the injection valve and a reduction process for making the gain of the feedback process smaller when the dither control process is executed than when the dither control process is not executed are executed.

In the above configuration, the feedback control gain is made smaller when the dither control process is being executed than when it is not being executed. As a result, even if the air-fuel ratio detected by the air-fuel ratio sensor due to the dither control process fluctuates significantly compared to when the dither control process is not executed, the stability of the feedback control is impaired. It is possible to prevent a situation from occurring, and in turn to prevent deterioration of controllability of the air-fuel ratio.

1 is a diagram showing a control device and an internal combustion engine according to one embodiment; FIG. FIG. 4 is a flowchart showing the procedure of processing executed by the control device according to the embodiment; FIG.

An embodiment of a control device for an internal combustion engine will be described below with reference to the drawings.
In the internal combustion engine 10 shown in FIG. 1 , air drawn from an intake passage 12 flows through a supercharger 14 into a combustion chamber 16 of each cylinder. The combustion chamber 16 is provided with a fuel injection valve 18 for injecting fuel and an ignition device 20 for generating spark discharge. In the combustion chamber 16, the mixture of air and fuel is combusted, and the combusted mixture is discharged to the exhaust passage 22 as exhaust. Downstream of the supercharger 14 in the exhaust passage 22, a three-way catalyst 24 having an oxygen storage capacity is provided.

The control device 30 controls the internal combustion engine 10 and operates operating units of the internal combustion engine 10 such as the fuel injection valve 18 and the ignition device 20 in order to control the control amounts (torque, exhaust components, etc.) of the internal combustion engine 10 . At this time, the control device 30 determines the air-fuel ratio Af detected by the air-fuel ratio sensor 40 on the upstream side of the three-way catalyst 24, the output signal Scr of the crank angle sensor 44, and the intake air amount Ga detected by the air flow meter 46. refer. The control device 30 includes a CPU 32, a ROM 34, and a RAM 36. The CPU 32 executes a program stored in the ROM 34 to control the control amount.

FIG. 2 shows one of the processes executed by the control device 30. As shown in FIG. The processing shown in FIG. 2 is implemented by the CPU 32 repeatedly executing a program stored in the ROM 34, for example, at predetermined intervals. In the following description, step numbers are represented by numerals prefixed with "S".

In the series of processes shown in FIG. 2, the CPU 32 calculates the base injection amount Qb based on the rotation speed NE calculated based on the output signal Scr of the crank angle sensor 44 and the intake air amount Ga (S10). The base injection amount Qb is an open-loop manipulated variable that is a manipulated variable for open-loop controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber 16 to the target air-fuel ratio. Next, the CPU 32 determines whether or not dither control is in effect (S12). When the CPU 32 determines that dither control is not being performed (S12: NO), the CPU 32 substitutes the normal gain KpH for the proportional gain Kp of the air-fuel ratio feedback control (S14). On the other hand, when the CPU 32 determines that dither control is being performed (S12: YES), it substitutes the dither gain KpL for the proportional gain Kp (S16). The dithering gain KpL is a value smaller than the normal gain KpH.

When the processes of S14 and S16 are completed, the CPU 32 calculates a feedback manipulated variable KAF, which is a manipulated variable for feedback-controlling the air-fuel ratio Af, which is a feedback controlled variable, to the target value Af* (S18). More specifically, the CPU 32 sets the sum of the output values of the proportional element, the integral element, and the differential element to the input of the difference Δ between the target value Af* and the air-fuel ratio Af as the correction ratio δ of the base injection amount Qb, and performs the feedback operation. Let the quantity KAF be "1+δ". Then, the CPU 32 substitutes the value obtained by multiplying the base injection amount Qb by the feedback operation amount KAF into the required injection amount Qd (S20).

Next, the CPU 32 determines whether or not there is a request to raise the temperature of the three-way catalyst 24 (S22). In this embodiment, if the logical sum of the three-way catalyst 24 warm-up request and the sulfur poisoning recovery processing execution request is true, it is determined that there is a temperature increase request. judge. Here, the warm-up request for the three-way catalyst 24 is based on the condition (a) that the integrated value InGa of the intake air amount Ga from the start of the internal combustion engine 10 is equal to or greater than the first specified value Inth1, and 2. It is assumed that this occurs when the logical AND with the condition (a) that it is equal to or less than the specified value Inth2 is true. Here, the second specified value Inth2 is greater than the first specified value Inth1. Condition (a) is a condition under which it is determined that the temperature of the upstream end of the three-way catalyst 24 is the activation temperature. Condition (a) is a condition under which the three-way catalyst 24 as a whole is not yet activated. On the other hand, it is assumed that the execution request for the sulfur poisoning recovery process is made when the amount of sulfur poisoning is equal to or greater than a predetermined amount. Here, the CPU 32 calculates the amount of sulfur poisoning based on the integrated value of the required injection amount Qd in a process different from that shown in FIG.

If the CPU 32 determines that there is no temperature increase request (S22: NO), it substitutes the required injection amount Qd for the injection amount command value Q* (S24). Then, the CPU 32 outputs an operation signal MS2 to the fuel injection valve 18 so that the fuel injection valve 18 injects an amount of fuel corresponding to the injection amount command value Q* (S26).

On the other hand, if the CPU 32 determines that there is a temperature increase request (S22: YES), it calculates and outputs a correction request value (injection amount correction request value α) for the required injection amount Qd (S28). The injection amount correction request value α targets the air-fuel ratio of the air-fuel mixture in which the components of the entire exhaust gas emitted from each of the cylinders #1 to #4 of the internal combustion engine 10 are combusted in all of the cylinders #1 to #4. This is the correction amount of the required injection amount Qd required by the dither control for making the air-fuel ratio of the air-fuel mixture to be combusted different between the cylinders while making it the same as in the case of using the air-fuel ratio. Here, in the dither control according to the present embodiment, one of the first cylinder #1 to the fourth cylinder #4 is a rich combustion cylinder in which the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio. and the remaining three cylinders are lean-burn cylinders in which the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. Then, the injection amount in the rich burn cylinder is set to "1+α" times the requested injection amount Qd, and the injection amount in the lean burn cylinder is set to "1-(α/3)" times the requested injection amount Qd. According to the setting of the injection amount for the lean-burn cylinder and the rich-burn cylinder, if the amount of air charged to each of the cylinders #1 to #4 is the same, then from each cylinder #1 to #4 of the internal combustion engine 10, The components of the entire discharged exhaust gas can be made equivalent to the case where the air-fuel ratio of the air-fuel mixture to be combusted in all of the cylinders #1 to #4 is set as the target air-fuel ratio. According to the setting of the injection amount, if the amount of air charged to each of the cylinders #1 to #4 is the same, the reciprocal of the average value of the fuel-air ratio of the air-fuel mixture to be combusted in each cylinder is is the target air-fuel ratio. The fuel-air ratio is the reciprocal of the air-fuel ratio.

Specifically, the CPU 32 variably sets the injection amount correction request value α based on the rotation speed NE and the load factor KL that define the operating point of the internal combustion engine 10 . Here, the load factor KL is a parameter indicating the amount of air charged into the combustion chamber 16, and is calculated by the CPU 32 based on the intake air amount Ga. The load factor KL is the ratio of the inflow air amount per cylinder per combustion cycle to the reference inflow air amount. Incidentally, the reference inflow air amount may be set variably according to the rotation speed NE.

Then, the CPU 32 determines whether or not the cylinder targeted for fuel injection is a rich combustion cylinder (S30). When the CPU 32 determines that it is a rich combustion cylinder (S30: YES), it substitutes "Qd·(1+α)" for the injection amount command value Q* (S32), and proceeds to the process of S26. On the other hand, if the CPU 32 determines that it is a lean combustion cylinder (S30: NO), it substitutes "Qd·{1−(α/3)}" into the injection amount command value Q* (S34), The process proceeds to S26.

It should be noted that the CPU 32 temporarily terminates the series of processes shown in FIG. 2 when the process of S26 is completed.
The operation and effects of this embodiment will be described below.

The CPU 32 executes dither control when a temperature increase request for the three-way catalyst 24 is generated. In this case, since the exhaust components of the rich burn cylinder and the exhaust components of the lean burn cylinder are different, the air-fuel ratio Af detected by the air-fuel ratio sensor 40 may fluctuate more than when the dither control is not executed. be. In that case, when the rotation speed NE changes, the control period of the air-fuel ratio feedback control and the fluctuation of the air-fuel ratio Af due to dither interfere with each other, and the feedback control falls into resonance and divergence, and the control of the air-fuel ratio control performance may decrease. Therefore, in this embodiment, when dither control is executed, the proportional gain Kp of feedback control is set to a smaller value than when dither control is not executed. As a result, compared to the case where the proportional gain Kp is not reduced, the feedback control is less likely to diverge, and thus a decrease in the controllability of the air-fuel ratio control can be suppressed.

Incidentally, in the above embodiment, the air-fuel ratio sensor 40 senses the exhaust components in the portion where the exhaust gases emitted from the cylinders #1 to #4 are merged. On the upstream side, it is conceivable to provide an air-fuel ratio sensor for sensing the components of the exhaust gas discharged from each cylinder. In this case, if the air-fuel ratio detected by each air-fuel ratio sensor is feedback-controlled to the target value of the cylinder, it is possible to prevent the feedback control from falling into resonance and divergence. However, in that case, the control becomes complicated.

<Correspondence>
Correspondence relationships between the items in the above embodiment and the items described in the "Means for Solving the Problems" column are as follows. The exhaust purification device corresponds to the three-way catalyst 24, the dither control process corresponds to the processes of S26 to S34, the feedback process corresponds to the processes of S18 and S20, and the reduction process corresponds to the processes of S12 to S16. handle.

<Other embodiments>
This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be implemented in combination with each other within a technically consistent range.

In the above embodiment, the proportional gain Kp is set to a smaller value when dither control is performed than when it is not performed, but the present invention is not limited to this. For example, in addition to the proportional gain Kp, the integral gain Ki may be set to a small value.For example, in addition to the proportional gain Kp, the differential gain Kd may be set to a small value.Further, in addition to the proportional gain Kp, the integral gain Ki and Differential gain Kd may be set to a small value. It is also not essential to set the proportional gain Kp to a small value. For example, only the integral gain Ki may be set to a small value, or only the differential gain Kd may be set to a small value. It should be noted that it is not essential that the correction ratio δ is the sum of the output values of the proportional element, the integral element and the differential element. and the sum of the differential elements, or, for example, the output value of the proportional element. Alternatively, for example, it may be the sum of an integral element and a differential element.

In the above embodiment, whether or not the air-fuel ratio Af detected by the air-fuel ratio sensor 40 is the output value itself of the air-fuel ratio sensor 40 was not specifically described. The resulting value may be used as the air-fuel ratio Af. For example, using the current output value AOUT(n), the previous air-fuel ratio Af(n-1), and a number N larger than "1", the current air-fuel ratio Af(n) is It can be realized by adding "{AOUT(n)-Af(n-1)}/N" to the air-fuel ratio Af(n-1). Even in this case, for example, when setting a time constant that allows detection of air-fuel ratio fluctuations for each cylinder to some extent, the air-fuel ratio Af fluctuates due to dither control, and feedback control becomes unstable. Therefore, it is effective to reduce the gain of feedback processing. In addition, as the injection amount correction request value α is increased, it becomes more difficult to remove fluctuations due to dither control from the air-fuel ratio Af by low-pass filter processing, so feedback control may become unstable even when the injection amount correction request value α is large. Therefore, it is effective to reduce the gain of feedback processing.

- The internal combustion engine is not limited to a four-cylinder internal combustion engine. Further, the fuel injection valve is not limited to one that injects fuel into the combustion chamber 16 , and may be one that injects fuel into the intake passage 12 .

Reference Signs List 10 Internal combustion engine 12 Intake passage 14 Supercharger 16 Combustion chamber 18 Fuel injection valve 20 Ignition device 22 Exhaust passage 24 Three-way catalyst 30 Control device 32 CPU, 34 -- ROM, 36 -- RAM, 40 -- air-fuel ratio sensor, 44 -- crank angle sensor, 46 -- air flow meter.

Claims (1)

Controlling an internal combustion engine comprising an exhaust purification device for purifying exhaust gas emitted from a plurality of cylinders and a fuel injection valve provided for each of the plurality of cylinders,
Some of the plurality of cylinders are rich combustion cylinders in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and cylinders other than the some of the plurality of cylinders have an air-fuel ratio. a dither control process for operating the fuel injection valve to create a lean combustion cylinder in which is leaner than the stoichiometric air-fuel ratio;
A feedback process for correcting the injection amount injected from the fuel injection valve to feedback-control the air-fuel ratio detected by an air-fuel ratio sensor provided upstream of the exhaust purification device to a target value;
and a control device for an internal combustion engine that performs a reduction process for making the gain of the feedback process smaller when the dither control process is being performed than when the dither control process is not being performed.

Images