JP7600840B2 - Control device for internal combustion engine - Google Patents

Description

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

For example, as seen in the following Patent Document 1, a control device that executes dither control processing is described. Dither control processing is processing in which some of the cylinders of an internal combustion engine are rich burn cylinders in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the remaining cylinders are lean burn cylinders in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. This control device makes the overall components of the exhaust gas discharged from the multiple cylinders equivalent to when the air-fuel ratio of the mixture to be burned by each of the multiple cylinders is set to a target air-fuel ratio. This control device also reduces the gain for feedback control of the detected value of the air-fuel ratio to the target value while dither control is being performed.

JP 2019-85948 A

The inventors considered executing a recovery process to supply excess oxygen to the exhaust system relative to the amount that reacts properly with the unburned fuel, in order to prevent the purification ability of a catalyst installed in the exhaust system from decreasing due to the influence of unburned fuel. Specifically, they considered stopping the supply of fuel to some of the multiple cylinders and continuing the supply of fuel to the remaining cylinders. In that case, it is not possible to accurately set a target value for the detection value of the air-fuel ratio sensor. However, if air-fuel ratio feedback control is stopped while the recovery process is being executed, inconveniences such as a decrease in controllability thereafter occur.

Means for solving the above problems and their effects will be described below.
a feedback process for correcting the injection amount by the fuel injection valve in response to a feedback control of a value obtained by feedback-controlling a value obtained by filtering a detection value of the air-fuel ratio sensor to a target value; a feedback process for correcting the injection amount by the fuel injection valve in response to an output of the feedback process; a partial stop process for stopping the supply of fuel from the fuel injection valve to some of the plurality of cylinders and continuing the supply of fuel from the fuel injection valve to the remaining cylinders of the plurality of cylinders; and a correction contribution rate reduction process for reducing a change in an output value of the filter process relative to a change in the detection value when the partial stop process is executed.

In the above configuration, a response delay occurs between the start of the partial stop processing and the change in the components in the exhaust. Also, a response delay occurs between the stop of the partial stop processing and the change in the components in the exhaust. Therefore, it is difficult to specify the period during which the partial stop processing makes it impossible to define a correct value as the target value or requires a large change in the target value. When the feedback processing is stopped for a certain period, the controllability of the air-fuel ratio may decrease depending on how the period is specified. Also, when the feedback processing is stopped, problems such as how to correct the amount of correction immediately after resuming the feedback processing may occur. Therefore, in the above configuration, the change in the output value of the filter processing relative to the change in the detection value is reduced over the period during which the partial stop processing is executed. This makes it possible to easily reduce the effect of the partial stop processing on the feedback processing, thereby suppressing the decrease in the controllability of the air-fuel ratio due to the partial stop processing.

1 is a diagram showing a drive system of a vehicle according to an embodiment; FIG. 2 is a block diagram showing a process executed by a control device according to the embodiment. 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment.

Hereinafter, an embodiment will be described with reference to the drawings.
As shown in Fig. 1, an internal combustion engine 10 has four cylinders #1 to #4. A throttle valve 14 is provided in an intake passage 12 of the internal combustion engine 10. A port injection valve 16 that injects fuel into an intake port 12a, which is a downstream portion of the intake passage 12, is provided. Air drawn into the intake passage 12 and fuel injected from the port injection valve 16 flow into a combustion chamber 20 when an intake valve 18 opens. Fuel is injected into the combustion chamber 20 from an in-cylinder injection valve 22. A mixture of air and fuel in the combustion chamber 20 is combusted in response to a spark discharge from an ignition plug 24. The combustion energy generated at this time is converted into the rotational energy of a crankshaft 26.

The air-fuel mixture burned in the combustion chamber 20 is discharged as exhaust gas into the exhaust passage 30 when the exhaust valve 28 opens. The exhaust passage 30 is provided with a three-way catalyst 32 with oxygen storage capacity and a gasoline particulate filter (GPF 34). In this embodiment, the GPF 34 is assumed to be a filter that collects particulate matter (PM) and supports a three-way catalyst with oxygen storage capacity.

The crankshaft 26 is mechanically connected to the carrier C of the planetary gear mechanism 50 that constitutes the power split device. The rotating shaft 52a of the first motor generator 52 is mechanically connected to the sun gear S of the planetary gear mechanism 50. The rotating shaft 54a of the second motor generator 54 and the drive wheels 60 are mechanically connected to the ring gear R of the planetary gear mechanism 50. An AC voltage is applied to the terminals of the first motor generator 52 by the inverter 56. An AC voltage is applied to the terminals of the second motor generator 54 by the inverter 58.

The control device 70 operates the operation parts of the internal combustion engine 10, such as the throttle valve 14, the port injection valve 16, the in-cylinder injection valve 22, and the spark plug 24, to control the torque and exhaust component ratio as the controlled variable of the internal combustion engine 10. The control device 70 also operates the inverter 56 to control the rotation speed, which is the controlled variable of the first motor generator 52. The control device 70 also operates the inverter 58 to control the torque, which is the controlled variable of the second motor generator 54. FIG. 1 shows the operation signals MS1 to MS6 of the throttle valve 14, the port injection valve 16, the in-cylinder injection valve 22, the spark plug 24, and the inverters 56 and 58. In order to control the controlled variable of the internal combustion engine 10, the control device 70 refers to the intake air amount Ga detected by the air flow meter 80, the output signal Scr of the crank angle sensor 82, and the water temperature THW detected by the water temperature sensor 84. The control device 70 also refers to an upstream air-fuel ratio Afu detected by an upstream air-fuel ratio sensor 86 provided upstream of the three-way catalyst 32, and a downstream air-fuel ratio Afd detected by a downstream air-fuel ratio sensor 88 provided downstream of the three-way catalyst 32. The control device 70 also refers to an output signal Sm1 of a first rotation angle sensor 90 that detects the rotation angle of the first motor-generator 52 in order to control the control amount of the first motor-generator 52. The control device 70 also refers to an output signal Sm2 of a second rotation angle sensor 92 that detects the rotation angle of the second motor-generator 54 in order to control the control amount of the second motor-generator 54. The control device 70 also refers to an accelerator operation amount ACCP, which is the amount of depression of the accelerator pedal detected by an accelerator sensor 94.

The control device 70 includes a CPU 72, a ROM 74, and a peripheral circuit 76, which are capable of communicating with each other via a communication line 78. Here, the peripheral circuit 76 includes a circuit that generates a clock signal that regulates the internal operation, a power supply circuit, a reset circuit, and the like. The control device 70 controls the control amount by the CPU 72 executing a program stored in the ROM 74.

In the following, the fuel injection processing performed by the control device 70 will be explained in the following order: basic processing, recovery processing for the three-way catalyst 32, and parameter setting processing depending on whether or not recovery processing is performed.

(Basic processing)
2 shows the process executed by the control device 70. The process shown in FIG.

The base injection amount calculation process M10 is a process for calculating a base injection amount Qb, which is a base value of the amount of fuel for making the air-fuel ratio of the mixture in the combustion chamber 20 the target air-fuel ratio, based on the charging efficiency η. In detail, when the charging efficiency η is expressed as a percentage, for example, the base injection amount calculation process M10 may be a process for calculating the base injection amount Qb by multiplying the fuel amount QTH per 1% of the charging efficiency η for making the air-fuel ratio the target air-fuel ratio by the charging efficiency η. The base injection amount Qb is a fuel amount calculated to control the air-fuel ratio to the target air-fuel ratio based on the amount of air charged in the combustion chamber 20. Incidentally, in this embodiment, the target air-fuel ratio is the theoretical air-fuel ratio. The charging efficiency η is calculated by the CPU 72 based on the intake air amount Ga and the rotation speed NE. The rotation speed NE is calculated by the CPU 72 based on the output signal Scr.

Filter processing M12 is a process for calculating an average air-fuel ratio Afa that suppresses changes in the upstream air-fuel ratio Afu. Here, the average air-fuel ratio Afa is an exponential moving average processing value of the upstream air-fuel ratio Afu. In detail, each time the upstream air-fuel ratio Afu is newly sampled, the average air-fuel ratio Afa is updated to the sum of the value obtained by multiplying the average air-fuel ratio Afa by a weighting coefficient α and the value obtained by multiplying the upstream air-fuel ratio Afu by "1-α".

The feedback correction coefficient calculation process M14 is a process for calculating and outputting the feedback correction coefficient KAF. The feedback correction coefficient KAF is a value obtained by adding "1" to the correction ratio δ of the base injection amount Qb, which is a feedback manipulated variable that is a manipulated variable for feedback-controlling the average air-fuel ratio Afa to the target value Afu*.

In detail, the deviation calculation process M16 outputs the difference between the average air-fuel ratio Afa and the target value Afu*. The normal deviation correction term calculation process M18 is a process that outputs the sum of the output values of the proportional element and the differential element, which input the output value of the deviation calculation process M16, and the output value of the integral element, which holds and outputs an integrated value according to the difference. The high-pass filter M20 is a process that extracts and outputs high-frequency components from the output value of the deviation calculation process M16. The proportional gain multiplication process M22 is a process that multiplies the output value of the high-pass filter M20 by the proportional gain Kph. The addition process M24 is a process that adds the output value of the proportional gain multiplication process M22 to the output value of the normal deviation correction term calculation process M18 to calculate the correction ratio δ. The correction coefficient calculation process M26 is a process that sets the feedback correction coefficient KAF to a value obtained by adding "1" to the correction ratio δ.

The switching process M30 is a process that alternately switches the target value Afu* from one of two values, the feedback rich air-fuel ratio Afr and the feedback lean air-fuel ratio Afl, to the other. The switching process M30 is a process that switches the target value Afu* to the feedback rich air-fuel ratio Afr when the logical sum of the following conditions is true:

The condition is that the oxygen storage amount OS is equal to or greater than the upper limit value OSfl for switching.
The downstream air-fuel ratio Afd is equal to or greater than "Afs+Δ". Here, the stoichiometric point Afs corresponds to the theoretical air-fuel ratio. The minute amount Δ is, for example, about 0.1 to 0.3.

The switching process M30 is a process for switching the target value Afu* to the feedback lean air-fuel ratio Afl when the logical sum of the following conditions is true:
The condition is that the oxygen storage amount OS is equal to or less than the switching lower limit value OSfr.

The condition is that the downstream air-fuel ratio Afd is equal to or less than "Afs-Δ".
The switching process M30 includes a process for calculating the oxygen storage amount OS based on the intake air amount Ga and the upstream air-fuel ratio Afu.

The switching process M30 aims to control the oxygen storage amount OS of the three-way catalyst 32 to a value significantly smaller than "1/2" of the maximum value. This is because there is a concern that a large amount of NOx will flow out downstream of the three-way catalyst 32 if the oxygen storage amount of the three-way catalyst 32 is large. If the oxygen storage amount of the three-way catalyst 32 is small, there is a concern that unburned fuel will flow out downstream of the three-way catalyst 32, but this amount is small compared to the amount of NOx that flows out. And even if a small amount of unburned fuel flows out downstream of the three-way catalyst 32, this is purified by the three-way catalyst equipped in the GPF 34.

The required injection amount calculation process M40 calculates the amount of fuel required in one combustion cycle (required injection amount Qd) by multiplying the base injection amount Qb by the feedback correction coefficient KAF.

The injector operation process M42 is a process that outputs an operation signal MS2 to the port injector 16 to operate the port injector 16, and outputs an operation signal MS3 to the in-cylinder injector 22 to operate the in-cylinder injector 22. In particular, the injector operation process M42 is a process that sets the amount of fuel injected from the port injector 16 and the in-cylinder injector 22 within one combustion cycle to an amount that corresponds to the required injection amount Qd.

(Recovery process of three-way catalyst 32)
As described above, when the oxygen storage amount of the three-way catalyst 32 is controlled to be small, there is a risk of HC poisoning, in which unburned fuel adheres to the surface of the three-way catalyst 32. When HC poisoning occurs, the purification ability of the unburned fuel decreases. Therefore, in this embodiment, a recovery process from HC poisoning is executed.

Figure 3 shows the procedure for recovery from HC poisoning. The process shown in Figure 3 is realized by the CPU 72 repeatedly executing a program stored in the ROM 74, for example at a predetermined interval. In the following, the step number of each process is given by a number preceded by "S."

In the series of processes shown in FIG. 3, the CPU 72 first determines whether the execution flag F is "1" (S10). When the execution flag F is "1", it indicates that recovery processing is being performed, and when the execution flag F is "0", it indicates that recovery processing is not being performed. When the CPU 72 determines that the execution flag F is "0" (S10: NO), it determines whether a fuel cut process is being performed (S12). The fuel cut process is a process that stops the supply of fuel to all cylinders #1 to #4. The conditions for executing the fuel cut process are that the torque required for the internal combustion engine 10 is equal to or lower than a predetermined value, such as when the accelerator pedal is released, and the rotation speed NE is equal to or higher than a predetermined speed.

When the CPU 72 determines that the fuel cut process is not being performed (S12: NO), it assigns the value obtained by adding the intake air amount Ga to the accumulated air amount InGa to the accumulated air amount InGa (S14). The accumulated air amount InGa is a quantity that has a correlation with the accumulated value of the injection amount, and is therefore a variable that indicates the degree of HC poisoning. Next, the CPU 72 determines whether the accumulated air amount InGa is equal to or greater than the threshold value InGath (S16). This process is a process for determining whether or not to perform HC poisoning recovery process. The threshold value InGath is set to the accumulated air amount InGa when the purification rate of unburned fuel becomes the lower limit of the allowable range due to HC poisoning of the three-way catalyst 32.

If the CPU 72 determines that the amount of air is equal to or greater than the threshold value InGath (S16: YES), it assigns "1" to the execution flag F and forcibly sets the required injection amount Qd for cylinder #1 to "0" (S18). If the CPU 72 completes the processing of S18 or makes a positive judgment in the processing of S12, it assigns "0" to the accumulated air amount InGa (S20).

On the other hand, when the CPU 72 determines that the execution flag F is "1" (S10: YES), it determines whether or not the cylinder #1 is at compression top dead center (S22). When the CPU 72 determines that the cylinder #1 is at compression top dead center (S22: YES), it increments a counter C that counts the number of times fuel supply to the cylinder #1 has been stopped by the processing of S18 (S24). The CPU 72 then determines whether or not the counter C is equal to or greater than a predetermined value Cth (S26). This processing is for determining whether or not to stop the recovery processing. The predetermined value Cth may be, for example, a value of "5" or less, or may be a value of "10" or less.

When it is determined that the difference is equal to or greater than the predetermined value Cth (S26: YES), the CPU 72 sets the execution flag F to "0" (S28).
It should be noted that the CPU 72 temporarily ends the series of processes shown in FIG. 3 when it completes the processes of S20 and S28, or when a negative determination is made in the processes of S16, S22, and S26.

(Parameter setting process depending on whether recovery process is performed or not)
In the above recovery process, the amount of oxygen in the exhaust gas discharged from the cylinders #1 to #4 into the exhaust passage 30 becomes excessive relative to the amount that reacts properly with the unburned fuel. Therefore, the target value Afu* when the recovery process is not being executed is not an appropriate value when the recovery process is being executed. Moreover, when the amount of oxygen is excessively large, the upstream air-fuel ratio Afu is guarded by the upper limit value of the output of the upstream air-fuel ratio sensor 86, and may be smaller than the actual value. Therefore, it is difficult to calculate an appropriate feedback correction coefficient KAF by the feedback correction coefficient calculation process M14. Therefore, in this embodiment, when the recovery process is executed, the settings of the parameters of the filter process M12 and the feedback correction coefficient calculation process M14 are changed.

Figure 4 shows the procedure for the process of the above change. The process shown in Figure 4 is realized by the CPU 72 repeatedly executing a program stored in the ROM 74, for example, at a predetermined interval.

In the series of processes shown in FIG. 4, the CPU 72 first determines whether or not the logical sum of the following condition (a) and condition (b) is true (S30).
Condition (A): The execution flag F is set to "1".

Condition (A): A predetermined time has elapsed since the execution flag F was switched from "1" to "0".
This process is a process for determining whether or not the period is one in which the influence of the recovery process affects the air-fuel ratio feedback control. Here, condition (B) determines the end point of the period in which the influence affects. The predetermined time in condition (B) is set according to the response delay time until the influence of the stop of the recovery process affects the upstream air-fuel ratio sensor 86. Condition (A) determines the start point of the period in which the influence affects. Immediately after the start of the recovery process, there is no influence on the upstream air-fuel ratio Afu by the recovery process due to the response delay caused by the flow of exhaust gas from cylinder #1 to the vicinity of the upstream air-fuel ratio sensor 86. However, since it is difficult to accurately grasp the timing at which the influence occurs, the start point of the period in which the influence affects is specified by condition (A).

When the CPU 72 determines that the logical sum is true (S30: YES), it assigns the recovery coefficient αL to the weighting coefficient α and the recovery gain KphL to the proportional gain Kph (S32). On the other hand, when the CPU 72 determines that the logical sum is false (S30: NO), it assigns the basic coefficient α0 to the weighting coefficient α and the normal gain Kph0 to the proportional gain Kph (S34). The basic coefficient α0 is smaller than the recovery coefficient αL, and the normal gain Kph0 is larger than the recovery gain KphL.

When the processes of S32 and S34 are completed, the series of processes shown in FIG. 4 is temporarily terminated. Incidentally, in the process of S32, a filter process may be performed to reduce the change in the downstream air-fuel ratio Afd input to the switching process M30.

Here, the operation and effects of this embodiment will be described.
When the cumulative air amount InGa is equal to or greater than the threshold value InGa, the CPU 72 determines that the purification rate of the unburned fuel by the three-way catalyst 32 reaches the lower limit of the allowable range due to HC poisoning, and executes the recovery process. The CPU 72 then increases the weighting coefficient α for a predetermined time period from the start of the recovery process to the end of the recovery process. This reduces the change in the average air-fuel ratio Afa relative to the change in the upstream air-fuel ratio Afu, thereby preventing the feedback correction coefficient KAF from changing significantly due to the recovery process. The CPU 72 also reduces the proportional gain Kph for a predetermined period of time. This reduces the output value of the proportional gain multiplication process M22. This prevents the correction ratio δ from becoming excessively large due to the start of the recovery process.

Moreover, the specified period is relatively short. Therefore, compared to stopping the feedback process only for a specified period, it is easier to simplify the control by maintaining the continuity of the air-fuel ratio feedback control.

According to the present embodiment described above, the following actions and effects can be obtained.
(1) The process of S32 is continued for a predetermined time after the recovery process is stopped. This makes it possible to take into account the delay until the exhaust gas discharged from the cylinders #1 to #4 affects the upstream air-fuel ratio Afu.

<Correspondence>
The correspondence between the matters in the above embodiment and the matters described in the "Means for solving the problem" section is as follows: The base injection amount calculation process corresponds to the base injection amount calculation process M10. The feedback process corresponds to the feedback correction coefficient calculation process M14 and the required injection amount calculation process M40. The injector operation process corresponds to the injector operation process M42. The partial stop process corresponds to the process of S18. The correction contribution rate reduction process corresponds to the process of S32.

<Other embodiments>
This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

- The variable indicating the degree of HC poisoning is not limited to the accumulated air amount InGa. For example, it may be the accumulated value of the charging efficiency η. It is also not limited to a variable indicating the amount of air taken into the cylinder, but may be, for example, the accumulated value of the injection amount, or in other words, any accumulated value of the load. It is not limited to the accumulated value of the load for all periods other than the time of fuel cut processing. For example, it may be the accumulated value of the load only when the load is equal to or above a certain value.

The filtering process M12 is not limited to the exponential moving average process, but may be a process using a first-order lag filter, for example.
The feedback process is not limited to the process exemplified in FIG. 2. For example, the high-pass filter M20, the proportional gain multiplication process M22, and the addition process M24 may be deleted. In that case, the output value of the normal deviation correction term calculation process M18 becomes the correction ratio δ. The normal deviation correction term calculation process M18 is not limited to a process that uses the output value of the deviation calculation process M16 as an input and outputs the sum of the output values of the proportional element, the integral element, and the differential element as an output value. For example, the process may use the sum of the output value of the proportional element and the output value of the integral element as an output value. Also, the process may use the output value of the integral element as an output value. The input of the high-pass filter M20 is not limited to the difference between the average air-fuel ratio Afa and the target value Afu*. For example, the input may be the difference between the upstream air-fuel ratio Afu and the target value Afu*.

- The condition for switching the target value Afu* to the feedback lean air-fuel ratio Afl is not limited to the logical sum of the oxygen storage amount OS being equal to or less than the switching lower limit value OSfr and the downstream air-fuel ratio Afd being equal to or less than "Afs-Δ". For example, it may be that the oxygen storage amount OS is equal to or less than the switching lower limit value OSfr. Also, it may be that the downstream air-fuel ratio Afd is equal to or less than "Afs-Δ".

- The condition for switching the target value Afu* to the feedback rich air-fuel ratio Afr is not limited to the logical sum of the oxygen storage amount OS being equal to or greater than the switching upper limit value OSfl and the downstream air-fuel ratio Afd being equal to or greater than "Afs+Δ". For example, it may be that the oxygen storage amount OS is equal to or greater than the switching upper limit value OSfl. Also, it may be that the downstream air-fuel ratio Afd is equal to or greater than "Afs+Δ".

10: internal combustion engine 30: exhaust passage 32: three-way catalyst 34: GPF
50... planetary gear mechanism 70... control device 86... upstream air-fuel ratio sensor

Claims (1)

The present invention is applied to an internal combustion engine equipped with an air-fuel ratio sensor in an exhaust passage,
the air-fuel ratio sensor is provided in a portion of the exhaust passage through which exhaust gas discharged from each of a plurality of cylinders of the internal combustion engine passes,
Executes a base injection amount calculation process, a feedback process, an injection valve operation process, a partial stop process, and a correction contribution rate reduction process,
the base injection amount calculation process is a process for calculating a base value of an injection amount by a fuel injection valve that supplies fuel to the cylinder,
the feedback processing is processing for correcting an injection amount by the fuel injection valve with respect to the base value so as to feedback control a filtered value of the detection value of the air-fuel ratio sensor to a target value,
the injector operation process is a process for operating the fuel injector in response to an output of the feedback process,
the partial stop processing is processing of stopping the supply of fuel from the fuel injection valve to some of the plurality of cylinders and continuing the supply of fuel from the fuel injection valve to the remaining cylinders of the plurality of cylinders,
A control device for an internal combustion engine, wherein the correction contribution rate reduction process is a process for reducing the change in the output value of the filter processing as a control variable of the feedback processing in response to a change in the detection value when the partial stop processing is executed , compared to before the partial stop processing is executed.