JP7107164B2 - Control device for internal combustion engine - Google Patents

Description

The present invention is applied to an internal combustion engine comprising a fuel injection valve, a catalyst having an oxygen storage capacity provided in an exhaust passage, and an air-fuel ratio sensor provided downstream of the catalyst in the exhaust passage. The present invention relates to a control device for an internal combustion engine.

Air-fuel ratio feedback control is well known in which a detected value of an upstream air-fuel ratio sensor provided upstream of a catalyst having an oxygen storage capacity in an exhaust passage is feedback-controlled to a target value. Further, in Patent Document 1 below, a downstream air-fuel ratio sensor is provided on the downstream side of the catalyst, and when the detected value of the downstream air-fuel ratio sensor is leaner than the stoichiometric air-fuel ratio, the target value is set to be leaner than the stoichiometric air-fuel ratio. A control device is described that makes the target value leaner than the stoichiometric air-fuel ratio when the detected value of the downstream air-fuel ratio sensor is richer than the stoichiometric air-fuel ratio (FIG. 11).

Patent No. 5949957

By the way, the detected value of the downstream side air-fuel ratio sensor may deviate due to individual differences, aged deterioration, temperature characteristics, etc. of the downstream side air-fuel ratio sensor. Then, for example, if control is performed to switch the target value while the deviation is occurring, as in the above device, the oxygen storage amount in the catalyst cannot be maintained at an appropriate value, and the exhaust purification ability of the catalyst decreases. Inconvenience may occur if the misalignment cannot be dealt with, such as when there is a risk of misalignment.

Means for solving the above problems and their effects will be described below.
1. The invention is applied to an internal combustion engine comprising a fuel injection valve, a catalyst having an oxygen storage capacity provided in an exhaust passage, and an air-fuel ratio sensor provided downstream of the catalyst in the exhaust passage, wherein the fuel injection air-fuel ratio control processing for controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine to a target value by operating a valve; and lean determination indicating that the detected value of the air-fuel ratio sensor is leaner than the theoretical air-fuel ratio. A rich control process for making the target value richer than the stoichiometric air-fuel ratio, and a rich judgment value indicating that the detected value of the air-fuel ratio sensor is richer than the stoichiometric air-fuel ratio. Triggered by the fact that the rich Based on the detected value of the air-fuel ratio sensor when the control process is performed, the deviation amount calculation process for calculating the deviation amount expression value, the target value set by the rich control process, and the lean control process are set. A control device for an internal combustion engine that executes a variable process of setting at least one of the two target values to be set to a different value depending on whether the execution condition is satisfied or not be.

When the detected value of the air-fuel ratio sensor is leaner than the stoichiometric air-fuel ratio, it can be considered that the oxygen storage amount of the catalyst is equal to or greater than a predetermined amount. When the rich control process is executed with the fact that the oxygen storage amount is equal to or greater than a predetermined amount as a trigger, the amount of fuel that reacts with oxygen in the unburned fuel in the fluid flowing into the catalyst is excessive. The unburned fuel flowing out downstream of the catalyst is negligible, since part reacts with the oxygen stored in the catalyst. Also, when the rich control process is performed, the amount of oxygen flowing downstream of the catalyst can be ignored. Therefore, the fluid to which the air-fuel ratio sensor is exposed when the rich control process is performed is equivalent to that when the air-fuel ratio of the mixture to be combusted is the stoichiometric air-fuel ratio. Therefore, it is possible to calculate the deviation amount expression value based on the deviation amount from the detected value assumed when the air-fuel ratio of the mixture to be combusted is the stoichiometric air-fuel ratio. Therefore, with the above configuration, deviations in the detected values of the air-fuel ratio sensor can be grasped, and the deviations can be dealt with.

Moreover, in the above configuration, by executing the variable process, at least one of the lean control process and the rich control process can be adjusted to a process suitable for the deviation amount calculation process. When acquired, it may be appropriate for that acquisition.

2. 2. The control of the internal combustion engine according to 1 above, wherein the variable processing includes processing for bringing the target value set by the rich control processing closer to the stoichiometric air-fuel ratio than when the shift amount calculation processing is executed and when it is not executed. It is a device.

When the target value set by the rich control process is brought closer to the stoichiometric air-fuel ratio, the timing at which the rich control process is switched to the lean control process is delayed, and the duration of the rich control process is increased. become longer. For this reason, in the above configuration, the duration of the rich control process can be extended by executing the variable process compared to when the variable process is not executed. enough to secure it.

3. 3. The control of the internal combustion engine according to 2 above, wherein the deviation amount calculation process includes a process of using a plurality of the detection values detected while the rich control process is continuing in the process of updating the deviation amount representation value once. It is a device.

In the above configuration, since one update process of the deviation amount expression value is performed based on a plurality of detected values, the above process 2 for lengthening the duration of the rich control process is particularly useful.
4. 4. The variable processing according to any one of 1 to 3 above, including processing for making the target value set by the lean control processing leaner than when the execution condition is not satisfied when the execution condition is satisfied. is a control device for an internal combustion engine.

When the target value set by the lean control process is made leaner, the timing at which the lean control process is switched to the rich control process is earlier than when the target value set by the lean control process is not made leaner, and the duration of the lean control process is shortened. becomes shorter. Therefore, in the above configuration, by executing the variable process, the duration of the lean control process can be shortened compared to when the variable process is not executed. It is possible to increase the proportion of the period in which the detected value can be acquired.

5. The air-fuel ratio sensor is a downstream air-fuel ratio sensor, the internal combustion engine includes an upstream air-fuel ratio sensor on the upstream side of the catalyst, and the air-fuel ratio control process detects a value detected by the upstream air-fuel ratio sensor. 5. The control apparatus for an internal combustion engine according to any one of 1 to 4 above, wherein the processing is feedback control to the target value.

In the above configuration, since the air-fuel ratio control process uses the feedback control, it is easier to improve the controllability of the air-fuel ratio of the air-fuel mixture as compared with the case where only the open loop control is used.
6. A deviation amount reflection process is executed to reflect the deviation amount representation value in the lean control process, and the deviation amount reflection process, when the deviation amount representation value is a deviation amount on the lean side, changes the deviation amount representation value to the lean control process. 6. The control device for an internal combustion engine according to any one of 1 to 5 above, including a process for advancing the actual switching timing from the rich control process to the lean control process before reflection to the lean control process. be.

When the detected value of the air-fuel ratio sensor deviates to the lean side, the timing at which the detected value becomes equal to or less than the rich determination value is delayed compared to when it does not deviate. Therefore, in the above configuration, even if the detected value of the air-fuel ratio sensor deviates to the lean side, the lean control process can be performed when the detected value of the air-fuel ratio sensor does not deviate by executing the deviation amount reflection process. It is possible to switch to lean control processing at a timing closer to the timing of switching to lean control processing.

1 is a diagram showing a control device and a drive system of a vehicle according to one embodiment; FIG. FIG. 3 is a block diagram showing processing executed by the control device according to the embodiment; 4 is a flowchart showing the procedure of sub-feedback processing according to the embodiment; FIG. 4 is a flowchart showing the procedure of stoichiometric point calculation processing according to the embodiment; FIG. 4 is a time chart for explaining a detection value sampling method for calculating a stoichiometric point according to the embodiment;

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 the intake passage 12 flows into the combustion chambers 14 of the cylinders #1 to #4. In the combustion chamber 14, the mixture of the fuel injected from the fuel injection valve 16 and the air flowing from the intake passage 12 is combusted by the spark discharge of the ignition device 18, and the energy generated by the combustion is transferred to the crankshaft 20. is converted into rotational energy of The combusted air-fuel mixture is discharged to the exhaust passage 22 as exhaust. The exhaust passage 22 is provided with an upstream three-way catalyst 24 and a downstream three-way catalyst 26 . Both of the three-way catalysts 24 and 26 have an oxygen storage capacity.

The crankshaft 20 is mechanically connected to a carrier C of a planetary gear mechanism 30 that constitutes a power split mechanism. A rotation shaft 32a of a motor generator 32 is mechanically connected to the sun gear S of the planetary gear mechanism 30, and a rotation shaft 34a of a motor generator 34 and a drive wheel 36 are mechanically connected to the ring gear R of the planetary gear mechanism 30. are linked together. As a result, the internal combustion engine 10 in this embodiment serves as one of the drive sources in the series/parallel hybrid vehicle.

Motor generator 32 is supplied with power from battery 44 via inverter 40 , and motor generator 34 is supplied with power from battery 44 via inverter 42 .

The ECU 50 controls the motor-generators 32 and 34 as objects to be controlled, and in addition to controlling the torque and rotational speed, which are the control amounts thereof, the ECU 50 controls the internal combustion engine 10 and the motor-generators 32 and 34 as objects to be controlled. It is a control device that executes processing to generate an output that

The control device 60 controls the internal combustion engine 10, and operates the operation units of the internal combustion engine 10 such as the fuel injection valve 16 and the ignition device 18 in order to control the torque, the exhaust component ratio, and the like, which are the control amounts. That is, for example, an operation signal MS1 is output to the fuel injection valve 16 to operate the fuel injection valve 16, and an operation signal MS2 is output to the ignition device 18 to operate the ignition device 18. FIG.

The control device 60 controls the amount of control by using the intake air amount Ga detected by the air flow meter 70, the output signal Scr of the crank angle sensor 72, and the upstream side air-fuel ratio sensor provided upstream of the three-way catalyst 24. The detection value Afu by 74 is referred to. The control device 60 also controls the detection value Afd of the downstream air-fuel ratio sensor 76 provided downstream of the three-way catalyst 24 and upstream of the three-way catalyst 26, and the internal combustion engine 10 detected by the water temperature sensor 78. refer to the temperature of the cooling water (water temperature THW). It should be noted that the upstream air-fuel ratio sensor 74 and the downstream air-fuel ratio sensor 76 are not so-called oxygen sensors having Z characteristics, but linearly increase the detected value as the amount of oxygen exceeding the amount of unburned fuel in the exhaust increases. It is a sensor that Also, the control device 60 has a function of communicating with the ECU 50 via the communication line 80 .

The control device 60 has a CPU 62 , a ROM 64 and a peripheral circuit 66 which are connected by a communication line 68 . The peripheral circuit 66 includes a circuit that generates a clock signal that defines internal operations, a power supply circuit, a reset circuit, and the like.

FIG. 2 shows processing executed by the control device 60 . The processing shown in FIG. 2 is implemented by the CPU 62 executing a program stored in the ROM 64 .
The base injection amount calculation process M10 is a process of calculating a base injection amount Qb, which is the base value of the fuel amount for making the air-fuel ratio of the air-fuel mixture in the combustion chamber 14 equal to the target air-fuel ratio, based on the charging efficiency η. Specifically, in the base injection amount calculation process M10, for example, when the charging efficiency η is expressed as a percentage, the charging efficiency η is added to the fuel amount QTH per 1% of the charging efficiency η for making the air-fuel ratio the target air-fuel ratio. A process of calculating the base injection amount Qb by multiplication may be performed. The base injection amount Qb is a fuel amount calculated for controlling the air-fuel ratio to the target air-fuel ratio based on the amount of air charged in the combustion chamber 14 . Incidentally, in this embodiment, the target air-fuel ratio is the stoichiometric air-fuel ratio. The charging efficiency η is calculated by the CPU 62 based on the intake air amount Ga and the rotational speed NE. Further, the rotation speed NE is calculated by the CPU 62 based on the output signal Scr.

The main feedback process M12 adds "1" to the correction ratio δ of the base injection amount Qb as the feedback manipulated variable, which is the manipulated variable for feedback-controlling the detected value Afu of the upstream side air-fuel ratio sensor 74 to the target value Afu*. This is a process of calculating and outputting the feedback correction coefficient KAF. More specifically, the main feedback process M12 is an integration that holds and outputs each output value of the proportional element and the differential element that receives the difference between the detected value Afu and the target value Afu*, and the integrated value of the value corresponding to the difference. Let the sum of the output values of the elements be the correction ratio δ.

The sub-feedback process M14 is a process of manipulating the target value Afu* in order to adjust the oxygen storage amount of the three-way catalyst 24 based on the detection value Afd of the downstream air-fuel ratio sensor 76.
The low temperature correction process M16 is a process for calculating a low temperature increase coefficient Kw to a value larger than "1" in order to increase the base injection amount Qb when the water temperature THW is lower than a predetermined temperature Tth (eg, 60°C). Specifically, the low temperature increase coefficient Kw is calculated to be a larger value when the water temperature THW is low than when it is high. When the water temperature THW is equal to or higher than the predetermined temperature Tth, the low temperature increase coefficient Kw is set to "1", and the correction amount of the base injection amount Qb based on the low temperature increase coefficient Kw is set to zero.

The required injection amount calculation process M18 is a process for calculating the fuel amount required in one combustion cycle (required injection amount Qd) by multiplying the base injection amount Qb by the feedback correction coefficient KAF and the low temperature increase coefficient Kw. .

The injection valve operation process M20 is a process of outputting an operation signal MS1 to the fuel injection valve 16 so that the fuel injection valve 16 is operated. In particular, the injection valve operation process M20 is a process for injecting the required injection amount Qd of fuel from the fuel injection valve 16 within one combustion cycle.

The stoichiometric point calculation process M22 is a process of calculating the detection value Afd of the downstream side air-fuel ratio sensor 76 when the air-fuel ratio of the air-fuel mixture to be combusted in the combustion chamber 14 is the stoichiometric air-fuel ratio as the stoichiometric point AfL.

FIG. 3 shows the procedure of the sub-feedback process M14. The processing shown in FIG. 3 is implemented by the CPU 62 repeatedly executing a program stored in the ROM 64, for example, at predetermined intervals. Note that, hereinafter, the step number of each process is represented by a number prefixed with “S”.

In the series of processes shown in FIG. 3, the CPU 62 first determines whether or not the lean determination flag Fl is "1" (S10). If the CPU 62 determines that it is "1" (S10: YES), the CPU 62 determines whether or not the detection value Afd is equal to or less than the value obtained by subtracting the rich side sub-offset amount εr from the stoichiometric reference value Afs (S12). . Here, the stoichiometric reference value Afs is the reference value of the detection value of the downstream side air-fuel ratio sensor 76 when the air-fuel ratio of the air-fuel mixture to be combusted in the combustion chamber 14 is the stoichiometric air-fuel ratio (reference air-fuel ratio sensor is the detected value). The process of S12 is a process of determining whether or not the flow rate of unburned fuel in the fluid flowing downstream of the three-way catalyst 24 is increasing.

If the CPU 62 determines that the stoichiometric reference value Afs is equal to or less than the value obtained by subtracting the rich side sub-offset amount εr from the stoichiometric reference value Afs (S12: YES), the CPU 62 substitutes "0" for the lean determination flag Fl and "1" for the rich determination flag Fr. ” is substituted (S14).

Next, the CPU 62 substitutes a value obtained by adding the lean side main offset amount δl to the stoichiometric reference value Afs into the target value Afu* (S16).
On the other hand, when the CPU 62 determines that the lean determination flag Fl is "0" (S10: NO), it determines whether the detected value Afd is equal to or greater than the sum of the stoichiometric reference value Afs and the lean side sub-offset amount εl. (S18). This process is a process for determining whether or not the flow rate of oxygen in the fluid flowing downstream of the three-way catalyst 24 is increasing as the amount of oxygen stored by the three-way catalyst 24 approaches the maximum value OSmax. . If the CPU 62 determines that it is less than the sum of the stoichiometric reference value Afs and the lean side sub-offset amount εl (S18: NO), the process proceeds to S16.

On the other hand, if the CPU 62 determines that the stoichiometric reference value Afs is equal to or greater than the sum of the lean side sub-offset amount εl (S18: YES), the CPU 62 sets the lean determination flag Fl to "1" and sets the rich determination flag Fr to " 0” (S20).

When the process of S20 is completed, or when the process of S12 makes a negative determination, the CPU 62 substitutes a value obtained by subtracting the rich side main offset amount δr from the stoichiometric reference value Afs into the target value Afu* (S22).

Incidentally, the rich-side sub-offset amount εr, the lean-side sub-offset amount εl, the rich-side main offset amount δr, and the lean-side main offset amount δl are determined by the oxygen This value aims at keeping the amount of storage unchanged.

When the processes of S16 and S22 are completed, the CPU 62 once terminates the series of processes shown in FIG.
FIG. 4 shows the procedure of the stoichiometric point calculation process M22. The processing shown in FIG. 4 is implemented by the CPU 62 repeatedly executing a program stored in the ROM 64, for example, at predetermined intervals.

In the series of processes shown in FIG. 4, the CPU 62 first determines whether or not the logical AND of the following conditions (a) to (e) is true (S30).
Condition (a): The condition is that the absolute value of the amount of change Δη in the charging efficiency η in a predetermined period is equal to or less than a predetermined amount Δηth. Here, the predetermined period may be, for example, the cycle of the series of processes shown in FIG. current value) and the sampled value (previous value) at the time of the previous execution. This condition is that the absolute value of the amount of change in the fluid flowing into the three-way catalyst 24 during a predetermined period is equal to or less than a predetermined amount. This condition is provided in view of the fact that the detection value Afd is more likely to fluctuate when the absolute value of the amount of change in the fluid flowing into the three-way catalyst 24 is larger than when it is small.

Condition (a): The condition is that the absolute value of the change amount ΔGa of the intake air amount Ga in a predetermined period is equal to or less than a predetermined amount ΔGath. Here, the predetermined period may be, for example, the cycle of the series of processes shown in FIG. 4, and in that case, the amount of change ΔGa may be the difference between the current value and the previous value regarding the intake air amount Ga. This condition is that the absolute value of the amount of change in the fluid flowing into the three-way catalyst 24 during a predetermined period is equal to or less than a predetermined amount.

Condition (c): The condition is that the water temperature THW is equal to or higher than the predetermined temperature Tth. This condition is for avoiding the influence of the air-fuel ratio error due to the low-temperature boost coefficient Kw as the open-loop manipulated variable from affecting the calculation of the stoichiometric point AfL.

Condition (d): The condition is that the integrated value InG of the intake air amount Ga from the start of the internal combustion engine 10 is equal to or greater than a predetermined value InGth. This condition is a condition that the three-way catalyst 24 is at the activation temperature.

Condition (e): The condition is that the intake air amount Ga is equal to or greater than the lower limit value GaL and equal to or less than the upper limit value GaH. Here, the upper limit value GaH is set to an upper limit value that does not excessively shorten the duration of the process of S22. Also, the lower limit value GaL is set to a value for idling or the like.

If the CPU 62 determines that the logical product of the conditions (a) to (e) is true (S30: YES), it substitutes the lean side detection offset amount δlH for the lean side main offset amount δl. The rich side detection offset amount δrL is substituted for the rich side main offset amount δr (S31).

Next, the CPU 62 determines whether the lean determination flag Fl has switched from "0" to "1" (S32). When the CPU 62 determines that the value of the lean determination flag Fl during the previous execution of the series of processes shown in FIG. (S32: YES), "1" is substituted for the permission flag Fp (S34).

When completing the process of S34 or when making a negative determination in the process of S32, the CPU 62 determines whether or not the logical product of the following conditions (f) to (h) is true (S36).
Condition (f): The condition is that the lean determination flag Fl is "1". In this process, the amount of unburned fuel in the fluid flowing into the three-way catalyst 24 in a state in which the amount of oxygen occluded in the three-way catalyst 24 can be regarded as being equal to or greater than a predetermined amount reacts with the unburned fuel in just the right amount. It is a condition that the amount of oxygen is greater than the amount of oxygen to be used. That is, the lean determination flag Fl is set to "1" when the detection value Afd becomes greater than the stoichiometric reference value Afs by the lean side sub-offset amount εl or more as a trigger. When it becomes, it can be considered that sufficient oxygen is occluded in the three-way catalyst 24 . When the processing of S22 is performed because the lean determination flag Fl becomes "1", the amount of fluid flowing into the three-way catalyst 24 is larger than the amount of unburned fuel that reacts with the oxygen in the fluid in just the right amount. including unburned fuel.

Condition (g): The condition is that the absolute value of the difference between the current value and the previous value of the detected value Afd is equal to or less than a specified amount ΔAfd. In FIG. 4, the current value is indicated by "n" and the previous value is indicated by "n-1".

This condition is that the amount of oxygen and the amount of unburned fuel in the fluid flowing out downstream of the three-way catalyst 24 are so small that they can be ignored. That is, after the processing of S22 is started, it takes time for the detection value Afu of the upstream air-fuel ratio sensor 74 to reach the target value Afu* determined by the processing of S22. The amount of oxygen in the fluid that Therefore, during that period, the amount of oxygen in the fluid flowing out downstream of the three-way catalyst 24 gradually decreases, and the amount of change in the detection value Afd also becomes relatively large. After that, when the detection value Afu of the upstream air-fuel ratio sensor 74 converges and stabilizes at the target value Afu* determined by the processing of S22, the absolute value of the amount of change in the detection value Afd of the downstream air-fuel ratio sensor 76 also decreases. Condition (g) specifies this point in time.

Condition (h): The condition is that the permission flag Fp is "1".
If the CPU 62 determines that the logical AND of the above conditions (f) to (h) is true (S36: YES), the CPU 62 adds the current sampling value to the integrated value InAfd of the detected value Afd to obtain the integrated value InAfd. is updated, and the number of integration times N of the detected value Afd is incremented (S38). When the process of S38 is completed, or when a negative determination is made in the process of S36, the CPU 62 determines whether or not the accumulated number of times N is equal to or greater than the reference number of times NH (S40). This processing is processing for determining whether or not the stoichiometric point AfL may be updated using the integrated value InAfd.

If the CPU 62 determines that the number of times is greater than or equal to the reference number of times NH (S40: YES), the CPU 62 substitutes the value obtained by dividing the integrated value InAfd by the number of times of integration N into the average value Afdave in order to calculate the simple average processing value of the detected value Afd. (S42). Next, the CPU 62 calculates the stoichiometric point AfL by exponential moving average processing of the average value Afdave (S44). Here, using a smoothing coefficient α having a value greater than “0” and less than “1”, the value obtained by multiplying the average value Afdave by the smoothing coefficient α and the stoichiometric point AfL are “1−α”. The stoichiometric point AfL is updated by the sum with the value multiplied by . The initial value of the stoichiometric point AfL may be, for example, the stoichiometric reference value Afs.

Next, the CPU 62 subtracts the value obtained by subtracting the stoichiometric reference value Afs from the stoichiometric point AfL from the initial value εr0 of the rich side sub-offset amount εr and adds it to the initial value εl0 of the lean side sub-offset amount εl. The rich side sub-offset amount εr and the lean side sub-offset amount εl are updated (S46). When the stoichiometric point AfL has not been calculated, the initial value εr0 is substituted for the rich side sub-offset amount εr, and the initial value εl0 is substituted for the lean side sub-offset amount εl in the process of FIG.

Then, the CPU 62 initializes the number of times of integration N and the integrated value InAfd, and substitutes "0" for the permission flag Fp (S48).
On the other hand, when a negative determination is made in the process of S40, the CPU 62 determines whether or not the value obtained by subtracting the previous value from the current value of the detection value Afd is smaller than the negative prescribed amount ΔAfdM (S50). This process determines whether the amount of oxygen stored by the three-way catalyst 24 has decreased and the unburned fuel in the fluid flowing into the three-way catalyst 24 has not been sufficiently oxidized by the oxygen stored in the three-way catalyst 24. This is a process for determining Note that, in the present embodiment, the absolute value of the specified amount ΔAfdM is equal to the specified amount ΔAfd. When the CPU 62 determines that it is smaller than the prescribed amount ΔAfdM (S50: YES), the CPU 62 determines whether or not the cumulative number N is equal to or greater than the lower limit value NL which is smaller than the reference value NH (S52). The lower limit NL is set to a lower limit that allows the integrated value InAfd to be reflected in the stoichiometric point AfL.

If the CPU 62 determines that it is equal to or greater than the lower limit value NL (S52: YES), it proceeds to the processing of S42.

On the other hand, when the CPU 62 makes a negative determination in the process of S30, it substitutes the lean side reference offset amount δlL into the lean side main offset amount δl and substitutes the rich side reference offset amount δrH into the rich side main offset amount δr. (S53). Here, the lean side reference offset amount δlL is smaller than the lean side detection offset amount δlH. Also, the rich side reference offset amount δrH is larger than the rich side detection offset amount δrL.

It should be noted that the CPU 62 temporarily terminates the series of processes shown in FIG. 4 when the processes of S48 and S53 are completed, or when a negative determination is made in the process of S50.
Here, the action and effect of this embodiment will be described.

FIG. 5 shows changes in the detected value Afd of the downstream side air-fuel ratio sensor 76 . Triggered by the detected value Afd exceeding the stoichiometric reference value Afs by the lean side sub-offset amount εl or more at time t1, the CPU 62 sets the target value Afu* to the rich side of the stoichiometric air-fuel ratio (S22). As a result, the air-fuel ratio of the air-fuel mixture to be combusted in the combustion chamber 14 is made richer than the stoichiometric air-fuel ratio, so that the fluid flowing into the three-way catalyst 24 reacts with oxygen in the fluid just enough. A larger amount of unburned fuel is included than the amount of unburned fuel required. Since this large amount of unburned fuel is oxidized by the oxygen stored in the three-way catalyst 24, the amount of oxygen and the amount of unburned fuel in the fluid flowing downstream from the three-way catalyst 24 are negligible. Become. The CPU 62 detects this when the absolute value of the amount of change in the detection value Afd becomes smaller in the process of S36 (time t2), samples the detection value Afd, and calculates the stoichiometric point AfL based on these sampled values. (S38-S44).

This stoichiometric point AfL is the downstream air-fuel ratio sensor 76 when the downstream side air-fuel ratio sensor 76 is exposed to the fluid flowing downstream of the three-way catalyst 24 when the air-fuel mixture to be combusted is constantly kept at the stoichiometric air-fuel ratio. It is considered to be the detection value of the side air-fuel ratio sensor 76 . Therefore, in the CPU 62, the value obtained by subtracting the stoichiometric reference value Afs from the stoichiometric point AfL is regarded as the deviation amount from the stoichiometric reference value Afs of the detection value of the downstream side air-fuel ratio sensor 76, and based on this, the rich side sub-offset is calculated. The amount εr and the lean side sub-offset amount εl are updated. As a result, due to the difference in the detection value of the downstream air-fuel ratio sensor 76, one of the oxygen and the unburned fuel flowing into the three-way catalyst 24 in one cycle between the processing of S16 and the processing of S22 It is possible to suppress the excess from the amount that reacts with each other just enough.

Incidentally, in this embodiment, when the difference in the detection value of the downstream side air-fuel ratio sensor 76 is so small that it can be ignored, the amount of change in the oxygen storage amount in the three-way catalyst 24 in one cycle between the processing of S16 and the processing of S22 is The rich side sub-offset amount εr and the lean side sub-offset amount εl are set so as to be several tens of percent (for example, 10%) or less of the maximum value OSmax. On the other hand, when the detection value Afd of the downstream air-fuel ratio sensor 76 deviates, the detection value Afd becomes the stoichiometric reference value Afs when the air-fuel ratio of the mixture to be combusted deviates from the stoichiometric air-fuel ratio. Therefore, if the rich side sub-offset amount εr and the lean side sub-offset amount εl are not updated based on the stoichiometric point AfL, one of the processing of S16 and the processing of S22 is excessively long, and the other is excessively long. Shorten. Therefore, one of the oxygen and the unburned fuel flowing into the three-way catalyst 24 in one cycle of the processing of S16 and the processing of S22 becomes more than the amount that reacts with the other without excess or deficiency, and the three-way catalyst 24 Oxygen storage capacity may change gradually. In that case, for example, when the fuel cut process or the like is not executed on the way and the steady operation is performed for a long time, the oxygen storage amount of the three-way catalyst 24 approaches zero or approaches the maximum value OSmax, There is a risk that the exhaust gas purification performance of the three-way catalyst 24 may deteriorate.

Furthermore, in the present embodiment, the rich side detection offset amount δrL is smaller than the rich side reference offset amount δrH. The amount of unburned fuel in the fluid flowing into the three-way catalyst 24 when executed is reduced. Therefore, the duration of the process of S22 can be lengthened, and a sufficient sampling period for the detected value Afd can be ensured.

Furthermore, in the present embodiment, since the lean-side detection offset amount δlH is larger than the lean-side reference offset amount δlL, the processing of S16 is performed more when the determination of S30 is affirmative than when it is not performed. The amount of oxygen in the fluid entering the three-way catalyst 24 when running is increased. Therefore, since the duration of the process of S16 can be shortened, the ratio of the execution period of the process of S22 to the operation period of the internal combustion engine 10 can be increased, and the detection time can be increased in the operation period of the internal combustion engine 10. The percentage of the period during which the value Afd can be sampled can be increased.

<Correspondence relationship>
Correspondence relationships between the items in the above embodiment and the items described in the "Means for Solving the Problems" column are as follows. Below, the corresponding relationship is shown for each number of the means for solving the problem described in the column of "means for solving the problem". The [1,2,4,5] catalyst corresponds to the three-way catalyst 24 and the air-fuel ratio sensor corresponds to the downstream air-fuel ratio sensor 76 . The air-fuel ratio control process corresponds to the base injection amount calculation process M10, the main feedback process M12, the low temperature correction process M16, and the required injection amount calculation process M18. The rich control process corresponds to the process of S22, and the lean control process corresponds to the process of S16. The deviation amount expression value corresponds to the stoichiometric point AfL. That is, the stoichiometric point AfL is a detected value of the target downstream air-fuel ratio sensor 76 when the air-fuel ratio of the air-fuel mixture to be combusted is the stoichiometric air-fuel ratio. The difference from the detected value (the stoichiometric reference value Afs) is the deviation amount, and is a parameter that expresses the deviation amount. The shift amount calculation process corresponds to the processes of S42 to S44. Variable processing corresponds to the processing of S31 and S53. [3] "Multiple detected values" correspond to detected values equal to or greater than the lower limit NL. [6] The deviation amount reflection process corresponds to the process of S46.

<Other embodiments>
In addition, this embodiment can be changed and implemented as follows. This embodiment and the following modifications can be implemented in combination with each other within a technically consistent range.

・"Rich control processing"
In the above embodiment, the sub-feedback process M14 constitutes the rich control process, but the present invention is not limited to this. For example, in view of the fact that the oxygen storage amount of the three-way catalyst 24 increases when the fuel cut process is performed, the target value Afu* may be made richer than the stoichiometric air-fuel ratio immediately after the fuel cut process is performed. good.

However, the process is not limited to controlling the air-fuel ratio of the air-fuel mixture to be combusted to the target value Afu*. It is good also as a process which adjusts a component.

・"About air-fuel ratio control processing"
It is not essential to use the low temperature correction process M16 in the process of calculating the required injection amount Qd.

In the above embodiment, the air-fuel ratio is controlled by two-degree-of-freedom control of open-loop control by the base injection amount calculation process M10 and feedback control by the main feedback process M12, but the air-fuel ratio control process is not limited to this. For example, it may be a process of open-loop control to the target value Afu* determined by a sub-feedback process.

・"About variable processing"
In the above embodiment, when the logical product of the above conditions (a) to (e) is true, the rich side main offset amount δr is used as the rich side detection offset amount δrL and the lean side main offset amount δl is used for lean side detection. Although the offset amount .delta.lH is used, the present invention is not limited to this. For example, although the rich side main offset amount δr is set to the rich side detection offset amount δrL, the lean side main offset amount δl may be set to the lean side reference offset amount δlL. Further, for example, the rich side main offset amount δr may be set to the rich side reference offset amount δrH while setting the lean side main offset amount δl to the lean side detection offset amount δlH.

・"Regarding deviation amount calculation processing"
In the above configuration, the stoichiometric point AfL is calculated as the deviation amount expression value indicating the deviation of the detection value Afd of the air-fuel ratio sensor, but the present invention is not limited to this. For example, it may be the amount of deviation itself from the detection value (stoichiometric reference value Afs) of the downstream side air-fuel ratio sensor, which is the reference when the air-fuel ratio of the mixture to be combusted is the stoichiometric air-fuel ratio. For example, in the processing of S38, the integrated value of the value obtained by subtracting the stoichiometric reference value Afs from the detected value Afd is obtained, and in the processing of S42, the average value of the values obtained by subtracting the stoichiometric reference value Afs from the detected value Afd is obtained. ,realizable.

It is not essential to calculate the stoichiometric point AfL by simple averaging and exponential moving averaging. For example, when correcting the rich side sub-offset amount εr and the lean side sub-offset amount εl with a value obtained by multiplying "AfL-Afs" by the gain K according to the method described in the section "Regarding deviation amount reflection processing" below, the stoichiometric The point AfL may be the average value Afdave. Alternatively, for example, simple averaging may be deleted and the exponentially moving averaged value of the detected value Afd may be used as the stoichiometric point AfL. Furthermore, it is not essential to include at least one of the simple average process and the exponential moving average process. For example, the stoichiometric point AfL may be a low-pass filter processed value such as first-order lag filter processing in which time-series data of the detection value Afd in a predetermined period is input.

・"Conditions for executing deviation amount calculation processing"
The conditions for executing the deviation amount calculation process do not necessarily include the condition that the logical product of the above conditions (a) to (e) is true. For example, the condition that the absolute value of the amount of change in the flow rate of the fluid flowing into the three-way catalyst 24 is equal to or less than a predetermined amount may be either condition (a) or condition (b). Further, for example, the above condition (c) may be deleted. Further, instead of the condition (d), a sensor such as a thermistor that senses the temperature of the three-way catalyst 24 may be provided, and a condition that the detected value is equal to or higher than a predetermined temperature may be provided. For example, instead of reducing the difference between the lower limit value GaL and the upper limit value GaH in the condition (e), the above condition (a) and condition (b) may be deleted.

Further, for example, instead of the condition (g), a condition that a predetermined time has passed since the lean determination flag Fl was switched to "1" may be used. Further, for example, instead of the condition (g), a condition that the absolute value of the difference between the detected value Afd and the stoichiometric reference value Afs is equal to or less than a predetermined value may be used.

As described in the section "Rich control process", when the rich control process is to be executed immediately after the fuel cut process, the execution condition may be that the process is immediately after the fuel cut process.

・"Regarding deviation amount reflection processing"
The processing for correcting “Afs−εr” as the rich judgment value and “Afs+εl” as the lean judgment value is not limited to the processing of S46. For example, it may be a process of adding "AfL-Afs" to the stoichiometric reference value Afs in the processes of S12 and S18 in FIG.

Instead of the process of S46, a value obtained by multiplying "AfL-Afs" by a gain K smaller than "1" and larger than "0" is subtracted from the rich side sub-offset amount εr, and the multiplied value is added to the lean side It may be added to the sub-offset amount εl.

In the above embodiment, the process of S48 constitutes the deviation amount reflection process, but the present invention is not limited to this. For example, a value obtained by subtracting "AfL-Afs" from the detection value Afd may be used as the detection value Afd to be the input for the processes of S12 and S18.

Note that the deviation amount reflection processing includes "Afs−εr" as the rich determination value, "Afs+εl" as the lean determination value, and the detection value Afd as a comparison target for the rich determination value and the lean determination value. The process is not limited to correcting either of them according to the stoichiometric point AfL. For example, if the output of the downstream side air-fuel ratio sensor 76 changes depending on the electrical amount (applied voltage, etc.) supplied to the downstream side air-fuel ratio sensor 76, the stoichiometric point AfL will approach the stoichiometric reference value Afs. It is good also as a process which adjusts an amount.

・"About the use of the deviation amount expression value"
The deviation amount expression value is not limited to that reflected in the sub-feedback process M14. For example, when the fuel injection valve 16 is operated so as to control the same air-fuel ratio of the mixture to be combusted in each of the cylinders #1 to #4, the mixture to be combusted is richer than the others. It may be used for determining the presence/absence of an abnormality (imbalance abnormality). Here, for example, in the determination process, the absolute value of the correction amount of the target value Afu* in the main feedback process M12 is small when the absolute value of the difference between the detection value Afd of the downstream side air-fuel ratio sensor 76 and the stoichiometric reference value Afs is large. On the premise that control is performed to make the imbalance larger than the case, the process of determining the presence or absence of an imbalance abnormality based on the correction amount may be performed. That is, when an imbalance abnormality occurs, the detection value Afu of the upstream side air-fuel ratio sensor 74 shifts to the rich side with respect to the air-fuel ratio of the air-fuel mixture to be combusted in each cylinder. The feedback processing M12 controls the combined air-fuel ratio to be leaner than the stoichiometric air-fuel ratio. Therefore, the detection value Afd of the downstream side air-fuel ratio sensor 76 is leaner than the stoichiometric air-fuel ratio, so the correction amount includes information regarding the degree of imbalance abnormality. In order to improve the accuracy of this determination process, the detection value Afd, which is the input to the correction amount calculation process, may be corrected based on the stoichiometric point AfL, as described in the section "Regarding deviation amount reflection process". In that case, no matter what the air-fuel ratio of the air-fuel mixture to be combusted is, the corrected detection value Afd will be the reference detection value of the air-fuel ratio sensor (the value that the control device 60 presupposes in the control). Since the values are close to each other, it is possible to improve the accuracy of determining the presence or absence of imbalance abnormality based on the correction amount.

・"Regarding the storage device of the deviation amount expression value"
In the above embodiment, the storage device for storing the stoichiometric point AfL was not specified, but it may be stored in a RAM as a volatile memory, for example. In this case, the stoichiometric point AfL is not stored in the RAM immediately after the start because the RAM is initialized when the control device 60 is newly started. However, instead of this, for example, the stoichiometric point AfL may be constantly stored regardless of whether control device 60 is activated or stopped. This can be realized, for example, by using, as a storage device, a backup RAM in which power supply is maintained regardless of the state of the main power supply of control device 60, or a non-volatile memory. Further, for example, a device including a RAM as a volatile memory and a nonvolatile memory may be used as a storage device for storing the stoichiometric point AfL. In this case, the stoichiometric point AfL stored in the RAM may be successively updated by the process of S44, and the stoichiometric point AfL may be stored in the non-volatile memory as post-processing prior to stopping the control device 60. FIG. In this case, the stoichiometric point AfL stored in the nonvolatile memory is stored in the volatile memory when the controller 60 is activated.

・"About the control device"
The control device is not limited to having the CPU 62 and the ROM 64 and executing software processing. For example, a dedicated hardware circuit (for example, an ASIC, etc.) that performs hardware processing at least part of what is software-processed in the above embodiments may be provided. That is, the control device may have any one of the following configurations (a) to (c). (a) A processing device that executes all of the above processes according to a program, and a program storage device such as a ROM that stores the program. (b) A processing device and a program storage device for executing part of the above processing according to a program, and a dedicated hardware circuit for executing the remaining processing. (c) have dedicated hardware circuitry to perform all of the above processes; Here, there may be a plurality of software processing circuits including a processing device and a program storage device, or a plurality of dedicated hardware circuits. That is, the processing may be performed by a processing circuit comprising at least one of one or more software processing circuits and one or more dedicated hardware circuits.

・"About the vehicle"
The hybrid vehicle is not limited to a series/parallel hybrid vehicle, and may be, for example, a parallel hybrid vehicle or a series hybrid vehicle. However, the vehicle is not limited to a hybrid vehicle, and may be a vehicle in which the internal combustion engine 10 is the only driving source of the vehicle.

·"others"
In the above embodiment, the absolute value of the specified amount ΔAfdM in the process of S50 is equal to the specified amount ΔAfd in the process of S36. Further, the processing of S34 is executed when the determination in S32 is affirmative and the condition (g) is satisfied, and the processing of S50 is executed when the condition (g) is not satisfied. It is good also as a process which transfers to. In this case, the integrated value InAfd is initialized when the condition (g) is no longer satisfied after the process of S38 is started.

Reference Signs List 10 Internal combustion engine 12 Intake passage 14 Combustion chamber 16 Fuel injection valve 18 Ignition device 20 Crankshaft 22 Exhaust passage 24, 26 Three-way catalyst 30 Planetary gear mechanism 32 Motor generator 32a Rotating shaft 34 Motor generator 34a Rotating shaft 36 Drive wheel 40, 42 Inverter 44 Battery 50 ECU 60 Control device 62 CPU 64 ROM 66 Peripheral circuit 68 Communication line 70 Air flow meter 72 Crank angle sensor 74 Upstream air-fuel ratio sensor 76 Downstream air-fuel ratio sensor 78 Water temperature sensor.

Claims (5)

Applied to an internal combustion engine comprising a fuel injection valve, a catalyst having an oxygen storage capacity provided in an exhaust passage, and an air-fuel ratio sensor provided downstream of the catalyst in the exhaust passage,
air-fuel ratio control processing for controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine to a target value by operating the fuel injection valve;
Rich control processing for making the target value richer than the stoichiometric air-fuel ratio, triggered by the fact that the detected value of the air-fuel ratio sensor is equal to or greater than a lean judgment value indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio;
lean control processing for making the target value leaner than the stoichiometric air-fuel ratio, triggered by the fact that the detected value of the air-fuel ratio sensor is equal to or less than a rich judgment value indicating that the air-fuel ratio is richer than the stoichiometric air-fuel ratio;
When the execution condition for the process of calculating the deviation amount expression value indicating the deviation amount of the detected value of the air-fuel ratio sensor is satisfied, the deviation is calculated based on the detected value of the air-fuel ratio sensor when the rich control process is performed. a deviation amount calculation process for calculating an amount expression value;
At least one of the target value set by the rich control process and the target value set by the lean control process is set depending on whether or not the execution condition is satisfied. Execute variable processing and set to different values ,
The control device for an internal combustion engine , wherein the variable processing includes processing for bringing the target value set by the rich control processing closer to the stoichiometric air-fuel ratio than when the shift amount calculation processing is executed and when it is not executed . Applied to an internal combustion engine comprising a fuel injection valve, a catalyst having an oxygen storage capacity provided in an exhaust passage, and an air-fuel ratio sensor provided downstream of the catalyst in the exhaust passage,
air-fuel ratio control processing for controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine to a target value by operating the fuel injection valve;
Rich control processing for making the target value richer than the stoichiometric air-fuel ratio, triggered by the fact that the detected value of the air-fuel ratio sensor is equal to or greater than a lean judgment value indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio;
lean control processing for making the target value leaner than the stoichiometric air-fuel ratio, triggered by the fact that the detected value of the air-fuel ratio sensor is equal to or less than a rich judgment value indicating that the air-fuel ratio is richer than the stoichiometric air-fuel ratio;
When the execution condition for the process of calculating the deviation amount expression value indicating the deviation amount of the detected value of the air-fuel ratio sensor is satisfied, the deviation is calculated based on the detected value of the air-fuel ratio sensor when the rich control process is performed. a deviation amount calculation process for calculating an amount expression value;
At least one of the target value set by the rich control process and the target value set by the lean control process is set depending on whether or not the execution condition is satisfied. Execute variable processing and set to different values ,
The control device for an internal combustion engine , wherein the variable processing includes processing for making the target value set by the lean control processing leaner than when the execution condition is not satisfied when the execution condition is satisfied . 3. The deviation amount calculation process according to claim 1, wherein the deviation amount calculation process includes a process of using a plurality of the detected values detected while the rich control process is continuing, in one update process of the deviation amount expression value. A control device for an internal combustion engine. The air-fuel ratio sensor is a downstream air-fuel ratio sensor,
The internal combustion engine includes an upstream air-fuel ratio sensor upstream of the catalyst,
The control apparatus for an internal combustion engine according to any one of claims 1 to 3 , wherein the air-fuel ratio control process is a process of feedback-controlling the detected value of the upstream side air-fuel ratio sensor to the target value. executing a deviation amount reflection process for reflecting the deviation amount expression value in the lean control process;
When the deviation amount representation value is a deviation amount on the lean side, the deviation amount reflection process includes switching timing from the rich control process to the lean control process before the deviation amount representation value is reflected in the lean control process. 5. The control device for an internal combustion engine according to claim 1 , further comprising a process of advancing the actual switching timing.

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