JP2010084671A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately correct behavior of correction quantity (sub correction quantity) by sub feedback control based on output of an exhaust gas sensor of a catalyst downstream side in an air-fuel ratio control system. <P>SOLUTION: When an output of an exhaust gas sensor provided at a downstream of a catalyst becomes a leaner value than a leanness determination value due to disturbance or the like during execution of main feedback control or sub feedback control, control parameter change processing is performed. In this control parameter change processing, behavior of sub correction quantity due to deterioration or individual difference of systems is accurately determined by comparing behavior of the sub correction quantity with predetermined reference behavior. The behavior of the sub correction quantity due to individual difference and deterioration of the system is accurately corrected by changing control parameters of sub feedback control (for example, a differential term, a proportional term, and an integration term or the like used for calculation of the sub correction quantity) to make the behavior of sub correction quantity coincide with reference behavior based on the comparison result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine in which sensors for detecting the air-fuel ratio or rich / lean of exhaust gas are installed on the upstream side and the downstream side of the exhaust gas purification catalyst of the internal combustion engine, respectively.

  In recent automobile exhaust gas purification systems, in order to increase the exhaust gas purification rate of the exhaust gas purification catalyst of the internal combustion engine, the exhaust gas emptied respectively upstream and downstream of the exhaust gas purification catalyst. A sensor (air-fuel ratio sensor or oxygen sensor) that detects the fuel ratio or rich / lean is installed, and the fuel injection amount is feedback corrected so that the air-fuel ratio upstream of the catalyst becomes the target air-fuel ratio based on the output of the upstream sensor “Main feedback control” is performed, and the target air-fuel ratio of the main feedback control is corrected based on the output of the downstream sensor, or the feedback correction amount or the fuel injection amount of the main feedback control is corrected. Some of them are designed to perform “control”.

  In such a system that performs main feedback control and sub-feedback control, Patent Document 1 (Japanese Patent Laid-Open No. 2002-2002) is required to ensure stable exhaust gas purification performance regardless of the operating state of the internal combustion engine and the state of the catalyst. As described in Japanese Patent No. 227689), the control gain of the sub-feedback control is corrected in accordance with the operation state (for example, rotation speed and intake air amount) of the internal combustion engine and the state of the catalyst (for example, the degree of deterioration). There is what I did.

Further, as described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-360605), the oxygen storage capacity is detected as information on the degree of deterioration of the catalyst, and the internal combustion is performed according to the degree of deterioration of the catalyst (oxygen storage capacity). Some have corrected the control parameters of the engine.
Japanese Patent Laid-Open No. 2002-227689 JP 2004-360605 A

  By the way, in a system that performs main feedback control and sub-feedback control, if the air-fuel ratio of exhaust gas flowing into the catalyst fluctuates due to disturbance or the like and the air-fuel ratio downstream of the catalyst (the output of the downstream sensor) fluctuates, Accordingly, the correction amount (sub correction amount) by the sub feedback control changes, and the main feedback control and the fuel injection amount are corrected by the sub correction amount, so that the exhaust gas is efficiently purified by the catalyst. The behavior of the sub-correction amount (output waveform) may change due to individual differences or deterioration (aging) of the system (catalyst, sensor, etc.), and the type of catalyst deterioration (for example, loss or reaction of ceria storing oxygen) The behavior of the sub correction amount also changes depending on the agglomeration of precious metals that contribute to the speed. If the change (shift) in the behavior of the sub correction amount due to such individual differences or deterioration of the system becomes large, there is a possibility that the exhaust gas cannot be purified efficiently by the catalyst.

  However, just by changing the control gain and the control parameter according to the degree of deterioration of the catalyst as in the techniques of Patent Document 1 and Patent Document 2, changes in the behavior of the sub correction amount due to individual differences or deterioration of the system. There is a possibility that the (displacement) cannot be corrected with accuracy and the exhaust gas cannot be efficiently purified by the catalyst.

  The present invention has been made in view of such circumstances, and therefore the object of the present invention is to accurately correct the change in behavior of the sub correction amount (correction amount by sub feedback control) An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can efficiently purify exhaust gas.

  In order to achieve the above object, the invention according to claim 1 is an internal combustion engine in which sensors for detecting the air-fuel ratio or rich / lean of exhaust gas are installed on the upstream side and downstream side of the exhaust gas purification catalyst of the internal combustion engine, respectively. In the engine air-fuel ratio control device, main feedback control means for performing main feedback control for feedback correction of the fuel injection amount so that the air-fuel ratio upstream of the catalyst becomes the target air-fuel ratio based on the output of the upstream sensor, and downstream Sub feedback control means for performing main feedback control or sub feedback control for correcting the fuel injection amount based on the output of the side sensor, and the output of the downstream sensor exceeds a predetermined value during execution of the main feedback control and the sub feedback control. Sometimes, the amount of correction by sub-feedback control or information related thereto (hereinafter These are collectively referred to as “sub-correction amount information”), and control parameter change processing for changing the control parameter of the sub-feedback control based on the comparison result between the behavior of the sub-correction amount information and a predetermined reference behavior And a control parameter changing means for performing the above.

  In this configuration, when the output of the downstream sensor fluctuates and exceeds a predetermined value due to disturbance or the like during execution of the main feedback control and the sub feedback control, the behavior of the sub correction amount information is detected, and the sub correction amount information By comparing the behavior of and the predetermined reference behavior, it is possible to accurately determine the behavior change (deviation) of the sub correction amount information due to individual differences and deterioration (time-dependent change) of the system, and based on the comparison result By changing the control parameters of the sub feedback control so that the behavior of the sub correction amount information matches the reference behavior, it is possible to accurately correct changes in the behavior of the sub correction amount information due to individual differences and deterioration of the system. The catalyst can efficiently purify the exhaust gas.

  In this case, as described in claim 2, during the operation of the internal combustion engine, the control parameter changing process may be executed at any time to correct the behavior of the sub correction amount information. In this way, the control parameter changing process is executed at any time during the operation of the internal combustion engine (for example, every time the output of the downstream sensor exceeds a predetermined value during the execution of the main feedback control and the sub feedback control) Changes in the behavior of the sub correction amount information due to individual differences and deterioration of the engine can be corrected, so that changes in the behavior of the sub correction amount information are corrected early during the operation of the internal combustion engine to prevent the exhaust emission from deteriorating. be able to.

  Further, as in claim 3, the control parameter changing process may be executed when the control system of the internal combustion engine is adapted so as to obtain an adapted value of the control parameter of the sub feedback control. In this way, the control parameter changing process of the present invention is executed at the time of adapting the control system in the development or design stage of the control system of the internal combustion engine, so that the behavior of the sub correction amount information matches the reference behavior. By changing the control parameter of the feedback control, the adaptive value of the control parameter of the sub feedback control can be obtained with high accuracy, and the optimal control parameter can be set. In addition, if the difference (difference) between the behavior of the sub correction amount information and the reference behavior is not reduced by the control parameter change process, the cause of the lack of catalyst capacity is clarified by the behavior of the difference and reflected in the catalyst design. Can be made.

  Further, as described in claim 4, the reference behavior may be set according to the ability of the catalyst. In this way, even if the capacity of the catalyst (for example, the maximum oxygen storage amount) changes due to individual differences or deterioration of the catalyst, it is possible to set an appropriate reference behavior according to the capacity of the catalyst.

  Further, as in claim 5, the reference behavior is such that when the output of the downstream sensor is leaner than the predetermined lean determination value, the fuel injection amount is increased and corrected stepwise by a predetermined rich step amount. Later, when the fuel injection amount increase correction amount is gradually reduced, and when the fuel injection amount increase correction amount by the rich input processing becomes zero or when the oxygen storage amount of the catalyst becomes zero In addition, after the fuel injection amount is corrected to be decreased stepwise by a predetermined lean step amount, a sub-type that performs a lean / lean input control that performs a lean input process for gradually decreasing the fuel injection amount decrease correction amount. It is better to set the behavior of correction amount information.

  In this way, the rich / lean input control can be executed with high accuracy by changing the control parameter of the sub feedback control so that the behavior of the sub correction amount information matches the reference behavior by the control parameter changing process. . In this rich / lean input control, due to the occurrence of a lean disturbance in which the air-fuel ratio of the exhaust gas flowing into the catalyst becomes lean, the oxygen storage amount of the catalyst becomes excessive and the NOx (lean component) purification rate decreases. When the downstream sensor output becomes leaner than the lean determination value, the rich input process is performed to supply the rich component to the catalyst, thereby quickly reducing the oxygen storage amount of the catalyst to almost zero. And the NOx purification rate can be promptly improved. Thereby, it is possible to reduce the NOx emission amount when the lean disturbance occurs. Furthermore, when the increase correction amount of the fuel injection amount by the rich input process becomes 0 or when the oxygen storage amount of the catalyst becomes 0, the lean input process is performed to supply the lean component to the catalyst. The oxygen storage amount of can be quickly increased to an appropriate value. At this time, since the lean input process can be performed to supply the lean component to the catalyst in a state where the oxygen storage amount of the catalyst is once substantially zero by the rich input process, oxygen is present in the upstream part (front part) of the catalyst. It can be in the occluded state. As a result, rich components such as HC and CO can be efficiently purified when a rich disturbance occurs after the occurrence of a lean disturbance.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 15 whose opening is adjusted by a motor (not shown) and a throttle opening sensor 16 for detecting the opening (throttle opening) of the throttle valve 15 are provided on the downstream side of the air flow meter 14. It has been.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes.

  On the other hand, a catalyst 22 such as a three-way catalyst for purifying harmful components (CO, HC, NOx, etc.) in the exhaust gas is installed in the middle of the exhaust pipe 21 of the engine 11. Sensors 23 and 24 for detecting the air-fuel ratio or rich / lean of the exhaust gas are installed on the upstream side and the downstream side of the catalyst 22, respectively. In this embodiment, the upstream sensor 23 is an air-fuel ratio sensor (linear A / F sensor) that outputs a linear air-fuel ratio signal corresponding to the air-fuel ratio of the exhaust gas, and the downstream sensor 24 is an empty exhaust gas sensor. An oxygen sensor whose output voltage is inverted depending on whether the fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio is used.

  A cooling water temperature sensor 25 that detects the cooling water temperature and a crank angle sensor 26 that outputs a pulse signal each time the crankshaft rotates a predetermined crank angle are attached to the cylinder block of the engine 11. A crank angle and an engine speed are detected based on the output signal.

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 27. The ECU 27 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount of the fuel injection valve 20 according to the engine operating state. The ignition timing of a spark plug (not shown) is controlled.

  At this time, the ECU 27 executes an air-fuel ratio feedback control routine (not shown) so that the air-fuel ratio (exhaust gas upstream) of the catalyst 22 matches the target air-fuel ratio based on the output of the upstream sensor 23. It functions as a main feedback control means for performing main feedback control for feedback correction of the fuel injection amount), and downstream so that the air-fuel ratio of the exhaust gas downstream of the catalyst 22 matches the control target value (for example, near the theoretical air-fuel ratio). Sub feedback control for correcting the fuel injection amount based on the output of the side sensor 24, correcting the target air-fuel ratio upstream of the catalyst 22, or performing sub feedback control for correcting the feedback correction amount of the main feedback control Functions as a means.

  Further, the ECU 27 executes a control parameter changing routine shown in FIG. 7 to be described later, and as shown in FIG. 2, during the execution of the main feedback control and the sub feedback control, the exhaust gas flowing into the catalyst 22 due to a disturbance or the like. When the air-fuel ratio fluctuates in the lean direction and the output of the downstream sensor 22 becomes leaner than a predetermined lean determination value, control parameter change processing is performed. In this control parameter changing process, the behavior of the correction amount (hereinafter referred to as “sub-correction amount”) by the sub-feedback control is detected, and the behavior of the sub-correction amount is compared with a predetermined reference behavior, thereby the system (catalyst 22). And the change (deviation) of the behavior of the sub correction amount due to individual differences and deterioration (change over time) of the sensor 23, 24, etc.) are accurately determined, and the behavior of the sub correction amount is matched with the reference behavior based on the comparison result. By changing the control parameters of the sub feedback control (eg, differential terms, proportional terms, integral terms used to calculate the sub correction amount), it is possible to accurately change the behavior of the sub correction amount due to individual differences and deterioration of the system. Correct it well.

  In this embodiment, the control parameter change process is executed at any time during engine operation (for example, every time the output of the downstream sensor 24 exceeds the lean determination value during execution of the main feedback control and the sub feedback control). Correct changes in the behavior of the sub correction amount due to individual differences and deterioration.

  In the control parameter changing process, for example, as shown in FIG. 3, when the peak portion of the behavior (output waveform) of the sub correction amount is shifted from the peak portion of the reference behavior, it is used for calculating the sub correction amount. Change the derivative term to correct the behavior of the sub correction amount to match the reference behavior. At this time, if the peak value (absolute value) of the behavior of the sub correction amount is smaller than the peak value (absolute value) of the reference behavior, the differential term is increased. On the other hand, if the peak value (absolute value) of the behavior of the sub correction amount is larger than the peak value (absolute value) of the reference behavior, the differential term is reduced.

  In addition, as shown in FIG. 4, when the behavior of the sub correction amount is deviated from the reference behavior as a whole, the proportional term used for calculating the sub correction amount is changed to change the behavior of the sub correction amount. Modify to match the standard behavior. At this time, if the change amount of the behavior of the sub correction amount is smaller than the change amount of the reference behavior, the proportional term is increased. On the other hand, when the change amount of the behavior of the sub correction amount is larger than the change amount of the reference behavior, the proportional term is decreased. Further, when the change time of the behavior of the sub correction amount (time until convergence) is longer than the change time of the reference behavior, the proportional term is increased. On the other hand, when the change time of the behavior of the sub correction amount is shorter than the change time of the reference behavior, the proportional term is reduced.

  Furthermore, as shown in FIG. 5, when the control center of the behavior of the sub correction amount is deviated from the control center of the reference behavior (when the behavior of the sub correction amount is translated with respect to the reference behavior). Changes the integral term used for calculation of the sub correction amount so as to make the behavior of the sub correction amount coincide with the reference behavior. At this time, if the control center of the behavior of the sub correction amount is shifted in the minus direction with respect to the control center of the reference behavior, the integral term is increased. On the other hand, when the control center of the behavior of the sub correction amount is shifted in the plus direction with respect to the control center of the reference behavior, the integral term is reduced.

  An intermediate target value is set between the detected air-fuel ratio of the downstream sensor 24 and the target air-fuel ratio downstream of the catalyst 22, and the sub correction amount is set based on the detected air-fuel ratio of the downstream sensor 24 and the intermediate target value. In the case of a system that calculates the intermediate target value, the intermediate target value may be changed based on the comparison result between the behavior of the sub correction amount and the reference behavior.

  The reference behavior is set according to the capacity of the catalyst 22. In this way, even if the capacity of the catalyst 22 (for example, the maximum oxygen storage amount) changes due to individual differences or deterioration of the catalyst 22, an appropriate reference behavior can be set according to the capacity of the catalyst 22. Note that the reference behavior may be set using a predetermined catalyst model.

  In this embodiment, the reference behavior is set to the behavior of the sub correction amount that executes the rich / lean input control shown in FIG. In this rich / lean input control, when the output of the downstream sensor 24 becomes leaner than a predetermined lean determination value, the fuel injection amount is corrected stepwise by a predetermined rich step amount, and then the fuel is injected. The rich input process for gradually decreasing the injection amount increase correction amount, and the fuel injection amount when the fuel injection amount increase correction amount by the rich input process becomes zero or when the oxygen storage amount of the catalyst 22 becomes zero. After the injection amount is corrected to be decreased step by step by a predetermined lean step amount, a lean input process for gradually decreasing the decrease correction amount of the fuel injection amount is performed.

  In this case, the control parameters of the sub feedback control (for example, the differential term, proportional term, integral term, etc. used for calculating the sub correction amount) are changed so that the behavior of the sub correction amount matches the reference behavior by the control parameter changing process described above. By doing so, rich / lean input control can be executed with high accuracy. In this rich / lean input control, due to the occurrence of a lean disturbance in which the air-fuel ratio of the exhaust gas flowing into the catalyst 22 becomes lean, the oxygen storage amount of the catalyst 22 becomes excessive and the NOx (lean component) purification rate decreases. Then, when the output of the downstream sensor 24 becomes leaner than the lean determination value, a rich input process is performed to supply a rich component to the catalyst 22, thereby quickly reducing the oxygen storage amount of the catalyst 22. Can be made. At this time, by setting the total amount of rich components supplied to the catalyst 22 to be equal to or greater than the oxygen storage capacity (maximum oxygen storage amount) of the catalyst 22, the oxygen storage amount of the catalyst 22 is quickly reduced to almost zero. Thus, the NOx purification rate can be promptly improved. Thereby, it is possible to reduce the NOx emission amount when the lean disturbance occurs.

  Further, when the fuel injection amount increase correction amount by the rich input process becomes 0 or when the oxygen storage amount of the catalyst 22 becomes 0, the lean input process is performed to supply the lean component to the catalyst 22. The oxygen storage amount of the catalyst can be quickly increased to an appropriate value. At this time, since the lean input process can be performed to supply the lean component to the catalyst 22 in a state where the oxygen storage amount of the entire catalyst 22 is once substantially zero by the rich input process, the upstream portion (front part) of the catalyst 22 ) Side oxygen can be occluded. As a result, rich components such as HC and CO can be efficiently purified when a rich disturbance occurs after the occurrence of a lean disturbance.

  Note that the rich step amount may be set based on the specifications of the catalyst 22 when the fuel injection amount is corrected to be increased step by step by the rich step processing of the rich / lean input control. In this way, based on the specifications (performance, specifications, etc.) of the catalyst 22, “slip-through” in which rich components such as CO do not participate in the adsorption reaction or desorption reaction does not occur in the catalyst 22. By setting the rich step amount as described above, the emission of rich components such as CO can be reduced, and the rich step amount is set so that the water gas shift reaction (CO + H 2 O → H 2 + CO 2) occurs in the catalyst 22. The NOx purification can be promoted by the strong reducing power of H2 produced by the water gas shift reaction.

  Further, when the fuel injection amount increase correction amount is gradually decreased by the rich / lean input control rich input process, the increase correction amount may be changed according to an index indicating the internal state of the catalyst 22. In this way, the supply amount of the rich component necessary for efficiently purifying NOx according to the indicators (oxygen storage amount, adsorption rate, desorption rate, reaction delay, etc.) indicating the internal state of the catalyst 22 is increased. In response to the change, the fuel injection amount increase correction amount can be changed to reduce the rich component supply amount while controlling it to an appropriate value (a supply amount necessary for efficiently purifying NOx). Further, NOx can be efficiently purified without causing a rich component (for example, CO) to pass through.

  Further, the total amount of lean components supplied to the catalyst 22 by the lean input process of rich / lean input control may be set according to the oxygen storage capacity of the catalyst 22. In this way, the oxygen storage amount of the catalyst 22 is quickly increased to an appropriate value (for example, 30 to 40% of the maximum oxygen storage amount) according to the oxygen storage capacity of the catalyst 22 by the lean input processing after the rich input processing. The catalyst 22 can be brought into a state where the exhaust gas purification rate is high (a state where the purification rate is high with respect to both the rich component and the lean component).

The control parameter changing process described above is executed by the ECU 27 according to the control parameter changing routine of FIG. The processing contents of this routine will be described below.
The control parameter change routine shown in FIG. 7 is repeatedly executed at a predetermined cycle during engine operation, and serves as a control parameter change means in the claims. When this routine is started, first, at step 101, it is determined whether or not the engine operating state is stable. If it is determined that the engine operating state is stable, the routine proceeds to step 102 and main feedback control is performed. It is determined whether or not sub feedback control is being executed.

  If it is determined in step 102 that the main feedback control is stopped, or if it is determined that the sub feedback control is stopped, this routine is executed without performing the processing after step 103. finish.

  On the other hand, if it is determined in step 102 that the main feedback control is being executed and the sub feedback control is being executed, the processing after step 103 is executed as follows.

  First, in step 103, it is determined whether the output of the downstream sensor 24 is leaner than the lean determination value, and it is determined that the output of the downstream sensor 24 is leaner than the lean determination value. Then, the process proceeds to step 104, and measurement of the sub correction amount (correction amount by sub feedback control) is started. Thereafter, the process proceeds to step 105, where it is determined whether or not the output of the downstream sensor 24 has converged to the control target value. When it is determined that the output of the downstream sensor 24 has converged to the control target value, step 106 is performed. Then, the measurement of the sub correction amount is finished.

  By the processing of these steps 103 to 106, the behavior (output waveform) of the sub correction amount during the period from when the output of the downstream sensor 24 becomes leaner than the lean determination value until it converges to the control target value is detected. .

  Thereafter, the process proceeds to step 107, where the behavior of the sub correction amount is compared with the reference behavior, and the difference between the behavior of the sub correction amount and the reference behavior (for example, peak portion deviation, change amount deviation, change time deviation). , The control center shift, etc.) is extracted, and then the process proceeds to step 108 to determine the comparison result between the behavior of the sub correction amount and the reference behavior.

  If it is determined in step 108 that the peak portion of the behavior of the sub correction amount is shifted from the peak portion of the reference behavior (see FIG. 3), the process proceeds to step 109 to calculate the sub correction amount. The differential term to be used is changed and corrected so that the behavior of the sub correction amount matches the reference behavior. At this time, if the peak value (absolute value) of the behavior of the sub correction amount is smaller than the peak value (absolute value) of the reference behavior, the differential term is increased. On the other hand, if the peak value (absolute value) of the behavior of the sub correction amount is larger than the peak value (absolute value) of the reference behavior, the differential term is reduced.

  If it is determined in step 108 that the behavior of the sub correction amount is entirely deviated from the reference behavior (see FIG. 4), the process proceeds to step 110 and is used to calculate the sub correction amount. Change the proportional term to correct the behavior of the sub correction amount to match the reference behavior. At this time, if the change amount of the behavior of the sub correction amount is smaller than the change amount of the reference behavior, the proportional term is increased. On the other hand, when the change amount of the behavior of the sub correction amount is larger than the change amount of the reference behavior, the proportional term is decreased. If the change time of the behavior of the sub correction amount is longer than the change time of the reference behavior, the proportional term is increased. On the other hand, when the change time of the behavior of the sub correction amount is shorter than the change time of the reference behavior, the proportional term is reduced.

  If it is determined in step 108 that the control center of the behavior of the sub correction amount is deviated from the control center of the reference behavior (see FIG. 5), the process proceeds to step 111, where the sub correction amount The integral term used for the calculation is changed to correct the behavior of the sub correction amount so as to match the reference behavior. At this time, if the control center of the behavior of the sub correction amount is shifted in the minus direction with respect to the control center of the reference behavior, the integral term is increased. On the other hand, when the control center of the behavior of the sub correction amount is shifted in the plus direction with respect to the control center of the reference behavior, the integral term is reduced.

  By the processing of these steps 109 to 111, the control parameter of the sub feedback control is changed so that the behavior of the sub correction amount matches the reference behavior, and the change in the behavior of the sub correction amount due to individual differences or deterioration of the system is corrected. To do.

  An execution example of the control parameter changing process of the present embodiment described above will be described with reference to the time chart of FIG. During engine operation, while the engine operation state is stable and the main feedback control and sub feedback control are being performed, the air-fuel ratio of the exhaust gas flowing into the catalyst 22 due to disturbance or the like fluctuates in the lean direction, and the downstream sensor 22 Measurement of the sub correction amount is started at the time t1 when the output of the sensor becomes leaner than the lean determination value, and then the sub correction amount is measured at the time t2 when the output of the downstream sensor 24 converges to the control target value. Exit. Thereby, the behavior (output waveform) of the sub correction amount during the period from when the output of the downstream sensor 24 becomes leaner than the lean determination value until it converges to the control target value is detected, and the behavior of the sub correction amount is detected. Control parameters of the sub feedback control (for example, a differential term, a proportional term, an integral term, etc. used for calculating the sub correction amount) so that the behavior of the sub correction amount matches the reference behavior based on the comparison result between the sub correction amount and the reference behavior. change.

  In the present embodiment described above, by comparing the behavior of the sub correction amount and the reference behavior, it is possible to accurately determine the change (deviation) in the behavior of the sub correction amount due to individual differences or deterioration of the system, By changing the control parameters of the sub feedback control so that the behavior of the sub correction amount matches the reference behavior based on the comparison result, the change in the behavior of the sub correction amount due to individual differences and deterioration of the system can be corrected with high accuracy. The exhaust gas can be efficiently purified by the catalyst 22.

  In this embodiment, the control parameter changing process is executed at any time during engine operation (for example, every time the output of the downstream sensor 24 exceeds the lean determination value during execution of the main feedback control and the sub feedback control) Changes in the behavior of the sub-correction amount due to individual differences and deterioration of the system can be corrected, so that changes in the behavior of the sub-correction amount can be corrected early during engine operation to prevent exhaust emission deterioration. .

  It should be noted that the control parameter change process may be executed when the engine 11 is adapted to the control system to obtain an appropriate value of the control parameter for the sub feedback control. In this case, for example, as shown in FIG. 9, when the control system is adapted at the development stage or design stage of the control system of the engine 11, the forced operation is performed during the execution of the main feedback control and the sub feedback control in a stable engine operating state. Thus, a lean disturbance is periodically generated in which the air-fuel ratio of the exhaust gas flowing into the catalyst 22 becomes lean, and the air-fuel ratio downstream of the catalyst 22 is periodically changed in the lean direction. Then, every time the output of the downstream sensor 22 becomes leaner than the lean determination value, the behavior of the sub correction amount is detected, and the sub correction amount is calculated based on the comparison result between the behavior of the sub correction amount and the reference behavior. The control parameter changing process for changing the control parameter of the sub feedback control (for example, the differential term, proportional term, integral term, etc. used for calculating the sub correction amount) so as to match the behavior with the reference behavior is repeated a plurality of times to obtain the sub feedback. Determine the conforming value of the control parameter of the control. As a result, it is possible to accurately obtain an appropriate value for the control parameter of the sub-feedback control, and to set an optimal control parameter.

  In the above embodiment, the control parameter changing process for changing the control parameter of the sub feedback control is executed based on the comparison result between the sub correction amount (correction amount by the sub feedback control) and the reference behavior. The control parameter changing process for changing the control parameter of the sub feedback control based on the comparison result between the behavior of information related to the sub correction amount (for example, the behavior of the output of the downstream sensor 24) and the reference behavior. May be executed.

  In the above embodiment, the control parameter changing process is executed when the output of the downstream sensor 22 is leaner than the lean determination value. However, the output of the downstream sensor 22 is more than the rich determination value. The control parameter changing process may be executed when the rich side is reached.

  1, the air-fuel ratio sensor is used for the upstream sensor 23 and the oxygen sensor is used for the downstream sensor 24. However, an air-fuel ratio sensor may also be used for the downstream sensor 24. An oxygen sensor may be used for both the upstream sensor 23 and the downstream sensor 24.

It is a schematic block diagram of the whole engine control system in one Example of this invention. It is a time chart explaining a control parameter change process. It is a figure explaining the change method of the control parameter when the peak part of the behavior of a sub correction amount has shifted. It is a figure explaining the change method of the control parameter when the behavior of the sub correction amount has shifted as a whole. It is a figure explaining the change method of the control parameter when the control center of the behavior of sub correction amount has shifted. It is a figure explaining rich / lean input control. It is a flowchart explaining the flow of a process of a control parameter change routine. It is a time chart explaining the example of execution of the control parameter change process of a present Example. It is a time chart explaining the example of execution of control parameter change processing of other examples.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 21 ... Exhaust pipe, 22 ... Catalyst, 23 ... Upstream sensor, 24 ... Downstream sensor, 27 ... ECU (main (Feedback control means, sub-feedback control means, control parameter change means)

Claims (5)

In the internal combustion engine air-fuel ratio control apparatus in which sensors for detecting the air-fuel ratio or rich / lean of the exhaust gas are installed on the upstream side and downstream side of the exhaust gas purification catalyst of the internal combustion engine, respectively.
Main feedback control means for performing main feedback control for feedback correction of the fuel injection amount so that the upstream air-fuel ratio of the catalyst becomes the target air-fuel ratio based on the output of the upstream sensor;
Sub-feedback control means for performing sub-feedback control for correcting the main feedback control or the fuel injection amount based on the output of the downstream sensor;
When the output of the downstream sensor exceeds a predetermined value during the execution of the main feedback control and the sub feedback control, the correction amount by the sub feedback control or information related thereto (hereinafter referred to as “sub correction”). Control parameter for performing a control parameter changing process for detecting the behavior of the sub correction amount information and changing the control parameter of the sub feedback control based on a comparison result between the behavior of the sub correction amount information and a predetermined reference behavior And an air-fuel ratio control apparatus for an internal combustion engine.   2. The internal combustion engine according to claim 1, wherein the control parameter changing means includes means for correcting the behavior of the sub correction amount information by executing the control parameter changing process at any time during operation of the internal combustion engine. Engine air-fuel ratio control device.   3. The control parameter changing means includes means for executing the control parameter changing process when adapting a control system of an internal combustion engine to obtain a conforming value of the control parameter of the sub feedback control. An air-fuel ratio control apparatus for an internal combustion engine.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the control parameter changing means includes means for setting the reference behavior according to the capacity of the catalyst.   The reference behavior is that when the output of the downstream sensor is leaner than a predetermined lean determination value, the fuel injection amount is corrected stepwise by a predetermined rich step amount, and then the fuel injection amount is calculated. A rich input process for gradually decreasing the increase correction amount, and a fuel injection amount when the fuel injection amount increase correction amount by the rich input process becomes zero or when the oxygen storage amount of the catalyst becomes zero. The sub correction amount set so as to execute rich / lean input control for performing a lean input process for gradually decreasing the fuel injection amount reduction correction amount after performing a stepwise reduction correction by a predetermined lean step amount The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, characterized in that the behavior is information.

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