JP5951068B1 - Air-fuel ratio control apparatus and air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

An air-fuel ratio control apparatus for an internal combustion engine that can suppress deterioration of drivability and exhaust gas and can diagnose deterioration of a three-way catalyst with high accuracy. The feedback control constant is reduced when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage, and the feedback control constant is decreased when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage. After the air-fuel ratio oscillation has shifted from the lean direction to the rich direction or from the rich direction to the lean direction, the air-fuel ratio at the timing when the output value of the upstream air-fuel ratio sensor first becomes equal to or higher than the set voltage is reduced. The feedback control value is learned as a rich learning value or lean learning value, and the rich learning value or lean learning is performed at the second or subsequent transition when the air-fuel ratio vibration shifts from the lean direction to the rich direction or from the rich direction to the lean direction. Set the value to the air-fuel ratio feedback control value. [Selection] Figure 2

Description

  The present invention relates to an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine mounted on a vehicle or the like, and in particular, air-fuel ratio feedback control for periodically oscillating an air-fuel ratio supplied to the internal combustion engine in a rich direction and a lean direction. About what to do.

  Generally, a three-way catalyst that simultaneously purifies harmful components HC, CO, and NOx in exhaust gas is installed in an exhaust passage of an internal combustion engine. Hereinafter, the three-way catalyst is also simply referred to as a catalyst. In this type of catalyst, the purification rate is high for any of the harmful components HC, CO, and NOx in the vicinity of the theoretical air-fuel ratio. Therefore, in an air-fuel ratio control apparatus for an internal combustion engine, an upstream O2 sensor is usually provided upstream of the catalyst, the fuel injection amount is adjusted so that the air-fuel ratio is close to the theoretical air-fuel ratio, and the air-fuel ratio is feedback-controlled. doing.

  Further, the catalyst has an oxygen storage capacity that acts like a primary filter, and absorbs a temporary fluctuation of the upstream air-fuel ratio corresponding to the output value of the upstream O2 sensor from the theoretical air-fuel ratio. It is like that. That is, the catalyst takes in and accumulates oxygen in the exhaust gas when the upstream air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and conversely, when the upstream air-fuel ratio is rich, the catalyst accumulates oxygen accumulated in the catalyst. discharge. Hereinafter, the upstream air-fuel ratio is referred to as upstream A / F. As a result, the temporary fluctuation of the upstream A / F is filtered in the catalyst and hardly appears in the air-fuel ratio downstream of the catalyst. Hereinafter, the air-fuel ratio on the downstream side of the catalyst is referred to as downstream A / F.

  Further, the maximum value of the oxygen storage amount of the catalyst is determined by the amount of the substance having the catalyst storage capacity attached at the time of production of the catalyst, and the oxygen storage amount is the maximum oxygen storage amount or the minimum oxygen storage amount (= 0) of the catalyst. When the value reaches, the fluctuation in the upstream A / F can no longer be absorbed, so the air-fuel ratio in the catalyst deviates from the stoichiometric air-fuel ratio, and the purification capacity of the catalyst decreases. At this time, since the air-fuel ratio on the downstream side of the catalyst greatly deviates from the stoichiometric air-fuel ratio, it can be detected that the oxygen storage amount of the catalyst has reached the maximum value or the minimum value (= 0).

  In addition, the catalyst is exposed to high-temperature exhaust gas, but it is designed so that the purification function of the catalyst does not rapidly deteriorate under use conditions normally considered in an internal combustion engine for a vehicle. However, the oxygen storage capacity of the catalyst may be significantly reduced due to some cause during use, for example, in-catalyst combustion that occurs when a misfire occurs. Also, even under normal use conditions, for example, when the mileage reaches tens of thousands of kilometers, the oxygen storage capacity gradually decreases due to deterioration over time.

  That is, when the catalyst deteriorates and the oxygen storage amount decreases, the upstream A / F, which is the output value of the upstream O2 sensor, cannot be absorbed by the catalyst, and the downstream side provided downstream of the catalyst. It is known that the fluctuation of the downstream A / F, which is the output value of the O2 sensor, increases.

  Therefore, an air-fuel ratio control device for an internal combustion engine that diagnoses catalyst deterioration by comparing fluctuations in the output value of the upstream O2 sensor and fluctuations in the output value of the downstream O2 sensor has been proposed (for example, Patent Document 1).

  In recent years, exhaust gas regulations have been strengthened from the improvement of awareness of the global environment, and it has been demanded to detect a more slight catalyst deterioration, that is, a decrease in the maximum oxygen storage amount. In addition, since the heat resistance of substances with oxygen storage capacity is improving year by year, the amount added to the catalyst can be increased, and the maximum oxygen storage amount of the catalyst that requires deterioration diagnosis is increased. Yes.

  Therefore, by increasing the period and width of the air-fuel ratio oscillation in the rich direction and lean direction of the output value of the upstream O2 sensor, the oscillation width of the oxygen storage amount of the catalyst is increased, thereby causing slight deterioration of the catalyst. An air-fuel ratio control apparatus for an internal combustion engine to be diagnosed has been proposed (see, for example, Patent Documents 2 and 3).

  However, in the air-fuel ratio control apparatus for an internal combustion engine described in Patent Documents 1 to 3, the air-fuel ratio oscillation period and vibration width need to be changed greatly according to the change in the maximum oxygen storage amount. There is a problem that various performances such as controllability, exhaust gas performance, air-fuel ratio feedback performance, and torque fluctuation increase are deteriorated.

  Therefore, as a method for solving this problem, an average air-fuel ratio oscillating means is provided, and this average air-fuel ratio oscillating means changes the average air-fuel ratio of the air-fuel ratio periodically oscillated by the air-fuel ratio feedback control means to a rich direction and a predetermined period. In order to vibrate in the lean direction, the means for alternately setting the predetermined rich period and the predetermined lean period of the average air-fuel ratio, and the average air-fuel ratio have a predetermined vibration width in the rich direction in the rich period, and in the lean period Means for setting a feedback control constant corresponding to the rich period and the lean period so as to have a predetermined vibration width in the lean direction, and the period or vibration width of the air-fuel ratio vibration focusing on air-fuel ratio feedback performance and torque fluctuation Without changing the setting, the vibration range of the oxygen storage amount can be changed freely to adapt to catalyst deterioration. Ratio control apparatus has been proposed (e.g., see Patent Document 4).

  However, in the air-fuel ratio control apparatus for an internal combustion engine described in Patent Document 4, when controlling with a predetermined vibration width in the rich direction in the rich period and controlling with a predetermined vibration width in the lean direction during the lean period, Since the air-fuel ratio correction coefficient continues to be added or subtracted until the predetermined period is reached, air-fuel ratio control is performed in a region where the upstream A / F greatly deviates from the stoichiometric air-fuel ratio, and drivability and exhaust gas deterioration are suppressed. There was a problem that it was not possible.

  Therefore, when the air-fuel ratio oscillates, the increase amount of the feedback control constant is reduced when the air-fuel ratio becomes equal to or higher than the voltage corresponding to the theoretical air-fuel ratio, and feedback is performed when the air-fuel ratio becomes equal to or lower than the voltage corresponding to the theoretical air-fuel ratio. It is conceivable to suppress drivability and deterioration of exhaust gas by reducing the amount of decrease in the control constant.

Japanese Patent Publication No. 6-39932 JP-A-6-26330 JP 7-259600 A JP 2008-157133 A

  In a conventional air-fuel ratio control apparatus for an internal combustion engine, the upstream A / F does not deviate from the stoichiometric air-fuel ratio by reducing the control gain of the feedback control constant at the timing when the air-fuel ratio crosses the voltage corresponding to the stoichiometric air-fuel ratio. Air-fuel ratio control in the region can be performed. However, even in this case, the feedback control amount calculated based on the feedback control constant changes due to variations in the combustion state of the internal combustion engine, so that the deterioration of the three-way catalyst cannot be accurately diagnosed. There is.

  The present invention has been made to solve the above-described problems. By performing air-fuel ratio control in a region where the upstream A / F does not deviate from the theoretical air-fuel ratio, drivability and exhaust gas deterioration are reduced. An object of the present invention is to obtain an air-fuel ratio control device and an air-fuel ratio control method for an internal combustion engine that can suppress the deterioration of the three-way catalyst with high accuracy.

  An air-fuel ratio control apparatus for an internal combustion engine according to the present invention is installed in an exhaust system of an internal combustion engine to purify exhaust gas from the internal combustion engine, and is provided upstream of the catalyst to detect an air-fuel ratio in upstream exhaust gas The air-fuel ratio supplied to the internal combustion engine is adjusted according to the upstream air-fuel ratio sensor, the various sensors that detect the operating state of the internal combustion engine, the output value of the upstream air-fuel ratio sensor, and the feedback control constant related to the operating state And an air-fuel ratio feedback control unit that periodically oscillates the air-fuel ratio in the rich direction and the lean direction, and the air-fuel ratio feedback control unit is configured so that the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage. Decrease the increase amount of the feedback control constant and decrease the decrease amount of the feedback control constant at the timing when the output value of the upstream air-fuel ratio sensor falls below the set voltage. After the control gain change unit and the air-fuel ratio oscillation shift from the lean direction to the rich direction, the air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor first becomes equal to or higher than the set voltage is learned as the rich learning value In addition, after the air-fuel ratio oscillation shifts from the rich direction to the lean direction, the feedback control that first learns the air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor is equal to or lower than the set voltage as the lean learning value. And a feedback control value learning unit, wherein the output value of the upstream air-fuel ratio sensor is greater than or equal to a set voltage at the second and subsequent transitions when the air-fuel ratio oscillation transitions from the lean direction to the rich direction. The air-fuel ratio feedback control value at the timing becomes a rich learning value, and the air-fuel ratio oscillation is rich. At the transition second and subsequent shifts to the lean direction from direction, and sets the air-fuel ratio feedback control value at the time when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than a set voltage to the lean learning value.

  An air-fuel ratio control method for an internal combustion engine according to the present invention includes a catalyst installed in an exhaust system of the internal combustion engine to purify exhaust gas from the internal combustion engine, and an air-fuel ratio in the upstream exhaust gas provided upstream of the catalyst. The air-fuel ratio supplied to the internal combustion engine according to the upstream air-fuel ratio sensor for detecting the engine, various sensors for detecting the operating state of the internal combustion engine, the output value of the upstream air-fuel ratio sensor, and the feedback control constant related to the operating state And an air-fuel ratio feedback control section that periodically oscillates the air-fuel ratio in the rich direction and the lean direction, and increases the feedback control constant at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage. An air-fuel ratio control device for an internal combustion engine that reduces the amount of feedback control constant at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage, with a large amount being reduced An air-fuel ratio control method to be executed, wherein after the air-fuel ratio oscillation shifts from the lean direction to the rich direction by the air-fuel ratio feedback control unit, the output value of the upstream air-fuel ratio sensor first becomes equal to or higher than the set voltage. A rich learning value learning step that learns the air-fuel ratio feedback control value as a rich learning value, and after the air-fuel ratio vibration has shifted from the rich direction to the lean direction, the output value of the upstream air-fuel ratio sensor is The lean learning value learning step for learning the air-fuel ratio feedback control value at the timing as the lean learning value, and the output of the upstream air-fuel ratio sensor at the second and subsequent transitions when the vibration of the air-fuel ratio shifts from the lean direction to the rich direction The air-fuel ratio feedback control value at the timing when the value exceeds the set voltage is set to the rich learning value. The air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor becomes lower than the set voltage at the learning value setting step and the second and subsequent transitions when the air-fuel ratio vibration shifts from the rich direction to the lean direction. And a lean learning value setting step for setting the lean learning value.

According to the air-fuel ratio control apparatus and the air-fuel ratio control method for an internal combustion engine according to the present invention, the increase amount of the feedback control constant is reduced at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage, Decrease the feedback control constant decrease at the timing when the output value of the fuel ratio sensor falls below the set voltage, and after the air-fuel ratio oscillation shifts from lean to rich or from rich to lean, first upstream The air-fuel ratio feedback control value at the timing when the output value of the air-fuel ratio sensor becomes equal to or higher than the set voltage is learned as the rich learning value or the lean learning value, and the air-fuel ratio oscillation changes from the lean direction to the rich direction or from the rich direction to the lean direction. At the time of the second and subsequent transitions, the rich learning value or lean learning value is set to the air-fuel ratio Set to back control value.
Therefore, by performing air-fuel ratio control in a region where the upstream A / F does not deviate from the stoichiometric air-fuel ratio, drivability and exhaust gas deterioration can be suppressed and deterioration of the three-way catalyst can be diagnosed with high accuracy.

1 is a configuration diagram schematically showing an air-fuel ratio control apparatus for an internal combustion engine according to Embodiment 1 of the present invention. FIG. It is a functional block diagram which shows the basic composition of the control circuit in FIG. It is a flowchart which shows the arithmetic processing operation | movement by the air fuel ratio feedback control part in FIG. 3 is a timing chart for supplementarily explaining the operation of the air-fuel ratio feedback control unit in FIG. 2. It is a flowchart which shows the arithmetic processing operation | movement by the feedback control value learning part in FIG.

  Hereinafter, preferred embodiments of an air-fuel ratio control apparatus and an air-fuel ratio control method for an internal combustion engine according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals. I will explain.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing the entire air-fuel ratio control apparatus for an internal combustion engine according to Embodiment 1 of the present invention, together with peripheral devices. In FIG. 1, an internal combustion engine 101 is provided with an intake pipe 105 having an air cleaner 102, a throttle valve 103, and a surge tank 104 as an intake system.

  The intake pipe 105 includes an air flow sensor 106 for detecting the intake air amount Qa, an injector 107 for injecting fuel, a throttle sensor 117 for detecting the throttle opening θ of the throttle valve 103, and an idle switch 118 for detecting idling. And are provided. The idle switch 118 generates an idle signal DL that is turned on at an idling opening, that is, when the throttle opening θ is in a fully closed state.

  The internal combustion engine 101 is provided with an exhaust pipe 108 as an exhaust system. In the exhaust pipe 108, a three-way catalyst 109 for purifying harmful components in the exhaust gas is disposed, and an upstream O2 sensor 110 that is disposed on the upstream side of the three-way catalyst 109 and detects an air-fuel ratio; A downstream O2 sensor 111 that is a λO2 sensor that detects an air-fuel ratio is provided on the downstream side of the three-way catalyst 109. Here, the case where the upstream O2 sensor 110 is also a λO2 sensor will be described as an example.

  An internal combustion engine control unit (ECU: Engine Control Unit) 112 includes a microcomputer, a central processing unit (CPU: Central Processing Unit) 113, a read only memory (ROM) 114, and a random access. It has a memory (RAM: Random Access Memory) 115, an input / output interface 116, a drive circuit 122, and a backup RAM 124. Hereinafter, the input / output interface 116 is referred to as I / O 116, and the backup RAM 124 is referred to as B-RAM 124.

  The internal combustion engine 101 also generates a water temperature sensor 119 for detecting the coolant temperature WT, a crank angle sensor 120 for generating a crank angle signal CA corresponding to the crank angle position, and a cam angle signal corresponding to the cam angle position. A cam angle sensor 121 is provided. A warning lamp 123 is connected to the I / O 116.

  The water temperature sensor 119, the crank angle sensor 120, and the cam angle sensor 121 are combined with other sensor means, that is, the air flow sensor 106, the upstream O2 sensor 110, the downstream O2 sensor 111, the throttle sensor 117, the idle switch 118, and the like. Various sensors that detect the operating state of the engine 101 are configured, and each detection signal is input to the ECU 112 as operating state information.

  In the internal combustion engine 101 shown in FIG. 1, the intake air cleaned by the air cleaner 102 is controlled to an intake amount corresponding to the load by the throttle valve 103, and is sent to each cylinder of the internal combustion engine 101 via the surge tank 104 and the intake pipe 105. Inhaled. At this time, the intake air amount Qa to the internal combustion engine 101 is detected by the air flow sensor 106. Further, fuel for each cylinder of the internal combustion engine 101 is injected into the intake pipe 105 through the injector 107. The intake air amount Qa may be estimated based on the operating point of the internal combustion engine 101 and the pressure in the surge tank 104 instead of being detected by the air flow sensor 106.

  The mixture of air and fuel sucked into each cylinder of the internal combustion engine 101 becomes exhaust gas through a combustion stroke, and the exhaust gas passes through the three-way catalyst 109 disposed in the exhaust pipe 108, so that harmful components are contained. Purified and exhausted into the atmosphere.

  At this time, the upstream O2 sensor 110 detects the oxygen concentration λO2 in the exhaust gas upstream of the catalyst to detect whether the atmosphere of the exhaust gas is rich or lean. Further, the downstream O2 sensor 111 detects the oxygen concentration λO2 in the exhaust gas downstream of the catalyst. The upstream O2 sensor 110 and the downstream O2 sensor 111 generate output values V1 and V2 as electrical signals having a voltage corresponding to the air-fuel ratio in the exhaust gas.

  In the ECU 112, operating state information from various sensors, that is, intake air amount Qa, throttle opening θ, idle signal DL, cooling water temperature WT, output value V1 from upstream O2 sensor 110, output value from downstream O2 sensor 111. V2, the crank angle signal CA, the cam angle signal from the cam angle sensor 121, and the like are taken into the CPU 113 via the I / O 116.

  ECU 112 constitutes an air-fuel ratio feedback control system, and is based on output values V1 and V2 from upstream O2 sensor 110 and downstream O2 sensor 111 disposed upstream and downstream of three-way catalyst 109. A drive signal for the injector 107 is generated and a required amount of fuel is injected.

  The ECU 112 functions as a device for detecting the deterioration of the three-way catalyst 109 together with a device for optimally controlling the internal combustion engine 101. The drive circuit 122 in the ECU 112 drives not only the injector 107 but also various actuators related to the internal combustion engine 101, such as an ISC valve (not shown).

  That is, the ECU 112 performs various controls such as ignition timing control and idle speed control in addition to air-fuel ratio control, and detects a failure of various components that cause exhaust gas deterioration as a self-diagnosis function. Further, the warning lamp 123 is turned on via the I / O 116 according to the detected information.

  The ROM 114 stores not only a control routine for the oxygen change amount of the three-way catalyst 109 but also a control program such as a deterioration detection routine for the three-way catalyst 109, and maps necessary for these control processes. Is also stored.

  FIG. 2 is a functional block diagram showing a basic configuration of the ECU 112 in FIG. 1, and each part in FIG. As described above, the ECU 112 includes the output value V1 of the upstream O2 sensor 110 that is the air-fuel ratio in the exhaust gas upstream of the three-way catalyst 109, and the downstream side that is the air-fuel ratio in the exhaust gas downstream of the three-way catalyst 109. The output value V2 of the O2 sensor 111 and detection information from other various sensors are input.

  In FIG. 2, the ECU 112 includes an air-fuel ratio feedback control unit 201 and a catalyst deterioration diagnosis unit 202. The air-fuel ratio feedback control unit 201 and the catalyst deterioration diagnosis unit 202 include an output value V1 of the upstream O2 sensor 110. Is entered. Further, the catalyst deterioration diagnosis unit 202 is inputted with the output value V2 of the downstream O2 sensor 111 and detection information from other various sensors.

  The air-fuel ratio feedback control unit 201 controls the drive circuit 122 of the injector 107 according to the output value V1 of the upstream O2 sensor 110 and the feedback control constant related to the operating state, thereby supplying the air-fuel ratio supplied to the internal combustion engine 101. Is adjusted to periodically oscillate the air-fuel ratio in the rich direction and the lean direction. Hereinafter, the feedback control constant is also simply referred to as a control constant.

  In addition, the air-fuel ratio feedback control unit 201 controls the control gain change unit 203 that changes the control gain of the air-fuel ratio feedback control unit 201 according to the output value V1 of the upstream O2 sensor 110, and the control period of the air-fuel ratio feedback control unit 201. A control period measuring unit 204 for measuring, and a feedback control value learning unit 205 for learning the air-fuel ratio feedback control value of the air-fuel ratio feedback control unit 201 are provided.

  The control gain changing unit 203 decreases the increase amount of the control constant at the timing when the output value V1 of the upstream O2 sensor 110 becomes equal to or higher than the voltage corresponding to the theoretical air-fuel ratio that is the set voltage, and the output value of the upstream O2 sensor 110. The decrease amount of the control constant is reduced at the timing when V1 becomes equal to or lower than the voltage corresponding to the theoretical air-fuel ratio. Hereinafter, when it is described as a set voltage, it means a voltage corresponding to the theoretical air-fuel ratio.

  After the air-fuel ratio oscillation has shifted from the lean direction to the rich direction, the control period measuring unit 204 is the control period until the increase in the control constant is reduced, or after the air-fuel ratio oscillation has shifted from the rich direction to the lean direction. Then, the control period until the decrease amount of the control constant is reduced is measured. Note that the air-fuel ratio feedback control unit 201 stops the air-fuel ratio vibration process when the control period is longer than a predetermined set period.

  The feedback control value learning unit 205 first performs rich learning of the air-fuel ratio feedback control value at the timing when the output value V1 of the upstream O2 sensor 110 first becomes equal to or higher than the set voltage after the vibration of the air-fuel ratio shifts from the lean direction to the rich direction. Learn as a value. Further, the feedback control value learning unit 205 first calculates the air-fuel ratio feedback control value at the timing when the output value V1 of the upstream O2 sensor 110 becomes equal to or lower than the set voltage after the air-fuel ratio oscillation shifts from the rich direction to the lean direction. Learn as lean learning value.

  Further, the feedback control value learning unit 205 performs the air-fuel ratio at the timing when the output value V1 of the upstream O2 sensor 110 becomes equal to or higher than the set voltage at the second and subsequent transitions when the vibration of the air-fuel ratio shifts from the lean direction to the rich direction. Set the feedback control value to the rich learning value. Further, the feedback control value learning unit 205 performs the air-fuel ratio at the timing when the output value V1 of the upstream O2 sensor 110 becomes equal to or lower than the set voltage at the second and subsequent transitions when the vibration of the air-fuel ratio shifts from the rich direction to the lean direction. Set the feedback control value to the lean learning value.

  When the catalyst deterioration diagnosis unit 202 determines that the catalyst deterioration diagnosis can be performed based on the detection information from the various sensors, the catalyst deterioration diagnosis unit 202 vibrates the air-fuel ratio upstream of the three-way catalyst 109 in the rich direction and the lean direction, Control constants and vibration cycles used in the air-fuel ratio feedback control unit 201 are manipulated so that the air-fuel ratio downstream of the three-way catalyst 109 vibrates in the rich direction and the lean direction. At this time, the catalyst deterioration diagnosis unit 202 may set a vibration cycle determined experimentally in advance according to the operating state of the internal combustion engine 101.

  Further, the catalyst deterioration diagnosis unit 202 has a deterioration index value calculation unit 206 that calculates the deterioration index value of the three-way catalyst 109. The deterioration index value calculation unit 206 calculates the degree of deterioration of the three-way catalyst 109 as a deterioration index value from the degree of approximation between the output value V1 of the upstream O2 sensor 110 and the output value V2 of the downstream O2 sensor 111. Further, the catalyst deterioration diagnosis unit 202 diagnoses the deterioration of the three-way catalyst 109 based on the deterioration index value calculated by the deterioration index value calculation unit 206, and outputs the diagnosis result to an alarm driving unit such as the warning lamp 123. .

  Next, referring to the flowchart of FIG. 3, the arithmetic processing operation by the air-fuel ratio feedback control unit 201 in FIG. 2, the arithmetic processing operation by the control gain changing unit 203 of the air-fuel ratio feedback control unit 201 in FIG. An arithmetic processing operation by the control period measurement unit 204 of the air-fuel ratio feedback control unit 201 in FIG. 2 will be described. The calculation processing routine of FIG. 3 shows a calculation control procedure of the fuel correction coefficient FAF based on the output value V1 of the upstream O2 sensor 110, and is executed by the air-fuel ratio feedback control unit 201 every predetermined period such as 5 msec. .

  In FIG. 3, the symbols “Y” and “N” of the branch portions from the respective determination processes indicate “YES” and “NO”, respectively. First, the output value V1 of the upstream O2 sensor 110 is A / D converted and captured (step S401), and it is determined whether the air-fuel ratio feedback F / B condition by the upstream O2 sensor 110, that is, the closed loop condition is satisfied. Determination is made (step S402).

  At this time, for example, during engine starting, during enrichment control at low water temperature, during enrichment control with high load power increase, during lean control for fuel efficiency improvement, during lean control after start, during fuel cut, etc. When an air-fuel ratio control condition other than the stoichiometric air-fuel ratio control is satisfied, or when the upstream O2 sensor 110 is in an inactive state or a failure, the closed-loop condition is determined to be not satisfied, and in other cases, the closed-loop condition is not satisfied. It is determined that the condition is satisfied.

  If it is determined in step S402 that the closed loop condition is not satisfied (ie, NO), the fuel correction coefficient FAF is set to “1.0” (step S441), and the delay counter CDLY is reset to “0” (step S441). S442), the counter TAF for measuring the control period from when the delayed air-fuel ratio flag F1 is inverted until the output value V1 of the upstream O2 sensor 110 becomes equal to or higher than the set voltage or lower than the set voltage is reset to “0” (S442). Step S443). Note that the fuel correction coefficient FAF may be a value immediately before the end of the closed loop control stored in the backup RAM 124 in the ECU 112 or a learned value.

  Subsequently, it is determined whether or not the output value V1 of the upstream O2 sensor 110 is equal to or lower than the comparison voltage VR1, that is, in a lean state (step S444), and the upstream A / F is in a lean state when V1 ≦ VR1 (that is, YES). ), The pre-delay air-fuel ratio flag F0 is set to “0” in the lean state (step S445), and the post-delay air-fuel ratio flag F1 is set to “0” in the lean state (step S446). Then, the process routine of FIG. 3 is exited (step S449). The comparison voltage VR1 is set to a lean determination reference voltage, for example, about 0.45V.

  If it is determined in step S444 that V1> VR1 (that is, NO), the upstream A / F is in the rich state, so the pre-delay air-fuel ratio flag F0 is set to “1” in the rich state (step S447). Then, the delayed air-fuel ratio flag F1 is set to “1” in the rich state (step S448), and the process routine of FIG. 3 is exited (step S449). By the above steps S441 to 448, the initial value when the air-fuel ratio closed loop condition is not established is set.

  On the other hand, if it is determined in step S402 that the closed loop condition is satisfied (that is, YES), then, whether or not the output value V1 of the upstream O2 sensor 110 is equal to or lower than the comparison voltage VR1, for example, 0.45V, that is, It is determined whether the upstream A / F of the three-way catalyst 109 is rich or lean with respect to the comparison voltage VR1 (step S403).

  If it is determined in step S403 that V1 ≦ VR1 (that is, YES), it is determined that the upstream A / F is in the lean state, and subsequently, it is determined whether or not the delay counter CDLY is equal to or greater than the maximum value TDR. (Step S404). The maximum value TDR corresponds to a “rich delay period” for holding a determination that the engine is in the lean state even if the output value V1 of the upstream O2 sensor 110 changes from lean to rich, and is a positive value. Defined by

  If it is determined in step S404 that CDLY ≧ TDR (ie, YES), the delay counter CDLY is reset to “0” (step S405), and the pre-delay air-fuel ratio flag F0 is set to “0” in the lean state. (Step S406), the process proceeds to step S416, which will be described later.

  If it is determined in step S404 that CDLY <TDR (that is, NO), it is subsequently determined whether or not the pre-delay air-fuel ratio flag F0 is “0” in the lean state (step S407). If it is determined that F0 = 0 (ie, YES), the delay counter CDLY is decremented by “1” (step S408), and the process proceeds to step S416.

  If it is determined in step S407 that F0 = 1 (ie, NO) in the rich state, the delay counter CDLY is incremented by “1” (step S409), and the process proceeds to step S416.

  On the other hand, if it is determined in step S403 that V1> VR1 (that is, NO), it is considered that the upstream A / F is in a rich state, and then whether or not the delay counter CDLY is equal to or smaller than the minimum value TDL is determined. Determination is made (step S410). Note that the minimum value TDL corresponds to a “lean delay period” for maintaining a determination that the upstream side O2 sensor 110 is in a rich state even if the output value V1 of the upstream O2 sensor 110 changes from rich to lean. Defined by

  If it is determined in step S410 that CDLY ≦ TDL (ie, YES), the delay counter CDLY is reset to “0” (step S411), and the pre-delay air-fuel ratio flag F0 is set to “1” in the rich state. (Step S412), the process proceeds to step S416.

  If it is determined in step S410 that CDLY> TDL (that is, NO), it is subsequently determined whether or not the pre-delay air-fuel ratio flag F0 is “0” in the lean state (step S413). If it is determined that F0 = 0 (ie, YES), the delay counter CDLY is decremented by “1” (step S414), and the process proceeds to step S416.

  If it is determined in step S413 that F0 = 1 (ie, NO) in the rich state, the delay counter CDLY is incremented by “1” (step S415), and the process proceeds to step S416.

  In step S416, it is determined whether or not the delay counter CDLY is equal to or smaller than the minimum value TDL. If it is determined that CDLY> TDL (that is, NO), the process proceeds to step S419 described later.

  If it is determined in step S416 that CDLY ≦ TDL (that is, YES), the delay counter CDLY is set to the minimum value TDL (step S417), and the post-delay air-fuel ratio flag F1 is set to “0” in the lean state. (Step S418). That is, when the delay counter CDLY reaches the minimum value TDL, the delay counter CDLY is guarded with the minimum value TDL, and the delayed air-fuel ratio flag F1 is set to “0” in the lean state.

  Subsequently, it is determined whether or not the delay counter CDLY is equal to or greater than the maximum value TDR (step S419). If it is determined that CDLY <TDR (that is, NO), the process proceeds to step S422 described later.

  If it is determined in step S419 that CDLY ≧ TDR (that is, YES), the delay counter CDLY is set to the maximum value TDR (step S420), and the post-delay air-fuel ratio flag F1 is set to “1” in the rich state. After setting (step S421), the process proceeds to step S422. That is, when the delay counter CDLY reaches the maximum value TDR, the delay counter CDLY is guarded with the maximum value TDR, and the delayed air-fuel ratio flag F1 is set to “1” in the rich state.

  In step S422, prior to execution of the skip increase / decrease process of the fuel correction coefficient FAF or the integration process, it is first determined whether or not the post-delay air-fuel ratio flag F1 has been reversed. Judge by whether or not.

  In step S422, if it is determined that the sign of the post-delay air-fuel ratio flag F1, that is, the air-fuel ratio is inverted (that is, YES), then the counter TAF is reset to “0” (step S423), and the rich It is determined whether the inversion from lean to lean or the inversion from lean to rich is based on whether the value of the post-delay air-fuel ratio flag F1 is “0” (step S424).

  If it is determined in step S424 that F1 = 0 (that is, YES), it is the reverse from rich to lean, so the fuel correction coefficient FAF is set to “FAF + RSR” and is increased by a constant RSR in a skipping manner (step S425). Then, the process proceeds to step S436 described later.

  If it is determined in step S424 that F1 = 1 (that is, NO), it is an inversion from lean to rich. Therefore, the fuel correction coefficient FAF is set to “FAF-RSL” and is decreased by a constant RSL in a skipping manner. (Step S426), the process proceeds to Step S436.

  On the other hand, in step S422, if it is determined that the sign of the post-delay air-fuel ratio flag F1, that is, the air-fuel ratio is not reversed (that is, NO), then the post-delay air-fuel ratio flag F1 is “0” in the lean state. (Step S427), and if it is determined that F1 = 0 (that is, YES), it is in a lean state, and the process proceeds to step S428.

  In step S428, it is determined whether or not the output value V1 of the upstream O2 sensor 110 is equal to or lower than the set voltage VR. If it is determined that V1 ≦ VR (that is, YES), the fuel correction coefficient FAF is set to “FAF + KIR”. As well as increasing the constant KIR (<RSR) (step S429), adding “1” to the counter TAF (step S430), and proceeding to step S436.

  On the other hand, if it is determined in step S428 that V1> VR (that is, NO), the process proceeds to step S451, where it is determined whether or not the vibration of the air-fuel ratio is the first time, and the first time (that is, Yes) is determined. If so, the fuel correction coefficient FAF is increased to “FAF + KIR2” using the constant KIR2 (<KIR) (step S431), and the process proceeds to step S436.

  On the other hand, if it is determined in step S451 that the air-fuel ratio oscillation is the second or later (that is, No), the rich learning value learned by the feedback control value learning unit 205 is set in the fuel correction coefficient FAF (step S452). The process proceeds to step S436.

  That is, in step S431, by using the constant KIR2 smaller than the constant KIR as the increase amount of the fuel correction coefficient FAF, the A / F control width after the fuel correction coefficient FAF has advanced to some extent in the rich direction can be suppressed. In addition, drivability and exhaust gas deterioration associated therewith can be suppressed. Note that the increase amount “KIR2” used in step S431 may be set to “0” so that the fuel correction coefficient FAF after the fuel correction coefficient FAF has advanced to some extent in the rich direction is not increased.

  Further, in step S428, when the setting voltage VR for switching the increase amount of the fuel correction coefficient FAF is set to a voltage corresponding to the theoretical air-fuel ratio of the upstream O2 sensor 110, the catalyst upstream atmosphere is in a lean state. When the atmosphere upstream of the catalyst is rich, the small increase amount “KIR2” can be set. Combining with the operation in the lean state in step S432, which will be described later, makes it possible to reliably perform the air-fuel ratio oscillation between the rich state and the lean state, and the A / F control range tends to increase due to acceleration / deceleration and the like. In this case, an effect of suppressing exhaust gas deterioration when the oxygen storage amount at the time of the deteriorated catalyst is reduced can be obtained.

  On the other hand, if it is determined in step S427 that F1 = 1 (that is, NO), the rich state is set, and the process proceeds to step S432.

  In step S432, it is determined whether or not the output value V1 of the upstream O2 sensor 110 is equal to or higher than the set voltage VL. If it is determined that V1 ≧ VL (that is, YES), the fuel correction coefficient FAF is set to “FAF− “KIL” is decreased by a constant KIL (<RSL) (step S433), and “1” is added to the counter TAF (step S434), and the process proceeds to step S436.

  On the other hand, if it is determined in step S432 that V1 <VL (that is, NO), the process proceeds to step S453, where it is determined whether or not the vibration of the air-fuel ratio is the first time, and the first time (that is, Yes) is determined. If so, the fuel correction coefficient FAF is reduced to “FAF−KIL2” using the constant KIL2 (<KIL) (step S435), and the process proceeds to step S436.

  On the other hand, if it is determined in step S453 that the air-fuel ratio oscillation is the second or later (that is, No), the lean learning value learned by the feedback control value learning unit 205 is set in the fuel correction coefficient FAF (step S454). The process proceeds to step S436.

  That is, in step S435, by using the constant KIL2 smaller than the constant KIL as the amount of decrease in the fuel correction coefficient FAF, the A / F control range after the fuel correction coefficient FAF has advanced to some extent in the lean direction can be suppressed. In addition, drivability and exhaust gas deterioration associated therewith can be suppressed. Note that the reduction amount “KIL2” used in step S435 may be set to “0” so that the fuel correction coefficient FAF after the fuel correction coefficient FAF has advanced to some extent in the lean direction is not reduced.

  Further, in step S432, when the setting voltage VL for switching the reduction amount of the fuel correction coefficient FAF is set to a voltage corresponding to the theoretical air-fuel ratio of the upstream O2 sensor 110, the catalyst upstream atmosphere is in a rich state. The large reduction amount “KIL” can be set, and when the atmosphere upstream of the catalyst is lean, the small reduction amount “KIL2” can be set. By combining with the operation in the rich state in step S428, the air-fuel ratio oscillation can be reliably performed between the rich state and the lean state, and the A / F control range tends to increase due to acceleration / deceleration and the like. In this case, an effect of suppressing the deterioration of exhaust gas can be obtained when the oxygen storage amount at the time of the deteriorated catalyst is reduced.

  The integral constants KIR, KIR2, KIL, and KIL2 are set to sufficiently small values compared to the skip constants RSR and RSL. Therefore, in steps S429 and 431, the fuel injection amount in the lean state, that is, F1 = 0 is gradually increased, and in steps S433 and 435, the fuel injection amount in the rich state, that is, F1 = 1 is gradually decreased. I will let you.

  In step S436, it is determined whether or not the counter TAF is smaller than the counter upper limit TAFH. If it is determined that TAF <TAFH (that is, YES), the process proceeds to step S449.

  On the other hand, if it is determined in step S436 that TAF ≧ TAFH (that is, NO), the process proceeds to step S441 to stop the air-fuel ratio vibration process.

  In other words, when the behavior of the upstream O2 sensor 110 is delayed due to a response delay or the like due to deterioration of the O2 sensor, and the period in which V1> VR is satisfied in step S428 or the period in which V1 <VL is increased in step S432. Then, it is determined that the A / F control range of the fuel correction coefficient FAF has become too large, and the execution of the air-fuel ratio oscillation process is stopped. As an effect thereof, it is possible to reduce the possibility of erroneously detecting a normal catalyst as a deteriorated catalyst at the time of diagnosis of the deteriorated catalyst.

  The calculation process in FIG. 3 is completed as described above, and the fuel correction coefficient FAF calculated in steps S401 to S454 is stored in the RAM 115 in the ECU 112.

  Next, the arithmetic processing operation shown in FIG. 3 will be supplementarily described with reference to the timing chart of FIG. In the timing chart of FIG. 4A, the output value V1 of the upstream O2 sensor 110 indicates the timing of switching the increase amount of the fuel correction coefficient FAF to KIR2 and the decrease amount to KIL2 in the conventional air-fuel ratio control device of the internal combustion engine. The timing when the set voltage VR1 is reached and the values of KIR2 and KIL2 are both “0”. The timing chart of FIG. 4B is the air-fuel ratio control of the internal combustion engine according to the first embodiment of the present invention. This is a case where the air-fuel ratio feedback control value in the apparatus is learned and the learning value is set in the fuel correction coefficient FAF.

  4A and 4B, when the comparison result of the rich / lean determination is obtained based on the output value V1 of the upstream O2 sensor 110, that is, the rich / lean determination result, the air / fuel ratio before the delay process is obtained. The pre-delay air-fuel ratio flag F0 that responds to the signal changes to a rich state or a lean state.

  The delay counter CDLY is counted up in response to the rich state of the pre-delay air-fuel ratio flag F0 corresponding to the pre-delay air-fuel ratio signal within the range between the maximum value TDR and the minimum value TDL. Counts down in response to a lean condition. As a result, the post-delay air-fuel ratio flag F1 indicates the delayed air-fuel ratio signal.

  For example, even when the comparison result of the air-fuel ratio signal before delay processing, that is, the output value V1, is inverted from lean to rich at time t1, the air-fuel ratio signal subjected to delay processing, that is, the post-delay air-fuel ratio flag F1 is It changes to rich at time t2 after being held lean for the period τDR.

  At this time, since the time up to time t1 or t5 and the value of the delay counter CDLY at that timing differ each time depending on the combustion, the value of the fuel correction coefficient FAF that is fixed after time t1 also differs for each vibration.

  Similarly, even at time t3, even if the air-fuel ratio signal before delay processing, that is, the upstream A / F changes from rich to lean, the air-fuel ratio signal after delay processing, that is, the post-delay air-fuel ratio flag F1, At time t4 after the period τDL is kept rich, it changes to lean.

  At this time, since the time until time t3 or t7 and the value of the delay counter CDLY at that timing differ each time depending on the combustion, the value of the fuel correction coefficient FAF fixed after time t3 also differs for each vibration.

  In the waveform of the fuel correction coefficient FAF in FIG. 4, the gradient in the increasing direction until the timing when the output value V1 of the upstream O2 sensor 110 becomes VR1 corresponds to the integration constant KIR, and the output of the upstream O2 sensor 110 The gradient in the increasing direction after the timing when the value V1 becomes VR1 corresponds to the integral constant KIR2, that is, “0” in FIGS.

  The inclination in the decreasing direction until the timing when the output value V1 of the upstream O2 sensor 110 becomes VR1 corresponds to the integration constant KIL, and decreases after the timing when the output value V1 of the upstream O2 sensor 110 becomes VR1. The inclination of the direction corresponds to the integral constant KIL2, that is, “0” in FIGS.

  4 (a) and 4 (b), the product of the fuel correction coefficient FAF and the vibration period, that is, the fuel correction coefficient FAF and the center line of the fuel correction coefficient FAF in FIGS. 4 (a) and 4 (b). As the area to be formed, the O2 manipulated variable used at the time of catalyst diagnosis is defined. At this time, if there is a difference in the feedback control amount due to variations in combustion, the O2 manipulated variable also varies, so that the output of the downstream O2 sensor 111 varies, and the deterioration of the three-way catalyst 109 cannot be diagnosed accurately. there were.

  Therefore, in the waveform of the fuel correction coefficient FAF in FIG. 4B, after the air-fuel ratio oscillation shifts from the lean direction to the rich direction, the output value V1 from the upstream O2 sensor 110 first becomes equal to or higher than the set voltage VR1. The air-fuel ratio feedback control value FAF at the timing t1 is learned as a rich learning value, and the output value V1 from the upstream O2 sensor 110 is set at the second and subsequent transitions when the air-fuel ratio vibration shifts from the lean direction to the rich direction. The air-fuel ratio feedback control value at timing t5 when the voltage VR1 or higher is set to the rich learning value.

  Further, in the waveform of the fuel correction coefficient FAF in FIG. 4B, after the air-fuel ratio oscillation shifts from the rich direction to the lean direction, the output value V1 from the upstream O2 sensor 110 first becomes equal to or lower than the set voltage VR1. The air-fuel ratio feedback control value FAF at the timing t3 is learned as a lean learning value, and the output value V1 from the upstream O2 sensor 110 is set at the second and subsequent transitions when the air-fuel ratio vibration shifts from the rich direction to the lean direction. The air-fuel ratio feedback control value at the timing t7 when the voltage VR1 or higher is set to the lean learning value.

  Further, during the period in which the integration constants KIR and KIL are used for the fuel correction coefficient FAF, the counter TAF is integrated. When the counter TAF becomes equal to or greater than TAFH, the execution of the air-fuel ratio oscillation process is stopped.

  In this way, by setting the first air-fuel ratio feedback control value as the learned value to the second and subsequent air-fuel ratio feedback control values, the difference in feedback control amount due to combustion variation is eliminated, and the variation in O2 manipulated variable is reduced. Since the output can be reduced, the output of the downstream O2 sensor 111 can be reliably shaken, and variations in the deterioration index value can be suppressed.

  That is, by accurately manipulating the O2 manipulated variable, the outputs of the upstream O2 sensor 110 and the downstream O2 sensor 111 are reliably shaken, so that variation in the degradation index value at the time of catalyst degradation diagnosis can be suppressed, and Diagnosis can be improved.

  Next, the calculation processing operation by the feedback control value learning unit 205 in FIG. 2 will be described with reference to the flowchart in FIG.

  First, it is determined whether or not the catalyst is being diagnosed (step S501). If it is determined that the catalyst is not being diagnosed (ie, No), the flowchart of FIG. 5 is terminated. On the other hand, if it is determined that the catalyst is being diagnosed (ie, Yes), the process proceeds to step S502.

  In step S502, it is determined whether the direction of air-fuel ratio oscillation is the lean direction or the rich direction. If it is determined in step S502 that the air-fuel ratio oscillation is from the lean direction to the rich direction (ie, Yes), the process proceeds to step S503, where the air-fuel ratio oscillation is from the rich direction to the lean direction (ie, No). ), The process proceeds to step S507.

  In step S503, it is determined whether the number of vibrations in the rich direction is the first time. If it is determined in step S503 that it is the first time (that is, Yes), the process proceeds to step S504, and the previous value V1 (n−1) of the output value V1 from the downstream O2 sensor 111 is less than VR1. It is determined whether or not.

  If it is determined in step S504 that V1 (n−1) is less than VR1 (ie, Yes), the current value V1 (n) of the output value V1 from the downstream O2 sensor 111 is equal to or greater than VR1. Whether or not V1 (n) is equal to or higher than VR1 (ie, Yes), the fuel correction coefficient FAF is stored in the rich learning value (step S506). The flowchart of FIG. 5 ends.

  On the other hand, if it is determined in step S503 that it is not the first time (that is, No), if it is determined in step S504 that V1 (n-1) is equal to or higher than VR1 (that is, No), and in step S505. , V1 (n) is determined to be less than VR1 (that is, No), the flowchart of FIG.

  In step S507, it is determined whether or not the number of vibrations in the lean direction is the first time. If it is determined in step S507 that the current time is the first time (that is, Yes), the process proceeds to step S508, and the previous value V1 (n−1) of the output value V1 from the downstream O2 sensor 111 is larger than VR1. It is determined whether or not.

  If it is determined in step S508 that V1 (n-1) is greater than VR1 (ie, Yes), the current value V1 (n) of the output value V1 from the downstream O2 sensor 111 is equal to or less than VR1. Whether or not V1 (n) is equal to or lower than VR1 (ie, Yes), the fuel correction coefficient FAF is stored in the lean learning value (step S510). The flowchart of FIG. 5 ends.

  On the other hand, if it is determined in step S507 that it is not the first time (that is, No), if it is determined in step S508 that V1 (n−1) is equal to or lower than VR1 (that is, No), and in step S509. , V1 (n) is determined to be larger than VR1 (ie, No), the flowchart of FIG.

  The deterioration diagnosis cycle of the three-way catalyst 109 is determined by experimentally measuring the diagnosis cycle in the steady state based on the operating state of the internal combustion engine 101, for example, the engine speed Ne, the load, the intake air amount Qa, the catalyst temperature, and the like. To set.

  As described above, the fuel correction coefficient FAF used for the upstream A / F air-fuel ratio oscillation is increased from the theoretical air-fuel ratio by decreasing the increase or decrease according to the output value V1 of the upstream O2 sensor 110. It will not come off. Therefore, as seen in the behavior of the output value V2 of the downstream O2 sensor 111, the vibration width of the actual air-fuel ratio becomes small, so that the exhaust gas fluctuation can be suppressed and the deterioration of the exhaust gas can be suppressed. Further, as seen in the behavior of the engine rotation, the vibration width of the actual air-fuel ratio becomes small, so that the rotation fluctuation can be suppressed and the deterioration of drivability can be suppressed. At the same time, variations in the degradation index value can be suppressed.

As described above, according to the first embodiment, the increase amount of the feedback control constant is reduced at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage, and the output value of the upstream air-fuel ratio sensor is set. The amount of decrease in the feedback control constant is reduced at the timing when the voltage becomes lower than the voltage, and after the air-fuel ratio oscillation shifts from the lean direction to the rich direction or from the rich direction to the lean direction, the output value of the upstream air-fuel ratio sensor is first The air-fuel ratio feedback control value at the timing when it becomes the set voltage or higher is learned as a rich learning value or lean learning value, and the air-fuel ratio oscillation changes from the lean direction to the rich direction or from the rich direction to the lean direction for the second and subsequent times. At the time of transition, the rich learning value or the lean learning value is set as the air-fuel ratio feedback control value.
Therefore, by performing air-fuel ratio control in a region where the upstream A / F does not deviate from the stoichiometric air-fuel ratio, drivability and exhaust gas deterioration can be suppressed and deterioration of the three-way catalyst can be diagnosed with high accuracy.

  In the first embodiment, a λ-type sensor is used as the downstream O2 sensor 111. However, the downstream O2 sensor 111 may be any sensor that can detect the purification state of the three-way catalyst 109 located on the upstream side. Other sensors may be used. For example, even if a linear O2 sensor, NOx sensor, HC sensor, CO sensor, or the like is used, the purification state of the three-way catalyst 109 can be controlled, so that the same effect can be obtained.

  DESCRIPTION OF SYMBOLS 101 Internal combustion engine, 102 Air cleaner, 103 Throttle valve, 104 Surge tank, 105 Intake pipe, 106 Air flow sensor, 107 Injector, 108 Exhaust pipe (exhaust system), 109 Three-way catalyst, 110 Upstream O2 sensor (Upstream air-fuel ratio sensor ), 111 downstream O2 sensor, 112 ECU, 113 CPU, 114 ROM, 115 RAM, 116 I / O, 117 throttle sensor, 118 idle switch, 119 water temperature sensor, 120 crank angle sensor, 121 cam angle sensor, 122 drive circuit , 123 warning lamp, 124 B-RAM, 201 air-fuel ratio feedback control unit, 202 catalyst deterioration diagnosis unit, 203 control gain change unit, 204 control period measurement unit, 205 feedback control value learning unit, 206 deterioration Target value calculation unit, the output value of V1 upstream O2 sensor output value V2 downstream O2 sensor, WT coolant temperature, CA crank angle, DL idle signal, theta throttle opening, Qa intake air amount.

Claims (4)

A catalyst installed in an exhaust system of the internal combustion engine to purify exhaust gas from the internal combustion engine;
An upstream air-fuel ratio sensor that is provided upstream of the catalyst and detects an air-fuel ratio in the upstream exhaust gas;
Various sensors for detecting the operating state of the internal combustion engine;
The air-fuel ratio supplied to the internal combustion engine is adjusted according to the output value of the upstream air-fuel ratio sensor and the feedback control constant related to the operating state, and the air-fuel ratio is periodically oscillated in the rich direction and the lean direction. An air-fuel ratio feedback control unit
The air-fuel ratio feedback control unit
The feedback control constant is decreased at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than a set voltage, and the feedback control constant is decreased at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage. A control gain changing unit for reducing the decrease amount of
After the air-fuel ratio oscillation shifts from the lean direction to the rich direction, the air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage is first learned as the rich learning value, Feedback control value learning that first learns, as a lean learning value, an air-fuel ratio feedback control value at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage after the oscillation of the fuel ratio shifts from the rich direction to the lean direction. And
The feedback control value learning unit
The air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage at the second and subsequent transitions when the air-fuel ratio vibration shifts from the lean direction to the rich direction is set to the rich learning value. As well as setting
The air-fuel ratio feedback control value at the timing when the output value of the upstream-side air-fuel ratio sensor becomes equal to or lower than the set voltage at the second and subsequent transitions when the air-fuel ratio vibration shifts from the rich direction to the lean direction becomes the lean learning value. Set an air-fuel ratio control device for an internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the set voltage is a voltage corresponding to a theoretical air-fuel ratio. After the air-fuel ratio oscillation shifts from the lean direction to the rich direction, the control period until the increase amount of the feedback control constant is reduced, or after the air-fuel ratio oscillation shifts from the rich direction to the lean direction, the feedback control constant A control period measuring unit that measures the control period until the decrease amount of
3. The internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control unit stops executing the air-fuel ratio oscillation process by the air-fuel ratio feedback control unit when the control period is longer than a set period. Air-fuel ratio control device. A catalyst installed in an exhaust system of the internal combustion engine to purify exhaust gas from the internal combustion engine;
An upstream air-fuel ratio sensor that is provided upstream of the catalyst and detects an air-fuel ratio in the upstream exhaust gas;
Various sensors for detecting the operating state of the internal combustion engine;
The air-fuel ratio supplied to the internal combustion engine is adjusted according to the output value of the upstream air-fuel ratio sensor and the feedback control constant related to the operating state, and the air-fuel ratio is periodically oscillated in the rich direction and the lean direction. An air-fuel ratio feedback control unit
When the output value of the upstream air-fuel ratio sensor becomes equal to or higher than a set voltage, the increase amount of the feedback control constant is reduced, and when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage, the feedback control constant An air-fuel ratio control method executed by an air-fuel ratio control device for an internal combustion engine that reduces an amount of decrease,
By the air-fuel ratio feedback control unit,
A rich learning value that first learns an air-fuel ratio feedback control value as a rich learning value at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage after the air-fuel ratio oscillation shifts from the lean direction to the rich direction. Learning steps,
A lean learning value that first learns an air-fuel ratio feedback control value as a lean learning value at a timing when the output value of the upstream air-fuel ratio sensor becomes equal to or lower than the set voltage after the air-fuel ratio oscillation has shifted from the rich direction to the lean direction. Learning steps,
The air-fuel ratio feedback control value at the timing when the output value of the upstream air-fuel ratio sensor becomes equal to or higher than the set voltage at the second and subsequent transitions when the air-fuel ratio vibration shifts from the lean direction to the rich direction is set to the rich learning value. A rich learning value setting step to be set;
The air-fuel ratio feedback control value at the timing when the output value of the upstream-side air-fuel ratio sensor becomes equal to or lower than the set voltage at the second and subsequent transitions when the air-fuel ratio vibration shifts from the rich direction to the lean direction becomes the lean learning value. A lean learning value setting step for setting an air-fuel ratio control method for an internal combustion engine.

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