JP2018159286A - Air-fuel ratio control device for internal combustion engine and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine capable of accurately estimating a state of an air-fuel ratio sensor and controlling an air-fuel ratio with good controllability by making an adjustment by using feedback correction amount corresponding to the state of the air-fuel ratio sensor, and a control method for the air-fuel ratio control device.SOLUTION: In an internal combustion engine for performing air-fuel ratio feedback control by adjusting fuel injection amount by using a catalyst-prior air-fuel ratio sensor 11 and a catalyst-posterior oxygen sensor 15, correction amounts of a catalyst inner central air-fuel ratio and a target air-fuel ratio are calculated based on a catalyst-prior air-fuel ratio sensor signal RABF, a catalyst-posterior oxygen sensor signal VO2R and intake air amount QAR, and a feedback gain corresponding to the catalyst inner central air-fuel ratio and the air-fuel ratio sensor state is adjusted by using the calculated correction amounts. At this time, the feedback gain is corrected by using a gain for determining feedback amount for shift correction of the air-fuel ratio sensor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a vehicle-mounted self-diagnosis regulation technology, and more particularly, to an air-fuel ratio control apparatus for controlling an air-fuel ratio of an internal combustion engine and a control method therefor.

  Practical use of feedback-type air-fuel ratio control device that controls air-fuel ratio based on information on exhaust gas components of internal combustion engines such as engines, as a means to reduce harmful exhaust gas of automobiles and improve fuel efficiency and drivability (For example, refer to Patent Document 1).

  In the above air-fuel ratio control apparatus, abnormalities in the exhaust gas component or the control system may occur due to failure or deterioration of a sensor used, for example, an air-fuel ratio sensor (LAF sensor). There are cases where it is impossible. In particular, since the air-fuel ratio sensor is installed at a position that directly receives engine exhaust, the air-fuel ratio sensor tends to deteriorate due to the influence of high temperature, high pressure, vibration, bad fuel, and the like. Further, in the case of a multi-cylinder engine, since it is affected by the combustion cycle of other cylinders, it is necessary to have extremely accurate detection accuracy.

In addition, North American automobiles must comply with the so-called OBDII regulations that require the installation of on-board self-diagnosis devices, and the air-fuel ratio sensor has an abnormality that exceeds 1.5 times the emission regulation value. It is required to promptly warn the driver and prompt repair.
Therefore, when the detection accuracy of the air-fuel ratio sensor decreases for some reason, it is necessary to take appropriate measures such as replacement of the air-fuel ratio sensor. For this reason, the abnormal state of the air-fuel ratio sensor is determined using the output signal of the oxygen sensor.

Japanese Patent No. 5851569

  However, since the state of the air-fuel ratio sensor cannot be accurately estimated, the correction amount for feedback according to the state of the air-fuel ratio sensor must be set to be uniformly small. If the correction amount for feedback is small, the controllability when the air-fuel ratio sensor is normal is good, but it takes time to absorb the error when a failure occurs, and the drivability deteriorates during the period until the error due to the failure is absorbed . On the other hand, if the correction amount for feedback is increased, the time required to absorb the error when the air-fuel ratio sensor fails can be shortened, but there is a problem that the controllability after absorbing the error due to the failure is deteriorated.

  The present invention has been made in view of the circumstances as described above. The object of the present invention is to accurately estimate the state of the air-fuel ratio sensor, and to adjust the feedback correction amount according to the state of the air-fuel ratio sensor. Another object of the present invention is to provide an air-fuel ratio control apparatus and a control method thereof that can control the air-fuel ratio of an internal combustion engine with good controllability.

An air-fuel ratio control apparatus for an internal combustion engine according to the present invention includes a first measuring means for measuring an air-fuel ratio on the upstream side of a catalyst provided in an exhaust system of the internal combustion engine, and a first measuring means for measuring an oxygen concentration on the downstream side of the catalyst. 2 measuring means, a third measuring means for measuring the intake air amount of the internal combustion engine, and an oxygen concentration control for calculating a target air-fuel ratio correction amount based on the measurement results of the first to third measuring means. An air-fuel ratio control apparatus for an internal combustion engine that feedback-controls the air-fuel ratio based on an output signal of the oxygen concentration control means, wherein the number of inversions, the inversion period, and the inversion of the detected value by the second measurement means A sensor state estimation unit that estimates the state of the second measurement unit from at least one of the times, and a gain calculation that determines a shift correction feedback amount based on an estimation result by the sensor state estimation unit It provided a feedback gain calculation means for performing, based on the amount of feedback shift correction output from the feedback gain calculation unit, and adjusting the target air-fuel ratio correction amount.
The air-fuel ratio control method for an internal combustion engine according to the present invention includes a detection signal of an air-fuel ratio sensor disposed upstream of a catalyst provided in an exhaust system of the internal combustion engine, and an oxygen sensor disposed downstream of the catalyst. In the air-fuel ratio control method for an internal combustion engine that feedback-controls the air-fuel ratio based on the detection signal, the step of calculating the oxygen accumulation amount of the catalyst based on the intake air amount of the internal combustion engine and the detection signal of the air-fuel ratio sensor Calculating a central air-fuel ratio in the catalyst based on the calculated oxygen accumulation amount, and calculating an operating parameter of the oxygen sensor when air-fuel ratio feedback control is performed based on a detection value of the air-fuel ratio sensor A step of calculating a feedback gain index that is a degree of deviation between the operating parameter and a predetermined value; and And adjusting at Kkugein index, the catalyst within the central air-fuel ratio and the adjustment, characterized by comprising the step of setting a base target air-fuel ratio of the air-fuel ratio feedback.

  According to the present invention, in the system that measures the air-fuel ratio upstream of the catalyst provided in the exhaust system of the internal combustion engine and the oxygen concentration downstream of the catalyst and feedback-controls the air-fuel ratio, the air-fuel ratio, Based on the oxygen concentration and the intake air amount, the correction amount of the center air-fuel ratio in the catalyst and the target air-fuel ratio is calculated, and the feedback gain is adjusted with the calculated correction amount according to the center air-fuel ratio in the catalyst and the state of the air-fuel ratio sensor. . At this time, by using a gain that determines the feedback amount of shift correction, the offset deviation of the pre-catalyst air-fuel ratio sensor can be corrected quickly and accurately, and a failure can be detected.

1 is a schematic diagram showing an example of a system configuration of an internal combustion engine to which an air-fuel ratio control apparatus of the present invention is applied. FIG. 2 is a block diagram schematically showing air-fuel ratio feedback control executed by a control device in the internal combustion engine system shown in FIG. 1 as a device. It is a figure for demonstrating the absorption operation | movement of the offset shift | offset | difference of the air fuel ratio sensor by oxygen concentration control. It is a functional block diagram of the air-fuel ratio control device according to the embodiment of the present invention. 6 is a flowchart showing a control method of the air-fuel ratio control apparatus shown in FIG. It is a flowchart which shows the control method following FIG. It is a wave form diagram for demonstrating the feedback gain when the frequency | count of inversion of the output voltage of an oxygen sensor is small. It is a wave form diagram for demonstrating a feedback gain when the frequency | count of inversion of the output voltage of an oxygen sensor is large. It is a wave form diagram for demonstrating the feedback gain when the inversion of the output voltage of an oxygen sensor is quick. It is a wave form diagram for demonstrating the feedback gain when the inversion of the output voltage of an oxygen sensor is slow. It is a figure for demonstrating the case where the detection signal of an air fuel ratio sensor has shifted offset.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of a system configuration of an internal combustion engine to which an air-fuel ratio control apparatus of the present invention is applied. The internal combustion engine 1 includes an intake system 2 and an exhaust system 3, and an ignition device 4, a fuel injection device 5, a rotation speed detection device 6 and the like are attached to an engine body 1a. The flow rate of the air flowing in through the air cleaner 7 is adjusted by the throttle valve 8a of the throttle 8, and the flow rate (intake air amount QAR) is measured by the flow rate detection device 9, and the intake passage 2a from the fuel injection device 5 is measured. Then, it is mixed with fuel injected at a predetermined angle and supplied to each cylinder 10. The throttle valve 8a is provided with a throttle opening sensor 8b for detecting the throttle valve opening (throttle position signal TPS).

A three-way catalyst 12 is provided in the exhaust passage 3a, and the exhaust gas is purified by the three-way catalyst 12 and then discharged into the atmosphere. An air-fuel ratio sensor (pre-catalyst air-fuel ratio sensor) 11 is attached to the upstream side of the three-way catalyst 12, and an oxygen sensor (post-catalyst oxygen sensor) 15 is attached to the downstream side.
On the other hand, the fuel in the fuel tank 16 is sucked and pressurized by the fuel pump 17 and then supplied to the pressure regulator 18 attached to the intake passage 2 a through the fuel pipe 19-1. Guided to the entrance. Excess fuel is returned to the fuel tank 16 through the fuel pipe 19-2.

  The control device 13 takes in the intake air amount QAR measured by the flow rate detection device 9 and the rotation speed Ne of the ring gear (or plate) 14 measured by the rotation number detection device 6, and calculates the fuel injection amount Ti of the fuel injection device 5. Calculate and control. Further, the control device 13 takes in the detection signal RABF of the air-fuel ratio sensor 11 and the detection signal VO2R of the oxygen sensor 15 and corrects the fuel injection amount Ti so that the air-fuel ratio of the internal combustion engine 1 becomes the stoichiometric air-fuel ratio. Then, air-fuel ratio feedback control is performed. Further, the control device 13 also transmits control signals to the ignition device 4, the throttle 8, the fuel pump 17, etc., and controls the ignition timing of the ignition device 4, the opening of the throttle valve 8a, the discharge amount of the fuel pump 17, and the like. Thus, an efficient operation of the internal combustion engine 1 is performed.

The control device 13 inputs / outputs data (measurement results from various sensors and control information to various devices), an analog input circuit 20, an A / D conversion circuit 21, a digital input circuit 22, an output circuit 23, and An I / O circuit 24 and the like are provided. In addition, an MPU 26, a ROM 27, a RAM 28, and the like are provided for processing data.
The analog input circuit 20 includes an intake air amount QAR measured by the flow rate detection device 9, a throttle position signal TPS indicating the throttle valve opening detected by the throttle opening sensor 8b, a detection signal RABF of the air-fuel ratio sensor 11, and an oxygen sensor. 15 detection signals VO2R and the like are input.

  The intake air amount QAR, the throttle position signal TPS, the detection signal RABF, and the detection signal VO2R input to the analog input circuit 20 are supplied to the A / D conversion circuit 21 and converted into digital signals, which are output on the bus 25. Is done. The rotational speed Ne of the plate (or ring gear) 14 input to the digital input circuit 22 is output on the bus 25 via the I / O circuit 24.

  An MPU 26, ROM 27, RAM 28, timer / counter (TMR / CNT) 29 and the like are connected to the bus 25, and data is exchanged via the bus 25. A clock signal is supplied from the clock generator (OSC) 30 to the MPU 26, and various operations and processes are executed in synchronization with the clock signal. The ROM 27 is composed of, for example, an EEPROM capable of erasing and rewriting data, and stores a program for operating the control device 13, setting data, initial values, and the like. The data is read into the RAM 28 and the MPU 26 through 25. Further, the ROM 27 stores the state of the internal combustion engine 1 and the operation by the driver as learning values as necessary, and the learning values are used to correct or adjust the calculation results and processing results by the MPU 26. The learning value is fetched and updated every time an update is instructed from the MPU 26.

The RAM 28 is used as a work area and temporarily stores calculation results and processing results by the MPU 26. The timer / counter 29 is used for measuring time and various times, for example, measuring the number of inversions of the detection signal of the oxygen sensor 15, the inversion period, and the inversion time.
Calculation results and processing results by the MPU 26 are output to the bus 25 and supplied from the output circuit 23 to the fuel pump 17, the ignition device 4, the fuel injection device 5, and the throttle valve 8a via the I / O circuit 24. And by controlling these and optimizing the air-fuel ratio, the harmful exhaust gas of the automobile is reduced and the fuel efficiency and drivability are improved.

  FIG. 2 schematically shows the air-fuel ratio feedback control executed by the control device 13 in the internal combustion engine system shown in FIG. 1 as a device. Normally, in the exhaust purification system using the three-way catalyst 12, the three-way catalyst is detected by PI control or the like using the detection signal RABF of the air-fuel ratio sensor 11 upstream of the three-way catalyst 12 attached to the exhaust system 3 of the engine body 1a. 12 is controlled to the target air-fuel ratio (theoretical air-fuel ratio or the like). At that time, the detection deviation of the air-fuel ratio sensor 11 is absorbed by correcting the target air-fuel ratio by the detection signal VO2R of the oxygen sensor 15 downstream of the three-way catalyst 12, and the air-fuel ratio required by the three-way catalyst 12 By matching the target air-fuel ratio to (in-catalyst center air-fuel ratio), more accurate air-fuel ratio feedback control is realized.

  That is, the oxygen concentration control device 40 has a feedback gain calculation that determines the intake air amount QAR measured by the flow rate detection device 9, the detection signal RABF of the air-fuel ratio sensor 11, the detection signal VO2R of the oxygen sensor 15, and the shift correction feedback amount. An output signal (gain) FBGAIN or the like of the unit 41 is input. This oxygen concentration control device 40 is for absorbing the offset deviation of the air-fuel ratio sensor 11, and generates the in-catalyst center air-fuel ratio correction amount CNTABF and the target air-fuel ratio correction amount TABFRO2, and the air-fuel ratio sensor offset failure diagnosis device 42 To supply. The air-fuel ratio sensor offset failure diagnosis device 42 diagnoses an offset failure (offset deviation) based on the in-catalyst center air-fuel ratio correction amount CNTABF and the target air-fuel ratio correction amount TABFRO2, and at least of these correction amounts CNTABF and TABFRO2 When one exceeds a predetermined value, a failure is diagnosed.

  The target air-fuel ratio correction amount TABFRO2 is supplied to the target air-fuel ratio calculation unit 43, and the output signal of the target air-fuel ratio calculation unit 43 and the detection signal RABF of the air-fuel ratio sensor 11 are supplied to the air-fuel ratio control unit 44. . The air-fuel ratio control unit 44 corrects the target air-fuel ratio with the detection signal VO2R of the oxygen sensor 15 downstream of the three-way catalyst 12, thereby absorbing the detection deviation of the air-fuel ratio sensor 11 and requesting the three-way catalyst 12. Match the target air-fuel ratio to the air-fuel ratio. The output signal of the air-fuel ratio control unit 44 and the intake air amount QAR measured by the flow rate detection device 9 are supplied to the fuel injection control unit 45 and controlled by controlling the amount of fuel injected from the fuel injection device 5 The air-fuel ratio upstream of the catalyst 12 is adjusted to the target air-fuel ratio.

Further, the detection signal VO2R of the oxygen sensor 15 is supplied to an air-fuel ratio sensor state estimation device 46 that estimates the state of the air-fuel ratio sensor 11, and an output signal of the air-fuel ratio sensor state estimation device 46 is supplied to the feedback gain calculation unit 41. It has come to be. The feedback gain calculation unit 41 calculates a gain that determines the feedback amount of shift correction.
As a means for realizing air-fuel ratio feedback control, there is oxygen concentration control. First, oxygen concentration control as a premise will be described. One purpose of oxygen concentration control is absorption of offset deviation of the air-fuel ratio sensor 11.

  FIG. 3 is a diagram for explaining the offset deviation absorption operation of the air-fuel ratio sensor 11 by oxygen concentration control. The vertical axis indicates the detected air-fuel ratio (detection signal RABF), and the horizontal axis indicates the actual air-fuel ratio. . In FIG. 3, when an offset deviation occurs in the normal characteristic indicated by the solid line, if the actual air-fuel ratio is 14.7, the operating point moves from point o to point a or a ′ as indicated by the up and down arrows. Then, it is controlled by the air-fuel ratio sensor control so that it becomes point b or b ′ (shown by a broken line). However, since the actual air-fuel ratio is a value at point c or c ′ (on the solid line), the air-fuel ratio at point c or c ′ appears in the detection signal VO2R of the oxygen sensor 15.

  Therefore, by using the detection signal VO2R of the oxygen sensor 15 and correcting the target air-fuel ratio, it is possible to perform control as if the air-fuel ratio sensor 11 having no offset deviation is used by absorbing the offset deviation. it can. That is, by moving the operating points at the points b and b ′ to the left and right to converge the operating point to the point o, the target air-fuel ratio is corrected by oxygen concentration control so that the air-fuel ratio becomes 14.7. Controls the offset deviation of the air-fuel ratio sensor.

  Another purpose of the oxygen concentration control is to correct the target air-fuel ratio according to the situation of the three-way catalyst 12. As the method, the amount of oxygen accumulated in the catalyst is estimated, and the central air-fuel ratio in the catalyst is calculated from the result. In the case of the ordinary three-way catalyst 12, it is desirable to control the air-fuel ratio to 14.7 which is the theoretical air-fuel ratio. However, the air-fuel ratio is necessarily controlled to 14.7 depending on the operation region, catalyst deterioration, and active state. Is not always good. Therefore, the oxygen accumulation amount in the three-way catalyst 12 is estimated by oxygen concentration sensor control, and the air-fuel ratio (in-catalyst center air-fuel ratio) with the highest exhaust gas purification rate is calculated according to the state of the three-way catalyst 12, and the target The best air-fuel ratio feedback control is realized by correcting the air-fuel ratio.

  FIG. 4 shows functional blocks of the air-fuel ratio control apparatus according to the embodiment of the present invention. The pre-catalyst air-fuel ratio sensor signal measuring unit 51 corresponds to the air-fuel ratio sensor 11 that measures the air-fuel ratio upstream of the three-way catalyst 12 in FIGS. 1 and 2, and the intake air amount measuring unit 52 is connected to the internal combustion engine 1. This corresponds to the flow rate detection device 9 that measures the amount of air sucked. The post-catalyst oxygen sensor signal measurement unit 53 measures the oxygen concentration on the downstream side of the three-way catalyst 12 and corresponds to the oxygen sensor 15. Furthermore, the oxygen accumulation amount calculation unit 54 in the catalyst, the proportional correction value calculation unit 55, the integral correction value calculation unit 56, the central air-fuel ratio correction amount calculation unit 57 in the catalyst, the target air-fuel ratio correction amount calculation unit 58, etc. A density control device 40 is configured.

  The diagnosis area determination unit 59 and the pre-catalyst air / fuel ratio sensor offset failure determination unit 60 constitute an air / fuel ratio sensor offset failure diagnosis device 42. The learning update determination unit 61, the post-catalyst oxygen sensor inversion number calculation unit 62, the post-catalyst oxygen sensor inversion period calculation unit 63, the post-catalyst oxygen sensor inversion time calculation unit 64, the inversion number learning update unit 65, and the inversion cycle learning update unit 66, an inversion time learning update unit 67, an air-fuel ratio sensor state first calculation unit 68, an air-fuel ratio sensor state second calculation unit 69, an air-fuel ratio sensor state third calculation unit 70, and the like constitute the air-fuel ratio sensor state estimation device 46. Has been. The output signals of the air-fuel ratio sensor state first calculation unit 68, the air-fuel ratio sensor state second calculation unit 69, and the air-fuel ratio sensor state third calculation unit 70 are respectively supplied to the feedback gain calculation unit 41, and the feedback amount of shift correction Is calculated and supplied to the central air-fuel ratio correction amount calculation unit 57 in the catalyst.

  The in-catalyst oxygen accumulation amount calculation unit 54 calculates the in-catalyst oxygen accumulation amount from the pre-catalyst air-fuel ratio sensor signal (pre-catalyst air-fuel ratio) RABF, the intake air amount QAR, and the in-catalyst center air-fuel ratio correction amount CNTABF. The proportional correction value calculator 55 calculates the proportional correction value PB from the oxygen accumulation amount in the catalyst and the post-catalyst oxygen sensor signal VO2R (post-catalyst oxygen concentration). The integral correction value calculator 56 calculates the integral correction value IB from the oxygen accumulation amount in the catalyst and the post-catalyst oxygen concentration. The in-catalyst center air-fuel ratio correction amount calculation unit 57 calculates the center in the catalyst from the amount of oxygen storage in the catalyst, the post-catalyst oxygen concentration, and the shift correction feedback amount indicated by the output signal (gain) FBGAIN of the feedback gain calculation unit 41. An air-fuel ratio correction amount CNTABF is calculated. Further, the target air-fuel ratio correction amount calculation unit 58 calculates the target air-fuel ratio correction amount TABFRO2 from the proportional correction value PB, the integral correction value IB, and the in-catalyst center air-fuel ratio correction amount CNTABF.

  The diagnosis area determination unit 59 determines permission of diagnosis execution. When the diagnosis execution is permitted, the pre-catalyst air / fuel ratio sensor offset failure determination unit 60 determines the offset of the pre-catalyst air / fuel ratio sensor 11 based on the in-catalyst center air / fuel ratio correction amount CNTABF and the target air / fuel ratio correction amount TABFRO2. It is determined whether or not a failure has occurred.

  Furthermore, the learning update determination unit 61 permits learning update determination from the rich / lean response state of the detection signal VO2R output from the post-catalyst oxygen sensor signal measurement unit 53. The post-catalyst oxygen sensor inversion number calculation unit 62 calculates the rich / lean inversion number O2K of the detection signal VO2R output from the post-catalyst oxygen sensor signal measurement unit 53. The post-catalyst oxygen sensor inversion cycle calculation unit 63 calculates the rich / lean inversion cycle O2S of the detection signal VO2R output from the post-catalyst oxygen sensor signal measurement unit 53. Further, the post-catalyst oxygen sensor inversion time calculation unit 64 calculates the rich / lean inversion time O2J of the detection signal VO2R output from the post-catalyst oxygen sensor signal measurement unit 53.

  The inversion number learning update unit 65 learns the inversion number O2K output from the post-catalyst oxygen sensor inversion number calculation unit 62 based on the learning update determination result of the learning update determination unit 61. The inversion cycle learning update unit 66 learns the inversion cycle O2S output from the post-catalyst oxygen sensor inversion cycle calculation unit 63 based on the learning update determination result of the learning update determination unit 61. Further, the inversion time learning update unit 67 learns the inversion time O2J output from the post-catalyst oxygen sensor inversion time calculation unit 64 based on the learning update determination result of the learning update determination unit 61.

  The air-fuel ratio sensor state first calculation unit 68 compares the output value (inversion number O2K) of the post-catalyst oxygen sensor inversion number calculation unit 62 with the learning value LRN_K of the inversion number learning update unit 65, and calculates a feedback gain index LAF_STATE1. To do. The air-fuel ratio sensor state second computing unit 69 compares the output value (reversal cycle O2S) of the post-catalyst oxygen sensor reversal cycle computing unit 63 with the learned value LRN_S of the reversal cycle learning update unit 66, and calculates the feedback gain index LAF_STATE2. To do. Further, the air-fuel ratio sensor state third calculating unit 70 compares the output value (reversing time O2J) of the post-catalyst oxygen sensor reversing time calculating unit 64 with the learning value LRN_J of the reversing time learning update unit 67, and feedback gain index LAF_STATE3. Is calculated.

  The feedback gain calculation unit 41 is based on the calculation result of the feedback gain index obtained by adding the outputs of the air-fuel ratio sensor state first calculation unit 68, the air-fuel ratio sensor state second calculation unit 69, and the air-fuel ratio sensor state third calculation unit 70. Then, a gain FBGAIN that determines the feedback amount of the shift correction is calculated and supplied to the central air-fuel ratio correction amount calculation unit 57 in the catalyst.

Next, the control method of the air-fuel ratio control apparatus shown in FIG. 4 will be described in detail with reference to the flowcharts of FIGS.
First, in step S1, the pre-catalyst air / fuel ratio sensor signal measuring unit 51 measures the air / fuel ratio from the detection signal (pre-catalyst air / fuel ratio sensor signal) RABF. In the next step S2, the intake air amount measurement unit 52 measures the intake air amount QAR. In step S3, the post-catalyst oxygen sensor signal measuring unit 53 measures the oxygen concentration from the detection signal (post-catalyst oxygen sensor signal) VO2R. In the following step S4, the oxygen accumulation in the catalyst is calculated from the measured pre-catalyst air / fuel ratio sensor signal RABF, the intake air amount QAR, the previous value OSEST_old of the in-catalyst oxygen accumulation amount OSEST, and the previous value CNTABF_old of the in-catalyst center air / fuel ratio correction amount CNTABF. The amount calculation unit 54 calculates the oxygen accumulation amount OSEST in the catalyst according to the following formula.
OSEST = OSEST_old + (RABF-CNTABE_old) × QAR

  In the next step S5, the post-catalyst oxygen sensor inversion number calculation unit 62 calculates the inversion number O2K of the post-catalyst oxygen sensor signal VO2R. In step S6, the post-catalyst oxygen sensor inversion period calculation unit 63 calculates the inversion period O2S of the post-catalyst oxygen sensor signal VO2R. Further, in step S7, the post-catalyst oxygen sensor inversion time calculation unit 64 calculates the inversion time O2J of the post-catalyst oxygen sensor signal VO2R.

  Then, the learning update determination unit 61 performs learning update determination (step S8). When learning update determination is permitted, learning update of the inversion number O2K, the inversion period O2S, and the inversion time O2J is performed based on each calculation result (step S9, S10, S11). Thereby, the learning value LRN_K is stored in the inversion number learning update unit 65, the learning value LRN_S is stored in the inversion period learning update unit 66, and the learning value LRN_J is stored in the inversion time learning update unit 67. The learning update is determined, for example, based on the travel distance of the automobile, and the learning values LRN_K, LRN_S, and LRN_J of the learning update units 65 to 67 are updated when the fuel is cut and the fuel is recovered after the initial traveling.

In step S12, the feedback gain index LAF_STATE1 of the air-fuel ratio sensor state is calculated by the air-fuel ratio sensor state first calculation unit 68 from the ratio between the number of inversions O2K of the post-catalyst oxygen sensor 15 and the learning value LRN_K of the number of inversions. Calculate.
LAF_STATE1 = O2K / LRN_K × α (weighting factor)
During steady running, as shown in FIG. 7, the output voltage of the post-catalyst oxygen sensor 15 does not invert in the rich or lean state as indicated by the solid line 80, or the number of inversions is small as indicated by the solid line 81. In this case, it is estimated that the air-fuel ratio sensor 11 is out of stoichiometry, and the feedback gain is corrected in a larger direction.
On the other hand, as indicated by the solid line 82 in FIG. 8, when the output voltage of the post-catalyst oxygen sensor 15 is frequently reversed between the rich state and the lean state, the air-fuel ratio sensor 11 estimates that the vicinity of the stoichiometric condition and the feedback gain Correct in a smaller direction.

In step S13, the feedback gain index LAF_STATE2 of the air-fuel ratio sensor state is calculated from the ratio between the reverse period O2S of the post-catalyst oxygen sensor 15 and the learned value LRN_S of the reverse period by the air-fuel ratio sensor state second calculation unit 69 according to the following equation. Calculate.
LAF_STATE2 = O2S / LRN_S × β (weighting factor)
The reversal cycle is the same as the number of reversals. During steady running, if the output voltage of the post-catalyst oxygen sensor 15 remains rich or lean and does not reverse, or if the reversal cycle is long, the air-fuel ratio sensor 11 is stoichiometric. The feedback gain is corrected in a larger direction.
In addition, when the output voltage of the post-catalyst oxygen sensor 15 is short in the period in which the rich state and the lean state are reversed, the air-fuel ratio sensor 11 estimates that the vicinity of the stoichiometric range and corrects the feedback gain in a smaller direction.

In step S14, the feedback gain index LAF_STATE3 of the air-fuel ratio sensor state is calculated from the ratio of the reverse time O2J of the post-catalyst oxygen sensor 15 and the learned value LRN_J of the reverse time by the air-fuel ratio sensor state third calculation unit 70 according to the following equation. Calculate.
LAF_STATE3 = O2J / LRN_J × γ (weighting factor)
When recovering from the fuel cut, as shown in FIG. 9, when the reversal of the output voltage of the air-fuel ratio sensor 11 is early from the timing t <b> 0 when the fuel cut is terminated by the fuel cut flag, the air-fuel ratio sensor 11 is The feedback gain is corrected in a larger direction, assuming that it is out of place (during a rich state).
On the other hand, as shown in FIG. 10, when the reversal of the output voltage of the air-fuel ratio sensor 11 is slow from the timing t0 when the fuel cut is ended by the fuel cut flag, the air-fuel ratio sensor 11 is out of stoichiometry (lean state). The feedback gain is corrected in a smaller direction.

In step S15, the feedback gain exponents LAF_STATE1, LAF_STATE2, and LAF_STATE3 of the air-fuel ratio sensor states in steps S12, S13, and S14 are added to calculate LAF_STATE. That is,
LAF_STATE = LAF_STATE1 + LAF_STATE2 + LAF_STATE3
It is.

In step S16, a feedback gain FBGAIN is calculated from the result of the air-fuel ratio sensor state LAF_STATE.
FBGAIN = TFBGAIN (LAF_STATE)
The steps S15 and S16 are executed by the feedback gain calculation unit 41.
In step S17, the proportional correction value PB is calculated based on the map 1 by the proportional correction value calculator 55 from the oxygen storage amount correction value OSESTN and the oxygen sensor signal correction value VO2RN.
PB = Map 1 (OSESTN, VO2RN)

In step S18, the integral correction value IB is calculated based on the map 2 by the integral correction value calculator 56 from the oxygen storage amount correction value OSESTN and the oxygen sensor signal correction value VO2RN.
IB = IB_old + Map 2 (OSESTN, VO2RN)
Here, IB_old is the previous value of the integral correction value IB.
In step S19, the in-catalyst center air-fuel ratio correction amount CNTABF is calculated based on the map 3 by the in-catalyst center air-fuel ratio correction amount calculation unit 57 from the oxygen storage amount correction value OSESTN and the oxygen sensor signal correction value VO2RN.
CNTABF = Map 3 (OSESTN, VO2RN)
In step S20, the target air-fuel ratio correction amount calculator 58 adds the calculated proportional correction value PB, integral correction value IB, and in-catalyst center air-fuel ratio correction amount CNTABF to calculate the target air-fuel ratio correction amount TABFRO2. That is,
TABFRO2 = PB + IB + CNTABF
It is.

In step S21, the previous values of the integral correction value IB, the catalyst center air-fuel ratio correction amount CNTABF, and the oxygen storage amount correction value OSESTN are set to IB_old, CNTABF_old, and OSESTN_old, respectively. The previous values of the integral correction value IB_old, the in-catalyst center air-fuel ratio CNTABF_old, and the oxygen accumulation amount OSEST_old are used for the calculations in step S4 and step S18. In the next step S22, a value obtained by multiplying the in-catalyst center air-fuel ratio correction amount CNTABF or the in-catalyst center air-fuel ratio correction amount CNTABF by a weighting coefficient is defined as CNTABF.
CNTABF = CNTABF
Or
CNTABF = CNTABF × ζ (weighting factor)

  In subsequent step S <b> 23, the diagnosis region determination unit 59 determines permission to execute diagnosis. If the diagnosis execution is permitted, the process proceeds to step S24. If the diagnosis execution is not permitted, the diagnosis is not executed. Next, the condition of step S24 executed by the pre-catalyst air-fuel ratio sensor offset failure determination unit 60 is determined. When the condition of step S24 is satisfied (intra-catalyst center air-fuel ratio correction amount CNTABF> upper limit determination value or in-catalyst center air-fuel ratio correction amount CNTABF <lower limit determination value), it is determined in step S25 that an offset failure has occurred. On the other hand, when the condition in step S24 is not satisfied, it is determined in step S26 that there is no offset failure (OK).

  As described above, in the present invention, the air-fuel ratio is measured by measuring the air-fuel ratio upstream of the three-way catalyst 12 provided in the exhaust system 3 of the internal combustion engine 1 and the oxygen concentration downstream of the three-way catalyst 12. In the feedback control system, based on the pre-catalyst air / fuel ratio sensor signal RABF, the post-catalyst oxygen sensor signal VO2R and the intake air amount QAR, the in-catalyst center air / fuel ratio correction amount CNTABF and the target air / fuel ratio correction amount TABFRO2 are calculated, and the in-catalyst center The feedback gain is adjusted according to the air-fuel ratio and the air-fuel ratio sensor state. At this time, the state of the air-fuel ratio sensor 11 can be accurately estimated by correcting using the gain FBGAIN that determines the feedback amount of the shift correction, and the air-fuel ratio of the internal combustion engine 1 can be controlled with good controllability. Further, the offset deviation of the air-fuel ratio sensor 11 can be corrected quickly and accurately to detect a failure.

  As shown in FIG. 3, the offset failure of the air-fuel ratio sensor 11 is an excessive state of the offset deviation, and the oxygen sensor control operation itself has a function of absorbing the offset deviation as described above. Therefore, the offset failure can be detected by monitoring the parameter in the oxygen concentration control. Then, next, it will be described that an offset failure can be accurately detected even when the post-catalyst oxygen sensor is affected by catalyst deterioration.

  FIG. 11 is a diagram showing the output failure state of the output of the air-fuel ratio sensor 11. When the air-fuel ratio sensor 11 has an offset failure, the detection signal VO2R of the oxygen sensor 15 is easily affected via the three-way catalyst 12, and the proportional correction value PB and the integral correction value IB change, resulting in empty The target air-fuel ratio correction amount TABFRO2 that becomes the output value of the fuel ratio sensor control changes. On the other hand, the correction amount of the in-catalyst center air-fuel ratio correction amount CNTABF is updated when a deviation from the target air-fuel ratio correction amount TABFRO2 occurs.

Therefore, the target air-fuel ratio is corrected in the target air-fuel ratio calculation, and the air-fuel ratio sensor signal RABF is controlled to the actual air-fuel ratio by the air-fuel ratio sensor control. That is, the offset failure of the air-fuel ratio sensor signal RABF is reflected in the in-catalyst center air-fuel ratio correction amount CNTABF. Therefore, it is possible to diagnose the offset failure of the air-fuel ratio sensor by monitoring the in-catalyst center air-fuel ratio correction amount CNTABF.
Further, by estimating the state of the air-fuel ratio sensor 11 from the post-catalyst oxygen sensor signal VO2R and switching the feedback gain, the offset state of the air-fuel ratio sensor 11 can be corrected and detected with a high degree of accuracy quickly.

Here, the technical idea that can be grasped from the above-described embodiment will be described together with the effects thereof.
An air-fuel ratio control apparatus for an internal combustion engine, in one aspect thereof, is provided with a catalyst provided in an exhaust system of the internal combustion engine and upstream and downstream sides of the catalyst, respectively, and detects a specific component concentration in the exhaust gas. In the control device for an internal combustion engine having an air-fuel ratio feedback control means for calculating an air-fuel ratio correction coefficient based on the signals of the pre-catalyst air-fuel ratio sensor and the post-catalyst oxygen sensor for correcting the reference fuel supply amount,
A pre-catalyst air-fuel ratio sensor signal measuring means for detecting an air-fuel ratio before the catalyst;
A post-catalyst oxygen sensor signal measuring means for detecting the post-catalyst oxygen concentration;
Intake air amount measuring means for measuring the intake air amount of the internal combustion engine;
Intra-catalyst oxygen accumulation amount calculation means for estimating the in-catalyst oxygen accumulation amount based on the measurement results of the pre-catalyst air-fuel ratio sensor signal measurement means and the intake air amount measurement means and the calculation result of the in-catalyst center air-fuel ratio calculation means. When,
Based on the calculation result of the oxygen sensor signal response time calculation means, a learning update determination means for permitting update of learning according to the response time until inversion to rich / lean;
Based on the measurement result of the post-catalyst oxygen sensor signal measurement means, the post-catalyst oxygen sensor inversion count calculating means for calculating the rich / lean inversion count of the oxygen sensor;
An inversion number learning update unit for calculating the rich / lean inversion number of the oxygen sensor signal for a predetermined period based on the determination result by the learning update determination unit and the calculation result of the post-catalyst oxygen sensor inversion number calculation unit;
Based on the oxygen sensor inversion number by the post-catalyst oxygen sensor inversion number calculating means and the oxygen sensor inversion number learning value of the inversion number learning update means, the ratio between the oxygen sensor inversion number and the oxygen sensor inversion number learning value is a feedback gain index. An air-fuel ratio sensor state first calculating means,
Based on the measurement result of the post-catalyst oxygen sensor signal measuring means, the post-catalyst oxygen sensor inversion period calculating means for calculating the rich / lean inversion period of the oxygen sensor;
An inversion cycle learning update unit for calculating a rich / lean inversion period of the oxygen sensor signal for a predetermined period based on a determination result of the learning update determination unit and a calculation result of the post-catalyst oxygen sensor inversion period calculation unit;
Based on the oxygen sensor inversion period of the post-catalyst oxygen sensor inversion period calculating means and the oxygen sensor inversion period learning value of the inversion period learning update means, the ratio of the oxygen sensor inversion period and the oxygen sensor inversion period learning value is a feedback gain index. An air-fuel ratio sensor state second calculating means,
Based on the measurement result of the post-catalyst oxygen sensor signal measuring means, the post-catalyst oxygen sensor inversion time calculating means for calculating the rich / lean inversion time of the oxygen sensor;
An inversion time learning update means for calculating the rich / lean inversion time of the oxygen sensor signal for a predetermined period based on the determination result of the learning update determination means and the calculation result of the post-catalyst oxygen sensor inversion time calculation means;
Based on the oxygen sensor inversion time of the post-catalyst oxygen sensor inversion time calculating means and the oxygen sensor inversion time learning value of the inversion time learning update means, the ratio of the oxygen sensor inversion time and the oxygen sensor inversion time learning value is expressed as a feedback gain index. An air-fuel ratio sensor state third calculating means,
Based on the calculation results of the air-fuel ratio sensor state first calculating means, the air-fuel ratio sensor state second calculating means, and the air-fuel ratio sensor state third calculating means, the air-fuel ratio sensor state is estimated, and shift correction feedback is performed. Feedback gain calculating means for calculating a gain for determining the amount;
A proportional correction value calculating means for calculating a proportional correction value based on the measurement result of the post-catalyst oxygen sensor signal measuring means and the calculation result of the in-catalyst oxygen accumulation amount calculating means;
An integral correction value calculating means for calculating an integral correction value based on the measurement result of the post-catalyst oxygen sensor signal measuring means and the calculation result of the in-catalyst oxygen accumulation amount calculating means;
Based on the measurement result of the post-catalyst oxygen sensor signal measurement means and the calculation result of the in-catalyst oxygen accumulation amount calculation means, the in-catalyst center air-fuel ratio correction amount calculation means for estimating the in-catalyst center air-fuel ratio;
Target air-fuel ratio calculating means for calculating a correction amount for correcting the target air-fuel ratio based on the calculation results of the proportional correction value calculating means, the integral correction value calculating means, and the central air-fuel ratio calculating means in the catalyst. It is characterized by comprising.
According to the above configuration, based on the air-fuel ratio detected by the pre-catalyst air-fuel ratio sensor signal measuring means, the oxygen concentration detected by the post-catalyst oxygen sensor signal measuring means, and the intake air amount detected by the intake air amount measuring means, The amount of correction for the center air-fuel ratio and the target air-fuel ratio is calculated and corrected using a gain that determines the feedback amount for shift correction according to the central air-fuel ratio in the catalyst and the state of the air-fuel ratio sensor measuring means. The offset state of the fuel ratio sensor measurement means can be corrected quickly and accurately.

In a preferred aspect of the air-fuel ratio control apparatus for the internal combustion engine, the pre-catalyst air-fuel ratio is determined based on the diagnosis region determination means for determining the diagnosis region, the determination result of the diagnosis region determination means, and the calculation result of the target air-fuel ratio calculation means. And a pre-catalyst air / fuel ratio sensor offset failure determining means for detecting an offset failure of the fuel ratio sensor signal measuring means.
In this way, it can be determined that the pre-catalyst air-fuel ratio sensor signal measuring means is an offset failure.

In another preferred aspect, the post-catalyst oxygen sensor inversion number calculating means calculates the number of times of inversion to rich / lean based on the output value of the post-catalyst oxygen sensor signal measuring means.
In still another preferred aspect, the inversion number learning update unit learns an output value of the post-catalyst oxygen sensor inversion number calculation unit based on a determination result of the learning update determination unit.

In another preferred aspect, the air-fuel ratio sensor state first calculating means compares the number of times of inversion to rich / lean based on the calculation result of the post-catalyst oxygen sensor inversion number calculating means with the learning value and the current value, The feedback gain index.
In another preferred aspect, the post-catalyst oxygen sensor inversion period calculating means calculates a period for inversion to rich / lean based on an output value of the post-catalyst oxygen sensor signal measuring means.
In another preferred aspect, the inversion cycle learning update unit learns an output value of the post-catalyst oxygen sensor inversion cycle calculation unit based on a determination result of the learning update determination unit.

In another preferred aspect, the second air-fuel ratio sensor state calculation means compares the rich / lean inversion period with the learning value and the current value based on the calculation result of the post-catalyst oxygen sensor inversion period calculation means, The feedback gain index.
In another preferred aspect, the post-catalyst oxygen sensor inversion time calculating means calculates a time for inversion to rich / lean based on an output value of the post-catalyst oxygen sensor signal measuring means.
In another preferred aspect, the inversion time learning update unit learns the output value of the post-catalyst oxygen sensor inversion time calculation unit based on the determination result of the learning update determination unit.

In another preferred aspect, the air / fuel ratio sensor state third calculating means compares the rich / lean inversion time with the learned value and the current value based on the post-catalyst oxygen sensor inversion time calculating means, and a feedback gain index And
In another preferred aspect, the feedback gain calculating means calculates each of feedback gain indexes of the air-fuel ratio sensor state first calculating means, the air-fuel ratio sensor state second calculating means, and the air-fuel ratio sensor state third calculating means. Based on the result, a feedback gain is selected.

In another preferred aspect, the in-catalyst center air-fuel ratio correction amount calculating means is based on the measurement results of the post-catalyst oxygen sensor signal measuring means and the calculation results of the in-catalyst oxygen accumulation amount calculating means and the feedback gain calculating means. Thus, the center air-fuel ratio in the catalyst is estimated.
In another preferred aspect, the learning update determination means makes a learning update determination from a time of reversal to rich / lean based on an output value of the post-catalyst oxygen sensor signal measurement means.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Intake system, 3 ... Exhaust system, 4 ... Ignition device, 5 ... Fuel injection device, 6 ... Rotation speed detection device, 7 ... Air cleaner, 8 ... Throttle, 8a ... Throttle valve, 8b ... Throttle Opening sensor, 9 ... Flow rate detection device, 10 ... Cylinder, 11 ... Air-fuel ratio sensor (pre-catalyst air-fuel ratio sensor), 12 ... Three-way catalyst, 13 ... Control device, 14 ... Plate (or ring gear), 15 ... Oxygen Sensor (post-catalyst oxygen sensor), 16 ... fuel tank, 17 ... fuel pump, 18 ... pressure regulator, 19-1, 19-2 ... fuel pipe, 40 ... oxygen concentration control device, 41 ... feedback gain calculation unit, 42 ... Air-fuel ratio sensor offset failure diagnosis device 43 ... Target air-fuel ratio calculation unit 44 ... Air-fuel ratio control unit 45 ... Fuel injection control unit 46 ... Air-fuel ratio sensor state estimation device 51 ... Air-fuel ratio before catalyst Sensor signal measuring unit 52 ... Intake air amount measuring unit 53 ... Post-catalyst oxygen sensor signal measuring unit 54 ... In-catalyst oxygen accumulation amount calculating unit 55 ... Proportional correction value calculating unit 56 ... Integral correction value calculating unit , 57 ... In-catalyst center air-fuel ratio correction amount calculation unit, 58 ... Target air-fuel ratio correction amount calculation unit, 59 ... Diagnosis region determination unit, 60 ... Pre-catalyst air-fuel ratio sensor offset failure determination unit, 61 ... Learning update determination unit, 62 ... post-catalyst oxygen sensor inversion number calculation unit, 63 ... post-catalyst oxygen sensor inversion period calculation unit, 64 ... post-catalyst oxygen sensor inversion time calculation unit, 65 ... inversion number learning update unit, 66 ... inversion period learning update unit, 67 ... Inversion time learning update unit, 68... Air-fuel ratio sensor state first calculation unit, 69... Air-fuel ratio sensor state second calculation unit, 70.

Claims (11)

First measurement means for measuring the air-fuel ratio upstream of the catalyst provided in the exhaust system of the internal combustion engine, second measurement means for measuring the oxygen concentration downstream of the catalyst, and intake air of the internal combustion engine A third measuring means for measuring the amount; and an oxygen concentration control means for calculating a target air-fuel ratio correction amount based on the measurement results of the first to third measuring means, and the output of the oxygen concentration control means An air-fuel ratio control apparatus for an internal combustion engine that feedback-controls an air-fuel ratio based on a signal,
Sensor state estimating means for estimating the state of the second measuring means from at least one of the number of inversions, the inversion period and the inversion time of the detected value by the second measuring means;
A feedback gain calculating means for calculating a gain for determining a feedback amount of shift correction based on an estimation result by the sensor state estimating means;
An air-fuel ratio control apparatus for an internal combustion engine, wherein the target air-fuel ratio correction amount is adjusted based on a shift correction feedback amount output from the feedback gain calculation means.   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the sensor state estimation means includes calculation means for calculating the number of inversions, the inversion period, and the inversion time from the detection value of the second measurement means.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the calculation means calculates the number of times of inversion to rich / lean based on the detection value of the second measurement means.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the calculation means calculates a cycle for reversing to rich / lean based on a detection value of the second measurement means.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the calculation means calculates a time for reversal to rich / lean based on a detection value of the second measurement means.   The sensor state estimating means further comprises learning means for learning the number of inversions, the inversion period and the inversion time of the detection value detected by the second measuring means, and the rich / lean detection signal output from the second measuring means The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 2 to 5, wherein the learning value is updated based on the response state.   The sensor state estimation means further comprises sensor state calculation means for calculating a feedback gain index of the sensor state based on the calculation result of the calculation means, the learning value of the learning means, and a predetermined weighting factor, and this sensor state calculation The air-fuel ratio control apparatus for an internal combustion engine according to claim 6, wherein the feedback gain index of the sensor state calculated by the means is supplied to the feedback gain calculation means. The oxygen concentration control means receives the measurement values of the first measuring means and the third measuring means and estimates the oxygen accumulation amount in the catalyst, and calculates the oxygen accumulation amount in the catalyst. A proportional correction value calculation unit that calculates a proportional correction value from the amount of oxygen storage in the catalyst calculated by the unit and the detection value measured by the second measuring means, and the amount of oxygen stored in the catalyst calculated by the oxygen storage amount calculation unit in the catalyst An integral correction value calculation unit for calculating an integral correction value from the oxygen accumulation amount and the detection value measured by the second measuring means; an in-catalyst oxygen accumulation amount calculated by the in-catalyst oxygen accumulation amount calculation unit; A center-of-catalyst air-fuel ratio correction amount calculation unit for calculating the center-of-catalyst air-fuel ratio correction amount from the detected value measured by the measuring means of 2 and the feedback amount of shift correction indicated by the output signal of the feedback gain calculating means; , Proportional correction value, integral And a target air-fuel ratio correction amount computing unit for computing a target air-fuel ratio from the positive and catalyst within the center air-fuel ratio correction amount,
The internal combustion engine according to any one of claims 1 to 7, wherein an in-catalyst center air-fuel ratio correction amount output from the in-catalyst center air-fuel ratio correction amount calculation unit is input to the in-catalyst oxygen accumulation amount calculation unit. Air-fuel ratio control device.   9. The air-fuel ratio control apparatus for an internal combustion engine according to claim 8, further comprising a diagnosis unit that determines that the first measurement unit is abnormal when the in-catalyst center air-fuel ratio correction amount is out of a predetermined range. An internal combustion engine that feedback-controls the air-fuel ratio based on a detection signal of an air-fuel ratio sensor arranged upstream of a catalyst provided in an exhaust system of the internal combustion engine and a detection signal of an oxygen sensor arranged downstream of the catalyst In the engine air-fuel ratio control method,
Calculating an oxygen accumulation amount of the catalyst based on an intake air amount of the internal combustion engine and a detection signal of the air-fuel ratio sensor;
Calculating a central air-fuel ratio in the catalyst based on the calculated oxygen accumulation amount;
Calculating an operating parameter of the oxygen sensor when air-fuel ratio feedback control based on a detection value of the air-fuel ratio sensor is performed;
Calculating a feedback gain index that is a degree of deviation between the operating parameter and a predetermined value;
Adjusting the central air-fuel ratio in the catalyst with the feedback gain index;
And a step of setting the adjusted central air-fuel ratio in the catalyst to a base target air-fuel ratio of the air-fuel ratio feedback.   11. The air-fuel ratio control method for an internal combustion engine according to claim 10, wherein the operating parameter of the oxygen sensor includes at least one of the number of inversions, the inversion period, and the inversion time of the detection signal of the oxygen sensor.