JP2681965B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention provides an air-fuel ratio such as an oxygen concentration sensor on the upstream side and the downstream side of a three-way catalyst inserted in the exhaust system of an internal combustion engine. The present invention relates to an air-fuel ratio control device for an internal combustion engine, which is provided with a sensor and executes air-fuel ratio feedback control based on a detection result of a downstream side air-fuel ratio sensor in addition to air-fuel ratio feedback control based on a detection result of an upstream side air-fuel ratio sensor.

[Prior Art] In a normal air-fuel ratio feedback control device, a so-called single oxygen concentration sensor system, an oxygen concentration sensor as an air-fuel ratio sensor for detecting oxygen concentration is arranged in the vicinity of the fuel chamber. It is provided in the exhaust manifold. However, there is a limit in improving the control accuracy of the air-fuel ratio due to individual differences in the output characteristics of the oxygen concentration sensor. Therefore, the individual difference in the output characteristics of the oxygen concentration sensor,
Furthermore, individual differences in components such as fuel injection valves, aging,
As a countermeasure against control accuracy deterioration due to aging, etc., an air-fuel ratio using a downstream oxygen concentration sensor disposed downstream of the catalytic converter and an upstream oxygen concentration sensor disposed upstream of the catalytic converter is used. A so-called double oxygen concentration sensor system that performs air-fuel ratio feedback control using the downstream oxygen concentration sensor in addition to the feedback control is known. In the double oxygen concentration sensor system, the response of the downstream oxygen concentration sensor is lower than the response of the upstream oxygen concentration sensor, but the output characteristics are relatively stable for the following reason.

(A) Since the exhaust gas temperature on the downstream side of the catalytic converter is lower than that on the upstream side, the adverse thermal effect on the downstream oxygen concentration sensor is relatively small.

(B) Since the harmful substances in the exhaust gas that adversely affect the output characteristics of the oxygen concentration sensor are adsorbed inside the catalytic converter, the oxygen concentration sensor is relatively less adversely affected by the exhaust gas on the downstream side.

(C) Since the exhaust gas on the downstream side of the catalytic converter is sufficiently mixed, the oxygen concentration in the exhaust gas is almost in an equilibrium state, so that it can be detected relatively accurately by the oxygen concentration sensor.

Therefore, the air-fuel ratio feedback control based on the outputs of the two oxygen concentration sensors (so-called double oxygen concentration sensor system) can correct the deterioration of the output characteristics of the upstream oxygen concentration sensor by the detection signal of the downstream oxygen concentration sensor. . That is, as shown in black in FIG. 24, in the double oxygen concentration sensor system, the emission amount of harmful components (HC, CO, NOx) in the exhaust gas is reduced even if the output characteristic of the upstream oxygen concentration sensor deteriorates. Almost no increase and no deterioration in exhaust characteristics is seen. On the other hand, as shown by a white outline in the figure, in the single oxygen concentration sensor system when the output characteristics are deteriorated, the harmful components in the exhaust are significantly increased, and the exhaust characteristics are significantly deteriorated.
Thus, in the double oxygen concentration sensor system, if the output of the downstream oxygen concentration sensor is stable, good exhaust characteristics are compensated.

In the double oxygen concentration sensor system as described above, during the execution of the air-fuel ratio feedback control based on the detection signal of the downstream oxygen concentration sensor, the control constant of the air-fuel ratio correction coefficient FAF obtained based on the detection signal of the upstream oxygen concentration sensor, For example,
A technique has been proposed in which the rich skip amount, the lean skip amount, and the like are changed based on the detection signal of the downstream oxygen concentration sensor.

For example, (1) a skip amount which is an air-fuel ratio feedback control constant is calculated according to the output of the downstream side air-fuel ratio sensor, and an air-fuel ratio correction amount corresponding to the output of the upstream side air-fuel ratio sensor is calculated using the skip amount. "Air-fuel ratio control device for internal combustion engine" (Japanese Patent Laid-Open No. 61-234241) that adjusts the air-fuel ratio of the engine to prevent the response speed from decreasing due to deterioration of the upstream air-fuel ratio sensor.

(2) An "air-fuel ratio control device for an internal combustion engine" that prevents the disturbance of the air-fuel ratio control by stopping the calculation of the air-fuel ratio feedback control constant by the downstream side air-fuel ratio sensor when the catalyst deterioration is detected. 61-286550).

In these technologies, for example, during start-up / warm-up, power increase, fuel cut, lean air-fuel ratio control, etc., when the air-fuel ratio feedback control based on the detection signal of the downstream oxygen concentration sensor is not executed, the air-fuel ratio feedback control is performed. The constant was set to a predetermined constant value or the final value at the time of the previous control.

[Problems to be Solved by the Invention] However, for example, at the time of switching from an operating state where the air-fuel ratio of the internal combustion engine is made to be a lean air-fuel ratio or a fuel supply cutoff state to an operating state where feedback control is performed to the stoichiometric air-fuel ratio. In the catalytic converter, oxygen molecules taken in due to the oxygen storage effect are released. For this reason,
Even if the air-fuel ratio on the upstream side of the catalytic converter changes to the rich side (Rich), the air-fuel ratio on the downstream side remains lean (Le
an), and the downstream air-fuel ratio sensor outputs a lean signal (lean side). Therefore, if the air-fuel ratio control is performed based on the output signal of the downstream side air-fuel ratio sensor, the rich side (Ri
ch) will be overcorrected. In particular, when the air-fuel ratio feedback control constant held at a constant value is corrected as described above as in the conventional technique, the overcorrection is further increased. That is, as shown in FIG. 25, when the catalytic converter is not deteriorated, when the fuel cut is performed at time T1, at time T2, the detection signal V2 of the downstream oxygen concentration sensor decreases and the lean side ( Lean output), but since the downstream side oxygen concentration sensor is arranged on the downstream side of the catalytic converter, the exhaust transportation delay time TD1 occurs. Meanwhile, time T3
When the fuel cut is changed to the air-fuel ratio feedback control (non-fuel cut), the detection signal V2 of the downstream side oxygen concentration sensor rises at time T4 and indicates the rich side (Rich output).
A delay of time TD2 occurs due to a delay in the transportation of exhaust gas and the oxygen storage effect of the catalytic converter. Therefore, even if the air-fuel ratio on the upstream side of the catalytic converter is actually on the rich side (Rich), the air-fuel ratio feedback control constant, for example, the skip amount is corrected to the rich side (Rich). That is,
The detection signal V2 of the downstream side oxygen concentration sensor changes as shown by a broken line in the figure without the oxygen storage effect of the catalytic converter, but actually changes as shown by a solid line in the figure due to the oxygen storage effect. . Especially when descending,
When racing is performed, the number of fuel cuts per unit time increases, and the rich overcorrection (Rich) overcorrection of the air-fuel ratio feedback control constant is accumulated, as shown at times T5 to T6. Such a problem is that the air-fuel ratio of the internal combustion engine is
The same occurs at the time of switching from an operating state in which the rich air-fuel ratio is set to an operating state in which feedback control is performed to the stoichiometric air-fuel ratio, such as an increase. Therefore, after a predetermined delay time has elapsed from the switching timing of the operating state of the internal combustion engine as described above, the air-fuel ratio feedback control based on the downstream side oxygen concentration sensor detection signal V2 is started, and it is less susceptible to the oxygen storage effect of the catalytic converter. The technique to do was also considered. However, the oxygen storage effect of the catalytic converter decreases with the deterioration of the catalytic converter. That is, as shown in FIG. 26, the oxygen storage time is greatly shortened as the traveling distance increases. Here, the oxygen storage time is the time from the time when the fuel cut is returned to the air-fuel ratio feedback control to the time when the detection signal of the downstream oxygen concentration sensor crosses 0.45 [V]. Therefore, as shown in FIG. 25, the exhaust transportation delay time TD10 that occurs when the fuel cut is performed at time T11 when the deterioration of the catalytic converter progresses.
Is shorter than the transport delay time TD1 when not deteriorated as described above. On the other hand, at time T13, the delay time TD20 that occurs when the fuel cut is switched to the air-fuel ratio feedback control is also shorter than the time TD2 when the oxygen storage effect of the deteriorated catalytic converter is not deteriorated.

Therefore, if the predetermined delay time until the start of the air-fuel ratio feedback control based on the downstream side oxygen concentration sensor detection signal is set to a fixed time without considering the decrease in the oxygen storage effect due to the deterioration of the catalytic converter, the catalytic converter Even if oxygen concentration sensors are provided on the upstream and downstream sides, respectively, there is a problem that the air-fuel ratio feedback control based on the detection signals of both oxygen concentration sensors cannot be executed with high accuracy for a long period of time.

The present invention, when the oxygen storage effect is reduced due to the deterioration of the catalytic converter with the increase in the degree of catalyst deterioration of the internal combustion engine, the fuel supply cutoff state, the lean burn control state, or the fuel increase operation state, An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which is capable of suitably preventing overcorrection of the air-fuel ratio feedback control constant to the rich side (Rich) when shifting to the air-fuel ratio feedback control state.

Structure of the Invention [Means for Solving the Problems] The present invention, which has been made to achieve the above object, is arranged in an exhaust passage of an internal combustion engine M1 and has an oxygen storage effect, as illustrated in FIG. A three-way catalyst M2 and a downstream side air-fuel ratio detecting means M4 arranged in the exhaust passage on the downstream side of the three-way catalyst M2 for detecting the air-fuel ratio of the internal combustion engine M2.
An operating state detecting means M6 for detecting the operating state of the internal combustion engine M1, and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the internal combustion engine M1 according to a control amount determined based on the operating state of the internal combustion engine M1. M5, based on the operating state detected by the operating state detection means M6, the operating state of the internal combustion engine M1, from the operating state to make the air-fuel ratio of the internal combustion engine M1 rich air-fuel ratio or lean air-fuel ratio The determination means M7 for determining whether or not it is the switching timing for switching to the operating state to be controlled to, and after the elapse of a predetermined delay time from the time when the determination timing is determined by the determination means M7, the internal combustion engine M1 becomes empty. Delay means for instructing the start of control for making the fuel ratio the stoichiometric air-fuel ratio
M8, in accordance with the start command output by the delay means M8, at least according to the detection result of the downstream air-fuel ratio detection means M4, to determine the control amount that makes the air-fuel ratio of the internal combustion engine M1 the stoichiometric air-fuel ratio,
An air-fuel ratio feedback control means M10 for instructing the air-fuel ratio adjusting means M5, and an air-fuel ratio control device for an internal combustion engine comprising: a catalyst deterioration degree calculating means for calculating a catalyst deterioration degree of the three-way catalyst M2. M11 and an empty space of an internal combustion engine comprising: a changing means M12 for shortening the predetermined delay time of the delay means M8 with an increase in the catalyst deterioration degree calculated by the catalyst deterioration degree calculating means M11. The gist of the invention is a fuel ratio control device.

Further, as illustrated in FIG. 2, the present invention is arranged in an exhaust passage of an internal combustion engine M101 and has a three-way catalyst M102 having an oxygen storage effect, and an exhaust passage upstream of the three-way catalyst M102. Upstream side air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine M101
M103, a downstream side air-fuel ratio detection means M104 arranged in the exhaust passage on the downstream side of the three-way catalyst M102, for detecting the air-fuel ratio of the internal combustion engine M101, and an operating state for detecting the operating state of the internal combustion engine M101. Detecting means M106, air-fuel ratio adjusting means M105 for adjusting the air-fuel ratio of the internal combustion engine M101 in accordance with a control amount determined based on the operating state of the internal combustion engine M101, and the operating state detected by the operating state detecting means M106. Based on the above, the operating state of the internal combustion engine M101 is switched from the operating state in which the air-fuel ratio of the internal combustion engine M101 is set to the lean side air-fuel ratio, or from the fuel supply cutoff state to the operating state in which the stoichiometric air-fuel ratio is controlled. A determination means M107 for determining whether or not there is a switching timing to be changed, and after a predetermined delay time has elapsed since the determination timing was determined by the determination means M107, the air-fuel ratio of the internal combustion engine M101 is set to the theoretical air-fuel ratio. For control of A delay means M108 for instructing the start, a control constant calculation means M109 for calculating an air-fuel ratio feedback control constant according to the detection result of the downstream air-fuel ratio detection means M104 according to the start command output by the delay means M108, According to the air-fuel ratio feedback control constant calculated by the control constant calculating means M109 and the detection result of the upstream side air-fuel ratio detecting means M103, the control amount for determining the air-fuel ratio of the internal combustion engine M101 as the theoretical air-fuel ratio is determined, and the air An air-fuel ratio feedback control means M110 for instructing a fuel ratio adjusting means M105, and an air-fuel ratio control device for an internal combustion engine comprising: a catalyst deterioration degree calculating means M111 for calculating a catalyst deterioration degree of the three-way catalyst M102. An internal combustion engine comprising: a changing means M112 for shortening the predetermined delay time of the delay means M108 with an increase in the catalyst deterioration degree calculated by the catalyst deterioration degree calculating means M111. It can be configured by the air-fuel ratio control apparatus.

Here, the oxygen storage effect of the three-way catalyst M2 (M102) is a characteristic of holding a predetermined amount of oxygen molecules in the exhaust gas inside the exhaust passage of the internal combustion engine M1 (M101) inside the three-way catalyst M2 (M102). The predetermined amount decreases as the three-way catalyst M2 (M102) deteriorates.

The upstream air-fuel ratio detecting means M103 is arranged in the exhaust passage upstream of the three-way catalyst M102 and detects the air-fuel ratio of the internal combustion engine M101. Further, the downstream side air-fuel ratio detection means M4 (M10
4) is arranged in the exhaust passage on the downstream side of the three-way catalyst M2 (M102) and detects the air-fuel ratio of the internal combustion engine M1 (M101). For example, it can be realized by a gas sensor that detects the concentration of specific components such as oxygen concentration and carbon monoxide in the exhaust gas.

The operating state detecting means M6 (M106) means the internal combustion engine M1 (M10
This is to detect the operating condition of 1). For example, it can be realized by various sensors capable of detecting the intake air amount, the intake pipe pressure, the throttle valve opening, the rotation speed, and the like.

The air-fuel ratio adjusting means M5 (M105) means the internal combustion engine M1 (M101)
The air-fuel ratio of the internal combustion engine M1 (M101) is adjusted according to the control amount that is determined based on the operating state of. For example, it can be realized by a fuel injection valve capable of controlling a fuel injection amount, a carburetor capable of controlling a bleed air flow rate, a secondary air introduction device capable of controlling a flow rate, and the like. As the operating state of the internal combustion engine M1 (M101), for example, the engine speed Ne, the engine load Q / Ne, the intake air amount Q, the output of the air-fuel ratio sensor, the water temperature, etc. can be used, and the operating state detecting means M6 ( What is detected by M106) can be used, but it may be detected by other means. The control amount based on this operating state can be determined by, for example, an electronic control device, but a dedicated arithmetic circuit may be provided.

The determining means M7 means that the operating state of the internal combustion engine M1 is based on the operating state detected by the operating state detecting means M6.
It is determined whether or not there is a switching timing at which the operating state in which the air-fuel ratio is set to the rich air-fuel ratio or the lean air-fuel ratio is switched to the operating state in which the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. For example, operating conditions at the lean side (Lean) air-fuel ratio such as so-called fuel cut and lean burn control, or so-called rich air-fuel ratio (Rich) air-fuel ratio such as so-called OTP increase, power increase, start increase, warm-up increase, etc. The operating speed of the internal combustion engine M1 depends on whether or not it is time to switch to the air-fuel ratio feedback control operating state in which the air-fuel ratio is changed to the stoichiometric air-fuel ratio according to the detection result of the downstream side air-fuel ratio detecting means M4. Alternatively, the determination can be made based on the throttle valve opening.

Further, for example, the determination means M107 is the operating state detection means M1.
Based on the operating state detected by 06, the operating state of the internal combustion engine M101 controls the air-fuel ratio of the internal combustion engine M101 from the operating state where the lean side air-fuel ratio is set, or from the fuel supply cutoff state to the theoretical air-fuel ratio. It can be configured to determine whether or not it is time to switch to an operating state. That is, the timing of switching from the lean air-fuel ratio control state with the lean side air-fuel ratio as the target value or the fuel cut state to the feedback control state with the theoretical air-fuel ratio as the target value may be determined.

The delay means M8 (M108) is a control for setting the air-fuel ratio of the internal combustion engine M (M101) to the stoichiometric air-fuel ratio after a lapse of a predetermined delay time from the time when the determination means M7 (M107) determines that the switching timing is reached. Command to start. For example, a timer may be used, or a count value of a counter that is counted every predetermined period may be compared with a value corresponding to a predetermined delay time, and a command may be issued by setting / resetting a flag.

The control constant calculation means M109 is for calculating an air-fuel ratio feedback control constant according to the detection result of the downstream side air-fuel ratio detection means M104 in accordance with the start command output from the delay means M108. For example, the integration constant, the lean / rich both skip amount, the lean / rich both delay time, the air-fuel ratio signal comparison voltage, etc. can be corrected and calculated according to the oxygen concentration on the downstream side.

The air-fuel ratio feedback control means M10 is the delay means M8.
According to the start command output by, at least in accordance with the detection result of the downstream side air-fuel ratio detection means M4, to determine the control amount that makes the air-fuel ratio of the internal combustion engine M1 the stoichiometric air-fuel ratio, to instruct the air-fuel ratio adjusting means M5. is there. For example, the lean and rich skip amounts may be determined according to the oxygen concentration on the downstream side, and feedback control may be performed using the skip amounts as the air-fuel ratio correction amount.

Further, for example, the air-fuel ratio feedback control means M110, the air-fuel ratio feedback control constant calculated by the control constant calculation means M109 and the detection result of the upstream side air-fuel ratio detection means M103, the theoretical air-fuel ratio of the internal combustion engine M101. The control amount to be the fuel ratio may be determined and the air-fuel ratio adjusting means M105 may be instructed. For example, control from integration constant, lean / rich both skip amount, lean / rich both delay time, air-fuel ratio signal comparison voltage, etc. and air-fuel ratio feedback correction coefficient calculated from upstream oxygen concentration, basic fuel injection amount, various correction coefficients It can be configured to determine and command a quantity.

The catalyst deterioration degree calculation means M11 (M111) means the three-way catalyst M2 (M
102) The degree of catalyst deterioration is calculated. For example, it can be realized by a timer that measures the time during which the internal combustion engine M1 (M101) is in the normal operation state. Further, for example, the internal combustion engine M
It can also be estimated based on the number of times (M101) is started.
Further, for example, it is calculated based on the intake air amount of the internal combustion engine M1 (M101), the rotational speed, the load, the throttle valve opening, the vehicle speed of the vehicle driven by the internal combustion engine M1 (M101), or the traveling distance. It may be configured as follows.
Furthermore, for example, when the width between the maximum value and the minimum value of the detection signal of the downstream oxygen concentration sensor exceeds a predetermined value, or
It can also be calculated based on an integrated value of the number of occurrences when the ratio of the detection signal cycle of the downstream oxygen concentration sensor and the detection signal cycle of the upstream oxygen concentration sensor exceeds a predetermined ratio.

Change means M12 (M112) means catalyst deterioration degree calculation means M11
The predetermined delay time of the delay means M8 (M108) is shortened as the catalyst deterioration degree calculated by (M111) increases. For example, it can be realized by a map, an arithmetic expression, or the like that regulates the decrease of the predetermined delay time equivalent amount with respect to the increase of the catalyst deterioration amount equivalent amount.

The determination means M7 (M107), the delay means M8 (M108), the control constant calculation means M109, the air-fuel ratio feedback control means M10
(M110), the catalyst deterioration degree calculating means M11 (M111) and the changing means M12 (M12) can be realized by, for example, independent discrete logic circuits. Also, for example, the well-known
It may be configured as a logical operation circuit together with a CPU, a ROM, a RAM, and other peripheral circuit elements, and may realize the above-described units according to a predetermined processing procedure.

[Operation] As shown in FIG. 1, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention detects the internal combustion engine M1 detected by the operating state detecting means M6.
That the operating state of the internal combustion engine M1 is at a switching timing to switch from an operating state in which the air-fuel ratio of the internal combustion engine M1 is set to a rich air-fuel ratio or a lean air-fuel ratio to an operating state in which the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.
After a lapse of a predetermined delay time from the time determined by, the air-fuel ratio feedback control means M10 is disposed at least in the exhaust passage of the internal combustion engine M1 according to the start command output by the delay means M8, and has three oxygen storage effects. Original catalyst
According to the detection result of the downstream side air-fuel ratio detecting means M4 arranged in the exhaust passage on the downstream side of M2, the control amount for determining the stoichiometric air-fuel ratio of the internal combustion engine M1 is determined, and the air-fuel ratio adjusting means M5 When instructing to, the change means M12 changes the catalyst deterioration degree calculation means M11.
With the increase in the catalyst deterioration degree calculated by, the delay means M8
To reduce the predetermined delay time of.

That is, the predetermined delay time until the start of the air-fuel ratio feedback control, which is set at the switching timing from the operating state in which the air-fuel ratio of the internal combustion engine M1 is set to the rich air-fuel ratio or the lean air-fuel ratio to the operating state in which the stoichiometric air-fuel ratio is controlled, The three-way catalyst M2 shortens as the degree of catalyst deterioration increases, and at least the three-way catalyst M2 decreases in accordance with the decrease in the oxygen storage effect of the three-way catalyst M2.
The start of the air-fuel ratio feedback control based on the air-fuel ratio detected on the downstream side of is accelerated.

Further, the present invention, as illustrated in FIG. 2, the operating state of the internal combustion engine M101 detected by the operating state detecting means M106 is such that the air-fuel ratio of the internal combustion engine M101 is changed to the lean side air-fuel ratio. Alternatively, according to the start command output from the delay means M108, after a predetermined delay time elapses from the time when the judgment means M107 determines that it is at the switching time to switch from the fuel supply cutoff state to the operating state in which the air-fuel ratio is controlled, the control is performed according to the start command output from the delay means M108. The constant calculating means M109 is provided in the exhaust passage of the internal combustion engine M101 and is provided in the exhaust passage on the downstream side of the three-way catalyst M102 having an oxygen storage effect, and the downstream side for detecting the air-fuel ratio of the internal combustion engine M101. The air-fuel ratio feedback control constant is calculated according to the detection result of the air-fuel ratio detection means M104, and the air-fuel ratio feedback control means M110 is used to remove the air-fuel ratio feedback control constant and the three-way catalyst M102 on the upstream side. According to the detection result of the upstream side air-fuel ratio detection means M103 arranged in the passage for detecting the air-fuel ratio of the internal combustion engine M101, the control amount for determining the air-fuel ratio of the internal combustion engine M101 as the stoichiometric air-fuel ratio is determined. When instructing the fuel ratio adjusting means M105, the changing means M112, along with the increase in the catalyst deterioration degree calculated by the catalyst deterioration degree calculating means M111,
It serves to reduce the predetermined delay time of the delay means M108.

That is, the air-fuel ratio of the internal combustion engine M101, from the operating state to make the lean air-fuel ratio, or from the fuel supply cutoff state, set at the switching time to the operating state to control the stoichiometric air-fuel ratio, until the air-fuel ratio feedback control start The predetermined delay time of the three-way catalyst M102 is shortened according to the increase of the catalyst deterioration degree,
In response to the decrease in the oxygen storage effect of the three-way catalyst M102,
An air-fuel ratio feedback control constant calculated from the air-fuel ratio detected on the downstream side of the three-way catalyst M102, and the three-way catalyst
That is, the start of the air-fuel ratio feedback control based on the air-fuel ratio detected on the upstream side of M102 is accelerated.

Therefore, the air-fuel ratio control device for an internal combustion engine of the present invention reduces the degree of catalyst deterioration by reducing the delay time from the rich air-fuel ratio operating state or the lean air-fuel ratio operating state, or from the fuel supply cutoff state to the start of air-fuel ratio feedback control. It works to suppress the overcorrection of the air-fuel ratio feedback control amount due to the decrease of the oxygen storage effect due to the increase of.

As described above, the technical problems of the present invention are solved by the operation of each component of the present invention.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 3 shows the system configuration of the engine air-fuel ratio control system according to the first embodiment of the present invention.

As shown in the figure, the air-fuel ratio control device 1 for the engine
The engine 2 and an electronic control device for controlling the engine 2
Simply called ECU. ) 3).

In the engine 2, a combustion chamber 7 is formed from a cylinder 4, a piston 5 and a cylinder head 6, and an ignition plug 8 is provided in the combustion chamber 7.

The intake system of the engine 2 includes an intake port 10 communicating with the combustion chamber 7 via an intake valve 9, an intake pipe 11, a surge tank 12 for absorbing pulsation of intake air, and an intake air amount in conjunction with an accelerator pedal 13. The throttle valve 14 and the air cleaner 15 adjust the pressure.

The exhaust system of the engine 2 includes an exhaust port 17 communicating with the combustion chamber 7 via an exhaust valve 16, an exhaust manifold.
18, a catalytic converter 19 and an exhaust pipe 20.

The ignition system of the engine 2 includes an igniter 21 having an ignition coil that outputs a high voltage required for ignition and a distributor 22 that supplies the high voltage generated by the igniter 21 to a spark plug in conjunction with a crankshaft (not shown). It is composed of

The fuel system of the engine 2 includes a fuel tank 23 for storing fuel, a fuel pump 24 for pumping the fuel, and an electromagnetic fuel injection valve 25 for injecting the pumped fuel near the intake port 10. ing.

The air-fuel ratio control device 1 of the engine is provided as a detector at an upstream side of the throttle valve 14 of the above-described intake pipe 11 to measure an intake air amount, and is provided inside the air flow meter 31 to detect the intake air temperature. An intake air temperature sensor 32 to be measured, a throttle position sensor 33 that detects the opening of the throttle valve 14 in conjunction with the throttle valve 14, an idle switch 34 that detects a fully closed state of the throttle valve 14, and cooling of the cylinder block 4a. A water temperature sensor 35 disposed in the system to detect a cooling water temperature, an upstream oxygen concentration sensor 36 provided in the exhaust manifold 18 to detect a residual oxygen concentration in exhaust gas before flowing into the catalytic converter 19, and an exhaust gas A downstream oxygen concentration sensor 37 provided in the pipe 20 for detecting the concentration of residual oxygen in the exhaust gas flowing out of the catalytic converter 19, For each rotation of the camshaft of the string Byuta 22, i.e., the cylinder discrimination sensor for outputting a reference signal every two rotations of the crank shaft (not shown)
38, a rotation angle sensor 39 that also functions as a rotation speed sensor that outputs a rotation angle signal for each 1/24 rotation of the camshaft of the distributor 22, that is, for each integral multiple of a crank angle of 0 ° to 30 °, and a vehicle-mounted gear shift An electromagnetic pickup type vehicle speed sensor 41 for detecting the vehicle speed from the rotation speed of the output shaft of the machine 40 is provided.

The detection signals of the above sensors and switches are input to the ECU 3, which controls the engine 2. ECU3 is CPU3a,
The ROM 3b, the RAM 3c, the backup RAM 3d, and the timer 3e are mainly configured as a logical operation circuit, and are connected to the input / output port 3g via the common bus 3f to perform input / output with the outside. CPU3a
The detection signals of the air flow meter 31, the intake air temperature sensor 32, and the throttle position sensor 33 described above are output through the A / D converter 3h and the input / output port 3g, and the detection signal of the idle switch 34 is output through the input / output port 3g. , Cylinder discrimination sensor 38,
The detection signals of the rotation angle sensor 39 are sent to the A / D converter 3j and the detection signals of the water temperature sensor 35, the upstream oxygen concentration sensor 36, and the downstream oxygen concentration sensor 37 via the waveform shaping circuit 3i and the input / output port 3g. The detection signal of the vehicle speed sensor 41 is input via the waveform shaping circuit 3k and the input / output port 3g via the output port 3g. On the other hand, the CPU 3a controls the drive of the igniter 21 via the input / output unit 3g and the drive circuit 3m. Further, the CPU 3a uses the input / output unit 3g, the down counter 3n, the flip-flop circuit 3p and the drive circuit 3r to inject the fuel injection valve 25.
Drive control. That is, a value corresponding to the fuel injection amount TAU calculated by the CPU 3a is preset in the down counter 3n, and the flip-flop circuit 3p is also set. Therefore, the drive circuit 3r opens the fuel injection valve 25, and fuel injection is started. On the other hand, when the down counter 3n counts the clock signal and the carry-out terminal finally becomes high level (1), the flip-flop circuit 3p is set, and the drive circuit 3r closes the fuel injection valve 25, and Ends. In this way, the amount of fuel corresponding to the fuel injection amount TAU is supplied to the engine 2. The ECU 3 operates by receiving power supply from the vehicle-mounted battery 43 via the ignition switch 42.

Next, the execution delay time calculation process executed by the ECU 3 is shown in FIG. 4, the fuel cut setting process is shown in FIG. 6, and the first air-fuel ratio feedback control process is shown in FIG. 8 (1), (2). The second air-fuel ratio feedback control process is shown in FIG. 10 (1),
The fuel injection control process (2) will be described with reference to the flowcharts of FIG.

The execution delay time calculation process shown in FIG. 4 is started every predetermined time after the ECU 3 is started.

First, in step 100, a process of reading each data obtained from the detection signal of each sensor described above is performed. In the following step 105, it is determined whether or not the engine 2 is in the normal operation state based on each data read in the above step 100. If the affirmative determination is made, the routine proceeds to step 115, while if the negative determination is made, This execution delay time calculation process is once terminated. Here, in the normal operation state, the starter signal is at a low level (OFF) and the rotation speed is 4
It must be over 00 [rpm]. Steps executed when it is determined that the engine 2 is in the normal operation state
In 115, backup the engine operating time TEG RAM3
The process of reading from d is performed. Next, in step 120, it is determined whether or not the engine operation cumulative time TEG read in step 110 exceeds a preset set time TEG0. If an affirmative judgment is made, the operation proceeds to step 130, while a negative judgment is made. Then, the process goes to step 125. In step 125, which is executed when the engine operation cumulative time TEG is still less than or equal to the set time TEG0, the execution delay time TEGS of the second air-fuel ratio feedback control process is set in advance in the ROM3.
After performing the processing for setting the long time TEGS1 stored in the map b shown in FIG. 5 and proceeding to step 140. On the other hand, in step 130, which is executed when it is determined in step 120 that the set time TEG0 has already been exceeded, the execution delay time TEGS of the second air-fuel ratio feedback control process is obtained from the map shown in FIG. Short time TEGS2
After performing the process of setting to, proceed to step 140. In step 140, the above step 125 or step 13
Processing for converting the execution delay time TEGS set at 0 into the execution delay count value C1 is performed. Next, the routine proceeds to step 145, where a process of adding the value AT to the engine operating cumulative time TEG and updating it is performed. In the following step 150, the engine operation cumulative time TEG updated in step 140 is set to the maximum cumulative time MAXTE.
The process of guarding within G is performed. Next, in step 155, after the process of storing the engine operation cumulative time TEG updated in step 145 in the backup RAM 3d,
This execution delay time calculation process is once terminated. Thereafter, the execution delay time calculation process is performed at the above-mentioned step 100 at every predetermined time.
Repeat ~ 155.

Next, the fuel cut setting process will be described based on the flowchart shown in FIG. This fuel cut setting process is EC
It is executed every predetermined time (for example, 4 [ms]) after starting U3. First, in step 205, a process of reading each data detected by each sensor described above and the execution delay count value C1 calculated in the execution delay time calculation process described above is performed. In the following step 210, it is determined whether or not the idle switch signal LL is at the high level (value 1), and if the determination is affirmative, the process proceeds to step 215, and if the determination is negative, the process proceeds to step 225. In step 215 executed when the throttle valve is fully closed, it is determined whether or not the rotation speed Ne of the engine 2 is equal to or higher than the fuel cut rotation speed NC, and in step 220, the rotation speed Ne is fuel cut. It is determined whether or not the speed is equal to or lower than the return rotation speed NR. If an affirmative decision is made in step 215, the routine proceeds to step 230, where after the processing of setting the fuel cut flag XFC to the value 1 (fuel cut) is performed, the routine proceeds to step 240. On the other hand, above step 2
When the negative judgment is made at 15, the routine proceeds to step 220. If an affirmative decision is made in step 220, the routine proceeds to step 225, where after the processing of setting the fuel cut flag XFC to the value 0 (non-fuel cut) is performed, the routine proceeds to step 240. Also, above step 2
If both 15,220 are denied, step 240 is performed.
Proceed to. That is, as shown in FIG. 7, when the rotation speed Ne of the engine 2 is equal to or lower than the fuel cut return rotation speed NR, the fuel cut flag XFC has a value 0 (non-fuel cut) and the rotation speed Ne is the fuel cut rotation speed. When it is NC or more, the fuel cut flag XFC has a value of 1 (fuel cut) and the rotation speed Ne.
Is higher than the fuel cut return rotational speed NR and is lower than the fuel cut rotational speed NC, the fuel cut flag XFC
Is retained at its previous value.

In steps 240 to 280, a process of setting the second air-fuel ratio feedback control process execution flag XFCFB1 based on the output signal V2 of the downstream oxygen concentration sensor 37 is performed.
The second air-fuel ratio feedback control processing execution flag
XFCFB1 has been reset to the value 0 by the initialization process.

In step 240, it is judged whether or not the fuel cut flag XFC is set to the value 1, and if the affirmative judgment is made, the routine proceeds to step 245, and if the negative judgment is made, the routine proceeds to step 260. In step 245 executed during the fuel cut, the elapsed time counter CF that counts the elapsed time after the fuel cut is returned.
The CR is reset to the value 0, the routine proceeds to step 250, where the second air-fuel ratio feedback control processing execution flag XFCFB1 is reset to the value 0, and at step 255, the value of the fuel cut flag XFC and the second air-fuel ratio feedback After the value of the control process execution flag XFCFB1 is stored in the RAM 3c, the fuel cut setting process is temporarily terminated. On the other hand, in step 260 that is executed when the fuel is not being cut, the value 1 is added to the count value of the elapsed time counter CFCR, and in step 265 it is determined whether the count value of the elapsed time counter CFCR is less than the maximum value CMAX. If it exceeds the maximum value CMAX, step 270
In the above, the count value of the elapsed time counter CFCR is limited to the maximum value CMAX, and further, in step 275, the count value of the above elapsed time counter CFCR is the execution delay count value C1 obtained in the execution delay time calculation process described above. It is determined whether or not it is exceeded, and if it is still below the execution delay count value C1, the fuel cut setting process is once terminated, while if it is above the execution delay count value C1, the routine proceeds to step 280 and the second empty After the fuel ratio feedback control processing execution flag XFCFB1 is set to the value 1, the above-mentioned step 255 is performed, and then the present fuel cut setting processing is once ended. After that, this fuel cut setting process is performed every predetermined time.
The above steps 205 to 280 are repeatedly executed.

Next, the first air-fuel ratio feedback control process will be described based on the flowcharts shown in FIGS. 8 (1) and 8 (2). The first air-fuel ratio feedback control process is executed every predetermined time (for example, 4 [msec]) after the ECU 3 is started. First, in step 302, processing for reading each data based on the detection signals of each sensor described above is performed. In the following step 304, it is determined whether or not the fuel cut flag XFC set in the above-described fuel cut setting process is reset to the value 0. If a negative determination is made, the fuel cut is in progress, so the first The air-fuel ratio feedback control process is finished, and if an affirmative decision is made, the routine proceeds to step 306. In step 306, it is determined whether or not the first air-fuel ratio feedback control execution condition is satisfied. If an affirmative decision is made, the routine proceeds to step 308, while if a negative decision is made, the value of the air-fuel ratio correction coefficient FAF is set to the previous value. Then, the first air-fuel ratio feedback control process is temporarily terminated. Note that the value of the air-fuel ratio correction coefficient FAF may be set to a constant value, an average value up to the end of the previous control, a learning value stored in the backup RAM 3d, or the like. Here, for example, when the cooling water temperature THW is equal to or lower than a predetermined temperature (for example, 60 [° C.]), the starting state, the amount after starting, the amount during warming up, the amount during acceleration increasing (asynchronous injection), during the power increasing, distillation When the output signal V1 of the side oxygen concentration sensor 36 never crosses the first comparison voltage VR1, the first air-fuel ratio feedback control execution condition is not satisfied. Does not meet the above conditions,
In step 308, which is executed when the first air-fuel ratio feedback control execution condition is satisfied, a process of A / D converting and reading the detection signal V1 of the upstream oxygen concentration sensor 36 is performed. In the following step 310, the detection signal V of the upstream oxygen concentration sensor 36
It is determined whether 1 is the first comparison voltage VR1 (for example, 0.45 [V]) or less, and if a positive determination is made, the air-fuel ratio is determined to be on the lean side (Lean), and the negative determination is made in step 312. If the air-fuel ratio is over-concentrated (Rich)
Proceed to 324 respectively. In step 312 which is executed when the air-fuel ratio is on the lean side (Lean), it is determined whether the count value of the delay counter CDLY is positive or negative, and when it is positive, the count value of the delay counter CDLY is reset to a value 0 in step 314. After that, the process proceeds to step 316. On the other hand, when the result is negative, step 3 is performed as it is.
Proceed to 16. In step 316, the count value of the delay counter CDLY is decremented by 1, and in subsequent steps 318 and 320, the count value of the delay counter CDLY is limited to the minimum value TDL, and when the value of the delay counter CDLY decreases to the minimum value TDL, , In step 322, the air-fuel ratio flag F1 is set to the value 0 {lean side (Lea
n)} and proceed to step 340. It should be noted that the minimum value TDL retains the determination that it is on the rich side (Rich) even if the detection signal V1 of the upstream oxygen concentration sensor 36 changes from the rich side (Rich) to the lean side (Lean). Is the lean delay time for and is defined as a negative value. On the other hand, in step 324, which is executed when it is determined in step 310 that the air-fuel ratio is on the rich side (Rich), it is determined whether the count value of the delay counter CDLY is positive or negative.
After the count value of the delay counter CDLY is reset to 0 at 6 and the process proceeds to step 328, while if it is positive, the process directly proceeds to step 328. In step 328, the count value of the delay counter CDLY is incremented by 1, and the subsequent steps 330, 33 are executed.
When the count value of the delay counter CDLY is limited to the maximum value TDR in 2 and the count value of the delay counter CDLY increases to the maximum value TDR, the air-fuel ratio flag F1 is set to 1 in step 334.
After setting to {rich side (Rich)}, the process proceeds to step 340. It should be noted that the maximum value TDR holds the judgment that the maximum value TDR is the lean side (Lean) even if the detection signal V1 of the upstream oxygen concentration sensor 36 changes from the lean side (Lean) to the rich side (Rich). Rich delay time of, defined as a positive value.

In the following step 340, it is determined whether or not the value of the air-fuel ratio flag F1 has been inverted.
On the other hand, if a negative determination is made, the process proceeds to step 348. Steps executed when the value of the air-fuel ratio flag F1 is reversed
At 342, processing is performed to determine whether the inversion is from the rich side (Rich) to the lean side (Lean) or from the lean side (Lean) to the rich side (Rich). From the rich side (Rich) to the lean side (Le
In step 344 executed at the time of reversal to (an), the rich skip amount RSR is added to the air-fuel ratio correction coefficient FAF to increase in a skip manner, while the lean side (Lean) to the rich side (Ric
In step 346 executed at the time of reversal to h), the lean skip amount RSL is subtracted from the air-fuel ratio correction coefficient FAF to be reduced in a skipping manner. Also, in step 348, which is executed when the value of the air-fuel ratio flag F1 does not reverse in step 340, it is determined whether the air-fuel ratio flag is lean (Lean).
A process for determining whether the image is on the rich side (Rich) is performed. In step 350 executed when the engine is on the lean side (Lean), the rich integration constant KIR is added to the air-fuel ratio correction coefficient FAF to gradually increase the value. On the other hand, the operation is executed when the engine is on the rich side (Rich). In step 352, the lean integration constant KIL is subtracted from the air-fuel ratio correction coefficient FAF to gradually decrease the value, and the process proceeds to step 356. Here, both integration constants KIR and KIL are set to be sufficiently smaller than those of both skips RSR and RSL. Therefore, in steps 344 and 346, the fuel injection amount is quickly increased and decreased, while in steps 350 and 352, the fuel injection amount is gradually increased and decreased. In the following steps 356 and 358, the value of the air-fuel ratio correction coefficient FAF is limited to, for example, the maximum value less than 1.2, and in the following steps 360 and 362, the minimum value is limited to 0.8 or more, and the value FAF of the air-fuel ratio correction coefficient is somehow. Even if it becomes too large or too small due to the above reason, the transition to the air-fuel ratio overrich state or the over lean state is prevented. Next, the routine proceeds to step 364, where the air-fuel ratio correction coefficient FAF calculated as described above is stored in the RAM 3c, and then the first air-fuel ratio feedback control process is temporarily ended. Thereafter, the first air-fuel ratio feedback control process repeatedly executes the above steps 302 to 364 at predetermined time intervals.

Next, an example of the above control will be described with reference to the timing chart of FIG. At time t1, the air-fuel ratio signal A / F based on the upstream oxygen concentration sensor detection signal is shifted to the lean side (Lea
When the value changes from n) to the rich side (Rich), the count value of the delay counter CDLY is counted up after reset, and reaches the maximum value TDR at time t2 after the lapse of the rich delay time TDR. Then, the air-fuel ratio signal A / Fd (the value of the air-fuel ratio flag F1) after the delay processing changes from the lean side (Lean) to the rich side (Rich). Further, at time t3, when the air-fuel ratio signal A / F based on the upstream oxygen concentration sensor detection signal changes from the rich side (Rich) to the lean side (Lean), the count value of the delay counter CDLY is counted down after reset. Reach the minimum value TDL at time t4 after the elapse of the lean delay time (-TDL). Then, the air-fuel ratio signal A / Fd (the value of the air-fuel ratio flag F1) after the delay processing changes from the rich side (Rich) to the lean side (Lean). However, for example, when the air-fuel ratio signal A / F based on the upstream oxygen concentration sensor detection signal is inverted in a time shorter than the rich delay time TDR as at times t5, t6, and t7, the count value of the delay counter CDLY becomes the maximum value. The time to reach TDR is extended, and at time t8, the delayed air-fuel ratio signal A / Fd is inverted. That is, the air-fuel ratio signal A / Fd (the value of the air-fuel ratio flag F1) after the delay processing is a value more stable than the air-fuel ratio signal A / F based on the upstream oxygen concentration sensor detection signal. Thus, the air-fuel ratio correction coefficient FAF is determined based on the air-fuel ratio signal A / Fd after the relatively stable delay processing.

Next, the second air-fuel ratio feedback control process will be described. The second air-fuel ratio feedback control process includes skip amounts RSR, RSL, integration constants KIR, KIL, and delay times TDR, TDL, which are control constants of the first air-fuel ratio feedback control process.
And a control for changing the first comparison voltage VR1 and a control for calculating the second air-fuel ratio correction coefficient FAF2.

Skip amounts RSR and RSL, which are control constants, and integration constants KIR and KI
In the control for changing L, the delay times TDR, TDL, and the first comparison voltage VR1, for example, the air-fuel ratio is shifted to the rich side (Rich) by correcting the increase of the rich skip amount RSR or correcting the decrease of the lean skip amount RSL. Control, on the other hand, the reduction correction of the rich skip amount RSR or the lean skip amount RSL
The air-fuel ratio can be controlled to the lean side (Lean) by the increase correction of. Therefore, according to the detection signal of the downstream oxygen concentration sensor 37, the rich skip amount RSR or the lean skip amount R
The air-fuel ratio can be controlled by correcting at least one of SL.
Further, for example, the air-fuel ratio can be controlled to the rich side (Rich) by increasing the rich integration constant KIR or decreasing the lean integration constant KIL, while decreasing the rich integration constant KIR or increasing the lean integration constant. The air-fuel ratio can be controlled to the lean side by increasing the KIL. in this way,
The air-fuel ratio can be controlled by correcting at least one of the rich integration constant KIR or the lean integration constant KIL according to the detection signal of the downstream oxygen concentration sensor 37. Further, for example,
When the rich delay time TDR is set relatively larger than the lean delay time (-TDL), the air-fuel ratio can be controlled to the rich side (Rich), while the rich delay time TDR is set relatively smaller than the lean delay time TDL. Then, the air-fuel ratio is set to the lean side (Lean).
Can be controlled. That is, the air-fuel ratio can be controlled by correcting at least one of the rich delay time TDR or the lean delay time TDL according to the detection signal of the downstream oxygen concentration sensor 37. Further, for example, when the first comparison voltage VR1 is corrected to decrease, the air-fuel ratio can be controlled to the lean side (Lean). Therefore, the air-fuel ratio can be controlled even if the first comparison voltage VR1 is corrected according to the detection signal of the downstream oxygen concentration sensor 37. By the way, when the skip amounts RSR, RSL, the integration constants KIR, RIL, the delay times TDR, TDL and the first comparison voltage VR1 are changed according to the detection signal of the downstream oxygen concentration sensor 37, for example, the delay times TDR, TDL Correction enables extremely delicate air-fuel ratio control, and skip amounts RSR and RSL can be controlled with high responsiveness without extending the air-fuel ratio feedback control cycle like the delay times TDR and TDL above. become. Therefore, control combining a plurality of the above control constants is effective.

Next, the second air-fuel ratio feedback control process will be described based on the flowcharts shown in FIGS. 10 (1) and 10 (2). The second air-fuel ratio feedback control process is executed every predetermined time (for example, 512 [msec]) after the ECU 3 is started, and corrects and calculates the skip amounts RSR and RSL. First, in step 402, a process of reading each data based on the detection signal of each sensor described above is performed. In the following step 404, it is determined whether or not the second air-fuel ratio feedback control processing execution condition is satisfied.
If the determination is negative, the skip amounts RSR, RSL
Is set to the value at the end of the previous control, and the second air-fuel ratio feedback control process is temporarily ended. The values of the skip amounts RSR and RSL may be set to an average value up to the end of the previous control, a learning value stored in the backup RAM 3d, or the like. Here, for example, when the cooling water temperature THW is equal to or lower than a predetermined temperature (for example, 60 [° C.]), the starting state, during the increase after the start, during the warm-up increase, during the acceleration increase (asynchronous injection), during the power increase, and during the upstream increase When the detection signal V1 of the side oxygen concentration sensor 36 has never crossed the first comparison voltage VR1, the conditions for executing the second air-fuel ratio feedback control process are not satisfied. When the second air-fuel ratio feedback control processing execution condition that does not correspond to each of the above conditions is satisfied, the routine proceeds to step 406 to step 416, and whether the cooling water temperature THW exceeds 70 [° C.] (step 406), throttle valve non-complete Whether or not it is in the closed state (step 408), whether or not the downstream oxygen concentration sensor 37 is in the active state {that is, the downstream oxygen concentration sensor
When the detection signal of 37 is changing across the second comparison voltage VR2} (step 410), the downstream oxygen concentration sensor 37
Is normal (ie, downstream oxygen concentration sensor)
When the diagnosis signal of 37 indicates normal} (step 412), it is determined whether or not the load of the engine 2 is a predetermined load or more (step 414), and the air-fuel ratio feedback control execution flag set in the fuel cut setting process described above. Whether or not XFCFB1 is set to a value of 1 (step 416) is respectively judged, and if affirmative judgment is made, the process proceeds to step 420 and below in order to execute the second air-fuel ratio feedback control, while either When a negative determination is made in step, the values of the skip amounts RSR, RSL are set to the values at the time of the previous control termination, and the second air-fuel ratio feedback control processing is temporarily terminated.

In step 420, which is executed when the second air-fuel ratio feedback control process execution condition is satisfied, a process of A / D converting and reading the detection signal V2 of the downstream oxygen concentration sensor 37 is performed. In the following step 421, processing for reading the previously calculated skip amounts RSR and RSL is performed. Following step 422
Then, it is determined whether or not the detection signal V2 of the downstream oxygen concentration sensor 37 is equal to or lower than a second comparison voltage VR2 (for example, 0.55 [V]). If the determination is affirmative, the air-fuel ratio is lean (Lean). , And on the other hand, if a negative determination is made, it is determined that the air-fuel ratio is on the rich side (Rich) and the process proceeds to step 444. In step 424 executed when the air-fuel ratio is on the lean side (Lean), the rich skip amount RSR is set to a constant value ΔRS.
Then, in steps 426 and 428, the value of the rich skip amount RSR is limited to an amount equal to or less than the maximum value RMAX, and in step 430, the value of the lean skip amount RSL is set to a constant value ΔRS.
In subsequent steps 432 and 434, the value of the lean skip amount RSL is limited to an amount equal to or more than the minimum value LMIN. here,
For example, the maximum value is 7.5 [%], and the minimum value is 2.5 [%]. Note that the maximum value is a value in a range where drivability does not deteriorate due to a change in the air-fuel ratio, and the minimum value is a value in a range where the transient followability does not decrease. In this manner, the rich skip amount RSR is corrected to increase, and the lean skip amount RSL is corrected to decrease, so that the air-fuel ratio can be easily shifted to the rich side (Rich). Next, proceeding to step 436, the rich skip amount RSR and the lean skip amount RSL corrected as described above are stored in the RAM 3c.
And after storing it in the backup RAM 3d,
Ends the air-fuel ratio feedback control process.

On the other hand, in the above step 422, the air-fuel ratio becomes rich (Rich).
In step 444 that is executed when it is determined that, the value of the rich skip amount RSR is subtracted by a constant value ΔRS, and in the subsequent steps 446 and 448, the value of the rich skip amount RSR is limited to an amount equal to or greater than the minimum value RMIN. Next, the routine proceeds to step 450, where the value of the lean skip amount RSL is added by a constant value ΔRS, and at the subsequent steps 452 and 454, the value of the lean skip amount RSL is limited to an amount equal to or less than the maximum value LMAX. In this manner, the rich skip amount RSR is corrected to decrease and the lean skip amount RSL is corrected to increase so that the air-fuel ratio can be easily shifted to the lean side (Lean). Thereafter, through the above-described step 436, the second air-fuel ratio feedback control process is once ended. Thereafter, the second air-fuel ratio feedback control process repeats the above steps 402 to 454 at predetermined time intervals.

Next, the fuel injection control process will be described based on the flowchart shown in FIG. This fuel injection control process is performed at every predetermined crank angle (for example, 360 [° CA]) after the ECU 3 is started.
Is executed. First, in step 500, a process of reading each data described above is performed. In the following step 510, it is determined whether or not the fuel cut flag XFC is reset to the value 0, and if a positive determination is made, the routine proceeds to step 520 to execute the air-fuel ratio feedback control, while if a negative determination is made, the step is made. After proceeding to 515 and performing the fuel cut processing, the present fuel injection control processing is once terminated. In step 520, which is executed when the air-fuel ratio feedback control is performed, a process of calculating the basic fuel injection amount TAU0 from the constant α, the intake air amount Q and the rotation speed Ne as in the following equation (1) is performed.

TAU0 = α × Q / Ne (1) In the following step 530, the warm-up increase coefficient FWL is calculated by interpolation calculation according to the map shown in FIG. 12 stored in the ROM 3b according to the cooling water temperature THW. Processing is performed.
Next, the routine proceeds to step 540, where the processing for calculating the actual fuel injection amount TAU as in the following equation (2) is performed. Where β, γ
Is a correction coefficient determined according to other operating state parameters.

TAU = TAU0 * FAF * (FWL + [beta] +1) + [gamma] (2) At the next step 550, the actual fuel injection amount TAU calculated at step 540 is set in the down counter 3n and the flip-flop circuit 3p is set. Is output to start the fuel injection, the present fuel injection control process is once ended. Note that, as described above, when the time corresponding to the actual fuel injection amount TAU elapses, the down counter 3n
Is reset, the flip-flop 3p is reset, and the fuel injection ends. After that, the present fuel injection control processing is repeatedly executed at the predetermined crank angle every steps 500 to 550.

Next, an example of the above control will be described with reference to the timing chart shown in FIG. From time t11 to time t12, the fuel is being cut (the fuel cut flag XFC is set to the value 1), so the coefficient value of the elapsed time counter CFCR is held at the value 0, and the second air-fuel ratio feedback control process is executed. The flag XFCFB1 is also held at the value 0. During this period, the first air-fuel ratio feedback control process based on the detection signal V1 of the upstream oxygen concentration sensor 36 and the downstream oxygen concentration sensor 37
The second air-fuel ratio feedback control process based on the detection signal V2 is stopped, and the air-fuel ratio is open-controlled to the lean side (Lean). In this case, the detection signal V2 of the downstream oxygen concentration sensor 37 indicates a low level (Lean output), and the rich skip amount RSR and the lean skip amount RSL (not shown) are held at the values immediately before the fuel cut. Eventually, at time t12, the fuel cut is restored (fuel cut flag XFC is reset to value 0) and counting of the elapsed time counter CFCR is started, but until the execution delay time count value C1 is increased. Is
Second air-fuel ratio feedback control process execution flag XFCFB1
Is held at the value 0. Therefore, the downstream oxygen concentration sensor 37
The second air-fuel ratio feedback control process based on the detection signal V2 is still stopped, and the rich skip amount RSR and the lean skip amount RSL are not corrected. However, since the first air-fuel ratio feedback control process based on the detection signal V1 of the upstream oxygen concentration sensor 36 is executed, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. Execution delay time TEG from time t12 above
At time t13 after the passage of S1, the count value of the elapsed time counter CFCR increases to the execution delay time count value C1, so
The air-fuel ratio feedback control process execution flag XFCFB1 is set to the value 1, and the detection signal V2 of the downstream oxygen concentration sensor 37
Since the second air-fuel ratio feedback control processing based on is executed, the rich skip amount RSR and the lean skip amount RSL are corrected. Therefore, after time t13, the first air-fuel ratio feedback control process based on the detection signal V1 of the upstream oxygen concentration sensor 36 and the second air-fuel ratio feedback control process based on the detection signal V2 of the downstream oxygen concentration sensor 37 are performed. Executed together. As described above, when the engine 2 is operated and the time t14 is reached, the cumulative driving time TEG exceeds the cumulative driving time reference value TEG0. Therefore, at the same time t14, the execution delay time count value C1 is shortened. The delay time TEGS2 is reduced and corrected to the converted value. After that, from time t15 to time t16, the fuel cut is performed again, so the count value of the elapsed time counter CFCR is reset to the value 0, and the second air-fuel ratio feedback control process execution flag XFCFB1 is also reset to the value 0. It During this period, both the first air-fuel ratio feedback control process and the second air-fuel ratio feedback control process are stopped, and the air-fuel ratio is open-controlled to the lean side (Lean). In this case, the rich skip amount RSR and the lean skip amount RSL (not shown) are held at the values immediately before the fuel cut. Eventually, at time t16, the fuel cut is restored, so the elapsed time counter CFCR starts counting,
Second air-fuel ratio feedback control process execution flag XFCFB1
Is held at the value 0, the second air-fuel ratio feedback control process is still stopped, and the rich skip amount RSR is
Also, the lean skip amount RSL is not corrected, only the first air-fuel ratio feedback control processing is executed, and the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. At the time t17 after the shortened and corrected execution delay time TEGS2 has elapsed from the time t16, the count value of the elapsed time counter CFCR increases to the decreased and corrected execution delay time count value C1. The feedback control process execution flag XFCFB1 is set to the value 1, and the second
Since the air-fuel ratio feedback control process is performed, the rich skip amount RSR and the lean skip amount RSL (not shown) are corrected as shown by the solid line in the figure, and the first air-fuel ratio feedback control process and the second air-fuel ratio feedback process are performed. Both control processes are properly executed. By the way, if the execution delay time is fixed to the constant value TEGS1 without considering the accumulated operation time TEG of the engine 2 as in the conventional case, the execution start of the second air-fuel ratio feedback control process is indicated by the broken line in the figure. As shown, from the above time t16, the execution delay time TEG
It will be delayed until time t18 after S1. Then, at the same time t
Up to 18, the rich skip amount RSR is not reduced and corrected as shown by the broken line in the figure, and the rich skip amount RSR (and the lean skip amount RSL (not shown) is overcorrected on the rich side (Rich), and control is performed. The deterioration of accuracy caused the air-fuel ratio to be disturbed.

In the first embodiment, the engine 2 is an internal combustion engine M1.
(M101), catalytic converter 19 is a three-way catalyst M2 (M102)
In addition, the upstream oxygen concentration sensor 36 is connected to the upstream air-fuel ratio detecting means M1.
In 03, the downstream side oxygen concentration sensor 37 is a downstream side air-fuel ratio detecting means.
The fuel injection valve 25 is connected to M4 (M104) by the air-fuel ratio adjusting means M5 (M10
In 5), the idle switch 34 and the rotation angle sensor 39 correspond to the operating state detecting means M6 (M106), respectively. Also, ECU3
In the processing executed by the ECU 3, step 240 is the determination means M7 (M107), step (260 to 280) is the delay means M8 (M108), step (402 to 454) is the control constant calculation means M109, and step (302 ~ 364,402 ~ 454,50
0-550) as the air-fuel ratio feedback control means M10,
Steps (302 to 364,500 to 550) serve as air-fuel ratio feedback control means M110, and steps (100,105,115,145 to 1)
55) functions as catalyst deterioration degree calculating means M11 (M111), and steps (120 to 140) function as changing means M12 (M112).

As described above, according to the first embodiment, when the oxygen storage effect decreases due to the deterioration of the catalytic converter 19 that accompanies the increase in the engine operating cumulative time TEG, the fuel cut process is performed first. When switching to the start of the air-fuel ratio feedback control process, the execution delay time TEGS is shortened, and the rich skip amount by the second air-fuel ratio feedback control process
By limiting overcorrection of RSR and lean skip amount RSL to the rich side (Rich), it is possible to prevent the generation of catalyst exhaust odor, reduce the emission of harmful components in the exhaust, and improve fuel consumption efficiency. The optimum air-fuel ratio feedback control can be continued.

In order to shorten and correct the execution delay time TEGS in consideration of the deterioration of the catalytic converter 19, the rich skip amount RSR and the rich skip amount RSR based on the detection signal V2 of the downstream side oxygen concentration sensor 36 arranged on the downstream side of the catalytic converter 19. Lean skip amount RSL
Of the upstream side oxygen concentration sensor 37 arranged on the upstream side of the catalytic converter 19 by using the second air-fuel ratio feedback control process for increasing / decreasing Since the first air-fuel ratio feedback control process for calculating the air-fuel ratio correction coefficient FAF according to the detection signal V1 can be executed while maintaining high control accuracy over a long operating time, the durability of the engine air-fuel ratio control device 1 is improved.・ Reliability is improved.

Further, the first air-fuel ratio feedback control process based on the detection signal V1 of the upstream oxygen concentration sensor 36 which fluctuates in a relatively short cycle is performed every 4 [msec], while the downstream oxygen concentration fluctuates in a relatively long cycle. Since the second air-fuel ratio feedback control process based on the detection signal V2 of the sensor 37 is executed every 512 [msec], the responsiveness and follow-up of the control can be compensated to a high level.

In the first embodiment, the engine operating cumulative time TEG is
Was calculated by measuring the time during which the engine 2 is in a normal operating state. For example, the operation of the ignition switch 42 (ON
/ OFF) It can also be calculated based on the number of times.

Further, in the above-described first embodiment, the description was given of the time of switching from the fuel cut processing to the air-fuel ratio feedback control processing, but for example, the lean side (Lean) of the air-fuel ratio such as lean burn control is described.
On the contrary, even when switching from the process of setting to the rich side (Rich) such as OTP increase and power increase to the air-fuel ratio feedback control process, the execution delay time TEGS is set according to the accumulated engine operation time TEG. When configured to shorten correction,
Similarly, it is possible to prevent the deterioration of the control accuracy due to the deterioration of the oxygen storage effect due to the deterioration of the catalytic converter 19.

Furthermore, in a so-called single oxygen concentration sensor system in which an oxygen concentration sensor is provided only on the downstream side of the catalytic converter 19 to perform air-fuel ratio feedback control, the air-fuel ratio correction calculated in the first air-fuel ratio feedback control process is performed. Instead of the coefficient FAF, the rich skip amount RSR and the lean skip amount RSL calculated in the second air-fuel ratio feedback control process may be used as the air-fuel ratio correction coefficient FAF to execute the air-fuel ratio feedback control.

Further, in the case of a so-called double oxygen concentration sensor system, other control constants used in the first air-fuel ratio feedback control process by the upstream oxygen concentration sensor 36, that is, the delay times TDL, TDR, the integration constants KIL, KIR. , The first comparison voltage VR1 and the like may be configured to be corrected by the detection signal V2 of the downstream oxygen concentration sensor 37, and the first air-fuel ratio feedback correction coefficient FAF and the second air-fuel ratio feedback correction coefficient The same effect can be obtained even if the configuration is used together with FAF2.

In addition, if you configure to correct multiple control constants among the skip amounts RSR, RSL, delay times TDL, TDR, integration constants KIL, KIR, and the first comparison voltage VR1, control accuracy and responsiveness / followability will be improved. It can be further improved.

Also, among the skip amounts RSR, RSL, the delay times TDL, TDR, the integration constants KIL, KIR, and the first comparison voltage VR1, the rich side (Rich),
Alternatively, one of the lean sides (Lean) is set to a constant value,
Only the other may be changed based on the detection signal V2 of the downstream oxygen concentration sensor 37.

Furthermore, in the first embodiment described above, the air flow meter 31
Is configured to determine the fuel injection amount TAU based on the intake air amount Q detected by the engine and the rotation speed Ne detected by the rotation angle sensor 39. For example, the intake air amount Q is measured by a Karman vortex sensor, a hot wire sensor, or the like. Alternatively, the fuel injection amount TAU may be calculated based on the intake pipe pressure PM and the rotation speed Ne, or the throttle valve opening TA and the rotation speed Ne.

In the above-described first embodiment, the oxygen concentration sensors 36, 37
However, for example, a gas sensor for detecting carbon monoxide CO or a so-called lean mixture sensor may be used.

Further, in the first embodiment described above, the air-fuel ratio control device 1 for the engine in which the fuel injection amount is controlled by the fuel injection valve 25 has been described. However, for example, an engine equipped with a carburetor, an engine that controls the amount of intake air with an air control valve (EACV), a bleed air control valve that adjusts the bleed air amount of the carburetor, and a main system passage and a slow system The present invention is also applicable to an engine that controls an air-fuel ratio by introducing air into a passage, an engine that adjusts an amount of secondary air supplied to an exhaust system, and the like. in this way,
In an engine equipped with a carburetor, the basic fuel injection amount is determined from the characteristics of the carburetor, and the amount of supply air that achieves a desired air-fuel ratio is calculated to perform air-fuel ratio control.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings. The difference between the second embodiment and the above-described first embodiment is that the execution delay time calculation processing is different, and the device configuration and other processing are exactly the same, so the same parts are denoted by the same reference numerals, The description is omitted.

The execution delay time calculation processing executed in the second embodiment is
Description will be made based on the flowchart shown in FIG. The execution delay time calculation process shown in FIG. 14 is started every predetermined time after the ECU 3 is started.

First, in step 610, a process of reading each data obtained from the detection signal of each sensor described above is performed. In the following step 620, it is determined whether or not the engine 2 is in the normal operation state based on each data read in the above step 610. If the affirmative determination is made, the processing proceeds to step 640, while if the negative determination is made, This execution delay time calculation process is once terminated. In step 640 that is executed when it is determined that the engine 2 is in the normal operation state, a process of reading the engine operation accumulated time TEG from the backup RAM 3d is performed. Next, proceeding to step 650, the execution delay time TEGS of the second air-fuel ratio feedback control processing is stored in the ROM 3b in advance. After performing the process of calculating from the map shown in FIG. 15, the process proceeds to step 660. In step 660, a process of converting the execution delay time TEGS calculated in step 650 into the execution delay count value C1 is performed. Then step 67
Proceeding to 0, a process of adding the value AT to the engine operation cumulative time TEG and updating it is performed. In the following step 680, a process of guarding the engine operating cumulative time TEG within the maximum cumulative time MAXTEG is performed. Next, the process proceeds to step 690, and after the process of storing the engine operation cumulative time TEG updated in step 670 in the backup RAM 3d, the present execution delay time calculation process is once ended. Thereafter, the execution delay time calculation process repeats the above steps 610 to 690 at predetermined time intervals.

In addition, in the second embodiment, the steps (640, 670 to 690) of the ECU 3 and the processing executed by the ECU 3 are the catalyst deterioration degree calculating means M11 (M111), and the steps (650 to 660) are the changing means M12 (M112). , Each works.

As described above, according to the second embodiment, the execution delay time TEGS that continuously corresponds to the engine operation cumulative time TEG at that time can be calculated, so that the control accuracy is further improved.

Next, a third embodiment of the present invention will be described in detail with reference to the drawings. The difference between the third embodiment and the above-described first embodiment is that the execution delay time calculation processing is different, and the device configuration and other processing are exactly the same, so the same parts are denoted by the same reference numerals, The description is omitted.

The execution delay time calculation process executed in the third embodiment is
Description will be made based on the flowchart shown in FIG. The execution delay time calculation process shown in FIG. 16 is started every predetermined time after the ECU 3 is started.

First, in step 710, a process of reading the vehicle speed V, the intake air amount Q, and the rotation speed Ne detected by the above-described sensors is performed. In the following step 720, a process of calculating the count-up value ΔSPD is performed according to the vehicle speed V and according to the map shown in FIG. 17, which is stored in advance in the ROM 3b. Next, at step 730, a process of adding the count-up value ΔSPD calculated at step 720 to the count value of the cumulative operation time counter CSPD stored in the backup RAM 3d. In the following step 740, the execution delay time TEGS of the second air-fuel ratio feedback control process is set in advance.
After performing the process of calculating from the map shown in FIG. 18 stored in the ROM 3b, the process proceeds to step 750. Step 750
Then, the execution delay time TEGS calculated in step 740 above
Is converted into the execution delay count value C1. Next, in step 760, the execution delay count value C1 converted in step 750 above is stored in RAM3c, and the cumulative operation time counter CSPD
After performing the process of storing the count value of each in the backup RAM 3d, the present execution delay time calculation process is once ended.
Thereafter, the execution delay time calculation process repeats the above steps 710 to 760 at predetermined time intervals.

In the third embodiment, the steps (710 to 730,760) of the ECU 3 and the processing executed by the ECU 3 are the catalyst deterioration degree calculating means M11 (M111), and the steps (740 to 750) are the changing means M12 (M112). , Each works.

As described above, according to the third embodiment, it is possible to estimate the traveling distance based on the vehicle speed V and calculate the cumulative operating time TEGS of the engine 2.

Instead of step 720 of the execution delay time calculation process of the third embodiment, for example, the count-up value ΔSPD is calculated from the intake air amount Q and the rotation speed Ne of the engine 2 according to a map as shown in FIG. It may be configured to calculate. In the case of such a configuration, there is an advantage that the cumulative operation time can be calculated from the operational state of the engine 2.

Further, for example, the count-up value ΔSPD can be calculated based on the intake pipe pressure PM of the engine 2, the throttle valve opening TA, the rotation speed Ne, and the like.

Next, a fourth embodiment of the present invention will be described. The difference between the present fourth embodiment and the above-described first embodiment is that the execution delay time calculation processing is different, and the device configuration and other processing are exactly the same, so the same parts are denoted by the same reference numerals, The description is omitted.

The oxygen concentration sensor output width / cycle calculation processing executed in the fourth embodiment will be described with reference to FIGS. 20 (1) and (2), and the execution delay time calculation processing with reference to the flowcharts shown in FIG. .

Output range of oxygen concentration sensor shown in Fig. 20 (1) and (2)
The cycle calculation process is performed at predetermined time intervals (for example,
4 [msec]). Step 802 to Step 836
Is performed on the detection signal V1 of the upstream oxygen concentration sensor 36, and steps 852 to 886 are performed on the detection signal V2 of the downstream oxygen concentration sensor 37.

First, in step 802, a process of A / D converting and reading the upstream oxygen concentration sensor detection signal V1 is performed. In the following step 804, the detection signal V1B read last time is compared with the detection signal V1 read this time.
Go forward each. In step 806, it is determined whether or not the upstream oxygen concentration sensor detection signal increase flag F1UP is set to the value 1, and if the decrease continues, the process proceeds to step 808.
On the other hand, when the decrease is reversed, the process proceeds to step 830.
When the decrease continues, the value 1 is added to the count value of the decrease period counter C1DN in step 808, the process proceeds to step 810, and the detection signal V1 read this time is replaced with the previous value V1B in preparation for the next process. Then, proceed to step 852 and below. On the other hand, if it is determined in step 804 that it is increasing, the process proceeds to step 812, it is determined whether or not the upstream oxygen concentration sensor detection signal increase flag F1UP is reset to a value 0, and the increase is continued. If so, the process proceeds to step 828. On the other hand, if the increase is reversed, the process proceeds to step 814. In the step 814 executed when reversing from decrease to increase, the count value of the decrease period counter C1DN is set to the decrease period TS1DN, and in the following step 816, the count value of the decrease period counter C1DN is reset to the value 0, and in step 818. Then, the previous detection signal V1B
Is set to a minimum value V1L, the upstream side oxygen concentration sensor detection signal increase flag F1UP is set to a value of 1 in step 820, and the decrease period TS1DN calculated in step 814 and step 830 of the previous process is set in step 822. Increase period TS1UP
And are added to calculate the cycle TS1 of the detection signal V1 of the upstream oxygen concentration sensor 36, and in step 824, the previous processing step
Calculate the width ΔV1 of the detection signal V1 of the upstream oxygen concentration sensor 36 by subtracting the minimum value V1L set in step 818 from the maximum value V1H set in 834, and in step 826 the upstream oxygen concentration sensor 36 Detection signal V1 period TS1 and width ΔV
After performing the process of storing 1 in the RAM 3c and the backup RAM 3d, the process proceeds to step 810 already described. That is, the 21st
As shown in the timing chart of the figure, the upstream side oxygen concentration sensor detection signal V1 is continuously decreasing from time t21 to t21.
In 22, the upstream oxygen concentration sensor detection signal increase flag P1UP
Is reset to the value 0, the count value of the increasing period counter C1UP is held at the value 0, while the decreasing period counter C1DN is maintained.
The count value of increases to TS1DN. However, when the upstream oxygen concentration sensor detection signal V1 reverses to increase at time t22, the upstream oxygen concentration sensor detection signal increase flag P1UP is set to the value 1, and the count value of the increase period counter C1UP starts to increase from the value 0. On the other hand, the count value of the decrease period counter C1DN is reset to 0 and held. Thus, while the increase of the upstream oxygen concentration sensor detection signal V1 continues, the control is
20. Steps 802, 804, 812, 828 in FIG.
Continue below 810. Eventually, when the upstream side oxygen concentration sensor detection signal V1 reverses from increase to decrease, control proceeds to step 802,
Proceed to 804, 806, 830, and in step 830, increment period counter
Set the count value of C1UP in the increment period TS1UP, and continue with Step 8
In 32, the increase period counter C1UP is reset to the value 0, in step 834, the previous detection signal V1B is set to the maximum value V1H, and in step 836, the upstream oxygen concentration sensor detection signal increase flag F1UP is reset to the value 0, Step 82 already mentioned
Go to 2 or less. That is, as shown in the timing chart of FIG. 21, the upstream oxygen concentration sensor detection signal V1 is continuously increasing, at times t22 to t23, the upstream oxygen concentration sensor detection signal increase flag P1UP becomes 1 When set, the count value of the increasing period counter C1UP increases to TS1UP, while the count value of the decreasing period counter C1DN is reset to 0 and held. However, when the upstream oxygen concentration set detection signal V1 reverses to decrease at time t23, the upstream oxygen concentration sensor detection signal increase flag P1UP is reset to the value 0, and the count value of the decrease period counter C1DN starts to increase from the value 0. On the other hand, the count value of the increment period counter C1UP is reset to 0 and held. In the same manner, step 852-
In each process of step 886, the downstream oxygen concentration sensor 37
The period TS2 and the width ΔV2 of the detection signal V2 are calculated and stored. In this way, the present oxygen concentration sensor output width / cycle calculation process is repeatedly executed at predetermined time intervals.

Next, the execution delay time calculation process will be described based on the flowchart of FIG. This execution delay time calculation process
After U3 is started, it is executed every predetermined time (for example, 4 [msec]).

First, in step 905, a process of reading each data detected by each sensor described above is performed. Continued Step 91
At 0, the cumulative time CC stored in the backup RAM 3d
Is read. Then go to step 915,
The width ΔV2 of the detection signal of the downstream side oxygen concentration sensor 37 calculated by the oxygen concentration sensor output width / cycle calculation process is 0.3.
[V] It is determined whether or not it exceeds V, and in step 920, whether the ratio of the period TS1 of the detection signal V1 of the upstream oxygen concentration sensor 36 to the period TS2 of the detection signal V2 of the downstream oxygen concentration sensor 37 exceeds 0.3. When it is determined whether or not, in either of the above steps 915 and 920, an affirmative determination is made, it is determined that the catalytic converter 19 has deteriorated, and the process proceeds to step 925. Assuming that the catalytic converter 19 has not deteriorated yet, the present execution delay time calculation process is once ended. In step 925, which is executed when the catalytic converter 19 is deteriorated, the cumulative time C
The process of adding the value 1 to C is performed. In the following step 930, the execution delay time TEGS of the second air-fuel ratio feedback control process is stored in advance in the ROM 3b according to the cumulative time CC. After performing the process of calculating from the map shown in FIG. 23, the process proceeds to step 935. In step 935, the execution delay time TEGS calculated in step 930 is used as the execution delay count value C.
Processing to convert to 1 is performed. Then proceed to step 940,
The execution delay count value C1 converted in step 935 above is stored in RAM3c
Further, after performing the process of storing the cumulative time CC in the backup RAM 3d, the present execution delay time calculation process is once ended. Thereafter, the execution delay time calculation process repeats the above steps 905 to 940 at predetermined time intervals.

In the fourth embodiment, the ECU 3 and the steps (910 to 925,940) of the processing executed by the ECU 3 are the catalyst deterioration degree calculating means M11 (M111), and the steps (930 to 935) are the changing means M12 (M112). , Each works.

As described above, according to the fourth embodiment, the detection signal V1 of the upstream oxygen concentration sensor 36 and the downstream oxygen concentration sensor 37
The degree of deterioration of the catalytic converter 19 having the oxygen storage effect is determined based on the ratio of the inversion period of the detection signal V2 and the output width, and the second empty space continuously corresponding to the degree of deterioration of the catalytic converter 19 is determined. The execution delay time TEGS of the fuel ratio feedback control process can be calculated. With such a configuration, since the degree of deterioration of the catalytic converter 19 can be grasped relatively accurately, it is possible to realize a favorable correction of shortening the execution delay time TEGS according to the degree of decrease of the oxygen storage effect.

The ratio TS1 / TS2 of the inversion cycle of the detection signal V1 of the upstream oxygen concentration sensor 36 and the detection signal V2 of the downstream oxygen concentration sensor 37
The execution delay time TEGS of the second air-fuel ratio feedback control process may be directly obtained.

Although several embodiments of the present invention have been described above,
The present invention is not limited to such embodiments at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

Effects of the Invention As described in detail above, the air-fuel ratio control device for an internal combustion engine of the present invention switches from an operating state in which the air-fuel ratio of the internal combustion engine is set to a rich air-fuel ratio or a lean air-fuel ratio to an operating state in which it is controlled to a stoichiometric air-fuel ratio. The predetermined delay time until the start of the air-fuel ratio feedback control set at the time is shortened according to the increase in the degree of catalyst deterioration of the three-way catalyst, and the three-way catalyst is reduced according to the decrease in the oxygen storage effect of the three-way catalyst. The air-fuel ratio feedback control based on the air-fuel ratio detected on the downstream side of the catalyst is started earlier. Therefore, when the oxygen storage effect decreases due to the deterioration of the three-way catalyst accompanying the increase in the degree of catalyst deterioration, the air-fuel ratio feedback is reduced by shortening the delay time from the predetermined air-fuel ratio operation state to the start of air-fuel ratio feedback control. Since the overcorrection of the control amount is suppressed, it is possible to prevent the generation of catalyst exhaust odor, and it is possible to improve the exhaust gas purification performance and the fuel consumption efficiency by improving the control accuracy.

Further, for example, the air-fuel ratio feedback control start set at the time of switching from the operating state where the air-fuel ratio of the internal combustion engine is changed to the lean air-fuel ratio, or from the fuel supply cutoff state to the operating state where the stoichiometric air-fuel ratio is controlled. Up to a predetermined delay time until the catalyst deterioration degree of the three-way catalyst increases,
Depending on the decrease in the oxygen storage effect of the three-way catalyst, the air-fuel ratio feedback control constant calculated from the air-fuel ratio detected on the downstream side of the three-way catalyst, and the air-fuel ratio detected on the upstream side of the three-way catalyst. If configured to accelerate the start of air-fuel ratio feedback control based on and, when the oxygen storage effect due to the deterioration of the three-way catalyst is reduced, the fuel supply is cut off or the lean-burn state is changed to the air-fuel ratio feedback control state. It prevents the air-fuel ratio feedback control constant from being overcorrected to the rich side (Rich) during the transition to, and does not cause adverse effects such as exhaust of catalyst exhaust odor and discharge of exhaust containing harmful components. Air-fuel ratio feedback control can be realized.

Furthermore, in order to shorten and correct the predetermined delay time in consideration of the deterioration of the three-way catalyst, the air-fuel ratio control that effectively utilizes both air-fuel ratio detection means provided on the upstream and downstream sides of the three-way catalyst can be used for a long period of time. Can continue with high accuracy.

[Brief description of the drawings]

1 and 2 are basic configuration diagrams conceptually illustrating the content of the present invention, FIG. 3 is a system configuration diagram of the first embodiment of the present invention, and FIG. 4 is a flowchart showing the same control, 5 is a graph showing the map, FIG. 6 is a flow chart showing the control, FIG. 7 is an explanatory view showing the control, and FIGS. 8 (1) and 8 (2) are flow charts showing the control. , FIG. 9 is a timing chart showing the state of the control, FIG. 10 (1), (2),
11 is a flow chart showing the same control, FIG. 12 is a graph showing the same map, FIG. 13 is a timing chart showing the state of the same control, and FIG. 14 is a control of the second embodiment of the present invention. Flow chart, FIG. 15 is a graph showing the same map, FIG. 16 is a flow chart showing control of the third embodiment of the present invention, FIG. 17, FIG. 18, FIG. 19 are graphs showing the same map, FIG. Figure (1),
(2) is a flow chart showing the control of the fourth embodiment of the present invention, FIG. 21 is a timing chart showing the state of the control, FIG. 22 is a flow chart showing the control, and FIG. 23 is the map. A graph, FIG. 24 is a graph showing an exhaust characteristic of the related art, FIG. 25 is a timing chart showing a control state of the related art, and FIG. 26 is a graph showing a relationship between oxygen storage time and mileage. M1 ... Internal combustion engine, M2 ... Three-way catalyst M4 ... Downstream air-fuel ratio detecting means M5 ... Air-fuel ratio adjusting means M6 ... Operating state detecting means M7 ... Determination means, M8 ... Delaying means M10 ... Air-fuel ratio feedback control means M11 ...... Catalyst deterioration degree calculation means M12 ...... Change means M101 ...... Internal combustion engine, M102 ...... Three-way catalyst M103 ...... Upstream side air-fuel ratio detection means M104 ...... Downstream side air-fuel ratio detection means M105 ... ... Air-fuel ratio adjusting means M106 ... operating state detecting means M107 ... judging means, M108 ... delaying means M109 ... control constant calculating means M110 ... air-fuel ratio feedback controlling means M111 ... catalyst deterioration degree calculating means M112 ... change Means 1 ... Engine air-fuel ratio control device 2 ... Engine 3 ... Electronic control unit (ECU) 3a ... CPU 19 ... Catalytic converter, 25 ... Fuel injection valve 31 ... Air flow meter 33 ... Throttle position sensor 34 …… idle switch 36 …… upstream The oxygen concentration sensor 37 ...... downstream oxygen concentration sensor 39 ...... rotation angle sensor, 41 ...... vehicle speed sensor 42 ...... ignition switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-237856 (JP, A) JP-A 63-147941 (JP, A) JP-A 61-215434 (JP, A)

Claims (2)

(57) [Claims] 1. A three-way catalyst provided in an exhaust passage of an internal combustion engine and having an oxygen storage effect, and a downstream provided in an exhaust passage downstream of the three-way catalyst for detecting an air-fuel ratio of the internal combustion engine. Side air-fuel ratio detecting means, operating state detecting means for detecting the operating state of the internal combustion engine, and air-fuel ratio adjustment for adjusting the air-fuel ratio of the internal combustion engine according to a control amount determined based on the operating state of the internal combustion engine. Means and the operating state detected by the operating state detecting means, the operating state of the internal combustion engine is controlled from the operating state in which the air-fuel ratio of the internal combustion engine is set to the rich air-fuel ratio or the lean air-fuel ratio to the stoichiometric air-fuel ratio. Determining means for determining whether or not it is the switching timing for switching to the operating state, and, after a predetermined delay time has elapsed from the time when the determining timing is determined by the determining means, changing the air-fuel ratio of the internal combustion engine to the theoretical air-fuel ratio. A delay means for instructing the start of control for controlling, and a control amount for making the air-fuel ratio of the internal combustion engine the stoichiometric air-fuel ratio in accordance with at least the detection result of the downstream air-fuel ratio detection means in accordance with the instruction from the delay means. An air-fuel ratio feedback control means for determining and instructing the air-fuel ratio adjusting means, and an air-fuel ratio control apparatus for an internal combustion engine, further comprising: An air-fuel ratio control device for an internal combustion engine, comprising: a changing means for shortening a predetermined delay time of the delay means with an increase in the catalyst deterioration degree calculated by the catalyst deterioration degree calculating means. 2. A three-way catalyst provided in an exhaust passage of an internal combustion engine and having an oxygen storage effect, and an upstream provided in an exhaust passage upstream of the three-way catalyst for detecting an air-fuel ratio of the internal combustion engine. A side air-fuel ratio detecting means, a downstream side air-fuel ratio detecting means arranged in the exhaust passage on the downstream side of the three-way catalyst for detecting the air-fuel ratio of the internal combustion engine, and an operating state for detecting the operating state of the internal combustion engine. Detecting means, air-fuel ratio adjusting means for adjusting the air-fuel ratio of the internal combustion engine in accordance with a control amount determined based on the operating state of the internal combustion engine, and the operating state detected by the operating state detecting means Whether the operating state of the internal combustion engine is at a switching time when the air-fuel ratio of the internal combustion engine is changed from the operating state in which the lean-side air-fuel ratio is set, or from the fuel supply cutoff state to the operating state in which the stoichiometric air-fuel ratio is controlled. Judgment to judge A delay means for instructing the start of control for making the air-fuel ratio of the internal combustion engine the stoichiometric air-fuel ratio after a lapse of a predetermined delay time from the time when the judging means judges that it is the switching timing, and the delay means. According to the detection result of the downstream air-fuel ratio detection means, a control constant calculation means for calculating an air-fuel ratio feedback control constant, an air-fuel ratio feedback control constant calculated by the control constant calculation means, and the upstream air-fuel ratio. An air-fuel ratio feedback control means for determining a control amount for making the air-fuel ratio of the internal combustion engine the stoichiometric air-fuel ratio according to the detection result of the fuel ratio detection means, and for instructing the air-fuel ratio adjusting means, A fuel ratio control device, further comprising a catalyst deterioration degree calculation means for calculating the catalyst deterioration degree of the three-way catalyst, and an increase in the catalyst deterioration degree calculated by the catalyst deterioration degree calculation means. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a changing unit that shortens the predetermined delay time of the delay unit.