JP2600771B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: Object of the Invention [Industrial application field] The present invention relates to an oxygen concentration disposed upstream and downstream of a three-way catalyst interposed in an exhaust system of an internal combustion engine. The present invention relates to an air-fuel ratio control device for an internal combustion engine that executes air-fuel ratio feedback control based on a detection result of an air-fuel ratio sensor such as a 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 disposed near a combustion chamber, so that the upstream side of a catalytic converter is disposed. 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 a decrease in control accuracy due to aging or the like, a downstream oxygen concentration sensor is provided downstream of the catalytic converter, based on a detection signal of an upstream oxygen concentration sensor provided upstream of the catalytic converter. A so-called double oxygen concentration sensor system that executes air-fuel ratio feedback control based on a detection signal of the downstream oxygen concentration sensor in addition to the air-fuel ratio 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 detection signals of the two oxygen concentration sensors (so-called double oxygen concentration sensor system) corrects the deterioration of the output characteristics of the upstream oxygen concentration sensor by the detection signal of the downstream oxygen concentration sensor. it can. That is, as shown in black in FIG. 9, in the double oxygen concentration sensor system, even if the output characteristics of the upstream oxygen concentration sensor deteriorate, the emission amount of harmful components (HC, CO, NOx) in the exhaust gas is reduced. There is almost no increase, and no deterioration in exhaust characteristics is observed. 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 characteristics of the downstream oxygen concentration sensor are 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,
There is known a technique for increasing / decreasing a rich skip amount, a lean skip amount, and the like in accordance with a detection signal of a downstream oxygen concentration sensor by a predetermined correction amount. As such, for example, an “air-fuel ratio control device for an internal combustion engine”
(JP-A-61-234241) and the like have been proposed. That is, the skip amount, which is the air-fuel ratio feedback control constant, is increased or decreased by a predetermined constant correction amount in accordance with the output of the downstream air-fuel ratio sensor, and the upstream air-fuel ratio sensor is corrected using the corrected skip amount. This is a technique for calculating an air-fuel ratio correction amount according to the output to adjust the air-fuel ratio of the engine, thereby preventing a reduction in response speed due to deterioration of the upstream air-fuel ratio sensor.

[Problems to be Solved by the Invention] By the way, when the air-fuel ratio of the internal combustion engine is on the lean side (Lean) and the air-fuel ratio on the upstream side of the three-way catalyst is also on the lean side (Lean), the downstream oxygen concentration By correcting the skip amount based on the sensor detection signal, the rich skip amount is corrected to a value larger than the lean skip amount, and the asymmetry between the rich skip amount and the lean skip amount may become remarkable.
In such a case, if the oxygen concentration in the exhaust gas becomes uneven due to insufficient mixing of the exhaust gas on the upstream side of the catalytic converter, depending on the contact state between the upstream oxygen concentration sensor and the exhaust gas, In some cases, the detection signal outputs a lean signal (Lean) such as a so-called lean spike in a short cycle. As described above, when the detection signal of the upstream oxygen concentration sensor is inverted in a short cycle between the lean side (Lean) and the rich side (Rich), the lean skip amount and the rich skip amount with high asymmetry are reduced. Since the air-fuel ratio feedback control amount is overcorrected to either one by the skip correction used, there is a problem that the exhaust gas purification performance is deteriorated due to a decrease in control accuracy, and an increase in the amount of harmful components discharged in the exhaust gas is caused. Was.

In addition, in order to remove a noise-like signal such as a so-called lean spike as described above, a delay time process for stabilizing the upstream oxygen concentration sensor detection signal by providing a delay time when determining the detection signal is also known. Have been. However, in the delay time processing or the like, it is not possible to remove a noise-like signal having an inversion cycle longer than the delay time. On the other hand, if the above delay time is extended to remove noise having a wide range of cycles, the frequency of the air-fuel ratio feedback control is reduced, thereby causing a problem that control responsiveness and followability are deteriorated. Therefore, it is impossible to remove all noise-like signals by delay time processing or the like, and the delay time processing has not been sufficient yet.

The present invention does not impair the responsiveness of the air-fuel ratio feedback control based on the detected air-fuel ratio of an internal combustion engine, even when the detected air-fuel ratio is reversed between a lean side and a rich side in a short cycle. It is another object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can appropriately suppress overcorrection of the air-fuel ratio.

Configuration of the Invention [Means for Solving the Problems] The present invention made to achieve the above object is provided in an exhaust passage of an internal combustion engine M1 to purify exhaust gas, as shown in FIG. A three-way catalyst M2; an upstream air-fuel ratio detecting means M3 for detecting a characteristic component concentration in exhaust gas on the upstream side of the three-way catalyst M2; and detecting a characteristic component concentration in exhaust gas on the downstream side of the three-way catalyst M2. According to the downstream air-fuel ratio detecting means M4 and the control amount externally commanded, the internal combustion engine M1
Air-fuel ratio adjusting means M5 for adjusting the air-fuel ratio of the air-fuel ratio, based on the detection result of the upstream air-fuel ratio detecting means M3,
When the air-fuel ratio of the internal combustion engine M2 is inverted from a lean side to a rich side, the lean skip amount is corrected based on the detection result of the downstream air-fuel ratio detection means M4 so that the air-fuel ratio can be quickly shifted to the lean side. On the other hand, when the air-fuel ratio of the internal combustion engine M1 is inverted from the rich side to the lean side, the air-fuel ratio can be quickly shifted to the rich side when the air-fuel ratio of the internal combustion engine M1 is reversed. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio feedback control unit M6 that instructs the air-fuel ratio adjustment unit M5 with a control amount that is increased and corrected by a rich skip amount that is corrected based on a detection result. Further, based on the detection result of the upstream air-fuel ratio detection means M3, a short cycle in which the lean-side reversal cycle from the previous lean-side reversal to the present lean-side reversal of the air-fuel ratio is less than a predetermined reversal cycle. Determines if it is in the inverted state Judgment means
M7, when the determination means M7 determines that the vehicle is in the short-cycle inversion state, the rich skip amount is slightly changed regardless of the correction based on the detection result of the downstream air-fuel ratio detection means M4. Change means M8 for changing to a possible rich skip amount and performing the increase correction of the control amount, or canceling the increase correction of the control amount due to the rich skip amount.
And an air-fuel ratio control device for an internal combustion engine, characterized by comprising:

Further, in the invention according to claim 2, in addition to the above configuration, the air-fuel ratio feedback control means M6 is configured such that the air-fuel ratio downstream of the three-way catalyst is lean, and the control amount is a predetermined value. If it exceeds, the downstream air-fuel ratio detecting means M4
The correction of the lean skip amount and the rich skip amount based on the detection result is stopped.

The upstream air-fuel ratio detecting means M3 detects the concentration of a specific component in exhaust gas on the upstream side of the three-way catalyst M2. For example,
It can be realized by various gas sensors such as a known oxygen concentration sensor, a lean mixture sensor, and a carbon monoxide (CO) sensor.

The downstream air-fuel ratio detecting means M4 detects the concentration of a characteristic component in exhaust gas downstream of the three-way catalyst M2. For example,
It can be realized by various gas sensors such as a known oxygen concentration sensor, a lean mixture sensor, and a carbon monoxide (CO) sensor.

The air-fuel ratio adjusting means M5 adjusts the air-fuel ratio of the internal combustion engine M1 according to a control amount commanded from the outside. 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.

The air-fuel ratio feedback control means M6 enables the air-fuel ratio to be quickly shifted to the lean side when the air-fuel ratio of the internal combustion engine M1 is reversed from the lean side to the rich side based on the detection result of the upstream side air-fuel ratio detecting means M3. The control amount reduced and corrected by the lean skip amount that is corrected based on the detection result of the downstream air-fuel ratio detection unit M4, while the air-fuel ratio is changed when the air-fuel ratio of the internal combustion engine M1 is inverted from the rich side to the lean side. The control amount increased and corrected by the rich skip amount corrected based on the detection result of the downstream air-fuel ratio detection unit M4 so that the air-fuel ratio can be quickly shifted to the rich side
It instructs M5. For example, in the configuration in which the oxygen concentration sensors are provided on the upstream side and the downstream side of the three-way catalyst, respectively, the lean skip amount, the rich skip amount, and the upstream oxygen concentration are changed and corrected based on the downstream oxygen concentration. The fuel injection amount may be determined based on the obtained air-fuel ratio correction coefficient and commanded.

The determination unit M7 is configured such that, based on the detection result of the upstream air-fuel ratio detection unit M3, the lean-side inversion cycle from the previous lean-side inversion of the air-fuel ratio to the current lean-side inversion is less than the predetermined inversion cycle. This is to determine whether or not a short-cycle inversion state exists. For example, the counter can measure the time from the previous lean-side inversion to the present lean-side inversion.

The changing means M8 can slightly change the air-fuel ratio regardless of the correction based on the detection result of the downstream air-fuel ratio detecting means M4 when the determining means M7 determines that the short cycle inversion state is established. In this case, the correction amount is changed to the rich skip amount and the control amount is increased, or the increase in the control amount due to the rich skip amount is stopped. For example, instead of the rich skip amount, the control amount can be increased and corrected by an integral term smaller than the rich skip amount value.
Alternatively, the rich skip amount may be set to the value 0, and the increase correction of the control amount due to the rich skip amount may be stopped.

The air-fuel ratio feedback control means M6, the determination means M7, and the change means M8 can be realized by, for example, independent and independent 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 device for an internal combustion engine of the present invention detects the air-fuel ratio detection means M3 upstream of the three-way catalyst M2 provided in the exhaust passage of the internal combustion engine M1. Based on the result, the air-fuel ratio of the internal combustion engine M1 is corrected based on the detection result of the downstream air-fuel ratio detection means M4 so that the air-fuel ratio can be quickly shifted to the lean side when the air-fuel ratio is reversed from the lean side to the rich side. On the other hand, when the air-fuel ratio of the internal combustion engine M1 is reversed from the rich side to the lean side, the air-fuel ratio can be quickly shifted to the rich side when the air-fuel ratio of the internal combustion engine M1 is reversed. When the air-fuel ratio feedback control unit M6 instructs the air-fuel ratio adjustment unit M5 to increase the control amount increased by the rich skip amount corrected based on the detection result of the detection unit M4, the detection of the upstream air-fuel ratio detection unit M3 is performed. Based on the result, the previous lean-side inversion of the air-fuel ratio From a dilute side reversal period to the current lean side when reversing it is, when it is determined by the determining means M7 in the short-period inversion state is less than a predetermined inversion period, changing means
M8 changes the rich skip amount to a rich skip amount capable of minutely changing the air-fuel ratio regardless of the correction based on the detection result of the downstream air-fuel ratio detection unit M4, and performs the increase correction of the control amount. Alternatively, it works to stop the increase correction of the control amount due to the rich skip amount.

That is, during the reversal of the air-fuel ratio from the rich side to the lean side, when correcting the control amount for adjusting the air-fuel ratio, if the lean-side reversal cycle is equal to or longer than the predetermined reversal cycle, the air-fuel ratio is quickly increased by the rich skip amount. When the lean side reversal cycle is shorter than the predetermined reversal cycle, the rich skip amount is changed to a rich skip amount capable of minutely changing the air-fuel ratio, and the control amount is increased and corrected. Alternatively, the increase correction of the control amount based on the rich skip amount is stopped, and the air-fuel ratio is gradually shifted to the target side.

Therefore, the air-fuel ratio control device for an internal combustion engine of the present invention functions to control over-correction of the air-fuel ratio even when the air-fuel ratio detection result reverses the lean side and the rich side in a short cycle.

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. 2 shows a system configuration of an air-fuel ratio control device for an engine according to an 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, catalytic converter 19 filled with three-way catalyst 19 and exhaust pipe
Consists of 20.

The ignition system of the engine 2 includes an igniter 21 having an ignition coil for outputting a high voltage required for ignition, and a distributor 22 for distributing and supplying a 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 combustion 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 also serving as a rotation speed sensor that outputs a rotation angle signal every 1/24 rotation of the camshaft of the distributor 22, that is, every integer multiple of the crank angle from 0 ° to 30 °. .

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 signal of the rotation angle sensor 39 is input to the A / D converter 3j and input to the detection signal 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. Input each through 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 is an input / output unit 3
g, the drive control of the fuel injection valve 25 via the down counter 3n, the flip-flop circuit 3p and the drive circuit 3r. 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 driving 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,
An amount of fuel corresponding to the fuel injection amount TAU is supplied to the engine 2. Note that the ECU 3 operates by receiving power supply from the vehicle-mounted battery 41 via the ignition switch 40. The backup RAM 3d is configured such that power is supplied from a path (not shown) without passing through the ignition switch 40, and the stored contents are retained regardless of the state of the ignition switch 40.

Next, the first air-fuel ratio feedback control process executed by the ECU 3 is shown in FIGS. 3 (1) and (2), and the second air-fuel ratio feedback control process is shown in FIGS. 4 (1) and (2). The fuel injection control process will be described with reference to each flowchart in FIG.

First, the first air-fuel ratio feedback control process will be described with reference to the flowcharts shown in FIGS. 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 102, a process of reading each data based on the detection signal of each sensor described above is performed. In the following step 104, it is determined whether or not the first air-fuel ratio feedback control execution condition is satisfied. If the determination is affirmative, the process proceeds to step 106. If the determination is negative, the value of the air-fuel ratio correction coefficient FAF is changed. The first air-fuel ratio feedback control process is temporarily terminated by setting the value at the end of the previous control. 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, 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 output signal V1 of the side oxygen concentration sensor 36 has never crossed the first comparison voltage VR1, the conditions for executing the first air-fuel ratio feedback control are not satisfied. In step 106, which is executed when the first air-fuel ratio feedback control execution condition that does not correspond to the above conditions is satisfied, the detection signal V1 of the upstream oxygen concentration sensor 36
Is A / D converted and read. Next step 1
At 08, a process of adding the value 1 to the count value of the lean inversion cycle counter CRSL is performed. Next, the routine proceeds to step 110, where the detection signal V1 of the upstream oxygen concentration sensor 36 is set to the first comparison voltage VR.
1 (for example, 0.45 [V]) is determined. If the determination is affirmative, the air-fuel ratio is determined to be on the rich side (Rich), and the routine proceeds to step 130. If the determination is negative, the air-fuel ratio is lean. It proceeds to step 112 as it is the side (Lean). Step 112 executed when the air-fuel ratio is on the lean side (Lean)
Then, a process of resetting the air-fuel ratio flag F1 to a value of 0 is performed. In the following step 114, 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 116. In step 116 executed when the value of the air-fuel ratio flag F1 is not inverted, a rich integration constant is added to the air-fuel ratio correction coefficient FAF.
After performing the process of adding and increasing the KIR gradually, the process proceeds to step 140. On the other hand, in step 118 executed when the value of the air-fuel ratio flag F1 is inverted, it is determined whether or not the count value of the lean inversion cycle counter CRSL is less than a determination value a (corresponding to α [msec]). If affirmative, step 12
On the other hand, if a negative determination is made, the process proceeds to step 126. Since the air-fuel ratio was inverted to the lean side (Lean) last time, the lean side (Le
In step 120, which is executed when a sufficient time has not yet passed until inversion to an), a process of clearing the lean inversion cycle counter CRSL to a value of 0 is performed. In the subsequent step 122, assuming that the current reversal is due to a lean spike, a process of gradually increasing the value by adding the rich integration constant KIR to the air-fuel ratio correction coefficient FAF is performed, and then proceeds to step 124. In step 124, after performing a process of setting the skip correction suspension control execution flag FRSL to a value of 1, step 14
Go to 0. On the other hand, in step 126, which is executed when it is determined in step 118 that sufficient time has already passed from when the air-fuel ratio was inverted to the lean side (Lean) last time to when it was now inverted to the lean side (Lean), A process is performed in which the rich skip amount RSR is added to the air-fuel ratio correction coefficient FAF to increase in a skip manner. In the following step 127, a process of clearing the lean inversion cycle counter CRSL to a value of 0 is performed.
Go to 140.

On the other hand, in step 110, the air-fuel ratio is shifted to the rich side (Rich).
In step 130, which is executed when it is determined that the air-fuel ratio has been set, the process of setting the air-fuel ratio flag F1 to the value 1 is performed. In the following step 132, 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 134. In step 134, which is executed when the value of the air-fuel ratio flag F1 is not inverted, a process is performed in which the lean integration constant KIL is subtracted from the air-fuel ratio correction coefficient FAF to gradually decrease the value, and then the process proceeds to step 140. On the other hand, in step 136 executed when the value of the air-fuel ratio flag F1 is inverted, the air-fuel ratio correction coefficient F
After the lean skip amount RSL is subtracted from the AF to decrease in a skip manner, the process proceeds to step 140. Where both integral constants K
IR and KIL are set sufficiently smaller than the two skip amounts RSR and RSL. Accordingly, in steps 126 and 136, the fuel injection amount is rapidly increased or decreased, while
In 4, the fuel injection amount is gradually increased or decreased. In the following steps 140 and 142, the value of the air-fuel ratio correction coefficient FAF is limited to, for example, a maximum value of 1.2 or less.
In 4,146, the minimum value is restricted to 0.8 or more, and even if the value FAF of the air-fuel ratio correction coefficient is excessively large or small for some reason, the air-fuel ratio is over-rich, or
Prevent transition to Ovaline state. Then step 14
8 and calculate the air-fuel ratio correction coefficient FAF calculated as described above.
After the data is stored in the RAM 3c and the backup RAM 3d, the first air-fuel ratio feedback control process is temporarily ended. Thereafter, the first air-fuel ratio feedback control process repeats the above steps 102 to 148 at predetermined time intervals.

Next, the second air-fuel ratio feedback control process will be described. The second air-fuel ratio feedback control process performs control for changing skip amounts RSR and RSL, which are control constants of the first air-fuel ratio feedback control process.

The second air-fuel ratio feedback control process executed in this embodiment will be described with reference to the flowcharts shown in FIGS. 4 (1) and 4 (2). The second air-fuel ratio feedback control process is performed for a predetermined time (for example, 512 [mse
c]), and the skip amounts RSR and RSL are corrected and calculated. First, in step 202, a process of reading each data based on the detection signal of each sensor described above is performed. In the following step 204, it is determined whether or not the air-fuel ratio feedback control process execution condition is satisfied. If the determination is affirmative, the process proceeds to step 206. If the determination is negative, the skip amounts RSR, RSL calculated in the previous process are determined. Is stored in the RAM 3c and the backup RAM 3d, and then the second air-fuel ratio feedback control process is temporarily terminated.

In the above step 204, 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 post-start increasing, during the warm-up increasing, during the acceleration increasing (asynchronous injection), during the power increasing. When the detection signal V1 of the upstream oxygen concentration sensor 36 has never crossed the first comparison voltage VR1, the conditions for executing the air-fuel ratio feedback control process are not satisfied. When the air-fuel ratio feedback control processing execution condition that does not correspond to the above conditions is satisfied, the process proceeds to step 206. In step 206, the cooling water temperature THW is set to a predetermined temperature (for example, 70
[° C.]) or more, at step 208, whether or not the throttle valve 14 is not fully closed, at step 210, whether or not the downstream oxygen concentration sensor 37 is in an active state, and at step 212, whether or not the downstream oxygen concentration sensor 37 is active. In step 214, it is determined whether the side oxygen concentration sensor 37 is normal or not.
It is determined whether or not there is more than one, and if affirmative determination is made in all the steps, it is determined that the second air-fuel ratio feedback control processing execution condition is satisfied, and the process proceeds to step 220 and subsequent steps. When it is determined that the second air-fuel ratio feedback control process execution condition is not satisfied, the values of the ship amounts RSR and RSL calculated in the previous process are stored in the RAM 3c and the backup RAM 3d, and then temporarily
The second air-fuel ratio feedback control process ends.

In step 220 executed when the second air-fuel ratio feedback control processing execution condition is satisfied, the downstream oxygen concentration sensor 3
The process of A / D converting and reading the detection signal V2 of 7 is performed.
In the following step 221, a process of reading the values of the air-fuel ratio correction coefficient FAF and the skip amounts RSR and RSL calculated in the previous process is performed. Next, the routine proceeds to step 222, where the detection signal V2 of the downstream oxygen concentration sensor 37 is changed to the second comparison voltage VR2 (for example, 0.55
[V]), and if affirmatively determined, the air-fuel ratio is determined to be on the rich side (Rich), and the process proceeds to step 244. If negatively determined, the air-fuel ratio is determined on the lean side (Lean). If so, the process proceeds to step 223. Air-fuel ratio is lean side (Lean)
In step 223 executed when is, it is determined whether or not the value of the air-fuel ratio correction coefficient FAF exceeds 1.0, and if a positive determination is made, the values of the skip amounts RSR and RSL calculated in the previous process are stored in the RAM 3c. And after storing it in the backup RAM 3d,
The second air-fuel ratio feedback control process ends, while if a negative determination is made, the process proceeds to step 224 and subsequent steps.

In step 224 executed when the value of the air-fuel ratio correction coefficient FAF is equal to or less than 1.0 and the air-fuel ratio is on the lean side (Lean), the skip correction amount ΔRS is added to the value of the rich skip amount RSR, and the following steps 226 and 228 And the rich skip amount RSR
Is limited to an amount equal to or less than the maximum value RMAX.
In 230, the skip correction amount ΔRS is subtracted from the value of the lean skip amount RSL, and in subsequent steps 232 and 234, 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 way, the rich skip amount RSR is increased and corrected, and the lean skip amount RSL is corrected.
Is reduced and the air-fuel ratio is easily shifted to the rich side (Lich). In the following step 236, a process of storing the rich skip amount RSR, the lean skip amount RSL, and the air-fuel ratio correction coefficient FAF corrected as described above in the RAM 3c and the backup RAM 3d is performed. Next, the routine proceeds to step 260, where the processing for resetting the skip correction suspension control execution flag FRSL to 0 is performed, and then the second air-fuel ratio feedback control processing is temporarily ended.

On the other hand, in step 222, the air-fuel ratio is
In step 244 executed when it is determined that the skip correction amount ΔRS
Is subtracted, and in subsequent steps 246 and 248, the rich skip amount R
Limit the value of SR to an amount equal to or greater than the minimum value RMIN, then step 25
Proceeds to 0, and the skip correction amount Δ
RS is added, and in steps 252 and 254, the value of the lean skip amount RSL is limited to an amount equal to or less than the maximum value LMAX. As described above, while the rich skip amount RSR is corrected to decrease, the lean skip amount RSL is increased and corrected to increase the air-fuel ratio on the lean side (Lea side).
Make it easier to move to n). Thereafter, steps 236 and 2 described above are performed.
After 60, the second air-fuel ratio feedback control process is temporarily ended. Thereafter, the second air-fuel ratio feedback control process repeats the above steps 202 to 260 at predetermined time intervals.

Next, the fuel injection control process will be described with reference to the flowchart shown in FIG. This fuel injection control process is performed at every predetermined crank angle after the ECU 3 is started (for example, 360 [° C. A]).
Is executed. First, in step 300, a process of reading each data described above is performed. In the following step 320, 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 330, the warm-up increase coefficient FWL is stored in the ROM 3b in advance according to the cooling water temperature THW. Processing for calculation by interpolation calculation according to the map shown in FIG. 6 is performed. Next, the routine proceeds to step 340, where 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 + β + 1) + γ (2) In the following step 350, a control signal for setting the actual fuel injection amount TAU calculated in step 340 to the down counter 3n and setting the flip-flop circuit 3p. Is output to start the fuel injection, and then the fuel injection control process is temporarily 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. Thereafter, the fuel injection control process is repeatedly executed at every predetermined crank angle by repeating steps 300 to 350 described above.

In this embodiment, the engine 2 is replaced by the internal combustion engine M1,
Catalytic converter 19 is three-way catalyst M2, upstream oxygen concentration sensor
36 is an upstream air-fuel ratio detecting means M3, and a downstream oxygen concentration sensor
37 corresponds to the downstream air-fuel ratio detecting means M4, and the fuel injection valve 25 corresponds to the air-fuel ratio adjusting means M5. ECU3 and ECU3
Steps (102 to 106, 110 to 116, 12
4,126,130 to 148,202 to 260,300 to 350) serve as the air-fuel ratio feedback control means M6 in steps (108,118,120,12).
7) is the determining means M7, and step (122) is the changing means M8.
Function as each.

As described above, according to the present embodiment, when a lean spike occurs, the air-fuel ratio correction coefficient FAF is integrated by the rich integration constant KIR instead of the skip correction by the rich skip amount RSR. The correction amount is appropriate and gradually reduced, and the air-fuel ratio correction coefficient FSF
Does not greatly deviate from the median value to the rich side (Rich), so hydrocarbons (HC) and carbon monoxide (C)
O) emission amount can be reduced, and an optimal air-fuel ratio feedback control that is not easily affected by a noise-like lean signal (Lean) such as a lean spike can be realized.

That is, as shown in the timing chart of FIG. 7, at time T1, the air-fuel ratio correction coefficient FAF is skip-corrected by the rich skip amount RSR with the shift of the upstream oxygen concentration sensor detection signal V1 to the lean side (Lean). You. At the same time T
From 1, the air-fuel ratio correction coefficient FAF is added and corrected by the rich integration constant KIR, and the lean inversion cycle counter CRSL starts counting after being reset. Eventually, at time T2, the air-fuel ratio correction coefficient FAF is skip-corrected by the lean skip amount RSL with the shift of the upstream oxygen concentration sensor detection signal V1 to the rich side (Rich), and lean integration is performed from the same time. Subtraction is corrected by the constant KIL. Similarly, also at time T3 and time T4, the lean side (Lean) of the upstream oxygen concentration sensor detection signal V1
With the shift to, the air-fuel ratio correction coefficient FAF is skip-corrected by the rich skip amount RSR, and from the times T3 and T4, the air-fuel ratio correction coefficient FAF is added and corrected by the rich integration constant KIR, and the lean inversion cycle counter CRSL is After resetting, counting starts. Eventually, at time T6, the upstream oxygen concentration sensor detection signal V1 shifts to the lean side (Lean) again.
However, the count value of the lean inversion cycle counter CRSL reset at the time of the previous lean (Lean) inversion (time T4) is still less than the determination value a. Therefore, at the same time T6, the lean inversion cycle counter CRSL is reset, and from time T6 to time T7, the air-fuel ratio correction coefficient FAF is integrated and corrected by the rich integration constant KIR. Eventually, at time T9, the count value of the lean reversal cycle counter CRSL has already exceeded the determination value a at time T8, so the upstream oxygen concentration sensor detection signal V1 shifts to the lean side (Lean). Accordingly, the air-fuel ratio correction coefficient FAF is skip-corrected by the rich skip amount RSR, and from the same time T9, the air-fuel ratio correction coefficient FAF is added and corrected by the rich integration constant KIR, and the lean inversion cycle counter CRSL is reset.
Start counting. Thereafter, the same increase / decrease correction of the air-fuel ratio correction coefficient FAF is executed. As a result, as shown by the solid line in the figure, even if the upstream oxygen concentration sensor detection signal V1 fluctuates with a lean spike (time T4 to time T7), the air-fuel ratio correction coefficient FAF does not influence the lean spike. Since it is corrected without receiving it, it does not greatly deviate from the center value to the rich side (Rich) {increase}. However, as shown by the broken line in the figure, in the prior art, the air-fuel ratio correction coefficient FAF is skip-corrected by the rich skip amount RSR at time T6 due to the influence of the lean spike. The oxygen concentration was far away from the increasing side, and from the same time T6 to the time T12, the upstream oxygen concentration was on the rich side (Rich). For this reason, in particular, between time T6 and time T10, the harmful component emission amount in the exhaust gas increased due to overcorrection toward the rich side (Rich).

Also, when the upstream oxygen concentration sensor detection signal V1 is determined, a delay process for setting the lean delay time TDL and the rich delay time TDR is not performed for the purpose of stabilizing the air-fuel ratio signal. Since this is not required, the control accuracy can be improved while maintaining the responsiveness and followability of the air-fuel ratio feedback control at a high level.

Further, when the downstream oxygen concentration sensor detection signal V2 is on the lean side (Lean) and the air-fuel ratio correction coefficient FAF exceeds 1.0, the second air-fuel ratio feedback control process is not executed, so the rich skip amount Since the asymmetry correction of the RSR and the lean skip amount RSL is not continued, it is possible to minimize the asymmetry between the rich skip amount RSR and the lean skip amount RSL.

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.

Further, in the above-described embodiment, the fuel injection amount TAU is determined based on the intake air amount Q detected by the air flow meter 31 and the rotation speed Ne detected by the rotation angle sensor 39. The intake air amount Q may be measured by a hot wire sensor or the like, or the intake pipe pressure PM and the rotation speed Ne, or the throttle valve opening degree
The fuel injection amount TAU may be calculated based on the TA and the rotation speed Ne.

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

Further, in the above-described embodiment, 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. As described above, in the engine having the carburetor, the basic fuel injection amount is determined from the characteristics of the carburetor, and the air-fuel ratio control is performed by calculating the supply air amount that achieves the desired air-fuel ratio by calculation.

Further, in place of the first air-fuel ratio feedback control process of the above-described embodiment, for example, a first air-fuel ratio feedback control process as shown in the flowcharts of FIGS. 8 (1) and (2) is executed. Even in this case, an effect similar to that of the above-described embodiment can be obtained.

That is, the first air-fuel ratio feedback control process shown in FIGS. 8A and 8B is executed every predetermined time (for example, 4 [msec]) after the ECU 3 is started. 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, a process of adding the value 1 to the count value of the lean inversion cycle counter CRSL is performed. Next, proceeding to step 405, it is determined whether or not the value of the rich skip amount RSR exceeds the sum of the lean skip amount RSL and the constant A. If the determination is affirmative, skip correction restriction processing with skip correction stop control is performed. The process proceeds to step 110a on the assumption that the process is to be performed. On the other hand, if a negative determination is made, the process proceeds to step 406 to execute the normal air-fuel ratio feedback control process. Here, the processing executed in step 110a is the same as that of the embodiment described above with reference to FIGS.
Of the first air-fuel ratio feedback control process shown in FIG.
This is the same processing as 104 to 148.

In step 406, it is determined whether or not the first air-fuel ratio feedback control execution condition is satisfied. If the determination is affirmative, the process proceeds to step 408. If the determination is negative, the value of the air-fuel ratio correction coefficient FAF is set to the previous value. At the end of the control of
The first air-fuel ratio feedback control process ends. 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, 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 output signal V1 of the side oxygen concentration sensor 36 has never crossed the first comparison voltage VR1, the conditions for executing the first air-fuel ratio feedback control are not satisfied. In step 408, which is executed when the first air-fuel ratio feedback control execution condition that does not correspond to the above conditions is satisfied, the detection signal V1 of the upstream oxygen concentration sensor 36 is set.
Is A / D converted and read. Next step 4
At 10, it is determined whether or not the detection signal V1 of the upstream oxygen concentration sensor 36 is equal to or lower than the first comparison voltage VR1 (for example, 0.45 [V]), and if the determination is affirmative, the air-fuel ratio becomes lean (Lean). ), The process proceeds to step 412. On the other hand, if a negative determination is made, the process proceeds to step 414 assuming that the air-fuel ratio is on the rich side (Rich). In step 412 executed when the air-fuel ratio is on the lean side (Lean), the process proceeds to step 420 after performing a process of resetting the air-fuel ratio flag F1 to a value of 0. On the other hand, in step 414 executed when it is determined in step 410 that the air-fuel ratio is on the rich side (Rich), the air-fuel ratio flag F
After the process of setting 1 to the value 1 is performed, the process proceeds to step 420.

In step 420, it is determined whether or not the value of the air-fuel ratio flag F1 has been inverted. When the determination is affirmative, the process proceeds to step 422, and when the determination is negative, the process proceeds to step 428. Step 42 executed when the value of the air-fuel ratio flag F1 is inverted
In 2, a process is performed to determine whether the reversal 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 424 executed at the time of inversion to (an), the rich skip amount RSR is added to the air-fuel ratio correction coefficient FAF to increase in a skipping manner, while the lean side (Lean) to the rich side (Ric
In step 426 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 skip manner, and the process proceeds to step 440. Also, in step 428, which is executed when the value of the air-fuel ratio flag F1 is not inverted in step 420, whether or not the value is on the lean side (Lean)
A process for determining whether the image is on the rich side (Rich) is performed. In step 430 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 432, 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 440.

In steps 440 and 442, the value of the air-fuel ratio correction coefficient FAF is limited to, for example, a maximum value of 1.2 or less, and in subsequent steps 444 and 446, the value is limited to a minimum value of 0.8 or more and the value of the air-fuel ratio correction coefficient Excessive depending on the cause, or
Even when the air-fuel ratio becomes too small, the air-fuel ratio is prevented from shifting to an over-rich state or an over-lean state. Next, the routine proceeds to step 448, where the air-fuel ratio correction coefficient FAF calculated as described above is stored in the RAM 3c and the backup RAM 3d, and then the first air-fuel ratio feedback control process is temporarily ended. Thereafter, the first air-fuel ratio feedback control process is repeatedly executed at predetermined time intervals by repeating steps 402 to 448 described above.

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

Effect of the Invention As described in detail above, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention corrects the control amount for adjusting the air-fuel ratio when the air-fuel ratio of the air-fuel ratio detection result is inverted from the rich side to the lean side. When the lean-side reversal cycle is equal to or longer than the predetermined reversal cycle, the air-fuel ratio is quickly shifted to the target side by the rich skip amount,
On the other hand, when the lean-side reversal cycle is less than the predetermined reversal cycle, the rich skip amount is changed to a rich skip amount capable of minutely changing the air-fuel ratio, and the control amount is increased or corrected. Is stopped, and the air-fuel ratio is gradually shifted to the target side. For this reason, even when the air-fuel ratio detection result is reversed in a short period between the lean side and the rich side, overcorrection of the air-fuel ratio feedback control amount can be reliably prevented, and the air-fuel ratio feedback control amount can always be corrected to the optimal control amount. In addition, there is an excellent effect that the exhaust purification performance is enhanced by improving the control accuracy.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram conceptually illustrating the contents of the present invention, FIG. 2 is a system configuration diagram of a first embodiment of the present invention, and FIG.
FIGS. (1) and (2), FIGS. 4 (1) and (2), and FIG. 5 are flowcharts showing the control, FIG. 6 is a graph showing the map, and FIG. FIGS. 8 (1) and 8 (2) are flow charts showing the control of another embodiment, and FIG. 9 is a graph showing the exhaust characteristics of the prior art. M1: internal combustion engine M2: three-way catalyst M3: upstream air-fuel ratio detecting means M4: downstream air-fuel ratio detecting means M5: air-fuel ratio adjusting means M6: air-fuel ratio feedback control means M7: determining means M8: changing means 1. engine Air-fuel ratio control device 2 ... Engine 3 ... Electronic control device (ECU) 3a ... CPU 19 ... Catalyst converter 25 ... Fuel injection valve 36 ... Upstream oxygen concentration sensor 37 ... Downstream oxygen concentration sensor

Claims (2)

(57) [Claims] A three-way catalyst disposed in an exhaust passage of an internal combustion engine for purifying exhaust gas; an upstream air-fuel ratio detecting means for detecting a concentration of a specific component in exhaust gas upstream of the three-way catalyst; Downstream air-fuel ratio detection means for detecting a specific component concentration in exhaust gas downstream of the three-way catalyst; air-fuel ratio adjustment means for adjusting the air-fuel ratio of the internal combustion engine in accordance with a control amount externally commanded; Based on the detection result of the side air-fuel ratio detecting means, when the air-fuel ratio of the internal combustion engine is reversed from a lean side to a rich side, the air-fuel ratio can be quickly shifted to the lean side so that the air-fuel ratio can be quickly shifted to the lean side. On the other hand, when the air-fuel ratio of the internal combustion engine is reversed from the rich side to the lean side, the air-fuel ratio can be quickly shifted to the rich side when the control amount reduced and corrected by the lean skip amount corrected based on the result, Compensation is performed based on the detection result of the downstream air-fuel ratio detection means. An air-fuel ratio feedback control means for instructing the air-fuel ratio adjustment means with a control amount increased by the corrected rich skip amount, the air-fuel ratio control device for an internal combustion engine comprising: Based on the detection result of the detecting means, it is determined whether or not the lean-side reversal cycle from the previous lean-side reversal of the air-fuel ratio to the present lean-side reversal is in a short cycle reversal state that is shorter than a predetermined reversal cycle. Determining means for determining, when the determining means determines that the vehicle is in the short-cycle inversion state, the air-fuel ratio is reduced by a small amount regardless of the correction based on the detection result of the downstream air-fuel ratio detecting means. Changing means for changing to a changeable rich skip amount and performing the increase correction of the control amount, or changing means for canceling the increase correction of the control amount due to the rich skip amount. An air-fuel ratio control device for an internal combustion engine. 2. The air-fuel ratio feedback control means of the downstream air-fuel ratio detection means when the air-fuel ratio downstream of the three-way catalyst is lean and the control amount exceeds a predetermined value. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the correction of the lean skip amount and the rich skip amount based on the detection result is stopped.