JPH03290039A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve controllability by determining the learning value of a feedback control value based on a value in the case when a feedback control value is switched from an increase side to a decrease side and a value in the case when it is reversibly switched. CONSTITUTION:A main O2 sensor 6 is arranged upstream from a Maniverter 14 which is a catalyst converter and on the other hand sub O2 sensor is arranged downstream from the Maniverter 14, and the output signals thereof are inputted to an electronic controller 9. A basic injection quantity TP is corrected by an air-fuel ratio feedback compensation Factor FAF and the like determined by a feedback signal (f) of the main O2 sensor 6 so as to determine a final electrification time T. At the time of an initial air-fuel ratio feedback control, the leaning of the feedback control value is carried out in the vicinity of the required value during a period until the control center of an air fuel ratio is adjusted from the starting of the control to the vicinity of the required time. At the time of next feedback control, the air-fuel feedback control is started immediately with the learning value considered as a starting point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control method for an internal combustion engine that is applied to automobiles and the like that are equipped with 02 sensors on the upstream and downstream sides of a catalytic converter.

[Prior art] A three-way catalyst, which is widely used as a means of purifying exhaust gas, maintains the air-fuel ratio of the air-fuel mixture within a narrow range (the window of the three-way catalyst) centered on the stoichiometric air-fuel ratio. Otherwise, it will not be possible to efficiently purify all of the Co, HC, and No elements contained in the exhaust gas. Therefore, in engines equipped with injectors, an air-fuel ratio feedback correction coefficient is provided to finely adjust the fuel injection amount, and the output voltage of the 02 sensor located upstream of the catalytic converter indicates a rich air-fuel ratio state. In this case, the correction coefficient is decreased after a predetermined delay time to throttle the fuel supply amount and change the air-fuel ratio of the air-fuel mixture toward the stoichiometric air-fuel ratio. Furthermore, when the output voltage indicates a lean air-fuel ratio state, the correction coefficient is increased after a predetermined delay time to increase the fuel supply amount and change the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio side. I try to let them do it.

However, when performing feedback control of the air-fuel ratio using a single 02 sensor, the desired air-fuel ratio control may not be performed due to variations in the output characteristics of the 0□ sensor, changes over time, variations in the fuel injection amount of the injector, etc. , the control center of the air-fuel ratio may deviate from within the window of the three-way catalyst. In addition, if a catalytic converter is connected to an exhaust manifold where the catalyst activation temperature can be easily ensured, and an 02 sensor is placed at the collection point of the exhaust manifold upstream, the 02 The output voltage of the sensor may be affected, and deterioration may be accelerated due to high heat, etc.

In order to avoid such problems, as a prior art of the present invention, for example, as shown in Japanese Patent Laid-Open No. 62-29738, the output voltage of the first 02 sensor disposed upstream of the catalytic converter is The control center of the air-fuel ratio is corrected to be within the window of the three-way catalyst based on the output voltage of the second 02 sensor located downstream of the catalytic converter while performing feedback control of the air-fuel ratio based on the catalytic converter. be. The control center of the air-fuel ratio may be changed based on the output voltage of the second 02 sensor, such as when changing the skip amount, rich integral, or lean integral of the air-fuel ratio feedback correction coefficient, or when changing the air-fuel ratio rich, air-fuel ratio There are cases where the fuel ratio lean determination delay time is changed.

[Problems to be Solved by the Invention] However, on the downstream side of the catalytic converter, the exhaust gas discharged from each cylinder is in an agitated state, and the oxygen concentration in the exhaust gas is close to an equilibrium state. 02
The output voltage of the sensor exhibits a slower change than the output voltage of the first 02 sensor.

That is, if the air-fuel mixture adjusted based on the output voltage of the first 02 sensor tends to be rich as a whole, the second
If the output voltage of the 02 sensor remains rich for a long time and the air-fuel mixture as a whole tends to be lean, the second
The time period during which the output voltage of the 02 sensor is in the lean state becomes longer. Then, the feedback control value for finely adjusting the fuel supply amount is gradually increased or decreased by minute values based on the output voltage of the second 02 sensor, and by repeating this control, the control center of the air-fuel ratio is is adjusted to near the stoichiometric air-fuel ratio. Therefore, as schematically shown in FIG. 8, even if the air-fuel ratio is feedback-controlled around the stoichiometric air-fuel ratio based on the feedback control value FACF, when the engine switch is turned OFF (key-off), When starting feedback next time, feedback control is restarted from the initial value. As a result, when feedback control is performed, the control center of the air-fuel ratio deviates from around the stoichiometric air-fuel ratio each time the feedback control is started, and emissions deteriorate during that time.

The present invention aims to eliminate such problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention employs the following configuration.

That is, in the air-fuel ratio control method for an internal combustion engine according to the present invention, a first 02 sensor that detects the oxygen concentration in exhaust gas is arranged upstream of a catalytic converter that purifies exhaust gas,
Based on the output voltage, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is feedback-controlled to near the stoichiometric air-fuel ratio, and the feedback control value is based on the output voltage of the second 02 sensor located downstream of the catalytic converter. An air-fuel ratio control method for an internal combustion engine configured to determine the feedback control value and change the control center of the air-fuel ratio to near the stoichiometric air-fuel ratio based on the feedback control value, the feedback control value changing from an increasing side to a decreasing side. A learning value of the feedback control value is determined based on the value when the feedback control value changes from the decreasing side to the increasing side, and the learning value is used as feedback when starting the feedback control. The feature is that the control is started.

The control center of the air-fuel ratio may be changed based on the feedback control value by changing the skip amount, rich integral, lean integral, etc. of the air-fuel ratio feedback correction coefficient determined based on the output voltage of the first 02 sensor. In some cases, the air-fuel ratio rich determination delay time and lean determination delay time may be changed.

[Operation] According to such a configuration, during the first air-fuel ratio feedback control, emissions deteriorate slightly from the start of the control until the control center of the air-fuel ratio is adjusted to around the required value, but the feedback is maintained around the required value. Once the control value is learned, the next time feedback control is performed, feedback control of the air-fuel ratio is immediately started using the learned value as the starting point.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 7.

The internal combustion engine schematically shown in FIG. 1 is used in an automobile, and includes an injector 1, a crank angle sensor 2, a pressure sensor 3, an idle switch 4,
It includes a water temperature sensor 5, a main 02 sensor 6 as a first 02 sensor, and a sub 02 sensor 7 as a second 02 sensor.

The injector 1 is attached to an intake pipe 8 and has a built-in electromagnetic coil and the like. When a fuel injection signal a is applied to the electromagnetic coil from the electronic control device 9, an amount of fuel corresponding to the application time is injected into the vicinity of the intake port. The crank angle sensor 2 is built into the distributor 10 and is configured to generate an engine rotation signal corresponding to the engine rotation speed. The pressure sensor 3 is provided in the surge tank 11,
The intake pressure signal C is output in proportion to the intake pressure. The idle switch 4 is connected to the throttle shaft 12
The throttle signal d is output by an ON-OFF switch that is connected to the throttle valve 13 and turns on when the throttle valve 13 is closed and turns off when the throttle valve 13 is open. The water temperature sensor 5 is
For example, it has a built-in thermistor or the like, and outputs a water temperature signal e in accordance with the engine cooling water temperature.

The main 02 sensor 6 is disposed upstream of the maniverter 14, which is a catalytic converter, and outputs a feedback signal f corresponding to the oxygen concentration in the exhaust gas. Specifically, as shown in Figure 3, when the air-fuel ratio A/F of the mixture is leaner than the judgment voltage that exists near the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas is high, It is configured to generate a low voltage and to generate a high voltage when the air-fuel ratio A/F of the mixture is richer than the determination voltage and the oxygen concentration in the exhaust gas is low. be. The sub 02 sensor 7 has the same configuration as the main 02 sensor 6, and outputs a feedback signal g in response to the oxygen concentration in the exhaust gas. In other words, if the air-fuel ratio of the air-fuel mixture is leaner than the judgment voltage that exists near the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas is high, a low voltage is generated, and the air-fuel ratio of the mixture is leaner than the judgment voltage that exists near the stoichiometric air-fuel ratio. It is on the richer side than the voltage and generates a high voltage when the oxygen concentration in the exhaust gas is low.

The electronic control device 9 has the role of adjusting the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 15, and the central processing unit 16
, a memory 17, a human interface 18, and a microcomputer unit equipped with one output interface. Human interface 1
8 includes at least an engine rotation signal from the crank angle sensor 2, an intake pressure signal C from the pressure sensor 3, a throttle signal d from the idle switch 4, and a water temperature signal e from the water temperature sensor 5. A feedback signal f from the main 02 sensor 6 and a feedback signal g from the sub 02 sensor 7 are respectively input.

From one output interface, the injector 1
The fuel injection signal a is output at the same time. The electronic control device 9 calculates the intake air amount from the engine rotation signal S, the intake pressure signal C, etc., and determines the basic injection amount TP in accordance with the intake air amount. Next, this basic injection amount TP is determined by the air-fuel ratio feedback correction coefficient F determined by the feedback signal f of the main 02 sensor 6.
The final energization time T to the injector 1 is determined based on the following formula by correcting the various correction coefficients determined according to the AF and engine operating conditions by 1 and the invalid injection time TAUV, and the time corresponding to that time T is determined based on the following formula. It plays the role of injecting a certain amount of fuel from the injector 1.

T = TPXFAF XK +TAUV Furthermore, the electronic control device 9 includes a program as schematically shown in FIG. First, in step 51, sub 02
It is determined whether the conditions for executing the feedback F/B by the sensor 7 are satisfied. If it is determined that the conditions are satisfied, the process proceeds to step 53; if it is determined that the conditions are not satisfied, the process proceeds to step 52. . In step 52, sub0
The learned value of the feedback control value determined by the output voltage of the second sensor 7 is held. In step 53, feedback F/B control of the air-fuel ratio by the sub-02 sensor 7 is executed, and the process proceeds to step 54. In step 54, it is determined whether the control direction of the feedback control value determined by the output voltage of the sub-02 sensor 7 has changed, and if it is determined that it has changed, the process proceeds to step 55. Step 5
5, as schematically shown in FIG. 6, the value when the feedback control value FACF changes from the increasing side to the decreasing side is updated as the maximum value MAX, and the value when changing from the decreasing side to the increasing side is updated as the maximum value MAX. After appropriately updating each as the minimum value MIN, the process proceeds to step 56.

In step 56, the learning value determined based on the procedure described later is set in a predetermined memory.

Next, feedback control by the main 02 sensor 6 and the sub 02 sensor 7 will be explained.

First, the conditions for feedback control of the air-fuel ratio by the main 02 sensor 6, for example, the engine cooling water temperature is 40°C or higher, the fuel is not being cut, the power is not being increased, a predetermined period of time has passed since the engine was started, and the main 02 If all conditions such as sensor 6 is active and pressure sensor 3 is normal are met, main 02
Feedback control is performed based on the output voltage of the sensor 6. Specifically, as shown in Figure 3, main 02
When the output voltage of the sensor 6 exceeds the determination voltage, the air-fuel ratio feedback correction coefficient FAF is skipped to the decreasing side by a predetermined value R3M after the rich determination delay time TDR;
Next, it is gradually decreased by a constant value based on the lean integral KIH. Therefore, the amount of fuel supplied from the injector 1 is reduced, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio. On the other hand, when the output voltage of the main 02 sensor 6 is lower than the determination voltage, the air-fuel ratio feedback correction coefficient FAF is changed to the predetermined value R3P after the lean determination delay time TDL.
, and then gradually increases by a constant value based on the Ricci integral KIP. As a result, the amount of fuel supplied from the injector 1 increases, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio.

If the feedback F/B condition by the sub-02 sensor 7 is satisfied during such feedback control, for example, a predetermined period of time has elapsed since the main 02 sensor 6 started performing air-fuel ratio feedback, or after the main 02 sensor 6 became active. A predetermined time has elapsed, the engine coolant temperature is 70'C or higher, the transient fuel correction amount is less than the predetermined amount, the engine is idling and the vehicle speed is 0.
or the engine is in a predetermined operating range in a non-idling state, and the number of learning times of the feedback control value determined by the output voltage of the sub-02 sensor 7 is less than the set number of times. , feedback F/B control is performed by the sub-02 sensor 7 (steps 51-53). In this feedback control, as shown in FIG.
A gate time CDLiTYSO (every 5 ec) is provided for control. Specifically, when it is continuously detected whether the output voltage of the sub-02 sensor 7 exceeds the determination voltage, the rich time DUTYSO is increased by the current at each set time. When the rich time DUTYSO counts up and reaches a certain value, the rich flag 5OFLG
is set to a signal 1 indicating that the air-fuel ratio is rich, and when the feedback control value FACF changes from a decreasing side to an increasing side, a signal 0 indicating that the air-fuel ratio is lean is set to the flag 5OFLG. When the signal 1 indicating that the air-fuel ratio is rich is set, the feedback control value FACF is decreased by a constant value based on the lean integral FACFKIM. On the other hand, rich flag 5OF
When the LG switches to a signal 0 indicating that the air-fuel ratio is lean, the feedback control value FACP is set to a constant value FACF.
After skipping only R8P to the increasing side, Rich integral FA
Gradually increase by a constant value based on CFKIP. Based on this procedure, the feedback control value PACF
is changed, and the feedback control value FACF
Based on this, the rich determination delay time TDR and the lean determination delay time TDL are determined from the map shown in FIG. Here, as the feedback control value PACF becomes larger, the rich determination delay time TDR becomes longer, while the lean determination delay time TDL becomes shorter. Therefore, the timing at which the air-fuel ratio feedback correction coefficient FAF changes from the increasing side to the decreasing side becomes later, and the timing at which it changes from the decreasing side to the increasing side becomes earlier, and the amount of fuel supplied from the injector 1 increases. It turns out. Conversely, if the feedback control value FACP becomes smaller, the fuel supply amount will decrease. Also, the feedback control value FACP
The maximum value MAX when reverses from the increasing side to the decreasing side,
While appropriately updating the minimum value KIN when reversing from the decreasing side to the increasing side, the learning value FK is calculated from these values based on the following formula.
G is determined (steps 54 to 56).

N XMAX +K XMIN PKG = N+K (N and K are positive integers) The above control is repeatedly executed during engine operation.

According to such a configuration, when feedback control of the air-fuel ratio is performed based on the output voltage of the main 02 sensor 6, if the control center of the air-fuel ratio shifts to the rich side or lean side, the output of the sub-02 sensor 7 By increasing/decreasing the feedback control value determined by the voltage, the
The air-fuel ratio of the air-fuel mixture is finely adjusted. At this time, as schematically shown in FIG. 6, learning of the feedback control value FACP is performed and the learned value is determined.

Therefore, as shown in FIG. 7, the stoichiometric air-fuel ratio is determined by the value MAX when the feedback control value FACF changes from the increasing side to the decreasing side, and the value MIN when the feedback control value FACF changes from the decreasing side to the increasing side. Therefore, the learned value becomes a value corresponding to the stoichiometric air-fuel ratio. Then, from the next operation, when feedback control is started, feedback control of the air-fuel ratio will be started using the learned value as the starting point.

Therefore, according to the above configuration, the main 02 sensor 6 may be affected by variations in the output characteristics of the main 02 sensor 6, changes over time, variations in the fuel injection amount of the injector 1, or by exhaust gas discharged from a specific cylinder. Even if a situation arises in which the output voltage of the air-fuel mixture is influenced and the predetermined air-fuel ratio control cannot be obtained, the air-fuel ratio of the air-fuel mixture is effectively converged within the window of the three-way catalyst through feedback control by the sub-02 sensor 7. be able to.

Moreover, according to this control method, during the first air-fuel ratio feedback control, emissions deteriorate slightly from the start of control until the air-fuel ratio control center is adjusted to around the required value, but when the air-fuel ratio control center is adjusted to around the required value, the feedback control value After learning, the next time feedback control is performed,
Feedback control of the air-fuel ratio can be performed immediately using the learned value as a starting point. Therefore, when air-fuel ratio feedback control is performed, emissions at the initial stage can be effectively improved.

Also, depending on the learning value, the rich judgment delay time TD)?
The lean determination delay time TDL is determined, and the control center to be set can be determined from this, so even when the feedpack control by the sub-02 sensor 7 is stopped when the engine is cold and the feedback control is performed by the main 02 sensor, Since feedback control can be immediately performed in the vicinity of the learned value starting from the learning value, deterioration of emissions during such feedback control can be suppressed.

Note that the feedback control value determined based on the output signal of the second 02 sensor is, of course, not limited to the case where it is determined based on the control procedure described above. Furthermore, it is also possible to adjust the control center of the air-fuel ratio by changing the rich integral, lean integral, and skip amount of the air-fuel ratio feedback correction coefficient based on the feedback control value.

[Effects of the Invention] Since the present invention has the above configuration, the first 02 sensor can prevent the air-fuel ratio of the mixture from deviating from around the stoichiometric air-fuel ratio, and the second 02 sensor can only prevent Since feedback control of the air-fuel ratio can be started from around the stoichiometric air-fuel ratio, it is possible to effectively avoid deterioration of emissions due to changes over time, etc. Emissions can be effectively improved.

[Brief explanation of drawings]

1 to 7 show one embodiment of the present invention, FIG. 1 is a schematic overall configuration diagram, FIG. 2 is a flowchart diagram schematically showing a control procedure, and FIG. 3 is a control mode. FIG. 4 is a timing chart diagram showing control modes, FIG. 5 is a diagram showing control setting conditions, and FIGS. 6 and 7 are operation explanatory diagrams. FIG. 8 is an operational explanatory diagram corresponding to FIG. 6 showing a conventional example. 1... Injector 6... First 02 sensor (main 02 sensor) 7...
・Second 02 sensor (sub 02 sensor) 14...Catalytic converter (maniverta) 15...Combustion chamber FACF...Feedback control value

Claims (1)

[Claims] A first O_2 sensor that detects the oxygen concentration in the exhaust gas is placed upstream of the catalytic converter that purifies the exhaust gas,
Based on the output voltage, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is feedback-controlled to near the stoichiometric air-fuel ratio, and the second O_2 disposed downstream of the catalytic converter
An air-fuel ratio control method for an internal combustion engine, comprising: determining a feedback control value based on the output voltage of a sensor; and changing the control center of the air-fuel ratio to near the stoichiometric air-fuel ratio based on the feedback control value; A learning value of the feedback control value is determined based on a value when the feedback control value changes from an increasing side to a decreasing side and a value when the feedback control value changes from a decreasing side to an increasing side, and the feedback An air-fuel ratio control method for an internal combustion engine, characterized in that feedback control is started using the learned value at the time of starting control.