JPH05141294A - Air/fuel ratio control method - Google Patents

Abstract

PURPOSE:To prevent overrich of an air fuel ratio by prohibiting change in an air/fuel ratio feedback correction coefficient till a predetermined time has elapsed since return from fuel cut and then, by changing this correction coefficient through combination of skip processing and integration processing. CONSTITUTION:An electronic control device 6 corrects a basic injection time with various correction coefficients determined according to engine conditions based on output signals a, b, etc., of an intake pressure sensor 13 and a revolution number sensor 14 so as to determine open time for a fuel injection valve and drives and controls a fuel injection valve 5. Also, fuel cut is executed which interrupts fuel supply in a predetermined engine operating state. In this case, when return form fuel cut is detected, open control is continued without changing an air/fuel ratio feedback correction coefficient for a predetermined period of time from the return from fuel cut. And after the predetermined time has passed, the air/fuel ratio feedback correction coefficient is changed by combining skip processing and integration processing based on an oxygen concentration detected by an O2 sensor 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method used in an engine of an automobile or the like equipped with an electronically controlled injection device.

[0002]

2. Description of the Related Art Conventionally, in this type of air-fuel ratio control method, open control is performed during fuel cut, rather than feedback control. In the case of open control, the output signal of the O ₂ sensor is not used, but in this case, since combustion is not performed, the O ₂ sensor outputs a signal indicating that the air-fuel ratio is lean. In the feedback control, for example, as disclosed in Japanese Patent Laid-Open No. 3-54338, when the output signal of the O ₂ sensor indicates lean, the supply air-fuel ratio approaches the stoichiometric air-fuel ratio, so the air-fuel ratio feedback correction coefficient FAF There is known a method in which a skip process is performed in which is temporarily increased by a certain value, and then feedback control is performed in which the process is gradually changed by an integration process. In such a case, when the fuel cut is forcibly returned to the feedback control, if the acceleration increase correction injection and the fuel cut return asynchronous injection are performed, the air-fuel ratio becomes lean during normal operation. Similarly, the air-fuel ratio feedback correction coefficient FAF also checks the state of the O ₂ sensor and executes the feedback control from the skip processing.

[0003]

However, the problem with the conventional skip processing including the above publication is that, as shown in FIG. 4, at the moment of returning from the fuel cut F / C,
That is, at the moment when the F / C flag that turns on / off corresponding to the fuel cut F / C state is turned off, it is a signal indicating the lean that is output by the O ₂ sensor, and therefore the air-fuel ratio feedback correction is performed based on the signal. The point is that the plus skip RSP for increasing the coefficient FAF is always executed. However, in reality, the actual air-fuel ratio A / F is often rich due to the above increase after the fuel cut F / C recovery,
In such a state, the air-fuel ratio feedback correction coefficient F
When the plus skip for increasing AF is executed, the effective injection time becomes longer, and the state in which the air-fuel ratio A / F is rich is promoted, resulting in deterioration of emission.

An object of the present invention is to eliminate such a problem.

[0005]

The present invention takes the following means in order to achieve such an object. That is, the air-fuel ratio control method according to the present invention detects the oxygen concentration in the exhaust gas and temporarily reduces the air-fuel ratio feedback correction coefficient based on the detected oxygen concentration. In combination with the changing integration process, the effective injection time of fuel is calculated using the changed air-fuel ratio feedback correction coefficient, and the fuel cut is stopped in the air-fuel ratio control method that approximates the supply air-fuel ratio to the theoretical air-fuel ratio. It detects that the fuel supply has been restarted, prohibits changing the air-fuel ratio feedback correction coefficient for a predetermined time set after the detection, and then changes the air-fuel ratio feedback correction coefficient based on the detected oxygen concentration. It is characterized in that the skip processing and the integration processing are combined and changed.

[0006]

With this structure, when the fuel cut is stopped and the fuel supply is restarted, the air-fuel ratio feedback correction coefficient corresponding to the detected oxygen concentration is changed for a predetermined time from that point. Do not do. Therefore, immediately after returning from the fuel cut, the air-fuel ratio feedback correction coefficient is not temporarily largely changed, and the amount of fuel increase corresponding to the increase in the air-fuel ratio feedback correction coefficient disappears. Then, at the time when the oxygen concentration is detected when the fuel cut return increase is executed after a lapse of a predetermined time after the fuel cut return is detected, the air-fuel ratio feedback correction coefficient corresponding to the detected oxygen concentration. Is changed. Therefore, it is possible to prevent the supply air-fuel ratio from becoming excessively rich immediately after returning from the fuel cut, and it is possible to reduce emissions.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is for an automobile, and its intake system 1 is provided with a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown), and a surge is provided downstream thereof. A tank 3 is provided.
Intake manifold 4 of intake system 1 communicating with surge tank 3
A fuel injection valve 5 is further provided in the vicinity of one end of the fuel injection valve 5, and the fuel injection valve 5 is controlled by the electronic control unit 6. Further, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to the exhaust system 20 at a position upstream of a three-way catalyst 22 arranged in a pipe line leading to a muffler (not shown). There is. This O ₂ sensor 21
Outputs a voltage signal h corresponding to the oxygen concentration.

The electronic control unit 6 is mainly composed of a microcomputer system including a central processing unit 7, a storage unit 8, an input interface 9 and an output interface 11, and the input interface 9 has Is the intake pressure signal a from the intake pressure sensor 13 for detecting the pressure in the surge tank 3, the rotation speed signal b from the rotation speed sensor 14 for detecting the engine speed NE, and the vehicle speed. The vehicle speed signal c from the vehicle speed sensor 15, the LL signal d from the idle switch 16 for detecting the opening / closing state of the throttle valve 2, the water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, and the above-mentioned O ₂ The voltage signal h or the like from the sensor 21 is input. On the other hand, from the output interface 11,
A fuel injection signal f is output to the fuel injection valve 5, and an ignition pulse g is output to the spark plug 18.

The electronic control unit 6 has an intake pressure signal a output from the intake pressure sensor 13 and a rotation speed signal b output from the rotation speed sensor 14 as main information, and various kinds of information are determined depending on the engine condition. The fuel injection valve opening time, that is, the injector final energization time T is determined by correcting the basic injection time with the correction coefficient, and the fuel injection valve 5 is controlled according to the determined energization time to supply the fuel according to the engine load. A program for injecting from the injection valve 5 to the intake system 1 is built in. In this program, fuel cut F /
The air-fuel ratio feedback correction coefficient FAF is not changed for a predetermined time after the return from C, the open control is continued, and after the predetermined time has elapsed, the air-fuel ratio feedback correction coefficient is changed corresponding to the detected oxygen concentration. It is programmed so that the effective injection time TAU is calculated by FAF and feedback control is performed to inject fuel.

The outline of this air-fuel ratio correction program is as shown in FIG. However, as the program itself for calculating the effective injection time TAU in consideration of various correction factors and then calculating the injector final energization time T, a conventionally known program can be used, and therefore illustration and description thereof will be omitted.

First, at step 51, the fuel cut F /
Fuel cut F / C
If it is medium, the process proceeds to step 61, and if not, the process proceeds to step 52. Whether or not the fuel cut F / C is performed, that is, the detection of the fuel cut F / C is determined by the state of the F / C flag that is turned on / off depending on the presence or absence of the fuel injection signal f output to the fuel injection valve 5. There is. In step 61, the elapsed counter for measuring the elapsed time after the fuel cut F / C recovery is cleared and the process proceeds to the main routine. This progress counter may be implemented by the central processing unit 7, and operates at the time when it is detected in step 51 that the fuel cut F / C is stopped and the supply of fuel is restarted, and starts time measurement. .. Step 52
Then, it is determined whether or not the elapsed time from the fuel cut F / C recovery has exceeded 1 second, and if it has exceeded 1 second, step 5
If not, go to step 54.

In step 53, after the fuel cut F / C is restored, more than 1 second, which is a predetermined time, has elapsed.
O ₂ sensor 2 to execute normal feedback control
The A / F feedback correction coefficient FAF is calculated corresponding to the voltage signal h output from the signal No. 1, and the process proceeds to step 55. In step 54, a predetermined time (delay time)
Has not elapsed, O is required to execute the open control.
₂ Regardless of the voltage signal h from the sensor 21, the A / F feedback correction coefficient FAF is fixed to a constant value, and step 5
Go to 5. In step 55, the effective injection time TAU is calculated using the A / F feedback correction coefficient FAF calculated in step 53 and step 54 together with other correction coefficients, and the effective injection time TAU is calculated in the main routine. Fuel injection is executed based on this.

In the above configuration, during the fuel cut F / C in which the F / C flag is on, the control proceeds from step 51 to step 61. Next, when the fuel cut F / C is stopped and the fuel cut F / C is restored, step 51 →
In step 52, if the elapsed counter does not count 1 second, that is, the elapsed time after the fuel cut F / C recovery is 1
If the time has not passed yet, the process proceeds from step 54 to step 55. In this case, as shown in FIG. 3, the A / F feedback correction coefficient FAF is fixed to a constant value irrespective of the output of the O ₂ sensor 21, and this state continues until a predetermined time elapses. In other words, the O ₂ sensor 21 outputs the voltage signal h corresponding to the operating condition of the engine after the fuel cut F / C recovery, but the A / F feedback correction coefficient FAF is fixed to a constant value for the open control. Therefore, the voltage signal h output within the predetermined time is not adopted and is all ignored. Therefore, until the predetermined time elapses, the supply air-fuel ratio A / F
Is slightly richer by the amount of fuel injection increased by the asynchronous increase at the time of return or the fuel cut recovery correction coefficient FFC, etc. You can

On the contrary, when the elapsed time after the fuel cut F / C recovery exceeds 1 second, the control is performed from step 51 to step 51.
The process proceeds from 53 to step 55. In this case, A / F feedback correction coefficient FAF is calculated corresponding to the output voltage signal of the O ₂ sensor 21 at the time the step 53 is executed, as shown in FIG. 3, the output of the O ₂ sensor 21 When the signal h indicates rich, it is calculated by performing a skip process for reducing it by a predetermined value, and thereafter, the value is gradually reduced by an integration process according to the situation of the output signal h. The control is repeated in this order until the fuel cut F / C is performed again, and the supply air-fuel ratio A / F is controlled so as to approximate the ideal air-fuel ratio by the normal feedback control.

As is clear from the above, the fuel cut F /
Supply air-fuel ratio A from the time C is restored until a predetermined time elapses
Since / F is reduced by an increase amount related to the A / F feedback correction coefficient FAF in the increase in the fuel injection amount immediately after the return, the emission can be reduced. There are two ways of returning the fuel cut F / C, for example, a natural return that is restored when the engine speed becomes equal to or lower than a predetermined number of revolutions, and a forced return that is restored by being accelerated during the fuel cut. , Transient air-fuel ratio correction coefficient FAEW
This is particularly effective when the forced recovery is performed in which the increase due to and the asynchronous increase are performed.

The present invention is not limited to the embodiment described above.

In addition, the configuration of each part is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0019]

As described in detail above, according to the present invention, the air-fuel ratio feedback correction coefficient is temporarily changed largely by the skip processing in the feedback control until the predetermined time elapses from the fuel cut recovery. Therefore, since the fuel amount corresponding to the increase in the air-fuel ratio feedback correction coefficient is eliminated, it is possible to prevent the supply air-fuel ratio from becoming overrich during the elapse of the predetermined time, and to reduce the emission during that time. It can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is an explanatory view of the operation of the same embodiment.

FIG. 4 is an operation explanatory view of a conventional example.

[Explanation of symbols]

5 ... fuel injection valve 7 ... central processing unit 8 ... storage device 9 ... input interface 11 ... output interface 21 ... _{O 2} sensor FAF ... A / F feedback correction coefficient TAU ... effective injection time

Claims (1)

[Claims] 1. A combination of a skip process for detecting an oxygen concentration in exhaust gas and temporarily changing the air-fuel ratio feedback correction coefficient largely based on the detected oxygen concentration, and an integration process for changing the air-fuel ratio feedback correction coefficient to a small value at regular intervals. In the air-fuel ratio control method in which the effective injection time of fuel is calculated by the changed air-fuel ratio feedback correction coefficient and the supplied air-fuel ratio is approximated to the stoichiometric air-fuel ratio, fuel cut is stopped and fuel supply is restarted. It is detected that the change of the air-fuel ratio feedback correction coefficient is prohibited for a predetermined time set from the detection, and thereafter the skip processing and the integration processing of the air-fuel ratio feedback correction coefficient are performed based on the detected oxygen concentration. An air-fuel ratio control method characterized by combining and changing.