JP3187534B2 - Air-fuel ratio correction method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting an air-fuel ratio of an internal combustion engine for an automobile, which is operated in a lean burn region having a high air-fuel ratio.

[0002]

2. Description of the Related Art In recent years, it has become increasingly necessary to operate an engine with the air-fuel ratio leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency. In response to such needs, in this type of internal combustion engine, the load of the engine is detected and the engine is in a predetermined transient state, for example, as in an air-fuel ratio control device described in Japanese Patent Application Laid-Open No. 62-162742. In this case, feedback control based on a stoichiometric air-fuel ratio is performed in a case where the fuel supply amount is controlled at an air-fuel ratio set leaner than the stoichiometric air-fuel ratio in a steady running state. To control the air-fuel ratio on the lean side, PID control is performed to a target air-fuel ratio using the output of the air-fuel ratio sensor. The air-fuel ratio sensor is usually disposed upstream of the three-way catalyst in the exhaust system.

[0003]

In the above configuration, the response of the air-fuel ratio sensor follows the change of the exhaust gas to be discharged due to the mounting position, but it always follows from the timing to be detected. It is late. When PID control is performed to achieve the target air-fuel ratio, a fuel cut is executed, and then the system returns and shifts to feedback control. Since exhaust gas in a lean atmosphere remains around the air-fuel ratio sensor, the exhaust gas Is output. Then, in response to the output signal, the air-fuel ratio control performs a correction to change the air-fuel ratio correction coefficient FLAF to the rich side so that the air-fuel ratio becomes rich ( FIG. 5 ). However, actually, since the exhaust gas at that time was in a rich atmosphere, hunting occurred in the control.

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

[0005]

In order to achieve the above object, the present invention takes the following measures. That is, the air-fuel ratio correction method for an internal combustion engine according to the present invention detects the operating state of the internal combustion engine by detecting the air-fuel ratio with at least the air-fuel ratio sensor, and performs feedback control based on the stoichiometric air-fuel ratio in accordance with the detected operating state. An air-fuel ratio correction method for an internal combustion engine that performs PID control for correcting a fuel injection amount with an air-fuel ratio correction coefficient including a proportional constant, an integral constant, and a differential constant so as to achieve a target air-fuel ratio set in a lean burn region. It is.

Then, it is detected that the fuel cut has been completed and the fuel supply has been restarted during the PID control, and the value obtained by subtracting the target air-fuel ratio in the lean burn region from the air-fuel ratio detected by the air-fuel ratio sensor thereafter is obtained. The PID control is stopped until it is detected that the air-fuel ratio has become less than the predetermined value, and the operation shifts to the PID control when the air-fuel ratio becomes less than the predetermined value.

[0007]

With this configuration, after the fuel cut is terminated and the fuel supply is restarted, the target air-fuel ratio in the lean burn region is subtracted from the air-fuel ratio detected by the air-fuel ratio sensor from that point. Until the value becomes less than the predetermined value, the PID control is stopped and the transition to the PID control is delayed. That is, after the fuel cut is restored, the PID control is started when the detected air-fuel ratio approximates the actual air-fuel ratio. Therefore, PID control in a state different from the actual air-fuel ratio due to a response delay of the air-fuel ratio sensor is not performed, and the hunting state does not occur due to the air-fuel ratio fluctuating to the rich side.

[0008]

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). 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 near one end of the fuel injection valve 5, and the fuel injection valve 5 is controlled by an electronic control device 6. In the exhaust system 20, a lean sensor 21 as an air-fuel ratio sensor for measuring the oxygen concentration in the exhaust gas is provided at a position upstream of a three-way catalyst 22 provided in a pipe leading to a muffler (not shown). Attached to. The lean sensor 21 has substantially the same configuration as a normal O ₂ sensor. By applying a constant voltage between the atmosphere-side electrode and the exhaust-side electrode, the lean sensor 21 has a stoichiometric air-fuel ratio during feedback control. And outputs an electric current in accordance with the oxygen concentration in the exhaust gas over the case of the air-fuel ratio in the lean burn region.

The electronic control unit 6 includes a central processing unit 7
, A storage device 8, an input interface 9, and an output interface 11. The microcomputer system mainly includes a microcomputer system having an input interface 9 for detecting a pressure in the surge tank 3. The intake pressure signal a from the intake pressure sensor 13, the rotational speed signal b from the rotational speed sensor 14 for detecting the engine rotational speed NE, the vehicle speed signal c from the vehicle speed sensor 15 for detecting the vehicle speed, the throttle valve 2 An LL signal d from the idle switch 16 for detecting the open / close state, a water temperature signal e from the water temperature sensor 17 for detecting the cooling water temperature of the engine, a current signal h from the above-described lean sensor 21 and the like are input. On the other hand, the output interface 11
After that, the fuel injection signal f is output to the fuel injection valve 5 and the ignition pulse g is output to the spark plug 18.

The electronic control unit 6 uses the intake pressure signal a output from the intake pressure sensor 13 and the rotational speed signal b output from the rotational speed sensor 14 as main information, and various types of information determined according to the engine conditions. The basic injection time is corrected by the correction coefficient to determine the fuel injection valve opening time, that is, the injector final energization time T. The fuel injection valve 5 is controlled based on the determined energization time, and the fuel corresponding to the engine load is supplied to the fuel. A program for injecting the fuel from the injection valve 5 to the intake system 1 is incorporated. In this program, at least the lean sensor 21 detects the air-fuel ratio to detect the operating state of the internal combustion engine, performs feedback control based on the stoichiometric air-fuel ratio according to the detected operating state, and sets the lean burn range. An air-fuel ratio correction method for an internal combustion engine that performs PID control for correcting a fuel injection amount by an air-fuel ratio correction coefficient including a proportional constant, an integration constant, and a differential constant so as to achieve a target air-fuel ratio. Is completed and fuel supply is restarted, fuel cut is terminated during PID control and fuel supply is restarted, and lean burn is detected based on the air-fuel ratio detected by the air-fuel ratio sensor thereafter. The PID control is stopped until it is detected that the value obtained by subtracting the target air-fuel ratio in the region is less than a predetermined value, and the air-fuel ratio is not higher than the predetermined value. Are those programmed to shift to PID control when it becomes.

The outline of the air-fuel ratio correction program is as shown in FIG. However, the program itself for calculating the effective injection time TAU in consideration of various correction coefficients and thereafter calculating the injector final energization time T can be a conventionally known program, and therefore, illustration and description thereof are omitted. The control switching between the feedback control and the PID control is determined based on the engine speed, the magnitude of the load, the cooling water temperature, and the like. The engine is being started, and the warm-up operation is performed during the warm-up operation. Except when the engine is in a steady state, the PID control is executed in the lean burn region except when the engine is in a transient state such as during acceleration.

First, at step 61, a fuel cut
Immediately after the flag (hereinafter referred to as flag) XAFFC
Is set or not, and 1 is set
If yes, go to step 62, if 0 is set
Proceed to step 64. This flag XAFFC is
This is set to 1 in the Elcut return processing routine.
is there. In step 62, the proportional constant DAF is
Determines when to restart PID control after returning to normal cut
Lean feedback start DAF level that is a predetermined value
(Hereinafter referred to as start level) less than KDAFFC
It is determined whether or not it is , if it is less, the process proceeds to step 63,
If so, the process returns to the subroutine. Step 63
Then, 0 is set to the flag XAFFC.

In step 64, the air-fuel ratio correction coefficient FLAF
Is an arithmetic processing routine. Specifically, as shown in FIG.
Thus, in step 53, the proportional constant DAF and the integral constant D
Air-fuel ratio consisting of AFTOTAL and differential constant DDAF
It is determined whether or not the cycle for calculating the correction coefficient FLAF has elapsed.
If it has passed, the process proceeds to step 54,
If not, return to the subroutine. In step 54,
The proportional constant DAF is calculated to calculate the air-fuel ratio correction coefficient FLAF. The calculation of the proportional constant DAF is performed by subtracting the target air-fuel ratio LAFT in the lean burn region from the current air-fuel ratio LAF detected by the lean sensor 21 as shown in the following equation (1). DAF = LAF-LAFT (1)

Next, at step 55, the integration constant DAFT
The calculation of OTAL is performed by the following equation (2). DAFTOTAL = ΣDAF (2)

Subsequently, in step 56, the differential constant DDAF is calculated by subtracting the previously calculated differential constant DAF0 from the proportional constant DAF calculated in step 54, as shown in the following equation (3). . DDAF = DAF-DAF0 (3)

In step 57, the air-fuel ratio correction coefficient FLAF is calculated by substituting the respective constants calculated in steps 54 to 56 into the following equation (4). FLAF = Kp * DAF + Ki * DAFTTOTAL + Kd * DDAF + 1.0 (4) where Kp, Ki, and Kd are coefficients.

[0018] Step 5 from this way, step 53
Up to 7, the air-fuel ratio correction coefficient FLAF in the PID control
Is executed at a predetermined calculation cycle during PID control. The calculation cycle may be the same as the detection cycle of the air-fuel ratio by the lean sensor 21, for example.

In the above-described configuration, this embodiment uses the PID based on the amount of change in the air-fuel ratio after fuel cut return.
The fuel cut is performed during the operation in the lean burn region, and then the fuel cut is restored. Goes to step 61 → 62 → subroutine. That is, during this time, the calculation of the air-fuel ratio correction coefficient FLAF is not executed, and as shown in FIG. 4 , the air-fuel ratio correction coefficient FLAF remains fixed at the value in the fuel cut (F / C in the figure), and the fuel cut Despite the return, the PID control is stopped (held). This means that by the time PID control is resumed,
The delay time is substantially set according to the operation state after the fuel cut recovery. On the other hand, during this time, the proportional constant DAF of the air-fuel ratio correction coefficient FLAF is calculated in the same manner as in the above equation (1). And the proportional constant D
When the AF falls below the start level KDAFFC, the control proceeds to steps 61 to 64, in which the first air-fuel ratio correction coefficient FLAF after the fuel cut recovery is calculated, and the fuel injection amount is corrected by the obtained air-fuel ratio correction coefficient FLAF. . Therefore, as shown in FIG. 4 , even when the output of the lean sensor 21 outputs a signal indicating a lean state at the time of return from the fuel cut, the difference between the target air-fuel ratio and the air-fuel ratio at that time is equal to the predetermined start level KDAFFC. If the air-fuel ratio does not decrease, the PID control is interrupted without calculating the air-fuel ratio correction coefficient FLAF during that time. Therefore, the fuel injection amount is not corrected so that the air-fuel ratio becomes rich, and the air-fuel ratio becomes rich. To prevent

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

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

[0022]

According to the present invention, as described in detail above, the restart timing of the PID control after the fuel cut is restored is determined by the air-fuel ratio detected by the air-fuel ratio sensor at that time and the target air-fuel ratio in the lean burn region. Is set at the point in time when it is detected that the difference becomes less than the predetermined value, the PID is deviated from the actual air-fuel ratio due to the response delay of the air-fuel ratio sensor.
Control can prevent want to consider performing some are, the air-fuel ratio can be prevented from being hunting state fluctuates to the rich side in the meantime.

[Brief description of the drawings]

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

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

FIG. 3 shows the air-fuel ratio correction coefficient in the control procedure of the embodiment.
The flowchart figure which shows a calculation procedure.

FIG. 4 is an operation explanatory view of the embodiment.

FIG. 5 is an operation explanatory view of a conventional example.

[Explanation of symbols]

 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 11 ... Output interface 21 ... Lean sensor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 395

Claims (1)

(57) [Claims] An air-fuel ratio is detected by at least an air-fuel ratio sensor to detect an operation state of the internal combustion engine, feedback control is performed based on a stoichiometric air-fuel ratio in accordance with the detected operation state, and a lean burn range is set. An air-fuel ratio correction method for an internal combustion engine that performs PID control for correcting a fuel injection amount by an air-fuel ratio correction coefficient including a proportional constant, an integration constant, and a differential constant so as to achieve a target air-fuel ratio. Is completed and the fuel supply is restarted, and the air-fuel ratio detected by the air-fuel ratio sensor thereafter
The PID control is stopped until it is detected that the value obtained by subtracting the target air-fuel ratio in the lean burn region from the predetermined value becomes smaller than a predetermined value, and when the air-fuel ratio becomes smaller than the predetermined value, the process shifts to PID control. An air-fuel ratio correction method for an internal combustion engine, comprising: