JPS63205451A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize air-fuel ratio by arranging a solenoid valve in a path communicating between a canister and an intake path in the downstream of a throttle valve, and resetting correction variables to ineffective values which substantially cause no variation on the fuel supply quantity, as required, when the solenoid valve is switched. CONSTITUTION:A fuel tank 25 communicates through a purge path 26 arranged with a canister 28, with an intake path 12 in the downstream of a throttle valve 18. Here, a purge control valve 30 is arranged in the purge path 26. An electronic control unit 16 controls a solenoid 30d in the valve 30 based on signals being fed from various sensors 14, 19-24 for detecting operational conditions of an engine 10 so as to open/close a valve body 30c. If open/close operation of the valve 30 is executed during feedback control operation of air-fuel ratio, correction variables are reset to ineffective values which cause substantially no variation of the fuel supply quantity even if fuel supply quantity is corrected, when the valve 30 is switched.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular, the present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular, the present invention relates to an air-fuel ratio control method for an internal combustion engine. The present invention relates to an air-fuel ratio control method during air-fuel ratio feedback control operation of an internal combustion engine.

(Prior Art) The amount of fuel supplied to an internal combustion engine is determined by adding various correction coefficients and correction values (these are called correction variables) to a basic amount determined by parameters representing engine load, such as air flow rate and engine rotation speed. For example, a correction coefficient (hereinafter referred to as "feedback correction coefficient") according to the concentration of a specific component in exhaust gas (for example, 1 degree ozt), a correction coefficient according to engine coolant temperature, a correction value according to battery voltage, etc. An air-fuel ratio control method that corrects by multiplying and/or adding the amount of fuel, injects and supplies the thus corrected fuel amount to the engine, and controls the air-fuel ratio to a required value (for example, a value that gives the stoichiometric air-fuel ratio of 14.6) has been widely adopted.

On the other hand, in order to prevent fuel that evaporates from the fuel tank, etc. from leaking into the atmosphere, the inside of the fuel tank is routed through a communication passage (hereinafter referred to as the "purge passage") into the intake passage downstream of the throttle valve. A canister is placed in the middle of this purge passage, and a solenoid valve (hereinafter referred to as a "purge control valve") is placed in the purge passage between the canister and the intake passage. Meanwhile, during specified operation, the purge control valve is opened to take in air from outside the canister, and the fuel separated from the activated carbon is discharged into the intake passage downstream of the throttle valve. .

Air containing evaporated fuel from the canister (hereinafter referred to as “
Purge air (referred to as "purge air") does not have a constant ratio of air to fuel, and if such purge air is discharged into the intake passage during specified low-load operation such as idling, engine operation will become unstable. During low-load operation, the purge control valve is closed to prevent purge air from being discharged into the intake passage.

When purge air is discharged into the intake passage during operation in which the air-fuel ratio is feedback-controlled to the required value by the feedback correction coefficient, the feedback correction coefficient value is leaner by the amount of purge air containing fuel vapor discharged into the intake passage. The air-fuel ratio is controlled to be maintained at the required value using the thus corrected feedback correction coefficient. Figure 4 shows changes in the output value of the 02 sensor that detects the 02 concentration in exhaust gas according to the on/off state of the purge control valve (PVC) during air-fuel ratio feedback control operation, and changes in the output value of the 0□ sensor. It shows the relationship between the time change of the feedback correction coefficient value IFB set by the engine and the time change of the air-fuel ratio of the air-fuel mixture supplied to the engine. As mentioned above, the feedback correction coefficient value IFB before time point 11 shown in Figure 4 is the value that corrects the air-fuel ratio to the lean side (Figure 4 (
Values shown by solid lines before time tI of cl. Typically this value is less than the value 1.0. ) is set.

(Problem to be Solved by the Invention) However, if the purge control valve is closed (off) during air-fuel ratio feedback control operation (1 in Fig. 4).
1), the fuel contained in the purge air is not suddenly supplied, and the air-fuel ratio suddenly changes to the fuel-lean side (see Figure 4 FDL). Therefore, feedback correction is required to maintain the air-fuel ratio at the required value. It is necessary to suddenly change the coefficient value IFB to a value that increases the amount of fuel commensurate with the amount of fuel contained in the purge air. However, in order to ensure the stability of the feedhack control system, the rate of change of the feedback correction coefficient rFH, which is set according to the change in the output value of the 0□ sensor, cannot be set to a large value. As shown by the solid line in Figure (C1), the feedback correction coefficient value IFB is gradually set to a larger value, and it takes time to reach the value necessary to maintain the air-fuel ratio at the required value (for example, In order to increase the feed hack correction coefficient value IFB to the value 1.0, it takes time from time 11 to time t2 as shown in FIG. 4 (el).During this time,
The air-fuel ratio supplied to the engine was on the overly lean side, and in some cases the engine stalled.

The present invention has been made to solve this problem, and when the purge control valve is opened or closed during air-fuel ratio feedback control operation, the air-fuel ratio is quickly stabilized to a desired value, thereby stabilizing engine operation. The present invention aims to provide an air-fuel ratio control method for an internal combustion engine that improves exhaust gas characteristics, improves fuel efficiency, etc.

(Means for Solving the Problems) In order to achieve the above-mentioned object, according to the present invention, the air-fuel ratio of an internal combustion engine in which the inside of the fuel tank is communicated with the intake passage on the downstream side of the throttle valve through the canister is adjusted. During feedback control operation, a correction variable value is set according to the concentration of a specific component in exhaust gas, and the amount of fuel supplied to the internal combustion engine is corrected according to the correction variable value to control the air-fuel ratio to a required value. In the fuel ratio control method, an electromagnetic valve for blocking and opening the communication passage is disposed in the middle of a communication passage connecting the canister and the intake passage downstream of the throttle valve, and the electromagnetic valve is opened during a predetermined operating state of the engine. and discharge the evaporated fuel into the intake passage, while when the opening/closing operation of the solenoid valve is executed during the feedback control operation, the correction variable value at the time of switching the solenoid valve is used as the correction variable value. An air-fuel ratio control method for an internal combustion engine is provided, which is characterized by resetting the fuel supply amount to an invalid value that does not substantially change the fuel supply amount even if the fuel supply amount is corrected.

(Function) The correction variable value at the time of switching the solenoid valve is used as an invalid value that does not substantially change the fuel supply amount even if the fuel supply amount is corrected, that is, the correction variable value is set as the correction variable value. By resetting the air-fuel ratio, which increases or decreases due to valve switching, to a value closer to the correcting value, the air-fuel ratio is quickly stabilized to the desired value.

(Example) An embodiment of the present invention will be described below based on the drawings.

First, the schematic configuration of a fuel supply control device for carrying out the method of the present invention will be described with reference to FIG. The intake pipe connected to the port is shown. An air cleaner 13 is attached to the open end of the intake pipe 12 on the atmosphere side, and a Karman vortex type air flow sensor 14 is also attached. This air flow sensor 1
4 is electrically connected to the input side of the electronic control unit (EC1J) 16 and supplies the Karman vortex generation periodic signal f to the electronic control unit 16.

A throttle valve 18 is disposed in the middle of the intake pipe 12, and an electromagnetic fuel injection valve 20 is disposed near the intake port of each cylinder, and each fuel injection valve 20 is connected to the output side of the electronic control device 16. The valve is driven to open by a drive signal from the electronic control unit 16. ! Reference numeral 15 indicates an exhaust pipe connected to the exhaust port of each cylinder, and a three-way catalyst 17 is disposed in the middle of the exhaust pipe 15 to purify harmful gas components such as unburned hydrocarbons and nitrogen oxides in the exhaust gas. An 02 sensor 21 is attached to the exhaust pipe 15 between the engine 10 and the three-way catalyst 17 to detect the 00□ concentration in the exhaust gas. 0□Sensor 21 is electronic control unit 1
6 and supplies the 02s degree detection signal ■0□ to the electronic control unit 16.

On the input side of the electronic control unit 16, there is an idle switch 19 that generates an on signal when the throttle valve 18 is closed to a predetermined idle opening position, and an idle switch 19 that generates an on signal when the throttle valve 18 is closed to a predetermined idle opening position. position)
a crank angle position sensor (N) 22 that detects the temperature of the engine, and an engine water temperature (Tw) sensor 23 that is attached to the cylinder block of the engine 10 and detects the engine cooling water temperature Tw.
, and sensors 24 for detecting other engine operating parameter values such as battery voltage and atmospheric pressure are electrically connected to each other.

Reference numeral 25 denotes a fuel tank, and the inside of the fuel tank 25 is communicated with the intake pipe 12 downstream of the throttle valve 18 via a purge passage (communication passage) 26.

The purge passage 26 is connected to either the fuel tank 25 side or the fuel tank 25 side.
- Yanista 28 and purge control valve (electromagnetic valve) 30 are arranged in this order. The canister 28 is filled with activated carbon 28a, and the inside of the canister 28 communicates with the atmosphere through an opening 211b opening at the bottom of the activated carbon 2Ba layer. Purge control pulp 3
0 is an on/off valve, and a port 30a is connected to the purge passage 26.

30b, and a valve body 30c that opens and closes the port 30a;
A spring (not shown) that presses the valve body 30c toward the port 30a so as to always close the port 30a and a biasing (on)
and a solenoid 30d that moves the valve body 30C in the valve opening direction against the spring force of the spring. It is energized by the energizing signal of.

Next, the operation of the fuel supply control device configured as described above will be explained.

First, the solenoid 30d of the purge control pulp 30 is activated by the energizing signal from the electronic control unit 16.
When the port 30a is energized and the port 30a opens, the canister 2
Atmospheric air (purge air) is sucked into the intake pipe 12 from the opening 28b of B, and the sucked air is absorbed into the activated carbon 28.
The fuel adsorbed on b is released and guided to the intake pipe 12.

Operation control of this purge control pulp 30, that is,
Purge air control is executed by an electronic control unit 16, which controls the engine 10 to shut off (purge cut) purge air from the canister 28 based on detection signals from the various engine operating parameter sensors described above. It is determined whether or not the engine is in a predetermined operating state in which discharge of the air into the intake pipe 12 should be prevented. The predetermined operating state to be purged is, for example, an operating state in which the engine water temperature 7W value detected by the engine water temperature sensor 23 is higher than a predetermined temperature (for example, 60° C.), a Karman vortex generation period f detected by the air flow sensor 14, etc. is below a value representing a predetermined air flow rate at a medium load or below, and the throttle valve 18 is closed and the idle switch 19 is in the on state, such as an operating state, and the electronic control unit 16 is in such a state that the persica 2 When one of the operating conditions to be detected is detected, the solenoid 30d of the purge control pulp 30 is deenergized, the port 30a is closed, and the purge air from the canister 28 is cut off.

Next, to explain the air-fuel ratio feedback control method by the electronic control unit I6, the electronic control unit 16 first determines whether the engine 10 should perform air-fuel ratio feedback control based on the detected values of the various engine operating parameters. When it is detected whether the engine 10 is in an operating state and it is detected that the engine 10 is in an operating state that requires air-fuel ratio feedback control, the valve opening time T of the fuel injection valve 20 is calculated based on the following equation.

T=Ktx (A/N)XIFBXK2+TnHere,
(A/N) indicates the intake air amount taken in one intake stroke of the engine 10, and is calculated from the air flow rate A detected by the airflow sensor 14 and the engine rotation speed N detected by the crank angle position sensor 22. be done. K1
is a constant for converting into a valve opening time corresponding to the (A/N) value, K2 is a correction coefficient set according to the engine water temperature TW detected by the engine water temperature sensor 23, atmospheric pressure, etc., and T
, are correction values determined according to battery voltage and the like.

Further, rFB is a feedback correction coefficient, and this correction coefficient rFB value is set according to the voltage value vO□ (value corresponding to the 0□ concentration) detected by the 0□ sensor 21. The method of setting this feedback correction coefficient value 1FB will be explained in more detail below with reference to the flowcharts shown in FIGS. 2 and 3.

The program flowchart shown in FIG. 2 is a timer routine program that is executed by an interrupt by a timing pulse (for example, a pulse generated every 25 m5ec) generated by the electronic control unit 16 at a predetermined time [1, 1]. The component 16 first reads the voltage value detected by the O2 sensor 21 in step 40, and converts it into 0. Store as a value. Next, the vO□ value is compared with a predetermined discrimination value Vx, and ■θ
□Determine whether the value is greater than the Vx value (Step 4
1).

If this determination result is affirmative (Yes), that is, if it is determined that the vO□ value is larger than the Vx value and the air-fuel ratio supplied to the engine 10 is on the Lynch side than the required value, the process proceeds to step 42. , subtracts a predetermined minute value Δ■ from the stored feedback correction coefficient value TFB, stores this as a new feedback correction coefficient value IFB, and ends the program.

If the determination result in step 4I is negative (No), that is,
If it is determined that the vO□ value is smaller than the Vx value and the air-fuel ratio supplied to the engine 10 is leaner than the required value, the process proceeds to step 43, where a predetermined small value Δ■ is calculated from the feedback correction coefficient value rFB. is added, this is stored as a new feedback correction coefficient value rFB, and the program is ended.

FIG. 3 shows a main routine program that is executed by the electronic control unit 16 each time, for example, a predetermined crank angle position is detected by the crank angle position sensor 22.
In step 50, a purge control valve (P
CV) 30 is opened (on). If this determination result is positive, the purge control valve 30 was opened (
(step 51).

If the determination result in step 51 is negative, that is, it was off last time and it is on this time, it means that the purge control valve 30 was opened from off to on during the previous execution of the program and the current execution time. If so, step 55
Then, the feedback correction coefficient value TFB is reset to the value 1.0, and the program ends.

If the determination result in step 51 is affirmative, that is, the purge control valve 30 is on both last time and this time, and there is no change in the operating state of the purge control valve 30, the program is ended without doing anything. .

On the other hand, if the determination result in step 50 is negative, that is, if the purge control valve 30 is closed (off) this time, the purge control valve 30 was also closed (off) when the program was executed last time. It is determined whether or not it has been completed (step 53). If the determination result in step 53 is negative, that is, it was on last time and off this time, it means that the purge control valve 30 was closed from on to off during the previous execution time and the current execution time of the program. In this case, the program proceeds to step 55 described above, resets the feedback correction coefficient value IFB to the value 1.0, and ends the program. If it is predicted that the air-fuel ratio will suddenly change to the lean side, the feedback correction coefficient value IFB
By setting 1.0 to a value larger than the current value, the air-fuel ratio can reach the theoretical air-fuel ratio more quickly (Figure 4 (C)).
(See the change in the feedback correction coefficient value IFB and the change in the air-fuel ratio shown by the broken line at time 11 of +dl).

On the other hand, if the determination result in step 53 is affirmative, that is, if the purge control valve 30 was off both last time and this time, and there is no change in the operating state of the purge control valve 30, the program is executed without doing anything. finish.

The feedback correction coefficient value IFB set as described above is applied to the arithmetic expression described above to calculate the valve opening time T of the fuel injection valve 20. electronic control unit) 1
6 supplies a drive signal corresponding to the valve opening time T thus calculated to the fuel injection valve 20 to open the fuel injection valve 20 and inject and supply the required amount of fuel to each cylinder of the engine 10.

In addition, in the above-mentioned embodiment, the feedback correction coefficient value IFB
is the vO□ value detected by the 02 sensor 21 as the predetermined judgment value V
The explanation has been given using an example of what is set by so-called integral term control, which adds or subtracts a minute value Δ■ to the IFB value depending on whether the vO□ value is larger than the VX value in comparison with x, but the feedback correction coefficient value The IFB setting method is not limited to this, but may be set by, for example, adding known proportional term control to the above-mentioned integral term control.

Furthermore, when the purge control valve 30 is opened from off to on, the feedback correction coefficient value IFB immediately before the valve opening is a normal value of 1.0 if the fuel supply system is well adjusted. In many cases, the purge control valve 30 is set to a value close to , so when the ON state of the purge control valve 30 is detected in step 50 of FIG. The current program may be terminated while keeping the numerical value IFB at its current value (the value set in the time routine program of FIG. 2).

Furthermore, in the above embodiment, the valve opening time T of the fuel injection valve 20
The calculation calculates the feedback correction coefficient IFB as K I
(A/N) value to correct this, and in the case of such a multiplication type correction coefficient, the K I X (A/N) value is multiplied as an invalid value, that is, a correction coefficient value. However, the value that does not substantially change the Klx (A/N) value is the value 1.
The feedback correction variable of the present invention is not limited to the multiplication type described above, but K 1 x
It may also be a type of correction variable that is added to the (A/N) value. The invalid value in this case is the value 0.

(Effects of the Invention) As described in detail above, according to the air-fuel ratio control method for an internal combustion engine of the present invention, the communication passage 1111 can be cut off or removed in the middle of the communication passage connecting the canister and the intake passage downstream of the throttle valve.
A solenoid valve that opens is provided, and the solenoid valve is opened during a specific operating state of the engine to discharge evaporated fuel into the intake passage, while the internal combustion engine When the opening/closing switching operation of the solenoid valve is executed during an air-fuel ratio feedback control operation in which the air-fuel ratio is controlled to a required value by correcting the amount of fuel supplied to the solenoid valve, the correction variable value at the time of switching of the solenoid valve is corrected. Since the variable value is reset to an invalid value that does not substantially change the fuel supply amount even if the fuel supply amount is corrected, the purge control valve is opened and closed during air-fuel ratio feedback control operation and the engine is not affected. Even if the supplied air-fuel ratio suddenly changes, it can be quickly stabilized to the required value, stabilizing engine operation, and improving exhaust gas characteristics and fuel efficiency. be effective.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a schematic configuration diagram of a fuel supply control device that executes the method of the present invention, and FIG. 2 shows a feedback correction system executed by the electronic control unit shown in FIG. 1. FIG. 3 is a flowchart showing the procedure for setting the numerical value IFB; FIG. The diagram is
This explains the inconvenience that occurs when the purge control valve is turned from on to off during air-fuel ratio foot bank control in the conventional air-fuel ratio control method, and describes the on-off state of the purge control valve (PCV), the output of the 02 sensor, and the feedback. 5 is a timing chart showing the relationship between the correction coefficient value IFB and each change over time in the air-fuel ratio. DESCRIPTION OF SYMBOLS 10... Internal combustion engine, 12... Intake pipe (intake passage), 16... Electronic control unit, 18...
Throttle valve, 20...Fuel injection valve, 21...o2
Sensor, 25... Fuel tank, 26... Purge passage (communication passage), 28... Canister, 3o... Purge control valve (electromagnetic valve). Applicant Mitsubishi Motors Corporation Agent Patent Attorney Kan Nagato Figure 3

Claims (1)

[Claims] During air-fuel ratio feedback control operation of an internal combustion engine in which the inside of the fuel tank is communicated with the intake passage on the downstream side of the throttle valve via the canister, a correction variable value is set according to the concentration of a specific component in the exhaust gas, and the correction variable is In the air-fuel ratio control method, the air-fuel ratio is controlled to a required value by correcting the amount of fuel supplied to the internal combustion engine according to the amount of fuel supplied to the internal combustion engine. A solenoid valve for blocking and opening a communication passage is provided, and the solenoid valve is opened during a predetermined operating state of the engine to discharge evaporated fuel into the intake passage, and the solenoid valve is switched to open and close during the feedback control operation. When the operation is executed, the correction variable value at the time of switching the solenoid valve is reset to an invalid value that does not substantially change the fuel supply amount even if the fuel supply amount is corrected as a correction variable value. An air-fuel ratio control method for an internal combustion engine, characterized in that: