JPH02286845A - Air-fuel ratio control method for engine - Google Patents

Abstract

PURPOSE:To have proper control of the air-fuel ratio in close accordance with the engine operating condition under running, by changing at least either of the skip value of an air-fuel ratio feedback correction factor and the integral constant in compliance with the car speed. CONSTITUTION:An electronic control device 4 corrects the fundamental injection amount determined from an engine rotation signal (b) and suction pressure signal (c) with an air fuel ratio feedback correction factor FAF etc. to serve determining of the fuel injection amount. In the case that the car speed is below the set value, the initial skip set value on the incremental side of correction factor FAF is set in a specified address. In the case over the set car speed value, a specified skip correction amount is added to the initial skip set value on the incremental side of correction factor FAF, and the result is set in specified address, followed by transfer to the main routine. Thereby the fundamental injection amount is corrected on the basis of initial correction factor FAF in case the car speed is below the set value, and in opposite case, the skip value on the incremental side of correction factor FAF is substituted with a larger value to cause shift of the value of air fuel ratio to the theoretical value side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an engine air-fuel ratio control method that can be suitably employed when feedback-controlling the air-fuel ratio of an air-fuel mixture to near the stoichiometric air-fuel ratio.

[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 (three-way catalyst window) centered around the stoichiometric air-fuel ratio. Otherwise, it will not be possible to efficiently purify all Go, HC, and NOX contained in the exhaust gas. Therefore, in engines equipped with fuel injection valves, the basic injection amount is finely adjusted using an air-fuel ratio feedback correction coefficient to maintain the air-fuel ratio of the air-fuel mixture within the window of the three-way catalyst. That is, when the output signal of the oxygen sensor that detects the oxygen concentration in exhaust gas indicates a rich air-fuel ratio, the correction coefficient is skipped to the decreasing side by the skip value, and then the correction coefficient is set to a constant value based on the integral constant. By gradually decreasing the value, the fuel supply amount is restricted and the air-fuel ratio of the air-fuel mixture is changed to the stoichiometric air-fuel ratio side. On the other hand, when the output signal of the oxygen sensor indicates a lean air-fuel ratio state, the correction coefficient is skipped to the increasing side by the skip value, and then gradually increased by a constant value based on the integral constant. The amount of fuel supplied is increased to change the air-fuel ratio of the air-fuel mixture toward the stoichiometric air-fuel ratio.

However, the actual required values for fuel and the like vary depending on the driving conditions of the vehicle. For this reason, some systems use parameters such as intake pipe pressure and engine speed to switch the air-fuel ratio feedback correction coefficient. In addition, as a prior art of the present invention, for example, as shown in Japanese Patent Application Laid-Open No. 191639/1982, the air-fuel ratio feedback correction coefficient is increased during acceleration and deceleration of the engine (and when the engine is in steady operation, There are also examples in which the air-fuel ratio feedback correction coefficient is made small.

[Problems to be Solved by the Invention] However, with such a configuration, the influence of the running wind when the vehicle is running is not taken into consideration, so it is difficult to perform air-fuel ratio control suitable for the engine condition when the vehicle is running. In other words, even if the intake pipe pressure and engine speed are the same, if the shift position of the transmission is different, the vehicle speed will change, various temperature conditions in the engine room will change, and the intake air temperature, fuel temperature, etc. will change. . Therefore, if intake pipe pressure or engine speed are used as parameters to substitute for these temperature changes when the vehicle is running, there is a high possibility that the fuel supply amount will not be adjusted accurately according to the engine status when the vehicle is running. .

The present invention aims to solve such problems.

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

That is, the engine air-fuel ratio control method according to the present invention changes the air-fuel ratio feedback correction coefficient based on the output signal of the oxygen sensor that detects the oxygen concentration in the exhaust gas, thereby adjusting the air-fuel ratio of the air-fuel mixture to the theoretical value. An engine air-fuel ratio control method that adjusts the air-fuel ratio to near the air-fuel ratio,
The present invention is characterized in that at least one of the skip value and the integral constant of the air-fuel ratio feedback correction coefficient is changed in accordance with the vehicle speed.

[Function] If the air-fuel ratio feedback correction coefficient is set to a small value when the inside of the engine room is relatively unaffected by the wind while the engine is running, the amount of increase or decrease in fuel will be small, and fluctuations in the air-fuel ratio of the air-fuel mixture will be suppressed. Ru. Therefore, it is possible to perform appropriate air-fuel ratio correction in response to temperature increases such as intake air temperature and fuel temperature during medium and low speed states of the vehicle.

On the other hand, if the air-fuel ratio feedback correction coefficient is increased when the engine compartment is easily affected by the wind while driving,
The responsiveness of air-fuel ratio control is increased along with the speed of fuel adjustment. Therefore, it is possible to quickly correct the air-fuel ratio in response to a tendency for the intake air temperature, fuel temperature, etc. to decrease when the vehicle is running at high speed.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

The engine schematically shown in FIG. 1 is used in an automobile and is equipped with an electronically controlled fuel injection device 1. The engine shown schematically in FIG. The electronically controlled fuel injection device 1 includes a fuel injection valve 3 attached to an intake pipe 2, and an electronic control device 4 that adjusts the amount of fuel injected from the fuel injection valve 3 according to engine conditions. Various information for adjusting the fuel injection amount and the like is input to the electronic control device 4.

The fuel injection valve 3 has a built-in electromagnetic coil, and when the fuel injection signal a is applied to the electromagnetic coil from the electronic control device 4, it injects fuel in an amount corresponding to the application time into the vicinity of the intake port. It is structured as follows.

The electronic control device 4 includes a central processing unit 5 and a memory 6.
It consists of a microcomputer unit equipped with an input interface 7 and an output interface 8. The input interface 7 receives at least an engine rotation signal from a crank angle sensor 9, an intake pressure signal C from a pressure sensor 10, a signal d from an idle switch IDL 11, and a signal for detecting vehicle speed. A vehicle speed signal e from the vehicle speed sensor 12, an output signal f from the oxygen sensor 13, and the like are respectively input. On the other hand, the output interface 8 outputs a fuel injection signal a toward the fuel injection valve 3.

The crank angle sensor 9 is configured to output an electrical signal corresponding to the engine speed, and is provided in the distributor 14. The pressure sensor 10 is attached to the surge tank 15 and is configured to output an electrical signal according to intake pipe pressure. The idle switch IDLII is an ONΦOFF switch that is turned on when the throttle valve 16 is in an idling position and turned off when it is in a non-idling position, and is coupled to the throttle shaft 17. The oxygen sensor 13 is for detecting the oxygen concentration in exhaust gas, and is arranged upstream of the three-way catalytic converter 18. This oxygen sensor 13 generates a low voltage when the air-fuel ratio of the air-fuel mixture is leaner than the conversion point that exists near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high. When the fuel ratio is on the richer side than the conversion point and the oxygen concentration in the exhaust gas is low, a high voltage can be generated.

The electronic control device 4 calculates the intake air amount from the engine rotation signal S, the intake pressure signal C, etc., and determines the basic injection amount TP according to the intake air amount. Then, the basic injection amount TP is corrected by the air-fuel ratio feedback correction coefficient FAP and various correction coefficients determined according to the engine condition to determine the fuel injection amount T. T = TPXPAF
XK), fuel is supplied to the combustion chamber 19 by opening the fuel injection valve 3 for a time corresponding to this fuel injection amount T.

Further, a program as schematically shown in FIG. 2 is set in the electronic control device 4 in order to change the air-fuel ratio feedback correction coefficient PAP in accordance with the vehicle speed state.

First, in step 51, it is determined based on the vehicle speed signal e whether the vehicle speed is equal to or higher than a set vehicle speed of 5PDo (for example, 80 km/h). If it is determined that the vehicle speed is not equal to or higher than the set vehicle speed SPD o, the process proceeds to step 52 and the set vehicle speed SPD o
If it is determined that the above is the case, the process proceeds to step 53. In step 52, the increasing side skip initial set value R3P0 of the air-fuel ratio feedback correction coefficient FAF selected from the map below is set at a predetermined address R8P, and the process proceeds to the main routine.

In step 53, the air-fuel ratio feedback correction coefficient PA
A predetermined skip correction amount A is added to the skip initial setting value R8P o on the increasing side of F, the value is set in a predetermined address R8P, and the process moves to the main routine.

AF According to such a configuration, when the vehicle speed is lower than the set vehicle speed SPD o in a predetermined driving range, the basic injection amount T is adjusted based on the initial air-fuel ratio feedback correction coefficient FAF.
P will be corrected. That is, the oxygen sensor 13
When the output voltage is leaner than the conversion point and the oxygen concentration in the exhaust gas is high, the air-fuel ratio feedback correction coefficient FAI' increases by the skip value R3P, as shown in Figure 3. After being skipped, the integral constant KIP
Based on o, - constant value P. It is gradually decreasing (
. Therefore, the fuel injection amount T supplied from the fuel injection valve 3
is increased, and the air-fuel ratio of the mixture changes to the stoichiometric air-fuel ratio side.

Further, when the output voltage of the oxygen sensor 13 is on the rich side than the conversion point and the oxygen concentration in the exhaust gas is low, after the air-fuel ratio feedback correction coefficient PAP is skipped to the decreasing side by the skip value R8M, Based on the integral constant KIN, it is gradually decreased by a constant value H (.For this reason,
The fuel injection amount T supplied from the fuel injection valve 3 is reduced,
The air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio.

On the other hand, when the vehicle speed exceeds the set vehicle speed SPD o, the skip value R8P o on the increasing side of the air-fuel ratio feedback correction coefficient FAF becomes a large value (RSP o +A).
replaced by Therefore, when the air-fuel ratio of the air-fuel mixture changes from rich to lean, the amount of fuel is quickly increased accordingly, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio.

When the throttle valve 13 is in a non-idle position (idle switch IDL/OFF >), except during warm-up, sudden acceleration, or sudden deceleration, the above control is repeatedly performed. The air-fuel ratio of the mixture is maintained near the stoichiometric air-fuel ratio.

Therefore, with such a configuration, the inside of the engine room is not easily affected by the running wind, and when the intake air temperature, fuel temperature, etc. tend to rise, the increase or decrease in fuel due to correction becomes small, Fluctuations in the fuel ratio are suppressed and maintained near the stoichiometric air-fuel ratio.

Therefore, combustion in the low and medium speed range can be stabilized, and exhaust gas purification efficiency, drivability, etc. can be improved.

On the other hand, if the air-fuel ratio changes to lean when the inside of the engine room is easily affected by the running wind and it is difficult for the intake temperature or fuel temperature to rise, the amount of fuel will be quickly increased and the air-fuel ratio will become the stoichiometric The fuel ratio is adjusted accordingly.

Therefore, combustion in the high-speed range can be stabilized, and exhaust gas purification efficiency, drivability, etc. can be improved.

In the above embodiment, only the increasing skip value of the air-fuel ratio feedback correction coefficient is changed, but the integral constant or both of these may be changed in accordance with the vehicle speed.

Furthermore, it goes without saying that the case where the increasing skip value is changed is not limited to the case where a correction value is added to the skip initial setting value. For example, as schematically shown in FIG. 4, there is a skip value R8P2 corresponding to a vehicle speed less than the set vehicle speed SPD o, and a skip value R8I corresponding to a vehicle speed equal to or higher than the set vehicle speed SPD o.
) and are set in advance, and these are selectively used based on vehicle speed determination (step 61) (step 62,
Step 63).

Further, in the above embodiment, the vehicle speed condition is set to two levels, but the vehicle speed condition may be set in detail as necessary. For example, if the vehicle speed is less than the set vehicle speed (
Vehicle speed < SPD o ) and within the setting range (SPD
o≦Vehicle speed≦SPD 1), and if it exceeds this (
It is also possible to subdivide into vehicle speed > SPD 1) and set corresponding skip values and integral constants. In this way, it becomes possible to perform air-fuel ratio control with even higher accuracy.

[Effects of the Invention] As described in detail above, the present invention changes the control value of the air-fuel ratio feedback correction coefficient in accordance with the vehicle speed, so that the control value of the air-fuel ratio feedback correction coefficient is changed accurately in accordance with the engine condition during actual driving. Air-fuel ratio control can be performed. As a result, it is possible to provide an engine air-fuel ratio control method with excellent controllability that can effectively improve exhaust gas purification efficiency, etc. within a wide range from low speed ranges to high speed ranges of a vehicle.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a schematic overall configuration diagram, FIG. 2 is a flowchart showing the control procedure, and FIG. 3 is a timing chart showing the control mode. It is. FIG. 4 is a flowchart corresponding to FIG. 2 showing another embodiment of the present invention. 1...Electronically controlled fuel injection device 3...Fuel injection valve 4...Electronic control device 12...Vehicle speed sensor 13...Oxygen sensor 18...Three-way catalytic converter

Claims (1)

[Claims] Engine air-fuel ratio control that adjusts the air-fuel ratio of the mixture to near the stoichiometric air-fuel ratio by changing the air-fuel ratio feedback correction coefficient based on the output signal of an oxygen sensor that detects the oxygen concentration in exhaust gas. 1. A method for controlling an air-fuel ratio of an engine, characterized in that at least one of a skip value and an integral constant of the air-fuel ratio feedback correction coefficient is changed in accordance with vehicle speed.