JP2902646B2 - Engine air-fuel ratio control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device capable of appropriately setting an air-fuel ratio feedback correction coefficient at the time of starting acceleration.

[Prior art] Conventionally, when an engine is operated near a stoichiometric air-fuel ratio,
It is known that NOx, CO, and HC in exhaust gas are purified by a catalytic reaction.

Therefore, in an electronically controlled engine having a catalytic converter, in order to set the air-fuel ratio to the stoichiometric air-fuel ratio, the basic fuel injection amount obtained from the intake air amount and the engine speed is calculated from various sensors that detect engine operating state parameters. A control means is provided for performing fuel injection correction based on the output signal and air-fuel ratio feedback correction to calculate the actual fuel injection amount for the injector.

By the way, when the throttle valve is suddenly opened, such as when starting acceleration, an air-fuel ratio sensor that measures this air-fuel ratio
Overlean is temporarily detected, and the air-fuel ratio feedback correction is set in the increasing direction accordingly. Then, the air-fuel ratio sensor detects rich, and the air-fuel ratio feedback correction is set in the decreasing direction by the rich signal.

In this way, the air-fuel ratio at the time of transition, such as when starting acceleration, repeats rich and lean while gradually narrowing the correction range and returning to normal air-fuel ratio control,
In the meantime, there is a problem that it takes time to return to normal air-fuel ratio control due to engine malfunction such as insufficient torque.

As a countermeasure, for example, in JP-A-59-32644, when an acceleration start state is detected, the proportional constant (skip amount) of the air-fuel ratio feedback correction signal set based on the output signal of the air-fuel ratio sensor and the integral are calculated. By temporarily increasing the constant, the air-fuel ratio during the transition can be immediately returned to the stoichiometric air-fuel ratio.

[Problems to be Solved by the Invention] However, in this prior art, as shown in FIG. 5A, the proportional constant P and the integral constant I of the air-fuel ratio feedback correction signal KF / B are increased at the time of acceleration start. In this case, the difference between the maximum value KkH of the increase correction and the maximum value KL of the decrease correction becomes too large, and as shown in FIG. 5 (b), hunting of the air-fuel ratio occurs during the transition, resulting in good startability. , Cannot get acceleration.

Further, there is a time lag between the air-fuel ratio set by the fuel injection amount discharged from the injector and the air-fuel ratio feedback correction coefficient set by detecting the air-fuel ratio by the air-fuel ratio sensor. As described above, when the proportional constant P and the integral constant I of the air-fuel ratio feedback correction signal KF / B are increased at the time of acceleration start, the difference between the actual required air-fuel ratio becomes too large, and the exhaust emission Deterioration, fuel consumption, and output reduction will be caused.

[Object of the Invention] The present invention has been made in view of the above circumstances, and can appropriately set an air-fuel ratio at the time of starting acceleration, thereby eliminating insufficient output, improving fuel efficiency, and improving exhaust emission. It is another object of the present invention to provide an air-fuel ratio control device for an engine capable of obtaining stable starting performance and acceleration performance.

[Means for Solving the Problems] The present invention provides an air-fuel ratio control device for an engine having a control means for calculating a fuel injection amount to an injector based on an output signal of each sensor for detecting an operating state parameter of the engine. The control means reduces at least one of the proportional constant value and the integral constant value of the air-fuel ratio feedback correction signal set based on the output signal of the air-fuel ratio sensor during the set time during the acceleration start, thereby increasing the air-fuel ratio to the rich side. An arithmetic unit for shifting to the second position is provided.

[Operation] In the present invention, at least one of the proportional constant value and the integral constant value of the air-fuel ratio feedback correction signal, which is set based on the output signal of the air-fuel ratio sensor, is reduced during the set time during the acceleration start, and the air-fuel ratio is reduced. To the rich side.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 to 4 show an embodiment of the present invention. FIG. 1 is a schematic diagram of an engine control system, FIG. 2 is a block diagram of a control means, and FIG. 3 (a) is an air-fuel ratio feedback correction signal. FIG. 3B is a waveform diagram of the air-fuel ratio, and FIG. 4 is a flowchart showing the control procedure.

Reference numeral 1 in FIG. 1 denotes an engine body, and a signal disc plate 2 mounted on a crankshaft 1a of the engine body 1 is provided with a rotation speed sensor 3 also serving as a crank angle sensor, and a water jacket. A water temperature sensor 4 is exposed.

Further, an injector 5 faces the intake port 1b of the engine body 1, and a throttle valve 7 is interposed in the middle of an intake passage 6 communicating with the intake port 1b.
An air chamber 6a is formed immediately downstream thereof. Further, a throttle position sensor 8 is connected to the throttle valve 7. An air flow meter 9 is provided upstream of the intake passage 6.

On the other hand, an O2 sensor 11, which is an example of an air-fuel ratio sensor, faces the exhaust passage 10 of the engine body 1. Reference numeral 12 is a catalytic converter.

Reference numeral 13 denotes air-fuel ratio control means, as shown in FIG. 2, which is constituted by an electronic control unit mainly composed of a microcomputer. The air flow meter 9, the throttle position sensor 8, the water temperature sensor 4, the rotation speed sensor 3, and the O2 sensor 11 are connected to the input interface 14 of the air-fuel ratio control means 13. In addition, an injector 5 disposed in each cylinder (# 1 to # 4) is connected to an output interface 15 of the air-fuel ratio control means 13 by a drive circuit.
Connected via 16.

Further, the air-fuel ratio control means 13 includes the input interface 14, the output interface 15, and a bus line.
Connect via 17. A CPU (central processing unit) 18, a ROM 19, and a RAM 20, which are operation units, are provided. The ROM 19 includes a proportional constant map MPp and an integral constant map MPi, which will be described later.
And fixed data such as data, and a control program.

The RAM 20 temporarily stores output signals of the sensors after data processing at predetermined addresses. Also,
The CPU 18 calculates a fuel injection amount for the injector 5 from various data stored in the RAM 20 according to a program stored in the ROM 19.

That is, in the CPU 18, the air flow meter 9
The basic fuel injection amount Tp is calculated from the intake air amount Q measured by the above and the engine speed N measured by the speed sensor 3 (Tp = KINJ × Q / N KINJ: constant).

Then, the basic fuel injection amount Tp is obtained by various fuel injection correction coefficients (COEF) obtained from the cooling water temperature Tw measured by the water temperature sensor 4, the throttle opening θ measured by the throttle position sensor 8, and the intake air temperature. At the same time, the actual fuel injection amount Ti for the injector 5 is calculated by correcting the air-fuel ratio feedback correction coefficient KA / F obtained from the air-fuel ratio feedback value measured by the O2 sensor 11 (Ti = Tp × KA / F × COE
F).

The signal of the air-fuel ratio feedback correction coefficient KA / F is composed of an integral constant I and a proportional constant P, as shown in FIG. 3 (a). Is retrieved from an integral constant map MPi and a proportional constant map MPp, which are obtained in advance through experiments or the like in accordance with the air-fuel ratio feedback signal.

Further, the air-fuel ratio control means 13 is provided with a calculation unit for setting an air-fuel ratio feedback correction signal at the time of starting acceleration. The control procedure of this calculation unit will be described with reference to the flowchart of FIG.

At every predetermined time (for example, 5 msec) during the normal air-fuel ratio feedback control, the output signal of the throttle position sensor 8 is taken in.
To determine if the idle switch is ON or OFF (Step 1
01).

When the idle switch is OFF (that is, when the throttle valve 7 is opened and the vehicle is starting or accelerating), the timer T provided in the CPU 18 subtracts from the time set by the timer in step 107 described later. Start (step 102).

Next, at step 103, the subtraction value of the timer T is determined, and if the subtraction is being performed (T> 0), that is, if the predetermined time has not elapsed since the start acceleration or the transition to the acceleration state, the process proceeds to step 104. , And the end of subtraction (T =
In the case of 0), the process proceeds to step 108.

If the timer T is in the process of subtraction, step 104
Sets the start correction amount K to a value a (a <1) smaller than 1. The value of a is preset at a uniform value such as 60%, or a certain width (for example, between 20% and 80%).
It is conceivable that the setting is made by, for example.

Next, at step 105, a proportional constant value P and an integral constant value I constituting an air-fuel ratio feedback correction coefficient are retrieved from the output signal of the O2 sensor 11 from the proportional constant map MPp and the integral constant map MPi stored in the ROM 19.

In step 106, the proportional constant P and the integral constant I of the actual air-fuel ratio feedback correction coefficient KA / F are calculated from the proportional constant value P and the integral constant value I, and the start correction amount K.

On the other hand, when it is determined in step 101 that the idle switch of the throttle position sensor 8 is ON (when the throttle valve 7 is fully closed and the vehicle is in an idle state in which the vehicle is stopped or in a coasting state in which the vehicle is running),
Proceeding from step 101 to step 107, the timer T
Is set by the timer. Then, after the starting correction amount is set to "K = 1" in step 108, the routine proceeds to step 105, where a normal air-fuel ratio feedback correction coefficient KA / F is calculated.

As described above, the proportional constant P and the integral constant I, which constitute the air-fuel ratio feedback correction coefficient, are set to 1 for a predetermined time during the start acceleration.
By correcting with a smaller coefficient K, as shown in FIG. 3A, the proportional constant value P and the integral constant value I are reduced, and the air-fuel ratio feedback correction coefficient KA / F is set. As a result, as shown by the solid line in FIG. 3 (b), during start acceleration, after the air-fuel ratio shifts to the rich side due to the increase in acceleration, the correction is slowly made until the air-fuel ratio becomes lean. As a result, the air-fuel ratio is slightly shifted to the rich side for a predetermined time during the start acceleration, and the air-fuel ratio during the transition does not show the hunting as shown by the one-dot chain line in the prior art, and the normal air-fuel ratio is smooth. The control can be returned to the fuel ratio control, and stable starting performance and acceleration performance can be obtained.

Note that the present invention is not limited to the above-described embodiment. For example, one of the proportional constant P and the integral constant I, which constitute the air-fuel ratio feedback correction coefficient, may be reduced at the time of starting acceleration.

[Effect of the Invention] As described above, according to the present invention, the set time during acceleration and start and the proportional constant value and the integral constant value of the air-fuel ratio feedback correction signal set based on the output signal of the air-fuel ratio sensor are set. At least one of them is decreased, and at least one of the proportional constant value and the integral constant value of the air-fuel ratio feedback correction is set smaller than usual, so that the control gain is reduced. From the state where the fuel ratio is forcibly shifted to the rich side, the air-fuel ratio can gradually and gradually converge to the stoichiometric air-fuel ratio,
Thereby, hunting of the air-fuel ratio at the time of acceleration start can be prevented.

In addition, since the air-fuel ratio hunting at the time of starting acceleration can be prevented and the air-fuel ratio can be set appropriately, it is possible to improve the fuel efficiency and the exhaust emission at the time of starting acceleration. Also, while preventing air-fuel ratio hunting,
At this time, since a rich air-fuel ratio is secured, an excellent effect is achieved such that output shortage can be resolved and stable starting performance and acceleration performance can be obtained.

[Brief description of the drawings]

1 to 4 show an embodiment of the present invention. FIG. 1 is a schematic diagram of an engine control system, FIG. 2 is a block diagram of a control means, and FIG. 3 (a) is an air-fuel ratio feedback correction signal. FIG. 3 (b) is a waveform diagram of the air-fuel ratio, FIG. 4 is a flowchart showing the control procedure, and FIG.
FIG. 5A is a waveform diagram of the air-fuel ratio feedback correction signal at the time of starting acceleration, and FIG. 5B is a waveform diagram of the air-fuel ratio. DESCRIPTION OF SYMBOLS 1 ... Engine body, 4, 8, 9, 11 ... Sensor, 5 ... Injector, 13 ... Air-fuel ratio control means, 18 ... Calculation part (CPU), KA / F ...
Air-fuel ratio feedback correction coefficient, I: proportional constant, P: integral constant, N, Tw, θ, Q, A / F: output signal.

Claims (1)

(57) [Claims] 1. An air-fuel ratio control system for an engine, comprising: control means for calculating a fuel injection amount to an injector based on an output signal of each sensor for detecting an operation state parameter of the engine. A setting unit for reducing at least one of the proportional constant value and the integral constant value of the air-fuel ratio feedback correction signal set based on the output signal of the air-fuel ratio sensor to shift the air-fuel ratio to the rich side. An air-fuel ratio control device for an engine, comprising: