JPS6238846A - Air-fuel ratio control method for engine - Google Patents

Abstract

PURPOSE:To prevent the fall in acceleration performance, by temporarily suspending theoretical air-fuel ratio control at the shifting of an engine from idling to non-idling when the engine is set to operate with a mixture at a theoretical air fuel ratio below a prescribed rotation speed. CONSTITUTION:When a throttle valve 17 is opened in idling in which a control valve 15 is regulated to feed a mixture at a theoretical air-fuel ratio, it is judged by a control unit 16 from an electric signal or non-idling signal from a position sensor 18 that an accelerating operation is under way. At that time, theoretical air-fuel ratio control based on an electric signal from an O2 sensor 22 is suspended, and the duty factor of a control valve drive signal is fixed to an optional value for a preset optional time to regulate the control valve 15. When the preset optional time has elapsed, the theoretical air-fuel ratio control is resumed. The air-fuel ratio is thus prevented from temporarily becoming thin at the accelerating operation. This results in enhancing acceleration performance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the air-fuel ratio of an engine, and is used for controlling the air-fuel ratio of an engine used as a power source for an automobile, a work vehicle, an industrial machine, etc. .

The technology of detecting the operating state of the engine and controlling the air-fuel ratio using a feedback method is widely known, and the basic supply amount of fuel is set according to the amount of intake air. Taking these factors into consideration, corrections are made in accordance with the operating conditions of the engine to achieve a predetermined air-fuel ratio. The air-fuel ratio is controlled by a control valve that is driven by a pulse waveform drive signal for either fuel or air. Normally, the output is from a control unit of a type.

Here, excluding the high output range (in the normal operating range, below a certain rotation speed and above the suction negative pressure, operation is performed at the stoichiometric air-fuel ratio to reduce emissions and take measures against exhaust gas, but above a certain rotation speed,
If you create a control system that measures fuel economy by operating at a lean air-fuel ratio below the suction negative pressure, the control will operate at the stoichiometric air-fuel ratio even when accelerating from an idle state, so depending on the degree of acceleration, The disadvantage is that the increase in fuel cannot correspond to the increase in air volume, resulting in a temporary lean air-fuel ratio, which may reduce acceleration performance.For this reason, a separate acceleration correction means must be provided, which complicates the control system. There is a problem.

Means for Solving the Problems The present invention controls an air-fuel ratio by driving a control valve that controls at least one of fuel and air using a pulse waveform drive signal.

The engine is set to operate at a stoichiometric air-fuel mixture below a certain rotational speed or above a negative suction pressure, and uses a throttle valve position sensor to distinguish between idle and off-idle to shift from idle to off-idle. The above-mentioned problem is solved by canceling the stoichiometric air-fuel ratio control based on the feedback method for an arbitrary period of time, fixing the duty value of the drive signal at an arbitrary value, and driving the control valve.

Example Embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a case where the present invention is implemented in an engine using LPG as fuel. LPG in a pressure-resistant container 1 is reduced in pressure to about atmospheric pressure in a vaporizer 2, passes through a main fuel passage 4 having a jet 3, and enters a venturi. The air enters an annular chamber 7 formed along the line 6, is sucked out through a slit-shaped main nozzle 8 into an intake passage 9, mixes with air, and is supplied to the engine 11 through an intake manifold IO. The exhaust gas is purified by a three-way catalytic converter 13 in an exhaust pipe 12 and released into the atmosphere.

An increase fuel passage 14 is provided which branches from the upstream side of the jet 3 in the main fuel passage 4 and is connected to the annular chamber 7, and this passage 14 is provided with an electromagnetically driven control valve 15.
The control valve 15 is opened and closed according to the duty value of the pulse waveform drive signal sent from the electronic control unit 16 to control the increased amount of fuel so that the required air-fuel ratio is achieved.

Here, the position sensor 1B of the throttle valve 17 installed in the mixer 5, the pressure sensor 19 installed in the intake manifold IO
．． Engine 11 rotational speed sensor 20 and temperature sensor 21. Oxygen sensor 22 provided in the exhaust pipe 12. Further, there are provided, as necessary, units (not shown) for detecting the intake air temperature, ignition switch, brake, and other operating conditions of the engine 11, and electrical signals from these units are sent to the control unit 16. , control unit 16
calculates the optimum conditions based on this information, issues a drive signal to open and close the control valve 15 at a predetermined duty ratio, or maintains the valve closed state or open state, and further changes the duty value of the drive signal. let Here, the 9-position sensor 18 used has the function of distinguishing between the idle state and the off-idle state of the throttle valve 17 and issuing a switching signal.

Further, as shown in the control map in Fig. 2, the rotational speed of the engine 11 is kept at a constant value No. 1 in the normal operating range excluding the high output operating range.
and below and the suction negative pressure is below the constant value Po (Al
and 2 the operating region (Bl) where the rotational speed is above a certain value No and the suction negative pressure is below a certain value Po, and the former operating region (
Al operates with a mixture at the stoichiometric air-fuel ratio and operates in the latter operating region (B
l is set to operate with a lean air-fuel mixture.

Further, the high output operating range (C) is set to operate with a mixture having an output air-fuel ratio.

In this embodiment with such a configuration, during idle linking, it is detected that the throttle valve 17 is at the idle position based on the electric signal from the position sensor 18, that is, the idle signal, so the electric signal from the temperature sensor 21 detects that the engine temperature is low. Except when this is detected, the control valve 15 is driven so as to supply the air-fuel mixture at the stoichiometric air-fuel ratio.

When the idle link ends and the throttle valve 17 opens, it is determined that acceleration operation is in progress based on the electric signal from the 2-position sensor 18, that is, the off-idle signal. At this time, oxygen
The stoichiometric air-fuel ratio control based on the two electric signals is canceled, and the duty value of the drive signal is fixed at an arbitrary value for a preset arbitrary time to drive the control valve 15.

The stoichiometric air-fuel ratio control is restarted when the above-mentioned time has elapsed, and an example of the operating range during acceleration with a fixed duty value is shown in range D in FIG.

FIG. 3 is an example of a waveform diagram of a drive signal for air-fuel ratio control, and when the 1-position sensor 18 is generating an idle signal, waveform a for controlling the stoichiometric air-fuel ratio is sent to the control valve 15. When the position sensor 18 issues an off-idle signal, a fixed value waveform is sent to keep the control valve 15 fully open.

After the set time has elapsed, waveform C is sent to the control valve 15 for controlling the stoichiometric air-fuel ratio again. The fixed value waveform may have a duty value larger than that of waveform a (it is not limited to the waveform shown in FIG. 2).

The suction negative pressure is below a certain value Po or the rotation speed is a certain value No.
In the lean air-fuel ratio operating region determined as above (in Bl, based on electrical signals from the oxygen sensor 22 and other sensors (feedback control is canceled and the control valve 15 is held in the closed state, the jet 3 is metered) ■ of the basic supply amount, only PG is sent to the mixer 5, and the mixture with a lean air-fuel ratio is sent to the engine 11.
to measure fuel economy.

The high output operating range (
Transition to C1 1 For example, when it is detected that the throttle valve 17 has opened at 60 degrees or more, the control valve 15 is driven at a large duty value so that a mixture with a high concentration output air-fuel ratio is supplied. or hold the valve in the open position.

The above is an explanation of the basic method of controlling the air-fuel ratio.1 For example, when the engine is off-idle.

It goes without saying that when the intake air is at a low temperature, the control valve 15 increases the amount of fuel necessary.
It is applied not only to gaseous fuels such as but also to those that supply liquid fuel by a vaporizer method or a fuel injection method.In a vaporizer method, at least one of the fuel and bleed air is controlled by a control valve, In this case, the injection valve constitutes the control valve.

According to the present invention, when the engine is set to operate with a mixture at a stoichiometric air-fuel ratio below a certain rotational speed or above a certain suction negative pressure, the stoichiometric air-fuel ratio control is temporarily canceled when transitioning from idle to off-idle. Therefore, the duty value of the control valve drive signal can be arbitrarily fixed.

It is possible to accelerate while maintaining the air-fuel mixture near the stoichiometric air-fuel ratio by increasing the amount of fuel in response to the increase in the amount of air, which not only does not reduce acceleration performance, but also eliminates the need for a separate acceleration correction means, resulting in simple control. A system can achieve a goal.

[Brief explanation of drawings]

11...engine, 14...°° increase fuel passage, 15...control valve, 16...control unit), 18...position setting /su, 22・old...
oxygen senna.

Claims (1)

[Claims] When controlling the air-fuel ratio by driving a control valve that controls at least one of fuel and air using a pulse waveform drive signal, the air-fuel ratio is lower than the stoichiometric air-fuel ratio below a certain rotational speed or above a negative suction pressure. In addition to setting the engine to operate with an air-fuel mixture, a throttle valve position sensor that detects and distinguishes between idle and off-idle is used to cancel stoichiometric air-fuel ratio control using a feedback method for an arbitrary period of time when transitioning from idle to off-idle. A method for controlling an air-fuel ratio of an engine, comprising driving a control valve while fixing a duty value of the drive signal to an arbitrary value.