JPS6238843A - Air-fuel ratio control method for engine - Google Patents

Abstract

PURPOSE:To secure good acceleration performance, by continuing an operation at a theoretical air-fuel ratio for a preset time before the operation is shifted from a theoretical air-fuel ratio operation range to a thin air-fuel ratio operation range. CONSTITUTION:When a throttle valve 17 is opened in a state of idling in which a control valve 15 regulated to feed a mixture at a theretical air-fuel ratio, the control valve is driven on the basis of the output of an O2 sensor 22 to feed the mixture at the theoretical air-fuel ratio, in a theoretical air-fuel ratio operation range in which it is judged by a control unit 16 from the outputs of a pressure sensor 19 and a rotation speed sensor 20 that the intake negative pressure is not less than a prescribed value Po or the rotation speed is not more than a prescribed value No. When the operation is to be shifted, after the acceleration of an engine, from the theoretical air-fuel ratio operation range to a thin air-fuel ratio operation range in which it is judged that the intake negative pressure is not more than the value Po or the rotation speed is not less than the value No, the shifting is delayed for a preset time so that the operation at the theoretical air-fuel ratio is continued.

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, or the like.

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 at least either fuel or air. It is usually output from the control unit.

Here, excluding the high output range (in the normal operating range, when the rotation speed is lower than the constant suction negative pressure, the engine is operated at the stoichiometric air-fuel ratio to reduce emissions and take measures against exhaust emissions, but the rotation speed is lower than the constant suction negative pressure). If a control system is created to measure fuel economy by operating at a lean air-fuel ratio above the rotational speed, the boundary between the two operating ranges will be constant, and as soon as this boundary is crossed, air-fuel ratio correction will be performed. When the operating state exceeds two operating ranges, it is detected by the suction negative pressure and the air-fuel ratio is switched.

In order to solve the above problem by aggravating the drawback that depending on the degree of acceleration, the system immediately shifts to a lean air-fuel ratio operating range and impairs acceleration performance, an acceleration correction means must be provided separately, so control is required. The problem is that the system becomes complicated.

The present invention controls the air-fuel ratio by driving a control valve that controls either fuel or air flow using a pulse waveform drive signal.

If the operating range is set so that when the suction negative pressure is below a certain level in the normal operating range, the air-fuel mixture is operated at a stoichiometric air-fuel ratio, and when the suction negative pressure is below a certain level, the air-fuel mixture is operated at a lean air-fuel ratio, then a simple control system can be used. The system is designed to provide acceleration performance that is set in advance even after the suction negative pressure exceeds the above-mentioned constant value when the operating state shifts from the stoichiometric air-fuel ratio operating region to the lean air-fuel ratio operating region. A passage 14 was provided to continue operation at the stoichiometric air-fuel ratio for a certain period of time, and this passage 14 was provided with electromagnetic drive means.

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 container 1 is reduced in pressure to about atmospheric pressure in a vaporizer 2, and passes through a main fuel passage 4 having a jet 3. The air enters the annular chamber 7 formed along the petulary 6, is sucked out through the slit-shaped main nozzle L/8 into the intake passage 9, mixes with air, and is supplied to the engine 11 through the intake manifold 10. 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 flow control valve 15 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 controls the duty of a pulse waveform drive signal sent from an electronic control unit 16. According to the value, the control valve 15 is opened and closed to control the increased amount of fuel so that the required air-fuel ratio is achieved.

Here, the position sensor 18 of the throttle valve 17 installed in the mixer 5. Pressure cassette 19 provided in the intake manifold 10
．． rotational speed sensor 20 and temperature sensor 21 of the mechanical/shifter 11. Oxygen sensor 22 provided in the exhaust pipe 12. Furthermore, sensors (not shown) for detecting intake air temperature, ignition switch, brake, and other operating conditions of the engine 11 are provided as necessary, and electrical signals from these sensors are sent to the 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

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 an operating region (Bl) in which the 1-rotation 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.

Furthermore, the high output operating range (C1 is set to operate with the air-fuel mixture at the output air-fuel ratio.The shift in operating state across the stoichiometric air-fuel ratio operating range (N) and lean air-fuel ratio operating range (Bl) indicates that It is identified by the suction negative pressure detected by the cell/cell 19.

In the present embodiment having such a configuration, during idle linking, the electric signal from the position sensor 18, that is, the idle signal, detects that the throttle valve 17 is at the idle position, so the electric signal from the temperature sensor 21 detects that the throttle valve 17 is in the idle position. The control valve 15 is driven to supply the air-fuel mixture at the stoichiometric air-fuel ratio except when it is detected that the engine temperature is low.

When the idle link ends and the throttle valve 17 opens, the electrical signals from the pressure sensor 19 and rotation speed sensor 20 indicate that the suction negative pressure of the engine/11 is below a certain value Po or the rotation speed is below a certain value No. The control valve 15 is driven so that a mixture of the stoichiometric air-fuel ratio is supplied based on the electric signal from the oxygen sensor 22 in the stoichiometric air-fuel ratio operating region (At). By setting the operating range (Al) so that the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio within the city running speed range,
It is possible to drive in a state where the exhaust gas purification efficiency by the three-way catalytic converter 13 is maximized.

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 (B) determined as above, feedback control based on electrical signals from the oxygen sensor 22 and other sensors is canceled, the control valve 15 is held in a closed state, and the jet 3 is used to measure the air-fuel ratio. Only the basic supply amount of LPG is sent to the mixer 5, and a mixture with a lean air-fuel ratio is supplied 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.

When the negative pressure signal or rotational speed signal detects that the engine has decelerated from the lean air-fuel ratio operating region (Bl) to the stoichiometric air-fuel ratio operating region (Al), the feedback control based on the electrical signal from the oxygen sensor 22 is resumed. The control valve 15 is driven so that the air-fuel mixture at the stoichiometric air-fuel ratio is supplied.

When the engine operating in the stoichiometric air-fuel ratio operating region accelerates and moves toward the lean air-fuel ratio operating region (B), the suction negative pressure decreases and becomes a constant value Po regardless of whether the engine is accelerating.
The following is true. In this way, when the suction negative pressure goes from above a certain value Po to below, the timer built into the control unit 16 is activated and the operation starts for a preset period of time or an arbitrary period of time set according to the degree of acceleration. This delays the region switching and continues operation at the stoichiometric air-fuel ratio. When the above-mentioned time has elapsed, the operation shifts to the lean air-fuel ratio operating range [Bl].

The above is an explanation of the basic method of controlling the air-fuel ratio.2 For example, when the engine is off-idle.

It goes without saying that when the intake air is at a low temperature, the necessary fuel amount is increased by the control valve 15. It is also applied to the supply of fuel, and in the carburetor method, there is a small amount of fuel and bleed air (either of which is controlled by a control valve, and the fuel injection method 11... Engine, 14... Increased fuel In the channel 15, the injection valve constitutes a control valve.

According to the present invention, the normal operating range of the engine is divided into the stoichiometric air-fuel ratio operating range and the lean air-fuel ratio operating range depending on the suction negative pressure, so that emission measures, drivability, and fuel economy can be adjusted according to the operating range. Not only can it be measured, but also the preset time can be theoretically measured even after the suction negative pressure exceeds a certain value set as a boundary, especially during acceleration when the operating state shifts from the stoichiometric air-fuel ratio operating range to the lean air-fuel ratio operating range. Since operation is continued based on the air-fuel ratio, a simple control system does not reduce acceleration performance.

[Brief explanation of drawings]

FIG. 1 is a layout diagram of an embodiment of the present invention, and FIG. 2 is a control map diagram. ... Control valve, 16 ... Control unit,
19... Pressure case/su, 22... Oxygen cell V. Figure 1

Claims (1)

[Claims] In 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 mixture of the stoichiometric air-fuel ratio is achieved at a constant suction negative pressure or higher in the normal operating range. The operating range is set so that the air-fuel mixture is operated with a lean air-fuel ratio below a certain suction negative pressure, and when the operating state shifts from the stoichiometric air-fuel ratio operating range to the lean air-fuel ratio operating range, the intake negative pressure is A method for controlling an air-fuel ratio of an engine, comprising continuing operation at a stoichiometric air-fuel ratio for a preset time even after the pressure exceeds the certain value.