JPS61283742A - Method of controlling air-fuel ratio of engine - Google Patents

Abstract

PURPOSE:To enhance the durability of an engine, by using the temperature of exhaust gas as one of compensating factors for the air-fuel ratio of the engine in a high output power range of the latter to control the amount of fuel when the temperature of exhaust gas exceeds a predetermined value, thereby it is possible to prevent a catalyst converter from overheating. CONSTITUTION:A feed-back control through an oxygen sensor 10 is released when a high output power range of an engine is detected in accordance with signals from a throttle valve opening degree sensor 4, an intake-air pipe pressure sensor 5 and an engine rotational speed sensor 12. Further, an electrical signal generated from an exhaust temperature sensor 11 is used as one of compensating factors for the air-fuel ratio of the engine, and when the temperature of exhaust gas exceeds a predetermined value, the amount of fuel is controlled to decrease the air-fuel ratio in order to lower the temperature below a predetermined temperature. With this arrangement, it is possible to prevent a catalyst converter from overheating and to enhance the durability of the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the air-fuel ratio of an engine, particularly in a high output range, and is used for controlling the air-fuel ratio of an engine equipped with a feedback type electronic fuel control system. .

Conventional technology and its problems When a feedback type electronic fuel control system is adopted for a fuel system using an injection method or a carburetor method to control the air-fuel ratio of the air-fuel mixture supplied to the engine, when the conditions are met, It is well known that the feedback control by the oxygen sensor is canceled to change the stoichiometric air-fuel ratio to a desired air-fuel ratio.

For example, in the high output range of the engine, that is, in the high load and high speed range, a high concentration mixture for output is supplied.

Feedback control is canceled in the high output range based on the throttle valve opening, suction pipe pressure, and engine speed. By the way, in engines equipped with a catalytic converter for exhaust purification, the amount of secondary air introduced into the exhaust system is controlled to prevent the catalyst from overheating and being damaged when the exhaust temperature reaches high temperatures. . Measures are taken to lower the exhaust temperature, such as by canceling feedback control and controlling the fuel to increase the air-fuel ratio.

Therefore, if the exhaust temperature becomes high while supplying a high-concentration air-fuel mixture with a small air-fuel ratio in the high output range, the air-fuel ratio will be increased in the engine without a secondary air control system. There is a problem in that the correction function that performs fuel control works and the output mixture cannot be obtained.

Means for Solving the Problems The present invention aims to reduce the combustion temperature as the air-fuel ratio decreases, and therefore the exhaust temperature (tends to decrease) in the high output range of engine/engine, especially at full throttle speed. The exhaust temperature is added to the air-fuel ratio correction factor when oxygen sensor/gas feedback control is canceled in the engine's high output range.

This is a means to solve the above problem by controlling the fuel to decrease the air-fuel ratio when the temperature of the exhaust gas reaches a certain level or higher to lower the temperature to a certain level or lower.

An embodiment of the present invention will be described based on the drawings.

The intake pipe system 2 of the engine 1 includes sensors 3.4.5 for air flow rate, throttle valve opening, and intake pipe pressure, and a throttle valve 6. A fuel injection valve 7 is provided, a three-way catalytic converter 9 and oxygen and exhaust temperature sensors 10 and 11 are provided in the exhaust pipe system 8, and a rotational speed sensor 12 is provided in the engine l. It is being

The electrical signals emitted by each of the units 3, 4, 5, 10, and 11.12 are sent to an electronic control unit (13), where they are processed and a mixture of a predetermined air-fuel ratio is supplied to the engine. A drive signal is sent to the fuel injection valve 7 so that the fuel injection valve 7 is activated.

When the air-fuel ratio is not corrected, the fuel injection valve 7 is driven to control the air-fuel mixture to the stoichiometric air-fuel ratio based on the electric signal sent from the oxygen sensor 10. When it is determined that the output is in the high output range based on the electrical signals from the rotational speed sensors 4, 5.12, the feedback control by the oxygen sensor IO is canceled and the fuel injection amount is increased to reduce the air-fuel ratio. This increase is limited to the amount required for high output operation at that time, taking into account the load and rotational speed of the engine 1. Also, when it is determined that the output is in the high output range, the exhaust temperature sensor 1
The electric signal emitted by 1 is added to the air-fuel ratio correction element, and the
1 and the temperature of the three-way catalyst co/parter 9 are monitored. When the exhaust gas reaches a certain temperature, for example, 800°C or higher, the fuel injection amount is increased to further reduce the air-fuel ratio if the sensor 5.12 for throttle valve opening and engine rotational speed determines that the engine is fully open at high speed. .

This lowers the combustion temperature and exhaust temperature. When the exhaust temperature exceeds a certain level in a high output range other than at full throttle high speed, depending on the engine speed, the fuel is controlled to increase the air-fuel ratio to lower the exhaust temperature at the expense of output.

In a carburetor type fuel system, fuel control is performed directly or indirectly by controlling fuel or bleed air.

According to the present invention, exhaust temperature is added to all air-fuel ratio correction elements in the high output range, and the exhaust temperature is kept constant by taking advantage of the fact that combustion temperature tends to decrease as the air-fuel ratio decreases when the engine is fully open and at high speed. When the temperature exceeds the temperature, the fuel is controlled to further reduce the air-fuel ratio to bring the temperature below a certain level, thereby preventing overheating of the catalytic converter while supplying the output air-fuel mixture and further improving the durability of the engine. It is something that can be done.

[Brief explanation of drawings]

The drawing is a layout diagram of an embodiment of the present invention. l...Engine, 2...Intake pipe system, 4
... Throttle valve opening degree, 5... Suction pipe pressure. 7...Fuel injection valve, 8...Exhaust pipe system,
9... Three-way catalytic converter, 10...
Oxygen sensor, 11... Exhaust temperature sensor, 12.
...Rotation speed sensor. 13... Control unit.

Claims (1)

[Claims] When the feedback control of the oxygen sensor is canceled in the high output range of the engine, the exhaust temperature is added to the air-fuel ratio correction element, and when the exhaust temperature exceeds a certain temperature, the fuel is controlled in the direction of reducing the air-fuel ratio. A method for controlling an air-fuel ratio of an engine, which is characterized by lowering the air-fuel ratio to below a certain temperature.