METHOD FOR FEEDBACK OR OPEN-LOOP CONTROLLING THE AIR-FUEL RATIO OF AN ENGINE CORRESPONDING TO TEMPERATURE OF CATALYST AND SURFACE TEMPERATURE OF AN EXHAUST MANIFOLD

摘要

PURPOSE: A control method of air-fuel ratio of an engine is provided to expand the feedback control range by feedback-controlling the air-fuel ratio of the engine according to the surface temperature of the exhaust manifold and the temperature of the catalyst. CONSTITUTION: An engine control unit decides the feedback and open-loop control coexistence range according to the detected air amount from an air flow sensor and engine rpm from an engine rpm sensor, and detects the sudden acceleration state based on the signals from a throttle valve position sensor(S1,S2). The engine control unit open-loop controls the air-fuel ratio to 13.5 in suddenly accelerating, and compares surface temperature of an exhaust manifold from a surface temperature sensor with the first reference surface temperature(S3,S4). The engine control unit compares the catalyst temperature from a catalyst temperature sensor with the first reference temperature, and feedback-controls with the theoretical air-fuel ratio of 14.5(S5,S6). The engine control unit open-loop controls with the rich air-fuel ratio if the catalyst temperature is over the first reference temperature, and compares the surface temperature of the exhaust manifold with the second reference surface temperature and the catalyst temperature with the second reference temperature(S7,S8).