Method for preventing overheating of an exhaust purifying device

Abstract

A method for preventing overheating of an exhaust purifying device by means of an air-flow sensor for sensing the amount of air drawn into an engine to generate an analog voltage corresponding to the amount of air drawn, an intake-air temperature sensor for sensing the temperature of the air drawn into the engine to generate an analog voltage corresponding to the temperature of the air drawn, a water temperature sensor for sensing the temperature of the engine cooling water temperature to generate an analog voltage corresponding to the cooling water temperature, a temperature sensor mounted on a converter, an RPM sensor for sensing the rotational speed of the engine to generating a pulse signal of a frequency corresponding to the engine speed, and a circuit responsive to the detection signals from the sensors for computing the desired amount of fuel injected. The computing circuit controls the ON and OFF periods of fuel injection valves to adjust the fuel injection quantity. When the exhaust temperature exceeds a predetermined value, the air-fuel ratio is compensated for the then current engine operating conditions and the compensation amount is then stored in a memory, whereby each time the same engine operating conditions are repeated, the air-fuel ratio is compensated in accordance with the stored compensation data to thereby prevent overheating of the exhaust purifying device.