To control an engine so as to retain high efficiency by detecting lowering of efficiency so that lowering of efficiency caused by deterioration by the long time operation of the catalyst of an internal combustion engine is prevented.
A catalyst is located in the exhaust pipe of an engine. Sensors 7, 8 for detecting exhaust gas conditions are arranged in front and behind the catalyst. These sensors 7, 8 may be an oxygen sensor whose output is changed stepwise when, for example, λ=1, or a sensor whose output is changed in proportion to an air-fuel ratio. The detected values from both the sensors 7, 8 are incorporated into a control unit, catalyst purifying efficiency and the degree of deterioration of the catalyst are estimated based on the compared result and an engine is controlled so as to have the best efficiency. Lowering of efficiency of the catalyst caused by longtime operation is detected and the engine is controlled so as to avoid lowering of efficiency, therefore, high exhaust gas purifying characteristics can be retained.
FUJIEDA MAMORU
KURIHARA NOBUO
