| 摘要 |
PURPOSE:To control the air fuel ratio so that it is coincided with the objective value both in the lean region and in the over rich region based on the operating condition of an engine, by changing the direction of a current flowing into an oxygen sensor element with a diaphragm structure. CONSTITUTION:A discriminating signal 30 is outputted based on an operating condition signal 10 which is inputted to a control unit 9. At the time of low and medium load operating conditions when the air fuel ratio required for the engine is on the lean side, switches 31A and 31B are turned ON by the high level signal 30 from the control unit 9, and a current IR is flowed to the sensor element 1 having the diaphragm structure from a constant current power source in the control unit 9. At the time of high load operation when the air fuel ratio required for rhe engine is on the over rich side, switches 32A and 32B are turned ON by the low level signal 30 from the control unit 9, and a current IR' is flowed to the sensor 1. The output of the sensor 1 is compared with a reference voltage in a comparator 16, and the control signal for an air fuel ratio control circuit 18 is obtained. |
