| 摘要 |
PURPOSE:To improve stability of a control system with a simple constitution by a method wherein a constant pre-specified theoretical air-fuel ratio signal is output when an air-fuel ratio corresponds to a theoretical air-fuel ratio so that fluctuation in air-fuel amount signals in the theoretical air-fuel ratio range is suppressed. CONSTITUTION:An output signal VS of an oxygen sensor 15 is input from an input terminal 37 of a signal processing circuit 20 to comparators 34, 35, of an identification circuit 31. The comparators 34, 35 compare the signal VS with standard voltage S1, S2, (S1>S2), respectively. When the voltage S1> voltage of the signal VS> the voltage S2, that is, the excess air ratio lambda is in the vicinity of 1.0, the comparator 34, 35 are in a continuity and a cut-off states, respectively. Since voltages at resistances R4, R5 of a conversion circuit 32 are equal to a voltage (voltage corresponding to a desired air-fuel ratio) resistance-divided by resistors R4 and R5, a power supply voltage VCC/2 is output from the circuit 32 to a buffer circuit 33. Therefore, when the air-fuel ratio is within a theoretical air-fuel ratio range, the voltage Vlambda of the output of the signal processing circuit 20 (air-fuel ratio signal) which is output from an output terminal 38 of the circuit 20 into an air-fuel ratio control circuit becomes VCC/2. |
