| 摘要 |
PURPOSE:To control the air-fuel ratio precisely in a broad range, by chaning the state, under which the generation of an output voltage proportional to an oxygen concentration is detected and the state, under which the generation of an output voltage indicating whether the air-fuel ratio is larger than the theoretical air-fuel ratio or not is detected, in response to the operating state of the engine. CONSTITUTION:A platinum thin film for a positive electrode and a platinum thin film for a negative electrode are coated on the inner and outer surfaces of oxygen ion conductive solid state electrolyte 21, whose outer surface is coated by porous ceramics 22. A voltage is applied to the positive electrode by a switching circuit 24. The first detecting state (solid line), under which the output voltage proportional to the oxygen concentration is generated and the second detecting state (broken line), under which the output voltage indicating whether the air-fuel ratio is larger than the theoritical air-fuel ratio or not are changed. An air-fuel ratio control unit judges whether the objective air-fuel ratio is on the lean side or equal to the theoretical air-fuel ratio based on the basic fuel injection time, and outputs a control signal to the switching circuit 24 so that the first detecting state and the second detecting state which are suitable for the respective controls are changed. |
