Abstract
OBD (On-Board Diagnosis) system is required in North America to prevent malfunction of automotive engine control systems and to keep emissions clean. Diagnosis of A/F (Air Fuel Ratio) sensor is one function of OBD system. In conventional methods, large amplitude vibration of fuel injection is required and the A/F sensors are diagnosed on the basis of their response to the vibration. In this paper, an A/F sensor diagnosis method without special fuel injection control is proposed. The proposed method detects changes in the A/F signal frequency which are caused by a decreased A/F sensor response. The change in the A/F signal frequency is detected on the basis of the fact that the gain of the differential filter is proportional to the input signal frequency. This method was evaluated using engine bench data. Even in the worst case, the required diagnosis was performed within 17 seconds.
