Using exhaust pressure pulsations to detect deteriorations of oxygen sensor dynamics

Wide-range oxygen sensors are widely used for the air–fuel ratio control in lean operation engines. However, the harsh environment in the exhaust pipe can deteriorate the sensor dynamics. Therefore, to satisfy emission legislation over the lifetime of the sensor, its dynamics must be monitored continuously. Conventional approaches for the diagnosis of sensor dynamics require for active external excitation or sufficient dynamic excitation induced by the driver. To overcome this dependency, this paper presents a new approach, which makes use of the sensor excitation caused by the reciprocating behavior of the engine that induces pressure pulsations in the exhaust pipe. The approach exploits the fact that wide-range oxygen sensors measure the oxygen partial pressure, which is proportional to the oxygen concentration as well as to the total pressure. Clogged protection tube holes of the oxygen sensor damp the pressure pulsations and slow down the sensor response. The relationship between the damping and the sensor response is analyzed with simulations and experiments. It is shown that the sensor time constant can be monitored with an average absolute accuracy of 0.25–0.3 s. Due to the continuous monitoring capability, the proposed approach is particularly suitable for applications where the engine experiences short-time and mainly stationary operation. Moreover, the proposed approach can be efficiently combined with conventional monitoring algorithms.