A Production Wide-Range AFR Sensor Response Diagnostic Algorithm for Direct-Injection Gasoline Application

A wide-range Air-Fuel Ratio sensor (WRAF) response diagnostic algorithm was developed for production application in Gasoline Direct Injection (Gas-DI) powertrains to fulfill On Board Diagnostic (OBD) legislative requirements [1] for wide-range oxygen sensors. The algorithm measures the response of a wide-range air-fuel ratio (AFR) sensor signal to an input AFR signal of known amplitude to determine whether degradation in sensor responsiveness is severe enough to cause a failure of legal emissions requirements.

A practical IIR (Infinite Impulse Response) digital bandpass filter design was used in series with a rectifier and low-pass filter to process the AFR sensor signal for comparison to a reference signal amplitude. The IIR filter was designed with a moveable pass-band to enable the algorithm to be used at variable frequencies during intrusive and non-intrusive sensor diagnostic tests.