Air-fuel modulation for oxygen sensor monitoring

For use with a vehicle including an electronic control unit for controlling fuel supply to an internal combustion engine having an oxygen sensor for sensing engine exhaust gas oxygen level, a method of monitoring operation of the sensor, the method comprising:

• generating a symmetrical air-fuel modulation signal;
• generating an asymmetrical air-fuel feedback signal based on an output signal from the oxygen sensor;
• summing the symmetrical air-fuel modulation signal and the asymmetrical air-fuel feedback signal to obtain a modulated air-fuel signal having an asymmetrical modified square-wave waveform designed to produce a particular engine exhaust response for interrogating the oxygen sensor;
• operating the engine based on the modulated air-fuel signal, the oxygen sensor producing an associated output signal in response to sensed exhaust gas oxygen levels;
• and
• processing the output signal of the oxygen sensor while operating the engine based on the modulated air-fuel signal so as to determine the operating condition of the oxygen sensor.

For use with a vehicle including an electronic control unit for controlling fuel supply to an internal combustion engine having an oxygen sensor for sensing engine exhaust gas oxygen level, a method of monitoring operation of the sensor, the method comprising:

• applying a plurality of forced fuel excursions at a predetermined frequency to the engine utilizing a modulated air-fuel signal having a modified square-wave waveform designed to produce a particular engine exhaust response for interrogating the oxygen sensor;
• comparing the number of forced fuel excursions applied to the engine to a predetermined fuel excursion threshold;
• processing an output signal of the oxygen sensor to determine a response frequency of the sensor to the applied forced fuel excursions;
• comparing the predetermined frequency of the forced fuel excursions to the response frequency of the sensor;
• and
• identifying an operating condition of the sensor based on the comparison of the predetermined frequency of the forced fuel excursions to the response frequency of the sensor.

An apparatus, for use with a vehicle including an internal combustion engine having an oxygen sensor for sensing engine exhaust gas oxygen level, for monitoring operation of the sensor, the apparatus comprising:

• means for generating a symmetrical air-fuel modulation signal;
• means for generating an asymmetrical air-fuel feedback signal based on an output signal from the oxygen sensor;
• combining means for summing the symmetrical air-fuel modulation signal and the asymmetrical air-fuel feedback signal to obtain a modulated air-fuel signal having an asymmetrical modified square-wave waveform designed to produce a particular engine exhaust response for interrogating the oxygen sensor, the engine being operated based on the modulated air-fuel signal, the oxygen sensor producing an associated output signal in response to sensed exhaust gas oxygen levels;
• and
• control means for processing the output signal of the oxygen sensor while operating the engine based on the modulated air-fuel signal so as to determine the operating condition of the oxygen sensor.