Onboard detection of oxygen sensor switch rate for determining air/fuel ratio control system failure

Claim 1

A method of determining air/fuel ratio control system failure in an internal combustion engine having an exhaust gas oxygen sensor feedback control loop as part of an engine control system including the steps of: determining an expected transport delay time of the engine; generating a signal indicative of an average of a plurality of previously determined expected transport delay times of the engine; detecting level switching of the exhaust gas oxygen sensor; generating a signal indicating level switching of the exhaust gas oxygen sensor; determining a time between the signal level switching of the exhaust gas oxygen sensor; generating a signal indicative of an average of a plurality of times between level switching of the exhaust gas oxygen sensor; comparing the signal indicating average transport delay time to the signal indicating average exhaust gas oxygen sensor level switching time; and determining an EGO sensor switching rate fault exists if the comparison indicates that one average is different from the other average by a predetermined amount.

Claim 2

A method of determining air/fuel ratio control system failure in an internal combustion engine having an exhaust gas oxygen sensor feedback control loop as part of an engine control system including the steps of: determining an expected transport delay time of the engine; generating a signal indicative of an average of a plurality of previously determined expected transport delay times of the engine; detecting level switching of the exhaust gas oxygen sensor; generating a signal indicating level switching of the exhaust gas oxygen sensor; determining a time between the signal level switching of the exhaust gas oxygen sensor; generating a signal indicative of an average of a plurality of times between level switching of the exhaust gas oxygen sensor; comparing the signal indicating average transport delay time to the signal indicating average exhaust gas oxygen sensor level switching time; and determining an EGO sensor switching rate fault exists if the comparison indicates that one average is different from the other average by a predetermined amount.

Claim 5

A method of determining air/fuel ratio control system failure in the internal combustion engine having an exhaust gas oxygen sensor feedback control loop as part of an engine control system including the steps of: storing transport delay times for various engine speed and load conditions in a memory table associated with the engine control system; determining an expected transport delay time based upon speed and load conditions of the engine; detecting a level change in the exhaust gas sensor output as an EGO sensor switch as indicated by signal level switching; calculating a simple average of previously determined expected transport delay times including maintaining, since the last EGO sensor switch, a transport delay time sum and the number of transport delay samples taken; calculating a rolling average of previously determined expected transport delay times; generating a signal indicative of the rolling average of a plurality of determined transport delay times of the engine; generating a signal indicating signal level switching of the exhaust gas oxygen sensor; calculating an exhaust gas oxygen sensor level switching time; calculating an exhaust gas oxygen sensor level switching time rolling average; generating a signal indicative of the rolling average of the times between signal level switching of the exhaust gas oxygen sensor; comparing the signal indicating exhaust gas oxygen level switching time rolling average to the signal indicating the transport delay time rolling average; determining a lazy exhaust gas oxygen sensor error exists if the exhaust gas oxygen sensor level switching time rolling average is larger than a first predetermined time average caused by slow switching; determining a buzzing exhaust gas oxygen sensor error exists if the exhaust gas oxygen sensor level switching time rolling average is smaller than a second predetermined time average, indicating fast level switching; and determining there is no fuel system error if the exhaust gas oxygen sensor level switching time rolling average is between the first and second time averages.

Claim 6

A method of determining air/fuel ratio control system failure in the internal combustion engine having an exhaust gas oxygen sensor feedback control loop as part of an engine control system including the steps of: storing transport delay times for various engine speed and load conditions in a memory table associated with the engine control system; determining an expected transport delay time based upon speed and load conditions of the engine; detecting a level change in the exhaust gas sensor output as an EGO sensor switch as indicated by signal level switching; calculating a simple average of previously determined expected transport delay times including maintaining, since the last EGO sensor switch, a transport delay time sum and the number of transport delay samples taken; calculating a rolling average of previously determined expected transport delay times; generating a signal indicative of the rolling average of a plurality of determined transport delay times of the engine; generating a signal indicating signal level switching of the exhaust gas oxygen sensor; calculating an exhaust gas oxygen sensor level switching time; calculating an exhaust gas oxygen sensor level switching time rolling average; generating a signal indicative of the rolling average of the times between signal level switching of the exhaust gas oxygen sensor; comparing the signal indicating exhaust gas oxygen level switching time rolling average to the signal indicating the transport delay time rolling average; determining a lazy exhaust gas oxygen sensor error exists if the exhaust gas oxygen sensor level switching time rolling average is larger than a first predetermined time average caused by slow switching; determining a buzzing exhaust gas oxygen sensor error exists if the exhaust gas oxygen sensor level switching time rolling average is smaller than a second predetermined time average, indicating fast level switching; and determining there is no fuel system error if the exhaust gas oxygen sensor level switching time rolling average is between the first and second time averages.