Adjustment of measured oxygen storage capacity based on upstream O2 sensor performance

A system for a vehicle, the system comprising:

• a catalyst test module that selectively commands a fueling transition from a fuel rich state to a fuel lean state;
• an upstream oxygen monitoring module that monitors an upstream oxygen sensor and sets an upstream transition period to the difference between the response of the upstream oxygen sensor to the rich-to-lean fueling transition and the time at which the rich-to-lean fueling transition was commanded, wherein the upstream oxygen sensor monitors an exhaust prior to an engine catalyst;
• a delay determining module that determines a delay period associated with a response of the upstream oxygen sensor to the rich-to-lean fueling transition based on catalyst temperature, intake air temperature, and mass air flow;
• an upstream correcting module that determines a corrected upstream transition period by subtracting the delay period from the upstream transition period;
• a downstream oxygen monitoring module that monitors a downstream oxygen sensor and sets a downstream transition period to the difference between the response of the downstream oxygen sensor to the rich-to-lean fueling transition and the time at which the rich-to-lean fueling transition was commanded, wherein the downstream oxygen sensor monitors the exhaust following the engine catalyst;
• an oxygen storage capacity (OSC) determining module that sets a OSC period to the difference between the downstream transition period and the corrected upstream transition period;
• a correcting module that determines a corrected OSC period by (i) determining a correction factor using a calibration table of correction factor values indexed by catalyst temperature and altitude, and (ii) multiplying the OSC period by the correction factor;
• an expected OSC module that determines an expected OSC period using a calibration table of expected OSC indexed by catalyst temperature and mass air flow;
• a normalizing module that sets an OSC ratio to the corrected OSC period divided by the expected OSC period;
• a ratio filtering module that determines a filtered OSC ratio using an exponentially weighted moving average filter;
• and
• a catalyst fault detection module that selectively adjusts operating parameters of an engine of the vehicle based on the filtered OSC ratio.

A method comprising:

• commanding a fueling transition from a fuel rich state to a fuel lean state;
• determining an upstream transition period based on the response of an upstream oxygen sensor to the rich-to-lean fueling transition, wherein the upstream oxygen sensor monitors an exhaust stream prior to an engine catalyst of a vehicle;
• determining a delay period associated with a response of the upstream oxygen sensor to the rich-to-lean fueling transition;
• determining a corrected upstream transition period based on the upstream transition period and the delay period;
• determining a downstream transition period based on the response of a downstream oxygen sensor to a rich-to-lean fueling transition, wherein the downstream oxygen sensor monitors the exhaust stream following the engine catalyst;
• determining an oxygen storage capacity (OSC) period based on the corrected upstream transition period and the downstream transition period;
• detecting a fault in a catalyst based on the OSC period;
• and
• selectively adjusting operating parameters of an engine of the vehicle.