Method of estimating catalyst temperature of a multi-displacement internal combustion engine

A method of estimating temperature of a catalyst associated with a cylinder bank of a multi-displacement internal combustion engine having multiple cylinder banks associated with multiple catalysts, comprising:

• a) setting temperature estimates of the catalysts associated with the multiple cylinder banks substantially equal to a base model temperature;
• b) determining deactivation of a cylinder bank of the multiple cylinder banks;
• c) incrementing a multi-displacement mode timer;
• d) identifying a catalyst cooldown correction for the catalyst associated with the deactivated cylinder bank from a catalyst cooldown model including time elapsed since deactivation of the cylinder bank as determined from the incremented multi-displacement mode timer;
• e) applying the catalyst cooldown correction to the temperature estimate of the catalyst associated with the deactivated cylinder bank to update the temperature estimate of the catalyst;
• f) identifying an ambient temperature adjustment for the catalyst cooldown correction from an ambient temperature model including outside ambient temperature;
• g) applying the ambient temperature adjustment to the catalyst cooldown correction to update the temperature estimate of the catalyst;
• h) determining reactivation of the cylinder bank;
• i) resetting the multi-displacement mode timer;
• j) comparing the temperature estimate of the catalyst to the base model temperature for the catalyst;
• k) using the base model temperature if the temperature estimate is greater than the base model temperature;
• l) but if the temperature estimate is less than the base model temperature,
• l1) identifying a catalyst warmup correction for the catalyst associated with the reactivated cylinder bank from a catalyst warmup model including cumulative heat associated with the cylinder bank, and
• l2) applying the catalyst warmup correction to the temperature estimate of the catalyst to update the temperature estimate of the catalyst;
• m) identifying a mass flow adjustment for the catalyst warmup correction from a mass flow model including mass flow associated with the reactivated cylinder bank;
• n) applying the mass flow adjustment to the catalyst warmup correction to update the temperature estimate of the catalyst;
• and
• o) using the temperature estimate of the catalyst as an input variable to determine whether to conduct on-board diagnostics of an exhaust system oxygen sensor.