Method and apparatus for catalyst temperature control

A method of minimizing the total quantity of hydrocarbons emitted from a catalytic converter located in the exhaust path of an internal combustion engine, the catalytic converter including a temperature sensor and a catalyst having a light-off temperature, the method comprising the steps of:

• continuously determining the catalyst temperature based on an output signal from the temperature sensor;
• adjusting at least one operating parameter of the engine to cause the catalyst temperature to rapidly rise when the catalyst temperature is less than the light-off temperature;
• and
• adjusting at least one operating parameter of the engine to achieve substantially stoichiometric conditions in the exhaust of the engine when the catalyst temperature is equal to or greater than the catalyst light-off temperature.

A method of diagnosing degradation of hydrocarbon conversion efficiency of a catalytic converter including a catalyst, located in the exhaust path of an internal combustion engine, based on measuring the temperature of the catalyst during a light-off period, the catalytic converter including a temperature sensor and the catalyst having a light-off temperature, the method comprising the steps of:

• adjusting an operating parameter of the engine to cause a controlled heating of the catalyst during the cold start period;
• continuously determining the temperature of the catalyst based on an output signal from the temperature sensor;
• computing a rate of change of the catalyst temperature;
• comparing the rate of change of the catalyst temperature during a first period of time when the catalyst temperature is less than the light-off temperature to the rate of change of the catalyst temperature during a second period of time when the catalyst temperature is greater than or equal to the light-off temperature;
• and
• generating an output signal indicative of the catalytic converter having a degraded hydrocarbon conversion efficiency if the rate of change of the catalyst temperature during the second period of time is less than or equal to the rate of change of catalyst temperature during the first period of time by at least a predetermined value.

A method of diagnosing degradation of hydrocarbon conversion efficiency of a catalytic converter located in the exhaust path of an internal combustion engine by measuring the temperature of a catalyst in the catalytic converter during a light-off period, the catalyst having a light-off temperature, the method comprising the steps of:

• continuously determining the temperature of the catalytic converter based on an output signal from a temperature sensor coupled to the catalytic converter;
• adjusting an operating parameter of the engine to cause a controlled heating of the catalyst during a cold start period;
• measuring the time period required for the catalyst temperature to exceed a predetermined target temperature;
• and
• generating an output signal indicative of the catalytic converter having a degraded hydrocarbon conversion efficiency if the time period required for the catalyst temperature to exceed the predetermined target temperature is greater than a predetermined value.

A method of simultaneously diagnosing degradation of hydrocarbon conversion efficiency of a catalytic converter in the exhaust path of an internal combustion engine and minimizing total hydrocarbon emissions from the catalytic converter, the catalytic converter including a catalyst having a light-off temperature, the method comprising the steps of:

• continuously determining the temperature of the catalyst based on a first output signal from a temperature sensor coupled to the catalytic converter;
• adjusting at least one operating parameter of the engine to cause substantially constant heating of the catalyst when the catalyst temperature is less than the light-off temperature whereby the catalyst temperature rapidly rises;
• adjusting at least one operating parameter of the engine to achieve substantially stoichiometric conditions in the exhaust of the engine when the catalyst temperature is equal to or greater than the catalyst light-off temperature;
• measuring the time required for the instantaneous temperature of the catalyst to exceed a predetermined target temperature;
• and
• generating a second output signal indicative of degraded hydrocarbon conversion efficiency if the time period required for the catalyst temperature to exceed the predetermined target temperature is greater than a predetermined value.