Method and system for estimating a midbed temperature of a catalytic converter

A method for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine having at least one cylinder, the exhaust system including an exhaust pipe for transporting exhaust gas from the engine to the catalytic converter, the method comprising:

• sensing a rate of change of the speed of the engine and generating a corresponding speed signal;
• estimating a rate of misfires occurring in the engine over a predetermined number of cylinder filling events based on the speed signal;
• determining an instantaneous temperature of exhaust gas at a first point on the exhaust pipe based on the estimated rate of misfires;
• and
• determining an instantaneous temperature at a midbed point of the catalytic converter based on the instantaneous temperature of exhaust gas at the first point on the exhaust pipe.

A system for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine, the exhaust system including an exhaust pipe for transporting exhaust gas from the engine to the catalytic converter, the system comprising:

• a sensor for sensing a rate of change of the speed of the engine and generating a corresponding speed signal;
• and
• a controller for performing the following:
• estimating a rate of misfires occurring in the engine over a predetermined number of cylinder filling events based on the speed signal;
• determining an instantaneous temperature of exhaust gas at a first point on the exhaust pipe based on the estimated rate of misfires;
• and
• determining an instantaneous temperature at a midbed point of the catalytic converter based on the instantaneous temperature of exhaust gas at the first point on the exhaust pipe.

A method for monitoring degradation of a catalytic converter in fluid communication with an internal combustion engine, comprising:

• detecting engine misfires;
• estimating catalyst temperature based in part on said detected misfires;
• and
• providing an indication of catalyst degradation when both a number of said detected misfires and said estimated temperature exceed respective preselected values during a predetermined test interval.