Adaptive exhaust temperature estimation and control

A method of estimating the temperature of a NO.sub.x trap located in an exhaust passage of an engine downstream from a catalytic converter, said trap including a sensor for measuring the temperature of the trap, said exhaust passage including a pierce point located between said converter and said trap for adding controlled amounts of air from an air pump to the exhaust prior to entry into said trap resulting in a total exhaust flow, said method comprising a sequence of the steps of:

• calculating the instantaneous temperature at a first location upstream of said pierce point based on a previous instantaneous temperature value at said first location, an estimated steady-state value, and a predetermined temperature rate of change at said first location as a function of engine air mass flow;
• calculating the total exhaust heat flow at a second location at the front face of the NO.sub.x trap before accounting for any exothermic reaction;
• calculating the heat capacity of said total exhaust flow;
• calculating the instantaneous temperature at said second location by dividing said heat flow by said heat capacity;
• calculating the total exhaust air/fuel ratio at said second location;
• if said total exhaust air/fuel ratio is rich, calculating the exothermic energy as a function of the amount of air pump air mass and the total exhaust air/fuel ratio;
• if said total exhaust air/fuel ratio is lean, calculating the exothermic energy as a function of the amount of engine air mass and the total exhaust air/fuel ratio;
• calculating the temperature generated by the exothermic energy at said second location;
• calculating the steady-state temperature at said second location by adding the calculated temperature before any exothermic reaction to the calculated temperature generated by the exothermic energy;
• calculating the instantaneous temperature at said second location based on a previous instantaneous temperature value at said second location, said estimated steady-state value at said second location, and a predetermined temperature rate of change at said second location as a function of the sum of engine air mass flow and air pump air mass flow;
• inferring the temperature within the NO.sub.x trap at the location of said sensor based on a previous estimated instantaneous temperature value at the sensor location, said estimated steady-state value at said sensor location, and a predetermined temperature rate of change of said sensor output as a function of total exhaust flow;
• calculating the error between the estimated temperature at the sensor location and the actual temperature measured by the sensor;
• learning an adaptive exotherm temperature correction term based on said error;
• and
• correcting the exothermic temperature calculation using said adaptive exotherm temperature correction term.

A method of correcting the estimated temperature of a catalytic converter located in an exhaust passage of an engine with a NO.sub.x trap located downstream from said catalytic converter, said trap including a sensor for measuring the temperature of the trap, said method comprising a sequence of the steps of:

• estimating the instantaneous midbed temperature of said converter;
• calculating the exothermic temperature at the trap entrance;
• estimating the temperature at the sensor location in the trap based on said midbed temperature and said exothermic temperature;
• calculating the temperature error between the estimated output of the sensor and the actual output of the sensor;
• learning a catalyst midbed temperature correction term based on said temperature error;
• and
• correcting said estimated midbed temperature using said midbed correction term.

A method of correcting the estimated temperature of a catalytic converter located in an exhaust passage of an engine, said converter including a sensor for measuring the temperature of the converter, said method comprising a sequence of the steps of:

• estimating the instantaneous midbed temperature of said converter;
• estimating temperature output of said sensor based on a previous estimate of said sensor output, said instantaneous midbed temperature of said converter, and a predetermined temperature rate of change of said sensor as a function of engine air mass flow;
• calculating the temperature error between the said estimated sensor output and the actual output of the sensor;
• learning a catalyst midbed temperature correction term based on said temperature error;
• and
• correcting said estimated midbed temperature using said midbed correction term.