Adaptive exhaust temperature estimation and control
First Claim
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1. A method of estimating the temperature of a NOx trap located in an exhaust passage of an engine, said trap including a sensor for measuring the temperature of the trap, said method comprising a sequence of the steps of:
- estimating the instantaneous temperature of said trap;
estimating temperature output of said sensor based on a previous estimate of said sensor output, said instantaneous trap temperature, 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 trap temperature correction term based on said temperature error; and
correcting said estimated trap temperature using said correction term.
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Abstract
A method and apparatus for inferring and controlling the temperature of a NOx trap located downstream from a three-way catalyst that employs a temperature sensor to correct a temperature estimation model under relatively steady-state conditions to provide a more accurate estimate of NOx trap temperature and three-way catalyst temperature. In a second embodiment, the three-way catalyst also includes a temperature sensor for improving the instantaneous catalyst temperature estimation.
145 Citations
12 Claims
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1. A method of estimating the temperature of a NOx trap located in an exhaust passage of an engine, said trap including a sensor for measuring the temperature of the trap, said method comprising a sequence of the steps of:
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estimating the instantaneous temperature of said trap; estimating temperature output of said sensor based on a previous estimate of said sensor output, said instantaneous trap temperature, 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 trap temperature correction term based on said temperature error; and correcting said estimated trap temperature using said correction term. - View Dependent Claims (2, 3, 4, 5)
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6. A method of estimating the temperature of a NOx 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:
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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 NOx 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 NOx 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. - View Dependent Claims (7, 8, 9, 10)
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11. A method of correcting the estimated temperature of a catalytic converter located in an exhaust passage of an engine with a NOx 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:
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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.
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12. 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:
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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.
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Specification