Degradation detection method for an engine having a NOx sensor
First Claim
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1. A method for determining degradation in an emission control system coupled to an internal combustion engine comprising:
- providing first and second signals from a sensor coupled downstream of the engine, said first output signal and said second output signal respectively indicative of a first exhaust gas constituent flowing through the emission control system and a second exhaust gas constituent flowing through the emission control system;
generating an estimate of said second exhaust gas constituent based at least on said first exhaust gas constituent and an engine operating condition; and
indicating when said estimate of said second exhaust gas constituent and said second exhaust gas constituent differ by a predetermined value at least during stoichiometric conditions.
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Abstract
An engine diagnostic system for use with an internal combustion engine coupled to a lean NOx trap with a NOx sensor coupled downstream of the trap is disclosed. Degradation of the NOx sensor is determined by estimating NOx exiting the trap based on engine out NOx and various other operating conditions. When the difference between the measured NOx and estimated NOx is greater than a predetermined value for a predetermined duration, degradation is indicated.
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Citations
10 Claims
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1. A method for determining degradation in an emission control system coupled to an internal combustion engine comprising:
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providing first and second signals from a sensor coupled downstream of the engine, said first output signal and said second output signal respectively indicative of a first exhaust gas constituent flowing through the emission control system and a second exhaust gas constituent flowing through the emission control system;
generating an estimate of said second exhaust gas constituent based at least on said first exhaust gas constituent and an engine operating condition; and
indicating when said estimate of said second exhaust gas constituent and said second exhaust gas constituent differ by a predetermined value at least during stoichiometric conditions. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An article of manufacture, comprising:
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a computer storage medium having a computer program encoded therein method for determining degradation in an emission control system coupled to an internal combustion engine, said computer storage medium comprising;
code for providing first and second signals from a sensor coupled downstream of the engine, said first output signal and said second output signal respectively indicative of a NOx concentration and an air-fuel ratio flowing through the emission control system;
code for generating an estimate of said NOx concentration based at least on said air-fuel ratio and an engine operating condition; and
code for indicating when said estimate and said NOx concentration differ by a predetermined value for a preselected duration at least during stoichiometric conditions.
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10. An emission control system for an internal combustion engine, comprising:
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a NOx absorbent disposed in an exhaust passage downstream of the internal combustion engine that stores and reacts NOx under certain operating conditions;
a NOx sensor disposed in the exhaust passage downstream of the NOx absorbent, a first output of the NOx sensor corresponding to a NOx concentration of exhaust gas flowing out of the NOx absorbent, and a second output of the NOx sensor corresponding to an oxygen concentration;
a controller controlling a lean operating condition of the internal combustion engine based on the first output value of the NOx sensor;
determining a deviation of the first output value of the NOx sensor from a predetermined value, said predetermined value based on said second output value of the NOx sensor, said deviation determined when preselected engine operating conditions, including stoichiometric operation conditions, are met; and
determining degradation of the NOx sensor based on said deviation; and
an electronically controlled throttle plate disposed in an intake passage of the internal combustion engine receiving a command from said controller.
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Specification