Method and apparatus for maintaining catalyst efficiency of a NO.sub.x trap
AssigneeFord Global Technologies, LLC
InventorsMichael John Cullen, David George Farmer, Arnold William Brandt, Jeffrey Scott Hepburn
Life of this patent
Estimating the term…
Abstract
An engine control computer estimates the cumulative SO.sub.x stored in a NO.sub.x trap and enters a SO.sub.x purge mode of operation when a maximum storage capacity limit is exceeded. SO.sub.x accumulation is estimated based on fuel flow to the engine, A/F and trap temperature. The purge mode is terminated when the estimated SO.sub.x storage level drops below a minimum threshold level during the purging operation.
Claims16
A method of estimating the amount of SO.sub.x accumulated in a NO.sub.x trap located in an exhaust passage of an engine comprising a sequence of the steps of:
- determining an amount of SO.sub.x accumulated per unit fuel flow, based on present A/F and present temperature of said trap;
- calculating the rate of SO.sub.x accumulation based on said determined amount of SO.sub.x and the flow rate of fuel supplied to said engine;
- and
- calculating the amount of S0.sub.x accumulation based on said calculated rate of SO.sub.x accumulation and the elapsed time since a previous calculation.
Apparatus for estimating the amount of SO.sub.x accumulated in a NO.sub.x trap located in an exhaust passage of an engine comprising:
- a read only memory containing experimentally determined data representing the expected amount of SO.sub.x that would be accumulated in said trap per quantity of fuel supplied to said engine at a specified A/F and trap temperature;
- an engine controller for estimating the temperature of said trap, and for calculating the desired fuel quantity to achieve a desired A/F;
- said controller calculating the incremental amount of SO.sub.x accumulated in said trap since the previous calculation based on the product of the read only memory data, corresponding to the present A/F and trap temperature, and the amount of fuel supplied to said engine since the previous calculation.
An article of manufacture comprising:
- a computer storage medium having a computer program encoded therein for controlling the amount of fuel supplied to an engine having an exhaust passage with a NO.sub.x trap located therein, said computer storage medium comprising:
- code for determining the temperature of said trap;
- code for calculating the amount of fuel to be delivered to said engine to achieve a desired A/F;
- and
- code for calculating the incremental amount of SO.sub.x accumulated in said trap at said A/F and trap temperature.
Dependencies are inferred from the claim text.