Closed loop control for desulfating a NO.sub.x trap
AssigneeFord Global Technologies, LLC
InventorJoseph Richard Asik
Life of this patent
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Abstract
A system and method for desulfating an NO.sub.x trap utilizes a closed loop control of the air-to-fuel (A/F) ratio to accurately maintain a precise A/F ratio during desulfation. An oxygen sensor is positioned in the middle of the trap to provide an actual A/F ratio measurement, which is subsequently compared to a target A/F ratio to generate a correction signal to adjust operation of the engine's fuel injector(s). The trap oxygen sensor can also be used to adaptively update engine state conditions for a more precise switch-over to a trap regeneration phase.
Claims15
A system for controlling an air-to-fuel ratio during a desulfation phase of an NO.sub.x trap used to reduce emission of NO.sub.x in an exhaust system of an engine, the desulfation phase comprising a trap heating phase in which the air-to-fuel ratio is used to raise the temperature within the trap to a desired desulfation temperature range, and a trap regeneration phase following the heating phase, said system comprising:
- a first oxygen sensor connected to the engine exhaust system and arranged to provide an output signal representative of the oxygen concentration present in the exhaust gases flowing through the trap;
- a fuel injection subsystem connected to the engine;
- a processor arranged to generate during the trap heating phase a signal responsive to said oxygen sensor output signal that is representative of an actual air-to-fuel ratio of the exhaust in the trap;
- an error signal generator responsive to said actual air-to-fuel signal and a target air-to-fuel ratio for generating an air-to-fuel ratio error signal;
- and
- a controller connected to said fuel injection subsystem for controlling the air-to-fuel ratio of the exhaust gases, wherein the controller is responsive to said error signal for adjusting the fuel concentration supplied to the engine during the trap heating phase, and is further responsive to the regeneration phase to reset the ratio to a predetermined ratio for a predetermined period of time.
A method for controlling an air-to-fuel ratio during a desulfation phase of an NO.sub.x trap used to reduce emission of NO.sub.x in an exhaust system of an engine, said method comprising the steps of:
- initiating a trap heating phase;
- measuring the oxygen concentration present in the exhaust flowing through the trap during the trap heating phase;
- determining an actual air-to-fuel ratio based on the measured oxygen concentration;
- comparing the actual air-to-fuel ratio to a target air-to-fuel ratio;
- generating an air-to-fuel ratio error signal based on the comparison between the actual and target air-to-fuel ratios;
- adjusting the fuel concentration supplied to the engine based on the air-to-fuel ratio error signal;
- and
- after completion of the trap heating phase, switching to an open loop air-to-fuel ratio control during a trap regeneration phase.
Dependencies are inferred from the claim text.