Patent ID: 6267937
Filing Date: 2001-07-31
Classification: B01D,F01N,F02D,Y02T,Y10S

Abstract:
A method of desulphating a lean NOx trap (LNT) in an exhaust system of a spark ignition internal combustion engine having a three-way catalyst and the lean NOx trap connected in series along the exhaust system, the NOx trap containing both NOx and oxygen storage components, the method comprising modulating the air to fuel ratio (AFR) calibration of the engine cyclically, first with a lean calibration for a sufficient time to result in the presence of excess air in the exhaust gases to provide oxygen to be stored within the lean NOx trap, then with a rich calibration for a sufficient time to result in the presence of excess fuel in the exhaust gases initially to react completely with any oxygen stored in the three-way catalyst itself and subsequently to react with the oxygen stored in the NOx trap so as to heat the NOx trap to a temperature in excess of 650.degree. C., wherein the AFR is performed at a plurality of frequencies so as to heat different parts of the lean NOx trap at different times.