Patent ID: 6497092
Filing Date: 2002-12-24
Classification: F01N,F02D,Y02T

Abstract:
A method of operating an internal combustion engine having a NOx adsorber coupled to said engine to receive exhaust gases produced by said engine, and having first and second oxygen sensors with said first oxygen sensor being located upstream of said NOx adsorber to output a first signal related to the air/fuel ratio of the exhaust gases entering said NOx adsorber and said second oxygen sensor being located downstreams of said NOx adsorber to output a second signal related to the air/fuel ratio of the exhaust gases exiting said NOx adsorber, said first and second signals being variable between a first value indicative of a lean combustion condition and a second value indicative of a rich combustion condition, the method comprising the steps of:(a) operating said engine at a lean combustion condition for a period of time sufficient to store O2 and NOx in said NOx adsorber and then switching operation of said engine to a rich combustion condition, (b) determining a NOx/O2 release time that is related to the amount of time between switching of said first signal from its first value to its second value and switching of said second signal from its first value to its second value, whereby the NOx/O2 release time is dependent upon the time required to release stored NOx and stored O2 from said NOx adsorber, (c) switching operation of said engine from a rich combustion condition to a lean combustion condition, (d) determining an O2 storage time that is related to the amount of time between switching of said first signal from its second value to its first value and switching of said second signal from its second value to its first value, (e) determining a NOx release time using said NOx/O2 release time and said O2 storage time, wherein said O2 storage time is used as an estimate of the time required to release stored O2 from said NOx adsorber, and (f) operating said engine in a lean combustion condition for a length of time that is dependent upon said NOx release time.