Method of on-board detection of automotive catalyst degradation

Abstract

A method of on-board detection of the degradation of an automotive catalyst which receives the emissions from an engine placed in a closed-loop feedback control with an A/F characteristic sensor immersed in the emissions. The method comprises: (a) artificially modulating the frequency and/or amplitude of the control for a predetermined burst period; (b) sensing an A/F characteristic by an independent sensor substantially immediately downstream of the catalyst at events prior to and during the burst period; and (c) determining if there is an absence of a substantial change between events in the independently sensed A/F characteristic, thus indicating a degraded catalyst. The artificial modulation changes the oxygen exposure of the catalyst during a short catalyst interrogation period in a manner to magnify the oxygen absorption characteristic of the noble metals within the catalyst. The artificial modulation may comprise a frequency change of a fixed uniform increase, such as 2-3 times the normal limit cycle frequency of the engine control, preferably about 2-4 Hz, or may comprise a variable change of frequency or amplitude such as ramping with or without steps or interruptions.

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