Patent ID: 6230485
Filing Date: 2001-05-15
Classification: F01N,F02D,Y02A,Y02T

Abstract:
An exhaust gas purification system (1) for an internal combustion engine, comprising:an internal combustion engine (2) having an exhaust conduit (4);an engine management system (8) with control means for controlling the engine (2) air/fuel ratio (10) alternately at a super-stoichiometric level and at a sub-stoichiometric level;a three-way catalyst (6) in-line with the exhaust conduit (4) and comprising noble metals selected from the platinum group and rhodium, the catalyst (6) exhibiting a three-way oxidizing activity on the exhaust gases; andthe efficiency of the three-way activity degrading over time when the engine (2) is operated at a super-stoichiometric level with the engine management system (8) comprising timer (12) and memory (14) to measure and store more than one cumulative time, including a first cumulative time over which the control means controls the engine (2) at the super-stoichiometric level and during which the efficiency of the three-way activity degrades, and also a second cumulative time over which the control means controls the engine (2) at a sub-stoichiometric level, the alternation between levels being such that the first cumulative time is greater than the second cumulative time, and the second cumulative time is between about one and ten hours to regenerate at least partially the efficiency of the three-way activity with timer (12) measuring a third cumulative time from the time engine (2) starts to operate, with the operation at a sub-stoichiometric level being overridden if necessary so that engine (2) operates at a super-stoichiometric level until a predetermined time sufficient for catalyst (6) to have reached a temperature of at least about 500.degree. C.