Importance

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Abstract

The suitability of diagnosing deterioration of a catalyst which purifies engine exhaust is determined based on estimated catalyst temperature. A value depending on condensation in the catalyst, and a value corresponding to a state without condensation, are respectively set as a reference heat amount for a cold start and a hot start. A catalyst temperature during steady state running condition of the engine is also computed based on the engine running conditions. The heat amount given by the exhaust to the catalyst is computed from this catalyst temperature and the engine intake air volume. When the total heat amount given to the catalyst after engine startup is equal to or less than the reference heat amount, a catalyst temperature estimated value is set to a fixed value. In all other cases, the catalyst temperature estimated value is calculated by a first order delay equation having catalyst temperature during steady running conditions as a parameter. In this way, the catalyst temperature is estimated with high precision.

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First Claim