Importance

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Abstract

A method and apparatus for controlling a vehicle engine. A catalyst in the exhaust system for reducing NOx emissions. When the catalyst is full, the air-fuel mixture is temporarily enriched for reducing the level of NOx. A primary control procedure regulates torque fluctuation or other characteristic during normal operation. For example, the primary control procedure may control the intake air. During the primary control procedure, a coefficient is determined, based on the operating state of the engine, to control the output characteristic. When the catalyst is full, a temporary control procedure varies the fuel-air ratio to increase the level of hydrocarbons delivered to the catalyst, which reduces the NOx. The temporary control procedure regulates the amount of fuel injected based on the same coefficient used in the primary control procedure. Therefore, the output characteristic is substantially unchanged by the temporary control procedure. The primary control procedure regulates torque fluctuation in one embodiment, and the coefficient may be based on the position of the throttle valve, the position of the EGR valve or the quantity of fuel injected into the combustion chambers. In another embodiment, the primary control procedure is for controlling the ignition timing, and the temporary control procedure uses a coefficient based on the timing retardation determined in the primary control procedure.

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First Claim