Air fuel ratio control apparatus for engine

Abstract

An air fuel ratio control apparatus for an engine equipped with an EGR device for refluxing a combustion gas from an exhaust pipe to an intake pipe and a fuel supply control device for controlling a fuel supply amount to the engine. The apparatus includes an air fuel ratio sensor for detecting an air fuel ratio of an air-fuel mixture to be introduced into said engine and an EGR rate sensor for detecting a reflux degree of the combustion gas to the intake pipe. In the apparatus a plurality of optimal feedback gains are set on the basis of a dynamic model of a system for controlling an air fuel ratio of an air-fuel mixture to the engine, and one of the plurality of set optimal feedback gains is selected in accordance with the reflex degree of the combustion gas detected by the EGR rate sensor. The apparatus determines a controlled amount of the fuel supply control device on the basis of the selected optimal feedback gain and the detected air fuel ratio so as to control the air fuel ratio for the engine to a target air fuel ratio. This arrangement can reduce the model error due to the EGR rate variation to improve the air fuel ratio control performance.

Dependencies are inferred from the claim text.