Exhaust gas re-circulation control unit for a diesel engine

Abstract

An EGR control unit for enhancing the performance as to the EGR rate and the engine acceleration, the unit being configured so as to control the EGR valve and the intake air valve with a simple control command signal that makes both the valves be operated in a coupled mode, whereby the response performance as to the engine speed during acceleration as well as the EGR gas flow rate is enhanced by means of compensation regarding the dead zones inherent in the intake air throttle valve and the EGR valve. An EGR control unit including; a dead zone evaluating meansthat calculates the estimation excess air ratio λ in consideration of the residual air in the EGR gas; thereby, it is judged that at least one of the EGR valveand the intake air throttle valveis operated in the dead zone based on the rate of change of the calculated estimation excess air ratio λ when the rate of change of the ratio λ is smaller than a prescribed level; and a dead zone compensating meansthat makes the revisions regarding the opening command signals as to the EGR valve and the intake air throttle valve so that the dead zones do not hinder the coupled operation between the valves when the dead zone evaluating means judges that at least one of the EGR valve and the air throttle valve is operated in the dead zone, and the engine is under a transient response condition.