Patent ID: 8479716

Claim:
An EGR control unit to control a diesel engine, the engine comprising: an EGR valve by which EGR flow rate of the engine is adjusted, an intake air throttle valve by which the intake air flow rate of the engine is adjusted, and a mechanism in which the opening of the EGR valve is operated in conjunction with the opening of the air throttle valve; wherein, each of opening determining lines (characteristic curves) and as to the opening of the EGR valve and the air throttle valve has a dead zone part where a flow rate stays unchanged even the opening of the valve is increased beyond a certain opening level; the EGR control unit is provided with a dead zone evaluating means that calculates an estimation excess air ratio λ in consideration of the residual oxygen in the EGR gas; thereby, it is judged that at least one of the EGR valve and the air throttle valve is operated in the dead zone based on a rate of change of the calculated estimation excess air ratio λ when the rate of change of the estimation excess air ratio λ is smaller than a prescribed level; and the EGR control unit is provided with a dead zone compensating means that makes revisions regarding opening command signals as to the EGR valve and the intake air throttle valve so that the dead zones do not hinder the mechanism regarding the conjunct opening operation 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.