Abstract: Disclosed is an engine control unit intended to prevent fuel vapors from a fuel tank from being released to the atmosphere and causing degradation of gas emission performance. In order to fulfill the object, a control unit according to an aspect of this invention includes means for discharging the fuel from a purging device constructed to adsorb the fuel vapors that rise from the fuel tank, and discharge the adsorbed fuel vapors into an air intake pipe, to an upstream side of a catalyst provided in an exhaust pipe, and when the control unit stops the engine that is running idle, the unit drives the discharge means to accelerate purification of the fuel vapors by sending the vapors to the catalyst under an active state immediately after the engine stop.

Abstract: Factors affecting the response time of a transfer system from the combustion of injected fuel to the detection of its oxygen concentration include a stroke delay time due to an engine speed, the dependence of an LAF sensor response time on an exhaust gas flow rate, a response time change of the LAF sensor due to its deterioration with time, and the like. If a hyperplane of the sliding mode is fixed without considering the above-mentioned factors affecting the response time of the transfer system, an overshoot or oscillation of a feedback system may occur at low speeds of the engine even if preferable feedback responsiveness can be achieved, for example, at high speeds of the engine. This results in aggravated exhaust emissions, degraded drivability due to torque fluctuations, and fluctuations in idle speed.