The variable valve control mechanism alters the valve stroke graph to produce an optimum engine load graph. The mechanism is fitted on either the induction valve (2) side or the exhaust valve (2) side. At the beginning of an alteration of the running mode of the engine from low revolutions to high revolutions, the valve open time of the induction valve or the exhaust valve is altered so that the overlap time of the two valves is increased. This may be done in two stages, acting on the open time and closed time of the two valves.
