Abstract: An internal combustion engine has at least three cylinders and induction conduits opening into the lower portion of the cylinders or into the crankcase. The induction conduits are intended at least for combustion air, comprising at least one rotary disc valve rotatably driven by the crankshaft of the engine. The valve has the form of a disc whose rotation axis crosses or intersects the crankshaft of the engine and is arranged in a valve housing through which the induction conduits extend, said valve being designed to alternately open and close the passages of the induction conduits through the valve housing. Said valve housing has at least three induction conduit inlets and is driven at an rpm which is lower than the crankshaft rpm and has a number of sets of recesses corresponding to the rpm reduction for control of the induction.