4-cycle engine

Abstract

A 4-cycle internal combustion engine including a crankcase, a cylinder, a cylinder head, a piston adapted to reciprocate within the cylinder, a combustion chamber formed by the piston, the cylinder and the cylinder head, and a crankshaft connected to the piston via a connecting rod, is improved in order to enhance its thermal efficiency, to reduce exhaust emissions and to make it possible to operate the engine while the engine is in any attitude. The improvements reside in an intake passage and an exhaust passage provided in the cylinder head, a rotary valve rotating synchronously with the crankshaft at a speed one-half of that of the latter for placing the intake passage and the exhaust passage in communication with the cylinder during an intake stroke and an exhaust stroke of the piston, respectively, a check valve through which the intake passage communicates with the interior of the crankcase so that only flow is allowed from the crankcase towards the intake passage, and a carburetor device for feeding a fuel mixture of air, fuel and lubricant oil into the crankcase. The suction of the fuel mixture into the crankcase chamber as well as the feeding of the fuel mixture within the crankcase to the intake passage are made possible by the variation in pressure within the crankcase chamber caused by the reciprocation of the piston.