Two-stroke cycle engine

A two-stroke cycle engine comprising:

• at least two two-stroke cycle power cylinder - piston assemblies each having a power cylinder provided with scavenging ports located near one axial end thereof and exhaust ports located near the other axial end thereof so as to perform uniflow scavenging, two horizontally opposed pistons disposed in said power cylinder and two crankcases which perform crankcase compression of scavenging charge and have the same total stroke volume as that of the power cylinder - piston assembly, said two power cylinder - piston assemblies operating with a phase difference of 180.degree. relative to each other, said scavenging ports being arranged substantially symmetrically around the central axis of each of said power cylinders so as to generate a spiral flow of scavenging charge through said power cylinder;
• at least one double acting pump cylinder - piston assembly which has a pump cylinder and two horizontally opposed pistons disposed in said pump cylinder and is driven by said power cylinder - piston assemblies so as to supply two separate scavenging charges to said two power cylinder - piston assemblies with a phase difference of 180.degree. therebetween;
• and a pair of common crankshafts adapted to rotate in synchronization with each other, each of said power cylinder - piston assemblies and said pump cylinder - piston assembly having a pair of crank mechanisms which incorporate said pair of common crankshafts so as to operate in synchronization with each other, wherein the sum of the total stroke volume of said pump cylinder - piston assembly and that of said crankcases is larger than the total stroke volume of said power cylinder - piston assemblies, and wherein the crank radius of each of said pair of common crankshafts with respect to said pump cylinder - piston assembly is substantially smaller than that with respect to said power cylinder - piston assemblies.