Abstract: An internal combustion engine includes at least one rotating, oscillating or reciprocating piston (20, 21) in a cylinder (11, 12). Each piston (20, 21) defines with the cylinder (11, 12) a combustion chamber (35). Each combustion chamber (35) has at least one inlet valve (36) and one exhaust valve (37), and a mechanism (40) to periodically open the inlet and exhaust valves. The valves are closed by a gas spring (80, 82) having a closing force proportional to the speed of the engine.

Abstract: An internal combustion engine comprising at least one pair of pistons (20, 21) rotating, oscillating or reciprocating in cylinder assemblies (11, 12) joined by a crankcase (13), each piston (20, 21) being driven by a crankshaft housed in the crankcase (13), the crankcase (13) including an inlet port (63) for entry of an air fuel mixture and an outlet port (65) for transfer of compressed air fuel mixture, each cylinder (11, 12) having a combustion chamber (35) and at least one inlet (36) and at least one exhaust (36) valve port communicating with the combustion chamber (35), the inlet valve port (36) being in communication with the crankcase (13) via the crankcase outlet port (65) whereby the engine is adapted to run on a four stroke cycle with the underside of the piston (20, 21) pressurising the air fuel mixture in the crankcase (13) and causing transfer of the pressurised air fuel mixture to the combustion chamber (35) via the crankcase outlet port (65) and inlet valve port (36).