Patent ID: 7559317

Claim:
An internal combustion engine comprising: a cylinder, a cylinder head closing an end of the cylinder, and a piston movable with reciprocating motion within an interior space of the cylinder, the piston motion providing a succession of four strokes including an induction stroke, a compression stroke, a power stroke and an exhaust stroke; wherein the engine is a gasoline engine or a diesel engine, and the cylinder head has an intake port, an exhaust port, and a return port which communicate with the interior space of the cylinder; wherein the compression stroke serves to compress gas within the cylinder in preparation for the power stroke, the compression-stroke gas being a mixture of air and fuel in the gasoline engine, or air without fuel in the diesel engine, the compression stroke providing a reduction in volume of the gas characterized by a compression ratio; the power stroke provides for an expansion in volume of gas within the cylinder, characterized by an expansion ratio, the gas in the power stroke being a mixture of air, fuel, and products of combustion; the engine further comprises reducing means for reducing the compression ratio to a value less than the expansion ratio; the reducing means comprises a holding tank for receiving a quantity of the gas from the cylinder via the return port during the compression stroke, and for returning the quantity of gas to the cylinder via the return port prior to a compression of cylinder gas in a subsequent compression stroke; and the cylinder head includes a return valve operative for closing and opening the return port, the return valve opening the return port during a part of the compression stroke for transferring said quantity of gas from the cylinder to the holding tank, the return valve opening the return port during a part of the induction stroke and/or an initial portion of the compression stroke for transferring said quantity of gas from the holding tank to the cylinder, and the return valve closing the return port during the power stroke and during the exhaust stroke to prevent communication of gas between the holding tank and said cylinder during said power stroke and said exhaust stroke.