High efficiency variable expansion ratio engine

In a spark-ignition, variable-expansion ratio, four-cycle engine of the type having a plurality of cylinders equipped with pistons all of which have a power output driving connection with a common crankshaft and including means directly connected to said common crankshaft for varying the cylinder clearance volume under different power demand conditions, that improvement which comprises:

• throttleless carburetor means for supplying a combustible charge to said cylinders, including a separate intake valve for each cylinder operatively connected to said crankshaft, and further including means for closing said intake valve selectively not later than bottom dead center of the intake stroke as necessary to provide a charge corresponding to torque output requirements between idling and full power, and means for closing said intake valves and for operating said means for varying the cylinder clearance volume in synchronism with the closure of said intake valves and thereby effective to maintain the engine compression ratio substantially constant over the full range of torque outputs and to increase the engine expansion ratio as the torque output is reduced.