Abstract: A two part variable compression ratio (VCR) piston assembly for use in a two cycle internal combustion engine, the piston assembly including an outer member movable relative to an inner member to vary the compression ratio of the engine and a hydraulic system utilizing oil from the lubrication system of the engine to automatically control the relative movement of the members to maintain a predetermined maximum combustion chamber pressure. The hydraulic circuit includes an upper and a lower chamber which expands and contracts conversely upon relative movement of the piston members and further includes a pumping system for pumping oil to the upper chamber and to the lower chamber through the upper chamber to thereby vary the compression ratio of the piston.

Abstract: A two part variable compression ratio (VCR) piston assembly having an outer member movable relative to an inner member to vary the compression ratio of an internal combustion engine and a hydraulic system utilizing oil from the lubrication system of the engine for automatically controlling the relative movement of the members to maintain a predetermined maximum combustion chamber pressure. A hydraulic circuit includes an upper and a lower chamber which expands and contracts conversely upon relative movement of the piston members and a system for supplying oil to the upper chamber and to the lower chamber via the upper chamber and for discharging the oil from the upper chamber in a manner which gradually changes the compression ratio of the piston until a predetermined maximum combustion chamber pressure has been achieved and which tends to maintain the maximum combustion chamber pressure after it has been achieved.

Abstract: A two part variable compression ratio (VCR) piston assembly having an outer member movable relative to an inner member to vary the compression ratio of an internal combustion engine and a hydraulic system utilizing oil from the lubrication system of the engine for automatically controlling the relative movement of the members to maintain a predetermined maximum combustion chamber pressure. A hydraulic circuit includes an upper and a lower chamber which expands and contracts conversely upon relative movement of the piston members and a system for supplying oil to the upper chamber and to the lower chamber via the upper chamber and for discharging the oil from the upper chamber in a manner which gradually changes the compression ratio of the piston until a predetermined maximum combustion chamber pressure has been achieved and which tends to maintain the maximum combustion chamber pressure after it has been achieved.