Patent ID: 7150250

Claim:
Method of operating a four-stroke internal combustion engine including a variable volume combustion chamber defined by a piston reciprocating within a cylinder between top-dead center and bottom-dead center points and an intake valve and an exhaust valve controlled during repetitive, sequential exhaust, intake, compression and expansion strokes of said piston comprising: providing an exhaust event during which the exhaust valve is open for expelling combusted gases from the combustion chamber; providing a rebreathe event wherein the intake valve is open during at least a portion of at least one of the expansion and exhaust strokes for expelling a portion of combusted gases from the combustion chamber to an intake passage; subsequent to the exhaust event, providing a period of simultaneous closure of the exhaust and intake valves during at least a portion of the intake stroke of the piston effective to establish a sub-atmospheric pressure condition within the combustion chamber; and, providing an intake event during which the intake valve is open for ingesting fresh air and combusted gases from the intake passage into the combustion chamber.