Patent ID: 7954463

Claim:
An engine comprising: a crankshaft rotatable about a crankshaft axis; an expansion piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston is operable to reciprocate through an expansion stroke and an exhaust stroke of a four stroke cycle during a single rotation of the crankshaft; a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston is operable to reciprocate through an intake stroke and a compression stroke of said four stroke cycle during a single rotation of the crankshaft; a crossover passage interconnecting the compression cylinder and the expansion cylinder, wherein the crossover passage includes a crossover valve proximate the expansion cylinder; wherein the ratio of volume in the expansion cylinder when the expansion piston is at the expansion piston's bottom dead center (BDC) position to the volume in the expansion cylinder when the expansion piston is that the expansion piston's top dead center (TDC) position is 20 to 1 or greater; and wherein the engine includes an ignition device that is operable to initiate a combustion event in the expansion cylinder while the expansion piston is descending from the expansion piston's top dead center (TDC) position towards the expansion piston's bottom dead center (BDC) position.