Abstract

The variable compression ratio piston system for an engine adjusts the compression ratio of the engine piston by way of hydraulic fluid distributed between a pair of chambers formed in a pair of bores receiving control pistons mechanically coupled to the engine piston. A control valve selectively permits flow of hydraulic fluid between the high compression ratio line and the low compression ratio line. A variable force solenoid controlled by an engine control unit preferably controls the position of the control valve. The position of the spool controls whether hydraulic fluid can flow toward the first chamber, toward the second chamber, or not at all. Flow of hydraulic fluid is actuated by alternating forces from inertial and combustion forces on a crankshaft from operation of the engine.