Patent ID: 7059280

Claim:
A variable compression ratio system for an internal combustion engine, comprising: a variable compression ratio mechanism for continuously varying a compression ratio of the internal combustion engine, the variable compression ratio mechanism including a control shaft rotatably moveable to a rotational position corresponding to the compression ratio; a hydraulic actuator driving the control shaft to the rotational position depending on operating conditions of the internal combustion engine; a hydraulic pressure source mechanically driven by the internal combustion engine to produce a hydraulic pressure supplied to the hydraulic actuator; and a hydraulic control mechanism to variably control the hydraulic pressure supplied to the hydraulic actuator on the basis of the operating conditions of the internal combustion engine, wherein the hydraulic control mechanism comprises a controller programmed to determine a target hydraulic pressure by selecting a larger one of a first hydraulic pressure required to allow rotation of the control shaft to vary the compression ratio of the internal combustion engine such that knocking does not occur in the engine and a second hydraulic pressure required for holding the control shaft at a rotational position to maintain the compression ratio of the internal combustion engine.