Patent ID: 7434548

Claim:
A control device for a hydraulic actuator in a piston comprising: an oil passage being provided through a connecting rod, a crankshaft and a crankcase supporting the crankshaft, one end of said oil passage being connected to a hydraulic chamber of a hydraulic actuator provided in a piston connected to the crankshaft via the connecting rod with another end of the oil passage being connected to an oil reservoir and a hydraulic pressure source via a main switching valve; said main switching valve being movable between a first switching position for allowing the oil passage to communicate with the oil reservoir, and a second switching position for allowing the hydraulic pressure source to communicate with the oil passage; and an auxiliary switching valve being provided in the connecting rod, said auxiliary switching valve causing a downstream side of the oil passage that leads to the hydraulic chamber to open into the crankcase when the main switching valve comes to the first switching position, and bringing the oil passage in a communicating state when the main switching valve comes to the second switching position.