Control device for hydraulic actuator in piston

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;
• a first 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;
• a second end of the oil passage being connected to an oil reservoir and a hydraulic pressure source;
• a main switching valve operatively connecting the second end of the oil passage to the oil reservoir and the hydraulic pressure source, 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 is positioned to the first switching position, and bringing the oil passage in a communicating state when the main switching valve is positioned to the second switching position.