Patent ID: 7931453

Claim:
A capacity variable device for a rotary compressor comprising: a casing that is provided with a gas intake pipe communicating with an evaporator and a gas discharge pipe communicating with a condenser; a cylinder that is fixedly installed inside the casing and has an intake hole penetratingly formed in a radial direction and directly communicating with a gas intake pipe, a valve hole penetratingly formed in a radial direction at a predetermined angle with respect to the intake hole, a bypass hole penetrating the middle portion of the valve hole in an axial direction and excluding a portion of a refrigerant, and a communication hole guiding to an intake chamber, the refrigerant excluded to the bypass hole; a plurality of bearing plates that form an internal space by covering both upper and lower sides of the cylinder together, a discharge hole communicating with an internal space of the cylinder and discharging a compression refrigerant, and a gas flow path provided at at least one side of the plurality of bearing plates, the gas flow path connecting the bypass hole with the communication hole; a rolling piston that is coupled to a rotary shaft of a driving motor rotating at a constant speed and compresses a refrigerant gas by a centrifugal force while orbiting within the cylinder; a vane that is coupled to the vane slit of the cylinder movably in a radial direction to pressingly contact with an outer circumferential surface of the rolling piston and divides the internal space of the cylinder into an intake chamber and a compression chamber; a sliding valve that is installed in the valve hole of the cylinder to slide in a radial direction and opens and closes the bypass hole of the cylinder, wherein the sliding valve is formed as a cylindrical body with both ends opened, wherein the sliding valve comprises a sub-valve at its end close to the cylinder so as to block the valve hole and exclude a portion of a compression gas when over-compression occurs within the cylinder, wherein the sub-valve is formed as a plate-shaped valve having a gas passing groove at its outer circumferential surface and sliding within the sliding valve, wherein a valve stopping protrusion that prevents a separation of the plate-shaped valve is formed at an inner circumferential surface of the sub-valve close to the cylinder, and wherein a sub-valve stopper limiting a distance that the plate-shaped valve moves is provided at a rear side of the plate-shaped valve; and a back pressure switching device that differentially supplies a back pressure to a rear surface of the sliding valve, such that the sliding valve slides within the valve hole according to an operation mode of the compressor to open and close the bypass hole.