Patent ID: 8608442

Claim:
A pitch driving unit for a wind-turbine rotor blade in which a wind turbine blade is mounted to a rotor head that is rotatably supported by and rotates about a nacelle, the pitch driving unit comprising: a hydraulic actuator that changes the pitch angle of the wind turbine blade; a hydraulic pump that supplies oil to the hydraulic actuator; a high-pressure oil line that guides the oil discharged from the hydraulic pump to the hydraulic actuator; a low-pressure oil line that returns the oil discharged from the hydraulic actuator to the hydraulic pump; and a pressure control unit that stores a predetermined surplus amount of the oil and that refills the low-pressure oil line with the stored oil while applying a minimum pre-pressure so that no negative pressure at an oil intake portion of the hydraulic pump is caused, wherein the hydraulic actuator, the hydraulic pump, the high-pressure oil line, the low-pressure oil line, and the pressure control unit constitute a closed hydraulic circuit that does not open to the atmosphere, the closed hydraulic circuit being filled with the oil, wherein the pressure control unit includes: an oil tank installed at the nacelle side; a connecting line that connects the oil tank to the low pressure oil line; and a gravity pre-pressurizing member that applies the minimum pre-pressure to the surface of the oil stored in the oil tank by gravity, wherein the low-pressure oil line is installed at the rotor head side, and the connecting line is connected to the low-pressure oil line via a rotary joint, and wherein the pressure control unit refills the low pressure oil line by the stored oil with said minimum pre-pressure during an operation of the pitch driving unit in which the pitch angle of the wind turbine blade is being adjusted in accordance with wind conditions in order to rotate the wind-turbine rotor blade at a desired rotational speed.