Abstract: A volume control valve for controlling the volume of a variable displacement type hydraulic rotary machine includes a valve housing provided with a bore in which a spool slides axially to selectively establish and block communication of a pressure oil feed/discharge port with a high pressure port and a tank port. A first pressure receiving portion is formed in the spool to receive a load pressure as a pilot pressure introduced from a pilot port for displacing the spool axially within the bore. A bottomed axial bore is formed in the spool which has a slidable piston therein defining an oil chamber between the piston end and the bottom of the bore to receive a hydraulic reaction force induced within the oil chamber. A second pressure receiving portion is formed by the bottom of the bore to receive an internal pressure of the oil chamber, thereby changing a total pressure receiving area of the spool in conjunction with the first pressure receiving portion.

Abstract: At the time of casting a structural material for a casing, metal pipes to be used as passages to and from a tilt actuator of a swash plate are integrally embedded in a cast body of the structural material. In a casting stage of the structural material for the casing, metal pipes are set in position within a casting mold, and then molten metallic material is introduced into the mold. A main casing for a hydraulic motor is formed out of the cast structural material by finishing its inner and outer peripheral surfaces and outer ends of embedded metal pipes. The resulting casing has the metal pipe conduits embedded in its cylindrical body portion from its open end toward its bottom portion with cylinders for a tilt actuator, the embedded metal pipe conduits providing passages on the inner peripheral side for supplying and discharging tilt control hydraulic fluid to and from the tilt actuator.

Abstract: A hydraulic-motor drive circuit system includes an auxiliary hydraulic source connected to one end of an auxiliary line, a low-pressure selector connected to the other end of the auxiliary line and a pair of main lines for causing the other end of the auxiliary line to communicate with one of the main lines on the low pressure side during rotation of a hydraulic motor for driving an inertia load, and a switching control arranged in the auxiliary line for supplying the hydraulic fluid from the auxiliary hydraulic source to the other end of the auxiliary line when the directional control valve is in a neutral position, cutting off the hydraulic fluid from the auxiliary hydraulic source to the other end of the auxiliary line when the directional control valve is in an operative position.

Abstract: A hydraulic drive traveling system has a pressure compensated low control valve connected between a hydraulic pump and a variable displacement type hydraulic motor for controlling a flow rate of the hydraulic fluid supplied to the motor. The flow rate is controlled in accordance with the delivery pressure of the pump and demanded traveling speed of the motor. When the delivery pressure of the pump is at a high level, the motor is shifted to a first capacity. When the delivery pressure of the pump is low, the motor is shifted to either the second capacity or the first capacity depending upon the demanded traveling speed.