Abstract: The present invention lowers energy loss while at the same time enhancing the responsiveness of a steering control system. When a steering controller is operated rapidly, the aperture area of a steering flow control valve 4 rapidly increases, and the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases. When the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases, a flow control valve 6 is biased by the spring force of a spring 6f and quickly moves to the side of a valve position 6b to increase the differential pressure (Pp?-PL) and make it correspond to a set pressure. Thus, the pressure oil of a surplus flow ?, which up to this point has been flowing to a discharge oil line 7, is quickly supplied from the flow control valve 6 to a steering hydraulic cylinder 5 via the steering flow control valve 4. Thus, an output Q? starts quickly relative to an input St.

Abstract: The present invention lowers energy loss while at the same time enhancing the responsiveness of a steering control system. When a steering controller is operated rapidly, the aperture area of a steering flow control valve 4 rapidly increases, and the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases. When the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases, a flow control valve 6 is biased by the spring force of a spring 6f and quickly moves to the side of a valve position 6b to increase the differential pressure (Pp?-PL) and make it correspond to a set pressure. Thus, the pressure oil of a surplus flow ?, which up to this point has been flowing to a discharge oil line 7, is quickly supplied from the flow control valve 6 to a steering hydraulic cylinder 5 via the steering flow control valve 4. Thus, an output Q? starts quickly relative to an input St.

Abstract: A hydraulic pipe arrangement of a working machine is not in contact with an obstacle and no torsion and no bending are generated. Accordingly, in a hydraulically driven type working machine provided with a boom (1) having a vertical swing supporting point supported at a base end side by a machine frame and a joint connection supporting point in a front end side, an arm (2) connected in a base end side to the joint connection supporting point, a boom driving hydraulic cylinder (6a) hoisting around a hoist supporting point provided in the machine frame so as to drive the boom, an arm driving hydraulic cylinder (7), and a working tool driving hydraulic cylinder (8), a swivel joint mechanism relaying a hydraulic pipe arrangement from a side of the machine frame is provided at a center of at least one of the vertical swing supporting point, the joint connection supporting point and the boom driving hydraulic cylinder hoist supporting point.

Abstract: First and second pistons are provided in a body, the first piston is restricted by the body and the second piston, and the second piston is restricted by the body and a second piston restricting part. Thus, the first piston can be stopped at three positions, and the respective stop positions can be adjusted. Therefore, when rotation speeds of left and right rotating bodies are switched among three levels by a hydraulic motor, a difference of the number of rotations between the left and right rotating bodies can be eliminated, and a vehicle can be suppressed from deviating from a course while it is going straight. Further, a mounting area of the hydraulic pump can be decreased and a structure can be made simple. The rotation speed of the hydraulic motor is changed among the three levels by a simple structure and simple control without using a complex structure such as a servo valve and complex control.

Abstract: A hydraulic pipe arrangement of a working machine is not in contact with an obstacle and no torsion and no bending are generated. Accordingly, in a hydraulically driven type working machine provided with a boom (1) having a vertical swing supporting point supported at a base end side by a machine frame and a joint connection supporting point in a front end side, an arm (2) connected in a base end side to the joint connection supporting point, a boom driving hydraulic cylinder (6a) hoisting around a hoist supporting point provided in the machine frame so as to drive the boom, an arm driving hydraulic cylinder (7), and a working tool driving hydraulic cylinder (8), a swivel joint mechanism relaying a hydraulic pipe arrangement from a side of the machine frame is provided at a center of at least one of the vertical swing supporting point, the joint connection supporting point and the boom driving hydraulic cylinder hoist supporting point.

Abstract: The invention can prevent a heat generation and a seizure due to a sliding friction between a piston and a cylinder in inclined shaft type and swash plate type hydraulic pumps even when they are made high speed.

Abstract: A travel drive apparatus for a hydraulic drive work vehicle of simple configuration, capable of preventing occurrence of cavitation which is predicted when a work vehicle is decelerated, descends a slope, or is changed from forward travel to reverse travel or from reverse travel to forward travel, and a control method thereof.

Abstract: A travel drive apparatus for a hydraulic drive work vehicle and control method therefor, the apparatus including: a travel hydraulic pump driven by the power of an engine; a hydraulic motor that receives discharged oil from the travel hydraulic pump and causes the vehicle to travel; a travel changeover valve that receives the discharged oil from the travel hydraulic pump, supplies the discharged oil to the hydraulic motor and discharges return oil from the hydraulic motor to a tank, in which the travel drive apparatus comprises; an accelerator for controlling an engine rotational speed; an operation unit for selecting vehicle forward travel, stop, and reverse travel; the travel changeover valve being adapted for receiving signals from the operation unit, switching the discharge oil supplied from the travel hydraulic pump to the hydraulic motor, and controlling vehicle forward travel, stop and reverse travel; a relief valve that regulates pressure for controlling the hydraulic motor when the vehicle has decele

Abstract: The present invention relates to a backpressure control circuit for a hydraulic drive device, which reduces the loss in drive power and which can suppress cavitation. Thus, the backpressure control circuit for hydraulic drive devices is a hydraulic drive circuit: for supplying to a hydraulic motor pressurized oil discharged from a hydraulic pump through a direction changeover valve, which is switched upon receipt of a pilot pressure; and for permitting at the time of braking by the hydraulic motor, a throttle valve to throttle return oil from the hydraulic motor and oil discharged from the hydraulic pump to generate a backpressure to supply pressurized oil to the hydraulic motor via a check valve for prevention of cavitation.

Abstract: In a counter balance valve, a valve body is provided with a valve bore having first and second pump-side ports, first and second motor-side ports and an auxiliary port. A spool is slidably fitted in the valve bore in a longitudinal direction thereof to establish and block communication between the respective ports. Left and right springs maintain the spool at a neutral position in which the respective ports are closed. A left pressure receiving chamber shifts the spool by a pressure oil supplied therein to a first travelling position at which the first pump-side port and the auxiliary port are communicated with each other and the second pump-side port and the second motor-side port are also communicated with each other.

Abstract: The present invention relates to a hydraulic circuit for a hydraulically driven working vehicle which allows the vehicle to travel at an almost constant speed during high-speed traveling, provides a great digging force during working, does not need a charging pressure for preventing cavitation, loses a small amount of energy, and has a simple structure. To this end, the hydraulic circuit has a hydraulic travel pump (2) and a working machine hydraulic pump (4) which are driven by the power of an engine (1) for discharging pressurized oil to a HST travel circuit and a working machine-driving hydraulic circuit, respectively, wherein pressurized oil from the working machine hydraulic pump (4) joins pressurized oil from the hydraulic travel pump (2) to effect high-speed traveling, while pressurized oil from the hydraulic travel pump (2) joins pressurized oil in the working machine hydraulic pump (4) to generate a large digging force to effect digging.

Abstract: A hydraulic motor driving apparatus includes a directional control valve for supplying discharge pressure fluid from a hydraulic pump into a first or second port of a hydraulic motor and returning the hydraulic fluid from the second or first port into a tank, and a pilot pressure applying valve for controlling the directional control valve. The directional control valve is urged to its neutral position by springs, to its first position by hydraulic pressure against its first pressure receiving portion and to its second position by hydraulic pressure against its second pressure receiving portion. Discharge pressure fluid from the hydraulic pump is supplied via a check valve into the first and second ports of the hydraulic motor when the directional control valve is at the neutral position. The discharge pressure fluid is supplied into the first port of the hydraulic motor and a hydraulic pressure fluid of the second port flows into the tank, when the directional control valve is at the first position.

Abstract: There is disclosed an apparatus for controlling the capacity of a hydraulic motor (5) in a hydraulically driven motor vehicle, which comprises: a hydraulic pump (2) adapted to be driven by an engine (1) having a variable rotation speed; the hydraulic motor of a variable capacity type adapted to be rotated by a discharge pressure fluid from the hydraulic motor for driving a traveling body that constitutes the motor vehicle allowed to travel; a capacity control section for reducing the capacity of the hydraulic motor when the rotation speed of the engine is increased and for increasing the capacity of the hydraulic motor when the rotation speed of the engine is reduced, the capacity control section having a variable operation rate and being operable at a variety of positions among a maximum capacity position, an intermediate capacity position and a minimum capacity position; and an operation rate control unit for accelerating the operation rate of the capacity control section when it is operating at a position

Abstract: There is provided a hydraulic braking apparatus, characterized in that it comprises: a first safety valve for draining a high pressure fluid at the side of a second port of a hydraulic motor into the side of a first port thereof; a second safety valve for draining a high pressure fluid at the side of the said first port of the said hydraulic motor into the side of the said second port thereof; and a braking valve adapted to be switched from a neutral position to a first position or a second position under a difference in pressure between the said first port and the said second port, the inlet side of each of the said first safety valve and the said second safety valve having a communication via the said braking valve with the side of each of the said first port and the said second port, and having an increased area of such communication when the said braking valve is set in the said neutral position and a reduced area of such communication when the braking valve is switched to the said first position or to th

Abstract: In a piston pump/motor of swash plate type which comprises: a cylinder block disposed in a casing to be rotatable jointly with a shaft therein; a plurality of pistons slidably inserted in the cylinder block parallel to the shaft; and a swash plate swingably attached to the casing for guiding the plurality of pistons on a front surface thereof and changing a displacement of each of the pistons by changing an inclination thereof, there is provided a swash plate angle changing apparatus in which the swash plate has a rear surface formed with a first contact surface and a second contact surface which make an angle between them. The casing has a swash plate support surface which is perpendicular to the shaft and with which the first contact surface and the second contact surface are each adapted to contact.

Abstract: A pressure control system in which a pressure in a back pressure chamber of a flow control valve is controlled according to a throttle opening of a pilot valve to locate stationary the valve body of the flow control valve at a position corresponding to the throttle opening of the pilot valve. In the system, a fixed throttle is provided in an oil passage extended to the back pressure chamber of the flow control valve, thereby applying a dampering action to the valve body.

Abstract: A pressure control system in which a pressure in a back pressure chamber of a flow control valve is controlled according to a throttle opening of a pilot valve to locate stationary the valve body of the flow control valve at a position corresponding to the throttle opening of the pilot valve. In the system, a fixed throttle is provided in an oil passage extended to the back pressure chamber of the flow control valve, thereby applying a dampering action to the valve body.

Abstract: A variable pressure control valve arranged to enable a pilot piston having a comparatively small diameter to be used thereby making the whole body of the valve compact. This variable pressure control valve comprises a spool (2) kept in pressure contact with the valve seat of a pressurized fluid inlet port (1) by the resilient force of a compression spring (3); a stationary valve shoe (5) fixed so as to support the base end of the compression spring; and an auxiliary compression spring (6) which urges the spool (2) to the side of the valve seat on one side thereof and is urged by a pilot piston (4) on the other side thereof.

Abstract: This invention relates to an electrohydraulic proportional control valve which continually provides pressurized oil into an oil path on the output side to prevent the existence of air therein and which can move a spool without any time delay when a solenoid is energized, thus improving response. The hydraulic proportional control valve includes a spool which establishes/cuts off communication between an inlet port communicating with a hydraulic pump and an outlet port on the output side, a spring disposed in such a manner as to apply to the base end of the spool such a spring force, which is in equilibrium with the oil pressure force acting on the tip of the spool so as to keep the spool at the position where the inlet port and the outlet port slightly communicate with each other, and a moving rod disposed in such a manner as to oppose the base end of the spool.

Abstract: An apparatus for supplying a pressure oil to a plurality of hydraulic cylinders of a working machine such as power shovels provided with working equipment such as shovels, wherein the cylinders are contracted at the same speed to move down or lower the working equipments at the same speed, so that the working equipment are prevented from suddenly dropping off in operation even if pressure oil passages (a, b) supplying the pressure oil to the cylinders are damaged during operation. The apparatus comprises: a lock valve assembly (B) provided with a valve housing (70) mounted on a cylinder tube of each of the hydraulic cylinders, in which valve housing (70) a check valve (77), a poppet valve (78) and a pilot valve (79) are mounted; and a directional control valve assembly (C) for selectively supplying the pressure oil to a lifting-movement pressure chamber (9a) and a lowering-movement pressure chamber (9b) of each of the hydraulic cylinders through the pressure oil passages (a, b), respectively.