A bi-directional pump connected to a motor by a pair of supply/discharge lines; a regulator changes the bi-directional pump tilting angle; and a controller controls the regulator based on a turning signal outputted from a turning operation valve. At the turning acceleration, at which the signal increases, the controller calculates a motor flow rate passing through the motor and an instruction flow rate determined based on the turning signal. If the instruction flow rate is greater than a reference flow rate obtained by adding a predetermined value to the motor flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the reference flow rate. If the instruction flow rate is not greater than the reference flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the instruction flow rate.

A booster device for a hydraulic circuit comprising a high-pressure circuit (12) and a low-pressure circuit (16) connected to a system generating the high pressure and to receivers, said booster device maintaining a minimum pressure in the low-pressure part, characterized in that it comprises a hydraulic motor (30) of which the inlet is connected to the high-pressure circuit (12) and the outlet to the low-pressure circuit (16), which drives a booster pump (20) sucking the fluid from a reservoir (24), in order to discharge it into this low-pressure circuit.

A construction machine, comprising a hydraulic pump, a swing hydraulic motor, a swing electric motor, a delivery capacity regulating device, and a control unit which controls the driving/braking of the swing structure, is configured to comprise an operation amount detection device for detecting the operation amount of the swing control lever and a speed detection device for detecting the speed of the swing electric motor. The control unit includes a hydraulic pump output reduction control unit which takes in an operation amount signal representing the operation amount of the swing control lever detected by the operation amount detection device and a speed signal representing the speed of the swing electric motor detected by the speed detection device and controls the delivery capacity regulating device by calculating a reduction rate of the output of the hydraulic pump based on the detection signals.

A variable displacement axial piston pump including a cylinder block defining a plurality of cylinder bores, each receiving a piston. A swash plate having a piston-supporting surface is pivotally supported relative to the cylinder block. A port block defines first and second pumping ports arranged in fluid communication with the plurality of cylinder bores such that, during operation of the pump, one of the first and second pumping ports is configured to supply fluid to the cylinder bores for pumping, and the other of the first and second pumping ports is configured to receive fluid pumped from the plurality of cylinder bores. The swash plate partially defines at least one variable volume control chamber, and the swash plate is operable to tilt with respect to the port block in response to a fluid pressure change in the at least one control chamber.

Systems are provided comprising at least one driving cylinder comprising a driving chamber and a driving piston within the driving chamber. The driving piston separates the driving chamber into a driving fluid zone for receiving a driving fluid and a buffer zone for receiving a buffer fluid. The driving piston is movable in the driving chamber by the driving fluid. The systems may also comprise a driven cylinder comprising a driven chamber and a driven piston moveable in the driven chamber. The driven piston is connected to and driven by the driving piston to move within the driven chamber. The driven chamber comprises an input port configured to receive a driven fluid at a first, lower pressure into the driven chamber and an output port configured to expel the driven fluid at a second, higher pressure from the driven chamber when the driven fluid is pressurized by the driven piston. The buffer fluid is different from the driving fluid and the driven fluid, and the buffer fluid in the buffer zone separates the driving fluid from the driven fluid.

A drive system for hydraulically driven working mechanisms of a working machine includes an axial piston pump, the pump capacity and flow direction of which is varied by changing the pivot angle of the axial piston pump. The drive system includes a hydraulic motor connected via a line to the axial piston pump and drivably connected to the working mechanisms, a control unit operated to set the pump capacity of the axial piston pump to zero and a control valve arrangement that is actuated by the control unit to actuate a limiting device such that the pivot angle of the axial piston pump can be mechanically set to zero degrees (0°).

A swash plate type piston pump includes a plurality of pistons, a cylinder block including a plurality of cylinders for housing the pistons, a swash plate for reciprocating the pistons to expand and contract volume chambers of the cylinders with the rotation of the cylinder block, a biasing mechanism for biasing the swash plate in a direction to increase a tilting angle, a first control pin for driving the swash plate in a direction to reduce the tilting angle according to a first load pressure, and a second control pin for driving the swash plate in a direction to reduce the tilting angle according to a second load pressure. The first and second control pins are connected in series.

Methods and systems are provided to adaptively control a hydraulic fluid supply to supply a driving fluid for applying a driving force on a piston in a gas compressor, the driving force being cyclically reversed between a first direction and a second direction to cause the piston to reciprocate in strokes. During a first stroke of the piston, a speed of the piston, a temperature of the driving fluid, and a load pressure applied to the piston is monitored. Reversal of the driving force after the first stroke is controlled based on the speed, load pressure, and temperature.

A hydraulic system of vehicle transmission device is provided. A heat exchanger configured downstream is used to cool working oil discharged from a torque converter, and the working oil is supplied, as lubricating oil, to a lubricating system hydraulic circuit. On the other hand, excess oil flowing out of a regulator valve for regulating line pressure returns to an input side of an oil pump through a recycle oil path. A bypass oil path is disposed in a manner of branching from the recycle oil path and connecting to an input side of the heat exchanger. A control mechanism is disposed, and when hydraulic pressure at the side of the recycle oil path is higher than that at the side of the heat exchanger, the bypass oil path is opened to guide oil at the side of the recycle oil path to the input side of the heat exchanger.

A hydraulic system of vehicle transmission device is provided. A heat exchanger configured downstream is used to cool working oil discharged from a torque converter, and the working oil is supplied, as lubricating oil, to a lubricating system hydraulic circuit. On the other hand, excess oil flowing out of a regulator valve for regulating line pressure returns to an input side of an oil pump through a recycle oil path. A bypass oil path is disposed in a manner of branching from the recycle oil path and connecting to an input side of the heat exchanger. A control mechanism is disposed, and when hydraulic pressure at the side of the recycle oil path is higher than that at the side of the heat exchanger, the bypass oil path is opened to guide oil at the side of the recycle oil path to the input side of the heat exchanger.