A hydraulic system includes: a cylinder in which an interior of a tube is divided by a piston into a first pressure chamber and a second pressure chamber; a first bidirectional pump connected to the first pressure chamber by a first supply/discharge line; a second bidirectional pump connected to the second pressure chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and an electric motor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

Provided is a construction machine on which a hydraulic closed circuit for driving a single rod-type hydraulic cylinder and a swing hydraulic motor is mounted and that has good swing deceleration responsiveness. In this construction machine that drives each of a single rod-type hydraulic cylinder and a swing hydraulic motor in a closed circuit, a minimum passage area from a second flushing valve to a tank in a case the second flushing valve is fully open is smaller than a minimum passage area from a first flushing valve to the tank in a case the first flushing valve is fully open.

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 steering device includes: a cylinder demarcated into first and second chambers by a piston; a main valve having first and second shuttle chambers; a hydraulic source having first and second discharge ports; a first oil passage configured to connect the first chamber and the first shuttle chamber; a second oil passage configured to connect the second chamber and the second shuttle chamber; a third oil passage configured to connect the first shuttle chamber and the first discharge port; a fourth oil passage configured to connect the second shuttle chamber and the second discharge port; and a tank connected to the main valve via the third oil passage and the fourth oil passage. One of the first shuttle chamber and the second shuttle chamber of the main valve is in an opened state when the hydraulic source is stopped.

An injection moulding system, water jet cutting machine or other industrial system has a synthetically controlled variable displacement fluid working machine which outputs hydraulic fluid to one or more fluid consumers, such as rams or hydraulic motors, through hydraulically stiff fluid retaining volumes and receives hydraulic fluid back from one or more fluid consumers through the same or other said hydraulically stiff fluid retaining volumes. Individual piston cylinder assemblies can be allocated to different outputs. There may be no valve between the machine and the consumers. A working chamber of the machine can be caused to undergo a motoring cycle to enable the machine to output more power than is received from a motor driving the machine. An accumulator can be used to provide a source of hydraulic compliance. The machine can be controlled using pressure control, flow control, feed forward control or variable power/variable power limit control.

Hydraulic fluid flushing valve for hydrostatic units usable in closed hydraulic circuit propel applications, having a flushing valve housing with a first inlet port connected to a first working line, a second inlet port connected to a second working line, and a discharge port for draining hydraulic fluid. A two-sided flushing valve flushing valve spool which can be shifted is mounted within the flushing valve housing in a cylindrical valve bore, which, in a shifted position, enables a fluid flow from one of the first or the second inlet port at which the lower hydraulic pressure is present, to the discharge port. The flushing valve spool includes on each side a pressure surface each of which is connected to one of the two inlet ports. At each side of the flushing valve spool a flushing valve spring is located in the flushing valve housing in such a manner that, when the flushing valve spool is in its centre, non-shifted position, at each side of the flushing valve spool a distance between a spring contact surface on the flushing valve spool and a spring support surface in the flushing valve housing is greater than the axial length of the corresponding flushing valve spring.

A linear actuator system includes a linear actuator and at least one proportional control valve and at least one pump connected to the linear actuator to provide fluid to operate the linear actuator. The at least one pump includes at least one fluid driver having a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from the pump inlet to the pump outlet. The linear actuator system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover and concurrently establishes an opening of the at least one proportional control valve to adjust at least one of a flow and a pressure in the linear actuator system to an operational set point.

The present disclosure relates to a hydraulic drive system having a hydraulic circuit architecture operable in first and second modes. In a first mode, a main hydraulic pump (22) is used to drive a hydraulic actuator (24) via a closed hydraulic circuit, and a charge pump (42) provides charge flow to the closed hydraulic circuit. In a second mode the main pump set to zero displacement and the charge pump (42) is used to drive the hydraulic actuator (24).

A mixer drum driving apparatus includes an auxiliary fluid pressure pump that is provided independently of a fluid pressure pump and is capable of supplying a working fluid to a fluid pressure motor so as to cause a mixer drum to perform agitation rotation, a plurality of motors configured to drive the auxiliary fluid pressure pump to rotate, and a control unit that controls rotation of the mixer drum. When an engine is stopped during the agitation rotation of the mixer drum, the control unit drives the auxiliary fluid pressure pump to rotate by operating the plurality of motors selectively in accordance with a load of the mixer drum.

The present invention relates to a closed hydraulic circuit between a hydraulic pump and a hydraulic motor that are connected to one another via working lines, a flushing pump being provided in order to feed a pressure medium into the working lines, and an output connection being provided in order to discharge excess pressure medium from the working lines. At least one hydraulic consumer, which is provided to convert at least some of the volume flow discharged from the hydraulic circuit into mechanical power, is connected downstream of the output connection.