An automatic residual load relief system for hydraulic compactors having rotary pumps relieves residual load inherent in the compacted material by releasing hydraulic fluid from the cylinder prior to reversal of the rotary pump while preventing the fluid from returning to the pump. The system comprises in general a rotary pump powered by a motor, one-way suction check valves, a flow check valve, a one-way, normally-open, pilot operated check valve, a cylinder comprising a reciprocating piston, the piston defining a disk void and an annular void within the cylinder, and a tank.

An electro hydrostatic actuator comprises a hydraulic pump driven by an electric motor to supply hydraulic fluid to a hydraulic actuator. The pump comprises an inlet and an outlet for the hydraulic fluid and an active flow path arranged therebetween such that, in an active mode of operation when the pump is driven by the electric motor, hydraulic fluid is actively drawn in through the inlet and exhausted out through the outlet. The pump further comprises a bypass flow path arranged to open between the inlet and outlet such that, in a damping mode of operation when the pump is not driven by the electric motor, hydraulic fluid is able to pass through the pump along the bypass flow path between the inlet and outlet.

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.

A device for actuating a parking lock of an automatic transmission for a motor vehicle. A piston, which a hydraulic medium can be applied from a reservoir by a valve apparatus in order to actuate the parking lock by a valve apparatus, which has a first valve and a second valve, which is arranged downstream of the first valve and upstream of the piston in the flow direction of the hydraulic medium from the reservoir to the piston and which has at least one device connection, by way of which the hydraulic medium can be applied to the piston, the second valve having at least two switching states, and a working chamber, which is bounded by the housing element and by the piston and into which the hydraulic medium can be introduced from the reservoir by the valve apparatus in order to apply the hydraulic medium to the piston.

A consumer control device, with which an external consumer device can be supplied with compressed air in a controlled manner, contains a compressed air maintenance unit, equipped with a proportional pressure regulating valve that can be electrically actuated, which is connectable via an outlet channel with the consumer device to be actuated. In the outlet channel an electrically controllable shut-off valve and an outlet pressure sensor are connected, both of which communicate with an internal electronic control unit, which is also supplied with information on the air flow in the outlet channel. The consumer control device can be operated according to a similarly proposed method, in that the consumer device in a normal operating phase is supplied with compressed air by the shut-off valve that is in the release position, which is regulated by a proportional pressure regulating valve adopting working mode at a working pressure value.

To provide a work machine capable of efficiently regenerating the energy owned by hydraulic fluid during a swing deceleration. In the present invention, when a swing deceleration detection section 57a detects the state of a revolving upperstructure 102 being decelerated, when an operation judgment section 57c judges the state that a double-tilting pump/motor 14 is not supplying hydraulic fluid to any of a boom cylinder 1 and an arm cylinder 3, and when the number of double-tilting pumps/motors 14, 18 having supplied hydraulic fluid to a swing hydraulic motor 7 in the state before the swing deceleration detection section 57a detects the state of the revolving upperstructure 102 being decelerated is equal to one or more, a pump valve control section 57d controls changeover valves 43a, 45b, 45d, 49d to open and increases the displacements of the double-tilting pumps/motors 14, 18 to the side to make suction pressures become higher than discharge pressures of the double-tilting pumps/motors 14, 18 so that the double-tilting pumps/motors 14, 18 operate as motors.

Disclosed is a hydraulic drive system capable of improving the fuel efficiency of a work machine by reducing the pressure loss and drag loss of a hydraulic pump. There are provided an electric motor M; a third pump P3 driven by the electric motor; a third pump hydraulic line L3 to which the delivered hydraulic fluid from the third pump is supplied; a third directional control valve V4 provided in the third pump hydraulic line, switch-operated by an arm operation device 19, and controlling the flow rate of the hydraulic fluid supplied to the arm cylinder 8 from the third hydraulic pump; and a controller 18 drive-controlling the electric motor, wherein the controller drives the third pump by the electric motor when a swing/arm combined operation is detected by pilot pressure sensors S6, S7, S10, S11.

In a construction machine with a hydraulic pilot type hydraulic control device, occurrence of jerking is prevented. A hydraulic excavator 1 having hydraulic pumps 51L and 51R, travel motors 22L and 22R, traveling operating levers 34L and 34R, a pilot pump 54, hydraulic pilot valves 55La, 55Lb, 55Ra, and 55Rb, and directional control valves 53L and 53R includes: changeover switches 35L and 35R which change the operating mode of the traveling operating levers 34L and 34R; pilot pressure adjusting devices 5L and 5R which adjust the pilot pressure applied to the directional control valves 53L and 53R; and pilot pressure sensors 56La, 56Lb, 56Ra, and 56Rb. The pilot pressure adjusting devices apply the pilot pressure at the time when the operating mode of the traveling operating levers 34L and 34R is changed to a control mode, to the directional control valves 53L and 53R.

A hydraulic unit is provided with: a manifold which forms a hydraulic circuit; a tank which is joined to the manifold; and a hydraulic pump which suctions hydraulic fluid in the tank and supplies the hydraulic fluid to the manifold, wherein the base end portion of a suction strainer is fitted into the hydraulic pump, and the suction strainer has such a shape that the base end portion of the suction strainer is not separated from the hydraulic pump in a state where the leading end portion of the suction strainer is in contact with the tank and an opening through which the hydraulic fluid is introduced from the tank is provided at the leading end portion.

Disclosed embodiments include travel motor hydraulic circuits for controlling the provision of hydraulic fluid to a travel motor. The travel motor hydraulic circuits include a counterbalance valve configured to block the flow of hydraulic fluid when in a neutral position to prevent unintended movement of a power machine, and an anti-cavitation valve configured to direct flow of hydraulic fluid back to the travel motor to prevent cavitation.