A hydraulic system includes: an operation device that outputs an operation signal corresponding to an operating amount of an operating unit; a variable displacement pump that supplies hydraulic oil to a hydraulic actuator; a control valve interposed between the actuator and pump, the control valve changing a meter-in opening area thereof, so an increase rate of the opening area increases in accordance with increase in the operation signal; a regulator that adjusts a tilting angle of the pump; an unloading valve that defines an unloading flow rate, at which the hydraulic oil is released to a tank; and a controller that, when the operation device is operated, determines a control valve required flow rate so rate is proportional to the meter-in opening area of the control valve, and controls the regulator so a discharge flow rate of the pump is a sum of the control valve and unloading flow rates.

To provide a construction machine that can highly precisely control branch flows from a hydraulic pump to a plurality of hydraulic actuators without being affected by load conditions. A controller (100) has a meter-out valve control section (140) configured to calculate a target opening area of a second meter-out valve (65a) (65b) according to a pressure difference between a supply pressure and a second meter-in pressure, or calculate a target opening area of a first meter-out valve (55a) (55b) according to a pressure difference between the supply pressure and the first meter-in pressure.

To provide a construction machine that can highly precisely control branch flows from a hydraulic pump to a plurality of hydraulic actuators without being affected by load conditions. A controller (100) has a meter-out valve control section (140) configured to calculate a target opening area of a second meter-out valve (65a) (65b) according to a pressure difference between a supply pressure and a second meter-in pressure, or calculate a target opening area of a first meter-out valve (55a) (55b) according to a pressure difference between the supply pressure and the first meter-in pressure.

To provide a work machine that makes it possible to drive actuators faster and more accurately by supplying flows to the actuators accurately at target rates without depending on load variations in a case where the machine body is controlled automatically by command inputs of a controller, while high operability is ensured for manual operation by an operator. In a case where a machine control function is cancelled via a machine control switch, a controller cancels limitation of the flow rate of a hydraulic fluid supplied to a plurality of directional control valves, the limitation being performed by the auxiliary flow rate control devices, and in a case where the machine control function is selected via the machine control switch, the controller causes the auxiliary flow rate control devices to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves.

Hydraulic pressure compensator units and hydraulic systems incorporating hydraulic pressure compensator units. The pressure compensator units include a main valve body defining a central axis and a first central passage, a compensation valve member positioned in the first central passage and defining a second central passage, the first central passage being in selective fluid communication with a port of hydraulic actuator. A load sense check component is positioned within the second central passage and adapted to move in a first axial direction to selectively open a fluid communication between a pump output and a load sense line. A reverse flow check component is positioned within the second central passage and adapted to move in a second axial direction opposite the first axial direction to selectively open a fluid communication between the hydraulic actuator and a tank line.

A discharge pressure scale (30) includes a valve housing (41) having a functional connector (A), a return flow connector (T) and a user connector (28). A valve piston (52) is guided such that it moves longitudinally against the effect of an energy accumulator (42), moving from a respective opening or regulating position, against a valve seat (94), into a closed position. The user connector (28) and return flow connectors (T) are separated from one another. The fluid pressure present at the user connector (28) can be guided onto a pressure-active surface (A.sub.1*) of the valve piston (52) by a pressure compensation device (70) in such a way that it moves into its respective opening or regulating position in a pressure-compensated manner due to the force of the energy accumulator (42).

A discharge pressure scale (30) includes a valve housing (41) having a functional connector (A), a return flow connector (T) and a user connector (28). A valve piston (52) is guided such that it moves longitudinally against the effect of an energy accumulator (42), moving from a respective opening or regulating position, against a valve seat (94), into a closed position. The user connector (28) and return flow connectors (T) are separated from one another. The fluid pressure present at the user connector (28) can be guided onto a pressure-active surface (A.sub.1*) of the valve piston (52) by a pressure compensation device (70) in such a way that it moves into its respective opening or regulating position in a pressure-compensated manner due to the force of the energy accumulator (42).

A hydraulic system includes first and second valve assemblies connected to a common pump. The first valve assembly includes a main valve housed inside a manifold. A pressure compensator valve maintains a constant pressure drop across a variable orifice of the main valve. A pressure limiter valve is in communication with the main valve and the pressure compensator valve, and allows an actuator connected to the first valve assembly to operate independently of the second valve assembly so that fluid flow to a work port of the first valve assembly is not interrupted by operation of the second valve assembly.

A valve device having an inlet port (ZA) of an inlet side for supplying a hydraulic consumer with hydraulic fluid, wherein said hydraulic consumer can be connected to the inlet port (ZA), having an outlet port (AA) of an outlet side for discharging pressurized fluid from the connectable consumer, wherein, depending on the direction of actuation of this consumer, the inlet side becomes the outlet side and the outlet side becomes the inlet side, having a pressure supply port (P), and having a return port (T), is characterized in that a pressure regulating device is acting on the respective inlet side and a volume flow regulating device is acting on the respective outlet side.

A hydraulic drive device for a cargo vehicle includes a hydraulic cylinder supplying and discharging of hydraulic oil, an operation member that operates the hydraulic cylinder, a hydraulic pump, a lowering oil path connecting the hydraulic cylinder and the hydraulic pump, an operation valve disposed in the lowering oil path, a bypass oil path that branches off from the lowering oil path, a bypass flow rate control valve disposed in the bypass oil path and that controls a bypass flow rate, and a resistance element that is disposed closer to the hydraulic cylinder than the operation valve in the lowering oil path and that increases a fluid resistance. A pilot flow path of the bypass flow rate control valve is connected to a part of the lowering oil path between the hydraulic cylinder and the resistance element.