A work machine includes: a main circuit that supplies a working fluid from a pump to an actuator; a pilot circuit that introduces part of the working fluid from the pump, to a pilot pressure receiving section of a control valve; a bleed-off passage that connects the pump and a tank. The pilot circuit is provided with: a first pressure reducing valve that generates a pilot primary pressure; and second and third pressure reducing valves that generate a pilot secondary pressure to be applied to the control valve and a bleed-off valve. A moving area of a spool of the bleed-off valve has a first moving area where an opening area of a restrictor changes stepwise, and a second moving area where the opening area of the restrictor changes continuously. A controller controls the third pressure reducing valve such that the spool is positioned in the first moving area at the time of non-operation of the actuator, and the spool is positioned in the second moving area at the time of operation of the actuator. The restrictor of the bleed-off valve has a restricting hole that gives a resistance to the working fluid passing therethrough in a case the spool is positioned in the first moving area.

A distributor (3) of the closed-center, load sensing type, connected to a variable displacement pump (1) comprises a valve device (10, 110), composed of a logic element, which is pilot-operated and configured to bring a high-pressure channel (2) into communication with a low-pressure channel (4), the connection being usually opened by the combined action of an equivalent pressure generated by an elastic member (12) and a counter-pressure which is generated, under operative conditions, in the low-pressure channel (4). The connection is closed in a switching position and it is pilot-operated to a closure position by the combined action of a high-pressure signal (P) and a load sensing signal (LS).

A cylinder driving apparatus includes a first passage connecting a first chamber of a cylinder to a first port of a pump; a second passage connecting a second chamber of the cylinder to a tank; a third passage connecting a second port of the pump to the tank; a throttle configured to apply resistance to a working fluid flowing through the third passage; and an operated check valve provided in the first passage to allow the working fluid to flow from the pump into the first chamber. The operated check valve is configured to allow the working fluid to flow from the first chamber into the pump in accordance with a fluid pressure of the working fluid in the third passage between the pump and the throttle.

A control arrangement for supplying a plurality of hydrostatic actuators includes a pump with an output connected to a circulating line that opens into a tank. The control arrangement has a metering port and an individual pressure compensator for each actuator. The individual pressure compensators are connected in series by the circulating line. Some of the pressure medium are configured to be branched off from the circulation channel for the respective actuator by the individual pressure compensators and fed to the metering port disposed downstream of the individual pressure compensator. The pressure medium that is not required is forwarded from each individual pressure compensator into the circulating line and is fed back from the last individual pressure compensator to the tank by the circulating line. The actuators are prioritized based on the order of their individual pressure compensators and move independently of the load pressure without expensive load sensing lines.

A hydraulic system according to an embodiment of the present invention comprises: a main hydraulic pump for discharging a hydraulic fluid; a plurality of driving apparatuses operating by receiving the hydraulic fluid; a parallel flow path through which the hydraulic fluid discharged by the main hydraulic pump flows; a plurality of control spools respectively connected to the parallel flow path in parallel to control the supply of hydraulic fluid to the plurality of driving apparatuses; and a plurality of electronic proportional decompression valves for adjusting a pilot pressure, applied to the respective control spools to be proportional to a current signal which has been input, wherein, if the plurality of control spools do not operate, the hydraulic fluid discharged by the main hydraulic pump is drained into an oil tank via the parallel flow path without passing through the plurality of control spools.

The invention relates to a wind energy system with at least one pitch adjustment system for adjusting the pitch of at least one rotor blade of the wind energy system, wherein the pitch adjustment system comprises at least one electrohydraulic drive that comprises an unregulated electromotor rotating in one direction of rotation for generating pressure.

During boom-midair lowering operation in which a front work implement 130 can be turned under the self-weight of a boom 131, a hydraulic pump/motor 7 is operated as a motor to operate a generator/electric motor 10 as a generator. Power generation operation is performed by the hydraulic fluid discharged from a bottom-side chamber 5b of a boom cylinder 5 to recover positional energy. During jack-up in which the front work implement 130 cannot be turned under the self-weight of the boom 131, the generator/electric motor 10 is operated as an electric motor to operate the hydraulic pump/motor 7 as a pump. The jack-up is performed by supplying the hydraulic fluid from the bottom-side chamber 5b to rod-side chamber 5a of the boom cylinder 5 without supplying the hydraulic fluid from the main pump 2 to the rod-side chamber 5a of the boom cylinder 5.

To reduce the cost by reducing the number of parts and simplify the control of regeneration in the hydraulic actuator even though the meter-in control and the meter-out control can be performed separately while the supply and the discharge of hydraulic fluid is controlled. A meter-in valve that controls supply flow from a hydraulic pump into a hydraulic cylinder is provided, and meter-out switching valve that switches the direction of supply and discharge of the hydraulic oil into the hydraulic cylinder and controls the discharge flow from the hydraulic cylinder to the oil tank is installed on the down stream side of the meter-in valve, and further, a regeneration control valve is installed on the down stream side of the meter-out switching valve.

To achieve improvement in work efficiency of calibration work and improvement in calibration accuracy, by performing control so that the time taken to increase the sweep of an applied current becomes substantially constant, upon the calibration of a valve opening position current value when a valve operated by electrical current applied to an electrical actuator opens a flow passage. There is provided a predicted value calculating means for predicting a calibration value of a valve opening position current value on the basis of information concerning valve opening position current values, and the sweep starting current value is set so that the time taken to increase the sweep to a predicted value predicted by the predicted value calculating means from a sweep start becomes a fixed time.

A hydraulic drive system for operating a hydraulic cylinder in first and second movement profiles. A hydraulic drive unit includes first and second hydraulic machines, each with first and second connections. In the first movement profile, a first cylinder chamber of the hydraulic cylinder is fluidly connected to a first fluid reservoir and a second cylinder chamber is fluidly connected to the second connection of the second hydraulic machine. In the second movement profile, the first connection of the first hydraulic machine is connected to the second connection of the second hydraulic machine.