A motor-generator (27) is connected mechanically to an engine (21) and a hydraulic pump (23). The hydraulic pump (23) delivers pressurized oil to cylinders (12D) to (12F) in a working mechanism (12), a traveling hydraulic motor (25) and a revolving hydraulic motor (26). The revolving hydraulic motor (26) drives a revolving device (3) in cooperation with a revolving electric motor (33). An HCU (36) reduces outputs of the revolving electric motor (33), the revolving hydraulic motor (26), the boom cylinder (12D) and the like such that a ratio of a revolving speed of an upper revolving structure (4) and a movement speed of raising a boom (12A) is held to a ratio in a normal mode (NMODE) at the time of performing a compound movement of a revolving movement and a boom-raising movement in a low speed mode (LSMODE).

A hydraulic actuator; a control valve that controls supply and discharge of hydraulic oil to and from the hydraulic actuator; a pilot operation valve connected to the operation valve by a pair of pilot lines; a proportional solenoid pressure-reducing valve provided on at least one of the pair of pilot lines; an operation detector that outputs an operation amount signal in accordance with an inclination angle of an operating lever of the pilot operation valve; and a controller that controls the proportional solenoid pressure-reducing valve such that, from immediately after a change amount per unit time in the operation amount signal outputted from the operation detector has decreased by a threshold value or more, a pilot port pressure of the control valve gradually decreases to zero due to communication of a secondary pressure port and a tank port of the proportional solenoid pressure-reducing valve with each other.

A hydraulic actuator; a control valve that controls supply and discharge of hydraulic oil to and from the hydraulic actuator; a pilot operation valve connected to the operation valve by a pair of pilot lines; a proportional solenoid pressure-reducing valve provided on at least one of the pair of pilot lines; an operation detector that outputs an operation amount signal in accordance with an inclination angle of an operating lever of the pilot operation valve; and a controller that controls the proportional solenoid pressure-reducing valve such that, from immediately after a change amount per unit time in the operation amount signal outputted from the operation detector has decreased by a threshold value or more, a pilot port pressure of the control valve gradually decreases to zero due to communication of a secondary pressure port and a tank port of the proportional solenoid pressure-reducing valve with each other.

Hydraulic systems for shrinking landing gear shrink are described. An example apparatus includes a landing gear strut, a transfer cylinder, aircraft hydraulics, a pressure vessel, and a pressure-operated check valve. The landing gear strut has an outer cylinder and an inner cylinder movable relative to the outer cylinder between a first position and a second position. The landing gear strut has a first length when the inner cylinder is in the first position and a second length less than the first length when the inner cylinder is in the second position. The transfer cylinder exchanges hydraulic fluid with the landing gear strut. The aircraft hydraulics exchange hydraulic fluid with the transfer cylinder. The pressure vessel exchanges gas with the landing gear strut. The pressure-operated check valve controls an exchange of gas between the pressure vessel and the landing gear strut based on hydraulic fluid received from the aircraft hydraulics.

A hydraulic system (600) and method for reducing boom dynamics of a boom (30), while providing counter-balance valve protection, includes a hydraulic actuator (110), first and second counter-balance valves (300, 400), first and second control valves (700, 800), and first and second blocking valves (350, 450). A net load (90) is supported by a first chamber (116, 118) of the hydraulic actuator, and a second chamber (118, 116) of the hydraulic actuator may receive fluctuating hydraulic fluid flow from the second control valve to produce a vibratory response (950) that counters environmental vibrations (960) on the boom. The first blocking valve prevents the fluctuating hydraulic fluid flow from opening the first counter-balance valve. The first blocking valve may drain leakage from the first counter-balance valve.

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.

This valve includes a first chamber, a second chamber, a seat with a liquid passage, a plug movable between i) an open position and ii) a closed position, and a biasing member for urging the plug toward the closed position. The valve includes an actuating member having a face which sustains an actuating pressure. The actuating member is movable between i) an actuation position for opening the plug and ii) a rest position. The valve operates, selectively: in a feed mode, where the plug is open and the actuating member is at rest, the liquid flowing in one direction throughout the second chamber, or in a latch mode, where the plug is closed and the actuating member is at rest, no liquid flowing in the valve, or in a drain mode, where the plug is open, the liquid flowing in the reverse direction throughout the second chamber.

A hydraulic system is disclosed. The hydraulic system may include a source of pressurized fluid; a tank; a hydraulic actuator including a first chamber and a second chamber; a first independent metering valve disposed between and fluidly connected to the source, the tank, and the first chamber of the hydraulic actuator; and a second independent metering valve disposed between and fluidly connected to the source, the tank, and the second chamber of the hydraulic actuator. Each of the first independent metering valve and the second independent metering valve may include a spool and a valve actuator disposed on one side of the spool. The valve actuator may include a push coil, a pull coil, and a force feedback mechanism configured to balance a force of the push coil and the pull coil.

A hydraulic drive system for an electrically-driven hydraulic work machine makes it possible to make a rated voltage of various electric equipment such as power storage devices common to one of an electrically-driven hydraulic work machine that is capable of being operated with lower horsepower and to prevent that only a power storage situation of one of the plurality of power storage devices significantly degrades together with operation of the electrically-driven hydraulic work machine and besides, to extend a time period within which each of actuators of the electrically-driven hydraulic work machine can obtain a predetermined speed. Accordingly, a controller 50 includes a virtual limitation torque calculation section 51 and electric motor rotational speed control sections 52 and 53. Variable horsepower control tables 52r and 53r are provided in the electric motor rotational speed control sections 52 and 53, and limit values q1*limit and q2*limit for a virtual displacement of the variable horsepower control tables 52r and 53r are changed such that a charge state of a power storage device 170 and a charge state of another power storage device 270 become equal to each other.

The invention provides a construction machine in which the load torque at the time of engine start-up can be reduced even when the engine stops against the will of the operator. A hydraulic excavator includes a control device (35) having a pump displacement control section (37) and an unload control section (38). The pump displacement control section (37) makes the displacement of a hydraulic pump (16) variable to a minimum displacement by controlling a regulator device (20) when the speed of an engine (14) detected by a speed sensor (41) becomes equal to or less than a preset low speed N3 at the time of driving of the engine (14). The unload control section (40) controls an unloading valve (24) to the open position at the time of start-up of the engine (14).