A time-based power boost control system. A fluid source supplies fluid. A relief device relieves pressure of the fluid supplied by the fluid source when the pressure of the fluid exceeds a relief pressure level. A control device controls the relief device. When a boost mode in which at least a first level of pressure and a second level of pressure, higher than the first level of pressure, are allowed to be selectively used as the relief pressure level is active, a length of a boost-on time in which the second level of pressure is used as the relief pressure level is shorter than a preset maximum boost-on time limit, and a length of a succeeding boost-off time succeeding the boost-on time in which the first level of pressure is used as the relief pressure level is equal to or longer than a preset minimum boost-off time limit.

A time-based power boost control system. A fluid source supplies fluid. A relief device relieves pressure of the fluid supplied by the fluid source when the pressure of the fluid exceeds a relief pressure level. A control device controls the relief device. When a boost mode in which at least a first level of pressure and a second level of pressure, higher than the first level of pressure, are allowed to be selectively used as the relief pressure level is active, a length of a boost-on time in which the second level of pressure is used as the relief pressure level is shorter than a preset maximum boost-on time limit, and a length of a succeeding boost-off time succeeding the boost-on time in which the first level of pressure is used as the relief pressure level is equal to or longer than a preset minimum boost-off time limit.

A working machine includes a lower body, a turning body, a turning manipulating member which turns the turning body, a hydraulic motor which rotationally drives the turning body, a brake device which brakes the hydraulic motor, a main hydraulic source which supplies hydraulic oil to the hydraulic motor, and a direction control valve which controls a flow direction of the hydraulic oil according to the manipulated variable of the turning manipulating member, in which in a state where the hydraulic motor is braked by the brake device based on a manipulation of a brake manipulating member, when the turning manipulation is performed by the turning manipulating member, a brake applied to the hydraulic motor by the brake device is released with respect to turning in an indication direction indicated by the turning manipulation such that the turning body turns in the indication direction.

A pressure booster having arranged therein drive cylinders on both sides of a boosting cylinder is provided with a pair of pilot valves that are actuated when pistons of the drive cylinders abut against the moving ends thereof. A pair of actuation valves switch the supply state of a pressure fluid to pressure chambers of the drive cylinders. When the pilot valves are actuated, the pressure fluid passes through the pilot valves and is supplied to the pair of actuation valves, and the supply state of the pressure fluid is switched.

The oscillation cylinder arrangement (100) comprises a working cylinder (10A) and a piston with a rod (27A), arranged to move therein, and a control valve structure (20) for the working cylinder (10A). The control valve structure (20) incorporates a main valve (24) for transmitting a pressure medium to a first sub-chamber or a second sub-chamber of the working cylinder (10A) for a linear movement (A, B) of the piston, as well as impulse valves (22, 23), and lever arms (25, 26) for controlling them, in order to set the operational state of the main valve (24). Control members (27B) fixed to the piston rod (27A) moving in the working cylinder (10A), the control members (27B) being arranged to contact the lever arms (25, 26) of the impulse valves in order to define the extreme positions of the movement of the piston rod (27A).

A hydraulic system in a work machine includes a hydraulic pump to supply pilot hydraulic oil. A work hydraulic actuator is to move a work device of the work machine. A control valve is to control the work hydraulic actuator based on a pilot pressure of the pilot hydraulic oil. A target pilot pressure of the pilot hydraulic oil is input through the work operation device to control, according to the target pilot pressure, the pilot pressure supplied from the hydraulic pump to the control valve. A pilot oil path connects the work operation device and the control valve to supply the pilot pressure to the control valve. A drain oil path is divided from the pilot oil path. A pressure adjustment valve is provided in the drain oil path to adjust the pilot pressure to be less than the target pilot pressure when a condition is satisfied.

A hydraulic system for a work machine includes a tank to store an operation fluid, a hydraulic device to be operated by the operation fluid, a control valve to control the hydraulic device, a first fluid tube connecting the hydraulic device and the control valve, the first fluid tube being to supply the operation fluid from the control valve to the hydraulic device, a second fluid tube branching from the first fluid tube and connected to the tank, a switch valve provided to the second fluid tube, the switch valve being to control a flow rate of the operation fluid, and an oil cooler provided to the second fluid tube between the switch valve and the tank.

A hydraulic drive including at least one hydraulic cylinder that includes a piston chamber, an annulus, and a piston that separates the piston chamber from the annulus. The hydraulic drive also includes a first hydraulic pump hydraulically connected with the piston chamber, a second hydraulic pump hydraulically connected with the annulus, a third hydraulic pump, and a directional control valve that has a first switching position and a second switching position. The third hydraulic pump in the first switching position of the directional control valve is hydraulically connected with the piston chamber, and the third hydraulic pump in the second switching position of the directional control valve is not hydraulically connected with the piston chamber.

A hydraulic drive including at least one hydraulic cylinder that includes a piston chamber, an annulus, and a piston that separates the piston chamber from the annulus. The hydraulic drive also includes a first hydraulic pump hydraulically connected with the piston chamber, a second hydraulic pump hydraulically connected with the annulus, a third hydraulic pump, and a directional control valve that has a first switching position and a second switching position. The third hydraulic pump in the first switching position of the directional control valve is hydraulically connected with the piston chamber, and the third hydraulic pump in the second switching position of the directional control valve is not hydraulically connected with the piston chamber.

A bypass line (35) having one end side connected to a pilot delivery line (23) between a pilot pump (16) and a throttle (32) and the other end side connected to the pilot delivery line (23) between a check valve (33) and a pressure reducing valve type pilot valve (25) so as to bypass the throttle (32), a gate lock valve (27), and the check valve (33) provided in order from a pilot pump (16) is provided in the pilot delivery line (23). A lock switching valve (36) shutting down a flow of a pilot pressure oil from the pilot pump (16) through the bypass line (35) at a normal time and allowing the flow of the pilot pressure oil through the bypass line (35) when a pressure generated in the pilot delivery line (23) exceeds a predetermined pressure between the gate lock valve (27) and the check valve (33) is provided in the bypass line (35).