A tilting angle control device includes pressure sensors. Each of the pressure sensors outputs to a control unit a pressure command signal corresponding to an operation amount. The control unit outputs to an electromagnetic proportional control valve a pressure control signal corresponding to the pressure command signal, and the electromagnetic proportional control valve outputs to a tilt adjustment mechanism pilot pressure corresponding to the pressure control signal. The tilt adjustment mechanism adjusts a tilting angle of a variable displacement pump such that the tilting angle becomes an angle corresponding to the pilot pressure. A pilot pressure sensor detects the pilot pressure to output a pressure feedback signal to the control unit. The control unit calculates the pressure control signal based on the pressure feedback signal and the pressure command signal and performs feedback control of the pilot pressure.

A hydraulic suspension system includes a suspension cylinder, a pump, and a control valve therebetween. The control valve includes a spool reciprocally movable between a pump flow position and a tank flow position in which a control port of the control valve is in communication with a pump and a tank, respectively. A piloted logic element in fluid communication with and interposed between the control valve and the suspension cylinder is selectively movable between a through-flow position in which fluid can flow in either direction between a chamber of the suspension cylinder and the control port of the control valve and a blocked position in which fluid is prevented from flowing in or out of the chamber of the suspension cylinder. The logic element is biased to the blocking position, moving to the through-flow position when subjected to a crack pressure delivered from the control port of the control valve.

A flow rate control apparatus for construction equipment includes: a boom cylinder driven by hydraulic fluid; a first control valve for controlling a hydraulic fluid flow supplied to the boom cylinder; an option actuator driven by hydraulic fluid; a second control valve for controlling a hydraulic fluid flow supplied to the option actuator; a boom cylinder manipulation lever and an option actuator manipulation lever; a confluence line selectively confluence the hydraulic fluid supplied to the boom cylinder with the hydraulic fluid of the option actuator; a center bypass switching valve provided at the furthest downstream side of a fluid supply path of the first hydraulic pump; a confluence switching valve selectively opening and closing the confluence line; a confluence selection valve applying a pilot pressure to the confluence switching valve; and a controller for controlling the confluence selection valve.

A fluid pressure control device for a power shovel including first, second, and third pumps, a first switching valve connected to the first pump, a second switching valve connected to the second pump, a first merge control valve connected to the third pump, and a second merge control valve provided downstream of the first merge control valve, in which the first merge control valve is switched by a pilot pressure of the first switching valve or the second switching valve to enable communication between the third pump and a downstream side, and the second merge control valve is switched by a pilot pressure of the second switching valve to block communication between the third pump and the first switching valve.

A hydraulic suspension system includes a suspension cylinder, a pump, and a control valve therebetween. The control valve includes a spool reciprocally movable between a pump flow position and a tank flow position in which a control port of the control valve is in communication with a pump and a tank, respectively. A piloted logic element in fluid communication with and interposed between the control valve and the suspension cylinder is selectively movable between a through-flow position in which fluid can flow in either direction between a chamber of the suspension cylinder and the control port of the control valve and a blocked position in which fluid is prevented from flowing in or out of the chamber of the suspension cylinder. The logic element is biased to the blocking position, moving to the through-flow position when subjected to a crack pressure delivered from the control port of the control valve.

Provided is an apparatus for driving a boom of a construction machine, allowing required power to be reduced. The apparatus includes a boom cylinder, a variable-displacement hydraulic pump , a control valve guiding hydraulic oil discharged by the hydraulic pump to the boom cylinder, a boom-raising-operation detector boom-cylinder pressure detectors, a supply selector valve switchable between a permitting position for permitting the hydraulic oil to be supplied from the hydraulic pump a head-side chamber of the boom cylinder and a blocking position for blocking the supply, a supply oil passage permitting hydraulic oil to be supplied to the head-side chamber during the blocking, and a controller which brings the supply selector valve into the blocking position and reduces volume of the hydraulic pump upon judging that excavation reaction force extends the boom cylinder even with no supply of hydraulic oil from the hydraulic pump to the head-side chamber.

The present disclosure relates to a hydraulic system of a construction machine. The hydraulic system of the construction machine includes: an electronic proportional pressure reducing valve configured to control a flow rate, to which a maximum pressure is input as a control current value, and which is set to a minimum flow rate; a gear pump configured to provide pilot operation oil to the EPPRV; a shuttle valve configured to compare a pressure of first pilot operation oil passing through the EPPRV and a pressure of a flow rate control signal, and output second pilot operation oil having the greater pressure; a hydraulic pump of which a swash plate angle is controlled by the second pilot operation oil; and a pump control device configured to control a pressure of the EPPRV to be decreased from a maximum pressure by a predetermined inclination when the flow rate control signal is generated.

A directional control valve device has: a plurality of spool valves; a first signal passage connected to the plurality of spool valves; and a second signal passage connected to the first signal passage at a connection site upstream from one or more of the plurality of spool valves for which shifting is to be detected.

A work machine capable of preventing cavitation more effectively. The work machine includes a work device, a variable displacement hydraulic pump, a hydraulic actuator, a posture detector, a control valve, an operation unit, an operation detector, and a controller. The controller judges whether or not a work operation detected by the operation detector is a low-pressure operation based on posture information acquired by the posture detector, and increases the pump capacity of the hydraulic pump when judging that the work operation is the low-pressure operation.