A hydraulic system includes a hydraulic pump, a first hydraulic actuator, a second hydraulic actuator, a first control valve to control the first hydraulic actuator, a second control valve to control the second hydraulic actuator, a return fluid tube in which a return fluid discharged from the first hydraulic actuator flows, the return fluid tube connecting the first control valve and the first hydraulic actuator, a first inner fluid tube provided in the first control valve and connected to the return fluid tube, an outer fluid tube connected to the first inner fluid tube, the outer fluid tube connecting the first control valve and the second control valve, a return-discharge fluid tube to discharge the return fluid, the discharge fluid tube being branched from the outer fluid tube, and a throttle provided in the return-discharge fluid tube.

A control system for construction machinery includes a first hydraulic pump, first and second actuators connected to the first hydraulic pump through first and second hydraulic lines respectively, first and second control valves installed in the first and second hydraulic lines respectively and configured to control operations of the first and second actuators, and a controller configured to adjust a spool displacement amount of the first control valve according to an amount of working oil to be supplied to the first actuator when the first actuator performs a single or multiple operation by self-load.

A fluid power system includes an electro-hydraulic variable displacement fluid pump driving fluid at a first displacement value. The system further includes a directional control valve, a sensor, and a controller. The directional control valve includes a valve member movable between a neutral position and at least one actuated position. The directional control valve diverts at least some fluid to an actuator while the valve member is in an actuated position, and the directional control valve exhausts fluid at an exhaust pressure through an outlet port to the fluid reservoir while the valve member is in the neutral position. The sensor measures a difference between the exhaust pressure and a nominal pressure and generates a signal based on the measured difference. The controller generates a flow command at least partially based on the pressure signal to modify the operation of the pump to drive fluid at a second displacement value.

An assembly for a fluid-filled piston-cylinder unit comprises a main body having an assembly longitudinal axis (24), a valve unit integrated in the main body and having an overflow channel, which valve unit seals the overflow channel when the assembly is moved along the assembly longitudinal axis in a first direction and releases the overflow channel, in dependence on the fluid pressure, when the assembly is moved along the assembly longitudinal axis in a second direction. Furthermore, the assembly comprises an outer seal element that is arranged on the main body so as to be moved along the assembly longitudinal axis, for abutting in a sealing manner against an inner surface of the housing, and at least one undercut element formed on the main body for engaging in an interlocking manner behind a mating element of the piston-cylinder unit.

A work vehicle includes a first frame, a second frame pivotally coupled to the first frame at an articulation joint, and a control circuit operable to control relative movement of the first and second frames about the articulation joint. The control circuit includes a pump, an actuator in fluid communication with the pump, and a first valve assembly coupled to a user-manipulable control. The first valve assembly is configured to direct fluid from the pump to the actuator in response to movement of the user-manipulable control to pivot the first and second frames. The control circuit also includes a second valve assembly configured to direct fluid from the pump to the actuator in response to receiving an electronic control signal to pivot the first and second frames.

In a method of controlling a main control valve of an excavator, when speeds of a boom cylinder and an arm cylinder is increased by handling a boom joystick and an arm joystick, a second arm control spool between a first hydraulic pump and the arm cylinder may be closed. A first boom control spool between the first hydraulic pump and the boom cylinder may be opened to supply a first flux generated from the first hydraulic pump to the boom cylinder. A second boom control spool between a second hydraulic pump and the boom cylinder may be closed. A first arm control spool between the second hydraulic pump and the arm cylinder may be opened to supply a second flux generated from the second hydraulic pump to the arm cylinder.

A position control system for an implement of a work vehicle. The implement, such as a blade, is operatively connected to a push arm rotatably coupled to a frame of the work vehicle. A hydraulic actuator is operatively connected to the push arm and is configured to adjust the position of the push arm with respect to the frame. A controller generates a control command to adjust the position of the hydraulic actuator to thereby raise and lower the blade. A proportional quick drop valve, coupled to the hydraulic actuator and to the controller, directs a flow of fluid to the hydraulic actuator in response to the operator control command. The proportional quick drop valve reduces a drop speed of the blade, reduces cavitation of the actuator valves, and also reduces the pressure drop and fluid flow forces acting on the spools of the actuator valves.

Provided is a hydraulic drive device that is provided in a work device and with which it is possible to obtain a high energy-saving effect with a low-cost configuration while being equipped with a plurality of hydraulic actuators. The hydraulic drive device is provided with: first and second actuator groups; closed circuits connected to hydraulic actuators included in the first actuator group; a pump section including closed circuit pumps; open circuits which include a plurality of variable throttle valves for changing the flow rate of working fluid supplied from a hydraulic pump included in the pump section to a hydraulic actuator; and circuit switching sections having a first state in which the closed circuits are opened and the opened circuits are blocked, and a second state in which the closed circuits are blocked and the open circuits are opened.

A hydraulic system for a work machine includes a first switch valve and a first return circuit. The first switch valve is switchable between a confluent position and an isolation position. The first switch valve is switched to the confluent position such that a first operation fluid tube is connected to a second operation fluid tube and a first transmission fluid tube is connected to a second transmission fluid tube. The first switch valve is switched to the isolation position such that the first operation fluid tube is disconnected from the second operation fluid tube and the first operation fluid tube is disconnected from the second operation fluid tube.

A control system for a dump truck includes a signal reception unit that receives a rising command signal to cause the dump truck including a vessel and a hydraulic cylinder configured to raise and lower the vessel to start a rising action of the vessel, and a vessel control unit that varies an extension speed of the hydraulic cylinder nonlinearly with respect to elapsed time when the signal reception unit receives the rising command signal.