A controller according to the present invention has: a storage section that stores a first relationship between manipulated variables of an operating lever preset for each vehicle-body weight and target delivery pressures of a hydraulic pump; a target delivery pressure computation section that applies the vehicle-body weight inputted through an input device and the manipulated variable of the operating lever corresponding to a pilot pressure detected by pilot pressure sensors, to a first relationship stored in the storage section in order to calculate a target delivery pressure of the hydraulic pump; and a feedback control section that performs feedback control on the center bypass selector valve such that the delivery pressure of the hydraulic pump detected by the delivery pressure sensor agrees with the target delivery pressure of the hydraulic pump calculated by the target delivery pressure computation section.

A hydraulic system for a work machine includes a hydraulic pump to supply a pilot fluid, and a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure. The pilot pressure is a pressure of the pilot fluid supplied from the hydraulic pump. The hydraulic system includes a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions. The hydraulic system includes a pressure applying device to apply a second pilot pressure to the hydraulic switch valve. The second pilot pressure is lower than the first pilot pressure.

A hydraulic system (600) and method for reducing boom dynamics of a boom (30), while providing counter-balance valve protection, includes a hydraulic cylinder (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 cylinder, and a second chamber (118, 116) of the hydraulic cylinder 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 method may include measuring first pressure ripples at the second chamber and reducing a magnitude of second pressure ripples at the first chamber. The pressure ripples may be transformed into a flow command by multiplying the pressure ripples by a gain and/or phase shifting. The gain and/or the phase shifting may be adjusted by feedback. The feedback may include the second pressure ripples at the load holding chamber, a position of the hydraulic actuator, and/or an operator input. A reference signal may be filtered with a moving average filter.

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.

A valve includes a bore within a valve body having a central axis. A plurality of galleries in the bore define flow paths for hydraulic fluid. A spool is positioned in the bore, and the spool is moveable along the central axis between a first position in which hydraulic fluid from a central pump gallery is prevented from flowing to first and second working galleries and from flowing to one or more tank galleries; a second position in which hydraulic fluid from the central pump gallery is in fluid communication with both the first and second working galleries simultaneously; and a third position in which the first and second working galleries are in fluid communication with the one or more tank galleries simultaneously.

A hydraulic circuit for a construction machine is disclosed, which can prevent a loss of pressure during a combined work. The hydraulic circuit includes a variable displacement hydraulic pump, at least two hydraulic actuators driven by hydraulic fluid that is supplied from the hydraulic pump, control valves installed in a center bypass path of the hydraulic pump and shifted to control a start, a stop, and a direction change of the hydraulic actuators, parallel flow paths having inlets branched and connected to predetermined positions on an uppermost stream side of the center bypass path and outlets connected to inlet ports of the control valves, bleed-off paths formed on the control valves other than the lowermost downstream side control valve among the control valves to selectively communicate with the center bypass path, the bleed-off paths communicating with the center bypass path when the plurality of control valves are shifted for a combined work, and a switching valve installed on a lowermost downstream side of the center bypass path to intercept the center bypass path when pilot signal pressure is applied.

A work machine operation assistance device enables setting of a manipulation gain appropriate for a skill level and habits of an operator and/or actual work contents. The work machine operation assistance device includes: a manipulation gain storage section storing a manipulation gain; a manipulated variable detection section detecting a manipulated variable of the operating device; a time integration section adding up time that the operating device is operated; a manipulated-variable frequency arithmetic section computing a manipulated-variable frequency of the operating device; a manipulated-variable frequency criterion setting section presetting a criterion value for the manipulated-variable frequency; a manipulation gain update arithmetic section performing a computation to update the manipulation gain; a manipulation gain display section displaying a result of the manipulation gain computed; and a manipulation gain update selection section to select whether or not an update to the manipulation gain displayed on the manipulation gain display section is performed.

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.

An optional-attachment-operating direction switching valve is provided in a part of an unloading passage which part is on the upstream of an arm-operating direction switching valve and a bucket-operating direction switching valve. The hydraulic circuit is arranged such that the optional-attachment-operating direction switching valve receives pressure oil from a pressure oil supply passage which branches from the part of the unloading passage on the upstream of the optional-attachment-operating direction switching valve, the arm-operating direction switching valve receives pressure oil from a pressure oil supply passage which branches from a part of the unloading passage which part is between the optional-attachment-operating direction switching valve and the arm-operating direction switching valve, and the bucket-operating direction switching valve receives the pressure oil from a pressure oil supply passage which branches from a part of the unloading passage which part is between the optional-attachment-operating direction switching valve and the bucket-operating direction switching valve.

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.