A hydraulic work system can include a continuously variable displacement hydraulic pump that is powered by an engine and is in communication with a hydraulic actuator. A run-time displacement of the hydraulic pump for movement of the hydraulic actuator can be controlled based on a speed of the engine.

A hydraulic system includes first and second valve assemblies connected to a common pump. The first valve assembly includes a main valve housed inside a manifold. A pressure compensator valve maintains a constant pressure drop across a variable orifice of the main valve. A pressure limiter valve is in communication with the main valve and the pressure compensator valve, and allows an actuator connected to the first valve assembly to operate independently of the second valve assembly so that fluid flow to a work port of the first valve assembly is not interrupted by operation of the second valve assembly.

A hydraulic work system can include a continuously variable displacement hydraulic pump that is powered by an engine and is in communication with a hydraulic actuator. A run-time displacement of the hydraulic pump for movement of the hydraulic actuator can be controlled based on a speed of the engine.

A valve, in particular for use as a pressure compensator or maintenance-type component (38) in hydraulically actuated hoisting devices (2), has a valve housing (54) with a control port (40), a fluid inlet (64) and a fluid outlet (66). A regulating piston (68) is longitudinally displaceably in the valve housing (54) and acts against an energy storage device (70) in the form of a compression spring, bringing the regulating piston (68) into positions forming a fluid-conveying connection between the fluid inlet (40) and the fluid outlet (66) or blocking this connection by a control pressure existing at the control port (40). A first orifice (88) in the regulating piston (68) connects the control port (40) to a receiving space (62) for the energy storage device (70) in a fluid-conveying manner. A second orifice (90) is in an intermediate part (72) in the valve housing (54). The receiving space (62) can be connected to a compensating chamber (92), which connected to the fluid outlet (66) in a fluid-conveying manner (98).

A valve, in particular for use as a pressure compensator or maintenance-type component (38) in hydraulically actuated hoisting devices (2), has a valve housing (54) with a control port (40), a fluid inlet (64) and a fluid outlet (66). A regulating piston (68) is longitudinally displaceably in the valve housing (54) and acts against an energy storage device (70) in the form of a compression spring, bringing the regulating piston (68) into positions forming a fluid-conveying connection between the fluid inlet (40) and the fluid outlet (66) or blocking this connection by a control pressure existing at the control port (40). A first orifice (88) in the regulating piston (68) connects the control port (40) to a receiving space (62) for the energy storage device (70) in a fluid-conveying manner. A second orifice (90) is in an intermediate part (72) in the valve housing (54). The receiving space (62) can be connected to a compensating chamber (92), which connected to the fluid outlet (66) in a fluid-conveying manner (98).

A construction machine is provided that can cause each hydraulic actuator to accurately operate according to operation by an operator in combined operation in which a hydraulic fluid of a hydraulic pump is subjected to flow dividing and is supplied to plural hydraulic actuators. A controller 10, in a case of determining that combined operation is being carried out, controls a regulator 7a in such a manner that the delivery flow rate of a hydraulic pump 7 becomes larger than the total target flow rate of plural hydraulic actuators 4a, 5a, and 6a, and controls the respective opening amounts of plural directional control valves 8a1, 8a3, and 8a5 in such a manner that the difference between the respective target flow rates of the plural hydraulic actuators and the respective inflow flow rates of the plural hydraulic actuators sensed by velocity sensors 12 to 14 becomes small.

A construction machine is provided that can cause each hydraulic actuator to accurately operate according to operation by an operator in combined operation in which a hydraulic fluid of a hydraulic pump is subjected to flow dividing and is supplied to plural hydraulic actuators. A controller 10, in a case of determining that combined operation is being carried out, controls a regulator 7a in such a manner that the delivery flow rate of a hydraulic pump 7 becomes larger than the total target flow rate of plural hydraulic actuators 4a, 5a, and 6a, and controls the respective opening amounts of plural directional control valves 8a1, 8a3, and 8a5 in such a manner that the difference between the respective target flow rates of the plural hydraulic actuators and the respective inflow flow rates of the plural hydraulic actuators sensed by velocity sensors 12 to 14 becomes small.

A control system for construction machinery includes a hydraulic cylinder operable by a working oil discharged from a hydraulic pump, a control valve arranged between the hydraulic pump and the hydraulic cylinder to control an operation of the hydraulic cylinder according to a position of a spool therein, the control valve having a first spool position for draining the working oil discharged from a chamber of the hydraulic cylinder to a drain tank, and a pressure compensated valve installed in a return hydraulic line through which the working oil discharged from the control valve at the first spool position is drained to the drain tank, the pressure compensated valve being configured to control a flow rate of the working oil passing through the pressure compensated valve according to a pressure difference between a front end and a rear end of the control valve.

A crane hydraulic system and a controlling method of the system is provided in order to fundamentally reduce impact in start and stop operations of a load sensing winch system. The load sensing subsystem is arranged, at the start and stop moments of a winch system, the pressure compensator can be opened, and the variable pump oil inlet line communicates with the oil return line to realize pressure relief, so as to reduce the pressure impact.

A hydraulic system includes: an operation device that outputs an operation signal corresponding to an operating amount of an operating unit; a variable displacement pump that supplies hydraulic oil to a hydraulic actuator; a control valve interposed between the actuator and pump, the control valve changing a meter-in opening area thereof, so an increase rate of the opening area increases in accordance with increase in the operation signal; a regulator that adjusts a tilting angle of the pump; an unloading valve that defines an unloading flow rate, at which the hydraulic oil is released to a tank; and a controller that, when the operation device is operated, determines a control valve required flow rate so rate is proportional to the meter-in opening area of the control valve, and controls the regulator so a discharge flow rate of the pump is a sum of the control valve and unloading flow rates.