To achieve reduction of fuel consumption and enhancement of operability, in a hydraulic control circuit provided with a bypass oil passage formed by being branched from a discharge line of a hydraulic pump and extending to an oil tank, and a bypass valve having variable opening area for controlling a flow rate of the bypass oil passage, and to accurately perform pump pressure control through opening area control of the bypass valve without being affected by a condition of each time. The hydraulic control circuit is configured to perform closed-loop control of the opening area of the bypass valve so that the pump pressure is maintained at a set pressure, during nonoperation of the operation lever; on the other hand, to perform open-loop control for reducing the opening area of the bypass valve depending on the operation input of the operation lever, during an operation of the operation lever, and further configured to correct on the basis of the opening area of the bypass valve during the closed-loop control, the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve during the open-loop control.

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.

To achieve reduction of fuel consumption and enhancement of operability, in a hydraulic control circuit provided with a bypass oil passage formed by being branched from a discharge line of a hydraulic pump and extending to an oil tank, and a bypass valve having variable opening area for controlling a flow rate of the bypass oil passage, and to accurately perform pump pressure control through opening area control of the bypass valve without being affected by a condition of each time. The hydraulic control circuit is configured to perform closed-loop control of the opening area of the bypass valve so that the pump pressure is maintained at a set pressure, during nonoperation of the operation lever; on the other hand, to perform open-loop control for reducing the opening area of the bypass valve depending on the operation input of the operation lever, during an operation of the operation lever, and further configured to correct on the basis of the opening area of the bypass valve during the closed-loop control, the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve during the open-loop control.

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.

An example valve includes a first port fluidly coupled to a source of fluid, a second port fluidly coupled to an actuator, a third port fluidly coupled to a reservoir, and a fourth port configured to export a load-sense (LS) fluid signal. The valve can operate in: a neutral state, wherein fluid is allowed to flow from the second port to the third port, while the first port and the fourth port are blocked; a first actuated state, wherein fluid flow is throttled from the second port to the third port, while the first port and the fourth port remain blocked; or a second actuated state, wherein fluid flow from the second port to the third port is blocked, while fluid flow is allowed from the first port to the second port and from the second port to the fourth port.

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 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 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: a single-rod hydraulic cylinder; a variable displacement pump driven by a rotating machine; a rod-side supply line and a head-side supply line that connect the pump to the hydraulic cylinder; a first tank line that is branched off from the rod-side supply line and connects to a tank; a second tank line that is branched off from the head-side supply line and connects to the tank; and a flow rate adjuster. The flow rate adjuster is configured to: switch a delivery capacity of the pump to a first setting value when a pressure of the head-side supply line is higher than a pressure of the rod-side supply line; and switch the delivery capacity of the pump to a second setting value less than the first setting value when the pressure of the rod-side supply line is higher than the pressure of the head-side supply line.

An example valve includes a first port fluidly coupled to a source of fluid, a second port fluidly coupled to an actuator, a third port fluidly coupled to a reservoir, and a fourth port configured to export a load-sense (LS) fluid signal. The valve can operate in: a neutral state, wherein fluid is allowed to flow from the second port to the third port, while the first port and the fourth port are blocked; a first actuated state, wherein fluid flow is throttled from the second port to the third port, while the first port and the fourth port remain blocked; or a second actuated state, wherein fluid flow from the second port to the third port is blocked, while fluid flow is allowed from the first port to the second port and from the second port to the fourth port.