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 control system for a construction machine includes a hydraulic pump group including a first hydraulic pump, a second hydraulic pump and a third hydraulic pump; a main control valve including a first spool group that controls a flow of pressurised fluid from the first hydraulic pump and the second hydraulic pump and that includes an operation apparatus spool, a driving spool and a merging spool, a second spool group that controls a flow of pressurised fluid from the third hydraulic pump and that includes a rotating spool, and a straight driving valve between the first spool group and the second spool group; a first pilot signal line connected to the operation apparatus spool that provides a supply path for a pilot pressurised fluid that is applied to switch the operation apparatus spool; a second pilot signal line connected to the driving spool that provides a supply path for a pilot pressurised fluid that is applied to switch the driving spool; and a direction changing valve on the second pilot signal line connecting the driving spool and a tank, that is connected to the first pilot signal line, and that is switched when the operation apparatus spool is switched so as to cut off the flow of a pilot pressurised fluid that is returning to the tank.

A hydraulic drive device for an industrial vehicle includes a tank, a hydraulic pump, a capacity control valve, a plurality of hydraulic cylinders, a plurality of direction switching valves, a first hydraulic oil passage, a second hydraulic oil passages, a pilot line, a relief valve, a relief pressure setting portion, a plurality of operation detecting portions, and a control unit. The control valve controls the hydraulic pumps so that a differential pressure between a discharge pressure of the hydraulic pump and a pilot pressure of the pilot line is to be a predetermined pressure. The control unit controls the relief pressure setting portion.

The present disclosure relates to a safety system for a construction machine, and the safety system for a construction machine according to the exemplary embodiment of the present disclosure includes: a pilot pump which supplies a pilot working fluid; multiple spools which are operated by the pilot working fluid to control a supply of a main working fluid and each have a signal unit formed in one region thereof; a signal line which sequentially connects the pilot pump and the signal units of the multiple spools and discharges the pilot working fluid, which is supplied by the pilot pump, to a hydraulic tank; and a pressure sensor which measures pressure in the signal line.

Pressure compensating valves not fully closing at the stroke end are employed, and upon the operator's operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine's hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.

A hydraulic working machine is provided that uses a variable displacement pump and open center type flow rate control valve for a controlling a hydraulic actuator, and has a negative control throttle disposed in a center bypass oil passage to generate a negative control pressure. A hydraulic pump control system performs virtual bleed-off control for reducing the bleed-off flow rate of the center bypass oil passage, and can operate the hydraulic actuator with the same performance as an open center control. The control system includes a bypass cut valve disposed upstream from the negative control throttle to reduce flow through the center bypass oil passages, and a negative control pressure output valve that outputs a virtual negative control pressure. The control system is configured to reduce the bleed-off flow rate by operating the bypass cut valve when virtual bleed-off control is performed, and to reduce the pump flow rate by the bleed-off reduction flow rate.

A hydraulic system for a working machine includes a variable displacement hydraulic pump, a plurality of hydraulic actuators, and a plurality of control valves. Each of the control valves includes an input port, an output port, and a flowrate reduction section. At least one of the control valves includes a flowrate increase section. The hydraulic actuators are a boom cylinder, a working tool cylinder, and an auxiliary actuator. The control valves are a boom control valve for controlling the boom cylinder, a working tool control valve for controlling the working tool cylinder, and a first auxiliary control valve for controlling the auxiliary actuator. The boom control valve and the working tool control valve each include the flowrate reduction section, and the first auxiliary control valve includes the flowrate reduction section and the flowrate increase section.

A hydraulic excavator is provided which can suppress the fuel consumption amount and improve the work efficiency by reducing the hydraulic pressure loss generated when a plurality of hydraulic actuators different in load are operated simultaneously. The hydraulic excavator includes a center bypass flow control valve that is arranged at the most downstream of a center bypass line and limits the flow rate of hydraulic fluid passing through the center bypass line in response to the operation amount of the second operation device in a case where a second operation device is operated, and a spool stroke limitation device that, in a case where a first operation device and the second operation device are operated simultaneously, limits the spool stroke amount of a second directional control valve in response to the operation amount of the first operation device in a state in which the spool stroke amount of a third directional control valve is controlled in response to the operation amount of the second operation device.

Different exemplary control systems for a hydraulically powered load-handling clamp, of the type usually mountable on industrial lift trucks or automatically guided vehicles, are disclosed. The disclosed systems variably limit a hydraulic force, by which load-clamping arms move a load substantially transversely, automatically depending on the weight of the load being moved, so as to avoid excessive transverse force applied to fragile loads.

A hydraulic control system for a construction machine includes a hydraulic pump group including a first hydraulic pump, a second hydraulic pump and a third hydraulic pump; a main control valve including a first spool group that controls a flow of pressurised fluid from the first hydraulic pump and the second hydraulic pump and that includes an operation apparatus spool, a driving spool and a merging spool, a second spool group that controls a flow of pressurised fluid from the third hydraulic pump and that includes a rotating spool, and a straight driving valve between the first spool group and the second spool group; a first pilot signal line connected to the operation apparatus spool that provides a supply path for a pilot pressurised fluid that is applied to switch the operation apparatus spool; a second pilot signal line connected to the driving spool that provides a supply path for a pilot pressurised fluid that is applied to switch the driving spool; and a direction changing valve on the second pilot signal line connecting the driving spool and a tank, that is connected to the first pilot signal line, and that is switched when the operation apparatus spool is switched so as to cut off the flow of a pilot pressurised fluid that is returning to the tank.