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 pressure increasing portion to increasing a pressure of the operation fluid, a first discharge fluid tube connected to any one of the first control valve and the second control valve and connected to the pressure increasing portion, a second discharge fluid tube connected to the first discharge fluid tube and configured to discharge the operation fluid, a float switching valve having an allowance position, a prevention position, and a float position, the allowance position blocking the second discharge fluid tube and allowing the operation fluid to flow to the pressure increasing portion, the prevention position unblocking the second discharge fluid tube and preventing the operation fluid from flowing to the pressure increasing portion.

A flow control valve for a construction machine includes a boom valve block connected lo a hydraulic pump; a boom spool coupled to the boom valve block so as to be slidably moved, and switched on by the supply of pilot signal pressure in order to carry out a boom-up or boom-down operation, thereby controlling the hydraulic oil supplied from the hydraulic pump to a boom cylinder; a boom-up flow control arrangement for supplying the hydraulic oil from the hydraulic pump to the large chamber of the boom cylinder through the boom spool, when switching on the boom spool in order to carry out the boom-up operation; and a boom-down flow control arrangement for returning a part of the hydraulic oil, which returns from the large chamber of the boom cylinder, to the hydraulic tank through the boom spool only at a predetermined pressure or higher, when the boom spool is switched on in order to carry out the boom-down operation, wherein the part of the hydraulic oil, which returns from the large chamber of the boom cylinder, is directly returned to the hydraulic tank through the boom spool, and the part of the hydraulic oil, which returns from the large chamber of the boom cylinder, is made to join, as regeneration flow, the small chamber side of the boom cylinder.

An excavator or other work machine includes a tilting bucket operated by a hydraulic actuator controlled by a bucket control valve responsive to control signals including a bucket shake control signal, which causes the bucket to move repeatedly in the rack and dump directions to shake debris from the bucket in a bucket shake operation. The actuator is powered by pressure from a hydraulic pump, and a control system includes an unloader valve to relieve pressure from the supply line to unload the pump when there is no demand for power. The control system is arranged to maintain a constant pressure signal in a load sensing line, to maintain the unloader valve constantly in a closed condition, for the duration of the bucket shake operation. This may be achieved by pressurising an actuator of a quick coupler to lock the bucket to the machine.

A control valve is provided for construction equipment having a holding valve which prevents the natural lowering of an operation apparatus due to the dead weight of the operation apparatus when an actuator is in a neutral position. A control valve for construction equipment according to the present invention includes: a valve body in which a supply path in communication with a pump path, through which a hydraulic fluid is supplied from a hydraulic pump, and actuator ports connected to an actuator are formed; a spool which is embedded in the valve body so as to be switchable; a holding valve having a holding poppet which is formed at the actuator port of any one of the actuator ports, and an auxiliary spool which is connected to a back pressure chamber of the holding poppet and releases the held load of the actuator at the time of switching; a control valve provided in the valve body; a pilot pressure control valve, embedded in the holding valve so as to be switchable, which applies or blocks a pilot pressure applied to switch the auxiliary spool on or off through a path when the pilot pressure control valve is switched on or off by means of the pressure of the hydraulic fluid which is drained from the back pressure chamber of the holding poppet at the time of switching the auxiliary spool on or off.

Control valves 100f, 100g, and 100h that reduce flow passage areas of parallel hydraulic fluid lines 41f, 41g, and 41h respectively when operating devices 34a, 34b for traveling are operated, are each disposed in the parallel hydraulic fluid line 41f, 41g, or 41h so that if saturation occurs during combined operations control likely to generate a significant difference in load pressure between any two actuators, the control valve prevents full closing of a pressure compensating valve lower in load pressure and thus prevents a slowdown and stop of the actuator undergoing the lower load pressure, and so that if saturation occurs during combined operations control likely to generate a particularly significant difference in load pressure between any two actuators, the control valve ensures a necessary supply of hydraulic fluid to the actuator higher in load pressure, thereby preventing a slowdown and stop of the actuator higher in load pressure.

A control system of a hybrid construction machine includes fluid pressure pumps configured to supply a working fluid to a fluid pressure actuator, a regeneration unit having a regeneration motor for regeneration to be rotated by the working fluid discharged from a load side pressure chamber of the fluid pressure actuator, a rotating electric motor coupled to the regeneration motor, and a storage battery configured to store electric power generated by the rotating electric motor, and a variable throttle configured to bleed a portion of the working fluid obtained by excluding a flow rate of the working fluid guided to the regeneration motor from the working fluid discharged from the load side pressure chamber.

Exemplary control valves that may be configured as a load sense, closed-center, and/or open-center valve. The control valve may include optional individual valve force sensing to potentially allow an operator to smoothly operate devices operating on low-load work ports even when a variable displacement pump is inducing pressure to operate a device connected to a high-load work port of a separate valve or worksection in the same stack. This optional force sensing may be employed on any or all worksections associated with any valve stack, and may further be included on one or both workports for any given worksection. Each worksection may include parallel and variable paths of fluid supplied by the pump. Also, flow priority to one or more worksections or external valves in a corresponding hydraulic system is optional and can be customized using the variable flow path and a corresponding fixed restriction.

When hydraulic fluid discharged from a hydraulic actuator is to be recovered for driving a different hydraulic actuator, the recovery frequency is increased to achieve further energy saving. To this end, a pressure increasing circuit 36 is provided in which a communication pressure increasing valve 12 is disposed in a communication passage 26 that connects a bottom side line 23 of and a rod side line 24 a boom cylinder 4. A recovery control valve 11 is controlled such that, when a first operation unit 5 is operated in a boom lowering direction (own weight falling direction of the boom) and a second operation unit 6 is operated simultaneously, only if the pressure at the bottom side of the boom cylinder 4 is higher than the pressure at the arm cylinder side that is a recovery destination of hydraulic fluid, the recovery control valve 11 is opened to recover the flow rate discharged from the bottom side of the boom cylinder 4 to the arm cylinder side.

A hydraulic system includes a hydraulic pump to output an operation fluid, first and second hydraulic devices to be operated by the operation fluid, first and second control valves to control the first and second hydraulic device, respectively, first and second communication tubes connecting the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve, first and second connection fluid tubes disposed on the first control valve, a discharge fluid tube connected to the first control valve, first and second branching fluid tubes branched from the first and second connection fluid tubes, respectively, first and second throttles disposed on the first and second branching fluid tubes, respectively, the second throttle being smaller than the first throttle.

The construction machine includes: a control valve that switchingly supplies hydraulic fluid from a hydraulic pump to a hydraulic actuator; a control valve drive device that supplies pilot secondary hydraulic fluid to the control valve in accordance with an operation of an operation lever device; a pilot hydraulic pump that supplies pilot primary hydraulic fluid to the control valve drive device; a pressure accumulation device that recovers return hydraulic fluid returned from the hydraulic actuator. The construction machine further includes: a check valve provided in a line between the pilot hydraulic pump and the control valve drive device; a pressure reducing valve that supplied the hydraulic fluid accumulated in the pressure accumulation device; a flow rate reduction device; and a controller that controls the flow rate reduction device in accordance with the pressure in the line between the check valve and the control valve drive device.