Hitachi Construction Machinery Co., Ltd.

Hitachi Construction Machinery

Yoshizumi Nishimura

Yusaku Nozawa

Kinya Takahashi

Mitsuhisa Tougasaki

Nobuhiko Ichiki

Minoru Aoki

A spool provided with a flange is inserted in a spool bore , and a pressing force of a spring is always applied through the flange to the spool at its one end in a second pressure chamber . A fluid groove is formed in an inner peripheral surface of the spool bore at a position near an abutment surface . A hydraulic fluid under the same pressure P as that in the second pressure chamber is introduced to the fluid groove through a fluid passage formed in a valve body . When the flange and the abutment surface are in contact with each other, the hydraulic fluid is allowed to enter the interface between them through the fluid groove . A rise of the cracking pressure, which occurs upon the flange coming into tightly close contact with the abutment surface, can be prevented without reducing the strength of the flange , and stable opening/closing characteristics of the spool can be achieved.

Unloading valve

To permit forcedly stopping combining flows of pressure fluid from two hydraulic pumps when a load pressure on a combined-flow-driven actuator in which the flows of pressure fluid are combined together exceeds a predetermined pressure and hence to permit driving the combined-flow-driven actuator with the pressure fluid from only one of the hydraulic pumps, a hydraulic drive system is provided with a flow-combining valve connected to a directional control valve in a first group of directional control valves via a center bypass passage , a flow-combining circuit communicating the flow-combining valve and a supply port of a flow-combining directional control valve with each other, and a combined-flow-driven actuator controlled by the flow-combining directional control valve and performs overall power control such that a total value of input torques to the two hydraulic pumps does not exceed an output torque from an engine The hydraulic drive system is provided with a canceling valve to cancel the combination of flows by the flow-combining valve when a load pressure on the combined-flow-driven actuator becomes higher than a predetermined pressure.

Hydraulic drive device of working machine

A hydraulic circuit system having a load sensing system including a hydraulic pump, a plurality of hydraulic actuators driven by a hydraulic fluid delivered from the hydraulic pump, a plurality of control valves disposed between the hydraulic pump and the plurality of acutators, a signal detecting hydraulic line to which a signal pressure based on a maximum load pressure among the plurality of hydraulic actuators is introduced, and pump control means for controlling a delivery pressure of the hydraulic pump to be held higher than the signal pressure by a predetermined value.

Hydraulic circuit device

A fixed throttle is provided in a delivery line of a fixed pump driven by an engine for rotation together with a hydraulic pump , and a differential pressure detecting valve is provided in association with the fixed throttle to detect a differential pressure across the fixed throttle and to output a pressure lower than the detected differential pressure by a predetermined value. The output of the differential pressure detecting valve is introduced, as a signal pressure, to a pressure bearing section of a load sensing valve , thereby setting a target differential pressure. With that arrangement, a pressure in link with an engine revolution speed can be directly employed as the set differential pressure of the load sensing valve, and the structure of the load sensing valve can be avoided from being complicated. Further, in the idling revolution range in which the work amount is relatively small, the displacement of the hydraulic pump can be reduced to improve fine operability and cut down fuel consumption.

Pump capacity control device and valve device

It is an object of the present invention to provide a control valve which can reduce the number of external lines connected to a hydraulic remote control valve. A control valve for controlling hydraulic cylinders &prime; is provided, in one of spool covers, with fluid passages &prime;, a shuttle valve for selecting higher one of pilot pressures to be transmitted to these fluid passages &prime;, and a fluid passage for transmitting the pressure selected by the shuttle valve . The fluid passages &prime; are in communication with pressure fluid ports &prime; as connection ports for pilot lines . The control valve is also provided, in the other spool cover , with fluid passages &prime;, a shuttle valve for selecting higher one of pilot pressures to be transmitted to these fluid passages &prime;, and a fluid passage for transmitting the pressure selected by the shuttle valve . The fluid passages &prime; are in communication with pressure fluid ports &prime; as connection ports for pilot lines

Control valve

A hydraulic line slit formed in a valve body of a flow distribution valve - , a control chamber , and a hydraulic line - are connected to a signal transmitting hydraulic line . A lap portion is formed in the hydraulic line slit , the lap portion having a check valve function with a lap amount X when the valve body is in a cutoff position. A 2-position, 3-way valve is disposed in the hydraulic line - . The valve connects the control chamber of the flow distribution valve - to only the signal transmitting hydraulic line when an external signal F is not applied, and to both the signal transmitting hydraulic line and a lower-pressure detecting hydraulic line , which is connected an outlet passage of a flow distribution valve - on the side of a hydraulic actuator - , when the external signal F is applied. With such an arrangement, during a combined operation including driving of an inertial body, a pressure on the lower load pressure side can be detected as a signal pressure without cutting off a load-pressure detecting hydraulic line on the higher load pressure side. Further, a portion for detecting a load pressure is simplified and the flow distributing function is not impaired.

Hydraulic circuit system

A recovery check valve,and a piston valve,are axially slidably disposed within a spool,in coaxial relation. An axial fluid passage,is formed within a cylindrical portion,of the piston valve,and a seat portion,for the recovery check valve is formed at an open end of the cylindrical portion,The cylindrical portion,of the piston valve is formed with a hole,through which a hydraulic fluid in the fluid chamber,is introduced to a bridge passage,when the spool,is operated so as to introduce a hydraulic fluid from a hydraulic pump to the bottom side of a hydraulic cylinder. Fluid passages,are formed within the spool so that a hydraulic fluid in the bridge passage,is introduced to the closed end of the piston valve through the fluid passages when the spool is operated in the opposite direction. With such a structure, the size of the valve apparatus can be set to the same size as the directional control valve not provided with the recovery check valve.

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Tsuchiura, Japan

Yoshizumi Nishimura