Hitachi Construction Machinery Co., Ltd.

Takeshi Yamaguchi

Sotaro Tanaka

Eiki Izumi

Yukio Aoyagi

Takashi Yagyu

Yasuo Sakaki

Kichio Nakajima

Kazuo Honma

Yukio Sumiya

Hiroshi Inamitsu

Eiji Minamiyama

Ultrasonic flaw detector

A hydraulic power system having a variable displacement hydraulic pump, a hydraulic motor driven by the hydraulic pump for actuating a load, with the pump and motor being connected to constitute a closed hydraulic circuit. A hydraulic servo controls the displacement volume of the pump, and a motor stop arrangement prevents, in its operative position, the motor from rotating. The system includes a control valve responsive to a main line pressure in the closed hydraulic circuit for controlling a hydraulic fluid supply to the hydraulic servo to prevent the main line pressure from substantially exceeding a predetermined level, and a control is responsive to the operation of the hydraulic servo for releasing the motor stop arrangement from the operative position when the hydraulic servo is operating.

Hydraulic power system

A hydraulic drive system including at least one hydraulic actuator, two variable displacement hydraulic pumps each connected to the hydraulic actuator to form a closed circuit therewith and connected in parallel with each other, two prime movers each driving one of the hydraulic pumps, and directional control valves each arranged between the hydraulic actuators and one of the hydraulic pumps. The directional control valves are each operative to shut, when one of the prime movers associated therewith is shut down, the hydraulic pump connected to the shutdown prime mover off the other hydraulic pump and the hydraulic actuator, to thereby prevent the hydraulic pump from being rotated by the pressure fluid delivered by the other hydraulic pump.

Hydraulic drive system having a plurality of prime movers

A hydraulic fluid circuit of a hydraulic shovel including a first directional control valve group connected to a first hydraulic pump and including a first directional control valve and a second directional control valve respectively connected to a first hydraulic cylinder and a second hydraulic cylinder. A second directional control valve group, connected to a second hydraulic pump, includes a third directional control valve having a first working port connected to one cylinder chamber of the first hydraulic cylinder and a second working port connected to one cylinder chamber of the second hydraulic cylinder. A switching device in the hydraulic fluid circuit is operative, when the first directional control valve is in a first position to switch the third directional control valve to a first position for supplying hydraulic fluid from the second hydraulic pump to the first hydraulic cylinder through the first working port, and also operative, when the second directional control valve is in a second position, to switch the third directional control valve to a second position for supplying hydraulic fluid from the second hydraulic pump to the second hydraulic cylinder through the second working port.

Hydraulic fluid circuit of hydraulic shovel

A hydraulic circuit for a hydraulic power shovel of the type having a swingable boom, swingable arm and a bucket attached to the end of the arm. The hydraulic circuit includes a levelling cylinder adapted to extend and contract in response to the swinging of the arm, and a switching valve device movable between a first position where it provides a communication between the levelling cylinder and a boom cylinder and a second position where it provides a communication between the levelling cylinder and an arm cylinder. When the switching valve device takes the first position, the levelling cylinder is communicated with the boom cylinder so that the boom is swung downwardly in response to the upward swinging of the arm, thereby to move the bucket horizontally. On the other hand, when the switching valve device takes the second position, the levelling cylinder and the boom cylinder are disconnected hydraulically so that the arm is allowed to swing independently of the boom.

Hydraulic circuit of hydraulic power shovel

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Tsuchiura, Japan

Takeshi Yamaguchi