Hitachi Construction Machinery Tierra Co., Ltd.

Hiroyuki Nobezawa

Yasutaka Tsuruga

Kiwamu Takahashi

Yasuharu Okazaki

Kenji Yamada

Yoshifumi Takebayashi

Kazushige Mori

Natsuki Nakamura

To make it possible to efficiently utilize rated output torque of a prime mover by performing total torque control with high precision through precise detection of absorption torque of another hydraulic pump by use of a purely hydraulic structure and feedback of the absorption torque to the side of one hydraulic pump, delivery pressure of a main pump and a load sensing drive pressure are supplied to a torque feedback circuit, which modifies the delivery pressure of the main pump to achieve a characteristic simulating the absorption torque of the main pump, and outputs the modified pressure. An output pressure of the torque feedback circuit is supplied to a torque feedback piston, which controls displacement of the main pump so as to decrease the displacement of the main pump and thereby decrease maximum torque as the output pressure increases.

Hydraulic drive system for construction machine

It is an object of the present invention to accurately detect the absorption torque of the other of two hydraulic pumps by a purely hydraulic structure and feed the absorption torque to one of the two hydraulic pumps, thereby to accurately perform a total torque control, effectively utilize a rated output torque of a prime mover, and enhance mountability. To achieve the object, there are provided: a torque feedback circuitto which the delivery pressure of a first hydraulic pumpand a load sensing drive pressure are introduced, which modifies the delivery pressure of a second hydraulic pumpto provide a characteristic simulating the absorption torque of the second hydraulic pump, and which outputs the modified pressure; and torque feedback pistons,to which the output pressure of the torque feedback circuitis introduced, and which control the capacity of the first hydraulic pumpto decrease the capacity of the first hydraulic pumpand decrease a maximum torque Tmax as the output pressure becomes higher. The torque feedback circuitincludes pressure dividing restrictor parts,, pressure dividing valves,, and relief valves,.

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Takaoka, Japan

Hiroyuki Nobezawa