Hitachi Construction Machinery Tierra Co., Ltd.

Kenji Yamada

Kiwamu Takahashi

Yasuharu Okazaki

Yasutaka Tsuruga

Yoshifumi Takebayashi

Kazushige Mori

Natsuki Nakamura

Hiroyuki Nobezawa

Masamichi Ito

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

In a hydraulic driving system for construction machines, when track motorsandare operated and the delivery pressure of a main pumpincreases to a second value PSof the set pressure of a main relief valve, the set pressure of a signal pressure relief valveincreases from a third value PAto a fourth value PA, which is smaller than the second value PSof the set pressure of the main relief valve, the difference between the second value PSand the fourth value PAbeing smaller than the target LS differential pressure. With such a structure, even if one of actuators reaches the stroke end and the delivery pressure of the hydraulic pump rises to the set pressure of the main relief valve, the other actuators do not stop, and further when the main relief valve is configured to increase the set pressure during operation of a specific actuator, the load pressure of the specific actuator does not increase to the increased set pressure of the main relief valve.

Hydraulic driving system for construction machine

The object is to make it possible to efficiently utilize rated output torque of the prime mover by performing total torque control with high precision through precise detection of absorption torque of the other hydraulic pump by use of a purely hydraulic structure and feedback of the absorption torque to the one hydraulic pump's side. For this purpose, the hydraulic drive system is equipped with: a torque feedback circuitwhich is supplied with delivery pressure of a main pumpand load sensing drive pressure, modifies the delivery pressure of the main pumpto achieve a characteristic simulating the absorption torque of the main pump, and outputs the modified pressure; and a torque feedback pistonwhich is supplied with output pressure of the torque feedback circuit and controls displacement of a main pumpso as to decrease the displacement of the main pumpand thereby decrease maximum torque Tas the output pressure increases. The torque feedback circuitincludes first and second variable pressure reducing valvesand

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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Toyama, Japan

Kenji Yamada