Hitachi Construction Machinery Co., Ltd.

Hitachi Construction Machinery Tierra Co., Ltd.

Yasuharu Okazaki

Yasutaka Tsuruga

Kiwamu Takahashi

Junya Kawamoto

Takashi Kanai

Satoshi Hamamoto

Kenji Yamada

Yukiaki Nagao

Yoshifumi Takebayashi

Kazushige Mori

Natsuki Nakamura

Kenichiro Nakatani

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,.

In a hydraulic drive system in which a target compensated differential pressure for each of pressure compensating valves is set in accordance with a differential pressure between a pump delivery pressure and a maximum load pressure, and a target LS differential pressure is set as a variable value depending on a revolution speed of an engine a fixed throttle and a signal pressure variable relief valve are disposed in a maximum load pressure line A relief setting pressure P of the signal pressure variable relief valve is set so as to satisfy P &equals;P &minus;P &plus;a (where a is a value smaller than P ) with respect to a target LS differential pressure P and a setting pressure P of the main relief valve

Hydraulic drive system

An actuator lock switching valve is provided which communicates a drain line and a pilot line with each other when the valve is in a position C, and which communicates pilot lines with each other when it is shifted to a position D. The pilot line is connected to a delivery line of a hydraulic pump , and the pilot line is connected to pressure receiving sections provided at ends of the pressure compensating valves on the side acting in the closing direction. The actuator lock switching valve has a pressure receiving section connected to the output side of a pilot lock switching valve , and is switched over in interlock with shifting of the switching valve . In a hydraulic drive system including pressure compensating valves controlled by an LS system, an actuator can be locked with a simple construction and can be prevented from malfunctioning in an inoperative condition while an engine is being driven, even when the system includes a mechanically shifted directional control valve, or even when a mechanically shifted directional control valve is retrofitted to the system.

Hydraulic driving device

A hydraulic drive system having a swing control system, includes a pump control unit for controlling a pump delivery rate such that a pump delivery pressure is held a predetermined value higher than a maximum load pressure among a plurality of actuators. Pressure compensating valves are each constructed to set, as a target compensation differential pressure, a differential pressure between a delivery pressure of a hydraulic pump and a maximum load pressure among the actuators. A pressure compensating valve for a swing section is given such a load dependent characteristic that when the load pressure rises, the target compensation differential pressure is reduced, the load dependent characteristic being set so as to provide a flow rate characteristic simulating constant-horsepower control of a swing motor.

Hydraulic drive device

A hydraulic drive system includes a pump control unit for controlling a pump delivery rate such that a pump delivery pressure is held at a predetermined value higher than a maximum load pressure among actuators . Pressure compensating valves are each constructed to set, as a target compensation differential pressure, a differential pressure between the delivery pressure of a hydraulic pump and the maximum load pressure among the actuators . The pressure compensating valve is given such a load dependent characteristic that the target compensation differential pressure is reduced when a load pressure rises. A lower limit setting spring for limiting the target compensation differential pressure from becoming smaller than a predetermined value is provided in the pressure compensating valve for the swing section.

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Namerikawa, Japan

Yasuharu Okazaki