Hitachi Construction Machinery Co., Ltd.

Hitachi, Ltd.

Shuichi Ichiyama

Yukio Aoyagi

Tomohiko Yasuda

Eiki Izumi

Yasuhiko Murata

Kunihiko Yoshida

Keiichiro Uno

A hydraulic drive system for a construction machine in which a hydraulic circuit has at least one hydraulic pump, at least first and second hydraulic actuators driven by a hydraulic fluid discharged from the pump, and at least first and second directional control valves connected to the pump in parallel with each other for controlling flows of hydraulic fluid supplied from the pump to the first and second actuators, respectively, and a control unit is responsive to first and second operation signals for driving the first and second actuators, respectively, to produce first and second control signals for actuating the first and second valves and deliver such control signals thereto, respectively, each of the first and second valves having a degree of opening changed in accordance with a level of the corresponding one of the first and second control signals for controlling a flow rate of hydraulic fluid supplied to the corresponding one of the first and second actuators. The control unit includes restriction means for restricting the level of the first control signal for restriction of the degree of opening of the first directional control valve when both of the first and second operation signals are entered in the control unit for instruction to perform simultaneous driving of the first and second hydraulic actuators.

Hydraulic drive system

A load weight calculating system for a load moving machine, such as a hydraulic excavator, including a support, and a front attachment pivotably supported by the support. The front attachment includes a first linkage element pivotably supported by the support, a second linkage element pivotably supported by the first linkage element, a loading section supported by the second linkage element, and first and second hydraulic actuators for moving the first and second linkage elements, respectively. The load weight calculating system includes a first displacement detector and a second displacement detector for obtaining displacements .alpha..sub.1 and .beta..sub.1 of at least the first and second linkage elements, respectively, a pressing force sensor for obtaining a pressing force K.sub.1 exerted by at least one of the first and second hydraulic actuators, a weight calculating unit for calculating the weight of a load carried by the loading section based on the values .alpha..sub.1, .beta..sub.1 and K.sub.1 obtained at least by the first and second displacement detector and pressing force sensor, and a weight indicating unit for indicating a value associated with the load weight obtained by the weight calculating unit.

Load weight indicating system for load moving machine

Control valve assembly

A hydraulic power system having a variable displacement hydraulic pump, a hydraulic motor driven by the hydraulic pump for actuating a load, the pump and motor being connected to constitute a closed hydraulic circuit, hydraulic servo for controlling the displacement volume of the pump, and motor stopping device including a brake arrangement adapted to release the motor from a braked condition when a control pressure from a hydraulic fluid source is received. 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 servo to prevent the main line pressure from substantially exceeding a predetermined level, first pressure transmission control interlocked with an input of the servo for transmitting the control pressure to the brake arrangement when the input is actuated, and a second pressure transmission control responsive to the pressure of a hydraulic fluid supply to the servo on the output side of the control valve for transmitting the control pressure to the brake arrangement when the supply pressure is substantially lower than a normal supply pressure of the hydraulic fluid source.

Hydraulic power system

Growing community of inventors

Tsuchiura, Japan

Shuichi Ichiyama