Hitachi Construction Machinery Co., Ltd.

Hitachi, Ltd.

Yukio Aoyagi

Eiki Izumi

Hiroshi Watanabe

Kichio Nakajima

Kazuo Honma

Tomohiko Yasuda

Shuichi Ichiyama

Gen Yasuda

Sotaro Tanaka

Takeshi Yamaguchi

Genroku Sugiyama

Toichi Hirata

Yasuo Tanaka

Yusuke Kajita

Koji Fujita

Hiroshi Onoue

Shigetaka Nakamura

Yasuhiko Murata

Kazuyoshi Narita

Takayuki Yamakawa

Tomohiko Yasudi

Keiichiro Uno

Kazuhiko Otsubo

Hydraulic drive system for construction machine

Hydraulic drive system with pressure compensting valve

Hydraulic drive system for construction machines

A hydraulic drive controlling apparatus for a construction machine has at least one variable displacement type hydraulic pump, a plurality of actuators driven with a hydraulic fluid from the hydraulic pump, directional control valves driven in accordance with amounts of manipulation of operation means for controlling the plurality of actuators, means for detecting a delivery pressure of the hydraulic pump, means for selecting maximum one of load pressures of the plurality of actuators, and first control means for controlling displacement of the hydraulic pump to bring a differential pressure between the delivery pressure and the maximum load pressure to a specified value. The hydraulic drive controlling apparatus further has second control means for controlling the displacement of the hydraulic pump to bring the delivery pressure thereof to a predetermined value, first command means for selecting a mode of control of the displacement of the hydraulic pump and outputting a corresponding command signal, and first selection means for selecting one of the first and the second control means depending upon the command signal from the first command means.

Pump controlling apparatus for construction machine

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

Method of and system for controlling hydraulic power system

A control system for a hydraulic circuit having a variable displacement hydraulic pump, and an actuator driven by the pump, in which a pump control controls a displacement volume varying member of the pump based on an operating signal giving a command with respect to the position thereof and a detector signal indicative of the actual position thereof while restricting the operating speed of the member to a level below a predetermined maximum speed. The control system has maximum speed setting device previously setting a first predetermined maximum speed and a second predetermined maximum speed higher than the first predetermined maximum speed for the operating speed of the variable displacement volume varying member and operative to select the first predetermined maximum speed when the direction of operation of the actuator commanded by the operating signal agrees with the actual direction of operation thereof, and select the second predetermined maximum speed when the position of the displacement volume varying member commanded by the operating signal is neutral or when the direction of operation of the actuator commanded by the operating signal is opposite to the actual direction of operation thereof. The pump control is constructed to effect the speed control of the displacement volume varying member based on the first or second predetermined maximum speed selected by the maximum speed setting device.

Control system for hydraulic circuit means

A control system for a hydraulic circuit including at least first and second variable displacement volume type hydraulic pumps, at least first and second hydraulic actuators driven by the pumps, and valves for controlling hydraulic connections between the pumps and the actuators. The control system includes a device for deciding the order of priority of hydraulic connections between the first actuator and the first and second hydraulic pumps and the order of priority of hydraulic connections between the second pump and the first and second actuators. A first sensor is provided for sensing maximization of the displacement volume of the first pump, sensing that the displacement volume of the second pump has become substantially zero. A device decides target displacement volumes of the first and second pumps based on information supplied at least by the priority order deciding device and first and second sensor. When the flow rate of hydraulic fluid supplied to the first actuator is increased, the displacement volume of the second pump is increased from substantially zero after the displacement volume of the first pump is maximized. When the flow rate of hydraulic fluid supplied to the first actuator is reduced, the displacement volume of the first pump is reduced after the displacement volume of the second pump has become substantially zero.

Control system for hydraulic circuit apparatus

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 control system for a hydraulic circuit having at least first and second hydraulic pumps of the variable displacement type, a first hydraulic actuator arranged for hydraulic connection with the first pump through first valve to be driven thereby, and a second hydraulic actuator arranged for selective hydraulic connection with said first and second pumps through second and third valve respectively to be driven thereby. The order of priority for hydraulic connection is preset so that, when an operation signal for the second actuator is received while the first pump is inoperative, the first pump takes priority over the second pump, and when an operation signal for the first actuator is received while the first pump is in hydraulic connection with the second actuator, the first actuator takes priority over the second actuator and the second actuator is brought into hydraulic connection with the second pump, and the displacement volume of the first pump and switching of the second valve means are controlled such that, when the first pump which is, in hydraulic connection with the second actuator, is to be brought into hydraulic connection with the first actuator, the displacement volume of the first pump is returned to zero before changing of the hydraulic connection. The control system includes a first judging device for determining if the first pump is in hydraulic connection with the second actuator when the operation signal for the first actuator is received, and for generating a command for backing up reduction in the supply of hydraulic fluid into the second actuator simultaneously when the displacement volume of the first pump begins to returns to zero. When judged that the first pump is in hydraulic connection with the second actuator, a command signal switches a third valve to an open position in accordance with the backup command. A command for initiating a displacement of the second pump is generated in accordance with the backup command.

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 flushing valve system suitable for use in a closed circuit hydrostatic transmission including a variable displacement hydraulic pump, a hydraulic actuator and two main lines. The flushing valve system includes poppet valves mounted in passages for respectively communicating the main lines with a fluid tank, passages mounting throttles for causing the pressure in the main lines to act on pressure chambers to keep poppets of the poppet valves from moving to an open position, and a change-over valve responsive to the pressure differential between the main lines to communicate the pressure chamber of the poppet valve connected to the main line on the lower pressure side with the fluid tank. The poppet valve connected to the main line on the lower pressure side opens when a predetermined pressure level is exceeded by the pressure in the main line, to thereby allow working fluid in the main line to be drained to the fluid tank.

Flushing valve system in closed circuit hydrostatic power transmission

Growing community of inventors

Ibaraki, Japan

Yukio Aoyagi