OIL PRESSURE CONTROL DEVICE FOR CONSTRUCTION MACHINE

Japanese Patent JP3490507

B2

PURPOSE: To maintain the amount of pressure oil which flows to a hydraulic actuator such as a hydraulic motor to a prescribed value so as to maintain its output condition in a constant condition even if load pressure of a hydraulic cylinder device for a working machine is fluctuated.
CONSTITUTION: An oil pressure control device is provided with a control valve 22a for controlling the flow amount of a hydraulic cylinder 4a for working which is driven by oil discharged from a hydraulic pump 20, a flow amount compensation valve 40 for maintaining the flow amount of a hydraulic motor 3 to a constant value by controlling the differential pressure between front and rear throttle 41 to a prescribed value, and a variable throttle valve 28 for controlling a flow amount supplied to the hydraulic cylinder 4a. And also it is provided with a controller 27 for controlling the displacement volume of a variable volume hydraulic pump 20 so as to set the differential pressure between the maximum value of load pressure of a hydraulic cylinder 4a and the hydraulic motor 3 and discharging pressure of the hydraulic pump 20 to a referential value, and also for reducing the opening degree of the variable throttle valve 28 until the differential pressure extends the prescribed value of the flow amount compensation valve 40 in the case where the displacement volume of the variable volume hydraulic pump 20 is a maximum value and the differential pressure not extend a referential value.

Makoto Mitsuhashi
Shiro Murakami

JP21581294A

January 26, 2004

September 09, 1994

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Hitachi Construction Machinery Co., Ltd.

B66C1/06; B66C1/08; F04B49/00; F15B11/00; F15B11/05; F15B11/16; (IPC1-7): F15B11/00; F15B11/05; F15B11/16

JP3157503A
JP478308U

Fuyuki Nagai

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