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1. (WO1991002905) HYDRAULIC DRIVING APPARATUS OF CIVIL ENGINEERING/CONSTRUCTION EQUIPMENT

Pub. No.:    WO/1991/002905    International Application No.:    PCT/JP1990/001062
Publication Date: Mar 7, 1991 International Filing Date: Aug 21, 1990
IPC: E02F 9/22
F15B 11/16
Applicants: HITACHI CONSTRUCTION MACHINERY CO., LTD.

NAKAMURA, Kazunori

Inventors: NAKAMURA, Kazunori

Title: HYDRAULIC DRIVING APPARATUS OF CIVIL ENGINEERING/CONSTRUCTION EQUIPMENT
Abstract:
A hydraulic driving apparatus of civil engineering/construction equipment of the present invention which includes a main hydraulic pump (2) of a variable capacity type, a plurality of actuators (3, 4) driven by pressure oil discharged from this main hydraulic pump, a plurality of flow rate regulation valves (5, 6) for controlling the flows of the pressure oil supplied to these actuators and pump controllers (30; 30A; 30B) for receiving the pressure difference between the discharge pressure of the main hydraulic pump and the maximum of load pressures of a plurality of actuators as a load sensing pressure difference and for controlling the discharge flow rate of the main hydraulic pump so that this load sensing pressure difference becomes equal to a predetermined target pressure difference, characterized by including flow rate maintaining means (8c; 18) which has zones (8c; 19) insensitive to the pressure difference between a load sensing pressure difference and the target pressure difference, suspends the control by the pump controllers (30; 30A; 30B) when the difference described above exists within the insensitive zones and maintains the discharge flow rate of the main hydraulic pump (2) at a substantially constant level.