HYDRAULIC DRIVING DEVICE FOR CONSTRUCTION MACHINE

摘要

The purpose of the invention is to reduce energy loss and improve energy efficiency while ensuring the same travel speed as in the past during a traveling action, and to minimize the effect of travel load fluctuations or a change in the pump discharge pressure and obtain a satisfactory travel operability when the travel operation lever is operated within a stroke region no greater than a half operation and a travel action is performed. A variable throttle valve (80) is disposed parallel to a flow rate detection valve (50) of an engine speed detection valve (13), a travel pilot pressure is made to act in the direction in which the variable throttle valve (80) opens, and the opening area of the variable throttle valve (80) is continuously increased from fully closed to the maximum opening area with the increasing travel pilot pressure. The travel flow rate control valves (5d, 6e) have a size that makes it possible to obtain a predetermined flow rate (QT) required for travel, even when the target LS differential pressure falls to a second stipulated value (Pa3) when the travel operation lever is being fully operated, and have an opening area similar to that for Comparative Example 1 in the first half of a spool stroke.