Patent ID: 6244048
Filing Date: 2001-06-12
Classification: E02F

Abstract:
A hydraulic drive system for hydraulic excavators equipped on a hydraulic excavator comprising an excavator body and a front device made up of a plurality of front members coupled to said body to be rotatable in the vertical direction, said front member including a boom, an arm and a bucket, said hydraulic drive system comprising a hydraulic reservoir provided on said body, at least one hydraulic pump, a plurality of hydraulic cylinders, including a boom cylinder, an arm cylinder, and a bucket cylinder for respectively driving said boom, arm and bucket, a plurality of pressure-uncompensated-type flow control valves provided on said body for respectively introducing a hydraulic fluid delivered from said hydraulic pump to said plurality of hydraulic cylinders by a flow rate variable according to a load pressure and controlling operation of the corresponding hydraulic cylinders, and a plurality of first connecting lines provided on said front device for respectively connecting said flow control valves and ones of the bottom and rod sides of the corresponding hydraulic cylinders, wherein:said hydraulic drive system further comprises at least one other hydraulic pump provided on said working machine body separately from said hydraulic pump,a delivery line to which is introduced a hydraulic fluid delivered from said other hydraulic pump and a reservoir line for introducing the hydraulic fluid to said hydraulic reservoir, said delivery line and said reservoir line being both provided on said body,a second connecting line provided on said front device and connected at one side thereof to said delivery line and extended so that the other side end portion thereof is positioned at least near said bucket cylinder and at least a part thereof is shared in common as to a supply of a hydraulic fluid to said boom cylinder, arm cylinder, and bucket cylinder,a plurality of first lines provided on said front device for forming another hydraulic fluid supplying route not passing said flow control valves and each having one side connected respectively to said second connecting line so as to be branched therefrom, the other side of each of said first lines on the opposite side to said one side connected respectively to at least those of said plurality of first connecting lines which are connected to the bottom sides of said hydraulic cylinders,a plurality of first flow control means provided respectively in said plurality of first lines for allowing the hydraulic fluid to flow from said other hydraulic pump toward said hydraulic cylinders through variable throttles which control respective flows of the hydraulic fluid to desired throttled flow rates, but cutting off flows of the hydraulic fluid from said hydraulic pump,a third connecting line provided on said front device and connected at one side thereof to said reservoir line and extended so that the other side end portion thereof is positioned at least near said bucket cylinder and at least a part thereof is shared in common as to a discharge of a hydraulic fluid from said boom cylinder, arm cylinder, and bucket cylinder,a plurality of second lines provided on said front device for forming another hydraulic fluid discharging route not passing said flow control valves and each having one end branched from and connected to said third connecting line, the other end of each of said second lines on the opposite side to said one end connected to said third connecting line being connected respectively to at least those of said plurality of first connecting lines which are connected to the bottom sides of said hydraulic cylinders,a plurality of second flow control means provided respectively in said plurality of second lines for allowing the hydraulic fluid to flow from said hydraulic cylinders toward said third connecting line through variable throttles which control respective flows of the hydraulic fluid to desired throttle flow rates, but cutting off flows of the hydraulic fluid from said third connecting line toward said hydraulic cylinders, andthird flow control means provided in a line branched from said delivery line within said working machine body for supplying the hydraulic fluid delivered from said other hydraulic pump to said first lines at a desired flow rate and returning the remaining hydraulic fluid to said hydraulic reservoir,said plurality of first lines including a first line for said boom connected to a part of said other side of said second connecting line near said boom cylinder so as to be branched therefrom, a first line for said arm connected to a part of said other side of said second connecting line near said arm cylinder so as to be branched therefrom, and a first line for said bucket connected to a part of said other side of said second connecting line near said bucket cylinder so as to be branched therefrom,said plurality of second lines including a second line for said boom connected to a part of said other side of said third connecting line near said boom cylinder so as to be branched therefrom, a second line for said arm connected to a part of said other side of said third connecting line near said arm cylinder so as to be branched therefrom, and a second line for said bucket connected to a part of said other side of said third connecting line near said bucket cylinder so as to be branched therefrom,said plurality of first flow control means including a first flow control means for said boom provided at a part of said first line for said boom near said boom cylinder, a first flow control means for said arm provided at a part of said first line for said arm near said arm cylinder, and a first flow control means for said bucket provided at a part of said first line for said bucket near said bucket cylinder,said plurality of second flow control means including a second flow control means for said boom provided at a part of said second line f o r said boom near said boom cylinder, a second flow control means for said arm provided at a part of said second line for said arm near said arm cylinder, and a second flow control means for said bucket provided at a part of said second line for said bucket near said bucket cylinder.