Hydraulic driving system of construction machinery

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism coupled to said swing body in a vertically angularly movable manner and made up of a boom and a bucket, wherein said hydraulic drive system comprises:

• a first hydraulic pump and a second hydraulic pump driven by prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder, and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm, and said bucket, respectively;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• a common high-pressure line having one side connected to the delivery side of said second hydraulic pump and the other side extended to the side of said front operating mechanism;
• a boom branch line branched from said common high-pressure line and connected on the side opposite to the branched side to a rod pushing-side chamber of said boom hydraulic cylinder;
• a boom inflow control valve disposed near a branch position at which said boom branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said boom hydraulic cylinder;
• an arm branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said arm hydraulic cylinder;
• an arm inflow control valve disposed near a branch position at which said arm branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said arm hydraulic cylinder;
• a bucket branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said bucket hydraulic cylinder;
• and
• a bucket inflow control valve disposed near the branch position (D2) at which said bucket branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said bucket hydraulic cylinder,
• said hydraulic system being configured such that when said boom hydraulic cylinder, said arm hydraulic cylinder and said bucket hydraulic cylinder are operated to extend, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chambers of said boom, arm and bucket hydraulic cylinders through said plurality of directional flow control valves, respectively, and the hydraulic fluid from said second hydraulic pump is supplied to said rod pushing-side chambers of said boom, arm and bucket hydraulic cylinders through said common high-pressure line, said boom branch line, said arm branch line and said bucket branch line and further said boom inflow control valve, said arm inflow control valve and said bucket inflow control valve, respectively, and being joined with the hydraulic fluid from said first hydraulic pump, while the fluids discharged from the rod drawing-side chambers of said boom, arm and bucket hydraulic cylinders are returned to said reservoir only through said plurality of directional flow control valves, respectively,
• wherein said hydraulic drive system further comprises at least one of three sets comprising:
• a boom return fluid joining line branched from said boom branch line at a position nearer to said boom hydraulic cylinder than said boom inflow control valve and connected on the side opposite to the branched side to a hydraulic reservoir, and a boom outflow control valve disposed in said boom return fluid joining line near a branch position at which said boom return fluid joining line is branched from said boom branch line and controlling a flow of a hydraulic fluid drained from said boom hydraulic cylinder to said hydraulic reservoir;
• an arm return fluid joining line branched from said arm branch line at a position nearer to said arm hydraulic cylinder than said arm inflow control valve and connected on the side opposite to the branched side to said hydraulic reservoir, and an arm outflow control valve disposed in said arm return fluid joining line near a branch position at which said arm return fluid joining line is branched from said arm branch line and controlling a flow of a hydraulic fluid drained from said arm hydraulic cylinder to said hydraulic reservoir;
• and
• a bucket return fluid joining line branched from said bucket branch line at a position nearer to said bucket hydraulic cylinder than said bucket inflow control valve and connected on the side opposite to the branched side to said hydraulic reservoir, and a bucket outflow control valve disposed in said bucket return fluid joining line near a branch position at which said bucket return fluid joining line is branched from said bucket branch line and controlling a flow of a hydraulic fluid drained from said bucket hydraulic cylinder to said hydraulic reservoir.

A hydraulic drive system for a construction machine, wherein said hydraulic drive system comprises:

• a first hydraulic pump and a second hydraulic pump driven by prime movers;
• a plurality of hydraulic cylinders driven by hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• at least one inflow control valve for controlling a flow of the hydraulic fluid delivered from said second hydraulic pump and supplied to at least one rod pushing-side chamber among said plurality of hydraulic cylinders without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• a recovery flow control valve for introducing the hydraulic fluid in at least one rod pushing-side chamber among said plurality of hydraulic cylinders to a rod drawing-side chamber thereof;
• said hydraulic system being configured such that when said plurality of hydraulic cylinders are operated to extend, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chambers of said plurality of hydraulic cylinders through said plurality of directional flow control valves, respectively, and the hydraulic fluid from said second hydraulic pump is supplied to said rod pushing-side chambers of said plurality of hydraulic cylinders through said plurality of inflow control valves respectively, and being joined with the hydraulic fluid from said first hydraulic pump, while the fluids discharged from the rod drawing-side chambers of said plurality of hydraulic cylinders are returned to said reservoir only through said plurality of directional flow control valves, respectively, and when said plurality of hydraulic cylinders are operated to contract, the hydraulic fluid from said first hydraulic pump is supplied to said rod drawing-side chambers of said plurality of hydraulic cylinders through said plurality of directional flow control valves, respectively, and part of the hydraulic fluid from said at least one rod pushing-side chamber amond said plurality of hydraulic cylinders is supplied to the rod drawing-side chamber of the corresponding hydraulic cylinder, while the remaining part of the fluid discharged from the rod pushing-side chamber of the corresponding hyraulic cylinder and the fluids discharged from the rold pushing-side chambers of the other hydraulic cylinders are returned to said reservoir only through said plurality of directional flow control valves, respectively.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism coupled to said swing body in a vertically angularly movable manner and made up of a boom, an arm and a bucket, wherein said hydraulic drive system comprises:

• a first hydraulic pump and a second hydraulic pump driven by prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm, and said bucket, respectively;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• at least one inflow control valve for controlling a flow of the hydraulic fluid delivered from said second hydraulic pump and supplied to a rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• at least one recovery flow control valve for introducing the hydraulic fluid in the rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders to a rod drawing-side chamber thereof;
• and
• said hydraulic system being configured such that when said boom hydraulic cylinder is operated to extend, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chamber of said boom hydraulic cylinder through the directional flow control valve for the boom hydraulic cylinder, and the hydraulic fluid from said second hydraulic pump is supplied to said rod pushing-side chamber of said boom hydraulic cylinder through said inflow control valve, and being joined with the hydraulic fluid from said first hydraulic pump, while the fluid discharged from the rod drawing-side chamber of said boom hydraulic cylinder is returned to said reservoir only throught the directional flow control valve for the boom hydraulic cylinder, and when said boom hydraulic cylinder is operatad to contract, the hydraulic fluid from said first hydraulic pump is supplied to said rod drawing-side chamber of said boom hydraulic cylinder through the directional flow control valve for the boom hydraulic cylinder, and part of the hydraulic fluid from said rod pushing-side chamber of the boom hydraulic cylinder is supplied to the rod drawing-side chamber of the boom hydraulic cylinder through said recovery flow control valve, while the remaining part of the fluid discharged from the rod pushing-side chamber of the boom hydraulic cylinder is returned to said reservoir only through the directional flow control valve for the boom hydraulic cylinder.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swingbody,an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open forward in a ground contact state, wherein said hydraulic drive system comprises:

• at least one first hydraulic pump and at least one second hydraulic pump driven by a plurality of prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively, and an opening/closing hydraulic cylinder supplied with the hydraulic fluids to open and close said bucket;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• a boom-raising inflow control valve, a bucket-crowding inflow control valve and a bucket-dumping inflow control valve for controlling respective flows of the hydraulic fluid delivered from said second hydraulic pump and supplied to rod pushing-side chamber of said boom hydraulic cylinder, a rod pushing-side chamber of said bucket hydraulic clyinder, and a rod drawing-side chamber of said bucket hydraulic cylinder without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• at least two recovery flow control valve for introducing the hydraulic fluids in the rod pushing-side chambers of at least said boom hydraulic cylinder and said arm hydraulic cylinder among said plurality of hydraulic cylinders to rod drawing-side chambers thereof;
• and
• said hydraulic system being configured such that when said boom hydraulic cylinder, said arm hydraulic cylinder and said bucket hydraulic cylinder are operated to extend as far as the boom and bucket hydraulic cylinders are concerned, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chambers thereof through the directional flow control valves for the boom and bucket hydraulic cylinders, respectively, and the hydraulic fluid from said second hydraulic pump is supplied to said rod pushing-side chambers thereof through said boom-raising and bucket-crowding inflow control valves, respectively, and being joined with the hydraulic fluid from said first hydraulic pump, and with respect to the arm hydraulic cylinder, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chamber thereof through the directional flow control valve for the arm hydraulic cylinder, while the fluids discharged from the rod drawing-side chambers of said boom arm and bucket hydraulic cylinders are returned to said reservoir only through the directional flow control valves for the boom, arm and bucket hydraulic cylinders, and when said boom hydraulic cylinder, said arm hydraulic cylinder and said bucket hydraulic cylinder are operated to contract, and with respect to said boom and arm hydraulic cylinders, the hydraulic fluid from said first hydraulic pump is supplied to said rod drawing-side chambers thereof through the directional flow control valves for the boom and arm hydraulic cylinders, respectively, and part of the hydraulic fluids from said rod pushing-side chambers thereof are supplied to the rod drawing-side chambers thereof through said recovery flow control valves and with respect to said bucket hydraulic cylinder, the hydraulic fluid from said first hydraulic pump is supplied to said rod drawing-side chamber thereof through the directional flow control valve for the bucket hydraulic cylinder, and the hydraulic fluid from said second hydraulic pump is supplied to the rod drawing-side chamber thereof through said bucket-dumping inflow control valve, and being joined with the hydraulic fluid from the first hydraulic pump, while the remaining part of the fluid discharged from the rod pushing-side chambers of the boom and arm hydraulic cylinders and all fluid discharged from the rod pushing-side chamber of the bucket hydraulic cylinder are returned to said reservoir only through the directional flow control valves for the boom, arm and bucket hydraulic cylinders.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open rearward in a ground contact state, wherein said hydraulic drive system comprises:

• at least one first hydraulic pump and at least one second hydraulic pump driven by a plurality of prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• a plurality of inflow control valve for controlling respective flows of the hydraulic fluid delivered from said second hydraulic pump and supplied to rod pushing-side chambers of said boom hydraulic cylinders, said arm hydraulic cylinder and said bucket hydraulic cylinder without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• at least one recovery flow control valve for introducing the hydraulic fluid in the rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders to a rod drawing-side chamber thereof;
• and
• said hydraulic system being configured such that when said boom hydraulic cylinder, said arm hydraulic cylinder and said bucket hydraulic cylinder are operated to extend, the hydraulic fluid from said first hydraulic pump is supplied to said rod pushing-side chambers of said boom, arm and bucket hydraulic cylinders through the directional flow control valves for the boom, arm and bucket hydraulic cylinders, respectively, and the hydraulic fluid from said second hydraulic pump is supplied to said rod pushing-side chambers thereof through said inflow control valves, respectively, and being joined with the hydraulic fluid from said first hydraulic pump, while the fluids discharged from the rod drawing-side chambers of said boom, arm and bucket hydraulic cylinders are returned to said reservoir only through the directional flow control valves for the boom, arm and bucket hydraulic cylinders, and when said boom hydraulic cylinder among said plurality of hydraulic cylinders is operated to contract the hydraulic fluid from said first hydraulic pump is supplied to said rod drawing-side clamber thereof through the directional flow control valve for the boom hydraulic cylinder, and part of the hydraulic fluid from said rod pushing-side chamber thereof is supplied to the rod drawing-side chamber thereof through said recovery flow control valve, while the remaining part of the fluid discharged from the rod pushing-side chamber thereof is returned to said reservoir only through the directional flow control valve for the boom hydraulic cylinders.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open forward in a ground contact state, wherein said hydraulic drive system comprises:

• six first hydraulic pumps and two second hydraulic pumps driven by a plurality of prime movers;
• a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively, and an opening/closing hydraulic cylinder supplied with the hydraulic fluids to open and close said bucket;
• a plurality of boom directional flow control valves, a plurality of arm directional flow control valves, a plurality of bucket directional flow control valves, and a plurality of opening/closing directional flow control valves for controlling respective flows of the hydraulic fluids supplied from said six first hydraulic pumps to said boom hydraulic cylinder, said arm hydraulic cylinder, said bucket hydraulic cylinder, and said opening/closing hydraulic cylinder;
• a boom-raising inflow control valve, a bucket-crowding inflow control valve and a bucket-dumping inflow control valve for controlling respective flows of the hydraulic fluids delivered from said two second hydraulic pumps and supplied to a rod pushing-side chamber of said boom hydraulic cylinder, a rod pushing-side chamber of said bucket hydraulic cylinder, and a rod drawing-side chamber of said bucket hydraulic cylinder without passing said plurality of boom directional flow control valves and said plurality of bucket directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluids delivered from said two second hydraulic pumps to a reservoir;
• a boom recovery flow control valve and an arm recovery flow control valve for introducing the hydraulic fluids in the rod pushing-side chambers of said boom hydraulic cylinder and said arm hydraulic cylinder to rod drawing-side chambers thereof;
• an opening/closing recovery flow control valve for introducing the hydraulic fluid in a rod drawing-side chamber of said opening/closing hydraulic cylinder to a rod pushing-side chamber thereof;
• and
• said hydraulic system being configured such that when said boom hydraulic cylinder, said arm hydraulic cylinder, said bucket hydraulic cylinder and said opening/closing hydraulic cylinder are operated to extend, and with respect to the boom and bucket hydraulic cylinders, the hydraulic fluids from said first hydraulic pumps are supplied to said rod pushing-side chambers thereof through the directional flow control valves for the boom and bucket hydraulic cylinders, respectively, and the hydraulic fluids from said second hydraulic pumps are supplied to said rod pushing-sides chambers thereof through said boom-raising and bucket-crowding inflow control valves, respectively, with being joined with the hydraulic fluids from said first hydraulic pumps, and with respect to the arm hydraulic cylinder, the hydraulic fluids from said first hydraulic pumps are supplied to said rod pushing-side chamber thereof through the directional flow control valves for the arm hydraulic cylinder, and with respect to the opening/closing hydraulic cylinder, the hydraulic fluids from said first hydraulic pumps are supplied to said rod pushing-side chamber thereof through the directional flow control valves for the opening/closing hydraulic cylinder, and part of the fluid discharged from said rod drawing-side chamber thereof is supplied to said rod pushing-side chamber thereof through said opening/closing recovery flow control valve, while all fluids discharged from the rod drawing-side chambers of said boom, arm and bucket hydraulic cylinders and the remaining part of the fluid discharged from the rod pushing-side chamber of the opening/closing, hydraulic cylinder are returned to said reservoir only through the directional flow control valves for the boom, arm, bucket and opening/closing hydraulic cylinders, and when said boom hydraulic cylinder, said arm hydraulic cylinder, said bucket hydraulic cylinder and said opening/closing hydraulic cylinder are operated to contract, and with respect to said boom and arm hydraulic cylinders, the hydraulic fluids from said first hydraulic pumps are supplied to said rod drawing-side chambers thereof through the directional flow control valves for the boom and arm hydraulic cylinders, respectively, and part of the hydraulic fluids from said rod pushing-side chambers thereof are supplied to the rod drawing-side chambers thereof through said boom and arm recovery flow control valves, and with respect to said bucket hydraulic cylinder, the hydraulic fluids from said first hydraulic pumps are supplied to said rod drawing-side chamber thereof through the directional flow control valves for the bucket hydraulic cylinder, and the hydraulic fluids from said second hydraulic pumps are supplied to the rod drawing-side chamber thereof through said bucket-dumping inflow control valve, and being joined with the hydraulic fluids from the first hydraulic pumps, and with respect to the opening/closing hydraulic cylinder, the hydraulic fluids from said first hydraulic pumps are supplied to said rod drawing-side chamber thereof through the directional flow control valves for the opening/closing hydraulic cylinder, while the remaining part of the fluids discharged from the rod pushing-side chambers of the boom and arm hydraulic cylinders and all fluids discharged from the rod pushing-side chambers of the bucket and opening/closing hydraulic cylinders are returned to said reservoir only through the directional flow control valves for the boom, arm, bucket and opening/closing hydraulic cylinders.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm, wherein said hydraulic drive system comprises:

• a boom hydraulic cylinder, an arm hydraulic cylinder, and a bucket hydraulic cylinder for driving said boom, said arm, and said bucket, respectively;
• at least one hydraulic pump mounted on said swing body;
• a common high-pressure line having one side connected to the delivery side of said at least one hydraulic pump and the other side extended to the side of said front operating mechanism;
• a boom branch line branched from said common high-pressure line and connected on the side opposite to the branched side to a rod pushing-side chamber of said boom hydraulic cylinder;
• a boom inflow control valve disposed near a branch position at which said boom branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said boom hydraulic cylinder;
• an arm branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said arm hydraulic cylinder;
• an arm inflow control valve disposed near a branch position at which said arm branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said arm hydraulic cylinder;
• a bucket branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said bucket hydraulic cylinder;
• and
• a bucket inflow control valve disposed near the branch position at which said bucket branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said bucket hydraulic cylinder;
• and
• wherein:
• said inflow control valves are all disposed together in one control valve unit.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm, wherein said hydraulic drive system comprises:

• a boom hydraulic cylinder, an arm hydraulic cylinder, and a bucket hydraulic cylinder for driving said boom, said arm, and said bucket, respectively;
• at least one hydraulic pump mounted on said swing body;
• a common high-pressure line having one side connected to the delivery side of said at least one hydraulic pump and the other side extended to the side of said front operating mechanism;
• a boom branch line branched from said common high-pressure line and connected on the side opposite to the branched side to a rod pushing-side chamber of said boom hydraulic cylinder;
• a boom inflow control valve disposed near a branch position at which said boom branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said boom hydraulic cylinder;
• an arm branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said arm hydraulic cylinder;
• an arm inflow control valve disposed near a branch position at which said arm branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said arm hydraulic cylinder;
• a bucket branch line branched from said common high-pressure line at a position downstream of the branch position of said boom branch line and connected on the side opposite to the branched side to a rod pushing-side chamber of said bucket hydraulic cylinder;
• and
• a bucket inflow control valve disposed near the branch position at which said bucket branch line is branched from said common high-pressure line, and controlling a flow of a hydraulic fluid supplied from said common high-pressure line to the rod pushing-side chamber of said bucket hydraulic cylinder;
• wherein said hydraulic drive system further comprises at least one of three sets comprising:
• a boom return fluid joining line branched from said boom branch line at a position nearer to said boom hydraulic cylinder than said boom inflow control valve and connected on the side opposite to the branched side to a hydraulic reservoir, and a boom outflow control valve disposed in said boom return fluid joining line near a branch position at which said boom return fluid joining line is branched from said boom branch line and controlling a flow of a hydraulic fluid drained from said boom hydraulic cylinder to said hydraulic reservoir;
• an arm return fluid joining line branched from said arm branch line at a position nearer to said arm hydraulic cylinder than said arm inflow control valve and connected on the side opposite to the branched side to said hydraulic reservoir, and an arm outflow control valve disposed in said arm return fluid joining line near a branch position at which said arm return fluid joining line is branched from said arm branch line and controlling a flow of a hydraulic fluid drained from said arm hydraulic cylinder to said hydraulic reservoir;
• and
• a bucket return fluid joining line branched from said bucket branch line at a position nearer to said bucket hydraulic cylinder than said bucket inflow control valve and connected on the side opposite to the branched side to said hydraulic reservoir, and a bucket outflow control valve disposed in said bucket return fluid joining line near a branch position at which said bucket return fluid joining line is branched from said bucket branch line and controlling a flow of a hydraulic fluid drained from said bucket hydraulic cylinder to said hydraulic reservoir;
• and
• wherein:
• said inflow control valves and said outflow control valves are all disposed together in one control valve unit.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open forward in a ground contact state, wherein said hydraulic drive system comprises:

• six first hydraulic pumps and two second hydraulic pumps driven by a plurality of prime movers;
• a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively, and an opening/closing hydraulic cylinder supplied with the hydraulic fluids to open and close said bucket;
• a plurality of boom directional flow control valves, a plurality of arm directional flow control valves, a plurality of bucket directional flow control valves, and a plurality of opening/closing directional flow control valves for controlling respective flows of the hydraulic fluids supplied from said six first hydraulic pumps to said boom hydraulic cylinder, said arm hydraulic cylinder, said bucket hydraulic cylinder, and said opening/closing hydraulic cylinder;
• a boom-raising inflow control valve, a bucket-crowding inflow control valve and a bucket-dumping inflow control valve for controlling respective flows of the hydraulic fluids delivered from said two second hydraulic pumps and supplied to a rod pushing-side chamber of said boom hydraulic cylinder, a rod pushing-side chamber of said bucket hydraulic cylinder, and a rod drawing-side chamber of said bucket hydraulic cylinder without passing said plurality of boom directional flow control valves and said plurality of bucket directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluids delivered from said two second hydraulic pumps to a reservoir;
• a boom recovery flow control valve and an arm recovery flow control valve for introducing the hydraulic fluids in the rod pushing-side chambers of said boom hydraulic cylinder and said arm hydraulic cylinder to rod drawing-side chambers thereof;
• and
• an opening/closing recovery flow control valve for introducing the hydraulic fluid in a rod drawing-side chamber of said opening/closing hydraulic cylinder to a rod pushing-side chamber thereof.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism coupled to said swing body in a vertically angularly movable manner and made up of a boom, an arm and a bucket, wherein said hydraulic drive system comprises:

• a first hydraulic pump and a second hydraulic pump driven by prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm, and said bucket, respectively;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• at least one inflow control valve for controlling a flow of the hydraulic fluid delivered from said second hydraulic pump and supplied to a rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump;
• and
• at least one recovery flow control valve for introducing the hydraulic fluid in the rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders to a rod drawing-side chamber thereof;
• and
• wherein:
• said inflow control valves are all disposed together in one control valve unit.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open forward in a ground contact state, wherein said hydraulic drive system comprises:

• at least one first hydraulic pump and at least one second hydraulic pump driven by a plurality of prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively, and an opening/closing hydraulic cylinder supplied with the hydraulic fluids to open and close said bucket;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• at least two inflow control valve for controlling respective flows of the hydraulic fluid delivered from said second hydraulic pump and supplied to rod pushing-side chambers of at least said boom hydraulic cylinder and said bucket hydraulic cylinder among said plurality of hydraulic cylinders without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• and
• at least two recovery flow control valve for introducing the hydraulic fluids in the rod pushing-side chambers of at least said boom hydraulic cylinder and said arm hydraulic cylinder among said plurality of hydraulic cylinders to rod drawing-side chambers thereof;
• and
• wherein:
• said inflow control valves are all disposed together in one control valve unit.

A hydraulic drive system for a construction machine comprising a travel body, a swing body swingably mounted onto said travel body, and a multi-articulated front operating mechanism made up of a boom rotatably coupled to said swing body, an arm rotatably coupled to said boom, and a bucket rotatably coupled to said arm to be open rearward in a ground contact state, wherein said hydraulic drive system comprises:

• at least one first hydraulic pump and at least one second hydraulic pump driven by a plurality of prime movers;
• a plurality of hydraulic cylinders including a boom hydraulic cylinder, an arm hydraulic cylinder and a bucket hydraulic cylinder supplied with hydraulic fluids delivered from said first hydraulic pump and said second hydraulic pump to drive said boom, said arm and said bucket, respectively;
• a plurality of directional flow control valves for controlling respective flows of the hydraulic fluid supplied from said first hydraulic pump to said plurality of hydraulic cylinders;
• a plurality of inflow control valve for controlling respective flows of the hydraulic fluid delivered from said second hydraulic pump and supplied to rod pushing-side chambers of said boom hydraulic cylinders, said arm hydraulic cylinder and said bucket hydraulic cylinder without passing said directional flow control valves;
• a bypass flow control valve for returning the hydraulic fluid delivered from said second hydraulic pump to a reservoir;
• and
• at least one recovery flow control valve for introducing the hydraulic fluid in the rod pushing-side chamber of at least said boom hydraulic cylinder among said plurality of hydraulic cylinders to a rod drawing-side chamber thereof;
• and
• wherein:
• said inflow control valves are all disposed together in one control valve unit.