Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
1998-01-23
2001-06-12
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S429000, C060S430000, C060S468000, C091S454000
Reexamination Certificate
active
06244048
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydraulic drive system for hydraulic working machines such as hydraulic excavators, and more particularly to a hydraulic drive system suitable for supersized construction machines.
BACKGROUND ART
A construction of a conventional hydraulic drive system, i.e., one example of a hydraulic circuit of the hydraulic drive system when applied to, e.g., a supersized hydraulic excavator in excess of 70 t-300 t, is shown in
FIG. 9
along with a control system thereof.
Specifically, a hydraulic drive system shown in
FIG. 9
comprises a first hydraulic pump
1
a
and a second hydraulic pump
1
b
both driven by a prime mover
4
a
, a third hydraulic pump
3
a
and a fourth hydraulic pump
3
b
both driven by a prime mover
4
b
, boom hydraulic cylinders
5
a
,
5
b
and an arm hydraulic cylinder
6
driven by a hydraulic fluid delivered from the first to fourth hydraulic pumps
1
a
,
1
b
,
3
a
,
3
b
, a bucket hydraulic cylinder
7
driven by the hydraulic fluid delivered from the first and third hydraulic pumps
1
a
,
3
a
, and a swing hydraulic motor
8
driven by the hydraulic fluid delivered from the second and fourth hydraulic pumps
1
b
,
3
b.
The first hydraulic pump
1
a
is connected to the boom hydraulic cylinders
5
a
,
5
b
, the arm hydraulic cylinder
6
and the bucket hydraulic cylinder
7
through a first boom control valve
10
c
, a first arm control valve
10
b
, and a first bucket control valve
10
a
, respectively. The second hydraulic pump
1
b
is connected to the boom hydraulic cylinders
5
a
,
5
b
, the arm hydraulic cylinder
6
and the swing hydraulic cylinder
8
through a second boom control valve
10
d
, a second arm control valve
10
e
, and a first swing control valve
10
f
, respectively. These control valves
10
a
-
10
f
constitute a first control valve group
10
.
The third hydraulic pump
3
a
is connected to the boom hydraulic cylinders
5
a
,
5
b
, the arm hydraulic cylinder
6
and the bucket hydraulic cylinder
7
through a third boom control valve
11
c
, a third arm control valve
11
b
, and a second bucket control valve
11
a
, respectively. The fourth hydraulic pump
3
b
is connected to the boom hydraulic cylinders
5
a
,
5
b
, the arm hydraulic cylinder
6
and the swing hydraulic cylinder
8
through a fourth boom control valve
11
d
, a fourth arm control valve
11
e
, and a second swing control valve
11
f
, respectively. These control valves
11
a
-
11
f
constitute a second control valve group
11
.
The bottom sides of the boom hydraulic cylinders
5
a
,
5
b
are connected to the first and second boom control valves
10
c
,
10
d
through main lines
105
and to the third and fourth boom control valves
11
c
,
11
d
through main lines
125
, while the rod sides of the boom hydraulic cylinders
5
a
,
5
b
are connected to the first and second boom control valves
10
c
,
10
d
through main lines
115
and to the third and fourth boom control valves
11
c
,
11
d
through main lines
135
. The bottom side of the arm hydraulic cylinder
6
is connected to the first and second arm control valves
10
b
,
10
e
through a main line
116
and to the third and fourth arm control valves
11
b
,
11
e
through a main line
136
, while the rod side of the arm hydraulic cylinder
6
is connected to the first and second arm control valves
10
b
,
10
e
through a main line
106
and to the third and fourth arm control valves
11
b
,
11
e
through a main line
126
. The bottom side of the bucket hydraulic cylinder
7
is connected to the first bucket control valve
10
a
through a main line
107
and to the second bucket control valve
11
a
through a main line
127
, while the rod side of the bucket hydraulic cylinder
7
is connected to the first bucket control valve
10
a
through a main line
117
and to the second bucket control valve
11
a
through a main line
137
. Further, the swing hydraulic motor
8
is connected to the first swing control valve
10
f
through main lines
108
,
118
and to the second swing control valve
11
f
through main lines
128
,
138
.
The control system for the hydraulic drive system includes a calculator
31
which receives operation signals output from control levers
32
,
33
and outputs command signals to the front control valves
10
a-f
and
11
a-f
. The control levers
32
,
33
are each moved in two orthogonal directions. Operating the control lever
32
in the two orthogonal directions outputs a swing operation signal and an arm operation signal, and operating the control lever
33
in the two orthogonal directions outputs a boom operation signal and a bucket operation signal.
In the above construction shown in
FIG. 9
, owing to later-described restrictions upon hose diameters available in the market, the main lines
105
-
107
,
115
-
117
,
125
-
127
and
135
-
137
, i.e., high-pressure lines, are each made up of two or three hoses (or steel pipes, etc.).
DISCLOSURE OF THE INVENTION
The above-explained structure is adapted for a supersized excavator and enables the hydraulic fluid to be supplied at flow rates about twice as much by adding the hydraulic pumps
3
a
,
3
b
, the second control valve group
11
and the main lines
125
,
126
,
127
,
128
,
135
,
136
,
137
,
138
to the construction of a conventional large-sized excavator including the hydraulic pumps
1
a
,
1
b
, the first control valve group
10
and the main lines
105
,
106
,
107
,
108
,
115
,
116
,
117
,
118
.
More specifically, a supersized excavator requires the hydraulic fluid to be supplied in a large amount to drive, in particular, the bottom sides of the hydraulic cylinders
5
a
,
5
b
,
6
,
7
. Meanwhile, to supply the hydraulic fluid at a super-high flow rate under a super-high pressure requires that each of the main lines be formed of, e.g., a hose or a steel pipe having a super-large diameter. In practice, however, since hoses available in the current market have a maximum diameter of about 2 inches, the main line must be constructed by arranging a plurality of hoses or the likes (e.g., two or three per main line) side by side, as mentioned above. This results in that the allowable capacity of the main line is restricted for a supply/return flow rate demanded by the hydraulic actuator and a relatively large pressure loss is generated in each of the hoses. Accordingly, in the entire hydraulic circuit of the supersized excavator including long lines made of up hoses, steel pipes or the likes, control valves, etc., a very large pressure loss is generated and an energy loss is increased correspondingly. Another problem is that the operating speed of the hydraulic actuator is lowered and the working efficiency is reduced.
Further, to arrange a plurality of hoses or the likes to construct one main line and install two or three main lines on each of the bottom and rod sides of the hydraulic cylinders
5
a
,
5
b
,
6
,
7
in the supersized excavator is not easy in itself. An additional problem is that the presence of many hoses or the likes makes poor visibility from a cab toward the lateral and rear sides of a working machine such as a hydraulic excavator.
An object of the present invention is to provide a hydraulic drive system which can reduce the total length of lines made up of hoses, steel pipes or the likes in a supersized hydraulic working machine, and can lessen a pressure loss in the entirety of a hydraulic circuit.
To achieve the above object, according to the present invention, there is provided a hydraulic drive system equipped on a hydraulic working machine comprising a working machine body and a front device made up of a plurality of front members coupled to the working machine body to be rotatable in the vertical direction, the hydraulic drive system comprising a hydraulic reservoir provided on the working machine body, at least one hydraulic pump, a plurality of hydraulic cylinders for respectively driving the plurality of front members, a plurality of flow control valves provided on the working machine body for respectively int
Kato Hideyo
Nozawa Yusaku
Ochiai Masami
Tanaka Sotaro
Yasuda Gen
Hitachi Construction Machinery Co. Ltd.
Lopez F. Daniel
Mattingly, Stanger & Malur
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