Excavating – Beneath a body of water – Grab
Reexamination Certificate
2001-08-07
2003-05-06
Pezzuto, Robert E. (Department: 3671)
Excavating
Beneath a body of water
Grab
C037S187000
Reexamination Certificate
active
06557277
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydraulic circuit for a working machine such as a hydraulic excavator, and more particularly to a hydraulic circuit for a working machine suitable for use with a working machine based on a hydraulic excavator and having a multistage expansion arm for caisson type excavation.
BACKGROUND ART
FIG. 8
is a schematic side elevational view showing a hydraulic excavator (working machine) to which a common multistage expansion arm is attached. The hydraulic excavator includes a lower traveling unit
1
, an upper revolving unit
2
coupled for revolution to the lower traveling unit
1
, a boom
3
mounted for swinging motion on the upper revolving unit
2
, a multistage expansion arm (expansible arm)
4
mounted for swinging motion at a tip end of the boom
3
and having an expansion/contraction function, a clamshell bucket
5
mounted at a tip end of the multistage expansion arm
4
, and so forth.
A boom cylinder
3
a
is provided between the boom
3
and the upper revolving unit
2
, and the boom
3
is driven to swing in response to an expansion/contraction movement of the boom cylinder
3
a
. Similarly, an arm cylinder
4
a
is provided between the boom
3
and the multistage expansion arm
4
, and the multistage expansion arm
4
is driven to swing in response to an expansion/contraction movement of the arm cylinder
4
a
. It is to be noted that a cylinder
11
[refer to FIG.
9
] is provided for the multistage expansion arm
4
and can expand and contract the multistage expansion arm
4
.
The clamshell bucket
5
is configured for opening and closing movement by causing a hydraulic cylinder
5
a
[refer to FIG.
9
] provided in the inside thereof to operate.
FIG. 9
is a schematic view showing a general configuration of a hydraulic circuit for the hydraulic excavator described above. It is to be noted that a pilot circuit is not shown in FIG.
9
. Referring to
FIG. 9
, reference numeral
6
denotes a prime mover, reference characters
7
a
,
7
b
denote each a hydraulic pump (pressure source) driven by the prime mover
6
, and reference numeral
8
denotes a control valve unit for controlling pressure oil (operating oil) from the hydraulic pumps
7
a
,
7
b
to distribute the flow rates of the pressure oil to various actuators which are hereinafter described. Reference numeral
9
denotes a revolving motor for driving the revolving motor
9
, and reference characters
10
a
,
10
b
denote each a traveling motor for driving a traveling apparatus not shown provided on the lower traveling unit
1
.
Reference character boom cylinder
3
a
denotes a boom cylinder,
4
a
an arm cylinder,
5
a
a bucket cylinder for opening and closing the clamshell bucket,
11
a telescopic cylinder for expanding and contracting the multistage expansion arm
4
,
12
a slow return valve provided in a rod side chamber
11
b
of the telescopic cylinder
11
, and
17
a tank.
When operating oil is supplied into a hydraulic chamber at an upper portion in the figure of the bucket cylinder
5
a
to move the bucket cylinder
5
a
downwardly in the figure, the clamshell bucket
5
is opened. A restrictor (orifice) is formed in the inside of the slow return valve
12
and prevents sudden expansion of the multistage expansion arm
4
by its own weight.
Reference numeral
13
denotes a telescopic control valve for expanding or contracting the telescopic cylinder
11
built in the control valve unit
8
,
14
a bucket control valve for operating the bucket cylinder
5
a
, reference characters
15
a
,
15
b
denote each a telescopic remote control valve for controlling the telescopic control valve
13
, reference numeral
15
denotes a telescopic remote control lever for controlling movement of the telescopic remote control valves
15
a
,
15
b
, valves
16
a
,
16
b
are bucket remote control valves for controlling the bucket control valve
14
, and reference numeral
16
denotes a bucket remote control valve for controlling operation of the bucket remote control valves
16
a
,
16
b.
Of the components given above, the telescopic remote control valve
15
a
is a remote control valve (opening operator) for expanding the telescopic cylinder
11
, and when the telescopic remote control lever
15
is tilted rightwardly in the figure, the telescopic remote control valve
15
a
is opened and a pilot pressure corresponding to the operation amount of the telescopic remote control lever
15
is outputted.
The bucket remote control valve
16
a
is a remote control valve (opening operator) for causing the clamshell bucket
5
to perform an opening movement, and when the bucket remote control lever
16
is tilted rightwardly in the figure, the bucket remote control valve
16
a
is opened and a pilot pressure corresponding to the operation amount of the bucket remote control lever
16
is outputted.
Reference characters
103
a
,
104
a
,
109
,
110
a
,
110
b
denote control valves for controlling movement of the boom cylinder
3
a
, arm cylinder
4
a
, revolving motor
9
, and traveling motors
10
a
,
10
b
, respectively, and reference numeral
120
denotes a traveling straightforward valve for keeping straightforward traveling of the hydraulic excavator. It is to be noted that detailed description of the valves just mentioned is omitted.
Referring to
FIG. 9
, if the telescopic remote control lever
15
is operated to open the telescopic remote control valve
15
a
, then a pilot pressure acts upon a pilot port
13
a
to change over the telescopic control valve
13
of the control valve unit
8
from a chamber N to another chamber X. Then, pressure oil is supplied from the hydraulic pumps
7
a
,
7
b
into a head side chamber
11
a
of the telescopic cylinder
11
while pressure oil in the rod side chamber
11
b
is introduced into the tank
17
through the slow return valve
12
and the telescopic control valve
13
.
At this time, since the weights of the multistage expansion arm
4
and the clamshell bucket
5
themselves act in the rod side chamber
11
b
of the telescopic cylinder
11
, a high pressure is generated in the rod side chamber
11
b
, but the pressure in the head side chamber
11
a
becomes low since no load is applied to the head side chamber
11
a.
Accordingly, if the bucket remote control lever
16
is operated in order to open the clamshell bucket
5
while the multistage expansion arm
4
is being extended, then most of pressure oil in the hydraulic pumps
7
a
,
7
b
flows into the head side chamber
11
a
of the telescopic cylinder
11
which has a lower working pressure. Consequently, sufficient pressure oil is not supplied into the bucket cylinder
5
a
and the speed at which the clamshell bucket
5
is opened is reduced, resulting in a subject that the operability is deteriorated.
The present invention has been made in view of such a subject as just described, and it is an object of the present invention to provide a hydraulic circuit for a working machine which prevents drop of the working speed of a clamshell bucket upon expansion of an expansion arm so that improvement in operability is achieved.
DISCLOSURE OF THE INVENTION
In order to attain the object described above, according to an aspect of the present invention, a hydraulic circuit for a working machine which includes an expansion arm and a clamshell bucket attached to a tip end of the expansion arm and is configured such that the expansion arm and the clamshell bucket are operated by pressure oil supplied from a common pressure source is characterized in that it comprises pressure reduction means for reducing an operating pressure for driving the expansion arm to the expansion side based on an operating pressure for opening the clamshell bucket.
Accordingly, with the hydraulic circuit for a working machine of the present invention, when an operation for opening the clamshell bucket is performed while the expansion arm is being expanded by reducing the operating pressure for driving the expansion arm to the expansion side based on the operating pressure for opening the cla
Hibi Yoshiyuki
Kubota Yorimichi
Matoba Nobuaki
Nozaki Shinya
Morrison & Foerster / LLP
Pezzuto Robert E.
Shin Caterpillar Mitsubishi Ltd.
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