Motors: expansible chamber type – Plural relatively movable or rigidly interconnected working... – Condition responsive means for modifying working member...
Reexamination Certificate
2000-12-07
2003-06-24
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Plural relatively movable or rigidly interconnected working...
Condition responsive means for modifying working member...
Reexamination Certificate
active
06581506
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of controlling supply of working fluid for an ordinary machine or a construction machine. The invention also relates to a control device used for such a method.
BACKGROUND OF THE INVENTION
FIG. 3
shows an example of a hydraulic excavator as a construction machine. The hydraulic excavator has a lower structure
1
and an upper structure
3
, which is revolvably attached to the lower structure
1
with a revolving bearing portion
2
therebetween. A front attachment
4
is mounted on the upper structure
3
. The front attachment
4
includes a boom
5
, an arm
6
and a bucket
7
. The base end of the boom
5
is rotatably fitted to the upper structure
3
, while the front end of the boom
5
is rotatably attached to the base end of the arm
6
. The bucket
7
is rotatably attached to the front end of the arm
6
. The boom
5
, the arm
6
and the bucket
7
are adapted to be rotated by a boom-cylinder
5
c,
an arm cylinder
6
c
and a bucket cylinder
7
c
respectively.
An example of conventional swing priority circuits is shown in
FIG. 4
, wherein working fluid is discharged from a hydraulic pump
10
. The working fluid is then divided and fed into a center bypass line
13
and a parallel line
14
in a control valve
12
, with a relief valve
11
controlling the pressure of the working fluid to a preset pressure.
A throttling selector valve dedicated to swinging motion (hereinafter called the swing selector valve)
15
, an arm-dedicated throttling selector valve (hereinafter called the arm-dedicated selector valve)
16
, and other throttling selector valves
28
,
29
are disposed in the control valve
12
. The swing selector valve
15
is adapted to control a revolution motor
3
m
for revolving the upper structure to the right or the left. The other throttling selector valves
28
,
29
are adapted to control other cylinders of the front attachment
4
and the drive motor of the lower structure
1
.
The swing selector valve
15
is designed to be pilot-operated by a remote-control valve dedicated to controlling hydraulic pressure for swinging motion and adapted to be manually operated with a swing operating lever. The arm-dedicated selector valve
16
is designed to be pilot-operated by an oil pressure remote-controlling valve that is dedicated to controlling the arm and adapted to be manually operated with another operating lever.
The swing selector valve
15
is disposed upstream from the arm-dedicated selector valve
16
, and a supply line
17
that leads to the swing selector valve
15
is connected to the parallel line
14
, thereby forming a so-called parallel circuit.
A supply line
18
leading to the arm-dedicated selector valve
16
is connected to the center bypass line
13
, thereby forming a so-called tandem circuit.
A supply line
19
extends between the parallel line
14
and the supply line
18
, and a swing priority valve
21
is disposed in the supply line
19
. The swing priority valve
21
is adapted to be changed over based on external pilot signal pressure fed from a solenoid valve
20
, which is of an on/off switching type. When the solenoid valve
20
is off, the external pilot signal pressure that is fed from a pilot pump
22
through the solenoid valve
20
is applied through a pilot line
23
to the swing priority valve
21
and switches said swing priority valve
21
so that the parallel line
14
communicates with the supply line
18
. When the solenoid valve
20
is at the ‘on’ position, the pilot line
23
communicates with a drain line
24
so that the swing priority valve
21
is at the neutral position as shown in the drawing. Therefore, the parallel line
14
and the supply line
18
are cut off from each other.
When the solenoid valve
20
is switched on, the working fluid is fed to the arm cylinder
6
c
solely from the center bypass line
13
, because the supply line
19
is blocked by the swing priority valve
21
, which is at the neutral position.
Therefore, when the revolution motor
3
m
operates in sync with the arm cylinder
6
c,
the working fluid fed to the arm cylinder
6
c
is limited by means of a bypass notch
25
of the swing selector valve
15
, and the working fluid fed to the revolution motor
3
m,
which serves to revolve the upper structure
3
, travels from the parallel line
14
to the arm cylinder
6
c
through the supply line
17
and a supply notch
27
.
In other words, the fluid is preferentially fed to the swing system. This mechanism is a so-called swing priority circuit, which is particularly effective for, for example, digging a groove by conducting an arm-in operation while pushing the bucket against the wall of the groove with revolving motion.
When the solenoid valve
20
is turned off, the external pilot signal pressure fed from the pilot pump
22
changes over the swing priority valve
21
so that the parallel line
14
communicates with the supply line
18
. Therefore, if the solenoid valve
20
is at the ‘off’ position when the revolution motor
3
m
operates in sync with the arm cylinder
6
c,
swing priority does not work, because the parallel line
14
feeds working fluid to the arm cylinder
6
c.
According to the prior art described above, the manner of controlling the swing priority valve
21
is on/off control by the solenoid valve
20
. Therefore, as described above, in case the swing priority valve
21
is in the blocked state in the swing priority circuit, the bypass notch
25
of the swing selector valve
15
limits the working fluid during the period when the revolution motor
3
m
operates in sync with the arm cylinder
6
c.
Along the nearly entire stroke of the swing selector valve
15
, the opening-area of the bypass notch
25
is normally much smaller than the opening-area of the bypass notch
27
as shown in
FIG. 5
so as to ensure a sufficient supply of working fluid to the revolution motor
3
m
during swinging operation.
As a result, in cases where there is a change in the degree of operation of the swing operating lever, in other words the distance of shifting the swing selector valve
15
, the working fluid fed through the supply line
18
to the arm-dedicated selector valve
16
is considerably reduced by the bypass notch
25
almost regardless of the degree of operation of the swing operating lever. Thus, the working fluid fed to the arm cylinder
6
c
is reduced to an extremely small quantity.
The way a machine is supposed to work is that when the degree of operation of the swing operating lever is increased, the quantity of the hydraulic fluid supplied to the arm cylinder
6
c
should increase accordingly. Likewise, when the degree of operation of the swing operating lever is reduced, the quantity of the hydraulic fluid supplied to the arm cylinder
6
c
should decrease accordingly. In other words, it is desirable that the working fluid fed from the hydraulic pump
10
be effectively and efficiently used. In reality, however, it is difficult with the conventional art to achieve effective use of working fluid. During minute swinging operation, too, the conventional art presents a problem in that large restriction at the bypass notch
25
hinders quick movement of the arm cylinder
6
c.
In order to solve the above problem, an object of the present invention is to make effective use of working fluid fed from a pump to a plurality of throttling selector valves. Another object of the invention is to make the machine more convenient to operate by ensuring smooth interactive operation among a plurality of hydraulic actuators.
DISCLOSURE OF THE INVENTION
A method of controlling supply of working fluid according to the present invention calls for feeding working fluid from a pump to a plurality of throttling selector valves adapted to respectively control a plurality of hydraulic actuators in such a manner that the working fluid flows through the throttling selector valves in sequence, while feeding working fluid from the pump to one located relatively upstream of the throttling selector valves, i.e. the first throttling sel
Darby & Darby
Shin Caterpillar Mitsubishi Ltd.
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