Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Reexamination Certificate
1999-11-23
2001-07-03
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
C091S450000, C091S461000
Reexamination Certificate
active
06253658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic control system for controlling a hydraulic operation machine such as a hydraulic shovel.
2. Description of Related Art
FIG. 11
shows a conventional hydraulic control system, which is for controlling a hydraulic operation machine such as a hydraulic shovel.
Pump
1
is connected with a cylinder device
3
via a control valve
2
.
The control valve
2
switches by a pilot pressure introduced into a pilot chamber
2
a
or
2
b
. The pilot pressure to be introduced into the pilot chambers
2
a
and
2
b
is controlled by a pilot valve
4
. For example, if the pilot pressure is introduced into the pilot chamber
2
a
, the control valve
2
switches to an upward position a (the left side of the drawing) in proportion to the volume of the introduced pilot pressure. If the pilot pressure is introduced into the pilot chamber
2
b
, the control valve
2
switches to a downward position b (the right side of the drawing) in proportion to the volume of the introduced pilot pressure.
Between the control valve
2
and a bottom pressure chamber
3
a
of the cylinder device
3
, a load supporting valve assembly
6
is arranged, and which includes a pilot check valve
7
, a selector valve
9
and an overload relief valve
10
.
As discussed in more detail further below, the control valve
2
is connected to a load supporting passage
5
, and the pilot check valve
7
is provided on the load supporting passage
5
.
The pilot check valve
7
passes flow only from the control valve
2
. A check function of the pilot check valve
7
is released in communication between a pilot passage
8
and a tank.
The pilot passage
8
of the pilot check valve
7
is connected to the selector valve
9
.
The selector valve
9
in a normal state shown in
FIG. 11
is in a blocking position for closing the pilot passage
8
. The pilot check valve
7
, therefore, causes its normal check function to be active. Whereas, on introduction of the pilot pressure into a pilot chamber
9
a
, the selector valve
9
switches to a communicating position so as to link the pilot passage
8
with the tank, thus the check function of the pilot check valve
7
is released.
The pilot pressure in the pilot chamber
2
b
of the control valve
2
is introduced into the pilot chamber
9
a
of the selector valve
9
designed as mentioned above. That is to say, the selector valve
9
is adapted to switch to the communicating position whenever the control valve
2
switches to the downward position b (the right side of the drawing).
The overload relief valve
10
is connected to a passage between the pilot check valve
7
and the bottom pressure chamber
3
a
of the cylinder device
3
. In a maintaining state of work load W. the overload relief valve
10
functions to prevent an extraordinary increase of a load pressure in the bottom pressure chamber
3
a
, thereby absorbing shock produced when an external force is applied to the work load W.
Operation of the conventional hydraulic control system will be explained below.
As shown in
FIG. 11
, if the control valve
2
is in a neutral position, oil discharged from the pump
1
is introduced into neither the bottom pressure chamber
3
a
nor a rod-side pressure chamber
3
b
of the cylinder device
3
.
The pilot pressure is not also introduced into the pilot chamber
9
a
, and the selector valve
9
is in the blocking position, so that the check function of the pilot check valve
7
is inactive. Thus, the flow from the bottom pressure chamber
3
a
of the cylinder device
3
is blocked and the work load W is assuredly maintained.
When the work load W needs to move up, the pilot pressure is introduced from the pilot valve
4
into the pilot chamber
2
a
, so that the control valve
2
switches to the upward position a (the left side of the drawing).
In this time, since the selector valve
9
keeps in the blocking position, the check function of the pilot check valve
7
is active. Hence, when the discharge pressure of the pump
1
is properly increased, the oil discharged from the pump
1
opens the pilot check valve
7
and then is introduced toward the bottom pressure chamber
3
a
of the cylinder device
3
, while the hydraulic fluid in the rod-side pressure chamber
3
b
is discharged to the tank, thus moving up the work load W.
On the other hand, when the work load W needs to move down, the pilot pressure is introduced from the pilot valve
4
into the pilot chamber
2
b
, so that the control valve
2
switches to the downward position b (the right side of the drawing).
In this time, the pilot pressure is also introduced into the pilot chamber
9
a
, and the selector valve
9
switches to the communication position, so that the check function of the pilot check valve
7
is inactive. Hence, the hydraulic fluid in the bottom pressure chamber
3
a
of the cylinder device
3
passes through the pilot check valve
7
and is discharged into the tank in accordance with the degree of opening control valve
2
, thus moving down the work load W.
Regarding the hydraulic control systems of prior art, in an operation for moving an objective downward with a hydraulic shovel in a craning work, for example, if the load supporting passage
5
is fractured, the hydraulic fluid in the bottom pressure chamber
3
a
of the cylinder device
3
may rapidly escape from the fractured section, whereby causing the objective to rapidly fall.
In this case, by returning the position of the control valve
2
to the neutral position, the selector valve
9
switches back to the blocking position, so that the check function of the pilot check valve
7
becomes active, whereby the falling objective can be stopped.
Actually, however, the objective must crashes on the ground due to its falling speed before the control valve
2
switches to the neutral position.
In the hydraulic control system of prior art, in order to absorb shock produced when the external force is applied to the work load W, in the supporting state of the work load W, the overload relief valve
10
must be connected to the passage between the bottom pressure chamber
3
a
of the cylinder device
3
and the pilot check valve
7
.
The load supporting valve assembly
6
is typically positioned close to the cylinder device
3
. In other words, the overload relief valve
10
that is included in the load supporting valve assembly
6
is also positioned closed to the cylinder device
3
, which is far away from the construction machine body.
However, the tank is typically placed around the construction machine body. Accordingly, as the overload relief valve
10
is distanced from the construction machine body, a pipe for connecting the overload relief valve
10
with the tank becomes longer.
The connecting pipe needs to be of significant capacity since the overload relief valve
10
is for the escape of overloading pressure. Therefore, such a long connecting pipe causes increases in cost and size.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a hydraulic control system capable of preventing an objective from rapidly dropping down, for example, when the load supporting passage
5
is fractured in an operation for moving the objective downward with a hydraulic shovel in a craning work. The second object of the present invention is to provide a hydraulic control system allowing reductions in cost and size due to needlessness of the arrangement of the overload relief valve
10
to connect to a passage between the bottom pressure chamber
3
a
of the cylinder device
3
and the pilot check valve
7
.
The present invention is based on the premises that a hydraulic control system has: a pump; a cylinder device; a pressure chamber provided in the cylinder device and generating a load pressure; a control valve blocking the cylinder device from the pump in its neutral position, and introducing a discharged oil from the pump into the pressure chamber of the cylinder device to move up a work load when switching to an upward position, and discharging
Kayaba Industry Co. Ltd.
Ryznic John E.
Steinberg & Raskin, P.C.
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