Valves and valve actuation – Fluid actuated or retarded – Pilot or servo type motor
Reexamination Certificate
1999-04-20
2001-06-05
Shaver, Kevin (Department: 3754)
Valves and valve actuation
Fluid actuated or retarded
Pilot or servo type motor
C251S035000, C137S460000
Reexamination Certificate
active
06241212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hose rupture control valve unit (often called a hose rupture valve) which is provided in a hydraulic machine, such as a hydraulic excavator, for preventing a drop of the load upon rupture of a cylinder hose.
2. Description of the Prior Art
In a hydraulic machine such as a hydraulic excavator, there is a need for preventing a drop of the load even if a hose or steel pipe for supplying a hydraulic fluid to a hydraulic cylinder, serving as an actuator for driving a load, e.g., an arm, should be ruptured. To meet such a need, a hose rupture control valve unit (often called a hose rupture valve) is provided in the hydraulic machine.
FIG. 8
is a hydraulic circuit diagram showing a typical conventional hose rupture control valve unit, and
FIG. 9
shows a sectional structure of the hose rupture control valve unit.
Referring to
FIGS. 8 and 9
, a hose rupture control valve unit
200
comprises a housing
204
provided with two input/output ports
201
,
202
and a reservoir port
203
. The input/output port
201
is directly attached to a bottom port of a hydraulic cylinder
502
, the input/output port
202
is connected to one of actuator ports of a control valve
503
via a hydraulic line (hose)
505
, and the reservoir port
203
is connected to a reservoir
509
via a drain line (hose)
205
. Within the housing
204
, there are provided a main spool
211
operated with a pilot pressure supplied as an external signal from a manual pilot valve
508
, a check valve
212
for fluid supply, a poppet valve body
214
controlled by a pilot portion
213
which is provided in the circumference of the main spool
211
, and an overload relief valve
215
for releasing an abnormal pressure.
In the conventional hose rupture control valve unit
200
having the above-described construction, supply of a hydraulic fluid to the bottom side of the hydraulic cylinder
502
is effected by supplying the hydraulic fluid from the control valve
503
to the bottom side through the fluid-supply check valve
212
. Also, discharge of the hydraulic fluid from the bottom side of the hydraulic cylinder
502
is effected by operating the main spool
211
of the valve unit
200
with the pilot pressure as an external signal to first open the poppet valve body
214
controlled by the pilot portion
213
which is provided in the circumference of the main spool
211
, and then open a variable throttle portion
211
a
also provided in the circumference of the main spool
211
, thereby draining the hydraulic fluid to the reservoir
509
while controlling the flow rate of the hydraulic fluid.
The poppet valve body
214
is provided in series with respect to the main spool
211
, and has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder
502
.
The overload relief valve
215
operates to drain the hydraulic fluid and prevent hose rupture in the event an excessive external force acts on the hydraulic cylinder
502
and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder
502
is brought into a high-pressure level.
Also, if the hydraulic hose
505
leading from the control valve
503
to the input/output port
202
should be ruptured, the check valve
212
and the poppet valve body
214
are closed to prevent a drop of the load borne by the hydraulic cylinder
502
. At this time, by operating the main spool
211
with the pilot pressure from the manual pilot valve
508
and adjusting an opening area of the variable throttle portion
211
a,
it is possible to slowly contract the hydraulic cylinder
502
under action of the weight of the load itself and to move the load to a safety position.
Numerals
507
a
and
507
b
denote main relief valves for limiting a maximum pressure in the circuit.
Further, JP, A, 3-249411 discloses a hose rupture control valve unit utilizing a proportional seat valve to reduce an overall size of the valve unit.
FIG. 10
shows the disclosed hose rupture control valve unit.
Referring to
FIG. 10
, a hose rupture control valve unit
300
comprises a housing
323
provided with an input port
320
, a work port
321
and a reservoir port
322
. The input port
320
is connected to one of actuator ports of a control valve
503
, the work port
321
is connected to a bottom port of a hydraulic cylinder
502
, and the reservoir port
322
is connected to a reservoir
509
via a drain line (hose)
205
. Within the housing
323
, there are provided a check valve
324
for fluid supply, a proportional seat valve
325
, an overload relief valve
326
, and a pilot valve
340
. The pilot valve
340
is operated with a pilot pressure supplied as an external signal from a manual pilot valve
508
(see FIG.
8
), and the proportional seat valve
325
is operated with the operation of the pilot valve
340
. The overload relief valve
326
is incorporated in the proportional seat valve
325
.
Supply of a hydraulic fluid to the bottom side of the hydraulic cylinder
502
is effected by supplying the hydraulic fluid from the control valve
503
to the bottom side through the fluid-supply check valve
324
of the valve unit
300
. Also, discharge of the hydraulic fluid from the bottom side of the hydraulic cylinder
502
is effected by operating the pilot valve
340
of the valve unit
300
with the pilot pressure, as an external signal, to open the proportional seat valve
325
, thereby draining the hydraulic fluid to the reservoir
509
while controlling the flow rate of the hydraulic fluid. The proportional seat valve
325
has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder
502
.
The overload relief valve
326
operates to open the proportional seat valve
325
for draining the hydraulic fluid and preventing hose rupture in the event an excessive external force acts on the hydraulic cylinder
502
and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder
502
is brought into a high-pressure level.
Also, if a hydraulic line (hose)
505
leading from the control valve
503
to the input port
320
should be ruptured, the check valve
324
and the proportional seat valve
325
are closed to prevent a drop of the load borne by the hydraulic cylinder
502
. At this time, by operating a spool
341
of the pilot valve
340
with the pilot pressure and adjusting an opening area of the proportional seat valve
325
, it is possible to slowly contract the hydraulic cylinder
502
under action of the weight of the load itself and to move the load to a safety position.
SUMMARY OF THE INVENTION
In the conventional hose rupture control valve unit shown in
FIGS. 8 and 9
, various components, i.e., the check valve
212
for fluid supply, the main spool
211
, the poppet valve body
214
controlled by the pilot portion
213
provided in the circumference of the main spool
211
, and the overload relief valve
215
, are separately provided corresponding to the respective functions. Therefore, incorporating all those components in the housing
204
of a restricted certain size imposes a limitation in sizes of the individual components. Also, there has been a difficulty in reducing the production cost.
On the other hand, since all of the hydraulic fluid discharged from the hydraulic cylinder
502
passes through the main spool
211
, a spool valve body of the main spool
211
is required to have a larger diameter. Further, because of the main spool
211
and the poppet valve body
214
being provided in series, the hydraulic fluid passes through these two valve elements at a large flow rate. However, when the main spool
211
and the poppet valve body
214
are incorporated besides the other components in the housing
204
of the restricted certain size, their sizes are necessarily limited. This may result in that a sufficient flow passage is not ensured and a pressure loss is in
Sugiyama Genroku
Takahashi Tarou
Toyooka Tsukasa
Bastianelli John
Hitachi Construction Machinery Co. Ltd.
Mattingly, Stanger & Malur
Shaver Kevin
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