Information
-
Patent Grant
-
6241212
-
Patent Number
6,241,212
-
Date Filed
Tuesday, April 20, 199925 years ago
-
Date Issued
Tuesday, June 5, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Shaver; Kevin
- Bastianelli; John
Agents
- Mattingly, Stanger & Malur
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
A hose rupture control valve unit includes a housing provided with two input/output ports. One input/output port is directly attached to a bottom port of a hydraulic cylinder, and the other input/output port is connected to one of actuator ports of a control valve via an actuator line. Within the housing, there are provided a poppet valve body serving as a main valve, a spool valve body serving as a pilot valve which is operated with a pilot pressure supplied as an external signal from a manual pilot valve, thereby operating the poppet valve body, and a small spool having the function of an overload relief valve. The above construction reduces the number of components arranged in a flow passage through which a hydraulic fluid passes at a large flow rate, and hence a pressure loss. A further reduction in overall size and production cost of the valve unit is achieved.
Description
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 increased. In addition, a pressure loss is also inevitable with such a construction that the hydraulic fluid passes at a large flow rate through the main spool
211
and the poppet valve body
214
provided in series.
The hose rupture control valve unit is mounted to the bottom side of a boom cylinder or the rod side of an arm cylinder. A boom and an arm, to which the boom cylinder and the arm cylinder are attached, are each a working member operated to be able to rotate in the vertical direction. If the size of the housing
204
is selected to a relatively large value in consideration of the problem of a pressure loss, a risk would be increased that the hose rupture control valve unit is damaged upon hitting against rocks, etc. during the operation of the boom or the arm. It has been thus difficult to design the hose rupture control valve unit in appropriate size.
Further, since all of the hydraulic fluid discharged from the hydraulic cylinder
502
passes through the overload relief valve
215
as well, the overload relief valve
215
is also required to have a rather large size. Correspondingly, the drain hose
205
leading to the reservoir port
203
is likewise required to have a rather large inner diameter. These requirements result in an increase of the production cost and a difficulty in routing the drain hose compactly.
FIG. 11
is a simplified diagram showing the case where the hose rupture control valve unit is attached to each of two boom cylinders. Referring to
FIG. 11
, symbols
502
a
,
502
b
denote two boom cylinders. Rod ends of the boom cylinders
502
a
,
502
b
are rotatably coupled through pins
230
a
,
230
b
to both sides of a boom
232
bearing a load
231
. Hose rupture control valve units
200
a
,
200
b
, each being the same as the above-mentioned valve unit
200
, are mounted respectively to the bottom sides of the boom cylinders
502
a
,
502
b.
In such an arrangement for practical use, during the operation with main spools
211
of the valve units
200
a
,
200
b
being open, bending loads would impose on the pins
230
a
,
230
b
due to a difference between driving forces acting on the pins
230
a
,
230
b
, thus causing breakage of the pins
230
a
,
230
b
, if there is a difference between metering characteristics of the main spools
211
due to a variation in machining carried out on the main spools
211
. For that reason, the main spools
211
of the valve units
200
a
,
200
b
are required to have the metering characteristics as identical as possible to each other.
In the hose rupture control valve unit disclosed in JP, A, 3-249411, shown in
FIG. 10
, the overload relief valve
326
is incorporated in the proportional seat valve
325
, which is controlled by the pilot valve
340
, so that the proportional seat valve
325
has not only the function of the main spool
211
in the above-described prior art, but also the functions of the poppet valve body
214
and the overload relief valve
215
. Therefore, the number of components is reduced as compared with that needed in the above-described prior art, and a reduction in size of the valve unit can be achieved to some extent while lessening a pressure loss. With this disclosed prior art, however, the check valve
324
for fluid supply is still an essential component. In other words, there is a demand for a further improvement in reducing the size of the valve unit and cutting down the production cost.
Also, although the overload relief valve
326
is incorporated in the proportional seat valve
325
to provide the proportional seat valve
325
with the overload relief function, the point that all of the hydraulic fluid discharged from the hydraulic cylinder
502
passes through the reservoir port
322
and returns to the reservoir
509
via the drain hose
205
is the same as in the above-described prior art shown in
FIGS. 8 and 9
. As a result, the drain hose
205
is required to have a rather large inner diameter, and a difficulty is encountered in routing the drain hose compactly.
Further, when the hose rupture control valve unit is mounted for each boom cylinder as shown in
FIG. 11
, the disclosed prior art also requires that metering characteristics of the valve units, each including the proportional seat valve
325
and the pilot valve
340
, on both sides are as identical as possible to each other like the above-described prior art shown in
FIGS. 8 and 9
. For the valve unit shown in
FIG. 10
, particularly, because the metering characteristics require to be made identical in consideration of variations in machining carried out on both the proportional seat valve
325
and the pilot valve
340
, adjustment of the metering characteristics becomes very difficult.
A first object of the present invention is to provide a hose rupture control valve unit which can reduce a pressure loss, an entire size of the valve unit, and a production cost while ensuring the various functions that are the least necessary as the hose rupture control valve unit.
A second object of the present invention is to provide a hose rupture control valve unit which requires no drain hose specific to an overload relief valve, and hence which can further reduce a production cost of the valve unit and simplify routing of hoses around the valve unit.
A third object of the present invention is to provide a hose rupture control valve unit with which, even when two hose rupture control valve units are arranged in parallel as encountered in application to boom cylinders, metering characteristics of the two valve units can be adjusted with good accuracy.
(1) To achieve the above objects, according to the present invention, in a hose rupture control valve unit provided between a supply/drain port of a hydraulic cylinder and a hydraulic hose for controlling a flow rate of a hydraulic fluid coming out from the supply/drain port to the hydraulic hose in accordance with an external signal, the valve unit comprises a poppet valve body serving as a main valve slidably disposed in a housing provided with a cylinder connecting chamber connected to the supply/drain port, a hose connecting chamber connected to the hydraulic hose, and a back pressure chamber, the poppet valve body being able to selectively interrupt and establish communication between the cylinder connecting chamber and the hose connecting chamber, and changing an opening area depending on the amount of movement thereof, and a spool valve body serving as a pilot valve disposed in a pilot passage connecting the back pressure chamber and the hose connecting chamber, and operated in accordance with the external signal to interrupt and control a rate of pilot flow passing through the pilot passage depending on the amount of movement thereof, the poppet valve body being provided with a feedback variable throttle passage which has an initial opening area when the poppet valve body is in a interrupting position, and increases an opening area thereof depending on the amount of movement of the poppet valve body, thereby controlling a value of the rate of pilot flow coming out from the cylinder connecting chamber to the back pressure.
In operation of supplying the hydraulic fluid to the bottom side of the hydraulic cylinder, since the feedback variable throttle passage has the initial opening area, the poppet valve body is opened when a pressure in the hose connecting chamber rises to a level higher than a load pressure, allowing the hydraulic fluid to be supplied to the bottom side of the hydraulic cylinder (conventional check valve function on the supply side).
In operation of discharging the hydraulic fluid from the bottom side of the hydraulic cylinder, when the spool valve body is operated in accordance with the external signal and the pilot flow is produced at a rate depending on the amount of movement of the spool valve body, the poppet valve body is opened and the amount of movement thereof is controlled depending on the rate of the pilot flow. Therefore, most of the hydraulic fluid on the bottom side of the hydraulic cylinder passes through the poppet valve body, whereas the remaining hydraulic fluid passes through the feedback variable throttle passage, the back pressure chamber and the spool valve body, both the flows of the hydraulic fluid being then drained to the reservoir (conventional main spool function).
In operation of holding the load pressure on the bottom side of the hydraulic cylinder, the poppet valve body is in the interrupting position and holds the load pressure, thereby reducing the amount of leakage (load check function).
Thus the hose rupture control valve unit of the present invention can fulfill the conventional check valve function on the supply side, main spool function, and load check function. Further, the poppet valve body is only one component arranged in a flow passage through which the hydraulic fluid passes at a large flow rate, and hence a pressure loss is reduced. In addition, it is possible to reduce an overall size and production cost of the valve unit.
(2) In the above (1), preferably, the valve unit further comprises communicating means for communicating the back pressure chamber with the reservoir when a pressure in the hose connecting chamber exceeds a preset value.
In the event an excessive external force acts on the hydraulic cylinder, the pressure in the cylinder connecting chamber rises, causing the communicating means to communicate the back pressure chamber with the reservoir, whereupon the pressure in the back pressure chamber lowers and the poppet valve body is opened. The hydraulic fluid, that is brought into a high-pressure level under action of the external force, is drained to the reservoir through a main overload relief valve which is disposed in an actuator line as conventional.
Thus, since the function of an overload relief valve is realized and the hydraulic fluid passes through the communicating means at a small flow rate, a size of the communicating means can be reduced. In addition, since the hydraulic fluid is released from the communicating means to the reservoir via a drain line that is identical to the drain line formed in the conventional valve unit, a drain hose specific to the overload relief valve is no longer required in the valve unit, and routing of the hose around the valve unit can be simplified.
(3) In the above (2), preferably, the communicating means is provided in parallel to the spool valve body.
(4) Also, in the above (2), the communicating means comprises a relief valve provided in parallel to the spool valve body, pressure generating means provided downstream of the relief valve, and means for causing a pressure generated by the pressure generating means to act as a driving force on the spool valve body on the same side as the external signal.
In the event an excessive force acts on the hydraulic cylinder and the pressure in the back pressure chamber rises, the relief valve is opened, whereupon a pressure generated by the pressure generating means operates the spool valve body. The operation of the spool valve body produces the pilot flow and opens the poppet valve body. As a result, the hydraulic fluid in the hydraulic cylinder can be released to the reservoir through the main overload relief valve in a similar manner as described in the above (2). Furthermore, the same function as that of the communicating means in the above (2) can be realized by the relief valve through which the hydraulic fluid passes at a smaller flow rate than through the communicating means in the above (2). Hence the component size can be reduced and the overall size of the valve unit can be further reduced.
(5) In the above (1), preferably, the poppet valve body has a dead zone set to maintain the poppet valve body in the interrupting position when the rate of pilot flow is not larger than a predetermined value.
According to this feature, even with two hose rupture control valve units arranged in parallel as encountered when attached to boom cylinders, metering characteristics of the two valve units can be adjusted with good accuracy by adjusting metering characteristics of only spool valve bodies in the range where poppet valve bodies are each in the dead zone.
(6) In the above (1), preferably, the spool valve body includes adjusting means capable of changing the amount of movement of the spool valve body with respect to the external signal.
According to this feature, the accuracy of metering characteristic of the spool valve body itself can be further improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a hydraulic circuit diagram showing a hose rupture control valve unit according to one embodiment of the present invention, along with a hydraulic drive system in which the valve unit is disposed.
FIG. 2
is a sectional view showing the structure of a portion, i.e., a poppet valve body and a spool valve body, of the hose rupture control valve unit shown in FIG.
1
.
FIG. 3
is a sectional view showing the structure of another portion, i.e., a small spool, of the hose rupture control valve unit shown in FIG.
1
.
FIG. 4
is a graph showing the relationships of an opening area of the poppet valve body and an opening area of a feedback slit with respect to the amount of movement (stroke) of the poppet valve body.
FIG. 5
is a graph showing the relationships of a rate of fluid flow passing through the spool valve body (pilot flow rate) and a rate of fluid flow passing through the poppet valve body (main flow rate) with respect to an external signal (pilot pressure).
FIG. 6
is a hydraulic circuit diagram showing a hose rupture control valve unit according to another embodiment of the present invention, along with a hydraulic drive system in which the valve unit is disposed.
FIG. 7
is a sectional view showing the structure of a portion, i.e., a small relief valve, of the hose rupture control valve unit shown in FIG.
6
.
FIG. 8
is a hydraulic circuit diagram showing a conventional hose rupture control valve unit, along with a hydraulic drive system in which the valve unit is disposed.
FIG. 9
is a sectional view showing the structure of a principal part of the conventional hose rupture control valve unit shown in FIG.
8
.
FIG. 10
is a hydraulic circuit diagram showing another conventional hose rupture control valve unit, along with a hydraulic drive system in which the valve unit is disposed.
FIG. 11
is a simplified diagram showing the case where the hose rupture control valve unit is attached to each boom cylinder.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1
is a hydraulic circuit diagram showing a hose rupture control valve unit according to one embodiment of the present invention, and
FIGS. 2 and 3
are sectional views each showing a structure of the hose rupture control valve unit.
Referring to
FIG. 1
, numeral
100
denotes a hose rupture control valve unit of this embodiment. A hydraulic drive system, in which the valve unit
100
is disposed, comprises a hydraulic pump
101
, a hydraulic actuator (hydraulic cylinder)
102
driven by a hydraulic fluid delivered from the hydraulic pump
101
, a control valve
103
for controlling a flow of the hydraulic fluid supplied from the hydraulic pump
101
to the hydraulic cylinder
102
, main overload relief valves
107
a
,
107
b
connected to actuator lines
105
,
106
, which are hydraulic lines (hoses) extended from the control valve
103
, for limiting a maximum pressure in the illustrated circuit, a manual pilot valve
108
, and a reservoir
109
.
As shown in
FIGS. 1 and 2
, the hose rupture control valve unit
100
comprises a housing
3
provided with two input/output ports
1
and
2
. The input/output port
1
is directly attached to a bottom port of a hydraulic cylinder
102
, and the input/output port
2
is connected two actuator ports of the control valve
103
via the actuator line
105
. Within the housing
3
, there are provided a poppet valve body
5
serving as a main valve, a spool valve body
6
serving as a pilot valve which is operated with a pilot pressure supplied as an external signal from the manual pilot valve
108
, thereby operating the poppet valve body
5
, and a small spool
7
serving as communicating means which has the function of an overload relief valve.
Further, within the housing
3
, there are defined a cylinder connecting chamber
8
connected to the input/-output port
1
, a hose connecting chamber
9
connected to the hydraulic hose constituting the actuator line
105
, and a back pressure chamber
10
. The poppet valve body
5
serving as a main valve is slidably disposed in the housing
3
such that it is subjected at its back surface to a pressure in the back pressure chamber
10
, and it selectively interrupts and establishes communication between the cylinder connecting chamber
8
and the hose connecting chamber
9
while its opening area is changed depending on the amount of movement (stroke) thereof. The poppet valve body
5
is provided with a feedback slit
11
serving as a feedback variable throttle passage which increases its opening area depending on the amount of movement of the poppet valve body
5
and controls a rate of pilot flow coming out from the cylinder connecting chamber
8
to the back pressure chamber
10
depending on the opening area thereof. The back pressure chamber
10
is closed by a plug
12
(see FIG.
2
), and a spring
13
is disposed in the back pressure chamber
10
for holding the poppet valve body
5
in the interrupting position as shown.
Pilot passages
15
a
,
15
b
are formed in the housing
3
to connect the back pressure chamber
10
and the hose connecting chamber
9
, and the spool valve body
6
serving as a pilot valve is disposed between the pilot passages
15
a
,
15
b.
The spool valve body
6
has a pilot variable throttle
6
a
capable of communicating the pilot passages
15
a
,
15
b
with each other. A spring
16
for setting an initial valve-opening force of the pilot variable throttle
6
a
is disposed at an operating end of the spool valve
6
in the valve-closing direction, and a pressure bearing chamber
17
, to which the pilot pressure is introduced as an external signal, is formed at an operating end of the spool valve
6
in the valve-opening direction. The amount of movement of the spool valve body
6
is determined by a control force given by the pilot pressure (external signal) introduced to the pressure bearing chamber
17
and an urging force produced by the spring
16
. The rate of pilot flow passing through the pilot passages
15
a
,
15
b
is interrupted and controlled depending on the amount of movement of the spool valve body
6
. The spring
16
is supported by a spring receiver
18
provided with a threaded portion
19
which enables an initial setting force of the spring (i.e., the initial valve-opening force of the pilot variable throttle
6
a
) to be adjusted. A spring chamber
20
, in which the spring
16
is disposed, is connected to the reservoir via a drain line
21
so that the spool valve body
6
smoothly moves in the spring chamber
20
.
The small spool
7
serving as communicating means, which has the function of an overload relief valve, is constructed to selectively open and close communication between a pilot passage
15
c
and a drain passage
15
d
, as shown in FIG.
3
. The pilot passage
15
c
is connected to the pilot passage
15
a
, and the drain passage
15
d
is connected to the drain line
21
. A spring
30
for setting a relief pressure is disposed at an operating end of the small spool
7
in the valve-closing direction, and a pressure bearing chamber
31
, to which a pressure in the pilot passage
15
c
is introduced via a pilot passage
15
e
, is formed at an operating end of the small spool
7
in the valve-opening direction. When the pressure in the pilot passage
15
c
exceeds the relief pressure set by the spring
30
, the pilot passage
15
c
is communicated with the reservoir.
The relationships of an opening area of the poppet valve body
5
and an opening area of the feedback slit
11
with respect to the amount of movement (stroke) of the poppet valve body
5
, and the relationships of a rate of fluid flow passing through the spool valve body
6
(pilot flow rate) and a rate of fluid flow passing through the poppet valve body
5
(main flow rate) with respect to the external signal (pilot pressure) will now be described.
FIG. 4
is a graph showing the relationships of an opening area of the poppet valve body
5
and an opening area of the feedback slit
11
with respect to the amount of movement (stroke) of the poppet valve body
5
. When the poppet valve body
5
is in the interrupting position, the feedback slit
11
has a predetermined initial opening area A
0
. As the poppet valve body
5
starts moving from the interrupting position and the amount of movement thereof increases, the opening areas of the poppet valve body
5
and the feedback slit
11
are increased proportionally. Because of the feedback slit
11
having the predetermined initial opening area A
0
, the poppet valve body
5
can perform not only the function of the conventional check valve for fluid supply, but also the function of the overload relief valve in cooperation with the small spool
7
(described later).
FIG. 5
is a graph showing the relationships of a rate of fluid flow passing through the spool valve body
6
(spool flow rate) and a rate of fluid flow passing through the poppet valve body
5
(main flow rate) with respect to the external signal (pilot pressure). The range of the pilot pressure from 0 to P
1
corresponds to a dead zone X of the spool valve body
6
. Even with the pilot pressure rising in that range, the spool valve body
6
is held stopped by the initial setting force of the spring
16
or, even if moved, it is kept in an overlap region before reaching the valve-opening position. The pilot variable throttle
6
a
of the spool valve body
6
therefore remains in the interrupting position. The pilot variable throttle
6
a
starts opening when the pilot pressure reaches P
1
, and the opening area of the pilot variable throttle
6
a
increases as the pilot pressure rises over P
1
. Correspondingly, the rate of fluid flow passing through the spool valve body
6
, i.e., the spool flow rate, also increases. The dead zone X of the poppet valve body
5
continues until the pilot pressure reaches P
2
(>P
1
). During the dead zone X, a pressure fall occurred in the back pressure chamber
10
is insufficient due to the presence of the feedback slit
11
even with the pilot flow rate produced to some extent, and therefore the poppet valve body
5
is held in the interrupting position by the initial setting force of the spring
13
. The poppet valve body
5
starts opening when the pilot pressure reaches P
2
, and the opening area of the poppet valve body
5
increases as the pilot pressure rises over P
2
. Correspondingly, the rate of fluid flow passing through the poppet valve body
5
, i.e., the main flow rate, also increases. A value of the pilot pressure P
2
can be adjusted by a value of the pilot pressure P
1
, and the value of the pilot pressure P
1
can be adjusted by turning the threaded portion
19
of the spool valve body
6
to adjust the stiffness (initial setting force) of the spring
16
.
By thus providing the dead zone X for the poppet valve body
5
, flow rate control in the initial low range before reaching the pilot pressure P
2
is carried out by the spool valve body
6
only, and an opening characteristic of the valve unit in such a range can be adjusted with good accuracy. In addition, since the spring
16
associated with the spool valve body
6
is adjustable in stiffness to make the value of the pilot pressure P
2
adjustable, the accuracy in adjustment can be further improved.
Next, the operation of the hose rupture control valve unit
100
thus constructed will be described.
1) Operation of Supplying Hydraulic Fluid to Bottom Side of Hydraulic Cylinder
102
When a control lever of the manual pilot valve
108
is operated in the direction A denoted in
FIG. 1
to shift the control valve
103
to take a right-hand position as viewed in the drawing, the hydraulic fluid from the hydraulic pump
101
is supplied to the hose connecting chamber
9
of the valve unit
100
through the control valve
103
, causing the pressure in the hose connecting chamber
9
to rise. At this time, since the pressure in the cylinder connecting chamber
8
of the valve unit
100
is equal to the load pressure on the bottom side of the hydraulic cylinder
102
and the feedback slit
11
has the initial opening area A
0
, the pressure in the back pressure chamber
10
is also equal to the load pressure. Accordingly, while the pressure in the hose connecting chamber
9
is lower than the load pressure, the poppet valve body
5
is held in the interrupting position. As soon as the pressure in the hose connecting chamber
9
becomes higher than the load pressure, the poppet valve body
5
starts to move upward in the drawing, allowing the hydraulic fluid to flow into the cylinder connecting chamber
8
. Thus the hydraulic fluid from the hydraulic pump
101
is supplied to the bottom side of the hydraulic cylinder
102
. While the poppet valve body
5
is moving upward, the hydraulic fluid in the back pressure chamber
10
displaces into the cylinder connecting chamber
8
through the feedback slit
11
for ensuring smooth opening of the poppet valve body
5
. The hydraulic fluid from the rod side of the hydraulic cylinder
102
is drained to the reservoir
109
through the control valve
103
.
2) Operation of Discharging Hydraulic Fluid from Bottom Side of Hydraulic Cylinder
102
to Control Valve
103
When the control lever of the manual pilot valve
108
is operated in the direction B denoted in
FIG. 1
to shift the control valve
103
to take a left-hand position as viewed in the drawing, the hydraulic fluid from the hydraulic pump
101
is supplied to the rod side of the hydraulic cylinder
102
through the control valve
103
. At the same time, the pilot pressure from the manual pilot valve
108
is introduced to the pressure bearing chamber
17
of the spool valve body
6
to move the spool valve body
6
, whereupon the pilot variable throttle
6
a
of the spool valve body
6
has an opening area corresponding to the amount of movement thereof. Accordingly, the hydraulic fluid passes through the pilot passages
15
a
,
15
b
at the pilot flow rate depending on the pilot pressure, and the poppet valve body
5
is opened and controlled in the amount of movement thereof depending on the pilot flow rate. As a result, most of the hydraulic fluid on the bottom side of the hydraulic cylinder
102
passes through the poppet valve body
5
from the cylinder connecting chamber
8
of the valve unit
100
, whereas the remaining hydraulic fluid passes through the feedback slit
11
, the back pressure chamber
10
, the pilot passage
15
a
, the spool valve body
6
, and the pilot passage
15
b
. These flows of the hydraulic fluid are led to the control valve
103
while the flow rates are controlled by the poppet valve body
5
and the spool valve body
6
, respectively, followed by being drained to the reservoir
109
. In this way, the flow rate of the hydraulic fluid discharged from the actuator
102
to the control valve
103
can be controlled.
3) Operation of Holding Load Pressure On Bottom Side of Hydraulic Cylinder
102
In a condition where the load pressure on the bottom side of the hydraulic cylinder
102
becomes high, as occurred in the case of holding a lifted load with the control valve
103
maintained at the neutral position, the poppet valve body
5
in the interrupting position retains the load pressure as with the conventional load check valve, thereby performing the function of reducing the amount of leakage (load check function).
4) Upon Excessive External Force Acting on Hydraulic Cylinder
102
In the event an excessive external force acts on the hydraulic cylinder
102
and the pressure in the cylinder connecting chamber
8
becomes high, the small spool
7
is moved by the hydraulic fluid introduced to a pressure bearing chamber
20
b
of the small spool
7
through the feedback slit
11
, the back pressure chamber
10
, and the pilot passages
15
a
,
15
e
, whereby the hydraulic pressure in the back pressure chamber
10
is released into the reservoir
109
and the pressure in the back pressure chamber
10
is reduced, causing the poppet valve body
5
to move upward as viewed in the drawing. With the upward movement of the poppet valve body
5
, the input/output port
1
and the input/output port
2
are subjected to the same level pressure, and therefore the hydraulic fluid, that is brought into a high-pressure level under action of the external force, is drained to the reservoir
109
through the overload relief valve
107
a
connected to the actuator line
105
. As a result, damage of the equipment is prevented. On that occasion, since the hydraulic fluid passes through the small spool
7
at a small flow rate, the function equivalent to that of the conventional overload relief valve can be realized with the small spool
7
having a small size.
5) Parallel Arrangement of Valve Units
100
as Encountered When Attached to Boom Cylinders
In the valve unit
100
of the present invention, because two valve bodies, i.e., the spool valve body
6
and the poppet valve body
5
, are operated, a metering characteristic tends to cause an error due to variations in machining carried out on individual components for each valve unit
100
. Particularly, in an example of practical use where two valve units
100
are arranged in parallel corresponding to respective boom cylinders, as described above in connection with
FIG. 11
, bending loads would impose on the pins
230
a
,
230
b
due to a difference between driving forces caused by a discrepancy in metering characteristic between the left and right valve units
100
, thus causing breakage of the pins
230
a
,
230
b
, unless the machining accuracy of individual components of each valve unit is remarkably improved. Taking into account that point, this embodiment sets the dead zone X for the poppet valve body
5
as described above in connection with FIG.
5
. With the provision of the dead zone X, in the initial low range before reaching the pilot pressure P
2
, the poppet valve body
5
remains standstill, and flow rate control in that range is carried out by the spool valve body
6
only. Therefore, a flow rate difference caused by differences in metering characteristic due to variations in machining carried out on the spool valve bodies
6
and the poppet valve bodies
5
of the left and right valve units
100
can be minimized. In addition, since the metering characteristic of the spool valve body
6
is adjustable by adjusting the stiffness of the spring
16
associated with the spool valve body
6
, the accuracy of metering characteristic in flow rate control performed by the spool valve body
6
can be further improved.
6) In the Event of Damage of Actuator Line
105
If the actuator line
105
leading from the control valve
103
to the input/output port
2
should be damaged, the poppet valve body
5
is closed and a drop of the load borne by the hydraulic cylinder
102
is prevented. On that occasion, by operating the spool valve body
6
with the pilot pressure from the manual pilot valve
108
and adjusting the opening area of the pilot variable throttle
6
a
, it is possible to slowly contract the hydraulic cylinder
102
under action of the weight of the load itself, and to move the load to a safety position.
With this embodiment, as described above, just by providing the poppet valve body
5
in a flow passage through which all of the hydraulic fluid supplied to and discharged from the hydraulic cylinder
102
passes, the poppet valve body
5
can fulfill the functions of the check valve for fluid supply, the load check valve, and the overload relief valve in the conventional hose rupture control valve unit. Therefore, a valve unit having a small pressure loss can be constructed, and highly efficient operation can be achieved with a less energy loss. Also, since the valve unit
100
has a smaller size than the conventional hose rupture control valve unit, a possibility that the valve unit may be damaged during works is reduced, and a degree of flexibility in design is increased. Further, the reduced number of components contributes to reducing the failure frequency, improving the reliability, and enabling the valve unit to be produced at a relatively low cost.
Moreover, since the hydraulic fluid, that is brought into a high-pressure level under action of an external force, can be released to the reservoir through the main overload relief valve
107
a
upon the poppet valve body
5
being opened, the hydraulic fluid passes through the small spool
7
at a small flow rate, and therefore the function equivalent to the conventional overload relief valve can be realized with the small spool
7
having a small size. In addition, since the hydraulic fluid is released from the small spool
7
to the reservoir via the drain line
21
that is identical to the drain line formed in the conventional valve unit, a drain hose specific to the overload relief valve is no longer required in the valve unit
100
, and routing of the hose around the valve unit
100
can be simplified.
Further, even with two hose rupture control valve units arranged in parallel as encountered when attached to boom cylinders, since only the spool valve body
6
is operated when the poppet valve body
5
is in the dead zone X, metering characteristics of the two valve units can be adjusted with good accuracy. Additionally, by adjusting the stiffness of the spring
16
associated with the spool valve body
6
, the accuracy of metering characteristic of the spool valve body
6
itself can be further improved.
Another embodiment of the present invention will be described with reference to
FIGS. 6 and 7
. In
FIGS. 6 and 7
, equivalent members to those in
FIGS. 1
to
3
are denoted by the same numerals.
Referring to
FIGS. 6 and 7
, a hose rupture control valve unit
100
A of this embodiment includes a small relief valve
7
A in place of the small spool
7
shown in
FIG. 7
, and a throttle
34
serving as pressure generating means which is disposed in a drain passage
15
d
of the small relief valve
7
A. Also, in addition to the pressure bearing chamber
17
to which the pilot pressure (external signal) is introduced, a spool valve body
6
A has another pressure bearing chamber
35
provided on the same side as the pressure bearing chamber
17
in series. The upstream side of the throttle
34
is connected to the pressure bearing chamber
35
via a signal passage
36
so that a pressure generated by the throttle
34
act, as a driving force, on the spool valve body
6
A on the same side as the pilot pressure (external signal).
In the event an excessive external force acts on the hydraulic cylinder
102
and the pressure in the back pressure chamber
10
rises, the small relief valve
7
A is opened, causing the hydraulic fluid to flow into the pilot passage
15
d
in which the throttle
34
is disposed. As a result, the pressure in the signal passage
36
rises to move the spool valve body
6
A, whereupon the pilot variable throttle
6
a
is opened, allowing the hydraulic fluid to flow into the pilot passages
15
a
,
15
b
. The poppet valve body
5
is also thereby opened. In this way, similarly to the above embodiment, the hydraulic fluid in the hydraulic cylinder
102
can be released to the reservoir through the main overload relief valve
107
a.
With this embodiment thus constructed, the same functions as those of the embodiment shown in
FIG. 1
can be realized by using the small relief valve
7
A through which the hydraulic fluid passes at a smaller flow rate than that in the embodiment shown in FIG.
1
. Hence the component size can be reduced and the overall size of the valve unit can be further reduced.
According to the present invention, as described above, just by providing a poppet valve body in a flow passage through which all of a hydraulic fluid supplied to and discharged from a hydraulic cylinder passes, the poppet valve body can fulfill the various functions needed for a hose rupture control valve unit. Therefore, a valve unit having a small pressure loss can be constructed, and highly efficient operation can be achieved with a less energy loss. Also, since the hose rupture control valve unit of the present invention has a smaller size than the conventional one, a possibility that the valve unit may be damaged during working is reduced, and a degree of flexibility in design is increased. Further, the reduced number of components contributes to reducing the failure frequency, improving the reliability, and enabling the valve unit to be produced at a relatively low cost.
Moreover, according to the present invention, since the hydraulic fluid, that is brought into a high-pressure level under action of an external force, can be released to a reservoir through a main overload relief valve upon the poppet valve body being opened, a drain hose specific to the overload relief valve is no longer required in the valve unit, and routing of the hose around the valve unit can be simplified.
According to the present invention, the hydraulic fluid at a high pressure can be released through the main overload relief valve while the poppet valve body is opened just by causing the hydraulic fluid to flow through a relief valve provided in the hose rupture control valve unit at a small flow rate. Therefore, the component size can be reduced and the overall size of the valve unit can be further reduced.
According to the present invention, even with two hose rupture control valve units arranged in parallel as encountered when attached to boom cylinders, metering characteristics of the two valve units can be adjusted with good accuracy because a dead zone is set for the poppet valve body and only a spool valve body is operated when the poppet valve body is in the dead zone.
Additionally, according to the present invention, the accuracy of metering characteristic of the spool valve body itself can be further improved by adjusting the stiffness of a spring associated with the spool valve body.
Claims
- 1. A hose rupture control valve unit which is provided between a supply/drain port of a hydraulic cylinder and a hydraulic hose connected to one of two actuator ports of a control valve for supplying a hydraulic fluid to and draining a hydraulic fluid from said hydraulic cylinder, and to which an external signal corresponding to a command signal for driving said control valve is given for controlling a flow rate of a hydraulic fluid coming out from said supply/drain port to said hydraulic hose in accordance with said external signal, said valve unit comprising:a poppet valve body serving as a main valve slidably disposed in a housing provided with a cylinder connecting chamber connected to said supply/drain port, a hose connecting chamber connected to said hydraulic hose, and a back pressure chamber, said poppet valve body being able to selectively interrupt and establish communication between said cylinder connecting chamber and said hose connecting chamber, and changing an opening area depending on the amount of movement thereof, and a spool valve body serving as a pilot valve disposed in a pilot passage connecting said back pressure chamber and said hose connecting chamber, and operated in accordance with said external signal to interrupt and control a rate of pilot flow passing through said pilot passage depending on the amount of movement thereof, said poppet valve body being provided with a feedback variable throttle passage which has an initial opening area when said poppet valve body is in an interrupting position, and which increases an opening area thereof depending on the amount of movement of said poppet valve body, thereby controlling a value of said rate of pilot flow coming out from the cylinder connecting chamber to the back pressure, said poppet valve body having a dead zone set to maintain said poppet valve body in the interrupting position when said rate of pilot flow is not larger than a predetermined value upon actuation of said spool valve body by said external signal, said spool valve body being configured to provide a metering characteristic for controlling said rate of pilot flow depending on said external signal when the pilot flow rate is not larger than said predetermined value.
- 2. A hose rupture control valve unit according to claim 1, further comprising communicating means for communicating said back pressure chamber with a reservoir when a pressure in said hose connecting chamber exceeds a preset value.
- 3. A hose rupture control valve unit according to claim 2, wherein said communicating means is provided in parallel to said spool valve body.
- 4. A hose rupture control valve unit according to claim 2, wherein said communicating means comprises a relief valve provided in parallel to said spool valve body, pressure generating means provided downstream of said relief valve, and means for causing a pressure generated by said pressure generating means to act as a driving force on said spool valve body on the same side as said external signal.
- 5. A hose rupture control valve unit according to claim 1, wherein said poppet valve body has a dead zone set to maintain said poppet valve body in the interrupting position when said rate of pilot flow is not larger than a predetermined value.
- 6. A hose rupture control valve unit according to claim 1, wherein said spool valve body includes adjusting means capable of changing the amount of movement of said spool valve body with respect to said external signal.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-110776 |
Apr 1998 |
JP |
|
US Referenced Citations (8)
Foreign Referenced Citations (2)
Number |
Date |
Country |
3-249411 |
Nov 1991 |
JP |
WO986949 |
Feb 1998 |
WO |