Title: Three-way switching valve
Abstract: The object of the present invention is to provide a three-way switching valve having a valve mechanism compact in size, and capable of changing a flow of a high-pressure fluid, without internal leakage of the fluid. A compact pilot-operated three-way switching valve changes a flow of a fluid introduced into an inlet port such that the fluid is caused to flow into a first outlet port or a second outlet port. Pressures in pressure-regulating chambers above pistons are selectively guided into a passage by a pilot valve having a pilot valve element, plugs including respective valve seats, and a spring. The passage leads one of the pressures to the first outlet port or the second outlet port via a check valve having valve, and a valve element. The check valve causes a very small amount of fluid permitted to flow so as to keep main valves open and closed, respectively, to flow to the downstream side of an open one of the main valves, whereby internal leakage of fluid is prevented.
Patent Number: 6,883,545 Issued on 04/26/2005 to Koyama
| Inventors:
|
Koyama; Katsumi (Tokyo, JP)
|
| Assignee:
|
TGK Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
457540 |
| Filed:
|
June 10, 2003 |
Foreign Application Priority Data
| Jun 13, 2002[JP] | 2002-172823 |
| Current U.S. Class: |
137/885 |
| Intern'l Class: |
F16K 011//20 |
| Field of Search: |
137/883,885
|
References Cited [Referenced By]
U.S. Patent Documents
| 3175581 | Mar., 1965 | Brandenberg et al.
| |
| 3894561 | Jul., 1975 | Thornbery.
| |
| 4149565 | Apr., 1979 | Jennings et al.
| |
| 4586531 | May., 1986 | Lindell.
| |
| 4733696 | Mar., 1988 | Baun.
| |
| 4816083 | Mar., 1989 | Bangyan.
| |
| 4909279 | Mar., 1990 | Nakamura et al.
| |
| Foreign Patent Documents |
| 1330663 | Jun., 1963 | FR.
| |
| 62-110083 | May., 1987 | JP.
| |
| 62-292973 | Dec., 1987 | JP.
| |
| 04-272588 | Sep., 1992 | JP.
| |
| 4-312276 | Nov., 1992 | JP.
| |
Primary Examiner: Fox; John
Attorney, Agent or Firm: Westerman, Hattori, Daniels & Adrian, LLP
Claims
1. A pilot-operated three-way switching valve for changing a flow of a fluid
introduced into an inlet port such that the fluid is caused to flow into a first
outlet port or a second outlet port,
characterized in that between a pilot valve for carrying out switching operation
to cause one of respective pressure-regulating chambers for two pistons interlocked
with two main valves to communicate with a low-pressure side, and the first outlet
port and the second outlet port located on downstream sides of the main valves,
there is provided a check valve that operates such that the pilot valve and a downstream
side of an open one of the main valves are communicated with each other by a differential
pressure between a pressure on a pilot valve side and a pressure on a downstream
side of a closed one of the main valves.
2. The three-way switching valve according to claim 1, wherein the check valve
includes a passage formed between spaces communicating with the first outlet port
and the second outlet port and having valve seats arranged on both end sides thereof,
and a plug disposed as valve elements associated with the valve seats in a chamber
communicating with the pilot valve and defined between the valve seats arranged
in the passage.
3. A three-way switching valve for changing a flow of a fluid introduced into
an inlet port such that the fluid is caused to flow into a first outlet port or
a second outlet port,
characterized by comprising:
a first main valve disposed between the inlet port and the first outlet port,
for opening and closing therebetween;
a second main valve disposed between the inlet port and the second outlet port,
for opening and closing therebetween;
a first piston having a larger pressure-receiving area than that of a first main
valve element of the first main valve, and operating in conjunction with the first
main valve element in directions of opening and closing operations of the first
main valve element;
a second piston having a larger pressure-receiving area than that of a second
main valve element of the second main valve, and operating in conjunction with
the second main valve element in directions of opening and closing operations of
the second main valve element;
a check valve disposed between the first outlet port and the second outlet port,
for operation such that a passage leading to a downstream side of a closed one
of the first and second main valves is closed;
a pilot valve for carrying out switching operation to selectively communicate
the check valve with respective pressure-regulating chambers for the first piston
and the second piston; and
a solenoid for actuating a pilot valve element of the pilot valve to switch the
pilot valve.
4. The three-way switching valve according to claim 3, wherein the check valve
includes a passage formed between spaces communicating with the first outlet port
and the second outlet port and having valve seats arranged on both end sides thereof,
and a plug disposed as valve elements associated with the valve seats in a chamber
communicating with the pilot valve and defined between the valve seats arranged
in the passage, the plug operating such that the passage leading to the downstream
side of the closed one of the first and second main valves is closed by a differential
pressure between a pressure on a pilot valve side and a pressure on the downstream
side of the closed one of the first and second main valves.
5. The three-way switching valve according to claim 3, wherein the first and
second main valves have flexible sealing materials at seating portions of either
the main valve elements or main valve seats.
6. The three-way switching valve according to claim 3, wherein the first and
second pistons are integrally formed with the main valve elements of the first
and second main valves, respectively.
7. The three-way switching valve according to claim 3, wherein the first and
second pistons have respective piston rings formed along circumferences thereof
such that a pressure of the fluid in the inlet port is introduced into the pressure-regulating
chambers via the piston rings, respectively.
8. The three-way switching valve according to claim 3, wherein the pilot valve
includes a pilot valve element for causing one of the pressure-regulating chambers
for the first and second pistons to communicate with the check valve, and causing
another of the pressure-regulating chambers to be closed, and a spring for urging
the pilot valve element toward the solenoid that actuates the pilot valve element.
9. The three-way switching valve according to claim 3, wherein the pilot valve
includes a pilot valve element disposed to have both ends thereof protruded from
both end faces of a plunger of the solenoid, a first valve seat formed on an end
face of a core of the solenoid in a manner opposed to one end of the pilot valve
element and having a valve hole communicating with the pressure-regulating chamber
for the first piston, a second valve seat disposed in a manner opposed to another
end of the pilot valve element and having a valve hole communicating with the pressure-regulating
chamber for the second piston, and a passage for causing spaces bounded by the
both end faces of the plunger to communicate with the check valve.
10. The three-way switching valve according to claim 9, wherein the pilot valve
element is a needle having conical both ends and axially movably disposed along
an axis of the plunger in a state where an amount of protrusion toward the second
valve seat is restricted, the pilot valve element being urged by a spring in a
direction in which the pilot valve element moves away from the first valve seat
formed on the core.
11. The three-way switching valve according to claim 10, wherein the needle is
divided in two.
12. The three-way switching valve according to claim 9, wherein the main valve
element of the first main valve and the first piston, and the main valve element
of the second main valve and the second piston are juxtaposed for parallel forward
and backward motion, the solenoid is arranged such that the plunger moves forward
and backward in a direction perpendicular to a direction of motion of the first
and second pistons.
13. The three-way switching valve according to claim 3, wherein the pilot valve
includes pilot valve elements disposed on both end faces of a plunger of the solenoid,
a first valve seat formed on an end face of a core of the solenoid in a manner
opposed to one of the pilot valve elements and having a valve hole communicating
with the pressure-regulating chamber for the first piston, a second valve seat
disposed in a manner opposed to another of the pilot valve elements and having
a valve hole communicating with the pressure-regulating chamber for the second
piston, and a passage for causing spaces bounded by the both end faces of the plunger
to communicate with the check valve.
14. The three-way switching valve according to claim 13, wherein the first valve
seat or the second valve seat has a valve hole communicated with the pressure-regulating
chamber for the first piston or the pressure-regulating chamber for the second
piston by a tube.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY
This application claims priority of Japanese Application No. 2002-172823 filed
on Jun. 13, 2002 and entitled "Three-Way Switching Valve".
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a three-way switching valve, and more particularly
to a pilot-operated three-way switching valve for switching a flow path of a fluid
through electromagnetic operation.
(2) Description of the Related Art
Conventionally, a three-way switching valve is known which operates
to cause selective flow of a fluid supplied from a pump or the like toward two
outlets. The three-way switching valve has two valve seats, and operates such that
when one of the valve seats is closed, the other is opened. The opening and closing
operations of the valve are carried out by actuating valve elements by a solenoid
or a motor, or by using the difference between fluid pressures. Some three-way
switching valves of the solenoid-operated type are configured to have two solenoids
for actuating two valve elements alternately. Further, some of the type making
use of the difference between pressures are required to introduce the difference
between pressures on the discharge side and the suction side of a pump into a valve
element or a portion for actuating the valve element, and some of the conventional
three-way switching valves generate the differential pressure by connecting a capillary
tube to the suction side of a pump.
On the other hand, a three-way switching valve is known e.g. from Japanese Unexamined
Patent Publication No. 4-312276, which is configured to have one solenoid, and
at the same time no external tube is provided so as to make its valve mechanism
compact in size. The three-way switching valve forms a three-way solenoid valve
having a solenoid and two valve elements arranged on the same axis and using a
diaphragm pilot mechanism. When the solenoid is in a deenergized state, a pilot
valve element formed on a plunger closes a pilot valve hole by the spring force,
whereby a valve element on the solenoid side is closed, and a valve element on
an opposite side of the solenoid is opened. Inversely, when the solenoid is energized,
the pilot valve element is opened whereby a pressure in a diaphragm chamber is
relieved to the downstream side of the valve to be opened, to thereby open the
valve element on the solenoid side and at the same time close the valve element
on the opposite side of the solenoid by the supplied fluid pressure.
However, the three-way switching valve constructed as above has a problem
in durability especially when it is used for switching flow of a fluid having a
very high pressure, since a diaphragm is employed in the pilot mechanism. In the
three-way switching valve, to open and close the two valve elements in an interlocked
fashion, a drive shaft is arranged such that it extends through a partition wall
that separates two outlet passages. This causes a very small amount of leakage
of the fluid through a portion slidably holding the drive shaft.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and an
object thereof is to provide a pilot-operated three-way switching valve having
a valve mechanism compact in size, capable of switching between flow paths of a
high-pressure fluid, and free from internal leakage of the fluid.
To solve the above problem, the present invention provides a pilot-operated three-way
switching valve for changing a flow of a fluid introduced into an inlet port such
that the fluid is caused to flow into a first outlet port or a second outlet port,
characterized in that between a pilot valve for carrying out switching operation
to cause one of respective pressure-regulating chambers for two pistons interlocked
with two main valves to communicate with a low-pressure side, and the first outlet
port and the second outlet port located on downstream sides of the main valves,
there is provided a check valve that operates such that the pilot valve and a downstream
side of an open one of the main valves are communicated with each other by a differential
pressure between a pressure on a pilot valve side and a pressure on a downstream
side of a closed one of the main valves.
The above and other objects, features and advantages of the present invention
will become apparent from the following description when taken in conjunction with
the accompanying drawings which illustrate preferred embodiments of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is cross-sectional views showing the internal construction of a three-way
switching valve according to a first embodiment of the invention, in a state with
its solenoid being OFF.
FIG. 2 is cross-sectional views showing the internal construction of the three-way
switching valve according to the first embodiment, in a state with its solenoid
being ON.
FIG. 3 is a time chart showing operating conditions of the three-way switching
valve according to the first embodiment.
FIG. 4 is a cross-sectional view showing the internal construction of a three-way
switching valve according to a second embodiment of the invention.
FIG. 5 is cross-sectional views taken on line B—B of FIG. 4, and taken
on line C—C of the same.
FIG. 6 is cross-sectional views showing the internal construction of a three-way
switching valve according to a third embodiment of the invention.
FIG. 7 is cross-sectional views showing the internal construction of a three-way
switching valve according to a fourth embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention will be described
in detail with reference to the drawings.
FIG. 1 provides cross-sectional views showing the internal construction of a
three-way switching valve according to a first embodiment, in a state with its
solenoid being OFF. FIG. 2 provides cross-sectional views showing the internal
construction of the three-way switching valve according to the first embodiment,
in a state with its solenoid being ON. FIG. 3 is a time chart showing operating
conditions of the three-way switching valve according to the first embodiment.
The three-way switching valve has a body
1 through which two cylinder
bores
2,
3 are formed for accommodating two main valves in parallel
with each other on the left side and right side thereof as viewed in FIGS. 1 and
2. The body
1 has an inlet port T
1 formed in the center thereof,
for introducing a fluid such that the inlet port T
1 communicates with both
of the cylinder bores
2,
3. At respective locations downward of the
cylinder bores
2,
3 are formed a first outlet port T
2 and
a second outlet port T
3.
The cylinder bores
2,
3 have respective main valve seats
4,
5 integrally formed with the body
1 between the inlet port T
1
and the first outlet port T
2, and between the inlet port T
1 and the
second outlet port T
3. Arranged in a manner opposed to the main valve seats
4,
5 are main valve elements
6,
7 which can move from
the inlet port T
1 side to and away from the main valve seats
4,
5.
The main valve elements
6,
7 are integrally formed with pistons
8,
9 slidably arranged in the cylinder bores
2,
3, respectively.
The pistons
8,
9 have larger pressure-receiving areas than those
of the main valve elements
6,
7, respectively.
The main valve elements
6,
7 have seal rings
10,
11
rigidly fitted on portions thereof via which they are seated on the main valve
seats
4,
5, by crimping via washers. The pistons
8,
9
have tension rings, and piston rings
12,
13 fitted in grooves formed
in outer peripheries thereof, respectively. This causes a very small amount of
fluid introduced from the inlet port T
1 to flow into each of pressure-regulating
chambers above the pistons
8,
9, via the piston rings
12,
13. It should be noted that the upward movement of the piston
8 on
the right side in the cylinder bore
2 as viewed in the figures is limited
by a C shaped snap ring fitted in the cylinder bore
2.
Above the piston
9 on the left side as viewed in the figures, there
is arranged a pilot valve formed by a three-way valve. The pilot valve comprises
a plug
15 including a valve seat
14 whose valve hole communicates
with the pressure-regulating chamber above the right-side piston
8, a plug
17 including a valve seat
16 whose valve hole communicates with the
pressure-regulating chamber above the left-side piston
9, a pilot valve
element
18 in the form of a needle, whose both ends are arranged in a manner
opposed to the valve seats
14,
16 such that the both ends can open
and close the valve holes of the valve seats
14,
16, and a spring
19 for urging the pilot valve element
18 in a direction in which
the pilot valve element
18 is seated on the valve seat
14.
The cylinder bore
2 formed on the right side of the body
1 has
an upper opening closed by a cap
20, while the cylinder bore
3 formed
on the left side of the same has an upper opening having a solenoid provided thereon
for actuating the pilot valve.
The solenoid has a core
21 integrally formed with the body
1 such
that the core
21 also serves as a lid for closing the upper opening of the
body
1. The core
21 has an upper half thereof fitted in a sleeve
22. The sleeve
22 has a plunger
23 inserted therein, and has
an upper end thereof closed by a cap
24. A solenoid coil
25 is arranged
on the outer periphery of the sleeve
22 and surrounded by a yoke
26.
The core
21 and the plunger
23 have a through hole extending along
a central axis thereof. The through hole of the plunger
23 has a stepped
portion at an intermediate part thereof such that an upper part of the hole has
a larger diameter than that of a lower part thereof. The upper part of the hole
having the larger diameter accommodates a holder
27 and a spring
28
for urging the holder
27 in a direction in which the holder
27 is
brought into abutment with the stepped portion. A shaft
29 is disposed in
the lower part of the hole of the plunger
23 having a smaller diameter and
the trough hole of the core
21. The shaft
29 has an upper end thereof
brought into abutment with the holder
27, and a lower end thereof brought
into abutment with a shaft
30 which is rigidly fixed to the pilot valve
element
18 and extends through the valve hole of the valve seat
14.
A space containing the pilot valve element
18 is communicated with a check
valve shown in a cross-sectional view of the body
1 taken on line A—A
of each figure and depicted in an upper part thereof. The check valve includes
a passage
31 communicating between the first outlet port T
2 and the
second outlet port T
3, and a valve seat
32 of the check valve is
integrally formed with the body
1 on the first outlet port side of the passage
31. On the second outlet port side of the passage
31 is arranged
a plug
34 that forms a valve seat
33. A space in the passage
31
between the valve seat
32 and valve seat
33 communicates with the
space containing the pilot valve element
18 via a passage
36 indicated
by a dotted line. A valve element
35 is arranged such that it can be seated
on either of the valve seats
32,
33.
In the three-way switching valve constructed as above, when the solenoid coil
25 is in a deenergized state, i.e. when the solenoid is OFF, with no fluid
being introduced into the inlet port T
1, no solenoid force for actuating
the pilot valve is generated, so that the pilot valve element
18 is pushed
upward as viewed in FIGS. 1 and 2 by the spring
19, whereby it is seated
on the valve seat
14. This causes an upper portion of the pilot valve to
be closed, and a lower portion thereof to be opened. As a result, the pressure-regulating
chamber above the right-side piston
8 is closed by the pilot valve, while
the pressure-regulating chamber above the left-side piston
9 communicates
with the check valve via the pilot valve and the passage
36. At this time,
although the main valve element
6 and the piston
8, and the main
valve element
7 and the piston
9 can assume arbitrary positions,
it is assumed here that the main valve elements
6,
7 are seated on
the main valve seats
4,
5, respectively, e.g. due to their own weights.
Further, the valve element
35 of the check valve is put in a position taken
when the supply of the fluid was stopped.
When the fluid is introduced into the inlet port T
1 with the solenoid
being OFF, the pressure of the fluid is introduced into the pressure-regulating
chambers above the pistons
8,
9 via the piston rings
12,
13
provided on the left-side and right-side pistons
8,
9. The pressure-regulating
chamber above the right-side piston
8 is closed by the pilot valve, while
the pressure-regulating chamber above the left-side piston
9 communicates
with the first outlet port T
2 and the second outlet port T
3 via the
pilot valve and the check valve. Therefore, the pressure in the pressure-regulating
chamber above the right-side piston
8 becomes high, whereas the pressure
in the pressure-regulating chamber above the left-side piston
9 becomes
low since the amount of fluid caused to flow out into the first outlet port T
2
or the second outlet port T
3 is larger than the amount of fluid introduced
from the inlet port T
1. The right-side piston
8 is designed to have
a larger pressure-receiving area than that of the main valve element
6,
and hence the piston
8 and the main valve element
6 are pushed downward
by the difference between pressures applied to the piston
8 and the main
valve element
6 to be brought to the state illustrated in FIG.
1.
Further, since the pressure on the side of the main valve element
7 is high
and the pressure within the pressure-regulating chamber above the left-side piston
9 is low, the left-side piston
9 and the main valve element
7
are pushed upward, and as shown in FIG. 1, the main valve in the cylinder bore
3 is opened. As a result, in the check valve, the pressure in the first
outlet port T
2 becomes low, and the pressure in the second outlet port T
3
becomes high, so that the valve element
35 of the check valve is seated
on the right-side valve seat
32 on the low-pressure side, to block communication
between the first outlet port T
2 and the second outlet port T
3. Thus,
the check valve is brought to the state illustrated in FIG.
1.
Next, when the solenoid is turned ON, first, the plunger
23 is pulled
and attracted by the core
21. As the plunger
23 is pulled by the
core
21, the holder
27 is pushed down toward the stepped portion
in the plunger
23 by the urging force of the spring
28. This causes
the holder
27 to push the shaft
29 downward, thereby pushing down
the shaft
30 rigidly fixed to the pilot valve element
18. Consequently,
the pilot valve element
18 is pushed downward against the urging force of
the spring
19 to be seated on the lower valve seat
16. That is, the
pilot valve element
18 is seated on the lower valve seat
16 by the
plunger-attracting operation, and thereafter, the pilot valve element
18
is held in the state seated on the lower valve seat
16, by the urging force
of the spring
28 within the plunger
23. This causes the upper portion
of the pilot valve to be opened, and the lower portion thereof to be closed.
As a result, the pressure-regulating chamber above the right-side piston
8
communicates with the second outlet port T
3 via the pilot valve, the passage
36, and the check valve. Since the fluid flows from the inlet port T
1
to the second outlet port T
3 to thereby cause a pressure loss therebetween,
the pressure in the second outlet port T
3 becomes lower than that of the
inlet port T
1, which acts to reduce the pressure in the pressure-regulating
chamber above the right-side piston
8 to a pressure as low as that of the
second outlet port T
3. On the other hand, there is no path for relieving
the pressure in the pressure-regulating chamber above the left-side piston
9,
so that the pressure in this chamber is increased to push the piston
9 downward.
This closes the left-side main valve element
7 to reduce the pressure in
the second outlet port T
3 so that the pressure within the pressure-regulating
chamber above the right-side piston
8 is sharply reduced. This causes the
right-side piston
8 to be moved upward, as viewed in the figure, by the
difference between the pressure in the pressure-regulating chamber above the right-side
piston
8 and that of the inlet port T
1, whereby the right-side main
valve element
6 is opened. Simultaneously, since the pressure in the first
outlet port T
2 becomes high, and the pressure in the second outlet port
T
3 becomes low, the valve element
35 of the check valve is seated
on the left-side valve seat
33 on the low-pressure side, and a route is
formed for relieving the pressure in the pressure-regulating chamber above the
right-side piston
8 to the first outlet port T
2 on a side where the
check valve is opened. As a result, the three-way switching valve is brought to
the state illustrated in FIG.
2.
Now, changes in pressure conditions in the three-way switching valve will be
described with reference to FIG.
3. It is assumed here that in a closed
fluid circuit, the inlet port T
1 of the three-way switching valve is connected
to the discharge side of a pump, while the first and second outlet ports T
2,
T
3 of the valve are connected to the suction side of the pump. In FIG. 3,
the pressure of a fluid introduced into the inlet port T
1 is represented
by a primary pressure, the pressure in the pressure-regulating chamber above the
left-side piston
9 is represented by a left-side piston pressure, the pressure
in the second outlet port T
3 on the downstream side of the left-side main
valve is represented by a left-side secondary pressure, the pressure in the pressure-regulating
chamber above the right-side piston
8 is represented by a right-side piston
pressure, the pressure in the first outlet port T
2 on the downstream side
of the right-side main valve is represented by a right-side secondary pressure,
the pressure in the central chamber accommodating the valve element
35 within
the check valve is represented by a check valve pressure, and the pressure in a
central chamber accommodating the pilot valve element
18 within the pilot
valve is represented by a pilot valve pressure. Further, the ordinate represents
a change in each of the above pressures, and the abscissa represents lapse of time.
First, let it be assumed that at a time t
0, the pump for supplying
the fluid to the three-way switching valve is started, and at the same time the
solenoid is turned ON. As the pressure of the fluid is increased by the start of
the pump, the primary pressure is also increased. Simultaneously, since the pressure-regulating
chamber above the left-side piston
9 is in a state closed by the pilot valve
actuated by the solenoid, the left-side piston pressure as well is increased similarly,
and both of the primary pressure and the left-side piston pressure become stable
at their highest pressures.
During the increases in the pressures, if the second outlet port T
3
on the closed chamber side is under suction by the pump, the left-side secondary
pressure has its residual pressure decreased. Further, the right-side piston pressure,
the right-side secondary pressure, the check valve pressure, and the pilot valve
pressure are each increased to a level obtained by subtracting a pressure loss
caused by flow of the fluid passing through the right-side main valve from the
primary pressure.
When the solenoid is turned OFF at a time t
1, although the primary pressure
is not changed, the pressure-regulating chamber above the left-side piston
9
is communicated with the second outlet port T
3, whereby the left-side piston
pressure attempts to be equal to the secondary pressure of the second outlet port
T
3, and hence is decreased. At the same time, since the pressure-regulating
chamber above the right-side piston
8 is closed by the pilot valve, the
right-side piston pressure is increased attempting to become equal to the primary pressure.
At a time t
2, when the left-side piston pressure becomes equal to the
secondary
pressure of the second outlet port T
3, and the right-side piston pressure
becomes equal to the primary pressure, the right-side main valve is closed, and
the left-side main valve is opened. This inverts the secondary pressure of the
first outlet port T
2 and the secondary pressure of the second outlet port
T
3, and hence the valve element
35 of the check valve is moved from
left to right. At this time, since the first outlet port T
2 and the second
outlet port T
3 temporarily communicate with each other via the passage
31
accommodating the valve element
35, the check valve pressure and the pilot
valve pressure are reduced (time t
3) during switching operation of the check
valve, and return to the secondary pressure of the open left-side main valve again
(time t
4). During switching operation of the check valve (t
2 to t
4),
the left-side secondary pressure is increased to the pressure obtained by subtracting
the pressure loss from the primary pressure, and the right-side secondary pressure
is reduced to the suction pressure of the pump.
At a time t
5, when the solenoid is turned ON again, first, the left-side
piston pressure is increased to the primary pressure, and the right-side piston
pressure is reduced to the secondary pressure of the right-side main valve. Now,
when the right-side main valve is opened, and the left-side main valve is closed,
during a time period t
6 to t
8 over which switching operation of the
check valve is carried out, the left-side secondary pressure is reduced to the
suction pressure of the pump, and the right-side secondary pressure is increased
to the level obtained by subtracting the pressure loss from the primary pressure.
The check valve pressure and the pilot valve pressure are temporarily reduced, respectively.
At a time t
9, when the pump is stopped, and the solenoid is turned OFF,
the primary pressure, the left-side piston pressure, the right-side piston pressure,
the right-side secondary pressure, the check valve pressure, and the pilot valve
pressure are reduced, and the left-side secondary pressure is increased, whereby
all the pressures become equal to each other.
FIG. 4 is a cross-sectional view showing the internal construction of a three-way
switching valve according to a second embodiment. FIG. 5 provides a cross-sectional
view taken on line B—B of FIG. 4, and a cross-sectional view taken on line
C—C of the same. In FIGS. 4 and 5, component parts and elements similar
to those of the three-way switching valve shown in FIGS. 1 and 2 are designated
by identical reference numerals, and detailed description thereof is omitted.
The three-way switching valve according to the second embodiment is configured
to be of a type in which a solenoid and a pilot valve are inserted from a lateral
side of a body
1 to reduce the height of the valve. More specifically, cylinder
bores
2,
3 formed in the body
1 have upper openings closed
by caps
20,
20a, respectively. The body
1 has an insertion
hole formed in the side thereof, for inserting the solenoid and the pilot valve
therein. The pilot valve comprises a plug
15 inserted into the insertion
hole and having a valve seat
14, a valve seat
16a integrally
formed with the body
1 and having a valve hole communicating with the cylinder
bore
3, and a pilot valve element
18 and a spring
19 disposed
between the valve seats
14,
16a. The plug
15 is formed
such that a valve hole of the valve seat
14 on the solenoid side communicates
with the cylinder bore
2. The solenoid is screwed into an inlet of the insertion
hole by a connecting member
37 forming part of a magnetic circuit. A space
accommodating the pilot valve element
18 communicates with a passage
36
to communicate with a space between valve seats
32,
33 of a check valve.
In the three-way switching valve constructed as above, operation thereof is similar
to that of the three-way switching valve according to the first embodiment. More
specifically, when the solenoid is OFF, a pressure-regulating chamber above a right-side
piston
8 is closed by the pilot valve, and a pressure-regulating chamber
above a left-side piston
9 communicates with the check valve for relieving
the pressure of a fluid to a low-pressure side via the pilot valve and the passage
36. Accordingly, the right-side piston
8 causes a main valve element
6 to be seated on a main valve seat
4, while the left-side piston
9 causes a main valve element
7 to move away from a main valve seat
5. As a result, a main valve between an inlet port T
1 and a first
outlet port T
2 is closed, and a main valve between the inlet port T
1
and a second outlet port T
3 is opened. In the check valve, a valve element
35 is seated on a valve seat
33 which is located on a side where
the pressure is reduced due to closing a main valve by the differential pressure
of the fluid between the first outlet port T
2 and the second outlet port
T
3. Thus, the pilot valve and the second outlet port T
3 on the downstream
side of the open main valve are communicated with each other by the check valve.
When the solenoid is ON, the pilot valve inverts the respective pressures in
the pressure-regulating chambers above the pistons
8,
9 to open the
right-side main valve and close the left-side main valve. This inverts the pressure
of the first outlet port T
2 and that of the second outlet port T
3
in magnitude, so that the check valve closes a side communicating with the second
outlet port T
3, and applies a pressure reduced by the amount of a pressure
loss caused by flow of the fluid through the right-side main valve to the pressure-regulating
chamber above the right-side piston
8 integrally formed with the right-side
main valve, thereby keeping the right-side main valve open, and the left-side main
valve closed.
FIG. 6 is a cross-sectional view showing the internal construction of a three-way
switching valve according to a third embodiment. In the figure, component parts
and elements similar to those of the three-way switching valve shown in FIGS. 1
and 2 are designated by identical reference numerals, and detailed description
thereof is omitted.
In the three-way switching valve according to the third embodiment, a solenoid
and a pilot valve are laterally arranged on top of a body
1 in a manner
bridging over two cylinder bores
2,
3, and the pilot valve is contained
in the solenoid.
The solenoid has a core
21 fitted in one end of a sleeve
22, and
a plunger
23 inserted into the sleeve
22. The core
21 has
a valve hole formed therethrough along the axis thereof such that a valve seat
14 of the pilot valve is formed. The valve hole is communicated with a pressure-regulating
chamber above a right-side piston
8 via a connecting member
38. In
the other end of the sleeve
22 is fitted one end of a connecting member
39 having a valve hole formed therethrough such that a valve seat
16
of the pilot valve is formed. The other end of the connecting member
39
is fitted in an upper opening of the left-side cylinder bore
3. The connecting
member
39 causes the valve hole of the valve seat
16 to communicate
with a pressure-regulating chamber above a left-side piston
9 such that
the valve seat
16 is formed. Further, the connecting member
39 includes
a passage
40 communicating with a space within the sleeve
22 having
the plunger
23 loosely fitted therein. The passage
40 communicates
with a check valve through a passage
36.
The plunger
23 has pilot valve elements
18a,
18b
arranged along the axis thereof. The pilot valve element
18a has
a flange on an opposite side of a needle facing the valve seat
14, and a
spring
19 is arranged between the flange and the core
21. The pilot
valve element
18b has a flange on an opposite side of a needle facing
the valve seat
16. The flange is held in the plunger
23. Therefore,
when a solenoid coil
25 is in a deenergized state, the plunger
23
and the pilot valve elements
18a,
18b are urged leftward,
as viewed in the figure, by the spring
19, whereby the pilot valve causes
the pressure-regulating chamber above the right-side piston
8 to communicate
with the check valve, and closes the pressure-regulating chamber above the left-side
piston
9. When the solenoid coil
25 is in an energized state, the
plunger
23 is attracted by the core
21 against the urging force of
the spring
19, and the pilot valve elements
18a,
18b
are urged rightward, as viewed in the figure, in a manner interlocked with
the attracting operation. Therefore, the pilot valve closes the pressure-regulating
chamber above the right-side piston
8, and causes the pressure-regulating
chamber above the left-side piston
9 to communicate with the check valve.
In the three-way switching valve constructed as above, operation thereof is substantially
similar to that of the three-way switching valve according to the first embodiment,
although left-side and right-side main valves thereof are opened and closed inversely
to those of the first embodiment. More specifically, when the solenoid is OFF,
the pressure-regulating chamber above the right-side piston
8 communicates
with the check valve for relieving the pressure of a fluid to the low-pressure
side, via the pilot valve and the passage
36, and the pressure-regulating
chamber above the left-side piston
9 is closed by the pilot valve. Therefore,
the right-side piston
8 causes a main valve element
6 to move away
from a main valve seat
4, while the left-side piston
9 causes a main
valve element
7 to be seated on a main valve seat
5. As a result,
a main valve between an inlet port T
1 and a first outlet port T
2
is opened, and a main valve between the inlet port T
1 and a second outlet
port T
3 is closed. In the check valve, a valve element
35 is seated
on a valve seat
33 on a side where the pressure is reduced by closing of
a main valve by a differential pressure between the first outlet port T
2
and the second outlet port T
3. Thus, the pilot valve and the first outlet
port T
2 on the downstream side of the open main valve are communicated with
each other by the check valve.
When the solenoid is ON, the pilot valve inverts pressures in the pressure-regulating
chambers above the pistons
8,
9 to close the right-side main valve
and open the left-side main valve. This inverts the pressure of the first outlet
port T
2 and that of the second outlet port T
3 in magnitude, so that
the check valve closes a side communicating with the first outlet port T
2,
and applies a pressure reduced by the amount of a pressure loss caused by the flow
of the fluid through the left-side main valve to the pressure-regulating chamber
above the left-side piston
9 integrally formed with the left-side main valve,
thereby keeping the right-side main valve closed, and the left-side main valve open.
FIG. 7 is a cross-sectional view showing the internal construction of a three-way
switching valve according to a fourth embodiment. In the figure, component parts
and elements similar to those of the three-way switching valve shown in FIGS. 1
and 2 are designated by identical reference numerals, and detailed description
thereof is omitted.
Although in the three-way switching valves according to the first and second
embodiments, the passage communicating between the pilot valve and the pressure-regulating
chamber above the right-side piston
8 is formed in the body
1, and
in the three-way switching valve according to the third embodiment, the passage
is formed in the connecting member
38, the three-way switching valve according
to the fourth embodiment is configured such that a pilot valve and a pressure-regulating
chamber above a right-side piston
8 are connected with each other by a tube
41. Further, the pilot valve is integrally formed with the solenoid, similarly
to the three-way switching valve according to the third embodiment.
The pilot valve includes valve sheets
42,
43 disposed in both end
faces of the plunger
23, respectively, and valve seats
14,
16
opposed to the valve sheets
42,
43, respectively. The upper valve
seat
14, as viewed in the figure, is integrally formed with a core
21,
and a valve hole in the core
21 communicates with the pressure-regulating
chamber above the right-side piston
8 through a tube
41. The lower
valve seat
16, as viewed in the figure, is integrally formed with a plug
17a disposed above a left-side piston
9, and a valve hole
in the plug
17a communicates with a pressure-regulating chamber above
the left-side piston
9. A space between the valve seat
14 and the
valve seat
16 communicates with a check valve via a passage
36. Further,
the plunger
23 also playing the role of a pilot valve element is urged by
a spring
44 in a direction in which it moves away from the core
21.
In the three-way switching valve constructed as above, operation thereof is substantially
similar to that of the three-way switching valve according to the first embodiment,
although left-side and right-side main valves thereof are opened and closed inversely
to those of the first embodiment. More specifically, when the solenoid is OFF,
the pressure-regulating chamber above the right-side piston
8 communicates
with the check valve for relieving the pressure of a fluid to the low-pressure
side, via the pilot valve and the passage
36, and the pressure-regulating
chamber above the left-side piston
9 is closed by the pilot valve. Therefore,
the right-side piston
8 causes a main valve element
6 to move away
from a main valve seat
4, while the left-side piston
9 causes a main
valve element
7 to be seated on a main valve seat
5. This opens a
main valve between an inlet port T
1 and a first outlet port T
2, and
closes a main valve between the inlet port T
1 and a second outlet port T
3.
In the check valve, a valve element
35 is seated on a valve seat
33
on a side where the pressure is reduced by closing of a main valve by the differential
pressure between the first outlet port T
2 and the second outlet port T
3.
Thus, the pilot valve and the first outlet port T
2 on the downstream side
of the open main valve are communicated with each other by the check valve.
When the solenoid is ON, the pilot valve inverts pressures in the pressure-regulating
chambers above the pistons
8,
9 to close the right-side main valve
and open the left-side main valve. This inverts the pressure of the first outlet
port T
2 and that of the second outlet port T
3 in magnitude, so that
the check valve closes a side communicating with the first outlet port T
2,
and applies a pressure reduced by the amount of a pressure loss caused by the flow
of the fluid through the left-side main valve to the pressure-regulating chamber
above the left-side piston
9 integrally formed with the left-side main valve,
thereby keeping the right-side main valve closed, and the left-side main valve open.
Although in the above embodiments, the seal rings provided for enhancing
the sealing performance of the main valves are arranged on the main valve elements,
they may be provided on the main valve seats.
As described above, according to the present invention, the three-way switching
valve is configured such that a check valve is provided on the downstream side
of a pilot valve used for selectively relieving pressures in respective pressure-regulating
chambers for pistons to a low-pressure side, and the check valve provides communication
to the down stream side of an open one of main valves. Due to this configuration,
a very small amount of fluid permitted to flow to keep the main valves open and
closed, respectively, is caused to flow to the downstream side of the open main
valve via the pilot valve and the check valve. This prevents internal leakage of
the fluid within the three-way switching valve.
Further, one of the pressure-regulating chambers above the piston integrally
formed with the open main valve has a pressure equal to a secondary pressure lower
than a primary pressure of the fluid in an inlet port by the amount of a pressure
loss caused by the flow of the fluid through the main valve to an outlet port.
The differential pressure of the fluid enables a main valve to maintain opening operation.
Further, only a small differential pressure between the primary pressure
and secondary pressure of the fluid, corresponding to the amount of the pressure
loss, is applied to the pilot valve, which requires only a very small solenoid
force for actuating a pilot valve element. This makes it possible to make the solenoid
compact in size.
The foregoing is considered as illustrative only of the principles of the present
invention. Further, since numerous modifications and changes will readily occur
to those skilled in the art, it is not desired to limit the invention to the exact
construction and applications shown and described, and accordingly, all suitable
modifications and equivalents may be regarded as falling within the scope of the
invention in the appended claims and their equivalents.
*
