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Patent Abstract
A solenoid valve comprises a solenoid portion 10 and a valve portion
20. The solenoid portion 10 is constructed by a stator core 12,
an electromagnetic coil 14 and a plunger 15. The valve portion 20
is constructed by a valve sleeve 21 and a spool 25 axially forming
plural lands 26a-26c in series. The plunger 15 is axially moved
by electromagnetic attraction and drives the spool 25. There are
formed the same pressurized areas at the plunger 15 and the land
of the spool 25 closest to the plunger 15. Therefore, the volume
in an intermediate space B between the plunger 15 and the spool
25 is constant and contaminants in the oil are not sucked into the
intermediate space B.
Patent Claims
What is claimed is:
1. A solenoid valve comprising: a solenoid portion comprising a
stator core, an electromagnetic coil wound around said stator core,
and a plunger axially moving in said stator core when said electromagnetic
coil is energized; a valve portion comprising a valve sleeve, a
spool forming plural lands and axially moving in said valve sleeve,
and a spring biasing said spool; and wherein said solenoid portion
and said valve portion are coaxially fixed in series such that said
plunger and the spool are coaxially disposed in series with an intermediate
space therebetween, whereby said spring biases said plunger via
said spool, which spool can be moved by said plunger due to an energization
of said electromagnetic coil, wherein the intermediate space is
defined in part by facing portions of said plunger and one of the
lands of said spool, and wherein said facing portions have equal
diameters so that the volume in the intermediate space does not
change during movement of the spool.
2. A solenoid valve according to claim 1, wherein said valve portion
comprises a supply port, a control port and a drain port, and further
comprises a feedback space formed between two of the lands of said
spool, which lands have different diameters, and wherein said feedback
space is arranged to receive a pressure in the control port.
3. A solenoid valve according to claim 2, wherein the land defining
said intermediate space is separated form said feedback space.
4. A solenoid valve according to claim 3, wherein said spring biases
said spool to a normally open position in which the supply port
communicates with the control port.
5. A solenoid valve according to claim 3, wherein said spring biases
said spool to a normally closed position in which the control port
communicates with the drain port.
6. A solenoid valve according to claim 1, wherein: said solenoid
portion comprises a cuplike cover wrapping said stator core and
said electromagnetic coil; and a tip space is formed at an end of
said plunger opposite said valve portion and connects to the outside
through a labyrinth passage formed at said cover.
7. A solenoid valve according to claim 6, wherein a cap forming
said labyrinth passage is attached to said cover.
8. A solenoid valve according to claim 7, wherein said cap forms
partial cylindrical portions arranged with angular phase differences.
9. A solenoid valve according to claim 6, wherein said spring biases
said spool to a normally open position in which the supply port
communicates with the control port.
10. A solenoid valve according to claim 6, wherein said spring
biases said spool to a normally closed position in which the control
port communicates with the drain port.
Patent Description
INCORPORATION BY REFERENCE
[0001] The present application claims priority under 35 U.S.C.
.sctn. 119 to Japanese Patent Application No. 2004-099094, filed
on Mar. 30, 2004. The contents of that application are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a solenoid valve whose sliding
plunger makes a valve spool move.
[0004] 2. Discussion of the Background
[0005] A conventional solenoid valve may be installed into an electronically
controlled automatic transmission. The solenoid valve is inserted
into a valve body formed in an oil pan of the automatic transmission.
Japanese patent laid open 01-242884 is prior art disclosing such
a solenoid valve. The prior art solenoid valve includes a solenoid
portion and a valve portion. In the solenoid portion, there is a
stator core which is coaxially constructed by a core and a yoke
in series. A bore is formed at the axial center of the stator core,
and a plunger is slidably fitted into the bore. The valve portion
coaxially adjoins the solenoid portion and is constructed by a valve
sleeve and a spool slidably fitted into the valve sleeve. The plunger
is axially moved against a spring by an electromagnetic coil through
the magnetized stator core and moves the spool. The solenoid valve
has a cover to separate the solenoid portion from the valve portion.
There is a space surrounded by the bore, one end of the plunger
and the cover. The volume in the space changes due to the sliding
of the plunger. In a conventional solenoid valve, the space is connected
with the outside via an inlet/outlet passage to absorb the volume
changes, so that contaminants in the oil may be sucked into the
space from the outside.
[0006] In the prior art, since the plunger slides in the bore,
the contaminants may become lodged between the bore and the plunger,
whereby the plunger may lock. To resolve such a problem, the plunger
of the prior art is constructed by a magnetic hollow slide and one
end of a shaft is inserted into the slide. The other end of the
shaft projects from the slide and is inserted into a concave portion
of the spool. Therefore, there reliably exists a gap between the
slide and the bore of the stator core. However, the wider gap increases
the magnetic reluctance in the magnetic circuit, which reduces magnetization
of the stator core and the slide. Therefore the magnetic attraction
force to the plunger is reduced and the valve characteristics become
unstable, or the electromagnetic coil must become larger to obtain
suitable valve characteristics.
[0007] To resolve the above problem, in Japanese laid open 2002-310322
a diaphragm is disposed at one end of the spool next to the plunger
in order to prevent the contaminants from being sucked in. In addition,
a cover is disposed at the end of the plunger opposite to the spool
and a breathing port is formed in the cover to connect the inside/outside
of the solenoid portion. In the second prior art, however, the diaphragm
requires a rubber material which has oil resistance and soft elasticity
even in a high/low temperature environment, whereby its product
costs are higher.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing, it is an object of the present
invention to provide an improved solenoid valve. In order to achieve
the above and other objects, an aspect of the present invention
provides a solenoid valve comprising a solenoid portion and a valve
portion. The solenoid portion is constructed by a stator core, an
electromagnetic coil and a plunger. The valve portion is constructed
by a valve sleeve and a spool axially forming plural lands in series.
The plunger is axially moved by electromagnetic attraction and drives
the spool. The pressurized areas of the plunger and the land of
the spool closest to the plunger have the same areas. Therefore,
the volume in an intermediate space between the plunger and the
spool is constant and contaminants in the oil are not sucked into
the intermediate space.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Various other objects, features and many of the attendant
advantages of the present invention will be readily appreciated
as the same becomes better understood by reference to the following
detailed description of the preferred embodiments when considered
in connection with the accompanying drawings, in which:
[0010] FIG. 1 is a longitudinal section view of a first embodiment
of a solenoid valve related to the invention;
[0011] FIG. 2 is a longitudinal section view of a second embodiment
of a solenoid valve related to the invention;
[0012] FIG. 3 is a part section view of a modification of the second
embodiment;
[0013] FIG. 4 is a part section view of another modification of
the second embodiment;
[0014] FIG. 5 is a longitudinal section view of a third embodiment
of a solenoid valve related to the invention;
[0015] FIG. 6 is a section view along line 6-6 of FIG. 5; and,
[0016] FIG. 7 is a part section view of a modification of a cap
of the third embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] A first embodiment of the present invention will be described
with reference to FIG. 1. A solenoid valve of the first embodiment
comprises a solenoid portion 10 and a valve portion 20, and is fixed
into a valve body 30, e.g., it is formed in an oil pan of an electronic
automatic transmission. As shown in FIG. 1, the solenoid portion
10 comprises a stator 11 and a plunger 15. The stator 11 is constructed
by a hollow cylindrical stator core 12 forming a central bore 12d,
an electromagnetic coil 14 wound around the stator core 12 and a
magnetic cover 13 wrapping the stator core 12 and the electromagnetic
coil 14. The stator core 12 is axially constructed by a magnetic
yoke 12a and a magnetic core 12b which are bridged via a non-magnetic
pipe 12c, and forms an air gap 12e as a resistance therebetween.
The electromagnetic coil 14 is wound around the stator core 12 to
magnetize the same. The cover 13 wraps the stator core 12 and the
electromagnetic coil 14, and magnetically connects both ends of
the stator core 12. The yoke 12a forms a large diameter portion
at one axial end opposite to the magnetic core 12b. The magnetic
core 12b forms a flange and a small diameter bore coaxially to the
central bore 12d at one axial end opposite to the yoke 12a. The
shape of the cover 13 is like a cup whose inner bottom contacts
with the end surface of the stator core 12a and whose open end is
caulked to connect with the flange of the magnetic core 12b and
a valve sleeve 21 of the valve portion 20.
[0018] The whole of the plunger 15 is a magnetic substance and
is slidably fitted into the central bore 12d of the stator core
12. The plunger 15 is able to slide between an advanced end position
where its one end closest to the valve portion 20 contacts the step
at the small diameter bore, and a retracted end position where the
other end contacts a central projection 13a formed in the inner
bottom of the cover 13. An intermediate space B is formed between
one end surface of the plunger 15 closest to the valve portion 20
and one end surface of a third land 26c of a spool 25, described
below, in the stator core 12 and the valve sleeve 21. Also, a tip
space A is formed between the other end surface of the plunger 15
and the inner bottom surface of the cover 13 in the central bore
12d of the yoke 12a.
[0019] As shown in FIG. 1, annular grooves 16b and 16d are respectively
formed on both sides of the large diameter portion of the yoke 12a
and are connected to each other via an axial passage 16c. A radial
passage 16a is formed on the end surface of the yoke 12a opposite
to the valve portion 20 and connects the annular groove 16b with
the tip space A. The passages 16a and 16c are formed at a 180 degree
mutual difference in circumferential position. In addition, an aperture
13b is formed in the circumference of the cover 13 in order to connect
the annular groove 16d to the outside at the same circumferential
position as the radial passage 16a. Since the cover 13 wraps the
large diameter portion of the yoke 12a, there is thus formed a labyrinth
inlet/outlet passage 16 between the yoke 12a and the cover 13. Therefore,
the tip space A is connected to the outside through the labyrinth
inlet/outlet passage 16 and the aperture 13b.
[0020] The valve portion 20 comprises the valve sleeve 21 and the
spool 25. The valve sleeve 21 coaxially forms a valve bore 22 where
the valve spool 25 is slidably fitted into. At one end of the valve
sleeve 21, a flange 21a contacts the flange of the core 12b, and
both portions 10 and 20 are coaxially fixed to each other by caulking
the opening of the cover 13 as mentioned above. A spring 28 is disposed
between the spool 25 and a tap 27 screwed into the end of the valve
sleeve 21 opposite to the solenoid portion 10 in order to force
the spool 25 toward the solenoid portion 10. When assembling, the
spool 25 and the spring 28 are put into the valve bore 22 from the
right side in FIG. 1 and then the tap 27 is secured to the valve
sleeve 21. A spindle 25a projects at the tip of the spool 25 and
contacts the end surface of the plunger 15 through the center of
the core 12b. Since the plunger 15 is biased by the spring 28 via
the spool 25, during rest, the plunger 15 is located at the retracted
end position where its end surface opposite to the valve portion
20 contacts the projection 13a formed at the center of the inner
bottom of the cover 13.
[0021] The spool 25 axially forms a pair of first lands 26a, a
second land 26b and a third land 26c in series toward the solenoid
portion 10. Sectional areas of those lands 26a-26c are different
from each other; the first lands 26 are the largest and the third
land 26c is the smallest. Namely, each of the first lands 26a has
a large diameter D4, the second land has a middle diameter D3 and
the third land has a small diameter D2. The valve bore 22 of the
valve sleeve 21 coaxially forms a first bore 22a, a second bore
22b and a third bore 22c in series in order to fit the first, second
and third lands 26a-26c into themselves respectively. The first
bore 22a forms an axially spaced series of a supply port 23a, a
control port 23b and a drain port 23c. The opening areas between
the supply port 23a and the control port 23b, and between the control
port 23b and the drain port 23c, open/close gradually and inversely
due to the axial slide of the first lands 26a of the spool 25.
[0022] A feedback space 24 is formed between the first and second
bores 22a and 22b. The pressure in the control port 23b is always
inputted into the feedback space 24 so that the pressure therein
forces the spool 25 against the spring 28 because of the pressurized
area difference between the first and second lands 26a and 26b,
which difference can be selected to match the electromagnetic attraction
force. The feedback space 24 thus stably adjusts the slide of the
spool 25 in relation with current applied to the electromagnetic
coil 14. Therefore, characteristics of the solenoid valve precisely
reflect the relation of the areas between the first and second lands
26a (diameter=D4) and 26b (diameter=D3), and depend on those diameters.
Between the second and third bores 22b and 22c, there is internally
formed an annular groove 22d connecting to the drain port 23c, whereby
the annular groove 22d separates the feedback space 24 and the intermediate
space B to prevent oil in one of these chambers from flowing into
the other.
[0023] The valve sleeve 21 is fixed to the stator core 12 to dispose
the third bore 22c next to the solenoid portion 10. The intermediate
space B is formed by the end surface of the third land 26c fitted
into the third bore 22c, the end surface of the plunger 15, a part
of the central bore 12d of the core 12b and a part of the valve
bore 22. Section areas of the plunger 15 and the third land 26c
are the same; namely the diameter D1 of the plunger 15 equals the
diameter D2 of the third land 26c, so that the volume in the intermediate
space B does not change even if the plunger 15 and the spool 25
move.
[0024] As shown in FIG. 1, in the solenoid valve of the first embodiment,
the valve sleeve 21 is fixed in the valve body 30 with liquid tightness.
Instead of the valve sleeve 21, the valve bore 22 and the ports
23a-23c may be formed in the valve body 30 itself.
[0025] During rest of the solenoid valve while the electromagnetic
coil 14 is not energized, the spring 28 forces the plunger 15 and
the spool 25 to contact each other and to set the plunger 15 on
the central projection 13a of the inner bottom of the cover 13 as
the retracted end position. This fully opens the opening between
the supply port 23a and the control port 23b, and closes the opening
between the control port 23b and the drain port 23c. In this situation,
an amount of oil supplied from a pump, not shown, to a hydraulic
equipment such as a clutch piston to be controlled, not shown, is
supplied via the supply port 23a and the control port 23b. When
the electromagnetic coil 14 is energized, the stator core 12 is
magnetized and attracts the plunger 15 toward the core 12b, against
the force of the spring 28. Therefore, the opening between the supply
port 23a and the control port 23b is gradually closed, and inversely
the opening between the control port 23b and the drain port 23c
is gradually opened, so that the amount of the oil supplied to the
hydraulic equipment decreases. When the current is maximum, the
plunger 15 contacts the end surface of the small diameter bore of
the core 12b as the advanced end position, wherein the opening between
the supply port 23a and the control port 23b is fully closed and
the opening between the control port 23b and the drain port 23c
is fully opened. In this situation, the oil supplied from the pump
is drained, so the hydraulic equipment becomes inactive.
[0026] In the first embodiment, because the plunger 15 and the
third land 26c have the same diameters (D1=D2), there is no change
in the volume of the intermediate space B between the plunger 15
and the third land 26c, even when the plunger 15 and the spool 25
move together. Therefore, even without a diaphragm or similar element,
contaminants in the oil will not be sucked into the intermediate
space B and cannot lodge between the plunger 15 and the central
bore 12d of the core 12, so that the plunger 15 will not lock.
[0027] The relation of the pressurized area difference between
the first and second lands 26a and 26b in the feedback space 24
is set in view of the desired valve force as mentioned above. However
the third land 26c does not face the feedback space 24, so that
there is no relation between the diameter D2 of the third land 26c
constructing the intermediate space B and the diameter D3 of the
second land 26b constructing the feedback space 24. Therefore, even
if the diameter D1 of the plunger 15 is restricted by the relation
between the current and the attraction force, the pressurized areas
of the first second lands 26a and 26b, namely diameters D4 and D3,
can be made larger while maintaining the same area difference. This
makes the solenoid valve of the embodiment respond rapidly.
[0028] The volume in the tip space A, formed between the bottom
of the cover 13 and the end surface of the plunger 15, changes according
to the slide of the plunger 15. However, since the tip space A connects
to the outside via the labyrinth inlet/outlet passage 16, the contaminants
in the oil hardly reach the tip space A and most of them are eliminated
during the opposite sliding movement of the plunger 15.
[0029] Iron powder is the contaminant which mainly makes the plunger
15 lock because the iron powder is inclined to be attracted and
accumulated around the resistance 12e which concentrates magnetic
lines of force. However, the resistance 12e is located next to the
intermediate space B opposite to the tip space A so that the iron
powder is rarely sucked through the labyrinth inlet/outlet passage
16 and rarely reaches the resistance 12e.
[0030] Next, a second embodiment referred to FIG. 2 will be described,
but there will be omitted the description of the same elements as
in the first embodiment. The second embodiment is also constructed
by the solenoid portion 10 and the valve portion 20, and is equipped
to the valve body 30 such as the oil pan of the electronically controlled
automatic transmission. Although the above mentioned first embodiment
is a normally open type of solenoid valve which opens the opening
between the supply and control ports 23a and 23b, respectively,
when the solenoid is inactive, the second embodiment is a normally
closed type of solenoid valve which closes the opening between the
supply and control ports 23a and 23b, respectively, when the solenoid
is inactive. The other construction and parts are substantially
the same as the first embodiment so that the differences will be
mainly described below.
[0031] Since the solenoid valve of the second embodiment is the
normally closed type, the second land 26b of the spool 25 is located
behind the pair of the first lands 26a, opposite to the solenoid
portion 10. However the third land 26c is located ahead of the first
lands 26a, close to the solenoid portion 10, just as in the first
embodiment. To permit putting the spool 25 into the valve bore 22
of the valve sleeve 21, there is formed a large diameter bore 22e
which is larger than the first bore 22a internal the flange 21a
of the valve sleeve 21 at the end of the valve bore 22, at the location
of the third bore 22c. The spool 25 is put into the valve bore 22
of the valve sleeve 21 from the side of the flange 21a, and then
a bush 21c coaxially forming the third bore 22c is press-fitted
and fixed into the large diameter bore 22e and slidably fits the
third land 26c of the spool 25 thereinto. Behind the bush 21c, there
is formed the annular groove 22d connecting to the outside via the
drain port 23c. The feedback space 24 is formed between the first
and the second bores 22a and 22b of the valve bore 22. The pressure
in the control port 23b is always inputted into the feedback space
24 and forces the spool 25 in the direction of assisting the spring
28. The construction of the second embodiment is otherwise the same
as the first embodiment.
[0032] In the second embodiment, when the solenoid is inactive,
the opening between the supply and the control ports 23a and 23b
is closed, but the opening between the control and the drain ports
23b and 23c is fully opened, whereby the oil from the pump is not
supplied to the hydraulic equipment but is instead drained through
the drain port 23c. When the solenoid becomes active, the openings
between the supply and the control ports 23a and 23b, and between
the control and the drain ports 23b and 23c, are controlled according
to the current flowing through the coil 14, and the oil from the
pump is supplied to the hydraulic equipment through the control
port 23b.
[0033] In the second embodiment, as in the first embodiment, the
pressurized area of the plunger 15 is as large as the third land
26c of the spool 25, namely the diameters D1 and D2 are the same,
so that the volume in the intermediate space B does not change even
if the plunger 15 and the spool 25 move together. Therefore, even
without a diaphragm, the contaminants cannot be sucked into the
intermediate space B so that the plunger 15 will not lock. In addition,
because the lands facing the intermediate space B (the third land
26c) and the feedback space 24 (the first and second lands 26a and
26b) are separated, the diameters D4 and D3 of the first and the
second lands can become larger without affecting the current and
the attraction. Therefore, the solenoid valve responds quicker.
[0034] The second embodiment, just as the first embodiment, forms
the tip space A which connects to the outside through the labyrinth
inlet/outlet passage 16 formed between the yoke 12a and the cover
13 around the end of the plunger 15 opposite to the valve portion
20, whereby the contaminants (iron powder) in the oil are hardly
sucked thereinto. Therefore, the contaminants are not attracted
and accumulated to the resistance 12e to cause locking of the plunger
15.
[0035] Additionally, in the first and second embodiments, although
the intermediate space B is shut off from the outside, as shown
in chain double-dashed lines in FIG. 1, an inlet/outlet passage
21b can be formed to connect the intermediate space B with the outside
on the end surface of the valve sleeve 21 to be fixed to the core
12b. As mentioned hereinbefore, since the volume in the intermediate
space B does not change, such an inlet/outlet passage does not cause
contaminants in the oil be sucked into the intermediate space B.
[0036] FIG. 3 shows a modification of the second embodiment shown
in FIG. 2. The second embodiment can be modified so that the third
land 26c and the spindle 25a are separated form the spool 25 to
form a free piston. The free piston integrally is formed of the
third land 26c and the spindle 25a, and is disposed between the
plunger 15 and the first land 26a of the spool 25. The third land
26c is slidably fitted into the third bore 22c of the bush 21c which
is press-fitted and fixed into the large diameter portion 22e of
the valve sleeve 21. In this modification of the second embodiment,
the concentricity between the third land 26c and the third bore
22c of the bush 21c can be adjusted and can be set separately from
the concentricity between the third bore 22c and the other bores
22a and 22b because the bush 21c and the valve sleeve 21 are separated
from each other. Therefore, the spool 25 smoothly moves.
[0037] FIG. 4 shows a further modification of the second embodiment.
In this modification, the third land 26c is separated from the spool
25, and further the spindle is separated from the third land 26c
and is press-fitted and fixed into the plunger 15.
[0038] A third embodiment will be described referring to FIGS.
5 and 6, but a description of the same elements as in the first
and second embodiments will be omitted. The solenoid valve of the
third embodiment is also constructed by the solenoid portion 10
and the valve portion 20, and is equipped to the valve body 30 such
as the oil pan of the electronically controlled automatic transmission.
The third embodiment is the same normally open type of solenoid
valve as the first embodiment. Unlike the first embodiment, however,
the solenoid valve of the third embodiment does not have the third
land 26c but forms the intermediate space B between the end surfaces
of the second land 26b and the plunger 15. Further, the constructions
of the stator core 12 and the inlet/outlet passage are also different
from the first embodiment. Hereinafter, the differences will be
mainly described.
[0039] As shown in FIG. 5, the solenoid portion 10 is constructed
by the stator 11 and the plunger 15. The stator 11 includes the
hollow cylindrical stator core 12 formed integrally, the electromagnetic
coil 14 wound around the stator core 12 and a magnetic cover 13
wrapping the stator core 12 and the electromagnetic coil 14 and
magnetically connecting both ends of the stator core 12. The integral
stator core 12 is magnetic, internally forms the central bore 12d
and includes an annular thin portion as the resistance 12e which
separates the integral stator core 12 into the yoke 12a and the
core 12b. At its end opposite to the yoke 12a, the core 12b forms
a flange which connects with the valve sleeve 21 by caulking with
the open end of the cover 13. The cuplike cover 13 outwardly forms
a step 13c around its bottom and an annular groove 13f at the base
of the step 13c. If small bores are formed at the thin portion,
magnetic resistance increases at the resistance 12e.
[0040] The whole of the plunger 15 is a magnetic substance and
is slidably fitted into the central bore 12d of the stator core
12. The plunger 15 is able to slide between the advanced end position
where its one end closest to the valve portion 20 contacts the spool
25 which is engaged with a projection 27a formed in the inner bottom
of the tap 27, and the retracted end position where the other end
contacts with the inner bottom of the cover 13. The intermediate
space B is formed in both the stator core 12 and the valve sleeve
21, between one end surface of the plunger 15 closest to the valve
portion 20 and one end surface of the second land 26b of the spool
25. Also, the tip space A is formed between the other end surface
of the plunger 15 and the inner bottom surface of the cover 13 in
the central bore 12d of the yoke 12a. An aperture 13e is formed
at the center of the bottom of the cover 13.
[0041] As shown in FIG. 5, a cap 17 is attached to the step 13c
of the cover 13 to form an inlet/outlet passage 18, and is integrally
molded from synthetic resin. As shown in FIGS. 5 and 6, the cap
17 forms a bottom portion 17a, a cylindrical outer portion 17b,
a partial cylindrical middle portion 17d and a partial cylindrical
inner portion 17e. At the internal tip of the outer portion 17b,
there is inwardly formed a clamp portion 17c which elastically clamps
to the annular groove 13f at the base of the step 13c. The partial
cylindrical middle and inner portions 17d and 17e are concentric
and have notches which are mutually circumferentially spaced by
180 degrees. Therefore, between cylindrical portions 17b, 17d and
17e there are formed an inner annular groove 18a and an outer annular
groove 18b in labyrinthine. Further, the cap 17 has an aperture
18c in the outer annular groove 18b at a location circumferentially
spaced 180 degrees from the notch of the outer portion 17e. Upon
attaching the cap 17 to the step 13c of the cover 13, the middle
and inner portions 17d and 17e contact the outer bottom 13d of the
cover 13, whereby the tip space A connects to the outside via the
aperture 13e and the labyrinth inlet/outlet passage 18 (the annular
grooves 18a-18b and the aperture 18c).
[0042] The valve portion 20 is constructed by the valve sleeve
21 and the spool 25 which is slidably fitted into the valve bore
22 of the valve sleeve 21. The spool 25 forms the first and second
lands 26a and 26b but does not have a third land 26c corresponding
to that of the first and the second embodiments. As a further difference
from the first and second embodiments, the tap 27 forming the projection
27a contacts the spool 25 to restrict the slide of the plunger 15
at its advanced position. In addition, on the flange 21a of the
valve sleeve 21 contacting the stator core 21, there may be formed
an inlet/outlet passage 21b1 to connect the intermediate space B
with the outside. In the third embodiment, the intermediate space
B is formed by the end surface of the second land 26b, the end surface
of the plunger 15, the central bore 12d of the core 12 and a part
of the valve bore 22. The pressurized area of the plunger 15 is
as large as the second land 26b, namely the diameters D1 of the
plunger 15 and D3 of the second land 26b are the same, so that the
volume in the intermediate space B does not change even if the plunger
15 and the spool 25 move.
[0043] During rest, as with the first embodiment, the plunger 15
and the spool 25 are located at the retracted end position where
the plunger 15 contacts to the bottom of the cover 13. This fully
opens the opening between the supply port 23a and the control port
23b, and closes the opening between the control port 23b and the
drain port 23c, whereby oil is supplied from the pump to the hydraulic
device through the supply and the control ports 23a and 23b. Upon
energizing the electromagnetic coil 14, the plunger 15 is attracted
to the core 12b and moves the spool 25 by a degree depending on
the current. The opening between the supply and the control ports
23a and 23b is thereby closed and the opening between the control
and the drain port 23b and 23c is opened, whereby the oil supply
to the hydraulic device decreases. When the maximum current is applied,
the spool 25 contacts the projection 27a of the tap 27 at the advanced
end position, the opening between the supply and the control ports
23a and 23b is fully closed, and the opening between the control
and the drain ports 23b and 23c is fully opened. In this situation,
the oil does not flow from the pump to the hydraulic device.
[0044] In the third embodiment, since the diameter D1 of the plunger
15 is the same as the diameter D3 of the second land 26b, the volume
in the intermediate space B formed between each end of the plunger
15 and the second land 26b does not change, whereby the oil including
the contaminants is not sucked into the intermediate space B. Therefore,
even without a diaphragm or similar element the plunger 15 is prevented
from locking due to contaminants lodged between the plunger 15 and
the central bore 12d.
[0045] The volume in the tip space A formed between the bottom
of the cover 13 and the end surface of the plunger 15 changes according
to the slide of the plunger 15. However, since the tip space A connects
to the outside via the aperture 13e of the cover 13 and the labyrinth
inlet/outlet passage 18, the contaminants in the oil hardly reach
the tip space A and most of them are eliminated during the opposite
movement of the plunger 15. Iron powder is the contaminant which
mainly makes the plunger 15 lock, because the iron powder is inclined
to be attracted and accumulated around the resistance 12e concentrating
the magnetic lines of force. However, the resistance 12e is located
next to the intermediate space B opposite to the tip space A so
that the iron powder is rarely sucked through the labyrinth inlet/outlet
passage 18 and rarely reaches the resistance 12e.
[0046] In the third embodiment, the cap 17 is integrally molded
from synthetic resin and forms the bottom portion 17a, the cylindrical
outer/inner/middle portions 17b/17d/17e for the labyrinth inlet/outlet
passage 18 and the clamp portion 17c to elastically clamp to the
annular groove 13f at the base of the step 13c of the cover 13.
Such a cap 17 can be easily fabricated to make the inlet/outlet
passage 18 from only one piece, and can reduce the product cost.
[0047] Next, referring to FIG. 7, a modification of the third embodiment
will be described. In this modification, the cap 17 firmly presses
each of the partial cylindrical portions 17d and 17e in the step
13c of the cover 13. The outer cylindrical portion of the cap 17
forms a middle step 17b1 at the middle in the axial direction, and
plural (ex. eight) extensions 17b2 which extend axially, curve inwardly
and have clamps 17c1 at each of the ends. The inner portion 17d
and the middle portion 17e have seal lips 17f at each of the tips
to contact the step 13c of the cover 13. The cap 17 is attached
into the cover 13 by clamping at the annular groove 13f1 formed
at the base of the step 13c via the clamps 17c1, as shown with chain
double-dashed lines in FIG. 7. The cap 17 elastically extends the
extensions 17b2, and firmly presses the tips of the middle step
17b1 and the partial cylindrical portions 17d-17e onto the cover
13 because of the elastic reaction force of the extensions 17b2.
Additionally, the seal lips 17f improve the seal at the tips of
the portions 17d-17e. Therefore, fluid leaks at the inlet/outlet
passage 18 decrease between the cap 17 and the cover 13 and the
contaminants in the oil are more rarely sucked thereinto.
[0048] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings.
It is thereby to be understood that within the scope of the appended
claims, the present invention may be practiced otherwise than as
specifically described herein.
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