SOLENOID VALVE ASSEMBLY
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to United States Provisional Patent
Application No. 61/062,363, which was filed on January 25, 2008.
TECHNICAL FIELD
The present invention generally relates to solenoid valves, and more
particularly, to variable force solenoid valves.
BACKGROUND OF THE INVENTION
Solenoid valves are useful for many applications requiring controlled
fluid flow. For example, solenoid valves may be used to control hydraulic pressure in
an automatic transmission of a vehicle. One type of solenoid valve, a variable force
solenoid valve, is often used to apply a clutch for smooth shifting or to control
transmission line pressure.
Problematically, however, existing solenoid valves often suffer from a
lack of concentricity among components, particularly among magnetically-attractive
surfaces. Such lack of concentricity may cause friction between components and a
resulting reduced solenoid valve response. Therefore, many existing solenoid valves
are unsuitable for applications requiring sensitive solenoid valve response for minimal
hydraulic pressure changes.
SUMMARY OF THE INVENTION
A solenoid valve assembly includes a bobbin supporting a coil and
having at least one protrusion on an inner surface. The solenoid valve assembly also
includes an adjustment member disposed within the bobbin and in contact with the at
least one protrusion. Further, the solenoid valve assembly includes a pole piece
disposed within the adjustment member and a valve body having a seat, wherein the

bobbin is disposed in contact with the seat. Additionally, the solenoid valve assembly
includes a spool slideably disposed within the valve body, and a resilient member
disposed in contact with the adjustment member and the spool.
[0006] In another embodiment, the spool is slideably disposed within the valve
body and spaced opposite the pole piece.
[0007] In a further embodiment, the solenoid valve assembly includes a bobbin
supporting a coil and having at least one annular protrusion on an inner surface.
Additionally, the solenoid valve assembly includes the adjustment member disposed
within the bobbin and in contact with the at least one annular protrusion. Further, the
solenoid valve assembly includes a pole piece having a first surface and disposed within
the adjustment member, and a valve body having a frusto-conical seat, wherein the
bobbin is disposed in contact with the frusto-conical seat. A spool is slideably disposed
within the valve body and spaced opposite the pole piece. The spool has a second
surface configured to correspond to the first surface to form a working air gap between
the pole piece and the spool. The spool is disposed substantially concentric with the
pole piece across the working air gap. The solenoid valve assembly also includes a
resilient member disposed in contact with the adjustment member and the spool. The
bobbin, the adjustment member, the pole piece, the spool, and the valve body are each
disposed substantially concentrically about a central longitudinal axis of the solenoid
valve assembly.
[0008] The above features and advantages and other features and advantages of
the present invention are readily apparent from the following detailed description of the
best modes for carrying out the invention when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 is a schematic cross-sectional view of a solenoid valve assembly
including a bobbin, an adjustment member, a pole piece, a valve body, a spool, and a
resilient member;

Figure 2 is a schematic cross-sectional view of another embodiment of
the solenoid valve assembly of Figure 1 including the spool spaced opposite the pole
piece; and
Figure 3 is a schematic cross-sectional view of a further embodiment of
the solenoid valve assembly of Figure 1 including an annular protrusion, a frusto-
conical seat, and a working air gap.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to the drawings, wherein like reference numerals refer to like
components, a solenoid valve assembly is shown generally at 10 in Figure 1. The
solenoid valve assembly may be useful for automotive applications, such as applications
relating to automatic transmissions. However, it is to be appreciated that the solenoid
valve assembly 10 may also be useful for other non-automotive applications, such as, but
not limited to, aerospace applications.
Referring to Figure 1, the solenoid valve assembly 10 includes a bobbin
12 supporting a coil 14. The bobbin 12 may provide an annular support for the coil 14
and may be formed from any suitable non-magnetic material known in the art. For
example, the bobbin 12 may be formed from molded plastic, such as a glass-filled
thermoplastic. The bobbin 12 may also include one or more flanges for supporting the
coil 14.
The coil 14 may be formed from an electrically-conductive material. For
example, the coil 14 may be formed from copper wire. The coil 14 may be wound
around the bobbin 12 in one or more turns, i.e., windings. In use, an electrical current
may be applied to the coil 14 from a power source, such as, for example, a controller of a
powertrain, to induce a magnetic flux.
Referring to Figure 1, the bobbin 12 has at least one protrusion 16 on an
inner surface 18. As used herein, the terminology "inner" refers to elements disposed
relatively closer to a central longitudinal axis C of the solenoid valve assembly 10. In
contrast, the terminology "outer" refers to elements disposed relatively farther from the
central longitudinal axis C. For example, the at least one protrusion 16 may protrude
from the bobbin 12 towards the central longitudinal axis C. In particular, the inner

surface 18 of the bobbin 12 may define a bore 20, whereas an outer surface of the bobbin
12 may support the coil 14.
The at least one protrusion 16 may be annular. Further, the at least one
protrusion 16 may have a frusto-conical cross-section. The at least one protrusion 16 is
configured to align the bobbin 12 with other components of the solenoid valve assembly
10, as set forth in more detail below. That is, without intending to be limited by theory, it
is believed that at least one protrusion 16, which may be frusto-conical, contributes to a
concentricity of the solenoid valve assembly 10 by stabilizing components within the
bore 20 of the bobbin 12. The at least one protrusion 16 may be unitary, i.e., integral,
with the bobbin 12. The solenoid valve assembly 10 may include one or more than one
protrusion 16.
Referring to Figure 1, the solenoid valve assembly 10 includes an
adjustment member 22. The adjustment member 22 generally provides preloading and
calibration adjustment of the solenoid valve assembly 10, as set forth in more detail
below. The adjustment member 22 is disposed within the bobbin 12 and in contact with
the at least one protrusion 16. As such, the adjustment member 22 may be generally
cylindrically-shaped so as to be disposed within the bore 20 defined by the inner surface
18 of the bobbin 12. Further, the adjustment member 22 may be hollow and define a
chamber which receives another component of the solenoid valve assembly 10, also as set
forth in more detail below.
In use, the adjustment member 22 may be aligned with the bobbin 12 via
the at least one protrusion 16 of the bobbin 12. That is, the at least one protrusion 16 may
be configured to align the bobbin 12 and the adjustment member 22 substantially
concentrically within the solenoid valve assembly 10. As used herein, the terminology
"concentrically" refers to elements or components having a common center along the
central longitudinal axis C of the solenoid valve assembly 10. Further, as used herein, the
terminology "substantially" is used to represent the inherent degree of uncertainty that
may be attributed to any quantitative comparison, value, measurement, or other
representation. As such, it refers to an arrangement of elements or features that, while in
theory would be expected to exhibit exact correspondence or behavior, may in practice
embody something slightly less than exact. The term also represents the degree by which

a quantitative representation may vary from a stated reference without resulting in a
change in the basic function of the subject matter at issue. Therefore, it is contemplated
that the bobbin 12 and the adjustment member 22 may be slightly less than or more than
concentrically aligned within the solenoid valve assembly 10.
Referring to Figure 1, the solenoid valve assembly 10 includes a pole
piece 24. The pole piece 24 generally provides an attractive surface for other
components of the solenoid valve assembly 10, as set forth in more detail below. The
pole piece 24 is disposed vrithin the adjustment member 22. As such, the pole piece 24
may be generally cylindrically-shaped so as to be disposed within the chamber defined by
the adjustment member 22. The pole piece 24 may also be solid. The pole piece 24 may
be formed from any suitable electrically-conductive metal known in the art. For
example, the pole piece 24 may be formed from steel.
The pole piece 24 and the adjustment member 22 may be close-fitting. As
used herein, the terminology "close-fitting" refers to a minimal distance between
surfaces. For example, an outer surface of the pole piece 24 and an inward surface of the
adjustment member 22 may be spaced apart by less than 0.1 mm. As used herein, the
terminology "inward" refers to elements disposed relatively closer to a central
longitudinal axis C of the solenoid valve assembly 10. Each of the pole piece 24 and the
adjustment member 22 may be formed of the same shape and may have a difference in
diameter of less than 0.1 mm. The pole piece 24 and the adjustment member 22 may be
close-fitting so that the pole piece 24 is disposed substantially concentric with the
adjustment member 22. The close-fitting pole piece 24 and adjustment member 22
contribute to the excellent concentricity of the solenoid valve assembly 10 by minimizing
radial movement of the pole piece 24.
The pole piece 24 may also be configured for attachment to the adjustment
member 22. For example, the pole piece 24 may include threads 25 configured for
threading the pole piece 24 into the adjustment member 22.
In use, the adjustment member 22 may be centered within the solenoid
valve assembly 10 between the bobbin 12 and the pole piece 24. As electrical current is
applied to the coil 14, a magnetic flux is induced through the pole piece 24 and the
adjustment member 22. Therefore, the pole piece 24 is magnetized and provides a

magnetically-attractive surface for other components of the solenoid valve assembly 10.
For optimal efficiency of the solenoid valve assembly 10, the pole piece 24 may be
substantially longitudinally stationary within the solenoid valve assembly 10, excluding
any adjustment via the adjustment member 22 for, for example, preloading and/or
calibration.
Referring to Figure 1, the solenoid valve assembly 10 includes a valve
body 26. The valve body 26 may be configured to contain hydraulic fluid, e.g., air or
hydraulic oil. Although the valve body 26 may have any shape, the valve body 26 may
have a generally cylindrical and elongated shape and may define a spool bore 28.
Further, the valve body 26 may include at least three ports, shown generally at 30A, 3 0B,
and 30C. The at least three ports 30A, 30B, and 30C are generally configured for fluidly
communicating with equipment external to the solenoid valve assembly 10. For example,
the at least three ports 30A, 3 0B, and 30C may communicate with a hydraulic fluid
supply line. In the embodiment for use with an automatic transmission of a vehicle, the
at least three ports may include a supply port 30A, a control port 30B, and an exhaust
port 30C. In general, oil may be supplied to the solenoid valve assembly 10 via the
supply port 30A, oil may flow to clutches or other automatic transmission components
via the control port 3 0B, and excess oil may bleed out of the solenoid valve assembly 10
via the exhaust port 30C. Therefore, as set forth in more detail below, in use, the
solenoid valve assembly 10 may balance hydraulic pressure between the supply port 30A
and the exhaust port 30C to maintain hydraulic pressure on the control port 30B.
The valve body 26 may be formed of any suitable material according to an
operating environment of the solenoid valve assembly 10. For example, the valve body
26 may be formed of steel or aluminum.
Referring to Figure 1, the valve body 26 has a seat 32, and the bobbin 12
is disposed in contact with the seat 32. That is, the seat 32 of the valve body 26 may be
configured to align the bobbin 12 and the valve body 26 substantially concentrically
within the solenoid valve assembly 10. The seat 32 may be frusto-conical. The seat 32
may be frusto-conical to provide an abutment, e.g., a shoulder, for the bobbin 12 so that
the bobbin 12 may not translate radially from the central longitudinal axis C of the
solenoid valve assembly 10. In this embodiment, a portion of the inner surface 18 of the

bobbin 12 may be tapered to complement the frusto-conical shape of the seat 32. The
seat 32 of the valve body 26 contributes to the excellent concentricity of the solenoid
valve assembly 10 by aligning the bobbin 12 and the valve body 26.
Further, the at least one protrusion 16 and the seat 32 may be spaced apart
at a distance of less than or equal to 10 mm. The aforementioned distance also
contributes to the excellent concentricity of the solenoid valve assembly 10 by
minimizing spacing between concentric components, e.g., the pole piece 24, the bobbin
12, and the valve body 26 along the central longitudinal axis C. That is, the distance of
less than or equal to 10 mm simplifies the maintenance of concentricity of components of
the solenoid valve assembly 10 as compared to existing valves, for example, by
minimizing potential radial movement between components.
Referring to Figure 1, the solenoid valve assembly 10 includes a spool 34
slideably disposed within the valve body 26. As used herein, the terminology "slideably
disposed" refers to an ability of the spool 34 to slide, i.e., translate along the central
longitudinal axis C of the solenoid valve assembly 10, within the valve body 26. As
such, the spool 34 may be similar in shape to the spool bore 28 of the valve body 26. For
example, the spool 34 may also have a generally cylindrical and elongated shape.
Further, the spool 34 may include a first sealing portion 36 and a second
sealing portion 38. The first sealing portion 36 may be disposed relatively closer to the
seat 32 of the valve body 26 than to the second sealing portion 38. Each of the first
sealing portion 36 and the second sealing portion 38 may have an axial length greater
than or equal to half an axial length of one of the at least three ports 30A, 30B, 30C In
an embodiment for use in an automatic transmission, the first sealing portion 36 may be
configured to at least partially seal off the exhaust port 30C. Likewise, the second
sealing portion 3 8 may be configured to at least partially seal off the supply port 30A of
the valve body 26.
The spool 34 also may define an annular recession 40 formed in an outer
periphery of the spool 34 between the first sealing portion 36 and the second sealing
portion 38. The annular recession 40 may be configured to allow fluid communication
between at least two of the at least three ports 30A, 30B, 30C. Therefore, the annular
recession 40 may extend along the central longitudinal axis C a distance sufficient to at

least partially expose each of the at least three ports 30A, 30B, 30C. The annular
recession 40 may fully expose at least one of the at least three ports 30A, 30B, 30C.
Stated differently, the spool 34 may be configured for balancing hydraulic pressure
between the at least three ports 30A, 3 OB, 30C.
The spool 34 may slide vrithin the valve body 26 in response to electrical
current applied to the coil 14. That is, when the electrical current is applied to the coil
14, the spool 34 may be attracted to the pole piece 24. As such, the spool 34 may be
formed from a magnetic material, e.g., steel. Further, the spool 34 and the valve body 26
may be close-fitting. For example, an outer surface of the first sealing portion 36 and an
inward surface of the valve body 26 may be spaced apart by less than 0.1 mm. A
distance between the outer surface of the first sealing portion 36 and the inward surface
of the valve body 26 may define a circular air gap 42. A sizeof the circular air gap, i.e., a
distance between the outer surface of the first sealing portion 36 and the inward surface
of the valve body 26, may be minimized so as to maximize the concentricity of the spool
34 and the valve body 26.
Similarly, the second sealing portion 3 8 and the inward surface of the
valve body 26 may also be spaced apart by less than 0.1 mm. That is, each of the first
sealing portion 36, the second sealing portion 38, and the adjustment member 22 may be
formed of the same shape and may have a difference in diameter of less than 0.1 mm.
The spool 34 and the valve body 26 may be close-fitting so that so that the spool 34 is
disposed substantially concentric with the valve body 26. The close-fitting spool 34 and
valve body 26 contribute to the excellent concentricity of the solenoid valve assembly 10
by minimizing radial movement between the spool 34 and the valve body 26. A
longitudinal position of the spool 34 within the valve body 26 may also be adjusted via a
dashpot 44.
Referring to Figure 1, the pole piece 24 may have a first surface 46 and the
spool 34 may have a second surface 48 configured to correspond with the first surface 46
to form a working air gap 50 between the pole piece 24 and the spool 34. For example,
the first surface 46 may form one of a pocket 52 and a projection 54 and the second
surface 48 may form another of the pocket 52 and the projection 54. That is, the first
surface 46 and the second surface 48 may be complementary. The first surface 46 of the

pole piece 24 may have a tapered portion forming the pocket 52 which corresponds and
cooperates with a similarly tapered portion of the spool 34 forming the projection 54.
Further, the spool 34 may be spaced opposite and disposed substantially concentric with
the pole piece 24 across the working air gap 50.
A size and configuration of the working air gap 50 generally determines a
magnitude -of a force produced by the magnetic flux in relation to the electric current
applied to the coil 14. The working air gap 50 may effect axial movement, i.e., sliding,
of the spool 34 along the central longitudinal axis C upon energization of the coil 14, e.g.
as electrical current is applied to the coil 14. A comparatively weaker force generally
results from a comparatively larger working air gap as compared to a smaller working air
gap. Further, the working air gap 50 of the solenoid valve assembly 10 may be
substantially concentric with the spool 34 and the pole piece 24.
Referring to Figure 1, the solenoid valve assembly 10 includes a resilient
member 58 disposed in contact with the adjustment member 22 and the spool 34. The
resilient member 58 may allow adjustment of the force effected by the working air gap 50
and may allow preloading and calibration of the solenoid valve body 26. The resilient
member 58 may be any suitable resilient member known in the art, such as, for example,
a spring. The resilient member 58 may be disposed adjacent an outer surface of each of
the pole piece 24 and the spool 34 and may abut an end of the adjustment member 22
disposed closest to the spool 34 along the central longitudinal axis C of the solenoid
valve assembly 10. In use, the force of the solenoid valve assembly 10 may be adjusted,
e.g., calibrated and/or preloaded, via a release 60. Further, the adjustment member 22
may adjust, e.g., compress or reduce, the resilient member 58. Since the adjustment
member 22 may be attached to and/or close-fitting with the pole piece 24, adjustment of
the resilient member 58 may move the pole piece 24 longitudinally so that the size of the
working air gap 50 may be reduced or enlarged. The resilient member 58 may be formed
from any suitable material known in the art.
Referring to Figure 1, the solenoid valve assembly 10 may also include a
housing 56. The housing may be configured for attachment to the adjustment member 22
and the valve body 26. For example, the housing 56 may be attached to the adjustment
member 22 via threads 25 and may be attached to the valve body 26 via an interference

fit. That is, an outer surface of the adjustment member 22 may include corresponding
threads 25 for attachment to the housing 56. The housing 56 contributes to the excellent
concentricity of the solenoid valve assembly 10 by aligning the adjustment member 22
and the valve body 26. Further, the seat 32 may be configured to align the bobbin 12 and
the valve body 26 substantially concentrically within the housing 56. Stated differently,
the bobbin 12, the adjustment member 22, the pole piece 24, the spool 34, and the valve
body 26 may each be disposed substantially concentrically about the central longitudinal
axis C of the solenoid valve assembly 10. In particular, the seat 32, the at least one
protrusion 16, the close-fitting adjustment member 22 and pole piece 24, and the close-
fitting spool 34 and valve body 26 may individually and collectively contribute to the
concentricity of the solenoid valve assembly 10, as set forth above.
Referring to Figure 2, in another embodiment, the solenoid valve assembly
110 includes a bobbin 112 supporting a coil 14 and having at least one protrusion 116 on
an inner surface 118 and an adjustment member 122 disposed within the bobbin 112 and
in contact with the at least one protrusion 116. Further, the solenoid valve assembly 110
includes a pole piece 124 disposed within the adjustment member 122. The solenoid
valve assembly 110 also includes a valve body 126 having a seat 132, wherein the bobbin
112 is disposed in contact with the seat 132. Additionally, the solenoid valve assembly
110 includes a spool 134 slideably disposed within the valve body 126 and spaced
opposite the pole piece 124. Further, the solenoid valve assembly 110 also includes a
resilient member 158 disposed in contact with the adjustment member 122 and the spool
134.
The spool 134 may be disposed substantially concentric with the pole
piece 124. Therefore, the bobbin 112, the adjustment member 122, the pole piece 124,
the spool 134, and the valve body 126 may each be disposed substantially concentrically
about a central longitudinal axis C of the solenoid valve assembly 110. In particular, the
seat 132, the at least one protrusion 116, the adjustment member 122 and pole piece 124,
and the spool 134 and valve body 126 may individually and collectively contribute to the
concentricity of the solenoid valve assembly 110.
Referring to Figure 3, in another embodiment, the solenoid valve assembly
210 includes a bobbin 212 supporting a coil 214 and having at least one annular

protrusion 216 on an inner surface 218 and an adjustment member 222 disposed within
the bobbin 212 and in contact with the at least one annular protrusion 216. Further, the
solenoid valve assembly 210 includes a pole piece 224 having a first surface 246 and
disposed within the adjustment member 222. The solenoid valve assembly 210 also
includes a valve body 226 having a frusto-conical seat 232, wherein the bobbin 212 is
disposed in contact with the frusto-conical seat 232. Additionally, the solenoid valve
assembly 210 includes a spool 234 slideably disposed within the valve body 226 and
spaced opposite the pole piece 224. The spool 234 has a second surface 248 configured
to correspond to the first surface 246 to form a working air gap 250 between the pole
piece 224 and the spool 234. The spool 234 is disposed substantially concentric with the
pole piece 224 across the working air gap 250. Further, the solenoid valve assembly 210
also includes a resilient member 258 disposed in contact with the adjustment member 222
and the spool 234. The bobbin 212, the adjustment member 222, the pole piece 224, the
spool 234, and the valve body 226 are each disposed substantially concentrically about a
central longitudinal axis C of the solenoid valve assembly 210. In particular, the frusto-
conical seat 232, the at least one annular protrusion 216, the adjustment member 222 and
pole piece 224, and the spool 234 and valve body 226 may individually and collectively
contribute to the concentricity of the solenoid valve assembly 210.
Referring to Figures 1-3, the solenoid valve assemblies 10,110,210 may
be a variable force solenoid valve for an automatic transmission. In use, and described
with respect to the solenoid valve assembly 10, the spool 34 translates along the central
longitudinal axis C in response to electric current applied to the coil 14. In a de-
energized state, e.g., when minimal electric current is applied to the coil 14, the spool 34
seals off a portion of each of the supply port 30A and the exhaust port 30C, thereby
allowing some hydraulic fluid to flow into the annular recession 40 of the spool 34 and
out each of the control port 3 0B and the exhaust port 30C. Further, an mcrease in electric
current applied to the coil 14 decreases hydraulic pressure through the control port 3 0B.
That is, as electrical current applied to the coil 14 increases, the spool 34 translates
toward the pole piece 24 and seals off an increasing portion of the supply port 30 A,
thereby decreasing an amount of fluid and hydraulic pressure available to the control port
3 0B. In contrast, a decrease in electric current applied to the coil 14 increases hydraulic

pressure through the control port 30B. That is, as electrical current applied to the coil 14
decreases, the spool 34 translates away from the pole piece 24 and seals off an increasing
portion of the exhaust port 30C, thereby increasing an amount of fluid and hydraulic
pressure available to the control port 3 OB. Therefore, a response of the solenoid valve
assemblies 10, 110, 210 is infinitely variable according to minimal pressure changes.
The solenoid valve assemblies 10, 110, 210 exhibit excellent
concentricity and minimal friction between components. As such, the solenoid valve
assemblies 10, 110, 210 exhibit sensitive solenoid valve response for minimal hydraulic
pressure changes. The solenoid valve assemblies 10, 110, 210 also nummize a total
number of components for simplified maintenance and fabrication of the solenoid valve
assemblies 10, 110, 210. Therefore, the solenoid valve assemblies 10, 110, 210 are
cost-effective, easily-assembled, and easily-maintained.
While the best modes for carrying out the invention have been described
in detail, those familiar with the art to which this invention relates will recognize various
alternative designs and embodiments for practicing the invention within the scope of the
appended claims.

WE CLAIM:
1. A solenoid valve assembly (10, 110, 210), comprising:
a bobbin (12, 112, 212) supporting a coil (14, 114, 214) and having at
least one protrusion (16, 116, 216) on an inner surface (18, 118, 218);
an adjustment member (22, 122, 222) disposed within said bobbin (12,
112, 212) and in contact with said at least one protrusion (16, 116, 216);
a pole piece (24, 124, 224) disposed within said adjustment member (22,
122, 222);
. a valve body (26, 126, 226) having a seat (32, 132, 232), wherein said
bobbin (12, 112, 212) is disposed in contact with said seat (32, 132, 232);
a spool (34, 134, 234) slideably disposed within said valve body (26,
126, 226); and
a resilient member (58, 158, 258) disposed in contact with said
adjustment member (22, 122, 222) and said spool (34, 134, 234).
2. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said pole piece (24, 124, 224) has a first surface (46, 146, 246) and said spool (34,
134, 234) has a second surface (48, 148, 248) configured to correspond with said first
surface (46, 146, 246) to form a working air gap (50, 150, 250) between said pole
piece (24, 124, 224) and said spool (34, 134, 234).
3. The solenoid valve assembly (10, 110, 210) of claim 2, wherein
said first surface (46, 146, 246) forms one of a pocket (52) and a projection (54) and
said second surface (48, 148, 248) forms another of said pocket (52) and said projection
(54).
4. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said seat (32, 132, 232) is frusto-conical.

5. The solenoid valve assembly (10, 110, 210) of claim 1, further
comprising a housing (56) configured for attachment to said adjustment member (22,
122, 222) and said valve body (26, 126, 226).
6. The solenoid valve assembly (10, 110, 210) of claim 5, wherein
said seat (32, 132, 232) is configured to align said bobbin (12, 112, 212) and said valve
body (26, 126, 226) substantially concentrically within said housing (56).
7. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said at least one protrusion (16, 116, 216) is annular.
8. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said at least one protrusion (16, 116, 216) is configured to align said bobbin (12, 112,
212) and said adjustment member (22, 122, 222) substantially concentrically within the
solenoid valve assembly (10, 110, 210).
9. The solenoid valve assembly (10, 110, 210) of claim 8, wherein
said pole piece (24, 124, 224) and said adjustment member (22, 122, 222) are close-
fitting.
10. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said spool (34, 134, 234) and said valve body (26, 126, 226) are close-fitting.
11. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said valve body (26, 126, 226) includes at least three ports (30A, 30B, 30C).
12. The solenoid valve assembly (10, 110, 210) of claim 11, wherein
said spool (34, 134, 234) is configured for balancing hydraulic pressure between said at
least three ports (30A, 30B, 30C).

13. The solenoid valve assembly (10, 110, 210) of claim 12, wherein
said spool (34, 134, 234) slides within said valve body (26, 126, 226) in response to
electrical current applied to said coil (14, 114, 214).
14. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said bobbin (12, 112, 212), said adjustment member (22, 122, 222), said pole piece
(24, 124, 224), said spool (34, 134, 234), and said valve body (26, 126, 226) are each
disposed substantially concentrically about a central longitudinal axis (C) of said
solenoid valve assembly (10, 110, 210).
15. The solenoid valve assembly (10, 110, 210) of claim 1, wherein
said at least one protrusion (16, 116, 216) and said seat (32, 132, 232) are spaced apart
at a distance of less than or equal to 10 mm.
16. A solenoid valve assembly (110, 210), comprising:
a bobbin (12, 112, 212) supporting a coil (14, 114, 214) and having at
least one protrusion (16, 116, 216) on an inner surface (18, 118, 218);
an adjustment member (22, 122, 222) disposed within said bobbin (12,
112, 212) and in contact with said at least one protrusion (16, 116, 216);
a pole piece (24, 124, 224) disposed within said adjustment member (22,
122, 222);-
a valve body (26, 126, 226) having a seat (32, 132, 232), wherein said
bobbin (12, 112, 212) is disposed in contact with said seat (32, 132, 232);
a spool (134, 234) slideably disposed within said valve body (26, 126,
226) and spaced opposite said pole piece (24, 124, 224); and
a resilient member (58, 158, 258) disposed in contact with said
adjustment member (22, 122, 222) and said spool (134, 234).

17. The solenoid valve assembly (110, 210) of claim 16, wherein said
spool (134, 234) is disposed substantially concentric with said pole piece (24, 124,
224).
18. A solenoid valve assembly (210), comprising:
a bobbin (212) supporting a coil (14, 114, 214) and having at least one
annular protrusion (216) on an inner surface (18, 118, 218);
an adjustment member (22, 122, 222) disposed within said bobbin (212)
and in contact with said at least one annular protrusion (216);
a pole piece (224) having a first surface (46, 146, 246) and disposed
within said adjustment member (22, 122, 222);
a valve body (226) having a frusto-conical seat (232), wherein said
bobbin (212) is disposed in contact with said frusto-conical seat (232);
a spool (134, 234) slideably disposed within said valve body (226) and
spaced opposite said pole piece (224);
wherein said spool (134, 234) has a second surface (48, 148, 248) configured to
correspond to said first surface (46, 146, 246) to form a working air gap (50, 150, 250)
between said pole piece (224) and said spool (134, 234) and is disposed substantially
concentric with said pole piece (224) across said working air gap (50, 150, 250); and
a resilient member (58, 158, 258) disposed in contact with said
adjustment member (22, 122, 222) and said spool (134, 234);
wherein said bobbin (212), said adjustment member (22, 122, 222), said pole piece
(224), said spool (134, 234), and said valve body (226) are each disposed substantially
concentrically about a central longitudinal axis (C) of said solenoid valve assembly
(210).

A solenoid valve assembly (10,110, 210) includes a
bobbin (12, 112, 212) supporting a coil 814, 114, 214)
and having at least one protrusion (IS, 116,216) on an
inner surface (18, 118, 218), an adjustment member (22,
122, 222) disposed within the bobbin and in contact
with the at least one protrusion, a pole piece (24,
124, 224) disposed within the adjustment member, a
valve body (26,126,226) having a seat (32, 132, 232),
wherein the bobbin is disposed in contact with the
seat, a spool (34, 134, 234) slideably disposed within
the valve body, and a resilient member (58, 158, 258)
disposed in contact with the adjustment member and the
spool.