U.S. patent application number 11/536022 was filed with the patent office on 2008-04-03 for temperature adaptive radial shaft seal assemblies using shape memory alloy elements.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Alan L. Browne, Nancy L. Johnson, Chandra S. Namuduri.
Application Number | 20080079222 11/536022 |
Document ID | / |
Family ID | 39277344 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080079222 |
Kind Code |
A1 |
Namuduri; Chandra S. ; et
al. |
April 3, 2008 |
Temperature adaptive radial shaft seal assemblies using shape
memory alloy elements
Abstract
A dynamic radial shaft assembly and methods of use for rotating
or reciprocating shafts include an elastic seal member having at
least a portion thereof in sealing communication with the rotating
or reciprocating shaft; and a shape memory alloy element in contact
with the elastic seal member, wherein the shape memory alloy
element is adapted to change a shape orientation and or modulus
property as a function of temperature change so as to change or
maintain a compressive force and/or sealing area of the seal member
portion against the rotating or reciprocating shaft at temperatures
from -55.degree. C. to about 250.degree. C.
Inventors: |
Namuduri; Chandra S.; (Troy,
MI) ; Browne; Alan L.; (Grosse Pointe, MI) ;
Johnson; Nancy L.; (Northville, MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21, P O BOX 300
DETROIT
MI
48265-3000
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
39277344 |
Appl. No.: |
11/536022 |
Filed: |
September 28, 2006 |
Current U.S.
Class: |
277/359 |
Current CPC
Class: |
F16J 15/3212 20130101;
F16J 15/164 20130101 |
Class at
Publication: |
277/359 |
International
Class: |
F16J 15/34 20060101
F16J015/34 |
Claims
1. A dynamic shaft seal assembly for sealing a rotating or
reciprocating shaft, the seal assembly comprising: an elastic seal
member having at least a portion thereof in sealing communication
with the rotating or reciprocating shaft; and a shape memory alloy
element in contact with the elastic seal member, wherein the shape
memory alloy element is adapted to change a shape orientation
and/or modulus property as a function of temperature change so as
to change or maintain a compressive force and/or sealing area of
the seal member against the rotating or reciprocating shaft at
temperatures from -55.degree. C. to about 250.degree. C.
2. The dynamic shaft seal assembly of claim 1, wherein the shape
memory alloy element is discontinuously disposed about the elastic
seal member.
3. The dynamic shaft seal assembly of claim 1, further comprising a
dust lip extending from the elastic seal member and contacting the
rotating or reciprocating shaft.
4. The dynamic shaft seal assembly of claim 1, wherein the elastic
seal member is formed of an elastomer.
5. The dynamic shaft seal assembly of claim 1, further comprising a
rigid casing in structural communication with the elastic seal
member.
6. The dynamic shaft seal assembly of claim 5, wherein the rigid
casing includes an axial portion and a radial portion.
7. The dynamic shaft seal assembly of claim 1, wherein the shape
memory alloy element is seated within a recess at about the portion
of the elastic seal member in sealing communication with the
rotating or reciprocating shaft.
8. The dynamic shaft seal assembly of claim 1, wherein the shape
memory element includes axial portions.
9. The dynamic shaft seal assembly of claim 1, wherein the shape
memory alloy element comprises a plurality of wires having
different transformation temperatures, wherein the wires are
circumferentially disposed about the portion of the elastic seal
member in sealing communication with the rotating or reciprocating
shaft.
10. A temperature adaptive seal, comprising: an elastomeric seal
body; and a shape memory alloy element in compressive contact with
the elastomeric seal body, wherein the shape memory alloy element
is adapted to change a shape orientation and/or modulus property as
a function of temperature change so as to change or maintain the
compressive contact force and/or sealing area of the seal member
portion against a component when the component is exposed to
ambient temperatures of about -55.degree. C. to about 250.degree.
C.
11. The temperature adaptive seal of claim 10, wherein the shape
memory alloy element is discontinuously disposed about the
elastomeric seal body.
12. The temperature adaptive seal of claim 10, wherein the
elastomeric seal body defines a selected one of an O-ring, a
V-ring, and U-ring.
13. The temperature adaptive seal of claim 10, wherein the shape
memory alloy element is embedded within the elastomeric body.
14. A method of mounting a radial shaft seal assembly onto a shaft,
wherein the shaft has an outer diameter larger than an inner
diameter of the seal assembly, the method comprising: mounting a
seal assembly onto the shaft, the seal assembly comprising a shape
memory element in compressive communication with an elastic seal
body portion, wherein the shape memory element is in an austenite
phase, wherein mounting the seal assembly onto the shaft stretches
the elastic seal body portion and the shape memory alloy element to
superelastically deform the shape memory element and change to a
martensite phase; and reverting to the austenite phase and a
smaller diameter once the deforming stresses are removed.
15. The method of claim 14, wherein the shape memory alloy element
comprises a plurality of wires having different transformation
temperatures, wherein the wires are circumferentially disposed
about the portion of the elastic seal member in sealing
communication with the shaft.
16. The method of claim 14, wherein the shape memory element
includes axial portions.
17. A method of sealing a rotatable or reciprocating shaft,
comprising: mounting a seal assembly onto the shaft, the seal
assembly comprising a shape memory element in compressive
communication with an elastic seal body portion, wherein the shape
memory alloy element is adapted to change a shape orientation and
or modulus property as a function of temperature change so as to
change or maintain a compressive force and/or sealing area of the
seal member portion against the rotating or reciprocating shaft;
and operating the seal assembly in an environment having a
temperature differential of at least 50.degree. C. and within a
temperature range of about -55.degree. C. to about 250.degree.
C.
18. The method of claim 17, wherein the shape memory alloy element
comprises a plurality of wires having different transformation
temperatures, wherein the wires are circumferentially disposed
about the portion of the elastic seal member in sealing
communication with the rotating or reciprocating shaft.
19. The method of claim 17, wherein the shape memory element
includes axial portions.
20. The method of claim 17, wherein the shape memory element is
discontinuously disposed about the elastic seal body portion.
21. A method of mounting a radial shaft seal assembly onto a shaft,
wherein the shaft has an outer diameter larger than an inner
diameter of the seal assembly, the method comprising: mounting a
seal assembly comprising a shape memory element in compressive
communication with an elastic seal body portion, wherein the shape
memory element is in an austenite phase, wherein mounting the seal
assembly onto the shaft stretches the elastic seal body portion and
the shape memory alloy element, wherein the shape memory element
exhibits a stress induced change to the martensite phase and
deforms superelastically; and maintaining a constant sealing force
over a range of moduli exhibited by the elastic seal body
portion.
22. The method of claim 21, further comprising operating the seal
assembly in an environment having a temperature differential of at
least 50.degree. C. and within a temperature range of about
-55.degree. C. to about 250.degree. C.
Description
BACKGROUND
[0001] The present disclosure relates to a temperature adaptive
radial shaft sealing device that provides improved sealing over a
wide range of temperatures while minimizing the friction and wear
associated with the same.
[0002] Most automotive sub-systems such as the engine,
transmission, driveline, suspension dampers, pumps, brakes and
other hydraulic/pneumatic actuators utilize seals to prevent
ingress of extraneous materials (dust, dirt, humidity, air etc.)
into the actuators and/or egress of fluids from the actuators. The
seals can be used in a static or a dynamic application. Most
dynamic seals have at least one part of the seal in contact with a
sliding or a rotating surface. As an example, a shock absorber has
a cylindrical piston rod that reciprocates axially through a sealed
bearing embedded at one end of a closed cylindrical tube that
encloses a hydraulic fluid. As another example, most rotating
elements in the transmission require the use of rotary dynamic
seals to prevent leakage of the pressurized hydraulic fluid, e.g.,
prevent leaking past the shaft bearings.
[0003] Many types of radial shaft seals suitable for individual
applications are available commercially. Each seal application has
specific requirements in terms of the leakage rate, operating
temperature range, maximum allowable friction, misalignment, cost,
cycle life, and the like. In automotive applications, the ambient
temperatures in which the seals must effectively operate typically
range from about -40.degree. C. to about 150.degree. C. while the
temperatures that some of the seals experience may be over an even
wider temperature range, such as -55.degree. C. to 250.degree. C.
or more. While commercially available radial shaft seals satisfy
most of the requirements of a given application at one temperature
extreme, it is difficult to satisfy all of the requirements at both
temperature extremes. For example, it is oftentimes difficult to
minimize seal friction at temperatures at the lower end of the
extremes (freezing and below) while maintaining adequate seal
friction/minimum leakage at the temperatures approaching the higher
end of the temperature extremes (temperatures in excess of
100.degree. C.). Most prior art seals utilize spring loaded
elastomer materials to maintain adequate sealing over time and
temperature. However, because of thermal expansion properties
inherent to the materials (e.g., spring steel, aluminum, brass, and
the like) used to form the spring, uniform spring loads do not
occur over the wide temperature ranges to which seals are exposed
such as experienced by dynamic seals used in the automotive
environment.
[0004] The disadvantages of prior art radial shaft seals include,
but are not limited to, excessive friction, excessive leakage,
excessive wear, reduced life/durability, and non-uniform
compliance/sealing pressure over the required operating temperature
range, among others. Interestingly, the first two properties are at
odds with each other in a dynamic sealing situation. Good
compression forces holding the seal against a reciprocating or
rotating member accelerate seal wear and shorten service life
whereas reducing the compressive force can result in leaking,
especially at the temperature extremes in which the dynamic seal
device can be used. Therefore, every dynamic seal design is a
compromise to produce an acceptable balance between these two
desirable properties.
[0005] Accordingly, what is needed is an improved seal assembly
that operates effectively and uniformly across a wide temperature
range.
BRIEF SUMMARY
[0006] Disclosed herein are dynamic shaft seal assemblies and
methods of use. In one embodiment, the dynamic shaft seal assembly
for sealing a rotating or reciprocating shaft comprises an elastic
seal member having at least a portion thereof in sealing
communication with the rotating or reciprocating shaft; and a shape
memory alloy element in contact with the elastic seal member,
wherein the shape memory alloy element is adapted to change a shape
orientation and or modulus property as a function of temperature
change so as to change or maintain a compressive force and/or
sealing area of the seal member portion against the rotating or
reciprocating shaft at temperatures from -55.degree. C. to about
250.degree. C.
[0007] In another embodiment, a temperature sensitive adaptive seal
comprises an elastomeric seal body; and a shape memory alloy
element in compressive contact with the elastomeric seal body,
wherein the shape memory alloy element is adapted to change a shape
orientation and/or modulus property as a function of temperature
change so as to change or maintain the compressive contact force
and/or sealing area of the seal member portion against a component
when the component is exposed to ambient temperatures of about
-55.degree. C. to about 250.degree. C.
[0008] A method of mounting a radial shaft seal assembly onto a
shaft, wherein the shaft has an outer diameter larger than an inner
diameter of the seal assembly comprises mounting a seal assembly
comprising a shape memory element in compressive communication with
an elastic seal body portion, wherein the shape memory element is
in an austenite phase, wherein mounting the seal assembly onto the
shaft stretches the elastic seal body portion and the shape memory
alloy element, wherein the shape memory element changes to a
martensite phase and superelastically deforms and reverts to the
austenite phase and a smaller diameter once the deforming stresses
are removed.
[0009] A method of mounting a radial shaft seal assembly onto a
shaft, wherein the shaft has an outer diameter larger than an inner
diameter of the seal assembly, the method comprises mounting a seal
assembly comprising a shape memory element in compressive
communication with an elastic seal body portion, wherein the shape
memory element is in an austenite phase, wherein mounting the seal
assembly onto the shaft stretches the elastic seal body portion and
the shape memory alloy element, wherein the shape memory element
exhibits a stress induced change to the martensite phase and
deforms superelastically; and maintaining a constant sealing force
over a range of moduli exhibited by the elastic seal body
portion.
[0010] A method of sealing a rotatable or reciprocating shaft
comprises mounting a seal assembly comprising a shape memory
element in compressive communication with an elastic seal body
portion, wherein the shape memory alloy element is adapted to
change a shape orientation and or modulus property as a function of
temperature change so as to change or maintain a compressive force
and/or sealing area of the seal member portion against the rotating
or reciprocating shaft at temperatures from -50.degree. C. to about
150.degree. C.; and operating the seal assembly in an environment
having a temperature differential of at least 50.degree. C. and
within a temperature range of about -55.degree. C. to about
250.degree. C.
[0011] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Referring now to the figures, which are exemplary
embodiments and wherein like elements are numbered alike:
[0013] FIG. 1 is a schematic representation of a cross sectional
view of a temperature adaptive radial seal assembly; and
[0014] FIG. 2 illustrates perspective views of exemplary shape
memory elements in accordance with the present disclosure.
DETAILED DESCRIPTION
[0015] The present disclosure addresses the issues associated with
the use of prior art dynamic radial shaft seal assemblies operating
in such wide temperature extremes. It has been discovered that by
integrating a shape memory alloy based element such as a spring,
garter band, ribbon, or the like in place of or in addition to the
standard metal garter spring or band used around a seal lip, and/or
the metal casing overcomes the problems noted with the prior art
seals. The shape memory alloy element is temperature sensitive and
can be used to provide enhanced seal performance over a wide
temperature range, reduced seal friction, reduced seal leakage,
reduced wear, increased seal life and/or durability, and improved
product reliability relative to prior art seal assemblies.
[0016] Shape memory alloys (SMA) exist in several different
temperature-dependent phases. The most commonly utilized of these
phases are the so-called martensite and austenite phases. In the
following discussion, the martensite phase generally refers to the
more deformable, lower temperature phase whereas the austenite
phase generally refers to the more rigid, higher temperature phase.
When the shape memory alloy is in the martensite phase and is
heated, it begins to change into the austenite phase. The
temperature at which this phenomenon starts is often referred to as
austenite start temperature (As). The temperature at which this
phenomenon is complete is called the austenite finish temperature
(Af). When the shape memory alloy is in the austenite phase and is
cooled, it begins to change into the martensite phase, and the
temperature at which this phenomenon starts is referred to as the
martensite start temperature (Ms). The temperature at which
austenite finishes transforming to martensite is called the
martensite finish temperature (Mf). Generally, the shape memory
alloys are softer and more easily deformable in their martensitic
phase and are harder, stiffer, and/or more rigid in the austenitic
phase. In view of the foregoing properties, expansion of the shape
memory alloy is preferably at or below the austenite transition
temperature (at or below As). Subsequent heating above the
austenite transition temperature causes the expanded shape memory
alloy to revert back to its permanent shape. Thus, a suitable
activation signal for use with shape memory alloys is a thermal
activation signal having a magnitude to cause transformations
between the martensite and austenite phases.
[0017] The temperature at which the shape memory alloy remembers
its high temperature form when heated can be adjusted by slight
changes in the composition of the alloy and through heat treatment.
In nickel-titanium shape memory alloys, for instance, it can be
changed from above about 100.degree. C. to below about -100.degree.
C. The shape recovery process occurs over a range of just a few
degrees and the start or finish of the transformation can be
controlled to within a degree or two depending on the desired
application and alloy composition. The mechanical properties of the
shape memory alloy vary greatly over the temperature range spanning
their transformation, typically providing shape memory effects,
superelastic effects, and high damping capacity.
[0018] Suitable shape memory alloy materials include, but are not
intended to be limited to, nickel-titanium based alloys,
indium-titanium based alloys, nickel-aluminum based alloys,
nickel-gallium based alloys, copper based alloys (e.g., copper-zinc
alloys, copper-aluminum alloys, copper-gold, and copper-tin
alloys), gold-cadmium based alloys, silver-cadmium based alloys,
indium-cadmium based alloys, manganese-copper based alloys,
iron-platinum based alloys, iron-palladium based alloys, and the
like. The alloys can be binary, ternary, or any higher order so
long as the alloy composition exhibits a shape memory effect, e.g.,
change in shape orientation, changes in yield strength, and/or
flexural modulus properties, damping capacity, superelasticity, and
the like. Selection of a suitable shape memory alloy composition
depends on the temperature range where the component will
operate.
[0019] FIG. 1 illustrates an exemplary dynamic radial shaft seal
assembly 10 utilizing a shape memory alloy element. The seal
assembly 10 is disposed in sealing communication with a rotating or
reciprocating radial shaft 12 and generally includes a compressible
seal body 14 having at least one seal lip 16 in sealing contact
with the shaft 12. Disposed in compressive communication with the
seal lip is a shape memory alloy element 18. The SMA element can be
seated within a recess provided in the seal body. The seal device
further includes a metal casing 20 for providing rigidity to the
seal device and further assists in defining the inner and outer
diameters of the seal device. The casing includes an axial portion
and a radial portion. The axial portion extends upward and then
bends inwardly at approximately 90.degree. forming the radial
portion.
[0020] Although reference has been made specifically to radial
shafts, one of skill in the art will recognize that the cross
sectional shape of a reciprocating shaft can vary and that the seal
assemblies disclosed herein can be readily adapted to sealingly
conform to the particular cross sectional geometry of the
shaft.
[0021] Optionally, the seal device 10 may further include
additional lips such as for preventing ingress of dust or other
contaminants beyond the seal device. The diameters of the seal
device 10 are such that it can snugly fit against an outer member
22 and the reciprocating or rotating shaft. The seal device is
preferably toroidal in shape so as to snugly fit about a shaft
circumference.
[0022] The SMA element can be configured in any structural form
such as a continuous wire or a ribbon embedded within and
conforming to the rotationally symmetric geometry of the seal body.
FIG. 2 illustrates exemplary shapes and is not intended to be
limiting. The elements could be of different geometries in the
circumferential or axial directions including straight, crown, or
wavy shape such as having a sinusoidal shape with hills and valleys
extending in the radial sealing direction. The particular shapes,
compositions, number of springs, and forms will generally depend on
the application and the desired compressive load. For example,
multiple individual wires/bands of SMA with different phase change
temperatures could also be used to increase the stiffness in steps
as the temperature increased to compensate for the continuing
decrease in elastic modulus of the seal material. Likewise, an SMA
wire/ribbon loop could be embedded within the seal body, which
wire/ribbon would be in its austenitic phase under installation and
normal operating temperatures for the seal device. This would
provide a seal device, wherein the seal body and SMA element could
be stretched dramatically to, for example, mount on a shaft; the
SMA wire exhibiting a stress induced phase change to martensite
form, i.e., superelasticity, which would cause it to revert to its
smaller diameter and snug the shaft once the deforming stresses
were removed.
[0023] In another embodiment, a method of mounting a radial shaft
seal assembly onto a shaft, wherein the shaft has an outer diameter
larger than an inner diameter of the seal assembly comprises
mounting a seal assembly generally includes a shape memory element
in compressive communication with an elastic seal body portion,
wherein the shape memory element is in an austenite phase, wherein
mounting the seal assembly onto the shaft stretches the elastic
seal body portion and the shape memory alloy element, wherein the
shape memory element exhibits a stress induced change to the
martensite phase and deforms superelastically, the magnitudes of
stress and deformation being sufficient to cause the shape memory
alloy element to remain in the martensite phase and because of this
maintain constant sealing forces over the range of moduli exhibited
by the elastic seal body portion, e.g., over the full operating
temperature range.
[0024] In yet another embodiment, discontinuous SMA elements are
utilized (see FIGS. 2C and E), e.g., wherein the SMA element is
impregnated, preferentially in circumferential and/or radial
patterns into the seal body material to achieve the desired
functionality. The shape memory alloy/composite material
characteristics are chosen based on the seal requirements. If the
base seal does not provide adequate sealing at high temperatures
and has excessive friction at the low temperatures, the SMA
characteristics can be tuned to increase the sealing pressure above
a threshold temperature to prevent leakage, while at lower
temperatures the excessive pressure may be released (due to the
lower modulus of the lower temperature martensitic phase of SMA) to
decrease seal friction or vice versa. The shape memory effect upon
heating would act to restore the seal geometry and sealing
pressure. While a lip type of dynamic shaft seal is shown as an
example, it is possible to adopt the disclosure into the other
types of seal geometries such as the O-rings, wear rings, V-rings,
U-rings and other shapes for various applications, to obtain a
temperature response adapted to the behavior and intended function
of the seal. Typical materials used to manufacture these types of
seals include, but are not limited to, nitrile, fluoroelastomer,
polytetrafluoroethylene (PTFE), polyurethane, and the like. The SMA
element can be embedded within or disposed, continuously or
discontinuously on a surface of any one of the above noted seal
geometries.
[0025] The body is preferably formed of an elastomer. Suitable
elastomers include, polybutadiene, polyisobutylene, polyisoprene,
styrene-butadiene-styrene, polyethylene, polysulfides,
fluoroelastomers, nitrites, and the like.
[0026] Advantageously, the seal assembly with the shape memory
elements improves seal wear and effectiveness over a wide
temperature range, e.g., about -40.degree. C. to about 150.degree.
C. for common automotive applications to as wide a range as
-55.degree. C. to 250.degree. C. for more extreme automotive
applications. In one embodiment, the temperature differential at
which the seal assembly is exposed is greater than 50.degree. C.,
and in other embodiments greater than 70.degree. C., and in still
other embodiments, greater than 100.degree. C.
[0027] As used herein, the terms "first", "second", and the like do
not denote any order or importance, but rather are used to
distinguish one element from another, and the terms "the", "a", and
"an" do not denote a limitation of quantity, but rather denote the
presence of at least one of the referenced items. Furthermore, all
ranges directed to the same quantity of a given component or
measurement are inclusive of the endpoints and independently
combinable.
[0028] While the disclosure has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *