U.S. patent application number 12/884383 was filed with the patent office on 2011-03-31 for system, method and apparatus for tolerance ring control of slip interface sliding forces.
This patent application is currently assigned to SAINT-GOBAIN PERFORMANCE PLASTICS RENCOL LIMITED. Invention is credited to Parag Natu, Andrew Slayne.
Application Number | 20110076096 12/884383 |
Document ID | / |
Family ID | 43252091 |
Filed Date | 2011-03-31 |
United States Patent
Application |
20110076096 |
Kind Code |
A1 |
Slayne; Andrew ; et
al. |
March 31, 2011 |
SYSTEM, METHOD AND APPARATUS FOR TOLERANCE RING CONTROL OF SLIP
INTERFACE SLIDING FORCES
Abstract
A tolerance ring comprising a metallic band for spring features
and a complementary low friction material for frictional
considerations is disclosed. The tolerance ring is designed to
operate within a precisely controlled torque or axial force band to
provide a defined amount of resistance and sliding force control
between components that move relative to each other. Isolated
portions of the tolerance ring form regions of contact with
adjacent ones of the components. Other surfaces of the tolerance
ring comprise portions with spring features that have geometry
suitable for their spring rate, rather than conforming to mating
surfaces of the adjacent components.
Inventors: |
Slayne; Andrew; (Bristol,
GB) ; Natu; Parag; (Neuss, DE) |
Assignee: |
SAINT-GOBAIN PERFORMANCE PLASTICS
RENCOL LIMITED
Bristol
GB
|
Family ID: |
43252091 |
Appl. No.: |
12/884383 |
Filed: |
September 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61245883 |
Sep 25, 2009 |
|
|
|
Current U.S.
Class: |
403/372 |
Current CPC
Class: |
Y10T 156/1041 20150115;
F16C 27/02 20130101; F16D 1/0835 20130101; F16D 3/06 20130101; Y10T
403/7058 20150115; Y10T 403/7061 20150115; F16D 7/021 20130101 |
Class at
Publication: |
403/372 |
International
Class: |
F16B 2/22 20060101
F16B002/22 |
Claims
1. An assembly, comprising: an outer component; an inner component
located in the outer component and movable relative thereto; a
tolerance ring mounted between the inner and outer components, the
tolerance ring providing: a radial stiffness that is greater than
about 20,000 N/mm; an axial sliding force in a range of about 10 to
600 N; and a diameter of at least 10 mm.
2. An assembly according to claim 1, wherein the tolerance ring
comprises an annular band formed from a metallic material and a low
friction material joined to the annular band.
3. An assembly according to claim 1, wherein the tolerance ring has
a plurality of projections extending in a radial direction, the
projections being compressed between the inner and outer components
such that the tolerance ring operates in a flattened portion of a
compression/retention force characteristic whereby the projections
initially exhibit elastic behavior and are plastically
deformed.
4. An assembly according to claim 2, wherein the annular band is
formed from spring steel and the low friction material has a
coefficient of friction in a range of 0.04 to 0.25, and is
laminated to at least one side of the annular band, the annular
band has a radial thickness of about 0.1 to 0.7 mm, and the low
friction material has a radial thickness in a range of about 0.05
to 0.50 mm.
5. (canceled)
6. An assembly according to claim 3, wherein the projections also
extend in an axial direction as axially-elongated ridges and the
tolerance ring also has circumferentially-extending rims at axial
ends of the projections.
7. An assembly according to claim 6, wherein the flat sections and
circumferentially-extending rims are contiguously formed in a
planar configuration, and the axially-elongated ridges have rounded
peaks and axial ends of each ridge terminates in a tapered shoulder
at the circumferentially-extending rims.
8. An assembly according to claim 6, wherein the projections are
circumferentially spaced apart from each other by flat
sections.
9. An assembly according to claim 6, wherein the projections
circumferentially abut one another.
10. An assembly, comprising: an outer component; an inner component
located in the outer component and movable relative thereto; a
tolerance ring mounted between the inner and outer components, the
tolerance ring providing: a radial stiffness that is greater than
about 20,000 N/mm; and parameters selected from the group
consisting of: (i) a slip torque in a range of 1 to 25 Nm, and a
diameter of less than about 40 mm; (ii) a slip torque in a range of
1 to 100 Nm, and a diameter of more than 40 mm; and (iii) an axial
sliding force in a range of 10 to 600 N, and a diameter of more
than 10 mm.
11. An assembly according to claim 10, wherein the tolerance ring
comprises an annular band formed from a metallic material and a low
friction material joined to the annular band.
12. An assembly according to claim 10, wherein the tolerance ring
has a plurality of projections extending in a radial direction, the
projections being compressed between the inner and outer components
such that the tolerance ring operates in a flattened portion of a
compression/retention force characteristic whereby the projections
initially exhibit elastic behavior and are plastically deformed,
and the tolerance ring provides an overload protection force of
less than 100 Nm.
13. An assembly according to claim 10, wherein the tolerance ring
is greater than 65 mm in diameter.
14. An assembly according to claim 11, wherein the annular band is
formed from spring steel and the low friction material has a
coefficient of friction in a range of 0.04 to 0.25, and is
laminated to one side of the annular band, the annular band has a
radial thickness of about 0.1 to 0.7 mm, and the low friction
material has a radial thickness in a range of about 0.05 to 0.50
mm.
15. (canceled)
16. An assembly according to claim 12, wherein the projections
extend in an axial direction as axially-elongated ridges and are
circumferentially spaced apart from each other by flat sections,
the tolerance ring also having circumferentially-extending rims at
axial ends of the projections.
17. (canceled)
18. A tolerance ring assembly, comprising: an outer component
having a bore with an axis therein; an inner component mounted in
the bore of the outer component, such that the inner component
mates with the outer component and is movable relative thereto; and
a tolerance ring located in the bore between the inner and outer
components, the tolerance ring comprising an annular band formed
from a metallic material and a low friction material joined to the
annular band, the tolerance ring also having a plurality of
projections extending relative to the axis, the projections being
compressed between the inner and outer components such that the
tolerance ring operates in a flattened portion of a
compression/retention force characteristic whereby the projections
initially exhibit elastic behavior and are plastically deformed,
and the tolerance ring provides an overload protection force of
less than 100 Nm.
19. A tolerance ring assembly according to claim 18, wherein the
tolerance ring is greater than 65 mm in diameter.
20. A tolerance ring assembly according to claim 18, wherein the
overload protection force is less than 25 Nm, and the tolerance
ring is less than 40 mm in diameter.
21. A tolerance ring assembly according to claim 18, wherein the
annular band is formed from spring steel and the low friction
material has a coefficient of friction in a range of 0.04 to 0.25,
and is laminated to one side of the annular band, the annular band
has a radial thickness of about 0.1 to 0.7 mm, and the low friction
material has a radial thickness in a range of about 0.05 to 0.50
mm.
22. (canceled)
23. A tolerance ring assembly according to claim 18, wherein a low
resistance to axial sliding in a range of about 10 and 600 N is
provided, and the tolerance ring has a diameter of at least 10
mm.
24. A tolerance ring assembly according to claim 18, wherein the
overload protection force comprises a torque overload protection
force of between 1 to 25 Nm, and the tolerance ring has a diameter
of less than 40 mm.
25. A tolerance ring assembly according to claim 18, wherein the
projections extend in an axial direction as axially-elongated
ridges and are circumferentially spaced apart from each other by
flat sections, the tolerance ring also having
circumferentially-extending rims at axial ends of the projections,
the flat sections and circumferentially-extending rims are
contiguously formed in a planar configuration.
26. (canceled)
27. A tolerance ring assembly according to claim 25, wherein the
axially-elongated ridges have rounded peaks and axial ends of each
ridge terminates in a tapered shoulder at the
circumferentially-extending rims.
28. A tolerance ring assembly according to claim 18, further
comprising a corrosion resistant layer on the annular band, the
corrosion resistant layer has a thickness of about 1 to 50 microns,
the corrosion resistant layer comprises an epoxy resin layer.
29. (canceled)
30. (canceled)
31. A tolerance ring assembly according to claim 28, wherein the
corrosion resistant layer further comprises an adhesion promoter
layer underlying the epoxy resin layer.
32. (canceled)
33. (canceled)
34. A tolerance ring assembly according to claim 28, wherein the
epoxy resin layer comprises a hardening agent.
35. (canceled)
Description
[0001] This application claims priority to and the benefit of U.S.
Provisional App. No. 61/245,883, filed Sep. 25, 2009, and is
incorporated herein by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The invention generally relates to tolerance rings that are
located between moving parts and, in particular, to an improved
system, method and apparatus employing a tolerance ring.
BACKGROUND
[0003] Tolerance rings constrain movement between relatively moving
parts, such as rotating shafts in housing bores. One type of
tolerance ring is an annular band located in the gap between the
outer surface of the shaft and the inner surface of the bore. This
tolerance ring limits radial motion of the shaft within the bore
while still permitting rotation.
[0004] In conventional tolerance ring configurations, a close fit
between the inner and outer components is sought. In addition,
either forces for providing maximal frictional engagement or
minimal variation in sliding forces are sought. A close fit between
the components is desirable because it reduces relative vibration
between the parts. These requirements between the inner and outer
components require strong and substantial contact, which increases
frictional forces.
[0005] Tolerance rings that provide torque overload protection for
applications with torques greater than 50 Nm, with relatively low
rates of rotation and small angular slip cycles also are known.
These applications include reduction gear mounts, power steps on
four wheel drive trucks and seat motors for fold away seats.
Tolerance rings for these applications tend to be heat-treated
carbon steel, greater than 0.40 mm thick, and have many strong,
high friction waves to provide the required torque. Although these
solutions are workable for some applications, improvements in
tolerance rings continue to be of interest.
SUMMARY OF THE INVENTION
[0006] Embodiments of a system, method and apparatus for a
tolerance ring comprise an assembly having an outer component, an
inner component located in the outer component and movable relative
thereto, and a tolerance ring mounted between the inner and outer
components.
[0007] In other embodiments, an assembly comprises an outer
component, an inner component located in the outer component and
movable relative thereto, and a tolerance ring mounted between the
inner and outer components. The tolerance ring provides a radial
stiffness that is greater than about 20,000 N/mm and parameters
selected from the following: a slip torque in a range of 1 to 25
Nm, and a diameter of less than about 40 mm; a slip torque in a
range of 1 to 100 Nm, and a diameter of more than 40 mm; or a low
resistance to axial sliding in a range of 10 to 600 N, and a
diameter of more than 10 mm. Applications having smaller diameters
may provide a lower radial stiffness.
[0008] In still other embodiments, a tolerance ring assembly
comprises an outer component having a bore with an axis therein and
an inner component mounted in the bore of the outer component, such
that the inner component mates with the outer component and is
movable relative thereto. A tolerance ring is located in the bore
between the inner and outer components, the tolerance ring
comprising a metallic annular band and a low friction material
joined to the metallic annular band, the tolerance ring also having
a plurality of projections extending relative to the axis, the
projections being compressed between the inner and outer components
such that the tolerance ring operates in a flattened portion of a
compression/retention force characteristic whereby the projections
initially exhibit elastic behavior and are plastically deformed,
and the tolerance ring provides an overload protection force of
less than 100 Nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the features and advantages are
attained and can be understood in more detail, a more thorough
description may be had by reference to the embodiments that are
illustrated in the appended drawings. However, the drawings
illustrate only some embodiments and therefore are not to be
considered limiting of the scope.
[0010] FIG. 1 is a perspective view of one embodiment of a
tolerance ring constructed in accordance with the invention;
[0011] FIG. 2 is a perspective view of another embodiment of a
tolerance ring constructed in accordance with the invention;
[0012] FIG. 3 is an axial sectional view of the ring of FIG. 2 in
an apparatus;
[0013] FIG. 4 is a radial sectional view of the ring of FIG. 3 in
the apparatus;
[0014] FIGS. 5A-E are various views of a third embodiment of a
tolerance ring constructed in accordance with the invention;
[0015] FIGS. 6A-E are various views of a third embodiment of a
tolerance ring constructed in accordance with the invention;
and
[0016] FIG. 7 is a schematic sectional side view of another
embodiment of a tolerance ring having corrosion resistance layers
and is constructed in accordance with the invention.
[0017] The use of the same reference symbols in different drawings
indicates similar or identical items.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIG. 1 depicts a tolerance ring 100 comprising one
embodiment. The tolerance ring 100 comprises a band 102 of
resilient material (e.g. spring steel) that is curved into a
ring-like (substantially annular) shape. The ends of the band 102
do not meet (e.g., it may be formed as a split ring), thereby
leaving an axially-extending gap 106 adjacent the circumference of
the band. In other embodiments, the band may be curved so that the
ends overlap with one another. In yet further embodiments, the band
may be a continuous, unbroken ring. The inner surface of the
tolerance ring 100 has a low friction layer 104 that conforms to
the shape of the band.
[0019] The tolerance ring 100 has a plurality of spaced projections
108 that extend radially outward from the outer surface of the
tolerance ring 100. There is a flat, circumferentially-extending
rim 109 of material at each axial end of the projections 108. Each
projection 108 also is separated from its neighboring projections
by a flat section 110 of the tolerance ring 100, which may be
contiguously formed with rims 109. The projections 108 are
axially-elongated ridges that are similar in shape to waves used on
conventional tolerance rings. The peak of each ridge is rounded,
and the axial ends of each ridge terminate at a tapered shoulder
111.
[0020] In some embodiments, the tolerance ring 100 may be formed
from a flat strip of resilient material (which forms the band 102).
Before the strip is bent into its curved shape, and before the
projections are formed, the low friction layer 104 is laminated
onto one surface thereof. In other embodiments, the low friction
layer 104 may be laminated onto both surfaces of the flat strip.
After the low friction layer 104 is attached to the flat strip, the
resulting layer structure is stamped (e.g., pressed using a
suitably shaped mold, rotary wave forming, etc.) to form the
projections 108. Thus, the projections 108 are formed from both the
strip of resilient material and from the low friction layer 104.
The material of the low friction layer 104 may be chosen to be
flexible to facilitate this stamping step. In the embodiment shown
in FIG. 1, the projections 108 project radially outward from the
band 102. In other embodiments they may project radially inward
from the low friction layer 104. After the projections 108 are
formed, the layered structure is curved into the ring-like
configuration shown in FIG. 1. In the embodiment shown, the band
102 is the outer material. In other embodiments, the band 102 may
be the inner material. In still other embodiments the projections
108 may extend radially inward or outward depending on the
particular situation and independently of whether the band 102
provides the inner or outer material for the tolerance ring
100.
[0021] In operation, the tolerance ring 100 is located between two
components. For example, it may be located in the annular space
between a shaft and a bore in a housing. The projections 108 are
compressed between the inner and outer components. Each projection
acts as a spring and deforms to fit the components together with
zero clearance therebetween. In other words, the inner component
contacts the inner surfaces of the tolerance ring and the outer
component contacts the outer surfaces of the tolerance ring.
[0022] If forces (e.g., rotational or linear) are applied to one or
both of the inner and outer components such that there is a
resultant force between the inner and outer components, the inner
and outer components can move relative to each other. Since some
embodiments have zero clearance between the components, there are a
pair of contacting surfaces that slide relative to each other. This
is the slip interface. In some embodiments, the slip interface
occurs at the surfaces of contact between the low friction layer
104 and the inner component (see, e.g., FIG. 3). The surfaces of
contact may include the inner surfaces of the flat rims 109 and the
"footprints" of each projection 108 (i.e., the regions around the
edges of each projection 108 where they meet the band 102). The
material for the low friction layer 104 and the configuration of
the projections 108 provide a slip force at the slip interface that
is substantially lower than an expected value derived from the
radial load force transmitted by the projections. This low slip
force facilitates motion between the moving contact surfaces.
[0023] In contrast, at the surfaces of contact between the outer
component and the outer surfaces of the band 102, there may be
sufficient frictional force to retain the tolerance ring 100 in
place relative to the outer component. In other embodiments, both
surfaces of the band 102 may be laminated with a low friction
layer. Thus, there may be two slip interfaces in such
embodiments.
[0024] FIG. 2 depicts another embodiment of a tolerance ring 200
comprising a band 202 curved into a tubular configuration with an
axial gap 206 in its circumference. In a similar way to FIG. 1, the
inner surface of the band 202 has a low friction layer 204
laminated thereon. The band 202 also has a plurality of projections
208 that extend radially outward from its outer surface. The
projections 208 may circumferentially abut one other as shown, or
be circumferentially spaced-apart as in the embodiment of FIG. 1.
The tolerance ring 200 may be manufactured in a manner as outlined
above, so the low friction layer 204 conforms to the shape of the
band 202, including indentations that match the various undulations
of the projections 208. The tolerance ring 200 includes flat rims
or collars 210 at each axial end of the projections 208.
[0025] The tolerance ring 200 shown in FIG. 2 differs from the one
depicted in FIG. 1 in that, for example, there are fewer
projections around the circumference of the band and there are
virtually no flat spaces between the neighboring projections.
[0026] FIG. 3 depicts an axial sectional view through an apparatus
300 comprising another embodiment. The apparatus 300 incorporates,
for example, the tolerance ring 200 shown in FIG. 2. The apparatus
300 comprises a housing 302 or outer component. The housing 302 has
an axial bore 304 formed therein, which receives a shaft 306 or
inner component. Tolerance rings may be used to transfer torque or
as torque limiters in such applications.
[0027] An annular gap exists between the outer surface 308 of shaft
306 and the inner surface 310 of bore 304. The size of this annular
gap is variable because the diameter of the shaft 306 and bore 304
may vary within manufacturing tolerances. To prevent vibration of
the shaft 306 within the bore 304, the annular gap is filled by
tolerance ring 200 to form a zero-clearance fit between the
components. FIG. 3 shows that the tolerance ring 200 comprises a
band 202 as an outer layer and a low friction layer 204 as an inner
layer that conforms to the shape of band 202. In use, the
circumferential projections 208 of the tolerance ring 200 are
radially compressed in the annular gap between the shaft 306 and
housing 302, such that the band 202 contacts the inner surface 310
of the bore 304. The slip interface is formed where the low
friction layer 204 contacts the outer surface 308 of the shaft 306.
The tolerance ring 200 therefore reduces the gap to zero so there
is no clearance between the components in apparatus 300.
[0028] The contact area between outer surface 308 and low friction
layer 204 is a slip interface at which relative motion between the
shaft 306 and the tolerance ring 200 occurs. The tolerance ring 200
is secured relative to the housing 302 by frictional engagement at
the contact area between the band 202 and the inner surface
310.
[0029] If, through use, wear of the shaft 306 or low friction layer
204 occurs at the slip interface, the projections 208 may
compensate by resiliently moving toward their rest state, thereby
maintaining contact with the shaft 306 and housing 302. The
lifetime of tolerance ring 200 may therefore be superior to
conventional, zero clearance tolerance rings without resiliently
compressible projections.
[0030] FIG. 4 illustrates a radial sectional view of the apparatus
comprising housing 302 and shaft 306. In the embodiment shown, the
tolerance ring 200 is retained on the shaft 306. The outer diameter
of the shaft 306 is greater than an inner diameter of the tolerance
ring 200 at rest. Thus, the tolerance ring must expand (axial gap
206 (FIG. 2) must widen) to fit the tolerance ring around the
surface 308 of the shaft. Inside the bore 304 of housing 302, the
projections 208 are compressed in the annular gap or space between
the components at inner surface 310. In this configuration, the
coefficient of friction at the slip interface (between shaft 306
and low friction layer 204) is very small compared to the
coefficient of friction at the contact area between the band 202
and housing 302. Thus, slipping is substantially limited to and
occurs substantially freely at the slip interface. In other
embodiments, the arrangement of the projections 208 and low
friction layer 204 may be such that the slip interface is between
the housing 302 and the tolerance ring 200.
[0031] FIGS. 5A-E depict various perspective, sectional, axial end
and side views of another embodiment of a tolerance ring 500.
Tolerance ring 500 comprises a band 502 curved into a tubular
configuration with an axial gap 506 in its circumference. The inner
surface of the band 502 has a low friction layer 504 laminated
thereon. The band 502 also has a plurality of projections 508 that
extend radially inward. The tolerance ring 500 may be manufactured
as described herein, so the low friction layer 504 has a uniform
thickness and conforms to the shape of the band 502, including
indentations that match the various undulations of the projections
508. The tolerance ring 500 may include tapered shoulders 511 and
flat circumferential rims or collars 509 at each axial end of the
projections 508, as well as flat spaces 510 between projections
508.
[0032] FIGS. 6A-E depict views of yet another embodiment of a
tolerance ring 600. The tolerance ring 600 comprises a band 602 of
resilient material that is curved into an annular) shape. In the
embodiment shown, the ends of the band 602 do not meet and leave a
gap 606, but it may be formed as a continuous ring. The inner
surface of the tolerance ring 600 has a low friction layer 604
laminated thereon, such as PTFE, which conforms to the band
602.
[0033] The tolerance ring 600 has a plurality of spaced projections
608 that extend radially outward from the outer surface of the
tolerance ring 600. There is a flat, circumferentially-extending
rim 609 at each axial end of the projections 608. Each projection
608 also is separated from its neighboring projections by a flat
section 610, which may be contiguously formed in a planar fashion
with rims 609. The projections 608 are axially-elongated ridges,
with the peak of each ridge being rounded, and the axial ends of
each ridge terminating at a tapered shoulder 611.
[0034] In some embodiments, the tolerance ring 600 may be formed
from a flat strip of resilient material as band 602). Before the
strip is bent into its curved shape, and before the projections are
formed, the low friction layer 604 is laminated onto one surface
thereof. In other embodiments, the low friction layer 604 may be
laminated onto both surfaces of the flat strip. After the low
friction layer 604 is attached, the resulting layered structure is
stamped to form the projections 608. Thus, the projections 608 are
formed from both the strip of resilient material 602 and from the
low friction layer 604. The material of the low friction layer 604
may be chosen to be flexible to facilitate this stamping step.
Although the projections 608 project radially outward from the band
602, they may project radially inward from the low friction layer
604. After the projections 608 are formed, the layered structure is
curved into the ring-like configuration. In the embodiment shown,
the band 602 is the outer material, but it may be the inner
material. In still other embodiments the projections 608 may extend
radially inward or outward depending on the particular situation
and independently of whether the band 602 provides the inner or
outer material for the tolerance ring 600.
[0035] In some embodiments for overload protection applications,
tolerance rings with torque overload protection forces of, for
example, less than 25 Nm and with an overall diameter of less than
40 mm are provided. Applications for these embodiments include, for
example, seat adjusters, hybrid dual clutch mechanisms, seat
headrest adjustment, door actuators, tire winches, etc.
[0036] Still other embodiments provide torque overload protection
forces of, for example, less than 100 Nm at diameters greater than
65 mm, such as for applications including starter motors, power
train applications, etc. These designs may utilize a stainless
steel band with a thickness of less than 0.40 mm in some
embodiments. Other embodiments may include diameters of, e.g., 40
to 65 mm with intermediate ranges of torque overload protection.
Moreover, no lubricant is required, which is particularly
advantageous for applications that must be grease-free for either
technical or aesthetic reasons.
[0037] In some embodiments, the tolerance ring is formed from
spring steel (e.g., cold rolled stainless steel) and has had a low
friction layer laminated thereto. For example, the stainless steel
may be 0.1 to 0.7 mm thick, and the low friction may be in a range
of about 0.05 to 0.50 mm thick (e.g., 0.25 mm) and bonded to the
steel before the tolerance ring is formed into its circular
shape.
[0038] The tolerance ring may be formed with geometrical wave that
are designed to achieve spring characteristics as required for the
particular force control application intended. The low friction
layer lowers the sliding forces, reduces force variation, and
provides a low friction slip surface that withstands many slips
without wear on the underlying materials. This allows tolerance
rings to be designed to fulfill force control functions not
possible within the usual envelope of performance achieved by
variation of tolerance ring geometry alone, such as low slip
torque, low sliding force, with little force degradation over many
slip cycles. For example, a tolerance ring in accordance with the
invention reduces sliding force or torque to approximately one-half
to one-third of what would be expected for an equivalent design,
metal-only tolerance ring. As a result, the embodiments disclosed
herein are much more stable than prior art designs.
[0039] In this disclosure, slip torque is defined as the torque at
which two components that are joined by a tolerance ring begin to
rotate with respect to each other due to any applied torque loading
to the system. The tolerance ring fixing will hold the mating
components together without relative rotation until this threshold
value is reached, at which point the frictional forces generated by
compression of the tolerance ring waves will be overcome and
respective rotation will occur, resisted by the frictional forces.
Similarly, axial sliding force is the same thing, but in an axial
direction. The tolerance ring will only permit axial sliding
between two components if the threshold force value is exceeded.
The threshold force is generated by the frictional forces generated
by compression of the tolerance ring waves. Overload protection
force, or torque, occurs where the tolerance ring slip torque or
sliding force is set to be below the safe capacity of the system.
The tolerance ring permits slippage if the system receives an
external load, above the threshold value, that may otherwise have
caused damage to the system.
[0040] Accordingly, embodiments of the tolerance ring waves have a
greater height than the radial space into which they are to be
assembled. Thus, as a result of assembly, the waves are compressed
and exert a force dependent on their stiffness and the amount of
compression, which is how they generate the force to hold the
assembly together.
[0041] Typically, the mating components of the assembly and the
tolerance ring waves themselves have dimensional variability within
given tolerances. Thus, the actual amount of compression of the
waves, and hence the forces generated in the assembly, can vary
from assembly to assembly. However, if the waves are compressed
beyond their `elastic zone` they behave progressively more
plastically, limiting further increase in force from any further
compression. This effect is important where tolerance rings provide
sliding force control (either axially or rotationally) to minimize
force variation due to compression variation, where the waves are
designed to be compressed into their `plastic zone.`
[0042] For example, in axial sliding force control applications
requiring low forces, such as axial sliding forces in a range of
about 30 to 300 N (and, in some embodiments, 10 to 600 N) with
component diameters of at least about 10 mm, and in torque
limitation applications requiring slip torque in a range of about 1
to 25 Nm with components of less than about 40 mm diameter and a
radial stiffness that is greater than about 20,000 N/mm, or a slip
torque in a range of about 1 to 100 Nm with component diameters of
more than about 40 mm diameter and a radial stiffness that is
greater than about 20,000 N/mm, it is very difficult to achieve
consistent sliding forces with conventional tolerance ring designs.
To achieve such low forces, thin materials and `weak` wave geometry
are needed in order to approach plastic spring performance,
resulting in very flimsy structures that are difficult to handle
and, once assembled, have very low radial stiffness.
[0043] For example, in one experiment a conventional tolerance ring
comprising a simple steel ring, and a tolerance ring constructed in
accordance with the invention low friction layer on an identical
steel ring were compared. Thus, the steel ring geometry was the
same for both rings, e.g., a 35 mm diameter, a 12 mm width and a
0.2 mm thickness, in which waves (e.g., 9 waves per ring) having a
1 mm height were pressed, with wave-spacing being identical for
both steel rings. The only difference in this experiment was that
the improved tolerance ring also included a PTFE ring having an
additional 0.25 mm thickness, in accordance with the invention.
Thus, the PTFE ring comprised a 0.2 mm steel thickness plus a 0.25
mm PTFE thickness. The spring stiffness for the conventional
steel-only ring and the PTFE-laminated ring were approximately
identical, as the PTFE has very little effect on the shape of the
load deflection curve if the steel wave geometry is maintained. The
sliding forces for these two experimental designs reached 1000 N
for the steel-only tolerance ring, but only 400 N for the
PTFE-laminated ring. Although the steel-only ring had just 0.2 mm
thickness, the sliding forces are much higher because of the higher
friction coefficient without PTFE, and the wear that occurs during
relative motion.
[0044] As another example and comparison of tolerance rings in a
torque slip application, tolerance rings having diameters of 20 mm,
widths of 18 mm, a wave height of 1 mm, and a wave-to-wave spacing
of 7 mm were tested. The application had a target slip torque of 4
Nm. To achieve this target goal, a tolerance ring in accordance
with the invention was formed from a band of stainless steel
material and had a thickness of 0.4 mm, plus a PTFE-laminated layer
with a thickness of 0.25 mm. This embodiment produced the slip
torque of only 4 Nm, but had a very significant radial stiffness to
an externally-applied load of about 50,000 N/mm.
[0045] In contrast, producing a target slip torque of only 4 Nm
with a conventional steel-only tolerance ring required the
thickness of the steel to be reduced to only 0.2 mm. As a
resultant, the radial stiffness of this conventional design was a
mere, by comparison, 12,000 N/mm. Thus, to achieve the target slip
torque, the thickness had to be reduced which rendered a radial
stiffness that was less than a fourth of that achievable by the
present embodiment of the invention. This experiment demonstrates
that embodiments of the invention provide a much stiffer assembly
in low torque slip application, which is particularly important
when external loading is required to be resisted. Moreover, in
practice the conventional metal-only tolerance ring quickly fails
in applications where multiple slips are required, due to the
significant wear on its steel-only contact surfaces.
[0046] Conventional reductions in sliding force also were possible
by reducing the number of waves, spacing the waves further apart,
and/or reducing the raw material thickness to about 0.1 mm to
reduce the stiffness of each wave. None of these conventional
solutions to reducing sliding force are viable. These simple
methods also detrimentally reduce the overall radial stiffness of
the assembly, so the result is far less stable and less able to
withstand external radial loading without undue deflection.
[0047] Maintaining the wave stiffness but reducing the number of
waves results in the same force per wave, so the same wear problems
occur as prior art designs without a low friction layer. Moreover,
reducing the thickness of the steel to 0.1 mm results in a very
flimsy ring that causes significant handling and assembling
difficulties.
[0048] The addition of the low friction material onto the surface
of the tolerance ring on which the sliding occurs has the effect of
lowering the contact friction coefficient and lowering the
resultant sliding forces. For example, the coefficient of friction
provided by the low friction layer may be in a range of about 0.04
to 0.25, and about 0.09 to 0.17 in other embodiments. This design
also avoids wear of the component surfaces during slip, maintaining
sliding forces over many slip cycles. With lowered forces, the
tolerance ring geometry can be made more robust for the same force
levels than would be possible with conventional tolerance rings.
The flow of the low friction material in the contract areas also
has the effect of helping minimize sliding force variation by
plastically deforming within itself, thereby providing a more
consistent force control.
[0049] Applications for such embodiments include, for example,
axial sliding force control (e.g., in steering column
`tube-in-tube` length adjustment sliding mechanisms), torque
overload protection in driven mechanisms (e.g., automotive
applications such as seat positioners, door mechanisms, etc.) The
low friction layer is on the surface of the tolerance ring that is
adjacent to the surface that will slip. It may be on the top or the
bottom of the waves depending on the application and the
configuration of the assembly. Alternative low friction materials
and/or thicknesses may be used depending on the required
properties, such as contract pressures, slip speeds, and desired
lubrication or wear characteristics.
[0050] The low friction layer may comprise many types of materials
including, for example, a polymer, such as a polyketone,
polyaramid, a thermoplastic polyimide, a polyetherimide, a
polyphenylene sulfide, a polyethersulfone, a polysulfone, a
polyphenylene sulfone, a polyamideimide, ultra high molecular
weight polyethylene, a thermoplastic fluoropolymer, a polyamide, a
polybenzimidazole, or any combination thereof. In an example, the
thermoplastic material includes a polyketone, a polyaramid, a
polyimide, a polyetherimide, a polyamideimide, a polyphenylene
sulfide, a polyphenylene sulfone, a fluoropolymer, a
polybenzimidazole, a derivation thereof, or a combination thereof.
In a particular example, the thermoplastic material includes a
polymer, such as a polyketone, a thermoplastic polyimide, a
polyetherimide, a polyphenylene sulfide, a polyether sulfone, a
polysulfone, a polyamideimide, a derivative thereof, or a
combination thereof. In a further example, the material includes
polyketone, such as polyether ether ketone (PEEK), polyether
ketone, polyether ketone ketone, polyether ketone ether ketone
ketone, a derivative thereof, or a combination thereof. An example
fluoropolymer includes fluorinated ethylene propylene (FEP),
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),
perfluoroalkoxy (PFA), a terpolymer of tetrafluoroethylene,
hexafluoropropylene, and vinylidene fluoride (THV),
polychlorotrifluoroethylene (PCTFE), ethylene tetrafluoroethylene
copolymer (ETFE), ethylene chlorotrifluoroethylene copolymer
(ECTFE), or any combination thereof. In an additional example, the
thermoplastic polymer may be ultra high molecular weight
polyethylene. An exemplary solid lubricant may include
polytetrafluoroethylene or a solid lubricant selected from
molybdenum disulfide, tungsten disulfide, graphite, graphene,
expanded graphite, boron nitride, talc, calcium fluoride, cerium
fluoride, or any combination thereof. An exemplary ceramic or
mineral includes alumina, silica, titanium dioxide, calcium
fluoride, boron nitride, mica, Wollastonite, silicon carbide,
silicon nitride, zirconia, carbon black, pigments, or any
combination thereof.
[0051] In some embodiments, the steel side of the tolerance ring
remains stationary against the other surface, in some embodiments.
Retention features such as flanges, tabs, scallops, flares or other
devices may be incorporated to anchor the steel surface to the
mating component to avoid slip.
[0052] In some embodiments, the tolerance ring provides zero
clearance with low slip force for rotational or axial movement. In
one aspect, the tolerance ring combines a low friction layer to
promote slipping with a tolerance ring to provide engagement across
a gap between two components that move relative to each other. The
structure is compressible and presents the additional advantages of
being operable in a variety of gap sizes (e.g., to compensate for
manufacturing variations in the dimensions of the components) and
present a smaller contact area than conventional tolerance rings.
In combination with the low friction layer, this design provides a
significant reduction in frictional forces that oppose relative
motion between the components even when the axial or radial load is
high.
[0053] Another advantage of the tolerance ring structure is its
resilience. Without the low friction layer, wear due to multiple
slips would occur and the sliding force would change. With the low
friction layer, however, wear is prevented. The low friction layer
wears instead of the mating components. The tolerance ring spring
effect takes up the wear in the PTFE, maintaining zero clearance
and helping maintain force levels.
[0054] The ring typically includes one or more flat
circumferentially extending rims, such as at the axial edges of the
ring, and a series of circumferentially spaced-apart projections
extending substantially in radial directions. The projections
extend radially from the ring either outwardly away from the ring,
or inwardly toward the radial center of the ring. The projections
may be discrete formations. They may be regular formations, such as
ridges, waves or fingers. Each projection may comprise a rounded
ridge (e.g., wave) that rises to and falls from a radial peak. In
such embodiments, the force transmitted by the projection is
concentrated in a small region around the edges where it meets the
band (i.e., its "footprint").
[0055] In use, each projection acts as a spring and exerts a radial
force against the components, thereby providing an interference fit
between them. Rotation of the inner or outer component produces
similar rotation in the other component as torque is transmitted by
the ring. Likewise, linear or axial movement of either component
produces similar linear movement in the other component as linear
force is transmitted by the ring.
[0056] It is known to provide tolerance rings that allow slipping
between components in exceptional circumstances. For example, if
relatively high forces (e.g., rotational or linear) are applied to
one or both of the inner and outer components such that the
resultant force between the components is above a threshold value.
In conventional tolerance rings that threshold value is high and is
based on an expected value based on the radial load force
experienced by the ring.
[0057] According to one aspect, there may be provided a system
comprising an inner component, an outer component arranged to
receive the inner component, and a tolerance ring mounted between
the inner and outer components to effect mating engagement
therebetween. The tolerance ring may comprise a deformable band of
a first material, the band having a flat circumferentially
extending rim and a plurality of circumferentially spaced radially
extending projections, and a low friction layer of a second
material having a lower coefficient of friction than the first
material to provide a slip interface to permit relative motion
between the inner and outer components. In use, the band provides a
zero clearance fit between the inner and outer components by
transmitting a load force therebetween. However, the low friction
layer functions to reduce frictional force at the slip interface
such that a slip force required to move the inner and outer
components relative to each other is significantly less than an
expected value derived from the load force.
[0058] The flat rim of the band may provide a circumferentially
extending contact surface with one of the inner and outer
components. A consistent region of contact around the circumference
of the tolerance ring can improve control over the slip force.
There may be two or more rims on the band, with multiple bands of
waves in some embodiments. A rim may be provided at each axial end
of the tolerance ring, with the projections being located between
the rims.
[0059] The projections may be arranged to project away from the rim
to provide a plurality of discrete contact surfaces with the other
of the inner and outer components. The projections may be
configured to deform. This may include elastic deformation at the
discrete contact surfaces to transmit the load force radially
through the tolerance ring between the inner and outer components.
The shape and size of each projection may be selected based on the
particular application. The slip force may depend on the shape of
the projections. Typically, tolerance ring projections or waves are
capable of transmitting relatively high radial forces (e.g., 200 N
or more) to locate stably and provide radial stiffness between the
inner and outer component. Each projection comprises a footprint
region where its edges meet the band. The slip interface may be at
the load transfer point between a footprint region and one of the
inner and outer components. For example, this may occur between the
tolerance ring and the one of the inner and outer components that
contacts the rims. The area of the footprint region may be
relatively small, which, in combination with the low friction
layer, reduces the frictional forces.
[0060] In some embodiments, the projections are self-contained
structures. For example, each projection may comprise a
circumferentially extending rounded ridge with tapered shoulders at
its axial ends. When the tolerance ring is mounted on the inner or
outer component in a pre-assembly, the tapered shoulders act as
guides to aid axial installation of the other component.
[0061] The projections are carefully selected and designed for
their force transfer or spring properties. The geometry of the
projections is selected to provide desired elastic/plastic
deformation characteristics. The deformation characteristics are
selected not only to take account of the manufacturing tolerances
of the inner and outer components, but also to compensate for
differential thermal expansion and wear that may occur between
dissimilar components in operation, thus ensuring the desired
performance is achieved throughout. These designs are applicable to
zero clearance tolerance rings to ensure that the assembled
components do not become loose at elevated temperatures.
[0062] In use, the band of the tolerance ring may deform
elastically when mounted on one of the components as a
pre-assembly. When the other of the components is mounted on the
pre-assembly, thereby compressing the ring in the gap between the
components, preferably only the projections deform. This
deformation may be elastic or plastic, depending on the shape
and/or profile of the projections and the size of the gap. If only
the projections deform in this way, the force transmitting contact
area at the slip interface is not substantially altered when the
ring is compressed. This enables a consistent slip force to be
achieved.
[0063] The low friction layer may be integral with or attached to
the band, and conforms in shape to the band. For example, the low
friction layer mold with and match the projections on the band.
This feature enables a compact construction. The low friction layer
comprises a series of discrete patches attached to or laminated on
the band. For example, the low friction layer may be provided at
contact points at the slip interface. In one embodiment, patches of
low friction material are attached to the band at the footprint
regions and the rims. The band may be exposed where there is no
contact at the slip interface.
[0064] The low friction layer may be attached to a surface of the
band facing the inner or outer component. The low friction layer
may be coated or bonded to the band. In one embodiment, the low
friction layer is laminated on the surface of the band. Laminating
the low friction layer provides an even thickness around the band
to avoid thin patches that may occur if the layer is coated by
immersing the band in a liquid form of the second material and
spinning or otherwise shaking off the excess.
[0065] In some embodiments, the tolerance ring is secured on one of
the inner or outer components, whereby the slip interface is
between the ring and the other of the components. For example, the
tolerance ring may be secured or retained by resilient gripping of
the band on the inner component. In this example, the low friction
layer is provided only on the inner surface of the band and the
projections may extend radially outwardly from the band, e.g.,
toward the outer component. With this arrangement, the slip
interface is at the contact area between the inner surface of the
tolerance ring and the inner component, where the footprints of the
projections and the rims of the tolerance ring contact the inner
component.
[0066] The tolerance ring is secured by frictional engagement of
the band on one of the components. In split ring embodiments, the
split ring is resilient so as to grip one component (e.g., a shaft)
that is larger than its diameter, or expand outward against an
outer component (e.g., a bore in a housing) that is smaller than
its diameter. It may be desirable to permit relative movement
between the inner and outer components in only one sense (e.g.,
rotational or axial). In this case, the tolerance ring may be
mechanically constrained with respect to one of the components to
prevent relative movement at the slip interface in the undesired
sense. For example, the tolerance ring may clip into an external
groove on the outer surface of a shaft. The edges of the groove
prevent axial movement of the tolerance ring relative to the shaft.
If the slip interface is provided on the inner surface of the
tolerance ring, relative axial movement of the shaft and bore at
that interface is prevented and must instead occur at the outer
surface of the tolerance ring. The outer surface may not have the
low friction layer and may therefore provide more resistance to
relative motion.
[0067] The band may comprise a resilient split ring, such as an
open loop of material extending partly around the perimeter of the
inner component. The configuration of projections may be
symmetrical around the circumference of the ring with respect to
the split. This arrangement may be particularly stable.
[0068] The inner component may be a shaft and the outer component
may be a housing having a bore for receiving the shaft. The
tolerance ring extends around the perimeter of the shaft to engage
the outer surface of the shaft and the inner surface of the bore.
As mentioned above, the band may extend entirely around the
perimeter of the shaft or only partly around the shaft.
[0069] The apparatus also may include a drive unit arranged to
cause relative rotation between the shaft and the housing, wherein
the ring is arranged to permit circumferential slipping between the
outer surface of the shaft and the inner surface of the bore.
[0070] The low friction layer may have substantially the same
circumferential extent as the band. The low friction layer may be
provided at all contact points between the ring and inner/outer
component at the slip interface. The band therefore does not
contact the component that is moving relative to it at the slip
interface, which can reduce friction.
[0071] Each indentation may be located opposite a projection. For
example, the projections may be formed by stamping, pressing or
roll-forming a strip of material such that indentations are
automatically formed in the backside of the strip when the
projections are made.
[0072] Where the projections are self-contained, discrete
structures having walls that enclose a volume when mounted between
the inner and outer components, they may retain any grease applied
before assembly and reduce or minimize subsequent leakage.
[0073] According to another aspect, there may be provided a
tolerance ring for mounting between inner and outer components to
effect mating engagement therebetween. The ring comprises a
deformable band of a first material, the band having a flat
circumferentially extending rim and a plurality of
circumferentially-spaced, radially-extending projections, and a low
friction layer of a second material having a lower coefficient of
friction than the first material to provide a slip interface to
permit relative motion between the inner and outer components. The
ring may have any of the features discussed above with respect to
other aspects.
[0074] According to still another aspect, there may be provided a
method of forming a tolerance ring for mounting between components
to effect mating engagement therebetween, the method comprising:
attaching a layer of slip material to a strip of base material to
form a layered structure, the slip material having a lower
coefficient of friction than the base material; forming a plurality
of spaced projections across the layered structure adjacent to a
flat region; bending the layered structure to form a ring, wherein
the flat region becomes a circumferentially-extending rim and the
plurality of projections extend radially from the layered
structure.
[0075] The base material again may be material suitable for forming
a tolerance ring, such as spring steel or the like. The slip
material may be laminated on to the base material to attach it
thereto. Laminating has an advantage in some applications because
the attached layer has a consistent thickness. The thickness of the
laminated layer may be selected to ensure that material performance
does not degrade if there is any wear at the slip interface. The
slip material may be any material suitable for forming the low
friction layer discussed above. The plurality of projections may be
formed by stamping, pressing or roll-forming the layered
structure.
[0076] Embodiments also are distinguished over conventional designs
that merely change the pitch and/or depth of their corrugations to
achieve a degree of resilience to avoid excessive torque. With
embodiments of the present tolerance ring, the design operates
within a well-defined torque band (e.g., with maximum and minimum
values) to functionally provide a defined amount of controlled
resistance. This design provides a means of torque or axial force
limitation within defined bands. Thus, it provides a high degree of
precise control of force, rather than a mere specification of
resilience for radial compensation. Embodiments of the tolerance
ring combine specific spring characteristics of the metallic band
with the friction and wear characteristics of a selected low
friction layer, into a tolerance ring that extends the performance
envelope of tolerance designs into the precise bandwidth control of
lower force, multi-slip applications that previously were not
possible.
[0077] FIG. 7 is a sectional view of another embodiment
illustrating various layers of a corrosion resistant tolerance ring
700. Tolerance ring 700 can include a load bearing substrate 702,
such as a metallic support layer (e.g., an annular band). The
metallic support layer can include a metal or metal alloy such as
steel including carbon steel, spring steel, and the like, iron,
aluminum, zinc, copper, magnesium, or any combination thereof. The
load bearing substrate 702 may be coated with temporary corrosion
protection layers 704 and 706 to prevent corrosion of the load
bearing substrate prior to processing. Additionally, a temporary
corrosion protection layer 708 can be applied over layer 704.
[0078] Each of layers 704, 706, and 708 can have a thickness of
about 1 to 50 microns, such as about 7 to 15 microns. Layers 704
and 706 can include a phosphate of zinc, iron, manganese, or any
combination thereof, or a nano-ceramic layer. Further, layers 704
and 706 can include functional silanes, nano-scaled silane based
primers, hydrolyzed silanes, organosilane adhesion promoters,
solvent/water based silane primers, chlorinated polyolefins,
passivated surfaces, commercially available zinc
(mechanical/galvanic) or zinc-nickel coatings, or any combination
thereof. Layer 708 can include functional silanes, nano-scaled
silane based primers, hydrolyzed silanes, organosilane adhesion
promoters, solvent/water based silane primers. Temporary corrosion
protection layers 704, 706, and 708 can be removed or retained
during processing.
[0079] A low friction or sliding layer 710 may be applied to the
load bearing substrate 702, such as with an adhesive layer 712 or
other means as described herein. The sliding layer 710 may comprise
the materials described herein. Additionally, sliding layer 710 can
include fillers, such as a friction reducing filler. Examples of
fillers that can be used in the sliding layer 710 include glass
fibers, carbon fibers, silicon, graphite, PEEK, molybdenum
disulfide, aromatic polyester, carbon particles, bronze,
fluoropolymer, thermoplastic fillers, silicon carbide, aluminum
oxide, polyamideimide (PAI), PPS, polyphenylene sulfone (PPSO2),
liquid crystal polymers (LCP), aromatic polyesters (Econol), and
mineral particles such as wollastonite and barium sulfate, or any
combination thereof. Fillers can be in the form of beads, fibers,
powder, mesh, or any combination thereof.
[0080] In some embodiments, the sliding layer may include a woven
mesh or an expanded metal grid. The woven mesh or expanded metal
grid can include a metal or metal alloy such as aluminum, steel,
stainless steel, bronze, or the like. Alternatively, the woven mesh
can be a woven polymer mesh. In an alternate embodiment, the
sliding layer may not include a mesh or grid. In another alternate
embodiment, the woven mesh or expanded metal grid may be embedded
between two adhesive layers.
[0081] The adhesive layer 712 may comprise a hot melt adhesive.
Examples of adhesives that can be used in adhesive layer 712
include fluoropolymers, an epoxy resins, a polyimide resins, a
polyether/polyamide copolymers, ethylene vinyl acetates, Ethylene
tetrafluoroethylene (ETFE), ETFE copolymer, perfluoroalkoxy (PFA),
or any combination thereof. Additionally, the adhesive layer 712
can include at least one functional group selected from --C.dbd.O,
--C--O--R, --COH, --COOH, --COOR, --CF.sub.2=CF--OR, or any
combination thereof, where R is a cyclic or linear organic group
containing between 1 and 20 carbon atoms. Additionally, the
adhesive layer 712 can include a copolymer. In an embodiment, the
hot melt adhesive can have a melting temperature of not greater
than about 250.degree. C., such as not greater than about
220.degree. C. In another embodiment, the adhesive layer 712 may
break down above about 200.degree. C., such as above about
220.degree. C. In further embodiments, the melting temperature of
the hot melt adhesive can be higher than 250.degree. C., even
higher than 300.degree. C.
[0082] On an opposing surface of the load bearing substrate 702
from sliding layer 710, a corrosion resistant coating 714 can be
applied. The corrosion resistant coating 714 can have a thickness
of about 1 to 50 microns, such as about 5 to 20 microns, and such
as about 7 to 15 microns. The corrosion resistant coating can
include an adhesion promoter layer 716 and an epoxy layer 718. The
adhesion promoter layer 716 can include a phosphate of zinc, iron,
manganese, tin, or any combination thereof, or a nano-ceramic
layer. The adhesion promoter layer 716 can include functional
silanes, nano-scaled silane based layers, hydrolyzed silanes,
organosilane adhesion promoters, solvent/water based silane
primers, chlorinated polyolefins, passivated surfaces, commercially
available zinc (mechanical/galvanic) or Zinc-Nickel coatings, or
any combination thereof.
[0083] The epoxy layer 718 can be a thermal cured epoxy, a UV cured
epoxy, an IR cured epoxy, an electron beam cured epoxy, a radiation
cured epoxy, or an air cured epoxy. Further, the epoxy resin can
include polyglycidylether, diglycidylether, bisphenol A, bisphenol
F, oxirane, oxacyclopropane, ethyleneoxide, 1,2-epoxypropane,
2-methyloxirane, 9,10-epoxy-9,10-dihydroanthracene, or any
combination thereof. The epoxy resin can include synthetic resin
modified epoxies based on phenolic resins, urea resins, melamine
resins, benzoguanamine with formaldehyde, or any combination
thereof. By way of example, epoxies can include
##STR00001##
or any combination thereof, wherein C.sub.XH.sub.YX.sub.ZA.sub.U is
a linear or ramified saturated or unsaturated carbon chain with
optionally halogen atoms X.sub.Z substituting hydrogen atoms, and
optionally where atoms like nitrogen, phosphorous, boron, etc, are
present and B is one of carbon, nitrogen, oxygen, phosphorous,
boron, sulfur, etc.
[0084] The epoxy resin can further include a hardening agent. The
hardening agent can include amines, acid anhydrides, phenol novolac
hardeners such as phenol novolac poly[N-(4-hydroxyphenyl)maleimide]
(PHPMI), resole phenol formaldehydes, fatty amine compounds,
polycarbonic anhydrides, polyacrylate, isocyanates, encapsulated
polyisocyanates, boron trifluoride amine complexes, chromic-based
hardeners, polyamides, or any combination thereof. Generally, acid
anhydrides can conform to the formula R--C.dbd.O--O--C.dbd.O--R'
where R can be C.sub.XH.sub.YX.sub.ZA.sub.U as described above
Amines can include aliphatic amines such as monoethylamine,
diethylenetriamine, triethylenetetraamine, and the like, alicyclic
amines, aromatic amines such as cyclic aliphatic amines, cyclo
aliphatic amines, amidoamines, polyamides, dicyandiamides,
imidazole derivatives, and the like, or any combination thereof.
Generally, amines can be primary amines, secondary amines, or
tertiary amines conforming to the formula R.sub.1R.sub.2R.sub.3N
where R can be C.sub.XH.sub.YX.sub.ZA.sub.U as described above.
[0085] In an embodiment, the epoxy layer 718 can include fillers to
improve the conductivity, such as carbon fillers, carbon fibers,
carbon particles, graphite, metallic fillers such as bronze,
aluminum, and other metals and their alloys, metal oxide fillers,
metal coated carbon fillers, metal coated polymer fillers, or any
combination thereof. The conductive fillers can allow current to
pass through the epoxy coating and can increase the conductivity of
the coated bushing as compared to a coated bushing without
conductive fillers.
[0086] In an embodiment, an epoxy layer can increase the corrosion
resistance of the bushing. For example, epoxy layer 718 can
substantially prevent corrosive elements, such as water, salts, and
the like, from contacting the load bearing substrate, thereby
inhibiting chemical corrosion of the load bearing substrate.
Additionally, the epoxy layer can inhibit galvanic corrosion of
either the housing or the load bearing substrate by preventing
contact between dissimilar metals. For example, placing an aluminum
bushing without the epoxy layer within a magnesium housing can
cause the magnesium to oxidize. However, epoxy layer 718 can
prevent the aluminum substrate from contacting the magnesium
housing and inhibit corrosion due to a galvanic reaction.
[0087] This written description uses examples, including the best
mode, and also to enable those of ordinary skill in the art to make
and use the invention. The patentable scope of the invention is
defined by the claims, and may include other examples that occur to
those skilled in the art. Such other examples are intended to be
within the scope of the claims if they have structural elements
that do not differ from the literal language of the claims, or if
they include equivalent structural elements with insubstantial
differences from the literal languages of the claims. For example,
embodiments may relate to rotational devices such as an electric
motor, such as a windshield wiper motor), or axial sliding
applications, such as a steering column adjustment mechanism.
[0088] While embodiments have been shown or described in only some
of forms, it should be apparent to those skilled in the art that
they are not so limited, but are susceptible to various changes
without departing from the scope of the invention.
* * * * *