U.S. patent number RE33,696 [Application Number 07/536,697] was granted by the patent office on 1991-09-24 for composite spring.
This patent grant is currently assigned to The Paton Corporation. Invention is credited to Andrew Stevenson.
United States Patent |
RE33,696 |
Stevenson |
September 24, 1991 |
Composite spring
Abstract
The spring includes a tubular elastomeric body, preferably
rubber, and a coil spring embedded in and bonded to it. The coil
spring controls the occurence of symmetric bulging instablity in
the body under axial load conditions. This bulging instability
occurs sequentially along the length of the body between adjacent
coils of the coil spring until it assumes the form of a continuous
coil of elastomer.
Inventors: |
Stevenson; Andrew (Hertford,
GB2) |
Assignee: |
The Paton Corporation (Seattle,
WA)
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Family
ID: |
27495899 |
Appl.
No.: |
07/536,697 |
Filed: |
June 12, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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886753 |
Jul 14, 1986 |
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680841 |
Dec 12, 1984 |
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Reissue of: |
149944 |
Jan 28, 1988 |
04817921 |
Apr 4, 1989 |
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Current U.S.
Class: |
267/33; 248/621;
248/634; 267/152; 267/140.4; 280/124.165; 280/124.179;
280/124.177 |
Current CPC
Class: |
F16F
3/12 (20130101); B60G 11/52 (20130101) |
Current International
Class: |
B60G
11/52 (20060101); B60G 11/32 (20060101); F16F
3/12 (20060101); F16F 3/00 (20060101); F16F
003/10 () |
Field of
Search: |
;267/33,140.4,152
;248/621,634 ;280/697,715 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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45497 |
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Feb 1982 |
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EP |
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662622 |
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Jul 1938 |
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DE2 |
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24676 |
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Feb 1977 |
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JP |
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118344 |
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Feb 1983 |
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JP |
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755186 |
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Aug 1956 |
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GB |
|
755808 |
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Aug 1956 |
|
GB |
|
1437525 |
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May 1976 |
|
GB |
|
Primary Examiner: Halvosa; George E. A.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Parent Case Text
This application is a continuation of application Ser. No. 886,753,
filed July 14, 1986, now abandoned, which is a continuation of
application Ser. No. 680,841, filed Dec. 12, 1984, now abandoned.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A spring having a force vs. deflection curve with a constant
rate region which persists for about the initial 20% of its
columnar deflection, a rising rate region which persists for about
the last 40% of its columnar deflection, and an intermediate
plateau region, said spring comprising: an elongated tubular
elastomeric body having a generally straight sided longitudinal
profile and a matching inner surface under zero columnar
deflection, and a coil spring embedded in said body for controlling
deformation of said body such that said plateau region persists for
a substantial portion of such columnar deflection so long as the
occurrence of a series of symmetric bulging instabilities at a
plurality of locations spaced apart along the length of said body
under a predetermined axial load condition, said body and said coil
spring being constructed and arranged according to the following:
##EQU3## where S=stability factor
E=reinforcing efficiency factor
H=total axial length of said body,
n=the total number of coils of said coil spring,
r=the internal radius of said body,
R=the external radius of said body,
(R-r)=the wall thickness of said body, and
t=the wire diameter of the coils of said coil spring,
wherein the value of S is between about 0.05 and 0.2 and the value
of E is between about 0.05 and .[.0.2.]. .Iadd.3. .Iaddend.
2. The spring of claim 1, wherein said bulging instability assumes
the form of a continuous coil of elastomer.
3. The spring of claim 1, wherein said coil spring is bonded to
said body.
4. The spring of claim 1, wherein the ratio of R/2H is less than
about 0.1.
5. The spring of claim 1, wherein said body is composed of a
material having a hardness selected in relation to said
predetermined load condition.
6. The spring of claim 1, wherein said body is composed of a
natural rubber compound.
7. The spring of claim 6, wherein said compound is
precompressed.
8. The spring of claim 6, wherein the ends of said body are
constructed and arranged with respect to the direction of force
application.
9. A spring having a force vs. deflection curve with a constant
rate region which persists for about the initial 20% of its
columnar deflection, a rising rate region which persists for about
the last 40% of its columnar deflection, and an intermediate
plateau region, said spring comprising:
an elongated tubular elastomeric body having first and second
longitudinal ends and substantially concentric inner and outer wall
surfaces extending between said first and second ends, said inner
and outer wall surfaces defining therebetween a body having a
minimum thickness at a longitudinally intermediate position and
having a progressively greater thickness proceeding toward each of
said first and second ends under zero columnar deflection; and
a coil spring embedded in said body controlling deformation of said
body such that said plateau region persists for a substantial
portion of such columnar deflection so long as the occurrence of a
series of symmetric bulging instabilities at a plurality of
locations spaced apart along the length of said body under a
predetermined axial load condition, the occurrence of said bulging
instabilities commencing proximate said intermediate position of
said body;
wherein said body and said coil spring are constructed and arranged
according to the following: ##EQU4## where S=stability factor,
E=reinforcing efficiency factor,
H=total axial length of said body,
n=the total number of coils of said coil spring,
r=the internal radius of said body,
R=the external radius of said body,
(R-r)=the wall thickness of said body, and
t=the wire diameter of the coils of said coil spring, wherein the
value of S is between about 0.05 and 0.2 and the value of E is
between about 0.05 and .[.0.2.]. .Iadd.3. .Iaddend.
10. A spring having a three part spring curve made up of a constant
rate region, a rising rate region and an intermediate plateau
region, said spring comprising: an elongated tubular elastomeric
body having a wall thickness at one location along its length which
is less than its wall thickness at another location spaced from
said location; a coil spring embedded in said body; said body and
said coil spring being constructed and arranged according to the
following: ##EQU5## where S=stability factor,
E=reinforcing efficiency factor,
H=total axial length of said body,
n=the total number of coils of said coil spring,
r=the internal radius of said body,
R=the external radius of said body,
(R-r)=the wall thickness of said body, and
t=the wire diameter of the coils of said coil spring,
wherein the value of S is between about 0.05 and 0.2 and the value
of E is between about 0.05 and .[.0.2.]. 3.
11. The spring of claim 10, wherein the ratio of R/2H is less than
about 0.1.
Description
BACKGROUND OF THE INVENTION
This invention relates to composite springs and, more particularly,
to composite springs made up of natural rubber or other elastomer
in combination with a coil spring or other reinforcement. At used
herein, the term "stiff" refers to those portions of the force
versus deflection curve of the composite spring that are of
relatively high spring rate, whether constant slope or generally
rising rate and is characteristic of progressively increasing
resistance to compressive deformation. The term "soft" refers to
and is characteristic of relatively lower spring rate or less
resistance to compressive deformation, whether increasing,
decreasing or none at all.
In the past, composite springs of this type have provided
force/deflection curves in which the spring is soft near the middle
of the curve and is stiff at each end. This result is obtained by
controlling deformation of the elastomer spring element under
certain conditions in which it is deformable according to different
but essentially stable characteristics. One example of such a
composite spring is found in the U.S. Pat. No. 2,605,099 by Brown.
This composite spring is made up of a rubber envelope that has an
undulatory wall section reinforced by and bonded to a steel spring.
Another generally similar composite spring is found in U.S. Pat.
No. 2,822,165 by Boschi.
The principle drawback of these composite springs is that the soft
region of the force/deflection curve, if any, is of very limited
duration. This is unsatisfactory in some applications in which it
is desireable to have a soft region of extended duration. One, but
not the only such application, is for vehicular suspension systems
and, in particular, suspension systems for automotive vehicles.
This is so because ride comfort often is associated with the ride
characteristics that are derived from the soft region of the
force/deflection curve of the suspension springs.
SUMMARY OF THE INVENTION
Accordingly, the principal object of this invention is to provide a
composite spring having a force/deflection curve with a "soft"
region of extended duration.
Another object of this invention is to provide a composite spring
in which the force/deflection curve is controllable to provide
selected "stiff" and "soft" regions in accordance with specific
requirements, particularly the provision of "soft" load bearing
characteristics over an extended deflection range at a
predetermined load.
Another object of this invention is to provide a composite spring
of the kind just mentioned that is "tunable" so that it can be
adapted easily to the force, deflection and other requirements of
specific applications.
These objects are achieved in accordance with principles of this
invention by providing a composite spring that comprises a tubular
elastomeric body and means for controlling deformation of the body
such that the force/deflection curve has two stiff regions, each
characterized by essentially stable compression of the body, and an
intermediate soft region characterized by unstable but symmetric
deformation of the body, preferably in the form of lateral bulging.
This instability occurs sequentially at predetermined locations
spaced apart along the length of the body until, in one preferred
embodiment, it assures the form of a continuous coil of elastomer.
Thus it is possible, by controlling the occurrence of this bulging
instability, to "tune" the composite spring so that its soft region
appears when and persists so long as desired for particular ride
characteristics or other specific requirements.
These and other features, objects and advantages of the present
invention will become apparent from detailed description and the
claims to follow, taken in conjunction with the accompanying
drawings in which like parts bear like reference numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph of force vs. deflection of one presently
preferred embodiment of the composite spring of this invention;
FIG. 2 is a side evelation, partially in longitudinal section, of
one presently preferred embodiment of the composite spring of this
invention, depicting it in its relaxed (no load) position;
FIG. 3 is a side elevation generally similar to FIG. 2, depicting
the FIG. 2 spring under axial load during the formation of
symmetric bulging instability;
FIG. 4 is a side elevation generally similar to FIG. 2, depicting
the FIG. 2 spring under axial load at the completion of the
formation of symmetric bulging instability;
FIG. 5 is a longitudinal section of one intracoil segment of the
FIG. 2 spring, depicting the manner in and the extent to which its
inner and outer walls bulge under axial load;
FIG. 6 is a graph of force vs. deflection of a FIG. 5 segment;
FIG. 7 is a graph of force vs. deflection of five FIG. 5 segments;
and
FIG. 8 is a graph of force vs. deflection of a first examplary
embodiment of the FIG. 2 spring.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 2, one presently preferred embodiment of the
composite spring of this invention is comprised of a tubular
elastomeric body 10 and reinforcement means in the form of a coil
spring 12 embedded in and bonded to the body for controlling
deformation of the body such that the spring's force/deflection
curve has two stiff regions, each characterized by essentially
stable compression of the body, and an intermediate soft region
characterized by unstable but symmetric bulging of the body.
Referring to FIG. 1, a typical force/deflection curve such as that
just described includes a lower stiff region 14 in which stiffness
is proportional to the shear modulus of the material forming body
10. In this region, essentially only uniaxial compression of the
body occurs, giving rise to a generally constant slope curve
approximating a linear spring rate. The force/deflection curve
further includes an upper stiff region 16 in which stiffness is
proportional to the shear modulus, but also is influenced by other
factors, as will be described. In this region the body is under
compression but, unlike region 14, the spring rae is of rising
rate. In both regions 14 and 16, however, the body is deformed
under conditions of essentially stable compression.
This invention stems from the discovery that, by causing instead of
preventing instability, an intermediate soft region 18 (FIG. 1) of
extended duration may be obtained, provided the instability is
controlled so that it is localized and symmetric; that is, so that
the body does not undergo columnar or other asymmetric buckling.
(The terms "symmetric" and "asymmetric" have as a reference the
longitudinal axis of the body 10.) This control is accomplished by
the coil spring 12. Being embedded in and bonded to the body 10
this spring restrains the cylindrical body wall from bulging along
a helical path 19 (FIGS. 3 and 4) that coincides with the
individual coils of spring 2. The body is free to bulge laterally,
however, in the axial spaces between adjacent convolutions of path
19 body (or between the individual coils of spring 12) at the
intervals corresponding to the pitch of spring 12. Thus, the
composite spring appears as a rubber coil spring, in which each
individual "coil" is formed by one of these lateral bulges.
In its undeflected state, the composite spring of this invention
has a simple cylindrical wall form that appears rectilinear in
longitudinal section, as shown (FIG. 2). As a columnar or axial
load is applied to body 10, uniaxial compression occurs until the
body has been deflected about twenty percent of its unloaded
length, or about 0.2H (FIG. 1). It is at this deflection that local
symmetric bulging instability begins to appear in sequence between
adjacent coils of spring 12. The force/deflection curve has by now
progressed upward along and through region 14 and is entering
region 18. As depicted in FIGS. 1 and 3, as deflection continues
beyond about 0.2H, this symmetric bulging instability appears as
lateral outward bulging between adjacent coils of spring 12, first
near the middle of body 10, as shown (FIG. 3) and subsequently
between other adjacent coils. As a consequence, the external
surface of the composite spring increasingly acquires an undulatory
configuration. The duration of region 18 corresponds to the range
of deflection during which the symmetric bulging instability grows
toward and eventually assume a continuous coil configuration, as
shown (FIG. 4). With continued deflection beyond about 0.6H,
adjacent undulations contact and "bottom out" upon one another, as
depicted in FIG. 4, and further growth of the bulging instability
essentially ceases. Continued deflection therefore produces further
compression of the body along region 16 of the force/deflection
curve (FIG. 1) under conditions of uniaxial compression similar to
region 14, except that further bottoming of the adjacent
undulations produces an increasing effective shape factor and hence
a rising instead of linear spring rate.
An important aspect of the present invention is that the composite
spring performance is the result of the cumulative effects of the
individual rubber "coils": that is, the segments of the body
between adjacent active coils of spring 12. In the single intracoil
body segment depicted in FIG. 5, the localized effects of axial
compression appear as both inward and outward bulging of its inner
wall 40 and its outer wall 50, respectively. As depicted by broken
lines, the magnitude of the inward bulging of wall 40 is
substantially less than that of the outward bulging of wall 50
under axial load conditions. The inner and outer circumferential or
hoop strains in and adjacent to walls 40 and 50 cause the
relatively incompressible material forming the body segment to
"flow" radially outward, producing the intracoil lateral bulging
and the overall appearance of a rubber coil spring as illustrated
in FIGS. 2-4. These strains become increasingly positive with
increases in axial compression, and are distributed axially along
the bulging surface such that the maximum strain appears about
midway between adjacent coils of spring 12 and are zero adjacent
the coils themselves. The "flow" obtained as a result of this
strain distribution causes the body segment to deflect momentarily
in an unstable manner as if it were buckling.
This may be understood by reference to the force/deflection
behavior of each of the FIG. 5 intracoil body segments or rubber
"coils", first individually and then cumulatively. Individually,
each rubber coil has a force deflection curve that resembles that
of the composite spring, except that, as depicted in FIG. 6, the
curve has a region 60 of negative slope. This is indicative of the
occurrence of symmetric bulging instability within the rubber coil.
Cumulatively, the bulging instability commences with the rubber
coils near the middle of the body, and proceeds toward the ends of
the body in alternate sequence. This is depicted in FIG. 3, in
which bulging instability between coils 22 and 24 is illustrated as
being the first to occur, and will be followed by similar
instability occurrences between coils 21, 22 or 24, 26, as the case
may be. Consequently, the rubber coils tend to reach the point of
symmetric bulging instability sequentially, so the cumulative
effects of coil instability occurrences appear as a plurality of
the FIG. 6 force/deflection curves. As depicted in FIG. 7, the
force/deflection curve for the composite spring therefore appears
as a superposition of multiple FIG. 6 force/deflection curves, from
which an average force/deflection curve 64 for the composite spring
may be derived. In making this derivation, the negative slope
regions of the individual rubber coils are offset by contrary
effects of the other rubber coils that are not then manifesting
this mode of deflection. Curve 64 therefore has a plateau-like
region that corresponds to region 18 of the FIG. 1 curve.
Referring again to FIG. 1, this plateau-like region may occur at a
predetermined load condition, as depicted by curves A, B and C. The
manner in which this is accomplished is described presently. As
will be apparent from FIG. 1, the slope of this region, whether
positive, zero or even negative, may vary, depending upon the load
condition at which the instability yielding the soft spring
behavior occurs and other factors. As a consequence, the actual
axial deflection force present during the occurrence of the
instability may in some cases vary in accordance with the point
along region 18 selected as the spring design load, or the load
level from which the spring is subjected to positive and negative
load inputs under the expected service conditions. The selection of
this design load will of course depend upon specific application.
For example, in most vehicular suspension applications, it should
be desirable to select a design load at point 66 (FIG. 1),
corresponding to the onset of region 18, to yield a soft ride over
the maximum available region of suspension deflections. The degree
of softness and the extent to which it may be desired to introduce
some stiffness within or bounding this deflection range is
controllable by "tuning" the spring according to further principles
of this invention.
The occurrence of symmetric bulging instability is controllable so
that the composite spring may be "tuned" such that its soft region
18 (FIG. 1) appears when and for the duration desired. Among the
factors that lend to this control are: wall thickness and length of
the body; the size, location, and spacing of the coils of spring
12; the properties of the material of which the body is composed;
and other factors that will become apparent from the description
and claims to follow.
The thickness of the body wall relative to coil spacing influences
the occurrence of bulging instabilities, the thinner the wall for a
given coil spacing the greater the tendency for the body to bulge.
It is preferred that the bulging instability occurs in a
predictable sequence in order to control the offsetting effects of
the FIG. 5 individual intracoil body segments. It is further
preferred that the bulging instability occurs first at or near the
middle of the body and progress toward its ends from there. To
accomplish this end, the body wall should be thinner at the middle
of the body and become progressively thicker proceeding toward its
ends. It is further preferred that the bulging instability
protrudes outwardly between the spring coils, rather than inward to
prevent or minimize undesirable surface stresses. To maximize the
tendency toward such outward bulging, spring 12 should be embedded
within body 10 nearer wall 40.
The number of active coils, coil diameter, and length of the body
all are additional stability factors ("Active" coils means all but
the end coils, which constitute "inactive" coils. As depicted in
FIG. 2, the active coils are designated by reference numerals 21,
22, 24 and 26 and the inactive coils are designated by reference
numerals 28 and 30.) For example, the greater the number of active
coils or greater the spacing between coils, the greater the
tendency of the body as a whole to buckle asymmetrically under
columnar loading. If the number of active coils is excessive, the
body is in essence divided into so many of the FIG. 5 intracoil
body that it tends to shift into asymmetric deformation conditions
unpredictably. Too few active coils engendered by excessive
intracoil spacing, on the other hand, promotes asymmetric buckling
within the individual segments.
The wire diameter or cross-sectional size of the individual coils
of spring 12 is still another stability factor. In the absence of
sufficient reinforcement due to inadequate coil diameter, the body
tends towards assymetric buckling, depending upon its length, in
accordance with well known principles of columnar loading. If its
individual coils are too large in diameter, however, spring 12
assumes a greater proportion of the load carrying capacity as
depicted by curve 20 in FIG. 1, and the beneficial effects of
elastomer loading are correspondingly sacrificed. The individual
coils should not be exposed and therefore preferably are of a
maximum diameter that is somewhat less than the thickness of the
body wall. In many practical cases, however, the individual coil
diameter will be substantially less than this wall thickness.
These considerations may be expressed as follows:
(a) Stability factor (S) ##EQU1##
(b) Reinforcing efficiency factor (E) ##EQU2##
Where (as depicted in FIG. 1):
H=total column height or length of body 10
n=number of active coils
r=internal radius of body 10
R=external radius of body 10
t=coil wire diameter of spring 12
(R-r)=body wall thickness
Preferably the stability factor(s) set forth in (1) above is
between about 0.03 and 0.8 and most preferably is between about
0.05 and 0.2. Preferably the reinforcement efficiency factor (E)
set forth in (2) above is between about 0.03 and 5 and most
preferably is between about 0.05 and 3. In addition to the
foregoing, unacceptable instabilities are likely to occur whenever
the ratio R/2H is less than about 0.1.
It is possible to control the point along the FIG. 1 vertical force
axis at which region 18 will occur, in accordance with the material
properties or wall thickness of body 10, or both. For a given
spring construction, an increase or decrease in the hardness or
shear modulus of the body material should produce a corresponding
variation in region 18 up and down along the force axis. Referring
to FIG. 1, curves A, B, and C respectively represent the effects of
progressive increases in shear modulus of the body material used.
Likewise, for a given shear modulus or material hardness, a similar
variation is attainable by increasing or decreasing the wall
thickness (R-r) of body 10 (FIG. 2). As a consequence, the
composite spring may be constructed with a predetermined design
load at which region 18 and its associated softness will occur.
Variations in regions 14, 16 and 18 may also be achieved by
adjusting the number of active coils within the limits set by (1)
and (2) above, or by adjusting the pitch of spring 12, or both.
This is particularly advantageous in vehicular suspension
applications in which it is desireable to "tune" the suspension
spring elements to provide soft ride effects at a certain design
load.
It presently is preferred to form body 10 of natural rubber
compounded with the usual ingredients to produce an engineering
grade of vulcanized rubber, although suitable synthetic elastomers
or blends of natural rubber with synthetic elastomers may be used.
In addition to acting as the primary load bearing material, the
rubber provides attenuation of vibration or shock transmitted from
the unsprung mass to the sprung mass by means of both isolation and
damping. Natural frequency is reduced by decreasing the spring
stiffness for a constant spring mass or by increasing the sprung
mass at constant stiffness. With the rubber coil spring of the
present invention, the static and dynamic stiffness at design load
is low and the natural frequency is also low, with corresponding
good vibration attenuation. The rubber coil spring provides
increasingly effective isolation of the sprung mass from
disturbances applied at frequencies above the natural frequency of
the spring/mass system, such that, as its resilience is increased,
vibration attenuation is reduced. The rubber coil spring has the
further advantages of being much less susceptible to the
transmission of higher order harmonics than an all-metal spring,
providing inherent damping that, in most practical applications, is
substantially greater than that of an all-metal spring and reducing
the effects of any resonance conditions that occur when a
disturbing frequency at the natural frequency of the spring/mass
system is encountered.
It is a well known consequence of increasing the inherent damping
of the rubber compound that the "set" remaining after the removal
of a compression load will increase, as will the creep under load.
These effects could lead in a particular application to a gradual
reduction in the length of the spring and hence in the height of
the sprung mass; for example, they could affect bumper height in
certain vehicle suspension applications. These effects may be
controlled and kept within acceptable limits, however, by
precompressing the rubber coil spring prior to installation. It is
well known that physical creep rates in rubber are approximately
constant with the logarithm of time typically involved with most
practical vehicle suspension applications. Thus, the effects of
creep may be minimized or eliminated simply by providing
precompression or prestressing of a rubber coil spring unit for a
period of time calculated to compensate for the amount of creep
anticipated for the service life of the spring.
It presently is preferred to use the coil spring 12 as the
reinforcement between which the localized bulging instability is
formed, and to both embed the spring in and bond it to the rubber
forming the body 10. Any suitable rubber bonding agent may be used
to accomplish this. It will be recognized, however, that other
types of forms of hoop-like restraints such as tire cord or fibers
arranged in a spiral pattern generally could be used in place of or
in combination with spring 12. Another possible construction is to
bond separate rings together in a stacked relationship, with
appropriate dividers bonded between them to promote lateral
bulging. Neither these rings nor body 10 need be of circular
transverse cross section, and could be of oval, multi-flat sided or
other cross-sections that yield acceptable deformation behavior in
accordance with the general principles of this invention. The
spring 12 itself preferably is of metallic composition, although it
could be formed of reinforced fibers, plastic or other nonmetallic
compositions having suitable structural properties. Likewise, it
may not always be necessary to bond the spring to the rubber, or to
embed it completely within the body wall, or both, provided the
frictional and other mechanical and thermal effects associated with
these variations in construction produce satisfactory results.
The rubber coil spring as illustrated and described thus far is
intended for axial columnar loading. As depicted in FIG. 1, the
ends of body 10 are planar and transverse to its longitudinal axis.
This composite spring therefore is suitable for axial columnar
loading between parallel platens as shown in FIGS. 70 and 72. It
may, however, be adapted easily for loading by non-parallel platens
and even by one or more pivoted platens, as may be encountered for
example in certain automotive suspension involving pivotal A-arms
or yokes. In these applications, the ends of the body may be formed
at angles to its longitudinal axis, or the platens may be angled
correspondingly, or both, provided the resultant force vector is
along the longitudinal axis. This could accommodate the swinging
motion of the sprung or unsprung mass, to the extent required to
achieve the controlled symmetric bulging instabilities described
earlier. It may also easily be adapted for use with non-planar
ends; for example, with spring ends cut square rather than ground
flat, producing a step like end to the RSC which can locate into a
suitable or fixture.
To illustrate the foregoing principles of this invention, but not
by way of limitation, the following example is disclosed.
EXAMPLE
A rubber coil spring generally similar to that illustrated in FIG.
2, in which internal radius (r) is 41 mm, outer radius (R) is 55
mm, unrestrained length (H) of 300 mm, five active coils, and
formulated of natural rubber of 50 IRHD. The force/deflection curve
and design load for this spring is depicted in FIG. 8. This spring
should yield generally "soft" ride characteristics in a vehicle
suspension system.
Although one presently preferred embodiment of the invention has
been illustrated and described herein, variations will become
apparent to one of ordinary skill in the art. Accordingly, the
invention is not to be limited to the specific embodiment
illustrated and described herein, and the true scope and spirit of
the present invention are to be determined by reference to the
appended claims.
* * * * *