Interlaced wave spring

An interlaced wave spring is formed from two constituent wave springs of similar thickness, amplitude and frequency. The two constituent wave springs are combined together by interlacing them so that the spring turns of each spring abut each other for substantially the entire length of the interlaced spring. This interlacing effectively increases the thickness of the spring turns of the interlaced spring to thereby provide increased loading and greater fatigue resistance characteristics.

BACKGROUND AND SUMMARY OF THE PRESENT INVENTION 
The present invention relates generally to wave springs, and more 
particularly to an interlaced wave spring having improved fatigue and 
operating characteristics. 
Springs are used in a variety of mechanical applications. Numerous types of 
springs are known in the art and each type has certain advantages and 
disadvantages which affect the use of the spring. Examples of known 
springs are coil springs, disc springs, Belleville springs, wave washers 
and wave springs. 
The coil spring is perhaps the best known type of spring. Coil springs are 
typically made from round wire by coiling wire around a mandrel at a 
helical pitch for a specific number of turns to provide a spring with a 
particular length. The ends of such springs may be finished with hook 
ends, for example, so that the spring may be engaged between two members. 
The ends may also be ground flat to provide end bearing surfaces when the 
spring is used in compression applications. Coil springs may be made in 
any length and for the most part, with any diameter of wire and are 
suitable for light and heavy-duty applications. An example of a heavy-duty 
coil spring is described in U.S. Pat. No. 1,523,225, issued Jan. 13, 1925. 
Belleville washers are another type of spring and are typically stamped 
from sheet metal. A Belleville washer acts like a spring because it is 
conical in shape and has an inherent flexibility due to the conical shape. 
Such washers may be used in a variety of light to medium duty 
applications. They are expensive to produce and require special tooling 
and also have a tendency to invert when overloaded so their deflection 
characteristics change. Such a spring washer is described in U.S. Pat. No. 
3,319,508, issued May 16, 1967. 
Disc springs are similar to Belleville washers and are also stamped out of 
a sheet or strip of metal. They are expensive to produce because they 
require special tooling. They may be used for heavy-duty applications 
where they must resist and support large loads. However, when overloaded, 
the deflection characteristics of these springs are different from that of 
compression coil springs because, when overloaded disc springs have a 
tendency to invert and collapse. 
Wave washers are also similar to Belleville washers in that they are 
stamped from sheet metal, but with a wave pattern formed in them. These 
type of washers include only a single turn. The wave pattern provides the 
operating length for the spring and provides a means for the washer to 
support loads. 
The wave pattern used for wave washers has also been used in wave springs 
such as that described in U.S. Pat. No. 4,752,178 issued Jun. 21, 1988, 
which is assigned to the assignee of the present invention. As shown in 
this patent, a wave spring which is particularly suitable for use in 
retaining ring-type applications, includes one or more flat wire turns 
which are circularly wound and waved in a sinusoidal pattern to provide a 
wave spring having a predesired thickness which thickness is defined by 
the total number of spring turns of the spring. 
The wave pattern has also been incorporated into springs wherein the spring 
turns have a sinusoidal shape. These type of wave springs are described in 
the art as "crest-to-crest" wave springs because the individual spring 
turns are oriented in a manner so that successive crest portions of one 
spring turn abut successive trough portions of each adjacent spring turn. 
Wave springs provide certain advantages over coil springs, primarily in 
terms of space-savings, because the wave spring provides the same load 
deflection characteristics as a coil spring but in a shorter length. Also, 
more precise spring loading is obtained with the use of wave springs 
because of their uniform waved structure. 
Wave springs may be made in many different styles and shapes. The 
crest-to-crest wave spring described above may be modified to include 
opposing, flat end portions which are usually formed by gradually reducing 
the amplitude and frequency of the waves in the spring turns down to a 
constant zero level to form opposing flat shim end portions. Such a 
construction is aptly described in U.S. Pat. No. 4,901,987, issued Feb. 
20, 1990, which patent is also owned by the assignee of the present 
invention. 
Although useful for most applications, wave springs, like coil springs may 
be subject to fatigue during long cycles of loading and unloading as well 
as repeatedly changing loads. Fatigue may affect the usefulness of wave 
springs in a detrimental manner because after repeated cycles of even or 
uneven loading, the operating stress within the spring may increase to a 
level at which the metal of the spring undergoes failure. One solution to 
fatigue is to increase the size of the spring cross-section undergoing the 
loading to reduce the stress created in it under load. In the spring art, 
this requires using a heavier and larger wire or flat wire to form the 
spring. This solution is not always practical. 
The present invention is therefore directed to an improved, interlaced wave 
spring which avoids the aforementioned shortcomings and develops new and 
improved performance characteristics not previously obtainable with 
crest-to-crest wave springs having a single thickness. 
In a wave spring incorporating the principles of the present invention, 
multiple constituent wave springs are interlaced, or interwound, together 
in order to effectively increase the thickness of each of the spring 
turns, while maintaining the spring turns in their crest-to-crest 
orientation and without increasing the base size of the wire used to form 
the spring. This interlacing results in either a reduction of the 
operating stress of the spring thereby increasing the fatigue life of the 
spring, or maintaining the operating stress of the spring while increasing 
the spring load. These operational parameters, and others, are affected 
proportionally by the number of constituent springs which make up the 
interlaced spring. 
In an interlaced wave spring incorporating the principles of the present 
invention, a plurality of constituent, multiple turn crest-to-crest wave 
springs are combined together to form a single spring. The constituent 
springs are formed with equal wave patterns in which the waves have 
substantially the same amplitudes and frequencies so that when they are 
interlaced, they act together under loading as a single spring. The 
constituent springs may be interlaced together. When the springs are 
interlaced together, they are aligned so that the successive crest and 
trough portions of adjacent spring turns "match up" and interfit together. 
In one preferred embodiment of the present invention, the successive crest 
and trough portions of adjacent spring turns generally share the same 
common centerpoint. When interlaced, the wave spring's operating 
parameters are increased or decreased by the number of interlaced springs. 
Accordingly, it is a general object of the present invention to provide a 
new and improved wave spring with increased beneficial spring 
characteristics. 
It is another object of the present invention to provide a multiturn 
crest-to-crest compression spring with multiple, interlaced springs. 
It is a further object of the present invention to provide an interlaced, 
crest-to-crest wave spring in which the interlacings have substantially 
identical wave amplitudes and frequencies. 
It is still yet a further object of the present invention to provide an 
improved crest-to-crest wave spring which includes a plurality of 
crest-to-crest wave springs interlaced together such that each spring turn 
abuts another spring turn and whereby the crests and troughs of the waves 
of adjacent interlacings lie substantially adjacent to each other, thereby 
decreasing the operating stress in the interlaced spring. 
It is still yet another object of the present invention to provide an 
interlaced crest-to-crest wave spring which provides the benefits normally 
obtained from either nesting a plurality of single-turn wave springs 
together or stacking a series of crest-to-crest wave springs together in 
series wherein the interlaced spring is formed from a plurality of flat 
wire strips, each of the strips being edgewound about a common edge and a 
longitudinal axis of the interlaced spring to define multiple wave 
springs, each having a plurality of spring turns, each spring turn having 
successive, distinct wave crest and trough portions arranged in generally 
sinusoidal wavepaths so that the crests portions abut the trough portions 
of adjacent spring turns, the plurality of springs being interlaced 
together such that the flat wire strips lie adjacent each other and abut 
each other for the length of the spring, thereby effectively increasing 
the thickness of the spring by the number of individual springs interwound 
together. 
These and other objects, features and advantages of the present invention 
will be clearly understood through a consideration of the following 
detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a conventional crest-to-crest wave spring 10 in which 
the spring 10 consists of a single strip of flat wire 12 formed in a wave 
pattern and having a number of circumferential spring turns 13. Each 
spring turn has successive waves formed from distinct crest portions 14 
and trough portions 15 which follow a substantially sinusoidal wavepath in 
a circular pattern around the longitudinal axis A of the spring 10. The 
crest portions 14 of one spring turn abuts the trough portions 15 of the 
spring turn lying adjacent to it either above or below it and hence the 
description, "crest-to-crest". The spring 10 illustrated has a operating 
length L.sub.L equal generally to the distance between the ends 16 of the 
spring 10. The thickness of each spring turn 13 consists of only the 
thickness of the single strip of wire which makes up the spring turn. Each 
spring turn is spaced apart from adjacent spring turns in the axial 
direction along the spring's longitudinal axis L.sub.A. 
The spring 10 is suitable for most applications. However, in certain 
applications, the loading condition to be experienced by the spring 10 may 
exceed the capacity of the spring 10. In order to provide a wave spring in 
this increased load application, and importantly where space is not a 
limiting factor, multiple springs 10 may be stacked end to end (so that 
the spring ends 16 abut each other) to meet the load requirements. 
FIG. 2 illustrates another known prior art wave spring 20 which is 
particularly useful for retaining ring-type applications. The wave spring 
20 is seen to consist of one or more adjacent flat wire turns 22 formed in 
define wave patterns having successive crest portions 23 and trough 
portions 24. The spring turns 22 of the spring lie parallel, or adjacent 
each other, that is, each successive 360.degree. spring turn abuts the 
spring turn either above or below it. Although the spring 20 is able to 
support a larger relative load than the spring 10, primarily due to the 
increased thickness of its spring turns 22, the spring 20 does not possess 
the inherent flexibility of the crest-to-crest wave spring 10 because it 
lacks a crest-to-crest configuration. 
The present invention is directed to a new and improved crest-to-crest wave 
spring which offers increased load carrying capacity, increased fatigue 
life and the spring flexibility normally found in crest-to-crest wave 
springs. FIG. 4 illustrates a wave spring 100 constructed in accordance 
with the principles of the present invention which provides the advantages 
of stacked crest-to-crest wave springs with increased load capacity by 
increasing the thickness of the spring turns, while maintaining the crest- 
to-crest configuration. 
As illustrated in FIGS. 4-7, the spring 100 is an "interlaced", or 
"interwoven" wave spring. These terms are believed to be new in the art of 
springs and will refer to, in the context of this detailed discussion, 
crest-to-crest wave springs in which the spring turns have multiple, 
adjacent layers which are formed by combining two or more wave springs 
together. In one preferred embodiment of the present invention and as 
illustrated specifically in FIG. 4, the interlaced wave spring 100 
comprises two constituent wave springs 100a, 100b which are interlaced 
together. 
The constituent wave springs 100a, 100b are formed from respective flat 
wire strips 102a, 102b which are spirally wound around respective common 
edges 104a, 104b and about their respective spring longitudinal axes 
L.sub.1, L.sub.2 to form a series of spring turns 105a, 105b. A "spring 
turn", as utilized herein refers to a complete 360.degree. of revolution 
around the spring longitudinal axis. For example, the spring illustrated 
in FIG. 1 has about five spring turns, the spring of FIG. 2 has about two 
spring turns and the springs of FIGS. 3-5 have about three turns. Each 
spring can be characterized as having an inner radius R.sub.I-1, R.sub.I-2 
and an outer radius R.sub.0-1, R.sub.0-2 which define respective widths 
W.sub.1 -W.sub.2 of the wire strips 102a, 102b taken radially from the 
longitudinal axes L.sub.1, L.sub.2 of the springs 102a, 102b, hereinafter 
referred to as the `radial width` of the wire strips 102a, 102b. 
Each spring 100a, 100b is further formed in a wave pattern which defines a 
wave path extending between the opposite ends 106a, 106b and 108a, 108b of 
the springs. This wavepath is preferably introduced during the winding of 
each spring 100a, 100b and includes a series of successive similar wave 
crests 110a, 110b and wave troughs 112a, 112b. Preferably, the wavepath of 
each spring 100a, 100b is continuous and sinusoidal in nature throughout 
its extent between the spring ends 106a, 106b and 108a, 108b. 
The waves of each spring 100a, 100b are formed at a particular amplitude 
("A"), which as used herein and as illustrated in FIG. 8 refers to the 
distance from the centerline C of the spring turn to the peak P of either 
the wave crests 110a, 110b or wave troughs 112a, 112b. In most 
applications for wave springs of the present invention, this distance will 
be generally equal to one-half of the true height of any individual wave. 
The waves of each spring 100a, 100b are further also formed at a particular 
frequency, which, as used herein, refers to the number of waves present in 
each spring turn 105a, 105b. Although the constituent wave springs 100a, 
100b and interlaced wave springs 100 illustrated in the Figures and 
described herein have about three waves per turn, it will be understood 
that such is merely an illustration and the number of waves per turn will 
be limited only by material and space requirements. 
In order to obtain the benefits and advantages of the present invention, it 
is preferred that the frequency and amplitudes of the waves of each of the 
constituent wave springs 100a, 100b are substantially equal so that when 
they are interlaced together as illustrated in FIG. 4, the resulting 
interlaced spring 100 presents and acts as an overall unitary structure. 
That is, the spring turns 105a, 105b of the constituent springs 100a, 100b 
should lie adjacent each other and substantially abut each other for the 
entire free length D (i.e. the length of the spring in an uncompressed 
state) of the interlaced wave spring 100. In other words, no significant 
gaps should occur between the interlaced constituent wave springs 100a, 
100b because the two spring turns 105a, 105b are, in effect, "matched" for 
their entire lengths. By "significant" is meant no gaps which exceed 10% 
of the thickness of the wire which makes up the spring. This matching also 
ensures that the wave crest portions 110a, 110b and wave trough portions 
112a, 112b are aligned together generally at their peaks, P, to form the 
unitary wave crest portions 110 and wave trough portions 112 of the 
interlaced wave spring 100. 
Due to this interlacing, the thickness of each of the spring turns 105 of 
the interlaced wave spring 100 is effectively increased by the number N of 
constituent wave springs. In FIG. 4, this thickness is effectively doubled 
as a result of two wave springs interlaced together, while in FIG. 5, it 
is effectively quadrupled as a result of four wave springs interlaced 
together. 
In effect, the present invention provides a way to obtain greater loads on 
an interlaced spring than on a single spring. The spring characteristics 
are affected in proportion to the number of interlacings or interwindings. 
The following two tables represent the beneficial physical characteristics 
which are obtained from interlaced wave springs formed from constituent 
wave springs having 2.00 inch diameter, a material thickness of 
approximately 0.018 inch, a radial width of about 0.143 inch and about 
31/2 waves per spring turn. The data set forth in them demonstrate the 
theoretical effect of the spring interlacings on various physical 
characteristics of the interlaced spring. 
TABLE 1 
______________________________________ 
Theoretical Increase in Load Carrying Ability of 
Interlaced Spring While Maintaining Operating 
Stress Constant 
Number of springs interlaced together (N) 
N = 
1(single 
spring) N = 2 N = 3 N = 4 
______________________________________ 
Spring 1.51 1.51 1.51 1.51 
Deflection 
Spring Load 
25 50 75 100 
(lbs.) 
Spring Rate 
16.5 33.1 49.7 66.2 
(lbs/in.) 
Operating 
255,262 255,262 255,262 255,262 
Stress 
(lbs/in.sup.2) 
Theoretical 
&lt;30,000 &lt;30,000 &lt;30,000 &lt;30,000 
Fatigue Life 
(Cycles) 
______________________________________ 
It can be seen from Table 1 that as the number of interlacings increase, 
the load capacity of the interlaced spring will increase by a factor of N, 
which is equal to the number of interlacings. Although the spring load is 
increased, the operating stress of the interlaced spring remains constant. 
Therefore, the use of two constituent wave springs permits the load on the 
spring to be doubled without any increase in operating stress, three 
constituent wave springs permits the load to be tripled and so on. 
TABLE 2 
______________________________________ 
Theoretical Decrease in Operating Stress of 
Interlaced Spring While Maintaining Load Constant 
Number of springs interlaced to ther (N) 
N = 
1(single 
spring N = 2 N = 3 N = 4 
______________________________________ 
Spring 1.51 .755 .503 .378 
Deflection 
(in.) 
Spring Load 
25 25 25 25 
(lbs.) 
Spring Rate 
16.5 33.1 49.7 66.1 
(lbs/in.) 
Operating 
255,262 127,631 85,087 63,815 
Stress 
(lbs./in.sup.2) 
Theoretical 
30,000 100,000- 1,000,000+ 
1,000,000+ 
Fatigue 200,000 
Life 
(Cycles) 
______________________________________ 
Table 2 demonstrates that when the load is maintained, as the number of 
constituent wave springs interlaced together increases, the spring 
deflection and operating stress will proportionally decrease by a factor 
of N, the number of constituent wave springs and the fatigue life of the 
interlaced spring increases. 
Apart from wave frequency and amplitude, it is also desirable, but not 
required, that the constituent wave springs 100a, 100b share other equal 
physical characteristics, such as substantially equal radial widths, 
thicknesses and materials of construction. This overall equalness of 
structure of the constituent springs 100a, 100b assists the interlaced 
spring 100 in acting as a unitary structure. Equal thicknesses and radial 
widths W.sub.1, W.sub.2 of the constituent springs will assist in the 
assembly of the springs by the interlacing thereof which may be done 
either manually or by machines. 
When the springs 100a, 100b have substantially equal radial widths, their 
inner and outer circumferential edges occurring at their associated inner 
and outer radii will be generally aligned together which will facilitate 
the application of the interlaced spring either within a recess or bore or 
on a shaft. This radial "matching" also assists in ensuring uniformity of 
loading on the spring 100, for if the wire strips 102a, 102b of the 
constituent springs do not match up in abutting engagement for the width 
and along their length, but rather are slightly displaced, such as in the 
case of where the peaks P of adjacent spring turn waves are slightly 
offset, the loading of the spring will not be entirely uniform during 
initial compressions of the interlaced wave spring until such time as the 
constituent wave springs move and align themselves together under loading. 
Additionally, where the radial matching is uniform, the factor N affecting 
the spring load and spring rate will be an integer such as shown in Tables 
1 and 2 above. 
The successive wave crest and wave trough portions 110a, 110b and 112a, 
112b of the constituent springs 100a, 100b may also include shoulder 
portions 114a, 114b defined thereon, primarily located around the crests, 
or peaks P of the waves. These shoulder portions 114a, 114b cooperate to 
provide workpiece engagement surfaces 114 at the opposing ends 106, 108 of 
the interlaced spring 100, which, as illustrated in FIGS. 6 and 7 engage a 
bore wall 120 shown in FIG. 6 or the groove wall 122 shown in FIG. 7. 
The constituent springs 100a, 100b are preferably formed by edge winding 
which avoids any abrupt peaks or ridges which typically occur in 
die-stamped springs and washers and retaining rings. The wire strips 102a, 
102b of the constituent wave springs 100a, 100b each have free ends 116, 
118 which remain free after the constituent springs are interlaced so that 
the interlaced spring 100 may be circumferentially expanded or contacted 
to simplify its installation on shafts or in bores. These free ends 116a, 
116b also facilitate the installation of the interlaced spring in some 
applications such as in the shaft application of FIG. 7 where the free 
ends of the interlaced spring may be inserted into a groove 121 and the 
remaining length of the spring 100 spiraled into the groove 121. The free 
ends 116a, 116b also facilitate interfacing the springs 100a, 100b 
together. 
The free ends 116a, 116b of the constituent springs 100a, 100b are 
preferably located off of the peak of any crest portions 110a, 110b and 
preferably located on either the incline of a wave so as not to introduce 
an additional thickness to the shoulder portions 114 of the interlaced 
spring 100. 
As for materials of construction, it is preferable that a metal flat wire 
be used in the forming of the constituent springs although it is 
contemplated that in some application high strength and/or reinforced 
plastics may be suitable for use. The spring wire strips may be produced 
from steel, copper and super alloys. Suitable carbon spring steels, may be 
used for normal applications, and stainless steel may be used in 
applications which require corrosion resistance. For nonmagnetic 
applications, copper; and particularly beryllium copper alloys, may be 
used as well as various bronzes, while high temperature applications may 
require the use of a super alloy such as Inconel or other nickel-chromium 
alloys. 
FIG. 5 illustrates another embodiment of an interlaced wave spring 200 
constructed in accordance with the principles of the present invention 
wherein the interlaced spring 200 is formed from four constituent wave 
springs 200a-d. It can be seen that the waves of each of the constituent 
wave springs are virtually identical so that they match up along their 
respective crest and trough portions. 
It will be appreciated that the embodiments of the present invention that 
have been discussed herein are merely illustrative of a few applications 
of the principles of the invention. Numerous modifications may be made by 
those skilled in the art without departing from the true spirit and scope 
of the invention.