Note: Descriptions are shown in the official language in which they were submitted.
CA 02266688 1999-03-1~
WO99/03725 PCT~S98/12987
BICYCLE FORK SUSPENSION HAVING A
SINGLE p~TM~y COMPRESSION SPRING SYSTEM
CROSS REFERENCE TO RE~TED PROVISIONAL APPLICATION
The present application claims the benefit of the
earlier filing date of pending U.S. Provisional Patent
Application Ser. No. 60/052,709, filed July 16, 1997.
BACKGROUND OF THE I~ENTION
The present invention relates to the design and
construction of bicycle fork suspension systems. More
particularly, the present invention relates to the use of
only one primary compression spring system in a bicycle
suspension fork.
Bicycle forks used for coupling a front or rear
bicycle wheel to a bicycle frame are well known. In addi-
tion, bicycle forks which include suspension systems forcushioning impacts or vibrations experienced by a rider when
the bicycle contacts bumps, ruts, rocks, pot holes or other
obstacles are also well known. Disturbances in the road are
absorbed by the suspension system, and their adverse impact
upon the vehicle and its rider is reduced or altogether
eliminated. One result of such impact reduction is that the
rider is better able to control the bicycle. In addition
bicycle suspension systems also serve the purpose of main-
taining the bicycle wheel in contact with the ground, thus
further improving the rider's steering and braking control
over the bicycle.
Bicycle suspension forks typically have a pair of
fork legs straddling the bicycle wheel, each leg including a
pair of inner and outer telescoping fork tubes. The inner
fork tubes usually are the upper tubular elements and the
outer fork tubes usually are the lower tubular elements.
However, the reverse arrangement may also be used.
A primary compression spring assembly is typically
provided in both fork legs, within the pairs of telescoping
CA 02266688 lgg9-o3-l~
W099/03725 PCT~S98/12987
fork tubes. The compression spring assembly biases the fork
tubes into a spaced apart condition when the suspension
system is under neutral (i.e., no external load) conditions.
The fork tubes are positioned to slidably move with respect
to each other upon impact to the frame, with the spring
assembly therein resisting the compression forces. The fork
tubes undergo a compression stroke when the tubes telescope
together (the inner tube slides into the outer tube), such
as when impact forces are applied to the fork. The spring
assembly absorbs the compression forces applied to the fork
tubes. Depending on the type of spring used, the spring
assembly stores some, if not all, of the energy imparted to
the system during compression and releases the energy to
return the fork tubes to their neutral position. The fork
tubes undergo an expansion stroke (or rebound stroke) when
the tubes telescope apart (the inner tube slides out from
the outer tube), such as after a compression stroke.
The primary spring assemblies typically comprise
coil springs, elastomeric members, air springs, arcuate
spring discs or other similar springs or combinations of
springs. Primary spring assemblies representative of those
known in the art are illustrated in U.S. Patent No.
2,708,112 to Seddon et al., U.S. Patent No. 5,193,833 to
Reisinger, U.S. Patent No. 4,971,344 to Turner, U.S. Patent
No. 5,238,259 to Wilson et al., U.S. Patent No. 5,310,203 to
Chen, U.S. Patent No. 5,284,352 to Chen, U.S. Patent No.
5,367,918 to Chang et al., U.S. Patent No. 5,449,155 to
Mack, U.S. Patent No. 5,449,189 to Chen, U.S. Patent No.
5,470,090 to Stewart et al., U.S. Patent No. 5,538,276 to
Tullis, and U.S. Patent No. 5,580,075 to Turner et al., the
disclosures of which are incorporated herein by reference in
their entireties.
In addition to the primary compression spring
assemblies, "bottom-out" springs have been used to cushion
abrupt impacts between the moving parts of the suspension
assembly when the inner and outer fork tubes are compressed
CA 02266688 1999-03-l~
WO99/03725 PCT~S98/12987
their maximum distance. Typically, bottom-out springs are
comprised of thin rubber or other elastomeric members posi-
tioned at the bottom of the outer fork tube and intended to
be used only at the very end of the compression stroke of
the fork legs. Similarly, "top-out" springs have been used
in combination with the primary compression spring assem-
blies in order to prevent abrupt impacts between the inner
fork tube and the outer fork tube when the fork tubes are
over-expanded during rebound of the suspension system.
"Bottom-out" or "top-out" spring systems representative of
those known in the art are illustrated in U.S. Patent No.
2,708,112 to Seddon et al., U.S. Patent No. 5,310,203 to
Chen, U.S. Patent No. 5,284,352 to Chen, and U.S. Patent No.
5,449,189 to Chen, the disclosures of which are incorporated
herein by reference in their entireties.
The use of a primary compression spring assembly
in only one fork leg, instead of a primary compression
spring assembly in each fork leg, would be advantageous for
reducing both the cost and weight of the bicycle. Cost
reductions are increasingly important given the competitive
nature of the bicycle and fork manufacturing industry.
Weight reductions are important for all bicycles, and par-
ticularly for bicycles used in cycling competitions, during
which weight can be a critical factor. Accordingly, there
is a need for a bicycle fork using only one primary compres-
sion spring assembly.
A significant disadvantage associated with the use
of a single primary compression spring assembly in only one
leg of a bicycle suspension fork is that, as the primary
spring assembly compresses and the inner fork tubes approach
the lower portion of their travel, the fork is increasingly
asymmetrically loaded. Asymmetrical loading is undesirable
as it results in unacceptably high stresses being transmit-
ted to the fork legs, the fork brace (the arch connecting
the fork legs), and/or other fork structures. To withstand
such loading, the fork structures would require reinforce-
CA 02266688 1999-03-1~
W099/03725 PCT~S98/12987
ment, resulting in added weight and increased bicycle
production costs, offsetting the reductions in cost and
weight achieved by eliminating the second primary compres-
sion spring assembly. Thus, there is a need for a bicycle
fork having a single primary compression spring system that
decreases the asymmetric loading that would otherwise be
created by the use of only a single primary compression
spring assembly.
SUMMARY OF THE INVENTION
It is an object of the present invention to pro-
vide a bicycle suspension fork that has a primary compres-
sion spring system in only one of the fork legs, yet is
configured to minimize any asymmetric loading that might be
caused by using such spring system.
This and other objects are accomplished in accor-
dance with the principles of the present invention by pro-
viding a suspension fork having a single primary compression
spring system in only one fork leg, and a method for assem-
bling such a suspension fork, such that loads in the fork
are more evenly distributed to reduce any asymmetric loading
that would otherwise be caused by the use of only a single
primary compression spring assembly on one side of the fork
is minimized. In particular, a load distributing assembly
is positioned in the fork leg not containing a primary com-
pression spring assembly, or in both fork legs. With re-
spect to either fork leg, the load distributing assembly of
the present invention is positioned so that compression of
the inner and outer telescoping tubes of the fork legs may
result in compression of the load distributing assembly.
Unlike the primary compression spring assembly,
the load distributing assembly is not intended to bias the
inner and outer fork tubes apart or resist compressive
forces applied to the fork legs throughout the entire travel
of the fork tubes, although in some embodiments the load
distributing assembly may provide some biasing assistance.
Instead, the load distributing assembly becomes effective
CA 02266688 1999-03-1~
WOs9/03725 PCT~S98/12987
after initial travel of the fork tubes. However, unlike a
typical bottom-out spring (which is effective only at the
end of a compression stroke), the load distributing assembly
is effective prior to a near-bottom-out condition. Specifi-
cally, the load distributing assembly provides resistance to
compressive forces applied to the fork legs through a por-
tion of the travel of the fork tubes toward the end of a
compression stroke. For example, the load distributing
assembly may comprise a spring positioned between the bottom
of the inner tube and the bottom of the outer tube so that,
while it provides some biasing force when the fork tubes are
in an uncompressed state, it provides meaningful resistance
to compressive forces only through about the last half of
the fork tubes' travel through a compression stroke. Pref-
erably, however, the load distributing assembly provides
such resistance through approximately the last one-third of
the fork tubes' travel through a compression stroke, as this
portion of the compression stroke is where the greatest
loads are usually experienced by the fork.
The load distributing assembly may include any
type of air spring, coil spring, arcuate spring members, or
elastomer spring, or any other type of spring or combination
of springs, provided that such spring or combination of
springs decreases asymmetrical compression forces caused by
the use of a single primary compression spring system on
only one side of a suspension fork and which would normally
require reinforcement of the legs, brace, or other fork
structure. In addition, as will be appreciated by those
skilled in the art, the load distributing assembly may be
positioned between the bottom of the inner fork tube and the
bottom of the outer fork tube, between the top of the inner
fork tube and a plunger extending into the inner fork tube
from the outer fork tube, or in some other operative posi-
tion, and may be disposed inside or outside of the inner
and/or outer fork tubes.
CA 02266688 1999-03-15
WO99/03725 PCT~S98/12987
The above and other objects, features, and advan-
tages of the present invention will be readily apparent from
the following detailed description of the invention taken in
conjunction with the accompanying drawings wherein like
reference characters represent like elements, the scope of
the invention being set out in the appended claims.
BRIEF DESCRIPTION OF TH~ DRAWINGS
In the drawings:
FIG. 1 is a partial sectional front elevational
view of a front bicycle suspension fork formed in accordance
with the principles of the present invention and including a
single primary compression spring assembly in only one of
the fork legs;
FIG. 2 is an exploded view of the single primary
compression spring assembly of FIG. 1; and
FIG. 3 is a partial sectional side elevational
view of the front bicycle suspension fork of FIG. 1, showing
a load distributing assembly within the leg not containing a
primary compression spring assembly.
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of a front suspension fork
10 having a single primary compression spring system 12
formed in accordance with the principles of the present in-
vention is illustrated in FIGS. 1-3. This application is
merely illustrative, however, as those having skill in the
art will recognize that the single primary compression
spring system 12 of the present invention may additionally
or alternatively be incorporated into a rear bicycle suspen-
sion fork or other suspension system utilizing two tele-
scoping fork legs.
Suspension fork 10 has two fork legs 14, 16, each
fork leg 14, 16 comprising an inner tube 18, 20 that tele-
scopes into an outer tube 22, 24. The first ends 26, 28 of
inner tubes 18, 20 are typically coupled together by a crown
30. The second ends 32, 34 of inner tubes 18, 20 telescope
into first ends 36, 38 of outer tubes 22, 24 and approach
CA 02266688 lssg-03-l~
W099l03725 PCT~S98/12987
second ends 40, 42 of outer tubes 22, 24 as fork 10 is
compressed. Outer tubes 22, 24 are typically coupled to-
gether by a fork brace 44.
Compression spring system 12 includes a single
primary compression spring assembly 50 within only one of
legs 14, 16 and a load distributing assembly 52 within at
least one of legs 14, 16. Preferably, as illustrated in
FIG. 1, primary compression spring assembly 50 is positioned
within the inner fork tube 20 of fork leg 16. However, it
will be appreciated that compression spring assembly 50 may
alternatively be disposed, for example, within outer fork
tube 24 of leg 16, within one of inner or outer fork tubes
18, 22 of leg 14, or externally of the inner or outer tubes
18, 20, 22, 24 with the inner or outer fork tube extending
through a bore or axial passage through the compression
spring assembly. As will be appreciated, only one compres-
sion spring assembly 50 is provided for the entire suspen-
sion fork 10.
FIG. 2 illustrates a preferred embodiment of the
primary compression spring assembly 50 of the present inven-
tion in isolation. Primary compression spring assembly 50
of FIG. 2 includes a biasing element 54 functioning as the
compression spring and a compression spring spacer 56.
Compression spring 54 preferably is an elastomer spring
which may be made from microcellular urethane ("MCU"). As
shown in FIG. 1, because primary compression spring assembly
50 is preferably positioned in the inner tube 20, which is
the upper tube of suspension fork 10, compression spring
spacer 56 is positioned between a top cap assembly 58 and
the compression spring 54.
As described in further detail below, the lower
end of compression spring 54 is supported and maintained
within inner fork tube 20 by a plunger assembly 60 including
a plunger shaft 62 having a first end 64 and a second end
66. An end plate 68 is provided on first end 64 of plunger
shaft 62 and is positioned within second end 34 of inner
.... ....
CA 02266688 1999-03-1~
W099/03725 PCT~S98/12987
tube 20 to provide a seat for compression spring 54. First
end 64 and end plate 68 are slidable within inner tube 20
and second end 66 of plunger shaft 62 is coupled to second
end 42 of outer tube 24 to permit compression of fork 16 and
of spring 54. A flange 70 is provided on second end 34 of
the inner tube 20 (FIG. 1) so that during extension of the
fork legs 14, 16, flange 70 will prevent shaft end plate 68
from being withdrawn from inner tube 20. Thus, plunger
shaft 62 and outer tube 24, with which shaft end plate 68 is
interconnected, are prevented from becoming disengaged from
the inner tube 20.
A top-out spring 72 is preferably provided at
first end 64 of plunger shaft 62 below shaft end plate 68.
Top-out spring 72 may be formed from any resilient material
known in the art. As may be seen in FIG. 1, when compres-
sion spring assembly 50 is positioned within fork 16, top-
out spring 72 is positioned between shaft end plate 68 and
the flange 70 of inner fork tube 20. Thus, top-out spring
72 cushions impacts between shaft end plate 68 and the
flange 70 when fork tubes 20, 24 are near their expansion
limit during rebound of the suspension system and second end
34 of inner tube 20 nears first end 38 of outer tube 24.
Preferably, plunger shaft 62 extends through an axial bore
in top-out spring 72 such that top-out spring 72 is posi-
tioned around plunger shaft 62.
In the preferred embodiment illustrated in FIGS.
1-3, compression spring system 12 also includes a load dis-
tributing system 52 which, as shown in FIG. 1, is preferably
located in the fork leg 14 that does not contain primary
compression spring assembly 50. However, if desired, load
distributing system 52 may be located in both fork legs 14,
16. As may be most clearly seen in FIG. 3, load distribut-
ing system 52 includes a load distributing spring 80, a load
distributing spring spacer 82, and plunger shaft 62.
Preferably, load distributing spring 80 and load distrib-
CA 02266688 lggg-03-l~
W099/03725 PCT~S98/12987
uting spring spacer 82 are annular such that plunger shaft
62 is passed therethrough.
Load distributing spring spacer 82 is preferably
an annular rigid or semi-rigid plastic spacer capable of
withstanding the compressive loads that may be applied to
load distributing spring assembly 52. Load distributing
spring 80 is preferably an annular elastomeric spring, and
most preferably an MCU elastomer. The use of an MCU elas-
tomer as the load distributing spring achieves two principle
advantages. First, the MCU elastomer has a progressive
spring rate that enables the elastomer to distribute, for
each incremental unit of distance the spring is compressed,
a nonlinearly increasing load increment to the fork leg not
containing the primary compression spring assembly. Second,
also as preferred, the MCU is lighter and less expensive
than many alternative spring structures. It will, nonethe-
less, be appreciated that the materials from which load dis-
tributing spring 80 and load distributing spring spacer 82
are formed are selected depending on the load distributing
characteristics desired for the system, and thus may com-
prise materials other than those explicitly listed herein,
so long as the desired load distribution is achieved.
As will be evident to those having skill in the
art, load distributing spring 80 will compress when engaged
by lower, second end 32, and particularly flange 92, of
inner fork tube 18. Upon compression, load distributing
spring 80 distributes a portion of the compressive loads to
the fork leg not containing a primary compression spring
assembly, thereby reducing the loading that would otherwise
be experienced by the fork leg containing the primary
compression spring assembly and alleviating the need to
reinforce the fork structure to withstand asymmetrical load-
ng .
Load distributing system 52 is preferably config-
ured and positioned to effectively distribute compressiveloads during the last one-half, and most preferably the last
CA 02266688 lgg9-o3-l~
WOs9/0372s PCT~S98/12987
one-third, of travel of the inner fork tubes 18, 20 into the
outer fork tubes 22, 24 (the compression stroke of fork 10).
This preferred range may vary in other forks or alternative
suspension assemblies, however, depending upon the particu-
lar design of the fork or device being considered. ~s ageneral rule, therefore, it is preferable that the load dis-
tributing spring assembly be configured and positioned to
redistribute asymmetric loads within the range of travel
where load redistribution is necessary in order to avoid the
need to reinforce the structural components of the fork or
other suspension assembly. It will be appreciated that
spacer 82 may be adjusted or replaced with a differently
sized or shaped spacer in order to modify the position of
load distributing spring 80 and thus the point at which load
distributing system 52 effectively distributes compressive
or other loads during compression of the bicycle fork.
Load distributing system 52 may be positioned in
any manner and on any surface permitting it to transfer
loads from the inner fork tube to the outer fork tube.
Thus, although FIGS. 1 and 3 show load distributing spring
80 of fork leg 14 being seated on a load distributing spring
spacer 82 disposed at the lower, second end 42 of outer fork
tube 22, it will be appreciated that another arrangement
that would provide the same load distribution is within the
scope of the principles of the present invention.
While the foregoing description and drawings
represent the preferred embodiments of the present inven-
tion, it will be understood that various additions, modifi-
cations and substitutions may be made therein without de-
parting from the spirit and scope of the present inventionas defined in the accompanying claims. In particular, it
will be clear to those skilled in the art that the present
invention may be embodied in other specific forms, struc-
tures, arrangements, proportions, and with other elements,
materials, and components, without departing from the spirit
or essential characteristics thereof One skilled in the
CA 02266688 1999-03-l~
W099/03725 PCT~S98/12987
art will appreciate that the invention may be used with many
modifications of structure, arrangement, proportions, mate-
rials, and components and otherwise, used in the practice of
the invention, which are particularly adapted to specific
environments and operative requirements without departing
from the principles of the present invention. The presently
disclosed embodiments are therefore to be considered in all
respects as illustrative and not restrictive, the scope of
the invention being indicated by the appended claims, and
not limited to the foregoing description.
