BACKGROUND OF THE INVENTION 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 for cushioning 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

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

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-

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

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.

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 THE 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

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

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-

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- ing.

Load distributing system 52 is preferably config- ured and positioned to effectively distribute compressive loads during the last one-half, and most preferably the last

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. As a general 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 invention as 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

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.