BICYCLE FORK SUSPENSION HAVING A SINGLE PRIMARY COMPRESSION SPRING SYSTEM

Abstract: A bicycle suspension fork (10) having a primary compression spring assembly (50) positioned in only one of the fork legs (14, 16). A load distributing assembly (52) is positioned in at least one of the fork legs (14, 16) in order to distribute loads transmitted to the fork (10) during a compression stroke. Thus, asymmetrical loading that would occur from the presence of only one compression spring assembly (50) on only one side of the fork is decreased if not completely eliminated. The load distributing assembly (52) preferably is arranged such that it begins load distribution during the last one-half, and most preferably the last one-third of compression stoke travel. A preferred embodiment of the load distributing assembly (52) includes a load distributing spring (80) and a load distributing spring spacer (82).

Description: BICYCLE FORK SUSPENSION HAVING A SINGLE PRIMARY COMPRESSION SPRING SYSTEM CROSS -REFERENCE TO RELATED 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 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 maintaining 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 positioned 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 assemblies 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 particularly 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 compression 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 transmitted 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 compression 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 provide a bicycle suspension fork that has a primary compression 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 accordance with the principles of the present invention by providing a suspension fork having a single primary compression spring system in only one fork leg, and a method for assembling 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 respect 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 portion 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 position, and may be disposed inside or outside of the inner and/or outer fork tubes. The above and other objects, features, and advantages 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 invention 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 suspension 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 telescopes 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 together 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 compression spring assembly 50 is provided for the entire suspension fork 10. FIG. 2 illustrates a preferred embodiment of the primary compression spring assembly 50 of the present invention 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 compression 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 distributing 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 distributing 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 elastomer 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, nonetheless, be appreciated that the materials from which load distributing 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 comprise 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 loading. 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 distributing 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 invention, it will be understood that various additions, modifications 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, structures, 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, materials, 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.

Claims: What is claimed is: 1. A bicycle suspension fork capable of undergo- ing a compression stroke and an expansion stroke, said bicycle fork comprising: a first fork leg and a second fork leg, each of said first and second fork legs comprising an inner fork tube telescopingly engaged within an outer fork tube, said inner fork tube and said outer fork tube each having a first and a second end, said second end of said inner fork tube telescoping into said first end of said outer fork tube during a compression stroke; a primary compression spring assembly posi- tioned for compression between said inner and outer fork tubes of only said first fork leg, such that only said first fork leg has a compression spring assembly therein and said second fork leg does not have a spring assembly therein; and at least one load distributing assembly posi- tioned between said inner and outer fork tubes of one of said first and second fork legs; whereby loads applied to said fork causing compression of said inner and outer fork tubes of said fork legs are transmitted in part through said load distributing assembly to said second fork leg. 2. A bicycle fork as in claim 1, wherein said load distributing assembly is positioned within said second fork leg. 3. A bicycle fork as in claim 2, wherein said load distributing assembly is positioned within both said second fork leg and said first fork leg. 4. A bicycle fork as in claim 2, wherein said load distributing assembly comprises a load distributing spring and a load distributing spring spacer. 5. A bicycle fork as in claim 1, wherein: said inner fork tubes travel into said outer fork tubes through the compression stroke; and said load distributing assembly is arranged to distribute compression forces through approximately the last one third of travel of said inner fork tube into said outer fork tube during a compression stroke. 6. A bicycle fork as in claim 5, further com- prising a load distributing spring and a load distributing spring spacer, the size and shape of said spring spacer permitting adjustment of the load distributing effect of said load distributing assembly to modify the point during compression of said bicycle fork at which compressive loads are distributed by said load distributing assembly. 7. A bicycle fork as in claim 1, wherein said spring assembly comprises a biasing element. 8. A bicycle fork as in claim 7, wherein said biasing element comprises an elastomer spring. 9. A bicycle fork as in claim 7, wherein said spring assembly further comprises a spring spacer. 10. A bicycle fork as in claim 7, wherein said spring assembly further comprises a plunger shaft. 11. A bicycle fork as in claim 10, wherein: said biasing element is positioned within one of said inner and outer fork tubes of said first fork leg; and said plunger shaft has a first end positioned within said one of said inner and outer fork tubes and a second end coupled to the other of said inner and outer fork tubes such that said first end slides within said one of said inner and outer fork tubes as said inner fork tube slides within said outer fork tube during compression of said bicycle fork. 12. A bicycle fork as in claim 11, wherein: said biasing element and said first end of said plunger shaft are positioned within said inner fork tube of said first fork leg; said second end of said plunger shaft is coupled to said second end of said outer fork tube; an end plate is provided on said first end of said plunger shaft; and a flange is formed on said second end of said inner fork preventing said end plate from being withdrawn from said inner fork upon movement of said inner fork tube apart from said outer fork tube. 13. A bicycle fork as in claim 12, further com- prising a top out spring positioned between said end plate and said flange on said inner fork tube of said first fork leg. 14. A bicycle fork as in claim 13, further com- prising a spring spacer positioned within said inner fork tube of said first fork leg between said first end of said inner fork tube and said biasing elemen . 15. A bicycle fork as in claim 11, further com- prising a spring spacer positioned within said one of said inner and outer fork tubes . 16. A bicycle fork as in claim 15, wherein: said biasing element is positioned within said inner fork tube of said first fork leg; said spring spacer is positioned between said first end of said inner fork tube and said biasing element; and said first end of said plunger shaft is positioned within said inner fork tube to support said biasing element and said second end of said plunger shaft is coupled to said second end of said inner fork tube. 17. A bicycle fork as in claim 11, wherein said load distributing spring assembly comprises a load distrib- uting spring at the second end of the other of said inner and outer fork tubes . 18. A bicycle fork as in claim 11, wherein said load distributing spring assembly comprises a load distrib- uting spring and a load distributing spring spacer at said second end of the outer fork tube of said second fork leg such that upon compression of said fork, said first end of said inner fork tube compresses against said load distribut- ing spring to distribute loads imparted to said bicycle fork. 19. A method of assembling a bicycle suspension fork capable of undergoing a compression stroke and an expansion stroke, said method comprising the steps of: providing a bicycle fork having a first fork leg and a second fork leg, each of said first and second fork legs comprising an inner fork tube telescopingly en- gaged within an outer fork tube, said inner fork tube and said outer fork tube each having a first and a second end, said second end of said inner fork tube telescoping into said first end of said outer fork tube during a compression stroke; positioning a primary compression spring assembly between said inner and outer fork tubes of only said first fork leg; and providing a load distributing assembly be- tween said inner and outer fork tubes of at least one of said first and second fork legs. 20. A method as in claim 19, further comprising the step of providing said load distributing assembly in said second fork leg. 21. A method as in claim 19, wherein said inner fork tubes travel into said outer fork tubes through the compression stroke, said method further comprising the step of arranging said load distributing assembly to distribute compression forces through approximately the last one third of travel of said inner fork tube into said outer fork tube during a compression stroke.

Inventors: MCANDREWS MICHAEL L, WINTER MARK J, MCANDREWS, MICHAEL, L., WINTER, MARK, J.
Applicants: ROCKSHOX INC, ROCKSHOX, INC.
Application year: 1998
Main classification: B62K25
IPC codes: B62K25, F16F1