Note: Descriptions are shown in the official language in which they were submitted.
101520253035CA 02264636 1999-03-08wo 99/0,1677 PCT/US98/13196PISTON ROD AND PISTON ASSEMBLYCROSS-REFERENCE To RELATED APPLICATIONThe present application claims the benefit of theearlier filing date of U.S. provisional patent application60/051,636, filed July 3, 1997.BACKGROUND OF THE INVENTIONSer. No.The present provisional patent application relatesto the design and construction of piston rod and piston assemâblies. More particularly, the present invention relates to anapparatus and method for manufacturing a lightweight, low costdamping assembly comprising a piston rod configured to have adamper piston injection molded directly thereon, for use inthe damping system of high-performance suspension systems,particularly high-performance bicycle suspension systems.A variety of systems utilize piston rods on which apiston assembly is mounted. A common use for a piston rod andpiston assembly is in hydraulic damping systems having a dampâing fluid cartridge. The piston rod is passed through thedamping cartridge such that the piston mounted thereon slidesthrough the damping fluid in the cartridge to effectuate dampâing. Such hydraulic damping systems have been known to beincorporated into suspension systems, such as those used inthe motorcycle and automotive fields, as well as in the fieldof bicycles. For example, U.S. Patent No. 5,456,480 to Turneret al. (the "'48O patent"), which patent has been assigned tothe assignee of the present invention and is hereby incorpo-rated by reference in its entirety, discloses a suspensionsystem for use in a bicycle fork and having a damping system.The suspension bicycle fork of the '48O patentincorporates a replaceable damping cartridge unit. The car-tridge unit is comprised of a cylindrical cartridge bodyfilled with hydraulic oil. on which a pistonassembly is mounted, is passed through the cartridge body sothat the piston assembly is slidable within the cartridgebody.A piston rod,The cartridge unit further has cartridge seals at both101520253035CA 02264636 1999-03-08W0 99/01677 PCT/US98/13196ends, sealing the points at which the piston rod is passedthrough the cartridge body ends. The piston rod extendsthrough the cartridge seals at both ends of the cartridgebody, and the piston divides the cartridge into two chambersand engages the inner surface of the cartridge body to sealthe first chamber from the second chamber. Ports extendthrough the piston as well as through the piston rod, so thatupon movement of the piston in the cartridge body, hydraulicoil passes from one side of the piston to the other. Therestriction of the passages determines the degree of resis-tance effected as the oil is forced through the passages, andthus determines the amount of damping achieved for a givenpiston speed.As illustrated in the '48O patent, a bicycle suspen-sion fork typically has a pair of telescoping struts, and thedamping cartridge attaches to one of the struts. The pistonrod and piston assembly attaches to the other strut so thatwhen the struts are compressed or expanded, the movement ofthe oil from one side of the piston to the other createsdamping.For applications such as bicycles, weight is a majorThus, piston rods such as the piston rod of the '48Opatent, as well as those not used in cartridge-type systems,concern .have typically been made from aluminum. Ideally, aluminumso that themovement of the rod against the damping system seals does notdegrade the integrity of the cartridge seals.piston rods are machined to a fine surface finish,However, thecost of finely finishing aluminum shafts is high, and as aresult, the aluminum shafts typically used in connection withdamped suspension systems are unnecessarily abrasive. Thenatural result of this is that damping system seals degrademore rapidly than is desirable, leading to hydraulic fluidleakage and the need for servicing at unnecessarily short timeintervals. It therefore would be desirable to provide alightweight piston rod that has a finely finished exterior101520253035CA 02264636 1999-03-08wo 99/01577 PCT/US98/13196surface, yet is also low in cost and has the requisitestrength to endure compressive forces applied thereto.In designs such as that illustrated in the '48O pat-ent, the piston rod comprises two rod sections which aresecuring the piston between them. In suchthe wall of the piston rod must be ofsufficient thickness to accommodate threads.threaded together,a design, however,Similarly, pis-tons have been attached to piston rods, for example, by usingsnap-rings positioned in grooves located on the outer surfaceof the piston rod on either side of the piston. thisattachment mechanism requires that the wall of the piston rodHowever,be sufficiently thick to accommodate snapâring grooves.In order to permit passage of damping fluid throughthe piston rod, and also in order to reduce weight, pistonrods typically are tubular. To reduce the weight of thepiston rod even further, especially if a material stronger andheavier than aluminum is used, the walls must be as thin aspossible. A common difficulty in providing for a lightâweighttubular piston rod is that the thin walls cannot be providedwith appropriate structural features, such as described above,for accommodating attachment mechanisms necessary for couplingthe rod with other elements. If the walls are made thickenough to accommodate such attachment mechanisms, then thepiston rod typically becomes unnecessarily heavy and costly tomanufacture.SUMARY OF THE INVENTIONIt is therefore an object of the present inventionto provide a lightweight and low cost piston rod having asufficiently fine finish that reduces wear on the seals of thedamping system in which the piston is used.It is another object of the present invention toprovide a piston rod that has the requisite strength for usein a suspension system, that is lightweight yet formed suchthat a piston may be securely mounted thereon.The above and other advantages are realized inaccordance with the principles of the present invention by. .. _...._....¢.....4...........m..a............., .. . , ... ..i._..., _.._.... .......,-. ...w~. ,101520253035CA 02264636 1999-03-08W0 99/01677 PCT/US98/13196providing a thinâwalled, preferably steel piston rod having achrOmeâplated exterior providing a finely finished surface forsliding against the seals of a damping system, preferably butnot necessarily including a damping cartridge, through whichthe piston rod is to be passed. A portion of the exterior ofthe piston rod is not provided with the chromeâplating, butinstead is formed such that a piston may be mounted thereonwithout additional mechanical connection elements. In partic-ular, the exterior of the unplated surface of the piston rodis preferably shaped such that a piston may be injectionmolded thereon for secure attachment thereto. For example,the unplated exterior may be provided with one or more holesor a series of shallow grooves in which the plastic of thepiston may anchor itself.The above and other objects, and advan-features,tages of the present invention will be readily apparent fromthe following detailed description of the invention taken inconjunction with the accompanying drawings wherein like refer-ence characters represent like elements, the scope of theinvention being set out in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGSIn the drawings:FIG. I is an elevational view, partly in section, ofa bicycle suspension fork having a damping cartridge incorpo-rating a preferred embodiment of the piston rod and pistonassembly Of the present invention;FIG. 2 is a perspective view of a preferred embodi-ment of the piston rod and piston assembly of the presentinvention;FIG. 3 is an elevational view Of a preferred embodi-ment of the piston rod of the present invention; andFIG. 4 is an enlarged isolated view of the pistonattachment portion of the piston rod of FIG. 3.DETAILED DESCRIPTION OF THE INVENTIONIn accordance with the principles of the presentinvention, a lightweight yet strong piston rod 10 (FIGS. 1-4)4101520253035CA 02264636 1999-03-08W0 99/0] 577 PCT/US98/13196having first and second ends 12, 14 is provided for use in asuspension system. Preferably, piston rod 10 is formed as atubular rod with a sufficiently thin wall such that the pistonrod has sufficient strength to withstand compression forcesexerted on the suspension system with which it is used, yet issufficiently lightweight for effective use in a suspensionsystem in which weight reduction is essential for optimum use.A preferred material that is strong enough to be used in aThe thinâwalledsteel piston rod of the preferred embodiment of the presentthinâwalled tubular piston rod is steel.invention can be made to weigh as little as or less than theweight of an aluminum piston rod that performs the same func-tions. Preferably, the wall thickness of a steel piston rod(O.6985 mm).A typical use of piston rod 10 is in bicycle suspen-Fork 22comprises two telescoping struts 24 each having an inner tubeIt will beappreciated that the inner tube need not be the upper tube, asshown in FIG. 1, but,10 is approximately 0.0275 inchession system 20 of bicycle fork 22 shown in FIG. 1.26 telescopingly received within an outer tube 28.instead, may be the lower tube. Suspen-sion system 2O preferably includes a biasing element 30 posi-tioned within inner tube 26 (although it is within the scopeof the present invention to instead provide biasing element 30in the outer tube 28,and outer tube 28)or external to and between inner tube 26and supported by piston rod 10. Prefera-bly, a flange or other support element 31 is provided on firstend 12 of piston rod 10 to support biasing element 30. Secondend 14 of piston rod 10 may be coupled to the outer tube 28 asdescribed in further detail below. Compression of fork 22causes inner tubes 26 to telescopingly slide into outer tubes28. As a result, biasing element 30 is compressed againstflange 31 on first end 12 of piston rod 10. As will be under-stood by one of ordinary skill in the art, piston rod 10, aspositioned within fork 22, must therefore be sufficientlystrong to endure the compressive forces exerted on fork 22.The formation of piston rod 10 from a thinâwalled chromed-101520253035CA 02264636 1999-03-08WO 99/01677 PCT/US98/13196steel in accordance with the principles of the present inven-tion provides the requisite strength for such use of pistonrod 10.As illustrated in FIG. 1, a damping system 32 pref-erably having at least one damping cartridge 34 may be pro-vided in at least one of struts 24 of fork 22. Ends 36, 38 ofdamping cartridge 34 are typically sealed in order to retaindamping fluid or gas therein. Piston rod 10 has a pistonassembly 40 mounted thereon, as shown in FIG. 2, and is passedthrough the seals on ends 36, 38 of damping cartridge 34 (or,where a damping cartridge is not used, through at least oneseal sealing the end of damping system 32) to effectuate thedamping function of damping system 32. Accordingly, a high-quality finely finished surface is typically desirable on theexterior of piston rod 10 to reduce wear of the seals ofdamping cartridge 34 resulting from the sliding of piston rodâ10 therethrough during use of fork 22. In a preferred embodi-ment, thin-walled steel piston rod 10 is provided with achrome-plated exterior. The finish achieved by chromeâplatingThus,damping cartridge 34 is far less likely to leak, and will re-the steel piston rod 10 improves the life of the seals.quire less servicing during use of the bicycle with which itis used.As described above, piston rod 10 is preferablyhollow to reduce weight. Additionally, when piston assembly40 is provided on piston rod 10 such that the combined pistonand rod assembly is used in a damping system such as system 32of FIG. 1, piston assembly 40 divides the interior of dampingcartridge 34 into two chambers. In order to permit dampingfluid to pass from one chamber to another and thereby damp thesystem, at least one throughâhole fluidly connecting thechambers must be provided within at least one, and preferablyboth, of piston rod 10 and piston assembly 40. When through-holes are provided in piston rod 10, piston rod 10 is typi-cally hollow from end 12 to end 14.However, as described101520253035CA 02264636 1999-03-08wo 99/01677 PCT/US98/13196above, the walls of piston rod 10 should be as thin as possi-ble to reduce the weight of the system.The thin walls of piston rod 10 must nonethelesspermit attachment of piston assembly 40 thereto. In a pre-ferred embodiment, as illustrated in FIG. 2, at least plasticpiston 42 of piston assembly 40 is injection-molded directlyonto piston attachment piston 44 of piston rod 10, shown inFIGS. 3 and 4. Although nylon 6,6 has been found to work wellfor the injection-molding of the piston, any type of plasticor other moldable material may be used.As described above, piston rod 10 is preferablychromeâplated. However, to facilitate attachment of piston 42to the exterior of piston rod 10, piston attachment portion 44is not chrome-plated.A variety of securing devices may be used to ensurethat piston 42 is fixed in place on the piston rod 10, such asa knurledâtype surface, a series of dimples or holes in pistonrod 10,groove in piston rod 10.or a rollâcrimped or machined groove or other type ofPreferably, however, piston attach-ment portion 44 of piston rod 10 includes one or more shallowgrooves,and more preferably still, includes a continuous,shallow spiral groove as shown in FIGS. 2 and 3. Such groovesprovide ample surface area with which the plastic of piston 42may anchor itself to rod 10, thus preventing piston 42 fromtraveling toward the first 12 or second 14 end of piston rod10. In addition, the spiral geometry of the grooves preventspiston 42 from rotating on piston rod 10.chrome plating on piston attachment 44 portion of piston rodThe absence of40 also helps to prevent movement of piston 42 with respect topiston rod 10.Thus, the injection-molded design of the presentpiston rod 10 and piston assembly 40 eliminates the need forspringâclip grooves or other fastener connections for attach-ing piston assembly 40 to piston rod 10, thereby reducing thenumber of parts required in,and the complexity of, the assem-bly. In addition, as a result of using shallow spiral grooves7101520253035CA 02264636 1999-03-08W0 99/01677 PCT/US98/13196to secure an injectionâmolded piston to piston rod 10, pistonrod 10 may be constructed of thin tubing, preferably thinsteel tubing, as described above.In accordance with a preferred embodiment, thepiston rod 10 and piston assembly 40 of the present inventionare used in a damping system 32 of a bicycle suspension rod 22as shown in FIG. 1, as described above. Preferably, cartridgebody 34 of damping system 32 is secured within inner tube 26,while first end 14 of piston rod 10 is secured to outer tube28.Because the walls of piston rod 10 are preferablyvery thin such that they cannot support a thread, an alterna-tive means is required to secure piston rod 10 to the outertube 28. In the preferred embodiment of the present inven-tion, an insert 50 couples second end 14 of piston rod 10 tothe bottom end of outer tube 28. Insert 50 is crimpable on afirst end 52 and configured for operative connection (such asby threaded connection) to the outer tube 28 on a second end54. The first end 52 of insert 50 is placed into and securelycrimped within second end 14 of piston rod 10 such that insert50 and piston rod 10 are securely coupled together. Thecrimping may be accomplished using a rollâcrimping or othercrimping process, but is preferably accomplished using acrimping process that effects a connection between insert 50and piston rod 10 such that piston rod 10 cannot rotate rela-tive to insert 50. Such a connection may be achieved, forexample, using a rollâcrimping device or a threeâjaw crimpingtool that crimps the rod and insert at three locations spacedapart by about 120 degrees. Alternatively, although perhapsnot as preferable, insert 50 may be configured at first end 52to be pressâfit into second end 14 of piston rod 10.In a preferred embodiment of the present invention,second end 54 of insert 50 has an internally threaded bore 56so that a bolt may be passed through an opening in the bottomof outer tube 28 to secure piston rod 10 to the outer tube 28.The outer surface 58 of second end 54 of insert 50 is to be10152025CA 02264636 1999-03-08wo 99/01577 PCT/US98/ 13196seated in a tapered bore in outer tube 28. To prevent insert50 from rotating relative to tapered bore, as may occur whenthe bolt passing through the lower end of outer tube 28 isthreaded into or out of insert 50, the outer surface 58 ofKnurl-ing or splining outer surface 58 of second end 54 of insert 50enables insert 50 to cut its own seat into the tapered bore ofsecond end 54 of insert 50 may be knurled or splined.outer tube 28 as insert 50 is bolted to the outer tube 28.While the foregoing description and drawings repre-sent the preferred embodiments of the present invention, itwill be understood that various additions, modifications andsubstitutions may be made therein without departing from thespirit and scope of the present invention as defined in theaccompanying exemplary claim. In particular, it will be clearto those skilled in the art that the present invention may beembodied in other specific forms, structures, arrangements,proportions, and with other elements, materials, and compo-nents, without departing from the spirit or essentialcharacteristics thereof. One skilled in the art will furtherappreciate that the invention may be used with many modifica-tions of structure, arrangement, proportions, materials, andcomponents and otherwise, used in the practice of the inven-tion, which are particularly adapted to specific environmentsand operative requirements without departing from the princi-ples of the present invention. The presently disclosed em-bodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and not limited to theforegoing description.
