Modular butt-jointed yoke for motorcycles

This application is a Continuation-in-Part of U.S. patent application Ser. No. 10/101,941 filed Mar. 21, 2002 now abandoned which claims priority from U.S. Provisional Patent Application No. 60/284,518 filed Apr. 19, 2001 entitled One-Piece Conventional-Fork Curved Yoke for Motorcycles.

This invention relates to the field of devices for securing motorcycle front forks to the head tube of the motorcycle frame, and in particular, to an improved yoke for the mounting of front forks to the head tube.

As seen in FIGS. 1 and 2, it is known in the prior art to use angularly shaped sharp or hard-edged yokes for pivotally mounting motorcycle front forks to the head tube of the motorcycle frame. For use on motorcycles such as Harley Davidson™ motorcycles, such components may be purchased from vendors such as Perse Performance™ of Englewood, Colo., for example components from that vendor referred to as Triple Trees™. Conventionally yokes such as the Triple Tree kits marketed by Perse Performance™ are manufactured as a kit of separate components that must be assembled to form the yoke. The yokes clamp around the outside of the fork tubes. The clamping of the yokes around the outside of the fork tubes may reduce the aesthetic appeal of the motorcycle. Further, it introduces the potential for a loss of rigidity of the yoke, such a loss of rigidity being undesirable in that the front wheel of the motorcycle is cantilevered from the yoke at the end of relatively long forks and thus subject to considerable force, bending moment and vibration.

There is a significant aftermarket in customizing motorcycles such as Harley Davidson™ motorcycles. One such example is the subject of FIG. 2, being a customized motorcycle used for display at motorcycle shows and the like. As may be seen, the customizing of the motorcycle results in a significantly rounded, flowing design where the conventional teardrop shape of the fuel tank is modified so that the fuel tank flows conformably into the seat pad saddle which itself then slows curvaceously into the swell of the rust fender. This lends the motorcycle a low elegantly curved profile. The curved low side-on profile is complemented by the use of aft-swept arcuately curved handlebars sweeping back from where they are mounted to the yoke immediately adjacent the head tube of the frame to which the motor and lower decorative fairings or cowlings are mounted. The yoke conventionally supports the forward extending forks, the front wheel and front fender mounted cantilevered on the distal end of the forks. Conventionally, the headlight is mounted to, so as to extend forwardly from between the uprights of the yoke.

The use of a prior art yoke on such a customized motorcycle, or for that matter other customized motorcycles which have rearwardly flowing curved lines in side-on profile, rather harshly interrupts the flowing lines of the profile due to the conventional hard-edged clamping of the corners of the generally triangular mounting plates around the exterior surface of the upper ends of the fork tubes or posts.

Thus in the present invention it is an object to provide a yoke which has, contrary to the motorcycle prior art of which applicant is aware, modular butt-jointed cross-bearing members or arches, where the yoke smoothly and aerodynamically curves rearwardly so as to complement the rearward flowing lines of the adjacent teardrop-shaped fuel tank on the motorcycle when the yoke is mounted to the head tube.

In summary the present invention is a modular butt-jointed front fork yoke for a motorcycle. The yoke may include upper and lower arches extending between a parallel pair of posts wherein the lower arch is butt-jointed to the pair of posts. Each post has an upper end and an opposite lower end. The upper arch extends from and between each upper end of the posts. Each upper end forms an impost at opposite ends of the upper arch.

The lower arch parallels the upper arch and is mounted to, so as to extend between, the lower ends of the pair of posts or adjacent the lower ends of the posts. The upper and lower arches each have a vertice lying on or adjacent an axis of rotation of the yoke when the yoke is mounted to a motorcycle frame so that a head tube of the frame is coaxial with the axis of rotation and is mountable snugly between the vertices of the upper and lower arches. The upper and lower arches each form a corresponding concavity under each arch which opens downwardly towards the lower ends of the posts.

The imposts form a pair of rounded-over shoulders between the upper arch and the posts. The shoulders are rounded in a plane containing the pair of posts so as to smoothly blend outer surfaces of the upper ends of the posts into outer surfaces of opposite ends of the upper arch, and are rounded-over between the front and rear of the yoke.

The pair of posts and the arches collectively have a front face, for facing forwardly from the motorcycle when the yoke is mounted to the motorcycle frame, and an opposite rear face. The arches have corresponding rear surfaces. Protrusions on the rear surfaces of the arches are curved so as to smoothly protrude rearwardly adjacent the vertices of the arches. The protrusions are adapted for vertically aligned mounting of the head tube therebetween. The front face is smoothly rounded over toward the rear face around forwardly exposed edges of the posts and the arches. The shoulders are rounded so as to smoothly blend from the front face at the upper ends of the posts, upwardly into the opposite ends of the upper arch and rearwardly so as to round smoothly into the rear face. The yoke is adapted so that the front face rakes, and is curved upwardly, aft when the yoke is mounted on the motorcycle frame, whereby a side profile of the yoke smoothly and aerodynamically blends into aft flowing curved lines of the motorcycle.

In one embodiment the pair of posts may be a pair of cylinders and the arches may each be generally semi-circular, that is, semi-circular or a lesser segment of a circle. The shoulders may be cupped so that each is shaped in the form of a cup-segment, that is, smoothly rounded as might be a well muscled human shoulder. Thus the arches and the shoulders may each have an upper surface which is rounded from the front face to the rear face of the yoke symmetrically about the above-defined plane, in which case the plane bisects the pair of posts so that longitudinal axes of symmetry of each post lie in the plane.

The lower arch parallels the upper arch and is butt-joint mounted to the posts or uprights at each end of the lower arch, so as to extend between the lower ends of the posts or adjacent the lower ends of the posts.

In one embodiment not intended to be limiting, each post has a symmetrical aperture in a sidewall thereof, and inside each post is a ledge adjacent the lower end of the post such that the ledge is below the aperture. Each post has an outer diameter, measured between the outer edges of one end of the post, and an inner diameter, measured between the inner edges of that end of the post.

Two hollow collars or cylinders are provided, each having an upper end and a lower end. Each cylinder is open at both ends. Each cylinder has an asymmetrical aperture, that is, a cammed aperture having an asymmetric cam surface. Each cylinder has an outer diameter, measured between the outer edges of one end of the cylinder, and an inner diameter, measured between the inner edges of that end of the cylinder. The outer diameter of each cylinder approximates, that is, is slightly less than the inner diameter of each post for snug flush sliding fitment of a cylinder into a corresponding post.

Thus, when a cylinder is inserted into each post, each cylinder rests on the ledge inside the corresponding post so as to align the cammed aperture on the cylinder with the symmetrical aperture in the post. A corresponding cammed nut is mounted into the cammed aperture so as to mate the asymmetrically cammed surfaces, thereby preventing rotation of the nut in the cammed aperture. Bolts are inserted through bolt-holes in the ends of the lower arch, through the symmetric apertures in the posts so as to threadably engage the cammed nuts mounted in the cammed apertures in the cylinders. Tightening the bolts draws the ends of the lower arch rigidly onto the opposed facing outer surfaces of the pair of posts.

FIG. 1 is, in perspective view, a prior art motorcycle yoke.

FIG. 2 is, in perspective view, a customized motorcycle incorporating the prior art yoke of FIG. 1 .

FIG. 3 is, in perspective view, the yoke of the present invention mounted to a motorcycle frame.

FIG. 4 is, in perspective view, the yoke of FIG. 3 mounted to front forks.

FIG. 5 is, in perspective view, the customized motorcycle of FIG. 2 employing the improved yoke of the present invention.

FIG. 6 is, in enlarged view, the yoke of FIG. 3 .

FIG. 7 is, in rear perspective view, the yoke of FIG. 5 .

FIG. 8 is, in front perspective partially exploded view, the yoke of FIG. 7 .

FIG. 9 is, in exploded partially cut-away view, the lower arch butt-jointing mechanism of the yoke of FIG. 8 .

FIG. 10 is a partially cut away exploded perspective view of the modular yoke according to the present invention.

FIG. 10 a is a perspective view of one post of FIG. 10 .

FIG. 10 b is a perspective bottom view of the lower arch of FIG. 10 .

FIG. 10 c is a perspective view of the post of FIG. 10 a showing the cammed nut protruding from the collar mounted within the post.

A prior art yoke 10 is illustrated in FIGS. 1 and 2, in FIG. 2 shown mounted on a customized motorcycle 12 such as a customized Harley Davidson™ motorcycle. In the illustrated example of FIG. 2, which is only intended to be by way of example and not intended to be limiting, the fuel tank 14 flows curvaceously aft, as indicated in FIG. 2 by direction arrow A, so as to conformably blend into saddle 16 and then swell arcuately over curved rear fender 18 . The flowing profile of fuel tank 14 , saddle 16 and fender 18 is complemented by the rearwardly arcuately swept shape of handlebars 20 and by the shape of front fender 22 which is conformably curved to front wheel 24 .

Front wheel 24 and fender 22 are mounted to the forward or distal ends of conventional forks 26 , forks 26 being rigidly mounted to, so as to extend cantilevered from, the base plate 28 of prior art yoke 10 .

As better seen in FIG. 1, prior art yoke 10 consists of base plate 28 mounted in parallel spaced apart relation to top plate 30 by three parallel spaced apart posts including a pair of laterally spaced posts 32 and a central post 34 . Central post 34 pivotally mounts into the correspondingly-sized head tube of the motorcycle frame so as to allow steering by pivoting of front wheel 24 about the longitudinal axis of the head tube. The parts are bolted together. In particular, the front corners of base plate 28 are formed as collar clamps 28 a which may be tensioned onto and around forks 26 by tightening bolts 29 into threaded bolt-holes 28 b.

As seen in FIGS. 3-6, the yoke 36 of the present invention is smoothly and aerodynamically contoured so that, once mounted to head tube 38 so as to be angled or raked aft, for example in the conventional 35 degree to horizontal orientation of forks 26 , the rounded pair of columnar uprights 40 smoothly blend at shoulders 42 upwardly and rearwardly into arch 44 which itself curves upwardly and rearwardly from shoulders 42 so as to medially intersect the axis of rotation B of head tube 38 . The upper arch 44 and shoulders 42 of yoke 36 are formed as a single unitary piece, for example milled, cast or forged. This reduces vibration and increases rigidity which provides advantages over the prior art. The surfaces of shoulders 42 and arch 44 are rounded-over from front to back so that a tangent to the curvature of the surfaces becomes approximately parallel to the curvature of fuel tank 14 along line A. A correspondingly formed lower arch 46 extends in generally parallel array with arch 44 between the lower ends of uprights 40 so as to medially intersect axis of rotation B below head tube 38 . As better described below, arch 46 is mounted to uprights 40 so as to be butt-jointed thereto, that is, without the use of external collars or clamps around the uprights.

Thus, once yoke 36 is mounted onto head tube 38 , the aft-raked flowing lines of yoke 36 such as illustrated by way of example by profile lines C, complement the flowing lines exemplified by profile line A in rearwardly flowing symmetry as would be expected if the design resulted from wind tunnel testing for aerodynamic efficiency. The flowing lines exemplified by lines C as they flow upwardly and rearwardly over yoke 36 also complement the aft-raked curvature of handlebars 20 and the smoothly rearwardly flowing profile of fuel tank 14 , saddle 16 and rear fender 18 , and appear a natural adjunct of the curvature of front wheel 24 and fender 22 .

As better seen in FIGS. 7-9, head tube 38 is mounted between arches 44 and 46 rotatably onto a removable central post 34 . The uppermost end of central post 34 mounts into a correspondingly sized bore 48 on the underside of arch 44 , bore 48 being coaxial with axis of rotation B. The uppermost end of head tube 38 may rotatably mount within seat 50 on the underside of arch 44 . Head tube 38 is held seated within seat 50 by means of adjustable collar 52 mounted snugged upwardly against the base of head tube 38 so as to snug upper collar flange 52 a upwardly against the base of the head tube.

The lower or base end of central post 34 is journalled along axis of rotation B through collar 52 . Arch 46 has a correspondingly sized bore 54 which extends through the arch for receiving collar 52 slidably mounted therein. With collar 52 slidably mounted within bore 54 , and with flange 52 a snugged upwardly against the base of head tube 38 , a cammed nut 56 is threadably mounted to bolt 58 through a further bore 60 bored through arch 46 perpendicularly to bore 54 . Cam surface 56 a on cammed nut 56 is aligned flush against planar lands 52 b on lower collar portion 52 c of collar 52 so as to both clamp collar 52 onto the lower end of central post 34 and to inhibit rotation of central post 34 relative to yoke 36 . Once the head of bolt 58 is tightened into cup washer 62 against cammed nut 56 , movement of collar 52 along axis B is inhibited.

In the butt-jointed mounting of lower arch 46 onto posts or uprights 40 as seen in FIGS. 10, 10 a , 10 b and 10 c , a collar or cylinder 120 is co-axially inserted into each upright 40 such that the lower surface 120 b of each cylinder 120 rests on the ledge 40 b inside each upright 40 . An asymmetric or cammed hole or aperture 120 a formed in the sidewall of each cylinder 120 is aligned with a symmetric hole or aperture 110 a on each upright 40 . The narrow end 118 a of each nut 118 is inserted from the inside of a cylinder 120 through aperture 120 a and into aperture 110 a until base 118 b of nut 118 prevents rotation of narrow end 118 a of nut 118 mounted in apertures 120 a and 110 a.

Each primary mounting bolt 114 of the pair of such bolts is inserted through a corresponding bolt hole 46 a in each end of lower arch 46 , then through washer 112 . Each bolt is then threaded into end 118 a of cammed nut 118 until bolt surface 114 a is flush against annular rim 46 b within bolt hole 46 a . A washer 112 may be sandwiched between bolt surface 114 a and the surface of rim 46 b.

A pair of tubes 122 are inserted into the upper ends of each upright 40 such that the lower surfaces 122 a of tubes 122 are flush with the upper surfaces 120 c of cylinders 120 when mounted inside uprights 40 .

Shoulders 42 of upper arch 44 are mounted onto the upper surfaces 122 b of tubes 122 such that each end surface 44 a of arch 44 is flush with each upper surface 122 b of tubes 122 .

The curved ends 46 c of lower arch 46 are shaped to conformably mate, adjacent apertures 110 a , onto the tubular outer surfaces of uprights 40 . Pins 124 protruding from uprights 40 mate into corresponding holes 46 d in the curved oppositely disposed end surfaces of curved ends 46 c . The primary mounting bolts 114 extend through the end surfaces of curved ends 46 c so as to engage the cammed nuts 118 mounted in the cammed apertures 120 a in cylinders 120 . Tightening of the primary mounting bolts 114 into the cammed mats 118 mates the pins 124 into the holes 46 d in the lower arch. Locking bolts 126 , transversely mounted in transverse holes 46 e the lower arch, once tightened, engage the heads of the primary mounting bolts 114 to prevent rotation of the primary mounting bolts once tightened into cammed nuts 118 .

Each cammed nut 118 has a flattened and asymmetrical narrow end 118 a and a flattened, asymmetrical base 118 b . The surface area of the base of each nut is larger than the surface area of the end of each nut. Inside each upright 40 , a cammed nut 118 is journalled through the cammed aperture 120 a in the cylinder 120 and then through the aperture 110 a in the upright 40 until the base 118 b of the nut 118 prevents further protrusion of the nut 118 into the upright 40 . Each bolt 114 is inserted through a washer 112 , then through a hole 46 a in one end 46 c of lower arch 46 , then through aperture 110 a in upright 40 and then threaded into end 118 a of cammed nut 118 . The result is that each end 46 c of lower arch 46 forms a butt-joint with each upright 40 .

Two 122 tubes are provided, each having an upper and a lower end for mating uprights 40 with shoulders 42 . The diameter of each tube 122 provides for snug mating of the tubes into uprights 40 . Each tube 122 is inserted into the upper end of an upright 40 , such that the lower end of the tube abuts the upper end of a cylinder 120 , and the upper end of tube 122 protrudes out of the upper end of upright 40 for mounting into shoulders 42 of upper arch 44 . The upper ends of tubes 122 are inserted into shoulders 42 at the ends of upper arch 44 , such that each end of the upper arch is flush with the upper end of an upright.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.