Fork stem assembly for a motorcycle

Abstract

Motorcycle (10), which includes: a main frame (12) configured to support a drive unit (24), at least one rear wheel (20) and at least one seat (23), a steering head (50) fixed to the main frame (12) and having a bore (54) between a first end (56) and a second end (64) of the steering head (50), the bore (54) defining a steering axis (A), and a steerer tube assembly (100) comprising: at least one steerable front wheel (14) which can be rotated about the steering axis (A) relative to the steering head (50), a first shaft member (112) extending into the bore (54) from the first end (56), and a second shaft member (124) extending into the bore (54) from the second end (64), wherein the first shaft member (112) is fixed to the second shaft member (124) within the bore (54), wherein none of the first (112) and second shaft members (124) extends completely through the bore (54), wherein the first shaft member (112) is removably attached to the second shaft member (124) at a connection (202) within the bore (54), the shaft members in the connected state define a shaft length (L), measured parallel to the steering axis (A), and the connection (202) between the two shaft members is arranged centrally along the length L.

Description

[0001] The present invention relates to a steering arrangement for a motorcycle.

[0002] The steering assembly of a motorcycle typically includes a fork stem that couples a front wheel and handlebars to a main frame to provide steering inputs to the front wheel of the motorcycle. The fork stem extends through a steering head of the main frame between an upper triple clamp and a lower triple clamp. Specifically, the upper triple clamp couples the fork stem, a pair of fork tubes, and a handlebar to the steering head. The lower triple clamp couples the fork stem and the front wheel, which is coupled to a pair of fork tubes, to an opposite side of the steering head. The fork stem is one-piece and can be inserted into the steering head from only one end to be retained by upper and lower bearings positioned therein. One or both bearings must be provided with a radial clearance on the fork stem to allow for mounting.Due to the radial clearance, a high steering link clamp load is desirable to limit sliding between the shaft and the inner races of the bearings. However, the clamp load can only be increased to a certain point without compromising ideal steering damping and handling.

[0003] US 2008 / 0 296 077 A1 describes a fork stem assembly with two stem members that are not arranged parallel to each other and can be connected to each other.

[0004] US 2010 / 0 283 219 A1 describes a bicycle front end assembly designed to reduce aerodynamic drag. A fork is attached to the head tube with an axle shaft. Bearings are preloaded using a headset cap to center the axle shaft on the head tube. After centering, the headset cap is attached to the axle shaft in a further step. Summary

[0005] According to one aspect, the invention provides a fork stem assembly for rotatably coupling a steering assembly to a steering head of a motorcycle main frame. The fork stem assembly includes a first stem member configured to support a first end of the steering assembly at a first end of the steering head, and a second stem member configured to support a second end of the steering assembly at a second end of the steering head. The second stem member is formed separately from the first stem member. A connection is defined between the first and second stem members and fixedly connects the first stem member to the second stem member.

[0006] According to another aspect, the invention provides a motorcycle comprising a main frame configured to support a drive unit, at least one rear wheel, and at least one seat. The motorcycle further comprises a steering head fixed to the main frame and having a bore between a first end and a second end of the steering head. The bore defines a steering axis. A fork stem assembly includes at least one steerable front wheel rotatable about the steering axis relative to the steering head. A first stem member extends through the bore from the first end, and a second stem member extends through the bore from the second end. The first stem member is fixedly connected to the second stem member within the bore.

[0007] According to another aspect, the invention provides a method for assembling a steering assembly of a motorcycle. A main frame is provided having a steering head including a bore defining opposite upper and lower ends. A first stem member is inserted into the lower end of the bore of the steering head, and a second stem member is inserted into the upper end of the bore of the steering head. The second stem member is fixedly connected to the first stem member at a joint within the bore.

[0008] Other aspects of the invention will become apparent from the following detailed description with reference to the accompanying drawings. Brief description of the drawings Fig. 1 is a side view of a motorcycle incorporating a two-piece fork stem assembly according to an embodiment of the invention. Fig. 2 is a side view of a steering assembly of the motorcycle of Fig. 1, with a portion cut away to show the two-piece steerer assembly. Fig. 3 is an exploded view of the steerer tube assembly of Fig. 2, which comprises a lower holding arrangement and an upper holding arrangement. Fig. 4 is a view of the lower support assembly of Fig. 3 in the unassembled state. Fig. 5 is a view of the lower support assembly of Fig. 3 in assembled state. Fig. 6 is a view of the upper support assembly of Fig. 3 in the unassembled state. Fig. Figure 7 is a view of the upper support assembly of Fig. 3 in assembled state. Fig. Figure 8 is a cross-sectional view of the steerer tube assembly taken along line 8-8 of Fig. 3. Detailed description

[0009] Before describing various aspects of the invention in detail, it should be noted that the invention is not limited in its application to the details of construction and arrangement described below and shown in the drawings. The invention may also be realized by other embodiments.

[0010] Fig. 1 shows a motorcycle 10 having a main frame 12, a front wheel 14 coupled to the main frame 12 via a pair of fork tubes 16 (only one of which is shown), a steering assembly 18, a rear wheel 20 connected to the main frame via a pivot arm 21, and at least one saddle seat 23 for supporting a rider and optionally a passenger. The steering assembly 18 includes a handlebar 22 for steering the motorcycle 10. The motorcycle 10 includes a drive unit (e.g., an engine such as an internal combustion engine) coupled to the main frame 12 and further drivingly coupled to the rear wheel 20. In the illustrated construction, the drive unit 24 includes a V-engine connected to the rear wheel 20 via a multi-speed transmission 26.

[0011] Fig. 2-3 show the steering assembly 18 in greater detail. The steering assembly 18 couples the front wheel 14, the fork tubes 16, and the handlebar 22 to the main frame 12. The steering assembly 18 is rotatably supported relative to the motorcycle 10 by a steering head 50 that is integrally coupled to the main frame 12 of the motorcycle 10. As shown in Fig. 2, Fig. 3 and Fig. 8, the steering head 50 defines a through hole or bore 54 that defines a steering axis A and extends between a first or lower end 56 of the steering head 50 and a second or upper end 64 of the steering head 50. A first counterbore 60 is provided at the first end 56 of the bore 54, and a second counterbore 68 is provided at the second end 64 of the bore 54. The steering head 50 retainingly receives a steerer tube assembly 100 that extends through the bore 54 of the steering head 50 to secure the front wheel 14 and the handlebar 22 on opposite sides of the steering head 50. The steering assembly 18 further includes a lower crown 72 and an upper crown 76 configured to couple to the steerer tube assembly 100. The lower fork bridge 72 contains a shaft receiving opening or a through hole 80 ( Fig. 8) and first and second fork receiving openings or through-holes 84a, 84b disposed on opposite sides of the stem receiving through-hole 80. Similarly, the upper triple clamp 76 includes a stem receiving opening or through-hole 88 and first and second fork receiving openings 92a, 92b. The through-holes 80, 84a, 84b of the lower triple clamp 72 are axially aligned with the corresponding through-holes 88, 92a, 92b of the upper triple clamp 76. The upper triple clamp 76 may also include one or more retaining members for mounting the handlebar 22 to the upper triple clamp 76 to provide rider control of the steering assembly 18. Fig. 2 shows a clamp 94 that clamps the handlebar 22 and mounts it to the upper fork bridge 76.

[0012] As continued in Fig. 2 and Fig. 3, one of the fork tubes 16 extends through the corresponding through-holes 84a, 92a of the two fork bridges 72, 76 on a first lateral side of the front wheel 14, while the other fork tube 16 extends through the corresponding through-holes 84b, 92b of the two fork bridges 72, 76 on a second lateral side of the front wheel 14. Each of the fork tubes 16 is fixed to both lower and upper fork bridges 72, 76, such that the front wheel 14 is pivoted relative to the steering head 50 in direct response to pivoting of the handlebar 22 attached to the upper fork bridge 76. In the embodiment shown, the fork receiving through holes 84a, 84b, 92a, 92b in the lower and upper triple clamps 72, 76 are tightened or clamped around the corresponding fork tubes 16 by means of a fastener such as a clamp screw (not shown).Accordingly, each of the stem-receiving through-holes 80, 88 receives and is secured to at least a portion of the steerer tube assembly 100. As explained in more detail below, the stem-receiving through-hole 88 in the upper crown 76 is secured to the steerer tube assembly 100 by means of a clamp screw or other fastener 96 that extends through an opening 98 oriented perpendicular to the axis A and tightens the stem-receiving through-hole 88 around the steerer tube assembly 100. In other constructions, other coupling methods may be implemented to couple the fork tubes 16 and the steerer tube assembly 100 to the upper crown 76.

[0013] The steerer tube assembly 100 includes a lower support assembly 104 ( Fig. 4-5) and an upper holding arrangement 108 ( Fig. 6-7). The lower support assembly 104 includes a first, or lower, shaft member 112; and the upper support assembly 108 includes a second, or upper, shaft member 124. The first and second shaft members 112, 124 are each formed separately. The first shaft member 112 extends through and is supported by the first end 56 of the steering head 50; and the second shaft member 124 extends through and is supported by the second end 64 of the steering head 50. In particular, at least a portion of the first shaft member 112 extends into the bore 54 from the first side 56 of the steering head 50. Correspondingly, at least a portion of the second shaft member 124 extends into the bore 54 from the second side 64 of the steering head 50. The first and second shaft members 112, 124 are arranged on opposite sides of the steering head 50. As shown at least in Fig. 3, the first shaft member 112 includes a female threaded portion 192 (a threaded bore) and the second shaft member 124 includes a male threaded portion 188 (a thread on at least a portion of the outer surface). Thus, the female threaded portion 192 is configured to threadably receive and secure the male threaded portion 188, thereby forming a connection 202 as shown in Fig. 8. In other constructions, the male and female threads are reversed on the first and second shaft members 112, 124.

[0014] And in still other structures, structures other than threads are provided to fix the connection 202 between the first and second shaft members 112, 124.

[0015] As in Fig. 8, the lower and upper support assemblies 104, 108 also each include first and second bearings 116, 128, which have substantially the same construction. Each of the bearings 116, 128 is a detachable, tapered roller bearing in the construction shown. As shown in Fig. 3 and Fig. 8, the first bearing 116 and the second bearing 128 each comprise a first inner race 132, 134 with a tapered outer surface 133, 135 and an outer race 140, 142 with a tapered inner surface 144, 145. Each of the bearings 116, 118 includes a cage member 150 in which a plurality of circumferentially distributed rolling elements 136, 138 (i.e., rollers) are received. The rollers 136, 138 are radially disposed between the inner race 132, 134 and the outer race 140, 142 of the corresponding bearing 116, 128 to allow low-friction rolling of the rollers 136, 138 between the inner races 132, 134 and the outer races 140, 142. The inner diameter 204, 206 of each inner race 132, 136 is dimensioned and shaped to receive and secure the corresponding shaft member 112, 124 with an interference fit (ie, without clearance).The outer races 140, 142 are sized and shaped to be received in the respective first and second ends 56, 64 of the bore 54 in the steering head 50. As shown in . Fig. 8, the counterbores 60, 68 at the ends of the bore 54 receive the corresponding outer races 140, 142. The counterbores 60, 68 serve as a stop surface for accurate positioning of the outer races 140, 142 relative to the steering head 50. The inner races 132, 134 are sized and shaped to be received by the corresponding outer races 140, 142. The inner races 132, 134 and the outer races 140, 142 are complementary to each other. In other words, the inner race 132, 134 of each of the bearings 116, 128 has a smaller outer diameter at a first end 156, 158, with the diameter gradually increasing toward a second end 160, 162. Accordingly, the outer race 140, 142 has a smaller inner diameter at a first end 164, 166, with the diameter gradually increasing towards a second end 168, 170.The bearings 116, 128 may have alternative or additional structures or features to those described and shown herein. The lower support assembly 104 and the upper support assembly 108 may also extend through through holes or openings in respective dust caps 146, 148 disposed between the lower and upper triple clamps 72, 76 and the respective bearings 116, 128, as shown in FIG. Fig. 4 - 7 are coupled.

[0016] As in Fig. 4, Fig. 5 and Fig. 8, the lower support assembly 104 is fixedly attached to the lower triple clamp 72 and rotatably coupled to the first end 56 of the steering head 50. As shown, the first stem member 112 extends through the stem-receiving through-hole 80 in the lower triple clamp 72 and into the first end 56 of the bore 54 of the steering head 50. The stem-receiving through-hole 80 of the lower triple clamp 72 includes a counterbore 172 that acts as a stop surface for a flange 176 of the first stem member 112 at its lowermost end. The inner race 132 of the first bearing 116 is forced onto the first stem member 112 until the lower triple clamp 72 prevents further movement. The inner race 132 or the adjacent dust cap 146 may abut a first or upper surface 180 of the lower triple clamp 72. The rollers 136 can be mounted on the inner race 132 before the lower support assembly 104 is inserted into the steering head bore 54.The outer race 140 is positioned in the counterbore 60 in the steering head 50 (e.g., by means of a press fit). The inner race 132 and rollers 136 are received by the outer race 140 when the first stem member 112 is inserted upwardly into the bore 54 from the lower end 56. As explained above, the counterbore 60 acts as a stop surface for the outer race 140 and limits the distance that the bearing 116, and thus the first stem member 112, can extend into the bore 54. The lower triple clamp 72 can be pre-assembled with the lower support assembly 104 into a subassembly before being coupled to the steering head 50.

[0017] As in Fig. 6, Fig. 7 and Fig. 8, the upper support assembly 108 is fixed to the upper triple clamp 76 and rotatably coupled to the second end 64 of the steering head 50. As shown in Fig. 6 and Fig. 7, the inner race 134 of the second bearing 128 is press-fitted onto the exterior of the second stem member 124 to a final position as close to the upper end as possible. The inner race 134 or the adjacent dust cap 148 may abut against a shoulder surface 182 of an upper end of the second stem member 124. The rollers 138 may be mounted onto the inner race 134 before the upper retainer assembly 108 is inserted into the steering head bore 54. The outer race 142 is positioned in the counterbore 68 in the steering head 50 (e.g., by means of a press fit). The inner race 134 and the rollers 138 are received by the outer race 142 when the second stem member 124 is lowered into the bore 54 from the upper end 64. In the assembled state, the upper fork bridge 76 is positioned such that the upper end of the second shaft member 124 passes through the shaft receiving through-hole 88 as in Fig. 8 shown.

[0018] As in Fig. 8 and explained above, the second shaft member 124 is threadably connected to the first shaft member 112 within the bore 54. When the first and second shaft members 112, 124 are connected together, they define a shaft length L ( Fig. 8) measured parallel to the steering axis A. Although the first and second shaft members 112, 124 define overlapping portions, each of the first and second shaft members 112, 124 defines less than 100 percent of the shaft length L and none of the first and second shaft members 112, 124 extends completely through the bore 54. As shown, each of the first and second shaft members 112, 124 has a terminal end disposed within the bore 54 when the steerer tube assembly 100 is assembled with the steering head 50.

[0019] As explained above and further in Fig. 8, the first and second stem members 112, 124 and their corresponding complementary threaded portions 188, 192 define a threaded connection 202. In particular, the connection 202 is located where the threaded portions 188, 192 of each of the first and second stem members 112, 124 mechanically engage each other within the bore 54. Because the stresses generated by operating loads (braking loads and shocks) are lowest in the steerer tube assembly 100, the connection 202 is located between the first and second bearings 116, 128. Thus, the connection 202 may be located at or adjacent to a point of minimum stress along the length L of the steering assembly 100. In the illustrated configuration, the connection 202 is located centrally along the length L. However, in other structures, the connection 202 can also be arranged at a different position along the shaft length L.

[0020] Another advantage of the steerer tube assembly 100 is that the interference fits with no clearance between the bearings 116, 128 and the corresponding stem members 112, 124 prevent sliding at the interfaces therebetween regardless of the axial mounting load of the steerer tube assembly 100. When the first and second stem members 112, 124 are coaxially fixed to each other at the joint 202 within the bore 54, the first bearing 116 is at least partially disposed within the bore 54 of the steering head 50 between the first end 56 of the steering head 50 and the first stem member 112 without a radial clearance. Similarly, the second bearing 128 is at least partially disposed within the bore 54 between the second end 64 of the steering head 50 and the second stem member 124 without a radial clearance.The steering damping and handling are controlled independently as a function of the axial mounting load set by tightening the first and second shaft members 112, 124.

[0021] As continued in Fig. 4 and Fig. 5, the steering assembly 18 of the motorcycle 10 is assembled by press-fitting the first stem member 112 through the stem-receiving through-hole 80 in the lower triple clamp 72. The dust cap 146 is slid onto the first stem member 112. The inner race 132 is positioned by press-fitting it onto the first stem member 112 adjacent the first surface 180 of the lower triple clamp 72. The lower triple clamp 72 is fixed to the first stem member 112 between the inner race 132 and the flange 176 of the first stem member 112. As shown in Fig. 8, the first shaft member 112 is inserted into the bore 54 at the first end 56 of the steering head 50, where the outer race 140 is positioned in the counterbore 60. After insertion of the first shaft member 112, the rollers 136 are wedged between the tapered outer surface 133 of the inner race 132 and the tapered inner surface 144 of the outer race 140. In doing so, the first shaft member 112 and the first bearing 116 are at least partially positioned within the first end 56 of the bore 54.

[0022] As continued in Fig. 6 and Fig. 7, after sliding the dust cap 148 onto the second shaft member 124, the inner race 134 of the second bearing 128 is positioned by press fitting onto the second shaft member 124. As shown in Fig. 8, the second shaft member 124 is inserted into the second end 64 of the bore 54, where the outer race 142 is positioned in the counterbore 68. After insertion of the second shaft member 124, the rollers 138 are wedged between the tapered outer surface 135 of the inner race 134 and the tapered inner surface 145 of the outer race 142. In doing so, the second shaft member 124 and the second bearing 128 are at least partially positioned within the second end 64 of the bore 54.

[0023] As continued in Fig.8, the second shaft member 124 is then coupled to the first shaft member 112 at the connection 202 within the bore 54. For example, in the embodiment shown, the male threaded portion 188 of the second shaft member 124 is threadably received and secured within the female threaded portion 192 of the first shaft member 112. Torque is applied to the second shaft member 124 to develop a clamping load through the upper support assembly 108 and also the lower support assembly 104. With the connection 202 secured, the upper yoke 76 is placed onto the upper end of the second shaft member 124 such that the second shaft member 124 extends through the shaft-receiving through-hole 88 in the upper yoke 76. The screw 96 in the upper triple clamp 76 is rotated to apply a radial clamping force to the upper end of the second shaft member 124.Accordingly, the radial clamping force secures the first and second stem members 112, 124, and thus the lower and upper support assemblies 104, 108, as a unitary structure that can be rotated relative to the steering head 50. The screw 96 allows adjustment of the clamping load during maintenance without requiring disassembly of other parts of the steering assembly 18 of the motorcycle 10.

[0024] The invention is defined by the appended claims.

Claims

[1] Motorcycle (10), which includes: a main frame (12) configured to support a drive unit (24), at least one rear wheel (20) and at least one seat (23), a steering head (50) fixed to the main frame (12) and having a bore (54) between a first end (56) and a second end (64) of the steering head (50), the bore (54) defining a steering axis (A), and a steerer tube assembly (100) comprising: at least one steerable front wheel (14) which can be rotated about the steering axis (A) relative to the steering head (50), a first shaft member (112) extending into the bore (54) from the first end (56), and a second shaft member (124) extending into the bore (54) from the second end (64), wherein the first shaft member (112) is fixed to the second shaft member (124) within the bore (54), wherein none of the first (112) and second shaft members (124) extends completely through the bore (54), wherein the first shaft member (112) is removably attached to the second shaft member (124) at a connection (202) within the bore (54), the shaft members in the connected state define a shaft length (L), measured parallel to the steering axis (A), and the connection (202) between the two shaft members is arranged centrally along the length L. [2] Motorcycle (10) according to claim 1, wherein the connection (202) is a screw connection. [3] Motorcycle (10), which includes: a main frame (12) configured to support a drive unit (24), at least one rear wheel (20) and at least one seat (23), a steering head (50) fixed to the main frame (12) and having a bore (54) between a first end (56) and a second end (64) of the steering head (50), the bore (54) defining a steering axis (A), and a steerer tube assembly (100) comprising: at least one steerable front wheel (14) which can be rotated about the steering axis (A) relative to the steering head (50), a first shaft member (112) extending into the bore (54) from the first end (56), and a second shaft member (124) extending into the bore (54) from the second end (64), wherein the first shaft member (112) is fixed to the second shaft member (124) within the bore (54), wherein none of the first (112) and second shaft members (124) extends completely through the bore (54), wherein the first shaft member (112) is removably attached to the second shaft member (124) at a connection (202) within the bore (54), a lower support assembly (104) comprising the first shaft member (112) and a first bearing (116) having an inner race (132), wherein the inner race (132) of the first bearing (116) is coupled to the first shaft member (112) by means of a press-fit engagement, and an upper support assembly (108) comprising the second shaft member (124) and a second bearing (128) having an inner race (134), wherein the inner race (134) of the second bearing (128) is coupled to the second shaft member (124) by means of a press-fit engagement. [4] The motorcycle (10) of claim 3, wherein the second shaft member (124) includes a male threaded portion (192) threadably received in a female threaded portion (188) of the first shaft member (112). [5] The motorcycle (10) of claim 3, wherein each of the first (116) and second bearings (128) includes an outer race (140, 142) separable from the inner race (132, 134), the inner race (132, 134) including tapered rollers (136, 138) configured to be brought into contact with a tapered outer surface (133, 135) of the outer race (140, 142). [6] The motorcycle (10) of claim 3, further comprising a lower fork bridge (72) secured to the lower support assembly (104) and an upper fork bridge (76) secured to the upper support assembly (108), the upper (76) and lower fork bridges (72) cooperating to support a pair of fork tubes (16).

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