Land vehicles – Wheeled – Occupant propelled type
Reissue Patent
1999-04-29
2004-12-14
DePumpo, Daniel G. (Department: 3611)
Land vehicles
Wheeled
Occupant propelled type
C280S279000, C280S280000, C188SDIG001
Reissue Patent
active
RE038669
ABSTRACT:
INTRODUCTION
This invention relates to front fork, telescoping type suspension systems for bicycles. The invention is comprised of an improved fork crown, a brake arch structure and attaching means to other fork components. The crown structure is that part of the suspension that connects the stanchion tubes (the upper part of the telescoping assembly) to the steerer tube. The brake arch attaches the upper portion of the right sliding fork leg or strut to the upper portion of the left sliding fork leg or strut, as well as supporting the brake cable stop and brake caliper assembly (in the case of cantilever brakes). The invention provides a simple and inexpensive means for reducing the overall fork weight and at the same time improving the bending and torsional stiffness and strength of the overall fork, and specifically the fork crown and brake arch components.
The invention provides an improved method for mounting the stanchion tubes to the fork crown and lower fork tubes to the brake arch, using a collet, wedge, pinch bolt or bonded assembly. Except in the case of the bonded assembly, these methods allow quick assembly and disassembly of the suspension system, for repairs and parts replacements.
BACKGROUND
In the design of competition bicycles and bicycle parts, weight and stiffness are critical issues. Extremely lightweight structures and structural components are used in the most serious competition bicycles. These lightweight components must be designed for a variety of severe riding environments. This results in a design that must operate at relatively high stresses, close to the strength limits of the materials being used. The demand for a minimum weight bicycle has led the industry into the use of modern, high performance structural materials, such as high strength aluminum, carbon fiber composite and titanium alloys. These high strength materials require more care in the design of fittings and joints because of, a) their susceptibility to fatigue cracking and b) the relatively high load levels at which the fittings and joints are required to operate.
A goal for a bicycle part manufacturer is to eliminate all unnecessary weight from a given part, without compromising its structural integrity and stiffness. There are numerous bicycle suspension forks currently on the market that are not very weight efficient. They have been designed for basic suspension function, without adequate consideration for weight optimization or steering and braking control. Most of the prior art telescoping front fork suspensions fall into this category. These designs tend to be relatively heavy and their stiffness to weight and strength to weight ratios are not very high. They are also relatively flexible laterally and in torsion and cannot provide the stability and accurate steering and braking control for the front wheel assembly that is desired for serious competition cycling. Laboratory tests show that some of the prior art fork designs have torsional spring rates as low as 84 in-lbf/deg and lateral spring rates as low as 140 lbf/in. Some of the heavier steel forks have torsional spring rates in the neighborhood of 230 in-lbf/deg and lateral spring rates of nearly 170 lbf/in, however, their weight exceeds 1500 grams. Based on studies, it has been found that a torsional spring rate in excess of 230 in-lbf/degree and a lateral spring rate in excess of 170 lbf/in is desirable for maximum steering control in competition cycling. The weight of the suspension should be less than 1000 grams.
Most of the prior art fork suspensions use brake arch designs that are inherently too flexible to control wheel wobble and braking action. The name “brake bridge” or “brake arch” says it all. The part was designed and located simply as a support for the brake cable hanger and possibly the brake mounts, similar to the part of the same name used on the rear seat stays of the bicycle. The prior art designs did not realize that the lower sliding tubes need to be rigidly linked to each other in torsion and bending in order to provide top performance of the cantilever brakes and the overall suspension fork assembly.
The present invention uses a unique design for the separate crown structure and brake arch assembly to dramatically increase the strength and stiffness of the fork while reducing weight. The crown structure and the brake arch play key parts in the overall stiffness of the front fork assembly. The invention also provides an improved method of assembly of the various key parts of the suspension fork to reduce manufacturing costs as well as make the system easier to assemble and disassemble for parts and repairs.
PRIOR ART DESIGNS
Prior art front fork suspensions come in a variety of sizes and shapes as shown in
FIGS. 1-5
(common components are identified by a numeral preceded by the figure number). Most of the more popular designs use telescoping struts, operating pneumatically, hydraulically, elastomerically or with metallic springs to achieve the suspension action.
FIG. 1
illustrates the structural arrangement typical of these designs. For example, some forks utilize a unicrown
3
type of construction (used on many non-suspended forks), consisting of a tight bend created in the top of the fork blade, where the fork blade is directly attached, through brazing, welding or other means to the steerer tube
2
.
FIG. 2
illustrates the unicrown type fork design. The integral blade and crown form the upper tube of the suspension. This type of construction has the advantage of not having a separate fork crown, but it also has several disadvantages. The curved tube upper structure coincides with the most highly stressed region of the fork. Under stress, the essentially round or elliptical sections deform significantly out of round, creating excessive movement and stress concentrations. The process of bending the curve into the tube stretches and thins the outer wall of the tube, weakening it. The welded or brazed joint to the steerer is a weakened area as a result of the thermal effects, residual stress and stress risers due to the joint configuration. The bent and welded type of construction does not lend itself to a highly accurate alignment of the two upper fork blades, or stanchion tubes, which make it difficult to make a high precision sliding structure.
For the separate fork crown member type of design (FIG.
1
), the stanchion tubes (the stationary part of the telescoping assembly—Items
1
L and
1
R) are connected to the steerer tube (
2
), by a common crown part (
3
). The crown is typically made of aluminum alloy, either machined out of solid or forged, with subsequent machining of the steerer and stanchion tubes fitting surfaces. In prior art, the stanchion tubes are retained by adhesive, interference fit or pinch bolts, or a combination of the above. The structural support between the steerer tube and the stanchion tube is typically either a solid rectangle or inverted channel shape.
Generally, one of the most critical and highly loaded parts of the suspension fork design is the crown structure (
3
). This part must be designed to handle both bending and torsional loads resulting from frontal and side impacts to the wheel. The crown acts as a structural transfer member to transmit the impact loads to the steerer where these loads are distributed to the head-set bearings and eventually to the bicycle frame.
Also, very important to the stability and performance of a telescoping type suspension fork is the brake arch or brake bridge, as it is sometimes called. The brake bridge connects the two struts and causes them to telescope together during wheel impact, thereby minimizing wheel “wobble”. If the two telescoping tubes are allowed to move independently, the wheel will wobble and create high stresses at dropout/axle connection. Neither condition is desirable. The brake bridge provides resistance against the up-down, for-aft and rotational (torsional) movements of the struts, forcing the wheel to run true during full suspension travel. The brake bridge (
4
) also serves as a structural support for
Klein Gary G.
Voss Darrell W.
DePumpo Daniel G.
Zegeer Jim
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