Abstract:
A bicycle stem and front loading handlebar clamp having a pair of C-shaped cradles provided with handlebar contacting surfaces which have an edge to edge maximum extent in the direction of the handlebar greater than the inside diameter of the cradles and wherein the cradles are characterized by the absence of straight lines and sharp corners.. Handlebar clamping stress concentrations are reduced by the configuration of the contact surfaces and further by a configuration of a moveable one of the cradles somewhat in the form of a laterally elongated cross with smooth curves at the ends and at the corners of the cross.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS, IF ANY  
     None 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     Field of the Invention 
     The present invention relates to parts for bicycles and other cycles, particularly lightweight bicycles for recreational riding, racing, mountain biking and off-road uses. As is known, cycles are steered by handlebars which in turn are connected to a steering tube which extends upwardly from the front wheel fork of the cycle. The connecting part is known as a stem and the stem may also include a forwardly extending boom to position the cycle handlebar at a desired location forwardly of the stem tube for comfort of the rider. Not all stems include booms, however. Various cycle parts including stems are usually manufactured from tubular metals such as alloys of aluminum, magnesium or steel and of composite materials such as carbon fiber reinforced resin. 
     Since reduction of weight is of extreme importance in human-powered cycles, increasing use has been made of very light weight but strong composite tubular structures instead of aluminum, titanium and steel tubular parts of cycle frames and handlebars. Such composites are relatively easily damaged not only cosmetically but also structurally by surface nicks and gouges such as are often incurred by clamping. The need therefore exists for a stem having a handlebar clamp to which a cycle handlebar made of composite material can be readily attached and removed for re-positioning or replacement without damaging the handlebar. 
     In general, the larger the clamping surface area which contacts the handlebar, the less clamping stress is transmitted from the clamping surfaces of the clamp to the handlebar. 
     OBJECTS OF PREFERRED EMBODIMENTS OF THE INVENTION 
     It is a primary object of the present invention to provide a stress reducing stem clamp in which a handlebar may be quickly and firmly attached without inducing significant clamping stress in the handlebar yet which will secure the handlebar by preventing relative rotation and longitudinal sliding movement of the handlebar. 
     Preferably, the stem clamp should also be readily attachable to cycle handlebars of various configurations including those having relatively short radius bends with little or no damage to the handlebar and without requiring removal of other components mounted on the handlebar such as hand grips, gear shifter controls and brake handles whenever field adjustment of the position of the handlebar is desired. 
     Various features and advantages of the invention will become apparent from reading the detailed description which follows. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cycle stem comprising:
         a) a tubular member having clamp structure thereon for attachment of the stem to the steering tube of a cycle; and   b) a handlebar clamp comprising a stationary C-shaped cradle integrally formed at one end of said tubular member, a moveable C-shaped cradle and means for fastening said cradles together, said cradles each having a handlebar contacting surface having a maximum dimension along an axially extending clamping length of a handlebar greater than an inside diameter of said cradles and wherein said cradles are characterized by the absence of straight lines and sharp corners.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of one preferred embodiment of a stem and handlebar clamp according to the present invention. 
         FIG. 2  is a plan view of the stem and clamp shown in  FIG. 1 . 
         FIG. 3  is a side elevation view of the stem and clamp shown in  FIG. 1 . 
         FIG. 4  is a front elevation view of the stem shown in  FIG. 1 . 
         FIG. 5  is a front elevation view of the stem with the moveable clamp attached. 
         FIG. 6  is a front elevation view of a first form of prior art handlebar clamp. 
         FIG. 7  is a front elevation view of a second form of prior art handlebar clamp. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In its broadest aspects, the cycle stem is comprised of a stem tube  10  which, in this embodiment includes a boom which, in use extends generally forwardly of the rider. The stem tube  10  has clamps  12 ,  14  at each end respectively for attaching the stem to a generally vertically extending steering tube of a cycle and to a handlebar. The stem tube  10  include a generally straight boom, as shown, but stems of other configurations are well known and well with in the scope of the present invention. The preferred embodiment of the invention shown in  FIG. 1  includes an elongated boom which extends forwardly and slightly downwardly although it will be appreciated at the angle of inclination, if any, of the boom between the steering tube clamp  12  and handlebar clamp  14  can be varied if desired. The manner in which the stem tube  10  is attached to the steering tube is not necessary to and forms no part of the present invention. 
     At the front end of the stem tube  10  (as viewed when sitting on a bicycle) a handlebar clamp  14  which opens to the front is provided. The handlebar clamp  14  is comprised of a stationary C-shaped cradle  20  and a moveable C-shaped cradle  30  connected by two threaded fasteners  40 ,  50  including nuts  41 ,  51 , to the stationary C-shaped cradle  20 . The handlebar clamp  14  preferably has a generally circular handlebar receiving cross-section at this location as seen if  FIG. 3 . Oval and other cross-sectional configurations such as hexagonal, octagonal, etc. are also within the scope of the invention as defined by the wording of the attached claims. The wall thickness of the stem tube  10  or boom is ordinarily substantially constant between the clamps  12 ,  14 , although this too is not essential. 
     It will be noted that the inner clamping surfaces  22 ,  32  of the C-shaped cradles  20 ,  30  are cylindrical as shown and extend for approximately 180° each to provide almost a full 360° contact around a handlebar when clamped therein. 
     The clamp assembly is completed by the fasteners  40 ,  50  preferably comprising threaded nuts and bolts received in apertures in opposed ears  24 ,  26 ;  34 ,  36  integrally formed on the stationary and moveable cradles  20 ,  30 . The apertures and fasteners are preferably centered in a vertical plane containing the axis of the stem tube clamp  12 . 
     Minimization of stresses in bicycle handlebars of composite construction is a primary safety concern, particularly for bicycles used in rigorous activities such as racing and off-road use since structural failure of bicycle handlebars may result in substantial injury and even death. Also, modern high tech handlebars made of composite materials to reduce weight and increase strength are usually expensive. Handlebar failure may be experienced, but not necessarily noticed, when the handlebar is improperly clamped into the stem too tightly or without due care taken to repeatedly alternate the tightening of the fasteners. Failure is also occasionally experienced during use and may be caused by a combination of dead load or stem bolt stresses induced by improper clamping and live load stresses induced due to strenuous riding which exceed the safety factor for the handlebar design. Other factors believed to contribute to handlebar failure include material fatigue and deterioration due to aging and long term exposure of the composite materials used in the handlebar to environmental conditions such as smog or acid rain, freezing, high temperature exposure and the like. 
     The stem and handlebar clamp described above is specially configured and designed to reduce stress concentrations in bicycle handlebars, particularly those made of composite materials, at all locations where the clamp surfaces engage the handlebar and may generally be characterized by the elimination of sharp edges and corners at the boundaries of the handlebar contact areas. Due to the higher design strength and materials of which the stem and C-shaped cradles  20 ,  30  are manufactured as compared with the design strength of the handlebar, failure of the stem tube  10 , cradles  20 ,  30  and fasteners  40 ,  50  is relatively unlikely. Accordingly, the cradles  20 ,  30  each are designed to have large handlebar contacting surfaces  22 ,  32 . The cradles  20 ,  30  have maximum edge to edge dimensions E—E as seen in  FIG. 5  which extend axially of the handlebar (horizontally as shown) a distance greater than the inside diameter of the cradles as best seen in  FIG. 3 . Also, the total area of the handlebar contacting surfaces  22  on the stationary cradle  20  ( FIG. 4 ) is preferably greater than the wall area seen in a transverse cross section of the stem tube  10  by a factor of about 3 due to the purposely flared configuration of the surfaces  22  of the cradle  20 . The area of the handlebar contacting surface  32  of the moveable cradle  30  (see  FIG. 1 ) is significantly greater than, and preferably at least twice as large as, the area of the handlebar contacting surface  22  on the stationary cradle  20 . 
     The opposed upper and lower ears  24 ,  26 ;  34 ,  36  on the stationary and moveable cradles  20 ,  30  include apertures  25 ,  27 ,  35 ,  37  through which the threaded fasteners  40 ,  50  extend and the ears  24 ,  34  and  26 ,  36  abut each other along an axial radial plane through the connecting area of the handlebar and are all centered on a line, (substantially vertical as seen in  FIG. 5  and which may be slightly angled from vertical as seen in the depicted embodiment in  FIG. 3 ) transverse to the central portion of the handlebar received in the cradles  20 ,  30 . The ears  24 ,  26 ;  34 ,  36  on the stem tube  10  and the stationary cradle  20  are all shaped to smoothly transition in gradual curves to merge with the outside arcuate surface of the stem tube  10 . The moveable cradle  30 , as viewed in  FIG. 5 , can be loosely described as a laterally elongated cross having arms each having smooth curves at their ends and at the corners of the arms. Integrally formed centrally extending reinforcing ribs  60 ,  62  on the outer surfaces of the arms provide greater thickness and strength in these areas. Finally, the sides of the ears  24 ,  26  on the outside of the stationary cradle  20  which face the stem tube  10  are recessed with non-circular configuration as best seen in  FIG. 1  to receive fastener nuts  41 ,  51  of complementary non-circular configuration into which the bolts of the fasteners  40 ,  50  are threaded. 
     To test the effectiveness of the stem configuration described and shown, five carbon reinforced resin composite handlebars of CE90 material from Easton Sports, Inc. of Van Nuys, Calif. were clamped in stem clamps of three different types (a total of 15 handlebars were consumed in the tests), respectively comprising (1) a four bolt magnesium clamp of EM90 material from Easton Sports, Inc. having two curved cradles each formed from a rectangular generally square plate  70  having curved corners and four fasteners  72  as shown in  FIG. 6 ; (2) a two bolt aluminum clamp of EA50 material, also from Easton Sports, Inc., having two curved cradles each formed from a rectangular plate  80  with two fasteners  82  and a central rectangular aperture  84  as shown in  FIG. 7 ; and (3) a two bolt aluminum clamp of EA 70 material configured as shown in  FIGS. 1–5 . In each test, the clamp connecting bolts were tightened in 5 pound increments until handlebar cracking was audibly or visually detected. The first clamp configuration resulted in handlebar cracking at an average of 61 inch pounds of torque. The second clamp configuration resulted in handlebar cracking at an average of 109 inch pounds of torque. The third clamp configuration resulted in handlebar cracking at an average of 163 inch pounds of torque—approximately a 50% increase compared to the next best second clamp configuration. Since all cracking occurred in the handlebars rather than in the clamps, the improvement is considered attributable solely to the new configuration of clamp parts rather than to differences in materials of which the clamps are made. Although a maximum bolt tightening torque of 70 inch pounds is generally recommended by the manufacturer, handlebars are usually not installed by the manufacturer and the consumer typically does not use a torque wrench or follow the manufacturer&#39;s instructions when attaching a handlebar to a stem, particularly in the field. For this reason, and due to the severe potential consequences of handlebar failure during riding, a high factor of safety is dictated and made possible by the present invention. 
     Persons skilled in the art will readily appreciate that various changes and modifications of an obvious nature can be made and all such changes and modifications are considered to fall within the scope of the appended claims.