Abstract:
A bicycle frame comprising a first tubular member having a first interface portion, and a second tubular member having a second interface portion engaged with the first interface portion to create a joint. The joint includes a peripheral channel having a depth that is greater than a wall thickness of the first tubular member, and a weld is positioned in the peripheral channel. To enhance the transition from the first main portion to the second main portion, the second tubular member can include a fillet surface between the second main portion and the second interface portion. The fillet surface is contoured to provide a smooth transition between the top tube and the head tube. An outer surface of the first interface portion can be offset from an outer surface of the first main portion to thereby create a shoulder.

Description:
BACKGROUND 
       [0001]    The present invention relates to bicycle frames, and particularly to weld joints of tubular bicycle frames. 
         [0002]    Bicycle frames are commonly manufactured from tubes that are coupled together into a desired configuration. When the tubes are metal (e.g., steel, aluminum, titanium, etc.), they can be welded together to form the bicycle frame. When manufacturing a welded bicycle frame, the ends of the tubes are pre-cut so that the tubes fit together to form pre-weld joints between the tubes. For example, one tube can be mitered so that it wraps snugly around the tube to which it will be welded. When tubes of similar size are coupled using a mitered joint, the geometry of the joint varies dramatically around the tube interface, from essentially a T-joint at the top and bottom to essentially a tangent joint on the sides, with the mitered tube having a razor thin wall thickness at the tangent joint. 
         [0003]    When welding tubes having mitered joints, a weld fillet is formed around the joint. Due to the varying joint geometry of the above-described mitered joint, creating a good, consistent weld is very difficult. At the location where the tubes are tangent, the weld bead commonly protrudes substantially above the surfaces of the tubes being welded. If a smooth joint is desired, one would need to grind or sand the weld bead. 
       SUMMARY 
       [0004]    The present invention relates to an improved weld joint structure between two parts. This improved joint structure is designed to make the weld bead more flush with the outer surfaces of the parts being welded to give the appearance of a smooth transition between the outer surfaces of the parts, and to reduce or eliminate post-weld finishing operations, such as grinding or sanding. 
         [0005]    The invention provides a bicycle frame comprising a first tubular member having a first main portion and a first interface portion (e.g., a first tapered portion), a second tubular member having a second main portion and a second interface portion (e.g., a second tapered portion) engaged with the first interface portion to create a joint. The joint includes a peripheral channel defined between the first interface portion and the second interface portion. The channel has a depth that is greater than a wall thickness of the first tubular member, and a weld is positioned in the peripheral channel. In one embodiment, a ratio of the channel depth to the wall thickness is at least 1.5:1, and is preferably at least 2:1. 
         [0006]    To enhance the transition from the first main portion to the second main portion, the second tubular member can include a fillet surface between the second main portion and the second interface portion. The fillet surface is contoured to provide a smooth transition between the top tube and the head tube. 
         [0007]    In order to create a visual guide to the welder, an outer surface of the first interface portion can be offset from an outer surface of the first main portion to thereby create a shoulder. In one embodiment, a ratio of a shoulder depth to the wall thickness is at least 1:10, preferably at least 1:5, and more preferably at least 1:3. 
         [0008]    In order to enhance the dry fit of the first and second tubular members, the first interface portion can be dimensioned to fit inside the second interface portion (e.g., a inner dimension of the first interface portion can be less than a corresponding inner dimension of the second interface portion. In a situation where one of the interface portions has a thinner wall thickness than the other interface portion, it is preferred that the thinner interface portion be positioned inside the thicker interface portion. 
         [0009]    It is anticipated that some aspects of this invention are applicable to bicycle components other than frames. Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a side view of a bicycle including a welded frame having features of the present invention. 
           [0011]      FIG. 2  is an enlarged partial side view of a portion of the frame prior to welding. 
           [0012]      FIG. 3  is an exploded perspective view of the portion of the frame depicted in  FIG. 2 . 
           [0013]      FIG. 4  is a section view of the portion of the frame depicted in  FIG. 2 . 
           [0014]      FIG. 5  is an enlarged view of one of the joints shown in  FIG. 2 . 
           [0015]      FIG. 6  is the section view of  FIG. 4  after the tubes are welded together. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0017]      FIG. 1  illustrates a bicycle  10  that includes a front wheel  12 , a rear wheel  14 , a frame  16 , and a steering assembly  18 . The frame  16  includes a top tube  20 , a head tube  22 , a down tube  24 , a seat tube  26 , seatstays  28 , chainstays  30 , and a bottom bracket  32 . Pedals  34  are attached to a crankset  36  to allow a user to rotate the crankset  36  and to propel the bicycle  10 , as is known in the art. 
         [0018]      FIG. 2  is an enlarged side view of the head tube  22  and portions of the top tube  20  and down tube  24  prior to those tubes being secured together. Each of the top tube  20  and down tube  24  includes a main portion  40  having a generally smooth outer surface  42  that is generally parallel to a longitudinal axis  44  of the tube. The illustrated main portions  40  are generally circular or oval in cross section. However, the present invention is not limited to tubes having circular or oval cross sections, but is applicable to tubes having a variety of cross sections. 
         [0019]    The end of each of the top tube  20  and down tube  24  includes an interface portion in the form of a tapered portion  50  that extends at an angle relative to the main portion  40  of each tube. The angle of the tapered portion  50  varies depending on the position around the perimeter of the tube. In this illustrated embodiment, the angle a of the tapered portion  50  of the top tube  20  relative to the longitudinal axis  44  of the top tube  20  varies from about 27 degrees to about 51 degrees. The angle B of the tapered portion  50  of the down tube  24  relative to the longitudinal axis  44  of the down tube  24  varies from about 8 degrees to about 66 degrees. 
         [0020]    With continued reference to  FIG. 2 , the head tube  22  comprises a main portion  52  having an outer surface  54  that generally mimics a cylindrical and/or slightly frustoconical configuration. The head tube  22  further includes an upper fillet surface  60  that is designed to provide a smooth transition from the outer surface  54  of the head tube  22  to the outer surface  42  of the main portion  40  of the top tube  20 . The head tube  22  also includes a lower fillet surface  62  that is designed to provide a smooth transition from the outer surface  54  of the head tube  22  to the outer surface  42  of the main portion  40  of the down tube  24 . More specifically, the upper and lower fillet surfaces  60 ,  62  are designed to mimic a weld fillet that would appear if substantially straight tubes were welded together (e.g., using a mitered joint) and sanded to provide a smooth, radiused transition between the head tube  22  and the top and down tubes  24 , respectively, thus giving the appearance of a molded frame  16 . 
         [0021]    The head tube  22  further includes an upper tapered portion  64  extending at an angle from the upper fillet surface  60 , and a lower tapered portion  66  extending at an angle from the lower fillet surface  62 . The upper and lower tapered portions  64 ,  66  are designed to fit with the tapered portions  50  of the top tube  20  and down tube  24 , respectively, to form pre-weld joints. The angle of the upper and lower tapered portions  64 ,  66  varies around the perimeter of the upper and lower fillet surfaces  60 , 62 . In the illustrated embodiment, the angle of the upper tapered portion  64  is about 36 degrees to about 91 degrees relative to the longitudinal axis  44  of the top tube  20 . The angle of the lower tapered  66  portion varies from about 30 degrees to about 59 degrees relative to the longitudinal axis  44  of the down tube  24 . 
         [0022]    Referring to  FIG. 4 , the end of the tapered portion  50  of the top tube  20  fits inside the end of the upper tapered portion  64  of the head tube  22 . In other words, an outer surface  70  of the tapered portion  50  of the top tube  20  engages an inner edge  72  or surface of the upper tapered portion  64 . In this regard, it can be seen that an inner dimension  74  of the tapered portion  50  of the top tube  20  is smaller than a corresponding inner dimension  76  of the upper tapered portion  64 . Similarly, the end of the tapered portion  50  of the down tube  24  fits within the end of the lower tapered portion  66  of the head tube  22 . This configuration provides for a relatively secure dry fit between the tubes prior to the welding operation, which facilitates the proper alignment and positioning of the tubes relative to each other. The above-described arrangement could be reversed, with one or both of the upper and lower tapered portions  64 ,  66  fitting inside the corresponding tapered portion  50  of the top tube  20  and down tube  24 , respectively. However, it is considered desirable to have the thinner tube (i.e., the top tube and down tube in the illustrated embodiment) positioned inside the thicker tube (i.e., the head tube in the illustrated embodiment). 
         [0023]    With further reference to  FIGS. 2 and 4 , the above-described configuration of top tube  20 , down tube  24 , and head tube  22  results in creation of a peripheral channel  80  around the joint between the top tube  20  and head tube  22  and the joint between the down tube  24  and head tube  22 . These channels  80  are dimensioned such that the cross-sectional area of each channel (i.e., the triangular region defined by the tapered portions) does not vary substantially around the perimeter of the joint. The result is a substantially uniform cross-section weld joint that is easier to weld. With skilled welders, it is believed that welding of these joints can result in a near finished products, with the weld bead substantially flush with the adjacent surfaces, thus requiring little or no grinding, filing, or sanding. 
         [0024]    The illustrated peripheral channels  80  are substantially V-shaped, and an angle γ at the base of the channel varies between about 80 degrees and about 96 degrees. In the illustrated embodiment, the channels have a depth  82  that is greater than the wall thickness  84  of the tubes being welded. For example, the depth  82  ( FIG. 5 ) of the channel between the top tube  20  and head tube  22  is about 5 millimeters, and a wall thicknesses  84  of the top tube and head tube at the joint (i.e., the interface portions) are about 2 mm and 2.5 mm, respectively. In this configuration, the ratio between the channel depth and the tube wall thickness is about 2.5:1 for the top tube and about 2:1 for the head tube. 
         [0025]    It should be understood that the channels do not need to have straight sidewalls, but instead could have curved sidewalls, such as when the tube ends are domed. 
         [0026]      FIG. 5  illustrates an enlarged view of one of the V-shaped channels  80  created by the above-described tapered portions  50 ,  64 . This enlarged view shows that the illustrated tapered portions  50 ,  64  do not extend directly from the ends of the outer surfaces  42 ,  60  of the tubes. Rather, each tapered portion  50 ,  64  is offset such that there is a shoulder  86  between the outer surfaces  42 ,  60  and the tapered portions  50 ,  64 . The illustrated shoulder  86  is radiused, but could instead be straight. The illustrated shoulder has a shoulder depth  88  of about 0.5 mm, thus creating shoulder depth  88  to wall thickness ratio of about 1:3. This offset between the tapered portions  50 ,  64  and the outer surfaces  42 ,  60  provides a guide for the welder, thus facilitating a better weld. It should be understood that the shoulder could be sized differently from the described embodiment, or the shoulder could be eliminated entirely without detracting from certain aspects of the present invention. 
         [0027]      FIG. 6  illustrates weld beads  92  (in broken lines) after the joints are welded. As illustrated, the weld beads  92  are substantially flush, or might protrude slightly outward from the joint beyond the outer surfaces of the tubes. The weld  92  can then be finished (e.g., ground, filed, sanded, etc.), if necessary, until it is flush with the outer surfaces of the tubes. The result is a welded bicycle frame that, once painted, will look like a single-piece molded bicycle frame. 
         [0028]    Various features and advantages of the invention are set forth in the following claims.