Abstract:
A bicycle frame having a replaceable flexible down tube assembly, wherein the down tube assembly includes a resilient arcuate down tube member with connectors in the form of releasable mounting clips removably attached to the ends of down tube member. The clips clamp on transverse mounting pins in stems attached to the bicycle frame at the ends of the down tube assembly. The clips are releasable to remove the down tube assembly from the frame for replacement or substitution of a down tube having different performance or appearance characteristics. The clips are removable from the down tube for separate replacement of clips and the down tube.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/802,840 filed Mar. 18, 2013, the entire disclosure of which is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention is related to a bicycle frame, in particular to a bicycle frame having a removable down tube, the down tube having removable clips on both ends for easy attachment to and removal from a frame and for separate replacement of the down tubes and clips. 
         [0003]    A bicycle frame having a removable down tube was previously disclosed in Applicant&#39;s Co-pending U.S. patent application Ser. No. 13/380,726, filed Jun. 28, 2010 the entire disclosure of which is incorporated by reference herein. As discussed in that application, there are several advantages to a bicycle having a flexible down tube that can be removed and replaced with a down tube having different characteristics. The replacement of the down tube allows for the modification of the flex characteristics of the frame as well as physical characteristics, such as head tube and seat tube angle, wheel base, and bottom bracket height. 
         [0004]    Another advantage of being able to replace a down tube is related to aesthetic appeal. Riders may desire the ability to change out an existing down tube for a down tube having a different style, color, or pattern. It would be expensive and often impractical to purchase a whole new frame just to get a tube with a different look. The ability to change out just the down tube makes a significant change in the appearance of the frame more affordable. 
         [0005]    There have, however, been some difficulties associated with previous designs. The set-ups used for previous removable down tubes have, at times, made it somewhat difficult for riders to change out down tubes quickly and easily. What is needed is an improved construction and method for mounting a removable down tube that facilitates replacement of the down tube while maintaining the secureness of the down tube connection and preserving the flex characteristic of the down tube. 
         [0006]    Another object of the present invention is to provide a down tube with easily replaceable end fittings or clips in the ends of the down tube such that end fittings and down tubes can easily be replaced separately, without the expense of replacement of both components at the same time. These and other objects are achieved with the improved frame construction of the present invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In accordance with the present invention, a bicycle frame employs a replaceable down tube assembly that is releasably mounted between forward and rearward mounting stems secured to the frame. The mounting stems include transverse mounting pins secured to the frame at positions where ends of the down tube assembly are attached to the frame. The down tube comprises an elongated down tube member having end fittings releasably attached to ends of the down tube member. The end fittings have transverse recesses in outer ends thereof that fit over the mounting pins in the stems. The end fittings permit at least limited pivotal movement of the down tube about the lateral axis of the mounting pins upon at least limited vertical deflection of the down tube in the frame. 
         [0008]    In one aspect of the invention, the down tube member comprises an elongated tube having a resilient arcuate portion. The end fittings are mounted on the ends of the tube and provide connector clips for releasably mounting the tube on the mounting pins in the stem. 
         [0009]    Desirably, the end fittings are formed from a synthetic resin having sufficient lubricity to permit pivotal movement of the end fittings on the pivot pins without requiring lubrication of the interface between the pivot pins and end fittings. 
         [0010]    In one aspect of the invention, at least one end fitting comprises an elongated body having an inner end that fits in the end of the tube and an outer end that protrudes outwardly from the end of the tube, the inner end being releasably attached to the end of the tube by releasable fasteners that extend through the side of the tube and into the inner end of the end fitting, the fasteners being releasable to permit replacement of the end fitting. 
         [0011]    In one aspect of the invention, the outer end of the end fitting includes an outwardly extending upper flange, with the upper flange having the transverse slot formed in an underside thereof. The locking mechanism comprises a locking plate that mounts on the underside of the upper flange below the mounting pin when the down tube is mounted in the frame. The locking plate is releasably attached to the upper flange by releasable fasteners that hold the locking plate to the upper flange. 
         [0012]    Preferably, the transverse slot has one or more inwardly extending projections at the outer edges of the transverse slot. The inwardly extending projections narrow the width of the slots at the outer edges to a distance less than the diameter of the mounting pins, so that the projections resiliently hold the mounting pins in the slots but are resiliently deflectable to permit the down tubes to be resiliently clipped on the locking pins in the mounts. 
         [0013]    Preferably, the down tube employed in the present invention has elongated, arcuate tubes that are at least partially oval, with the down tube having a major oval axis in a horizontal direction when the down tube is mounted. 
         [0014]    In another aspect of the invention the transverse mounting pins are removable from the clip members. In such a case, the clip members can, if desired, employ a one piece clip having a transverse bore therethrough. The clips can then be mounted on the stem by aligning the transverse bore in the clip with the mounting pin openings in the stem and inserting the removable pin therethrough. 
         [0015]    These and other features and advantages of the present invention will become apparent from the detailed description of the invention set forth below and shown in the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a side view of a bicycle having a frame employing the down tube of the present invention. 
           [0017]      FIG. 2  is a perspective view of the frame of  FIG. 1  showing the lower end of the down tube disconnected from that frame. 
           [0018]      FIG. 3  is a side perspective view of the frame of  FIG. 1  with the lower end of the down tube disconnected from the frame. 
           [0019]      FIG. 4  is a perspective view of a bike frame showing the front section of the down tube disconnected from the frame. 
           [0020]      FIG. 5  is a perspective view similar to  FIG. 4  but showing the front end of the down tube connected to the frame. 
           [0021]      FIG. 6  is a partially-exploded perspective view of the front end of the down tube and clip set shown in  FIG. 11  and showing an optional tube cover. 
           [0022]      FIG. 7  is a side perspective view of a clip set showing a top clip section attached to a bottom clip section. 
           [0023]      FIG. 8  is an inverted perspective view of the top and bottom clip sections shown in  FIG. 7 . 
           [0024]      FIG. 9 a    is a side view of the top and bottom clip sections, showing the fasteners for connecting the sections. 
           [0025]      FIG. 9 b    is a top view of the top clip section of the present invention. 
           [0026]      FIG. 10  is a side perspective view of the top clip section shown in  FIG. 9 . 
           [0027]      FIG. 11 a    is a perspective view of the front mounting stem attached to the bottom bracket shell shown in  FIG. 1 . 
           [0028]      FIG. 11 b    is a top view of the mounting stem of  FIG. 11 . 
           [0029]      FIG. 12 a    is a perspective view of the rear mounting stem attached to the bottom bracket shell shown in  FIG. 1 . 
           [0030]      FIG. 12 b    is a perspective view of the mounting stem of  FIG. 12 a   , showing the bottom bracket shell in phantom. 
           [0031]      FIGS. 13 a  and 13 b    are a perspective view of a universal down tube mounting stem that connects to both the bottom bracket shell and head tube of the frame, showing the frame components in phantom. 
           [0032]      FIG. 14  is a fragmentary view showing a down tube connected to a frame using the universal mounting stem of  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Referring to the drawings, a first embodiment of bicycle  10  employing a flexible frame  12  in accordance with the present invention is shown in  FIG. 1 . Bicycle  10  is illustrated as a mountain bike. However, the invention can be used for road bikes, BMX bikes, trail bikes, time trial bikes, city bikes, casual use bikes, and other styles of bike. 
         [0034]    Bicycle frame  12  shown in  FIG. 1  comprises a top tube  14 , a seat tube  16 , a seat stay  18 , a chain stay  20 , a down tube  22 , a head tube  24 , and a bottom bracket shell  26 . The frame includes two chain stays  20  and two seat stays  18 , on opposite sides of rear wheel  28 , with the rear ends of seat stays  18  and chain stays  20  being connected to a rear drop out  29  that engages the axle  30  on rear wheel  28 . The frame and the seat stay and chain stay members  18  and  20  may be formed of aluminum or other metal or carbon fiber material or other conventional materials. A seat  34  mounted on a seat post  36  is mounted to the upper end of seat tube  16 , with seat post  36  fitting downwardly inside the hollow upper end of seat tube  16 . 
         [0035]    A handlebar assembly  38 , comprising handlebar  40  and handlebar mount  42 , mounts on the upper end of head tube  24 , with mount  42  being rotatably mounted on bearings in an open upper end of head tube  24 . A fork assembly  44  comprises a pair of spaced forks  46  on each side of front wheel  48 , with a conventional fork steerer tube (not shown) extending upwardly into the interior of head tube  24 , where it operably engages with the handlebar mount  42 . 
         [0036]    The bicycle  10  is powered by a conventional pedal mechanism attached to the bottom bracket shell  26  at the bottom of the seat tube  16 . A bottom bracket spindle  55  mounted on bearings inside the bottom bracket shell  26  extends outwardly from the sides of the bottom bracket shell and engages a conventional crank set comprising crank arms  54  mounted at the ends of the bottom bracket spindle  55  and having pedals  56  mounted on the outer ends. A chain ring or sprocket  58  is mounted on the spindle for rotation with the pedals. A rear sprocket  60  drivingly engaged to rear wheel  28  is driven by a chain  62  by chain ring or front sprocket  58  in a conventional manner. 
         [0037]    As shown in  FIG. 1 , bicycle  10  employs a flexible arcuate down tube  22 , which is preferably similar in shape and flex characteristics to the down tubes described in detail in Applicant&#39;s Co-pending U.S. patent application Ser. No. 13/380,726, which is incorporated by reference. An arcuate hollow tubular down tube is described, but an arcuate solid leaf spring could be employed. Either can be regarded as a down tube (i.e. the component extending from the head tube to the bottom bracket shell). In this embodiment, the down tube  22  has replaceable connectors or mounting clips at the ends and is connected at a front end  70  to rear-facing stem  72  which is mounted on head tube  24 . At its rear end  80 , the down tube  22  is connected to forward-facing stem  82 . The forward facing stem  82  is mounted to the bottom bracket shell  26 , at or near the base of the seat tube  16 . In the alternative, it is also contemplated that the forward-facing stem  82  could be welded to the seat tube  16  near the bottom bracket shell  26  or to both at the junction between the bottom bracket shell  26  and the seat tube  16 . The connections between the down tube  22  and rear-facing  72  and forward-facing  82  stems are discussed in more detail below. 
         [0038]    The connector attached to each end of the down tube  22  is a clip set  90 . Each clip set  90  combines a top clip member  92  and a bottom clip member  100 . As shown in isolation in  FIGS. 9 and 10 , each top clip member  92  includes a frame engagement section  94  and a tube engagement section  96 . The bottom face  98  of the frame engagement section  94  of each top clip member  92  includes a rounded transverse groove or indentation  102 . 
         [0039]    Preferably, the indentation  102  has an inwardly extending lip  103  on each side of the outer edge thereof, so that the clip can be resiliently clipped on a transverse mounting shaft on the frame (see  FIG. 10 ). As is shown in  FIG. 7 , the tube engagement section  96  of each top clip member  92  has a cross shape, the cross shape comprising a large vertical rectangular prism  104  with “T”-shaped arms  106  extending from both sides of the middle of the prism portion  104 . Arms  106  comprise outwardly extending legs  107  and vertical flanges  109  ( FIG. 7  orientation). When the down tube is a leaf spring, the engagement section can be a flat end portion attached by fasteners to the front of the spring. The end portion alternatively can be a socket member that fits over the end of the spring and is fastened thereto by fasteners. 
         [0040]    As shown in  FIG. 8 , each top clip member  92  preferably includes two main screw holes  110  aligned on the bottom face  108  of its tube engagement section  96  and two secondary screw holes  112  on the bottom face  98  of its shaft engagement section  94  that are in alignment with holes  120  in the bottom clip member  100  (see  FIG. 8 ). 
         [0041]    One embodiment of the bottom clip member  100  of each clip set  90  is shown in  FIGS. 6-8 . Each bottom clip member  100  has a width and a length that is roughly equivalent to the length and width of the shaft engagement section  94  of the corresponding top clip member  92 . When placed beneath the shaft engagement section  94 , a rear face of the bottom clip member  100  abuts a lateral face  116  of the tube engagement section  96  of the top clip member  92 , as shown in  FIG. 4 . Also as shown in this figure, each bottom clip member  100  has two secondary screw holes  120  on its bottom face  118  that are aligned with corresponding holes in the top clips. The top and bottom clip members are screwed together through these openings. 
         [0042]    Other embodiments of the clip sets are also contemplated. In another embodiment, each bottom clip member is significantly thinner relative to the corresponding top clip member, as compared to the relative thicknesses shown in the embodiments of  FIGS. 7 and 8 . 
         [0043]    In still another embodiment, when the clip is to be affixed to a pivot pin that is easily removable, such as a clevis pin, it is not essential to make the clip in two separate parts so that the clip can be mounted on the pin while the pin is in place. Instead, the top clip and bottom clip members can be formed as single clip members, with a transverse bore hole formed through the clip. When this construction is employed, the end of the clip can be positioned between the flanges of the stem with the opening in the clip in alignment with the holes in the stem flanges. A mounting pin in the form of a clevis pin, bolt, or other removable pivot pin is inserted through the aligned openings and locked into place. Since with either type of clips, the clip member is formed of a resin with inherent lubricity, lubrication between the clips and the pivot pin is provided by the clip member and supplemental lubrication is not required. This embodiment can be used when the pivot pin is removable, however, the clip on nature of the foregoing embodiment has desirable features and may be employed even when the pivot pin is removable. 
         [0044]    Referring to  FIG. 3 , the use of the two clip sets  90  is shown. One clip set  90  is used to connect the front end  70  of down tube  22  to rear-facing stem  72 . To achieve this attachment, the tube engagement section  96  of the top clip member  92  is inserted into the front end  70  of the down tube  22  such that indentation  102  in the shaft engagement section  94  is oriented downwardly. Screws  122  are inserted through openings in the down tube and into screw holes  110 . As shown in  FIGS. 4 and 5 , the indention  102  in the shaft engagement portion  94  of the top clip member  92  fits downwardly into a gap between a pair of spaced, opposed flanges  124 ,  126  on the rear-facing stem  72 . The indentation  102  is fitted over a stainless steel lateral shaft or mounting pin  128  that extends between flanges  124  and  126 . Pin  128  desirably is formed of stainless steel or other rust resistant material. Pin  128  can be press fit into the flanges of the stem. Alternatively, the pin can be a clevis pin or bolt, any of which is replaceable if necessary. 
         [0045]    To complete the attachment of the front end  70  of the down tube  22  to the rear-facing stem  72 , the bottom clip member  100  is positioned against the bottom face  108  of the top clip member  92 , such that the lateral shaft  128  is captured between the top  92  and bottom  100  clip members, within the clip set  90 . Two screws  130  are screwed through the screw holes  120  of the bottom clip member and into the aligned screw holes in the the top clip member, whereby the top  92  and bottom  100  clip members are securely attached together, locking the down tube on the bicycle frame. 
         [0046]    As shown in  FIG. 3 , at the rear end  80  of the down tube  22 , a near mirror image of the connection described above is employed to connect the rear end  80  of the down tube to the forward facing stem  82 . Once both the top and bottom clips sets  90  are secured in their respective positions, the bicycle can be used by the rider. 
         [0047]    Desirably, the clips members are formed of a synthetic resin such as super tough nylon, which has good inherent lubricant characteristics. This provides natural lubrication and obviates the need to lubricate the joints. 
         [0048]    When desired by the rider, the down tube  22  can be removed and replaced in a simple manner by a replacement down tube  22 A. Replacement down tubes of the present invention can have several different characteristics from the original down tubes. For example, the outer coloring scheme, flexibility, and degree of arc can all vary between down tubes, in order to change the flex characteristics or appearance of the down tube. 
         [0049]    To change the down tubes, the original down tube  22  must first be removed. To achieve this, the steps described above are reversed, with the screws  122 ,  130  being unscrewed and the top  92  and bottom  100  clip members of the clip sets  90  being pulled apart and separated from the stems  72 ,  82 . A replacement down tube  22 A is then connected to the stems  72 ,  82  in the same manner as described above. If desired the clip sets for down tube  22  can be removed and reused in down tube  22 A. 
         [0050]    With the foregoing down tube assembly construction, down tube clip sets can easily be installed on and removed from down tubes. This makes it possible to replace the tubular portion of the down tube (which may be relatively inexpensive) without replacing possibly more expensive end connectors. It also makes it possible to replace end connectors without discarding the down tube. 
         [0051]    In  FIG. 6 , an optional tube end cover  140 , preferably formed of tubular plastic, is shown. Tube end covers  140  can be used to encircle and cover the connections between the down tube ends  70 ,  80  and the respective lateral shafts  128  of the stems  72 ,  82 . The covers  140  cover pinch points, improve appearance and serve to protect the connections from undue wear potentially caused by unwanted dirt and other materials getting into these connection points. 
         [0052]    The frame mounting stems employed for mounting the down tubes to the frame are shown in  FIGS. 11-14 . In one embodiment of the invention, different rear facing and forward facing stems  72  and  82  are employed. See  FIGS. 11 and 12 . Rear facing stem  72  ( FIG. 11 ) is mounted on the rear side of head tube  24  at an upper portion of the frame and is connected to the clip member at the front end of the down tube, while forward facing stem  82  ( FIG. 12 ) is mounted at the base of the seat tube on bottom bracket shell  26  and is connected to the clip member at the rear end of the down tube. 
         [0053]    Rear facing stem  72  is formed of aluminum or other suitable material. When the stem  72  and the bike frame are aluminum the stem typically is welded to the frame. When they are formed of a composite material the stems can be integrally molded into the frame. Stems that are welded to the frame are described herein. 
         [0054]    Stem  72  includes a front end  73  that mates with and is attached to head tube  24 . A vertically extending arcuate indentation or recess  75  in the front end of the stem mates with the head tube and is welded securely to the head tube. A rear end  77  of stem  72  comprises a pair of laterally spaced flanges  124  and  126 , with a vertical slot  127  therebetween. The outer sides of the flanges have an oval outer contour that corresponds with the end of the down tube. The flanges have aligned pivot pin mounting holes  129  therein. A lateral shaft or mounting pin  128  is mounted in the openings  129  so as to inventoried and purchased) and facilitates installation (the same stem is used at both ends of the down tube). 
         [0055]    It should be understood that the foregoing is merely an exemplary of the preferred practice of the present invention and that various modifications may be made in the arrangements and details of construction of the embodiments disclosed herein without departing from the spirit and scope of the present invention, as defined in the appended claims.