Abstract:
A tube for use in a bicycle frame in which the tube has a first end and a second end, and a middle section extending between the ends. The first end, second end, and middle sections each have oval-shaped planar cross-sections. In the cross-sections of the first and second ends, the height is greater than the width. In the cross-section of the middle section, the width is greater than the height. This arrangement allows the middle section of the tube to flex vertically between it is narrower in the vertical direction. Likewise, this arrangement provides a strong connection point at the first and second ends which resists flex and movement vertically because the tube is thicker in the vertical direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application 62/117,736, which was filed on Feb. 18, 2015, the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention pertains to a tube for use in a bicycle frame. More particularly, the present invention pertains to a tube for use in a bicycle frame having a cross-sectional shape that is variable along the length of the tube. 
         [0004]    2. Description of the Prior Art 
         [0005]    Bicycle frames have traditionally been designed to be as rigid and stiff as possible. The common belief was that any flex in the frame led to a loss of energy or weakness in the frame. 
         [0006]    However, it has been determined by the inventor that this premise is not entirely true. Even more so, it has been determined that a bicycle frame that is specifically designed to have a degree of flex can function like a spring which stores and releases potential energy through each revolution of the pedals. 
         [0007]    A bicycle frame having a flexible, removable down tube was previously disclosed in the Applicant&#39;s U.S. Pat. No. 8,991,848, the entire disclosure of which is hereby incorporated by reference. As discussed in that patent, 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 increased vertical flexibility in the frame provided by the flexible down tube can increase the comfort for the rider by increasing the shock absorbency of the frame, and may also actually increase efficiency by reducing energy loss during pedaling. These benefits are achieved or enhanced by having a flexible top tube as well. 
         [0008]    One potential problem with a flexible top tube, or with flexible frames in general, is that the flexing of the frame can increase stress on the joints between the tubes. This increased flex means more stress at the joints than is found in traditional bicycles with stiffer frames. This stress can be detrimental over time and can cause joints, particularly those that are welded together, to become weak or even to fail from fatigue. 
         [0009]    Traditional frames often employ tubes that have consistent cross-sections through the entire length of the tubes. Often these cross-sections are circular. This is not ideal in frames where there is an attempt to increase the amount of flex in the tube. In these frames, a tube with a cross-section that has a lesser maximum vertical axis (referred to hereafter as “height”) than maximum horizontal axis (referred to hereafter as “width”) may be more flexible than its counterpart with a circular cross-section. For example, a top tube having oval-shaped cross-sections with a greater width than height (e.g., where the major axis is horizontal) will tend to allow more vertical flex than. a similar top tube with a circular cross-section. 
         [0010]    As a frame becomes more flexible, however, this structure can become less than optimal. In the top tube of the previous example, for instance, the increased vertical flex may be found throughout the entire length of the tube. This means that there will be increased stress at the joints, namely, the first end point and second end point of the tube where the top tube is joined to the head tube and to the seat tube, respectively. That is to say, the result of the increased vertical flex in the top tube as a whole is an increase in flex at the potentially weak joints where the ends of op tube are attached to other parts of the frame. 
         [0011]    Thus, there remains a need for a bicycle frame with an improved tube design that allows for increased vertical flex but decreases the stress on the joints between the top tube and other parts of the frame. 
       SUMMARY OF THE INVENTION 
       [0012]    According to a first embodiment of the present invention, there is provided a tube for use in a bicycle frame extending along a length l from a first end to a second end, the tube comprising: 
         [0013]    the first end having a first planar cross-section, the first planar cross-section having a cross-sectional area a 1 , a maximum height h 1 , and a maximum width w 1 ; 
         [0014]    the second end having a second planar cross-section, the second planar cross-section having a cross-sectional area a 2 , a maximum height h 2 , and a maximum width w 2 ; and 
         [0015]    a middle section located along the length l of the tube between the first end and the second end, the middle section having a middle cross-section, the middle cross-section having a cross-sectional area a m , a maximum height h m , and a maximum width w m ; wherein h 1 &gt;h m  and h 2 &gt;h m , and w 1 &lt;w m  and w 2 &lt;w m . 
         [0016]    Although the cross-sectional areas a 1 , a 2 , and a m  may be any suitable type of shape, preferably the cross-sectional areas a 1 , a 2 , and a m  are oval or elliptical in shape. 
         [0017]    Preferably, the maximum width along the length of the entire tube is w m , and the maximum height along the length of the entire tube is preferably h 1  or h 2 . The height h 1  may also be equal to h 2 , although not necessarily. 
         [0018]    In addition, any of the three areas a 1 , a 2 , and a m  may be equal in size to each other, although not necessarily. 
         [0019]    Furthermore, the tube is preferably a top tube or a down tube, although it is possible that any other tube on the bicycle frame can utilize the tri-oval construction described herein. In addition, the tube can form any suitable shape in which the tube may be straight, arcuate, or the like. 
         [0020]    According to a second embodiment of the present invention, there is provided a bicycle frame comprising: 
         [0021]    a top tube, the top tube having a first end and a second end, the tube extending along a length l from the first end to the second end, and further having a middle point located along the top tube between the first end and the second end; 
         [0022]    a seat tube connected to the second end; 
         [0023]    a head tube connected to the first end; 
         [0024]    a down tube connected to the seat tube at a point on the seat tube below the second end of the top tube, and the down tube connected to the head tube at a point on the head tube below the first end of the top tube; 
         [0025]    the first end of the top tube having an oval-shaped first cross-section along a plane that is perpendicular to the length l of the top tube, wherein the first cross-section is greater in height than width; 
         [0026]    the second end of the top tube having an oval-shaped second cross-section along a plane that is perpendicular to the length l of the top tube, wherein the second cross-section is greater in height than width; and 
         [0027]    the middle point having an oval-shaped third cross section along a plane that is perpendicular to the length l of the top tube, wherein the third cross-section is greater in width than height. 
         [0028]    Optionally, the top tube can include a second middle point located between the first end and the middle point, and a third middle point located between the second middle point and the middle point. The top tube decreases gradually in height and increases gradually in width between the second middle point and the third middle point. 
         [0029]    Optionally, the top tube can also include a fourth middle point located between the second end and the middle point, and a fifth middle point located between the fourth middle point and the middle point. The top tube decreases gradually in height and increases gradually in width between the fourth middle point and the fifth middle point. 
         [0030]    Preferably, the down tube is flexible and has an arcuate shape. 
         [0031]    Furthermore, the height and width of the top tube is preferably substantially constant between the first end and the second middle point, and the height and width of the top tube is preferably substantially constant between the second end and the fourth middle point. 
         [0032]    In addition, the height and width of the top tube is preferably substantially constant between the third middle point and the fifth middle point. 
         [0033]    According to a third embodiment of the present invention, there is provided a bicycle frame comprising a top tube and a down tube in which the top tube and the down tube each have a “tri-oval” construction in which the height is the oval&#39;s major axis along a cross-section of the respective tube at the opposed ends of the top tube and down tubes where the respective tubes connect to a head tube and a seat tube, and the width is the oval&#39;s major skis along a cross-section of the respective tube at a medial point of the top tube and down tube. 
         [0034]    For a more complete understanding of the present invention, reference is made to the following detailed description and accompanying drawings. In the drawings, like reference characters refer to like parts throughout the views in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]      FIG. 1  is a side elevational view of a bicycle frame of an embodiment of the present invention having a tri-oval top tube and tri-oval down tube showing cross-sectional views in  FIGS. 1 a -1 f    of the frame at various locations along the frame members; 
           [0036]      FIG. 2  is a top side view of a top tube; 
           [0037]      FIG. 3  is a side view of a top tube, shown 90° from the view shown in  FIG. 2 ; 
           [0038]      FIG. 4  is a perspective side view of a bicycle frame having a tri-oval top tube and having a replaceable down tube; and 
           [0039]      FIG. 5  is a perspective view of a bicycle frame having a tri-oval top tube that is arcuate in shape along the length thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0040]    In accordance with the present invention and as shown generally in  FIG. 1 , a bicycle frame  10  constructed in accordance with the present invention comprises a top tube  12 , a down tube  14 , a seat tube  16 , a head tube  34 , and a front fork  18  comprising spaced forks  20  on opposite sides of a front wheel  22 . Chain stays  24  and seat stays  26  are positioned on opposite sides of a rear wheel  28 , with ends of the seat stays  26  and chain stays  24  being connected to a rear dropout  30  that engages an axle  29  on the rear wheel  28  and upwardly extending slot  32 . A seat (not shown) is mounted on the upper end of a seat tube  16  in a conventional manner. 
         [0041]    A handlebar assembly (not shown) is mounted on the upper end of head tube  34  at the front end of the frame  10 . The bicycle is powered by a conventional pedal mechanism (not shown) attached to the bottom bracket shell  36  positioned at the bottom of the seat tube  16 . 
         [0042]    As referenced herein, the terms “height” and “width” are intended to generally refer to a vertical and horizontal orientation, respectively. However, more specifically the various cross-sections described herein are along a plane that is perpendicular to the length of the particular tube. In other words, the tube has an axis along the length thereof, and the plane of each cross-section is oriented 90° from the axis, such that the axis extends perpendicular from the plane. Thus, it is understood that the “height” and “width” of each cross-section is not necessarily vertical and horizontal, respectively. This is particularly true when the tube is arcuate and only a portion of the tube extends along a horizontal axis. The cross-sectional drawings of the tube from  FIG. 1  and  FIGS. 1 a -1 f    should make apparent the orientation of each cross-sectional plane. 
         [0043]    In the present invention, the bicycle frame  10  includes the top tube  12  that extends along a length l from a first end  38  to a second end  40 . The top tube  12  has an oval cross-section near the first end  38  and second end  40  of the top tube  12  wherein the major axis is the height, and having an oval cross-section in the intermittent portion of the tube  12  wherein the major axis is the width. 
         [0044]    As shown in  FIGS. 1 a -1 c   , the first end  38  has a first planar cross-section having a cross-sectional area a 1 , a maximum height h 1 , and a maximum width w 1 . The second end  40  has a second planar cross-section having a cross-sectional area a 2 , a maximum height h 2 , and a maximum width w 2 . There is also provided a middle section  42  located along the length l of the tube  12  between the first end  38  and the second end  40 . The middle section  42  has a middle cross-section which has a cross-sectional area a m , a maximum height h m , and a maximum width w m . As described in greater detail below, the height and width dimensions of the first end  38 , second end  40 , and middle section  42  are such that h 1  and h 2  are both greater than h m , and w m  is greater than both w 1  and w 2 . 
         [0045]    The cross-sectional areas a 1 , a 2 , and a m  may be any suitable type of shape, however, preferably the cross-sectional areas a 1 , a 2 , and a m  are oval or elliptical in shape. 
         [0046]    Preferably, the maximum width along the length l of the entire tube is w m , and the maximum height along the length l of the entire tube is preferably h 1  or h 2 . The height h 1  may also be equal to h 2 , although not necessarily. In addition, any of the three areas a 1 , a 2 , and a m  may be equal in size to each other, although not necessarily. 
         [0047]    This structure allows for, and in fact encourages, more flex in the middle section  42  of the top tube  12  than at its ends. This flex in the middle section  42  of the top tube  12  tends to be in a vertical direction and can have an overall positive impact on the shock absorbing aspects and efficiency of the frame  10 . The greater height of the cross-sections of the top tube  12  near the ends  38 , 40  of the tube  12  increases the resilience of the tube  12  at the ends  38 , 40  and restrains the tube  12  from flexing vertically as much at those ends. This is preferable in most instances because reducing flex at the ends helps to avoid undue stress on the connections between the top tube  12  and the seat tube  16 , and between the top tube  12  and the head tube  34 . This helps transfer stress away from the ends  38 , 40  of the tube  12 . 
         [0048]    In one embodiment of the invention, shown in  FIG. 4 , the down tube  14  has an arcuate shape and is removably mounted to the frame  10  by connectors. The arcuate tube of this embodiment, however, does not employ a tri-oval tube design. 
         [0049]    It is also contemplated that this type of tri-oval tube construction could also be used for tubes in the frame  10  other than the top tube  12 . It may be particularly well-suited for a down tube  14 , for example. This concept is employed in another embodiment of the invention, shown in  FIG. 5 , wherein the present invention is used for the down tube  14 , and the down tube  14  has an arcuate shape similar to one or more of the down tubes  14  shown in U.S. Pat. No. 8,991,848, but differing in that it has the tri-oval geometry. In this embodiment of the invention, the down tube  14  is formed in an arcuate manner and is fastened securely to the frame  10  by welding or the like. In both the embodiment shown in  FIG. 4  and the embodiment shown in  FIG. 5 , the down tubes  14  are flexible vertically. 
         [0050]    It is contemplated that the tubes in the bicycle frame  10  can be connected to each other using any suitable connector that is well-known in the art. For example, this could include the connectors shown in U.S. Pat. No. 8,991,848, or even clips, preferably of the type shown in the Applicant&#39;s co-pending U.S. patent application Ser. No. 14/778,486, filed Sep. 18, 2015. Preferably, the top tube  12  is welded at one end to the head tube  34  and at the other end to the seat tube  16 . 
         [0051]    The top tube  12  has an oval-shaped cross-section at the first end  38 , second end  40 , and a middle point  44 . According to one embodiment, the relative proportion of the major and minor axes of the oval-shaped cross-section at the first end  38  of the tube  12  is approximately 5:4. The cross-section of the tube  12  maintains this constant proportion from the first end  38  of the tube to a distance of about 10% of the total length of the tube, this location being defined as a second middle point  46 . Approximately the next 22% of the length of the tube  12  has an oval-shaped cross-section that gradually decreases in height and increases in width, this location being defined as a third middle point  48 . The decrease in height is caused by an upward slant in the bottom of the tube  12  while the top of the tube  12  maintains a consistent arcuate path. The increase in width is caused by a gradual outward bulging on both sides of the tube  12 . 
         [0052]    Continuing to move along the length of the tube  12  away from the head tube  34 , approximately the next 41% of the length of the tube forms a middle portion, or middle section, which spans the middle point  44 , and terminates at a location defined as a fifth middle point  50 . In this middle portion, the cross-section of the tube  12  maintains a consistent proportion of about 5:3 between the major and minor axes, with the width of the tube  12  being the major axis. 
         [0053]    Adjacent to the middle portion  42 , and moving beyond the fifth middle point  50 , the next approximate 13% of the length of the tube  12  has an oval-shaped cross-section that gradually increases back in height and decreases in width, this section terminating at a location defined as a fourth middle point  52 . The increase in height is caused by a downward slant in the bottom of tube  12 , while the top of the tube  12  maintains a consistent arcuate direction. The decrease in width is caused by a gradual inward draw on both sides of the tube  12 . During the remaining approximate 14% of the length of the tube  12 , the cross-section maintains a consistent proportion between the major axis (height) and the minor axis of about 5:4 until it terminates at the second end  40 . 
         [0054]    This top tube  12  has significant advantages. For example, by having a middle section  42  of the tube  12  that is less in height than width, there is a significant vertical flex in that portion of the tube  12 . This is contrasted with the end portions (which are located between the first end  38  and the second middle point  46 , and between the second end  40  and the fourth middle point  52 ), which have greater heights than widths, and which will tend to flex less in the vertical direction and thus place less stress on the welded joints. 
         [0055]    In the preferred embodiment, there are oval-shaped cross-sections over the entire length of the tube  12 , notwithstanding the two circular cross-sectional planes which may occur as the geometry of the tube  12  switches the major and minor axes between the height and the width. However, any other suitable shapes for the cross-sections are also contemplated, including ellipses, polygonal shapes, or even irregular shapes. 
         [0056]    In addition, in the preferred embodiment, the top tube  12  is composed primarily of a flexible material, such as carbon fiber or titanium. 
         [0057]    The foregoing describes applications of the present invention for a bicycle frame. Other features and applications of a similar nature are within the scope of the invention. 
         [0058]    As is apparent from the preceding, the present invention provides a bicycle frame with an improved tube design that allows for increased vertical flex but decreases the stress on the joints between the top tube and other parts of the frame.