Abstract:
A bicycle steerer tube is adapted to reside in a plane of travel of the bicycle. A thickness at a point on the wall of the steerer tube body in a lower section thereof varies as a function of the cross-sectional angle of the point to the plane of travel, with the wall thickness being at a maximum in the plane of travel. An inner wall of the lower section may be elliptical, with a minor axis aligned with the plane of travel and a major axis orthogonal to the plane of travel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates in general to bicycles, and more particularly to bicycle steerer tubes. 
         [0002]    A conventional bicycle (a mountain bike is shown at  100  in  FIG. 1 ) is steered by varying the plane of its front wheel  102  out of a plane of travel P, which is aligned with the running direction of the bicycle. This is done by linking the front wheel  102  to a rider-operated handlebar  104 . The front wheel  102  is rotatably suspended between left and right tubes  106 ,  108  of a fork indicated generally at  110 . The left and right fork tubes  106 ,  108  are joined, either in solid fashion or by shock absorbing apparatus, to a fork crown  112  positioned upward from the front wheel. 
         [0003]    Referring to  FIGS. 1 and 2 , a steerer tube  200  has its lower end  202  affixed to the fork crown  112  and is disposed along an upwardly and usually rearwardly extending steering axis X. Axis X is within the plane of travel P. The steerer tube  200  is inserted into a coaxial head tube  204  that is part of a bicycle frame  206 . Bearings are mounted between the steerer tube  200  and the head tube  204  to permit the free rotation of the steerer tube  200  relative to the head tube  204 . The handlebar  104  is affixed in some fashion (as by a star nut, not shown) to an upper end  212  of the steerer tube, and permits the rider to impart torque to the steerer tube  200 , the fork  110  and the front wheel  102 , which in response rotate around the steering axis X as a unit. Thus, the rider may steer the bicycle  100  right or left as desired. 
         [0004]    Many conventional steerer tubes are circularly cylindrical. A perfectly cylindrically circular steerer tube, having a uniform wall thickness, will exhibit a uniform stiffness longitudinally, or fore-and-aft and in alignment with plane of travel P, and laterally, or side-to-side and perpendicular to plane of travel P and axis X. But uniformly thick and stiff steerer tubes do not take into account the differences in loads on the steerer tube and stability, comfort and steering requirements. 
       SUMMARY OF THE INVENTION 
       [0005]    According to one aspect of the invention, a bicycle steerer tube has an elongate hollow body that is arranged around a steering axis of the bicycle. The steering axis is located in a vertical plane of travel of the bicycle. A segment of an upper section of the body is adapted to be joined to a bicycle handlebar. A segment of a lower section of the steerer tube body is adapted to be joined to a crown of a front wheel fork. The lower and upper sections of the steerer tube body are joined together. The body of the steerer tube is formed by a wall. The thickness of the wall at any point in the lower section of the body varies as a function of the cross-sectional angle of the point relative to the plane of travel, the wall thickness being at a maximum in the plane of travel of the bicycle. 
         [0006]    In some embodiments of the invention, the outer surfaces of the upper and lower sections of the steerer tube body are circular in cross section. In some embodiments of the invention, the wall thickness is at a minimum in a plane containing the steering axis and orthogonal to the plane of travel of the bicycle. In some embodiments of the invention, at least a portion of the inner surface of the wall is formed as an ellipse in cross section, with a major diameter of the ellipse being formed to be perpendicular to the plane of travel, and a minor diameter of the ellipse being formed to be in the plane of travel. 
         [0007]    Steerer tubes according to the invention have a large stiffness and strength in the fore and aft plane of travel of the bicycle. But since side bending stiffness isn&#39;t as critical due to lighter side loads, the wall thickness outside of the plane of travel may be reduced. This permits a lighter weight steerer tube that nonetheless meets all loading requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further aspects of the invention and their advantages can be discerned in the following detailed description, in which like characters denote like parts and in which: 
           [0009]      FIG. 1  is a perspective view of a representative bicycle; 
           [0010]      FIG. 2  is a front view of a bicycle fork as incorporating a steerer tube according to one embodiment of the invention; 
           [0011]      FIG. 3  is a bottom end view taken substantially along line  3 - 3  of  FIG. 2 ; 
           [0012]      FIG. 4  is a top end view taken substantially along line  4 - 4  of  FIG. 2 ; 
           [0013]      FIG. 5 a    is a side view of the steerer tube shown in  FIG. 2 ; 
           [0014]      FIG. 5 b    is a perspective view of the steerer tube shown in  FIG. 2 ; 
           [0015]      FIG. 6  is an axial sectional view taken substantially along line  6 - 6  of  FIG. 3 ; 
           [0016]      FIG. 7  is an axial sectional view taken substantially along line  7 - 7  of  FIG. 3 ; 
           [0017]      FIG. 8  is a bottom end view of the steerer tube of  FIG. 6 ; 
           [0018]      FIG. 9  is a sectional view taken substantially along line  9 - 9  of  FIG. 6 ; 
           [0019]      FIG. 10  is a sectional view taken substantially along line  10 - 10  of  FIG. 6 ; 
           [0020]      FIG. 11  is a sectional view taken substantially along line  11 - 11  of  FIG. 6 ; 
           [0021]      FIG. 12  is a front view of a bicycle fork as incorporating a steerer tube according to another embodiment of the invention; 
           [0022]      FIG. 13  is an axial sectional view of a steerer tube according to another embodiment of the present invention; 
           [0023]      FIG. 14  is an axial sectional view taken substantially along line  14 - 14  of  FIG. 13 ; 
           [0024]      FIG. 15  is a bottom end view of the steerer tube of  FIG. 13 ; 
           [0025]      FIG. 16  is a sectional view taken substantially along line  16 - 16  of  FIG. 13 ; 
           [0026]      FIG. 17  is a sectional view taken substantially along line  17 - 17  of  FIG. 13 ; 
           [0027]      FIG. 18  is a sectional view taken substantially along line  18 - 18  of  FIG. 13 ; 
           [0028]      FIG. 19  is an axial sectional view of a steerer tube according to another embodiment of the invention; 
           [0029]      FIG. 20  is an axial sectional view taken substantially along line  20 - 20  of  FIG. 19 ; 
           [0030]      FIG. 21  is a bottom end view of the steerer tube of  FIG. 19 ; 
           [0031]      FIG. 22  is a sectional view taken substantially along line  22 - 22  of  FIG. 19 ; 
           [0032]      FIG. 23  is a sectional view taken substantially along line  23 - 23  of  FIG. 19 ; 
           [0033]      FIG. 24  is a sectional view taken substantially along line  24 - 24  of  FIG. 19 ; 
           [0034]      FIG. 25  is an axial sectional view of a steerer tube according to another embodiment of the invention; 
           [0035]      FIG. 26  is an axial sectional view taken substantially along line  26 - 26  of  FIG. 25   
           [0036]      FIG. 27  is a bottom end view of the steerer tube of  FIG. 25 ; 
           [0037]      FIG. 28  is a sectional view taken substantially along line  28 - 28  of  FIG. 25 ; 
           [0038]      FIG. 29  is a sectional view taken substantially along line  29 - 29  of  FIG. 25 ; 
           [0039]      FIG. 30  is a sectional view taken substantially along line  30 - 30  of  FIG. 25 ; 
           [0040]      FIG. 31  is an axial sectional view of a steerer tube according to another embodiment of the invention; 
           [0041]      FIG. 32  is an axial sectional view taken substantially along line  32 - 32  of  FIG. 31 ; 
           [0042]      FIG. 33  is a bottom end view of the steerer tube of  FIG. 31 ; 
           [0043]      FIG. 34  is a sectional view taken substantially along line  34 - 34  of  FIG. 31 ; 
           [0044]      FIG. 35  is a sectional view taken substantially along line  35 - 35  of  FIG. 31 ; and 
           [0045]      FIG. 36  is a sectional view taken substantially along line  36 - 36  of  FIG. 31 . 
       
    
    
     DETAILED DESCRIPTION 
       [0046]      FIG. 2  illustrates a steerer tube  200  as used as a component of a mountain bike fork, although the present invention may be used with any bicycle type, including road bicycles and triathlon bicycles. The steerer tube  200  is particularly advantageous as used with a mountain bike, as the steerer tube stiffness within the plane of travel P ideally is enhanced relative to its stiffness orthogonal to plane P. 
         [0047]    The embodiment of the steerer tube  200  shown in  FIGS. 2-11  has an upper section  214  and a lower section  213  that in turn has a first or upper portion  216  and a second or lower portion  218 . The upper section  214  extends from the upper end  212  of the steerer tube  200  to a lower end  220  of the upper section. A segment  215  of the upper section, adjacent to end  212 , is adapted to be joined to handlebar  104 . The upper section  214  has an outer surface  222  which is circularly cylindrical throughout the length of the upper section  214 , and an inner surface  224  which is also circularly cylindrical throughout the length of the upper section  214 . Upper section  214  has an invariant outer diameter O A , which in one embodiment may be in the range of 25 mm to 40 mm and more preferably can be about 28.5 mm, and an invariant inner diameter I A , which in one embodiment may be in the range of 20 mm to 36 mm and more preferably can be about 24.6 mm. While the segment  215  of the upper section  214  is circularly cylindrical so as to be more easily compatible with a star nut (not shown), in an alternative embodiment, the segment  215  of the upper section  214  could be tapered or elliptical in cross section and still be compatible with a star nut. 
         [0048]    In this embodiment, the upper portion  216  of lower section  213  has an outer surface  226  which is frustoconical. The lower end  220  of the upper section  214  acts as the upper end of the upper portion  216  of lower section  213 . The upper portion  216  extends from its upper end  220  to a lower end  228 ; the lower end  228  is defined by the termination of the sloped outer surface  226 . In this embodiment, the outer surface  226  is circular in cross section and has an outer diameter O B  which increases linearly from outer diameter O A , at its upper end  220 , to an outer diameter O C  at its lower end  228 . Said another way, the outer surface  226  of upper portion  216  gradually tapers in diameter from O C  to O A  as one proceeds upwardly along axis X. More generally, outer diameter O C  can be greater than outer diameter O A  In one embodiment, the outer diameter O C  can be in the range of 25 mm to 50 mm and more preferably can be about 39.9 mm. Upper portion  216  can be about 76 mm long. 
         [0049]    In this embodiment, the inner surface  230  of upper portion  216  has a shape which changes as a function of the distance from upper end  220 . At upper end  220 , the inner surface  230  is circular in cross section. As one proceeds towards upper portion lower end  228 , the cross section becomes more and more elliptical.  FIG. 6  is an axial sectional view aligned with the minor axis of the ellipse formed by the inner surface  230  of upper portion  216 . The minor diameter I B1  of surface  230  linearly increases as a function of distance from upper end  220 , but the rate of increase is relatively small. As shown in  FIG. 7 , the major diameter I B2  of surface  230  is the same as I A  at upper end  220  but then increases linearly as a function of the distance away from upper end  220 . 
         [0050]    The wall thickness of the tube  200  at the crown  112  is generally greater than the wall thickness of the upper section  214 , as the stress on tube  200  is highest at its junction with crown  112 . The lower portion  218  of the lower section  213  of steerer tube  200  is characterized in that its outer surface  232  is circularly cylindrical. Lower portion  218  extends downwardly from upper portion end  228 , which is the same as the lower end of upper portion  216 , to lower end  202  of the steerer tube. A segment  234  of lower portion  218 , adjacent to the lower end  202 , is formed in this embodiment to include a ring of increased diameter (such as about 42 mm) and is adapted for affixation to fork crown  112 . In another embodiment shown in  FIG. 12 , a steerer tube  260  and a fork crown  262  may be integrally formed rather than assembled and in those embodiments a raised ring may be missing. An outer diameter O C  of the outer surface  232  may be in the range of 25 mm to 50 mm and more preferably can be chosen to be 39.9 mm. Lower portion  218  can be at least 25 mm long. 
         [0051]    In this embodiment, lower portion  218  has an inner surface  236  which continues to change cross-sectional shape as one proceeds to tube end  202 . In this illustrated embodiment, while the outer surface  232  makes a shoulder with outer surface  222  of the upper portion  216  at end  228 , the shape of inner surface  236  changes continuously and linearly from upper portion inner surface  230 , with no discernable break or bend at portion end  228 . In this illustrated embodiment, the lower portion inner surface minor diameter I C1  will continue to slowly increase as steerer tube end  202  is approached. The lower portion inner surface major diameter I C2  will continue to linearly increase at a faster rate. 
         [0052]    In this and other embodiments, a ratio of I C2  to I C1 , taken at tube end  202 , can be in the range of 1.05 to 1.3, and more preferably is in the range of 1.10 to 1.25. The combined lengths of upper portion  216  and lower portion  218  can be chosen to be between 40 mm and 200 mm and in one embodiment can be about 101 mm. In this and other embodiments, a ratio of the upper section inner diameter I A  to the upper section outer diameter O A  can be chosen to be in the range of 0.75 to 0.95. 
         [0053]    Steerer tube  200  (and the other embodiments  300 ,  400 ,  500  and  600  herein described) may be fabricated of aluminum, steel, magnesium, titanium or carbon fiber reinforced composite. Steerer tube  200  may be made of a material that is the same or different from the rest of fork  110 . 
         [0054]    In the embodiment illustrated in  FIGS. 13-18 , a steerer tube indicated generally at  300  continues to have an upper section  302  and a lower section  303 , the lower section in turn having an upper portion  304  and a lower portion  306 , similar to the embodiment shown in  FIGS. 2-11 . An upper segment  308  adjacent to an upper tube end  310  is adapted to be affixed to a bicycle handlebar  104 . A lower segment  312  adjacent to a lower tube end  314 , herein shown as including a raised annulus or ring, is adapted to be affixed to a fork crown  112 . 
         [0055]    Upper section  302  extends from upper tube end  310  to a lower end  316  of upper section  302 . An outer surface  318  and an inner surface  320  of upper section  302  are circularly cylindrical throughout the length of upper section  302 , as before. Upper section  302  may have an outer diameter O A  and an inner diameter I A  with measurements and/or ratios to each other similar to those described for the embodiment illustrated in  FIGS. 2-11 . 
         [0056]    First or upper portion  304  of lower section  303  extends from its upper end  316  (which is the same as the lower end of the upper section  302 ) to a lower end  322 . An outer surface  324  of the upper portion  304  is frustoconical in shape; its outer diameter O B  increases linearly from upper end  316  to lower end  322 . The lower end  322  is defined by the termination of the sloped outer surface  324 . An inner surface  326  of the upper portion  304  changes cross-sectional shape from circular to elliptical, and the eccentricity of the ellipse increases as the lower end  322  is approached. A major diameter I B2  of upper portion inner surface  326  increases linearly as the lower end  322  is approached. A minor diameter I B1  of upper portion inner surface  326  stays the same as upper section inner diameter I A . 
         [0057]    Second or lower portion  306  of lower section  303  extends from its upper end  322 , which is the same as the lower end of upper portion  304 , to lower tube end  314 . The lower portion  306  has an outer surface  330  that is circularly cylindrical. The lower portion  306  has an inner surface  328  which continues to change cross-sectional shape as one proceeds to lower tube end  314 . In this illustrated embodiment, while the outer surface  330  makes a shoulder with outer surface  324  of the upper portion  304  at end  322 , the shape of the inner surface  328  changes continuously and linearly from the upper portion inner surface  326 , with no discernable break or bend at end  322 . The lower portion inner surface major diameter I C2  increases linearly as steerer tube end  314  is approached. The lower portion inner surface minor diameter I C1  stays the same as upper section inner diameter I A . 
         [0058]    In the embodiment illustrated in  FIGS. 19-24 , a steerer tube indicated generally at  400  continues to have an upper section  402  and a lower section  403 , the lower section in turn having an upper portion  404  and a lower portion  406 , similar to the embodiment shown in  FIGS. 2-11 . An upper segment  408  adjacent to an upper tube end  410  is adapted to be affixed to bicycle handlebar  104 . A lower segment  412  adjacent to a lower tube end  414 , herein shown as including a raised annulus or ring, is adapted to be affixed to fork crown  112 . 
         [0059]    Upper section  402  extends from tube end  410  to a lower end  416  of upper section  402 . An outer surface  418  and an inner surface  420  of upper section  402  are circularly cylindrical throughout the length of upper section  402 , as before. Upper section  402  may have an outer diameter O A  and an inner diameter I A  with measurements and/or ratios to each other similar to those described for the embodiment illustrated in  FIGS. 2-11 . 
         [0060]    First or upper portion  404  of lower section  403  extends from its upper end  416  (which is the same as the lower end of the upper section  402 ) to a lower end  422 . An outer surface  424  of the upper portion  404  is frustoconical in shape; its outer diameter O B  increases linearly from end  416  to end  422 . An inner surface  426  of the upper portion  404  changes cross-sectional shape from circular to elliptical, and the eccentricity of the ellipse increases as the lower end  422  of upper portion  404  is approached. A major diameter I B2  of upper portion inner surface  426  increases linearly as lower end  422  is approached. A minor diameter I B1  of upper portion inner surface  426  also increases linearly as lower end  422  is approached, but at a slower rate than the rate of increase of I B2 . 
         [0061]    The second or lower portion  406  of lower section  403  extends from its upper end  422  (which is the same as the lower end of upper portion  404 ) to the lower tube end  414 . An outer surface  428  of the lower portion  406  is circularly cylindrical and has an outer diameter O C , of dimensions similar to those chosen for the embodiment shown in  FIGS. 2-11 . An inner surface  430  of the lower portion  406  is elliptically cylindrical; the cross-sectional ellipse taken at end  422  is the same as the cross-sectional ellipse taken at end  414 . Major inner diameter I C2 and minor inner diameter I C1  are the same at end  422  as they are at end  414 . 
         [0062]      FIGS. 25-30  illustrate another embodiment of a steerer tube  500  of the invention. The steerer tube  500  has an upper end  502  and a lower end  504 . The steerer tube  500  is divided into an upper section  506  and a lower section  508 ; section  508  has no distinct upper and lower portions. An upper segment  510  adjacent tube upper end  502  is adapted to be affixed to handlebar  104 . A lower segment  512 , here including a raised ring, is disposed adjacent lower tube end  504  and is adapted to be affixed to fork crown  112 . 
         [0063]    Upper section  506  extends from upper tube end  502  to a lower end  514 . Both an outer surface  516  of section  506  and an inner surface  518  of section  506  are circularly cylindrical throughout the length of upper section  506 . Inner surface  518  has a constant diameter I A  and outer surface  516  has a constant outer diameter O A . 
         [0064]    Lower section  508  extends from its upper end  514 , which is the same as the lower end of the upper section  506 , to the tube end  504 . An outer surface  520  of the lower section  508  is circularly cylindrical and may have an outer diameter O C.  Outer diameter O C  may be chosen to be the same as outer diameter O A  and in this instance outer surface  520  will be linearly continuous with outer surface  516  of upper section  506 . The dimension of outer diameter O C  can be chosen to be similar to that described in the first embodiment ( FIGS. 2-11 ). 
         [0065]    An inner surface  522  of the lower section  508  changes shape as one proceeds from its upper end  514  to the tube end  504 . At end  514 , the inner surface  522  has a circular cross section such that its minor diameter I C1  is the same as its major diameter I C2 , and at end  514  these are the same as upper section inner diameter I A . As one approaches tube end  504 , major diameter I C2  will increase linearly. Minor diameter I C1  will also increase linearly, but at a slower rate. Therefore, the eccentricity of the cross-sectional ellipse of inner surface  522  will increase and will be greatest at end  504 . At end  504 , the ratio of I C2  to I C1  can be chosen from the range of 1.05 and 1.3, and more preferably from within the range of 1.10 to 1.25, similar to the ratios expressed for the embodiment shown in  FIGS. 2-11 . 
         [0066]    While the above embodiments show an inner surface of the steerer tube transitioning between a circular cross section and an elliptical cross section, in another embodiment the inner surface of a steerer tube may have an elliptical cross section throughout the length of the steerer tube as shown in  FIGS. 31-36 . The steerer tube  600  has the upper section  614  and a lower section  613 . The lower section  613  has an upper portion  616  and a lower portion  618 . The upper section  614  extends from an upper end  612  of the steerer tube  600  to a lower end  620  of the upper section  614 . A segment  615  of the upper section, adjacent to end  612 , is adapted to be joined to handlebar  104 . The upper section  614  has an outer surface  622  which is circularly cylindrical throughout the length of the upper section  614  and an inner surface  624  which is elliptical in cross section throughout the length of the upper section  614 . Upper section  614  has an invariant outer diameter O A  and an invariant inner minor diameter I A1  and an invariant inner major diameter I A2 . 
         [0067]    The upper section  616  of lower section  613  has an outer surface  626  which is frustoconical. The lower end  620  of the upper section  614  acts as the upper end of the upper portion  616  of lower section  613 . The upper portion  616  extends from its upper end  620  to a lower end  628 ; the lower end  628  is defined by the termination of the sloped outer surface  626 . In this embodiment, the outer surface  626  is circular in cross section and has an outer diameter O B  which increases linearly from outer diameter O A  at is upper end  620 , to an outer diameter O C  at its lower end  628 . 
         [0068]    The inner surface  630  of upper section  616  has a shape which changes as a function of the distance from upper end  620 . At upper end  620 , the inner surface  630  is elliptical in cross section. As one proceeds towards upper portion lower end  628 , the cross section becomes more and more elliptical.  FIG. 31  is an axial sectional view aligned with the minor diameter of the ellipse formed by the inner surface of upper portion  616 . The minor diameter I B1  of surface  630  linearly increases as a function of distance from upper end  620 , but the rate of increase is relatively small. As shown in  FIG. 32 , the major diameter I B2  of surface  630  is the same as I A2  at upper end  620  but then increases linearly as a function of the distance away from upper end  620 . 
         [0069]    The lower section  618  of the lower section  613  of steerer tube  600  is characterized in that its outer surface  632  is circularly cylindrical. Lower portion  618  extends downwardly from upper portion end  628 , which is the same as the lower end of upper portion  616 , to lower end  602  of the steerer tube. A segment  634  of lower portion  618 , adjacent to the lower end  602 , is adapted for affixation to the fork crown  112 . 
         [0070]    In this embodiment, lower portion  618  has an inner surface  636  which continues to change cross-sectional shape as one proceeds to tube end  602 . While the outer surface  632  makes a shoulder with outer surface  622  of the upper section  616  at end  628 , the shape of the inner surface  636  changes continuously and linearly from upper portion inner surface  630 , with no discernable break or bend at portion end  628 . The lower portion inner surface minor diameter I C2  will continue to slowly increase as steerer tube end  602  is approached. The lower portion inner surface major diameter I C2  will continue to linearly increase at a faster rate. At end  602 , the ratio of I C2  and I C1  can be chosen from the range of 1.05 and 1.3, and more preferably from within the range of 1.10 to 1.25, similar to the ratios expressed for the embodiment shown in  FIGS. 2-11 . 
         [0071]    In summary, steerer tube embodiments have been illustrated and described which have lower sections, or portions of same, with a wall thickness in the plane of travel that is greater than the wall thickness outside of the plane of travel, and which therefore exhibit a greater stiffness fore and aft than they do side-to-side. The outer surface of the lower portion of the lower tube section nonetheless may be specified as circularly cylindrical as an aid to its assembly to other fork elements. 
         [0072]    While illustrated embodiments of the present invention have been described and illustrated in the appended drawings, the present invention is not limited thereto but only by the scope and spirit of the appended claims.