Abstract:
An axle used to mount a wheel for rotation on the body of a wood hobby vehicle is provided with three axially separate cylindrical lands that engage with and support the wheel for rotation, and four axially spaced cylindrical grooves that are interspersed among the lands and reduce the friction between the wheel and the axle as well as provide areas for lubrication between the wheel and the axle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention pertains to the design of an axle used to mount a wheel for rotation on the body of a wood hobby vehicle. In particular, the present invention pertains to a metal axle that has three axially separate cylindrical lands that engage with and support the wheel for rotation, and four axially spaced cylindrical grooves that are interspersed among the lands and reduce the friction between the wheel and the axle as well as provide areas for lubrication between the wheel and the axle. 
         [0003]    2. Related Art 
         [0004]    In the construction of wood hobby vehicles, for example the wood hobby vehicles that are raced in the Pinewood Derby® of the Boy Scouts of America®, the wheels of the hobby vehicles, whether they are constructed of wood or an other material, are typically mounted for rotation on the wood body of the vehicle by a small metal nail, brad, a pin, or a wood screw. The nail has the typical construction of a narrow length with a tip and a head at opposite ends of the nail. The nail tip is inserted through a hole in the center of the wheel and then is inserted into the side of the wood vehicle body in mounting the wheel for rotation on the body. 
         [0005]    The friction between the nail axle and the wheel center hole of the hobby vehicle obviously affects the speed of rotation of the wheel and the speed of the hobby vehicle. To reduce the friction and increase the speed of rotation of the wheel on the axle, lubricants such as graphite have been employed between the axle and the wheel. In addition to or as an alternative to lubricating, prior art axles have been provided with polished surfaces to reduce friction. Still further, it is a known practice to file the axles of the hobby vehicle to reduce their diameter and reduce the contact surface between the axle and the wheel center hole, or to form a groove in the axle to reduce the area of contact between the axle and the center hole of the wheel. Although all of these techniques can increase the speed of a hobby vehicle, there is still a competition to find new ways to increase a vehicle&#39;s speed. 
       SUMMARY OF THE INVENTION 
       [0006]    The hobby vehicle axle of the invention is designed to be used in mounting a wheel for rotation on the body of a wood vehicle, for example a vehicle constructed to compete in the Pinewood Derby® of the Boy Scouts of America®, and increase the speed of the vehicle. The length dimensions and the diameter dimensions of the axle are generally the same as those of an axle typically used in constructing a vehicle to compete in the Pinewood Derby®. However, the construction of the axle of the invention is modified from that of the prior art Pinewood Derby® axle to reduce the friction between a wheel mounted for rotation on the axle and thereby increase the speed of a hobby vehicle employing the axle of the invention. 
         [0007]    The axle has a generally cylindrical length with opposite proximal and distal ends, and a center axis. The axle is constructed of the same metal materials employed in the prior art axles, and could also have a polished exterior surface to reduce friction. 
         [0008]    The axle is provided with a pointed tip at the axle proximal end. The tip is employed in driving the axle into the wood vehicle body, as is conventional. Other configurations of the tip, for example a screw thread, could also be employed to drive the tip into the wood vehicle body. 
         [0009]    The opposite distal end of the axle is provided with a head, as is also conventional. In the preferred embodiment an inboard surface of the head tapers as it extends both axially and radially toward the axle distal end. This tapered surface is provided to reduce surface contact between the head of the axle and the wheel of the vehicle, and thereby reduce friction between the axle and wheel. 
         [0010]    The mounting length of the axle that extends between the tip at the proximal end and the head at the distal end is comprised of a shank portion of the axle and a wheel support portion of the axle. The shank portion of the axle is provided to be driven into the wood of the hobby vehicle body in mounting the axle to the vehicle body. This shank portion has a cylindrical exterior surface with a constant exterior diameter. 
         [0011]    The wheel support portion of the vehicle axle has a novel construction designed to reduce friction between the axle and a wheel mounted for rotation on the axle. In the preferred embodiment of the invention, the wheel support portion of the axle is formed with three land sections that each have a cylindrical exterior surface. Each of the cylindrical land sections have a same exterior diameter dimension. In the preferred embodiment of the invention the lands are finished and the exterior diameter dimension of the three cylindrical land sections is slightly smaller than that of the shank portion of the axle. 
         [0012]    A total of four grooves are formed in the exterior surface of the axle. The three land sections of the wheel support portion of the axle are separated axially from each other by two of the four grooves. The two grooves have exterior diameter dimensions that are smaller than the exterior diameter dimensions of the three land sections. A third of the four cylindrical grooves separates the three cylindrical land sections of the axle from the shank portion of the axle, and the fourth groove separates the three cylindrical land sections of the axle from the head portion of the axle. 
         [0013]    With the wheel mounted on the wheel support portion of the axle, the wheel rotates on the cylindrical exterior surfaces of the three land sections of the axle. The grooves formed in the exterior surface of the axle reduce the area of surface contact between the axle and the center hole of the wheel, and thereby reduce the friction between the axle and the wheel. In addition, the cylindrical grooves that axially separate the three cylindrical land sections of the axle and separate the land sections from the shank portion and head portion of the axle provide areas around the axle for lubricant retention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Further features of the hobby vehicle axle of the invention are set forth in the following detailed description and in the drawing figures. 
           [0015]      FIG. 1  is a side view of the axle of the invention. 
           [0016]      FIG. 2  is a representation of the axle of  FIG. 1  mounting a wheel for rotation on a wood hobby vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    As stated earlier, the hobby vehicle axle of the invention  12  is designed to be used in mounting a wheel for rotation on the body of a wood vehicle, for example a vehicle constructed to compete in the Pinewood Derby® of the Boy Scouts of America®, and to increase the speed of the vehicle. Because the axle  12  is designed to replace conventional axles used in constructing vehicles to compete in the Derby, the length dimension of the axle  12  is essentially the same as that of the conventional axle. In addition, the materials employed in constructing the axle  12  of the invention can also be those materials employed in constructing conventional axles. 
         [0018]    A side view of the axle of the invention  12  is shown in  FIG. 1 .  FIG. 2  is a representation of the axle  12  shown mounting a wheel  14  to the wood body  16  of a hobby vehicle. With the axle of the invention  12  being an improvement over the conventional axles used in constructing the wood hobby vehicles, the axle  12  can be used in any conventional method of assembling the wheel  14  to the wood body of the vehicle  16 . 
         [0019]    Referring to  FIG. 1 , the axle  12  has a length with a center axis  18 . The axle length is comprised of a tip portion  22 , a shank portion  24 , a wheel support portion  26 , and a head portion  28 . Each of these portions of the axle  12  are constructed integrally from a single piece of metal or other material typically employed in nails or screws. 
         [0020]    The tip portion  22  shown in  FIG. 1  has an exterior surface with a conical configuration, as is typical in many axles. The smooth conical surface of the tip portion  22  facilitates driving the tip portion into the wood body of a hobby vehicle. In other configurations of the tip portion  22 , the exterior surface could be provided with a screw thread to facilitate driving the tip portion into the wood hobby vehicle body. 
         [0021]    The axle shank portion  24  has a length with opposite proximal  32  and distal  34  ends. The length of the shank portion  24  is coaxial with the tip portion  22 . The shank portion  24  has a cylindrical exterior surface  36 . The exterior surface  36  is unfinished and has a constant diameter dimension for the entire axial length of the shank portion  24  from the proximal end  32  to the distal end  34 . In the illustrative embodiment shown in  FIG. 1 , the exterior diameter dimension of the shank portion exterior surface  36  is 2.23 mm. The combined axial lengths of the shank portion  24  and the tip portion  22  are conventional and are determined to securely hold the axle  12  to the wood body of a hobby vehicle  16  when the tip portion  22  and shank portion  24  are driven into the hobby vehicle body. 
         [0022]    The shank portion distal end  34  is formed with an annular end surface  42 . The annular end surface  42  is positioned in a plane that is perpendicular to the axle center axis  18  and perpendicular to the shank portion exterior surface  36 . In the illustrative embodiment shown in  FIG. 1 , the annular end surface  42  has a radial dimension that extends radially inwardly from the shank portion exterior surface  36  a dimension of 0.53 mm. 
         [0023]    The axle has a first groove defined by a first cylindrical groove surface  44  that extends axially from the shank portion distal end  34  and axially from the interior of the annular end surface  42 . In the illustrative embodiment of  FIG. 1 , the first groove surface  44  has an axial length of 1 mm. With the first groove surface  44  being positioned inside the annular end surface  42 , the first groove surface has a constant diameter dimension of 1.17 mm for the entire axial length of the surface. 
         [0024]    A second annular end surface  46  extends radially outwardly from the first groove surface  44 . The second annular end surface  46  has a slightly smaller radial dimension of 0.050 mm compared to the radial dimension of the first annular end surface  42 . Like the first annular end surface  42 , the second annular end surface  46  is positioned in a plane that is perpendicular to the axle center axis  18 . 
         [0025]    A first cylindrical land  48  having a cylindrical exterior surface extends axially from the second annular end surface  46 . The cylindrical exterior surface of the first land  48  is finished, and therefore the exterior diameter dimension of the first land  48  is slightly smaller than the exterior diameter dimension of the shank portion  24  of the axle. In the illustrative embodiment shown in  FIG. 1 , the exterior diameter dimension of the first land  48  is 2.18 mm. Also, in the illustrative embodiment shown in  FIG. 1 , the axial length of the first land  48  is 1.25 mm. 
         [0026]    A third annular end surface  52  is provided on the axially opposite side of the first land  48  from the second annular end surface  46 . The third annular end surface  52  has the same radial dimensions as the second annular end surface  46 , and is also positioned in a plane that is perpendicular to the axle center axis  18 . 
         [0027]    A second groove defined by a second cylindrical groove surface  54  extends axially from the third annular end surface  52 . The second cylindrical groove surface  54  has the same axial dimension and the same diameter dimension as the first groove surface  44 . 
         [0028]    A fourth annular end surface  56  extends radially outwardly from the second groove surface  54  on the axially opposite side of the second groove surface  54  from the third annular end surface  52 . The fourth annular end surface  56  has the same radial dimensions as the third annular end surface  52  and is positioned in a plane that is perpendicular to the axle center axis  18 . 
         [0029]    A second land having a second cylindrical land surface  58  extends axially from the fourth annular end surface  56 . The second land  58  has the same exterior diameter dimension as the first land surface  48 . However, in the illustrative embodiment of  FIG. 1 , the cylindrical exterior surface of the second land  58  has an axial length dimension of 1.5 mm. 
         [0030]    A fifth annular end surface  62  extends radially inwardly from an opposite side of the second land surface  58  from the fourth annular end surface  56 . The fifth annular end surface  62  has the same radial dimensions as the fourth annular end surface  56  and is positioned in a plane that is perpendicular to the axle axis  18 . 
         [0031]    A third groove in the axle  12  is defined by a third cylindrical groove surface  64  that extends axially from the fifth annular end surface  62 . The third groove surface  64  has the same exterior diameter dimension as the second groove surface  54  and also has the same axial dimension as the second groove surface  54 . 
         [0032]    A sixth annular end surface  66  extends radially outwardly from the third groove surface  64  on an opposite side of the third groove surface  64  from the fifth annular end surface  62 . The sixth annular end surface  66  has the same radial dimension as the fifth annular end surface  62  and it is positioned in a plane that is perpendicular to the axle center axis  18 . 
         [0033]    A third land is defined by a third cylindrical land surface  68  that extends axially from the sixth annular end surface  66 . The third land surface  68  has the same exterior diameter dimension as the second land surface  58  and also has the same axial length dimension as the second land surface  58 . 
         [0034]    A seventh annular end surface  72  extends radially inwardly from the third land surface  68  on an opposite side of the third land surface  68  from the sixth annular end surface  66 . The seventh annular end surface  72  has the same radial dimensions as the sixth annular end surface  66  and is positioned in a plane that is perpendicular to the axle center axis  18 . 
         [0035]    A fourth groove in the axle  12  is defined by a fourth cylindrical groove surface  74  that extends axially from the seventh annular end surface  72 . The fourth groove surface  74  has the same exterior diameter dimension as the third groove surface  64  and also has the same axial dimension as the third groove surface  64 . 
         [0036]    The axle head portion  28  extends both radially and axially from the fourth groove surface  74  on an opposite side of the fourth groove surface from the seventh annular end surface  72 . The axle head portion has an inboard surface  76  that faces toward the axle wheel support portion  26 . As seen in the illustrative embodiment of  FIG. 1 , the head portion inboard surface  76  simultaneously extends both axially and radially away from the fourth groove surface  74 . In the illustrative embodiment of  FIG. 1 , the inboard surface  76  forms an angle of substantially 30 degrees relative to a plane positioned perpendicular to the axle center axis  18 . The inboard surface  76  extends radially outwardly to a maximum exterior diameter dimension of the head portion  28  that is conventionally determined to be larger than the hole through the wheel  14  of a Derby vehicle. 
         [0037]    The axle head portion  28  also has an outboard surface  78  as shown in  FIG. 1 . In the embodiment of the axle  12  shown in  FIG. 1 , the head portion outboard surface  78  has a generally convex configuration. In alternate embodiments of the axle  12 , the outboard surface  78  could have another configuration, and could also be substantially flat. 
         [0038]      FIG. 2  gives an illustrative example of the axle  12  mounting a wheel  14  to the body of a hobby vehicle  16 . As shown in  FIG. 2 , the axle  12  is mounted on the vehicle body  16  by driving the tip portion  22  and the shank portion  24  into the wood body. Thus, the first annular end surface  42  of the axle is positioned substantially parallel to a side surface of the vehicle body  16 . The wheel  14  is mounted on the axle  12  so that the interior surface of the wheel center hole  82  is supported in sliding engagement against the exterior surfaces of the first land surface  48 , the second land surface  58 , and the third land surface  68 . Due to the presence of the first groove surface  44 , the second groove surface  54 , the third groove surface  64 , and the fourth groove surface  74 , the total area of friction contact between the axle  12  and the wheel  14  and the friction force associated with that contact is reduced. In this way, the axle  12  of the invention mounts a wheel  14  for rotation while substantially reducing the friction between the wheel  14  and axle  12  from that present in prior art axles. In addition, the presence of the multiple grooves between the center hole of the wheel  14  and the groove surfaces  44 ,  54 ,  64 ,  74  of the axle  12  allows for the retention of a lubricant in the grooves that will further reduce the friction between the wheel  14  and the axle  12  of the invention. 
         [0039]    In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. 
         [0040]    As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.