Abstract:
A system and method for a motorcycle to automatically variably adjust the wheelbase length including a rear swing arm having a length and a rear wheel attached thereto, a prime mover that generates a motive force for selectably extending or retracting the length of the swing arm to extend or retract the rear wheel, and means for lengthening or retracting a motorcycle driveline providing power to the rear wheels.

Description:
[0001]    The present application claims priority to U.S. Provisional Application Ser. No. 61/289,873 filed Dec. 23, 2009, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to vehicles having a variable length wheelbase and in a particular embodiment to a motorcycle having a variable length wheelbase. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vehicle wheelbase has a large effect on the stability, ride comfort, turning responsiveness and turning radius of a vehicle. Wheelbase is the horizontal distance between the centers (or the ground contact points) of the front and rear wheels of a vehicle. In a motorcycle, wheelbase cannot vary during operation of the motorcycle and is a function of rear frame length, steering axis angle (caster), and fork offset. Different types of motorcycles have different dynamics and these play a role in how a motorcycle performs in given conditions. For example, a longer wheelbase provides more stability in a straight line and a smoother ride at the sacrifice of turning radius and responsiveness. A shorter wheelbase in turn provides greater steering responsiveness and a shorter turning radius at the sacrifice of stability and smoothness. 
         [0004]    As discussed above, wheelbase has a major influence on the longitudinal stability of a bike, along with the height of the center of mass of the combined bike and rider. Short wheelbase motorcycles, such as sport bikes, can easily generate enough torque at the rear wheel, and enough stopping force at the front wheel, to lift the opposite wheel off the pavement. These actions, if performed on purpose, are known as wheelies and stoppies, respectively. If carried past the point of recovery, the resulting upset is known as an “endo” (short for “end-over-end”), which can injure or kill the rider. Stoppies and wheelies can be particularly tricky for motorcycle riders to intentionally perform without resulting in an endo because as the wheelie or stoppie is performed, the effective wheelbase of the motorcycle and reduced and, therefore, the amount of braking or accelerating force needs to be reduced or the driver will be thrown from the vehicle. 
         [0005]    Because any particular wheelbase for a vehicle is inherently a comprise between responsiveness and stability, a vehicle with an adjustable wheelbase will allow the greatest flexibility for the use of that vehicle. However, because most performance vehicles have an engine attached to a frame and a driveline providing torque from that frame to the rear wheel, the driveline must be able to accommodate a change in driveline length associated with the change in wheelbase. As such, no suitable systems for varying the wheelbase of a vehicle have been developed. Therefore, there is a need in the art for a vehicle having a variable wheelbase. 
       SUMMARY OF THE INVENTION 
       [0006]    A system and method for a motorcycle to automatically variably adjust the wheelbase length including a rear swing arm having a length and a rear wheel attached thereto, a prime mover that generates a motive force for selectably extending or retracting the length of the swing arm to extend or retract the rear wheel, and means for lengthening or retracting a motorcycle driveline providing power to the rear wheels. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a side view of a motorcycle according to an embodiment of the present invention; 
           [0008]      FIG. 2  is a left side view of a motorcycle swing arm according to an embodiment of the present invention; 
           [0009]      FIG. 3  is a right side view of a motorcycle swing arm according to an embodiment of the present invention; 
           [0010]      FIG. 4  is a top view of a motorcycle swing arm according to an embodiment of the present invention; 
           [0011]      FIG. 5  is a perspective view of a bridge support according to an embodiment of the present invention; 
           [0012]      FIG. 6  is an enlarged side view of an idler and slider gear arrangement according to an embodiment of the present invention; 
           [0013]      FIG. 7  is a side view of the slip joint drive shaft according to an embodiment of the present invention; and 
           [0014]      FIG. 8  is a left side view of a motorcycle swing arm according to an alternate embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
         [0016]    A preferred embodiment of the present invention is a motorcycle having a wheelbase selectively adjustable via a remote control for lengthening and shortening the driveline to accommodate the lengthened or shortened wheelbase. Referring to the Figures generally and to  FIG. 1  specifically, there is provided a motorcycle having a swing arm  10 , a rear wheel  12  attached to the swing arm  10  and a drive chain  14 . The swing arm  10  is pivotally attached to a motorcycle frame  16 . 
         [0017]    Referring to  FIGS. 2-4 , the swing arm  10  comprises a swing arm frame  18  which attaches to the motorcycle frame  16  ( FIG. 1 ). The swing arm frame  18  comprises two swing arm bars  19  that extend from the motorcycle frame  16  toward a rear of the motorcycle and each swing arm bar  19  terminates at a respective bridge support  20 . Referring to  FIG. 5 , the bridge support  20  comprises two upwardly extending guard plates  22  attached to a vehicle support plate  24  that defines a horizontal surface. Attached to the vehicle support plate  24  is a wheel flange  26  for attachment to a rear wheel support assembly  28  through which a rear wheel axle is mounted. 
         [0018]    As shown in  FIGS. 2-4 , the termination of the swing arm bars  19  are located between the guard plates  22  of the bridge support  20  and rest upon the vehicle support plate  24 . Also, attached to the motorcycle frame  16  are a pair of hydraulic rams  30 . The rams  30  are attached to the motorcycle frame  16  at a pivot point  32  and also at a second point  33  to a lower swing arm bar  34 . The ram  30  comprises an extension rod  36  that is attached to the wheel flange  26  or rear wheel support assembly  28 . 
         [0019]    In this manner, by extending or retracting the extension rods  36  from the hydraulic rams  30 , the rear wheel support assembly  28  can be moved rearwardly and forwardly by mere operation of the hydraulic ram  30 . The bridge support  20  allows sliding movement between the swing arm bar  19  and the vehicle support plate  24 , but the vehicle support plate  24  continues to act to support the weight of the vehicle. 
         [0020]    While the use of hydraulic rams is shown and described, after viewing the present disclosure, one of ordinary skill in the art would recognize that various devices for extending the rear wheel support assembly can be implemented in place of hydraulic rams, including for example, the use of stepper motors  202  and helically threaded rod  204  ( FIG. 8 ). The stepper motors would precisely rotate to extend or retract the threaded rod to extend or retract the wheel support assembly  28 . 
         [0021]    In order to accommodate the resulting increase or decrease in length of the driveline, the preferred embodiment of the invention comprises a driveline adjustment system. In the embodiment described, an idler gear  40  and a slider gear  42  ( FIG. 3 ) are implemented to accommodate the additional length of drive chain  14  necessary for extension of wheel support assembly  28  as the wheelbase is adjusted. The idler gear  40  is attached to the lower swing arm bar  34 . The slider gear  42  is located within a slotted lower bracket  44  attached to the lower swing arm bar  34 . The slider gear  42  is moveable within the slot  46  of the lower bracket  44 . The slider gear  42  is attached to a threaded slider gear linkage rod  48  that is in turn attached the rear wheel support assembly  28  in the preferred embodiment by means of a bracket  50 . The slider gear linkage rod  48  and the lower bracket  44  each include flat surfaces  52  and  54  that oppose one another to provide additional support for the slider gear  42 . The threaded slider gear linkage rod  48  may be threaded in and out to change the relative distance of the idler gear  40  and the slider gear  42  to accommodate manufacturing tolerances for the length of the chain  14  and to accommodate chain stretch and the chain ages. 
         [0022]    When the hydraulic ram  30  is operated to extend or retract the wheelbase of the vehicle as described above, the relative distance between the idler gear  40  and the slider gear  42  is likewise changed because the position of the idler gear  42  remains fixed with respect to the lower swing arm bar  34  and the slider gear  40  extends with respect to the ram  30  with the extension of the extension rod  36 . The ram  30  is extended or retracted through the operation of a remote control switch, preferably mounted on the handlebars of the motorcycle. The resulting difference in distance between the idler gear  40  and the slider gear  42  provides additional chain length between the motorcycle transmission (not shown) and the rear wheel  12  when the wheelbase is lengthened. Likewise, a decrease in wheelbase by the hydraulic ram  30  causes the distance between the idler gear  40  and the slider gear  42  to increase, thereby taking up slack chain created by the shortening of the vehicle wheelbase. Moreover, the arrangement of the gears  40  and  42  having fixed positions with respect to one another in any position of the rear wheel  12  (rather than being in a spring loaded arrangement as with derailers on bicycles) allows the idler gear  40  and the slider gear  42  to accept the negative torque that occurs upon deceleration of the vehicle, also known as engine braking. 
         [0023]    Finally, one of ordinary skill in the art upon viewing this disclosure would understand that for a shaft driven vehicle, as opposed to a chain driven vehicle, a slip joint drive shaft  100  may be used to provide a drivetrain that will accommodate a change in vehicle wheelbase ( FIG. 7 ). 
         [0024]    Further other systems of the vehicle may also require modification to accommodate a changing wheelbase, including rear wheel brake connections (hydraulic or mechanical) that can accommodate changing wheelbase and also exhaust systems including flexible mounts or flexible sections of pipe to accommodate wheelbase length changes. 
         [0025]    The above examples show that the invention, as defined by the claims, has far ranging application and should not be limited merely to the embodiments shown and described in detail. Instead the invention should be limited only to the explicit words of the claims, and the claims should not be arbitrarily limited to embodiments shown in the specification. The scope of protection is only limited by the scope of the accompanying claims, and the Examiner should examine the claims on that basis.