Patent Publication Number: US-2007119645-A1

Title: Motorcycle Drive Shaft Offset Assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/740,917 filed Nov. 30, 2005. 
    
    
     FIELD OF THE INVENTION  
      The invention relates to power transmission assemblies in motorcycles and more specifically to a power transmission shaft for transmitting rotational torque to a rear wheel of a vehicle.  
     BACKGROUND OF THE INVENTION  
      Motorcycles and two-wheeled vehicles are typically equipped with standard equally sized front and rear wheels. It is however, a popular pastime among motorcycle enthusiasts to alter their motorcycles with customizations, such as paint and/or structural modifications. A popular custom feature is the installation of an oversized rear wheel. One such custom modification is to provide an oversized rear wheel having a width which is wider than the original equipment manufacturer wheel. Installation of an oversized tire adds to the aesthetic appearance of the motorcycle.  
      However, installation of an oversized rear wheel presents a number of challenges, most particularly, in routing power from the transmission to the oversized rear wheel. There are two principle drive designs in use in motorcycles: (1) belt or chain drives found on many Harley-Davidson® motorcycles, and (2) shaft drive assemblies found on motorcycles such as the Honda® Aero 750 and the BMW® K11200S. Several designs have been presented for routing power to a rear wheel in belt or chain drive motorcycles retrofitted with an oversized rear wheel, such as those disclosed in U.S. Pat. Nos. 6,755,272 and 6,575,260.  
      However, with shaft-driven designs, the problem of transferring torque to a wider rear wheel becomes exceptionally difficult as the oversized rear wheel will block the path of the drive shaft to the rear drive coupling. Therefore, the previously known systems for accommodating and oversized rear wheel cannot be used in a shaft drive assembly.  
     SUMMARY OF THE INVENTION  
      What is desired therefore is a system and method for transmitting driving torque to the rear wheel of a shaft drive motorcycle, where the rear wheel is provided as an oversized wheel.  
      It is further desired to provide a system and method for retrofitting a motorcycle with an oversized rear wheel that accommodates the drive shaft assembly of the motorcycle.  
      It is still further desired to provide a system and method that provides a reliable, simply design for repositioning the drive shaft of a motorcycle to a position outboard of an oversized rear wheel.  
      These and other objects are achieved in one advantageous embodiment by the provision of an intermediate offset power transmission assembly and rear drive shaft.  
      The drive shaft of a standard motorcycle typically extends rearward toward an outboard position adjacent to the rear wheel of the motorcycle. The drive shaft is designed to engage with a wheel having a particular width, typically the same width as the front wheel. However, when an oversized wheel (a wheel having an increased width) is used, the drive shaft provided from the factory extends into the oversized wheel.  
      The present invention provides a front drive shaft coupled to one end of an intermediate offset power transmission assembly which is in turn coupled to a rear drive shaft which transmits output torque to the oversized rear wheel. The intermediate offset power transmission assembly transmits rotational torque input from the front drive shaft to the rear drive shaft, which is longitudinally offset from the front drive shaft. The intermediate offset power transmission assembly is provided to longitudinally offset a portion of the drive shaft to a position that is outboard of the oversized rear wheel. The axis of the front drove shaft is offset from the axis of the rear drive shaft so that the two shafts may be considered axially offset relative to each other. The intermediate offset power transmission assembly may comprise torque transmission devices including, for example, chain and sprocket drives, belt drives, a gear set, or even a hydraulic drive system. The front drive shaft, intermediate offset power transmission assembly, and rear drive shaft are built into the swingarm of the motorcycle rear wheel and serve as the left side of the swingarm.  
      Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of one advantageous embodiment of the present invention.  
       FIG. 2  is a block diagram of the intermediate offset power transmission assembly according to  FIG. 1 .  
       FIG. 3  is an illustration of an advantageous embodiment of the present invention according to  FIG. 1 .  
       FIG. 4  is an exploded view of the advantageous embodiment according to  FIG. 3 .  
       FIG. 5  is a top view of the advantageous embodiment according to  FIG. 3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views.  
      The present assembly allows for retrofitting of a wider rear wheel onto an existing motorcycle frame. The retrofitting process includes replacing the existing swingarm with the swingarm  121 . While a particular sized rear wheel is illustrated, many different sized wheels may effectively be used with the assembly. The wider oversized rear wheel  112 , the longer elongated housing  118  must be to position rear drive shaft  106  outboard of the wheel. It is contemplated that a number of standard sized housing may be made to coincide with standard wheel widths.  
       FIG. 1  is a block diagram depicting power transmission assembly  100 . Power transmission assembly  100  generally comprises, front drive shaft  102 , intermediate offset power transmission assembly  104  and rear drive shaft  106 . As shown in  FIG. 1 , front drive shaft  102  is located after the motorcycle engine torque output and the transmission output  108  and extends to the intermediate offset power transmission assembly  104 . Front drive shaft  102  is provided to transmit rotational torque from the motorcycle engine/transmission assembly to the intermediate offset power transmission assembly  104 . Rear drive shaft  106  receives rotational torque from intermediate offset power transmission assembly  104  and transmits the torque to oversized rear wheel  112 . Rear drive shaft  106  extends from the intermediate offset power transmission assembly  104  to a rear drive mechanism  110 . Rear drive mechanism  110  is typically a ring gear or bevel gear mechanism transferring power from the rear drive shaft  106  to oversized rear wheel  112 .  
      Turning now to  FIG. 2 , intermediate offset power transmission assembly  104  is shown in greater detail. Intermediate offset power transmission assembly  104  couples rotational torque from front drive shaft  102  to rear drive shaft  106 . The intermediate offset power transmission assembly  104  allows the drive shaft extending from the motorcycle engine to be axially offset to an outboard position relative to oversized rear wheel  112 . In this manner, a standard OEM rear wheel, which is much thinner and substantially aligns with the longitudinal axis of front drive shaft  102 , may be replaced with an oversized wheel. Intermediate offset power transmission assembly  104  is provided to transmit rotational torque to longitudinally offset shaft members. Intermediate offset power transmission assembly  104  may comprise a number of differing power transfer mechanisms including for example offset sprockets connected by an endless chain loop, or pulley members connected by an endless belt loop, or cogged pulleys connected by a cogged belt, or a gear set, or a hydraulic power transmission assembly using vaned turbines mounted on the front and rear drive shafts. Most preferably the power transfer mechanism contains two parallel power transfer mechanisms, for example, two sets of sprocket/chain combinations or two sets of pulley/belt combinations.  
       FIG. 2  further contains an interface  114  for interfacing front drive shaft  102  with intermediate offset power transmission assembly  104 . Additionally, interface  116  provides an interface between intermediate offset power transmission assembly  104  and rear drive shaft  106 . It is contemplated that interface  114 ,  116  may comprise one or more parts, including for example, bushings, washers, nuts, spacers, connectors, and the like for coupling the drive shafts to the intermediate offset power transmission assembly  104 .  
      Referring now to  FIGS. 3-5 , a perspective exterior view of power transmission assembly  100  is shown in  FIG. 3 , while a top view is shown in  FIG. 5 . Power transmission assembly  100  is integrated in the swingarm  121  having a pivot tube  138 , which couples to the motorcycle frame (not shown) and allows the assembly to pivot with respect to the motorcycle frame. The pivoting swing arm  121  hold the axle of the rear wheel but pivots vertically to allow the suspension to absorb bumps in the road. The right arm  134  of swingarm  121  extends outboard of oversized rear wheel  112  on the side opposite to the drive shaft side, as seen in  FIGS. 4 and 5 . Oversized rear wheel  112  is driven by the drive shaft extending along the left arm  135  on the left side of the swingarm  121 . While the drive shaft is illustrated on the left side of oversized rear wheel  112 , it is contemplated that the drive shaft may also be positioned on the right side of oversized rear wheel  112  in some applications. The right arm  134  has a substantial offset to accommodate the oversized rear wheel  112 , however, other different configurations and shapes may effectively be used. As can further be seen in  FIGS. 3-5 , swingarm  121  includes the front shaft cover  120  and a support member  136 , which provides a robust coupling for the left and right sides of the swingarm  121 .  
      Front drive shaft  102  is coupled to the motorcycle engine by way of a motorcycle transmission. As best seen in  FIG. 4 , front drive shaft  102  is contained in front shaft cover  120 . Front shaft cover  120  is welded or otherwise affixed to front wall  124  of an elongated housing  118  in which intermediate offset power transmission assembly  104  is located. An opening  126  is located in the front wall  124  and front drive shaft  102  extends into elongated housing  118 . Elongated housing  118  extends perpendicularly to front shaft cover  120  and rear shaft cover  122 . Bearing  113  and circlip  115  center the front drive shaft  102  in the opening  126 . Sprocket  114  is located at the rear end of the front drive shaft  102  and is positioned within the elongated housing  118 . A rear cover  128  for elongated housing  118  is detachably affixed to housing  118  by means of screws  132  or other attachment devices. Rear cover  118  has an opening  130  and the front end of rear drive shaft  106  extends through the opening. Bearing  117  and circlip  119  center the rear drive shaft  106  in the opening  130 . Sprocket  116  is located at the front end of the rear drive shaft  106  and is positioned within the elongated housing  118 . Sprockets  114  and  116  are connected by a loop of chain so that power received by the front drive shaft  102  is transferred to the rear drive shaft  106 . Rear drive shaft  106  is contained in rear shaft cover  122 . Rear shaft cover  122  is has a flange  140 , which is provided to interface with a rear drive mechanism  110  (shown schematically in  FIG. 1 ). The rear drive mechanism  110  is a driven flange assembly such as the mechanism disclosed in U.S. Pat. No. 6,516,912, the disclosure of which is incorporated by reference. The gear end  107  at the rear of rear drive shaft  106  transfers power to the rear drive mechanism  110  to drive the oversized rear tire via a driven flange.  
      It should be noted that, while various functions and methods have been described and presented in a sequence of steps, the sequence has been provided merely as an illustration of one advantageous embodiment, and that it is not necessary to perform these functions in the specific order illustrated. It is further contemplated that any of these steps may be moved and/or combined relative to any of the other steps. In addition, it is still further contemplated that it may be advantageous, depending upon the application, to utilize all or any portion of the functions described herein. Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.