Abstract:
A motorcycle frame including a base portion and a removable portion that both bear operating loads of the motorcycle. The removable portion and base portion are fastened together at a joint comprising a first end cap having a protrusion, a second end cap having a recess, and a fastener having a fastener axis and extending through the first and second end caps. The protrusion and the recess are characterized by angled walls oriented at an acute angle with respect to the fastener axis. The angled wall engagement of the end caps ensures that substantially all shear loads in the joint are born by the end caps and not by the fastener. The motorcycle footpeg position can be changed by replacing the removable portion with a second removable portion having footpeg mounting structure at a different location than the removable portion.

Description:
FIELD OF THE INVENTION 
   The invention relates to motorcycle frames, and more particularly to motorcycle frames having a removable portion. 
   BACKGROUND 
   Virtually all motorcycles utilize some type of frame structure to carry loads encountered during vehicle operation. One type of frame structure known as a twin-spar frame typically uses a pair of large cross section aluminum beams that extend from the motorcycle steering head and around the sides of the engine to the swingarm pivot. As such, the engine is at least partially surrounded by frame structure on its right and left sides. Another type of frame structure is known as a cradle frame. The cradle frame generally includes one or more structural members extending over the top of the engine, and one or more structural members extending below the engine. Both types of frames support a wide variety of motorcycle components including the engine, fuel tank, seat, and footpegs, as well as other items. 
   Most motorcycle frames, whether twin-spar or cradle style, are fabricated (e.g. cast and/or welded) as one-piece assemblies. Several limitations arise when a motorcycle frame is fabricated as a single piece. While the unitary construction is generally very strong, installation and removal of the engine are often difficult, especially when it is aesthetically desirable to package the engine as tightly within the frame as possible. Furthermore, alterations to the frame, such as relocation of the footpegs or other items that mount to the frame, can be difficult and time consuming. For a consumer, such alterations generally require cutting, grinding, and welding of the frame, all of which may weaken the frame as well as detract from its appearance. For a manufacturer that may want to develop an entire vehicle line using a single style of frame, such minor alterations often require expensive new tooling and/or fabrication equipment. 
   Therefore, a new motorcycle frame that facilitates installation and removal of the engine and simplifies the process of relocating certain motorcycle components, while simultaneously fulfilling the structural requirements of a motorcycle frame would be welcomed by those in the art. 
   SUMMARY 
   The invention provides a method for relocating the position of a footpeg on a motorcycle frame having a base portion and a first removable portion removably mounted to the base portion at a joint. The first removable portion has footpeg mounting structure affixed thereto at a first footpeg position. The method includes providing a second removable portion that is removably mountable to the base portion at the joint and includes footpeg mounting structure at a second footpeg position different from the first footpeg position. The position of the footpeg may therefore be changed by removing the first removable portion from the base portion, and replacing it with the second removable portion. The original footpeg, or a new footpeg if desired, may then be mounted to the footpeg mounting structure of the second removable portion in the second footpeg position. 
   The invention also provides a joint for fastening the removable portion to the base portion. The joint includes male and female profile end caps mounted to the removable portion and to the base portion. The male and female profiles snugly engage each other, and a fastener is extended through the joint along a fastener axis. The male and female profiles include walls that are oriented at an acute angle with respect to the fastener axis. The snug engagement of the male and female end caps and the angled engagement of the walls in the joint cause the walls to bear a substantial majority of the shear stress in the joint, and substantially reduce the shear stress on the fastener. 
   Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a motorcycle embodying the invention. 
       FIG. 2  is a perspective view of the frame of the motorcycle. 
       FIG. 3  is an exploded view of the frame. 
       FIG. 4  is a cross-section view taken along line  4 — 4  in FIG.  1 . 
       FIG. 5  is an enlarged exploded view of the portion of the frame encircled in FIG.  3 . 
       FIG. 6  is a cross-section view taken along line  6 — 6  in FIG.  2 . 
       FIG. 7  is a cross-section view taken along line  7 — 7  in FIG.  2 . 
       FIG. 8  is a perspective view of the frame with a second removable portion substituted for the removable portion illustrated in FIG.  2 . 
   

   Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. 
   DETAILED DESCRIPTION 
     FIG. 1  illustrates a motorcycle  10  comprising a cradle-style frame  14 , an engine and drive train assembly  18  isolatingly mounted to the frame  14  by resilient mount assemblies  19 ,  20 , front and rear wheels  22 ,  26  supporting the frame  14 , a steering assembly  30  including handlebars  34  and a fork  38  mounted to the front wheel  22  and pivotal with respect to the frame  14 , and a swing arm  40  (partially hidden) interconnecting the rear wheel  26  to the frame  14 . Although the invention is illustrated and described with respect to a cradle-style frame, the teachings are also applicable to twin-spar frames as well as other frame types. 
   As seen in  FIGS. 2 and 3 , the frame  14  includes a base portion  42 , two removable portions  46  mounted to the base portion  42  at joints  48 , and a cross-brace  50  between the removable portions  46 . The removable portions  46  are substantial mirror images of each other, except as pointed out below. Therefore, only one of the removable portions  46  will be described. Referring to  FIG. 3 , each removable portion  46  includes opposite mating ends  54  having central axes  56 , and the base portion  46  includes free ends  58 . Both the base portion  42  and the removable portion  46  include mounting points to which the engine and power train assembly  18  is mounted. The illustrated frame  14  is configured to isolatingly support the motorcycle engine  18 . The resilient mount assemblies  19 ,  20  mount to mounting portions  59  of the base portion  42  and resiliently secure the engine  18  within the frame  14  as described further below. A tie link  60  substantially prevents lateral movement of the engine  18  with respect to the frame  14  while allowing limited fore-aft and up-down movement of the engine  18  within the frame  14 . The tie link  60  is pivotally intercoupled between the engine  18  and a mounting tab  61  on one of the removable portions  46 . As illustrated, the mounting tab  61  is provided on the left removable portion  46 , however the mounting tab  61  could be provided on the right removable portion  46 , if desired. 
   Referring to  FIG. 2 , the front mount assembly  19  includes a frame mounting bracket  62 , a front mount  63  and an engine mounting bracket  64 . The frame mounting bracket  62  is secured to the front mounting portion  59  and the front mount  63  is secured to the frame mounting bracket  62 . The engine mounting bracket  64  is secured to the front mount  63  and is secured to a front cylinder head  68  (see  FIG. 1 ) of the engine  18 . The front mount  63  is made of a resilient material (e.g. rubber) such that the engine and power train assembly  18  and the frame  14  are movable with respect to each other. 
   Referring to  FIG. 4 , the rear resilient mount assembly  20  includes a pair of substantially cylindrical rear mounts  69  that are made of a resilient material (e.g. rubber) and include flange portions  70  received by the rear mounting portions  59 . The swingarm  40  includes first and second pivot ends  71 ,  72  and the engine and drive train assembly  18  includes a pivot boss  73 . A pivot shaft  76  extends through the first pivot end  71 , the rear mounts  69 , the pivot boss  73 , and the second pivot end  72 . The pivot shaft  76  pivotally couples the engine  18  to the swingarm  40 . Also, the pivot shaft  76  engages the rear mounts  69  such that the pivot shaft  76 , and thus the engine and drive train assembly  18  and the swingarm  40  are resiliently coupled to the frame  14 . Clearance is provided between the pivot shaft  76  and the rear mounting portions  59  to allow the pivot shaft  76 , the engine and drive train assembly  18 , and the swingarm  40  to move with respect to the frame  14 . 
   Because the engine  18  is isolatingly supported within the frame  14 , the frame  14  is preferably significantly stronger and stiffer than a frame having an engine and transmission assembly rigidly mounted thereto. The reason for this is that stresses applied to the frame  14  due to, for example, bumps in the road, acceleration and braking maneuvers, as well as other vehicle handling maneuvers, are carried almost exclusively by the frame  14 . In contrast, when an engine and transmission assembly is rigidly mounted to a frame, the engine and transmission assembly bears a greater portion of the operating loads, which effectively stiffens the frame. 
   Vehicle torsional loads (e.g. such as those generated during cornering maneuvers) are generally transmitted from the rear wheel  26  through the swingarm  40  to the pivot shaft  76 . Due to the configuration of the frame  14 , the engine and transmission assembly  18 , and the mount assemblies  19 ,  20 , the pivot shaft  76  transmits the torsional loads to the engine and transmission assembly  18  and subsequently to the tie link  60 , thereby subjecting the tie link  60  to tensile and compressive loads. Because the tie link  60  is pivotally coupled to the removable portion  46  as well as the engine and transmission assembly  18 , the tie link generally only transmits the vehicle torsional loads to the removable portion  46  in an axial manner. In this respect, the loads transmitted by the tie link, to the removable portion  46  via the mounting tab  61  are substantially single-axis loads (e.g. substantially no bending loads are transmitted by the tie link). Thus the removable portion is subjected to stresses transmitted by the frame  14  as well as by the engine and transmission assembly  18 . Although the illustrated embodiment of the invention is configured for use with a motorcycle having a resiliently supported engine, the teachings of the present invention are also applicable to motorcycles having engines that are rigidly mounted to the frame. 
   With reference to  FIG. 5 , both the removable portion  46  and base portion  42  include tubular bodies  78  having open ends. The mating end  54  of the removable portion  46  and the free end  58  of the base portion  42  include female and male end caps  79 ,  80 , respectively, that have chamfered or reduced diameter ends  81 . The reduced diameter ends  81  are inserted into and welded to the open ends of the respective tubular bodies  78 . 
   The female end cap  79  includes a recessed socket  82  having bolt holes  84 . The socket  82  is characterized by slanted or angled walls  86  that cause the socket  82  to narrow from its top to its bottom. The male end cap  80  includes a protrusion  90  having bolt holes  94 . The protrusion  90  is characterized by slanted or angled walls  98  that cause the protrusion  90  to narrow from its bottom to its top. The angled walls  86 ,  98  extend in a direction that is substantially parallel to the central axis  56  of the respective mating end  54 . It should be noted that the female and male end caps  79 ,  80  may be switched so that the male end cap  80  is welded to the removable portion  46  and the female end cap  79  is welded to the base portion  42 . Also, although the mating surfaces of the illustrated walls  86 ,  98  are substantially planar, the mating surfaces could alternatively be curved. 
   As seen in  FIGS. 5 and 6 , the socket  82  snugly receives the protrusion  90  such that the angled walls  86 ,  98  are in intimate contact with each other and the bolt holes  84 ,  94  are aligned with each other. Fasteners, such as the illustrated bolts  102 , extend through the bolt holes  84 ,  94  and are secured with nuts  108  to fasten the mating ends  54  of the removable portion  46  to the free ends  58  of the base portion  42 . Alternatively, one of the bolt holes  84 ,  94  may be threaded such that the bolts  102  threadedly engage one of the end caps  79 ,  80  directly. 
   The bolts  102  each define a fastener axis  112  (FIG.  7 ), and the angled walls  86 ,  98  are angled α (about 45° in the illustrated construction) with respect to the fastener axis  112 . Due to the angle α of the wall engagement, and the snug engagement between the socket  82  and the protrusion  90 , the walls  86 ,  98  bear substantially all shear stress (e.g., from bumps and/or handling maneuvers as discussed above) transmitted through the joint  48  such that the fasteners  102  are exposed to substantially no shear stress. 
   With reference to  FIGS. 2 and 3 , a footpeg mounting structure is affixed to the removable portion  46 . The footpeg mounting structure includes a cylindrical boss  116  that is welded to the removable portion  46 . The cylindrical boss  116  includes a longitudinal bore  120  and a cross-bore  124  extending perpendicular to the longitudinal bore  120 . A foot pedal  128  that may actuate, among other things the brake, clutch, or transmission, of the vehicle includes a pedal bore  132  that is aligned with the longitudinal bore  120  of the cylindrical boss  116 , and a clevis pin  136  extends through the pedal bore  132  and into the longitudinal bore  120 . A cross pin  140  extends through the cross-bore  124  to anchor the clevis pin  136  within the cylindrical boss  116 , and to mount the pedal  128  to the cylindrical boss  116 . A footpeg  144  is pivotally mounted to the clevis pin  136  by positioning a tongue portion  148  of the footpeg  144  in the forked end of the clevis pin  136 , and extending a footpeg pin  152  through the forked end and tongue portion  148 . 
     FIG. 8  illustrates the frame  14  with alternative removable portions  160  substituted for the above-described removable portions  46 . The alternative removable portions  160  are substantially identical to the above-described removable portions  46 , except that they have cylindrical bosses  164  welded at locations different from the locations on the above-described removable portions  46 . The position of the motorcycle footpegs  144  may therefore be changed by removing the above-described removable portions  46  of the frame  14  and replacing them with the alternative removable portions  160  of the frame  14 . The original pedals  128  and footpegs  144  may then be mounted to the cylindrical bosses  164  of the alternative removable portion  160  or new pedals and footpegs may be provided. 
   Various features of the invention are set forth in the following claims.