Patent Publication Number: US-2005139407-A1

Title: Motorcycle with coaxial swingarm pivot and drive sprocket

Description:
RELATED APPLICATIONS  
      This application is a continuation-in-part of U.S. patent application Ser. No. 10/633,296 entitled “Vehicle with Separate Gearbox Clutch and Back-Torque-Limiting Slipper Clutch” filed Jul. 31, 2003 by Michael Czysz, and a continuation-in-part of U.S. patent application Ser. No. 11/001,164 entitled “Motorcycle Rear Suspension with Linear Spring Rate and Linkage Controlled Shock Rate” filed Dec. 1, 2004 by Michael Czysz, and a continuation-in-part of U.S. patent application Ser. No. 10/704,929 entitled “Motorcycle with Dual Drive Chains” filed Nov. 10, 2003 by Joshua S. Bryan, all of which are commonly assigned with the present application. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Technical Field of the Invention  
      This invention relates generally to motorcycle rear suspension, and more specifically to swingarm pivot location.  
      2. Background Art  
      Motorcycles are most commonly chain driven. The rear wheel has a large sprocket of approximately 48 teeth, and the engine&#39;s output shaft has a small sprocket of approximately 16 teeth. The front sprocket is coupled to an output shaft or sprocket shaft of the engine&#39;s transmission or gearbox. Some motorcycles use belts rather than chains, but in a similar geometric arrangement.  
      Motorcycles typically include a rear swingarm which has a rear end coupled to the rear wheel, and a front end coupled to the frame or to the engine at a pivot point. The location of the swingarm pivot is a key factor in the overall performance and characteristics of the motorcycle&#39;s rear suspension.  
      Most commonly, the swingarm pivot is located to the rear of the sprocket shaft, such that the swingarm pivot lies within the perimeter of the chain. One undesirable side-effect of this geometry is that, as swingarm rises and falls, rotating up and down around its swingarm pivot, the chain tension changes significantly. In many applications, the tension changes so much that a separate chain tensioner mechanism is required, to prevent the chain from jumping sprocket teeth when the chain tension is at its loosest. The different locations of the sprocket shaft and the swingarm pivot have other effects, as well, such as contributing to “squat” or “rise” of the rear end under acceleration.  
       FIG. 6  is a photograph of a 2005 Yamaha R1 sportbike with its bodywork removed. The sprocket shaft is approximately at location  102 ; it is hidden by the sprocket cover which protects the rider from the sprocket and chain. The swingarm pivots in the frame at location  104 .  
       FIG. 7  is a photograph of a 2005 Yamaha YZF450F dirtbike. The sprocket shaft is at location  106 , and the swingarm pivots at location  108 .  
       FIG. 8  is a photograph from Tony Foale&#39;s excellent motorcycle suspension website http://www.tonyfoale.com and illustrates what Mr. Foale indicates is a Kawasaki Z1R engine (evidently from the 1970s). Mr. Foale indicates at http://tonyfoale.com/gallery/StrFrame/home.htm that the Z1R&#39;s “swingarm was concentric with the gearbox sprocket to maintain constant chain tension. Two magnesium castings were made to hold the bearings for the swingarm pivot. One replaced the clutch cover and can be seen in [ FIG. 8 ], the other covered the sprocket and incorporated the clutch release actuating lever.” In other words, the Z1R&#39;s swingarm pivots  110  were outboard from the sprocket, and were not directly coupled to the engine casings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a generally side view showing one embodiment of a motorcycle engine having a sprocket shaft which is coaxial with its swingarm pivot.  
       FIG. 2  is a generally top view of the motorcycle engine of  FIG. 1  with various engine components removed for better visibility of others.  
       FIG. 3  is a generally front cross-sectioned view of the motorcycle engine of  FIG. 1 , showing the coaxial relationship of the sprocket shaft and the swingarm pivot.  
       FIG. 4  is a generally front cross-sectioned view of another embodiment of a motorcycle engine having a pair of sprocket shafts—one out each side of the engine—which are coaxial with the swingarm pivots at their respective sides of the engine.  
       FIG. 5  shows a motorcycle according to one embodiment of this invention.  
       FIG. 6  shows a 2005 Yamaha R1 motorcycle, in which the swingarm pivot is behind the sprocket shaft.  
       FIG. 7  shows a 2005 Yamaha YZF450F motorcycle, in which the swingarm pivot is behind the sprocket shaft.  
       FIG. 8  shows a 1970s era Kawasaki Z1R motorcycle engine which had its swingarm pivots outboard of its sprocket in lightweight castings which were bolted to the engine. 
    
    
     DETAILED DESCRIPTION  
      The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only.  
       FIG. 1  illustrates a motorcycle engine  10  and swingarm  12  according to one embodiment of this invention. The engine includes an output shaft or sprocket shaft  14  to which is coupled a chain drive sprocket  16  (or belt drive wheel in belt-driven applications). The engine includes a cylinder block  18  which is coupled to a crankcase  20 . In one embodiment, the sprocket shaft exits the engine at a mating seam between the cylinder block and the crankcase.  
      The crankcase may include a separate gearbox case  22  which can be dropped away without removing the various gearbox components (not shown) from their respective bearings and other retainers (not shown). In one embodiment, the crankcase may include a lower crankcase half  24  which is disposed between the upper crankcase half  20  and the gearbox case. In one embodiment, the engine includes a primary gearbox clutch  26  and a separate slipper clutch unit  28 . In one embodiment, the slipper clutch unit is disposed at the seam between the upper and lower crankcase halves. The engine further includes one or more heads  30  coupled to the cylinder block to provide intake, exhaust, valving, and so forth as is conventionally known in engines.  
       FIG. 2  illustrates the motorcycle engine  10  and swingarm  12  with the cylinder block and heads removed, providing visibility into some of the internal engine components. The engine includes one or more crankshafts  32  which are driven by pistons (not shown) in the cylinder block. Power is transmitted from the crankshafts down into the gear box by e.g. a gear train  34 . After passing through the gearbox, power is transmitted to a final drive output gear  36  which is coupled to the output shaft  14 , which in turn drives the sprocket  16 .  
      The structure  37  of the swingarm which extends about the swingarm pivot is inboard of the sprocket  16 . In other words, the mounting point of the swingarm is narrower from the midline of the swingarm, than is the sprocket. This enables the swingarm to be coupled directly into the structure of the crankcase and/or cylinder block, whereas in the few prior art examples of coaxial swingarm mounting, the swingarm pivots were outside the sprocket and the swingarm was coupled into to an intermediate subframe or casing that is coupled to a frame or engine casing. For example, as shown in  FIG. 6 , in the Kawasaki Z1R, the swingarm mounted to the outside of the clutch cover, which was in turn bolted to the engine casings. In Bimota Tesi motorcycles, the swingarm mounted to a subframe plate that was bolted to the frame and was not coupled to the engine at all; the swingarm pivot was well outside the drive sprocket.  
       FIG. 3  illustrates the motorcycle engine  10  and swingarm of  FIG. 1  in cutaway or cross-sectioned view. The sprocket shaft  14  carries the sprocket  16  and exits the engine at the seal where the crankcase  20  meets the cylinder block  18 . The sprocket shaft is driven by a final output gear  36  which is driven by a gear  38  coupled to the slipper clutch  28 . The slipper clutch is disposed at the seam or gasket where the upper crankcase half  20  meets the lower crankcase half  24 .  
      The sprocket shaft rotates in bearings  40 ,  42  which are journaled in the crankcase and engine block. The slipper clutch rotates in a bearings  44 ,  46  which are journaled in the crankcase halves. In one embodiment, in which the gearbox shafts (not shown) are oriented longitudinally with respect to the direction of travel of the motorcycle, the slipper clutch is driven by a bevel gear  48  which mates with another bevel gear (not shown) coupled to the gearbox secondary shaft (not shown).  
      The swingarm includes a portion  50  which rotates on bearings  52  which are coupled to the engine by mounting brackets  54  which, in one embodiment, thread into the engine. The sprocket shaft exits the assembly substantially coaxial with the swingarm pivot bearings.  
       FIG. 4  illustrates another embodiment of an engine  60  and swingarm  12  in which the swingarm pivot is coaxial with the sprocket shaft  62 . In addition to the first chain sprocket  16  on one side of the motorcycle, there is also a second chain sprocket  64  on the other side of the motorcycle. The extended sprocket shaft  62  may ride in additional bearings  66  at the other side of the engine.  
      This extended sprocket shaft with dual sprockets, one at either end, enables the motorcycle to use dual drive chains, one on either side of the motorcycle, to provide symmetrical pull and other forces on the swingarm. The more symmetrical these forces are, the less the swingarm will tend to flex or torque. This enables the swingarm to be made lighter. It also enables the use of two, lighter chains (not shown) and correspondingly lighter sprockets front and rear (not shown). In some embodiments, the swingarm is substantially symmetrical.  
       FIG. 5  illustrates one embodiment of a motorcycle  70  according to this invention. The motorcycle includes an engine  10  and a swingarm  12 , in which the swingarm pivot is coaxial with the sprocket shaft  14 .  
     Conclusion  
      When one component is said to be “adjacent” another component, it should not be interpreted to mean that there is absolutely nothing between the two components, only that they are in the order indicated.  
      The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown.  
      Those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention. CLMMS