Abstract:
The invention provides a motorcycle having a frame, an engine coupled to the frame, and a crankshaft assembly. The crankshaft assembly includes a first flywheel half having an aperture, a crank pin including a first end portion, a second end portion opposite the first end portion, and a bearing surface between the first and second end portions. The first end portion is press-fit into the aperture of the first flywheel half. The first end portion, the second end portion, and the bearing surface are coated with a fiction enhancer. A bearing is positioned at least partially onto the bearing surface, and a connecting rod has an aperture that at least partially receives the bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application 60/830,965, filed Jul. 14, 2006, and U.S. Provisional Application No. 60/865,183, filed Nov. 10, 2006. The entire contents of these provisional applications are incorporated by reference. 
     
     BACKGROUND 
       [0002]    The present invention relates to a crankshaft assembly with a coated crank pin, and more particularly, to a crankshaft assembly with a coated crank pin used with a roller element bearing. 
         [0003]    It is known for a motorcycle engine, and specifically a V-twin style engine, to include a crankshaft assembly including first and second flywheel halves coupled together with a single crank pin. The crank pin is connected to the flywheel halves in a variety of ways. One option is to extend threaded ends of the crank pin through holes in the opposed flywheel halves and to thread nuts onto the ends of the crank pins to secure the assembly together. Another method is to press-fit non-threaded ends of the crank pin into the holes of the opposed flywheel halves. 
         [0004]    Sometimes, the press-fit can be strengthened by using a press-soldering process which creates a thin layer (approximately 5 μm) of solder between the press-fit components. Other methods of strengthening the press-fit connection include pressing a solid plug into a bore of the crank pin after it is press-fit into the holes of the flywheel halves, case hardening one or both of the press-fit components, or keying the press-fit. 
         [0005]    In some assemblies, friction enhancers (e.g., platings or coatings) on the crank pin are used to enhance a press-fit connection for a crank pin on a crankshaft assembly. However, these enhancers were believed to be incompatible with roller element bearings resulting in an adverse effect on the performance of the roller element bearings. To overcome this perceived deficiency, masking of the bearing contact surface of the crank pin was introduced. However, masking is labor intensive and inefficient, and if masking is not done properly, bearing performance could be adversely impacted. 
       SUMMARY 
       [0006]    In one embodiment, the invention provides a motorcycle having a frame, an engine coupled to the frame, and a crankshaft assembly. The crankshaft assembly includes a first flywheel half having an aperture, a crank pin including a first end portion, a second end portion opposite the first end portion, and a bearing surface between the first and second end portions. The first end portion is press-fit into the aperture of the first flywheel half and the second end portion is press-fit into the aperture of the second flywheel half. The first end portion, the second end portion, and the bearing surface are coated with a friction enhancer. A bearing is positioned at least partially onto the bearing surface, and a connecting rod receives the bearing. 
         [0007]    In another embodiment the invention provides a method of manufacturing a crankshaft assembly for a motorcycle. The method includes providing a crank pin including a first end portion, a second end portion opposite the first end portion, and a bearing surface between the first and second end portions. The method further includes coating the first end portion, the second end portion, and the bearing surface with a friction enhancer. The method further includes press-fitting the first coated end portion into a corresponding aperture in a first flywheel half, positioning a bearing at least partially onto the coated bearing surface, and receiving the bearing at least partially inside an aperture of a connecting rod. 
         [0008]    In some embodiments of the invention, the crank pin is provided with a metallic layer on substantially its entire outer surface. The metallic layer is preferably made from a zinc alloy and is simultaneously used in the area of the bearing surface as a wear resistant inner slide track for the roller body of the roller bearing. Because the metallic layer of high adhesiveness, which is produced from a zinc alloy, but also from other metals, such as copper, it is suitable not only for increasing the stability of a press-fit connection, but also as a tribological partner within a roller bearing, if the roller bodies roll over the coated bearing surface, this has no disadvantageous consequences for the service life of the roller bearing. Moreover, such metallic layers can be deposited onto the crank pins with especially high dimensional stability, so that the bearing surface satisfies the high precision requirements in terms of its cylindrical shape and its diameter for its property as an inner slide track for the roller body of the roller bearing even after the coating process. Based on this characteristic, the outer surface of the crank pin can be provided completely with the metallic layer, so that, in a time-saving and cost-saving way, the added expense for generating only local coating zones before or after the coating process can be eliminated. 
         [0009]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a motorcycle including an engine embodying to the present invention. 
           [0011]      FIG. 2  is a cross-section view of a crankshaft assembly of the engine of  FIG. 1 . 
           [0012]      FIG. 3  is a cut-away section view taken along line  3 - 3  of  FIG. 2 . 
           [0013]      FIG. 4  is a perspective view of a crank pin of the crankshaft assembly of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be 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,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0015]    The motorcycle  10  of  FIG. 1  includes a frame  12 , a steering assembly  14  pivotably mounted to a forward portion of the frame  12 , a front wheel  16  rotatably mounted to an end of the steering assembly  14 , a rear wheel  18  rotatably mounted to a swing arm  20  that is pivotably connected to a rearward portion of the frame  12 , and an engine  22  and transmission  24  mounted to the frame  12  and operably coupled to the rear wheel  18 . A seat  26  is coupled to the frame  12  above the rear wheel  18  to support an operator. The steering assembly  14  includes a fork  28 , handlebars  30 , and controls  32 , such as a throttle grip  34 , coupled to the handlebars  30 . The operator manipulates the controls  32  to power the engine  22  and transmission  24 , drive the rear wheel  18 , and propel the motorcycle  10 . The operator maneuvers the handlebars  30  to pivot the steering assembly  14  and front wheel  16  to steer the motorcycle  10  while the motorcycle  10  is moving. 
         [0016]    The engine  22  is an internal combustion engine including a first or front cylinder  36  and a second or rear cylinder  38 . In other embodiments, the engine  22  can include more or less than two cylinders arranged in any suitable fashion such as, for example, a “V” configuration, an opposed configuration, or an inline configuration. 
         [0017]    As shown in  FIGS. 2 and 3 , the engine also includes a crankshaft assembly  40  having first and second crankshaft ends  42 ,  44  rotatably coupled to a crankcase (not shown) of the engine  22 . The assembly  40  includes first and second flywheel halves  46 ,  48  coupled together with a single crank pin  50 . The crank pin  50  is connected to each of the flywheel halves  46 ,  48  by press-fitting the crank pin  50  into the corresponding holes  52 ,  54  of the flywheel halves  46   48 . The first and second flywheel halves  46 ,  48  are not necessarily equal in size, but are positioned generally on opposite sides of the crankpin  50 . In some embodiments, only one of the first and second flywheel halves  46 ,  48  is included, such that the crankpin  50  is cantilevered off of the only one of the first and second flywheel halves  46 ,  48 . 
         [0018]    The crankshaft assembly  40  also includes a first connecting rod  56  rotatably coupled at one end  58  to a piston (not shown) reciprocally disposed within the first cylinder  36  and a second connecting rod  60  rotatably coupled at one end  62  to another piston (not shown) reciprocally disposed within the second cylinder  38 . The opposite ends  64 ,  66  of the first and second connecting rods are rotatably connected to the crank pin  50  with a roller element bearing  68 . In other embodiments, this bearing could be a caged roller bearing, a needle bearing, ball bearing, or other type of roller element bearing. The end  66  of the second connecting rod  60  is split such that the end  64  of the first connecting rod  56  can be received between the split portions  70  of the second connecting rod  60 . In other embodiments, the opposite ends of the connecting rods could be similarly shaped and connected in a side-by-side relationship to the crank pin. 
         [0019]    In the illustrated embodiment, the roller element bearing  68  is a needle bearing having center needle rollers  72  and end needle rollers  74  on opposite sides of the center needle rollers  72 . A bore  76  in the end  64  of the first connecting rod  56  defines the outer race of the center needle rollers  72 , and bores  78  in the split portions  70  of the second connecting rod  60  define the outer races of the end needle rollers  74 . 
         [0020]    As shown in  FIG. 4 , the crank pin  50  is a cylindrical pin including an inside diameter  80 , outside diameter  82 , annular end faces  84 , and a length  86  extending between the end faces  84 . The inside diameter  80  defines an inner cylindrical surface  88  over the length  86 , and the outer diameter  82  defines an outer cylindrical surface  90  over the length  86 . The end faces  84  of the crank pin  50  are chamfered. The chamfer on the outside diameter is blended into the finished outside diameter  82  such that no ridges or discontinuities of any kind are visible. 
         [0021]    The outer cylindrical surface  90  includes three zones. The first zone  92  is the area of the outer surface  90  that is positioned within the hole  52  of the first flywheel half  46  when press-fit together, and the second zone  94  is the area of the outer surface  90  that is positioned within the hole  54  of the second flywheel half  48  when press-fit together. The third zone  96  is disposed between the first and second zones  92 ,  94  and is the area in contact with the roller element bearing  68  when assembled together. The third zone  96  is also referred to as the bearing surface of the crank pin  50 . The bearing surface  96  defines the inner race of the center and end needle rollers  72 ,  74  of the needle bearing  68 . In the illustrated embodiment, the outer cylindrical surface  90  includes a surface roughness of about R a =6 μm. 
         [0022]    The crank pin  50  is made of bearing quality 8620 steel. The crank pin  50  is carburized, tempered, frozen to −40 degrees Fahrenheit (F), and tempered again at 300-375 degrees F for 1 hour at temperature. 
         [0023]    In one embodiment, the crank pin  50  is coated all over with ZnFe 0.0005 mm-0.005 mm (per DIN 50962—Deutsches Institut fur Normung e. V.). The illustrated crank pin  50  does not undergo passivation. In other embodiments of the invention, the zinc alloy can involve a binary alloy, such as zinc/iron, zinc/cobalt, zinc/nickel. Here, the zinc/iron alloy can be, for example, approximately 99% zinc and approximately 1% iron. Alternatively, the zinc alloy can involve a ternary alloy, such as zinc/iron/cobalt, zinc/nickel/cobalt, with the zinc/iron/cobalt being made from approximately 98% to 99% zinc, approximately 0.5% to 1% iron, and approximately 0.5% to 1% cobalt. In some embodiments, the ternary alloy is combined with the binary allow. The mentioned compositions of the zinc/iron alloy and the zinc/iron/cobalt alloy, however, do not exclude process-specific and technically harmless impurities of the respective alloy due to other elements, such as phosphorus or sulfur in small amounts. 
         [0024]    For example, suitable zinc coatings have coefficients of friction μ of approximately 0.31 to 0.37 that are favorable for the non-positive action of the press fit connections. In comparison, the coefficient of friction of an uncoated axle or hub equals approximately 0.1 to 0.15, so that in the case of a zinc coating, the load that can be transferred statically by the press-fit connection is increased by the factor 2 to 3.7. 
         [0025]    In some embodiments, the thickness of the zinc layer equals, for example, on average, about 2.5 μm, with maximum layer thickness of about, for example, 5 μm. Such a layer thickness lies on the order of magnitude of the surface roughness of the outer surface of the crank pin, so that a change in dimension of the crank pin caused by the coating is negligible in terms of the function-specific geometrical requirements on the press surfaces and on the bearing surface. 
         [0026]    The metallic layer of high adhesiveness is produced from a zinc alloy, or other suitable metals, such as copper, and is used for increasing the stability of a press-fit connection. Moreover, such metallic layers can be deposited onto the crank pins with especially high dimensional stability, so that the bearing surface satisfies the high precision requirements in terms of its cylindrical shape and its diameter for its property as an inner slide track for the roller body of the roller bearing even after the coating process. Based on this characteristic, the outer surface of the crank pin can be provided completely with the metallic layer. In some embodiments, only the crank pin is provided with the metallic layer, while the aligned bores of the crank arms can remain uncoated. In addition, the metallic layers can be electroplated. Other known coating methods can also be used, such as, for example, thermal sputtering, etc. 
         [0027]    To assemble the crankshaft assembly  40 , the crank pin  50  is machined, heat treated, and then coated entirely with ZnFe, or other suitable metal alloy. This coating enhances the corrosion resistance and enhances the frictional characteristics of the crank pin  50 . Next, the end  64  of the first connecting rod  56  is positioned between the split portions  70  of the second connecting rod  60  to align the bores  76 ,  78  of the ends  64 ,  66 . Then, with the bores  76 ,  78  aligned, the roller element bearing  68  is inserted into the bores  76 ,  78 , and the crank pin  50  is press-fit into the holes  52 ,  54  of the flywheel halves  46 ,  48 . In other embodiments, the crank pin can be press-fit into a single flywheel half prior to assembling the connecting rods and roller element bearing to the crank pin. 
         [0028]    The ZnFe or suitable metallic alloy coating improves the strength of the press-fit retention. In some embodiments, the press-fit retention is increased by 25% or more. In addition, the coating does not materially negatively affect the performance of the roller element bearing contact with the crank pin  50 . The roller element bearing is allowed to function normally without the need for masking during the coating operation. 
         [0029]    Various features and advantages of the invention are set forth in the following claims.