Abstract:
An idler wheel assembly, for example a rear idler wheel assembly, for a snowmobile and includes at least one cross-member that permits load transfer and possible load damping as between a pair of rear idler wheels. The cross-member may be configured to transfer lateral loads, bending loads and other types of loads between the idler wheels. The cross-member is arranged between the wheels in such a manner that it is free to rotate with the idler wheels without interference to or from other structure of a skid frame assembly of the snowmobile. In one embodiment, each idler wheel includes a cross-member that extends inward to connect to the other wheel.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to an idler wheel assembly for a snowmobile and, more specifically, to a lighter and more robust rear idler wheel assembly for a snowmobile skid frame assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional snowmobiles typically have a skid frame assembly for supporting an endless flexible drive track. The skid frame assembly generally includes low-friction wearstrips respectively coupled to slide rails, a number of crossbrace axles extending from one slide rail to the other, a suspension system, one or more idler wheel assemblies, and other structural support. By way of example, a rear idler wheel assembly is coupled to an aft portion of the skid frame assembly and provides a surface on which the continuous track makes approximately a 160 degree turn. Because the rear idler wheel assembly is located sufficiently aft of the snowmobile&#39;s center of gravity it is desirable to reduce the weight of the rear idler wheels in order to more effectively centralize the overall mass for better handling. Therefore, the rear idler wheels are typically made of a lightweight, structural material and have spokes or lightening holes for weight reduction purposes. 
         [0003]    A snowmobile rides on various non-uniform surfaces and all types of on- and off-trail conditions, as such it must be able to contend with many different riding environments. The terrain may change from smooth trails to large bumps and jumps to deep snow with occasional hidden rocks or stumps. Snow conditions can vary from grippy hard-pack to bottomless powder, from smooth trails to rough and bumpy ones. In turn, the idler wheel assemblies, and specifically the rear idler wheel assembly, should be optimized to strike a balance between weight and load capacity or structural robustness. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to an idler wheel assembly for a skid frame assembly of a snowmobile and in one embodiment to a rear idler wheel assembly that is lightweight and more structurally robust as compared to conventional idler wheel assemblies. By way of example, the rear idler wheel assembly includes at least one cross-member that permits load transfer and possible load damping as between a pair of rear idler wheels. The cross-member may be configured to transfer lateral loads or the lateral component of a load, bending loads, and other types of loads between the idler wheels. Lateral loads are generally side loads directed approximately parallel to a rotational axis of the wheel. The cross-member is connected between the wheels in such a manner that it is free to rotate with the idler wheels without interference to or from other structure of the skid frame assembly. 
         [0005]    In accordance with an aspect of the invention, a snowmobile includes a powertrain system, a pair of front skis, a steering assembly, a skid frame, and an idler wheel assembly. The powertrain system includes an engine, a drivetrain, and an endless flexible track propelled by the drivetrain. The steering assembly is maneuverable to turn the front skis. The skid frame assembly has at least one pair of slide rails. The idler wheel assembly is coupled to the skid frame assembly. The idler wheel assembly includes at least two idler wheels aligned on a common rotational axis. The idler wheels are interconnected to transfer loads between the idler wheels. 
         [0006]    In accordance with another aspect of the invention, a skid frame assembly configured to receive a track of a snowmobile includes a pair of slide rails and a pair of idler wheels coupled to the slide rails. Each idler wheel includes an outer diameter surface and a hub. A cross-member extends from one idler wheel and interconnects with the other idler wheel. The cross-member is substantially aligned with a common rotational axis of the idler wheels. The cross-member is located between the outer diameter surface and the hub. 
         [0007]    In accordance with yet another aspect of the invention, a method for arranging idler wheels of a snowmobile includes the steps of (1) coupling a first idler wheel to an inner surface of a skid frame assembly; (2) coupling a second idler wheel to another inner surface of the skid frame assembly, the idler wheels sharing a common rotational axis; and (3) structurally coupling the first and second idler wheels together with a cross-member that extends substantially parallel to the common rotational axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0009]      FIG. 1  is a perspective view of a snowmobile having a skid frame assembly with an idler wheel assembly according to an embodiment of the present invention; 
           [0010]      FIG. 2  is another perspective view looking into the skid frame assembly for a closer view of the rear wheel assembly of  FIG. 1 ; 
           [0011]      FIG. 3  is a perspective view of the skid frame assembly without the endless drive track, but showing the idler assembly with cross-members according to an embodiment of the present invention; 
           [0012]      FIG. 4A  is an isometric view looking outward toward an idler wheel of an idler wheel assembly according to an embodiment of the present invention; 
           [0013]      FIG. 4B  is an isometric view looking inward toward another idler wheel of an idler wheel assembly according to an embodiment of the present invention 
           [0014]      FIG. 5  is a side elevational view of the idler wheel of  FIG. 4B ; and 
           [0015]      FIG. 6  is a cross-sectional view of the idler wheel of  FIG. 5  taken along LINE  6 - 6  of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    As will be described in further detail below, at least one embodiment of the invention includes a snowmobile having a lighter weight and more structurally robust idler wheel assembly in which the wheels are coupled together by one or more cross-members. As discussed above, snow conditions (i.e., loading conditions) can vary from hard-packed to bottomless powder, from smooth trails to rough and bumpy ones. While idler wheel assemblies, and rear idler wheel assemblies in particular, may be designed with a balance between weight and load capacity or structural robustness, it is axiomatic that overload conditions may occur and still cause damage to one or more of the idler wheels. For example if a rear idler wheel takes a sharp blow in a direction not aligned with the plane of its face, the lateral load may misalign the wheel at the same time the track is pulling on the wheel to increase the load on the misaligned wheel. Such action may fold the wheel to the point that it fails through excessive plastic yielding or by having a bearing become misaligned or released from its center. Using the rear idler wheel assembly as an example, an aggressive driver may be more apt to cause damage to one of the rear idler wheels when taking corners sharply or maneuvering over rough terrain. Unfortunately if damage does occur to one of the rear idler wheels it will likely cause the snowmobile to be essentially immovable or non-drivable. While idler wheels are not difficult to remove and replace, they are also not one of the components that many riders carry as a spare part. Thus in some instances, snowmobiles have been stranded overnight or longer until the rider or another can obtain a spare idler wheel or wheels. Accordingly, at least one embodiment of the present invention provides an idler wheel assembly that is lightweight and more structurally robust than a conventional idler wheel assembly. 
         [0017]      FIG. 1  shows a snowmobile  100  having a front body panel  102 , handlebars  104 , a seat  106 , a tunnel  108 , a front ski and suspension assembly  110 , and a skid frame/track assembly  112 . Referring now to  FIG. 2 , the skid frame/track assembly  112  includes an endless flexible drive track  114  and a skid frame assembly  116  about which the track  114  moves. The endless flexible drive track  114  may take the form of one of the drive tracks described in U.S. Pat. Nos. 7,422,295 and 7,712,846, which are incorporated by reference herein in their entireties. 
         [0018]      FIG. 3  shows the skid frame assembly  116  having a skid framework  118  with wearstrips  120  attached thereto. End caps  122  are attached to the end portions of the skid framework  118 . The skid frame assembly  116  includes a front suspension assembly  124 , a rear suspension assembly  126 , a front shock  128 , and a rear shock  130 . In addition, the skid frame assembly  116  may include a plurality of idler wheel assemblies. In the illustrated embodiment, the skid frame assembly  116  includes a front idler wheel assembly  132 , an intermediate-lower idler wheel assembly  134 , an intermediate-upper idler wheel assembly  136 , and a rear idler wheel assembly  138 . The idler wheel assemblies may be located on an outside of the skid frame assembly  116  such as the front idler wheel assembly  132  or on an inside of the skid frame assembly  116  such as the rear idler wheel assembly  138 . 
         [0019]    The skid frame assembly  116  also includes a plurality of cross-braces or cross-bars. Again referring to the illustrated embodiment, the skid frame assembly  116  includes a front cross-brace  139  coupled to the front suspension assembly  124  with limiter straps  140 . Respective intermediate cross-braces  142 ,  144 ,  146  and  148  are arranged in the skid frame assembly  116  at desired locations. 
         [0020]      FIGS. 4A and 4B  show left and right rear idler wheels  152   a,    152   b , respectively of the rear idler wheel assembly  138  ( FIG. 3 ). In the illustrated embodiment, the idler wheels  152   a,    152   b  are identical, so for purposes of brevity only the left idler wheel  152   a  will be described in detail and identical features will have the same reference numeral in  FIG. 4B , but appended with the small letter “b.” The left idler wheel  152   a  includes an outer periphery or diameter surface  154   a,  a central hub  156   a,  and cross-members  158   a.  The idler wheel  152   a  may include lightening holes or spaces  160   a  and structural spokes  162   a  that couple the hub  156   a  to the outer diameter surface  154   a.  The idler wheel  152   a  may be made from a variety of materials such as, but not limited to, thermoplastics, rubber, reinforced composites, metals, or a combination of the above, etc. The illustrated embodiment shows three cross-members  158   a  equally spaced, however the number of cross-members and spacing may be varied based on design or aesthetic considerations. The left and right cross members are secured together with fasteners (not shown) through the small holes in the inner ends of the cross members to form the interconnected idler wheel assembly or unit. In one alternate embodiment, the left and right idler wheels are constructed with no individual cross members at all, but rather with a continuous cylindrical wall from one to the other. The wall in such an embodiment is preferably recessed from the diameter surface  154 , such that the track does not ride on the wall. In this and other embodiments, the left and right wheels can be integrally coupled together to form a single unit. They can even be formed together as a single unit, without having to fasten the left and right cross members with fasteners. 
         [0021]      FIG. 5  shows a side elevational view of the right, rear idler wheel  152   b  from  FIG. 4   b . The cross-members  158   b  may be sized to sufficiently fill the spaces between respective spokes  162   b;  however the cross-members  158   b  may be larger or smaller than illustrated. Further, the cross-members  158   b  are radially located between an outside diameter  164   b  of the idler wheel  152   b  and the hub  156   b.  The cross members are placed and shaped to most effectively address torsional and lateral loads on the completed idler wheel assembly without interfering with the operation of the track or suspension components. Thus, for example, the cross members are place near the outer diameter  154   b  to provide good mechanical support for lateral loads, but are not all the way at the outer diameter  154   b,  so they don&#39;t contact the track as it rotates. Although an intermediate wheel or outer diameter may alternatively be provided between the two wheels in another embodiment. 
         [0022]      FIG. 6A  shows a cross-sectional view of the right, rear idler wheel  152   b.  A bearing  166   b  positioned in the hub  156   b  permits the idler wheel  152   b  to rotate relative to its axle (not shown). In the illustrated embodiment, the cross-members  158   b  have a cavities  168   b  for purposes of weight reduction and for fastener placement. The cavity  168   b  is defined by walls  170   b  and an end portion  172   b.  Further, the cross-members  158   b  may be integrally formed with the wheel  152   b  as indicated by a transition radius  174   b.  After assembly, the end portions  172   b  of each cross-member  158   b  for the right, rear idler wheel  152   b  are in contact with the corresponding cross-member end portions of the left, rear idler wheel  152   a  ( FIG. 4A ) and fastened together through the holes in the ends of the cross members. By way of example, a length  176   b  of the cross-members may be sufficient to permit contact with another cross-member and be fastened together. Therefore in operation, the end portions and walls of the cross-members provide the structural load path from one wheel to the other. Further, the cross-members help prevent the idler wheels from bending or deforming in an undesired manner. 
         [0023]    Note in  FIG. 6A  that the outer perimeter of wheel  152   b  includes a rubber “tire” member  178   b  to increase traction between the wheel and the track. However, especially when the wheel is used as a rear idler wheel, the traction between the polyethylene wheel material and the track is sufficient that the rubber member  178   b  is not necessary. As a rear wheel, more than a third of the circumference is typically engaged with the track as the track is held rearward by the wheel. In this situation, wheel slippage on the track is not an issue. Thus, the traction member can be omitted as shown in  FIG. 6B . 
         [0024]    While the preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiments. Instead, the invention should be determined by reference to the claims that follow.