Abstract:
The present invention provides a snowmobile suspension system comprising a slide frame for engagement with an endless track, a suspension arm, a bracket arm, and a rocker arm. The suspension arm has an upper portion adapted to be pivotally mounted relative to a chassis on a snowmobile and a lower portion adapted to be pivotally mounted relative to the slide frame. The bracket arm has an end fixedly connected to the lower portion of the suspension arm. The rocker arm has an upper end pivotally connected to the other end of the bracket arm and a lower end supporting a lower end of a shock absorber, the lower end of said shock absorber being pivotally attached thereto. The upper end of the shock absorber is pivotally interconnected to the chassis. The rocker arm is constructed and arranged such that a lower end thereof is disposed beneath the lower portion of the suspension arm.

Description:
The present application claims priority to U.S. Provisional Application of Mallette, filed Feb. 9, 2000, Ser. No. 60/181,231, the entirety of which is hereby incorporated into the present application by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a rear shock linkage system for a suspension system of a snowmobile. 
     BACKGROUND OF THE INVENTION 
     Tracked vehicles such as snowmobiles have rear suspensions generally consisting of front and rear suspension arms pivotally mounted on shafts, which are rotatably connected to a slide frame. The slide frame comprises a pair of laterally spaced apart slide rails or longitudinal skids interconnected transversely on opposing lateral sides of the snowmobile. The slide rails are in sliding contact with an endless track which contacts the snow surface and drives the snowmobile. The front and rear suspension arms pivotally interconnect the chassis of the snowmobile to the slide frame. 
     In many current arrangements, front and rear suspension arms pivotally interconnect the chassis to the slide frame. In one typical arrangement, the rear suspension system includes a pair of shock absorbers pivotally interconnected to the chassis, extending downward to a transverse tube that is pivotally mounted relative to the slide frame by connecting parts. Also, to attach the rear shock absorber to the transverse tube, the conventional approach is to pivotally mount the shock absorber to a bracket arm that, in turn, is fixedly attached to the transverse tube. Such a system is shown in U.S. Pat. No. 5,664,649 to Thompson et al., with the above-mentioned bracket arm designated as element  90 . 
     In the above arrangement, it is preferable to make the bracket arm as short as possible so that the shock absorber is attached at the lowest possible point to thereby provide greater suspension travel within the confines defined by the endless track. However, a short bracket arm length creates the possibility that the shock absorber will become jammed with other suspension components and/or belt during large angular displacements of the pivoting shaft, and, correspondingly, the bracket arm. Therefore, a short bracket arm length limits flexibility in the design of the suspension linkage system. 
     One way to alleviate the concerns over the restriction on the design options and also provide for sufficient shock absorber travel is to attach the shock absorber to an end of an additional component that permits a higher or lower pivoting point for the additional component. Such a prior art system is shown in FIG.  1 . Here, shock absorber  1  is attached to a rocker arm  2 , which is pivotally attached via a bolt  3  to an additional component designated as plate bracket  4 . Plate bracket  4  is in turn fixed to transverse tube  5 , which is fixed to the slide frame. Thus, rocker arm  2  pivots about plate bracket  4  via bolt  3 . Because of the large forces experienced by the system, plate bracket  4  and rocker arm  2  require additional support. To provide such support, plate bracket  4  includes a C-shaped portion  6 , which is more clearly shown in the exploded view in FIG.  2 . This C-shaped portion  6  is in sliding contact with transverse portion  8  of front suspension arm  7 . Thus, plate bracket  4  is supported at both ends for additional strength. As can be seen from FIG. 1, shock absorber  1  is thus attached to a low position that allows for sufficient suspension travel. Because rocker arm  2  is long and can pivot freely about pivot  3 , the concerns about the restrictions in the suspension linkage system are reduced. 
     However, the prior art apparatus shown in FIG. 1 has three problems. First, the added components of the plate bracket  4  and support tube  5  add weight. Second, the forces involved combined with the friction between the C-shaped portion  6  and transverse portion  8  create significant wear of both the transverse portion  8  and the C-shaped portion  6 . Third, because of the forces between the C-shaped portion  6  and the transverse portion  8 , “stiction” occurs between the two components, preventing free movement of the front suspension arm and thereby reducing the overall performance of the suspension system. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention, therefore, to overcome the problems associated with the prior art noted above. In achieving this object, the present invention provides a snowmobile suspension system comprising a slide frame for engagement an endless track, a suspension arm, a bracket arm, and a rocker arm. The suspension arm has an upper portion adapted to be pivotally mounted relative to a chassis on a snowmobile and a lower portion adapted to be pivotally mounted relative to the slide frame. The bracket arm has an end fixedly connected to the lower portion of said suspension arm. The rocker arm has an upper end pivotally connected to the other end of the bracket arm and a lower end supporting a lower end of a shock absorber, the lower end of the shock absorber being pivotally attached thereto. The upper end of the shock absorber is pivotally interconnected to the chassis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described in the detailed description which follows, by reference to the noted drawings by way of non-limiting exemplary embodiments, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
     FIG. 1 shows a prior art suspension system which utilizes a rocker arm, a plate bracket, and a C-shaped support portion for additional support; 
     FIG. 2 illustrates an expanded view of a portion of the prior art system shown in FIG. 1; 
     FIG. 3 shows an overall view of a snowmobile with its major components, including the preferred embodiment of the snowmobile suspension system of the present invention; 
     FIG. 4 shows a perspective view of the preferred embodiment of the snowmobile suspension system of the present invention; and 
     FIG. 5 shows a two dimensional view of FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     While the present invention will hereinafter be described in connection with at least one exemplary embodiment thereof, it should be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     Referring to FIG. 3, a snowmobile  10  is generally shown having a forward end  13  and a rearward end  15  (that are defined consistently with the travel direction of the vehicle). Snowmobile  10  includes a body  17  (i.e., the exterior upper portions) and a chassis  12 . While not shown in FIG. 3, an engine is carried by chassis  12  at its forward end. In addition, two skis  11  are attached to the forward end of chassis  12  through a front suspension  19 . An endless, drive track  16  of the rear suspension  18  is disposed under chassis  12  and is connected operatively to the engine for propulsion of the vehicle. As is shown more clearly in FIG. 4, rear track support wheels  24  are supported on the slide rails  28  of a slide frame  20  by an axle shaft  32 . 
     At the front of chassis  12 , snowmobile  10  includes fairings  25  that enclose the engine to protect it and to provide a external shell that can be decorated so that the snowmobile is aesthetically pleasing. Typically fairings  25  comprise a hood and a bottom pad (neither of which have been individually identified in the Figures). A windshield  26  may be connected to fairings  25  near the forward end  13  of snowmobile  10 . Windshield  26  acts as a windscreen to lessen the force of the air on a rider when snowmobile  10  is moving. 
     A seat  14  extends from rearward end  15  of snowmobile  10  to the fairings  25 . A steering device  27 , such as a handlebar, is positioned forward of the rider and behind the engine. Two footrests (not shown) are positioned on either side of seat  14  to accommodate the rider&#39;s feet. 
     Referring to FIGS. 4 and 5, the rear suspension system of the snowmobile  10  comprises a slide frame  20  that is connected to the chassis  12  through the front and rear suspension assemblies generally indicated as  29  and  49 , respectively. Each of the front and rear suspension assemblies  29 ,  49  comprises, among other things, front and rear suspension arms  30  and  50 , respectively, and front and rear shock absorbers  60  and  70 , respectively. In the embodiment shown in FIG. 4, the rear shock absorber  70  is preferably of the piston-damper type, while the front shock absorber  60  of the coil-over piston-damper type. The slide frame  20  comprises two longitudinally extending transversely spaced apart slide rails  28  that are transversely interconnected by suitable cross structures to form a generally rigid structure. The lower surfaces of the slide rails  28  are coated in a known manner with a suitable low friction material such as nylon, Teflon®, and preferably UHMW (ultra high molecular weight polyethylene), for sliding contact with the drive track  16 . 
     As shown in FIG. 4, front and rear suspension arms  30  and  50 , respectively, interconnect the slide rails  28  with the chassis  12 . The front suspension arm  30  is a trapezoidally-shaped structure that includes an upper tube portion  34  and a lower tube portion  38  that are connected by two tubes  30   a  and  30   b . In the preferred embodiment, the components are all welded together to form an integral structure. The upper portion  34  of front suspension arm  30  is pivotally mounted on a first transverse shaft (not shown) that is fixedly attached to the chassis  12  by means of bolts  34   a . Likewise, the lower tube portion  38  of front suspension arm  30  is pivotally mounted on a second transverse shaft (not shown) that is fixedly attached to the respective slide rails  28 . Therefore, as the slide frame  20  displaces vertically, front suspension arm  30  is able to pivot about the first transverse shaft relative to the chassis  12  and simultaneously pivot about the second transverse shaft relative to the slide frame  20 . 
     A front shock absorber  60  extends from the upper tube portion  34  of the front suspension arm  30  downwardly and rearwardly to fixedly connect to a lower transverse shaft  22 , which is fixedly attached to slide rails  28  by bolts  60   b , as shown in FIG.  5 . The front shock absorber  60  is pivotally attached to a bracket arm  42  of the upper tube portion  34  by a bolt  60   a . Bracket arm  42  is in turn fixedly attached to the upper tube portion  34  of front suspension arm  30 . 
     The rear suspension assembly  49  comprises, among other things, a rear suspension arm  50 , a rear shock absorber  70 , and a location rod  90 . The rear suspension arm  50  comprises a transverse rear upper tube that is pivotally mounted on a third transverse shaft (not shown), which is connected to the chassis  12  in known manner by a bolt  54 , as shown in FIG.  4 . Rear suspension arm  50  is a rectangularly-shaped structure that includes a transverse rear upper tube  52  and a transverse rear lower tube  56  that are connected at intermediate locations thereon by a metal plate  51 . Although shown being connected by a metal plate  51 , the transverse rear upper and lower tubes  52  and  56  can also be connected with at least one bar or tube, in which case the components of the rear suspension arm  50  would all be welded together to form a single unit. 
     The rear suspension arm  50  extends from the upper tube  52  downwardly and rearwardly to the lower tube  56 . The transverse rear lower tube  56  is connected to a lower arm  55  which is in turn pivotally connected to the slide frame  20 . The axial ends of the rear lower tube  56  have blocks  59   a  and  59   b  which are movable within the block stoppers  57   a  and  57   b  located on each slide rail  28 . 
     A rear shock absorber  70  extends from the transverse rear upper tube downwardly and forwardly to pivotally attach to a rocker arm  80 , which will be discussed below. The other end of the rear shock absorber  70  is pivotally interconnected to the chassis  12 . That is, the upper end of rear shock absorber  70  is pivotally attached by a bolt  70   a  to a bracket arm  40 , which in turn is fixedly attached to the transverse rear upper tube  52 . Additionally, the rear suspension assembly  49  further comprises a location rod  90  that at one end (lower end) is pivotally attached to the lower end of rocker arm  80  by a bolt  90   b . The location rod  90  runs adjacent the rear shock absorber  70  and is pivotally interconnected to the chassis  12 . That is, the other end (upper end) of the location rod  90  is pivotally connected by a bolt  90   a  to bracket arm  92 , which in turn is fixedly attached to the transverse rear upper tube  52 . Therefore, as the slide frame  20  displaces vertically, rear suspension arm  50  is able to pivot about the third transverse shaft relative to the chassis  12 . 
     Biasing elements are provided in both front and rear suspension assemblies  29  and  49 , respectively, for urging the slide rails  28  away from the chassis  12 . The biasing elements on the rear suspension assembly  49  preferably include a pair of torsion springs  72  around the transverse upper tube  52  of the rear suspension arm  50 . One end  74  of each torsion spring  72  is connected to its corresponding slide rail  28  and the other end  76  of each is engaged with the rear suspension arm  50 . The biasing element on the front suspension assembly  29  includes a helical spring  63  that is incorporated into the shock absorber  60 . A pair of extension limiters, such as straps  64  shown in FIG. 4, is used to prevent over-extension of the slide rails  28  by the springs  63  and  72 . 
     As mentioned earlier, the rear shock absorber  70  extends downwardly and forwardly to pivotally attach to rocker arm  80 . Rocker arm  80  and its attachment to the front suspension arm  30  represents a major aspect of the preferred embodiment. Rocker arm  80  is made of two spaced apart flat plates which, when connected, together form one rocker arm  80 . Of course, an integral cast, forged or manufactured rocker arm  80  can also be used. One end of rocker arm  80  is pivotally attached to bracket arm  84  by a bolt  82 , and bracket arm  84  is in turn fixedly attached to the transverse lower tube portion  38  of the front suspension arm  30 . Rocker arm  80  curls around and extends rearwardly beneath tube portion  38 . Pivotally attached to the other end of rocker arm  80  are the lower end of the rear shock absorber  70  by a bolt  70   b  and the lower end of the location rod  90  by a bolt  90   b . Bushings can be provided at one or more of the rocker arm/bracket arm, rocker arm/shock absorber and rocker arm/location rod pivot joints, as is known, to reduce friction between the components during operation. The positioning of bracket arm  84  is designed so that when the displacement of the slide frame  20  has reached its maximum compression point, i.e., bottomed out, the top of bracket arm  84  is close to or touches the underside of the snowmobile track  16 . It can be appreciated that the orientation angle between the bracket arm  84  and the front suspension arm  30  remains fixed, and as the front suspension arm  30  moves up vertically due to a displacement of slide frame  20 , bracket arm  84  likewise moves upward and also pivotally rotates about bolt  32 . 
     With this structure, fewer parts are required to ensure sufficient suspension travel, thereby reducing the complexity and weight of the system, while providing greater flexibility in designing the suspension linkage systems. Additionally, the rocker arm  80  linkage arrangement of the illustrated embodiment eliminates the wear and stiction problems associated with the prior art. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments and elements, but, on the contrary, is intended to cover various modifications, equivalent arrangements, and equivalent elements included within the spirit and scope of the appended claims.