Abstract:
A cambered surfaced tensioning block is provided that is used in conjunction with the rear suspension of a typical snowmobile when sufficient lateral force is applied. The tensioning block fits within an open ended block housing which is attached to the slide rail components of the rear suspension in a position that is just rearward of the point at which the spring arms are attached. The upper surface of the tensioning block is formed in a curve in a manner so that the radius of that curve lessens as you move rearward thus, creating a cambered surface. The cambered upper surface of the tensioning block is utilized to move the load point of the suspension spring arm closer to the point of force application as the lateral force applied to the suspension increases. Therefore, the use of the present invention provides a rear suspension spring characteristic that grows increasingly stiff as more and more lateral force is applied to it. This improves the handling of snowmobiles in rough terrain which is very desirable in high performance machines.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improvement in the manner in which the rear suspension of a typical snowmobile is constructed. More specifically, to a method of varying the vertical force that is necessary to compress the spring component of the rear suspension. This has the effect of stiffening the ride at the rear of the snowmobile which improves its handling and performance characteristics under certain riding conditions and is especially advantageous for use in snowmobiles that are used for racing. 
     It has long been known by motor sports enthusiasts that a key to improving the handling characteristics of any given vehicle that is to be used for racing or any other situation in which a premium is placed on performance is to increase the stiffness of its suspension components. The reason for this is that the stiffer suspension will flex less under a load which has the effect of keeping the suspended drive or steering components of the vehicle in contact with the surface over which the vehicle is traveling. A stiffer suspension also lessens the amount of roll (a horizontal change in attitude) of the body of the vehicle in relation to its drive and steering components as it is driven over rough terrain and through corners. A lesser amount of body roll allows an operator to travel faster through corners and over rough terrain because it keeps the weight of the vehicle&#39;s body and operator centered over its drive and steering components which provides more traction and steering impetus to the vehicle in these conditions. Therefore, as a general rule in high performance vehicles, the stiffer that the suspension can be set up, the faster the vehicle will be able to travel over a given set of course obstacles or configurations. 
     Problems also arise from a vehicle which is set up with a suspension that is too stiff. The first of these is that if the vehicle&#39;s suspension is too stiff the resulting roughness of the ride in difficult terrain will make it impossible for the driver to control the vehicle as he would be bounced around to such a degree that he would be unable to focus on the road or track ahead. Additionally, an extremely stiff suspension would also create problems in the drive and steering mechanisms of a vehicle as they would tend to bounce over surface irregularities and lose contact with the surface over which they are traveling. This loss of surface contact would make the vehicle very difficult to control and, thus, force the vehicle to be driven at a slower rate of speed in order to maintain control over it. Therefore, finding the proper balance between suspension stiffness and controllability is critical to the performance of all types of racing and high performance vehicles. 
     The stiffness and controllability of the rear suspension of a snowmobile is controlled by the use of a pair of coiled springs that have a spring arm which angles downward and are fixedly attached to a lower suspension component. It is the flexing of the spring arm which primarily facilitates and controls the vertical movement of the suspension as a whole as the snowmobile travels over uneven terrain. The problem with this design is that the only way the spring rate can be varied to either stiffen or soften the suspension to compensate for different terrain conditions is to change out the springs themselves. This is a very time consuming operation which requires that the entire rear suspension assembly be unassembled, resulting in a lot of down time. Therefore, it is desirable to provide a method of varying the stiffness of the rear suspension of a snowmobile without the need of replacing the suspension springs. 
     SUMMARY OF THE INVENTION 
     It is the primary objective of the present invention to provide a method of stiffening the rear suspension of a typical snowmobile that can be used in conjunction with the original components of the rear suspension. 
     It is an additional objective of the present invention to provide such a method of stiffening the rear suspension of a snowmobile that provides a greater degree of resistance corresponding to the occurrence of a higher degree of force being placed on the snowmobile. 
     It is still a further objective of the present invention to provide such a method of stiffening the rear suspension of a snowmobile that works equally effectively with a wide variety of makes and models and that is inexpensive to construct and to sell. 
     These objectives are accomplished by the use of a cambered surfaced tensioning block that engages the forward portion of the spring arm component of the rear suspension of a snowmobile when sufficient lateral force is applied to the suspension. The spring arms pass through an open ended block housing just above the upper surface of the tensioning block. The tensioning block fits within an open ended block housing which is attached to the slide rail components of the rear suspension in a position that is just rearward of the point at which the spring arms are attached. 
     The spring arm functions within the rear suspension by flexing downwards and upwards when lateral forces are applied to the snowmobile and serves to both contain these forces and to maintain the suspension in a neutral position during normal operation. This flexing of the spring arm generally occurs within the relatively short portion of the arm that is located directly behind the point of attachment to the slide rail components of the rear suspension. The positioning of the flex or load point of the spring arm creates a relatively soft spring action as the application of force to it is at the furthest possible point from the flex or load point. 
     The use of the present invention effectively moves the flex or load point of the spring arm rearward and closer to the point at which the force is applied. This is accomplished because as the spring arm begins to flex downward, it contacts the upper surface of the tensioning block which changes the load point from its original position to that at which it is in contact with the tensioning block. Additionally, the upper surface of the tensioning block is formed in a curve in a manner so that the radius of that curve lessens as you move rearward which creates a cambered surface. The cambered upper surface of the tensioning block is utilized to move the load point closer still to the point of force application as the lateral force applied to the suspension increases. Therefore, the use of the present invention provides a rear suspension spring characteristic that grows increasingly stiff as more and more lateral force is applied to it. This improves the handling of snowmobiles in rough terrain which is very desirable in high performance machines. 
     For a better understanding of the present invention reference should be made to the drawings and the description in which there are illustrated and described preferred embodiments of the present invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a typical snowmobile with the rear suspension exposed illustrating the orientation of the spring components in relation to the whole of the existing prior art. 
     FIG. 2 is a side elevation view of the rear suspension of the prior art illustrating the orientation of its major components. 
     FIG. 3 is a top elevation view of the rear suspension of the prior art illustrating the orientation of its major components. 
     FIG. 4 is a side elevation view of the rear suspension spring component of the prior art. 
     FIG. 5 is a side elevation view of the present invention detailing the manner in which it is used in conjunction with the prior art. 
     FIG. 6 is a side elevation view of the rear suspension spring component of the prior art illustrating the manner in which a downward force affects the spring arm. 
     FIG. 7 is a side elevation view of the present invention illustrating the manner in which it works to change the spring rate of the existing spring arm. 
     FIG. 8 is a side elevation cut-away view of the present invention showing the orientation of the spring block within the block housing. 
     FIG. 9 is a front elevation view of the present invention showing the orientation of the spring block within the block housing. 
     FIG. 10 is a perspective view of the spring block component of the present invention detailing its cambered upper surface. 
     FIG. 11 is a side elevation cut-away view of an alternative embodiment of the present invention showing the orientation of the spring block within the block housing when the spring arm retainer is not employed. 
     FIG. 12 is a perspective view of an alternative embodiment of the spring block component of the present invention in which a spring arm groove is formed into the cambered upper surface of the spring block. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more specifically to FIG. 1 which is an illustration of the prior art, a typical snowmobile  10  consists of a aerodynamically shaped fiberglass body  11  which is attached to a frame  13 . The rear portion of the body  11  is equipped with a seat  12  which provides positioning for one or two people. The body  11  of the snowmobile  10  is also generally equipped with a transparent windscreen  28  which extends in an upward fashion and provides some protection from the wind as the snowmobile  10  moves forward over the snow. Located directly behind the windscreen  28  and in front of and above the seat  12  is the steering yolk  14  which is directly connected to the front suspension  16  of the snowmobile  10 . It is the steering yolk  14  that the operator uses to control the forward direction of the snowmobile  10 . 
     The front suspension  16  of the snowmobile  10  is primarily made up of a pair of skis  18  which are the components of the front suspension  16  which contact the snow and provide the directional imputes for the snowmobile  10 . The skis  18  are pivotally connected at their upper center point to the suspension spindles  20 . The suspension spindles  20  extend upwardly in a slightly rearward angle and are connected to the upper linkage  24  and the lower linkage  26  which allow the suspension spindles  20  to move up and down along with the skis  18  to compensate for irregularities encountered in the terrain as the snowmobile travels forward. This upward and downward movement is controlled by the use of the front shocks  22  which also contain the springs which hold the front suspension in the proper position in relation to the body  11  of the snowmobile  10 . 
     The rear suspension  30  of a snowmobile  10 , which is an example of the prior art, is detailed in FIGS. 1,  2 , and  3 . The rear suspension  30  components of a snowmobile  10  are all contained within the interior of the drive track  50  which is drive by the engine of the snowmobile  10  and provides the forward imputes for the vehicle. The rear suspension  30  of the snowmobile  10  allows the rear end to make adjustments for uneven terrain encountered during travel and is designed in a manner that ensures that the majority of the drive track  50  will remain in contact with the snow as the vehicle moves forward in all types of conditions. 
     The rear suspension  30  of a typical snowmobile  10  is primarily made up of a pair of slide rails  34  which extend from the most rearward portion of the drive track  50  to just rear of the most forward end of the track  50 . The slide rails  34  form a solid support surface upon which the portion of the flexible drive track  50  runs that contacts the upper surface of the snow during wheel operation. For this purpose, approximately the most forward twenty five percent of slide rails  34  are upwardly curved to provide this support to the leading edge of the drive track  50  to ensure that this portion of the track is supported when encountering irregularities in the surface over which the snowmobile  10  is traveling. 
     The suspension slide rails  34  also are the components of the present invention to which the rest of the suspension parts are attached. Located at the most rearward end of the slide rails  34  and at the points that correspond to the outer edge of the drive track  50  are the rear idler wheels  32 , The rear idler wheels  34  are the components of the present invention which contacts the inner surface of the drive track  50  and provide the point of rotation at which the reward direction of the lower surface of the drive track  50  is changed to the forward direction of travel of the drive track  50  at its upper surface. Thus, the rear idler wheels  32  function to guide the rotation of the drive track  50  around the most reward portion of the rear suspension  30  and also aid in maintaining the drive track  50  within the confines of the rear suspension  30 . 
     Just forward of the rear idler wheels  32  along the upper surfaces of the slide rails  34  are located the rear arms  36  which extend upwards and are pivotal in nature. The rear arms  36  provide the mounting point for the raised idler wheels  38 . The raised idler wheel&#39;s  38  primary function is very similar to that of the rear idler wheel&#39;s  36  in that they provide a point of directional change for the drive track  50  and help to maintain it in the proper orientation during vehicle operation. Additionally, the system of which the raised idler wheels  38  are a part also houses the rear suspension spring  40  which is the component of the rear suspension  30  which provides the adjustment capabilities that are necessary for the operation of a snowmobile  10  in uneven terrain. 
     The rear suspension spring  40  is mounted to the rear suspension  30  on the raised idler axle  60  which also provides at its outer ends the mounting point for the raised idler wheels  38 . The rear suspension spring  40  consists of two suspension spring coils  54  which each fit over the opposite ends of the raised idler axle  60 , just inside of the two raised idler wheels  38 . Each of the spring coils  54  have a spring arm  56  that extends in a downward and forward manner (in relation to the snowmobile  10 ) and that attach to the slide rails  34  by means of the spring arm retainers  58 . Thus, when a vertical force is exerted on the rear suspension  30 , it is the rear suspension spring  40  which absorbs this force and this force is mostly absorbed through the flexing of the spring arm  56  at a point just above its connection with the spring arm retainer  58 . 
     The raised idler axle  60  also serves as the point of attachment for the rear end of the rear arm shock  42 . The rear arm shock  42  is attached to the rear suspension  30  at its front end at a point that is midway between the two slide rails and just rearward of the forward point of the slide rails  34  at which they begin to curve upwards as previously described. The rear arm shock  42  functions to dampen the movement of the rear suspension  30  as the rear suspension spring  40  operates to absorb vertical forces. The purpose of the dampening effect of the rear arm shock  42  is to control the vertical movement of the rear suspension  30  in order that the drive track  50  will maintain the highest possible degree of contact with the surface over which it is traveling. 
     The rear suspension  20  of a typical snowmobile  10  also contains a drive track tensioning apparatus  76 , which purpose maintains the correct tension on the drive track  50  as the rear moves to adjust for irregularities in the terrain. The use of the track tensioning apparatus  76  is critical for the operation of the rear suspension  30  because as vertical forces are applied to it and as the rear suspension spring  40  compresses, the distance between the raised idler wheels  38 , which control the orientation of the drive track  50  at their point of contact, and the lower surface of the drive track  50 , is considerably shortened. If there was no way to compensate for this variance, the drive track  50  could easily become dislodged from its position on the rear suspension  30 . 
     The track tensioning apparatus  76  compensates for this variability in the drive track  50  primarily through the use of a front arm shock  48 . The front arm shock  48  is attached at its lower end to the slide rails  34  at a central point between the front idler wheels  46  (the form and function of which are similar to the other idler wheels discussed above). At its upper end, the front arm shock  48  is attached to the central portion of the guide axle  80  which holds at specific points along its length a plurality of front idler guides  78 . The front idler guides  78  again function like the raised idler wheels  38  in that they hold the front portion of the drive track  50  in the proper orientation during vehicle operation by engaging its interior surface just above the front of the slide rails  34 . 
     The tensional compensation function of the track tensioning apparatus  76  is primarily accomplished by the operation of the front arm shock  48 . The front arm shock  48  contains a relatively large compression spring that operates to place upward pressure on the entire system. This upward pressure serves to ensure that the front idler guides  76  place pressure upon and remain in contact with the inner surface of the drive track  50  which keeps the drive track at the proper tension. The contact with the drive track  50  also acts to contain a certain amount of the compressed force within the spring, which ensures that there is always upward force on the interior surface of the drive track  50 . Therefore, when the rear suspension spring  40  compresses due to a vertical force and the drive track  50  is loosened due to the change in position of the raised idler wheels  38 , the track tensioning apparatus  76  maintains the proper tension on the drive track  50 . This is done by forcing the front idler guides  78  in an upward fashion through the front arm shock  48  which pushes against the front portion of the drive track  50 . It is this upward motion of the track tensioning apparatus  76  that compensates for any changes in the outer configuration of the track  50  due to the movement of the raised idler wheels  38  while the snowmobile  10  is in motion. 
     FIGS. 4 and 5 illustrate the method of construction of the rear suspension spring  50  in both the prior art (FIG. 4) and its configuration when used with the spring tensioning device  62  (FIG.  5 ). In the prior art, the rear suspension spring  40  is attached to the raised idler axle  60  inside of the raised idler wheel  38 . From this configuration, the spring arm  56  component of the rear suspension spring  40  extends forward and downward to the point at which it is attached to the slide rail  34  by means of the spring arm retainer  58 . The attachment of the spring arm retainer  58  to the slide rail  34  is accomplished in a manner so that it is held in a fixed position. This means that any change in attitude in the rear suspension spring  40  in relation to the slide rail and spring arm retainer  58  is compensated for in the length of the spring arm  56  and not by the spring arm retainer  58 . 
     With the use of the spring tensioning device  62  in conjunction with the rear suspension spring  40 , the basic configuration of the rear suspension spring  40  is the same as with the prior art with the exception that the present invention is attached to the slide rail  34  through the use of the block housing  72  in a position so that it can interact with the spring arm  56 . This interaction with the spring arm  56  is the pivotal point of the invention as the placement of the tensioning block  64  serves to limit the travel of the spring arm  56  as the rear suspension spring  40  changes its orientation in relation to the slide rail  34  in response to terrain anomalies encountered by the moving snowmobile  10 . 
     The manner in which the tensioning block  64  changes the action of the spring arm is illustrated in FIG. 6 (which shows the action of the spring arm  56  in the prior art without the use of the present invention) and in FIG. 7 (which shows the action of the spring arm  56  with the use of the present invention). As a vertical force is placed on the rear suspension  30  of a snowmobile  10  it causes a spring compression motion as indicated by the arrow labeled as  68 . This action causes the spring arm to load at a specific point which is illustrated in both FIGS. 6 and 7. 
     Without the use of the present invention, the load point  66  is relatively close to the point at which the spring arm  56  is joined to the spring arm retainer  58 . This creates a relatively soft spring arm  56  as the point of origin of the spring load  68  is comparatively a long distance from the point at which the spring arm retainer  58  is fixedly attached. This configuration creates a long lever which requires a relatively small amount of force to flex the load point  66  of the spring arm  56  which in turn creates a rear suspension  30  with a softer feel and, thus, a snowmobile  10  with a soft ride quality. 
     Conversely, when the present invention is used with a spring arm  56  and spring arm retainer  58 , it effectively moves the load point of the spring arm closer to the point of origin of the spring load  68 . This creates a relatively hard or stiff spring arm  56  as the point of origin of the spring load  68  is comparatively a short distance from the point at which the spring arm retainer  58  is fixedly attached. This configuration creates a short lever which requires a relatively large amount of force to flex the load point  66  of the spring arm  56  which in turn creates a rear suspension  30  with a harder or stiffer feel and, thus, a snowmobile  10  with a hard ride quality. The advantage of a snowmobile  10  which has a stiffer rear suspension  30  is that it will be more responsive and provide a greater degree of operator control which is especially desirable in high performance machines. 
     The manner of construction of the present invention is further illustrated in FIGS. 8,  9 , and  10 . The spring tensioning device  62  consists primarily of a tensioning block  64  which is located within the block housing  72  and attached therein by the use of the two attachment holes that are drilled through its side surfaces. This entire configuration is mounted to the rear suspension  30  of a snowmobile  10  in a location so that the spring arm  56  passes through the open ended block housing  72  just above the tensioning block  64 . This manner of construction allows the rear suspension to operate normally until enough lateral force has been applied for the spring arm to engage the tensioning block  64 . 
     The tensioning block contains an upper cambered tensioning surface  70  which is the portion of the invention that is used to engage the spring arm  56  of the rear suspension  30 . The cambered surface of the tensioning block  64  allows the spring arm  56  to contact it in a variety of different places that progress further away from the point of attachment at the spring arm retainer  58  depending upon the amount of lateral force that is placed on the rear suspension  30 . Thus, as the amount of lateral force applied to the spring arm  56  is increased, the load point  66  moves closer to the point of origin for the spring load  68  which has the effect of progressively stiffening the rear suspension  30 . Effectively, this means that the rougher and more demanding the terrain over which the snowmobile  10  is being driven, the stiffer the rear suspension will be and, therefore, the more control the operator will have. 
     Additionally, two further alternative embodiments of the present invention are illustrated in FIGS. 11 and 12. FIG. 11 illustrates an alternative embodiment of the spring tensioning device  62  of the present invention in which the spring arm retainer  58  of the previous embodiment has been removed and the most forward portion of the spring arm  56  is left unfixed. In this embodiment, the downward tension placed on the spring arm  56  supplies enough force to keep the spring arm  56  in contact with the tensioning surface  70  of the tensioning block  64  during all phases of the operation of the invention. Also, the tensioning block  64  in this embodiment has been moved forward, in relation to the vehicle as a whole, within the block housing  72 . This design feature serves to further alter the loading characteristic of the spring arm  56 , which also enhances the handling characteristics of the vehicle with which the invention is used. 
     Finally, FIG. 12 illustrates an alternative embodiment of the tensioning block  64  component of the present invention. In this embodiment, the upper tensioning surface  70  is equipped with a shallow concave spring arm retainer groove  77  which extends along the length of the upper tensioning surface  70  and matches the outside diameter of the spring arm  56  in form and size. The purpose of the spring arm retainer groove  77  is to hold the spring arm  56  in the proper orientation along the upper tensioning surface  70  and it is especially useful when used in conjunction with the previously described embodiment in which the spring arm retainer  58  has been removed. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.