Abstract:
A suspension system for a tracked vehicle providing a wide range of performance characteristics via a user-adjustable overload spring assembly which engages a rear suspension element. An optimum spring force can depend on the both operator characteristics and local operating conditions. A user is afforded the ability to adjust a rear suspension system to provide desired ride characteristics. A suspension system including a movable stop to define a mechanical relation between a rear suspension arm and a front suspension arm is also disclosed.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. Pat. No. 7,533,750, which claimed priority from U.S. Provisional Application No. 60/721,296, filed on Sep. 28, 2005, the disclosure of each being hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to snowmobiles and more particularly to suspension systems for snowmobiles providing for efficient reconfiguration based on anticipated load conditions. 
       BACKGROUND OF THE INVENTION 
       [0003]    Performance characteristics of snowmobiles, including ride comfort and weight balance, depend upon a variety of systems and components, including the snowmobile suspension. Modern snowmobile suspensions typically include two systems, a front suspension system for the skis and a rear suspension system for the track. 
         [0004]    The rear suspension of a snowmobile supports an endless track driven by the snowmobile engine to propel the machine. The track is supported beneath the vehicle chassis by a suspension that is designed to provide proper weight balance and ride comfort by absorbing some of shock as the snowmobile traverses uneven terrain. Most modern snowmobiles utilize a slide rail suspension which incorporates a slide rail along with several idler wheels to support the track. The slide rail typically is suspended beneath the chassis by two or more suspension arms, each arm being attached at its upper end to the chassis of the snowmobile and attached at its lower end to the slide rail. The mechanical linkage of the slide rail to the suspension arms and to the snowmobile chassis typically is provided with springs and one or more shock absorbers, the springs being loaded to urge the slide rails downwardly away from the snowmobile chassis, and the shocks providing dampening forces for improved ride comfort. 
         [0005]    A variety of configurations of suspension arms, springs, shocks, and shock rods have been utilized to alter the characteristics and feel of the ride given by a particular suspension system. U.S. Pat. No. 5,265,692 shows a snowmobile track suspension having a pair of generally parallel suspension arms connecting the slide rail to the snowmobile chassis. The lower end of the rear suspension arm has a pivot mount that is movable longitudinally of the slide rail. When this pivot is located at its forward most portion of longitudinal movement (i.e., at the forward end of a longitudinal slot), the suspension arms form a parallelogram with the snowmobile chassis and the slide rail so that upward movement of the front suspension arm is transmitted through the slide rail to the rear suspension arm, causing the slide rail to move upward in an orientation that is generally parallel to the snowmobile chassis. Thus, the front end of the slide rail cannot move higher than the back end of the slide rail. The longitudinal slot into which the lower end of the rear suspension arm is pivotally mounted permits the back end of these slide rails to move higher than the front end of the rails. 
         [0006]    In light of the varying characteristics that can be built into a suspension system, a variety of competing suspension systems have been made commercially available, and different types of suspension systems commonly are employed on different types of machines, depending upon their primary usage (e.g., racing, touring, etc.). A need remains for an adjustable suspension system adaptable to perform across a variety of terrain and under diverse conditions. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention relates to a suspension system for a snowmobile that is adjustable by the rider to match the riding conditions and desired performance characteristics. In one embodiment, a system includes a slide rail for engagement with a lower portion of the snowmobile track and suspension arms mounted to the snowmobile chassis and the slide rail. Shocks and springs are provided for urging the slide frame downwardly away from the chassis. The front suspension arms have pivot connections at both ends, one end connected to the snowmobile chassis and the other end connected to the slide frame. The rear suspension arms are pivotally connected to the snowmobile chassis at upper ends and include a pivot connection at lower ends to the slide frame to permit some longitudinal movement of the lower end of the rear suspension arms with respect to the slide frame. An overload assembly provides an additional force tending to bias the slide rail away from the chassis. The overload force is applied at a location of the rear suspension arm between the upper and lower ends thereof. The position of the applied spring force can be user-adjusted, such as via a movable transfer block mechanism as further described hereinafter in order to modify performance characteristics of the snowmobile. 
         [0008]    Benefits of a suspension incorporating one or more of the present inventions include: improved comfort; controlled machine attitude across a variety of operation speeds and conditions; and minimization of the change or variability of track tension across a variety of operational conditions. 
         [0009]    One object of the present invention is the application of an overload force to a rear suspension arm at a location between the upper end and the lower end thereof. 
         [0010]    Another object of the present invention is efficient user adjustment of the location of overload force application to control the force level transferred to the rear suspension arm. 
         [0011]    Another object of the present invention is the application of a helical spring to provide the overload spring force. In one embodiment, the helical spring has an elongated spring arm for transferring the overload spring forces to the rear suspension arm. 
         [0012]    Yet another object of the invention is the provision of a user-adjustable assembly for controlling overload force to a rear suspension arm. Suspension characteristics of the machine can be adjusted by changing spring force and/or transfer locations. In one embodiment of the present invention, a movable transfer block capable of sliding along the rear suspension arm is used to change the location of spring force transfer. A plurality of spaced apertures along the rear suspension arm provides a plurality of different positions for coupling the transfer block to the rear suspension arm, thereby providing an operator with a plurality of different suspension performance characteristics. An operator-accessible pin provides for efficient repositioning of the transfer block between locations along the rear suspension arm. In another embodiment of the invention, an overload spring force is applied at an upper extent of the rear suspension arms. An overload arm provides an overload force which is transferred to an rear suspension arm axle or directly to a rear suspension arm. 
         [0013]    Yet another object of the present invention is the provision of a control means for selectively controlling a degree of mechanical coupling between rear and front suspension arms during various load conditions. 
         [0014]    Yet another object of the present invention is the provision of a user-adjusted control means which provides a movable stop at different distances relative to ends of the rear suspension arms. Depending on the particular position of the movable stop, the degree of mechanical coupling between the front and rear suspension arms can be effectively controlled. 
         [0015]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
           [0017]      FIG. 1  is an illustration of a snowmobile in accordance with the present application. 
           [0018]      FIG. 2  illustrates a portion of the snowmobile of  FIG. 1  including components of a rear suspension of the machine of  FIG. 1 . 
           [0019]      FIG. 3  is an illustration of a portion of the rear suspension of the snowmobile of  FIG. 1  shown in assembled and exploded format. 
           [0020]      FIGS. 4-7  are illustrations of a portion of the rear suspension of  FIG. 1 . 
           [0021]      FIG. 8  illustrates components of the rear suspension in a compressed state. 
           [0022]      FIG. 9  illustrates components of the rear suspension in a fully compressed state. 
           [0023]      FIGS. 10 and 11  illustrate another embodiment of a rear suspension in accordance with the present invention. 
           [0024]      FIG. 12-14  illustrate portions of a rear suspension of a snowmobile. 
           [0025]      FIG. 15  is a side elevational view of another embodiment of a suspension system of a snowmobile in accordance with the present invention. 
           [0026]      FIG. 16  is an assembly drawing illustrating portions of the rear suspension of  FIG. 15 . 
           [0027]      FIG. 17  is a depiction of the suspension assembly of  FIG. 15  as under a fully loaded condition. 
           [0028]      FIG. 18  is a perspective view of the suspension assembly of  FIG. 15 . 
           [0029]      FIG. 19  is a side elevational view of another embodiment of a suspension system in accordance with the present invention. 
           [0030]      FIG. 20  is a perspective view of elements of a control means within the suspension system of  FIG. 19 . 
           [0031]      FIGS. 21-23  are perspective views of the control means of  FIG. 20  shown under different operating orientations. 
           [0032]      FIGS. 24-25  are depictions of the suspension system of  FIG. 15  under certain load conditions. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Applicant has found that prior art suspension systems appear optimized for certain conditions, but perform less optimally in other conditions. For example, in relatively deep powder, it may be particularly desirable to permit the front end of the slide rail suspension to move higher than the rear of the suspension, making it somewhat easier for the snowmobile track to plane out or rise above the powdery snow. Similarly, deep powder handling and performance are related to the degree to which the back end of the slide rails is permitted to rise above the front end of the slide rails (or, in other words, the extent to which the machine is permitted to “rock backwards” on the suspension). 
         [0034]      FIGS. 1-14  depict portions of a snowmobile  10  having a rear suspension system for supporting the machine and for defining the path of the track  12  which propels the machine across the snow. Although the invention can be utilized in connection with a variety of rear suspension configurations, the invention will be described in the context of a particular preferred rear suspension illustrated in the drawings. Such a suspension includes a front suspension arm  14  and a rear suspension arm  16 , each arm extending downwardly and rearwardly from pivot connections to the snowmobile frame or chassis (often referred to as the “tunnel”). The lower end of each such arm  14 ,  16  is secured, either directly or indirectly, to the slide rail  30 , beneath which the track slides. As the snowmobile tunnel obscures the rear suspension,  FIGS. 2-14  depict the suspension elements as removed from the machine  10 . 
         [0035]    Springs and shock absorbers  31  are provided to urge the slide rail  30  down and away from the snowmobile tunnel. Springs and shocks  31  act to control the relative movement of the suspension with respect to the chassis as the snowmobile moves over terrain of varying contours. Preferably, the rear suspension arm  16  is centrally positioned between the pair of rear shock absorbers  31  as shown in  FIG. 3 . The relative lengths and orientations of the suspension arms  14  and  16  also control the movement and orientation of the suspension as it is compressed upwardly toward the chassis. 
         [0036]    Shock absorbers  31  are connected between upper axle  34  and slide rail  30 . Shocks  31  include shock stem  82  attached to an upper shock mount  81 . Shock mount  81  is retained upon upper axle  34  by a journal bearing, etc. and is generally free to rotate relative to upper axle  34 . A plurality of spacers  84  position the upper shock mount upon axle  34 . Shocks  31  compress and retract in a direction of elongation  85  which is aligned to generally intersect the center axis of axle  34 . Shocks  31  include shock stems  82  which are aligned in the direction of elongation  85  so that shock stems  82  are aligned to generally intersect the center of axle  34 . In comparison, the shock center of typical prior art suspensions is offset relative to the axle  34  as shown in  FIG. 16 . Similarly, the front shock of the suspension system of  FIG. 16  is offset relative to the front axle. 
         [0037]    Referring to  FIGS. 2-5 , upper end  32  of rear arm  16  is pivotally connected to the snowmobile chassis via upper axle  34 . The lower end of arm  16  is connected to a pair of lower pivot arms  38 , which in turn are pivotally connected to slide rail  30 . The linkage of arm  16  with pivot arms  38  permits the front of the slide rail  30  to rise substantially independently of the rear portion of the slide rail. A pivot axis  36  is generally defined as the center of stub shaft  37 . The lower ends of pivot arms  38  are pivotably couple to the slide rail  30  via shaft  39 . Upper axle  34  also carries a pair of upper idler wheels  90 . Rear idler wheels  91  are carried on the slide rail  30 . 
         [0038]    Referring to  FIGS. 5-9 , the suspension system includes an overload spring  40  which provides an overload spring force to the rear suspension arm tending to bias the rear suspension arm away from the machine chassis. Overload spring  40  is shown as a helical coil spring connected to the slide rail  30  by a shaft  42  and bearing  44  and including a pair of extended spring arms  46 ,  48 . A portion of arm  46  is received within and retained by a retainer  50  which is connected to stub shaft  37 . Arm  46  may slide into and out of an aperture  51  of retainer  50  during machine operation. Retainer  50  is generally freely journaled about stub shaft  37 . Another embodiment of spring retainer  50  is illustrated in  FIGS. 11 and 12 . In the embodiment of  FIGS. 11 and 12 , spring retainer  50  has a plurality of apertures  51   a ,  51   b ,  51   c  into which the portion  46  of spring arm  40  can be received. The spring force, F, applied to the rear suspension arm  16  can be varied by selecting a different aperture  51   a ,  51   b ,  51   c . Alternative embodiments of a spring retainer  50  would be appreciated by those of ordinary skill in the art. For example, a spring retainer  50  may have opposed apertures  51  having different distances away from the shaft  37  so that the spring force is varied depending on the particular aperture chosen. 
         [0039]    Referring again to  FIGS. 5-9 , arm  48  of overload spring  40  extends generally upwardly relative to the slide rail  30  and engages a transfer block  60  connected to the rear suspension arm  16 . Arm  48  of spring  40  engages the transfer block  60  in a sliding relationship and transfers an overload spring force, F, to the rear suspension arm  16  tending to bias the slide rail  30  away from the chassis. Transfer block  60  slides within a channel  64  defined within suspension arm  16 . A plurality of spaced apertures  66  are provided on suspension arm  16 . Apertures  66  are sized relative to an aperture  68  of transfer block  60  and a removable retaining pin  70  so that pin  70  is capable of retaining the transfer block  60  at an intermediate location between the upper end and lower end of rear suspension arm  16 . 
         [0040]      FIGS. 7 and 8  depict the rear suspension in a load-carrying condition.  FIG. 9  depicts the rear suspension at a fully compressed load-carrying condition. 
         [0041]      FIGS. 13 and 14  illustrated another embodiment of an upper shock adjuster, generally indicated as numeral  110 . Upper shock adjuster  110  includes a plate  112  having a plurality of stops  114  which are differently spaced from a center  114 . Stops  114  engage a pin  116  coupled to the chassis. Axle  34  engages the plate center  114  so that as plate  112  is rotated the distance between the axle  34  center and the pin  116  changes. A duplicate assembly would be located at the opposite end of axle  34  (not shown) and together the assemblies  110  would be used to position the axle  34  relative to the chassis. As the rear suspension arm  16  and shock absorbers  31  are directly coupled to axle  34 , the movement of axle  34  relative to chassis also adjusts the angular orientation of the rear suspension arm  16  and the shock absorbers  31  relative to the chassis. A threaded fastener (not shown) similar to the second threaded fastener  108  of  FIG. 12  can be used to secure the plate  112  to the chassis and temporarily fix the orientation of axle  34 , shock absorbers  31  and rear suspension arm  16  relative to the slide rail  30 . 
         [0042]    One aspect of the present invention is the application of an overload spring force to a downwardly angled rear suspension arm  16  at an intermediate location between the upper end and the lower end thereof. The operator is afforded efficient adjustment of the location of the overload spring force application by manipulation of a user-adjustable transfer block  60 . Upon removal of pin  70 , the transfer block  60  is capable of sliding along the rear suspension arm  16  during repositioning to change the location of spring force transfer. The use of a plurality of spaced apertures  66  along the rear suspension arm  16  provides a plurality of positions for coupling the transfer block  60  to the rear suspension arm  16 . Movement of the transfer block  60  along the rear suspension arm  16  effectively changes the level of spring force applied by the overload spring  40  to the rear suspension arm  16 . For example, the spring force will be greater when the transfer block  60  is closer to the spring  40  center and decrease as the transfer block  60  is positioned further away along the rear suspension arm  16 . 
         [0043]      FIGS. 15-19  illustrate another embodiment of a suspension system of the present invention. In this embodiment, the overload force is applied via a pivoting overload arm  400 . The overload force is transferred to the rear suspension arm only after a predetermined compression of the suspension system. 
         [0044]      FIG. 15  illustrates a side elevational view of aspects of a second embodiment of a snowmobile suspension system of the present invention. Slide rail  30  is movably coupled to a snowmobile chassis via front and rear suspension arms  140 ,  160 . Each of a pair of front suspension arms  140  is pivotally connected at one end to the chassis and at the other end to the slide rail  30 . A front shock  170  is connected between an upper end of front suspension arm  140  and slide rail  30 . A rear shock  172  is connected between slide rail  30  and a shock mount  398 . Shock  170 ,  172  may include coil-over springs (not shown for clarity purposes) or may be an air-shocks without a coil-over springs. 
         [0045]      FIG. 16  is an exploded view of portions of the suspension system of  FIG. 15 . Each of the pair of rear suspension arms  160  is pivotally connected at one end to the snowmobile chassis via an upper axle  340  and to a movable lower pivot arm  380 . Pivot arms  380  are pivotally connected to slide rail  30  via shaft  390  and to rear suspension arms  160  via upper shaft  392 . Covers  394 ,  396  are provided over shafts  392 ,  340 , respectively. Covers  394 ,  396  are preferably of resilient construction. Portions of an upper shock mount  398  are also connected near an upper end of the rear suspension arms  160 . 
         [0046]    Referring again to  FIG. 15  the suspension system includes an overload arm  400  for providing an overload force to the rear suspension arm assembly during certain operating conditions. Overload arm  400  is pivotally supported relative to slide rail  30  via a pivot  402  provided on arm support  404 . A shock assembly  406  is coupled between the overload arm  400  and the slide rail  30 . The overload arm  400  includes an engaging surface  410  which engages upper axle  340  during certain overload conditions. In a light load condition, the overload arm  400  is spaced away from the rear suspension arms  160  and not engaged by shaft  340 . As depicted by the phantom lines in  FIG. 15 , rear suspension arm  160  rotates during operation of the snowmobile and depending on the load conditions the overload arm  400  is engaged by the rear suspension arm assembly. Such contact between overload arm  400  and the rear suspension arm assembly causes rotation of the overload arm about pivot  402 . As rotation of the overload arm is controlled via shock assembly  406 , a force tending to resist motion between the chassis and the slide rail  30  is transferred via overload arm  400 . 
         [0047]      FIG. 17  is a side view of the suspension assembly of  FIG. 15  depicted in a fully loaded condition. As shown, the overload arm  400  has been rotated about its pivot  402  by engagement with the upper axle  340 /upper end of the rear suspension arms  160 . The cover  396  on upper axle  340  is in sliding contact with a flat portion of the engaging surface  410 . As depicted, the overload spring assembly  406  provides a force tending to resist collapse of the rear suspension assembly into the configuration of  FIG. 17 . 
         [0048]      FIG. 18  is a perspective view of a snowmobile having the suspension system of  FIG. 15 . The connection between the second shock assembly  31  and the slide rail  30  may be adjusted by repositioning a shaft  420  between different apertures  422  of the slide rail  30 . By changing the location of shaft  420 , the overload arm  400  is rotated about its pivot  402 . Adjustments to overall ride/performance characteristics of the snowmobile may be made by adjusting this connection between the slide rail  30  and shock assembly  406 . 
         [0049]      FIG. 18  also illustrates that the shock assembly  172  is positioned between the pair of rear suspension arms  160 . The suspension system of  FIG. 15  includes single rear shock assembly  172  coupled between the slide rail  30  and the rear suspension arm assembly. In other embodiments, two or more shock assemblies may be utilized to control movement of the rear suspension arm assembly. 
         [0050]    The shock assembly  406  provides a force tending to resist movement of the overload arm  400 . In one embodiment of the invention, the shock assembly  406  provides a controlled damping force tending to resist movement of the rear suspension arm assembly in a vertical direction. The shock assembly  406  controls movement of the rear suspension arm assembly during certain load conditions. Once the suspension system is released from a collapsed condition, the shock assembly  406  may not necessarily provide a force to the rear suspension arm  160  tending to restore the rear suspension arm assembly into a pre-load condition. That is, the shock assembly  172  may accelerate the rear suspension arm assembly away from contact with the overload arm  400 . In this regard, the overload arm and shock assembly  406  may provided a controlled application of forces tending to resist movement of the rear suspension arm assembly in one or both directions of collapse and return. 
         [0051]    In the embodiment of  FIGS. 15-18 , the overload arm  400  transfers an overload force tending to resist motion of the slide rail  30  toward the chassis. In this embodiment, the axle  340  is positioned at the end of rear suspension arms  160 . In other example, the overload force applied by overload arm  400  could be transferred away from the end of the rear suspension arms  160 . For example, the overload arm  400  could be extended to contact the rear suspension arms  160  between its upper and lower ends. While the contact between overload arm  400  and axle  340  includes a sliding motion, in alternative embodiments a roller can be attached to axle  340  allowing the roller to roll along the engaging surface  410  of overload arm  400 . 
         [0052]      FIG. 19  illustrates another embodiment of a suspension assembly further include an adjustable control means  500  for selectively coupling the front and rear suspension arms  160 ,  140  during certain operational load conditions. As described herein, contact is only made between the control means  500  and the rear suspension arm assembly during particular load operations. 
         [0053]      FIG. 20  is a perspective view of components of control means  500 . A shaft  502  is held between a pair of supports  504  which are coupled to the slide rail  30  via threaded fasteners (not shown) passing through apertures  506  of the supports  504 . Ends of shaft  502  are threaded and receive portions of threaded fasteners  510  which pass through an aperture  512  on adjuster plates  514  and through angled slot apertures  516  on the supports  504 . The adjuster plates  514  include a hex coupling  518  for engaging a standard hex socket or wrench during an adjustment procedure. The adjusters  514  include a plurality of stops  520  which are spaced with varying degrees relative to aperture  512 . Control means  500  includes a pair of pins  522  which engage stops  520 . A resilient cover  524  on shaft  502  engages portions of the rear suspension arm assembly during certain load conditions. Cover  524  prevents a hard contact between portions of the rear suspension arm assembly and shaft  502 . 
         [0054]    As a result of the stops  520 , the adjusters  514  have a tendency to rest when stops  520  are aligned with pins  522 . Thus, since the adjusters  514  tend to stop wherever a new stop  520  is encountered, this arranged can be termed “indexed.” An indexed mechanism is simpler to use and allows the user to visually confirm that the adjusters  514  have been correctly set. 
         [0055]      FIGS. 21-23  are perspective views of the adjustable control means  500  on a suspension assembly shown in different configurations whereby adjusters  514  have been rotated to move shaft  502  forward (toward the machine front). To move adjusters  514 , fasteners  510  are first loosened and hex coupling  518  is then engaged by a wrench or socket and adjusters  514  are rotated about the fasteners  510  into a desired position. The fasteners  510  are then secured to retain adjusters  514  in the desired position. 
         [0056]    While the control means  500  is preferably operated using a hex socket or wrench coupled to hex coupling  518 , it should be noted that it is also possible to rotate axle adjusters  514  by means of a remote mechanism. For example, the adjusters  514  could be rotated via a hydraulic system. Other systems involving pneumatic actuation or push-pull cables could be implemented to allow the rider to adjust the suspension while seated on the snowmobile. 
         [0057]      FIG. 24  depicts the suspension assembly and slide rail  30  after a forward-located force, F 1 , has collapsed the front suspension arm  140 . Under such a load condition, the control means  500  does not engage the rear suspension assembly and rear suspension arms  160  are free to move independently relative to the front suspension arms  140 . The suspension assembly would also assume this orientation under a loading condition with a generally centrally-located force. 
         [0058]      FIG. 25  depicts the suspension assembly and slide rail  30  after a rearward-located force, F 2 , has collapsed both the rear and front suspension arms  160 ,  140 . Such a force may be generated, for example, during machine acceleration, operating in a steep climb or across large moguls or other aggressive terrain. As force F 2  is applied, the rear suspension arms  160  rotate toward slide rail  30  and contact is made between the suspension arms  160  and the control means  500 . Further application of force, F 2 , results in a “coupling” of the rear suspension arms  160  with the front suspension arms  140 . As a result of this coupling effect, the front suspension arms  140  are forced to rotate toward the slide rail  30  as the rear suspension arms  160  are further loaded. Under such conditions, forces are transferred via the chassis tunnel causing the front suspension arms  140  to rotate toward the slide rail  30  as the rear suspension arms are further rotated under the load of force, F 2 . 
         [0059]      FIG. 26  is provided for comparison purposes and illustrates the suspension assembly of  FIG. 25  but without the control means  500 .  FIG. 25  depicts an operating condition where a force, F 2 , is applied to a rear portion of the assembly. Without the coupling effect provided by control means  500 , the front suspension arms  140  are not forcibly biased toward the slide rail  30  as depicted in  FIG. 25 . 
         [0060]    In many load conditions, contact is not made between control means  500  and the rear suspension assembly. That is control means  500  does not limit the range of motion of rear suspension arms  160 . However under some conditions, when contact is made between control means  500  and the rear suspension arm assembly, a coupling is generated between the rear suspension arms  160  and the front suspension arms  140 . The degree of inclination lower pivot arm  380  is allowed before the suspension becomes coupled is a function of overall suspension system geometry and the orientation of the adjustable control means  500 . By providing a selective control means  500 , the rider is able to efficiently adjust the snowmobile suspension based on anticipated operating conditions. 
         [0061]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.