Tracked vehicle suspension
BACKGROUND OF THE INVENTION 
     This invention generally relates to track laying vehicles and more particularly to suspensions for tracked vehicles such as, for example, snowmobiles and the like. 
     In the suspension of tracked vehicles, bogie wheel as well as slide-type suspensions or combinations thereof, are generally well known and used in the industry. A bogie wheel suspension is costly by virtue of the number and complexity of mechanical parts and is an inefficient system in deep snow due to the high rolling resistance of the small bogie wheels. A slide suspension is less costly than the bogie wheel suspension and is more efficient in deep snow giving more support and stability to the vehicle, but it must have snow for a lubricant and for cooling of the rub surfaces between the slide rail and track. Therefore, it is not suitable for use on ice, hard-packed snow, or where dry ground conditions exist. Furthermore, the track must be configured with rub surfaces, such as for example, metal clips and the like, to lower the coefficient of friction between the track and the slide. Such modifications to the track naturally increase its cost. 
     These and other factors and influences have been limitations to the useful operational range of this type vehicle and it is, therefore, a primary object of the instant invention to provide a suspension for tracked vehicles that is operationally simple, easily adapted to presently designed vehicles and is not limited by a lack of snow or other lubrication or by the operating conditions. Still another object is to provide a suspension that allows for the use of a much simplified track having no requirement for embedded metal slide surfaces and the like. 
     In its broad aspect, the invention envisions a belt-type suspension wherein one or more belts are supported by one or more pulleys, which belt or belts operate in conjunction with the vehicle track to hold the track to the ground as it rolls over the terrain. More specifically, the invention provides a belt-type suspension that is mounted in a relative position to the track, on its inside pathway between the track drive and adjusting pulleys and in engagement with the track to run at the same speed as the track. Belts of the type alluded to that may be applied to the suspension that is the subject of this invention are described in a copending application Ser. No. 944,485 filed concurrently herewith and entitled, Anti-Backbend Belts. The teaching of said application is incorporated by reference herein and the subject belts may be applied to the suspension of this invention when an anti-backbend characteristic is required, as will be more fully appreciated from the detailed description that follows. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view with portions broken away showing a tracked vehicle and the suspension that is the subject of this invention; 
     FIG. 2 is a top plan view with portions broken away of the suspension shown in FIG. 1; 
     FIG. 3 is a side elevational view with portions broken away of the belt suspension shown in FIG. 2; and 
     FIG. 4 is an enlarged elevational view of the rear portion of the suspension showing the belt and track pulley tension adjustment. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a tracked vehicle of the snowmobile type is generally indicated by reference numeral 10 and generally comprises a body 12 on a suspension 14 that carries a flexible track 16 driven by a motor 18. The vehicle normally also includes a front steering mechanism 20 controlled by the operator through handle grips 22. This invention is particularly directed to the suspension 14 that carries the vehicle body 12 and track 16 and, therefore, is not considered limited by the particular vehicle configuration shown in the drawing. The track 16 normally comprises a reinforced elastomeric belt having ground-engaging grousers 24 located on the outwardly facing surface and in a transverse orientation to the direction of travel of the track and drive lugs 26 on the inside surface thereof for engagement with a drive pulley 28 associated with the drive motor 18 through a conventional transmission (not shown). At the rearward end of the vehicle the track 16 is passed around pulleys 38 that are adjustably mounted for tension control of the track. 
     In accordance with this invention, the suspension 14 comprises one or more belts 30 mounted on a pair of pulleys 32, 34 on a framework 36 that provides mounting and cushioning means for the vehicle body 12. The framework 36 is positioned on the longitudinal axis of the vehicle and is positioned such that the belts 30 engage the snow track 16 along its bottom inside surface. Thus, it must be appreciated that the snow track 16 is driven by the motor 18 through a typical transmission and drive pulley 28 and engages a suspension belt 30 which rolls at the same speed as the track 16. 
     Referring to FIGS. 2 and 3, the suspension of this invention is generally indicated by reference numeral 40. Conventional snowmobiles generally utilize a single track 42 (shown in ghost lines) that is approximately 15 inches in width and is characterized by a plurality of grouser bars 24 on its outside surface. As clearly shown in FIG. 2, the suspension 40 may comprise two belts 30a and 30b in parallel aligned position with the longitudinal axis A--A of the track 42. 
     The framework 36 is generally rectangular having upper and lower horizontal braces 44 and 46, respectively, and a plurality of substantially vertical braces 48 and cross braces 49 positioned within the framework where needed for the strength integrity of the suspension. The framework 36 carries a front axle 50 and a rear axle 52, the front axle supporting suspension belt pulleys 32a and 32b while the rear axle supports suspension belt pulleys 34a and 34b. Of course, the pulleys are all bearing or bushing-mounted following well known practice in the industry. As more clearly shown in FIG. 4, the rear axle 52 is horizontally adjustable within the framework 36 to provide tension adjustment of the suspension belts 30 and this adjustment is effected through at least one adjusting bolt 54 that is threaded through a vertical flange 56 that is welded to a base plate 58. The base plate 58 is rigidly attached to the framework by welding or the like. The rearward portion of the framework 36 also carries a yoke structure generally indicated by reference numeral 60 that supports the track pulleys 38a and 38b. The yoke is horizontally adjustable to provide tension control of the track 42 and this adjustment is effected through adjusting bolts 62 that are threaded through the rear axle 52 to abut a vertical flange 64a on a yoke-mounting plate 64 such as at 66 in FIGS. 2 and 4. The yoke-mounting plate 64 is secured to the base plate 58 by reason of bolts 68 that are mounted in slots 70 in the plate 64 such that by turning down the adjusting bolts 62 the yoke assembly 60 is moved rearwardly to increase the tension on the track 42. When the proper track tension is realized, the bolts 68 are tightened down to rigidly hold the plate 64 in place. 
     The vehicle body 12 is attached to the suspension 40 at two forward mounts 72 and 74 interconnected by a cross-member 73 and two rearward mounts 76 and 78 interconnected by a cross-member 77. The body attachments are made through conventional bushing mounts, and the forward bushing mounts 72, 74 are attached to the lower framework braces 46 through suspension springs 80. The spring rate of each spring 80 is adjustable by reason of connecting rods 82 in a well-recognized manner. In similar fashion, the rearward body mounts 76, 78 are connected to the framework lower braces 46 through suspension springs 84 which have their spring rate adjusted through rods 86. The rearward vehicle mounting assembly is further isolated from shock by virtue of a conventional shock absorber 90 that has its piston end 90a attached to the cross-member 77 while the piston rod end 90b is connected to a framework cross-brace 49 through mounting brackets 92. 
     As herebefore mentioned, the suspension is positioned on the inside pathway of the snowtrack 16 such that the suspension belts 30 engage the track on its bottom inside surface. The belts 30 may be any of the configurations described in Applicant&#39;s copending application or any other type of rubber, plastic or chain link belt which may be used to support the track in an anti-backbending mode. For example, the belts 30a and 30b shown in FIGS. 2 and 3 are a simple form of anti-backbend belt characterized in that the tension cords of the belt are located closest to the inside surface of the belt, which surface engages the pulleys 32 and 34. In this circumstance, the compression compound of the belt faces outwardly, comprises at least 50% of the total surface-to-surface thickness of the belt, and is siped to form blocks 30c of substantially imcompressible material such that the belts are sufficiently flexible to pass around the pulleys 32, 34 but when in the area between the pulleys and in a straightened condition, the blocks of incompressible material are in an end-to-end abutting relationship and resist a load force exerted in the direction of arrow 98. This is the direction of loading on the suspension belts by the track as it conforms to the terrain. In other configurations, to accomplish an anti-backbending characteristic, the belts 30 may have cut-out portions or notches that match the sequence and engage the drive lugs 26 on the inside surface of the track 16. In this circumstance, the engagement of the lugs with the suspension belt and the separation of the tension cords of the two results in a resistance to backbending and an anti-backbending characteristic is accomplished that provides support for the track and effects its conforming to the terrain over which it travels. 
     Further, and while the invention is shown and described with respect to the use of two belts 30a and 30b, it will become apparent to those skilled in the art that a single belt may be applied in a similar manner. For example, a single wider belt that possess an anti-backbend characteristic may be mounted centrally along the longitudinal axis of the framework 40 such as to engage and support the track along its central area. In this circumstance, the track pulley adjustment may be through a modified yoke wherein the adjusting bolts are positioned outside of the width of the suspension belt. 
     While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.