Abstract:
An ATV endless track conversion using sprocket rings fit over each of the tires of the rear wheels which are inflated into a tight driving connection. A swing arm extension is pivoted to the ATV swing arm and has its own spring-shock absorber suspension in addition to the existing ATV spring-shock absorber. A return idler wheel set is mounted at the rear of the swing arm extension as well as two track band shaping wheel sets which engage track band upper and lower segments forward of the idler return wheel set to maintain the track band tension and footprint without substantial friction losses.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application U.S. Serial No. 60/274,047, filed Mar. 7, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns all terrain vehicles (ATV&#39;s) used for recreational and utility purposes. These vehicles are open topped with two large rear wheels having large tread tires powered to propel the vehicle over various terrain. 
     While providing effective traction in most conditions, wheeled propulsion has its limitations, such as are encountered in snow and mud. Endless tracks have been used for many years in various types of vehicles intended for off road travel, and provide more effective drive in snow and other difficult terrain conditions. For example, recreational snowmobiles use endless tracks for propulsion in snow. Snowmobiles lack the maneuverability of ATV&#39;s and the slider mounting used in snowmobiles relies on the presence of snow to reduce the high friction otherwise developed in the slider guide. 
     There have been prior attempts to convert ATVs to a track drive so as to allow their use in snowy conditions, and thus to provide an all season vehicle. 
     This conversion has in the past been attempted by installing endless tracks so as to be driven by the rear wheel drive. In the past, this has been done by installing sprockets on the rear wheel axle replacing the rear wheels, as shown in U.S. Pat. No. 6,095,275. The track band is circulated around idler wheels spaced to the rear from the sprockets. See also U.S. Pat. No. 4,699,229. The tracks must have a linear footprint as they circulate in order to produce an extended ground contact developing the improved traction enabled by use of the endless track drive. 
     A slider guide has been used in such conversions to guide and tension each track band, similar to that in use on conventional snowmobiles. As noted above, there is a high friction loss created in the slide assembly when not used in snow, which reduces the horsepower available to drive the track bands, adversely affecting the performance of the vehicle. The use of heavy sprockets replacing the wheels and tires adds to the time and cost of carrying out the conversion. 
     U.S. Pat. No. 4,635,740 shows an ATV conversion in which the tracks are directly driven by the rear tires, but such engagement is not effective at high speeds and is subject to slippage in snow or mud. An auxiliary set of wheels and tires is also used in lieu of the slider assembly, but this is a costly alternative. 
     It is an object of the present invention to provide a low cost ATV track conversion which maximizes the performance of the vehicle by providing a track drive and support which is efficient in not generating large frictional losses even when not operated in snow, and which drives, guides and supports the track bands effectively even at high speeds. 
     SUMMARY OF THE INVENTION 
     The above object and others which will be understood upon a reading of the following specification and claims are achieved by a conversion having several unique features. 
     First, the drive to a pair of endless tracks includes a lightweight molded plastic sprocket ring mounted to each existing rear tire of the ATV by being slipped over a partially deflated tire, with the tire then reinflated to be expanded to tightly engage the inside of the sprocket ring to be held in place on the tire very securely. The inside of each sprocket ring has pocket features interfit with the tire tread raised areas to establish a positive drive between each tire and the associated sprocket ring. 
     The exterior of each sprocket ring is formed with features engaged with corresponding raised engagement features on the inside of the associated endless track band. 
     According to a second unique feature of the present invention, each endless track band passes around one of a pair of idler wheel assemblies supported on an auxiliary axle housing mounted to the rear of the ATV drive axle by a swing arm extension pivotally attached to the end of the ATV swing arm which mounts the rear wheel drive axle. 
     Each idler wheel assembly includes an angled swing link pivoted on a stub shaft projecting from a respective end of the auxiliary axle housing and coupled to a torsion spring in the auxiliary axle assembly. The idler wheel assembly includes a pair of sets of return idler wheels mounted on one arm of the angled link around which the associated endless track band is circulated to define the rearmost extent of the track band, and passing around the associated sprocket ring at the forward end of the track band. 
     Two sets of track shape defining wheels are also included in each idler wheel assembly, a lower set supported on the other arm of the link forward of the return idler wheel set and engaging the inside of the lower segment of the track band. The other track shaping defining wheel set is supported on a pivoted link spring urged to swing up from the angled link so that the second set of track shape defining wheels engages the inside of the upper, return segment of the associated track band. 
     The swing arm extension itself has a spring-shock absorber unit attached at one end thereto, connected to the ATV swing arm to create an independent suspension for the idler wheel assemblies which augments the main ATV suspension, normally including the swing arm and an ATV spring and shock absorber unit. The provision of an auxiliary track-idler wheel suspension is a third unique feature of the track conversion according to the invention, allowing the track to be held in proper contact with the ground even at high speeds. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational outline view of an ATV with a detailed view of the track conversion according to the present invention with front ski replacements shown for the original front wheels, shown in phantom lines. 
     FIG. 2 is a downward perspective fragmentary view from one side of an ATV having the track conversion according to the invention but with the track bands removed. 
     FIG. 3 is a fragmentary perspective view of rear portions of the ATV track conversion according to the present invention. 
     FIG. 4 is a plan view in partial section of the track conversion components and the associated components of the ATV. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     Referring to FIG. 1, an ATV vehicle  10  is shown in outline, equipped with a track conversion  12  which incorporates the original rear wheels  14  (with the tires). Since this conversion may be intended for when the ATV is used in snow, the front wheels  16  (shown in phantom lines) may be replaced with skis  18  as are used with snowmobiles. 
     The track conversion includes a pair of endless track bands  20  each driven by a respective rear wheel around which the track band  20  passes, which also passes around an associated one of a pair of idler wheel assemblies  22  to the rear of the rear wheels  14 . The idler wheel assemblies  22  are both supported on a swing arm extension  24  trailing and pivotally mounted to the rear end of the existing ATV swing arm  26  which mounts the rear wheel axle  28  to allow movement thereof in the manner known in the art. 
     The swing arm extension  24  has a lower tongue  30  which is pivotally mounted to the trailing end of the swing arm  26 . The pivotal attachment of the swing arm extension  24  to the ATV swing arm  26  varies in its details with the particular ATV vehicle. The rear wheel drive axle  28  are driven by a chain  32  and sprocket  34  (FIG.  2 ). The ATV axle housing  36  normally is adjustably mounted to the swing arm  26  to enable tightening the chain  32 , and the particular pivotal attachment  38  of the tongue  30  for a given vehicle must be designed to not interfere with the adjustment movement of the ATV axle housing  36 . 
     A combination shock absorber-spring  40  is connected at one end to a clevis  42  projecting up over the tongue  30  of the swing arm extension  24  and at the other end to the swing arm  26  at a point located to the rear of the ATV swing arm combination spring-shock absorber  44 . 
     The swing arm extension  24  also includes a pair of rearwardly extending members  46 , the ends of which hold jaw brackets  54  which in turn adjustably receive an auxiliary axle housing  48 . 
     A pair of stabilizer rods  50 a each connected at their forward and to a respective ball bearing  52  received on a respective segment of the rear wheel drive axle  28  and at their rear end to the auxiliary axle housing  48 . The stabilizer rods  50  reinforce and stabilize the positioning of the auxiliary axle housing  48  with respect to the drive axle  28 . 
     The position of auxiliary axle housing  48  may be adjusted within receiving jaw brackets  54 , with a threaded end  58  on each rod stabilizer  50  allowing tensioning of the track bands  20  (adjusting bolts  56  shown in FIG.  4 ). 
     In order to create a positive drive to the endless track bands  20 , a pair of sprocket rings  60  are provided installed on each tire  14  by partially deflating the same and slipping a sprocket ring  60  over the tire  14  and reinflating the same. The sprocket rings  60  are preferably molded using a high strength material such as ultra high molecular weight plastic (UHMW). 
     The interior of each of the sprocket rings  60  are formed with axially extending features  62  which are located so as to be engaged with the particular tire tread features  64  (FIG. 2) of the ATV being converted to insure a positive connection. The exterior of the sprocket rings  60  is also formed with axial features  66  configured and spaced to define pockets  69  receiving the inner drive features  68  of the associated endless track band  20 . 
     The endless track bands  20  are of the same type as have previously been used in snowmobiles, and have molded exterior cleats  70  to gain better traction in snow, mud, etc. 
     The idler wheel assemblies  22  define the shape of the endless track bands  20  as the bands circulate as the ATV traverses the terrain. A main idler wheel set  72  is included, located rearmost from the wheels  14 , and the associated track band  20  passes around the same in returning to the sprocket ring  60 . The return idler wheel set  72  may include two spaced pairs of wheels  74 ,  76  which each straddle the row of outermost features  68 A,  68 B on the bands  20  as shown in FIG. 3, and are rotatably supported on an axle  78  carried on one set of arms  80  on angled links  82 . This straddling engagement tends to prevent the lose of a track band  20 . 
     The angled links  82  are fixed to rotate with stub axles  84  projecting from a respective end of housing  48 . The stub axles  84  are bonded to an elastomeric mass contained within square cavities in housing  48  covered with plates  86  to be prevented from rotating. This creates a torsional spring acting to generate a restoring torque while allowing wind up of the links  82  and swinging of the arms  80 . 
     A lower shape band defining wheel set  88  is located forward of return wheel set  72 , rotatably supported by an axle  89  on second arm  90  of each of the angled links  82  the return idler wheel set  72 . 
     The lower band shape defining wheel set  88  is swung on the links  82  as the return idler wheel set  72  is swung. An axle shaft  90  provides rotational support for the individual wheels  92  in the set  88 . The wheels  92  may be received between respective rows of track features  68 . 
     A set  94  of upper track band shape defining wheels  100  is supported on a pair of upwardly angled arms  96  freely swingable on the shafts  84 . A spring  98  is mounted to urge the arms  96  to swing up and force wheel set  94  into engagement with the inside of the associated track band  20 . 
     The wheel set  94  comprises a pair of closely spaced wheels  100  supported on either end of an axle  102 . 
     The wheels  100  may also run between the rows of features  68  on the inside of the track band  20  to help the retention of the track bands  20  on the vehicle. 
     The wheels of each set  74 ,  88 , and  94  are of a light weight construction commonly used to support snowmobile tracks. 
     As the terrain varies, the return idler wheel set  72  may lift up, allowing the links  82  to rotate counterclockwise, causing wheel set  88  to push down into the track band  20 , while wheel set  94  rotates down, the net effect to keep the track band  20  taut and its shape roughly triangular and to maintain tension. 
     If the return idler wheel set  88  moves up, the wheel set moves down and wheel set  94  moves up. 
     Thus, the three wheel sets  72 ,  88 ,  94  arranged in a triangle insure that the extended track footprint on the surface is maintained as the ATV traverses any type of terrain, and the tension of track bands  20  is maintained despite up and down motion of the return wheel set  22 . 
     The idler wheel assembly  22  has its own suspension acting independently of the ATV suspension which establishes superior performance. The swing arm extension  24  can swing up against the resistance of the combination spring-shock absorber  40 , and this does not offset the ability of the rear wheel  14  to swing up to accommodate the dynamics of the ATV as it travels at high speeds across rough terrain. 
     The frictional losses are minimal even when the ATV is not being driven in snow, to provide high performance over all types of terrain and conditions. The track bands  20  are securely retained and positively driven to allow operation at high speeds.