Abstract:
A tracked vehicle produces a pressure no more than 3 psi on the ground by increasing the number of contact points on the inner surface of the track. The stiffness of the track is also selected to minimize bowing between the idler wheels or rollers. The track is therefore kept substantially straight between the rollers so increase the efficiency associated with transferring power to track. The drive sprocket is positioned above the ground so as to eliminate complexity in the design and yet effectively transmit power to the tracks. Positioning the drive sprocket above ground also prevents derailing of the track. The track is also held in a constant state of tension on the driver sprocket and the roller. This too prevents derailment. The undercarriage of the vehicle includes torsion axles and sealed bearings to provide for a lower maintenance track. Components associated with the undercarriage do not require constant greasing and cleaning of the idler wheels. The track is beveled so that it does not rip up surfaces. The drive sprocket is provided with roller sleeves that accommodate the changes in the pitch line of an elastomeric flat track. The sprocket does not “scrub” the areas between the driving lugs. The drive sprocket includes a pair of scrapers and a pair of conical shields which provide self cleaning and which remove debris from the sprocket area.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a multi-surface vehicle, and more particularly to the suspension and drive mechanism associated with a multi-surface vehicle with a rubber track.  
         BACKGROUND OF THE INVENTION  
         [0002]    A variety of track driven vehicles have been around for many years. Tracked vehicles vary from 100 ton military tanks and bull-dozers to 300 pound snowmobiles. Track types vary from segmented steel tracks to one piece molded rubber tracks.  
           [0003]    One of the major design challenges with all types of tracks and vehicles is to find the most efficient way to transfer the torque of the drive mechanism to the track with minimum power loss. There are many torque transmission systems. The three most common torque transmission systems are an external drive, a friction drive and an internal drive. External drives include a sprocket with a fixed number of teeth around the circumference that drives against a rigid member attached to the track. The sprocket teeth protrude through the track to a point where the rigid members can not slip back under a heavy load. Friction drives include a wheel attached to the drive axle and drive against the inside surface of a track. The outside of the wheel and the inside of the track are typically made of resilient material such as rubber or other composites. The track tension must be extremely tight to prevent slippage. The track tension also results in power loss. Internal drive systems, also known as involute drives, have a track with drive lugs attached to the inside surface of the track. The drive lugs may be molded to the inside surface of a rubber track. The drive sprocket is made by attaching rigid drive teeth to a rigid radius wheel. The sprocket teeth drive against the internal drive lugs on the track.  
           [0004]    Internal drive systems are generally considered the most efficient drive for tracks made of elastomeric material such as rubber when the drive lugs and drive sprockets are properly matched. They are properly matched when the pitch diameter of the sprocket matches the pitch line of the track. Another way of determining whether they are properly matched is when the pitch diameter of the sprocket causes the drive teeth to match perfectly with the center to center distance between the track drive lugs. In practice, proper matching is difficult to achieve especially when using an elastomeric or rubber track. Tracks made of elastomeric materials are resilient. As a result, the elastomeric material stretches or contracts slightly depending on a number of factors. One of the more common factors that causes changes in the pitch length is the variation in the load applied to a track during operation of the multi-surface vehicle. The load on the track and on the internal lugs will be higher when the vehicle is pulling a log as compared to the load on the track applied to merely move the vehicle over terrain. The tracks may be loaded differently when turning. An outside track will typically be loaded to a higher degree when compared to an inside track. The pitch length of the track varies with the variations in the load applied to the track.  
           [0005]    Variations in the pitch length of the track results in a mismatch between the pitch length of the track and the pitch diameter of the sprocket. When using a sprocket having rigid drive teeth, the change in the pitch length along the track causes the sprocket teeth to “scrub in” or “scrub out” or both. In other words, the rigid tooth is rubbing between the individual drive lugs on the internal surface of the flat belt. This causes a loss in efficiency. Scrubbing in or out can result in extreme power loss and excessive wear on the track drive lugs and sprocket teeth.  
           [0006]    Another common problem with flat tracks such as those made from an elastomeric material is that foreign matter or sticky material builds up in the sprocket area. Metal tracks usually have openings through which at least some foreign matter may be passed. The buildup is worse on a flat track. When foreign matter builds up in the sprocket area the pitch diameter or the pitch line of the flat track is likely to change. This results in power loss and excessive wear. Rocks, sticks, grass, mud, snow and other materials may build up in the sprocket area.  
           [0007]    Military tanks and bull-dozers are two common vehicles featuring metal tracks. Metal tracks are typically mounted on drive wheels and idler wheels that are mounted on springs or suspension systems that allow the drive wheel to move slightly from a fixed position. The use of rollers on the track drive segments of a metal track reduces noise and reduces wear between the individual segments of the metal track. The springs or suspension associated with the idler wheels allows the metal track to accommodate obstacles encountered by the metal track. At the drive wheels, the springs also accommodate slight variations in pitch diameter.  
           [0008]    Metal tracked vehicles have many problems. One of the problems is that metal tracked vehicles are very heavy and tend to sink in and damage relatively soft surfaces. The pressure produced by a metal tracked vehicle is relatively high. For example, when a metal tracked vehicle operates in mud, the vehicle typically sinks to solid ground rather than passing over such a surface. The tracks also are tough on surfaces such as grass or lawns. The pressure produced by the metal track of a bull-dozer or a tank typically produces indentations in a surface. For example, if a bull-dozer passes over a residential lawn, the pressure is high enough to compact the earth and form a permanent indentation. A home owner would have to fill in the impressions with additional soil to fix the lawn. In addition, the metal tracks typically have square edges which dig into surfaces during turns. A turning bull-dozer would rec havoc with residential lawns. Metal tracks can also become derailed.  
           [0009]    Some tracked vehicles have used rubber tracks. Typically, designers of metal tracked vehicles carry over many of the design characteristics into flat track vehicles using elastomeric or rubber tracks. Many of the problems encountered with metal tracks are also encountered with rubber tracks. For example, many rubber track designs include a track mounted on drive wheels or sprockets which are spring mounted. The problem of matching the pitch line of the track to the pitch diameter of the sprocket is further exacerbated. The drive wheels do not maintain the track near a constant state of tension so the pitch line can fluctuate widely.  
           [0010]    In addition, the drive sprocket is positioned so that it in contact with the surface. Typically, the drive sprocket will be at the rear of the vehicle and positioned so that the track passes between the drive wheel and the ground. In such designs, the rear drive wheel has two jobs. The rear drive wheel drives the track and maintains the alignment of the track. When the rear drive wheel is on the ground, the two jobs the rear drive wheel is called on to do work against one another. When driven, the track tends to want to leave the drive wheel or “jump off the sprocket”. It is necessary to maintain alignment to prevent derailing. Rear drive wheels on the ground are more prone to derailing since the forces associated with doing the two jobs counteract one another. Another problem with rear drive wheels on the ground is that they tend to require additional complexity. Elongated gear boxes must be used to transfer power to these rear on the ground drive wheels.  
           [0011]    Another problem associated with flat elastomeric tracked vehicles is that there are few idler wheels that contact the ground. The track tends to bow between the idler wheels which results in a loss of traction. In addition, with fewer points on the ground and bowing between the wheels, the effective surface pressure at various points under the wheels is high. The tracked vehicle does not have an even pressure across the flat track. Still another problem is that these vehicles are high maintenance. Each individual wheel must be greased periodically. In addition, since the environment for use includes foreign matter such as dirt, the individual idler wheels tend to wear. Because of the high maintenance and cost, there is a tendency to use lesser numbers of wheels in various designs.  
           [0012]    As a result of high pressure per wheel, most designs of tracked vehicles using elastomeric or steel tracks are not environmentally friendly. Current designs still indent soft surfaces and tear up grass lands. In addition, the current vehicles are high maintenance. High maintenance is needed to assure that the components of the undercarriage do not prematurely wear.  
           [0013]    Thus, there is a need for a for a tracked vehicle that produces a low pressure on the surface and which is environmentally friendly. In addition, there is a need for a lower maintenance vehicle not prone to derailing the track. In addition, there is a need for a vehicle which has many contact points, and therefore has lower pressure per wheel, on the track as it passes over the surface. There is also a need for a vehicle which does not require constant greasing and cleaning of the wheels in contact with the track. There is also a need for a vehicle which places the drive sprocket off the ground so as to eliminate complexity in the design and yet effectively transmit power to the tracks. In addition, there is a need for a sprocket which will accommodate the changes in the pitch line of an elastomeric flat track. In addition, there is a need for a sprocket which will not “scrub” between the driving lugs. There is also a need for a sprocket which is self cleaning and which removes debris from the sprocket area to minimize problems associated with debris build up changing the pitch relationship between the sprocket and the flat track.  
         SUMMARY OF THE INVENTION  
         [0014]    A tracked vehicle produces a pressure no more than 3 psi on the ground and less than 190 pounds per contact point on the inner surface of the track. Multiple wheels across the width of the track eliminate bowing between the idler wheels or rollers. The track is therefore kept substantially straight across the rollers to increase the efficiency associated with transferring power to track. The drive sprocket is positioned above the ground so as to eliminate complexity in the design and yet effectively transmit power to the tracks. Positioning the drive sprocket above ground also prevents derailing of the track. The track is also held in a constant state of tension on the driver sprocket and the roller. This too prevents derailment. The undercarriage of the vehicle includes torsion axles and sealed bearings to provide for a lower maintenance track. Components associated with the undercarriage do not require constant greasing and cleaning of the idler wheels. The track is beveled so that it does not rip up surfaces. The drive sprocket is provided with roller sleeves that accommodate the changes in the pitch line of an elastomeric flat track. The sprocket does not “scrub” the areas between the driving lugs. The drive sprocket includes a pair of scrapers which provide self cleaning and which remove debris from the sprocket area.  
           [0015]    Advantageously, the vehicle will travel over soft surfaces without causing damage to the surface. In addition, unlike other vehicles, the vehicle sinks little in soft mud or snow. The resulting vehicle is very effective in transmitting power to the surface over which it passes. The vehicle requires very low maintenance since the bearings associated with the undercarriage are sealed. Other suspension units are simple and straightforward and require little or no maintenance. The vehicle also is less prone to track derailment.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The following detailed description of the preferred embodiments can best be understood when read in conjunction with the following drawings, in which:  
         [0017]    [0017]FIG. 1 is a side view of the multi-surface vehicle.  
         [0018]    [0018]FIG. 2 is perspective view of the undercarriage of the multi-surface vehicle.  
         [0019]    [0019]FIG. 3 is perspective view of the rubber track used with the multi-surface vehicle.  
         [0020]    [0020]FIG. 4 is a top view of the track showing the tread pattern.  
         [0021]    [0021]FIG. 5 is a cross-sectional view along line  5 - 5  in FIG. 4.  
         [0022]    [0022]FIG. 6 is a cross-sectional view along line  6 - 6  in FIG. 4 showing the idler wheels in phantom engaging the lugs of the track.  
         [0023]    [0023]FIG. 7 is an exploded perspective view showing multiple wheels attached to a single tubular axle having multiple wheels and sealed bearings.  
         [0024]    [0024]FIG. 8 is a perspective view of an axle  710  and the wheel plate.  
         [0025]    [0025]FIG. 9 is a perspective view of the drive sprocket which engages the drive lugs on the track and a scraper.  
         [0026]    [0026]FIG. 10 is a cross-sectional view showing the suspension unit, also called the rear torsion axle and swing joint.  
         [0027]    [0027]FIG. 11 is a partial perspective view of the undercarriage of the multi-surface vehicle as it engages an obstacle on the surface being traversed.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.  
         [0029]    [0029]FIG. 1 shows a perspective view of a multi-surface vehicle  100  on a surface  110 . The multi-surface vehicle  100  includes a frame  102  which carries an engine  120  such as an eighty horsepower, 4.5 liter John Deere PowerTech Diesel or a one hundred fifteen horsepower, 4.5 liter John Deere PowerTech Turbo Diesel. Both of these engines are available from John Deere and Company of Moline, Ill. The engine  120  powers a hydrostatic transmission which powers hydraulic drive motors with planetary gear boxes which eliminates additional chains and sprockets, thereby lessening the complexity and increasing the efficiency of the drive system. Two auxiliary pumps are used to power different accessories. As shown, the vehicle includes a loader/bucket accessory  130 . The engine  120  powers hydraulic pumps used to drive the hydraulic cylinders  132  and  134  for operation of the loader  130 . Other accessories, such as a blade or logging device may be substituted for the loader  130 . The vehicle  100  also includes an operator cab  140 . The operator cab is equipped with controls for controlling the loader  130  and for operating the multi-surface vehicle  100 . Attached to the frame  102  of the multi-surface vehicle  100  is an undercarriage  200 . A duplicate undercarriage is attached to the other side of the frame  102 . The undercarriage  200  is attached to the frame  102  via torsion axle type suspension units  1000 . The undercarriage  200  includes a drive sprocket  900  for driving a flat elastomeric or rubber track  300 . It should be noted that the drive sprocket  900  is positioned off the surface  110  so that it will stay clean for a longer life. The undercarriage  200  features multiple idler wheels  700  on axles (shown in FIG. 2) which engage the inner portion of the track  300  as the track engages the surface  110 . The wheels  700  are of a selected diameter and spaced so that track  300  will not bow between the contact points as the track travels over the surface  110 . The properties of the elastomeric track  300  also are selected so that the track has a sufficient stiffness so that the track  300  stays substantially straight between the contact points of the various idler wheels  700 . As shown in FIG. 1, eight different axles carrying wheels  700  are shown in contact with the track  300 . The wheels  700  provide multiple contact points which more evenly distribute the weight of the vehicle  100  and its load over the two tracks  300 . By keeping the individual tracks  300  substantially straight between the various contact points, the track  300  is also better able to grip the surface  110 .  
         [0030]    [0030]FIG. 2 is perspective view of one side of the undercarriage  200  of the multi-surface vehicle  100 . The As can be seen from this view, there are two frame members  202  and  204  which are part of the frame  102  of the vehicle  100 . The undercarriage  200  includes an undercarriage frame  210  which includes an upper portion  212  and a side skirt  214 . Attached to the upper portion  212  of the undercarriage frame  210  are cross members  220 ,  222 , and  224 . The cross members include a channel each of which accommodates a suspension unit or torsion axle  1000 . The torsion axle type suspension unit  1000 , which will be described in more detail in FIG. 9, provides an essentially maintenance free suspension member which does not require greasing or regular cleaning. Attached to each end of a cross member is a wheel plate  230  and a wheel plate  232 . The wheel plates for cross member  222  are described here. For the sake of clarity, the other wheel plates are not numbered. The other wheel plates are attached to cross members  220  and  224  are substantially identical to the wheel plates  230  and  232  attached to cross member  222 . Each wheel plate carries two wheel axles  710  and  712 . Each wheel axle carries three wheels  700 . The wheels  700  have a rubber or plastic outer annulus  702  attached to a central wheel  704  made of either plastic or metal. The outer annulus provides for enhanced contact with the flat track or belt. The wheels  700  attached to first end axle  714  and to second end axle  718  are fixed with respect to the undercarriage frame  210 . The end axles  714  and  718  are actually in a fixed position in a notch in the side skirt  214  of the undercarriage frame  210 .  
         [0031]    Also attached to the undercarriage frame  210  at a position above the end axle  718  is the drive sprocket  900 . The drive sprocket  900  is in a fixed position with respect to the undercarriage frame  210 . It should be noted that the wheels on the end axle  714 , the wheels on the end axle  718 , and the drive sprocket  900  are all in fixed position with respect to the undercarriage frame  210 . These particular wheels and the drive sprocket  900  define the outer limits of the flat track  300 . It is important to have a fixed position for these wheels and the drive sprocket  900  so that the elastomeric track  300  is held in a substantially constant state of tension. The pitch length of an elastomeric track, such as those made of rubber, will vary slightly. The pitch length will stretch slightly as variable loads are applied to the track  300 . The use of springs or other suspension means at these points will allow for the track to collapse inward too much when a load is placed on the track  300 . Springs or other suspension means, commonly used to keep metal tracks, will allow the elastomer tracks to dislodge or come off. Therefore, it is imperative that no springs or anything are used to maintain the tension on the track.  
         [0032]    As can be seen, the wheels  700  provide for a plurality of contact points onto the internal surface of the track. In fact the eight axles each having 3 wheels provide for a total of 24 contact points to the internal surface of the flat track  300 . The vehicle has a duplicate undercarriage on the other side of the vehicle. The end result is at any given time there is approximately 2,844 square inches in contact with the ground or surface  110 . Forty eight wheels or contact rollers spread the weight evenly over the two tracks  300  so that superior traction and flotation are achieved. There is also a minimal amount of force at each contact point. The ground pressure associated with the vehicle  100  is no more than 3 psi (pounds per square inch) which means that the vehicle has the capability to work on soft ground or lawns without forming ruts or compacting soil.  
         [0033]    Of course to keep the soil from compacting or forming ruts, the elastomeric track  300  is formed of a material which is stiff enough such that it will not bow between the contact points of the wheels  700 . This the track  300  substantially flat and in contact with the ground or surface  300 .  
         [0034]    [0034]FIG. 3 is perspective view of the elastomeric or rubber track  300  used with the multi-surface vehicle  100 . The track  300  has an outer surface  310  which has a tread pattern  312 . The track  300  also has an inner surface  320 . Attached or molded to the inner surface of the track  300  are a plurality of drive lugs  322 . The drive lugs  322  are arranged in two rows  330  and  332 . The spacing between the rows  330  and  332  is selected so that the width of the middle wheels on a three wheel axle fits between the first row  330  of drive lugs  322  and the second row  332  of drive lugs  322 . Typically approximately one-half inch of clearance is provided so that the track  300  can shift an appropriate amount during a turn or other operation. The outer wheels  700  fit between one row of lugs  322  and the outer edge of the track  300 . The spacing from one lug  322  to another within a row is selected so that the lugs  322  will properly engage the sprocket  900 . Proper engagement would match the pitch diameter of the drive sprocket  900  to the pitch line of the track  300 . Of course, this is difficult to achieve since there are different forces on the track  300  at various times.  
         [0035]    [0035]FIG. 4 is a top view of the outer surface  310  of a section of the track  300  showing the tread pattern  312 . The tread patten  312  includes a series of transverse grooves  340 ,  341 ,  342 ,  343 , and  344 . The tread pattern  312  also includes a first beveled edge  314  and a second beveled edge  316 . The beveled edges  314  and  316  allow some side-to-side movement which accommodates turns made with the elastomeric or rubber track  300 . The allowance of the side-to-side motion from turning makes for a very environmentally friendly track. Unlike square tracks that typically dig into the ground and produce track damage, the beveled edges  314  and  316  on the track  300  can slip over the ground during a turn to leave the terrain substantially undamaged. The transverse grooves  340 ,  341 ,  342 ,  343 , and  344  are at a selected spacing and at a selected depth so as to leave ribs between the grooves. The ribs formed between the grooves  340 ,  341 ,  342 ,  343 , and  344  are dimension so that after the track passes over the wheels  700  associated with the end axle  714  and into contact with the ground, the ribs close and grip the vegetation or the ground surface  110  for added traction.  
         [0036]    [0036]FIG. 5 is a cross-sectional view along line  5 - 5  in FIG. 4. Both the inner surface  320  and the outer surface  310  of the track are shown in this view. The track also includes stiffeners  350 ,  352 , and  354 . The stiffeners  350 ,  352  and  354  increase the stiffeners of the track  300  across the width of the track  300 . The stiffeners  350 ,  352  and  354  are fiberglass rods which are molded into the track. The stiffeners  350 ,  352  and  354  are placed in the wider ribs such as those formed between grooves  341  and  342 , and formed between grooves  343  and  344 . The driving lugs  322  are shown molded or attached to the inner surface  320  of the track  300 . The distance between the lugs  322 , depicted by the reference number  360  is selected so that the engaging portions of the drive sprocket  900  engages the portion of the inner surface  320  between adjacent lugs  322  in a row. Ideally, the “teeth” of the drive sprocket  322  would engage the lugs  322  with little or no backlash or extra spacing located between the lugs  322 . This is difficult to achieve given that the pitch of the elastomeric track  300  will stretch slightly as a function of the load placed on the track  300 .  
         [0037]    [0037]FIG. 6 is a cross-sectional view along line  6 - 6  in FIG. 4. The rollers or idler wheels  700  engaging the lugs of the track have been added in phantom to FIG. 6. As can be seen, the rollers or idler wheels  700  do not fit tightly with respect to the rows  330  and  332  of lugs  322 . This allows for slight movement of the track with respect to the wheels  700  attached to a single axle, such as axle  710  (shown in FIGS. 2 and 7). The rows  330  and  332  are spaced such that the wheels  700  of the undercarriage fit between the rows  330  and  332 . The drive lugs  322  thus prevent the track from dislodging or jumping off since the engaging drive lugs control or stop the side-to-side motion of the track  300 . The drive lugs  322  have beveled sides  323  and  324  which allow the beveled sides of the multiple wheels to butt up against the tracks. Another aspect of these driving lugs  322  is that the spacing on them allows the track some lateral movement. The lateral movement enhances the turnability of the vehicle  100 .  
         [0038]    One stiffener  350  is shown in FIG. 6. The stiffener  350  is molded into the track  300  and is a fiberglass rod positioned transverse to the path of travel. The transverse fiberglass rods strengthen the track. The fiberglass rod  350  terminates well short of the beveled edges  314  and  316  so as to prevent the stiffener  350  from releasing from the flat track  300 . On other flat tracks, the release of a fiberglass rod from the track was a precursor to track failure. As a result, the fiberglass rod  350  is stopped well short of the end of track  300  and then enveloped in five to seven layers of Kevlar or another tire cording material. This prevents the stiffener  350  from leaving the flat track  300  thereby forming a weak spot in the track.  
         [0039]    [0039]FIG. 7 is an exploded perspective view showing multiple flanges  720 ,  721 ,  722 , and  724  rotatably attached to a single tubular axle  710 . FIG. 8 shows an assembled axle and attached wheels. Now turning to FIGS. 7 and 8, the idler wheels or rollers  700  are attached to a the flanges  720 ,  721 ,  722  and  724 . There are two types of rollers or idler wheels  700 . The first type of roller or idler wheel  700  is an outside wheel  702  which fits one of the ends of the shaft  710 . The second type of roller or idler wheel  700  is an intermediate wheel  704 . The intermediate wheel  704  attaches to flanges  721  and  722  intermediate the two ends of the wheel shaft  710 . The intermediate wheel  704  comprises a first half  706  and a second half  708 . Each of the two halves  706  and  708  is split along a diameter of the wheel  704  to form two semicircular halves. The two semicircular halves  706  and  708  are bolted to the flange  722  on the axle  710  to form an intermediate wheel  704 . The outside wheels  702  and the intermediate wheel  704  form a circular plastic rim with a rubber outer diameter. The plastic rims are bolted to the flanges  720 ,  721 ,  722 , and  724 . The outside wheels are provided with an endcap  732  and an endcap  734 .  
         [0040]    The axle  710  is a hollow tubular element. The flanges  720 ,  722 , and  724  are attached to the hollow tubular element. The axle  710  or hollow tubular element is mounted on a shaft  730 . The shaft  730  has two ends which protrude from the ends of the hollow tubular axle  710 . The tubular axle  710  is rotatably attached to the shaft  730  by a first roller bearing set  750  and a second roller bearing set  752 . The entire inner portion of the axle is filled with oil or grease. The roller bearings  750  and  752  are both sealed bearings. The roller bearings  750  and  752  are provided with multiple seals so that a sealed bearing for all three wheels  700  (shown in FIG. 8) is formed. Use of a sealed bearing sharply reduces maintenance time and keeps the life of the bearings high. Including three rollers or idler wheels  700  on an axle  710  is less expensive to manufacture and also provides for a maintenance free part that lasts up to the life of the vehicle  100 . Each end is provided with three seals. The bearing has a first seal  760 , an annular plastic or rubber element that fits over one side of the bearings, which comes with the bearing set. A second seal  762  is positioned outside of the bearing set. A third seal  764  includes seven different seals in one. The third seal  764  has a tortuous path to prevent dirt from getting into the bearing or into the space between the axle  710  and the shaft  730 . If dirt or other contaminants get into the grease or the oil covering the bearing sets  750  and  752 , the life of the bearings will be shortened. However, dirt entering through the first seal  760 , the second seal  762  and the third seal  764  would have to pass through nine seals in order to get to the lubricant. The rollers in each of the bearing sets are in a cage. The roller cage and the bearings are submersed in the oil or grease found within the hollow tubular axle  710 .  
         [0041]    [0041]FIG. 8 shows the wheels  700  attached to the tubular axle  710 . The single shaft  730  is shown protruding from the sealed end of the tubular axle  710 . The shaft  730  extends beyond the endcap  734 . The shaft  730  includes a flat or keyway  740  that engages the wheel plate  230 . The wheel plate  230  includes an axle capture plate  231  which, when bolted to the wheel plate  230 , captures the axle  730 . Only one axle capture plate is shown in FIG. 8.  
         [0042]    [0042]FIG. 9 is a perspective view of the drive mechanism including the sprocket  900  which engages the drive lugs  322  on the track  300 . A first scraper  940  and a second scraper  942  are positioned near the inner diameter of the drive sprocket to clear the drive sprocket of debris that may otherwise accumulate. The driver sprocket  900  includes a central drive plate  902 . A number of tubular elements  904  are welded or otherwise attached to the central drive plate  902 . Attached to the central drive plate is a first annular unit  910  and a second annular unit  911 . As shown, the first annular unit  910  and a second annular unit  911  are attached to the central drive plate  902  using a long bolt or pin  912 . A set of spacers  914  and  916  are used to define the spatial relationships between the central drive plate  902  and the first annular unit  910  and the second annular unit  911 . Spacers  914  and  916  also carry roller sleeves  920  and  922 . The roller sleeves roll with respect to the spacers and with respect to the central drive plate  902 . In other words, the roller sleeves  920  and  922  fit between the drive plater  902  and the first annular unit  910 , and and between the drive plater  902  and the second annular unit  911 . The roller sleeves  920  and  922  are dimensioned and spaced so that they can engage the spaces between the drive lugs  322  on the inside portion  320  of the rubber or elastomeric track  300 . The roller sleeves are advantageous in that they are self adjusting. As the rubber track passes over a roller sleeve  920  and  922 , the pitch of the track  300  actually changes since the track is elastomeric. The roller sleeves accommodate such changes in pitch since they can roll between the drive lugs  322  rather than scrub the inner surface  320  between the drive lugs  322 . The end result is that the roller sleeves  920  and  922  also prevent chatter or extra vibrations at various speeds of the track.  
         [0043]    The drive plate  902  is attached to a sprocket driver  930 . The sprocket driver  930  is attached to portion of the frame of the vehicle and which includes a first scraper  940 . Also attached to the sprocket driver  930  is a hydraulic pump  932 . The hydraulic pump is attached to a source of hydraulic fluid. As hydraulic fluid is passed through the hydraulic pump  932  an output shaft  934  turns a planetary transmission system housed within the sprocket driver  930 . The central drive plate  902  is attached to an annular ridge  909  on the sprocket driver  930 . A second scraper  942  is attached a plate  907  which is attached to the undercarriage frame  210 . The sprocket driver  930  is attached to the plate  907 . There are a series seals and a cap  905  that prevents contamination of the sprocket driver  930  with dirt or other contaminants.  
         [0044]    The scrapers  940  and  942  force and remove the debris from the drive sprocket  900  and deposit it outside the drive sprocket  900 . This is critical since build up of debris within the sprocket will generally tend to change the pitch line of the track further. In addition, debris build up tends to act to dislodge or derail the track  300  from the drive sprocket  900 . The first scraper  940  and the second scraper  942  are cantilevered in toward the central drive plate  902  of the drive sprocket  900 . The second scraper  942  is cantilevered from another plate  907  that is typically attached to the undercarriage frame  210 . The first scraper  940  and the second scraper  942  are positioned near the inner diameter of the rollers  920  and  922  of the driver sprocket  900 . The scrapers  940  and  942  remove debris from the rollers and force the debris away from the sprocket driver  930  and the track  310 . The scrapers  940  and  942  are cantilevered and stick into the inside diameter of the driver sprocket  900 . Without the scrapers  940  and  942 , mud and other debris would accumulate and eventually lift the track  300  from the drive sprocket  900  to dislodge it from its operating position. The scrapers  940  and  942  are arcuate in shape. By dislodging mud and other debris from the driver sprocket  900  and placing the debris elsewhere, the scrapers  940  and  942  keep the driver sprocket  900  clean and clear of mud or other debris.  
         [0045]    The placement of the driver sprocket  900  enhances the ability of the track to stay on or not become dislodged, when compared to other vehicles. Now referring FIGS. 1, 2 and  9 , the driver sprocket  900  is placed off the ground or surface  110 , and toward the rear of the vehicle. Placing the driver sprocket above the ground prevents derailing for several reasons. The force of the driver sprocket  900  on the track tends to act to dislodge the track  300  from the driver sprocket  900 . When the driver is on the ground, not only is the driver sprocket driving the track  300 , it is also trying to maintain the alignment of the track. Thus, when the driver sprocket  900  is on the ground the two jobs counteract one another. In other words, the track is undergoing a force tending to dislodge or derail the track  300  while also being used to keep the track  300  aligned. Placing the driver sprocket  900  above the ground removes the function of maintaining alignment. The above ground driver sprocket&#39;s only function is to drive the track  300 . In addition, placing the driver sprocket  900  above ground and near the rear of the vehicle prevents dislodgment of the track  300 . In the elevated position, the driver sprocket applies a large force to the track at the last or rear axle carrying three roller or idler wheels  700 . The drive sprocket  900  pulls the track  300  into alignment with the wheels associated with the rear axle thereby keeping the track from being dislodged or coming off the rollers. It should be noted that dislodgement or track derailing is very costly and time consuming. Many times the track  300  is ruined or damaged due as a result of being dislodged.  
         [0046]    [0046]FIG. 10 is a cross-sectional view showing the axle mounting bracket  1010  which uses a several suspension units also called a torsion axle  1000 . Each torsion axle  1000  is comprised of a shell  1020  of a length of square tubular material. An inner bar  1030  having a substantially square cross section is positioned within the shell  1020 . Rubber cords  1040  are placed between the shell  1020  and the inner bar  1030 . The inner bar is placed on a diagonal with respect to the inside square cross section of the tubular material comprising the shell  1020 . Within the square tubular stock of the shell  1020 , there is fitted a square cross-sectional piece of rectangular stock referred to as the inner bar  1030 . The inner bar  1030  has a diagonal which is slightly less than the shortest dimension between the walls of the square tubular stock of the shell  1030 . The inner bar  1030  makes a diamond inside or is fitted within the square tubular stock so that it looks like a diamond within the perimeter of the square tubular stock shell  1020 . Positioned in the corners of the square tubular stock of the shell  1020  are four elastomeric cords or rubber cords  1040  which run the entire length of the shell  1020 .  
         [0047]    This arrangement provides for a stiff suspension unit or torsion axle that never requires lubrication and is therefore maintenance free and very reliable. The torsion axles  1000  are used throughout the undercarriage  200 . Turning briefly to FIG. 2, the x&#39;s shown in that figure depict attachments which use the torsion axle  1000 . For example, two wheel plates  230  and  232  carry two axles  710  and  712 . Each of the axles  710  and  712  have three wheels attached thereto. The wheel plates are attached to one another via a torsion axle  1000 . The torsion axle  1000  is a stiff suspension member used to attach two axles of three wheels a piece to the undercarriage frame  210 . The end result is an inexpensive, simple, and straightforward suspension member that is impervious to dirt, requires little or no maintenance, and which does not need to be sealed.  
         [0048]    [0048]FIG. 11 is a partial perspective view of the undercarriage  200  of the multi-surface vehicle  100  as it engages an obstacle  1100  on the surface  110  being traversed. The resulting amount of stiffness produced by the torsion axles  1000  allows the wheels to hug the ground  110  even when a rock or other obstacle  1100  is encountered so as to keep more tread  312  of the track  300  on the ground  110  at any given time. When an obstruction is not encountered, the torsion axle  1100  is sufficiently stiff so that the belt or rubber track maintains a substantially unbowed state between the wheels  700  associated with the undercarriage  200 .  
         [0049]    Advantageously, the vehicle will travel over soft surfaces without causing damage to the surface. In addition, unlike other vehicles, the vehicle sinks little in soft mud or snow. The resulting vehicle is very effective in transmitting power to the surface over which it passes. The vehicle requires very low maintenance since the bearings associated with the undercarriage are sealed. Other suspension units are simple and straightforward and require little or no maintenance. The vehicle also is less prone to track derailment.  
         [0050]    Although specific embodiments have been illustrated and described herein, it is appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.