Abstract:
A wheel and tire assembly for recreational vehicles, such as mountainboards, motorized carts and pedaled carts is provided. The tire comprises a tire made of substantially inelastic material that will not stretch under a load. Thus, the tire will flatten under a load to provide a high level of traction on soft and irregular surfaces, as well as on hard and flat surfaces. The tire includes protrusions on its inner diameter surface for securely engaging the wheel. The wheel includes a rim that supports the tire and includes protrusions for engaging the protrusions of the tire in an interdigitating manner. The interdigitating engagement of the protrusions on the tire with the protrusions on the wheel prevents slippage and rotation of the tire relative to the wheel. The wheel also includes support flanges that extend radially inward from the rim in order to protect the tire from damage as the tire deforms under a load.

Description:
This application claims the benefit of U.S. provisional application No. 60/589,835 filed Jul. 22, 2004. 

   BACKGROUND OF THE INVENTION 
   Recreational vehicles, such as mountainboards, motorized carts and pedal-operated carts are operated over a variety of terrains. These terrains can include many different types of surfaces, including hard, soft, smooth and irregular (i.e., rough or bumpy) surfaces. It is difficult to design wheel and tire assemblies that provide optimum performance characteristics on a variety of surfaces. Therefore, the wheels and tires that are provided on recreational vehicles are often designed for optimum performance on a particular type of surface only, or are designed to provide compromised performance on a variety of surfaces. 
   Traditional wheel and tire assemblies for recreational vehicles include a wheel and a tubed or tubeless pneumatic tire mounted on the wheel. To ensure adequate load bearing capacity, to retain the tires on their rims and to ensure that the tires resist the torque applied to rotate and stop rotation of the wheels and tires, the tires are typically constructed of tough, relatively hard materials and are inflated to high operating pressures, typically in excess of 10 psi. When the typical wheel and tire assemblies are mounted on a vehicle and subjected to an axial load by a rider/operator, the tires flatten only very slightly and generally retain the appearance of deflated, unloaded tires. As a result, the contact areas between the tires and the support surfaces underlying the tires are small, so that the pressure per unit area on the support surfaces is high, which causes the wheels and tires to sink partially into soft support surfaces such as sand and loose dirt. The high operating pressures to which the tires are inflated also make the tires less yielding to obstacles, bumps and irregularities on the support surface, which can lead to a bumpy ride, and thus a loss of speed while traversing terrain and diminished control of the vehicle by a rider/operator. 
   The invention aims to provide an improved wheel and tire assembly for recreational vehicles to allow for optimum performance on a wide variety of surfaces. Additionally, it is an object of the invention to provide a wheel and tire assembly wherein the tire is securely mounted to the wheel without being permanently attached to the wheel, in order to ensure safe operation and ease of replacement for the tire and/or wheel. The invention further aims to provide a wheel and tire assembly that can be manufactured relatively quickly and inexpensively. 
   BRIEF SUMMARY OF THE INVENTION 
   Recognizing that recreational vehicles traverse surfaces having a variety of compositions and characteristics, and that recreational vehicles are also subjected to a wide range of loads during operation, a need exists for a wheel and tire assembly that can perform well on various types of surfaces and under various loads. The invention provides an improved wheel and tire assembly including a tire-supporting rim and a low-pressure, all-terrain tire that provides superior performance regardless of variations in terrain or load. The wheel and tire assembly also provides secure attachment of the tire to the wheel and protection of the tire from potential damage during extreme acceleration, braking and turning of vehicles. 
   The tire of the invention comprises a substantially torus-shaped member (or “torus”) constructed of substantially inelastic material that will not deform at temperatures up to at least 225° F. The tire includes an inner diameter wall portion for engaging the rim and an outer diameter wall portion for contacting a support surface. The tire can flatten under load (i.e., axial load) to facilitate movement of the tire over various types of surfaces. Due to flattening of the tire, the tire is able to easily traverse soft and irregular surfaces as well as smooth and hard surfaces. 
   The inner diameter wall portion of the tire and the outer surface of the rim include interdigitating protrusions for securing the wheel and tire together and preventing rotation of the tire relative to the wheel. The rim further includes flanges extending radially inward towards the center of the wheel to support side portions of the tire as the tire flattens under load with side torque, such as when a rider or operator is turning the vehicle on which the tire is mounted. The flanges therefore prevent the sidewall portions of the tire from incurring damage that could otherwise be caused by extreme pressure against outer edges of the rim. 
   Various objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only exemplary embodiments of the invention. As will be realized, the invention is capable of modification in various obvious respects without departing from the scope of the invention. Accordingly, the drawings and description are illustrative in nature and are not intended to be restrictive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a disassembled wheel and tire assembly, with end caps removed from the wheel, according to one embodiment. 
       FIG. 2  is a partially transparent side view showing the wheel and tire assembly of  FIG. 1  in its fully assembled form. 
       FIG. 3  is a cross-sectional view of the wheel and tire assembly of  FIG. 1 , taken along line A—A. 
       FIG. 4  is a cut-away view of the cross-section of  FIG. 3 , showing the wheel and tire in more detail. 
       FIG. 5  is a side view of the tire of  FIG. 1 . 
       FIG. 6  is a more detailed cross-sectional taken along line B—B of  FIG. 2 . 
       FIG. 7  is a partially transparent side view of the wheel of  FIG. 1  with the end caps removed. 
       FIGS. 8A and 8B  show an end cap of the wheel of  FIG. 1 . 
       FIG. 9  shows a disc brake for the assembly of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A wheel and tire assembly according to the invention includes a tire made of a flexible, substantially inelastic material and a wheel adapted to support the tire for rotation. The tire and wheel of the present invention, when secured together, securely engage one another to resist relative rotation between the tire and the wheel. By definition, the tire may deform under load, but will not stretch, or will stretch very little under load. This characteristic is opposite to the tendency of elastic materials, such as rubber or rubber-like materials, to stretch under load. 
   Polyurethane is an example of a material that may be utilized in the construction of the tire. The polyurethane may be thermoplastic and may additionally be a polyether-based grade polyurethane, such as TEXIN 985U polyurethane available from the Bayer corporation. This polyurethane has a Shore hardness of about 85 A. Naturally, other polyurethanes or other materials having similar characteristics, such as Shore hardness, abrasion resistance, impact strength, toughness, flexibility, temperature resistance and resistance to UV exposure could be utilized. 
   The wall thickness of a tire according to the present invention can vary greatly with the diameter and/or width of the tire as well as the particular application for which the tire is intended. Due to the nature of the molding process for making a tire according to the invention, the entire wall of the tire is typically uniformly thick. However, the tire may be differentially thick. 
   A tire according to the present invention may be utilized in extreme temperatures. For example, a tire, such as a tire made of polyurethane, could be used on hot concrete, asphalt, or metal, or could be left inside hot vehicles in the sun, where temperatures can exceed 225° F. without experiencing deformation. Many plastic tires have limits on the conditions in which they may be utilized. For example, an elastomeric plastic tire may begin to deform at temperatures of about 120° F. to about 150° F. Since concrete, asphalt, metal and other surfaces may exceed 120° F. in summer seasons, such elastomeric plastic tires could not be utilized on such surfaces. Additionally, potential storage areas, such as the interior of a motor vehicle, can exceed 225° F. in the summer, and an elastomeric plastic tire would deform under such conditions. 
   A wheel and tire assembly  100  according to an embodiment of the present invention is shown in  FIG. 1 . The assembly  100  includes a low pressure tire  200  and a wheel  300  for supporting the tire  100 . The tire  200  is substantially torus-shaped and is constructed of substantially inelastic material, such as polyurethane as described above. The tire  200  is described as “substantially torus-shaped” because it does not have a perfect donut shape, but generally has a modified donut shape that is formed to fit supporting surfaces of the wheel  300 , as shown best in  FIGS. 3 and 4 . 
   Referring to  FIG. 3 , the cross section of tire  200  is substantially annular in shape. The tire  200  includes an inner diameter wall portion  210  and sidewall portions  220  for engaging a tire supporting rim  310  of the wheel  300 , and an outer diameter wall portion  230  for contacting a supporting surface on which the tire supports the vehicle (not shown) for rolling motion. As illustrated in  FIGS. 1 and 5 , the inner diameter wall portion  210  includes transverse ribs or protrusions  212  extending in the direction of the axial width W of the tire  200 . Preferably, each protrusion  212  extends across nearly the entire axial width of the inner diameter wall portion  210 , and includes a substantially flat top surface  214  and two side surfaces  216  oriented substantially perpendicular to the top surface  212 . Adjacent protrusions  212  are separated by recesses  219 . Preferably, the protrusions  212  are disposed around the entire periphery of the inner diameter wall portion  210 . The exterior surface of the outer diameter wall portion  230  may be smooth, or it may have a tread pattern suitable for a particular application. 
   The tire  200  may be substantially or entirely free from reinforcing fabrics or cords. However, such reinforcing materials may be included in areas where the tire  200  engages the wheel  300  in order to reinforce those areas. The absence of any reinforcing material may help the tire  200  to flatten or deform as desired under load. 
   As indicated in  FIG. 4 , the tire  200  may also include a sealable opening  240  for inflating and deflating the tire. The sealable opening  240  may be any typical structure for inflating a tire or other inflatable structure. For example, the sealable opening  240  could include a conventional valve stem member or needle valve such as the type used in inflatable balls. Preferably, the sealable opening  240  is located in a lower part of a sidewall portions  220  such that it is recessed behind the wheel  300 . 
   As previously stated, the tire  200  typically deforms but does not stretch when encountering an obstacle under a load. When inflated to lower pressure levels, the tire may spread out under load to facilitate movement over soft or irregular support surfaces. Typically, in such conditions, the tire  200  may be inflated to a pressure of no more than about 1 psi to help insure that the tire will flatten to help provide sufficient contact surface and reduce rolling friction between the tire and the soft or irregular support surface. The tire  200  may thereby permit a vehicle or device on which the tire is mounted to move easily over soft or irregular support surfaces. The contact surface of the tire may increase as a load on the tire increases. Although the tire  200  may be inflated to pressures up to 6 psi, pressures as low as 1 psi to 4 psi would be suitable use on soft or irregular surfaces. Generally speaking, when the tire  200  is inflated to lower pressures, the tire is better suited for use on soft and irregular surfaces, as the tire  200  will flatten more under a load than it would when inflated to higher pressures. By flattening, the tire  200  provides an enlarged contact area between its outer diameter surface  230  and the underlying support surface. 
   Typically, the tire  200  is formed by a blow molding method. Blow molding is typically more economical, more efficient and less labor intensive than other methods of forming flexible polyurethane products. However, other suitable methods may be used to make such a tire. 
   Turning to  FIG. 6 , the wheel  300  is constructed of two mating axial wheel halves  302  that are adapted to be fastened to each other and two end caps  330  that are each adapted to be fastened to a respective one of the wheel halves  302 . The wheel  300  includes bolt holes  304  extend through both wheel halves  302 . Each end cap includes an axle hole  331  for receiving the axle (not shown) and bolt holes  332  that are adapted to be aligned with the bolt holes  304 . Bolts (not shown) may be inserted through the bolt holes  304  and  332  to assemble the wheel  300 . 
   With reference to  FIGS. 1 and 6 , the wheel  300  includes the aforementioned tire supporting rim  310  connected to a hub  320  for receiving an axle (not shown). Bearings (not shown) are retained inside the hub  320  in bearing seats  321 , shown in  FIGS. 3 and 6 . The rim  310  includes a cylindrical center section  312  for engaging the inner diameter surface  210  of the tire, a pair of substantially conical portions  314  extending from opposite ends of cylindrical center section  312  for supporting a lower section of the tire sidewall portion  220 , and rounded outer lips  316  extending from the conical portions  314 . Additionally, as shown in  FIG. 4 , at least one of the conical portions  314  may include an opening  318  providing access to the sealable opening  240  of the tire. The end caps  330  may also include one or more openings  334  (shown in  FIGS. 4 and 8   a – 8   b ) that can be aligned with the opening  318  in order to allow access to the sealable opening  240  when the end cap  330  is in place. 
   Referring to  FIG. 8   a,  each end cap  330  includes a rounded lip  336  at its outer circumference. When the end caps  330  are attached to the wheel halves  302 , each rounded lip  338  mates with an outer lip  316  of the rim  310  to form a support flange that extends radially inward from the outer diameter of the wheel  300  (see  FIGS. 3 and 8   a ). The end caps  330  also secure bearings  321  within the hub  320 . 
   As best shown in  FIGS. 1 and 7 , the center section  312  of the rim  310  includes transverse ribs or protrusions  342  extending in the direction of the axial width of the wheel  300 . Preferably, each protrusion  342  extends across nearly the entire width of center section  312 , and includes a substantially flat top surface  344  and two side surfaces  346  oriented substantially perpendicular to the top surface  344 . Adjacent protrusions  342  are separated by recesses  349 . Preferably, the protrusions  342  are disposed around the entire periphery of the center section  312 . 
   As shown in  FIGS. 3 and 4 , when the assembly  100  is fully assembled, the inner diameter wall portion  210  of the tire  200  is supported on the wheel  300  such that the center section  312  and conical portions  314  of the rim  310  secure the tire  200  in place. Each protrusion  212  of the tire  200  is received within a recess  349  of the rim center section  312 , and the protrusions  342  of the rim center section  312  are received within the recesses  219  tire  200 . Thus, the protrusions  212  and  342  engage each other in an interdigitating or intermeshing manner. To ensure optimum engagement between the protrusions  212  and  342 , it is generally preferable that the side engaging surfaces  216  and  346  be within the range of about 0.25 inches to about 0.50 inches in depth. However, the depth of the surfaces  216  and  346  may be outside this range in some applications, depending on the size of the tire  200  and the wheel  300 . 
   The intermeshing engagement of the protrusions  212  and  342  positively secures the tire  200  and wheel  300  together and resists rotation and slippage of the tire  200  relative to the wheel  300  during acceleration and braking of the vehicle or device to which the assembly  100  is mounted. As a result of the interdigitating arrangement of the protrusions  212  and  342 , the tire  200  is securely mounted on the wheel  300  without requiring the tire  200  to be glued, bonded, fused or otherwise permanently attached to the wheel  300 . 
   The support flanges  338 , shown best in  FIGS. 3 and 6 , serve to further support the tire sidewall portions  220  under a load when side torque is applied to the tire  200 . Under a side torque load, such as during turning of the vehicle or device on which the assembly  100  is mounted, the tire  200  may deform axially by a significant amount, in addition to flattening. In such circumstances, if there were no means for further supporting the tire  200 , part of the inner diameter wall portion  210  of the tire  200  might deform axially inward and rub against edges of the rim  310  or other parts of the wheel  300 . Such rubbing could result in rapid wear and damage to the tire  200 , including blowouts that could cause the operator of the vehicle to have a serious accident. However, according to the present invention, the rounded, radially inward-extending support flanges  338  will prevent the tire sidewall portions  220  from deforming excessively in the axially inward direction. The flanges  338  are further advantageous in that they protect the tire  200 , without requiring extension of the rim  310  in the axial direction, thereby making the wheel  300  more compact in width. 
     FIG. 9  shows a brake disc  400  which can be mounted to the wheel  300 . The brake disc  400  includes axle hole  402  for receiving the axle (not shown) and bolt holes  404  that can be aligned with bolt holes  304  and  332  for fastening the brake disc  400  to the wheel  300 . The brake disc may be part of a braking system for stopping rotation of the wheel  300 . 
   Although the foregoing describes preferred embodiments of the invention, it should be understood that the invention is capable of various other combinations and modifications within the scope of the invention disclosed herein. Accordingly, the embodiments described hereinabove are intended to be illustrative, and are not intended to limit the invention to the form disclosed herein. Thus, it is understood that the invention is covered by the following claims.