Abstract:
A wheel for a skateboard, roller skate or the like has a radial surface arranged to provide contact with the ground, said radial surface comprising areas of at least a first material and areas of a second material, said second material having at least one mechanical property differing from that of the first material. The first and second materials are arranged in such a way that they form a pattern on the radial surface which varies around the circumference of the wheel. This enables the adaptation of the behavior of the wheel in a very flexible way.

Description:
The present invention relates to the field of wheels for sports or leisure equipment such as skateboards, inlines and the like, and more specifically to wheels having a radial surface comprising at least two different materials having different mechanical properties. 
     BACKGROUND AND PRIOR ART 
     The wheels of a skateboard are typically made of polyurethane and come in many different sizes and shapes adapted to different types of skating. 
     It is also well known that the properties of the surface material affect the behavior of the skateboard. Polyurethane, which can be found with different friction coefficients, rolling resistance, and rebound depending on the mechanical properties of the material, such as its hardness. Hardness is usually measured on a Shore durometer scale in the range of Shore A 75 to Shore A 100 or harder. For example, hard wheels can slide more easily while softer wheels are can maintain higher speeds without sliding. Skateboard wheels have a wide surface engaging the ground, ranging from approximately 1 cm to over 5 cm. Traditionally, skateboarders have had to make compromises between control and a smooth ride on one hand and high speed on the other. Thinner wheels are generally made of relatively hard urethane, facilitating slides, grinds and other tricks. Thicker wheels are typically made with softer urethane for more control, making them suitable for, for example, downhill racing. 
     U.S. Pat. No. 6,953,225 discloses a skateboard wheel as initially defined. This wheel has a radial surface comprising outer portions and an inner portion between the outer portions, with a substantially linear border between them. Each of the three portions extends completely around the circumference of the wheel. The outer portions are made from a harder material than the inner portion, giving the outer portions a lower friction and thereby properties suitable for making tricks, especially involving sliding, while the inner portion has a higher friction thereby providing a higher degree of control, according to U.S. Pat. No. 6,953,225. The wheel has an axle passage through the centre with a bearing surface facing a hub for mounting the wheel on a skateboard. Hence, a designer of skateboard wheels can vary the properties of the wheels through selection of the hardness and friction coefficient of the materials used on the surface, and the width of the outer and inner portions of the wheels Similar considerations apply to other types of wheels, for example for roller skates or inline roller skates. 
     U.S. Pat. No. 4,699,432 discloses a safety wheel for use with, for example, roller skates or skateboards. The wheel is designed to provide improved traction and performance and comprises portions of a first material having a relatively low friction coefficient and a second material, softer than the first material and having a higher friction coefficient. 
     SUMMARY OF THE INVENTION 
     The invention relates to a wheel for sports equipment, such as a skateboard, a scooter, a snakeboard, a roller skate or an inline roller skate. The wheel has a radial surface arranged to provide contact with the ground comprising areas of at least a first material and areas of at least one additional material, said additional material or materials having mechanical properties differing from that of the first material. The first and additional second materials are arranged in such a way that they form a pattern on the radial surface which varies around the circumference of the wheel. The first and additional materials are chosen in such a way that they will form molecular bonding between them. Typically both materials will be polyurethane. 
     Said mechanical properties include but are not limited to hardness, rebound, abrasion, rate, coefficient of friction. Typically, a harder polyurethane material is used as the first material and a softer polyurethane is used as the second material. It would also be possible to use materials that have essentially the same mechanical properties but different colours. This would achieve a pattern in the wheel that would not be worn off in the same way as printed patterns on the surface. 
     By using polyurethane for both materials a molecular bonding can be achieved between the different areas. In contrast, when different types of materials are used, some sort of mechanical bonding must be used to keep the areas of different materials together. In practice, a wheel comprising two or more different types of polyurethane material can be made to function as one integral piece where the different areas cannot be separated from each other. As a consequence, there is no space between the different areas and no risk of rifts or crevices forming between the different areas. Such imperfections in the surface of the wheel serve to reduce the performance of the wheel so avoiding them is a major advantage. Further, the manufacturing process can be made more cost-efficient, since less effort will be needed to bond the areas of different materials together. 
     Varying the pattern of the two materials over the radial surface enables the wheel designer to modify the performance of the wheel beyond limitations in urethane materials. A design having different urethanes in alternating contact with the riding surface would give the rider the individual benefits of each material. The wheel can be adapted according to the intended use of the wheel, skills of the intended user, the surface on which the user will ride, or any other parameter. 
     Further, the visible differentiation a mix of materials in a pattern conveys a marketing benefit, since the patterns may be designed to look cool. Patterns may even be designed to reflect, for example, the logotype of a company or any other attractive image. This enables the differentiation of wheels from a particular manufacturer, or wheels having a particular set of properties just by looking at them. 
     In a preferred embodiment the surface is arranged so that only one of the first and additional second materials is in constant contact with the riding surface. The other material or materials form isolated areas, or islands, on parts of the radial surface. With alternating contact, the hard material gives stability and controls deformation and rolling resistance, the softer material gives better grip and higher rebound. By alternating materials we can engineer and optimize the wheel beyond previous limitations. 
     It would be possible to use a combination of more than two different materials as well. 
     In a preferred embodiment, the blended center surface is the principal weight supporting surface which interacts with the riding surface, because of its mix of materials in alternating contact enables the ability to manage the mechanical properties, tribology, and performance of the wheel. 
     In an alternative preferred embodiment, the blended center surface is combined with one or two outer portions of a similar type as in the prior art. In this case, the friction of the outer portions will be minimized, to facilitate tricks, while the friction of the center portion can be adapted as desired. 
     At any given moment more than one of the materials will normally be in contact with the riding surface, but the distribution between the materials will vary. By varying the design, size and pattern of the different materials we can affect the ride in the same way that alternating patterns on studded tires affect grip in snow. One material is engineered to give stability, while a second material gives grip and rebound. The degree of which any one material or a combination of two materials that is in alternating contact with the riding surface will vary depending upon the properties optimal for each type of skateboard wheel which is manufactured according to the patent technology. 
     In one embodiment the pattern of two different materials extends to at least one side of the wheel. This is particularly useful for applications in which the wheel may be tilted, for example for inline rollerskates. 
     The physics of wheels are the same for skateboarding, roller skating, inline skating, and scooters. All of these products utilize polyurethane wheels and therefore benefit from the ability to engineer the wheels properties through design. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following embodiments of the invention will be described in detail, with reference to the appended drawings, in which 
         FIGS. 1A-1C  show different views of skateboard wheel according to a first embodiment of the invention. 
         FIGS. 2A and 2B  show examples of what a section through the wheel of  FIGS. 1A to 1C  might look like. 
         FIG. 3A  is a view of part of the circumference of a skateboard according to an embodiment of the invention. 
         FIG. 3B  is a section through the skateboard wheel of  FIG. 2A . 
         FIG. 4A  shows a third embodiment of a wheel according to the invention. 
         FIG. 4B  is a section view of the wheel of  FIG. 4A . 
         FIG. 5  shows a fourth embodiment of a wheel according to the invention. 
         FIG. 6  shows a section trough a wheel according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1A  is a perspective view of an embodiment of a wheel  1  according to the invention. The wheel has a hub  3 , which exhibits an axle passage  5  for mounting on a skateboard, a rollerskate or the like. A bearing (not shown) is typically provided around the axle passage for smooth rotation of the wheel. The wheel has a tapered edge  7  and an outer surface  9  which forms the interface towards the ground. The tapered edge  7  and the outer surface  9  are primarily made from a first material  11  having a first set of mechanical properties, including a first hardness, shown in white in the Figure. Around the circumference of the wheel, a second material  13  having a second set of mechanical properties, including a second hardness, is applied in such a way that the outer surface  9  and/or the tapered edge  7  comprises areas of the first material  11  and areas of the second material  13 . In this particular embodiment, the exterior surface around the circumference of the wheel comprises a central narrow line of the first material  11  surrounded by a feather-like pattern in which areas of the second material  13  extend from the central line to the edge outer surface around the whole circumference, interrupted by curved lines of the first material  11 . In this embodiment, the edges  7  of the wheel are beveled, so that the first material surfaces at the edges and sides of the wheel. 
     The wheel may be made entirely from the first material, with only the areas of the second material applied as shown, or one or more other materials or compositions may be used for the interior or portions of the interior of the wheel. Alternatively, the wheel may have hollow portions inside, such as the chambers shown in  FIG. 1 . 
       FIG. 1B  is a view of the wheel of  FIG. 1 a   , seen from the side, including the hub  3 , the axel passage  5  and the tapered edge  7 . The pattern around the circumference is seen in the narrow outer circle as wider areas of the second material  13  interrupted by narrow areas of the first material  11 . 
       FIG. 1C  is a view of the wheel of  FIGS. 1 a  and 1 b   , as seen towards the circumference of the wheel. The outer surface  9  is seen having a narrow central line of the first material  11  around its circumference and a feather-like pattern of the second material  13  extending from the narrow central line across the outer surface  9  towards the tapered edges  7 . 
       FIG. 2A  shows a section through the wheel of  FIGS. 1A-1C  according to a first embodiment. As can be seen, a core  15  made from the material forming the hub  3  extends radially from the axel passage  5  to form the major part of the wheel. This core  15  is covered, around the areas that are adapted to connect to the ground, by a layer of the first material  11  constituting the main part of the wheel. The areas of the second material  13  extend a relatively short distance into the first material as can be seen in the Figure. 
       FIG. 2B  shows a section through the wheel of  FIGS. 1A-1C  according to an alternative embodiment. As can be seen, the hub  3  in the middle is surrounded by an area of the first material  11  constituting the main part of the wheel. The areas of the second material  13  extend a longer distance into the first material as can be seen in the Figure. Of course, the areas of the second material  13  could extend longer or shorter into the first material. For example, it could extend halfway, or more than halfway in, or approximately as shown in  FIG. 2A .  FIG. 6  below shows yet another possible implementation. 
     Although the Figures show wheels suitable for a skateboard, using two or more different materials having different mechanical properties in the outer surface of the wheel can be utilized in wheels for a number of different applications, including rollerskates, inlines, snakeboards and scooters. How to make such wheels is well known in the art, including dimensions, shapes, how to arrange the hub, the use of bearing, etc. The only change that is made according to the invention lies in how the surface material is applied to the wheel. 
       FIG. 3A  shows a second embodiment of the wheel, seen towards the circumference of the wheel. The side view would be essentially as shown in  FIG. 1A . In this embodiment, the second material is applied in three areas: a first and a second band  13 ′ around the edges of the wheel and a band  13 ″ in the middle. The borders between the first and second bands  13 ′ and the areas  11 ′ of the first material have a serrated shape. Of course, the borders could have any shape that was not entirely linear, since a variation should be provided around the circumference of the wheel. 
       FIG. 3B  shows a section through the line A-A of  FIG. 3B . As in  FIG. 2B , the second material forms the main part of the wheel, extending from the hub  3  all the way to the circumference. In the example shown, areas of the second material extend a short way into the first material around the circumference. Of course, the wheel of  FIG. 3A  could also be implemented in the different ways discussed in connection with  FIGS. 2A and 3A . 
       FIG. 4A  shows a third embodiment of the wheel. As in  FIG. 1A , a hub  103  is surrounded by a first material  111  making up the main part of the wheel. Areas of a second material  113  are placed in the beveled portions of the wheel, only.  FIG. 2B  shows a section through the wheel of  FIG. 2A , in which areas of the second material  113  extend a short distance into the first material at the beveled side portions of the wheel. 
       FIG. 4B  shows a section through the wheel of  FIG. 4A . In this example, the second material  113  extends only a short distance into the first material  111 . Of course, the wheel of  FIG. 4A  could also be implemented in the different ways discussed in connection with  FIGS. 2A and 3A . 
       FIG. 5A  shows a fourth embodiment of a wheel to illustrate that the first  211  and second  213  materials may be arranged in any pattern on the circumference of the wheel. In this particular example, the areas of the second material are heart shaped. The section through the wheel could be as any of the embodiments discussed above, or as discussed in connection with  FIG. 6 . 
       FIG. 6  shows an alternative section through a wheel having a hub  303  around an axel passage  305 . In this embodiment the second material is arranged to form a band  313  around the hub. The first material  311  is arranged around the band  313  and extends to the circumference. The band has arms  313 ′ extending radially through the first material towards the circumference of the wheel, to form areas of the second material in the first material on the surface. The cross-section of the arms  313 ′ may have any shape, typically corresponding to the pattern that should be made around the circumference of the wheel. For example in the wheel of  FIG. 5  the cross-section could be heart-shaped. 
     The wheel according to the invention may be produced in a number of different ways, as will be clear to the person skilled in the art. For example, the core of the wheel is made of the first material and extends from the hub  3  of the wheel all the way to the outer surface. The core is then place in a mold shaped like the outer shape of the wheel. The second material is poured into the mold and forms the outer surface of the wheel fused with the first material of the core. Alternatively, it would be possible to make the wheel of the second material and apply the first material only around the outer surface. 
     Alternatively a patterned insert ring with an outer diameter matching the outer surface of the wheel is molded. This ring is then placed in a mold and the second material is poured into the mold and forms the outer surface of the wheel fused with the first material of the ring. An optimal thickness of the ring would be in the range from 2 mm to 10 mm. 
     A third option would be to make a wheel of the first material with cavities in the first material and fill in the cavities using the second material. The cavities can be made as deep as desired, from extending about 1 millimeter into the wheel to 25 millimeters into the wheel, or extending all the way to the hub. A preferred thickness would be 6 mm to 7 mm. 
     The diameter of the wheel varies depending on the type of wheel, as the skilled person will be aware. For skateboard wheels, the diameter is typically within the range from 45 mm to 60 mm for a street wheel, between 55 mm and 70 mm for a park/vert/transition wheel. A longboard speed wheel typically has a diameter between 60 mm and 120 mm. 
     The shape of a wheel and the width of the wheel contacting the riding surface also depends on the type of wheel. An inline, snakeboard or scooter wheel has an elliptical form and the portion contacting the riding surface is very narrow, from 2 mm to 15 mm. 
     A skateboard wheel the width of the portion contacting the riding surface starts at 15 mm for a 360 freestyle wheel. For a street skateboard wheel it is typically between 20 mm and 30 mm, and for a park/vert/transition wheel it is typically between 25 mm and 40 mm. The contacting portion of a longboard wheel is typically 35 mm to 80 mm. 
     As the skilled person will understand, the dimensions given above are merely intended as examples and are not limiting in any way. Further, the wheel according to invention is not limited to the uses mentioned. The wheel can be made in the conventional way for the intended use, apart from the combination of two or more surface materials as discussed in this document.