Abstract:
A tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness having a compliant tread band and a plurality of web spokes for bearing the load in tension extending transversely across and inward from a compliant tread band for attachment to a hub. The web spokes have an increasing draft angle and decreasing width as they extend from the compliant tread band to the hub reducing the lateral stiffness of the wheel thereby reducing steering force feedback to the steering mechanism.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter of the present disclosure relates generally to tension-based non-pneumatic, structurally supported tires and wheels. More particularly, the invention relates to a tension-based non-pneumatic wheel having a reduced lateral stiffness that supports a load with its structural components and has pneumatic tire-like performance capabilities to serve as a replacement for a pneumatic tire. 
         [0002]    The web spokes of a tension-based non-pneumatic tire have a high effective stiffness in tension and a low effective stiffness in compression. The low stiffness in compression allows the web spokes attached to the ground-contacting portion of the compliant band to accommodate deformation of the ground-contacting portion of the compliant band without transmitting significant vertical load. The web spokes are relatively thin compared to their length and, typically, will bend in compression. The lack of substantial compressive load support by the web spokes in the contact region facilitates the formation of the contact patch and absorption of obstacles. In addition, because the majority of the supported load and road shock must travel around the compliant band and through the tensioned web spokes, the tension-based non-pneumatic compliant wheel has improved comfort and shock absorption compared to pneumatic wheels. One example of a non-pneumatic wheel is described in U.S. Pat. No. 7,013,939, incorporated in its entirety herein by reference. 
         [0003]    To facilitate the bending of the web spokes of the ground contacting portion of the tread, the spokes can be curved. Alternatively, the web spokes can be shaped during molding to have a predisposition to bend in a particular direction. Another alternative is to provide a connection between the hub and web spokes or between the compliant band and web spokes that acts in tension but allows relative movement of the web spoke in compression. 
         [0004]    A non-pneumatic structurally supported wheel incorporating a compliant band and a plurality of tension-based load bearing structural components has a lateral stiffness inherent in the design of the wheel. Under certain circumstances it is desirable to adjust the lateral stiffness of the wheel to a desired lateral stiffness for a given application. For instance, when a non-pneumatic wheel with relatively high lateral stiffness is used off-road, for instance in an All-Terrain Vehicle (ATV), it creates a high force feedback into the steering mechanism. 
       SUMMARY OF THE INVENTION 
       [0005]    According to a one embodiment, a tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness is achieved by tapering and twisting each web spoke by reducing the width of each web spoke and increasing the magnitude of the draft angle as each web spoke extends from the compliant tread band to the inner wheel portion of the wheel. 
         [0006]    A tension-based non-pneumatic structurally supported wheel comprises a hub; a compliant, load supporting band disposed radially outward and concentrically with the hub; and a plurality of tension-based web elements, otherwise referred to as web spokes, extending between the hub and the compliant band, wherein each web spoke has a tapered lateral width which is greater near the compliant band than near the hub and a changing draft angle which is greater near the hub than near the compliant band. Generally, the compliant band comprises a reinforcing membrane or ply embedded in the band. The reinforcing ply comprises cords aligned in the circumferential direction embedded in an elastomeric layer. According to this embodiment, the decreasing tapered width and increasing draft angle of the plurality of webs as they extend radially inward from the compliant band decrease the lateral stiffness of the wheel, reducing force feedback into the steering mechanism of the vehicle while maintaining stability of the wheel. 
         [0007]    Another embodiment of the structurally supported wheel comprises: a compliant band; a plurality of web spokes extending transversely across and radially inward from said compliant band; the plurality of web spokes attaching to a hub, each of the plurality of web spokes having a spoke width extending in an axial direction, a spoke length extending in a radial direction, a spoke thickness perpendicular to the other dimensions, a draft angle measured as the angle each of the plurality of web spokes make compared to the transverse axis of the wheel at a given position along the spoke length, the spoke width decreasing and the magnitude of the draft angle increasing as measured at a radially outward position to a radially inward position. 
         [0008]    Another embodiment of the invention could include a structurally supported wheel comprising: a compliant band; a plurality of twisted web spokes extending transversely across and radially inward from the compliant band; the plurality of web spokes attaching to a hub, each of the plurality of web spokes having a spoke width extending in an axial direction, a spoke length extending in a radial direction, a spoke thickness perpendicular to the other dimensions, a draft angle measured as the angle each of the plurality of web spokes make compared to the transverse axis of the wheel at a given position along said spoke length, the spoke width decreasing and the magnitude of the draft angle increasing as measured at a radially outward position to a radially inward position. 
         [0009]    In another embodiment the draft angle of the web spokes proximal to the compliant band is 0.5 degrees while the draft angle of the web spokes proximal to the hub is greater than 0.5 degrees. 
         [0010]    In another embodiment the draft angle of the web spokes proximal to the compliant band is 4 degrees while the draft angle of the web spokes proximal to the hub is 12 degrees. 
         [0011]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
           [0013]      FIG. 1  is a perspective view of the tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness. 
           [0014]      FIG. 2  is a close-up perspective view of the wheel. 
           [0015]      FIG. 3  is a side view in the equatorial plane of the wheel. 
           [0016]      FIG. 4  is a close up partial side view in the equatorial plane of the wheel view showing two adjacent web spokes 
           [0017]      FIG. 5  is a section view of the outer radial end of the web spokes taken on line  5 A- 5 A of  FIG. 4 . 
           [0018]      FIG. 6  is a section view of the middle portion of the web spokes taken on line  6 - 6  of  FIG. 4 . 
           [0019]      FIG. 7  is a section view of the inner radial end of the web spokes taken on line  7 - 7  of  FIG. 4 . 
           [0020]      FIG. 8  is a section view of the wheel taken along the equatorial plane of the wheel. 
           [0021]      FIG. 9  is a section view of the wheel taken on line  9 - 9  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    For the purposes of the following description, the term “hub” refers to any device or structure for supporting the wheel and mounting it to a vehicle. 
         [0023]    The compliant band is formed of a material capable of deforming under load, including bending of the band, to envelope obstacles and to conform to a contact surface, such as a road or floor. In particular, bending deformation of the band under load forms a contact patch with the contact surface, which provides pneumatic tire-like transmission of traction and steering forces. One aspect of the compliance of the wheel material is that the amount of bending of the band relates to the magnitude of the load on the wheel. 
         [0024]    The compliant band may be formed of an elastomeric material, such as natural or synthetic rubber, polyurethane, foamed rubber and foamed polyurethane, segmented copolyesters and block co-polymers of nylon. Preferably, the material has an elastic modulus of about 9 MPa to about 60 MPa. The band may be unreinforced, or may include a reinforcing ply to increase the band&#39;s circumferential inextensibility. 
         [0025]    The web spokes interconnect the hub and compliant band and act in tension to transmit load forces between the hub and the band. This provides, among other functions, support for the mass of a vehicle. Load support forces are generated by tension in the web spokes not connected to the ground-contacting portion of the band. The loaded hub can be said to hang from the upper portion of the compliant band, which defines an arch supporting the load. The web spokes may also be interconnected forming a plurality of web elements comprising a plurality of polygonal openings. It should be understood that when a web spoke is referred to, it may refer to a single row of web spokes spanning from the hub to the compliant band, or a plurality of rows of web spokes segments spanning from the hub to the compliant band. 
         [0026]    For purposes of describing the invention, reference now will be made in detail to the tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0027]    The tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness  100 , shown in perspective in  FIG. 1 , the tread portion  105  is shown connected to the hub  10  by a plurality of tension transmitting elements, illustrated as web spoke elements  150 . The web spokes  150  are shown here connected together at their inner radial ends by an inner band  160  and at their outer radial ends by an outer band  170 . The inner band  160  anchors the wheel  100  to the hub  10 . The outer band  170  anchors the tread portion  105  to the wheel  100 . Tread features may be formed in the tread portion  105  and may include grooves, ribs, divots, protrusions and other tread features for traction and aesthetics. Each web spoke  150  possesses a front surface  156  and a rear surface  158 . 
         [0028]      FIG. 2  shows a close-up perspective partial view of an embodiment of the wheel  100 . In this embodiment, each web spoke  150  possess a three radius blended profile that reduces stress concentration and encourages predictable flexing in compression. The tension carrying spokes may be interconnected and/or branched. 
         [0029]      FIG. 3  shows the embodiment from a view perpendicular to the equatorial plane of the wheel  100 . The tread portion  105  forms the outer surface of the compliant band  110 . In this embodiment, each web spoke  150  is angled such that the front surface  156  or rear surface  158  of each web spoke lies out of plane with the transverse axis of the wheel. In this embodiment, the draft angle varies from the outer radial end  152  of the web spoke  150  to the inner radial end  154  of the web spoke. At the inner radial end  154  of the web spoke, the draft angle is greater in magnitude than the draft angle at the outer radial end  152 . In the view perpendicular to the equatorial plane of the embodiment, as shown in  FIG. 3 , the draft angle and web width appears constant from the inner radial end  154  to the outer radial end  152 . This appearance is due to the embodiment having a variable draft angle that is less in magnitude at the outer radial end  152  than at the inner radial end  154  while the width of the spoke is greater at the outer radial end  152  than at the inner radial end  154 . While this appearance is present in the embodiment, it may not be present, or as pronounced in other embodiments of the wheel where the draft angle change chosen is different and or the taper of the width of the web spoke chosen is different than the embodiment. 
         [0030]      FIG. 4  shows a close up partial view perpendicular to the equatorial plane of the tension-based non-pneumatic structurally supported wheel with reduced lateral stiffness showing two adjacent web spokes  150  having opposite draft angles. 
         [0031]      FIG. 5  is a section view of the adjacent web spokes  150  taken on line  5 - 5  of  FIG. 4  which is at the outside radial end  152  of the web spoke  150 . In the embodiment, the draft angle is small, if nearly parallel, to the transverse axis of the wheel  100 . 
         [0032]      FIG. 6  is a section view of the adjacent web spokes  150  taken on line  6 - 6  of  FIG. 4  which is at a middle location along the length of the web spoke  150 . In the embodiment, the magnitude of the draft angle is greater than at the outside radial end of the web spoke  150 . The width of the web spoke  150  is less in the middle portion of the web spoke  150  than the width at the outside radial end  152  of the web spoke. 
         [0033]      FIG. 7  is a section view of the adjacent web spokes  150  taken on line  7 - 7  of  FIG. 4  which is at the inside radial end location  154  along the length of the web spoke  150 . In the embodiment, the magnitude of the draft angle is greater than at the outside radial end  152  of the web spoke  150 . The width of the web spoke  150  at the inside radial end  154  of the web spoke is less than the middle portion of the web spoke and less than the width of the web spoke at the outside radial end  152 . In the embodiment, the draft angle is  12  degrees at the inner radial end  154  of the web spoke. 
         [0034]    The draft angle changes from a smaller draft angle at the outside radial end to a greater draft angle at the inner radial end of the web spoke  150 . The increased draft angle allows reduction of the lateral stiffness of the wheel. When discussing smaller or larger draft angles herein, it should be obvious that a “smaller” draft angle refers to a draft angle that is closer to having zero draft, while a larger draft angle is an angle that has a larger draft regardless of whether the spoke is angled clockwise or counterclockwise. 
         [0035]    The change of draft angle along the length of the web spoke creates a web spoke  150  which is twisted. This twist is due to the variation of the draft angle as the web spoke  150  moves inward radially from the outer band  170  to the inner band  160 . When the wheel  100  tread surface  105  is placed against a flat surface and the wheel  100  is loaded, for instance by the vehicle weight, the compliant band  110  flattens in the area of contact of the ground with the tread portion  105 , this area of contact also generally referred to as the “footprint.” This flattening of the compliant band reduces the distance from the outer band  170  to the inner band  160  resulting in web spokes  150  above the wheel  100  footprint to both bend along length of the web spoke  150  and deform across width of the web spoke  150  near the outer band  170  due to the equatorial flattening and any lateral deformation of the compliant band  110  that may be present due to tread sculpture or lateral curvature of the surface. This web spoke deformation can create a structural instability in the web spoke  150  which is reduced when the draft angle is reduced near the outer band. Thus, the twist allows for reduced lateral stiffness in the wheel  100  while reducing structural instability in each individual web spoke  150  when bending by allowing a smaller draft angle near the outer band  170  but a larger draft angle near the inner band  160 . 
         [0036]      FIG. 8  shows a section view along the equatorial plane of the wheel  100 . In the embodiment as shown, the tread portion  105  of the wheel forms the outer periphery of the compliant band  110 . Alternatively, the tread portion may be an additional layer bonded to the outer surface of the compliant band. The web spokes  150  possess a three curved radius blend profile aimed at reducing stress concentrations when the web spokes  150  are bearing the vehicle weight while encouraging predictable flexing in compression. Alternatively the spokes may be straight. Alternatively the web spoke  150  may be molded curved then straightened by thermal shrinkage during cooling to predispose them to curve in a particular direction. The web spokes are joined at the inner radial ends  154  by an inner band  160 , which is secured to a hub  10 . At the outer radial end  152  of the web spokes  150 , each spoke is joined together by an outer band  170  which interconnect the web spokes together. In the embodiment, the inner band  160 , web spokes  150  and outer band  170  are molded from a single material as a unit. 
         [0037]      FIG. 9  shows a cross section of the wheel  100  taken on line  9 - 9  of  FIG. 3  which is a view along a plane through the transverse axis of the tire. In the embodiment, each web spoke tapers from the inner radial end  154  to the outer radial end  152  generally increasing in diameter. This taper may be non-linear, such as, for example the taper as shown, or alternatively the taper may be linear. In the embodiment shown, the web spoke  150  taper is non-linear having a concave left edge  153  and right edge  155 . 
         [0038]    It should be understood that many other variations are apparent to one of ordinary skill in the art from a reading of the above specification. These variations and other variations are within the spirit and scope of the instant invention as defined by the following appended claims.