Abstract:
A structurally supported tire includes a ground contacting annular tread portion, an annular shear band and geodesic ply.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to vehicle tires and non-pneumatic tires, and more particularly, to a non-pneumatic tire. 
       BACKGROUND OF THE INVENTION 
       [0002]    The pneumatic tire has been the solution of choice for vehicular mobility for over a century. The pneumatic tire is a tensile structure. The pneumatic tire has at least four characteristics that make the pneumatic tire so dominate today. Pneumatic tires are efficient at carrying loads, because all of the tire structure is involved in carrying the load. Pneumatic tires are also desirable because they have low contact pressure, resulting in lower wear on roads due to the distribution of the load of the vehicle. Pneumatic tires also have low stiffness, which ensures a comfortable ride in a vehicle. The primary drawback to a pneumatic tire is that it requires compressed fluid. A conventional pneumatic tire is rendered useless after a complete loss of inflation pressure. 
         [0003]    A tire designed to operate without inflation pressure may eliminate many of the problems and compromises associated with a pneumatic tire. Neither pressure maintenance nor pressure monitoring is required. Structurally supported tires such as solid tires or other elastomeric structures to date have not provided the levels of performance required from a conventional pneumatic tire. A structurally supported tire solution that delivers pneumatic tire-like performance would be a desirous improvement. 
         [0004]    Non pneumatic tires are typically defined by their load carrying efficiency. “Bottom loaders” are essentially rigid structures that carry a majority of the load in the portion of the structure below the hub. “Top loaders” are designed so that all of the structure is involved in carrying the load. Top loaders thus have a higher load carrying efficiency than bottom loaders, allowing a design that has less mass. 
         [0005]    Thus an improved non pneumatic tire is desired that has all the features of the pneumatic tires without the drawback of the need for air inflation is desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention will be better understood through reference to the following description and the appended drawings, in which: 
           [0007]      FIG. 1  is a perspective view of a first embodiment of a non-pneumatic tire of the present invention; 
           [0008]      FIG. 2  is a perspective view of a second embodiment of a non-pneumatic tire of the present invention; 
           [0009]      FIG. 3  is a cross-sectional view of the non-pneumatic of  FIG. 1  or  FIG. 2 ; 
           [0010]      FIG. 4  is a cross-sectional view of the non-pneumatic of  FIG. 1  or  FIG. 2  having a double reinforcement layer; 
           [0011]      FIG. 5  is a close up side view of the tire of  FIG. 1  having geodesic ply spokes. 
           [0012]      FIG. 6  is a perspective view of an embodiment of the invention with geodesic ply spokes; 
           [0013]      FIG. 7  is a side view of a third embodiment of the invention with geodesic ply spokes having a turnup. 
           [0014]      FIG. 8 a    is a cross-sectional view of the invention showing the ply positioned in the shear band between the reinforcement layers of the shear band. 
           [0015]      FIG. 8B  illustrates an alternate embodiment of the ply clamped around an optional elastic member. 
           [0016]      FIG. 9  illustrates a fourth embodiment of the invention. 
           [0017]      FIG. 10  is a cross-sectional view of the invention showing ply spokes embedded in the shear band. 
           [0018]      FIG. 11 a    illustrates a spring rate test for a shear band, while  FIG. 11 b    illustrates the spring rate k determined from the slope of the force displacement curve. 
           [0019]      FIG. 12  is the deflection measurement on a shear band from a force F. 
       
    
    
     DEFINITIONS 
       [0020]    The following terms are defined as follows for this description. 
         [0021]    “Equatorial Plane” means a plane perpendicular to the axis of rotation of the tire passing through the centerline of the tire. 
         [0022]    “Meridian Plane” means a plane parallel to the axis of rotation of the tire and extending radially outward from said axis. 
         [0023]    “Hysteresis” means the dynamic loss tangent measured at 10 percent dynamic shear strain and at 25° C. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    A non-pneumatic tire  100  of the present invention is shown in the enclosed figures. The non-pneumatic tire of the present invention includes a radially outer ground engaging tread  200 , a shear band  300 , and one or more reinforcement layer  400 . The non-pneumatic tire of the present invention is designed to be a top loaded structure, so that the shear band  300  and the reinforcement layer  400  efficiently carries the load. The shear band  300  and the reinforcement layer  400  are designed so that the stiffness of the shear band is directly related to the spring rate of the tire. The reinforcement layer is designed to be a stiff structure that buckles or deforms in the tire footprint and does not compress or carry a compressive load. This allows the rest of structure not in the footprint area the ability to carry the load, resulting in a very load efficient structure. It is desired to minimize this load for the reason above and to allow the shearband to bend to overcome road obstacles. The approximate load distribution is such that approximately 95-100% of the load is carried by the shear band and the upper radial portion of the reinforcement layer  400 , so that the lower portion of the reinforcement structure undergoing compression carries virtually zero of the load, and preferably less than 10%. 
         [0025]    The tread portion  200  may be a conventional tread as desired, and may include grooves or a plurality of longitudinally oriented tread grooves forming essentially longitudinal tread ribs there between. Ribs may be further divided transversely or longitudinally to form a tread pattern adapted to the usage requirements of the particular vehicle application. Tread grooves may have any depth consistent with the intended use of the tire. The tire tread  200  may include elements such as ribs, blocks, lugs, grooves, and sipes as desired to improve the performance of the tire in various conditions. 
       Shear Band 
       [0026]    The shear band  300  is preferably annular. A cross-sectional view of the shear band is shown in  FIG. 3 . The shear band  300  is located radially inward of the tire tread  200 . The shear band  300  includes a first and second reinforced elastomer layer  310 , 320 . In a first embodiment of a shear band  300 , the shear band is comprised of two inextensible reinforcement layers  310 , 320  arranged in parallel, and separated by a shear matrix  330  of elastomer. Each inextensible layer  310 , 320  may be formed of parallel inextensible reinforcement cords  311 , 321  embedded in an elastomeric coating. The reinforcement cords  311 , 321  may be steel, aramid, nylon, polyester or other inextensible structure. The shear band  300  may further optionally include a third reinforced elastomer layer  340  (not shown) located between the first and second reinforced elastomer layers  310 , 320 . 
         [0027]    It is additionally preferred that the outer lateral ends  302 , 304  of the shear band be radiused in order to control the buckled shape of the sidewall and to reduce flexural stresses. 
         [0028]    In the first reinforced elastomer layer  310 , the reinforcement cords are oriented at an angle Φ in the range of 0 to about +/−10 degrees relative to the tire equatorial plane. In the second reinforced elastomer layer  320 , the reinforcement cords are oriented at an angle φ in the range of 0 to about +/−10 degrees relative to the tire equatorial plane. Preferably, the angle Φ of the first layer is in the opposite direction of the angle φ of the reinforcement cords in the second layer. That is, an angle +Φ in the first reinforced elastomeric layer and an angle −φ in the second reinforced elastomeric layer. 
         [0029]    The shear matrix  330  may have a radial thickness in the range of about 0.10 inches to about 0.2 inches, more preferably about 0.15 inches. The shear matrix is preferably formed of an elastomer material having a shear modulus G m  in the range of 15 to 80 MPa, and more preferably in the range of 40 to 60 MPA. 
         [0030]    The shear band has a shear stiffness GA. The shear stiffness GA may be determined by measuring the deflection on a representative test specimen taken from the shear band. The upper surface of the test specimen is subjected to a lateral force F as shown below. The test specimen is a representative sample taken from the shear matrix material, having the same radial thickness. 
         [0031]    The shear stiffness GA is then calculated from the following equation: 
         [0000]    
       
      
       GA=F*L/ΔX  
      
     
         [0032]    The shear band has a bending stiffness EI. The bending stiffness EI may be determined from beam mechanics using the three point bending test subjected to a test specimen representative of the shear band. It represents the case of a beam resting on two roller supports and subjected to a concentrated load applied in the middle of the beam. The bending stiffness EI is determined from the following equation: EI=PL 3 /48*ΔX, where P is the load, L is the beam length, and ΔX is the deflection. 
         [0033]    It is desirable to maximize the bending stiffness of the shearband EI and minimize the shear band stiffness GA. The acceptable ratio of GA/EI would be between 0.01 and 20, with a preferred range between 0.01 and 5. EA is the extensible stiffness of the shear band, and it is determined experimentally by applying a tensile force and measuring the change in length. The ratio of the EA to EI of the shearband is acceptable in the range of 0.02 to 100 with a preferred range of 1 to 50. The shear band  300  preferably can withstand a maximum shear strain in the range of 15-30%. 
         [0034]    The shear band  300  has a spring rate k that may be determined experimentally by exerting a downward force on a horizontal plate at the top of the shear band and measuring the amount of deflection as shown in  FIG. 11 a   . The spring rate k is determined from the slope of the Force versus deflection curve, as shown in  FIG. 11   b.    
         [0035]    The non-pneumatic tire has an overall spring rate k t  that is determined experimentally. The non-pneumatic tire is mounted upon a rim, and a load is applied to the center of the tire through the rim. The spring rate k t  is determined from the slope of the Force versus deflection curve. The spring rate k t  is preferably in the range of 500 to 1000 for small low speed vehicles such as lawn mowers. 
         [0036]    The invention is not limited to the shear band structure disclosed herein, and may comprise any structure which has a GA/EI in the range of 0.01 to 20, or a EA/EI ratio in the range of 0.02 to 100, or a spring rate k t  in the range of 500 to 1000, as well as any combinations thereof. More preferably, the shear band has a GA/EI ratio of 0.01 to 5, or an EA/EI ratio of 1 to 50 and any subcombinations thereof. The tire tread is preferably wrapped about the shear band and is preferably integrally molded to the shear band. 
       Reinforcement Structure 
       [0037]    A first embodiment of the non-pneumatic tire of the present invention is shown in  FIG. 2 . The reinforcement structure  400  functions to carry the load transmitted from the shear layer. The reinforcement structure  400  is primarily loaded in tension and shear, and carries no load in compression. As shown in  FIGS. 2 and 3 , the reinforcement layer  400  has a first end  402   a,b  that extends from a first radius to a second radius in order to form the non-pneumatic tire sidewall. At the first radius, the first end  402   a,b  is clamped to a rim via clamp rings  500  connected to the rim, as shown in  FIG. 3 , without the need for a bead. Each first end  402   a,b  extends radially outward and terminates in a respective second end  405   a,b . As shown in  FIG. 3 , the reinforcement layer extends radially outward of the shear band  300  and terminates axially inward of the lateral edges  302 , 304  of the shear band. Thus the sidewall may be formed from one or more reinforcement layers. The second end  405   a,b  may optionally extend completely across the crown of the tire, although not required, as shown in  FIG. 4 . 
         [0038]    The reinforcement layer  400  may comprise any fabric or flexible structure such as nylon, polyester, cotton, rubber. Preferably, the reinforcement layer  400  comprises a reinforced rubber or ply layer formed of parallel reinforcements that are nylon, polyester or aramid. Preferably, the reinforcements are oriented in the radial direction. It is preferred that tire ply be used as a reinforcement layer for several reasons. First, tire ply is an ideal connecting structure for the non-pneumatic tire application because it is thin, and has a low bending stiffness with no resistance to compression or buckling. Tire ply has a high tensile stiffness and strength which is needed in the non-pneumatic tire application. Tire ply is also cheap, has a known durability, and is readily available. Furthermore, a continuous ply reinforcement layer eliminates debris which can be caught into spoke or web non pneumatic tire designs, and does not contribute to tire noise or high frequency harmonics associated with discrete spokes. 
         [0039]    The reinforcement layer forming the sidewalls is preferably oriented so that it makes an angle alpha with respect to the radial direction, as shown in  FIG. 3 . The angle alpha can help pretension the reinforcement  400  and also increase and tune the lateral stiffness of the tire. This results in a non-pneumatic tire having angled sidewalls. The angle alpha is measured with respect to the radial direction, and may be −10 to 45 degrees, and more preferably, 0 to 45 degrees, and even more preferably 10-25 degrees as measured with respect to the radial direction. The angle alpha can be tuned as desired using an axial adjustment feature of the rim  502 . The rim  502  may be axially adjusted to narrow or expand the axial rim width. This axial adjustment controls the ply tension, allowing the tire lateral stiffness to be adjusted independent of the radial stiffness. The rim may be adjusted by a tensioning member or bolt  504  that is mounted in the opposed rim parallel walls  506 , 508 . The clamp rings  500  are secured to the outer end of the rim walls  506 , 508 . Alternatively, the angle may be adjusted by the radial length of the sidewalls. 
         [0040]      FIG. 1  illustrates a second embodiment of the invention wherein the reinforcement layer is formed by a plurality of strips  401 , that are preferably geodesic, and more preferably the strips are oriented in the radial direction. The strips are preferably about 0.25 to 0.5 inches wide. Each strip preferably includes one or more parallel reinforcements, such as nylon, polyester or aramid reinforcements which are preferably oriented in the radial direction when mounted on the tire.  FIG. 3  is representative of the cross-section of  FIG. 1 , wherein the strips may be arranged in a single reinforcement layer. The strips may overlap as shown in  FIG. 5 . Alternatively, the reinforcement structure  400  may comprise two or more layers of reinforcement for the embodiments of  FIG. 1 or 2  as shown in  FIG. 4,5 . As shown in  FIG. 4 , the ply layer has a first inner layer  400  that extends completely (axially) across the crown portion of the tire, and is located radially outward of the shear band  300 . The inner ply layer  400  extends radially inward and forms a looped end  402   a,b  that is clamped or secured to the rim, wherein the ply forms a second layer that extends radially outward of the rim clamps and then radially outward of the shear band terminating in folded over ends  408   a,b . Thus the sidewalls are formed of a dual layer of reinforcement ply. An optional flexible o-ring or flexible rubber band  800  may be used to form the looped end, as shown in  FIG. 6 , wherein the flexible o-ring  800  and ply ends are then securing to rim clamps  500  as shown in  FIG. 8   b.    
         [0041]    Alternatively, the reinforced ply strip may be continuously wound from one side of the tire to the other in order to form a plurality of geodesic ply spokes. The reinforced strips are wound in a continuous manner so that the geodesic ply spokes extend from the inner radius R 1  to the outer radius R 2 , as shown in  FIG. 8 a   . Preferably, the ply spokes are oriented in the radial direction. The reinforced strip may optionally extend over the full axial width of the crown and then radially inward to form the other sidewall. The ply spokes or strip are preloaded in tension. 
         [0042]    Alternatively, the first end  402   a,b  may be wound around a portion of the rim, or otherwise secured or fastened to the outer radial portion of the rim. 
         [0043]    Alternatively, the first end  402   a,b  may be looped around a portion of the rim and secured to the down portion of the ply forming a looped end or beadless turnup as shown in  FIG. 7 . The looped end may be received in clamps and may further include an optional annular flexible member  800  mounted on the rim. The optional flexible member  800  may be an o-ring or flexible rubber band, which may be included to facilitate the mounting of the reinforcement structure on the rim clamp as shown in  FIG. 6  and  FIG. 8 b   . Thus the invention has eliminated the need for a bead or annular tensile member, which reduces the weight, cost and complexity of the design. 
         [0044]    The reinforcement structure  400  need not be positioned radially outward of the shear band. The reinforcement structure may be positioned radially inward of the shear band, and underneath the shear band as shown in  FIG. 9 . Alternatively, a portion of the reinforcement layer may even be positioned between the reinforcement layers of the shear band, as shown in  FIG. 8A . However, it is advantageous to locate the reinforcement layer radially outward of the shear band because it eliminates the tensile stress on the bond between the shear band and load carrying member or connecting structure. This advantage is especially important when the shear band and the play are dissimilar materials. 
         [0045]    Alternatively as shown in  FIG. 10 , a first end  432  of a ply spoke may terminate in the crown portion of the tire and in the shear band, and the terminal end  431  of the ply spoke may partially extend up the sidewall of the tire. 
         [0046]    Applicants understand 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 present invention as defined by the following appended claims.