Abstract:
A structurally supported tire includes a ground contacting annular tread portion, an annular shear band and at least one spoke disk connected to the shear band, wherein the spoke disk has at least one spoke, wherein the spoke extends between an outer ring and an inner ring in a first parabolic curve. The spoke disk may further includes a second spoke having a second parabolic curve different from the first curve, and overlapping with the first spoke.

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 front view of the non-pneumatic tire of  FIG. 1 ; 
           [0009]      FIG. 3  is a front view of the non-pneumatic tire of  FIG. 1  shown with the spoke disks in phantom; 
           [0010]      FIG. 4  is a cross-sectional view of the of the non-pneumatic tire of  FIG. 1 ; 
           [0011]      FIG. 5  is a perspective cross-sectional view of the of the non-pneumatic tire of  FIG. 1 ; 
           [0012]      FIG. 6  is a partial cross-sectional view of the non-pneumatic tire of  FIG. 1  illustrating the tread and shear band; 
           [0013]      FIG. 7  is a front view of first embodiment of a spoke disk of the present invention; 
           [0014]      FIG. 8  is a cross-sectional view in the direction  8 - 8  of the spoke disk of  FIG. 7 ; 
           [0015]      FIG. 9  is a front view of second embodiment of a spoke disk of the present invention; 
           [0016]      FIGS. 10A-10B  are perspective and side views of a rim assembly of the present invention. 
           [0017]      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. 
           [0018]      FIG. 12 a    illustrates a spring rate test for a spoke disk, while  FIG. 12 b    illustrates the spring rate k determined from the slope of the force displacement curve. 
           [0019]      FIG. 12 c    is the deflection measurement on a shear band from a force F. 
           [0020]      FIG. 13 a    illustrates a spring rate test for a spoke disk, while  FIG. 13 b    illustrates the tire spring rate k determined from the slope of the force displacement curve. 
           [0021]      FIG. 14  is a perspective view of a second spoke disk under load. 
           [0022]      FIG. 15  is a perspective view of a tire of the present invention under load. 
           [0023]      FIG. 16  is an exploded view of a tire of the present invention. 
           [0024]      FIG. 17  illustrates the disposition of adhesive on tire components. 
       
    
    
     DEFINITIONS 
       [0025]    The following terms are defined as follows for this description. 
         [0026]    “Equatorial Plane” means a plane perpendicular to the axis of rotation of the tire passing through the centerline of the tire. 
         [0027]    “Meridian Plane” means a plane parallel to the axis of rotation of the tire and extending radially outward from said axis. 
         [0028]    “Hysteresis” means the dynamic loss tangent measured at 10 percent dynamic shear strain and at 25° C. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A first embodiment of a non-pneumatic tire  100  of the present invention is shown in  FIGS. 1-6 . The non-pneumatic tire of the present invention includes a radially outer ground engaging tread  200 , a shear band  300 , one or more spoke disks  400 , 500 , and a rim  700 . The spoke disks  400 , 500  may have different designs, as described in more detail, below. The non-pneumatic tire of the present invention is designed to be a top loading structure, so that the shear band  300  and the one or more spoke disks  400 , 500  efficiently carry the load. The shear band  300  and the spoke disks are designed so that the stiffness of the shear band is directly related to the spring rate of the tire. The spokes of each disk are designed to be stiff structures that deform in the tire footprint. This allows the rest of the spokes not in the footprint area the ability to carry the load. Since there are more spokes outside of the footprint than in, the load per spoke would be small enabling smaller spokes to carry the tire load which gives a very load efficient structure. Not all spokes will be able to elastically deform and will retain some portion of the load in compression in the footprint. 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 90-100% of the load is carried by the shear band and the upper spokes, so that the lower spokes carry virtually zero of the load, and preferably less than 10%. 
         [0030]    The non-pneumatic tire may have different combination of spoke disks in order to tune the non-pneumatic tire with desired characteristics. For example, a first spoke disk  500  may be selected that carries both shear load and tensile load. A second spoke disk may be selected that carries a pure tensile load. 
         [0031]    The tread portion  200  may have no grooves or may have 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 
       [0032]    The shear band  300  is preferably annular, and is shown in  FIG. 6 . 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 . The shear band  300  may be formed of two inextensible 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, or other inextensible structure. The shear band  300  may optionally include a third reinforced elastomer layer  333  located between the first and second reinforced elastomer layers  310 , 320  and between shear matrix layers  330 , 331 . 
         [0033]    In the first reinforced elastomer layer  310 , the reinforcement cords  311  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  321  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. 
         [0034]    The shear matrix  330  has a 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 Gm in the range of 0.5 to 10 MPa, and more preferably in the range of 4 to 8 MPA. 
         [0035]    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 band and having the same radial thickness as the shearband. The shear stiffness GA is then calculated from the following equation: 
         [0000]    
       
      
       GA=F*L/ΔX  
      
     
         [0036]    The shear band has a bending stiffness EI. The bending stiffness EI may be determined from beam mechanics using the three point bending test. 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. 
         [0037]    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 an ideal 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 an ideal range of 1 to 50. 
         [0038]    The shear band  300  preferably can withstand a maximum shear strain in the range of 15-30%. 
         [0039]    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, as shown in  FIG. 13 a   . The spring rate k t  is determined from the slope of the force versus deflection curve, as shown in  FIG. 13 b   . Depending upon the desired application, the tire spring rate k t  may vary. The tire spring rate k t  is preferably in the range of 650 to 1200 lbs/inch for a lawn mower or slow speed vehicle application. 
         [0040]    The shear band 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 is determined from the slope of the Force versus deflection curve as shown in  FIG. 11   b.    
         [0041]    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 in the range of 20 to 2000, 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, or a spring rate of 170 lb/in, and any subcombinations thereof. The tire tread is preferably wrapped about the shear band and is preferably integrally molded to the shear band. 
       Spoke Disk 
       [0042]    One example of a load bearing member suitable for use in the non-pneumatic tire is shown in  FIG. 7 . As shown in  FIG. 7 , the load bearing member may be a solid annular disk  400  having an outer edge  406  and an inner edge  403 . As shown in  FIG. 8 , the solid disk  400  is curved, having a maximum curvature at a location of ½ the radial height of the disk. The solid disk  400  has a curvature that projects axially outward (away from the tire center) or convex. The inner edge  403  of the solid spoke disk is received over and mounted on the outer surface  602  of the cylindrical rim  600 . The rim  600  is shown in for receiving a metal or rigid reinforcement ring  405  to form a hub. The solid disk  400  has an axial thickness A that is substantially less than the axial thickness AW of the non-pneumatic tire. The axial thickness A is in the range of 5-20% of AW, more preferably 5-10% AW. If more than one disk is utilized, than the axial thickness of each disk may vary or be the same. The solid disk has a thickness t. The ratio of the spoke axial width W to thickness t, W/t is in the range of 8-28, more preferably 9-11. 
         [0043]    Each spoke disk has a spring rate SR which may be determined experimentally by measuring the deflection under a known load, as shown in  FIG. 12 a   . One method for determining the spoke disk spring rate k is to mount the spoke disk to a hub, and attaching the outer ring of the spoke disk to a rigid test fixture. A downward force is applied to the hub, and the displacement of the hub is recorded. The spring rate k is determined from the slope of the force deflection curve as shown in  FIG. 12 b   . It is preferred that the spoke disk spring rate be greater than the spring rate of the shear band. It is preferred that the spoke disk spring rate be in the range of 3 to 12 times greater than the spring rate of the shear band, and more preferably in the range of 3 to 4 times greater than the spring rate of the shear band. Each spoke disk preferably has a spring rate k in the range of 800 to 1400 lb/in, and more preferably 900 to 1300 lb/in. Preferably, if more than one spoke disk is used, all of the spoke disks have a spring rate within 10% of each other. The spring rate of the non-pneumatic tire may be adjusted by increasing the number of spoke disks. Alternatively, the spring rate of each spoke disk may be different by varying the geometry of the spoke disk or changing the material. It is additionally preferred that if more than one spoke disk is used, that all of the spoke disks have the same outer diameter. 
         [0044]      FIG. 9  illustrates a second embodiment of a spoke disk  500 . The spoke disk  500  has an axial thickness A substantially less than the axial thickness AW of the non-pneumatic tire. The solid disk  500  has a plurality of spokes that extend radially between an inner ring  510  and an outer ring  520 . The shear band  300  is mounted radially outward of the spoke disks. The spoke disk  500  has a first spoke  530  that intersects with a second spoke  540  at a joint  550 . The first spoke  530  forms an angle Beta with the outer ring  520  in the range of 20 to 80 degrees, more preferably in the range of 55-65 degrees. The solid disk  500  further includes a second spoke  540  that extends from the outer ring  520  to the inner ring  510 , preferably in a curved shape. The second spoke  540  has a radially outer portion  540   a  that extends radially outward of the joint  550 , and a radially inner portion  540   b  that is radially inward of the joint  550 . Likewise, the first spoke  530  has a radially outer portion  530   a  that is radially outward of the joint  550 , and a radially inner portion  530   b  that is radially inward of the joint  550 . For the first spoke  530 , the curvature of the radially inner portion  530   b  is opposite the curvature of the radially outer portion  530   a . Preferably, the curvature of the radially outer portion  530   a  is concave, and the curvature of the radially inner portion  530   b  is convex or straight. For the second spoke  540 , the curvature of the radially inner portion  540   b  is opposite the curvature of the radially outer portion  540   a . Preferably, the curvature of the radially outer portion  540   a  is convex, and the curvature of the radially inner portion  540   b  is concave. The shaping or curvature of the first and second spokes control how the blades bend when subject to a load. See  FIG. 14  which illustrates the second spoke disk  500  under load. The blades of the spoke disk  500  are designed to bend in the angular direction theta. 
         [0045]    The joining of the first spoke  530  to the second spoke  440  by the joint  550  results in an approximate shape of a radially outer triangle  560  and an approximate shape of a radially inner triangle  570 . The radial height of the joint  550  can be varied, which thus varies the size of the approximate outer and inner triangles  560 , 570 . The ratio of  540   b / 540   a  and/or  530   b / 530   a  may be in the range of 0.2 to 5, and preferably in the range of 0.3 to 3, and more preferably in the range of 0.4 to 2.5. The spokes  530 , 540  have a spoke thickness t 2  in the range of 2-5 mm, and an axial width W in the axial direction in the range of about 25-70 mm. The ratio of the spoke axial width W 2  to thickness t 2 , W 2 /t 2  is in the range of 8-28, more preferably 9-11. 
         [0046]    Preferably, the spoke disk  500  has a spoke width W to spoke axial thickness ratio, W 2 /t 2 , in the range of about 15 to about 80, and more preferably in the range of about 30 to about 60 and most preferably in the range of about 45 to about 55. 
         [0047]    A first embodiment of a non-pneumatic tire is shown in  FIGS. 3-5 . The spoke disks on the outer axial ends of the tire are the solid disks  400 , and are oriented so that they deform axially outward, as shown in  FIG. 15 . Although not shown, there may be two solid spoke disks on each end of the tire. The solid disks  400  may also be located at any desired axial location. The first embodiment may optionally include one or more spoke disks  500  located between the solid spoke disks  400 . The solid disks  400  are designed to carry both shear and tension loads, while the spoke disks  500  are designed to carry loads in tension only. The number of spoke disks  500  may be selected as needed. The orientation of the spoke disks  500  may be such that the spokes are axially and radially aligned, as shown in  FIG. 3 . Preferably the spoke disks  500  may be rotationally staggered at angular intervals in the range of 5-60 degrees, more preferably 10-30 degrees. Optionally, the spoke disks  500  may be rotated 180 degrees about a central axis so that the disks bend in an opposite angular direction. The solid disks  400  bend or deform axially outward, while the spoke disks bend in an angular plane theta. The disks  400 , 500  are designed to be laterally stiff, so that they can be combined to tune the tire lateral stiffness. 
         [0048]    A second embodiment of the non-pneumatic tire eliminates the solid spoke disks  500  from the tire. The second embodiment includes at least two spoke disks  500 , and preferably 6-8 spoke disks  500 . The orientation of the spoke disks  500  may be such that the spokes are axially and radially aligned, as shown in  FIG. 3 . Preferably the spoke disks  500  may be rotationally staggered at angular intervals in the range of 5-60 degrees, more preferably 10-30 degrees. Preferably, the spoke disks are oriented so that the bend in the direction of the tire rotation. Optionally, the spoke disks  500  may be rotated 180 degrees about a central axis so that the disks bend in an opposite angular direction. 
         [0049]    The spoke disks are preferably formed of an elastic material, more preferably, a thermoplastic elastomer. The material of the spoke disks is selected based upon one or more of the following material properties. The tensile (Young&#39;s) modulus of the disk material is preferably in the range of 45 MPa to 650 MPa, and more preferably in the range of 85 MPa to 300 MPa, using the ISO 527-1/-2 standard test method. The glass transition temperature is less than −25 degree Celsius, and more preferably less than −35 degree Celsius. The yield strain at break is more than 30%, and more preferably more than 40%. The elongation at break is more than or equal to the yield strain, and more preferably, more than 200%. The heat deflection temperature is more than 40 degree C. under 0.45 MPa, and more preferably more than 50 degree C. under 0.45 MPa. No break result for the Izod and Charpy notched test at 23 degree C. using the ISO 179/ISO180 test method. Two suitable materials for the disk is commercially available by DSM Products and sold under the trade name ARNITEL PL 420H and ARNITEL PL461. 
         [0050]      FIGS. 16 and 17  show schematic illustrations of the assembly of the non-pneumatic tire  100 . With reference to  FIG. 16 , non-pneumatic tire  100  is shown in expanded view indicating the orientation of the various assembled components. In the illustrated embodiment, the tire  100  includes rim  100  with spoke disks  500  disposed concentrically and axially along the outer surface  750  of rim  700 . Spoke disks  500  engage rim  700  via an adhesive bond between radially innermost surface  580  of the spoke disk  500  and radially outermost surface  750  of the rim  700 . Shear band  300  is disposed concentrically over the axially disposed spoke disks  500 . Shear band  300  engages spoke disks  500  via an adhesive bond between radially innermost surface  350  of shear band  300  and radially outermost surfaces  590  of spoke disks  500 . Tread  200  radially overlays shear band  300  and is bonded to shear band  300  via co-curing of the elastomer compositions. 
         [0051]    The adhesive bonds between the spoke disks  500  and the rim  700 , and between the spoke disks  500  and the shear band  300 , is accomplished using an appropriate adhesive that bonds effectively between metal and thermoplastic, and between thermoplastic and elastomer. In one embodiment, the adhesive is a cyanoacrylate type adhesive comprising an alkyl-2-cyanoacrylate monomer. In one embodiment, the alkyl group includes from one to ten carbon atoms, in linear or branched form. In one embodiment, the alkyl-2-cyanoacrylate monomers include methyl-2-cyanoacrylate, ethyl-2-cyanoacrylate, butyl-2-cyanoacrylate, and octyl-2-cyanoacrylate. In one embodiment, the adhesive is an ethyl-2-cyananoacrylate available as Permabond® 268. 
         [0052]    As seen in  FIG. 16 , the adhesive is applied in thin layers  360 ,  760  to radially innermost surface  350  of shear band  300  and to radially outermost surface  750  of rim  700 , followed by assembly of the various components as shown in  FIG. 15 . The adhesive may be applied for example manually using a brush, sponge, trowel, spatula or the like. 
         [0053]    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.