Abstract:
A pneumatic tire having a carcass and a belt reinforcing structure, the belt reinforcing structure comprising: a zigzag belt reinforcing structure formed of a strip of reinforcement cords, the strip of reinforcement cords being inclined at 5 to 30 degrees relative to the centerplane of the tire extending in alternation to turnaround points at each lateral edge, wherein the strip of cords is formed from two different cords made of different materials.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to pneumatic tires having a carcass and a belt reinforcing structure, more particularly to high speed heavy load tires such as those used on aircraft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Pneumatic tires for high speed applications experience a high degree of flexure in the crown area of the tire as the tire enters and leaves the area of the footprint. This problem is particularly exacerbated on aircraft tires wherein the tires can reach speed of over 200 mph at takeoff and landing. 
         [0003]    When a tire spins at very high speeds the crown area tends to grow in dimension due to the high angular accelerations and velocity, tending to pull the tread area radially outwardly. Counteracting these forces is the load of the vehicle which is only supported in the small area of the tire known as the footprint area. 
         [0004]    Current tire design drivers are an aircraft tire capable of high speed, high load and with reduced weight. It is known in the prior art to use zigzag belt layers in aircraft tires, such as disclosed in the Watanabe U.S. Pat. No. 5,427,167. Zigzag belt layers have the advantage of eliminating cut belt edges at the outer lateral edge of the belt package. The inherent flexibility of the zigzag belt layers also help improve cornering forces. However, a tire designed with zigzag belt layers may result in too many layers at the belt edges which may reduce durability. Further, there is generally a tradeoff between load capacity and weight. Thus an improved aircraft tire is needed, which is capable of meeting high speed, high load and with reduced weight. 
       Definitions 
       [0005]    “Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads. 
         [0006]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
         [0007]    “Cord” means one of the reinforcement strands of which the plies in the tire are comprised. 
         [0008]    “Equatorial plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread. 
         [0009]    “Modulus of elasticity” of a cord at a given strain or stress means the extension secant modulus calculated at the given strain or stress. A high elastic modulus means a secant elastic modulus over 1000 cN/tex and a low elastic modulus means a secant modulus under 600 cN/tex. 
         [0010]    “Ply” means a continuous layer of rubber-coated parallel cords. 
         [0011]    “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire. 
         [0012]    “Radial-ply tire” means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire. 
         [0013]    “Section width” is the distance between a tire&#39;s sidewalls measured at the widest part of the tire when inflated to rated pressure and not under load. 
         [0014]    “Tangent modulus of elasticity” of a cord at a given strain or stress means the extension tangent modulus of the cord. At a given stress or strain, the tangent modulus of elasticity is the value of the slope of the tangent to the stress strain curve, and can be determined using ASTM E111-04 entitled “Standard Test Method for Young&#39;s Modulus, Tangent Modulus and Chord Modulus.” 
         [0015]    “Zigzag belt reinforcing structure” means at least two layers of cords or a ribbon of parallel cords having 1 to 20 cords in each ribbon and laid up in an alternating pattern extending at an angle between 5° and 30° between lateral edges of the belt layers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic cross-sectional view of a first embodiment of half of a tire according to the invention; 
           [0017]      FIG. 2  is a schematic perspective view of a zigzag belt layer in the middle of the formation; 
           [0018]      FIG. 3  is a schematically enlarged cross-sectional view of a first embodiment of half of a composite belt package for a tire showing the belt layer configuration; 
           [0019]      FIG. 4  is a schematically enlarged cross-sectional view of a second embodiment of a composite belt package showing the belt layer configuration; 
           [0020]      FIG. 5  is a first embodiment of a belt reinforcement strip; and 
           [0021]      FIG. 6  is a second embodiment of a belt reinforcement strip. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  illustrates a cross-sectional view of one half of a radial aircraft tire  10  of the present invention. The tire is symmetrical about the mid-circumferential plane so that only one half is illustrated. As shown, the aircraft tire comprises a pair of bead portions  12  each containing a bead core  14  embedded therein. One example of a bead core suitable for use in an aircraft tire is shown in U.S. Pat. No. 6,571,847. The bead core  14  preferably has an aluminum, aluminum alloy or other light weight alloy in the center portion  13  surrounded by a plurality of steel sheath wires  15 . A person skilled in the art may appreciate that other bead cores may also be utilized. 
         [0023]    The aircraft tire further comprises a sidewall portion  16  extending substantially outward from each of the bead portions  12  in the radial direction of the tire, and a tread portion  20  extending between the radially outer ends of the sidewall portions  16 . The tire is shown mounted on a rim flange having a rim flange width extending from one bead to the other bead and indicated as W BF  in  FIG. 1 . The section width of the tire is indicated in  FIG. 1  as W and is the cross-sectional width of the tire at the widest part when inflated to normal pressure and not under load. 
         [0024]    Furthermore, the tire  10  is reinforced with a carcass  22  toroidally extending from one of the bead portions  12  to the other bead portion  12 . The carcass  22  is comprised of inner carcass plies  24  and outer carcass plies  26 , preferably oriented in the radial direction. Among these carcass plies, typically four inner plies  24  are wound around the bead core  14  from inside of the tire toward outside thereof to form turnup portions, while typically two outer plies  26  are extended downward to the bead core  14  along the outside of the turnup portion of the inner carcass ply  24 . 
         [0025]    The aircraft may preferably be an H type tire having a ratio of W BF /W in the range of about 0.65 to 0.7, and more preferably in the range of about 0.65 to about 0.68. 
         [0026]    Each of these carcass plies  24 , 26  may comprise any suitable cord, typically nylon cords such as nylon-6,6 cords extending substantially perpendicular to an equatorial plane EP of the tire (i.e. extending in the radial direction of the tire). Preferably the nylon cords have an 1890 denier/2/2 or 1890 denier/3 construction. One or more of the carcass plies  24 ,  26  may also comprise an aramid and nylon cord structure, for example, a hybrid cord, a high energy cord or a merged cord. Examples of suitable cords are described in U.S. Pat. No. 4,893,665, U.S. Pat. No. 4,155,394 or U.S. Pat. No. 6,799,618. The ply cords may have a percent elongation at break greater than 8% and less than 30%, and more preferably greater than 9% and less than 28%. 
         [0027]    The aircraft tire  10  further comprises a belt package  40  arranged between the carcass  22  and the tread rubber  28 .  FIG. 3  illustrates a first embodiment of one half of a belt package  40  suitable for use in the aircraft tire. The belt package  40  is symmetrical about the mid-circumferential plane so that only one half of the belt package is illustrated. The belt package  40  as shown comprises a first belt layer  50  located adjacent the carcass. The first belt layer  50  is preferably formed of reinforcement cords forming an angle of 10 degrees or less with respect to the mid-circumferential plane, and more preferably, 5 degrees or less. Preferably, the first belt layer  50  is formed of a first rubberized strip  41  of two or more cords made by spirally or helically winding the cords relative to the circumferential direction. The first belt layer  50  is the narrowest belt structure of the belt package  40 , and has a width in the range of about 13% to about 100% of the rim width (width between flanges). 
         [0028]    The belt package  40  further comprises a second belt layer  55  located radially outward of the first belt layer  50 . The second belt layer  55  is preferably formed of cords having an angle of 10 degrees or less with respect to the mid-circumferential plane. Preferably, the second belt layer  55  is formed of a rubberized strip  41  of two or more cords made by spirally or helically winding the cords relative to the circumferential direction. The second belt layer has a width in the range of about 13% to about 100% of the rim width. Preferably the second belt layer  55  has a width the same or slightly greater than the first belt layer  50 . The belt package  40  may further comprise a third belt layer  60  and a fourth belt layer  61 . The third belt layer  60  is located radially outward of the second belt layer  55 , and may be substantially wider than the second belt layer. The fourth belt layer is located radially outward of the third belt layer  60 , and may be the same width as the third belt layer  60  or slightly wider. The third and fourth belt layers  60 , 61  are low angle belts, typically with a belt angle of 10 degrees or less with respect to the mid-circumferential plane. Preferably, the third and fourth belt layers  60 ,  61  are formed of a first rubberized strip  41  of two or more cords made by spirally or helically winding the cords relative to the circumferential direction. 
         [0029]    The belt package  40  further comprises at least one zigzag belt reinforcing structure  70 ,  92 . The zigzag belt reinforcing structures  70 ,  92  are comprised of two layers of cord interwoven together formed as shown in  FIG. 2 . Each zigzag belt structure  70 ,  92  is formed from a rubberized composite strip  43  of two or more cords. The composite strip  43  is shown in  FIG. 5  and described in more detail, below. The composite strip  43  is wound generally in the circumferential direction to extend between alternating lateral edges  44  and  45  of a tire building drum  49  or core. The strip is wound along such zigzag path many times while the strip  43  is shifted a desired amount in the circumferential direction so as not to form a gap between the adjoining strips  43 . As a result, the cords extend in the circumferential direction while changing the bending direction at a turnaround point at both ends  44 ,  45 . The cords of the zigzag belt structure cross with each other, typically at a cord angle A of 5 degrees to 30 degrees with respect to the equatorial plane EP of the tire when the strip  43  is reciprocated at least once between both side ends  44  and  45  of the ply within every 360 degrees of the circumference as mentioned above. The two layers of cords formed in each zigzag belt structure are embedded and inseparable in the belt layer and wherein there are no cut ends at the outer lateral ends of the belt. 
         [0030]    In the embodiment of  FIG. 3 , it is preferred that one or more of the low angle belts  50 , 55 , 60 ,  61  are formed of a strip of reinforcement cords having an EPI of  18 . It is preferred that the strip of reinforcement cords are formed of reinforcement cords made of aramid, nylon, or a merged reinforcement cord blend of aramid and nylon. It is additionally preferred that the strip have a width of 0.5 inches, with 9 reinforcement cords. The zigzag belt strips are preferably formed of a 0.5 inch composite strip of 8 reinforcement cords having an EPI of 16. 
         [0031]    In order to reduce the number of overlapping strips at the belt edges, it is preferred that the amplitude or width of the zigzag belt winding be varied. Generally, a zigzag belt is formed to have a constant amplitude or width. In order to reduce the number of layers at the belt edges, the amplitude (distance from the drum center to the axial end of the drum) of the zigzag can be varied. The amplitude can be varied randomly, or it can be carried by a pattern. In one example, a first zigzag winding on the drum has a first winding pattern of W1W2, wherein W1 is a first amplitude, and W2 is a second amplitude which immediately follows the first amplitude, wherein W1 is not equal to W2. A second winding is overlayed on the first winding, and has a second winding pattern of W2W1. Each winding pattern is repeated as often as necessary to complete the winding on the drum. Strip Configuration 
         [0032]    The composite strip  43  is shown in  FIG. 5 , may be used to form any of the above described belt structures, and is preferably used to form at least one of the zigzag belt structures. More preferably, the composite strip is used to form all of the zigzag belt structures. The composite strip is made of two or more parallel reinforcement cords, wherein the reinforcement cords are different from each other. The reinforcement cords are embedded in rubber. More preferably, the composite strip  43  is formed of reinforcements made from different materials. The width of the strip may vary as desired, but it is preferably about 0.5 inches, with a variation of +/−5%. The gauge or thickness of the strip may vary depending upon the application. If the reinforced strip is utilized for spiral (helically wound) or low angle belts, then the gauge or thickness of the strip may be 0.062 inches. If the reinforced strip is used for zigzag belts, then the strip thickness is greater than for low angle/spiral belts. The strip thickness for zigzag belts is preferably 0.065 inches. 
         [0033]    In a first embodiment shown in  FIG. 5 , the first cord reinforcement  44  has a higher tangent modulus than the second cord reinforcement  46 . Preferably, the composite strip has at least two higher tangent modulus reinforcement cords  44  located laterally inward (ie, towards the center of the strip) on the strip, and at least two lower tangent modulus reinforcement cords. Preferably, the lower tangent modulus reinforcement cords  46  are located on the lateral outer ends of the composite strip. The higher tangent modulus reinforcement cords  44  have a tangent modulus at 80% break greater than 4500 MPA, and more preferably greater than 10,000 MPA and less than 31,000 MPA. The lower tangent modulus cords  46  have a tangent modulus at 80% break of less than 4500 MPA. 
         [0034]    In the example shown in  FIG. 5 , there are  8  total reinforcement cords arranged in parallel relationship to each other. The composite strip  43  has a 0.5 inch width. The composite strip  43  has an EPI (ends/inch) of 16. The composite strip  43  has a nylon reinforcement cords  46  located on each lateral edge of the strip. There could also be four outer reinforcement cords  46 , with two reinforcement cords  46  located at each lateral edge. The lower modulus reinforcement cords  46  may be formed of any desired materials, such as nylon or nylon 6,6. It is preferred that the lower modulus cords  46  be Nylon having a 2100 denier/2/2 construction. The composite strip  43  as shown in  FIG. 5  has six higher modulus reinforcement cords  44  located laterally inward of the lower modulus reinforcement cords  46 . The inner reinforcement cords  44  may be formed of any higher modulus material such as aramid, POK or a merged or hybrid cord made of aramid and nylon. One example of a suitable cord construction may comprise a composite of aramid and nylon, containing two cords of a polyamide (aramid) with construction of 3300 dtex with a 6.7 twist, and one nylon or nylon 6/6 cord having a construction of 1860 dtex, with a 4.5 twist. The overall merged cable twist is 6.7. A second example of a suitable high modulus cord construction contains three cords of a polyamide with a construction of 1670 denier/1/3 construction. 
         [0035]      FIG. 6  illustrates a second embodiment of a strip suitable for the invention. The composite strip  100  has a strip width of 0.5 inches, and nine reinforcement cords. The composite strip  100  has an epi (ends/inch) of 18. The laterally outer reinforcement cords  146  located at each lateral end of the strip are formed of a lower modulus material having a tangent modulus at 80% of break of less than 4500 MPA. Preferably, the outer reinforcement cords  146  are formed of nylon. The composite strip further includes higher modulus cords  144 , which are preferably located between the lower modulus reinforcement cords  146 . 
         [0036]      FIG. 4  illustrates a second embodiment of the present invention. The second embodiment includes a first and second zigzag belt structure  80 ,  90 . The second zigzag belt structure  90  is located radially outward of the first zigzag belt structure  80 . The second zigzag belt structure  90  has a width less than the first zigzag belt structure  80 . 
         [0037]    It is additionally preferred that the ply cords have a greater elongation at break than the belt cords elongation at break. The cord properties such as percent elongation at break, linear density and tensile strength are determined from cord samples taken after being dipped but prior to vulcanization of the tire. 
         [0038]    Variations of the present invention are possible in light of the description as provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject inventions, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the subject inventions.