Abstract:
A pneumatic tire having a carcass and a belt reinforcing structure wherein the belt reinforcing structure is a composite belt structure having at least one pair of radially outer zigzag layers and at least one spirally wound belt layer with cords inclined at an inclination of 5 degrees or less relative to the tire&#39;s centerplane and located radially inward of and adjacent to the at least two radially outer belt layers. The at least two radially outer zigzag belt layers have cords inclined at 5 degrees to 30 degrees relative to the tire&#39;s centerplane and extending in alternation to turnaround points at each lateral edge of the belt layer. At each turnaround point the cords are folded or preferably bent to change direction across the crown of the carcass thus forming a zigzag cord path.

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 radial ply 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 contact patch. 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 contact patch.  
           [0004]    In U.S. Pat. No. 5,427,167, Jun Watanabe of Bridgestone Corporation suggested that the use of a large number of belt plies piled on top of one another was prone to cracks inside the belt layers which tended to grow outwardly causing a cut peel off and scattering of the belt and the tread during running. Therefore, such a belt ply is not used for airplanes. Watanabe found that zigzag belt layers could be piled onto the radially inner belt layers if the cord angles progressively increased from the inner belt layers toward the outer belt layers. In other words the radially inner belt plies contained cords extending substantially in a zigzag path at a cord angle A of 5 degrees to 15 degrees in the circumferential direction with respect to the equatorial plane while being bent at both sides or lateral edges of the ply. Each of the outer belt plies contains cords having a cord angle B larger than the cord angle A of the radially inner belt plies.  
           [0005]    In one embodiment each of the side end portions between adjoining two inner belt plies is provided with a further extra laminated portion of the strip continuously extending in the circumferential direction and if the radially inner belt plies have four or more in number then these extra laminated portions are piled one upon another in the radial direction. The inventor Watanabe noted the circumferential rigidity in the vicinity of the side end of each ply or the tread end can be locally increased so that the radial growth in the vicinity of the tread end portion during running at high speed can be reduced.  
         SUMMARY OF THE INVENTION  
         [0006]    A pneumatic tire having a carcass and a belt reinforcing structure wherein the belt reinforcing structure is a composite belt structure having at least one pair of radially outer zigzag layers and at least one spirally wound belt layer with cords inclined at an inclination of 5 degrees or less relative to the tire&#39;s centerplane and located radially inward of and adjacent to the at least two radially outer zigzag belt layers.  
           [0007]    The at least two radially outer zigzag belt layers have cords inclined at 5 degrees to 30 degrees relative to the tire&#39;s centerplane and extending in alternation to turnaround points at each lateral edge of the belt layer. At each turnaround point the cords are folded or preferably bent to change direction across the crown of the carcass thus forming a zigzag cord path.  
           [0008]    In a preferred embodiment at least two radially inner zigzag belt layers are positioned between the carcass and the at least one spirally wound belt layer. Each of the radially inner zigzag belt layers has cords wound at an inclination of 5 degrees to 30 degrees relative to the centerplane of the tire and extending in alternation to turnaround points at each lateral edge of the belt layers.  
           [0009]    The cords of the at least two radially inner spirally wound belt layers are wound from a single cord or from a group of 2 to 20 cords which continuously extend to form spirally wound belt layer and the at least two radially outer belt layers.  
           [0010]    Alternatively, the cords of the spirally wound belt layer in a single cord or a group of 2 to 20 cords may be continuously wound to form the at least two radially outer belt layers.  
           [0011]    As described above the tire should have three belt layers, preferably five, as a minimum as measured at the tire&#39;s center.  
           [0012]    The tire is well suited for high speeds and large loads such as found in aircraft tires.  
         DEFINITIONS  
         [0013]    “Apex” means a non-reinforced elastomer positioned radially above a bead core.  
           [0014]    “Aspect ratio” of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.  
           [0015]    “Axial” and “axially” mean lines or directions that are parallel to the axis of rotation of the tire.  
           [0016]    “Bead” means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.  
           [0017]    “Cut belt or cut breaker reinforcing structure” means at least two cut layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 10 degrees to 33 degrees with respect to the equatorial plane of the tire.  
           [0018]    “Bias ply tire” means a tire having a carcass with reinforcing cords in the carcass ply extending diagonally across the tire from bead core to bead core at about a 25°-50° angle with respect to the equatorial plane of the tire. Cords run at opposite angles in alternate layers.  
           [0019]    “Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.  
           [0020]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.  
           [0021]    “Chafers” refer to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire.  
           [0022]    “Chippers” mean a reinforcement structure located in the bead portion of the tire.  
           [0023]    “Cord” means one of the reinforcement strands of which the plies in the tire are comprised.  
           [0024]    “Equatorial plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread.  
           [0025]    “Flipper” means a reinforced fabric wrapped about the bead core and apex.  
           [0026]    “Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.  
           [0027]    “Innerliner” means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.  
           [0028]    “Net-to-gross ratio” means the ratio of the tire tread rubber that makes contact with the road surface while in the footprint, divided by the area of the tread in the footprint, including non-contacting portions such as grooves.  
           [0029]    “Nominal rim diameter” means the average diameter of the rim flange at the location where the bead portion of the tire seats.  
           [0030]    “Normal inflation pressure” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.  
           [0031]    “Normal load” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.  
           [0032]    “Ply” means a continuous layer of rubber-coated parallel cords.  
           [0033]    “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.  
           [0034]    “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.  
           [0035]    “Section height” (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.  
           [0036]    “Zigzag belt reinforcing structure” means at least two layers of cords or a ribbon of parallel cords having 2 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  
       [0037]    [0037]FIG. 1 us a schematically section view of a first embodiment of the tire according to the invention;  
         [0038]    [0038]FIG. 2 is a partially cutaway top view of the tire shown in FIG. 1;  
         [0039]    [0039]FIG. 3 is a schematically perspective view of an inner or outer zigzag belt layer in the middle of the formation;  
         [0040]    [0040]FIG. 4 is a schematically developed view of the inner or outer zigzag belt layers In the middle of the formation;  
         [0041]    [0041]FIG. 5 is an enlargedly developed view of the inner or outer zigzag belt layers in the vicinity of the side end of the ply in the middle of the formation;  
         [0042]    [0042]FIG. 6 is an enlargedly developed view of another embodiment of the inner belt layer in the vicinity of the side end of the ply in the middle of the formation;  
         [0043]    [0043]FIG. 7 is a schematically enlarged section view of the composite belt layers in the vicinity of side end portions of these plies;  
         [0044]    [0044]FIG. 8 is a schematically developed view of the inner layer located at an outmost side;  
         [0045]    [0045]FIG. 9 is a schematically enlarged section view of another embodiment of plural inner belt plies in the vicinity of side end portions of these plies. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]    In FIGS. 1 and 2, numeral  21  is a radial tire of the preferred embodiment of the invention, as shown, to be mounted onto an airplane, which comprises a pair of bead portions  23  each containing a bead core  22  embedded therein, a sidewall portion  24  extending substantially outward from each of the bead portions  23  in the radial direction of the tire, and a tread portion  25  of substantially cylindrical shape extending between radially outer ends of these sidewall portions  24 . Furthermore, the tire  21  is reinforced with a carcass  31  toroidially extending from one of the bead portions  23  to the other bead portion  23 . The carcass  31  is comprised of at least two carcass plies  32 , e.g. six carcass plies  32  in the illustrated embodiment. Among these carcass plies  32 , four inner plies are wound around the bead core  22  from inside of the tire toward outside thereof to form turnup portions, while two outer plies are extended downward to the bead core  22  along the outside of the turnup portion of the inner carcass ply  32 . Each of these carcass plies  32  contains many nylon cords  33  such as nylon-6,6 cords extending substantially perpendicular to an equatorial plane E of the tire (i.e. extending in the radial direction of the tire). A tread rubber  36  is arranged on the outside of the carcass  31  in the radial direction.  
         [0047]    A belt  40  is arranged between the carcass  31  and the tread rubber  36  and is comprised of plural inner belt plies or layers  41  located near the carcass  31 , i.e. two radially inner belt layers  41  in the illustrated embodiment and plural radially outer belt layers  42  located near to the tread rubber  36 , i.e. two radially outer belt layers  42  in the illustrated embodiment. As shown in FIGS. 3 and 8, each of the radially inner belt plies  41  is formed by providing a rubberized strip  43  of one or more cords  46 , winding the strip  43  generally in the circumferential direction while being inclined to extend between side ends or lateral edges  44  and  45  of the layer forming a zigzag path and conducting such a winding many times while the strip  43  is shifted at approximately a width of the strip in the circumferential direction so as not to form a gap between the adjoining strips  43 . As a result, the cords  46  extend substantially zigzag in the circumferential direction while changing the bending direction at a turnaround point at both ends  44 ,  45  and are substantially uniformly embedded in the first inner belt layer  41  over a full region of the first inner belt layer  41 . Moreover, it is intended to form the radially inner belt layer  41  by the above method, the cords  46  lie one upon another, so that two first and second inner belt layers  41  are formed while crossing the cords  46  of these plies with each other. Similarly the radially outer belt layers  42  are made using the same method. Interposed between the inner layers  41  and outer layers  42  is at least one spirally wound layer  39  of cords  46 , the cords being wound at an angle of plus or minus 5 degrees or less relative to the circumferential direction.  
         [0048]    In the pneumatic radial tire for airplanes, there are various sizes, the tire illustrated is a 42×17. OR18 with a  26  ply rating and the tire  21  has the belt composite reinforcing structure as shown in FIG. 9. As shown the tire of FIG. 9 has two inner zigzag layers  41  and three spiral layers  39  and two outer zigzag layers  42 . In any such tire size, the cords  46  of the inner belt plies  41  cross with each other at a cord angle A of 5 degrees to 15 degrees with respect to the equatorial plane 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.  
         [0049]    In the illustrated embodiment, the widths of the inner belt layers  41  become narrower as the ply  41  is formed outward in the radial direction or approaches toward the tread rubber  36 . Further, when the inner belt layers  41  is formed by winding the rubberized strip  43  containing plural cords  46  arranged in parallel with each other as mentioned above, a period for forming the ply layer  41  can be shortened and also the cord  46  arrangement can be made accurate. However, the strip  43  is bent at the side ends  44 ,  45  of the ply with a small radius of curvature R as shown in FIG. 5, so that a large compressive strain is produced in a cord  46  located at innermost side of the curvature R in the strip  43  to remain as a residual strain. When the cord  46  is nylon cord, if the compressive strain exceeds 25%, there is a fear of promoting the cord fatigue. However, when a ratio of R/W (R is a radius of curvature (mm) of the strip  43  at the side ends  44 ,  45  of the layer, and W is a width of the strip  43 ) is not less than 2.0 as shown in FIG. 6, the compressive strain produced in the cord  46  can be controlled to not exceed 25%. Therefore, when the inner belt layer  41  is formed by using the rubberized strip  43  containing plural nylon cords  46  therein, it is preferable that the value of R/W is not less than 2.0. In addition to the case where the strip  43  is bent at both side ends  44 ,  45  of the ply in form of an arc as shown in FIG. 5, the strip  43  may have a straight portion extending along the side end  44  ( 45 ) and an arc portion located at each end of the straight portion as shown in FIG. 6. Even in the latter case, it is favorable that the value of R/W in the arc portion is not less than 2.0. Furthermore, when the strip  43  is wound while being bent with a given radius of curvature R at both side ends  44 ,  45  of the ply, a zone  47  of a bent triangle formed by overlapping three strips  43  with each other at a half width of the strip as shown in FIG. 7 is repeatedly created in these bent portions or in the vicinity of both side ends  44 ,  45  of the ply in the circumferential direction as shown in FIG. 5. These two strips  43  are usually overlapped with each other by each forming operation. The width changes in accordance with the position in the circumferential direction continuously in the circumferential direction. Moreover, these laminated bent portions  47  turn inward in the axial direction as they are formed outward in the radial direction as shown in FIG. 7 because the widths of the inner belt layers  41  become narrower toward the outside in the radial direction as previously mentioned. In the bent portion  47 , the outer end in widthwise direction of the middle strip  43   c  sandwiched between upper and lower strips  43   a  and  43   b  overlaps with the zone  47  located inward from the middle strip  43   c  in the radial direction as shown in FIG. 7. When the belt  40  is constructed with these inner belt layers  41 , the total number of belt layers or plies can be decreased while maintaining total strength but reducing the weight and also the occurrence of standing wave during the running at high speed can be prevented.  
         [0050]    The middle layers  39  of the composite belt structure  40  are spirally wound around the radially inner belt layers  41 . As shown in FIG. 7 the spirally wound layer  39  extends completely across the two radially inner belt layers  41  and ends at  39   a  just inside the end  41   a . The cords  46  within each strip  39  extend at an angle of 5 degrees or less relative to the circumferential equatorial plane. As shown four cords are in each strip. In practice the strips  41 ,  39 ,and  42  could be wound using a single cord  46  or plural cords  46  in a strip or ribbon having plural cords in the range of 2 to 20 cords within each strip. In the exemplary tire  21  of the size 42×17.OR18 strips  43  having 8 cords per strip  42  were used. The strips  43  had a width W, W being 0.5 inches. It is believed preferable that the strip width W should be 1.0 inch or less to facilitate bending to form the zigzag paths of the inner and outer layers  41 ,  42 .  
         [0051]    In the most preferred embodiment the layers  41 ,  39 , and  42  are all formed from a continuous strip  43  that simply forms the at least two radially zigzag layers  41  and then continues to form the at least one spirally wound layer  39  and then continues on to form the at least two radially outer layers  42 . Alternatively, the spirally wound layers  39  could be formed as a separate layer from a strip  43 . This alternative method of construction permits the cords  46  to be of different size or even of different materials from the zigzag layers  41  and  42 . What is believed to be the most important aspect of the invention is the circumferential layer  39  by being placed between the zigzag layers  41  and  42  greatly-reduces the circumferential growth of the tire  21  in not only the belt edges  44 ,  45  but in particular the crown area of the tread  36 . The spirally wound circumferential layer  39 , by resisting growth in the crown area of the tire, greatly reduces the cut propensity due to foreign object damage and also reduces tread cracking under the grooves. This means the tire&#39;s high speed durability is greatly enhanced and its load carrying capacity is even greater. Aircraft tires using multiple layers of only zigzag ribbons on radial plied carcasses showed excellent lateral cornering forces. This is a common problem of radial tires using spiral layers in combination with cut belt layers which show poor cornering or lateral force characteristics. Unfortunately, using all zigzag layered belt layers have poor load and durability issues that are inferior to the more conventional spiral belt layers in combination with cut belt layers.  
         [0052]    The present invention has greatly improved the durability of the zigzag type belt construction while achieving very good lateral force characteristics as illustrated in FIG. 10. The all zigzag belted tire A is slightly better than the tire B of the present invention which is shown better than the spiral belt with a combination of cut belt layers of tire C in terms of lateral forces. Nevertheless the all zigzag belted tire A cannot carry the required double overloads at inflation whereas the tire B of the present invention easily meets these load requirements.  
         [0053]    The tire of the present invention may have a nylon overlay  50  directly below the tread. This overlay  50  is used to assist in retreading.