Patent Publication Number: US-2019184765-A1

Title: Pneumatic tire with a robust ply ending structure

Description:
FIELD OF THE INVENTION 
     The invention relates to pneumatic tires. More particularly, the invention relates to the structure of radial ply tires. Specifically, the invention is directed to a pneumatic radial tire that includes a ply ending structure which improves the durability of the bead area of the tire. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of a pneumatic tire, the tire is typically built on the drum of a tire-building machine, which is known in the art as a tire building drum. Numerous tire components are wrapped about and/or applied to the drum in sequence, forming a cylindrical-shaped tire carcass. The tire carcass is then expanded into a toroidal shape for receipt of the remaining components of the tire, such as a belt package and a rubber tread. The completed toroidally-shaped unvulcanized tire carcass, which is known in the art at that stage as a green tire, is then inserted into a mold or press for forming of the tread pattern and curing or vulcanization. 
     One of the components of the tire is the bead area. The bead area includes a core, which is an annular tensile member wrapped by ply cords and shaped to fit the wheel rim. Typically, a bead core is integrated into each side of the tire to provide a secure fit of the tire on each side of the wheel rim. 
     Durability of the bead area of the tire is an item that is sought to be improved in the tire industry. For example, in applications such as short distance delivery in city or urban environments, the frequent starting and stopping of a vehicle such as a truck may create high load conditions on the bead area of the tire. 
     A tire of the prior art is shown in  FIGS. 1 and 2  and indicated at  10 . The tire  10  includes a pair of bead areas  12  and a respective bead core  14  embedded in each bead area. A respective sidewall  16  extends radially outward from each bead area  12  to a ground-contacting tread  18 . The tire  10  is reinforced by a carcass  20  that toroidally extends from one of the bead areas  12  to the other one of the bead areas. The carcass  20  includes at least one ply  22  that preferably winds around each bead core  14 . A belt reinforcement package  24  is disposed between the carcass  20  and the tread  18 . 
     What is conventionally considered a main portion  26  of the carcass reinforcing ply  22  extends radially inward toward the tire rim (not shown) and is turned about each bead core  14  to form a carcass ply turn up  28 . The carcass ply turn up  28  extends at a single angle μ relative to a radial line tangent to the axially outermost point of the bead core  14  and parallel to the equatorial plane of the tire  10 . A chafer  30  is disposed about the radially inward surface of the carcass ply turn up  28  to resist chafing of the tire  10  by the rim. 
     Due to the configuration and nature of the radial carcass  20 , when the tire  10  is expanded, the main portion  26  of the carcass ply  22  is put under tension, pulling the carcass main portion radially outward and the carcass ply turn up  28  radially inward. After inflation and during operation of the tire  10 , when the tire is under deflection, the carcass ply  22  is subject to bending forces and the carcass main portion  26  moves radially inward while the carcass turn up  28  moves radially and axially outward. Due to the adhesion relationship between the rubber and the reinforcing cords of the ply  22 , the rubber surrounding the carcass main portion  26  and the carcass turn up  28  also is forced to move during both tension and deflection, resulting in the rubber being stressed. The movement of the carcass ply  22  and the surrounding rubber may thus result in cracking of the rubber in each tire bead area  12 , thereby potentially decreasing durability of the tire  10 . 
     Therefore, it is desirable to provide a tire that includes a structure that improves the durability of the bead area. 
     SUMMARY OF THE INVENTION 
     According to an aspect of an exemplary embodiment of the invention, a pneumatic radial tire includes a pair of opposing bead areas, in which each bead area includes a bead core and a bead apex. At least one carcass reinforcing ply includes a turn up at each bead core, and each turn up includes a radially outward end. A pair of chippers is disposed at each turn up, in which the pair of chippers includes a first chipper and a second chipper. The first chipper is disposed axially inwardly of the second chipper and includes a radially outward end that is disposed radially outwardly of the radially outward end of the turn up. The second chipper includes a radially outward end that is disposed radially outwardly of the radially outward end of the first chipper, in which forces due to deflection of the tire are absorbed by the pair of chippers to reduce stresses along each turn up. 
     Definitions 
     “Axial” and “axially” mean lines or directions that are parallel to the axis of rotation of the tire. 
     “Axially inward” and “axially inwardly” refer to an axial direction that is toward the equatorial plane of the tire. 
     “Axially outward” and “axially outwardly” refer to an axial direction that is away from the equatorial plane of the tire. 
     “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. 
     “Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads. 
     “Chafer” means a layer of reinforcing material around the bead in the rim flange area to prevent chafing of the tire by the rim. 
     “Chipper” means a band of fabric or steelcord located in the bead area with the function of reinforcing the bead area and stabilizing the lower sidewall of the tire. 
     “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
     “Cord” means one of the reinforcement strands of which the plies in the tire are comprised. 
     “Equatorial plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread. 
     “Inboard” and “inboardly” refer to an axial direction that is toward the equatorial plane of the tire. 
     “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. 
     “Outboard” and “outboardly” refer to an axial direction that is away from the equatorial plane of the tire. 
     “Radial” and “radially” mean lines or directions that are perpendicular to the axis of rotation of the tire. 
     “Radially inward” and “radially inwardly” refer to a radial direction that is toward the central axis of rotation of the tire. 
     “Radially outward” and “radially outwardly” refer to a radial direction that is away from the central axis of rotation of the tire. 
     “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 about 65 to about 90 degrees with respect to the equatorial plane of the tire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of example and with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic cross-sectional view of an exemplary tire of the prior art; 
         FIG. 2  is an enlarged fragmentary view of a bead area of the tire shown in  FIG. 1 ; 
         FIG. 3  is an enlarged fragmentary view of a bead area of a first exemplary embodiment of the tire of the present invention; and 
         FIG. 4  is an enlarged fragmentary view of a bead area of a second exemplary embodiment of the tire of the present invention. 
     
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A first exemplary embodiment of the tire of the present invention is shown in  FIG. 3  and is indicated generally at  50 . The general construction of the tire  50  is somewhat similar to that of prior art tire  10 , with the principal differences to be described in detail below. 
     The tire  50  includes a pair of bead areas  52  (only one shown) and a respective bead core  54  embedded in each bead area. A carcass  56  includes at least one ply  58  that preferably winds around each bead core  54 . A main portion  60  of the carcass reinforcing ply  58  extends radially inward toward the tire rim (not shown) and is turned about each bead core  54  to form a carcass ply turn up  62 . The carcass reinforcing ply  58  is also wrapped about a bead apex  64 . In this manner, the carcass reinforcing ply  58  envelopes the bead core  54  and a lower portion of the bead apex  64  in each bead area  52 . The carcass ply turn up  62  terminates at a radially outward end  66 . A chafer  68  is disposed about the radially inward surface of the carcass ply turn up  62  to resist chafing of the tire  50  by the rim, and may include an end cap  70 . 
     Axially outward of the carcass ply turn up  62  is an axially outer chipper  72 , which is a reinforced layer, as will be described in greater detail below. The axially outer chipper  72  includes a radially inward end  74 , a radially outward end  76 , an inboard surface  78  and an outboard surface  80 . Axially inward of the carcass ply turn up  62  is an axially inner chipper  82 , which is a reinforced layer, as will be described in greater detail below. The axially inner chipper  82  includes a radially inward end  84 , a radially outward end  86 , an inboard surface  88  and an outboard surface  90 . 
     The inboard surface  78  of the outer chipper  72  adjacent its radially inward end  74  is bonded to an outboard surface  92  of the carcass ply turn up  62  near the turn up end  66 . The outboard surface  90  of the inner chipper  82  adjacent its radially inward end  84  is bonded to an inboard surface  92  of the carcass ply turn up  62  near the turn up end  66 . The outer chipper  72  and the inner chipper  82  extend radially outwardly past the end  66  of the carcass ply turn up  62 . Once past the carcass ply turn up end  66 , the inboard surface  78  of the outer chipper  72  is bonded to the outboard surface  90  of the inner chipper  82 . In this manner, the outer chipper  72  and the inner chipper  82  form a sandwich-layer construction with the carcass ply turn up  62 . 
     The outer chipper  72  and the inner chipper  82  preferably are of similar lengths. The radially inward end  74  of the outer chipper  72  is offset in a radially outward direction from the radially inward end  84  of the inner chipper  82  by a distance of at least 5 millimeters (mm). As a result, the radially outward end  76  of the outer chipper  72  extends radially outwardly past the radial outward end  86  of the inner chipper  82  by a distance of at least 5 mm. 
     By way of example, the outer chipper  72  and the inner chipper  82  may each be about 35 mm long. In such a case, the radially outward end  76  of the outer chipper  72  extends radially outwardly past the radially outward end  86  of the inner chipper  82  by a distance indicated by A. Distance A is at least about 5 mm, or at least about 15 percent of the length of the outer chipper  72  and the inner chipper  82 . Preferably, distance A is about 6 mm, or at least about 17 percent of the length of the outer chipper  72  and the inner chipper  82 . The radially inward end  84  of the inner chipper  82  extends radially inwardly past the radially inward end  74  of the outer chipper  72  by a distance indicated by B. Distance B is at least about 5 mm, or at least about 15 percent of the length of the outer chipper  72  and the inner chipper  82 . Preferably, distance B is about 6 mm, or at least about 17 percent of the length of the outer chipper  72  and the inner chipper  82 . 
     The inboard surface  78  of the outer chipper  72  is bonded to the outboard surface  90  of the inner chipper  82  for a distance indicated by C. Distance C is about 12 mm, or about 34 percent of the length of the outer chipper  72  and the inner chipper  82 . The inboard surface  78  of the outer chipper  72  is bonded to the outboard surface  92  of the carcass ply turn up  62  for a distance indicated by D. Distance D is about 13 to 14 mm, or about 35 to about 40 percent of the length of the outer chipper  72  and the inner chipper  82 . The outboard surface  90  of the inner chipper  82  is bonded to the inboard surface  92  of the carcass ply turn up  62  for a distance indicated by D plus B. Distance D plus distance B is at least about 18 mm to about 20 mm, or about 50 percent to about 57 percent of the length of the outer chipper  72  and the inner chipper  82 . 
     The outer chipper  72  is formed of an elastomer or polymer compound known to those skilled in the art. The inner chipper  82  may be formed of the same elastomer or polymer compound as the outer chipper  72 , or of a different elastomer or polymer compound. 
     Both the outer chipper  72  and the inner chipper  82  are reinforced with substantially inextensible cords. Preferably the cords are made of steel having a mesh of parallel cords between about 8 and 18 ends per inch, and more preferably between about 12 and 16 ends per inch. The wire cord gauge of each chipper  72  and  82  is preferably between about 0.6 mm and 1.5 mm. Alternatively, the cords in each chipper  72  and  82  may be made of a polyamide monofilament cord of any cross-sectional shape, such as round, oval or star. The cords of each chipper  72  and  82  preferably are oriented at an angle of between about 25 degrees and about 85 degrees with respect to the radially oriented steel cords that reinforce the carcass ply  58 . More preferably, the cords of each chipper  72  and  82  are oriented between about 25 and about 45 degrees. 
     The outer chipper  72  and the inner chipper  82 , when assembled as shown, preferably have generally equal, but oppositely oriented cord angles. Having the cord angles biased oppositely at the locations where the chippers  72  and  82  are joined causes the stresses that would normally tend to initiate a crack at the end  66  the carcass ply turn up  62  to be absorbed first by the radially outward end  76  of the outer chipper  72 . Such absorption causes shear stresses to progress radially inwardly to the area where the inner chipper  82  is joined to the outer chipper  72 , which in turn causes the shear forces to be absorbed in both the outer and inner chippers above or radially outwardly of the carcass ply turn up  62 . This absorption of forces lowers the shear forces absorbed by the carcass ply turn up  62 , while also transferring stress to the inner chipper  82  without unduly loading the carcass ply turn up. 
     In this manner, the tire  50  of the present invention provides a structure in which forces due to deflection are absorbed by the outer chipper  72 , as its radially outward end  76  extends radially outwardly past the inner chipper  82  and the carcass ply turn up  62 . Those forces are then absorbed by the outer chipper  72  and the inner chipper  82 . Such absorption of forces by the outer chipper  72  and the inner chipper  82  lowers shear stresses along the carcass ply turn up  62 . Lowering or reducing the stresses in the carcass ply turn up  62  enables the tire  50  to resist fatigue cracking in the bead area  52 , thereby improving the durability of the bead area. 
     A second exemplary embodiment of the tire of the present invention is shown in  FIG. 4  and is indicated generally at  100 . The general construction of the tire  100  is somewhat similar to that of the first embodiment of the tire  50  of the present invention, with the principal differences to be described in detail below. The second embodiment of the tire  100  finds particular application when cost and/or manufacturing considerations are a particular concern, as the second embodiment of the tire may be more economical to manufacture than the first embodiment of the tire  50 . 
     As with the first embodiment of the tire  50 , the second embodiment of the tire  100  includes a pair of bead areas  52  (only one shown) and a respective bead core  54  embedded in each bead area. A carcass  56  includes at least one ply  58  that preferably winds around each bead core  54 . A main portion  60  of the carcass reinforcing ply  58  extends radially inward toward the tire rim (not shown) and is turned about each bead core  54  to form a carcass ply turn up  62 . The carcass reinforcing ply  58  is also wrapped about a bead apex  64 . In this manner, the carcass reinforcing ply  58  envelopes the bead core  54  and a lower portion of the bead apex  64  in each bead area  52 . The carcass ply turn up  62  terminates at a radially outward end  66 . A chafer  68  is disposed about the radially inward surface of the carcass ply turn up  62  to resist chafing of the tire  50  by the rim. 
     Axially outward of the carcass ply turn up  62  is a first axially outer chipper  102 , which a reinforced layer, as will be described in greater detail below. The first outer chipper  102  includes a radially inward end  104 , a radially outward end  106 , an inboard surface  108  and an outboard surface  110 . Axially outwardly of the first outer chipper  102  is a second axially outer chipper  112 , which is a reinforced layer, as will be described in greater detail below. The second axially outer chipper  112  includes a radially inward end  114 , a radially outward end  116 , an inboard surface  118  and an outboard surface  120 . 
     The inboard surface  78  of the first outer chipper  102  is bonded to the chafer  68  and the carcass ply turn up  66 . More particularly, the chafer  68  includes an axially outer end  122  and an outboard surface  124 , and the carcass ply turn up  62  includes an outboard surface  126  that extends radially outwardly past the outer end of the chafer. The inboard surface  78  of the first outer chipper  102  is bonded to the outboard surface  124  of the chafer  68  and to the outboard surface  126  of the carcass ply turn up  62 . The radially inward end  104  of the first outer chipper  102  is disposed below or radially inwardly of the axially outer end  122  of the chafer  68 , and extends radially outwardly past the end  66  of the carcass ply turn up  62 . In this manner, the first outer chipper  102  covers the axially outer end  122  of the chafer  68  and the end  66  of the carcass ply turn up  62 . 
     The inboard surface  118  of the second outer chipper  112  is bonded to the outboard surface  110  of the first outer chipper  102 . The first outer chipper  102  and the second outer chipper  112  preferably are of similar lengths. The radially inward end  114  of the second outer chipper  112  is offset in a radially outward direction from the radially inward end  104  of the first outer chipper  102  by a distance of at least 5 mm. As a result, the radially outward end  116  of the second outer chipper  112  extends radially outwardly past the radial outward end  106  of the first outer chipper  102  by a distance of at least 5 mm. 
     By way of example, the first outer chipper  102  and the second chipper  112  may each be about 72 mm long. In such a case, the radially outward end  116  of the second outer chipper  112  extends radially outwardly past the radially outward end  106  of the first outer chipper  102  by a distance indicated by E. Distance E is at least about 5 mm, or at least about 7 percent of the length of the first outer chipper  102  and the second outer chipper  112 . Preferably, distance A is about 8 mm, or at least about 11 percent of the length of the first outer chipper  102  and the second outer chipper  112 . The radially inward end  104  of the first outer chipper  102  extends radially inwardly past the radially inward end  114  of the second outer chipper  112  by a distance indicated by F. Distance F is at least about 5 mm, or at least about 7 percent of the length of the first outer chipper  102  and the second outer chipper  112 . Preferably, distance F is about 8 mm, or at least about 11 percent of the length of the first outer chipper  102  and the second outer chipper  112 . In such a case, the inboard surface  118  of the second outer chipper  112  is bonded to the outboard surface  110  of the first outer chipper  102  for a distance of about 56 mm, which is about 78 percent of the length of the first outer chipper and the second outer chipper. 
     The first outer chipper  102  is formed of an elastomer or polymer compound known to those skilled in the art. The second outer chipper  112  may be formed of the same elastomer or polymer compound as the first outer chipper  102 , or of a different elastomer or polymer compound. 
     Both the first outer chipper  102  and the second outer chipper  112  are reinforced with substantially inextensible cords. Preferably the cords are made of steel having a mesh of parallel cords between about 8 and 18 ends per inch, and more preferably between about 12 and 16 ends per inch. The wire cord gauge of each chipper  102  and  112  is preferably between about 0.6 mm and 1.5 mm. Alternatively, the cords in each chipper  102  and  112  may be made of a polyamide monofilament cord of any cross-sectional shape, such as round, oval or star. The cords of each chipper  102  and  112  preferably are oriented at an angle of between about 25 degrees and about 85 degrees with respect to the radially oriented steel cords that reinforce the carcass ply  58 . More preferably, the cords of each chipper  102  and  112  are oriented between about 25 and about 45 degrees. 
     The first outer chipper  102  and the second outer chipper  112 , when assembled as shown, preferably have generally equal, but oppositely oriented cord angles. Having the cord angles biased oppositely at the locations where the chippers  102  and  112  are joined causes the stresses that would normally tend to initiate a crack at the end  66  the carcass ply turn up  62  to be absorbed first by the radially outward end  116  of the second outer chipper  112 . Such absorption causes shear stresses to progress radially inwardly to the area where the first outer chipper  102  is joined to the second outer chipper  112 , which in turn causes the shear forces to be absorbed in both the first and second outer chippers above or radially outwardly of the carcass ply turn up  62 . This absorption of forces lowers the shear forces absorbed by the carcass ply turn up  62 , while also transferring stress to the first outer chipper  102  without unduly loading the carcass ply turn up. 
     In this manner, the tire  100  of the present invention provides a structure in which forces due to deflection are absorbed by the second outer chipper  112 , as its radially outward end  116  extends radially outwardly past the first outer chipper  102  and the carcass ply turn up  62 . Those forces are then absorbed by the second outer chipper  112  and the first outer chipper  102 . Such absorption of forces by the second outer chipper  112  and the first outer chipper  102  lowers shear stresses along the carcass ply turn up  62 . Lowering or reducing the stresses in the carcass ply turn up  62  enables the tire  100  to resist fatigue cracking in the bead area  52 , thereby improving the durability of the bead area. 
     The pneumatic radial tire of the invention  50 ,  100  thus includes a layered ply ending or chipper structure  72 ,  82 ,  102 ,  112  that improves the durability of the respective bead areas  52  of the tire and the life of the tire. In each tire of the present invention  50 ,  100 , an advantage includes increased bead durability under heavy loads or high heat conditions, as is seen in commercial vehicles such as buses, tractors and medium commercial truck tires designed for heavy loads. Such tires  50 ,  100  typically have large rim diameters of about 20 inches (508 mm) or greater, and are designed to be retreaded such that the bead portions of the carcass  20  may be exposed to many hundreds of thousand miles. The ability to provide a more durable bead portion or area  52  as accomplished by the tire of the present invention  50 ,  100  thereby also provides a longer-lasting tire carcass  20 . 
     The present invention also includes a method of forming a tire  50 ,  100  with improved durability of the bead area  52 . The method includes steps in accordance with the description that is presented above and shown in  FIGS. 3 and 4 . 
     It is to be understood that the structure of the above-described tire  50 ,  100  may be altered or rearranged, or components or steps known to those skilled in the art omitted or added, without affecting the overall concept or operation of the invention. For example, the teachings herein are applicable to a broad range of tires and may be useful in tire lines such as, but not limited to, passenger tires, radial medium truck tires, aircraft tires, and off-the-road tires, run-flat tires, and the like. Moreover, the invention applies to tires formed with any type of belt structure or tread configuration. 
     The invention has been described with reference to preferred embodiments. Potential modifications and alterations will occur to others upon a reading and understanding of this description. It is to be understood that all such modifications and alterations are included in the scope of the invention as set forth in the appended claims, or the equivalents thereof.