Patent Publication Number: US-2011056606-A1

Title: Pneumatic tire

Description:
RELATED APPLICATIONS 
     This application is a divisional of co-pending U.S. application Ser. No. 11/936,241 entitled “Pneumatic Tire” filed Nov. 7, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a pneumatic tire. More specifically, the present invention is directed to a pneumatic radial tire wherein the bead portion of the tire is designed for improved durability due to the configuration of the turn-up portion of the carcass reinforcing ply. 
     BACKGROUND OF THE INVENTION 
     Bead area durability is one of the concerns of the tire industry. A conventional tire bead portion  100  is illustrated in prior art  FIG. 4 . What is conventionally considered the main portion  104  of a carcass reinforcing ply extends radially inward toward the tire rim and is turned about an inextensible bead core  106  to form a carcass ply turnup  108 . The carcass ply turn up  108  extends at a single angle μ relative to a radial line tangent to the axially outermost point of the bead core  106  and parallel to the tire equatorial plane. 
     Due to the configuration and nature of the radial carcass, when a tire is expanded, the main portion of the carcass is put under tension, pulling the carcass main portion  104  radially upward and the carcass turn up  108  radially inward. After inflation and during operation of the tire, when the tire is under deflection, the carcass ply is subject to bending forces and the carcass main portion  104  moves radially inward while the carcass turnup  108  moves radially and axially outward. During both tension and deflection, the rubber surrounding the carcass main portion  104  and the carcass turn up  108 , due to the adhesion relationship between the rubber and the reinforcing cords of the ply, also is forced to move and the rubber is stressed. The movement of the carcass ply and the surrounding rubber may result in cracking of the rubber in the tire bead portion, decreasing durability of the tire. 
     Other attempts have been made to improve the durability of the bead portion. U.S. Pat. No. 6,260,597 (Miyazono) discloses a pneumatic tire having multiple organic fiber cord reinforced layers in the bead portions outward of a carcass ply. Axially outward of the carcass ply turnup, the terminal ends of the organic fiber layers are all at the same height or radially outward of the terminal end of the carcass ply turnup. Because the axially outer organic fiber layers are predominately radially outward of the carcass ply terminal end, when the bead portion is subjected to strain during operation, it is the organic fiber layer ends that are subjected to the greater load and where crack initiation may begin, resulting in reduced bead durability. Miyazono teaches that to improve durability, the ends of the organic fiber layers are bent in various different embodiments while the carcass ply turnup is maintained at a single angle. 
     Several prior art patents similarly propose applying textile cord layers adjacent the turnup ends of a pneumatic tire to improve durability as in U.S. Pat. No. 4,234,029 and U.S. Pat. No. 4,093,014 having a folded over U shaped chipper. U.S. Pat. No. 6,962,183 uses an axially outer short steel cord chipper terminating radially below the turnup end wherein both the chipper and the turnup end are covered by a nylon patch. 
     In U.S. Pat. No. 4,842,033 gum strips are proposed to cover the turnup ends to improve durability. 
     In U.S. Pat. No. 6,962,183 and U.S. Pat. No. 6,877,538 the use of an axially outer steel or organic cord reinforced chipper layer is taught wherein the outer end terminates below preferably well below the high ply turnup terminal end which is encased in insulation rubber. 
     All of these exemplary prior art patents where attempts to improve tire bead area durability and to reduce crack propagation which is a common issue in heavy duty commercial truck tires, particularly such tires using a steel reinforced carcass ply. 
     SUMMARY OF THE INVENTION 
     A pneumatic radial tire has a pair of opposing bead portions, each bead portion has a bead core and a bead apex; at least one carcass reinforcing ply having radially oriented steel cords, the at least one carcass reinforcing ply has a main portion and two turnups, one turnup extending from each end of the main portion and having a terminal end, the carcass reinforcing ply main portion extends between the opposing bead cores and turnups are located axially outward of the bead core and a portion of the bead apex; and two pairs of steel cord reinforced chippers, one pair adjacent each turnup, each pair having one inner chipper being adjacent and on an axially inner side of the turnup and one outer chipper being adjacent on an axially outer side of the turnup, the inner and outer chippers adjacent the turnup each have a terminal end extending radially outward of the terminal end of the turnup. 
     The inner chipper has the steel cords oriented on a bias angle in relative to a circumferential or radial plane of the tire and the outer chipper has the steel cords oriented in a bias angle opposite in direction relative to the inner chipper, the steel cords of the chippers are oriented on a bias angle in the range of 25 to 85 degrees. The steel cords of the inner and outer chippers are oriented preferably at equal but oppositely oriented bias angles. Each chipper has the steel cords arranged substantially parallel in the range of 8 to 15 ends per inch (3 to 6 ends per cm). Additionally, a second axially inner chipper having steel cords lying adjacent to and axially inward of the inner chipper, may be provided. 
     The pneumatic radial tire also has a belt reinforcement structure having three or more steel cord reinforced belt layers disposed radially outward of the at least one carcass reinforcing ply; and a tread radially outward of the belt reinforcing structure. Preferably, the axially outer chipper extends to a radially inner end extending between the bead core and a rim seating base of the bead portion, while the radially outer terminal end of the axially inner chipper extends outwardly by 5 mm or more relative to the terminal end of the axially outer chipper. The radially outer terminal end of the axially outer chipper also extends outwardly by 5 mm or more relative to the terminal end of the turnup. The axially inner chipper has a radially inner end extending toward the bead core terminating above a location of contact of bead core and the turnup. The pneumatic radial tire of the present invention is typically a commercial truck tire having nominal bead diameter of 22.5 inches (88 mm) or greater. In a second embodiment, two pairs of polyamide monofilament cord reinforced chippers may be used instead of chippers having steel cords. Also, the pneumatic radial tire may further be constructed having a top belt layer covering the at least three or more steel cord belt layers, the top belt having cords being made of nylon or polyamide. 
     DEFINITIONS 
     The following definitions are applicable to the present invention. 
     “Inner” means toward the inside of the tire and “outer” means toward its exterior. 
     “Outer” means toward the tire&#39;s exterior. 
     “Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire. 
     “Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load. The tread has a depth conventionally measured from the tread surface to the bottom of the deepest groove 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 cross-sectional view of half of a pneumatic tire; 
         FIG. 2  is a close up of the bead portion of the tire of  FIG. 1 ; 
         FIG. 3  is an alternative bead portion construction; and 
         FIG. 4  is a prior art tire bead. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the drawings are the same as those referred to in the specification. For purposes of this application, the various embodiments illustrated in the figures each use the same reference numeral for similar components. The structures employ basically the same components with variations in location or quantity thereby giving rise to the alternative constructions in which the inventive concept can be practiced. 
     A pneumatic tire in accordance with a first embodiment of the present invention is illustrated in  FIGS. 1 and 2 . The pneumatic tire has a carcass, a belt structure  8  radially outward of the carcass, and a tread  10  radially outward of the belt structure  8 . The belt structure  8  may be any of the type conventionally used for a pneumatic tire, and generally will include at least two reinforcement plies of angled, inclined cords and may include a ply of zero degree cords. The actual belt structure of the tire will be dictated by the intended end use of the tire. Similarly, the exact tread configuration will be dictated by the intended end use of the tire. 
     The carcass has at least one carcass reinforcing ply  12 , a pair of opposing bead portions  14  and a pair of opposing sidewalls  16 . The ply  12  has a main portion  18  extending through the opposing sidewalls  16  and two carcass turnups  20  initiating in the bead portions  14 . Each carcass turnup  20  of the carcass reinforcing ply  12  extends from the main portion  18  of the carcass reinforcing ply  12 , and is wrapped about a bead core  23  and a bead apex  24  in the bead portion  14 ; thus enveloping, at a minimum, the bead core  23  and the lower portion of the bead apex  24  in each bead portion  14 . The carcass turnup  20  terminates at a distance H T  from the tire bead base line BL; the distance H T  is at least 20% of the section height SH. The tire bead base line BL is an imaginary line, perpendicular to the equatorial plane EP of the tire, from the intersection of the radially extending outer side of the bead portion and the bead base of the tire. 
     Outward of the carcass ply  12  in the bead portion  14  is a steel cord reinforced layer referred to as the axially outer chipper  30 . The axially outer chipper  30  extends from axially inward of the bead core  23  to axially outward of the bead core  23 , being turned up around the bead core  23  similar to the carcass ply  12 . The radially outer end  31  of the outer chipper  30  terminates radially outward of the terminal end  21  of the turnup  20  of the carcass ply  12 . The axially outer chipper  30  extends radially inwardly along and adjacent to the turnup  20  and wraps about a portion of the bead core  23  and the carcass ply  12  terminating at an axially inner end  33  between the bead core  23  and a rim seating bead base  26 . 
     To reduce the effect of the shear forces acting on both the carcass main portion  18  and the turnup portion  20 , the minimum distance D min  between the carcass main portion  18  and the carcass turnup  20 , as measured perpendicular to the EP, is not less than 50%, preferably not less than 75% of the maximum bead core width W B  as measured perpendicular to the EP. Preferably, to maintain the spacing, the carcass turnup  20  also does not pass axially inward of a radial line BT that is tangent to the axially outermost point of the bead core  23  and parallel to the tire equatorial plane EP. 
     Outward of the main portion  18  of the carcass ply  12  in the bead portion  14  is another steel cord reinforced layer referenced to as the axially inner chipper  40 . The axially inner chipper  40  extends from a radially inner end  43  located above and in close proximity to the bead core  23 . The axially inner chipper  40  extends axially inward along and adjacent to the turnup  20  extending to a radially outer end  41  which extends radially outward of both the terminal end  21  of the turnup  20  and the radially outer end  31  of the axially outer chipper  30 . 
     As shown in both  FIGS. 1 and 2 , the axially outer chipper  30  has the end  31  extending 5 mm or more beyond the terminal end  21  of the turnup  20 , while the inner chipper  40  extends even further beyond both the terminal end  21  and the end  31  to an end  41  which extends at least 5 mm or more beyond the end  31 . In this region the radially outer portions of the inner chipper  40  and the outer chipper  30  join creating an interlocking adjoining region just radially above the terminal end  21  of the ply turnup  20 . 
     Both the inner and outer chippers  30 ,  40  are reinforced with substantially inextensible cords  32 ,  42 . Preferably the cords  32 ,  42  are made of steel having a mesh of parallel cords between about 8 and 18 ends per inch, preferably between about 12 and 16 ends per inch. The wire cord gauge of each chipper is preferably between about 0.6 mm and 1.5 mm. The chipper cords  32 ,  42  are oriented at an angle of between about 25 degrees and about 85 degrees with respect to the radially oriented steel cords  22  that reinforce the ply  20 , most preferably cords  32 ,  42  are oriented between 25 and about 45 degrees. Alternatively the cords  32 ,  42  can be made of a polyamide monofilament cord of any cross sectional shape such as round, oval or star. These polyamide cords  32 ,  42  although being a synthetic material are very strong and similarly substantially inextensible as compared to polyester or nylon cords. 
     Both chipper layers  30 ,  40  when assembled as shown preferably have generally equal, but oppositely oriented cord angles. By having the cord angles biased oppositely at the locations where the chipper  30  and  40  are joined causes the stresses that would normally tend to initiate a crack at the terminal end  21  of the ply turnup  20  absorbed first by the end  41  of the axially inner chipper  40  causing these shear stresses to progress radially inwardly to the area wherein the outer chipper  30  is joined to the inner chipper  40  causing the shear forces to be absorbed in both the chippers  30  and  40  directly above the turnup  20 . This greatly lowers the shear forces absorbed by the turnup  20  while also providing a way in which the inner chipper  40 , can in a disconnected way relative to the bead core  23 , transfer the stress to the outer chipper  30  which is anchored between the bead core  23  and bead base  26  without unduly loading the turnup  20 . Textile or otherwise high elongation cords used to protect the turnup  20  could not absorb nor transfer the shear stresses in such an efficient manner. The stretching of such textile cords would simply cause the turnup  20  when reinforced with steel cords  22  to absorb the shear forces and the typical cracking in this area of the bead  14  would continue to occur. 
     An important feature of the present invention is the fact that the initial forces are absorbed by the inner chipper  40  because of its end  41  extending above the end  31 . This structure insures the inner chipper  30 , unanchored by the bead core  23 , takes the initial shear stresses caused by deflection of the tire. Attempts to extend the end  31  of the outer chipper  30  to the same height or beyond the end  41  of the inner chipper  40  would have caused the anchored outer chipper  30  to take the initial shear stress and its end  31  would initiate a crack propagation due to the stiffness of the steel or polyamide cords  32  being anchored at the bead core  23 . The present invention insures the stresses due to deflection of the tire are first taken in the longer end  41  of the chipper  40 . 
     With reference to  FIG. 3  an alternative embodiment bead portion  14  is shown wherein an additional second inner chipper  50  is added to the bead portion  14 . The second chipper  50  has a radial outer end  51  and radial end  53  lying adjacent next to the inner chipper  40 . The second inner chipper  50  has steel or polyamide cords  52  oriented on a bias angle preferably equal but opposite to the cords  42  of the inner chipper  40 . In this alternative embodiment the added chipper  50  increases the stiffness of the bead portion  14  inward of the ply turnup  20  to further insure the transfer of shear stresses along both the inner chippers  40 ,  50  and outer chipper  30 . 
     In each of the present tire construction, the primary advantage is increasing 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 typically have large rim diameters of 22.5 inches (88 mm) or greater and are designed to be retreaded such that the bead portions of the carcass may be exposed to many hundreds of thousand miles. The ability to provide a more durable bead portion as is accomplished by the present invention provides a more reliable longer lasting carcass. 
     As shown by sandwiching the ply turnup  20  between the chippers  30  and  40  or optionally, also chipper  50 , the present invention has been shown to enable the bead area to actually be made slightly lighter in weight which helps reduce hear build up. In a preferred embodiment the main portion  18  of the ply  12  preferably has a ply line approximately a neutral ply path to further help reduce shear forces on the ply  12 . Experimental testing has shown the bead portions  14  employing the chippers  30 ,  40  provide a cool running tire with lower shear stresses along the ply turnup  20  evidencing greatly improved bead area durability with a much lower probability of end cracking along the ply turnup terminal end  21 . 
     The tire of the present invention has an improved life and improved bead durability. 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. The teachings may also be useful in improving bead durability for run-flat tires of any type. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.