Abstract:
A pneumatic tire construction is described suitable for severe loading conditions. The tire includes a bead portion further having an apex which extends radially outward of the bead core, and a turn-up pad located adjacent said chafer. The turn-up pad has a minimum specified width and a maximum specified width at a Radius R as measured from the bead center. The turn-up pad is formed of a material having a specified G′ and G″.

Description:
TECHNICAL FIELD 
     This invention relates to heavy duty pneumatic tires such as are commonly used on earthmoving equipment, aircraft, and agricultural tires. 
     BACKGROUND 
     The invention concerns the reduction of ply cord compression and shear strain/stress in the lower sidewall of large, heavy load tires or Off-The-Road tires of radial construction that are used in heavily loaded vehicles. The lower sidewall of a typical radial OTR construction consists of a ply around the bead and chipper reinforcements that restrict the circumferential deformation of the ply. Under heavy load, the lower sidewall of the tire bends over the rim flange, and the ply reinforcement rotates in the circumferential direction. The severe deformation results in high ply cord compression in the turn-up near the rim flange region, and high in-plane shear strains in the turn-up pad. The deformation also results in rubbing of the chafer against the rim flange, resulting in wear of both the tire and rim. It is desired to have an improved tire design to reduce the ply cord compression, shear stresses and rim chafing of the tire against the rim. 
     DISCLOSURE OF THE INVENTION 
     Definitions 
     “Aspect ratio” of the tire means the ratio of its section height (SH) to its section width (SW); 
     “Axial” and “axially” mean lines or directions that are parallel to the axis of rotation 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; 
     “Belt reinforcing structure” means at least two 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 17 degrees to 27 degrees with respect to the equatorial plane of the tire; 
     “Bias Ply Tire” means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about a 25-50° angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers; 
     “Carcass” means the tire structure apart from the belt structure, tread, under tread, and sidewall rubber over the plies, but including the beads; 
     “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction; 
     “Chafers” refers 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; 
     “Chippers” means a reinforcement structure located in the bead portion of the tire; 
     “Cord” means one of the reinforcement strands of which the plies in the tire are comprised; 
     “Design rim” means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim width are as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical Organization—Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer&#39;s Association. 
     “Equatorial plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread; 
     “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; 
     “Normal rim diameter” means the average diameter of the rim flange at the location where the bead portion of the tire seats; 
     “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; 
     “Normal load” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire; 
     “Ply” means a continuous layer of rubber-coated parallel cords; 
     “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire; 
     “Radial-ply tire” means belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from the bead to bead are laid at cord angles between 65 degrees and 90 degrees with respect to the equatorial plane of the tire; 
     “Section height” (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane; and, 
     “Section width” (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands. 
     “Turn-up pad” means a strip of elastomer located between the chafer and the turnup end of the ply in the lower sidewall of the tire near the bead general area. 
     SUMMARY OF THE INVENTION 
     The invention provides in a first aspect a pneumatic tire comprising a carcass, the carcass having one or more cord reinforced plies and a pair of bead portions, each bead portion having at least one annular inextensible bead core about which the cord reinforced plies are wrapped, a tread and a belt reinforcing structure disposed radially outward of the carcass, the bead portion further comprising an apex which extends radially outward of the bead core, and a chafer, the tire further comprising a turn-up pad located adjacent said chafer, wherein the turn-up pad has a minimum thickness in the range of about 1.0 inches to about 2.0 inches. The turn-up pad may have a maximum thickness in the range of about 2 inches to about 3 inches. The minimum thickness may be located within a range of radius R from about 4 inches to about 8 inches, wherein the R is measured from the bead center. The maximum thickness may be located within a range of R from about 4 inches to about 8 inches. The bead core may have a width in the range of about 2.4 inches to 2.7 inches, or a width in the range of about 2.5 inches to 2.7 inches. The gauge between the turnup portion of the ply and the turndown portion of the ply may be between 0.25 inches and 0.8 inches. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention may take physical form and certain parts and arrangements of parts, several preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part whereof and wherein: 
         FIG. 1  is a cross-sectional view illustrating one side or one-half of a symmetrical heavy duty tire according to a first embodiment of the invention; 
         FIG. 2  is an enlarged cross-sectional view of the bead portion of the tire shown in  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view illustrating the bead portion of a baseline tire; 
         FIG. 4  illustrates an enlarged cross-sectional view of a lower sidewall portion of a tire illustrating how the turnup ply-turndown ply gauge, the turn-up pad gauge and the bead width are measured; 
         FIG. 5  illustrates a graph of ply cord compression for the tire of Ex. 1 versus the base line tire; 
         FIG. 6  illustrates a graph of rim chafing indicator for the tire of Ex. 1 versus the base line tire; 
         FIG. 7  illustrates a graph of turn-up pad strain for the tire of Ex. 1 versus the base line tire; and 
         FIG. 8  illustrates a computer model of the ply cord compressive force calculated for the tire of Ex. 1 and the baseline tire for both the rated load and severe load conditions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 and 2 , a cross-sectional view of one half of a tire of the present invention  10  is illustrated. The tire  10  has a carcass  14  which includes a crown region having a radially outer tread  12  disposed over the crown region of the carcass  14 . The outer surface of the tread may further include a plurality of lands and grooves or a plurality of tread blocks and grooves, as commonly known to those skilled in the art. The carcass further includes an optional inner liner  17  that covers the entire interior facing surface of the tire carcass and serves to hold the air or gas mixture that is used to inflate the tire. The inner liner of the tire is typically made of butyl rubber. The carcass  14  further includes a pair of tire sidewalls  18  which extend radially inward from the outer radial surface of the of the tire carcass, terminating in the vicinity of a pair of inextensible annular tensile members or beads  16 . 
     The annular beads  16  illustrate an asymmetrical cross sectional shape having a lower half with a rounded outer surface  15  and an upper half portion  33  with angular outer edges similar to half of a hexagon. The annular beads may comprise other shapes such as, for example, round, hexagonal or a combination of shapes. Preferably, the radially innermost surface  15  of the bead wire is rounded. 
     The carcass further includes one or more steel cord reinforced plies  19  wrapped about each bead  16  forming a turnup portion  20 , more preferably an envelope turnup. The portion of the ply which extends from the crown towards the bead and is axially inwards of the bead is referred to as the down portion of the ply or down ply, while the portion of the ply which extends radially and axially outwards from the bead is referred to as the up ply or turnup portion. The one or more plies  19  are oriented in the radial direction. Disposed radially outwardly of the ply  19  in the crown area of the tire is a steel reinforced belt package  21  formed of two or more belts. A pair of sidewalls  18  extend radially inward from the tread  12  to the bead area. Located radially outward of the bead  16  is an elastomeric apex  24 . The apex as shown may have a triangular cross-sectional shape. Wrapped around the bead  16  is an optional flipper  26 . The flipper  26  is located adjacent the bead  16  and the carcass ply  19 . Located on the axially outer edge of the bead area is a chafer  28 . 
     A turn-up pad  30  is located adjacent the chafer  28  in the bead portion of the tire. The turn-up pad  30  has a first end  32  located in the vicinity of the bead wire  16 , and more preferably in line with the radially outer surface  33  of the bead wire. The turn-up pad  30  has a second end  34  located between the first end  32  and the ply turnup  20 . The length of the turn-up pad  30  is sized so that it is positionable over the 90 degree bend of the rim when the tire is under heavy load. The turn-up pad  30  has a thickness in the range of about 1 to about 2 inches, and more preferably in the range of about 1.2 to about 1.7 inches, and more preferably in the range of about 1.2 to about 1.5 inches, as measured at a Radius R of 4 inches from the bead center. The thickness of the turn-up pad is measured across the cross-section of the pad and perpendicular to the pad longitudinal axis. As measured at a radius of 8 inches from the bead center, the turn-up pad  30  has a thickness in the range of about 2 to about 3 inches, and more preferably in the range of about 2.2 to about 2.7 inches, and more preferably in the range of about 2.4 to about 2.6 inches. The length of the turn-up pad  30  may range from about 200 mm to about 400 mm. The turn-up pad  30  is comprised of an elastomeric or rubber material having a storage modulus G′ which ranges from about 0.5 MPA to about 2.0 MPA and more preferably in the range of 0.6 to 1.5 MPA and more preferably in the range of 0.8 to 1.2 MPA. The turn-up pad  30  is made of a material having a G″ which ranges from about 0.05 MPA to about 0.1 MPA. 
     Unless otherwise noted, all G′ values are measured on a rubber sample at a sample temperature of 90° C., at a measurement frequency of 10 Hz and at a strain amplitude of 50%. The rubber sample is taken from a cured tire manufactured to the desired manufacturer specifications. For the purposes of this invention, the storage modulus property G′ is a viscoelastic property of a rubber composition and may be determined by a dynamic mechanical analyzer over a range of frequencies, temperature and strain amplitude. One example of a dynamic mechanical analyzer (DMA) suitable for measuring G′, G″ is model number DMA +450 sold by the 01-dB Metravib company. The DMA instrument uses dynamic mechanical analysis to evaluate rubber compositions. A cured sample of the respective rubber composition is subjected to a precisely controlled dynamic excitation (frequency and amplitude) at a frequency (Hertz) and temperature (° C.) and the sample stress response is observed by the instrument. The observed sample response can be separated, by the instrument, into viscous or loss modulus (G″) and elastic or storage modulus (G′) components. Unless otherwise indicated, all G″ are measured at the same conditions as G′. 
     Durability issues in the lower sidewall may be due to several factors such as large ply cord compression in the region adjacent to rim flange, chafing between the tire and rim and large strains in rubber components in lower sidewall. The current invention is focused on achieving significant reduction in strain/stress in the turn-up pad and ply cord compression while maintaining similar level of chafing potential between rim and chafer as the baseline. When there is a durability issue in the lower sidewall, tire designers have historically increased the bead diameter in order to reduce the stress/strain in the lower sidewall. An increase in bead width increases the compressive force in the ply cord while achieving only moderate decrease in the stress/strain in the lower sidewall. The inventor has found that a combination of reduction in bead width and increase in turn-up pad thickness yields the most desirable results that are not intuitive. It is desirable to reduce the bead width Bw of the annular tensile member  16  to the range of about 2.0 to 3 inches, more particularly in the range of about 2.4 to 2.7 inches, and more preferably about 2.5 to 2.7 inches. 
     It has also been determined that by reducing the gauge or distance between the ply turnup and the ply turndown (hereinafter “turnup-turndown gauge”) as shown in  FIG. 7 , that the ply cord compression is reduced. The inventor has found that the effect of decreasing the gauge between ply turnup and ply turndown on the ply cord compression is more pronounced as the turn-up pad gauge increases. The distance or gauge is measured perpendicular to the longitudinal axis of the ply. It is thus desired to have the turnup-turndown gauge to be in the range of about 0.25 inches to about 0.8 inches, and more particularly in the range of about 0.4 inch to about 0.6 inches, and most preferably about 0.4 to about 0.5 inches. The turnup-turndown gauge is measured over a range of radius R from the center of annular tensile member. It is additionally preferred that the turnup-turndown gauge previously stated occur at a radius of 8 inches from the bead center. At a radius of 4 inches from the bead center, it is desired to have the turnup-turndown gauge to be in the range of about 1.25 inches to about 1.75 inches, and more particularly in the range of about 1.4 inches to about 1.7 inches, and most preferably about 1.5 inches to about 1.6 inches. 
     A significant reduction in the ply cord compression as well as stress/strain in the lower sidewall is achieved through the combination of bead width, turn-up pad gauge and turnup-turndown gauge proposed in this invention.  FIGS. 8 through 10  illustrate the results from a numerical simulation study of a tire of the invention in a 63 inch size as compared to a baseline design in both a 57 inch and 63 inch rim size. The baseline design had a bead width of 3.15 inch and a turnup-turndown gauge of 1.894 inches and a turn-up pad gauge of 1.324, both measured at a radius of 4 inches from the bead center. The baseline tire had a turn-up pad gauge of 1.75 inches and a turnup-turndown ply gauge of 1.1 inches, both values measured at a radius of 8 inches from the bead center. The Ex. 1 tire had a 63 inch rim size, an annular tensile member (or bead width) having a cross-sectional width of 2.65 inches, and a turn-up pad thickness of 2.62 inches as measured at a radius R of 8 inches from the annular tensile member center. The turn-up pad was formed of the same rubber material as the baseline tire. The Ex. 1 tire had a ply turnup-ply turndown gauge of 0.42 inches at a radius of 8 inches from the bead center. A numerical model was made of both tires and subjected to rated load and a high severity load of 1.2 times rated load. 
       FIG. 5  illustrates the computer simulation results, showing a significant 57% reduction of ply cord compression for the inventive tire of Ex. 1 as compared to the baseline design.  FIG. 6  illustrates that the rim chafing potential between chafer and rim is about the same for the base line design and the tire of Ex. 1.  FIG. 7  illustrates a reduction of 14% in the strain in the turn-up pad component in the lower sidewall of the tire of Ex. 1 as compared to the baseline tire.  FIG. 8  illustrates the ply cord compression in the tire of Ex. 1 for both the rated load and high severity. 
     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.