PNEUMATIC TIRE WITH A ROBUST PLY ENDING STRUCTURE

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.

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 inFIGS. 1 and 2and indicated at10. The tire10includes a pair of bead areas12and a respective bead core14embedded in each bead area. A respective sidewall16extends radially outward from each bead area12to a ground-contacting tread18. The tire10is reinforced by a carcass20that toroidally extends from one of the bead areas12to the other one of the bead areas. The carcass20includes at least one ply22that preferably winds around each bead core14. A belt reinforcement package24is disposed between the carcass20and the tread18.

What is conventionally considered a main portion26of the carcass reinforcing ply22extends radially inward toward the tire rim (not shown) and is turned about each bead core14to form a carcass ply turn up28. The carcass ply turn up28extends at a single angle μ relative to a radial line tangent to the axially outermost point of the bead core14and parallel to the equatorial plane of the tire10. A chafer30is disposed about the radially inward surface of the carcass ply turn up28to resist chafing of the tire10by the rim.

Due to the configuration and nature of the radial carcass20, when the tire10is expanded, the main portion26of the carcass ply22is put under tension, pulling the carcass main portion radially outward and the carcass ply turn up28radially inward. After inflation and during operation of the tire10, when the tire is under deflection, the carcass ply22is subject to bending forces and the carcass main portion26moves radially inward while the carcass turn up28moves radially and axially outward. Due to the adhesion relationship between the rubber and the reinforcing cords of the ply22, the rubber surrounding the carcass main portion26and the carcass turn up28also is forced to move during both tension and deflection, resulting in the rubber being stressed. The movement of the carcass ply22and the surrounding rubber may thus result in cracking of the rubber in each tire bead area12, thereby potentially decreasing durability of the tire10.

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.

“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'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.

DETAILED DESCRIPTION OF THE INVENTION

A first exemplary embodiment of the tire of the present invention is shown inFIG. 3and is indicated generally at50. The general construction of the tire50is somewhat similar to that of prior art tire10, with the principal differences to be described in detail below.

The tire50includes a pair of bead areas52(only one shown) and a respective bead core54embedded in each bead area. A carcass56includes at least one ply58that preferably winds around each bead core54. A main portion60of the carcass reinforcing ply58extends radially inward toward the tire rim (not shown) and is turned about each bead core54to form a carcass ply turn up62. The carcass reinforcing ply58is also wrapped about a bead apex64. In this manner, the carcass reinforcing ply58envelopes the bead core54and a lower portion of the bead apex64in each bead area52. The carcass ply turn up62terminates at a radially outward end66. A chafer68is disposed about the radially inward surface of the carcass ply turn up62to resist chafing of the tire50by the rim, and may include an end cap70.

Axially outward of the carcass ply turn up62is an axially outer chipper72, which is a reinforced layer, as will be described in greater detail below. The axially outer chipper72includes a radially inward end74, a radially outward end76, an inboard surface78and an outboard surface80. Axially inward of the carcass ply turn up62is an axially inner chipper82, which is a reinforced layer, as will be described in greater detail below. The axially inner chipper82includes a radially inward end84, a radially outward end86, an inboard surface88and an outboard surface90.

The inboard surface78of the outer chipper72adjacent its radially inward end74is bonded to an outboard surface92of the carcass ply turn up62near the turn up end66. The outboard surface90of the inner chipper82adjacent its radially inward end84is bonded to an inboard surface92of the carcass ply turn up62near the turn up end66. The outer chipper72and the inner chipper82extend radially outwardly past the end66of the carcass ply turn up62. Once past the carcass ply turn up end66, the inboard surface78of the outer chipper72is bonded to the outboard surface90of the inner chipper82. In this manner, the outer chipper72and the inner chipper82form a sandwich-layer construction with the carcass ply turn up62.

The outer chipper72and the inner chipper82preferably are of similar lengths. The radially inward end74of the outer chipper72is offset in a radially outward direction from the radially inward end84of the inner chipper82by a distance of at least 5 millimeters (mm). As a result, the radially outward end76of the outer chipper72extends radially outwardly past the radial outward end86of the inner chipper82by a distance of at least 5 mm.

By way of example, the outer chipper72and the inner chipper82may each be about 35 mm long. In such a case, the radially outward end76of the outer chipper72extends radially outwardly past the radially outward end86of the inner chipper82by 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 chipper72and the inner chipper82. Preferably, distance A is about 6 mm, or at least about 17 percent of the length of the outer chipper72and the inner chipper82. The radially inward end84of the inner chipper82extends radially inwardly past the radially inward end74of the outer chipper72by 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 chipper72and the inner chipper82. Preferably, distance B is about 6 mm, or at least about 17 percent of the length of the outer chipper72and the inner chipper82.

The inboard surface78of the outer chipper72is bonded to the outboard surface90of the inner chipper82for a distance indicated by C. Distance C is about 12 mm, or about 34 percent of the length of the outer chipper72and the inner chipper82. The inboard surface78of the outer chipper72is bonded to the outboard surface92of the carcass ply turn up62for 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 chipper72and the inner chipper82. The outboard surface90of the inner chipper82is bonded to the inboard surface92of the carcass ply turn up62for 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 chipper72and the inner chipper82.

The outer chipper72is formed of an elastomer or polymer compound known to those skilled in the art. The inner chipper82may be formed of the same elastomer or polymer compound as the outer chipper72, or of a different elastomer or polymer compound.

Both the outer chipper72and the inner chipper82are 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 chipper72and82is preferably between about 0.6 mm and 1.5 mm. Alternatively, the cords in each chipper72and82may be made of a polyamide monofilament cord of any cross-sectional shape, such as round, oval or star. The cords of each chipper72and82preferably 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 ply58. More preferably, the cords of each chipper72and82are oriented between about 25 and about 45 degrees.

The outer chipper72and the inner chipper82, when assembled as shown, preferably have generally equal, but oppositely oriented cord angles. Having the cord angles biased oppositely at the locations where the chippers72and82are joined causes the stresses that would normally tend to initiate a crack at the end66the carcass ply turn up62to be absorbed first by the radially outward end76of the outer chipper72. Such absorption causes shear stresses to progress radially inwardly to the area where the inner chipper82is joined to the outer chipper72, 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 up62. This absorption of forces lowers the shear forces absorbed by the carcass ply turn up62, while also transferring stress to the inner chipper82without unduly loading the carcass ply turn up.

In this manner, the tire50of the present invention provides a structure in which forces due to deflection are absorbed by the outer chipper72, as its radially outward end76extends radially outwardly past the inner chipper82and the carcass ply turn up62. Those forces are then absorbed by the outer chipper72and the inner chipper82. Such absorption of forces by the outer chipper72and the inner chipper82lowers shear stresses along the carcass ply turn up62. Lowering or reducing the stresses in the carcass ply turn up62enables the tire50to resist fatigue cracking in the bead area52, thereby improving the durability of the bead area.

A second exemplary embodiment of the tire of the present invention is shown inFIG. 4and is indicated generally at100. The general construction of the tire100is somewhat similar to that of the first embodiment of the tire50of the present invention, with the principal differences to be described in detail below. The second embodiment of the tire100finds 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 tire50.

As with the first embodiment of the tire50, the second embodiment of the tire100includes a pair of bead areas52(only one shown) and a respective bead core54embedded in each bead area. A carcass56includes at least one ply58that preferably winds around each bead core54. A main portion60of the carcass reinforcing ply58extends radially inward toward the tire rim (not shown) and is turned about each bead core54to form a carcass ply turn up62. The carcass reinforcing ply58is also wrapped about a bead apex64. In this manner, the carcass reinforcing ply58envelopes the bead core54and a lower portion of the bead apex64in each bead area52. The carcass ply turn up62terminates at a radially outward end66. A chafer68is disposed about the radially inward surface of the carcass ply turn up62to resist chafing of the tire50by the rim.

Axially outward of the carcass ply turn up62is a first axially outer chipper102, which a reinforced layer, as will be described in greater detail below. The first outer chipper102includes a radially inward end104, a radially outward end106, an inboard surface108and an outboard surface110. Axially outwardly of the first outer chipper102is a second axially outer chipper112, which is a reinforced layer, as will be described in greater detail below. The second axially outer chipper112includes a radially inward end114, a radially outward end116, an inboard surface118and an outboard surface120.

The inboard surface78of the first outer chipper102is bonded to the chafer68and the carcass ply turn up66. More particularly, the chafer68includes an axially outer end122and an outboard surface124, and the carcass ply turn up62includes an outboard surface126that extends radially outwardly past the outer end of the chafer. The inboard surface78of the first outer chipper102is bonded to the outboard surface124of the chafer68and to the outboard surface126of the carcass ply turn up62. The radially inward end104of the first outer chipper102is disposed below or radially inwardly of the axially outer end122of the chafer68, and extends radially outwardly past the end66of the carcass ply turn up62. In this manner, the first outer chipper102covers the axially outer end122of the chafer68and the end66of the carcass ply turn up62.

The inboard surface118of the second outer chipper112is bonded to the outboard surface110of the first outer chipper102. The first outer chipper102and the second outer chipper112preferably are of similar lengths. The radially inward end114of the second outer chipper112is offset in a radially outward direction from the radially inward end104of the first outer chipper102by a distance of at least 5 mm. As a result, the radially outward end116of the second outer chipper112extends radially outwardly past the radial outward end106of the first outer chipper102by a distance of at least 5 mm.

By way of example, the first outer chipper102and the second chipper112may each be about 72 mm long. In such a case, the radially outward end116of the second outer chipper112extends radially outwardly past the radially outward end106of the first outer chipper102by 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 chipper102and the second outer chipper112. Preferably, distance A is about 8 mm, or at least about 11 percent of the length of the first outer chipper102and the second outer chipper112. The radially inward end104of the first outer chipper102extends radially inwardly past the radially inward end114of the second outer chipper112by 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 chipper102and the second outer chipper112. Preferably, distance F is about 8 mm, or at least about 11 percent of the length of the first outer chipper102and the second outer chipper112. In such a case, the inboard surface118of the second outer chipper112is bonded to the outboard surface110of the first outer chipper102for 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 chipper102is formed of an elastomer or polymer compound known to those skilled in the art. The second outer chipper112may be formed of the same elastomer or polymer compound as the first outer chipper102, or of a different elastomer or polymer compound.

Both the first outer chipper102and the second outer chipper112are 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 chipper102and112is preferably between about 0.6 mm and 1.5 mm. Alternatively, the cords in each chipper102and112may be made of a polyamide monofilament cord of any cross-sectional shape, such as round, oval or star. The cords of each chipper102and112preferably 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 ply58. More preferably, the cords of each chipper102and112are oriented between about 25 and about 45 degrees.

The first outer chipper102and the second outer chipper112, when assembled as shown, preferably have generally equal, but oppositely oriented cord angles. Having the cord angles biased oppositely at the locations where the chippers102and112are joined causes the stresses that would normally tend to initiate a crack at the end66the carcass ply turn up62to be absorbed first by the radially outward end116of the second outer chipper112. Such absorption causes shear stresses to progress radially inwardly to the area where the first outer chipper102is joined to the second outer chipper112, 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 up62. This absorption of forces lowers the shear forces absorbed by the carcass ply turn up62, while also transferring stress to the first outer chipper102without unduly loading the carcass ply turn up.

In this manner, the tire100of the present invention provides a structure in which forces due to deflection are absorbed by the second outer chipper112, as its radially outward end116extends radially outwardly past the first outer chipper102and the carcass ply turn up62. Those forces are then absorbed by the second outer chipper112and the first outer chipper102. Such absorption of forces by the second outer chipper112and the first outer chipper102lowers shear stresses along the carcass ply turn up62. Lowering or reducing the stresses in the carcass ply turn up62enables the tire100to resist fatigue cracking in the bead area52, thereby improving the durability of the bead area.

The pneumatic radial tire of the invention50,100thus includes a layered ply ending or chipper structure72,82,102,112that improves the durability of the respective bead areas52of the tire and the life of the tire. In each tire of the present invention50,100, 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 tires50,100typically 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 carcass20may be exposed to many hundreds of thousand miles. The ability to provide a more durable bead portion or area52as accomplished by the tire of the present invention50,100thereby also provides a longer-lasting tire carcass20.

The present invention also includes a method of forming a tire50,100with improved durability of the bead area52. The method includes steps in accordance with the description that is presented above and shown inFIGS. 3 and 4.

It is to be understood that the structure of the above-described tire50,100may 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.