Abstract:
The present invention relates to a pneumatic tire, specifically to improvements to the bead region of tires designed for runflat operations. The improvements comprise the addition of cavities or indentation ( 126 ) on the surface of the bead ( 127 ) that contacts the wheel rim ( 128 ). In a first embodiment a series of circular cavities ( 126 ) are located on the radial innermost surface of the bead in the proximity of the bead toe. In a second embodiment, a continuous groove-like torus cavity ( 226 ) is located in the radially innermost surface of the bead in the proximity of the bead toe. The series of cavities or torus cavity increase the adherence of the bead to the rim as a small volume of air at a low pressure, significantly inferior to the atmospheric pressure (air vacuum situation) is trapped in the void spaces created by the cavities or torus cavity and the bead seat.

Description:
TECHNICAL FIELD 
   The present invention relates to a pneumatic tire, specifically to improvements to the bead region of tires designed for runflat operations. 
   BACKGROUND OF THE INVENTION 
   An important design consideration in the development of a run-flat tire is insuring that the uninflated tire remains seated on the rim. Solutions have been developed employing bead restraining devices as well as special rims to accomplish this requirement. 
   The design of the bead region for extended mobility technology (EMT) tires requires the balance of two opposing criteria. The design of the bead region must provide the means for the bead to remain seated on the rim during uninflated operation and the design should be compatible with conventional wheel rims. The design should also allow the tire to be installed on a conventional wheel without special equipment or procedures and removed from a conventional wheel without damage to the tire. The prior art shows a variety of approaches, however, none provide a completely satisfactory solution to the problem or an optimum balance of operating characteristics when uninflated and compatibility with conventional wheels, tires, and mounting procedures. 
   The compressive force of the air in typical pneumatic tire is confined by the carcass plies in tension. The tensile force in the carcass plies is transmitted to the bead cores, placing the bead cores in tension. The bead core holds the bead seat radially inward against the rim of the wheel and in the case of tubeless tires maintains an air tight seal between the bead and rim bead seat of the wheel. The compressive force of the air in the tire also exerts an axial outward force on the bead region of the tire pressing the axially outward facing surfaces of bead seat against the rim flange. The relatively thin and flexible sidewalls of a normally inflated conventional tire do not transmit significant compressive forces, bending moments or axially inward forces to the bead region except possibly under conditions of severe cornering or breaking. 
   In comparison, EMT tires often rely on a thickened and reinforced sidewall construction to provide uninflated operation. These thickened and reinforced sidewalls are capable of transmitting compressive and bending stresses to the bead regions of the tire particularly during under-inflated or uninflated operation. These compressive and bending stresses conspire to unseat the bead from the rim particularly when combined with the additional lateral forces encountered in cornering. The compressive loading of the reinforced sidewalls carries an axial inward component tending to unseat the bead. The bending stresses tend to lift the radially and axially innermost edge of the bead or bead toe facilitating the slippage of the bead over any humps or protrusions that may be provided axially inward of the bead seat. 
   The prior art shows a considerable variety of approaches to the design a bead-wheel interface capable of resisting the axially inward forces that may be encountered during uninflated operation. Many of these approaches require modifications to the wheel rim as well as the bead region of the tire to provide and interlocking geometry where circumferential grooves or humps on the bead are matched by complementary grooves or humps on the flange and bead seat regions of the wheel. However the use of non-standards wheels and tires has not received wide application. 
   A more simple solution is to increase the size and strength of the bead core to improve the runflat operation. However, as the strength of the bead core is increased, mounting the tire on a wheel becomes more difficult and may require special equipment. 
   Another approach is to redesign the wheel and tire bead with a non-conventional geometry. For example, U.S. Pat. No. 5,145,536 (&#39;536) discloses a bead profile with an elastomeric projection or toe extending radially and axially inward from the bead core and a wheel rim provided with a complementary groove. The wheel rim of the &#39;536 patent is designed with an annular groove and hump that accommodate the toe and groove respectively of the tire bead. 
   U.S. Pat. No. 4,015,652 discloses a radial tire where at least one bead portion is adhered to the rim at one of the seats with a cement having sufficient bonding strength to retain the bead portion on the rim during operation of the tire in the deflated condition. 
   Despite the variety of ingenious approaches to improving the interface between the bead and the rim to provide more robust runflat operation, none of the existing designs have provided an entirely satisfactory solution. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improvement to the interface between the bead region of the tire and the wheel rim to maintain bead seating at very low inflation pressures and to resist the tendency the tire bead to rotate and roll off the bead seat of the tire rim when operated in an under-inflated or uninflated condition. A tire having a tread, a belt structure and a carcass structure comprising a pair of sidewalls, a pair of bead regions and one or more plies anchored in each bead region the tire is provided with a series or plurality of cavities in a surface of the bead regions that is in contact with a wheel rim during normal inflated operation. 
   In one embodiment the present invention the cavities are circular in their area of contact with the bead seat. The void spaces bounded by the cavities and the rim of the wheel are lenticular in shape having a partial spherical shape defined by the surface of the bead and having a cylindrical or conical shape defined by the bead seat. The cavities are arranged with uniform spacing around the circumference of the bead regions and are aligned in a circumferential pattern with a uniform minimum distance from the edges of the cavities to the axially inward edge of the bead toe. 
   During the process of installing the tire upon the wheel, the cavities are flattened against the bead seat and the air contained by void spaces defined by the bead cavities and the bead seat is substantially expelled from the void space. The cavities are surrounded by elastomeric material that provides an air-tight seal preventing air from leaking back into the void spaces defined by the cavities and the rim once the tire has been installed in the wheel. The cavities are held in a flattened condition against the bead seat by the bead core which generate compression on the rim when the tire is installed on a wheel rim and operated in a normally inflated condition on a vehicle. 
   Once the cavities have been flattened by installation or operation of the tire, the bead will resist separation from the wheel rim bead seat. Due to adherence force generated by the air vacuum, cavities in the vicinity of the bead toe, once flattened by installation or operation, will resist rotation of the bead region that would tend to lift or separate the bead toe from the rim bead seat. 
   In a second embodiment of the present invention, a pneumatic tire having a tread, a belt structure and a carcass structure comprising a pair of sidewalls, a pair of bead regions, one or more plies anchored in each bead region is provided with a torus cavity in a section of a surface of one or both bead regions that are in contact with a wheel rim during normal inflated operation. The torus cavity is aligned in a circumferential pattern with a uniform minimum distance from the edges of the torus cavity to the axially inward edge of the bead toe, having a minimum distance from the edges of the torus cavity to the axially inward edge of the bead toe. 
   The process of installing the tire upon the wheel causes the torus cavity to flatten against the bead seat and the air contained by void spaces defined by the torus cavity and the bead seat to be substantially expelled from the void space creating adherence force via vacuum. The surrounding elastomeric material of the torus cavity provides an air-tight seal preventing air from leaking back into the void spaces defined by the torus cavity and the rim once the tire has been installed in the wheel. The torus cavity may also be flattened or held in a flattened condition against the bead seat by the bead core when the tire is installed on a wheel rim and operated in a normally inflated condition on a vehicle. The torus cavity may also be flattened or held in a flattened condition against the wheel rim by the bead core when the tire is installed on a wheel rim and operated in an inflated or uninflated condition on a vehicle traveling in a straight line and at a constant speed. 
   Once the torus cavity has been flattened by installation or operation of the tire, the bead will resist separation from the wheel rim bead seat and resist rotation of the bead region that would tend to lift or separate the bead toe from the rim bead seat. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The drawings are intended to be illustrative, not limiting. Certain elements in selected ones of the drawings may be illustrated not-to-scale, for illustrative clarity. 
     Often, similar elements throughout the drawings may be referred to by similar references numerals. For example, the element  199  in a figure (or embodiment) may be similar in many respects to the element  299  in an other figure (or embodiment). Such a relationship, if any, between similar elements in different figures or embodiments will become apparent throughout the specification, including, if applicable, in the claims and abstract. In some cases, similar elements may be referred to with similar numbers in a single drawing. For example, a plurality of elements  199  may be referred to as  199   a ,  199   b ,  199   c , etc. 
     The cross-sectional views presented herein may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity. 
     The structure, operation, and advantages of the present preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a cross-sectional view of a tire incorporating a first embodiment of the present invention; 
       FIG. 1   a  is a detailed cross-sectional view of the bead region of the tire of  FIG. 1  showing a first embodiment of the present invention as a series of cavities in the seat of the bead; 
       FIG. 1   b  is a detailed view of the radially innermost surface of the bead region of  FIG. 1   a  showing a series of cavities according to a first embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of a tire incorporating a second embodiment of the present invention; 
       FIG. 2   a  is a detailed cross-sectional view of the second embodiment of the present invention wherein the bead region includes a circumferential, torus cavity; and 
       FIG. 2   b  is a detailed view of the radially innermost surface of the bead region of  FIG. 2   a  showing a circumferential torus cavity according to a second embodiment of the present invention. 
   

   DEFINITIONS 
   “Axial” and “Axially” means the lines or directions that are parallel to the axis of rotation of the tire. 
   “Axially Inward” means in an axial direction toward the equatorial plane. 
   “Axially Outward” means in an axial direction away from the equatorial plane. 
   “Bead” or “Bead Core” generally means that part of the tire comprising an annular tensile member of radially inner beads that are associated with holding the tire to the rim; the beads being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers. 
   “Bead Seat” refers to the area of the wheel comprising a portion of the wheel rim and the flange that are normally in contact with the rim of the tire during normal inflated operation. 
   “Bead Toe” refers to a projection of the bead region radially and axially inward of the bead core. 
   “Bead Heel” refers to that portion of the bead that is axially outward and radially inward from the bead core. 
   “Belt Structure” or “Reinforcement Belts” or “Belt Package” means at least two annular layers or 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 18 degrees to 30 degrees relative to the equatorial plane of the tire. 
   “Carcass” means the tire structure apart from the belt structure, tread, undertread over the plies, but including the beads. 
   “Circumferential” most often means circular lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread, as viewed in cross section. 
   “Crown” or “Tire Crown” means the tread, tread shoulders and the immediately adjacent portions of the sidewalls. 
   “Equatorial Plane” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread; or the plane containing the circumferential centerline of the tread. 
   “Lateral” means a direction parallel to the axial direction. 
   “Ply” means a cord-reinforced layer of rubber coated radially deployed or otherwise parallel cords. 
   “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire. 
   “Radial Ply Structure” means the one or more carcass plies or which at least one ply has reinforcing cords oriented at an angle of between 65 degrees and 90 degrees with respect to the equatorial plane of the tire. 
   “Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles between 65 degrees and 90 degrees with respect to the equatorial plane of the tire. 
   “Rim-Bead Interface” refers to the area of contact between the rim of the wheel and the bead of the tire during normal inflated operation. 
   “Section Height” means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane. 
   “Section Width” 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. 
   “Shoulder” means the upper portion of sidewall just below the tread edge. 
   “Sidewall” means that portion of a tire between the tread and the bead. 
   “Tangential” and “Tangentially” refer to segments of circular curves that intersect at a point through which can be drawn a single line that is mutually tangential to both circular segments. 
   “Tread Cap” refers to the tread and the underlying material into which the tread pattern is molded. 
   “Tread width” means the arc length of the tread surface in the plane includes the axis of rotation of the tire. 
   “Wheel Flange” refers to a radially outward projection of the wheel rim at one or both of the axially outermost edges of the wheel. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Prior Art Embodiment 
   The present invention provides a general means to improve the interface between a tire bead and a wheel rim particularly for extended mobility technology (EMT) tires during under-inflated or uninflated operation. The tire bead of a conventional tire during normal inflated operation is held in place by tension in the bead core and pressure in the tire. However, in the design of EMT tires, conventional bead designs have been found inadequate to fully resist the forces on the bead region that occur when the tire is operated in an under-inflated or uninflated condition. A variety of designs have been developed that depend on modifications to the wheel rim and the tire bead to provide enhanced runflat capabilities. However, most of these designs are not compatible with either conventional tires or conventional rims and have not met with widespread acceptance. The present invention provides an improvement to the bead design that is compatible with conventional wheel rim designs. 
   The surfaces of conventional and EMT beads are normally smooth over the normal area of contact with the rim. U.S. Pat. No. 5,769,981 (&#39;981) discloses a radial tire having bead regions with between two and ten circumferentially extending ribs projecting outward of the bead region outer surface to improve uniformity when mounted on a wheel rim. The present invention provides a series of cavities or circumferential indentation groove in the bead that would increase the adherence of the bead to the rim bead seat. Also by increasing the adherence of the bead to the rim in the vicinity of the bead toe the resistance of the bead region to bending forces can be increased. 
   Preferred Embodiment of the Present Invention 
   The present invention relates to improving the retention of the bead region of a tire on the bead seat of a conventional wheel rim and is particularly applicable to improving the runflat performance of EMT tires. One aspect of the present invention relates to providing a series of discrete cavities on the surface of the bead region of a tire. The invention anticipates many varieties of patterns, sizes and locations of the cavities on the surface of the bead region that would meet the essential objectives of the present invention with essentially equivalent means that fall within the scope of this invention. 
   Detailed Description of the First Embodiment 
   Referring to  FIG. 1 , there is illustrated a cross-sectional view of a runflat tire  110  incorporating a series of discrete cavities  126  on the surface of the bead region  120  of the tire in accordance with the first embodiment of the invention. The tire  110  has a tread  112 , a belt structure  114 , and a carcass structure  116 , comprising a pair of sidewalls  118 , a pair of bead regions  120 , and one or more reinforcing carcass plies  122  anchored in each bead region  120 . A series of cavities  126  are located in the surface  127  of the bead region  120  which contacts the wheel rim  128 . 
   When the tire  110  is installed on a wheel  130 , the cavities  126  are flattened against the rim bead seat  132  causing at least a 95 percent reduction in the volume of the cavities and causing the expulsion of about 90 percent of the air contained by the cavities. In addition, the initial size and shape of the cavities  126 , the elasticity of the surrounding elastomeric material  134  in the bead region  120  and the nominal tension in the bead cores  136  may be designed to continue to flatten the cavities  126  in surface  127  against the bead seat  132 . These design characteristics are selected so that the cavities  126  are maintained at a reduced volume which in turn causes any air or other gases to be substantially expelled from the cavities in the course of normal tire operation. Referring to  FIG. 1 , the volume of the cavity  126  prior to installation on the wheel  130 , is indicated by a dashed line. 
   Furthermore, when the tire  110  of the present invention incorporates reinforced sidewalls  118  to provide extended runflat capability, the reinforced sidewall structure may be designed to flatten each of the cavities  126  against the bead seat  132  at least once during each rotation of the tire  110 . This flattening assists in reducing the volume of the cavities  126  to substantially expel any gasses that may be contained by the cavities. 
   Referring to  FIGS. 1A and 1B  showing a detailed cross-section of the bead region  120  and a partial view of the radially innermost surface  127  of the bead region, respectively, the cavities  126  are evenly spaced about the radially innermost surface  127  of each bead region  120  in the proximity of the bead toe  138 . In an exemplary tire, which is shown and described for illustration purposes only, the cavities  126 , in their area of contact with the bead seat  132 , have a diameter “d” of typically between 30% and 50% of the overall axial width “w” of the bead region  120 . “w” measured from heel  140  to toe  138  is typically from 20 mm to 28 mm as measured in an axial direction. The axially located innermost point of the cavities  126  are located a distance “a” of typically between 1 mm to 4 mm from the radially innermost edge or toe  138  of the bead region  120 . The minimum distance “b” between cavities  126  is close to the distance “a” value. The maximum initial depth “p” of the cavities  126 , measured in a radial direction relative to the cylindrical plane of the nominal bead seat  132 , is typically from 1 mm to 3 mm. In shape, the radially outermost surfaces of the cavities  126  conforms to a portion of a sphere. Thus formed with a radially outward spherical shape, the cavities  126  may be considered as having a lenticular shapes with one side having a spherical shape and the other side having a more or less cylindrical shape conforming to the shape of the rim bead seat  132 . However, the cavities  126  of the present invention may have any shape providing that the quantity of air or other gasses contained by the cavity is substantially decreased by the installation or operation of the tire upon a wheel and that the surrounding elastomeric material  134  prevents air or other gasses from leaking back into the cavities  126 . 
   Referring to  FIG. 2 , a second embodiment of the present invention is illustrated. The tire  210  has a tread  212 , a belt structure  214 , and a carcass structure  216 , comprising a pair of sidewalls  218 , a pair of bead regions  220 , one or more reinforcing carcass plies  222  anchored in each bead region. 
   As shown by  FIGS. 2A and 2B , which provide a detailed cross-section view of the bead region  220  and a partial view of the radially innermost surface  227  of the bead region  220 , respectively, the radially innermost surface  227  of the bead region is provided with a circumferential torus cavity  226  located adjacent to bead toe  238 . As shown in  FIG. 2A  the torus cavity  226  has a curved radially outermost surface that appears similar to that of the cavities  126  of first embodiment when seen in cross section. However,  FIG. 2B , providing a plan view of the bead surface  227 , shows that the torus cavity  226  is continuous in the second embodiment and extends circumferentially over the radially innermost surface of the bead region  220 . 
   When the tire  210  is installed on a wheel  230 , the torus cavity  226  is flattened against the rim bead seat  232  causing a substantial reduction in the volume of the torus cavity  226  and causing most of the air contained by the torus cavity  226  to be expelled. In addition, the initial size and shape of the torus cavity  226 , the elasticity of the surrounding elastomeric material  234  and the nominal tension in the bead cores  236   a ,  236   b  may be designed to continue to flatten the torus  128  against the bead seat  232  causing the torus cavity  226  to be maintained at a reduced volume and causing any air or other gases to be substantially expelled from the cavities in the course of normal operation. 
   Referring to  FIG. 2B , the torus cavity  226  provides a uniform cavity extending over the radially innermost surface of each bead region  220  in the proximity of the bead toe  238 . In the exemplary tire  210 , which is shown and described for illustration purposes only, the torus cavity  226  has a width “x” of typically between 30% and 50% of the overall axial width “y” of the bead region  220 . The overall width “y” of the bead region  220 , measured from heel  240  to toe  238  is from 2 mm to 28 mm as measured in an axial direction. Preferably, the axially innermost edges  226  of the torus cavity  226  is located from 1 to 6 mm from the radially innermost edge or toe  238  of the bead region  220 . The maximum initial depth “e” of the torus cavity  226 , measured in a radial direction relative to the cylindrical plane of the nominal bead seat  232 , is typically from 1 mm to 3 mm. In shape, the radially outermost surfaces of the torus cavity  226  conforms to a portion of a torus having a radius typically from 6 mm to 12 mm in the axial direction and radius more or less equal to the radius of the bead in the radial direction. However, the torus cavity  226  may have any cross-sectional shape providing that the quantity of air or other gasses contained by the torus cavity  226  is substantially decreased by the installation or operation of the tire upon a wheel  230  and that the surrounding elastomeric material  234  prevents air or other gasses from leaking back into the torus cavity  226 . 
   Dynamic Operation of the Inventive Concept 
   The dynamic operation of the inventive concept is described relative to the details of the first embodiment. However the basic principles of operation and the essential results are equivalent for the two embodiments described above as well as for a range of applications that could vary considerably in detail but not the spirit of the present invention. One skilled in the art will find no difficulty in applying the following discussion to both embodiments as well as to a variety of easily conceived alternatives. 
   Once the cavities  126  of the first embodiment have been flattened against the bead seat  132  reducing their volume and expelling a substantial portion of any gasses that may have been contained by the cavities, the surrounding elastomeric material  134  seals the edges of the cavities to the bead seat  132  preventing air or other gasses from leaking back into the cavities  126 . Any attempt to separate a bead surface  127  provided with such cavities  126  will require an expansion in the volume of the cavities. However, since the quantity of the air or other gasses contained by the cavities  126  has been substantially reduced, small absolute increase in the volume of the cavities  126  will require a relatively large percentage increase in the volume of the cavities  126  with a large resulting decrease in the pressure of the air or other gasses contained within each the cavities  126 . As a result, the pressure within the cavities  126  will be substantially reduced relative to the pressure of the air surrounding the bead region  126 , and this net difference in pressure will resist the further separation of the bead region from the rim. 
   With the loss of air pressure, the sidewalls  118  bulge axially outward so that the compressive force is applied to the bead region  120  with an axially inward component. In addition, the bulging of the sidewalls  118  also introduces a bending stress which tends to rotate the bead regions  120  lifting the axially and radially innermost edge of the bead region, also known as the bead toe  138  from the bead seat  132 . The rotation of the bead region  120  reduces the area of contact between the bead region  120  and the rim bead seat  132  of the wheel  130 . The rotation also lifts the toe  138  of the bead from the rim bead seat  132  and facilitates the axially inward movement of tire  130  over any axially inward humps  142  in the rim. 
   The present invention provides a means to prevent the toe  138 , 238  from being separated from the rim bead seat  132 . By placing a series of cavities  126  or a circumferential torus cavity  226  in the proximity of the toe  138 , 238  of a bead region  120 , 220 , the separation of the toe  138 , 238  from the bead seat  132 , 232  is resisted by the net difference in pressure between the small volume of air and other gasses trapped in the cavities  138 , 238  and the surrounding air pressure. Preventing the toe  138 , 238  from being rotated out of position will cause the heel  140 , 240  of the bead region  120 , 220  to bear more firmly against the bead seat, increasing the frictional resistance of the bead to axial movement. In addition, if the wheel rim is provided with a hump  142  placed axially inward of the bead seat  132 , the bead toe  138 , 238  will be held in position against the hump  142  where it can also provide resistance to axially inward movement. If the bead toe  138 , 238  were not held in position the bending moment transmitted to the bead region  120 , 220  could rotate the bead region and lift the bead toe  138 , 238  over the hump  142  in a process leading to the unseating of the bead region from the rim. However, while the use of a wheel  130 , incorporating a hump  142  located axially inward of the bead seat  132  provides certain advantages, a hump  142  is not essential to the operation or benefits provided by the present invention.