Patent Application
20120085474
The present invention relates to a pneumatic tire, and more particularly, to a radial runflat passenger tire or a high performance tire with low rolling resistance and high durability.
A pneumatic tire typically includes a pair of axially separated inextensible beads. A circumferentially disposed bead filler apex extends radially outward from each respective bead. At least one carcass ply extends between the two beads. The carcass ply has axially opposite end portions, each of which is turned up around a respective bead and secured thereto. Tread rubber and sidewall rubber is located axially and radially outward, respectively, of the carcass ply. A belt structure is typically disposed between the carcass ply and the tread rubber.
The bead area is one part of the tire that contributes a substantial amount to the rolling resistance of the tire, due to cyclical flexure which also leads to heat buildup. Under conditions of severe operation, as with runflat and high performance tires, the flexure and heating in the bead region can be especially problematic, leading to separation of mutually adjacent components that have disparate properties, such as the respective moduli of elasticity. In particular, the ply turnup ends may be prone to separation from adjacent structural elements of the tire.
A conventional ply may be reinforced with materials such as nylon, polyester, rayon, and/or metal, which have much greater stiffness (i.e., modulus of elasticity) than the adjacent rubber compounds of which the bulk of the tire is made. The difference in elastic modulus of mutually adjacent tire elements may lead to separation when the tire is stressed and deformed during use.
A variety of structural design approaches have been used to control separation of tire elements in the bead regions of a tire. For example, one method has been to provide a “flipper” surrounding the bead and the bead filler. The flipper works as a spacer that keeps the ply from making direct contact with the inextensible beads, allowing some degree of relative motion between the ply, where it turns upward under the bead, and the respective beads. In this role as a spacer, a flipper may reduce disparities of strain on the ply and on the adjacent rubber components of the tire (e.g., the filler apex, the sidewall rubber, in the bead region, and the elastomeric portions of the ply itself).
The flipper may be made of a square woven cloth that is a textile in which each fiber, thread, or cord has a generally round cross-section. When a flipper is cured with a tire, the stiffness of the fibers/cords becomes essentially the same in any direction within the plane of the textile flipper.
In addition to the use of flippers as a means by which to reduce the tendency of a ply to separate, or as an alternative, another method that has been used involves the placement of “chippers.” A chipper is a circumferentially deployed metal or fabric layer that is disposed within the bead region in the portion of the tire where the bead fits onto the wheel rim. More specifically, the chipper lies inward of the wheel rim (i.e., toward the bead) and outward (i.e., radially outward, relative to the bead viewed in cross section) of the portion of the ply that turns upward around the bead. Chippers serve to stiffen, and increase the resistance to flexure of, the adjacent rubber material, which itself is typically adjacent to the turnup ply endings.
A pneumatic tire in accordance with the present invention includes a carcass having at least one reinforced ply, a tread disposed radially outward of the carcass, and a belt structure disposed radially between the carcass and the tread. The belt structure includes a single woven layer of crimped metallic cords extending in the radial direction and in the circumferential direction.
In one aspect of the present invention, the crimped metallic cords have crimp angles between 10° and 60°.
In another aspect of the present invention, the crimped metallic cords have straight lengths between the crimp angles. The straight lengths are between 0.8 mm and 20.0 mm.
In still another aspect of the present invention, the woven layer has between 10 EPI to 18 EPI.
In yet another aspect of the present invention, the crimped metallic cords each comprise a monofilament.
In still another aspect of the present invention, the crimped metallic cords each comprise twisted metallic filaments.
In yet another aspect of the present invention, the pneumatic tire is a radial runflat passenger tire.
In still another aspect of the present invention, the pneumatic tire is a high performance tire.
In yet another aspect of the present invention, the crimped metallic cords are constructed of steel.
In still another aspect of the present invention, the crimped metallic cords are constructed of titanium.
“Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.
“Annular” means formed like a ring.
“Aspect ratio” means the ratio of its section height to its section width.
“Axial” and “axially” are used herein to refer to 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 structure” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having cords inclined respect to the equatorial plane of the tire. The belt structure may also include plies of parallel cords inclined at relatively low angles, acting as restricting layers.
“Bias tire” (cross ply) means a tire in which the reinforcing cords in the carcass ply extend diagonally across the tire from bead to bead at about a 25°-65° angle with respect to equatorial plane of the tire. If multiple plies are present, the ply cords run at opposite angles in alternating layers.
“Breakers” means at least two annular layers or plies of parallel reinforcement cords having the same angle with reference to the equatorial plane of the tire as the parallel reinforcing cords in carcass plies. Breakers are usually associated with bias tires.
“Cable” means a cord formed by twisting together two or more plied yarns.
“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
“Casing” means the carcass, belt structure, beads, sidewalls and all other components of the tire excepting the tread and undertread, i.e., the whole tire.\
“Chipper” refers to a narrow band of fabric or steel cords located in the bead area whose function is to reinforce the bead area and stabilize the radially inwardmost part of the sidewall.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tire parallel to the Equatorial Plane (EP) and 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.
“Cord” means one of the reinforcement strands of which the reinforcement structures of the tire are comprised.
“Cord angle” means the acute angle, left or right in a plan view of the tire, formed by a cord with respect to the equatorial plane. The “cord angle” is measured in a cured but uninflated tire.
“Denier” means the weight in grams per 9000 meters (unit for expressing linear density). Dtex means the weight in grams per 10,000 meters.
“Elastomer” means a resilient material capable of recovering size and shape after deformation.
“Equatorial plane (EP)” means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread; or the plane containing the circumferential centerline of the tread.
“Fabric” means a network of essentially unidirectionally extending cords, which may be twisted, and which in turn are composed of a plurality of a multiplicity of filaments (which may also be twisted) of a high modulus material.
“Fiber” is a unit of matter, either natural or man-made that forms the basic element of filaments. Characterized by having a length at least 100 times its diameter or width.
“Filament count” means the number of filaments that make up a yarn. Example: 1000 denier polyester has approximately 190 filaments.
“Flipper” refers to a reinforcing fabric around the bead wire for strength and to tie the bead wire in the tire body.
“Gauge” refers generally to a measurement, and specifically to a thickness measurement.
“High Tensile Steel (HT)” means a carbon steel with a tensile strength of at least 3400 MPa @ 0.20 mm filament diameter.
“Inner” means toward the inside of the tire and “outer” means toward its exterior.
“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.
“LASE” is load at specified elongation.
“Lateral” means an axial direction.
“Lay length” means the distance at which a twisted filament or strand travels to make a 360 degree rotation about another filament or strand.
“Mega Tensile Steel (MT)” means a carbon steel with a tensile strength of at least 4500 MPa @ 0.20 mm filament diameter.
“Normal Load” means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
“Normal Tensile Steel (NT)” means a carbon steel with a tensile strength of at least 2800 MPa @ 0.20 mm filament diameter.
“Ply” means a cord-reinforced layer of rubber-coated radially deployed or otherwise parallel cords.
“Radial” and “radially” are used to 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° and 90° 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° and 90° with respect to the equatorial plane of the tire.
“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.
“Sidewall” means that portion of a tire between the tread and the bead.
“Super Tensile Steel (ST)” means a carbon steel with a tensile strength of at least 3650 MPa @ 0.20 mm filament diameter.
“Tenacity” is stress expressed as force per unit linear density of the unstrained specimen (gm/tex or gm/denier). Used in textiles.
“Tensile” is stress expressed in forces/cross-sectional area. Strength in psi=12,800 times specific gravity times tenacity in grams per denier.
“Toe guard” refers to the circumferentially deployed elastomeric rim-contacting portion of the tire axially inward of each bead.
“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.
“Tread width” means the arc length of the tread surface in a plane including the axis of rotation of the tire.
“Turnup end” means the portion of a carcass ply that turns upward (i.e., radially outward) from the beads about which the ply is wrapped.
“Ultra Tensile Steel (UT)” means a carbon steel with a tensile strength of at least 4000 MPa @ 0.20 mm filament diameter.
“Yarn” is a generic term for a continuous strand of textile fibers or filaments. Yarn occurs in the following forms: 1) a number of fibers twisted together; 2) a number of filaments laid together without twist; 3) a number of filaments laid together with a degree of twist; 4) a single filament with or without twist (monofilament); 5) a narrow strip of material with or without twist.
The structure, operation, and advantages of the invention will become more apparent upon contemplation of the following description taken in conjunction with the accompanying drawings, wherein:
The carcass ply 14 may be a rubberized ply having a plurality of substantially parallel carcass reinforcing members made of such material as polyester, rayon, or similar suitable organic polymeric compounds. The carcass ply 14 engages the axial outer surfaces of two flippers 32a, 32b.
The example tire of
The LENO weave fabric flipper 54 wraps around the bead 52b and extends radially outward into the sidewall regions of the example tire. The axially inward portion 55 of LENO weave fabric flipper 54 terminates within the bead-filler apex 59b. The axially outward portion 60b of the LENO weave fabric flipper 54 lies radially beyond a turnup end 62b, which itself is located radially beyond the radially outermost reach of the chipper 56 (discussed separately below). The axially outwardmost portions 62b of the turnup end 62b of the carcass ply 50 may extend radially outward about 15-30 millimeters beyond the top of a wheel rim flange 72 of a wheel rim 70.
As shown in
The LENO weave fabric chipper 56 is disposed adjacent to the portion of the carcass ply 50 that is wrapped around the bead 52b. More specifically, the LENO weave fabric chipper 56 is disposed on the opposite side of the portion of the carcass ply 50 from the LENO weave fabric flipper 54. The axially inwardmost portion of the LENO weave fabric chipper 56 lies in the portion of the bead region that, when the tire is mounted on the wheel rim 70, would lie closest to a circularly cylindrical part 74 of the wheel rim. The axially and radially outwardmost portion of the LENO weave fabric chipper 56 lies in the portion of the bead region that, when the tire is mounted on the wheel rim 70, would lie axially inward of the circular portion of the wheel rim 70, being separated from the circular portion of the wheel rim by tire rubber such as a toe guard 64.
In other words, as can be seen in
The LENO weave fabric chipper 56 protects the portion of the carcass ply 50 that wraps around the bead 52b from the strains in the rubber that separates the LENO weave fabric chipper from the wheel rim 70. The LENO weave fabric chipper 56 reinforces the bead area and stabilizes the radially inwardmost part of the sidewall 57. In other words, the LENO weave fabric chipper 56 may absorb deformation in a way that minimizes the transmission of stress-induced shearing strains that arise inward from the wheel rim 70, through the toe guard 64, to the turned up portion 62b of the carcass ply 50, where the LENO weave fabric chipper is most immediately adjacent to the rigid bead 52b.
The patch 58 shown in
The net effect of the incorporation of the LENO weave fabric flipper 54 and the LENO weave fabric chipper 56 is to provide strain buffers that relieve or absorb differential shearing strains that otherwise, were the flippers and chippers not present, could lead to separation of the adjacent materials that have disparate shearing moduli of elasticity. Furthermore, this reinforced construction may increase durability of the tire by means of the incorporation of a smaller number of components than for standard constructions with gum strips.
In accordance with the present invention, the belts 18, 20 of the conventional belt structure 16 may be replaced with a single woven structure 200 of crimped metal cords 210 (
Analysis of the structural and thermal response of the structure 200 has revealed tire radial stiffness similar to the dual belts 18, 20. Socketing was dissipated along the length of the intersecting cords 210. Rubber gauge of the belt structure 16 was reduced, thus markedly improving tire rolling resistance. The crimp configuration may have straight lengths L of between 0.8 mm and 20.0 mm and crimp angles {acute over (α)} of between 10° and 60° (
Further, an annular ring of the woven steel belt may be formed such that the woven structure 200 may slip over the carcass 14 in a one step process. This improves efficiency and cost compared to conventionally building and cutting two plies (18, 120 in opposite directions to form an opposed belt angle structure. A tire with the structure 200 in accordance with the present invention may thus dissipate strain energy at the edges of the structure at the juncture points 220 of the woven structure.
The structure 200 may be treated with an adhesion promoter, such as brass. The selection of materials for the adhesion promoter may depend upon the materials selected for use in the tire.
As stated above, a structure 200 in accordance with the present invention produces excellent rolling resistance performance and durability in a pneumatic tire 10. This structure 200 thus enhances the performance of the pneumatic tire 10, even though the complexities of the structure and behavior of the pneumatic tire are such that no complete and satisfactory theory has been propounded. Temple, Mechanics of Pneumatic Tires (2005). While the fundamentals of classical composite theory are easily seen in pneumatic tire mechanics, the additional complexity introduced by the many structural components of pneumatic tires readily complicates the problem of predicting tire performance. Mayni, Composite Effects on Tire Mechanics (2005). Additionally, because of the non-linear time, frequency, and temperature behaviors of polymers and rubber, analytical design of pneumatic tires is one of the most challenging and underappreciated engineering challenges in today's industry. Mayni. A pneumatic tire has certain essential structural elements. United States Department of Transportation, Mechanics of Pneumatic Tires, pages 207-208 (1981). An important structural element is the belt structure, typically made up of many flexible, high modulus cords of natural textile, synthetic polymer, glass fiber, or fine hard drawn steel embedded in, and bonded to, a matrix of low modulus polymeric material, usually natural or synthetic rubber. Id. at 207 through 208.
The flexible, high modulus cords are usually disposed as a single layer. Id. at 208. Tire manufacturers throughout the industry cannot agree or predict the effect of different twists of belt ply cords on noise characteristics, handling, durability, comfort, etc. in pneumatic tires. Mechanics of Pneumatic Tires, pages 80 through 85.
These complexities are demonstrated by the below table of the interrelationships between tire performance and tire components.
As seen in the table, belt ply characteristics affect the other components of a pneumatic tire (i.e., belt affects apex, carcass, overlay, etc.), leading to a number of components interrelating and interacting in such a way as to affect a group of functional properties (noise, handling, durability, comfort, high speed, and mass), resulting in a completely unpredictable and complex composite. Thus, changing even one component can lead to directly improving or degrading as many as the above ten functional characteristics, as well as altering the interaction between that one component and as many as six other structural components. Each of those six interactions may thereby indirectly improve or degrade those ten functional characteristics. Whether each of these functional characteristics is improved, degraded, or unaffected, and by what amount, certainly would have been unpredictable without the experimentation and testing conducted by the inventors.
Thus, for example, when the structure (i.e., twist, cord construction, weave, etc.) of the belt ply or plies of a pneumatic tire is modified with the intent to improve one functional property of the pneumatic tire, any number of other functional properties may be unacceptably degraded. Furthermore, the interaction between the belt ply and the apex, carcass, and tread may also unacceptably affect the functional properties of the pneumatic tire. A modification of the belt ply or plies may not even improve that one functional property because of these complex interrelationships.
Thus, as stated above, the complexity of the interrelationships of the multiple components makes the actual result of modification of a belt ply, in accordance with the present invention, impossible to predict or foresee from the infinite possible results. Only through extensive experimentation have the woven structure 200 of the present invention been revealed as an excellent, unexpected, and unpredictable option for a tire belt.
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.
