Patent Application
20150041039
The present invention relates to a pneumatic tire, and more particularly, to a radial runflat passenger tire or a high performance tire with a reinforced flipper and/or chipper.
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.
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 polyamide/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 reinforced by a carcass ply extending from a first bead to a second bead, at least one belt ply disposed radially outward of the carcass ply in a crown portion of the pneumatic tire, and a bead reinforcement disposed adjacent the first bead and the second bead. The bead reinforcement includes at least one hybrid cord having at least one first core yarn with at least one second aramid wrap yarn wrapped around the first core yarn such that the first core yarn has a modulus less than a modulus of the second wrap yarn.
According to another aspect of the pneumatic tire, the first core yarn has a linear density value in the range between 700 dtex to 900 dtex.
According to still another aspect of the pneumatic tire, the cord has a structure of one single polyamide/nylon core yarn and one single aramid wrap yarn.
According to yet another aspect of the pneumatic tire, the bead reinforcement has an end count of cord ends per inch in the range between 15-32.
According to still another aspect of the pneumatic tire, the second wrap yarn has a linear density value in the range between 900 dtex to 1100 dtex.
According to yet another aspect of the pneumatic tire, the bead reinforcement is a flipper.
According to still another aspect of the pneumatic tire, the bead reinforcement is a chipper.
“Apex” or “bead filler apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup plies.
“Axial” and “Axially” mean the lines or directions that are parallel to the axis of rotation of the tire.
“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.
“Carcass” means the tire structure apart from the belt structure, tread, undertread 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” 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.
“Cord” means one of the reinforcement strands, including fibers, with which the plies and belts are reinforced.
“Equatorial Plane” 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.
“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 thickness.
“Inner Liner” 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.
“Lateral” means a direction parallel to the axial direction.
“Normal Load” means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
“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° 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.
“Toe guard” refers to the circumferentially deployed elastomeric rim-contacting portion of the tire axially inward of each bead.
“Tread width” means the arc length of the tread surface in the plane includes 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.
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 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 the flipper 54 terminates within the bead-filler apex 59b. The axially outward portion 60b of the 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 chipper 56 may be adjacent the portion of the carcass ply 50 that is wrapped around the bead 52b. More specifically, the chipper 56 may be disposed on the opposite side of the portion of the carcass ply 50 from the flipper 54. The axially inwardmost portion of the chipper 56 may lie 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 chipper 56 may lie 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 chipper 56 may protect the portion of the carcass ply 50 that wraps around the bead 52b from the strains in the rubber that separates the chipper from the wheel rim 70. The chipper 56 reinforces the bead area and stabilizes the radially inwardmost part of the sidewall 57. In other words, the 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 chipper is most immediately adjacent to the rigid bead 52b.
The patch 58 shown in
The net effect of the incorporation of the flipper 54 and the chipper 56 may be 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 flippers 54 and chippers 56 of the example tires of
Materials for the low modulus core yarn(s) 132 may include, but are not limited to, rayon, polyamide/nylon, polyamide 6 and 6,6, polyethylene terephthalate (PET), polyketone (PK), and polyethylene napthalate (PEN). Materials for the higher modulus wrap yarn/filament may include, but are not limited to, aramid, Normal Tensile Steel, High Tensile Steel, Super Tensile Steel, Ultra Tensile Steel, Mega Tensile Steel, titanium, stainless steel, aluminum, and/or any alloys thereof.
Material selection may be based on the desired stress/strain characteristics of the hybrid cord 130 as a whole. However, a main criteria may be that the outer wrap yarn(s)/metallic filament(s) 134 has a moduli greater than the core yarn(s) 132. Thus, for example, a single wrap yarn 134 may be aramid with a single polyamide/nylon core yarn 132.
In the example cord 130, both the core yarn 132 and wrap yarn 134 may be twisted a given number of turns per unit of length, usually expressed in turns per inch (TPI). Additionally, the core yarn 132 and the wrap yarn 134 may each be twisted together a given number of turns per unit of length (TPI) for the yarns, such as between 3 mm and 25 mm, for the yarns 132, 134 of the cord 130. The direction of twist refers to the direction of slope of the spirals of a yarn or cord when it is held vertically.
Visually, if the slope of the spirals appears to conform in direction to the slope of a letter “S,” then the twist is termed “S” or “left handed.” If a slope of the spirals appears to visually conform in direction to the slope of a letter “Z,” then the twist is termed “Z” or “right handed.” An “S” or “left handed” twist direction is understood to be a direction opposite to a “Z” or “right handed” twist. “Twist” is understood to mean the twist imparted to a yarn or filament/yarn component before the yarn or filament/yarn component is incorporated into a cord. “Cord twist” is understood to mean the twist imparted to two or more yarns and filaments/yarns when twisted together with one another to form the cord. “Dtex” is understood to mean the weight in grams of 10,000 meters of a yarn before the yarn has a twist imparted thereto.
For example, a core yarn 132, such as polyamide/nylon and a twist of 2-10 TPI, may be helically wrapped with a wrap yarn 134, such as aramid. The core yarn 132 and wrap yarn 134 may have twists of S, Z, or S & Z. Such a cord 130 in a flipper 54 and/or chipper 56 thus produces good fatigue performance. The cord targets may be Modulus >5000 MPa at 100° C., 100% Adhesion, and Glass Transition (tg) >85° C. for a gauge less than 0.022 inches (0.56 mm).
One cord construction in accordance with the present invention may be (900-1100/1 Aramid+700-900/1 Polyamide/Nylon)[(4-6)Z+(4-6)S]/(4-6)S where the polyamide/nylon core yarn 132 has a lower polyamide/nylon Dtex than conventional cords. The twist per inch (TPI) may be optimized at the yarns level (x and y) and at the cord level (z) to ensure equal/balanced structural response. One specific example cord 130 may be (1000/1 Aramid+840/1 Polyamide/Nylon)[4.7Z+5.5S]/4.75 where the lower Dtex polyamide/nylon core yarn 132 has replaced the conventional higher polyamide/nylon Dtex core yarn.
Such a cord 130 may be utilized in a flipper 54 and/or chipper 56 of a high performance or runflat tire, such as the example tire 10. The lower polyamide/nylon Dtex advantageously does not adversely affect the structural response/characteristics of the cord 130. Such an advantage may thus be realized in the improved rolling resistance and enhanced thermal stability due to the reduced volume of polyamide/nylon and superior durability performance due to higher insulation gauges. Additionally, the cord 130 may require a lower total tire cost because of the smaller amount of polyamide/nylon.
As stated above, a flipper 54 and/or chipper 56 of hybrid cords 130 in accordance with the present invention produces unexpectedly improved performance in a tire 10. This flipper 54 and/or chipper 56 thus enhances the performance of the 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 overlay, 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 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, bead/apex cord characteristics affect the other components of a pneumatic tire (i.e., bead/apex affects overlay, belt, carcass ply, 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, etc.) of the flipper and/or chipper cords 130 of a pneumatic tire 10 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 bead/apex cords (e.g., the flipper/chipper cords, etc.) and the overlay, belt, carcass, and tread may also unacceptably affect the functional properties of the pneumatic tire. A modification of the flipper/chipper cords 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 an overlay, in accordance with the present invention, impossible to predict or foresee from the infinite possible results. Only through extensive experimentation have the flipper 54, chipper 56, and cords 130 of the present invention been revealed as an excellent, unexpected, and unpredictable option for a tire overlay.
The previous descriptive language is of the best presently contemplated mode or modes of carrying out the present invention. This description is made for the purpose of illustrating an example of general principles of the present invention and should not be interpreted as limiting the present invention. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the schematic drawings are the same as those referred to in the specification. For purposes of this application, the various examples illustrated in the figures each use a same reference numeral for similar components. The examples structures may employ similar components with variations in location or quantity thereby giving rise to alternative constructions in accordance with the present invention.
