Tire bead

Abstract

A tire for a motor vehicle having at least one carcass ply comprised of a crown portion and two axially opposite side portions terminating in beads for mounting the tire on a rim. A tread band and a belt structure are interposed between the carcass structure and the bead. Each bead includes on elongated cord comprised of a first yarn, such as aramid, having a melting or decomposition point T.sub.1, and a second yarn, such as nylon, having a melting point T.sub.2, wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C.

Claims

1. A tire for a motor vehicle, comprising: a carcass structure comprising at least one carcass ply, said carcass structure comprising a crown portion and two axially opposite side portions terminating in beads for mounting the tire on a rim; a tread band; and a belt structure interposed between said carcass structure and said tread band, wherein each bead includes elongated cord comprised of a first yarn having a melting or decomposition point T.sub.1, and a second yarn having a melting point T.sub.2 wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C. and wherein each bead is comprised of a plurality of said elongated cords arranged parallel to one another to form between 12 and 18 wraps, said wraps forming a concentric ring, said ring having a circumference of at least about 40 inches, said beads having an average diameter of between about 0.3 and 0.4 inches, and said beads having a breaking strength of at least 20,000 (N) and a weight of less than 100 grams.

2. The tire of claim 1 wherein the T.sub.1 yarn is comprised of aramid and the T.sub.2 yarn is comprised of nylon.

3. The tire of claim 1 wherein the T.sub.1 yarn comprises between 85 and 97% by weight of the cord and the T.sub.2 yarn comprises between 3 and 15% by weight of the cord.

4. The tire of claim 1 wherein each cord is comprised of between 3 to 1 and 5 to 1 of the first yarn relative to the second yarn.

5. The tire of claim 1 wherein said first yarn is at least substantially untwisted.

6. The tire of claim 5, wherein said second yarn has less than 2 twists per mm.

7. The tire of claim 1 wherein said cord comprises a diameter of at least 0.05.

8. A tire bead consisting essentially of a plurality of polymeric cords arranged parallel to one another to form a plurality of wraps, said wraps forming a concentric ring, said cords being comprised of a combination of polymeric yarns having a melting or decomposition point T.sub.1 and polymeric yarns having a melting point T.sub.2, wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C.

9. The tire bead of claim 8 wherein said T.sub.1 polymer consists essentially of aramid and said T.sub.2 polymer consists essentially of nylon.

10. The tire bead of claim 9 wherein said aramid comprises between 85 and 97% and nylon comprise between 3 and 15% by weight of each cord.

11. The tire bead of claim 8 consisting of a plurality of polymeric cords arranged parallel to one another to form a plurality of wraps, said wraps forming a concentric ring, said cords being comprised of a combination of polymeric yarns having a melting or decomposition point T.sub.1 and polymeric yarns having a melting point T.sub.2, wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C.

12. A tire for a motor vehicle, comprising: a carcass structure comprising at least one carcass ply, said carcass structure comprising a crown portion and two axially opposite side portions terminating in beads for mounting the tire on a rim; a tread band; and a belt structure interposed between said carcass structure and said tread band, wherein each bead includes elongated cord comprised of a first yarn having a melting or decomposition point T.sub.1, and a second yarn having a melting point T.sub.2 wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C. and wherein each bead is comprised of a plurality of said elongated cords arranged parallel to one another to form between 6 and 18 wraps, said wraps forming a concentric ring, said ring having a circumference of at least about 40 inches, said beads having an average diameter of between about 0.25 and 0.4 inches and said beads having a breaking strength of at least 11,000 (N) and a weight of less than 100 grams.

13. A tire for a motor vehicle, comprising: a carcass structure comprising at least one carcass ply, said carcass structure comprising a crown portion and two axially opposite side portions terminating in beads for mounting the tire on a rim; a tread band; and a belt structure interposed between said carcass structure and said tread band, wherein each bead includes elongated cord comprised of a first yarn having a melting or decomposition point T.sub.1, and a second yarn having a melting point T.sub.2 wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C. and wherein each bead is comprised of a plurality of the elongated cords arranged parallel to one another to form between 20 and 50 wraps, said wraps forming a concentric ring, said ring having a circumference of at least about 59 inches, said beads having a minimum dimension of 0.10 and a maximum dimension of 1.00, and said beads having a breaking strength of at least 106,000 (N) and a weight of less than 1500 grams.

14. The tire of claim 13 wherein the beads include a fabric wrap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated samples, however, are not exhaustive of the many possible embodiments of the disclosure. Other advantages and novel features of the disclosure will be set forth in the following detailed description of the disclosure when considered in conjunction with the drawings, in which:

(2) FIG. 1 is a cross sectional view of a first prior art tire bead;

(3) FIG. 2 is a cross sectional view of a second prior art tire bead;

(4) FIG. 3 illustrates a tire including a polymeric bead bundle;

(5) FIG. 4 is a perspective view of a conventional bead line winder; and

(6) FIG. 5 is a graphical depiction of vehicle dry braking from the Examples.

DETAILED DESCRIPTION

(7) The present disclosure is directed to a vehicle tire including a bead constructed of at least two polymers, such as aramid and nylon. One benefit of using a single treated aramid cord to form hex (see FIG. 1) or ribbon (see FIG. 2) beads is that current steel bead forming equipment can be utilized. Moreover, a treated aramid cord can be spooled off and sent through an extrusion die where it is coated with rubber.

(8) The present embodiment is advantageous because handling and shipping of spools of aramid cord is relatively easy, economical and moreover, can be implemented commercially in the same manner as traditional spooled wire. Particularly, the rubber coated aramid cord can be processed through steel bead hex or ribbon forming equipment to produce aramid beads. Final tire weight can be lighter (2% to 6% expected) and vehicle fuel consumption can be improved by the lighter weight tire.

(9) However, in order for the current bead forming equipment to work, the aramid cord must be stiff. This is accomplished by interweaving a strand of thermoplastic material with the aramid cord which melts during the heat treating process. Once the thermoplastic re-hardens, it produces a stiff aramid cord. The stiff cord allows it to be processed through current steel cord bead processing equipment.

(10) The cord of the present disclosure used for winding into a tire bead can be the type of cord described in U.S. Pat. No. 6,921,572, the disclosure of which is herein incorporated by reference. The cord can be made up of at least two yarns, the first being a yarn having a melting or decomposition point T.sub.1, and the second being a yarn have a melting point T.sub.2, wherein T.sub.1>T.sub.2, and T.sub.2 is greater than 40 C. The ratio of the linear density of the first yarn to the linear density of the second yarn can be between 1,000:1 and 1:1, between 100:1 and 4:1, or between 35:1 and 15:1.

(11) Suitable materials for the yarn with the relatively higher melting or decomposition point (T.sub.1) include aromatic polyamides (e.g. aramid), such as poly(para-phenylene terephthalamide). Suitable materials for yarns with the relatively lower melting point (T.sub.2) can be polyesters, polyamides, polyolefins, elastanes, thermoplastic vulcanizates, and acrylics. According to one embodiment, the T.sub.1 polymer can be aramid and the T.sub.2 polymer can be nylon.

(12) To provide a suitable combination of strength and stiffness the cord can contain between about 85 and 97% by weight T.sub.1 polymer and between about 3 and 15% by weight T.sub.2 polymer. In certain embodiments, between about 88 and 95% by weight T.sub.1 polymer and between about 5 and 12% by weight T.sub.2 polymer will be present. Of course, it is also contemplated that a minor portion of a third or fourth yarn could be included in the cord.

(13) The distribution of the second yarn is controlled by intertwining according to appropriate twisting schemes and is dependent on the type of cord construction. The twisting scheme and the amount of second yarn relative to the first yarn used depend on the desired bundle cohesion and can be determined by those skilled in the art. Twisting regimens are well-known in the art. The twisting can be carried out with any suitable twisting equipment. Typically, the yarn will include less than 2 twists per mm. However, in certain embodiments an untwisted yarn may be desirable. Examples of suitable cord materials include Twaron D1014, Twaron D2200 (3220 dtex24+thermal adhesive) and Twaron D2200 (3220 dtex14+thermal adhesive) available from Teijin Limited of Wuppertal, Germany.

(14) The method of manufacturing the cord comprises the steps of intertwining the first and the second yarn and then heating the intertwined cord at a temperature between T.sub.1 and T.sub.2. The heating step is performed to fixate the first yarn bundles by melting the second yarn. The molten filaments embrace the single plies, thereby interlocking the filaments and holding them in place. In some embodiments, the heating step can be integrated with or followed by a step wherein the cord is subjected to a dipping treatment with a rubber adhesion material.

(15) More particularly, in order to ensure that the cord has good adhesion with the matrix material of the tire in which it will be embedded, it is desirable to coat the cords with an adhesive. Suitable adhesive coatings include epoxy compounds, polymeric methyl diphenyl diisocyanate and polyurethanes having ionic groups. Highly suitable adhesive coatings for use in the case of poly(para-phenylene terephthalamide) is a resorcinol/formaldehyde/latex (RFL) system. Typically, the coated cord of the present disclosure will have a gauge size of greater than 0.05 and less than 0.20.

(16) For technical and economic reasons, the fusion step can take place as a part of the dipping process. By selecting a thermoplastic adhesive with a melting point within the range of temperatures used for the dipping treatment, the heat setting can be combined with the dip-curing steps. The aqueous emulsion is preferably applied to cord as an overfinish after drawing has been completed in any of the conventional ways of applying finishes. A satisfactory manner of applying the finish is by feeding the emulsion to a trough equipped with a rotatable roll dipping therein and passing the cord in contact with the roll. The rate of rotation of the roll can be adjusted to provide desired pick-up of coating by the yarn. By selecting a thermoplastic adhesive with a melting point between 200-250 C., the heat-setting can be combined with the curing step in a conventional dipping process. Integrated RFL dipping and heat setting is one example.

(17) In the construction of vehicle tires it is the usual practice to incorporate a stiffening bead at both the inside and outside openings where the tire is to be mounted upon a rim. With reference to FIG. 3, a pneumatic tire 40 made incorporating a polymeric bead ring 10 is illustrated. The tire is made as is conventional in the tire building art and includes at least a pair of bead rings 10, carcass plies 44 which are wrapped around the bead rings 10, an optional inner liner 42 disposed inwardly of the carcass plies, optional belts or breakers 46 disposed in a crown area of the tire over the carcass plies, tread 50 disposed over the crown area of the tire and sidewalls 48 between the tread 50 and beads 10.

(18) The tire illustrated in FIG. 3 represents a typical passenger vehicle tire. Of course, the present embodiment is equally suitable for use in vehicle tires, such as, motorcycle, truck and/or bus. In fact, because of the relative increase in weight reduction, the present disclosure may have particular benefit in large tire vehicles where the bead bundle has a large internal circumference (e.g. >59) and/or includes a large number of cord wraps (e.g. >20).

(19) Listed in the following Table are typical bead breaking strengths for various types of vehicle tires.

(20) TABLE-US-00001 Bead Breaking Strength by segment Passenger Truck/Bus Motorcycle Vehicle Vehicle Bead Breaking Strength Min 11,000N 20,000N 106,000N Bead Breaking Strength Max 50,000N 120,000N 315,000N
All of these values can be obtained using the instant invention by controlling the number of wraps of cord in the bead bundles. It is noted that in the case of large vehicle tires such as bus and truck which may have a greater number of cord wraps, it may be advantageous to provide the bead bundle with a fabric wrap to help maintain its integrity. An exemplary fabric wrap material is rubber coated nylon or polyester cord or square woven fabric.

(21) One method of forming the polymeric tire beads of the present embodiment is to grip the leading end of a polymer cord and wind multiple turns of the cord in a groove on a drum and to cut the cord, forming a trailing end of the cord on the wound bead and a leading end to be gripped for winding the next bead. Pre-assembled tire polymeric cord based bead assemblies can be built on a conventional bead line winder. A suitable conventional bead winding apparatus is illustrated in FIG. 4 and more fully described in U.S. Patent Publication 2008/0196812, the disclosure of which is herein incorporated by reference. Suitable equipment is available from Bartell Machinery Systems, LLC of Rome, N.Y.

(22) According to one aspect of the disclosure, the cords are coated with rubber or a similar synthetic covering before and/or during the winding process used to form the bead. By maintaining a sufficient temperature to render the coating tacky, adjacent cords in the bead adhere to one another. Exemplary coating materials include SBR rubber compounds, BR rubber compounds, natural rubber compounds or blends thereof.

(23) Characteristics of a suitable polymeric bead bundle are reflected in the following Table.

(24) TABLE-US-00002 Aramid Cord Bead Properties Treatment RFL (resorcinol formaldehyde latex) Thermo Adhesive Thermal Polyamide Perlon Polyamide Thermoplastic Size/Denier of the individual 2.14 mm diameter, cord forming the bead 80-90 mil thickness Breaking Strength 4000-4500 kN Hex Wraps 7 to 15 wraps

Examples

(25) Two different aramid cords were formed into hex beads using current bead forming equipment. In each example, an aramid nylon cord including a cord coating of Cooper Tire bead insulation was wound into a substantially consistent internal circumference (IC), 2-3-4-3-2 hex bead using a Bartell Manufacturing bead forming apparatus. Example A used Teijin Twaron D1014 cord having a gauge size 0.087, and a cord breaking strength of 4000N. Example B used Teijin Twaron D2200 cord having a gauge size of 0.083, and a cord breaking strength of 4000N. An average diameter of the Example A and B beads was about 0.34 inches. The beads of Examples A and B were then compared to a control bead of 3-4-3 high tensile steel wire having a gauge of 0.062 inches by evaluating in a 225/60R16 tire of conventional design.

(26) Testing:

(27) SAE: J1561 High speed test: Four tires were tested for a T speed rating.

(28) Hydroburst testTwo tire using each bead was filled with water under pressure until the tire burst. In a successful test, the tire does not fail at the bead.

(29) CFR571.139 S6.2High speed performance test mandated by DOT

(30) CFR571.139 S6.3Tire Endurance test mandated by DOT

(31) CFR571.139 S6.4Low inflation performance mandated by DOT

(32) TABLE-US-00003 Test: Pass/Fail SAE: Hydro- CFR571.139 CFR571.139 CFR571.139 Example J1561 burst S6.2 S6.3 S6.4 Control - Pass Pass Pass Pass Pass Steel bead A D1014 Pass Pass Pass Pass Pass bead B D2200 Pass Pass Pass Pass Pass bead
Dry Brakingas shown in FIG. 5, the Example A tire provided directionally better test results than the control. The Example B tire had test results equivalent to the control tire.

(33) The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.