Patent Application
20090038731
The present invention relates to a pneumatic radial tire, and more particularly, to the structure of the beads and carcass reinforcement means of the pneumatic radial tire.
A tire with a radial carcass reinforcement usually comprises a reinforcing bead core in each bead portion of the tire, about which the carcass reinforcement is anchored by winding or forming an upturn. The bead cores provide a clamping force for the tire when the tire is mounted upon the beads seats of a wheel rim. The clamping produces a certain compression of the bead portion between the bead core and the wheel rim, the clamping generally being brought about by a difference in the angles of the bead seat and the rim seat respectively, and/or by a difference in the diameters of said seats.
The bead clamping force of the tire is particularly important in designing a run-flat tire or tire system. One such tire system that uses the clamping force to maintain operation of the tire during underinflated or uninflated operating conditions is disclosed in U.S. Pat. Nos. 5,785,781 and 5,971,047. The radial carcass reinforcement of the tire, which is anchored within each bead to at least one inextensible annular reinforcement element, has a profile, when the tire is mounted on its operating rim and inflated to its operating pressure, with a direction of curvature which is constant in the sidewalls and bead regions which ends in the bead toe. The preferred bead region of this type of tire is more fully disclosed in U.S. Pat. No. 5,971,047, wherein the carcass reinforcement has a hooking structure, and which is also shown in FIG. 5.
In the tire of the above disclosed run-flat system, when the tire system is inflated at reduced or zero pressure, the beads of the tire remain in place when travelling because the structure creates an increase of the clamping of the bead toe on the mounting rim as a function of the tension of the carcass reinforcement. The structure also makes it possible to have initial clamping on rim of low value, given that said clamping will increase when the tire is inflated to its recommended pressure.
However, due to the turn back of the carcass reinforcement ply below the bead core, the above tire structure is complicated and difficult to manufacture in an accurate and consistent basis. Further, the tire structure requires the use of non-standard tire building machinery such as special tire building drums. Thus a simpler tire structure design that does not require special tire building machinery yet retains the bead clamping benefits is desired.
The present invention is directed toward a run-flat tire. The wheel rim has a bead seat, the bead seat has an axially outer end closer to the axis of rotation than the axially inner end thereof. The tire is has a pair of opposing sidewalls and two bead portions. At least one of the bead portions terminates axially to the outside by a tip and is intended to be mounted on one of the wheel rim bead seats. Located within the bead portion are an inextensible bead ring and a bead apex. The tire has a radial carcass reinforcement ply extending through the tire sidewalls and anchored in each bead portion.
The invention will be described by way of example and with reference to the accompanying drawings in which:
The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the drawings are the same as those referred to in the specification. For purposes of this application, the various embodiments illustrated in the figures each use the same reference numeral for similar components. The structures employed basically the same components with variations in location or quantity thereby giving rise to the alternative constructions in which the inventive concept can be practiced.
The bead portion 14 has an outer cross-sectional profile wherein as the profile moves from the axially outer side of the bead portion 14 to the axially inner side, the bead profile slopes radially upward, resulting in the bead toe 18 being both axially outward and radially inward of the bead heel 20. Above the bead toe 18 is a rib 22 that assists in locking the tire onto a wheel rim having a correspondingly profiled bead rim seat. This bead profile is contrary to a conventional tire wherein the bead toe is radially and axially inward of the bead heel and wherein the bead heel fits into the curved portion of the wheel rim where the rim seat and the wheel flange meet. In addition to the carcass reinforcement ply 12, the bead portion 14 contains therein a bead ring 24. The illustrated bead ring 24 has a circular configuration and is formed of a plurality of steel wires or cords. The ring 24 may have a different cross-sectional configuration and be formed from alternative materials. The bead ring 24 is located within a hard elastomeric component 26; the component 26 surrounds the bead ring 24 all on sides and the geometric center C of the bead ring 24 is axially offset from the axial center of the component 26, as measured along the greatest width of the component 26. The component 26 extends radially upwards in a triangular like fashion.
The carcass reinforcement ply 12 has a main portion 28 extending about the main toroidal portion of the tire 10. The turn-up portions 30 of the carcass reinforcement ply 12 are the outer ends of the reinforcement ply 12, each turn-up portion 30 passes radially under the bead ring 24 and component 26. When the tire 10 is mounted on a corresponding wheel (not illustrated), as the carcass reinforcement ply 12 is placed in tension by air pressure inside the tire 10, the reinforcement ply main portion 28 is expanded radially outward. As the main portion 28 expands, it pulls on the turnup portion 30, pulling the bead toe 18 radially inward into the wheel rim and flange, effectively acting to lock the bead portion 14 of the tire 10 onto the wheel.
In the tire of
In each tire side, preferably axially inward of the main carcass portion 28, there is at least one insert 34. The insert 34 has a curved configuration with the middle third of the insert 34 having a substantially constant thickness and the ends of the insert 34 being tapered. The insert 34 extends from the bead portion 14 to radially inward of the belt structure 16. When the insert 34 extends through the entire sidewall, it has a radially inner end located axially inward of the bead ring 24. The insert 34 is formed from a hard rubber, with a Shore A hardness at 100° C. in a range of about 55 to about 90, with a preferred range of 60 to 70. Regarding additional properties of the insert, the properties disclosed in U.S. Pat. No. 6,230,773 are suitable for the insert 34 of the present invention. The properties may be achieved by the compound disclosed in the referenced US patent, or other compounds may be selected which yield the disclosed properties. The rubber forming the insert 34 may also be flock loaded or blended with reinforcing fibers. Fibers useful may be either natural or man-made, and are characterized by having a length at least 100 times its diameter or width. Flock are particles smaller than fibers. And either may be formed from cotton, aramid, nylon, polyester, PET, PEN, carbon fiber, steel, fiberglass, or any combination thereof. The fiber or flock loading of the rubber is in the range of 5 to 35 parts per hundred parts rubber. The insert's lenticular configuration maintains the carcass main portion in a desired configuration.
In the embodiment illustrated in
In the tire bead of
In
In comparison to the prior art tire,
A key requirement of a tire is for the tire to stay on the wheel rim while pressurized and under load; i.e. the tire must stay seated. To test for this, tires are subjected to a bead unseat resistance test. In the test, depending on the tire size, the tire is inflated to a pressure greater than the recommended operating inflation pressure, the pressure being dependant upon the tire size and tire application. For a tire of the type and general size disclosed herein, the tire should not unseat at pressures less than 160 psi (1100 KPa). Because the turn-up of the disclosed tire has a different configuration than the configuration turn-up for this type of bead profile, the reinforcement ply, under tension, may function differently. Bead unseat pressures were determined by computer FEA analysis for the disclosed tire and the prior art tire (identified below as the control tire).
The only variation in the tires identified in the table below is the turn up structure path and placement.
From the above results, it can be seen that, when the terminal point of the turn-up extends too high up into the sidewall and thus closer to the ply turndown portion 12a, the bead unseat pressure is significantly reduced and is below the desired minimum unseat pressure. As the terminal point of the turn up is radially lowered, and is at or below the line P, the unseat pressure is above the minimum value and is comparable to the control tire. Thus, the tire seating characteristics are maintained, while the ease and uniformity in manufacturing is improved.
For each of the tires illustrated and discussed above, the opposing bead rings 24 and sidewalls 40 may have an identical diameter and height, respectively; that is, the non-illustrated portion of the tire is a mirror image of that illustrated. However, it is also within the scope of the present invention to form any of the discussed tires such that the diameters of the opposing beads 24 are different, as seen in
