GB2074954A

GB2074954A - A Pneumatic Tire

Info

Publication number: GB2074954A
Application number: GB8106352A
Authority: GB
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1980-03-24
Filing date: 1981-02-27
Publication date: 1981-11-11
Also published as: GB2074954B; DE3108886A1; CA1144463A; FR2478545B1; AU537768B2; IT1135703B; IT8120668A0; JPS56146402A; AU6766881A; MX151991A; FR2478545A1; BR8101623A

Abstract

A pneumatic tire (10) has first and second carcass reinforcing structures (23), (24), the first structure (23) passing from the tire crown region first to the axially inner surface of bead cores (20), (21), and then on around the cores and the second structure (24) passing from the crown region first to the axially outer surface of the bead cores and then on around the cores, in the as-cured state of the tire the neutral contour of bead and side wall regions of each structure (23), (24) coinciding with a natural equilibrium curve of the respective structure. Each structure (23), (24) may consist of one or more plies whose cords may be at 75 DEG -90 DEG to the circumferential, and the tire may have a crown reinforcement with cords at 15 DEG -30 DEG to the circumferential. The beads may have reinforcements (31), (34) which are made of rubber with a dynamic modulus of at least 125 kg/cm<2> and whose radially outer extremities are at a distance A from the type bead heals of at least 25% of the tyre section height CSH. <IMAGE>

Description

SPECIFICATION A Pneumatic Tire The foregoing abstract is not to be taken as limiting the invention of this application, and in order to understand the full nature and extent of the technical disclosure of this application, reference must be made to the accompanying drawings in the following detailed description.

Background of the Invention This invention relates to a pneumatic tire, and more particularly, to a novel and improved pneumatic tire.

It is well known in the prior art that it is desirable to cure a tire in a configuration such that the carcass ply structure follows the natural equilibrium curve for at least a portion of its length. The natural equilibrium curve is the shape the carcass ply structure tends to assume as prescribed by its cord path and dimensions when mounted on the rim for which it is designed and inflated to design inflation pressure. This concept is thoroughly discussed and explained in "Mathematics Underlying The Design of Pneumatic Tire" by John F. Purdey. U.S. Patent Nos. 3,757,8443,910,336; and 3,938,575 are illustrative of the prior art wherein at least a portion of the carcass ply structure follows the natural equilibrium curve.

During normal operation of a pneumatic tire, the bead area is subject to torsional forces and stress concentrations which can substantially detract from the durability, handling and overall performance of the tire. The prior art does not take into account these forces. In the prior art the carcass ply layers are all immediately adjacent one another or are disposed at positions symmetrically about the natural equilibrium curve in the bead area. The carcass ply structure does not contribute to the lateral stability of the tire or improve bead durability under lateral forces.

Applicant has designed an improved pneumatic tire which has the advantages of a tire having the carcass plies located at the natural equilibrium curves while at the same time providing improved handling and durability.

Summary of the Invention A tire made in accordance with the present invention comprises at least two carcass ply structures wherein one carcass ply structure is wrapped adjacent the axially inner surface of the bead core and the second carcass ply structure is wrapped adjacent the axially outer surface of the bead core. The neutral contour line of each carcass ply structure follows the natural equilibrium curve in at least the bead area of the tire.

Description of the Figures Fig. 1 is a radial cross-sectional view of a pneumatic tire made in accordance with the present invention; and Fig. 2 is a radial cross-sectional view of the tire of Figure 1 when experiencing a lateral force.

Detailed Description of the Invention Referring to Fig. 1, there is illustrated a pneumatic tire 10 made in accordance with the present invention. The tire 10 has a circumferentially extending ground engaging tread portion 1 2 which terminates in a pair of shoulder portions 14, 1 5 at the lateral ends thereof. A pair of sidewall portions 1 6, 1 7 extend radially inward from the shoulder portions 1 4, 1 5 respectively terminating in a pair of bead portions 1 8, 1 9. Each of the bead portions 1 8, 1 9 have embedded therein a substantially inextensible bead core 20, 21 respectively. The bead cores 20, 21 in the embodiment illustrated are preferably made of steel wires.A carcass reinforcing ply structure 22 extends from bead portion 18 through sidewall 16, tread portion 1 2 and sidewall 1 7 to bead portion 1 9. The reinforcing ply structure 22 comprises two reinforcing ply structures 23 and 24.The carcass reinforcing structure 22 is of the one-up one-down construction, that is, wherein the ends of the axially innermost ply structure 23 are wrapped adjacent the axially innermost surface of each of the bead cores 20, 21 in each of the respective bead areas 1 8 and 1 9 and the ends of the axially outermost ply structure 24 is wrapped adjacent the axially outermost surface of each of the bead cores 20, 21 in each respective bead area 1 8, 1 9. In the particular embodiment illustrated, the reinforcing ply structures 23 and 24 each comprise one layer of rubber coated fabric.The fabric comprises of a plurality of parallel cords which may be made of any material used for rubber reinforcement, for example, and not by way of limitation, rayon, nylon, polyester and steel and may form many desired angles with respect to the midcircumferential centerplane CP of the tire. The cords of reinforcing ply structures 23 and 24 form an angle of from about 75 to about 90 with respect to the mid-circumferential centerplane CP. While the particular embodiment illustrated shows reinforcing ply structures 23 and 24 as having a single layer each, it is understood that each ply structure 23 and 24 may be comprised of any multiple of layers, preferably ply structures 23 and 24 each having the same number of fabric layers.

Placed circumferentially about the radially outermost surface of the carcass ply structure 22 is a tread reinforcing belt structure 28 having two cut reinforcing plies 30, 32 of parallel cords coated with a thin layer of rubber. The cords of plies 30, 32 may be comprised of any material used for rubber reinforcement, for example, and not by way of limitation, nylon, rayon, steel and aramid. While the belt structure 28 is shown as having two cut plies 30, 32 belt structure 22 may be of any desired configuration and be omitted entirely if desired.The cords of plies 30 and 32 preferably form an angle of from about 15O to 300 with respect to the mid-circumferential centerplane CP of the tire and in the particular embodiment illustrated is approximately 21 . Preferably the plies 30 and 32 are oriented such that the cords of ply 30 form an angle equal and opposite to the angle formed by the cords of belt ply 32.

In each of the bead portions 18, 1 9 there is provided a hard rubber reinforcement 34, 36 respectively which extends radially outward from the respective bead core in between the carcass reinforcing ply structures 23 and 24. The hard rubber reinforcement 34 and 36 extend radially outward terminating a distance A from the nominal rim diameter NRD of at least twenty-five (25) percent of the carcass section height CSH, preferably at least thirty (30) percent and in the particular embodiment illustrated the distance A is about thirty-six (36) percent of the maximum carcass section height CSH.

For the purposes of this invention, the nominal rim diameter NRD is the distance from the axis of rotation as designated in the size designation of the tire and the maximum carcass section height OSH is the maximum radial distance between the neutral contour of the carcass reinforcing structure 22 beneath the tread portion 12 and the nominal rim diameter NRD. The hard rubber reinforcement 34 and 36 comprises a material having a dynamic modulus of elascity of at least 125 Kg/cm2. The dynamic modulus being determined by the Goodyear Vibra Tester (ASTM-2233 1).

The tire 10 is cured in configuration such that the neutral contour line of each of the reinforcing ply structures 23, 24 follow its respective natural equilibrium curve. Preferably the reinforcing ply structures 23 and 24 follow the natural equilibrium curve radially outward to wherein it first meets the belt structure 28.

For the purposes of this invention the neutral contour line of each carcass reinforcing ply structure 23, 24 respectively, is the line located midway between the outermost and innermost reinforcing ply of each reinforcing ply structure 23, 24.

The natural equilibrium curve for each of the reinforcing ply structures 23 and 24 are determined in accordance with the following relationship:

wherein y is the perpendicular distance from the mid-circumferential plane of radius p0 to any point on the tire carcass for any specified p; p is the distance from the axis of rotation to a point on the tire; Pm is the radius from the axis of rotation to the point on the tire carcass where y is maximum; a is the cured cord angle, the outer angle which the cord makes with the circumference of any circle in the circumferential direction of the tire;; p01 is the radius from the axis of rotation of the tire to a point determined by an iterative method such that the curve defined by equation (1) will pass through a point Pst Ys (specified in the shoulder area) and tangent to a line determined by Ym, pb, Yb determined for the carcass structure in the bead area; ps is the distance from the axis of rotation to a point in the shoulder area where the carcass contour deviates from equation (1); Yb, pb is the point at which the carcass contour deviates from equation (1); pb is the distance from the axis of rotation to the point on the tire carcass in the bead area; Yb is the distance from the mid-circumferential plane of radius po to the point on the tire carcass bead area; ; The above equation is used when a belt reinforcing structure 28 is present in the tire 10. When there is no belt reinforcing structure the po' term is replaced by the po term which is defined as the radius from the axis of rotation to a point on the tire at the tread center.

For the purposes of this invention, the maximum carcass section width OSW is the maximum distance measured parallel to the axis of rotation of the tire between the neutral contour of the reinforcing structure 22.

During normal operation of a pneumatic tire, the bead area is subject to torsional forces and stress concentrations which can substantially detract from the durability and handling characteristics of a tire. This is of particular importance in tires of radial type construction, that is, a tire in which the cords form an angle of from about 750 to 900 with respect to the mid-circumferential centerplane. The carcass ply layers of a radial tire do not contribute substantially to the lateral stability of the tire on proved bead durability under lateral forces. The one-up one-down carcass ply construction provides bead durability and improves the lateral stability of the tire during turning maneuvers.

Referring to Fig. 2, there is illustrated the tire 10 undergoing a lateral force. The one-up one-down construction puts one of the reinforcing ply structures 23 or 24 in compression while the other is in tension depending upon which bead portion is being considered. The reinforcing ply structure that is being put under tension adds to the stability of the tire. Curing the tire in the configuration such that each of the reinforcing ply structures follow its own natural equilibrium curve minimizes the stresses and tension variations in the cords of each ply structure while at the same time allows the carcass reinforcing ply structures to go into tension as the condition requires improving lateral stability of the tire. A tire made in accordance with the present invention exhibits improved lateral stability and bead durability without adversely affecting the normal performance characteristics of the tire. Applicant's invention is particularly well suited for radial type tires, that is, tires wherein the cords of the reinforcing ply structure form an angle from about 750 to 900 with respect to the mid-circumferential plane of the tire, wherein improved lateral stability is desired.

While certain representative embodiments and details have been shown for purposes if illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims

1. A pneumatic tire comprising: a ground engaging tread portion, said tread portion terminating in a pair of shoulder portions, one at each lateral end thereof, a pair of sidewall portions extending radially inward from said shoulder portions terminating in a pair of bead portions respectively, each of said bead portions having at least one inextensible bead core, a first carcass reinforcing ply structure extending from bead core to bead core, the terminal ends of said first carcass ply structure each being wrapped adjacent the axially inner surface of each respective bead core and, a second carcass reinforcing ply structure extending from bead core to bead core the terminal ends of said carcass reinforced ply structure being wrapped adjacent the axially outermost surface of said respective bead cores, characterized by said tire being cured in the configuration such that the neutral contour line of each of said first and second carcass reinforcing ply structures coincides with the respective natural equilibrium curve of said structures.

2. A tire according to claim 1 further characterized by said first and second carcass reinforcing ply structures comprising one layer of cord reinforcement.

3. A tire according to claim 2 further characterized by the cords of said layers forming an angle in a range of from 750 to 900 with respect to the mid-circumferential centerplane of the tire.

4. A tire according to claim 1 further characterized by a circumferentially extending belt reinforcing structure in a ground engaging tread portion radially outward of said first and second carcass reinforcing ply structures.

5. A tire according to claim 1 further characterized by each of said bead portions further including a hard rubber reinforcement positioned between said first and second reinforcing structures and extending radially outward from said bead cores and terminating at a distance from the nominal rim diameter of at least twenty-five percent (25%) of the carcass section heiqht.