WO2022091117A1

WO2022091117A1 - Heavy duty tire

Info

Publication number: WO2022091117A1
Application number: PCT/IN2021/050835
Authority: WO
Inventors: Ambalal Bharat Patil
Original assignee: Ceat Limited
Priority date: 2020-10-27
Filing date: 2021-08-30
Publication date: 2022-05-05

Abstract

The present invention is directed towards improving the durability of a tire (1) under heavy load conditions. The tire (1) comprises a tread portion (4), a pair of 5 circumferentially and continuously extending shoulder portion (5). Each of the pair of shoulder portion (5) comprises an inner surface (1'') and an outer surface (1'), the outer surface (1') being divided between a pair of upper sidewall portion (1'b) and a lower sidewall portion (1'a). The tire (1) also comprises a body plyline (2) extending between bead portions and turned up around a bead core (3) in each 10 bead portion (6) from inside to outside of the tire (1) so as to form a pair of turnup portion (2') and a main portion (7) therebetween, wherein, in loaded condition, the body plyline (2) forms a straight portion (S) across the lower sidewall portion (1'a).

Description

HEAVY DUTY TIRE

TECHNICAL FIELD

[0001] The subject matter described herein, in general, relates to a radial tire for heavy load, and in particular relates to a radial tire for heavy load whose durability, resistance to wire fatigue, and resistance to uneven wear may be improved.

BACKGROUND

[0002] These days radial tires have become an essential requirement in passenger cars, sports utility vehicles (SUVs), commercial vans, light trucks, trailers, commercial trucks, and buses, etc., to meet modern transportation needs. Further, the radial tires are continuously being improvised for safe and efficient operation.

[0003] A radial tire is an assembly of numerous components such as sidewalls, plies, beads, inner liner, belt system, treads, etc. The bead is made up of bands of high tensile-strength steel wires and lies in a bead core of the radial tire. The bead connects the radial tire to the rim and holds the entire wheel together. The steel wires move perpendicular to the tread and radially from one bead core to another bead core. An area adjacent to the bead core is filled with rubber having hardness different from that of the bead core. Furthermore, a reinforcing layer of the steel wires surrounds the plies for providing better strength to the bead core.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0005] FIG. 1 shows a cross-section view of a radial tire about a mid- circumferential plane, as per an implementation of the present subject matter; [0006] FIG. 2 shows a schematic view of an optimized body plyhne profile across lower sidewall in bead area, as per an implementation of the present subject matter; and

[0007] FIG. 3 shows a schematic view of a body plyline optimization along shoulder portion of a radial tire, as per an implementation of the present subject matter.

DETAILED DESCRIPTION

[0008] The present invention relates to the construction of a body plyline of a radial tire (hereinafter referred to as tire), to improve durability, resistance to wire fatigue, and resistance to uneven wear of the tire in a heavy load condition, in accordance with the present subject matter.

[0009] In a heavy load tire, growth in a radius markedly occurs in a vicinity of a shoulder portion on both sides of a tread portion in a tire width direction, and the radius growth ranges unevenly in the tire width direction. This uneven radius growth may cause separation of the body plyline from the bead core at the plyline turnup ends. Separation of the body plyline causes loss of durability, wire fatigue, and uneven wear to the tire.

[0010] Various prior art systems have been devised to overcome the aforementioned problems. In some prior art solutions, a heavy-duty pneumatic radial tire that comprises a carcass of at least one rubberized cord ply of radial arrangement toroidally extending between a pair of bead core embedded in bead portions and wound around the bead core from inside of the tire toward the outside to form a turnup portion is provided. Further, at least one rubberized organic fibre cord layer extending outside the turnup portion over an end of the turnup portion outward in a radial direction of the tire is used, in which the organic fibre cord layer is arranged so as to extend from a position near to an outside of the bead core over the end of the turnup portion toward the outside of the tire and spread apart to the turnup portion.

[0011] In some other prior art solutions, a tire that has a carcass, a tread, and a belt reinforcing structure located radially outward of the carcass and radially inward of the tread is provided. The carcass is comprised of a reinforcing ply extending between a pair of bead portions, a pair of sidewalls, each sidewall located radially outward of one of the pair of bead portions, and a pair of inserts located in each sidewall. The first insert is positioned between an inner liner and the first reinforcing ply, and the second insert is positioned axially outward of the first reinforcing ply.

[0012] In yet other prior art solutions, a tire has a carcass having a pair of sidewall plies and a bridge ply, wherein each ply is reinforced with cords. The sidewall plies each have a first end which is received between the bridge ply and a belt reinforcing structure. Each sidewall ply extends axially outward along the sidewall and extending radially inwardly to the bead core and folded from a position axially outside the bead core to a position axially inside and around the bead core to an axially inner turnup end. The bridge ply has ends which overlap with a respective inner turnup end of said sidewall ply.

[0013] However, none of the aforementioned prior art solutions suggest a way to optimize the body plyline profile so that separation of the ply layers from the bead core may be prevented and the durability of the tire under heavy load conditions may be improved.

[0014] In light of the foregoing discussions, there exists a need to overcome various problems associated with a conventional tire for heavy loading, and accordingly, there is a need to optimize body plyline profile to improve the durability, resistance to wire fatigue, and resistance to uneven wear of the tire.

[0015] To this end, approaches for optimizing the body plyline profile design in a lower sidewall portion of a tire are discussed, which substantially prevents the separation of the ply layers from the bead core and improves the durability of the tire under heavy load conditions.

[0016] An implementation of the present subject matter describes a radial pneumatic tire. The tire includes a tread portion and a pair of circumferentially and continuously extending shoulder portions arranged on either side of the tread portion. Each of the pair of shoulder portions comprises an inner surface and an outer surface. The outer surface is divided between a pair of upper sidewall portions and a lower sidewall portion, wherein the upper sidewall portion and the lower sidewall portion are provided on either side of the tread portion. Each of the pair of lower sidewall portions comprises a bead portion that is located at a distal end of a respective lower sidewall portion. The bead portion has a bead core therein.

[0017] The tire also includes a body plyline that extends on and between the bead portion on both sides of the tire and extends along the tread portion and the sidewalls. The body plyline is turned up around each bead core from the inner side to the outer side, with respect to the bead core, in an axial direction. Due to this tuming-up, a main portion and tumed-up portions are formed in the body plyline. According to the present invention, in loaded condition, the body plyline forms a straight portion along the lower sidewall portion, wherein the straight portion initiates from a center of the bead core which is defined by a maximum limit and a minimum limit, respectively. The loaded condition of the tire in the present invention may be defined as per the standard load condition given by the Indian Tyre Technical Advisory Committee (ITTAC) or European Tire and Rim Technical Organization (ETRTO) standard manual, for example.

[0018] With the implementation of the present subject matter, the body plyline profile in the bead portion of the tire is optimized, wherein the optimization includes straighter body plyline across the lower sidewall portion so as to define shape of tire in loaded condition. The straighter profile of the body plyline reduces the separation of the ply layers from the bead core and thus contributes to durability of the tire in heavy load conditions. Implementation of the present subject matter also eliminates the stresses and strains that are developed due to the shearing and straining at the turnup area in the bead portion.

[0019] The above and other features, aspects, and advantages of the subject matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly descnbed or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components.

[0020] FIG. 1 shows a meridional cross section of radial truck tire for heavy vehicles.

[0021] The cross-sectional view of FIG. 1 is a radial cut of a radial tire 1 showing only half of the cross-section of the radial tire 1, as per an implementation of the present subject matter. The radial cross-section of the radial tire 1 is symmetrical with respect to a mid-circumferential plane Y of the tire 1. The top portion of the tire 1 includes a tread portion 4 constituting a tread surface for contacting a ground surface to support a vehicle by transferring vehicular loads from the rim through the tire 1 to the ground surface. The tire 1 further comprises a shoulder portion 5 disposed laterally on each side of said mid- circumferential plane Y and the shoulder portion 5 comprises an inner surface 1 ’ ’ and an outer surface 1 ’ .

[0022] The outer surface 1 ’ of the shoulder portion 5 is divided between a pair of upper sidewall portion 1’b and a lower sidewall portion 1’a, wherein the upper sidewall portion 1’b and the lower sidewall portion 1’a are provided on either side of the tread portion 4, respectively. In an embodiment, the pair of upper sidewall portion 1’b and the lower sidewall portion 1’a may be demarcated in 60 to 40 ratios or 50 to 50 ratios depending upon the type of the tire. The sidewalls of the tire serve to increase the lateral stability of the vehicle. Further, each of the pair of lower sidewall portion 1’a comprises a bead portion 6 located at a distal end of a respective lower sidewall portion 1’a, wherein the bead portion 6 has a bead core 3 therein.

[0023] In an example, the tire 1 may also include a plurality of reinforced belt plies, interior to the tread portion 4, forming belt packages in a band around the tire 1. The belt packages may extend laterally over the top of the tire 1 from shoulder to shoulder. [0024] The bead core 3 of the tire 1 is composed of steel wires in varying numbers to form a loop in the bead portion 6 that seals against a rim and forms an anchor on which a body plyline 2 is wound. The body plyline 2 may be composed of steel cords that gives sufficient strength to hold the air pressure and provide impact resistance to the sidewalls. The body plyline 2 extends on and between the bead portion 6 on both sides and extends along the tread portion 4 and the sidewalls. The body plyline 2 is turned up around each bead core 3 from the inner side to the outer side in the axial direction which is parallel to the height of the tire. Due to this turning-up, a main portion 7 and a turned-up portion 2' are formed in the body plyline 2.

[0025] The sidewall portion 5 protects the body plyline 2 from flex fatigue and abrasion. Further, the tire 1 may include an inner liner layer (not illustrated). The inner liner layer may be used to retard or minimize the escape of air used to inflate the tire 1, thereby maintaining tire pressure. The inner liner layer may be adhered to the inner surface of the tire 1 and, in another embodiment, may extend over the entire inner surface of tire 1. The inner liner layer may be made of a material (e.g., butyl or a halo butyl rubber or natural rubber) which has low air permeability and high elongation and flex resistance over the tire temperature range likely to be encountered by a tire in service.

[0026] In an example implementation of the present subject matter, the tire 1 may also include a chafer (not illustrated) positioned around the tire's 1 bead portion 6 and intended for contacting a rigid rim of the vehicle wheel. The chafer may be made up of a rubber composition and is designed to contact the rigid wheel rim and, therefore, act as an interface between the tire 1 and the wheel rim. The chafer rubber composition is very abrasion resistant, tough, and has a relatively high modulus while also having acceptable flex and rubber fatigue properties as well as good resistance to cut growth. The chafer may be placed adjacent to the bead portion 6 of the tire 1, leaving the rubber portion of the chafer to contact the rigid wheel rim when the tire 1 is mounted on such rim and inflated. The chafers, their intended interface between the tire bead portion and rigid wheel rim, as well as their rather demanding physical properties, are well known to those skilled in the art and have not been elaborated in the present description.

[0027] Further, the tire 1 may be provided with a rim-cushion (not illustrated) so that the tire 1 has the ability of absorbing shock or cushioning effects due to the bumpy vehicle running surface. In some implementations of the tire 1, a shoulder pad (not illustrated), may be provided in the tire 1 to reduce inflation pressures and to further improve the off-road traction. The shoulder pad may also help in controlling bulging in the shoulder areas, reducing in those areas of the tire 1, a risk of puncture.

[0028] In another example embodiment, in the tire 1, a belt cover layer (not illustrated) may be provided which may consist of a nylon material or the like with lower rigidity than the belt packages, as described above. The belt cover layer may be disposed on the belt plies in a tire circumferential direction in order to improve high speed durability of the tire 1. Since, the belt cover layer does not directly affect the performance to which the present invention pertains and already known in the art, therefore further description on the belt cover layer is skipped here for the sake of brevity.

[0029] Although the foregoing description has described belt plies primarily as utilizing steel or like metal cords or cables as the reinforcing elements, it will be understood that the principles of the invention are applicable to belts made up of cords of other high modulus materials, such as rayon, glass fiber, and the like, well known in the art.

[0030] Further, in yet another example implementation of the present subject matter, the bead portion 6 may be provided with bead filler (not illustrated) disposed radially inside the bead core 3 and between the main portion 7 and the turned-up portion 2' of the body plyline 2. The bead filler generally has triangular cross-sectional shape, an axially outer side and an axially inner side. The construction of bead filler and the bead filler's constituents is well known in the art. [0031] In one embodiment of the present subject matter, the tire may have an aspect ratio in a range of 80 -120. Furthermore, in another embodiment, the aspect ratio may vary, depending upon the types of tires used.

[0032] FIG. 2 illustrates a schematic view of an optimized body plyline profile across the lower sidewall portion 1’a in the bead portion 6 of the tire 1, as per an implementation of the present subject matter.

[0033] As shown in FIG. 2, the body plyline 2 is forming a straight portion S along the lower sidewall portion 1’a, wherein straightness initiation Si of the straight portion S occurs from a center of the bead core 3. The straightness initiation Si is defined by a maximum limit Si max and a minimum limit Si min, respectively.

[0034] In an embodiment, the minimum limit Si min and the maximum limit Si max of the straightness initiation Si may lie in a range of 9% to 13 % of section height SH of the tire 1, wherein the section height SH is the height of the tire 1 measured from outer diameter of the tire 1 to sitting of the tire 1. In another embodiment, value of Si max may lie in a range of: +13% to 15% of the section height SH of the tire 1 and value of Si min may lie in a range of - 5% to -9% of the section height SH of the tire 1.

[0035] In another embodiment, a variation of the straight portion S of the body plyline 2 and gauge W with respect to the straightness initiation Si is given by:

S = -0.0015Si² - 1.1122Si + 98.146,

W= 0.012Si² - 0.8175Si + 40.212, wherein the gauge W is defined from the outer surface 1’ of the tire 1 and measured from a centre of the straight portion S. Further, length of the straight portion S of tire 1 may lie in a range of 17% to 30% with respect to the section height SH-

[0036] FIG. 3 shows a schematic view of the body plyline 2 optimization along the shoulder portion 5 of the tire 1, as per an implementation of the present subject matter. In an example embodiment, the main portion 7 of the body plyline 2 in the upper sidewall portion 1’b may have a profile that comprises a radially outward outer portion O that from a maximum cross-sectional width point A of the main portion 7 of the body plyline and have a radius of first curvature R2. The radius of the first curvature R2 may be tangent to the straight portion S of the body plyline 2. Further, centre of the first curvature may lie on a reference height RH of the tire 1. The reference height RH of the tire 1 is a height of the tire 1 at which maximum section width is achieved. Tangency of radius curvature gives uniform pressure and tension distribution throughout the plyline that reduces the stress and strain development near bead area.

[0037] In yet another example embodiment, the main portion 7 of the body plyline 2 in the lower sidewall portion 1’a may have a profile comprising an inner portion I that extends radially outwards from a maximum cross-sectional width point A of the main portion 7 of the body plyline 2, wherein a radius of second curvature R1 may be larger than radius R2.

[0038] Further, in another example embodiment, radius R2 of second curvature may be tangent to arc drawn from radius R1 such that R1/R2-1.5, wherein R2 is measured from the same line from where the R1 is being measured. This type of curvature profiles may bring the upper sidewall portion 1’b sufficiently inward thereby reducing the shearing stresses and increasing the durability of tires.

[0039] In yet another example embodiment, a length of the straight portion S may be 17% to 30% of the length of the section height SH and the length of the reference height R_H may be 30% to 60% of the length of the section height SH- Further, the straight portion S of the body plyline 2 have an inclination angle (theta) with respect to a straight line (K), wherein the inclination angle may be in a range of 40 to 70 degrees.

[0040] The embodiments of this invention can be used in combination or individually to form tires made by improved manufacturing processes and/or with improved performance features. The combinations depend on the intended use of the tire and includes conventional as well a run-flat tire uses. The overall design of the body plyline of the invention disclosed herein results in a straighter plyline profile along the turpup portion of body plyline thus reducing the bead unwrapping, improving the durability of the tire and driving performances of the vehicle, especially the heavy-duty vehicle.

Claims

I/We claim:

1. A tire (1) comprising: a tread portion (4); a pair of circumferentially and continuously extending shoulder portion (5) arranged on either side of the tread portion (4), each of the pair of shoulder portion comprising: an inner surface (1”); and an outer surface (1’), the outer surface (1’) being divided between a pair of upper sidewall portion (l’b) and a lower sidewall portion (l’a) provided on either side of the tread portion (4), each of the pair of lower sidewall portion (l’a) comprising: a bead portion (6) located at a distal end of a respective lower sidewall portion (l’a), the bead portion (6) having a bead core (3) therein; and a body plyline (2) extending between bead portions and turned up around the bead core (3) in each bead portion (6) from inside to outside of the tire (1) so as to form a pair of turnup portion (2') and a main portion (7) there between, wherein, in loaded condition, the body plyline (2) forms a straight portion (S) across the lower sidewall portion (l’a) and wherein straightness initiation (Si) of the straight portion (S) occurs from a center of the bead core (3) which is defined by a maximum limit (Si max) and a minimum limit (Si min), respectively.

2. The tire (1) as claimed in claim 1, wherein the minimum limit (Si min) and the maximum limit (Si max) of the straightness initiation (Si) lies in a range of 9% to 13 % of section height (SH), the section height (SH) being the height of the tire (1) measured from outer diameter to sitting of the tire (1).

3. The tire (1) as claimed in claim 1, wherein the main portion (7) of the body plyline (2) in the upper sidewall portion (l’b) has a profile comprising an outer portion (O) extending radially outwards from a maximum cross sectional width point (A) of the main portion (7) of the body plyline and having a radius of first curvature (R2) and wherein the radius of the first curvature (R2) is tangent to the straight portion (S) of the body plyline (2).

4. The tire (1) as claimed in claim 3, wherein centre of the first curvature lies on a reference height (R_H), the reference height (R_H) being a height of the tire at which maximum section width is achieved.

5. The tire (1) as claimed in claim 1, wherein a length of the straight portion (S) lies in a range of 17% to 30% with respect to the length of the section height (S_H).

6. The tire (1) as claimed in any one of the preceding claims 2-4, wherein the length of the reference height (RH) lies in a range of 30% to 60% with respect to the length of the section height (SH)-

7. The tire (1) as claimed in claim 1, wherein the main portion (7) of the body plyline (2) in the lower sidewall portion (l’a) has a profile comprising an inner portion (I) extending radially outwards from a maximum cross sectional width point (A) of the main portion (7) of the body plyline and having a radius of second curvature (Rl) larger than radius (R2).

8. The tire (1) as claimed in any one of the preceding claims 3-7, wherein relation between the radius of the first curvature (R2) and radius of the second curvature (Rl) is given by R1/R2-1.5.

9. The tire (1) as claimed in claim 1, wherein a variation of the straight portion (S) of the body plyline (2) and gauge (W) with respect to the straightness initiation (Si) is given by:

S = -0.0015Si² - 1.1122Si + 98.146, W= 0.012Si² - 0.8175S1 + 40.212, the gauge (W) being defined from the outer surface (1’) of the tire and measured from a centre of the straight portion (S).

10. The tire (1) as claimed in claim 1, wherein the straight portion (S) of the body plyline (2) has an inclination angle (theta) in a range of 40 to 70 degrees with respect to a straight line (K).