WO2002030686A1

WO2002030686A1 - Tire with optimized interior contour

Info

Publication number: WO2002030686A1
Application number: PCT/EP2001/011569
Authority: WO
Inventors: Roger C. Cottrell; Walter L. Willard, Jr.
Original assignee: Michelin Recherche et Technique SA Switzerland; Societe de Technologie Michelin SAS
Current assignee: Michelin Recherche et Technique SA Switzerland; Societe de Technologie Michelin SAS
Priority date: 2000-10-10
Filing date: 2001-10-08
Publication date: 2002-04-18
Anticipated expiration: 2003-04-10
Also published as: AU2002223600A1

Abstract

The invention provides a tire comprising a carcass structure anchored in each side of the tire in a bead, each bead having a base which is intended to be mounted on the tire's design mounting rim, each bead being extended radially upward by a sidewall portion, a reinforced summit, the sidewall portions joining said summit, said tire having an inner and an outer contour, wherein the sidewall inner contour comprises a convex portion with a radius of curvature superior to H/2, B being the Section Height of the tire.

Description

TIRE WITH OPTIMIZED INTERIOR CONTOUR

BACKGROUND OF THE INVENTION

The invention relates to a tire, more specifically to a pneumatic tire capable of continued mobility in a deflated condition.

Various tire constructions have been proposed for pneumatic runflat tires; that is tires, which normally operate in an inflated condition but which also permit a limited operation in a deflated condition. These tires constructions are generally formed of one or more generally radial carcasses which are turned up around one or more bead wires arranged in each bead. To obtain the desired mobility in the deflated condition, many of these tires further employ sidewalls which are reinforced and thickened by interposing additional rubber layers between the carcasses or between the carcasses and the tire inner liner.

Usually, the runflat tires have an inner contour of their sidewall portions with a concave curvature, i. e. a curvature the center of which is disposed towards the inside of the tire cavity. FR 2 344 413 presents a runflat tire with the sidewalls reinforced by inserts made of foam. These inserts, in the embodiment of figure 1 , are placed radially under the sides of the belt of the summit of the tire in order to support it when deflated. The inner side of this tire has a pronounced convex curvature.

Inflated and deflated performance also depends on the carcass structural arrangement, materials and on the carcass path. In known runflat tires, the carcass path is such that, in operation, at least a portion of the carcass may be placed in a compressive stress due to its position at the axially outward side of the bead/sidewall structure. Tensile-compressive cyclic stress may affect the product durability. For instance tires having carcasses turned up around bead wires necessarily have a discontinuity at the radially uppermost extent of the turned up portion of one or more of the carcasses. When the turned up portion is axially positioned to the exterior of a median axis of the tire cross section, deformation of the bead portion due to loading the tire places the turned up portion in a state of compressive stress. This stress state and the aforementioned discontinuity lead to design constraints resulting in tire performance compromises between the inflated and deflated states.

BRIEF SUMMARY OF THE INVENTION

The invention provides a tire comprising a carcass structure anchored in each side of the tire in a bead, each bead having a base which is intended to be mounted on the tire's design mounting rim, each bead being extended radially upward by a sidewall portion, a reinforced summit, the sidewall portions joining said summit, said tire having an inner and an outer contour, wherein the sidewall inner contour comprises a convex portion with a radius of curvature superior to H/2, H being the Section Height of the tire.

This convex portion, i. e. that this portion has a center of curvature placed outwardly of the tire cavity, has the advantage to provide an even distribution of the stress-strain cycles in the rubber mixes of the sidewall during deflated operation. As a consequence, this gives a better 0-psi durability.

Preferably, the height of this convex portion is comprised between 0,3 and 0,5 H.

This convex portion may have a radius of curvature substantially infinite.

Advantageously, the convex portion is adjacent a concave portion placed radially inwardly with a radius of curvature between 0,2 and 0,3 H.

The sidewall inner contour may further comprise a substantially linear portion.

Specifically, advantageously, radially inwardly from the summit to the bead, the sidewall inner contour may comprises a first concave zone with a first radius of curvature, a convex portion with a second radius of curvature, a second concave zone with a third radius of curvature and a substantially linear portion. Preferably, the first radius of curvature is between 0,15 H and 0,25 H and is inferior to the third radius of curvature. The third radius of curvature may be between 0,2 H and 0,3 H.

The tire of the invention further comprises a bead with an anchoring zone for anchoring of the carcass structure wherein the carcass structure has at least one circumferential alignment of cords in this anchoring zone, which progressively divides in the sidewall portion in at least two circumferential alignments of cords.

This carcass structure is very flexible and allows placing the carcass cords where they are most useful. For instance, the density of cords of the axially exterior carcass layer is preferably superior to the density of cords of the axially interior carcass layer.

Preferably, a runflat insert is disposed between these two carcass circumferential cord alignments and this runflat insert is in direct contact with the cords of the two circumferential alignments.

The direct contact between the runflat insert and the cords of the two adjacent carcass layers gives an excellent homogeneity of the mechanical properties of the structure, which drives to a better durability in 0-psi performance. The construction is also simplified due to the least number of rubber mixes necessary for its building.

Preferably, the carcass structure of the tire of the invention comprises only one circumferential alignments of cords in the summit portion of the tire.

Preferably, the anchoring zone is provided with at least one first bead reinforcement, at least partially bordering said carcass structure and a high modulus rubber mix cooperating with said bead reinforcement and with said carcass structure for anchoring said a carcass structure in the bead. The bead reinforcement advantageously includes at least one substantially circumferentially oriented cord laterally bordering the carcass structure on at least one side.

This type of cooperation between the carcass structure and bead reinforcements provides design flexibility in many aspects. Moreover, such an anchoring zone is compact and very strong.

Such an arrangement provides the possibility of taking up the tension developed in the carcass during inflated or deflated use of the tire.

According to a preferred embodiment, the carcass structure comprises only one circumferential alignment in the summit portion of the tire. This has the advantage of limiting the thickness of the summit of the tire. Such a tire has reduced weight and rolling resistance and improved inflated and deflated performances.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the sidewall and bead portion of a runflat tire according to the invention, taken along a meridian plane through the axis of rotation;

Figure 2 illustrates the sidewall and bead portion of a second embodiment of a runflat tire according to the invention, taken along a meridian plane through the axis of rotation, with two carcass layers in the bead and three in the sidewall;

Figure 3 is an enlarged perspective view of the bead portion of a runflat tire corresponding to the second embodiment of the invention showing the common circumferential disposition of the first and second carcass layers; and

Figure 4 illustrates the evolution of the sidewall inner contour from a prior art tire to the tire of the invention. DETAILED DESCRIPTION OF THE INVENTION

"Axial" and "axially" mean the lines or directions that are parallel to the axis of rotation of the tire.

"Equatorial plane (EP)" means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

"Radial" and "radially" mean directions radially toward or away the axis of rotation of the tire.

"Section Height (H)" means the radial distance from the nominal rim diameter (D) to the outer diameter of the tire at its equatorial plan (EP).

As illustrated in figure 1 , the tire 1 of the invention comprises a bead 3 provided with a seat 6, specially adapted to fit on the tire's mounting rim 2. The bead 3 extends substantially radially to the sidewall 7. The sidewall 7 joins the tire summit 8. The tire summit comprises a usual belt structure 9.

The tire comprises a carcass structure 5, extending from bead to bead or leaving a gap between two half structures, for instance in the substantially median portion of the summit. The radially inwardmost extent of the carcass structure 5 terminates in an anchoring zone 4 of the bead 3.

Advantageously, the carcass structure is not turned up around bead cores or other bead reinforcement. That is to say, each axial coordinate defining the profile of the carcass structure has a unique radial position for each radial position less than that of the tire equator.

The carcass structure is anchored in the bead portion by a bead reinforcement. A preferred embodiment of such a reinforcement comprises a cord arrangement 10 provided with at least one substantially circumferentially oriented cord 41 laterally bordering the carcass structure on at least one side. In the embodiment of figure 1 , there are two circumferentially oriented cord windings 41 and 42 laterally bordering the carcass structure 5 on both sides. In this instance "anchored" in the bead portion means that the arrangement resists the tension developed in the carcass structure during inflated or deflated use of the tire by the adherence of the carcass reinforcing structure laterally with the cords 41 and 42 rather than being wound around a traditional bead core.

The mechanical properties of the anchoring zone 4 are optimized in using a bead filler having a very high elastic modulus. For instance, typical values may be within the following range: the shore A hardness may be equal or greater than 95 and the modulus at 10 % greater than 60 MPa.

Other examples of carcass anchorings or dispositions of the carcass layers in the bead portion have been disclosed in US 5,660,656 to Herbelleau et al and are incorporated herein by reference.

The carcass structure 5 of the tire 1 has more than one carcass layer within some portion of the tire. The carcass structure 5 comprises one circumferential alignment of cords in the summit 8. In the sidewall portion 7 of the tire, the carcass structure 5 is divided in two circumferential alignments of radial cords 51 and 52. These two circumferential alignments of cords progressively move axially away from each other. In the bead 1 , the two circumferential alignments of cords 51 and 52 join and give a common circumferential alignment of cords 5. Accordingly, in the bead 1 , there is only one circumferential alignment of cords.

This carcass structure is very flexible and allows placing the carcass cords where they are most useful. For instance, the density of cords of carcass layer 52 is advantageously superior to the carcass density of cords of the carcass layers 51.

The cords of the outer carcass layer are subjected to high-tension stress-strain cycles in inflated and deflated operation. These cords are well designed to support these high-tension cycles and the number of cords is defined accordingly. The cords of the inner carcass layer are subjected in deflated operation to stress-strain cycles with compression. In this case, it is the rubber mixes, which are well designed to support these compression stresses. The number of cords needs not to be high. It allows also a limited thickness of the carcass structure in the summit and an appropriate anchoring in the bead portion.

Advantageously, runflat inserts are placed in the sidewall between the carcass layers 51-52 - insert 92 and also between the carcass structure 5 and the inner side of the tire - insert 91 - in order to have a good 0-psi performance.

Preferably, these runflat inserts are in direct contact of the cords of the adjacent carcass layers. This means that the rubber mixes constituting the runflat inserts are in intimate contact with at least part of the outer circumference of the cord, and that during the building of the tire, no usual cushion rubber mix of low modulus of elasticity has been used. Accordingly, the sidewall structure has a better durability in deflated operation.

The tire comprises an outer contour 12 and an inner contour 13. In its sidewall portion, the inner contour 13 comprises, from the summit side towards the bead, a first concave zone 14 having a first radius of curvature R1 , a convex portion 15 having a high radius of curvature R2, a second concave zone 16 having a third radius of curvature R3 and a substantially linear portion 17. This substantially linear portion 17 joins the bead inner contour.

The convex portion 15 has a curvature with a radius R2 superior to half the Section Height of the tire:

R2 > H/2

The radius of curvature R1 of the first concave zone 14 is preferably between 15 % and 25 % of the Section Height H of the tire. R3 is between 20 % to 30 % of the Section Height H of the tire 1. The length L1 of the convex portion of the inner contour of the sidewall, measured in a radial direction, is between 30 % and 50 % of the Section Height H of the tire 1. Accordingly, the length L2 of the substantially linear portion of the sidewall inner contour may vary with the type of the tire considered.

It is to be quoted that the substantially linear portion 17 and the carcass alignment of cords in the bead are substantially parallel. They are also parallel to the two windings of circumferentially oriented cords 41 and 42 and to the anchoring zone as a whole. This results in a very stiff, compact and resistant bead structure, the durability of which is excellent, notably in deflated operation.

As illustrated in figure 1 , the previous dimensions are calculated with the tire 1 being mounted on its design rim 2, inflated but unloaded.

Such an inner contour of sidewall of the tire 1 has the advantage to provide to the rubber mixes constituting the sidewall a more even distribution of the stress-strain cycles during deflated operation. As a consequence, the durability performance of the tire in deflated operation is improved.

Figure 2 illustrates a second embodiment of the invention in which the convex portion 25 has a very high radius of curvature, substantially infinite. In this embodiment, the carcass structure 5 comprises one circumferential alignment of cords in the summit 5. In the sidewall portion 7 of the tire, the carcass structure 5 is divided in three circumferential alignments of radial cords 511, 512 and 52.

These three circumferential alignments of cords progressively move axially away from each other. In the bead 1 , the two circumferential alignments of cords 511 and 512 join and give a common circumferential alignment of cords 51. Accordingly, in the bead 1 , there are two circumferential alignments of cords 51 and 52.

The density of cords of carcass layer 52 is advantageously superior to the carcass density of cords of the carcass layers 511 and 512. This structure allows a limited thickness of the carcass structure in the summit and an appropriate anchoring in the bead portion. The anchoring of the carcass structure 5 is achieved by three windings 41 , 42, 43 of circumferential oriented cords, which axially border the two circumferential alignments of cords 51 and 52 of the carcass structure with the interposition as in the previous embodiment of figure 1 of a high modulus rubber layer.

Advantageously, another runflat insert 93 is placed in the sidewall between the carcass layers 512 and 52 in order to improve the 0-psi performance. Preferably, as in the first embodiment the runflat inserts are in direct contact of the cords of the adjacent carcass layers.

Figure 3 illustrates the structure of the radial and circumferential cords in the bead 3 of the second embodiment. In the anchoring zone, axially outward, we have the first circumferentially oriented winding 41 , the first carcass circumferential alignment 51 , the second circumferentially oriented winding 42, the second carcass circumferential alignment 52 and the third circumferentially oriented winding 43. Radially outwardly from the anchoring zone, the first carcass circumferential alignment 51 is divided in two carcass circumferential alignments 511 and 512. The rubber mixes are not represented in this figure for clarity. All these cords are embedded, at least in the anchoring zone, by a high modulus rubber mix. Preferably, this rubber mix has a shore A hardness over 80.

All the carcass cords presented in figure 3 are placed with a circumferentially shifted position, which allows them to form one sole alignment in the summit portion of the tire. This allows minimizing the thickness of the summit portion.

The cords 41 , 42 and 43 are advantageously made of steel. Monofilament or cable structure cords may be used. Textiles type cords, such as aramid, nylon, PET, PEN, or hybrids such as aramid/nylon, etc., may also be used alone or in combination with metallic cords.

Within the scope of the invention, the carcass structure can also present one circumferential alignment of cords in the summit and the bead, which divide in three in the sidewall. Figure 4 illustrates the evolution of the sidewall inner contour from a prior art tire to the tire of the invention. The broken line 20 gives the usual sidewall inner contour. This contour is concave.

The line 21 gives the optimized contour of the inventive tire with the first transition region 14 (R1), the convex region 15 (R2), the second transition region 16 (R3) and the linear portion 17 adjacent the bead.

The following table gives the value of the relative peak stress level at the equator of the tire (0,5 H) in a deflated loaded region:

The optimized contour tire, a P 225/60 R16 MXV4 ZP, has a more efficient use of its mass. The amelioration of the durability in deflated condition is very sensitive.

In order to position the reinforcement cords as precisely as possible, it is very advantageous to build the tire on a rigid support, for instance a rigid core imposing the shape of its inner cavity.

All the components of the tire, which are disposed directly in their final place, are applied onto this core in the order required by the final architecture, without undergoing shaping at any moment of the building. In this case, the tire can be molded and vulcanized in the manner explained in US 4,895,692. While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.

Claims

1. A tire comprising a carcass structure anchored in each side of the tire in a bead, each bead having a base which is intended to be mounted on the tire's design mounting rim, each bead being extended radially upward by a sidewall portion, a reinforced summit, the sidewall portions joining said summit, said tire having an inner and an outer contour, wherein the sidewall inner contour comprises a convex portion with a radius of curvature superior to H/2, H being the Section Height of the tire.

2. A tire according to claim 1, wherein, the height L1 in a radial direction of said convex portion is comprised between 0,3 H and 0,5 H.

3. A tire according to claim 1 or 2, wherein the radius of curvature of said convex portion is substantially infinite.

4. A tire according to any one of preceding claims, wherein said convex portion is adjacent a concave portion placed axially inward with a radius of curvature between 0,2 H and 0,3 H.

5. A tire according to any one of preceding claims, being adapted for continued mobility in a substantially deflated condition.

6. A tire according to any one of preceding claims, further comprising a runflat insert provided in the axially inner portion of the sidewall.

7. A tire according to any one of preceding claims, wherein said bead further comprises an anchoring zone for anchoring said carcass in said bead, and wherein said carcass structure comprises at least one circumferential alignment of cords in said anchoring zone of the bead which progressively divides in the sidewall portion in at least two circumferential alignments of cords.

8. A tire according to claim 7, wherein a runflat insert is disposed between said two carcass circumferential cord alignments and wherein said runflat insert is in direct contact with the cords of said two circumferential alignments.

9. A tire according to claim 7 or 8, wherein said carcass structure comprises only one circumferential alignment in the summit portion of the tire.

10. A tire according to any one of preceding claims, wherein the sidewall inner contour further comprises a substantially linear portion.

11.A tire according to any one of preceding claims, wherein said carcass structure in the bead is substantially parallel to said substantially linear portion.

12. A tire according to any one of preceding claims, wherein said bead further comprises an anchoring zone for anchoring said carcass in said bead and wherein said anchoring zone is substantially parallel to the substantially linear portion.

13. A tire according to any one of preceding claims, wherein, radially inwardly from the summit to the bead, the sidewall inner contour comprises a first concave zone with a first radius of curvature, a convex portion with a second radius of curvature, a second concave zone with a third radius of curvature and a substantially linear portion.

14. A tire according to claim 13, wherein said first radius of curvature is between 0,15 H and 0,25 H.

15. A tire according to claim 13 or 14, wherein said third radius of curvature is superior to the first radius of curvature and between 0,2 H and 0,3 H.

16. A tire according to any one of preceding claims, wherein said bead further comprises an anchoring zone for anchoring said carcass in said bead and wherein said anchoring zone is provided with at least one first bead reinforcement, at least partially bordering said carcass structure and a high modulus rubber mix cooperating with said bead reinforcement and with said carcass structure.

17. A tire according to claim 16, wherein said bead reinforcement includes at least one substantially circumferentially oriented cord laterally bordering the carcass structure on at least one side.

18. A tire according to claim 16, wherein said bead reinforcement is substantially parallel to the substantially linear portion.