WO2009020460A1

WO2009020460A1 - Run-flat tire with multi-layer sidewall

Info

Publication number: WO2009020460A1
Application number: PCT/US2007/075340
Authority: WO
Inventors: Robert C. Lawson
Original assignee: Societe De Technologie Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2007-08-07
Filing date: 2007-08-07
Publication date: 2009-02-12

Abstract

A run-flat tire comprises a tread portion for contacting the ground during tire operation, a bead portion for mounting the tire on a rim, a sidewall portion, and the sidewall portion comprises at least three sidewall reinforcements. The first sidewall reinforcement has a thickness Tl and is in contact on its axially outer surface with a second sidewall reinforcement; the second sidewall reinforcement has a thickness T2 and is located axially outward of the first sidewall reinforcement and is in contact on its axially outer surface with a third sidewall reinforcement; and the third sidewall reinforcement has a thickness T3 and is located axially outward of the second sidewall reinforcement. The thickness T3 is greater than or equal to the thickness T2 and the thickness T2 is greater than or equal to the thickness Tl.

Description

RUN-FLAT TIRE WITH MULTI-LAYERED SIDEWALL

BACKGROUND

[0001] Numerous extended mobility solutions exist in the market, each having their own unique advantages and disadvantages. Self-supporting tires are those that, following a partial or total loss of inflation pressure, support most of the load through a sidewall construction having additional reinforcement compared to a conventional tire. This type of run-flat tire has the advantage of reduced complexity when compared to other run-flat solutions. However, they also tend to have the disadvantages of increased mass, rolling resistance and inflated stiffness due to the additional sidewall material required for the tire to operate a sufficient distance under run-flat conditions. There is a need for a run-flat tire construction that reduces the compromise between run-flat endurance and other tire performance attributes.

SUMMARY

[0002] A run-flat tire with a multi-layer sidewall construction obtains an improved set of performances through a more efficient distribution of material thicknesses and material properties throughout the sidewall. This construction enables improved run-flat endurance with the same amount of sidewall material or mass, or alternatively, an acceptable run-flat endurance with significantly less sidewall material or mass.

[0003] A run-flat tire comprises a tread portion for contacting the ground during tire operation, a bead portion for mounting the tire on a rim, a sidewall portion, the sidewall portion connecting the tread portion to a bead portion, a carcass extending from the tread portion through the sidewall portion and extending into the bead portion, the carcass having at least one layer of reinforcement and being anchored in the bead regions, a tread reinforcement interposed between the carcass and the tread, and the sidewall comprising at least three sidewall reinforcements. Each of the sidewall reinforcements has a thickness measured in the sidewall portion at a location corresponding to a maximum axial width of the tire. The first sidewall reinforcement has a thickness Tl and is in contact on its axially outer surface with a second sidewall reinforcement; the second sidewall reinforcement has a thickness T2 and is located axially outward of the first sidewall reinforcement and is in contact on its axially outer surface with a third sidewall reinforcement; and the third sidewall reinforcement has a thickness T3 and is located axially outward of the second sidewall reinforcement. The thickness T3 is greater than or equal to the thickness T2 and the thickness T2 is greater than or equal to the thickness Tl .

[0004] In one example of a run-flat tire with the multi-layer sidewall reinforcement, the thickness Tl of the first sidewall reinforcement is between about 10 and 20 percent of the total sidewall reinforcement thickness TT; the thickness T2 of the second sidewall reinforcement is between about 15 and 25 percent of the total sidewall reinforcement thickness TT, and the thickness T3 of the third sidewall reinforcement is between about 55 and 75 percent of the total sidewall reinforcement thickness TT.

[0005] In another example of a run-flat tire with multi-layer sidewall reinforcement, the sum of the thickness Tl of the first sidewall reinforcement and the thickness T2 of the second sidewall reinforcement is less than or equal to 35 percent of a total sidewall reinforcement thickness TT.

[0006] The run-flat tire with multi-layer sidewall reinforcement may be further optimized when a tensile modulus of the first sidewall reinforcement is less than a tensile modulus of the second sidewall reinforcement and the tensile modulus of the second sidewall reinforcement is less than a tensile modulus of the third sidewall reinforcement. [0007] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is a meridian plane cross-section view of a run-flat tire 100 corresponding to the prior art and having a single layer sidewall reinforcement.

[0009] Fig. 2 is a meridian plane cross-section view of an improved run-flat tire 200 having a multi-layer sidewall reinforcement.

[0010] Fig. 3A is an enlarged meridian plane cross-section view of a run-flat tire 200 illustrating the three sidewall reinforcements.

[0011] Fig. 3B is a further enlarged meridian plane cross-section view of a run-flat tire 200 illustrating the relative thicknesses of the each of the three sidewall reinforcements.

[0012] Fig. 4 is a graphical representation of the estimated stresses in the sidewall of a run- flat tire 100 having a single-layer sidewall construction.

[0013] Fig. 5 is a graphical representation of the estimated stresses in the sidewall of a tire 200 having a multi-layer sidewall construction.

DETAILED DESCRIPTION

[0014] Throughout this disclosure, and in the several examples, common nomenclature and numeric identifiers will be used to identify similar or like components. The term "axial" means in a direction generally parallel to the axis of rotation of the tire. The term "radial" means in a direction generally parallel to a meridian plane and passing through the axis of rotation of the tire. The terms "outward" and "inward" mean in a direction away from or towards, respectively, the inner surface of the tire.

[0015] Figure 1 illustrates an example of a pneumatic run-flat tire 100 having a construction to allow continued mobility after loss of normal inflation pressure. The tire 100 has a crown portion with a tread 1 10 for contacting the ground during operation, a bead portion to allow the tire to be mounted on a wheel, and a sidewall portion connecting the tread to the bead region. Figure 1 shows only the left half of the tire relative to an equatorial plane. The crown portion contains reinforcements. In the example of tire 100, there are three layers of crown reinforcements or belts. The first two belts 11 1 and 1 12 comprise cord reinforced layers posed at mutually oblique angles to the circumferential direction. The third belt 1 13 is a layer of generally circumferentially oriented cords, commonly referred to as zero-degree, reinforcements. Other crown reinforcement constructions are possible, such as reinforced bands or composite shear bands. The bead portion provides anchoring of the tire to a rim for mounting on the vehicle. The bead portion contains a bead reinforcement 122, shown in this example as a winding of steel wires. A sidewall portion extends from the tread portion to the bead portion. The sidewall is reinforced with a carcass layer 121 extending from the tread portion to the bead portion. In the illustrative example of tire 100, the carcass layer 121 is a single layer of reinforcements, although multiple carcass layers are among the design alternatives. The carcass layer 121 wraps around the bead reinforcement 122, and then extends radially outward to terminate in the sidewall portion. Alternative bead constructions are known where the carcass layer is vertically anchored in one or more circumferential windings of bead reinforcement, thereby eliminating the turned-up portion. A rubbery filler material 123, extending radially outward from the bead reinforcement 122, is interposed between the main and turned-up portion of the carcass layer 121. Finally, a protector 124 is wrapped around the outer part of the bead portion. An innerliner 125, usually a high butyl content rubber composition aids in air retention during normal operation of the tire. The innerliner 125 may be eliminated, for example by the use of impermeable barrier coatings or the like. The particular construction of tire 100 has a thin, constant thickness backer product 126 having a low tensile modulus of elasticity and posed between the innerliner 125 and the sidewall reinforcement 130. A rubber composition having a tensile modulus on the order of 2.0 MPa is suitable. However, this product is optional. The sidewall portion is protected by a rubber layer 120 posed axially outward of the carcass layer 121.

[0016] The foregoing paragraph provides an illustrative example of the construction of a pneumatic tire. To facilitate continued mobility after a loss of normal operating inflation pressure, the run-flat tire 100 further comprises a thick sidewall reinforcement 130. The reinforcement 130 provides increased rigidity to the sidewall portion relative to a conventional, non run-flat tire. As long as the tire 100 is inflated to its proper pressure, then the load of the vehicle is carried by tension in the carcass layer 121. However, after a partial or complete loss of inflation pressure, that tension is significantly reduced. In that event, the reinforcement 130 provides a structural load support capability for extended mobility. The actual distance that the tire can continue to run is a function of the stress and strain states and the heat build up in the reinforcement 130.

[0017] Figure 2 depicts an example of an improved run-flat tire 200. Tire 200 has a construction in the crown portion and in the bead portion that is similar to the previously described tire 100. However, in the sidewall portion, the single-layer sidewall reinforcement 130 is now replaced by a multi-layer construction having a first reinforcement 231 , a second sidewall reinforcement 232, and a third sidewall reinforcement 233, all of which extend radially in the sidewall. The first sidewall reinforcement 231 is the innermost member. In the example shown for tire 200, the reinforcement 231 is in contact with the innerliner 225 and with the second sidewall reinforcement 232. The second sidewall reinforcement 232 extends axially outward from the first reinforcement 231 and is in contact with the third sidewall reinforcement 233. The third sidewall reinforcement 233 extends axially outward from the second reinforcement 232 and is in contact with the carcass layer 221. Optionally, the construction of tire 200 also has a thin, constant thickness backer product 226 having a low tensile modulus of elasticity and posed between the innerliner 225 and the first sidewall reinforcement 231. A rubber composition having a tensile modulus on the order of 2.0 MPa is suitable.

[0018] Figure 3A provides an enlarged view of the sidewall portion of tire 200 to describe better the geometry of the three sidewall reinforcements. The thickness of the sidewall reinforcements is measured at or near the equator E of the tire. The equator E is the axially outermost extent of the mounted and inflated tire as depicted in Fig. 3 A. The thicknesses of the sidewall reinforcements are measured along a line parallel to the axis of the tire and passing through the equator E of the tire. Now referring to the detail view do Fig. 3B, the first sidewall reinforcement 231 has a thickness Tl , the second sidewall reinforcement 232 has a thickness T2, and the third sidewall reinforcement has a thickness T3. The total sidewall reinforcement thickness TT is the sum of three sidewall reinforcements; Tl , T2, and T3.

[0019] A mathematical model was constructed to predict the mechanical behavior of the sidewall portion under conditions simulating a tire operating under a vertical load, as would be imposed by a vehicle, and without inflation pressure. The model predicts the stress and strain in each of the sidewall components. These simulations were then used to determine optimized thicknesses and material properties for the sidewall reinforcements. From these results, it was determined that the multi-layer arrangement of the tire 200 provided superior results over the single-layer arrangement of the tire 100. The three sidewall reinforcements are distinguished from each other by their respective material properties and their physical dimensions. It was determined that the thicknesses Tl , T2, and T3 should increase in the outward direction. Therefore, the thickness T3 of reinforcement 233 is greater than or equal to the thickness T2 of reinforcement 232, and the thickness T2 of reinforcement 232 is greater than or equal to the thickness Tl of reinforcement 231.

[0020] The preferred ranges of the sidewall thickness will vary according to the physical dimensions of the tire. For, example, one skilled in the art of run-flat tire design knows that as the radial height of the sidewall portion increases, the total thickness of the sidewall reinforcement must increase. Thus, to provide design information that is not limited to the specific examples disclosed herein, the relative thicknesses of the sidewall reinforcements are expressed herein as percentages of the thickness of the particular reinforcement to the total sidewall reinforcement thickness TT. Therefore, the thickness Tl of reinforcement 231 should be in the range of about 10 to 20 percent of the total sidewall reinforcement thickness TT. The thickness T2 of reinforcement 232 should be in the range of about 15 to 25 percent of the total sidewall reinforcement thickness TT. Finally, the thickness T3 of reinforcement 233 should be in the range of about 55 to 75 percent of the total sidewall reinforcement thickness TT. The particular choice of thickness within each of the suggested ranges must still respect the relation that the thickness T3 of reinforcement 233 is greater than or equal to the thickness T2 of reinforcement 232, and the thickness T2 of reinforcement 232 is greater than or equal to the thickness Tl of reinforcement 231. An advantageous arrangement of the sidewall reinforcements is obtained when the third reinforcement 233 is much thicker than combined thickness of the first reinforcement 231 and the second reinforcement 232. This is satisfied when the sum of the thicknesses Tl and T2 is less than or equal to the 35 percent of the total sidewall reinforcement thickness TT.

[0021] Figure 3 depicts a more detailed view of the sidewall portion of the tire 200 for a particular arrangement of the radial extent and thickness variation of the three reinforcements. The first and second reinforcements have a relatively uniform thickness with little variation, whereas the third reinforcement has a distinctly crescent shape. One skilled in the art could readily adapt the overall geometry of the reinforcements using the parametric relationships described above.

[0022] The hardness or stiffness of the materials used for the sidewall reinforcements is specified by the tensile modulus of elasticity, which is the secant modulus determined from the stress developed in a tensile test sample at 10 percent strain and at a temperature of 25 degrees Celsius. It was determined from the model that the modulus of elasticity of the rubber compositions chosen for the three reinforcements should be relatively soft for the first reinforcement 231, and then become progressively harder for the second reinforcement 232 and third reinforcement 233. The first reinforcement 231 has a modulus of elasticity in the range of about 2.5 MPa to 3.5 MPa; the second reinforcement 232 has a modulus of elasticity in the range of about 5.0 MPa to 7.0 MPa, and the third reinforcement 233 has a modulus of elasticity in the range of about 9 MPa to 13 MPa. A preferred arrangement would have the modulus of each of the three layers progress in the ratio of 1 :2:4, meaning that the second reinforcement 232 is twice as stiff as the first reinforcement 231 and the third reinforcement 233 is twice as stiff as the second reinforcement 232. The hysteretic properties of the materials should be chosen to minimize heat build-up in the tire.

[0023] Example: Prototype tires in the size 225/50 Rl 7 were constructed to compare the run- flat performance of the reference tire construction with a single sidewall reinforcement, similar to the tire 100 and the improved construction with three sidewall reinforcements, similar to the tire 200. The constructions and geometries of the prototype tires were identical, except for the number and arrangement of sidewall reinforcements. The reference numerals used to describe the prototype tires correspond to the reference tire 100 of Fig. 1 and the improved tire 200 of Fig. 2. In the reference tire, a single sidewall reinforcement 130 had a thickness Tl (and by default TT) of 8.20 mm. The modulus of elasticity of the reinforcement was 6.2 MPa. The improved tire had a first reinforcement 231 with a thickness of 1.00 mm and a modulus of 3.1 MPa, a second reinforcement 232 with a thickness of 1.24 mm and a modulus of 6.2 MPa, and a third reinforcement 233 with a thickness of 5.96 mm and a modulus of 1 1.5 MPa. This arrangement yields thickness ratios of 12 percent, 15 percent, and 73 percent, respectively, and a modulus ratio very close to 1 :2:4. Both the reference and improved tires used a backer, 126 and 226, having a tensile modulus of 1.9 MPa.

[0024] The prototype tires were then subjected to a test procedure designed to assess run-flat capability of the two constructions. In this test, the tires were mounted and inflated to a pressure of 250 kPa, and then stored in an environment at 38 degrees Celsius for three hours. The tires were then deflated, mounted on a 1.7 m diameter test roadwheel, and loaded to 65% of the rated European Tire & Rim Technical Organization (ETRTO) load index for the 225/50 R 17 tire size. For the 225/50 Rl 7 tire size, the test load is calculated as 436 kg. The tire test was conducted a speed of 80 kph and an environmental temperature of 38 degrees Celsius. The loaded radius of the tire, measured as the distance from the roadwheel surface to the axis of rotation of the tire was monitored throughout the test. The test was stopped when the loaded radius decreased by at least 20% from the value measured at the start of the test. The reference tires achieved a run-flat distance of 173 km, whereas the improved tires achieved a result of 321 km, an 85 percent increase in run-flat durability.

[0025] The aforementioned mathematical model provides the details to explain this unexpectedly good performance. Figure 4 presents the graphical output from the model for the tire 100 having a single sidewall reinforcement. The horizontal axis shows the axial postion through the thickness of the sidewall and shows all sidewall products. The notation "inner" and "outer" denote, the inside surface and outside surface of the tire, respectively.

The vertical axis plots the maximum normal stress, which is the stress in the direction following the path of the carcass reinforcement 121 or 221. A positive value indicates a tensile stress, and a negative value indicates a compressive stress. In general, the portions of the sidewall towards the inside surface of the tire are in a state of compressive stress, and the portions of the sidewall towards the outside surface of the tire are in a state of tensile stress. For the reference tire, one will immediately notice that the magnitude of the normal stress becomes sharply compressive to a value of about -3.4 MPa at the boundary between the sidewall reinforcement 130 and the backer 126. Figure 5 provides the comparison to the improved tire 200 having a multi-layer sidewall construction. The normal stress at the boundary between the first sidewall reinforcement 231 and the backer 226 was reduced to about -1.4 MPa. Furthermore, the maximum compressive stress in the sidewall portion, now occurring at the interface between the second and third reinforcements, is reduced to about - 1.9 MPa. Therefore, the improved tire gives the result where the maximum compressive stress was reduced from -3.4 MPa to -1.9 MPa, a 45 percent reduction; and the stress magnitude throughout each of the sidewall reinforcements is more uniformly distributed. Thus, compared to a single-layer tire, the multi-layer tire makes more efficient use of the sidewall reinforcements.

[0026] While the present subject matter has been described in detail with respect to specific examples showing specific arrangements of the tire components, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and this disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.

Claims

1. A run-flat tire comprising a tread portion for contacting the ground during tire operation, a bead portion for mounting the tire on a rim, a sidewall portion, the sidewall portion connecting the tread portion to a bead portion, a carcass extending from the tread portion through the sidewall portion and extending into the bead portion, the carcass having at least one layer of reinforcement and being anchored in the bead regions, a tread reinforcement interposed between the carcass and the tread, and the sidewall comprising at least three sidewall reinforcements and each of the sidewall reinforcements has a thickness measured in the sidewall portion at a location corresponding to a maximum axial width of the tire; wherein a first sidewall reinforcement having a thickness Tl is in contact on its axially outer surface with a second sidewall reinforcement, the second sidewall reinforcement having a thickness T2 is located axially outward of the first sidewall reinforcement and in contact on its axially outer surface with a third sidewall reinforcement, and the third sidewall reinforcement having a thickness T3 located axially outward of the second sidewall reinforcement, and the thickness T3 is greater than or equal to the thickness T2 and the thickness T2 is greater than or equal to the thickness Tl .

2. The tire according to claim 1 , wherein the thickness Tl of the first sidewall reinforcement is between about 10 and 20 percent of the total sidewall reinforcement thickness TT.

3. The tire according to claim 1 , wherein the thickness T2 of the second sidewall reinforcement is between about 15 and 25 percent of the total sidewall reinforcement thickness TT.

4. The tire according to claim 1, wherein the thickness T3 of the third sidewall reinforcement is between about 55 and 75 percent of the total sidewall reinforcement thickness TT.

5. The tire according to claim 1, wherein a sum of the thickness Tl of the first sidewall reinforcement and the thickness T2 of the second sidewall reinforcement is less than or equal to 35 percent of the total sidewall reinforcement thickness TT.

6. The tire according to claim 1 , wherein a tensile modulus of the first sidewall reinforcement is less than a tensile modulus of the second sidewall reinforcement and the tensile modulus of the second sidewall reinforcement is less than a tensile modulus of the third sidewall reinforcement.

7. The tire according to claim 1 , wherein the first sidewall reinforcement has a tensile modulus between about 2.5 MPa and 3.5 MPa.

8. The tire according to claim 1 , wherein the second sidewall reinforcement has a tensile modulus between about 5.0 MPa and 7.0 MPa.

9. The tire according to claim 1 , wherein the third sidewall reinforcement has a tensile modulus between about 9 MPa and 13 MPa.