JP7187882B2 - run flat tires - Google Patents

Description

TECHNICAL FIELD The present invention relates to a run-flat tire capable of improving ride comfort performance during normal running.

2. Description of the Related Art Conventionally, there is known a run-flat tire in which a sidewall portion is provided with a thick reinforcing rubber strip having a crescent-shaped cross section (see Patent Document 1 below). In this type of runflat tire, the flexural rigidity of the sidewall portion is increased by the thick reinforcing rubber strip, so that the sidewall portion can support the gross weight of the vehicle even in the event of a puncture. It is possible to continuously run for several tens of kilometers at a speed of .

Patent No. 3971831

On the other hand, since the run-flat tire has a sidewall portion with high bending rigidity, there is a problem that the ride comfort tends to deteriorate during normal running when the tire is filled with high-pressure air.

SUMMARY OF THE INVENTION The present invention has been devised in view of the actual situation as described above, and its main object is to provide a run-flat tire capable of enhancing ride comfort performance during normal running.

The present invention comprises a carcass extending from a tread portion to a bead core of a bead portion via sidewall portions on both sides, and a side reinforcing rubber having a crescent-shaped cross section and disposed axially inside the carcass of the sidewall portion. A run-flat tire, wherein the tread portion has a main region having a width of 80% of the tread width centered on the tire equator, and the tire thickness of the main region is greater than the maximum tire thickness of the sidewall portion. is also small.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 95% or less of the maximum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 85% or less of the maximum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 75% or less of the maximum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is desirable that the minimum tire thickness of the sidewall portion is 60% or more of the maximum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 70% to 125% of the minimum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 80% to 115% of the minimum tire thickness of the sidewall portion.

In the run-flat tire according to the present invention, it is preferable that the tire thickness of the main region is 85% to 105% of the minimum tire thickness of the sidewall portion.

The inventors found that when the tire runs straight, a large ground contact pressure acts on the main area of the tread portion, which is an area of 80% of the tread width centered on the tire equator. found to have a significant impact on In the present invention, since the tire thickness of the main region is formed to be smaller than the maximum tire thickness of the sidewall portion, the tread portion undergoes moderate vertical deflection during normal running. Therefore, the run-flat tire of the present invention can improve ride comfort during normal running.

BRIEF DESCRIPTION OF THE DRAWINGS It is a tire meridian sectional view which shows one Embodiment of the run-flat tire of this invention.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a tire meridional cross-sectional view including a tire rotation axis (not shown) in a normal state of a run-flat tire (hereinafter sometimes simply referred to as "tire") 1 showing an embodiment of the present invention. In this embodiment, a tire 1 for a passenger car is shown as a preferred aspect. However, the present invention may be employed, for example, as a tire 1 for heavy loads such as trucks and buses.

The "normal condition" is a state in which the tire 1 is mounted on a normal rim (hereinafter sometimes simply referred to as "rim") R, is filled with normal internal pressure, and is unloaded. Hereinafter, unless otherwise specified, the dimensions and the like of each part of the tire 1 are values measured in a normal state.

"Regular rim R" is the rim R defined for each tire by the standard in the standard system including the standard on which the tire 1 is based. ", or "Measuring Rim" for ETRTO.

"Regular internal pressure" is the air pressure specified for each tire by each standard in the standard system including the standard that Tire 1 is based on. LIMITSAT VARIOUSCOLD INFLATION PRESSURES", and "INFLATION PRESSURE" for ETRTO.

As shown in FIG. 1 , the tire 1 of this embodiment includes a carcass 6 , a belt layer 7 and side reinforcing rubbers 9 .

The carcass 6 is composed of at least one, in this embodiment, one carcass ply 6A extending in a toroidal shape. The carcass ply 6A is formed, for example, by covering carcass cords (not shown) arranged at an angle of, for example, 75 to 90° with respect to the tire equator C direction with a topping rubber. The carcass 6 may be composed of, for example, two carcass plies.

The carcass ply 6A of this embodiment includes a main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a folded portion 6b folded back from the axially inner side to the outer side around the bead core 5. Consists of The folded portion 6b of the present embodiment is wound up to a high position so as to terminate between the belt layer 7 and the main body portion 6a. As a result, the rigidity of the carcass 6 can be effectively increased with a small number of plies, which in turn improves steering stability and run-flat running performance.

In this embodiment, a bead apex 8 is arranged between the main body portion 6a and the folded portion 6b. The bead apex 8 of this embodiment extends from the outer surface of the bead core 5 to the outside in the tire radial direction in a tapered shape. The bead apex 8 preferably has a complex elastic modulus E* of, for example, 5 to 20 MPa. Also, the bead apex 8 preferably has a loss tangent tan δ of 0.05 to 0.11, for example. As a result, high bending rigidity of the bead portion 4 is ensured, and stability performance and ride comfort performance during running are maintained in a well-balanced manner. In addition, the bead apex 8 is not limited to such a mode, and may be configured by, for example, two layers of apex portions (not shown) having different complex elastic moduli.

The belt layer 7 is composed of at least two belt plies 7A and 7B arranged outside the carcass 6 in the tire radial direction and inside the tread portion 2. In this embodiment, two belt plies 7A and 7B are arranged inside and outside the tire radial direction. Each belt ply 7A, 7B has highly elastic reinforcing cords, for example made of steel, aramid or rayon, inclined at an angle of 15-40° with respect to the tire equator C. A band layer (not shown) for suppressing lifting of the belt layer 7 may be arranged on the outer side of the belt layer 7 in the tire radial direction.

The side reinforcing rubber 9 of the present embodiment is arranged inside the carcass 6 of the sidewall portion 3 in the axial direction of the tire. In this embodiment, the side reinforcing rubber 9 is formed to have a crescent-shaped cross-section whose thickness gradually decreases from the central portion in the tire radial direction toward the inner end 9i in the tire radial direction and the outer end 9e in the tire radial direction. there is Since the side reinforcing rubber 9 can increase the bending rigidity of the sidewall portion 3, vertical deflection at the time of puncture is restricted, and run-flat running performance is ensured.

The side reinforcing rubber 9 of this embodiment preferably has a complex elastic modulus E* of 11 to 21 MPa. If the complex elastic modulus E* of the side reinforcing rubber 9 is less than 11 MPa, there is a possibility that the bending rigidity of the side reinforcing rubber 9 cannot be sufficiently maintained during run-flat running. Conversely, if the complex elastic modulus E* of the side reinforcing rubber 9 exceeds 21 MPa, the longitudinal deflection of the tire 1 may become excessively large. From this point of view, the complex elastic modulus E* of the side reinforcing rubber 9 is more preferably 14 MPa or more, and more preferably 18 MPa or less.

Further, the side reinforcing rubber 9 preferably has a loss tangent tan δ of 0.03 to 0.05. If the loss tangent tan δ of the side reinforcing rubber 9 is less than 0.03, the energy loss is small, so the impact absorption capacity may be reduced, and the ride comfort may be deteriorated. If the loss tangent tan δ of the side reinforcing rubber 9 exceeds 0.05, the heat generated by the side reinforcing rubber 9 will increase, possibly deteriorating the run-flat running performance. The loss tangent tan δ of the side reinforcing rubber 9 is more preferably 0.035 or more and more preferably 0.045 or less.

In the present specification, "complex elastic modulus E*" and "loss tangent tan δ" are measured using a "viscoelastic spectrometer" manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions according to the provisions of JIS-K6394. This is the value measured by
Initial strain: 10%
Amplitude: ±1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70°C

As the rubber polymer used for the side reinforcing rubber 9, for example, diene rubber, more specifically natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, or a blend of two or more of them. Used.

In this specification, the sidewall portion 3 is defined as an area between the ground contact edge Te and the rim separation point P where the rim R and the tire 1 come into contact with each other on the outermost side in the tire radial direction. be. The sidewall portion 3 may be appropriately provided with marks such as characters and patterns, and a rim protector (not shown) capable of protecting the rim R. Also, the tread portion 2 is defined as a region between the ground edges Te, Te on both sides. The tread portion 2 may be appropriately provided with drainage grooves or the like. The bead portion 4 is defined as a region radially inward of the rim separation point P. As shown in FIG.

The tread portion 2 of the tire 1 includes a main region 2A having a width of 80% of the tread width TW centered on the tire equator C, and a pair of side regions 2B disposed on both sides of the main region 2A in the tire axial direction. there is The main area 2A is an area where a large ground contact pressure acts during straight traveling. The side region 2B is a region on which a relatively small ground pressure acts compared to the main region 2A. It was found that the vertical deflection of the main region 2A greatly contributes to ride comfort performance.

The "tread width TW" is defined as the distance between the contact points Te, Te, which is the outermost contact point in the tire axial direction when the tire 1 in the normal state is applied with a normal load and is grounded on a flat surface with a camber angle of 0 degrees. is the axial distance of the tire.

"Normal load" is the load defined for each tire by each standard in the standard system including the standards on which the tire 1 is based. Maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", "LOAD CAPACITY" for ETRTO.

The tire 1 further includes a tread rubber 2G, a sidewall rubber 3G, a clinch rubber 4G and an inner liner 10. - 特許庁

In this embodiment, the tread rubber 2G is arranged on the outer side of the belt layer 7 in the tire radial direction and forms a tread surface 2a in contact with the road surface. In the present embodiment, the tread rubber 2G extends axially outward of the ground contact edge Te and terminates radially outward of the carcass maximum width position M in the tire radial direction. The carcass maximum width position M is the position where the main body portion 6a of the carcass 6 protrudes most outward in the axial direction of the tire 1 in the normal state.

The complex elastic modulus E* of the tread rubber 2G is preferably 3-7 MPa, for example. The loss tangent tan δ of the tread rubber 2G is preferably 0.10 to 0.15, for example. Such tread rubber 2G enhances ride comfort performance. The tread rubber 2G may be composed of, for example, two layers of rubber members having different complex elastic moduli E*.

In this embodiment, the sidewall rubber 3G is continuous with the tread rubber 2G and extends radially inward and outward on the axially outer side of the carcass 6 to form the outer surface of the sidewall portion 3 .

The complex elastic modulus E* of the sidewall rubber 3G is preferably smaller than the complex elastic modulus E* of the side reinforcing rubber 9 . As a result, while the side reinforcing rubber 9 suppresses the deflection of the sidewall portion 3 during run-flat running, the sidewall rubber 3G is less likely to separate from the carcass 6 even when the sidewall portion 3 is greatly deflected. Flat durability can be improved. The complex elastic modulus E* of the sidewall rubber 3G is preferably 1 to 10 MPa, for example.

The loss tangent tan δ of the sidewall rubber 3G is preferably larger than the loss tangent tan δ of the side reinforcing rubber 9 . Since the sidewall rubber 3G is in contact with the outside air, it can efficiently release the heat generated by running to the outside air, and can improve ride comfort while maintaining high run-flat running performance. The loss tangent tan δ of the sidewall rubber 3G is desirably 0.06 to 0.14, for example.

In the present embodiment, the clinch rubber 4G continues to the sidewall rubber 3G and is arranged outside the folded-back portion 6b of the carcass 6 in the tire axial direction. The clinch rubber 4G constitutes the outer surfaces of the sidewall portion 3 and the bead portion 4, for example. The clinch rubber 4G contacts the rim R when the tire 1 is assembled on the rim R.

The complex elastic modulus E* of the clinch rubber 4G is desirably 3 to 20 MPa in order to prevent damage due to contact with the rim R, for example. Also, the loss tangent tan δ of the clinch rubber 4G is desirably about 0.05 to 0.11, for example.

In this embodiment, the inner liner 10 is arranged in a toroidal shape across the bead portions 4 , 4 so as to form the inner cavity surface 1 b of the tire 1 . The inner liner 10 is made of a rubber material such as, for example, butyl rubber, halogenated butyl rubber and/or brominated butyl rubber, and is air impermeable.

In order to suppress the occurrence of cracks in the inner liner 10 and improve the run-flat running performance, the complex elastic modulus of the inner liner 10 is desirably 2 to 5 MPa, for example. The loss tangent tan δ of the inner liner 10 is preferably 0.10 to 0.15, for example.

The tire thickness ta of the main region 2A is formed smaller than the maximum tire thickness tx of the sidewall portion 3 . As a result, the tread portion 2 causes the tire 1 to have an appropriate vertical deflection during normal running, thereby improving ride comfort. As used herein, each tire thickness is the distance between the outer surface 1a and the bore surface 1b of the tire 1 in the direction normal to the bore surface 1b of the tire 1 in the tire meridian section. When the outer surface 1a or the inner cavity surface 1b is provided with an inward concave portion such as a groove or serration, each tire thickness is measured on a smooth virtual surface obtained by filling the concave portion. is. It is desirable that the tire thickness ta over the entire range of the main region 2A is smaller than the maximum tire thickness tx of the sidewall portion 3 .

In this embodiment, the maximum tire thickness tx is a region located inside the carcass maximum width position M in the tire radial direction, where the bead apex 8, the sidewall rubber 3G, the side reinforcing rubber 9 and the inner liner 10 are formed. It is in. Note that the region where the maximum tire thickness tx is formed is not limited to such an aspect, and for example, some of the bead apex 8, the sidewall rubber 3G, the side reinforcing rubber 9 and the inner liner 10 may be formed. Also, the region where the maximum tire thickness tx is formed may be a region where other rubber members are formed in addition to these.

In the maximum tire thickness tx of the present embodiment, when the thickness t1 of the sidewall rubber 3G, the thickness t2 of the bead apex 8, and the thickness t3 of the side reinforcing rubber 9, the following formula (1) is satisfied. It is desirable to
t3>t1>t2 (1)

The tire thickness ta of the main region 2A is desirably 95% or less, more desirably 85% or less, and even more desirably 75% or less of the maximum tire thickness tx. If the tire thickness ta of the main region 2A is excessively smaller than the maximum tire thickness tx, the durability performance of the tread portion 2 may deteriorate. Therefore, the tire thickness ta of the main region 2A is desirably 50% or more, more desirably 55% or more, of the maximum tire thickness tx.

When the tire 1 runs straight, a relatively small contact pressure is generated in the vicinity of the axially outer end 2e of the main region 2A from the contact end Te. Therefore, in order to improve ride comfort performance, it is desirable to minimize the tire thickness ta at the position of the outer end 2e in the main region 2A. In order to effectively exhibit the action, the tire thickness ta of the main region 2A preferably increases from the outer end 2e of the main region 2A toward the tire equator C, and gradually increases from the outer end 2e to the tire equator C. It is even more desirable to

When the minimum tire thickness tn of the sidewall portion 3 is reduced, the vertical deflection of the tire 1 is increased to improve ride comfort. On the other hand, if the minimum tire thickness tn is excessively small, run-flat driving performance is reduced. Therefore, by reducing the difference between the tire thickness ta and the minimum tire thickness tn, ride comfort performance and run-flat running performance can be enhanced in a well-balanced manner. Through various experiments conducted by the inventors, it was found that it is preferable to define the ratio between the tire thickness ta and the minimum tire thickness tn as follows. The tire thickness ta is desirably 70% or more, more desirably 80% or more, and even more desirably 85% or more of the minimum tire thickness tn. The tire thickness ta is preferably 125% or less, more preferably 115% or less, and even more preferably 105% or less of the minimum tire thickness tn.

In this embodiment, the minimum tire thickness tn is a region radially outward of the carcass maximum width position M, where the sidewall rubber 3G, the side reinforcing rubber 9 and the inner liner 10 are arranged. The rubber thickness t4 of the sidewall rubber 3G and the rubber thickness t5 of the side reinforcing rubber 9 at the minimum tire thickness tn are desirably as shown in the following formula (2). Note that the region having the minimum tire thickness tn is not limited to such an aspect, and for example, a region formed by some of the sidewall rubber 3G, the side reinforcing rubber 9 and the inner liner 10 can be used. good. Also, the region may be a region formed by further including another rubber member.
t5>t4 (2)

If the difference between the minimum tire thickness tn and the maximum tire thickness tx becomes large, the portion having the minimum tire thickness tn is likely to be deformed during rim assembly, and there is a risk that unevenness in the tire axial direction may occur in the tire circumferential direction. Moreover, such a tire 1 may be greatly distorted at the position of the minimum tire thickness tn, and the run-flat running performance may not be maintained. Therefore, the minimum tire thickness tn is desirably 60% or more, more desirably 65% or more, and even more desirably 70% or more of the maximum tire thickness tx. If the minimum tire thickness tn is too large, the flexural rigidity becomes excessively large, and there is a risk that the ride comfort during normal running will deteriorate. Therefore, the minimum tire thickness tn is desirably 90% or less, more desirably 85% or less, and even more desirably 80% or less of the maximum tire thickness tx.

The tire thickness tb of the side region 2B is not particularly limited. is desirable.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the specific embodiments described above and can be modified in various ways and implemented.

Based on the basic structure shown in FIG. 1 and the specifications shown in Table 1, run-flat tires of size 225/45RF18 were prototyped and tested for the following performance. Main common specifications are as follows.
Each rubber is molded so that its complex elastic modulus E* and loss tangent tan .delta. The positions of the minimum tire thickness and the maximum tire thickness are the same in each example and each comparative example.

<Run-flat driving performance>
Each test tire was mounted on a regular rim, the valve core was removed, the internal pressure was set to 0 kPa, the tire was run on a drum tester at a speed of 80 km/h, and the distance traveled until the tire was destroyed was measured. The results are shown as indices with the value of Comparative Example 1 being 100, and the larger the value, the better.

<Riding comfort performance>
A static tester was used to measure the longitudinal spring constant of each sample tire. The vertical spring constant is the ratio of vertical load/vertical deflection under the following conditions. The results are expressed as indices with the value of Comparative Example 1 being 100. The smaller the numerical value, the better the ride comfort performance.
Internal pressure: 240kPa
Load: Regular load x 80%

<Uniformity>
Each test tire was mounted on a rim, and the unevenness (difference in the height of protrusion in the axial direction) was measured at multiple points on the tire circumference at a position where the height of the sidewall portion in the tire radial direction was constant. . In addition, irregularities such as marks and designs are excluded. The results are expressed as real numbers, and the smaller the number, the better.
Test results are shown in Table 1.

As a result of the test, it was confirmed that the tire of the example was superior to the tire of the comparative example in ride comfort performance.

REFERENCE SIGNS LIST 1 run-flat tire 2 tread portion 2A main region 3 sidewall portion 6 carcass 9 side reinforcing rubber C tire equator

Claims (5)

A run-flat tire comprising a carcass extending from a tread portion to a bead core of a bead portion via sidewall portions on both sides, and a side reinforcing rubber having a crescent-shaped cross section and arranged axially inward of the carcass of the sidewall portion. There is
The tread portion has a main region having a width of 80% of the tread width centered on the tire equator,
The tire thickness of the main region is smaller than the maximum tire thickness of the sidewall portion,
including a sidewall rubber forming the outer surface of the sidewall portion;
A rubber thickness t5 of the side reinforcing rubber at the minimum tire thickness of the sidewall portion is greater than a rubber thickness t4 of the sidewall rubber at the minimum tire thickness,
The tire thickness of the main region is 85% or less of the maximum tire thickness of the sidewall portion.
run-flat tires. The maximum tire thickness of the sidewall portion is located radially inward of the carcass maximum width position M,
2. The run-flat tire according to claim 1, wherein a rubber thickness t3 of said side reinforcing rubber at the maximum tire thickness of said sidewall portion is greater than a rubber thickness t1 of said sidewall rubber at said maximum tire thickness. . The run-flat tire according to claim 1 or 2, wherein the tire thickness of the main region is 75% or less of the maximum tire thickness of the sidewall portion . A run-flat tire comprising a carcass extending from a tread portion to a bead core of a bead portion via sidewall portions on both sides, and a side reinforcing rubber having a crescent-shaped cross section and arranged axially inward of the carcass of the sidewall portion. There is
The tread portion has a main region having a width of 80% of the tread width centered on the tire equator,
The tire thickness of the main region is smaller than the maximum tire thickness of the sidewall portion,
including a sidewall rubber forming the outer surface of the sidewall portion;
A rubber thickness t5 of the side reinforcing rubber at the minimum tire thickness of the sidewall portion is greater than a rubber thickness t4 of the sidewall rubber at the minimum tire thickness,
The minimum tire thickness of the sidewall portion is 60% or more of the maximum tire thickness of the sidewall portion,
The tire thickness of the main region is 80% to 115% of the minimum tire thickness of the sidewall portion.
run-flat tires. The runflat tire according to claim 4 , wherein the tire thickness of the main region is 85% to 105% of the minimum tire thickness of the sidewall portion .

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