JP2003011623A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering stability, comfortableness, and durability, while retaining superior low rolling resistance. SOLUTION: A short fiber reinforced rubber layer extending along the outside surface of bead apex rubber, passing the outer end of the bead apex rubber, and extending along the outside of a ply body part is disposed in a sidewall part. The short fiber reinforced rubber layer is formed of multiple rubber regions divided into the inside/outside in the radial direction and having different mixing rates of the short fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire having improved rolling resistance by reducing carcass turn-up height and bead apex height, which is a pneumatic tire capable of improving steering stability, riding comfort and durability. Regarding

[0002]

2. Description of the Related Art For example, as shown in FIG. 5, it is possible to suppress the height of a folded portion b1 of a carcass folded around a bead core a and a bead apex rubber c rising radially outward from the bead core a. It has been conventionally known that it is effective for reducing rolling resistance.

However, when such a structure is adopted, the tire rigidity is reduced, and the steering stability is particularly deteriorated. When such a sidewall portion of a tire is reinforced with a steel cord reinforcing layer, there is a problem that the riding comfort is deteriorated and the rolling resistance reducing effect is impaired.

Therefore, the present applicant has filed Japanese Patent Application Laid-Open No. 8-1751.
In JP-A-19, it is proposed to use a short fiber reinforced rubber layer in place of the cord reinforcement layer. Such a short fiber reinforced rubber layer can appropriately increase the bending rigidity of the tire, and can improve both steering stability and riding comfort while maintaining excellent low rolling resistance.

[0005]

However, in the tire having such a structure, since the deformation is large and the stress is concentrated at the bead portion, the short fibers contained therein cause damage to the short fiber reinforced rubber layer g. It tends to occur and tends to impair durability.

Therefore, the present invention is based on the fact that the short fiber reinforced rubber layer is formed by a plurality of rubber regions divided inward and outward in the radial direction and having different blending amounts of short fibers.
To provide a pneumatic tire that can suppress damage to the short fiber reinforced rubber layer in the bead part, maintain excellent low rolling resistance, and improve not only steering stability and riding comfort but also durability Has an aim.

[0007]

In order to achieve the above-mentioned object, the invention of claim 1 of the present application is such that the ply main body portion extending from the tread portion to the side wall portion to the bead core of the bead portion is provided around the bead core. Folding ply A carcass composed of one carcass ply integrally provided with a folding back portion, and a bead apex rubber that extends from the bead core toward the tire radial outer side through a space between the ply body portion and the ply folding portion. The carcass ply has a height h from a bead base line at a radially outer end of the ply turnback portion.
1 is 0.12 to 0.15 times the tire cross-section height H, and the bead apex rubber has a height h2 from the bead base line at the radially outer end thereof that is 0.20 to the tire cross-section height H. 0.25 times, and in addition to arranging a short fiber reinforced rubber layer along the outer surface of the bead apex rubber and along the outer surface of the ply body portion along the outer surface of the bead apex rubber in the sidewall portion,
The short fiber reinforced rubber layer is characterized in that it is formed by connecting a plurality of rubber regions that are divided inward and outward in the radial direction and have different blending amounts of short fibers.

In the invention of claim 2, the radial inner end of the short fiber reinforced rubber layer starts from a position where the inner end in the radial direction crosses the outer end of the ply turn-up portion in the outer radial direction, and the outer end in the radial direction is It is characterized in that it is located in the vicinity of the maximum tire width point and the outer end of the radially innermost rubber region is located radially outside of the outer end of the bead apex rubber.

Further, the invention of claim 3 is characterized in that the blending amount of the short fibers in the rubber region on the outer side in the radial direction is larger than the blending amount of the short fibers in the rubber region adjacent on the inner side in the radial direction.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below.
This will be described together with the illustrated example. FIG. 1 shows a meridional sectional view illustrating a case where the pneumatic tire 1 of the present invention is a radial tire for passenger cars. FIG. 2 is an enlarged sectional view showing the bead portion.

As shown in FIG. 1, the pneumatic tire 1 is
Bead part 4 from tread part 2 to sidewall part 3
A carcass 6 reaching the bead core 5, and a belt layer 7 arranged inside the tread portion 2 and outside the carcass 6,
A bead apex rubber 8 extends from the bead core 5 to the outer side in the tire radial direction.

The belt layer 7 includes two or more, in this example, two belt plies 7 in which high-elasticity belt cords are arranged at an angle of, for example, 10 to 35 ° with respect to the tire circumferential direction.
It is composed of A and 7B. Belt ply 7A, 7B
The belt cords are stacked so that the plies intersect with each other with different inclinations, and the triangle structure of the cords enhances the belt rigidity and reinforces substantially the entire width of the tread portion 2 with a hoop effect. As the belt cord, a steel cord or a high modulus organic fiber cord comparable to the steel cord, such as an aromatic polyamide fiber, is preferably used.

In this example, the band layer 9 is provided outside the belt layer 7 for the purpose of enhancing the restraining force on the belt layer 7 and improving the high-speed durability.
The band layer 9 has a band cord that is spirally wound at an angle of, for example, 5 degrees or less with respect to the tire circumferential direction, and extends to cover at least the tire axial direction outer end portion of the belt layer 7.

The carcass 6 comprises a carcass ply 6A having carcass cords arranged at an angle of 75 to 90 degrees with respect to the tire circumferential direction.
A is a ply body portion 6a extending between the bead cores 5 and 5.
The ply turn-back portions 6b that turn back from the inside to the outside around the bead core 5 are integrally provided at both ends of the. As a carcass cord, nylon, rayon, polyester,
In addition to organic fiber cords such as aromatic polyamide, steel cords can be appropriately used, but organic fiber cords are preferable from the viewpoint of weight reduction.

The bead apex rubber 8 is made of a relatively hard rubber having a rubber hardness (durometer A hardness) of about 65 to 95 degrees, and passes through between the ply body 6a and the ply folded portion 6b. The taper extends outward in the tire radial direction.

What is important here is that, in the tire 1 of the present embodiment, in order to reduce rolling resistance, the carcass 6 has a radial outer end 6e (sometimes referred to as a turn-back end 6e) of the ply turn-back portion 6b. The height h1 from the bead base line BL (may be referred to as the turn-up height h1) is 0.12 of the tire cross-section height H.
The bead apex rubber 8 is regulated in the range of 0.15 times and the outer end 8 thereof is used.
The height e of the e (sometimes called the apex end 8e) from the bead base line BL (the apex height h2
May be said) is 0.20 of the tire cross-sectional height H
It is to regulate in the range of 0.25 times.

In this way, by controlling the apex height h2 to be small, not only the weight is reduced, but also the energy loss due to the heat generation of the bead apex rubber 8 is reduced. Further, since the contour shape of the ply body portion 6a is linear from the bead portion 4 to the sidewall portion 3, the carcass cord path is shortened, and uniform and sufficient tension is applied to the entire carcass cord. Bending is also suppressed overall. These synergistic effects reduce rolling resistance. The folding height h1 is also the apex height h.
Since it is smaller than 2, it is possible to further reduce the weight while suppressing damage at the folded end 6e, and it is possible to further enhance the effect of reducing the rolling resistance.

However, in such a structure, on the other hand, the tire rigidity is reduced and the steering stability tends to be lowered.

Therefore, in the tire 1 of the present embodiment, in order to improve the steering stability and the riding comfort and to secure sufficient durability while maintaining the above-mentioned excellent low rolling resistance, The short fiber reinforced rubber layer 1 is provided on the sidewall portion 3.
0 is arranged, and the short fiber reinforced rubber layer 10 is formed by a plurality of rubber regions 11 divided inward and outward in the radial direction.

More specifically, the short fiber reinforced rubber layer 10 is
As shown in FIG. 2, it is a thin rubber layer having a substantially constant rubber thickness t, which extends radially outward along the tire axial outer surface of the bead apex rubber 8 and also has the apex end 8e. After passing, the ply body 6a extends along the outer surface in the tire axial direction.

At this time, the short fiber reinforced rubber layer 10 is
The radial inner end EL is preferably positioned radially outward beyond the folding end 6e so as not to overlap with the ply folded-back portion 6b, and further, the interval between the inner end EL and the folding-back end 6e. It is preferable that j is controlled to be as small as possible within the range of 0 to 10 mm from the viewpoint of ensuring durability.

Further, in the short fiber reinforced rubber layer 10, it is preferable that the radial outer end EU thereof is located in the vicinity Y of the tire maximum width point TM, and if the position of the outer end EU is too low, the reinforcing effect is obtained. It becomes too small, and it becomes difficult to sufficiently improve the steering stability. On the other hand, if it is too high, low rolling resistance and riding comfort tend to be impaired. The “vicinity Y” means a range in which the radial distance from the tire maximum width point TM is 0.1 times or less the tire cross-sectional height H.

Next, the short fiber reinforced rubber layer 10 is made of short fiber compounded rubber in which short fibers are compounded in a rubber base material,
Particularly, 90% or more of short fibers are ± 2 in the tire radial direction.
It is preferable to orient at a small angle of 0 degree or less. Due to the orientation of the short fibers, specifically, the complex elastic modulus E * a in the orientation direction (radial direction) of the short fibers and the complex elastic modulus E * b in the direction perpendicular to the orientation direction (circumferential direction). Ratio (E * a /
The E * b) ratio can be, for example, larger than 1.0, more preferably 5 or more, and further preferably about 7 to 20. As a result, in the sidewall portion 3, compression and bending rigidity in the tire radial direction can be effectively compensated, and steering stability and riding comfort can be improved while maintaining excellent low rolling resistance. It will be possible.

The complex elastic modulus was measured by using a viscoelasticity spectrometer VESF-III type manufactured by Iwamoto Seisakusho Co., Ltd., and the measurement conditions were as follows: temperature 70 ° C., frequency 10 Hz, initial strain 10
%, Dynamic strain ± 1%.

Here, examples of the rubber base material of the short fiber reinforced rubber layer 10 include diene such as natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoplane rubber (IR). One or a combination of a plurality of rubbers can be preferably used.

The short fibers are preferably organic fibers such as nylon, polyester, aramid, rayon, vinylon, cotton, cellulose resin and crystalline polybutadiene, but other than these, for example, metal fibers, whiskers, boron. Inorganic fibers such as glass fibers can be used, and these can be used alone or in combination of two or more kinds. More preferably, the short fibers may be subjected to an appropriate surface treatment in order to improve the adhesiveness with the rubber substrate.

The average diameter (D) of the short fibers is preferably, for example, 0.1 to 1.0 μm. If the average diameter (D) is less than 0.1 μm, the reinforcing effect tends to relatively decrease, and conversely. If it is larger than 1.0 μm, cracks or cracks are likely to occur at the interface with the rubber, and the adhesive strength with the rubber tends to relatively decrease. The short fibers have a ratio (L / D) of the average length (L) to the average diameter (D) of 5 or more, more preferably 50 or more, and further preferably 50 to.
The value of 2000 is preferable. This ratio (L / D) is 5
If it is less than the above range, the reinforcing effect due to the orientation of the short fibers cannot be sufficiently exhibited. The average length (L) of the short fibers is
It is preferably 20 μm or more, more preferably 50 to 1000 μm.

In addition to the short fibers, the short fiber reinforced rubber layer 10 can be appropriately blended with a rubber reinforcing agent such as carbon black or silica, and a conventional tire rubber additive such as sulfur or an antioxidant.

Further, the rubber thickness t of the short fiber reinforced rubber layer 10 is
Is preferably in the range of 0.3 to 1.0 mm, and the rubber thickness t
Is less than 0.3 mm, the rigidity is insufficient, the effect of improving the steering stability and the like cannot be sufficiently exhibited, and the productivity is deteriorated. On the other hand, if the rubber thickness t exceeds 1.0 mm, the orientation of the short fibers deteriorates, and the reinforcing effect of the short fibers diminishes, while the weight unnecessarily increases and the low rolling resistance is impaired. Become.

Further, in this embodiment, in order to suppress damage to the short fiber reinforced rubber layer 10 and enhance tire durability, the short fiber reinforced rubber layer 10 is divided into a plurality of radially inner and outer sections. In addition to being formed by the rubber regions 11, each rubber region 11 is formed by a different rubber composition G having a different compounding amount of the short fibers.

In this example, the short fiber reinforced rubber layer 10 is used.
Is the radially innermost rubber region 11A, the radially outer rubber region 11B, and the radially outermost rubber region 1
1C and three rubber regions 11 and each rubber region 11
The case where A, 11B, and 11C are formed by the rubber compositions GA, GB, and GC in which the amounts of fibers are different is illustrated.

At this time, the rubber compositions GA, GB, G
It is necessary for the damage suppressing effect to have the following relationships in the short fiber blending amounts ga, gb, and gc of C. ga <gb <gc, that is, the rubber region 1 on the outer side in the radial direction
It is necessary to make the blending amount of the short fibers of No. 1 larger than the blending amount of the short fibers of the rubber regions 11 adjacent to each other in the radial direction.

In the tire 1 of this embodiment having a low apex height h2, the bead portion 4 is largely deformed and the stress is concentrated.
It is easy for cracks and the like to occur. Therefore, it is effective to suppress damage by reducing the compounding amount of the short fibers in the rubber region 11 on the inner side in the radial direction where the degree of stress concentration is high and relatively enhancing the flex cracking performance of the rubber. On the contrary, as the rubber region 11 on the outer side in the radial direction becomes stiffer, it becomes easier to balance steering stability and riding comfort, and further improvement in performance can be expected.

In order to prevent damage to the rubber layer 10, it is preferable that the innermost rubber region 11A extends to a position where the outer end AU in the radial direction of the innermost rubber region 11A extends outwardly in the radial direction beyond the apex end 8e. . This is because stress is most likely to be concentrated in the vicinity of the apex end 8e. Therefore, it is preferable to dispose the innermost rubber region 11A in at least this portion in order to suppress damage. From the viewpoint of ensuring rigidity, the height h3 of the outer end AU from the bead base line BL is preferably set to 0.3 times the height H of the tire cross section or less.

Here, in the rubber composition G, when the amount of the short fibers is less than 10 parts by weight, the effect of containing the short fibers is not exerted, and when it exceeds 30 parts by weight, the rubber composition G is formed. When kneading, it is difficult to knead and extrude rubber, and productivity is significantly deteriorated. Therefore, the short fiber content of the rubber composition G is preferably in the range of 10 to 30 parts by weight. In particular, in order to maximize the effect of the division of the short fiber reinforced rubber layer 10, the rubber composition GA is used. 10 to 20 parts by weight with respect to 100 parts by weight of the rubber substrate, 15 to 25 parts by weight of the short fiber compounding amount gb in the rubber composition GB, and the short fiber compounding amount in the rubber composition GC. The amount gc is preferably 20 to 30 parts by weight.

Further, as shown in FIG. 3, the short fiber reinforced rubber layer 10 is provided with a rubber innermost rubber region 11A made of the rubber composition GA and a radially outermost rubber region 11C made of the rubber composition GC. It is also possible to form the two rubber regions 11 and. At this time, the short fiber blending amounts ga and gc of the rubber compositions GA and GC are ga <gc, the short fiber blending amount ga is 10 to 20 parts by weight, and the short fiber blending amount gc is 2
The short fiber reinforced rubber layer 10 has a content of 0 to 30 parts by weight.
This is preferable in order to maximize the effect of the division of.

When the number n of the rubber regions 11 is 4 or more, not only the effect due to the classification cannot be expected, but also the work efficiency of forming the short fiber reinforced rubber layer 10 tends to be impaired. Therefore, as described above, It is preferable that n is 2 or 3.

Further, each rubber region 11 is connected in series by abutting each end thereof, and a boundary line N (corresponding to the abutting surface of the end) between the rubber regions 11 is shown in FIG.
As in (B), it may be parallel to the thickness direction or may be inclined with respect to the thickness direction. Note that it is preferable to incline the boundary line N from the viewpoint of durability because the abutting area is large and the connection strength is increased.

When the boundary line N is inclined, the length J of the boundary line N in the radial direction along the rubber region 11 is the narrow rubber region 1 among the inner and outer rubber regions 11 to be connected.
The width Wj of 1 is preferably 0.5 times or less. 0.5
If it exceeds twice, the effect due to the division of the short fiber reinforced rubber layer 10 cannot be sufficiently achieved.

When the boundary line N is inclined, it is preferable that the radially inner point of the boundary line N is radially outside the apex end 8e for the purpose of suppressing damage, and from the viewpoint of ensuring rigidity. The height h3 of the radial outer side point of the boundary line N from the bead base line BL is preferably set to 0.3 times or less of the tire section height H.

In each rubber region 11, it is preferable that the types of short fibers to be blended are the same, but the types of short fibers may be different according to requirements. The difference in the type of the short fibers means that any one of the material, the average diameter, and the average length of the fibers is different.

Although a particularly preferred embodiment of the present invention has been described above in detail, the present invention is not limited to the illustrated embodiment and can be modified in various modes.

[0043]

Example: The tire size is 205 / 65R15,
A tire having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and rolling resistance, steering stability, riding comfort and durability of each sample tire were tested. The structure other than the short fiber reinforced rubber layer is the same for each tire as shown in Table 2. The test method is as follows.

(1) Rolling resistance: Using a rolling resistance tester, each tire was subjected to rim (15 × 6.5 JJ) and internal pressure (2).
00kPa), speed (80km / h), load (4.5k)
Under the conditions of N), the measured rolling resistance value was measured, and is displayed as an index with the conventional example being 100. The smaller the index, the smaller the resistance and the better.

(2) Steering stability and riding comfort: Tires are mounted on four wheels of a passenger vehicle (2000 cc, FF vehicle) under the conditions of rim (15 × 6.5 JJ) and internal pressure (200 kPa), and dry asphalt is used. The steering stability and riding comfort when traveling on a test course on the road surface are displayed as an index with the conventional example being 100 by sensory evaluation of the driver.
The larger the index, the better.

(3) Durability: Using a drum tester, under the conditions of rim (15 × 6.5 JJ) and internal pressure (200 kPa), in accordance with the load / speed performance test specified by ECE30, the step speed It was carried out by the method. In the test, the traveling speed is successively increased and the speed at the time when the tire is broken is displayed as an index with the conventional example being 100. The larger the index, the better.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

As described above, according to the present invention, since the short fiber reinforced rubber layer is formed by a plurality of rubber regions which are divided inward and outward in the radial direction and have different short fiber compounding amounts, the folding height of the carcass is increased. It is possible to improve steering stability, riding comfort and durability of a tire having improved rolling resistance by reducing the height of the bead apex and the height of the bead apex.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a tire according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a bead portion together with a short fiber reinforced rubber layer.

FIG. 3 is a cross-sectional view showing another example of a short fiber reinforced rubber layer.

4A and 4B are schematic cross-sectional views illustrating boundary lines between rubber regions.

FIG. 5 is a diagram illustrating a conventional technique.

[Explanation of symbols]

3 Side wall part 4 bead section 5 bead core 6 carcass 6A carcass ply 6a ply body 6b Ply turn-up part 8 bead apex rubber 10 Short fiber reinforced rubber layer 11 Rubber area

Claims (3)

[Claims] 1. A ply turn-back portion, which turns back around the bead core, is integrally provided in a ply body portion extending from a tread portion to a side wall portion to a bead core of a bead portion.
A pneumatic tire comprising a carcass consisting of a sheet of carcass plies, and a bead apex rubber that extends in a tapered shape from the bead core toward the tire radial outer side through a space between the ply body part and a ply folded part. In the carcass ply, the height h1 from the bead base line of the radial outer end of the ply turn-up portion is 0.12 to 0.15 times the tire cross-sectional height H, and the bead apex rubber is in the radial direction. The height h2 from the bead base line at the outer end is 0.20 to 0.
25 times, and a short fiber reinforced rubber layer extending along the outer surface of the bead apex rubber and beyond the outer end of the bead apex rubber is provided in the sidewall portion, and The pneumatic tire characterized in that the short fiber reinforced rubber layer is formed by connecting a plurality of rubber regions which are divided inward and outward in the radial direction and have different blending amounts of short fibers. 2. The short fiber reinforced rubber layer has a radial inner end as a starting point at a position beyond the outer end of the ply folded portion outward in the radial direction, and the radial outer end is near a tire maximum width point. 2. The pneumatic tire according to claim 1, wherein the outermost end of the innermost rubber region in the radial direction is located further outward in the radial direction than the outer end of the bead apex rubber. 3. The pneumatic material according to claim 1, wherein the compounding amount of the short fibers in the rubber region on the outer side in the radial direction is larger than the compounding amount of the short fibers in the rubber region adjacent on the inner side in the radial direction. tire.