JPH11321250A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly reduce the lower end position height of an adjacent area and attain the more improvement in bead durability and a lighter weight by providing a substantially triangular sectional hollow cavity part surrounded by a ply body part, a ply folded part and a bead core on a bead part. SOLUTION: This tire is provided with a hollow cavity part 8 surrounded by a ply body part 6A, a ply folded part and a bead core 5. By the formation of the cavity part 8, the lower end position of the adjacent area G of the ply body part 6A and the ply folded part 6B corresponding to the bead apex height or the cavity height LI can be reduced while forming the adjacent part G. Consequently, the ply folded part 6B is closed to the neutral line of stress in tire deformation, and the shearing stress of the ply body part 6A and the ply folded part 6B can be reduced to effectively suppress the breakage or damage of the cord. Accordingly, the improvement in bead durability and a lighter weight can be attained while keeping the steering stability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of improving bead durability while reducing weight at a bead portion.

[0002]

2. Description of the Related Art For example, in heavy duty tires for trucks and buses, and tires for light trucks and the like, in order to maintain bead durability, conventionally, as shown in FIG. Part a1 and ply turn-back part a
By increasing the rubber volume of the bead apex rubber b to be filled in between the two and increasing the bead rigidity significantly, the tire deformation itself due to the load applied is reduced.

On the other hand, bead structures have recently been reviewed to reduce the weight of tires, and as shown in FIG.
Conversely, the volume and height of the bead apex rubber b are greatly reduced, and the bend durability is maintained by raising the ply turn-up portion a2 to be close to the ply body portion a1 (hereinafter referred to as a slim bead structure). Meanwhile, a technique for reducing the weight has been proposed.

In the slim bead structure, there is a strong correlation between the height h of the bead apex rubber b and the bead durability, and it has been found that the height h is preferably as small as possible for the bead durability. .

[0005]

However, in the ply turn-up portion a2, an area g2 below the adjacent area g1 is provided.
The degree of bending caused by the above-mentioned increases significantly as the height h decreases. As a result, especially when a steel cord having high bending rigidity is used as the carcass cord, the bending rigidity influences the bead apex rubber b.
Is limited, and it is difficult to reduce the height h to, for example, 2.4 times or less the rim flange height Lf.

Therefore, the present invention is based on removing the conventional bead apex rubber b and hollowing this portion, and increasing the height of the lower end position of the proximity area g1 corresponding to the height h of the bead apex rubber b. An object of the present invention is to provide a pneumatic tire that can be reduced in width and that can further improve bead durability and reduce weight.

[0007]

In order to achieve the above object, a pneumatic tire according to the present invention comprises a ply body portion extending from a tread portion to a bead portion through a sidewall portion to a bead portion of a bead portion. The carcass consists of a radially arranged carcass ply with a ply turn-up part that turns back from the inside to the outside in the direction.
An upper portion of the ply turn-up portion has a proximity region extending substantially parallel to and close to the ply body portion,
The bead portion is provided with a hollow cavity having a substantially triangular cross section surrounded by the ply body, the ply turn-up portion, and a bead core.

[0008] By covering the periphery of the cavity with a covering rubber layer, it is possible to prevent structural members such as bead wires and carcass cords from being exposed in the cavity. Therefore, the exposed portion serves as a starting point for rubber peeling, cracking, and so on. Damage such as corrosion, that is, new damage caused by the cavity can be prevented. Moreover, the cavity functions as an elastic body by the internal air sealed by the covering rubber layer, so that traveling performance such as steering stability can be maintained. In particular, when the covering rubber layer includes an airtight layer portion made of butyl rubber, higher airtightness can be ensured, and maintenance of the running performance and prevention of damage can be performed more reliably.

The effect of the present invention can be more remarkably exhibited in a tire in which the carcass is formed of one or more carcass plies of a steel cord.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a meridional section in a non-loaded standard state in which a pneumatic tire 1 (hereinafter referred to as a tire 1) is mounted on a regular rim J and filled with a regular internal pressure.
In this example, a case where the tire 1 is a tubeless heavy-load radial tire used for a truck, a bus, or the like is illustrated.

In this specification, "regular rim" is defined as a standard rim defined by JATMA, and "normal internal pressure" is defined as a maximum air pressure defined by JATMA.

In the figure, a tire 1 has a tread 2
And a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 located at an inner end of each sidewall portion 3. The tire 1 is provided with a toroidal carcass 6 extending between the beads 4 and a belt layer 7 located radially outside the carcass 6 and inside the tread portion 2.

The carcass 6 has a ply body 6A extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the side wall portion 3 on both sides of the ply body portion 6A. The carcass ply 6a includes one or more carcass plies 6a in which a plurality of ply turn-up portions 6B are continuously provided.

The carcass ply 6a is in the form of a sheet in which carcass cords are arranged in an angle range of 70 to 90 ° with respect to the tire equator C, and both sides of which are covered with topping rubber. As the carcass cord, preferably, a steel cord is used, but if necessary, an organic fiber cord such as nylon, rayon, polyester, or aromatic polyamide can also be used. In this example,
The carcass 6 is formed from one carcass ply 6a in which steel cords are arranged at an angle of about 90 ° with respect to the tire equator C.

The belt layer 7 is composed of two or more belt plies. In this embodiment, the innermost belt plies 7a in which the belt cords are inclined at an angle of, for example, about 60 ± 10 ° with respect to the tire equator C. A belt layer ply 7b, 7c, 7d inclined at a small angle of 30 ° or less with respect to the tire equator C is provided in one or more places where the belt cords intersect each other between the plies, and has a four-layer structure. Eggplant As the belt cord, a steel cord is preferable, but if necessary, an organic fiber cord such as rayon, nylon, or aromatic polyamide may be used.

The bead portion 4 is provided with a hollow cavity 8 surrounded by the ply body 6A, the ply turn-up portion 6B and the bead core 5.

In the present embodiment, the bead core 5 is formed by spirally winding a steel bead wire a predetermined number of times to form a substantially hexagonal cross section, and then covering the rubber with a lower side 5i. 10 to 17 °, in this example, about 15 °, that is, along the inclination of the rim seat surface J1 of the rim. The bead core 5 may be made of an aromatic polyamide wire material in addition to steel.

As shown in FIG. 2, the hollow portion 8 has a substantially triangular cross-section extending radially outward and has a bead base line BL at an outer end (apex) 8e.
Height from the bead base line BL of the rim flange Jf to 0.7 to 3.0.
And double. Thereby, the effect of improving the bead durability by the slim bead structure is achieved. here,
The “bead base line BL” refers to the JATMA
Means the tire axial line passing through the rim diameter defined by the standard. It is difficult to reduce the cavity height L1 to less than 0.7 × Lf in terms of tire production, and it is difficult to reduce the cavity height L1 to 3.0 × Lf.
If the thickness exceeds the above range, the effect of improving the bead durability is weakened, but the volume of the cavity 8 becomes excessively large and the strength of the cavity 8 itself is reduced, so that the merit of the hollowing of the present application cannot be obtained.

The periphery of the cavity 8 is covered with a coating rubber layer 20.
The inner pressure is maintained in a pressurized state of 1 atm or more. In this example, in order to obtain higher airtightness, as shown in FIG. Sheet-shaped airtight layer 20B made of butyl rubber having high permeability
And formed from The butyl rubber means a rubber containing 30 phr or more of halogenated butyl rubber, and the topping rubber is formed of a non-butyl rubber containing a diene rubber as a main component.

Here, the thickness Ta of the hermetic layer portion 20B depends on the content of the halogenated butyl rubber, but is preferably 0.2 mm or more for hermeticity. Especially the thickness Ta
As for (unit mm), when the content (unit phr) of the halogenated butyl rubber is X, it is preferable that Ta ≧ 20 / X. Further, the upper limit of the thickness Ta is set at 1.
The thickness is preferably 5 mm or less, and particularly preferably Ta ≦ 50 / X. The base layer 20 as a topping rubber
The thickness of A is usually about 0.15 to 1.0 mm.

Further, as the covering rubber layer 20, as shown in FIG. 4, the airtight layer portion 20B may be configured to pass through the lower surface of the bead core 5. Further, the covering rubber layer 20 may be formed only of the base layer portion 20A without providing the airtight layer portion 20B. Further, the base layer portion 20A may be formed of a non-butyl rubber having the same composition or a different composition as the topping rubber. A layer portion may be provided. Also at this time, for example, rubber damage, cracks, or corrosion damage such as cords due to exposure of the carcass cords 21 and bead wires can be prevented to some extent.

Next, the ply turn-up portion 6B of the carcass 6 is once bent in a concave arc shape along the hollow portion 8, and then from the outer end 8e of the hollow portion 8, the ply body portion 6A
And extends substantially parallel to and close to the tire, and terminates at a position radially inward of the tire maximum width point.

More specifically, in the present application, as shown in FIG. 2, by reducing the cavity height L1 to a large extent, the outermost point BP (where the wire portion extends from the bead core 5 most outwardly in the tire axial direction) is formed. The ply folded portion 6 with respect to a straight line Y connecting the outer end 8e of the cavity 8 with the ply folded portion 6e.
The curved portion 12 of B passes on the straight line Y or sharply curves beyond the straight line Y inward in the tire axial direction.

At this time, the carcass cord has a reaction force which tends to return due to its bending rigidity. In the present invention, this reaction force is balanced by the pressing force of the chafer rubber 9 adjacent to the outside, and the curved portion 12 is bent. It is kept stable. On the other hand, when there is a bead apex rubber as in a conventional tire, since the bead apex rubber and the chafer rubber are balanced, the reaction force functions, and therefore, the degree of bending of the bending portion 12 is increased. thing,
That is, there was a limit to reducing the bead apex rubber.

As described above, in the present application, the formation of the hollow portion 8 forms the proximity region G between the ply body portion 6A and the ply turnover portion 6B, while forming the proximity region G corresponding to the conventional bead apex height. The lower end position, that is, the cavity height L1 can be greatly reduced.

As a result, the ply turn-up portion 6B approaches the neutral line of the stress at the time of tire deformation, the shear stress between the ply turn-up portion 6B and the ply body portion 6A is reduced, and cord breakage damage and the like are effectively suppressed. it can. Further, the formation of the cavity 8 shortens the cord path of the ply body 6A such that the ply body 6A has a substantially linear shape in a wide area range from the bead core 5 to the proximity area G, and when the regular internal pressure is filled, Furthermore, when a load is applied, the carcass 6 can be prevented from protruding outward, and the amount of deformation of the bead portion 4 can be effectively reduced. Further, by being substantially linear, the thickness of the bead portion 4 is further reduced to suppress internal heat generation, and the ply turn-up portion 6B comes closer to the neutral line of the stress, so that the ply turn-up portion 6B and the ply body portion 6A prevents damage to the plyulose and damage to the cord due to fatigue rupture.

In the standard state, the length L2 of the proximity region G is 0.5 to 5.0 times the maximum cross-sectional width BW of the bead core 5 (measured for the wire portion), more preferably 1 times. 0.0 to 4.0 times, and the length L2 is equal to 0.0.
When it is less than 5 × BW, the bead durability is significantly reduced. Conversely, if the value exceeds 5.0 × BW, the effect of improving the bead durability is not expected, and the outer end of the ply turn-up portion 6B is disposed at a position where the rubber gauge in the sidewall portion 3 is thin. Above and below, a stepped line is generated, and the distortion of the sidewall to the rubber is increased, resulting in an appearance damage such as a rubber crack. Also, the effect of weight reduction due to the increase in weight is reduced.

As shown in FIG. 5, the carcass cords 2 of the ply body 6A adjacent to each other in the proximity area G are formed.
1 and the inter-cord rubber thickness N between the carcass cord 21 of the ply turn-back portion 6B is 0.15 to 4.5 times, preferably 1.3 to 3.5 times the maximum diameter K of the carcass cord 21. It is desirable that the shear force acting between the adjacent carcass cords 21 be reduced by the elasticity of the rubber material 22 interposed between the carcass cords 21. When the inter-cord rubber thickness N is less than 0.15 × K, the effect of alleviating the shearing force becomes insufficient, and sometimes the carcass cords 21 may partially contact and cause cord loose. Maybe. The rubber thickness between cords N
However, when it exceeds 4.5 × K, even when the ply body 6A and the ply turn-up portion 6B extend in parallel, the ply turn-up portion 6B is liable to cause compression breakage damage, and the thickness of the bead portion 4 is reduced. It is not preferable from the viewpoint of heat generation, such as unnecessary increase. The rubber material 22 may be a topping rubber of the carcass ply 6a, but in this example, a cushion rubber layer 23 having a hardness substantially equal to that of the topping rubber is separately provided between the ply body 6A and the ply turn-up portion 6B. FIG.

In this embodiment, the upper end of the airtight layer portion 20B penetrates between the ply body 6A and the ply turnover 6B in the proximity area G. Since the butyl rubber forming the airtight layer portion 20B has a weak adhesive force, if the penetration length L5 is excessively large, there is a possibility that peel damage may be induced between the ply body portion 6A and the ply folded portion 6B. In order to prevent this peeling damage, the penetration length L5 is preferably as small as 5 mm or less, and more preferably, the height L6 from the bead base line BL up to the upper end portion of the hermetic layer portion 20B is set to the flange length. The height Lf is preferably set to 3.0 times or less.

If the cavity height L1 is greatly reduced as described above, there is a possibility that bead rigidity is reduced and running performance such as steering stability tends to decrease. Therefore, in this example, the height L of the chafer rubber 9 for preventing rim displacement is set.
3 is larger than the cavity height L1 (L3> L1), so that the chafer rubber 9 has a function of improving bead rigidity.

More specifically, the chafer rubber 9 extends radially outward from the bead core 5 below the bead core 5 while being in contact with the ply turn-up portion 6B, and the outer end thereof is formed of a soft sidewall rubber forming the sidewall portion 3. Adjacent to 10.

The chafer rubber 9 has a 100% modulus of the sidewall rubber 10 of 10 to 20.
Whereas it is kgf / cm ^2, it is formed the 100% modulus of a high elasticity of rubber and 55~75kgf / cm ^2. The 100% modulus of chafer rubber 9 is 5
If it is less than 5 kgf / cm ² , the bead rigidity becomes insufficient and
If it exceeds 5 kgf / cm ² , heat generation of the bead portion 4 increases, and conversely, durability performance decreases. Also the side wall rubber 10-1
If the 00% modulus is less than 10 kgf / cm ² , the carcass 6 cannot be protected from trauma, and if it exceeds 20 kgf / cm ² , flexibility is impaired and cracks occur on the outer surface.

The chafer rubber 9 forms a contact surface with the rim J including the bead bottom surface 4S by the exposed surface 9S exposed on the outer surface of the tire. The exposed surface height L4 from the bead base line BL at the radially outer end of the exposed surface 9S.
Is preferably 1.2 to 2.5 times the flange height Lf. When the exposed surface height L4 is less than 1.2 × Lf, the lower end of the sidewall rubber 10 comes into contact with the rim flange Jf when the tire is deformed, causing the sidewall rubber 10 to be locally worn. On the other hand, when it exceeds 2.5 × Lf, heat generation of the bead portion 4 increases, and cracks are caused on the surface of the chafer rubber 9 to reduce durability.

The boundary surface 11 between the chafer rubber 9 and the side wall rubber 10 forms a smooth slope extending radially inward from the carcass 6 toward the tire outer surface.
This alleviates the stress concentration between the rubbers 9 and 10 due to the difference in rubber elasticity.

Although the present application can be most preferably adopted as a heavy-duty tire for trucks, buses and the like as in the present embodiment, it is formed as a pneumatic tire for various uses such as a tire for a small truck or a tire for a passenger car. be able to.

Next, a method of manufacturing the pneumatic tire 1 will be described. As shown in FIGS. 6 to 9, as shown in FIGS. 6 to 9, the inner liner rubber 30, the chafer rubber 9 and the sidewall rubber 10
And a carcass ply 6a are sequentially wound and attached to form a ply base forming step S1 for forming a cylindrical ply base 32. The bead cores 5, 5 are set on both sides of the ply base 32. A bead mounting step S2; a shaping step S3 for shaping the green tire main body 33 by expanding the main forming former 40 and the side former 41.

The main forming former 40 is provided with an inflatable bladder 41A at both ends of a cylindrical drum 42 having a bladder (not shown) which expands in a toroidal shape by internal pressure filling via a bead lock 43 for fixing a bead core. The side former 41 is arranged concentrically.

In the ply substrate forming step S1, as shown in FIG. 6, the inner liner rubber 30 wound on the cylindrical drum 42 and the tire outer rubber 31 wound on the side former 41 are formed in the same manner as in the prior art. The carcass ply 6a is wound in a cylindrical shape over the straddle.

In the bead mounting step S2, as shown in FIG. 7, only the bead core 5 is inserted to a predetermined position, and the bead lock 43 is expanded to fix the bead core 5. Thereafter, an airtight layer portion 20 is placed on the bead core 5.
A butyl-based rubber sheet 34 for forming B is stuck on both ends of the carcass ply 6a and attached. In the structure shown in FIG. 4, the butyl rubber sheet 34 is placed at a predetermined position on the carcass ply 6a before the bead core 5 is inserted.
Then, the bead core 5 is inserted and fixed on the sheet 34.

In the shaping step S3, as shown in FIGS.
Each of the bladders is inflated, and the side of the ply body 6A that expands in a toroidal shape is provided with a folded ply folded portion 6B.
Are pressed and bonded. At this time, a gap surrounded by the butyl rubber sheet 34 is formed on the bead core 5, and the gap forms the cavity 8. An annular tread ring 36 including a belt layer 7 and a tread rubber 35 is pressed and bonded to the center of the ply body 6A.

The raw tire body 33 thus formed
Is vulcanized and molded in a vulcanizing mold as in the past, but the vulcanizing pressure at that time causes the cavity 8 of the finished tire to
The pressure is increased to 1 atm or more.

[0042]

EXAMPLE A radial tire for heavy load having a tire size of 11R22.5 was prototyped based on the specifications in Table 1, and
The bead durability, steering stability, and tire weight of the sample tire were measured. The common specifications of the tires are as follows. <Carcass> ・ Number of plies: 1 ・ Cord composition Steel cord (3 × 0.17 + 7 × 0.20) ・ Cord angle 90 degrees to tire equator ・ Cord density 21 / 5cm (center of tread) <Belt layer>・ Number of plies 4 ・ Cord configuration Steel cord (3 × 0.20 + 6 × 0.35) ・ Cord angle +67 degrees / + 18 degrees / -18 degrees / -18 degrees from inner ply to tire equator ・ Code density 26 / 5 cm The contents of the test are as follows.

<Bead Durability> A sample tire was subjected to 8.25 ×
Attached to a regular rim of 22.5, filled with an internal pressure of 1000 kPa, run on a drum at a load of 9000 kgf and a speed of 20 km / h, and when damage that can be visually confirmed was observed, the running was terminated and damage occurred. Distance Li and finish distance Lo
(10000 km), the ratio Li / Lo is 10
It was evaluated by an index of 0. The higher the value, the better.

<Steering Stability> A sample tire was 8.25 × 2.
Mounted on a regular rim of 2.5 and filled with an internal pressure of 800 kPa, mounted on all wheels of a 10-ton car, run on general roads, and evaluated the characteristics of steering wheel responsiveness, rigidity, grip, etc. by sensory evaluation of the driver It is indicated by an index with the conventional example as 100. The higher the value, the better.

<Tire Weight> The weight per tire was evaluated by an index with the conventional example being 100. The smaller the value, the lighter. Table 1 shows the test results.

[0046]

[Table 1]

As a result of the test, the tires of the examples can greatly improve bead durability and weight reduction while maintaining steering stability.

[0048]

As described above, the pneumatic tire of the present invention has the following features.
By removing the conventional bead apex rubber and hollowing out this part, it is possible to greatly reduce the height of the lower end position of the proximity area, further improving bead durability while maintaining steering stability Improvement and weight reduction can be achieved.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view showing a bead portion.

FIG. 3 is an enlarged cross-sectional view showing a covering rubber layer covering a hollow portion.

FIG. 4 is a cross-sectional view showing another example of the coating rubber layer.

FIG. 5 is a diagram showing a rubber thickness between cords in an adjacent area.

FIG. 6 is a diagram illustrating a ply base forming step.

FIG. 7 is a diagram illustrating a bead mounting process.

FIG. 8 is a diagram illustrating a shaping step.

FIG. 9 is a diagram showing a shaped raw tire main body.

FIGS. 10A and 10B are cross-sectional views of a bead portion for explaining a conventional technique.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6a Carcass ply 6A Ply body part 6B Ply folded part 8 Cavity part 20 Coating rubber layer 20B Airtight layer part G Proximity area

Claims (4)

[Claims] 1. A carcass ply having a radial arrangement in which a ply turn-up portion is provided in a ply main body portion extending from a tread portion to a bead portion of a bead portion through a sidewall portion to a bead core of a bead portion. A carcass, wherein the carcass has an adjacent area in which an upper portion of the ply turn-up portion extends substantially parallel to the ply body portion, and the bead portion has the ply body portion and the ply turn-up portion. A pneumatic tire having a hollow cavity having a substantially triangular cross section surrounded by a bead core. 2. The pneumatic tire according to claim 1, wherein a periphery of the cavity is covered with a covering rubber layer. 3. The pneumatic tire according to claim 2, wherein the covering rubber layer includes an airtight layer made of butyl rubber. 4. The pneumatic tire according to claim 1, wherein the carcass comprises one or more carcass plies using a steel cord.