JP3005190B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire which can improve the durability of a bead portion and can be suitably used particularly as a heavy-duty tire for trucks and buses used at high internal pressure and high load.

[0002]

2. Description of the Related Art In pneumatic tires, particularly tubeless pneumatic tires, the internal pressure of the tire is maintained by tightly assembling the rim with the bead portion of the tire. A bead core that does not substantially extend is embedded in a bead portion of such a tire. And this bead core
Continuously winding and laminating steel wires, the cross section is circular,
Generally, a desired shape corresponding to the tire, such as a square or a hexagon, is used.

FIG. 7 illustrates a bead portion a (before rim assembly) of a heavy-duty pneumatic tire, and a rim j is a 15 ° deep rim specified by JIS. In this example,
The bead core b has a substantially hexagonal shape with a horizontally long cross section, around which the carcass ply c is folded and locked.
The bead core b generally has a substantially flat inner surface G1 in the cross section in a radial direction, and this flat portion is formed substantially parallel to the rim sheet surface j1 of the rim.

When designing such a bead core b, first, the interference ratio (interference h / substantial rubber thickness T) of the total rubber gauge existing radially inside the bead core b is, for example, 50 to 60. %, And the bead core diameter d is determined based on the value.

In the conventional bead core shape as described above, when the tire is vulcanized and formed, the topping rubber of the carcass ply c, the topping rubber of the wire of the bead core b, and the beading canvas bw wound around the bead core b A part of the topping rubber or the like moves between the inner surface of the bead core b and the carcass ply c, and a rubber accumulation region A (shown by hatching) is formed.

[0006] In such a rubber reservoir area A, the deformation of the folded shape of the carcass and the variation in the amount of rubber of the topping rubber are complicatedly affected by the tension acting on the carcass cord during tire vulcanization molding. Due to this, even with one tire, there is variation in each part,
Also, the tires are different from each other.

Therefore, it is very difficult to consider the area A of the rubber pool at the design stage.
Has to determine the substantial rubber thickness T and design the bead core diameter d on the assumption that the bead core b is not compressed.

[0008]

However, in an actual tire, the portion of the rubber reservoir region A is formed so that the actual rubber thickness T changes and the tire is mounted on the rim j. In this case, there is a problem that the bead compression between the bead base surface a1 and the rim seat surface j1 becomes lower than a design value.

As a result, the bead compression between the outer surface of the bead portion a in the tire axial direction and the rim flange j2 becomes relatively high, which causes the wound portion f of the carcass ply to be easily damaged and the bead portion to be damaged. The problem that the durability of a was greatly reduced was found. Such a problem is particularly remarkable in a heavy-duty pneumatic tire that is rim-assembled on a deep rim and used under a high load and a high internal pressure and has a large bead compression.

Further, the conventional bead core has a problem that the number of times of winding the wire is large and the productivity is poor.

According to the present invention, an appropriate bead compression is obtained between the bead base surface a1 and the rim seat surface j1 so that the outer surface of the bead portion and the rim flange j2 can be obtained.
It is an object of the present invention to provide a pneumatic tire that can prevent an increase in bead compression between the tire and the tire, and can improve durability of a bead portion.

Still another object of the present invention is to improve the productivity of bead cores in a pneumatic tire that achieves the above object.

The present invention as described above can be preferably applied to a tubeless type heavy-duty pneumatic tire that is rim-assembled on a deep rim.

[0014]

Means for Solving the Problems In the present invention, claim 1 is provided.
The described invention is a pneumatic tire having a carcass that is folded back and locked by an annular bead core embedded in a bead portion from a tread portion to a sidewall portion,
The bead core is formed by continuously spirally winding a belt-shaped body having a width W, and protrudes radially inward at a width-direction central portion of a radial inner surface of the bead core in a cross section including the tire axis. A swollen portion is formed .

Further, according to the first aspect of the present invention, the width of the bulging portion is
Radius of curvature of an arc piece connecting both ends in the radial direction and the radially projecting end
Is set to 0.5 to 1.0 times the width W of the strip, and
The outer surface and the inner surface of the band 10 are each formed at the center of the thickness of the band.
Eccentric with the same radius of curvature R, R
By forming the belt-shaped body 10 from the center (thickness t)
It is characterized in that it is gradually thinned toward the end (thickness t ') .

According to the second aspect of the present invention, the bulging portion is provided.
It is formed from a single arc piece over the entire width of the bead core
It is characterized by that.

According to the third aspect of the present invention, the belt-like body is provided.
Is characterized in that a rivet is provided so that a widthwise central portion of a surface which is radially inward by lap winding projects inward.

Further, in the invention according to claim 4 , the carcass includes a main body extending from the tread portion to the sidewall portion and extending inward in the tire axial direction of the bead core of the bead portion; A carcass ply having a winding portion folded back from the inside in the tire axial direction to the outside, and a bead apex extending radially outward from the upper surface of the bead core between the main body portion and the winding portion; The portion has an adjoining portion extending along the main body portion outside the outer end of the bead apex by positioning the tip end radially outward of the radial outer end of the bead apex, and further comprising the bead apex. The height AH of the bead apex from the rim baseline when the outer end of the rim is assembled is the rim flange of the rim flange. With a 0.5 to 3.0 times the RH is, the bead core, the radially inner surface width direction center
In the rim assembly state, the inner diameter φBC of the innermost end point where the radial inner surface is located most inward is set to be less than or equal to the rim diameter φBT, and the bead core has a bulge portion protruding inward in the radial direction. The minimum distance z between the inner surface in the radial direction of the rim and the rim sheet surface of the rim is set to 0.8 to 6.0 mm.

[0019]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the present invention applied to a tubeless type heavy duty radial tire mainly used for trucks, buses, and the like. As a rim J, a rim seat surface J1 has an angle of 15 ° with a tire axial direction line. 15 ° deep rim.

In the figure, the radial tire for heavy load is
From the tread section 2 to the side wall section 3 to the bead section 4
A main body 6A extending inward in the tire axial direction of the bead core 5 embedded in the main body 6A, and the bead core 5 is formed integrally with the main body 6A and along the contour of the inner surface of the bead core 5 in this example.
And a carcass 6 having a carcass ply having a winding portion 6B that is smoothly turned from the inside to the outside in the tire axial direction, and a belt layer 7 disposed outside the carcass 6 and inside the tread portion 2. are doing.

The carcass 6 is made of nylon, rayon,
An organic fiber cord such as polyester or aromatic polyamide or a steel cord is 70-90 to the tire equator CO.
The carcass ply is composed of one or more carcass plies having a radial or semi-radial structure in which the carcass plies are arranged in an inclined angle range and both surfaces are covered with topping rubber.

In the present embodiment, the carcass 6 is formed from a single carcass ply 6a in which a steel cord is inclined at an angle of 90 ° with respect to the tire equator CO.

In the present embodiment, the belt layer 7 is made of steel cord, for example, 60 ± 10 ° with respect to the tire equator CO.
The innermost belt ply 7A inclined at an angle of about and the belt plies 7B, 7C, 7D in which steel cords are arranged at a small angle of 30 ° or less with respect to the tire equator CO,
For example, the steel cord has a four-layer structure in which the steel cords are overlapped so as to cross each other.

A bead apex 9 made of hard rubber is provided between the main body 6A and the winding portion 6B of the carcass 6 and extends radially outward from the upper surface of the bead core 5. .

The winding portion 6B has a tip located radially outward from a radial outer end 9A of the bead apex 9 so that the outer end 9 of the bead apex 9 can be formed.
It has an adjacent portion 6b extending along the body portion 6A outside A.

In the adjacent portion 6b, a rubber gauge of 0.3 mm or more, more preferably 1.6 mm or more is provided between the main body portion 6A and the winding portion 6B, so that shearing caused by deflection during tire running is provided. Ply peeling due to force can also be prevented.

When the tire shown in FIG. 2 is not assembled to the rim J, the bead base surface 15 of the bead portion 4 is radially outward with respect to the tire axial line L with respect to the tire axial line L. Incline outward upward at an angle θ, and this angle θ
Is not less than 1.0 times and not more than 1.9 times, more preferably not less than 1.2 times and 1.9 times, the angle α at which the rim seat surface J1 of the rim J on which the bead base surface 15 is seated is inclined outward and upward. It is set in the following range.

By setting the value of the ratio θ / α to 1.0 to 1.9, the bead portion 4 can be firmly contacted with the rim J while securing the rim assembling performance. The resultant force can be increased to improve the rim displacement resistance.

If the angle θ is smaller than 1.0 times the angle α, the fitting force with the rim J cannot be sufficiently increased, and the rim displacement resistance cannot be effectively improved. If it is larger than 0.9 times, the bead part 4
Must be excessively compressed, which adversely affects rim assembly performance.

In addition, the bead apex height AH from the rim base line RB of the outer end 9A of the bead apex 9 in the rim assembled state is set to 0 of the rim flange height RH from the rim base line RB at the inner end of the rim flange J2 . It is set to not less than 0.5 times and not more than 3.0 times.

The rim baseline RB is a JAT
MA (Japan Automobile Tire Association), TRA (US Tire
It is defined as a tire axial direction line that determines the rim diameter φBT defined by the rim standards of the Rim Association and ETRTO (European Tire and Rim Technical Organization).

By setting the value of the ratio AH / RH to 3.0 or less, the compressive strain applied to the winding portion 6B when the tire is bent can be reduced, the durability of the winding portion 6B can be improved, and the volume of the bead apex 9 can be improved. Can be reduced,
Bead heat generation can be effectively suppressed.

However, when the value of the ratio AH / RH is smaller than 0.5, air accumulation is likely to occur between the winding portion 6B and the bead apex 9, and many defective products are not preferred, and therefore it is more preferred. Is 1.0
That is all.

Next, in the present invention, the bead core 5 comprises:
As shown in FIG. 2 and FIG. 3 (C),
It is formed by winding a plurality of layers in a continuous spiral with uniform width and in this embodiment, three layers.

For example, as shown in FIG. 3 (B), when the belt-shaped body 10 is overlap-wound, the band-shaped body 10 is previously provided with a radially inwardly protruding center portion in the width direction by the overlap winding. This is desirable from the viewpoint of increasing productivity. In addition, any method can be used for this customizing.

The strip 10 may be made of, for example, a strip of high carbon steel material, or an aramid fiber, carbon fiber, glass fiber, carbon silicon A belt-like material made of a composite material reinforced with an inextensible fiber material such as fiber or boron fiber can be used as appropriate.

As shown in FIG. 3B, the thickness t of the band 10 is preferably, for example, 0.6 to 2.0 mm. If the thickness t is less than 0.6 mm, the rigidity tends to be low, and it tends to be difficult to maintain the shape. Conversely, when the thickness t of the band 10 exceeds 2.0 mm, a large step occurs at the winding start and end positions of the band 10,
In addition to the occurrence of the rigidity step of the bead core 5 itself, the end face of the band-shaped body 10 is not usually plated, and tends to cause poor adhesion to rubber. The “thickness t of the strip 10” is specified at the center in the width direction.

The width W of the belt-shaped body 10 in the tire axial direction is:
For example, 4 to 40 mm is preferable. The width W of this band 10
Is smaller than 4 mm, the bulging portion 5a of the bead core 5 described later.
The effect is unlikely to occur even if the bead core 5 is formed.
, The carcass 6 tends to be easily damaged. Conversely, if the width W of the strip 10 exceeds 40 mm, it tends to be difficult to obtain a smooth arc when the carcass 6 is folded. From such a viewpoint, it is desirable that the value of the ratio W / t between the width W of the belt-shaped body 10 and the thickness t be approximately 4 to 40.

FIG. 3A shows a bead core b of a conventional heavy duty pneumatic tire. The bead core b is formed by winding a wire having a diameter D of about 1.55 mm 51 times, and a bead wrapping canvas bw made of a rubber-coated organic fiber cord is wound around the bead core b.
The bead core 5 according to the present embodiment can be manufactured with the same cross-sectional area as that of the related art by winding the belt-shaped body 10 having the dimensions shown in FIG.

In FIG. 3B, each dimension is R
= 9.7 mm, t = 2.0 mm, γ = 123 °, and strip 1
The cross-sectional area of 0 is about 32.2 mm ² . Therefore, the productivity of the bead core 5 can be significantly improved as compared with the related art. In addition,
After winding the belt-shaped body 10, it is desirable to wrap the periphery with rubber or the like.

The bead core 5 has a bulged portion 5a projecting radially inward toward the rim seat surface J1 side of the rim J at the center in the width direction of the radial inner surface i in the cross section including the tire shaft. The bulging portion 5a is formed by connecting both ends 5e, 5e in the width direction of the bulging portion 5a and the radially protruding end 5c by an arc piece 12.

Accordingly, the arc piece 12 can be present at the center in the width direction of the bead core 5, and the carcass ply 6a can be smoothly folded back along the arc piece. A straight portion or an arc piece having a curvature different from that of the arc piece 12 may be connected to both ends 5e, 5e in the width direction of the bulging portion 5a of the bead core 5.
2 itself may be a composite arc.

In this embodiment, the cross section of the bead core 5 is
As shown in FIG. 3C, an example is shown in which the projecting end 5c has a symmetrical structure and the protruding end 5c is located at the center in the width direction.
In this embodiment, the most preferable mode is shown in which the bulging portion 5a is formed from an arc piece 12 having a single radius of curvature R over the entire width of the bead core 5.

Such a bead core 5 is used in this embodiment.
Is such that the radius of curvature R of the arc piece 12 is approximately 0.55 times the width W of the strip 10.

The radius of curvature R of the arc segment 12 is
If the width W is less than 0.35 times the width W, the radius of curvature is relatively too small, and it is difficult to lap the belt-shaped body 10,
There is a problem that the productivity of the bead core 5 is reduced.

The radius of curvature R of the arc piece 12 is
If the width W is 0.35 times or more and less than 0.5 times the width W, the arc piece 12 cannot be formed over the entire width of the belt-shaped body 10.

In this case, as shown in FIG. 6 (A), a straight piece 13 is formed at least at one end of the arc piece 12, and this end may exert a heavy load on the carcass cord. Accordingly, the curvature radius R of the circle arc piece 12, to 0.50 times the width W of the strip 10, more preferably 0.55 times or more, it is desirable to minimize the proportion of straight pieces 13.

The radius of curvature R of the arc piece 12 is
When the width W exceeds 2.0 times the width W, the radius of curvature becomes relatively large, and the corner portion of the radially inner surface i of the bead core 5 tends to approach a right angle, which similarly promotes the fatigue of the carcass cord. There's a problem. Therefore, preferably, the arc piece 1
2 is 1.0 or less times the width W of the belt-shaped body 10,
More preferably, it is desirably 0.7 times or less.

As a prior art, a tubeless tire having a bead core in which a strip of steel is wound is disclosed in
No. 53904. However, this proposal aims to prevent the relative movement of the strips overlapping each other, and does not suggest that the bulge is formed at the center of the inner surface of the bead core. Are basically different.

FIGS. 5A to 5C show an embodiment of the bead core 5 in which different strips 10 are wound around each other. The number of windings of the bead core 5 can be variously adjusted in accordance with the thickness t of the belt-shaped body 10, and it is preferable that the number of layers be about 3 to 6 as shown in the figure because of excellent productivity. FIG.
(C) shows a bead core 5 in which a straight piece 13 is provided on one end side of the inner surface.

Further, when the above-mentioned band-shaped body 10 is wrapped around,
If a gap is formed between the layers of each strip, the durability of the bead core 5 will be reduced. Accordingly, for example, as shown in FIG. 3B, the outer surface and the inner surface of the band 10 have the same radius of curvature R with their centers decentered in the thickness direction of the band.
The belt-shaped body 10 is formed by an arc piece of R, and the center of the belt-shaped body 10 (thickness t).
To both ends (thickness t ′) .

In addition, it is preferable that both ends of the belt-shaped body 10 are smoothly rounded, so that both ends can be prevented from damaging the carcass cord.

In the present embodiment described above, the bead core 5 has the radially inner surface i formed on the basis of the circular arc piece 12 having the specific radius of curvature R, and has no portion parallel to the rim sheet surface J1. . Therefore, carcass 6
When folded back around the bead core 5, the bead core 5 can be smoothly folded back along the inner surface shape, that is, along the arcuate piece 12, so that the rubber pool between the bead core 5 and the carcass 6 as in the related art is formed. Since the area A hardly occurs, in the actual tire, it is possible to maintain the closing rate targeted at the design stage as it is, so that the bead compression between the bead base surface 15 and the rim seat surface J1 is reduced. Can be prevented. In addition, variations among tires can be eliminated.

Further, since the bead compression between the bead base surface 15 and the rim seat surface J1 can be prevented from lowering, the bead portion 4 and the rim flange J2 can be prevented.
The bead compression between the carcass 6 can be properly maintained, and the bead compression can be prevented from being excessively increased. Therefore, the wound portion 6B of the carcass 6 can be prevented from being damaged, and the durability of the bead portion 4 is greatly improved. Can.

As a precautionary measure, a pressure sensor is embedded at each position of the bead portion of the tire as shown in FIG.
The rim J was assembled into a rim, filled with a regular internal pressure, and the contact pressure at each position was measured. FIG. 9B shows the result, with the solid line indicating the product of the present invention (Example 2 described later) and the chain line indicating the conventional product (the conventional example). The position or the position is a position where the width of the bead portion in the tire axial direction is divided into four equal parts, and the position is specified as a position where the flange arc angle ε of the rim flange J2 is 45 °.

As is apparent from the figure, it was confirmed that the product of the present invention can maintain a higher compression than the conventional one at each position facing the rim seat surface J1 of the rim J. And, in the conventional product, it was also confirmed that the compression of the position was extremely high due to the inverse correlation of the low compression of the position.

Further, in the product of the present invention, the compression at the positions facing the rim seat surface J1 of the rim J is maintained at a high level, so that the position facing the rim flange J2 is opposite to the conventional product at the position facing the rim flange J2. , The compression was low.

In the rim assembly state shown in FIG. 1, the inner diameter φBC of the innermost end point where the radially inner surface i of the bead core 5 is located most inward is equal to or less than the rim diameter φBT, more preferably 2 mm from the rim diameter φBT. Is set to a value less than or equal to

Thus, the bead core 5 can be brought closer to the rim sheet surface J1 of the rim J, so that the interference of the rubber inside the bead core 5 can be increased, and the movement of the carcass 6 and the rubber around the bead core 5 can be reduced so that under heavy load. The deformation of the bead portion 4 is reduced, and the risk of ply loose is reduced. As a result, the durability of the bead portion 4 can be improved, and the bead reinforcing layer can be removed, so that the tire weight can be reduced.

By setting the difference between the rim diameter φBT and the inner diameter φBC to 2 mm or more, the deformation of the bead portion 4 can be reduced more effectively, and the toe portion of the bead portion 4 can be prevented from floating. In order to prevent the carcass 6 passing radially inward of the bead core 5 from being exposed from the bead base surface 15, in the rim assembled state, the radial length between the radial inner end of the carcass 6 and the rim seat surface J1 1.5mm
It is desirable to keep the above.

In the rim assembled state, the bead core 5
By setting the shortest distance z between the radially inner surface i of the rim J and the rim sheet surface J1 of the rim J in a range of 0.8 mm or more and 6.0 mm or less, ply separation is prevented, and the durability of the bead portion 4 is improved. This is desirable because it can be further improved.

If the shortest distance z is smaller than 0.8 mm, the durability of the rubber inside the bead core 5 in the radial direction is sharply reduced, cracks are generated in the chafer rubber, air enters from there, and the clinch is generated. The risk of inducing ply separation in the part is greater, while conversely 6.0.
mm, the inner diameter φBC becomes larger than the rim diameter φBT.
There is a possibility that the bead portion 4 may be larger than the above, and the durability of the bead portion 4 is reduced.

Further, a separation point A at which the main body 6A of the carcass 6 starts to separate from the bead core 5, and a radial line passing through a maximum swelling end C of the swelling portion 5a from a line connecting both ends in the width direction of the bead core 5 The angle β formed by the straight line 16 connecting the LR with the ply point B crossing the main body 6A and the tire axial direction line L is set in a range of 45 ° or more and 60 ° or less.

By setting the range of the angle β in this manner, the inclination of the carcass 6 can be made closer to the carcass line at the time of filling the internal pressure, and the rubber thickness of the bead portion 4 can be reduced.
The heat generation can be reduced to prevent damage.

If the angle β is smaller than 45 °, the bead core 5 moves excessively inward in the tire axial direction, and the rubber thickness of the bead core 5 outward in the tire axial direction becomes excessively large, causing heat generation. On the other hand, if the angle is larger than 60 °, the rubber thickness of the bead core 5 inside the tire axial direction becomes too large, which is not preferable.

A side packing rubber 19 extending vertically in the radial direction is provided between the radially inner portion of the sidewall rubber 17 forming the outer surface of the sidewall portion 3 and the winding portion 6B of the carcass 6. At the same time, the bead portion 4 is provided with a chafer rubber 20 which covers the side packing rubber 19 from its bottom surface and forms the bead base surface 15 and the rising surface 14 which comes into contact with the rim flange J2 in the rim assembled state. ing.

Further, 10 of the sidewall rubber 17
The 0% modulus MS is 10 to 20 kgf / cm ² , and the 100% modulus MP of the side packing rubber 19 is 14 to 4 kg.
7 kgf / cm ² , 100% modulus MA of Bead Apex 9 is 14 to 84 kgf / cm ² , chafer rubber 20
55~71kgf / cm ² 100% modulus MC of 100% modulus MT of the topping rubber of the carcass 6 and 37~47kgf / cm ^2.

As described above, the bead apex 9, the side packing rubber 19, and the chafer rubber 20
Since the rubber having the 0% modulus in the above range is used, the rigidity of the bead portion 4 can be moderately reduced, and the deformation of the bead portion 4 can be dispersed over a wide range. This can prevent the bead apex 9 from being locally bent at the outer end 9A in the radial direction, prevent the strength of the carcass cord near the outer end 9A from decreasing, and improve the followability with the carcass 6 to improve the carcass 6 Separation, pry loose, etc. can be prevented.

Since the 100% modulus MS of the side wall rubber 17 is set to a low value of 10 to ²⁰ kgf / cm ^2, the side wall rubber 17 can expand and contract following the carcass 6, and the rim displacement resistance is improved by the high modulus of the chafer rubber 20. While preventing separation from the carcass 6, propagation of stress to the bead portion 4 can be prevented.

The 100% modulus MA is 84 kg.
greater than f / cm ² , MP greater than 47 kgf / cm ² , 1
Than 100% modulus MS is 20 kgf / cm ² large, and when 100% modulus MC of greater than 71kgf / cm ^2, the rigidity of the bead portion 4 becomes excessively large, radially outer end 9A vicinity of the bead apex 9 Induces strong carcass cords, prizes, etc.

100% modulus MA, MP is 14 kg
smaller than f / cm ² , 100% modulus MS is 10kgf
/ Cm ² and 55% 100% modulus MC
If it is smaller than f / cm ² , the required rigidity of the bead portion 4 cannot be obtained, and the running performance is greatly impaired. The bead apex 9 and the side packing rubber 19 are rubber parts which are located inside the bead and require higher rigidity than the side wall rubber 17, so that the 100% modulus MA is 64 kgf / cm ² or more. 100% modulus M
P is preferably 37 kgf / cm ² or more.

Note that the 100% modulus MT is 10
Since the modulus is larger than 0% modulus MA and MP and smaller than MC, the carcass 6 can follow the deformation of the bead portion 4, and the ply loose or the like can be prevented.

As described above, the rim is not limited to the 15 ° deep rim. For example, the rim sheet may be 5 °, but the effect of the present invention is obtained in the case of a deep rim where the bead compression of the tire is relatively high (the intersection angle between the tire axial line and the rim sheet surface is 13 to 33 °). Is remarkable.

[0074]

EXAMPLES Table 1 is based on a heavy duty radial tire having a tire size of 11R22.5 and a structure shown in FIG.
Prototypes were manufactured according to the specifications in Table 2 (conventional examples, Examples 1 to 11 and Comparative Examples 1 to 6 ), and the effects of the present invention were tested. The test conditions are as follows.

1) Heat generation of a bead A test tire was mounted on a 22.5 × 8.25 15 ° deep rim, filled with an internal pressure of 8.00 ksc, and loaded with a load of 9000 kg.
Running on the drum at a speed of 20 km / h,
The tire temperature at the bead portion was measured every 00 km, and the average value was indicated by an index with the conventional example being 100. The smaller the value, the lower the heat generation.

2) Bead damage The test tire was mounted on a 22.5 × 8.25 15 ° deep rim, filled with an internal pressure of 10.00 ksc, and loaded with a load of 9000 k.
After running 8000 km on the drum at g and a speed of 20 km / h, each test tire was disassembled and examined for the presence of carcass ply loose. If any damage could be visually confirmed during the test, the test was stopped at that point.

3) Tire Weight The weight of each sample tire was indicated by an index with the conventional example being 100. A smaller value indicates a lighter weight.

4) Productivity of bead core and cost of bead core O is good, Δ is inferior in productivity or cost, and X is inferior in productivity.

[0079] 5) samples the carcass up portion of the code prototyped tires after remaining strong bead damage test of the carcass cord, as well as measuring the breaking strength of each code was indicated by an index to the first embodiment and 100.
The larger the value, the greater the residual strength and the better. The test results are shown in Tables 1 and 2, and the results of the bead damage test are described below.

[0080]

[Table 1]

[0081]

[Table 2]

Bead Damage Test Results Conventional Example For all five tires, damage was visually observable at 3800 to 6100 km (cord loose at the carcass turnaround portion near the separation point where the rim flange starts to separate from the tire). The swelling was suspected) and the test was stopped.

Comparative Examples 4, 5, and 65 All of the tires completed the run, but when disassembled, one of the tires was placed at the carcass turn-up portion on the outer side in the tire axial direction of the bead core.
The carcass cord was frayed. For the remaining four, no damage occurred.

Examples 1 to 11 All five tires completed the run, and no damage occurred even when disassembled.

COMPARATIVE EXAMPLE 1 Five tires completed the run, but when disassembled, two tires were placed in the carcass turn-up portion on the outer side in the tire axial direction of the bead core.
The carcass cord was frayed. For the remaining three, no damage occurred.

Comparative Example 2 All five tires completed the run, but when disassembled, the carcass cords were frayed at the carcass folded-back portions of the bead cores outside the tire axial direction.

COMPARATIVE EXAMPLE 3 In all five tires, visible damage was observed at 4900 to 6100 km (a bulge caused by a cord loose at the folded portion of the carcass near the separation point of the rim flange). And aborted the test.

As a result of the above test, it was confirmed that the samples of Examples 1 to 11 generate less heat than the conventional example and the comparative example, and that the durability of the bead portion is greatly improved. In addition, it was confirmed that the tires of Examples 1 to 11 also reduced the tire weight because the bead apex could be reduced based on the shape of the bead core.

[0089]

As described above, the pneumatic tire of the present invention has the following features.
According to the configuration of the first aspect, a region where the topping rubber or the like stays between the bead core and the winding portion of the carcass ply hardly occurs. Particularly, in the invention of the third aspect, this region can be completely eliminated. By being
In a real tire, the bead compression targeted at the design stage can be maintained, so that the bead compression between the bead base surface and the rim seat surface can be prevented from lowering. In addition, variations among tires can be eliminated.

Further, since the bead compression between the bead base surface and the rim seat surface can be prevented from lowering, the bead compression between the bead portion and the rim flange can be prevented from being excessively increased. The wound portion can be prevented from being damaged, and the durability of the bead portion can be greatly improved.

Further, with the bead core, the number of times of winding the belt-like body can be greatly reduced as compared with the conventional case, and the productivity is remarkably improved.

[Brief description of the drawings]

FIG. 1 is a right half sectional view of a tire showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a bead portion showing the embodiment of the present invention.

FIG. 3A is a cross-sectional view of a conventional bead core, and FIG.
Is a cross-sectional view of the belt-like body, and (C) is a cross-sectional view showing a state in which the belt-like body is overlapped and wound.

FIG. 4A is a view showing a measurement position of a bead portion;
(B) is a diagram comparing bead compression between the present invention and a conventional one.

FIGS. 5A to 5C are cross-sectional views of a bead core showing an embodiment of the present invention.

FIG. 6A is a cross-sectional view showing another embodiment of the present invention,
(B) is a sectional view of a bead core of a comparative example.

FIG. 7 is an enlarged sectional view of a conventional bead portion.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 5a Swelling part 5c Protruding end 5e Both ends of swelling part 6 Carcass 6A Body part 6B Winding part 6b Adjacent part 7 Belt layer 9 Bead apex 10 Band 12 Arc-shaped piece i Bead core Radial inner surface of J rim J1 rim seat surface J2 rim flange

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-191611 (JP, A) JP-A-1-272445 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 15/04 B29D 30/48

Claims (4)

(57) [Claims] 1. A pneumatic tire having a carcass which is folded back and locked by an annular bead core embedded in a bead portion from a tread portion to a sidewall portion, wherein the bead core has a width W. The bead core is formed by continuously spirally wrapping, and a bulging portion protruding radially inward is formed at the center in the width direction of the radial inner surface of the bead core in a cross section including the tire shaft. The radius of curvature of an arc piece connecting both ends in the width direction and the radially protruding end of the bulging portion is 0.5 to 1.0 times the width W of the strip.
In addition, the outer surface and the inner surface of the band 10
Circles of the same radius of curvature R, R eccentric in the thickness direction of the body
The central portion (thickness) of the belt-shaped body 10
A pneumatic tire characterized in that the thickness is gradually reduced from t) to both ends (thickness t ′) . 2. The pneumatic tire according to claim 1, wherein the bulging portion is formed from a single arc piece over the entire width of the bead core. 3. The belt-like body according to claim 1, wherein the band-shaped body is provided with a curl so that a widthwise central portion of a surface which is radially inward by lap winding projects inward. The pneumatic tire as described. 4. The carcass has a main body extending from the tread portion to the sidewall portion and extending inward in the tire axial direction of the bead core of the bead portion, and the carcass extends from the inner side in the tire axial direction to the periphery of the bead core. A carcass ply having a winding portion to be folded back, and a bead apex extending radially outward from the upper surface of the bead core between the main body portion and the winding portion, and the winding portion has a tip of a bead apex. By being located radially outward from the radial outer end, the outer end of the bead apex has an adjacent portion extending along the main body outside the outer end, and further, the outer end of the bead apex is in a rim assembly state. Apex height AH from rim baseline
Is 0.5 to rim flange height RH of the rim flange.
3.0 times, and the bead core has a half in the center in the width direction of the inner surface in the radial direction.
In the rim assembly state, the inner diameter φBC of the innermost end point where the inner surface in the radial direction is located most inward is set to be equal to or less than the rim diameter φBT, and the bead core has a radially inwardly projecting portion. The pneumatic tire according to any one of claims 1 to 3, wherein the shortest distance z between the inner surface and the rim seat surface of the rim is set to 0.8 to 6.0 mm.