JP3124937B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can exhibit high rim assembling performance while improving the durability of a bead portion, and is particularly suitably used as a heavy duty tire for trucks and buses used under high internal pressure and high load. And pneumatic tires.

[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. As this bead core, generally, a steel wire is continuously wound and laminated, and its cross section is generally in a desired shape such as a circle, a square, or a hexagon according to a tire.

FIG. 10 illustrates a bead portion a (before rim assembly) of a pneumatic tire for heavy load, 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. In addition, the bead core b is usually provided with a radially inner surface G1 of a cross section.
Is substantially flat, and this flat portion is the rim seat surface j1 of the rim.
And are formed substantially in parallel.

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 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] Such a rubber accumulation region A is caused by the fact that 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. , There is variation in each part even with one tire,
Also, the tires are different from each other.

Therefore, since it is very difficult to consider the rubber accumulation region A at the design stage, the substantial rubber thickness T is determined on the assumption that the region A is not compressed by the bead core b. The diameter d had to be designed.

[0008]

However, in an actual tire, the tire is mounted on the rim j by changing the substantial rubber thickness T and the like due to the formation of the rubber accumulation region A. 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.

[0010] In addition, such a conventional bead core having a substantially horizontally long hexagonal shape or the like has extremely high rigidity, so that the rim assembly performance is impaired and the tire weight is increased.

The present invention is based on forming a bulged portion and a concave portion at a central portion of an inner surface and a central portion of an outer surface of a bead core in a radial direction, respectively, and can suppress formation of a conventional rubber accumulation region below the bead core. It is an object of the present invention to provide a pneumatic tire capable of reducing bead compression between a rim flange and a bead portion by optimizing a bead compression between the rim flange and the bead portion.

Further, according to the present invention, in a pneumatic tire that achieves the above object, while improving the rim assembling performance and reducing the weight of the tire, the installation accuracy and installation work of the bead apex rubber installed on the outer surface of the bead core are improved. The aim is to improve efficiency, increase productivity and improve tire uniformity.

[0013]

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 winding one or more bead wires in a circumferential direction, and furthermore, in a cross section including the tire shaft, a bulging portion protruding radially inward is provided at a center in a width direction of a radial inner surface of the bead core. Is formed, and at the center in the width direction of the radially outer surface of the bead core, a concave portion is formed which is depressed inward in the radial direction, and the bulging portion has a contour shape formed of a smooth curve. Is characterized in that the radius of curvature R of an arc curve connecting both ends in the width direction and the radially protruding end is 0.35 to 2.0 times the width W of the bead core in the tire axial direction.

Further, the invention according to claim 2 is characterized in that the bead core is formed by continuously winding one bead wire in a spiral and in multiple stages.

The invention according to a third aspect is characterized in that the bead core is formed by winding a tape-like strand formed by aligning a plurality of bead wires in the axial direction in an annular and multistage manner.

[0016]

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.
Represents a 15 ° deep rim in which the rim seat surface J1 forms an angle of 15 ° with the tire axial line.

In the figure, a radial tire 1 for heavy load
A main body 6A extending from the tread portion 2 through the sidewall portion 3 to the inside of the bead core 5 embedded in the bead portion 4 in the tire axial direction, and integrally connected to the main body portion 6A;
In the present example, a carcass 6 having a carcass ply having a winding portion 6B that is smoothly turned from the inside in the tire axial direction to the outside around the bead core 5 along the contour of the inner surface of the bead core 5, and the carcass 6 It has a belt layer 7 disposed outside and inside the tread portion 2.

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 about 90 ° with respect to the tire equator CO.

In this embodiment, the belt layer 7 is formed by applying a steel cord to the tire equator CO by, for example, 60 ± 10.
° 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. It has a four-layer structure in which the directions intersect each other.

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

The winding portion 6B has a tip located radially outward of a radial outer end 9A of the bead apex 9 so that the outer end 9 of the bead apex 9 is 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 achieved. Ply peeling due to force can also be prevented.

FIG. 2 shows the bead portion 4 in a state where the tire 1 is not assembled to the rim J. The bead base surface 15 of the bead portion 4 is located outside the tire axial direction L with respect to the tire axial direction. Is inclined outward at an angle θ that is radially outward, and this angle θ is at least 1.0 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. And 1.9 times or less, more preferably 1.2 times or more and 1.9 times or less.

By setting the value of the ratio θ / α to 1.0 to 1.9, the bead portion 4 can be brought into firm contact 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.

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 outer end of the rim flange J2. It is set to be not less than 0.5 times and not more than 3.0 times.

Note that 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, if the value of the ratio AH / RH is smaller than 0.5, air accumulation tends to occur between the winding portion 6B and the bead apex 9, which is not preferable because many defective products are generated. Is 1.0
That is all.

Next, in the present invention, the bead core 5
As shown in FIGS. 3 and 4, the core is a so-called single-wind type or tape bead type core formed by winding one or more bead wires 30 in a circumferential direction.
A conventional steel wire made of a hard steel wire of about 55 mm can be used.

In the cross section including the tire axis, the bead core 5 is located at the center in the width direction of the inner surface Si in the radial direction.
While having the bulging part 10 protruding inward in the radial direction,
At the center in the width direction of the radially outer surface So, a concave portion 11 is provided which is depressed inward in the radial direction. In the present application, the radially inner side between the points or sides V1 and V1 of the points or sides where the bead core 5 protrudes most on both sides in the tire axial direction is referred to as the inner surface Si, and the radially outer side is referred to as the outer surface So. Is referred to as a width W of the bead core 5 in the tire axial direction.

The bulging portion 10 has a contour shape formed of a smooth curve. For example, as shown in FIG. 4, both sides of the bulging portion 10 are in contact with both ends 10e in the width direction of the bulging portion 10. By providing the straight portion 13 having a tangent line inclined upward, the bulging portion 10 and the straight portions 13 can form the inner surface Si. Further, as shown in FIG. 3, the bulging portion 10 may be formed over the entire width of the inner surface Si, that is, the entire inner surface Si may be formed only by the bulging portion 10. As the “smooth curve”, various curves other than a straight line, such as a single arc, a plurality of arcs, and an elliptic parabola, and a composite curve obtained by smoothly combining these curves can be adopted.

The bulging portion 10 has two ends 10e, 1e.
0e and the radially protruding end 10c, the radius of curvature R of the single circular arc curve 16 determined by the three points
Is set to 0.35 to 2.0 times the width W of the bead core 5 to regulate the degree of protrusion of the bulging portion 10. The contour of the bulging portion 10 does not need to follow the arc curve 16 as long as it is formed by a smooth curve such as an ellipse as shown in an enlarged view in FIG. As shown in FIG. 3, it is preferable that the inner surface Si is formed substantially over the entire width of the inner surface Si.

As described above, the bead core 5 has its inner surface Si
In addition, since the bulging portion 10 having a restricted degree of protrusion is provided with a smooth curve, the carcass 6 can be smoothly folded back along the inner surface shape of the bead core 5, that is, along the bulging portion 10. In addition, the formation of the bulging portion 10 eliminates the rubber accumulation region A which has conventionally occurred between the carcass 6 and the actual tire, so that it is possible to keep the interference rate targeted in the design stage as it is. . As a result, it is possible to prevent the bead compression between the bead base surface 15 and the rim seat surface J1 from being illegally reduced, and it is possible to eliminate variations in compression among tires.

Further, by preventing the bead compression from lowering between the bead base surface 15 and the rim seat surface J1, the bead compression between the bead portion 4 and the rim flange J2 can be properly maintained without excessively increasing. This can prevent the wound portion 6B of the carcass 6 from being damaged, and can greatly improve the durability of the bead portion 4.

If the radius of curvature R of the arc curve 16 is smaller than 0.35 times the width W of the bead core 5, the effect of eliminating the rubber accumulation region A becomes insufficient, and the bead compression is not optimized.

If the radius of curvature R is at least 0.35 times the width W but less than 0.5 times, the bead core 5
The bulge 10 cannot be formed over the entire width of the inner surface Si. In this case, as shown in FIG. 4, the rubber accumulation region A is eliminated by forming the linear portion 13 on at least one end of the bulging portion 10. The end of the straight portion 13 may put a heavy load on the carcass cord. Therefore, it is preferable that the radius of curvature R be at least 0.50 times, more preferably at least 0.55 times the width W, and the proportion occupied by the linear portion 13 be as small as possible. When the straight portion 13 is provided, the bulging portion 10
Is preferably provided so that the width W1 occupied by the bead core 5 is 50% or more of the width W of the bead core 5.

When the radius of curvature R exceeds 2.0 times the width W, the effect of eliminating the rubber accumulation region A is reduced, and the corners of the inner surface Si of the bead core 5 tend to approach a right angle. However, there is a problem that the fatigue of the carcass cord is promoted. Therefore, it is desirable that the radius of curvature R be 1.0 times or less of the width W, more preferably 0.7 times or less.

The width W of the bead core 5 is preferably, for example, 4 to 40 mm. If the width W is less than 4 mm, the effect of the bulging portion 10 is unlikely to occur, and the carcass 6 tends to be damaged on the side surface of the bead core 5. Become. Conversely, if the width W exceeds 40 mm, it tends to be difficult to obtain a smooth arc when the carcass 6 is folded.

It is preferable that the concave portion 11 provided on the outer surface So of the bead core 5 has the contour shape formed by a smooth curve similarly to the bulging portion 10. 10 is substantially parallel.

The recess 11 cooperates with the bulging portion 10 to reduce the rigidity of the bead core 5 and to improve the rim assembling performance. Note that, even when the rigidity is relaxed, the bead compression is properly maintained by eliminating the rubber accumulation region A, so that a necessary fitting force with the rim J is maintained. The concave portion 11 also contributes to the weight reduction of the bead core 5, and in order to make the bead core 5 lighter, the concave portion 11 is formed over the entire width of the outer surface So, and the outer surface So of the bead core 5 is formed.
And the inner surface Si is more preferably substantially parallel.

The bead apex 9 has, on its inner surface in the radial direction, a fitting projection that fits into the recess 11, so that the bead apex 9 is placed on the outer surface So when forming a green tire. Also functions as positioning when setting to As a result, the positional accuracy of the installation of the bead apex 9 is improved, and the uniformity is improved. On the other hand, there is an advantage that the work efficiency of the installation is increased and the productivity can be improved.

Such a bead core 5 can be formed by, for example, a tape bead method. According to this method, as shown in FIG. 6, a plurality of bead wires 30 are aligned in the axial direction in parallel with each other and fitted to a tape-like strand 32 covered with a topping rubber 31 and the inner surface shape of the bead core 5. A winding mold 34 having a molding recess 33 is prepared. Then, in a state where the strands 32 are formed in a flat state or in a state in which the strands are molded so as to conform to the molding recesses 33, the beads 32 are wound annularly and in multiple stages in the molding recesses 33 of the mold 34.

The bead core 5 can also be formed by a single wind system. In this method, rubber
The bead wire 30 is inserted into the molding recess 33 of the mold 34.
Spirally wound from one side to the other side in the tire axial direction along the bottom surface of the tire to form a first stage, and further continuously spirally wound thereon to form a second stage Nth stage Form. As another method, only one central portion is spirally wound from the first stage to the Nth stage on the bottom surface of the forming concave portion 33 by one of the bead wires 30, and then the one side portion is formed. From the first stage to the Nth stage, and the other side
It may be formed sequentially and continuously from the stage to the Nth stage. Thus, various winding methods can be adopted.

In the rim assembled state shown in FIG. 1, the core inner diameter φBC between the innermost end points where the inner surface Si of the bead core 5 is located at the innermost position is equal to or less than the rim diameter φBT, more preferably 2 mm from the rim diameter φBT. Is set to be equal to or less than the value obtained by subtracting.

As a result, the bead core 5 can be brought closer to the rim sheet surface J1 to increase the interference of the rubber inside the bead core 5, the carcass 6 around the bead core 5 and the movement of the rubber can be reduced, and the bead portion 4 under a large load can be reduced. Less deformation and reduce the risk of pry loose. As a result, the durability of the bead portion 4 can be further 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 core 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. However, 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 gap between the radial inner end of the carcass 6 and the rim seat surface J1 1.
It is desirable to keep 5 mm or more.

In the rim assembled state, the bead core 5
Shortest distance z between the inner surface Si and the rim sheet surface J1
Is set in the range of 0.8 mm or more and 6.0 mm or less in that the ply separation can be prevented and the durability of the bead portion 4 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 20, and air enters from there. On the other hand, when the risk of inducing ply separation at the clinch portion is increased, when the diameter is larger than 6.0 mm, the core inner diameter φBC is likely to be larger than the rim diameter φBT. The property will be reduced.

In the rim assembled state, the shape of the outer surface 3s between the maximum width point P1 at which the side wall portion 3 projects most outward in the tire axial direction and the separation point P2 at which the bead portion 4 separates from the rim flange is: A convex arc portion 24 having a radius of curvature R1 having a center point at a tire axial direction line L1 passing through the maximum width point P1 and a convex arc portion 24 extending from a lower end point P3 of the convex arc portion 24 to the separation point P2. And a concave curved portion 25 extending inward in the axial direction of the tire and extending mainly in a concave shape rather than an extended arc (indicated by a dashed line). The convex arc portion 24 and the concave curve portion 25 are smoothly connected, and the maximum separation distance D of the concave curve portion 25 from the extended arc is the rim base line R of the maximum width point P1.
It is set to 0.03 to 0.20 times the height HS from B.

By adopting such a shape of the outer surface 3s, the structure of the bead core 5 having the bulging portion 10 and the concave portion 11, and further, the difference between the rim diameter φBT and the core inner diameter φBC is set to 2 mm or more. By organically combining with the structure, the heat generation of the bead can be reduced while suppressing the bead deformation, and the durability of the bead portion can be further improved and the weight reduction of the tire can be promoted.

Further, as shown in FIG. 2, a separation point B1 at which the main body 6A of the carcass 6 starts to separate from the bead core 5, and a radial line L passing through the protruding end 10c of the bulging portion 10.
An angle β formed by a straight line 18 connecting the ply point B2 at which R intersects the main body portion 6A with the tire axial direction line L is set in a range of 45 ° or more and 60 ° or less.

By setting the angle β in the above range, the inclination of the carcass 6 can be made closer to the carcass line at the time of filling the internal pressure, the rubber thickness of the bead portion 4 is reduced, and the heat generation is reduced. It can 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 too large to generate heat. Invite a rise. On the other hand, if it is larger than 60 °, the rubber thickness of the bead core 5 inside the tire axial direction becomes too large, which is not preferable.

Between the radially inner portion of the side wall rubber 17 forming the outer surface of the side wall portion 3 and the winding portion 6B of the carcass 6, it rises from the bead base surface 15 and abuts the rim flange J2. The chafer rubber 20 forming the rising surface 14 for use is provided.

Further, 10 of the sidewall rubber 17
10% to 20 kgf / cm ^{2 of} 0% modulus MS and 14 to 84 kg of 100% modulus MA of Bead Apex 9
f / cm ² , 100% modulus M of chafa rubber 20
C is 55 to 71 kgf / cm ² , and the 100% modulus MT of the topping rubber of the carcass 6 is 37 to 47 kgf / cm ² .

As described above, since the bead apex 9 and the chafer rubber 20 are made of rubber having a modulus of 100% within the above range, 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. Can be done. This can prevent the bead apex 9 from being locally bent at the outer end 9A in the radial direction, and can prevent the strength of the carcass cord near the outer end 9A from decreasing.
Followability with the carcass 6 is enhanced, and separation, ply loose, etc. of the carcass 6 can be prevented.

Also, since the 100% modulus MS of the sidewall rubber 17 is set to a low value of 10 to ²⁰ kgf / cm ² , it can be expanded and contracted 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.
Larger than f / cm ² , 100% modulus MS is 20kgf
/ Cm ² and 71% 100% modulus MC
When it is larger than f / cm ² , the rigidity of the bead portion 4 becomes excessively large, and the strength of the carcass cord is reduced near the outer end 9A of the bead apex 9 in the radial direction, and ply loose is induced.

The 100% modulus MA is 14 kgf / cm.
Smaller than ² , 100% modulus MS is 10 kgf / cm ²
Smaller and 100% modulus MC is 55kgf / cm
^When it is smaller than ² , the required rigidity of the bead portion 4 cannot be obtained, and the running performance is greatly impaired. The bead apex 9 is located inside the bead,
The rubber part requires higher rigidity than that of No. 7, so that the 100% modulus MA is preferably 64 kgf / cm ² or more.

The 100% modulus MT is set to 10
Since the modulus is larger than the 0% modulus MA and smaller than the 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.

[0064]

Embodiment 1 FIG. 1 shows a tire size of 11R22.5.
A heavy-duty radial tire having the configuration shown in Table 1 was prototyped based on the specifications in Table 1, and the bead heat (bead durability), tire weight, and rim set of the test tires (conventional examples, Examples 1 to 8, and Comparative Examples 1 to 3) were prepared. The performance was compared. The bead core shape of the conventional example is schematically shown in FIG. 9, and the bead core shape of Comparative Example 3 is schematically shown in FIG.

The test conditions are as follows. 1) Bead heat generation: The test tire was 22.5 × 8.25.
Attached to 5 ° deep rim and filled with internal pressure 8.00 ksc,
The tire was run on the drum at a load of 9000 kg and a speed of 20 km / h, and the tire temperature of the bead portion was measured at every running distance of 1000 km. The smaller the value, the lower the heat generation. 2) Tire weight: The weight of each sample tire was set to 100 based on the conventional example.
It was indicated by an index. A smaller value indicates a lighter weight. 3) Rim assembly performance: ○ indicates good, Δ indicates slightly poor rim assembly performance, and X indicates extremely poor rim assembly performance.

[0066]

[Table 1]

As shown in the test results shown in Table 1, Example 1
No. 8 to No. 8 exhibit excellent rim assembly performance, can reduce bead heat generation to 81 to 88, and have improved bead durability. Also, the tire weight has been reduced to 86 to 90, and the weight has been reduced.

In Comparative Examples 1 and 2, although the bulge and the recess were formed in the bead core, the degree of protrusion of the bulge, that is, the ratio R / W was too small or too large. The effect of improving durability (bead heat generation) is inferior, and almost no improvement in rim assembly performance is observed. In the case of Comparative Example 3, since the contour of the swollen portion is different from a smooth curve such as a V-shape, there is no effect of eliminating the rubber accumulation region between the carcass and the bead durability (bead heat generation) is improved. The effect is not achieved. Also, there is almost no improvement in rim assembly performance.

[0069]

EXAMPLE 2 The compression (contact pressure) between the bead and the rim was measured using the tires of the conventional example and the example 2 in Table 1, and the fitting state with the rim was compared. The measurement is performed by embedding a pressure sensor at each position of the bead portion as shown in FIG. 7A, assembling the rim into a rim J, filling the internal pressure, and measuring the contact pressure at each position. FIG. 7B shows the result. The solid line indicates Example 2 and the dashed line indicates the conventional product. 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 at a position where the flange arc angle ε of the rim flange J2 is 45 °.

As apparent from FIG. 7B, it was confirmed that the product 2 of the present invention, which is the product of the present invention, can maintain a higher compression with the rim seat surface J1 than the conventional one. Further, in the conventional product, it was also confirmed that the compression with the rim flange J2 at the position was extremely high due to the inverse correlation of the low compression at the position.

Further, in the product of the present invention, the compression with the rim flange J2 at the position is reduced by the synergistic effect of maintaining the compression with the rim seat surface J1 at each position higher than that of the conventional product.
It could be confirmed that it was optimized.

[0072]

As described above, the pneumatic tire of the present invention has the following features.
According to the configuration of the first aspect, the rubber accumulation area below the bead core between the carcass and the carcass is eliminated, so that the bead compression targeted at the design stage can be maintained in the actual tire. As a result, the bead compression between the rim flange and the rim flange is optimized without excessively increasing, and the durability of the bead portion can be greatly improved, for example, the damage of the carcass winding portion can be prevented.

Further, the rigidity of the bead core can be reduced while maintaining the necessary fitting force with the rim J, and the rim assembling performance can be improved. Further, by forming the concave portion, the bead core can be reduced in weight, and the positional accuracy of the installation of the bead apex can be improved to improve the uniformity, while the work efficiency of the installation can be 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. 3 is an enlarged sectional view showing an example of a bead core.

FIG. 4 is an enlarged sectional view showing another example of the bead core.

FIG. 5 is a diagram showing still another example of the contour shape of the bulging portion of the bead core.

FIG. 6 is a diagram illustrating a process of forming a tape bead type bead core;

FIG. 7A is a diagram showing measurement positions of bead compression, and FIG. 7B is a diagram comparing bead compression values of a product of the present invention and a conventional product.

FIG. 8 is a schematic sectional view of a bead core used in the tire of Comparative Example 3 in Table 1.

FIG. 9 is a schematic sectional view of a bead core used in the conventional tire shown in Table 1.

FIG. 10 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 6 Carcass 10 Bulging part 10e Both ends of bulging part 10c Bulging part protruding end 11 Concave 16 Circular curve 30 Bead wire 32 Strand Si Radius inner surface of bead core So radial outer surface of bead core

Continuation of the front page (56) References JP-A-53-102389 (JP, A) JP-A-54-57703 (JP, A) JP-A-58-191611 (JP, A) JP-A-59-199309 (JP) JP-A 9-315112 (JP, A) JP-A 7-1925 (JP, A) JP-A 7-279070 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) B60C 15/04 B29D 30/48

Claims (3)

(57) [Claims] 1. A pneumatic tire having a carcass that is folded and locked by an annular bead core embedded in a bead portion from a tread portion to a sidewall portion, wherein the bead core includes one or more bead wires. In the cross section including the tire axis, a bulging portion projecting inward in the radial direction is formed at the center in the width direction of the radial inner surface of the bead core, and the radial direction of the bead core is formed. At the center in the width direction of the outer surface, a concave portion is formed which is depressed inward in the radial direction. A pneumatic tire characterized in that the radius of curvature R of an arc curve connecting the following is 0.35 to 2.0 times the width W of the bead core in the tire axial direction. 2. The pneumatic tire according to claim 1, wherein the bead core is formed by continuously winding one bead wire spirally and in multiple stages. 3. The pneumatic tire according to claim 1, wherein the bead core is formed by winding a plurality of bead wires in the axial direction into a tape-like strand formed in an annular shape and in multiple stages.