JP2000016034A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a width of a bead core without causing weight increase, rise of bead core rigidity, or decrease in the number of stages, and improve bead durability. SOLUTION: A bead core 5 is of a roughly hexagonal form having a flat cross section comprising wire lines Li of bead wires 10 disposed in a lateral direction along a bead bottom part by winding the bead wires 10 and stacked in plural stages in a vertical direction perpendicular to the bead bottom part. A cross section of the bead wire 10 is roughly of an elipse form in which a ratio B/C of a lateral wire width B and a vertical wire height C is 1.15-4.00.

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 bead durability without increasing weight and is particularly suitable for heavy load vehicles.

[0002]

2. Description of the Related Art Conventionally, as a bead structure of a tire for a heavy load vehicle such as a truck or a bus, as shown schematically in FIG. By increasing the rubber volume of the filled bead apex b and increasing the bead rigidity,
With improved bead durability by reducing deformation due to applied load, or as shown schematically in FIG. 7 (B), the rubber volume of bead apex b is significantly reduced,
It is known that the ply winding portion a2 is raised to be close to the ply body a1 to reduce the weight while maintaining bead durability.

On the other hand, in recent years, the bead structure has been further reviewed, and in order to improve the bead durability, as shown in FIGS. 7A and 7B, the radial direction of the bead core d is changed. It has been found that securing a distance X in the tire axial direction from the lowest bead heel point P is extremely important.

That is, according to the experiment of the present inventor, FIG.
As shown in the figure, when the distance X is in the range of about 17 mm or more, extremely high bead durability is exhibited. this is,
When the distance X is large, the profile of the ply body a1 extending from the bead core d is lying close to the profile at the time of tire deformation (the inclination angle with respect to the tire axial direction is small).
Therefore, it is inferred that the amount of deformation of the tire itself is reduced and durability is improved.

[0005]

In order to secure the distance X, it is proposed to increase the width of the bead core. However, simply increasing the number of wires in the wire row (lateral direction) of the bead core causes an increase in weight and lowers the rim assembly performance due to an increase in bead core rigidity. At this time, if the number of steps in the wire row is reduced, an increase in weight and a decrease in rim assemblage can be suppressed, but this reduction in the number of steps causes a new problem of impairing the fracture resistance of the bead core.

Accordingly, the present invention provides a bead wire in which the ratio B / C of the wire width B to the wire height C is 1.15 to 4.0.
The width of the bead core can be increased without increasing the weight, increasing the rigidity of the bead core, and reducing the number of steps, based on the use of an approximately elliptical wire having a flat cross section and a flattened cross section, and the bead durability can be improved. It aims to provide pneumatic tires.

[0007]

In order to achieve the above object, the present invention provides a pneumatic tire having a carcass which turns around a bead core embedded in a bead portion from a tread portion to a sidewall portion, The bead core is formed by winding a bead wire so that a wire row in which the bead wires are arranged in the horizontal direction along the bead bottom is superposed in a plurality of stages in a vertical direction perpendicular to the bead bottom, and the number of wires in the wire row in the middle section in the vertical direction is reduced. The cross section of the bead wire has a cross section of the bead wire in which the width B in the horizontal direction is larger than the height C in the vertical direction, and the cross section of the bead wire is larger than the number of steps in the vertical direction. The ratio B / C of the width B to the wire height C is 1.15 to 4.00.
It is characterized by having a substantially elliptical shape.

It is preferable that the distance X in the tire axial direction from the bead heel point of the lower inner edge of the bead wire at the lowermost step in the longitudinal direction and the innermost part in the lateral direction of the bead core is 17 to 22 mm in terms of bead durability.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates a case where the pneumatic tire 1 is a heavy-duty vehicle tire. The pneumatic tire 1 has a tread portion 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 reinforced by a carcass 6 extending between the bead portions 4 and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

The carcass 6 is formed of one carcass ply in which steel carcass cords are arranged at an angle of 75 to 90 degrees with respect to the tire equator C0. The carcass ply includes a ply body 6 extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the sidewall portion 3.
On both sides of A, a ply winding portion 6B that winds the bead core 5 from inside to outside in the tire axial direction is provided. Also, between the ply body 6A and the ply winding portion 6B,
A bead apex rubber 8 is tapered from the bead core 5 toward the outside in the tire radial direction.

As shown in FIG. 2, the bead core 5 is a so-called single-wind type ring formed by continuously winding a bead wire 10 in the tire circumferential direction. , A wire row Li (i = n) in which the bead wires 10 are laterally arranged along the bead bottom 4S.
Is formed into a flat and substantially hexagonal shape in which a plurality of stages n are stacked in the vertical direction perpendicular to the bead bottom 4S.

More specifically, in the bead core 5, the number of wires Nj of the wire row Lj at the middle stage in the vertical direction is larger than the number n of upper and lower stages in the vertical direction, and from the middle stage in the vertical direction to the uppermost stage and the lowermost stage in the vertical direction. , The number Ni of wires in the wire row Li is gradually reduced one by one. In this example, in the five rows (n = 5) of rows L1 to L5, the numbers N1 to N5 of the wires are set to 6, 7, 8,.
7 and 6 are illustrated.

The cross section of the bead wire 10 is, as shown in FIG.
And the ratio B / C of the vertical wire height C to 1.15
It is in the shape of a horizontally long flat ellipse of 4.00. As shown in FIG. 3 (B), this flat bead wire 10 is a conventional bead wire g having a circular cross section made of a hard steel wire in this example.
Is deformed by being crushed in the vertical direction, and has substantially the same cross-sectional area as the conventional bead wire g. Therefore,
When the diameter of the conventional bead wire g is A, in other words, the diameter of a bead wire having a circular cross section having the same cross-sectional area as that of the flat bead wire 10 is A, B × C ≒ A ^2. {0.93-0.
5, the ratio B / A ≒ 1.07 to 2.00.

This is because the core width WB can be increased to 1.07 to 2.00 times the conventional one while maintaining the same tensile strength (cross-sectional area) as the conventional bead core, and the core height WC can be reduced to 0. .93 to 0.5 times.

As a result, the distance X in the tire axial direction from the bead heel point P of the lower inner edge of the bead wire 10a located at the lowermost step in the vertical direction and the innermost direction in the lateral direction of the bead core 5 is set to a range of 17 to 22 mm without increasing the weight. Can be secured. The bead heel point P is the outer end point of the bead bottom surface in the tire axial direction, and is a reference point for the applicable rim diameter.

The distance X is, as described with reference to FIG.
By securing a value of 17 mm or more, the profile of the ply body 6A extending from the bead core 5 becomes a lying state close to the profile at the time of tire deformation, the amount of tire deformation itself is reduced, and bead durability can be improved. is there. If the distance X is larger than 22 mm, further improvement in bead durability cannot be expected, and the protrusion of the bead portion 4 inward in the tire axial direction becomes excessively large, resulting in an increase in weight. Further, the distance X is increased by increasing the core width WB.
Is maintained in the above range, the rubber thickness of the chafer rubber 15 from the bead core 5 to the side surface of the bead can be reduced, and reduction in weight and cost can be expected.

Further, as the core width WB increases, the fitting width with the rim sheet also increases, so that the fitting property with the rim is enhanced, and the carcass 6 can be firmly locked, so that the cord loose at the carcass end can be suppressed.

On the other hand, in the present invention, the core height WC is 0.93 to 0.93.
Since it is reduced by 0.5 times, the shear rigidity toward the central axis is reduced, and the rim assemblability can be improved. In addition, since the bead wire on the outer side in the radial direction has a larger length in the circumferential direction than that on the inner side, the function of receiving a load such as the amount of elongation against tensile stress itself becomes large, so that the bead wire on the inner side. It tends to be inferior. However, in the present application, since the core height WC is reduced and the outer bead wire 10 is shifted inward in the radial direction while maintaining the number of steps n, the bead core 5
The overall load supporting effect is enhanced, and the breakdown pressure can be improved. On the contrary, it is also possible to reduce the number of wires in each wire row Li by about 1 while maintaining the breakdown resistance and increasing the core width WB, as compared with the conventional bead core.
In this case, further weight reduction can be achieved.

The bead wire 10 may be an ellipse having a substantially straight portion 10e extending in the lateral direction as shown in FIGS. 4A and 4B, in addition to the ellipse. In such a case, the ratio C / A = 0.95 to 0.4, the ratio B
/A=1.10 to 1.80 is preferred.

Next, the bead apex rubber 8 is
As shown in FIG. 5, the bead apex height h1 from the tire axial line (bead base line) passing through the bead heel point P at the outer end in the radial direction is 6 of the carcass sectional height H (shown in FIG. 1). ~ 31%, more preferably 8 ~ 2
It has been reduced to the 2% range.

The carcass ply winding section 6B
In the present example, while extending radially outward in a concave arc shape along the outer surface of the bead apex rubber 8, from the vicinity of the outer end of the bead apex rubber 8,
An adjacent portion G extending substantially parallel to and near the ply body 6A is formed. The proximity portion G terminates radially inward from the tire maximum width point P1, that is, at a position of a height h2 where the amount of distortion under load is relatively small, and an outer end height h thereof.
2 is 15% to 50% of the carcass sectional height H, more preferably about 20 to 40%.

As described above, since the bead apex height h1 is greatly reduced and the proximity portion G is formed, the ply winding portion 6B approaches the neutral line of the stress at the time of tire deformation, and the ply winding portion The compression force to 6B is reduced, and cord breakage damage and the like can be effectively suppressed.

The ply body 6A is formed substantially linearly in a region along the bead apex rubber 8 and in a region forming the proximity portion G. Thereby, the cord path of the ply body 6A is shortened, 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 reduced.
In addition, by making the shape substantially linear, the thickness of the bead apex 8 is further reduced, and the ply winding portion 6B further approaches the neutral line of the stress, which further helps to suppress breakage damage of the cord. Note that the length LG of the proximity portion G along the ply is in the range of 35 to 70 mm, thereby providing a necessary bead rigidity.

The belt layer 7 has at least two sheets,
In the present example, the first belt ply 11 is composed of four belt plies 11 to 14 arranged in order from the carcass side toward the tread surface. The second to fourth belt plies 12 to 14 are arranged at an angle of about 50 to 70 degrees.
The belt cords are arranged at an angle of about 0 to 30 degrees.
In addition, the inclination direction of the cord is different between the second and third belt plies 12 and 13, thereby forming a strong truss structure and imparting necessary belt rigidity to maintain steering stability.

The bead core 5 is provided in the same manner as in FIG.
As shown in the above, the rubber volume of the bead apex is increased, and it is naturally applicable to tires with a structure in which the bead deformation is reduced by drastically increasing the bead rigidity.In particular, the rubber volume of the bead apex is greatly reduced. Further, the tire having the structure as in the present example exerts a more excellent effect.

The tire of the present invention is not limited to a heavy duty tire, and may be formed as various tires such as a tire for a passenger car and a tire for a small truck.

[0027]

Since the pneumatic tire of the present invention is constructed as described above, the width of the bead core can be increased without increasing the weight, increasing the rigidity of the bead core, and reducing the number of steps, and improving the bead durability. Can improve.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating an example of a bead core.

FIG. 3A is a sectional view showing an example of a bead wire used in the present application, and FIG. 3B is a sectional view showing a conventional bead wire.

FIGS. 4A and 4B are cross-sectional views showing another example of a bead wire.

FIG. 5 is an enlarged sectional view showing a bead portion.

FIG. 6 is a diagram showing a relationship between a distance X and bead durability.

7A and 7B are cross-sectional views showing the structure of a conventional bead portion.

[Explanation of symbols]

 2 Tread section 3 Side wall section 4 Bead section 5 Bead core 6 Carcass 10 Bead wire 4S Bead bottom Li wire row Ni wire row P wire heel point

Claims (2)

[Claims] 1. A pneumatic tire having a carcass that turns around a bead core embedded in a bead portion from a tread portion to a sidewall portion, wherein the bead core is formed by winding a bead wire so that the bead wire has a bead bottom portion. The wire rows lined up in the horizontal direction along the bottom are superposed in a plurality of stages in the vertical direction perpendicular to the bottom of the bead, and the number of wires of the wire rows in the middle in the vertical direction is larger than the number of the upper and lower stages in the vertical direction, so that the cross section is flattened. The bead wire has a hexagonal shape, and the cross section of the bead wire is such that the horizontal wire width B is larger than the vertical wire height C, and the wire width B
A pneumatic tire having a substantially elliptical shape with a ratio B / C of 1.15 to 4.00 with respect to a wire height C. 2. The air according to claim 1, wherein a distance X in a tire axial direction from a bead heel point of a lower inner edge of a bead wire located at a lowermost portion in a longitudinal direction and an innermost portion in a lateral direction of the bead core is 17 mm to 22 mm. Containing tires.