JPH01215607A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To prevent the deformation and the decrease in airtightness of a bead core by forming the section of the bead core in a polygonal shape with each upper, lower, right and left side areas, and setting the inclination of each side area with a specific relation. CONSTITUTION:The section of bead core 1 is formed in a polygonal shape consisting of a base (a) on a bead base side, a left side (b) on a bead toe side, an upper side (c) on a bead filler side, and a right side (d) on a bead heel side. And the inclination theta1 of the base (a) to tire axial direction is set so as to be the same as the inclination of a rim base to tire axial direction. And an angle beta formed by the intersection of the base (a) and the left side (b) is set at 70 deg.-90 deg., and the inclination theta2 of the upper side (c) to tire axial direction is made smaller than the said inclination theta1 of the base (a) and set in the opposite direction to that of the inclination of the base (a). Consequently, the rigidity of the bead core 1 on the bead toe side can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pneumatic tire with improved rigidity on the bead toe side of a bead core, particularly a radial tubeless tire for heavy loads such as trucks and buses.

[Prior art]

For example, radial tubeless tires for heavy loads are
It has a bead structure as shown in Figure (A). Fourth
In Figure (A), a bead core 1 in a bead portion 10
A carcass layer 2 is rolled up around the tire from the inside to the outside, and a reinforcing layer 3 is placed on the outside of this carcass j12.
is located. A lower bead filler 4 and an upper bead filler 5 are arranged above the bead core 1, and a reinforcing layer 6 is arranged outside the carcass layer turn-up edge 2u, reinforcing layer 3, and upper bead filler 5.

7 represents a bead toe portion, 8 represents a bead heel portion, and 9 represents a bead base portion. The bead base portion 9 is a rim base portion (
(not shown) at approximately the same angle of inclination.

An example of a bead core is shown in FIG. 4(B) and FIG. 4(C), respectively. In FIG. 4(B), the bead core has a hexagonal cross section made up of a plurality of bead wires 11 with a circular cross section, and in FIG. 4(C), the bead core has a rectangular cross section made of a plurality of bead wires 11 with a rectangular cross section. be. Further, the bead core shown in FIGS. 4(B) and 4(C) is inclined at an angle α with respect to the tire axial direction E, substantially the same as the rim base portion.

It is well known that in such tires, tensile forces of the type that form in the bead core act upon internal pressure filling or load transfer. In particular, in radial tires that use substantially non-stretchable cords for the carcass cords in the carcass layer, the carcass cords are arranged in the normal direction of the annular bead core. As shown in the figure, the force exerted by the internal pressure during internal pressure filling or load transfer is transmitted to the bead core l, so the force acting in the normal direction of the bead core is smaller than that of a bias tire in which the carcass cord is made of plies laminated on the bias. becomes large. In FIG. 5(A), 12 represents a rim, and 13 represents a rim base portion.

Furthermore, in radial tubeless tires for trucks and buses, the demand for which is increasing rapidly due to the development of expressway networks in recent years, the rim diameter of the rim base part generally has an inclination of 156 with respect to the tire axial direction E in order to maintain airtightness. Since the inner diameter is smaller than that of the rim 12 and the bead base is inclined in the same way as the rim base, the reaction force from the rim 12 becomes extremely large as shown in Fig. 5 (B), and the tire A large force m acts outward in the radial direction F.

Therefore, the bead base portion 9 rises from the position indicated by the dotted line to the position indicated by the solid line.

As a result, when the tire is transferred, compressive deformation is repeated in the rim base due to the bending deformation of the com-haheed core in the bead toe, and when the tire is used for a long period of time, the rubber properties deteriorate due to the high temperature of the air inside the tire. ), the rubber at the bead toe part undergoes permanent deformation that cannot be recovered. In FIG. 5(C), the dotted line shows the shape before use, and the solid line shows the shape after use. Further, T represents the deformed length in the axial direction E, and S represents the deformed length in the radial direction F. Such deformation occurs in a narrow range at the tip of the bead toe portion 7 at the initial stage of use, but once such deformation occurs, the contact area between the bead base portion 9 and the rim base portion is narrowed, and this As a result, the rim reaction force per unit width of the bead base portion increases, which causes the deformation to progress further toward the bead heel portion 8.

When this deformation occurs, the area of the bead base that can substantially contact the rim base becomes smaller, which impairs the airtightness of the tire, makes it difficult to inflate when assembling the rim, and furthermore, the area of the bead base that can substantially contact the rim base becomes smaller. Vibration will occur due to unstable fitting of the bead base to the bead base.

Furthermore, when the contact area between the rim base and the bead base decreases, the firm fixation of the carcass cord under the bead core is impaired, which increases the movement of the carcass cord and increases the movement of the carcass layer turn-up edge. , separation of this edge portion will be induced.

Conventionally, in order to solve these problems, for example, as shown in FIG. 6, a bead wire 11 is further laminated on the dotted line portion of the bead core l to reinforce the bead core l without destroying the hexagonal cross-sectional shape of the bead core l. However, in this case, the overhang amount wl toward the bead toe side increases to the overhang amount W2, which causes new problems such as a lack of stability in the shape of the bead core 1 and an increase in the weight of the bead core 1. It ends up.

Therefore, the inventor of the present invention analyzed a large number of tires regarding the deformation of the bead toe of radial tubeless tires, and found that radial tubeless tires that have been used for a long period of time
The inclination angle of the bead base part with respect to the axial direction E that was originally held (when new) was not maintained, and as shown in Fig. 7, the bead core 1 deformed as shown by the dotted line, and the bead toe part rose up. We discovered that the slope of the bead base changes slightly in the horizontal direction. Furthermore, as a result of a detailed study of the physical properties of the bead wires in various parts of the bead core of radial tubeless tires that have been used for a long period of time, as shown in Figure 8, the physical properties of the bead wires on the bead toe side deteriorated, and the bead wires on the bead core central area and bead heel side decreased. (The elongation index at break of the bead wire on the bead toe side is small.)

It has also been found that as the period of use (mileage) of the tire increases, the deterioration in the physical properties of the bead wire tends to gradually expand from the bead toe side to the central region of the bead core. For this reason, we have come to the conclusion that in order to prevent deformation of the bead toe of a radial tubeless tire, it is better to place more bead wires in the part of the bead core on the bead toe side to increase the strength and rigidity of the bead core in this part. .

[Purpose of the invention]

The present invention has been made in view of these circumstances, and by improving the rigidity of the bead toe side of the bead core, deformation of the bead toe part after long-term use is suppressed, and a decrease in airtightness is prevented. It is an object of the present invention to provide a pneumatic tire that improves air injectability during rim assembly and prevents separation of the turn-up edge of the carcass layer.

[Structure of the invention]

For this reason, the present invention provides a pneumatic tire having an annular bead core, in which the cross section of the bead core has a polygonal shape consisting of a bottom side a on the bead base side, a left side on the bead toe side, an upper side C on the bead filler side, and a right side d on the bead heel side. The angle of inclination θ of the base a with respect to the tire axial direction is
1 is almost the same as the inclination angle of the rim base portion with respect to the tire axis direction, and the intersection angle β between the base a and the left side is 7.
0° to 90'', and the inclination angle θ2 of the upper side C with respect to the tire axis direction is smaller than the inclination angle θ, and the inclination direction of the upper side C is opposite to the inclination direction of the base a. This article focuses on pneumatic tires.

Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 1(A) is an explanatory cross-sectional view showing an example of the bead structure of the pneumatic tire of the present invention, and FIG. 1(B) is an explanatory cross-sectional view showing the main part thereof.

In FIG. 1(A), as in FIG. 4(A), a carcass layer 2 is rolled up around the bead core l in the bead portion 10 from the inside of the tire to the outside. A reinforcing layer 3 is arranged.

A lower bead filler 4 and an upper bead filler 5 are arranged above the bead core 1, and a reinforcement M6 is arranged outside the carcass layer turn-up edge 2u, reinforcing layer 3, and upper bead filler 5. 7 represents a bead toe portion, 8 represents a bead heel portion, and 9 represents a bead base portion.

The bead base portion 9 is inclined with respect to the tire axial direction E at approximately the same angle of inclination as the rim base portion in order to ensure good fitting to the rim base portion.

In the present invention, as shown in FIG. 1(B), the bead core l
has a polygonal cross section consisting of a bottom side a on the bead base side, a left side on the bead toe side, an upper side C on the bead filler side, and a right side d on the bead heel side. Tire axial direction E of base a
The inclination angle θ with respect to the tire axial direction is approximately the same as the inclination angle of the beam base portion with respect to the tire axial direction.

The intersection angle β between the base a and the left side is 70° to 90@.

If β is less than 70", the lowest point on the bead toe side of the bead core 1 will be sharp, and there is a risk of damage to the carcass cord due to rubbing between the carcass cord and the bead core at this part. On the other hand, if β exceeds 90°, the bead core 1 will be sharp. The amount of overhang of the upper part on the bead toe side of No. 1 becomes large, and the physical properties of the bead wire in this part are likely to deteriorate.In addition, in order to increase the rigidity of the bead toe part, the inclination angle θ2 of the upper side C with respect to the tire axial direction E is set to be smaller than the inclination angle θ1. is also small, and the upper side C
The direction of inclination of the base a is opposite to the direction of inclination of the base a.

A specific example of the bead core 1 shown in FIG. 1(B) is shown in FIG.
) to (E), respectively. The left side is not limited to a straight line, but may be a curved line in which the substantial outer ring line of the bead wire is constituted by a circular arc, as shown in FIG. 2(D).

Note that the cross-sectional shape of the bead wire constituting the bead core may be circular, square, or other shapes, but it is preferable to have a circular shape in consideration of friction between each corner of the bead core and the carcass cord, productivity of the bead core, etc. preferable.

Examples are shown below.

Example The following tires were manufactured.

(11 Tires of the present invention.

Tire size IIR22,514PR, bead structure shown in FIG. 3(A). FIG. 3(A) is substantially the same as FIG. 1(A). β=80°.

(2) Conventional tire 10 Tire size IIR22,514PR, bead structure shown in FIG. 3(B). FIG. 3(B) is substantially the same as FIG. 4(A), and the structure of other parts and the constituent materials of the tire are the same as the above-described tire of the present invention.

(3) Conventional tire 2° tire size IIR22,514PR, bead portion structure shown in FIG. 3(C). FIG. 3(C) is substantially the same as FIG. 3(B) except that the bead core 1 has a rectangular cross section. The structure of other parts and the constituent materials of the tire are the same as those of the tire of the present invention described above.

(4) Comparison tires.

Tire size IIR22,514PR, bead structure shown in FIG. 3(D). As mentioned earlier, Figure 3 (D) shows
This is a tire that aims to improve the strength and rigidity of the bead core using the conventional method shown in FIG. The structure of other parts and the constituent materials of the tire are the same as those of the tire of the present invention described above.

These tires are installed on a 10 ton vehicle 2/D-D model vehicle and meet the JATMA standard Too kgf/cJ.

After driving for 150,000 km under the condition of 2500 kg, it was removed and the amount of deformation after driving with respect to the shape of the bead toe when new (
am) was measured by the method shown in FIG. 5(C).

In addition, the inflatability during rim assembly was evaluated by once removing the tire from the rim, reassembling the rim, and investigating the difficulty of inflating at that time. At this time, if a single worker was able to inject air into all tires with the same specifications that were submitted for evaluation without using a special tire bead sealing jig, the rating was "O".
The evaluation of tires consisting of several tires with the same structure is as follows.
If the evaluation of another tire was rXJ, the evaluation of that tire was shown as “△”. In the case where a single worker was unable to inject air during the above work and used a jig to seal the bead portion, it was rated "x".

The fit with the rim was expressed as the amount of variation in the distance between the rim flange and the tire rim check line over the entire circumference when the tire was filled with the maximum air pressure according to the JATMA standard.

Furthermore, the tires were finally cut after running, and the presence or absence of separation at the turn-up edge of the carcass layer was investigated, and for tires in which separation had occurred, the maximum crank length was measured.

These results are shown in Table 1 below.

(Leaving space below)] As can be seen from Table 1, the tire of the present invention has sufficiently improved rigidity on the bead toe side of the bead core, and has just recently shown sufficient effectiveness in suppressing deformation of the bead toe. This improved the air injectability when assembling the rim, the fitability with the rim when assembling the rim again, and it was also effective in preventing separation of the carcass layer turn-amp edge. I understand.

〔Effect of the invention〕

As explained above, since the bead core of the tire of the present invention is configured as described above, the deformation of the bead toe after long-term use is suppressed, the deterioration of airtightness is prevented, and the inflatability during rim assembly is improved. It is possible to improve this and also to prevent the occurrence of separation of the turn-up edge of the carcass layer.

[Brief explanation of the drawing]

FIG. 1(A) is a cross-sectional explanatory diagram showing an example of the bead structure of the pneumatic tire of the present invention, FIG. 1(B) is a cross-sectional explanatory diagram showing the main part thereof, and FIGS. ) are cross-sectional explanatory views showing specific examples of the bead core in the present invention, and FIGS. 3(A) to (D) are cross-sectional explanatory views each showing an example of the bead portion structure. FIG. 4(A) is a cross-sectional explanatory diagram showing an example of the bead structure of a conventional pneumatic tire, and FIGS. 4(B) and (C) are cross-sectional explanatory diagrams showing an example of the bead core in FIG. 4(A), respectively. Figures 5(A) and 5(B) are cross-sectional explanatory diagrams showing how internal pressure acts on the bead of a conventional pneumatic tire, respectively, and Figure 5(C) is a conventional pneumatic tire used for long periods of time. A cross-sectional explanatory diagram showing how the bead toe portion deforms later. Fig. 6 is a cross-sectional explanatory diagram showing another example of the bead core in a conventional pneumatic tire. Fig. 7 is a cross-sectional explanatory diagram showing the bead core of a conventional pneumatic tire after long-term use. FIG. 8 is an explanatory diagram showing the physical properties of the bead wires in various parts of the bead core after long-term use of a conventional pneumatic tire. ■...Bead core, 2...Carcass layer, 2u...
Carcass layer turn-up edge, 3... Reinforcement layer, 4.
...Lower bead filler, 5...Upper bead filler, 6
... Reinforcement layer, 7... Bead toe part, 8... Bead heel part, 9... Bead base part, 10... Bead part, 11... Bead wire, 12... Rim, 13...
...Rim base part. Figure 3 (A) Figure 3 CB) Figure 2 (A) Figure 2 (C) Figure 2 (E) Figure 2 (B) Figure 2 (D) Figure 4 (A) E 4 Figure (B) Figure 4 (C)
Figure 5 (A) Figure 5 (B) Figure 5 (C) Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] In a pneumatic tire having an annular bead core, the cross section of the bead core has a bottom side a on the bead base side, a left side b on the bead toe side, and an upper side c on the bead filler side.
The bead heel side right side d has a polygonal shape, and the inclination angle θ_1 of the base a with respect to the tire axial direction is almost the same as the inclination angle of the rim base with respect to the tire axial direction. Intersection angle β is 70°~
90°, an inclination angle θ_2 of the upper side c with respect to the tire axial direction is smaller than the inclination angle θ_1, and the inclination direction of the upper side c is opposite to the inclination direction of the base a. tire.