JP4699836B2 - Pneumatic bias tire - Google Patents

Description

  The present invention relates to a pneumatic bias tire, and more particularly to a pneumatic bias tire including a plurality of bead cores in a bead portion.

Conventionally, as a means for improving the bead portion durability of a heavy-duty bias tire, it has been generally reinforced by a method of increasing the number of strand beads (see, for example, Patent Document 1). Basically, in addition to the strength for maintaining the internal pressure, it is necessary to withstand the strain generated by the tire deformation caused by the load.
There is a case where a problem of bead burst occurs in a tire for a mineral excavator (wheel loader) having a rim diameter of 57 inches, which is currently operating in a mine having a very limited use condition.

As a phenomenon, the separation generated around the bead core extends over the entire circumference in the cross section, and when it spreads in the circumferential direction, the internal air is ejected to the outside.
Usually, reinforcement is achieved by increasing the number of needles of the bead core as in the past, and it is possible to respond by increasing the strength, but due to dimensional restrictions on the rim on which the tire is mounted, the product bead width limit has been reached. As described above, the number of stitches of the bead core cannot be increased in the width direction, and there is no choice but to increase in the height direction.
On the other hand, as the mechanism of this phenomenon is elucidated, increasing the number of needles in the radial direction of the bead core increases the distortion of the core of separation, so there is no way to deal with it. It was.
JP 08-216632 A

  The present invention has been made to solve the above-mentioned problem, and is a heavy-duty vehicle capable of improving the durability of the bead portion by suppressing the bead burst caused by the separation generated around the bead core while suppressing the cost. It is an object of the present invention to provide a pneumatic bias tire suitable for the above.

The inventors have conducted various experimental studies and found the following.
First, as a result of the actual product confirmation, it was found that separation occurred from the outermost one in the width direction and the second bead core among the plurality of bead cores.
The mechanism of the occurrence of this separation was as follows.

First of all, the tire deforms when the tire supports the load.At this time, the greatest distortion occurs in the core part of the separation. It was found to be near the part.
The movement of the carcass in this portion will be described from the deformation of the tire. (1) As shown in FIG. 3A, the tire 100 bends to support the load. (2) When the tire 100 is bent, the tire tread surface portion in the vicinity of the stepped-in portion and the kick-out portion is pushed upward obliquely (in the direction of arrow A). (3) As shown in FIG. 3B, one cord 102 of the carcass ply layer intersecting from the vicinity of the side to the bead portion is pulled, and the other cord 104 receives a compressive force. As a characteristic of nylon, which is a material for carcass cords, deformation at the time of compression is many times larger than that at the time of pulling, so that deformation due to pulling becomes dominant. (4) The movement of the core part of the separation is caused by the above deformation (see FIG. 3). As shown in FIG. 4, the carcass ply layer 106 in which a plurality of cords (shown by dotted lines) are embedded is a bead core. 5 is used to move back and forth in the circumferential direction (arrow B direction) with the lower end portion (radially inner end portion) of 108 as a fulcrum, so that shear deformation (arrow C direction) as shown in FIG. Will occur.
It was found that this caused the separation 110 around the bead core.

  Therefore, suppressing tire deformation (deflection) reduces distortion at the core of separation, so there is a corresponding method such as increasing the carcass ply layer to increase the internal pressure. There is a limit value for the product bead width, and it cannot be increased.

The point of the present invention lies in the above-mentioned “back and forth in the circumferential direction with the lower end of the core as a fulcrum”. It can be seen that the displacement of the carcass ply layer is larger as the upper end portion (radially outer end portion) of the bead core that is the core of the separation is higher, and the displacement is smaller as it is lower.
From this, it can be seen that reducing the core height of the bead core on the outer side in the width direction, which is a separation nucleus, is an effective method for reducing distortion.

Further, when the strength cannot be reduced, it is also an effective means to add the number of stitches reduced at the first and second from the outside to the first and second inside.
However, if you lower it too much, it will lower the basic durability, so there is a limit to lowering it. By clarifying the limit level that can reduce the distortion reduction effect, It became possible to keep costs down.

The invention according to claim 1 is a pneumatic bias tire comprising four bead cores in a bead portion, and a carcass ply wound around each bead core, wherein the inner ends in the tire radial direction of the four bead cores are connected to each other. The connecting virtual line is set in parallel with the bead seat when the rim is mounted , and among the four bead cores, the height measured in the radial direction from the virtual line when the two bead cores on the outer side in the tire width direction are mounted. The height dimension is set to be lower than the height dimension of the two bead cores on the inner side in the tire width direction, and the two bead cores on the inner side in the tire width direction are set to have the same height, and the two bead cores on the outer side in the tire width direction are set. Is characterized by having the same height.

Next, the operation of the pneumatic bias tire according to claim 1 will be described.
An imaginary line connecting the inner ends in the tire radial direction of the four bead cores is set in parallel with the bead seat when the rim is mounted, and the imaginary when the rim of the two bead cores on the outer side in the tire width direction is mounted among the four bead cores. The height measured in the radial direction from the line is set lower than the height of the two bead cores on the inner side in the tire width direction, and the two bead cores on the inner side in the tire width direction are set to have the same height. The two bead cores on the outer side in the direction can be set to have the same height, so that the displacement of the carcass ply around which the bead core is wound can be reduced when the tire is loaded on the tire. Generation of separation as a nucleus can be suppressed.

In addition, since addition of a member etc. is not performed for generation | occurrence | production suppression of the said separation, cost can be held down.
In addition, the arrangement | positioning area | region of a bead core here means between the tire width direction outermost end of the bead core of a tire width direction outermost side, and the tire width direction innermost end of the bead core of a tire width direction innermost side.

  Since the imaginary line connecting the tire radial inner ends of multiple bead cores is set parallel to the bead seat when the rim is mounted, the surface pressure distribution of the bead base is made uniform, preventing separation that occurs around the bead core. I can do it.

In the pneumatic bias tire according to claim 1, when the height of the lowest bead core among the plurality of bead cores is H1, and the height of the highest bead core is H2, = 0.8-0.9H2 is satisfied.

Next, the operation of the pneumatic bias tire according to claim 2 will be described .
When H1 <0.8H2, the cross-sectional area of the bead core becomes too small, and the basic durability is impaired.
On the other hand, when H1> 0.9H2, the effect of suppressing the occurrence of separation is insufficient.

  As described above, according to the pneumatic bias tire of the present invention, it is possible to improve the durability of the bead portion by suppressing the bead burst caused by the separation generated around the bead core while suppressing the cost. It has the effect.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the bead portion 14 of the pneumatic bias tire 10 of the present embodiment attached to the rim 12 has a first bead core 16, a second bead core 18, a third bead core 20, and the like from the inner side in the tire width direction. A fourth bead core 22 is disposed.
In the present embodiment, an imaginary line FL connecting the inner ends in the tire radial direction of each bead core is set in parallel with the bead seat 24 of the rim 12.

Here, at least one bead core disposed on the outer side in the tire width direction with respect to the center portion in the tire width direction of the arrangement region 26 in which the first bead core 16 to the fourth bead core 22 are disposed is a bead seat 24 when the rim is mounted. It is necessary to set the height dimension H measured in the radial direction to be lower than the height dimension H of the bead core disposed on the inner side in the tire width direction with the center portion in the tire width direction of the arrangement region 26 as a boundary.
As shown in FIG. 2, when the height of the lowest bead core is H1, and the height of the highest bead core is H2, it is preferable to satisfy the relationship of H1 = 0.8 to 0.9H2.

  Each bead core is formed by winding a bead wire (not shown) a plurality of times so as to be rectangular in cross-sectional shape. In the first bead core 16 and the second bead core 18, the bead wires are adjacent to each other. The first row is formed side by side, and each step is formed by winding 38 steps outward in the radial direction. In the third bead core 20 and the fourth bead core 22, the bead wires are arranged in 19 rows adjacent to each other. Each step is formed by winding 32 steps radially outward. As shown in FIG. 2, in this embodiment, the third bead core 20 and the fourth bead core 22 have a radial height. Is H1, the radial height of the first bead core 16 and the second bead core 18 is H2, and the relationship between H1 and H2 is H1 = 0.84H2.

  The first bead core 16 includes a plurality of first carcass plies 28, the second bead core 18 includes a plurality of second carcass plies 30, and the third bead core 20 includes a plurality of third carcass plies 32. A plurality of fourth carcass plies 34 are wound around the fourth bead core 22 from the inner side to the outer side in the tire width direction.

Each of these carcass plies has a general configuration in which a plurality of nylon cords arranged in a hook shape are covered with rubber, and the inclination directions of the cords are adjacent to each other in order to make the tire a bias structure. Has been.
In the bead portion 14, a reinforcing layer 36 is embedded from the inner side in the tire radial direction of each bead core to the outer side of the bead portion.

(Function)
Next, the operation of the pneumatic bias tire 10 of this embodiment will be described.
In the pneumatic bias tire 10 of the present embodiment, the height H1 of the third bead core 20 on the outer side in the tire width direction and the fourth bead core 22 that is likely to become a core of separation among the four is set as the first bead core on the inner side in the tire width direction. 16 and the second bead core 18 is set lower than the height H2 of the second bead core 18, so that the displacement of the third carcass ply 32 wound around the third bead core 20 at the time of tire load rolling and the fourth bead core 22 are wound around. The displacement of the fourth carcass ply 34 at the time of rolling with a tire load can be reduced, and the occurrence of separation with the third bead core 20 and the fourth bead core 22 as the core can be suppressed.

Further, in the pneumatic bias tire 10 of the present embodiment, since no member is added to suppress the occurrence of the separation, the cost can be suppressed.
When H1 <0.8H2, the cross-sectional area of the bead core becomes too small, and the basic durability is impaired. On the other hand, when H1> 0.9H2, the effect of suppressing the occurrence of separation is insufficient.
Since the imaginary line FL connecting the tire radial inner ends of the plurality of bead cores is set in parallel with the bead seat 24 when the rim is mounted, the surface pressure distribution of the bead base portion is made uniform and the separation generated around the bead cores. Can be suppressed.

[Other Embodiments]

As long as the above-described conditions are satisfied, the number of rows and stages of bead wires, the number of bead cores, and the cross-sectional shape of the bead core are not limited to those of the present embodiment.
Further, the height of the bead core on the inner side in the tire width direction may be increased by the amount corresponding to the decrease in the height of the bead core on the outer side in the tire width direction.

上記表内の「※タイヤ断面内コア周りセパレーション長さ」とは、タイヤ周上８箇所を等間隔にラジアル方向に切断した断面にて、ビードコア周りのセパレーションを各断面にて測定し、一番大きい長さを示している。 (Test example)
In order to confirm the effect of the present invention, an endurance test of the bead portion was conducted at three mines using an actual vehicle. In addition, the test vehicle used the same vehicle as three places. Test conditions and test results are as described in Table 1 below.

In the above table, “* Separation length around the core in the tire cross section” is a cross section obtained by cutting the 8 circumferences of the tire in the radial direction at equal intervals, and measuring the separation around the bead core in each cross section. It shows a large length.

  From the test results, it can be seen that the durability of the tire of the example to which the present invention is applied is greatly improved as compared with the tire of the conventional example.

It is sectional drawing of the bead part of the pneumatic bias tire which concerns on embodiment. It is sectional drawing of a bead core. (A) is a side view which shows a part of tire, (B) is a side view which shows a part of carcass. It is a perspective view which shows a bead core and a part of carcass. (A) is sectional drawing of bead core vicinity, (C) is explanatory drawing which shows the shearing force concerning the rubber | gum of the arrow D part of FIG. 5 (A).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pneumatic bias tire 12 Rim 14 Bead part 16 1st bead core 18 2nd bead core 20 3rd bead core 22 4th bead core 24 Bead seat 26 Arrangement area 28 1st carcass ply 30 2nd carcass ply 32 3rd carcass ply 34 4th Carcass ply

Claims (2)

A pneumatic bias tire having four bead cores in a bead portion, and a carcass ply wound around each bead core,
The imaginary line connecting the tire radial direction inner ends of the four bead cores is set in parallel with the bead seat when the rim is mounted,
Of the four bead cores, the height dimension measured in the radial direction from the imaginary line when the rim of the two bead cores on the outer side in the tire width direction is mounted is lower than the height dimension of the two bead cores on the inner side in the tire width direction. A pneumatic bias characterized in that the two bead cores on the inner side in the tire width direction are set to the same height, and the two bead cores on the outer side in the tire width direction are set to the same height. tire. 2. The relationship of H1 = 0.8 to 0.9H2 is satisfied, where H1 is the lowest bead core height and H2 is the highest bead core among the plurality of bead cores. The pneumatic bias tire described in 1.

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