JPH06143921A - Tire for heavy load - Google Patents

Abstract

PURPOSE:To improve the dimensional stability and durability of a tread part and maintain the travelling performance of the same for a long period. CONSTITUTION:In a tire for heavy load having 70% or less of flatness rate a belt layer 7 comprises a belt ply7A having the maximum width and an adjacent belt ply 7B adjacent thereto. The ply width WB of the maximum width belt pry is set to 0.72-0.8 times the tire width W and the dimensional difference 2 in the axial direction of the tire between the outer ends of the adjacent belt ply and maximum width belt ply is set to 3 or less times the diameter of a belt cord of the adacent belt ply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty tire capable of improving the dimensional stability of the tread portion and maintaining the running performance for a long period of time, and at the same time, improving wear resistance and heat resistance to improve tire durability. Regarding

[0002]

2. Description of the Related Art Heavy duty tires for buses and trucks used under severe conditions such as heavy loads and high internal pressure,
The belt layer is formed by stacking a plurality of belt plies. Further, between two adjacent belt plies, the belt cords are arranged so as to intersect with each other, thereby exhibiting the hoop effect and increasing the rigidity of the tread portion.

The belt plies a and b have different belt widths as shown in FIG. 5, and by avoiding the matching of the belt end portions, the rigidity difference in the tread portion is eliminated. Conventionally, the dimensional difference z between the end portions of the belt plies has been set to be 4 to 6.5 times the diameter d of the belt cord forming the belt plies.

On the other hand, in the belt layer, at a part of the belt ply end, as shown in FIG. 5, the plies are separated from each other to have a rubber gauge y.

As a result, the restraining force of the belt layer sharply decreases at the end e of the belt layer as shown in the graph of FIG.

[0006]

Further, the tire cross-section height H
The flatness ratio H / W, which is the ratio of the tire width W to the tire width W, is 70% or less, and in a tire with improved high-speed running performance, the tread surface tends to be flat in the tire axial direction. As described above, as the restraint force of the belt layer decreases, the dimensional growth amount hs of the tread shoulder portion over time on the tread surface is equal to the growth rate hc at the central portion.
As a result of the test, it was confirmed that the amount was 1.5 times.

Since the amount of dimensional growth is not the same in the central portion of the tread surface and the tread shoulder portion, the cross-sectional shape of the tread surface changes with time as the vehicle travels, which lowers the traveling performance. However, uneven wear is likely to occur, and heat resistance is poor, so durability is reduced.

In addition, since the dimensional growth amount is not uniform, it is troublesome for the tire rehabilitation work due to the end of the primary life, such as reworking the tread portion after correcting the dimensional amount. There is.

In view of such a situation, the inventors of the present invention have conducted extensive research and as a result, have found that the unevenness in the dimensional growth amount is affected by the structure of the belt end in the tread shoulder portion. By regulating the size and relative position of the belt plies forming the end of the layer,
The inventors have completed the present invention by discovering that the dimensional growth amounts of the tread central portion and the tread shoulder portion on the tread surface can be made evenly close to each other.

The present invention is based on restricting the position of each end of a plurality of belt plies forming a belt layer.
The expansion over time in the central portion and the tread shoulder portion of the tread surface can be made to approach evenly,
An object of the present invention is to provide a heavy-duty tire that can maintain running stability for a long period of time, prevent uneven wear, suppress heat generation during running, and improve durability.

[0011]

According to the present invention, there is provided a carcass which is folded from a tread portion through a sidewall portion and around a bead core of a bead portion, and a carcass which is arranged radially outside the carcass and inside the tread portion. A heavy-duty tire comprising a belt layer composed of a plurality of belt plies having cords aligned with each other and having an aspect ratio H / W, which is a ratio of a tire cross-section height H to a tire width W, of 70% or less, In a standard state in which the belt layer is assembled to the regular rim and filled with the regular internal pressure, the belt layer is provided with a maximum width belt ply having a maximum distance between the outer ends of the plies in the tire axial direction, and a belt layer adjacent to the maximum width belt ply. And the belt cord includes the belt cord of the maximum width belt ply and the adjacent belt ply arranged in a different direction with respect to the tire equator, and The ply width WB of the large width belt ply is 0.72 times or more and 0.8 times or less the tire width W, and the belts at the outer end of the adjacent belt ply and the outer end of the maximum width belt ply. The tire for heavy load is characterized in that the dimension difference Z in the tire axial direction from the outer end of the cord is set to 3 times or less the diameter D of the belt cord of the adjacent belt ply.

The belt layer has a belt cord of the adjacent belt ply with respect to the shortest distance Y between the belt cord of the adjacent belt ply and the belt cord of the maximum width belt ply at the outer end of the adjacent belt ply. Ratio Y of diameter D
It is preferable that / D is 2 or more and 3.4 or less.

[0013]

Since the ply width WB of the maximum width belt ply is increased in the range of 0.72 to 0.8 times the tire width W, the required rubber gauge thickness between the belt end and the buttress surface is maintained. , The tread portion can be restrained with a wider width. As a result, it is possible to effectively suppress the change in the shape of the contact surface due to the outer diameter growth during traveling. The ply width WB is the tire width W
If it is less than 0.72 times, the difference in dimensional growth will be remarkably large, and if it exceeds 0.8, the amount of rubber at the end of the belt layer will be small and damage due to cutting will be large.

Further, the dimensional difference Z between the outer end of the cord of the adjacent belt ply and the outer end of the cord of the maximum width belt ply is set to not more than 3 times the diameter D of the belt cord. This is based on the technical idea of spreading the hoop effect by each ply of the belt layer in the tread shoulder portion as much as possible, and compared with the conventional tire having the ratio Z / D of 4 to 6.5, The dimensional difference Z is greatly reduced. Due to this, the binding force of the belt comes close to the tread shoulder part and the central part,
The dimensional growth over time in the tread portion can be made to approach evenly. If the ratio Z / D exceeds 3, the dimensional growth in the tread shoulder portion becomes large, and the above-mentioned effect cannot be obtained.

As described above, according to the present invention, since the above-mentioned respective components are organically integrated, the temporal expansion of the central portion of the tread surface and the tread shoulder portion can be made evenly close to each other. Since the sectional shape of the part can be maintained for a long period of time,
While the traveling performance is stable, uneven wear is prevented, heat generation during traveling is suppressed, and durability is improved, while rehabilitation work accompanying the end of the first life can be performed easily and economically.

When the shortest distance Y between the cord of the maximum width belt ply and the cord of the adjacent belt ply at the outer end of the belt ply is set to 2 to 3.4 times the cord diameter, the effect of relaxing the shearing force is obtained. By this, the occurrence of belt separation can be suppressed and the durability can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, which shows a standard state in which a regular rim R determined by JATMA, TRA, ETRTO or the like is assembled into a rim and a standard internal pressure is filled, a heavy load tire 1 extends from a tread portion 2 and both ends thereof inward in a radial direction of the tire. The sidewall portion 3 and the bead portion 4 located at the inner end of each sidewall portion 3 are provided. Further, between the bead portions 4 and 4, the carcass 6 whose both ends are folded back around the bead core 5 of the bead portion 4 from the tread portion 2 through the sidewall portion 3
A tough belt layer 7 is wound around the outside of the carcass 6 with a hoop effect, and the flatness ratio H / W is restricted to 70% or less.

The carcass 6 is composed of at least one carcass ply in which carcass cords made of organic fibers or metal fibers such as nylon, rayon and polyester are arranged at an angle of 75 to 90 degrees with respect to the tire equator C. In this example, a steel cord is used as the carcass cord.

The belt layer 7 is composed of a plurality of belt plies in which steel belt cords are arranged in parallel with each other, and in this example, the first, second, and third layers are sequentially stacked from the carcass 6 side to the tread surface S side. 3, the fourth belt ply 11,
A four-layer structure composed of 12, 13, and 14 is formed. The ply width W2, which is the length between the outer ends of the second belt ply 12 in the tire axial direction, is larger than the ply width W1 of the first belt ply 11, and the ply width W3 of the third belt ply 13 is Fourth
Is larger than the ply width W4 of the belt ply 14 and substantially the same as the ply width W1. Therefore, in this example, the second belt ply 12 forms the maximum width belt ply 7A.

As shown in FIG. 2, the belt cords of the first and second belt plies 11 and 12 are the tire equator C, respectively.
And the third and fourth belt plies 13 and 14 are arranged in the same direction, that is, in the present example, in the upward left direction.
The belt cords for the tires are the first with respect to the tire equator C,
The second belt ply is arranged in a direction different from that of the belt cord, that is, in the present example, in an upward right direction.

The belt cord has an inclination angle θ of 5 to 70 degrees with respect to the tire equator C, and the first belt ply 1
The inclination angle θ1 of 1 is 50 to 70 degrees, for example 68 degrees, the second,
Inclination angle θ of the belt plies 12, 13 and 14 of 3 and 4
2, θ3, θ4 are set to 14 to 22 degrees, for example, 17 degrees. By using such a coding sequence, ply 11
The belt cords 13 to 13 form a truss structure in which the belt cords cross each other, exhibiting a high hoop effect and improving tire rigidity. In addition, by increasing the inclination angle θ1
The shear strain between the belt ply 11 and the carcass 6 is relaxed. In this embodiment, the third belt ply 13 forms an adjacent belt ply 7B which is adjacent to the maximum width belt ply and whose belt cord is arranged in a direction different from the belt cord of the maximum width belt ply.

The tread surface S forms an arc having a radius of curvature TR centered on the equatorial plane of the tire, while the maximum width belt ply 7A, which is the second belt ply 12, is substantially concentric with the tread surface S. It is curved in an arc with a radius of curvature TB, and the distance L in the normal direction between the maximum width belt ply 7A and the tread surface S is within a variation range of about ± 1.5 mm over almost the entire width of the ply 7A. , That is, kept almost constant. The radius of curvature TR of the tread surface S is the tire width W.
The range is 1.85 to 2.5 times.

The belt layer 7 is the adjacent belt ply 7B.
Of the belt cord 20B located at the outermost end in the axial direction of the tire and the outer end of the belt cord 20A located at the outermost end of the maximum width belt ply 7A have a dimensional difference Z in the tire axial direction between adjacent belt plies. 3 times or less of the diameter D of the belt cord 20A. In the conventional tire, the dimensional difference Z is 4 to 6.5 times the diameter D, but in the present example, the dimensional difference Z is extremely small, which allows the restraining force of the belt layer 7 to be reduced. It affects a wide range of areas.

Further, in this embodiment, the belt cord 20B of the adjacent belt ply 7B and the maximum width belt ply 7 are
The ratio Y / D of the diameter D of the belt cord 20B of the adjacent belt ply 7B to the shortest distance Y from the belt cord 20A of A is set to 2 or more and 3.4 or less.

The setting range was found from a running test conducted by the inventors. That is, tires for flat heavy loads of various sizes having different shortest distances Y and maximum ply widths WB were made on a trial basis, and the wear indicators were exposed to the wear limit at which the wear indicator was exposed at 100% load determined by JATMA, TRA, and ETRTO. As the actual vehicle runs,
The presence or absence of belt separation after the running was confirmed.

When the shortest distance Y is 2.0 times or more of the cord diameter D, the rubber G interposed between the cords absorbs and relaxes the shearing force concentrated on the outer end E of the belt to suppress the separation. You can. However, since the rubber volume excessively increases in a range of more than 3.4 times, the internal temperature rise of the rubber is increased as compared with the above-mentioned shearing force relaxation effect, and on the contrary, separation is promoted. Note that such a shortest distance Y can be easily secured by covering the outer end E of the adjacent belt ply 7B with the covering rubber layer 15 having a predetermined thickness as shown in FIG.

In order to exert a shearing force relaxing effect,
The rubber G interposed between the cords needs to expand and contract following the cords. For this reason, the rubber G has a 100% modulus of 40 to 70 kg / cm ² and an elongation at break of 200 to.
300% and the stress at break 150-300kg / cm ²
Is preferred.

The maximum width belt ply 7A ply width WB
Is 0.72 times or more and 0.8 times or less of the tire width W.

This is because the restraint force of the belt can be increased over a wider width of the tread portion 2 by the above regulation, the outer shape growth of the tread during running is prevented, and the change of the ground contact surface shape is suppressed. is there. If the ply width WB is less than 0.72 times the tire width W, the difference in dimensional growth over time (hs-hc) between the central portion of the tread portion 2 and the tread shoulder portion becomes significantly large, and conversely, the ply width is increased. W
Belt code 7A when B exceeds 0.8 times the tire width W
The rubber gauge between the outer end of the buttress and the outer surface 16 of the buttress becomes small, the rubber of the tread portion 2 is destroyed early, and the external force from the outer surface 16 of the buttress easily causes damage to the belt end. Therefore, the ratio WB / W is more preferably 0.7.
It is 4 or more and 0.77 or less.

[0030]

SPECIFIC EXAMPLE A tire having a tire size of 385 / 65R22.5 and having the configuration shown in FIG. 1 was prototyped and the stability of tire dimensions during running was investigated.

In the investigation, the outer diameter DCO on the tire equator C and the outer diameter DSO at the tread edge were measured in advance in a standard condition for the sample tire, and a load of 140% of the normal load was further measured using a drum tester. In addition, after running for 10 hours at a speed of 50 km / H, the test tire was removed from the tester, the outer diameter DC1 on the tire equator after the test and the outer diameter DS1 at the tread edge were measured, and the difference DC1-DC
0 = hc and DS1-DS0 = hs were calculated.

As a result of the test, the tire according to the constitution of the present application has a ratio hs / hc of 1.0 to 1.2, which is a significant improvement over the ratio of 1.5 in the conventional tire. I was able to confirm that.

[0033]

As described above, since the heavy duty tire of the present invention has the above-mentioned structure, the dimensional change of the tread portion over time can be equalized in substantially the entire area of the tread portion, and the running performance can be maintained for a long time. In addition, the uneven wear resistance and the heat generation resistance can be improved to improve the durability, and the tire can be easily rehabilitated due to the end of the primary life.

[Brief description of drawings]

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

FIG. 2 is a plan view illustrating a code arrangement of a belt layer.

FIG. 3 is an enlarged cross-sectional view showing an end portion of a belt layer.

FIG. 4 is a cross-sectional view illustrating an example of a rubber layer.

FIG. 5 is a partial cross-sectional view showing an end portion of a belt layer of a conventional tire.

FIG. 6 is a diagram illustrating the distribution of the binding force of the belt on the tread surface.

FIG. 7 is a diagram illustrating a dimensional change of a tread surface over time.

[Explanation of symbols] 2 tread portion 3 sidewall portion 4 bead portion 5 bead core 6 carcass 7 belt layer 7A maximum width belt ply 7B adjacent belt ply 11, 12, 13, 14 belt ply D belt cord diameter H tire section height R Regular rim W Tire width WB Maximum width Belt ply ply width Y Shortest distance between cords Z Dimensional difference

Claims (2)

[Claims] 1. A carcass folded from a tread part through a sidewall part around a bead core of a bead part, and a plurality of carcass arranged radially outside the carcass and inside the tread part and having belt cords aligned with each other. And a flatness ratio H / W, which is the ratio of the tire cross-section height H to the tire width W, of 70% or less.
% Or less, in a standard state in which the tire is mounted on a regular rim and filled with a regular internal pressure, the belt layer is a belt having a maximum width that maximizes the distance between the outer ends of the ply in the tire axial direction. A ply and an adjacent belt ply which is adjacent to the maximum width belt ply and in which the belt cord is arranged in a different direction with respect to the belt cord of the maximum width belt ply and the tire equator, The ply width WB is 0.72 of the tire width W
Double or more and 0.8 times or less, and the dimensional difference Z in the tire axial direction between the outer end of the belt cord at the outer end of the adjacent belt ply and the outer end of the belt cord at the outer end of the maximum width belt ply is determined by the adjacent belt. Ply belt cord diameter D 3
A heavy-duty tire characterized by not more than double. 2. The belt cord of the adjacent belt ply with respect to the shortest distance Y between the belt cord of the adjacent belt ply and the belt cord of the maximum width belt ply at the outer end of the adjacent belt ply. Ratio of diameter D of Y /
The heavy duty tire according to claim 1, wherein D is 2 or more and 3.4 or less.