JPS5847363B2 - heavy duty pneumatic tires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pneumatic tire used under heavy loads,
In particular, the present invention relates to a novel structure for increasing the durability of a pneumatic tire having a bias-structured carcass body made of a multi-ply laminate in which a large number of organic fiber cords are arranged and coated with rubber.

This type of pneumatic tire is mainly used for construction vehicles, industrial vehicles, large trucks, and large buses.
In order to give the tire strength suitable for the carcass structure, a large number of rubber-coated plies are laminated in a biased manner, but in this case, the number of laminated plies becomes a large number.

For this reason, the strength per cord is 1890d instead of a thick denier cord, such as a 1260d/2 cord.
By using a /2 cord or increasing the number of cord ends (increasing the number of cord sequences per unit width), the strength per ply layer is increased, and the actual number of plies is reduced while maintaining the strength that meets the usage conditions. Conventionally, it has been common practice to realize this and thereby rationalize production efficiency, manufacturing costs, or reduce tire weight.

However, as a result of repeated actual measurements, it has become clear that when the number of carcass plies is reduced by the above-mentioned means, ply separation (separation of plies), which is a cause of fatal tire failure, is likely to occur.

By the way, as a result of various studies based on actual measurements, we found that the greater the compressive strain and shear strain when the tire runs under high load, the greater the cord spacing in the carcass plies and the cord spacing between adjacent plies. It has been found that ply separation is more likely to occur as the spacing becomes smaller.

Moreover, after carefully observing and analyzing the structures of conventional tires in which ply separation failure occurred, the present inventors found that in addition to separation failures near the breaker-carcass interface and the breaker-tread interface that are generally seen here and there, force It has been found that separation between flies is likely to occur within the cusply layer, especially in the inner layer of the carcass where compressive strain is thought to be large.

Based on this knowledge, the present inventors first made a detailed observation of the carcass ply in the vicinity of the area where the ply separation failure occurred, and as a result, discovered a surprising fact.

In other words, cracks occur in the rubber in the vicinity of a large number of rubber-coated ply cords, and the cracks extend and connect with cracks extending from adjacent ply cords, resulting in ply separation. I discovered the fact that

In view of the actual situation, the present invention addresses the drawbacks of the conventional branching technique as described above, namely, the reduction in the number of plies due to the increase in strength per ply layer due to the use of thick denier cord and the increase in the number of cord ends. This invention was developed as a result of repeatedly investigating tire behavior through repeated experiments and considerations, in light of the contradictory problem of unavoidable ply separation failure when striving to improve tire performance and reduce tire weight. By keeping the cord spacing of the carcass plies appropriate, especially in areas where ply separation failures are likely to occur, it is possible to reduce the number of carcass plies, improve productivity, reduce tire weight, and prevent ply separation failures from occurring. The company's unique feature lies in its ability to provide highly durable pneumatic tires.

Further, the content of the present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of an example of the tire of the present invention taken along a plane including its rotational axis, in which 1 is a bead portion consisting of three bead cores 1a, 1b, and 1c, and a ply 2 constituting the carcass body. consists of a laminate of multiple plies of organic fiber cords, such as nylon cords, arranged in large numbers and coated with rubber, and the cord direction of about half of the plies in each layer and the cord direction of the remaining plies are opposite to each other. It has a so-called bias structure.

This carcass body consists of a ply layer wound around the bead cores 1atlb and 1c from the inside of the tire to the outside, and a ply layer wrapped around the bead core from the outside to the inside, and the inner layer group and middle layer group are different between the ply cords. Although it is composed of three groups, a ply layer group and an outer layer group, these different ply layer groups can of course be wound on the same bead core.

A tread portion 3 on the outside of the plies 2 is provided with a breaker 4 made of organic fiber cord.

In the pneumatic tire having the above structure, the feature of the present invention lies in that the structure of the ply 2 meets the following conditions, namely, for the three layer groups, the spacing between the organic fiber cords is The cords are different within the same ply layer and between adjacent ply cords, while the diameter and twist of each cord are approximately the same.

In this case, the cord spacing within the same ply layer and the cord spacing between adjacent ply cords are set to the following conditions.

In other words, with the middle group as the reference, the inner group,
Inter-adjacent ply code spacing indices ri and I'o of the outer layer group
and the intra-ply chord spacing index Ai and Ao, respectively, 1.1<7'i<3.0, 1.1<7'o<
3.0, 1.5<, 4i <4.0, 1.5<A
The relationship is such that it exists within the range o < 4.0.

Therefore, each index 7'i, 7'o, 4i, A
o is determined by the following equation, and its specifications are as illustrated in FIG.

? 1; Cord gauge (mrtt) used in carcass inner layer group 2a, dm; Cord gauge (mi) used in carcass middle layer group 2b, do; Cord gauge (mu) used in carcass outer layer group 2c. , Δt1; Cord spacing (distance) between adjacent plies in the carcass inner layer group 2a, Δt. 1; Cord spacing (distance) between adjacent plies in carcass middle layer group 2b, △to; Cord spacing (mrn) between adjacent plies in carcass outer layer group 2c, △ei; Cord spacing within the same ply in carcass inner layer group 2a ( △erT1; Cord spacing within the same ply in the carcass middle layer group 2b (關); △eo; Cord spacing within the same ply in the carcass outer layer group 2c (關); γi: Cord between adjacent plies in the carcass inner layer group 2a The ratio of the spacing to the cord gauge, γ; The ratio of the cord spacing between adjacent plies in the carcass middle group 2b to the cord gauge, γ.

; the ratio of the cord spacing between adjacent plies in the carcass outer layer group 2C to the cord gauge; λi; the ratio of the cord spacing within the same ply in the carcass inner layer group 2a to the cord gauge; λm: the cord spacing within the same ply in the carcass middle layer group 2b is the ratio to the cord gauge, λ.

: The ratio of the cord spacing within the same ply in the carcass outer layer group 2c to the cord gauge. By having the carcass body with the structure described above, the disadvantages of conventional pneumatic tires, such as the use of thick denier cords and the increase in the number of cord ends, can be overcome. The reduction in the number of plies due to the increase in strength per ply layer has made it possible to eliminate the inconvenience of unavoidable ply separation failure when trying to improve productivity and reduce tire weight.

To further explain this point, firstly, the middle layer group 2b contributes to reducing the number of plies while maintaining the necessary strength of the carcass by increasing the cord density to a level that maintains the minimum necessary cord spacing. , On the other hand, the inner layer group 2a is said to have larger compressive strain and shear strain than the middle layer group 2b.
In the outer layer group 2c, the cord spacing is made larger than in the middle layer group 2b, thereby contributing to suppressing the occurrence of ply separation failures.

In this case, as is clear from the comparative experiment example described later, F
If i and 7'o are less than 1.1, the effect of ply separation resistance cannot be obtained sufficiently, so 1.1 is set as the lower limit.On the other hand, if it exceeds 3.0, the wall thickness of the Kerr force sply body increases. 3. This also causes an increase in compressive strain in the carcass, making it impossible to obtain a sufficient anti-ply separation effect.

The upper limit is 0. Also, for JH and Ao, 1
．． If it is less than 5, the effect of ply separation resistance cannot be sufficiently obtained, as is the case with Fi and Fo, and therefore 1.5 is set as the lower limit.

Furthermore, if Ai and Ao exceed 4.0 in the same way,
In order to maintain the necessary carcass strength, it is necessary to increase the number of plies, and by departing from the spirit of the present invention, increasing the number of plies will also result in an increase in the carcass thickness, which will reduce the ply separation resistance effect as described above. Therefore, the upper limit is set at 4.0.

In this way, by using equal denier cords and changing the cord arrangement in each layer group of the three-layer group, efficiency and costs can be rationalized by unifying the cord members and making the cord spreading work easier. This prevents the occurrence of rubber cracks in the vicinity, resulting in an anti-ply separation effect.

Next, performance comparisons were made between specific examples of the present invention and selected comparative tires, and the following results were obtained.

Example 1 For tire sizes 2400-49 and 48PR, the structure of the carcass ply body was as shown in Table 1. A test was conducted using an indoor drum testing machine to compare tire performance when each cord spacing index Fi, Fo, Ai, and Ao was changed in the inner layer group and the outer layer group with respect to the middle ply layer group.

※※ All test conditions are the same and the rims are regular rims 17.
00X49Tl3 is used, tire internal pressure is 3. <) k9
/CIIL, load &! 2 6 0 0 0 $ speed c1
0 lvhr theal.

The test results are as shown in Table 2, and the present invention tire (
A1) completed the test without any ply separation occurring.

Example 2 A tire of the present invention in which the tire size was 1600-2524PR, the carcass ply cord was made of 1890 d/2 twisted nylon tire cord with a cord diameter of about 0.79, and the structure of the carcass ply body was set as shown in Table 3. (A
A durability test and measurement of plunger energy were conducted under the following test conditions to compare the performance of this tire and the comparative tire (E).

Test conditions (drum test) Tire pressure '7''/ant
*Note 1 Note 2 Weight: 650 kg Degree: 10 to 5 oIarL/hr Step speed durability was measured by measuring the time until failure occurred and expressed as a ratio of 100 minutes.

Measurement of plunger energy is based on US Automobile Safety Standard F.
According to the method specified in MVSS-119,
Expressed as a 100 minute ratio.

The test results are shown in Table 4, and it is clear that the tire durability and tire strength as seen in plunger energy are excellent.

To summarize the above test results, if Fi, Fo is 3.0 or more, and jH, Ao is 4.0 or more, the tire strength will be inferior even if the tire durability is the same, and Fi
, Fo is 1.1 or less, and Ai, Ao is 1.5 or less, it is obvious that the tire durability is poor.

Note that in order to maintain tire strength, it is possible to increase the number of layers in the middle layer group, but this can be achieved by reducing the actual number of plies, which is the gist of the present invention, and streamlining production efficiency and manufacturing costs. In addition, it deviates from the point of reducing tire weight, and it goes without saying that there is a limit to the total number of plies in the carcass body, as shown in Example Tire (AI) (A2). The optimum condition can be obtained by setting the number of plies in the middle layer group to 0.8n = 0.6n and the number of plies in the inner layer group and outer layer group to 0.1n = 0.2n. .

As is clear from the above description, the present invention increases the cord spacing of the inner layer group and outer layer group where ply separation failures are likely to occur, in other words, where rubber cracks are likely to occur and grow, compared to the middle layer group, and the tire By appropriately maintaining the cord spacing of the middle layer group, which affects strength, it has become possible to provide a pneumatic tire that has high load resistance while reducing the number of carcass plies, and is a process that contributes to this industry. It's a huge pneumatic tire.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view of an example of the tire of the present invention, and FIG. 2 is an enlarged cross-sectional view for explaining the structure of the carcass portion. 1...Bead portion, 1at1b, 1c-bead core, 2...Ply, 2a...Inner layer group,
2b...middle group, 2c...outer group, 3
...Tread section, 4...Breaker

Claims (1)

[Scope of Claims] 1. A pneumatic tire comprising a carcass body with a bias structure consisting of a plurality of ply laminates arranged with a large number of organic fiber cords and coated with rubber, each of the carcass bodies having a plurality of layers. The spacing between organic fiber cords within the same ply and the spacing between organic fiber cords between adjacent plies are determined according to the inner layer group, middle layer group, and outer layer group. and the inter-ply chord spacing indexes Fi and I' of the inner layer group and the outer layer group with respect to the middle layer group.
o and the intra-ply chord spacing indices Ai and Ao are within the following ranges: 1.1<Fi, I"o<3.0 1.5<Ai, Ao<4.0 2. A highly durable pneumatic tire in which the carcass body has a total number n of plies, the number of plies in the middle layer group is 0.8n = 0.6H, and the number of plies in the inner layer group and the outer layer group is O- 1 n, respectively. 2. A highly durable pneumatic tire according to claim 1, comprising three layer groups defined by n = 0.2 n.