JPH01111504A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To improve an appearance and prevent the occurrence of any separation of ply terminals by specifying the extension structure of a fold where at least one of plies in a carcass main body is wound up around a bead core from the inside to the outside of a tire. CONSTITUTION:In the tire in the caption, at least one of plies in a carcass main body 1 is folded over from the inside to the outside of the tire around a bead core 4 so as to provide the reinforced portion of a bead portion. In this case, a fold 3 extends away from the bead core 4 in such a way as to once come close to the pass line of the carcass main body 1 and then separate therefrom. The terminal portion of the fold 3 extends substantially straight between a normal (n) drawn on the pass line through the terminal (e) thereof and a virtual straight line l1, which is parallel to the normal (n) and spaced toward the bead core with a distance corresponding to 5% of a tire sectional height, and as well with a crossing angle theta of 60-80 deg. with respect to the normal (n). Moreover, the ratio of distances L1, L2 is specified in the range of 0.20-0.50.

Description

Detailed description of the invention (Industrial field of application) So-called heavy duty pneumatic radial tires such as trucks, buses, etc. In particular, at least one ply consisting of a cord of metal, for example steel wire, is used as the main reinforcement of the carcass body. The folded shape of the carcass ply at the bead of the pneumatic radial tire, the outer contour shape of the bead, and the arrangement of the rubber stock at the bead have been improved to create a pneumatic radial tire for heavy loads that has excellent bead durability. The company aims to provide tires.

(Prior technology) By bending the carcass ply at the bead part so that it is longer than the shortest distance between the end and the bead core, separation between the carcass ply and the rubber is prevented and the durability of the bead part is improved. An attempt was made to
Although it is disclosed in Publication No. 4-564, an example of using an organic fiber such as polyamide as the ply cord is cited, and a method of arranging the folded part of the carcass that can use a particularly light carcass is discussed. There is.

(Problem to be Solved by the Invention) By separating the folded end of the carcass ply from the carcass body as much as possible, the amount of rubber stock interposed between them can be increased, which has the advantage of reducing stress concentration at the end. However, in this case, when a steel wire with extremely high rigidity is used as the ply cord, the following problems peculiar to this occur.

-a, when the tire is filled with internal pressure, the bead part is stretched as a whole, and at this time, there is a difference in rigidity above and below the stiff turn, and as a result, above the end of the turn, The rubber surface layer at the bead part stretches more than the lower part, causing the rubber surface layer to become indented.This indentation is caused by the folding of the carcass radially inward as the tire shifts under the load of running on the road. The repeated deformation of the rubber surface layer near the end of the folding process eventually leads to fatigue, and the above-mentioned dents become the starting point for cranking, and the above-mentioned elongation occurs. This also causes separation at the end of the fold, and these factors combine to reduce the durability of the bead portion of this type of tire.

Therefore, a first object of the present invention is to prevent the occurrence of the above-mentioned dents, thereby eliminating the cause of deterioration in durability of the rubber surface layer of the bead portion due to cranking.

On the other hand, the above-mentioned separation at the end of the fold is caused by a crack in the surrounding rubber at the end, which progresses, and this crack is caused by the deformation of the bead under load. The cause of this is a decrease in the interfacial adhesion between the steel wire cord and the rubber and a deterioration in the crack propagation resistance of the rubber itself due to repeated stress concentration and temperature rise due to repeated deformation.
The second object of the present invention is to solve such problems and advantageously prevent the occurrence and propagation of cracks that start at the end of the folded end portion while minimizing the increase in tire weight and cost.
The purpose of

(Means for solving the problems) Each of the above objectives can be effectively achieved by making the following matters into the main structure.

A heavy-duty pneumatic tire is constructed in which the main reinforcement is a carcass body using at least one ply of steel wire cord, and at least one of the plies is inserted around the bead core from the inside to the outside of the tire on both sides of the ply. In addition, in addition to providing a reinforcing element in the bead portion, the above-mentioned folds are wound in an arrangement substantially occupying the radial plane of the tire, and while the above-mentioned folds extend away from the bead core, the folds pass through the carcass body. At the end of the turn, which passes through a reversal path in which it approaches the line and then moves away, the normal n that passes through the end e and stands on the path line, and this normal n
An imaginary straight line extending parallel to 2. by a distance equivalent to 5% of the tire cross-sectional height toward the bead core. almost straight across the line, and at an intersection angle θ of 60 to 80° with respect to the normal line.
The bead portion with this fold as a reinforcing element is stretched along the straight line 11.
Let us also imagine a parallel second straight line 2□ which has the same distance from the above normal line n and sandwiching the cough normal line n, and each of these straight lines n,
The intersection of L and 12 and the reference outer surface of the tire is Pa, P1
, and Pi,2, and the distance between Pn and the folded end e is L
1. Normal n and line segment Pjl! , when the distance between the intersection P3 and the intersection Pa1 with PA□ is L2, the ratio of the distance L2 to the distance is within the range of 0.20 to 0.50. A pneumatic radial tire for heavy loads (first invention).

A heavy-duty pneumatic tire whose main reinforcement is a carcass body using at least one ply of steel wire cord, and at least one of the plies is extended from the inside of the tire to the outside of the tire around the bead core at each side edge thereof. In addition to providing a reinforcing element for the bead portion, the folds are formed by winding the cord in an arrangement that substantially occupies the radial plane of the tire. At the end of the turn, which passes through the reversal path where the vehicle approaches and then leaves, a normal line n is drawn to the pass line through the end e, and a line parallel to this normal line n is 5% of the cross-sectional height of the tire. 1.1, extending the corresponding distance toward the bead core, almost straight, and at a distance of 60 to 80 degrees with respect to the normal line.
The bead portion with this fold as a reinforcing element is stretched at an intersection angle θ of
The distance from the normal n to the above normal n is the same (and the parallel second straight line 2 □ sandwiching the normal n is also imaginary, and each of these straight lines n,
f, and! 2 and the reference outer surface of the tire are Pa, P
I! , and P2□, and when the distance between Pa and the folded end e is L1, and the distance between the intersection P3 of the normal n and the line segment Pf and P12 with respect to the intersection Pa1 is L2, the distance with respect to the distance is between the carcass body and the flap, rubber A adjacent to the carcass body and the bead core, rubber adjacent to the carcass body and the flap; It has three types of rubber stocks: rubber B, rubber B, and rubber C adjacent to the fold, where rubber A has a 100% modulus of 60 kgf/c [Rubber B has a 100% modulus of 15 to 35 kgf/cti
Resilience in l 65-85 Rubber C has 100% modulus 35-60 kgf/cr
1, the resilience is 50 to 65, and the ratio of the thickness t of the rubber C to the total rubber stock thickness T measured along the normal line n is 0.3 to 0.
A pneumatic radial tire for heavy loads (second invention), characterized in that the pneumatic radial tire is a combination of the following:

Now, FIG. 1 illustrates a cross-section of a bead portion of a heavy-duty tire according to the first invention, in which 1 is a carcass body, 2 is a chafer, 3 is a fold, and 4 is a bead core.

The carcass body 1 consists of at least one ply of steel wire cords arranged in the radial plane of the tire, and at least one of the plies is wound around the bead core 4 from the inside to the outside of the tire at each side edge of the ply. A fold 3 is formed as a reinforcing element of the section and cooperates with the chafer 2.

The fold 3 extends in a direction away from the bead core 4 together with the chafer 2 in many cases, reaching the end portion and extending longer than the chafer 2.

During this stretching, it passes through a reversal path in which it approaches the pass line of the carcass body and then moves away from it.

The terminal part of this turnback 3 passes through the terminal e and extends a distance corresponding to 5% of the cross-sectional height of the tire to the bead core, parallel to the normal line n set on the pass line of the carcass body 1. An imaginary straight line separated by 4! , and at an intersection angle θ of 60 to 80° with respect to the normal line.
It shall be stretched to form a shape.

Here, the tire cross-sectional height refers to the maximum distance of the pass line of the carcass body 1 measured from the bead base line.
As is customary.

The bead portion having the above-mentioned fold 3 as a reinforcing element is formed by the above-mentioned straight line 1,
The above law! A second straight line 12 sandwiching the normal n with the same distance to an is further assumed, and these straight lines n,
j! The intersections of + and 2□ and the above outer surface are Pfi and Pf
, and the distance between P2□, Pa and the folded end e is L.
I, when the distance between the intersection P3 of the normal n and the line segment Pfi, Pj22 and the intersection Pa is defined as L2, the distance LI
The ratio of the distance L2 to the distance L2 is determined to be within the range of 0.2 to 0.5.

Next, in the second invention, in the above-mentioned place, a bead filler 3 is further provided between the carcass body 1 and the fold 3.
A rubber stock consisting of seed rubbers A, B and C is arranged.

Here, the rubber A is arranged to be adjacent to the carcass body 1 and the bead core 4, the rubber B is in contact with the rubber A, the carcass body 1 and the flap 3, and the rubber C is in contact with the rubber B and the flap 3, in that order. 10oz modulus is 60kgf
/cJ or more, 15-35kgf/aJ, 35-60kg
f/d, and Rubbers B and C are assumed to have physical properties with resilience of 65 to 85. The ratio of the thickness t of the rubber C to the total thickness T of the rubber C is in the range of 0.3 to 0.75.

(Function) In general, the principal strain originating from the tire displacement under load that occurs at the fold 2 of the carcass body 1, especially at the end e of the end portion, is indicated by the arrow in Fig. 2 for the conventional tire of this type. Analysis results using the finite element method have revealed that the rotation occurs approximately in the radial direction of the tire.

In this regard, according to the shape of the folded part of the carcass body shown in the above-mentioned Japanese Patent Publication No. 54-564, the terminal part of the folded part is separated from the carcass body, so that the above-mentioned upper strain is
The disadvantages that occur along the direction of folding are reduced, and in such a direction the intervening rubber thickness between the carcass body and the carcass body increases, so that the influence of distortion can be reduced. However, as mentioned at the outset, when the carcass body is made of steel wire cord, it poses a particular problem.

The inventors used several types of models to analyze the relationship between the ply direction and the above-mentioned upper strain at the folded end of a radial carcass consisting of at least plies of steel wire cord. The folded end part is separated from the end part, inverted, and extends straight, in a direction that intersects at an angle θ of 60 to 80 degrees, more preferably 65 to 75@, with respect to the normal line erected to the carcass body 1 passing through the end e. I have found that it is optimal to do so.

If the intersection angle θ is larger than 80", the effect of reducing strain will not be sufficient, and the durability of the bead will not be improved much. On the other hand, if the intersection angle θ is too small than 60°, the outer rubber from the end e to the outer surface of the bead will be damaged. As the thickness becomes thinner, there is a concern that cracks may form there.

Originally, when the end part of this turn-up 3 is separated from the carcass body 1, the difference in the normal direction of the end e to the carcass body 1, that is, the total thickness T of the rubber stock shown in FIG. It is necessary to make the width wider than the maximum width W of the tire, while at the same time reducing the weight of the tire or
From the viewpoint of suppressing heat generation in the bead part, the bead part is desired to be as slim as possible, so the carcass body 1
The distance from the bead to the tire surface cannot be made too thick, and in this respect, in the conventional tire shown in Fig. 2, the distance T' is narrower than the maximum width of the bead core, and therefore there is a considerable distance outside the end e. This is in contrast to the thick rubber skin used in the

For example, in the conventional bead structure shown in FIG. 2 in a heavy-duty pneumatic radial tire of size 1000 R20, the rubber thickness was about 8 to 12 mm on the outside of the end e, but in this invention, the rubber thickness was about 4 to 6 nn. halved to
Therefore, in the above-mentioned separation arrangement of simple folding, the above-mentioned dents occur and the durability of the bead portion deteriorates due to cracks caused by these dents.

To advantageously overcome this point, as shown in Figure 1, /
It is essential to keep the L ratio in the range of 0.2 to 0.5.

In other words, in the case of the above-mentioned size, the dent that occurs near the point Pa of the bead portion shown in Fig. 2 is conventionally less than 0.5 m, but in the comparative example shown in Fig. 3, it exceeds 0.5 mm. Therefore, in this invention, when molding in a mold, the part where the dent will occur is made particularly convex in order to avoid the disadvantage of the dent. . FIG. 4 shows a tire according to the invention in which the folded end portion is separated from the carcass body 1, and 5. The relationship between the value of L2 and the amount of denting when Omm is determined by experiment. Here the amount of dent is 0
．． In the range of 5 to -0.5 mm, there is no appearance defect.
Therefore, it can be said that L2/L of 0.2 to 0.5 is appropriate.

Therefore, if L, /L is less than 0.2, the occurrence of dents cannot be completely prevented, while if it exceeds 0.5, the area becomes convex, which is unfavorable in terms of appearance.

Next, regarding the bead filler rubber, refer to the symbol A again in Figure 2.
As the conventional rubber stock arrangement is shown in ', B', the one in contact with the carcass body 1' and the bead core 4, and the rubber stock A
Two types of bead parts were mainly used: a bead that overlaps the carcass body 1 and the flap 3 and overlaps the rubber B', but most of the bead failures occur when the bead crosses the rubber B' at the end of the flap 3 inward. A crack that propagates further along the boundary between rubber A' and rubber B' is generated.

During this process, the peeling at the end of the cord, which is very small at first, progresses little by little within the coating rubber of the ply cord, but when a crack appears in the rubber B', its growth occurs rapidly;
It is necessary for the rubber B' to reduce heat generation at the bead part,
This is due to the fact that it is formulated with a focus on low loss and is significantly inferior to ply cord coating rubber in terms of crack propagation resistance.
As is generally well known, such loss characteristics and crack growth resistance are antinomy.

As already mentioned, improving the bead durability by slimming down the bead of heavy-duty pneumatic radial tires in line with the demands for weight reduction and cost reduction is more effective than reducing heat generation. It is advantageous to aim at reducing strain and increasing crack resistance.

In the second invention, first of all, by arranging the rubber C having relatively high elasticity and high loss physical properties considerably thickly, the crack propagation resistance is considerably inferior because it is placed away from the end e of the fold where strain tends to be concentrated. This prevents cracks from propagating to Rubber B, which is a low-loss rubber compound that is unavoidable.

Since rubber C is thermally disadvantageous compared to rubber B, it is not preferable to make the thickness of rubber B too small.

Results of investigating the relationship between the ratio of the thickness of rubber C to the total rubber stock (rubber B and C) thickness T on the normal line to the carcass body 1 across rubber C and rubber B on bead durability. As is clear from FIG. 5, which shows 0.
It is clear that a range of 3 to 0.75 is useful for improving durability. When t/T exceeds 0.75, it is disadvantageous for heat generation and durability is impaired, while when it is less than 0.3, sufficient effects cannot be achieved.

(Example) Example 1 An example of a bead portion of a heavy-duty tire of tire size 1000 R20 is shown in FIG.

The carcass body 1 is made by winding one piece of metal cord from the inside to the outside of the bead core 4, and the folds 3 are arranged radially outward from a position adjacent to the bead core 4 so as to first approach the carcass body 1. It extends radially outwardly and axially outwardly so as to approach and then move away from the carcass body 1, and is disposed farthest from the carcass body l at the end e.

In this embodiment, the distance between the carcass main body l and the carcass fold 3 is 10 mm at the closest point (=f)
, set at 15 pus at the terminal end (·T). At this time, the inclination θ with respect to the normal at the end of the ply was 70°, and the thickness from the end e of the ply to the tire surface was 6 m. The maximum width of bead core 4 is 12 mm, and the tire section hide SR is 268 mm.

Further, the distance (L2) between points P1 and Pa was set at 1.7 degrees.

Other ply folding height E is 70 valence, chafer folding outer set height F is 55 mm, chafer inner set height G is 38 mm, ply cord angle is 90° to the circumferential direction, chafer cord The angle is 30° with respect to the circumferential direction.

Here, T/D = 1.2 to 1.7, E is 20χ to 40χ of section hide SH (see Figure 6), and F is 7 of E.
Preferably, the range is 0x to 90x, and G is in the range OE, and the chafer cord angle is 25 to 60° with respect to the circumferential direction.

Example 2 Carcass ply main body 1 and folding 3 are formed at the bead part of a radial tire of tire size 1000 R20 shown in Fig. 1.
The following rubber stock was placed between the This rubber stock consists of three rubber layers, labeled A, B, and C as shown.

Rubber A has MIoo = 65 kg/allll rubber amount. . = 25 kg/cil Resilience = 72 Rubber C is Ml. . = 42 kg/cJ Resilience = 60 Total rubber stock thickness T at the end of fold 3 is 15.0 s SC rubber layer thickness t is 7.0 m
m and t/T is set to 0.47. Rubber A here
The height of the top end is 60mm, and the height of the top end of rubber B is 120mm.
Decoration, the distance from the end e of the flap 3 to the bottom end of the rubber C is 2
0III11, the distance to the top was also 28M.

(Effects of the Invention) The first invention makes it possible to improve the appearance and prevent the occurrence of ply end separation by preventing the formation of recesses on the tire surface near the carcass ply ends when the tire is running.
It is possible to simultaneously reduce tire weight and improve bead durability.

Further, the second invention can suppress cracks in the end rubber of the carcass ply and their propagation, especially under heavy loads, and improve bead durability.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional view showing the first and second inventions in a common view of the bead reinforcement structure of a pneumatic radial tire for heavy loads; Fig. 2 is a cross-sectional view of main parts of a conventional tire; Fig. 3 is a comparative tire. FIG. 4 is a graph of the occurrence behavior of concavities or convexities occurring on the outer surface of the bead portion, FIG. 5 is an effect diagram, and FIG. 6 is a cross-sectional view of a typical tire. ■... Carcass body 2... Chafer 3.
...Return 4...Bead core Fig. 2 Fig. 4 Fig. 5 □ min Fig. 6

Claims (1)

[Scope of Claims] 1. A heavy-duty pneumatic tire whose main reinforcement is a carcass body using at least one ply of steel wire cord, and at least one of the plies has bead cores on both sides thereof. From the inside of the tire around to the outside,
In addition to providing a reinforcing element for the bead portion, the above-mentioned folds are wound in an arrangement that substantially occupies the radial plane of the tire. At the end of the turn, which passes through the reversal path where the vehicle approaches and then leaves, a normal line n is drawn to the pass line through the end e, and a line parallel to this normal line n is 5% of the cross-sectional height of the tire. Almost straight across the virtual straight line l_1 by extending the corresponding distance toward the bead core, and at a distance of 60~60° to the normal line.
Stretching at an intersection angle θ of 80°, and the bead portion with this fold as a reinforcing element forms a parallel second straight line l_2 sandwiching the normal line n with the same distance from the normal line n of the straight line l_1. also hypothetically,
The intersection points of these straight lines n, l_1, and l_2 with the reference outer surface of the tire are P_n, Pl_1, and Pl_2, and P
The distance between _n and the folded end e is L_1, the normal n and the line segment @
When the distance between the intersection P_a with Pl_1Pl_2@ and the intersection P_n is L_2, the ratio of the distance L2 to the distance L_1 is within the range of 0.20 to 0.50. A pneumatic radial tire for heavy loads that is characterized by: 2. A heavy-duty pneumatic tire whose main reinforcement is the carcass body using at least one ply of steel wire cord, and at least one of the plies is inserted from inside the tire around the bead core on both sides of the ply. Out,
In addition to providing a reinforcing element for the bead portion, the above-mentioned folds are wound in an arrangement that substantially occupies the radial plane of the tire. At the end of the turn, which passes through the reversal path where the vehicle approaches and then leaves, a normal line n is drawn to the pass line through the end e, and a line parallel to this normal line n is 5% of the cross-sectional height of the tire. Almost straight across the virtual straight line l_1 by extending the corresponding distance toward the bead core, and at a distance of 60~60° to the normal line.
Stretching at an intersection angle θ of 80°, and the bead portion with this fold as a reinforcing element forms a parallel second straight line l_2 sandwiching the normal line n with the same distance from the normal line n of the straight line l_1. also hypothetically,
The intersection points of these straight lines n, l_1 and l_2 with the reference outer surface of the tire are P_n, Pl_1 and Pl_2, and P_
The distance between n and the folded end e is L_1, the normal n and the line segment @P
When the distance between the intersection P_a with l_1Pl_2@ and the intersection P_n is L_2, the distance L with respect to the distance L_1
It has an outer contour with a ratio of _2 within the range of 0.20 to 0.50, and between the carcass body and the flap, rubber A is adjacent to the carcass body and the bead core, and rubber B is adjacent to the carcass body and the flap. It also has three types of rubber stocks: this rubber B and the rubber C adjacent to the fold. Rubber A has a 100% modulus of 60 kgf/cm^2 or more, and Rubber B has a 100% modulus of 15 to 35 kgf/cm^2.
2, resilience 65-85 Rubber C has 100% modulus 35-60 kgf/cm^
2, each physical property has a resilience of 50 to 65, and the ratio of the thickness of rubber C to the total rubber stock thickness T measured along the normal line n is 0.3 to 0.2.
A pneumatic radial tire for heavy loads, characterized in that the pneumatic radial tire has a combination of 75 and 75.