JPH05155205A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To prevent the coulisse to a tire and improve the durability of a bead part by forming at least one step for lessening the thickness of a sidewall, between the contact part with A rim flange of the outside surface of the tire and the largest width position of the tire. CONSTITUTION:Two steps 6 and 7, which form step shapes within the step range of 0.2-5mm, are made, respectively, in the direction of reducing the thickness of a sidewall 5, toward the side of the largest width position of a tire from the side of a rim flange, within required area between the contact part with the rim flange 3 of the outside surface of the tire and the tire largest width position 4. And, for these steps 6 and 7, main curves 8 and 9, the centers of the curvatures of which lie inside the tire, and following curves 10 and 11, the centers of the curvatures of which lie outside the tire, are continued. Hereby, the durability can be improved by effectively reducing the deflection of the bead part and the heat occurrence, and besides at molding by vulcanization, the occurrence of the coulisse to each step 6 and 7 can be prevented effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention not only improves the durability of the bead portion, but also almost completely eliminates the cris caused by vulcanization and causing cracks. The present invention relates to a pneumatic tire for heavy load of 80% or less.

[0002]

2. Description of the Related Art Conventionally, in order to improve durability of a bead portion, a carcass ply is wound around a bead core from the inside of a tire toward the outside,
Place a chafer as a reinforcing layer on the outside of the winding end of the carcass ply at the bead part, or consider the rubber hardness and placement of the stiffener on the outer peripheral side of the bead core, and consider whether a large rigidity step At some point, it has been widely practiced to arrange a rubber having an intermediate rigidity.

However, when a large number of reinforcing layers are used in the bead portion, in addition to the large amount of heat generated in the bead portion,
There is an inconvenience that both the tire weight and the cost increase, and in the case where the stiffener is composed of plural kinds of rubber, there is an inconvenience that the productivity is lowered.

Therefore, as shown in FIG. 3, a relatively large dent portion b extending continuously in the circumferential direction is formed on the outer surface of the tire at a position slightly outside the bead portion a, and the dent portion b is formed. JP-A-57-191104 discloses that by reducing the thickness of the sidewall of the portion where the tire is formed, the flexibility of that portion is increased, and thereby the distortion of the bead portion during load rolling of the tire is reduced. This is disclosed in the publication, and according to this, the durability of the bead portion can be improved without requiring addition of a tire constituent material.

[0005]

However, Japanese Patent Laid-Open No. 57-1
According to such a conventional technique disclosed in Japanese Patent No. 91104, at the time of vulcanization molding of a tire, a recess b having a relatively large depth and a wide radial region is formed in a sidewall by a mold. Since it is supposed to be formed, when molding a raw tire by molding, as shown in FIG.
As exaggeratedly shown in a schematic partial sectional view in the radial direction of the mold, one ridge d provided on the mold c is attached to a green tire e.
When pushing into the raw tire, the flow distance of the raw tire portion that first comes into contact with the ridge or other mold protrusion becomes considerably long, and therefore, when the pushing of the mold ridge d into the raw tire is completed, The outer surfaces of the raw tire fluidized portions come into contact with each other, and so-called Chris is generated at the contacted portions, in which rubbers are not completely adhered to each other.

Since this Chris remains almost as it is even after the vulcanization of the raw tire is completed, the appearance of the tire is impaired by it, and cracks are generated from the crack during rolling of the tire. There was a problem that it was easy to do.

The present invention has been made to solve the above-mentioned problems of the prior art, and its object is to sufficiently prevent the occurrence of chris in the tire, (EN) It is possible to provide a heavy duty pneumatic tire capable of greatly improving the durability of the bead portion.

[0008]

The heavy duty pneumatic tire of the present invention has a contact portion with a rim flange on the outer surface of the tire in a tire width direction cross section in a state in which the tire is mounted on a prescribed rim and filled with a prescribed internal pressure. Between the tire maximum width position, the main curve that has the center of curvature inside the tire and the secondary curve that is connected between the main curves and has the center of curvature outside the tire, and the tire maximum width from the rim flange side. 0.2 to 5 in the direction of decreasing the wall thickness toward the position side
At least one step portion having a step shape with a step of mm is formed.

More preferably, the amount of the step is set to 0.
The range is 5 to 3 mm, and the ratio of the length of the sub-curve to the length of the main curve is 1 to 30%, preferably 1 to 15%. More preferably, two or more steps are provided, and at least one step is formed on the outer side in the tire radial direction from the folded carcass ply end.

[0010]

In the heavy duty pneumatic tire of the present invention, at least two step portions for reducing the sidewall thickness are formed between the contact portion of the tire outer surface with the rim flange and the tire maximum width position. Then, by sufficiently reducing the total thickness of the sidewall at the required position, distortion and heat generation at the bead portion during tire load rolling are effectively reduced, and the durability of the bead portion is improved. Can be made

In this case, a plurality of steps are used without forming a single recess in the sidewall,
By providing the required sidewall thickness, it is possible to sufficiently reduce the flow distance and flow amount of the surface rubber at each step during vulcanization molding of the raw tire,
As a result, it is possible to effectively prevent the occurrence of chris.

Here, if the step is less than 0.2 mm, the effect of providing the step is poor, and the total thickness of the sidewall cannot be made sufficiently thin, so that the bead portion at the time of load rolling of the tire is not formed. Distortion and heat generation cannot be effectively reduced. On the other hand, if it exceeds 5 mm, the flow amount of the surface rubber at the step cannot be sufficiently reduced, and the occurrence of cres cannot be effectively prevented.

Further, here, most of the steps are formed by a main curve having a center of curvature inside the tire, so that the raw tire and the mold are brought into contact with each other in a substantially parallel manner over a wide range, and the rubber of the raw tire surface portion is made. The flow can be suppressed and the generation of Chris can be prevented more effectively.

When the ratio of the length of the sub-curve to the length of the main curve is less than 1%, a substantial step portion cannot be formed, and the wall thickness of the sidewall is effective. Since it cannot be made as thin as possible, it is not effective in reducing the distortion and heat generation of the bead portion. Meanwhile, the ratio
If it exceeds 30%, the flow distance of the raw tire portion when coming into contact with the mold becomes long and creases easily occur.

More preferably, the radius of curvature of the main curve is set to 80 mm or more and the radius of curvature of the secondary curve is set to 50 mm or less so that the entire radius of curvature of the outer surface portion including each step is sufficiently large. By contacting the green tire and the mold substantially parallel to each other, it is possible to further effectively prevent the occurrence of Chris.

That is, when the radius of curvature of the main curve is less than 80 mm, the overall radius of curvature of the outer surface including the step cannot be increased, and the radius of curvature of the secondary curve is 50 mm.
If the value exceeds mm, a large curvature is formed on the outer side, and in any case, it is not effective in preventing the occurrence of Chris.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view in the tire width direction showing an embodiment of the present invention, in which 1 is a pair of bead cores and 2 is a radial carcass extending from one bead core 1 to the other bead core 1. Are shown respectively. Note that the other reinforcing structure of the tire is similar to that of a general radial tire for heavy load, and is not shown.

Here, in the required area between the contact portion of the outer surface of the tire with the rim flange 3 and the maximum tire width position 4, the sidewall is extended from the rim flange side toward the maximum tire width position. In the direction of decreasing the wall thickness of 5, 0.
Two step portions 6 and 7 each having a step shape in a step range of 2 to 5 mm are formed, and each of these step portions 6 and 7 is a main curve 8 and 9 having a center of curvature inside the tire, and a tire. It is configured by connecting the secondary curves 10 and 11 with the center of curvature outside of, and the ratio of the lengths of the secondary curves 10 and 11 to the lengths of the primary curves 8 and 9 is 1 to 30%. The range is. In such a tire, the radius of curvature of the main curves 8 and 9 is more preferably 80 mm or more, and the radius of curvature of the secondary curves is 50 mm or less.

Incidentally, the size shown in FIG.
100 from pied heel on 11/70 R 22.5 tires
A curve with an arc length of 44 mm under a radius of curvature of mm, followed by one step 6 close to the bead, with a parabola 10 with an arc length of 1.5 mm under a radius of curvature of 10 mm, 250 Under the radius of curvature of mm, the step is defined as 1 mm by the main curve 8 having an arc length of 15.5 mm and the other step 7
Is subdivided as 1 mm with a minor curved surface 11 having an arc length of 1.5 mm under a radius of curvature of 10 mm and a main curve 9 having an arc length of 15.5 mm under a radius of curvature of 250 mm. As a result, the ratio of each of the secondary curves 10 and 11 to each of the primary curves 8 and 9 is set to 9.7%. By the way, the step referred to here indicates the amount of deviation between the extension lines of the respective main curves 8 and 9, as shown in the enlarged sectional view of FIG.

Further, in the illustrated example, by continuing an arc having a radius of curvature of 10 mm and having a center of curvature on the outside of the tire on the main curved surface 9, the artificial thin portion 13 of the sidewall 5 is maintained and continued. With a transition area 14 with a radius of curvature of 165.5 mm, it is smoothly continuous to the tire maximum width position 4.

According to the tire constructed as described above, the thickness of the sidewall 5 is reduced between the contact portion of the outer surface of the tire with the rim flange and the tire maximum width position 4. By providing two steps 6 and 7,
The distortion and heat generation of the bead portion can be effectively reduced, and the durability of the bead portion can be greatly improved.

Further, by reducing the wall thickness of the sidewall 5 with the two step portions 6 and 7, as described above, in forming each step portion during vulcanization molding, the flow distance of the surface partial rubber is increased. And, the flow rate is made sufficiently small, and thereby, it is possible to effectively prevent the generation of creases in the step portions 6 and 7. Here, by setting each step in the range of 0.5 to 3 mm, distortion of the bead portion and heat generation can be effectively reduced, and crease can be effectively prevented.

Each step 6 and 7 is composed of a main curve 8 and 9 having a center of curvature inside the tire and sub curves 10 and 11 having a center of curvature outside the tire. By setting the ratio of the curves 10 and 11 to the main curves 8 and 9 to be in the range of 1 to 30%, the overall shape of the outer surface portion including the step portions 6 and 7 is convex outward, As a result, the green tire and the mold are brought into contact with each other substantially in parallel over a wide range, and the rubber flow on the surface portion of the green tire can be suppressed to more effectively prevent the generation of Chris.

Further, in the illustrated tire, the radii of curvature of the main curves 8 and 9 are both 80 mm or more, and the radii of curvature of the secondary curves 10 and 11 are both 50 mm or less. By making the entire radius of curvature of the surface portion sufficiently large, it is possible to further suppress the rubber flow on the surface portion of the green tire and prevent the occurrence of creases more effectively.

[0025]

[Comparative Example] A comparative test concerning the occurrence of strain in the bead portion, the durability of the beat portion, and the occurrence of Chris between the invention tire and the comparative tire will be described below. ◎ Test tire size 11/70 R22.5 tires specified rim (7.50 × 22.
It was attached to 5) and filled with the specified internal pressure (8 kg / cm ² ). Inventive tire Tire having the configuration and dimensions shown in FIG. 1 Comparative tire 1 Tire having a side recess as shown in FIG. 3 Curvature radius of the center of the recess 30 mm (outward center of curvature) Comparative tire 2 Normal tire having no recess 230 mm center radius of curvature from flange to maximum width (center of curvature inward)

◎ Test Method The bead strain was determined by measuring the compressive strain generated at the radially outer end of the carcass turnup portion when a standard load of 100% (2500 kg) was applied. Also, regarding the durability of the bead part, a drum test was performed with a load of 140% of the standard (3500 kg), and at a rotation speed of 60 km / h,
The distance traveled until damage occurred was measured. Then, the state of crease formation was visually inspected for the presence or absence of crease formation at the time of removal from the mold after vulcanization.

◎ Test results Table 1 shows these results. The bead portion strain and the bead portion durability were indexed using the comparative tire 2 as a control. Here, the larger the index value, the better the result.

[0028]

[Table 1] According to Table 1, it is clear that the invention tire can effectively improve the durability of the bead portion as a result of the bead portion strain being smaller than that of the comparative tire 2, and compared with the comparative tire 1. It is clear that Chris can be almost completely prevented from occurring.

[0029]

As is apparent from the above comparative example, according to the present invention, it is possible to substantially completely prevent the formation of creases and to further greatly improve the durability of the bead portion.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view of a step portion.

FIG. 3 is a sectional view similar to FIG. 1 showing a conventional technique.

FIG. 4 is a schematic diagram showing the occurrence state of Chris.

[Explanation of symbols]

 3 Rim flange 4 Tire maximum width position 5 Side wall 6,7 Step section 8,9 Main curve 10, 11 Secondary curve 13 Thin section

Claims (3)

[Claims] 1. A curvature inward of a tire between a contact portion of a tire outer surface with a rim flange and a tire maximum width position in a tire width direction cross section in a state where the tire is assembled to a prescribed rim and filled with a prescribed internal pressure. In the direction of decreasing the sidewall wall thickness from the rim flange side toward the tire maximum width position side, which is composed of a main curve having a center and a subsidiary curve connected between the main curves and having a center of curvature on the outside of the tire. 0.2-5
A heavy-duty pneumatic tire, characterized in that at least one stepped portion having a step of mm is formed. 2. The pneumatic tire for heavy load according to claim 1, wherein the ratio of the arc length of the sub-curve to the arc length of the main curve adjacent to the outer side in the tire radial direction is in the range of 1 to 30%. 3. The radius of curvature of the main curve is 80 mm or more, and the radius of curvature of the secondary curve is 50 mm or less.
The pneumatic tire for heavy load described.