JP3499346B2 - Pneumatic tire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a land portion having a convex portion on the tire center side formed by a main groove, and more specifically, a land which is formed on a tread surface by a two-piece mold. The present invention relates to a pneumatic tire that suppresses the occurrence of chipping or cracks in the convex portions of the parts.

[0002]

2. Description of the Related Art Conventionally, when a pneumatic tire provided with a land portion composed of a block or a rib having a convex portion on the tire center side by a main groove extending in the tire circumferential direction is vulcanized and molded by a two-piece mold, When pulling out the mold along the tire axial direction after vulcanization, a large frictional resistance acts between the main groove wall and the protrusion of the main groove forming mold protruding in the direction intersecting the tire axial direction. . Therefore, chipping or cracking is likely to occur at the tip corner portion of the tread surface of the convex portion, which is weak in strength. This tendency is particularly remarkable in a tire having a deep main groove, in which the angle of the convex portion with respect to the tire circumferential direction is 65 ° or less.

As measures against the above, a lubricant such as silicon is applied to the convex portion, or the groove wall angle and the block shape on the convex portion side are changed so that the mold can be easily removed. Also, a sectional type mold is used. However, the method of applying the lubricant has a problem that the cost increases as much as it is used, and that if the groove wall angle, the block shape or the like is changed, the tire performance is significantly deteriorated. Further, when a sectional type mold is used, there is a drawback that the product cost of the tire becomes expensive because the mold is expensive. Therefore, if the tread pattern including blocks and ribs having a convex portion on the tire center side can be molded by using a two-division mold without applying a lubricant such as silicon, the product cost can be reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a convex land portion which is molded on a tread surface by a two-divided mold without applying a lubricant such as silicon or using a sectional type mold. It is an object of the present invention to provide a pneumatic tire capable of suppressing the occurrence of cracks and cracks in a portion and maintaining the tire performance at substantially the same level.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a tire having a main groove extending in the tire circumferential direction on a tread surface.
In a pneumatic tire in which a land portion formed of a block having a convex portion on the tire center side is formed by a lateral groove extending in the width direction, the convex portion is notched only over the tread surface and the side wall of the main groove, and up to the tread surface. With the side that extends
A stepped portion having a bottom surface extending from the side surface to the main groove is provided along the main groove .

Since the stepped portion which is cut out is provided on the convex portion on the tire center side of the land portion as described above, after the vulcanization is formed by using the two-divided mold, the mold is moved in the tire axial direction. Even when a large frictional resistance is applied between the side wall of the main groove and the protrusion of the mold for forming the main groove that protrudes in the direction intersecting the extraction direction, the notched step The frictional resistance acting on the convex portion in the vicinity of the portion is lower than that of the conventional one, and the mold is likely to come off. As a result, it is possible to suppress cracks and cracks that have conventionally occurred in the convex portions of the land portion.

Further, unlike the conventional method of changing the groove wall angle, the block shape, etc., it is only necessary to provide the stepped portion at the corner portion facing the main groove of the convex portion, so that the steering stability is greatly reduced. Never.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention will be specifically described below with reference to the embodiments shown in the drawings. FIG. 1 is a tire center C of the tread surface of the pneumatic tire of the present invention.
The main part on the left side from L is shown. The tread surface 1 is provided with a zigzag-shaped main groove 2 extending in the tire circumferential direction T, and a lateral groove 3 extending in the tire width direction. The main groove 2 and the lateral groove 3 form the tire center CL side. A plurality of land portions 4 each formed of a block that is convex toward are formed. The bottom of the main groove 2 is formed in an arc shape in cross section,
Both side walls 2a of the main groove 2 continuing from the bottom to the tread surface 1
Is formed to have a linear cross section and expands outward.

According to the present invention, in the pneumatic tire having the above-described structure, the tire center-side convex portion 4A of the land portion 4 is provided.
Only at the bottom, a stepped portion 5 cut out is provided over the tread surface 1 and the side wall 2a of the main groove 2. This stepped part 5
Is formed so as to include the tip corner portion 4a of the convex portion 4A,
Is provided on the convex portion 4A. The stepped portion 5 is
It has a flat side surface 5a extending to the tread surface 1 and a flat bottom surface 2b extending from the lower end of the side surface 5a to the side wall 2a of the main groove 2.

By providing the stepped portion 5 on the convex portion 4A on the tire center CL side of the land portion 4 as described above, when the two-piece mold is pulled out along the tire axial direction, it intersects with the pulling direction. Even if a large frictional resistance acts between the protrusion of the die for forming the main groove and the side wall 2a of the main groove, the stepped portion cut out from the tread surface 1 to the side wall 2a of the main groove 2 Since the frictional resistance acting on the convex portion 4A in the vicinity of 5 is reduced to facilitate the removal, it is possible to suppress the chipping and cracks generated in the convex portion 4A of the land portion 4. Therefore, the land portion 4 having the convex portion 4A in which the generation of chips and cracks is suppressed by the two-division mold without using a lubricant such as silicon and without using a sectional mold.
Since it is possible to mold, the product cost can be reduced. Further, unlike the conventional case, it is only necessary to form the stepped portion 5 on the convex portion 4A without changing the groove wall angle, the block shape, or the like, so that the steering stability is not significantly reduced.

In the above-described embodiment, the side surface 5 of the stepped portion 5 is in the tire longitudinal section orthogonal to the extending direction of the main groove 2.
A tire with respect to the tread surface 1 that passes through a tangent line X connecting a point a where a intersects with the tread surface 1 and a point B where the bottom surface 5b of the stepped portion 5 intersects with the side wall 2a of the main groove 2 and the tire center CL of the tread surface 1. The angle α with the normal direction Z is 10 to 30
It is preferable to set in the range of °. This angle α corresponds to the apparent angle at the corner when the mold is pulled out in the axial direction of the tire. Generally, the larger this angle, the smaller the frictional resistance when pulling out the mold, and the tip corner portion. It is effective in preventing cracks and cracks in 4a. However, the angle α is 30
If the angle exceeds 50 °, the contact area of the land portion 4 will decrease, and the steering stability will be significantly reduced. If the angle α is less than 10 °,
The effect of reducing frictional resistance is small, and cracks and cracks are likely to occur.

The notch width a between the points A and B of the stepped portion 5 is 0.5 to 5 mm, and the depth b from the tread surface (tread surface 1) to the point B is the depth of the main groove 2. It is better to set it to 0.05 to 0.5 D with respect to the size D. The stepped portion 5 is
As shown in FIG. 2, the side surface 5a extends in a direction orthogonal to the tangent line drawn to the point A where the tread surface 1 intersects (the tire normal direction to the tread surface 1 passing through the point A), and the bottom surface 5b extends to the side surface 5a. On the other hand, it is preferable that the main groove 2 is extended to the side wall 2a at an angle of 90 °, but the present invention is not limited to this.

Also, the tread surface 1 and the side surface 5a of the stepped portion 5
Corner 4b surrounded by and bottom surface 5b of stepped portion 5
In the corner portion 4c surrounded by the side wall 2a of the main groove 2,
As shown by the dotted line in the figure, it is preferable to chamfer, and this further reduces the frictional resistance at the time of removing the mold from the corners, so that cracks and cracks can be more suppressed.

This chamfering is preferably performed on both corners 4b and 4c, but at least one of them may be chamfered. The chamfered shape is not particularly limited, but an arcuate cross section having a predetermined curvature as shown in FIG. 2 is preferable, and in that case, the radius of curvature r is in the range of 0.2 to 1.5 mm. Can be Figure 3
7 shows another embodiment of the present invention. In the above-described embodiment, the step portion 6 that projects toward the main groove 2 side is further provided below the side wall 2a of the main groove 2. The depth of the step 6 from the tread surface 1 is 0.5 with respect to the depth D of the main groove 2.
The protrusion is provided on the side wall 2a of the main groove 2 of 1D. By providing the step portion 6 below the side wall 2a of the main groove 2 as described above, the frictional resistance when the mold is pulled out from the corner portion 4b is further reduced, and the cracks and cracks in the convex portion 4A are further suppressed. Can be done on a regular basis.

In this embodiment, the side surface 5a of the stepped portion 5 in the tire longitudinal section orthogonal to the direction in which the main groove 2 extends.
Point A at which the tread surface 1 intersects with the tread surface 1, and the planar upper surface 6a of the stepped portion 6 has a planar side surface 6b of the stepped portion 6.
It is preferable that an angle β formed by a tangent line Y connecting a point C intersecting with and a tire normal direction Z with respect to the tread surface 1 that passes through the tire center CL of the tread surface 1 is within a range of 10 to 30 °. If the angle β is smaller than 10 °, the improvement effect is small, and if it exceeds 30 °, the volume of the main groove 2 is reduced, and the drainage performance is deteriorated. The projecting width c of the stepped portion 6 can be 0.5 to 5 mm.

The corner portion 6c surrounded by the upper surface 6a and the side surface 6b of the stepped portion 6 may be chamfered so that a cross section having a predetermined curvature becomes an arc shape or the like, as in the above, and a radius of curvature thereof. r1 can also be 0.2 to 1.5 mm as described above . In the present invention, in particular, the depth D of the main groove 2 is 7.
It can be preferably used when the angle θ of the convex portion 4A with respect to the tire circumferential direction T is 5 mm or more and 65 ° or less.

[0017]

EXAMPLE A tire of the present invention having a common tire size of 145R12 8PR and provided with a stepped portion as shown in FIG. 1, and a conventional tire 1 having no stepped portion in FIG.
~ 3 and so on were manufactured as follows. In each of the test tires, the depth of the main groove was 11.1 mm, the notch width a of the stepped portion in the tire of the present invention was 1.5 mm, and the depth b of the stepped portion was 28% of the depth D of the main groove. The radius of curvature of the chamfer of the corner portion is 0.5 mm, the angle α is 26 °, and the angle θ of the convex portion is 50 °. The tire of the present invention: vulcanization molding without applying a lubricant using a two-piece mold. Conventional tire 1: Vulcanization molding without applying lubricant using a two-piece mold. Conventional tire 2: A vulcanization molding was performed by applying a lubricant using a two-piece mold. Conventional tire 3: Vulcanization molding using a sectional type mold.

Each of these test tires was subjected to an evaluation test for chipping of land and steering stability by the following measuring method, and the results shown in Table 1 were obtained. Chips on land After vulcanization molding of each test tire as described above, the number of chips generated on the convex part of the block was measured, and the result was evaluated as good (no or little chipping) or good (chipless). Is within the allowable range) and is not possible (there are many defects and is outside the allowable range). Steering stability Rim size of the tire of the present invention and the conventional tire is 12 × 4.
It is attached to the rim of 00B, and the air pressure is set to 200 kPa.
It was mounted on a 0 cc vehicle and a driving test was conducted by a test driver to evaluate steering stability. The larger this value, the better the steering stability.

[0019]

[Table 1]

As is clear from Table 1, the tire of the present invention provided with the stepped portion has the same block defect as the conventional tire 2 coated with the lubricant and the conventional tire 3 manufactured by the sectional type mold. In comparison with the above, it is possible to maintain the steering stability at about the same level within a permissible range (allowing a decrease of 10%), without applying a lubricant such as silicone or reducing the tire performance. It can be seen that the two-divided mold can suppress the occurrence of chipping in the convex portion of the land portion that is molded on the tread surface.

In the tire of the present invention, the angle α
Was changed as shown in Table 2 to prepare test tires 1 to 5 using a two-divided mold. When each of these test tires was subjected to an evaluation test for chipping of land and steering stability by the above-described measuring method, the results shown in Table 2 were obtained.

[0022]

[Table 2] As is clear from Table 2, the test tire with the angle α of 10 to 30 ° can effectively suppress the occurrence of chipping without significantly lowering the steering stability as compared with the conventional tire. .

[0023]

As described above, the present invention can be applied to the tread surface.
A main groove extending in the tire circumferential direction and a lateral groove extending in the tire width direction
From the block that has a convex portion on the tire center side due to the groove
A pneumatic tire formed with land portions made, the protrusions
Only on the tread surface and the side surface of the main groove, which is notched over the side surface extending to the tread surface and from the side surface to the main groove.
Since a stepped portion having an extending bottom surface is provided along the main groove, a tread surface is formed on the tread surface by a two-piece mold without applying a lubricant such as silicon or using a sectional mold. It is possible to suppress the occurrence of cracks or cracks in the convex portion of the land portion to be molded, and thereby reduce the product cost of the tire. Moreover, the tire performance can be maintained at substantially the same level.

[Brief description of drawings]

FIG. 1 is a plan view of relevant parts showing an example of a tread surface of a pneumatic tire of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view of essential parts showing another embodiment of the pneumatic tire of the present invention.

[Explanation of symbols]

1 tread surface 2 main groove 2a Side wall 4 Land area 4A convex portion 4a tip corner portion 4b, 4c corner part 5 stepped part 5a side 5b bottom 6 step 6a upper surface 6b Side 6c Corner CL tire center T tire circumferential direction

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B60C 11/04 B60C 11/11

Claims (8)

(57) [Claims] 1. A main groove extending in a tire circumferential direction on a tread surface.
And a pneumatic tire in which a land portion formed of a block having a convex portion on the tire center side is formed by a lateral groove extending in the tire width direction, the tread surface is notched only on the convex portion and the sidewall of the main groove, and the tread is formed. Extend to the plane
A pneumatic tire having a stepped portion provided with a side surface and a bottom surface extending from the side surface to the main groove along the main groove . 2. A point A where a side surface of the stepped portion intersects a tread surface and a point B where a bottom surface of the stepped portion intersects a side wall of the main groove in a tire cross section orthogonal to a direction in which the main groove extends.
The pneumatic tire according to claim 1, wherein an angle α formed by a tangent line X that connects to the tread surface and a tire normal direction Z with respect to the tread surface that passes through the tire center is in the range of 10 to 30 °. 3. A notch width a between the points A and B of the stepped portion is 0.5 to 5 mm, and a depth b from the tread surface to the point B.
3. The pneumatic tire according to claim 2, wherein is set to 0.05 to 0.5 D with respect to the depth D of the main groove. 4. A corner portion surrounded by the tread surface and a side surface of the stepped portion, and at least one of a corner portion surrounded by a bottom surface of the stepped portion and a side wall of the main groove,
The pneumatic tire according to claim 1, which is chamfered. 5. A step portion protruding to the main groove side is provided at a portion of the side wall of the main groove whose depth from the tread surface is 0.5 to 1D with respect to the depth D of the main groove. The pneumatic tire according to claim 1. 6. A tire cross section orthogonal to a direction in which the main groove extends, a point A where a side surface of the stepped portion intersects with a tread surface, and a point C where an upper surface of the stepped portion intersects with a side surface of the stepped portion. The pneumatic tire according to claim 5, wherein an angle β formed by a tangent line Y connecting the two and a tire normal direction Z with respect to the tread surface, which passes through the tire center of the tread surface, is in a range of 10 to 30 °. 7. The pneumatic tire according to claim 6, wherein the protruding width c of the step portion is 0.5 to 5 mm. 8. The pneumatic tire according to claim 5, wherein a corner portion surrounded by an upper surface and a side surface of the step portion is chamfered.