JPH05169917A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire which is restrained from cracking at both ends or the bent bottom of an open calf arranged on a block. CONSTITUTION:A tread 1 has blocks 4 formed with main grooves 2 extended to a tire peripheral direction and auxiliary grooves extended to a tire cross direction. The block 4 is provided with a calf 5 having the bent portion 5a to be extended to the tire cross direction and having both ends connected to the main grooves 2 or the groove 2 and a shoulder edge to be formed as an open calf. Both ends and the bent portion 5a of the calf 5, at least, have the depths 1.1-1.3 times the depth of the calf 5 in a main area, and the total length of the calf in an deep area is not more than 50% of the whole length (m) of the calf.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of suppressing cracks at the bottom of a kerf placed on a block.

[0002]

2. Description of the Related Art In many pneumatic tires provided with a block pattern mainly for improving the performance on ice, the block is provided with an open kerf so that both ends of the kerf are connected to the main groove or the sub groove. In addition, in order to increase the edge effect in the tire lateral direction and the kerf length, there is also a case where the open kerf has a bent shape.

However, the tire provided with the open kerf as described above has a problem that cracks are likely to occur at both ends of the kerf and the bottom of the bent portion. Conventionally,
As a measure for preventing cracks in the kerf, it has been proposed to increase the width of the kerf bottom portion in the entire longitudinal direction. However, merely widening the width of the kerf bottom in this way does not always sufficiently prevent cracks at both ends of the kerf connected to the main groove and the bent portion. Moreover, since the width of the bottom of the kerf is wide, there is a problem that it is difficult to remove the tire from the bone portion of the mold kerf during vulcanization of the tire.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire capable of suppressing cracks generated at both ends of an open calf arranged in a block and the bottom of a bent portion.

[0005]

According to the present invention for achieving the above object, a block is formed on a tread surface by a plurality of main grooves extending in the tire circumferential direction and a plurality of auxiliary grooves extending in the tire width direction. In this pneumatic tire, the block is provided with a kerf that extends in the tire width direction and has a bent portion, and both ends of the kerf are open kerfs that connect the main groove or the main groove and the shoulder edge, at least the above. The depths of both ends of the kerf and the bent portion were 1.1 to 1.3 times the depth of the main region of the kerf, and the total length of the deep kerf region was 50% or less of the total length of the kerf. It is characterized by

As described above, since the depths of both ends and the bent portion of the bent open calf are 1.1 to 1.3 times the depth of the main kerf region, the rigidity of the deep kerf portion is localized. It is possible to prevent the movement of the block from reaching the bottom of the kerf so much that cracks can be reduced. Further, since the total length of the deep kerfs is limited to 50% or less of the total length of the kerfs, the cracks can be suppressed while maintaining the required block rigidity.

In the present invention, it is more preferable to form an enlarged block in which the width of the kerf bottom is 1.1 to 1.3 times the kerf width of the surface in the region not deep kerfed, whereby. Even if a crack occurs at the end of the bottom of the kerf, the propagation of the crack to the main region can be stopped. Hereinafter, the tire of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a tread pattern of a pneumatic tire according to an embodiment of the present invention. The tread 1 is provided with a plurality of main grooves 2 extending in the tire circumferential direction and a large number of sub grooves 3 extending in the tire width direction, and a large number of blocks 4 divided into the main grooves 2 and the sub grooves 3 are formed. .. A plurality of kerfs 5 extending in the tire width direction are arranged in the block 4 in the tire circumferential direction. The calf 5 has a bent portion 5a that is bent in a V-shape with its tip facing in the tire rotation direction.
The both ends 5b of the tread 1 are connected to the main groove 2 in the central region of the tread 1, and the shoulder end kerf is an open kerf connecting the inner end to the main groove 2 and the outer end to the shoulder edge. There is.

As shown in FIGS. 2 and 3, the kerf 5, which is the open kerf, has both ends 5b and a bent portion 5a.
The calf depth L'in the is the calf depth L of the remaining main area
1.1 to 1.3 times that of the depth c (= L'-
L) is deeper. By providing such a deep kerf region, the block rigidity at both ends 5b and the bent portion 5a is locally reduced, the stress on the kerf bottom of these portions is relaxed, and the occurrence of cracks is suppressed. If the kerf depth L ′ is smaller than 1.1 times L, the above effect cannot be expected, and if the kerf depth L ′ is larger than 1.3 times, the rigidity of the entire block is lowered.

The depths of the kerf provided on the both end portions 5b and the bent portion 5a are the length from the connection point to the main groove 2 or the shoulder edge of the both end portions 5b, and the bent portion 5a.
The length from the bending point C is a and the total length of these is limited to 50% or less with respect to the total length m of the kerf 5. By limiting the length of the deep kerf region as described above, the block rigidity required for tire running is maintained while achieving the crack prevention effect. The length a per side is preferably 0.3 times or less of the depth L ′ of the kerf depth region (a ≦ 0.3L ′).

Further, as shown in FIGS. 4 and 5, the calf 5 has a thickness of width t, and the thickness t is 0.3 to
A range of 1.0 mm is preferably used. In the kerf 5 having such a thickness t, in the main region where the kerf depth is L, an enlarged portion 5c having a round bottom and a circular arc shape with a width t ′ wider than the thickness t is formed on the kerf bottom. Has been done. By providing such an enlarged portion 5c, even if a crack occurs in the deep kerf region, it becomes possible to prevent the crack from propagating to the main region.

As the width t'of the enlarged portion 5c,
The thickness t of the kerf on the block surface side should be 1.5 to 3.0 times. If it is less than 1.5 times, the crack propagation preventing effect is small, and if it is more than 3.0 times, tire vulcanization is performed. Make it difficult to release from the mold later. In the present invention, as described above, the kerf depth region of the depth L ′ may be provided between the both end portions 5b and the bent portion 5a over the length b, if necessary, as shown in FIG. Good. However, if the deep kerf region provided in this intermediate region is made too large, the overall block rigidity will be reduced, so the total total length of both end portions 5b and the bent portion 5a is the total length of the kerf m. Must remain below 50%.

The kerf 5 described above can be formed by providing a kerf bone on a tire molding die. In particular, the kerf bone of the portion forming the enlarged portion 5c may be formed as shown in FIGS. 7 and 8. FIG. 7 is formed by folding back the tip of the plate-shaped kerf bone 7. Further, in FIG. 8, another plate piece 7'is formed by bending it into a U shape and mounting it on the tip of the kerf bone 7. The top of each calf bone is bent to form a tapered shape.
It is designed to make it easy to release from.

[0014]

As described above, according to the present invention, the depth of both ends and the bent portion of the open kerf in the bent shape is 1.1 to 1.3 times the depth of the kerf main region. Since the strain of the part is locally reduced, the movement of the block does not reach the bottom of the groove to a large extent, and the occurrence of cracks is reduced. Further, since the total length of the deep kerfs is limited to 50% or less of the total length of the kerfs, the required block rigidity can be maintained and the cracks can be suppressed.

In the present invention, it is more preferable to form an enlarged block in which the width of the kerf bottom is 1.1 to 1.3 times the kerf width of the surface in the region which is not deep kerfed. Even if a crack occurs at the end of the bottom of the kerf, the propagation of the crack to the main region can be stopped.

[Brief description of drawings]

FIG. 1 is a plan view of a tread pattern showing an embodiment of a tire of the present invention.

2 is an enlarged plan view showing a part of a block of the tread pattern of FIG. 1. FIG.

3 is a cross-sectional view taken along line X-C-X 'of FIG.

4 is a cross-sectional view taken along the line AA of FIG.

5 is a sectional view taken along line BB of FIG.

FIG. 6 is a cross-sectional view corresponding to FIG. 3 of a tire according to another embodiment of the present invention.

FIG. 7 is a side view showing an example of a calf bone used for molding the tire of the present invention.

FIG. 8 is a side view showing another example of the calf bone used for molding the tire of the present invention.

[Explanation of symbols]

 1 tread 2 main groove 3 auxiliary groove 4 block 5 calf 5a bent portion 5b end portion 5c enlarged portion

Claims (1)

[Claims] 1. A block is formed on the tread surface with a plurality of main grooves extending in the tire circumferential direction and a plurality of sub-grooves extending in the tire width direction, and the block has a bent portion extending in the tire width direction. In a pneumatic tire in which a kerf is provided and both ends of the kerf are open kerfs that connect the main groove or the main groove and the shoulder edge, at least the depths of the both ends of the kerf and the bent portion are A pneumatic tire in which the depth is 1.1 to 1.3 times the depth of the main region and the total length of the deep kerf region is 50% or less of the total length of the kerf.