JPH06143943A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To disperse stress concentrated on the bottom of a sipe for restraining the occurrence of cracks by providing a cylindrical expanded part limited in the bottom of a portion communicating to a main groove by a sipe and specified of the diameter, length and length extended from the bottom of the sipe. CONSTITUTION:The bottom of a sipe 5 is provided in a portion communicating to a main groove 2 with an expanded cylindrical part 6 having a diameter (d) larger than the width (t) of the sipe 5. The ratio of diameter (d) of the expanded part 6 to the width (t) of the sipe 5 falls within the range of 0.2t<=d<=3t. The length (a) of the expanded part 6 to the diameter (d) and length (b) of the sipe 5 is defined as 2d<=(a)<=(b)/3. Further, the expanded part 6 sets the relation between the depth (h) from the surface of a block 4, the length (h)-(H) extending from the depth L of the sipe 5 and the diameter (d) to 0.1d<h-H<=1.45d. When the extension length h-L is smaller than 0.1d, the deformation of the bottom of the sipe 5 cannot be restrained so that an effect of mitigating stress cannot be obtained.

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 generated at the bottom of sipes arranged on a block of a tire having a block pattern.

[0002]

2. Description of the Related Art In a pneumatic tire provided with a block pattern mainly for the purpose of improving the performance on ice, sipes extending in the tire width direction are provided in the blocks. However, since the sipe is a thin cut, there is a problem that stress is likely to be concentrated at the bottom of the sipe due to the strain of the block that is received when the tire rotates, and cracks are easily generated at the bottom.

Conventionally, as a measure for preventing the occurrence of such a crack, it has been proposed to form the bottom of the sipe into an arc having a radius of 1/2 of the sipe width. However, since the radius of curvature is small, a sufficient crack suppressing effect can be obtained. I couldn't do it. For this reason, as an improvement, it has been proposed to provide a cylindrical enlarged portion having a larger radius of curvature over the entire length of the sipe. However, in this proposal, since the enlarged part having a radius of curvature larger than the sipe width extends over the entire length of the sipe, it may be difficult to release the mold from the mold after tire vulcanization, and in some cases, the block may be damaged. It was

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire capable of preventing cracks at the bottom of a sipe while allowing smooth demolding after tire vulcanization.

[0005]

According to the present invention for achieving the above object, a plurality of main grooves extending in the tire circumferential direction and sub-grooves intersecting with the main groove are provided on a tread surface, and these main grooves are provided. In a pneumatic tire in which a large number of blocks divided into sub-grooves are formed and the blocks are provided with sipes extending in the tire width direction, a cylindrical enlarged portion is formed at the bottom of the portion where the sipes communicate with the main groove. The diameter d of the enlarged portion is 1.2t ≦ d ≦ 3t with respect to the width t of the sipe, and the length a of the enlarged portion along the longitudinal direction of the sipe is the diameter d and the length of the sipe. 2b ≦ a ≦ b /
3, and the depth (h−L) of the depth h of the enlarged portion from the block surface extending from the depth L of the sipe is 0.1d <h−L ≦ 1. It is characterized in that it is set to 45d.

In this way, a cylindrical enlarged portion is formed at the bottom of the portion where the sipe communicates with the main groove, and the enlarged portion is formed into a cylindrical shape having a diameter larger than the width of the sipe. By specifying the relative position to the bottom of the sipe, the stress concentrated on the bottom of the sipe is efficiently dispersed, and the occurrence of cracks is suppressed. Further, since these enlarged portions are arranged only in the portion communicating with the main groove of the sipe bottom, the resistance at the time of demolding after tire vulcanization is reduced and damage to the block can be eliminated compared to the case where it is provided over the entire length of the sipe. it can.

That is, according to the study by the present inventor, the cracks generated at the bottom of the sipe are mostly localized in the portion where the sipe communicates with the main groove, and the enlarged portion is provided over the entire length of the sipe as in the conventional case. If it is found that it is not necessary, and if the enlarged portion is locally provided in the communicating portion with the main groove as described above, the effect of facilitating the mold releasing can be obtained.

In the present invention, the sipe means a thin cut having a width t of 2 mm or less, and is distinguished from a large groove such as a main groove or a sub groove. less than,
The present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is an example of a tread pattern used in the present invention, and FIG. 2 is an enlarged view of a part thereof. 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. . The block 4 is provided with sipes 5 extending in a thin notch in the tire width direction so as to bend or straighten so that both ends 5a thereof communicate with the main groove 2, respectively. The sipe 5 provided on the block 4 at the shoulder end communicates the outer end side with the shoulder edge.

As shown in FIG. 3, at the bottom of the sipe 5,
A cylindrical enlarged portion 6 having a diameter d larger than the width t of the sipe 5 is formed in a portion communicating with the main groove 2. In the present invention, the enlarged portion 6 has the diameter d and the sipe 5
The length a along the length direction of is set as follows. First, the diameter d is in the range of 1.2t ≦ d ≦ 3t with respect to the width t of the sipe 5. If the diameter d is smaller than 1.2t, there is no effect of relieving stress, and if it is larger than 3.0t, it becomes difficult for the tire to come off from the mold during demolding after tire vulcanization, which causes block damage.

The length a of the enlarged portion 6 is 2d≤a≤b / 3 with respect to the diameter d and the length b of the sipe. If the length a is less than 2d, the deformation of the bottom of the sipe is suppressed and the effect of relaxing the stress cannot be obtained. Also, b /
When it is larger than 3, it becomes difficult to remove the mold from the mold, and the rigidity of the block end portion is lowered, so that uneven wear is likely to occur in the block.

Further, the enlarged portion 6 has a length (h- which extends a depth h from the surface of the block 4 from a depth L of the sipe 5).
L) must be regulated. The length of extension (h
-L) is 0.1d <h-L≤1.45d with respect to the diameter d. If the extension length (h−L) is smaller than 0.1 d, the deformation of the bottom of the sipe 5 cannot be suppressed, and the effect of stress relaxation cannot be obtained. On the other hand, if it is larger than 1.45d, the rigidity of the end portion of the block is lowered, so that uneven wear is likely to occur in the block.

In the above-described embodiment, the case where both ends of the sipes communicate with the main grooves or shoulder end sides on both sides has been described, but the present invention also applies to the case where only one side of the sipes communicates with the main groove. Can be applied.

[0013]

Example A tire of the present invention having a tire size of 11R22.5 14PR, having the tread pattern shown in FIG. 1, and having the specifications of the sipe provided on the block and the enlarged portion as follows was manufactured. Sipe width t: 0.8 mm Depth L: 12.0 mm Total length b: 24.0 mm Enlarged portion Diameter d: 1.6 mm Depth h: 12.6 mm Length a: 4.0 mm For comparison, the tire of the present invention is also used. In Comparative tire 1, a comparative tire 1 in which an enlarged portion is not formed at the bottom of the sipe and a comparative tire 2 in which the bottom of the sipe is formed in an arc shape over the entire length are manufactured.

Each of these three types of tires has a rim of 22.5
When mounted on a × 8.25 and examined the total crack length at the bottom of the sipe by the evaluation method under the following conditions, the results shown in Table 1 were obtained. Crack generation evaluation method: 20 at an average speed of 40 km / h
After traveling 000 km, the surface length of cracks generated at the bottom of the sipe was measured, and the total sum in each block was obtained. The evaluation results are compared by using the reciprocal of the measured value, and comparison tire 1
Was set as 100 and indicated by an index. The larger the index value, the better.

[0015] From the results in Table 1, it is understood that the tires of the present invention have less cracks than the comparative tires 1 and 2.

[0016]

As described above, according to the present invention, since the sipe is limited to the bottom portion of the portion which communicates with the main groove, the cylindrical enlarged portion having the specified diameter, length and length extending from the sipe bottom portion is provided. The stress concentrated on the bottom of the sipe can be dispersed, and the occurrence of cracks can be suppressed. Further, since these enlarged portions are arranged only in the portion communicating with the main groove on the bottom of the sipe, the resistance at the time of demolding after tire vulcanization can be reduced and damage to the block can be eliminated.

[Brief description of drawings]

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

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

3 is a view taken along the line X-C-X 'in FIG.

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

[Explanation of symbols]

 1 Tread 2 Main groove 3 Secondary groove 4 Block 5 Sipe 6 Enlarged part

Claims (1)

[Claims] 1. A tread surface is provided with a plurality of main grooves extending in the tire circumferential direction and sub-grooves intersecting with the main grooves to form a large number of blocks divided into the main grooves and the sub-grooves.
In a pneumatic tire having a sipe extending in the tire width direction in the block, a cylindrical enlarged portion is formed at a bottom portion of a portion where the sipe communicates with the main groove, and a diameter d of the enlarged portion is set to a width of the sipe. 1.2t ≦ d ≦ 3t with respect to t, the length a of the enlarged portion along the longitudinal direction of the sipe is 2d ≦ a ≦ b / 3 with respect to the diameter d and the length b of the sipe, and The depth h of the enlarged portion from the block surface is the depth L of the sipe.
The pneumatic tire having a length (hL) extended from 0.1d <hL <1.45d with respect to the diameter d.