JPH0858317A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To prevent partial the wear produced on the side part of a land part and prevent degradation of running performance on roads. CONSTITUTION: In a pneumatic tire having a plurality of land parts 3 divided with a plurality of longitudinal grooves almost rectilinearly extending in the circumferential direction of the tire, many upper sipes 8 opening on the surface and the side part of the land part 3 and extending from the opening end of the side part 8 to a groove bottom 6 are spacedly arranged on the groove wall 4 of the side part of the land part 3, and further many lower sipes 9 opening on the way of the groove wall 4, the opening upper end parts of which enter into the territories between the upper sipes 7 and the opening lower end parts extend to the groove bottom 6, are arranged in the territories between these upper sipes 7, 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly, to a pneumatic tire for heavy load, which is improved in uneven wear resistance and wet resistance at high speed on a generally good road.

[0002]

2. Description of the Related Art Conventionally, pneumatic radial tires, whether in a rib pattern or a block pattern, have uneven wear generated in a plurality of circumferentially extending land portions divided by a plurality of longitudinal grooves, and in particular, in the longitudinal groove of the land portion. In order to improve the river wear that occurs along the vertical groove adjacent to the tire, including the improvement of running resistance on wet roads, the sipe that opens laterally to the tread and the groove wall, respectively, in the tire circumferential direction, A large number of arrays have been arranged at intervals.

That is, in order to improve the uneven wear resistance and the wet resistance at the same time, a large number of sipes extending in the tire width direction are arranged in the groove wall to reduce the frictional energy due to slippage and thereby the tire in the rib or block. Prevents wear on the widthwise ends and prevents uneven wear, which is often called the river wear in the tire circumferential direction when there are no sipes, and reduces resistance to circumferential slip at the widthwise ends of the land. The trackability has been improved, and the running performance on wet roads has been secured by the edge effect of sipes.

[0004]

However, in order to secure the uneven wear resistance, it is necessary to make the intervals of the sipes considerably small. However, if the intervals of the sipes are made very small, the uneven wear resistance is improved. However, the rigidity in the small area between sipes becomes too small, and the small area between sipes does not work effectively as the area of the land part that provides wear resistance, and the wear resistance decreases and external force is applied. It was weak and was the cause of chipping, chipping and cracking.

On the other hand, with respect to wet resistance, this type of sipe is originally an auxiliary, and since it is often formed on the upper part of the side surface of the land part, it becomes difficult to function as the wear progresses. Generally, for wet resistance, drainage from the ground plane based on the size of the cross-sectional area of the vertical groove and the horizontal groove has an important effect, but the horizontal groove disappears or the vertical groove becomes shallow and the drainage from the ground plane becomes large. As the property becomes smaller, the wet road running performance also deteriorates.

An object of the present invention is to provide a pneumatic radial tire capable of preventing uneven wear occurring at the widthwise end of a land portion and preventing deterioration of running performance on wet roads.

[0007]

As described above, the ability to follow slippage in the circumferential direction in a small area surrounded by sipes plays an important role in preventing uneven wear. This uneven wear increases the slip because the movement in the width direction of the land tread due to the vertical load on the tread lowers the friction coefficient for the slip in the circumferential direction according to its momentum, that is, the friction energy increases, It is caused by the selective wear of the ends over the others.

Therefore, it seems that the smaller the sipes distance is, the better it is. However, when the sipes distance is made quite fine as in the prior art, for example, 5 to 8 mm, the rigidity in a small area between sipes becomes too small and the sipes are small. As mentioned above, the area does not work effectively as a land area that provides wear resistance, wear resistance decreases, and it is weak against external force, causing chipping, chipping, and cracking. is there.

However, according to the result of the test, it was found that the uneven wear suppressing effect does not change so much when the sipe interval is below a certain level. This means that the circumferential force transmitted from the surface of the road surface is 4 out of 6 for blocks in small areas.
This is because the surface is fixed at the land, so the smaller the surface area, the less it reaches the bottom. Therefore, it is important to transmit this circumferential force to the lower part,
For that purpose, it was found that it is necessary to make the gap smaller in the lower part of the sipe than in the upper part. In addition, the decrease in running performance on wet roads becomes more remarkable in combination with the decrease in groove depth because the width of the conventional sipe is often smaller toward the groove bottom.

Based on the above findings, the present invention provides a pneumatic tire having a plurality of land portions divided by a plurality of longitudinal grooves extending substantially linearly in the tire circumferential direction, in the groove wall of the side surface portion of the land portion. , A large number of upper sipes, which are open to the land surface and side surfaces and extend from the land surface toward the groove bottom, are arranged at intervals, and in the region between these upper sipes, on the groove wall from the middle thereof. A configuration is adopted in which a plurality of lower sipes that are opened and the upper end of the opening enters the region between the upper sipes and that extends from that position toward the groove bottom.

The lengths of the openings in the groove walls of the upper sipe and the lower sipe are not particularly limited, but it is desirable that they are approximately 1/2 of the vertical groove depth. This is because in order to bring out the tire characteristics of both sipes well, it is advantageous to make the sipes longer in the range where the maximum length is limited to the groove depth or less.

The lower sipe can be adopted in the groove wall on the side surface of the land as long as the upper end of the opening enters into the region between the upper sipe. In that sense, the lower sipe is placed between the upper sipe. Not only the structure in which the lower sipes are alternately inserted, but also a structure in which a plurality of lower sipes are arranged and entered in the region between the upper sipes can be adopted.

The depth of the lower sipe is not particularly limited, either.
The upper end portion of the opening and the lower end portion of the opening may be the same or may be different. However, it is more desirable that the depth is shallower toward the upper end of the opening and deeper toward the lower end of the opening.

[0014]

According to the present invention, in the groove wall of the side surface of the land portion, a large number of upper sipes which are open to the surface of the land portion and the side surface portion and extend from the open end of the land portion surface toward the groove bottom are arranged at intervals. In addition, in the region between these upper sipes, there are a number of lower sipes that open from the middle of the groove wall, the upper end of the opening enters the region between the upper sipes, and the lower end of the opening extends toward the groove bottom. Because it is a pneumatic radial tire that has been placed,
The presence of this lower sipe, which penetrates into the area between the upper sipe, causes discontinuous but overlapping overlap between the upper and lower sipe, reducing the sipe spacing in that part and relatively close to the surface. In some cases, the circumferential force from the surface of the road surface is easily transmitted to the bottom of the block by the upper sipe, which increases the trackability of the land circumferential edge in the circumferential direction and resists uneven wear. Is improved.

Also, due to the action of the lower sipe, the distance between the upper sipe is set to, for example, the dimension 1 when only the upper sipe is installed.
Since the distance can be set to about 0 to 15 mm, it is not necessary to unnecessarily narrow the sipe interval as in the conventional case, so that chipping, chipping and cracking can be prevented.

Further, since the lower sipe appears on the surface as the wear progresses, good wet performance is exhibited until the end of wear. In particular, if the lower sipe has a depth that is shallower toward the upper end of the opening and deeper toward the lower end of the opening, a wide sipe gradually appears on the tread surface during the wear progressing period to ensure wet performance. Further, even if a structure in which a large number of lower sipes are arranged and entered in the region between the upper sipes is adopted, the number of sipes increases during the wear progressing period, so that good wet performance is exhibited.

When the upper sipe and the lower sipe appear on the tread surface at the same time during the progress of wear, the sipe interval becomes small, but at this time, the depth of the vertical groove and the horizontal groove is already shallow. Therefore, chipping, chipping, etc. are less likely to occur in a small area between sipes.

[0018]

1 is a schematic pattern diagram of a tread portion showing an embodiment of a pneumatic radial tire according to the present invention, FIG.
FIG. 3 is an enlarged perspective view of the same main part.

In the figure, 1 is a plurality of longitudinal grooves extending substantially linearly in a circumferential direction on a tire tread portion 3, 3 is a land portion divided by the longitudinal grooves 1, 1 and 4 is a side surface portion of the land portion 3. It is a groove wall that constitutes. Further, 5 is a shoulder ground contact end, 6 is a groove bottom, TC is a tire center, and SI is a sipe interval. In addition, 1a is a center side vertical groove, 1b is a shoulder side vertical groove.

Reference numeral 7 is an upper sipe formed on the groove wall 4 on the side surface of the land portion 3. The upper sipe 7 is open to the surface of the land portion 3 and the groove wall 4 of the side surface, extends from the opening end 8 of the land portion 3 toward the groove bottom 6, and is arranged in large numbers at intervals in the tire circumferential direction. ing.

A lower sipe 9 is formed so as to open from the middle of the groove wall 4. The lower sipe 9 has an opening upper end portion 9a which is inserted into a region 10 between the upper sipe 7, 7, and an opening lower end portion 9b extends toward the groove bottom 6. In the present embodiment, as illustrated, the depth of the lower sipe 9 is shallower toward the opening upper end 9a side and deeper toward the opening lower end 9b side. FIG. 3 is a conceptual diagram of this embodiment showing an arrangement state of the upper sipe 7 and the lower sipe 9 on the groove wall 4, and in the present embodiment, as shown in the same figure, the upper sipe 7 and the lower sipe 9 are arranged around the tire circumference. The grooves are arranged alternately one by one in the direction, and in the middle of the groove wall 4, a so-called overlapping portion 11 is formed although it is discontinuous.

FIG. 4 is an enlarged perspective view of an essential part of a tread portion showing another embodiment of the pneumatic radial tire according to the present invention, and FIG. 5 is a conceptual diagram showing an arrangement state of the upper sipe 7 and the lower sipe 9 on the groove wall. Is. In this embodiment, the upper end portions 9a of the openings of the plurality of lower sipes 9 enter into the region 10 between the upper sipes 7, 7. Further, the depth of the lower sipe 9 is shallower toward the opening upper end 9a side and deeper toward the opening lower end 9b side, as in the above-described embodiment.

Next, a tire having a surface size shown in FIG. 1 and having the conditions shown in Table 1 was formed on the land portion.
00R20 14PR, rim size 7.00 × 20, a prototype radial tire is a pressure 7.5~8Kg / cm ^2,
This is attached to the front wheel of the truck, and the constant volume of 90-100
Running on a good road with a pavement ratio of 100% under% load condition, uneven wear resistance performance and wet performance were evaluated. For comparison, a conventional tire in which only the upper sipe was formed was also evaluated. The design conditions of the sipes in the table are as shown in FIGS. 8 to 10 listed in the schematic view of Table 1. 8 to 10
The unit of dimensions is mm. In FIGS. 9 and 10, the lengths of the upper sipe 7 and the lower sipe 9 at the groove wall openings are respectively 1/2 of the groove depth + 1/2 of the overlap of the sipes.

In the table, in the sipe type, the one-stage type means a tire in which only the upper sipe is formed, and the two-stage type means the tire of the present invention having the upper sipe and the lower sipe. In addition, all the tires are tires having a rib pattern of four vertical grooves, and the tires of Examples 1 to 3 are tires in which upper sipes and lower sipes are alternately arranged, and in Example 4, there are 2 lower sipes between upper sipes. The tire formed as shown in FIG. 4 and Example 5 is a tire in which the depth of the lower sipe is the same at the upper end and the lower end.

As for the uneven wear resistance performance, as shown in FIG. 6, the uneven wear amount S represented by the product of the uneven wear width b and the uneven wear depth h was measured for the tire fitted with the front wheels of the vehicle after traveling 50,000 km. However, the uneven wear amount S of Comparative Example 1 is indexed to 100. The smaller the index value, the better the uneven wear resistance. Note that FIG. 7 shows the uneven wear resistance with respect to the sipe distance for the comparative tires including only the upper sipes (including Comparative Examples 1 and 2).

The wet performance, that is, the running performance on a wet road, means that when the land portion wears 60% of the depth of the longitudinal groove, it runs on the wet road at a speed of 40 km / h and the distance to the stop (braking) The distance) was indexed with Comparative Example 1 set to 100. The results are shown in Table 1. The smaller the index value, the better the wet road running performance.

[0027]

[Table 1]

As shown in FIG. 7, in the case of the tire having only the upper sipe, the effect is small when the sipe interval is 11.3 mm or more, but the effect of the uneven wear resistance is not so different even when the sipe interval is set to 10 mm or less. It was found that there was no. Rather, as the sipe spacing becomes narrower, chipping and chipping,
A crack had occurred (Comparative Example 2).

On the other hand, in the case of the tire of this embodiment in which the upper sipe and the lower sipe are formed, as shown in Table 1, the uneven wear resistance is improved and, moreover, chipping, chipping,
No cracks were found.

Further, from Table 1, it is recognized that the example tires have improved wet performance as compared with Comparative Example 1. In addition, the wet performance is improved as the overlapping size of the sipes is increased. Further, the tire of Example 4 in which two lower sipes are formed between the upper sipes, shows a performance superior to that of Comparative Example 1 although it is slightly inferior to Example 1 in which the sipes are almost the same.

When the depth of the lower sipe is made deeper at the lower end than at the upper end, the sipe arrangement is the same, and the tire of the embodiment 3 is compared to the tire of the embodiment 5 in which the depth of the upper end of the lower sipe is the same. Has good uneven wear and wet road running performance.

By the way, the present invention is not limited to the above embodiment. For example, although the above embodiment is a rib pattern tire, a block pattern having lateral grooves is also applicable. Further, the arrangement of the lower sipes does not necessarily have to be in the middle of the region between the upper sipes, and it is possible to dispose the lower sipes toward one of the upper sipes. Further, although this type of sipe is formed on the groove walls of all the land side surfaces of the tire tread portion in the above-described embodiment, it may be formed on a part of the land side surface groove walls. Preferably, it is suitable to form the groove wall on the side surface of the land portion on the shoulder side where uneven wear is likely to occur.

[0033]

As described above, according to the present invention, a large number of upper sipes, which are open to the land surface and the side surface and extend from the land surface toward the groove bottom, are arranged in the groove wall of the land side surface at intervals. In addition, in the region between these upper sipes, there are a number of lower sipes that open into the groove wall from the middle, the upper end of the opening enters the region between the upper sipes, and extend from that position toward the groove bottom. Since the pneumatic radial tires are arranged, it is possible to effectively prevent uneven wear that occurs at both ends of the land surface in the tire rotation axis direction, particularly river wear, and also improve wet road running performance.

[Brief description of drawings]

FIG. 1 is a schematic pattern diagram of a tread portion showing an embodiment of a pneumatic radial tire according to the present invention.

FIG. 2 is an enlarged perspective view of the main part.

FIG. 3 is a conceptual diagram showing an arrangement state of the upper sipe and the lower sipe.

FIG. 4 is an enlarged perspective view of a main part of a tread portion showing another embodiment of the pneumatic radial tire according to the present invention.

FIG. 5 is a conceptual diagram showing an arrangement state of the upper sipe and the lower sipe.

FIG. 6 is an enlarged perspective view of an essential part showing an uneven wear state.

FIG. 7 is a relationship diagram showing a relationship between an uneven wear index and a sipe interval.

FIG. 8 is a schematic enlarged perspective view of a main part having a conventional sipe.

FIG. 9 is a schematic enlarged perspective view of an essential part having the sipe of the embodiment according to the present invention in which the upper sipe and the lower sipe are alternately repeated.

FIG. 10 is a schematic enlarged perspective view of a main part having a sipe according to another embodiment of the present invention in which two lower sipe are formed between the upper sipe.

[Explanation of symbols]

 1 Vertical Groove 1a Center Side Vertical Groove 1b Shoulder Side Vertical Groove 2 Tire Tread 3 Land 4 Groove Wall 5 Shoulder Ground End 6 Groove Bottom 7 Upper Sipe 8 Side Opening 9 Lower Sipe 9a Upper Opening 9b Opening Lower 10 Area 11 Overlap

Claims (2)

[Claims] 1. A pneumatic tire having a plurality of land portions sectioned by a plurality of longitudinal grooves extending substantially linearly in a tire circumferential direction, wherein a groove wall of the land portion side surface portion has a land portion surface and a side surface portion. A large number of upper sipes that open toward the groove bottom from the open end of the land surface are arranged at intervals, and further open in the groove wall in the region between these upper sipes from the middle of the opening. A pneumatic radial tire characterized in that a plurality of lower sipes, each of which has an upper end that enters into a region between the upper sipes and an opening lower end that extends toward a groove bottom, are arranged. 2. The pneumatic radial tire according to claim 1, wherein the depth of the lower sipe is shallower toward the upper end of the opening and deeper toward the lower end of the opening.