JP4442160B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire, and more specifically, suppresses a decrease in drainage on a wet road surface without impairing the appearance even when wear progresses, and achieves both driving stability on a wet road surface and a dry road surface. Relates to a pneumatic radial tire.

  In order to ensure drainage on a wet road surface, a tread pattern in which a main groove extending in the tire circumferential direction is formed on the tread surface is employed. In this way, it is advantageous to increase the groove volume to improve drainage and ensure steering stability on wet road surfaces, but if the groove volume is too large, the rigidity of the tread surface will be insufficient. There is a problem that steering stability on the road surface is lowered. On the other hand, on wet road surfaces with a relatively shallow water depth, a large groove volume is not required to ensure drainage, so some of the multiple main grooves are shallower than the main grooves. A technique has been adopted in which the emphasis is placed on improving the driving stability on a dry road surface while changing to a minor groove while ensuring the driving stability on a wet road surface.

  However, tires with a main groove and a sub-groove with a shallower groove depth than the main groove on the tread surface lose the sub-groove before reaching the wear life, and the appearance of the tread surface before and after the sub-groove disappears. As a result, the water drainage on the wet road surface deteriorates.

  On the other hand, in order to secure the groove volume of the tread surface at the stage where wear has progressed and to suppress the decrease in wet performance, there is a proposal to embed rubber with low wear resistance inside the tread land portion (for example, Patent Document 1). reference.).

However, since this proposal assumes that the groove depth of the circumferential groove formed on the tread surface is uniform, the trade-off relationship between securing the tread rigidity and securing the groove volume is the same as when the wear progresses from when it is new. It is difficult to keep a good balance through the road, and it is not always sufficient as a measure for achieving both steering stability on wet and dry road surfaces. Furthermore, when the wear progresses and the low wear-resistant rubber embedded in the tread land portion is exposed on the tread surface, the appearance of the tread surface is impaired.
Japanese Patent Laid-Open No. 11-147403

  The object of the present invention is to eliminate such problems and suppress deterioration of drainage on wet road surfaces without impairing the appearance even when wear progresses, and achieve both steering stability on wet road surfaces and dry road surfaces. An object of the present invention is to provide a pneumatic radial tire.

In order to achieve the above object, the pneumatic tire of the present invention includes a main groove extending in the tire circumferential direction on the tread surface, and a secondary groove having drainage extending in the tire circumferential direction having a shallower groove depth than the main groove. In the pneumatic radial tire, the sub-grooves are arranged between the main grooves, and the main grooves are alternately arranged in the tire width direction on the left and right sides around the sub-grooves via circumferential ribs, respectively. together so as to, characterized in that a rubber of a small groove bottom of abrasion resistance coefficient than the tread rubber below the groove bottom of the minor groove.

In the pneumatic tire of the present invention, the groove depth rubber having a smaller wear resistance coefficient than the tread rubber is arranged under the groove bottom of the sub-groove having a shallow drainage property compared to the main groove, so that the water depth is compared. On a normal shallow road surface, drainage is ensured by the main groove and sub-groove when it is new, and when the wear has progressed to some extent, the rubber at the bottom of the groove located on the bottom of the sub-groove is exposed to the tread surface. Since the rubber at the bottom of the groove is worn away by the frictional force with the road surface and sinks into a concave shape with respect to the tread surface, it serves as a sub-groove at the time of a new article, thereby suppressing the deterioration of drainage on the wet road surface, It is possible to achieve both steering stability on the wet road surface and the dry road surface through the stage where the wear has progressed since the new article.

  In addition, since the rubber at the bottom of the groove recessed in the tread surface remains in the stage where the wear has progressed, the appearance of the tread surface is not impaired through the stage in which the wear has progressed from the beginning.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a partial plan view showing an example of a tread surface of a pneumatic radial tire according to the present invention, and FIG. 2 is a cross-sectional view taken along the line AA showing the main part of FIG.

On the tread surface 1 of the pneumatic radial tire, there are four main grooves 2 extending in the tire circumferential direction, and three sub- drains having a shallow drainage performance compared to the main groove 2 (groove depth H). Grooves 3 (groove depth h) are alternately formed in the tire width direction with the subgroove 3 as the center. A circumferential block row is formed by a widthwise inclined groove 4 that opens from the main groove 2 on both shoulder sides to the main groove 2 and extends to the shoulder side, and from the main groove 2 to the sub-groove 3 at the center side thereof. Two circumferential ribs each having left and right projecting grooves 5 projecting in the width direction are formed, and two circumferential straight ribs are formed on the center side with the sub-groove 3 interposed therebetween.

Below the groove bottom of the sub- groove 3, a rubber 6 at the groove bottom having a smaller wear resistance coefficient than the tread rubber G is disposed. The rubber constituting the groove bottom rubber 6 is preferably a rubber having a wear resistance coefficient of 85% or less of the wear resistance coefficient of the tread rubber G. As a result, as will be described later, the tread rubber G is worn and the rubber at the bottom of the groove is worn. When 6 is exposed to the tread surface 1, the groove bottom rubber 6 wears earlier than the surrounding tread rubber G due to the difference in the degree of wear with the tread rubber G caused by the frictional force received by the road surface 6 from the road surface. Form.

  The composition of the rubber constituting the rubber 6 at the bottom of the groove is not particularly limited. For example, the composition of carbon black and the amount of oil extended may be changed from those of the tread rubber G, or additives such as resins may be blended. It is good to get.

The rubber 6 at the bottom of the groove disposed under the groove bottom of the sub- groove 3 is exposed to the tread surface 1 from the state shown in FIG. Since the amount of wear is larger than that of the rubber G, as shown in FIG. 3 (b), it sinks into a concave shape and exhibits a function as a new groove.

The width W of the rubber 6 at the bottom of the groove disposed below the bottom of the sub- groove 3 is illustrated in FIG. 3A as being the same width as the width R of the sub-groove 3. It is preferable to be 1 mm or more in the direction. Further, the arrangement in the depth direction of the rubber 6 at the groove bottom is preferably such that the depth H ′ from the tread surface 1 to the bottom surface of the rubber 6 at the groove bottom is equal to the depth H of the main groove 2.

  Thereby, rubber | gum 6 of the groove bottom maintains the function as a favorable groove | channel until it reaches the last stage of wear of the tread surface 1, and can maintain the steering stability on a wet road surface without deteriorating drainage. Further, since the rubber 6 at the bottom of the concave groove remains as a groove on the tread surface 1 until the end of wear, the appearance of the tread surface 1 is not deteriorated.

In the embodiment described above, the case where the rubber 6 at the bottom of the groove is disposed below the bottom of the sub- groove 3 is shown. However, the rubber 6 at the bottom of the groove is shallower than the main groove 2 in the width direction. The inclined groove 4 or the protruding groove 5 may be disposed at the bottom of the groove, whereby the same effect can be obtained.

As described above, the pneumatic radial tire of the present invention has a main groove 2 that extends in the tire circumferential direction on the tread surface 1 and a secondary drainage that extends in the tire circumferential direction with a shallower groove depth than the main groove 2. In the pneumatic radial tire in which the groove 3 is disposed, the sub-groove 3 is disposed between the main grooves 2, and the main groove 2 extends in the tire width direction via circumferential ribs on both the left and right sides of the sub-groove 3. By arranging the rubber 6 at the bottom of the groove having a wear resistance coefficient smaller than that of the tread rubber G under the groove bottom of the sub-groove 3, the main groove 2 and the sub-groove 3 at the time of a new product are arranged alternately. At the stage where drainage is ensured and wear has progressed to some extent, the rubber 6 at the bottom of the groove disposed below the bottom of the sub-groove 3 is exposed to the tread surface 1 and plays the role of the sub-groove 3 when new. To the tread through the stage of wear from the beginning Without impairing the appearance, and suppressing the deterioration of the drainage performance on a wet road surface, it is possible to achieve both the steering stability in the wet road surface and dry road surface.

  Conventional tires (conventional examples), tires of the present invention (examples) and comparative tires (comparative examples 1 to 3) were respectively produced with the tire size common to 205 / 55R16 89V and the following configuration.

The above five types of tires were evaluated for DRY and WET handling stability when new, 50% wear appearance, DRY and WET handling stability by the following evaluation methods, and the results are shown in Table 1. .
[DRY and WET handling stability evaluation when new]
Each tire is assembled in a rim (16 × 61 / 2JJ), filled with air pressure of 230 kPa, mounted on a domestic rear wheel drive sedan vehicle, run on dry and wet road surfaces, and subjected to sensory tests by three panelists. The results were evaluated by a five-point method in which the conventional tire was set to 3, and the result on a dry road surface was displayed as DRY steering stability and the result on a wet road surface was displayed as WET steering stability. The higher the number, the better.
[Appearance at 50% wear, DRY and WET handling stability evaluation]
Prepare tires whose main groove depth is 50% of that of new tires in advance, and visually observe the tread surface appearance of these tires to evaluate good (◯) or bad (×). Performed and displayed the results.

Furthermore, each of these tires was assembled in a rim (16 × 61 / 2JJ), filled with 230 kPa of air pressure, mounted on a domestic rear-wheel drive sedan vehicle, and run on dry and wet road surfaces. The result of the sensory test was evaluated by the five-point method with the conventional tire as the result of the sensory test at the time of a new article, and the result on the dry road surface was DRY steering stability and the result on the wet road surface was stable by WET Displayed as sex. The higher the number, the better.
[Conventional example]
With the pattern shown in FIG. 1, the groove depth h of the sub-groove 3 is set to 30% of the depth H of the main groove 2.
〔Example〕
Underneath the groove bottom of the sub-groove 3 of the conventional example, a rubber 6 at the groove bottom having a thickness corresponding to 70% of the depth H of the main groove 2 was disposed.
[Comparative Example 1]
The sub-groove 3 was not formed on the tread surface 1 of the conventional example.
[Comparative Example 2]
The groove depth h of the sub-groove 3 of the conventional example is made equal to the depth H of the main groove 2.
[Comparative Example 3]
The auxiliary groove 3 of Comparative Example 3 was filled with rubber having the same quality as the rubber 6 at the bottom of the groove.

  From Table 1, it can be seen that the tire according to the present invention suppresses a decrease in steering stability on a wet road surface without impairing the appearance even when the wear proceeds.

  The pneumatic radial tire of the present invention is preferably applied as a tire for passenger cars that is commonly used for dry road surfaces and wet road surfaces.

It is a partial top view which shows an example of the tread surface of the pneumatic radial tire of this invention. It is AA arrow sectional drawing which shows the principal part of FIG. It is a perspective view explaining the form at the time of a new article of the subgroove of the pneumatic radial tire of the present invention. It is a perspective view explaining the form at the time of wear progress of the minor groove of the pneumatic radial tire of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread surface 2 Main groove 3 Sub groove 4 Inclination groove 5 Protrusion groove 6 Rubber of groove bottom

Claims (4)

In a pneumatic radial tire in which a main groove extending in the tire circumferential direction on the tread surface and a secondary groove having drainage extending in the tire circumferential direction with a shallow groove depth compared to the main groove are arranged,
Wherein the minor groove and disposed between the main groove, thereby be arranged alternately in the tire width direction the main groove via the respective circumferential rib on the right and left sides around the minor groove, said sub-grooves Pneumatic radial tire with rubber at the bottom of the groove that has a smaller wear resistance coefficient than the tread rubber.   2. The pneumatic radial tire according to claim 1, wherein a wear resistance coefficient of rubber at the groove bottom is 85% or less of a wear resistance coefficient of the tread rubber.   The pneumatic radial tire according to claim 1 or 2, wherein the rubber at the groove bottom is disposed over a width of 1 mm or more in the width direction of the sub-groove. The pneumatic radial tire according to claim 1, 2, or 3, wherein a depth from the tread surface to a bottom surface of the rubber at the bottom of the groove is equal to a depth of the main groove.

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