JP2001010308A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire to use rubbers, different in hardness, in the central part area and the shoulder part areas on both sides of a tread part, reduce the generation of car noise, such as road noise, without damaging maneuvering stability, and make two types of performance compatible with each other. SOLUTION: In a pneumatic radial tire having a plurality of main grooves 2 in the peripheral direction of a tire in the outer periphery of a tread part, a tread part 1 is divided into a central part area Ce inside the main groove 2 situated in a most outside position and shoulder part areas Sh on both sides situated at the outside thereof. The central part area and the shoulder part areas are different in rubber hardness, and a comparatively high hardness rubber 1a is situated in the shoulder part area Sh and a low hardness rubber 1b in the central part area Ce. An exposed boundary part 3 between the two rubbers is situated on the inside side wall surface of the main groove 2, and a base rubber layer 1c formed of the high hardness rubber is formed below the low hardness rubber 1b of the central part area. Rubber hardness (a) of the high hardness rubber is set to 63 deg.<=(a)<=75 deg. and rubber hardness (b) of the low hardness rubber to 50 deg.<(b)<=63 deg. and a hardness difference between two rubbers is 4 deg. or more.

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 having a plurality of main grooves having a tread pattern extending in a tire circumferential direction.

[0002]

2. Description of the Related Art Conventionally, tread rubber has been used as a means for reducing road noise in which vehicle interior noise in such a pneumatic radial tire, particularly vibration of the tread surface of the tire, is transmitted to the interior of the vehicle through an axle. There is known a method of reducing the hardness of the tire to reduce the input from the road surface due to the grounding of the tread surface.

However, when the hardness of the tread rubber is reduced,
The pattern rigidity of the tread is reduced, and the steering stability is reduced. Increasing the rigidity of the tread shoulder is also effective in reducing road noise,
When the hardness of the tread rubber is reduced as described above, the rigidity of the shoulder portion is reduced, which is disadvantageous for the effect of reducing road noise.

[0004] For this reason, it has been difficult to achieve both significant reduction of road noise and securing of steering stability by changing only the rubber composition and hardness of a single tread.

The present invention has been made in view of the above, and by using rubbers having different hardnesses in the central portion of the tread portion and the shoulder portions on both sides, road noise and the like can be obtained without impairing steering stability. The present invention provides a pneumatic radial tire that can reduce the in-vehicle sound of the vehicle and achieve both performances.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is a pneumatic radial tire having a plurality of main grooves extending in a tire circumferential direction on an outer periphery of a tread portion. It is divided into a central region inside the main groove at the outermost position in the tire width direction and outer shoulder portions on both sides, and the center shoulder region and both shoulder portions have different rubber hardnesses, and the both shoulder portions are different. A relatively high hardness rubber (hereinafter, referred to as high hardness rubber) is disposed in the region, and a lower hardness rubber (hereinafter, referred to as low hardness rubber) is disposed in the central region, and the low hardness rubber in the central region is provided. An exposed boundary portion between the main groove and the high hardness rubber in the shoulder region on both sides is provided in a side wall surface of the main groove.

[0007] Thus, the low-hardness rubber in the central portion in the width direction of the tread portion can absorb and mitigate the input from the road surface due to the grounding of the tread surface, thereby suppressing road noise. In addition, by arranging high-hardness rubber in the shoulder regions on both sides, the effect of suppressing vibration is large, and the steering stability can be maintained or improved satisfactorily.

In addition, since the boundary between the low hardness rubber in the central region and the high hardness rubber in the shoulder regions on both sides is provided in the inner side wall surface of the main groove, blocks or ribs of the tread pattern are provided. There is no danger of occurrence of step wear and groove bottom cracks due to differences in rigidity because they are not present on the land surface such as the main surface or the groove bottom such as the main groove.

In the above pneumatic radial tire,
It is preferable to provide a base rubber layer made of high-hardness rubber integrated with the shoulder regions on both sides below the low-hardness rubber in the central region. As a result, the input from the road surface is moderated by the low-hardness rubber in the central region, and the vibration caused by the input from the road surface can be suppressed by the high-hardness base rubber layer thereunder, and the steering stability can be further improved. .

The rubber hardness (a) of the high hardness rubber is 63 °
<(A) ≦ 75 °, the rubber hardness (b) of the low hardness rubber is 50 ° <(b) ≦ 63 °, and the hardness difference between the two rubbers is 4
° or more is preferable. More preferably, the hardness difference is set to 6 ° or more.

That is, if the hardness (b) of the low-hardness rubber is higher than the above range, the effect of reducing road noise cannot be obtained, and if the hardness (b) is lower than the above range, the central region becomes too soft and the shoulder portions on both sides become too soft. Even if the rubber hardness (a) in the region is increased, the steering stability decreases, which is not preferable. Also, if the hardness (a) of the high-hardness rubber in the shoulder regions on both sides is lower than the above range, the steering stability is deteriorated, and if it is higher than the above range, the grip property at the time of WET decreases. It is not preferable because it occurs.

If the difference in hardness between the low-hardness rubber and the high-hardness rubber is smaller than the above, the above-mentioned effects due to the use of rubbers having different hardnesses cannot be sufficiently obtained.
If the hardness difference is too large, the uniformity of the tire may be reduced and the steering stability may be worsened. Therefore, it is practical to set the hardness difference in the range of 6 ° to 20 °. Especially desirable.

Further, in the case of the one having a high hardness base rubber layer under the low hardness rubber, the thickness of the low hardness rubber under the bottom of the main groove existing in the central region is 0.5 mm or more, and The thickness is 0.5 mm or more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic cross-sectional view in the width direction of a pneumatic radial tire (T) of the present invention, and FIG. 2 is an enlarged cross-sectional view of a part of the tire.

The radial tire (T) has a bead portion (12) having bead cores (11) on both sides and the bead portion (1).
Side wall part (1) extending radially outward from 2)
3) and a tread (1) connecting its upper end
It has a carcass (14) which is folded and supported at both ends by a bead core (11) along its inner circumference, and a belt layer (15) between the tread portion (1) and the carcass (14). Since the reinforcing structure is the same as that of a general radial tire, a detailed description is omitted.

In the figure, reference numeral (2) denotes a plurality (usually 3 to 5) of main grooves formed on the outer peripheral surface of the tread portion (1) and extending linearly or zigzag in the tire circumferential direction. Although not shown in the cross-sectional views of the drawings,
A lateral groove in a direction intersecting with the main groove (1), and an auxiliary groove connecting a sub-groove and a lateral groove which are narrower than the main groove in the tire circumferential direction are formed to form a predetermined tread pattern.

The tread portion (1) has a central region (Ce) inside a region inside the main grooves (2) and (2) at the outermost position (position closer to the shoulder) in the tire width direction, and a region outside the central region (Ce). Divided into shoulder regions (Sh) and (Sh) on both sides, the central region (Ce) and shoulder regions on both sides (Sh)
The rubber used for (Sh) is made of a rubber compound having different hardness, and the rubber (1a) having relatively high hardness is provided in the shoulder regions (Sh) and (Sh) on both sides, and the rubber (1a) is provided in the central region (Ce). Low hardness rubber (1b) is provided. An exposed boundary portion (3a) appearing on the tire surface between the low hardness rubber (1b) and the high hardness rubber (1a) is formed on an inner side wall surface (2) of the main groove (2).
a) and extends circumferentially along the main groove (2). Since the exposed boundary portion (3a) is set as described above, it is particularly preferable that the main groove (2) is substantially linear and continuous in the tire circumferential direction. The exposed boundary may be set in the outer side wall surface of the main groove (2).

The exposed boundary portion (3a) is provided in the main groove (2).
From the boundary with the groove bottom (2b) at the tread (1)
The tread wear indicator (not shown) provided in the main groove (2) may be anywhere in the side wall surface (2a) up to the boundary with the land surface such as a block or a rib. It is more preferable to be located above in order to suppress the occurrence of cracks in the treadwear indicator portion. Further, when the exposed boundary portion is located near the land surface such as a rib or a block, the exposed boundary portion is exposed to the land surface at a relatively early stage of wear of the tread portion. Therefore, it is desirable to set as close to the treadwear indicator as possible.

A boundary surface (3) between the high-hardness rubber (1a) and the low-hardness rubber (1b) extends inward from a side wall surface (2a) inside the main groove (2). 15) It is preferable to be inclined to the side. The boundary surface (3) is not necessarily required to be linear, but may be a shape in which the outer rubber (1a) and the inner rubber (1b) enter each other and are deformed.

Further, in the case of the illustrated embodiment, the high hardness rubber (1a) of the shoulder regions (Sh) and (Sh) on both sides is integrated below the low hardness rubber (1b) of the center region (Ce). A base rubber layer (1c) made of high-hardness rubber is provided.
This base rubber layer (1c) has a low hardness rubber (1b) on it
The interface (3) may be of any thickness as long as it is less than or equal to the exposed boundary portion (3a) on the side wall surface (2a) of the main groove (2). The thickness (t1) of the low hardness rubber (1b) below the bottom surface of the main groove (2) existing in the base groove (2) is 0.5 mm or more, and the thickness (t2) of the base rubber layer (1c) thereunder is 1.5 mm or more. The central area (Ce)
The boundary between the two rubbers is not exposed to the other main groove (2), and the effect of suppressing vibration by the base rubber layer (1c) can be secured well, which is particularly preferable in practice.

The base rubber layer (1c) may be extruded integrally with the high hardness rubber (1a) in the shoulder regions (Sh) (Sh) on both sides, or the high hardness rubber (1a) may be used. It is also possible to use a sheet rubber extruded separately from the same rubber material. In each case, the low hardness rubber (1b) is placed on the base rubber layer (1c), molded and vulcanized,
Can be integrated.

The rubber used for the high hardness rubber (1a) and the base rubber layer (1c) has a rubber hardness (a) [JI
Room temperature (23 ° C) by the measurement method specified in S-K6253
Rubber hardness at 63 ° <(a) ≦ 75
°, the rubber used for the low hardness rubber (1b) is a rubber compound having a hardness (b) in the range of 50 ° <(b) ≦ 63 °, and the difference in hardness between these two rubbers is 4 ° or more, especially Preferably, the angle is set to 6 ° or more.

The pneumatic radial tire (T) of the embodiment described above uses the low-hardness rubber (1b) having the tread portion (1) in the widthwise central region (Ce) in the use state in which the tire is mounted on a vehicle. , Can absorb and mitigate the input from the road surface due to the grounding of the tread surface, can suppress road noise and pattern noise, can reduce the sound inside the car, and have a high hardness rubber (1b) in the shoulder area (Sh) on both sides Even if they are arranged, it is possible to maintain good ride comfort. In addition, by arranging the high hardness rubber (1a) in the shoulder regions (Sh) and (Sh) on both sides, the effect of suppressing vibration is large and the steering stability can be maintained or further improved. In particular, by having the high hardness base rubber layer (1c), the effect of suppressing the vibration due to the input from the road surface is large, and the steering stability is further improved.

Further, the exposed boundary (3a) between the low hardness rubber (1b) in the central area (Ce) and the high hardness rubber (1a) in the shoulder area (Sh) is formed on the side wall surface of the main groove (2). (2a), it is not present on the land surface such as blocks or ribs of the tread pattern or on the groove bottom (2b) of the main groove (2). No groove bottom cracks occur.

(Embodiment) Table 1 below shows, for each of the tires of the embodiment and the comparative example set under the following tire conditions, the driving stability of DRY and WET, ride comfort, pattern noise, road noise and the like. The results of performing a comparison test of each performance are shown. The test tires
This is a tire having the same structure (the same tread pattern) of two steel belts having a tire size of 215 / 45ZR17. Among them, the tires of Examples 1 to 3 and the tire of Comparative Example 2 show a case where a base rubber layer continuous from the shoulder region is provided in the central region.

The evaluation of each performance is indicated by an index with Comparative Example 1 which is a conventional tire made of one type of rubber having the same hardness in both the central region and the shoulder regions on both sides taken as 100, and the larger the numerical value, the larger the value. This indicates that the performance is good.

The test vehicle was a 2000 cc domestic passenger vehicle having a tire inner pressure of 220 kPa, and each was subjected to a sensory evaluation by the driver.

[0029]

[Table 1] As described above, the tires of Examples 1 to 4 of the present invention were able to suppress road noise without impairing steering stability, unlike the comparative examples.

In particular, the rubber hardness in the shoulder region was set to be the same as that of the conventional tire (Comparative Example 1) and the rubber hardness in the central region was set low so that the hardness difference between the two rubbers was maintained at 6 ° or more. In the case (Example 1), the pattern noise and the road noise can be greatly reduced and the riding comfort is good, and the rubber hardness in the central region is the same as that of the conventional tire, and the rubber hardness in the shoulder region is increased ( In Example 3), the road noise was reduced, and the steering stability was significantly improved.

Further, when the rubber hardness in the central region is set lower than that of the conventional tire and the rubber hardness in the shoulder region is set higher than that of the conventional tire (Example 2), the effect of reducing road noise and pattern noise, ride comfort, All of the steering stability has been improved over conventional tires.

[0032]

As described above, according to the present invention, rubbers having different hardnesses are used for the central portion of the tread portion and the shoulder portions on both sides. By using hard rubber, it is possible to drastically reduce in-vehicle noise such as road noise while maintaining or improving the steering stability satisfactorily. There is no risk of occurrence.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a pneumatic radial tire according to the present invention.

FIG. 2 is an enlarged sectional view of a part of the above.

[Explanation of symbols]

 (T) Pneumatic radial tire (Ce) Central area (Sh) Shoulder area (1) Tread (1a) High hardness rubber (1b) Low hardness rubber (1c) Base rubber layer (2) Main groove (2a) Side wall surface (2b) Groove bottom (3) Boundary surface (3a) Exposed boundary

Claims (4)

[Claims] 1. A pneumatic radial tire having a plurality of main grooves extending in a tire circumferential direction on an outer periphery of a tread portion, wherein the tread portion has a central region inside a main groove at an outermost position in a tire width direction. It is divided into outer both side shoulder portions, and the center portion and the two side shoulder portions have different rubber hardnesses, and the both side shoulder portions have relatively high hardness rubber, and the center portion has a lower hardness than the above. A rubber having hardness is provided, and an exposed boundary portion between the low hardness rubber in the central region and the high hardness rubber in the shoulder regions on both sides is provided in the side wall surface of the main groove, and is pneumatically filled. Radial tire. 2. The pneumatic radial tire according to claim 1, wherein a base rubber layer made of high-hardness rubber integrated with the shoulder regions on both sides is provided below the low-hardness rubber in the central region. 3. The high hardness rubber has a rubber hardness (a) of 63 °.
<(A) ≦ 75 °, the rubber hardness (b) of the low hardness rubber is 50 ° <(b) ≦ 63 °, and the hardness difference between the two rubbers is 4
The pneumatic radial tire according to claim 1 or 2, wherein the angle is not less than 0 °. 4. The method according to claim 2, wherein the thickness of the low hardness rubber below the bottom surface of the main groove existing in the central region is 0.5 mm or more, and the thickness of the base rubber layer thereunder is 0.5 mm or more. The described pneumatic radial tire.