JP3364259B2 - Pneumatic radial tires with excellent handling stability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire for passenger cars, and more particularly, to a pneumatic radial tire which improves steering stability of a vehicle without impairing the durability of the tire.

[0002]

2. Description of the Related Art Conventionally, it has been widely practiced to increase the lateral rigidity of a tire, that is, the rigidity in the width direction of a tire for the purpose of improving the steering stability of a vehicle. It is known that it is effective to change the structure of the sidewall portion in addition to changing the structure.

In changing the structure of the side wall portion, the side wall rubber forming the side wall portion is made to have a high elastic modulus, and the side wall portion is reinforced by steel, aramid fiber, organic fiber or the like. The addition of members is often performed.

[0004]

However, when the entire sidewall rubber is made to have a high elastic modulus in order to increase the lateral rigidity of the tire, the tire is not durable due to the large strain generated in the sidewall portion. In addition, there is a disadvantage that it significantly decreases, and when a reinforcing member made of steel or the like is added to the side wall portion, the reinforcing member, the winding end portion of the carcass, the radially outer end portion of the bead filler, and other reinforcing members. There is a disadvantage that it is difficult to accurately dispose the individual constituent members at the intended positions in order to avoid the overlap with the side wall. It was particularly important in low profile tires.

The present invention has been made as a result of studies aimed at solving such problems of the prior art, and the object of the present invention is not to bring about a decrease in tire durability, and , If each component can be placed exactly in the intended position,
(EN) It is possible to provide a pneumatic radial tire having excellent steering stability which can effectively increase the lateral rigidity of the tire.

[0006]

A pneumatic radial tire having excellent steering stability according to the present invention has a pair of left and right bead portions, respective side wall portions connected to the respective bead portions, and both side wall portions. And a continuous car tread portion, and a radial carcass consisting of at least one carcass ply with each end wound up around a bead core embedded in each bead portion. , Flatness rate 55%
In addition to the following, each side wall portion is composed of two layers of inner and outer side wall rubber, and the inner layer side wall rubber has an elastic modulus of 10 × 10 ⁷ at 30 ° C.
˜200 × 10 ⁷ dyn / cm ^2, and the same elastic modulus of the outer side wall rubber is 3 × 10 ⁷ to 8 × 10.
^{It is 7} dyn / cm ² .

Here, preferably, the outer end portion in the tire radial direction of the inner layer side wall rubber is arranged to abut against the tread rubber forming the tread portion or to be overlapped with the tread rubber, and preferably Is
The radially inner end portion of the inner layer side wall rubber is arranged so as to abut on a rubber chafer provided on the outer surface side of the bead or to overlap the rubber chafer. Further, the thickness of the inner side wall rubber is preferably in the range of 0.5 to 2 mm.

[0008]

In a tire having an aspect ratio of 55% or less, the tire height, and consequently the sidewall height, becomes low.
When adding a new reinforcing member made of steel or the like to the sidewall portion, ideally treat each end portion of the reinforcing member inside and outside the radial direction without overlapping with other constituent members. This is especially important when other reinforcing members are already embedded in the sidewall portion, and therefore the sidewall portion is formed in order to further increase the lateral rigidity of the tire. It is effective to increase the elastic modulus of the sidewall rubber. However, when all the sidewall rubbers are made highly elastic, as described above, the fracture durability when a large strain is generated in the sidewall portion is lowered.

Therefore, in the pneumatic radial tire of the present invention, the sidewall portion is made up of two layers of sidewall rubber, the inner layer side located near the strain neutral line and having a relatively small amount of strain. The sidewall rubber is a rubber having a high elastic modulus, and the sidewall rubber on the outer layer side, which is located away from the strain neutral line and has a relatively large strain amount,
By using a rubber having a relatively small elastic modulus, even if a large strain occurs in the sidewall portion, the lateral rigidity of the tire is increased without fear of lowering the durability of the sidewall portion.

This means that the inner side wall rubber has an elastic modulus at 30 ° C. of 10 × 10 ^{7 to} 20.
0 × 10 ⁷ dyn / cm ² and the elastic modulus of the outer layer side wall rubber is 3 × 10 ⁷ to 8 × 10 ⁷ dyn / cm, which is the same as that widely used as a side wall rubber from the past.
It is particularly remarkable when set to ² .

In this tire, the inner and outer ends in the radial direction of the inner layer side wall rubber having a high elastic modulus are respectively against the rubber chafer provided on the outer surface side of the bead and the tread rubber forming the tread portion. When they are abutted or overlapped with each other, it is possible to sufficiently prevent the durability of the sidewalls from being deteriorated due to the rigidity difference. This means that both the tread rubber and the rubber chafer are made of rubber with a high elastic modulus, but since both of them are the same rubber material as the inner side wall rubber, the inner side Not only when arranging the side wall rubbers butting, but also when arranging them side by side, a large rigidity step such as when superposing a reinforcing material made of steel or other dissimilar material on the tread rubber, rubber chafer, etc. occurs. That is not the case, and therefore the sidewall portion can exhibit excellent durability.

On the other hand, when the inner and outer ends in the radial direction of the inner layer side wall rubber are located apart from the tread rubber and the rubber chafer, the rigidity is remarkably reduced in these gaps, and the sidewall part Cause deterioration of durability.

By the way, in this tire, when the thickness of the inner layer side wall rubber is less than 0.5 mm,
The effect of increasing the lateral rigidity of the tire becomes small, and if it is set to a value exceeding 2 mm, the surface of the inner layer side wall rubber is too far from the strain neutral line, and the inner layer side wall rubber is Since it is not possible to sufficiently prevent the occurrence of a large strain on the inner wall of the side wall portion and the deterioration of the durability of the side wall portion, it is preferable that the thickness of the inner side wall rubber is in the range of 0.5 to 2 mm.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view in the tire width direction showing an embodiment of the present invention with a half portion omitted. In this tire having a flatness ratio of 55% or less, in the figure, 1 is a pair of left and right bead portions, 2 is continuous with each of these bead portions 1,
This also shows a pair of left and right sidewall portions, and 3 indicates a tread portion which extends over both sidewall portions 2 and is continuous with them. Although the tread portion 3 has a two-layered structure including the base rubber layer 3a and the cap rubber layer 3b in the figure, it may have a single-layered structure.

Here, each bead portion 1 has a bead core 1a embedded therein, and in this example, a carcass ply 4 on the inner layer side around these bead cores 1a.
The respective end portions of a are rolled up from the inner side to the outer side, and the respective end portions of the carcass ply 4b on the outer layer side are extended from the outer side of the bead core 1a and terminated at the radially inner position of the bead core 1a. Thus, the radial carcass 4 is constructed.

In each bead portion 1, a reinforcing member 5a made of aramid fiber is provided inside the rolled-up end portion of the inner layer side carcass ply 4a and between the rolled-up end portion and the main body portion of the outer layer side carcass ply 4b. , 5b are arranged respectively, and the bead filler 6 is arranged between the reinforcing member 5a and the main body portion of the inner carcass ply 4a at the radially outer position of the bead core 1a.
A rubber chafer 7 is arranged further outside the outer carcass ply 4b.

Further, here, the sidewall portion 2 is
Inner layer side wall rubber 2a having a large elastic modulus and outer layer side wall rubber 2b having a smaller elastic modulus than that
And, preferably, the inner layer side wall rubber 2
The elastic modulus of a is in the range of 10 × 10 ⁷ to 200 × 10 ⁷ dyn / cm ² , and the elastic modulus of the outer side wall rubber 2 b is 3
The range is from × 10 ⁷ to 8 × 10 ⁷ dyn / cm ² . The thickness of the inner layer side wall rubber 2b is preferably in the range of 0.5 to 2 mm as described above.

By the way, the inner end portion in the radial direction of the inner layer side wall rubber 2a having a high elastic modulus is, as shown in FIG.
In addition to being located inside the rubber chafer 7, it can also be located outside the rubber chafer 7 as shown in FIG. 2, or as abutting against the rubber chafer 7 as shown in FIG. As shown in FIG. 1 and FIG. 2, the outer end portion of the side sidewall rubber 2a in the radial direction is located in abutment with the tread rubber including both the base rubber layer 3a and the cap rubber layer 3b. It is also possible to position them on the inner side of the tread rubber as shown in FIG. 4 or on the outer side of the tread rubber as shown in FIG.

According to the tire constructed as described above, there is no fear that the durability of the tire, especially the sidewall portion 2, will be deteriorated due to the action of the sidewall rubbers 2a and 2b of the inner and outer layers. In addition, the lateral rigidity of the tire can be effectively increased, and as a result, the steering stability of the vehicle can be greatly improved. According to the present invention, in addition to the above-described configuration, it is possible to add a wire insert or other reinforcing member in a range that does not cause a large rigidity step that impairs durability.

(Comparative Example 1) A comparative test on the lateral rigidity of the invention tire, the conventional tire and the comparative tire will be described below. ◎ Test tire size is 205/55 R16 tire ○ Invention tire A tire having a structure in which the reinforcing members 5a and 5b are omitted from the configuration shown in FIG. 3, and the elastic modulus of the inner layer side wall rubber is 70 × 10 ^7. dyn / cm ² , thickness: 1 mm, outer layer side wall rubber elastic modulus: 4 × 10 ⁷ dyn / cm ² , thickness: 3 mm. ○ The elastic modulus of the entire conventional tire sidewall is 4 × 10 ⁷ dyn / cm.
^2. A tire having the same construction as the invention tire except that it is made of one kind of sidewall rubber having a thickness of 3 mm. ○ Comparative tire A steel wire insert member is added to the conventional tire. The additional positions of the steel wire insert members were the respective positions of the reinforcing members 5a and 5b shown in FIG.

◎ Test method The lateral rigidity of each tire is 6.5JJ × 16 for each tire.
Mounted on the rim of the vehicle, filled with 2.0 kg / cm ^{2 of} internal pressure, and pressed against the flat plate with the safety walk attached by a load of 495 kg, when the flat plate is moved in the lateral direction of the tire, the lateral force applied to the flat plate is applied. The force was measured and evaluated.

◎ Test Results Table 1 shows the results of the above tests. The larger the index value in the table, the better the result.

[Table 1]

According to Table 1, it is clear that the invention tire can bring about a lateral rigidity equal to or higher than that with the addition of the steel wire insert shown as a comparative product. Moreover, in the invention tire, the adhesive strength is naturally higher than that of the comparative tire to which the steel wire insert member is added, so that it is possible to exhibit more excellent durability.

(Comparative Example 2) Another comparative test on the lateral rigidity and durability of the tire will be described below. ◎ Tire with test tire size of 225/50 R16 ○ Inventor tire 1 A tire having a structure in which the reinforcing members 5a and 5b are omitted from the configuration shown in FIG. 4, and the elastic modulus of the inner side wall rubber is 70 × 10. ⁷ dyn / cm ² , thickness 1 mm, the elastic modulus of the outer side wall rubber is 7 × 10 ⁷ dyn / cm ² , thickness
2.8 mm. Inventive tire 2 An invention tire 2 has the same configuration as the invention tire 1 except that the thickness of the inner side wall rubber is 0.4 mm. Inventive tire 3 Inventive tire 1 is obtained by adding two layers of reinforcing members 5a and 5b made of aramid fiber. ○ The elastic modulus of the entire conventional tire sidewall is 7 × 10 ⁷ dyn / cm.
^{2. A} tire having the same structure as the tire 1 of the invention except that it is made of one kind of sidewall rubber having a thickness of 2.8 mm. Comparative tire A conventional tire with a three-layer reinforcing member made of aramid fiber added.

◎ Test method The lateral rigidity of the tire was measured by mounting each tire on an 8JJ × 16 rim, filling the internal pressure of 2.0 kg / cm ² , and applying a load of 565 kg thereto. Measurement and evaluation were performed in the same manner as described above.

◎ Test Results The results of the above tests are shown in Table 2. The larger the index value in the table, the better the result.

[Table 2]

From Table 2, it is clear that each of the invention tires has a higher lateral rigidity than the conventional tire in which the sidewall reinforcing member is not embedded. It turns out that it can be effectively increased. By the way, in the tire 2 of the invention, the lateral rigidity cannot be significantly increased because the thickness of the sidewall rubber on the inner layer side is thin. Further, although the invention tire 3 shows the same lateral rigidity as the comparative tire, as a result of the durability test, the failure occurred only in the sidewall portion of the comparative tire. Therefore, the method according to the present invention is effective for effectively improving the durability of the sidewall portion.

[0028]

As is clear from the above description, according to the present invention, in particular, the side wall portion is composed of inner and outer side wall rubber layers, and
The inner layer side wall rubber has an elastic modulus at 30 ° C. of 10 × 10 ⁷ to 200 × 10 ⁷ dyn / cm ² , and the outer layer side wall rubber has the same elastic modulus of 3 × 10 ⁷ to 8 × 10 ^7.
By setting the dyn / cm ² , it is possible to sufficiently enhance the lateral rigidity of the tire and thus the steering stability of the vehicle without impairing the durability of the sidewall part of the tire.

[Brief description of drawings]

FIG. 1 is a widthwise sectional view showing an embodiment of the present invention with a half portion omitted.

FIG. 2 is a sectional view similar to FIG. 1, showing another embodiment of the present invention.

FIG. 3 is a sectional view similar to FIG. 1, showing another embodiment of the present invention.

FIG. 4 is a sectional view similar to FIG. 1, showing still another embodiment of the present invention.

[Explanation of symbols] 1 bead part 1a bead core 2 Side wall part 3 tread section 4a, 4b carcass ply 4 radial carcass 5a, 5b Reinforcing member 6 bead filler 7 rubber chafer

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Claims (4)

(57) [Claims] 1. A pair of left and right bead portions, a pair of left and right sidewall portions that are connected to these bead portions, and a tread portion that straddles both sidewall portions. A pneumatic radial tire with a radial carcass consisting of at least one carcass ply with each end wound up around a bead core embedded in the bead part, with a flatness rate of 55% or less and each side. The wall portion is composed of two layers of inner and outer side wall rubbers, and the inner layer side wall rubber has an elastic modulus at 30 ° C. of 10 × 10 ⁷ to 200 × 10 ⁷ dyn / cm ² , which is similar to the outer layer side wall rubber. Elasticity of 3 × 10 ⁷ to 8 × 1
A pneumatic radial tire with excellent handling stability of 0 ⁷ dyn / cm ² . 2. The tire according to claim 1, wherein an outer end portion in the tire radial direction of the inner layer side wall rubber is arranged to abut against a tread rubber forming a tread portion or to be overlapped with the tread rubber. Pneumatic radial tire with excellent steering stability as described. 3. The inner layer side wall rubber is arranged such that the inner end portion in the tire radial direction is abutted against a rubber chafer provided on the outer surface side of the bead portion or is overlapped with the rubber chafer. Alternatively, the pneumatic radial tire described in 2 is excellent in driving stability. 4. The thickness of the sidewall rubber on the inner layer side is 0.5.
The pneumatic radial tire according to any one of claims 1 to 3, which has a steering stability of up to 2 mm.