JP3047200B2 - Pneumatic radial tires for passenger cars - 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 radial tire for a passenger car, which has an improved steering stability while reducing the weight of a tread / belt structure.

[0002]

2. Description of the Related Art Recently, the problem of environmental pollution, which is expanding on a global scale, has led to a strong demand for further reduction in fuel consumption of vehicles. As part of this, weight reduction of tires has been highlighted as a major technical issue. ing. On the other hand, pneumatic radial tires for passenger cars, in which the belt layer is made of steel cord, have high handling stability because the steel cord has very high strength and high modulus compared to other fiber cords. It is known to exert However, the steel cord has a drawback that the specific gravity is large, so that the tire weight is increased and the fuel efficiency is reduced, so that it is difficult to cope with the above-mentioned technical problems.

Hitherto, an aramid fiber cord has been proposed as a tire cord material having characteristics close to those of a steel cord. This aramid fiber cord has a high strength and a high elastic modulus comparable to a steel cord, and has a lower specific gravity than a steel cord, so that it can contribute to the weight reduction of a tire. For example, simply replacing the belt layer of steel cord with aramid fiber cord will result in about 5-
It has been found that the weight can be reduced by as much as 8%.

[0004] However, the aramid fiber cord has a drawback that the bending rigidity when subjected to bending deformation is low because its compressive rigidity is almost equal to zero. for that reason,
The cornering power obtained by replacing the belt layer using the steel cord with the aramid fiber cord while keeping the same structure was up to 75% of the cornering power obtained from the belt layer using the steel cord. Therefore, it has been considered that it is almost impossible to improve the steering stability of some aramid fiber cords as well as a tire having a belt structure using a steel cord.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to use aramid fiber cords for the belt structure to reduce the weight while exhibiting more steering stability than a tire of a belt layer using a conventional steel cord. An object of the present invention is to provide a pneumatic radial tire for a passenger car.

[0006]

A pneumatic radial tire for a passenger car according to the present invention is provided with a plurality of grooves extending at least in the tire circumferential direction on a tread surface, and a plurality of grooves are provided inside the tread.
In a pneumatic radial tire provided with a belt layer of a plurality of layers, the groove depth of the groove is in the range of 6.0 to 8.5 mm, and the rubber thickness under the groove from the groove bottom to the outermost belt layer is 0. 0.5 to 2.5 mm, and at least one of the belt layers is formed by coating an aramid fiber cord with a coating rubber, and the coating rubber has a short length of 1 to 10 parts by weight with respect to 100 parts by weight of the rubber. It is a rubber composition containing fibers.

[0007] In addition to forming at least one belt layer of aramid fiber cord as described above, the groove depth and the rubber thickness under the groove are set to be smaller than those of the conventional tire, so that the tire weight can be reduced. The weight can be reduced as compared with the case using a steel cord belt layer. In addition, the groove depth of the tread surface and the thickness of the rubber under the groove are set to be small, and the in-plane rigidity of the belt layer is increased by blending short fibers with the coated rubber of the aramid fiber cord, and the cornering power is increased. Can be higher than that obtained from a belt-layer tire using a conventional steel cord.

In the present invention, the groove depth (d) refers to
Means the distance measured perpendicular to the tread surface to the deepest groove bottom, and the rubber thickness under the groove (t) is the distance from the deepest groove bottom to the cord surface of the outer belt layer (4u). Refers to distance. 1 and 2 illustrate a pneumatic radial tire for a passenger vehicle having the configuration of the present invention.
In the drawing, 1 is a tread portion, and 2 is a carcass layer made of an organic fiber cord such as a nylon cord or a polyester cord. The carcass layer 2 is wound around the pair of left and right bead cores 5 from the inside to the outside of the tire. The cord angle of the carcass layer 2 with respect to the tire circumferential direction EE ′ is substantially 90 °. In the tread portion 1, two inner belt layers 4d and outer belt layers 4u made of aramid fiber cords are arranged outside the carcass layer 2 over one circumference of the tire. Each belt layer 4
In the d and 4u coat rubbers, 1 to 10 parts by weight of short fibers are mixed with 100 parts by weight of the coat rubber. The cord angles of the inner belt layer 4d and the outer belt layer 4u with respect to the tire circumferential direction EE ′ are 5 to 40 ° and cross each other.

On the surface of the tread portion 1, a main groove 6 extending in the tire circumferential direction and a sub groove 7 intersecting the main groove 6 are provided. The groove depth d of the main groove 6 is set in the range of 6.0 to 8.5 mm, and the rubber thickness t under the groove is set in the range of 0.5 to 2.5 mm. In order to realize the above-described invention, the present inventors have multifacetedly searched for factors that influence the cornering power of a radial tire on the premise of a technical problem of reducing the weight of a tire. As a result, as will be described in detail in an experimental example described later, the groove depth and the rubber thickness under the groove mainly provided in the tire circumferential direction on the tread surface are large factors that determine the cornering power, and the grooves of these grooves are further increased. It was found that the cornering power was increased as the depth and the rubber thickness under the groove were smaller. In this case, the groove in the tire circumferential direction was not related to whether it was a straight groove or a zigzag groove, and was not related to whether or not it had a sub-groove in the tire width direction. However, as described above, when the cord of the belt layer is replaced with steel cord from aramid fiber cord, there is a reduction in cornering power of about 25%. It has also been found that it is almost impossible to cover a 25% reduction in cornering power.
Therefore, in addition to these factors, the aim of improving steering stability while reducing weight is achieved by increasing the in-plane rigidity of the belt layer by blending short fibers with the coated rubber of the aramid fiber cord. Was found.

Hereinafter, the present invention will be described in detail with reference to experimental examples. FIG. 3 shows an experimental result on the relationship between the groove depth d and the cornering power CP. In this experiment, the tire structure was made common as follows, and only the groove depth d was changed to 6 mm, 7 mm, 8 mm, 8.5 mm, and 9 m.
The results were obtained for eight types of radial tires having different sizes of m, 10 mm, 11 mm, and 12 mm.

Tread structure: Fig. 1 Tire size: 185 / 70R13 Belt structure: 2 belt layers Cord angle 21 ° Width of belt layer Upper / lower layers 120mm / 130mm Cord aramid fiber 1500D / 2 Number of ends 45 / 50mm Coated rubber 50 % Elasticity at elongation 25 kgf / cm ² Rubber thickness under the groove: 3.0 mm The cornering power CP is 4 in the drum test.
When traveling at 50 kgf and a speed of 10 km / hr, the lateral force when the slip angle is 1 ° to the right and the lateral force when the slip angle is 1 ° to the left are each measured, and the average value of both measured values (average absolute value) Is indicated by an index when the measured value of a tire having a groove depth of 6 mm is set to 100.

The elastic modulus at 50% elongation of the coated rubber is a value measured at room temperature by the method specified in JIS K6301. On the other hand, FIG. 4 shows an experimental result on the relationship between the rubber thickness t under the groove and the cornering power CP. This experiment has the same tread structure, tire size, and belt structure as the tire used in the above experiment, and the point that the groove depth is 8.5 mm in common.
0.5mm, 1.5mm, 2.0
mm, 2.5mm, 3.0mm, 3.5mm, 4.0m
m for seven different radial tires. The cornering power CP was measured by the same method as described above, and was represented by an index when the measured value of a tire having a rubber thickness under the groove t of 0.5 mm was set to 100.

First, as for the groove depth, as shown in FIG. 3, the cornering power CP increases as the groove depth decreases.
It can be seen that the cornering power CP sharply increases below 5 mm. It is recognized that the above-mentioned tendency is not limited to the tires of the tire sizes used in the test, and the same tendency applies to tires of other sizes. In a conventional radial tire, the groove depth is generally set to 8 to 11 mm, but in the present invention, the groove depth is set to 6.0 based on the result of FIG.
To 8.5 mm, preferably 6.0 to 7.5 mm. The lower limit of 6.0 mm is determined from the wear life, and if it is shallower than this, the tire becomes less practical.

As for the thickness of the rubber under the groove, it can be seen from FIG. 4 that the cornering power CP increases as the thickness of the rubber under the groove t becomes thinner, and increases sharply particularly at 2.5 mm or less. The same tendency is observed for tires of other sizes. In the conventional radial tire, the thickness of the rubber under the groove is generally set to 2.5 to 4 mm, but in the present invention, the thickness of the rubber under the groove is set to 0.5 to 2.5 mm from the result of FIG. Preferably 1.0 to 2.0
mm. The lower limit of 0.5 mm is a limit for protecting the belt cord and preventing its breakage and failure.

As described above, the smaller the groove depth d of the groove (main groove) provided in the tread and the thickness t of the rubber under the groove, the more the cornering power CP can be increased. However, the effect of improving the cornering power CP by the former groove depth d is only up to about 9% compared to the lower limit groove depth of the conventional tire of 8.5 mm even when the lower limit of the groove depth is 6.0 mm. And the latter rubber thickness t under the groove
The effect of improving the cornering power CP by the method described above is only about 19% at most as compared with the lower limit of the under-groove rubber thickness of 3.0 mm of the conventional tire even when the lower-limit rubber thickness below the groove is 0.5 mm. For this reason, the low bending stiffness of the aramid fiber cord belt layer cannot be compensated for only from the groove depth d and the rubber thickness t under the groove, and it is impossible to increase the cornering power beyond the conventional steel cord belt layer. difficult.

According to the present invention, the cornering power, which is insufficient only by the groove depth d and the rubber thickness t under the groove, is increased by increasing the in-plane rigidity by blending short fibers with the coat rubber of the aramid fiber cord belt layer. To supplement the cornering power obtained from the steel cord belt layer. FIG. 5 shows the results of an experiment on the relationship between the blending amount of short fibers in the coated rubber and the cornering power CP, and the same tread structure, tire size, and belt structure as the tire used in the experiment of FIG. The groove depth is 7.0mm and the rubber thickness under the groove is 1.5m
m, and only the blending amount of the short fiber with respect to 100 parts by weight of the coated rubber was changed to 0 parts by weight, 1 part by weight, 2.5 parts by weight, 5 parts by weight, and 10 parts by weight.
Experiments were conducted on various types of radial tires. The cornering power CP is measured in the same manner as in FIG.
It is indicated by an index when the measured value of a tire containing no short fiber is taken as 100.

As is apparent from FIG. 5, the cornering power CP increases in proportion to the blending amount of the short fibers. In the present invention, the low bending stiffness of the aramid fiber cord is compensated for by blending short fibers in a proportion of 1 to 10 parts by weight with 100 parts by weight of the coated rubber of the aramid fiber cord belt layer. The blending amount of the short fiber with respect to 100 parts by weight of the coated rubber is 1 part by weight or more, and the more the amount, the more desirable. However, if the amount is too large, the elongation at break decreases and the fatigue resistance of the belt layer decreases.
0 parts by weight. Even if short fibers are added to the coated rubber, the viscosity of the unvulcanized coated rubber hardly changes, so that the workability of the belt layer does not decrease.

In the present invention, it is preferable that the short fibers to be uniformly blended in the coated rubber have an average diameter of 1 μm or less. Fatigue properties can be improved. In addition, the length of the short fiber is preferably set to 100 μm or more because the effect of increasing the rigidity is insufficient if the length is too short, but if the length is longer than 5000 μm, it is cut at the time of mixing of the coated rubber and 5000 μm or less. Becomes shorter. Such short fibers suitable for the present invention include:
Natural fibers such as cotton and silk; cellulose fibers; polyamide fibers such as nylon; polyester fibers; polyvinyl alcohol fibers such as vinylon; and carbon fibers.

In the present invention, the aramid fiber cord used for the belt layer has a total denier of 500 to 500.
It is desirable that the yarn is a twist of 5000D, preferably 2000 to 3000D filament. Further, this twisted yarn is surface-treated with an adhesive such as epoxy resin or resorcinol-formalin latex (RFL) in order to improve the adhesiveness with the coat rubber. The surface treated code is
It is woven in a drip-like form, and the coated rubber obtained by blending short fibers with the obtained drip-like woven fabric is 0.1 to 1.0 times the cord diameter.
mm thick. Preferably, it is coated so as to have a thickness of the cord diameter + 0.1 to 0.6 mm.

In the present invention, it is desirable that both belt layers are made of an aramid fiber cord, but if necessary, one layer may be made of an aramid fiber cord and the other layer may be made of a steel cord. . The two belt layers have a cord angle of 5 to 4 with respect to the tire circumferential direction.
0 degrees, preferably 15 to 30 degrees, and the belt cords are laminated so as to intersect with each other, so that the width in the tire meridian direction is 80 to 130%, preferably 90 to 110% of the tire contact width. Is good.

[0021]

Example 1 A rubber composition having the tire structure shown in FIG. 1 and the tire specifications shown in Table 1 was used, and rubber compositions A to E shown in Table 2 were used as a coating rubber for a belt layer. The tires 1 to 3 of the present invention and the comparative tires 1 to 3 were prepared by setting the thickness t to the size shown in Table 4 and forming the following tread pattern on the tread surface.
Was made. For comparison with the prior art, a cord structure of 1 × 5 (0.25 mm) was used instead of the aramid fiber cord.
A conventional tire having the same specifications as the tire 1 of the present invention was produced, except that the steel cord was used and the rubber composition was changed to A.

Tread pattern: Four straight main grooves having a width of 6 mm are provided in the tread contact surface along the tire circumferential direction, and five ribs having substantially equal widths are formed. A plurality of sub-grooves having a width of 4 mm and the same depth as the straight main groove were formed at intervals of about 26 mm in the radial direction, the ribs were divided, and 72 rectangular blocks were arranged on the tire circumference. A block pattern was formed.

With respect to these seven types of tires, the cornering power CP was evaluated in the same manner as in FIG. 3 described above, and the evaluation results were compared with the weight per tire as shown in Table 4.
It was shown to. The CP value was indicated by an index with the value of the conventional tire being 100, and the tire weight was indicated based on the weight of the conventional tire.

[0024]

[0025] In Table 2, the amounts of the respective components are parts by weight.

¹⁾ : Sumica 610 manufactured by Sumitomo Chemical Co., Ltd. ²⁾ : Abbreviation of hexamethoxymethyl melamine ³⁾ : Gobalt naphthenate (manufactured by Dainippon Ink and Chemicals, Inc.) ⁴⁾ : “Nocrack 6C” manufactured by Ouchi Shinko Chemical Co., Ltd. ^{5 )} : 80% insoluble sulfur ⁶⁾ : "Noxeller MSA-G" (OB
S) ⁷⁾ : FRR-NR manufactured by Ube Industries (average diameter 0.3 μm)

[0027] In Table 3, ¹⁾ : Styrene-butadiene copolymer rubber “Nipol 1712” manufactured by Zeon Corporation ²⁾ : “Nocrack 6C” manufactured by Ouchi Shinko Chemical Co., Ltd. ³⁾ : “Sunnoc” manufactured by Ouchi Shinko Chemical Co., Ltd. ⁴⁾ : "Sancellar 232" manufactured by Sanshin Chemical Industry Co., Ltd.
-MG "

[0028]

From Table 4, it can be seen that the tire weight can be reduced by 525 g by simply replacing the steel cord of the conventional tire with the aramid fiber cord as in Comparative Tire 1, but the cornering power CP is reduced by 25%. On the other hand, the tire 1 of the present invention in which the thickness t of the rubber under the groove was set to 2.5 mm and 10 parts by weight of the short fiber was mixed with 100 parts by weight of the coated rubber.
Can reduce tire weight and improve cornering power CP over conventional tires while using aramid fiber cords. In addition, the tire 2 of the present invention having the groove depth d of 6.0 mm as the lower limit has the same cornering power CP as the tire weight can be significantly reduced even if the amount of short fibers of the coated rubber is lower than that of the tire 1 of the present invention. Could be larger than the tires. The comparative tires 2 and 3 have the groove depth d and the rubber thickness t under the groove set to the lower limits of 6.0 mm and 0.5 mm, respectively, but the short fiber content of the coated rubber is less than 1 part by weight. Therefore, the elastic modulus M50 at the time of 50% elongation was low, and the cornering power CP was equal to or less than that of the conventional tire. On the other hand, the tire 3 of the present invention in which the groove depth d and the rubber thickness t under the groove were the same as those of the comparative tires 2 and 3 and the blending amount of the short fiber of the coated rubber was 2.5 parts by weight, the cornering power CP was higher than that of the conventional tire. Was also getting bigger. Example 2 A tire 4 of the present invention having the same specifications as the tire 2 of Example 1 except that only the inner belt layer constituting the two belt layers was replaced with a steel cord constituting the belt layer of the conventional tire. did.

The cornering power CP of the tire 4 of the present invention was evaluated in the same manner as in FIG. The evaluation value was 127 as an index value when the CP value of the conventional tire was set to 100. At this time, the tire weight could be reduced by 1100 g. That is, even if one of the two belt layers is a steel belt, the cornering power CP can be improved while reducing the weight of the tire by mixing short fibers with the coat rubber of the belt layer.

[0031]

According to the present invention, at least one of the two belt layers is made of aramid fiber cord as described above, and the groove depth and the rubber thickness under the groove are adjusted. Since the tire is set smaller than the conventional tire, the weight can be reduced as compared with the conventional tire having a belt layer using a steel cord. In addition, the fact that the groove depth and the rubber thickness under the groove are set small, and that the in-plane rigidity of the belt layer is increased by blending short fibers with the coated rubber of the aramid fiber cord, synergistically to reduce the steel cord. The cornering power can be improved and the steering stability can be improved as compared with the tire of the belt layer used.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a radial tire for a passenger car according to an embodiment of the tire of the present invention, partially cut away.

FIG. 2 is an enlarged sectional view of a main groove portion provided in a tread portion of the tire of the present invention.

FIG. 3 is a graph showing a relationship between a groove depth d of a groove and a cornering power CP.

FIG. 4 is a graph showing a relationship between a rubber thickness t under a groove and a cornering power CP.

FIG. 5 is a graph showing a relationship between a blending amount of short fibers in a coated rubber and a cornering power CP.

[Explanation of symbols]

 Reference Signs List 1 tread portion 6 main groove 2 carcass layer 7 sub groove 4d inner belt layer d groove depth 4u outer belt layer t rubber thickness under groove 5 bead core

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI B60C 11/04 B60C 11/06 Z (56) References JP-A-62-85702 (JP, A) JP-A-1-240303 ( JP, A) JP-A-54-132646 (JP, A) JP-A-57-70705 (JP, A) JP-A-58-112805 (JP, A) JP-A-3-42306 (JP, A) 56-79005 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 9/18-9/20 B60C 11/00 B60C 11/04 B60C 1/00

Claims (1)

(57) [Claims] 1. A pneumatic radial tire in which a plurality of grooves extending at least in the circumferential direction of a tire are provided on a tread surface and two belt layers are provided inside the tread, the groove depth of the grooves is 6.0 to 8 0.5 mm, and the rubber thickness under the groove from the groove bottom to the outermost belt layer is 0.5 to 0.5 mm.
In a range of 2.5 mm, at least one of the belt layers is formed by coating an aramid fiber cord with a coating rubber, and the coating rubber contains 1 to 10 parts by weight of short fibers with respect to 100 parts by weight of the rubber. A pneumatic radial tire for a passenger car, characterized in that the rubber composition is a rubber composition.