JPH04314604A - Pneumatic radial tire for passenger car - Google Patents

Abstract

PURPOSE:To exhibit steering stability beyond a tire with a belt layer using a conventional steel cord while enhancing a reduction in weight by using an aramid fiber cord in belt structure. CONSTITUTION:In a pneumatic radial tire comprising a plurality of grooves extending at least in the tire circumferential direction on a tread surface and two belt layers disposed in the tread in such a manner their belt cords are mutually crossed, the groove depth of the groove is set within the range of 6.0-8.5mm, and the groove under rubber thickness from the groove bottom to the surface belt layer is within the range of 0.5-2.0mm. This belt layer is disposed without turning up both the end parts, and at least one layer is formed from aramid fiber cord. Further, at least both the end parts of the belt layer is covered with a belt cover layer having a cord angle to the tire circumferential direction not more than 30 deg.. The belt cover layer is formed from an organic fiber cord with a cord diameter not more than 0.7mm, and its placing density is 35-90%.

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 passenger cars that has a lighter tread/belt structure and improved handling stability.

0002

[Background Art] Due to the environmental pollution problem that has recently been expanding on a global scale, there has been a strong demand for further improvements in vehicle fuel efficiency, and as part of this, reducing the weight of tires has also been highlighted as a major technical issue. ing. On the other hand, pneumatic radial tires for passenger cars whose belt layer is composed of steel cords have high strength and high elastic modulus, which is superior to other fiber cords, resulting in high handling stability. is known to exhibit. However, steel cord has a disadvantage that it increases the weight of the tire due to its high specific gravity and reduces fuel efficiency, which makes it difficult to meet the above-mentioned technical problems.

Conventionally, aramid fiber cords have been proposed as a tire cord material having characteristics similar to steel cords. This aramid fiber cord has high strength and high elastic modulus comparable to steel cord, and has a lower specific gravity than steel cord, so it can contribute to reducing the weight of the tire. For example, by simply replacing the steel cord belt layer with aramid fiber cord, approximately 5~
It is known that the weight can be reduced by as much as 8%.

[0004] However, aramid fiber cords have a disadvantage in that their compressive stiffness is approximately zero, and therefore their bending stiffness is low when subjected to bending deformation. Therefore,
The cornering power obtained by replacing the belt layer using steel cord with an aramid fiber cord while maintaining the same structure was up to 75% of the cornering power obtained from the belt layer using steel cord. Therefore, it has been considered that it is almost impossible to improve steering stability using aramid fiber cords to the same level as tires with a belt structure using steel cords.

[0005]

[Problems to be Solved by the Invention] An object of the present invention is to reduce weight by using aramid fiber cords in the belt structure, while achieving greater handling stability than tires with belt layers that use conventional steel cords. An object of the present invention is to provide a pneumatic radial tire for a passenger car.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a tread surface with a plurality of grooves extending at least in the circumferential direction of the tire, and has two belt layers inside the tread with belt cords crossing each other. In a pneumatic radial tire arranged so that the groove depth of the groove is 6.0~
8.5 mm, the under-groove rubber thickness from the groove bottom to the outermost belt layer is in the range of 0.5 to 2.0 mm, and both ends of the belt layer are arranged without folding back. , at least one layer is composed of aramid fiber cord, and further, at least both ends of the belt layer are covered with a belt cover layer having a cord angle of 30° or less with respect to the tire circumferential direction, and the belt cover layer has a cord diameter of 0.
．． Organic fiber cord of 7 mm or less is implanted with a density of 35 to 9.
This feature is characterized in that it is configured at 0%.

In the present invention, the groove depth (d) refers to the distance measured to the deepest groove bottom in the direction perpendicular to the tread surface, as shown in FIG. 2, and the groove bottom rubber thickness (t) , refers to the distance from the bottom of the deepest groove to the cord surface of the outer belt layer (4u). In addition, the implantation density ρ (%) is expressed by the following formula, where a is the diameter of the organic fiber cords constituting the belt cover layer, and p is the distance (pitch) between the centers of two adjacent organic fiber cords. A defined value.

ρ (%) = (a ÷ p) × 100 As mentioned above, by setting the groove depth and the rubber thickness under the groove to be smaller than that of conventional tires, and by constructing the belt layer with an aramid fiber cord, The weight of the tire can be reduced compared to tires using conventional steel cord belt layers. In addition, the groove depth on the tread surface and the rubber thickness under the grooves have been set small, and the belt cover layer has a specified cord diameter and driving density of the organic fiber cords. It becomes possible to exceed that obtained from belt layer tires using cords.

FIGS. 1 and 2 illustrate a pneumatic radial tire for passenger cars having the structure of the present invention. In the figure, 1 is a tread portion, and 2 is a carcass layer made of organic fiber cords such as nylon cords and polyester cords. The carcass layer 2 is folded back and rolled up from the inside of the tire to the outside around a pair of left and right bead cores 3. The cord angle of this carcass layer 2 with respect to the tire circumferential direction EE' is substantially 90°. In the tread portion 1, a belt layer consisting of two layers, an inner belt layer 4d and an outer belt layer 4u made of aramid fiber cords, is arranged outside the carcass layer 2 over one circumference of the tire. Both of the belt layers are of a so-called step-cut type in which both ends are not folded back and the belt width of the outer belt layer 4u is smaller than that of the inner belt layer 4d. Moreover, the inner belt layer 4d and the outer belt layer 4u are
The cords have an angle of 5 to 40 degrees with respect to the tire circumferential direction EE' and intersect with each other.

Furthermore, a belt cover layer 5 having a width W in the tire radial direction is disposed on the outside of the outer belt layer 4u so as to cover the entire width W of these belt layers. The cord angle of the belt cover layer 5 with respect to the tire circumferential direction EE' is 30° or less, preferably approximately 0°. Moreover, this belt cover layer 5 has a cord diameter of 0.7 m.
35 to 90% driving density from organic fiber cord of less than m
It consists of

[0011] On the surface of the tread portion 1, there is a tire circumferential direction E.
A main groove 6 extending in the direction E' and a sub groove 7 intersecting the main groove 6 are provided. The groove depth d of this main groove 6 is 6.0 to 8.5 mm.
The groove bottom rubber thickness t is set within the range of 0.5 to 2.
It is set in the range of 0mm. In making the above-described invention, the present inventors conducted a multifaceted search for factors that influence the cornering power of radial tires based on the technical problem of reducing the weight of tires. As a result, as will be shown in detail in the experimental examples below, the depth of the grooves provided on the tread surface mainly in the circumferential direction of the tire and the thickness of the rubber under the grooves are important factors that determine cornering power. It was discovered that the smaller the depth and the thickness of the rubber under the groove, the greater the cornering power. In this case, it does not matter whether the grooves in the circumferential direction of the tire are straight grooves or zigzag grooves, and whether or not there are sub-grooves in the width direction of the tire does not matter. However, as mentioned above, when the belt layer cord is replaced from steel cord to aramid fiber cord, cornering power decreases by about 25%. It was also found that it was almost impossible to compensate for the 25% decrease in cornering power, so in addition to this, the belt layer was covered with a belt cover layer.
Moreover, it has been found that the object can be achieved by specifying the cord diameter and implant density of the organic fiber cords constituting the belt cover layer.

The details of the present invention will be explained below with reference to experimental examples. FIG. 3 shows experimental results regarding the relationship between groove depth d and cornering power CP. In this experiment, the tire structure was the same as shown below, and only the groove depth d was 6 mm, 7 mm, 8 mm, 8.5 mm, and 9 mm.
, 10 mm, 11 mm, and 12 mm.

Tread structure: In Figure 1, a structure without a belt cover layer Tire size: 185/70R13 Belt structure: 2 belt layers Cord width Outside/Inside 120mm/130mm Cord angle 21° Cord Aramid fiber 1500D/2 ends number 4
5 pieces/50mm Rubber thickness under the groove t: 3.0mm Cornering power CP is determined by load 4 in the drum test.
When running at 50 kgf and a speed of 10 km/hr, measure 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, and average the two measured values (average of absolute values). is expressed as an index when the measured value of a tire with a groove depth of 6 mm is set as 100.

On the other hand, FIG. 4 shows experimental results regarding the relationship between the groove bottom rubber thickness t and the cornering power CP. In this experiment, the same tread structure, tire size, and belt structure as the tires used in the above experiment were used, and the groove depth was 8.5 mm, and only the groove bottom rubber thickness t was changed to 0.5 mm, 1. 5mm, 2.0mm, 2.5mm
, 3.0 mm, 3.5 mm, and 4.0 mm. Cornering power CP is measured using the same method as in Figure 3 above.
The measured value of a tire with a groove bottom rubber thickness t of 0.5 mm is 100
It is expressed as an index when .

First, regarding the groove depth, from FIG. 3, the shallower the groove depth, the higher the cornering power CP.8.
It can be seen that the cornering power CP increases rapidly below 5 mm. It is recognized that the above-mentioned tendency is not limited to tires of the tire size used in the test, but also exists for tires of other sizes. In conventional radial tires, the groove depth is generally 8 to 11 mm, but in the present invention, the groove depth is set to 6.0 mm based on the results shown in Fig. 3.
8.5 mm, preferably 6.0 to 7.5 mm. The lower limit of 6.0 mm is determined based on the wear life, and if the depth is shallower than this, the tire will be impractical.

Regarding the groove bottom rubber thickness, from FIG. 4, the cornering power C decreases as the groove bottom rubber thickness t becomes thinner.
It can be seen that P increases, particularly rapidly below 2.5 mm. Similar trends are observed for tires of other sizes as well. In conventional radial tires, the thickness of the rubber under the groove is generally 2.5 to 4 mm, but in the present invention, the thickness of the rubber under the groove is 0.5 to 2.0 mm, based on the results shown in FIG. Preferably 1.0-2.0m
Let it be m. The lower limit of 0.5 mm is a limit for protecting the belt cord and preventing its breakage.

As described above, the cornering power CP can be increased as the groove depth d of the groove (main groove) provided in the tread and the groove bottom rubber thickness t are made smaller. However, the cornering power CP due to the former groove depth d
Even when the lower limit groove depth is set to 6.0 mm, the improvement effect is at most 9% compared to the lower limit groove depth of 8.5 mm for conventional tires.
Furthermore, even if the lower limit of the groove rubber thickness t is set to 0.5 mm, the latter effect of improving cornering power CP due to the groove groove rubber thickness t is limited to 3 mm, which is the lower limit of the groove groove rubber thickness of the conventional tire. It is only about 19% at most compared to .0mm. Therefore, it is not possible to compensate for the low bending rigidity of the aramid fiber cord belt layer from only the groove depth d and the bottom rubber thickness t, and it is impossible to increase the cornering power beyond that obtained from the conventional steel cord belt layer. difficult.

In the present invention, cornering power which is insufficient with only the groove depth d and groove bottom rubber thickness t can be achieved by at least both ends of the belt layer using aramid fiber cords at a cord angle of 30 mm with respect to the tire circumferential direction. The cornering power obtained from a belt layer using steel cords is increased by covering the belt cover layer with a belt cover layer that has a cornering power of less than or equal to that obtained from a belt layer using steel cords. It is possible to do this.

FIG. 6 shows experimental results regarding the relationship between the cord diameter and driving density of the nylon cord constituting the belt cover layer and the cornering power CP. In this experiment, the tire size and belt structure were the same as those used in the experiment in Figure 3, and the groove depth was 7.0 mm.
, the common features are that the rubber thickness under the groove is 1.5 mm and that a belt cover layer made of nylon cord is used with a cord angle of 0° with respect to the tire circumferential direction. Regarding the belt cover layer, the cord diameter was 0.6 mm and the implant density ρ was changed to 36%, 60%, and 84%, respectively.
Two types with a cord diameter of 0.7 mm and a driving density ρ of 42% and 70%, respectively, and a cord diameter of 1.0
One type of radial tire with a driving density ρ of 60% in mm and one type of radial tire without a belt cover layer were tested. The cornering power CP was measured in the same manner as in FIG. 3 above, and is expressed as an index when the measured value of the tire without the belt cover layer is set as 100.

From FIG. 6, it can be seen that a belt cover layer with a cord diameter of 1.0 mm does not contribute much to the improvement of cornering power CP. In tires provided with belt cover layers having cord diameters of 0.7 mm and 0.6 mm, the cornering power CP increases as the driving density ρ increases. As is clear from FIG. 6, it can be seen that the cornering power CP significantly differs depending on the cord diameter and implant density of the organic fiber cords constituting the belt cover layer. In the present invention, the cord diameter is set to 0.7 mm or less, and the driving density ρ is set to 35% or more, preferably 50% or more. However, if the implantation density ρ is too large, the cord spacing becomes too narrow and the durability decreases, so the upper limit thereof needs to be 90%. Preferably it is 85%.

In the present invention, it is desirable that the cord angle of the belt cover layer 5 with respect to the tire circumferential direction be approximately 0°, but substantially the same effect can be provided as long as it is 30° or less. Further, this belt cover layer 5 may be a full cover that covers the entire outer surface of a laminate consisting of two superimposed outer belt layers 4u and inner belt layers 4d, or may be a full cover that covers the entire outer surface of the laminate, or both ends of the laminate. An edge cover may be used that covers the tread but does not cover the tread center region. In the case of an edge cover, it is desirable that the width per side be 10% or more of the total belt layer width, and that the implant density ρ of the organic fiber cord be 50% or more. In addition, in the case of this edge cover, the depth of the groove provided in the tread part is 6 to 7 mm, and the thickness of the rubber under the groove is 0.5 to 1.5 mm.
It is desirable that the range be within mm.

The organic fiber cord constituting the belt cover layer is preferably a heat-shrinkable textile cord such as a nylon cord or a polyester cord. These codes are resorcinol formalin latex (RFL)
) After surface treatment with an adhesive such as ), it is used by covering it with a coated rubber. In the present invention, both ends of the belt layer are not folded back, but are preferably step-cut, and at least one layer is made of aramid fiber cord. Thereby, the weight can be further reduced, and the aramid fiber cord having high rigidity can be easily handled, and productivity can be increased. When only one belt layer is made of aramid fiber cords, it is desirable that the other layer is made of steel cords.

[0023] The aramid fiber cord used for this belt layer has a total denier D of 500 to 5000D.
, preferably a twisted yarn consisting of filaments of 2,000 to 3,000 D. Furthermore, in order to improve the adhesion of this twisted yarn with the coating rubber, epoxy resin,
The surface is treated with an adhesive such as resorcinol formalin latex (RFL). The surface-treated cord is woven into a sag, and the coated rubber is coated on the resulting sag so that it is 0.1 to 1.0 mm thicker than the diameter of the cord. Preferably cord diameter + 0.1 to 0.6 mm
Cover to a thickness of .

The two belt layers are stacked so that the cord angle with respect to the tire circumferential direction is 5 to 40 degrees, preferably 15 to 30 degrees, and the cords intersect with each other between the belt layers. The width of the belt layer in the tire meridian direction is 80 to 130% of the tire ground width, preferably 90 to 1%.
It is better to set it to 10%.

[0025]

【Example】

Example 1 A tire 1 of the present invention was manufactured, having the tire structure shown in FIG. 1 and the tire specifications shown in Table 1, and having the following tread pattern formed on the tread surface. Tread pattern: Four straight grooves (main grooves) with a width of 6 mm are provided in the tread contact surface along the circumferential direction of the tire, forming five ribs of approximately equal width. Width of multiple pieces 4m
A block pattern in which grooves (minor grooves) with the same depth as the straight grooves are formed at intervals of about 26 mm in the radial direction, the ribs are divided into rectangular blocks, and 72 rectangular blocks are arranged on the circumference of the tire. In addition, the groove depth d, groove bottom rubber thickness t, belt cover layer width w (mm), driving density ρ (%), and cord angle with respect to the tire circumferential direction (°) were changed as shown in Table 3. Six types of tires were manufactured: inventive tires 2, 3, 4, and 5, and comparative tires 1 and 2, which had the same specifications as inventive tire 1 except for the above (comparative tire 1).
(without belt cover layer).

For comparison, a conventional tire without a belt cover layer having the specifications shown in Table 3 was manufactured using a steel cord with a cord structure of 1×5 (0.25 mm) in place of the aramid fiber cord. Regarding these eight types of tires,
Cornering power CP was evaluated using the same method as in FIG. 3, and the evaluation results are shown in Table 3 along with a comparison of the weight per tire. The cornering power CP is expressed as an index when the measured value of the conventional tire is set as 100, and the comparison of tire weight is expressed based on the weight of the conventional tire.

[0027]

In Table 2, 1): Styrene-butadiene copolymer rubber “Nipol 1712” manufactured by Nippon Zeon Co., Ltd.
2): “Nocrack 6C” manufactured by Ouchi Shinko Kagaku Co., Ltd.
3): “Sunnock” manufactured by Ouchi Shinko Kagaku Co., Ltd. 4)
: “Suncellar 232” manufactured by Sanshin Chemical Industry Co., Ltd.
-MG”

Note: In Table 3, the total width indicates full coverage, and the edge indicates edge coverage.

From Table 3, when the steel cord of the conventional tire is simply replaced with an aramid fiber cord and no belt cover layer is provided, as in Comparative Tire 1, the tire weight is 53.
Although it reduces by 0g, cornering power CP decreases by 25%. Further, like Comparative Tire 2, even if the entire width of the belt layer is covered with the belt cover layer, the groove bottom rubber thickness t is 2.
With a thickness of 5 mm, it is not possible to obtain the same cornering power CP as a conventional tire. However, when the under-groove rubber thickness t is set to 2.0 mm, which is the upper limit of the present invention, as in the tire 1 of the present invention, the tire weight is reduced and it is comparable to the conventional tire. A cornering power CP equivalent to that can be obtained.

Further, as in the tire 2 of the present invention, the bottom groove rubber thickness t is set to 2.0 mm, and the groove depth d is made shallow.6.
When it is set to 0 mm, the tire weight is significantly reduced and the cornering power CP is increased to 107. Furthermore, as in the tire 3 of the present invention, the groove bottom rubber thickness t is set to the lower limit of 0.5 m.
When the tire is thinned to m, the weight of the tire is significantly reduced and the cornering power CP becomes 115, which is a significant improvement.

[0032] Even in the case of an edge cover like the tire 4 of the present invention, the groove depth d is 7.0 mm and the groove bottom rubber thickness t.
By setting 1.5mm, cornering power C
P can be made larger than that of conventional tires. In this case, when the belt cover layer is made into a full cover like the tire 5 of the present invention, the cornering power CP is further improved. Example 2 Inventive tire 6 was manufactured with the same tire specifications as inventive tire 1 of Example 1 except that only the inner belt layer was replaced with a belt layer made of steel cord with a cord structure of 1×5 (0.25 mm). did.

The cornering power CP of this invention tire 6 was evaluated according to the same method as in FIG. 3 described above. The evaluation value is an index value of 121 when the value of cornering power CP of the conventional tire of Example 1 is 100,
Furthermore, the tire weight can be reduced by 695g, which indicates that the steering stability can be improved while reducing the weight.

[0034]

According to the present invention, as described above, the groove depth and the rubber thickness under the groove are set smaller than those of conventional tires, and the belt layer is made of aramid fiber cord, thereby reducing the weight of the tire. The weight can be reduced compared to those using a steel cord belt layer. In addition, the groove depth on the tread surface and the rubber thickness under the groove have been set small, and a belt cover layer made of organic fiber cords has been arranged, and the cord diameter of the organic fiber cords has been reduced to increase the driving density. By synergistically,
Cornering power can be increased beyond that obtained from conventional steel cord belt layer tires.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a main part of a radial tire for a passenger car, which is an embodiment of the tire of the present invention.

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

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

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

FIG. 5 is a graph showing the relationship between the cord diameter a and the cord driving density ρ of the belt cover layer and the cornering power CP.

[Explanation of symbols]

1 Tread section
4d Inner belt layer 4u Outer belt layer
5 Belt cover layer 6 Main groove
7 Minor groove d Groove depth of the groove
t Groove rubber thickness W
Total belt layer width
w Belt cover layer width

Claims (1)

[Claims] 1. A pneumatic radial tire in which a plurality of grooves extending at least in the circumferential direction of the tire are provided on the tread surface, and two belt layers are arranged inside the tread so that the belt cords intersect with each other, wherein the grooves of the grooves Depth 6.
The thickness of the rubber under the groove from the bottom of the groove to the outermost belt layer is within the range of 0.5 to 2.0 mm, and both ends of the belt layer are arranged without folding back. At the same time, at least one layer is made of aramid fiber cord, and further, at least both ends of the belt layer are covered with a belt cover layer having a cord angle of 30 degrees or less with respect to the tire circumferential direction, and the belt cover layer has a cord diameter of 30 degrees or less. Organic fiber cord of 0.7 mm or less is implanted to a density of 35
A pneumatic radial tire for passenger cars made up of ~90%.