JPH0446804A - Pneumatic radial tire for passenger car - Google Patents

Abstract

PURPOSE:To increase the lightening of a tire, the riding quality of a car and the stability of steering, and decrease the rusting and separating of a steel belt layer, by forming a fiber cord belt layer out of the belt layer of the tread layer of a double belt layer. CONSTITUTION:Double layers 5, 6 are provided between a tread 1 and a carcass 3. Between them, the belt layer on the carcass side is the steel belt layer 5 consisting of steel cords 7, and the other belt layer on the tread side is the fiber cord belt layer 6 consisting of polyamid monofilaments 8 with an unstranded flat cross section. On these polyamid monofilaments 8, the major axis directions of their flat cross sections are disposed in order along the plane direction of the belt layer 6. Both the end parts of the steel belt layer 5 are wider at least by about 5mm than those of the fiber cord belt layer 6.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a pneumatic radial tire for passenger cars having a steel belt layer, and more specifically, to a pneumatic radial tire for passenger cars that has a steel belt layer and is lightweight, and has a well-balanced improvement in riding comfort and handling stability. This invention relates to a pneumatic radial tire for passenger cars that reduces rusting and separation of steel belts due to tread trauma.

[Prior art] Generally, high-performance pneumatic radial tires for passenger cars have two steel belt layers made of steel cords with high strength and modulus as the heald layer in the tread, thereby achieving excellent high-speed durability and handling. I'm trying to get stability. As described above, the steel belt layer has great advantages in improving tire performance, but on the other hand, the out-of-plane bending rigidity of the steel belt layer is too high, so the impact force when driving over bumps on the road surface is large, which reduces ride comfort. However, since the specific gravity of the steel cord is very high, the weight of the tire becomes large, which increases the fuel consumption rate.

Conventionally, as a countermeasure to eliminate such drawbacks associated with steel heald layers, the belt layer on the tread side of the two steel belt layers was replaced with a belt layer made of high-strength, high-modulus aramid fiber cord. Tires are suggested. However, since aramid fiber cords are made up of a large number of small-diameter multifilaments twisted together, if trauma to the tread reaches the fiber cord belt layer, moisture and impurities will be trapped due to the capillary action of the fiber cords. was sucked into the cord, which caused rusting and separation of the inner steel belt layer.

(Problems to be Solved by the Invention) An object of the present invention is to reduce the weight of the tire, improve riding comfort and handling stability in a well-balanced manner in a radial tire with a steel belt layer, and to prevent the tread from suffering from external damage. To provide a pneumatic radial tire for a passenger car which reduces rusting and separation of a steel belt layer when the steel belt layer is worn.

(Means for Solving the Problems) A pneumatic radial tire for a passenger car according to the present invention that achieves the above object has two belt layers arranged on the outside of the carcass in the trend part with their cord directions intersecting each other. Among the belt layers, the belt layer on the carcass side is a steel belt layer, and the belt layer on the tread side is a fiber cord belt layer made of untwisted polyamide monofilament with a flat cross section, and the polyamide monofilament of the fiber cord belt layer is made of a steel belt layer. It is characterized in that the major axis direction of the flat cross section is arranged along the surface direction of the belt layer.

In this way, by using the fiber cord belt layer as the belt layer on the tread side of the two belt layers, the weight of the tire is reduced compared to the case where both layers are steel belt layers. In addition, although untwisted polyamide monofilament has a higher modulus (stiffness) than steel cord, it has a higher modulus than a twisted cord made of multifilament, so by using a fiber cord belt layer made of polyamide monofilament, By reducing the out-of-plane bending stiffness of the belt layer, ride comfort is improved, and it is also possible to obtain steering stability close to that obtained from two steel belt layers.

Furthermore, since polyamide monofilament does not have capillary action unlike twisted cords, it does not absorb moisture and cause rusting or separation of the steel belt layer.

The present invention will be explained below with reference to embodiments shown in the drawings.

In the pneumatic radial tire for a passenger car shown in FIG. 1, 1 is a tread, and 2 is a sidewall. 3 is a carcass made of fiber cord provided inside the tire, and the cord angle is approximately 90° with respect to the circumferential direction of the tire. This carcass 3 has bead cores 4 at both ends.
It is wrapped around the tire from the inside to the outside.

Between the tread 1 and the carcass 3 there are two belt layers 5.
6 is provided. Of these two layers, the belt layer on the carcass side is a steel belt layer 5 made of steel cord 7.
The belt layer on the tread side is a fiber cord belt layer 6 made of untwisted polyamide monofilament 8 having a flat cross section. In addition, these belt layers 5.6 have their cords crossed with each other, and the angles are 5" to 40 degrees, more preferably 15 to 30" on opposite sides with respect to the tire circumferential direction.
It forms an angle of . As shown in FIG. 2, the polyamide monofilaments 7 having a flat cross section constituting the fiber cord heald layer 6 are arranged in an orderly manner so that the major axis direction of the flat cross section is along the surface direction of the heald layer.

In the above embodiment, both belt layers 5 and 6 are step cut at both ends, and the steel belt layer 5 has a smaller length at both ends than the fiber cord belt layer 6 (both 5ffl).
The width is increased by n+.

However, this is shown in Figure 3 (A), (B), (C).
As shown in FIG. 2, both ends of the fiber cord belt layer 6 are bent inward to form a fallout portion 6a, and the entire width of the fiber cord belt layer after folding is wider than the width of the steel belt layer 5. You can. In FIG. 3(A), the fallout portion 6a of the fiber cord belt layer 6 is bent toward the tread side, but in FIG. 3(B), it is bent toward the carcass side, and furthermore, in FIG.
), the fall part 6a wraps around the end of the steel belt layer 5.

In the present invention described above, since the polyamide monofilament used in the belt layer constitutes the tire cord with only one large diameter polyamide monofilament in an untwisted state, it has a higher modulus than a conventional twisted cord. That is, in conventional twisted cords, a large number of small-diameter multifilaments are twisted together to give the cord convergence and fatigue resistance, but the twisting reduces the modulus. However, in the case of monofilament, since it consists of only one large-diameter filament, twisting for convergence is not necessary, and the non-twisting allows it to exhibit high modulus.

In addition, if the monofilament is not twisted, the fatigue resistance will decrease, but in the present invention, the cross-sectional shape of the monofilament is made flat, and the major axis direction of the flat cross section is aligned with the surface direction of the belt layer. This is to compensate for the decrease in fatigue resistance. That is, with the above arrangement, when the monofilament undergoes bending deformation, the maximum distance from the neutral axis of bending is shortened compared to the case of a circular cross-section cord, so the maximum value of bending strain becomes smaller, and the fatigue resistance described above decreases. can be supplemented.

The fiber cord belt layer made of polyamide monofilament as described above is of course lighter than the steel belt layer, but it is also lighter in weight because the major axis direction of the flat cross section is aligned with the in-plane direction of the belt layer. Since the thickness t (see FIG. 2) after rubberization can be made thinner than when a circular cross-section cord is used, the weight can be further reduced. In addition, by using this fiber cord belt layer, the out-of-plane bending rigidity of the belt layer (stiffness against bending deformation of the belt layer when the tire runs over a protrusion) is improved compared to when both layers are steel belt layers. reduce In addition, by arranging the polyamide monofilaments so that the long axis direction of the flat cross section is along the in-plane direction of the belt layer, the fiber cord heald layer itself has low out-of-plane bending rigidity, so these combine to reduce the stiffness when passing over protrusions. This reduces impact force and improves riding comfort.

In addition, polyamide monofilament has a high modulus, although it is not a steel cord, and by arranging the long axis direction of the flat cross section along the surface direction of the belt layer, the number of cord ends (cord density) can be reduced substantially. It is possible to obtain the same effect as an increase in the number of tires, and in combination with the steel belt layer placed on the carcass side, it is possible to increase the in-plane bending rigidity (stiffness against bending deformation of the belt layer when the tire corners).

Therefore, it is possible to improve the steering stability of the tire while maintaining a balance with the above-mentioned improvement in ride comfort.

In the present invention, in order to exhibit such an effect more markedly, the flatness ratio R (
=longer axis/breadth axis) is 1.5 or more, more preferably 2.
It is desirable to set it to 0 or more. Furthermore, the number of polyamide monofilament ends e in the fiber cord heald layer
It is desirable that (the number of cords per 50 mm in the direction orthogonal to the tire circumferential direction) be 20 min. or more, 150 mm or more, and that the distance W between the monofilaments (see FIG. 2) be 0.1 m+n or more. End number e is 20 knd 150
When it is less than mm, the shared tension per polyamide monofilament becomes large, reducing the original effect of the heald layer. Also, the distance W between the monofilaments is 0
If it is smaller than ゜11Il11, it is not preferable from the viewpoint of durability of the belt layer.

Further, as a means for further enhancing the effects of the present invention described above, the fiber cord heald layer has both ends thereof connected to the third layer as described above.
It is preferable to bend it inward to form a fold structure as shown in Figures (A), (B), and (C). Among these, the structure shown in FIG. 3(A) is particularly preferable.

In the present invention, the polyamide constituting the monofilament is not particularly limited, but polyhexamethylene adipamide (nylon 66), polyepsilon caprolactam (nylon 6), and the like are preferably used.

In addition, in the present invention, the polyamide monofilament used in the fiber cord belt layer weighs 2.25 g when used in a green tire after being treated with an adhesive.
/dThe elongation rate under load is 6.5% or less, and 150
It is desirable that the dry heat shrinkage rate at °C is 4.5% or less. By suppressing the elongation rate after adhesive treatment to 6.5% or less, it is possible to increase the initial modulus of the reinforcing cord used in the fiber cord belt layer and further improve the handling stability of the radial tire. can. Further, by controlling the dry heat shrinkage rate to 4.5% or less, it is possible to suppress a decrease in durability at the end portion due to cord shrinkage during vulcanization molding.

〔Example〕

The belt structure has the following specifications: the belt layer on the tread side has a step structure as shown in Figure 1, and the belt layer as shown in Figure 3 (
For these belt structures, steel belt layers, aramid belt layers, and borerimid monofilament belt layers with the following specifications were used in various combinations as shown in A). A total of nine types of pneumatic tires for passenger cars were prototyped, including the conventional example, Examples 1.2, and Comparative Examples 1 to 6.

The tire size for both was 175/70R13.

(1) Step structure belt layer width on carcass side = 130mm Belt layer width on treading surface = 12On+m (2) Fold structure belt layer width on carcass side = 120o+m Belt layer width on treading surface - 1301III11 foot Width (per side) = 40mm (1) Steel belt layer (1) Steel cord 1 x 5 (0,25) Number of ends
44 threads 150mm Cord angle (relative to the tire circumferential direction) 21° (2) Aramid belt layer: Aramid cord 1500 D/2 Number of ends 52 threads 150mm Cord angle (relative to the tire circumferential direction) 21° (3) Polyamide monofilament Belt layer: Nylon 66 monofilament 4000D Number of ends 20 threads 150mm Cord angle (relative to the tire circumferential direction) 21° ξ belt structure Two-step tread side belt layer Two steel belt layers Carcass side belt layer Two steel belt layers - Belt structure Two-step tread side belt layer: Polyamide monofilament belt layer Carcass side belt layer Two steel heald layers Two steel heald layers Belt structure: Fold Tread side belt layer: Polyamide monofilament root layer Carcass side heald layer Two steel heald layers Earth comparison held structure Two-step tread side belt layer: Aramid belt layer Carcass side belt layer Two-step tread side belt layer 1 Belt structure Two-step tread side belt layer Core aramid heald layer Carcass side heald layer: Aramid helt layer North side group Two-step tread side belt layer: Polyamide monofilament belt layer Carcass side belt layer: Aramid belt layer 1 Soil belt structure Two-step tread side belt layer: Aramid belt layer Carcass side belt layer: Polyamide monofilament belt layer Anti-fog Evert structure Two-step tread side belt layer: Polyamide monofilament belt layer Carcass side belt layer: Polyamide monofilament belt layer Northern base Tread side belt layer Two steel belt layers Carcass side belt layer: Polyamide monofilament belt layer Prototype was manufactured as above 9 The various types of radial tires were subjected to a riding comfort test, a steering stability test, and a belt layer durability test as described below, and the tire weight was measured, and the results shown in the table were obtained.

From the results in the table, it can be seen that the tire of the present invention of Example 1.2 is lightweight and has excellent ride comfort, handling stability, and belt layer durability.

Ride comfort test> A protrusion was fixed on the surface of a rotating drum, and the impact force (reaction force) generated over the protrusion was measured when a prototype tire was pressed against the rotating drum and rotated under the following conditions.

The measured values were expressed as an index with the conventional tire set as 100. The smaller the index, the better the ride comfort.

Air pressure: 1. 9 kg/cffl rim: 13
X5-J Load: 405kg Traveling speed: 60km/h Projection 2 Semicircular projection with radius 10IIIn <Steering stability test> When rotating a prototype tire on the surface of a rotating drum under pressure to give a slip angle under the following conditions. The cornering force generated was measured.

The measured values were expressed as an index with the conventional tire set as 100. The larger the index, the better the steering stability.

Air pressure: 1.9kg/c+a Rim: 13X5-J Load + 405kg Running speed: 10km/h Slip angle: 26 Durability test of held layer> Drill a hole in the trend surface of the prototype tire until it reaches the belt layer, and then drill the hole until it reaches the belt layer. After injecting salt water in advance into the test vehicle, the test vehicle was mounted on a test vehicle of the same model, and the test vehicle was driven on the road under the following conditions, and the amount of separation at the edge of the heald layer was measured after the vehicle was driven.

The measured values were expressed as an index with the conventional tire set as 100. The smaller the index, the better the durability.

Air pressure: 1. 9 kg/cJ Rim: 13X'5-J Travel path M: 110000k Note that the weight is expressed as an index with the conventional tire as 100. The smaller the index, the lighter the weight.

(Margins below this page) (Numbers in the table indicate indexes) [Effects of the invention] As described above, the pneumatic radial tire for passenger cars of the present invention has a steel belt layer on the carcass side as a belt layer in the tread portion. The tire is made up of 24° layers with a fiber cord belt layer made of untwisted flat cross-section polyamide monofilament placed on the tread side, making it lighter than conventional tires consisting of two steel belt layers. Combined with the fact that the polyamide monofilaments in the layer are arranged so that the major axis direction of the flat cross section is along the plane direction of the belt layer, riding comfort and steering stability can be improved in a well-balanced manner. In addition, polyamide monofilament does not have the same capillary action as multifilament twisted cords and absorbs moisture.

Since it does not have a diffusion effect, rusting and separation of the steel belt reinforcing layer can be reduced.

[Brief explanation of drawings]

FIG. 1 is a partially sectional perspective view showing a main part of a pneumatic radial tire for a passenger car according to an embodiment of the present invention, FIG. 2 is a sectional view of a main part of a fiber cord belt layer of the same radial tire, and FIG. Figures (A), (B), and (C) are schematic diagrams showing other examples of belt layer structures, respectively. DESCRIPTION OF SYMBOLS 1... Tread, 3... Carcass, 5... Steel belt layer, 6... Fiber cord heald layer, 7... Steel cord, 8... Polyamide monofilament.

Claims (1)

[Claims] Two belt layers are arranged outside the carcass of the tread portion with their cord directions crossing each other, and among the two belt layers, the belt layer on the carcass side is a steel belt layer, and the belt layer on the tread side is blank. A pneumatic radial tire for a passenger car, in which a fiber cord belt layer is formed by twisting polyamide monofilaments with a flat cross section, and the polyamide monofilaments of the fiber cord belt layer are arranged so that the major axis direction of the flat cross section runs along the surface direction of the belt layer.