JPS6112406A - Radial tire - Google Patents

Abstract

PURPOSE:To reduce the amount of steel cord thus to reduce the weight by coating specific coat rubber over the steel cord in belt layer while setting the tensile resiliency factor of organic fiber cord in carcass to specific level. CONSTITUTION:A carcass 2 composed of organic fiber cords is arranged in parallel with the meridian cross-section of tire while a belt layer 3 composed of rubbered steel cord is arranged between the carcass 2 and the tread 1. Here the steel cord in the belt layer 3 is coated with rubber coat having has the breakdown strength F(kg) defined by the formula I (where, n: number of strands, d: diameter of strand mm.) and 50% modulus within the range of 10-40kgf/cm<2>. The organic fiber cords in the carcass 2 are set such that the tensile resiliency factor of single cord will be higher than 1,800kgf/mm.<2>. With such arrangement, the purpose can be achieved without deteriorating the steering stability and the fuel consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radial tire that is significantly lighter in weight without reducing the steering stability and fuel consumption efficiency of the tire.

[Prior art]

Steel radial tires have two to four layers of unidirectionally reinforced composite material made of metal cords and reinforcing rubber placed on the belt layer to increase the rigidity of the tread, resulting in excellent maneuverability and wear resistance.

Demonstrates low fuel consumption.

However, since the specific gravity of the steel cord used for the belt layer is approximately 7.86, which is significantly higher than that of rubber or organic fiber reinforcing materials, the centrifugal force generated by high-speed rotation of the tire is significantly large, resulting in peeling between the belt layers. tends to occur. For this reason, especially in tires used for high-speed running, in order to overcome the centrifugal force that occurs due to high-speed rotation and to obtain circumferential properties of the belt layer, the amount of metal cord used increases further, resulting in a vicious cycle. To maintain balance, steel radial tires used for high-speed driving require a large amount of metal cord. Further, the large amount of metal cord used in the belt layer is disadvantageous in terms of uniformity during tire rotation. Furthermore, increasing the amount of steel cord used increases the weight of the entire tire and fuel consumption, which is undesirable. For this reason, attempts have been made in the past to reduce the amount of steel cord used.
As stated in Publication No. 03, the tensile strength of the steel cord is increased by increasing the carbon content of the steel cord,
As a result, the amount of steel cord used can be reduced while maintaining the durability of the cord.

However, steel cords with increased carbon content have problems as can be seen from FIGS. 2 and 3. That is, as shown in Figure 2, when comparing the stress-strain curves of steel cords with a carbon content of 0.82% by weight and a carbon content of o, 72% by weight, the strength at break is determined by the carbon content. Although the elastic modulus increases as the strain increases, it is difficult to find a difference between the two in terms of the elastic modulus in the straight line portion where the strain is 0% to 1.5%.

Since the strain imposed on the metal cord in the belt layer during normal running is less than 1.0 inch, steel cords with a high carbon content have no advantage during normal running.

Further, FIG. 3 shows the relationship between the amount of steel cord used and cornering power, and it is clear that reducing the amount of steel cord used causes a decrease in belt rigidity and reduces cornering power.

Therefore, if we try to reduce the amount of cord used only by using steel cord with high carbon content,
The belt circumferential rigidity clearly decreases, leading to a decrease in the transverse spring constant, resulting in a decrease in steering stability.

Furthermore, while reducing tire weight generally reduces transfer resistance and improves fuel consumption, reducing tire weight by reducing the amount of steel cord used increases the movement of the belt layer during driving. Therefore, there were problems such as worsening resistance to transfer and lowering fuel consumption efficiency.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lightweight radial tire that reduces the amount of steel cord used without reducing the handling stability and fuel efficiency of the steel radial tire.

[Structure of the invention]

For this reason, the present invention provides a radial tire comprising a carcass made of organic fiber cords arranged parallel or substantially parallel to the meridional section of the tire, and a belt layer made of rubberized steel cords arranged between the carcass and the tread. In the tire, (1) the steel cord of the belt layer:
(a) Breaking strength F (Kgf) is 195 X rI X (11,872≦F≦225
A cord that is within the range of X n The tire is coated with rubber, and (2) the organic fiber cord of the carcass has a tensile modulus of elasticity of 1800 Kff/ld or more per cord.

In addition, here, the tensile elastic modulus E of one organic fiber cord is
is the value measured in accordance with JISL1017 J Chemical Fiber Tire Cord Testing Method, Sections 7 and 8, Initial Tensile Resistance Measurement Method, and the tensile conditions are: grip interval 20crIL
1 tensile rate is 10 cIrL/min.

Hereinafter, the present invention will be specifically explained based on the drawings.

FIG. 1 is an explanatory diagram of a meridional cross section of an example of the radial tire of the present invention, in which 1 is a tread, 2 is a carcass of radial structure in which cords are arranged parallel or almost parallel to the meridional cross section of the tire, and this carcass 2 and A belt layer 3 made of rubberized steel cord is arranged between the treads 1 so as to surround the outer periphery of the carcass 2.

The carcass 2 usually consists of one or two organic fiber cords/rubber coverings, and the organic fiber cords are usually made of nylon or polyester fibers. Further, it is sufficient that at least one belt layer 3 is disposed,
In addition, the steel cord that makes up the belt layer 3 is usually 3~
It consists of 12 steel filaments.

In the present invention, the carcass 2 and belt layer 3 are defined as follows.

(1) Regarding belt layer 3: (al Tensile breaking strength per steel cord F(
Kri f/code) is 195 X n X d18”≦F≦225 X n
Must be within the range of X d1872. However, n: the number of strands composing the code.

d: Diameter (mm) of the wire composing the cord.

The reason for determining F in this way is as follows.

In other words, tires generally act as pressure vessels that hold high-pressure air inside and support the load of the automobile, so it is desirable for safety to reduce the internal pressure and the breaking strength of the fiber-reinforced material that supports the load. It's not a thing.

Therefore, as a result of research on the breaking strength of steel cords, the present inventor found that the breaking strength F of steel cords depends on the diameter d of the strands that make up the steel cords, and naturally, the breaking strength F of steel cords depends on the diameter d of the strands that make up the steel cords. It depends on the number n, and the breaking strength F (K9f
) has a diameter d of 0.06 to 0.45III! It has been found that the following formula is satisfied in a normal single-strand tire steel cord having a number of strands n of 3 to 28 and a twist pitch of 8.0 to 20.

F=kX. x dl, 872 is a constant that depends on the steel wire, and in the case of a steel cord for normal tires, k = around 175.

By the way, in order to reduce the weight of tires, it is necessary to increase the value of k to 195 to 225.

In addition, measures to increase the breaking strength include (a) increasing the carbon content, (b) increasing the degree of wire drawing, and (c) adjusting the putting temperature, or a combination of these. I can do it. However, the value of k is 225
If it is increased beyond this value, internal cranking is likely to occur during wire drawing, and it is also unfavorable in terms of fatigue resistance. Therefore, as mentioned above, the cord breaking strength F (Kgf/cord) that achieves weight reduction and does not reduce durability must be within the following range.

195×nXdI872≦F≦225 X n X d
Note that the steel cord used in the tire of the present invention may be either a closed cord or an open cord.

(b) The 50% modularity and X value M (K9f/crI) of the rubber surrounding the steel cord is in the range of 10≦M≦40.

The reason for this is that the 50% modulus of the coated rubber is 9 to 10.
In the region below f/7, the so-called belt edge separation resistance decreases due to the increase in strain at the belt edges.On the other hand, when the 50 thymodules of the coated rubber increases to 40Kff/di or more, the belt layer deteriorates as it runs. This is because the steel cord tends to buckle when subjected to compressive force, which is unfavorable in terms of tire durability.

(2) Regarding carcass 2: The tensile modulus of one organic fiber cord is 1800 Kyf
/md or more.

As mentioned above, even if the breaking strength of the steel cord is increased to ensure safety as a pressure vessel, the modulus of elasticity will not increase, so if the amount of cord used is reduced by an amount commensurate with the breaking strength, the belt rigidity will decrease. , the transverse spring constant decreases, resulting in a decrease in steering stability, and the movement of the belt layer increases, resulting in a decrease in fuel consumption efficiency.

Therefore, a means is needed to compensate for the decrease in belt rigidity and ensure the total rigidity of the tire. Table 1 in the experimental examples described later shows the steering stability and steering stability of prototype tires by varying the tire stiffness by varying the carcass cord/belt cord combination.
The results of evaluating the fuel consumption rate show that the breaking strength F (Kpf) is 195 X n X d1872≦F≦
225 X n It was concluded that weight reduction could be achieved without reducing the consumption rate.

The reason why the tire of the present invention exhibits such characteristics is that the total rigidity as a radial tire is ensured by the combination of the belt cord and carcass cord, so the contribution rate of the belt rigidity becomes small. Conceivable.

〔Effect of the invention〕

As explained above, according to the present invention, the steel cord of the belt layer has the following properties: 195 X n X d18'''≦F≦225 X n
Using a high-strength steel wire material of
In addition to the above, since we used a coated rubber whose 50% modulus value M (K9fβ) of the rubber surrounding the steel cord was 10≦M≦40, handling stability and
It is possible to reduce tire weight without reducing fuel consumption.

Experimental examples are illustrated below.

Experimental Example Table 1 shows the results of this experiment. Tire size is 1655R
130 passenger car tire (the cord used for the belt layer has a 1×5 structure, and the twist pinch is 9.5 mm).

There are various evaluation methods for the steering stability of tires, but here we have used cornering power as a substitute characteristic.

The test conditions are shown below.

Internal pressure: 1.9 f/7 Load: 420 Kqf Slip angle: 2° to 4° Rim: 4 J-13 Evaluation is expressed as an index when tire number 6 is set as 100, and the larger the number, the better. It has large cornering power and high maneuverability.

Next, regarding the fuel consumption rate, a test was conducted under the following conditions using a rolling resistance of 1η obtained by an indoor drum test as a substitute characteristic.

Internal pressure: 1.9 Kqf/cr/1 Load: 420 Nirf Speed: 40 KrrV/h to 130 Km/h Average evaluation is
It is expressed as an index when tire number 6 is set as 100, and the larger the number, the greater the transfer resistance and the poorer the fuel consumption rate.

Based on the above-mentioned evaluation method, evaluation was performed on tires with tire numbers 1 to 6.

Tire numbers 1 and 2 correspond to examples of the present invention, and it can be seen that weight reduction can be achieved without impairing the characteristics in terms of both steering stability and fuel consumption rate.

On the other hand, as seen in tire numbers 3 and 4.5,
If the belt cord is simply replaced with a high-strength steel cord, not only will the steering stability deteriorate, but the fuel consumption rate will also decrease.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a meridional cross section of an example of the radial tire of the present invention, Fig. 2 is a diagram showing the relationship between elongation rate (chi) and load (Kqf) due to differences in carbon content of steel cords, Fig. 3 FIG. 3 is a diagram showing the relationship between code usage and cornering power. 1...Tread, 2...Carcass, 3...Belt layer.

Claims (1)

[Claims] A radial tire comprising a carcass made of organic fiber cords arranged parallel or substantially parallel to the meridional cross section of the tire, and a belt layer made of rubberized steel cords arranged between the carcass and the tread, (1) the above-mentioned The steel cord of the belt layer has (a) breaking strength F(K
gf) is 195×n×d^1^. ^8^7^2≦F≦2
25×n×d^1^. ^8^7^2 (n: number of strands composing the cord, d: diameter of strands composing the cord (mm)
)) and (b) 50% modulus is 10 to 4.
(2) The organic fiber cord of the carcass has a tensile modulus of elasticity of 1800 Kgf/mm^2 or more per cord. tire.