JP2604709B2 - Radial tires for passenger cars - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radial tire for a passenger car, and more particularly, to a vibration riding comfort (hereinafter referred to as “shocking property”) and a steering stability (hereinafter referred to as “steering stability”) by improving a ply cord. The present invention relates to a radial tire in which both of the above-mentioned features are improved, and in particular, the resilience at a high speed is remarkably improved.

(Conventional technology) Riding performance and maneuverability are considered the most important basic performances required for radial tires for passenger cars, and other fuel-saving performance, low-noise performance, braking performance when wet, etc. It can be said that it is an incidental performance whose importance differs depending on the purpose and field.

Various researches and developments have been made to improve the basic performance of the rideability and maneuverability.Also, with regard to the incidental performance, improvement measures according to the purpose have been taken by improving the tire structure, rubber quality and the like. Have been.

(Problems to be Solved by the Invention) However, it is very difficult to improve both the swinging property and the maneuverability at the same time, because the swinging property and the maneuverability of the basic performance have a great trade-off factor. Has been considered.

That is, in general, it is desirable to reduce the tire rigidity as a means for improving the riding performance. However, if the tire rigidity is small, the steerability is reduced, and the tire becomes a so-called soft tire. This is because if the tire stiffness is increased, the riding performance is reduced. For this reason, it was not an exaggeration to say that achieving both maneuverability and swinging performance was an eternal issue in tire design.

The trade-off between the above-mentioned oscillating performance and maneuverability is also observed in the ply cord forming the skeleton of the tire.A tire using aramid or the like having a high cord modulus as the ply cord improves the operability, but the shaking is improved. Is reduced,
Tires using nylon or the like having a low cord modulus as a ply cord have improved rideability but have reduced steering stability. In order to specifically show this phenomenon, a test as shown in FIG. 5 was performed. FIG. 5 shows a case where various general-purpose codes are used as ply codes with the same number of shots.
Shows the rideability and maneuverability of each tire. In the figure, the maneuvering stability index is represented by a 6,6-nylon (66N) code, and the vibration riding comfort index is represented by a Kevlar (trade name, Aramid manufactured by DuPont) code as 100. The larger the value, the better. From FIG. 5, it is suggested that it is difficult to achieve a balance between maneuverability and maneuverability only by improving the ply cord, and this means that in the past tire designs, depending on what kind of cord is used as the ply cord. It can be seen that the design flexibility had to be significantly reduced. That is, conventional radial tires for passenger cars are given only the freedom to select general-purpose ply cords such as nylon, polyester, and aramid in response to the above trade-off and maneuverability of handling, and the tires are not provided with the same flexibility. There is a drawback that the use code must be selected from various general-purpose ply cords according to the purpose of use. In other words, heretofore, there has been no means for simultaneously improving and improving both the swinging property and the maneuverability by at least a ply cord.

(Means for Solving the Problems) The inventor of the present invention aims at simultaneously improving both the swaying property and the maneuverability by the ply cord, and aims at improving the swaying property and the operability of the tire with the ply cord. As a result of a detailed study of the relationship, it was found that, under predetermined conditions, it was possible to achieve both stability and oscillating performance by increasing the modulus of the ply cord and reducing the number of shots. Reached.

That is, the present invention includes a tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions formed on the inner periphery of the side portion, respectively, and In a radial tire for a passenger car, which is reinforced with a carcass in which ply cords made of organic fibers are arranged and a belt buried inside the tread portion on the outer periphery of the carcass, the ply cord is made of aramid fiber and polyester fiber The composite fiber cord has a breaking strength S and a modulus M expressed in grams (g) per denier (d), and a value of a ratio M / S of the modulus M to the breaking strength S, S> 8.0 (g / d) M ≧ 78 (g / d) M / S ≦ 15, and the ply cord is applied to the crown center per 5 cm in the tire circumferential direction. The number N of the cords is more than 10 and the number of cords is 30 or less.
And the modulus M have the following relationship: S × N> 240 ((g / d) × (books / 5cm)) M × N ≧ 2340 ((g / d) × (books / 5cm)) The present invention relates to a radial tire for a passenger car.

In the present invention, it is not sufficient that the modulus M (g / d, hereinafter abbreviated) of the ply cord composed of the composite cord of the aramid fiber and the polyester fiber is merely high. For example, if the modulus M of the ply cord is increased while the breaking strength S (g / d, hereinafter omitted) is kept the same, and the number of driving N in the tire circumferential direction at the crown center (N / 5cm, hereinafter omitted) is reduced. The safety factor has dropped,
This is a safety issue for tires. Therefore, it is preferable that the modulus M of the ply cord is proportional to the breaking strength S. For example, if the modulus M is twice the current polyester cord, the breaking strength S is preferably doubled. From the above, in order to maintain the tire rigidity represented by the product M × N of the modulus M of the ply cord and the number of shots N in a predetermined range, the breaking strength S of the ply cord is simultaneously increased with the modulus M of the ply cord. It is necessary to reduce the number N, and if S is less than 8.0 (g / d, omitted below) or S × N
If it is less than 240, the desired effect cannot be obtained.

In addition, in order to improve the vertical axial force and the longitudinal axial force (which will be described in detail later) as factors governing the oscillating property, it is essential to reduce the number of hits N. There must be a smaller number of shots N for some. However, when N is 10 or less, the driving becomes too coarse, and concavities and convexities on the tire side portion are conspicuous, and there are disadvantages in tire molding, such as an increase in the overlap width of the ply joint, and there are practical difficulties. Therefore, it is necessary that the number of shots N is 30 ≧ N> 10.

In general, reducing the number of hits N as described above leads to a decrease in the tire rigidity represented by M × N, but the lower the tire rigidity, the lower the tire stability. At present, it is 6,
6 nylon, polyester, etc. are used, but 6,6 nylon with low modulus M generally has good shaking performance but cannot be said to have sufficient maneuverability. For ply cords with lower modulus than 6,6 nylon, It is difficult to ensure sufficient maneuverability. By the way, in case of nylon tire cord M
× N is approximately 1100 <M × N <1500, and M × N is 23
Tires of less than 40 are not possible because the improvement in steerability aimed at by the present invention is impaired.

Therefore, in the present invention, the modulus M must be high in order to prevent the tire rigidity M × N from lowering even if the number of hits N is reduced as described above. It needs to be. By increasing M in this way, it is possible to improve the high-speed oscillating property, which is one of the features of the present invention.

However, in the case of extremely high modulus such as aramid fiber (M = 350, S = 18), the number of driving cords is required to make the safety factor of the tire equal to that of the current polyester tire cord (M = 65, S = 7.2). It is only necessary to increase N by 0.4 times (18 / 7.2 = 0.4), but in such an aramid ply cord tire with the same safety factor, the equivalent value of modulus M out of tire rigidity M × N is 140 (350 × 0.4) And reached more than twice the current polyester tire cord modulus M65,
This leads to an increase in tire rigidity M × N. For this reason, the effect of improving the longitudinal axial force by reducing the number of shots is also offset by the increase in the vertical axial force (details will be described later), which is a dominant factor in the oscillating performance, and as a result, the effect of improving the oscillating performance Can not. Further, if the tire rigidity is made the same, the safety factor is excessively reduced, which is a problem in tire safety. Therefore, it is reasonable to consider the value of M / S from the above when reducing the number of shots N, where the value of M / S is less than or equal to 15 in balance with the swinging performance, maneuverability, and number of shots N. And preferably the M / S is about 9.

(Action) The present inventor studied the relationship between the ply cord and the tire performance in detail, and obtained the following findings.

First of all, as a result of examining the drivability and shaking performance by greatly changing the denier number and the number of driving N of general-purpose cords such as nylon, polyester, rayon, aramid, etc. It has been found that maneuverability can be significantly improved. That is, as described above, conventionally, it was thought that the rolling property was uniquely determined by the tire stiffness and, consequently, the modulus M of the ply cord. And the effect of reducing the number of shots N or the number of deniers are synergistic, and the wheeling performance is significantly improved without lowering the steerability of the tire.
The following test was conducted in order to further clarify the cause of the effect of improving the shaking property obtained by reducing the number of shots N or making the cord thinner.

In general, the oscillating property of a tire is determined by the sum of vectors of the vertical axial force and the longitudinal axial force applied to the tire. Therefore, a test was performed using the tester shown in FIG. 1 to measure the magnitude of each vector component. The vertical and axial forces, which are the components of each vector, were obtained by measuring the pp values in the figure. A specific method for measuring the pp value will be described in detail in Examples.

Table 1 below shows the relationship between the vertical and longitudinal axial forces and longitudinal axial forces at 40 km / h and 120 km / h, the number of ply cords, the number of deniers, etc., obtained with tires using ply cords of various cord materials. Show. Note that the values of the vertical and axial forces in the table are the indices with the control tire having tire stiffness = 100 (index value) as 100 among tires using 6,6 nylon ply cord. In accordance with the formula in the description of the protrusion overshoot vibration test described later. The tires used for the tests were radial tires for passenger cars and the size was 165SR13
Therefore, tires of the same size were used in various tests described below.

First, as for the vertical axial force, as shown in Table 1, by changing the number of hits N of various ply cords having different moduli, the tire rigidity determined by the modulus M x the number of hits N is set to the same 100 (index). It can be seen that the vertical axial force at a relatively low speed is exactly the same regardless of the material of the ply cord. Also, in the case of a tire rigidity of 50 (index) where the number of shots N is half of each ply cord material, the vertical axial force is the same regardless of the material at 40 km / h, but a tire with a tire rigidity of 100 (index) It can be seen that it is more improved.

On the other hand, paying attention to the vertical axial force at a high speed of 1200 km / hour, the vertical axial force may decrease as the material of the ply cord, that is, the modulus M of the ply cord increases, regardless of the number N of ply cords to be driven. I understand.

In order to further clarify the relationship between the vertical axial force, the number N of ply cords to be driven, and the material as described above, as an example, the size of the 6,6 nylon is large (33.3 / 5cm) and small (16.7 / 5cm). ) And large size of rayon (13.9 pcs / 5cm)
FIG. 2 shows the result of examining the relationship between the vertical axial force and the speed of the tire having a small driving force (7 tires / 5 cm).

As described above, the rigidity of the tire is 6,6 nylon driving large (33.3 pcs / 5cm) tire and rayon driving large (13.9 pcs)
/ 5cm) tires are the same. Nylon (16.7 // 5cm) tires and rayon (7/5)
cm) tires have the same tire stiffness.

As can be seen from FIG. 2, in the low-speed range of 80 km / h or less, the vertical axial force depends on the tire rigidity regardless of the material of the ply cord, and the higher the tire rigidity (the larger the number of hits), the larger the vertical axial force. The lower the tire rigidity (the smaller the number of hits), the smaller the vertical axial force. Also, 80
At a running speed of less than Km / hour, a decrease in the vertical axial force due to a reduction in tire stiffness due to a reduction in the number of hits by half was generally recognized for each ply cord. These test results support the test results shown in Table 1. Therefore, it can be seen that the tire stiffness can be improved in the swinging property involving the vertical axial force component in the low speed range of 80 km / h or less. However, in the high-speed region exceeding 80 km / h, the modulus of the ply cord determines the vertical axial force irrespective of the tire rigidity, and this test result also supports the test result of Table 1, and therefore, in the case of a rayon cord having a high code modulus M, the result is as follows. Irrespective of the number of hits N, the oscillating property involving the vertical axial force component at high speed is improved.

Next, from Table 1, tire rigidity = 10
In both the cases of 0 and 50, and in the case of both speeds of 40 km / h and 120 km / h, the axial force decreases as the modulus M of the ply cord increases, and the degree of the decrease does not change at both speeds. It can be seen that 50 has a slightly larger tendency. Among these, the point that the longitudinal axial force at a speed of 40 km / hour decreases as the modulus M of the ply cord increases becomes a significant difference from the vertical axial force described above.

Therefore, the longitudinal axial force shown in Table 1 will be examined in more detail from one side of the number of hits N. As an example, two types of tires of 6,6 nylon with the number of hits of 33.3 / 5cm and 16.7 / 5cm are used. FIG. 4 (a) shows the result of measuring the axial force pp value. From this figure, it can be seen that when the number N of hits is reduced, the front-rear axial force decreases in the entire speed range shown, and the front-rear axial force is proportional to the number N of hits.

FIG. 4 (b) shows the relationship between the longitudinal axial force at a speed of 40 km / h, the ply cord material and the number of shots N in FIG. 4 (a). From this figure, it can be understood that the longitudinal axial force is determined by the number N of shots regardless of the material of the ply cord.

As described above, from Table 1 and FIGS. 4 (a) and 4 (b), the reduction of the longitudinal axial force from the low speed region to the high speed region is due to the product M × N of the modulus M of the ply cord and the number of shots N. It is advantageous to make the modulus M as high as possible and to reduce the number of shots N as much as possible, and to make the value of the product M × N as small as possible when the tire rigidity determined by Clarified.

In consideration of this longitudinal force and the vertical force described above,
The oscillating properties determined by the magnitudes of the vector sums of these two axial forces are, in the end, to make the modulus M of the ply cord as high as possible and the number of shots N as small as possible in the low to high speed range. By making the value of × N as small as possible, it is possible to greatly improve.

In a tire with a small number of driving N, the rubber layer between the cords reduces input in the tire longitudinal direction during rotation of the tire, thereby lowering the longitudinal axial force. The same result can be obtained even if the denier number of the ply cord is reduced without changing the number N of shots. Therefore, it can be said that the longitudinal force is controlled by the ratio of the rubber layer of the ply cord to the ply cord.

Actually, when the deformation of the tire during high-speed rotation exceeding 80 km / h was measured with a stereo camera, the tire using a ply cord made of nylon or the like with a low modulus M had large side deformation, and the tire width at the time of contact with the ground It has been found that the amount of side protrusion in the direction is significantly uneven, and that the vibration of the side portion is random and large. On the other hand, it was clarified that a tire using a ply cord such as Kevlar or rayon having a high modulus M had a small amount of protrusion in the side tire width direction such as a rotating ground, and a uniform vibration waveform.

From the above, at the time of high-speed rotation, the influence of the number of hits N is small and the modulus M of the ply cord directly governs the vibration of the tire size part. As a result, in the high modulus cord, the uniform overhang of the side part is a kind of force transmission function. On the other hand, in tires using ply cords with low modulus, force transmission is not eased due to the generation of random vibration waveforms on the side parts, and therefore vertical input during contact with the ground is directly detected as tire axial force. Can be considered.

In terms of maneuverability, tires with the same tire stiffness show almost the same performance in all speed ranges regardless of the ply cord material. The code was recognized in common. This means that the tire rigidity shown in FIG.
It can be confirmed by the relationship between the maneuverability and the number of driving N in a tire selected by combining the number of driving N with the ply cord material so that the same is obtained at the two levels. Third
In the figure, in the case of a tire having a maneuverability index of 100, when a cord having a high ply cord modulus M is used, the number N of cords of the tire is reduced. Number of cords N
And the so-called tire stiffness is made the same. On the other hand, in the tire having the maneuverability index of 92, the number N of the ply cords of each material is reduced by half, and the so-called tire stiffness is reduced to half that of the tire having the maneuverability index of 100.

The present invention has been made on the basis of the above-described study results, and has made it possible to achieve both excellent shaking performance and maneuverability which have been considered impossible with the improvement of the ply cord in the past. That is, it is advantageous to increase the modulus M of the ply cord as much as possible and to reduce the number of shots N as much as possible and / or to reduce the value of the product M × N in order to improve the shaking performance. Needless to say, there is a limit in terms of maintaining stability, so that the modulus M is set to 78 or more, and the number of driving N is set to more than 10 and less than 30 per 5 cm in the tire circumferential direction at the crown center portion of the ply cord, Further, by providing a ply cord having a product M × N value of 2340 or more, a radial tire for a passenger car can be provided which is capable of significantly improving the swaying performance while maintaining excellent steering stability. You can do it.

Further, as described above, by setting the breaking strength S to a value exceeding 8.0 and the M / S value to 15 or less, an appropriate safety factor, excellent shaking performance, and maneuverability of the radial tire for a passenger car can be obtained. Can be realized.

When the modulus M is less than 78, the modulus M of the ply cord and the breaking strength S preferably increase and decrease in proportion to each other in the present invention. It is not possible to use the number N of shots because the shaking performance is reduced.

(Examples) Next, the present invention will be described based on examples and comparative examples.
The radial tire for passenger cars in each case is size 165SR13
It is.

In the present example and the comparative example, the ply cord was prepared by changing the material and the number of twists of the ply cord and the ply twist, and the modulus M and the breaking strength S of the ply cord were measured, respectively. Next, using these ply cords, tires having different numbers of hits N were trial-produced, and the tire safety factor index of the control and the vertical axial force index and the front-rear axial force index of the control at speeds of 40 km / h and 120 km / h (shock) Sex index)
I asked. In addition, the maneuverability of these tires was indexed by the so-called cornering power, and at the same time, an actual vehicle feeling test was conducted to index the actual vehicle feeling in comparison with the control. Further, in order to examine the unevenness of the tire side portion due to the decrease in the number of hits, the unevenness of the side portion of each tire was measured using a surface roughness meter.

 Hereinafter, a specific method of the above-described test will be described.

(A) Measurement of ply cord breaking strength and modulus According to JIS L 1017, the ply cord was brought to room temperature by an autograph, and the tensile breaking strength S of the ply cord collected from the center of the tire crown was determined. The modulus M is plotted on the vertical axis with the load (g / d), and on the horizontal axis, the SS curve of the ply cord is calculated by dividing the elongation (%) by 100. When the load is 2.25 g / d, From the curve on the curve and the origin of the SS curve.

In addition, the denier number used the original yarn denier before twisting. This is to avoid complication due to a change in denier due to a change in cord length due to twisting, dipping and shrinkage during tire vulcanization.

(B) Tire safety factor index The ply cord collected from the tire is pulled in accordance with the item (a), and the product of its breaking strength S and the number N of hits per 5 cm width in the circumferential direction of the tire crown center portion is obtained as a control tire 100. Indexed. A tire having a larger breaking strength S or a larger number of hits N has a larger tire safety factor index, and thus has improved safety.

As shown in FIG. 1 (c) projection Norikoshi vibration test, iron protrusion (upper base 19 mm, the lower base 38mm, height 9.5 mm) were fixed in one location on the drum outer diameter 2000 mm, the inner pressure 1.70 kg / cm ² Test tire adjusted to 395 kg load
After pre-running at a speed of 80 km / h for 20 minutes,
The internal pressure under no-load conditions readjusted to 1.70kg / cm ^2, 20Km speed
The load was adjusted to 395 kg / h, and thereafter, the speed was increased every 5 km / h, and at each speed, the average waveform of the variation in the load on the fixed shaft of the tire at the time of passing over the protrusion was calculated, and the pp value was calculated. Note that p
The -p value is an amplitude from the maximum value to the minimum value of the fluctuation amplitude of the tire shaft load when the vehicle goes over the protrusion as is apparent from FIG.

The axial load fluctuation direction of the tire fixed shaft when riding on the protrusion is measured in two directions, the tire traveling direction (front-back direction) and the tire vertical direction, and the respective axial forces are measured. As representative values, the speed is 40 km / hour and 120 km / hour. The vertical and vertical axial forces and the longitudinal axial force are indexed. In addition, indexing is 10 for control tires.
It was indicated by the following equation as 0.

For indexing, the test tire pp value is the control tire p
The smaller the value is compared to the -p value, the larger the index is, and the larger the index is, the better the oscillating property is.

(D) Maneuverability A test tire adjusted to an internal pressure of 1.70 kg / cm ² was placed on a drum with an outer diameter of 2500 mm, and after a load of 395 kg was loaded, it was preliminarily run at a speed of 30 km / h for 30 minutes. 1.70kg internal pressure
/ cm ² was readjusted, and a 395 kg load was applied again, and positive and negative slip angles were continuously applied on the drum at the same speed up to a maximum of 14 °. Measure the corner linag force (CF) at each positive and negative angle, and calculate the following formula: The cornering power (CR) was determined at.

The index was calculated by dividing the CP of each test tire by the CP of the control tire to obtain an index, and the control tire was set to 100. The larger the index, the better the maneuverability.

(E) Side unevenness Using a surface roughness meter, unevenness in the tire circumferential direction at the tire side portion (the maximum width position in the radial direction) was measured over the entire circumference.
The tire was adjusted to an internal pressure of 2.5 kg / cm ² in a room at a temperature of 25 ± 2 ° C., allowed to stand for 24 hours, readjusted the air pressure, and measured. When this measured value is 0.50 mm or more, the internal pressure is 1.70 kg / cm ²
Occasionally, there is a problem in appearance in which unevenness on the side is sufficiently visually observed. Therefore, a tire having an inner pressure of 2.5 kg / cm ² and an unevenness of 0.5 mm or more was made large in side unevenness.

The test results obtained for the tires manufactured in the following Examples and Comparative Examples according to the above test methods are summarized in Table 2 described later. In the table, the size of the side unevenness is indicated by a mark x.

Comparative Examples 1 and 2 The raw yarn for a tire cord of 1500 denier made of normal polyester was twisted into a twist, a bottom twist, and 40T / 10 cm, respectively.
The tire used as a control was this double-twisted cord used as a ply cord, with 36 cords / 5 cm being driven in the circumferential direction of the crown center portion.

The tire of Comparative Example 1 is exactly the same as the tire currently on the market.

In Comparative Example 2, the number of tires of Comparative Example 1 was 36/5 cm.
It is reduced to 30 pieces / 5cm.

As is clear from Table 2, the tire of Comparative Example 2 has a reduced tire safety factor index and has a problem in safety. The vertical force at low speeds (50 km / h) was improved, but the stability was reduced.

Example 1, Comparative Example 3 A 1500 denier polyester yarn was twisted at 40 T / 10 cm, and a 1500 denier aramid yarn was 50 T / 10 cm.
A ply cord was prepared by twisting the two strands with a twist of 41 T / 10 cm and then twisting the two strands to form a ply cord. The modulus M and the breaking strength S when the ply cord was removed from the tire were 78 and 8.6, respectively, as shown in Table 2.

Example 1 is a tire in which this ply cord is used in the circumferential direction of the crown center portion with the number of driving 30 pieces / 5 cm, and the number of driving is reduced by the increase of the modulus M of the ply cord and the breaking strength S.

As apparent from Table 2, the longitudinal force was improved by reducing the number of hits N and the vertical force at high speed was increased by increasing the cord modulus M without impairing the steering performance.

In Comparative Example 3, since the ply cord was used with the same number of indentations of 36 pieces / 5 cm as in Comparative Example 1, the vertical axial force at 40 km / h was increased by the increased tire stiffness, and the actual vehicle feeling index in the riding performance Decreased.

Comparative Example 4 1500 d / 2, 40 × 40 T / 1 of the polyester cord of Comparative Example 1
The condition of 0 cm was changed to 1500d / 2, 32 × 32T / 10cm, and a cord that had been subjected to a tension heat treatment to just before the yarn breakage during dipping was used as a ply cord.

Since the modulus M of the ply cord was increased by the reduction in the number of twists and the increase in stress due to the dipping treatment, the tire safety factor index became equal to that of the control, but the tire rigidity was improved and the shaking performance was reduced.

Example 2, Comparative Example 5 A 1500 denier polyester yarn was twisted at 35 T / 10 cm, and a 1500 denier aramid yarn was 42 T / 10 cm.
A ply cord was obtained by twisting the two strands with a twist of 38 T / 10 cm, and then applying heat treatment at 240 ° C. after applying an adhesive by a conventional method. The modulus M and the breaking strength S when the ply cord was removed from the tire were 91 and 10.1, respectively, as shown in Table 2.

Example 2 is a tire in which the ply cord is used in a number of 26 // 5 cm in the circumferential direction of the crown center portion. The safety factor index of this tire is 100 as shown in Table 2,
It also reduces the number of shots and the ply cord modulus M
Due to the increase in the speed, the choking performance at both low speed and high speed was greatly improved.

On the other hand, in Comparative Example 5, since the ply cord was used with the same number of injections as that of the control of Comparative Example 1 at 36 yarns / 5 cm, the longitudinal force was increased due to an increase in the number of injections N,
As a result, the shaking property was reduced.

Examples 3 and 4, Comparative Examples 6,7 A polyester yarn of 1500 denier was subjected to a 26 T / 10 cm sub-twist, and a 1500 denier aramid yarn was 26 T / 10 cm.
A double-twisted cord obtained by twisting both yarns with a twist of 20 T / 10 cm was used as a ply cord, and a heat treatment was performed at 240 ° C. after applying an adhesive by a conventional method. As shown in Table 2, the modulus M and the breaking strength S when the ply cord was removed from the tire were 130 and 14.4, respectively.
Met.

In Examples 3 and 4, the number of such ply cords was 30 and 5 cm and 19 and 5 cm, respectively, in the circumferential direction of the crown center portion.
The tires used in

In the tires of Examples 3 and 4, the vertical axial force at 40 km / h was slightly reduced as compared with the control due to a slight improvement in tire rigidity. However, since the front-rear axial force was improved, the actual vehicle feeling index was improved, and the handling was also improved.

On the other hand, in Comparative Example 6, the number of the ply cords was 36
The number was equal to the number of tires of the control / 5cm. For this reason, the rigidity of the tire became too high and the oscillating property was lowered.

In Comparative Example 7, the number of shots was set as low as 15/5 cm, so that the tire safety factor index was reduced and the tire rigidity was insufficient, resulting in inferiority to the control.

Comparative Examples 8 to 10 Each of the aramid yarns was twisted to 32T / 10cm for both the upper and lower twists, and the double-twisted cord was used as a ply cord in the circumferential direction of the crown center at 30,15 and 10 / 5cm. The tires used were Comparative Examples 8 to 10, respectively.

In all of these tires, the cord modulus M was too high, so that the balance between the tire rigidity and the safety factor was poor, and it was not possible to achieve a balance between riding and maneuverability.

Example 5, Comparative Example 11 1500 denier aramid yarn was subjected to 40 T / 10 cm ply twist, and 1500 denier polyester ether yarn.
In the case of Example 5, both of the twiddles of 40T / 10cm were twisted to 40T / 10cm.
In the case of Comparative Example 11, a two-ply cord was obtained by twisting 10 cm and twisting it by 32 T / 10 cm.

In Example 5, the ratio M / S between the modulus M and the breaking strength S of the obtained cord was 14.0. Tires using such cords as ply cords with the number of shots of N30 were inferior to the control in the vertical axis force, but the actual vehicle feeling index was equivalent to the control due to the effect of improving the front and rear axial force by reducing the number of shots. .

On the other hand, in the tire using the cord obtained as Comparative Example 11 as the ply cord with the same number of shots, the decrease in the vertical axial force index of 40 km / hour cannot be covered by the improvement of the longitudinal axial force, and therefore, the actual vehicle feeling index Was slightly inferior to the control. At this time, the M / S value of the ply cord was 16.3.

The embodiments of the present invention are not limited to the above, and when new fibers that satisfy the conditions of the present invention appear, these fibers can be replaced with the above-described composite fibers.

(Effect of the Invention) As described above, the radial tire for a passenger car of the present invention is considered to be extremely difficult to achieve compatibility by increasing the modulus of the ply cord under a predetermined condition to reduce the number of hits. It is possible to improve both the swaying performance and the maneuverability, and the effect of remarkably improving the swaying performance particularly at high speed is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a protrusion overshoot vibration test, FIG. 2 is a diagram showing a relationship between vertical axial force and speed measured using ply cord materials and tires having different tire rigidities, and FIG. FIG. 4 (a) is a diagram showing the relationship between the steerability index and the number of shots of tires using various ply cords. FIG. FIG. 4 (b) is a diagram showing the relationship between the measured longitudinal axial force and the speed, FIG. 4 (b) is a diagram showing the relationship between the longitudinal axial force and the ply cord material and the number of shots in FIG. 4 (a), The figure is a diagram showing the relationship between the swingability and controllability of each tire and the modulus index of the ply cord when various general-purpose cords are used as ply cords with the same number of shots.

Claims (1)

(57) [Claims] 1. A tire comprising: a tread portion; a pair of side portions connected on both sides of the tread portion; and a pair of bead portions formed on an inner periphery of the side portion, respectively. A carcass in which ply cords composed of organic fibers are arranged, and a radial tire for a passenger car which is reinforced with a belt buried inside a tread portion on the outer periphery of the carcass, wherein the ply cords are aramid fibers and polyester fibers. And the ratio of the modulus (M) to the breaking strength (S) of the composite fiber cord, expressed in grams (g) per denier (d), and the modulus (M) to the breaking strength (S) ( M / S) satisfies the relationship of S> 8.0 (g / d) M ≧ 78 (g / d) M / S ≦ 15, and the ply cord is in the tire circumferential direction at the crown center. The number of hits per 5 cm (N) in the array is more than 10 and 30 or less, and the number of cords (N) and the breaking strength (S) and modulus (M) are S × N> 240 ((g / d) × (book / 5cm)) M × N ≧ 2340 ((g / d) × (book / 5cm)) A radial tire for a passenger car, characterized by having the following relationship.