JP2001233014A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having various improved characteristics on a high level such as maneuvering stability, riding quality against vibration, the side appearance of a tire, and uniformity. SOLUTION: In a pneumatic radial tire having a carcass 2 comprising at least one of plies formed by radially disposing cords between a pair of beads 1 as a skeleton, the carcass is an annulus body comprising plies formed by rubberizing a large number of polyester fiber cords and having no overlapping joint of the cords in the circumferential direction of the tire, the intermediate percentage of elongation of the polyester fiber cord under a loaded condition and the percentage of dry heat contraction under a loaded condition are numerically restricted, and the bead core is structured by laminating layers formed by spirally winding a rubber coated wire having a restricted diameter side by side and one by one on the outside in its radius direction, by restricting a distance between the axial centers of adjacent wires in a cross section in a tire width direction, and by having one more wire arranged side by side in a second layer on the furthest inside than those in a first layer.

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, in which the carcass ply cord and the bead core are both improved in synergy, without impairing the steering stability of the tire, the vibration comfort of the tire and the tire. The present invention relates to a pneumatic radial tire having simultaneously improved side appearance and uniformity characteristics.

In recent years, the performance required for passenger car tires has become stricter. In particular, tires to be mounted on luxury-oriented passenger cars have not only improved handling stability and vibration riding comfort, but also
Uniformity necessary to suppress vibration and blurring that occur when the tire is uneven (collapse from roundness, etc.)
It is required to improve each of the smoothness of the side portions that are conspicuous in the tire appearance.

[0003]

2. Description of the Related Art It is well known that the basic performance of a tire, such as steering stability and vibration riding comfort, is greatly affected by the performance of a carcass serving as a skeleton of the tire. Conventionally, nylon fiber cords and rayon fiber cords have been used for carcass plies of pneumatic radial tires, especially pneumatic radial tires for passenger cars. However, nylon fiber cord has low elasticity, high dry heat shrinkage rate, and high creep limit.If nylon fiber cord is used for carcass ply, dimensional stability of tire is hindered,
Also, nylon has a flat spot problem,
Its usage tends to decrease. In addition, the flat spot means that the tire generates heat by running, stops running with the carcass ply cord stretched, and when the tire cools down after a certain period of time, only the part that was in contact with the tire's road surface, A phenomenon in which vibration is generated when running is started again as a result of the cord being held in an extended state.

On the other hand, rayon fiber cords have lower strength than nylon fiber cords. Therefore, when tires are manufactured based on the design of tire safety strength, the amount of cords used must be increased, and as a result, the weight of the tires increases. , And undesirably results in various performances such as rolling resistance. In addition, since the raw material is pulp, there is concern about future supply.

In recent years, by using polyester fiber cords having excellent dimensional stability and high strength in place of these fiber cords, handling stability and vibration comfort have been improved particularly in the field of pneumatic radial tires for passenger cars. Significant improvements in basic performance such as gender have been made.

On the other hand, characteristics such as the appearance and uniformity of the tire side are affected by the characteristics of the bead portion, especially the characteristics of the bead core. Conventionally, a so-called strand bead has been used for this bead core, in which a plurality of wires are arranged in parallel, rubber-coated and formed into a plate shape, and a rubber-coated wire is formed by winding several times and winding.
However, the bead core has end portions at the beginning and end of winding of a plate-shaped rubber-coated wire, and a nonuniform rigidity step always occurs on the circumference. As a result, vibration and blurring during running were caused. In addition, in order to rubber coat a plurality of wires at a time, in the tire width direction cross-section of the bead core, between the adjacent layers of the plate-shaped rubber coating wire wound in a pile, the wires are arranged to overlap in the radial direction, so the tire The cross-sectional shape of the bead core is likely to collapse at the time of manufacturing, and as a result, it causes vibration and blur during traveling as in the above.

In recent years, by using a bead core formed by spirally winding a single rubber-coated wire on the strand bead, non-uniformity on the periphery of the bead core has been improved. This bead core structure
It is possible to arrange the wires in a densely packed arrangement in the cross section of the bead core, thereby avoiding the shape collapse during tire production and suppressing vibration and runout during running.

[0008]

SUMMARY OF THE INVENTION Steering stability of tires,
The application of the above-mentioned polyester fiber cord to the carcass ply and the application of the bead core structure by winding a single wire are effective for vibration comfort, tire side appearance and various properties of uniformity, but are merely effective. By combining these, it has been difficult to achieve the above four characteristics at the same time, and at a level that sufficiently satisfies the requirements for tires to be mounted on high-grade passenger cars.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic radial tire in which the steering stability, vibration comfort, tire side appearance and uniformity are all improved to a high level. It is in.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies focusing on the joining method of the carcass ply, the physical properties of the carcass ply cord, and the cross-sectional structure of the bead core. It has been found that by making it appropriate, it is possible to simultaneously satisfy the desired tire characteristics, and the present invention has been completed.

That is, the gist of the present invention is as follows. (1) In a pneumatic radial tire having a carcass composed of at least one ply of cords arranged in a radial direction between a pair of bead cores as a skeleton, the carcass has rubberized a number of polyester fiber cords, The polyester fiber cord has an intermediate elongation of 4 to 6% under a load of 1.98 cN / dtex, and 177 under an initial load of 50 g. C. and a dry heat shrinkage rate of 2.5% or less at 30 minutes, and a sum of the intermediate elongation rate and the dry heat shrinkage rate of 7.0% or less, and a bead core having a diameter of 1.2 to 2.2 mm. A layer in which one of the rubber-coated wires is spirally wound in parallel in a spiral pattern is sequentially laminated on the outer side in the radial direction, and the layer is formed in the tire width direction cross section of the bead core. The distance between the axial centers of adjacent wire portions is 1.01 to 1.20 times the wire diameter, and the second parallel number is one more than the number of parallel wires of the innermost first layer in the radial direction. A pneumatic radial tire comprising a layer.

(2) In the above (1), the polyester fiber cord is characterized in that the dry heat shrinkage is 2.0% or less and the sum of the intermediate elongation and the dry heat shrinkage is 6.5%. Pneumatic radial tires.

(3) The pneumatic radial tire according to (1) or (2), wherein the bead core has a three- to five-layer structure.

[0014]

FIG. 1 shows a cross section of a pneumatic radial tire according to the present invention. In the figure, 1 is a pair of bead cores, 2 is a carcass formed by extending at least one ply, in the illustrated example, two plies between the pair of bead cores 1, 3 is a belt composed of at least two layers, and 4 is a belt. The tread. In addition, the tread surface portion and the side wall portion may be made of ordinary materials, shapes, and arrangements.

It is important that the number of the carcass 2 is the same in the entire tire circumferential direction. In other words, when winding the carcass ply on the forming drum at the time of molding the tire, it is important to join the joints of the carcass plies so that the cords do not overlap. That is, by avoiding the weight joining of the carcass plies, uniformity can be secured in the circumferential direction of the carcass, which serves as an index of the uniformity of the tire and is easy for the driver to feel while driving, and is referred to as a radial force variation (hereinafter referred to as a radial force variation). , RFV) is reduced, resulting in improved uniformity. Furthermore, making the carcass uniform in the circumferential direction also effectively works to suppress irregularities which are likely to occur on the tire side portion, and a good appearance can be obtained.

Here, various factors such as the rubber material of the tread tread, the tread pattern, the belt rigidity, and the side shape affect the steering stability and vibration riding comfort of the pneumatic radial tire for passenger cars. However, when the uniformity on the tire circumference is impaired, it is very difficult to improve steering stability and vibration riding comfort.
Therefore, it is important to ensure the uniformity on the tire circumference. For this purpose, it is advantageous to first form the carcass ply so that the cords do not overlap at the ply joint.

That is, if there is a portion where the cords overlap each other on the periphery of the carcass ply, when the tire is filled with the internal pressure, the tension applied to one cord is reduced only at that portion, and the side portion is dented and the outer appearance is reduced. Not only is this not preferable, but only the weight of the portion is different on the circumference. In the worst case, vibration due to vibration occurs during running, which is a factor that deteriorates steering stability and vibration comfort. Further, R
This may cause an increase in the FV value, and may impair high-speed durability. Therefore, it is important for the carcass to have a structure in which there is no cord overlap joint in the circumferential direction of the tire.

Further, a polyester fiber cord is used as a cord constituting the carcass ply, and the cord is 1.98 cN / dtex when collected from a tire.
The intermediate elongation under load is 4 to 6%, and the dry heat shrinkage when applying 177 ° C. heat for 30 minutes under an initial load of 50 g is 2.5% or less, and the above intermediate elongation and dry heat shrinkage Is preferably 7.0% or less, more preferably 2.0% or less, and the sum of the intermediate elongation and the dry heat shrinkage is 6.0%.
It is important that it be 5%.

That is, regarding the physical properties of the carcass ply cord, when the intermediate elongation is less than 4%, vulcanization and post-cure inflation (hereinafter referred to as PC) during tire production.
In step (I), the expansion tension that propagates from the ply cord to the bead core increases, so that the bead core is likely to lose its shape, while the intermediate elongation exceeds 6% or the dry heat shrinkage increases 2.5%. If it exceeds this, or if the sum of the intermediate elongation and the dry heat shrinkage exceeds 7.0%, the expansion and contraction of the ply cord in the vulcanization and PCI processes will increase, and this expansion and contraction will vary around the tire circumference. In each case, it is difficult to ensure uniformity around the tire circumference,
It becomes difficult to ensure steering stability and vibration riding comfort.

Next, as shown in FIGS. 2 to 8, the bead core 1 has a layer in which one rubber-coated wire 5 having a diameter of 1.2 to 2.2 mm is spirally wound in parallel. , And are sequentially laminated outward in the radial direction. Incidentally, the bead core shown in FIG. 2 has a three-layer laminated structure. Similarly, the bead cores shown in FIGS. 3 to 6 have a four-layer structure, and the bead cores shown in FIGS. 7 and 8 have a five-layer structure. The cross-sectional shape of the bead core is not limited to those shown in FIGS. 2 to 8, and the number of layers in each layer and the number of layers can be appropriately changed.

That is, the bead core 1 is formed by spirally winding a single rubber-coated wire 5 to improve the non-uniformity on the periphery thereof and to densely fill the cross-sectional arrangement of the cord, thereby providing a tire. It is possible to suppress the shape of the bead core from being lost during manufacturing, and to suppress vibration and vibration during traveling. However, when the wire diameter is less than 1.2 mm, it is necessary to increase the number of windings in terms of maintaining the tire strength, which causes a bias in the stress distribution to each cord in the cross section of the bead core. As described above, it is necessary to increase the number of windings, and there is a possibility that rolling resistance is deteriorated with an increase in tire weight. On the other hand, if the wire diameter exceeds 2.2 mm, the bending stiffness of one wire increases, making it difficult to attach and detach the tire to and from the rim. In the worst case, it causes bead deformation, resulting in steering stability and vibration riding. It also has an adverse effect on comfort.

As shown in FIG. 10, in the cross section of the bead core 1 in the tire width direction, the distance H between the axes P of the adjacent wires 5 is defined as 1.01 to 1.01 of the wire diameter D.
1.20 times. If the distance H is less than 1.01 times the wire diameter D, the steel cords rub against each other during running, so that there is a problem that the breaking strength of the bead core is reduced. However, since the distribution of the stress applied to the cords in the cross section of the bead core is deviated, there is a problem that the number of windings must be increased more than necessary as described above.

Further, it is important to configure the second layer with the number of parallel wires one greater than the number of parallel wires of the first layer on the radially innermost side of the bead core. That is, in the bead core shown in FIGS. 2 and 3, the number of parallel wires in the first layer is two, and thus the number of parallel wires in the second layer is three.
Similarly, in the example of FIG. 4, the number of parallel wires in the first layer is three, and thus the number of parallel wires in the second layer is four. In the examples of FIGS. 5 and 7, since the number of parallel wires of the first layer is four,
The number of parallel wires in the second layer is 5, and in the examples of FIGS. 6 and 8, the number of parallel wires in the first layer is 5, so the number of parallel wires in the second layer is 6.

[0024] As described above, since the laminated structure has a structure that does not easily lose its shape when subjected to expansion tension from the ply cord in the vulcanization during manufacturing of the tire or the PCI process, the stress on each cord in the cross section of the bead core is reduced. The load distribution becomes more uniform, and the breaking strength of the bead core can be increased.

[0025]

EXAMPLES Various specifications shown in Tables 1 to 3 were applied to a bead core 1 and a carcass 2 of a pneumatic radial tire having the structure shown in FIG. 1, and a tire having a size of 205/65 R15 was prototyped. In addition, other structures conformed to the general structure of the tire.

The tires thus obtained were evaluated for various characteristics described below, and the results are also shown in Tables 1 to 3. In addition, the evaluation method of various characteristics is as follows.

(A) Cord elongation After removing excess rubber attached to the periphery of the carcass ply cord taken out of the tire with scissors, JIS L10
According to 17, the code was autographed at room temperature (25 ± 2
° C), and the elongation (%) under a load of 1.98 cN / dtex was determined. In addition, the denier number used the original yarn denier before twisting.

(A) Dry heat shrinkage of cord A carcass ply cord taken out in the same manner as in (A) above is weighed with a 50 g weight and left standing for 30 minutes in an oven maintained at 177 ° C in advance. The cord was shrunk, the cord length at that time was measured, and the portion shorter than the cord length before placing in the oven was divided by the cord length before placing in the oven to obtain a dry heat shrinkage. That is, it was calculated based on the following equation (1).

(Equation 1)

(C) Tire projection riding vibration test (ride comfort) An iron projection (upper base 19 mm, lower base 38 mm and height 9.5 mm) was fixed at one place on a drum having an outer diameter of 2000 mm, and the internal pressure was increased to 196 kPa. Load 1 on the adjusted test tire.
After applying 1760N and preliminarily running at a speed of 80km / h for 20 minutes, the internal pressure was readjusted to 196kPa under no load, the speed was increased to 20km / h and a load of 11760N, and thereafter the speed was increased every 5km / h. At each speed, the average waveform of the change in the load on the fixed shaft of the tire at the time of riding over the protrusion at each speed was determined, and the peak-to-peak value of the waveform was calculated. The axial load fluctuation direction at the time of overhanging the protrusion on the tire national fixed axis is the tire advancing direction (back and forth spring), and the pp value (N) in the speed range of 30 to 40 km / h was calculated. Then, the calculated pp value was indexed according to the following equation (2), with the control tire of Comparative Example 1 as 100. This indexing is such that the smaller the pp value, the larger the index, and therefore, the larger the index, the better the ride comfort.

(Equation 2)

(D) Maneuvering stability The maneuvering stability was determined by first mounting each test tire on a car,
After performing a preliminary run of km for 3 minutes,
A feeling test was conducted using a real vehicle at a speed of 200 km / h, and (i) straight running stability, (ii) turning stability, and (ii)
i) Regarding items such as rigidity and (iv) handling, 1
A rating of 10 to 10 was given, and each item was averaged to obtain a rating of steering stability. The evaluation was carried out by two professional drivers, and the average of the scores of the two drivers was obtained. The results were indicated by an index when the control tire of Comparative Example 1 was set to 100. When this value is large, it indicates that the steering stability is good.

(E) Side appearance (tire 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 196 kPa at a room temperature of 25 ± 2 ° C., left for 24 hours, readjusted the air pressure, and measured _. When the measured value is 0.5 mm or more, the side irregularities are sufficiently recognized visually, which causes a problem in appearance.

(F) Uniformity (RFV value) The uniformity was measured in accordance with JASO C607, "Method of testing uniformity of automobile tires".

(G) Tire burst pressure The tire burst pressure was measured by a water pressure burst test.

(H) Rim assembling operation Rim assembling and rim releasing operations were performed five times in succession, and the presence or absence of deformation of the bead portion was confirmed. "×"
It was determined.

(G) Tire Durability The tire high load durability is controlled by controlling the ambient temperature to 30 ± 3 ° C. by using a drum tester having a smooth drum specification and a diameter of 1.707 m. And the test internal pressure is 294 kPa,
The vehicle was driven under a load of 1300 kg until a failure occurred. The longer this travel distance poison, the higher the tire durability. The running distance until the failure occurred was evaluated with the control tire of Comparative Example 1 taken as 100. In the judgment, those having a running distance of less than 60 were evaluated as "x".

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

In Tables 1 to 3, the content of Comparative Example 1 is the current control tire. Compared with Comparative Example 1, the tire of the invention example according to the present invention has better handling stability, vibration riding comfort, and It can be seen that both the omity (RFV value) and the side appearance (the amount of unevenness) are greatly improved.

That is, Invention Examples 2 and 3 correspond to Invention Example 1.
However, according to the tire evaluation results, it is understood that the invention example 1 has an excellent performance balance. In addition, in Invention Examples 4 and 5, the wire diameter was changed, and in Invention Examples 6 and 7, the center-to-center distance between adjacent wire portions was changed.
It turns out that the balance of the invention example 1 is the most excellent.

Further, in Comparative Examples 2 to 7, the effect of combining the conventional technique alone or in combination with the control tire of Comparative Example 1, such as the presence of ply cord, bead, and ply overlap, was confirmed. However, in each case, the improvement effect was slight, and the magnitude of the improvement effect of the invention example can be understood.

Comparative Examples 8 to 12 include ply cord characteristics,
The results were shown when either the bead wire diameter or the bead adjacent wire diameter deviated. In any case, no improvement in performance was observed, or the tire became very poorly balanced. In particular, Comparative Examples 10 and 11 Are tires without marketability.

[0043]

According to the present invention, by satisfying specific conditions such as the characteristics of the carcass ply cord and the structure of the bead core, tire steering stability, vibration riding comfort,
The four required characteristics of uniformity and side appearance can be satisfied at a high level and at the same time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the width direction of a tire according to the present invention.

FIG. 2 is a schematic diagram showing a bead core structure according to the present invention.

FIG. 3 is a schematic view showing another bead core structure of the present invention.

FIG. 4 is a schematic view showing another bead core structure of the present invention.

FIG. 5 is a schematic diagram showing a bead core structure according to the present invention.

FIG. 6 is a schematic view showing another bead core structure of the present invention.

FIG. 7 is a schematic view showing another bead core structure of the present invention.

FIG. 8 is a schematic view showing another bead core structure of the present invention.

FIG. 9 is a schematic diagram showing a distance between axial centers of adjacent wire portions in a bead core.

[Explanation of symbols]

 1 bead core 2 carcass 3 belt 4 tread 5 wire

Claims (3)

[Claims] 1. A pneumatic radial tire having, as a skeleton, a carcass composed of at least one ply of cords radially arranged between a pair of bead cores, the carcass rubberizes a large number of polyester fiber cords. A polyester fiber cord having an intermediate elongation of 4 to 6% under a load of 1.98 cN / dtex, and an initial load of 50 g. Lower one
The dry heat shrinkage at 77 ° C. and 30 minutes is 2.5% or less, and the sum of the intermediate elongation and the dry heat shrinkage is 7.0%.
The bead core has a diameter of 1.2 to 2.2.
mm of a rubber-coated wire is spirally wound in parallel, and the layers are sequentially laminated radially outwardly. In the cross-section of the bead core in the tire width direction, the distance between the axial centers of adjacent wire portions. Is the wire diameter of 1.01 to 1.20
A pneumatic radial tire characterized in that the second layer is doubled and the number of parallel wires is one greater than the number of parallel wires of the first layer on the innermost side in the radial direction. 2. The air according to claim 1, wherein the polyester fiber cord has a dry heat shrinkage of 2.0% or less and a sum of an intermediate elongation and a dry heat shrinkage of 6.5%. Included radial tire. 3. The pneumatic radial tire according to claim 1, wherein the bead core has a three- to five-layer structure.