JP7417030B2 - pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire having a carcass layer made of organic fiber cord, and more particularly to a pneumatic tire that is capable of achieving both shock burst resistance and steering stability during high-speed running.

One of the causes of failure of pneumatic tires is known to be damage (shock burst) in which the carcass is destroyed when the tire receives a large shock while driving. Durability against such damage (shock burst resistance) can be determined, for example, by a plunger energy test. In other words, the plunger energy test is a test in which a plunger of a predetermined size is pressed against the center of the tread to measure the breaking energy when the tire breaks. It can be used as an index of fracture energy (fracture durability against protrusion input of the tread portion).

It is known that one way to obtain good results from such plunger energy tests (that is, to improve shock burst resistance) is to, for example, increase the rubber gauge at the tire equator where the plunger comes into contact during the test. (For example, see Patent Document 1). However, with these methods, there is a risk that the amount of rubber used will increase and the weight of the tire will increase. Therefore, it is also being considered to use an organic fiber cord with a large elongation at break as the carcass cord constituting the carcass layer to allow for deformation during testing (when pressed by a plunger). However, in this case, since the rigidity of the carcass layer is reduced, buckling of the belt layer is likely to occur, and there is a possibility that the steering stability during high-speed running may be reduced. Therefore, there is a need for measures to achieve a high degree of both shock burst resistance and handling stability during high-speed running in pneumatic tires having a carcass layer made of organic fiber cords.

Japanese Patent Application Publication No. 2010-247700

The object of the present invention is to provide a pneumatic tire with a carcass layer made of organic fiber cord, and more specifically, to provide a pneumatic tire that is capable of achieving both shock burst resistance and handling stability during high-speed running. It is about providing.

To achieve the above object, the pneumatic tire of the present invention includes a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and these sidewall portions. a pair of bead portions disposed on the inside in the radial direction of the tire, at least one carcass layer mounted between the pair of bead portions, and at least one carcass layer disposed on the outer peripheral side of the carcass layer in the tread portion. In a pneumatic tire having a plurality of belt layers and a belt reinforcing layer disposed on the outer peripheral side of the belt layer, the carcass layer is a carcass cord made of an organic fiber cord made of twisted filament bundles of polyethylene terephthalate fibers. The elongation at break of the carcass cord is 20% or more, and the elongation of the carcass cord at a load of 1.5 cN/dtex on the inner peripheral side of the belt layer is more than 6.0 % and no more than 7.0% , and The belt reinforcing layer is composed of a belt reinforcing cord made of an organic fiber cord made by twisting filament bundles of polyethylene terephthalate fibers, and the elongation of the belt reinforcing cord when loaded at 2.0 cN/dtex is 2.0% to 4.0. %.

In the present invention, as mentioned above, since the elongation at break of the carcass cord constituting the carcass layer is 20% or more, deformation during the plunger energy test (when pressed by the plunger) can be sufficiently tolerated. This makes it possible to improve the fracture energy (fracture durability against protrusion input of the tread portion). That is, the shock burst resistance of the pneumatic tire can be improved. In addition, the elongation of the carcass cord on the inner circumferential side of the belt layer is more than 6.0 % but less than 7.0% , and the rigidity of the carcass cord on the inner circumferential side of the belt layer is kept low. The shock burst resistance of the tire can be improved. On the other hand, the elongation of the belt reinforcing cord constituting the belt cover layer under a load of 2.0 cN/dtex is 2.0% to 4.0%, and the belt reinforcing layer has sufficient rigidity, so it can be used near the grip limit. This suppresses out-of-plane buckling of the belt layer, suppresses a decrease in cornering force, and improves steering stability during high-speed driving. Due to these cooperation, the pneumatic tire of the present invention can achieve both shock burst resistance and steering stability during high-speed running.

In the present invention, the elongation at break of the carcass cord is preferably 22% to 24%. Further , it is preferable that the twist coefficient K of the carcass cord after dipping, expressed by the following formula (1), is 2000 to 2500. By setting each physical property value in this manner, the physical properties of the carcass cord are further improved, which is advantageous in achieving both shock burst resistance and steering stability during high-speed running.

K=T×D ^1/2 ...(1)
(However, T is the number of twists of the cord (twists/10cm), and D is the total fineness (dtex) of the cord.)
In the present invention, it is preferable that the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex is 2.5% to 3.5%. This further improves the physical properties of the belt reinforcing cord, which is advantageous in achieving both shock burst resistance and steering stability during high-speed running.

In the present invention, the organic fibers constituting the carcass cord are polyethylene terephthalate fibers . Further, the organic fibers constituting the belt reinforcing cord are polyethylene terephthalate fibers . By using polyethylene terephthalate fibers in each layer in this manner, its excellent physical properties (high elastic modulus) make it advantageous in achieving both shock burst resistance and steering stability during high-speed running.

In the present invention, it is preferable that the belt reinforcing cord covers the entire area of the belt layer in the tire width direction. With this arrangement, it is possible to better exhibit the effects of the belt reinforcing cord.

1 is a meridian cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 placed on both sides of the tread portion 1, and a pair of sidewall portions 2 placed on the inside of the sidewall portions 2 in the tire radial direction. A pair of bead portions 3 are provided. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-sectional view, the tread portion 1, sidewall portion 2, and bead portion 3 each extend in the circumferential direction of the tire and form an annular shape, which makes the pneumatic tire toroidal. The basic structure of The following description using FIG. 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the tire circumferential direction and forms an annular shape.

In the illustrated example, a plurality of main grooves (four in the illustrated example) extending in the tire circumferential direction are formed on the outer surface of the tread portion 1, but the number of main grooves is not particularly limited. In addition to the main grooves, various grooves and sipes including lug grooves extending in the width direction of the tire can also be formed.

A carcass layer 4 including a plurality of reinforcing cords (carcass cords) extending in the tire radial direction is mounted between the pair of left and right bead portions 3. A bead core 5 is embedded in each bead portion, and a bead filler 6 having a substantially triangular cross section is arranged on the outer periphery of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from the inner side in the tire width direction to the outer side. As a result, the bead core 5 and the bead filler 6 are formed in the main body part of the carcass layer 4 (the part from the tread part 1 through each sidewall part 2 to each bead part 3) and the folded part (around the bead core 5 in each bead part 3). (a portion that is folded back and extends toward each sidewall portion 2).

On the other hand, a plurality of belt layers 7 (two layers in the illustrated example) are embedded in the outer peripheral side of the carcass layer 4 in the tread portion 1 . Each belt layer 7 includes a plurality of reinforcing cords (belt cords) that are inclined with respect to the tire circumferential direction, and the belt cords are arranged so as to cross each other between layers. In these belt layers 7, the angle of inclination of the belt cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. For example, a steel cord is used as the belt cord.

A belt cover layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability and reducing road noise. The belt reinforcing layer 8 includes reinforcing cords (belt reinforcing cords) oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the belt reinforcing cord with respect to the tire circumferential direction is set to, for example, 0° to 5°. In the present invention, the belt cover layer 8 necessarily includes a full cover layer 8a that covers the entire area of the belt layer 7, and optionally includes a pair of edge cover layers 8b that locally cover both ends of the belt layer 7. (In the illustrated example, both the full cover layer 8a and the edge cover layer 8b are included). The belt cover layer 8 is preferably constructed by winding a strip of material in which at least one belt reinforcing cord is aligned and coated with a coated rubber in a spiral shape in the tire circumferential direction, and it is particularly desirable to have a jointless structure.

Since the present invention relates to the carcass cord constituting the above-mentioned carcass layer 4 and the belt cord constituting the belt reinforcing layer 8, the basic structure of the entire tire is not limited to that described above.

In the present invention, the carcass cord constituting the carcass layer 4 is composed of an organic fiber cord in which filament bundles of organic fibers are twisted together. The elongation at break of this carcass cord (organic fiber cord) is 20% or more, preferably 22% to 24%. Further, the elongation at the inner peripheral side of the belt layer 7 of the carcass cord under a load of 1.5 cN/dtex is 5.5% or more, preferably 5.5% to 7.0%. The type of organic fiber constituting the carcass cord is not particularly limited, but for example, polyester fiber, nylon fiber, aramid fiber, etc. can be used, and among them, polyester fiber can be preferably used. Examples of polyester fibers include polyethylene terephthalate fibers (PET fibers), polyethylene naphthalate fibers (PEN fibers), polybutylene terephthalate fibers (PBT), and polybutylene naphthalate fibers (PBN). It can be suitably used. In addition, "elongation at break" and "elongation at 1.5 cN/dtex load" are based on JIS L1017 "Chemical fiber tire cord test method" under the conditions of gripping interval 250 mm and tension speed 300 ± 20 mm/min. It is the elongation rate (%) of the sample cord measured by conducting a tensile test. "Elongation at break" is the value measured when the cord breaks, and "elongation at 1.5 cN/dtex load" is 1.5 cN. /dtex This is the value measured under load.

In the present invention, the belt reinforcing cord constituting the belt cover layer 8 is composed of an organic fiber cord in which filament bundles of organic fibers are twisted together. The elongation of this belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is 2.0% to 4.0%, preferably 2.5% to 3.5%. The type of organic fiber constituting the belt reinforcing cord is not particularly limited, but for example, polyester fiber, nylon fiber, aramid fiber, etc. can be used, and among them, polyester fiber can be preferably used. Examples of polyester fibers include polyethylene terephthalate fibers (PET fibers), polyethylene naphthalate fibers (PEN fibers), polybutylene terephthalate fibers (PBT), and polybutylene naphthalate fibers (PBN). It can be suitably used. In addition, in the present invention, the elongation under a load of 2.0 cN/dtex was determined by a tensile test in accordance with JIS L1017 "Chemical Fiber Tire Cord Test Method" under the conditions of a grip interval of 250 mm and a tensile speed of 300 ± 20 mm/min. This is the elongation rate (%) of the sample cord measured under a load of 2.0 cN/dtex.

As described above, by using a combination of the carcass layer 4 made of organic fiber cords having specific physical properties and the belt cover layer 8 made of organic fiber cords having specific physical properties, the pneumatic tire of the present invention has shock burst resistance. It is possible to achieve a high level of balance between performance and steering stability during high-speed driving. That is, in the carcass layer 4, the carcass cord has a large elongation at break, so deformation during the plunger energy test (when pressed by the plunger) can be sufficiently tolerated, and the break energy (protrusion of the tread part) can be sufficiently tolerated. It is possible to improve the shock burst resistance of the pneumatic tire. Further, it is also advantageous for the rigidity of the carcass layer 4 on the inner peripheral side of the belt layer 8 to be kept low in order to improve the shock burst resistance of the pneumatic tire. On the other hand, in the belt cover layer 8, the belt reinforcing cord with the above-mentioned physical properties can suppress out-of-plane buckling of the belt layer near the grip limit, suppressing a decrease in cornering force, and suppressing the reduction in cornering force. The steering stability during driving can be improved.

At this time, if the elongation at break of the carcass cord (organic fiber cord) is less than 20%, deformation during the plunger energy test cannot be sufficiently tolerated, and shock burst resistance cannot be improved. If the elongation at the inner circumferential side of the belt layer 8 of the carcass cord under a load of 1.5 cN/dtex is less than 5.5%, the rigidity of the carcass layer on the inner circumferential side of the belt layer 8 becomes high, and the plunger energy test It is not possible to sufficiently tolerate deformation over time, and it is not possible to improve shock burst resistance. If the elongation of the belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is less than 2.0%, the rigidity of the belt reinforcing layer 8 will be high, and the deformation during the plunger energy test will be sufficiently tolerated. There is a risk that the shock burst resistance will be impaired. If the elongation of the belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is greater than 4.0%, the rigidity of the belt reinforcing layer 8 will decrease, buckling cannot be sufficiently suppressed, and the Driving stability decreases.

In addition to the above-mentioned physical properties, the carcass cord of the present invention preferably has a twist coefficient K expressed by the following formula (1) of 2000 to 2500. Note that this twist coefficient K is a numerical value of the carcass cord after dipping treatment. Setting the twist coefficient K to a large value in this manner is advantageous in improving high-speed durability. When the twist coefficient K is less than 2000, fatigue is likely to occur in the carcass layer 4 due to repeated compressive deformation of the rolled-up portion of the carcass layer 4 due to collapse of the bead portion during tire rolling, improving high-speed durability. There is a possibility that the effect will not be sufficiently obtained.

K=T×D ^1/2 ...(1)
(However, T is the number of twists of the cord (twists/10cm), and D is the total fineness (dtex) of the cord.)

The tire size is 275/40ZR20 and has the basic structure illustrated in Fig. 1, and the material and physical properties of the carcass cord constituting the carcass layer (elongation at break, at a load of 1.5 cN/dtex on the inner peripheral side of the belt layer) Conventional Example 1, Comparative Examples 1 to 4, in which the material and physical properties (elongation when loaded with 2.0 cN/dtex) of the belt reinforcing cord constituting the belt protective layer were varied as shown in Tables 1 and 2. Pneumatic tires of Examples 1 to 7 were manufactured (in addition, examples in which the elongation at the inner peripheral side of the belt layer of the carcass cord when a load of 1.5 cN/dtex was outside the scope of the present invention , and the type of organic fiber were nylon). 66 (N66), ie, Examples 1, 3 to 7 , are reference examples).

In either example, the belt cover layer is a joint in which a strip made of one organic fiber cord (nylon 66 fiber cord or PET fiber cord) aligned and coated with rubber is wound spirally in the circumferential direction of the tire. It has a non-resistance structure. The cord driving density in the strip is 50 cords/50 mm. Further, each organic fiber cord (nylon 66 fiber cord or PET fiber cord) has a structure of 1100 dtex/2.

Regarding the organic fiber type column, nylon 66 fiber cord was indicated as "N66", and PET fiber cord was indicated as "PET".

These test tires were evaluated for shock burst resistance and steering stability during high-speed running using the following evaluation methods, and the results are also shown in Tables 1 and 2.

Shock burst resistance Each test tire was assembled to a wheel with a rim size of 9 1/2J (ETRTO standard rim), the air pressure was set to 240 kPa (Reinforced/Extra Load Tires), and a plunger with a plunger diameter of 19 ± 1.6 mm was set at the loading speed. A tire breaking test was conducted in which the tire was pressed against the center of the tread at a plunger pushing speed of 50.0±1.5 m/min, and tire strength (tire breaking energy) was measured. The evaluation results were expressed as an index, with the measured value of Conventional Example 1 being 100. The larger this value is, the larger the fracture energy is, meaning that the shock burst resistance is excellent. Incidentally, if this index value is "110" or less, it means that a sufficient improvement effect was not obtained.

Steering stability during high-speed driving Each test tire was assembled to a wheel with a rim size of 9 1/2J and mounted on a test vehicle (4-wheel drive vehicle with a displacement of 2000cc), the air pressure was set to 240kPa, and the number of passengers was 2. Sensory evaluation was conducted by three test drivers on a test course consisting of a paved road with regard to steering stability during high-speed driving at speeds of 100 km/h to 120 km/h. The evaluation results were scored using a 5-point system with the result of Conventional Example 1 as 3 points (standard), and the average value of the scores of the three test drivers is shown. The higher the score, the better the steering stability during high-speed driving. Incidentally, if this index value is "3.5" or less, it means that a sufficient improvement effect was not obtained.

As can be seen from Tables 1 and 2, the tires of Examples 1 to 7 achieved a high degree of both shock burst resistance and handling stability during high-speed running, compared to Conventional Example 1, which is the standard. On the other hand, in Comparative Example 1, because the elongation at break of the carcass cord was small, it was not possible to sufficiently secure the breaking energy of the tire measured by the plunger test, and the effect of improving shock burst resistance was not sufficiently obtained. There wasn't. In Comparative Example 2, the elongation at the inner peripheral side of the belt layer of the carcass cord under a load of 1.5 cN/dtex was small, and therefore the effect of improving steering stability during high-speed running could not be sufficiently achieved. In Comparative Example 3, the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex was small, so the cord was difficult to deform, and the effect of improving shock burst resistance was not sufficiently obtained. In Comparative Example 4, the elongation of the belt reinforcing cord at a load of 2.0 cN/dtex was large, so that the effect of improving steering stability during high-speed running could not be sufficiently achieved.

1 Tread portion 2 Sidewall portion 3 Bead portion 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer CL Tire equator

Claims (5)

A tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed inside the sidewall portions in the tire radial direction. comprising: at least one carcass layer mounted between the pair of bead portions; a plurality of belt layers disposed on the outer circumferential side of the carcass layer in the tread portion; and a plurality of belt layers disposed on the outer circumferential side of the belt layer. In a pneumatic tire having a belt reinforcing layer,
The carcass layer is composed of a carcass cord made of an organic fiber cord made by twisting filament bundles of polyethylene terephthalate fibers, and the carcass cord has an elongation at break of 20% or more, and 1. The elongation under a load of 5 cN/dtex is more than 6.0 % and less than 7.0% ,
The belt reinforcing layer is composed of a belt reinforcing cord made of an organic fiber cord made by twisting filament bundles of polyethylene terephthalate fibers, and the belt reinforcing cord has an elongation of 2.0% to 4.0% under a load of 2.0 cN/dtex. 0% pneumatic tires. The pneumatic tire according to claim 1, wherein the carcass cord has an elongation at break of 22% to 24%. The pneumatic tire according to claim 1 or 2, wherein the carcass cord has a twist coefficient K of 2000 to 2500 after dipping, expressed by the following formula (1).
K=T×D ^1/2 ...(1)
(However, T is the number of twists of the cord (twists/10cm), and D is the total fineness (dtex) of the cord.) The pneumatic tire according to any one of claims 1 to 3, wherein the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex is 2.5% to 3.5%. The pneumatic tire according to any one of claims 1 to 4 , wherein the belt reinforcing cord covers the entire area of the belt layer in the tire width direction.

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