JP2024080104A - Pneumatic tires - Google Patents

Abstract

[Problem] To provide a pneumatic tire with improved tire performance. [Solution] The tire has a cap rubber that forms a contact patch and has pinholes for driving stud pins into it, and a belt reinforcing layer that is arranged on the radially inward side of the cap rubber. The cap rubber has a plurality of main grooves extending in the circumferential direction of the tire. The number of pinholes in a shoulder region that is axially outward of a first main groove that is the axially outermost of the plurality of main grooves is greater than the number of pinholes in a center region that is axially inward of the first main groove. The maximum number of layers of the belt reinforcing layer in the shoulder region is greater than the maximum number of layers of the belt reinforcing layer in the center region. [Selected Figure] Figure 2

Description

This disclosure relates to a pneumatic tire that is used with stud pins attached to the tread.

In regions with harsh winters, such as Northern Europe, studded tires are used as winter tires. Studded tires have multiple pinholes in the tread for metal stud pins to be driven into. The studs driven into the pinholes allow the tires to perform well on icy and snowy roads.

For example, Patent Document 1 discloses that pin removal performance can be improved by adjusting the ratio of rubber hardness and modulus.

JP 2018-188503 A

In addition to the pin removal performance mentioned above, studded tires are required to have various improved tire performance.

This disclosure provides a pneumatic tire with improved tire performance.

The pneumatic tire disclosed herein comprises a cap rubber that forms a contact surface and has pinholes for driving stud pins, and a belt reinforcing layer that is disposed radially inward of the cap rubber, the cap rubber having a plurality of main grooves extending in the tire circumferential direction, the number of pinholes in a shoulder region that is axially outward of a first main groove that is the outermost of the plurality of main grooves in the tire axial direction is greater than the number of pinholes in a center region that is axially inward of the first main groove, and the maximum number of layers of the belt reinforcing layer in the shoulder region is greater than the maximum number of layers of the belt reinforcing layer in the center region.

1 is a cross-sectional view of a pneumatic tire according to a first embodiment, the cross-sectional view passing through a tire meridian. FIG. FIG. 4 is a partially enlarged plan view showing the tread pattern with the stud pins 8 driven into the pinholes 37. 4 is a cross-sectional view taken along the line A1-A1 in FIG. 3. FIG. 4 is a partially enlarged plan view showing the tread pattern before the stud pins 8 are driven into the pinholes 37. 6 is a cross-sectional view taken along the line A2-A2 in FIG. 5 . FIG. 2 is a cross-sectional view of the pneumatic tires of Comparative Examples 1 and 2, passing through the tire meridian.

[First embodiment]
Hereinafter, a pneumatic tire according to a first embodiment of the present disclosure will be described with reference to the drawings. In the drawings, "CD" means the tire circumferential direction, "AD" means the tire axial direction, and "RD" means the tire radial direction. Each drawing shows the shape of a new tire.

Figure 1 is a cross-sectional view of a pneumatic tire according to the first embodiment, taken along the tire meridian. Figure 2 is a plan view showing a tread pattern. As shown in Figure 1, the pneumatic tire includes a pair of beads 1, sidewalls 2 extending from each bead 1 to the tire radially outer side RD1, and a tread 3 connecting the tire radially outer RD1 ends of the sidewalls 2. The bead 1 includes an annular bead core 1a formed by rubber-coating a bundle such as a steel wire, and a bead filler 1b made of hard rubber. The bead 1 is attached to a bead seat of a rim (not shown), and if the air pressure is a predetermined pressure (for example, an air pressure determined by JATMA), the tire is fitted to the rim by the tire internal pressure, and the tire is fitted to the rim.

The tire also has a toroidal carcass 4 that extends from the tread 3 through the sidewall 2 to the bead 1. The carcass 4 is provided between a pair of beads 1, and its ends are wound up and secured via the bead core 1a. An inner liner rubber 5 for maintaining air pressure is arranged on the inner side RD2 of the carcass 4 in the tire radial direction.

On the tire radial outer side RD1 of the carcass 4 in the tread 3, a plurality of belts 6 (two in the first embodiment) are arranged to reinforce the carcass 4. The belts 6 have cords that extend at a predetermined angle with respect to the tire circumferential direction CD. The cords of the belts 6 are made of metal such as steel. The belts 6 are stacked so that the cords of each belt 6 cross each other in opposite directions. A belt reinforcing layer 7 is arranged on the tire radial outer side RD1 of the belts 6. The cords of the belt reinforcing layer 7 are made of organic fibers such as nylon fibers and polyamide fibers. A base rubber 31 is arranged on the tire radial outer side RD1 of the belt reinforcing layer 7. Furthermore, a cap rubber 30 is arranged on the tire radial outer side RD1 of the base rubber 31.

As shown in Figures 1 and 2, the surface of the tread 3 (cap rubber 30) is formed with multiple main grooves 32 extending in the tire circumferential direction CD, and lands 33 that are partitioned by the main grooves 32 and extend in the tire circumferential direction CD. In the first embodiment, the main grooves 32 form shoulder lands 33a, quarter lands 33b, and center lands 33c. The center lands 33c are the lands closest to the tire equatorial plane CL. The shoulder lands 33a are lands formed axially outboard of the first main grooves 32a, which are the axially outermost of the multiple main grooves 32. The quarter lands 33b are lands arranged between the shoulder lands 33a and the center lands 33c.

In the first embodiment, two main grooves 32 are formed on one side of the tire, and there are four main grooves 32 in total, but this is not limited to the above. For example, there may be three main grooves 32 in total, or five or more. Depending on the number of main grooves 32, the quarter land 33b may be omitted, and the number of lands 33 may be changed as appropriate.

As shown in FIG. 2, the land 33 of the tread 3 forms a contact surface 34 that can come into contact with the road surface. The contact edge LE is the outermost end of the contact surface 34 in the tire axial direction AD. The contact surface 34 refers to the surface that comes into contact with the road surface when the tire is mounted on a standard rim, inflated to the standard internal pressure, placed vertically on a flat road surface, and a standard load is applied.

A genuine rim is a rim that is determined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is a standard rim, and in the cases of TRA and ETRTO, it is a "Measuring Rim."

The normal internal pressure is the air pressure set for each tire by the standard system that includes the standard on which the tire is based. For truck and bus tires and light truck tires, it is the maximum air pressure for JATMA, the maximum value listed in the table IRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES for TRA, and INFLATION PRESSURE for ETRTO. For passenger car tires, it is usually 180 kPa, but for tires that are labeled Extra Load or Reinforced, it is 220 kPa.

The normal load is the load determined for each tire by the standards, including the standards on which the tire is based. For JATMA, it is the maximum load capacity. For TRA, it is the maximum value listed in the TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES table. For ETRTO, it is the LOAD CAPACITY. If the tire is for passenger cars, it is a load equivalent to 88% of the above load. If the tire is for racing karts, the normal load is 392N.

As shown in FIG. 2, in the first embodiment, the shoulder land 33a and the quarter land 33b are divided in the tire circumferential direction CD by slits 35 and have multiple blocks in the tire circumferential direction CD. The center land 33c is a rib and is continuous in the tire circumferential direction CD. The shoulder land 33a, the quarter land 33b, and the center land 33c have sipes 36 extending in the tire axial direction AD. The edge effect of the sipes 36 provides excellent performance on icy road surfaces.

In this specification, the main groove 32 is not particularly limited, but may have a groove width of 4.0 mm or more. In addition, the main groove 32 is not particularly limited, but may have a groove width of, for example, ...

The shoulder land 33a and the quarter land 33b are formed with pinholes 37 for embedding the stud pins 8. The center land 33c does not have a pinhole 37. FIG. 2 shows the pinhole 37 with the stud pins 8 driven into it. FIG. 3 is a partially enlarged plan view showing the tread pattern with the stud pins 8 driven into the pinholes 37. FIG. 4 is a cross-sectional view of the A1-A1 portion in FIG. 3. As shown in FIGS. 3 and 4, the stud pins 8 are made of metal such as aluminum or steel. The stud pins 8 have a main body 80 exposed from the opening of the pinhole 37, a protrusion 81 protruding from the main body 80 to the road surface, a flange portion 82 extending in the radial direction of the stud pin 8, and a constricted portion 83 connecting the flange portion 82 and the main body 80. As shown in FIG. 4, the bottom of the pinhole 37 terminates in the cap rubber 30 and does not reach the base rubber 31. The sides and bottom of the pinhole 37 are formed with the cap rubber 30, and the stud pin 8 is covered with the cap rubber 30 from the tire radial inner side RD2. As shown in FIG. 3, in a block in which the pin hole 37 is formed, no sipes 36 are formed on either side of the pinhole 37 in the tire circumferential direction CD. In a block having the pinhole 37, the pinhole 37 and the sipes 36 are arranged in positions that do not overlap with each other when projected parallel to the tire circumferential direction CD on the tire meridian cross section.

Figure 5 is a partially enlarged plan view showing the tread pattern before the stud pin 8 is driven into the pinhole 37. Figure 6 is a cross-sectional view of the A2-A2 area in Figure 5. As shown in Figures 5 and 6, the pinhole 37 before the stud pin 8 is driven into is in a state in which the diameter of the pinhole 37 is smaller than the diameter of the stud pin 8. As shown in the figure, the pinhole 37 is formed so that the diameter of the bottom is larger than the diameter of the opening to correspond to the flange portion 82 of the stud pin 8.

<Belt reinforcing layer 7>
As shown in FIG. 1, in the first embodiment, the number of layers of the belt reinforcement layer 7 arranged at a position covering the end of the belt 6 on the outer side AD1 in the tire axial direction is greater than the number of layers of the belt reinforcement layer 7 arranged at the center of the tread 3 in the tire axial direction AD. Specifically, the region on the outer side AD1 in the tire axial direction of the first main groove 32a, which is the outermost of the main grooves 32 in the tire axial direction AD, is the shoulder region Sh, and the region on the inner side AD2 in the tire axial direction of the first main groove 32a is the center region Ce. In this case, the maximum number of layers (2 layers) of the belt reinforcement layer 7 in the shoulder region Sh may be greater than the maximum number of layers (1 layer) of the belt reinforcement layer 7 in the center region Ce in the tire axial direction AD of the shoulder land 33a. The number of layers (2 layers) of the belt reinforcement layer 7 arranged at the center of the shoulder land 33a in the tire axial direction AD may be greater than the number of layers (1 layer) of the belt reinforcement layer 7 arranged at the tire equatorial plane CL. The center of the shoulder land 33a in the tire axial direction AD is half the distance along the tire axial direction AD from the first main groove 32a to the ground contact end LE. In the first embodiment, both ends of one belt reinforcing layer 7 in the tire axial direction AD are folded back to form one belt reinforcing layer 7 in the center of the tire axial direction AD and two belt reinforcing layers 7 in the end on the tire axial outer side AD1, but the method of increasing the number of layers is not limited to this. For example, separate belt reinforcing layers 7 may be laminated by being stuck on top of each other, or multiple belt reinforcing layers 7 may be arranged and laminated while shifting the pitch.

<Effect of the number of belt reinforcing layers 7 and the number of pinholes 37>
The belt reinforcement layer 7 has a function of suppressing the tire from expanding in the tire radial direction RD. By making the number of layers of the belt reinforcement layer 7 at both ends of the tire axial direction AD greater than the number of layers of the belt reinforcement layer 7 at the center of the tire axial direction AD, the expansion of the shoulder region Sh of the tire toward the tire radial direction outer side RD1 is suppressed, and conversely, the center region Ce of the tire is likely to expand toward the tire radial direction outer side RD1. As a result, the ground pressure of the center region Ce during tire rolling is increased, and the ground pressure of the shoulder region Sh is decreased. Therefore, the road damage suppression performance can be improved by reducing the number of pinholes 37 in the center region Ce where the ground pressure is not reduced and increasing the number of pinholes 37 in the shoulder region Sh where the ground pressure is reduced. On the other hand, during braking, the ground pressure of the shoulder region Sh is higher than the ground pressure of the center region Ce. By increasing the number of pinholes 37 in the shoulder region Sh where the ground pressure is high during braking, the ice braking performance can be improved.

<Effect of physical properties of cap rubber>
It is believed that the rubber hardness at 23°C and -5°C of the cap rubber 30 (the cap rubber 30 that forms the pinhole 37) surrounding the stud pin 8 is related to the ease of movement of the stud pin 8. In order to improve the pin removal performance described below, it is preferable that the rubber hardness of the cap rubber 30 at 23°C is 50 degrees or more. This is to ensure pin removal performance in seasons when tires are changed (spring and autumn). It is also preferable that the rubber hardness of the cap rubber 30 at -5°C is 60 degrees or more. This is to suppress distortion acting on the bottom of the stud pin 8 during the main season of use (winter) when mileage is high.

The rubber hardness is JIS K6253-1-2012 3.2 durometer hardness, and is measured using a type A durometer for general rubber (medium hardness) in an atmosphere of 23°C or -5°C.

We believe that the tear strength of the rubber (cap rubber 30) that comes into contact with the bottom of the stud pin 8 is related to the degree of wear of the rubber that comes into contact with the bottom of the stud pin 8. To improve the pin removal performance described below, it is preferable that the tear strength of the cap rubber 30 is 55 kN/m or more. If wear of the cap rubber 30 that comes into contact with the bottom of the stud pin 8 can be suppressed, the pin removal performance can be improved.

The tear strength [kN/m] is determined in accordance with JIS K6252 by using a test piece punched into a crescent shape with a 0.50±0.08 mm notch in the center of the indentation, and performing a tear test at a tensile speed of 500 mm/min using a Shimadzu tensile tester to measure the tear force.

We believe that the storage modulus (E') at -5°C of the rubber (cap rubber 30) that contacts the bottom of the stud pin 8 is related to ice braking performance. To improve the ice braking performance described below, it is preferable that the storage modulus (E') of the cap rubber 30 at -5°C is 35 MPa or less.

The storage modulus (E') [MPa] of the cap rubber 30 at -5°C is measured using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd. under the conditions of a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±5%, and a temperature of -5°C.

To concretely demonstrate the effects of the pneumatic tires disclosed herein, the following evaluations were performed on the following examples.

The configuration of the belt reinforcement layer 7 in Comparative Examples 1 and 2 will be described. Figure 7 is a cross-sectional view passing through the tire meridian of the pneumatic tires in Comparative Examples 1 and 2. As shown in Figure 7, one belt reinforcement layer 7 covers the entire belt 6, and the number of layers of the belt reinforcement layer 7 in the shoulder region Sh and the center region Ce is the same (one layer). The belt reinforcement layer 7 in Comparative Example 3 and Examples 1 to 3 is as shown in Figure 1, and the number of layers of the belt reinforcement layer 7 in the shoulder region Sh and the center region Ce is two and one, respectively.

For Comparative Examples 1 to 4 and Examples 1 to 3, the rubber hardness of the cap rubber 30 at 23°C, the rubber hardness of the cap rubber 30 at -5°C, the tear strength of the cap rubber 30, the storage modulus (E') of the cap rubber 30, the configuration of the belt reinforcement layer 7 (maximum number of layers of the belt reinforcement layer 7 in the shoulder region Sh: maximum number of layers of the belt reinforcement layer 7 in the center region Ce), the number of stud pins 8 in the shoulder region Sh, the number of stud pins 8 in the center region Ce, and the ratio of the number of pins (number of stud pins 8 in the shoulder region Sh/number of stud pins 8 in the center region Ce) are as shown in the table.

Road surface damage performance was measured by testing studded tires in accordance with the standard SFS 7503:2018, which is mentioned in the regulations on technical requirements for studded tires prescribed by the Finnish Transport and Communications Agency under the Vehicle Act (82/2021). Specifically, a specified number of times was run on a specified uneven road surface, and the amount of road surface wear (weight) after the run was measured, and an index evaluation was performed with Comparative Example 1 set at 100, with the larger the value, the less wear and better the result.

Ice braking performance: On an icy road at -3±3°C, a 2000cc 4WD vehicle was operated at 40km/h with the ABS activated, and the braking distance was measured (average value of n=10). The evaluation was done by indexing Comparative Example 1 as 100, with a larger value indicating a shorter braking distance and better performance.

Pin removal performance A vehicle fitted with tires with stud pins 8 embedded in pinholes 37 was driven a predetermined distance and the number of stud pins 8 remaining in the tire was counted. The evaluation was made using an index rating with Comparative Example 1 set at 100, with a larger value indicating a larger number of remaining stud pins 8 and better performance.

Comparative examples 1 and 2 in Table 1 show that by increasing the number of pins in the shoulder region Sh compared to the number of pins in the center region Ce, the ice braking performance is improved by increasing the number of pins in the shoulder region Sh where the ground pressure is high during braking. On the other hand, it can be seen that increasing the number of pins in the shoulder region Sh where the ground pressure is high during rolling damages the road surface and worsens the road damage performance.

According to Comparative Examples 1 and 2 and Example 1 in Table 1, by making the number of layers of the belt reinforcement layer 7 in the shoulder region Sh greater than that in the center region Ce, the bulging of the shoulder region Sh toward the tire radial outer side RD1 during rolling is suppressed, and the ground pressure in the shoulder region Sh during rolling can be reduced. As a result, it can be seen that it is possible to improve road damage suppression performance by reducing the number of pinholes 37 in the center region Ce where the ground pressure is not reduced and increasing the number of pinholes 37 in the shoulder region Sh where the ground pressure is reduced. In addition, looking at Comparative Examples 1 and 3, it can be seen that since there is no change in the road damage performance and ice braking performance simply by configuring the number of layers of the belt reinforcement layer 7 in the shoulder region Sh to be greater than that in the center region Ce, both the ice braking performance and the road damage performance can be improved by two configurations, the ratio of the number of pins and the number of layers of the belt reinforcement layer 7.

According to Examples 1 and 2 in Table 1, it can be seen that increasing the number of stud pins 8 in the shoulder region Sh improves ice braking performance. However, it can be seen that the ice braking performance is not improved when the pin number ratio (Sh/Ce) is 2.33, as in Comparative Example 4. This is because it is believed that by increasing the number of stud pins 8 in the shoulder region Sh, the stud pins 8 arranged in the contact patch are aligned in the tire circumferential direction CD, and the stud pins 8 are less likely to catch on the ice road surface, resulting in no improvement in ice braking performance. Therefore, it can be seen that the pin number ratio (number of stud pins 8 in the shoulder region Sh/number of stud pins 8 in the center region Ce) is preferably 1.2 or more and 2.0 or less. If the pin number ratio is less than 1.2, no improvement in road damage performance can be expected, and if the pin number ratio exceeds 2.0, as in Comparative Example 4, ice braking performance is not improved.

According to Examples 2 and 3 in Table 1, it can be seen that both ice braking performance and pin removal performance can be improved by setting the rubber hardness of the cap rubber 30 at 23°C to 50 degrees or more, the rubber hardness of the cap rubber 30 at -5°C to 60 degrees or more, the tear strength of the cap rubber 30 to 55 kN/m or more, and the storage modulus (E') of the cap rubber 30 to 35 MPa or less.

[1]
Like the pneumatic tire of the first embodiment, the tire comprises a cap rubber 30 that forms a contact surface 34 and that forms pinholes 37 for inserting stud pins 8, and a belt reinforcement layer 7 that is arranged on the radially inner side RD2 of the cap rubber 30, and the cap rubber 30 has a plurality of main grooves 32 extending in the tire circumferential direction CD, and the number of pinholes 37 in a shoulder region Sh that is axially outer than a first main groove 32a that is the outermost of the plurality of main grooves 32 in the tire axial direction AD1 is greater than the number of pinholes 37 in a center region Ce that is axially inner than the first main groove 32a, and the maximum number of layers of the belt reinforcement layer 7 in the shoulder region Sh is greater than the maximum number of layers of the belt reinforcement layer 7 in the center region Ce.

This configuration can improve road damage performance.

[2]
In the pneumatic tire described in [1] above, a value obtained by dividing the number of pinholes 37 in the shoulder region Sh by the number of pinholes 37 in the center region Ce may be 1.2 or more and 2.0 or less.

This configuration makes it possible to improve both road damage performance and ice braking performance.

[3]
In the pneumatic tire described in [1] or [2] above, the cap rubber 30 may have a rubber hardness of 50 degrees or more at 23°C, a rubber hardness of 60 degrees or more at -5°C, a tear strength of 55 kN/m or more, and a storage modulus of 35 MPa or less.

This configuration makes it possible to improve both ice braking performance and pin removal performance.

Although the embodiments of the present disclosure have been described above with reference to the drawings, the specific configuration should not be considered to be limited to these embodiments. The scope of the present disclosure is indicated not only by the description of the above embodiments but also by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

The structures employed in each of the above embodiments can be employed in any other embodiment. The specific configurations of each part are not limited to the above-mentioned embodiments, and various modifications are possible without departing from the spirit of this disclosure.

6: Belt 7: Belt reinforcing layer 8: Stud pin 30: Cap rubber 32: Main groove 32a: First main groove 34: Ground contact surface 37: Pinhole AD: Tire axial direction AD1: Tire axial outer side AD2: Tire axial inner side CD: Tire circumferential direction Ce: Center region RD: Tire radial direction RD2: Tire radial inner side Sh: Shoulder region

Claims (3)

A cap rubber that forms a ground contact surface and also forms pinholes for inserting stud pins, and a belt reinforcing layer that is disposed on the inner side of the cap rubber in the tire radial direction,
The cap rubber has a plurality of main grooves extending in the tire circumferential direction,
the number of the pinholes in a shoulder region axially outward of a first main groove, which is an axially outermost groove among the plurality of main grooves, is greater than the number of the pinholes in a center region axially inward of the first main groove,
a maximum number of layers of the belt reinforcing layer in the shoulder region is greater than a maximum number of layers of the belt reinforcing layer in the center region. The pneumatic tire according to claim 1, wherein the value obtained by dividing the number of pinholes in the shoulder region by the number of pinholes in the center region is 1.2 or more and 2.0 or less. The cap rubber has a rubber hardness of 50 degrees or more at 23° C.
The rubber hardness of the cap rubber at −5° C. is 60 degrees or more,
The tear strength of the cap rubber is 55 kN/m or more,
The pneumatic tire according to claim 1 or 2, wherein the cap rubber has a storage modulus of 35 MPa or less.