JP2024080078A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire improved in tire performance.

SOLUTION: A pneumatic tire includes: cap rubber which forms a ground contact surface and forms a pin hole for driving a stud pin therein; and base rubber disposed on a tire radial direction inner side of the cap rubber. The cap rubber forms a bottom surface of the pin hole. The thickness of the base rubber on a tire radial direction inner side of the pin hole is 1.0 mm or more. The rubber thickness of the cap rubber on the tire radial direction inner side of the pin hole is 1.0 mm or more. The base rubber has a rubber hardness of 70 degrees or more at -5°C.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

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 other tire performance improvements.

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 also forms a pinhole for inserting a stud pin, and a base rubber that is arranged on the tire radial inside of the cap rubber, the cap rubber forms the bottom surface of the pinhole, the thickness of the base rubber on the tire radial inside of the pinhole is 1.0 mm or more, the rubber thickness of the cap rubber on the tire radial inside of the pinhole is 1.0 mm or more, and the rubber hardness of the base rubber at -5°C is 70 degrees or more.

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. 4 is a cross-sectional view of a modified pneumatic tire passing through a tire meridian. 4 corresponding to Comparative Examples 6 to 8.

[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 of 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 side 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 side 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 the block in which the pinhole 37 is formed, the sipes 36 are not formed on either side of the pinhole 37 in the tire circumferential direction CD. In the 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.

In the first embodiment, the number of pinholes 37 in the shoulder region Sh is greater than the number of pinholes 37 in the center region Ce, but this is not limited to the above. The number of pinholes 37 in the shoulder region Sh may be the same as the number of pinholes 37 in the center region Ce, or the number of pinholes 37 in the shoulder region Sh may be less than the number of pinholes 37 in the center region Ce.

<Effect of physical properties of base rubber 31>
The rubber hardness of the base rubber 31 at -5°C is considered to be related to dry steering stability and pin removal performance. By making the base rubber 31 harder, the rigidity of the entire land increases, making the land less likely to move, improving dry steering stability. Furthermore, by making the land less likely to move, the stud pins 8 become less likely to move, improving pin removal performance. The rubber hardness of the base rubber 31 at -5°C is preferably 70 degrees or more.

<Thickness of Cap Rubber 30 and Base Rubber 31>
As shown in FIG. 4, in a state where the stud pin 8 is driven into the pinhole 37, the sum (D1+D2) of the rubber thickness D1 of the cap rubber 30 and the rubber thickness D2 of the base rubber 31 at the tire radial inner side RD2 of the pinhole 37 is preferably 2.0 mm or more. The sum (D1+D2) is the rubber thickness at the tire radial outer side RD1 than the belt 6, and the thicker the sum (D1+D2), the lower the land rigidity of the tread 3 and the worse the dry steering stability. On the other hand, the thicker the sum (D1+D2), the thicker the rubber that holds the stud pin 8, and the better the pin removal performance. Dry steering stability and pin removal performance are contradictory performances. By making the sum (D1+D2) 2.0 mm or more, it becomes easier to balance the dry steering stability and pin removal performance by other means (such as increasing the hardness of the base rubber 31).
The rubber thicknesses D1 and D2 when the stud pin 8 is driven into the pinhole 37 shown in Figure 4 are the same as the rubber thicknesses D1 and D2 before the stud pin 8 is driven into the pinhole 37 shown in Figure 6.

As shown in FIG. 4, the thickness D1 of the cap rubber 30 along the tire radial direction RD from the bottom of the pinhole 37 to the base rubber 31 is preferably 1.0 mm or more. If the thickness D1 of the cap rubber 30 is less than 1.0 mm (including the case where the thickness D1 is 0 as shown in FIG. 8), the pin removal performance will be significantly deteriorated. In addition, the thickness D1 of the cap rubber 30 is preferably 1.5 mm or less. If the thickness D1 of the cap rubber 30 is 1.0 mm or more and 1.5 mm or less, the effect of improving the dry steering stability performance and pin removal performance is appropriately achieved.

As shown in FIG. 4, the thickness D2 of the base rubber 31 at the portion RD2 on the radially inner side of the pinhole 37 is preferably 1.0 mm or more. If the thickness D2 is less than 1.0 mm, the function of the base rubber 31 (improved dry steering stability and pin removal performance due to high hardness) is not easily achieved. In addition, if the thickness D2 of the base rubber 31 is 1.0 mm or more and 2.0 mm or less, the effect of improving dry steering stability and pin removal performance is appropriately achieved.

<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.

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 structure around the pinhole 37 in Comparative Examples 6 to 8 will be described. Figure 8 is a diagram corresponding to Figure 4 for Comparative Examples 6 to 8. In Comparative Examples 6 to 8, as shown in Figure 8, there is no thickness from the bottom of the pinhole 37 in the cap rubber 30 to the base rubber 31, and the bottom of the pinhole 37 does not terminate inside the cap rubber 30, but reaches the base rubber 31. The stud pin 8 is in contact with the base rubber 31.

For Comparative Examples 1 to 8 and Examples 1 to 8, 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 rubber hardness of the base rubber 31 at -5°C, the thickness D1 [mm] of the cap rubber 30 at the bottom of the stud pin 8, the thickness D2 [mm] of the base rubber 31 at the bottom of the stud pin 8, and the total rubber thickness (D1 + D2) at the bottom of the stud pin 8 are as shown in the table.

Dry Driving Stability Performance The tires were mounted on a vehicle and driving was performed on a dry asphalt-paved road surface, accelerating, braking, turning, and changing lanes. The evaluation conditions were a tire size of 225/50R17, a rim of 17X7.5J, and an internal tire pressure of 220kPa. The test vehicle was a passenger car with an engine displacement of 1984cc. A professional driver made a relative evaluation and expressed it as an index with Comparative Example 1 being 100. The higher the index value, the better the driving stability performance on a dry road surface.

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 to 4 in Table 1 show that the smaller the total rubber thickness (D1 + D2) of the cap rubber 30 and base rubber 31 at the bottom of the stud pin 8, the more the dry steering stability tends to improve, and conversely, the more the pin removal performance tends to deteriorate. In particular, in a configuration in which the rubber thickness D1 of the cap rubber 30 shown in Figure 8 is 0 mm, as in comparative example 6, the deterioration of pin removal performance becomes significant.

It can be seen that if the rubber hardness of the base rubber 31 at -5°C is set to 70 degrees or more as in Comparative Example 7, both the dry steering stability performance and the pin removal performance are improved compared to Comparative Example 6. However, even if the base rubber 31 is made to have a high hardness to improve the pin removal performance, it is not possible to compensate for the deterioration of the pin removal performance caused by the rubber thickness D1 of the cap rubber 30 being 0 mm, and it is therefore not possible to ensure the pin removal performance of Comparative Example 1.

A comparison of Comparative Examples 4 and 5 shows that the dry steering stability and pin removal performance are improved by increasing the rubber hardness of the cap rubber 30. A comparison of Comparative Examples 7 and 8 also shows that the dry steering stability and pin removal performance are improved by increasing the rubber hardness of the cap rubber 30. However, in the configuration shown in FIG. 8 in which the thickness D1 of the cap rubber 30 is 0 mm, it can be seen that the pin removal performance of Comparative Example 1 is not achieved even if the rubber hardness of both the cap rubber 30 and the base rubber 31 is increased to improve the pin removal performance.
Therefore, it can be seen that by making the total rubber thickness (D1 + D2) at the bottom of the stud pin 8 neither too thin nor too thick, it is possible to achieve a balance between dry steering stability performance and pin removal performance.

According to Comparative Example 1 and Examples 1 to 6, if the thickness D1 of the cap rubber 30 at the bottom of the stud pin 8 is 1.0 mm or more and the thickness D2 of the base rubber 31 at the bottom of the stud pin 8 is 1.0 mm or more, it is possible to ensure the same high pin removal performance as that of Comparative Example 1, in which the rubber thickness (D1 + D2) at the bottom of the stud pin 8 is 4.0 mm. Furthermore, it is found that if the rubber thickness D1 of the cap rubber 30 at the bottom of the stud pin 8 is 1.5 mm or more, it is possible to improve the pin removal performance compared to Comparative Example 1.

According to Examples 1 and 3 to 6, it can be seen that the larger the total rubber thickness (D1 + D2) is, the worse the dry steering stability becomes. Example 6 has improved dry steering stability compared to Comparative Example 1, and there is no example where the total rubber thickness (D1 + D2) is greater than that of Example 6, but if the total rubber thickness becomes too large, it is expected that there may be cases where the deterioration of dry steering stability becomes a problem. Therefore, it is preferable that the total rubber thickness (D1 + D2) is 2.0 mm or more and 4.0 mm or less. It is even more preferable that it is 2.0 mm or more and 3.5 mm or less.

According to Examples 1, 2, 7, and 8, it is clear that by setting the rubber hardness of the cap rubber 30 at 23°C to 50 degrees or more and the rubber hardness of the cap rubber 30 at -5°C to 60 degrees or more, it is possible to improve both the dry steering stability performance and the pin removal performance.

<Modification>
(A) In the first embodiment, the number of layers of the belt reinforcement layer 7 in the shoulder region Sh is different from the number of layers of the belt reinforcement layer 7 in the center region Ce, but this is not limited to the above. Fig. 7 is a cross-sectional view of a modified pneumatic tire passing through the tire meridian. As shown in Fig. 7, one belt reinforcement layer 7 may cover 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 may be the same (one layer).

[1]
Like the pneumatic tire of the first embodiment, the tire may include a cap rubber 30 that forms a contact surface 34 and a pinhole 37 for inserting a stud pin 8, and a base rubber 31 that is arranged on the tire radial inner side RD2 of the cap rubber 30, wherein the cap rubber 30 forms the bottom surface of the pinhole 37, the thickness D2 of the base rubber 31 at the tire radial inner side RD2 of the pinhole 37 is 1.0 mm or more, the rubber thickness D1 of the cap rubber 30 at the tire radial inner side RD2 of the pinhole 37 is 1.0 mm or more, and the rubber hardness of the base rubber 31 at -5°C is 70 degrees or more.

This configuration ensures the high pin removal performance of Comparative Example 1, where the rubber thickness (D1 + D2) at the bottom of the pinhole 37 is 4.0 mm, while improving dry steering stability by ensuring the rubber thickness D2 of the high hardness base rubber 31. This ensures pin removal performance and improves dry steering stability.

[2]
In the pneumatic tire described in the above [1], the rubber thickness D1 of the cap rubber 30 at the tire radially inner side RD2 of the pinhole 37 may be 1.5 mm or less.

This configuration improves pin removal performance by ensuring the rubber thickness D1 of the cap rubber 30, making it possible to improve both dry steering stability and pin removal performance.

[3]
In the pneumatic tire described in the above [1] or [2], the cap rubber 30 may have a rubber hardness of 50 degrees or more at 23° C., and the cap rubber 30 may have a rubber hardness of 60 degrees or more at −5° C.

This configuration can further improve both dry steering stability and pin-out 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.

8: Stud pin 30: Cap rubber 31: Base rubber 34: Ground contact surface 37: Pinhole D1: Rubber thickness of cap rubber D2: Rubber thickness of base rubber RD: Tire radial direction RD2: Tire radial inner side

Claims (3)

The tire has a cap rubber that forms a contact surface and a pinhole for inserting a stud pin, and a base rubber that is disposed radially inward of the cap rubber,
the cap rubber forms a bottom surface of the pinhole,

a thickness of the base rubber on the radially inner side of the pinhole in the tire radial direction is 1.0 mm or more;
The rubber thickness of the cap rubber on the radially inner side of the pinhole is 1.0 mm or more,
The base rubber has a rubber hardness of 70 degrees or more at -5°C. The pneumatic tire according to claim 1, wherein the rubber thickness of the cap rubber on the radially inner side of the pinhole is 1.5 mm or less. The cap rubber has a rubber hardness of 50 degrees or more at 23° C.
The pneumatic tire according to claim 1 or 2, wherein the cap rubber has a rubber hardness of 60 degrees or more at -5°C.