JP7464833B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire having an embedded transponder covered by a coating layer, and more specifically, to a pneumatic tire that makes it possible to improve the communication performance of the transponder while maintaining good tire balance.

It has been proposed to embed an RFID tag (transponder) in a pneumatic tire (see, for example, Patent Document 1). When embedding a transponder in a tire, the transponder is covered with a coating layer and the relative dielectric constant of the coating layer is reduced, thereby improving the communication performance of the transponder. However, if the coating layer is insufficient, the communication performance of the transponder deteriorates, and if the coating layer is excessive, a localized weight increase occurs around the tire, which may cause the tire balance to deteriorate.

Japanese Patent Application Laid-Open No. 7-137510

The object of the present invention is to provide a pneumatic tire that makes it possible to improve transponder communication while maintaining good tire balance.

In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions,
The tire is characterized in that a transponder is embedded in the sidewall portion so as to extend along the tire circumferential direction, the transponder is covered with a covering layer, the covering layer has a relative dielectric constant lower than the relative dielectric constant of a surrounding rubber member adjacent to the covering layer, and the length Lc of the covering layer in the tire circumferential direction and the length Lr of the transponder in the tire circumferential direction satisfy the relationship: 1.1≦Lc/Lr≦2.0.

In the present invention, the transponder is covered with a covering layer, the relative dielectric constant of the covering layer is lower than the relative dielectric constant of the surrounding rubber member adjacent to the covering layer, and the circumferential length Lc of the covering layer and the circumferential length Lr of the transponder satisfy the relationship 1.1≦Lc/Lr≦2.0. This sufficiently isolates the transponder from the surrounding rubber members and encases it in a covering layer with a low relative dielectric constant, thereby improving the communication performance of the transponder. In addition, by specifying the upper limit of the circumferential length Lc of the covering layer relative to the circumferential length Lr of the transponder, the tire balance can be maintained well.

In the present invention, it is preferable that the transponder has a substrate and an antenna extending from both ends of the substrate, and the distance L between the terminal of the antenna in the tire circumferential direction and the terminal of the covering layer in the tire circumferential direction satisfies the relationship 0.05≦L/Lr≦0.50 with respect to the length Lr of the transponder in the tire circumferential direction. This ensures that the entire transponder is covered by the covering layer, thereby ensuring a sufficient communication distance for the transponder and further ensuring sufficient durability of the tire.

It is preferable that the total thickness Gac of the coating layer and the maximum thickness Gar of the transponder satisfy the relationship 1.0 mm ≦ Gac - Gar ≦ 3.0 mm. This ensures that the transponder is reliably covered by the coating layer, ensuring a sufficient communication distance for the transponder. Furthermore, by specifying the upper limit of Gac - Gar, it is possible to maintain good tire balance and ensure sufficient tire durability.

The transponder has a substrate and an antenna extending from both ends of the substrate, and it is preferable that the antenna extends within a range of ±20° with respect to the tire circumferential direction. By restricting the inclination of the antenna constituting the transponder in this way, the durability of the transponder can be sufficiently ensured.

It is preferable that the center of the transponder in the thickness direction is located within a range of 25% to 75% of the total thickness Gac of the coating layer from the surface on one side in the thickness direction of the coating layer. This ensures that the transponder is reliably covered by the coating layer, ensuring a sufficient communication distance for the transponder.

The coating layer is made of elastomer or rubber, and the dielectric constant of the coating layer is preferably 7 or less. By specifying the dielectric constant of the coating layer in this way, the communication performance of the transponder can be effectively improved.

It is preferable that the center of the transponder is located at least 10 mm away from the splice portion of the tire component in the tire circumferential direction. This can effectively improve the durability of the tire.

It is preferable that the transponder is disposed between a position 15 mm radially outward from the upper end of the bead core of the bead portion and the maximum tire width position. This allows the transponder to be disposed in an area where the stress amplitude during driving is small, effectively improving the durability of the transponder and preventing a decrease in the transponder's communication capability or the tire's durability.

1 is a meridian half cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. 2 is an enlarged cross-sectional view showing a main part of the pneumatic tire of FIG. 1. 1A and 1B are perspective views showing a transponder that can be embedded in a pneumatic tire according to the present invention. FIG. 2 is a cross-sectional view showing a transponder embedded in a pneumatic tire while being covered with a covering layer. FIG. 4 is a meridian half cross-sectional view showing a modified example of a pneumatic tire according to an embodiment of the present invention. 1A to 1C are plan views showing a transponder embedded in a pneumatic tire while being covered with a covering layer. 1A and 1B are plan views showing a transponder embedded in a pneumatic tire while being covered with a covering layer. FIG. 2 is a meridian cross-sectional view illustrating the pneumatic tire of FIG. 1 . FIG. 2 is an equatorial cross-sectional view that illustrates the pneumatic tire of FIG. 1 . FIG. 2 is an explanatory diagram showing radial positions of transponders in a test tire.

The configuration of the present invention will be described in detail below with reference to the attached drawings. Figures 1 to 8 show a pneumatic tire according to an embodiment of the present invention.

As shown in FIG. 1, the pneumatic tire of this embodiment has a tread portion 1 that extends in the circumferential direction of the tire and forms an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the radially inner side of the sidewall portions 2.

Between a pair of bead portions 3, at least one carcass layer 4 (one layer in FIG. 1) is mounted, which is made of a plurality of carcass cords arranged in the radial direction. The carcass layer 4 is covered with rubber. As the carcass cords constituting the carcass layer 4, organic fiber cords such as nylon and polyester are preferably used. An annular bead core 5 is embedded in each bead portion 3, and a bead filler 6 made of a rubber composition with a triangular cross section is arranged on the outer periphery of the bead core 5.

On the other hand, multiple belt layers 7 (two layers in FIG. 1) are embedded on the tire outer circumferential side of the carcass layer 4 in the tread portion 1. The belt layers 7 include multiple reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers 7.

At least one belt cover layer 8 (two layers in FIG. 1) is arranged on the tire outer periphery side of the belt layer 7, in which reinforcing cords are arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction, in order to improve high-speed durability. In FIG. 1, the belt cover layer 8 located on the inner side in the tire radial direction constitutes a full cover that covers the entire width of the belt layer 7, and the belt cover layer 8 located on the outer side in the tire radial direction constitutes an edge cover layer that covers only the ends of the belt layer 7. As the reinforcing cords of the belt cover layer 8, organic fiber cords such as nylon and aramid are preferably used.

In the above pneumatic tire, both ends 4e of the carcass layer 4 are folded back from the inside to the outside of the tire around each bead core 5, and are arranged to encase the bead core 5 and the bead filler 6. The carcass layer 4 includes a main body portion 4A that extends from the tread portion 1 through each sidewall portion 2 to each bead portion 3, and a rolled-up portion 4B that is rolled up around the bead core 5 in each bead portion 3 and extends toward each sidewall portion 2.

An inner liner layer 9 is disposed along the carcass layer 4 on the inner surface of the tire. A cap tread rubber layer 11 is disposed in the tread portion 1, a sidewall rubber layer 12 is disposed in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed in the bead portion 3.

In the pneumatic tire, the transponder 20 is embedded in the sidewall portion 2 at a location on the outer side of the carcass layer 4 in the tire width direction so as to extend along the tire circumferential direction. As shown in FIG. 2, the transponder 20 is covered by a covering layer 23. The covering layer 23 covers the entire transponder 20 by sandwiching both the front and back sides of the transponder 20.

As the transponder 20, for example, an RFID (Radio Frequency Identification) tag can be used. As shown in Figs. 3(a) and (b), the transponder 20 has an IC board 21 that stores data and an antenna 22 that transmits and receives data in a non-contact manner. By using such a transponder 20, information about the tire can be written or read at appropriate times, and the tire can be managed efficiently. RFID is an automatic recognition technology that is composed of a reader/writer with an antenna and a controller, and an ID tag with an IC board and an antenna, and can wirelessly communicate data.

The overall shape of the transponder 20 is not particularly limited, and may be, for example, columnar or plate-shaped as shown in Figs. 3(a) and (b). In particular, the columnar transponder 20 shown in Fig. 3(a) is preferable because it can follow the deformation of the tire in each direction. In this case, the antenna 22 of the transponder 20 protrudes from both ends of the IC board 21 and has a spiral shape. This allows it to follow the deformation of the tire during driving, improving the durability of the transponder 20. Furthermore, communication can be ensured by appropriately changing the length of the antenna 22.

In a pneumatic tire configured in this manner, the dielectric constant of the coating layer 23 that covers the transponder 20 is set lower than the dielectric constant of the surrounding rubber members adjacent to the coating layer 23 (e.g., the bead filler 6, the inner liner layer 9, the sidewall rubber layer 12, the rim cushion rubber layer 13, and the coating rubber of the carcass layer 4), and as shown in FIG. 5(a), the tire circumferential length Lc of the coating layer 23 and the tire circumferential length Lr of the transponder 20 satisfy the relationship 1.1≦Lc/Lr≦2.0.

In the above-mentioned pneumatic tire, the transponder 20 is covered with the covering layer 23, and the relative dielectric constant of the covering layer 23 is lower than that of the surrounding rubber member adjacent to the covering layer 23. The tire circumferential length Lc of the covering layer 23 and the tire circumferential length Lr of the transponder 20 satisfy the above relationship, so that the transponder 20 is sufficiently isolated from the surrounding rubber member and wrapped with the covering layer 23 having a low relative dielectric constant, thereby improving the communication performance of the transponder 20. In other words, since the radio wave wavelength is shortened in the dielectric, the length of the antenna 22 of the transponder 20 is set to resonate with the shortened radio wave wavelength. In this way, optimizing the length of the antenna 22 of the transponder 20 greatly improves the communication efficiency. However, in order to optimize the communication environment of the transponder 20, it is necessary to sufficiently isolate the transponder 20 from the surrounding rubber member adjacent to the covering layer 23. Therefore, by satisfying the relationship of 1.1≦Lc/Lr≦2.0, it is possible to improve the communication performance of the transponder 20. In addition, by defining the upper limit of the circumferential length Lc of the coating layer 23 relative to the circumferential length Lr of the transponder 2, it is possible to maintain good tire balance. This makes it possible to improve the communication performance of the transponder 20 while maintaining good tire balance.

Here, if the value of Lc/Lr is less than 1.1, the effect of improving the communication performance of the transponder 20 is not obtained, and conversely, if it is greater than 2.0, the tire balance deteriorates. In particular, it is desirable that the length Lc of the coating layer 23 in the tire circumferential direction and the length Lr of the transponder 20 in the tire circumferential direction satisfy the relationship 1.1≦Lc/Lr≦1.5.

Furthermore, in the above-mentioned pneumatic tire, the transponder 20 is embedded outside the carcass layer 4 in the tire width direction, so there is no tire component that blocks radio waves during communication of the transponder 20, and the communication performance of the transponder 20 can be ensured well. In the present invention, the transponder 20 is disposed in the sidewall portion 2, but the position in the tire axial direction is not particularly limited. When the transponder 20 is embedded outside the carcass layer 4 in the tire width direction, the transponder 20 can be disposed between the rolled-up portion 4B of the carcass layer 4 and the rim cushion rubber layer 13, or between the carcass layer 4 and the sidewall rubber layer 12. As another structure, the transponder 20 can be disposed between the rolled-up portion 4B of the carcass layer 4 and the bead filler 6, or between the main body portion 4A of the carcass layer 4 and the bead filler 6. Also, as shown in FIG. 5, the transponder 20 may be disposed between the carcass layer 4 and the inner liner layer 9.

In the above pneumatic tire, as shown in Figs. 6(a) to (c), the transponder 20 has a substrate 21 and an antenna 22 extending from both ends of the substrate 21, and the transponder 20 extends along the tire circumferential direction Tc. More specifically, the inclination angle α of the transponder 20 with respect to the tire circumferential direction is preferably within the range of ±20°. In addition, the distance L between the terminal of the antenna 22 in the tire circumferential direction and the terminal of the covering layer 23 in the tire circumferential direction preferably satisfies the relationship 0.05≦L/Lr≦0.50 with respect to the length Lr of the transponder 20 in the tire circumferential direction. As a result, the entire transponder 20 is reliably covered by the covering layer 23, so that the communication distance of the transponder 20 can be sufficiently ensured, and furthermore, the durability of the tire can be sufficiently ensured.

Here, if the absolute value of the inclination angle α of the transponder 20 with respect to the tire circumferential direction Tc is greater than 20°, the durability of the transponder 20 against repeated tire deformation during running is reduced. Also, if the distance L between the terminal of the antenna 22 in the tire circumferential direction and the terminal of the coating layer 23 in the tire circumferential direction is smaller than 0.05×Lr, the effect of improving the communication performance of the transponder 20 is reduced, and the terminal of the antenna 22 in the tire circumferential direction protrudes from the coating layer 23 during running, which may cause stress to concentrate on the terminal of the antenna 22 and reduce the durability of the tire. On the other hand, even if the distance L is made greater than 0.50×Lr, the effect of improving the communication performance of the transponder 20 is not further improved, and an unnecessary increase in weight occurs. In particular, it is desirable that the distance L between the terminal of the antenna 22 in the tire circumferential direction and the terminal of the coating layer 23 in the tire circumferential direction satisfy the relationship of 0.05≦L/Lr≦0.30 with respect to the length Lr of the transponder 20 in the tire circumferential direction.

In the above pneumatic tire, as shown in FIG. 4, it is preferable that the total thickness Gac of the covering layer 23 and the maximum thickness Gar of the transponder 20 satisfy the relationship 1.0 mm≦Gac-Gar≦3.0 mm. This ensures that the transponder 20 is reliably covered by the covering layer 23, thereby ensuring a sufficient communication distance for the transponder 20. In addition, by specifying the upper limit value of Gac-Gar, it is possible to maintain good tire balance and ensure sufficient tire durability.

Here, if the value of Gac-Gar is less than 1.0 mm, the effect of improving the communication performance of the transponder 20 is reduced. On the other hand, if the value of Gac-Gar is greater than 3.0 m, there is concern that the tire balance and durability of the tire may deteriorate. The total thickness Gac of the coating layer 23 is the total thickness of the coating layer 23 at a position including the transponder 20, and is, for example, the total thickness on a straight line that passes through the center C of the transponder 20 in the tire meridian cross section and is perpendicular to the carcass cord of the nearest carcass layer 4, as shown in FIG. 4. In addition, the thickness of the coating layer 23 formed on the outside of the transponder 20 on the straight line is preferably 0.3 mm to 1.5 mm. The cross-sectional shape of the coating layer 23 is not particularly limited, but may be, for example, a triangular, rectangular, trapezoidal, or spindle shape.

In the above pneumatic tire, as shown in Figures 7(a) and (b), the transponder 20 has a substrate 21 and antennas 22 extending from both ends of the substrate 21, and at least one of the antennas 22 may extend so as to be bent relative to the substrate 21. In this case, it is preferable that the angle β of each antenna 22 with respect to the tire circumferential direction Tc is within the range of ±20°. By restricting the inclination of the antennas 22 constituting the transponder 20 in this manner, the durability of the transponder 20 can be sufficiently ensured.

Here, if the absolute value of the inclination angle β of the transponder 20 with respect to the tire circumferential direction Tc is greater than 20°, stress will be concentrated at the base end of the antenna 22 due to repeated tire deformation during driving, reducing the durability of the transponder 20. Note that since the antenna 22 is not necessarily straight, the inclination angle β of the antenna 22 is the angle that the straight line connecting the base end and tip end of the antenna 22 makes with respect to the tire circumferential direction Tc.

As shown in FIG. 4, in the above pneumatic tire, it is preferable that the center C of the transponder 20 in the thickness direction is located within a range of 25% to 75% of the total thickness Gac of the covering layer 23 from the surface on one side in the thickness direction of the covering layer 23. This ensures that the transponder 20 is reliably covered by the covering layer 23, so that the surrounding environment of the transponder 20 is stable, no deviation in the resonant frequency occurs, and the communication distance of the transponder 20 can be sufficiently secured.

The coating layer 23 is preferably composed of rubber or elastomer and 20 phr or more of white filler. By configuring the coating layer 23 in this manner, the dielectric constant of the coating layer 23 can be made relatively low compared to when carbon is contained, and the communication properties of the transponder 20 can be effectively improved. In this specification, "phr" means parts by weight per 100 parts by weight of the rubber component (elastomer).

The white filler constituting the coating layer 23 preferably contains 20 phr to 55 phr of calcium carbonate. This allows the dielectric constant of the coating layer 23 to be relatively low, effectively improving the communication performance of the transponder 20. However, if the white filler contains an excessive amount of calcium carbonate, it becomes brittle and the strength of the coating layer 23 decreases, which is not preferable. In addition to calcium carbonate, the coating layer 23 can optionally contain 20 phr or less of silica (white filler) or 5 phr or less of carbon black. When a small amount of silica or carbon black is used in combination, the dielectric constant of the coating layer 23 can be reduced while maintaining the strength of the coating layer 23.

The dielectric constant of the coating layer 23 is preferably 7 or less, and more preferably 2 to 5. By appropriately setting the dielectric constant of the coating layer 23 in this way, radio wave permeability when the transponder 20 emits radio waves can be ensured, and the communication performance of the transponder 20 can be effectively improved. The dielectric constant of the rubber constituting the coating layer 23 is 860 MHz to 960 MHz at room temperature. Here, the room temperature conforms to the standard conditions of the JIS standard, which are 23±2°C and 60%±5% RH. The dielectric constant of the rubber is measured by the capacitance method after being treated at 23°C and 60% RH for 24 hours. The above-mentioned range of 860 MHz to 960 MHz corresponds to the currently allocated frequency of UHF RFID, but if the above-mentioned allocated frequency is changed, the dielectric constant of the range of the allocated frequency can be specified as above.

In the above pneumatic tire, as shown in FIG. 8, the transponder 20 is preferably arranged between a position P1 15 mm outward from the upper end 5e (the outer end in the tire radial direction) of the bead core 5 and a position P2 at the maximum tire width as the tire radial arrangement area. That is, the transponder 20 is preferably arranged in the area S1 shown in FIG. 8. When the transponder 20 is arranged in the area S1, the transponder 20 is located in an area where the stress amplitude during driving is small, so that the durability of the transponder 20 can be effectively improved, and further, the communication performance of the transponder 20 and the durability of the tire are not deteriorated. Here, if the transponder 20 is arranged inward in the tire radial direction from the position P1, the transponder 20 tends to deteriorate in communication performance because it is close to metal members such as the bead core 5. On the other hand, if the transponder 20 is disposed outside the position P2 in the tire radial direction, the transponder 20 is located in an area where the stress amplitude during running is large, and the transponder 20 itself is likely to be damaged or the interface around the transponder 20 is likely to peel off, which is not preferable. In particular, the transponder 20 is preferably disposed in a tire radial direction between a position 20 mm outward from the upper end 5e of the bead core 5 and the upper end of the bead filler 6, or between a position 20 mm outward from the upper end 5e of the bead core 5 and a position 40 mm outward from the upper end 5e of the bead core 5. In this case, the communication capability of the transponder 20 and the durability of the tire can be achieved at a high level.

As shown in FIG. 9, there are a number of splice sections on the circumference of the tire, which are formed by overlapping the ends of tire constituent members. FIG. 9 shows the tire circumferential position Q of each splice section. It is preferable that the center of the transponder 20 is located 10 mm or more away from the splice section of the tire constituent member in the tire circumferential direction. That is, the transponder 20 is preferably located in the region S2 shown in FIG. 9. Specifically, it is preferable that the IC board 21 constituting the transponder 20 is located 10 mm or more away from the position Q in the tire circumferential direction. Furthermore, it is more preferable that the entire transponder 20 including the antenna 22 is located 10 mm or more away from the position Q in the tire circumferential direction, and it is most preferable that the entire transponder 20 in a state where it is covered with the covering rubber is located 10 mm or more away from the position Q in the tire circumferential direction. In addition, it is preferable that the tire constituent member in which the splice section is located away from the transponder 20 is a member adjacent to the transponder 20. Examples of such tire components include the carcass layer 4, the bead filler 6, the inner liner layer 9, the sidewall rubber layer 12, and the rim cushion rubber layer 13. By disposing the transponder 20 at a position away from the splice portion of the tire components, the durability of the tire can be effectively improved.

More specifically, when the transponder 20 is disposed between the carcass layer 4 and the inner liner layer 9, it is preferable that the splice portion of the carcass layer 4 and/or the splice portion of the inner liner layer 9 are disposed away from the transponder 20. When the transponder 20 is disposed between the carcass layer 4 and one of the sidewall rubber layer 12 and the rim cushion rubber layer 13, and the carcass layer 4 has a low turn-up structure, it is preferable that for the transponder 20 located radially inward of the apex of the bead filler 6, the splice portion of the bead filler 6 and/or one of the splice portions of the sidewall rubber layer 12 and the rim cushion rubber layer 13 are disposed away from the transponder 20, and for the transponder 20 located in the flex zone radially outward of the apex of the bead filler 6, the splice portion of the carcass layer 4 and/or one of the splice portions of the sidewall rubber layer 12 and the rim cushion rubber layer 13 are disposed away from the transponder 20. When the transponder 20 is disposed between the carcass layer 4 and either the sidewall rubber layer 12 or the rim cushion rubber layer 13, and the carcass layer 4 has a high turn-up structure, it is preferable that the splice portion of the carcass layer 4 and/or the splice portion of either the sidewall rubber layer 12 or the rim cushion rubber layer 13 is disposed away from the transponder 20.

In the embodiment of FIG. 9, the tire circumferential positions Q of the splices of each tire component are arranged at equal intervals, but this is not limited to the embodiment. The tire circumferential positions Q can be set at any position, and in any case, the transponder 20 is arranged so as to be 10 mm or more away from the splices of each tire component in the tire circumferential direction.

In the above embodiment, an example is shown in which the terminal 4e of the turned-up portion 4B of the carcass layer 4 is positioned near the upper end 6e of the bead filler 6, but this is not limited to this, and the terminal 4e of the turned-up portion 4B of the carcass layer 4 can be positioned at any height.

In a pneumatic tire having a tire size of 235/60R18 and including a tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radial inside of these sidewall portions, a columnar transponder is embedded in the sidewall portion so as to extend in the tire circumferential direction on the tire width direction outer side of the carcass layer, the transponder is covered by a covering layer, and the ratio Lc/Lr of the tire circumferential length Lc of the covering layer to the tire circumferential length Lr of the transponder is The tires of Comparative Examples 1 and 2 and Examples 1 to 22 were manufactured with the following settings as shown in Tables 1 and 2: the ratio L/Lr of the distance L between the antenna's circumferential terminal and the coating layer's circumferential terminal and the transponder's circumferential length Lr, the difference Gac-Gar between the coating layer's total thickness Gac and the transponder's maximum thickness Gar, the antenna's angle β relative to the circumferential direction of the tire, the position of the transponder's center in the coating layer, the dielectric constant of the coating layer, the circumferential distance from the transponder center to the splice of the tire constituent member, and the radial position of the transponder.

In Comparative Examples 1 and 2 and Examples 1 to 22, the dielectric constant of the coating layer is lower than the dielectric constant of the surrounding rubber member. The ratio L/Lr is the smaller of the ratios L/Lr at both ends of the transponder. The position of the transponder center within the coating layer is expressed as the ratio of the distance from the surface of the coating layer on the carcass layer side to the transponder center to the total thickness Gac of the coating layer.

In Tables 1 and 2, the radial positions of the transponders in the tire correspond to positions A through E shown in Figure 10.

For these test tires, tire evaluation (tire balance and durability) and transponder evaluation (communication and durability) were performed using the following test methods, and the results are shown in Tables 1 and 2.

Communication (transponder):
A reader/writer was used to communicate with the transponder for each test tire. Specifically, the longest communication distance was measured with the reader/writer at an output of 250 mW and a carrier frequency of 860 MHz to 960 MHz. The evaluation results were shown in three stages: a communication distance of 1000 mm or more was indicated as "◎ (excellent)", a communication distance of 500 mm to 1000 mm was indicated as "○ (good)", and a communication distance of less than 500 mm was indicated as "△ (fair)".

Tire balance:
Each test tire was mounted on a standard rim wheel, and tire balance (dynamic) was measured under the conditions of an air pressure of 200 kPa, no load, and a rotation speed of 60 rpm. The evaluation results were shown on a three-level scale: "◎ (excellent)" indicates that the tire balance was not substantially worse than when there was no transponder or coating layer, "○ (good)" indicates that the tire balance was worsened but there was no vibration, and "△ (fair)" indicates that the tire balance was worsened and there was vibration.

Durability (tires and transponders):
Each test tire was mounted on a standard rim wheel, and a running test was performed using a drum test machine under the conditions of an air pressure of 120 kPa, 102% of the maximum load, and a running speed of 81 km, and the running distance when the tire broke down was measured. The evaluation results were shown in three stages: "◎ (excellent)" for a run of 6480 km, "○ (good)" for a run of 4050 km to 6480 km, and "× (not good)" for a run of less than 4050 km. Furthermore, for each test tire after the run, the transponder was checked for communication and damage, and if communication was possible and there was no damage (same as when it was new), it was shown in two stages: "○ (good)" for a run of communication possible but the communication distance was reduced due to antenna damage, and "△ (passable)".

As can be seen from Tables 1 and 2, the pneumatic tires of Examples 1 to 22 were able to improve the transponder communication performance while maintaining good tire balance in comparison with Comparative Example 1. In Comparative Example 1, Lc/Lr = 1.0, so the transponder communication performance was insufficient. In Comparative Example 2, Lc/Lr = 3.0, so the tire balance deteriorated.

REFERENCE SIGNS LIST 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 9 inner liner layer 11 tread rubber layer 12 sidewall rubber layer 13 rim cushion rubber layer 20 transponder 21 substrate 22 antenna 23 covering layer CL tire center line

Claims (8)

A pneumatic tire including a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions,
a transponder is embedded in the sidewall portion so as to extend along the tire circumferential direction, the transponder is covered with a covering layer, the covering layer has a relative dielectric constant lower than a relative dielectric constant of a peripheral rubber member adjacent to the covering layer, and a length Lc of the covering layer in the tire circumferential direction and a length Lr of the transponder in the tire circumferential direction satisfy the relationship: 1.1≦Lc/Lr≦2.0. The pneumatic tire according to claim 1, characterized in that the transponder has a substrate and an antenna extending from both ends of the substrate, and the distance L between the terminal of the antenna in the tire circumferential direction and the terminal of the coating layer in the tire circumferential direction satisfies the relationship 0.05≦L/Lr≦0.50 with respect to the length Lr of the transponder in the tire circumferential direction. The pneumatic tire according to claim 1 or 2, characterized in that the total thickness Gac of the coating layer and the maximum thickness Gar of the transponder satisfy the relationship 1.0 mm ≦ Gac - Gar ≦ 3.0 mm. A pneumatic tire according to any one of claims 1 to 3, characterized in that the transponder has a substrate and an antenna extending from both ends of the substrate, and the antenna extends within a range of ±20° with respect to the tire circumferential direction. A pneumatic tire according to any one of claims 1 to 4, characterized in that the center of the transponder in the thickness direction is located within a range of 25% to 75% of the total thickness Gac of the coating layer from the surface on one side in the thickness direction of the coating layer. A pneumatic tire according to any one of claims 1 to 5, characterized in that the coating layer is made of elastomer or rubber and has a relative dielectric constant of 7 or less. A pneumatic tire according to any one of claims 1 to 6, characterized in that the center of the transponder in the longitudinal direction is disposed at a distance of 10 mm or more in the circumferential direction of the tire from the splice portion of the tire constituent member. A pneumatic tire according to any one of claims 1 to 7, characterized in that the transponder is disposed between a position 15 mm radially outward from the upper end of the bead core of the bead portion and the maximum width position of the tire.

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