JP5302729B2 - Pneumatic tire and strain sensor used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance economic efficiency by efficiently attaching a strain sensor at an accurate position and permitting replacement of the strain sensor, and to ensure high measurement accuracy of the strain sensor during straight line traveling and during cornering. <P>SOLUTION: In a tire body 10 in which a sensor attachment hole 20 for attaching the strain sensor is recessedly disposed in an external surface Gs of a sidewall rubber 3G, the strain sensor 21 is fitted in the sensor attachment hole 20 while being compressed in the direction of the length thereof. Before fitting, a length L1 of the strain sensor 21 is larger than a length L0 of the sensor attachment hole 20, and the width W1 of the strain sensor 21 is not more than that W0 of the sensor attachment hole 20. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a strain sensor used for detecting a force acting on a tire by outputting a strain output obtained by measuring a strain of a sidewall portion, and a pneumatic tire including the strain sensor.

  In recent years, three or more strain sensors are attached to different positions in the tire circumferential direction on at least one side wall of the tire, and tire strain is simultaneously measured at a predetermined tire rotation angle position. A technique for estimating the longitudinal force, lateral force, and vertical force acting on the tire (hereinafter sometimes collectively referred to as three component forces) by a plurality of simultaneous sensor outputs (distortion outputs), for example, It is proposed in Patent Document 1 and the like. Patent Document 1 shows a case where three component forces are estimated from three sensor outputs.

And in this patent document 1, as the attachment method of the said strain sensor,
(1) Before the tire is vulcanized, the strain sensor is embedded in the sidewall portion or attached to the inner surface or the outer surface of the sidewall portion, and attached by vulcanization adhesion by subsequent vulcanization, or (2) It is disclosed that a strain sensor is attached to an inner surface or an outer surface of a sidewall portion after vulcanization by bonding with an adhesive.

Japanese Patent Laid-Open No. 2005-126008

  However, in any case, it is difficult to attach the strain sensor to an accurate position, and there are problems that the estimation accuracy of the three component force is impaired and the attachment work efficiency or the tire manufacturing efficiency is impaired. In addition, since the strain sensor is integrally fixed to the tire, even if one of the plurality of strain sensors fails, it is necessary to replace the entire tire, resulting in poor economic efficiency. In the former case, there is also a problem that the vulcanization pressure may cause a failure of the strain sensor.

  Therefore, the present inventors have provided a sensor mounting hole in the outer surface of the sidewall portion, and fitted a rectangular parallelepiped strain sensor in which a magnet and a magnetic sensor element are embedded in the sensor mounting hole. Proposed to wear. The maximum gain line of the strain sensor is arranged in the direction that is the length direction of the rectangular parallelepiped shape. However, in this case, due to the lateral force received when the tire corners, the sensor mounting hole is subjected to compressive deformation in two directions, ie, the length direction and the width direction, or tensile deformation is generated in the two directions. . Therefore, when a strain sensor of approximately the same size is fitted in the sensor mounting hole, the strain sensor cannot follow the tensile deformation in the two directions in the sensor mounting hole, and the tire strain Can not be measured.

  Even when the sensor mounting hole is compressed and deformed in two directions, as shown in FIG. 9, it is difficult to accurately measure the tire strain. The figure shows an example of the result of measuring the tire strain in the sidewall portion when cornering at a slip angle of -1 ° using a strain sensor. Sample 1 has a sensor mounting hole in the side wall, and the sensor output when the strain sensor is directly attached to the opposite side in the length direction by bonding. Sample 2 has a sensor output in the side wall. Sensor outputs when a rectangular parallelepiped strain sensor is fitted in the sensor mounting holes are shown.

  In the same figure, at the ground contact position PA where the rotation angle is about 150 °, the force is properly transmitted from the sensor mounting hole in the sample 2 because it is strongly compressed and deformed in two directions. 3100 mV) is measured. However, as the compressive deformation decreases gradually away from the ground contact position PA, the force transmission from the sensor mounting hole in Sample 2 becomes worse, and the difference in sensor output from Sample 1 gradually increases. For example, the tire rotation angle is 225 °. An output difference Δ of about 200 mV occurs in the vicinity of the position PB. Note that sample 3 in the figure shows the sensor output when measuring the tire distortion of the sidewall portion in the straight running using the strain sensor attached to the sensor mounting hole by fitting. Sensor output is decreasing near position PB.

  This is explained as follows. FIG. 10 exaggerates the state of the sensor mounting hole a at the position PB. The length La of the sensor mounting hole a is the longest when traveling straight, and the length is increased by two-way compression deformation during cornering. The length La and the width Wa are gradually shortened. However, the strain sensor b arranged in the sensor mounting hole a cannot extend to the length La of the sensor mounting hole a when going straight, and the length direction is between the strain sensor b and the sensor mounting hole a. The gap d is generated. Further, even when compressive deformation in two directions occurs due to cornering, the strain sensor b cannot completely fill the gap d with the sensor mounting hole a in the length direction. In other words, even on the compression side during straight traveling and cornering, the strain sensor b is difficult to deform following the sensor mounting hole a in the length direction in which the maximum gain line faces, and the measurement accuracy is lowered. The problem to be left remains.

  Therefore, the present invention is based on the principle that the length of the strain sensor is larger than the length of the sensor mounting hole, and the strain sensor is fitted in a compressed state in the length direction, so that the strain sensor is efficiently mounted at an accurate position. An object of the present invention is to provide a pneumatic tire capable of exchanging a strain sensor and improving economy by enabling the replacement of the strain sensor, and ensuring high measurement accuracy by the strain sensor even during straight running and cornering, and a strain sensor used therefor It is said.

In order to solve the above problems, the invention of claim 1 of the present application is a pneumatic tire including a strain sensor used for detecting a force acting on a tire by outputting a strain output obtained by measuring a strain of a sidewall portion. There,
It has at least a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a sidewall rubber disposed on the outside of the carcass and having an outer surface forming the sidewall surface, and on the outer surface of the sidewall rubber. A tire body having a sensor mounting hole for mounting a strain sensor formed of a rectangular parallelepiped square hole,
And a rubber base made of a rubber elastic material to form a rectangular parallelepiped shape in which a magnet body and a magnetic sensor element facing the magnet body are embedded, and the gain is maximized in the direction of the length direction of the rectangular parallelepiped shape. It has a strain sensor with a line,
In addition, the strain sensor is compressed in the length direction and inserted into the sensor mounting hole, so that at least the side wall surfaces on both sides in the length direction of the strain sensor and the side wall surfaces on both sides in the length direction of the sensor mounting hole. And the pressure contact,
Before the insertion, the length L1 of the strain sensor is larger than the length L0 of the sensor mounting hole, and the width W1 of the strain sensor is not more than the width W0 of the sensor mounting hole.

  In the invention of claim 2, before the insertion, the length L1 of the strain sensor is 1.10 to 1.40 times the length L0 of the sensor mounting hole, and the width W1 of the strain sensor is It is characterized by being 0.90 to 1.00 times the width W0 of the mounting hole.

  According to a third aspect of the present invention, the strain sensor is provided with a hollow portion extending through the rubber base in the width direction and / or the height direction between the magnet body and the magnetic sensor element. Thus, the volume of the cavity is reduced.

  According to a fourth aspect of the present invention, the volume V1 of the hollow portion before insertion is 0.7 to 0.7 (V2−V3) of the difference (V2−V3) between the apparent volume V2 of the strain sensor and the volume V3 of the sensor mounting hole before insertion. It is characterized by being 1.50 times.

  According to a fifth aspect of the present invention, the magnet body is made of a samarium cobalt magnet.

The invention of claim 6 is a strain sensor used for detecting a force acting on a tire by outputting a strain output obtained by measuring a strain of a sidewall portion,
A maximum gain line in which a magnet body and a magnetic sensor element facing the magnet body are embedded in a rubber base made of a rubber elastic material, and the gain is maximized in the lengthwise direction of the rectangular body shape. Is arranged,
The rubber base includes a hollow portion extending through the rubber base in the width direction and / or the height direction between the magnet body and the magnetic sensor element.

  The apparent volume V2 of the strain sensor means the volume of the strain sensor when it is assumed that the cavity is not disposed.

  The present invention has a rectangular parallelepiped shape in which a magnet and a magnetic sensor element facing the magnet are embedded in a rubber base made of a rubber elastic material, and a maximum gain line is arranged in the direction of the length of the rectangular parallelepiped shape. The strain sensor is fitted into a sensor mounting hole provided on the outer surface of the sidewall rubber. At this time, the length L1 of the strain sensor before insertion is larger than the length L0 of the sensor mounting hole and the width W1 of the strain sensor is set to be equal to or smaller than the width W0 of the sensor mounting hole, and the strain sensor is compressed in the length direction. ing.

  Therefore, even when the sensor mounting hole is stretched and deformed in the length direction during straight running and cornering, the strain sensor is previously compressed in the length direction, so that it is stretched and deformed following the sensor mounting hole. Measurement accuracy can be improved.

  Further, since the sensor mounting hole can be formed by a vulcanization mold at the time of tire vulcanization molding, the strain sensor can be mounted at an accurate position. Further, the mounting is efficient because the strain sensor is inserted, so that the working efficiency and the tire manufacturing efficiency can be improved, and the economical strain can be improved because the failed strain sensor can be replaced.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. It is a side view of the pneumatic tire which shows the arrangement state of a strain sensor schematically. It is a disassembled perspective view which shows a sensor attachment hole with a distortion sensor. It is a diagram which shows the attachment direction of a strain sensor. (A), (B) is the top view and side view which show one Example of a strain sensor. (A) is a graph showing changes in sensor output of a strain sensor before and after vulcanization when a samarium cobalt magnet is used for the magnet body, and (B) is a vulcanization when a neodymium magnet is used for the magnet body. It is a graph which shows the change of the sensor output of the distortion sensor before and behind. The graph which shows the change of a sensor output by the temperature change in a strain sensor when a samarium cobalt magnet is used for a magnet body and when a neodymium magnet is used. (A), (B) is the top view and side view of a strain sensor which show the other Example of a cavity part. It is a graph which shows the result of having measured the tire distortion of the sidewall part at the time of cornering with a slip angle of -1 degrees using a strain sensor. It is a diagram which exaggerates and shows the state of a deformation | transformation of a sensor attachment hole.

  Hereinafter, embodiments of the present invention will be described in detail. In FIG. 1, a pneumatic tire 1 according to the present embodiment includes a tire body 10 having a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a sidewall surface of the tire body 10. And a strain sensor 21 that is fitted into a sensor mounting hole 20 provided in the sensor.

  The tire body 10 is a vulcanized tire that has been vulcanized by a vulcanization mold, and a sidewall rubber 3G having an outer surface Gs forming a sidewall surface is disposed outside the carcass 6.

  The carcass 6 is formed of one or more carcass plies 6A in this example, in which carcass cords are arranged at an angle of, for example, 70 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A includes a series of ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the ply main body portion 6 a that extends between the bead cores 5 and 5. A bead reinforcement bead apex rubber 8 having a triangular cross-section extending outward from the bead core 5 in the tire radial direction is disposed between the ply main body portion 6a and the ply turn-up portion 6b.

  A tread reinforcing belt layer 7 is wound in the tire circumferential direction inside the tread portion 2 and outside the carcass 6 in the radial direction. The belt layer 7 is formed from two or more belt plies 7A and 7B in which belt cords are arranged at an angle of, for example, 10 to 35 ° with respect to the tire circumferential direction, and each belt cord is between plies. By crossing each other, the belt rigidity is enhanced, and the substantially entire width of the tread portion 2 is firmly reinforced with a tagging effect. In this example, on the outer side in the radial direction of the belt layer 7, a band cord is spirally wound at an angle of 5 degrees or less with respect to the circumferential direction for the purpose of improving high-speed running performance and high-speed durability. A band layer 9 is provided.

  Next, the sidewall rubber 3G is made of a soft rubber having a rubber hardness Hs (durometer A hardness) of, for example, 48 to 53, and covers and protects the carcass 6 from an injury. The outer surface Gs of the side wall rubber 3G is provided with at least one sensor mounting hole 20 for mounting a strain sensor, preferably three or more, and more preferably six or more. In the case where a plurality of sensor mounting holes 20 are formed, as shown in FIG. 2, it is convenient to arrange them at equal intervals on the same circumferential line i centered on the tire axis. From the viewpoint of properties and the like. The figure illustrates the case where eight sensor mounting holes 20 are formed on the same circumferential line i at equal intervals.

  As shown in an enlarged view in FIG. 3, the sensor mounting hole 20 is a rectangular parallelepiped-shaped rectangular hole, and includes a bottom surface 22 parallel to the outer surface Gs, and a peripheral wall surface 23 surrounding the bottom surface 22. With The peripheral wall surface 23 includes side wall surfaces 23A and 23A on both sides in the length direction, and side wall surfaces 23B and 23B on both sides in the width direction perpendicular to the length direction. Thus, by forming the sensor mounting hole 20 in a rectangular parallelepiped shape, the strain sensor 21 can be stably mounted in an accurate posture, and the deformation of the sensor mounting hole 20 can be accurately applied to the strain sensor 21. Can contribute to the improvement of distortion measurement accuracy.

  As conceptually shown in FIG. 4, the sensor mounting hole 20 has a rectangular parallelepiped width center line c1 of 30 to 60 °, more preferably 40 to 50 °, still more preferably 45 with respect to the tire radial direction line. Inclined at an angle θ of °.

  Next, as shown in FIGS. 5A and 5B, the strain sensor 21 faces the magnet body 11 and the magnet body 11 with a gap in a rubber base 13 made of a rubber elastic material. It has a rectangular parallelepiped shape in which the magnetic sensor element 12 is embedded. A maximum gain line K that maximizes the gain is arranged in the direction of the length of the rectangular parallelepiped shape.

  The rubber elastic material forming the rubber base 13 is an already vulcanized rubber, for example, a raw rubber base in which the magnet body 11 and the magnetic sensor element 12 are embedded in a mold. It is formed by sulfur molding. Therefore, vulcanization heat of, for example, around 150 ° C. acts on the magnet body 11 and the magnetic sensor element 12 when the strain sensor is manufactured. Therefore, as the magnetic sensor element 12, a sensor element having excellent heat resistance, for example, a Hall element, an MR element (magnetoresistance effect element), a TMF-MI element, a TMF-FG element, an amorphous sensor, etc. can be adopted. A Hall element can be suitably employed from the viewpoint of sensitivity, ease of handling, and the like.

  The magnet body 11 is preferably a rare earth magnet capable of obtaining a high magnetic flux density. However, depending on the type, demagnetization occurs due to the vulcanization heat, and the initial sensor output cannot be obtained. Therefore, the magnet body 11 is preferably a samarium cobalt magnet (so-called samacoba magnet) having a high Curie temperature and a small change in magnetic flux density due to temperature. 6A shows the sensor output (indicated by Δ) when a samarium cobalt magnet is used for the magnet body 11 and the strain sensor 21 is vulcanized under a vulcanization condition of 150 ° C. for 30 minutes. The results of comparison with the sensor output (indicated by the solid line) of the unvulcanized strain sensor before vulcanization are shown. In the figure, the horizontal axis represents the distance between the magnet body 11 and the magnetic sensor element 12 (Hall element is used), and the vertical axis represents the sensor output at that time. In the case of a samarium cobalt magnet, it can be confirmed that there is no change in the sensor output before / after vulcanization. In addition, although the result when the same test was performed using a neodymium magnet for the magnet body 11 is shown in FIG. 6 (B), in the case of a neodymium magnet, demagnetization occurs after vulcanization, compared with that before vulcanization. It can be confirmed that the sensor output decreases.

  The samarium cobalt magnet is also preferable from the viewpoint of keeping the change in the sensor output low because the change in the magnetic flux density is small even with respect to the temperature change within the ambient temperature (25 to 35 ° C.) when the tire travels in the actual vehicle. A sample A of a strain sensor using a samarium cobalt magnet as the magnet body 11 and a sample B of a strain sensor using a neodymium magnet were prototyped under the vulcanization conditions, and the sensor output with respect to a temperature change within the environmental temperature. The results of testing the change are shown in FIG. As shown in the figure, it can be confirmed that sample A (using samarium-cobalt magnet) has a substantially constant sensor output with respect to a temperature change within the environmental temperature during actual vehicle travel, and can exhibit high measurement accuracy.

  Here, in the strain sensor 21, as shown in FIG. 3, the length L <b> 1 in the length direction of the strain sensor 21 is set to the length of the sensor mounting hole 20 before being inserted into the sensor mounting hole 20. It is important that the strain sensor has a width W1 that is greater than L0 and is not more than the width W0 of the sensor mounting hole. As a result, the strain sensor 21 is inserted into the sensor mounting hole 20 in a compressed state in the length direction, and the length of the side wall surface 33A on both sides of the strain sensor 21 in the length direction and the sensor mounting hole 20 is lengthened. The side wall surfaces 23A on both sides in the direction can be pressed.

  When the strain sensor 21 is attached in a compressed state as described above, the strain sensor 21 itself is in a length direction that is released from compression in response to tensile deformation in the length direction of the sensor attachment hole 20 during straight traveling or cornering. Can stretch and deform. That is, the strain sensor 21 can be extended and deformed following the tensile deformation of the sensor mounting hole 20, and the amount of deformation can be measured with high accuracy.

  The ratio L1 / L0 between the length L1 of the strain sensor 21 and the length L0 of the sensor mounting hole 20 before the insertion is 1.10 to 1.40, the width W1 of the strain sensor 21, and the sensor mounting hole 20 The ratio W1 / W0 to the width W0 is preferably 0.90 to 1.00. When the ratio L1 / L0 is less than 1.10, the compression amount of the strain sensor 21 is too small to follow the large tensile deformation of the sensor mounting hole 20, and a gap is generated between the side wall surfaces 33A and 23A. Reduce measurement accuracy. On the contrary, if the ratio L1 / L0 exceeds 1.40, the amount of compression becomes excessive, and the mounting work to the sensor mounting hole 20 becomes difficult.

  On the other hand, if the ratio W1 / W0 exceeds 1.00, the resistance between the side wall surfaces 33B on both sides in the width direction of the strain sensor 21 and the side wall surfaces 23B on both sides in the width direction of the sensor mounting hole 20 increases. If the ratio W1 / W0 is less than 0.9, a gap is generated between the side wall surfaces 33B and 23B, and the strain sensor 21 in the sensor mounting hole 20 is deformed. The stability of seating is impaired, and the measurement accuracy and the mounting strength tend to be reduced.

  In order to ensure the above-described high compression amount, in this example, the strain sensor 21 is provided between the magnet body 11 and the magnetic sensor element 12 as shown in FIGS. 5 (A) and 5 (B). A hollow portion 14 extending through the rubber base 13 in the width direction and / or the height direction is provided.

  In this example, the cavity 14 has one or more (five in this example) vertical hole portions 14A extending in the height direction in the rubber base 13 in the height direction, and the length direction of each side wall surface 33B. One or more (two in this example) circular cross-sections extending in the width direction in the rubber base 13 and the vertical cut-out recesses 14B made of, for example, cross-section arc-shaped cuts extending in the height direction at the center. The horizontal hole portion 14C. These cavities 14 are preferably formed symmetrically with respect to both the width center line and the length center line of the strain sensor 21.

  Such a cavity 14 is elastically deformed with respect to the compression in the length direction of the strain sensor 21, and by reducing the volume thereof, the high compression deformation and the compression from which the ratio L1 / L0 is 1.10 or more are achieved. It is possible to allow elongation deformation. For this reason, the total volume V1 of the cavity 14 before insertion is 0.7 to 0.7 (V2−V3) of the difference (V2−V3) between the apparent volume V2 of the strain sensor 21 and the volume V3 of the sensor mounting hole 20 before insertion. It is preferably 1.50 times. If the volume ratio V1 / (V2-V3) is less than 0.7, the cavity portion 14 is completely crushed by the insertion, so that it is difficult to attach the strain sensor 21 to the sensor attachment hole 20. On the other hand, if the ratio V1 / (V2-V3) exceeds 1.50, the cavity portion 14 becomes excessive and the rubber elastic force of the strain sensor 21 is reduced, so that the elastic deformation of the strain sensor 21 is reduced. Decreases. From such a viewpoint, the ratio V1 / (V2-V3) has a lower limit value of preferably 1.0 or more, and an upper limit value of 1.2 or less.

  The rubber elastic material forming the rubber base 13 has a rubber hardness Hs (durometer A hardness) equal to or less than the rubber hardness Hs of the side wall rubber 3G in order to ensure followability with respect to the sensor mounting hole 20. The difference in rubber hardness Hs is preferably 3 to 8 °.

  The strain sensor 21 has a built-in transmission means (not shown) for transmitting a strain output of the measured strain to an electronic control unit (ECU) of a vehicle control system provided in the vehicle. This transmitting means is composed of a semiconductor in which a transmission / reception circuit, a control circuit, a memory, etc. are made into a chip, and an antenna. The distortion output data can be transmitted as response radio waves.

  Next, FIGS. 8A and 8B show another embodiment of the cavity 14. In this example, the hollow portion 14 includes one or more (in this example, one) rectangular hole-like vertical hole portions 14A each having a rectangular cross section (including a square) extending in the height direction in the rubber base 13, One or more longitudinal notch recesses 14B made of, for example, arc-shaped cutouts extending in the height direction at the center in the longitudinal direction of the side wall surface 33B, and one or more circular cross-sections extending in the width direction in the rubber base 13 It is comprised from the horizontal hole part 14C (one in this example). The total volume V1 of the cavity 14 before insertion is 0.7 to 1.50 times the difference (V2−V3) between the apparent volume V2 of the strain sensor 21 and the volume V3 of the sensor mounting hole 20 before insertion. Is set in the range. Such a square hole-shaped vertical hole portion 14A is a preferable mode in securing a large volume V1.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 3G Side wall rubber 4 Bead part 5 Bead core 6 Carcass 10 Tire main body 11 Magnet 12 Magnetic sensor element 13 Rubber base 14 Cavity part 20 Sensor attachment hole 21 Strain sensor 23A Side wall surface 33A Side wall surface Gs on both sides in length direction Outer surface K Maximum gain line

Claims (6)

A pneumatic tire comprising a strain sensor used for detecting a force acting on the tire by outputting a strain output obtained by measuring the strain of the sidewall portion,
It has at least a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a sidewall rubber disposed on the outside of the carcass and having an outer surface forming the sidewall surface, and on the outer surface of the sidewall rubber. A tire body having a sensor mounting hole for mounting a strain sensor formed of a rectangular parallelepiped square hole,
And a rubber base made of a rubber elastic material to form a rectangular parallelepiped shape in which a magnet body and a magnetic sensor element facing the magnet body are embedded, and the gain is maximized in the direction of the length direction of the rectangular parallelepiped shape. It has a strain sensor with a line,
In addition, the strain sensor is compressed in the length direction and inserted into the sensor mounting hole, so that at least the side wall surfaces on both sides in the length direction of the strain sensor and the side wall surfaces on both sides in the length direction of the sensor mounting hole. And the pressure contact,
Before insertion, the length L1 of the strain sensor is greater than the length L0 of the sensor mounting hole, and the width W1 of the strain sensor is equal to or less than the width W0 of the sensor mounting hole. Tires.   Before the insertion, the length L1 of the strain sensor is 1.10 to 1.40 times the length L0 of the sensor mounting hole, and the width W1 of the strain sensor is 0 of the width W0 of the sensor mounting hole. The pneumatic tire according to claim 1, wherein the pneumatic tire is .90 to 1.00 times.   In the strain sensor, a cavity extending through the rubber base in the width direction and / or the height direction is provided between the magnet body and the magnetic sensor element, and the volume of the cavity is increased by the fitting. The pneumatic tire according to claim 1, wherein the pneumatic tire decreases.   The volume V1 of the cavity before the insertion is 0.7 to 1.50 times the difference (V2−V3) between the apparent volume V2 of the strain sensor and the volume V3 of the sensor mounting hole before the insertion. The pneumatic tire according to claim 3.   The pneumatic tire according to claim 1, wherein the magnet body is made of a samarium cobalt magnet. A strain sensor used for detecting a force acting on a tire by outputting a strain output obtained by measuring a strain of a sidewall portion,
A maximum gain line in which a magnet body and a magnetic sensor element facing the magnet body are embedded in a rubber base made of a rubber elastic material, and the gain is maximized in the lengthwise direction of the rectangular body shape. Is arranged,
The strain sensor according to claim 1, wherein the rubber base includes a hollow portion extending through the rubber base in a width direction and / or a height direction between the magnet body and the magnetic sensor element.

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