JP4939210B2 - Tire longitudinal force detection method and pneumatic tire used therefor - Google Patents

Description

  The present invention relates to a method for detecting a longitudinal force of a tire for measuring a torsional deformation in a rotational direction of the tire and detecting a longitudinal force acting on the pneumatic tire, and a pneumatic tire used therefor.

  In recent years, various vehicle control systems such as ABS (anti-lock brake system), TCS (traction control system), and VSC (vehicle stability control) have been developed in order to ensure the stability and safety of a running vehicle. Yes. In order to control these systems, it is necessary to accurately grasp the rolling state of the running tire. For example, in ABS, it is necessary to grasp the slip condition of a tire. For that purpose, a longitudinal force (circumferential force) acting on the tire is detected, and the slip condition is related to the detected longitudinal force. It has been proposed to estimate the road surface friction coefficient and road surface adhesion ability of tires.

  As a method for detecting the longitudinal force, the one disclosed in Patent Document 1 is known. In Patent Document 1, a mark is provided on a sidewall portion of a tire, and a mark sensor attached to a vehicle body detects passage of the mark during tire rotation. Further, a wheel speed sensor having a disk body with a tooth groove, which can rotate integrally with the axle and has tooth grooves formed on the outer peripheral edge at equal pitch intervals, is attached to the vehicle body. The disc body has one missing portion with a tooth gap missing, and the wheel speed sensor detects the rotational speed and phase angle of the axle by detecting the passage of the tooth gap and the missing portion. sell.

  Then, based on the time point when the wheel speed sensor detects the passage of the defective part, the change of the time difference at the time when the mark sensor detects the passage of the mark of the tire is read, thereby acting on the tire from the change of the time difference. The longitudinal force can be detected.

JP-A-2005-221385

  However, the detection method requires two sensors and is affected by errors from each sensor, so that it is difficult to sufficiently increase measurement accuracy. Further, when the tire is attached or detached, the relative position in the circumferential direction between the tire and the axle is shifted, so that there is a problem that the time difference from the reference itself changes.

  Therefore, the present invention does not change the time difference from the reference itself even when the tire is attached and detached, and can measure the torsional deformation in the rotational direction of the tire with a single sensor and can detect the longitudinal force of the tire with high accuracy. It is an object to provide a method and a pneumatic tire used therefor.

In order to achieve the above-mentioned object, the invention of claim 1 of the present application is a tire longitudinal force detection method for detecting a circumferential longitudinal force acting on a tire, wherein the first circumference around a tire axial center is provided. A magnetic body set comprising: a first magnetic body positioned on a line; and a second magnetic body positioned on a second circumferential line that is concentrically arranged radially outward of the first circumferential line. And the first and second magnetic bodies include a pneumatic tire embedded in a protruding portion protruding from the surface of the sidewall portion , the first circumferential line and the second circumferential line. A magnetic sensor attached to the vehicle body at an intermediate position and capable of sequentially detecting the passage of the first magnetic body and the passage of the second magnetic body; and from the passage of the first magnetic body Detecting the longitudinal longitudinal force based on the change of the passage time until the passage of the magnetic body 2 It is a symptom.

  According to a second aspect of the present invention, the magnetic sensor is attached to a grounding opposite region on the opposite side of the tire shaft center from the grounding portion where the tire is grounded.

The invention of claim 3 is a pneumatic tire used in the longitudinal force detection method of claim 1 or 2,
A first magnetic body located on a first circumferential line centered on the tire axis and a second circumference concentrically disposed radially outward of the first circumferential line in the sidewall portion; A magnetic body set comprising a second magnetic body located on the line,
The first and second magnetic bodies are embedded in a protruding portion protruding from the surface of the sidewall portion.

  According to a fourth aspect of the present invention, in the magnetic body set, a radial distance between the first magnetic body and the second magnetic body is 15 to 40 mm.

  According to the invention of claim 5, in the magnetic body set, the first magnetic body and the second magnetic body are displaced in the tire circumferential direction and the magnetic body on the circumferential line passing through the tire maximum width position. The positional deviation distance Lc is set to 3 to 30 mm, and the magnetic pole direction of the first magnetic body and the magnetic pole direction of the second magnetic body are respectively set in the tire radial direction.

  The invention according to claim 6 is characterized in that a plurality of magnetic body sets are arranged in the circumferential direction, and the magnetic body sets adjacent to each other in the circumferential direction have different positional displacement distances Lc of the magnetic bodies.

  According to a seventh aspect of the invention, the first circumferential line and the second circumferential line are arranged inside and outside in the radial direction across the tire maximum width position.

  According to an eighth aspect of the present invention, the protruding portion includes a hole extending from the first magnetic body and the second magnetic body to the surface of the protruding portion.

  As described above, in the present invention, the first and second magnetic bodies are attached to the sidewall portion of the tire so as to be separated from the inside and outside in the tire radial direction, and the first and second magnetic bodies are attached to the vehicle body side. A magnetic sensor is attached at an intermediate position in the tire radial direction. By arranging the magnetic sensor at the intermediate position, the passage of both the first magnetic body and the second magnetic body can be sequentially detected by one sensor.

Therefore, the longitudinal force in the circumferential direction can be detected based on the change in the passage time from the passage of the first magnetic body to the passage of the second magnetic body. In addition, calculation of the longitudinal force from the change of passage time can be performed by following Formula.
(Front / rear force) = (change in transit time) × (tire rotation speed) × (tire circumferential spring constant)
The tire circumferential spring constant is a value unique to the tire, and the relationship between the longitudinal force acting on the tire tread and the amount of twist deformation at the mounting position of the magnetic sensor generated in the tire at that time, for example, the tire It can be obtained in advance by measuring at the time of manufacture, shipment, etc.

  As described above, since two magnetic bodies are detected by one sensor, for example, the influence of noise due to vibrations at the sensor mounting portion can be halved and the accuracy is high compared to the case where two sensors are used. Measurement can be performed. It can also contribute to cost reduction and simplification of the structure. In addition, since the magnetic body as the detection target is attached only to the tire, the measurement reference position can be kept constant even when the tire is attached or detached.

  On the other hand, since a large distortion occurs during running on the sidewall portion of the tire, when a magnetic material is attached to the sidewall portion, there arises a problem that peeling occurs at the interface and the magnetic material is dropped. However, as a result of the inventor's research, when, for example, a block-like protrusion is provided on the surface of the sidewall portion, the distortion concentrates near the base of the protrusion, so that the distortion inside the protrusion becomes very small. Therefore, by embedding a magnetic material in the projecting portion, it is possible to suppress dropping of the magnetic material and tire damage caused by the magnetic material.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a cross-sectional view showing a pneumatic tire used in the method for detecting longitudinal force of a tire according to the present invention, FIG. 2 is a cross-sectional view showing an enlarged main portion thereof, and FIG. 3 is a tire showing an arrangement state of magnetic body sets. It is a side view.

As shown in FIG. 1, the longitudinal force detection method of this embodiment includes
(1) a pneumatic tire 21 in which a magnetic body set 5 composed of a first magnetic body 3A and a second magnetic body 3B is attached to a sidewall portion 23, and (2) the first tire 1A attached to a vehicle body 6 One magnetic sensor 7 capable of sequentially detecting the passage of the magnetic body 3A and the passage of the second magnetic body 3B is used.

Then, by operating the watch counter using the detection signal (or detection output) of this passage as a switch, the second magnetic field 3A is passed through the second magnetic material 3A as shown in FIGS. 6 (A) and 6 (B). A change Δt in the passage time t until the magnetic body 3B passes (may be a change Δt in the passage time t from the passage of the second magnetic body 3B to the passage of the first magnetic body 3A). Can do. Further, the change Δt in the passage time t corresponds to the torsional deformation in the circumferential direction of the tire, and is in a substantially proportional relationship with the longitudinal force F acting on the tire. Therefore, based on the change Δt in the passage time t, The longitudinal force F can be detected.

  Specifically, as shown in FIG. 3, the magnetic body set 5 includes one first magnetic body 3 </ b> A located on a first circumferential line J <b> 1 centered on a tire axis i, and the first It is formed by a pair with one second magnetic body 3B located on the second circumferential line J2 concentrically arranged on the outer side in the radial direction of one circumferential line J1. At this time, the first circumferential line J1 and the second circumferential line J2 are preferably provided inside and outside in the radial direction of the circumferential line Jp passing through the tire maximum width position P (shown in FIG. 2). FIG. 3 illustrates a case where a plurality of sets (12 sets in this example) of magnetic body sets 5 are arranged on the sidewall portion 23 of the tire, but only one set of magnetic body sets 5 is arranged. You may do it. The first and second magnetic bodies 3A and 3B are so-called magnets, and are not particularly restricted. For example, those having a magnetic flux density of about 2500 to 4500 gauss can be suitably used.

  In each magnetic body set 5, the first and second magnetic bodies 3 </ b> A, 3 </ b> B have the magnetic pole direction f as the tire radial direction, and the first magnetic body 3 </ b> A and the second magnetic body 3 </ b> B are tires. They are displaced from each other in the circumferential direction. The magnetic pole direction f means the direction of a magnetic pole line that is a line connecting the N pole and the S pole through the center of the magnetic body.

  At this time, as shown in an enlarged view in FIG. 4, the positional displacement distance Lc in the tire circumferential direction between the magnetic bodies 3A and 3B measured on the circumferential line Jp passing through the tire maximum width position P is in the range of 3 to 30 mm. The tire radial distance Lr between the magnetic bodies 3A and 3B is preferably in the range of 15 to 40 mm. The “position displacement distance Lc” means a circumferential distance on the circumferential line Jp between the magnetic pole lines. The “tire radial direction distance Lr” means a radial distance between the inward magnetic pole surfaces 3s and 3s on the magnetic bodies 3A and 3B facing each other. In the first and second magnetic bodies 3A and 3B, the directions of the N pole and the S pole are random, and any magnetic pole surface may face inward in the radial direction.

  Next, as the magnetic sensor 7, for example, one using a Hall element, MR element (magnetoresistance effect element), TMF-MI element, TMF-FG element or the like can be adopted. The magnetic sensor 7 is attached to an intermediate position between the first circumferential line J1 and the second circumferential line J2, thereby passing the first magnetic body 3A and the second magnetic body 3B. Both can be detected sequentially.

  Here, in order to more accurately detect the torsional deformation in the circumferential direction of the tire due to the longitudinal force F, as shown in FIG. 3, the ground contact portion QL where the tire contacts the road surface is opposite to the tire shaft core i. It is preferable that the magnetic sensor 7 is attached to the opposite grounding region GU and the change Δt of the passage time t is measured in the grounding opposite region GU. The reason is that when a longitudinal force F (for example, braking force Fr) is applied to the ground contact portion QL, the torsional deformation Δθ1 due to the longitudinal force F occurs uniformly over the entire tire circumference. This is because the torsional deformation Δθ2 due to the longitudinal load is further applied in the region other than the region GU, and the longitudinal force F cannot be accurately obtained from the total torsional deformation Δθ. Further, it is difficult to provide the magnetic sensor 7 in the grounding portion QL because it is easily damaged from the road surface. Therefore, the magnetic sensor 7 is attached to the grounding opposite region GU. Strictly speaking, the “grounding opposite region GU” is defined as an angle region in which the central angle α around the vertical line passing through the tire core i is 30 °.

  At this time, in order to sequentially detect the passage of the two magnetic bodies 3A and 3B with one magnetic sensor 7, as described above, the first magnetic body 3A and the second magnetic body 3B are arranged in the tire circumferential direction. It is important to shift the position, and it is preferable to secure a position shift distance Lc of 3 mm or more.

  FIG. 7 shows a Hall element magnetic sensor 7 and a magnetic body 3 having a magnetic flux density of 3000 gauss (magnetic bodies 3A and 3B are collectively referred to as magnetic body 3), and an inward magnetic pole of the magnetic body. The detection output of the magnetic sensor 7 (the output voltage of the Hall element) at a position where the distances X and Y are different, where X is the distance in the magnetic pole direction from the surface 3s and Y is the distance perpendicular to the magnetic pole direction from the magnetic pole line. The measurement results are shown. From FIG. 7, when the distance Y in the direction perpendicular to the magnetic pole direction is increased to 3.0 mm or more, the detection output of the magnetic sensor is greatly reduced as compared with the case where Y = 0.0 mm. This means that if the distance Y is 3.0 mm or more, when the magnetic sensor 7 reacts to one magnetic body (Y = 0), the influence of the magnetic force received from the other magnetic body can be greatly reduced. This means that the passage of both magnetic bodies 3A and 3B can be identified, that is, it can function as a switch of the clock counter. Therefore, the distance Y, that is, the positional displacement distance Lc in the circumferential direction is preferably 3.0 mm or more, and more preferably 5.0 mm or more in order to increase the reliability of the switch operation of the timepiece counter.

  On the other hand, the measurement time by the magnetic sensor 7 becomes longer as the positional deviation distance Lc becomes larger and the traveling speed becomes slower. Therefore, the minimum speed that can be measured is regulated based on the relationship between the capacity of the watch counter and the positional deviation distance Lc. For example, when the timepiece counter has a counting capability of 100,000 times in 0.25 microseconds, if the positional deviation distance Lc exceeds 27.7 mm, measurement at a traveling speed of 4 km / h or less becomes difficult. Therefore, from the viewpoint of the minimum measurable speed and the capacity of the watch counter, the upper limit of the positional deviation distance Lc is preferably 30.0 mm or less, and more preferably 27.7 mm or less.

  Further, as the distance Lr in the tire radial direction between the magnetic bodies 3A and 3B increases, the change Δt of the passage time t increases, so that the measurement accuracy tends to increase. On the other hand, since the magnetic sensor 7 is separated from the magnetic bodies 3A and 3B, the detection output of the magnetic sensor 7 (the output voltage of the Hall element) is reduced and the detection accuracy of passage is lowered. From such a viewpoint, the tire radial direction distance Lr has a lower limit value of preferably 15.0 mm or more, more preferably 25.0 mm or more, and an upper limit value of 40.0 mm or less, further 35.0 mm or less. Is preferable. In order to increase the detection accuracy of the passage, the magnetic pole lines of the magnetic bodies 3A and 3B and the sensitivity center of the magnetic sensor 7 are aligned on one plane S (shown in FIG. 2) parallel to the tire equatorial plane. It is preferable to make it. The sensitivity center of the magnetic sensor 7 is also directed in the tire radial direction.

  Next, it is preferable for the control of the vehicle control system to continuously measure the longitudinal force during traveling in order to control the vehicle control system. For this purpose, a plurality of magnetic body sets 5 are provided in this example. At this time, the first magnetic body 3A in each magnetic body set 5 is disposed on the first circumferential line J1, and the second magnetic body 3B is disposed on the first circumferential line J2. When the magnetic bodies 3A and 3B are not arranged on the respective circumferential lines J1 and J2, the detection output of the magnetic sensor 7 (the output voltage of the Hall element) varies for each magnetic body set 5. Although a threshold value is set for the detection output as a switch of the clock counter, if the detection output varies, the threshold value must be set smaller by the variation. As a result, it becomes easy to react to a noise signal, resulting in a problem that malfunction is likely to occur.

  When a plurality of sets of magnetic bodies 5 are arranged, it is preferable that the magnetic body set 5 adjacent to each other in the circumferential direction has a different positional displacement distance Lc between the magnetic bodies.

Here, in the longitudinal force detection method of the present application, as described above, the change Δt in the passage time t from the passage of the first magnetic body 3A to the passage of the second magnetic body 3B is obtained for one magnetic body set 5. The longitudinal force is detected based on the change Δt. For example, as conceptually shown in FIGS. 5A and 6A, the passage time t0 between the magnetic bodies 3A and 3B in the case of no load (F = 0) is used as a reference. As shown in FIGS. 5B and 6B, when a longitudinal force F (braking force Fr) acts on the tire, a torsional deformation in the circumferential direction occurs, and the passing time between the magnetic bodies 3A and 3B. t1 changes by Δt from the reference passage time t0. The longitudinal force F can be calculated from the change Δt in the passage time by the following equation.
(Longitudinal force F) = (change in passing time Δt) × (tire rotational speed V) × (tire circumferential spring constant K)

  The tire circumferential spring constant K is a value unique to the tire, and the relationship between the longitudinal force F acting on the tire tread and the amount of twist deformation at the mounting position of the magnetic sensor 7 generated at the tire at that time, for example, It can be obtained in advance by measuring at the time of tire manufacture or shipment.

  However, when a plurality of magnetic body sets 5 are arranged, the first and second magnetic bodies 3A and 3B in one magnetic body set 5 are compared with each other and between the adjacent magnetic body sets 5 and 5. There is a possibility that the comparison between the first and second magnetic bodies 3A and 3B may be mistakenly performed. Therefore, in order not to make a mistake in the comparison, as shown in FIG. 4, the positional deviation distance Lc between the magnetic bodies 3A and 3B in the magnetic body set 5 and the magnetic body set adjacent to the magnetic body set 5 in the circumferential direction. 5 is preferably made different from the positional deviation distance Lc between the magnetic bodies 3A and 3B. In particular, the magnetic body set 5 is composed of two types, a magnetic body set 5A having a small displacement distance Lc (Lc1) and a magnetic body set 5B having a large displacement distance Lc (Lc2). It is preferable to arrange 5A and 5B alternately. As a result, the passage time t is detected with reference patterns of large, small, large, small..., So that a comparison error can be easily recognized.

  Next, when the magnetic bodies 3A and 3B are attached to the sidewall portion 23 of the pneumatic tire 21, peeling occurs at the interface between the magnetic bodies 3A and 3B and the tire rubber due to repeated deformation of the sidewall portion 23 during traveling. There arises a problem that the magnetic bodies 3A and 3B are dropped. Therefore, as a result of the study by the present inventor, as shown in FIG. 8, when, for example, a block-like protruding portion 8 is provided on the surface 23S of the sidewall portion 23, a concentration ε1 of strain ε is generated near the root of the protruding portion 8. However, on the other hand, it has been found that the strain ε is very small inside the protrusion 8.

  Therefore, in the pneumatic tire 21 of the present embodiment, as shown in FIG. 2, the sidewall portion 23 is provided with a block-like protruding portion 8 protruding from the surface 23 </ b> S, and the magnetic body is provided in the protruding portion 8. By embedding 3A and 3B, dropping off of the magnetic bodies 3A and 3B and tire damage caused by the magnetic bodies 3A and 3B are suppressed. At this time, the magnetic bodies 3A and 3B need to be arranged outside the surface 23S in order to avoid the influence of the strain ε. Further, as described above, in order to align the magnetic poles of the magnetic bodies 3A and 3B on the plane S parallel to the tire equatorial plane, the magnetic bodies 3A and 3B are separated inward and outward in the radial direction of the tire maximum width position P. In particular, it is preferable that the tires are attached at equal distances from the tire maximum width position P inward and outward in the radial direction.

  Further, as shown in FIGS. 9, 10 </ b> A and 10 </ b> C, the protrusion 8 has one or more holes 9 extending from the magnetic body 3 to the surface of the protrusion 8. It is. In this example, the case where the magnetic body 3 has a rectangular shape is illustrated, and the hole 9 has, for example, two lower holes 9a extending from the inward magnetic pole surface 3s, and the tire of the magnetic body 3. A case is shown in which a total of five holes 9 including one hole 9b extending from each circumferential side surface and one end hole 9c extending from the outer side surface of the magnetic body 3 in the tire axial direction are shown. Yes.

  The hole 9 is formed when the magnetic body 3 is positioned in the mold 30 when the tire 21 is vulcanized. In order to increase the detection accuracy of the longitudinal force F, it is necessary to attach the magnetic body 3 to an accurate position. In particular, the position of the magnetic pole surface 3s facing inward and the magnetic pole direction of the magnetic body 3 are very important.

  For this purpose, as shown in FIGS. 11A and 11C, a concave portion 31 for forming the protruding portion 8 is provided in the mold 30 and the magnetic body 3 is attracted to the inner wall surface of the concave portion 31 by the magnetic force. For example, the fixing protrusion 32 is preferably formed. It is particularly preferable that the fixed protrusion 32 includes a rail-shaped lower fixed protrusion 32 a that attracts the inward magnetic pole surface 3 s and stably holds the magnetic body 3 across the magnetic body 3. In order to increase the accuracy of the positional displacement distance Lc, the fixing protrusion 32b on the side that adsorbs and holds both sides of the tire 3 in the circumferential direction of the magnetic body 3, and the magnetic body 3 in order to increase the positional accuracy in the tire axial direction. It is also preferable to provide a fixed protrusion 32c at the end for adsorbing and holding the outer surface of the body 3 in the tire axial direction. When such a mold 30 is used for vulcanization molding, the hole 9 is formed as a trace of the fixed protrusion 32.

  Further, during vulcanization molding, a strong rubber flow is generated outward in the tire axial direction due to the inflow of the rubber into the concave portion 31, and the magnetic body 3 is likely to be displaced. Therefore, it is preferable to incline the outward wall surface 31w facing the outward magnetic pole surface 3so out of the inner wall surface of the recess 31 in the direction approaching the outward magnetic pole surface 3so outward in the tire axial direction. As a result, a rubber flow is generated in such a direction that the magnetic body 3 is pressed against the lower fixing protrusion 32a, and an effect of suppressing displacement to the magnetic body 3 is produced.

  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.

  A radial tire for a passenger car (245 / 40ZR18) in which 18 sets of magnetic bodies 5 using a columnar magnetic body 3 having a diameter of 6.0 mm, a height of 3.0 mm, and a magnetic flux density of 3850 gauss are formed on the sidewall portion 23 is used. Prototype. Each magnetic body 3 is embedded in a rectangular block-shaped projecting portion 8 of 10 mm (circumferential width) × 10 mm (radial height) × 10 mm (projection height) with the tread-side magnetic pole as an N pole. Two protrusions 32 a having a width of 1 mm are formed on the protrusion 8. The radial distance Lr between the magnetic bodies 3A and 3B is 30 mm, and the circumferential displacement Lc is 10 m.

  This sample tire was mounted on the front wheel of a vehicle (3000 cc, FR vehicle) under the conditions of a rim (18 × 8 JJ) and internal pressure (230 kPa), and a braking test was performed on a tire test course. The longitudinal force at that time was measured using a 6-component force meter, and at the same time, it was detected using a magnetic sensor (Hall element: MLX90251 manufactured by Melexis) according to the longitudinal force detection method of the present invention. Then, as shown in FIG. 12, the measurement result by the 6-component force meter is plotted on the horizontal axis, and the measurement result of Example 1 using the detection method of the present invention is plotted on the vertical axis. As shown in FIG. 12, it can be confirmed that the longitudinal force equivalent to that of the 6-component force meter can be measured.

  Next, the sample tire was run for 30000 km on the drum under the conditions of a rim (18 × 8JJ), internal pressure (230 kPa), longitudinal load (8.26 km), and speed (80 km / h). The tire damage caused by falling off or the magnetic material was visually inspected. It was confirmed that the sample tire did not cause the magnetic body to drop off or damage to the tire as in the conventional tire.

It is sectional drawing which shows the pneumatic tire used for the longitudinal force detection method of the tire of this invention. It is sectional drawing which expands and shows the principal part. It is a side view of the pneumatic tire which shows the arrangement state of a magnetic body set roughly. It is drawing explaining the position shift distance of a magnetic body. (A) is a drawing showing the passing state of the first and second magnetic bodies when there is no load, and (B) is a drawing showing the passing state of the first and second magnetic bodies when the longitudinal force is applied. is there. (A) is drawing which shows passage time in the case of no load, (B) is drawing which shows the change of passage time when a longitudinal force acts. It is a graph which shows the output change of a magnetic sensor when the attachment position of the magnetic sensor with respect to a magnetic body is changed. It is drawing which shows the relationship between a protrusion part and surface distortion. It is a perspective view which shows a protrusion part with a magnetic body. (A) is sectional drawing which shows a protrusion part with a magnetic body, (B) is the BB sectional view taken on the line, (C) is the CC sectional view taken on the line. (A) is sectional drawing which shows the metal mold | die which forms a protrusion part, (B) is the bb sectional view taken on the line, (C) is the cc sectional drawing. It is the graph which compared the measurement result with the detection method of this invention, and the case where a 6 component force meter is used.

Explanation of symbols

3A 1st magnetic body 3B 2nd magnetic body 3s Magnetic pole surface 5 Magnetic body set 6 Car body 7 Magnetic sensor 8 Protruding part 9 Hole part 21 Pneumatic tire 23 Side wall part F Longitudinal force i Tire axial center J1 1st circle Circumferential line J2 Second circumferential line P Tire maximum width position QL Grounding part QU Grounding opposite area

Claims (8)

A tire front-rear force detection method for detecting a circumferential front-rear force acting on a tire,
A first magnetic body located on a first circumferential line centered on the tire axis, and a first magnetic body located on a second circumferential line concentrically arranged radially outward of the first circumferential line; A pneumatic tire comprising a magnetic body set comprising two magnetic bodies , and the first and second magnetic bodies are embedded in a protruding portion protruding from a surface of the sidewall portion ;
One magnetic sensor attached to the vehicle body at an intermediate position between the first circumferential line and the second circumferential line and capable of sequentially detecting passage of the first magnetic body and passage of the second magnetic body And
A method for detecting the longitudinal force of a tire, comprising: detecting a longitudinal longitudinal force based on a change in passage time from the passage of the first magnetic body to the passage of the second magnetic body.
  2. The method for detecting the longitudinal force of a tire according to claim 1, wherein the magnetic sensor is attached to a grounding opposite region opposite to a grounding portion where the tire is grounded, with the tire shaft core interposed therebetween. A pneumatic tire used in the longitudinal force detection method according to claim 1 or 2,
A first magnetic body located on a first circumferential line centered on the tire axis and a second circumference concentrically disposed radially outward of the first circumferential line in the sidewall portion; A magnetic body set comprising a second magnetic body located on the line,
The pneumatic tire according to claim 1, wherein the first and second magnetic bodies are embedded in a protruding portion protruding from a surface of the sidewall portion.   The pneumatic tire according to claim 3, wherein a radial distance between the first magnetic body and the second magnetic body in the magnetic body set is 15 to 40 mm. In the magnetic body set, the first magnetic body and the second magnetic body are displaced in the tire circumferential direction, and the positional deviation distance Lc of the magnetic body on a circumferential line passing through the tire maximum width position is 3 to 30 mm. And

5. The pneumatic tire according to claim 3, wherein the magnetic pole direction of the first magnetic body and the magnetic pole direction of the second magnetic body are respectively the tire radial direction.   The pneumatic tire according to claim 5, wherein a plurality of magnetic body sets are arranged in the circumferential direction, and the magnetic body sets adjacent to each other in the circumferential direction have different positional displacement distances Lc of the magnetic bodies.   The pneumatic tire according to any one of claims 3 to 6, wherein the first circumferential line and the second circumferential line are arranged inside and outside in the radial direction across the tire maximum width position. .   The pneumatic tire according to claim 3, wherein the protrusion includes a hole extending from the first magnetic body and the second magnetic body to the surface of the protrusion.

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