Patent ID: 12214626

DETAILED DESCRIPTION

Configurations according to embodiments of the present technology will be described in detail below with reference to the accompanying drawings.FIG.1illustrates a wear state detection device according to an embodiment of the present technology.

In order to sense a progress condition of wear in a tread portion1of a tire T (seeFIG.7, for example), a wear state detection device10detects voltage based on deformation of the tread portion1during tire rotation and vehicle speed or tire rotation speed, and stores waveform data over time of the voltage together with the vehicle speed or the tire rotation speed detected. Then, the wear state detection device10calculates frequency of exceedance of a predetermined threshold value based on the waveform data in a predetermined speed range and a predetermined time period, and determines the progress condition of the wear in the tread portion1of the tire T based on the calculated frequency of exceedance of the predetermined threshold value. This makes it possible to sense the progress condition of the wear in the tread portion1of the tire T which is a sensing target.

As illustrated inFIG.1, the wear state detection device10includes an element11configured to generate voltage based on deformation of the tread portion1during tire rotation, a voltage detection unit12configured to detect the voltage generated by the element11, a speed detection unit16configured to detect vehicle speed or tire rotation speed, a storage area13configured to store waveform data over time of the voltage detected by the voltage detection unit12together with the vehicle speed or the tire rotation speed detected by the speed detection unit16, a calculation unit14configured to calculate frequency of exceedance of a predetermined threshold value based on the waveform data in a predetermined speed range and a predetermined time period stored in the storage area13, and a determination unit15configured to determine a progress condition of wear of the tread portion1based on the frequency of exceedance of the predetermined threshold value calculated by the calculation unit14.

The wear state detection device10may include an air pressure detection unit17configured to detect air pressure inside a tire, or a temperature detection unit18configured to detect temperature inside the tire, in addition to the voltage detection unit12and the speed detection unit16. Further, devices such as an input device, an output device, and a display may be appropriately added to the wear state detection device10.

In the wear state detection device10, the storage area13, the calculation unit14, and the determination unit15function as a data processing device19. The data processing device19processes data input from a detection unit represented by the voltage detection unit12. Data input to the data processing device19may be performed either by wire or wirelessly.

Further, in the wear state detection device10, a sensor module20configured to acquire tire information can be used as a module including at least the element11and the voltage detection unit12. The sensor module20can be mounted with sensors so as to include the air pressure detection unit17and the temperature detection unit18, as appropriate, together with the element11and the voltage detection unit12.

The element11is a component of the voltage detection unit12, and is included in the voltage detection unit12. The element11is not particularly limited as long as the element11generates voltage in proportion to the amount of deformation (deformation energy) of the tread portion1during tire rotation. As such an element11, for example, a piezoelectric element can be used. The piezoelectric element is disposed so as to be directly or indirectly in contact with a tire inner surface, and is configured to be capable of sensing deformation of the tread portion1. The element being indirectly in contact with the tire inner surface means that deformation of the tread portion1can be sensed even when another member intervenes between the element and the tire inner surface, such as in the case where the element is in contact with the tire inner surface via a housing of the sensor module20or where the element is covered with a protective layer made of rubber or the like and is in contact with the tire inner surface via the protective layer. The piezoelectric element has a structure to generate voltage based on deformation of the tread portion1during tire rotation as described above, and thus is less likely to be affected by noise and capable of performing an accurate sensing.

The voltage detection unit12is a voltage sensor configured to detect potential difference in the element11that is electrically charged. The voltage detection unit12includes the element11that generates voltage based on deformation of the tread portion1during tire rotation, and thus is different from a strain sensor that detects strain. The speed detection unit16may detect measurement data (vehicle speed) by a speed meter on a vehicle side, or may detect a tire rotation speed by using a sensor capable of detecting the tire rotation speed. Further, a pressure sensor may be used as the air pressure detection unit17, and a temperature sensor may be used as the temperature detection unit18.

The storage area13stores the waveform data over time of the voltage detected by the voltage detection unit12together with the vehicle speed or the tire rotation speed detected by the speed detection unit16. That is, the vehicle speed or the tire rotation speed and the waveform data of the voltage are linked to each other and integrally stored in the storage area13. Here, the storage area13can be composed of an external storage device such as a hard disk or an internal storage device such as a RAM (random access memory), or a combination thereof.

FIG.2illustrates waveform data stored in the storage area13. InFIG.2, the vertical axis represents voltage (V), the horizontal axis represents elapsed time (μs), and waveform data corresponding to one rotation of the tire T is illustrated. During one rotation of the tire T, the waveform (voltage) reaches a peak (a maximum value or a minimum value) when a point on the circumference of the tire T comes to a ground contact leading edge and to a ground contact trailing edge. Waveform data d1 is data of when the tire T is in new condition, and waveform data d2 is data of when the wear of the tread portion1of the tire T has progressed (late stage of wear). That is, as the wear of the tread portion1of the tire T progresses, the peak values of the voltage at the positions of the ground contact leading edge and the ground contact trailing edge tend to increase. Note that the waveform data illustrated inFIG.2is a typical example, and is not limited thereto.

FIG.3illustrates waveform data for a predetermined time period stored in the storage area13. That is, the waveform data in the predetermined time period includes waveform data for a plurality of rotations of the tire T. The dotted lines inFIG.3indicate predetermined threshold values, and, as can be seen, there are a plurality of portions exceeding the predetermined threshold values in the waveform data for the predetermined time period.

In a case where the wear state detection device10includes the air pressure detection unit17and the temperature detection unit18, the storage area13stores the waveform data of the voltage detected by the voltage detection unit12together with the air pressure and the temperature detected by the air pressure detection unit17and the temperature detection unit18, respectively. That is, the air pressure and the temperature and the waveform data of the voltage are linked to each other and integrally stored in the storage area13.

The calculation unit14calculates the frequency of exceedance of the predetermined threshold value based on the waveform data in the predetermined speed range and the predetermined time period stored in the storage area13. Further, the calculation unit14can store the calculated waveform data in the storage area13, and can read out the stored waveform data and perform calculation. The calculation unit14can be composed of, for example, a memory or a CPU (central processing unit).

Here, the predetermined speed range is a speed range in which a lower limit is −5 km/h with respect to an arbitrary speed [km/h] and an upper limit is +5 km/h with respect to the arbitrary speed. The arbitrary speed can be set, for example, within a range of 30 km/h to 60 km/h. The predetermined time period can be set, for example, within a range from 0.1 [sec] to 10.0 [sec]. Further, the predetermined threshold value can be set to a voltage [V] at which it can be determined that the tread portion1is worn based on the predetermined speed range and the predetermined time period described above. The predetermined threshold value can be set for both or either of an upper limit range and a lower limit range. Furthermore, for example, the predetermined threshold value can be appropriately defined based on a tire size.

In a case where the wear state detection device10includes the air pressure detection unit17and the temperature detection unit18, the calculation unit14can correct the waveform data or the predetermined threshold value based on the air pressure detected by the air pressure detection unit17and the temperature detected by the temperature detection unit18. At that time, the calculation unit14reads out the waveform data in the predetermined speed range and the predetermined time period or the predetermined threshold value stored in the storage area13and performs correction, and stores the corrected waveform data or the corrected predetermined threshold value in the storage area13.

The determination unit15determines the progress condition of the wear of the tread portion1based on the frequency of exceedance of the predetermined threshold value calculated by the calculation unit14. At that time, the determination unit15reads out the waveform data in the predetermined speed range and the predetermined time period from the storage area13and performs determination. Note that determination results by the determination unit15can be indicated on a display provided on a vehicle, for example.

FIG.4illustrates a procedure of a sensing method using a wear state detection device according to an embodiment of the present technology. In detecting the progress condition of the wear in the tread portion1of the tire T, in step S1, the voltage detection unit12of the wear state detection device10detects voltage generated based on deformation of the tread portion1during the rotation of the tire T. At that time, the storage area13stores the waveform data over time of the voltage detected by the voltage detection unit12.

Further, in step S1, the speed detection unit16detects vehicle speed or tire rotation speed, and the storage area13stores the waveform data of the voltage detected by the voltage detection unit12together with the vehicle speed or the tire rotation speed detected by the speed detection unit16. In addition, the air pressure detection unit17and the temperature detection unit18detect air pressure and temperature, respectively, and the storage area13stores the waveform data of the voltage detected by the voltage detection unit12together with the air pressure and the temperature detected by the air pressure detection unit17and the temperature detection unit18.

Next, the process proceeds to step S2, and the calculation unit14of the wear state detection device10corrects the waveform data of the voltage or the predetermined threshold value based on the air pressure and the temperature detected by the air pressure detection unit17and the temperature detection unit18, respectively. At that time, as a correction operation by the calculation unit14, for example, when the air pressure detected by the air pressure detection unit17is relatively low, the amount of change in the entire tire tends to increase, and consequently the waveform data also tends to increase as a whole. Thus, the calculation unit14performs correction such that the waveform data of the voltage is reduced in a predetermined ratio. By performing the correction by the calculation unit14in this manner, it is possible to improve the accuracy of determining the progress condition of the wear in the tread portion1. Then, the calculation unit14stores the corrected waveform data or the corrected predetermined threshold value in the storage area13. Note that air pressure inside a tire varies depending on temperature inside the tire, and thus the temperature detected by the temperature detection unit18is used for correction of the air pressure.

Next, the process proceeds to step S3, and the calculation unit14of the wear state detection device10calculates the frequency of exceedance of the predetermined threshold value based on the waveform data in the predetermined speed range and the predetermined time period stored in the storage area13. At that time, the calculation unit14performs masking of the waveform data based on the predetermined threshold value and calculates the frequency of exceedance. Specifically, the frequency of exceedance can be calculated by performing masking for extracting portions exceeding the predetermined threshold value and by counting the number of the portions exceeding the predetermined threshold value in the waveform data after the masking (seeFIG.5). Then, the calculation unit14stores the calculated waveform data in the storage area13.

Next, the process proceeds to step S4, and the determination unit15of the wear state detection device10determines the progress condition of the wear of the tread portion1based on the frequency of exceedance of the predetermined threshold value calculated by the calculation unit14. For example, in a case where a determination criterion for frequency of exceedance is set to 15 times in advance, the determination unit15concludes that the determination criterion is not satisfied when the frequency of exceedance in waveform data at a certain point in time is 10 times, and that the determination criterion is satisfied when the frequency of exceedance in waveform data at another point in time is 15 times. The determination criterion can be set, for example, as the number of exceedances of the predetermined threshold value, or as a ratio to the number of exceedances of when in new condition. The determination operation terminates when the determination criterion is satisfied as described above. On the other hand, when the determination criterion is not satisfied, the process returns to step S1.

Since the wear state detection device10described above includes the element11configured to generate voltage based on deformation of the tread portion1during tire rotation, the voltage detection unit12configured to detect over time the voltage generated by the element11, the speed detection unit16configured to detect vehicle speed or tire rotation speed, the storage area13configured to store waveform data over time of the voltage detected by the voltage detection unit12together with the vehicle speed or the tire rotation speed detected by the speed detection unit16, the calculation unit14configured to calculate frequency of exceedance of a predetermined threshold value based on the waveform data in a predetermined speed range and a predetermined time period stored in the storage area13, and the determination unit15configured to determine a progress condition of wear of the tread portion1based on the frequency of exceedance of the predetermined threshold value calculated by the calculation unit14, the progress condition of the wear in the tread portion1can be accurately sensed. In particular, since the frequency of exceedance of a predetermined threshold value is used, there is no dependence on a road surface state, and thus the influence of an unexpected error can be reduced. Accordingly, determination accuracy can be improved.

FIG.6illustrates a modified example of a procedure of a sensing method using a wear state detection device according to an embodiment of the present technology. InFIG.6, the determination unit15of the wear state detection device10performs at least two determination operations, and conclusively determines the progress condition of the wear of the tread portion1based on the results of these determination operations. The procedure illustrated inFIG.6is identical to that illustrated inFIG.4up to step S4. Next, the process proceeds to step S5from step S4, and the voltage detection unit12detects the voltage generated by the element11, and the speed detection unit16detects vehicle speed or tire rotation speed. Next, the process proceeds to step S6, and the calculation unit14corrects the waveform data or the predetermined threshold value based on the air pressure and the temperature detected by the air pressure detection unit17and the temperature detection unit18, respectively. Then, the calculation unit14stores the corrected waveform data or the corrected predetermined threshold value in the storage area13. Next, the process proceeds to step S7, and the calculation unit14calculates the frequency of exceedance of the predetermined threshold value based on the waveform data in the predetermined speed range and the predetermined time period stored in the storage area13. Then, the calculation unit14stores the calculated waveform data in the storage area13. Next, the process proceeds to step S8, and the determination unit15performs the second determination operation. At that time, the determination operation terminates when an arbitrary determination criterion is satisfied. On the other hand, when the determination criterion is not satisfied, the process returns to step S5. As for the second determination operation by the determination unit15, the first determination operation (steps S1to S4) and the second determination operation (steps S5to S8) may be performed on the same day, or the first determination operation and the second determination operation may be performed on different days.

By performing at least two determination operations by the determination unit15as described above, the occurrence of an unexpected error in conclusive determination results can be reduced, and the accuracy of determining the progress condition of the wear in the tread portion1can be improved.

In the embodiment ofFIG.6, an example in which the number of times of determination by the determination unit15is two has been described, but the number of times of determination is not particularly limited thereto, and may be set to any number of times equal to or greater than two times. Also, in the embodiment ofFIG.6, an example in which the process returns to step S5when the determination criterion is not satisfied in step S8, but the process may be configured to return to step S1when the determination criterion is not satisfied in step S8.

FIG.7illustrates a pneumatic tire (tire T) that is a detection target of the wear state detection device10according to an embodiment of the present technology.FIGS.8to10illustrate the sensor module20or the container30mounted on the tire T. InFIGS.8and10, an arrow Tc represents a tire circumferential direction, and an arrow Tw represents a tire width direction.

As illustrated inFIG.7, the tire T includes the tread portion1extending in the tire circumferential direction and having an annular shape, a pair of sidewall portions2,2disposed on both sides of the tread portion1, and a pair of bead portions3,3disposed on inner sides of the sidewall portions2in a tire radial direction.

A carcass layer4is mounted between the pair of bead portions3,3. The carcass layer4includes a plurality of reinforcing cords extending in the tire radial direction and is folded back around a bead core5disposed in each of the bead portions3from a tire inner side to a tire outer side. A bead filler6having a triangular cross-sectional shape and formed of a rubber composition is disposed on the outer circumference of the bead core5. Furthermore, an innerliner layer9is disposed in a region between the pair of bead portions3,3on a tire inner surface Ts. The innerliner layer9forms the tire inner surface Ts.

On the other hand, a plurality of belt layers7are embedded on an outer circumferential side of the carcass layer4in the tread portion1. Each of the belt layers7includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and the reinforcing cords are disposed so as to intersect each other between the layers. In the belt layers7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to fall within a range of from 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers7. To improve high-speed durability, at least one belt cover layer8, formed by disposing reinforcing cords at an angle of, for example, 5° or less with respect to the tire circumferential direction, is disposed on an outer circumferential side of the belt layers7. Organic filament cords such as nylon and aramid are preferably used as the reinforcing cords of the belt cover layer8.

Note that the tire internal structure described above represents a typical example for a pneumatic tire, but the pneumatic tire is not limited thereto.

At least one container30made of rubber is fixed in a region corresponding to the tread portion1of the tire inner surface Ts of the tire T. The sensor module20is inserted into the container30. The container30includes an opening portion31into which the sensor module20is inserted, and is bonded to the tire inner surface Ts via an adhesive layer32. Since the sensor module20is configured to be freely housed in the container30, the sensor module20can be replaced as necessary at the time of replacement, failure, or the like. In addition, since the container30is made of rubber, the container30suitably expands and contracts when the sensor module20is inserted into and taken out of the opening portion31.

Examples of the material of the container30include chloroprene rubber (CR), butyl rubber (IIR), natural rubber (NR), acrylonitrile-butadiene copolymer rubber (NBR), butadiene rubber (BR), styrene-butadiene rubber (SBR), or the like, and a single material or a blend of two or more materials can be used. Since these materials are excellent in adhesiveness to butyl rubber constituting the tire inner surface Ts, when the container30is formed of any of the above materials, sufficient adhesiveness between the container30and the tire inner surface Ts can be secured.

As illustrated inFIG.10, the sensor module20includes a housing21and an electronic component22. The housing21has a hollow structure, and accommodates the electronic component22inside. The electronic component22may be configured to include a transmitter, a receiver, a control circuit, a battery, and the like, as appropriate, together with a sensor23that acquires the above-described tire information such as voltage, speed, air pressure, and temperature of the tire T. As the sensor23, for example, a speed sensor (the speed detection unit16), a pressure sensor (the air pressure detection unit17), or a temperature sensor (the temperature detection unit18) can be used together with a piezoelectric sensor (the element11and the voltage detection unit12). In particular, the piezoelectric sensor includes the element11that generates voltage based on deformation of the tread portion1during tire rotation. The piezoelectric sensor is different from a piezoelectric type acceleration sensor. An acceleration sensor or a magnetic sensor other than the sensors described above can also be used. In addition, the sensor module20is configured to be capable of transmitting the tire information acquired by the sensor23to the storage area13. Further, in order to make it easy to hold the sensor module20, a knob portion24protruding from the housing21may be provided, and the knob portion24can have a function of an antenna. Note that the internal structure of the sensor module20illustrated inFIG.10is an example of the sensor module, and the internal structure is not limited thereto.

The container30is bonded to the tire inner surface Ts via the adhesive layer32. The container30includes a base portion33having a plate shape and joined to the tire inner surface Ts, a tube portion34having a cylindrical shape and protruding from the base portion33, and a housing portion35formed in the tube portion34. The housing portion35communicates with the opening portion31having a circular shape. Thus, the housing portion35has a substantially quadrangle cross-sectional shape with the base portion33as a bottom surface and the opening portion31as an upper surface. The sensor module20having a cylindrical shape with a tapered upper surface is housed in the housing portion35. Note that the shapes of the base portion33, the tube portion34, and the housing portion35are not particularly limited, and can be appropriately changed according to the shape of the sensor module20to be inserted into the container30.

The adhesive layer32is not particularly limited as long as it can bond the rubber composition. Examples thereof include an adhesive agent, an adhesive tape, a vulcanized adhesive that is naturally vulcanized (vulcanizable at normal temperature), and a puncture repair agent used as an emergency treatment when a pneumatic tire is punctured. In particular, a vulcanized adhesive is preferably used as the adhesive layer32because the vulcanized adhesive can make it unnecessary to perform a primer treatment needed for fixing the container using an adhesive tape and thus can improve productivity. Note that the primer treatment (base coat treatment) is preliminarily applied to the tire inner surface to improve adhesiveness.

The above-described pneumatic tire includes, on the tire inner surface Ts, at least one container30made of rubber and configured to be used for insertion of the sensor module20. The container30includes the base portion33having a plate shape and joined to the tire inner surface Ts via the adhesive layer32, the tube portion34protruding from the base portion33, the housing portion35formed in the tube portion34, and the opening portion31communicating with the housing portion35. Accordingly, it is possible to easily perform an operation of inserting the sensor module20into the container30, and securely hold the sensor module20by tightening of the container30so as to prevent the sensor module20from falling off.

Preferably, in the above-described pneumatic tire, the container30is bonded to the tire inner surface Ts via the adhesive layer32, and as roughness of the tire inner surface Ts, an arithmetic mean height Sa ranges from 0.3 μm to 15.0 μm, and a maximum height Sz ranges from 2.5 μm to 60.0 μm. By appropriately setting the arithmetic mean height Sa and the maximum height Sz as the roughness of the tire inner surface Ts in this manner, the adhesion area between the tire inner surface Ts and the adhesive layer32can be increased, and the adhesiveness between the tire inner surface Ts and the container30can be improved effectively. When the arithmetic mean height Sa exceeds 15.0 μm and the maximum height Sz exceeds 60.0 μm, the adhesive layer32cannot follow the unevenness of the tire inner surface Ts, and the adhesiveness tends to decrease. Note that the arithmetic mean height Sa and the maximum height Sz are values measured in accordance with ISO25178, and can be measured using a commercially available surface properties measuring machine (e.g., a shape analysis laser microscope or a 3D shape measuring machine). The measurement method may be any of a contact type or a non-contact type.

InFIGS.7and9, the container30is disposed on an inner side of the ground contact edge in the tire width direction. The sensor23in the sensor module20inserted into the container30can accurately acquire tire information.

In the above-described pneumatic tire, the container30may be set to have the following dimensions. A width Lc1 of the opening portion31of the container30and an inner width Lc2 of the bottom surface of the container30preferably satisfy a relationship of Lc1<Lc2. By making the width Lc1 of the opening portion31narrower than the inner width Lc2 of the bottom surface of the container30in this manner, a restricting force on the upper surface side of the container30is increased, and the sensor module20inserted into the container30can be effectively prevented from falling off. Accordingly, both workability for inserting the sensor module20and holding property of the container30can be provided in a compatible manner. Both the width Lc1 of the opening portion31and the inner width Lc2 of the bottom surface of the container30are measured in a state where the sensor module20is not inserted into the container30.

Additionally, an average thickness of the container30preferably ranges from 0.5 mm to 5.0 mm. By appropriately setting the average thickness of the container30in this manner, it is possible to improve the workability for inserting the sensor module20, the holding property of the container30, and the breaking resistance of the container30in a well-balanced manner. Here, when the average thickness of the container30is thinner than 0.5 mm, the container30is easily broken when the sensor module20is inserted. When the average thickness of the container30is thicker than 5.0 mm, the rigidity of the container30becomes excessively large, and the sensor module20cannot be easily inserted. The average thickness of the container30is obtained by measuring the thickness of the rubber constituting the container30.

In particular, the container30and the sensor module20preferably satisfy the following dimensional relationship. The width Lc1 of the opening portion31of the container30and a maximum width Lsm of the sensor module20to be inserted into the container30preferably satisfy a relationship of 0.10≤Lc1/Lsm≤0.95, more preferably satisfy a relationship of 0.15≤Lc1/Lsm≤0.80, and most preferably satisfy a relationship 0.15≤Lc1/Lsm≤0.65. By appropriately setting the ratio of the width Lc1 of the opening portion31of the container30to the maximum width Lsm of the sensor module20in this manner, it is possible to effectively prevent the sensor module20from falling off, and it is possible to improve the workability for inserting the sensor module20and the holding property of the container30. In the sensor module20illustrated inFIG.10, the maximum width Lsm corresponds to a width Ls2 of the lower surface.

Further, the width Lc1 of the opening portion31of the container30, the inner width Lc2 of the bottom surface of the container30, a width Ls1 of the upper surface of the sensor module20, and a width Ls2 of the lower surface of the sensor module20preferably satisfy a relationship of Lc1<Ls1≤Ls2≤Lc2. Furthermore, the upper surface of the sensor module20is preferably formed in a tapered shape so as to satisfy a relationship of Ls1<Ls2. By appropriately setting the widths of the container30and the sensor module20in this manner, it is possible to effectively prevent the sensor module20from falling off. Alternatively, in the sensor module20, it is also possible to employ a form in which the diameter is gradually decreased from the upper surface thereof toward the lower surface. In that case, it is preferable to satisfy a relationship of Ls2<Ls1, and Ls2≤Lc2, and Lc1<Ls1.

Furthermore, the ratio of a height Hc of the container30with the sensor module20inserted to a height (maximum height) Hs of the sensor module20preferably ranges from 0.5 to 1.5, more preferably ranges from 0.6 to 1.3, and most preferably ranges from 0.7 to 1.0. By appropriately setting the ratio of the height Hc of the container30to the height Hs of the sensor module20in this manner, it is possible to effectively prevent the sensor module20from falling off. When the knob portion24is provided in the sensor module20, the height Hs of the sensor module20is a height including the knob portion24(seeFIG.10). Also, the height Hc of the container30does not include the height of the base portion33, and is a height of the cylindrical portion34(seeFIG.10).

In the above-described pneumatic tire, the rubber constituting the container30preferably has the following physical properties. The elongation at break EB preferably ranges from 50% to 900%, and the modulus at 300% elongation (M300) preferably ranges from 2 MPa to 15 MPa. By appropriately setting the elongation at break EB and the modulus (M300) in this manner, it is possible to improve the workability for inserting the sensor module20, the holding property of the container30, and the breaking resistance of the container30in a well-balanced manner.

Example

Tires of Examples 1 to 6 having a tire size of 275/40R21 were manufactured. The tires include a wear state detection device having an element configured to generate voltage based on deformation of a tread portion during tire rotation, a voltage detection unit configured to detect over time the voltage generated by the element, a speed detection unit configured to detect vehicle speed or tire rotation speed, a storage area configured to store waveform data over time of the voltage detected by the voltage detection unit together with the vehicle speed or the tire rotation speed detected by the speed detection unit, a calculation unit configured to calculate frequency of exceedance of a predetermined threshold value based on the waveform data in a predetermined speed range and a predetermined time period stored in the storage area, and a determination unit configured to determine a progress condition of wear of the tread portion based on the frequency of exceedance of the predetermined threshold value calculated by the calculation unit. A sensor module including the element and the voltage detection unit is fixed to a tire inner surface via a container configured to house the sensor module. The container includes an opening portion into which the sensor module is inserted. The ratio of a width Lc1 of the opening portion to a maximum width Lsm of the sensor module (Lc1/Lsm) is set according to Table 1.

The test tires were evaluated for wear sensing performance, workability for inserting the sensor module, and durability by test methods described below, and the results are collectively indicated in Table 1.

Wear Sensing Performance:

For each test tire, the progress condition of the wear of the tread portion was determined by the wear state detection device. For example, in Example 1, the waveform data in the predetermined speed range and the predetermined time period as illustrated inFIG.11was obtained. As illustrated, the frequency of exceedance of the predetermined threshold values (the dotted lines indicated) increased as wear of the tread portion progressed in a new condition A and a late stage of wear B (as a ratio of a groove depth in the late stage of wear to a groove depth when in new condition decreased). That is, a correlation between the frequency of exceedance of the predetermined threshold value and the progress condition of the wear of the tread portion was observed. Also for Examples 2 to 6, when there was a similar correlation, “Good” is indicated in Table 1.

Workability for Inserting Sensor Module:

For each test tire, the time required for inserting the sensor module into the container provided on the tire inner surface was measured. The evaluation results are expressed as index values using the reciprocal of the measurement values, with Example 1 being assigned an index value of 100. The larger the index value is, the easier the insertion of the sensor module is.

Durability:

Each test tire was mounted on a wheel having a rim size of 21×9.5 J, and a running test was performed by using a drum testing machine under the conditions of an air pressure of 120 kPa, a load at 102% with respect to the maximum load, a running speed of 81 km/h, and a running distance of 10000 km. After the test was performed, presence of breakage of the container or falling off of the sensor module was visually confirmed. The evaluation results are expressed as the presence or absence of breakage of the container and the presence or absence of falling off of the sensor module.

TABLE 1ExampleExampleExampleExampleExampleExample123456Ratio of width Lc1 of0.090.100.500.900.900.95opening portion tomaximum width Lsm ofsensor module (Lc1/Lsm)Wear sensing performanceGoodGoodGoodGoodGoodGoodWorkability for inserting100101103105105106sensor moduleDurability (presence orPresenceAbsenceAbsenceAbsenceAbsenceAbsenceabsence of breakage ofcontainer)Durability (presence orAbsenceAbsenceAbsenceAbsenceAbsencePresenceabsence of falling off ofsensor module)

As can be seen from Table 1, the wear state detection devices of Examples 1 to 6 had good wear sensing performance. Examples 2 to 6 had improved workability for inserting the sensor module as compared with Example 1. Examples 3 to 5 had no breakage of the container and no falling off of the sensor module.