Patent Publication Number: US-2022222396-A1

Title: Tire failure prediction system and tire failure prediction method

Description:
TECHNICAL FIELD 
     The present technology relates to a tire failure prediction system and a tire failure prediction method. 
     BACKGROUND ART 
     For tires mounted on trucks and buses, tread separation may be caused by internal failure. The occurrence of tread separation poses a problem in that tire burst may occur, making the vehicle inoperable. Thus, a method for predicting tire internal failure has been proposed (for example, Japan Unexamined Patent Publication No. H06-211012). 
     The technology described above determines a tire abnormality based on the temperature of tires mounted on a traveling vehicle. The technology described above has room for improvement in predicting failure in the tires with higher accuracy. 
     SUMMARY 
     The present technology provides a tire failure prediction system and a tire failure prediction method that can perform tire abnormality determination with higher accuracy to predict failure. 
     A tire failure prediction system according to an aspect of the present technology includes a setting unit configured to set a predetermined master curve indicating a relationship between a speed of a vehicle on which a tire is mounted and a heat build-up temperature of the tire, a determination unit configured to determine a tire condition of the tire based on a difference between the master curve set by the setting unit and a measured value of the heat build-up temperature of the tire, and an update unit configured to update the master curve set by the setting unit. 
     Preferably, the update unit updates the master curve in a case where the determination unit determines that the tire is normal. 
     Preferably, the tire failure prediction system further includes a warning unit configured to output a warning in a case where the determination unit determines that the tire is abnormal. 
     The update unit may update the master curve set by the setting unit in a case where a difference between the master curve and the measured value of the heat build-up temperature of the tire exceeds a predetermined range, and refrain from updating the master curve set by the setting unit in a case where the difference between the master curve and the measured value of the heat build-up temperature of the tire is equal to or less than a predetermined threshold value. 
     The vehicle may include a plurality of the tires, and the setting unit may set the master curve for each of the plurality of tires, and the determination unit may compare a difference between the master curve set by the setting unit and the measured value of the heat build-up temperature of the tire with a difference between the master curve for another tire and the measured value of the heat build-up temperature of the other tire to determine the tire condition of the tire. 
     The determination unit may compare the differences between the tires mounted at positions that are symmetrical in the vehicle and determine the tire condition of the tire. 
     The determination unit may determine the tire condition of the tire in a predetermined cycle and based on a determination result from the determination unit, determine the tire condition of the tire in a cycle shorter than the predetermined cycle. 
     The setting unit may set the master curve for the tire of the vehicle based on the master curve for a tire of another vehicle other than the vehicle. 
     In order to solve the problems described above and achieve an object, a tire failure prediction method according to an aspect of the present technology includes a first step of setting a predetermined master curve indicating a relationship between a speed of a vehicle on which the tire is mounted and a heat build-up temperature of the tire, a second step of determining a tire condition of the tire based on a difference between the master curve set in the first step and a measured value of the heat build-up temperature of the tire, and a third step of updating the master curve set in the first step. 
     According to the tire failure prediction system and the tire failure prediction method of the present technology, tire abnormality determination can be performed with higher accuracy to predict failure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of a tire failure prediction system according to a first embodiment. 
         FIG. 2  is a diagram illustrating an example of a placement position of a temperature sensor. 
         FIG. 3  is a diagram illustrating an example of a master curve set by a setting unit. 
         FIG. 4  is a diagram illustrating an example of a master curve set by the setting unit. 
         FIG. 5  is a flowchart illustrating an operation example of the tire failure prediction system according to the first embodiment. 
         FIG. 6  is a diagram illustrating another example of the master curve. 
         FIG. 7  is a diagram illustrating another example of the master curve. 
         FIG. 8  is a flowchart illustrating an operation example of a tire failure prediction system according to a second embodiment. 
         FIG. 9  is a diagram illustrating an example of positions where temperature sensors are provided. 
         FIG. 10  is a diagram illustrating another example of positions where the temperature sensors are provided. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present technology are described in detail below with reference to the drawings. In the embodiments described below, identical or substantially similar components to those of other embodiments have identical reference signs, and descriptions of those components are either simplified or omitted. The present technology is not limited by the embodiments. Constituents of the embodiments include elements that are substantially identical or that can be substituted and easily conceived by one skilled in the art. Note that it is possible to combine the configurations described below as desired. 
     Master Curve 
     The heat build-up temperature of a tire mounted on a traveling vehicle is proportional to the product of the load applied to the tire and the vehicle speed. The load applied to the tire depends on the vehicle. For example, in a case where the vehicle is a truck, a large cargo carrying capacity corresponds to a heavy load, and a small cargo carrying capacity corresponds to a light load. In a case where the vehicle is a bus, the load is higher when it runs on a route with many passengers, and lower when it runs on a route with few passengers. In this manner, the load applied to the tire is not constant and varies depending on the amount of cargo and the number of passengers. A heavy load increases the amount of heat generated in the tire, leading to an increased likelihood of internal failure of the tire. Additionally, a high vehicle speed increases the amount of heat generated in the tire, leading to an increased likelihood of internal failure of the tire. However, even with the heat build-up temperature of the tire and the vehicle speed known, an unknown load leads to difficulty in determining the likelihood of internal failure of the tire. 
     Thus, the tire failure prediction system of the present example sets a master curve for a variation in the heat build-up temperature of the tire with respect to the vehicle speed. The master curve indicates the relationship between the speed of the vehicle on which the tire is mounted and the heat build-up temperature of the tire. The master curve indicates a reference value for a variation in temperature with respect to the vehicle speed. Accordingly, in a case where the tire has no abnormality (the tire is normal), the heat build-up temperature of the tire varies along the master curve, which is the reference value, as the vehicle speed increases. 
     Additionally, the tire failure prediction system of the present example updates the set master curve by machine learning. Using the master curve set and updated allows tire abnormality determination to be performed with higher accuracy to predict failure. 
     First Embodiment 
     A tire failure prediction system according to a first embodiment will now be described. 
     Configuration 
       FIG. 1  is a block diagram illustrating a configuration of a tire failure prediction system  100  according to the first embodiment. In  FIG. 1 , the tire failure prediction system  100  includes a control unit  10 , a storage unit  20 , and a warning unit  30 . The control unit  10  is a device that comprehensively controls the operation of the tire failure prediction system  100 , and includes, for example, a central processing unit (CPU), a read-only memory (ROM), a random-access memory (RAM), and the like. The control unit  10  includes a setting unit  11 , a master curve storage unit  12 , a temperature acquisition unit  13 , a speed acquisition unit  14 , a determination unit  15 , an update unit  16 , and an input/output unit (I/O)  40 . Specifically, the functions of the setting unit  11 , the master curve storage unit  12 , the temperature acquisition unit  13 , the speed acquisition unit  14 , the determination unit  15 , the update unit  16 , and the input/output unit (I/O)  40  are realized by the CPU of the control unit  10  loading and executing programs in the storage unit  20 . 
     The setting unit  11  sets a master curve. The master curve indicates the relationship between the speed of the vehicle on which the tire is mounted and the heat build-up temperature of the tire. The master curve indicates a reference value for a variation in temperature with respect to the vehicle speed. Accordingly, in a case where the tire has no abnormality (the tire is normal), the heat build-up temperature of the tire varies along the master curve as the vehicle speed changes. Hereinafter, a master curve first set by the setting unit  11  is referred to as an initial master curve. For example, a master curve for a tire at an identical mounting position in another vehicle other than the vehicle described above can be set as the initial master curve. In particular, a master curve for a tire at an identical mounting position in a vehicle of an identical type or a vehicle with an identical tire arrangement can be set as the initial master curve. A master curve for another vehicle previously stored in the storage unit  20  may be utilized, or a master curve stored in an external database may be utilized. 
     When setting the master curve, the setting unit  11  accesses the master curve storage unit  12 . The setting of the master curve is processing for storing, in the master curve storage unit  12 , data related to a master curve used to determine a tire failure. The master curve set is to be compared with a measured value of the heat build-up temperature of the tire. 
     The master curve storage unit  12  stores data related to the master curve used to determine a tire failure. The data related to the master curve is data identifying the master curve, for example, a function corresponding to the master curve, a coefficient value indicating the inclination of the master curve, and an address value at which the data indicating the master curve is stored. The storage contents of the master curve storage unit  12  are updated by the update unit  16 . The storage contents of the master curve storage unit  12  are referenced by the determination unit  15 . In other words, the setting unit  11  stores data related to the master curve in a storage area in which the determination unit  15  can reference the master curve. 
     The temperature acquisition unit  13  acquires temperature data from temperature sensors  1 L and  1 R. The temperature acquisition unit  13  acquires temperature data in a predetermined cycle. The temperature data acquired by the temperature acquisition unit  13  is stored in the storage unit  20 . The temperature sensors  1 L and  1 R are provided in an inner cavity of the tire.  FIG. 2  is a diagram illustrating an example of a placement position of a temperature sensor. As illustrated in  FIG. 2 , the temperature sensor  1  ( 1 L,  1 R) is provided in an inner cavity of the tire P. The temperature acquisition unit  13  acquires temperature data from temperature sensors  1 L and  1 R at one-minute intervals, for example. The temperature acquisition unit  13  wirelessly acquires data from the temperature sensors  1 L and  1 R. The control unit  10  may acquire data directly from each sensor, or, with a relay provided, the control unit  10  may acquire data from each sensor via the relay. The heat build-up temperature of the tire is obtained by subtracting the atmospheric temperature from the temperature value obtained by the temperature sensor. 
     Returning to  FIG. 1 , the speed acquisition unit  14  acquires data regarding the vehicle speed from the speed sensor  2 . The speed acquisition unit  14  acquires the speed data from the speed sensor  2  at one minute intervals, for example. The speed acquisition unit  14  acquires the data related to the vehicle speed in a predetermined cycle. The speed acquisition unit  14  acquires the data related to the vehicle speed in a case where the temperature acquisition unit  13  acquires temperature data, for example. The speed sensor  2  detects the vehicle speed, for example, by generating a pulse signal proportional to the number of rotations of the axle in the vehicle. The speed sensor  2  may use a Global Positioning System (GPS) to calculate the vehicle speed. For example, the speed sensor  2  may utilize a Doppler effect of a radio wave received from a positioning satellite to calculate the vehicle speed. Additionally, for example, the speed sensor  2  may calculate the vehicle speed based on a movement distance of the vehicle and the time required for the movement of the vehicle, the distance and time being determined from a radio wave from the positioning satellite. 
     By referencing the storage contents of the master curve storage unit  12 , the determination unit  15  can recognize the master curve set by the setting unit  11 . The determination unit  15  determines a tire condition based on the difference between the master curve set by the setting unit  11  and the measured value of the temperature acquired by the temperature acquisition unit  13 . As described below, the determination unit  15  determines that the update unit  16  is to perform an update in a case where the difference between the master curve and the measured value of the temperature is a value within a first predetermined range. Additionally, in a case where the difference between the master curve and the measured value of the temperature is a value within a second predetermined range, the determination unit  15  determines that the tire condition is normal (i.e., the tire condition is not abnormal). In a case where the difference between the master curve and the measured value of the temperature is a value exceeding the second predetermined range, the determination unit  15  determines that the tire condition is not normal (i.e., the tire condition is abnormal). 
     The update unit  16  updates the master curve set by the setting unit  11 . Updating the master curve is processing for rewriting the storage contents of the master curve storage unit  12 . For example, the update unit  16  sets another master curve that is more appropriate instead of the currently set master curve. More specifically, the update unit  16  overwrites data related to the master curve stored in the master curve storage unit  12 , with other data. For example, a function corresponding to the master curve, a coefficient value indicating the inclination of the master curve, and the address value in which the data indicating the master curve is stored are rewritten. Note that changing the coefficient indicating the inclination of the master curve means changing the inclination of the straight line. 
     The update unit  16  updates the master curve based on a determination result from the determination unit  15 . The update unit  16  updates the master curve in a case where the determination unit  15  determines that the tire condition is normal (i.e., the tire condition is not abnormal). 
     The update unit  16  may overwrite with data identical to the data related to the master curve stored in the master curve storage unit  12 . In other words, the update unit  16  may replace data related to the master curve stored in the master curve storage unit  12 , with the same data. 
     The input/output unit (I/O)  40  functions as an input unit that receives data from the temperature sensors  1 L,  1 R, and the like. Additionally, the input/output unit (I/O)  40  functions as an output unit that outputs data based on a determination result from the determination unit  15 . 
     The storage unit  20  is a device for storing various types of programs  21  and various types of data  22  used for processing in the control unit  10 . The storage unit  20  includes, for example, a non-volatile memory or a magnetic storage device. The storage unit  20  may be provided inside the control unit  10 , and the control unit  10  and the storage unit  20  may be integrated with each other. The various programs  21  include programs for making determinations described below. The various data  22  include threshold values for making the determinations described below. 
     The warning unit  30  is a device for outputting a warning. The warning unit  30  outputs a warning based on a warning signal output from the control unit  10 . The control unit  10  outputs a warning signal in a case where the determination unit  15  determines that the tire condition is not normal (i.e., the tire condition is abnormal). The warning unit  30 , for example, outputs the warning to a driver of the vehicle. The warning is provided by, for example, a voice output or a display output. Additionally, the warning unit  30  may output a warning to an external device. The warning unit  30  may output a warning to the driver of the vehicle and output a warning to the external device. Outputting a warning allows the possibility of a tire failure to be notified to the driver of the vehicle or an external device. Note that the warning unit  30  does not output a warning in a case where the determination unit  15  determines that the tire condition is normal (i.e., the tire condition is not abnormal). 
       FIGS. 3 and 4  are diagrams illustrating an example of a master curve set by the setting unit  11 . In  FIG. 3 , the horizontal axis is the speed (km/h) of the vehicle on which the tire is mounted, and the vertical axis is the heat build-up temperature (° C.) of the tire. In  FIG. 3 , reference signs Th 1 , Th 2 , Th 3 , and Th 4  indicate measured values of the heat build-up temperature with respect to the vehicle speed. 
     Here, in this example, in a case where the difference between the measured value and the heat build-up temperature obtained from the master curve MC is a value exceeding the second predetermined range (for example, a range of ±20° C.), the system determines that the tire is abnormal (the tire is not normal). In  FIG. 3 , the measured values Th 1 , Th 2 , Th 3 , and Th 4  are values where the differences between the measured values Th 1 , Th 2 , Th 3 , and Th 4  and the heat build-up temperature obtained from the master curve MC are within the second predetermined range. Thus, for the measured values Th 1 , Th 2 , Th 3 , and Th 4 , the tire is determined to be not abnormal (the tire is determined to be normal). 
     As illustrated in  FIG. 3 , the measured value Th 2  matches the heat build-up temperature obtained from the master curve MC, and thus the present system updates the master curve as illustrated by the dashed line in  FIG. 3 . An updated master curve MC′ passes through the measured value Th 2 . Thus, the measured value Th 2  matches the heat build-up temperature obtained by the updated master curve MC′. That is, the present system updates the master curve in such a manner as to eliminate the difference from the measured value Th 2  to match the master curve with the measured value Th 2 . The present system updates the master curve by, for example, changing a coefficient indicating the inclination of the master curve to eliminate the difference from the measured value Th 2  to match the master curve with the measured value Th 2 . 
     Additionally, for example, the measured values Th 1 , Th 3 , and Th 4  illustrated in  FIG. 3  match the heat build-up temperature obtained from the master curve MC. Thus, even in a case where the master curve MC is updated in the present system, the master curve MC remains unchanged. 
     On the other hand, in a case where the measured value does not match the heat build-up temperature obtained from the master curve MC and the difference is a value exceeding the second predetermined range, the present system determines that the tire is abnormal. For example, as illustrated in  FIG. 4 , in a case where the difference between the measured value Th 2 ′ and the heat build-up temperature obtained from the master curve MC is a value exceeding ±20° C. used as the second predetermined range, the present system determines that the tire is abnormal. In a case where the system determines that the tire is abnormal, the present system outputs a warning to the driver or the like. 
     Update of Master Curve 
     In the tire failure prediction system of the present example, the heat build-up temperature of the tire is acquired in a predetermined cycle. In the tire failure prediction system of the present example, in a case where the measured value of the heat build-up temperature of the tire does not match the temperature obtained from the master curve and the difference is within the first predetermined range, the master curve is preferably updated. Updating the master curve refers to setting another master curve instead of the already set master curve. 
     Additionally, in a case where the measured value of the heat build-up temperature of the tire does not match the temperature obtained from the master curve and is a value within the first predetermined range that is close to that temperature, the master curve is preferably updated. For example, in a case where the measured value of the heat build-up temperature of the tire does not match the temperature obtained from the master curve, but the difference is within the range of ±10° C. (i.e., within the first predetermined range), the master curve is updated. Updating the master curve allows setting of a master curve that is closer to an actual variation in heat build-up temperature. This allows determination to be made based on a more appropriate master curve. 
     Operation Example 
       FIG. 5  is a flowchart illustrating an operation example of a tire failure prediction system  100  according to the first embodiment. In  FIG. 5 , for example, in a case where a vehicle power generation device (not illustrated) is started, the tire failure prediction system  100  performs the following processing. The power generation device is, for example, an engine or an electric motor. For example, when it is detected that an ignition switch of the vehicle has been turned on, it may be determined that the power generation device has started. 
     The tire failure prediction system  100  according to the first embodiment performs processing for each of the tires mounted on the vehicle in accordance with the flowchart illustrated in  FIG. 5 . The tire failure prediction system  100  periodically performs processing in accordance with the flowchart illustrated in  FIG. 5 . 
     In step S 101 , the tire failure prediction system  100  sets an initial master curve. The initial master curve is set by the setting unit  11 . Then, in step S 102 , the tire failure prediction system  100  acquires the measured value of the heat build-up temperature of the tire and the vehicle speed. The measured value of the heat build-up temperature of the tire is acquired by the temperature acquisition unit  13 . The vehicle speed is acquired by the speed acquisition unit  14 . 
     In step S 103 , the tire failure prediction system  100  determines whether the tire is abnormal based on the difference between the temperature obtained from the vehicle speed acquired by the speed acquisition unit  14  and the master curve set by the setting unit  11 , and the heat build-up temperature of the tire acquired by the temperature acquisition unit  13 . The determination unit  15  determines whether the tire is abnormal. 
     In response to the determination in step S 103  that the tire is not abnormal (No in step S 103 ), the tire failure prediction system  100  determines that the master curve is to be updated, and updates the master curve in step  5104 . The master curve is updated by the update unit  16 . Subsequently, the tire failure prediction system  100  determines in step S 105  whether to end the processing. In step S 105 , in a case of not ending the processing (No in step S 105 ), the tire failure prediction system  100  returns to step S 102  to continue the processing. 
     In response to the determination, in step S 103 , that the tire is abnormal (Yes in step S 103 ), the tire failure prediction system  100  outputs a warning in step  5107 . Subsequently, the tire failure prediction system  100  transitions to step S 105  to determine whether to end the processing. 
     Note that in a case of ending the processing in step S 105  (Yes in step S 105 ), the tire failure prediction system  100  transitions to step S 106 . Thus, the tire failure prediction system  100  ends the processing. 
     As described above, in a case where, with respect to the vehicle speed, the measured value of the heat build-up temperature of the tire matches the temperature obtained from the master curve or is a value within the second predetermined range that is close to that temperature, it can be determined to be normal. In other words, the tire can be determined to be normal. In a case where the tire is determined to be normal, no warning is given to the driver of the vehicle or the like. 
     On the other hand, in a case where, with respect to the actual vehicle speed, the measured value of the heat build-up temperature of the tire does not match the heat build-up temperature obtained from the master curve and is a value exceeding the second predetermined range, it can be determined to be abnormal. In other words, the tire can be determined to be abnormal. In a case where the tire is determined to be abnormal, a warning can be given to the driver of the vehicle or the like. 
     Second Embodiment 
     Now, a second embodiment of the present system will be described. In response to the determination, in step S 103  in  FIG. 5 , that the tire is not abnormal (the tire is normal), the update unit  16  may refrain from performing an update in a case where the difference is a value within the first predetermined range. For example, in a case where the difference is within the range of ±10° C. (that is, within the first predetermined range), the update unit  16  may refrain from performing the update. In other words, in a case where the tire is determined to be not abnormal (the tire is determined to be normal), when the temperature obtained based on the vehicle speed and the master curve MC does not perfectly match the measured value of the heat build-up temperature of the tire, but the difference is small, the master curve need not be updated. This is because a small difference from the measured value can be considered to be within the margin of error in the measurement of the heat build-up temperature. 
     On the other hand, in the second embodiment of the present system, in step S 103  in  FIG. 5 , in a case where the tire is determined to be not abnormal (tire is determined to be normal), when the difference is a value exceeding the first predetermined range, the present system updates the master curve. For example, in a case where the difference is a value exceeding the range of ±10° C., the present system updates the master curve. However, for example, in a case where the difference exceeds the range of ±10° C., corresponding to the first predetermined range, and the difference is a value exceeding the range of ±20° C., corresponding to the second predetermined range, the present system determines that the tire is abnormal. In the present system, in a case where the determination unit  15  determines that the tire is abnormal, the warning unit  30  outputs a warning to a driver or the like. In the present system, in a case where the determination unit  15  determines that the tire condition is normal (i.e., the tire condition is not abnormal), the warning unit  30  does not output a warning. 
       FIGS. 6 and 7  are diagrams illustrating other examples of master curves.  FIG. 6  is a diagram illustrating an example of a master curve set by the setting unit  11  in the second embodiment of the present system. In  FIG. 6 , the measured values Th 1 , Th 21 , Th 3 , and Th 4  are values within the second predetermined range (for example, in the range of ±20° C.) of the difference from the heat build-up temperature obtained by the master curve MC. Thus, for the measured values Th 1 , Th 21 , Th 3 , and Th 4 , the tire is determined to be not abnormal (the tire is determined to be normal). In this case, the difference between the measured value Th 21  and the heat build-up temperature obtained from the master curve MC is a value within the first predetermined range (e.g., in the range of ±10° C.), and thus the master curve MC is not updated. 
     On the other hand, in a case where the difference is outside the first predetermined range (e.g., the range of ±10° C.), the master curve MC is updated. In a case where the difference between the measured value Th 22  and the heat build-up temperature obtained from the master curve MC is within the second predetermined range (e.g., in the range of ±20° C.) (i.e., the tire is not abnormal) but exceeds the first predetermined range (e.g., the range of ±10° C.), the present system updates the master curve as illustrated by the dashed line in  FIG. 7 . For example, the master curve is updated by changing the coefficient indicating the inclination of the master curve to eliminate the difference from the measured value Th 22  to match the master curve with the measured value Th 22 . Thus, the updated master curve MC″ passes through the measured value Th 22 . Thus, the measured value Th 22  matches the heat build-up temperature obtained from the updated master curve MC″. 
       FIG. 8  is a flowchart illustrating an operation example of the tire failure prediction system  100  according to the second embodiment. The tire failure prediction system  100  according to the second embodiment performs processing on each of the tires mounted on the vehicle in accordance with the flowchart illustrated in  FIG. 8 . The tire failure prediction system  100  periodically performs processing in accordance with the flowchart illustrated in  FIG. 8 . The flowchart illustrated in  FIG. 8  differs from the flowchart illustrated in  FIG. 5  in that in a case where in step  5103 , the tire is determined to be not abnormal (No in step S 103 ), the determination unit  15  further determines in step S 103 A whether to update the master curve. 
     In step S 103 A, in a case where the difference is a value within the first predetermined range, the update unit  16  does not perform the update (No in step S 103 A), and the processing transitions to step S 105 . On the other hand, in step S 103 A, in a case where the difference is a value exceeding the first predetermined range, the update unit  16  performs the update (Yes in step S 103 A), and the processing transitions to step S 104 . 
     As described above, instead of updating the master curve every time, the tire failure prediction system  100  according to the second embodiment refrains from updating the master curve for a slight difference, enabling a reduction in power consumption. 
     Third Embodiment 
     A third embodiment of the present system will now be described. For a tire mounted on the vehicle, the tire failure prediction system  100  references data regarding the heat build-up temperature of another tire mounted on an identical axle at a symmetrical position to determine whether the tire has an abnormality. In other words, in step S 103  in  FIG. 5  and in step S 103  in  FIG. 8 , when determining whether the tire is abnormal, the determination may be made by referencing data regarding the heat build-up temperature of a second tire, the second tire being mounted on the identical axle at the symmetrical position. 
     In other words, in a case where the difference between the measured value of the heat build-up temperature of one tire and the heat build-up temperature obtained from the master curve is comparable to the difference for another tire mounted at a symmetrical position on the same axle, the difference for the one tire can be determined to be not abnormal. On the other hand, in a case where the difference between the measured value of the heat build-up temperature of a tire P and the heat build-up temperature obtained from the master curve is significantly different from the difference for another tire P′ mounted at a symmetrical position with respect to the tire P on the same axle as the axle on which the tire P is mounted, the difference for the tire P can be determined to be abnormal. For example, in a case where the difference exceeds  10 % of the heat build-up temperature of the tire P and the difference exceeds  10 % of the difference for the other tire P′, the tire may be determined to be abnormal. 
       FIG. 9  is a diagram illustrating an example of positions where the temperature sensors  1 L and  1 R are provided. In the present example, the vehicle  50  includes two front wheels on one axle and four rear wheels on one axle. The advancement direction of the vehicle  50  corresponds to the direction of arrow Y. On an axle JF for the front wheels, a tire P 1 L is mounted on the left side in the advancement direction and a tire P 1 R is mounted on the right side in the advancement direction. On an axle JR for the rear wheels, a tire P 2 L is mounted on a left outer side in the advancement direction and a tire P 2 R is mounted on a right outer side in the advancement direction. Additionally, on the axle JR for the rear wheels, a tire P 3 L is mounted on a left inner side in the advancement direction and a tire P 3 R is mounted on a right inner side in the advancement direction. The two left tires and the two right tires mounted on the rear wheels constitute double tires. The double tires have a configuration in which two tires are respectively mounted on a vehicle outer side and a vehicle inner side of one wheel. Note that the tires mounted on the vehicle may be collectively referred to as the tires P. 
     In the present embodiment, for tires mounted at symmetrical positions in the vehicle, the above-described difference is compared to determine abnormality. “Mounted at symmetrical positions” refers to the first tire and the second tire being mounted on the same axis at left-right symmetrical positions with respect to an imaginary line X from the front side (advancement direction) toward the rear side (reverse direction). 
     In a vehicle including two front wheels on one axle, a first tire (for example, the left tire P 1 L) mounted on the axle JF for the front wheels and a second tire (for example, the right tire P 1 R) mounted on the same axle JF for the front wheels are mounted at symmetrical positions. 
     In a vehicle including four rear wheels on one axle, a first tire mounted on the outer side of the axle JR for the rear wheels (for example, the left outer tire P 2 L) and a second tire (for example, the right outer tire P 2 R) mounted on the outer side of the same axle JR of the rear wheels are mounted at symmetrical positions. Additionally, a first tire (for example, the left inner tire P 3 L) mounted on the inner side of the axle JR for the rear wheels and a second tire (for example, the right inner tire P 3 R) mounted on the inner side of the same axle for the rear wheels are mounted at symmetrical positions. Note that in  FIG. 9 , illustration of the storage unit  20  is omitted. 
       FIG. 10  is a diagram illustrating another example of positions where the temperature sensors  1 L and  1 R are provided. In the present example, a vehicle  51  includes two front wheels on one axle and eight rear wheels on two axles. The advancement direction of the vehicle  51  corresponds to the direction of arrow Y. On the axle JF for the front wheels, the tire P 1 L is mounted on the left side in the advancement direction and the tire P 1 R is mounted on the right side in the advancement direction. On the rear-side axle JR for the rear wheels, the tire P 2 L is mounted on the left outer side in the advancement direction, and the tire P 2 R is mounted on the right outer side in the advancement direction. Additionally, on the rear-side axle JR for the rear wheels, the tire P 3 L is mounted on the rear inner side in the advancement direction, and the tire P 3 R is mounted on the right inner side in the advancement direction. On a front-side axle JM for the rear wheels, a tire P 4 L is mounted on the left outer side in the advancement direction, and a tire P 4 R is mounted on the right outer side in the advancement direction. Additionally, on the front-side axle JM for the rear wheels, a tire P 5 L is mounted on the left inner side in the advancement direction, and a tire P 5 R is mounted on the right inner side in the advancement direction. The two left tires on each of the front and rear sets of the rear wheels and the two right tires on each of the front and rear sets of the rear wheels constitute double tires. The double tires have a configuration in which two tires are respectively mounted on a vehicle outer side and a vehicle inner side of one wheel. Thus, in the case of a double tire, two tires are mounted on the same wheel. 
     In  FIG. 10 , a first tire (for example, the left tire P 1 L) mounted on the axle JF for the front wheels, and a second tire (for example, the right tire P 1 R) mounted on the same axle JF for the front wheels are mounted at symmetrical positions. 
     A first tire (for example, the left outer tire P 2 L) mounted on the outer side of rear-side axle JR for the rear wheels and a second tire (for example, the right outer tire P 2 R) mounted on the outer side of the same rear-side axle JR for the rear wheels are mounted at symmetrical positions. Additionally, a first tire (for example, the left inner tire P 3 L) mounted on the inner side of rear-side axle JR for the rear wheels and a second tire (for example, the right inner tire P 3 R) mounted on the inner side of the same rear-side axle JR for the rear wheels are mounted at symmetrical positions. 
     A first tire (for example, a left outer tire P 4 L) mounted on the outer side of the front-side axle JM for the rear wheels and a second tire (for example, a right outer tire P 4 R) mounted on the outer side of the same front-side axle JM for the rear wheels are mounted at symmetrical positions. Additionally, a first tire (for example, a left inner tire P 5 L) mounted on the inner side of the front-side axle JM for the rear wheels, and a second tire (for example, a right inner tire P 5 R) mounted on the inner side of the front-side axle JM for the rear wheels are mounted at symmetrical positions. 
     As illustrated in  FIG. 10 , also for a vehicle including two front wheels on one axle and eight rear wheels on two axles, the above-described difference is compared between the first tire and the second tire mounted on the same axle at left-right symmetrical positions to determine whether there is an abnormality. 
     In the present example, the temperature sensors  1 L and  1 R are provided inside the tires. The control unit  10  wirelessly acquires data of the temperature sensors  1 L and  1 R. The control unit  10  may acquire data directly from each sensor, or, with a relay provided, the control unit  10  may acquire data from each sensor via the relay. Note that in  FIG. 10 , illustration of the storage unit  20  is omitted. 
     For other vehicles with different wheel arrangements as well, a temperature sensor is provided in each of the tires P, and it is determined whether the tire P has an abnormality by referring to the data regarding the heat build-up temperature of another tire mounted at a symmetrical position on the same axle. 
     Fourth Embodiment 
     The temperature acquisition unit  13  acquires temperature data in a predetermined cycle. The speed acquisition unit  14  acquires the data related to the vehicle speed in a predetermined cycle. Thus, the control unit  10  can determine the tire condition in a predetermined cycle. 
     Additionally, based on the determination result from the determination unit  15 , the tire condition may be determined in a cycle shorter than the predetermined cycle. For example, in a case where the difference between the measured value and the heat build-up temperature obtained from the master curve MC is greater than a predetermined threshold value, the condition of the tire may be determined in a shorter cycle. For example, in a case where data regarding the temperature and data regarding the vehicle speed are acquired at intervals of five minutes and the tire condition is determined, the data may be acquired at shorter intervals of one minute to determine the tire condition. 
     More specifically, in a case where the difference exceeds the range of ±10° C., corresponding to the first predetermined range, the data regarding the temperature and the data regarding the vehicle speed may be acquired in a shorter cycle to determine the tire condition. In this way, tire abnormality can be detected early by changing the cycle for determining the tire condition to a shorter cycle. 
     MODIFIED EXAMPLES 
     Although the case has been described in which the master curve storage unit  12  is provided in the control unit  10 , the master curve storage unit  12  may be provided at any other position. For example, the master curve storage unit  12  may be provided in the storage unit  20 . Additionally, the master curve storage unit  12  may be provided in the setting unit  11  or the determination unit  15 . 
     The case in which the temperature varies linearly with respect to the vehicle speed has been described for ease of explanation. The temperature may vary along a curve with respect to the vehicle speed. Even in such a case, by updating the master curve, it is possible to set a master curve that is closer to the actual change in heat build-up temperature. This allows determination to be made based on a more appropriate master curve. 
     Tire Failure Prediction Method 
     According to the tire failure prediction system described above, a tire failure prediction method as described below is realized. Specifically, a tire failure prediction method is implemented that includes a first step of setting a predetermined master curve indicating a relationship between a speed of a vehicle on which a tire is mounted and a heat build-up temperature of the tire, a second step of determining a tire condition of the tire based on a difference between the master curve set in the first step and the measured value of the heat build-up temperature of the tire, and a third step of updating the master curve set in the first step. According to this method, abnormality determination can be performed with higher accuracy to predict failure. 
     Additionally, in the third step, the master curve is preferably updated in a case where the tire is determined to be normal in the second step. This allows determination to be made based on a more appropriate master curve. 
     The method may further include a fourth step of outputting a warning in a case where the tire is determined to be abnormal in the second step. Outputting a warning allows the possibility of a tire failure to be notified to the driver of the vehicle or an external device.