JP5384137B2 - Tire internal failure determination method and tire internal failure determination device - Google Patents

Description

  The present invention relates to a method and an apparatus for detecting a failure inside a running tire.

The tire has a structure in which members such as carcass plies and belts or a metal cord coated with rubber are laminated. For this reason, when an excessive load is input to the bonded portion of the member during traveling of the vehicle, a phenomenon called socketing occurs in which the cord end portion and the coating rubber are peeled off and the rubber is cracked. When the socketing generated in each part on the tire circumference is coupled, the separation develops into a separation in which the laminated members are separated.
Further, the separation between the belts causes the both ends of the belt in the width direction to rise, and as a result, the steering stability performance may deteriorate.

By the way, when an internal failure such as separation occurs in the tire, heat generation at the failure location increases, and the temperature near the failure location increases.
Thus, a method has been proposed in which a temperature sensor is embedded in the tire shoulder portion to measure the temperature of the running tire and an internal failure of the tire is detected from this temperature change (see, for example, Patent Document 1).

  In addition, a temperature-sensitive ferrite having a Curie point in a predetermined temperature range is arranged at a predetermined pitch along the circumferential direction in the annular portion of the tire, and a magnet and an annular magnet forming an annular magnetic path intersecting the annular portion on the vehicle body side. A coil wound around the outer circumference of the road, and the electromotive force excited by the coil due to the change in magnetic flux density accompanying the rotation of the tire is measured. There has also been proposed a method of detecting abnormal distortion in an annular portion of a tire and detecting an internal failure of the tire (for example, see Patent Document 2).

There has also been proposed a method for detecting an internal failure of a tire by directly detecting deformation of a shoulder portion of the running tire.
Specifically, an acceleration sensor that measures the acceleration in the circumferential direction of the tire and an acceleration sensor that measures the acceleration in the width direction of the tire are embedded in the tire shoulder portion, and the tire circumferential portion of the running tire shoulder portion is embedded in the tire shoulder portion. After calculating the amount of deformation and the amount of deformation in the tire width direction, using these two amounts of deformation, the time series deformation of the tire shoulder is defined as the x-axis and y-axis in the tire circumferential direction and the tire width direction, respectively. Expressed as a trajectory in an orthogonal coordinate system, the size and form of deformation of the tire shoulder portion are detected from the trajectory, and an internal failure of the tire is detected (see, for example, Patent Document 3).

JP 2005-67447 A JP 2004-69462 A JP 2007-191038 A

However, in the conventional tire internal failure detection method, the sensor is embedded in the shoulder near the belt end where separation occurs, so the boundary surface between the sensor and the surrounding rubber has a new rubber crack. There is a risk of causing tire failure as a core.
In addition, when the sensor is disposed at the belt end portion where a large stress acts when the tire rolls, the belt end portion is broken and the possibility of causing separation is high.

  The present invention has been made in view of conventional problems, and a tire internal failure determination method capable of accurately determining whether or not a tire internal failure due to separation has occurred without affecting the behavior of the tire. And an apparatus for the same.

  As a result of intensive investigations, the present inventor, in the case of a tire in which an internal failure due to separation has occurred, the vibration spectrum obtained by frequency analysis of vibration in the tire width direction of the tread of the running tire is 4 kHz to 10 kHz. Since the size of frequency components in the frequency band (hereinafter referred to as the band value) has increased significantly compared to normal tires, if the band value is used as a separation measure, the presence or absence of internal tire failures can be determined. The inventors have found that accurate determination can be made and have arrived at the present invention.

That is, the present invention is a method for determining whether or not an internal failure due to separation has occurred in a tire, the step of detecting acceleration in the tire width direction with an acceleration sensor disposed on the inner surface of the tire, and the acceleration sensor A step of calculating a band value that is a magnitude of a frequency component within a frequency band of 4 kHz to 10 kHz of the tire width direction acceleration waveform obtained from the output signal of the tire, and a tire width direction acceleration waveform obtained from the output signal of the acceleration sensor A step of detecting a vibration level within a frequency band of 0.5 kHz to 3.5 kHz, and a road surface measured using a normal tire in which separation is not generated in the detected vibration level and a predetermined inside. Estimating the road surface state from the relationship between the state of the vehicle and the vibration level, and the normal type A step of the threshold is changed according to the estimated road surface state separation within the band value measured by mounting is set on the basis of the bandwidth value measured by mounting the tire generated, said operation determining a bandwidth values, by comparing the changed threshold, when the previous SL computed bandwidth value exceeds the modified threshold, an internal failure due separation in the tire has occurred And a step.
In addition, “separation” generally refers to a phenomenon in which a rubber and a belt constituting a tire and a rubber and a rubber are peeled and damaged, and a socketing phenomenon in which a cord end part and a coating rubber are peeled is also referred to as “separation”. "include.

Further, the present invention, a threshold for determining whether the internal mechanical failure due to the separation has occurred, in which be changed according to said estimated road surface condition and wheel speed.

Further, the present invention is an apparatus for determining whether or not an internal failure due to separation has occurred in a tire, an acceleration sensor disposed on the inner surface of the tire for detecting acceleration in the tire width direction, and an output of the acceleration sensor A width direction acceleration waveform extracting means for extracting a tire width direction acceleration waveform from the signal, and a band value calculation for calculating a band value which is a magnitude of a frequency component within a frequency band of 4 kHz to 10 kHz from the tire width direction acceleration waveform. And a vibration level detecting means for detecting a vibration level in a frequency band of 0.5 kHz to 3.5 kHz from the acceleration waveform in the tire width direction, and a normal tire in which separation is not generated is mounted. Set based on the band value when driving with a tire with separation generated inside First storage means for storing the threshold was, first stores a table showing pre-determined internal separation had been the state of the road surface was measured using a normal tire does not occur the relationship between the vibration level And a threshold value changing means for changing the threshold value in accordance with the estimated road surface condition from the stored vibration level and the table. And the calculated band value and the threshold value changed by the threshold value changing means, and when the calculated band value exceeds the changed threshold value, an internal failure due to separation occurs in the tire. It is characterized by comprising determination means for determining that it is present.

Further, the present invention provides a means for detecting the wheel speed, and the threshold value changing means
Characterized the Turkey to change the threshold stored in said first storage means in accordance with said estimated road surface state and the detected wheel speed.

According to the present invention, whether or not a tire internal failure has occurred from the magnitude of the frequency component in the frequency band of 4 kHz to 10 kHz of the tire width direction acceleration waveform output from the acceleration sensor arranged in the tire tread portion. Therefore, it is possible to determine whether or not a tire internal failure due to separation has occurred without affecting the behavior of the tire. Further, the threshold value used for the determination was set based on the bandwidth value separation was measured by mounting the tire that occurred band value and an inner portion as measured by mounting the normal tire separation within has not occurred Therefore, the occurrence of separation can be reliably determined.
Moreover, since the threshold value used for the determination is changed according to the road surface condition, the accuracy of the tire internal failure determination can be further improved.
Specifically, a tire width direction acceleration waveform of 0.5 kHz to 3 with little difference between a band value measured with a normal tire mounted and a band value measured with a tire with separation inside. Since the vibration level in the frequency band of 5 kHz is detected, the road surface state is estimated from the detected vibration level, and the threshold value is changed according to the estimated road surface state, regardless of the road surface state. Therefore, it is possible to accurately determine the internal failure of the tire.

In addition, since the difference between the band value measured with a normal tire mounted and the band value measured with a tire with separation inside is dependent on the wheel speed, the threshold used for the determination is estimated. if the change in accordance with the road conditions and the wheel speed, it is possible to further improve the accuracy of the internal failure determination of the tire.

  The summary of the invention does not list all necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

It is a figure which shows the structure of the tire internal failure determination apparatus which concerns on this Embodiment. It is sectional drawing which shows the structure of a tire. It is a figure which shows the generation | occurrence | production location of a separation. It is a figure which shows the footprint at the time of separation generation | occurrence | production. It is a figure which shows the difference in the frequency spectrum of the width direction acceleration by the presence or absence of generation | occurrence | production of a separation (wheel speed; 20 km / hr). It is a figure which shows the difference in the frequency spectrum of the width direction acceleration by the presence or absence of generation | occurrence | production of a separation (wheel speed; 30 km / hr). It is a figure which shows the difference in the frequency spectrum of the width direction acceleration by the presence or absence of generation | occurrence | production of a separation (wheel speed; 40 km / hr). It is a figure which shows the relationship between a wheel speed and a zone | band value. It is a flowchart which shows the tire internal failure determination method by this invention. It is a figure which shows the other structure of the tire internal failure determination apparatus by this invention.

  Hereinafter, the present invention will be described in detail through embodiments, but the following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

FIG. 1 is a diagram illustrating a configuration of a tire internal failure determination device 1.
The tire internal failure determination apparatus 1 includes an acceleration sensor 11, a wheel speed sensor 12, an acceleration waveform extraction unit 13, a frequency analysis unit 14, a band value calculation unit 15, a first storage unit 16, and a threshold setting unit 17. A failure determination unit 18, an alarm unit 19, a vibration level detection unit 21, a second storage unit 22, and a road surface state estimation unit 23.
Each means from the acceleration sensor 11 to the warning means 19 constitutes the tire internal failure determination means 10, and the road surface state is estimated from the acceleration sensor 11, the acceleration waveform extraction means 13, the frequency analysis means 14, and the vibration level detection means 21. Each means up to means 23 constitutes traveling road surface estimating means 20. The acceleration sensor 11, the acceleration waveform extraction means 13, and the frequency analysis means 14 are common components of the tire internal failure determination means 10 and the traveling road surface estimation means 20.

FIG. 2 is a cross-sectional view showing the configuration of the tire 30. In the figure, 31 is a bead portion, 31C is a bead core, 32 is a carcass layer, 33 is a first belt layer, 34 is a second belt layer, 35 is a tread, and 36 is an inner liner.
The carcass layer 32 is a member constituting the skeleton of the tire 30 and is provided so as to straddle a pair of bead cores 31 </ b> C disposed in the bead portion 31 in a toroidal shape. Two belt layers (first and second belt layers) 33 and 34 are disposed outside the crown portion of the carcass layer 32 in the tire radial direction. The first and second belt layers 33 and 34 are respectively arranged such that steel cords or cords made by twisting organic fibers intersect at an angle of 20 ° to 70 ° with respect to the equator direction. . The first belt layer 33 disposed on the inner side in the tire radial direction is formed wider than the second belt layer 34 disposed on the outer side in the tire radial direction. The extension direction of the cord of the second belt layer 34 intersects with each other.
The socketing in which the cord end portion and the coating rubber peel and the rubber cracks mainly occurs at the end portions of the first and second belt layers 33 and 34, and when this progresses, as shown in FIG. In addition, the tire shoulder portion 37 develops into a separation in which the first belt layer 33 and the second belt layer 34 are separated.

In the present example, the acceleration sensor 11 is disposed at substantially the center of the inner liner 36 of the tire 30 on the tire air chamber side. The acceleration sensor 11 is arranged so that the detection direction is the tire width direction, and detects vibration in the tire width direction that is input from the road surface to the contact surface of the tread 35.
The wheel speed sensor 12 detects the wheel speed V and includes a rotation speed detection means 12a. As the rotation speed detection means 12a, for example, a type that detects the rotation of the transmission using a magnetoresistive element can be used.
The acceleration waveform extraction means 13 extracts a time series waveform of tire width direction acceleration (hereinafter referred to as width direction acceleration waveform) from the output signal of the acceleration sensor 11.
The frequency analysis means 14 performs frequency analysis on the width direction acceleration waveform to obtain a frequency spectrum.

Hereinafter, the characteristics of the failed tire in which separation has occurred will be described.
FIG. 4 (a) is a footprint showing the shape of the ground contact surface of the tire and is symmetrical when traveling straight. This is because the cords of the first belt layer 33 and the cords of the second belt layer 34 are arranged at an axially symmetric angle with respect to the tire center, and therefore the first belt layer 33 and the second belt. When the layer 34 is adhered to each other, the ground contact shapes are left-right symmetrical because the deformations due to the belt angle (shear deformation) are constrained to cancel each other.
On the other hand, when separation occurs and the end portion of the first belt layer 33 and the end portion of the second belt layer 34 are separated, the mutual restraining force is lost, so that deformation due to the belt angle is caused by the contact shape and the tire inner surface. Appear in Therefore, as shown in FIG. 4B, the shape of the contact surface becomes asymmetric, and as a result, in the tire in which separation occurs, high-frequency vibration is generated in the tire width direction as shown in FIGS. .

5 to 7 are diagrams showing frequency spectra of the acceleration in the width direction when the wheel speed V is 20 km / hr, 30 km / hr, and 40 km / hr on the road surface of the DRY asphalt, respectively. The horizontal axis is the frequency (kHz), the vertical axis is the width direction acceleration level, the solid line in each figure is the frequency spectrum when running with a new tire, and the broken line is when running with a tire with separation Is the frequency spectrum.
As is clear from the figure, in the failed tire in which the separation occurred, the width direction acceleration level in the frequency band of 4 kHz or more of the frequency spectrum is remarkably increased as compared with the new tire.
Further, as shown in FIG. 8, the way of increase depends on the wheel speed V. Specifically, the band value increases as the wheel speed V increases, whether it is a new tire or a failed tire.
Therefore, it is possible to estimate whether or not separation has occurred in the tire by obtaining the wheel speed V and the width direction acceleration level within a frequency band of 4 kHz or more of the frequency spectrum.

The band value calculation means 15 calculates the width direction acceleration level (hereinafter referred to as the band value P) of the frequency component in the frequency band of 4 kHz to 10 kHz from the frequency spectrum obtained by the frequency analysis means 14.
The band value P may be a width direction acceleration level at a specific frequency in the 4 kHz to 10 kHz band, or may be an average value of the width direction acceleration levels at a plurality of frequencies in the preset 4 kHz to 10 kHz band. There may be. Alternatively, it may be the sum or integral value of the width direction acceleration levels in a predetermined frequency band (for example, 5 kHz to 8 kHz) in a preset 4 kHz to 10 kHz band.

The first storage means 16 obtains in advance a band value P ₀ when running with normal tires attached and a band value P _s when running with tires with separation inside. The threshold value K set based on is stored.
In this example, the threshold value K is changed according to the road surface state and the wheel speed.
Specifically, it is known that when the road surface becomes slippery, the width direction acceleration level increases in a frequency band of 0.5 kHz or more of the width direction acceleration even in a normal tire in which separation does not occur. Further, as described above, the band value P depends on the wheel speed V. Therefore, the threshold value K is set to the threshold value K _j (V) corresponding to the road surface state and the wheel speed V.
That is, the road surface condition is divided into three, a high μ road corresponding to a DRY asphalt road surface, a low μ road corresponding to a snow road or an ice road, and a middle μ road in the middle, and the threshold value on the high μ road is set to K _h ( V), the threshold value for the medium μ road is K _m (V), the threshold value for the low μ road is K _l (V), and the first storage means 16 uses the threshold value K _h (V), the threshold value K. _m (V) and threshold value K _l (V) are obtained for each wheel speed V, and these threshold values K _j (V) (j = h, m, l) are stored.

The threshold value setting means 17 is based on the wheel speed V detected by the wheel speed sensor 12 and the road surface state estimated by the road surface state estimating means 23 described later, and the threshold value K _j for the band value P calculated by the band value calculating means 15. Select (V) and set.
The failure determination unit 18 compares the band value P calculated by the band value calculation unit 15 with the threshold value K _j (V) set by the threshold value setting unit 17, and the band value P exceeds the threshold value K _j (V). It is determined that an internal failure has occurred in the tire 30 due to separation.
The alarm means 19 issues an alarm to the driver by flashing a lamp or the like arranged near the driver's seat or generating a warning sound from a speaker when an internal failure occurs in the tire 30.

As described above, when the road surface becomes slippery, even in a normal tire, the width direction acceleration level increases in a frequency band of 0.5 kHz or more. Therefore, in this example, the road surface state is estimated using the traveling road surface estimation means 20, and the threshold value is changed according to the estimated road surface state.
Specifically, in the frequency band of 0.5 kHz or more that increases or decreases depending on the slipperiness of the road surface, the acceleration level in the width direction of the tire in the frequency band of 0.5 kHz to 3.5 kHz, which is hardly affected by the occurrence of separation. To estimate the road surface condition.
That is, the vibration level detection means 21 calculates the vibration level M, which is the magnitude of the frequency component within the frequency band of 0.5 kHz to 3.5 kHz, from the frequency spectrum obtained by the frequency analysis means 14.

The second storage means 22 is a road surface created using vibration levels M (μ) obtained in advance by running a vehicle equipped with normal tires on road surfaces having various road surface friction coefficients μ. A table 22T indicating the relationship between the friction coefficient μ and the vibration level M (μ) is stored.
The road surface state estimating means 23 determines whether the road surface state during traveling is a high μ road based on the vibration level M calculated by the vibration level detecting means 21 and the table 22T stored in the second storage means 22. It is estimated whether the road is a μ road or a medium μ road.

Next, operation | movement of the tire internal failure determination apparatus 1 is demonstrated with reference to the flowchart of FIG.
First, vibration in the tire width direction of the running tire 30 is detected by the acceleration sensor 11, and the detection signal is output to the acceleration waveform extraction means 13 (step S11). The acceleration waveform extraction means 13 extracts a width direction acceleration waveform, which is a time series waveform of the tire width direction acceleration, from the output waveform of the acceleration sensor 11 (step S12), and outputs this to the frequency analysis means 14.
The frequency analysis means 14 performs frequency analysis on the widthwise acceleration waveform to obtain a frequency spectrum (step S13), and outputs this frequency spectrum to the band value calculation means 15 and the vibration level detection means 21.
The band value calculation means 15 calculates a band value P which is the magnitude of the frequency component within the frequency band of 4 kHz to 10 kHz from the frequency spectrum of the tire width direction acceleration (step S14), and this is calculated to the failure determination means 18. Output.

On the other hand, the vibration level detection means 21 calculates a vibration level M which is the magnitude of the frequency component in the frequency band of 0.5 kHz to 3.5 kHz from the frequency spectrum of the tire width direction acceleration (step S15). Is output to the road surface state estimating means 23.
The road surface state estimating means 23 estimates the road surface state from the table 22T showing the relationship between the vibration level M, the road surface friction coefficient μ stored in the second storage means 22 and the vibration level M (μ) (step S 16), this estimation result is output to the threshold setting means 17.
On the other hand, the wheel speed sensor 12 is used to detect the wheel speed V and output this to the threshold setting means 17 (step S17).

The threshold value setting means 17 uses the wheel speed V detected by the wheel speed sensor 12 and the road surface state estimated by the road surface state estimation means 23 to determine the threshold value K _j (V) (j = h, m, l) is set (step S18).
The failure determination means 18 determines whether or not the band value P sent from the band value calculation means 15 exceeds the threshold value K _j (V) (step S19). When the band value P exceeds the threshold value K _j (V), it is determined that an internal failure due to separation has occurred in the tire 30, and this determination result is sent to the alarm means 19. The warning means 19 notifies the driver that an internal failure has occurred in the tire (step S20).

According to the present embodiment, the time series waveform of the acceleration in the tire width direction input from the road surface to the contact surface of the tread 35 is extracted from the output waveform of the acceleration sensor 11 arranged on the tire chamber side of the inner liner 36 of the tire 30. After that, from the frequency spectrum obtained by frequency analysis of this, the band value P which is the size of the frequency component within the frequency band of 4 kHz to 10 kHz is calculated, and this band value P and a normal tire are mounted. The threshold value K _j (V) set on the basis of the band value measured in this way and the band value measured based on the measurement of the tire with separation generated inside the tire is compared. Since it was determined whether or not it occurred, there was a tire internal failure due to separation without affecting the tire behavior. It can be determined whether or not the.

Further, the threshold value K _j (V) used for the determination is changed according to the wheel speed V detected by the wheel speed sensor 12 and the road surface state estimated by the road surface state estimating means 23. A tire internal failure due to occurrence can be reliably determined.
Further, when estimating the road surface condition, a vibration level M that is a magnitude of a frequency component within a frequency band of 0.5 kHz to 3.5 kHz is calculated from a frequency spectrum of acceleration in the tire width direction, and the vibration level M Since the road surface state is estimated from the table 22T indicating the relationship between the road surface friction coefficient μ and the vibration level M (μ) stored in the second storage unit 22, the threshold value K _j used for the determination (V) can be selected accurately. Therefore, the accuracy of the tire internal failure determination can be improved.

Moreover, since the determination of a tire internal failure and the estimation of the road surface condition can be performed with one acceleration sensor 11, the apparatus can be simplified.
Further, when it is determined that an internal failure due to separation has occurred in the tire 30, the alarm means 19 notifies the driver that the internal failure has occurred in the tire 30, so as to call the driver attention. Therefore, the running stability of the vehicle can be improved.

In the above-described embodiment, one threshold value K _j (V) is set for each combination of the wheel speed V and the road surface state, and it is determined whether or not an internal failure due to separation has occurred in the tire 30. The threshold value K _j (V) may be increased. As a result, according to the separation progress state, for example, determination of multiple stages such as “normal”, “failure occurrence”, “failure progress”, and the like can be performed, so that the tire internal failure determination can be performed with higher accuracy.
The frequency band for calculating the band value P may be changed depending on the tire type, size, tire internal pressure, and the like.

  In the above example, the band value P and the vibration level M are obtained from the frequency spectrum of the width-direction acceleration obtained by using the frequency analysis unit 14. However, instead of the frequency analysis unit 14, a bandpass filter is used. Also good. Specifically, a first filter that extracts a time series waveform in a frequency band of 4 kHz to 10 kHz from a time series waveform of acceleration in the tire width direction and a second filter that extracts a time series waveform in a frequency band of 0.5 kHz to 3.5 kHz. A filter may be provided, the RMS value of the output signal of the first filter may be the band value P, and the RMS value of the output signal of the second filter may be the vibration level M.

  In the above example, the road surface state is divided into three stages of a high μ road surface, a medium μ road surface, and a low μ road surface. However, the present invention is not limited to this, and the road surface state may be divided into two stages of a high μ road surface and a low μ road surface. Good. Alternatively, the road surface state may be represented by the value of the road surface friction coefficient μ itself. In this case, however, the threshold value K is finely set and an error is more likely to occur. Therefore, it is preferable to divide into about three stages as in this example.

Further, a road surface state estimation device 40 as shown in FIG. 10 may be used instead of the traveling road surface estimation means 20.
In the road surface state estimating device 40, a pressure sensor 41 is installed in the tire, and the frequency analysis means 42 performs frequency analysis on the minute vibration component (AC component) of the gas pressure in the tire chamber detected by the pressure sensor 41. Obtain the pressure fluctuation spectrum. Then, after the pressure fluctuation level detecting means 43 detects the pressure fluctuation level of 0.5 kHz to 3.5 kHz of the pressure fluctuation spectrum, the road surface state estimating means 45 detects the pressure detected by the pressure fluctuation level detecting means 43. An estimated value of the road surface friction coefficient μ is obtained from the fluctuation level and the G-table 44G indicating the relationship between the road surface friction coefficient μ and the pressure fluctuation level stored in the pressure fluctuation level storage means 44 in advance.

  In addition, when the road surface state estimation device 40 and the tire internal failure determination unit 10 according to the present invention are combined to form the tire internal failure determination device 2 as in the present embodiment, the road surface state estimation unit 45 includes the road surface friction coefficient μ. It is estimated that the road surface during traveling is a high μ road, a low μ road, or a medium μ road, and this is sent to the threshold setting means 17. That's fine.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the embodiment. It is apparent from the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  As described above, according to the present invention, it is possible to accurately detect the destruction inside the tire without affecting the behavior of the tire, so it is possible to detect the failure of the tire in advance, and the safety of the vehicle. Can be improved.

1 tire internal failure determination device, 10 tire internal failure determination means,
11 acceleration sensor, 12 wheel speed sensor, 13 acceleration waveform extraction means,
14 frequency analysis means, 15 band value calculation means, 16 first storage means,
17 threshold setting means, 18 failure determination means, 19 alarm means,
20 traveling road surface estimation means, 21 vibration level detection means, 22 second storage means,
22T table, 23 road surface state estimation means,
30 tires, 31 bead parts, 31C bead core, 32 carcass layers,
33 1st belt layer, 34 2nd belt layer, 35 tread, 36 inner liner.

Claims (4)

Detecting the acceleration in the tire width direction by an acceleration sensor disposed on the inner surface of the tire;
Calculating a band value that is a magnitude of a frequency component within a frequency band of 4 kHz to 10 kHz of a tire width direction acceleration waveform obtained from an output signal of the acceleration sensor;
Detecting a vibration level within a frequency band of 0.5 kHz to 3.5 kHz of a tire width direction acceleration waveform obtained from an output signal of the acceleration sensor;
Estimating the road surface state from the detected vibration level and the relationship between the road surface state and vibration level measured using normal tires that have not been separated in the interior determined in advance;
A step of changing a threshold value set based on a band value measured by mounting the normal tire and a band value measured by mounting a tire in which separation occurs inside according to the estimated road surface condition When,
Wherein the computed bandwidth value, comparing the modified threshold, when the previous SL computed bandwidth value exceeds the modified threshold, an internal fault by separation on the tires has occurred And a step of determining the tire internal failure. The threshold for determining whether the internal mechanical failure due to the separation has occurred, the tire internal mechanical failure determination according to claim 1, characterized in that to change in accordance with said estimated road surface condition and wheel speed Way . An acceleration sensor arranged on the inner surface of the tire to detect acceleration in the tire width direction;
A width direction acceleration waveform extracting means for extracting a tire width direction acceleration waveform from an output signal of the acceleration sensor;
Band value calculation means for calculating a band value that is a magnitude of a frequency component within a frequency band of 4 kHz to 10 kHz from the tire width direction acceleration waveform;
Vibration level detection means for detecting a vibration level in a frequency band of 0.5 kHz to 3.5 kHz from the tire width direction acceleration waveform;
A threshold value set based on a band value when running with a normal tire without separation inside and a band value when running with a tire with separation inside is stored . 1 storage means;
Second storage means for storing a table indicating a relationship between a road surface state and a vibration level measured using a normal tire in which separation is not generated in the interior obtained in advance;
From the detected vibration level and the table, road surface state estimating means for estimating the state of the road surface during traveling,
Threshold change means for changing the threshold according to the estimated road surface condition;
The calculated bandwidth value is compared with the threshold value changed by the threshold value changing means, and when the calculated bandwidth value exceeds the changed threshold value, an internal failure due to separation has occurred in the tire. A tire internal failure determination device, comprising: a determination unit that determines While providing means for detecting wheel speed ,
The threshold value changing means includes
Tire internal mechanical failure determination device according to claim 3, wherein the benzalkonium to change the threshold stored in said first storage means in accordance with said estimated road surface state and the detected wheel speed.

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