JP2003252191A - Method and device for estimating road surface condition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for detecting a road surface condition with high accuracy by inhibiting cavernous resonance generated in a tire. <P>SOLUTION: A tire air chamber 5 is divided in to a tire main air chamber 6 and a sub-air chamber 7 by a lid member 4, the tire main air chamber 6 and the sub-air chamber 7 are communicated through a communication hole 8 to configurate a wheel 1 comprising a Helmholtz resonance sound absorber. A fixed-type pressure sensor unit 10 formed by mounting a pressure sensor, a battery, a sensor driving circuit, and a radio transmission circuit, is attached to a well part 3w of a rim 3, a signal of minute pressure fluctuation of detected tire internal pressure is transmitted to a car body side not shown in a drawing, the frequency of the signal of minute pressure fluctuation is analyzed, the pressure fluctuation value is calculated within a predetermined frequency band, and the road surface condition in traveling is estimated on the basis of the calculated pressure fluctuation value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for estimating a road surface condition when a vehicle is running.

[0002]

2. Description of the Related Art In order to improve the running stability of an automobile, it is required to accurately estimate a friction coefficient between a tire and a road surface (road surface friction coefficient) or a road surface condition and feed it back to vehicle control. In particular, if the road surface friction coefficient can be estimated in advance before a risk-avoidance operation such as braking / driving or steering is performed, for example, it will be possible to perform higher-level control of the ABS brake and further improve safety. To be In addition, it is possible to expect a reduction in accidents by allowing the driver to carry out a deceleration operation earlier by simply notifying the driver of the degree of danger. The applicant is, for example, Japanese Patent Application No. 200
1-36048 proposes a road surface state estimation method and apparatus capable of accurately estimating a road surface state during traveling and feedback controlling the traveling state of a vehicle based on the estimated road surface state. . This method is based on the fact that the tire slips in the tread even during steady running, detects minute fluctuations of the gas in the propagated tire, and analyzes the frequency of this.
The road friction coefficient is estimated by detecting the pressure fluctuation level in a predetermined frequency band of the obtained pressure fluctuation spectrum. More specifically describing the above technique, the tire causes slippage due to wiping deformation on the tread surface even during steady running, and the slip amount increases when the road surface friction coefficient decreases. Due to this phenomenon, the high frequency vibration of the tire of 1 kHz or more increases, and this vibration also propagates to the gas in the tire. Therefore, by monitoring minute pressure fluctuations in the tire and performing frequency analysis, further obtaining pressure fluctuation levels (band values) in some required frequency bands, and performing arithmetic processing such as multiplication by a coefficient,
The road friction coefficient can be estimated. Here, as the frequency band, a plurality of bands having a large road surface input such as speed and unevenness of the road surface are selected with respect to a plurality of bands in which the contribution of the road surface is large, and a correction calculation is performed to determine the speed etc. The road friction coefficient can be estimated without information.

[0003]

However, in the above system, the road surface friction coefficient can be accurately estimated during straight traveling at a constant speed, or during gentle acceleration / deceleration and steering. In a tire, a cavity resonance sound that produces a very large peak may increase, leading to a decrease in estimation accuracy. That is, the cavity resonance sound becomes a disturbance factor in detecting the tire internal pressure and estimating the road surface slip vibration.

The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a method and apparatus for suppressing a cavity resonance noise generated in a tire and detecting a road surface condition with high accuracy. .

[0005]

According to a first aspect of the present invention, there is provided a road surface state estimating device for detecting a tire internal pressure, which is attached to a wheel having a Helmholtz resonance sound absorber and a tire air chamber side of the wheel. Pressure detection means, a wireless communication device for transmitting a signal of a minute pressure fluctuation of the tire internal pressure detected by the pressure detection means to the vehicle body side, a frequency analysis of the signal of the minute pressure fluctuation, and within a predetermined frequency band. A pressure fluctuation value calculating means for calculating a pressure fluctuation value, and a road surface state estimating means for estimating a road surface state during traveling from the calculated pressure fluctuation value are provided, and by the Helmholtz resonance sound absorber,
The cavity resonance sound in the tire, which is a noise component for the signal of the minute pressure fluctuation of the tire internal pressure, is reduced so that the road surface condition can be accurately detected. The Helmholtz resonance sound absorber forms a sub air chamber by using a lid member or the like in the wheel, and communicates the sub air chamber with the tire main air chamber through a communication hole to absorb resonance of sound by the sub air chamber. The inventors of the present invention have studied that the volume of the tire cavity resonance sound is reduced by utilizing the phenomenon. As a result, the volume of the auxiliary air chamber is V (cm ³ ), and the total cross-sectional area of the communication hole is S (cm ^2). ), The communication hole length is L (cm), and the number of communication holes is N, the resonance frequency F ₀ (Hz) of the Helmholtz resonance sound absorber can be expressed by the following equation. However, c is the sound velocity (cm / sec) in the tire air chamber. Therefore, by appropriately setting the design values of the Helmholtz resonance sound absorber, the sound in the frequency band around the cavity resonance sound can be significantly reduced.

In the road surface condition estimating device according to the second aspect of the present invention, in order to improve the accuracy of estimating the road surface condition by detecting the slipping vibration of the tire with high accuracy, the pressure detecting means serves as at least the minute pressure fluctuation. A device having a response of 1 kHz or higher is used.

According to a third aspect of the road surface condition estimating apparatus of the present invention, the cavity resonance frequency of the tire mounted on the wheel, which is determined by the size of the tire (average circumference in the tire air chamber), is F _c.
Then, the setting range of the resonance frequency F ₀ of the Helmholtz resonance absorber is F _c −100 Hz ≦ F ₀ ≦ F _c +10
Since it is set to 0 Hz, the cavity resonance noise of the tire can be reliably and significantly reduced, and the road surface condition estimation accuracy can be significantly improved.

According to a fourth aspect of the present invention, in the road surface state estimating device, the Helmholtz resonance sound absorber is formed between a rim of a wheel and a plurality of lid members arranged radially outside the rim, and is circumferentially spaced. It is composed of a plurality of sub air chambers divided by at least three or more hermetically-sealed partition walls provided with a space, and a communication hole communicating the tire main air chamber with the sub air chamber. The communication hole may be provided in the lid member, or the communication hole may be formed by providing a gap between adjacent lid members.

In the road surface state estimating device according to the fifth aspect, in order to efficiently reduce the tire cavity resonance noise while ensuring the steering stability, the total volume of the sub air chamber is set to be equal to that of the tire main air chamber.
% And 25% or less.

A road surface condition estimating method according to a sixth aspect of the present invention uses the road surface state estimating device according to any of the first to fifth aspects of the present invention to detect a time variation of a tire internal pressure and perform a frequency analysis. An average value of pressure fluctuations in at least two frequency bands is calculated, and a road surface condition during traveling is estimated from the calculated average value of pressure fluctuations.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of the present invention, 1 is a wheel for mounting a tire 2, 3 is a wheel rim (hereinafter referred to as rim) which is a tire mounting portion of the wheel, and 4 is a rim 3. A lid member, which is arranged between the tire 2 and the rim 3 and is arranged on the outer side in the radial direction, for separating the tire air chamber 5 into a tire main air chamber 6 and a sub air chamber 7, and 8 is the tire A communication hole 10 for communicating the main air chamber 6 and the sub air chamber 7 has a pressure sensor, a battery, a sensor drive circuit, a wireless transmission circuit, etc., housed in one case,
A valve fixed type pressure sensor unit integrated with a snap-in type tire valve provided on the rim 3, and a well portion 3w of the rim 3 so that a detection surface of the pressure sensor is located on the main air chamber 6 side. To be installed. In this example, as shown in FIG. 2 (a), a plurality of lid members 4 are arranged in the circumferential direction, and at least three or more closed partition walls are circumferentially spaced from the lid member 4. 9 are provided to form a plurality of auxiliary air chambers 7 (7a, 7b, ...) Discontinuous in the circumferential direction, and the auxiliary air chambers 7a, 7b ,. By forming a communication hole 8 (8a, 8b, ...) Which communicates with the air chambers 7a, 7b ,. As a result, the wheel 1 is easy to manufacture and has a sufficient cavity resonance effect.
Can be obtained. Note that, as shown in FIG.
It is also possible to form the slit-shaped communication holes 81 by arranging the respective lid members 41 at regular intervals in the circumferential direction.
In this case, for positioning, it is necessary to devise a spacer 41z for forming a fitting structure on the rim 3 and the lid member 41 at the end portion of the lid member 41, but this is man-hourly. It is possible to obtain the desired morphology with a minimum.

The resonance frequency F ₀ (Hz) of the Helmholtz resonance sound absorber is V (cm ³ ) for the volume of each sub-air chamber, S (cm ² ) for the total cross-sectional area of the communication hole, and for the communication hole length. L (cm),
The number of communication holes is N, and the sound velocity in the tire air chamber is c (cm / cm
sec) can be expressed by the following equation. On the other hand, as is known, F _c is the cavity resonance frequency of the tire to be mounted, determined by the size of the tire (the average circumferential length of the tire chamber). Therefore, in this example, the auxiliary air chamber 7 (7
a, 7b, ...) and the communication hole 8 (8a, 8b ,.
), The design values of the Helmholtz resonance sound absorber such as the total cross-sectional area S are appropriately set, and the setting range of the resonance frequency F ₀ of the Helmholtz resonance sound absorber is ± 100 Hz of the cavity resonance frequency F _c of the tire. Range (F _c −100 Hz ≦ F ₀ ≦
F _c +100 Hz)
The tire cavity resonance noise is greatly reduced.
The total volume of the auxiliary air chamber 7 is 2 times the volume of the tire main air chamber 6.
When it is less than%, the effect of reducing the cavity resonance sound becomes small and 2
If it is more than 5%, the tire spring constant is lowered too much, which is not preferable because the vibration damping property and the steering stability are deteriorated. Therefore, the sub air chamber total volume is 2 times the volume of the tire main air chamber 6.
% To 25%, more preferably 3 to 25%
15% is good.

The wheel 1 of the present invention comprises, in particular, a rim 3
Is the well portion 3w wider than the conventional product in the axial direction,
Alternatively, the structure is deep in the radial direction. The structure deep in the radial direction means that the diameter difference between the bead portion 2a and the wheel base portion 3a is large. Therefore, if there is a sufficient brake space, the diameter of the wheel base portion 3a can be reduced to increase the diameter difference. You can, but if you can't afford the beat part 2a
The diameter difference is increased by increasing the diameter and reducing the tire height (making the tire outer diameter the same), so-called an inch-up method. In addition, there is no substantial restriction on widening the well portion 3w in the axial direction. However,
Although the required auxiliary air chamber volume can be obtained even if the width of the well portion 3w is widened, it is preferable to make it deeper in the radial direction from the viewpoint of ensuring a larger volume. The wheel 1 having the above structure can be manufactured by a conventional casting method or a forging method, and can be manufactured at low cost.

The outer peripheral surfaces of the plurality of lid members 4 which are connected to the outer side of the rim 3 in the radial direction and which form the plurality of sub air chambers 7, and the outer peripheral surface of the rim 3 which is not covered by the lid member 4 are formed. The profile is a normal JATMA having a well portion 3w.
It is set so that the line conforms to the standard. Further, the material of the lid member 4 (or the lid member 41) may be the same metal material as the wheel 1 main body, or may be a different metal material or resin. Welding is preferably selected as the joining method for the lid members if they are made of the same metal material, but if they are different members, fixing methods such as bolts, bonding, and fitting are used. The thickness of the lid member 4 (or the lid member 41) depends on the material, but can be made thin within a range that does not plastically deform when the tire rim is assembled and that does not significantly deform due to centrifugal force during traveling. It is preferable because it suppresses an increase in weight. However, since the thickness of the communication hole is an element that affects the resonance frequency, it is necessary to strictly set the thickness. With such a configuration, the auxiliary air chamber can be formed only by coupling the lid member 4 manufactured separately from the wheel 1 main body, so that the number of manufacturing steps, cost, and weight are small, and the rotation balance is conventional. The auxiliary air chamber can be easily formed after ensuring the level. Further, since the lid member 4 is arranged in the wheel 1 main body and the tire 2 to form the auxiliary air chamber 7, there is no concern about air leakage. Further, the wheel 1 main body and the lid member 4 (or the lid member 41)
After coupling with the wheel 1, the rim shape of the wheel 1 has the same profile as the rim of the conventional wheel.

As a result of the study, it was found that the number of the auxiliary air chambers 7 should be three or more. That is, the auxiliary air chamber 7
If the number is smaller, resonance sound absorption delay occurs, and as a result, the cavity resonance sound in the tire cannot be effectively reduced. In this case, it is effective to increase the number of partition walls 9, and for example, even if only the communication holes 8 are dispersed in the circumferential direction, the effect is not improved. Preferably, the number of the auxiliary air chambers 7 is preferably 4 or more, more preferably 5 or more. Further, it is preferable that the partition walls 9 have the same size and are installed at equally distributed positions on the circumference so that the rotation balance is not deteriorated. There is no particular restriction on the thickness of the partition wall 9, and it is preferable to reduce the thickness in order to suppress weight. In addition, the material is not particularly limited, and if it is made integrally with the wheel 1 main body, the wheel 1 made of aluminum, iron, etc.
The same material as the body may be used. Alternatively, from the viewpoint of improving the hermeticity, a material such as rubber having a compressibility and a low specific gravity can be preferably used.

Next, a road surface state estimating method according to the present invention will be described. FIG. 3 shows a road surface state estimating device 20 of the present invention.
In this figure, the present device 20 is a rolling side (wheel side) A to which a valve fixed type pressure sensor unit 10 having a pressure sensor 11 and integrated with a tire valve is attached.
And a later-described calculation unit on the vehicle body side B, which is the non-rolling side, are wirelessly connected. The valve fixed type pressure sensor unit 10 on the wheel side A includes a pressure sensor 11 that detects the pressure of gas in the tire, and a minute vibration component (AC) on the time axis of the output of the pressure sensor 11.
Component), a pressure sensor circuit 12 for detecting the minute pressure fluctuation, an A / D converter 13a, an information compression circuit 13b,
The transmitter 13c is provided, and the information signal of the pressure fluctuation of the gas in the tire detected is converted into a digital signal and compressed,
A transmission circuit 13 for wirelessly transmitting the compressed signal from the antenna 14 to the vehicle body side B, a pressure sensor 11, a pressure sensor circuit 12, and a battery 15 for driving the transmission circuit 13 are provided. Here, the pressure sensor unit 1
0 is at least 1 kHz or higher, preferably 5 kHz
A sensor including a pressure sensor 11 and a pressure sensor circuit 12 having a response of Hz or more, and more preferably 10 kHz or more is used. Thereby, the measurement accuracy of the pressure fluctuation can be improved. In addition, as shown in FIG. 1, the fixed valve pressure sensor unit 10 has a wheel 1
It is integrated with the snap-in type tire valve provided on the rim 3 and is attached to the well portion 3w of the rim 3. Also,
In this example, the tire valve is provided with the antenna mechanism, but the antenna 14 may be separately provided.
Further, on the vehicle body side B, a receiver 22 having an antenna 21 for receiving the compressed vibration information signal, and an FFT analyzer which is a frequency analysis means for restoring the received pressure fluctuation information signal and analyzing the frequency. 23 and a calculation circuit 24 for estimating the road surface friction coefficient from the pressure fluctuation spectrum obtained by the FFT analyzer 23. Further, on the vehicle body side B, a μ indicator 31 for displaying the value of the estimated road surface friction coefficient, and an ABS brake controller (vehicle control means) 32 for controlling the hydraulic pressure of the ABS brake based on the road surface friction coefficient. Is installed.

Next, the operation of the road surface state estimating device 20 having the above configuration will be described. In the valve fixed type pressure sensor unit 10, the pressure sensor 11 and the pressure sensor circuit 12 detect the pressure fluctuation of the gas filled in the running tire, and the transmission circuit 13 A / D-converts the data to compress it. Then, the signal is transmitted from the antenna 14 to the vehicle body side B. On the vehicle body side B, the transmitted compressed signal is received by the receiver 22 via the antenna 21, and this is received by the FFT analyzer 2
3, and frequency analysis is performed to obtain a pressure fluctuation spectrum. The arithmetic circuit 24 calculates an average value of pressure fluctuations in at least two frequency bands of the pressure fluctuation spectrum, and calculates an estimated value of the road surface friction coefficient μ from the calculated average value of pressure fluctuations. In Figure 4, the tire size is 1
It is a figure which shows an example of the pressure fluctuation spectrum in a tire obtained by running a dry asphalt road and an icy road at a speed of 60 km / hr using a 1800 CC passenger car equipped with a 95 / 60R15 tire. As is clear from the figure, in the pressure fluctuation spectrum in the ice-based road where the road surface friction coefficient is low, the pressure fluctuation level is higher in the frequency band of 1.5 kHz or more than in the case of the dry asphalt road. . Therefore, in the obtained pressure fluctuation spectrum, there is a large difference between the pressure fluctuation average value in the 300 Hz to 1000 Hz band which is less affected by the slipperiness of the road surface and the pressure fluctuation level depending on the road surface condition.
The average value of the pressure fluctuation average value in the 000 Hz to 5000 Hz band is calculated, the ratio of the calculated average value of the pressure fluctuation is calculated, and the road surface friction coefficient μ is calculated in advance by the same running test as the above. An estimated value of the road surface friction coefficient can be obtained by comparing the pressure fluctuation value ratio data.

By the way, when the unevenness of the road surface is severe,
In the tire, the cavity resonance sound that produces a very large peak increases, so that the estimation accuracy of the road surface friction coefficient may decrease. FIG. 5 shows tires when a vehicle equipped with a normal wheel and a vehicle equipped with the wheel 1 with a Helmholtz resonance sound absorber according to the present invention are run on a dry asphalt road having large road surface irregularities at a speed of 60 km / hr. It is a figure which shows the frequency-analysis result of internal pressure, and the pressure fluctuation spectrum in a tire measured by the road surface state estimation apparatus 20 provided with the wheel 1 of this invention WHEREIN: The peak of the pressure fluctuation level by generation | occurrence | production of a cavity resonance sound is large. It can be seen that the disturbance factor is reduced.

The value of the road surface friction coefficient estimated by the road surface state estimating device 20 is sent to and displayed on the μ display 31.
Further, it is sent to the ABS brake controller 32 to control the hydraulic pressure of the ABS brake according to the estimated road surface friction coefficient. In the present example, as described above, the Helmholtz resonance sound absorber is used to significantly reduce the cavity resonance noise in the tire that becomes a noise component for the signal of the minute pressure fluctuation of the tire internal pressure. Accurate estimation can be performed, and the traveling state of the vehicle can be stably controlled.

In the above embodiment, the pressure sensor 1
Although the value of the road surface friction coefficient was estimated from the fluctuation information of the tire internal pressure detected in 1 and displayed on the μ display 31, the road surface condition where the tire is in contact with the ground is normal, caution, dangerous. It may be possible to display the degree of slippage of the road surface during driving = the degree of danger by classifying into states and the like. Further, in the above example, the road surface friction coefficient calculating means 25 is provided on the vehicle body side B, but it is provided on the wheel side A, and the transmission circuit 13 calculates the road surface friction coefficient estimated by the road surface friction coefficient calculating means 25. The value may be transmitted to the vehicle body side B.
Further, in the above example, the estimated value of the road surface friction coefficient is calculated from the ratio of the pressure fluctuation values, but the pressure fluctuation level (band value) of several required frequency bands is calculated and multiplied by the coefficient. The road surface friction coefficient may be estimated by performing arithmetic processing. Here, as the frequency band, a plurality of bands having a large road surface input such as speed and unevenness of the road surface are selected with respect to a plurality of bands having a large contribution of the slip of the road surface, and a correction calculation is performed. Even without it, the road surface friction coefficient can be accurately estimated.

<Embodiment> A road surface state estimating apparatus 20 of the present invention.
Fig. 6 shows the results of continuously measuring the road surface friction coefficient of a vehicle equipped with a vehicle running on a dry asphalt repair road with large unevenness on the road surface. Further, as a comparative example, the results of estimating the road surface friction coefficient by arranging a pressure sensor unit similar to that of the present invention on an ordinary wheel without a Helmholtz resonance sound absorber are also shown. The road surface friction coefficient of the road surface was 0.91 as measured by a normal braking test.
As is clear from the figure, the friction coefficient estimated value of the product of the present invention is stable. This is because the factor of disturbance is reduced by significantly reducing the cavity resonance noise, and it was confirmed that the road surface friction coefficient can be accurately obtained by the present invention.

[0022]

As described above, the road surface condition estimating apparatus of the present invention comprises a wheel having a Helmholtz resonance sound absorber, and pressure detecting means for detecting the tire internal pressure, which is attached to the tire air chamber side of the wheel. Pressure fluctuation value calculating means for frequency-analyzing the signal of the minute pressure fluctuation to calculate a pressure fluctuation value within a predetermined frequency band, and road surface condition estimation for estimating a road surface condition during traveling from the calculated pressure fluctuation value. Means, and by means of the Helmholtz resonance sound absorber, it is possible to significantly reduce the cavity resonance noise in the tire that becomes a noise component for the signal of the minute pressure fluctuation of the tire internal pressure, so that the road surface friction coefficient is accurately estimated. Therefore, the running state of the vehicle can be controlled stably.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a wheel according to the present embodiment.

FIG. 3 is a diagram showing a configuration of a road surface state estimating device according to the present embodiment.

FIG. 4 is a diagram showing variation spectra of tire internal pressure on a dry asphalt road and an iced road.

FIG. 5 is a diagram showing a damping effect of cavity resonance sound.

FIG. 6 is a diagram showing an estimation result of a road surface friction coefficient according to the present invention.

[Explanation of symbols]

1 wheel, 2 tire, 2a bead part, 3 wheel rim, 3a wheel base part, 3w well part,
4 lid members, 5 tire air chambers, 6 tire main air chambers, 7
Sub air chamber, 8 communication holes, 9 partition walls, 10 valve fixed type pressure sensor unit, 11 pressure sensor, 12 pressure sensor circuit, 13 transmission circuit, 13a A / D converter, 13
b information compression circuit, 13c transmitter, 14 transmission antenna, 15 battery, 20 road surface friction coefficient estimation device, 21 reception antenna, 22 receiver, 23 F
FT analyzer, 24 arithmetic circuit, 25 road surface friction coefficient arithmetic means, 31 μ display, 32 ABS brake controller.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B60B 21/02 G08C 17/00 BF term (reference) 2F073 AA21 AA35 AB02 AB03 BB01 BC02 CC01 FG20 GG01 GG04 GG09 3D046 BB23 BB28 HH16 HH46 HH50 JJ16 KK11

Claims (6)

[Claims] 1. A wheel provided with a Helmholtz resonance sound absorber, pressure detection means for detecting tire internal pressure, which is mounted on the tire air chamber side of the wheel, and minute pressure fluctuations of the tire internal pressure detected by this pressure detection means. Wireless communication device for transmitting the signal of the above to the vehicle body side, a pressure fluctuation value calculation means for frequency-analyzing the signal of the minute pressure fluctuation to calculate a pressure fluctuation value within a predetermined frequency band, and the calculated pressure fluctuation. A road surface state estimating device comprising: a road surface state estimating means for estimating a road surface state during traveling from a value. 2. The road surface state estimating device according to claim 1, wherein the pressure detecting means has a responsiveness of at least 1 kHz or more to the minute pressure fluctuation. 3. The resonance frequency F ₀ of the Helmholtz resonance sound absorber is set in the following range, where F _c is the cavity resonance frequency of the tire mounted on the wheel. Alternatively, the road surface state estimating device according to claim 2. _{F c -100Hz ≦ F 0 ≦ F} c + 100Hz 4. The Helmholtz resonance sound absorber is formed between the rim of the wheel and a plurality of lid members arranged radially outside the rim, and at least three or more are provided at intervals in the circumferential direction. 4. A plurality of sub air chambers divided by the closed partition wall of claim 1, and a communication hole that communicates the tire main air chamber with the sub air chamber. Road surface condition estimation device. 5. The total volume of the sub air chamber is 2% or more and 25% or less of the tire main air chamber.
~ The road surface state estimating device according to claim 4. 6. The road surface condition estimating apparatus according to claim 1, wherein time variation of tire internal pressure is detected and frequency analyzed to detect pressure variation within at least two frequency bands. A road surface state estimating method, comprising: calculating an average value and estimating a road surface state during traveling from the calculated average value of the pressure fluctuations.