JP2002340863A - Road surface determination device and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect a road surface condition with a practical sampling frequency. SOLUTION: An acceleration sensor 10 and a sound pressure sensor 12 are arranged inside a tire. A waveform comparison circuit 18E determines a road surface according to an acceleration reference waveform and a waveform of an acceleration signal. A waveform comparison circuit 20E determines the road surface according to a sound pressure reference waveform and a waveform of a sound pressure signal. A power spectrum comparison circuit 18F determines the road surface according to comparison between an acceleration reference power spectrum and an acceleration power spectrum obtained from the acceleration signal. A power spectrum comparison circuit 20F determines the road surface according to comparison between a sound pressure reference power spectrum and a sound power spectrum obtained from the sound pressure signal. A road surface determination circuit 22 determines the road surface according to a majority of the surface determination results.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road surface determination device and a road surface determination system, and more particularly to a road surface determination device and a road surface determination system capable of accurately determining a road surface at a practical sampling frequency.

[0002]

2. Description of the Related Art Japanese Patent Laying-Open No. 6-258196 focuses on the fact that the resonance level of rubber on the tread surface caused by a lateral slip caused by a toe-in during straight traveling varies with the road surface μ. Calculates the PSD value (power spectrum density) of the resonance level based on the signal from the acceleration sensor attached to the suspension arm, and uses the calculated PSD value as the P of the specific frequency.
A road surface state detection device using a tire acceleration for detecting a road surface state in comparison with an SD table value is described.

However, in this technique, the target frequency band is around 6 kHz, and sampling at around 60 kHz (16 ns in terms of period), which is at least 10 times, is required to perform accurate frequency analysis.
As described above, in the technique focusing on the resonance of the rubber on the tread surface, there is a problem that the sampling frequency must be increased to an impractical level because the resonance frequency needs to be extremely high.

In Japanese Patent Application Laid-Open No. 8-298613, a microphone is installed on a vehicle body near a tire, a running sound caused by friction between the tire and a road surface is measured by the microphone, and a bandpass filter is used. A technique is described in which frequency analysis is performed by Fourier transform, and a spectrum at a specific frequency is compared with a table value of each road surface to detect a road surface state.

However, in this technique, since the microphone is installed outside the tire, there is a problem that the microphone is easily affected by external sounds such as an engine sound and a wind noise, and the road surface determination accuracy is reduced.

The present invention has been made to solve the above problems, and provides a road surface determination device and a road surface determination system capable of accurately detecting a road surface state at a practical sampling frequency of about 1 kHz to 5 kHz. The purpose is to do.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an acceleration sensor which is disposed inside a tire and detects acceleration generated inside the tire as the tire rotates and outputs an acceleration signal. A detection unit including a sound pressure sensor that is disposed close to the acceleration sensor inside the tire and detects a sound pressure generated inside the tire with rotation of the tire and outputs a sound pressure signal; The road surface is determined based on the reference waveform of the acceleration and the waveform of the acceleration signal detected by the acceleration sensor, and based on the reference waveform of the predetermined sound pressure and the waveform of the sound pressure signal detected by the sound pressure sensor. A first road surface determination unit that determines a road surface based on the acceleration waveform and outputs a road surface determination result based on the acceleration waveform and a road surface determination result based on the sound pressure waveform; and a predetermined acceleration reference power spectrum. The road surface is determined by comparing the acceleration power spectrum obtained from the speed signal with the reference power spectrum of a predetermined sound pressure and the power spectrum of the sound pressure obtained from the sound pressure signal. Output a road surface determination result based on the power spectrum of the sound pressure and a road surface determination result based on the power spectrum of the sound pressure.
From the road surface determination means, the road surface determination result based on the acceleration waveform, the road surface determination result based on the sound pressure waveform, the road surface determination result based on the power spectrum of the acceleration, and the road surface determination result based on the power spectrum of the sound pressure, Preferably, a third road surface determining means for determining a road surface from the result of majority decision of the road surface determination results is provided.

First, the principle of the present invention will be described. During steady running on a dry road, when the part of the tire that is not in contact with the road surface is in contact with the road surface (during contact), a constant acceleration and sound pressure are generated inside the tire due to deformation of the tread. Occurs. Therefore, the waveforms of the constant acceleration and sound pressure can be used as a reference.

If a water film is present between the tire road surfaces, the deformation of the tread is suppressed, so that each waveform of the acceleration and sound pressure at the time of contact with the ground changes with respect to the reference.

Further, when the coefficient of friction between the tire road surfaces is reduced, slippage occurs at the leading edge of the tread contact portion, so that the waveforms of acceleration and sound pressure at the time of contact change with respect to the reference.

If the unevenness of the road surface is large, the waveforms of acceleration and sound pressure at the time of contact with the ground greatly change.

Therefore, it is possible to determine the road surface by detecting a change from the reference during running on the basis of the waveforms of the acceleration and sound pressure inside the tire when the vehicle is steadily running on the dry road.

[0013] Furthermore, when the vehicle is running on a dry road in a steady state, the tire rubber vibrates due to micro unevenness on the road surface,
Acceleration and sound pressure occur inside the tire. The vibration of the tire rubber in the road noise frequency range (around 100 to 500 Hz) changes with respect to the reference due to the difference in unevenness between road surfaces such as an icy road and an asphalt road.

Therefore, it is possible to determine the road surface by detecting a change from the reference power spectrum at a specific frequency during running on the basis of the acceleration and sound pressure spectrum inside the tire when the vehicle is steadily running on a dry road. it can.

The acceleration sensor and the sound pressure sensor of the present invention
Each of them is arranged close to the inside of the tire, detects acceleration and sound pressure generated inside the tire as the tire rotates, and outputs an acceleration signal and a sound pressure signal, respectively.

The first road surface determination means determines the road surface based on the reference waveform of the acceleration and the waveform of the acceleration signal, and determines the road surface based on the reference waveform of the sound pressure and the waveform of the sound pressure signal. The road surface determination result based on the acceleration waveform and the road surface determination result based on the sound pressure waveform are output. The second road surface determination means compares the reference power spectrum of the acceleration with the power spectrum of the acceleration obtained from the acceleration signal, and also compares the reference power spectrum of the sound pressure with the power of the sound pressure obtained from the sound pressure signal. The road surface is determined by comparing the spectrum with the spectrum, and a road surface determination result based on the power spectrum of the acceleration and a road surface determination result based on the power spectrum of the sound pressure are output. The third road surface determining means includes a road surface determination result based on the acceleration waveform, a road surface determination result based on the sound pressure waveform, a road surface determination result based on the power spectrum of the acceleration, and a road surface determination result based on the power spectrum of the sound pressure. The road surface is determined from the determination result. In this case, it is effective to determine the road surface from the result of majority decision of these road surface determination results.

In the present invention, since the acceleration sensor and the sound pressure sensor are housed inside the tire, the road surface can be accurately determined without being affected by external sounds. Also,
Since the road surface is determined by comparing the acceleration waveform inside the tire and comparing the power spectrum, it is not necessary to increase the sampling frequency as in the related art, and sampling can be performed within a practical range.

According to the present invention, the first road surface determining means determines the waveform of the acceleration signal and the waveform of the sound pressure signal output in a predetermined section including a section where the tire detecting means arrangement portion is in contact with the road surface. The road surface is determined using the power spectrum of the acceleration and the power spectrum of the sound pressure obtained from each of the acceleration signal and the sound pressure signal output in the predetermined section. Is determined. As described above, by using the acceleration signal and the sound pressure signal output in a predetermined section including the section where the tire detection unit arrangement portion is in contact with the road surface,
Since the determination of the road surface can be performed using only the signal of the necessary section, the road surface determination time can be reduced. When determining the road surface by the first road surface determination means, a variance value between the acceleration reference waveform and the acceleration signal waveform and a variance value between the sound pressure reference waveform and the sound pressure signal waveform are calculated. The road surface can be determined by comparing the calculated variance value with a threshold value predetermined according to the road surface. Note that a correlation coefficient may be used instead of the variance value. During braking and driving, the acceleration waveform and the sound pressure waveform with respect to the wheel pressure and the vehicle speed are different depending on the road surface μ. Therefore, it is preferable to change the threshold value according to the wheel pressure and the vehicle speed.

The above-described road surface determination device can be configured as a road surface determination system in combination with a preview road surface determination device used for vehicle control. This road surface determination system is configured to irradiate any one of the above-described road surface determination devices with light toward the road surface, compare the level of light reflected from the road surface with a threshold value, and determine a fourth road surface state. Road surface determining means for irradiating an ultrasonic wave toward the road surface and comparing the level of the reflected wave from the road surface with a threshold value to determine the road surface state.
A preview road surface provided with at least one of a road surface determination unit and a sixth road surface determination unit that captures a road surface and compares a feature amount of the captured image with a threshold value of the feature amount to determine the road surface. A determination device and at least one threshold value of the preview road surface determination device, or a determination result of the fourth road surface determination device, a fifth road surface determination device, based on a determination result of the third road surface determination device. And a correcting means for correcting at least one of the determination results of the sixth road surface determining means. As image features,
The brightness of the image can be used.

As described above, since the road surface determination using the acceleration and sound pressure signals inside the tire directly detects the contact state between the tire and the road surface, a highly accurate determination result can be obtained. it can. Therefore, the accuracy of the preview road surface determination is improved by correcting at least one of the threshold values of the preview road surface determination or the at least one of the preview road surface determination results based on the road surface determination result with high accuracy. Can be.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the present embodiment, a road surface determination device is mounted on a vehicle to determine a road surface state (a type of road surface).

As shown in FIG. 1, the road surface judging device mounted on the vehicle according to the present embodiment detects an acceleration generated inside the tire as the tire rotates and outputs an acceleration signal (G signal). An acceleration sensor (G sensor) 10 housed inside the tire, a microphone (microphone) housed inside the tire that detects a sound pressure generated inside the tire as the tire rotates and outputs a sound pressure signal (S signal) ) 1
2, and an encoder 14 that is arranged near the axis of the tire and outputs one pulse every predetermined rotation angle according to the rotation of the tire. Acceleration sensor 10 and microphone 12
Are located close to each other. G sensor 1
For 0, a sensor that detects acceleration in one to three directions (one to three axes) can be used. When one direction is detected, acceleration in the front-rear direction of the vehicle is detected.

Numeral 17 denotes a tire tread. Usually, the acceleration and the sound pressure are measured when a portion of the tire that is not in contact with the road surface is in contact with the road surface, and when the tire is in contact with the road surface. Indicates a peak value when the vehicle leaves the road surface.

The vehicle has a vehicle speed sensor for detecting a vehicle speed (vehicle speed) and outputting a vehicle speed signal, and a wheel for detecting wheel pressure (oil pressure in a wheel cylinder of a hydraulic brake) and outputting a wheel pressure signal. A pressure sensor and a steering angle sensor for detecting a steering angle of the steering and outputting a steering angle signal are attached.

The encoder 14 is connected via a slip ring 15 to an encoder processing circuit 16 for performing waveform processing of a pulse signal output from the encoder. The G sensor 10 has an internal G signal for performing waveform processing of the G sensor signal.
G sensor signal processing circuit 18A provided in processing circuit 18
The microphone 12 is connected to a microphone sound signal processing circuit 20A provided in the internal sound processing circuit 20 for performing waveform processing of the microphone sound signal.

The internal G processing circuit 18 performs the G processing described above.
The sensor signal processing circuit 18A stores a reference acceleration waveform and a reference power spectrum, which are reference values, and thresholds L1 to L4 for road surface determination, and the magnitudes of the thresholds L1 to L4 according to the vehicle speed signal and the wheel pressure signal. A reference value storage circuit 18B for changing the steering angle, a time-series value storage circuit 18 for determining whether or not the vehicle is traveling straight in accordance with the steering angle signal and storing a time-series G sensor signal in the straight traveling according to the sampling period.
C, a frequency analysis circuit 1 for frequency-analyzing the G sensor signal input from the G sensor signal processing circuit 18A when traveling straight ahead
8D, a waveform comparison circuit 18E for estimating a road surface state (determining a road surface) based on a reference acceleration waveform and a waveform of a time-series G sensor signal stored in the time-series value storage circuit 18C, and a reference power spectrum and a G sensor It comprises a power spectrum comparison circuit 18F that estimates the road surface state by comparing the power spectrum of the signal with the power spectrum of the signal.

The reference value storage circuit 18B receives the vehicle speed signal and the wheel pressure signal, and the time series value storage circuit 18C receives the steering angle signal, the output of the encoder processing circuit 16, and the output of the G sensor signal processing circuit 18A. The steering angle signal and the G sensor signal processing circuit 18 are provided in the frequency analysis circuit 18D.
The G sensor signal output from A is input, and the reference acceleration waveform output from the reference value storage circuit 18B and the G sensor signal waveform output from the time-series value storage circuit 18C are input to the waveform comparison circuit 18E. The power spectrum comparison circuit 18F receives the reference power spectrum from the reference value storage circuit 18B and the power spectrum of the G sensor signal output from the frequency analysis circuit 18D.

The internal sound processing circuit 20 stores the microphone sound signal processing circuit 20A described above, the reference sound pressure waveform and the reference power spectrum as reference values, and the threshold values L1 'to L4' for road surface determination. A reference value storage circuit 20B for changing the magnitudes of the threshold values L1 'to L4' in accordance with the vehicle speed signal and the wheel pressure signal, and determining whether or not the vehicle is traveling straight in accordance with the steering angle signal and traveling straight in accordance with the sampling cycle. A time-series value storage circuit 20C for storing a time-series microphone sound signal during traveling, a frequency analysis circuit 20D for frequency-analyzing a microphone sound signal input from the microphone sound signal processing circuit 20A during straight traveling, a reference sound pressure waveform and time series A waveform comparison circuit 20E for estimating a road surface state by comparing the time series microphone sound signal stored in the value storage circuit 20C, and a reference power spectrum and a microphone sound signal It is constituted by the power spectral comparison circuit 20F for comparing the word spectrum estimating a road surface condition.

The reference value storage circuit 20B receives the vehicle speed signal and the wheel pressure signal, and the time series value storage circuit 20C receives the steering angle signal, the output of the encoder processing circuit 16, and the output of the microphone sound signal processing circuit 20A. The frequency analysis circuit 20D includes a steering angle signal and a microphone sound signal processing circuit 20.
The microphone sound signal output from A is input, and the waveform of the reference sound waveform output from the reference value storage circuit 20B and the waveform of the sound pressure signal output from the time-series value storage circuit 20C are input to the waveform comparison circuit 20E. , Power spectrum comparison circuit 2
At 0F, the reference power spectrum from the reference value storage circuit 20B and the power spectrum of the sound pressure signal output from the frequency analysis circuit 20D are input.

The waveform comparing circuits 18E and 20E and the power spectrum comparing circuits 18F and 20F are connected to a road surface judging circuit 22 for judging a road surface by a majority decision of the road surface state estimated by each comparing circuit.

From the reference value storage circuit 18B to the waveform comparison circuit 1
8E, the reference acceleration waveform and the threshold values L1 to L4 changed according to the vehicle speed and the wheel pressure are input. The reference sound pressure waveform and the vehicle speed are input from the reference value storage circuit 20B to the waveform comparison circuit 20E. And threshold values L1 ′ to L4 ′ changed according to the wheel pressure and the reference value storage circuit 18
B, the reference power spectrum of the acceleration is input to the power spectrum comparison circuit 18F, and the reference value storage circuit 20B
The reference power spectrum of the sound pressure is input to the power spectrum comparison circuit 20F. Next, the road surface state estimation processing routine of the present embodiment will be described with reference to FIG. Steps 100 to 108 are processes executed in each of the time-series value storage circuits 18C and 20C, and Step 110 is a waveform comparison circuit 18E and 20E.
, But will be described together.
A dry road is given in advance as an initial value of the road surface state estimation result in the road surface state estimation processing routine.

In step 100, it is determined whether or not the vehicle is traveling straight based on the steering angle signal. If the vehicle is traveling straight, in step 102, the time-series value storage circuit 18C stores the sampling cycle. If so, the G signal and the encoder output signal are fetched, and the time series value storage circuit 20C fetches the S signal and the encoder output signal during the sampling period. It is to be noted that each signal is not taken in except at the sampling time.

In the next step 104, based on the encoder output signal, it is determined whether or not the portion corresponding to the mounting portion of the tire tread where the G sensor 10 and the microphone 12 are grounded, that is, the portion corresponding to the sensor mounting portion is determined. It is determined whether or not it is located in the contact section, and step 10
At 6, it is determined whether or not the touchdown is completed. If the grounding is not completed, that is, if the portion corresponding to the sensor mounting portion is located in the grounding section, in step 108, the time series value storage circuit 18B stores the G signal and the encoder output signal, and The storage circuit 20B stores the S signal and the encoder output signal.

As a result, the time-series value storage circuit 18B stores
The G signal and the encoder output signal are sequentially stored as time series values for each sampling period, and the time series value storage circuit 20B
, The S signal and the encoder output signal are sequentially stored as time-series values for each sampling period.

On the other hand, when it is determined in step 106 that the grounding has ended, in step 110, the time series values from the start of grounding to the end of grounding stored in the time series value storage circuit 18C are input to the waveform comparison circuit 18E. Using the reference acceleration waveform and the threshold value input from the reference value storage circuit, the road surface is estimated using the acceleration waveform, and the time series from the start of touchdown to the end of touchdown stored in the time series value storage circuit 20C. The value is input to the waveform comparison circuit 20E, and a road surface estimation process is performed using the sound pressure waveform using the reference sound pressure waveform and the threshold value input from the reference value storage circuit 20B. The details of this road surface determination will be described later.

In step 112, the time-series data stored in each of the time-series value storage circuits 18C and 20C is erased in order to determine the road surface when the sensor is attached to the ground at the next time.

Next, referring to FIG.
The details of the road surface state estimation processing in step 110 executed in each of E and 20E will be described. The processing performed by each of the waveform comparison circuits 18E and 20E is the same, and only one of them will be described. In the description, a reference acceleration waveform (or reference sound pressure waveform) is simply referred to as a reference value, and a time series value of a G signal (or an S signal) is simply referred to as a time series value. The threshold values L1 to L4 are used in the case of the road surface state estimation processing using the acceleration waveform, and the threshold values L1 ′ to L4 ′ are used in the case of the road surface state estimation processing using the sound pressure waveform.

In step 116, the variance σ between the reference value and the time series value is calculated. The variance σ is calculated using a reference value and a time-series value at each of the same tire rotation angle positions obtained from the encoder output signal. Note that a correlation coefficient or the like representing a correlation between a reference value and a time-series value may be used instead of the variance value σ.

In the next step 118, it is determined whether or not the variance value σ is larger than the threshold value K. If the variance value σ is larger than the threshold value K, the vehicle is traveling on a road surface different from the reference road surface, that is, on a icy road (low μ road) where hydroplaning is occurring. , Running on a snowy road (middle μ road), or running on a bad road, the cumulative value co2 of the variance σ weighted in step 124 is calculated according to the following equation. Calculate.

Co2 = k1 · co2 + k2 · σ (1) Here, k1 and k2 are weighting coefficients, and the past variance σ
Weight coefficient k1 for the cumulative value co2 of
And the current variance value σ
Is suddenly changed so that the cumulative value co2 of the variance value σ does not suddenly change accordingly. by this,
Even when the variance σ greatly changes temporarily when the vehicle travels on a partly rough part (or uneven part) on the road surface, it is possible to prevent erroneous determination of the road surface.

Also, during braking / driving, the instantaneous waveform of the acceleration on each road surface becomes remarkably different as the vehicle speed and the wheel pressure rise as described below. In step S122, it is determined whether or not braking / driving is being performed. In step 122, the weight coefficient k1 is reduced (for example, 0) to calculate the accumulated value co2. As a result, the road surface state is estimated based only on the current variance value, so that the surface state can be determined instantaneously.

In steps 126 to 140, the road condition is estimated by comparing the accumulated value co2 with one of the threshold values. In the case of estimating the road surface state using the acceleration waveform, the magnitudes of the thresholds L1 to L4 are L1 <L2 <L3 <L4, as described later. In the case of estimating the road surface state using the sound pressure waveform, Also, threshold values L1 'to L4'
The size of L1 ′ <L2 ′ <L3 ′ <
L4 ′, and the threshold values L1 to L4 and L1 ′ to L4 ′ are changed in magnitude in the reference value storage circuit according to running conditions such as vehicle speed and wheel pressure.

The estimation of the road surface condition based on the acceleration waveform will be described in detail. In step 126, the accumulated value co2 is compared with the threshold value L1, and if the accumulated value co2 is equal to or less than the threshold value L1, the road surface condition estimation result is obtained. No change, cumulative value co
If 2 exceeds the threshold value L1, the accumulated value co2 is compared with the threshold value L2 in step 128, and the accumulated value co2
Is less than or equal to the threshold L2, it is estimated at step 130 that the road is on ice.

On the other hand, if the cumulative value co2 exceeds the threshold value L2, the cumulative value co2 is compared with the threshold value L3 in step 132, and if the cumulative value co2 is equal to or less than the threshold value L3, step 134 It is estimated that hydroplaning has occurred in. If the cumulative value co2 exceeds the threshold value L3, the cumulative value co2
Is compared with the threshold value L4.
If it is 4 or less, it is estimated that the road is on snow at step 138,
If the accumulated value co2 exceeds the threshold value L4, it is estimated in step 140 that the road is bad such as gravel. In the case of estimating the road surface condition by using the sound pressure waveform, the road surface condition can be estimated in the same manner as described above only by changing the threshold value.

When it is determined in step 122 that the variance value σ is equal to or smaller than the threshold value K, in step 142, a predetermined value n is subtracted from the cumulative value co2 to obtain the cumulative value co2.
Is determined in step 144 to determine whether or not the accumulated value co2 has become negative.
In step 148, the accumulated value co2 is set to 0, and a dry road is estimated. If the accumulated value co2 is equal to or greater than 0, this routine ends without changing the road surface state estimation result.

Next, the estimation of the road surface condition will be described in detail. 4 (a) and 4 (b), the acceleration in the vehicle running front-rear direction when the studless tire is in contact with the ground when the vehicle is running at a vehicle speed of 30 km / h in a steady state is shown on each road surface (dry road, snowy road, icy road, and bad road). (Road) shows an instantaneous waveform measured by a G sensor, and a dry road reference waveform obtained by averaging the instantaneous waveforms for each contact at the time of traveling on a dry road at each contact position. FIG.
The horizontal axis of (a) and (b) indicates the grounding position of the tread portion corresponding to the mounting portion of the G sensor obtained by the encoder output signal, and the tread portion corresponding to the mounting portion of the G sensor corresponds to the grounding section. With the case where the tread portion is located at the center as the reference (0), the grounding section is defined as the grounding section from the stepping side where the tread portion corresponding to the G sensor attachment site is grounded to the kickout side where the tread portion corresponding to the G sensor attachment site is separated from the road surface. , The acceleration waveform when the tread corresponding to the attachment site of the G sensor moves from −25 cm to +25 cm.

From the comparison between the instantaneous waveform and the reference waveform, FIG.
In the case of the dry road shown in FIG. 4A, since the deformation of the tire at the time of the ground contact is the same every time, the instantaneous waveform in the ground contact section and the reference waveform substantially match, and the snowy road shown in FIG. In this case, the instantaneous waveform of the ground contact section does not match the reference waveform because of the surface layer collapse of the road surface. In the case of the icy road shown in FIG. ,
In the case of the bad road shown in FIG. 4D, the acceleration waveform vibrates violently due to gravel or the like, and it can be understood from these that the shape of the instantaneous waveform changes depending on the road surface other than the dry road.

FIG. 5 shows the instantaneous acceleration in the longitudinal direction of the vehicle when the tire is in contact with the ground when the tire is constantly running on an artificial low μ road at a vehicle speed of 50 km / h using normal tires, and the longitudinal direction of the vehicle when the tire is lifted. And the instantaneous acceleration are shown in comparison with the dry road reference waveform. From the figure, it is understood that the instantaneous waveform when the tire is in contact with the ground substantially matches the dry road reference waveform as described above, but the instantaneous waveform when the tire is lifted does not match the dry road reference waveform. it can.

FIG. 6 (a) shows the longitudinal direction of the vehicle obtained on each road surface (dry road, snowy road, icy road, and bad road) when the vehicle travels at a constant vehicle speed of 30 km / h. FIG. 6B shows time-series data of the variance value of acceleration, and FIG. As can be seen from the figure, it can be understood that the variance value decreases on average on the rough road, the snowy road, the icy road, and the dry road.

FIG. 7A shows a time series of the variance of the acceleration of the normal tire in the longitudinal direction of the vehicle running on each of the low μ road, the medium μ road, and the high μ road when the vehicle travels at a constant speed of 50 km / h. The data is shown in FIG. 7B, and the vehicle speed is 70 km / h.
7 shows time-series data similar to that of FIG. From the figure, it can be understood that the dispersion value at the moment when hydroplaning occurs increases as the vehicle speed increases.

Therefore, the threshold values L1 to L4 for estimating the road surface state using the acceleration waveform are L1 <L2 <L3, respectively.
It can be understood that <L4 should be satisfied.

The measurement results in FIGS. 4 to 7 are the same for the sound pressure. Therefore, the threshold values L1 ′ to L4 ′ for estimating the road surface state when using the sound pressure waveform are as follows:
It can be understood that L1 '<L2'<L3'<L4' should be satisfied.

From the above results, it can be understood that the road surface condition can be determined by comparing the magnitude of the variance between the reference waveform and the time series value with the threshold value. In the above description, an example is described in which the acceleration waveform and the sound pressure waveform on a dry road are used as the reference values. However, the acceleration waveform and the sound pressure waveform when traveling on another road surface may be used as the reference values.

FIG. 8 shows the vehicle speed using studless tires.
When the vehicle is running at a constant speed of 30 km / h and a vehicle speed of 50 km / h
Shows the dry road reference acceleration waveform (when the wheel pressure is 0)
It is a thing. From the figure, the acceleration at the contact point is the vehicle speed.
About 100m / s at 30km / h ^TwoAt a vehicle speed of 50 km / h
About 300m / s^Two, During the ground contact section. This
The reason will be described below.

FIG. 9 shows how the tire is deformed when the tire is in contact with the ground. At the time of contact, the tire contact surface is forcibly deformed to be flat along the road surface, so that the tire radius R ₀ instantaneously changes at the contact front edge Cf and the contact rear edge Cr, and the contact front edge Cf and At the trailing edge Cr, the mass system moves in the radial direction while rotating. In addition, the acceleration of the tire contact surface becomes zero during steady running because the tire contact surface comes into contact with the road surface and translates during the contact.

FIG. 10 shows a vector diagram of the acceleration of the motion in which the point P at the tip of the vector R moves in the direction of the vector R while rotating, where ω is the wheel speed. In FIG. 10, the wheel speed ω is dR / d
The direction of each vector when t> 0, d ² R / dt ² > 0, and dω / dt> 0 is shown.

Assuming that the periphery of the portion where the G sensor is attached is a mass system existing at the point P at the tip of the vector R,
At the front contact edge Cf and the rear contact edge Cr during steady running, an acceleration α expressed by the following equation is generated by the Coriolis force with respect to the mass system.

Α = 2 (dR / dt) · ω (2) Equation (2) shows the tangential acceleration in a steady state when no frictional force acts.

FIG. 11 shows the positional relationship of the mass system from the reference line with the straight line connecting the center of the ground contact surface and the rotation center as the reference line. The turning radius R (same as the magnitude of the vector R) at the time of contact of the mass system rotating at the rotation speed ω on the tire radius R ₀ is expressed by the following equation from FIG.

R = R ₀ · cos θ / cos θωt (3) where θ is the angle (ground length) formed by a reference line and a straight line connecting the ground edge (front or rear edge) and the center of rotation. And t is the elapsed time based on the position of the reference line.

When R in the above equation (3) is differentiated with respect to time, the change dR / dt in the radius of gyration is expressed by the following equation. _{dR / dt = R 0 · cosθ} · sinωt · ω / (cosθωt) 2 ··· (4) (4) Equation (2) is substituted into equation the following equation is obtained.

Α = 2 · R ₀ · cos θ · sin ωt · ω ² / (cos θωt) ² (5) From the above equation (5), the acceleration α at the moment when the tire is in contact with the ground is obtained.
Is proportional to the square of the wheel speed, so that the threshold values L1 to L4
Needs to be changed according to the wheel speed or the vehicle speed.

Here, the tire radius R ₀ is 0.314 m,
Assuming that θ calculated from the contact length is 14.5 °, the vehicle speed is 30k
The following table shows the acceleration α at the front contact edge Cf and the rear contact edge Cr (ωt = ± θ) at a speed of 50 m / h and a vehicle speed of 50 km / h.
Have the same magnitude but opposite directions.

[0064]

[Table 1]

FIGS. 12 (a) to 12 (c) show acceleration waveforms (instantaneous waveform and steady running) at the time of braking from running 50 km / h on a dry road, a snowy road, or an icy road using studless tires. At the time of drying). Numerical values described on the left side of the figure indicate the wheel pressure Pc, the vehicle speed V, and the slip ratio λ at the time when the plot data is obtained.

As can be understood from FIG. 12, even at substantially the same wheel pressure, the respective instantaneous waveforms are different. In other words, on a snowy road, the surface layer of the road surface is severely collapsed, and the waveform is oscillating. On an icy road, the region where the acceleration is 0 is widened at the leading edge of the tire contact with the ground, and the mountain having the acceleration peak as the peak is thin. The cause of this is that the tread movement speed becomes slower due to slippage, and the G sensor stays longer at the same ground contact position than during steady running, so the tire radius change speed is small and Coriolis during ground contact This is because the acceleration due to the force is observed as converging. In the above, the acceleration at the time of braking has been described, but the same applies to the time of driving, and the same applies to the sound pressure.

As described above, during braking / driving, the deviation from the reference acceleration waveform on the dry road becomes large. Therefore, the threshold values L1 to L4 for estimating the road surface state from the acceleration waveform and the sound pressure waveform during the steady running on the dry road. , L1 'to L4' need to be changed. That is, the threshold values L1 to L4, L1
It is necessary to change the size of 'to L4' according to the vehicle speed and the wheel pressure. Further, at the time of braking / driving, the difference in the instantaneous waveform of the acceleration for each road surface becomes conspicuous as the wheel pressure increases, so that the weight coefficient k1 is reduced (for example, 0) as described above so that the road surface can be determined instantaneously. Is preferred.

Next, the frequency analysis circuit 1 of the above embodiment
8D, 20D and power spectrum comparison circuit 18F, 2
The road surface state determination processing routine at 0F will be described. The road surface state determination processing in the power spectrum comparison circuits 18F and 20F is the same, and the power spectrum comparison circuit 18F analyzes the specific frequency spectrum (reference power spectrum) of the acceleration when the vehicle is steadily traveling on the dry road and the analyzed acceleration. And the power spectrum comparing circuit 20F compares the specific frequency spectrum of the sound pressure (reference power spectrum) when the vehicle is steadily traveling on the dry road with the spectrum of the specific frequency of the analyzed sound pressure. Since the road surface condition is estimated by comparison, it will be described together.

In step 160, each frequency analysis circuit determines whether or not the vehicle is traveling straight based on the steering angle signal.
If the vehicle is traveling straight, in step 162, the frequency analysis circuit 18D takes in the G signal at the sampling time, the frequency analysis circuit 20D takes in the S signal at the sampling time, and otherwise, the G signal (or S signal). Do not take in.

In the next step 164, the frequency analysis circuit 1
In 8D, the spectrum value at the specific frequency of the G signal is extracted, and in the frequency analysis circuit 20D, the spectrum value at the specific frequency of the S signal is extracted and output to each of the power spectrum comparison circuits. For the extraction of the spectrum, a technique such as FFT, band-pass filter, wavelet transform and the like can be used. In step 166, the spectrum value extracted by the power spectrum comparison circuit is compared with the reference power spectrum at the specific frequency input from the reference value storage circuit, and the road surface state is estimated.

FIGS. 14 (a) and 14 (b) show that the vehicle steadily traveled on each road surface (dry road, snowy road, icy road and badly gravel road) at a vehicle speed of 30 km / h and a vehicle speed of 50 km / h using studless tires. 4 shows a frequency spectrum of acceleration at the time. Around 300-500Hz for each vehicle speed (road noise frequency range)
Are different on each road surface. Therefore, the road surface condition can be estimated by comparing the spectrum of the specific frequency (reference power spectrum) when traveling on the dry road with the spectrum of the specific frequency (power spectrum) from the frequency analysis circuit. Although the frequency spectrum of the acceleration has been described above, the same applies to the frequency spectrum of the sound pressure. The road surface state can be estimated by comparing the frequency spectrum with the reference power spectrum.

The estimation result of the waveform comparison circuit 18E (the estimation result by the G waveform comparison), the estimation result of the waveform comparison circuit 20E (the estimation result by the S waveform comparison), and the power spectrum comparison circuit 18F estimated as described above. (Estimation result by G spectrum comparison) and estimation result by power spectrum comparison circuit 20F (Estimation result by S spectrum comparison) are input to the road surface determination circuit 22 as shown in FIGS. The road surface is determined by majority decision. As a result, two or more estimation results having the same estimation result are determined as the current traveling road surface.

As described above, according to the present embodiment, since the G sensor and the sound pressure sensor are arranged inside the tire, the influence of external sound is small and the practical sampling frequency of 1 to 5 kHz is used. Can be used to determine the road surface.

Next, a second embodiment of the present invention will be described. As described above, the road surface determination using the acceleration and sound pressure signals inside the tire according to the first embodiment is performed by:
Since the contact state between the tire and the road surface is directly detected, a highly accurate determination result can be obtained. Therefore, the second
In the second embodiment, the threshold value for the preview road surface determination in the vehicle control device that controls the vehicle based on the preview road surface determination result is modified using the road surface determination result of the first embodiment.

In this embodiment, as shown in FIG. 16, the road surface judging device 50, the preview road surface judging device 52, the mottle road detecting circuit 54, the preview result majority circuit 56, and the threshold described in the first embodiment. It comprises a value correction circuit 58 and a vehicle control device 60.

The preview road surface judging device 52 comprises an irradiator for irradiating infrared light toward the road surface and a light receiving device for receiving reflected light of the irradiated infrared light from the road surface and outputting an electric signal. A road surface state determination device 52A using infrared light, which determines a road surface state by utilizing a difference between an absorption wavelength of infrared light for water (liquid) and an absorption wavelength of infrared light for ice (solid), is used. Is provided. In this road surface condition determination device 52A, infrared light is irradiated onto the road surface and passes through a first filter that passes light in an absorption wavelength range of water and a second filter that passes light in an absorption wavelength range of ice. the reflected light received by the light receiver, and compares the received light level I _R of the first light-receiving level of the reflected light passed through the filter I _L and the reflected light which has passed through the second filter. When I _R < _IL , it is determined that the infrared light is absorbed by the ice and the light reception level I _R is reduced, and the frozen road is determined. Conversely, if I _R > _IL , it is determined that the infrared light is absorbed by water and the light receiving level _IL is reduced, and the wet road is determined.

When only the road surface condition judging device 52A is used, the judgment result of only one of the frozen road and the wet road is output, and the erroneous judgment is made when the vehicle is traveling on other road surfaces. For this reason, the threshold value Iice of the light receiving level on the frozen road and the threshold value Iwet of the light receiving level on the wet road are provided, and the determination is made as follows. · I _R <I _L, and when I _L <Iice, determines that the frozen road. When I _R > I _L and I _R <Iwet, it is determined that the road is wet.・ If neither of the above is satisfied, the road will be replaced with another road surface.

Further, the threshold value correction circuit 58 increases or decreases the threshold values Iice and Iwet of the light receiving level based on the determination result of the road surface determination device 50 as shown in the following table.

[0079]

[Table 2]

As can be understood from Table 2, when the determination result based on the tire internal signal is a frozen road and the determination result based on the infrared light is other than that, it is highly possible that the road is a frozen road. When the determination result based on the tire internal signal is a wet road and the determination result based on the infrared light is other than that, the possibility of the wet road is high.
reduce et. Further, when the determination result based on the tire internal signal is other, since the determination result based on the infrared light is likely to be other even on a frozen road or a wet road, each of the threshold values Iice and Iwet is set. increase.

The preview road surface determination device 52 includes:
An irradiator that irradiates light toward the road surface and a light receiver that receives reflected light from the road surface of the illuminated light through a slit array having a plurality of slits and outputs an electric signal, and includes a slit array. Road condition judging device 5 that judges the road surface condition by using the fact that the spectrum of the light received via the light varies depending on the road surface in a low frequency region.
2B are provided. In the road surface state determination device 52B, light is emitted to the road surface, and the reflection levels of the regular reflection light and the diffuse reflection light of the light received through the slit array are compared with the threshold values of each road surface.

A value obtained by normalizing the intensity Db of the frequency component in a predetermined low frequency band by the intensity Da of the spatial center frequency f0 corresponding to the moving speed of the vehicle (frequency component intensity ratio Db / Da) in the road surface condition determination device 52B. , The intensities Da and D of the components included in the frequency band centered on each spatial center frequency for each of the specular reflected light and the diffuse reflected light
f (reflected light ratio Df / Da), diffused reflected light reflectance Rv (ratio of reflected light amount to light projected on road surface LD)
And threshold values TH1, TH2, TH3, THc,
The road surface state is determined as follows by comparing THd1, THd2, and THe. Db / Da ≦ TH1, Db / Da ≦ TH2, and Df
When / Da> THd1, it is determined that the road is wet. Db / Da ≦ TH1, Db / Da ≦ TH2, and Df
When / Da ≦ THd1, or when Db / Da ≦ TH3 and Df / Da ≦ THd2, it is determined that the road is dry. -When Db / Da ≦ TH1 and Db / Da> TH2, or when Db / Da> TH3 and Rv ≦ THc, it is determined to be a gravel road surface. When Db / Da> TH1, or when Db / Da> TH
3, and when Rv> THc, it is determined that the road is a snowy road. When Db / Da ≦ TH3 and Df / Da> THd2, the road is determined to be a frozen road.

When only the road surface condition judging device 52B is used, the reflection intensity changes on snowy roads and frozen roads depending on the degree of dirt on the road surface. Therefore, accurate road surface judgment can be made by using a fixed threshold value. Disappears. Therefore, the threshold value correction circuit 58 increases or decreases the related threshold value as shown in Table 3 below.

That is, based on the determination result based on the tire internal signal, when the determination result of the road surface state determination device 52B is different from the determination result based on the tire internal signal, the determination result based on the tire internal signal is performed by the road surface determination device 52B. The threshold is increased or decreased in the direction in which is obtained.

[0085]

[Table 3]

For example, when the determination result based on the tire internal signal is a dry road and the determination result of the road surface state determination device 52B is a wet road, the threshold value THd1 is decreased.
The threshold value THc is increased when the determination result of the road surface state determination device 52B is a snowy road, and the threshold value TH3 is decreased when the determination result of the road surface state determination device 52B is a frozen road.

The preview road surface determination device 52 includes:
It is composed of an irradiator that irradiates the ultrasonic wave toward the road surface and a receiver that receives the reflected wave of the irradiated ultrasonic wave from the road surface and outputs an electric signal, and the level of the received reflected wave is a dry path (or a wet path). A road surface state determination device 52C that uses ultrasonic waves to determine a road surface state by using the difference between a road and a snowy road (or a frozen road) is provided. In this road surface condition determination device 52C, an ultrasonic wave is applied to the road surface, and if the reception level of the reflected wave is within the set allowable range, it is determined that the road is a dry road (or wet road), and the reception level of the reflected wave is outside the set allowable range. If so, it is determined that the road is a snowy road (or a frozen road).

In the road surface state determination device 52C, if the set allowable range is not appropriate, an erroneous determination may occur in the road surface determination result based on the ultrasonic wave. When the determination result of the state determination device 52C is different from the determination result based on the tire internal signal, the setting allowable range is increased or decreased in a direction in which the determination result based on the tire internal signal is obtained by the road surface state determination device 52C.

For example, when the determination result based on the tire internal signal is a dry road (or wet road), while the road surface determination result by the road surface state determination device 52C is a snowy road (or a frozen road), Reduce the allowable setting range.

[0090]

[Table 4]

The preview road surface judging device 52 photographs the road surface with a camera, converts the image information from the camera into black and white image information, judges the state of the color brightness distribution of the black and white image information, and reduces the brightness. A road surface condition determination device 52D that determines that snow is present when the threshold value is exceeded is provided. In this road surface state determination device 52D, the color of the road surface changes depending on the degree of dirt on the snowy road, and therefore, using a fixed threshold value may cause an erroneous determination of the road surface state.

[0092] Therefore, as shown in Table 5, the road surface state determination device 5
If the 2D determination result is different from the determination result based on the tire internal signal, the threshold value is increased or decreased by the road surface state determination device 52D in a direction in which the determination result based on the tire internal signal is obtained.

For example, when the result of the determination based on the tire internal signal is a dry road and the result of the road surface determination by the road surface condition determination device 52D is a snowy road, the threshold value is decreased.

[0094]

[Table 5]

In the present embodiment, the road surface judging device 50 is used for correcting the threshold value and the like in the threshold value correcting circuit 58, and the judgment result is not output to the vehicle control device 60 in a normal state.

However, when the mottle detecting circuit 54 connected to the camera of the road surface condition judging device 52D detects a road surface (mottled road) in which snow, ice, dry parts and the like are mixed in the image taken by the camera. Switches the switching device 62 according to the output from the mottle detection circuit 54, and performs vehicle control based on the determination result of the road surface determination device 52.

In the second embodiment, an example in which the threshold value of the preview road surface determination device is corrected has been described. However, the determination result of the road surface state determination device provided in the preview road surface determination device is corrected. You may make it. Further, in the second embodiment, an example in which four road surface state determination devices are used has been described. However, the number is not limited, and at least one may be provided.

[0098]

As described above, according to the present invention, the acceleration sensor and the sound pressure sensor are arranged inside the tire, and the judgment result based on the reference waveform and the detected acceleration waveform is obtained. Since the road surface is determined by a majority decision of the determination result by the degree waveform, the determination result by the reference power spectrum and the power spectrum of the detected acceleration, and the determination result of the reference power spectrum and the power spectrum of the detected sound pressure, The effect is obtained that the road surface can be accurately determined at a practical sampling frequency without being affected by external sounds.

The threshold value or the determination result of the preview road surface determination device is corrected based on the determination result of the road surface determination device capable of accurately determining the road surface at a practical sampling frequency without being affected by external sounds. Therefore, it is possible to obtain an effect that an accurate preview determination result can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a flowchart showing a processing routine of a waveform comparison circuit of FIG. 1;

FIG. 3 is a flowchart showing details of a road surface determination process in FIG. 2;

4A is a diagram illustrating an acceleration waveform inside the tire on a dry road, FIG. 4B is a diagram illustrating an acceleration waveform inside the tire on a snowy road, and FIG. 4C is an acceleration waveform inside the tire on an icy road; And (d) is a diagram showing an acceleration waveform inside the tire on a rough road.

FIG. 5 is a diagram showing a comparison between acceleration waveforms inside the tire when the tire is in contact with the ground and when it is not.

FIG. 6A is a diagram showing a variance value on each road surface, and FIG. 6B is an enlarged view of FIG.

FIG. 7A is a diagram illustrating a change in variance value on each road surface when the vehicle speed is 50 km / h, and FIG. 7B is a diagram illustrating a change in variance value on each road surface when the vehicle speed is 70 km / h. FIG.

FIG. 8 is a diagram showing a change in an acceleration waveform according to a vehicle speed.

FIG. 9 is a schematic diagram illustrating deformation of a tire when the tire is in contact with the ground.

FIG. 10 is a diagram showing a vector diagram of acceleration at a point P when the vector R rotates while changing in the length direction.

FIG. 11 is a diagram illustrating Coriolis force generated by tire deformation at the time of tire contact.

12A is a diagram illustrating an acceleration waveform inside the tire when braking on a dry road, FIG. 12B is a diagram illustrating an acceleration waveform inside the tire when braking on a snowy road, and FIG. FIG. 3 is a diagram showing an acceleration waveform inside the tire at the time of braking.

FIG. 13 is a flowchart showing a processing routine of the power spectrum comparison circuit of FIG. 1;

14A is a diagram showing a frequency spectrum of the tire internal acceleration on each road surface when the vehicle speed is 30 km / h, and FIG. 14B is a diagram showing the frequency of the tire internal acceleration on each road surface when the vehicle speed is 50 km / h. It is a diagram which shows a spectrum.

FIG. 15 is a flowchart showing a processing flow of the road surface determination device of FIG. 1;

FIG. 16 is a block diagram of a second embodiment of the present invention.

[Explanation of symbols]

 10 G Sensor 12 Microphone 14 Encoder 15 Slip Ring 17 Tire Tread

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshitoshi Watanabe 1-41, Chuchu-ji, Yokomichi, Nagakute-cho, Aichi-gun, Aichi F-term in Toyota Central Research Laboratory, Inc. (reference) 2G047 AA10 BA04 BC04 EA10 GA19 GD02 GG06 GG10 GG19 GG33 GG36

Claims (4)

[Claims] An acceleration sensor that is arranged inside the tire and detects acceleration generated inside the tire as the tire rotates, and outputs an acceleration signal; and a tire arranged inside the tire in close proximity to the acceleration sensor. Detecting means including a sound pressure sensor for detecting a sound pressure generated inside the tire due to rotation of the tire and outputting a sound pressure signal; a reference waveform of a predetermined acceleration and a waveform of an acceleration signal detected by the acceleration sensor And the road surface is determined based on the road surface, a road surface is determined based on a predetermined reference sound pressure waveform and a waveform of the sound pressure signal detected by the sound pressure sensor, and a road surface determination result based on the acceleration waveform and First road surface determination means for outputting a road surface determination result based on a sound pressure waveform; and a reference power spectrum of a predetermined acceleration and a power spectrum of an acceleration obtained from an acceleration signal. The road surface is determined by comparing the reference power spectrum of the predetermined sound pressure with the power spectrum of the sound pressure obtained from the sound pressure signal, and the road surface determination result based on the power spectrum of the acceleration and the sound pressure are compared. A second road surface determination unit that outputs a road surface determination result based on the power spectrum of: a road surface determination result based on an acceleration waveform; a road surface determination result based on a sound pressure waveform; a road surface determination result based on a power spectrum of acceleration; And a third road surface determining means for determining a road surface from a road surface determination result based on a power spectrum of sound pressure. 2. The first road surface determination means uses a waveform of an acceleration signal and a waveform of a sound pressure signal output in a predetermined section including a section in which a portion where the detection means of the tire is disposed on the road surface. The second road surface determining means,
The road surface determination device according to claim 1, wherein the road surface is determined using an acceleration power spectrum and a sound pressure power spectrum obtained from each of the acceleration signal and the sound pressure signal output in the predetermined section. 3. The method according to claim 1, wherein the first road surface determining means calculates a variance value or a correlation coefficient between the acceleration reference waveform and the acceleration signal waveform, and calculates a difference between the reference sound pressure waveform and the sound pressure signal waveform. The road surface is determined by calculating a variance value or a correlation coefficient, and comparing each of the calculated variance value or the correlation coefficient with a threshold value predetermined according to the road surface. Road surface determination device. 4. A road surface determining apparatus according to claim 1, wherein the road surface is illuminated with light, and the level of reflected light from the road surface is compared with a threshold value to determine a road surface state. A fourth road surface determining unit that irradiates an ultrasonic wave toward the road surface, compares the level of a reflected wave from the road surface with a threshold value to determine a road surface state, and captures an image of the road surface. A preview road surface determination device including at least one of a sixth road surface determination unit that determines a road surface by comparing a feature amount of a captured image with a threshold value of the feature amount; and the third road surface determination. Means for determining at least one of the threshold values of the preview road surface determination device, the determination result of the fourth road surface determination means, the determination result of the fifth road surface determination means, and the sixth road surface determination based on the determination result of the means. Correcting means for correcting at least one of the determination results of the means; State road system, including.