JP3427246B2 - Road surface condition determination device and vehicle equipped with this device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for determining the condition of the road surface of a vehicle such as an automobile, and a vehicle equipped with this device.

[0002]

2. Description of the Related Art As a conventional device of this type, there is a vehicle-mounted road surface condition determining device proposed by the applicant (International Publication WO95 / 01549).
This device emits light from a traveling vehicle toward the road surface, receives the reflected light through a spatial filter, and performs spatial frequency analysis on the output signal from the spatial filter to determine the road surface condition. Is.

The spatial filter, as shown in FIG. 19, sequentially passes the reflected light P of the light irradiated to a predetermined position on the road surface through a plurality of slit holes 50, and then collects the passing light. As a result, a signal including a sine wave having a constant period T1 as shown in FIG. 20 is output.

Specifically, the spatial frequency analysis processing is as follows.
As shown in FIG. 21, the output signal from the spatial filter is taken in at every predetermined time interval T ₀ , N sampling data showing an output waveform while the vehicle is moving for a predetermined distance is taken out, and these sampling data It executes a Fourier transform.

FIG. 22 shows a result of performing fast Fourier transform (hereinafter abbreviated as "FFT") on the sampling data, which is N in the frequency range of 0 to 1 / 2T _0.
/ 2 pieces of signal strength data are extracted. The frequency f ₀ (corresponding to the number of data n) at which the intensity takes a peak value is extracted as the center frequency corresponding to the moving speed of the vehicle.

As will be described later, this center frequency f ₀
The intensity of the component included in the lower frequency band reflects the road surface condition of the traveling road, and the value obtained by normalizing the intensity of this low frequency component by the intensity of the intermediate frequency component is compared with a predetermined threshold value. As a result, the road surface condition determination process is performed.

Therefore, in order to determine the road surface condition with high accuracy, it is necessary to sample the output signal from the spatial filter at time intervals corresponding to the current speed of the vehicle and to accurately extract the target frequency component. Here, if the sampling interval T ₀ is set to a time interval that is ½ or more of one cycle T1 of the sine wave corresponding to the center frequency component, aliasing occurs and the original intermediate frequency is generated, as shown in FIG. A frequency component 52 different from the component 51 is extracted.

On the other hand, as shown in FIG. 24, sampling is performed at a time interval corresponding to a quarter of the cycle T1, and the return point of the sine wave to the baseline and the maximum / minimum values are 4 If the points are extracted, the center frequency component can be properly extracted. Therefore, if the sampling interval T ₀ is controlled to be always about ¼ of the period T1, then n becomes N / 4, and the extraction position of the center frequency component in the spatial frequency distribution curve is It can be set near the center of.

However, the sampling interval T
_{When 0} is set to be shorter than a quarter of the period T1, the extraction accuracy of the center frequency component is improved, but at the same time, the extraction range of the high frequency component is increased, so that the center frequency in the intensity distribution of the frequency shown in FIG. There is a problem that the extraction position of f ₀ is closer to the low frequency, and the center frequency component and the low frequency component cannot be accurately separated. Therefore, in order to detect the center frequency component and the low frequency component with high accuracy and stably determine the road surface condition, the sampling interval T ₀ is controlled to be about ¼ of the period T1. There is a need. Therefore, in the conventional road surface state determination device, the center frequency f ₀ obtained from the output signal from the spatial filter is converted into the moving speed v of the vehicle, and the next sampling interval T ₀ is set using the conversion result. I have to.

From the spatial frequency analysis result of FIG. 22, the center frequency f ₀ is calculated by the following equation (1). Further, the moving speed v of the vehicle is calculated by applying the result of the equation (1) to the equation (2) using one period (that is, the arrangement interval of the slit holes) m of the spatial filter.

[0011]

[Equation 1]

[0012]

[Equation 2]

[0013]

However, when the sampling interval T ₀ is determined based on the output signal from the spatial filter, if the center frequency is missing from this output signal, an erroneous velocity will be detected, There is also a problem that a malfunction occurs in subsequent road surface determination processing. For example, when reflected light from a metal part such as a bridge seam is incident on the spatial filter, the output signal in the incident period A becomes saturated as shown in FIG. 25, and extraction of the center frequency component becomes impossible. . Further, when light is applied to a portion having a hole such as a groove, the reflection target is missing in this portion, so that the output signal from the spatial filter is flat in the lacking period B as shown in FIG. Then, it becomes impossible to extract the center frequency.

The present invention has been made in view of the above problems. The moving speed of a vehicle is measured by using a plurality of speed detecting means which are not affected by the loss of the center frequency component from the reflected light at the same time. By determining the sampling interval of the reflected light using the measurement value, it is a technical object to avoid the malfunction of the road surface state determination processing due to the incorrect extraction of the speed and to stably perform the road surface state determination.

[0015]

According to a first aspect of the present invention, there is provided light projecting means for radiating light from a traveling vehicle toward a road surface.
Sampling means for receiving the reflected light from the road surface and sampling the reflected light at a predetermined interval, and reflecting the center frequency component corresponding to the moving speed of the vehicle and the road surface condition from the spatial frequency distribution of the sampled reflected light In a road surface state determination device comprising extraction means for extracting a predetermined low frequency component, and determination means for determining the road surface state based on the intensity ratio of each frequency component extracted by the extraction means, from the reflected light Speed measuring means for measuring the moving speed of the vehicle by using a plurality of speed detecting means which are not affected by the lack of the center frequency component of the same, and the sampling interval of the reflected light of the sampling means based on the measured value by the speed measuring means. And a sampling interval determining means for determining.

According to a second aspect of the present invention, the speed measuring means includes at least a first speed detecting means for detecting the moving speed of the vehicle using at least a spatial frequency component contained in the specularly reflected light from the road surface, and from the road surface. Second speed detecting means for detecting the moving speed of the vehicle using the spatial frequency component contained in the diffusely reflected light.

In the invention of claim 3, the speed measuring means comprises at least a first speed detecting means having a short measuring time and a second speed detecting means having a sufficiently longer measuring time than the first speed detecting means. And means.

In the invention of claim 4, the speed measuring means at least counts the wave number of the center frequency component contained in the reflected light within a predetermined period to detect the moving speed of the vehicle. And a second speed detecting means for detecting the moving speed of the vehicle by using the result of the discrete Fourier transform of the reflected light.

According to the invention of claim 5, the second measuring means is set with a measuring time sufficiently longer than the measuring time of the first measuring means.

In the invention of claim 6, the speed measuring means determines the fastest speed among the moving speeds detected by the plurality of speed detecting means as the moving speed of the vehicle.

According to a seventh aspect of the present invention, a vehicle equipped with the above-mentioned road surface state determining device is constructed.

[0022]

When the center frequency component is missing from the reflected light from the road surface, the sampling interval of the reflected light is determined by using the detection value of the speed detecting means that is not affected by the lack of the center frequency component. By setting an appropriate sampling interval, it becomes possible to accurately extract the spatial frequency components necessary for determining the road surface condition.

According to the second aspect of the present invention, the velocity is extracted by using the spatial frequency components contained in the regular reflection light and the diffuse reflection light from the road surface respectively, so that the center frequency component is lost in either one of the reflection light. However, an accurate speed can be measured using the other reflected light.

According to the invention of claim 3, the first measuring time is short.
The speed detecting means of 1 corresponds to the acceleration and deceleration of the vehicle, and the second speed detecting means having a long measurement time corresponds to the lack of the center frequency component from the reflected light.

According to the invention of claim 4, the first speed detecting means for counting the wave number of the center frequency component contained in the reflected light corresponds to the acceleration and deceleration of the vehicle, and the reflected light undergoes the discrete Fourier transform. The speed detecting means of 1 corresponds to the lack of the center frequency component from the reflected light.

In the invention of claim 5, the measurement time of the first speed detecting means using the wave number of the center frequency component is set short, and the measurement time of the second speed detecting means using discrete Fourier transform is set long. By doing so, both acceleration and deceleration of the vehicle and lack of the center frequency component from the reflected light can be reliably accommodated.

According to the sixth aspect of the present invention, the speed detecting means affected by the lack of the center frequency component from the reflected light has a detection speed slower than the actual speed, so that the speed detecting means is the fastest among the plurality of speed detecting means. By adopting the fast detection speed as the measurement value, it is possible to measure the accurate speed that is not affected by the lack of the center frequency component.

According to the seventh aspect of the present invention, by mounting the above-mentioned road surface condition determination device on a vehicle, it is possible to stably determine the road surface condition while the vehicle is traveling.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration example of a vehicle equipped with a road surface condition determining device of the present invention, and a preferred embodiment of the road surface condition determining device will be described with reference to FIGS. explain.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a state in which a road surface condition determining device 1 according to an embodiment of the present invention is installed in a vehicle 5. The road surface state determination device 1 includes a reflected light measuring sensor 2 that measures the amount of light reflected from the road surface LD, and a control device 3 that receives a detection signal from the sensor 2 and performs a road surface state determination process. The control device 3 is further connected to the alarm device 4. The alarm device 4 is composed of a voice, a light emitting lamp, or the like, and outputs predetermined warning information to the driver when the control device 3 determines that the road surface LD is in a dangerous state.

FIG. 2 shows a detailed structure of the reflected light measuring sensor 2, which is composed of two lights 6, 7, a light receiving system 8 and a spatial filter optical system 9. The first light source 6 is composed of a plurality of LEDs 6a arranged in a matrix, and the second light source 7 is composed of a single LED 7a. The light sources 6, 7 and the light receiving system 8 and the spatial filter optical system 9 are As shown in FIG. 3, they are housed and arranged in the same housing 10. Each light source 6 and 7 is a road surface LD
It is arranged to irradiate light toward the
The optical axis of the spatial filter optical system 9 is adjusted so as to capture the diffuse reflection light of the irradiation light from the first light source 6 and the specular reflection light of the irradiation light from the second light source 7. .

As shown in FIG. 4, control pulses are given to the LEDs 6a and 7a of the light sources 6 and 7 so as to alternately emit light at predetermined time intervals, and the spatial filter optical system 7 is The road surface L is synchronized with the control pulse to each light source.
The specular reflection light and the diffuse reflection light from D are alternately processed, and a signal indicating the characteristics of each reflection light is output to the control device 3.

The light receiving system 8 comprises a light receiving lens 11, a slit plate 12, and a collimating lens 13. The reflected light from the road surface LD is condensed by the lens 11, and then the slit hole of the slit plate 12 is formed. The light enters the collimator lens 13 via 12a and is collimated.

The spatial filter optical system 9 comprises a slit array 14, a prism array 15, a condenser lens 16, two photodetectors 17a and 17b, two mirrors 19 and 19, and the like. The slit array 14 has elongated slit holes 14a arranged along the traveling direction B of the vehicle 1, and the light collimated by the collimating lens 13 of the light receiving system 8 passes through these slit holes 14a. It is incident on the prism array 15. Prism array 15
Is formed by continuously forming prisms with a period twice as long as the arrangement period of the slit array 14. The incident light is refracted alternately in each prism and is separated into two directions.

The photodetectors 17a and 17b are arranged at an interval corresponding to the arrangement period of the prism array 15 and the magnification of the condenser lens 16, and the prism array 15 is provided.
The light passing therethrough is condensed by the condenser lens 16 in each separation direction, and is incident on the respective photodetectors 17a and 17b. Furthermore, the output signals from these photodetectors 17a and 17b are input to the control device 3, and as will be described later, spatial frequency components reflecting the unevenness of the road surface LD are extracted from the differential signals of these output signals. The mirror 19 is for reflecting the light not condensed on the light receiving surfaces of the photodetectors 17a and 17b and guiding it to the light receiving surfaces. 2 in FIG.
Reference numeral 0 indicates a temperature sensor (which is composed of an infrared radiation thermometer) for measuring the road surface temperature.

FIG. 5 shows the reflected light measuring sensor for three types of road surfaces: dry asphalt or concrete road surface (hereinafter collectively referred to as "dry paved road surface"), gravel road surface (including soil and sand road), and snowy road surface. The result of having analyzed the spatial frequency of the diffused light from 2 is shown. Here, each analysis result is shown by being normalized by the spatial center frequency f ₀ corresponding to the moving speed of the vehicle so that the difference in the frequency distribution in each road surface state becomes clear.

In the illustrated example, focusing on the intensity of frequency components in a band lower than the spatial center frequency f ₀ , there is a clear difference between the road surface states, and the difference becomes larger as the spatial frequency becomes lower. ing. Based on this principle, in this road surface state determination device, the intensity Db of the frequency component in a predetermined low frequency band is normalized by the intensity Da of the spatial center frequency component f ₀ (hereinafter, this is referred to as “frequency component intensity ratio Db / “Da”) is set as an index for determining the road surface condition.

Further, in this road surface condition discriminating apparatus, a threshold value T1 for discriminating a snowy road surface and a gravel road surface and a gravel road surface and a dry paved road surface are discriminated on the basis of actually measured values for each road surface state. The threshold value T2 and the threshold value T2 are set and stored in the memory of the control device 3, and the calculated frequency component intensity ratio Db / Da is set to the threshold value T1,
Compared with T2, the road surface condition is dry paved road surface, gravel road surface,
Determine which of the snowy roads.

In order to determine the road surface condition in more detail, it is necessary to measure not only diffuse reflected light but also specular reflected light from the road surface LD. Particularly in the case of a paved road, when the road surface is wet due to rain or in a frozen state, the road surface becomes a state close to a mirror surface, so that the amount of specularly reflected light from the road surface is significantly increased as compared with the dry state.

FIG. 6 shows the relationship between the intensities of the central frequency components of the diffuse reflectance and the regular reflectance on the pavement road surface in association with the road surface conditions of dry, wet, frozen, and snow. , The intensity of the central frequency component of diffusely reflected light on a snowy road surface is significantly higher than other road surface conditions. Although there is almost no difference in the central frequency component of the diffuse reflected light between the dry, wet, and frozen states, comparing the central frequency component intensities of the specularly reflected light shows that the dry road surface and the wet / frozen road surface There is a clear difference between them. In addition,
The measured value of the road surface temperature by the temperature sensor 20 is used to determine the wet state and the frozen state.

FIG. 7 shows the electrical construction of the road surface condition-dependent device. The control device 3 includes a pulse oscillator circuit 21, a differential amplifier circuit 22, two conversion circuits 23a and 23b, a discrimination circuit 24, a speed feedback circuit 25, and the like.

Each photodetector 1 of the spatial filter optical system 9
The output signals from 7a and 17b are input to the differential amplifier circuit 22 and subjected to differential amplification processing, and then the conversion circuits 23a and 2b.
It is input to 3b. The conversion circuits 23a and 23b are for converting the input differential amplified signal of the reflected light amount into a spatial frequency, and are each a comb filter 26, an A / D conversion circuit 27, a memory 28, a fast Fourier transform circuit 29 (hereinafter (Abbreviated as "FFT circuit 29") and the like.

The pulse oscillating circuit 21 is, as described above,
The drive pulses to the light sources 6 and 7 are alternately output. Further, the drive pulse to the LED 6a for diffuse reflection is input to the first conversion circuit 23a, and the drive pulse to the LED 7a for regular reflection is input to the second conversion circuit 23b, respectively. The conversion circuit 23a outputs the analysis result of the spatial frequency of the diffuse reflection light, and the second conversion circuit 23b outputs the analysis result of the spatial frequency of the specular reflection light.

The LEDs 6a and 6b of each light source receive the drive pulse shown in FIG. 4 from the pulse oscillation circuit 21 and irradiate pulsed light. As a result, the photodetectors 17a, 1
Although a rectangular signal synchronized with each drive pulse is also output from 7b, disturbance light other than the reflected light also enters at the same time, so that the level of the output signal waveform varies as shown in FIG. Has occurred.

The comb filter 26 is for removing the influence of the ambient light and smoothing the rectangular signal of the reflected light. As shown in FIG.
It is composed of five and three sample-hold circuits (hereinafter abbreviated as "S / H circuits") 36a, 36b, 36c, and an arithmetic circuit 37.

The timing generating circuit 35 receives the drive pulse from the pulse oscillating circuit 31 and generates a timing signal at the rising time t1, the falling time t3, and the intermediate time t2 of these. This timing signal is applied to each S / H circuit 36a, 36b, 36c.
The signal levels V1, V2 and V3 from the light receiving unit at each time point are sampled and held as shown in FIG.

The arithmetic circuit 37 includes S / H circuits 36a and 36a.
an adder circuit 38 for inputting the output from c, and an S / H circuit 3
2b circuit 39 for inputting the output from 6b and adder circuit 3
8 and the doubling circuit 39, the subtraction circuit 40 which inputs the output
And, the output level V is determined by executing the arithmetic processing of the following equation (3). As a result, the level change due to ambient light is removed, and the amount of reflected light can be accurately grasped.

[0048]

[Equation 3]

Returning to FIG. 7, the waveform data of the reflected light amount passing through the comb filter 26 is sampled by the A / D conversion circuit 27 at a predetermined sampling interval T ₀ ,
Digitally converted. The digital-amount waveform data extracted by this conversion process is stored in the memory 28, then is acquired by the FFT circuit 29, and the fast Fourier transform process is executed.

The discrimination circuit 24 includes conversion circuits 23a, 23.
The intensity Da of the high frequency band and the intensity Db of the low frequency band including the spatial center frequency are extracted from the conversion result of b,
Further, by using the extraction result and the measurement value obtained by the temperature sensor for measuring the road surface temperature, the road surface state determination process (details will be described later) is executed. Note that the configuration described up to this point is the same as in the configuration examples of FIGS.

When reflected light from a portion having a high regular reflectance such as a metal portion is incident on the reflected light measuring sensor 2, the output result of the regular reflected light is saturated as shown in FIG. The diffusely reflected light components are extracted relatively unaffected. Further, in the case of a road surface having a large light absorptance, the output of diffusely reflected light is almost flat as shown in FIG. 12, but the regular reflectance is relatively high, so the center frequency component should be extracted without omission. You can

As described above, since the positive and diffuse reflected lights are not easily affected by the lack of the center frequency component at the same time, either of them can be detected by detecting the velocity for each reflected light amount as in the above configuration example. Even if an error occurs in one speed detection value, the traveling speed of the vehicle can be accurately measured by the other detection value. In both cases of FIGS. 11 and 12, the speed detected by the reflected light that is affected by the lack of the center frequency component is slower than the actual moving speed of the vehicle, so that the detection of each speed is performed. It is considered that the faster one of the values represents the actual traveling speed of the vehicle.

Therefore, the traveling speed of the vehicle is accurately measured using both reflected lights, and the next sampling interval T ₀ of the A / D conversion circuit is determined to be a quarter of the measured value. By doing so, in the result of the spatial frequency analysis by the FFT circuit 29, it is possible to control so that the center frequency component always comes to the ideal position on the distribution curve, and it becomes possible to stably determine the road surface condition.

Returning to FIG. 7 again, the speed feedback circuit 25 converts the speed data detected by either the positive or the diffused reflected light into the conversion circuit 2 based on the above principle.
3a, 23b for feedback, and two tracking bandpass filters 30,
31 (hereinafter abbreviated as “tracking BPF 30, 31”), pulse counting circuits 32, 33, and a speed measuring circuit 34.

The tracking BPFs 30 and 31 take in the waveform signals of the respective reflected lights of the positive and diffused light which have passed through the comb filters 26 and 26, respectively, and extract the frequency component corresponding to the center frequency f ₀ . Pulse counting circuit 32,
As for the input intermediate frequency component 33, as shown in FIG. 13, 33 performs pulse conversion of the sine wave based on the level of the base line, and sequentially counts pulse signals generated during a predetermined measurement time t, The count value is output to the speed measuring circuit 34.

The speed measuring circuit 34 calculates the moving distance L of the vehicle within the measuring time t from the count value n of the pulse signals output from the pulse counting circuits 32 and 33, and further from this distance the moving speed of the vehicle. Calculate v.
Now, assuming that one cycle of the spatial filter is 4 mm, the output interval of the pulse signal corresponds to half the cycle thereof, so that the distance L traveled by the vehicle during the measurement period t is 4 * n / 2. Therefore, the moving speed v of the vehicle is calculated by the following equation (4).

[0057]

[Equation 4]

The above velocity calculation processing is performed for both positive and diffuse reflected light. The velocity measurement circuit 34 adopts the faster velocity of these two calculated values as the measured velocity. The adopted measured value is fed back to the A / D conversion circuits 27, 27 and the tracking BPFs 30, 31. As a result, each A / D conversion circuit 2
The sampling interval T _{0 at 7} and 27 and the range of the cutoff frequency at the tracking BPFs 30 and 31 are determined, and the center frequency component can be extracted at an appropriate position also in the spatial frequency distribution of the next stage.

FIG. 14 shows another example of the structure related to speed feedback. The speed feedback circuit 25 of this illustrated example measures the moving speed of the vehicle by using the diffused reflected light from the road surface. The tracking BPF 30, the two pulse counting circuits 32a, 3 similar to the embodiment of FIG.
2b, speed measurement circuit 34 is included as a configuration.

The pulse counting circuits 32a and 32b are
Both of them count pulse signals indicating the wave number of the spatial frequency component of the diffuse reflected light extracted by the tracking BPF 30, and each pulse count circuit 32
a and 32b have different measurement times T _A ,
T _B is set.

In the first pulse count circuit 32a, specifically, a short measurement time T _A (for example, 1/16 ms) that can cope with acceleration / deceleration of the vehicle is determined. In this case, as shown in FIG. 15, when the central frequency component is missing from the diffuse reflected light, the pulse count circuit 32a cannot perform the counting process at the time of the missing, and detects an incorrect speed. In order to cope with this malfunction, the second pulse count circuit 32b is set with a measurement time T _B (for example, 1 sec) that is sufficiently longer than the measurement time T _{A of} the first pulse count circuit 32a. Since the speed detected in this case is average data within this measurement time T _B , even if the center frequency component is missing at one point within the measurement time, there is little error in the detected speed value. Therefore, an appropriate speed can be fed back to the conversion circuits 23a and 23b.

However, when the vehicle accelerates or decelerates, the second pulse counting circuit 32b having a long measurement period is used.
Then, it is impossible to perform detection that follows changes in the speed of the vehicle. In this case, since the speed measuring circuit 34 adopts the speed obtained from the count value of the first pulse counting circuit 32a having a short measurement period as the measured value, it is possible to perform the feedback operation corresponding to the speed change of the vehicle. Become.
The signal input to the above speed feedback circuit is
Not limited to diffuse reflected light, specular reflected light may be input.

FIG. 16 shows a third configuration example relating to speed feedback. Also in this embodiment, similar to the embodiment of FIG. 14, the moving speed v of the vehicle is measured using diffused reflected light, and the speed measuring circuit 34 uses the same pulse counting circuit 32 as described above to determine a predetermined speed. The velocity is detected from the wave number of the center frequency component within the measurement time. At the same time, the speed measuring circuit 34 controls the FF of the conversion circuit 23a for diffuse reflected light.
The extraction result of the center frequency f ₀ by the T circuit 29 is applied to the equations (1) and (2) to detect the speed, and the faster one of these detection results is adopted as the measured value.

In the case of the above configuration, the pulse count circuit 32
_A short measurement period T _A that can cope with acceleration / deceleration of the vehicle is set for the same as in the embodiment of FIG. In this case, if the center frequency component is missing from the reflected light, the velocity cannot be detected, but the data collection period required for the processing of the FFT circuit 29 is much longer than this measurement period T _A , The velocity can be detected without being affected by the lack of the center frequency component.

FIG. 17 shows the FFT processing result (shown by the broken line in the figure) for the waveform having no missing center frequency component.
The FFT processing result (shown by the solid line in the figure) for a waveform in which a lack of the center frequency component is recognized is shown in association with each other. In this way, when the missing part of the center frequency component is included in the processing period, the missing part is only reflected on the component strength of the center frequency and does not significantly affect the speed detection.

However, when the sampling interval T _{0 of the} A / D conversion circuit 27 does not correspond to the moving speed of the vehicle due to acceleration / deceleration of the vehicle, the speed detection value by the FFT circuit 29 becomes erroneous. In this case, the speed measurement circuit 34 uses the count value from the pulse count circuit 32 to detect the moving speed v reflecting the speed change of the vehicle so as to normalize the detection value on the FFT circuit 29 side. Various feedback processes. As a result, the FFT circuit 2
The extraction position of the center frequency in the frequency analysis result of 9 is kept in an ideal state, and the stabilization of the road surface state determination processing is realized.

FIG. 18 shows the procedure of the road surface state discrimination processing by the discrimination circuit 17. In the figure, TH
1, TH2, TH3, TH _c , TH _d1 , TH _d2 , TH _e
Indicates a threshold value for discriminating the road surface state (TH1 and TH2 among these are for comparison with the frequency component intensity ratio of the diffuse reflection light described above).

First, in step 1, the temperature sensor 1
The road surface temperature De measured by 9 is compared with the threshold value TH _e . This threshold TH _e is set near 0 ° C. which is the freezing temperature of water, and when the temperature De exceeds the threshold TH _e , there is no possibility that the road surface is frozen. Therefore, the process proceeds to step 2 and subsequent steps.

In steps 2 and 3, the frequency component intensity ratio Db / Da and the threshold value TH are set for the diffuse reflection light.
1 and TH2 are compared. In this case, the frequency component intensity ratio Db / Da is calculated according to the principle described with reference to FIG.
Is greater than the threshold value TH1, it is determined that the traveling road surface is a snowy road surface (step 5). If the frequency component intensity ratio Db / Da is between the threshold values TH2 and TH1, the traveling road surface is It is determined that the road is a gravel road surface (step 6).

On the other hand, when the frequency component intensity ratio Db / Da is less than or equal to the threshold value TH2, it is determined that the road surface is a paved road surface. In this case, in step 4,
For both the positive and diffuse reflected lights, the intensities Da and D of the components included in the frequency band centered on the spatial center frequency, respectively.
f is taken out, the ratio Df / Da of these intensities (hereinafter referred to as “reflected light ratio Df / Da”) and the threshold value TH _d1.
Is compared with.

As described above, when the paved road is wet, the road surface is close to a mirror surface, so that the amount of specularly reflected light increases and the value of the reflected light ratio Df / Da accordingly increases. The threshold value TH _d1 is set to an intermediate level between the reflected light ratio Df / Da when the road surface is in the wet state and the reflected light ratio Df / Da when the road surface is in the dry state, and the calculated reflected light If the ratio Df / Da exceeds this threshold value TH _d1 , it is determined that the road surface is a wet road surface (step 8). On the other hand, when the reflected light ratio Df / Da is less than or equal to the threshold value TH _d1, it is determined that the traveling road is a dry road surface (step 7).

When the road surface temperature De is equal to or lower than the threshold value TH _e , the routine proceeds to step 9, where the frequency component intensity ratio Db / Da is compared with a predetermined threshold value TH3. As a result, when the frequency component intensity ratio Db / Da exceeds the threshold value TH3, it is recognized that the road surface is a snowy road surface or a gravel road surface, and it is further determined in the next step 10 which road surface state it is. Is done.

In this step 10, the reflectance ratio Rv of the diffuse reflected light (the ratio of the reflected light amount to the projected light amount on the road surface LD).
Is compared with a predetermined threshold value TH _c, and if the diffuse reflection light ratio Rv exceeds the threshold value TH _c , the road surface is judged to be a snow surface (step 5), and the diffuse reflection light If the ratio is less than or equal to the threshold value TH _c , the road surface is judged to be a gravel road surface (step 6).

In step 9, the frequency component intensity ratio Db
When / Da is less than or equal to the threshold value TH3, it is determined that the road surface is a paved road surface, and in step 11, the reflected light ratio Df / Da and the threshold value TH _d2 are compared to determine that Detailed determination of the road surface condition is performed. Since the frozen road surface is close to a mirror surface, the amount of specularly reflected light is significantly increased, and as a result, the reflected light ratio Df / Da is increased. Therefore, when the reflected light ratio Df / Da exceeds the threshold value TH _d2 , it is determined that the road surface is frozen (step 12), and when the reflected light ratio Df / Da is the threshold value TH _d2 or less, The road surface is judged to be dry (step 7).

As described above, while traveling on the road, the spatial frequencies of the specular reflection light and the diffuse reflection light at a predetermined position are analyzed, and the road surface temperature is checked to obtain a wet road surface, a dry road surface, a gravel road surface, a snowy road surface, Frozen road surface 5
It is possible to determine the type of road surface condition.

In this embodiment, the warning information is output to the driver when it is determined that the road surface is in a dangerous state such as a frozen road surface or a snowy road surface.
Not limited to this, the function of the control device may be introduced into an ECU for ABS (anti-lock brake system) to perform appropriate brake control according to the road surface condition. It is also possible to configure a system in which a communication device is provided in this vehicle and the determination result of the road surface condition is transmitted to a road management center or the like to integrally manage the road surface condition at each position of the road.

[0077]

As described above, according to the present invention, based on the spatial frequency distribution obtained by sampling the reflected light from the road surface at a predetermined interval, the low frequency reflecting the center frequency component corresponding to the moving speed of the vehicle and the road surface condition is obtained. In the device for extracting the component and determining the road surface condition, when the central frequency component is missing from the reflected light, the sampling interval of the reflected light is determined by using the detection value by the speed detecting means that is not affected by the missing. Thus, the sampling interval is always set according to the moving speed of the vehicle, the spatial frequency component necessary for determining the road surface condition can be accurately extracted, and the road surface condition can be stably determined.

According to the second aspect of the present invention, the traveling speed of the vehicle is measured using the spatial frequency components contained in at least the specular reflection light and the diffuse reflection light from the road surface. Even if is missing, the accurate speed can be measured using the other reflected light.

According to the third aspect of the present invention, at least the first speed detecting means having a short measuring time and the second speed detecting means having a measuring time sufficiently longer than the measuring time are used. Since the moving speed is measured, it is possible to deal with the acceleration and deceleration of the vehicle and the lack of the center frequency component from the reflected light.

According to the fourth aspect of the present invention, at least the first velocity detecting means that uses the wave number of the center frequency component included in the reflected light and the second velocity detecting means that performs the discrete Fourier transform on the reflected light are used. Since it measures the moving speed of the vehicle,
It is possible to cope with acceleration / deceleration of the vehicle and lack of the center frequency component from the reflected light.

In the invention of claim 5, the measurement time of the first speed detecting means using the wave number of the center frequency component is set short, and the measurement time of the second speed detecting means using the discrete Fourier transform is set long. Therefore, both acceleration and deceleration of the vehicle and lack of the center frequency component from the reflected light can be reliably accommodated.

According to the sixth aspect of the invention, the fastest detected speed of the plurality of speed detecting means is adopted as the measured value.
It is possible to obtain a measurement value that is not easily affected by the lack of the center frequency component, and to determine the sampling interval of the reflected light with high accuracy.

According to the seventh aspect of the present invention, since the above-mentioned road surface condition determining device is mounted on the vehicle, the road surface condition can be stably determined while the vehicle is traveling.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a vehicle equipped with a road surface state determination device according to the present invention.

FIG. 2 is a perspective view showing a detailed configuration of a reflected light measurement sensor.

FIG. 3 is an explanatory diagram showing a positional relationship of each optical system of the reflected light measurement sensor.

FIG. 4 is a timing chart showing an output timing of a drive pulse to each light projecting unit.

FIG. 5 is an explanatory diagram showing spatial frequency characteristics of diffusely reflected light for each road surface state.

FIG. 6 is an explanatory diagram showing the relationship between the intensities of the central frequency components of diffusely reflected light and specularly reflected light in association with each type of road surface state.

FIG. 7 is a block diagram showing an electrical configuration example of a road surface state determination device.

FIG. 8 is an explanatory diagram showing a state of an output signal from the photodetector.

9 is a block diagram showing a detailed configuration of the comb filter in FIG. 7. FIG.

10 is an explanatory diagram showing a processing method for the output signal of FIG. 8. FIG.

FIG. 11 is an explanatory diagram showing a relationship between specular reflection light and diffuse reflection light from a road surface.

FIG. 12 is an explanatory diagram showing a relationship between specular reflection light and diffuse reflection light from a road surface.

13 is an explanatory diagram showing a counting processing method in the pulse counting circuit of FIG. 7. FIG.

FIG. 14 is a block diagram showing another configuration example of the road surface state determination device.

15 is a timing chart showing the relationship between the measurement time of each pulse counting circuit of FIG. 14 and the lack of an intermediate frequency component from reflected light.

FIG. 16 is a block diagram showing another configuration example of the road surface state determination device.

FIG. 17 is an explanatory diagram showing the influence of lack of a center frequency from reflected light on FFT processing.

FIG. 18 is a flowchart showing a procedure of road surface determination.

FIG. 19 is an explanatory diagram showing an optical processing method using a spatial filter.

FIG. 20 is an explanatory diagram showing an output signal of reflected light that has passed through a spatial filter.

FIG. 21 is an explanatory diagram showing a sampling process for an output signal from a spatial filter.

FIG. 22 is an explanatory diagram showing a spatial frequency distribution curve obtained by using FFT.

FIG. 23 is an explanatory diagram showing the relationship between the cycle of the center frequency and the sampling cycle.

FIG. 24 is an explanatory diagram showing the relationship between the cycle of the center frequency and the sampling cycle.

FIG. 25 is an explanatory diagram showing an example of missing spatial frequencies from reflected light.

FIG. 26 is an explanatory diagram showing an example of missing a spatial frequency from reflected light.

[Explanation of symbols]

1 Road surface condition determination device 2 Reflected light measurement sensor 3 control device 23 Conversion circuit 24 Discrimination circuit 25 Speed feedback circuit

Claims (7)

(57) [Claims] 1. A light projecting means for radiating light from a traveling vehicle toward a road surface, a sampling means for receiving reflected light from the road surface and sampling the reflected light at a predetermined interval, and sampled reflection Based on the intensity ratio of each frequency component extracted by the extracting means for extracting the center frequency component corresponding to the moving speed of the vehicle and the predetermined low frequency component reflecting the road surface state from the spatial frequency distribution of light, A road surface condition determination device comprising a determination means for determining a road surface condition, wherein a speed at which the moving speed of the vehicle is measured by using a plurality of speed detection devices that are not affected by the lack of the central frequency component from the reflected light at the same time Measuring means, and sampling interval determining means for determining the sampling interval of the reflected light of the sampling means based on the measurement value by the speed measuring means. With the road surface state detecting apparatus comprising. 2. The speed measuring means includes at least a first speed detecting means for detecting a moving speed of the vehicle by using a spatial frequency component included in the regular reflection light from the road surface, and a diffuse reflection light from the road surface. The road surface state determination device according to claim 1, further comprising a second speed detecting unit that detects a moving speed of the vehicle using the included spatial frequency component. 3. The speed measuring means comprises at least a first speed detecting means having a short measuring time and a second speed detecting means having a sufficiently longer measuring time than the first speed detecting means. Item 1. A road surface condition determination device described in item 1. 4. The speed measuring means includes at least a first speed detecting means for detecting a moving speed of a vehicle by counting the wave number of a center frequency component included in the reflected light within a predetermined period, and the reflected light. The road surface state determination device according to claim 1, further comprising a second speed detection unit that detects a moving speed of the vehicle by using a result of performing a discrete Fourier transform on the. 5. The road surface condition determining device according to claim 4, wherein the second measuring means is set with a measuring time sufficiently longer than the measuring time of the first measuring means. 6. The road surface state determination device according to claim 1, wherein the speed measuring means determines the fastest speed among the moving speeds detected by the plurality of speed detecting means as the moving speed of the vehicle. 7. A vehicle on which the road surface state determination device according to claim 1 is mounted.