JP3473158B2 - Road surface condition detection 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 detecting the condition of a road surface on which a tire is in contact with the ground.

[0002]

2. Description of the Related Art The road surface condition detecting apparatus described above urges a driver to perform a driving operation suitable for an actual road surface condition, or sets a control condition of a vehicle behavior to match an actual road surface condition so as to drive and brake. It helps to increase the stability of.

As this road surface state detecting device, for example,
As disclosed in Japanese Patent Laid-Open No. 174543/1994, the sound generated from the tire is collected by a microphone, and the road surface on which the tire is in contact with the ground is based on the sound pressure level within the set frequency range. There is one that determines whether or not

[0004]

In the conventional device as disclosed in the above publication, the road surface condition is detected based on the sound pressure level within the set frequency, so that the sound pressure generated from the tire due to the change in vehicle speed is There is a possibility that the road surface condition may be erroneously detected due to a change (as seen from FIG. 3, the sound pressure increases as the vehicle speed increases).

If the behavior of the vehicle is controlled on the basis of erroneous information, it has an adverse effect on safety. Therefore, in this type of device, it is extremely important to improve the detection accuracy.

An object of the present invention is to meet the demand for improvement in detection accuracy in this road surface state detecting device.

[0007]

In order to solve the above-mentioned problems, in the present invention, the sound detecting means detects a contact sound between a tire and a road surface, and among the detected contact sounds, a sound within a plurality of preset frequency ranges is detected. The ratio of pressure levels is calculated, and the condition of the road surface on which the tire is in contact is determined by the road surface condition detection means depending on whether the ratio exceeds a reference value determined according to the road surface condition. I decided to do it.

[0008]

As for the contact sound between the tire and the road surface, the sound pressure level changes when the vehicle speed changes, but the frequency characteristic changes a lot even if the vehicle speed changes, as can be seen from FIG. do not do. On the other hand, when the road surface condition changes, a characteristic change appears in a specific frequency range. Therefore, select a frequency range in which characteristic changes appear due to changes in road surface condition and a frequency range in which the changes are small as a plurality of set frequency ranges, find the ratio of the sound pressure levels within the set frequency range, and use that ratio as the reference value. By checking whether or not the road surface has been exceeded (whether or not a characteristic change has appeared in a specific frequency range), it is possible to know whether or not the road surface condition has changed, and what kind of condition the currently running road surface is. . In the detection based on this principle, since there is nothing to depend on the change in the sound pressure level, erroneous detection due to the change in vehicle speed that causes the change in the sound pressure level does not occur.

[0009]

FIG. 1 shows an example in which a microphone (sound detecting means) 1 used in the detecting device of the present invention is attached to a vehicle. The microphone 1 detects the contact sound between the tire and the road surface while suppressing the entry of noise as much as possible. Therefore, the microphone 1 is directed to the contact point between the tire and the road surface at a place where it is not easily affected by water, mud, stones, etc. splashed by the tire. To install.

FIG. 2 is an outline of the first embodiment of the detecting device of the present invention. In this device, the output of the microphone 1 is passed through the frequency analysis device 2 for frequency analysis, and then the result is input to the road surface condition determination device 3, where the condition of the road surface currently touched by the tire is determined.

FIG. 3 shows frequency analysis results when the vehicle runs on a dry road surface and a flooded road surface at a speed of 40 km / h and a speed of 60 km / h. In this way, as the traveling speed increases, the sound pressure level increases on both the dry road surface and the submerged road surface, which makes it difficult to discriminate by the conventional method and may cause erroneous detection. On the other hand, the frequency characteristic of the contact sound is characteristic depending on the road surface condition, and it is about 1.5k on a submerged road surface without depending on the traveling speed.
The frequency component of Hz is large.

Therefore, in this embodiment, the ratio of the average of the sound pressure levels within the range of 1 to 2 kHz to the average of the sound pressure levels within the range of 0.5 to 1 kHz within the road surface condition determining device 3 is determined. I chose The ratio is calculated by the following formula. Sound pressure level ratio = (average value of sound pressure level in the range of 1 to 2 kHz) / (average value of sound pressure level in the range of 0.5 to 1 kHz) Result of obtaining ratio of sound pressure levels by this formula Is shown in FIG. The ratio is 60 km / h at 40 km / h on dry road surface.
It is much smaller than 1.5 at m and far exceeds 1.5 in case of flooded road surface. Therefore, in this embodiment, the reference value is set to 1.5, and if the ratio of the sound pressure levels obtained by the road surface condition determination device 3 is greater than 1.5, it is determined to be a flooded road surface, and otherwise the road surface is determined to be a dry road surface. I made a decision. FIG. 5 shows a flowchart of road surface condition determination used in the illustrated apparatus. A display device is added to notify the driver of the determination result.

Further, in this embodiment, since a characteristic peak appears in the vicinity of about 1.5 kHz on the surface of the submerged road, (average sound pressure level in the range of 1 to 2 kHz) /
The ratio of (average of sound pressure levels within the range of 0.5 to 1 kHz) was used as the reference material for the road surface condition. As can be seen from FIG.
Even in the region of 2 kHz or more (10 kHz or less), the output is high on the flooded road surface and low on the dry road surface. Therefore,
For example (average sound pressure level in the range of 2-3 kHz)
The ratio of / (average of sound pressure levels within the range of 0.5 to 1 kHz) may be used as the reference material for determining the road surface condition.

FIG. 6 shows a road surface state detecting device according to the second embodiment.

In this embodiment, the sound wave from the microphone 1 is first transmitted.
It was passed through a filter 11 and a second filter 12 and sieved. The first filter 11 is a bandpass filter that passes a sound wave of 0.5 to 1 kHz, and the second filter 12 is 1 to 2 kHz.
The band-pass filters that pass the sound waves are used, and the AC signal outputs from these filters are converted into DC signals by the first rectifier circuit 13 and the second rectifier circuit 14, and then input to the road surface state determination device 15. The output from the first rectifying circuit 13 corresponds to the average value of the sound pressure level of 0.5 to 1 kHz in the first embodiment, and the output from the second rectifying circuit 14 corresponds to the sound pressure level of 1 to 2 kHz. Corresponding to the average value of. The road surface condition determination device 15 determines the ratio of these outputs, compares this ratio with a reference value, and determines whether the road surface is flooded or dry based on the flowchart similar to FIG.

By the same reason as above, it is possible to detect the road surface condition by obtaining the ratio of the sound pressure levels within three or more set frequency ranges. An example of the flowchart of the determination in this case is shown in FIGS. Further, FIG. 8 shows the frequency analysis result of the contact sound on the snow-compacted road surface and the icy road surface determined based on the flowchart.

In the case of FIG. 7A, first, the average value S1 of the sound pressure levels in the three set frequency ranges (here,
0.5 to 1 kHz average value), S2 (0.1 to 0.5 kHz)
(Average value of Hz) and S3 (average value of 1 to 2 kHz), and the ratio of S2 to S1 is the reference value L1 (for example, 1.
If it is larger than 5), the road surface is determined to be snowy. Also S2 / S
If the condition of 1> L1 is not satisfied, then it is checked whether the ratio of S3 to S1 is larger than the second reference value L2 (for example, 1.5). If YES, it is determined to be a flooded road surface, and if NO, it is determined to be a dry road surface.

Meanwhile, in the case of FIG. 7 (b), first, 3
Average value S1 of sound pressure level within one set frequency range (here
Then, an average value of 0.6 to 0.8 kHz), S2 (here,
0.8 to 1 kHz average value), S3 (here, 1 to 1.
2kHz average value), and the ratio of S2 to S1 is
Greater than the quasi value L1 (eg 1.5) and corresponding to S1
The ratio of S3 is larger than the reference value L2 (for example, 1.5).
For example, the road surface is determined to be on ice, and if not, it is determined to be dry, submerged, or snowy.

As described above, the apparatus for determining the ratio of the sound pressure levels in three or more set frequency ranges and comparing the ratio with the reference value is three as shown in FIG. 7A. It can also be used to detect the above road surface conditions.

The frequency characteristic of the contact sound between the tire and the road surface is characteristic according to the road surface condition, and if the same road surface condition does not change even if the vehicle speed changes, the characteristic is If the ratio of the sound pressure level in the frequency range where characteristic changes appear and the sound pressure level in the frequency range where there is not much change is found and it is judged whether this ratio is larger than the reference value of the comparison target, the coefficient of friction with the tire The road surface in which you are currently driving is one of many road conditions, such as a large dry road surface, a small dry road surface, a slightly wet flood surface, a fairly wet flood surface, an icy road surface, and a snowy road surface. Can be detected.

[0021]

As described above, the road surface condition detecting device of the present invention has a frequency range in which a characteristic change occurs in the contact sound between the tire and the road surface in accordance with a change in the road surface state and a frequency range in which the change is small. Select the sound pressure level ratio in that frequency range and determine the road surface state based on this ratio, so changes in sound pressure level will not affect detection accuracy,
Accurate information can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of mounting a microphone on a vehicle.

FIG. 2 is a block diagram of a detection device according to the first embodiment.

FIG. 3 is a diagram showing an example of frequency analysis results.

FIG. 4 is a chart showing sound pressure level ratios.

FIG. 5 is a diagram showing an example of a flowchart for determining a road surface condition.

FIG. 6 is a block diagram of a detection device according to a second embodiment.

FIG. 7A is a diagram showing another example of a flowchart for determining the road surface condition, and FIG. 7B is a diagram showing still another example of the flowchart for determining the road surface condition.

FIG. 8A is a diagram showing an example of a frequency analysis result on a compressed snow road surface, and FIG. 8B is a diagram showing an example of a frequency analysis result on an ice road surface.

[Explanation of symbols]

1 microphone 2 Frequency analyzer 3 Road surface condition determination device 11 First filter 12 Second filter 13 First rectifier circuit 14 Second rectifier circuit 15 Road surface condition determination device

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-138018 (JP, A) JP-A-6-174543 (JP, A) JP-A-6-50878 (JP, A) Actual Kaihei 2- 75562 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 29/00-29/28 B60R 21/00

Claims (6)

(57) [Claims] 1. A sound detecting means for detecting a contact sound between a tire and a road surface, and a ratio of sound pressure levels within a plurality of set frequency ranges among the detected contact sound between the tire and the road surface, the ratio being a road surface condition. And a road surface condition detecting means for determining a condition of a road surface on which the tire is in contact with the road surface condition detecting device. 2. A road surface is selected by selecting a low frequency region and a high frequency region as the plurality of set frequency ranges, obtaining a ratio of sound pressure levels in these regions, and determining whether or not the ratio exceeds a certain reference value. The road surface condition detecting device according to claim 1, wherein the condition is determined. 3. The low frequency region is set within a range of 1 kHz or less, and the high frequency region is set within a range of 1 to 10 kHz, and the high frequency side is set with respect to the average of the sound pressure level in the low frequency side set range. 3. The road surface condition detecting device according to claim 2, wherein if the average ratio of the sound pressure levels in the setting range is larger than a certain reference value, it is determined to be a flooded road surface, and if it is smaller, it is determined to be a dry road surface. 4. The low frequency region is 0.1 to 0.5 kH
Within the range of z , the high frequency region is set within the range of 0.5 to 1 kHz, and the average of the sound pressure level in the setting range on the high frequency side is set to the average of the sound pressure level in the setting range on the low frequency side. 3. The road surface state detecting device according to claim 2, wherein if the average ratio is larger than a certain reference value, it is determined that the road surface is snowy. 5. The low frequency region is 0.6 to 0.8 kHz.
Within the range of z , the high frequency range is 0.8 to 1 kHz and 1
Each of them is set in the range of 1.2 kHz, and the ratio of the average of the sound pressure levels in the setting range on the low frequency side to the average of the sound pressure levels in the setting range on the high frequency side is both.
3. The road surface condition detecting device according to claim 2 , wherein both of the persons judge that the road surface is on ice if it is larger than a certain reference value. 6. A contact sound between a tire and a road surface is detected by a sound detecting means, and a ratio of sound pressure levels within a plurality of set frequency ranges among the detected contact sound between the tire and the road surface is obtained, and the ratio is a road surface state. Depending on whether the standard value set according to
A road surface condition detecting method for determining a condition of a road surface on which the tire is in contact with the ground.