JP2005106728A - Road surface condition detection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a road surface condition detection apparatus which constantly detects a road surface condition by using tire cavity resonance. <P>SOLUTION: A box 2 made from a metallic plank or a die casting and having a natural frequency of 500 to 1,000 Hz is placed on a vehicle floor 3. A microphone 1 as sound pressure detection means which detects sound is placed in a closed space formed within the box 2. A processor 5 connected to the microphone 1 through a connecting cable 4 detects two, high and low peak frequencies F_low and F_high and sound pressure levels P_low and P_high corresponding to F_low and F_high, respectively, from cavity resonance by a tire detected by the microphone 1. The processor 5 determines (detects) the condition of a road surface on which a vehicle is travelling from the detected sound pressure levels and the frequency difference between the two, high and low peak frequencies. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a road surface state detection device mounted on a vehicle device or the like.

  2. Description of the Related Art Conventionally, as a device for detecting the state of a road surface on which a vehicle travels, for example, there is a device that estimates the road surface state based on a change in tire air pressure associated with traveling. Specifically, the tire pressure Pe at a predetermined time after the start of travel is estimated from the tire air pressure Po at the start of travel of the vehicle, the outside air temperature T, and the like, and the estimated tire air pressure Pe and the actual time after the predetermined time has elapsed after the start of travel The road surface state is estimated based on the comparison with the tire pressure Pa (see, for example, Patent Document 1). In addition, there is a technique that performs frequency analysis by detecting a change in air pressure in a tire (see, for example, Patent Document 2). Furthermore, a detecting means for detecting the rotational speed of each wheel is provided, and a slip condition between each wheel and the road surface is estimated from the traveling speed of the vehicle and the rotational speed of each wheel, and the braking force for braking each wheel is controlled. (For example, refer to Patent Document 3).

  On the other hand, a technique for reducing in-vehicle noise (generally referred to as road noise) generated by road surface unevenness and tires when a vehicle travels is disclosed (for example, see Non-Patent Document 1). According to the description of Non-Patent Document 1, road noise is generated when a resonance mode of a doughnut-shaped hollow acoustic system composed of a tire and a disc wheel (hereinafter referred to as a wheel) is excited by input from a road surface. It is explained that the cavity resonance has the following three characteristics.

Specifically, in FIG. 4, the horizontal axis indicates the cavity resonance sound frequency and the vertical axis indicates the sound pressure level.
(A) The peak frequency of the cavity resonance sound is one when the tire is not deformed, but two appear when the tire is partially deformed by grounding.
(B) Of the two peak frequencies, the wheel vibrates back and forth at the lower natural frequency (hereinafter referred to as F_low), and the wheel vibrates up and down at the higher natural frequency (hereinafter referred to as F_high). To do.

Further, in FIG. 5, the horizontal axis indicates the vehicle traveling speed (vehicle speed), and the vertical axis indicates the cavity resonance sound frequency.
(C) During traveling, F_low becomes lower and F_high becomes higher as the traveling speed (vehicle speed) of the vehicle increases.
It has the characteristics.
JP-A-8-156537 JP 2002-240520 A Japanese Patent Laid-Open No. 9-109871 Yuji Yamauchi, Shinji Akiyoshi, “Proposal for improving tire cavity resonance sound”, Automotive Technology, Japan Society for Automotive Engineers, August 2003, Vol. 57, no. 7, p. 59-63

Incidentally, the conventional techniques described in Patent Document 1 to Patent Document 3 have a problem that the road surface state cannot always be detected. Specifically, in the technique described in Patent Document 1, in order to reliably determine whether the road surface is a dry road surface or a wet road surface, it is necessary to wait for the time to elapse from the start of traveling of the vehicle. was there. In the technique described in Patent Document 2, the state between the road surface and the tire is detected by utilizing the fact that the state where the hydroplaning phenomenon is likely to occur can be determined from the tread vibration in the high frequency region of 800 [Hz] or higher. Therefore, the control value could not be calculated unless it was just before the hydroplaning phenomenon occurred. Furthermore, with the technique described in Patent Document 3, it is only possible to perform braking within a range that does not exceed a predetermined slip ratio during braking, and it has not been possible to detect a road surface state during normal traveling in which no slip occurs.
Therefore, the conventional technology has a problem in that it is difficult to perform active vehicle control in a normal traveling state by always detecting the road surface state.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a road surface state detection device that can always detect a road surface state using tire cavity resonance sound.

  In order to solve the above-mentioned problem, a road surface state detection device according to the invention of claim 1 is disposed in a transmission path of vibration transmitted from a road surface through a tire to a vehicle body, and is closed by a solid material. A gas chamber (for example, a box 2 in an embodiment to be described later), a sound pressure detecting means (for example, a microphone 1 in an embodiment to be described later) that is disposed in the gas chamber and detects sound, and the sound pressure detecting means. And an arithmetic device (for example, an arithmetic processing unit 5 in an embodiment described later) that obtains information related to the road surface condition where the vehicle is traveling.

  The road surface state detection device having the above configuration detects vibration transmitted from the road surface through the tire to the vehicle body as sound, using sound pressure detection means provided in a gas chamber of a constant volume closed by a solid material. In addition, when the arithmetic device performs the frequency analysis of the sound, information relating to the road surface state where the vehicle is traveling can be obtained whenever the vehicle is traveling.

  According to a second aspect of the present invention, there is provided a road surface condition detecting device according to the first aspect, wherein the arithmetic unit is configured to output two high and low peak frequencies (for example, implementation described later) in the output of the sound pressure detecting means. And detecting a sound pressure level corresponding to at least one of the two peak frequencies (for example, sound pressure levels P_low and P_high in the embodiments described later) and the sound pressure. Based on the level and the frequency difference, information related to a road surface state where the vehicle is traveling is obtained.

  The road surface condition detection apparatus having the above configuration is such that the tire cavity resonance sound level is high, the low two peak frequencies and the frequency difference thereof, and the sound pressure level corresponding to the two peak frequencies are the conditions of the road surface on which the tire contacts the ground. By utilizing the fact that there is a close relationship with the vehicle, it is possible to accurately obtain information related to the road surface state where the vehicle is traveling, whenever the vehicle is traveling.

  A road surface condition detection apparatus according to a third aspect of the present invention is the road surface condition detection apparatus according to the first or second aspect, wherein the frequency band of the sound detected by the sound pressure detection means is from 100 [Hz] to 300 [Hz]. [Hz].

  The road surface state detection device having the above configuration is detected by the sound pressure detection means specialized for tires having a center of gravity diameter of about 36 [cm] to 110 [cm], for example, which is generally used. By limiting the frequency band of sound from 100 [Hz] to 300 [Hz], it is possible to obtain optimum cost performance.

According to the road surface state detection device of the first aspect, information relating to the road surface state in which the vehicle is traveling can be obtained whenever the vehicle is traveling. Therefore, it is possible to obtain an effect that it is possible to always detect the road surface condition and execute the active vehicle control in the normal traveling state. Moreover, according to the road surface state detection device of the second aspect, information relating to the road surface state in which the vehicle is traveling can be obtained accurately whenever the vehicle is traveling. Therefore, an effect that a high-performance road surface state detection device can be realized and vehicle control with high accuracy in the normal traveling state can be performed.
Furthermore, according to the road surface state detection device of the third aspect, the optimum cost performance can be obtained by limiting the frequency band of the sound detected by the sound pressure detecting means. Therefore, the effect that a high-performance and low-priced road surface state detection device can be realized is obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

(overall structure)
FIG. 1 is a diagram illustrating a configuration and an installation example of a road surface state detection device according to an embodiment of the present invention. The road surface state detection apparatus according to the present embodiment detects a road surface state by using a cavity resonance sound that is excited when an external force is input from a road surface to a donut-shaped hollow acoustic system including tires and wheels. . For this reason, the road surface condition detection apparatus of the present embodiment detects and utilizes the cavity resonance sound transmitted from the wheel to the vehicle interior via the vehicle suspension and body.

In FIG. 1, a microphone 1 is sound pressure detecting means for detecting sound, and is installed inside a box 2 (a space closed with a solid) made of a thick metal plate or die cast (die cast).
On the other hand, the vehicle floor surface 3 is a vehicle floor surface on which the road surface condition detection device of the present embodiment is mounted. On the vehicle floor surface 3, a box 2 and a microphone installed inside the box 2 are provided. An arithmetic processing unit 5 that is connected via a connection cable 4 that is electrically connected to 1 and that executes a road surface state detection process using a cavity resonance sound detected by the microphone 1 is attached. In addition, a vehicle speed signal indicating the traveling speed of the vehicle is input to the arithmetic processing unit 5 from a vehicle speed sensor (not shown) that detects the traveling speed (vehicle speed) of the vehicle.

  The connection between the microphone 1 installed inside the box 2 by the connection cable 4 and the arithmetic processing unit 5 installed outside the box 2 is made by connecting the terminal installed on the wall surface of the box 2 and the connection cable 4. It is assumed that the connection means such as a connector provided in the connector is connected so as to maintain the airtightness of the internal space of the box 2 in which the microphone 1 is installed. Details of the operation of the arithmetic processing unit 5 will be described later.

  FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and the box 2 will be described in more detail. In FIG. 2, the box 2 has, for example, an L-shaped cross section welded to the box 2. Are attached to the vehicle floor 3 by bolts 7. The box 2 has a natural frequency of 500 [Hz] to 1000 [Hz], for example, and a closed space is formed inside. The lid 2a is opened and closed by a bolt 8 at the top of the box 2 It is attached freely. The microphone 1 attached to the inside of the box body 2 is fixed to a bottom wall (bottom surface) 9 inside the box body 2 by a bracket 10 so that the microphone 1 is positioned at a substantially central portion in the space. Accordingly, the cavity resonance sound of the tire is transmitted to the air inside the box body 2 through the box body 2, so that the microphone 1 detects this.

  That is, for example, if the microphone 1 is installed outside the vehicle or in the passenger compartment, it is difficult to separate with a filter or the like due to a mixture of disturbance due to other sounds and cavity resonance sound. By installing the microphone 1 inside the body 2, it is possible to utilize the point that the cavity resonance sound is transmitted through the solid part of the vehicle, and to insulate the microphone 1 from the sound other than the cavity resonance sound, thereby accurately performing the cavity resonance. The effect that sound can be detected is obtained.

  The microphone 1 corresponds to the cavity resonance sound frequency calculated based on the following formula (1) so that the tire can have a center-of-gravity diameter of the tire cavity cross section of 36 [cm] to 110 [cm]. For example, the cost performance can be optimized by selecting a sound whose frequency range (frequency band) can be detected from 100 [Hz] to 300 [Hz]. Further, if the frequency range of sound that can be detected is limited to the tire size for each vehicle, the accuracy of frequency analysis can be further improved, and cost performance is improved. In the following formula (1), R is the center-of-gravity radius [m] of the tire cavity cross section. The sound speed is 340 [m / sec].

Cavity resonance sound frequency = (sound speed) / (2 × π × R) (1)

  In the above description, the box 2 is described as being attached to the vehicle floor 3 with the bolts 7 via the bracket 6 welded to the box 2, for example, but the box 2 is welded to the vehicle floor 3. It may be sufficient if it is mechanically fixed by contact. Furthermore, although the box 2 and the arithmetic processing unit 5 have been described as separate units, the arithmetic processing unit 5 may be accommodated in the box 2 together with the microphone 1, and in this case, the arithmetic processing unit 5 is accommodated. The volume of the box 2 may be constant before and after the operation.

(Road surface detection process)
Next, the road surface state detection processing operation of the road surface state detection device of this embodiment will be described with reference to the drawings. FIG. 3 is a flowchart showing a road surface state detection processing operation by the arithmetic processing unit 5 of the road surface state detection device of the present embodiment.
In FIG. 3, the arithmetic processing unit 5 first acquires the cavity resonance sound by the microphone 1 (step S1) and also acquires the traveling speed (vehicle speed) of the vehicle at this time from the vehicle speed sensor (step S2).

  Next, sound pressure levels P_low and P_high corresponding to F_low and F_high and F_low and F_high, which are two high and low peak frequencies, are detected from the cavity resonance sound caused by the tire detected by the microphone 1 shown in FIG. (Step S3). Specifically, the two high and low peak frequencies F_low and F_high shown in FIG. 4 are obtained when the tire is partially deformed by grounding, as described in Non-Patent Document 1 described above. The two peak frequencies of the cavity resonance sound that appear, here, as an example, shows the case where the center of gravity diameter of the tire cavity cross section is 47 [cm] and the basic cavity resonance sound frequency is 230 [Hz]. In FIG. 4, the horizontal axis indicates the cavity resonance sound frequency [Hz] and the vertical axis indicates the sound pressure level [dB].

  Further, the arithmetic processing unit 5 is characterized in that the two high and low peak frequencies F_low and F_high are characterized in that F_low is low and F_high is high as the vehicle traveling speed (vehicle speed) increases. Based on the calculation example of the vehicle traveling speed (vehicle speed) and the cavity resonance sound frequency shown in FIG. 5, for example, the vehicle traveling speed (vehicle speed) is calculated based on the detected high and low peak frequencies of the cavity resonance sound. The cavity resonance sound at the time of “zero” is converted into high and low peak frequencies (step S4), and the frequency difference between the high and low peak frequencies is calculated (step S5). FIG. 5 shows F_low and F_high, with the horizontal axis representing the vehicle traveling speed (vehicle speed) [km / h] and the vertical axis representing the cavity resonance sound frequency [Hz]. F_ave represents an average value of F_low and F_high.

Then, the arithmetic processing unit 5 determines (detects) the road surface state in which the vehicle is traveling from the detected sound pressure level and the frequency difference between the high and low two peak frequencies (step S6).
More specifically, FIG. 6 is a determination map for determining a road surface state obtained experimentally by traveling on a known road surface. For example, the horizontal axis represents the sound pressure level P_high corresponding to the peak frequency F_high. However, the vertical axis indicates the frequency difference between the high and low peak frequencies of the cavity resonance sound when the vehicle traveling speed (vehicle speed) is “zero”.

  Further, the road surface states classified in association with the sound pressure level and the frequency difference between the two high and low peak frequencies, as shown in FIG. 6, are indicated by the sound pressure level P_high shown on the horizontal axis and the vertical axis. For example, (1) gravel road surface, (2) uneven road surface, (3) normal paved road surface, (4) low friction coefficient paved road surface, and so on. It is divided. Therefore, the arithmetic processing unit 5 determines the road surface state in which the vehicle is currently traveling according to the determination map shown in FIG. 6 from the detected sound pressure level and the frequency difference between the high and low peak frequencies.

  In step S4 described above, the vehicle traveling speed (vehicle speed) is “zero” based on the traveling speed (vehicle speed) of the vehicle at that time, based on the two high and low peak frequencies of the cavity resonance sound detected by the microphone 1. It was converted to two high and low peak frequencies of the cavity resonance sound at the time of this, but this is to make it possible to obtain a certain result in determining the road surface condition under any driving conditions, The vertical axis of the determination map used for determination of the road surface shown in FIG. 6 shows the frequency difference between the high and low peak frequencies of the cavity resonance sound when the vehicle traveling speed (vehicle speed) is “zero”. Corresponds to the state classification.

  That is, the vertical axis of the determination map used for determining the road surface shown in FIG. 6 shows the high and low two peak frequencies of the cavity resonance sound when the vehicle traveling speed (vehicle speed) is 20 km / h, for example. In the case where the road surface condition classification is shown by showing the frequency difference, in step S4, the high and low two peak frequencies of the cavity resonance sound detected by the microphone 1 are determined based on the traveling speed (vehicle speed) of the vehicle at that time. When the vehicle traveling speed (vehicle speed) is 20 [km / h], it is necessary to perform processing by converting the cavity resonance sound into high and low two peak frequencies.

  Further, the horizontal axis of the determination map used for road surface determination shown in FIG. 6 shows the sound pressure level P_high corresponding to the peak frequency F_high, but the value shown on the horizontal axis of the determination map is the peak frequency F_low. May be the sound pressure level P_low corresponding to, or an average value of the sound pressure levels P_high and P_low. Furthermore, because the cavity resonance sound frequency also changes due to the change in sound speed due to temperature, it is equipped with a temperature sensor that measures outside air noise, road surface temperature, tire temperature, etc., and by correcting by the measured temperature, A more reliable determination of the road surface condition can be executed.

  As described above, according to the road surface condition detection apparatus of the present embodiment, the natural frequency of a thick metal plate or die-cast (die-cast) on the vehicle floor 3 is 500 [Hz] to 1000 [Hz]. The microphone 1 is installed in a closed space formed inside the box 2 as sound pressure detecting means for detecting sound. Then, the arithmetic processing unit 5 connected to the microphone 1 via the connection cable 4 first acquires the cavity resonance sound by the microphone 1 and acquires the traveling speed (vehicle speed) of the vehicle at this time from the vehicle speed sensor. Next, sound pressure levels P_low and P_high corresponding to F_low and F_high, and F_low and F_high, respectively, are detected from the cavity resonance sound by the tire detected by the microphone 1.

  Further, the arithmetic processing unit 5 uses two low and high peak frequencies of the cavity resonance sound detected by the microphone 1, for example, two high and low peak frequencies of the cavity resonance sound when the vehicle traveling speed (vehicle speed) is “zero”. Converted to the peak frequency, the frequency difference between the two high and low peak frequencies is calculated. Then, the arithmetic processing unit 5 determines (detects) the road surface state in which the vehicle is traveling from the detected sound pressure level and the frequency difference between the two high and low peak frequencies. Thereby, the vibration transmitted from the road surface through the tire to the vehicle body is detected as sound (cavity resonance sound) using the microphone 1 provided in the box 2 having a constant volume closed by the solid material, and the calculation processing is performed. By executing the frequency analysis of this sound, the unit 5 can obtain information related to the road surface state where the vehicle is traveling whenever the vehicle is traveling.

  Therefore, it is possible to realize a high-performance road surface state detection device, and to obtain an effect that the road surface state is constantly detected and the vehicle control can be executed positively and highly in the normal driving state. Furthermore, since the optimum cost performance can be obtained by limiting the frequency band of the sound detected by the microphone 1, an effect of realizing a high-performance and low-priced road surface state detecting device can be obtained.

It is a figure which shows the structure and installation example of the road surface state detection apparatus in one Example of this invention. It is sectional drawing along the AA line of FIG. It is a flowchart which shows the road surface state detection processing operation by the arithmetic processing part of the road surface state detection apparatus of the Example. It is a figure which shows the cavity resonance sound by the tire detected by the microphone. It is a figure which shows the relationship between the travel speed (vehicle speed) of a vehicle, and a cavity resonance sound frequency. It is a figure which shows the map for determination for driving | running | working a known road surface and determining the road surface state calculated | required experimentally.

Explanation of symbols

1 Microphone (Sound pressure detection means)
2 Box (gas chamber)
5 Arithmetic processing part (arithmetic unit)

Claims (3)

A gas chamber of a constant volume that is disposed in a vibration transmission path that is transmitted from the road surface through the tire to the vehicle body and that is blocked by the solid material,
A sound pressure detecting means disposed in the gas chamber for detecting sound;
A road surface state detection apparatus comprising: an arithmetic unit that obtains information related to a road surface state where the vehicle is traveling by performing frequency analysis on the output of the sound pressure detection unit. The arithmetic device detects the sound pressure level corresponding to at least one of the high and low two peak frequencies in the output of the sound pressure detecting means, the frequency difference thereof, and the two peak frequencies, and the sound pressure level. The road surface state detection device according to claim 1, wherein information related to a road surface state where the vehicle is traveling is obtained based on the frequency difference. The road surface condition detection device according to claim 1 or 2, wherein a frequency band of sound detected by the sound pressure detection means is set to 100 [Hz] to 300 [Hz].

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