JPH04105082A - Road condition detecting device - Google Patents

Abstract

PURPOSE:To enable a road condition to be accurately detected by extracting a signal having a frequency shifted to such an extent as corresponding to a Doppler shift computed from the frequency of an ultrasonic wave transmitted to the road on the basis of a ground speed. CONSTITUTION:A transmitter 21 sends an ultrasonic wave having a frequency of a f0 to a road on the basis of an electrical signal having a frequency of f0 generated with an ultrasonic wave supply source 10. A receiver 22 is so positioned as to be capable of receiving irregular reflection waves giving an effective Doppler shift, among reflection waves generated on the road. The received ultrasonic waves are converted into electrical signals and amplified in a preamp circuit 31. In a tracking filter 32, only signals having a frequency of f0 + DELTAf (Doppler shift) are extracted from pure irregular reflection waves from the road. The aforesaid DELTAf is computed on the basis of a vehicle speed V detected with a speed sensor 23. The noise component of the signal is eliminated with a low pass filter 35 via an AM detection circuit 34, thereby obtaining a signal D accurately detecting a road condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a road surface condition detection device, and particularly to a road surface condition detection device using ultrasonic waves.

[Conventional technology]

When controlling the driving of a vehicle, the condition of the road surface on which the vehicle is currently traveling is an important control parameter. As a physical quantity expressing the road surface condition, a value quantitatively indicating the degree of unevenness of the road surface is usually used.

Generally, two types of devices are used as devices for detecting such road surface conditions. The first device is a device that uses ultrasonic pulses, which emits ultrasonic pulses from a direction perpendicular to the road surface and receives reflected pulses from the road surface.

By measuring the round trip time of this pulse, the distance between the vehicle and the road surface is determined. The unevenness of the road surface is
It is detected as a minute change in the distance between the vehicle and the road surface. The second device emits ultrasonic waves as continuous waves instead of pulses from a direction perpendicular to the road surface, and receives reflected waves from the road surface. Then, information regarding the unevenness of the road surface is obtained based on the intensity of this reflected wave. In this case, the less uneven the road surface is, the smoother it is, the stronger the reflected waves will be.

A detection device based on this principle is known, for example, from Japanese Patent Application Laid-Open No. 62-12
It is disclosed in Japanese Patent No. 6377.

[Problem to be solved by the invention]

However, the conventional device described above has a problem in that it cannot accurately detect the road surface condition.

In the first device described above, since the distance between the vehicle and the road surface changes due to vibrations of the vehicle, the influence of the vehicle vibrations directly appears as a detection error. On the other hand, the second device described above does not detect the distance between the vehicle body and the road surface, so it is less susceptible to the influence of vehicle body vibrations. However,
Detecting the intensity of pure reflected waves from the road surface is
Another problem is that it is technically very difficult to perform accurate detection in practice. In other words, the ultrasonic waves detected by the receiver include not only pure reflected waves from the road surface, but also ultrasonic waves that have come around from the transmitter, multiple reflected waves that have reflected multiple times between the road surface and the vehicle body, etc. Noise waves are mixed in, and it is difficult to distinguish pure reflected waves from other noise waves.

Therefore, the ultrasonic intensity detected by the receiver is not the intensity of pure reflected waves, but contains errors.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a road surface condition detection device that can accurately detect road surface conditions.

[Means to solve the problem]

The present invention provides a road surface condition detection device that includes means for transmitting ultrasonic waves of frequency f towards the road surface, means for receiving ultrasonic waves diffusely reflected from the road surface, and means for receiving the transmitted ultrasonic waves based on the speed with respect to the road surface. means for calculating a Doppler shift amount Δf; means for extracting a signal of a frequency shifted from the frequency fo by the Doppler shift amount false from the received ultrasonic wave; and outputting a signal indicating a road surface condition based on the intensity of the extracted signal. A means for doing so is provided.

[For production]

When ultrasonic waves are emitted onto a road surface, reflected waves and diffusely reflected waves (scattered waves) are generated on the road surface. To clearly distinguish between the two,
Hereinafter, in this specification, a normal reflected wave will be referred to as a regular reflected wave. The generation ratio of specularly reflected waves and diffusely reflected waves is determined by the unevenness of the road surface. In other words, if the road surface is smooth like a mirror, most of the waves will be specularly reflected. On the other hand, if the surface has a so-called rough surface with a large number of concavities and convexities on the order of the wavelength of the ultrasonic wave, most of the reflection will be diffused. Therefore, both the specularly reflected wave and the diffusely reflected wave have information indicating the road surface condition. Conventional devices detect road surface conditions using specularly reflected waves. In contrast, the device of the present invention detects the road surface condition using diffusely reflected waves. A characteristic of the diffusely reflected waves is that when the vehicle is running, it undergoes a Doppler shift depending on the vehicle speed. Therefore, by calculating the Doppler shift amount according to the vehicle speed, the wavelength of the pure diffusely reflected wave from the road surface can be determined. In the device of the present invention, only the wavelength component of the pure diffusely reflected wave is extracted from the ultrasonic waves detected by the receiver, and its intensity is determined. Therefore, it is possible to accurately detect the road surface condition by eliminating errors caused by noise waves such as ultrasonic waves that have come around from the transmitter and multiple reflected waves that have been reflected multiple times between the road surface and the vehicle body.

〔Example〕

The present invention will be described below based on illustrated embodiments. FIG. 1 is a block diagram showing the configuration of a road surface condition detection device according to an embodiment of the present invention. The components illustrated here are:
All will be installed on vehicles. Ultrasonic source 10
is the frequency f. Based on this electric signal, the transmitter 21 transmits ultrasonic waves of frequency fo to the road surface. On the road surface, specularly reflected waves and diffusely reflected waves are generated based on this ultrasonic wave. The receiver 22 is placed at an appropriate position to receive the diffusely reflected waves. Generally, diffusely reflected waves spread out from the road surface in a hemispherical manner, so
The arrangement of the receiver 22 does not require precise directionality as is required when receiving specularly reflected waves.

However, it is preferable to arrange it so that it receives diffusely reflected waves that have undergone an effective Doppler shift. In this embodiment, an arrangement is adopted in which ultrasonic waves are transmitted diagonally downward and forward in the direction of travel of the vehicle, and diffusely reflected waves from approximately the same direction are received.

The receiver 22 converts the received ultrasound into an electrical signal,
This is given to the preamplifier circuit 31. Preamplifier circuit 3
1 amplifies this electrical signal. Now, let's consider the frequency components of this electrical signal. It is now assumed that the vehicle is traveling at a speed V, and due to this speed V, the pure diffusely reflected wave from the road surface undergoes a Doppler shift by +Δfv. In this case, the frequency of the pure diffusely reflected wave from the road surface is fo + Δfv, but the ultrasonic waves detected by the receiver 22 also include the ultrasonic waves with the frequency fo that have come around from the transmitter 21, and the ultrasonic waves between the vehicle and the road surface. The frequency f reflected multiple times between
Multiple reflected waves of o + nΔfv (n>2) are mixed. Therefore, the electrical signal amplified by the preamplifier 31 includes signals of these various frequency components. Therefore, in the tracking filter 32, the frequency f of the pure diffusely reflected wave from the road surface. Extract only the +Δfv signal. However, since this extracted frequency value changes depending on the vehicle speed V, the vehicle speed V is detected from the rotational speed of the tires by the vehicle speed sensor 23, and the Doppler shift amount Δfv is calculated based on the vehicle speed V at that time. In this way, the tracking filter 32
This filter has the function of moving the passing signal frequency band in synchronization with the vehicle speed V. After the frequency component of the pure diffusely reflected wave is thus extracted by the tracking filter 32, this signal is amplified by the amplifier circuit 33.

An example of the output signal of this amplifier circuit 33 is shown in FIG. 2(a).

Subsequently, the AM detection circuit 34 performs AM detection processing. That is, an AM detection signal whose voltage value is the amplitude of the signal output from the amplifier circuit 33 is generated. The result of performing AM detection processing on the signal shown in Figure 2 (a) is shown in Figure 2 (b).
). This AM detection signal contains noise components due to the influence of wind and the like. Therefore, by removing this noise component using the low-pass filter 35, an accurate road surface condition detection signal can be obtained. The result of noise removal performed on the signal shown in FIG. 2(b) is shown in FIG. 2(C). When the gain of this signal is large, it means that the intensity of the diffusely reflected wave is large, which indicates that the degree of unevenness of the road surface is large. For example, in the signal shown in Figure 2 (C), the signal gain decreases halfway, but such a signal is difficult to detect when moving from a highly uneven road such as a gravel road to a smooth road such as asphalt. This indicates information such as changes in road surface conditions. This road surface condition detection signal is input to a control unit 40 that controls the running of the vehicle. The control unit 40 performs processing such as changing brake control parameters based on this information regarding the road surface condition.

Finally, the results of a road surface condition detection experiment conducted using a prototype device of the above-described embodiment will be shown. FIG. 3 is a graph showing the results of a simulation experiment using this prototype device and the results obtained by calculation.

In this simulation experiment, instead of using an actual road surface as a detection target, a belt with an uneven surface was used as a detection target. The horizontal axis represents the depth of the belt groove to be detected (dragon), the vertical axis represents the signal strength (dB) of the road surface condition detection signal detected by the prototype device, and the frequency f of the ultrasonic wave to be transmitted. . , 200kHz, 100kHz, 40kHz,
The experimental results for each case are shown below. The value of each signal strength is OdB when the depth of the belt groove is about 2.0.
It has been standardized so that Each circular plot represents an actually measured value, and each curve represents a calculated value. The measured values almost match the calculated values, indicating that road surface conditions can be detected accurately.

FIG. 4 shows the results of a field experiment in which this prototype device was mounted on an actual vehicle. The type of road surface targeted for detection is clearly indicated next to each circular plot. The road surface condition on the horizontal axis of the graph indicates that the road surface becomes smoother as it goes to the right.

In this way, an accurate output that can sufficiently identify the type of road surface can be obtained in practical use.

〔Effect of the invention〕

As described above, according to the road surface condition detection device according to the present invention,
Only pure diffusely reflected waves from the road surface are frequency-selected and extracted, and the road surface condition is detected based on the intensity of these diffusely reflected waves, so it is not affected by vehicle vibration and errors caused by various noise waves are eliminated. Accurate detection that eliminates contamination becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of a road surface condition detection device according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of signals of each part in the device shown in FIG. 1, and FIG. FIG. 4 is a graph showing the results of a simulation experiment using the device shown in FIG. 1, and FIG. 4 is a graph showing the results of a practical experiment using the device shown in FIG.

Claims (1)

[Claims] means for transmitting ultrasonic waves of frequency f_0 toward the road surface;
means for receiving ultrasonic waves diffusely reflected from the road surface; means for calculating a Doppler shift amount Δf received by the transmitted ultrasonic wave based on the speed with respect to the road surface; means for extracting a frequency signal from the received ultrasound;
A road surface condition detection device comprising: means for outputting a signal indicating a road surface condition based on the intensity of the extracted signal.