JPH02293611A - Road surface state detector - Google Patents

Abstract

PURPOSE:To exactly discriminate the road surface state during traveling by transmitting ultrasonic waves to the road surface while sweeping a frequency and deciding the road surface state in accordance with the frequency and max. value of the reflected waves. CONSTITUTION:The ultrasonic waves are transmitted at a prescribed angle thetafrom a signal transmitter 1 driven by an oscillator 7 and a driving circuit 9 to the road surface 3. A signal transmitter 7 is so constituted as to automatically sweep the predetermined oscillation frequency. The reception signal from a signal receiver 5 is supplied via a preamplifier 13 to a multiplier 11 and only the frequency shifted from the frequency fo of the transmission signal is extracted and is outputted to a low-pass filter 19. The signal near the Doppler shift frequency is outputted from the filter 19 to a vehicle speed computing part 15 and a road surface state identifying section 17. The road surface state is identified in accordance with the SN ratio of the Doppler signal and the peak wavelength by a peak-hold circuit 21, an average processing circuit 25 and a road surface deciding circuit 27 in the identifying section 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a road surface condition detection device that is installed in a vehicle and detects the road surface condition while the vehicle is running.

(Prior art) As a conventional road surface condition detection device, for example, the
There is something like the one shown in No. 887. This road surface condition detection device is installed on a road in order to provide information on road surface conditions such as road ice to traveling vehicles. This device transmits sound waves while sweeping the frequency vertically from above the road, and records the intensity of the reflected waves as a time-varying pattern regarding the swept frequency. Considering that the intensity of the reflected wave changes depending on the transmission frequency and this pattern of change is correlated with the road surface condition, the device is preset with a pattern of change of the intensity of the reflected wave with respect to the transmission frequency. , the road surface condition is determined based on this.

(Problem to be Solved by the Invention) By the way, when the above-mentioned road surface condition detection device is installed in a vehicle to detect the road surface condition while the vehicle is running, a piezoelectric microphone, for example, is used as a means for transmitting and receiving a sound wave. However, due to its characteristics, there are the following problems.

First, in piezoelectric microphones, the physical properties of the materials that make up the microphone, such as the voltage output coefficient of the piezoelectric material, the Young's modulus of the adhesive that bonds the piezoelectric element and the vibration case, or the elastic modulus of the vibration case, change with temperature. They each have a temperature dependence for the resulting sensitivity, and in addition, this temperature dependence changes depending on the frequency of the sound wave.

In other words, the temperature dependence and deviation of the sensitivity of the microphone are such that, since the sensitivity of the microphone changes according to each frequency, the intensity of the reflected wave for each frequency changes depending on the temperature conditions of the microphone and the temperature conditions associated with the deployment in the vehicle. This will vary for each individual microphone. As a result,
If the intensity of the received signal for the frequency received by the microphone constituting the receiving means has a pattern that changes significantly depending on the road surface condition, it is possible to identify the road surface, but if the pattern changes only small, it is possible to identify the road surface. This may make it difficult to identify the state.

Next, when a road surface condition detection device is installed in a vehicle, the microphone is directly exposed to the outside world, so foreign matter may adhere to the surface of the microphone's vibration surface, and this foreign matter on the microphone's vibration surface may cause changes in sensitivity over time. Conceivable. In this case, it is necessary to appropriately change the road surface identification pattern that has been set in advance as the sensitivity of the microphone changes over time, but since the state of foreign matter adhering to the microphone changes depending on the environment (vehicle driving), etc. , it is impossible to predict changes in sensitivity characteristics. Therefore, it is not possible to appropriately change the pattern in accordance with changes in the sensitivity of the microphone over time, and there is a possibility that the road surface condition cannot be accurately identified.

The present invention has been made in view of the above, and an object of the present invention is to provide a road surface condition detection device that enables accurate identification of road surface conditions during driving even when installed in a vehicle.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention is a device that is installed in a vehicle and detects the condition of a road surface while the vehicle is running, which sweeps the frequency of sound waves at a predetermined angle with respect to the road surface. a transmitting means for transmitting the transmitted sound wave while transmitting the sound wave, a receiving means for receiving the reflected wave of the transmitted sound wave from the road surface, and an identifying means for identifying the road surface condition based on the detected frequency and maximum value of the received reflected wave. The gist is:

(Function) In the road surface condition detection device according to the present invention, the Doppler signal, which is a signal reflected from the road surface when a sound wave is transmitted from a running vehicle toward the road surface at a predetermined angle, is detected when the road surface is rough. focuses on the characteristic that the signal-to-noise ratio (S/N ratio) of the Doppler signal increases regardless of the vehicle's running speed, and the peak wavelength at which the S/N ratio is maximum shifts to the longer wavelength side. A sound wave is transmitted at a predetermined angle while sweeping the frequency, and the road surface condition is determined based on the detected frequency and maximum value of the reflected waves from the road surface.

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

First, the principle of the present invention will be explained.

A device for measuring the absolute vehicle speed of an automobile using the Doppler effect of ultrasonic waves has already been proposed (for example, Japanese Patent Application Laid-open No. 76678/1983).

This device transmits an ultrasonic wave having an ultrasonic frequency fO toward a road surface at a predetermined angle θ, and a reception microphone receives a portion of the ultrasonic signal reflected from the road surface. This received signal is shifted by fd (Doppler shift frequency) with respect to the frequency fO of the transmitted signal, and since this Doppler shift frequency fd has the relationship given by the following equation with respect to the absolute vehicle speed V of the automobile, The vehicle speed V is calculated based on the formula.

(d. 2 f o V cos θC-Vcos
θ where C is the speed of sound.

The inventor of the present application discovered the following experimental results while proceeding with the development of a ground vehicle speed sensor that utilizes the ultrasonic Doppler effect.

FIG. 2 shows an example of the experimental results, which are based on the experimental results shown in FIGS. 3 to 6.

FIGS. 3 and 4 show changes in the signal level with respect to the frequency of the received signal on a rough road surface and a smooth road surface, respectively, at a vehicle speed of 40 km/h and a transmission frequency of 115 KHz. Also, in Figures 5 and 6, the transmission frequency is 120K at a vehicle speed of 401aa/h.
Figure 3 shows the variation of the signal level with respect to the frequency of the received signal on a rough road surface and a smooth road surface, respectively, in Hz. Figure 2 shows the changes in the S/N ratio of the Doppler signal with respect to the frequency or wavelength in Figures 3 to 6. In Figure 2, when the road surface is rough, it is smooth. It can be seen that the S/N ratio of the Doppler signal is relatively higher than that of the road surface, and the wavelength indicating the peak value of the S/N ratio of the Doppler signal is shifted to the longer wavelength side. That is,
The road surface condition can be identified based on the SZN ratio and peak wavelength of the Doppler signal. Note that in FIGS. 3 to 6, the S/N ratio is the ratio between the signal strength S of the peak value of the Doppler signal and the background noise signal level N. In addition, FIGS. 2 and 3 to 6 are
The experimental results were obtained when the vehicle speed over the ground was 40 ks+/h, but the results were also obtained when the vehicle speed over the ground was 20 km/h, 60 km/h, and 80 km/h as shown in Figure 2.
The wavelength of the ultrasonic wave, which indicates the peak value of the SZN ratio of the Doppler signal on two road surfaces, hardly changes;
Wavelength equivalent to 15KHz, 120K on smooth road surface
Experimental results have shown that the S/N ratio of the Doppler signal takes a maximum value at a wavelength of Hz.

FIG. 1 is a diagram showing a configuration block of a road surface condition detection device according to an embodiment of the present invention. In the same figure, 1 is the road surface 3
3 is a transmitter consisting of a microphone that transmits ultrasonic waves (hereinafter simply referred to as "sound waves") at a predetermined angle θ to be. The transmitter 1 is driven and controlled by an oscillator 7 and a drive circuit 9, and the oscillator 7 is configured to automatically sweep the oscillation frequency with a predetermined oscillation frequency width and period. As a result, a sound wave having a frequency corresponding to the sweeping operation of the oscillator 1 is transmitted.

Note that the transmitter 1 operates within a predetermined transmission frequency range (
For example, the transmission sensitivity characteristic is flat from 106 KHz to 130 KHz (in other words, from 3.2 KHz to 2.6 KHz in terms of the wavelength of a sound wave).

A received signal from the receiver 5 is supplied to a multiplier 11 via a preamplifier 13. The multiplier 11 extracts only a signal having a frequency component reshifted from the frequency fO of the transmission signal from the supplied signal, and outputs the extracted signal to the low-pass filter 19. The low-pass filter 19 has a filtering width determined according to the value of the Doppler shift frequency fd, which is predetermined from the vehicle speed V of the automobile and the transmission angle θ of the sound wave from the transmitter 1.
9, a signal near the Doppler shift frequency is output to the vehicle speed calculation section 15 and the road surface condition identification section 17.

The vehicle speed calculation section 15 and the road surface condition identification section 17 identify the absolute vehicle speed and the road surface condition, respectively, based on the signal from the low-pass filter 19. The vehicle speed calculation unit 15 is detailed in the above-mentioned Japanese Patent Application Laid-Open No. 60-76678, so a description thereof will be omitted here.

The road surface condition identification section 17 has a configuration including a peak hold circuit 21, a frequency calculation circuit 23, an average processing circuit 25, and a road surface judgment circuit 27. The peak hold circuit 21 is
It holds the peak value of the signal from the low-pass filter 19, and the frequency calculation circuit 23 reads the frequency of the peak-held peak value. Specifically, since the sound wave frequency from the transmitter 1 is swept with a frequency of a predetermined width at a predetermined time timing, the frequency calculation circuit 23 generates a peak hold value that is measured in synchronization with the oscillator 7, for example. This is a circuit that measures the time until. Thereafter, the average processing circuit 25 calculates the average value of several frequency values indicating this peak hold value, and the road surface judgment circuit 27
Output to. This road surface judgment circuit 27 includes an average processing circuit 2
The frequency value from 5 (specifically, the time signal from the predetermined frequency at which oscillation starts to the frequency at which the peak value appears in the peak hold circuit 21) is converted into a voltage, and the magnitude of this voltage level is The condition of the road surface 3 is determined according to the condition of the road surface 3.

As a concrete determination by the road surface determination circuit 27, it is possible to divide the roughness of the road surface into, for example, four representative types, and identify the road surface based on the wavelength showing the peak of the S/N ratio of the Doppler signal. . That is, for example, the roughness of the sandy ground or asphalt road shown in FIG. The frequency of the sound wave that indicates the peak of the S/N ratio of the Doppler signal on a smooth road surface, such as an icy road that is close to a mirror surface, a water surface road, or a road surface where water has accumulated slightly on the asphalt surface and the asphalt surface has become flat. 122KH
z, and the frequency of the sound wave is 118 KHz when the road surface is rougher than a standard road surface, such as an uneven asphalt road or an uneven concrete road, and the frequency of the sound wave is 118 KHz. For rough road surfaces such as rough roads or uneven roads, the frequency of the sound waves is set to 115 KHz. On top of that. In the road surface determination circuit 27, there is a linear relationship in which the analog voltage resulting from conversion increases as the frequency of the sound wave increases, so the road surface condition is classified into four types according to the level of this analog voltage. It is to identify.

As an example of use when the road surface condition detecting device as described above is mounted on a car, the following modes can be considered, for example.

First, we will discuss how to use it as a device to switch the damping force of an automobile's shock absorber. An automobile occupant feels vertical acceleration depending on the roughness of the road surface, so when the road surface is rough, the change in damping force is increased depending on the action of the shock absorber. Specifically, the size of the oil inflow/outflow hole of the orifice that determines the damping force is set to be large depending on the roughness of the road surface. In this way, the vertical vibrations that occur when driving on rough road surfaces are absorbed by the damping force of the Shipqua absorber.

Next, the amount of oil pressure protrusion of the power steering system can be changed. The rougher the road surface, the worse the tires' contact with the ground, and the more likely they are to slip. In this case, if the road surface is rough for the same steering angular acceleration, the amount of hydraulic pressure of the power steering may be increased to improve steering performance.
By increasing the steering angle, the steering can be stabilized on slippery roads.

Another example is brake control. In this case,
Tires tend to slip when braking when the road surface is rougher than a certain level of roughness, and when the road surface is narrower than a certain level of roughness. In such a state, it is appropriate to take a longer braking oil pressure generation change time for the same brake stroke and gradually apply the brakes.

Therefore, according to this embodiment, the ultrasonic Since the road surface is identified by reading the frequency of the ultrasonic wave that indicates the peak value of the Doppler signal, it is possible to identify the road surface condition without being affected by the temperature dependence of the sensitivity of ultrasonic microphones, changes over time, etc. can be identified accurately.

Note that in this embodiment, the road surface condition is ultimately identified mainly based on the frequency that indicates the peak of the SZN ratio, but it is also possible to identify the road surface condition based on the difference in the relative level of the S/N ratio due to the difference in the road surface condition. Of course you can.

〔Effect of the invention〕

As explained above, according to the present invention, the Doppler signal, which is a reflected signal from the road surface when a sound wave is transmitted from a running vehicle toward the road surface at a predetermined angle, Focusing on the characteristic that as the signal-to-noise ratio (S/N ratio) of the Doppler signal increases regardless of the
The system sends sound waves at a predetermined angle to the road surface while sweeping the frequency, and judges the road surface condition based on the detected frequency and maximum value of the waves reflected from the road surface. It is possible to accurately identify the road surface condition.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIGS. 2 to 6 are diagrams for explaining the embodiment. 1... Transmitter 3... Road surface 5... Receiver 7... Oscillator 9... Drive circuit 11... Multiplier 13... Preamplifier 15... Vehicle speed calculation section 17... Road surface condition identification section 19...Low-pass filter 21...Peak hold circuit 23...Frequency calculation circuit 25...Average processing circuit 27...Road surface judgment circuit 2nd

Claims (1)

[Claims] This device is installed in a vehicle to detect the condition of the road surface while driving, and includes a transmitting means that transmits sound waves while sweeping the frequency at a predetermined angle with respect to the road surface, and a device that detects reflected waves of the transmitted sound waves from the road surface. 1. A road surface condition detection device comprising: a receiving device that receives a received reflected wave; and an identifying device that identifies a road surface condition based on a frequency and a maximum value detected for the received reflected wave.