JPH08334561A - Ultrasonic doppler-type ground speed measuring apparatus - Google Patents

Abstract

PURPOSE: To obtain an ultrasonic Doppler-type ground speed measuring apparatus by which a precise ground speed can be computed by receiving reflected waves of ultrasonic waves from road surface and finding the frequency and the magnitude of Doppler waves on the basis of received waves. CONSTITUTION: By using continuous waves which are output by an oscillator 1, an ultrasonic transmitter 2 transmits ultrasonic waves to a road surface. Reflected waves from the road surface which contains Doppler waves are received by an ultrasonic receiver 3 so as to be amplified 4. A multiplier 5 multiplies a received signal by the continuous waves of the oscillator 1, and only a Doppler signal is taken out by a low-pass filter 6. The output of the filter 6 is digital-converted digitally by a zero-crossing comparator 7, and a counter 8 finds a Doppler frequency. In addition, a voltmeter 9 finds an amplitude value on the basis of the output of the filter 6. At this time, the amplitude value differs according to the unevenness or the wet state of the road surface, and a frequency is dropped at a high speed or the like. Consequently, the relationship among a vehicle speed, the amplitude value and the frequency is computed in advance so as to be found, the relationship is stored in a vehicle- speed computation circuit 10, and a precise vehicle speed can be computed on the basis of the frequency and the amplitude value of the counter 8 and the voltmeter 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground speed measuring device using ultrasonic Doppler and is used for an ABS device for a mobile body such as an automobile or a navigation system.

[0002]

2. Description of the Related Art Conventionally, a ground speed measuring method using ultrasonic Doppler has been proposed. As shown in FIG. 2, this method measures the ground speed from the Doppler frequency of the received wave obtained by transmitting ultrasonic waves to the road surface.
When the speed of sound is c, the transmission / reception angle is θ, and the transmission frequency is f ₀ ,
The Doppler frequency f _d is theoretically obtained from the following equation (1).

F _d = (2Vcos θ / c + V · cos θ) f ₀ (1)

However, in actuality, there is a problem that the Doppler frequency becomes smaller than the above equation at high speed or on a wet road surface, and the speed is measured low. The cause of the error at high speed is that the sound speed is not so high compared to the vehicle speed, so that the transmission / reception point shifts in the time from transmission to reception, which has been clarified by analysis and experiments. Therefore, there is a method in which the deviation of the transmission / reception point is improved by using a correction formula obtained geometrically (JP-A-4-357486, JP-A-4-25298).
Five). However, because the transceiver is directional,
Many ultrasonic waves are transmitted in addition to the front of the transmitter. Therefore, it is necessary to correct not only the propagation path of the ultrasonic wave transmitted only to the front side but also the propagation path of the ultrasonic wave transmitted to the direction other than the front side.

Unlike dry asphalt roads, wet roads wet with rainwater and the like have no irregularities due to water, ultrasonic waves are specularly reflected, and scattered waves from roads are less likely to return, resulting in low S / N and Doppler. It becomes difficult to find the frequency. Further, it is experimentally known that the Doppler frequency is measured low and the variation is large as in the case of high speed. For this reason, conventionally, there is a method in which a vehicle speed is obtained by determining a wet state from frequency variations and removing low Doppler frequency components which are not scattered waves from the front of the sensor (Japanese Patent Laid-Open No. 2-176491). However, this has a practical problem that it takes time to obtain the frequency distribution and variations.

[0006]

The Doppler frequency is expressed by the equation (1).
The factors that are measured to be lower are (1) the positions of the transmitter and the receiver are misaligned because the ultrasonic wave propagation speed is not so high compared to the ground speed according to the ultrasonic wave propagation analysis performed by the present inventors. (2) Both ultrasonic transmitters and receivers have frequency characteristics and directivity, and the scattering characteristics of ultrasonic waves on the road surface differ depending on the shape. (3) There is a difference in ultrasonic wave reflection characteristics between a dry road surface and a wet road surface. I know.

What kind of problems will be described below with reference to the drawings. The above (1) has been conventionally pointed out as shown in FIG. 3, and since the transmission / reception angle changes due to the positional deviation of the transmitter and the receiver, the received wave has a Doppler frequency different from that of the equation (1). However, since an actual ultrasonic transmitter has directivity, as shown in FIG. 4, ultrasonic waves are transmitted to other than the front of the transmitter. In addition, since the receiver also has directivity, the area a where the output of the transmitter is high and the sensitivity of the receiver is high
The reflected waves from will be strongly received. The distribution of the reflected wave from the road surface is calculated using the intensity and the Doppler frequency.
As shown in the figure, it becomes lower than the Doppler frequency f _d of the equation (1). When the ground speed becomes higher, the area a becomes narrower, the received wave becomes weaker, and the Doppler frequency distribution becomes lower.

The reflection characteristics of the road surface include a specular reflection component that reflects in the direction opposite to the incident direction like a mirror surface and a diffuse reflection component that reflects in all directions. According to the results of the acoustic analysis performed by the present inventors, as shown in FIG. 6, when an ultrasonic wave is incident on a road surface having irregularities, if the shape shown in FIG. Such a reflected wave can be obtained. In the figure, λ is the wavelength of ultrasonic waves. FIG. 7 and FIG. 8 also show the case where the unevenness becomes small due to the entry of water. From this figure, the diffuse reflection is strong on the road surface with large irregularities, and the regular reflection is strong on the road surface with small irregularities or on a road surface wet with water. This tendency is more remarkable as the angle of incidence on the road surface is smaller. Since the transmitter and the receiver have directivity, when the unevenness is small or on a road surface with strong regular reflection such as a road surface wet with water, as shown in FIG. The reflected wave in the area becomes stronger. Therefore, considering the combination of the road surface reflection and the directivity of the transmitter and the receiver, the width and size of the Doppler distribution are as shown in FIG. 10, which is slightly lower than that of Equation 1 on a road surface with strong irregularities of reflected waves. It becomes even lower on a small uneven or uneven road surface where the reflected wave from is weak.

Therefore, in reality, due to the directivity of the transmitter and the receiver and the reflection characteristics of the road surface, the reflected wave becomes weak and the magnitude of the Doppler wave becomes small at high speed or on a road surface with small unevenness or a wet road surface. The frequency is also lower than that of equation (1). In order to reduce the deviation from the equation (1), the directivity of the transmitter and the receiver may be narrowed to reduce the overlapping area a, but when the ground speed is high, the high output area and the high sensitivity area are No overlapping (no area a exists) and no received wave can be obtained. For that purpose, the directivity of the transmitter or receiver should be narrowed.However, if the directivity of the receiver is wide, it is easy to pick up not only the transmitted waves but also other acoustic noise. Is desirable. The directivity of the transmitter is set so that an overlapping area a is generated in the speed measurement area.
Needless to say, the mounting positions and angles of the transmitter and receiver are relevant.

In actual transmitters and receivers, there is a region called a main lobe where the output sound pressure or the reception sensitivity is high and a region called a side lobe where the output sound pressure or the sensitivity is high other than the front. If the transmitter has side lobes,
As shown in, strong ultrasonic waves are transmitted in the side lobe direction b other than the frontal direction a. Therefore, the distribution of the Doppler frequency received at this time becomes large in the low part,
Decrease the average frequency of Doppler. Since such a side lobe causes a similar problem in the receiver, it needs to be sufficiently small in the front direction.

Further, as described above, since the Doppler frequency is not a single frequency but has a distribution, if the frequency characteristics of the receiver are not flat, the received wave will be changed as shown in FIGS. 12 (a) and 12 (b). The included Doppler distributions have different amplitudes. Therefore, since the Doppler frequency is different from the true value and a velocity error occurs, it is necessary to use a receiver having a flat frequency characteristic. As described above, in the ground speed measuring device using ultrasonic Doppler, the directivity of the transmitter, the directivity and frequency characteristics of the receiver, the reflection characteristics of the road surface, the distribution and magnitude of the received wave Doppler frequency It becomes lower than (1).

An object of the present invention is to consider the directivity of the transmitter, the directivity of the receiver and the frequency characteristics, and the smaller the magnitude of the Doppler wave from the road surface, the more the Doppler frequency becomes as expressed by equation (1).
It is an object of the present invention to provide an ultrasonic Doppler-type ground speed measuring device that is highly accurate in obtaining the ground speed from the magnitude and frequency of a Doppler wave by utilizing the fact that it becomes smaller.

[0013]

The ultrasonic Doppler type ground speed measuring device (the invention according to claim 1) of the first invention is shown in FIG.
As shown in, the ultrasonic wave transmitting means for transmitting ultrasonic waves at a predetermined angle to the road surface, the ultrasonic wave receiving means for receiving the reflected wave from the road surface, and the Doppler frequency calculation for obtaining the frequency of the Doppler wave from the received wave Means, a Doppler wave analysis means for obtaining the magnitude of the Doppler wave from the received wave, and a vehicle speed calculation means for obtaining the ground speed from the magnitude and frequency of the Doppler wave.

The ultrasonic Doppler type ground speed measuring device of the second invention (the invention according to claim 2) has an ultrasonic transmitting means having a wide directional characteristic with almost no side lobes and a narrow directional characteristic with almost no side lobes. This is a configuration having an ultrasonic wave reception means.

[0015]

The Doppler type ground speed measuring device of the first aspect of the present invention transmits ultrasonic waves to the road surface from the transmitting means and receives reflected waves from the road surface by the receiving means. The ground speed can be accurately obtained from the strength and the Doppler frequency. The Doppler frequency calculation means finds the frequency of the Doppler wave from the received wave, and the Doppler wave analysis means finds the magnitude of the Doppler wave. The vehicle speed calculation means can accurately obtain the ground speed from the Doppler frequency and the magnitude of the reflected wave from the road surface.

In the ultrasonic Doppler type ground speed measuring device of the second invention, the error of the Doppler frequency of the reflected wave from the road surface is small due to the characteristics of the ultrasonic wave transmitting means and the ultrasonic wave receiving means, and the ground speed can be accurately obtained. it can. That is, the ultrasonic Doppler type ground speed measuring device of the second invention is attached so that the transmission area determined by the directivity of the transmission means and the reception area determined by the directivity of the reception means overlap in the measurement speed area, The ground speed can be obtained with high accuracy from the intensity of ultrasonic wave reflection on the road surface and the Doppler frequency.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention will be described below with reference to the drawings.

[First Embodiment] As shown in FIG. 13, an ultrasonic Doppler type ground speed measuring apparatus according to the first embodiment includes an oscillator 1 and an ultrasonic transmitter 2 for transmitting a continuous wave output from the oscillator 1. When,
An ultrasonic receiver 3 for receiving a reflected wave from the road surface, an amplifier 4 for amplifying the received wave, a multiplier 5 for multiplying the received wave and the transmitted wave, a low-pass filter 6 for extracting a Doppler wave from the received wave, Zero cross comparator 7 for converting the Doppler wave into a digital signal, counter 8 for calculating the Doppler frequency, voltmeter 9 for calculating the amplitude of the Doppler wave, vehicle speed calculation for calculating and outputting the ground speed from the amplitude value of the Doppler wave and the Doppler frequency It consists of a circuit 10.

Next, the operation and effect of the ultrasonic Doppler type ground speed measuring apparatus of the first embodiment will be briefly described. In the ultrasonic Doppler type ground speed measuring device of the first embodiment, a continuous wave is output from the transmitter 1 to the ultrasonic transmitter 2, and the ultrasonic transmitter 2
Ultrasonic waves are transmitted to the road surface. The reflected wave from the road surface including the Doppler wave is received by the ultrasonic receiver 3, and this received signal is amplified by the amplifier 4. The received signal is multiplied by the continuous wave output from the oscillator 1 by the multiplier 5. Further, the output signal of the multiplier 5 is passed through the low-pass filter 6 to extract only the Doppler signal. The output of the filter 6 is digitally converted by the zero cross comparator 7,
The Doppler frequency is obtained by obtaining the frequency using the counter 8.

Further, the output of the filter 6 uses a voltmeter 7 to obtain an amplitude value. The amplitude value of the Doppler signal differs depending on the size of the unevenness of the road surface and the degree of wetting of the road surface (a condition in which the road surface unevenness is lost by being wet), and the Doppler frequency is lower than that of equation (1). The relationship between the vehicle speed and the amplitude value and frequency of the Doppler signal includes the directivity of the transmitter and the frequency characteristic of the output sound pressure, the directivity of the receiver and the frequency characteristic of the receiving sensitivity, the mounting position and angle of the transmitter and the receiver, and road reflection. It can be calculated in advance based on the characteristics and the attenuation rate of ultrasonic waves in the air. For example, according to the acoustic analysis result of the inventor, the relationships shown in FIGS. 14A and 14B are required. This relationship is stored in the vehicle speed calculation circuit 10, and the vehicle speed is calculated and output.

With the ultrasonic Doppler type ground speed measuring apparatus of the first embodiment, the amplitude value and the frequency of the Doppler wave are thereby reduced even at high speed or on a road surface with small unevenness or a road surface wet with rain. It is possible to estimate the vehicle speed from the vehicle and accurately calculate the vehicle speed, which is excellent in practical use.

[0021]

[Second Embodiment] Next, an ultrasonic Doppler type ground speed measuring apparatus of a second embodiment will be described with reference to FIG. The ultrasonic Doppler type ground speed measuring device of the second embodiment is almost the same as that of the first embodiment, and the description will be focused on the differences.
The ultrasonic transmitter 2 has a wide directivity with almost no side lobes as shown in FIG. 15, and the ultrasonic receiver 3 has a narrow directivity with almost no side lobes as shown in FIG. Here, “there is almost no side lobe” means that the side lobe is smaller than the main lobe by 30 dB or more. In addition, as shown in FIGS. 17 (a) and 17 (b), from the low speed to the highest speed in the measurement speed range, the mounting position is such that the high output area of the transmitter 2 and the high receiving sensitivity area of the receiver 3 overlap. , The angle is set. The operation from the transmitter 1 to the vehicle speed calculation circuit 10 is the same as that of the device of the first embodiment, so the description thereof is omitted.

The relationships shown in FIGS. 14 (a) and 14 (b) are the transmission output frequency characteristics and directivity of the transmitter, the receiving sensitivity and directivity of the receiver, the mounting position of the transmitter and the receiver, and It depends on the propagation attenuation of ultrasonic waves. In FIG. 14, only three representative correction curves are entered, and the ground speed is calculated by interpolating between them in the first embodiment device, but various road surface reflections are obtained by changing the road surface shape. If the acoustic analysis is performed on the characteristics and the relational expression is derived, the ground speed can be accurately obtained from the magnitude and frequency of the Doppler wave. Note that the relationships shown in FIGS. 14A and 14B are not limited to those in the above-described embodiment, but in addition to this, it is also possible to calculate and use a relational expression obtained by experiments without using acoustic analysis. Further, the relationship between the magnitude and frequency of the Doppler wave and the ground speed can be applied by directly making a lookup table and referring to it.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment device.

FIG. 2 is an explanatory view of the measurement principle of the ultrasonic Doppler type ground speed meter.

FIG. 3 is a diagram showing a deviation from a Doppler frequency calculation formula caused by movement of a transmitter and a receiver.

FIG. 4 is a diagram showing a deviation from a Doppler frequency calculation formula caused by directivity of a transmitter and a receiver.

FIG. 5 is a diagram showing the reflection characteristics of ultrasonic waves on the road surface.

FIG. 6 is a diagram showing how ultrasonic waves are reflected by uneven road surfaces.

FIG. 7 is a diagram showing a road surface shape and a situation where the road surface shape changes depending on water.

8 is a diagram showing the magnitude of reflected waves from a road surface having the shape of FIG.

FIG. 9 is a diagram showing that the Doppler frequency from a road surface having small unevenness or a road surface wet with water becomes low.

FIG. 10 is a diagram showing the Doppler frequency distribution and the size of a road surface having small unevenness or a road surface wet with water.

FIG. 11 is a diagram showing a deviation from a Doppler frequency calculation formula caused by side lobes of a transmitter and a receiver.

FIG. 12 is a diagram illustrating changes in Doppler frequency distribution caused by frequency characteristics of receiver sensitivity of a receiver.

FIG. 13 is a specific configuration diagram of the first embodiment device.

FIG. 14 is a diagram showing the relationship between the magnitude and frequency of Doppler waves from the road surface and the vehicle speed.

FIG. 15 is a diagram showing the directivity of the ultrasonic transmitter of the second embodiment.

FIG. 16 is a diagram showing the directivity of the ultrasonic receiver of the second embodiment.

FIG. 17 is a diagram showing how the transmission area of the transmitter and the reception area of the receiver of the second embodiment overlap when the ground speed changes.

[Explanation of symbols]

 1 Transmitter 2 Ultrasonic transmitter 3 Ultrasonic receiver 4 Amplifier 5 Multiplier 6 Low-pass filter 7 Zero cross comparator 8 Counter 9 Voltmeter 10 Vehicle speed calculation circuit

Claims (2)

[Claims] 1. An ultrasonic wave transmitting means for transmitting an ultrasonic wave at a predetermined angle to a road surface, an ultrasonic wave receiving means for receiving a reflected wave from the road surface, and a Doppler frequency calculation for obtaining a frequency of a Doppler wave from the received wave. Means, a Doppler wave analyzing means for obtaining the magnitude of the Doppler wave from the received wave, and a ground speed calculating means for obtaining the ground speed from the magnitude and frequency of the Doppler wave, the ultrasonic Doppler ground speed Measuring device. 2. The ultrasonic wave transmitting means according to claim 1, has a wide directional characteristic with almost no side lobes, and the ultrasonic wave receiving means has a narrow directional characteristic with almost no side lobes, and within the measurement speed range. An ultrasonic Doppler type ground speed measuring device, characterized in that the ultrasonic Doppler type ground speed measuring device is mounted so that a transmission area determined by the directivity of the ultrasonic transmission means and a reception area determined by the directivity of the ultrasonic reception means overlap.