JPH0357985A - Ground vehicle speed meter by ultrasonic doppler method - Google Patents

Abstract

PURPOSE:To enable reduction of an error due to variation of an irradiation angle without providing a special sensor or the like, by calculating a ground vehicle speed by using a real irradiation angle computed from a Doppler shift (DS) frequency and a Doppler signal band width. CONSTITUTION:A reflected signal wave of an ultrasonic signal 4 striking on a road surface 5 and reflected diffusedly therefrom is received 6 and a Doppler signal thereof is amplified 7 and then subjected to high-speed Fourier transform 13. From informations obtained by the fourier transform, subsequently, a DS frequency fd and a Doppler frequency band width fw are detected 14, 15. A real irradiation angle computing device 16 determines a real irradiation angle thetacontaining a variation due to the effect of pitching of a vehicle, by using an equation theta = tan<-1> {fw/2fd.Sin(2<1/2>alpha)} (where alpha denotes a half angle of a half value sound pressure in relation to a front main beam of an ultrasonic receiver 2). Next, a vehicle speed is calculated by a vehicle speed computing device 17 on the basis of the data on the angle, the DS frequency, a sound velocity and an oscillation frequency. Then a more precise measured speed value of which an error due to the pitching of the vehicle is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technique for improving the measurement accuracy of an ultrasonic Doppler ground vehicle speed meter. [Prior Art] As a conventional ultrasonic Doppler speed meter, there is one described in, for example, Japanese Patent Laid-Open No. 60-76678. Figure 2 is a block diagram showing the structure of the above speedometer. In FIG. 2, an oscillator 1 generates a signal of a predetermined wavelength,
The drive means 3 amplifies the above signal and drives the transmitter 2 with its output. The wave transmitter 2 is, for example, a piezoelectric type wave transmitter, and generates an ultrasonic signal 4 having the wavelength of the above signal, and radiates it toward the road surface 5.

Further, the receiver 6 receives a reflected wave signal obtained by diffusely reflecting the ultrasonic signal 4 upon hitting the road surface 5 .

Preamplifier 7 amplifies the received signal and sends it to multiplier 8. Multiplier 8 multiplies the oscillation frequency of oscillator 1 and the frequency of the received signal to find the difference between the two.

The output signal of this multiplier 8 is passed through a low-pass filter 9 to remove unnecessary noise, and then a zero-cross comparator 1
The waveform of the Doppler signal component is shaped by 0, and the frequency is read by the pulse counter 11. Then, the vehicle speed calculation circuit 12 converts the frequency of the Doppler signal into vehicle speed. The frequency changed by the above Doppler effect, that is, the Doppler shift frequency fd, changes the oscillation frequency to f0,
The sound speed is C, the vehicle speed is V, and the irradiation angle of ultrasonic waves to the road surface is θ.
In this case, fd:2vf.・cosθ/C ・It is shown by (1). In the above equation (1), since f0, C, and θ are each constant values, the vehicle speed V can be determined by determining the Doppler shift frequency fd. [Problems to be Solved by the Invention] In the conventional ultrasonic Doppler velocimeter as described above, the irradiation angle θ in the equation (1) is a fixed constant value.

However, in an actual vehicle. Since the angle between the vehicle body and the road surface changes due to the pitching of the vehicle, the angle of the transmitter 2 fixed to the vehicle body with respect to the road surface, that is, the irradiation angle θ changes in accordance with the pitching angle of the vehicle body. Therefore, there was a problem in that a total error of 8 m occurred due to the variation in the irradiation angle of 0. For example, in the case of a beam angle of 456, a total of 81! based on the variation of the pitching angle! l error is approximately ±4.5
%. In order to solve the above problem, it is sufficient to provide a sensor that detects the pitching angle of the vehicle body, calculate the actual illumination angle θ according to the pitching, and use that value to calculate the vehicle speed. However, providing the above-mentioned special sensors increases costs, and also increases the installation location, installation man-hours, inspection man-hours, etc. The present invention was made in order to solve the problems of the prior art as described above, and is an ultrasonic Doppler method that can reduce errors caused by fluctuations in the irradiation angle θ without adding any special sensors etc. The purpose is to provide a ground vehicle speedometer. [Means for Solving the Problems] In order to achieve the above object, the present invention is configured as described in the claims. That is, in the present invention, the actual illumination angle is calculated from the Doppler shift frequency and the bandwidth of the Doppler signal, and this is used to calculate the accurate ground vehicle speed. Both the Doppler shift frequency and Doppler signal bandwidth mentioned above can be calculated from the ultrasound signal received by a normal receiver, so by simply adding a simple electronic circuit, a special sensor etc. can be installed. Errors caused by variations in the illumination angle can be reduced without any problems. [Embodiment] FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, an oscillator 1 generates a signal of a predetermined wavelength,
The drive means 3 amplifies the above signal and uses its output to drive the transmitter 2. The transmitter 2 is, for example, a piezoelectric type transmitter, and generates an ultrasonic signal 4 having the wavelength of the above-mentioned signal, and radiates it toward the road surface 5. Further, the receiver 6 receives a reflected wave signal obtained by diffusely reflecting the ultrasonic signal 4 upon hitting the road surface 5 .

Next, the received Doppler signal is amplified by a preamplifier 7 and then Fourier transformed by a fast Fourier transformer 13. Further, the Doppler shift frequency detector l4 detects the Doppler shift frequency from the information obtained by Fourier transform, and the Doppler signal bandwidth detector 15 detects the Doppler signal bandwidth from the information obtained by Fourier transform.

Further, the actual irradiation angle calculation unit 16 calculates the irradiation angle of the sound wave with respect to the road surface from the Doppler shift frequency and the Doppler signal bandwidth (details will be described later). Further, the vehicle speed calculator 17 calculates the vehicle speed based on the actual illumination angle determined by the actual illumination angle calculator 16 and the Doppler shift frequency detected by the Doppler shift frequency detector 14. [Function] The transmitting sound frequency in the ultrasonic Doppler speedometer is set to f.
. , the irradiation angle of the sound wave with respect to the road surface is θ, the speed of sound is C, and the vehicle speed is V, then the Doppler shift frequency fd detected by the Doppler shift frequency detector l4 is approximately expressed as (
1) It is expressed as the formula. Furthermore, the bandwidth fw detected by the Doppler signal bandwidth detector 15 is expressed as in equation (2) below. Note that the bandwidth here is defined as the frequency width at which the peak level of the signal is -12 dB, but it is -6 dB or -3 dB.
It doesn't matter if it's dB. fw:4vf,・sinθ・sin (v'T a )
/ C − (2) In the above equation (2), α represents the angle at which the sound pressure is halved with respect to the main beam in front of the ultrasonic wave #l2, that is, the half-reduction half angle. This value α is a value unique to each transmitter. By the way, when pitching occurs in the vehicle body and the angle between the vehicle body and the road surface changes, the actual illumination angle becomes the reference illumination angle when the vehicle is at rest plus the pitching angle θ'. The measurement speed error due to this pitching is due to the irradiation angle of 45 when stationary.
'', it is expected to be approximately ±4.5%. In order to prevent deterioration of measurement accuracy due to the influence of pitching described above, in the embodiment shown in FIG.
) is used to determine the actual illumination angle θ, which is then used to calculate the vehicle speed. That is, (1) above, (
2) In the equation, the variable is fw. fd. Since they are v and θ, by eliminating V from both equations, θ can be expressed as fw and fd. and Doppler shift frequency detector 1
Doppler shift frequency fd obtained in step 4 and Doppler signal band obtained by Doppler signal bandwidth detector 15 @ f w
By using , we can find the actual illumination angle θ. To find θ by eliminating V from equations (1) and (2) above, calculate equation (1)/(2) and use the following (
3) It can be obtained as shown in the formula.

tanθ= f w/ (2 f d-sin(v'
T (E)) θ=tan-”(f w/ (2 f
d-sin(v'd-a))=(3) The actual illumination angle calculator 16 in FIG. 1 performs the calculation of equation (3) above.

The actual illumination angle θ obtained by calculating the above equation (3) is a value that also includes fluctuations due to the influence of pitching. Next, using the actual illumination angle θ obtained as described above and the value of the Doppler shift frequency fd obtained by the Doppler shift frequency detector 14, the vehicle speed V is calculated in the vehicle speed calculator 17 based on the following equation (4). v = fclc/2f, ・cos θ
The vehicle speed value obtained using equation (4) is a value that has been corrected for errors due to pitching. [Effects of the Invention] As explained above, the present invention is configured to calculate the actual illumination angle from the Doppler shift frequency and the bandwidth of the Doppler signal, and use it to calculate the ground vehicle speed. The effect is that it is possible to correct the variation in the illumination angle caused by the pitching of the vehicle, making it possible to measure speed with higher accuracy.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, and Figure 2 is a block diagram of a conventional ultrasonic Doppler ground speed meter. <Explanation of symbols> 1... Oscillator 2... Transmitter 3... Drive circuit 4... Ultrasonic wave 5... Road surface 6... Receiver 7... Preamplifier 8... Multiplier 9...Low-pass filter 10...Zero cross comparator 1l...Pulse counter l2...Vehicle speed calculation circuit 13...Fast Fourier transformer 14...Doppler shift frequency detector 15... Doppler signal bandwidth detector l6... Irradiation angle calculator 17... Vehicle speed calculator

Claims (1)

[Scope of Claims] Ultrasonic transmitting means for transmitting ultrasonic signals diagonally at a predetermined irradiation angle with respect to the road surface, ultrasonic receiving means for receiving the ultrasonic signals reflected from the road surface, and the above-mentioned method using the Doppler effect. An ultrasonic Doppler ground vehicle speedometer mounted on a vehicle, comprising: a first means for calculating a Doppler shift frequency from a received signal; a second means for calculating the bandwidth of the Doppler signal from the signal; a third means for calculating the actual illumination angle from the Doppler shift frequency and the bandwidth of the Doppler signal obtained by both of the above means; and the first means above. and a fourth means for calculating the ground vehicle speed from the Doppler shift frequency obtained by the above-mentioned Doppler shift frequency and the actual irradiation angle obtained by the third means, and corrects the variation in the irradiation angle caused by the inclination of the vehicle. Ultrasonic Doppler ground vehicle speed meter.