JPS6213632B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a vehicle speed measuring device that applies the Doppler effect using ultrasonic waves. In particular, the present invention relates to a vehicle speed measuring device that applies the Doppler effect using ultrasonic waves. In particular, it is possible to calculate the vehicle speed at each fixed Doppler wave number from the relationship between the vehicle speed and the Doppler frequency. This is what I did.

When ultrasonic waves are emitted from an ultrasonic transducer installed in the direction in which a vehicle on the road is moving, the frequency of the reflected waves received after being reflected by the vehicle will vary depending on the speed of the vehicle. deviate. This is well known as the Dotsupura effect.

The difference in frequency between the reflected wave and the emitted wave, ie, the Doppler frequency _d , is generally expressed by the following equation.

_d = 2・V・cosφ/C−V・cosφ・_p ……
(1) Here, _p is the emitted wave frequency, C is the speed of sound, V is the vehicle speed, and φ is the angle between the vehicle traveling direction and the received reflected wave.

From equation 1, vehicle speed V is as follows: V= _d / _d + 2・_p・C/cosφ (2) However, calculating vehicle speed V from equation 2 requires a complicated arithmetic circuit. Conventionally, vehicle speed has been measured using a simplified calculation method in which C≫V·cosφ is assumed in Equation 1. The vehicle speed measurement value V _s at this time is V _s = _d /2· _p ·C/cosφ (3), which is obtained as a value proportional to the Doppler frequency _d and can be easily calculated. However, the vehicle speed measurement error at this time is C=
Since it is 346m/sec, the vehicle true speed V=160Km/
When h and cosφ=0.9, it is approximately 13%.

In addition, the Doppler frequency dm in the microwave Doppler radar vehicle speed measuring device that utilizes the Doppler effect of microwaves is expressed by the following equation.

dm=2・V・cosφ/Cm−V・cosφ・_pn
...(4) Here, _pn is the microwave oscillation frequency, Cm is the microwave propagation speed, and Cm=3×10 ⁸ (m/
sec), so it can be considered that Cm≫V・cosφ, and the vehicle speed V is V= _dn /2・_pn・Cm/cosφ...(5), and the vehicle speed can be calculated using the same calculation method as Equation 3. I can do it. There are many practical examples of vehicle speed calculation methods of this microwave radar vehicle speed measuring device, and three types of calculations can be performed using these methods. An example of the conventional method will be described below with reference to FIGS. 1 and 2.

The example shown in FIG. 1 is called the fixed time method, and is a method in which the speed is calculated in proportion to the Doppler wave number counted within a certain period of time. The Doppler signal is waveform-shaped by a Schmitt circuit 1, and based on the pulse waveform, a continuous detection circuit 2 outputs only continuous Doppler signal pulses. The counter 3 counts these Doppler signal pulses during the gate time width T _s that the counting time generating circuit 4 outputs. By setting this gate time width T _s to T _s =C/2· _p ·cosφ (6), the count value of the counter 3 becomes the vehicle speed V _s as it is. For example, _p = 20kHz,
If cosφ=0.9 and C=346 m/sec, the gate time width T _s =34.6 m sec and the count value becomes V _s (Km/h).

The example shown in FIG. 2 is called the constant wave method, and is a method in which the time required to count a constant Doppler wave number is measured and the reciprocal thereof is determined. The Doppler signal is waveform-shaped by a Schmitt circuit 5, and the pulse waveform thereof is outputted by an n-wave continuous detection circuit 6 as a time width pulse n/ _d of n consecutive Doppler signal pulses. The counter 8 counts the clock _c output from the clock generation circuit 7 during the gate time 〓.
The counted value is n/ _d・_c . The constant generation circuit 10 sends out a constant K expressed as K= _n.c / _2.p.C /cosφ (7). However, _p
is the emitted wave frequency, C is the speed of sound, and φ is the vehicle speed.

The division circuit 9 divides the constant K of the constant generation circuit 10 by the signal n/ _d · _c of the counter 8, and sends out an output D as a result. That is, becomes. Furthermore, the denominator and numerator of equation 9 are (2・_p・
_d ), D= _d /2・_p・C/cosφ (10), and Equation 10 is exactly the same as Equation 3, and the vehicle speed _Vs can be obtained.

In the above two conventional examples, since the calculation is based on the three formulas, vehicle speed measurement errors are inevitable, and as mentioned above, the errors are approximately
It will be 13%.

The present invention enables highly accurate vehicle speed measurement by calculating vehicle speed using two more precise equations. FIG. 3 is a block diagram of an ultrasonic vehicle speed measuring device according to an embodiment of the present invention, and FIGS. 4a to 4g are signal waveform diagrams of the same embodiment. Examples thereof will be described below using FIG. 3 and FIGS. 4 a to 4 g. The Doppler signal is waveform-shaped by the Schmitts circuit 11 (Fig. 4a), and its pulse waveform is output as a time width pulse n/ _d of n consecutive Doppler signal pulses by the n-wave continuous detection circuit 12 (Fig. 4b). do. The timer 13 outputs a time width pulse n/2· _p (FIG. 4c). The gate time switching circuit 14 first passes the output 〓 of the n-wave continuous detection circuit 12, and when the output n/ _d ends, starts the timer 13 and subsequently passes the output n/2/ _p of the timer 13. It is something. Therefore, the gate time switching circuit 14 outputs a pulse with a time width of (n/ _d + n/2· _p ) (FIG. 4d).

The counter 16 counts the clock _c output from the clock generation circuit 15 (Fig. 4e) during the gate time (n/ _d + n/2· _p ), and the counted value is (n/ _d + n/2·p). _p )・_c . The division circuit 17 divides the output K (Fig. 4) of the constant generation circuit 18 by the output of the counter 16, and the output Q is becomes.

Here, if the value of K is K=n・_c /2・_p・C/cosφ...(12) Furthermore, multiplying the denominator and numerator by (2・_p・_d ) gives Q= _d / _d + 2・_p・C/cosφ... (14), and equation 14 becomes exactly the same as equation 2, and from equation 14 , a precise vehicle speed V (Fig. 4g) can be obtained.

As is clear from the above embodiment, the present invention obtains the n/ _d signal from the Doppler frequency _d using an n-wave continuous detection circuit, and uses the gate time switching circuit to obtain the n/ _d and timer n/ _2p signals. Synthesize (n
/ _d + n/2 _p ) signal, and use the counter to calculate the above (n/2 p ) signal.
_d + n/2 _p ) by the clock generation circuit signal _c to obtain (n/ _d + n/2 _p )・_c , and the division circuit multiplies the constant generation circuit signal (K=n _c /2 _p・C /cosφ
) by the signal of the counter, the vehicle speed can be calculated with high precision using _{a relatively} simple device _.
This has the effect that φ can be determined.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional ultrasonic vehicle speed measuring device, and FIG. 3 is a block diagram of an ultrasonic vehicle speed measuring device according to an embodiment of the present invention.
FIG. 4 is a signal waveform diagram of the same embodiment. 11... Schmitt circuit, 12... N wave continuous detection circuit, 13... Timer, 14... Gate time switching circuit, 15... Clock generation circuit, 16... Counter, 17... Division circuit, 18... Constant generator circuit.

Claims (1)

[Claims] 1. A Schmitt circuit that inputs the reflected wave of an ultrasonic wave emitted toward a moving object and converts this Doppler frequency _d into a rectangular wave, and a Schmitt circuit that converts the signals of this Schmitt circuit into a fixed number (n At the end of the counting time width n/ _d , a fixed number (n waves ₎ of the oscillation frequency _2p signal of the oscillation circuit is stored. ), and the timer that sends out the counting time width n/ _2p , the counting time width n/ _d of the n-wave continuous detection circuit, and the counting time width n/ _2p of the above timer are added to obtain a composite time width ( A gate time switching circuit that sends out the signal (n/ _d + n/2 _p ), and a clock for the above synthetic time width (n/ _d + n/2 _p ).
A counter that sends out (n/ _d + n/2 _p )・_c by passing _c , and a constant K (=n _c /2 _p・C/cos) (where _p : firing frequency, C: sound speed,: vehicle A constant generating circuit that sends out the angle between the traveling direction and the received reflected wave) and the constant K of the constant generating circuit as the signal of the counter (n/ _d + n/2 _p )
・Divide by _c , vehicle speed V= _d / _d + 2・_p・C/c
An ultrasonic vehicle speed measuring device comprising a division circuit for determining os.