JPH01314987A - Doppler type speedometer - Google Patents

Abstract

PURPOSE:To always enable highly accurate speed measurement even if an S/N of a reflected beam may be worsened being affected by conditions of an ultrasonic beam reflecting surface by providing a bandpass filter synchronizing with a center frequency of a Doppler frequency. CONSTITUTION:A transmitter 10 carried on a vehicle is given a signal with a specified frequency generated by an oscillation circuit 14 from a driving circuit 16 to radiate an ultrasonic beam with a specified transmission frequency at an angle of inclination to a moving surface. Reflected beam of the ultrasonic beam is received 12 to be amplified 18, a receiving signal thereof is applied to a mixer 20 to be mixed with signals of transmission and reception frequencies of signals from the circuit 14. Then, a difference between the transmission and reception frequencies, namely, a signal of a Doppler frequency alone is picked up with a low-pass filter 22. This signal is turned to a DC voltage signal via an F-V converter 26 or a voltage synchronization type bandpass filter 28 and an F-V counter 32. A higher one of the voltages is selected 34 and the filter 28 has the feed back control of a center frequency by the signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a Doppler speedometer that detects the moving speed of a vehicle such as an automobile or other moving object using the Doppler effect.

(Prior art) An ultrasonic beam is emitted from a moving object such as an automobile onto a moving surface such as a road surface, the reflected beam from the moving surface is received, and the ultrasonic beam is detected by a detection means such as a low-pass filter. Detects the difference between the transmitting frequency and receiving frequency,
Doppler speedometers that detect the speed of a moving object based on this frequency difference, that is, the Doppler frequency, have been known for a long time.
No. 0-76678.

When a Doppler speedometer is used in a vehicle such as an automobile, the reflecting surface of the ultrasonic beam is the ground, which is the road surface on which the vehicle travels, so it is called a Doppler ground vehicle speedometer.

(Problem to be Solved by the Invention) In a Doppler speedometer, the S/N ratio of the reflected beam fluctuates under the influence of the state of the reflecting surface of the ultrasonic beam. When the driving road surface, which is the reflecting surface of the ultrasonic beam, changes from a dry state to a wet state due to rain and snow, or a frozen state, the received waves weaken and the S/N ratio deteriorates. The center frequency of the Doppler frequency changes accordingly. This phenomenon can be observed from the power spectrum of the signal after passing through the low-pass filter.

Because of the above-mentioned situation, if the detection means is only a simple low-pass filter, the speed measurement accuracy will be reduced depending on the type of reflection surface of the ultrasonic beam.

(Object of the Invention) In view of the above-mentioned problems, the present invention has been made to
It is an object of the present invention to provide an improved Doppler speedometer in which speed measurement accuracy does not deteriorate even if the N ratio deteriorates due to the influence of the state of the reflecting surface of the ultrasonic beam.

(Means for Solving the Problems) In order to achieve the above objects, the Doppler speedometer according to the present invention includes a bandpass filter tuned to the center frequency of the frequency difference, that is, the Doppler frequency, as a detection means. It is characterized by

The bandpass filter that is tuned to the center frequency of the Doppler frequency may be a voltage-tuned bandpass filter that changes the center frequency of the bandpass filter by an external voltage, and this external voltage control changes the center frequency of the bandpass filter depending on the output of the bandpass filter itself. By doing so, a self-tracking tracking bandpass filter is constructed.

(Description of Examples) The present invention will be described in detail below based on Examples with reference to the accompanying drawings.

FIG. 1 shows one embodiment of a Doppler speedometer according to the present invention. In FIG. 1, reference numeral 10 indicates a transmitter, and reference numeral 12 indicates a receiver, which are mounted on the vehicle in the case of a vehicle-mounted speedometer used in a vehicle such as an automobile.

The transmitter 10 may be an ultrasonic speaker, which:
A signal of a predetermined frequency generated by the oscillation circuit 14 is transmitted to the drive circuit 1.
6, an ultrasonic beam having a predetermined transmission frequency is emitted at a predetermined angle of inclination to a moving surface, for example, a running road surface.

The receiver 12 may be an ultrasound microphone adapted to receive the reflected beam of the ultrasound beam emitted by the transmitter 10 towards the moving surface.

The reflected beam received by the receiver 12 is amplified by an amplifier 18 and input to a hybridizer 20.

Hybridizer 20 may be a multiplier, for example, and receiver 12
It receives a received signal from the oscillator circuit 14 and a signal having the same frequency as the transmitting frequency from the oscillation circuit 14, mixes the signal at the transmitting frequency and the signal at the receiving frequency, and outputs this mixed signal to the low-pass filter 22. There is.

The low-pass filter 22 receives the mixed signal and extracts only the difference component signal between the transmitting frequency and the receiving frequency, that is, only the Doppler frequency signal. The power spectrum of this Doppler shift component signal is
Illustrated in the figure.

The output signal of the low-pass filter 22, ie, the Doppler frequency signal, is provided to a comparator 24 and a voltage-tuned band-pass filter 28, respectively.

Comparator 24 is a pulse width modulator that pulses the low-pass filter output signal (Doppler frequency signal); The output signal, ie, the Doppler frequency signal, is pulsed. The comparator 24 is the S/N of the Doppler frequency signal.
It is configured as a hysteresis type comparator which has a relatively large dead zone due to hysteresis in consideration of times when the ratio is poor, and a specific example of pulsing the Doppler frequency signal by this comparator 24 is shown in FIG. . In FIG. 3, (a) shows the Doppler frequency signal which is the low-pass filter output signal, and (b) shows the pulse width modulation signal which is the output signal of the comparator 24. The output signal of the comparator 24, ie, the pulse width modulation signal, is applied to the F-V converter 26.

The F-V converter 26 converts the pulse width modulation signal from the comparator 24 into a DC voltage signal with a proportional characteristic as shown in FIG. 5 depending on the pulse period, that is, the frequency. There is.

The output signal of the F-V converter 26 is applied to a selection circuit 34.

The selection circuit 34 receives DC voltage signals from each of the F-V converter 26 described above and another F-V converter 32 described below, selects the higher voltage signal among them, and converts it into a voltage. The signal is output to a tuned bandpass filter 28.

The voltage-tunable band-pass filter 28 is a type of band-pass filter that changes the center frequency of the band-pass filter, in other words, the band-pass frequency range, depending on an external voltage, and changes the band-pass frequency range by the DC voltage signal from the selection circuit 34. It is designed to be set variably. An example of the center frequency characteristic of the bandpass filter 28 with respect to the input voltage from the selection circuit 34 is shown in FIG.

The output signal of the bandpass filter 28 is the comparator 3
It is set to be given to 0.

Comparator 30 is a pulse width modulator that pulses the analog signal from bandpass filter 28, and the comparator 30 pulses the analog signal from bandpass filter 28 with a relatively low second threshold B as shown in FIG. It is designed to convert analog signals into pulses. The comparator 30 has a relatively small dead zone compared to the other comparator 24, that is, it is configured as a hysteresis type comparator that can accurately pulse even a very small signal. This reduction of the dead zone is made possible because the output signal of the voltage-tunable band-pass filter 28 has an improved S/N ratio compared to that of the low-pass filter 22. A specific example of pulsing the analog signal by the comparator 30 is shown in FIG. In FIG. 4, (a) shows an analog signal that is the output signal of the bandpass filter 28, and (b) shows a pulse width modulation signal that is the output signal of the comparator 30.

The output signal of the comparator 30 is taken out as an analog output indicating the speed due to the Doppler effect, and is provided to another F-V converter 32.

The F-V converter 32 may be a converter equivalent to the F-V converter 26 described above, and is configured to generate a DC voltage proportional to the frequency of the pulse modulated wave signal from the comparator 3o. The F-V conversion characteristic of the F-V converter 32 is
- It may be equivalent to that of V converter 26, an example of which is shown in FIG. A DC voltage signal which is an output signal of the F-V converter 32 is applied to a selection circuit 34.

The selection circuit 34 selects the higher voltage of the DC voltage signals from the two F-V converters 26 and 32 and supplies it to the voltage-tuned bandpass filter 28 as a control voltage signal.

A specific circuit diagram of the selection circuit 34 is shown in FIG. 7, and is composed of a combination of two OP amplifiers 36 and 38 and two diodes 4o and 42.

With the above-described configuration, the F-V converter 26 converts the Doppler frequency signal from the low-pass filter 22 directly into F-V.
The F-V converter 32 performs F-V conversion on the Doppler frequency signal that has passed through the bandpass filter 28 to generate a Doppler frequency signal. A fine adjustment signal having a DC voltage corresponding to the voltage is generated. Selection diagram H@34
selects the signal with the higher voltage from the two F-V converters 26 and 32 and supplies it to the bandpass filter 28 as a control voltage, so the bandpass filter 28 operates in a closed loop. Tracking is performed under feedback control, and its center frequency is feedback-controlled. Further, the bandpass filter 28 is activated for tracking by the rough adjustment signal from the FV2 converter 26, and is prevented from deviating significantly from the tracking range.

The Doppler frequency signal that has passed through the bandpass filter 28 becomes a signal with an improved S/N ratio, as shown by the broken line in FIG. is set to a lower value than the second threshold B,
Accordingly, a highly accurate output corresponding to the center frequency of the Doppler frequency signal can be obtained.

The reflected beam from the reflecting surface of the ultrasonic beam used in the Doppler speedometer is influenced by the state of the reflecting surface, and the S
/N ratio, for example, in a Dotsupura ground vehicle speedometer,
When the driving road surface, which is the reflecting surface of the ultrasonic beam, changes from a dry state to a wet state due to rain and snow, or a mirror state due to frozen ice, the received waves weaken and the S/N ratio deteriorates. is known and is shown in FIGS. 8 to 10. Figure 8 shows the power spectrum of the Doppler frequency signal on each road surface at the same vehicle speed, and Figure 9 shows the signal waveform when the S/N ratio is relatively large, such as when driving on a dry asphalt road. , Fig. 10 shows the surface of a wet road or a mirror surface.
This shows a signal waveform when the /N ratio is relatively small.

Therefore, when the road surface on which the vehicle is running shifts from a dry asphalt road surface to a wet road surface or a mirror surface road surface, the output of the low-pass filter 22, that is, the Doppler frequency signal, has its amplitude greatly reduced, as shown in FIG. 3(a). death,
Almost all of the amplitude falls within the dead area of the comparator 24. For this reason, if the output signal of the low-pass filter 22 is converted into a pulse as it is, accurate vehicle speed measurement will not be possible when the vehicle is running on a wet road surface or a mirror surface road surface.

On the other hand, in the Doppler speedometer according to the present invention,
The comparator 30 converts the output of the bandpass filter 28, which is feedback-controlled, or in other words, a self-tracking tracking bandpass filter, into a pulse, so that the vehicle speed can be measured even when driving on a wet road or a mirror surface. It will be done accurately. That is, since the output of the bandpass filter 28 is a signal with an improved S/N ratio as shown in FIG. 4, the comparator 30 reduces the hysteresis, that is, the dead area. Accordingly, even a signal with a minute amplitude can be accurately pulsed, and vehicle speed can be measured accurately.

(Effects of the Invention) As described above, the Doppler speedometer according to the present invention is configured to include a bandpass filter tuned to the center frequency of the Doppler frequency, so that the S/N ratio of the reflected beam is lower than that of the reflected ultrasonic beam. It has the effect of always being able to accurately measure the speed even if it deteriorates due to the influence of the surface condition.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the Doppler speedometer according to the present invention, Fig. 2 is a graph showing the power spectrum of the Doppler frequency signal, and Fig. 3 (a) and (b) are extracted from a low-pass filter. Figure 4 is a graph showing the waveform of the Doppler frequency signal and its pulse modulation signal after passing through a bandpass filter, Figure 5 is a graph showing the waveform of the Doppler frequency signal and its pulse modulation signal.
Graph showing an example of F-V conversion characteristics of a -V converter, No. 6
The figure is a graph showing the center frequency characteristics of a voltage-tunable bandpass filter, Figure 7 is a circuit diagram of the selection circuit, Figure 8 is a graph showing the power spectrum of the Doppler frequency signal that is the low-pass filter output signal, and Figure 9 is a graph showing the power spectrum of the Doppler frequency signal that is the low-pass filter output signal. A graph showing the waveform of the Doppler frequency signal when the reflecting surface of the ultrasonic beam is a dry asphalt road surface. FIG. 10 shows the waveform of the Doppler frequency signal when the reflecting surface of the ultrasonic beam is a wet road surface or a mirror surface road surface. It is a graph. 10... Transmitter 12... Receiver 14... Oscillation circuit 20... Hybridizer 22... Low pass filter 28... Voltage tuned band pass filter Patent applicant
Nissan Motor Co., Ltd

Claims (1)

[Claims] 1. Emit an ultrasonic beam from a moving object to a moving surface, receive the reflected beam from the moving surface, use a detection means to detect the difference between the transmitting frequency and receiving frequency of the ultrasonic beam, and based on the frequency difference. A Doppler speedometer for detecting the speed of a moving object, wherein the detection means includes a bandpass filter tuned to the center frequency of the frequency difference.