JPH05264733A - Ultrasonic doppler type ground speed meter - Google Patents

Abstract

PURPOSE:To obtain a ultrasonic Doppler type ground speed meter which can automatically adjust reception frequency of a ultrasonic signal into peak frequency of a wave receiver varying according to a temperature. CONSTITUTION:When an automobile speed calculating part 14A calculates speed zero, a transmission frequency sweep controlling part 14D is used to sweep and control the transmission frequency of a wave transmitter 3, and a received signal level at a wave receiver 6 at this time is observed via a signal level detection circuit 13 by a peak frequency determining part 14. Frequency when the received signal intensity is at the peak is made to be reception frequency of the wave receiver 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler type ground speed meter for measuring the speed of a moving body such as a vehicle utilizing the Doppler effect.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional ultrasonic Doppler type ground speed meter disclosed in Japanese Patent Laid-Open No. 2-287183. In FIG. 3, reference numeral 1 is an oscillator, 2 is a drive circuit for amplifying an oscillation signal from the oscillator 1, 3 is a wave transmitter driven by the drive circuit 2, and the wave transmitter 3 is for a moving body such as a vehicle. In front,
The ultrasonic wave 4 is applied to the road surface 5 obliquely from above. Reference numeral 6 is a wave receiver for receiving the ultrasonic waves reflected by the road surface 5. 7
Is a preamplifier that amplifies the reception output of the wave receiver 6, and 8 is an analog multiplier that multiplies the oscillation signal from the oscillator 1 and the reception signal of the wave receiver 6 to obtain a Doppler signal,
Reference numeral 9 is a low-pass filter that passes only the Doppler shift frequency component from the output signal of the analog multiplier 8. Reference numeral 10 is a zero-cross comparator 10 that waveform-shapes the Doppler shift frequency signal that has passed through the low-pass filter 9 and sends a pulse signal. A pulse counter for detecting the Doppler shift frequency by counting the pulse signals from the comparator 10, 12 is a calculation control unit using a CPU or the like, and includes a vehicle speed calculation unit 12A and a transmission frequency setting unit 12B.

In the conventional ultrasonic Doppler type ground velocity meter constructed as described above, when the ultrasonic wave 4 of the wave transmitter 3 driven according to the oscillation frequency signal is applied to the road surface 5,
A part of the ultrasonic waves diffusely reflected on the road surface 5 is received by the wave receiver 6. The reception output of the wave receiver 6 is input to the analog multiplier 8 through the preamplifier 7 and mixed with the oscillation signal from the oscillator 1 to extract a signal having a Doppler shift frequency corresponding to the difference between the two. This Doppler shift frequency signal is input to the zero-cross comparator 10 after passing through the low-pass filter 9, a waveform-shaped pulse signal is output from the zero-cross comparator 10, and this pulse signal is counted by the pulse counter 11 to obtain the Doppler shift signal. The frequency is detected. The vehicle speed calculation unit 12A of the calculation control unit 12 calculates the vehicle speed based on the count value of the pulse counter 11 and outputs it as the vehicle speed value. Further, in the transmission frequency setting unit 12B, the count value of the pulse counter 11, i.e. on the basis of the Doppler shift frequency f _d which corresponds to the vehicle speed, the frequency F of the ultrasound signal (the reception frequency of the receivers) is the vehicle speed to be received The frequency of the oscillator 1 (f ₀ = F−f _d ) is controlled so that it is always constant regardless of the relationship. That is, the oscillation frequency of the oscillator 1 is controlled according to the vehicle speed so that the frequency of the ultrasonic signal received by the wave receiver will be a constant value.

In FIG. 4, (a) shows the frequency characteristic of the wave receiver 6, and (b) shows the frequency characteristic of the wave transmitter 3.

In the fixed reception frequency type ultrasonic Doppler type ground velocity meter as described above, the transmission frequency of the wave transmitter is set so that the frequency of the ultrasonic signal received by the wave receiver is always constant regardless of the vehicle speed. Since the control is performed, as shown in FIG. 4A, a wave receiver having a frequency characteristic with a large Q value in which the reception frequency peaks at a predetermined frequency (130 kHz in the illustrated example) can be used as the wave receiver. .. On the other hand, the frequency dependency of the transmitted sound pressure of the wave transmitter has a flat characteristic within the used frequency band corresponding to the detected vehicle speed range, as shown in FIG. 4B. This is because the value of the transmission frequency is changed according to the value of the Doppler shift frequency, and as a result, the frequency of the received ultrasonic signal is kept constant.

In such a fixed reception frequency type speedometer, since the reception sensitivity at the resonance point of the receiver is high, there is an advantage that the strength of the reception signal can be increased.
Since the resonance Q value of the wave receiver is large, the wave receiver functions as a bandpass filter, and it is possible to remove frequency components unnecessary for vehicle speed calculation in reflected ultrasonic waves from the road surface. As a result, there is an advantage that only the frequency component that is truly necessary for vehicle speed calculation can be extracted.

[0007]

However, in such a conventional fixed reception frequency type ultrasonic Doppler type ground velocity meter, the measurement accuracy depends on the temperature of the wave receiver in the velocity meter for the following reason. There was a problem that

That is, the frequency at which the sensitivity of the receiver reaches its peak changes with temperature as shown in FIG. Therefore, in the above-described conventional example, the peak frequency at room temperature is stored in advance in the memory of the arithmetic control unit, and the transmission frequency control is performed so that the frequency of the received ultrasonic signal matches the set frequency.

FIG. 6A shows the relationship between the reception frequency, the reception sensitivity, and the Doppler signal level near room temperature (25 ° C.). In this case, the frequency of the received signal and the peak frequency of the sensitivity of the receiver coincide with each other, which enables accurate vehicle speed calculation. On the other hand, when the temperature of the wave receiver becomes lower than the normal temperature, the peak frequency of the wave receiver shifts to the low frequency side as shown in FIG. 5 (see the upper part of the graph of FIG. 6B). At this time, the transmission frequency setting unit operates so as to maintain the reception frequency at the peak frequency 130 kHz of the wave receiver at room temperature.

However, the peak frequency of the receiver is
Since it is lower than 130 kHz (129.1 kHz in the illustrated example) as shown in FIG. 6B, the spectrum of the ultrasonic signal dragged by it is also shown in FIG.
As shown by the solid line at the bottom of the graph in (b), 130 kHz
Is shifted to the lower frequency side. At this time, the value of the frequency counted by the pulse counter 11 coincides with the frequency (129.5 kHz in the illustrated example) that is the peak of the Doppler signal spectrum in the frequency space. That is, in this case, the Doppler shift frequency f _d becomes lower than expected, and thus the calculated vehicle speed becomes lower than it actually is. Similarly, when the temperature is high, the calculated vehicle speed becomes higher than the actual speed. Further, if the peak frequency is extremely deviated, the reflected signal is received at a frequency with low sensitivity of the receiver, so that the vehicle speed calculation accuracy may be deteriorated due to the decrease in reception intensity.

As a solution to such a problem, it is conceivable to detect the temperature of the wave receiver using a thermistor or the like and adjust the reception frequency of the wave receiver using this detected value. However, it is generally difficult to mount the thermistor inside the wave receiver and measure the temperature. In addition, it is necessary to add new parts to the vehicle speed calculation unit, which is disadvantageous in terms of cost. In addition, even if the temperature is actually corrected by such a thermistor, the temperature characteristics of the wave receiver have inherent variations, so the characteristics of the speedometer are not constant, and much adjustment is required. There is a problem of this.

An object of the present invention is to provide an ultrasonic Doppler type ground speed meter capable of automatically adjusting a reception frequency of an ultrasonic signal to a peak frequency (resonance frequency) of a receiver which changes according to temperature. To provide.

[0013]

The present invention will be described with reference to FIG. 1 showing an embodiment. In the present invention, the ultrasonic wave 4 is transmitted toward the front of the vehicle and obliquely to the road surface 5. An ultrasonic wave transmitting means 3, an ultrasonic wave receiving means 6 for receiving the ultrasonic wave reflected by the road surface 5, a Doppler signal detecting means 8 for extracting a Doppler signal from the transmitted ultrasonic wave and the received ultrasonic wave, and Doppler shift frequency calculation means 10 and 11 for calculating the Doppler shift frequency from the Doppler signal.
Then, the vehicle speed calculating means 14A for calculating the vehicle speed from the Doppler shift frequency, and the ultrasonic wave transmitted from the ultrasonic wave transmitting means 3 so that the frequency of the received ultrasonic wave is always constant based on the vehicle speed value. It is applied to an ultrasonic Doppler type ground speed meter equipped with frequency control means 14B for controlling the transmission frequency. And the above-mentioned purpose is the vehicle speed calculation means 14A.
When the vehicle speed is calculated to be zero, the transmission frequency sweep control means 14D operates to control the transmission frequency of the ultrasonic transmission means 3 within a predetermined frequency range, and the signal level for detecting the reception signal level of the ultrasonic reception means 6. The detection means 13 and the peak frequency determination means 14C that detects the frequency at which the received signal level detected by this signal level detection means 13 has a peak and uses this frequency as the reception frequency of the ultrasonic wave reception means 6
This is achieved by including and.

[0014]

The transmission frequency sweep control means 14D sweep-controls the transmission frequency of the ultrasonic transmission means 3 within a predetermined frequency range when the vehicle speed value becomes zero, and the signal level detection means 13 performs each sweep-controlled transmission. The received signal level of the ultrasonic receiving means 6 at the frequency is detected. Then, the peak frequency determining means 14C determines the frequency when the received signal level reaches a peak, and sets this frequency as the receiving frequency of the ultrasonic receiving means 6. Therefore, even if the resonance frequency of the ultrasonic wave receiving means 6 fluctuates due to a temperature change, the reception frequency can be matched with the resonance frequency following this.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the sake of easy understanding of the present invention. It is not limited to.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an ultrasonic Doppler type ground speed meter according to the present invention. In FIG. 1, the same components as those of FIG. 3 are designated by the same reference numerals, and the description thereof will be briefly described.

The ultrasonic Doppler ground velocity meter of this embodiment is similar to the speedometer of the conventional example described above, and includes an oscillator 1, a drive circuit 2, a wave transmitter 3, a wave receiver 6, a preamplifier 7, and an analog. In addition to having a multiplier 8, a low-pass filter 9, a zero-cross comparator 10 and a pulse counter 11, a newly provided reception level detection means 13 and a newly added receiver peak frequency determination section 14C and transmission frequency sweep control section 14D are provided. The arithmetic and control unit 14 is provided.

The signal level detection circuit 13 is a means for detecting the level of the received signal output from the preamplifier 7, and as an example, a RMS / DC converter for converting the effective value of the received signal into a DC voltage value. Composed. The arithmetic and control unit 14 is composed of a microcomputer including a CPU, and has a vehicle speed arithmetic unit 14A for arithmetically calculating the vehicle speed from the count value (Doppler shift frequency) of the pulse counter 11 and the pulse counter 11 as in the conventional example. The transmission frequency setting unit 14B is provided to control the frequency of the oscillator 1 so that the reception frequency becomes constant based on the count value (Doppler shift frequency). Receiver peak frequency determination unit 14C
Determines the peak frequency of the wave receiver 6 from the reception level signal output from the signal level detection means 13 and the transmission frequency output from the transmission frequency sweep control unit 14D. The transmission frequency sweep controller 14D operates when the vehicle speed calculator 14A calculates the vehicle speed of 0 km / h, sweeps a predetermined transmission frequency range at a predetermined sweep speed, and outputs a sweep command signal at that time to the oscillator 1. To be done.

In the correspondence between the above embodiment and the claims, the wave transmitter 3 is an ultrasonic wave transmitting means, the wave receiver 6 is an ultrasonic wave receiving means, the analog multiplier 8 is a Doppler signal detecting means, and a zero cross. The comparator 10 and the pulse counter 11 are Doppler shift calculating means, the signal level detecting circuit 13 is the receiving signal level detecting means, the vehicle speed calculating section 14A is the vehicle speed calculating means, the transmission frequency setting section 14B is the frequency controlling means, and the receiver peak. The frequency determination unit 14C constitutes a reception peak frequency determination unit, and the transmission frequency sweep control unit 14D constitutes a transmission frequency sweep control unit.

Next, the operation of this embodiment will be described.
During a normal vehicle speed detection operation, the same operation as the conventional example is performed.
When the vehicle speed calculation unit 14A detects the zero vehicle speed, the operation of the transmission frequency setting unit 14B is stopped based on the command from the vehicle speed calculation unit 14A at that time. Then, instead, the transmission frequency sweep control unit 14D starts the operation. Here, a predetermined transmission frequency region is swept at a predetermined sweep speed, and the sweep command signal is sent to the oscillator 1.

FIG. 2 shows the state of the transmission frequency sweep. Here, the frequency range to be swept is set from the temperature characteristics shown in FIG. 5 and the operating temperature range. The sweep speed may be set according to the time required for peak frequency detection. In this embodiment, the set frequency range is swept in 1 second as shown in FIG. Transmission frequency sweep controller 1
When the sweep command signal sent from 4D is applied to the oscillator 1, the oscillator 1 outputs the frequency range (1
An oscillation signal of 29.1 kHz to 130.1 kHz) is transmitted. This oscillation signal is amplified to a predetermined level by the drive circuit 2 and then applied to the wave transmitter 3 to drive the wave transmitter 3. At this time, the frequency dependence of the transmission sound pressure of the wave transmitter 3 may have the characteristic shown in FIG. 4A, and at least the frequency range to be swept (from 129.1 kHz in the illustrated example to
It is sufficient that a constant sound pressure can be obtained at 130.1 kHz).

The wave receiver 6 receives a wraparound wave that directly arrives from the wave transmitter 3 without being reflected on the road surface or an ultrasonic wave reflected by the road surface. The received ultrasonic signal is amplified to a predetermined level by the preamplifier 7, and a part of it is sent to the multiplier 8. After that, the vehicle speed calculation unit 14A calculates the vehicle speed through the same process as the conventional example. It The vehicle speed at this time is 0 km / h. On the other hand, a part of the signal output from the preamplifier 7 is also sent to the signal level detection circuit 13. This signal level detection circuit 13
The DC voltage value corresponding to the received signal level of the wave receiver is sent to the wave receiver peak frequency determination unit 14C. The receiver peak frequency determination unit 14C determines the magnitude of the signal level value corresponding to the transmission frequency value obtained from the transmission frequency sweep control unit 14D. After the sweep in the transmission frequency sweep control unit 14D is completed, the receiver peak frequency determination unit 14C determines the frequency at which the received signal level reaches a peak, and sets this frequency as the received frequency corrected by the temperature of the receiver 6. ..

After that, the operation mode of the arithmetic and control unit 14 is returned to the normal mode, and the vehicle speed is calculated and the frequency is controlled by the received frequency. That is, using this reception frequency F, the vehicle speed v is calculated based on the following equation.
Calculated by A.

[Equation 1]

In such an embodiment, when the vehicle speed calculator 14A calculates the zero vehicle speed (when the vehicle stops).
Then, the transmission frequency sweep control unit 14D is operated to sweep control the drive frequency of the wave transmitter 3, and at this time, while observing the intensity of the signal level by the wave receiver 6 with the peak frequency determination unit 14C, Since the peak frequency is detected and this frequency is used as the reception frequency, even if the resonance frequency of the receiver changes due to temperature changes, the frequency of the ultrasonic signal received following this changes. It can be adjusted to match the resonant frequency of the receiver, thus enabling a highly accurate speedometer. In addition, since the control method for matching the reception frequency with the resonance frequency of the wave receiver is adopted, it is possible to provide a stable and highly reliable speedometer at low cost without an unstable element such as a thermistor.

The ultrasonic Doppler type ground velocity meter of the present invention is not limited to the structure shown in the above embodiment, and various modifications can be made without departing from the scope of the claims.

[0026]

As described above, according to the present invention, when the vehicle speed value becomes zero, the transmission frequency of the ultrasonic wave transmission means is swept-controlled, and the ultrasonic wave signal transmitted from this ultrasonic wave transmission means is controlled. By observing the signal strength of the ultrasonic wave receiving means, the frequency at which the signal strength reaches its peak is detected, and this frequency becomes the receiving frequency that matches the resonance frequency depending on the temperature of the ultrasonic wave receiving means. Since the control is performed in accordance with the above, it is possible to adjust so that the resonance frequencies of the ultrasonic wave receiving means coincide with each other due to the temperature change, which has the effect of enabling highly accurate speed measurement.

[Brief description of drawings]

FIG. 1 is a block diagram showing an ultrasonic Doppler type ground speed meter which is an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a transmission frequency sweep according to the present embodiment.

FIG. 3 is a block diagram showing a conventional ultrasonic Doppler type ground speed meter.

FIG. 4A is a characteristic diagram showing the relationship between the frequency of the wave receiver and the receiving sensitivity, and FIG. 4B is a characteristic diagram showing the relationship between the frequency of the wave transmitter and the transmitted sound pressure.

FIG. 5 is a characteristic diagram showing the relationship between the temperature of the wave receiver and the reception peak frequency.

FIG. 6 is a characteristic diagram showing the relationship between the receiving sensitivity of the wave receiver and the Doppler signal level.

[Explanation of symbols]

 1 oscillator 2 drive circuit 3 wave transmitter 4 road surface 5 ultrasonic wave 6 wave receiver 8 analog multiplier 9 low-pass filter 10 zero-cross comparator 11 pulse counter 13 signal level detection circuit 14 arithmetic and control unit 14A vehicle speed arithmetic unit 14B transmission frequency setting unit 14C Receiver peak frequency determination unit 14D Transmission frequency sweep control unit

Claims (1)

[Claims] 1. An ultrasonic wave transmitting means for transmitting an ultrasonic wave forward of a vehicle and obliquely to a road surface, an ultrasonic wave receiving means for receiving an ultrasonic wave reflected on the road surface, and an ultrasonic wave transmitted. Doppler signal detection means for extracting a Doppler signal from the sound waves and the received ultrasonic waves, a Doppler shift frequency calculation means for calculating a Doppler shift frequency from the Doppler signal, a vehicle speed calculation means for calculating a vehicle speed from the Doppler shift frequency, and An ultrasonic Doppler type ground speed provided with frequency control means for controlling the transmission frequency of the ultrasonic wave transmitted from the ultrasonic wave transmitting means so that the frequency of the received ultrasonic wave is always constant based on the vehicle speed value. In the meter, when the vehicle speed calculation means calculates the vehicle speed to be zero, the operation is performed and the transmission frequency of the ultrasonic wave transmission means is swept controlled within a predetermined frequency range. Transmission frequency sweep control means, signal level detection means for detecting the reception signal level of the ultrasonic wave reception means, frequency at which the reception signal level detected by the signal level detection means reaches a peak, and this frequency An ultrasonic Doppler-type ground speed meter, comprising: a peak frequency determining unit that determines a reception frequency of the ultrasonic receiving unit.