JPH05273346A - Vehicle speed measuring instrument - Google Patents

Abstract

PURPOSE:To accurately measure the absolute ground speed of a vehicle. CONSTITUTION:The title instrument measures the speed of its own vehicle from the deviated frequency component of reflected waves of ultrasonic waves of a fixed frequency from the road surface corresponding to the speed of the vehicle by transmitting the ultrasonic waves against the road surface. A band- pass filter 11 is provided between a detector 7 and amplifier circuit 8. The passing band of the filter 11 is changed by means of a comparator 10 in accordance with the measured speed of the vehicle. Therefore, the deviated frequency component caused by the movement of the vehicle body is removed by only passing the extracted output of the deviated frequency component in the near band corresponding to the measured speed of the vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transmits an ultrasonic wave having a constant frequency to a road surface, extracts a frequency shift component corresponding to the vehicle speed of a reflected wave from the road surface, and extracts the vehicle speed from the frequency shift component. The present invention relates to a vehicle speed measuring device of a Doppler system for measuring.

[0002]

2. Description of the Related Art In a conventional vehicle speed measuring device used for an automobile or the like, the speed is obtained from the wheel speed. By the way, recently, in order to improve the braking performance, ABS (anti-lock braking system)
The number of cars that have introduced is increasing. The key to the performance of this ABS is the vehicle speed detection capability.

The wheel speed of the vehicle itself is such that when the driver steps on the panic brake, the rotation of the wheel itself stops, and the vehicle slides on the road surface with the tire locked, resulting in a wheel speed of 0 km / It will be h. Therefore, an ABS has been developed that has been devised as a software so as not to reduce the performance. However, if the absolute vehicle speed to the ground can be easily detected by the vehicle itself, a more complete ABS should be commercialized.

Some examples of such a vehicle speed measuring device for detecting an absolute vehicle speed to the ground have been devised and prototyped. As a vehicle speed measuring device which can be used as a product base in the present situation, one adopting the Doppler system is used. It is considered effective. A typical example of the Doppler type vehicle speed measuring device is shown in FIG. In this vehicle speed measuring device, the output of the oscillation circuit 1 is amplified by the amplification circuit 2 to drive the ultrasonic microphone 3, and the ultrasonic wave of the oscillation frequency f ₀ is transmitted. Here, the ultrasonic microphone 3 is shown in FIG.
It has the output characteristics shown in b) and converts the electric signal of frequency f ₀ into ultrasonic waves and sends them out into the air. Further, as shown in FIG. 17, the ultrasonic microphone 3 transmits ultrasonic waves in a direction having an inclination of an angle θ in the direction opposite to the traveling direction of the vehicle A vertically downward. The angle θ will be referred to as a ground incident angle in the following description.

The ultrasonic wave of frequency f ₀ sent from the ultrasonic microphone 3 is reflected on the road surface and received by the ultrasonic microphone 4. Here, the ultrasonic microphone 4
The ultrasonic wave received at 1 has a frequency f ′ that is Doppler-shifted by the traveling of the vehicle. Frequency f'at this time
Is given by the following equation.

[0006]

[Equation 1]

However, C is the speed of sound (331.5 + 0.6
t), V is the vehicle speed, θ is the angle of incidence on the ground, and f ₀ is the transmission frequency. The ultrasonic microphone 4 has the reception band characteristic shown by B in FIG. 16A, and has received the Doppler shift from the frequency f ₀ . It has a characteristic that the frequency f ′ can be received in a wide band. The received output of the ultrasonic microphone 4 is amplified by the amplification circuit 5 and mixed with the oscillation signal of the oscillation circuit 1 by the mixer 6, and the difference Δf of f ₀ −f ′ is a beat signal, that is, a Doppler beat signal ( Hereinafter, it is output as a Doppler signal). The carrier component f ₀ from the oscillation circuit 1 is removed from this Doppler signal and only the Doppler signal of Δf is extracted. The Doppler signal is amplified by the amplifier circuit 8 and converted into a voltage according to the frequency (speed) by the FV conversion circuit 9. In this way, the Doppler vehicle speed measuring device can detect the absolute vehicle speed to the ground. The amplifier circuit 8 has a low-pass band characteristic shown in FIG. 16 (b) so that the maximum speed to be detected is 0 km.
It also has the function of a filter that allows the Doppler signal to pass through / h.

[0008]

By the way, in the detection method of the absolute vehicle speed to the ground adopting the above-mentioned Doppler method, it is easy to be affected by the noise and vibration of the running vehicle or the pitching and rolling of the vehicle depending on the road surface, For example, in addition to the Doppler shift (cos θ component) that occurs when the vehicle moves slowly up and down and the vehicle speed measuring device travels, a shift in vertical movement (U sin θ component ... U is the vertical movement speed of the vehicle). ) Is affected. That is, FIG.
As shown in (b), in the amplifier circuit 8 having a wide band active filter characteristic, all Doppler shift components are allowed to pass, and even if the vehicle actually travels at 100 km / h, the circuit output, for example, the FV conversion circuit. The output of 9 may output a signal of several km / h. Generally, the vertical movement of the car is much slower than the speed while driving, so the output depending on the speed while driving may suddenly drop or may not be output, which is referred to as noise. There were many Therefore, it has been evaluated that the measurement of the absolute vehicle speed with respect to the ground by the Doppler method using the above-mentioned ultrasonic waves is a step forward in terms of reliability and performance.

The present invention has been made in view of the above points, and an object thereof is to provide a vehicle speed measuring device capable of accurately measuring an absolute vehicle speed to ground.

[0010]

In order to achieve the above object, in the invention of claim 1, the output of the frequency deviation extracting section is passed to a section for inputting to the speed measuring section according to the measured vehicle speed. The band-pass filter means has a variable band and passes the extracted output of the frequency deviation only in the vicinity region corresponding to the measured vehicle speed.

According to the second aspect of the present invention, the low-range cutoff frequency is changed in accordance with the measured vehicle speed in the portion for inputting the output of the frequency shift extracting section to the speed measuring section, and corresponds to the measured vehicle speed. High-pass filter means is provided to prevent the extracted output having a frequency deviation lower than the specified frequency from being input to the speed measurement unit. According to the invention of claim 3, the output of the frequency shift extraction unit is binarized, the characteristic component of the output is extracted, the abnormal output is discriminated, and the abnormal output is removed as a noise component. ..

[0012]

According to the first aspect of the present invention, the frequency shift component generated by the movement of the vehicle itself is removed by the bandpass filter means to prevent inaccurate measurement of the absolute vehicle speed with respect to ground. In the invention of claim 2, paying attention to the fact that the frequency shift component generated by the movement of the vehicle itself exists in the low frequency region,
The frequency shift component caused by the movement of the vehicle itself is removed by the high-pass filter means to prevent inaccurate measurement of the absolute vehicle speed with respect to ground.

According to the third aspect of the present invention, the frequency shift component caused by the movement of the vehicle itself is removed by software to prevent inaccurate measurement of the absolute vehicle speed with respect to ground.

[0014]

【Example】

(Embodiment 1) FIGS. 1 to 4 show an embodiment of the present invention.
The vehicle speed measuring device according to the present embodiment is based on the above-mentioned ultrasonic Doppler system, and basically has the same structure as described in FIG. Therefore, the same components are designated by the same reference numerals, detailed description thereof will be omitted, and only the characteristic features of the present invention will be described in the following description.

The present embodiment is characterized by the configuration of the post-stage circuit of the detector 7. Specifically, as shown in FIG. 2, the band characteristic of allowing the output of the detector 7 to pass the detected output in accordance with external control is a variable band pass filter (hereinafter, BP).
11). Here, the BPF 11
Is configured by using, for example, an analog switch IC capable of switching in multiple stages, and the width of the pass band at each swinging is set to a width (for example, about several kHz) that can cope with sudden acceleration / deceleration of the vehicle. The output of the BPF 11 is amplified by the amplifier circuit 8 and input to the FV conversion circuit 9. However, the order of the BPF 11 and the amplifier circuit 8 may be reversed, and the amplifier circuit 8 may have the same function as the BPF 11.

The FV conversion circuit 9 outputs a voltage according to the Doppler signal Δf.
Is output to the comparator 10. That is, the pass band of the BPF 11 is variably set by the comparator 10.
Here, a large number of threshold values Th _{1 to} Th ₄ shown in FIG. 3 are set in the comparator 10, and the FV conversion circuit 9 is set.
The pass band of the BPF 11 is variably controlled by monitoring the analog output of. In this way, as shown in FIG. 2, if the frequency of the Doppler signal Δf becomes higher (the vehicle speed becomes faster), the pass band of the BPF 11 becomes higher as shown in FIGS. It is possible to shift to one direction and cut extremely low Doppler signal components such as vertical movement of the vehicle, so that the absolute vehicle speed to the ground can be detected stably during high speed running. 4 shows the output waveform of each circuit in FIG.

(Embodiment 2) FIG. 5 shows another embodiment of the present invention. In this embodiment, an amplifier circuit 8 is provided at the output of the detector 7, and the Doppler signal Δf amplified by the amplifier circuit 8 is waveform-shaped by the waveform shaping circuit 12 and converted into a digital signal. Here, the waveform shaping circuit 12 may be composed of, for example, a Schmitt trigger circuit. And
In the case of this embodiment, since the waveform shaping circuit 12 converts the digital signal, a digital filter 13 is provided instead of the BPF 11. In this digital filter 13, the period of the digital pulse is varied by the comparator 10 that monitors the output of the FV conversion circuit 9, and the pulse width of the digital signal to be passed is variably controlled. Also in the case of the present embodiment, basically, as in the case of the first embodiment, if the frequency of the Doppler signal Δf becomes higher (the vehicle speed becomes faster), the digital signal which can be passed through the digital filter 13 is changed. Only the high frequency is used, and the extremely low Doppler signal components such as the vertical movement of the car are cut, and the absolute vehicle speed to ground can be detected stably at high speed.

(Embodiment 3) FIGS. 6 and 7 show still another embodiment of the present invention. In this embodiment, instead of the BPF 11 in the first embodiment, a high-pass filter (hereinafter, HPF) is used.
14), and the HPF 14 is capable of varying the low-frequency cutoff frequency under the control of the comparator 10. That is, the movement such as vertical movement during actual driving of the vehicle is much lower than the frequency of the Doppler signal Δf generated by high-speed running. Therefore, as in the first embodiment, the detector 7
It is possible to remove components due to movement such as vertical movement during driving of the vehicle without changing the band for passing the output of, that is, without changing the wide range cutoff frequency. In the HPF 14 of the present embodiment, as shown in FIG. 7, the low cutoff frequency is increased as the vehicle speed increases,
The components due to movements such as vertical movement are removed.

The digital filter 13 that functions as a so-called bandpass filter in the second embodiment.
May function as a high-pass filter as in the present embodiment. (Embodiment 4) FIGS. 8 and 9 show still another embodiment of the present invention. This embodiment is an embodiment in which the HPF 14 and the comparator 10 in Embodiment 3 are simplified.
The HPF 14 whose low-frequency cutoff frequency is variable is composed of a capacitor C ₁ and resistors R ₁ and R ₂ , and the comparator 1
Instead of 0, a transistor Q ₁ connected in parallel across the resistor R ₂ is used, and this transistor Q ₁ is turned on / off by the output of the FV conversion circuit 9. Here, the resistance of the resistor R ₁ is small, and the resistance of the resistor R ₂ is large.
The circuit unit will be referred to as the filter unit 15.

[0020] Now, when the output of the FV converter 9 is equal to or less than the threshold voltage of the transistor Q ₁ (approximately 0.6V), the transistor Q ₁ is off, the low frequency cut-off of the high-pass filter of the filter unit 15 Frequency is Figure 9
Has become as shown by the solid line low at the output of the FV converter 9 exceeds a threshold voltage of the transistor Q _1, the transistor Q ₁ is turned on, both ends are short-circuited resistor R _2, the filter unit 15 The low-pass cutoff frequency of the high-pass filter is increased as shown in FIG.

(Fifth Embodiment) FIGS. 10 to 12 show still another embodiment of the present invention. In the case of the above-described embodiment, the processing is performed by hardware to remove the component due to the vertical movement of the vehicle, but in the present embodiment, the component is removed by software. Therefore, in this embodiment, the amplifier circuit 8
An arithmetic processing unit 18 including a CPU is provided at the output of the.

In the arithmetic processing section 18, the output of the amplifier circuit 8 which has a high amplification factor and whose output is binarized into a high level and a low level is continuously supplied at a predetermined timing pulse, and the sampling number is set to 10 pulses, for example. Then, the pulse width of the output of the amplifier circuit 8 is obtained, stored and initialized. Then, by comparing the obtained pulse width with the previous pulse width, it is determined whether or not it is an abnormal value. Here, if there is no abnormality, the FV conversion circuit is operated to output a voltage corresponding to the pulse width. Now, when an abnormal pulse width t ₂ is obtained as shown in FIG. 12,
This pulse width t ₂ is judged to be abnormal, and the previous pulse width t
Output voltage based on ₁ . The abnormal pulse width t ₂ is not used in the pulse width determination process. When the operation of the arithmetic processing unit 18 is shown in a circuit form, as shown in FIG. 11, the sampling unit 19, the initialization unit 20,
The comparison / determination unit 21 and the FV conversion unit 22 are included.

That is, the speed is continuous and analog
It changes, and it changes continuously with it.
Far from the process of pulse width change, eg 10% or more
Difference appears and when the original pulse width is restored again,
Pulse is treated as noise. in this way
Even so, the effect of the vertical movement of the car can be eliminated. by the way,
The frequency of the Doppler signal Δf sharply changes with the acceleration.
In the process of shortening, the pulse width of the output of the amplifier circuit 8
Is t as shown in FIG.₁To t₈And changes. This place
Pulse width t₁~ T₈FV conversion according to
Output, the output appears as a sudden change.
Not a desirable output for circuits that use force. There
Output by averaging the obtained pulse width
The rate of change is smoothed. In addition, such a state
The same can be said for the situation when the vehicle decelerates rapidly. This
Where t₁> T₂＞ …… ＞ t₈Or t₁<T ₂<……
<T₈And the pulse width change in one direction, the average
If it does, you can't get out of the true absolute vehicle speed.
Furthermore, in the process of continuous pulse width change,
When a different pulse is input, that pulse
Should be removed.

[0024]

As described above, according to the present invention, the pass band is changed in accordance with the measured vehicle speed in the portion for inputting the output of the frequency deviation extraction unit into the speed measuring unit, and the measured vehicle speed is supported. Since it is equipped with bandpass filter means for passing the extracted output of the frequency deviation only in the vicinity region, the frequency deviation component generated by the movement of the vehicle itself is removed by the bandpass filter means, and the absolute vehicle speed to ground can be measured. You can prevent inaccuracies.

According to the second aspect of the present invention, the low-range cutoff frequency is changed according to the measured vehicle speed in the portion for inputting the output of the frequency deviation extraction section to the speed measuring section, and corresponds to the measured vehicle speed. Since the high-pass filter means for preventing the extraction output of the frequency deviation lower than the frequency to be input to the speed measuring unit is provided, the frequency deviation component generated by the movement of the vehicle itself is removed by the high-pass filter means. , It is possible to prevent inaccurate measurement of the absolute vehicle speed to ground.

According to the third aspect of the present invention, the output of the frequency shift extraction unit is binarized, the characteristic component of the output is extracted to discriminate the abnormal output, and the abnormal output is removed as a noise component. Since it is provided, the frequency shift component generated by the movement of the vehicle itself can be removed by software, and the measurement of the absolute vehicle speed with respect to ground can be prevented from becoming inaccurate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the above bandpass filter.

FIG. 3 is an operation explanatory diagram of the above comparator.

FIG. 4A to FIG. 4G are output waveform charts of respective parts of the same.

FIG. 5 is a configuration diagram of another embodiment.

FIG. 6 is a configuration diagram of still another embodiment.

FIG. 7 is an explanatory diagram of the operation of the above high-pass filter.

FIG. 8 is a configuration diagram of yet another embodiment.

FIG. 9 is an explanatory diagram of the operation of the above filter unit.

FIG. 10 is a configuration diagram of still another embodiment.

FIG. 11 is a specific configuration diagram of the arithmetic processing unit of the above.

FIG. 12 is an explanatory diagram of an operation of the arithmetic processing unit of the above.

FIG. 13 is a specific configuration diagram of another arithmetic processing unit.

FIG. 14 is an explanatory diagram of an operation of the above.

FIG. 15 is a configuration diagram of a conventional example.

16A and 16B are a characteristic diagram of an ultrasonic microphone and a characteristic diagram of an amplifier circuit.

17 (a) and 17 (b) are an explanatory view showing a method of measuring an absolute vehicle speed with respect to ground and an enlarged view of a main part thereof.

[Explanation of symbols]

 7 Detector 8 Amplification Circuit 9 FV Conversion Circuit 10 Comparator 11 Band Pass Filter 13 Digital Filter 14 High Pass Filter 15 Filter Section 18 Arithmetic Processing Section

Claims (3)

[Claims] 1. A vehicle speed measuring device for transmitting an ultrasonic wave having a constant frequency to a road surface, extracting a frequency deviation component according to the vehicle speed of a reflected wave from the road surface, and measuring the vehicle speed from the frequency deviation component. That is, the passband is varied according to the measured vehicle speed in the portion where the output of the frequency deviation extraction unit is input to the speed measurement unit, and the frequency deviation of only the vicinity region corresponding to the measured vehicle speed is A vehicle speed measuring device comprising bandpass filter means for passing an extracted output. 2. A vehicle speed measuring device for transmitting an ultrasonic wave having a constant frequency to a road surface, extracting a frequency shift component according to the vehicle speed of a reflected wave from the road surface, and measuring the vehicle speed from the frequency shift component. In the part for inputting the output of the frequency deviation extraction unit to the speed measurement unit, the low-range cutoff frequency is changed according to the measured vehicle speed, and the frequency lower than the frequency corresponding to the measured vehicle speed. A vehicle speed measuring device comprising high-pass filter means for preventing a deviation extraction output from being input to a speed measuring unit. 3. A vehicle speed measuring device for transmitting an ultrasonic wave having a constant frequency to a road surface, extracting a frequency shift component according to the vehicle speed of a reflected wave from the road surface, and measuring the vehicle speed from the frequency shift component. Where the output of the frequency shift extraction unit is binarized, the characteristic component of the output is extracted, and the abnormal output is determined,
A vehicle speed measuring device comprising an arithmetic processing means for removing an abnormal output as a noise component.