JPH06313795A - Measuring apparatus of inter-vehicle distance - Google Patents

Abstract

PURPOSE:To prevent mutual interference with a radio wave sent from another vehicle, by a method wherein a non-modulated part is provided in a transmission wave, discriminative information is inserted into the non-modulated part causing no hindrance to sampling and is transmitted and an inter-vehicle distance is measured only when the discriminative information is received from a reception wave. CONSTITUTION:A non-modulated part NM is provided in a transmission wave by utilizing an unused beat frequency part other than sampling parts SMP1 and SMP2 being necessary for measuring an inter-vehicle distance, and information ID for discriminating a user's own vehicle is inserted into the non-modulated part NM and transmitted. When the transmission wave is reflected by a vehicle in front and returned, the non-modulated part NM is present also in a reception wave, and by determining a beat frequency of this reception wave and the transmission wave, therefore, a sampling part SMP3 for a discriminative information discriminating processing, of which the frequency is definite, is obtained. By executing an inter-vehicle distance measuring processing based on the SMP1 and the SMP2 only when the discriminative information ID on the user's own vehicle is detected from the sampling part SMP3, radio interference with the opposite vehicle can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance measuring device, and more particularly to a device (distance measuring device) for measuring an inter-vehicle distance to a vehicle in front using FM-CW waves.

[0002]

2. Description of the Related Art FIG. 5 schematically shows a conventionally well-known inter-vehicle distance measuring device using FM-CW waves. FM-CW waves transmitted from a radio wave transmitting device 21 are transmitted by a transmitting antenna. 22. At this time, for example, when there is a vehicle ahead, the FM-C reflected by the vehicle ahead
The W wave is received by the receiving antenna 23 and is received by the radio wave receiving device 24.

The mixer 25 mixes the beat frequencies of the waveform emission wave and the reception wave, and the distance derivation processor 26 outputs a signal obtained by measuring the inter-vehicle distance (and relative speed) to the preceding vehicle. is there.

FIG. 6 shows the change over time of the mixing waveform, and FIG. 6 (a) shows the emission wave shown by the solid line and the reception wave shown by the dotted line, and when these waves are mixed by the mixer 25, they are the same. A waveform of the beat frequency is obtained as shown in FIG.

In the distance derivation processor 26 from such a waveform of the beat frequency, sampling portions SMP1 and SMP2 including a portion where the frequency before and after the beat frequency becomes "0" become constant as shown in FIG. It is set to be used for arithmetic processing.

In this case, as shown in FIG. 7A showing the state of frequency analysis for the sampling portion SMP1, the signal strength in the sampling portion SMP1 is maximum at the frequency f1 and the sampling portion SMP2. As shown in the same figure (b) showing the state of the frequency analysis for, the frequency f2 has the maximum signal strength in the sampling portion SMP2.

Therefore, in the distance derivation processor 26, these frequencies f1 and f2 are combined, the distance (and the relative speed) is calculated by the Doppler's principle formula, and it is output as a measurement signal.

[0008]

In the conventional inter-vehicle distance measuring apparatus as described above, it is premised that the radio wave sent from the transmitting antenna is reflected by the vehicle in front, but normally it is as shown in FIG. Since there are also radio waves emitted from oncoming vehicles, the radio waves emitted from oncoming vehicles like this are used as reception waves and the beat frequency is calculated by mixing with the emission waves as described above, and the error due to mutual interference of radio waves occurs. There was a problem that it brought about the measurement result.

Therefore, according to the present invention, the FM-CW wave is transmitted as a launch wave to the front of the vehicle, the received wave reflected by the vehicle ahead is mixed with the launch wave to generate a beat signal, and the beat signal is subjected to frequency analysis. It is an object of the present invention to prevent mutual interference with radio waves emitted from other vehicles in an apparatus for measuring an inter-vehicle distance with respect to a vehicle in front of the vehicle so that an accurate inter-vehicle distance can be measured.

[0010]

In order to achieve the above object, in the inter-vehicle distance measuring apparatus according to the present invention, the FM-CW emission wave is provided with a non-modulation portion, and the non-modulation portion is provided in the own vehicle. The peculiar identification information is inserted into a portion other than the sampling portion necessary for measuring the inter-vehicle distance and transmitted, and the inter-vehicle distance is measured only when the identification information is detected from the received wave.

This will be explained with reference to the principle waveform diagram shown in FIG. 1. As shown in FIGS. 6B and 6B, beat frequencies not used other than the sampling portions SMP1 and SMP2 necessary for measuring the inter-vehicle distance are shown. It can be seen that the part exists.

Therefore, in the present invention, as shown in FIG. 1 (a), the emission wave is first provided in the non-modulation portion NM, and an information ID for identifying the own vehicle is inserted into the non-modulation portion NM to emit the emission wave. And

When this is reflected by the vehicle ahead and returns, there is still an unmodulated portion NM in the received wave, and when the beat frequencies of this received wave and the emitted wave are determined,
As shown in FIG. 9B, the sampling portion SMP3 for the identification information discrimination processing with a constant frequency is obtained.

Only when the identification information of the own vehicle is detected from the sampling portion SMP3, the inter-vehicle distance measuring process by the sampling portions SMP1 and SMP2 shown in the figure may be executed.

In this way, the unmodulated part is inserted into the launch wave,
Since the reflected wave also has an unmodulated portion, the inter-vehicle distance can be read only when the identification information in the beat frequency portion of the emission wave of the waveform received as the reflected wave is decoded and it is determined that it is the identification information of the own vehicle. The process of deriving the distance (and the relative speed) can be performed.

[0016]

FIG. 2 is a block diagram showing an embodiment of an inter-vehicle distance measuring apparatus according to the present invention, in which 1 is a transmitting antenna, 2 is a transmitting circuit, and 3 is a VCO (voltage controlled oscillator). 5 is a receiving antenna, 5 is a receiving circuit, and 6 is a mixer. The transmitting circuit 2 and the modulating circuit 3 correspond to the radio wave transmitting device 21 shown in FIG. The circuit 5 also corresponds to the radio wave receiving device 24, and the mixer 6 corresponds to the mixer 25.

The signal applied to the modulation circuit 3 is generated by the signal generation circuit 8, and the signal generation circuit 8 always receives the clock signal from the synchronization signal generation circuit 9, and C
Upon receiving the identification information from the PU 10, the identification information unique to the own vehicle as shown in FIG. 3 is generated.

The output signal of the mixer 6 is supplied to the demodulation circuit 7. The output signal of the demodulation circuit 7 is supplied to the frequency-voltage (F / V) conversion circuit 12 and converted into a voltage signal. The converted signal is further applied to the A / D conversion circuit 11 and converted into a digital signal.

The output signals of the A / D conversion circuit 11 are both sent to the frequency analysis section 13 and the identification information decoding section 14, and the respective analysis results and decoding results are given to the CPU 10 to output a measurement signal. is there.

The demodulation circuit 7, the frequency-voltage conversion circuit 11, the A / D conversion circuit 12, and the frequency analysis unit 13 constitute the distance derivation processor 26 shown in FIG. Further, the conversion circuits 11 and 12 are also configured to receive the synchronization signal from the synchronization signal generation circuit 9.

Next, the operation of the above embodiment will be described below with reference to the waveform charts shown in FIGS. 3 shows the waveform of the output signal of the signal generation circuit 8 shown in FIG. 2, and FIG. 4 also shows the waveform of the output signal of the modulation circuit 3.

First, the identification information I of the own vehicle used in the present invention.
D is intended to be realized by the ON / OFF timing of the VCO in the modulation circuit 3. One pulse of the synchronization signal from the synchronization signal generation circuit 9 is set as one unit, and the VCO
If "1" is set when turning ON, and "0" is set when turning OFF, the identification information ID becomes "0101" in the example shown in FIG. In order to detect the identification information ID in the received wave, it is desirable to set the first bit to "0".

Further, when the identification information ID is 4 bits in this way, after the completion of the 4 bits, the signal is not raised again but is held at a constant value as shown in the figure. This means that the unmodulated portion NM (see FIG. 1A) is provided in the emitted wave and the received wave shown in FIG. 6A, and the identification information “0101” of the own vehicle is provided in this unmodulated portion NM. Has been inserted.

Further, since the non-modulated portion NM exists after the identification information ID, the sampling portion SMP3 for determining the identification information in which the beat frequency becomes constant as described later (see FIG. 1B). This is because it is necessary to provide.

The modulation circuit 3 receiving the signal shown in FIG. 3 controls the VCO in accordance with this voltage, and the transmission circuit 2 produces a frequency modulation (FM) signal as shown in FIG.
Send to.

The received wave transmitted from the FM-CW wave based on the signal as described above and reflected by the vehicle in front and returned is received by the receiving circuit 5 via the receiving antenna 4 and is received by the mixer 6.
By mixing with the emission wave at, the signal as shown in FIG. 1B is obtained from the demodulation circuit 7.

Since a non-modulation portion in which the modulation frequency does not change is created in the signal, a point P when the beat frequency becomes "0" occurs as shown in FIG. 1 (b),
Since the identification information ID is always inserted after this point P (several clocks after the synchronizing signal), the continuity of the signal in this portion is read.

Therefore, in the frequency-voltage conversion circuit 12, the beat frequency signal shown in FIG. 1 (b) is converted into a voltage, and the A / D conversion circuit 12 further converts it into a digital signal corresponding to the voltage. It is given to the frequency analysis unit 13 and the identification information decoding unit 14.

Then, in the identification information decoding unit 14, the A / D
When the digital signal from the conversion circuit 12 becomes the first "0" from the time point P, it is judged that the sampling portion SMP3 has started, and the identification information ID peculiar to the own vehicle described above.
= “0101” is detected and notified to the CPU 10.

The signal output from the demodulation circuit 7 is A
When converted to a digital signal by the / D conversion circuit 11 and given to the frequency analysis unit 13, the digital values in the sampling portions SMP1 and SMP2 also shown in FIG. 6B, that is, FIG. Since the signal level at each frequency shown can be obtained, this means that the frequency analysis shown in FIG.
Can be output as a measurement signal of the inter-vehicle distance (and relative speed).

In the A / D conversion circuit 11, if the signal for one clock is continuous at the same voltage, it is "1". If the voltage changes and is not continuous with the voltage of the previous clock, it is "0" for identification. Information can be deciphered.

[0032]

As described above, according to the inter-vehicle distance measuring apparatus of the present invention, the unmodulated portion is inserted into the FM-CW emission wave, and the reflected wave also has the unmodulated portion. Configured so that the inter-vehicle distance (and relative speed) measurement signal is obtained only when the identification information in the beat frequency part of the emission wave of the waveform received as the reflected wave is decoded and it is determined that it is the identification information of the own vehicle. Therefore, it is possible to prevent malfunction due to mutual interference of radio waves between radar-type inter-vehicle distance measuring devices mounted on an oncoming vehicle or a parallel traveling vehicle. Further, there are no restrictions on the arrangement of the radio wave antennas in consideration of the polarization plane of the radio wave, and the antennas with better measurement conditions can be arranged.

[Brief description of drawings]

FIG. 1 is a waveform diagram for explaining the principle of an inter-vehicle distance measuring device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of an inter-vehicle distance measuring device according to the present invention.

FIG. 3 is a diagram showing a waveform of a control signal for the modulation circuit shown in FIG.

4 is a diagram showing a waveform of an output signal from the modulation circuit shown in FIG.

FIG. 5 is a block diagram schematically showing an inter-vehicle distance measuring device using FM-CW waves, which is generally known in the past.

FIG. 6 is a diagram showing a temporal change of a mixing waveform in a conventional example.

FIG. 7 is a waveform diagram showing a conventional general frequency analysis.

FIG. 8 is a diagram showing an example of radio wave interference between vehicles.

[Explanation of symbols]

 1 Transmission Antenna 2 Transmission Circuit 3 Modulation Circuit 4 Reception Antenna 5 Reception Circuit 6 Mixer 7 Demodulation Circuit 8 Signal Generation Circuit 9 Synchronous Signal Generation Circuit 10 CPU 11 A / D Conversion Circuit 12 Frequency-Voltage (F / V) Conversion Circuit 13 Frequency Analysis unit 14 Identification information decoding unit In the figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An FM-CW wave is transmitted as a launch wave to the front of a vehicle, a received wave reflected by a vehicle in front is mixed with the launch wave to generate a beat signal, and the beat signal is frequency-analyzed to produce the beat signal. In a device for measuring a vehicle-to-vehicle distance, an unmodulated portion is provided in the emitted wave, and identification information unique to the own vehicle is inserted in the unmodulated portion in a portion other than a sampling portion required for measuring the vehicle-to-vehicle distance and transmitted An inter-vehicle distance measuring device characterized in that the inter-vehicle distance is measured only when the identification information is detected from the received wave.