JPH05107351A - Measuring apparatus for distance to vehicle ahead having means for determining threshold - Google Patents

Abstract

PURPOSE:To provide a measuring apparatus for the distance to a vehicle ahead capable of defining a threshold as a function of frequency and having a means for determining an appropriate threshold according to the ambient temperature. CONSTITUTION:A measuring apparatus for the distance to a vehicle ahead comprises a radar 101 for measuring the distance to the vehicle ahead, a means 102 for subjecting radar output signals to frequency analysis, a means 103 for storing the results of frequency analysis as thresholds when there is no vehicle ahead, and a processing means 104 for removing noise from the results of frequency analysis according to the thresholds stored. The threshold storage means 103 has at least two storage areas and also has a means for detecting atmospheric temperature around the radar, a means for switching according to the ambient temperature the threshold storage areas in which the thresholds are stored, and a means for selecting a threshold according to the ambient temperature and outputting it to the processing means 104.

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 apparatus using a radar, and more particularly to an inter-vehicle distance measuring apparatus having threshold value determining means for separating significant frequency components and noise components.

[0002]

2. Description of the Related Art In order to prevent a rear-end collision of a vehicle, an inter-vehicle distance measuring device has been put into practical use, which detects whether or not an obstacle is present within a predetermined area in front of the vehicle. In such an inter-vehicle distance measuring device, a so-called FM-CW radar is generally used as a sensor, and the inter-vehicle distance is obtained by analyzing the frequency of this output signal and identifying the peak frequency.

That is, in the FM-CW type radar, a signal emitted toward an obstacle is FM-modulated within a range of ± ΔF / 2 centering on a frequency f ₀ to obtain a so-called beat between a transmission signal and a reception signal. Then, the inter-vehicle distance and the relative speed are obtained by identifying the beat frequency f _up while the frequency of the transmission signal is increasing and the beat frequency f _down while the frequency of the transmission signal is decreasing.

It is therefore necessary to process the radar output signal to identify the two beat frequencies f _up and f _down , for which it is common to frequency analyze the radar output signal. FIG. 5 is a block diagram of a conventional inter-vehicle distance measuring apparatus, in which an output signal of a radar 301 is digitized by an analog / digital converter 3012 after passing through a low pass filter 3011 for removing aliasing noise.

The frequency of the digitized signal is analyzed by the frequency analysis unit 3
After frequency analysis in 02, it is sent to the frequency identification unit 5502. The frequency analysis unit 302 and the frequency identification unit 550
Reference numeral 2 is a digital signal processor (DSP). The frequency identifying unit 5502 removes frequency components equal to or lower than the threshold set by the threshold setting unit 5501, identifies the peak frequency, obtains the inter-vehicle distance, and outputs the inter-vehicle distance to the processing unit 5503. Then, when it is detected that the distance is equal to or less than the predetermined distance, an alarm is issued in process 5503.

Therefore, in order to obtain an accurate measurement result, it is necessary to remove the frequency component below a predetermined power as noise. Conventionally, the threshold setting unit 5501 sets the noise and the peak frequency in order to separate them. The threshold to be set was a fixed value.

[0007]

As described above, in the inter-vehicle distance measuring apparatus using the FM modulation, the peak of the frequency component of the modulation frequency appears in the frequency analysis result when there is no obstacle in front, so that the noise level is uniform. Not like. Therefore, if the threshold value is a constant value regardless of the frequency, it must be a relatively large value, and the peak value cannot be detected when the reflection intensity of the obstacle is small.

Further, the noise characteristic of the radar is affected by the atmospheric temperature. The present invention has been made in view of the above problems, and it is possible to provide an inter-vehicle distance measuring device that can determine a threshold value as a function of frequency and that has means for determining an appropriate threshold value according to ambient temperature. To aim.

[0009]

FIG. 1 is a basic configuration diagram of an inter-vehicle distance measuring apparatus according to a first invention, which is a radar 101 for measuring an inter-vehicle distance and a frequency analysis for frequency-analyzing an output signal of the radar 101. Means 102, a threshold storage means 103 for storing the analysis result of the frequency analysis means 102 as a threshold when there is no obstacle ahead, and a threshold storage means 10.
Processing unit 104 that removes noise from the analysis result of the frequency analysis unit 102 according to the threshold value stored in No. 3.

FIG. 2 is a basic block diagram of an inter-vehicle distance measuring apparatus according to the second invention, in which the threshold value storage means 103 has at least two storage areas 1031, 1032 ... 103.
An ambient temperature detecting means 105 configured to detect the atmospheric temperature around the radar 101, and at least two threshold storage areas 1031 for storing thresholds according to the ambient temperature detected by the ambient temperature detecting means 105.
First switching means 1061 for switching 1032 ... 103N and at least two storage areas 103 according to the ambient temperature detected by the ambient temperature detecting means 105.
Second switching means 106 for selecting the threshold value stored in 1, 1032 ... 103N and outputting it to the processing means 104
2 and.

[0011]

In the first aspect of the present invention, since the threshold value is set according to the frequency, the measurement accuracy and sensitivity are improved. In the second aspect, an appropriate threshold value is set according to the atmospheric temperature, and the measurement accuracy is further improved.

[0012]

FIG. 3 is a block diagram of an embodiment of an inter-vehicle distance measuring apparatus according to the present invention, in which a so-called FM-CW is used as a sensor.
The type radar 301 is used. The millimeter wave or laser light emitted from the radar 301 is reflected by the obstacle 310 and received by the radar 301.

The signal emitted as described above has a frequency f _0.
Since the signal is modulated in the range of ± ΔF / 2 with respect to, a beat occurs between the emitted signal and the received signal. This beat frequency signal becomes the output signal of the radar 301, and the analog-digital converter 301 is passed through the low-pass filter 3011 for removing the aliasing noise.
2 is supplied.

The beat frequency signal is digitized by the analog / digital converter 3012 and input to the digital signal processor (DSP) 302. DSP
In 302, frequency analysis is performed on the beat frequency signal by a fast Fourier transform (FFT) algorithm, and power is calculated for each discretized frequency.

FIG. 4 is a spectrum diagram of the frequency analysis result of the output signal of the radar 301, where the horizontal axis represents frequency and the vertical axis represents power. (A) shows the spectrum when the obstacle 310 is not present, but the power is a function of frequency. The spectrum in the absence of this obstacle is stored as a threshold value in the memory in the controller 350.

As the threshold to be stored, this spectrum may be multiplied by a constant K of 1 or more. (B)
Is a spectrum in the presence of the obstacle 310, and a peak (marked with a circle) equal to or higher than a threshold as a function of frequency stored in a memory in the controller 350 is detected, and an inter-vehicle distance and a relative speed are calculated. ..

Since the radar 301 is affected by the ambient temperature, the detection accuracy can be improved by changing the threshold value according to the ambient temperature. That is, in the embodiment of the second invention, the temperature detection sensor 305 is provided near the radar 301 and the output signal is input to the controller 350. Then, the spectrum is calculated by changing the ambient temperature of the radar 301 without the obstacle 310.

For example, the ambient temperature is divided into three parts every 20 degrees from -20 degrees to 40 degrees and the spectrum in each temperature zone is stored in three memory areas provided in the controller 350. During traveling, the threshold values stored in the three memory areas can be selected according to the ambient temperature of the radar 301 detected by the temperature detection sensor 305.

[0019]

According to the first aspect of the present invention, when the information about the inter-vehicle distance is extracted from the output signal of the radar, noise is removed by an appropriate threshold value determined as a function of frequency to improve the measurement accuracy. Is possible. According to the second aspect of the present invention, since the threshold value according to the ambient temperature of the radar is used, it is possible to further improve the measurement accuracy.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a first invention.

FIG. 2 is a basic configuration diagram of a second invention.

FIG. 3 is a hardware configuration diagram of an embodiment of the present invention.

FIG. 4 is a spectrum diagram of a frequency analysis result.

FIG. 5 is a configuration diagram of a conventional inter-vehicle distance measuring device.

[Explanation of symbols]

 101 ... Radar 102 ... Frequency analysis means 103 ... Threshold storage means 104 ... Processing means 105 ... Ambient temperature detection means 1061 ... First switching means 1062 ... Second switching means

Claims (2)

[Claims] 1. A radar (101) for measuring an inter-vehicle distance, a frequency analysis means (102) for frequency-analyzing an output signal of the radar (101), and a frequency analysis means () when there is no obstacle ahead. 1
02) storing the analysis result as a threshold, and a processing means (104) for removing noise from the analysis result of the frequency analyzing means (102) by the threshold stored in the threshold storing means (103). ), And an inter-vehicle distance measuring device having a threshold value determining means. 2. The threshold storage means (103) has at least two storage areas (1031, 1032 ... 103).
N) and further includes the radar (10
1) Ambient temperature detecting means (10) for detecting the ambient atmospheric temperature
5) and first switching means (1061) for switching the at least two threshold value storage areas (1031, 1032 ... 103N) for storing threshold values according to the ambient temperature detected by the ambient temperature detecting means (105). ) And the at least two storage areas (1031, 1) according to the ambient temperature detected by the ambient temperature detecting means (105).
032 ... 103N), and a second switching means (1062) for selecting a threshold value stored in the processing means (104) and outputting it to the processing means (104). apparatus.