JPH04315080A - Measuring device for distance between cars - Google Patents

Abstract

PURPOSE:To enable reducing the time ratio for processing in a DSP by determin ing a frequency analysis range according to the speed of the driver's own car. CONSTITUTION:A device has a radar 101 loaded in a part of a car to emit and receive millimeter wave or laser beam to an obstruction existing in front, a signal conversion means 102 to convert the output signal to digital signal and a frequency analyzing means 103 to analyze the frequency of digitized signal. Also, it has a car distance determination means 104 to determine the distance between cars based on the result of the frequency analysis, a running velocity detection means 105 to detect the running velocity of the driver's own car, and an analyzed frequency upper limit determination means 106 to determine the upper limit of frequency for analyzing in the frequency analyzing means 103 based on the running velocity of the driver's own car.

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 using a radar, and more particularly to an inter-vehicle distance measuring device that can vary the processing range of radar measurement results depending on the speed of the own vehicle.

0002

2. Description of the Related Art In order to prevent rear-end collisions of automobiles, inter-vehicle distance measuring devices have been put into practical use that detect whether or not an obstacle exists within a predetermined range in front of the vehicle. In such inter-vehicle distance measuring devices, a so-called FM-CW type radar is generally used as a sensor, and the inter-vehicle distance is determined by digitizing this output signal and then frequency-analyzing it to identify the peak frequency. ing.

That is, in the FM-CW type radar, the signal emitted toward the obstacle is set at ±ΔF/2 with the frequency f0 as the center.
FM modulation is performed in the range of , and the so-called beat between the transmitted signal and the received signal is taken. Then, the inter-vehicle distance and relative speed are determined by identifying the beat frequency fup while the frequency of the transmitted signal is increasing and the beat frequency fdown while the frequency of the transmitted signal is decreasing.

It is therefore necessary to process the radar output signal to identify the two beat frequencies fup and fdown, and for this purpose it is common to perform frequency analysis on the radar output signal. FIG. 4 is a block diagram of a conventionally used inter-vehicle distance measuring device, in which the output signal of a radar 201 passes through a low-pass filter 2011 to remove aliasing noise, and then is digitized by an analog-to-digital converter 202. .

The digitized signal is frequency-analyzed by a digital signal processor (DSP) 203, and then the peak frequency is identified by a controller 204 to determine the inter-vehicle distance.
An alarm is generated at 41. According to the so-called sampling theorem, the upper limit of the frequency ful that can be analyzed by the DSP 203 is 1/2 of the sampling frequency fs of the analog-to-digital converter 202, and if fs = 200 kHz, then ful = 100 kHz.

In this device, for example, the peak frequency fp
If the inter-vehicle distance d is calibrated to 2 m when = 1.5 kHz, the upper limit of measurement of the device is fp = ful = 100 kHz
z, and dmax = 133m.

[0007]

[Problem to be solved by the invention] However, when a car is traveling at a speed of A kilometers per hour, it is generally said that it is sufficient to maintain a distance between the vehicles of A meters, so if frequency analysis is always performed up to the upper limit frequency ful, DSP This means that processing time is wasted. The present invention has been made to solve such problems, and is a method for measuring inter-vehicle distance that determines the frequency analysis range according to the traveling speed of the own vehicle and makes it possible to use the remaining time for other processing. The purpose is to provide equipment.

[0008]

[Means for Solving the Problems] Fig. 1 is a basic configuration diagram of the present invention, and the first invention is installed in a part of a vehicle and emits millimeter waves or laser light to obstacles and collects reflected waves. A receiving radar 101, a signal conversion means 102 that converts the output signal of the radar 101 into a digital signal, a frequency analysis means 103 that analyzes the frequency of the signal digitalized by the signal conversion means 102, and a frequency analysis result by the frequency analysis means 103. Inter-vehicle distance determining means 104 determines the inter-vehicle distance based on the following; traveling speed detecting means 105 detects the traveling speed of the own vehicle; and frequency analyzing means 103 based on the traveling speed of the own vehicle detected by the traveling speed detecting means 105. The analysis frequency upper limit determining means 106 determines the upper limit of the frequency to be analyzed.

Furthermore, in the second invention, there is a driving condition detecting means 107 for detecting the driving condition of the own vehicle, and an analysis frequency upper limit value determining means 106 determined based on the output of the driving condition detecting means 107. It further includes analysis frequency upper limit value correction means 108 for correcting the frequency upper limit value.

0010

According to the present invention, the frequency analysis range for identifying the peak frequency is limited to the necessary range depending on the traveling speed of the own vehicle, so that frequency analysis time is saved. Furthermore, according to the second invention, the frequency analysis range is corrected depending on the driving conditions of the own vehicle.

[0011]

[Embodiment] FIG. 2 is a block diagram of an embodiment of the inter-vehicle distance measuring device according to the present invention, in which a so-called FM-CW sensor is used as a sensor.
type radar 201 is used. Millimeter waves or laser light emitted from radar 201 is reflected by obstacle 210 and received by radar 201 .

As mentioned above, the emitted signal has a frequency f0
Since the signal is modulated in the range of ±ΔF/2 with the center at , a beat occurs between the emitted signal and the received signal. This beat frequency signal becomes the output signal of the radar 201, and is sent to the analog-to-digital converter 202 via a low-pass filter 2011 for removing aliasing noise.
supplied to

The beat frequency signal is digitized by an analog-to-digital converter 202 at a sampling frequency fs kHz and then processed by a digital signal processor (DS).
P) 203. Frequency analysis is performed on the beat frequency signal within the DSP 203 using a well-known Fast Fourier Transform (FFT) algorithm.

According to the sampling theorem, the range in which frequency analysis is significant is fs/2kHz, but since the processing time required for FFT varies depending on the width of the band in which frequency analysis is performed, the maximum frequency is There is no need to perform frequency analysis on the bandwidth. In other words, if the traveling speed of the own vehicle is V kilometers per hour, the upper limit of frequency analysis f
ul can be determined using the following formula.

[0015] ful=k·V

(1) Here k is a constant. In this embodiment, a magnetic switch type speed sensor 205 is used to detect the traveling speed of the own vehicle. That is, the speed sensor 205 is installed near the magnet 250 attached to the propeller shaft, and is repeatedly turned on and off in proportion to the number of rotations of the propeller shaft.

This on/off signal is taken in via the speed sensor interface 2051 to the controller 204 composed of, for example, a microprocessor. The controller 204 determines the upper limit value ful for frequency analysis using equation (1), and sends it to the DSP 203 . By limiting the upper limit of the frequency analysis in this way, the DS
The processing time ratio of P203 (processing time required for analysis up to the upper limit value ful of frequency analysis/processing time required for analysis up to fs/2) is less than 1.0 as shown in the following equation, and the free time is used to Other appropriate processing can then be performed.

D=ful/(fs/
2)
(2) However, when frequency analysis is performed up to fs/2kHz, D=1.0. Then, from the processing results in the DSP 203, the beat frequency fup when the frequency increases and the beat frequency fdown when the frequency decreases of the signal emitted from the radar 201 are identified, and the inter-vehicle distance is calculated in the controller 204 based on a well-known radar equation. When the distance is less than a predetermined distance, a warning device 2041, such as a buzzer, notifies the driver of the danger.

Furthermore, it is possible to further reduce the processing time ratio D by correcting the upper limit value ful of frequency analysis according to the driving condition of the own vehicle. For example, if the own vehicle is climbing a slope, it is easy to stop the vehicle, so the upper limit value ful can be set low. Conversely, if the vehicle is descending a slope, safety can be increased by setting the upper limit value ful high.

That is, a vehicle body tilt signal detected by a tilt sensor 207 attached to the vehicle body is input to the controller 204 via a tilt sensor interface 2071. FIG. 3 is a graph showing an example of the correction value of the upper limit value of frequency analysis due to the inclination of the vehicle body, where the correction value when the vehicle body is in a horizontal state is 1.0, and the higher the climbing angle becomes, the smaller the upper limit value ful becomes. The upper limit value ful is corrected so that the larger the downhill angle is, the larger the upper limit value ful is.

Furthermore, when the atmospheric temperature is measured as part of the driving condition and a temperature lower than a predetermined temperature is detected, it is assumed that there is a risk that the road surface may freeze, and the upper limit value ful can be corrected to be large. Further, when the humidity is measured by an atmospheric humidity sensor and a predetermined humidity or higher is detected, it is assumed that it is raining and the upper limit value ful can be corrected to be large.

[0021]

[Effects of the Invention] According to the present invention, the processing time ratio of the DSP is reduced by performing frequency analysis on the necessary frequency range according to the running speed of the own vehicle, and the surplus time is used to perform other processing. It becomes possible to do so.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an inter-vehicle distance measuring device according to the present invention.

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

FIG. 3 is a graph showing correction values depending on the inclination of the vehicle body.

FIG. 4 is a configuration diagram of a conventional inter-vehicle distance measuring device.

[Explanation of symbols]

101...Radar 102...Signal conversion means 103...Frequency analysis means 104... Inter-vehicle distance determining means 105... Traveling speed detection means 106...Analysis frequency upper limit value determining means 107...Driving condition detection means 108...Analysis frequency upper limit value correction means

Claims (2)

[Claims] 1. A radar (101) installed in a part of a vehicle that emits millimeter waves or laser light to obstacles and receives reflected waves, and converts the output signal of the radar (101) into a digital signal. A signal converting means (102) for converting signals, a frequency analyzing means (103) for frequency analyzing the signal digitalized by the signal converting means (102), and an inter-vehicle distance based on the frequency analysis result by the frequency analyzing means (103). inter-vehicle distance determining means (104) for determining;
An inter-vehicle distance measuring device comprising: a traveling speed detecting means (105) for detecting the traveling speed of the own vehicle; and the frequency analyzing means (103) based on the traveling speed of the own vehicle detected by the traveling speed detecting means (105). analysis frequency upper limit determining means (106) for determining the upper limit of the frequency to be analyzed;
An inter-vehicle distance measuring device characterized by having: 2. A driving condition detecting means (107) for detecting the driving condition of the own vehicle, and an analysis frequency upper limit determining means (106) based on the output of the driving condition detecting means (107).
2. The inter-vehicle distance measuring device according to claim 1, further comprising analysis frequency upper limit value correction means (108) for correcting the analysis frequency upper limit value determined by the method.