JPH08211145A - Radar unit carried on vehicle - Google Patents

Abstract

PURPOSE: To obtain a radar unit in which the modulation frequency of carrier waves is changed on the basis of the relative distance of a computed target object, in which the relative velocity of a target object is detected with high accuracy at a short distance and in which the pairing operation of peaks in the frequency rise section and the fall section of a plurality of target objects is performed easily at a long distance. CONSTITUTION: A target recognition device 30 detects peaks of powere spectrums in a frequency rise section and a fall section so as to perform a pairing operation, and it finds a relative distance and a relative velocity simultaneously. A danger judgment device 32 compares magnitudes of a predetermined safe distance and the relative distance so as to judge a danger. Then, the resolution of a relative velocity obtained from a relative velocity frequency appearing as a frequency difference becomes large, the larger a modulation frequency is. When the modulation frequency is large, the relative velocity frequency becomes relatively smaller with reference to a relative distance frequency, and the measuring accuracy of the relative velocity becomes worse. However, when a plurality of target objects exist, the difference between a peak in the frequency rise section and a peak in the fall section becomes smaller, and the pairing operation of the target objects can be performed easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-vehicle radar device, and more particularly to an on-vehicle radar device for detecting a preceding vehicle.

[0002]

2. Description of the Related Art Conventionally, an on-vehicle radar device has been developed which irradiates a radar beam in front of its own vehicle to detect a relative distance and a relative speed to a target object such as a preceding vehicle. For example, Japanese Patent Application Laid-Open No. 2-198380 discloses that a carrier wave is frequency-modulated by a trapezoidal wave and the relative velocity of a target object is accurately detected from the frequency of a beat signal in a period in which the carrier wave frequency is constant. .

[0003]

When there are a plurality of target objects to be detected, the beat signals of the transmitted wave and the received wave are generated for the plurality of target objects, and the beat signals and the target objects are generated. There was a problem that it was difficult to know the correspondence relationship with.

[0004] The present invention has been made in view of the above points,
By changing the modulation frequency of the carrier wave based on the relative distance of the target object, the relative speed of the target object can be detected with high accuracy at a short distance, and the frequency rising section and the frequency falling section of a plurality of target objects can be detected at a long distance. It is an object of the present invention to provide an on-vehicle radar device that facilitates pairing of the peaks of 1.

[0005]

As shown in FIG. 1, the present invention transmits and receives a frequency-modulated carrier wave from a radar apparatus main body M1 and forms pairs in the power spectrum of the beat signal in each of the frequency rising section and the frequency falling section. An in-vehicle radar device that calculates a relative distance and a relative speed to a target object from the frequency of a peak formed has a modulation frequency changing means M2 that changes the modulation frequency of a carrier wave based on the calculated relative distance of the target object. .

[0006]

In the present invention, since the modulation frequency of the carrier is changed based on the calculated relative distance of the target object,
When the target object is at a short distance, the relative frequency of the target object can be detected with high accuracy by decreasing the modulation frequency and increasing the relative speed frequency, and when the target object is at a long distance, the modulation frequency Is increased to relatively reduce the relative velocity frequency, which facilitates pairing of peaks in the frequency rising section and the frequency falling section of the plurality of target objects.

[0007]

FIG. 2 shows a block diagram of the device of the present invention. In the figure, the transmission side circuit includes a carrier wave generator 10 and a frequency modulator 1.
2. The modulation voltage generator 14, the directional coupler 16, and the transmission antenna 18 are included. A carrier wave is output from the carrier wave generator 10 and supplied to the frequency modulator 12. On the other hand, the modulation voltage generator 14 outputs a triangular wave having a repeating frequency fm whose amplitude changes in a triangular shape, and is supplied to the frequency modulator 12 as a modulating wave. As a result, the carrier wave from the carrier wave generator 10 is frequency-modulated, and a transmission signal whose frequency changes in a triangular shape over time is output. This transmission signal is supplied to the transmission antenna 18 via the directional coupler 16 and radiated toward the object to be detected. On the other hand, a part of the transmission signal is supplied to the mixer 22 of the receiving side circuit described later via the directional coupler 16.

The receiving side circuit includes a receiving antenna 20, a mixer 22, an amplifier 24, a filter 26, a fast Fourier transform processor (FFT signal processor) 28, and a target recognizer 3.
0, a risk determiner 32, and an alarm 34.
The reflected wave from the detected object is received by the receiving antenna 20 and supplied to the mixer 22. In the mixer 22, the reception signal and a part of the transmission signal from the directional coupler 16 are combined by a difference calculation to generate a beat signal. The beat signal from the mixer 22 is amplified by the amplifier 24, and is supplied to the FFT signal processor 28 and the target recognizer 30 via the anti-aliasing filter 26. The FFT signal processor 28 obtains a power spectrum in each of the frequency rising section and the frequency falling section, and supplies the power spectrum to the target recognizer 30.

The target recognizer 30 has a frequency increasing section,
The peaks of the power spectrum of each descending section are detected and pairing is performed to form a peak pair corresponding to each target object. The relative velocity frequency fd and the relative distance frequency fr fd = (fdown-fup) / 2 (1) fr = (fdown +) obtained from the peak frequency fup in the frequency rising section and the peak frequency fdown in the frequency falling section of this peak pair. fup) / 2 (2) and fd = 2 · V · f0 / C (3) fr = 4 · fm · Δf / C · R (4) where V: relative velocity, C: speed of light, f0: Center frequency, f
m: modulation frequency, Δf: frequency shift width of, for example, 75 MH
z, R: Relative distance R and relative velocity V are simultaneously obtained from After that, the size of the safety distance and the relative distance, which is predetermined by the risk determiner 32 or calculated according to the running state of the vehicle, is compared. If the safety distance is less than or equal to the safety distance, it is determined to be dangerous, The driver is notified by the alarm device 34.

By the way, the relative velocity frequency fd is simply a function of the relative velocity V, as is apparent from the equation (3). However, it can be seen from the equation (4) that the relative distance frequency fr changes depending on the modulation frequency fm of the triangular wave. Further, ΔT = 1/2 · fm in each of the frequency rising section and the frequency falling section. When the peak frequency is calculated by performing FFT signal processing in each section, if the sampling period is constant, the frequency difference Δf between adjacent peaks, that is, the resolution is Δf = 1 / ΔT.
Therefore, Δf = 2 · fm. The relative velocity resolution ΔVd obtained from the relative velocity frequency fd appearing as the frequency difference Δf increases as the modulation frequency fm increases, as shown by the solid line in FIG. That is, the smaller the modulation frequency fm, the smaller the resolution of the relative velocity and the better.

Therefore, when the modulation frequency fm is small, the relative speed frequency fd becomes relatively large with respect to the relative distance frequency fr, and the measurement accuracy of the relative speed V is improved. However, when there are a plurality of target objects, the peaks u1, u2, and u3 in the frequency increasing section (up section) shown in FIG. 4A and the frequency falling section (down section) shown in FIG. When the difference between the frequencies of the peaks d1, d2 and d3 becomes large and the relative speed of each target object is large, for example, the frequency of the peak d1 becomes larger than the frequency of the peak d2, and the peaks u1 and d1. , It is difficult to pair the peaks u2 and d2 and the peaks u3 and d3.

On the contrary, when the modulation frequency fm is high, the relative velocity frequency fd becomes relatively small with respect to the relative distance frequency fr, and the measurement accuracy of the relative velocity V deteriorates. However, when there are a plurality of target objects, FIG.
Peaks u1 and u in the frequency increase section (up section) shown in
2 and u3, and the frequency falling section (do
(during wn interval), the frequency difference between the peaks d1, d2, d3 becomes small, and even if the relative velocity of each target object is large, the arrangement of the frequencies of the peaks u1, u2, u3 and the peaks d1, d3.
Since the frequencies of 2 and d3 are arranged in the same order, pairing of each target object is easy.

FIG. 6 shows a flow chart of an embodiment of the modulation frequency control processing as the modulation frequency changing means M2 executed by the target recognizer 30. In the figure, step S1
At 0, a command is issued to the modulation voltage generator 14,
The modulation frequency fm is, for example, a frequency fm of 780 Hz.
Set to.

Next, in step S20, target recognition is performed. Here, the power spectrum supplied from the FFT signal processor 28 is taken in, and each target object is expressed by using the formulas (1) to (4) for each peak pair of the frequency rising section and the frequency falling section, that is, for each target object. The relative distance R and the relative velocity V of V are calculated.

After that, the process proceeds to step S30, and it is determined whether or not the relative distance D _T to the recognized target object is less than the threshold value D _L. Here, when there is a single target object, its relative distance R is D _T, and when there are multiple target objects, the minimum relative distance R is D _T. The threshold value D _L is, for example, 30 m.

When D _T <D _L , the target object is in a short distance less than D _L , so that the time for avoiding danger is short and it is necessary to know the relative speed of the target object with high accuracy. Since the spread of the radar beam is small at a short distance and a plurality of target objects are unlikely to be detected, the process proceeds to step S40 to issue a command to the modulation voltage generator 14 to set the modulation frequency fm to the frequency fmL of 390 Hz, for example. And the process proceeds to step S20.

D in step S30_T≧ D_LIn case of
Relative distance D_TIs the threshold D_H(D_HIs an example
For example, it is determined whether or not it exceeds 70 m. Where D_T
> D _HIf the target object is D_HOver a long distance
Therefore, it takes a long time to avoid danger,
You do not need to know the speed with high accuracy,
The spread of the beam is large and it is possible to detect multiple target objects.
Since there is a high need for high efficiency and easy pairing,
In step S60, the modulation voltage generator 14 is
Issue a command and set the modulation frequency fm to 1500 Hz, for example.
To the frequency fmH, and the process proceeds to step S20.

In step S50, D_T<D_Hin the case of
Proceeds to step S70, and the target object is D_LTo D_HUntil
The modulation frequency fm is equal to the frequency f
Set to mM and proceed to step S20. by this,
Relative distance D to the target object_TIs D_L≤D_T≤D_HMiddle distance
In the case of, the modulation frequency fm is fmM shown by the solid line in FIG.
Be done. Relative distance D_TIs D_T<D _LModulation for close range of
The frequency fm is set to fmL indicated by the alternate long and short dash line in FIG.
Therefore, the relative velocity frequency fd is compared with the relative distance frequency fr.
The relative speed of the target object with high accuracy
Can be detected.

Further, when the relative distance D _T is a long distance D _T > D _H , the modulation frequency fm is set to fmH shown by a broken line in FIG. 7, whereby the relative velocity frequency fd is relative to the relative distance frequency fr. It becomes relatively small, and the peaks in the frequency rising section and the frequency falling section of the plurality of target objects are arranged in the same frequency order, which facilitates pairing of the peaks.

[0020]

As described above, according to the present invention, the modulation frequency of the carrier wave is changed based on the calculated relative distance of the target object. Therefore, when the target object is in a short distance, the modulation frequency is reduced. The relative velocity of the target object can be detected with high accuracy by increasing the relative velocity frequency relatively, and the modulation frequency is increased and the relative velocity frequency is relatively decreased when the target object is at a long distance. Thus, the pairing of peaks between the frequency rising section and the frequency falling section of a plurality of target objects becomes easy, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of the device of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between modulation frequency and resolution.

FIG. 4 is a diagram showing correspondence between beat signals in a frequency rising section and a frequency falling section.

FIG. 5 is a diagram showing correspondence between beat signals in a frequency rising section and a frequency falling section.

FIG. 6 is a flowchart of a modulation frequency control process.

FIG. 7 is a diagram showing a modulation signal waveform.

[Explanation of symbols]

 10 carrier wave generator 12 frequency modulator 14 modulation voltage generator 16 directional coupler 18 transmission antenna 20 reception antenna 22 mixer 24 amplifier 26 filter 28 FFT signal processor 30 target recognizer 34 alarm device M1 radar device body M2 modulation frequency change means

Claims (1)

[Claims] 1. A vehicle-mounted device that transmits and receives a frequency-modulated carrier wave and calculates a relative distance and a relative velocity with respect to a target object from frequencies of a pair of peaks in a power spectrum of a beat signal in each of a frequency rising section and a frequency falling section. The radar apparatus has a modulation frequency changing means for changing the modulation frequency of a carrier wave based on the calculated relative distance of the target object.