JPS6343715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to improvements in FM-CW radar devices for automobiles.

PRIOR ART Recently, as a safety measure for automobiles mainly aimed at protecting occupants, radar devices are installed in automobiles to measure the distance and relative speed between them and other automobiles or obstacles. The development of inter-vehicle distance control or collision prevention systems that prevent collisions by warning the driver or applying automatic braking is currently underway.

Conventionally, this type of radar device is a dual-frequency Doppler radar that measures the distance and relative speed of an object based on the Doppler frequency shift that occurs due to the relative speed of the reflected waves of radio waves emitted toward the object. and pulse radar, which calculates the distance to the target by measuring the round trip time of radio waves emitted toward an object until it is reflected and transmitted, and the distance is determined from the beat frequency caused by the phase shift between the transmitted and received waves. FM-CW radars are widely used, but dual-frequency Doppler radars do not work unless there is a relative velocity between them and the target, whereas pulse radars and FM-CW radars cannot operate even if the relative velocity is zero. Since it is possible to measure the distance of , an adaptive radar will naturally be determined when targeting an obstacle whose relative speed is zero.

In addition, especially with the latter type of radar equipment, pulse radar cannot measure distances below the distance corresponding to its output pulse width, so the output pulse width must be made extremely small in order to measure close ranges. Therefore, the structure of the pulse oscillator itself and the reception of its reflected waves are technically difficult, but in contrast, FM-CW radar has a relatively simple structure and excellent controllability. , and has the advantage of being able to easily perform measurements up to close range.

In the present invention, an FM-
It uses a CW radar method to measure the distance and relative speed to the object.

Before explaining the automotive FM-CW radar device according to the present invention, the operating principle will be described first. As shown in FIG. 1, the oscillation frequency
Radio wave D ₁ of f ₀ with period Tm and frequency deviation Δf
Modulate the wave to raise it to f ₀ + Δf and lower it to f ₀ , emit the modulated radio wave toward the object, receive the reflected wave D ₂ , and compare it with the previously emitted radio wave on the same time axis. Then, the round trip time t _R of the radio wave
This phase shift generates a beat frequency f _R , which is determined by the round trip time of _the radio wave as shown in the second equation below.
Since t _R is proportional to the distance x to the object,
By measuring the magnitude of the beat frequency f _R , it becomes possible to detect the distance x. Also,
By determining the time change in the distance x to the detected object, the relative velocity can be calculated as shown in the third equation.
VR can be detected.

t _R =2x/c (1) where c is the propagation speed of the radio wave.

f _R = 2/Tm・Δf・t _R ………(2) dx/dt=Vr ………(3) Figure 2 shows how this FM-CW radar is mounted on a car, and as described above. Detects the distance and relative speed to the object, calculates the appropriate inter-vehicle distance at that time according to a preset function based on the detection results and the own vehicle's speed signal, and compares it with the actual inter-vehicle distance. This figure shows a conventional device that is configured to make a judgment and appropriately send a necessary command to a sound alarm, an automatic brake, or the like to the outside. That is, the automotive FM-CW radar device modulates the oscillation frequency f ₀ from the oscillator 1 at a constant frequency using the modulator 2, and transmits the modulated output to the antenna 5 via the directional coupler 3 and the circulator 4. The reflected wave from the object received by the antenna 5 is sent to the mixer 6 via the circulator 4, where it is branched from the directional coupler 3. The weak beat frequency _signal is amplified as required by the video amplifier 7, and the amplified signal is sent to the frequency counter 8. The frequency is read here, and the value of the read beat frequency is sent to the signal processing device 9, where the following distance x
In addition to calculating the relative speed Vr by the above calculation, the appropriate vehicle distance is determined in advance based on the speed signal Vs sent from the own vehicle's speedometer, etc., and the calculated relative speed Vr with respect to the other vehicle. The system determines the appropriate inter-vehicle distance Xs at that time according to a predetermined function in which distance characteristics are stored, and compares the appropriate inter-vehicle distance Xs with the actual inter-vehicle distance x. If Xs<x, an alarm or brake command is issued to the outside. configured to send.

However, such conventional FM-CW radar devices have the disadvantage that the negative image detected by the FM-CW radar itself deteriorates its performance and causes malfunction. That is, when there are multiple objects, for example, when there are two cars A and B running parallel to each other at different distances in front of own car C as shown in Fig. The device receives reflected radio waves from both cars A and B, resulting in a mixed beat frequency, making it impossible to distinguish between A and B. In addition, since there is a limit to the directivity of radio waves emitted from the antenna installed in a car, the reflected waves may be received even on a flat road surface. False signals are generated by objects. Furthermore, with conventional FM-CW radar equipment, when the sensitivity of the receiver is increased to detect small objects, it also detects many reflected waves from the road surface, making it impossible to distinguish between them. There are drawbacks.

Purpose The present invention has been made with these points in mind, and is an FM-CW for automobiles that solves the problem of negative images detected by the FM-CW itself and improves the accuracy of detecting objects. It provides radar equipment.

Configuration The automotive FM-CW radar device according to the present invention includes:
The beat frequency band corresponding to the detection distance targeted by the radar is subdivided, and the mixed beat frequencies from multiple targets are decomposed so that the beat frequencies corresponding to each distance range can be received separately and independently. At the same time, the magnitude of each decomposed frequency component of the reflected wave from the road surface (which is reflected from a wide range of road surfaces in front of the antenna and produces a mixed beat frequency) is converted into a level in advance, and the level value is calculated. This makes it possible to extract only the necessary information by removing noise caused by road reflection from each frequency component of the received wave.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 4, the automotive FM-CW radar device according to the present invention is constructed using
In the figure), there is a signal extraction circuit _S1 consisting of a channel divider 10 and a filter gate 11 connected in series between the video amplifier 7 and the frequency counter 8, and the channel divider 10 and a signal processing unit (CPU). A channel selection circuit S2 consisting of a detector 12, an offset level circuit 13, a multiplexer 14 and an A/D converter 15 is provided between the channel selection circuit S2 and the channel selection circuit _S2 connected in series between the channel selection circuit S2 and the channel selection circuit S2.

Automotive device according to the present invention configured as described above
In the FM-CW radar device, as described above, frequency-modulated continuous wave radio waves are emitted from the antenna 5, and the radio waves reflected from multiple objects including the road surface are received by the antenna 5 and sent to the mixer. 6
The received wave and the transmitted wave are mixed to generate a beat frequency, which is a signal component. Note that the beat frequency is synthesized from reflected waves from various objects received by the antenna 5.
Since the beat frequency is a weak signal, it is amplified as required by the video amplifier 7 in the next stage and then sent to the channel divider 10, where it is divided into a certain narrow frequency bandwidth that covers the beat frequency band to be detected. 5th filter group with channels
The frequency is resolved as shown in the figure. Next, the frequency-resolved beat frequency signal for each channel is sent to the filter gate 11 and the detector 12, respectively. At this time, the filter gate 11 opens and closes the gate to select a channel in response to a command from a signal processing unit (CPU) 9', and allows only the frequency signal of the selected channel to pass.
Then, the frequency counter 8 reads the frequency and sends the content to the signal processing unit (CPU) 9', where the distance x and relative velocity Vr to the specific object are calculated in the same manner as described above. The appropriate inter-vehicle distance is calculated and determined according to the own vehicle speed Vs.
Xs is determined, and a warning or brake command is issued to the outside as appropriate based on the comparison result between x and Xs.

On the other hand, in order to provide the signal processing unit (CPU) 9' with information for determining the channel selection described above, the beat frequency signal for each channel from the channel divider 10 is sent to the detector 12, where each converted to DC voltage level. The output voltage of each channel in the detector 12 is essentially no signal when there is no object on the road, so each channel is at a constant reference level as shown in Figure 7, but in reality Due to reflected waves from the road surface, the voltage levels of each channel become uneven as shown in FIG. 6, making it impossible to accurately detect a real object on the road. Therefore, the output of the detector 12 is connected to the offset level circuit 1.
3, where the noise due to road reflection is offset. In the offset level circuit 13, the voltage level of each channel when there is no object on the road within the detectable distance range of the object is registered in advance as an offset value. FIG. 8 shows the voltage level state of each channel after offset adjustment when there are two objects A and B at different distances from each other on the road (see FIG. 3). Then, each output of the offset level circuit 13 is sent to the multiplexer 1.
4, where it is sequentially switched and swept starting from the first channel signal, and then sent to the next stage A/D converter 1.
5, the signal is converted into a digital signal, and then sent to a signal processing unit (CPU) 9'. The signal processing unit (CPU) 9' selects, for example, the channel with the highest voltage level (in the case of FIG. 8, channel 4) corresponding to the target object from the output level of each channel from the A/D converter 15. A gate opening command is sent to the filter gate 11 of the selected channel to extract only the beat frequency signal of the necessary channel as described above.

Effects As described above, the FM-CW radar device for automobiles according to the present invention emits radio waves whose oscillation frequency is modulated at a constant frequency, receives the radio waves reflected by the target object, and adjusts the distance between the transmitted and received waves. Means for decomposing the beat frequency signal generated between transmitted and received waves into multiple channels with a constant frequency bandwidth, in a device that calculates the distance or relative velocity to an object based on the beat frequency generated by the wave. and,
Means for converting the decomposed frequency signals for each channel into voltage signals, and the voltage level for each channel when there is no object on the road registered in advance from the voltage level for each channel. and means for selecting the frequency signal of the channel in which the offset voltage level is maximum as the beat frequency signal due to the reflected wave from the target object, and based on the selected beat frequency signal. It is designed to find the distance or relative speed to a target object, and it is possible to separate and extract the mixed beat frequency of multiple objects for each object. It has the excellent advantage of being able to accurately perform distance detection and the like. Furthermore, even when selecting a channel, the beat frequency component due to waves reflected from the road surface is canceled in advance as noise, so there is no false detection. Since it can be canceled, it has various excellent advantages, such as increasing the sensitivity of the receiver and reducing the lower limit of the detectable range of objects.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the operating principle of a general FM-CW radar, and Figure 2 is a conventional FM-CW radar for automobiles.
A block configuration diagram of a CW radar device, FIG. 3 is a diagram showing a state in which there are a plurality of objects in front of the own vehicle, and FIG. 4 is a block configuration diagram showing an embodiment of the present invention.
FIG. 5 is a diagram showing the output characteristics of the channel divider in the same embodiment, FIG. 6 is a diagram showing one characteristic of the output voltage level for each channel of the detector according to the road reflected waves in the same embodiment, and FIG. 8 and 8 are diagrams respectively showing the characteristics of the output voltage level for each channel of the offset level circuit when there is no object and when there is an object in the same embodiment. DESCRIPTION OF SYMBOLS 1... Oscillator, 2... Modulator, 3... Directional coupling part, 4... Circulator, 5... Antenna,
6... Mixer, 7... Video amplifier, 8... Frequency counter, 9,9... Signal processing device, 10...
Channel divider, 11... filter gate,
12...Detector, 13...Offset level circuit, 14...Multiplexer, 15...A/D converter, _S1 ...Signal extraction circuit, _S2 ...Channel selection circuit.

Claims (1)

[Claims] 1 Emit radio waves with the oscillation frequency modulated at a constant frequency, receive the radio waves reflected by the target object,
In an FM-CW radar device that calculates the distance or relative velocity to an object based on the beat frequency generated between the transmitted and received waves, the beat frequency signal generated between the transmitted and received waves has a fixed frequency bandwidth. A means for decomposing the frequency signal into a plurality of channels, a means for converting the frequency signal of each decomposed channel into a voltage signal, and a means for detecting an object on a road registered in advance from the voltage level of each channel. means for offsetting the voltage level of each channel when there is no voltage level, and means for selecting the frequency signal of the channel in which the offset voltage level is maximum as the beat frequency signal due to the reflected wave from the target object. For automobiles, the distance or relative speed to a target object is determined based on the selected beat frequency signal.
FM-CW radar equipment.