JP2020012702A - Radar device for vehicles - Google Patents

Abstract

To provide a radar device for vehicles with which it is possible to realize wide-angle detection without performing a beam scan, and which is advantageous in detecting a moving object to either side or ahead of a vehicle.SOLUTION: The radar device comprises a transmit antenna oriented in a direction that interests the longitudinal direction of a vehicle, a first and a second receive antenna arranged by being shifted in the longitudinal direction of the vehicle, a millimeter wave transmit unit capable of transmitting by switching non-modulated CW and modulated CW from the transmit antenna, and a signal processing unit for processing the received signal of each receive antenna. The radar device executes a first detection mode in which, with a non-modulated CW transmitted by the millimeter wave transmit unit, the relative speed and direction of a moving object are detected from a first Doppler signal (Δf1) obtained from the reflected wave received by the first receive antenna and the transmitted wave and a second Doppler signal (Δf2) obtained from the reflected wave received by the second receive antenna and the millimeter wave, and executes a second detection mode in which, when the relative speed of the moving object is greater than or equal to a threshold, the transmitted wave is changed to a modulated CW and the distance to the moving object is calculated from the received signal component.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a radar apparatus for a vehicle, and more particularly, to a radar apparatus for a vehicle for detecting a moving body on a side or a front side of a vehicle.

  Vehicles are equipped with sensors for detecting other moving or stationary objects. For example, a camera, a millimeter wave radar, a lidar, and the like are mounted on the front of the vehicle, but the camera has a problem in detection accuracy at night or in bad weather. LIDER is advantageous for detecting a three-dimensional shape of a stationary object at a wide angle, but has a problem that a complicated system is required for detecting the relative speed of a moving object.

  Millimeter-wave radar is suitable for long-distance monitoring because it has a long detection distance regardless of the weather, and is used for monitoring vehicles ahead and obstacles in high-speed regions.However, high gain is used to secure detection sensitivity. Then, there is a problem that the radiation angle becomes narrow.

  By the way, as the road conditions where other moving objects should be detected, there are moving objects (eg, four-wheeled vehicles, two-wheeled vehicles, and bicycles) approaching from the left and right directions at the intersection, in addition to detecting the preceding vehicle and the following vehicle on the own vehicle's running path. . Particularly, at an intersection where there is no signal, an intersection where the priority is unclear, or an intersection where visibility is poor, a head accident is likely to occur. Since the intersecting roads do not always intersect at a right angle, it is necessary to detect a wide range. In addition, since a vehicle having a high relative speed is assumed, a high detection sensitivity is also required.

  When performing detection over a wide range while maintaining detection sensitivity with a millimeter wave radar, there is also a method of performing beam scanning by electronic control (for example, see Patent Document 1). However, it is necessary to mount the radar device in a limited space inside the bumper when detecting a moving object on the side or the front side of the vehicle without complicating the device.

JP 2014-6072 A

  The present invention has been made in view of the above situation, and has as its object to realize wide angle detection without performing beam scanning, and to detect a moving object on the side or front side of a vehicle. It is another object of the present invention to provide a vehicle radar apparatus which is advantageous.

In order to solve the above problems, the present invention provides
A vehicle radar device for monitoring a side or a front side,
A transmitting antenna oriented in a direction intersecting the vehicle length direction,
First and second receiving antennas arranged offset in the vehicle length direction;
A millimeter-wave transmitting unit capable of switching and transmitting unmodulated CW / modulated CW from the transmitting antenna;
A signal processing unit that processes a signal received by each of the receiving antennas,
An unmodulated CW is transmitted from the transmitting antenna by the millimeter wave transmitting unit, and a reflected wave received by the first receiving antenna and a first Doppler signal obtained from the transmitted wave, and received by the second receiving antenna Executing a first detection mode for detecting the relative speed and direction of the moving object from the reflected wave and the second Doppler signal obtained from the millimeter wave;
When the relative speed of the moving object is equal to or greater than a threshold, a second detection mode in which the transmission wave from the transmitting antenna by the millimeter wave transmitting unit is switched to modulation CW and the distance of the moving object is calculated from a received signal component. Configured to run.

  As described above, the vehicular radar device according to the present invention transmits the unmodulated CW at a wide angle in the first detection mode, and determines the relative speed and direction of the moving body approaching from a wide area on the side or front side of the vehicle. If a moving object whose relative speed is equal to or higher than the threshold is detected, the transmission wave is switched to the modulation CW in the second detection mode, and the distance to the moving object is calculated. Angle detection can be realized, and a moving body approaching from the side or front side of the vehicle can be detected with high sensitivity by a simple configuration. Moreover, since the antenna itself does not require a high gain, it is suitable for miniaturization, and is advantageous for installation in a limited space inside a vehicle bumper.

It is a block diagram showing a radar device of an embodiment of the present invention. 1 is a plan view of a vehicle including a radar device according to an embodiment of the present invention. It is a schematic diagram which shows the moving body detection by the radar device of the embodiment of the present invention. (A) is a schematic diagram which shows the detection of the relative speed and azimuth of the moving body approaching from the front side, (b). 5 is a flowchart illustrating an operation of the radar device according to the embodiment of the present invention. FIG. 4 is an explanatory diagram showing a transition from a first detection mode to a second detection mode.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a radar apparatus 1 according to an embodiment of the present invention. In FIG. 1, a radar apparatus 1 according to an embodiment of the present invention includes a transmitting antenna 10, first and second receiving antennas 11, 12, It includes a millimeter wave transmitting unit 20, first and second receiving amplifiers and mixers 21, 22, a signal modulating unit 30, band pass filters 31, 32, AD converters 41, 42, and a signal processing unit 40.

  As shown in FIG. 2, the radar devices 1 (L, R) are directed sideways to the left and right front sides of the vehicle 4 so as to detect a moving body approaching from the left or right side or the front side of the vehicle 4. Are located. The left and right radar devices 1 (L, R) have the same structure as the target, and the respective transmitting antennas 10 and receiving antennas 11, 12 are arranged in the vehicle length direction x and fixedly arranged on a common mounting frame, It is arranged inside the bumper fascia (resin bumper). In addition, the vehicle 4 is equipped with a millimeter wave radar device 2 for forward monitoring and a camera device 3 including a stereo camera or a monocular camera.

  The transmitting antenna 10 is disposed at the center of the two receiving antennas 11 and 12 and is oriented in a direction intersecting the vehicle length direction x of the vehicle 4. In the illustrated example, the transmitting antenna 10 is at 65 degrees with respect to the traveling direction a of the vehicle 4. Orientation. The beam width (radiation angle, half-value angle) of the transmission antenna 10 is set to be a wide angle of ± 30 to 45 degrees in a horizontal plane and 60 to 90 degrees as a whole with respect to the radiation direction. In the illustrated example, the angle is set to about 85 degrees so that it can be detected.

  Of the two receiving antennas 11 and 12, the first receiving antenna 11 is arranged at a predetermined distance from the transmitting antenna 10 on the front side in the vehicle length direction, and the second receiving antenna 12 is And is arranged at the rear side in the vehicle length direction by the predetermined dimension. The beam widths 11a and 12a of the two receiving antennas 11 and 12 are set so as to have a wide angle of ± 30 to 45 degrees in a horizontal plane with respect to the radiation direction as in the transmitting antenna 10, and 60 to 90 degrees as a whole, In the illustrated example, the angle is set to about 85 degrees.

  Although the two receiving antennas 11 and 12 can be oriented in the same direction as the transmitting antenna 10, as shown in the illustrated example, the first receiving antenna 11 is located on the front side in the vehicle length direction with respect to the transmitting antenna 10, The receiving antenna 12 can be oriented rearward of the transmitting antenna 10 in the vehicle length direction so as to have a declination of 1 to 5 degrees, respectively. As the transmitting antenna 10 and the receiving antennas 11 and 12, a small planar patch array antenna can be suitably used.

  The millimeter wave transmitting unit 20 includes a millimeter wave (76 GHz) oscillator serving as a transmission wave, a directional coupler for distributing a part of the transmission wave to the reception amplifiers / mixers 21 and 22, a power amplifier, and the like. By turning on / off the signal modulating unit 30 that generates a signal, it is possible to switch between a non-modulated continuous wave (CW) and a frequency modulated continuous wave (FMCW) and output the same from the transmitting antenna 10.

  The receiving amplifiers / mixers 21 and 22 mix the reflected wave received by the receiving antennas 11 and 12 with the local wave distributed from the millimeter wave transmitting unit 20, respectively. It is composed of a mixer that generates a beat signal.

  The signal processing unit 40 performs FFT (Fast Fourier Transform) processing for analyzing the frequency of the generated beat signal, and calculates the relative speed and direction of the moving object from the received signal components at the time of unmodulated continuous wave (CW) transmission. ROM that stores a program for executing processing (first detection mode) and secondary processing (second detection mode) for calculating the distance of a moving object from a received signal component at the time of frequency-modulated continuous wave (FMCW) transmission. It is implemented as a computer (MPU) including a (flash memory), a CPU for performing arithmetic processing, a RAM from which the program is read out, and a working area of the CPU and a temporary storage area for calculation results, and an input / output interface.

  The radar apparatus 1 configured as described above executes the first detection mode for detecting the relative speed and direction of a moving object located in a wide area by the unmodulated CW method, and when the moving object is detected by the first detection mode. The mobile unit is configured to perform two-stage detection of executing a second detection mode for detecting a precise distance by the FMCW method.

  Wide-angle detection is indispensable for detecting a moving body approaching from the side or front side of the vehicle. However, if the beam width (radiation angle) is widened, the antenna gain relatively decreases and the detection sensitivity also decreases. That is as described above. The maximum range of the radar is proportional to the antenna gain and inversely proportional to the noise bandwidth of the receiver. The noise intensity of the receiving unit is proportional to the frequency bandwidth of the signal.

  Then, by transmitting the unmodulated CW having a narrow frequency bandwidth in the first detection mode, it is possible to detect a moving object in a wide range while suppressing the noise of the receiving unit and securing the detection sensitivity. Generally, the frequency bandwidth at the time of FM modulation is several thousand MHz, whereas the frequency bandwidth of the unmodulated CW is only several MHz.

  Further, when a moving object is detected by the non-modulation CW method, the frequency band of the received signal is determined. Therefore, the band-pass filters 31 and 32 can be inserted in accordance with the frequency band, and a signal without noise can be obtained. Becomes

(First detection mode)
FIG. 3 illustrates, as an example of the moving object detection by the radar device 1 of the vehicle 4, a case where there is a moving object 5 (another vehicle) traveling from right to left so as to cross the path ahead of the vehicle 4. . As shown in the figure, when a non-modulated CW (millimeter wave) having a wide-angle beam width is radiated from the transmission antenna 10 of the radar apparatus 1R to the right side or the right front side with respect to the traveling direction a of the vehicle 4 as a transmission wave 10w. The reflected waves 11w and 12w from the moving body 5 reach the first and second receiving antennas 11 and 12, respectively.

  The reflected waves 11w and 12w are Doppler-shifted according to the relative speed of the moving body 5, and are mixed with the local waves (transmitted waves) by the reception amplifiers / mixers 21 and 22 to obtain a Doppler frequency (difference frequency). The beat signal corresponding to is detected. At this time, since the two receiving antennas 11 and 12 are arranged to be shifted forward and backward in the vehicle length direction (the traveling direction a) with respect to the transmitting antenna 10, the relative speed of the moving body 5 is determined as follows. Direction can be detected.

  As shown in FIG. 4A, when the moving body 5a is approaching the vehicle 4 from just beside at a speed V, the distance between the moving body 5a and the two receiving antennas 11 and 12 is equal to the azimuth. The Doppler frequencies Δf1 and Δf2 are equal, and the relative speed Vc is equal to the speed V of the moving object 5.

  On the other hand, as shown in FIG. 4B, when the moving object 5b is traveling at a speed V so as to cross the front of the path of the vehicle 4, the distance and the azimuth between the moving object 5b and the two receiving antennas 11 and 12 are determined. Is different, and the Doppler frequencies Δf1 and Δf2 are different accordingly, so that the azimuth of the moving object 5b can be obtained from the difference between Δf1 and Δf2.

  If the moving object 5 is on the front side of the vehicle 4, the detection distance of the receiving antenna 11 is shorter than that of the receiving antenna 12, so that the Doppler frequency is Δf1> Δf2. Conversely, if the moving body 5 is behind the host vehicle 4, the detection distance of the receiving antenna 11 is longer than that of the receiving antenna 12, so that the Doppler frequency is Δf1 <Δf2.

  That is, when the moving body is right beside, in other words, when the azimuth angle of the moving body with respect to the traveling direction a of the vehicle 4 is 90 degrees, the difference between the Doppler frequencies Δf1 and Δf2 is zero, and the moving body is located on the front side. In other words, the difference between the Doppler frequencies Δf1 and Δf2 increases as the azimuth angle of the moving body with respect to the traveling direction a decreases. This shows the correlation between the azimuth angle and the cosine of the traveling direction a, and the azimuth can be estimated from the difference between the frequencies Δf1 and Δf2.

  The azimuth can be calculated from the phase difference between the Doppler frequencies Δf1 and Δf2 and the interval between the two receiving antennas 11 and 12, but as described above, the azimuth of the moving object is directly estimated from the difference between the Doppler frequencies Δf1 and Δf2. This simplifies the processing, and is suitable for the purpose of the radar apparatus 1 for detecting a moving body approaching from the side or the front side of the vehicle 4.

The relative speed Vc of the moving object 5 can be obtained from the following equation from the Doppler frequencies Δf1 and Δf2. Here, C is the speed of light.
Vc = (C / 2f) (Δf1 + Δf2) / 2

  Further, since the two receiving antennas 11 and 12 are arranged shifted from each other in the vehicle length direction x, if only the front receiving antenna 11 is detected, it is a moving body in front, and only the rear receiving antenna 12 is used. The detected moving object is a rear moving object. When the two receiving antennas 11 and 12 are oriented with a declination in the front and back, the possibility of detection by any of the front and rear receiving antennas 11 and 12 increases, and the overlapping area and the It will have three detection areas, the front and rear, non-overlapping areas.

(Second detection mode)
When the relative speed and azimuth of the moving object 5 (5a, 5b) are detected in the first detection mode based on the non-modulation CW method as described above, and the relative speed is a significant value equal to or more than a predetermined threshold, the signal is output. The modulation unit 30 is turned on, the mode shifts to the second detection mode based on the FMCW method, and the distance to the moving object 5 is measured. In the second detection mode, the bandwidth is widened and the reception signals of the two reception antennas 11 and 12 are substantially the same, so that only one signal may be used.

In the FMCW method, the transmission wave is subjected to FM modulation (triangular wave) having a modulation period T and a frequency modulation width ΔF, so that the reception wave reflected by the moving object 5 is Doppler shifted according to the relative speed Vc with respect to the moving object 5. Since the beat signals f _BH and f _BL according to the Doppler frequency (difference frequency) are detected, and the round trip propagation delay time τ = 2L / C according to the distance L from the moving object 5 occurs, the distance L , Relative speed Vc is obtained by the following equation.
L = CT (f _BH + f _BL ) / 8ΔF
_{Vc = C (f BH -f BL} ) / 4f

FIG. 6 shows a transition from the first detection mode using the unmodulated CW method to the second detection mode using the FMCW method. First, in the first detection mode, the Doppler signal fd is detected and subjected to FFT processing using a band-pass filter (BPF) to specify a Doppler frequency. At this time, the relative speed of the moving object (Tg) is determined. Then, the FM modulation is started, the mode is shifted to the second detection mode, the beat signals f _BH and f _BL are detected, and the distance to the moving object (Tg) is calculated.

Even when a plurality of moving objects (Tg, Tg '...) Are present, the relative speeds and azimuths are not exactly the same, so that they are simultaneously or sequentially detected as different Doppler signals fd' in the first detection mode. Further, in the second detection mode, different beat signals f _BH 'and f _BL ' are detected, and are detected as different moving objects (Tg ') having different distances and directions.

  In general, a target having no relative speed is detected by the FMCW method. In the second detection mode, a moving object having a significant relative speed is detected in the first detection mode, and a band-pass filter (BPF) is used. In addition, since the mode is shifted to the second detection mode based on the FMCW method in a state where the mobile object is locked on, the load on the calculation process is small, and only the target with high importance can be reliably detected.

(Operation flow of moving object detection)
Next, an operation of the vehicle radar device based on the above embodiment will be described with reference to FIG.
When the external detection system of the vehicle 4 is activated, the radar device 1 enters the first detection mode, the signal modulation unit 30 is kept off, and the millimeter wave transmission unit 20 transmits the unmodulated CW millimeter wave from the transmission antenna 10. Radiation is performed at a wide angle on the side or front side in the traveling direction a (step 100).

  At the same time, the signal processing unit 40 starts detection of a Doppler signal (beat signal) obtained from the reflected wave and the transmitted wave via the receiving antennas 11 and 12, the receiving amplifier / mixers 21 and 22, and the AD converters 41 and 42 ( Step 101).

  When a Doppler signal is detected from the reflected waves received by the receiving antennas 11 and 12, it is considered that a moving object has been detected, and the band-pass filters 31 and 32 that pass only the frequency band of the Doppler signal are used. Then, the Doppler frequencies Δf1 and Δf2 are specified by FFT (step 102).

  Next, the signal processing unit 40 calculates the relative speed Vc and direction of the moving object based on the respective Doppler frequencies Δf1 and Δf2 (step 103), and determines whether the relative speed Vc is equal to or higher than a predetermined threshold (step 103). 104). If the relative speed Vc is less than the threshold, the urgency is considered to be low, and the moving object detection in the first detection mode (non-modulation CW method) is continued.

  If the relative speed Vc is equal to or higher than the threshold, the signal modulation section 30 is turned on, the transmission wave is FM-modulated, and the mode shifts to the second detection mode based on the FMCW method (step 110). A bead frequency is obtained by applying FFT to a bead signal generated from the FM-modulated transmission wave and its reflected wave, and a distance L to the moving object is calculated based on the bead frequency (step 111).

  If the predicted arrival time TTC calculated from the distance L to the moving object and the relative speed Vc is within a predetermined time (step 112), it is determined that the moving object is approaching the danger area, and a sound, a display lamp, An alarm is output to an alarm means such as a screen display to warn the driver of the approach of the moving body (step 113). Alternatively, avoidance measures such as outputting a braking command to the ESP / ABS controller of the vehicle 4 and activating the automatic brake are performed.

  As described above, the vehicular radar device according to the present invention can detect a wide range of moving objects on the side or front side of the vehicle as shown in FIG. It is suitable for detecting a wheelchair, a two-wheeled vehicle, and a bicycle, and is particularly advantageous in preventing a head-on accident at an intersection where there is no traffic light, an intersection where the priority is unclear, or an intersection with poor visibility.

In the above-described embodiment, the case has been described in which FM modulation is performed with a triangular wave from which two beat signals f _BH and f _BL are obtained in the second detection mode. Can also. Further, instead of the FMCW method, signal processing may be performed by a two-frequency CW method to determine the distance of the moving object.

  Further, in the above embodiment, the case where the transmitting antenna 10 is arranged at the center of the first and second receiving antennas 11 and 12 has been described, but it is not always necessary to arrange the transmitting antenna 10 at the center.

  As described above, some embodiments of the present invention have been described, but the present invention is not limited to the above embodiments, and various modifications and changes can be made based on the technical idea of the present invention. Is added.

1, 1L, 1R radar device 4 Vehicle 5, 5a, 5b Moving object 10 Transmitting antenna 11 First receiving antenna 12 Second receiving antenna 20 Millimeter wave transmitting unit 21 First receiving amplifier / mixer 22 Second receiving amplifier・ Mixer 30 Signal modulation unit 40 Signal processing unit

Claims (5)

A vehicle radar device for monitoring a side or a front side,
A transmitting antenna oriented in a direction intersecting the vehicle length direction,
First and second receiving antennas arranged offset in the vehicle length direction;
A millimeter-wave transmitting unit capable of switching and transmitting unmodulated CW / modulated CW from the transmitting antenna;
A signal processing unit that processes a signal received by each of the receiving antennas,
An unmodulated CW is transmitted from the transmitting antenna by the millimeter wave transmitting unit, and a first Doppler signal obtained from a reflected wave and a transmitted wave received by the first receiving antenna, and received by the second receiving antenna Executing a first detection mode for detecting the relative speed and direction of the moving object from the reflected wave and the second Doppler signal obtained from the millimeter wave,
A second detection mode for switching a transmission wave from the transmission antenna by the millimeter wave transmission unit to a modulation CW when a relative speed of the moving body is equal to or more than a threshold, and calculating a distance to the moving body from a received signal component; Vehicle radar device configured to execute the following.   The first receiving antenna is arranged to be shifted to the front in the vehicle length direction with respect to the transmitting antenna, and the second receiving antenna is arranged to be shifted to the rear in the vehicle length direction with respect to the transmitting antenna. The vehicle radar device according to claim 1.   The vehicle radar device according to claim 1, wherein the modulation CW is an FMCW.   The transmission antenna, the first reception antenna, and the second reception antenna, wherein an overlap of a beam width between a side of the vehicle and a front side of the vehicle is 70 degrees or more. A radar device for a vehicle according to claim 1.   With respect to the radiation direction of the transmitting antenna, the beam direction of the first receiving antenna is oriented so as to have a declination forward in the vehicle length direction, and the beam direction of the second receiving antenna is deflected backward in the vehicle length direction. The vehicle radar device according to claim 4, wherein the radar device is oriented to have an angle.

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