JP5284035B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that is mounted on a vehicle and scans a predetermined scanning range with a radar wave, and more particularly to a radar apparatus that controls the output of a transmission radio wave.

  Today, an on-vehicle radar device is used as a means for supporting automatic control of driving of an automobile. In the case of assisting control (following traveling control) in which the preceding vehicle is automatically followed while maintaining a desired inter-vehicle distance, as described in Patent Document 1, the radar apparatus uses the own vehicle. Scanning is performed by transmitting radar waves (radio waves) to the scanning range ahead, and a preceding vehicle to be followed is detected.

  On the other hand, various regulations are provided today in order to avoid radio wave interference between various radio wave services. For example, according to the Radio Law in Japan, the frequency band of radio waves that can be used for each commercial radio wave service is limited, and a millimeter wave band of 76.0-77.0 GHz band is allocated to an on-vehicle radar device. It has been. Then, as the number of on-vehicle radar devices increases, the possibility of radio wave interference between radar devices that use radio waves in the same band increases. Therefore, in-vehicle radar devices are required to suppress unnecessary transmission radio waves as much as possible. In addition, the FCC (Federal Communications Commission) regulations in the United States set different standards for the transmission power of the on-vehicle radar device when the vehicle is running and when the vehicle is stopped. Therefore, it is required to suppress transmission power when the vehicle is stopped.

For this reason, as one method of suppressing unnecessary transmission radio waves, a method of stopping radio wave transmission from the on-vehicle radar device when the vehicle is stopped has been proposed.
Japanese Patent Laid-Open No. 10-325865

  By the way, the following traveling of the vehicle generally includes the following traveling at the time of cruising on an expressway and the following traveling at the time of traffic congestion in the vicinity of the exit of the expressway or in an urban area. In the former, the preceding vehicle normally continues to travel at a certain constant traveling speed, and the host vehicle travels so that the desired inter-vehicle distance is maintained by constantly monitoring the relative speed and relative distance from the preceding vehicle. A control action to adjust the speed is required. On the other hand, in the latter case, the preceding vehicle intermittently stops and travels at a low speed. Therefore, when the preceding vehicle stops, the own vehicle is stopped, and when the preceding vehicle starts traveling at a low speed, the preceding vehicle follows this. A control operation is also required in which the vehicle starts to travel at a low speed. Therefore, in the follow-up running control at the time of traffic congestion, the radar device needs to continuously detect the preceding vehicle and monitor its behavior even when the own vehicle is stopped.

  However, since the radar apparatus according to the above-described prior art stops the radio wave transmission while the vehicle is stopped, the preceding vehicle cannot be detected. For this reason, when the preceding vehicle starts traveling, the driver must start the own vehicle by his / her driving operation to start radio wave transmission to the radar device, thereby enabling follow-up traveling control. As described above, the conventional technique has a problem that the convenience in the follow-up traveling control at the time of traffic congestion is poor.

  Therefore, an object of the present invention is to provide a radar device that can suppress unnecessary radio wave transmission and can detect a preceding vehicle even when the vehicle is stopped.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a radar device that is mounted on a vehicle and scans a predetermined scanning range with a radar wave, and the traveling speed of the vehicle is a first speed. In this case, a radar wave is transmitted for each first unit angle within the scanning range, and when the traveling speed is a second speed slower than the first speed, the first unit angle within the scanning range. A radar having transmission control means for transmitting the radar wave for each wider second unit angle, and target object detection means for detecting the target object by receiving a reflected wave of the transmitted radar wave from the target object An apparatus is provided.

  According to a second aspect of the present invention, there is provided a radar apparatus that is mounted on a vehicle and that alternately transmits and receives radar waves at a predetermined switching period using a common antenna, wherein the traveling speed of the vehicle Is the first speed, the transmission time ratio in the switching period is the first ratio, and when the traveling speed is the second speed slower than the first speed, the transmission time ratio is the first speed. A radar apparatus comprising: a transmission / reception control unit having a second ratio smaller than a ratio of the target; and a target object detection unit configured to detect the target object based on a reflected wave of the transmitted radar wave by the target object. Is provided.

  According to the first aspect, the transmission control unit transmits a radar wave for each first unit angle within the scanning range when the traveling speed of the vehicle is the first speed, and the traveling speed is When the second speed is slower than the first speed, the radar wave is transmitted for each second unit angle wider than the first unit angle within the scanning range, and therefore transmission unnecessary for the entire radar apparatus is performed. The radio wave can be suppressed, and a reflection point of the radio wave necessary for detecting this can be obtained from the target object at a short distance. Therefore, it is possible to accurately detect a preceding vehicle in a short distance by following traveling in a traffic jam.

  Further, according to the second aspect, when the travel speed of the vehicle is the first speed, the transmission control means sets the ratio of the transmission time in the switching period to the first ratio, and the travel speed is When the second speed is slower than the first speed, the ratio of the transmission time is set to a second ratio smaller than the first ratio, so that unnecessary transmission radio waves can be suppressed as a whole radar apparatus and the target object It is possible to obtain a reflected wave necessary for detecting. Therefore, it is possible to accurately detect a preceding vehicle in a short distance by following traveling in a traffic jam.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 1 is a diagram for explaining a usage state of a radar apparatus according to the present embodiment. The radar apparatus 10 is mounted in a front portion of the vehicle 1, for example, a front grille, transmits and receives radar waves (radio waves) through the front grille front surface, and scans a scanning range in front of the vehicle 1 with radar waves. Here, as the scanning range, when the own lane width is set to 2 to 3 meters, an angle range in which a preceding vehicle located within a distance range of several meters to about 200 meters in front of the own lane can be detected, for example, the front is 0 degree. An angle range of about ± 5 to 20 degrees is used. Further, the radar device 10 is cooled by the traveling wind received through the front grill when the circuit elements inside the radar device 10 generate heat when operated. The radar device 10 can be mounted at a location other than the above as long as it is cooled by the traveling wind, for example, near a bumper portion or a fog lamp unit.

  When the radar apparatus 10 detects the preceding vehicle, information such as the relative speed, the relative distance, and the azimuth angle is output to the vehicle control system 100 that executes the tracking traveling control of the vehicle 1. Based on such information, the vehicle control system 100 drives various actuators of the vehicle 1 so that the vehicle 1 follows the preceding vehicle at a desired inter-vehicle distance, and adjusts the traveling speed of the vehicle 1.

  FIG. 2 is a diagram illustrating the configuration of the radar apparatus 10. FIG. 2A shows the overall configuration of the radar apparatus 10. For example, the radar apparatus 10 transmits a millimeter-wave continuous wave (radio wave) subjected to frequency modulation as a radar wave, receives a reflected wave from the target object, and detects the target object based on the frequency difference between the transmitted and received waves. This is a CW (Frequency Modulated-Continuous Wave) type radar apparatus.

  The radar transceiver 30 transmits a transmission wave, which is frequency-modulated with a triangular wave, toward the scanning range in front of the vehicle, receives a reflected wave from the target object, and mixes the transmission / reception wave to a beat frequency corresponding to the frequency difference of the transmission / reception wave. Generate a beat signal. The beat signal is A / D converted and the digital data is output to the signal processing device 14.

  Here, FIG. 3A shows an example of the frequency change of the transmission / reception wave. First, the frequency of the transmission wave rises and falls linearly at the center frequency f0 and the frequency modulation width ΔF according to the frequency modulation signal of the triangular wave of the frequency fm. Is repeated (illustrated by a solid line). On the other hand, the received wave reflected and returned by the target object is subjected to a time delay ΔT due to the relative distance of the target object and a frequency shift corresponding to the Doppler frequency corresponding to the relative velocity (illustrated by a broken line). As a result, the transmission / reception wave has a frequency difference α during the frequency rise period (up period) of the transmission wave and a frequency difference β during the frequency fall period (down period). Then, when the frequency (beat frequency) change of the beat signal generated at this time is shown in FIG. 3B, the beat frequency becomes the frequency α in the up period and the frequency β in the down period.

  The signal processing device 14 processes the frequency spectrum of the beat signal with an arithmetic processing device such as a DSP (Digital Signal Processor) that performs FFT (Fast Fourier Transform) processing on the above-described beat signal converted into digital data. And a microcomputer for detecting the target object. The microcomputer includes a CPU (Central Processing Unit), a ROM (Read Only Memory) in which various processing programs and control programs executed by the CPU are stored, and a RAM (Random Access) in which the CPU temporarily stores various data. Memory).

  The target object detection unit 14b includes a DSP that performs FFT processing on a beat signal, a CPU that detects a target object based on the FFT processing result, and a processing program that describes its operation. The transmission control instruction means 14a is composed of a CPU for controlling the radar wave transmission of the radar transceiver 30 by various control signals and a processing program describing its operation, as will be described in detail later. Moreover, the transmission control means 14a detects the traveling speed of the vehicle 1 from the vehicle speed signal input from the vehicle speed sensor of the vehicle 1, and uses it for transmission control.

  Here, there are a mechanical scanning method and an electronic scanning method for the radar device 10 to scan the scanning range with a radar wave. The detailed configuration of the radar transceiver 30 varies depending on the scanning method of the radar apparatus 10.

  FIG. 2B shows a configuration of a mechanical scanning type radar transceiver 30. In the radar transceiver 30, when the frequency modulation instruction unit 16 generates a triangular wave-shaped frequency modulation signal in response to the instruction signal from the signal processing device 14, the voltage controlled oscillator (VCO) 18 generates the frequency modulation instruction unit 16. As shown in FIG. 3A, a transmission wave whose frequency rises linearly in the rising period of the triangular wave and linearly falls in the falling period of the triangular wave is output as shown in FIG. This transmission wave is power-distributed by the distributor 20, and a part of the transmission wave is input to a transmission power amplifier 40 including a multistage amplifier having an FET as an active element. Then, the transmission power amplifier 40 amplifies the transmission wave and outputs it to the antenna 11 via the switch SW1.

  The antenna 11 is a transmission / reception antenna configured to be capable of switching between transmission and reception, and is switched by a transmission / reception switching instruction signal (for example, a pulse signal of about several hundred kHz to 2 MHz) input from the transmission control instruction means 14a of the signal processing device 14. SW1 switches the connection destination of the antenna 11. That is, a transmission wave is supplied from the transmission power amplifier 40 to the antenna 11 during the transmission time corresponding to the duty ratio of the transmission / reception switching instruction signal, the antenna 11 performs transmission, and the reception wave received by the antenna 11 is mixed during the reception time. 22 is input.

  The mixer 22 mixes a part of the power-distributed transmission wave and the reception wave, and generates a beat signal having a frequency corresponding to the frequency difference between the two. The beat signal is converted into digital data by the AD converter 24 and output to the signal processing device 14.

  Further, the radar transceiver 30 includes a rotating unit 26 that includes a mechanism that reciprocally rotates the antenna 11 and an encoder that detects a rotation angle of the antenna 11. Here, the rotation operation of the antenna 11 and the modulation period of the transmission wave are synchronized so that when the antenna 11 rotates by a predetermined unit angle (for example, 1 degree), a pair of up period and down period correspond. Be taken. Then, a rotation angle signal indicating the rotation angle of the antenna 11 is output from the encoder of the rotation unit 26 to the signal processing device 14.

  In the case of the mechanical scanning method, the signal processing device 14 sets a target object for each detection cycle, with a period in which the antenna 11 rotates once on one side of the angle range corresponding to the scanning range and scans the scanning range once as one detection cycle. The detection means 14b detects the target object. That is, the target object detection unit 14b detects the rotation angle of the antenna 11 when the level of the beat signal forms a peak for each detection cycle based on the rotation angle signal, and the direction of the target object based on the rotation angle. Detect corners.

  In the mechanical scanning method, by configuring the antenna 11 to be used for both transmission and reception as described above, the area of the antenna 11 can be made wider than when separate antennas for transmission and reception are provided, and a steep antenna pattern can be formed. That is, the beam width can be narrowed, and the angular resolution when detecting the azimuth angle of the target object can be improved.

  Further, the target object detection unit 14b uses the beat frequency α in the up period and the beat frequency β in the down period of the beat signal forming the peak to calculate the relative distance of the target object according to the following equations (1) and (2). R and relative speed V are calculated. Here, ΔF is the frequency modulation width of the transmission wave, f0 is the center frequency, fm is the frequency of the triangular wave, and C is the speed of light.

R = C · (α + β) / (8 · ΔF · fm) Equation (1)
V = C · (β−α) / (4 · f0) Equation (2)
FIG. 2C shows the configuration of an electronic scanning type radar transceiver 30. The same components as those in FIG. 2B are denoted by the same reference numerals. The radar transceiver 30 includes a transmitting / receiving antenna 11 and a plurality of receiving antennas 11_1, 11_2,. Here, the number of receiving antennas can be any number of two or more. Further, the radar transceiver 30 responds to the reception switching instruction signal input from the signal processing device 14 and inputs the received waves from the antennas 11, 11_1, 11_2,... To the mixer 22 in a time division manner. Have The mixer 22 mixes each of the reception waves from the antennas 11, 11_1, 11_2,... With the transmission wave to generate a beat signal.

  In the electronic scanning method, the target object detection unit 14b performs target object detection processing with the transmission wave up period and down period as one detection cycle. The target object detection means 14b changes the directivity of the whole antenna by controlling the phase difference of the received wave between the antennas. Then, by obtaining the directivity when the level of the received wave is maximum, the azimuth angle of the target object corresponding to the directivity is detected. Alternatively, in the phase monopulse method that is one form of the electronic scanning method, the target object detection unit 14b directly detects the azimuth angle of the target object that is the arrival direction of the received wave from the reception phase difference between at least one pair of antennas. To do.

  Also in the case of the electronic scanning method, by configuring the antenna 11 for both transmission and reception as described above, it is possible to provide more receiving antennas in the same space than when providing separate antennas for transmission and reception, and the radar transceiver 30 as a whole. As a result, a steep antenna pattern can be formed. Therefore, the angular resolution when detecting the azimuth angle of the target object can be improved. However, a configuration in which the antenna 11 is exclusively used for transmission without using the switch SW1 is also included in this embodiment.

  Further, the target object detection unit 14b uses the beat frequency α in the up period and the beat frequency β in the down period at which the beat signals for the antennas 11, 11_1, and 11_2 form peaks, and the above-described equations (1) and (2 ) To detect the relative distance and relative speed of the target object.

  FIG. 4 is a flowchart for explaining the target object detection procedure by the signal processing device 14, that is, the operation procedure of the target object detection means 14b. The procedure shown in FIG. 4 is executed for each detection cycle in both the mechanical scanning method and the electronic scanning method.

  The target object detection means 14b first performs FFT processing on the beat signal and detects its frequency spectrum (S2). Then, beat signals whose levels are peaked in each of the up period and the down period are paired (associated) with each other (S4), and the azimuth angle, relative distance, and relative speed of the target object using each beat frequency. Is detected (S6). Then, the target object detection unit 14b determines whether the detected azimuth angle and the level of the beat signal at that time have continuity in a plurality of past detection cycles (S8), and the target object detection unit 14b exceeds a certain level (for example, three times) or more. About the target object which has continuity, the azimuth, relative speed, and relative distance are output to the vehicle control apparatus 100 of the vehicle 1 (S10).

  The radar device 10 configured as described above detects a preceding vehicle by scanning a scanning range in front of the vehicle 1 with a radar wave when the vehicle 1 travels, and determines the relative speed, relative distance, azimuth angle, and the like of the vehicle control device. Output to 100. The vehicle control device 100 performs follow-up running control of the vehicle 1 based on information supplied from the radar device 10.

  Here, when the speed of the vehicle 1 is below a certain level or when the vehicle 1 is stopped, such as when there is a traffic jam, the transmission of radar waves is controlled by the method described below to reduce unnecessary radio wave transmission. By doing so, radio wave interference with other radar devices can be reduced, and a preceding vehicle can be detected even when the speed of the vehicle 1 is below a certain level or when the vehicle is stopped. Therefore, in the following description, the transmission control instruction means 14a of the signal processing device 14 that instructs the control of the transmission operation of the transmission wave, and the radar transceiver 30 that controls the transmission operation in response to the instruction are in the present invention. This corresponds to “transmission control means”.

  Also, in the United States, the so-called FCC (Federal Communications Commission) regulations require that the output of the transmitted radio wave when the vehicle is stopped to be lower than the output of the transmitted radio wave when the vehicle is running. It is possible to perform control conforming to such regulations.

  Moreover, since the power consumption of the entire radar apparatus can be reduced by suppressing unnecessary transmission radio waves, heat generation of the radar apparatus can be suppressed. As described above, the radar device 10 dissipates heat by the traveling wind received through the front grille. However, the traveling wind is weakened during low speed traveling or when the vehicle is stopped, and the heat radiation efficiency is reduced. Therefore, by suppressing heat generation, it is possible to reduce damage to circuit elements due to a decrease in heat dissipation efficiency.

[First transmission radio wave reduction method]
First, the first transmission radio wave reduction method is applied to the mechanical scanning method. In the first transmission radio wave reduction method, the radar apparatus 10 is configured so that the antenna 11 is in a normal traveling state where the vehicle 1 travels at a constant reference speed (for example, 10 to 20 kilometers per hour) or more as shown in FIG. Each time the unit angle θ (for example, 1 degree) rotates, a radar wave corresponding to the up period and the down period is transmitted, and the azimuth angle of the target object is determined based on the rotation angle of the antenna 11 when the received wave is obtained. The relative distance and relative speed are detected from the beat frequency. On the other hand, when the vehicle is traveling at a low speed below the reference speed (including when the vehicle is stopped), as shown in FIG. 5B, for example, for each unit angle 2θ every unit angle θ, A radar wave corresponding to the down period is transmitted. That is, the transmission of radar waves is thinned out.

  The transmission control instruction means 14a detects the rotation angle of the antenna 11 from the rotation angle signal indicating the rotation angle of the antenna 11, and stops the output of the transmission wave amplifier 40 at a unit angle for thinning transmission. Such an operation is performed.

  Here, FIG. 6 shows a detailed configuration of the transmission power amplifier 40. The transmission power amplifier 40 includes a multi-stage amplifier 40a using an FET as an active element, a drain voltage supply circuit 41 that receives a power supply from an in-vehicle power source, generates a constant voltage, and supplies the drain voltage to each drain of the multi-stage amplifier 40a. The switch SW2 is capable of disconnecting the drain voltage supply to the final stage amplifier of the multistage amplifier 40a, and the switch SW3 is capable of disconnecting the drain voltage supply to all the amplifiers of the multistage amplifier 40a. The switches SW2 and SW3 are opened and closed in response to the instruction signals Con_1 and 2 generated by the signal processing device 14. The gate voltage GV generated by the signal processing device 14 is applied to each gate of the multistage amplifier 40a.

  In such a configuration, when a certain level of gate voltage GV and drain voltage DV is applied to the multistage amplifier 40a, the amplified transmission wave output from the multistage amplifier becomes saturated and stabilizes at a constant level.

  Therefore, in the first transmission radio wave reduction method, the transmission control instruction unit 14a connects the switches SW2 and SW3 during normal traveling of the vehicle 1 so that the drain voltage DV that saturates the transmission wave is generated in the multistage amplifier 40a. Apply to all amplifiers. By doing so, the transmission wave is amplified to a desired level and output. When the vehicle 1 travels at a low speed, the supply of the drain voltage DV to all the amplifiers of the multistage amplifier 40a is stopped by opening the switch SW3 for each unit angle at which transmission is thinned. Then, the output of the transmission wave from the multistage amplifier 40a is stopped.

  In this way, the transmission control instruction means 14a executes the operation of thinning out the radar wave, whereby the transmission radio wave when time averaged can be reduced.

  Here, since the preceding vehicle to be detected when traveling at a low speed in a traffic jam is located at a shorter distance than during normal traveling, the number of reflection points per reflection sectional area is greater than when the preceding vehicle is located at a long distance. Therefore, even if the unit angle for transmitting the radar wave is thinned, a reflected wave from a reflection point sufficient for detecting the preceding vehicle can be obtained. Moreover, since the distance is short, the amount of attenuation of the reflected wave is small. Therefore, the preceding vehicle can be detected without reducing the detection accuracy. Note that the interval between the unit angles to be thinned may be 2θ or more, and can be arbitrarily set to an angle at which a necessary reflection point can be obtained.

  Also, according to the method of thinning out the unit angle for processing the beat signal by the signal processing device 14 without thinning out the unit angle for transmitting the radar wave, the power consumption of the entire radar device can be reduced. An effect of suppressing heat generation of the device can be obtained.

[Second transmission radio wave reduction method]
The second transmission radio wave reduction method can be applied to either a mechanical scanning method or an electronic scanning method using a transmission / reception antenna. In the second transmission radio wave reduction method, the radar apparatus 10 switches transmission / reception of the antenna 11 with a transmission / reception switching instruction signal having a duty ratio of 50%, as shown in FIG. Therefore, the radar apparatus 10 transmits a radar wave at a transmission time TS of 50% when the transmission / reception switching instruction signal becomes H level in one cycle of transmission / reception switching instruction signal, that is, one transmission / reception switching period, and the remaining 50% when it becomes L level The reflected wave is received at the reception time TR.

  On the other hand, when the vehicle 1 travels at a low speed, as shown in FIG. 7B, the ratio of the transmission time TS in the transmission / reception switching cycle is reduced to, for example, 25% (at this time, the ratio of the reception time TR is 75%). To change the duty ratio of the transmission / reception switching instruction signal. By doing so, the transmission radio wave when time averaged can be reduced.

  In this case, the received radio wave as a whole of the radar apparatus is reduced by reducing the transmitted radio wave. However, since the preceding vehicle to be detected is at a short distance, the attenuation amount in the round trip of the radio wave is small. Therefore, a received wave having a level sufficient to detect the preceding vehicle can be obtained. However, when a transmission / reception antenna is used, the level of the received wave may decrease at a very short distance (close distance). Here, such a case will be described with reference to FIG.

  FIG. 8 shows the transmission time (TS) / reception time (TR) based on the transmission / reception switching instruction signal, the reflected wave of the transmission wave transmitted during the transmission time, and the reception time during the reception time, with the horizontal axis as time. It is a figure explaining the correspondence of a received wave. Here, the reflected wave returns when a delay time corresponding to the relative distance of the target object has elapsed. FIG. 8A shows the case where the target object is at a short distance and the reflected wave delay time ΔT1, and FIG. 8B shows the case where the target object is at a close distance and the reflected wave delay time ΔT2 (<ΔT1). . Note that the duty ratio of the transmission / reception switching instruction signal in FIGS. 8A and 8B is the same.

  As shown in FIGS. 8A and 8B, the received radio wave corresponds to the reflected wave that has returned during the reception time. Then, as shown in the comparison of both figures, the received radio wave as a whole is smaller when the delay time is ΔT2 (<ΔT1). That is, when the delay time is small, that is, when the relative distance of the target object is small, the received radio wave is reduced. As described above, even when the attenuation amount of the radio wave at the relative distance is taken into consideration, the level of the received wave may be lowered at a close distance when the transmission / reception antenna is used.

  Therefore, in the second transmission radio wave reduction method, the frequency of the transmission / reception switching instruction signal is increased in order to compensate for the decrease in the reception wave level at a close distance caused by using the transmission / reception antenna. In other words, the switching cycle between the transmission time and the reception time is shortened.

  Here, FIG. 8C shows a case where the frequency of the transmission / reception switching instruction signal in FIG. 8B is doubled. Then, as shown in the comparison between FIGS. 8B and 8C, the received radio wave per unit time is increased by doubling the frequency of the transmission / reception switching signal in the case of the reflected wave delay time ΔT2. be able to. The received wave levels in the cases of FIGS. 8B and 8C are shown in FIG.

  In FIG. 9, the horizontal axis indicates the relative distance of the target object, that is, the delay time of the reflected wave returning from the target object, and the vertical axis indicates the level of the received wave when the reflected wave is received. Curve B corresponds to the case of FIG. 8B, and curve C corresponds to the case of FIG. As shown in the figure, the curve C corresponding to the case of FIG. 8C in which the frequency of the transmission / reception switching signal is doubled has a higher received wave level at a close distance. In this way, even when a transmission / reception antenna is used, it is possible to compensate for a decrease in received wave level at a close distance.

  By the way, in the comparison of the delay time when the reflected wave returns and the reception time, if the delay time exceeds the reception time, the reflected wave may reach the antenna 11 after the reception time of the same transmission / reception period has elapsed. . That is, since the reflected wave returns during the transmission time of the next cycle, it cannot be received. Therefore, in this case, the target object cannot be detected. The relative distance of the target object corresponding to the delay time at this time is called a null point. The null point appears at a short distance because the reception time is shortened as the frequency of the transmission / reception switching instruction signal is increased (that is, the transmission / reception switching period is shortened).

  In FIG. 9, null points Nb and Nc in curves B and C are shown. Then, for the reason described above, the null point Nc in the curve C when the frequency of the transmission / reception switching instruction signal is high is closer than the null point Nb in the curve B when the frequency is low. For this reason, when the second transmission radio wave reduction method is executed, the process of increasing the frequency of the transmission / reception switching instruction signal as a modification thereof is suitable when the relative distance of the target object is a close distance shorter than the null point. Applied. That is, if the frequency of the transmission / reception switching instruction signal is increased, the null point becomes closer, but if the relative distance of the target object is a close distance closer to the null point, the detection of the received wave will not occur without failing the target object detection. The level can be increased.

[Third transmission radio wave reduction method]
The third transmission radio wave reduction method can be applied to both a mechanical scanning method and an electronic scanning method (including both a configuration using a transmission / reception antenna and a configuration using a transmission dedicated antenna). In the third transmission radio wave reduction method, the radar apparatus 10 reduces the transmission power by controlling the transmission power amplifier 40. Specifically, in the configuration of the transmission power amplifier 40 shown in FIG. 6, the transmission control instruction means 14a amplifies the transmission wave to a desired level and outputs it by connecting the switches SW2 and 3 when the vehicle 1 is traveling normally. When the vehicle 1 travels at a low speed, the switch SW2 is opened. Here, when the switch SW2 is opened with the transmission wave reaching the saturation level, the drain voltage to the final stage amplifier is turned off. However, since the transmission wave has a high frequency of millimeter wavelength, leakage power passes through the final stage amplifier and is output as a transmission wave. By utilizing this fact, the transmission power can be reduced without stopping the transmission wave by turning off the drain voltage to the amplifier at the final stage.

  By reducing the transmission power in this way, transmission of unnecessary radio waves can be suppressed.

  In the case of a configuration using a transmission / reception antenna of the mechanical scanning method and the electronic scanning method, the transmission power amplifier 40 is controlled to lower the transmission power, and as a modification, the frequency of the transmission / reception switching instruction signal is increased. Thus, the level of the received wave of the target object at a close distance can be increased. Therefore, the target object at a close distance can be detected with high accuracy by compensating for the decrease in the level of the received wave.

Here, an operation procedure when the first to third transmission radio wave reduction methods are executed will be described.
FIG. 10 is a flowchart for explaining an operation procedure when the radar apparatus controls a transmission wave. The procedure in FIG. 10 is executed after the target object detection process (procedure S6) in the procedure shown in FIG.

  The transmission control instruction means 14a detects the traveling speed from the vehicle speed signal (S22), and determines whether the traveling speed is during normal traveling above the reference value or at low speed traveling below the reference value (S24). During normal travel (YES in S24), the process ends without controlling radio wave transmission. On the other hand, during low-speed traveling (NO in S24), any one of the above-described first to third transmission radio wave reduction methods that can be adopted according to the scanning method of the radar apparatus is executed, thereby transmitting radio waves. Can be reduced. Here, a procedure for categorizing which method to adopt depending on whether or not the vehicle is stopped is shown.

  First, when the vehicle is stopped (YES in S26), the preceding vehicle is also stopped, and there is a high probability that the distance is a close distance ahead of about 2 to 3 meters. Therefore, the transmission power is reduced by executing any one of the first to third transmission radio wave reduction methods described above (S28). In particular, when executing the second transmission radio wave reduction method (changing the duty ratio of the transmission / reception switching instruction signal), the frequency of the transmission / reception switching instruction signal is increased in order to compensate for a decrease in the level of the received wave at a close distance. Process.

  On the other hand, when the vehicle is not stopped (NO in S26), that is, when the vehicle is traveling at a low speed, the preceding vehicle is also traveling, and the distance and the azimuth are likely to change within a certain range. Therefore, the transmission radio wave reduction method is properly used according to the distance of the preceding vehicle detected in the target object detection process (step S6 in FIG. 4).

  That is, when the distance is less than a reference value (for example, 2 to 3 meters) (YES in S30), that is, when the distance is very close, the transmission radio wave is transmitted by either the first transmission radio wave reduction method or the third transmission radio wave reduction method. Decrease (S32). This is because the first or third transmission radio wave reduction method that does not reduce the transmission time is closer than the second transmission radio wave reduction method that reduces the transmission time by changing the duty ratio of the transmission / reception switching instruction signal. This is because the possibility of a decrease in the received wave level is small. However, it is also possible to employ the second transmission radio wave reduction method by using a process for increasing the frequency of the transmission / reception switching instruction signal together. In this case, if the reference value in the distance determination in step S30 is closer to the null point when the frequency of the transmission / reception switching instruction signal is made higher, it is possible to prevent a situation where the reflected wave cannot be received by the null point, The second transmission radio wave reduction method can be suitably used. Even when the third method for reducing the transmission radio wave is executed, a decrease in the level of the reception wave may be compensated by using a process for increasing the frequency of the transmission / reception switching instruction signal.

  On the other hand, when the distance is equal to or greater than the reference value (NO in S30), that is, when the distance is short, the transmission radio wave is reduced by either the second or third method (S34). This is because the error in the azimuth angle of the preceding vehicle is larger at a short distance than at a close distance. Therefore, the second or third transmission that does not thin out the transmission radio wave is more effective than the first transmission radio wave reduction method that thins out the transmission wave. This is because the radio wave reduction method has higher azimuth resolution. In particular, when the second transmission radio wave reduction method for changing the duty ratio of the transmission / reception switching instruction signal is executed, a process for increasing the frequency of the transmission / reception switching instruction signal to compensate for a decrease in the level of the reception wave at a close distance. Do. Even when the third method for reducing the transmission radio wave is executed, a decrease in the level of the reception wave may be compensated by using a process for increasing the frequency of the transmission / reception switching instruction signal.

  According to the above procedure, it is possible to reduce the transmission radio wave by selecting the optimum method based on the traveling speed of the host vehicle and the distance of the preceding vehicle.

  In addition, the Example which uses together two or more among the 1st-3rd transmission radio wave reduction methods in said procedure S28 is contained in this embodiment. Further, an embodiment in which the first transmission radio wave reduction method and the third transmission radio wave reduction method are used in combination in the above step S32, or an embodiment in which processing for increasing the frequency of the transmission / reception switching instruction signal is used in combination with the present embodiment. include. Further, in the present embodiment, an example in which the second transmission radio wave reduction method and the third transmission radio wave reduction method are used in combination in S34, or an example in which a process for further increasing the frequency of the transmission / reception switching instruction signal is used in this embodiment. It is. In any case, the transmission radio wave can be further suppressed in the range of the transmission output in which the preceding vehicle can be detected as compared with the case where only the single transmission radio wave reduction method is used.

  As described above, according to the present embodiment, unnecessary transmission radio waves can be suppressed, and a reflected wave necessary for detecting a target object at a short distance can be obtained. Therefore, it is possible to accurately detect a preceding vehicle in a short distance by following traveling in a traffic jam.

It is a figure explaining the use condition of the radar apparatus in this embodiment. 1 is a diagram illustrating a configuration of a radar apparatus 10. FIG. It is a figure which shows the example of the frequency change of a transmission / reception wave. It is a flowchart explaining the operation | movement procedure of the target object detection means 14b. It is a figure which shows a response | compatibility with the rotation angle of the antenna 11, and transmission operation | movement. 3 is a diagram illustrating a detailed configuration of a transmission power amplifier 40. FIG. It is a figure explaining the transmission time by a transmission / reception switching instruction | indication signal. It is a figure explaining the correspondence of the transmission time and reception time based on a transmission / reception switching instruction | indication signal, the reflected wave of the transmission wave transmitted during transmission time, and the reception wave received during reception time. It is a figure which shows the level of the received wave for every relative distance of a target object according to the frequency of a transmission / reception switching instruction | indication signal. It is a flowchart figure explaining the operation | movement procedure when a radar apparatus controls a transmission wave.

Explanation of symbols

1: vehicle, 10: radar device, 14: signal processing device, 14a: transmission control instruction means, 14b: target object detection means, 30: radar transceiver

Claims (2)

In a radar apparatus mounted on a vehicle and scanning a predetermined scanning range with a radar wave,
When the traveling speed of the vehicle is a first speed, a radar wave is transmitted for each first unit angle within the scanning range, and when the traveling speed is a second speed slower than the first speed, Transmission control means for transmitting the radar wave for each second unit angle wider than the first unit angle within a scanning range;
Target object detecting means for detecting the target object based on a reflected wave of the transmitted radar wave by the target object ;
The transmission control means is configured for each second unit angle within the scanning range when the traveling speed of the vehicle is the second speed and the detected distance of the target object is less than a reference value. A radar apparatus that transmits the radar wave . Oite to claim 1,
The radar apparatus according to claim 1, wherein the transmission control means reduces the output of the radar wave to be transmitted according to the traveling speed of the vehicle.

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