JP3454767B2 - Automotive radar equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device for detecting an obstacle in a vehicle, and more particularly to a foreign substance that reflects or absorbs radio waves in a cover (hereinafter referred to as a radome) covering an antenna of the radar device. The present invention relates to a vehicle-mounted radar device capable of detecting that the detection capability has deteriorated due to the adherence of particles.

[0002]

2. Description of the Related Art As an obstacle detection radar device for a vehicle,
For example, radar devices utilizing so-called millimeter waves such as 76 GHz have been studied.

This millimeter-wave radar device is different from a radar device using a laser beam in that it has a feature that its detection ability does not deteriorate so much even under environmental conditions such as rainfall, fog, and snow.

As a known example of this type of radar device, there is JP-A-5-40168.

[0005]

However, millimeter-wave radio waves have a low ability to pass through a water film. For example, when snow that is half melted during snowfall adheres to the antenna surface of a radar device, obstacles, etc. The detection ability of is extremely reduced. In such a case, it is difficult to perform a correct operation because it is unknown whether or not an obstacle or the like actually exists or whether the detection capability is deteriorated.

[0006] as described above as an example that can be easily detected without using a special sensor that radar detection performance is lowered with respect to the millimeter wave, JP 10- 2
There is an FM radar device described in Japanese Patent No. 82229 .

The FM radar device described in Japanese Patent Application Laid- Open No. 10-282229 collects the frequency spectrum data of the low frequency component and the detected frequency spectrum data of the low frequency component when the radome is not contaminated. The comparison is made, and based on the result, it is detected whether or not dirt is attached to the radome.

However, this Japanese Patent Laid- Open No. 10-282229
In the FM radar device described in the publication, there is a reflected wave from a short-distance road surface even if dirt is not attached, and it is difficult to distinguish this from a reflected wave due to dirt. However, it was difficult to accurately determine that the radome had dirt.

The present invention has been made in consideration of the above matters, and an object thereof is to simply and accurately detect the attachment of a foreign matter near the surface of a radar antenna without using a special device. It is to realize an on-vehicle radar device capable of

[0010]

In order to achieve the above object, the present invention is configured as follows. (1) In a vehicle-mounted radar device that detects a reflected wave from an object by radiating a radio wave in front of or in the vicinity of a vehicle by a radio wave radiating means, at a plurality of frequency points of the detected reflected wave
The strength of the intermediate frequency signal whether decreased from a predetermined reference value to determine whether foreign matter on the surface of the radio wave emitting means is attached.

[0011]

( 2 ) Further, preferably, in the above (1), the predetermined reference value is a value obtained from a frequency analysis result of an intermediate frequency signal obtained when the vehicle is stopped.

( 3 ) Further, preferably, in the above (1), as a judgment value for judging that the strength of the signal has decreased below a predetermined value, the characteristics of each radar device are measured in advance and stored in a built-in memory. To use.

( 4 ) In a monopulse type on-vehicle radar device that radiates radio waves to the front or the periphery of the vehicle by radio wave radiating means and detects a reflected wave from an object, it corresponds to a sum signal and a difference signal of two receiving antennas. Obtain each spectrum of the intermediate frequency signal, and
By comparing the intensity of the sum signal and the difference signal and determining that the intensity difference is less than or equal to a reference value, it is determined whether or not a foreign matter has adhered to the surface of the radio wave radiating means. .

According to the present invention, when a vehicle is traveling, a so-called background noise, which is observed by reflecting a part of radio waves emitted by the radar device on, for example, a road surface, is observed to judge foreign matter adhesion. is there.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a circuit block diagram of the vehicle-mounted radar device 1 to which the first embodiment of the present invention is applied. In FIG. 2, a timing circuit 101 generates a timing signal at a constant cycle, and a driving circuit 102 and a DS
Supply to P111. The drive circuit 102 controls a voltage controlled oscillator (VCO) 103 to generate a frequency-modulated signal as shown in FIG. 3, for example. This radar system is a known system called the FM-CW system, and the frequency repeatedly changes linearly with time.

The modulated signal is radiated as a radio wave from the transmitting antenna 105 via the duplexer 104. The radio wave radiated from the transmitting antenna 105 hits the obstacle 2, is reflected, and is received by the receiving antenna 106.

The signal received by the antenna 106 is supplied to the mixer 107. In this mixer 107,
With the signal demultiplexed by the demultiplexer 104, the signal supplied from the antenna 106 is down-converted and converted into a so-called intermediate frequency (IF) signal.

The IF signal is a reduction filter (LPF) 108.
The high frequency component is removed by and is amplified by the amplifier 109 to a predetermined level. Then, the amplified signal is supplied to the analog-digital converter (ADC) 110, and converted into a digital value by the analog-digital converter (ADC) 110. The signal converted into a digital value is taken into a signal processor (DSP) 111 and subjected to radar signal processing.

The DSP 111 executes a fast Fourier transform or the like to calculate the distance to the target and the relative speed.

There are some DSPs 111 that receive a vehicle transmission signal from the vehicle speed sensor 4.

FIG. 4 is a view showing a state in which the radar device 1 is mounted on the vehicle 3. In reality, a beam called a side lobe is emitted from the antenna of the laser device 1 in addition to the main lobe. As shown, part of the side lobes hit the road surface and are reflected.

When the vehicle is running, the spectrum of the IF signal as shown in FIG. 5 is obtained. This Figure 5
Indicates the frequency on the horizontal axis and the signal strength (noise level) on the vertical axis. In FIG. 5, the frequency component represents the relative speed of the road surface viewed from the antenna, and the signal reflected from the area directly below the antenna has a frequency near DC, and is close to the road surface. Therefore, the reflection level is large and the signal strength is large. Become.

Then, as the distance from the radar apparatus 1 increases, the relative speed increases and the Doppler shift increases.
For this reason, in general, the spectrum tends to show a downward sloping spectrum. That is, the signal strength tends to decrease as the frequency increases. The signal having this tendency is called a ground clutter signal.

However, for example, when semi-molten snow or the like adheres to the surface of the radar device 1, the situation changes.

FIG. 6 is a sectional view of the radar device 1 as seen from the side. In FIG. 6, in order to protect the surfaces of the antennas 105 and 106, a radome 112 for protection is usually installed. The radome 112 is made of a material, such as plastic, which is a material that transmits radio waves well and has mechanical strength.

FIG. 6 shows a state in which snow has adhered to the surface of the radome 112. In this state, the antenna 10
Since the radio wave radiated from 5 does not pass through, the ground clutter signal does not appear as shown in FIG. That is,
The signal strength near DC is high, but at other frequencies, the signal strength is uniformly low.

The present invention has been made by paying attention to the above-mentioned phenomenon, that is, the phenomenon of change in signal intensity shown in FIGS. 5 and 7.

That is, the level of the ground clutter signal is observed and an abnormal state is judged. The determination of this abnormal state is performed by the program of the DSP 111.

FIG. 1 is a flowchart showing a part of the processing of the processing program of the DSP 111. In FIG. 1, first, in step S1, the IF signal sampled at a constant cycle from the ADC 110 is captured in the form of a digital signal. In this case, the number of samples is 1024, for example.

Next, in step S2, step S
The FFT operation of the digital signal sampled at 1 is performed.

As described above , the relative speed of the ground clutter signal increases as the distance from the radar device 1 increases.
Since it is observed only during running, abnormality determination processing S3
Prior to step S2A, it is determined in step S2A whether the vehicle speed is equal to or higher than a certain value (for example, 10 km / h). The vehicle speed may be determined by the signal from the vehicle speed sensor 4 shown in FIG.

The vehicle speed sensor signal is input to the radar device 1 in a pulse format, and generally represents a constant distance per pulse. That is, the speed can be calculated by counting the pulses within a fixed time. If the vehicle speed is less than the certain speed, the process proceeds to step S5 and the normal process is continued.

If it is determined in step S2A that the vehicle speed is equal to or higher than a certain speed, it is possible to determine an abnormality. Therefore, an abnormality determination process is performed in step S3. In step S31,
Based on the result of the FFT calculation, a plurality of N points are sampled from the frequency range exceeding the frequency of the reflected wave from the surface of the radome. Next, in step S32, it is determined whether or not all of the N points are at or below a predetermined value.

That is, when foreign matter adheres to the surface of the radome, a characteristic curve as shown in FIG. 7 is obtained, and all N points are at a level below a predetermined value. On the other hand, when no foreign matter is attached to the surface of the radome, a ground clutter signal as shown in FIG. 5 appears.

Therefore, a plurality of N points from the frequency region exceeding the frequency of the reflected wave from the radome surface are
When all are less than or equal to the predetermined value, the characteristics are as shown in FIG. 7, and it can be determined that the foreign matter is attached to the surface of the radome.

If it is determined in step S32 that all the N points are at a level equal to or lower than the predetermined value, the abnormality flag is turned on in step S33, and the process proceeds to step S4. If it is determined in step S32 that any of the N points exceeds the predetermined value, the abnormality flag is turned off in step S34, and the process proceeds to step S4.

In step S4, the abnormality flag reflecting the determination result is referred to, and if the abnormality flag is on,
Abnormality processing is performed in step S6. In this abnormality processing, for example, a message is output to a display (not shown) to prompt the driver to remove the foreign matter. The message in this case may be an alarm sound or a voice. Further, even if there is no dedicated display device, the foreign substance removal can be similarly promoted by using, for example, a navigation device or a television device. Then, the process proceeds to step S5.

If the abnormality flag is off in step S4, the process proceeds to step S5 and the normal processing is continued.

The predetermined value for making the determination in step S32 is based on the noise shown in FIG.
You can use a value above 2 dB.

As described above, according to the first embodiment of the present invention, it depends on whether or not the plurality of N points in the frequency region exceeding the frequency of the reflected wave from the radome surface are all below a predetermined value, that is, Since it is configured to judge whether foreign matter is attached to the radome surface based on whether the ground clutter signal appears, foreign matter is easily attached near the radar antenna surface without using a special device. It is possible to realize an on-vehicle radar device that can accurately detect the above.

The characteristics of the ground clutter signal change depending on the characteristics of the antenna pattern and the receiving system. If these characteristics are small in individual devices and have good reproducibility, the above judgment values may be constant, for example, ROM (Read Only).
You can use what is fixedly written in Memory).

However, when the above characteristics vary due to various reasons, a value corresponding to the characteristics of each radar device should be used as the judgment value. FIG. 8 is a block diagram of the circuit configuration of the radar device 1 according to the second embodiment of the present invention, which can use a value according to the characteristics of each radar device as a determination value. The difference between the example of FIG. 8 and the example of FIG. 1 is that a nonvolatile memory 113 that can be accessed and controlled by the DSP 111 is provided.

The memory 113 is an electrically rewritable ROM (EEPROM), flash memory, or
A battery-backed SRAM or the like may be used.

The memory 113 stores the noise level of the circuit.
It is stored in advance and used for later judgment. As for the noise level of the circuit, a radio wave blocker may be placed on the surface of the radome 112 when the radar apparatus 1 is adjusted, and the level of the required sample point of the FFT result of the IF signal at that time may be stored.

As described above, according to the second embodiment of the present invention, the same effect as that of the first embodiment can be obtained, and the characteristics of the ground clutter signal are the antenna pattern of the individual device, It is possible to realize an on-vehicle radar device that can accurately detect that a foreign substance has adhered to the vicinity of the radar antenna surface easily without using a special device even when the characteristics of the receiving system vary. .

As a simple method, it can be considered that the stop of the vehicle is determined using the signal of the vehicle speed sensor 4 and the FFT result at that time is used. However, it is usually considered that various vehicles may come into the field of view of the radar device 1 even when the vehicle is stopped, and therefore a countermeasure is required.

Here, the present invention is not limited to the radar system of the above example, but can be applied to other radar systems. Next, an example in which the present invention is applied to another radar system will be described.

FIG. 9 is a circuit block diagram of a radar device called a monopulse system which is a third embodiment of the present invention. In the example of FIG. 9, the same symbols as those in FIG. 2 represent the same items. The difference between the example of FIG. 9 and the example of FIG. 2 is that the example of FIG. 9 has two receiving systems.

That is, the reflected radio wave from the obstacle 2 is received by the antennas 106 and 116. Next, in the hybrid circuit 114, the sum signal and the difference signal of the two antennas 106 and 116 are generated, and the mixers 107 and 1 are respectively generated.
It is input to 17 and down-converted to an IF signal. The signals demultiplexed by the demultiplexer 104 are locally input to the mixers 107 and 117.

The IF signals from the mixers 107 and 117 are band-limited by the LPFs 108 and 118, and are amplified to a predetermined level by the amplifiers 109 and 119.

Next, the respective signals from the amplifiers 109 and 119 are converted into digital signals by the ADCs 110 and 120, and are taken into the DSP 111.

FIG. 10 shows an example of the angle characteristic of the sum / difference signal. As shown in FIG. 10, the pattern (characteristic) of the difference signal has a characteristic that the sensitivity drops in the direction of zero angle. On the contrary, the sum signal has the characteristic of showing the maximum sensitivity in the zero angle direction.

Therefore, as for the image of the spectrum of the road surface clutter signal of each sum / difference signal, for example, as shown in FIG. 11, the difference signal appears to have a lower clutter signal level than the sum signal.

Thus, by observing the difference between the signal levels of the sum signal and the difference signal, it is possible to determine the abnormality. That is, if the spectrum characteristics of both of the sum difference signals are close (if the difference between the sum signal and the difference signal is less than a predetermined value),
It can be judged as an abnormal state.

FIG. 12 is a flow chart of the judgment processing in the DSP 111 of the example of FIG. First, step S
7, the data of the sum signal and the difference signal is sent to the DSP 111.
Take in. Next, in step S8, FFT calculation is performed on each of the sum signal and the difference signal. next,
In step S2A, it is determined whether the vehicle speed is a certain value or higher. If the vehicle speed is less than the certain speed, the process proceeds to step S5 and the normal process is continued.

If the vehicle speed is equal to or higher than the predetermined speed in step S2A, an abnormality determination is performed in step SA using the result of step S8.

Next, details of the abnormality determination processing SA will be described. In step SA1, each F of the sum difference signal is
Data of frequencies at N points are sampled from the FT result. Next, in step SA2, the sum signal and the difference signal are compared for all the data at N points. If the difference between the sum signal and the difference signal at all points is equal to or greater than a predetermined value (predetermined value), it is determined to be normal, the abnormality flag is turned off in step SA4, and the process proceeds to step S4.

In step SA2, if the difference between the sum signal and the difference signal is less than the predetermined value at any of N points, the abnormality flag is turned on in step SA3, and the process proceeds to step S4. The processes after step S4 are the same as those in the example shown in FIG.

It should be noted that the above-mentioned predetermined determination value in step SA2 must be determined in consideration of the gain and frequency characteristics of the two receiving systems. When the characteristics of the individual radar devices 1 vary, the measures shown in the example of FIG. 8 may be taken. In this case, the determination process using the vehicle speed signal becomes unnecessary.

As described above, according to the third embodiment of the present invention, the same effect as that of the first embodiment can be obtained, and the sum signal and the difference signal can be obtained without providing a judgment reference value. It is possible to determine whether or not there is an abnormality from the difference between and.

[0062]

According to the present invention, whether or not a plurality of N points from the frequency region exceeding the frequency of the reflected wave from the radome surface are all below a predetermined value, that is, whether or not the ground clutter signal appears. Depending on whether it is attached to the surface of the radome or not, it is possible to easily detect the attachment of the foreign object near the surface of the radar antenna easily without using a special device. It is possible to realize a vehicle-mounted radar device that can be used.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an abnormality determination flow according to a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of an in-vehicle radar device 1 to which the first embodiment of the present invention is applied.

FIG. 3 is a diagram illustrating frequency modulation of radio waves radiated from the radar device of FIG.

FIG. 4 is a diagram illustrating a radio wave pattern emitted from a radar device mounted on a vehicle.

FIG. 5 is a diagram illustrating a spectrum image of a ground clutter signal reflected from a road surface.

FIG. 6 is a diagram illustrating snow adhering to a radar device.

FIG. 7: IF when radio waves are blocked on the surface of the radar device
It is a figure explaining the spectrum image of a signal.

FIG. 8 is a block diagram of a radar device including a nonvolatile memory according to a second embodiment of the present invention.

FIG. 9 is a block diagram of a monopulse type radar device according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating an angular gain characteristic of a sum difference signal of a monopulse radar device.

FIG. 11 is a diagram illustrating a spectrum image of a road surface clutter signal of a sum difference signal of the monopulse radar device.

FIG. 12 is a diagram illustrating an abnormality determination flow by the monopulse radar device.

[Explanation of symbols]

1 Radar device 2 obstacles 3 vehicles 4 vehicle speed sensor 101 Timing circuit 102 drive circuit 103 Voltage controlled oscillator 104 duplexer 105, 106 antenna 107, 117 mixer 108, 118 Low pass filter 109,119 Amplifier 110, 120 Analog-to-digital converter 111 DSP 112 radome 113 memory

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-109030 (JP, A) JP-A-10-160836 (JP, A) JP-A-11-166973 (JP, A) JP-A-61- 7486 (JP, A) JP 11-183611 (JP, A) JP 6-331742 (JP, A) JP 2000-19242 (JP, A) JP 2000-321348 (JP, A) JP 2001-42034 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/40 G01S 13/00-13/95

Claims (4)

(57) [Claims] 1. An in-vehicle radar device for detecting a reflected wave from an object by radiating an electric wave to the front or the vicinity of a vehicle by a radio wave radiating means, the intermediate frequency signal at a plurality of frequency points of the detected reflected wave.
No. of intensity depending on whether or not reduced below a predetermined reference value, the in-vehicle radar apparatus characterized by determining whether foreign matter on the surface of the radio wave emitting means is attached. 2. The on-vehicle radar according to claim 1, wherein the predetermined reference value is a value obtained from a frequency analysis result of an intermediate frequency signal obtained when the vehicle is stopped. apparatus. 3. The on-vehicle radar device according to claim 1, wherein a characteristic value of each radar device is measured in advance and stored in a built-in memory as a judgment value for judging that the intensity of the signal has decreased below a predetermined value. An on-vehicle radar device characterized by being used. 4. A monopulse type on-vehicle radar device for detecting a reflected wave from an object by radiating an electric wave to the front or in the vicinity of the vehicle by an electric wave radiating means, and an intermediate signal corresponding to a sum signal and a difference signal of two receiving antennas. determined each spectrum of frequency signals, performs intensity comparison between the sum and difference signals in a single or more frequency points, its
The in-vehicle radar device is characterized in that it is determined whether or not a foreign matter adheres to the surface of the radio wave radiating means by determining that the intensity difference between the two is less than or equal to a reference value.