JPH1048332A - Radar equipment for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable snow deposited on an antenna to be detected by detecting a low frequency component appearing in a mixer output when snow is deposited on the antenna. SOLUTION: When snow is deposited on an antenna 2, electromagnetic waves generated by an oscillator 1 are supplied through a circulator 11 to the antenna, while a portion of the waves is reflected by the snow and returned again to a mixer 5 through the circulator 11. When the electromagnetic waves of the oscillator 1 are mixed with the electromagnetic waves reflected by the snow, a peat signal having an extremely small frequency is generated and measured as a low frequency current output. A low frequency current measuring section 9 measures the low frequency current value outputted from the mixer 5. As the thickness of the snow deposited on the antenna is increased, the electromagnetic waves reflected by the snow is also increased, so that the low frequency current value is increased in proportion to the thickness of the snow deposited on the antenna.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device mounted on an automobile for transmitting radio waves and receiving reflected waves of the radio waves. INDUSTRIAL APPLICABILITY The present invention is used as a device which is mounted on an automobile and automatically measures an inter-vehicle distance with a preceding vehicle during traveling, and issues an alarm when the inter-vehicle distance becomes short. The present invention relates to a technique for determining whether or not there is snow on an antenna of a radar device.

[0002]

2. Description of the Related Art Radio waves in the tens of GHz band are transmitted toward the front of a vehicle, reflected waves of the radio waves are received, and the distance to an object in front of the vehicle is measured based on the time difference between the transmission timing and the reception timing. Automotive radars are being developed. In recent years, the use of the 60 GHz (wavelength 5 mm) band as the frequency of in-vehicle radar has been specified in Japan,
Inter-vehicle distance warning devices in this frequency band are being studied. FIG. 8 shows the concept of this conventional example. FIG. 8 is a diagram illustrating a running example of a radar-equipped vehicle and a target vehicle during snowfall.

The mounting state of an antenna of a vehicle equipped with a radar will be described with reference to FIG. FIG. 9 is a diagram illustrating an example of mounting an antenna. In the example of FIG. 9, the antenna 2 is mounted on a bumper of an automobile by providing a square hole with a side of about several cm. At the time of snowfall as shown in FIG. 8, snow is clogged in this hole and hinders transmission and reception of radio waves, so a snow removal device is provided. As one example, a blower for blowing off by air pressure is provided. This blower blows off snow by injecting compressed air from an electric air pump, but the activation of the air pump is linked to the wiper switch.

[0004]

However, the wiper switch is operated not only at the time of snowfall but also at the time of rainfall. For example, in temperate regions such as Japan, the use of wipers for rainfall is overwhelmingly more prevalent than in snowfall.

Therefore, in the case of a snow removal device linked to a wiper switch as shown in the conventional example, the snow removal device works even during rainfall, and wasteful power is consumed. In addition, the life of the snow removal device is unnecessarily shortened.

[0006] Alternatively, when the snow removal device is started manually, the radar device may not operate normally due to reasons such as forgetting to start the air pump during snowfall.

The present invention has been made in such a background, and has as its object to detect snowfall of an antenna. An object of the present invention is to provide an on-vehicle radar device that operates normally even when snow falls.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an on-vehicle radar device, which includes an oscillator having an oscillation frequency of several tens of GHz, and transmits the output of the oscillator as a radio wave to a space in a traveling direction of a vehicle. An on-vehicle radar device comprising: an antenna for receiving a reflected wave; and a calculation circuit for calculating a distance to an object in front of the vehicle from a time difference between a transmission timing of the radio wave and a reception timing of the reflected wave. A feature of the present invention is that, in the arithmetic circuit, means for detecting the level of the reflected wave with respect to the time difference corresponding to the distance from the radiation end of the antenna to the transmission / reception separation circuit; Means for detecting snowfall on the vehicle.

That is, when snow is present on the antenna, part of the radio wave transmitted via the antenna is reflected by the snow. Therefore, a radio wave reciprocating between the transmission / reception separation circuit and the radiation end of the antenna is generated. By detecting the level of this reflected wave, it is possible to detect snow accretion on the antenna.

The means for detecting the level of the reflected wave includes means for continuously detecting the level of the reflected wave having a very small time difference, and the means for detecting snow accretion includes the means for detecting the level of the reflected wave at a predetermined value. It is desirable to include a means for sending an alarm when the value exceeds the limit. This makes it possible to continuously detect snowfall, notify the driver of snowfall, and activate a device that removes snowfall.

According to another aspect of the present invention, there is provided an arithmetic circuit for calculating a distance to an object in front of the vehicle by detecting a beat frequency between the transmitted wave frequency of the radio wave and the reflected wave frequency. A vehicle-mounted radar device. A feature of the present invention is that the arithmetic circuit includes means for detecting snowfall on the antenna when the signal level near the zero frequency of the beat signal exceeds a predetermined value. Therefore, snow accumulation can be detected by including means for detecting the low-frequency current in the arithmetic circuit.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of the arithmetic circuit.

The present invention relates to an on-vehicle radar device, which includes an oscillator 1 having an oscillation frequency of 60 GHz band, and transmits the output of the oscillator 1 as a radio wave to a traveling direction space of a vehicle and receives a reflected wave of the radio wave. An on-vehicle radar device comprising: an antenna 2; and a calculation circuit 4 that calculates a distance to an object in front of the vehicle from a time difference between a transmission timing of the radio wave and a reception timing of the reflected wave.

Here, the feature of the present invention is that the arithmetic circuit 4 detects the level of the reflected wave with respect to the time difference corresponding to the distance from the radiation end of the antenna 2 to the circulator 11 as a transmission / reception separation circuit. A low-frequency current measuring unit 9 as a means, and a snow accretion detecting unit 4 as a means for detecting snow accretion on the antenna 2 based on the magnitude of this level.
3 is included.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a diagram showing an example of a waveform of a transmission radio wave generated by an oscillator. FIG. 4 is a diagram showing a reception spectrum in fine weather. FIG. 5 is a diagram showing a reception spectrum at the time of snowfall. 4 and 5, the horizontal axis represents the mixer output frequency and the vertical axis represents the received power. FIG. 6 is a diagram showing the relationship between the thickness of snow accumulation and the low-frequency current, in which the horizontal axis indicates the thickness of snow accumulation and the vertical axis indicates the low-frequency current value. FIG. 7 is a flowchart showing the operation of detecting snow accumulation.

The oscillator 1 is a 60G oscillator as shown by a solid line in FIG.
Hz radio waves are continuously oscillated. This radio wave is 60G
The frequency is modulated between Hz and 60.075 GHz, and the center frequency is 60.0375 GHz. The repetition frequency of the frequency modulation is 750 KHz. This radio wave is input to the circulator 11 and is emitted from the antenna 2 toward the front of an automobile equipped with the on-vehicle radar device 10. The radio wave reflected by the target vehicle shown in FIG. The received radio wave is input to the circulator 11 and input to the mixer 5. In the mixer 5, the radio wave generated by the oscillator 1 and the radio wave received by the antenna 2 input via the circulator 11 are mixed. As a result, a beat signal generated from the phase difference between the two radio waves is output from the mixer 5. The beat signal is converted from analog to digital by the AD converter 6, the gain is adjusted, and the frequency is analyzed by the frequency analyzer 7. The frequency analyzer 7 is an FFT (Fast Fourier Tr).
ansform: Fast Fourier Transform). The output of the frequency analyzer 7 is input to the received power measuring unit 41 of the arithmetic circuit 4, and the frequency distribution and the received power are measured. The distance to the target vehicle and the relative speed are measured from the frequency distribution and the value of the received power. That is, if the distance to the target vehicle is short, the frequency of the beat signal is low, and if the distance to the target vehicle is long, the frequency of the beat signal is high. As shown in FIG. Measure the distance.

More specifically, the radio wave reflected by the target vehicle and returning to the antenna 2 is, as shown by a broken line in FIG.
2L / c (L is the distance between the target vehicle and the vehicle equipped with radar,
(c is the speed of the electromagnetic wave). Accordingly, the frequency shifts by Δf. This Δf becomes the frequency of the beat signal. This Δf increases in proportion to the distance L. The distance calculation unit 42 measures the distance to the target vehicle and the relative speed according to the frequency distribution of the received power. The alarm generator 44 outputs the distance and relative speed information from the distance calculator 42 to the display 8, and outputs an alarm when the distance and relative speed information exceeds a predetermined value. The alarm output can perform both output to the display 8 and external output.

FIG. 4 shows a reception spectrum in fine weather.
The reception spectrum of the reception power P measured as described above generates a power waveform such as the waveform P0 as shown in FIG. FIG. 5 shows a reception spectrum at the time of snowfall. When the antenna 2 receives snow, the radio wave generated by the oscillator 1 is supplied to the antenna 2 via the circulator 11, but a part of the radio wave is reflected by the snow and returns to the mixer 5 via the circulator 11 again. Since the propagation distance of the radio wave in this case is limited to a very short distance inside the device, when the radio wave of the oscillator 1 is mixed by the mixer 5 with the radio wave reflected by the snow, a beat signal having an extremely small frequency is generated.

The beat signal having a very low frequency is measured as a low-frequency current output from the mixer 5.
Therefore, when the output frequency of the mixer 5 is extremely low, as shown in FIG. 5, a power waveform such as the waveform P1 occurs near the extremely low frequency value. The waveform P0 'is a power waveform due to the radio wave reflected on the target vehicle, and decreases in inverse proportion to the increase in the waveform P1. The low-frequency current measuring section 9 measures the low-frequency current value output from the mixer 5. As the thickness of the snow on the antenna 2 increases, the radio wave reflected by the snow also increases. Therefore, FIG.
As shown in the figure, this low-frequency current value increases in proportion to the thickness of the snow on the antenna 2.

The operation of the snow detection unit 43 will be described with reference to FIG. S1 to S4 are as described above. The low-frequency current measuring unit 9 obtains the low-frequency current I0 from the mixer 5 (S5). If the relationship between the reception power L0 measured by the reception power measurement unit 41 and the low-frequency current I0 measured by the low-frequency current measurement unit 9 exceeds the threshold for snow accumulation, a snow removal device such as an air pump Start (S
7). Here, the principle of detecting snowfall from the relationship between the received power L0 and the low-frequency current I0 will be described. That is,
As shown in FIG. 5, the reception power L0 of the radio wave reflected by the target vehicle shown by the waveform P0 'and the reception power of the radio wave reflected by snow accumulation shown by the waveform P1 are in inverse proportion. Since the received power level of the radio wave reflected by snow accretion is proportional to the low frequency current I0, if the value of the low frequency current I0 increases, it means that a part of the radio wave to be transmitted to the target vehicle arrives. Reflects on snow to indicate that it does not play its intended role. Therefore, the value of the received power L0 of the radio wave reflected back to the target vehicle decreases. Therefore, a threshold is provided for each of the two values of the received power L0 and the low-frequency current I0. For example, when the received power L0 falls below the threshold A and the low-frequency current I0 exceeds the threshold B, it is determined that snow has arrived. . The threshold may be set only to the value of the low-frequency current I0, and the snowfall may be determined when the low-frequency current I0 exceeds the threshold B. Furthermore, if the snow that has arrived cannot be removed even though the snow removal device has been activated, a snowfall warning is issued (S9).

[0022]

As described above, according to the present invention,
Snowing of the antenna can be detected. Therefore,
An in-vehicle radar device that operates normally even during snowfall can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of an arithmetic circuit.

FIG. 3 is a diagram showing a waveform of a transmission radio wave generated by an oscillator.

FIG. 4 is a diagram showing a reception spectrum in fine weather;

FIG. 5 is a diagram showing a reception spectrum when snow accumulates.

FIG. 6 is a diagram showing a relationship between the thickness of snow accumulation and a low-frequency current.

FIG. 7 is a flowchart illustrating an operation of detecting snow accumulation.

FIG. 8 is a diagram showing a running example of a radar-equipped vehicle and a target vehicle during snowfall.

FIG. 9 illustrates an example of mounting an antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator 2 Antenna 4 Operation circuit 5 Mixer 6 AD converter 7 Frequency analyzer 8 Display 9 Low frequency current measurement unit 10 In-vehicle radar device 11 Circulator 41 Received power measurement unit 42 Distance calculation unit 43 Snow accretion detection unit 44 Alarm generation Department

[Procedure amendment]

[Submission date] October 24, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (3)

[Claims] An oscillator having an oscillation frequency of several tens of GHz;
An antenna that transmits the oscillator output as a radio wave toward the traveling direction space of the vehicle and receives a reflected wave of the radio wave, and an object in front of the vehicle based on a time difference between the transmission timing of the radio wave and the reception timing of the reflected wave. An on-vehicle radar device comprising an arithmetic circuit for calculating the distance of the antenna, wherein the arithmetic circuit detects the level of the reflected wave with respect to the time difference corresponding to the distance from the radiation end of the antenna to the transmission / reception separation circuit. Means for detecting snowfall on the antenna based on the magnitude of this level. 2. The means for detecting the level of the reflected wave,
Means for continuously detecting the level of the reflected wave having a very small time difference; means for detecting the snow accumulation including means for sending an alarm when the level of the reflected wave exceeds a predetermined value. 2. The on-vehicle radar device according to 1. 3. A frequency modulation oscillator having an oscillating frequency of several tens of GHz band, an antenna transmitting an output of the oscillator as a radio wave toward a space in a traveling direction of a vehicle and receiving a reflected wave of the radio wave, and a transmission wave of the radio wave. An arithmetic circuit for calculating a distance to an object in front of the vehicle by detecting a beat frequency between the frequency and the reflected wave frequency, wherein the arithmetic circuit includes a zero frequency of the beat frequency. An on-vehicle radar apparatus comprising means for detecting snowfall on an antenna when a nearby signal level exceeds a predetermined value.