JPH11183611A - Vehicle-mounted radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve driving safety, by detecting a level of a reflection wave for a time difference equivalent to distance from an antenna radiation edge to a signal transmission/ reception separation circuit, and setting and changing an alarm limit value. SOLUTION: An operation circuit 3 detects a reflection wave level based on a time difference equivalent to distance from a radiation edge of an antenna 2 to a signal transmission/reception separation circuit and detects the snow accretion of the antenna 2. While a vehicle is driving, snow accretion a constantly detected and a snow accretion elimination device 7 is started or stopped according to the presence or absence of snow-accretion. When the period of a snow accretion operation is smaller than a lower-limit judgment value, it is judged that a heavy snowfall including a snowstorm resulted and an alarm limit value is automatically set to a far mode. When a snow removal period is larger than the lower limit judgment value and smaller than a middle judgment value, it is judged that a medium degree of snowfall resulted and then alarm limit value is automatically set to a far mode. When snow removal period is larger than a middle judgment value and smaller than an upper-limit judgment value, it is judged that a light snowfall or rain resulted and the alarm limit value is automatically set to a middle mode. When the period of the snow removal operation is larger than the upper-limit judgment value, a normal mode is automatically set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention is applied to automobiles.
The present invention mounts a radar device on an automobile, irradiates the radar beam mainly in the traveling direction forward, measures an inter-vehicle distance,
The present invention relates to an improvement in a device for issuing an alarm. The present invention relates to an improvement for using a radar device in cold regions.

[0002]

2. Description of the Related Art Radar technology for detecting the distance from an antenna to an object by transmitting a directional radio wave from an antenna and measuring the time required for the reflected wave to return to the object is measured. Are known. It became an indispensable device for ships or aircraft.

Attempts have been made to mount this device on an automobile, and many proposals have been made. In recent years, it has been decided that the frequency to be used is 60 to 77 GHz. The applicant of the present application
In order to enhance the safety of car driving, we focused on radar equipment for cars from an early stage and conducted research. Then, in order to mount this device on a practical vehicle, the operation under various environmental conditions that the vehicle experiences was tested.

As a part of this, what is the problem of the radar device when it is used in a cold region is examined.
No. 225 and Japanese Patent Application No. 8-202257 (both were not disclosed at the time of filing the present application). In snowy areas in cold regions, the transmission of radar radio waves is hindered by snow and the sensitivity of radar equipment deteriorates.Therefore, when there is snowfall, radio wave output is increased, or snow or ice attached to the antenna is increased. Improvements such as removal. The present invention is to further improve the radar device to solve the problems found from the results of the test in a cold region.

[0005]

When a vehicle is traveling at a low speed, it is not always dangerous even if a preceding vehicle approaches the vehicle considerably. For example, when the road is congested, it is not dangerous even if the distance between the vehicle and the preceding vehicle is several meters. For this reason, conventionally, in-vehicle radar devices have been provided with a means for prohibiting an alarm so that an alarm is not generated even when the distance to a preceding vehicle is below the alarm limit when the vehicle speed is lower than, for example, 35 km / h. However, it has been found that when snow falls, the distance (field of view) that the driver can visually recognize becomes short, and in such a special state, a radar device may be required even at an extremely low vehicle speed. It has been found that such a condition especially occurs during a snowstorm.

SUMMARY OF THE INVENTION The present invention has been made in view of such a background, and is capable of automatically changing ordinary conditions without the driver's operation during a snowstorm to enable effective use. It is an object of the present invention to provide a radar apparatus for a vehicle. An object of the present invention is to provide a device in which a driver does not neglect the driving operation by operating the radar.

[0007]

SUMMARY OF THE INVENTION The present invention detects a snowfall condition and automatically changes and sets an alarm limit value set for an inter-vehicle distance in accordance with the snowfall condition, so that the vehicle can be safely driven in bad weather. It is characterized by enhancing the performance.

That is, according to the present invention, the oscillation frequency is several tens G
An oscillator in the Hz band, an antenna for transmitting the output of the oscillator as a radio wave toward the traveling direction space of the vehicle and receiving a reflected wave of the radio wave, and an antenna in front of the vehicle from the time from transmission of the radio wave to reception of the reflected wave An arithmetic circuit for calculating the distance to an object at a distance, and an alarm circuit for generating an alarm when the distance obtained at the output of the arithmetic circuit is smaller than the alarm limit value, wherein the arithmetic circuit is Means for detecting the level of the reflected wave with respect to a time difference corresponding to the distance from the radiation end of the antenna to the transmission / reception separation circuit; and Means for automatically changing the alarm limit value to a large distance based on the detection output of the means for detecting snow. This is to change the alarm limit value so as to increase the inter-vehicle distance when the weather is bad.

Means for automatically activating the snow removal device of the antenna based on the detection output of the snow detection device, and the snow removal device when the detection output of the snow detection device is lost. Means for automatically stopping, means for detecting the degree of snowfall by detecting the repetition period of the means for starting or means for stopping, and automatically when the degree of snowfall is equal to or more than a certain It is desirable to have a means for setting a snowstorm mode and a means for changing the response start speed of the radar to a value smaller than a standard value by the snowstorm mode.

When the vehicle is running at a vehicle speed equal to or higher than a predetermined value, an output generated by an oscillator in the tens of GHz band is transmitted as a radio wave from the antenna to the traveling direction space, and a reflected wave of the radio wave is transmitted to the antenna. Receive. The arithmetic circuit calculates the distance to the reflecting object (preceding vehicle) based on the time from the transmission of the radio wave to the reception of the reflected wave, and the distance obtained at the output of the arithmetic circuit is smaller than the set inter-vehicle distance alarm limit value. The alarm circuit generates an alarm when it becomes true.

In this manner, the inter-vehicle distance from the preceding vehicle is detected. When the inter-vehicle distance is detected, the level of the reflected wave is detected for a time difference corresponding to the distance from the radiation end of the antenna to the transmission separation circuit. Based on the magnitude of this level, it is detected whether or not the antenna has snowed, that is, whether or not it is in a snowfall state, and the alarm limit value of the inter-vehicle distance is automatically changed to the safe side based on the snow detection output.

When the antenna has snow, a part of the radio wave transmitted by the oscillator is reflected by the snow and returns.
Therefore, when there is snowfall, the signal level near the zero frequency of the beat frequency increases. Snow accumulation is detected by the increase in the signal level.

When snowfall on the antenna is detected, the snow removal device is automatically activated to remove snowfall, and when the snowfall is removed and the snowfall detection output is lost, the snow removal device is driven. To stop automatically.

Even in a snowfall state, the state is different, such as light snow, heavy snow, and snowstorm, and the state of snow on the antenna is also different. The degree of the snowfall is determined by measuring a cycle from activation to stop of the snow removal device for a predetermined number or time, and detecting the magnitude of the repetition cycle.

When the degree of snowfall detected in this way is equal to or more than a predetermined value, a snowstorm mode is automatically set. In this snowstorm mode, the threshold value of the vehicle speed at which the radar starts to respond is set to a value smaller than a standard value. Change to The snowstorm mode includes a heavy snow condition, and it is desirable that the threshold value of the radar response speed be changed stepwise.

As described above, snowfall on the antenna is automatically detected, the alarm limit value is changed to the safe side, and
By detecting the degree of snowfall and changing and setting the vehicle speed at which the radar starts to respond according to the degree of snowfall, the traveling safety of the vehicle can be maintained even in heavy snow or snowstorm conditions. In addition, since the detection of snowfall, the detection of the degree of snowfall, and the setting of an alarm limit value corresponding to the vehicle speed are automatically performed, it is possible to prevent the driver from neglecting the driving operation by operating the radar device. Can be avoided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

[0018]

Next, an on-vehicle radar device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a main part of a vehicle-mounted radar device according to an embodiment of the present invention.

In the embodiment of the present invention, the oscillation frequency is several tens GHz.
A high-frequency oscillator 1 for transmitting a high-frequency band, an antenna 2 for transmitting the output of the high-frequency oscillator 1 as a radio wave toward the space in the traveling direction of the vehicle and receiving a reflected wave of the radio wave, and receiving a reflected wave from transmission of the radio wave An arithmetic circuit 3 for calculating the distance to the object in front of the vehicle from the time up to the vehicle, an alarm circuit 4 for generating an alarm when the distance obtained from the output of the arithmetic circuit 3 is smaller than an alarm limit value, and an antenna 2 And a display device 8 for removing snow accretion.

The arithmetic circuit 3 includes means for detecting the level of the reflected wave with respect to a time difference corresponding to the distance from the radiation end of the antenna 2 to the transmission / reception separation circuit, and detecting snowfall on the antenna 2 based on the magnitude of the level. Means for automatically changing the alarm limit to a large distance based on the detection output of the means for detecting snow accretion, and the snow removal device 7 for the antenna 2 based on the detection output of the means for detecting snow accretion. , A means for automatically stopping the snow removal device 7 when the detection output of the means for detecting snow disappears, and a means for automatically starting the snow removal device 7 A means for detecting the degree of snowfall by detecting a repetition period of the means for stopping, a means for automatically setting a snowstorm mode when the degree of snowfall is equal to or more than a certain value, Means for further changing the sensitive initial rate of the radar to the standard value smaller value is provided.

Further, in the apparatus of the present invention, the first attenuator 11 and the second attenuator 12 for adjusting the attenuation rate of the radio wave generated by the high-frequency oscillator 1 and the output from the first attenuator 11 are branched. Directional coupler 13
A circulator (transmission / reception separating circuit) 14 for transmitting a radio wave from the directional coupler 13 to the antenna 2 and receiving a reflected wave from the antenna 2, a radio wave from the second attenuator 12, and a radio wave from the circulator 14. , An A / D converter 16 for converting the output of the mixer 15 from analog to digital,
A frequency analyzer 17 that analyzes the frequency of the output from the converter 16 and outputs the result to the arithmetic circuit 3 and a low-frequency current measuring device 18 that measures the low-frequency current value output from the mixer 15 are provided.

The vehicle-mounted radar device and the display 8 according to the present invention are mounted on a vehicle as shown in FIG. 2, and the display 8 is arranged at a position which is easy for the driver to operate and easy to see as shown in FIG. You.

FIG. 4 is a diagram showing an example of the configuration of the display surface of the display unit relating to the vehicle-mounted radar device according to the embodiment of the present invention. On the display 8, a power switch 20, an inter-vehicle distance setting switch 21 for setting an inter-vehicle distance by operation, a distance setting indicator lamp 22 for displaying the set inter-vehicle distance, and an actual inter-vehicle distance from a preceding vehicle are displayed. Inter-vehicle distance indicator 23, a danger warning lamp 24 for displaying a red danger warning when the distance between vehicles becomes a danger area, and a caution alarm lamp 25 for displaying a yellow danger warning when the inter-vehicle distance becomes a danger area. , A speaker 26 for generating an alarm sound and a snow arrival alarm lamp 27 are arranged. In addition, a dirt indicator lamp, a failure indicator lamp, a volume down switch, and a volume down indicator lamp are arranged.

The on-vehicle radar device and the display 8 are activated by turning on the power switch, and the distance set by the distance setting indicator lamp 22 by operating the inter-vehicle distance setting switch 21 shown in FIG.・
The middle and near modes are displayed. This inter-vehicle distance mode is set by pressing the inter-vehicle distance setting switch 21, and each time the inter-vehicle distance setting switch 21 is pressed, the inter-vehicle distance setting switch 21 shown in FIGS.
The lighting of the distance setting indicator lamp 22 switches between far, middle, and near as shown in FIG.

The setting of far / middle / near is selected according to the condition of the road and the type of road. For example, on a crowded road or an uphill road with many curves, the vehicle speed is not high, so the inter-vehicle distance is set to medium or close, and slippery roads, highways, or snowy roads where the vehicle speed tends to increase On roads, the distance is set to far or middle to increase the distance between vehicles.

FIG. 6 is a diagram showing an example of an alarm operation characteristic of an inter-vehicle distance alarm relating to the vehicle-mounted radar device according to the embodiment of the present invention. As shown in this characteristic, the alarm limit value of inter-vehicle distance at a certain vehicle speed V _i, large in the far-mode, small in the near mode, in the middle mode a value in between. A caution alarm limit value and a danger alarm limit value are set for each of these inter-vehicle distance modes.

Next, the operation of the thus-configured on-vehicle radar apparatus according to the embodiment of the present invention will be described. First, the operation of measuring the distance between vehicles and generating an alarm by the on-vehicle radar device according to the embodiment of the present invention will be described. FIG. 7 is a flowchart showing a flow of an inter-vehicle distance measurement and an alarm generation operation by the on-vehicle radar device according to the embodiment of the present invention.

When the power switch is turned on, the on-vehicle radar device and the display 8 are activated, and as shown by the solid line in FIG. 8, a 60-GHz radio wave is continuously output from the high-frequency oscillator 1 in this example. . The attenuation rate of this radio wave is adjusted by the first attenuator 11, and the radio wave is emitted from the antenna 2 in the traveling direction via the directional coupler 13 and the circulator 14.

The radiated radio wave is reflected by the preceding vehicle, received by the antenna 2, and output from the circulator 14 to the mixer 15. A beat signal is generated and output from the mixer 15 based on the phase difference between the radio wave input via the directional coupler 13 and the second attenuator 12 and the reflected wave from the circulator 14. This beat signal is supplied to the AD converter 1
The analog / digital conversion is performed by 6, the gain is adjusted, and the frequency is analyzed by the frequency analyzer 17. The output from the frequency analyzer 17 is input to the arithmetic circuit 3, where the frequency distribution and its received power are measured, and the distance to the preceding vehicle and the relative speed are calculated based on the measured frequency distribution.

That is, as shown by the broken line in FIG. 8, the radio wave reflected by the preceding vehicle and returned to the antenna 2 is proportional to the radio wave oscillated by the high-frequency oscillator 1, Δt = 2L / C (L =
The phase is shifted by the distance between the preceding vehicle and the own vehicle, and C is the speed of the electromagnetic wave), and accordingly, the frequency is shifted by Δf. This Δf becomes the frequency of the beat signal and increases in proportion to the distance L. The distance to the preceding vehicle and the relative speed are calculated according to the frequency distribution of the received power. FIG. 8 shows an example in which the radio wave is modulated between 60 GHz and 60.75 GHz, and the center frequency is 60.0375 GHz.

It is determined whether the calculated inter-vehicle distance to the preceding vehicle is smaller than the inter-vehicle distance alarm limit value set by operating the inter-vehicle distance setting switch 21 shown in FIG. An alert is generated as too much.

This warning is displayed on the danger warning lamp 24 or the caution warning lamp 25 of the display 8 shown in FIG. In the case of a caution alarm, the caution alarm lamp 25 is illuminated in yellow, and the speaker 26 displays the sound of "beep, beep, ...". In the case of a danger warning, the danger warning lamp 24 is illuminated in red, and the speaker 26 displays the sound of “Piro, Piro, Piro,...”.

Here, the operation of changing the setting of the alarm limit value of the inter-vehicle distance in bad weather by the on-vehicle radar device according to the embodiment of the present invention will be described. A feature of the present invention is that, for a time difference corresponding to the distance from the radiation end of the antenna 2 to the transmission / reception separation circuit (the circulator 14 in the present embodiment), the reflected wave of the radio wave transmitted toward the traveling direction space of the vehicle is changed. The purpose is to detect a level, detect snowfall on the antenna 2 based on the magnitude of the level, and automatically change the alarm limit value to a safe side based on the detection output.

First, the snow removal cycle detecting operation will be described. FIG. 9 is a flowchart showing the flow of the snow removal cycle detection operation by the on-vehicle radar device according to the embodiment of the present invention.

During traveling of the vehicle, it is always detected whether or not there is snow on the antenna 2. If there is snow, the snow removal device 7 is activated, and a snow removal device activation signal is transmitted. When the snow removal of the antenna 2 is removed by the snow removal device 7,
The activation of the snow removal device 7 is stopped, and a snow removal device activation stop signal is transmitted. If snow accumulates again after the snow accretion is removed, the same operation is repeated.

The detection of snow accretion is performed according to the flow shown in FIG. Radio waves emitted from the antenna 2 are reflected by the preceding vehicle and received by the antenna 2. A beat signal generated from the phase difference between the received reflected wave and the radio wave from the second attenuator 12 is converted into an analog signal by the AD converter 16.
The digital signal is converted, the frequency is analyzed by the frequency analyzer 17, and the output is input to the arithmetic circuit 3. on the other hand,
The output from the mixer 15 has a low-frequency current value measured by a low-frequency current measuring device 18 and is output to the arithmetic circuit 3. The arithmetic circuit 3 calculates the received power and the low-frequency current from these outputs, and determines whether or not the relationship between the calculated received power and the low-frequency current has exceeded a predetermined snowfall threshold. The presence or absence is determined.

This determination is made based on the following principle.
That is, the radio wave reflected by the attached snow increases as the thickness of the snow on the antenna 2 increases. Therefore, the low-frequency current value increases in proportion to the thickness of snow accumulation. Therefore, the reception power of the radio wave reflected by the preceding vehicle and the reception power of the radio wave partially reflected by the snow on the antenna 2 have an inversely proportional relationship. The received power level of the radio wave partially reflected by the snow accretion is proportional to the low-frequency current, so if the value of the low-frequency current increases, a part of the radio wave to be transmitted to the preceding vehicle arrives. It does not play its original role by reflecting off the snow. Therefore, the value of the received power of the radio wave reflected back to the preceding vehicle decreases. Therefore, thresholds are provided for the received power and the low-frequency current, and it is determined that snow has arrived when the received power falls below the predetermined threshold and the low-frequency current exceeds the predetermined threshold.

FIG. 11 is a flow chart showing the flow of the operation of changing the setting of the inter-vehicle distance alarm limit value in bad weather by the on-vehicle radar device according to the embodiment of the present invention.

A timer is set by an operation signal of the snow removal device 7, and a snow removal cycle from when snow removal is performed to when an operation stop signal is output is measured. Snow removal device 7
Is started when the mixer current reaches a predetermined value, as shown in FIG. 12A, and stopped when the mixer current becomes zero. FIG. 12B shows a snow removal device 7 for the antenna 2.
Is a diagram showing a voltage waveform applied to the heater when a heater is used. A predetermined voltage is applied at the time of starting the device, the voltage value decreases as the mixer current decreases, and the device stops at a voltage value of zero. FIG. 12C is a diagram showing activation and stop of the washer and the wiper when a washer or a wiper is used as the snow removal device 7.

When such a snow removal operation is performed a predetermined number of times n, the average snow removal period T is calculated by T = (T ₁ + T ₂ +... + T _n ) / n, and a predetermined lower limit judgment is made. Value T _L
(For example, 1 minute). If the detected cycle T is smaller than the lower limit determination value _TL , the snow removal operation is performed in a very short cycle, so that it is determined that the snow includes a snowstorm, and the radar response start speed is set to a first threshold (for example, 1 km / h). ) Is set. As a result, the vehicle speed is 1k
Even at m / h, the inter-vehicle distance of the preceding vehicle can be detected by the radar.

Next, by operating the inter-vehicle distance setting switch 21 shown in FIG. 4, it is determined whether or not the "far" mode is set as the alarm limit value on the distance setting indicator lamp 22, and the "far" mode is set. If not, the "far" mode is set automatically. Accordingly, the snow alarm lamp 27 is turned on, and the first attenuator 11 is turned on.
The output of the radio wave is adjusted by the second attenuator 12 and the output level of the radio wave is increased until the received power becomes equal to or higher than a predetermined value.

If the calculated period T is larger than the lower limit judgment value T _L, it is judged whether or not it is smaller than the intermediate judgment value T _M (for example, 10 minutes). If the period T is smaller than the intermediate determination value T _M , it is determined that the vehicle is in the middle of snow, and a second threshold value (for example, 20 km / h) is set for the radar start response speed. As a result, if the vehicle speed exceeds 20 km / h, the inter-vehicle distance of the preceding vehicle can be detected by the radar.

Next, it is determined whether or not the "far" mode is set as the alarm limit value as in the case of heavy snowfall.
If "far" mode is not set, "far"
The mode is set. Also in this case, since the amount of snowfall is large, the snowfall warning lamp 27 shown in FIG. 4 is turned on, and the output level of the oscillating radio wave is similarly increased.

If the calculated cycle T is smaller than the intermediate judgment value T _M, it is judged whether it is smaller than the upper limit judgment value T _U (for example, 20 minutes). If the cycle T is smaller than the upper limit determination value T _U , it is determined that light snow or rain is present, and the response start speed of the radar is set to a standard threshold value similar to the normal mode (for example, 35 km).
/ H) is set. Next, "medium" as the alarm limit value
It is determined whether the mode is set or not. If the "medium" mode is not set, the "medium" mode is automatically set. In this case, there is no snowfall on the antenna 2 and the received power is maintained at a predetermined value or more, so that the snowfall warning lamp 27 is not turned on and the output level of the radio wave is not increased.

If the calculated period T is larger than the upper limit judgment value T _U , the field of view will not be lost, so that the normal mode is automatically set, the inter-vehicle distance measurement based on the standard radar-sensitive start speed, and an alarm. The generating action is performed.

[0046]

As described above, according to the present invention, when heavy snow or snowstorm occurs, normal conditions are automatically changed without operation of the driver, and measurement of the following distance and generation of an alarm are performed. Since the operation is performed, the radar device can be effectively used, and the safety of traveling of the vehicle can be improved.

Further, since the arrival of snow on the antenna is automatically detected and snow is removed, and the reception level of the reflected wave is automatically changed. The distance between vehicles can be measured with an accuracy of. Since the detection of snowfall and the setting change of the output level of the radio wave are automatically performed, it is possible to prevent the driver from neglecting the driving operation for operating the radar device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of an on-vehicle radar device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of disposition of a vehicle-mounted radar device and a display device according to an embodiment of the present invention in a vehicle.

FIG. 3 is a diagram showing an example of disposition of a display device in a driver's seat related to the vehicle-mounted radar device according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration example of a display surface of a display unit related to the vehicle-mounted radar device according to the embodiment of the present invention.

FIGS. 5A, 5B, and 5C are diagrams showing display examples of a distance setting indicator lamp related to the on-vehicle radar device according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of an alarm operation characteristic of an inter-vehicle distance alarm related to the on-vehicle radar device according to the embodiment of the present invention.

FIG. 7 is a flowchart showing a flow of an inter-vehicle distance measurement and an alarm generation operation by the on-vehicle radar device according to the embodiment of the present invention;

FIG. 8 is a diagram showing a waveform example of a radio wave generated by a high-frequency oscillator of the vehicle-mounted radar device according to the embodiment of the present invention.

FIG. 9 is a flowchart showing a flow of a snow removal cycle detection operation by the on-vehicle radar device according to the embodiment of the present invention;

FIG. 10 is a flowchart showing a flow of a snow accretion detection operation by the vehicle-mounted radar device according to the embodiment of the present invention;

FIG. 11 is a flowchart showing a flow of an operation of setting an alarm limit value of an inter-vehicle distance in bad weather by the on-vehicle radar device according to the embodiment of the present invention.

12A is a diagram showing an example of starting and stopping of a snow removal device of the on-vehicle radar device according to the embodiment of the present invention, and FIG. 12B is a diagram showing repeated start and stop when a heater is used as the snow removal device. The figure which shows the example of a cycle, (c) The figure which shows the example of the repetition cycle of starting and stopping of a snow removal apparatus when a washer or a wiper is used as a snow removal apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency oscillator 2 Antenna 3 Operation circuit 4 Alarm circuit 5 Vehicle speed sensor 7 Snow removal device 8 Display 11 First attenuator 12 Second attenuator 13 Directional coupler 14 Circulator 15 Mixer 16 AD converter 17 Frequency analyzer 18 Low frequency current measuring device 20 Power switch 21 Inter-vehicle distance setting switch 22 Distance setting indicator lamp 23 Inter-vehicle distance indicator 24 Danger alarm lamp 25 Caution alarm lamp 26 Speaker

Claims (4)

[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 a distance from a time from transmission of the radio wave to reception of the reflected wave to an object in front of the vehicle. And a warning circuit that generates a warning when a distance obtained at the output of the calculation circuit is smaller than a warning limit value. The calculation circuit includes a radiation end of the antenna. Means for detecting the level of the reflected wave for the time difference corresponding to the distance from the transmission / reception separation circuit to the transmission / reception separation circuit, and means for detecting snowfall on the antenna based on the magnitude of the level, and means for detecting the snowfall. Means for automatically changing the alarm limit value to a large distance based on the detection output of the radar. 2. A means for automatically activating a snow removal device of an antenna based on a detection output of said means for detecting snow accretion, and said snow accretion when the detection output of said means for detecting snow accretion disappears. 2. The on-vehicle radar device according to claim 1, further comprising means for automatically stopping the removing device. 3. The on-vehicle radar device according to claim 2, further comprising means for detecting a degree of snowfall by detecting a repetition period of said activating means or said stopping means. 4. A means for automatically setting a snowstorm mode when the degree of snowfall is equal to or greater than a predetermined value, and means for changing the radar start speed to a value smaller than a standard value by the snowstorm mode. The on-vehicle radar device according to claim 3.