JPH08147585A - Device for alarming start of vehicle in front - Google Patents

Abstract

PURPOSE: To detect the reflection intensity of reflected waves received in the reception part of a radar head, to judge the start of a vehicle in front when a detected value becomes lower than a prescribed value after becoming higher than the prescribed value and to raise an alarm. CONSTITUTION: When the signals of present vahicle stopping are inputted from a stopping detector 33 to a signal processing circuit 30, start pulses are outputted from the signal processing circuit 30 to a trigger circuit 21 and trigger signals are outputted from the trigger circuit 21 to a driving circuit 11. The driving circuit 11 lets a light emitting element 12 emit light every time the trigger signals are inputted and radiates transmission pulse signals in front of the present vehicle through a lens 13. Reception output from a light receiving element 15 is amplified in a limiter amplifier 16 and then, reception signals converted into binarized signals are generated depending on whether or not it has exceeded a threshold value in a zero-cross comparator 23. The trigger signals of the trigger circuit 21 are also inputted to a sampling pulse generator 22 and the signal processing circuit 30 performs the addition processing of reception data inside respective memories and detects a target in front.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front vehicle start warning device which detects the start of a front vehicle and informs the driver of an alarm when the vehicle is stopped.

[0002]

2. Description of the Related Art As a conventional forward vehicle start warning device,
For example, JP-A-57-182545 and Japanese Utility Model Publication No.
As disclosed in Japanese Patent Publication No. 8-6646, etc. Such a conventional device radiates an electromagnetic wave to a forward vehicle using, for example, a Doppler radar and receives the reflected wave, and based on the frequency of the radiated wave and the frequency of the received wave, determines the distance and the relative speed to the forward vehicle. It is calculated and an alarm is sounded when the relative speed changes over a predetermined speed to notify the driver that the preceding vehicle is approaching or moving away.

[0003]

However, in such a conventional device, since the distance to the vehicle in front and the relative speed are parameters of the alarm logic, a signal processing circuit for calculating the distance from the received signal is required. In particular, when an optical radar is used, there is a problem that the signal processing unit is complicated because a circuit that performs time differential processing of the distance is required to obtain the relative velocity. Further, when the preceding vehicle approaches or moves away at an extremely low speed less than or equal to a predetermined relative speed, the alarm may not be issued.

Further, when the above-mentioned conventional vehicle start warning device is realized by using an optical radar, in order to obtain a sufficient vehicle detection distance, it is necessary to collect and emit the transmitted light so as to hit the reflector of the vehicle ahead. Therefore, the light emission area (vehicle detection area) on the left, right, top, and bottom is narrowed. Therefore,
When the optical axis of the transmitted light is deviated, the transmitted light is likely to be separated from the reflector of the vehicle in front, and when it is separated, only weak reflected light from the vehicle body can be received and accurate distance measurement may not be possible.

The present invention has been made by paying attention to such a conventional problem, and the strength of a signal reflected from the front is used as a parameter of an alarm logic to simplify the signal processing circuit. An object is to provide a vehicle start warning device.

[0006]

For this reason, in the forward vehicle start warning device according to the first aspect of the present invention, as shown in FIG. 1, the radiating portion for radiating an electromagnetic wave forward of the host vehicle and the radiated electromagnetic wave are provided. A radar head having a receiving unit for receiving the reflected wave, a reflection intensity detecting means for detecting the reflection intensity of the reflected wave received by the receiving unit of the radar head, and the reflection intensity of the detected reflected wave is a predetermined value or more. After that, an alarm control means for determining that the vehicle ahead has started and issuing an alarm from the alarm means when the value falls below the predetermined value.

According to the second aspect of the present invention, as shown in FIG. 2, the reflection intensity detection means includes a reception data binarization means for binarizing the reception data from the reception section, and the radiation section. Sampling means for sampling and storing the binarized reception data at predetermined intervals at each cycle of the radiated electromagnetic wave pulse signal, and the reception data at each sampling point stored in the sampling means for the electromagnetic wave pulse signal And the addition means for inputting for each radiation period and adding for each sampling point, and the addition value of the addition means is used as the reflection intensity.

Further, in the invention described in claim 3, as shown by a broken line in FIG. 2, in addition to the configuration described in claim 2, the sampling means is connected to the binary data output line to
A monitor lamp that uses the digitized data output as the drive power supply,
The optical axis of the radar head can be adjusted based on the lighting state of the monitor lamp. In the invention according to claim 4,
As shown by the broken line in FIG. 3, the optical axis of the radar head is adjusted based on the alarm sound of the alarm means instead of the monitor lamp, and mode switching means for switching between the start alarm mode and the optical axis adjustment mode is provided. The alarm means is connected to the alarm control means at the start alarm mode position and connected to the output line of the sampling means at the optical axis adjustment mode position.

According to the fifth aspect of the invention, the stop detection means for detecting the stop of the own vehicle is provided, and the power is turned on when the stop of the own vehicle is detected.

[0010]

According to the first aspect of the invention, the radar head radiates an electromagnetic wave from the radiating section, and the reflected wave is received by the receiving section. The reflection intensity detection means detects the reflection intensity of the reflected wave received by the receiver of the radar head. The alarm control means determines that the preceding vehicle has started when the detected reflection intensity of the reflected wave is less than or equal to a predetermined value and then issues an alarm from the warning means.

As described above, if the parameter of the warning logic in the forward vehicle start warning device is only the reflected signal strength, the signal processing circuit can be simplified, and even if the forward vehicle moves at an extremely low speed, it can be reduced. It is possible to detect. Further, in the invention of claim 2,
The received data binarization means binarizes the received data, and the sampling means samples the binarized data at predetermined intervals for each cycle of the electromagnetic wave pulse signal radiated from the radiating portion of the radar head at a constant cycle. Memorize and by adding means,
The binarized data sampled by the sampling means is added at each sampling point, and the added value is output to the alarm control means as the reflection intensity.

As described above, according to the method of binarizing the received signals and adding them to calculate the reflection intensity, it is possible to easily distinguish the random noise from the true reflection signal, and the reliability of the apparatus. Can be increased. Further, in the invention described in claim 3, since the binarized data output is substantially fixed to "1" or "0" when the reflected wave from the front object is reliably received, the monitor lamp Turns on or off. On the other hand, when the reflected wave from the front object is weakened due to the shift of the optical axis, "1" and "0" are generated in the binarized data output substantially alternately, and the monitor lamp blinks. Therefore, it is possible to determine whether the optical axis position is normal or not based on the lighting state of the monitor lamp, and it is possible to easily add a monitoring function for adjusting the optical axis of the radar head.

In the invention according to claim 4, since the alarm device can also be used for the optical axis adjustment monitor of the radar head, it is not necessary to provide a component dedicated to the optical axis adjustment monitor. Further, according to the invention described in claim 5, when the own vehicle stops, the start warning function of the preceding vehicle can be automatically activated.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram showing a concrete configuration of the first embodiment of the present invention. In FIG. 4, the radar head 10 is
In front of the host vehicle, a radiator that emits, for example, a light pulse signal as an electromagnetic wave, and a receiver that receives the reflected pulse of the emitted optical pulse signal reflected by the vehicle ahead are provided.
The radiating unit is a drive circuit 11 driven in response to a trigger signal output from a trigger circuit 21 described later, the drive circuit 11
It is composed of a light emitting element 12 such as an LED or a laser diode which emits light in accordance with the driving of the vehicle and a lens 13 which condenses the light emitted from the light emitting element 12 so as to hit a predetermined portion such as a reflector of a vehicle ahead. Further, the receiving unit is a lens that focuses the reflected pulse toward the light receiving surface of the light receiving element 15 described later while focusing the light.
14, a light receiving element 15 such as a photodiode that converts the light that has passed through the lens 14 and is condensed into an electric signal, and a limiter amplifier 16 that appropriately amplifies the electric signal output by the light receiving element 15.

The logic circuit 20 takes in a clock signal (for example, 15 MHz) from the clock oscillator 31, and
Upon receiving a start pulse from a signal processing circuit 30 described later, a trigger circuit 21 that outputs a trigger pulse to the drive circuit 11 and a sampling pulse generator 22 described later at regular intervals,
A sampling pulse generator 22 that takes in a clock signal from the clock oscillator 31, generates a sampling pulse for controlling the sampling operation by a trigger pulse from the trigger circuit 21, and generates an end pulse indicating the end of sampling, the radar head 10 The output of the limiter amplifier 16 is converted into a binary value of 5V and 0V, for example, 5V is a logical value 1 and 0V is a logical value 0, and the received data is converted into a binary logic level and output, and a sampling pulse. Is composed of an 8-bit shift register 24 for sampling, shifting, and storing the binary logic output from the zero-cross comparator 23 for each input.

The signal processing circuit 30 is constructed by incorporating, for example, a microcomputer, takes in the clock signal from the clock oscillator 31, outputs a start pulse to the trigger circuit 21, and controls the light emission timing of the radar head 10. In addition, by inputting an end pulse indicating the end of sampling from the sampling pulse generator 22, the binary sampling data stored in the 8-bit shift register 24 is respectively taken in from the 8-bit data terminal, added, and stored in the memory for 8-bit shift. It is provided for each bit of the register 24. Then, based on the added value (corresponding to the reflection intensity) for each sampling point stored in each memory, it is determined whether or not an alarm is to be issued, and the drive of the alarm device 32 is controlled. Therefore, the zero cross comparator 23 receives the received data 2
It corresponds to a value conversion means. Also a sampling pulse generator
The 22 and 8-bit shift register 24 constitutes a sampling means. Further, the memory of the signal processing circuit 30 corresponds to the adding means, and the function of the alarm control means is that of the signal processing circuit 30.
It is equipped with software.

Further, the signal processing circuit 30 recognizes the vehicle speed zero signal from the vehicle stop detection device 33 including a vehicle speed sensor as a vehicle stop signal and supplies power to the radar head 10, the logic circuit 20, the clock oscillator 31, and the like. Note that the vehicle stop detection device
As 33, a handbrake switch that is turned on by the operation of the handbrake may be used. Monitor lamp 35
Is connected to, for example, the 1-bit data terminal of the 8-bit shift register 24 of the logic circuit 20 via the buffer circuit 34, and turns on / off the output voltage of the 1-bit data terminal as a power source. It is used to adjust the optical axis of. The buffer circuit 34 is provided so that the drive of the monitor lamp 35 does not affect the received signal taken into the signal processing circuit 30 for the start warning process.

Next, the operation will be described. When a signal indicating that the vehicle has stopped is input to the signal processing circuit 30 from the vehicle stop detection device 33, a start pulse is output from the signal processing circuit 30 to the trigger circuit 21. Then, the trigger signal shown in the time chart of FIG. 5 is output from the trigger circuit 21 to the drive circuit 11. This trigger signal is generated a predetermined number of times (8192 times in this embodiment) which is set in advance at a predetermined interval, for example, every 4 μs. Drive circuit 11
Each time the trigger signal is input, the light emitting element 12 is caused to emit light, and the sending pulse signal shown in FIG. In addition, the received output from the light receiving element 15 is amplified by the limiter amplifier 16, and then the zero cross comparator is used.
At 23, it is converted into a binary signal of 5V and 0V depending on whether or not a predetermined threshold value (for example, 0V) is exceeded, and the reception signal shown in FIG. 5 is generated. The received signal, together with the noise signal, is reflected at each transmission timing of the emitted transmission pulse signal at a position delayed by a delay time Td proportional to the distance from the transmission timing to the target, as shown in FIG. Appears.

The trigger signal of the trigger circuit 21 is also input to the sampling pulse generator 22, and the sampling pulse generator 22 generates the sampling pulse of FIG. 5 every time the trigger signal is input. This sampling pulse is
It occurs at a predetermined constant period Δt, and the number is, for example, 8
Individual. Then, the sampling pulse is output to the 8-bit shift register 24. 8-bit shift register 24
For each input of the sampling pulse, the binary signal from the zero-cross comparator 23 is sampled, sequentially shifted and stored.

When the eighth sampling pulse is generated, the sampling pulse generator 22 outputs an end pulse to the signal processing circuit 30 in synchronism with this, and the signal processing circuit 30
8-bit shift register 24 for each input of this end pulse
The eight binarized received data stored in 1 are taken in and stored in each memory corresponding to each bit. This operation is repeated 8192 times, the reception data in each memory is added, and the front target is detected.

Next, the drive control operation of the alarm device 32 by the signal processing circuit 30 will be described with reference to the flowchart of FIG. In step 1 (indicated by S1 in the figure, the same applies hereinafter), binary-level (1 or 0) received data of logic level in the 8-bit shift register 24 is fetched by the end pulse input from the sampling pulse generator 22. .

In step 2, the fetched received data is added to the stored value in each memory and the added value is stored. In step 3, it is determined whether or not the data addition operation is performed 8192 times, and when it is repeated 8192 times, the process proceeds to step 4, and the maximum value Amax of the addition values in each memory is detected.

In step 5, the flag F is checked. Here, when the flag F = 1, it indicates that there is a maximum value Amax that is equal to or more than a predetermined threshold value A ₀ described later (the front vehicle exists), and when the flag F = 0, the front vehicle does not exist. Shows. Therefore, when the operation of detecting the maximum value Amax is the first time, the flag F = 0 in step 5, and the process proceeds to step 6.

In step 6, the addition detected in step 4 is added.
The maximum value Amax of the calculated value is the predetermined threshold A ₀Determine whether or not
And Amax ≧ A₀If it is, it is judged that there is a detected vehicle in front.
Then, in step 7, the flag F = 1 is set and the step is restarted.
Return to step 1 and repeat the operations of steps 1 to 4. Soshi
Then, the determination in step 5 is flag F = 1,
Go to 8.

In step 8, it is judged whether the maximum value Amax exceeding the threshold value A ₀ is smaller than the threshold value, and Amax
When it is determined that the detected vehicle has decreased to <A ₀ , it is determined that the detected vehicle in front of the own vehicle has started, and an alarm output command is generated in step 9, and an alarm is issued from the alarm device 32 to the front of the driver. Notify the start of the vehicle. In step 10, the flag F = 0 is set.

That is, when there is no target in front and the received signal is only random noise that is a background noise, the zero-cross comparator 23 alternately outputs "1" and "0". , "1" is output and "0" is output. Therefore, in the case of only random noise, the addition value obtained by the addition processing of 8192 times in one target detection operation is 4096, which is half that value. When a target is present, the number of output of "1" from the data terminal of the 8-bit shift register 24 corresponding to the sampling point indicating the position where the front target is present increases due to the presence of the reflection pulse from the target, The added value is 4
Increase from 096. Then, when the value is equal to or larger than the predetermined threshold value A ₀ , it is determined that the received signal includes the reflection pulse from the target, and it is determined that the target is present.

The relation between the reflection intensity E and the distance R to the target is represented by the radar equation as E = B / R ⁴ (B: constant), and the distance to the target and the reflection intensity are relative. Since there is such a relationship, it is possible to detect the approaching or separating operation of the vehicle in front based on the reflection intensity. Therefore, the added value of such received data is regarded as the reflection intensity from the vehicle in front,
If this reflection intensity is used as a parameter for the start warning, the number of parameters is smaller than the conventional one that uses both the distance and the relative speed as the start warning parameter, and the circuit can be simplified. Further, even when the preceding vehicle moves at an extremely low speed, it is possible to reliably detect the difference due to the difference in the reflection intensity.

Further, in the case of the reception data addition method in which the addition value of the reception data is used as the reflection intensity, since the distinguishability between the random noise and the reflection pulse from the true target becomes good, the detection reliability of the preceding vehicle is high. And the reliability of the start warning device can be improved. Next, the optical axis adjusting function of the radar head 10 provided in this embodiment will be described. As shown in FIG. 7, each time the pulse signal is emitted, the 8-bit shift register 24
Is input with 8 clocks, 8 received data are taken into the signal processing circuit 30, and this is repeated 8192 times. By adding 8192 received data, one distance measuring operation is completed. . In this distance measuring operation, "1" is output to the data output line of the first bit of the 8-bit shift register 24 (corresponding to the distance closest to the host vehicle in the detected distance) when the reflected pulse intensity is strong. If it is weak, "0" occurs. When the 1st bit of the received data is "1", a voltage of 5V is applied to the monitor lamp 35 to light it, and when it is "0", the applied voltage is 0V and the monitor lamp 35 is turned off. Therefore, when the reflected pulse from the distance corresponding to the first bit sampling point of the 8-bit shift register 24 is weak, that is, when there is no object and only random noise, or when there is a vehicle in front, the radar head 10 When the weak reflection pulse from the vehicle body is input due to the deviation of the optical axis of, the output of the 1st bit is alternately repeated "1" and "0". In this case, the monitor lamp 35 Flashing operation. The added value is 4
It is 096. On the other hand, there is a vehicle in front and the radar head 10
If the optical axis of is normal and a strong reflection pulse is received from the reflector of the vehicle ahead, the output probability of the 1st bit “1” increases, the added value increases above the threshold, and the monitor lamp
35 turns on.

Therefore, when the vehicle is ahead, the position of the radar head 10 is adjusted while looking at the monitor lamp 35,
By aligning the position of the radar head 10 with the position where the monitor lamp 35 is turned on, the optical axis of the radar head 10 can be aligned. As described above, if the monitor lamp 35 for adjusting the optical axis of the radar head 10 is connected to the data output line of the 8-bit shift register 24 and the output of the output line is used as a power source,
By adding a simple circuit without adding a memory or the like, the optical axis of the radar head 10 can be easily adjusted based on the reflection intensity. By providing such a monitor lamp 35, it is possible to always confirm whether or not the detection status of the reflection intensity is normal, so that it is possible to prevent the occurrence of a non-alarm in advance and eliminate the anxiety of malfunction such as giving the driver. it can. Furthermore, the light emitting element 12
If the deterioration occurs, the received data addition value does not become the maximum, so that it is possible to easily judge from the lighting state of the monitor lamp 35.

Next, another embodiment relating to the optical axis adjustment will be described with reference to FIG. The same elements as those of the first embodiment shown in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. In FIG.
In this embodiment, instead of the monitor lamp 35, an alarm device 32 for starting alarm is used. That is, the alarm device 32 is provided with a mode switching switch 40 capable of switching between the start warning mode and the optical axis adjustment mode of the radar head 10. When the X terminal side of the switch 40 is selected, the optical axis adjustment mode is set, and Y When the terminal side is selected, the start alarm mode is set.

Next, the operation will be described. When the mode changeover switch 40 is connected to the X terminal side to select the optical axis adjustment mode, the alarm device 32 is connected to the first bit of the 8-bit shift register 24. In this case, when the optical axis of the radar head 10 is displaced from the reflector of the vehicle ahead and the reflection intensity received by the light receiving element 15 is weak reflection from the vehicle body,
Since the output of the first bit of the bit shift register 24 is "1" and "0" alternately, the alarm of the alarm device 32 is generated intermittently, the optical axis is normal, and the strong light from the reflector of the vehicle ahead. If it is a reflection, the output of the first bit continues to be "1", so that the alarm device 32 issues a continuous alarm.

On the other hand, when the start alarm mode is selected by connecting the mode changeover switch 40 to the Y terminal side, the alarm device 32 is connected to the signal processing circuit 30 side. In this case, the alarm generation of the alarm device 32 is controlled by determining whether or not the vehicle ahead is starting based on the added value calculated by the signal processing circuit 30. According to the embodiment shown in FIG. 8, the alarm device 32 for starting warning can also serve as the optical axis adjustment of the radar head 10, and it is not necessary to provide the monitor lamp 35 dedicated to the optical axis adjustment, and the number of parts can be reduced. Can be reduced.

In each of the embodiments, the monitor lamp 35 is connected to the first bit data output line of the 8-bit shift register 24, but the received data is sampled by the 8-bit shift register 24 from the generation of the trigger signal. In consideration of the operation delay of the circuit intervening in the route up to the above, the connection bit of the monitor lamp 35 should be connected to the data output line of the second bit onward depending on the distance to be detected by the preceding vehicle. desirable.

In the optical axis adjustment, the monitor lamp 35 is turned on when the optical axis is normal in this embodiment. For example, an inverter for inverting the output of the data output line is provided in the preceding stage of the monitor lamp 35. Therefore, the monitor lamp 35 may be turned off when the optical axis is normal. Furthermore,
In each embodiment, the number of times of addition of data in one distance measuring operation is 8192, but the number of times of addition is not limited to this.
Although it may be at least larger than this, the larger the number of additions, the higher the accuracy of discrimination from random noise, and the higher the reliability of alarm generation.

Further, in each of the embodiments, the vehicle stop detection device is provided and the start alarm device is automatically activated when the own vehicle is stopped. However, the vehicle stop detection device is omitted and a manual operation switch is provided. The driver may operate the operation switch of the start warning device.

[0036]

As described above, according to the first aspect of the present invention, electromagnetic waves are radiated to the vehicle ahead and the presence or absence of the vehicle ahead is detected by using the reflected intensity of the radiated electromagnetic waves as a parameter of the vehicle start warning. Since the configuration is such that a warning is issued, the number of warning parameters can be smaller than in the conventional case, the circuit for signal processing can be simplified, and the cost of the warning device can be reduced.

According to the second aspect of the invention, since the addition type radar system is adopted in which the received data for each radiation of electromagnetic waves is added a predetermined number of times and the added value is used as the reflection intensity to detect the front vehicle, Since the reflected wave and the random noise can be discriminated well, the reliability of the alarm device can be improved. Also,
According to the invention of claim 3, a monitor lamp is connected to the output line of the reception data to be subjected to the addition processing, and the optical axis of the radar head can be aligned while the monitor lamp is lit. The optical axis adjustment function of the radar head can be added just by adding it, and it is possible to always check whether the detection status of the reflection intensity is normal or not, so it is possible to prevent the occurrence of unwarned alarms in advance and give the driver an action. You can eliminate anxiety such as defects. Further, it is possible to easily determine the deterioration of the electromagnetic wave radiation element of the radar head from the lighting state of the monitor lamp.

If the alarm device also serves as the optical axis adjustment monitor of the radar head as in the fourth aspect of the present invention, a monitor lamp dedicated to the optical axis adjustment of the radar head can be dispensed with, and the number of parts can be reduced. It is possible to reduce. Also,
According to the fifth aspect of the present invention, the operation of the start warning device is automatically started when the host vehicle stops, so that the driver does not have to operate the vehicle and the usability is good.

[Brief description of drawings]

FIG. 1 is a block configuration diagram for explaining the invention according to claim 1.

FIG. 2 is a block diagram for explaining the invention according to claims 2 and 3.

FIG. 3 is a block diagram for explaining the invention according to claim 4;

FIG. 4 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 5 is a time chart of various output signals according to the embodiment.

FIG. 6 is a flowchart for explaining the operation of the above embodiment.

FIG. 7 is a time chart for explaining an optical axis adjusting operation.

FIG. 8 is an overall configuration diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 10 Radar head 12 Light emitting element 15 Light receiving element 20 Logic circuit 21 Trigger circuit 22 Sampling pulse generator 23 Zero cross comparator 24 8-bit shift register 30 Signal processing circuit 31 Clock oscillator 32 Alarm device 33 Stop detection device 35 Monitor lamp 40 Mode changeover switch

Claims (5)

[Claims] 1. A radar head including a radiation unit that radiates an electromagnetic wave in front of the host vehicle and a reception unit that receives a reflected wave of the radiated electromagnetic wave; and a reflection intensity of the reflected wave received by the reception unit of the radar head. A reflection intensity detecting means, and an alarm control means that, when the detected reflection intensity of the reflected wave falls below a predetermined value after reaching a predetermined value, determines that a vehicle ahead is in motion and issues an alarm from the alarm means. A forward vehicle start warning device comprising: 2. The reflection intensity detecting means, the receiving data binarizing means for binarizing the receiving data from the receiving part, and the binarizing at each period of the electromagnetic wave pulse signal emitted from the emitting part. Sampling means for sampling and storing the received data at predetermined intervals, and the received data for each sampling point stored in the sampling means is input for each radiation period of the electromagnetic pulse signal and added for each sampling point. An addition means is provided, and the addition value of the addition means is used as the reflection intensity.
The preceding vehicle start warning device. 3. A monitor lamp connected to the data output line of the sampling means and using this binary data output as a drive power source is provided, and the optical axis of the radar head can be adjusted based on the lighting state of the monitor lamp. The forward vehicle start warning device according to claim 2. 4. A structure for performing optical axis adjustment of a radar head based on an alarm sound of the alarm means in place of the monitor lamp, and mode switching means for switching between a start alarm mode and an optical axis adjustment mode. 3. The forward vehicle start alarm device according to claim 2, wherein the alarm means is connected to the alarm control means at the start alarm mode position and connected to the data output line of the sampling means at the optical axis adjustment mode position. 5. The front according to any one of claims 1 to 4, wherein stop detection means for detecting the stop of the own vehicle is provided, and the power is turned on when the stop detection means detects the stop. Vehicle start alarm device.