JPH1148884A - Inter-vehicle distance alarm device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To issue an inter-vehicle distance alarm so as to prevent collision onto a car in front in creep even in the state where a brake pedal is depressed during low-speed driving. SOLUTION: In this inter-vehicle distance alarm device, it is determined by a first alarm judging means 20a whether an inter-vehicle distance detected by an inter-vehicle distance detecting means 1 is less than an alarm distance determined according to the relative speed between its own vehicle speed and the speed of a vehicle in front or not, and it is also determined by a second alarm judging means 20b whether, after its own vehicle is stopped, the distance is less than an alarm distance at low speed determined according to its own speed and an inter-vehicle distance at the speed less than a predetermined car speed. And an alarm output control means 20d outputs an inter-vehicle alarm when the first alarm judging means judges the alarm output and a brake is not operated, and outputs the inter-vehicle alarm when the second alarm judging means judges an alarm output at low speed even when the brake is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inter-vehicle distance alarm device.

[0002]

2. Description of the Related Art Conventionally, as an inter-vehicle distance alarm device which issues an inter-vehicle distance alarm and warns a driver when the inter-vehicle distance to a vehicle in front falls below a predetermined warning distance from the relationship between the own vehicle speed and the relative speed, FIG. 8 is known. This conventional inter-vehicle distance warning device emits a laser beam forward like a laser radar device, receives reflected light that is reflected back to the tail of a preceding vehicle and returns, and from the emission timing to the reflected light reception timing. Distance detection device 1 for detecting the distance between vehicles based on the time difference of the vehicle
And the vehicle speed signal output from the vehicle speed sensor 6 for detecting the own vehicle speed is input to calculate the own vehicle speed, and the relative speed with respect to the preceding vehicle is calculated from the temporal change of the inter-vehicle distance output from the inter-vehicle distance detection device 1. An alarm determining unit 2a that compares a warning distance set in advance based on the own vehicle speed and the relative speed with an actual inter-vehicle distance at that time to determine whether to output an inter-vehicle distance warning, and An alarm output control unit 2b for inputting a signal of the brake switch 5 for outputting an ON signal when the foot brake is operated and controlling whether to output the alarm output signal from the alarm determination unit 2a as it is or to stop the output is provided. The alarm processor 2 and the alarm processor 2
The display device 3 displays an inter-vehicle distance warning by receiving an alarm output signal from the alarm output control unit 2b, and an alarm buzzer 4 that similarly receives the alarm output signal and outputs an inter-vehicle distance alarm sound.

FIG. 9 is a graph showing a vehicle speed / relative speed-warning distance characteristic graph referred to by an alarm judging section 2a of an alarm processing device 2 which has been widely used in the related art. This is given by an alarm distance calculation formula determined from the relationship between the vehicle speed Vf-the relative speed Vr), the reaction time t1 of the driver, and the deceleration α generated by the deceleration operation. When the traveling condition enters the area below the characteristic line in FIG. 9, the alarm condition is satisfied, and the inter-vehicle distance alarm output is determined.

In such a conventional inter-vehicle distance warning device,
As shown in the flowchart of FIG. 10, when the following distance warning system starts (step S100), the signal of the vehicle speed sensor 6 is input to calculate the own vehicle speed (step S101), and then the following distance output device 1 outputs Then, the relative speed is calculated from the inter-vehicle distance change per unit time between the previous inter-vehicle distance data and the preceding inter-vehicle distance data (steps S102 and S103).
Next, regarding the vehicle speed, the inter-vehicle distance, and the relative speed, it is determined whether or not the alarm condition is satisfied by referring to the above-described vehicle speed / relative speed-warning distance characteristic (step S10).
4).

If the alarm condition is not satisfied, it is determined that the safe inter-vehicle distance is being maintained, and step S10 is performed.
It returns to 1 and continues inter-vehicle distance monitoring. On the other hand, if the alarm condition is satisfied, it is next determined whether an ON signal indicating a brake operation is input from the brake switch 5 (step S105). If the brake switch 5 is ON, the driver considers that the driver has stepped on the brake to reduce the speed because the inter-vehicle distance has become short, and stops the alarm output (step S106).
If is kept off, an inter-vehicle distance alarm is output to issue an inter-vehicle distance alarm to the driver (step S107).

For example, referring to the characteristic line in FIG. 9, when the own vehicle speed is approaching 70 km / h and the relative speed is approaching 10 km / h, the alarm distance L is 28 m. If the warning distance is 28 m or less, it is determined that an inter-vehicle distance alarm has been output, and if the distance becomes less than the alarm inter-vehicle distance without the brake being depressed, an inter-vehicle distance warning is displayed, and an inter-vehicle distance warning sound is output to warn the driver. You do it.

[0007]

However, such a conventional inter-vehicle distance warning device has the following problems. In other words, under running conditions where the driver repeatedly stops and starts on a congested road while stopping due to a traffic light, the driver must take care of the driver while standing on the brake pedal and stopping while neglecting to look forward. As a result, the depression force of the brake pedal is weakened, and in particular, there may be a situation in which the vehicle moves forward at a low speed due to the creep phenomenon of the automatic vehicle, and abnormally approaches the stopped vehicle ahead. However, since the brake switch is kept on because the foot is put on the brake pedal, the alarm output is stopped even in the case of operating the inter-vehicle distance alarm device, and the driver neglected the forward gaze. There is a risk that the driver may not notice the approaching distance between vehicles.

[0008] Such a situation may also occur in a manual transmission vehicle as well as in an automatic vehicle when the position where the vehicle stops is on a downhill.

The present invention has been made in view of such a conventional problem, and in addition to the conventional inter-vehicle distance alarm function, an alarm judgment function particularly in an extremely low speed region of a vehicle creep phenomenon is newly set. However, at the time of outputting the inter-vehicle distance warning in the extremely low speed range, the inter-vehicle distance warning is further stopped even if the brake switch is turned on, thereby further enhancing the support function for rear-end collision prevention. It is intended to provide a device.

[0010]

According to a first aspect of the present invention, there is provided an inter-vehicle distance alarm device for detecting an inter-vehicle distance with a preceding vehicle, and an inter-vehicle distance between the preceding vehicle detected by the inter-vehicle distance detecting device. First alarm determining means for determining whether or not the distance is equal to or less than a predetermined warning distance corresponding to the speed of the own vehicle and the relative speed with respect to the preceding vehicle; and changing the own vehicle speed from a running state to a stopped state. A second warning determining means for determining whether or not the speed is below a predetermined low speed warning distance corresponding to the speed of the own vehicle and the inter-vehicle distance to the vehicle ahead at a predetermined vehicle speed or less after the vehicle speed has been detected. Alarm output means for outputting an inter-vehicle distance alarm, brake detection means for detecting that the brake operation of the own vehicle has been performed, and the first alarm determination means determines that the alarm condition is satisfied. And when the brake detecting means does not detect a braking operation, the warning output means outputs an inter-vehicle distance warning, and the second warning determining means determines that the low-speed warning condition is satisfied. Alarm output control means for causing the alarm output control means to output an inter-vehicle distance alarm at the time of occurrence.

[0011] In the inter-vehicle distance warning device according to the first aspect of the present invention,
The first alarm determining means determines whether or not the inter-vehicle distance to the preceding vehicle detected by the inter-vehicle distance detecting means is equal to or less than a predetermined warning distance corresponding to the speed of the own vehicle and the relative speed to the preceding vehicle. Judgment, and after it is detected that the own vehicle speed has changed from the running state to the stopped state, at a predetermined low vehicle speed or less, a low speed predetermined in accordance with the speed of the own vehicle and the inter-vehicle distance to the preceding vehicle. Whether the distance is equal to or less than the warning distance is determined by the second warning determining means. Then, the alarm output control means causes the alarm output means to output an inter-vehicle distance alarm when the first alarm determination means determines that the alarm condition is satisfied and the brake detection means has not detected the brake operation; When the second warning determining means determines that the low-speed warning condition is satisfied, control is performed to output the following distance warning to the warning output means even if the brake operation is detected.

Accordingly, when the vehicle is stopped following the preceding vehicle at the intersection or when extremely low-speed driving is repeated intermittently on a congested road, even if the brake is depressed, the vehicle approaches the preceding vehicle below the low-speed warning distance. If it does, it will output an inter-vehicle distance warning,
Avoid situations where the driver's carelessness causes the brake pedal force to loosen and approach the vehicle in front abnormally.

According to a second aspect of the present invention, there is provided the inter-vehicle distance warning device according to the first aspect, further comprising an idle speed detecting means for detecting an idle speed, and an idle speed detected by the idle speed detecting means. Idle speed determining means for comparing with an idle speed setting value, wherein the second alarm determining means determines that the idle speed determining means is equal to or higher than the normal idle speed setting value. The warning output is determined using a second low-speed warning distance in which a longer distance than a normal low-speed warning distance for an idle rotation speed equal to or less than the set value is set.

[0014] According to a second aspect of the present invention, there is provided an inter-vehicle distance warning device.
The idling speed is monitored, and particularly when the idling speed increases and the creep force becomes larger than usual during stop or extremely low-speed operation, the second low-speed warning distance is set to be larger than usual. By judging the inter-vehicle distance alarm output based on the low-speed alarm distance, it is possible to reliably maintain a safe inter-vehicle distance that avoids a rear-end collision with a preceding vehicle.

[0015]

According to the first aspect of the present invention, when the vehicle is stopped following the preceding vehicle at an intersection or when extremely low-speed driving is repeated intermittently on a congested road, even when the brake is depressed, the vehicle is driven at a low speed. If the vehicle approaches the vehicle ahead of the warning distance or less, an inter-vehicle distance warning is output, so that it is possible to avoid a situation in which the driver's carelessness causes the brake pedal force to loosen and the vehicle approaching the vehicle in front of the vehicle abnormally. improves.

According to the second aspect of the present invention, the idling speed is monitored, and even when the idling speed increases and the creep force becomes larger than usual during stop or extremely low speed operation, By judging the inter-vehicle distance warning output based on the second low-speed warning distance larger than usual as the low-speed warning distance, it is possible to reliably maintain a safe inter-vehicle distance that avoids a rear-end collision with a preceding vehicle.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. An inter-vehicle distance warning device according to the first embodiment includes an inter-vehicle distance detection device 1 such as a laser radar device similar to a conventional example, and a vehicle. An alarm processing device 20 which is a feature of the embodiment, a display device 3 for displaying an inter-vehicle distance warning similar to the conventional example, and an alarm buzzer 4 for outputting an inter-vehicle distance alarm sound;
The vehicle includes a brake switch 5 for outputting a brake on / off signal to an alarm processing device 20 and a vehicle speed sensor 6 for detecting the speed of the host vehicle.

The alarm processing device 20 calculates the own vehicle speed by inputting the vehicle speed signal output from the vehicle speed sensor 6 for detecting the own vehicle speed, similarly to the alarm judging section 2a of the conventional example. The relative speed with the preceding vehicle is calculated from the temporal change of the output inter-vehicle distance, the warning distance based on the preset own vehicle speed and the relative speed is compared with the actual inter-vehicle distance at that time, and the inter-vehicle distance alarm is generated. A normal alarm judging unit 20a for judging whether or not to output, a low speed alarm judging unit 20b for judging whether or not an alarm condition is set in an extremely low speed running region such as a creep phenomenon; A vehicle speed determination unit 20c that receives a vehicle speed signal from the vehicle speed sensor 6 and determines a vehicle speed change state in order to switch which of the determination units 20b performs the alarm determination;
In response to an alarm output signal from the normal alarm judgment unit 20a or the low speed alarm judgment unit 20b, an alarm output that controls whether to output or stop an alarm signal to the display device 3 and the alarm buzzer 4 according to the signal of the brake switch 5 It is composed of a control unit 20d.

The alarm output characteristics referred to by the normal alarm judging section 20a are those shown in FIG. 9 similarly to the conventional example. Then, the low-speed alarm determining unit 20b refers to the low-speed alarm characteristic shown in FIG. It is assumed that the vehicle travels at a low speed of 10 km / h or less and is applied when the relative speed with respect to the preceding vehicle is not zero. In such a low-speed running range, after the brake operation, 3
Assuming that a complete stop is possible at about m or less, the characteristics are set as shown in the figure by considering about 1 second as the reaction time from when the driver confirms the alarm and starts the brake operation. For example, if the vehicle speed is 6-7 km / h
Then, 5 m is set as the low-speed warning distance.

Next, the operation of the inter-vehicle distance warning device according to the first embodiment having the above configuration will be described. As shown in the flowchart of FIG. 2, when the present system starts (step S200), first, the vehicle speed determination unit 20c measures the own vehicle speed based on a signal from the vehicle speed sensor 6 (step S2).
01), it is determined whether or not the vehicle speed at this time has completely stopped from running, that is, whether or not the vehicle speed has changed to zero (step S202).

When the vehicle speed has changed to zero and the vehicle has not been completely stopped, the routine branches to NO and the normal alarm determination section 20a
Then, the inter-vehicle distance is measured based on the inter-vehicle distance data of the inter-vehicle distance detection device 1 (step S203), and the relative speed is calculated based on the inter-vehicle distance change amount per unit time with the previously acquired inter-vehicle distance (step S203). Step S204). Then, using the inter-vehicle distance information, the own vehicle speed information, and the relative speed information, it is determined whether or not the current traveling condition satisfies the inter-vehicle distance alarm condition by referring to the vehicle speed / relative speed-warning distance characteristic (step S205). ).

Here, if the alarm condition is not satisfied, the safe inter-vehicle distance is maintained, and the process returns to the vehicle speed measurement without outputting an alarm (step S201). On the other hand, when the current driving condition satisfies the alarm condition, the normal
Outputs an alarm output command to the alarm output control unit 20d. The alarm output control unit 20d considers that the driver has operated the brake in order to increase the inter-vehicle distance if the brake switch 5 is turned on after seeing the input of the brake switch 5. Output stop control is performed, and if an alarm has been output to the display device 3 and the alarm buzzer 4 so far, the alarm is stopped. If a new alarm output command is issued, the alarm output is not performed and the process returns to the vehicle speed measurement. (Steps S206, S207).

The warning output control unit 20d receives a warning output command from the normal warning determination unit 20a and outputs a warning to the display device 3 and the warning buzzer 4 if it does not receive an ON signal from the brake switch 5, and displays an inter-vehicle distance warning display. The driver is notified by an inter-vehicle distance warning sound (steps S206 and S20).
8). Then, the normal speed warning judgment mode is repeated (step S201).

On the other hand, as a result of the vehicle speed measurement in step S201, when the vehicle speed becomes zero and the vehicle stops once,
In step S202, the flow branches to YES to enter a low-speed warning determination mode. In the low-speed alarm determination mode, the low-speed alarm determination unit 20b temporarily stops the alarm output regardless of whether the brake switch 5 is on or off (step S209).
Next, the vehicle speed is measured (step S210), and it is confirmed whether the vehicle speed is in a low speed region, that is, 10 km / h. The process returns to the normal speed determination mode (steps S211, S201).

However, after complete stoppage, 10k
When the low-speed traveling of m / h or less is continued (when branching to YES in step S211), the low-speed warning determination unit 20b measures the following distance (step S21).
2) The relative speed is calculated using the previous inter-vehicle distance data and the new inter-vehicle distance data (step S213).

Here, it is determined whether or not the alarm condition is satisfied by referring to the low-speed alarm characteristic shown in FIG. 3 (step S214). If the alarm condition is not satisfied, the safe inter-vehicle distance is maintained at a low speed. It is assumed that the vehicle is traveling while the vehicle is running, and the low speed warning determination mode is continuously repeated (steps S214 and S210).

On the other hand, if the low-speed alarm condition is satisfied, the low-speed alarm determination unit 20b outputs an alarm output command, and in response to this, the alarm output control unit 20d sets the brake switch 5
Irrespective of ON / OFF of the vehicle, an alarm output is given to the display device 3 and the alarm buzzer 4 to output an inter-vehicle distance alarm (steps S214 and S215). Then, the low speed alarm determination mode is repeated (step S210).

The operation shown in the timing chart of FIG. 4 can be realized in the following distance alarm apparatus of the first embodiment. It is assumed that the host vehicle is initially traveling at a constant speed of about 70 km / h. Now, there is a stopped vehicle ahead, and the inter-vehicle distance gradually decreases, so that the vehicle enters the normal alarm area at timing t1 and outputs an inter-vehicle distance alarm. When the inter-vehicle distance alarm is sounded, the driver performs the brake operation at timing t2, starts deceleration, and stops at timing t3 with the inter-vehicle distance of 7 m between the host vehicle and the preceding vehicle.

Thereafter, at time t4, if the vehicle starts moving at a speed of about 8 km / h with the brake switch being on while the brake switch is on, the inter-vehicle distance with the preceding vehicle is further reduced. It is determined that the alarm distance has fallen below the alarm distance 5 m of the low-speed alarm characteristic, and an alarm is output again here. When the driver hears the inter-vehicle distance warning and depresses the brake pedal more strongly, the vehicle stops completely at timing t6, and a rear-end collision is avoided. Thereafter, the preceding vehicle starts at timing t7, and the own vehicle also starts at timing t8.

As described above, in the first embodiment of the present invention, the inter-vehicle distance alarm is determined to be output in the normal speed range, and the inter-vehicle distance alarm is output if the brake switch remains off, and the brake switch is turned on. When the vehicle stops, the inter-vehicle distance warning is stopped. However, if the inter-vehicle distance becomes shorter than the low-speed warning distance after the vehicle has stopped once and the vehicle is traveling at low speed, the inter-vehicle distance is always constant regardless of the on / off state of the brake switch. By outputting an alarm, especially when the vehicle is stopped following the preceding vehicle at an intersection or when extremely low speed driving is repeated intermittently on congested roads, the driver's carelessness causes the brake pedal force to loosen and the preceding vehicle is abnormal. Can be avoided.

Next, a second embodiment of the present invention will be described with reference to FIGS.
A description will be given based on FIG. The features of the second embodiment are as follows.
In addition to the configuration of the first embodiment shown in FIG.
Engine speed sensor 7 that senses engine speed
, The idle speed is measured, the normal speed or the high speed is determined, and the result is given to the low speed warning determining unit 20b.
b, when the idle rotation determining unit 20e determines that the rotation speed is the normal rotation speed, the warning determination is performed by referring to the normal characteristic line N1 in the low speed warning distance characteristic of FIG. The point is that when it is determined that the value is a number, an alarm determination is made with reference to the high-speed characteristic line N2.

Normally, the idling speed is set at 1000 rpm or less, but especially at warm-up operation, 1000 rpm.
The rotation speed may be increased to over pm. Therefore, especially when driving on a general road without sufficient warming up in winter, the engine control system may automatically increase the idling speed to 1000 rpm or more. Since it generates a creep force larger than the creep force due to the number of revolutions,
If the driver does not depress the brake pedal with a greater force than usual during the stop, it may advance naturally, and if the driver has stepped on the brake to stop it,
The stopping distance becomes longer than in the case of normal idle rotation.

Therefore, in the second embodiment, a plurality of low-speed warning distance characteristics N1,
By preparing N2 and changing the alarm distance characteristic to be used according to the idle speed, it is possible to more reliably assist in preventing rear-end collision regardless of whether the idle speed is high or low.

Next, the operation of the inter-vehicle distance warning device according to the second embodiment will be described with reference to the flowchart of FIG. The flowchart shown in FIG. 6 corresponds to steps S209-S in the low-speed warning mode in the flowchart shown in FIG.
215 is to be replaced.
Therefore, step S in the flowchart of FIG.
At 201, the own vehicle speed is measured, and when it is not zero, the normal alarm determination unit 20a and the alarm output control unit 20d
Thus, steps S203 to S208, which are the normal speed warning mode, are executed as in the first embodiment.

However, once the vehicle speed becomes zero, the mode shifts to the low-speed warning mode, and the flow proceeds to step S in FIG.
The processing after 209 is executed. Here, once the own vehicle is completely stopped, the alarm is stopped (step S209), and the own vehicle speed is measured (step S209).
210). If the vehicle speed is equal to or higher than 10 km / h, the process exits from the low speed warning mode to shift to the normal speed inter-vehicle distance warning mode (steps S211 and S201).

If the vehicle speed is lower than 10 km / h and the vehicle is traveling at a low speed, the following distance is measured (step S21).
2) calculate the relative speed with respect to the preceding vehicle (step S)
213) Further, the determination result of the idle rotation determination unit 20e is obtained, and during high-speed idling (idle rotation speed> 100
0 rpm), the creep force is large, so the alarm distance characteristic line N2 side is used (steps S216, S216).
217), it is determined whether or not to output an inter-vehicle distance alarm by using an alarm distance longer than the normal idle speed (step S214). If the inter-vehicle distance is shorter than the alarm distance during the high-speed idling, the inter-vehicle distance alarm output is output to the display device 3 and the alarm buzzer 4 through the alarm output control unit 20d to output the inter-vehicle distance alarm (step S).
215). On the other hand, when the idling speed is smaller than 1000 rpm, it is compared with the actual inter-vehicle distance using the low-speed alarm distance characteristic line N1 similar to that of the first embodiment, and it is determined whether the output of the inter-vehicle distance alarm is necessary. Determine (Step S21)
6, S214, S215).

As described above, in the headway distance warning device according to the second embodiment, for example, referring to the characteristic lines N1 and N2 in FIG. 7, when the idling speed is smaller than 1000 rpm, the vehicle speed is 6 to If the inter-vehicle distance becomes about 5 m or less at 7 km / h, an inter-vehicle distance warning is output, but if the idling speed exceeds 1000 rpm, the same vehicle speed 6 to
At 7 km / h, an inter-vehicle distance warning is issued when the inter-vehicle distance becomes about 6 m or less, so that rear-end collision can be reliably prevented even when the idling speed is high and the creep force is strong.

The numerical value of 10 km / h or less as the low-speed region exemplified in the above-described embodiment and the low-speed alarm characteristic are not limited, and can be changed according to the current situation. In addition, the idling speed is set to be higher than 1000 rpm, but this is not particularly limited, and it is also possible to set a larger value or a smaller value.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram according to a first embodiment of the present invention.

FIG. 2 is a flowchart of an inter-vehicle distance warning process according to the embodiment.

FIG. 3 is a graph showing low-speed alarm characteristics used in the embodiment.

FIG. 4 is a timing chart showing an example of an inter-vehicle distance warning output operation of the embodiment.

FIG. 5 is a circuit block diagram according to a second embodiment of the present invention.

FIG. 6 is a flowchart of an inter-vehicle distance warning process according to the embodiment.

FIG. 7 is a graph showing low-speed alarm characteristics used in the embodiment.

FIG. 8 is a circuit block diagram of a conventional example.

FIG. 9 is a graph showing general inter-vehicle distance warning characteristics.

FIG. 10 is a flowchart of a conventional inter-vehicle distance warning process.

[Explanation of symbols]

 Reference Signs List 1 inter-vehicle distance detection device 20 alarm processing device 20a normal alarm judgment unit 20b low speed alarm judgment unit 20c vehicle speed judgment unit 20d alarm output control unit 20e idle rotation judgment unit 3 display device 4 alarm buzzer 5 brake switch 6 vehicle speed sensor 7 engine rotation sensor

Claims (2)

[Claims] 1. An inter-vehicle distance detecting means for detecting an inter-vehicle distance to a preceding vehicle, and an inter-vehicle distance to the preceding vehicle detected by the inter-vehicle distance detecting means corresponds to a speed of the own vehicle and a relative speed to the preceding vehicle. First warning determining means for determining whether the vehicle speed is equal to or less than a predetermined warning distance, and detecting that the vehicle speed has changed from a running state to a stopped state. Second alarm determining means for determining whether or not the distance is equal to or less than a predetermined low-speed warning distance corresponding to the speed and the inter-vehicle distance to a vehicle in front; an alarm output means for outputting an inter-vehicle distance alarm; Brake detection means for detecting that the brake operation has been performed; and the first alarm determination means determines that the alarm condition is satisfied, and the brake detection means detects the brake operation. When not, the warning output means outputs an inter-vehicle distance alarm, and when the second alarm determination means determines that the low-speed alarm condition is satisfied, an inter-vehicle distance alarm is output to the alarm output means. An inter-vehicle distance alarm device comprising: an alarm output control unit for causing the vehicle to output an alarm. 2. The inter-vehicle distance warning device according to claim 1, further comprising: an idle speed detecting means for detecting an idle speed, and a normal idle speed detected by the idle speed detecting means. An idle speed determination unit that compares the set value with the set value. The second alarm determination unit determines that the idle speed determination unit determines that the idle speed is equal to or greater than the normal idle speed set value. An inter-vehicle distance alarm device that determines an alarm output using a second low-speed alarm distance in which a longer distance is set than a normal low-speed alarm distance for an idle rotation speed equal to or less than a value.