JPH07172208A - Speed controller for automobile - Google Patents

Abstract

PURPOSE:To avoid the contact of a preceding car or the following car with a driver's own car by proper control when a following car approaches the driver's own car during the following control of the driver's own car against the preceding car. CONSTITUTION:A first radar unit 7 for detecting a distance between one's own car and the preceding car, a second radar unit 8 for detecting a distance between the driver's own car and the following car and a control unit 4 for control the vehicle speed so that a distance between the driver's own car and the preceding car is kept to a predetermined desired distance between both car approaches one's own car by a distance less than the predetermined one is set longer than that when the following car is spaced from one's own car by the predetermined distance. When the preceding car is decelerated while the following car approaches one's own car by a distance less than the predetermined distance and the following car is spaced from the driver's own car by the predetermined distance, the following car is decelerated gently compared with the deceleration of the preceding car.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle speed control device for a vehicle which controls a vehicle speed so as to keep a vehicle-to-vehicle distance constant between an own vehicle and a preceding vehicle, and more particularly to control when a following vehicle approaches.

[0002]

2. Description of the Related Art Conventionally, in an auto cruise function of a vehicle, a vehicle speed type feedback control for automatically maintaining the vehicle speed of the vehicle at a preset target vehicle speed and a distance between the preceding vehicle and a preceding vehicle are preset. There is a vehicle-type feedback control that maintains a fixed distance. The vehicle speed control device that performs the latter control basically sets an inter-vehicle distance detection means such as a radar device that detects an inter-vehicle distance between the own vehicle and a preceding vehicle, and a target inter-vehicle distance based on the vehicle speed of the preceding vehicle. Target vehicle distance setting means, and control means for controlling the vehicle speed so that the actual vehicle distance detected by the vehicle distance detecting means becomes equal to the target vehicle distance.

Further, in Japanese Patent Laid-Open No. 60-244629, in addition to a front inter-vehicle distance detecting means for detecting the inter-vehicle distance between the own vehicle and the preceding vehicle, a rear portion for detecting the inter-vehicle distance between the own vehicle and the following vehicle. Equipped with inter-vehicle distance detection means, when a following vehicle approaches, it accelerates when a safe inter-vehicle distance is secured for the preceding vehicle and secures a safe inter-vehicle distance for the following vehicle, It is disclosed that an alarm is issued when it is not secured.

[0004]

However, in the case of the above-mentioned publication, when the following vehicle approaches the own vehicle while performing the inter-vehicle feedback control with the safe inter-vehicle distance as the target inter-vehicle distance, a warning is simply issued. It is only emitted and is not sufficient as a measure to avoid contact with the following vehicle. Further, when the own vehicle is brought closer to the preceding vehicle than the safe inter-vehicle distance, the own vehicle may come into contact with the preceding vehicle when the preceding vehicle suddenly decelerates.

The present invention has been made in view of the above points, and an object of the present invention is to provide a following vehicle with respect to the own vehicle while performing feedback control while maintaining a predetermined inter-vehicle distance with respect to the preceding vehicle. An object of the present invention is to provide a vehicle speed control device for an automobile, which can perform appropriate control when approaching and can avoid contact with a preceding vehicle and a following vehicle.

[0006]

In order to achieve the above object, the invention according to claim 1 is, as a vehicle speed control device for an automobile, a first vehicle distance detecting device for detecting an inter-vehicle distance between a host vehicle and a preceding vehicle in front of the vehicle. Vehicle distance detection means, second vehicle distance detection means for detecting a vehicle distance between the own vehicle and a succeeding vehicle behind the vehicle, and the vehicle distance between the vehicle and the preceding vehicle is kept at a predetermined target vehicle distance. Control means for controlling the vehicle speed, and target vehicle distance setting means for setting the target vehicle distance. And, in the target inter-vehicle distance setting means, the target inter-vehicle distance when the following vehicle is closer to the own vehicle than the predetermined distance is set to be longer than that when the following vehicle is farther than the predetermined distance. is there.

The invention according to claim 2 is dependent on the invention according to claim 1, wherein in the control means, when the following vehicle is decelerated while the following vehicle is closer than the own vehicle by a predetermined distance, The vehicle speed is controlled so that when the vehicle is away from the predetermined distance, the vehicle decelerates more slowly than when the preceding vehicle decelerates.

The invention according to claim 3 is, as a vehicle speed control device for an automobile, first inter-vehicle distance detecting means for detecting an inter-vehicle distance between the own vehicle and a preceding vehicle existing in front of the own vehicle, and the own vehicle and thereafter. Second inter-vehicle distance detecting means for detecting an inter-vehicle distance to a succeeding vehicle existing on one side, control means for controlling a vehicle speed so as to keep the inter-vehicle distance between the own vehicle and the preceding vehicle at a predetermined target inter-vehicle distance, and the following vehicle When the vehicle approaches the own vehicle by a predetermined distance or more, the control means for stopping the control of the control means is provided.

The invention according to claim 4 is dependent on the invention according to claim 3, and in addition to the constituent elements thereof, when the following vehicle comes closer to the own vehicle than a predetermined distance, Almost at the same time as the control is stopped, a configuration is provided in which a warning unit is provided that issues a warning to the driver to increase the inter-vehicle distance to the preceding vehicle.

[0010]

With the above construction, in the invention according to claim 1,
Under the vehicle speed control of the control means, when the following vehicle comes closer to the preceding vehicle than the predetermined distance while following the preceding vehicle while keeping a predetermined vehicle distance (target vehicle distance), In the target inter-vehicle distance setting means that is detected by the inter-vehicle distance detecting means 2 and receives the signal of the detecting means, the target inter-vehicle distance is set to be longer than that when the following vehicle is farther than the predetermined distance. The vehicle is decelerated, and the inter-vehicle distance to the preceding vehicle is changed to be long so as to be equal to the target inter-vehicle distance. Therefore, even when the preceding vehicle suddenly decelerates, the own vehicle can be gently decelerated so as to avoid contact with the following vehicle, and contact with the preceding vehicle and the following vehicle can be avoided.

According to the second aspect of the present invention, when the following vehicle is decelerated while the following vehicle is closer than the own vehicle by a predetermined distance, the following vehicle is separated from the predetermined distance by the control means. Since the vehicle speed is controlled so as to decelerate gently when the preceding vehicle decelerates when the vehicle is present, contact with the preceding vehicle and the following vehicle can be reliably avoided.

According to the third aspect of the present invention, the following vehicle has a predetermined distance with respect to the own vehicle when the vehicle is following the preceding vehicle while keeping a predetermined distance between the preceding vehicles (target distance) under the vehicle speed control of the control means. When the distance from the vehicle is approaching, the second inter-vehicle distance detecting means detects that, and the control stopping means that receives the signal of the detecting means stops the control of the control means.
For this reason, the driver himself / herself can decelerate to increase the inter-vehicle distance with the preceding vehicle, and even when the preceding vehicle suddenly decelerates, the own vehicle avoids contact with the following vehicle. As described above, it is possible to gently decelerate and avoid contact with the preceding vehicle and the following vehicle.

Here, in the invention according to claim 4, when the following vehicle comes closer to the own vehicle than a predetermined distance, the alarm means is activated to drive at substantially the same time as the control of the control means is stopped by the control stop means. Since the warning is issued to the driver to increase the inter-vehicle distance to the preceding vehicle, the driver himself surely increases the inter-vehicle distance to the preceding vehicle.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure of a vehicle speed control system for an automobile according to an embodiment of the present invention. 1 is a throttle control system for automatically adjusting the opening of a throttle valve (not shown) of an engine intake system. Is a control device for an electronically controlled automatic transmission (EAT), and 3 is a brake control device for automatically adjusting the braking force applied to each wheel.
Each of the actuators 3 has an actuator (not shown), and each actuator is controlled by the control unit 4. That is, the control unit 4
Is a control means for controlling the vehicle speed, which outputs a target throttle opening signal to the actuator of the throttle control device 1 for control, and outputs a target brake amount signal to the actuator of the brake control device 3. Take control. The control unit 4 receives a shift position signal from a sensor (not shown) for detecting the shift position of the EAT control device 2 and outputs a shift control signal to an actuator of the EAT control device 2 to perform control. .

Reference numeral 6 denotes an information display device provided on an instrument panel or the like in the vehicle compartment. The information display device 6 is turned on upon receiving an alarm signal from the control unit 4 although not shown. An alarm lamp and a display unit for displaying a screen upon receiving a self-diagnosis signal from the control unit 4 are provided. Reference numeral 7 is a radar device as a first inter-vehicle distance detecting means for detecting an inter-vehicle distance (hereinafter referred to as a front inter-vehicle distance) between the own vehicle and a preceding vehicle existing in front of the own vehicle, and 8 is a succeeding vehicle present behind the own vehicle and behind the vehicle. Radar devices as second inter-vehicle distance detecting means for detecting inter-vehicle distance (hereinafter, referred to as rear inter-vehicle distance), 9 and 10 are third and third radars for detecting automobiles on the left and right sides of the own vehicle, respectively. 4 radar devices, and these radar devices 7 to 10
Both basically emit radar waves in front of the own vehicle and receive reflected waves that are reflected by the preceding vehicle, and depending on the time difference between the reception time and the transmission time, Is configured to measure the distance to and from the car. However, the third and fourth radar devices 9 and 1
Since 0 is sufficient to detect the presence or absence of a side vehicle, its distance detection accuracy is inferior to that of the first and second radar devices 7 and 8. Inter-vehicle distance signals, which are detection signals of the radar devices 7 to 10, are input to the control unit 4.

Further, 11 is a throttle opening sensor that detects the opening of the throttle valve, 12 is a vehicle speed sensor that detects the vehicle speed, and 13 is a steering wheel steering angle (hereinafter, simply referred to as steering angle).
A yaw rate sensor for detecting a yaw rate generated in the own vehicle, a lateral G sensor for detecting a lateral acceleration generated in the own vehicle, a brake switch 16 that is turned on when the brake pedal is depressed, Reference numeral 17 is a clutch switch which is turned on according to the operating state of the clutch, 18 is a main switch for starting the auto cruise, and 19 is a set switch for the driver to set a target vehicle speed. These sensors and switches 11-19
All the detection signals of are input to the control unit 4. Incidentally, detection signals of other sensors and switches (not shown) such as an engine speed sensor are also input to the control unit 4.

The control by the control unit 4 is performed according to the flow charts shown in FIGS. Hereinafter, these figures will be sequentially described.

FIG. 2 shows a main routine of control by the control unit 4. In FIG. 2, after starting, it is first determined in step S1 whether or not the driver has turned on the main switch 18 to start the auto cruise. If the determination is NO, step S7
In step S8, the set flag Fset is cleared, and in step S8, the automatic cruise is deactivated, and then the process returns.

On the other hand, when the determination in step S1 is YES, it is determined in step S2 whether or not the set switch 19 is turned on. When this judgment is NO, it is judged in step S6 whether or not the set flag Fset is set. Since the set flag Fset is not set unless the set switch 19 is turned on (step S3), when the set switch 19 is turned off, the process proceeds to step S8 and the automatic cruise is deactivated. Therefore, in the case of the present embodiment, in order to actually start the auto cruise, not only the driver pushes the main switch 18 to turn it on, but also the set switch 1
It is also necessary to press 9 once to turn it on.

When the determination in step S2 is YES,
That is, when the set switch 19 is pressed and turned on, the set flag Fset is set in step S3,
After setting the vehicle speed V0 at the time when the set switch 19 is pressed in step S4 to the target vehicle speed TGV, the automatic cruise is activated in step S5 and the process returns. Even if the set switch 19 is turned on and then turned off again, the set flag F is set unless the main switch is turned off.
Since set is still set, the process proceeds to step S1 → step S2 → step S6 → step S5, and the automatic cruise operation is performed.

FIG. 3 shows a subroutine of the automatic cruise operation (step S5). In FIG. 3, first, in step S11, the front inter-vehicle distance L detected by the first radar device 7, the own vehicle speed V0 detected by the vehicle speed sensor 12, the relative speed V1 between the own vehicle and the preceding vehicle, and the target vehicle speed TGV (FIG. 2). Step S4) is read. The relative speed V1 between the own vehicle and the preceding vehicle is obtained by continuously measuring the front inter-vehicle distance L and calculating the amount of change per unit time.

Then, in step S12, the deceleration start inter-vehicle distance L0, the deceleration release inter-vehicle distance L1 and the warning inter-vehicle distance L2 are calculated using the map shown in FIG. In the map shown in FIG. 6, the three types of inter-vehicle distances L0, L1, and L2 all increase in a quadratic curve as the vehicle speed of the preceding vehicle (the preceding vehicle speed) increases, and the magnitude relationship between them is L0>L1> L2
Is. Next, in step S12, the above three types of inter-vehicle distances L
Correct 0, L1 and L2. This correction will be described later. Target inter-vehicle distance setting means 2 for setting a target inter-vehicle distance for follow-up control (inter-vehicle distance control) through steps S12 and S13.
1 is configured.

After setting the target inter-vehicle distance in this way, in step S14, it is determined whether or not the relative speed V1 between the own vehicle and the preceding vehicle is zero or more, that is, whether the own vehicle is approaching the preceding vehicle or separated. Determine whether you are doing. When the determination is YES, it is determined in step S15 whether the front inter-vehicle distance L is shorter than the deceleration start inter-vehicle distance L0. When the determination is YES, the vehicle is decelerated in step S16 and follows the preceding vehicle. Then, in step S18, it is determined whether or not the front inter-vehicle distance L is shorter than the warning inter-vehicle distance L2. If the front inter-vehicle distance L is shorter than the warning inter-vehicle distance L2, an alarm signal is output to the information display device 6 to issue an alarm and return. When it is long, it returns as it is. When the determination in step S15 is NO, that is, when the front inter-vehicle distance L is longer than the deceleration start inter-vehicle distance L0, normal vehicle speed control is performed in step S17, and the process returns. The normal vehicle speed control is for controlling the own vehicle speed to the target vehicle speed TGV.

On the other hand, when the determination in step S14 is NO, it is determined in step S20 whether the front inter-vehicle distance L is shorter than the deceleration release inter-vehicle distance L1. If the determination is YES, step S21 While the follow-up deceleration control is continued and the process returns, if the determination is NO, it is further determined in step S22 whether or not the current own vehicle speed V0 is smaller than the target vehicle speed TGV of the vehicle speed control. This judgment is YE
When S, in step S23, the follow-up acceleration control is performed to follow the preceding vehicle while increasing the speed, and while returning, the determination is N
When it is O, the normal vehicle speed control is returned to in step S24,
To return.

FIG. 4 shows the various inter-vehicle distances L0, L1, L2.
The subroutine of the correction (step S13) is shown. In FIG. 4, first, in step S31, various inter-vehicle distances, that is, deceleration start inter-vehicle distance L0, deceleration release inter-vehicle distance L1 and warning inter-vehicle distance L2 are recognized, and the front inter-vehicle distance L detected by the first radar device 7 in step S32, Second radar device 8
And the information on the presence / absence of a side vehicle from the third and fourth radar devices 9 and 10 is read.

Subsequently, in step S33, a correction value α1 corresponding to the approaching degree of the following vehicle is set using a map. The correction value α1 is set so that it gradually increases as the rear inter-vehicle distance Lb becomes shorter than the predetermined distance k, and the maximum value becomes a.

After setting the above correction value α1, step S
In step S35, it is determined whether or not there is a side vehicle. When the side vehicle is present, the correction value α2 is set to a positive value b in step S35.
Set 0 to the correction value α2 at 36. Here, the meaning of the correction value α2 is to eliminate this when another vehicle runs alongside the host vehicle in the lane adjacent to the traveling lane of the host vehicle during follow-up travel. Therefore, the value of b is about the same as the entire length of the automobile.

Subsequently, in step S37, the front inter-vehicle distance L is continuously measured to determine whether or not the amount of change is large.
When the amount of change is large, it is determined that the preceding vehicle is in an unstable state by repeating acceleration and deceleration, and a positive value c is set to the correction value α3 in step S38 in order to increase the inter-vehicle distance in the following running. . On the other hand, when the amount of change is not large, the correction value α3 is set to 0 in step S39. As an element for determining the instability of the preceding vehicle, the amount of change in the left-right direction (vehicle width direction) of the preceding vehicle (so-called meandering amount) may be used in addition to the amount of change in the front inter-vehicle distance L.

After setting the correction values α1 to α3, the correction values α1 to α3 are added to the various vehicle-to-vehicle distances L0, L1, and L2 to make corrections in step S40. That is, the conversion of L0 ← L0 + (α1 + α2 + α3) L1 ← L1 + (α1 + α2 + α3) L2 ← L2 + (α1 + α2 + α3) is performed and the process is returned.

FIG. 5 shows the following deceleration (step S in FIG. 3).
16 and S21) and the follow-up acceleration (step S23) control subroutine. In FIG. 5, first, step S51.
After reading the actual inter-vehicle distance (front inter-vehicle distance) L, the target inter-vehicle distance (deceleration start inter-vehicle distance) L0 and the rear inter-vehicle distance Lb detected by the second radar device 8 in step S52, An inter-vehicle distance deviation .DELTA.L (= L-L0) between the actual inter-vehicle distance L and the target inter-vehicle distance L0 is calculated.

Then, in step S53, the target acceleration / deceleration G is set. The target acceleration / deceleration G is a linear function value of the inter-vehicle distance deviation ΔL, and the target acceleration / deceleration G is a positive value in a region where the inter-vehicle distance deviation ΔL is positive (when the actual inter-vehicle distance L is longer than the target inter-vehicle distance L0). That is, the acceleration becomes and the acceleration gradually increases as the inter-vehicle distance deviation ΔL increases,
Further, in a region where the vehicle-to-vehicle distance deviation ΔL is negative (when the actual vehicle-to-vehicle distance L is shorter than the target vehicle-to-vehicle distance L0), the target acceleration / deceleration G becomes a negative value, that is, deceleration, and the deceleration is increased as the vehicle-to-vehicle distance deviation ΔL increases. Will gradually increase. However, the target acceleration / deceleration G has a maximum value of 0.
It is limited to 4g (gravitational acceleration).

Then, in step S54, the target acceleration / deceleration G is corrected by accumulating a correction value α corresponding to the rear inter-vehicle distance Lb. The correction value α is 1 when the rear inter-vehicle distance Lb is longer than the predetermined distance k, and the rear inter-vehicle distance Lb is
Is set to be gradually smaller from 1 as the distance becomes shorter than the predetermined distance k. That is, the rear inter-vehicle distance Lb
When is short, the acceleration / deceleration (target acceleration / deceleration) G of the vehicle is reduced.

After that, the vehicle speed is feedback-controlled so that the corrected target acceleration / deceleration G is obtained, and the process returns.

By the follow-up control routine as described above,
Control means 22 is configured to control the vehicle speed so that the actual vehicle-to-vehicle distance L between the own vehicle and the preceding vehicle is maintained at the target vehicle-to-vehicle distance L0.
In the present embodiment, the control means 22 decelerates the preceding vehicle when the following vehicle is closer than the own vehicle by a predetermined distance or decelerates the preceding vehicle when the following vehicle is further than the predetermined distance. The vehicle speed is controlled so that the vehicle decelerates more slowly (with a small target deceleration G) than when the vehicle is operated.

Next, the operation and effect of the above-described embodiment will be described. When the following vehicle approaches the own vehicle while the following vehicle travels while keeping a predetermined distance from the preceding vehicle, The second inter-vehicle distance Lb between the host vehicle and the following vehicle is detected by the second radar device 8, and the rear inter-vehicle distance Lb is short in the target inter-vehicle distance setting means 21 in the control unit 4 which receives the detection signal of the radar device 8. A relatively large correction value α1 is set (step S33 in FIG. 4), and various target inter-vehicle distances including the deceleration start inter-vehicle distance L0 are corrected long (step S40). By this correction, the inter-vehicle distance between the own vehicle and the preceding vehicle is changed to be longer. Therefore, even when the preceding vehicle suddenly decelerates, the own vehicle can be gently decelerated so as to avoid contact with the following vehicle, and contact with the preceding vehicle and the following vehicle can be avoided.

Further, in the control of the following running, when the preceding vehicle decelerates and the inter-vehicle distance L with the own vehicle becomes shorter and decelerates, the target deceleration G is the following inter-vehicle distance L with the following vehicle.
The shorter b is, the smaller it is corrected (step S54 in FIG. 5).
Since the vehicle speed is controlled so that the vehicle gradually decelerates, it is possible to reliably avoid contact with the preceding vehicle and the following vehicle.

In the above embodiment, when the following vehicle approaches the subject vehicle while following the preceding vehicle, the vehicle speed is controlled so as to increase the inter-vehicle distance from the preceding vehicle. In such a case, the vehicle speed control may be stopped, and the driver may issue an alarm so that the inter-vehicle distance to the preceding vehicle is lengthened.

[0039]

As described above, according to the first aspect of the present invention, the following vehicle comes closer to the own vehicle than the predetermined distance while following the preceding vehicle while keeping the predetermined inter-vehicle distance. Sometimes, the distance between you and the preceding vehicle is changed, so
Even when the preceding vehicle suddenly decelerates, the vehicle can be gently decelerated to avoid contact with the preceding vehicle and the following vehicle, and safety can be improved.

In particular, according to the second aspect of the present invention, when the preceding vehicle decelerates when the following vehicle is closer to the vehicle than the predetermined distance, and when the following vehicle is farther than the predetermined distance. Since the vehicle speed is controlled so as to decelerate more slowly than when the preceding vehicle decelerates, it is possible to reliably avoid contact with the preceding vehicle and the following vehicle.

According to the third aspect of the present invention, when the following vehicle comes closer than the own vehicle by a predetermined distance while following the preceding vehicle while keeping a predetermined inter-vehicle distance, the follow control is stopped. As a result, the driver can decelerate to increase the distance between the preceding vehicle and the preceding vehicle.Also, even when the preceding vehicle suddenly decelerates, the driver gradually decelerates to the preceding vehicle and the following vehicle. Contact can be avoided and safety can be improved.

In particular, according to the invention as set forth in claim 4, when the following vehicle comes closer to the own vehicle than the predetermined distance, the driver is made to increase the distance between the preceding vehicle and the preceding vehicle substantially at the same time when the follow-up control is stopped. Since the warning is issued, the driver himself surely increases the inter-vehicle distance to the preceding vehicle, and it is possible to more surely avoid contact with the preceding vehicle and the following vehicle.

[Brief description of drawings]

FIG. 1 is a block diagram showing a vehicle speed control device for an automobile according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a main routine of vehicle speed control.

FIG. 3 is a flowchart showing an automatic cruise operation routine.

FIG. 4 is a flowchart showing a routine for correcting various inter-vehicle distances.

FIG. 5 is a flowchart showing a follow-up control routine.

FIG. 6 is a diagram showing a map used for setting a target inter-vehicle distance.

[Explanation of symbols]

 4 Control Unit 7 First Radar Device (First Inter-Vehicle Distance Detection Means) 8 Second Radar Device (Second Inter-Vehicle Distance Detection Means) 21 Target Inter-Vehicle Distance Setting Means 22 Control Means

Front page continuation (72) Inventor Satoru Ando 3-1, Shinchu, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Kazunori Okuda 3-3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture (72) ) Inventor Chizumi Izumi, 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Kenji Shimizu 3-1-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture (72) Inventor, Yoshi Sugamoto Akira 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (4)

[Claims] 1. A first inter-vehicle distance detecting means for detecting an inter-vehicle distance between an own vehicle and a preceding vehicle existing in front of the own vehicle, and a second inter-vehicle distance detecting means for detecting an inter-vehicle distance between an own vehicle and a following vehicle existing behind the own vehicle. The vehicle-interval distance detection means, the control means for controlling the vehicle speed so as to keep the vehicle-interval distance between the own vehicle and the preceding vehicle at a predetermined target inter-vehicle distance, and the target inter-vehicle distance setting means for setting the target inter-vehicle distance. The target inter-vehicle distance setting means is provided to set the target inter-vehicle distance when the following vehicle is closer to the host vehicle than a predetermined distance, longer than that when the following vehicle is farther than the predetermined distance. A vehicle speed control device for an automobile. 2. The control means, when the following vehicle decelerates when the following vehicle is closer than the own vehicle by a predetermined distance,
2. The vehicle speed control device for a vehicle according to claim 1, wherein the vehicle speed is controlled such that when the following vehicle is separated from a predetermined distance, the vehicle speed is gradually reduced compared to when the preceding vehicle is decelerated. 3. A first inter-vehicle distance detecting means for detecting an inter-vehicle distance between a host vehicle and a preceding vehicle existing in front of the host vehicle, and a second inter-vehicle distance detecting means for detecting an inter-vehicle distance between the host vehicle and a following vehicle behind the host vehicle. Inter-vehicle distance detecting means, a control means for controlling the vehicle speed so as to keep the inter-vehicle distance between the own vehicle and the preceding vehicle at a predetermined target inter-vehicle distance, and the control means when the following vehicle comes closer to the own vehicle than the predetermined distance. And a control stopping means for stopping the control of the vehicle speed control device for an automobile. 4. When the following vehicle comes closer to the own vehicle than a predetermined distance, an alarm urging the driver to increase the inter-vehicle distance from the preceding vehicle substantially at the same time as the control of the control means is stopped by the control stop means. 4. The vehicle speed control device for an automobile according to claim 3, further comprising an alarm means for issuing.