JP2000280782A - Vehicle travel control device - Google Patents

Abstract

(57) [Summary] [Problem] To greatly improve safety by enabling a driver to operate without misunderstanding and returning from traveling at a constant inter-vehicle distance to traveling at a constant speed with optimal acceleration according to road conditions. improves. A target vehicle speed setting unit sets a target vehicle speed.
A target inter-vehicle distance setting unit 44 sets a target inter-vehicle distance. The constant speed constant inter-vehicle distance traveling control section 48 selectively performs constant speed traveling while traveling at a target vehicle speed and constant inter-vehicle traveling while traveling at a target inter-vehicle distance, and performs constant speed constant inter-vehicle traveling. Here, if the target inter-vehicle distance is not set even if the target vehicle speed is set, the control determination unit 45
Canceling entering into the constant speed constant inter-vehicle distance running control. Further, the constant speed constant inter-vehicle distance traveling control unit 48 transitions at the return acceleration calculated by the return acceleration calculating unit 47 according to the radius of curvature of the curve and the road surface μ when transitioning from the constant inter-vehicle distance traveling to the constant speed traveling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle travel control device having a function of traveling at a constant vehicle speed and a function of traveling at a constant inter-vehicle distance from a preceding vehicle.

[0002]

2. Description of the Related Art Conventionally, in vehicles such as automobiles,
Particularly, in order to reduce the driver's driving operation while driving on a highway and to improve safety, a constant-speed traveling control device that automatically keeps the vehicle speed at a target vehicle speed set in advance by the driver and controls traveling is practically used.

[0003] In recent years, a target in which a driver sets in advance a distance between the vehicle and a preceding vehicle based on information on the preceding vehicle ahead of the traveling road obtained by a radio wave radar device, a laser radar device or an image system mounted on the vehicle. Various types of constant inter-vehicle traveling control devices (follow-up traveling devices) that control traveling while maintaining the inter-vehicle distance have been proposed and started to be put into practical use.

Recently, for example, Japanese Patent Application Laid-Open No. 9-2
As shown in Japanese Patent Application Publication No. 07610, when the preceding vehicle exists by combining the above-mentioned constant-speed traveling control device and the above-mentioned constant inter-vehicle traveling control device, the inter-vehicle distance with the preceding vehicle is maintained at the target inter-vehicle distance, and the constant When the vehicle travels a long distance and there is no preceding vehicle or when the preceding vehicle is far away, there is proposed a technology of a constant speed constant inter-vehicle distance traveling control in which the vehicle speed is automatically maintained at a target vehicle speed and the vehicle travels at a constant speed. .

[0005]

However, in the above prior art, in order to execute the function of the constant speed traveling control and the function of the constant inter-vehicle traveling control in combination, the switch of the constant speed traveling control and the traveling of the constant inter-vehicle distance are required. The control switch must be turned on. For this reason, for example, when the driver is running at a constant speed for a long time by turning on only the switch for the constant speed running control, the driver turns on the switch for the constant inter-vehicle distance running control.
If you forget to do that, if the distance between you and the preceding vehicle is equal to the target distance, you will assume that you will run a certain distance, and perform appropriate deceleration operation even if the distance between you and the preceding vehicle is short Therefore, there is a risk that sudden braking will be applied thereafter.

Further, in the above prior art, after the preceding vehicle exists and travels for a fixed distance, if the preceding vehicle is no longer present due to lane change or the like, the vehicle returns to constant speed traveling. At that time, the vehicle is approaching a curve, or If the road surface μ of the traveling road is significantly reduced, the return acceleration may be too large, and the vehicle may not be able to pass the curve stably or may spin.

[0007] In view of the above circumstances, the present invention enables the driver to operate without misunderstanding, and enables the vehicle to return from running at a constant inter-vehicle distance to running at a constant speed at an optimum acceleration according to road conditions, thereby improving safety. It is an object of the present invention to provide a travel control device for a vehicle that can be significantly improved.

[0008]

To achieve the above object, a first vehicle traveling control device according to the present invention comprises a target vehicle speed setting means for setting a target vehicle speed, and a target inter-vehicle distance to a preceding vehicle. A target inter-vehicle distance setting means for setting the vehicle speed and traveling at a constant speed while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and setting the inter-vehicle distance to the preceding vehicle by the target inter-vehicle distance setting means. In a travel control device for a vehicle including control means for selectively performing a constant inter-vehicle distance traveling while maintaining the target inter-vehicle distance and performing a constant speed constant inter-vehicle distance travel, the target inter-vehicle distance is set even if the target vehicle speed is set. When the distance is not set, a control judging means for prohibiting the constant speed constant inter-vehicle distance traveling control by the control means is provided.

That is, in the first vehicle travel control device, the target vehicle speed is set by the target vehicle speed setting means, and the target inter-vehicle distance to the preceding vehicle is set by the target inter-vehicle distance setting means. In the control means, a constant speed running while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and a constant speed running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means. Distance traveling is selectively performed to control traveling at a constant speed and a constant inter-vehicle distance. At this time, if the target speed is set by the control determining means but the target inter-vehicle distance is not set, the constant speed constant inter-vehicle distance traveling control of the control means is prohibited.

The second vehicle travel control device according to the present invention comprises a target vehicle speed setting means for setting a target vehicle speed and a target inter-vehicle distance setting means for setting a target inter-vehicle distance with a preceding vehicle. A constant speed running while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and a constant speed running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means. In a vehicle travel control device provided with a control means for selectively performing distance travel and controlling travel at a constant speed and a constant inter-vehicle distance, if the target vehicle speed is set but the target inter-vehicle distance is not set, the target A control determining means for setting the inter-vehicle distance to a preset maximum target inter-vehicle distance is provided.

That is, in the traveling control device for the second vehicle, the target vehicle speed is set by the target vehicle speed setting means, and the target inter-vehicle distance to the preceding vehicle is set by the target inter-vehicle distance setting means. In the control means, a constant speed running while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and a constant speed running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means. Distance traveling is selectively performed to control traveling at a constant speed and a constant inter-vehicle distance. At this time, if the target vehicle speed is set but the target inter-vehicle distance is not set by the control determination means, the target inter-vehicle distance is set to the preset maximum target inter-vehicle distance, and the constant speed constant inter-vehicle distance is set. Run control.

Further, the traveling control device for a third vehicle according to the present invention is the traveling control device for the first or second vehicle, wherein the acceleration of the vehicle is set to at least one of a curvature radius of a curve of a traveling road and a road surface frictional resistance. And an acceleration setting means for setting the acceleration when the control means shifts from the constant inter-vehicle distance traveling to the constant speed traveling to a value set by the acceleration setting means.

That is, in the traveling control device for a third vehicle, in the traveling control device for the first or second vehicle, the control means, when shifting from traveling at a constant inter-vehicle distance to traveling at a constant speed, reduces the acceleration of the vehicle. The acceleration setting means sets a value set according to at least one of the radius of curvature of the curve of the traveling road and the road surface frictional resistance.

A fourth vehicle traveling control device according to the present invention comprises a target vehicle speed setting means for setting a target vehicle speed and a target inter-vehicle distance setting means for setting a target inter-vehicle distance with a preceding vehicle. A constant speed running while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and a constant speed running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means. A travel control device for a vehicle, comprising a control means for selectively performing distance travel and controlling travel at a constant speed and a constant distance between vehicles, wherein the acceleration of the vehicle is set according to at least one of a radius of curvature of a curve of a travel road and a road surface frictional resistance. Wherein the control means sets the acceleration at the time of transition from the constant inter-vehicle distance traveling to the constant speed traveling to a value set by the acceleration setting means. .

That is, in the fourth vehicle travel control device, the target vehicle speed is set by the target vehicle speed setting means, and the target inter-vehicle distance with the preceding vehicle is set by the target inter-vehicle distance setting means. In the control means, a constant speed running while maintaining the vehicle speed at the target vehicle speed set by the target vehicle speed setting means, and a constant speed running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means. Distance traveling is selectively performed to control traveling at a constant speed and a constant inter-vehicle distance. At this time, the control means sets the acceleration of the vehicle to a value set by the acceleration setting means according to at least one of the radius of curvature of the curve of the traveling road and the road surface frictional resistance when shifting from traveling at a constant inter-vehicle distance to traveling at a constant speed. Set to.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show a first embodiment of the present invention.
FIG. 1 is a functional block diagram of a travel control device, FIG. 2 is a schematic configuration diagram of a vehicle equipped with the travel control device, FIG. 3 is a flowchart of a travel control program, and FIG. 4 is a method of obtaining a radius of curvature of a curve. FIG. 5 is an explanatory diagram of correction of the radius of curvature of the obtained curve, and FIG. 6 is a characteristic explanatory diagram of the return acceleration setting map.

In FIG. 2, reference numeral 1 denotes a vehicle (own vehicle) which is an example of a four-wheel drive vehicle having a center differential device and an automatic transmission. The driving force of the engine 2 disposed at the front of the vehicle is transmitted from an automatic transmission (including a torque converter and the like) 3 behind the engine 2 to a center differential device 4 via a transmission output shaft 3a. The center differential device 4 distributes the torque to the rear wheels and the front wheels at a predetermined torque distribution ratio.

The driving force distributed from the center differential device 4 to the rear wheels is input to a rear wheel final reduction device 8 via a rear drive shaft 5, a propeller shaft 6, and a drive pinion 7. The driving force distributed from the center differential device 4 to the front wheels is input to the front wheel final reduction gear 10 via the front drive shaft 9.
Here, the automatic transmission 3, the center differential device 4, the front wheel final reduction gear 10, and the like are integrally provided in a case (not shown).

The driving force input to the rear wheel final reduction gear 8 is applied to the left rear wheel 12rl via the rear wheel left drive shaft 11rl.
The power is transmitted to the right rear wheel 12rr via the rear wheel right drive shaft 11rr. The driving force input to the front wheel final reduction gear 10 is transmitted to the left front wheel 12 via the front wheel left drive shaft 11fl.
and transmitted to the right front wheel 12fr via the front wheel right drive shaft 11fr.

Reference numeral 13 denotes a hydraulic unit comprising a hydraulic pump and various valves, which is provided as a brake drive unit. A master cylinder 15 connected to a brake pedal 14 operated by a driver is connected to the brake driving unit 13. Therefore, when the driver operates the brake pedal 14, the master cylinder 15 causes the brake drive unit 1 to operate.
3, wheel cylinders of the four wheels 12fl, 12fr, 12rl, and 12rr (left front wheel cylinder 16fl, right front wheel cylinder 16fr, left rear wheel cylinder 1
6rl, the rear right wheel cylinder 16rr) is adapted to apply a brake pressure, whereby the four wheels are braked and braked.

The throttle valve 17 of the engine 2
Is openably and closably provided by an accelerator pedal 18 and connected to a throttle actuator 19.
The actuator can be opened and closed freely by an actuator drive unit 20 that operates the throttle actuator 19.
The actuator drive unit 20 includes a motor pump and various solenoid valves.

In the first embodiment of the present invention, the automatic transmission 3 is an electronically controlled four-speed full automatic transmission, and includes a parking range (P range), a reverse range (R range), and a neutral range (N range). , And 1st range, 2nd range, 3rd range,
A drive range (D range) to which the fourth speed of overdrive is added is provided, and the position of each of these ranges is detected by the inhibitor switch 21 and output to a control device 40 described later.

A pair of CCD cameras 22 using a solid-state image pickup device such as a charge-coupled device (CCD), which stereoscopically image the front of the outside traveling road from different viewpoints, are fixed in front of the ceiling in the cabin of the vehicle 1. It is attached with an interval of. The pair of CCD cameras 22 are connected to an image processing device 23.
For a pair of stereo images captured by the CD camera 22, a process of obtaining distance information over the entire image from the corresponding positional deviation amount based on the principle of triangulation is performed to obtain a distance image representing a three-dimensional distance distribution. It is generated and output to the control device 40.

Further, the vehicle 1 has a navigation device 2
4 is mounted, and this navigation device 24 is
As a general example, as shown in FIG. 1, it mainly includes a vehicle position detection sensor unit 24a, an auxiliary storage device 24b, an information display unit 24c, an operation unit 24d, and a calculation unit 24e.

The vehicle position detecting sensor unit 24a is, specifically, a global positioning satellite system (Global Positioning S).
ystem (GPS) to receive a radio wave from a GPS satellite to measure its own position, a GPS receiver for detecting the absolute traveling direction of the vehicle 1, and a wheel speed sensor for detecting the wheel speed. The connection is made so that traveling information relating to the vehicle position is collected.

The auxiliary storage device 24b is a CD-ROM device, and is formed as a read-only storage device in which a CD-ROM storing road map information including road information and terrain information is set. In the CD-ROM, road map information is stored at each of a plurality of hierarchical levels having different scales. Further, road type information such as expressways, general national roads, and local roads, and traffic conditions such as intersections, etc., are stored. Information is stored. The road data in the road map information includes point data (node information) input at predetermined intervals and line data (link information) formed by continuously connecting these points.

The information display section 24c is formed of a liquid crystal display which displays a map, a position of the vehicle (latitude, longitude, altitude), a direction, a position of the vehicle on the map, an optimum route to a destination, and the like. Then, a touch panel as an operation unit 24d is connected integrally with the information display unit 24c (liquid crystal display), and an operation input for changing a scale of a map, a detailed display of a place name, a display of area information, route guidance, and the like is performed. You can do it.

The calculation unit 24e combines the travel information of the vehicle 1 obtained from the vehicle position detection sensor unit 24a with the map information read from the auxiliary storage device 24b while performing calculations such as map matching, and combines the results. The information is sent to the information display unit 24c based on an operation signal sent from the operation unit 24d to display the current position of the vehicle 1, a map around the vehicle 1, an optimal route to a destination, and the like. Further, the information on the road shape ahead of the traveling road of the host vehicle 1 is read by the control device 40 as needed.

The vehicle 1 has a vehicle speed sensor 25 for detecting a vehicle speed, a steering wheel angle sensor 26 for detecting a steering wheel angle,
Each of a lateral acceleration sensor 27 for detecting a lateral acceleration and a yaw rate sensor 28 for detecting a yaw rate are connected to the control device 40. Furthermore, brake pedal 1
Brake pedal switch 2 for detecting ON-OFF of 4
9. Driver ON-O for constant speed constant inter-vehicle distance control
A main switch 30 for performing FF, a vehicle speed set switch 31 for the driver to set a target vehicle speed at constant speed traveling, a coast switch 32 for the driver to mainly change and set the target vehicle speed to the downside, a driver to mainly increase the target vehicle speed to the upside The control device 40 is connected to a resume switch 33 for changing and setting the distance to the vehicle and an inter-vehicle distance set switch 34 for the driver to set a target inter-vehicle distance for traveling at a constant inter-vehicle distance by numerical input or the like.

The control device 40 is composed of a microcomputer and various peripheral circuits such as an A / D converter and a driving circuit.
Navigation device 24, sensors 25, 26, 27,
28, each switch 21, 29, 30, 31, 32, 3
3, 34 are connected. An actuator drive unit 20 is connected to an output port of the control device 40. The actuator drive unit 20 is driven by an output signal from the control device 40 to open and close the throttle valve 17 through the throttle actuator 19.

That is, the control device 40 performs a constant speed running while maintaining the vehicle speed at the target vehicle speed set by the driver, and a constant inter-vehicle distance running while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the driver. Is selectively performed to control traveling at a constant speed and a constant inter-vehicle distance. Then, the control device 40
As shown in FIG. 1, a road shape recognition unit 41, a preceding vehicle information detection unit 42, a target vehicle speed setting unit 43, and a target inter-vehicle distance setting unit 4
4, a control determining unit 45, a road surface μ calculating unit 46, a return acceleration calculating unit 47, and a constant speed constant inter-vehicle distance running control unit 48.

The road shape recognizing section 41 is provided with the image processing device 23
The travel path is recognized by performing histogram processing on the distance distribution of the distance image from, and the road width of the travel path is calculated. Specifically, for example, a white line is approximated by a polygonal line, and a range surrounded by left and right polygonal lines is recognized as the own lane,
The road width is calculated from the interval between the left and right polygonal lines of the own lane. In addition, the above-described road width data, and data relating to the position from the navigation device 24 (data such as node information, link information, road type information, and current position of road data).
Is read as necessary, and the road shape including the bending state (curve information) ahead of the traveling road is recognized. Here, the curve information is obtained by, for example, a technique proposed by the present applicant in Japanese Patent Application No. Hei 9-155409. Hereinafter, this technique will be briefly described.

From the point data of the road input from the navigation device 24, for example, three points on the road within a range of about 100 m ahead are sequentially arranged at predetermined intervals (for the vehicle) as shown in FIG. These are sequentially read as a first point Pn-1, a second point Pn, and a third point Pn + 1 (from the closest point). Here, the representative point of this curve is Pn. Therefore, the curve at point P1 is from points P0, P1, P2, the curve at point P2 is from points P1, P2, P3,..., And the curve at point Pn is at point Pn-1.
, Pn, and Pn + 1.

In the curve of the point Pn, the first point Pn-1
The first point Pn-1 and the second point Pn-1 are based on the position information of the second point Pn and the second point Pn.
Calculate the linear distance connecting the point Pn of the second point Pn and the third point Pn
The second point Pn and the third point Pn based on the position information of the point Pn + 1
Calculate the straight line distance connecting n + 1.

Then, a straight line distance connecting the first point Pn-1 and the second point Pn is compared with a straight line distance connecting the second point Pn and the third point Pn + 1. Is determined. As a result, based on each data (position, distance) of the short straight line, a half distance of the short straight line distance is calculated, and the midpoint position on the short straight line is determined. Here, for example, a straight line connecting the first point Pn-1 and the second point Pn is a short straight line, and the middle point is Pn-1, n.

On the other hand, each data (position,
Distance) and half the shorter linear distance,
A midpoint equidistant point is determined on the longer straight line at a position that is half of the shorter straight line distance from the second point. Here, for example, it is assumed that a straight line connecting the second point Pn and the third point Pn + 1 is a long straight line, and a midpoint equidistant point is Pn, n + 1.

Then, based on the position data of the midpoint Pn-1, n and the calculated position data of the midpoint equidistant point Pn, n + 1, a shorter straight line (here, Pn -1 Pn) and the straight line perpendicular to the longer straight line (here, Pn Pn + 1) at the midpoint equidistant point Pn, n + 1 is defined as the center position On of the curve of the travel road. Then, the radius of curvature Rn of the traveling road is calculated based on the curve center position On.

Further, as shown in FIG.
And the distance Lon from the curve center position On to the second point Pn
Is calculated, and when the difference Deln exceeds a preset error setting value described later, the curvature radius Rn is corrected to always keep the difference Deln within the error setting value. That is, the error set value is varied according to both the road width D and the shorter straight line distance, and (error set value)
= Αh · D (αh is a constant set in accordance with the shorter straight line distance: hereinafter, referred to as a point interval correction coefficient).

It should be noted that the road width D usually employs the value of the road width obtained based on the image. However, when data based on this image cannot be obtained, the value obtained from the navigation device 24 is used. The road width D is set based on road type information such as a highway, a general national road, and a local road. Here, as the road width D increases, the error set value increases and no correction is performed. This expresses that the radius of curvature Rn increases as the road width increases on an actual road. . In addition, the fact that the straight line distance is short means that correction is not performed because the point data is set finely and it can be regarded that the road is correctly represented. Therefore, the point interval correction coefficient αh is in a direction in which the shorter the straight line distance is, the larger the point interval correction coefficient αh becomes, the larger the error set value becomes, and no correction is performed. For example, αh = 1.2 when the shorter linear distance is shorter than 20 m, αh = 0.6 when the intermediate distance is shorter than 100 m, and αh = 0.3 when the shorter straight distance is longer than 100 m.
And

Thus, the final curve information (the position of the representative point Pn of the curve, the distance Ln between the point Pn-1 and the point Pn, the final radius of curvature Rn, the curve center position On, the straight line Pn-1)
The curve angle θn of each point determined from the angle between Pn and the straight line Pn Pn + 1, and the curve start point Lsn (curve center position O
n from Pn-1 perpendicular to the straight line Pn-1 Pn) and Pn-1
Distance, distance L from vehicle position to representative point of each curve
ssn etc.) are calculated. Thus, of the curve information obtained, the curve radius of curvature Rn in front of the traveling road is:
It is output to the return acceleration calculation section 47.

Further, the preceding vehicle information detecting section 42 performs image processing such as extracting features of a box-shaped pattern on the distance image from the image processing device 23, and performs, in a three-dimensional object, the front of the own vehicle 1. An object existing in the vehicle 1 and serving as an obstacle to the host vehicle 1 is identified, a preceding vehicle is detected, and a distance from the preceding vehicle (inter-vehicle distance) is determined. Then, the change of the inter-vehicle distance with time is calculated to calculate the relative speed of the preceding vehicle with respect to the own vehicle, and the relative speed of the preceding vehicle is added to the vehicle speed from the vehicle speed sensor 25 to obtain the preceding vehicle speed. The calculated preceding vehicle information (inter-vehicle distance, relative speed of the preceding vehicle with respect to the own vehicle, preceding vehicle speed) is stored in the constant speed constant inter-vehicle distance traveling control unit 4.
8 is output.

Further, the target vehicle speed setting section 43 serves as target vehicle speed setting means. The vehicle speed is input from the vehicle speed sensor 25, and the vehicle speed set switch 31, coast switch 32, and resume switch 33 are turned on and off by the driver. An OFF signal is input. Then, the vehicle speed can be set in a speed setting range (for example, about 40 km / h to 100 km / h).
When an ON signal is input from the vehicle speed set switch 31 while the vehicle is traveling, the vehicle speed at the time when this signal is turned OFF is set as the target vehicle speed. When an ON signal is input from the coast switch 32 during traveling at a constant speed, the speed is gradually reduced while the coast switch 32 is ON, and the vehicle speed at the time when the coast switch 32 is turned OFF is set as a new target vehicle speed. You. Conversely, when an ON signal is input from the resume switch 33 during traveling at a constant speed, the vehicle is accelerated gradually while the resume switch 33 is ON, and the vehicle speed at the time the resume switch 33 is turned OFF is set as a new target vehicle speed. Is done. Then, a signal indicating whether or not the target vehicle speed has been set is output to the control determining unit 45, and the set target vehicle speed is output to the constant speed constant inter-vehicle distance traveling control unit 48.

The target inter-vehicle distance setting section 44 serves as target inter-vehicle distance setting means, receives a numerical signal from the inter-vehicle distance set switch 34, and sets a range in which the inter-vehicle distance with the preceding vehicle can be set. It is set as the target inter-vehicle distance within about 3 m to 30 m). Then, a signal indicating whether or not the target inter-vehicle distance has been set is output to the control determination unit 45, and the set target inter-vehicle distance is output to the constant speed and constant inter-vehicle distance travel control unit 48.

The control determining section 45 receives an ON-OFF signal from the driver from the main switch 30 and receives a signal indicating whether or not the target vehicle speed has been set from the target vehicle speed setting section 43.
A target inter-vehicle distance setting presence / absence signal is input from the target inter-vehicle distance setting unit 44. Then, the main switch 30 is turned off.
If any one of the condition, the target vehicle speed is not set, and the target inter-vehicle distance is not set is satisfied, the constant-speed constant inter-vehicle traveling control unit 48 controls the constant-speed constant inter-vehicle traveling. Is canceled. That is, the control determination unit 45 is a control determination unit, and when the target vehicle speed is set but the target inter-vehicle distance is not set by the control determination unit 45, the constant speed constant inter-vehicle distance traveling control is prohibited. Is done.

The road surface μ calculating section 46 receives the vehicle speed from the vehicle speed sensor 25, the steering wheel angle from the steering wheel angle sensor 26, the lateral acceleration from the lateral acceleration sensor 27, and the yaw rate from the yaw rate sensor 28, and inputs the road surface μ of the running road. The estimation of the road surface μ is, for example,
It is determined by the present applicant using the technology proposed in Japanese Patent Application No. 10-242030. In this technique, a high μ road reference vehicle body slip angle corresponding to a steering wheel angle and a vehicle speed is calculated by a vehicle motion model based on a predetermined vehicle motion equation on a high μ road, and is set in advance. Based on a vehicle motion model based on the equation of motion of the vehicle on a low μ road, a low μ road reference body slip angle corresponding to the steering wheel angle and the vehicle speed is calculated. Based on the steering wheel angle, vehicle speed, lateral acceleration, high μ road reference vehicle slip angle, and low μ road reference vehicle slip angle, the estimated vehicle slip angle is estimated by the An estimated road surface μ is calculated based on a predetermined relationship between a high μ road reference vehicle slip angle, a low μ road reference vehicle slip angle, and an estimated vehicle slip angle. The road surface μ estimated in this way is output to the return acceleration calculation unit 47.

The return acceleration calculating section 47 receives the curve radius of curvature Rn in front of the traveling road from the road shape recognition section 41 and the road surface μ of the traveling road from the road surface μ computing section 46. From the map in which Rn and the road surface μ are respectively set as parameters, a safe and optimum acceleration limit value for passing through the traveling road is obtained. Then, the limit value of the acceleration is read as required by the constant speed constant inter-vehicle distance traveling control unit 48 as the return acceleration, and is set as the acceleration at the time of transition from the constant inter-vehicle distance traveling to the constant speed traveling. That is, the return acceleration calculator 47 is provided as acceleration setting means.

As shown in FIG. 6, the map for obtaining the return acceleration is such that as the curve radius of curvature Rn increases,
A characteristic line having a large return acceleration is set and formed for each of the plurality of road surfaces μ. Here, the larger the curve curvature radius Rn becomes, the larger the return acceleration becomes. This means that the greater the curve becomes, the greater the acceleration can be made. Also, the slope of the characteristic line of the curve radius of curvature Rn-return acceleration increases as the road surface μ increases. This expresses that the higher the road μ, the greater the acceleration. is there.

A constant speed constant inter-vehicle distance traveling control unit 48
Is a control means for selectively performing a constant speed running while maintaining the vehicle speed at the target vehicle speed and a constant inter-vehicle traveling while maintaining the inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance as a control means for controlling the constant speed and the inter-vehicle distance. The vehicle speed sensor 25 sends the vehicle speed, the coast switch 32, the resume switch 33 sends an ON-OFF signal from the driver, the inhibitor switch 21 sends a range position, and the brake pedal switch 29 sends an ON-OFF signal to the brake pedal 14. Is entered. Further, the preceding vehicle information detecting unit 42 outputs the preceding vehicle information (inter-vehicle distance, relative speed of the preceding vehicle to the own vehicle,
A preceding vehicle speed), a target vehicle speed from the target vehicle speed setting unit 43, and a target inter-vehicle distance from the target inter-vehicle distance setting unit 44.
The control determination unit 45 executes or cancels the constant speed constant inter-vehicle distance traveling control, or reads the return acceleration from the return acceleration calculation unit 47 as necessary.

Then, a constant speed constant inter-vehicle distance traveling control unit 4
When the control determination unit 45 executes the constant speed constant inter-vehicle distance traveling control, if the preceding vehicle does not exist or does not exist within the preset distance range, the vehicle travels at a constant speed. In this case, first, the target vehicle speed from the target vehicle speed setting unit 43 and the vehicle speed from the vehicle speed sensor 25 are compared. When the vehicle speed is higher than the target vehicle speed, a signal for driving the actuator drive unit 20 to close the throttle valve 17 is output. On the other hand, when the vehicle speed is lower than the target vehicle speed, a signal for driving the actuator drive unit 20 to open the throttle valve 17 is output.

When the preceding vehicle is traveling within a preset distance range and travels at a constant inter-vehicle distance during execution of the constant speed and constant inter-vehicle distance traveling control, the target inter-vehicle distance setting unit 44 Is compared with the target inter-vehicle distance from the preceding vehicle information detection unit 42. When the inter-vehicle distance from the preceding vehicle is shorter than the target inter-vehicle distance, a signal for driving the actuator drive unit 20 to close the throttle valve 17 is output. On the other hand, if the inter-vehicle distance from the preceding vehicle is longer than the target inter-vehicle distance, a signal to drive the actuator drive unit 20 to open the throttle valve 17 is output.

A constant speed constant inter-vehicle distance traveling control unit 48
When the constant speed inter-vehicle traveling control is executed, when the preceding vehicle is no longer present due to a lane change, a right or left turn, etc. during the constant inter-vehicle traveling, it is determined before the vehicle enters the constant inter-vehicle distance traveling. The vehicle returns to the constant speed running at the target vehicle speed. The return acceleration at this time is set by reading from the return acceleration calculation section 47. For this reason, even if there is no preceding vehicle on a sharp curve or on a slippery road surface, there is no sudden acceleration to return to constant speed running, and constant speed running with safe and appropriate return acceleration is always available. The return is made.

Further, when executing the constant speed constant inter-vehicle distance traveling control, if the preceding vehicle approaches within a preset distance range during the constant speed traveling, it is determined before the vehicle enters the constant speed traveling. The vehicle returns to running at a constant inter-vehicle distance at the target inter-vehicle distance.

A constant speed constant inter-vehicle distance traveling control unit 48
Then, when traveling at a constant speed, the coast switch 32
When the N signal is input, while the coast switch 32 is ON, a signal for driving the actuator drive unit 20 to close the throttle valve 17 is output to gradually reduce the speed. And the coast switch 32
The vehicle speed at the time of turning off is input from the target vehicle speed setting unit 43 as a new target vehicle speed, and the vehicle travels at a constant speed. Further, when traveling at a constant speed, the resume switch 33
When the N signal is input, the resume switch 33 is turned on.
During this operation, a signal for driving the actuator drive unit 20 to open the throttle valve 17 is output to gradually increase the speed. Then, the vehicle speed at the time when the resume switch 33 is turned off is input from the target vehicle speed setting unit 43 as a new target vehicle speed, and the vehicle travels at a constant speed.

The constant speed constant inter-vehicle distance traveling control unit 48
Then, in addition to the cancellation of the constant speed constant inter-vehicle distance traveling control by the control determination unit 45, when an ON signal is input from both the coast switch 32 and the resume switch 33,
When the brake pedal 14 is depressed and an ON signal is input from the brake pedal switch 29, and when an N range input is received from the inhibitor switch 21, the constant speed constant inter-vehicle distance traveling control is canceled.

Next, the control device 4 according to the first embodiment of the present invention will be described.
The control at 0 will be described based on the flowchart of FIG.
This travel control program is executed by an ignition switch O
After N, it is repeatedly executed at set time intervals.

First, step (hereinafter abbreviated as “S”) 1
01, vehicle speed, steering wheel angle sensor 2 from vehicle speed sensor 25
6, the steering wheel angle, the lateral acceleration sensor 27, the lateral acceleration,
The yaw rate is read from the yaw rate sensor 28, the range position is read from the inhibitor switch 21, and each switch position is read from the brake pedal switch 29, the main switch 30, the vehicle speed set switch 31, the coast switch 32, the resume switch 33, and the following distance set switch 34. Read. Further, a distance image is read from the image processing device 23, and various data relating to the position (data such as road data node information, link information, road type information, and current position) are read from the navigation device 24.

Then, the program proceeds to S102, in which it is determined whether or not the traveling speed control at a constant speed and a constant distance has been canceled by the switch state, that is, the coast switch 32 and the resume switch 33.
The brake pedal 14 is depressed and the brake pedal switch 29 is turned on
It is determined whether there is a signal input or whether there is an N-range input from the inhibitor switch 21. An ON signal is input from both the coast switch 32 and the resume switch 33, an ON signal is input from the brake pedal switch 29 when the brake pedal 14 is depressed, or an N range input is provided from the inhibitor switch 21. If any one of the conditions is satisfied, the constant speed constant inter-vehicle distance traveling control is stopped. If none of the above conditions are satisfied, the control proceeds to step S103 to execute the constant speed constant inter-vehicle distance traveling control.

In S103, the main switch 30 is turned on.
If the main switch 30 is ON, the process proceeds to S104, and if the main switch 30 is OFF, the constant speed constant inter-vehicle distance traveling control is stopped.

When the main switch 30 is turned on in S103 and the operation proceeds to S104, it is determined whether or not the target vehicle speed is set in the target vehicle speed setting section 43. If the target vehicle speed is set, the operation proceeds to S105. If the target vehicle speed has not been set, the constant speed constant inter-vehicle distance traveling control is stopped.

When it is determined in S104 that the target vehicle speed has been set and the routine proceeds to S105, it is determined whether or not the target inter-vehicle distance is set in the target inter-vehicle distance setting section 44.
If the target inter-vehicle distance has been set, the process proceeds to S106. If the target inter-vehicle distance has not been set, the constant speed constant inter-vehicle distance traveling control is stopped.

That is, S103 to S105 are processes executed by the control determination unit 45. In particular, even if the target vehicle speed is set, if the target inter-vehicle distance is not set, the process is executed by the control determination unit 45. Since the vehicle does not enter into the distance running control, the vehicle automatically shifts from the constant speed running to the constant inter-vehicle distance running, so that the driver can operate without misunderstanding.

Next, when it is determined in S105 that the target inter-vehicle distance has been set, and the routine proceeds to S106, the image processing apparatus 2
From the preceding vehicle information (inter-vehicle distance, relative speed of the preceding vehicle to the own vehicle, preceding vehicle speed) obtained by the preceding vehicle information detecting unit 42 based on the distance image from 3, the preceding vehicle is captured in the own lane. A determination is made as to whether or not it is. If the preceding vehicle has been captured, the process proceeds to S107, and if the preceding vehicle has not been captured, the process jumps to S115.

When the preceding vehicle is captured in S106 and the process proceeds to S107, it is determined whether or not the vehicle is approaching the preceding vehicle, that is, whether or not the preceding vehicle is present within a predetermined distance range. If so, the process proceeds to S108. If the preceding vehicle is not approaching (the preceding vehicle is far from the host vehicle), the process jumps to S115.

In S108, it is determined whether or not the preceding vehicle exists in the own lane. As a result, if there is a preceding vehicle in the own lane, the process proceeds to S109, and if there is no preceding vehicle in the own lane, the process proceeds to S111. In the first process in which it is determined that the preceding vehicle has approached in S107 and the process proceeds to S108, since the preceding vehicle has already been confirmed in S107, S1
09.

Then, in S109, a constant inter-vehicle distance control for traveling at a constant inter-vehicle distance is executed. That is, the target inter-vehicle distance from the target inter-vehicle distance setting unit 44 and the preceding vehicle information detection unit 42
If the following distance is shorter than the target following distance, a signal for driving the actuator driving unit 20 to close the throttle valve 17 is output. On the other hand, if the inter-vehicle distance from the preceding vehicle is longer than the target inter-vehicle distance, a signal to drive the actuator drive unit 20 to open the throttle valve 17 is output.

Thereafter, the process proceeds to S110, where new preceding vehicle information is read from the preceding vehicle information detecting section 42, and the determination processing of S108 is performed. For this reason, constant inter-vehicle distance control is continuously performed as long as the preceding vehicle exists.

When the preceding vehicle no longer exists due to a lane change or a left / right turn, the process proceeds from S108 to S111,
Data on the distance image from the image processing device 23 and the position from the navigation device 24 (data such as node information, link information, road type information, and current position of road data)
The road shape recognition unit 41 calculates road shape data (curve information such as a curve radius of curvature Rn) in front of the road on the basis of the above.

Then, the program proceeds to S112, in which the road surface μ calculating section 46 estimates and calculates the road surface μ of the running road based on the vehicle speed, the steering wheel angle, the lateral acceleration and the yaw rate.

Then, the program proceeds to S113, in which the return acceleration calculating section 47 refers to a map based on the curve radius of curvature Rn and the road surface μ to determine a safe and optimum acceleration limit value for passing through the traveling road. This limit value of the acceleration is set as the return acceleration when the vehicle travels from the constant inter-vehicle distance traveling to the constant speed traveling.

Thereafter, the program proceeds to S114, in which the return acceleration calculated by the return acceleration calculating section 47 when the vehicle travels from the constant inter-vehicle distance to the constant speed travel is set, that is, the throttle opening amount is equal to the return acceleration. Output to the actuator drive unit 20 as shown in FIG.
At the target vehicle speed, and the process proceeds to S115.

In S106, the preceding vehicle is not captured, or
When the preceding vehicle is far from the host vehicle in S107, or when the process proceeds from S114 to S115, the constant vehicle speed control of the constant speed traveling is executed. That is, the target vehicle speed setting unit 43
When the vehicle speed is greater than the target vehicle speed, a signal for driving the actuator drive unit 20 to close the throttle valve 17 is output. On the other hand, when the vehicle speed is lower than the target vehicle speed, a signal for driving the actuator drive unit 20 to open the throttle valve 17 is output. Thus, the program is repeated again.

As described above, according to the first embodiment,
Even if the target vehicle speed is set, if the target inter-vehicle distance is not set, the vehicle will not enter the constant speed constant inter-vehicle distance traveling control. The driver can operate without misunderstanding and safety can be greatly improved.

Further, when the constant speed constant vehicle-to-vehicle distance running control is executed, when the preceding vehicle does not exist due to lane change, right / left turn or the like from the constant vehicle-to-vehicle distance, and returns to the constant speed driving,
As the return acceleration, a safe and optimal return acceleration is used to pass through the traveling road according to the curve radius of curvature Rn and the road surface μ, so even if there is no preceding vehicle on a sharp curve or on a slippery road surface, The vehicle does not suddenly accelerate to return to the constant speed traveling, but always returns to the constant speed traveling at a safe and appropriate return acceleration, so that the safety can be greatly improved.

Next, FIGS. 7 and 8 show a second embodiment of the present invention.
7 is a functional block diagram of the travel control device, and FIG. 8 is a flowchart of a travel control program. still,
The second embodiment differs from the first embodiment in that a target inter-vehicle distance setting unit 44 and a control determination unit 45 of the control device 40 in the first embodiment are different, and other configurations and operations are the same as those in the first embodiment. The same reference numerals are given and the description is omitted.

For this reason, the control device 4 according to the second embodiment of the present invention
0 is a road shape recognition unit 41, a preceding vehicle information detection unit 42, a target vehicle speed setting unit 43, a target inter-vehicle distance setting unit 51, a control determination unit 52, a road surface μ calculation unit 46, a return acceleration calculation, as shown in FIG. It mainly comprises a unit 47 and a constant speed constant inter-vehicle distance traveling control unit 48.

The target inter-vehicle distance setting unit 51 serves as target inter-vehicle distance setting means. When a numerical signal is input from the inter-vehicle distance set switch 34, the inter-vehicle distance to the preceding vehicle can be set (for example, approximately 3 m to 30 m) is set as the target inter-vehicle distance. When the setting from the inter-vehicle distance set switch 34 is not performed, a preset maximum target inter-vehicle distance (for example, about 30 m) is set from a signal from the control determination unit 52. The set target inter-vehicle distance including the maximum target inter-vehicle distance is output to the constant speed / constant inter-vehicle distance traveling control unit 48.

The control determining section 52 receives an ON / OFF signal from the driver from the main switch 30 and receives a signal indicating whether or not the target vehicle speed has been set from the target vehicle speed setting section 43.
A target inter-vehicle distance setting presence / absence signal is input from the target inter-vehicle distance setting unit 44. Then, the main switch 30 is turned off.
In a state or a state in which the target vehicle speed is not set, the constant speed constant inter-vehicle distance traveling control unit 48 cancels the constant speed constant inter-vehicle distance traveling control. When the main switch 30 is ON and the target inter-vehicle distance is not set even if the target vehicle speed is set, the target inter-vehicle distance setting unit 44 sets the maximum target inter-vehicle distance as the target inter-vehicle distance. Is output. That is, the control determination unit 52 is a control determination unit. When the target vehicle speed is set but the target inter-vehicle distance is not set by the control determination unit 52, the target inter-vehicle distance becomes the maximum target inter-vehicle distance. Is set.

Next, the control device 4 according to the second embodiment of the present invention
The control at 0 will be described with reference to the flowchart of FIG.
This travel control program is repeatedly executed at set time intervals after the ignition switch is turned on, as in the first embodiment.

After performing the same processing as in the first embodiment from S101 to S104, if it is determined in S104 that the target vehicle speed has been set, the process proceeds to S201, where the target inter-vehicle distance setting unit 51 It is determined whether or not the target inter-vehicle distance has been set. If the target inter-vehicle distance has been set, the process proceeds to S106, while if the target inter-vehicle distance has not been set, the process proceeds to S202, and the target inter-vehicle distance setting unit 51 sets the maximum target inter-vehicle distance as the target inter-vehicle distance. Thereafter, the process proceeds to S106.

After S106, the same processing as in the first embodiment is performed. Thus, the second embodiment of the present invention
According to the embodiment, even when the target vehicle speed is set, the target inter-vehicle distance is not set, and the maximum target inter-vehicle distance is set as the target inter-vehicle distance. From high-speed running, the vehicle automatically shifts to running at a constant inter-vehicle distance, so that the driver can operate without misunderstanding and safety can be greatly improved.

In each of the above embodiments, the preceding vehicle information is obtained based on the distance image obtained from the pair of CCD cameras 22 and the image processing device 23. However, the present invention is not limited to this. For example, a radio wave radar device, a laser radar device, or the like) may be used. In addition, a display device that indicates the operation of the traveling control device of the vehicle may be provided so that the driver can clearly understand the state of traveling at a constant speed and the state of traveling at a constant inter-vehicle distance. Further, at the time of transition from traveling at a constant speed to traveling at a constant inter-vehicle distance, or at the time of transition from traveling at a constant inter-vehicle distance to traveling at a constant speed, a notification may be given by a chime or buzzer sound. In addition, acceleration / deceleration control
Other than the throttle valve, it may be performed by, for example, changing the gear setting of an automatic brake or an automatic transmission.

[0082]

As described above, the first embodiment according to the present invention is described.
According to the vehicle traveling control device, when the target vehicle speed is set but the target inter-vehicle distance is not set, the constant speed constant inter-vehicle distance traveling control is prohibited. As a result, the vehicle shifts to the constant vehicle-to-vehicle distance running state, the driver can operate without misunderstanding, and the safety can be greatly improved.

According to the second vehicle travel control device of the present invention, when the target vehicle speed is set but the target inter-vehicle distance is not set, the maximum target inter-vehicle distance is set as the target inter-vehicle distance. Since the constant-speed constant inter-vehicle traveling control is performed, the vehicle automatically shifts from the constant speed traveling state to the constant inter-vehicle traveling state at all times. Can be operated as if
Safety can be greatly improved.

Further, according to the traveling control device for a third vehicle of the present invention, the traveling control device for the first or second vehicle sets the return acceleration at the time of transition from traveling at a constant inter-vehicle distance to traveling at a constant speed. Since the setting is made in accordance with at least one of the radius of curvature of the curve of the traveling road and the road surface frictional resistance, a safe and optimal return acceleration for passing through the traveling road is adopted in accordance with at least one of the curve radius of curvature and the road surface frictional resistance. Even if there is no preceding vehicle on a sharp curve or on a slippery road, the vehicle will not suddenly accelerate to return to constant speed driving, and will always return to constant speed driving with safe and appropriate return acceleration. Therefore, in addition to the effects of the travel control device for the first or second vehicle, the safety can be greatly improved.

Further, according to the fourth vehicle travel control device of the present invention, the return acceleration at the time of transition from traveling at a constant inter-vehicle distance to traveling at a constant speed is determined by at least the radius of curvature of the curve of the traveling road and the road surface frictional resistance. Since it is set according to one side, a safe and optimal return acceleration for passing through the traveling road is adopted according to at least one of the curve radius of curvature and the road surface frictional resistance, and the leading vehicle is driven on a sharp curve or on a slippery road surface. Even if the vehicle disappears, it will not suddenly accelerate to return to constant speed driving, and will always return to constant speed driving with safe and appropriate return acceleration, greatly improving safety. .

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a travel control device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a vehicle equipped with the travel control device.

FIG. 3 is a flowchart of a traveling control program according to the first embodiment;

FIG. 4 is an explanatory diagram of a method for obtaining a curvature radius of a curve according to the first embodiment;

FIG. 5 is an explanatory diagram of correction of a radius of curvature of a calculated curve;

FIG. 6 is a diagram illustrating characteristics of a return acceleration setting map according to the first embodiment;

FIG. 7 is a functional block diagram of a travel control device according to a second embodiment of the present invention.

FIG. 8 is a flowchart of a travel control program according to the first embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vehicle 17 Throttle valve 19 Throttle actuator 20 Actuator drive unit 40 Control device 41 Road shape recognition part 42 Leading vehicle information detection part 43 Target vehicle speed setting part (target vehicle speed setting means) 44 Target inter-vehicle distance setting part (target inter-vehicle distance setting means) 45 control determination unit (control determination unit) 46 road surface μ calculation unit 47 return acceleration calculation unit (acceleration setting unit) 48 constant speed constant inter-vehicle distance travel control unit (control unit)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D044 AA01 AA11 AA14 AA25 AA27 AA35 AB01 AC01 AC22 AC24 AC26 AC31 AC55 AC56 AC59 AD04 AD17 AD21 AE01 AE03 AE04 AE15 AE19 AE21 3G093 AA03 AA05 BA04 DB09 DB23 DB13 CB11 DB11 DB15 DB16 DB18 EA09 EB03 EB04 EC02 FA01 FA02 FA07 FA08 FA10 FA12

Claims (4)

[Claims] 1. A target vehicle speed setting means for setting a target vehicle speed, and a target inter-vehicle distance setting means for setting a target inter-vehicle distance with a preceding vehicle, wherein the vehicle speed is set by the target vehicle speed setting means. A constant speed constant vehicle running while maintaining the target vehicle speed and a constant vehicle distance running while maintaining the target inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means are selectively performed. In a travel control device for a vehicle having control means for controlling travel, when the target vehicle speed is set and the target inter-vehicle distance is not set, the constant speed constant inter-vehicle distance travel control of the control means is prohibited. A travel control device for a vehicle, comprising a control determination unit. 2. A vehicle control apparatus comprising: a target vehicle speed setting means for setting a target vehicle speed; and a target inter-vehicle distance setting means for setting a target inter-vehicle distance to a preceding vehicle, wherein the vehicle speed is set by the target vehicle speed setting means. A constant speed constant vehicle running while maintaining the target vehicle speed and a constant vehicle distance running while maintaining the target inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means are selectively performed. In a travel control device for a vehicle having control means for controlling travel, a maximum target inter-vehicle distance in which the target inter-vehicle distance is set in advance if the target inter-vehicle distance is not set even if the target vehicle speed is set A travel control device for a vehicle, comprising: a control determining means for setting the vehicle speed. 3. The vehicle according to claim 1, further comprising acceleration setting means for setting the acceleration of the vehicle according to at least one of a radius of curvature of a curve of a traveling road and a road surface frictional resistance, wherein said control means switches from said constant inter-vehicle distance traveling to said constant speed traveling. 3. The vehicle travel control device according to claim 1, wherein the acceleration at the time of shifting is set to a value set by the acceleration setting means. 4. A target vehicle speed setting means for setting a target vehicle speed, and a target inter-vehicle distance setting means for setting a target inter-vehicle distance with a preceding vehicle, wherein the vehicle speed is set by the target vehicle speed setting means. A constant speed constant vehicle running while maintaining the target vehicle speed and a constant vehicle distance running while maintaining the target inter-vehicle distance with the preceding vehicle at the target inter-vehicle distance set by the target inter-vehicle distance setting means are selectively performed. A travel control device for a vehicle comprising control means for controlling travel, comprising: acceleration setting means for setting the acceleration of the vehicle according to at least one of a radius of curvature of a curve of a travel road and a road surface frictional resistance, wherein the control means A travel control device for a vehicle, wherein an acceleration at the time of shifting from the constant inter-vehicle distance traveling to the constant speed traveling is set to a value set by the acceleration setting means.