Vehicle Control Apparatus, Vehicle Control Method, and Adaptive Cruise Control System

A lead vehicle (1) in an adaptive cruise control system that non-mechanically connects a following vehicle (2) to the lead vehicle (1) sequentially and that causes the following vehicle (2) to follow its immediately preceding vehicle calculates vehicle velocity limit (V1max) for limiting a velocity of the lead vehicle (1) based on maximum allowable vehicle velocity (V2max) of the following vehicle (2), maximum allowable vehicle velocity (V2max) satisfying a turning performance of the following vehicle (2), and controls a brake apparatus and a drive apparatus such that the velocity of the lead vehicle (1) will not exceed vehicle velocity limit (V1max).

TECHNICAL FIELD

The present invention relates to a vehicle control apparatus, to a vehicle control method, and to an adaptive cruise control system. In particular, it relates to adaptive cruise control that non-mechanically connects following vehicles to a lead vehicle sequentially and causes each of the following vehicles to follow its immediately preceding vehicle.

BACKGROUND ART

Adaptive cruise control has been known. In this adaptive cruise control, a vehicle controls its driving and braking forces to follow its immediately preceding vehicle that is running in the same lane in accordance with a set velocity (see Patent Document 1, for example). In the adaptive cruise control, if it is determined that the vehicle is the lead vehicle of a convoy, the vehicle changes its set velocity to a first upper limit. If it is determined that the vehicle is not the lead vehicle, the vehicle changes its set velocity to a second upper limit greater than the first upper limit.

REFERENCE DOCUMENT LIST

Patent Document

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

There is a situation in which a lead vehicle is on a straight path and a following vehicle that is controlled to follow this lead vehicle is on a curve. In this situation, if the lead vehicle accelerates, the lateral acceleration of the following vehicle may excessively increase. This lateral acceleration occurs in a direction orthogonal to the driving direction of the following vehicle. While conventional adaptive cruise control limits the velocity of the lead vehicle such that the following vehicle can follow the lead vehicle, conventional adaptive cruise control does not take into consideration the lateral acceleration that occurs in the following vehicle. Thus, the following vehicle may, for example, experience deteriorated ride quality, slipping, or freight collapsing.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a vehicle control apparatus, a vehicle control method, and an adaptive cruise control system that prevent excessively large lateral acceleration that adaptive cruise control may cause in a following vehicle on a curve.

Means for Solving the Problem

A vehicle control apparatus according to the present invention includes a control unit which is mounted on a lead vehicle in an adaptive cruise control system that non-mechanically connects a following vehicle to the lead vehicle sequentially and that causes the following vehicle to follow its immediately preceding vehicle and which outputs a calculation result obtained based on input information to a brake apparatus or a drive apparatus as a control command, wherein the control unit calculates a vehicle velocity limit for limiting a velocity of the lead vehicle based on a maximum allowable vehicle velocity of the following vehicle, the maximum allowable vehicle velocity satisfying a turning performance of the following vehicle, and wherein the control unit outputs the control command to the brake apparatus and/or the drive apparatus such that the velocity of the lead vehicle will not exceed the vehicle velocity limit.

In addition, in a vehicle control method according to the present invention, a lead vehicle in an adaptive cruise control system that non-mechanically connects a following vehicle to the lead vehicle sequentially and that causes the following vehicle to follow its immediately preceding vehicle calculates a vehicle velocity limit for limiting a velocity of the lead vehicle based on a maximum allowable vehicle velocity of the following vehicle, the maximum allowable vehicle velocity satisfying a turning performance of the following vehicle, and controls a brake apparatus and/or a drive apparatus such that the velocity of the lead vehicle will not exceed the vehicle velocity limit.

In addition, an adaptive cruise control system according to the present invention non-mechanically connects a following vehicle to a lead vehicle sequentially and causes the following vehicle to follow its immediately preceding vehicle, wherein the lead vehicle includes: a control unit, a brake apparatus, and a drive apparatus. The control unit calculates a vehicle velocity limit for limiting a velocity of the lead vehicle based on a maximum allowable vehicle velocity of the following vehicle, the maximum allowable vehicle velocity satisfying a turning performance of the following vehicle, and outputs a control command for limiting acceleration or deceleration of the lead vehicle such that the velocity of the lead vehicle will not exceed the vehicle velocity limit. The brake apparatus controls braking force based on the control command, and the drive apparatus controls driving force based on the control command.

Effects of the Invention

The vehicle control apparatus, the vehicle control method, and the adaptive cruise control system according to the present invention can prevent excessively large lateral acceleration that adaptive cruise control may cause in a following vehicle on a curve.

MODE FOR CARRYING OUT THE INVENTION

First Example

Outline of Adaptive Cruise Control System

An outline of an adaptive cruise control system according to a first example will be described with reference toFIGS.1to3. In this adaptive cruise control system, at least one following vehicle is non-mechanically connected to a lead vehicle sequentially, and each of the following vehicles follows its immediately preceding vehicle. The vehicles in the present description are automobiles that run on roads.

FIG.1illustrates a convoy formed by a plurality of vehicles in an adaptive cruise control system. The convoy inFIG.1includes a lead vehicle1that leads the convoy and a plurality of following vehicles2that run after lead vehicle1. Each following vehicle2follows its immediately preceding vehicle while maintaining a certain inter-vehicle distance from the immediately preceding vehicle.

FIG.2illustrates an example of the driving state of a convoy including only one following vehicle in the adaptive cruise control system. InFIG.2, lead vehicle1is on a straight path after passing through a curve, and following vehicle2is on the curve.

A turning performance unique to following vehicle2is previously set in following vehicle2, to prevent at least one of deteriorated ride quality, slipping, and freight collapsing. The turning performance of following vehicle2is set based on the upper limit of a lateral acceleration (lateral acceleration limit) aylimor the upper limit of a yaw rate (yaw rate limit) rlim. To satisfy this turning performance, for the velocity of the following vehicle2, an upper limit (maximum allowable vehicle velocity) V2maxis set based on the driving path on which following vehicle2runs. Maximum allowable vehicle velocity V2maxof following vehicle2is the velocity of following vehicle2when an actual lateral acceleration ayreaches lateral acceleration limit aylim. Alternatively, maximum allowable vehicle velocity V2maxof following vehicle2is the velocity of following vehicle2when an actual yaw rate r reaches yaw rate limit rlimof following vehicle2.

When following vehicle2is on a driving path having a relatively large curvature, the actual lateral acceleration and the actual yaw rate increase more easily as the vehicle velocity of following vehicle2increases than those when following vehicle2is on a driving path having a relatively small curvature. Thus, when following vehicle2is on a driving path having a relatively large curvature, the actual lateral acceleration and the actual yaw rate of following vehicle2reach lateral acceleration limit aylimand yaw rate limit rlimat a relatively low vehicle velocity. Thus, maximum allowable vehicle velocity V2maxof following vehicle2on a driving path having a relatively large curvature is less than maximum allowable vehicle velocity V2maxof following vehicle2, which is on a driving path that has a relatively small curvature (including a straight path).

Referring back toFIG.2, if lead vehicle1accelerates on a straight path after passing through the curve, the velocity (turning velocity) of following vehicle2following lead vehicle1also increases while maintaining a certain inter-vehicle distance therefrom on the curve. If the velocity of following vehicle2exceeds its maximum allowable vehicle velocity V2maxon the curve, the actual lateral acceleration or the actual yaw rate of following vehicle2exceeds its upper limit aylimor rlimused to set the turning performance, possibly resulting in deteriorated ride quality, slipping, or freight collapsing.

Thus, following vehicle2calculates its maximum allowable velocity V2max(=u1) that satisfies its turning performance at its driving location and transmits information about maximum allowable velocity V2max(=u1) to lead vehicle1via inter-vehicle communication. Next, lead vehicle1sets a vehicle velocity limit V1maxfor controlling its vehicle velocity to the same value as maximum allowable velocity V2max(=u1) and performs vehicle velocity control such that the vehicle velocity will not exceed vehicle velocity limit V1max. In this way, the velocity of following vehicle2does not exceed maximum allowable vehicle velocity V2max, and the actual lateral acceleration and the actual yaw rate of following vehicle2are maintained at or below their respective upper limits aylimand rlimused to set the turning performance.

FIG.3illustrates an example of the driving state of a convoy including three following vehicles in the adaptive cruise control system. InFIG.3, lead vehicle1and a first following vehicle2A following lead vehicle1are on a straight path after passing through a curve. A second following vehicle2B following first following vehicle2A is on the curve, and a third following vehicle2C following second following vehicle2B is on a straight path before entering the curve.

As in the case of the above convoy including only one following vehicle, each of following vehicles2A to2C calculates its maximum allowable vehicle velocity V2maxbased on its turning performance at its driving location and transmits information about maximum allowable vehicle velocity V2maxto lead vehicle1via inter-vehicle communication. Specifically, first following vehicle2A calculates its maximum allowable vehicle velocity V2max(=u1) on the straight path on which first following vehicle2A is running and transmits information about maximum allowable vehicle velocity V2max(=u1) to lead vehicle1. Second following vehicle2B calculates its maximum allowable vehicle velocity V2max(=u2) on the curve on which second following vehicle2B is running and transmits information about maximum allowable vehicle velocity V2max(=u2) to lead vehicle1. Third following vehicle2C calculates its maximum allowable vehicle velocity V2max(=u3) on the straight path on which second following vehicle2C is running and transmits information about maximum allowable vehicle velocity V2max(=u3) to lead vehicle1.

Lead vehicle1sets the lowest one of maximum allowable vehicle velocities V2maxof following vehicles2A to2C as vehicle velocity limit V1max. If following vehicles2A to2C have the same turning performance, maximum allowable vehicle velocity V2max(=u2) of second following vehicle2B running on the curve is the lowest. Thus, lead vehicle1sets maximum allowable vehicle velocity V2max(=u2) of second following vehicle2B as vehicle velocity limit V1maxand performs vehicle velocity control such that the vehicle velocity of lead vehicle1will not exceed vehicle velocity limit V1maxset as described above. In this way, the velocities of following vehicles2A to2C are maintained below their respective maximum allowable vehicle velocities V2max, and the actual lateral accelerations and the actual yaw rates of following vehicles2A to2C are maintained at their respective upper limits aylimand rlimor less used to set their respective turning performances. First to third following vehicles2A to2C may have mutually different turning performances.

In short, according to the first example, each of following vehicles2calculates its maximum allowable vehicle velocity V2maxthat satisfies its turning performance at its driving location, and lead vehicle1performs vehicle velocity control so that its vehicle velocity will not exceed vehicle velocity limit V1maxset based on maximum allowable vehicle velocities V2maxof following vehicles2.

Adaptive Cruise Control System of Following Vehicle

FIG.4illustrates an example of an adaptive cruise control system mounted on a following vehicle. The adaptive cruise control system mounted on following vehicle2includes a vehicle control apparatus20as a main component including a microcomputer as a control unit. The adaptive cruise control system also includes an external information recognition apparatus21, a vehicle state acquisition apparatus22, a reception apparatus23, a first transmission apparatus24, a second transmission apparatus25, a drive apparatus26, and a brake apparatus27.

For example, external information recognition apparatus21recognizes objects present in front of corresponding following vehicle2by using a camera, a radar, a sonar, or the like. Specifically, external information recognition apparatus21measures an inter-vehicle distance d between corresponding following vehicle2and its immediately preceding vehicle and outputs information about inter-vehicle distance d.

Vehicle state acquisition apparatus22acquires the vehicle state of corresponding following vehicle2and includes a vehicle velocity acquisition unit221, a longitudinal acceleration acquisition unit222, a yaw rate acquisition unit223, a lateral acceleration acquisition unit224, and a steering angle acquisition unit225.

Vehicle velocity acquisition unit221acquires a vehicle velocity V2of corresponding following vehicle2based on a vehicle velocity pulse signal output from a vehicle-mounted vehicle velocity sensor or a vehicle velocity estimation result obtained by a vehicle behavior control apparatus such as an ABS (Anti-lock Braking System) and outputs information about vehicle velocity V2. Longitudinal acceleration acquisition unit222acquires a longitudinal acceleration ax of corresponding following vehicle2by performing measurement using a vehicle-mounted longitudinal acceleration sensor and outputs information about longitudinal acceleration ax. Longitudinal acceleration acquisition unit222may calculate longitudinal acceleration ax based on change of vehicle velocity V2acquired by vehicle velocity acquisition unit221.

Yaw rate acquisition unit223acquires yaw rate r of corresponding following vehicle2by performing measurement, for example, using a vehicle-mounted yaw rate sensor and outputs information about yaw rate r. Yaw rate acquisition unit223may calculate yaw rate r by using measured values of physical amounts such as vehicle velocity V2and a steering angle δ, without performing measurement using a yaw rate sensor. Lateral acceleration acquisition unit224acquires lateral acceleration ayof corresponding following vehicle2by performing measurement, for example, using a vehicle-mounted lateral acceleration sensor and outputs information about lateral acceleration ay. Lateral acceleration acquisition unit224may calculate lateral acceleration ayby using measured values of physical amounts such as vehicle velocity V2and steering angle δ, without performing measurement using a lateral acceleration sensor. Steering angle acquisition unit225acquires steering angle δ of corresponding following vehicle2by performing measurement, for example, using a vehicle-mounted steering angle sensor and outputs information about steering angle δ.

Reception apparatus23receives, from the immediately preceding vehicle of corresponding following vehicle2, information about a velocity Vf of the immediately preceding vehicle (immediately preceding vehicle velocity) via inter-vehicle communication between following vehicle2and the immediately preceding vehicle in accordance with an instruction from vehicle control apparatus20. If following vehicle2is not the last vehicle in a convoy, first transmission apparatus24transmits the output information of vehicle velocity acquisition unit221and longitudinal acceleration acquisition unit222to the vehicle immediately behind following vehicle2via inter-vehicle communication between corresponding following vehicle2and the vehicle immediately behind following vehicle2(the following vehicle) in accordance with an instruction from vehicle control apparatus20. Second transmission apparatus25transmits, to lead vehicle1, information about maximum allowable vehicle velocity V2maxof corresponding following vehicle2calculated by vehicle control apparatus20via inter-vehicle communication between corresponding following vehicle2and lead vehicle1in accordance with an instruction from vehicle control apparatus20.

Drive apparatus26includes a drive source (an engine, an electric motor, or a combination thereof) that generates driving force for wheels of corresponding following vehicle2and a drive controller that controls the driving force based on an acceleration command from vehicle control apparatus20.

Brake apparatus27includes a brake mechanism (a friction brake, a drum brake, or the like) that applies braking force to wheels of corresponding following vehicle2, and a brake controller that controls the braking force based on a deceleration command from vehicle control apparatus20.

The microcomputer in vehicle control apparatus20includes a processor such as a central processing unit (CPU), a non-volatile memory such as a read-only memory (ROM), a volatile memory such as a random access memory (RAM), and an input-output port, which are connected to a bus. The same applies to various microcomputers, which will be described below.

The microcomputer in vehicle control apparatus20receives various kinds of information output from external information recognition apparatus21, vehicle state acquisition apparatus22, and reception apparatus23and outputs calculation results obtained based on various kinds of information to second transmission apparatus25, drive apparatus26, and brake apparatus27. Vehicle control apparatus20has two main functions, which are an inter-vehicle control unit201that causes corresponding following vehicle2to follow its immediately preceding vehicle while maintaining the inter-vehicle distance between corresponding following vehicle2and the immediately preceding vehicle at a target value and a maximum allowable vehicle velocity calculation unit202that calculates maximum allowable vehicle velocity V2maxthat satisfies the turning performance of corresponding following vehicle2at an individual driving location.

The individual functions of vehicle control apparatus20are realized by causing, in the microcomputer, the processor to read out a control program from the non-volatile memory to the volatile memory and to execute the control program. Alternatively, the functions of vehicle control apparatus20may be entirely or partly realized by hardware components. The same applies to various vehicle control apparatuses, which will be described below.

To maintain the inter-vehicle distance between corresponding following vehicle2and the immediately preceding vehicle at a target value during convoy driving, inter-vehicle control unit201outputs an acceleration command value Acomas an acceleration command to drive apparatus26, and outputs a deceleration command Dcomas a deceleration command to brake apparatus27. The target value of the inter-vehicle distance may be a constant value or a variable value. That is, the target value of the inter-vehicle distance may be changed as the driving state changes. For example, the target value of the inter-vehicle distance may be increased as the vehicle velocity increases. Inter-vehicle control unit201calculates acceleration command value Acomin accordance with the following mathematical equation (1), for example.

In mathematical equation (1), Δx denotes the difference between inter-vehicle distance d acquired based on the output information of external information recognition apparatus21and a target value d* of inter-vehicle distance d (Δx=d−d*). When inter-vehicle distance d is greater than target value d*, Δx is calculated as a positive value. When inter-vehicle distance d is less than target value d*, Δx is calculated as a negative value. In addition, Δv denotes the difference between immediately preceding vehicle velocity Vfacquired based on the output information of reception apparatus23and vehicle velocity V2of corresponding following vehicle2acquired based on the output information of vehicle velocity acquisition unit221(Δv=Vf−V2). When the immediately preceding vehicle velocity Vfis faster than vehicle velocity V2of corresponding following vehicle2, Δv is calculated as a positive value. When immediately preceding vehicle velocity Vfis slower than vehicle velocity V2of corresponding following vehicle2, Δv is calculated as a negative value.

In mathematical equation (1), axfdenotes the longitudinal acceleration of the immediately preceding vehicle acquired based on the output information of reception apparatus23. When the immediately preceding vehicle accelerates and immediately preceding vehicle velocity Vfincreases, axfis given as a positive value. When the immediately preceding vehicle decelerates and immediately preceding vehicle velocity Vfdecreases, axe is given as a negative value. In addition, Kx and Kv are positive gain constants, which are control constants stored in the non-volatile memory of the microcomputer.

When acceleration command value Acomcalculated in accordance with mathematical equation (1) is a positive value, inter-vehicle control unit201outputs acceleration command value Acomas an acceleration command to drive apparatus26. In contrast, when acceleration command value Acomcalculated in accordance with mathematical equation (1) is a negative value, inter-vehicle control unit201calculates deceleration command Dcomas Dcom=|Acom| and calculated outputs deceleration command Dcomas a deceleration command to brake apparatus27.

Other than mathematical equation (1), inter-vehicle control unit201may use a different mathematical equation for calculating acceleration command value Acom. For example, inter-vehicle control unit201may use a different mathematical equation as needed, depending on a control request. For example, inter-vehicle control unit201may use a mathematical equation including a derivative term or an integral term or may modify and use information about longitudinal acceleration axe or immediately preceding vehicle velocity Vfof the immediately preceding vehicle. Alternatively, inter-vehicle control unit201may use a mathematical equation that does not use these items of information.

Maximum allowable vehicle velocity calculation unit202calculates maximum allowable vehicle velocity V2maxbased on lateral acceleration limit aylimor yaw rate limit rlimused to set the turning performance of corresponding following vehicle2and a curvature κ2of the driving path on which corresponding following vehicle2is running.

Lateral acceleration limit aylimand yaw rate limit rlimcan be stored as fixed values in the non-volatile memory of the microcomputer. Alternatively, a vehicle user may specify any values as lateral acceleration limit aylimand yaw rate limit rlimby operating a switch or the like. For example, if lateral acceleration limit aylimor yaw rate limit rlimis defined to prevent slip, lateral acceleration limit aylimor yaw rate limit rlimmay be set changeably depending on the road conditions of the driving path. If lateral acceleration limit aylimor yaw rate limit rlimis defined to prevent collapsing of the freight, lateral acceleration limit aylimor yaw rate limit rlimmay be set changeably depending on the load weight or load height.

In accordance with the following mathematical equation (2), maximum allowable vehicle velocity V2maxis calculated as the square root of a value obtained by dividing lateral acceleration limit aylimby curvature κ2. Alternatively, in accordance with the following mathematical equation (3), maximum allowable vehicle velocity V2maxmay be calculated as a value obtained by dividing yaw rate limit rlimby curvature κ2.

Curvature κ2of the driving path on which following vehicle2is running is calculated by suitably assigning physical amounts indicating the vehicle state at an actual driving location of following vehicle2to any one of various relational expressions indicating basic motion characteristics of following vehicle2. Examples of the physical amounts include vehicle velocity V2, lateral acceleration ay, yaw rate r, and steering angle δ of following vehicle2. For example, if vehicle velocity V2and lateral acceleration ayof following vehicle2at the driving location of following vehicle2have already been acquired, curvature κ2can be calculated as a value obtained by dividing lateral acceleration ayby the square of vehicle velocity V2(κ2=ay/V22). If vehicle velocity V2and yaw rate r of following vehicle2at the driving location of following vehicle2have already been acquired, curvature κ2can be calculated as a value obtained by dividing yaw rate r by vehicle velocity V2(κ2=r/V2). In addition, if vehicle velocity V2and steering angle δ of following vehicle2at the driving location of following vehicle2have already been acquired, and a stability factor A and a wheelbase L that are constants unique to following vehicle2are known, curvature κ2can be calculated in accordance with a relational expression (κ2=δ/(1+A×V22)×L).

Maximum allowable vehicle velocity calculation unit202may calculate maximum allowable vehicle velocity V2maxby using yaw rate r or lateral acceleration ayacquired at the driving location of following vehicle2, instead of using curvature κ2of the driving path on which following vehicle2is running. Specifically, maximum allowable vehicle velocity calculation unit202may calculate maximum allowable vehicle velocity V2maxas a value obtained by dividing lateral acceleration limit aylimby yaw rate r in accordance with the following mathematical equation (4) or as a value obtained by dividing lateral acceleration ayby yaw rate limit rlimin accordance with the following mathematical equation (5).

Vehicle control apparatus20of following vehicle2may use a different method for calculating maximum allowable vehicle velocity V2maxas necessary, depending on a specific configuration of vehicle state acquisition apparatus22of following vehicle2. After maximum allowable vehicle velocity calculation unit202outputs information about maximum allowable vehicle velocity V2maxcalculated thereby from vehicle control apparatus20to second transmission apparatus25, second transmission apparatus25transmits the information to lead vehicle1.

Another Example of Adaptive Cruise Control System of the Following Vehicle

FIG.5is a schematic diagram illustrating another example of the adaptive cruise control system of the following vehicle. InFIG.5, lead vehicle1is on a straight path after passing through a curve, and a certain following vehicle2is on a straight path before entering the curve. In the above adaptive cruise control system, following vehicle2calculates maximum allowable vehicle velocity V2maxthat satisfies its turning performance on the straight path on which following vehicle2is actually running. However, in this example, as illustrated inFIG.5, following vehicle2calculates its maximum allowable vehicle velocity V2maxthat satisfies its turning performance on the curve on which following vehicle2is about to enter. That is, following vehicle2calculates its maximum allowable vehicle velocity V2max(=u2) based on curvature (forward curvature) κ2estof the curve into which following vehicle2is about to enter and its turning performance. In addition, when lead vehicle1sets vehicle velocity limit V1max, lead vehicle1uses maximum allowable vehicle velocity V2max(=u2). In this way, since lead vehicle1can reduce velocity limit V1maxbefore following vehicle2enters the curve, and the lateral acceleration generated on the curve on which following vehicle2is about to enter is reduced more reliably.

Specifically, vehicle control apparatus20of following vehicle2calculates its maximum allowable vehicle velocity V2maxby assigning lateral acceleration limit aylimand forward curvature κ2estin place of curvature κ2to mathematical equation (2) or by assigning yaw rate limit rlimand forward curvature κ2estin place of curvature κ2to mathematical equation (3). Next, vehicle control apparatus20compares maximum allowable vehicle velocity V2maxcalculated based on forward curvature κ2estand the turning performance of following vehicle2with maximum allowable vehicle velocity V2maxthat satisfies the turning performance of following vehicle2at the driving location on which following vehicle2is actually running. As a result of the comparison, the vehicle control apparatus20transmits information about the lower one of maximum allowable vehicle velocities V2maxto lead vehicle1. When setting vehicle velocity limit V1max, lead vehicle1uses the lower maximum allowable vehicle velocity V2max.

Forward curvature κ2estcan be estimated based on external information recognized by external information recognition apparatus21. For example, if external information recognition apparatus21is configured to recognize road demarcation lines (white lines) by processing its camera images, forward curvature κ2estcan be estimated from the recognized road demarcation lines. If external information recognition apparatus21can acquire a relative location and a relative angle, in addition to inter-vehicle distance d between corresponding following vehicle2and the immediately preceding vehicle thereof, by processing its camera images, forward curvature κ2estcan be estimated based on a curve obtained by interpolation as the driving path of the immediately preceding vehicle from the acquired data. In another example, from the acquired data, a line extending in the front-back direction of corresponding following vehicle2and a line extending in the front-back direction of the immediately preceding vehicle on a two-dimensional plane are determined, and forward curvature κ2estcan be estimated based on a curve that is into contact with these lines and that connects corresponding following vehicle2and the immediately preceding vehicle without an inflection point.

In addition, forward curvature κ2estcan be estimated by determining the road shape of the forward driving path from map information. For example, if following vehicle2can acquire its vehicle location from a global positioning system (GPS), a locator, or the like, forward curvature κ2estcan be estimated by reading out map information about the acquired vehicle location from a map information database and determining the road shape of the forward driving path.

In addition, forward curvature κ2estcan be estimated by acquiring past records of the vehicle state of the immediately preceding vehicle. For example, reception apparatus23of corresponding following vehicle2receives physical amounts (longitudinal acceleration ax, lateral acceleration ay, yaw rate r, vehicle velocity V2, etc.) relating to the vehicle state acquired by vehicle state acquisition apparatus22of the immediately preceding vehicle of corresponding following vehicle2, and the driving path of the immediately preceding vehicle can be estimated by performing dead reckoning using integral values of these physical amounts. Corresponding following vehicle2can estimate forward curvature κ2estbased on the estimated driving path. Alternatively, if the immediately preceding vehicle is configured to acquire and transmit its own vehicle location, corresponding following vehicle2can estimate the driving path from past records of the vehicle location of the immediately preceding vehicle and can estimate forward curvature κ2estbased on this estimated driving path.

Adaptive Cruise Control System of the Lead Vehicle

FIG.6illustrates an example of an adaptive cruise control system mounted on the lead vehicle. The adaptive cruise control system mounted on lead vehicle1includes a vehicle control apparatus10as a main component including a microcomputer as a control unit. The adaptive cruise control system also includes a vehicle state acquisition apparatus11, a reception apparatus12, an accelerator operation unit13, a brake operation unit14, a drive apparatus15, and a brake apparatus16. Vehicle state acquisition apparatus11includes a vehicle velocity acquisition unit111. Since vehicle velocity acquisition unit111is configured in the same way as vehicle velocity acquisition unit221of following vehicle2, description thereof will be omitted.

Reception apparatus12receives information about maximum allowable vehicle velocities V2max(1) to V2max(n) from following vehicles2via inter-vehicle communication with following vehicles2and outputs the information to vehicle control apparatus10, and n is an integer (a natural number) or 1 or greater for indicating identification numbers of following vehicles2. For example, identification numbers are allocated to following vehicles2following lead vehicle1in ascending order via inter-vehicle communication.

Accelerator operation unit13is a mechanism (for example, an accelerator pedal) that receives an acceleration operation amount (for example, an accelerator position) allowing the vehicle user to accelerate lead vehicle1and includes an acceleration operation amount sensor (not illustrated) that detects the acceleration operation amount and that outputs information about the acceleration operation amount. The acceleration operation amount is a positive value, and the vehicle velocity of lead vehicle1increases as the acceleration operation amount increases.

Brake operation unit14is a mechanism (for example, a brake pedal) that receives a brake operation amount (for example, a brake position) for allowing the vehicle user to decelerate lead vehicle1and includes a brake operation amount sensor (not illustrated) that detects the brake operation amount and that outputs information about the brake operation amount. The brake operation amount is a positive value, and the vehicle velocity of lead vehicle1decreases as the brake operation amount increases.

Drive apparatus15includes a drive source (an engine, an electric motor, or a combination thereof) that generates driving force for wheels of lead vehicle1, and a drive controller that controls the driving force based on a control command from vehicle control apparatus10. Vehicle control apparatus10outputs, to drive apparatus15, a normal acceleration command or a limited acceleration command as a control command.

Brake apparatus16includes a brake mechanism (a friction brake, a drum brake, or the like) that applies braking force to wheels of lead vehicle1and a brake controller that controls the braking force based on a control command output from vehicle control apparatus10. The vehicle control apparatus10outputs, to brake apparatus16, a normal deceleration command or a forced deceleration command as a control command.

The microcomputer of vehicle control apparatus10receives various kinds of information output from vehicle velocity acquisition unit111, reception apparatus12, accelerator operation unit13, and brake operation unit14and outputs calculation results obtained based on various kinds of information as control commands to drive apparatus15and brake apparatus16. Vehicle control apparatus10has two main functions, which are a vehicle velocity limit setting unit101and a vehicle velocity control unit102.

Vehicle velocity limit setting unit101acquires maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number) of following vehicles2from the output information of reception apparatus12and sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2max(1) to V2max(n). Specifically, if there is only one following vehicle2, vehicle velocity limit setting unit101sets maximum allowable vehicle velocity V2max(1) as vehicle velocity limit V1max. If there are a plurality of following vehicles2, vehicle velocity limit setting unit101sets the lowest one of maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number of 2 or more) as vehicle velocity limit V1max.

Vehicle velocity control unit102acquires vehicle velocity V1, the acceleration operation amount, and the brake operation amount from the output information of vehicle velocity acquisition unit111, accelerator operation unit13, and brake operation unit14and outputs control commands generated based on the acceleration operation amount, vehicle velocity V1, vehicle velocity limit V1max, and the brake operation amount to drive apparatus15and brake apparatus16. Vehicle velocity control unit102performs vehicle velocity control in this way.

Basically, vehicle velocity control unit102outputs a normal acceleration command generated based on an acceleration operation amount associated with an acceleration request from the vehicle user to drive apparatus15as a control command. However, when velocity V1exceeds a predetermined vehicle velocity V1dless than vehicle velocity limit V1max, vehicle velocity control unit102generates a limited acceleration command based on a corrected acceleration operation amount that is less than the acceleration operation amount, to limit the acceleration of lead vehicle1. Next, vehicle velocity control unit102outputs this limited acceleration command to drive apparatus15as a control command. Specifically, if vehicle velocity V1is between vehicle velocity limit V1maxand predetermined vehicle velocity V1d, vehicle velocity control unit102reduces the acceleration operation amount to a value within a range in which lead vehicle1can be accelerated. Vehicle velocity control unit102may perform greater reduction from the acceleration operation amount to the corrected acceleration operation amount when the difference (=V1max−V1) between vehicle velocity limit V1maxand vehicle velocity V1is less. If vehicle velocity V1is over vehicle velocity limit V1max, vehicle velocity control unit102reduces the acceleration operation amount to a value that does not substantially accelerate lead vehicle1(for example, 0).

In the case of vehicle control apparatus10, predetermined vehicle velocity V1dmay be set variably depending on the acceleration operation amount. For example, as the acceleration operation amount increases (that is, as the longitudinal acceleration increases), predetermined vehicle velocity V1dmay be separated further from vehicle velocity limit V1max. In the case of vehicle control apparatus10, even when vehicle velocity V1is over predetermined vehicle velocity V1d, if no acceleration operation amount is input, or if the acceleration operation amount is not a value indicating an acceleration request from the vehicle user, outputting of the limited acceleration command can be omitted.

In addition, basically, vehicle velocity control unit102outputs a normal deceleration command generated based on a brake operation amount associated with a brake request from the vehicle user to brake apparatus16as a control command. However, if vehicle velocity V1exceeds vehicle velocity limit V1max, vehicle velocity control unit102outputs the forced deceleration command as a control command to brake apparatus16for forcibly decelerating lead vehicle1, so as to reduce vehicle velocity V1to vehicle velocity limit V1maxor less. The brake operation amount, when the forced deceleration command is output, may be set as a fixed value or a value that varies depending on the excess of vehicle velocity V1from vehicle velocity limit V1max.

There is a case in which the vehicle user generates a brake request while a forced deceleration command is being output. That is, there may be a situation in which a brake operation amount acquired from the output information of brake operation unit14of vehicle control apparatus10indicates a value indicating a brake request given by the vehicle user. In this situation, if vehicle velocity control unit102predicts that the change by the deceleration of lead vehicle1based on the brake operation in accordance with the normal deceleration command will be greater than the change by the deceleration of lead vehicle1based on the brake operation in accordance with the forced deceleration command, vehicle velocity control unit102outputs the normal deceleration command to brake apparatus16as a control command. In contrast, if vehicle velocity control unit102predicts that the change by the deceleration of lead vehicle1based on the brake operation in accordance with the normal deceleration command will be less than the change by the deceleration of lead vehicle1based on the brake operation in accordance with the forced deceleration command, vehicle velocity control unit102continues to output the forced deceleration command to the brake apparatus16as a control command.

The prediction of whether the change by the deceleration based on the brake operation in accordance with the normal deceleration command will be greater than the change by the deceleration based on the brake operation in accordance with the forced deceleration command can be performed as follows. For example, vehicle velocity control unit102can predict which one of the changes will be greater by comparing the brake operation amount that outputs the forced deceleration command with the brake operation amount acquired from the output information of brake operation unit14.

If vehicle velocity control unit102determines that the change by the deceleration based on the brake operation in accordance with the forced deceleration command is the same as the change by the deceleration based on the brake operation in accordance with the normal deceleration command, vehicle velocity control unit102may output either the forced deceleration command or the normal deceleration command as a control command.

Main Part of Control Processing Performed by the Following Vehicle

FIG.7illustrates a part of an example of processing that realizes maximum allowable vehicle velocity calculation unit202of the vehicle control apparatus of a following vehicle, the processing being included in the control processing repeatedly performed when the ignition switch of the following vehicle is turned on.

In step S1001(which is abbreviated “S1001” inFIG.7, and the same abbreviation will also apply to the following flowcharts), vehicle control apparatus20of following vehicle2calculates maximum allowable vehicle velocity V2maxthat satisfies the turning performance of following vehicle2. Specific methods for calculating maximum allowable vehicle velocity V2maxhave already been described in the above description of the adaptive cruise control system of following vehicle2and another example thereof.

In step S1002, vehicle control apparatus20of following vehicle2instructs second transmission apparatus25to transmit information about calculated maximum allowable vehicle velocity V2maxto lead vehicle1.

Main Part of Control Processing Performed by the Lead Vehicle

FIG.8illustrates a part of an example of processing that realizes vehicle velocity limit setting unit101and vehicle velocity control unit102of the vehicle control apparatus of a lead vehicle, the processing being included in the control processing repeatedly performed when the ignition switch of the lead vehicle is turned on.

In step S2001, vehicle control apparatus10of lead vehicle1instructs reception apparatus12to receive information about maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number) from following vehicles2.

In step S2002, vehicle control apparatus10of lead vehicle1sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number) of following vehicles2acquired from the output information of reception apparatus12.

In step S2003, vehicle control apparatus10of lead vehicle1determines whether vehicle velocity V1is greater than vehicle velocity limit V1max. If vehicle control apparatus10of lead vehicle1determines that vehicle velocity V1is greater than vehicle velocity limit V1max(YES in step S2003), the processing proceeds to step S2004. However, if vehicle control apparatus10of lead vehicle1determines that vehicle velocity V1is less than or equal to vehicle velocity limit V1max(NO in step S2003), the processing proceeds to step S2007.

In step S2004, vehicle control apparatus10of lead vehicle1outputs a limited acceleration command to drive apparatus15. As described above, the limited acceleration command is generated based on a corrected acceleration operation amount obtained by reducing the acceleration operation amount associated with the acceleration request from the vehicle user to a value that does not substantially accelerate lead vehicle1.

In step S2005, vehicle control apparatus10of lead vehicle1outputs a forced deceleration command to brake apparatus16. In step S2006, vehicle control apparatus10of lead vehicle1determines whether outputting the forced deceleration command is appropriate. A specific processing content of this determination of whether outputting the forced deceleration command is appropriate will be described below.

In step S2007, vehicle control apparatus10of lead vehicle1determines whether vehicle velocity V1is greater than predetermined vehicle velocity V1d. If vehicle control apparatus10of lead vehicle1determines that vehicle velocity V1is greater than predetermined vehicle velocity V1d(YES in step S2007), the processing proceeds to step S2008. However, if vehicle control apparatus10of lead vehicle1determines that vehicle velocity V1is less than or equal to predetermined vehicle velocity V1d(NO in step S2007), vehicle control apparatus10ends the present control processing without limiting vehicle velocity V1.

In step S2008, vehicle control apparatus10of lead vehicle1outputs a limited acceleration command to drive apparatus15. Unlike the limited acceleration command output in step S2004, as described above, the limited acceleration command output in this step is generated based on a corrected acceleration operation amount obtained by reducing the acceleration operation amount associated with the acceleration request from the vehicle user to a value within a range in which lead vehicle1can be accelerated.

Determination of Whether Outputting Forced Deceleration Command is Appropriate

FIG.9is a subroutine illustrating an example of the determination of whether outputting the forced deceleration command is appropriate in step S2006included in the control processing inFIG.8performed by the vehicle control apparatus of the lead vehicle.

In step S3001, vehicle control apparatus10of lead vehicle1determines whether there is a brake request from the vehicle user. As described above, whether there is a brake request from the vehicle user can be determined based on the value of a brake operation amount acquired from the output information of brake operation unit14.

In step S3002, vehicle control apparatus10of lead vehicle1determines whether the change by the deceleration of lead vehicle1based on the brake operation in accordance with the normal deceleration command is greater than the change by the deceleration of lead vehicle1based on the brake operation in accordance with the forced deceleration command. If vehicle control apparatus10of lead vehicle1determines that the change by the deceleration of lead vehicle1based on the brake operation in accordance with the normal deceleration command is greater than the change by the deceleration of lead vehicle1based on the brake operation in accordance with the forced deceleration command (YES in step S3002), vehicle control apparatus10determines that outputting the forced deceleration command is not appropriate, and the processing proceeds to step S3003. In contrast, if vehicle control apparatus10of lead vehicle1determines that the change by the deceleration of lead vehicle1based on the brake operation in accordance with the normal deceleration command is not greater than the change by the deceleration of lead vehicle1based on the brake operation in accordance with the forced deceleration command (NO in step S3002), vehicle control apparatus10determines that outputting of the forced deceleration command is appropriate and ends the present subroutine by skipping step S3003.

In step S3003, vehicle control apparatus10of lead vehicle1generates the normal deceleration command based on the brake operation amount acquired from the output information of brake operation unit14and outputs the normal deceleration command, instead of the forced deceleration command, to brake apparatus16as a control command.

As described above, in the adaptive cruise control system according to the first example, each following vehicle2calculates its maximum allowable vehicle velocity V2maxthat satisfies its turning performance, and lead vehicle1calculates vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2maxtransmitted from following vehicles2and performs vehicle velocity control such that vehicle velocity V1will not exceed vehicle velocity limit V1max. In this way, following vehicle2running on a curve is prevented from experiencing excessively large lateral acceleration that causes at least one of deteriorated ride quality, slipping, and freight collapsing.

Second Example

Outline of Adaptive Cruise Control System

Hereinafter, an outline of an adaptive cruise control system according to a second example will be described with reference toFIG.10. The present example will focus on the difference from the first example. The same components in the first and second examples will be denoted by the same reference numerals, and description thereof will be omitted or simplified.

FIG.10illustrates an example of the driving state of a convoy including three following vehicles in the adaptive cruise control system. InFIG.10, first following vehicle2A, second following vehicle2B, and third following vehicle2C are non-mechanically connected to lead vehicle1sequentially, and each of following vehicles2A to2C follows its immediately preceding vehicle. In the above adaptive cruise control system, each of the following vehicles2A to2C calculates its maximum allowable vehicle velocity V2maxthat satisfies its turning performance on its driving path on which the corresponding following vehicle is actually running or is about to run. However, in the present example, lead vehicle1calculates, for the following vehicles, maximum allowable vehicle velocities V2maxthat satisfy their respective turning performances on the driving path in the convoy section from lead vehicle1to third following vehicle2C, of the entire driving path that lead vehicle1has already passed (driven path).

Specifically, lead vehicle1calculates the curvature of the driving path on which lead vehicle1is running while sequentially storing the curvature and determines a maximum curvature κmaxon the driving path in the convoy section of the entire driven path. Next, lead vehicle1calculates maximum allowable vehicle velocity V2maxfor each of the following vehicles based on maximum curvature κmaxand the turning performances of following vehicles2A to2C. Next, lead vehicle1sets the lowest one of calculated maximum allowable vehicle velocities V2maxof following vehicles2A to2C as vehicle velocity limit V1maxand performs vehicle velocity control such that the vehicle velocity will not exceed vehicle velocity limit V1max. Although not illustrated, when only one following vehicle2A follows lead vehicle1, lead vehicle1sets maximum allowable vehicle velocity V2maxcalculated based on maximum curvature κmax1and the turning performance of following vehicle2A as vehicle velocity limit V1max.

Adaptive Cruise Control System of the Following Vehicle

FIG.11illustrates an example of an adaptive cruise control system mounted on a following vehicle. The adaptive cruise control system mounted on following vehicle2includes a vehicle control apparatus20aas a main component, external information recognition apparatus21, a vehicle state acquisition apparatus22a, reception apparatus23, first transmission apparatus24, second transmission apparatus25, drive apparatus26, and brake apparatus27.

While vehicle control apparatus20aincludes a microcomputer as a control unit and inter-vehicle control unit201described above as a main function, vehicle control apparatus20adoes not include maximum allowable vehicle velocity calculation unit202. In addition, vehicle control apparatus20ainstructs second transmission apparatus25to transmit, instead of information about maximum allowable vehicle velocity V2max, information about inter-vehicle distance d output from external information recognition apparatus21to lead vehicle1.

While vehicle state acquisition apparatus22aincludes longitudinal acceleration acquisition unit222and vehicle velocity acquisition unit221necessary for vehicle velocity control, vehicle state acquisition apparatus22adoes not include yaw rate acquisition unit223, lateral acceleration acquisition unit224, and steering angle acquisition unit225necessary for calculating maximum allowable vehicle velocity V2max.

Adaptive Cruise Control System of the Lead Vehicle

FIG.12illustrates an example of an adaptive cruise control system mounted on the lead vehicle. The adaptive cruise control system mounted on lead vehicle1includes a vehicle control apparatus10aas a main component including a microcomputer as a control unit. The adaptive cruise control system also includes a vehicle state acquisition apparatus11a, reception apparatus12, accelerator operation unit13, brake operation unit14, drive apparatus15, and brake apparatus16. In addition to vehicle velocity acquisition unit111, vehicle state acquisition apparatus11aincludes a yaw rate acquisition unit112, a lateral acceleration acquisition unit113, and a steering angle acquisition unit114.

Because yaw rate acquisition unit112, lateral acceleration acquisition unit113, and steering angle acquisition unit114are configured in the same way as yaw rate acquisition unit223, lateral acceleration acquisition unit224, and steering angle acquisition unit225of following vehicle2according to the first example, description thereof will be omitted.

The microcomputer of vehicle control apparatus10areceives various kinds of information output from vehicle state acquisition apparatus11a, reception apparatus12, accelerator operation unit13, and brake operation unit14and outputs calculation results obtained based on various kinds of information to drive apparatus15and brake apparatus16as control commands.

In addition to the two main functions which vehicle velocity limit setting unit101and vehicle velocity control unit102have as described above, vehicle control apparatus10ahas another main function of acquiring information necessary for setting vehicle velocity limit V1max. This function is realized by five units of a driving distance acquisition unit103, a driving path information acquisition unit104, a driven path information storage unit105, a convoy length estimation unit106, and a maximum allowable vehicle velocity calculation unit107.

Driving distance acquisition unit103acquires vehicle velocity V1from the output information of vehicle velocity acquisition unit111and acquires driving distance B of lead vehicle1based on vehicle velocity V1. For example, driving distance B of lead vehicle1can be acquired by multiplying vehicle velocity V1acquired per control cycle of the microcomputer of vehicle control apparatus10aby control cycle time and by adding up the calculated products.

Driving path information acquisition unit104acquires physical amounts indicating the vehicle state at an actual driving location of lead vehicle1from the output information of vehicle state acquisition apparatus11aand acquires, based on these physical amounts, information about the shape of the driving path at the actual driving location of lead vehicle1(driving path information).

Examples of the driving path information include a curvature κ1of the driving path at the driving location of lead vehicle1. Curvature κ1is calculated by suitably assigning vehicle velocity V1, lateral acceleration ay, yaw rate r, and steering angle δ to any one of various relational expressions indicating basic motion characteristics of lead vehicle1. Because these various relational expressions indicating basic motion characteristics of lead vehicle1are the same as those used for calculating curvature κ2of the driving path on which following vehicle2is running according to the first example, description thereof will be omitted. Regarding various relational expressions that lead vehicle1uses to calculate curvature κ1, a suitable relational expression may be selected depending on which acquisition units are included in vehicle state acquisition apparatus11aof lead vehicle1.

For example, there are cases in which there is only one following vehicle2, the convoy section is relatively short, or lead vehicle1has run at a constant velocity on the driving path in the convoy section. In any one of these cases, it can be assumed that the vehicle velocity of lead vehicle1has not changed much from the location of following vehicle2at the end of the convoy to the location of lead vehicle1and that the vehicle velocity of lead vehicle1has been constant on the driving path in the convoy section. Thus, in these cases, it is reasonable to say that the individual values of the yaw rate, the lateral acceleration, and the steering angle acquired on the driving path in the convoy section indirectly indicate curvature κ1on the driving path in the convoy section. Thus, when the vehicle velocity of lead vehicle1can be regarded as being constant on the driving path in the convoy section, yaw rate r or lateral acceleration ayacquired by vehicle state acquisition unit11amay be acquired as the driving path information, instead of curvature κ1.

Each time that driven path information storage unit105acquires driving distance B and driving path information, driven path information storage unit105associates driving distance B with the driving path information and stores the associated information as driven path information in the volatile memory or the like of the microcomputer. The driven path information is information about the shape of the driving path on which lead vehicle1has already run.

Convoy length estimation unit106estimates a convoy length C corresponding to the length of the convoy section based on inter-vehicle distances d(1) to d(n) (n is a natural number) acquired from the output information of reception apparatus12. As described above, n is a natural number for indicating identification numbers of following vehicles2. Specifically, while convoy length estimation unit106estimates convoy length C based on a sum of inter-vehicle distances d(1) to d(n) (n is a natural number), if the vehicle length of following vehicle2is known, this vehicle length may be added to convoy length C.

Maximum allowable vehicle velocity calculation unit107sets maximum allowable vehicle velocity V2maxas follows, based on driving distance B acquired by driving distance acquisition unit103, the driven path information stored in driven path information storage unit105, and convoy length C estimated by convoy length estimation unit106.

First, maximum allowable vehicle velocity calculation unit107subtracts convoy length C from driving distance B of lead vehicle1and determines a driving distance Bendof lead vehicle1, driving distance Bendcorresponding to the driving location of the last vehicle in the convoy. Next, maximum allowable vehicle velocity calculation unit107refers to the driven path information and determines maximum curvature κmaxon the driving path in the convoy section from curvatures κ1from driving distance B to driving distance Bend. To save memory resources, of all the driven path information stored in the volatile memory or the like, driven path information less than driving distance Bendmay be deleted.

Next, maximum allowable vehicle velocity calculation unit107calculates maximum allowable vehicle velocity V2maxfor each of following vehicles2based on maximum curvature κmaxand the turning performance of corresponding following vehicles2. Maximum allowable vehicle velocity calculation unit107may calculate maximum allowable vehicle velocity V2maxby replacing curvature κ2in mathematical equation (2) or mathematical equation (3) by maximum curvature κmax. That is, maximum allowable vehicle velocity calculation unit107may calculate maximum allowable vehicle velocity V2maxas the square root of a value obtained by dividing lateral acceleration limit aylimby maximum curvature κmaxor a value obtained by dividing yaw rate limit rlimby maximum curvature κmax. If a plurality of following vehicles2have the same turning performance, maximum allowable vehicle velocity calculation unit107may calculate maximum allowable vehicle velocity V2maxfor only one following vehicle2, without calculating maximum allowable vehicle velocity V2maxfor each following vehicle2.

If driving path information acquisition unit104has acquired yaw rate r or lateral acceleration ayas the driving path information, maximum allowable vehicle velocity calculation unit107refers to the driven path information and determines the maximum value of yaw rate r or lateral acceleration ayon the driving path in the convoy section. This is because it is conceivable, when yaw rate r or lateral acceleration ayon the driving path in the convoy section reaches its maximum value, the curvature on the driving path in the convoy section reaches maximum curvature κmax. Next, maximum allowable vehicle velocity calculation unit107assigns the maximum value of yaw rate r to mathematical equation (4) or the maximum value of lateral acceleration ayto mathematical equation (5), to calculate maximum allowable vehicle velocity V2maxfor each following vehicle2.

Vehicle velocity limit setting unit101sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number) of following vehicles2calculated by maximum allowable vehicle velocity calculation unit107. Specifically, if there is only one following vehicle2, vehicle velocity limit setting unit101sets maximum allowable vehicle velocity V2max(1) as vehicle velocity limit V1max. If there are a plurality of following vehicles2, vehicle velocity limit setting unit101sets the lowest one of maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number of 2 or greater) as vehicle velocity limit V1max.

Vehicle velocity control unit102acquires vehicle velocity V1, the acceleration operation amount, and the brake operation amount from the output information of vehicle velocity acquisition unit111, accelerator operation unit13, and brake operation unit14and outputs control commands generated based on the acceleration operation amount, vehicle velocity V1, vehicle velocity limit V1max, and the brake operation amount to drive apparatus15and brake apparatus16. Vehicle velocity control unit102performs vehicle velocity control in this way. Since other specific contents about vehicle velocity control unit102are the same as those according to the first example, description thereof will be omitted.

Main Part of Control Processing Performed by the Following Vehicle

FIG.13illustrates a part of an example of a main part of the control processing repeatedly performed by the vehicle control apparatus of a following vehicle when the ignition switch of the following vehicle is turned on. The processing that realizes inter-vehicle control unit201, the processing being included in the main part, is not included in this example.

In step S4001, vehicle control apparatus20aof following vehicle2acquires inter-vehicle distance d from its immediately preceding vehicle from the output information of external information recognition apparatus21.

In step S4002, vehicle control apparatus20aof following vehicle2instructs second transmission apparatus25to transmit information about inter-vehicle distance d to lead vehicle1.

Main Part of Control Processing Performed by the Lead Vehicle

FIG.14illustrates a part of an example of processing that realizes the above main functions of all the control processing repeatedly performed by the vehicle control apparatus of a lead vehicle when the ignition switch of the lead vehicle is turned on.

In step S5001, vehicle control apparatus10aof lead vehicle1acquires vehicle velocity V1from the output information of vehicle velocity acquisition unit111and calculates driving distance B based on vehicle velocity V1.

In step S5002, vehicle control apparatus10aof lead vehicle1acquires physical amounts indicating the vehicle state at its actual driving location from the output information of vehicle state acquisition apparatus11aand acquires driving path information (for example, curvature κ1) from the physical amounts. Step S5002may be performed before step S5001.

In step S5003, vehicle control apparatus10aof lead vehicle1associates the driving path information acquired in step S5002with driving distance B acquired in step S5001and stores the associated information in the volatile memory or the like of the microcomputer as driven path information.

In step S5004, vehicle control apparatus10aof lead vehicle1estimates convoy length C based on inter-vehicle distances d(1) to d(n) (n is a natural number) acquired from the output information of reception apparatus12. Step S5004may be performed before step S5003.

In step S5005, vehicle control apparatus10aof lead vehicle1calculates maximum allowable vehicle velocities V2maxbased on driving distance B acquired in step S5001, convoy length C estimated in step S5002, and driven path information stored in step S5003. Since specific methods for calculating maximum allowable vehicle velocity V2maxare the same are those described with maximum allowable vehicle velocity calculation unit107, description thereof will be omitted.

In step S5006, vehicle control apparatus10aof lead vehicle1sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2max(1) to V2max(n) (n is a natural number) of following vehicles2calculated in step S5005. Since steps S5007to S5012are the same as steps S2003to S2008, description thereof will be omitted.

As described above, while each following vehicle2measures inter-vehicle distance d from its immediately preceding vehicle so that lead vehicle1can estimate convoy length C, inter-vehicle distance d may be measured in a different way. For example, if there is only one following vehicle2, lead vehicle1can measure inter-vehicle distance d from following vehicle2by using a rear side recognition apparatus that can recognize objects behind lead vehicle1. In this way, following vehicle2does not need to transmit information about inter-vehicle distance d to lead vehicle1. If there are a plurality of following vehicles2, in addition to have lead vehicle1measure inter-vehicle distance d from the vehicle immediately following lead vehicle1by using a rear side recognition apparatus, each following vehicle2may measure inter-vehicle distance d from the vehicle immediately following this following vehicle2by using a rear side recognition apparatus equivalent to that of lead vehicle1. In this way, the last vehicle in the convoy does not need to transmit information about inter-vehicle distance d to lead vehicle1.

When the target value of the inter-vehicle distance in the inter-vehicle control unit of following vehicle2is a constant value and when actual convoy length C will not probably change by the inter-vehicle control, vehicle control apparatus10aof lead vehicle1may be configured without convoy length estimation unit106. In this case, maximum allowable vehicle velocity calculation unit107of vehicle control apparatus10aof lead vehicle1calculates maximum allowable vehicle velocity V2maxassuming that convoy length C is a known fixed value stored in advance in the non-volatile memory or the like of the microcomputer.

As described above, in the adaptive cruise control system according to the second example, lead vehicle1calculates maximum allowable vehicle velocities V2maxbased on maximum curvature κmaxof the driving path in the convoy section in the driven path and the turning performances of following vehicles2. Next, lead vehicle1sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2maxof following vehicles2and performs vehicle velocity control such that the vehicle velocity of lead vehicle1will not exceed vehicle velocity limit V1max. In this way, in addition to preventing following vehicle2on a curve from experiencing excessively large lateral acceleration that causes at least one of deteriorated ride quality, slipping, and freight collapsing, the following significant advantageous effects can be provided. That is, following vehicles2do not need to calculate maximum allowable vehicle velocities V2max. In addition, when the convoy length will not probably change, each following vehicle2does not need transmit information about inter-vehicle distance d. Thus, since following vehicle2has less processing load, calculation resources can be allocated to other control processing such inter-vehicle control processing.

As describe above, inFIG.12, maximum allowable vehicle velocity calculation unit107calculates maximum allowable vehicle velocities V2maxof following vehicles2and supplies calculated maximum allowable vehicle velocities V2maxto vehicle velocity limit setting unit101, which then calculates vehicle velocity limit V1max. However, alternatively, vehicle velocity limit V1maxmay directly be determined based on the driven path information stored in driven path information storage unit105.

Although the present invention has thus been described in detail with reference to preferable examples, the individual technical concepts described in the above first and second examples can be appropriately combined and used as long as there is no conflict. In addition, it is apparent to those skilled in the art that various types of modifications, as described below, are possible, based on the basic technical concept and teaching of the present invention.

In the above first and second examples, lead vehicle1sets vehicle velocity limit V1maxbased on maximum allowable vehicle velocities V2maxof following vehicles2and performs vehicle velocity control such that the vehicle velocity of lead vehicle1will not exceed vehicle velocity limit V1max. Alternatively, lead vehicle1may simply perform vehicle velocity control such that lead vehicle1does not accelerate when following vehicle2enters a curve. For example, when following vehicle2determines that following vehicle2has entered a curve based on the output information of yaw rate acquisition unit223, lateral acceleration acquisition unit224, or steering angle acquisition unit225, following vehicle2transmits a limitation request signal requesting lead vehicle1to limit the vehicle velocity of lead vehicle1. Upon receiving this limitation request signal, lead vehicle1performs vehicle velocity control that prevents acceleration of lead vehicle1. In this way, it is possible to reduce the risk that following vehicle2on a curve will experience excessively large lateral acceleration that causes at least one of deteriorated ride quality, slipping, and freight collapsing.

In the above first and second examples, the processing for determining whether outputting the forced deceleration command is appropriate is performed in a predetermined step in the control processing of lead vehicle1. However, alternatively, this determination processing may be performed as interrupt processing performed when a brake request is issued from the vehicle user while the forced deceleration command is being output.

In each of the above adaptive cruise control systems of following vehicles2, for convenience of description of the functions, three functions that perform inter-vehicle communication have been described. However, reception apparatus23, first transmission apparatus24, and second transmission apparatus25may be configured as a single communication apparatus.

In each of the above adaptive cruise control systems of lead vehicles1, vehicle velocity control unit102selects the normal acceleration command or the limited acceleration command and selects the normal deceleration command or the forced deceleration command. However, the drive controller of drive apparatus15may select the normal acceleration command from accelerator operation unit13or the limited acceleration command from vehicle velocity control unit102, and the brake controller of brake apparatus16may select the normal deceleration command from brake operation unit14or the forced deceleration command from vehicle velocity control unit102.

REFERENCE SYMBOL LIST

1lead vehicle10,10avehicle control apparatus12reception apparatus13accelerator operation unit14brake operation unit15drive apparatus16brake apparatus101vehicle velocity limit setting unit102vehicle velocity control unit103driving distance acquisition unit104driving path information acquisition unit105driven path information storage unit106convoy length estimation unit107maximum allowable vehicle velocity calculation unit111vehicle velocity acquisition unit112yaw rate acquisition unit113lateral acceleration acquisition unit114steering angle acquisition unit2,2A,2B,2C following vehicle20,20avehicle control apparatus21external information recognition apparatus25second transmission apparatus202maximum allowable vehicle velocity calculation unit221vehicle velocity acquisition unit223yaw rate acquisition unit224lateral acceleration acquisition unit225steering angle acquisition unitaylateral accelerationaylimlateral acceleration limitr yaw raterlimyaw rate limitV1vehicle velocity of lead vehicleV1dpredetermined vehicle velocityV1maxvehicle velocity limitV2maxmaximum allowable vehicle velocity of following vehicleκ1curvature at driving location of lead vehicleκmaxmaximum curvature of driving path in convoy sectionκ2curvature at driving location of following vehicleκ2estforward curvature of following vehicle