Patent Description:
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 <NUM>, 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.

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 control method, an adaptive cruise control system and a convoy of vehicles that prevent excessively large lateral acceleration that adaptive cruise control may cause in a following vehicle on a curve.

A control method for a convoy of vehicles, an adaptive cruise control system and a convoy of vehicles according to the present invention are defined in the independent claims <NUM>, <NUM> and <NUM>.

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

Hereinafter, examples of the present invention will be described in detail with reference to the accompanying drawings.

An outline of an adaptive cruise control system according to a first example will be described with reference to <FIG>. 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> illustrates a convoy formed by a plurality of vehicles in an adaptive cruise control system. The convoy in <FIG> includes a lead vehicle <NUM> that leads the convoy and a plurality of following vehicles <NUM> that run after lead vehicle <NUM>. Each following vehicle <NUM> follows its immediately preceding vehicle while maintaining a certain inter-vehicle distance from the immediately preceding vehicle.

<FIG> illustrates an example of the driving state of a convoy including only one following vehicle in the adaptive cruise control system. In <FIG>, lead vehicle <NUM> is on a straight path after passing through a curve, and following vehicle <NUM> is on the curve.

A turning performance unique to following vehicle <NUM> is previously set in following vehicle <NUM>, to prevent at least one of deteriorated ride quality, slipping, and freight collapsing. The turning performance of following vehicle <NUM> is set based on the upper limit of a lateral acceleration (lateral acceleration limit) aylim or the upper limit of a yaw rate (yaw rate limit) rlim. To satisfy this turning performance, for the velocity of the following vehicle <NUM>, an upper limit (maximum allowable vehicle velocity) V2max is set based on the driving path on which following vehicle <NUM> runs. Maximum allowable vehicle velocity V2max of following vehicle <NUM> is the velocity of following vehicle <NUM> when an actual lateral acceleration ay reaches lateral acceleration limit aylim. Alternatively, maximum allowable vehicle velocity V2max of following vehicle <NUM> is the velocity of following vehicle <NUM> when an actual yaw rate r reaches yaw rate limit rlim of following vehicle <NUM>.

When following vehicle <NUM> is 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 vehicle <NUM> increases than those when following vehicle <NUM> is on a driving path having a relatively small curvature. Thus, when following vehicle <NUM> is on a driving path having a relatively large curvature, the actual lateral acceleration and the actual yaw rate of following vehicle <NUM> reach lateral acceleration limit aylim and yaw rate limit rlim at a relatively low vehicle velocity. Thus, maximum allowable vehicle velocity V2max of following vehicle <NUM> on a driving path having a relatively large curvature is less than maximum allowable vehicle velocity V2max of following vehicle <NUM>, which is on a driving path that has a relatively small curvature (including a straight path).

Referring back to <FIG>, if lead vehicle <NUM> accelerates on a straight path after passing through the curve, the velocity (turning velocity) of following vehicle <NUM> following lead vehicle <NUM> also increases while maintaining a certain inter-vehicle distance therefrom on the curve. If the velocity of following vehicle <NUM> exceeds its maximum allowable vehicle velocity V2max on the curve, the actual lateral acceleration or the actual yaw rate of following vehicle <NUM> exceeds its upper limit aylim or rlim used to set the turning performance, possibly resulting in deteriorated ride quality, slipping, or freight collapsing.

Thus, following vehicle <NUM> calculates 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 vehicle <NUM> via inter-vehicle communication. Next, lead vehicle <NUM> sets a vehicle velocity limit V1max for 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 vehicle <NUM> does not exceed maximum allowable vehicle velocity V2max, and the actual lateral acceleration and the actual yaw rate of following vehicle <NUM> are maintained at or below their respective upper limits aylim and rlim used to set the turning performance.

<FIG> illustrates an example of the driving state of a convoy including three following vehicles in the adaptive cruise control system. In <FIG>, lead vehicle <NUM> and a first following vehicle 2A following lead vehicle <NUM> are on a straight path after passing through a curve. A second following vehicle 2B following first following vehicle 2A is on the curve, and a third following vehicle 2C following second following vehicle 2B 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 vehicles 2A to 2C calculates its maximum allowable vehicle velocity V2max based on its turning performance at its driving location and transmits information about maximum allowable vehicle velocity V2max to lead vehicle <NUM> via inter-vehicle communication. Specifically, first following vehicle 2A calculates its maximum allowable vehicle velocity V2max (= u1) on the straight path on which first following vehicle 2A is running and transmits information about maximum allowable vehicle velocity V2max (= u1) to lead vehicle <NUM>. Second following vehicle 2B calculates its maximum allowable vehicle velocity V2max (= u2) on the curve on which second following vehicle 2B is running and transmits information about maximum allowable vehicle velocity V2max (= u2) to lead vehicle <NUM>. Third following vehicle 2C calculates its maximum allowable vehicle velocity V2max (= u3) on the straight path on which second following vehicle 2C is running and transmits information about maximum allowable vehicle velocity V2max (= u3) to lead vehicle <NUM>.

Lead vehicle <NUM> sets the lowest one of maximum allowable vehicle velocities V2max of following vehicles 2A to 2C as vehicle velocity limit V1max. If following vehicles 2A to 2C have the same turning performance, maximum allowable vehicle velocity V2max (= u2) of second following vehicle 2B running on the curve is the lowest. Thus, lead vehicle <NUM> sets maximum allowable vehicle velocity V2max (= u2) of second following vehicle 2B as vehicle velocity limit V1max and performs vehicle velocity control such that the vehicle velocity of lead vehicle <NUM> will not exceed vehicle velocity limit V1max set as described above. In this way, the velocities of following vehicles 2A to 2C are maintained below their respective maximum allowable vehicle velocities V2max, and the actual lateral accelerations and the actual yaw rates of following vehicles 2A to 2C are maintained at their respective upper limits aylim and rlim or less used to set their respective turning performances. First to third following vehicles 2A to 2C may have mutually different turning performances.

In short, according to the first example, each of following vehicles <NUM> calculates its maximum allowable vehicle velocity V2max that satisfies its turning performance at its driving location, and lead vehicle <NUM> performs vehicle velocity control so that its vehicle velocity will not exceed vehicle velocity limit V1max set based on maximum allowable vehicle velocities V2max of following vehicles <NUM>.

<FIG> illustrates an example of an adaptive cruise control system mounted on a following vehicle. The adaptive cruise control system mounted on following vehicle <NUM> includes a vehicle control apparatus <NUM> as a main component including a microcomputer as a control unit. The adaptive cruise control system also includes an external information recognition apparatus <NUM>, a vehicle state acquisition apparatus <NUM>, a reception apparatus <NUM>, a first transmission apparatus <NUM>, a second transmission apparatus <NUM>, a drive apparatus <NUM>, and a brake apparatus <NUM>.

For example, external information recognition apparatus <NUM> recognizes objects present in front of corresponding following vehicle <NUM> by using a camera, a radar, a sonar, or the like. Specifically, external information recognition apparatus <NUM> measures an inter-vehicle distance d between corresponding following vehicle <NUM> and its immediately preceding vehicle and outputs information about inter-vehicle distance d.

Vehicle state acquisition apparatus <NUM> acquires the vehicle state of corresponding following vehicle <NUM> and includes a vehicle velocity acquisition unit <NUM>, a longitudinal acceleration acquisition unit <NUM>, a yaw rate acquisition unit <NUM>, a lateral acceleration acquisition unit <NUM>, and a steering angle acquisition unit <NUM>.

Vehicle velocity acquisition unit <NUM> acquires a vehicle velocity V2 of corresponding following vehicle <NUM> based 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 unit <NUM> acquires a longitudinal acceleration ax of corresponding following vehicle <NUM> by performing measurement using a vehicle-mounted longitudinal acceleration sensor and outputs information about longitudinal acceleration ax. Longitudinal acceleration acquisition unit <NUM> may calculate longitudinal acceleration ax based on change of vehicle velocity V2 acquired by vehicle velocity acquisition unit <NUM>.

Yaw rate acquisition unit <NUM> acquires yaw rate r of corresponding following vehicle <NUM> by performing measurement, for example, using a vehicle-mounted yaw rate sensor and outputs information about yaw rate r. Yaw rate acquisition unit <NUM> may calculate yaw rate r by using measured values of physical amounts such as vehicle velocity V2 and a steering angle δ, without performing measurement using a yaw rate sensor. Lateral acceleration acquisition unit <NUM> acquires lateral acceleration ay of corresponding following vehicle <NUM> by performing measurement, for example, using a vehicle-mounted lateral acceleration sensor and outputs information about lateral acceleration ay. Lateral acceleration acquisition unit <NUM> may calculate lateral acceleration ay by using measured values of physical amounts such as vehicle velocity V2 and steering angle δ, without performing measurement using a lateral acceleration sensor. Steering angle acquisition unit <NUM> acquires steering angle δ of corresponding following vehicle <NUM> by performing measurement, for example, using a vehicle-mounted steering angle sensor and outputs information about steering angle δ.

Reception apparatus <NUM> receives, from the immediately preceding vehicle of corresponding following vehicle <NUM>, information about a velocity Vf of the immediately preceding vehicle (immediately preceding vehicle velocity) via inter-vehicle communication between following vehicle <NUM> and the immediately preceding vehicle in accordance with an instruction from vehicle control apparatus <NUM>. If following vehicle <NUM> is not the last vehicle in a convoy, first transmission apparatus <NUM> transmits the output information of vehicle velocity acquisition unit <NUM> and longitudinal acceleration acquisition unit <NUM> to the vehicle immediately behind following vehicle <NUM> via inter-vehicle communication between corresponding following vehicle <NUM> and the vehicle immediately behind following vehicle <NUM> (the following vehicle) in accordance with an instruction from vehicle control apparatus <NUM>. Second transmission apparatus <NUM> transmits, to lead vehicle <NUM>, information about maximum allowable vehicle velocity V2max of corresponding following vehicle <NUM> calculated by vehicle control apparatus <NUM> via inter-vehicle communication between corresponding following vehicle <NUM> and lead vehicle <NUM> in accordance with an instruction from vehicle control apparatus <NUM>.

Drive apparatus <NUM> includes a drive source (an engine, an electric motor, or a combination thereof) that generates driving force for wheels of corresponding following vehicle <NUM> and a drive controller that controls the driving force based on an acceleration command from vehicle control apparatus <NUM>.

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

The microcomputer in vehicle control apparatus <NUM> includes 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 apparatus <NUM> receives various kinds of information output from external information recognition apparatus <NUM>, vehicle state acquisition apparatus <NUM>, and reception apparatus <NUM> and outputs calculation results obtained based on various kinds of information to second transmission apparatus <NUM>, drive apparatus <NUM>, and brake apparatus <NUM>. Vehicle control apparatus <NUM> has two main functions, which are an inter-vehicle control unit <NUM> that causes corresponding following vehicle <NUM> to follow its immediately preceding vehicle while maintaining the inter-vehicle distance between corresponding following vehicle <NUM> and the immediately preceding vehicle at a target value and a maximum allowable vehicle velocity calculation unit <NUM> that calculates maximum allowable vehicle velocity V2max that satisfies the turning performance of corresponding following vehicle <NUM> at an individual driving location.

The individual functions of vehicle control apparatus <NUM> are 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 apparatus <NUM> may 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 vehicle <NUM> and the immediately preceding vehicle at a target value during convoy driving, inter-vehicle control unit <NUM> outputs an acceleration command value Acom as an acceleration command to drive apparatus <NUM>, and outputs a deceleration command Dcom as a deceleration command to brake apparatus <NUM>. 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 unit <NUM> calculates acceleration command value Acom in accordance with the following mathematical equation (<NUM>), for example.

In mathematical equation (<NUM>), Δx denotes the difference between inter-vehicle distance d acquired based on the output information of external information recognition apparatus <NUM> and 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 Vf acquired based on the output information of reception apparatus <NUM> and vehicle velocity V2 of corresponding following vehicle <NUM> acquired based on the output information of vehicle velocity acquisition unit <NUM> (Δv = Vf - V2). When the immediately preceding vehicle velocity Vf is faster than vehicle velocity V2 of corresponding following vehicle <NUM>, Δv is calculated as a positive value. When immediately preceding vehicle velocity Vf is slower than vehicle velocity V2 of corresponding following vehicle <NUM>, Δv is calculated as a negative value.

In mathematical equation (<NUM>), axf denotes the longitudinal acceleration of the immediately preceding vehicle acquired based on the output information of reception apparatus <NUM>. When the immediately preceding vehicle accelerates and immediately preceding vehicle velocity Vf increases, axf is given as a positive value. When the immediately preceding vehicle decelerates and immediately preceding vehicle velocity Vf decreases, axf 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 Acom calculated in accordance with mathematical equation (<NUM>) is a positive value, inter-vehicle control unit <NUM> outputs acceleration command value Acom as an acceleration command to drive apparatus <NUM>. In contrast, when acceleration command value Acom calculated in accordance with mathematical equation (<NUM>) is a negative value, inter-vehicle control unit <NUM> calculates deceleration command Dcom as Dcom= |Acom| and calculated outputs deceleration command Dcom as a deceleration command to brake apparatus <NUM>.

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

Maximum allowable vehicle velocity calculation unit <NUM> calculates maximum allowable vehicle velocity V2max based on lateral acceleration limit aylim or yaw rate limit rlim used to set the turning performance of corresponding following vehicle <NUM> and a curvature κ2 of the driving path on which corresponding following vehicle <NUM> is running.

Lateral acceleration limit aylim and yaw rate limit rlim can 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 aylim and yaw rate limit rlim by operating a switch or the like. For example, if lateral acceleration limit aylim or yaw rate limit rlim is defined to prevent slip, lateral acceleration limit aylim or yaw rate limit rlim may be set changeably depending on the road conditions of the driving path. If lateral acceleration limit aylim or yaw rate limit rlim is defined to prevent collapsing of the freight, lateral acceleration limit aylim or yaw rate limit rlim may be set changeably depending on the load weight or load height.

In accordance with the following mathematical equation (<NUM>), maximum allowable vehicle velocity V2max is calculated as the square root of a value obtained by dividing lateral acceleration limit aylim by curvature κ2. Alternatively, in accordance with the following mathematical equation (<NUM>), maximum allowable vehicle velocity V2max may be calculated as a value obtained by dividing yaw rate limit rlim by curvature κ2. <MAT> <MAT>.

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

Maximum allowable vehicle velocity calculation unit <NUM> may calculate maximum allowable vehicle velocity V2max by using yaw rate r or lateral acceleration ay acquired at the driving location of following vehicle <NUM>, instead of using curvature κ2 of the driving path on which following vehicle <NUM> is running. Specifically, maximum allowable vehicle velocity calculation unit <NUM> may calculate maximum allowable vehicle velocity V2max as a value obtained by dividing lateral acceleration limit aylim by yaw rate r in accordance with the following mathematical equation (<NUM>) or as a value obtained by dividing lateral acceleration ay by yaw rate limit rlim in accordance with the following mathematical equation (<NUM>). <MAT> <MAT>.

Vehicle control apparatus <NUM> of following vehicle <NUM> may use a different method for calculating maximum allowable vehicle velocity V2max as necessary, depending on a specific configuration of vehicle state acquisition apparatus <NUM> of following vehicle <NUM>. After maximum allowable vehicle velocity calculation unit <NUM> outputs information about maximum allowable vehicle velocity V2max calculated thereby from vehicle control apparatus <NUM> to second transmission apparatus <NUM>, second transmission apparatus <NUM> transmits the information to lead vehicle <NUM>.

<FIG> is a schematic diagram illustrating another example of the adaptive cruise control system of the following vehicle. In <FIG>, lead vehicle <NUM> is on a straight path after passing through a curve, and a certain following vehicle <NUM> is on a straight path before entering the curve. In the above adaptive cruise control system, following vehicle <NUM> calculates maximum allowable vehicle velocity V2max that satisfies its turning performance on the straight path on which following vehicle <NUM> is actually running. However, in this example, as illustrated in <FIG>, following vehicle <NUM> calculates its maximum allowable vehicle velocity V2max that satisfies its turning performance on the curve on which following vehicle <NUM> is about to enter. That is, following vehicle <NUM> calculates its maximum allowable vehicle velocity V2max (= u2) based on curvature (forward curvature) κ2est of the curve into which following vehicle <NUM> is about to enter and its turning performance. In addition, when lead vehicle <NUM> sets vehicle velocity limit V1max, lead vehicle <NUM> uses maximum allowable vehicle velocity V2max (= u2). In this way, since lead vehicle <NUM> can reduce velocity limit V1max before following vehicle <NUM> enters the curve, and the lateral acceleration generated on the curve on which following vehicle <NUM> is about to enter is reduced more reliably.

Specifically, vehicle control apparatus <NUM> of following vehicle <NUM> calculates its maximum allowable vehicle velocity V2max by assigning lateral acceleration limit aylim and forward curvature κ2est in place of curvature κ2 to mathematical equation (<NUM>) or by assigning yaw rate limit rlim and forward curvature κ2est in place of curvature κ2 to mathematical equation (<NUM>). Next, vehicle control apparatus <NUM> compares maximum allowable vehicle velocity V2max calculated based on forward curvature κ2est and the turning performance of following vehicle <NUM> with maximum allowable vehicle velocity V2max that satisfies the turning performance of following vehicle <NUM> at the driving location on which following vehicle <NUM> is actually running. As a result of the comparison, the vehicle control apparatus <NUM> transmits information about the lower one of maximum allowable vehicle velocities V2max to lead vehicle <NUM>. When setting vehicle velocity limit V1max, lead vehicle <NUM> uses the lower maximum allowable vehicle velocity V2max.

Forward curvature κ2est can be estimated based on external information recognized by external information recognition apparatus <NUM>. For example, if external information recognition apparatus <NUM> is configured to recognize road demarcation lines (white lines) by processing its camera images, forward curvature κ2est can be estimated from the recognized road demarcation lines. If external information recognition apparatus <NUM> can acquire a relative location and a relative angle, in addition to inter-vehicle distance d between corresponding following vehicle <NUM> and the immediately preceding vehicle thereof, by processing its camera images, forward curvature κ2est can 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 vehicle <NUM> and a line extending in the front-back direction of the immediately preceding vehicle on a two-dimensional plane are determined, and forward curvature κ2est can be estimated based on a curve that is into contact with these lines and that connects corresponding following vehicle <NUM> and the immediately preceding vehicle without an inflection point.

In addition, forward curvature κ2est can be estimated by determining the road shape of the forward driving path from map information. For example, if following vehicle <NUM> can acquire its vehicle location from a global positioning system (GPS), a locator, or the like, forward curvature κ2est can 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 κ2est can be estimated by acquiring past records of the vehicle state of the immediately preceding vehicle. For example, reception apparatus <NUM> of corresponding following vehicle <NUM> receives 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 apparatus <NUM> of the immediately preceding vehicle of corresponding following vehicle <NUM>, 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 vehicle <NUM> can estimate forward curvature κ2est based on the estimated driving path. Alternatively, if the immediately preceding vehicle is configured to acquire and transmit its own vehicle location, corresponding following vehicle <NUM> can estimate the driving path from past records of the vehicle location of the immediately preceding vehicle and can estimate forward curvature κ2est based on this estimated driving path.

<FIG> illustrates an example of an adaptive cruise control system mounted on the lead vehicle. The adaptive cruise control system mounted on lead vehicle <NUM> includes a vehicle control apparatus <NUM> as a main component including a microcomputer as a control unit. The adaptive cruise control system also includes a vehicle state acquisition apparatus <NUM>, a reception apparatus <NUM>, an accelerator operation unit <NUM>, a brake operation unit <NUM>, a drive apparatus <NUM>, and a brake apparatus <NUM>. Vehicle state acquisition apparatus <NUM> includes a vehicle velocity acquisition unit <NUM>. Since vehicle velocity acquisition unit <NUM> is configured in the same way as vehicle velocity acquisition unit <NUM> of following vehicle <NUM>, description thereof will be omitted.

Reception apparatus <NUM> receives information about maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) from following vehicles <NUM> via inter-vehicle communication with following vehicles <NUM> and outputs the information to vehicle control apparatus <NUM>, and n is an integer (a natural number) or <NUM> or greater for indicating identification numbers of following vehicles <NUM>. For example, identification numbers are allocated to following vehicles <NUM> following lead vehicle <NUM> in ascending order via inter-vehicle communication.

Accelerator operation unit <NUM> is 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 vehicle <NUM> and 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 vehicle <NUM> increases as the acceleration operation amount increases.

Brake operation unit <NUM> is 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 vehicle <NUM> and 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 vehicle <NUM> decreases as the brake operation amount increases.

Drive apparatus <NUM> includes a drive source (an engine, an electric motor, or a combination thereof) that generates driving force for wheels of lead vehicle <NUM>, and a drive controller that controls the driving force based on a control command from vehicle control apparatus <NUM>. Vehicle control apparatus <NUM> outputs, to drive apparatus <NUM>, a normal acceleration command or a limited acceleration command as a control command.

Brake apparatus <NUM> includes a brake mechanism (a friction brake, a drum brake, or the like) that applies braking force to wheels of lead vehicle <NUM> and a brake controller that controls the braking force based on a control command output from vehicle control apparatus <NUM>. The vehicle control apparatus <NUM> outputs, to brake apparatus <NUM>, a normal deceleration command or a forced deceleration command as a control command.

The microcomputer of vehicle control apparatus <NUM> receives various kinds of information output from vehicle velocity acquisition unit <NUM>, reception apparatus <NUM>, accelerator operation unit <NUM>, and brake operation unit <NUM> and outputs calculation results obtained based on various kinds of information as control commands to drive apparatus <NUM> and brake apparatus <NUM>. Vehicle control apparatus <NUM> has two main functions, which are a vehicle velocity limit setting unit <NUM> and a vehicle velocity control unit <NUM>.

Vehicle velocity limit setting unit <NUM> acquires maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number) of following vehicles <NUM> from the output information of reception apparatus <NUM> and sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max(<NUM>) to V2max(n). Specifically, if there is only one following vehicle <NUM>, vehicle velocity limit setting unit <NUM> sets maximum allowable vehicle velocity V2max(<NUM>) as vehicle velocity limit V1max. If there are a plurality of following vehicles <NUM>, vehicle velocity limit setting unit <NUM> sets the lowest one of maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number of <NUM> or more) as vehicle velocity limit V1max.

Vehicle velocity control unit <NUM> acquires vehicle velocity V1, the acceleration operation amount, and the brake operation amount from the output information of vehicle velocity acquisition unit <NUM>, accelerator operation unit <NUM>, and brake operation unit <NUM> and outputs control commands generated based on the acceleration operation amount, vehicle velocity V1, vehicle velocity limit V1max, and the brake operation amount to drive apparatus <NUM> and brake apparatus <NUM>. Vehicle velocity control unit <NUM> performs vehicle velocity control in this way.

Basically, vehicle velocity control unit <NUM> outputs a normal acceleration command generated based on an acceleration operation amount associated with an acceleration request from the vehicle user to drive apparatus <NUM> as a control command. However, when velocity V1 exceeds a predetermined vehicle velocity V1d less than vehicle velocity limit V1max, vehicle velocity control unit <NUM> generates 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 vehicle <NUM>. Next, vehicle velocity control unit <NUM> outputs this limited acceleration command to drive apparatus <NUM> as a control command. Specifically, if vehicle velocity V1 is between vehicle velocity limit V1max and predetermined vehicle velocity V1d, vehicle velocity control unit <NUM> reduces the acceleration operation amount to a value within a range in which lead vehicle <NUM> can be accelerated. Vehicle velocity control unit <NUM> may perform greater reduction from the acceleration operation amount to the corrected acceleration operation amount when the difference (= V1max - V1) between vehicle velocity limit V1max and vehicle velocity V1 is less. If vehicle velocity V1 is over vehicle velocity limit V1max, vehicle velocity control unit <NUM> reduces the acceleration operation amount to a value that does not substantially accelerate lead vehicle <NUM> (for example, <NUM>).

In the case of vehicle control apparatus <NUM>, predetermined vehicle velocity V1d may 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 V1d may be separated further from vehicle velocity limit V1max. In the case of vehicle control apparatus <NUM>, even when vehicle velocity V1 is 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 unit <NUM> outputs a normal deceleration command generated based on a brake operation amount associated with a brake request from the vehicle user to brake apparatus <NUM> as a control command. However, if vehicle velocity V1 exceeds vehicle velocity limit V1max, vehicle velocity control unit <NUM> outputs the forced deceleration command as a control command to brake apparatus <NUM> for forcibly decelerating lead vehicle <NUM>, so as to reduce vehicle velocity V1 to vehicle velocity limit V1max or 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 V1 from 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 unit <NUM> of vehicle control apparatus <NUM> indicates a value indicating a brake request given by the vehicle user. In this situation, if vehicle velocity control unit <NUM> predicts that the change by the deceleration of lead vehicle <NUM> based on the brake operation in accordance with the normal deceleration command will be greater than the change by the deceleration of lead vehicle <NUM> based on the brake operation in accordance with the forced deceleration command, vehicle velocity control unit <NUM> outputs the normal deceleration command to brake apparatus <NUM> as a control command. In contrast, if vehicle velocity control unit <NUM> predicts that the change by the deceleration of lead vehicle <NUM> based on the brake operation in accordance with the normal deceleration command will be less than the change by the deceleration of lead vehicle <NUM> based on the brake operation in accordance with the forced deceleration command, vehicle velocity control unit <NUM> continues to output the forced deceleration command to the brake apparatus <NUM> as 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 unit <NUM> can 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 unit <NUM>.

If vehicle velocity control unit <NUM> determines 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 unit <NUM> may output either the forced deceleration command or the normal deceleration command as a control command.

<FIG> illustrates a part of an example of processing that realizes maximum allowable vehicle velocity calculation unit <NUM> of 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" in <FIG>, and the same abbreviation will also apply to the following flowcharts), vehicle control apparatus <NUM> of following vehicle <NUM> calculates maximum allowable vehicle velocity V2max that satisfies the turning performance of following vehicle <NUM>. Specific methods for calculating maximum allowable vehicle velocity V2max have already been described in the above description of the adaptive cruise control system of following vehicle <NUM> and another example thereof.

In step S1002, vehicle control apparatus <NUM> of following vehicle <NUM> instructs second transmission apparatus <NUM> to transmit information about calculated maximum allowable vehicle velocity V2max to lead vehicle <NUM>.

<FIG> illustrates a part of an example of processing that realizes vehicle velocity limit setting unit <NUM> and vehicle velocity control unit <NUM> of 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 apparatus <NUM> of lead vehicle <NUM> instructs reception apparatus <NUM> to receive information about maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number) from following vehicles <NUM>.

In step S2002, vehicle control apparatus <NUM> of lead vehicle <NUM> sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number) of following vehicles <NUM> acquired from the output information of reception apparatus <NUM>.

In step S2003, vehicle control apparatus <NUM> of lead vehicle <NUM> determines whether vehicle velocity V1 is greater than vehicle velocity limit V1max. If vehicle control apparatus <NUM> of lead vehicle <NUM> determines that vehicle velocity V1 is greater than vehicle velocity limit V1max (YES in step S2003), the processing proceeds to step S2004. However, if vehicle control apparatus <NUM> of lead vehicle <NUM> determines that vehicle velocity V1 is less than or equal to vehicle velocity limit V1max (NO in step S2003), the processing proceeds to step S2007.

In step S2004, vehicle control apparatus <NUM> of lead vehicle <NUM> outputs a limited acceleration command to drive apparatus <NUM>. 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 vehicle <NUM>.

In step S2005, vehicle control apparatus <NUM> of lead vehicle <NUM> outputs a forced deceleration command to brake apparatus <NUM>. In step S2006, vehicle control apparatus <NUM> of lead vehicle <NUM> determines 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 apparatus <NUM> of lead vehicle <NUM> determines whether vehicle velocity V1 is greater than predetermined vehicle velocity V1d. If vehicle control apparatus <NUM> of lead vehicle <NUM> determines that vehicle velocity V1 is greater than predetermined vehicle velocity V1d (YES in step S2007), the processing proceeds to step S2008. However, if vehicle control apparatus <NUM> of lead vehicle <NUM> determines that vehicle velocity V1 is less than or equal to predetermined vehicle velocity V1d (NO in step S2007), vehicle control apparatus <NUM> ends the present control processing without limiting vehicle velocity V1.

In step S2008, vehicle control apparatus <NUM> of lead vehicle <NUM> outputs a limited acceleration command to drive apparatus <NUM>. 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 vehicle <NUM> can be accelerated.

<FIG> is a subroutine illustrating an example of the determination of whether outputting the forced deceleration command is appropriate in step S2006 included in the control processing in <FIG> performed by the vehicle control apparatus of the lead vehicle.

In step S3001, vehicle control apparatus <NUM> of lead vehicle <NUM> determines 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 unit <NUM>.

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

In step S3003, vehicle control apparatus <NUM> of lead vehicle <NUM> generates the normal deceleration command based on the brake operation amount acquired from the output information of brake operation unit <NUM> and outputs the normal deceleration command, instead of the forced deceleration command, to brake apparatus <NUM> as a control command.

As described above, in the adaptive cruise control system according to the first example, each following vehicle <NUM> calculates its maximum allowable vehicle velocity V2max that satisfies its turning performance, and lead vehicle <NUM> calculates vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max transmitted from following vehicles <NUM> and performs vehicle velocity control such that vehicle velocity V1 will not exceed vehicle velocity limit V1max. In this way, following vehicle <NUM> running on a curve is prevented from experiencing excessively large lateral acceleration that causes at least one of deteriorated ride quality, slipping, and freight collapsing.

Hereinafter, an outline of an adaptive cruise control system according to a second example will be described with reference to <FIG>. 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> illustrates an example of the driving state of a convoy including three following vehicles in the adaptive cruise control system. In <FIG>, first following vehicle 2A, second following vehicle 2B, and third following vehicle 2C are non-mechanically connected to lead vehicle <NUM> sequentially, and each of following vehicles 2A to 2C follows its immediately preceding vehicle. In the above adaptive cruise control system, each of the following vehicles 2A to 2C calculates its maximum allowable vehicle velocity V2max that 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 vehicle <NUM> calculates, for the following vehicles, maximum allowable vehicle velocities V2max that satisfy their respective turning performances on the driving path in the convoy section from lead vehicle <NUM> to third following vehicle 2C, of the entire driving path that lead vehicle <NUM> has already passed (driven path).

Specifically, lead vehicle <NUM> calculates the curvature of the driving path on which lead vehicle <NUM> is running while sequentially storing the curvature and determines a maximum curvature κmax on the driving path in the convoy section of the entire driven path. Next, lead vehicle <NUM> calculates maximum allowable vehicle velocity V2max for each of the following vehicles based on maximum curvature κmax and the turning performances of following vehicles 2A to 2C. Next, lead vehicle <NUM> sets the lowest one of calculated maximum allowable vehicle velocities V2max of following vehicles 2A to 2C as vehicle velocity limit V1max and performs vehicle velocity control such that the vehicle velocity will not exceed vehicle velocity limit V1max. Although not illustrated, when only one following vehicle 2A follows lead vehicle <NUM>, lead vehicle <NUM> sets maximum allowable vehicle velocity V2max calculated based on maximum curvature κmax<NUM> and the turning performance of following vehicle 2A as vehicle velocity limit V1max.

<FIG> illustrates an example of an adaptive cruise control system mounted on a following vehicle. The adaptive cruise control system mounted on following vehicle <NUM> includes a vehicle control apparatus 20a as a main component, external information recognition apparatus <NUM>, a vehicle state acquisition apparatus 22a, reception apparatus <NUM>, first transmission apparatus <NUM>, second transmission apparatus <NUM>, drive apparatus <NUM>, and brake apparatus <NUM>.

While vehicle control apparatus 20a includes a microcomputer as a control unit and inter-vehicle control unit <NUM> described above as a main function, vehicle control apparatus 20a does not include maximum allowable vehicle velocity calculation unit <NUM>. In addition, vehicle control apparatus 20a instructs second transmission apparatus <NUM> to transmit, instead of information about maximum allowable vehicle velocity V2max, information about inter-vehicle distance d output from external information recognition apparatus <NUM> to lead vehicle <NUM>.

While vehicle state acquisition apparatus 22a includes longitudinal acceleration acquisition unit <NUM> and vehicle velocity acquisition unit <NUM> necessary for vehicle velocity control, vehicle state acquisition apparatus 22a does not include yaw rate acquisition unit <NUM>, lateral acceleration acquisition unit <NUM>, and steering angle acquisition unit <NUM> necessary for calculating maximum allowable vehicle velocity V2max.

<FIG> illustrates an example of an adaptive cruise control system mounted on the lead vehicle. The adaptive cruise control system mounted on lead vehicle <NUM> includes a vehicle control apparatus 10a as a main component including a microcomputer as a control unit. The adaptive cruise control system also includes a vehicle state acquisition apparatus 11a, reception apparatus <NUM>, accelerator operation unit <NUM>, brake operation unit <NUM>, drive apparatus <NUM>, and brake apparatus <NUM>. In addition to vehicle velocity acquisition unit <NUM>, vehicle state acquisition apparatus 11a includes a yaw rate acquisition unit <NUM>, a lateral acceleration acquisition unit <NUM>, and a steering angle acquisition unit <NUM>.

Because yaw rate acquisition unit <NUM>, lateral acceleration acquisition unit <NUM>, and steering angle acquisition unit <NUM> are configured in the same way as yaw rate acquisition unit <NUM>, lateral acceleration acquisition unit <NUM>, and steering angle acquisition unit <NUM> of following vehicle <NUM> according to the first example, description thereof will be omitted.

The microcomputer of vehicle control apparatus 10a receives various kinds of information output from vehicle state acquisition apparatus 11a, reception apparatus <NUM>, accelerator operation unit <NUM>, and brake operation unit <NUM> and outputs calculation results obtained based on various kinds of information to drive apparatus <NUM> and brake apparatus <NUM> as control commands.

In addition to the two main functions which vehicle velocity limit setting unit <NUM> and vehicle velocity control unit <NUM> have as described above, vehicle control apparatus 10a has 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 unit <NUM>, a driving path information acquisition unit <NUM>, a driven path information storage unit <NUM>, a convoy length estimation unit <NUM>, and a maximum allowable vehicle velocity calculation unit <NUM>.

Driving distance acquisition unit <NUM> acquires vehicle velocity V1 from the output information of vehicle velocity acquisition unit <NUM> and acquires driving distance B of lead vehicle <NUM> based on vehicle velocity V1. For example, driving distance B of lead vehicle <NUM> can be acquired by multiplying vehicle velocity V1 acquired per control cycle of the microcomputer of vehicle control apparatus 10a by control cycle time and by adding up the calculated products.

Driving path information acquisition unit <NUM> acquires physical amounts indicating the vehicle state at an actual driving location of lead vehicle <NUM> from the output information of vehicle state acquisition apparatus 11a and acquires, based on these physical amounts, information about the shape of the driving path at the actual driving location of lead vehicle <NUM> (driving path information).

Examples of the driving path information include a curvature κ1 of the driving path at the driving location of lead vehicle <NUM>. Curvature κ1 is 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 vehicle <NUM>. Because these various relational expressions indicating basic motion characteristics of lead vehicle <NUM> are the same as those used for calculating curvature κ2 of the driving path on which following vehicle <NUM> is running according to the first example, description thereof will be omitted. Regarding various relational expressions that lead vehicle <NUM> uses to calculate curvature κ1, a suitable relational expression may be selected depending on which acquisition units are included in vehicle state acquisition apparatus 11a of lead vehicle <NUM>.

For example, there are cases in which there is only one following vehicle <NUM>, the convoy section is relatively short, or lead vehicle <NUM> has 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 vehicle <NUM> has not changed much from the location of following vehicle <NUM> at the end of the convoy to the location of lead vehicle <NUM> and that the vehicle velocity of lead vehicle <NUM> has 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 κ1 on the driving path in the convoy section. Thus, when the vehicle velocity of lead vehicle <NUM> can be regarded as being constant on the driving path in the convoy section, yaw rate r or lateral acceleration ay acquired by vehicle state acquisition unit 11a may be acquired as the driving path information, instead of curvature κ1.

Each time that driven path information storage unit <NUM> acquires driving distance B and driving path information, driven path information storage unit <NUM> associates 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 vehicle <NUM> has already run.

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

Maximum allowable vehicle velocity calculation unit <NUM> sets maximum allowable vehicle velocity V2max as follows, based on driving distance B acquired by driving distance acquisition unit <NUM>, the driven path information stored in driven path information storage unit <NUM>, and convoy length C estimated by convoy length estimation unit <NUM>.

First, maximum allowable vehicle velocity calculation unit <NUM> subtracts convoy length C from driving distance B of lead vehicle <NUM> and determines a driving distance Bend of lead vehicle <NUM>, driving distance Bend corresponding to the driving location of the last vehicle in the convoy. Next, maximum allowable vehicle velocity calculation unit <NUM> refers to the driven path information and determines maximum curvature κmax on the driving path in the convoy section from curvatures κ1 from 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 Bend may be deleted.

Next, maximum allowable vehicle velocity calculation unit <NUM> calculates maximum allowable vehicle velocity V2max for each of following vehicles <NUM> based on maximum curvature κmax and the turning performance of corresponding following vehicles <NUM>. Maximum allowable vehicle velocity calculation unit <NUM> may calculate maximum allowable vehicle velocity V2max by replacing curvature κ2 in mathematical equation (<NUM>) or mathematical equation (<NUM>) by maximum curvature κmax. That is, maximum allowable vehicle velocity calculation unit <NUM> may calculate maximum allowable vehicle velocity V2max as the square root of a value obtained by dividing lateral acceleration limit aylim by maximum curvature κmax or a value obtained by dividing yaw rate limit rlim by maximum curvature κmax. If a plurality of following vehicles <NUM> have the same turning performance, maximum allowable vehicle velocity calculation unit <NUM> may calculate maximum allowable vehicle velocity V2max for only one following vehicle <NUM>, without calculating maximum allowable vehicle velocity V2max for each following vehicle <NUM>.

If driving path information acquisition unit <NUM> has acquired yaw rate r or lateral acceleration ay as the driving path information, maximum allowable vehicle velocity calculation unit <NUM> refers to the driven path information and determines the maximum value of yaw rate r or lateral acceleration ay on the driving path in the convoy section. This is because it is conceivable, when yaw rate r or lateral acceleration ay on 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 unit <NUM> assigns the maximum value of yaw rate r to mathematical equation (<NUM>) or the maximum value of lateral acceleration ay to mathematical equation (<NUM>), to calculate maximum allowable vehicle velocity V2max for each following vehicle <NUM>.

Vehicle velocity limit setting unit <NUM> sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number) of following vehicles <NUM> calculated by maximum allowable vehicle velocity calculation unit <NUM>. Specifically, if there is only one following vehicle <NUM>, vehicle velocity limit setting unit <NUM> sets maximum allowable vehicle velocity V2max(<NUM>) as vehicle velocity limit V1max. If there are a plurality of following vehicles <NUM>, vehicle velocity limit setting unit <NUM> sets the lowest one of maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number of <NUM> or greater) as vehicle velocity limit V1max.

Vehicle velocity control unit <NUM> acquires vehicle velocity V1, the acceleration operation amount, and the brake operation amount from the output information of vehicle velocity acquisition unit <NUM>, accelerator operation unit <NUM>, and brake operation unit <NUM> and outputs control commands generated based on the acceleration operation amount, vehicle velocity V1, vehicle velocity limit V1max, and the brake operation amount to drive apparatus <NUM> and brake apparatus <NUM>. Vehicle velocity control unit <NUM> performs vehicle velocity control in this way. Since other specific contents about vehicle velocity control unit <NUM> are the same as those according to the first example, description thereof will be omitted.

<FIG> illustrates 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 unit <NUM>, the processing being included in the main part, is not included in this example.

In step S4001, vehicle control apparatus 20a of following vehicle <NUM> acquires inter-vehicle distance d from its immediately preceding vehicle from the output information of external information recognition apparatus <NUM>.

In step S4002, vehicle control apparatus 20a of following vehicle <NUM> instructs second transmission apparatus <NUM> to transmit information about inter-vehicle distance d to lead vehicle <NUM>.

<FIG> illustrates 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 apparatus 10a of lead vehicle <NUM> acquires vehicle velocity V1 from the output information of vehicle velocity acquisition unit <NUM> and calculates driving distance B based on vehicle velocity V1.

In step S5002, vehicle control apparatus 10a of lead vehicle <NUM> acquires physical amounts indicating the vehicle state at its actual driving location from the output information of vehicle state acquisition apparatus 11a and acquires driving path information (for example, curvature κ1) from the physical amounts. Step S5002 may be performed before step S5001.

In step S5003, vehicle control apparatus 10a of lead vehicle <NUM> associates the driving path information acquired in step S5002 with driving distance B acquired in step S5001 and stores the associated information in the volatile memory or the like of the microcomputer as driven path information.

In step S5004, vehicle control apparatus 10a of lead vehicle <NUM> estimates convoy length C based on inter-vehicle distances d(<NUM>) to d(n) (n is a natural number) acquired from the output information of reception apparatus <NUM>. Step S5004 may be performed before step S5003.

In step S5005, vehicle control apparatus 10a of lead vehicle <NUM> calculates maximum allowable vehicle velocities V2max based 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 V2max are the same are those described with maximum allowable vehicle velocity calculation unit <NUM>, description thereof will be omitted.

In step S5006, vehicle control apparatus 10a of lead vehicle <NUM> sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max(<NUM>) to V2max(n) (n is a natural number) of following vehicles <NUM> calculated in step S5005. Since steps S5007 to S5012 are the same as steps S2003 to S2008, description thereof will be omitted.

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

When the target value of the inter-vehicle distance in the inter-vehicle control unit of following vehicle <NUM> is a constant value and when actual convoy length C will not probably change by the inter-vehicle control, vehicle control apparatus 10a of lead vehicle <NUM> may be configured without convoy length estimation unit <NUM>. In this case, maximum allowable vehicle velocity calculation unit <NUM> of vehicle control apparatus 10a of lead vehicle <NUM> calculates maximum allowable vehicle velocity V2max assuming 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 vehicle <NUM> calculates maximum allowable vehicle velocities V2max based on maximum curvature κmax of the driving path in the convoy section in the driven path and the turning performances of following vehicles <NUM>. Next, lead vehicle <NUM> sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max of following vehicles <NUM> and performs vehicle velocity control such that the vehicle velocity of lead vehicle <NUM> will not exceed vehicle velocity limit V1max. In this way, in addition to preventing following vehicle <NUM> on 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 vehicles <NUM> do not need to calculate maximum allowable vehicle velocities V2max. In addition, when the convoy length will not probably change, each following vehicle <NUM> does not need transmit information about inter-vehicle distance d. Thus, since following vehicle <NUM> has less processing load, calculation resources can be allocated to other control processing such inter-vehicle control processing.

As describe above, in <FIG>, maximum allowable vehicle velocity calculation unit <NUM> calculates maximum allowable vehicle velocities V2max of following vehicles <NUM> and supplies calculated maximum allowable vehicle velocities V2max to vehicle velocity limit setting unit <NUM>, which then calculates vehicle velocity limit V1max. However, alternatively, vehicle velocity limit V1max may directly be determined based on the driven path information stored in driven path information storage unit <NUM>.

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, the scope of the invention being defined by the subject-matter of the appended claims.

In the above first and second examples, lead vehicle <NUM> sets vehicle velocity limit V1max based on maximum allowable vehicle velocities V2max of following vehicles <NUM> and performs vehicle velocity control such that the vehicle velocity of lead vehicle <NUM> will not exceed vehicle velocity limit V1max. Alternatively, lead vehicle <NUM> may simply perform vehicle velocity control such that lead vehicle <NUM> does not accelerate when following vehicle <NUM> enters a curve. For example, when following vehicle <NUM> determines that following vehicle <NUM> has entered a curve based on the output information of yaw rate acquisition unit <NUM>, lateral acceleration acquisition unit <NUM>, or steering angle acquisition unit <NUM>, following vehicle <NUM> transmits a limitation request signal requesting lead vehicle <NUM> to limit the vehicle velocity of lead vehicle <NUM>. Upon receiving this limitation request signal, lead vehicle <NUM> performs vehicle velocity control that prevents acceleration of lead vehicle <NUM>. In this way, it is possible to reduce the risk that following vehicle <NUM> on 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 vehicle <NUM>. 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 vehicles <NUM>, for convenience of description of the functions, three functions that perform inter-vehicle communication have been described. However, reception apparatus <NUM>, first transmission apparatus <NUM>, and second transmission apparatus <NUM> may be configured as a single communication apparatus.

Claim 1:
A control method for a convoy of vehicles (<NUM>, <NUM>, 2A, 2B, 2C), wherein:
- the convoy of vehicles (<NUM>, <NUM>, 2A, 2B, 2C) is formed by a plurality of vehicles (<NUM>, <NUM>, 2A, 2B, 2C) which comprises a lead vehicle (<NUM>) and at least one following vehicle (<NUM>, 2A, 2B, 2C) and wherein (i) the at least one following vehicle (<NUM>, 2A, 2B, 2C) runs after the lead vehicle (<NUM>) and (ii) a respective following vehicle (<NUM>, 2A, 2B, 2C) follows its immediately preceding vehicle (<NUM>, <NUM>, 2A, 2B, 2C),
- the method is to be performed in an adaptive cruise control system that non-mechanically connects the following vehicles (<NUM>, 2A, 2B, 2C) to the lead vehicle (<NUM>) sequentially, and that causes a respective following vehicle (<NUM>, 2A, 2B, 2C) to follow its immediately preceding vehicle (<NUM>, <NUM>, 2A, 2B, 2C), and
- the method comprises:
- calculating a vehicle velocity limit (V1max) for limiting a velocity of the lead vehicle (<NUM>) based on maximum allowable velocities (V2max) of the following vehicle (<NUM>, 2A, 2B, 2C), wherein each of the maximum allowable velocities (V2max) satisfies a turning performance of a respective following vehicle (<NUM>, 2A, 2B, 2C); and
- controlling a brake apparatus (<NUM>, <NUM>) and/or a drive apparatus (<NUM>, <NUM>) of the lead vehicle (<NUM>) such that the velocity of the lead vehicle (<NUM>) will not exceed the vehicle velocity limit (V1max).