Vehicle speed control method and vehicle speed control device

Abstract

To set a target vehicle speed of traveling on a target travel track so as not to exceed a limit of a steering angle that can be achieved by a steering mechanism.SOLUTION: A vehicle control method includes: setting a target travel track of an own vehicle 1 and setting a maximum steering angle as a maximum value of a steering angle that a steering mechanism can achieve according to a vehicle speed of the own vehicle 1 (S12); setting a target vehicle speed at which the own vehicle travels on the target travel track such that a the steering angle of the own vehicle 1 does not exceed the maximum steering angle (S10, S11, S13 to S17); and controlling the vehicle speed of the own vehicle on the basis of the target vehicle speed (S4).SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a vehicle speed control method and a vehicle speed control device. [Background technology]

[0002] Patent Document 1 listed below describes a technique for setting a target speed so that the turning acceleration does not exceed the coefficient of road friction while an autonomously driven vehicle is traveling autonomously. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-121874 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, the target vehicle speed is set by focusing on the lateral acceleration at the center of gravity of the vehicle. However, if the steering mechanism cannot actually achieve the steering angle required to turn at the lateral acceleration and target vehicle speed, there is a risk that the ability to follow the target driving trajectory generated by the automatic driving control will decrease. An object of the present invention is to set a target vehicle speed for traveling on a target traveling trajectory so as not to exceed the limit of the steering angle that can be realized by the steering mechanism. [Means for solving the problem]

[0005] A vehicle speed control method according to one aspect of the present invention sets a target driving trajectory for a vehicle, sets a maximum steering angle that is the maximum steering angle that can be achieved by a steering mechanism depending on the vehicle speed, sets a target vehicle speed at which the vehicle will travel on the target driving trajectory without the steering angle of the vehicle exceeding the maximum steering angle, and controls the vehicle speed based on the target vehicle speed. [Effects of the Invention]

[0006] According to the present invention, the target vehicle speed for traveling on the target traveling trajectory can be set so as not to exceed the limit of the steering angle that can be realized by the steering mechanism. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic configuration diagram of a driving assistance device according to an embodiment; [Figure 2] FIG. 1 is an explanatory diagram illustrating an example of architecture of autonomous driving control by a driving assistance device according to an embodiment. [Figure 3] 2 is a block diagram showing an example of a functional configuration of an automatic driving control unit of the driving assistance device according to the embodiment; FIG. [Figure 4] 2 is a block diagram illustrating an example of a functional configuration of a vehicle control unit illustrated in FIG. 1. FIG. [Figure 5] 1A is an explanatory diagram of an example of a first vehicle speed profile, FIG. 1B is an explanatory diagram of an example of a second vehicle speed profile, and FIG. 1C is an explanatory diagram of an example of a third vehicle speed profile. [Figure 6] 5 is a block diagram illustrating an example of a functional configuration of a backward calculation unit illustrated in FIG. 4. FIG. [Figure 7] 5 is a block diagram illustrating an example of a functional configuration of a forward calculation unit illustrated in FIG. 4. FIG. [Figure 8] 3 is a flowchart illustrating an example of a vehicle speed control method according to an embodiment. [Figure 9] 9 is a flowchart illustrating an example of the process of step S2 in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) (composition) See Figure 1. The host vehicle 1 is either a front-wheel steering vehicle capable of steering a right front wheel 2FR and a left front wheel 2FL, or a four-wheel steering vehicle capable of steering a right front wheel 2FR, a left front wheel 2FL, a right rear wheel 2RR, and a left rear wheel 2RL. Hereinafter, the right front wheel 2FR and the left front wheel 2FL will be collectively referred to as "front wheels 2F," the right rear wheel 2RR and the left rear wheel 2RL will be collectively referred to as "rear wheels 2R," and the front wheels 2F and rear wheels 2R will be collectively referred to as "wheels 2." The host vehicle 1 is equipped with a driving assistance device 10 that provides driving assistance for the host vehicle 1. Driving assistance provided by the driving assistance device 10 may include automatic driving control that automatically drives the host vehicle 1 without the involvement of the driver based on the driving environment around the host vehicle 1, and driving assistance control that assists the driver in driving the host vehicle 1. The driving assistance control may include driving control that controls at least one of the steering device, drive device, and braking device of the host vehicle 1, such as automatic steering, automatic braking, constant speed control, lane keeping control, and merging assistance control.

[0009] The driving assistance device 10 includes an object sensor 11, a vehicle sensor 12, a positioning device 13, a map database (map DB) 14, a navigation device 15, a controller 17, and an actuator 18. The object sensor 11 detects objects around the host vehicle 1. The object sensor 11 is a plurality of sensors mounted on the host vehicle 1, such as a laser radar, a millimeter wave radar, a camera, and a LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), that detect objects around the host vehicle 1. It is equipped with different types of object detection sensors.

[0010] The vehicle sensor 12 is mounted on the host vehicle 1 and detects various information (vehicle signals) obtained from the host vehicle 1. The vehicle sensor 12 includes, for example, a vehicle speed sensor that detects the vehicle speed (traveling speed) V of the host vehicle 1, a wheel sensor that detects the rotational speed and amount of rotation of the wheels 2, a three-axis acceleration sensor (G sensor) that detects the acceleration (including deceleration) in three axial directions of the host vehicle 1, a steering angle sensor that detects the steering angle (including the turning angle), a gyro sensor that detects the angular velocity generated in the host vehicle 1, a yaw rate sensor that detects the yaw rate, an accelerator sensor that detects the accelerator opening of the host vehicle 1, and a brake sensor that detects the amount of brake operation by the driver.

[0011] The positioning device 13 includes a Global Navigation System (GNSS) receiver and receives radio waves from multiple navigation satellites to measure the current position of the vehicle 1. The GNSS receiver may be, for example, a Global Positioning System (GPS) receiver. The positioning device 13 may also be, for example, an inertial navigation system. The map database 14 may store high-precision map data (hereinafter simply referred to as "high-precision map") suitable as a map for automated driving. The high-precision map is map data with higher precision than map data for navigation (hereinafter simply referred to as "navigation map"), and includes more detailed information on a lane-by-lane basis than on a road-by-road basis. The navigation device 15 recognizes the current position of the vehicle 1 using the positioning device 13, etc. The navigation device 15 acquires road information and traffic information around the vehicle 1 based on the recognized current position, and outputs the information to the controller 17. The navigation device 15 also provides route guidance to the occupant, and road and traffic information.

[0012] The controller 17 is an electronic control unit (ECU) that includes a processor and peripheral components such as a storage device, and performs driving assistance control of the host vehicle 1. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device may include a semiconductor storage device, a magnetic storage device, an optical storage device, etc. The storage device may include a register, a cache memory, a ROM (Read Only Memory) used as a main memory device, etc. The memory may include memory such as a memory card (RAM) and a random access memory (RAM). The processor of the controller 17 executes a computer program stored in the storage device, causing the controller 17 to function as an automatic driving control unit 20, an input arbitration unit 21, and a vehicle control unit 22. These functions will be described later.

[0013] The controller 17 may be formed by dedicated hardware for executing each of the information processes described below. For example, the controller may comprise functional logic circuits configured in a general-purpose semiconductor integrated circuit. For example, the controller may comprise a programmable logic device (FPGA) such as a field-programmable gate array (FPGA). The memory may include a programmable logic device (LD).

[0014] The actuator 18 operates the steering device, drive device, and braking device of the host vehicle 1 in response to a control signal from the controller 17 to generate vehicle behavior of the host vehicle 1. The actuator 18 includes a steering actuator, an accelerator opening actuator, and a brake control actuator. When the host vehicle 1 is a front-wheel steering vehicle, the steering actuator controls the front wheel steering angle δ F When the host vehicle 1 is a four-wheel steering vehicle, the steering actuator controls the front wheel steering angle δ F In addition, the rear wheel steering angle δ R Control.

[0015] The steering actuator may be, for example, a steering assist motor that applies a steering assist force in an electric power steering system, or a steering motor that steers the wheels 2 in a steering-by-wire system in which the steering wheel and the wheels 2 are mechanically separated. The accelerator opening actuator controls the accelerator opening of a drive device (for example, an engine or an electric motor) that is a power source that generates driving force for the host vehicle 1. The brake control actuator controls the braking operation of the host vehicle 1's brake device. The combination of the drive device, the brake device, the controller 17 and the actuator 18 is an example of a "speed control device" as defined in the claims.

[0016] Next, an example of driving support control by the driving support device 10 of the embodiment will be described. FIG. 2 shows an example of architecture of automatic driving control by the driving support device. The automatic driving control is performed by an automatic driving layer (AD Layer) 30, an arbitration unit (Arbitration) 31, and a reference model unit (Reference Model). The control is executed by a vehicle body motion control unit (Body Motion Control) 32, a vehicle body motion control unit (Body Motion Control) 33, a wheel motion control unit (Wheel Motion Control) 34, and the actuator 18 described above. The autonomous driving layer 30 sets a destination for the vehicle 1 and sets a driving route from the current position of the vehicle 1 to the destination. The destination may be a final destination set by the driver, or may be a point a predetermined distance ahead of the current position of the vehicle 1 (for example, the center position of the lane a predetermined distance ahead on the lane in which the vehicle is traveling). The autonomous driving layer 30 generates a target driving trajectory of the vehicle 1 traveling along a driving route, i.e., a driving trajectory on the road from the current position of the vehicle 1 to the destination, as an autonomous driving input (AD input), which is an instruction input from the autonomous driving layer 30.

[0017] The arbitration unit 31 arbitrates between manual driving input (MD input) which is input by the driver to operate the steering wheel, accelerator, and brake, and automatic driving input from the automatic driving layer 30, and sets the vehicle motion that the host vehicle 1 should perform. The normative model unit 32 sets the parameters of the vehicle motion model (e.g., yaw moment of inertia, cornering stiffness of the wheels 2, etc.) used to calculate the body behavior of the host vehicle 1 so that the host vehicle 1 realizes the vehicle motion set by the arbitration unit 31. The vehicle behavior control unit 33 controls the vehicle based on the vehicle motion model set by the reference model unit 32. Then, arbitration unit 31 calculates the vehicle body behavior (for example, vehicle speed, acceleration / deceleration, yaw rate, yaw angular acceleration, yaw moment, etc.) for realizing the vehicle motion set by arbitration unit 31.

[0018] The wheel behavior control unit 34 calculates the control amount (steering angle, braking amount, driving amount, etc.) of the wheel 2 to cause the vehicle 1 to produce the vehicle body behavior calculated by the vehicle body behavior control unit 33, and controls the wheel behavior using the actuator 18. For example, the functions of the autonomous driving layer 30 may be performed by the autonomous driving control unit 20 shown in Figure 1, the functions of the arbitration unit 31 may be performed by the input arbitration unit 21, and the functions of the normative model unit 32, the vehicle body behavior control unit 33, and the wheel behavior control unit 34 may be performed by the vehicle control unit 22.

[0019] Next, an example of the functional configuration of the automatic driving control unit 20 will be described with reference to Fig. 3. The automatic driving control unit 20 includes a localization unit 40 and a destination setting unit 41. a route planning unit (Route Planning) 42, an action decision unit (Decision Making) 43, and an action decision unit (Action Decision Making) 44. It is equipped with a Drive Zone Planning unit 44 and a Trajectory generation unit 45. do.

[0020] The localization unit 40 recognizes the surrounding environment of the vehicle 1 based on the detection signal of the object sensor 11. The localization unit 40 determines the current position of the vehicle 1 on the high-precision map by map matching between the recognition result and the high-precision map in the map database 14. Furthermore, based on the result of the recognition of the surrounding environment, a local model 47, which is a model of the surrounding environment of the vehicle 1, is generated. Furthermore, the local model 47 and a high-precision map are By combining this information with road information and traffic information from the navigation device 15, a world model 46 is generated.

[0021] The destination setting unit 41 sets the destination of the vehicle 1 based on an operational input by the driver via the navigation device 15. The route planning unit 42 calculates a planned driving route from the current position to the destination based on road information from the navigation device 15. Note that the planned driving route is not limited to this, and may be, for example, a planned route from the current position to a predetermined distance ahead of the vehicle. Alternatively, without using road information from the navigation device 15, the planned route from the predetermined distance ahead of the vehicle may be detected from an image captured by a camera or the like of the area ahead of the vehicle. The behavior decision unit 43 decides a driving behavior plan for the vehicle 1 to be executed by the driving assistance device 10 based on the recognition result of the surrounding environment, the current position of the vehicle 1, the world model 46, and the planned driving route.

[0022] Driving actions include, for example, stopping the vehicle 1, stopping temporarily, adjusting driving speed, slowing down, accelerating, changing lanes, turning right, turning left, going straight, changing lanes in merging sections or on multiple lanes, staying in lane, overtaking, and dealing with obstacles. The behavior decision unit 43 generates a driving behavior plan for the host vehicle 1 based on the current position and attitude of the host vehicle 1, the surrounding environment of the host vehicle 1, and the world model .

[0023] The driving zone planning unit 44 calculates a driving zone, which is an area in which the host vehicle 1 can travel, based on the generated driving action plan, the motion characteristics of the host vehicle 1, and the local model 47. The trajectory generation unit 45 generates a target driving trajectory for the host vehicle 1 so that the host vehicle 1 travels within the driving zone calculated by the driving zone planning unit 44 .

[0024] See Fig. 1. The input arbitration unit 21 arbitrates between the automatic driving input of the target driving trajectory set by the automatic driving control unit 20 and the manual driving input by the driver, and sets the vehicle motion that the host vehicle 1 should perform. The vehicle control unit 22 controls the behavior of the host vehicle 1 so as to realize the vehicle motion set by the input arbitration unit 21 .

[0025] Next, a description will be given of vehicle speed control by the vehicle control unit 22. In order for the host vehicle 1 to travel along a target travel trajectory, it is necessary to set a target vehicle speed so that the frictional force of the wheels 2 due to the lateral acceleration at the center of gravity of the host vehicle 1 does not exceed the friction limit. Furthermore, there is a limit to the steering angle of the steered wheels that the steering actuator can actually achieve, depending on the vehicle speed. If the steering mechanism cannot actually achieve the steering angle required to turn at the lateral acceleration and target vehicle speed, there is a risk that the ability to follow the target driving trajectory will decrease. For example, when turning with high lateral acceleration, the turning speed increases compared to when turning with low lateral acceleration, so a large steering command (e.g., command values ​​for steering angle, steering torque, steering force, etc.) is generated. If the steering command exceeds the limits of the steering mechanism, the required steering angle cannot be realized, and there is a risk that the ability to follow the target driving trajectory will decrease.

[0026] Therefore, the vehicle control unit 22 sets a maximum steering angle, which is the maximum value of the steering angle that the steering mechanism can achieve depending on the vehicle speed of the vehicle 1, and sets a target vehicle speed at which the vehicle 1 travels on the target driving trajectory without the steering angle of the vehicle 1 exceeding the maximum steering angle. This allows the target vehicle speed to be set so as not to exceed the limit of the steering angle that can be achieved by the steering mechanism, improving the ability to follow the target driving trajectory. Fig. 4 is a block diagram showing an example of the functional configuration of vehicle control unit 22 shown in Fig. 1. Vehicle control unit 22 includes a geometric calculation unit 50, a backward calculation unit 51, and a forward calculation unit 52.

[0027] The geometric calculation unit 50 calculates the turning curvature ρ of the target traveling trajectory generated by the trajectory generation unit 45 in FIG. 3 and the maximum lateral acceleration setting value A that is preset as the maximum allowable lateral acceleration. yMax Based on this, the lateral acceleration of the center of gravity of the host vehicle 1 is set to the maximum lateral acceleration setting value A yMax , so as not to exceed the target vehicle speed of the host vehicle. in Calculate. For example, the turning curvature at point i on the target driving trajectory is ρ i Then, the geometric calculation unit 50 calculates the target vehicle speed V at point i based on the following equation (1): i may be set.

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[0028] Figure 5(a) shows the first vehicle speed profile V in In the figure, the horizontal axis indicates the travel distance from the current position of the vehicle 1 to each point ahead of the vehicle on the target travel path, and the vertical axis indicates the target vehicle speed at each point. The leftmost point on the horizontal axis of FIG. 5(a) is the current position of the vehicle 1, and the rightmost point is the first vehicle speed profile V in is the point on the generated target driving trajectory that is the farthest from the vehicle 1 (hereinafter referred to as the "farthest point"). The same applies to Figures 5(b) and 5(c).

[0029] See Fig. 4. At each point on the target driving trajectory, backward calculation unit 51 calculates, based on the loads acting on front wheels 2F and rear wheels 2R in accordance with the deceleration of host vehicle 1, a maximum backward speed at which the resultant force of the braking force on each of front wheels 2F and rear wheels 2R and the lateral force does not exceed the friction limit and the steering angle required to turn along the target driving trajectory does not exceed the limit of the steering mechanism. The backward calculation unit 51 calculates the first vehicle speed profile V in By limiting the maximum backward speed, the second vehicle speed profile V B Set. Figure 5(b) shows the second vehicle speed profile VB An example is shown below.

[0030] Here, the first vehicle speed profile V at point i is limited by the friction limit. in Target vehicle speed V in From (i), the target vehicle speed V at the forward point (i+1) in If the vehicle speed cannot be reduced to (i+1), the first vehicle speed profile V in If this is exceeded, the vehicle will no longer be able to travel along the target travel trajectory. Therefore, the backward calculation unit 51 calculates the target vehicle speed V at a point (i+1) ahead of the target point i. in (i+1), the target vehicle speed V at the point of interest i is calculated. in Limit (i). Specifically, the target vehicle speed V at point (i+1) in (i+1) and the turning curvature ρ(i+1), the maximum deceleration A allowed for the host vehicle 1 at the point (i+1) x Calculate (i+1). And the maximum deceleration A at point (i+1) x Based on the loads applied to the front wheels 2F and the rear wheels 2R according to (i+1), the maximum backward speed is calculated as the maximum speed at which the resultant force of the braking force and the lateral force of the front wheels 2F and the rear wheels 2R at the point of interest i does not exceed the friction limit, and the steering angle required to turn along the target driving trajectory does not exceed the limit of the steering mechanism, and the first vehicle speed profile V at the point of interest i is calculated. in The target vehicle speed is limited by the maximum backward speed. This calculation is repeated while moving the attention point i backward one step at a time from the farthest point toward the current position of the host vehicle 1.

[0031] See Fig. 4. At each point on the target driving trajectory, forward calculation unit 52 calculates, based on the loads acting on front wheels 2F and rear wheels 2R in accordance with the acceleration of host vehicle 1, a maximum forward speed at which the resultant force of the driving force and lateral force on each of front wheels 2F and rear wheels 2R does not exceed the friction limit and the steering angle required to turn along the target driving trajectory does not exceed the limit of the steering mechanism. The forward calculation unit 52 calculates the second vehicle speed profile V BBy limiting the forward speed to the maximum, the third vehicle speed profile V out Set. The vehicle control unit 22 determines the third vehicle speed profile V out The speed of the host vehicle 1 is controlled by driving the accelerator opening actuator and the brake control actuator of the actuator 18 based on the above.

[0032] Contrary to the backward calculation unit 51, the forward calculation unit 52 calculates the target vehicle speed V at a point (i-1) one position behind the target vehicle 1, while moving the target point i forward one position at a time from the current position of the vehicle 1 toward the farthest point. in (i-1) and the turning curvature ρ(i-1), the maximum acceleration A allowed for the host vehicle 1 at the point (i-1) x Calculate (i-1). And the maximum acceleration A at point (i-1) x Based on the loads applied to the front wheels 2F and the rear wheels 2R in accordance with (i-1), the maximum forward speed is calculated as the maximum speed at which the resultant force of the driving force and lateral force of the front wheels 2F and the rear wheels 2R at the point of interest i does not exceed the friction limit and the steering angle required to turn along the target driving trajectory does not exceed the limit of the steering mechanism, and the second vehicle speed profile V at the point of interest i is calculated. B The target vehicle speed is limited to the maximum forward speed.

[0033] In the examples of FIG. 4 and FIG. 5(a) to FIG. 5(c), the backward calculation unit 51 calculates the first vehicle speed profile V in By limiting the second vehicle speed profile V B is set, and the forward calculation unit 52 calculates the second vehicle speed profile V B By limiting the third vehicle speed profile V out Instead, the forward calculation unit 52 calculates the first vehicle speed profile V in The second vehicle speed profile V B The backward calculation unit 51 sets the second vehicle speed profile V B The third vehicle speed profile V out may be set.

[0034] Next, a detailed description will be given of the backward calculation unit 51 and the forward calculation unit 52. FIG. The backward calculation unit 51 sets a point one position behind the farthest point as the first attention point i, and calculates the maximum deceleration A at the attention point i while sequentially moving the attention point i backward one position at a time to the current position of the vehicle 1. x (i) and target vehicle speed V Tar (i) is calculated respectively. The backward calculation unit 51 includes a maximum speed calculation unit 51a, selectors 51b and 51k, a load calculation unit 51c, a target lateral force calculation unit 51d, a maximum lateral force calculation unit 51e, a maximum steering angle calculation unit 51f, a maximum lateral force limiting unit 51g, a target longitudinal force calculation unit 51h, a maximum longitudinal force calculation unit 51i, and a maximum acceleration / deceleration calculation unit 51j.

[0035] In the calculation at the first point of interest i, the maximum speed calculation unit 51a calculates the target vehicle speed V at the point (i+1) immediately before the point of interest i. Tar (i+1), the first vehicle speed profile V in Set the target vehicle speed and the maximum deceleration A at point (i+1). x (i+1) is the maximum allowable deceleration preset value A xMax Set. In the calculation at the second or subsequent point of interest i, the target vehicle speed V calculated at the previous point of interest (i.e., point (i+1)) is used. Tar (i+1) and maximum deceleration A x Enter (i+1). The maximum speed calculation unit 51a calculates the target vehicle speed V at the previous point (i+1). Tar (i+1) and maximum deceleration A x The speed limit value of the following equation (2) is set according to (i+1).

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[0036] The selector 51b selects the first vehicle speed profile V at the point of interest i. in Target vehicle speed V in (i) according to the following equation (3), the target vehicle speed V Tar Set (i).

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[0037] The load calculation unit 51c calculates the maximum deceleration A at the point (i+1) immediately ahead based on the following equations (4) and (5): x (i+1), the front wheel load Fz, which is the load on the front wheel 2F based on the pitch motion of the body of the host vehicle 1. F (i) and the rear wheel load Fz, which is the load on the rear wheel 2R R Calculate (i).

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[0038] The target lateral force calculation unit 51d calculates the target vehicle speed V at the target point i based on the following equations (6) and (7): Tar (i) and the turning curvature ρ(i) of the target running trajectory, the target front wheel lateral force Fy ReqF (i) and the target rear wheel lateral force Fy ReqR (i) is calculated respectively.

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[0039] The maximum lateral force calculation unit 51e calculates the front wheel load Fz based on the following equations (8) and (9). F (i) and rear wheel load Fz R (i) and the target vehicle speed V Tar (i) and the maximum lateral acceleration setting value A yMax and a maximum yaw rate setting value γ Max Based on this, the maximum front wheel lateral force Fy is the maximum lateral force that can be generated on the front wheel 2F. MaxF (i) and the maximum rear wheel lateral force Fy, which is the maximum lateral force that can be generated on the rear wheel 2R. MaxR (i) is calculated respectively.

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[0040] The maximum steering angle calculation unit 51f calculates the target vehicle speed V Tar (i) The maximum front wheel steering angle δ that can be realized MaxF Calculate (i). For example, the rack axial force SF of the front wheel 2F is calculated by the following equation (10) in relation to the vehicle speed V and the front wheel steering angle δ F It is assumed that restrictions will be imposed depending on the SF=f const f(V) |δ F |≦SF Max …(10) f in equation (10) const and f(V) are fixed parameters and speed-sensitive parameters determined according to the vehicle specifications, respectively, and SF Max is the upper limit of the rack axial force SF.

[0041] In this case, the maximum steering angle calculation unit 51f calculates the target vehicle speed V based on the following equation (11): Tar(i) The maximum front wheel steering angle δ that changes depending on MaxF (i) may be calculated.

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[0042] The maximum lateral force limiting portion 51g is F is the maximum front wheel steering angle δ MaxF (i) Upper limit of front wheel lateral force Fy Max-F (i) is calculated, and the maximum front wheel lateral force Fy MaxF (i) is the upper limit of the front wheel lateral force Fy Max-F (i) The values ​​are limited to the following values ​​and output to the target longitudinal force calculation unit 51h, maximum longitudinal force calculation unit 51i, and maximum acceleration / deceleration calculation unit 51j. When the host vehicle 1 is a four-wheel steering vehicle, the maximum lateral force limiting unit 51g limits the front wheel lateral force upper limit value Fy Max-F In addition to (i), the rear wheel steering angle δ R The upper limit of the rear wheel lateral force Fy Max-R (i) and the lower limit of rear wheel lateral force Fy Min-R Calculate (i). The maximum lateral force limiting section 51g is the maximum front wheel lateral force Fy MaxF (i) is the upper limit of the front wheel lateral force Fy Max-F (i) The maximum rear wheel lateral force Fy is limited to the following value. MaxR (i) is the rear wheel lateral force Lower limit Fy Min-R (i) or more and the upper limit of rear wheel lateral force Fy Max-R (i) The values ​​are limited to the following values ​​and output to the target longitudinal force calculation unit 51h, maximum longitudinal force calculation unit 51i, and maximum acceleration / deceleration calculation unit 51j.

[0043] Lateral force on front wheel 2F Fy F , cornering stiffness C FIf the vehicle speed is V, the yaw rate is γ, and the slip angle (vehicle attitude angle) is β, the front wheel steering angle during turning is δ F can be expressed by the following equation (12): From the following equation (12), the following equation (13) is obtained.

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[0044] The slip angle characteristic G in equation (13) β (i) and ΔG β (i) is the front wheel steering angle δ when turning on a trajectory with curvature ρ(i). F and rear wheel steering angle δ R is a transfer function that gives the slip angle generated by the vehicle 1, and is given by the following equations (14) and (15). When the vehicle 1 is a front-wheel steering vehicle, ΔG β (i)=0.

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[0045] The following equation (16) is obtained from the above equation (13). The maximum lateral force limiting unit 51g calculates the front wheel lateral force upper limit value Fy based on the following equation (16). Max-F Calculate (i).

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[0046] Furthermore, the maximum lateral force limiting section 51g is configured to limit the rear wheel lateral force upper limit Fy Max-R (i) and rear wheel lateral force lower limit FyMin-R Calculate (i). As shown in the following equation (17), the steering angle δ of the rear wheel 2R R Maximum steering angle δ MaxR (For example, the limit steering angle to the right) and the minimum steering angle δ MinR (For example, the maximum steering angle to the left) δ MinR ≦δ R ≦δ MaxR …(17) The maximum lateral force limiting unit 51g calculates the rear wheel lateral force upper limit value Fy based on the following equations (18) and (19): Max-R (i) and rear wheel lateral force lower limit Fy Min-R Calculate (i).

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[0047] For example, the front wheel steering angle δ F Based on the rear wheel steering angle δ R When the upper limit of the front wheel lateral force Fy is Max-F (i) Maximum front wheel lateral force Fy after limiting to the following value: MaxF (i) is substituted into the above equation (13) to obtain the front wheel steering angle δ Max-F (i), and calculate the minimum steering angle δ of the rear wheel 2R based on the following equations (21) and (22): MinR and maximum steering angle δ MaxR may be calculated.

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[0048] The target longitudinal force calculation unit 51h calculates the maximum deceleration setting value Ax based on the following equation (23): Max and the front wheel target lateral force Fy ReqF (i) and the rear wheel target lateral force Fy ReqR (i) and the maximum front wheel lateral force Fy MaxF (i) and the maximum rear wheel lateral force Fy MaxR (i) A target longitudinal force Fx to be generated in the host vehicle 1 Req Calculate (i).

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[0049] The target longitudinal force calculation unit 51h calculates the target longitudinal force Fx based on the following equations (24) and (25): Req (i) is the brake distribution ratio κ of the front wheel 2F and the rear wheel 2R F :(1-κ F ) based on the target longitudinal force Fx of the front wheels, which is the target longitudinal force to be generated on the front wheels 2F. ReqF (i) and the target rear wheel longitudinal force Fx, which is the target lateral force to be generated on the rear wheel 2R. ReqR (i) is calculated respectively.

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[0050] The maximum longitudinal force calculation unit 51i calculates the front wheel load Fz F(i) and rear wheel load Fz R (i) The friction circles of the front wheel 2F and the rear wheel 2R according to (i) and the maximum lateral force Fy MaxF (i) and the maximum rear wheel lateral force Fy MaxR Based on (i), the maximum longitudinal force that can be generated on the front wheel 2F is the maximum longitudinal force Fx MaxF (i) and the maximum rear wheel longitudinal force Fx, which is the maximum longitudinal force that can be generated on the rear wheel 2R. MaxR (i) and (ii) are calculated respectively. Specifically, the maximum longitudinal force calculation unit 51i calculates the front wheel maximum longitudinal force Fx based on the following equations (26) and (27): MaxF (i) and maximum rear wheel longitudinal force Fx MaxR Calculate (i).

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[0051] The maximum acceleration / deceleration calculation unit 51j calculates the front wheel target longitudinal force Fx ReqF (i) and maximum front wheel longitudinal force Fx MaxF (i) The smallest value min(Fx ReqF (i),Fx MaxF (i)) and the rear wheel target longitudinal force Fx ReqR (i) and maximum rear wheel longitudinal force Fx MaxR (i) The smallest value min(Fx ReqR (i),Fx MaxR (i)) and the ratio of the target lateral force to the maximum lateral force Fy ReqF (i) / Fy MaxF (i), Fy ReqR (i) / Fy MaxR (i) respectively, and the sum of these is the maximum longitudinal force Fx at which the frictional force of the front wheel 2F and the rear wheel 2R does not exceed the friction limit. Max (i) (the following formula (28)).

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[0052] Selector 51k is the maximum longitudinal force Fx Max The deceleration caused by (i) (Fx Max (i) / m) and maximum deceleration setting value A xMaxThe smaller of these two is the maximum deceleration A at the point of interest i. x The calculated value (i) is output to the maximum speed calculation unit 51a and the load calculation unit 51c. This completes the calculation for the target point i. Then, when the target point i is moved backward by one and calculation for the next target point i is started, the maximum deceleration A calculated at the previous target point (i.e., point (i+1)) is x (i+1) is the target vehicle speed V at the new target point i Tar (i) and maximum deceleration A x Used in the calculation of (i).

[0053] FIG. 7 is a block diagram showing an example of the functional configuration of the forward calculation unit 52. As shown in FIG. The forward calculation unit 52 sets a point one position ahead of the current position of the vehicle 1 as the first point of interest i, and calculates the maximum acceleration A at the point of interest i while sequentially moving the point of interest i forward one position at a time until it reaches the farthest point. x (i) and target vehicle speed V Tar (i) is calculated respectively. The forward calculation unit 52 includes a maximum speed calculation unit 52a, selectors 52b and 52k, a load calculation unit 52c, a target lateral force calculation unit 52d, a maximum lateral force calculation unit 52e, a maximum steering angle calculation unit 52f, a maximum lateral force limiting unit 52g, a target longitudinal force calculation unit 52h, a maximum longitudinal force calculation unit 52i, and a maximum acceleration / deceleration calculation unit 52j.

[0054] In the calculation at the first point of interest i, the maximum speed calculation unit 52a calculates the target vehicle speed V at the point (i-1) immediately after the point of interest i. Tar (i-1) is the first vehicle speed profile V in Set the target vehicle speed and the maximum acceleration A at point (i-1). x (i-1) is the maximum allowable acceleration preset value A xMax Set. In the calculation at the second or subsequent point of interest i, the target vehicle speed V calculated at the previous point (i.e., point (i-1)) is used. Tar (i-1) and maximum acceleration A x Enter (i-1). The maximum speed calculation unit 52a calculates the target vehicle speed V at the previous point (i-1). Tar (i-1) and maximum acceleration A x The speed limit value of the following equation (29) is set according to (i-1).

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[0055] The selector 52b selects the first vehicle speed profile V at the point of interest i. in Target vehicle speed V in (i) according to the following equation (30), the target vehicle speed V Tar Set (i).

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[0056] The load calculation unit 52c calculates the maximum acceleration A at the point (i-1) immediately ahead based on the following equations (31) and (32): x In response to (i-1), a front wheel load Fz, which is the load on the front wheel 2F based on the pitch motion of the body of the host vehicle 1, is calculated. F (i) and the rear wheel load Fz, which is the load on the rear wheel 2R R Calculate (i).

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[0057] The functions of the target lateral force calculation unit 52d, maximum lateral force calculation unit 52e, maximum steering angle calculation unit 52f, maximum lateral force limiting unit 52g, target longitudinal force calculation unit 52h, maximum longitudinal force calculation unit 52i, maximum acceleration / deceleration calculation unit 52j, and selector 52k of the forward calculation unit 52 are similar to the functions of the target lateral force calculation unit 51d, maximum lateral force calculation unit 51e, maximum steering angle calculation unit 51f, maximum lateral force limiting unit 51g, target longitudinal force calculation unit 51h, maximum longitudinal force calculation unit 51i, maximum acceleration / deceleration calculation unit 51j, and selector 51k of the backward calculation unit 51. However, the "maximum deceleration A" in the explanation of the backward calculation unit 51 is omitted. x ", "Maximum deceleration setting value A xMax " and "Brake distribution ratio" are set to "Maximum acceleration A x ", "Maximum acceleration setting value A xMax "," shall be read as "driving force distribution ratio."

[0058] (operation) 8 is an explanatory diagram of an example of a vehicle speed control method according to an embodiment. In step S1, the geometric calculation unit 50 calculates a first vehicle speed profile V, which is a profile of a target vehicle speed of the host vehicle. in Calculate. In step S2, the backward calculation unit 51 calculates the first vehicle speed profile V so as not to exceed the friction limit during deceleration. in By limiting the second vehicle speed profile V B Set. Fig. 9 is a flowchart of an example of the process of step S2 in Fig. 8. Here, the process of steps S10 to S17 is repeated while moving the attention point i backward one step at a time from the point immediately behind the farthest point toward the current position of the vehicle 1.

[0059] In step S10, the maximum speed calculation unit 51a and the selector 51b calculate the maximum deceleration A at the point (i+1) immediately before the target point i. x (i+1) at the point of interest i 1 Vehicle speed profile V in Target vehicle speed V in (i) is limited to the second vehicle speed profile V B Target vehicle speed V B Calculate (i). In step S11, the target lateral force calculation unit 51d calculates the front wheel target lateral force Fy ReqF (i) and rear wheel target lateral force Fy ReqR Calculate (i). In step S12, the maximum steering angle calculation unit 51f calculates the target vehicle speed V Tar In (i), the maximum steering angle that can be achieved by the steering mechanism is calculated.

[0060] In step S13, the maximum lateral force calculation unit 51e calculates the front wheel maximum lateral force Fy MaxF (i) and maximum rear wheel lateral force Fy MaxR The maximum lateral force limiting unit 51g calculates the maximum front wheel lateral force Fy so that the steering angle of the steered wheels does not exceed the maximum steering angle. MaxF (i) is limited. In the case of a four-wheel steering vehicle, the maximum rear wheel lateral force Fy is also limited. MaxR (i) may be restricted. In step S14, the target longitudinal force calculation unit 51h calculates the front wheel target longitudinal force Fx ReqF (i) and rear wheel target longitudinal force Fx ReqR Calculate (i). In step S15, the maximum longitudinal force calculation unit 51i calculates the front wheel maximum longitudinal force Fx MaxF (i) and maximum rear wheel longitudinal force Fx MaxR (i) and (ii) are calculated respectively.

[0061] In step S16, the maximum acceleration / deceleration calculation unit 51j calculates the maximum front wheel longitudinal force Fx MaxF (i), Rear wheel maximum longitudinal force Fx MaxR (i) Front wheel target longitudinal force Fx ReqF (i) Rear wheel target longitudinal force Fx ReqR (i) is limited, and the maximum longitudinal force Fx that can be generated on the vehicle 1 without the frictional force of the front wheel 2F and the rear wheel 2R exceeding the friction limit is calculated. Max Calculate (i). In step S17, the selector 51k selects the maximum longitudinal force Fx Max The deceleration caused by (i) (Fx Max (i) / m) is the maximum deceleration setting value A xMax The maximum deceleration is A x (i) is calculated, and then the process proceeds to step S3 in FIG.

[0062] 8, in step S3, the forward calculation unit 52 calculates the second vehicle speed profile V so as not to exceed the friction limit during acceleration. B By limiting the third vehicle speed profile V out Set. The processing of the forward calculation unit 52 is similar to the processing of the backward calculation unit 51 in step S2, except for the following points (1) and (2). (1) The target point i is moved forward one point at a time from the point one point ahead of the current position of the vehicle 1 to the farthest point. (2) "Maximum deceleration A x ", "Maximum deceleration setting value A xMax " and "Brake distribution ratio" are set to "Maximum acceleration A x ", "Maximum acceleration setting value A xMax "," shall be read as "driving force distribution ratio." In step S4, the vehicle control unit 22 calculates the third vehicle speed profile V out The actuator 18 is driven based on this to control the speed of the host vehicle 1. Then, the process ends.

[0063] (Effects of the embodiment) (1) Controller 17 sets a target driving trajectory for host vehicle 1, sets a maximum steering angle that is the maximum value of the steering angle that can be realized by the steering mechanism according to the vehicle speed of host vehicle 1, sets a target vehicle speed at which host vehicle 1 drives on the target driving trajectory without the steering angle of host vehicle 1 exceeding the maximum steering angle, and controls the vehicle speed of host vehicle 1 based on the target vehicle speed. This makes it possible to set the target vehicle speed so as not to exceed the limit of the steering angle that can be realized by the steering mechanism, improving the ability to follow the target driving trajectory.

[0064] (2) The controller 17 may calculate a maximum lateral force, which is the maximum value of the lateral force that can be generated on the wheels of the vehicle 1, based on the maximum steering angle, and may calculate a maximum longitudinal force, which is the maximum value of the longitudinal force that can be generated on the wheels of the vehicle 1, based on the friction circle of the wheels of the vehicle 1 and the maximum lateral force, and may set a target vehicle speed based on the maximum longitudinal force. This allows the target vehicle speed to be set so that the lateral force and longitudinal force generated on the wheels do not exceed the friction limit.

[0065] (3) The controller 17 may set a first vehicle speed profile, which is a profile of the target vehicle speed of the host vehicle 1, so that the lateral acceleration of the center of gravity of the host vehicle 1 is equal to or less than a predetermined value at each point on the target driving trajectory, calculate the maximum speed at which either the deceleration or the acceleration is equal to or less than a first predetermined value at each point on the target driving trajectory as a first maximum speed, set a second vehicle speed profile by limiting the first vehicle speed profile by the first maximum speed at each point on the target driving trajectory, calculate the maximum speed at which the other of the deceleration or the acceleration is equal to or less than a second predetermined value at each point on the target driving trajectory as a second maximum speed, set a third vehicle speed profile by limiting the second vehicle speed profile by the second maximum speed at each point on the target driving trajectory, and control the vehicle speed of the host vehicle 1 based on the third vehicle speed profile. This allows the vehicle speed to be controlled so as not to exceed the deceleration and acceleration allowable for the host vehicle.

[0066] (4) When one of the points on the target driving trajectory, one closer to the vehicle 1 or one farther ahead of the vehicle 1, is designated as a first point, and the other is designated as a second point, the controller 17 may set the maximum steering angle based on the target vehicle speed at the first point, and set the target vehicle speed at the second point based on the maximum longitudinal force. This allows a target vehicle speed profile that does not exceed the limits of the steering mechanism to be planned in a time series.

[0067] (5) The controller 17 may calculate a target lateral force, which is a target value of the lateral force to be generated on the wheels of the host vehicle 1, based on the curvature of the target driving trajectory and the target vehicle speed at the first point, calculate a target longitudinal force, which is a target value of the longitudinal force to be generated on the wheels of the host vehicle 1, based on the friction circle of the wheels of the host vehicle 1 and the target lateral force, set a maximum acceleration / deceleration, which is the maximum value of the acceleration / deceleration allowable for the host vehicle 1, based on the target longitudinal force limited by the maximum longitudinal force, and set a target vehicle speed at the second point based on the maximum acceleration / deceleration. This allows the target vehicle speed to be set based on the acceleration / deceleration limited by the friction circle of the wheels of the host vehicle 1 and the target lateral force. [Explanation of symbols]

[0068] 22...vehicle control unit, 50...geometric calculation unit, 51...backward calculation unit, 51a, 522a...maximum speed calculation unit, 51b, 51k, 52b, 52k...selector, 51c, 52c...load calculation unit, 51d, 52d...target lateral force calculation unit, 51e, 52e...maximum lateral force calculation unit, 51f, 52f...maximum steering angle calculation unit, 51g, 52g...maximum lateral force limiting unit, 51h, 52h...target longitudinal force calculation unit, 51i, 52i...maximum longitudinal force calculation unit, 51j, 52j...maximum acceleration / deceleration calculation unit

Claims

1. Set a target driving trajectory for the vehicle, setting a first vehicle speed profile, which is a profile of a target vehicle speed of the host vehicle, so that a lateral acceleration of the center of gravity of the host vehicle is equal to or less than a predetermined value at each point on the target traveling trajectory; setting a maximum steering angle that is a maximum value of the steering angle that can be realized by the steering mechanism according to the vehicle speed of the host vehicle; At each of the points, a maximum speed at which the steering angle of the host vehicle does not exceed the maximum steering angle and one of deceleration and acceleration is equal to or less than a first predetermined value is calculated as a first maximum speed; establishing a second vehicle speed profile by limiting the first vehicle speed profile at the first maximum speed at each of the locations; At each of the points, a maximum speed at which the steering angle of the host vehicle does not exceed the maximum steering angle and the other of the deceleration and the acceleration is equal to or less than a second predetermined value is calculated as a second maximum speed; establishing a third vehicle speed profile by limiting the second vehicle speed profile at the second maximum speed at each of the locations; controlling the vehicle speed of the host vehicle based on the third vehicle speed profile; A vehicle speed control method comprising:

2. calculating a maximum lateral force that is a maximum value of a lateral force that can be generated on a wheel of the host vehicle based on the maximum steering angle; calculating a maximum longitudinal force that is a maximum value of a longitudinal force that can be generated on a wheel of the host vehicle based on a friction circle of the wheel of the host vehicle and the maximum lateral force; setting the target vehicle speed based on the maximum longitudinal force; 2. The vehicle speed control method according to claim 1.

3. one of the points on the target traveling trajectory that is closer to the host vehicle and the point on the target traveling trajectory that is farther from the host vehicle is designated as a first point, and the other point is designated as a second point; setting the maximum steering angle based on the target vehicle speed at the first location; setting the target vehicle speed at the second point based on the maximum longitudinal force; 3. The vehicle speed control method according to claim 2.

4. calculating a target lateral force, which is a target value of a lateral force to be generated on a wheel of the host vehicle, based on the curvature of the target traveling trajectory at the first point and the target vehicle speed; calculating a target longitudinal force, which is a target value of a longitudinal force to be generated in a wheel of the host vehicle, based on the friction circle of the wheel of the host vehicle and the target lateral force; setting a maximum acceleration / deceleration that is a maximum value of acceleration / deceleration allowable for the host vehicle based on the target longitudinal force limited by the maximum longitudinal force; setting the target vehicle speed at the second location based on the maximum acceleration / deceleration; 4. The vehicle speed control method according to claim 3.

5. a drive device that generates a drive force for the host vehicle; a braking device that generates a braking force for the host vehicle; a controller that sets a target traveling trajectory of the host vehicle, sets a first vehicle speed profile that is a profile of a target vehicle speed of the host vehicle so that a lateral acceleration of a center of gravity of the host vehicle is equal to or less than a predetermined value at each point on the target traveling trajectory, sets a maximum steering angle that is a maximum value of a steering angle that can be realized by a steering mechanism according to the vehicle speed of the host vehicle, calculates, at each point, a maximum speed at which the steering angle of the host vehicle does not exceed the maximum steering angle and one of deceleration or acceleration is equal to or less than a first predetermined value as a first maximum speed, sets a second vehicle speed profile by limiting the first vehicle speed profile at each point, calculates, at each point, a maximum speed at which the steering angle of the host vehicle does not exceed the maximum steering angle and the other of deceleration or acceleration is equal to or less than a second predetermined value as a second maximum speed, sets a third vehicle speed profile by limiting the second vehicle speed profile at each point, and controls at least one of the drive device or the brake device based on the third vehicle speed profile; A vehicle speed control device comprising:

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