Vehicle control method and vehicle control device

Abstract

To provide a vehicle control method and a vehicle control device capable of returning a vehicle to a target track when the vehicle deviates from the target track in a state where steering control is limited according to a state of friction with a road surface.SOLUTION: When the tire force of the front wheel is limited within the range of the friction limit and the vehicle deviates from the target trajectory, update the range of the friction limit so that the range of the friction limit expands as a deviation amount of the vehicle from the target trajectory increases, generate a return steering command so that the vehicle returns to the target trajectory within the updated range of the friction limit, and perform steering control of the vehicle based on the return steering command.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A technology is known in which parameters included in an assist amount optimization problem are adjusted according to the vehicle's driving conditions, including the friction conditions with the road surface, the optimal assist amount is determined sequentially using the adjusted parameters, and the vehicle's driving control is performed based on the determined optimal assist amount (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-30659 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology disclosed in Patent Document 1 has a problem in that when the steering amount is limited by an upper limit value set according to the friction conditions with the road surface, if the vehicle deviates from the target trajectory, the steering control may be limited to the steering amount necessary to return the vehicle to the target trajectory, and the vehicle may not be able to return to the target trajectory.

[0005] The problem to be solved by the present invention is to provide a vehicle control method and a vehicle control device that can return a vehicle to a target trajectory when the vehicle deviates from the target trajectory while steering control is limited depending on the friction condition with the road surface. [Means for solving the problem]

[0006] The present invention solves the above problem by steering and controlling a vehicle so that it follows a target trajectory, and when the tire force of the front wheels is limited within the friction limit range and the vehicle deviates from the target trajectory, updating the friction limit range so that the greater the deviation of the vehicle from the target trajectory, the wider the friction limit range is, generating a return steering command so that the vehicle returns to the target trajectory within the updated friction limit range, and steering and controlling the vehicle based on the return steering command. [Effects of the Invention]

[0007] According to the present invention, when a vehicle deviates from a target trajectory while steering control is limited depending on the frictional conditions with the road surface, the vehicle can be returned to the target trajectory. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a vehicle control system including a vehicle control device according to the present invention. [Figure 2] FIG. 2 is a diagram for explaining a scene in which the vehicle control method according to this embodiment is executed. [Figure 3] FIG. 3 is a block diagram showing an example of each functional unit of the vehicle control device according to this embodiment. [Figure 4] FIG. 4 is an example of a flowchart showing the procedure of the vehicle control method according to this embodiment. [Figure 5] FIG. 5 is a diagram for explaining the relationship between the constraint value of the operation amount and the deviation amount of the vehicle from the target trajectory in this embodiment. [Figure 6] FIG. 6 is a block diagram showing an example of each functional unit of the vehicle control device according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] FIG. 1 is a block diagram showing a vehicle control system including a vehicle control device according to the present invention. The vehicle control system 100 is an in-vehicle system that drives a vehicle using autonomous driving control. Autonomous driving control refers to autonomously controlling the driving behavior of a vehicle using a vehicle control device 1, and the driving behavior includes all driving behaviors such as acceleration, deceleration, starting, stopping, steering to the right or left, changing lanes, and pulling over. Furthermore, autonomously controlling driving behavior refers to the vehicle control device 1 controlling the driving behavior using a device in the vehicle. In other words, the vehicle control device 1 intervenes in and controls these driving behaviors within a predetermined range. Driving behaviors that are not intervened in are manually operated by the driver.

[0011] Vehicle control system 100 can be applied not only to vehicle driving under autonomous driving control, but also to assisting vehicle driving under manual driving by a driver. When vehicle control system 100 is applied to autonomous vehicle driving control, it can be applied to cases where both speed control and steering control are autonomously controlled, or where one of speed control and steering control is autonomously controlled and the other is manually controlled.

[0012] 1, the vehicle control system 100 includes a vehicle control device 1, a map DB 2, a detection device 3, and a drive mechanism 4. These devices included in the vehicle control system 100 are in-vehicle devices, are connected via a CAN or other in-vehicle LAN, and can exchange information with each other.

[0013] The map DB2 is a high-precision three-dimensional map that describes road structures, including road surface markings that indicate lanes and destinations. The map DB2 is a database containing information used for generating a target trajectory and / or controlling vehicle travel. The map DB2 includes two-dimensional and / or three-dimensional position information for each map coordinate, road information for each map coordinate, lane boundary information, road attribute information, lane incline / descent information, lane identification information, destination lane information, facility information, and attribute information thereof. The road information includes information such as road width, curvature radius, road shoulder structures, road traffic regulations (speed limits, lane change permission / prohibition), road merging points, branching points, and locations where the number of lanes increases or decreases. The map DB2 may be stored in a readable state on a recording medium provided in the vehicle control device 1 or a server device, as well as in the on-board device.

[0014] The map DB2 also includes information on lane boundaries that indicate the boundaries between the lane in which the vehicle is traveling and other lanes. Lane boundaries exist on both the left and right sides of the vehicle's traveling direction. The form of the lane boundaries is not particularly limited, and examples thereof include road markings and road structures. Examples of lane boundaries that are road markings include lane boundary lines and center lines. Examples of road boundary structures include medians, guardrails, curbs, and side walls of tunnels or expressways. Note that lane boundaries are preset in the map DB2 for points where lane boundaries cannot be clearly identified (for example, within intersections). The preset lane boundaries are imaginary road boundaries and are not actually existing road markings or road structures.

[0015] The detection device 3 is a device that detects various types of information. The detection device 3 includes sensors for detecting the driving environment around the vehicle. The driving environment around the vehicle includes objects around the vehicle. Examples of objects include lane markings on roads, zebra strips, center lines, road markings, medians, guardrails, curbs, highway sidewalls, road signs, traffic lights, crosswalks, construction sites, accident sites, traffic restrictions, advertising billboards, road signs, roadside trees, buildings, and road structures. Objects also include automobiles (other vehicles) other than vehicles, motorcycles, bicycles, and pedestrians. Objects also include obstacles that obstruct the vehicle's travel. The detection device 3 acquires the position, attitude (orientation), and speed of the detected objects.

[0016] The detection information of the detection device 3 is acquired by the vehicle control device 1 at predetermined time intervals. The vehicle control device 1 acquires information about objects around the vehicle from the detection device 3. The detection device 3 includes, for example, a camera. The camera recognizes objects around the vehicle from images. The detection device 3 may also be equipped with a distance measuring device for calculating the relative distance and relative speed between the vehicle and surrounding objects (preceding vehicles, obstacles). The distance measuring device is, for example, a laser radar or LIDAR. A single vehicle may be provided with a plurality of such devices.

[0017] The detection device 3 includes a sensor for detecting the vehicle state of the vehicle. The vehicle state of the vehicle includes, for example, the vehicle speed, yaw rate, frictional conditions with the road surface on which the vehicle is traveling, and the current position of the vehicle. The detection device 3 includes a vehicle speed sensor and a yaw rate sensor. The vehicle speed sensor measures the rotational speed of the drive train, such as the drive shaft, and detects the traveling speed of the host vehicle (hereinafter also referred to as vehicle speed) based on this. The yaw rate sensor is a sensor, such as a gyro sensor, that detects the vehicle attitude, such as the yaw rate of the vehicle. The friction information includes the friction coefficient (μ) between the vehicle wheels and the road surface. The detection device 3 estimates the friction coefficient based on, for example, the rate of change of the steering angle relative to a steering angle command value. The detection device 3 may also estimate the friction coefficient from the state of the road surface recognized from a camera image.

[0018] The detection device 3 includes a vehicle position sensor. The vehicle position sensor is composed of, for example, a GPS unit, a gyro sensor, etc. The vehicle position sensor detects radio waves transmitted from multiple satellite communications by the GPS unit, periodically acquires vehicle position information, and detects the current position of the vehicle based on the acquired vehicle position information, angle change information acquired from the gyro sensor, and vehicle speed acquired from the vehicle speed sensor. The detection device 3 also acquires, for example, the position of the vehicle within the road (the lateral position of the vehicle in the left-right direction) as the current position of the vehicle. For example, the detection device 3 recognizes the road surface around the vehicle from a camera image and estimates the lateral position of the vehicle within the road. The lateral position of the vehicle within the road is based, for example, on the position of the center of gravity of the vehicle. The detection information of the detection device 3 is acquired by the vehicle control device 1 at predetermined time intervals.

[0019] The vehicle control device 1 is a device that controls the running of a vehicle by controlling and cooperating with devices included in the vehicle control system 100. In this embodiment, the vehicle control device 1 includes a processor 10, which realizes a vehicle control function. The processor 10 is a computer that includes a ROM that stores a program, a CPU that is an operating circuit that functions as the vehicle control device 1 by executing the program stored in the ROM, and a RAM that functions as an accessible storage device.

[0020] The processor 10 electronically controls the drive mechanism 4, which governs the operation of the vehicle. The processor 10 controls the drive mechanism 4 to drive the vehicle so that it follows a target trajectory at a target speed. The target trajectory is the trajectory along which the vehicle travels within a road. The drive mechanism 4 includes an electric motor and / or an internal combustion engine as a driving source, a power transmission device including a drive shaft and an automatic transmission that transmits output from these driving sources to the drive wheels, a drive device that controls the power transmission device, and a braking device that brakes the wheels. The processor 10 calculates the target speed, generates a control signal including a braking / driving force command value so that the vehicle speed becomes the target speed, and sends the control signal to the drive mechanism 4. The drive device and braking device perform braking / driving control of the vehicle based on the control signal obtained from the processor 10.

[0021] The processor 10 controls the steering device included in the drive mechanism 4 so that the vehicle travels while maintaining a predetermined lateral position relative to the target trajectory. The steering device is equipped with a steering actuator. The steering actuator includes a motor attached to the steering column shaft, etc. The processor 10 generates a target trajectory, generates a control signal including a steering angle command value so that the vehicle follows the target trajectory, and sends the control signal to the drive mechanism 4. The steering device performs steering control of the vehicle based on the control signal obtained from the processor 10. Below, each functional unit of the processor 10 according to this embodiment will be described in detail.

[0022] The processor 10 includes, as functional blocks, a vehicle state acquisition unit 11, a road boundary generation unit 12, a target trajectory generation unit 13, an operation amount calculation unit 14, a target behavior generation unit 15, and a control command unit 16. The processor 10 of this embodiment executes each function through cooperation between the above-mentioned hardware and software for realizing each function or executing each process.

[0023] The vehicle state acquisition unit 11 acquires the vehicle state from the detection device 3. The vehicle state includes the vehicle speed, yaw rate, friction condition with the road surface on which the vehicle is traveling, and the current position of the vehicle. The vehicle state is acquired at regular intervals.

[0024] The lane boundary generation unit 12 generates the boundaries of the lane along which the vehicle will travel, based on the current position of the vehicle and information from the map DB2. The lane boundary generation unit 12 acquires surrounding lane information, including information about the area ahead of the vehicle, from the map DB2. For example, the lane boundary generation unit 12 acquires lane information including the lane boundary lines of the lane along which the host vehicle is traveling. The lane information includes the position of the lane boundary lines and the width of the lane. The lane boundary generation unit 12 may also acquire lane information including the lane boundary lines of the host lane from an image of the area around the vehicle captured by a camera included in the detection device 3. The lane boundary generation unit 12 generates left and right boundaries of the lane along the acquired left and right lane boundary lines of the host lane. In other words, the lane is the area between the left and right lane boundary lines of the host lane.

[0025] The target trajectory generating unit 13 generates a target trajectory based on the boundary of the road located ahead of the vehicle. More specifically, the target trajectory generating unit 13 generates a target trajectory within the road. For example, the target trajectory generating unit 13 generates a target trajectory along the center line between the left and right boundaries of the road. The target trajectory generated by the target trajectory generating unit 13 is a target trajectory during normal driving, and is a target trajectory for the vehicle to drive within the road. The target trajectory is, for example, a trajectory that has a predetermined trajectory length and curvature, starting from the center of gravity of the vehicle.

[0026] The operation amount calculation unit 14 calculates continuous operation amounts that can be realized by the vehicle. The operation amount is an operation amount for controlling the position of a traveling vehicle, for example, a tire force generated on each wheel of the vehicle. The tire force includes either or both of longitudinal forces (braking force and driving force) and lateral forces. The position of a traveling vehicle is controlled by generating tire forces on the tires of each wheel. In this embodiment, the operation amount calculation unit 14 calculates the longitudinal force based on a target speed. The calculated longitudinal force is also referred to as a target longitudinal force. The target speed is generated based on detection information obtained by detecting a target trajectory and the traveling environment around the vehicle. The surrounding traveling environment includes, for example, a preceding vehicle, an obstacle, etc. The operation amount calculation unit 14 calculates a lateral force so that the vehicle travels while maintaining a predetermined lateral position with respect to the target trajectory. The calculated lateral force is also referred to as a target lateral force.

[0027] Here, calculation of tire force will be described using the tire force of the front wheels as an example of each wheel of the vehicle. In this embodiment, the operation amount calculation unit 14 calculates the tire force of the front wheels within the range of the friction limit. The range of the friction limit is set according to the friction condition with the road surface on which the vehicle is traveling. The correspondence relationship between the friction condition (for example, the friction coefficient μ) and the range of the friction limit is stored in advance. The operation amount calculation unit 14 sets the range of the friction limit according to the friction coefficient acquired by the vehicle state acquisition unit 11. The friction coefficient used to set the range of the friction limit is an estimated value acquired from the detection device 3. The operation amount calculation unit 14 calculates the tire force of the front wheels so that the resultant force of the longitudinal force and the lateral force does not exceed the range of the friction limit.

[0028] If the tire force of the front wheels is limited within the friction limit range, when the vehicle deviates from the target trajectory, the lateral force required for the vehicle to return to the target trajectory cannot be generated by steering control, making it difficult for the vehicle to return to the target trajectory. For example, assume a case in which the vehicle deviates from the target trajectory, as shown in FIG. 2. FIG. 2 is a diagram illustrating a scenario in which the vehicle control method according to this embodiment is executed. Circles set around the front and rear wheels of the vehicle indicate an example of the friction limit range for each wheel. That is, the area inside the circle indicates the friction limit range. The left diagram of FIG. 2 illustrates a scenario in which a conventional vehicle deviates from the target trajectory. The friction limit range Fr1 is the friction limit range for the front wheels of the vehicle, which is the friction limit range corresponding to the friction coefficient (estimated value) with respect to the road surface obtained from the detection device 3. In the left diagram of FIG. 2, a vehicle traveling on the target trajectory Ta at vehicle position V1 deviates from the target trajectory Ta and moves to vehicle position V1′.

[0029] At this time, the vehicle needs to be steered to the right to return to the target trajectory Ta before the deviation. However, because the friction limit range is set according to the friction coefficient with the road surface, the steering control necessary to return to the target trajectory may not be realized, and the vehicle may travel along the predicted trajectory Tb and deviate from the road. The friction limit range Fr1 is based on an estimated value of the friction coefficient. If the friction limit range corresponding to the actual friction coefficient is the friction limit range Fr2, as shown in the center diagram of Figure 2, the friction limit range Fr2 may be larger than the friction limit range Fr1. In this case, the tire force limited by the friction limit range can also be set to a larger value. Therefore, if the vehicle is steered based on the lateral force calculated within the friction limit range Fr2, there is a possibility that the vehicle will be able to return to the target trajectory Ta. Therefore, in this embodiment, as shown in the right diagram of FIG. 2, if a vehicle traveling on a target trajectory Ta at vehicle position V1 deviates from the target trajectory Ta and moves to vehicle position V1′, the operation amount calculation unit 14 updates the friction limit range to a friction limit range Fr3, which is wider than the friction limit range Fr1 set according to the estimated value of the friction coefficient, and calculates the lateral force within the updated friction limit range. The vehicle performs steering control based on the lateral force calculated within the updated friction limit range. Thus, in this embodiment, compared to when the vehicle is only steered within the friction limit range corresponding to the friction coefficient with the road surface, additional steering control allows the vehicle to return to the target trajectory. This prevents the vehicle from going off course. An example of a specific calculation method will be described in detail below.

[0030] Here, an example of a functional unit included in the manipulated variable calculation unit 14 according to this embodiment will be described with reference to FIG. 3. FIG. 3 is a block diagram illustrating an example of each functional unit of the vehicle control device according to this embodiment. As shown in FIG. 3, the manipulated variable calculation unit 14 includes, as functional units, a constraint value calculation unit 140, a pre-processing manipulated variable calculation unit 141, and a limit processing unit 142. The constraint value calculation unit 140 first determines whether the tire force of the front wheels of the vehicle is limited within the range of the friction limit corresponding to the friction coefficient with the road surface on which the vehicle is traveling. If the tire force of the front wheels of the vehicle is limited within the range of the friction limit, the constraint value calculation unit 140 acquires the friction coefficient (estimated value) of the road surface on which the vehicle is traveling, the boundary of the road, and the target trajectory (lateral position, yaw angle) to calculate a constraint value for calculating a target lateral force. The constraint value calculation unit 140 calculates, as a constraint value, the maximum value of the lateral force at which the resultant force of the longitudinal force and the lateral force generated at the front wheels does not exceed the range of the friction limit corresponding to the friction coefficient of the road surface. In other words, the constraint value is the upper limit value of the target lateral force.

[0031] Furthermore, when the tire force of the front wheels of the vehicle is limited within the friction limit range, the constraint value calculation unit 140 determines whether the vehicle has deviated from the target trajectory. A method for determining whether the vehicle has deviated from the target trajectory will be described. The constraint value calculation unit 140 determines whether the vehicle has deviated from the target trajectory based on the current position of the vehicle and the target trajectory. Specifically, the constraint value calculation unit 140 acquires the current position of the vehicle from the detection device 3 and acquires the target trajectory from the target trajectory generation unit 13. For example, the current position is the position of the center of gravity of the vehicle. The constraint value calculation unit 140 determines that the vehicle has deviated from the target trajectory when the current position of the vehicle is away from the target trajectory by more than a predetermined distance. The predetermined distance is, for example, the distance from the position of the center of gravity of the vehicle to the position of the side of the vehicle.

[0032] If the vehicle deviates from the target trajectory, the constraint value calculation unit 140 updates the friction limit range so that it is larger than the friction limit range corresponding to the road surface friction coefficient (estimated value). More specifically, the friction limit range is updated so that the friction limit range expands as the amount of deviation of the vehicle from the target trajectory increases. The amount of deviation is, for example, the distance between the vehicle's current position and the target trajectory. The amount of deviation increases due to nonlinearity of the tires or vehicle. The constraint value calculation unit 140 calculates a constraint value for the lateral force based on the updated friction limit range. That is, the constraint value calculation unit 140 calculates the maximum value of the lateral force at which the resultant force of the longitudinal force and the lateral force does not exceed the updated friction limit range.

[0033] The constraint value calculation unit 140 may also calculate the distance between the boundary of the road and the current position of the vehicle, and update the friction limit range so that the shorter the distance, the wider the friction limit range. The constraint value calculation unit 140 may also update the friction limit range so that the friction limit range is wider, with the upper limit set to a limit range corresponding to the upper limit of the tire force that can be achieved by the steering actuator of the vehicle (hereinafter also referred to as the steering actuator limit range). In other words, the updated friction limit range is larger than the friction limit range corresponding to the road surface friction coefficient (estimated value) and smaller than the steering actuator limit range. Note that, when the vehicle does not deviate from the target trajectory, as described above, the constraint value calculation unit 140 calculates the lateral force constraint value based on the friction limit range corresponding to the friction coefficient with the road surface.

[0034] In this embodiment, the constraint value calculation unit 140 may calculate a target tire force for the vehicle to follow the target trajectory during steering control so that the steering speed does not exceed a predetermined steering speed, the target steering amount does not exceed a predetermined steering amount, or the vehicle body yaw resonance frequency of the vehicle does not exceed a predetermined frequency. More specifically, the constraint value calculation unit 140 calculates the constraint value so as to satisfy the above-mentioned constraint conditions on the steering speed, the target operation amount, or the vehicle body yaw resonance frequency.

[0035] The pre-processing operation amount calculation unit 141 calculates, as the pre-processing operation amount, an operation amount that is feasible and continuous for the vehicle based on the target trajectory (lateral position, yaw angle). In this embodiment, the pre-processing operation amount calculation unit 141 calculates, as the pre-processing operation amount, a pre-processing lateral force so that the vehicle travels while maintaining a predetermined lateral position with respect to the target trajectory.

[0036] The limit processing unit 142 limits the pre-processing operation amount calculated by the pre-processing operation amount calculation unit 141 using the constraint value calculated by the constraint value calculation unit 140. This calculates a target operation amount that is limited based on information about friction with the road surface. In this embodiment, the limit processing unit 142 calculates a target lateral force by performing limit processing on the pre-processing lateral force calculated by the pre-processing operation amount calculation unit 141. For example, the limit processing unit 142 compares the constraint value with the pre-processing lateral force, and if the pre-processing lateral force is equal to or greater than the constraint value, calculates the constraint value as the target lateral force. The limit processing unit 142 compares the constraint value with the pre-processing lateral force, and if the pre-processing lateral force is less than the constraint value, calculates the pre-processing lateral force as the target lateral force. The calculated target operation amount is output to the target behavior generating unit 15.

[0037] The target behavior generator 15 generates a target behavior of the vehicle calculated from target operation variables including the target lateral force. The target behavior includes, for example, a standard yaw rate calculated from a standard vehicle model. For example, the target behavior generator 15 generates a standard yaw rate by an inverse system consisting of the standard vehicle model using the target operation variables calculated and limit-processed by the operation variable calculator 14. The generated standard yaw rate is output to the control command unit 16.

[0038] In this embodiment, the control command unit 16 outputs a control command to the drive mechanism 4 to achieve a target behavior of the vehicle. The target behavior of the vehicle includes, for example, a standard yaw rate. In this embodiment, the control command unit 16 calculates a target steering amount for the vehicle to follow a target trajectory based on the standard yaw rate, and generates a control command including the target steering amount. The steering amount is, for example, a steering angle. The control command unit 16 outputs the control command to a steering device of the drive mechanism 4. In addition, the control command unit 16 calculates a deviation between the target steering amount and the actual steering amount, and applies a yaw moment to the vehicle to reduce the deviation. The yaw moment is applied according to the magnitude of the deviation between the target steering amount and the actual steering amount.

[0039] For example, the control command unit 16 compares the target behavior of the vehicle with the actual behavior of the vehicle resulting from steering control, and if the target behavior of the vehicle is not achieved by the steering control of the vehicle, it applies a yaw moment to the vehicle. The actual behavior of the vehicle is, for example, the actual yaw rate achieved by the actual steering amount. If there is a deviation (yaw rate deviation) of the actual yaw rate from the standard yaw rate achieved by steering control based on the target steering amount, the control command unit 16 generates a yaw moment (target yaw moment) to reduce the yaw rate deviation. The control command unit 16 generates a control command to apply the target yaw moment to the vehicle and outputs the control command to the drive mechanism 4. For example, if the vehicle is understeered with respect to the target trajectory, the control command unit 16 applies a yaw moment to turn the vehicle body toward the inside of the turn. In this way, by creating a slip angle of the vehicle body, the vehicle can ensure rear wheel lateral force.

[0040] Here, a specific method for applying a yaw moment will be described. For example, a yaw moment is applied to a vehicle by distributing the braking / driving force for braking / driving the vehicle to the left and right wheels of the vehicle, distributing the braking / driving force to the front and rear wheels of the vehicle, or by controlling the load on each wheel of the vehicle. When the control command unit 16 has determined the braking / driving force and / or load to be distributed to each wheel of the vehicle in order to apply a target yaw moment to the vehicle, it outputs a control command to the drive mechanism 4 that includes the braking / driving force and / or load to be distributed to each wheel.

[0041] A method for distributing braking / driving forces to the left and right wheels of a vehicle will be described. For example, the control command unit 16 applies a target yaw moment to the vehicle by distributing braking forces between the left and right front wheels so as to create a difference between the left and right braking forces. Specifically, the braking forces are distributed so that the braking force of the front wheel on the inside of a turn is greater than the braking force of the front wheel on the outside of a turn. The control command unit 16 also applies a target yaw moment to the vehicle by distributing driving forces between the left and right front wheels so as to create a difference between the left and right driving forces. Specifically, the driving forces are distributed so that the driving force of the front wheel on the outside of a turn is greater than the driving force of the front wheel on the inside of a turn. The control command unit 16 also applies a target yaw moment to the vehicle by distributing regenerative torque between the left and right front wheels so as to create a difference between the left and right regenerative torques. Specifically, the regenerative torque is distributed so that the regenerative torque of the front wheel on the inside of a turn is greater than the regenerative torque of the front wheel on the outside of a turn.

[0042] A method for distributing braking / driving forces to the front and rear wheels of a vehicle will be described. The lateral force generated on the front wheels increases as the braking / driving force of the front wheels approaches zero. Therefore, the braking / driving force is distributed so that the braking / driving force of the front wheels is reduced. For example, when there is a yaw rate deviation, the control command unit 16 distributes the braking / driving force to the front and rear wheels of the vehicle so that the braking / driving force of the rear wheels of the vehicle is greater than when there is no yaw rate deviation. Furthermore, when there is a yaw rate deviation, the control command unit 16 distributes the braking / driving force to the front and front wheels of the vehicle so that the reduction in the driving force of the front wheels of the vehicle is smaller than when there is no yaw rate deviation. The control command unit 16 may also set the reduction in the driving force to zero. The reduction in the driving force is a deceleration force generated by the drive unit, such as the braking force of an engine brake or a regenerative brake of a motor.

[0043] A method for controlling the load on each wheel of the vehicle will now be described. The lateral force generated on the front wheels increases as the load on the front wheels increases. Therefore, the loads on the front and rear wheels are distributed so that the load on the front wheels increases. For example, when there is a yaw rate deviation, the control command unit 16 controls the load on each wheel of the vehicle so that the load on the front wheels of the vehicle is greater than when there is no yaw rate deviation by reducing the driving force on the front wheels of the vehicle or by generating or increasing braking force on the front wheels of the vehicle.

[0044] Furthermore, in this embodiment, when the vehicle deviates from the target trajectory, the control command unit 16 generates a return steering command for returning the vehicle to the target trajectory and performs steering control of the vehicle based on the return steering command. The return steering command includes a target steering amount for returning the vehicle to the target trajectory. The target steering amount for returning the vehicle to the target trajectory is calculated based on a target lateral force calculated within the updated friction limit range. The generated return steering command is output to the drive mechanism 4. Specifically, when the target behavior generator 15 generates a normative yaw rate based on the target lateral force calculated within the updated friction limit range and outputs the normative yaw rate to the control command unit 16, the control command unit 16 generates a return steering command including a target steering amount for returning the vehicle to the target trajectory based on the output normative yaw rate. Furthermore, when vehicle steering control based on the return steering command is not achieved, the control command unit 16 calculates the deviation between the target steering amount included in the return steering command and the actual steering amount and applies a yaw moment to the vehicle to reduce the calculated deviation. In this embodiment, the steering command for the vehicle to follow the target trajectory before it is determined that the vehicle has deviated from the target trajectory may be distinguished from the return steering command and referred to as a following steering command.

[0045] Furthermore, the control command unit 16 generates a control command including braking / driving forces for realizing the target speed and outputs the control command to the drive mechanism 4. The control command includes braking / driving forces and / or loads to be distributed to each wheel in order to apply a target yaw moment to the vehicle.

[0046] Next, a procedure in which the vehicle control device 1 executes the vehicle control method according to this embodiment will be described with reference to Fig. 4. Fig. 4 is an example of a flowchart showing the procedure of the vehicle control method according to this embodiment.

[0047] In step S10, processor 10 acquires the vehicle state of the vehicle. The vehicle state of the vehicle includes the vehicle speed, the vehicle yaw rate, and the coefficient of friction with the road surface on which the vehicle is traveling. In step S20, processor 10 generates road boundaries. Specifically, processor 10 acquires the current position of the vehicle, acquires lane information including lane boundaries in the vehicle's traveling direction from map DB2, and generates road boundaries along the lane boundaries. In step S30, processor 10 generates a target trajectory within the road based on the road boundaries acquired in step S20.

[0048] In step S40, the processor 10 calculates the amount of manipulation required for the vehicle to follow the target trajectory. For example, the processor 10 first calculates a constraint value for the amount of manipulation based on the target trajectory, the boundary of the road, and the vehicle state. The processor 10 calculates the amount of manipulation so as not to exceed the constraint value. In step S50, the processor 10 calculates a target behavior based on the amount of manipulation. In step S60, the processor 10 imparts a yaw moment to the vehicle so as to achieve the target behavior through steering control.

[0049] Here, an example of a method for generating constraint values ​​for the manipulated variable will be described. First, the processor 10 calculates the distance L between the target trajectory and the current position of the vehicle. VT Calculate the distance L VT is calculated as a positive value when the vehicle is located to the right of the target trajectory, and as a negative value when the vehicle is located to the left of the target trajectory. In addition, the processor 10 calculates the distances L between the target trajectory and the left and right boundaries of the road. TBL , L TBR Calculate the following.

[0050] The processor 10 calculates the distance L between the target trajectory and the current position of the vehicle. VTDetermine whether the distance L between the target trajectory and the current position of the vehicle is greater than 0 m. VT is greater than 0 m, the processor 10 determines that the distance L between the target trajectory and the right boundary of the track is TBR and the distance L between the target trajectory and the current position of the vehicle. VT Based on the ratio of est and the constraint value μ аct Between the constraint value μ ex The constraint value μ est is a constraint value based on the range of friction limits corresponding to the friction coefficient of the road surface. аct is a constraint value based on the limited range of the steering actuator. The limited range of the steering actuator corresponds to the upper limit of the tire force that can be achieved by the steering actuator. The constraint value μ ex is a constraint value based on the range of the friction limit after updating. Specifically, as shown in the following formula (1), the constraint value μ ex is calculated, where μ est ≦μ ex ≦μ аct is.

number

[0051] Distance L between the target trajectory and the vehicle's current position VT is not greater than 0 m, i.e., is less than 0 m, the processor 10 determines the distance L between the target trajectory and the left boundary of the track. TBL and the distance L between the target trajectory and the current position of the vehicle. VT Based on the ratio of est and the constraint value μ аct Between the constraint value μ ex Specifically, as shown in the following formula (2), the constraint value μ ex is calculated, where μ est ≦μ ex ≦μ аct is.

number

[0052] Here, referring to FIG. 5, the constraint value μ of the manipulated variable in this embodiment ex An example of a calculation method for the above will be described. FIG. 5 is a diagram for explaining the relationship between the constraint value of the operation amount and the deviation amount of the vehicle from the target trajectory in this embodiment. FIG. 5 shows a graph representing the positional relationship between the target trajectory T and the vehicle V, and the constraint value, in a scene where the vehicle V is traveling between the left boundary Bl and the right boundary Br of the road. When the distance between the vehicle V and the target trajectory T is the distance L VT , the distance between the target trajectory and the right boundary of the track is distance L TBR , the distance between the target trajectory and the left boundary of the track is distance L TBL In the graph of the constraint value, the horizontal axis (x-axis) indicates the distance between the vehicle V and the target trajectory T, and the vertical axis (y-axis) indicates the constraint value μ ex This shows:

[0053] As shown in the graph of the constraint value, when the vehicle V is traveling on the target trajectory T, that is, when the distance between the target trajectory T and the vehicle V is 0, the constraint value μ ex The value of is a constraint value μ based on the range of friction limits corresponding to the friction coefficient μ of the road surface. est In addition, when the vehicle is traveling on the boundary Bl or Br of the road, that is, when the distance between the target trajectory T and the vehicle V is equal to the distance L TBR , or distance L TBL In the case of ex The value of is a constraint value μ based on the limited range of the steering actuator. аct In the example of Figure 5, as shown in the graph of the constraint value, the distance L between the target trajectory T and the vehicle V VT The corresponding constraint value μ ex The value of is calculated.

[0054] Next, another example of a method for calculating the constraint value of the operation amount will be described. First, the processor 10 calculates the distance L between the center line between the left and right boundaries of the lane and the current position of the vehicle. Vc The processor 10 also calculates the distance L between the center line between the left and right boundaries of the track and each of the left and right boundaries of the track. C (=L CBL =LCBR Then, the processor 10 calculates the distance L between the center line between the left and right boundaries of the track and each of the left and right boundaries of the track. C and the distance L between the center line between the left and right boundaries of the lane and the current position of the vehicle. Vc Based on the ratio of est and the constraint value μ аct Between the constraint value μ ex Specifically, as shown in the following formula (3), the constraint value μ ex is set, where μ est ≦μ ex ≦μ аct is.

number

[0055] Furthermore, in this embodiment, the processor 10 is not limited to calculating tire forces for the vehicle to follow the target trajectory based on the target trajectory. It may also predict future vehicle behavior based on vehicle dynamics using a vehicle model and the coefficient of friction with the road surface, and calculate tire forces based on the future vehicle behavior. Here, another example of each functional unit of the manipulated variable calculation unit according to this embodiment will be described with reference to FIG. 6. FIG. 6 is a block diagram showing an example of each functional unit of the vehicle control device according to this embodiment. As shown in FIG. 6, the manipulated variable calculation unit 14 includes, as functional units, a lateral force constraint value calculation unit 143, a predicted trajectory generation unit 144, and an optimum calculation unit 145.

[0056] The lateral force constraint value calculation unit 143 acquires the friction coefficient of the road surface on which the vehicle is traveling, the boundary of the road, the target vehicle speed, and the target trajectory (lateral position and yaw angle), and calculates a lateral force constraint value for calculating the target lateral force. The lateral force constraint value is calculated so that the resultant force of the longitudinal force and the lateral force does not exceed the friction limit range corresponding to the friction coefficient with the road surface on which the vehicle is traveling. The friction limit range is set according to the friction coefficient μ of the road surface. The lateral force constraint value calculation unit 143 also determines whether the vehicle has deviated from the target trajectory, and if the vehicle has deviated from the target trajectory, updates the friction limit range and calculates the lateral force constraint value within the updated friction limit range. Specifically, the lateral force constraint value calculation unit 143 updates the friction limit range so that the greater the amount of deviation of the vehicle from the target trajectory due to nonlinearity of the tires or vehicle, the wider the friction limit range.

[0057] The predicted trajectory generation unit 144 generates a predicted trajectory that the vehicle will travel in the future based on the target vehicle speed, the current vehicle speed (V), initial values ​​(current lateral position (Y) and yaw angle (θ)), and the previous value of the target lateral force. The predicted trajectory generation unit 144 may also have a vehicle model. The predicted trajectory generation unit 144 generates the predicted trajectory by predicting the future behavior of the vehicle based on information on vehicle dynamics using the vehicle model and friction with the road surface.

[0058] The optimum calculation unit 145 calculates operation variables, including a continuous lateral force, that can be realized by the vehicle so as to minimize the difference between the target trajectory and the predicted trajectory within the range of the lateral force constraint value. The optimum calculation unit 145 outputs the calculated lateral force as the target lateral force and the target operation variables, including the target lateral force, to the target behavior generator 15. The configurations and functions of the target behavior generator 15 and the control command unit 16 are the same as those in Fig. 3, so their explanations will be omitted and the explanation of Fig. 3 will be used as appropriate.

[0059] As described above, in the vehicle control method and vehicle control device according to this embodiment, the processor generates a target trajectory based on the boundary of the road ahead of the vehicle, steers the vehicle based on the target steering amount so that the vehicle follows the target trajectory, calculates the deviation between the target steering amount and the actual steering amount, applies a yaw moment to the vehicle to reduce the deviation, determines whether the tire force of the front wheels of the vehicle is limited within a friction limit range corresponding to the friction coefficient with the road surface on which the vehicle is traveling, determines whether the vehicle has deviated from the target trajectory, and if the tire force of the front wheels is limited within the friction limit range and the vehicle has deviated from the target trajectory, updates the friction limit range so that the friction limit range expands as the deviation of the vehicle from the target trajectory increases, generates a return steering command including the target steering amount so that the vehicle returns to the target trajectory within the updated friction limit range, and steers the vehicle based on the return steering command. This allows the vehicle to return to the target trajectory when the vehicle deviates from the target trajectory while steering control is limited depending on the friction with the road surface.

[0060] In addition, in the vehicle control method and vehicle control device according to this embodiment, when the steering control of the vehicle based on the return steering command is not realized, the processor calculates the deviation between the target steering amount included in the return steering command and the actual steering amount, and applies a yaw moment to the vehicle to reduce the calculated deviation. This makes it possible to reduce the amount of deviation of the vehicle from the target trajectory even when the steering control of the vehicle is insufficient.

[0061] In the vehicle control method and vehicle control device according to this embodiment, the processor applies a yaw moment to the vehicle by distributing braking / driving forces for braking / driving the vehicle to the left and right wheels of the vehicle, distributing braking / driving forces to the front and rear wheels of the vehicle, or controlling the loads on each wheel of the vehicle, thereby making it possible to reduce the amount of deviation of the vehicle from the target trajectory even when steering control of the vehicle is insufficient.

[0062] In the vehicle control method and vehicle control device according to this embodiment, the processor calculates a target tire force for the vehicle to follow a target trajectory during steering control of the vehicle so that the steering speed does not exceed a predetermined steering speed, the target steering amount does not exceed a predetermined steering amount, or the vehicle body yaw resonance frequency does not exceed a predetermined frequency, and calculates a target steering amount for the vehicle to follow the target trajectory based on the target tire force. This makes it possible to calculate a steering amount that can be realized by the vehicle.

[0063] In the vehicle control method and vehicle control device according to this embodiment, the processor predicts future vehicle behavior based on information about vehicle dynamics using a vehicle model and friction with the road surface, calculates target tire forces for the vehicle to follow a target trajectory based on the future vehicle behavior, and calculates a target steering amount for the vehicle to follow the target trajectory based on the target tire forces. This makes it possible to calculate a steering amount that can be realized by the vehicle.

[0064] In the vehicle control method and vehicle control device according to this embodiment, the processor calculates the deviation of the actual yaw rate of the vehicle from the standard yaw rate achieved by steering control based on the target steering amount as a yaw rate deviation, and applies a yaw moment to the vehicle so as to reduce the yaw rate deviation. As a result, the application of the yaw moment can reduce the amount of deviation of the vehicle from the target trajectory.

[0065] In the vehicle control method and vehicle control device according to this embodiment, the processor updates the friction limit range so as to expand the friction limit range, with the upper limit being the limit range corresponding to the upper limit of the tire force that can be achieved by the steering actuator of the vehicle. This makes it possible to reduce the amount of deviation of the vehicle from the target trajectory within a range that does not exceed the control limit of the steering actuator.

[0066] In the vehicle control method and vehicle control device according to this embodiment, the processor calculates the distance between the lane boundary and the vehicle, and updates the range of the friction limit so that the smaller the distance, the wider the range of the friction limit becomes. This allows the range of the friction limit to be wider as the vehicle approaches the lane boundary.

[0067] Furthermore, in the vehicle control method and vehicle control device according to this embodiment, the processor distributes braking / driving forces to the front and rear wheels of the vehicle so that, when there is a yaw rate deviation, the braking / driving forces of the rear wheels of the vehicle are greater than when there is no yaw rate deviation, thereby making it possible to reduce the amount of deviation of the vehicle from the target trajectory while accelerating and decelerating the vehicle.

[0068] In the vehicle control method and vehicle control device according to this embodiment, the vehicle is a front-wheel drive vehicle, and the processor distributes braking and driving forces to the front and rear wheels of the vehicle so that, when there is a yaw rate deviation, the reduction in driving force of the front wheels of the vehicle is smaller than when there is no yaw rate deviation. This makes it possible to accelerate the vehicle while reducing the amount of deviation of the vehicle from the target trajectory.

[0069] Furthermore, in the vehicle control method and vehicle control device according to this embodiment, when there is a yaw rate deviation, the processor controls the load on each wheel of the vehicle so that the load on the front wheels of the vehicle is greater than when there is no yaw rate deviation, by reducing the driving force on the front wheels of the vehicle or by generating or increasing braking force on the front wheels of the vehicle. In this way, by applying a front load to the vehicle through braking / driving control, it is possible to reduce the amount of deviation of the vehicle from the target trajectory.

[0070] It should be noted that the above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above-described embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. [Explanation of symbols]

[0071] 100...Vehicle control system 1...Vehicle control device 2. Map database 3. Detection device 4...Drive mechanism 10...Processor 11...Vehicle status acquisition unit 12...Run boundary generation section 13…Target trajectory generation unit 14...Manipulated amount calculation section 15... Target behavior generation unit 16...Control command section

Claims

1. 1. A vehicle control method executed by a processor, comprising: The processor: generating a target trajectory based on a boundary of a road located ahead of the vehicle; steering the vehicle based on the target steering amount so that the vehicle follows the target trajectory; Calculating a deviation between the target steering amount and the actual steering amount; applying a yaw moment to the vehicle to reduce the deviation; determining whether the tire force of the front wheels of the vehicle is limited within a friction limit range corresponding to a friction coefficient with the road surface on which the vehicle is traveling; determining whether the vehicle deviates from the target trajectory; When the tire force of the front wheels is limited within the range of the friction limit and the vehicle deviates from the target trajectory, updating the range of the friction limit so that the range of the friction limit increases as the deviation amount of the vehicle from the target trajectory increases; generating a return steering command including the target steering amount so that the vehicle returns to the target trajectory within the range of the updated friction limit; A vehicle control method for controlling the steering of the vehicle based on the return steering command.

2. 2. The vehicle control method according to claim 1, The processor: When the steering control of the vehicle based on the return steering command is not realized, the deviation between the target steering amount included in the return steering command and the actual steering amount is calculated; A vehicle control method for applying the yaw moment to the vehicle in order to reduce the calculated deviation.

3. 3. A vehicle control method according to claim 1 or 2, The processor: A vehicle control method that applies the yaw moment to the vehicle by distributing a braking / driving force for braking / driving the vehicle to the left and right wheels of the vehicle, distributing the braking / driving force to the front and rear wheels of the vehicle, or controlling the load of each wheel of the vehicle.

4. 3. A vehicle control method according to claim 1 or 2, The processor: calculating a target tire force of the vehicle for causing the vehicle to follow the target trajectory so that the steering speed does not exceed a predetermined steering speed, so that the target steering amount does not exceed a predetermined steering amount, or so that the vehicle body yaw resonance frequency does not exceed a predetermined frequency during steering control of the vehicle; a vehicle control method for calculating the target steering amount for the vehicle to follow the target trajectory based on the target tire force;

5. 3. A vehicle control method according to claim 1 or 2, The processor: predicting future behavior of the vehicle based on information about vehicle dynamics and friction with the road surface using a vehicle model; calculating a target tire force of the vehicle for the vehicle to follow the target trajectory based on a future behavior of the vehicle; a vehicle control method for calculating the target steering amount for the vehicle to follow the target trajectory based on the target tire force;

6. 4. The vehicle control method according to claim 3, The processor: calculating a deviation of an actual yaw rate of the vehicle from a standard yaw rate realized by steering control based on the target steering amount as a yaw rate deviation; A vehicle control method for applying the yaw moment to the vehicle so as to reduce the yaw rate deviation.

7. 3. A vehicle control method according to claim 1 or 2, The processor: A vehicle control method for updating the friction limit range so that the friction limit range is expanded, with an upper limit set to a limit range corresponding to an upper limit value of the tire force achievable by a steering actuator of the vehicle.

8. 3. A vehicle control method according to claim 1 or 2, The processor: Calculating the distance between the boundary of the road and the vehicle; A vehicle control method for updating the range of friction limits such that the range of friction limits increases as the distance decreases.

9. 7. A vehicle control method according to claim 6, The processor: A vehicle control method for distributing the braking / driving forces to the front and rear wheels of the vehicle when there is a yaw rate deviation so that the braking / driving forces of the rear wheels of the vehicle are greater than when there is no yaw rate deviation.

10. 7. A vehicle control method according to claim 6, The vehicle is a front-wheel drive vehicle, The processor: A vehicle control method in which, when there is a yaw rate deviation, the braking / driving force is distributed to the front and rear wheels of the vehicle so that the amount of reduction in the driving force of the front wheels of the vehicle is smaller than when there is no yaw rate deviation.

11. 7. A vehicle control method according to claim 6, The vehicle control method includes, when the yaw rate deviation exists, controlling the load on each wheel of the vehicle by reducing the driving force of the front wheels of the vehicle or generating or increasing a braking force on the front wheels of the vehicle so that the load on the front wheels of the vehicle is greater than when the yaw rate deviation does not exist.

12. A vehicle control device including a processor, The processor: generating a target trajectory based on a boundary of a road located ahead of the vehicle; steering the vehicle based on the target steering amount so that the vehicle follows the target trajectory; Calculating a deviation between the target steering amount and the actual steering amount; applying a yaw moment to the vehicle to reduce the deviation; determining whether the tire force of the front wheels of the vehicle is limited within a friction limit range corresponding to a friction coefficient with the road surface on which the vehicle is traveling; determining whether the vehicle deviates from the target trajectory; When the tire force of the front wheels is limited within the range of the friction limit and the vehicle deviates from the target trajectory, updating the range of the friction limit so that the range of the friction limit increases as the deviation amount of the vehicle from the target trajectory increases; generating a return steering command including the target steering amount so that the vehicle returns to the target trajectory within the range of the updated friction limit; A vehicle control device that controls the steering of the vehicle based on the return steering command.

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