KR20200081524A - Vehicle, and control method for the same - Google Patents

Abstract

The vehicle according to an embodiment may control steering by predicting an understeer or oversteer situation that may occur in a curved section included in a driving trajectory during autonomous driving.
To this end, a vehicle according to an embodiment includes a steering device; A camera that acquires an image of a driving lane; A sensor for acquiring vehicle behavior information; And calculating a target driving trajectory along the center of the driving lane based on the behavior information of the vehicle, calculating a first steering torque to follow the target driving trajectory, and predicting occurrence of understeer or oversteering. It includes a control unit for correcting the driving trajectory, calculating a second steering torque for following the modified target driving trajectory, and controlling the steering device based on the first steering torque and the second steering torque.

Description

Vehicle and its control method{VEHICLE, AND CONTROL METHOD FOR THE SAME}

The present invention relates to a vehicle for controlling steering by predicting understeer or oversteer when autonomous driving along a driving trajectory and a control method thereof.

In general, in an autonomous driving system, a Lane Keeping Assist System or a Lane Following Assist System recognizes a lane to generate a driving trajectory, and controls the vehicle to travel according to the driving trajectory, Make sure you stay in the lane without steering wheel manipulation. At this time, the vehicle is generally controlled to travel in the center of the lane.

However, the conventional autonomous driving system is controlling steering without considering an understeer or oversteer situation that may occur in a curved section included in the driving trajectory, so the steering stability is poor and ride comfort is reduced. There was this falling issue.

The present invention provides a vehicle for controlling steering by predicting an understeer or oversteer situation that may occur in a curved section included in a driving trajectory during autonomous driving, and a control method thereof.

As a technical means for achieving the above-described technical problem, a vehicle according to an embodiment includes a steering device; A camera that acquires an image of a driving lane; A sensor for acquiring vehicle behavior information; And calculating a target driving trajectory along the center of the driving lane based on the behavior information of the vehicle, calculating a first steering torque to follow the target driving trajectory, and calculating a yaw rate gain error to understeer or over. Predict the steer occurrence, correct the target travel trajectory according to the understeer or oversteer occurrence prediction, and calculate a second steering torque for tracking the modified target travel trajectory as a value proportional to the yaw rate gain error And a control unit controlling the steering device based on the first steering torque and the second steering torque.

The control unit may calculate a current driving trajectory based on the position of the vehicle in the driving lane, and calculate the first steering torque based on a difference value between the target driving trajectory and the current driving trajectory.

The controller predicts yaw rate based on the curvature radius of the target travel trajectory and the current speed of the vehicle, predicts yaw rate gain based on the yaw rate and the front wheel rotation angle, and between the yaw rate gain and the front wheel to rear wheel. The yaw rate gain error can be calculated based on the wheelbase of.

If the yaw rate gain error value falls within a predetermined range, it is determined as a neutral steer. If the yaw rate gain error value is positive (+) outside the predetermined range, it is set as an over steer. If the yaw rate gain error value is negative (-) outside the predetermined range, it may be determined as an under steer.

The control unit may calculate the radius of curvature using the coordinate value of the target travel trajectory, and predict the yaw rate by setting the current speed as the turning speed of the vehicle in a curved section of the target travel trajectory.

The controller accelerates or decelerates the speed of the vehicle so that the corrected target travel trajectory falls within the allowable error range when the corrected target travel trajectory is out of the allowable error range, and re-corrects the corrected target travel trajectory. Can.

The controller may accelerate and control the speed of the vehicle when the oversteer is predicted, and decelerate and control the speed of the vehicle when the understeer is predicted.

The controller may accelerate and control the speed of the vehicle below a threshold speed when the occurrence of the oversteer is predicted.

The control unit may increase the second steering torque when the understeer occurrence is predicted, and decrease the second steering torque when the oversteer occurrence is predicted.

A control method of a vehicle according to an embodiment includes detecting a driving lane and acquiring behavior information of a vehicle; Calculating a target driving trajectory along the center of the driving lane based on the behavior information of the vehicle; Calculating a first steering torque for following the target travel trajectory; Calculating a yaw rate gain error to predict the occurrence of understeer or oversteer; Modifying the target driving trajectory according to the understeer or oversteer occurrence prediction; Calculating a second steering torque for tracking the modified target driving trajectory as a value proportional to the yaw rate gain error; And controlling the steering device based on the first steering torque and the second steering torque.

The calculating of the target driving trajectory may include calculating a current driving trajectory based on the position of the vehicle in the driving lane. The calculating of the first steering torque may include calculating the target driving trajectory and the current driving. And calculating the first steering torque based on the difference value of the trajectory.

The predicting the occurrence of the understeer or oversteer may include predicting a yaw rate based on a radius of curvature of the target driving trajectory and a current speed of the vehicle; Predicting a yaw rate gain based on the yaw rate and the front wheel rotation angle; And calculating a yaw rate gain error based on the yaw rate gain and a wheelbase between the front and rear wheels.

In the step of predicting the occurrence of the understeer or oversteer, if the yaw rate gain error value falls within a predetermined range, it is determined as a neutral steer, and the yaw rate gain error value is a positive number outside the predetermined range (+ ). If the yaw rate gain error value is negative (-) outside the predetermined range, it is determined as an under steer.

The step of predicting the yaw rate may include calculating the radius of curvature using a coordinate value of the target travel trajectory; And predicting the yaw rate by setting the current speed as a turning speed of the vehicle in a curved section of the target driving trajectory.

A control method of a vehicle according to an embodiment may include: accelerating or decelerating the speed of a vehicle so that the modified target driving trajectory falls within the tolerance range when the modified target driving trajectory is out of the tolerance range; And re-modifying the modified target driving trajectory.

The step of accelerating or decelerating the vehicle speed may include accelerating and controlling the vehicle speed when the oversteer occurrence is predicted, and decelerating and controlling the vehicle speed when the understeer occurrence is predicted. .

The step of accelerating or decelerating the speed of the vehicle may include controlling the speed of the vehicle below a threshold speed when the occurrence of the oversteer is predicted. The calculating of the second steering torque may include And increasing the second steering torque when the understeer generation is predicted, and decreasing the second steering torque when the oversteer generation is predicted.

According to the vehicle and its control method of the present invention, it is possible to predict an understeer or oversteer situation that may occur in a curved section included in a driving trajectory during autonomous driving, and control steering accordingly.

Therefore, the vehicle and its control method of the present invention can improve steering stability and ride comfort during autonomous driving.

1 shows a configuration of a vehicle according to an embodiment.
2 is a view for explaining the generation and modification of a target driving trajectory.
3 is a view for explaining a method of calculating a radius of curvature of a target travel trajectory.
4 is a view showing the relationship between the yaw rate gain and the speed and steering state of the vehicle.
5 is a flowchart of a vehicle control method according to an embodiment.
6 illustrates a method of determining a steering state based on a yaw rate gain error.

The same reference numerals refer to the same components throughout the specification. This specification does not describe all elements of the embodiments, and overlaps between general contents or embodiments in the technical field to which the present invention pertains are omitted. The term'unit, module, member, block' used in the specification may be implemented by software or hardware, and according to embodiments, a plurality of'unit, module, member, block' may be implemented as one component, It is also possible that one'part, module, member, block' includes a plurality of components.

Throughout the specification, when a part is "connected" to another part, this includes not only a direct connection but also an indirect connection, and an indirect connection includes connecting through a wireless communication network. do.

Also, when a part “includes” a certain component, this means that other components may be further included instead of excluding other components, unless otherwise specified.

Terms such as first and second are used to distinguish one component from other components, and the component is not limited by the above-mentioned terms.

Singular expressions include plural expressions, unless the context clearly has an exception.

In each step, the identification code is used for convenience of explanation. The identification code does not describe the order of each step, and each step can be executed differently from the specified order unless a specific order is clearly stated in the context. have.

Hereinafter, working principles and embodiments of the present invention will be described with reference to the accompanying drawings.

1 shows a configuration of a vehicle according to an embodiment.

Referring to FIG. 1, the vehicle 10 includes a camera 110, a radar 120, a sensor 130, a steering device 140, an acceleration device 150, a braking device 160, and a control unit 200 can do.

The camera 110 may collect video data by photographing an image around the vehicle 10. Specifically, the camera 110 may photograph the front of the vehicle 10 and recognize other vehicles, pedestrians, cyclists, lanes, and road signs. The camera 110 may include a plurality of lenses and an image sensor. The image sensor may include a plurality of photodiodes that convert light to an electrical signal, and the plurality of photodiodes may be arranged in a two-dimensional matrix.

The camera 110 may be electrically connected to the control unit 200. For example, the camera 110 is connected to the control unit 200 through a vehicle communication network NT, or is connected to the control unit 200 through a hard wire, or a printed circuit board, PCB ) Can be connected to the control unit 200.

The camera 110 may photograph a periphery of the vehicle 10 to detect a driving lane, and acquire an image of an object around the vehicle (front, rear, left and right). Objects around the vehicle may include structures on a road such as a median, surrounding vehicles, obstacles on a driving lane, and the like. Further, the camera 110 may detect a curved section, a shoulder road, and a side slope of the road.

The radar 120 may acquire location information, distance information, speed information, and the like of objects (eg, preceding vehicles, pedestrians, etc.) around the vehicle 10. The radar 120 is provided at the front, rear and side of the vehicle 10 to transmit and receive radio waves.

The radar 120 calculates the distance to the preceding vehicle based on the phase difference (or time difference) between the transmitted and reflected radio waves, and the speed or relative speed of the preceding vehicle based on the frequency difference between the transmitted and reflected radio waves. Can be calculated. Meanwhile, the radar 120 may be implemented as a lidar.

The radar 120 may be connected to the control unit 200 through a vehicle communication network NT or a hard wire or a printed circuit board. The radar 120 may transmit radar data to the controller 200.

The sensor 130 may acquire behavior information of the vehicle 10. Various sensors 130 may be provided in the vehicle 10 to acquire behavior information of the vehicle 10. For example, the vehicle 10 includes a speed sensor 132 that detects speed, an acceleration sensor that detects acceleration of the vehicle, a yaw rate sensor 131 that detects the rotational angular velocity of the vehicle 10, and a vehicle tilt. It may include a gyro sensor, a steering angle sensor 133 for detecting the rotation and steering angle of the steering wheel.

The sensor 130 may be connected to the control unit 200 through a vehicle communication network NT or a hard wire or a printed circuit board. The sensor 130 may transmit sensing data to the control unit 200.

The camera 110, the radar 120, and the sensor 130 may be mounted on the front windshield, front radiator grille, or front headlamp of the vehicle 10, and heat rays on the rear side of the roof panel and the upper side of the rear window glass. It is also possible to be integrally implemented together. That is, there is no limitation on the installation location.

The steering device 140 may change the driving direction of the vehicle 10. The steering device 140 may be implemented as an electronic power steering device (EPS). The steering device 140 may adjust the driving direction of the vehicle 10 so that the vehicle 10 can follow the driving trajectory formed along the lane. The steering device 140 may include a steering wheel, a steering output shaft, or a motor that rotates and moves the rack bar.

The acceleration device 150 includes an engine and an engine management system (EMS) that generate power for the vehicle 10, and a transmission and transmission control unit that transmits power generated by the engine to the wheels. TCU). The accelerator 150 may generate power by controlling the engine according to a control command of the control unit 200, and may control the transmission in response to the driving speed of the vehicle 10 determined by the control unit 200.

The braking device 160 may decelerate or stop the vehicle 10 through friction with the wheel. The braking device 160 may temporarily release or maintain braking of the wheel in response to slippage of the wheel sensed when braking the vehicle 10 under the control of the controller 200.

In addition, the braking device 160 may selectively release or maintain braking of the wheel in response to an oversteer or understeer sensed when the vehicle 10 is steered under the control of the controller 200. have.

The vehicle 10 may further include various safety devices for driver and passenger safety. The safety device of the vehicle 10 includes an airbag control device for the safety of the occupant, such as a driver in the event of a vehicle collision, and an electronic stability control device (ESC) that controls the vehicle's posture when accelerating or cornering the vehicle. There are several types of safety devices.

In addition, the vehicle 10 detects a lane so as not to deviate from the driving lane and generates an auxiliary steering torque to control the steering device 140, such as a Lane Keeping Assist System and a Lane Following Assist. And the like.

The various devices or systems described above may communicate with each other through a vehicle communication network NT. For example, electronic components can transmit data through Ethernet, MOST (Media Oriented Systems Transport), Flexray, CAN (Controller Area Network), and LIN (Local Interconnect Network). Can send and receive

Meanwhile, the vehicle 10 may include a communication unit (not shown) that communicates with an external device. The communication unit may receive road traffic information from an external device. Road traffic information may include speed limit information, traffic jam information, and the like.

The communication unit (not shown) may use various communication technologies. The communication unit is wireless such as vehicle-to-vehicle (V2V) communication, Wi-Fi, wireless local area network (WLAN), ultra-mobile broadband (UMB), GPS, and long term evolution (LTE). Data can be received from the outside using a mobile communication technology.

The control unit 200 may control various devices provided in the vehicle 10. The control unit 240 may mean an electronic control unit (ECU), and although it is expressed as the control unit 200, this is only an expression to be interpreted in a broad sense and is not limited thereto.

The controller 200 may include at least one memory 220 in which programs for performing the above-described operations and operations described below are stored, and at least one processor 210 for executing the stored programs. When the memory 220 and the processor 210 are plural, it is possible that they are integrated in one chip, and it is also possible to be provided in a physically separate location.

The memory 220 is used to store various types of information such as cache, read only memory (ROM), programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EPMROM), and flash memory. It may be implemented as at least one of a volatile memory device or a volatile memory device such as RAM (Random Access Memory) or a storage medium such as a hard disk drive (HDD), CD-ROM, but is not limited thereto.

Hereinafter, the operation of the control unit 200 will be described in detail.

2 is a view for explaining the generation and modification of a target driving trajectory.

Referring to FIG. 2, the control unit 200 detects a driving lane from an image obtained by the camera 110 and based on the behavior information of the vehicle 10 obtained by the sensor 130, centers the driving lane. The following target driving trajectory T1 and the current driving trajectory T2 can be calculated.

The control unit 200 may calculate the current driving trajectory T2 based on the position of the vehicle 10 in the driving lane. The vehicle 10 may not be able to follow the target driving trajectory T1 as it is due to various reasons such as a road condition. In other words, a difference D1 may exist between the current travel trajectory T2 and the target travel trajectory T1.

When the vehicle 10 is driven in the autonomous driving mode, it is generally safe to drive along the center of the lane. Therefore, it is necessary to compensate for the difference D1 between the current driving trajectory T2 of the vehicle 10 and the target driving trajectory T1, and to control the vehicle 10 to travel along the target driving trajectory T1. The difference D1 between the current driving trajectory T2 and the target driving trajectory T1 may mean a separation distance between two trajectories.

The control unit 200 may calculate a first steering torque for compensating for a difference D1 between the current travel trajectory T2 and the target travel trajectory T1. The control unit 200 may transmit the calculated first steering torque to the steering device 140. The steering device 140 may rotate the steering wheel according to the first steering torque and adjust the direction of the front wheel.

On the other hand, if the target driving trajectory T1 includes a curved section, understeering or oversteering may occur when the vehicle 10 turns the curved section.

Under steer is a phenomenon in which the vehicle 10 is pushed out of the target driving trajectory T1 when the vehicle 10 enters the curved section at a high speed. When understeer occurs, the rotation angle of the vehicle body becomes smaller than the input steering angle. If the degree of understeer is severe, slip may occur as the traction of the front wheels is lost. This case is defined as Under steer with slip.

Over steer is a phenomenon in which the rotation angle of the vehicle body becomes larger than the input steering angle. That is, when an oversteer occurs, the vehicle 10 turns inside the target travel trajectory T1. If the oversteer degree is severe, slip may occur as the rear wheel loses grip. This case is defined as Over steer with slip.

When such understeer or oversteer occurs, control of the vehicle 10 may become impossible and an accident may occur. Therefore, when the vehicle 10 travels while following the target travel trajectory T1, it is necessary to predict and avoid the occurrence of understeer or oversteer.

The control unit 200 may predict whether an understeer or oversteer is generated, and if it is predicted that an understeer or oversteer will occur, the target driving trajectory T1 may be corrected.

The control unit 200 may predict the occurrence of understeer or oversteer using the yaw rate gain error. Specifically, the controller 200 predicts the yaw rate ψ based on the radius of curvature R of the target travel trajectory and the current speed V of the vehicle, and the yaw rate ψ and the front wheel rotation angle δ _f . The yaw rate gain can be predicted based on the yaw rate, and the yaw rate gain error can be predicted based on the yaw rate gain and the wheelbase L between the front and rear wheels.

In addition, the control unit 200 calculates the radius of curvature R using the coordinate values of the target travel trajectory T1, and calculates the current speed V of the vehicle 10 in the curved section of the target travel trajectory T1. The yaw rate (ψ) can be predicted by setting the rotation speed of (10).

If the above-described content is expressed by the following equation, it is as follows.

[Equation 1]

ψ = V/R

(ψ: yaw rate, V: vehicle speed, R: radius of curvature)

[Equation 2]

Yaw rate gain = ψ/δ _f

(ψ: yaw rate, δ _f : front wheel rotation angle)

[Equation 3]

Yaw rate gain error = ψ/δ _f -V/L

(ψ/δ _f : yaw rate gain, V: vehicle speed, L: wheelbase)

If the yaw rate gain error value falls within a predetermined range, it is determined as a neutral steer, and if the yaw rate gain error value is positive (+) outside the predetermined range, it is determined as an over steer. And, if the yaw rate gain error value is a negative number (-) outside the predetermined range, it may be determined as an under steer.

The control unit 200 controls the vehicle 10 to travel with the target driving trajectory T3 modified to avoid understeering or oversteering. That is, the control unit 200 may calculate the second steering torque for following the modified target travel trajectory T3. The control unit 200 transmits the calculated second steering torque to the steering device 140, and the steering device 140 adjusts the steering wheel and the front wheel according to the second steering torque.

The control unit 200 may calculate the second steering torque with a value proportional to the yaw rate gain error. In addition, the control unit 200 may calculate the second steering torque by setting the proportional constant between the yaw rate gain error and the second steering torque to a negative number (-). If the oversteer is predicted, the yaw rate gain error is calculated as positive (+). In the oversteer situation, the steering angle must be reduced. Therefore, the control unit 200 may reduce the second steering torque by setting the proportional constant to a negative number (-). Conversely, if the understeer is predicted, the yaw rate gain error is calculated as a negative (-), and in the understeer situation, the steering angle must be increased. Therefore, the control unit 200 increases the second steering torque.

In other words, the control unit 200 includes a first steering torque for compensating for a difference D1 between the current travel trajectory T2 and a target travel trajectory T1 and a second steering torque for avoiding understeer or oversteer. Can be calculated, and the steering device 140 can be controlled based on the first steering torque and the second steering torque.

On the other hand, to avoid the occurrence of understeer or oversteer, the modified target travel trajectory T3 must exist within the tolerance range ER of the target travel trajectory T1 before modification. This is because when the modified target driving trajectory T3 is out of the tolerance range ER, the driving trajectory of the vehicle 10 may be changed differently than intended. For example, if the modified target driving trajectory T3 is out of the tolerance range ER, the vehicle 10 may leave the lane and an accident may occur.

When the modified target driving trajectory T3 is out of the tolerance range ER, the controller 200 determines the speed V of the vehicle 10 so that the modified target driving trajectory T3 falls within the tolerance range ER. ) Can be accelerated or decelerated, and the corrected target driving trajectory can be corrected.

Specifically, the controller 200 accelerates and controls the speed of the vehicle 10 when an oversteer is predicted, and decelerates and controls the speed of the vehicle 10 when an understeer is predicted. As described above, since the understeer is pushed outward in the curved section, it can be avoided by reducing the speed of the vehicle 10. In addition, since the oversteer digs inward in a curved section, it can be avoided by increasing the speed of the vehicle 10 rather than reducing the speed of the vehicle 10.

On the other hand, when the oversteer occurrence is predicted, the control unit 200 accelerates and controls the speed of the vehicle 10 below the critical speed Vcr. This is because when the speed V of the vehicle 10 exceeds the threshold speed Vcr in a situation in which oversteering is predicted, slip may occur and control of the vehicle 10 may become impossible.

The control unit 200 may recalculate the first steering torque for tracking the re-corrected target travel trajectory, and may predict whether under-steer or over-steer occurs for the re-corrected target travel trajectory, and generate under-steer or over-steer. The second steering torque for avoiding can be calculated again.

3 is a view for explaining a method of calculating a radius of curvature of a target travel trajectory.

Referring to FIG. 3, the control unit 200 calculates the radius of curvature R using the coordinate values of the target travel trajectory T1, and calculates the current speed V of the vehicle 10 of the target travel trajectory T1. The yaw rate ψ can be predicted by setting the turning speed of the vehicle 10 in a curved section.

Specifically, the controller 200 calculates the radius of curvature R using Equation 4 below. In FIG. 3, the coordinates of the point P are x(1) and y(1), and the coordinates of the point Q are assumed to be x(2) and y(2).

[Equation 4]

∴

As described above, by calculating the radius of curvature R using the coordinate values of the target driving trajectory T1, the yaw rate without information about tire cornering stiffness of the front and rear wheels and specific resources of the vehicle 10 is calculated. Can predict.

On the other hand, when predicting the yaw rate, in addition to the method of setting the current speed V of the vehicle 10 to the turning speed of the vehicle 10 in the curved section of the target driving trajectory T1, the current speed V of the vehicle 10 ) And when the difference value between the speed limit of the driving road is within a predetermined range, a method of setting the speed limit of the driving road as a turning speed in a curved section may also be used.

4 is a view showing the relationship between the yaw rate gain and the speed and steering state of the vehicle.

4, the horizontal axis represents the speed V of the vehicle 10, and the vertical axis represents the yaw rate gain of Equation (2). The slope of the straight line 310 representing the neutral steer is 1/L. As described above, L means the wheelbase between the front and rear wheels. In Equation 3 described above, since the wheelbase L is a constant value, the yaw rate gain error is determined by the yaw rate gain and the speed of the vehicle 10.

When the yaw rate gain error value falls within a predetermined range, the control unit 200 determines that it is a neutral steer. That is, when the value of the yaw rate gain error is within a predetermined range from the neutral steer straight line 310, the neutral steer is predicted.

If the yaw rate gain error value is positive (+) outside the predetermined range, the control unit 200 determines that it is an over steer 320. In addition, if the yaw rate gain error value is positive (+) outside the predetermined range when the speed V of the vehicle 10 is greater than or equal to the critical speed Vcr, the control unit 200 is an unstable oversteer as a slipped oversteer. over steer) (321).

If the yaw rate gain error value is negative (-) outside the predetermined range, the control unit 200 determines that it is an under steer (330). In addition, if the yaw rate gain error value is negative (-) outside the predetermined range when the speed (V) of the vehicle 10 is greater than or equal to the characteristic speed (Vch), the control unit 200 slips under steer with slip ) (331).

On the other hand, if the characteristic speed (Vch) and the threshold speed (Vcr) are defined based on the yaw rate gain, the characteristic speed (Vch) is the speed of the vehicle 10 in which the yaw rate gain becomes maximum during understeer. It means (V), and the critical speed (Vcr) means the speed (V) of the vehicle 10 where the yaw rate gain becomes infinite when oversteering.

The controller 200 is a characteristic velocity squared value (Characteristic Speed Square; Vch ²⁾ of the sign (positive or negative), and a characteristic velocity squared value characteristic speed (Vch), or critical speed (Vcr) which is derived from (Vch ²⁾ and present The understeer or oversteer may be determined based on the magnitude relationship of the vehicle speed V.

The controller 200 may calculate the characteristic velocity squared value Vch ² and the critical velocity squared value Vcr ² using Equation 5 below.

[Equation 5]

(V: vehicle speed, δ _st : steering angle, ψ: yaw rate, i _st : steering angle (δ _st )/front wheel rotation angle (δ _f ), L: wheel base)

The control unit 200 determines that the characteristic speed square value (Vch ² ) is positive (+) as an understeer, and slips understeer when the current speed (V) of the vehicle 10 is greater than or equal to the characteristic speed (Vch). Judging by.

When the characteristic speed square value Vch ² is negative (-) or the threshold speed square value Vcr ² is positive (+), the controller 200 determines the overspeed, and the current speed V of the vehicle 10 ) Is determined as a slipped oversteer when the threshold speed is greater than or equal to Vcr.

5 is a flowchart of a vehicle control method according to an embodiment.

Referring to FIG. 5, the control unit 200 detects a driving lane from an image acquired by the camera 110, and based on the behavior information of the vehicle 10 acquired by the sensor 130, centers the driving lane. The following target driving trajectory T1 and the current driving trajectory T2 are calculated (501).

The controller 200 calculates the current driving trajectory T2 based on the position of the vehicle 10 in the driving lane, and calculates the first steering torque for the vehicle 10 to follow the target driving trajectory T1. (502). The control unit 200 predicts the yaw rate ψ based on the curvature radius R of the target driving trajectory and the current speed V of the vehicle (503), the yaw rate (ψ) and the front wheel rotation angle (δ _f ) The yaw rate gain is predicted based on (504).

The control unit 200 predicts the occurrence of understeer or oversteer using the yaw rate gain error (505). The method for predicting the occurrence of understeer or oversteer is as described above.

When the occurrence of understeer or oversteer is predicted, the control unit 200 corrects the target travel trajectory T1 to avoid understeer or oversteer (506).

If the occurrence of understeer or oversteer is not predicted, the controller 200 controls the steering device 140 according to the first steering torque (510).

The controller 200 determines whether the corrected target travel trajectory T3 is within the tolerance range ER of the target travel trajectory T1 before modification (507). When the modified target driving trajectory T3 is out of the tolerance range ER, the control unit 200 controls the speed V of the vehicle 10 so that the modified target driving trajectory T3 falls within the tolerance range ER. ) Is accelerated or decelerated, and the modified target travel trajectory is re-modified (508).

When the modified target travel trajectory T3 is within the tolerance range ER, the controller 200 calculates a second steering torque for following the modified target travel trajectory T3 (509). At this time, the control unit 200 calculates the second steering torque with a value proportional to the yaw rate gain error.

The control unit 200 controls the steering device 140 according to the first steering torque and the second steering torque (510).

6 illustrates a method of determining a steering state based on a yaw rate gain error.

Referring to FIG. 6, the controller 200 may calculate a yaw rate gain error according to Equation 3 described above (601). The neutral steer, under steer, or over steer may be determined based on the yaw rate gain error.

If the yaw rate gain error value falls within a predetermined range (ψ/δ _f -V/L≒0), the controller 200 determines that the neutral steer is a neutral steer (602, 603). If the yaw rate gain error value is a positive number outside the predetermined range (ψ/δ _f -V/L>0), the control unit 200 determines that it is over steer (604, 605). If the yaw rate gain error value is a negative number (ψ/δ _f -V/L<0) outside the predetermined range, the control unit 200 determines that it is an under steer (604, 606).

As described above, according to the vehicle and its control method of the present invention, it is possible to predict an understeer or oversteer situation that may occur in a curved section included in a driving trajectory during autonomous driving, and control steering accordingly.

Therefore, the vehicle and its control method of the present invention can improve steering stability and ride comfort during autonomous driving.

Meanwhile, the disclosed embodiments may be implemented in the form of a recording medium that stores instructions executable by a computer. Instructions may be stored in the form of program code, and when executed by a processor, may generate program modules to perform operations of the disclosed embodiments. The recording medium may be embodied as a computer-readable recording medium.

The computer-readable recording medium includes all types of recording media storing instructions that can be read by a computer. For example, there may be a read only memory (ROM), a random access memory (RAM), a magnetic tape, a magnetic disk, a flash memory, and an optical data storage device.

As described above, the disclosed embodiments have been described with reference to the accompanying drawings. Those skilled in the art to which the present invention pertains will understand that the present invention may be practiced in different forms from the disclosed embodiments without changing the technical spirit or essential features of the present invention. The disclosed embodiments are illustrative and should not be construed as limiting.

1: Vehicle
110: camera
120: radar
130: sensor
140: steering system
150: accelerator
160: braking system
200: control unit

Claims (18)

Steering device;
A camera that acquires an image of a driving lane;
A sensor for acquiring vehicle behavior information; And
Calculate a target travel trajectory along the center of the driving lane based on the behavior information of the vehicle, calculate a first steering torque to follow the target travel trajectory, calculate yaw rate gain error, and calculate understeer or oversteer Predicting the occurrence, correcting the target driving trajectory according to the prediction of the understeer or oversteering, and calculating a second steering torque to follow the modified target driving trajectory as a value proportional to the yaw rate gain error, , A control unit for controlling the steering device based on the first steering torque and the second steering torque. According to claim 1,
The control unit
A vehicle that calculates a current driving trajectory based on a position of a vehicle in the driving lane, and calculates the first steering torque based on a difference value between the target driving trajectory and the current driving trajectory. According to claim 1,
The control unit
Predict yaw rate based on the curvature radius of the target driving trajectory and the current speed of the vehicle, predict yaw rate gain based on the yaw rate and front wheel rotation angle, and wheelbase between the yaw rate gain and front wheel to rear wheel A vehicle that calculates a yaw rate gain error based on a vehicle. According to claim 3,
The control unit
If the yaw rate gain error value falls within a predetermined range, it is determined as a neutral steer. If the yaw rate gain error value is positive (+) outside the predetermined range, it is determined as an over steer. If the yaw rate gain error value is negative (-) outside the predetermined range, the vehicle determines that it is under steer. According to claim 3,
The control unit
A vehicle for calculating the radius of curvature using a coordinate value of the target driving trajectory, and predicting the yaw rate by setting the current speed as the turning speed of the vehicle in a curved section of the target driving trajectory. According to claim 1,
The control unit
A vehicle that accelerates or decelerates or controls the speed of a vehicle so that the modified target driving trajectory falls within the tolerance range when the modified target driving trajectory is out of the tolerance range, and re-corrects the modified target driving trajectory. The method of claim 6,
The control unit
A vehicle that accelerates and controls the speed of the vehicle when the oversteer is predicted, and decelerates and controls the speed of the vehicle when the understeer is predicted. The method of claim 7,
The control unit
A vehicle that accelerates and controls the speed of the vehicle below a threshold speed when the occurrence of the oversteer is predicted. According to claim 1,
The control unit
A vehicle that increases the second steering torque when the understeer is predicted, and decreases the second steering torque when the oversteer is predicted. Detecting a driving lane and obtaining behavior information of the vehicle;
Calculating a target driving trajectory along the center of the driving lane based on the behavior information of the vehicle;
Calculating a first steering torque for following the target travel trajectory;
Calculating a yaw rate gain error to predict the occurrence of understeer or oversteer;
Modifying the target driving trajectory according to the understeer or oversteer occurrence prediction;
Calculating a second steering torque for tracking the modified target driving trajectory as a value proportional to the yaw rate gain error; And
And controlling a steering device based on the first steering torque and the second steering torque. The method of claim 10,
The step of calculating the target driving trajectory
And calculating a current driving trajectory based on the position of the vehicle in the driving lane.
The step of calculating the first steering torque is
And calculating the first steering torque based on a difference value between the target driving trajectory and the current driving trajectory. The method of claim 10,
The step of predicting the occurrence of the understeer or oversteer is
Predicting a yaw rate based on a radius of curvature of the target driving trajectory and a current speed of the vehicle;
Predicting a yaw rate gain based on the yaw rate and the front wheel rotation angle; And
And calculating a yaw rate gain error based on the yaw rate gain and a wheelbase between the front and rear wheels. The method of claim 12,
The step of predicting the occurrence of the understeer or oversteer is
If the yaw rate gain error value falls within a predetermined range, it is determined as a neutral steer. If the yaw rate gain error value is positive (+) outside the predetermined range, it is determined as an over steer. If the yaw rate gain error value is negative (-) outside the predetermined range, determining an under steer (Under steer); control method of a vehicle comprising a. The method of claim 12,
The step of predicting the yaw rate is
Calculating the radius of curvature using the coordinate value of the target driving trajectory; And
And predicting the yaw rate by setting the current speed as a turning speed of the vehicle in a curved section of the target driving trajectory. The method of claim 10,
Accelerating or decelerating the speed of the vehicle so that the corrected target travel trajectory falls within the tolerance range when the modified target travel trajectory is out of the tolerance range; And
And re-modifying the modified target driving trajectory. The method of claim 15,
The step of controlling the acceleration or deceleration of the vehicle speed is
And controlling the speed of the vehicle when the oversteer occurrence is predicted, and decelerating and controlling the speed of the vehicle when the understeer occurrence is predicted. The method of claim 16,
The step of controlling the acceleration or deceleration of the vehicle speed is
And controlling the speed of the vehicle at a threshold speed or less when the occurrence of the oversteer is predicted. The method of claim 10,
The step of calculating the second steering torque is
And increasing the second steering torque when the understeer generation is predicted, and decreasing the second steering torque when the oversteer generation is predicted.

Images