JP7020750B2 - How to generate a target trajectory - Google Patents

Description

The present invention relates to a method of generating a target trajectory when a following vehicle follows (tracks) a preceding vehicle in platooning.

The platooning in which a plurality of vehicles such as trucks run in a platoon is said to be one form in which autonomous driving is embodied. In the follow-up running (tracking) in such platooning, the lateral deviation amount of the following vehicle is detected with respect to the preceding vehicle, and the steering angle of the own vehicle is adjusted so that the lateral deviation amount is sufficiently reduced by using it as a control amount. It controls.

As such a control technique, Patent Document 1 uses a detection device installed in the front part of the own vehicle (following vehicle), a marker installed in the rear part of the vehicle preceding the own vehicle, and a rear vehicle body of the preceding vehicle. In addition to detecting both ends, the distance between the marker and both ends of the vehicle body and the irradiation angle are detected, the lateral deviation of the own vehicle with respect to the preceding vehicle is calculated from this detection information, and the target position of the own vehicle is calculated based on the result. It is disclosed that the actual steering angle of the front wheels is controlled by setting.

In Patent Document 2, the own vehicle is made to follow the preceding vehicle based on the steering angle information of the preceding vehicle acquired by vehicle-to-vehicle communication, and the difference between the steering angle of the preceding vehicle and the own vehicle when traveling straight is obtained. It is described that control is performed so that the error is reduced by setting the center of the rudder angle.

Patent Document 3 proposes to use the vehicle position information from GPS for automatic driving. Specifically, the inertial navigation calculation unit receives the 3-axis angular speed signal and the 3-axis acceleration signal from the MEMS inertial sensor, and each output from the inertial navigation calculation unit, GPS sensor, tire speed sensor, and steering angle sensor. It is described that the error is estimated and corrected by subtracting the output.

Further, Patent Document 4 describes that a clothoid curve is set in a part of a traveling track when the vehicle is automatically driven. Since this clothoid curve is a curve drawn by a vehicle traveling at a constant vehicle speed and a constant angular velocity, it is also used in the curved portion of a highway.

Further, non-patent documents 1 to 3 can be mentioned as documents relating to obstacle avoidance and course change in automatic driving.

Japanese Patent No. 6109998 Japanese Unexamined Patent Publication No. 2013-107571 Japanese Unexamined Patent Publication No. 2016-17796 Japanese Unexamined Patent Publication No. 2018-79823

"Basic Automotive Engineering (Late)" by Masaichi Kondo, Yokendo, 1967.4p226-229 "High-speed generation method for self-driving cars" Naoki Suganuma et al., Automobile Technology Papers, Vol.42 No.6.November2011.p1281-1286 "Proposal of target trajectory generation and control method for autonomous vehicles that follow the preceding vehicle" Kohei Nishizaki et al., Proceedings of the Japan Society of Mechanical Engineers, Vol.83, No.852, 2017

The content disclosed in Patent Document 1 is to detect a marker installed at the rear of the preceding vehicle and both ends of the rear vehicle body by using a detection device, and does not describe any relationship with GPS. In particular, it is unclear how to deal with the following vehicle when the preceding vehicle travels irregularly or unstablely due to some cause such as lack of driving knowledge or driving skill, fluctuation of traffic environment, and the like.

As disclosed in Patent Document 2, even if the steering angle information of the preceding vehicle is acquired, the specifications of the steering device of each vehicle constituting the platooning are different, and various matters related to vehicle motion such as vehicle mass and wheelbase. If the originals are different, the value calculated based on the steering information of the preceding vehicle will not be equal to the lateral deviation of the own vehicle, so the lateral deviation of the own vehicle in the vehicle direction with respect to the preceding vehicle may not be sufficiently small. ..

Patent Document 3 describes a method for improving the accuracy of the own vehicle position by GPS, but does not describe how to utilize the calculated own vehicle position for automatic driving of platooning.

Patent Document 4 only discloses that a clothoid curve is connected to a partial orbit having an arc shape to make the curved orbit smoothly continuous, and does not describe GPS information or suggestion of relevance to platooning.

In addition, all of Non-Patent Documents 1 to 3 have problems peculiar to platooning, that is, how to convey the position and direction of the preceding vehicle to the following vehicle, and when the traveling posture of the preceding vehicle has an adverse effect on the following vehicle. It does not solve anything about how to solve it.

In order to solve the above-mentioned problems, the method for generating a target locus according to the present invention transmits the GPS travel locus of the preceding vehicle to the following vehicle by vehicle-to-vehicle communication when a plurality of vehicles are traveling in a platoon on a curved portion by automatic driving. Then, the following vehicle generates an interpolation curve of the preceding vehicle trajectory in real time based on the received GPS travel trajectory of the preceding vehicle, sets the arrival target point of the following vehicle on the interpolation curve, and determines the arrival target point. I tried to connect smoothly between the position of the vehicle and the position of the own vehicle with a relaxation curve.

Here, the preceding vehicle means the leading vehicle forming a platoon. For example, when forming a platoon with four vehicles, the second to fourth vehicles are all following vehicles, and each following vehicle is a preceding vehicle. A target locus is generated based on the GPS travel locus of.

In Patent Document 1 and the like, a marker or the like installed at the rear of the immediately preceding vehicle is detected, but in the present invention, the third and subsequent vehicles are also based on the GPS traveling locus of the preceding vehicle and other trailing vehicles. A unique target trajectory different from the target trajectory of the vehicle is generated.

Further, if the steering speed is too fast with respect to the vehicle speed, steering wheel vibration occurs. Therefore, when generating the target locus of the following vehicle, it is preferable to generate it under the condition that the steering wheel vibration does not occur.

According to the method for generating a target trajectory according to the present invention, when a truck or the like travels in a platoon, the following vehicle can smoothly follow the preceding vehicle even if the preceding vehicle freely selects a traveling route. can.

Further, since the reference of the target trajectory of the following vehicle is not the steering angle information of the preceding vehicle disclosed in the prior art but the traveling trajectory of the preceding vehicle itself, each following vehicle does not lag behind the preceding vehicle. The target trajectory can be obtained in real time.

In particular, by interpolating with a relaxation curve such as a clothoid curve, it is possible to obtain a target locus that can be accurately and stably followed.

The flowchart of the method of generating the target locus which concerns on this invention. The figure explaining the clothoid curve as a relaxation curve Explanatory diagram of the target trajectory of the following vehicle with the correction of the traveling trajectory of the preceding vehicle Explanatory drawing of the method to obtain the actual rudder angle from the radius of curvature The figure explaining the relationship between the vehicle speed which suppresses the steering wheel vibration and the steering speed

As shown in FIG. 1, the preceding vehicle converts the acquired GPS information (longitude, latitude, direction) into plane orthogonal coordinates and transmits it to each following vehicle by vehicle-to-vehicle communication (760MHz V2V transmission interval 0.1 seconds).

Each subsequent vehicle that receives this converts the GPS information (longitude, latitude, azimuth) acquired by its own vehicle into plane orthogonal coordinates, and N points (N points) on a crossoid curve between the coordinates of the preceding vehicle and the coordinates of its own vehicle. x ₁ , x ₂ , ... x _n, y ₁ , y ₂ , ... y _n, φ ₁ , φ ₂ , ... φ _n , ...) Interpolate and trace coordinates of point N (x, y) ), The azimuth angle (φ1), and the curvature (ρ1) are obtained and used as the target locus of the preceding vehicle (h: see).

Each following vehicle detects the tracking deviation (lateral deviation e2, angle deviation e3) with respect to the target trajectory of the preceding vehicle, calculates the tracking trajectory (crossoid interpolation path of the following vehicle) from the position of the following vehicle to the target trajectory of the preceding vehicle, and steers. Derive the angle.

As shown in FIG. 2A, the clothoid curve is a locus drawn by the vehicle when the steering wheel is turned at a constant ratio (angle speed) when the vehicle is traveling at a constant speed, and is a line segment (segment) P ₀ . -The product of P ₁ and the radius of curvature of the locus becomes a constant value. The path angle continuously changes to φo, φv, and φu, which indicates the change in the curvature of the line segment (h) in b), and the curvature of the line segment (h) continuously changes. φ ₀ is the initial direction, φ v is the arc having the initial curvature, and φ u is the increment of the tangential angle due to the addition of the clothoid component.

FIG. 2C shows clothoid interpolation from one of the following vehicles to the preceding vehicle. The following vehicle is at Po (same as P ₀ in FIG. 3) at a path angle φo, and P1 of the preceding vehicle trajectory. Since it is about to reach the point (same as P1 in FIG. 3), the path angle deviation of the following vehicle with respect to the preceding vehicle trajectory is "φ1-φ0", and the position deviation is L.

The above relationship is shown in FIG. FIG. 3A is a partially enlarged view of FIG. 3B, and FIG. 3B is a diagram showing the positional relationship of the following vehicle following the preceding vehicle on the earth plane coordinates.
The curvature ρ2 of the following vehicle flowing into the trajectory of the preceding vehicle is determined from the lateral deviation e2 and the angular deviation e3. That is, the position deviation between the locus point P1 of the preceding vehicle and the current position P0 of the following vehicle is expressed by the equation ( 1 ), and the angle deviation e3 is φ _1i − φ _2i . From the integral equation (2) of this angular deviation, the path curvature (ρ2) of the following vehicle is obtained. This equation (2) is a clothoid interpolation equation, and the equation (3) is a trigonometric function equation.

If the curvature is not large for both the generation of the target locus of the following vehicle from the locus of the preceding vehicle and the curve flowing into the target locus from the current position of the following vehicle, the time is not limited to the crossoid curve whose path length is a variable. It may be a triangular function expression as a variable or a polynomial curve approximation (minimum square method, exponential function, etc.).

FIG. 4 is an explanatory diagram of a method of determining the actual steering angle from the radius of curvature, the front wheel actual steering angle is obtained from the path curvature (ρ2) of the following vehicle obtained above, and the steering wheel angle (steering angle) is obtained from the actual steering angle. Ask.

Specifically, a steady circular turning state in which the steering wheel is fixed to the left portion of FIG. 4 and the vehicle turns at a constant vehicle speed is shown. The vehicle turns with a revolution that rotates around the center of the circle and a rotation that rotates around the center of gravity of the own vehicle. Since it is necessary to generate a centripetal force that is commensurate with the centrifugal force, the front axle tire and the rear axle tire slip sideways to generate a tire lateral force (cornering force).

The vehicle body skid angle (β) is required to skid the rear axle tires. Therefore, there is a relationship between the absolute speed (V), the front-back speed (Vx), and the lateral speed (Vy) in contact with the turning circle. The speed measured by GPS is the absolute speed (V), and the speed measured from the wheel rotation of the vehicle is the front-back speed (Vx).

As the vehicle speed increases, the skid angle and turning radius change due to the relationship between the vehicle lateral acceleration and the tire lateral force. The change in the skid angle is given by Eq. (4), the change in turning radius is given by Eq. (5), and the relationship between the curvature and the actual steering angle is given by Eq. (6). When the overall gear ratio of the steering system is multiplied by the equation (6), the steering angle (steering angle) is obtained.

5A and 5B are views for explaining the “relationship between vehicle speed and steering speed” that suppresses steering wheel vibration, FIG. 5A is a three-dimensional view of the steering system, and FIG. 5B is a plan view of vehicle turning.
The vehicle should run smoothly if the speed is controlled and the steering is controlled so as to follow the clothoid curve, but it is necessary to pay attention to the relationship between the rotation speed due to the vehicle speed and the rotation speed due to the steering regarding the rotation of the actual steering wheel.

In the three-dimensional view (a), the steering wheel rotation speed is applied to the gear ratio of the power steering, and is passed through the pitman arm, the drag link, and the steering arm.
The right steering angle (δr) is centered on the right kingpin axis, and the left steering angle (δl) is similarly centered on the left kingpin axis via the tie rod and tie rod arm.

Explaining the rotational speed of the left front wheel in the plan view (b) as an example, the wheel speed (Vs) due to steering is generated in the wheel speed (Vc) due to the vehicle speed. (Refer to Masaichi Kondo, Yokendo, 1967.4, p.116-117, Basic Automotive Engineering (Late Edition))
Since the wheel speed (Vc) and the wheel speed (Vs) are in opposite directions, when a high steering speed is applied under a low vehicle speed condition, a condition that Vc-Vs becomes negative arises. Under this condition, the friction of the tire contact patch changes to sliding friction instead of rolling friction, and steering vibration occurs. The relationship between the vehicle speed and the steering speed is controlled by the equation (7) so as not to fall within the limit of this relationship.

Claims (3)

It is a method to generate the target trajectory of the following vehicle when multiple vehicles are traveling in a platoon on a curved part by automatic driving, and the GPS traveling trajectory of the preceding vehicle is transmitted to the following vehicle by vehicle-to-vehicle communication, and the following vehicle receives it. Based on the GPS travel locus of the preceding vehicle, a part of the preceding vehicle locus is set as an interpolation curve in which the following vehicle merges in real time, and the arrival target point of the following vehicle is set on this interpolation curve, and the arrival target point is set as the arrival target point. A method for generating a target locus, which comprises connecting the positions of the own vehicle with a relaxation curve such as a crossoid curve to form a target locus. In the method for generating a target locus according to claim 1, the relaxation curve from the position of the following vehicle to the target point of arrival is calculated based on the lateral deviation and the angle deviation between the current position of the following vehicle and the target point of arrival. A method of generating a target trajectory characterized by. In the method for generating the target locus according to claim 1 or 2, the condition for connecting with the relaxation curve is that the wheel speed of the steering wheel by steering does not exceed the wheel speed due to the vehicle speed in order to suppress the steering wheel vibration. A method of generating a target trajectory, which is characterized by doing so.

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