WO2018215709A1

WO2018215709A1 - System for planning the trajectory of a motor vehicle

Info

Publication number: WO2018215709A1
Application number: PCT/FR2018/051029
Authority: WO
Inventors: Sergey ABRASHOV; Francois Aioun; Franck Guillemard; Xavier Moreau; Rachid Malti
Original assignee: Psa Automobiles Sa; Centre National De La Recherche Scientifique; Institut Polytechnique De Bordeaux; Universite de Bordeaux
Priority date: 2017-05-22
Filing date: 2018-04-24
Publication date: 2018-11-29
Also published as: FR3066627A1; FR3066627B1; EP3635499A1

Abstract

The invention relates to a method for autonomous control of the steering of a motor vehicle during a lane change. The method uses a decision-making computer (2) determining the lane to be used, as well as a positioning system (7) for positioning the vehicle in relation to the various lanes. A reference generator (4) calculates a filtered reference signal (df n) from the error between a reference value and a measured value in order to make it possible to have a smoothed trajectory correction. The correction of this position error is obtained via a control loop (8), using a regulator (5). The latter outputs a control signal (51) which acts on the steering mechanism of the vehicle (6).

Description

MOTOR VEHICLE TRACK PLANNING SYSTEM

The invention relates to the field of motor vehicles equipped with autonomous or semi-autonomous driving system. More particularly, the invention relates to the field of trajectory planning systems for a motor vehicle in autonomous or semi-autonomous driving during a lane change.

Lateral trajectory regulators play a vital role in controlling the trajectory of motor vehicles. They intervene in particular to control and maintain the vehicle on a trajectory calculated by an external system. Three cases usually occur. The first concerns the case where the curvature of the road varies. The vehicle must adjust its trajectory to align with the variation in the shape of the road, usually modeled by a clothoid curve. The second case concerns in particular the disturbances of the trajectory, due for example to an involuntary manipulation of the steering wheel or to the meteorological conditions (wind). The vehicle must be able to quickly return to its original trajectory. The third case concerns trajectory calculations where a lane change is planned. In order to preserve the stability of the vehicle and the comfort of the passenger, this change of lane must not lead to a sudden change of the trajectory.

In this sense, published patent document US 8,428,843 B2 discloses a method requiring a complete modeling of the route taken by the vehicle. Once this estimate is made, a preferred trajectory is predictively generated, adapted to be smooth when changing lanes. The algorithm therefore relies on polynomial approximations requiring substantial computing power.

The lateral control method disclosed in the state of the art requires the analysis of a road horizon in order to plan in advance the trajectory of the vehicle over that horizon. The object of the invention is to provide a method for autonomously controlling the steering of a motor vehicle, in the event of a lane change, which overcomes at least one disadvantage of the abovementioned prior art. More particularly, the invention aims to provide a method of autonomous control of the steering of a motor vehicle, in case of a lane change, requiring less computational capabilities than the methods of the state of the art. The invention relates to a method for autonomously controlling the direction of a motor vehicle during a lane change, comprising the following steps: receiving a lane change signal to a target channel; and calculating a vehicle direction control signal based on the lane change signal; remarkable in that the calculation of the steering control signal comprises, upon reception of the lane change signal, the determination of a function of the lateral deviation of the vehicle with respect to the target lane and a smoothing of said function by means of a low-pass filter.

Autonomous control of the steering of a motor vehicle means an automated control of the direction of the vehicle with or without the supervision and / or intervention of the driver.

The target track is the path on which the vehicle must align its trajectory and continue its movement. The target path may be changed depending on the planned trajectory calculations. According to an advantageous embodiment of the invention, the calculation of the steering control signal further comprises a servocontrol loop of said control signal, with, as a reference, the function of the smoothed lateral deviation.

According to an advantageous mode of the invention, the control loop comprises a regulator of the PID type. According to an advantageous embodiment of the invention, the servo control loop further comprises a function representative of the dynamics of the vehicle.

According to an advantageous embodiment of the invention, the control loop further comprises a disturbance signal at the input of the function representative of the dynamics of the vehicle. The disturbances acting on the servo system are therefore a component of the signal processed by the representative function of the dynamics of the vehicle.

According to an advantageous embodiment of the invention, the servo-control loop comprises a measurement of the lateral deviation of the vehicle relative to a reference track and the calculation of the difference between said measured difference and the smoothed lateral deviation. According to an advantageous embodiment of the invention, the low-pass filter is executed by means of a transfer function F (s) of the second order which is stated:

according to a Laplace s operator, with a cutoff frequency and a damping coefficient ζf

According to an advantageous embodiment of the invention, the cutoff frequency is greater than or equal to 0.25 and / or less than or equal to 2.

According to an advantageous embodiment of the invention, the damping coefficient is greater than or equal to 0.85. The invention also relates to a motor vehicle comprising an autonomous driving system with a power steering and a computer electrically connected to said direction, and wherein the computer is configured to perform the method described above according to the invention.

The measurements of the invention are interesting in that the method makes it possible to generate, in a simplified manner, the trajectory of the vehicle when it changes its lane. This trajectory generation is simplified in that it is based on a smoothing of the function of the lateral deviation of the vehicle with respect to the target channel, this function forming, by its nature, a step. This function is calculated from two external data, which correspond to the lateral distance of the vehicle relative to a reference path, as well as that relative to a target path.

The measures of the invention are interesting in that they make it possible to distinguish the different situations at the origin of a variation of the values of these lateral distances. Indeed, the reference generator makes it possible to distinguish the variations due to a movement of the vehicle following a spacing of its intended trajectory (turn, weather disturbance or involuntary handling of the steering wheel), those due to a change of target path. Thus, only the component of the function of the lateral deviation due to a change of lane is smoothed by a low-pass filter.

The method therefore makes it possible to adapt the effect of the lateral position regulator to each situation. If it is a separation of the vehicle from its trajectory, the loop of control acts so that the vehicle quickly returns to its position. If the target channel has changed, the vehicle then starts a smooth deflection, thanks to a damping of the instruction upstream of the command.

In addition, the measurements of the invention are interesting in that the degree of smoothing is adjustable, in particular by acting on the damping coefficient and the cut-off pulse of the filter placed upstream of the control loop.

Other features and advantages of the present invention will be better understood from the description and the drawings, among which:

- Figure 1 models the differences between the tracks and the vehicle; FIG. 2 is a block diagram of the invention;

FIG. 3 is a graph showing the setpoint variation during a lane change without signal processing;

FIG. 4 is a block diagram of the reference generator, which contributes to the smoothing of the trajectory; FIG. 5 is a block diagram of the control loop;

FIG. 6 is a graph of the reference trajectory as a function of the cut-off pulse of the filter.

- Figure 7 illustrates the marks associated with the vehicle.

Figure 1 models the differences between the different tracks and the vehicle. Each of the paths is indexed i, and each of said deviations is denoted by. A Frenet base (T, N) can be associated with the position of the vehicle at each moment, T being a vector tangent to the vehicle trajectory, and N a vector normal to T at the point modeling the position of the vehicle 1. The index i then varies incrementally from 0, in the positive direction of the vector N. The channel 0 therefore represents the furthest path situated to the right of the driver, according to the direction of advance of the vehicle 1.

The invention is implemented by a device as shown in Figure 2. The vehicle is equipped with a positioning computer 2 of the vehicle on the road. It implements a decision algorithm that determines the trajectory of the vehicle, and therefore the way to follow at every moment. This path is called "target path" and is noted n. The corresponding data is transformed into a signal 3 at the input of the reference generator 4.

In order to implement such a device, the vehicle is also equipped with a positioning system 7, which generally includes position sensors and cameras to identify road features, such as the white side lines. These measured position data are sent to the input of the reference generator 4 by means of a control loop 8.

When a difference is found between the actual position of the vehicle and the target path, the device acts to cancel and reposition the vehicle on its calculated path. This adjustment is achieved by the step 40 of calculating a control signal of the direction of the vehicle, implementing the reference generator 4 and the lateral position controller 5.

The repositioning of the vehicle on its trajectory is therefore ensured by a control signal 51 emitted by the lateral position controller 5. In case of deviation, the repositioning trajectory of the vehicle is linked to the shape of the signal of the trajectory setpoint df ⁿ received by the lateral position regulator 5. In fact, the position controller 5 converts the setpoint df ⁿ into a control 51 applied to the steering mechanism of the vehicle 6.

Figure 3 shows the variation of the reference reference Δd ⁿ during a change of channel without signal processing. At the moment of the change, the distance between the vehicle and the middle of the target path varies abruptly, according to a spatial and temporal level. The reference setpoint Δd ⁿ , as indicated in the figure, is calculated from these variations of deviation.

Figure 4 is a block diagram of the reference generator 4, which contributes to the smoothing of the trajectory. The reference generator 4 comprises a selector 42, a subtractor 44, and a filter 46. The selector 42 receives as input the number of the target channel n, transmitted by the decision-making calculator 2 (FIG. 2), as well as the differences of to all routes i. The selector 42 emits at its output only the data of two deviations: d ° and d ⁿ . The subtractor 44 calculates the difference between d ⁿ and d °, referred to as the reference reference Δd ⁿ . The advantage of this selection step 41 and then subtraction 43 lies in the fact that a lane change influences only the distance d ⁿ and not d °. In the event of a disturbance of the trajectory, on the other hand, the vehicle starts moving, which results in the variation of d ° and d ⁿ at a time. The subtraction step 43 of a gap from one another makes it possible to distinguish one case from the other.

It is thus necessary to eliminate from the signal the component related to a possible disturbance, to keep only the part of the trajectory related to the change of target lane:

Indeed, if there is no change of lane, and assuming that the respective tangents of the lanes are parallel to the instant t, the variations of the differences d ° and d ⁿ at this instant are equal, as illustrated. by the following proposition:

During step 45, the reference setpoint Δd ⁿ is processed by a low-pass filter 46 to emit at its output the filtered reference Δdf ⁿ , which constitutes the regulation setpoint.

The trajectory error to be canceled by the lateral position regulator, said trajectory setpoint df ⁿ , is induced at the output of the generator by means of a closed-loop control 8.a, and is obtained according to the following formula:

By noting F the filter transfer function, the regulation setpoint Δdf ⁿ is obtained according to the following relation:

Where is the operator of the Laplace inverse transform, * is the convolution operator, s is a Laplace operator, ω _f is the filter cutoff pulse, and ζ _f is the damping coefficient of the filter. ζ _f is usually chosen greater than 0.85 to avoid oscillations. FIG. 5 is a block diagram of the control loop 8.b, including the lateral position regulator 5 and the function representative of the dynamics of the vehicle 6. The servocontrol loop 8b makes it possible to provide the regulator with an error of position e (s) to be canceled, given by:

J _ref.f (s) corresponds to a set value obtained by filtering a reference value y _ref (s), thanks to the low-pass filter 46 of the transfer function F. The equations (E1) and (E2) are therefore equivalent:

A disturbance signal is taken into account upstream of the function representative of the dynamics of the vehicle 6, which can advantageously be the steering mechanism.

The control loop 8.b makes it possible to bring the distance between the channel 0 and the vehicle - represented by the measured value noted y, - to equalize the target value noted y _ref , which represents the distance between the channel 0 and the new target path n. It constitutes a reference value towards which the value of measurement must tend thanks to successive iterations of calculation.

As illustrated in FIG. 6, ω _f makes it possible to impose the degree of "smoothing": for the pulsation values ω _f less than or equal to 0.35rad.s-1, the trajectory is smooth. For values greater than 0.35rad.s-1, switching from one channel to another becomes abrupt.

The marks associated with the vehicle 1 are given in FIG. 7. The values of the deviations of are algebraic values, their sign depending on the position of the vehicle 1 with respect to each of the respective channels.

The signals y and y _ref are given by the following formulas:

To establish the transfer relationship between the reference and the output:

As well as the transfer between the output and the perturbation p:

Claims

CLAIMS.

1. A method of autonomously controlling the steering of a motor vehicle (1) during a lane change, comprising the following steps:

- receiving a lane change signal (3) to a target channel (n);

calculating (40) a control signal (51) of the vehicle direction on the basis of the lane change signal (3);

characterized in that

the calculation of the steering control signal comprises, upon reception of the lane change signal (3), determining a function (Δd ⁿ ) of the lateral deviation of the vehicle with respect to the target lane (n ) and smoothing (45) said function by means of a low-pass filter (46).

2. Method according to claim 1, characterized in that the calculation of the control signal of the direction (51) further comprises a control loop (8.b) of said control signal, with, for regulation setpoint , the function of the target lateral deviation smoothed (Δdf ⁿ ).

3. Method according to claim 2, characterized in that the control loop comprises a PID type regulator (5).

4. Method according to claim 3, characterized in that the control loop further comprises a function representative of the dynamics of the vehicle (6).

5. Method according to claim 4, characterized in that the control loop (8.b) further comprises a disturbance signal at the input of the function representative of the dynamics of the vehicle (6).

6. Method according to one of claims 2 to 5, characterized in that the servocontrol loop (8.b) comprises the measurement (y) of the lateral deviation of the vehicle relative to a reference channel and the calculation the difference between said measured difference (y) and the smoothed target lateral deviation (Δdf ⁿ ).

7. Method according to one of claims 1 to 6, characterized in that the low-pass filter is executed (45) by means of a transfer function F (s) of the second order: according to an operator

of Laplace s, with a cut-off frequency ω _f and a damping coefficient ζf

8. The method of claim 7, characterized in that the cutoff frequency ω _f is greater than or equal to 0.25 and / or less than or equal to 2.

9. Method according to one of claims 7 or 8, characterized in that the damping coefficient is greater than or equal to 0.85.

Motor vehicle (1) comprising an autonomous driving system with a power steering and a computer electrically connected to said direction, characterized in that the computer is configured to execute the method according to one of claims 1 to 9. .