Method for controlling the trajectory of a vehicle enabling obstacle avoidance

Abstract

The present invention relates to a method (1) for controlling the trajectory of a vehicle when approaching an obstacle, comprising a step (12) of controlling a steering angle of the wheels implementing a calculation of a yaw rate setpoint (I) of the vehicle and a control loop of the steering angle of the wheels as a function of the calculated yaw rate setpoint (II), the step (12) of controlling the steering angle of the wheels using a longitudinal speed of the vehicle, the control method (1) being characterised in that it further comprises a step (10) of controlling a speed of the vehicle, and in that the longitudinal speed of the vehicle is a set longitudinal speed (Vox) determined during the step (12) of controlling the speed of the vehicle.

Description

Description Title of the invention: Method for controlling the trajectory of a vehicle allowing obstacle avoidance

[0001] The present invention relates to the field of the automotive industry, and more specifically concerns a method for controlling the trajectory of an autonomous vehicle or one equipped with an advanced driving assistance system.

[0002] These vehicles are equipped with sensors to understand their environment, and actuators to act on the transmission and steering of the vehicle, without intervention from the driver, the actuators themselves being controlled by one or more computers generally embedded in the vehicle. Such a vehicle therefore manages the trajectory of the vehicle itself, at least in certain driving contexts of the vehicle.

[0003] Such a vehicle must handle generally complex scenarios. In order for a vehicle computer to make and execute an optimal decision regarding the trajectory to follow, for example in terms of steering angle or speed to be set by the vehicle, it is necessary to make several software modules cooperate and to merge information from these modules in real time.

[0004] One of the recurring complex problems that such a vehicle must solve is the avoidance of obstacles at high speed. Indeed, this problem requires cooperation between a lateral vehicle control system, managing the steering angle of the vehicle wheels, and a longitudinal vehicle control system, managing the vehicle speed. An integration of the data from these systems to solve this problem results in a non-linear and difficult-to-solve equation in real time to regulate both the vehicle speed and the steering angle of the vehicle wheels.

[0005] Existing control solutions for obstacle avoidance maneuvers are mainly based on vehicle steering regulation only, which depending on a measured longitudinal vehicle speed, dynamically modifies a vehicle yaw rate towards a new reference trajectory generated by the vehicle's computer.

[0006] Because the generation of a yaw rate command is closely linked to the measured longitudinal speed of the vehicle, at high speeds during an obstacle avoidance maneuver the vehicle will reach its physical limits and will be unable to turn as fast as requested and follow the yaw rate command. This can cause oscillations or even instability of the vehicle even if it finally manages to avoid the obstacle and reach a new reference trajectory.

[0007] These solutions do not take into account the longitudinal evolution of the vehicle in their calculation of the yaw rate, nor the physical limitations of the vehicle's braking and steering systems, which may prevent the vehicle from performing the avoidance maneuver satisfactorily.

[0008] The invention aims to remedy at least in part the drawbacks of the state of the art by providing a method for controlling the trajectory of a vehicle when approaching an obstacle, in which longitudinal speed and yaw setpoints of the vehicle are optimized so that the physical limits of a steering system of the vehicle can be respected at high speed, thus allowing the vehicle to avoid the obstacle by a rapid maneuver without creating instability.

[0009] To this end, the invention proposes a method for controlling the trajectory of a vehicle when approaching an obstacle, comprising a step of controlling a steering angle of the wheels implementing a calculation of a yaw rate setpoint of the vehicle and a loop for controlling the steering angle of the wheels as a function of the calculated yaw rate setpoint, the step of controlling the steering angle of the wheels using a longitudinal speed of the vehicle, the control method being characterized in that it further comprises a step of controlling a speed of the vehicle, and in that said longitudinal speed of the vehicle is a set longitudinal speed determined during the step of controlling the speed of the vehicle.

[0010] By means of the invention, a complex obstacle avoidance problem is simply achieved by decoupling the vehicle speed control step on the one hand and the vehicle wheel steering angle control step on the other hand, the wheel steering angle control step using only an exogenous parameter from the vehicle speed control step. Indeed, these two steps are executed in parallel, and the vehicle wheel steering angle control step does not influence the vehicle speed control step in any way. Conversely, only the vehicle's set longitudinal speed influences the vehicle wheel steering angle control step. In this application, the longitudinal direction of the vehicle is oriented parallel to the length of the vehicle. By using this decoupling, each step can take into account the limits specific to the vehicle's braking system or steering system.

[0011] According to an advantageous characteristic of the trajectory control method according to the invention, the step of controlling the speed of the vehicle comprises a sub-step of optimizing an objective function taking into account a distance calculated as a function on the one hand of a distance measured between the vehicle and the obstacle and on the other hand of a yaw angle of the vehicle, the optimization sub-step being capable of providing a set longitudinal acceleration of the vehicle, the integration of which provides said set longitudinal speed. Thanks to this characteristic, information from the vehicle sensors is added to the control loop. In fact, the set longitudinal speed takes this information into account and requires the vehicle to slow down when approaching the obstacle, which allows the yaw rate to adapt to a lower set longitudinal speed than in the prior art, and to perform avoidance without oscillations. The calculated distance is a function of the distance measured at least for a certain period of time preceding the avoidance of the obstacle. The set longitudinal acceleration is here a value that can be positive or negative, i.e. it can be a longitudinal acceleration or deceleration setpoint.

[0012] In one embodiment of the invention, the calculated distance is a function of a minimum safety distance between the vehicle and the obstacle to be avoided. Thus, the obstacle is avoided with a configurable safety margin.

[0013] Advantageously, the calculated distance increases as a function of the vehicle's yaw angle at least until the yaw angle allows the obstacle to be avoided. Thus, as the vehicle approaches its objective of avoiding the obstacle, braking is reduced, allowing the vehicle to resume the direction of a new trajectory without excessive deceleration.

[0014] In one embodiment of the invention, the optimization sub-step responds to a constraint according to which a distance traveled by the vehicle during a predetermined number of calculation steps is less than said calculated distance. This realization of the optimization sub-step allows an adaptation of the braking distance in real time and configurable.

[0015] According to an advantageous characteristic of the trajectory control method according to the invention, as soon as the yaw angle allows the obstacle to be avoided, the calculated distance is updated so as to no longer depend on the distance measured between the vehicle and the obstacle, according to a predefined choice of driving mode. Thus, the deceleration of the vehicle once it is steered so as to avoid the obstacle is configurable according to a driving choice, for example selected by a user of the vehicle. In particular, the user can choose the speed of execution of the complete obstacle avoidance maneuver by selecting a fast or sporty mode or a mode with a safer and more flexible feel.

[0016] For example, as soon as the yaw angle allows the obstacle to be avoided, the calculated distance is updated so as to no longer constrain the objective function, or to constrain it according to another obstacle on the trajectory of the vehicle, instead of said obstacle to be avoided. Alternatively, the constraint on the calculated distance is removed in the objective function optimization sub-step. This removal of the dependence of the set longitudinal speed on the calculated distance allows the vehicle to regain speed as soon as it is no longer heading towards the obstacle, and to reach its new trajectory very quickly.

[0017] Alternatively, the vehicle's environment being divided orthogonally to an initial trajectory of the vehicle, into a first zone not including the obstacle and comprised between the vehicle and a first end of the obstacle, and a second zone including the obstacle and comprised between the first end of the obstacle and a second end of the obstacle, as long as the vehicle is in the first zone, as soon as the yaw angle allows the obstacle to be avoided, the calculated distance is updated so as to no longer depend only on the yaw angle and a distance between the vehicle and a target trajectory of the vehicle. In this alternative, the vehicle only really picks up speed when the vehicle begins to pass the obstacle, which makes its maneuver more flexible than in the previous example.

[0018] In yet another alternative, the vehicle's environment being divided orthogonally to an initial trajectory of the vehicle, into a first zone not including the obstacle and comprised between the vehicle and a first end of the obstacle, and a second zone including the obstacle and comprised between the first end of the obstacle and a second end of the obstacle, as long as the vehicle is in the first or second zone, as soon as the yaw angle allows the obstacle to be avoided, the calculated distance is updated so as to no longer depend only on the yaw angle and a distance between the vehicle and a target trajectory of the vehicle. In this other alternative, the vehicle only really picks up speed when the vehicle has passed the obstacle, which makes its maneuver even more comfortable and flexible than in the previous alternative.

[0019] The invention also relates to a computer program comprising program code instructions for executing the steps of the control method according to the invention, when said program is executed on one or more computers of a vehicle. The computer program according to the invention has advantages similar to those of the control method according to the invention.

[0020] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0021] [Fig.1] schematically illustrates markers for the positioning of a vehicle implementing a control method according to the invention, these markers being used by this control method according to the invention, in one embodiment of the invention,

[0022] [Fig.2] illustrates means and steps used or implemented by the control method according to the invention, in this embodiment of the invention,

[0023] [Fig.3] illustrates a vehicle environment as modeled by the method of control of [Fig.2],

[0024] [Fig.4] represents the trajectory taken by a vehicle not implementing the control method according to the invention, during an obstacle avoidance maneuver,

[0025] [Fig.5] represents yaw rates of the vehicle of [Fig.4] during this obstacle avoidance maneuver,

[0026] [Fig.6] represents trajectories taken by the vehicle of [Fig.1] implementing the control method of [Fig.2] during an obstacle avoidance maneuver,

[0027] [Fig.7] represents longitudinal speeds of the vehicle of [Fig.1] during the trajectories taken by it and represented [Fig.6],

[0028] [Fig.8] represents angles at the steering wheel of the vehicle of [Fig.1] during the trajectories taken by it and represented [Fig.6], and

[0029] [Fig.9] represents lateral accelerations of the vehicle of [Fig.1] during the trajectories taken by it and represented [Fig.6].

[0030] In one embodiment of the invention, a vehicle 2 represented in figure 1 according to a so-called “bicycle” model implements a trajectory control method 1 according to the invention (referenced figure 2), and has a center of gravity G. Its position is located in an orthonormal reference frame (O, X, Y) fixed relative to the vehicle 2, and in which a yaw rate of the vehicle is measured. The axis (OX) is parallel to an initial trajectory of the vehicle, on which there is an obstacle Obs (referenced [Fig.3]).

[0031] In the so-called "bicycle" model, the rear wheels of vehicle 2 are merged into a single wheel Wr and the front wheels of vehicle 2 into a single wheel Wf. An orthonormal reference frame (G,x,y) integral with vehicle 2 has a longitudinal axis (Gx) passing through the center of gravity G of vehicle 2, through the center of the merged wheels Wr, Wf, and oriented towards the front of vehicle 2. This longitudinal axis (Gx) is called the longitudinal axis of vehicle 2. The orthonormal reference frame (G,x,y) has a lateral axis (Gy) passing through the center of gravity G of the vehicle, parallel to the floor of the vehicle and orthogonal to the longitudinal axis (Gx) of vehicle 2. This lateral axis (Gy) is directed here towards the left side of vehicle 2 and is called the lateral axis of vehicle 2.

[0032] In the orthonormal reference frame (G,x,y) fixed to the vehicle 2, a measured speed (relative to the fixed orthonormal reference frame (O,X,Y)) of the vehicle 2 is decomposed along the longitudinal axis (Gx) into a longitudinal speed , and along the lateral axis (Gy) of the vehicle 2, into a lateral speed . The front wheel Wf has a steering angle δ with the longitudinal axis (Gx) of the vehicle 2. This steering angle δ is a steering angle of the wheels of the vehicle 2, representative of the direction taken by the latter at a given instant.

[0033] As shown [Fig.2], the vehicle 2 comprises means 20 for perceiving the immediate environment of the vehicle 2, these means 20 for perceiving a or several sensors such as radars, LiDAR (from the English “Light Detection And Ranging”) or cameras. The perception means 20 deduce from these sensors, a measured distance Dobs between the vehicle 2 and the obstacle Obs appearing on the initial trajectory of the vehicle 2.

[0034] The vehicle 2 further comprises a positioning means 21 such as a GPS module (from the English “Global Positioning System”) capable of providing a position (X,Y) of the vehicle 2 in the fixed orthonormal reference frame (O,X,Y).

[0035] The vehicle 2 also includes a gyroscope 25 providing the measured yaw rate of the vehicle 2, and a speed sensor 26 providing the measured speed of the vehicle 2.

[0036] In this embodiment of the invention, the control method 1 is implemented in a computer of the vehicle 2, which receives for example via a central computer bus of the vehicle 2 (also called “CAN bus” for the English “Controller Area Network”), the measured distance Dobs to the obstacle Obs, the position (X,Y) of the vehicle 2 in the fixed orthonormal reference frame (O,X,Y), the measured yaw rate and the measured speed of the vehicle 2, these data being updated in real time by the various means and sensors of the vehicle 2.

[0037] The computer of the vehicle 2 comprises a navigation module 22 which establishes from the position (X, Y) of the vehicle 2, and from the measured distance Dobs to the obstacle Obs, a new trajectory Tr (referenced figure 3) to be followed for the vehicle 2, with a reference speed and a reference yaw angle ψr which follows the curve of this new trajectory Tr.

[0038] The computer of the vehicle 2 also includes a module 27 for estimating the lateral state of the vehicle 2. This estimation module 27 estimates a lateral speed of the vehicle 2 in the orthonormal reference frame (G,x,y) of the vehicle 2, and uses a model to provide a corrected yaw rate c based in particular on the measured yaw rate.

[0039] The computer of the vehicle 2 implements a step 10 of controlling the speed of the vehicle 2, this step 10 using a longitudinal planner 23, which optimizes the reference speed in particular as a function of the physical characteristics of the braking, propulsion and transmission systems of the vehicle 2, and of the measured distance Dobs to the obstacle Obs. The longitudinal planner 23 provides as output a set longitudinal speed Vox, the obtaining of which will be detailed later in relation to [Fig.3].

[0040] Vehicle speed control step 10 also uses a longitudinal controller 24 which applies a setpoint acceleration or deceleration ax_cons to actuators of vehicle 2 to make it take the longitudinal speed of Vox instruction.

[0041] In parallel with this step 10 of controlling the speed of the vehicle 2, the computer of the vehicle 2 implements a step 12 of controlling the yaw rate of the vehicle 2, using a lateral planner 28 whose operation will be detailed later in relation to FIG. 3. The lateral planner 28 receives as input the lateral speed of the vehicle 2 estimated by the estimation module 27, the corrected yaw rate c by the estimation module 27, the reference yaw angle ψr provided by the navigation module 22, and the set longitudinal speed Vox from the longitudinal planner 23. The lateral planner 28 uses these inputs to provide a yaw rate setpoint o. This setpoint takes into account the physical limits of the steering system of the vehicle 2.

[0042] Step 12 of controlling the yaw rate of the vehicle 2 also uses a lateral controller 29 which implements a control loop, as a function of the yaw rate setpoint o, of a wheel steering angle setpoint δcons, sent to actuators of the vehicle 2 to make it take this yaw rate setpoint o.

[0043] In step 10 of controlling the speed of the vehicle 2, the longitudinal planner 23 determines a calculated distance Dmax represented [Fig.3], as follows:

[0044] Dmax = Dobs – Ds, where Ds is a safety distance of a few meters around the obstacle Obs.

[0045] Then the longitudinal planner 23 determines a variable Ytr (referenced [Fig.3]) such that:

[0046] Ytr = Wobs – Dmax / tan(ψ) where Wobs is the dimension of the obstacle orthogonally to the OX axis and therefore to the initial trajectory of vehicle 2, and tan(ψ) the tangent to the yaw angle ψ of the vehicle measured by the estimation module 27 of the lateral state of vehicle 2, this yaw angle ψ being representative of the change of direction of vehicle 2 with respect to the axis (OX) of the fixed orthonormal reference frame (O, X, Y), and therefore with respect to its initial trajectory.

[0047] If the variable Ytr has a negative value, this means that the immediate direction of vehicle 2 towards its new trajectory Tr is such that vehicle 2 should not encounter the obstacle Obs. If, on the contrary, the variable Ytr has a strictly positive value, this means that the immediate direction of vehicle 2 towards its new trajectory Tr is such that vehicle 2 would encounter the obstacle Obs if it maintained this direction. In [Fig.3], the critical point Pc corresponds to the zero value of the variable Ytr and therefore to the target point that the longitudinal axis (Gx) of vehicle 2 must strive to encounter by turning towards its new trajectory Tr.

[0048] The longitudinal planner 23 then modifies the value of the calculated distance Dmax according to the variable Ytr and a driving mode, selected by example by a user of vehicle 2.

[0049] According to a first sporty driving mode, when the variable Ytr is of strictly positive value, the longitudinal planner 23 increases the calculated distance Dmax as a function of the yaw angle ψ of the vehicle, more precisely in an inversely proportional manner to the cosine of this measured yaw angle ψ:

[0050] Dmax = Dmax / cos(ψ)

[0051] In other words, the calculated distance Dmax is taken equal not to the actual distance Dobs to the obstacle Obs but to a travel distance of the vehicle to the obstacle Obs with a constant vehicle direction and oriented according to the yaw angle ψ measured at a processing time by the longitudinal planner 23, a safety distance (Ds / cos(ψ)) being subtracted from this travel distance.

[0052] When, on the contrary, the variable Ytr has a negative value, in this first sporty driving mode, the longitudinal planner 23 gives the calculated distance Dmax a very high value, for example one hundred meters, so as to no longer force braking on the vehicle 2:

[0053] Dmax =100

[0054] The distance Dobs to the obstacle being updated in real time, the calculated distance Dmax is also updated before modification by the longitudinal planner 23 according to the variable Ytr. The calculated distance Dmax being used to determine the set longitudinal speed Vox, the smaller this calculated distance Dmax is, the more the set longitudinal speed Vox brakes the vehicle 2. In this first sporty driving mode, the modifications of the planner 23 let the vehicle 2 brake until the vehicle 2 is steered so as to avoid the obstacle Obs, then when the target point Pc is reached by the longitudinal axis (Gx) of the vehicle 2, the latter is no longer braked by the obstacle Obs, but can be by other trajectory constraints.

[0055] According to a second flexible driving mode, three distinct zones are distinguished in which the vehicle 2 moves during its obstacle avoidance maneuver. A first zone z1 extends parallel to the initial trajectory of the vehicle 2, in the fixed orthonormal reference frame (O, X, Y), between an initial position of the vehicle 2 and the obstacle Obs. A second zone z2 extends parallel to the initial trajectory of the vehicle 2, in the fixed orthonormal reference frame (O, X, Y), over the entire dimension Lobs of the obstacle Obs parallel to the axis (OX), that is to say between a first end of the obstacle Obs located on a straight line orthogonal to the initial trajectory of the vehicle 2, proximal to the vehicle 2, and a second end of the obstacle Obs located on a straight line orthogonal to the initial trajectory of the vehicle 2, distal to the vehicle 2.A third zone z3 extends parallel to the initial trajectory of vehicle 2, in the fixed orthonormal reference frame (O, X, Y), from the second end of the obstacle Obs.

[0056] In this second flexible driving mode, when the variable Ytr is of value strictly positive, the longitudinal planner 23 also increases the calculated distance Dmax as a function of the yaw angle ψ of the vehicle, inversely proportional to the cosine of this measured yaw angle ψ:

[0057] Dmax = Dmax / cos(ψ)

[0058] When, on the contrary, the variable Ytr has a negative value, in this second flexible driving mode, as long as the vehicle is in zone z1, the longitudinal planner 23 gives the calculated distance Dmax a value which no longer depends on the distance Dobs measured at the obstacle, but which depends on the yaw angle ψ measured and a distance Ycg between the vehicle and the new trajectory Tr of vehicle 2, which is a target trajectory:

[0059] Dmax =Ycg / sin(ψ)

[0060] It should be noted that the target trajectory Tr is parallel to the initial trajectory of the vehicle but laterally offset from this initial trajectory.

[0061] Dmax being taken equal to the distance Ycg between vehicle 2 and the new trajectory Tr of vehicle 2, divided by the sine of the measured yaw angle ψ, this means that once vehicle 2 is steered so as to avoid obstacle Obs, the braking of vehicle 2 is a function of the travel distance of vehicle 2 to the new trajectory Tr with constant vehicle direction and oriented according to the yaw angle ψ measured at the instant of processing by the longitudinal planner 23. In other words, vehicle 2 continues to brake in zone z1 after having steered so as to avoid obstacle Obs, so that it moves more gently than in the first driving mode, towards its new trajectory Tr.

[0062] According to a third driving mode perceived as safer by a user, when the variable Ytr is of strictly positive value, the calculated distance Dmax is always taken equal, by the longitudinal planner 23, to:

[0063] Dmax = Dmax / cos(ψ)

[0064] When, on the contrary, the variable Ytr has a negative value, in this third driving mode, as long as the vehicle is in zones z1 and z2, the longitudinal planner 23 gives the calculated distance Dmax a value which no longer depends on the distance Dobs measured at the obstacle, but which depends on the yaw angle ψ measured and the distance Ycg between the vehicle and the new trajectory Tr of vehicle 2:

[0065] Dmax =Ycg / sin(ψ)

[0066] In other words, as in the second driving mode, in this third mode, once the vehicle 2 is steered so as to avoid the obstacle Obs, the braking of the vehicle 2 is a function of the travel distance of the vehicle 2 up to the new trajectory Tr with constant vehicle direction and oriented according to the yaw angle ψ measured at the instant of processing by the longitudinal planner 23. Thus the vehicle 2 continues to brake until it passes the obstacle Obs, in its redirection maneuver towards the new Tr trajectory, which provides a safer feeling than in the second driving mode.

[0067] The calculated distance Dmax modified by the longitudinal planner 23, is used by the latter in a sub-step of optimization of an objective function J which provides as output the longitudinal acceleration (or deceleration) ax_cons of the vehicle, the integration of which provides the longitudinal speed of the vehicle Vox. It is therefore a predictive control of the longitudinal speed of the vehicle, subject to given constraints. We have:

[0068] and where is the instantaneous longitudinal acceleration of vehicle 2, on the longitudinal axis (Gx) of vehicle 2, is the instantaneous longitudinal speed of vehicle 2, on the longitudinal axis (Gx) of vehicle 2, and is the distance traveled by vehicle 2 from an initial position of vehicle 2, taken for example when vehicle 2 is on its initial trajectory. These data are discretized by calculation step and noted , and to designate their value at any calculation step k.

[0069] The predictive control consists of finding, at each calculation step k, the longitudinal acceleration which minimizes the objective function J:

[0072]

[0073]

[0074]

[0075] Or :

[0076] - is a maximum acceleration value not to be exceeded,

[0077] - is a reference longitudinal speed of the vehicle 2 corresponding to the projection of the reference speed provided by the navigation module 22, on the longitudinal axis (Gx) of the vehicle 2, and - is a maximum acceleration increment or decrement between a calculation step k+i and the calculation step k.

[0078] The number N of calculation steps considered in the objective function J is fixed by the person skilled in the art, for example following various operating tests of the longitudinal planner 23 on a given braking or powertrain system.

[0079] The minimizing longitudinal acceleration of the objective function J is then taken as the longitudinal acceleration (or deceleration) ax_cons of the vehicle 2, and allows, by integrating this instruction, to determine the longitudinal speed of the instruction Vox. This longitudinal speed of the instruction Vox is then provided as input to the lateral planner 28.

[0080] During step 12 of controlling the steering angle of the vehicle wheels, the lateral planner 28 uses a control loop of the steering angle δ of the wheels as a function of a yaw rate setpoint o which is a virtual reference determined in real time by solving an optimization problem, this being for example to minimize the quadratic distance between a previous yaw rate and a yaw rate making it possible to reach the new trajectory Tr, as a function of constraints, in particular linked to the steering system of the vehicle 2.

[0081] The paper “A Reference Governor approach for Lateral Control of Autonomous Vehicles” by Dimitrios Kapsalis et al, presented in September 2021 at the IEEE (Institute of Electrical and Electronics Engineers) ITSC2021 conference, describes a similar control step, which uses a measured longitudinal speed of the vehicle 2.

[0082] In this embodiment of the invention, step 12 of controlling the steering angle of the wheels uses the method described in this document, but instead of using the longitudinal speed measured in the lateral control loop, uses the set longitudinal speed Vox. Thus the yaw speed setpoint o takes into account the longitudinal approach strategy of the vehicle 2, implemented by the longitudinal planner 23, which makes the control method 1 according to the invention more efficient.

[0083] To illustrate this improvement over the prior art, tests were carried out on the one hand with an autonomous vehicle not implementing the control method 1 according to the invention, and on the other hand with the vehicle 2 implementing the control method 1 according to the invention. During these tests, the vehicles perform an obstacle avoidance maneuver under the same initial conditions. Each autonomous vehicle approaches an obstacle positioned 17 meters away from it at 14 m / s (meters per second), while being laterally 3.2 meters from a new lane on which it must place itself to avoid the obstacle. The new lane corresponds to a new trajectory or target trajectory T. The minimum safety distance is set at 3.2 meters in front of the obstacle.

[0084] Figure 4 shows the trajectory 3(t) taken by the autonomous vehicle not implementing the control method 1 according to the invention, and Figure 5 shows the reference yaw rate deduced from a reference yaw angle provided by a navigation module of autonomous, the measured yaw rate of this autonomous vehicle, and the yaw rate instruction given to the of steering of this autonomous vehicle.

[0085] This data shows that the autonomous vehicle's navigation module provides a reference yaw angle that the autonomous vehicle cannot follow (the speed measured yaw rate does not follow the reference yaw rate, because the demand of the module exceeds the limits of the autonomous vehicle's steering capabilities. This is due to the fact that the vehicle's longitudinal speed is very high and influences the reference yaw rate so that it changes too quickly to be followed by the autonomous vehicle's steering system. This is why the autonomous vehicle oscillates around its target trajectory T and exhibits instability.

[0086] In the case of the vehicle 2 implementing the control method 1 according to the invention, the different driving modes are tested. Thus [Fig.6] shows the trajectory 2_1(t) followed by the vehicle 2 during the obstacle avoidance maneuver when the first sporty driving mode is selected, the trajectory 2_2(t) followed by the vehicle 2 during the obstacle avoidance maneuver when the second flexible driving mode is selected, and the trajectory 2_3(t) followed by the vehicle 2 during the obstacle avoidance maneuver when the third driving mode with a safer feel is selected.

[0087] Similarly, Figures 7, 8 and 9 respectively show the longitudinal speed vx_1(t), wheel steering angle δ_1(t) and lateral acceleration ay_1(t) of vehicle 2 during the obstacle avoidance maneuver when the first sporty driving mode is selected, the longitudinal speed vx_2(t), wheel steering angle δ_2(t) and lateral acceleration ay_2(t) of vehicle 2 during the obstacle avoidance maneuver when the second smooth driving mode is selected, and the longitudinal speed vx_3(t), wheel steering angle δ_3(t) and lateral acceleration ay_3(t) of vehicle 2 during the obstacle avoidance maneuver when the third driving mode with a safer feeling is selected. The wheel steering angles are expressed in degrees in [Fig.8].

[0088] These data show that when the set longitudinal speed Vox is used by the lateral planner 28, in particular to determine the yaw rate setpoint o, the vehicle 2 reaches the target trajectory T without oscillating and without instability. This is due to the fact that the speed of the vehicle 2 is reduced before the obstacle, which allows the lateral planner 28 to issue a yaw rate setpoint o that is suitable for the physical limits of the steering system of the vehicle 2. Indeed, from the first second the longitudinal speed of the vehicle is reduced as well as the lateral acceleration. These figures also show that the first driving mode corresponds to the fastest of the three maneuvers shown in Figures 6 to 9, and that the third driving mode corresponds to the smoothest and most comfortable of these three maneuvers.

[0089] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

Claims

Claims

1. Method for controlling (1) the trajectory of a vehicle (2) when approaching an obstacle (Obs), comprising a step (12) of controlling a steering angle of the wheels (δ) implementing a calculation of a yaw rate setpoint ( ) of the vehicle (2) and a loop for controlling the steering angle of the wheels as a function of the calculated yaw rate setpoint, the step (12) of controlling the steering angle of the wheels (δ) using a longitudinal speed of the vehicle (2), the control method (1) being characterized in that it further comprises a step (10) of controlling a speed of the vehicle (2), and in that said longitudinal speed of the vehicle (2) is a set longitudinal speed (Vox) determined during the step (12) of controlling the speed of the vehicle (2).

2. Control method (1) according to claim 1, in which the step (10) of controlling the speed of the vehicle (2) comprises a sub-step of optimizing an objective function (J) taking into account a calculated distance (Dmax) as a function on the one hand of a measured distance (Dobs) between the vehicle (2) and the obstacle (Obs) and on the other hand of a yaw angle (ψ) of the vehicle (2), the optimization sub-step being capable of providing a set longitudinal acceleration (ax_cons) of the vehicle (2), the integration of which provides said set longitudinal speed (Vox).

3. Control method (1) according to claim 2, in which the calculated distance (Dmax) is a function of a minimum safety distance (Ds) between the vehicle (2) and the obstacle (Obs) to be avoided.

4. Control method (1) according to any one of claims 2 to 3, wherein the calculated distance (Dmax) increases as a function of the yaw angle (ψ) of the vehicle (2) at least until the yaw angle (ψ) makes it possible to avoid the obstacle (Obs).

5. Control method (1) according to any one of claims 2 to 4, wherein the optimization sub-step responds to a constraint according to which a distance traveled by the vehicle (2) during a predetermined number of calculation steps is less than said calculated distance (Dmax).

6. Control method (1) according to any one of claims 2 to 5, wherein as soon as the yaw angle (ψ) makes it possible to avoid the obstacle (Obs), the calculated distance (Dmax) is updated so as to no longer be. make it depend on the measured distance (Dobs) between the vehicle (2) and the obstacle (Obs), according to a predefined choice of driving mode.

7. Control method (1) according to claim 5 or 6, in which as soon as the yaw angle (ψ) allows the obstacle (Obs) to be avoided, the calculated distance (Dmax) is updated so as to no longer constrain the objective function (J), or to constrain it according to another obstacle on the trajectory of the vehicle (2), instead of said obstacle (Obs) to be avoided.

8. Control method (1) according to claim 5 or 6, wherein the environment of the vehicle (2) is divided orthogonally to an initial trajectory of the vehicle (2), into a first zone (z1) not comprising the obstacle (Obs) and comprised between the vehicle (2) and a first end of the obstacle (Obs), and a second zone (z2) comprising the obstacle (Obs) and comprised between the first end of the obstacle (Obs) and a second end of the obstacle (Obs), as long as the vehicle (2) is in the first zone (z1), as soon as the yaw angle (ψ) allows the obstacle (Obs) to be avoided, the calculated distance (Dmax) is updated so as to no longer depend only on the yaw angle (ψ) and a distance between the vehicle (2) and a target trajectory (Tr) of the vehicle (2).

9. Control method (1) according to claim 5 or 6, wherein the environment of the vehicle (2) is divided orthogonally to an initial trajectory of the vehicle (2), into a first zone (z1) not comprising the obstacle (Obs) and comprised between the vehicle (2) and a first end of the obstacle (Obs), and a second zone (z2) comprising the obstacle (Obs) and comprised between the first end of the obstacle (Obs) and a second end of the obstacle (Obs), as long as the vehicle (2) is in the first (z1) or the second zone (z2), as soon as the yaw angle (ψ) allows the obstacle (Obs) to be avoided, the calculated distance (Dmax) is updated so as to no longer depend only on the yaw angle (ψ) and a distance between the vehicle (2) and a target trajectory (Tr) of the vehicle (2).

10. Computer program comprising program code instructions for executing the steps of the control method (1) according to any one of claims 1 to 9, when said program is executed on one or more computers of a vehicle (2).

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