Method of steering a motor vehicle in the center of its lane

Abstract

The invention relates to a method for assisting the steering of a motor vehicle to keep it in the center of its traffic lane, comprising steps of: - acquiring values ​​of parameters relating to the dynamics of the motor vehicle and to its position in its traffic lane, a first of said parameters being an integral function of a position datum of the motor vehicle in its traffic lane, - determining a steering angle setpoint of the motor vehicle by means of a controller, as a function of the acquired values ​​and of nominal reference values ​​of said parameters. According to the invention, when the implementation of the steering method has been suspended and then resumes, the steering angle is acquired and the reference value of said first parameter is modified so as to minimize the difference between the acquired steering angle and the steering angle setpoint. Figure for the abstract: Fig.2

Description

Title of the invention: Method for steering a motor vehicle in the center of its traffic lane Technical field of the invention

[0001] The present invention relates generally to driving aids for motor vehicles.

[0002] It applies more particularly to cars and other motorized vehicles traveling on roads, but also applies to other fields such as robotics.

[0003] The invention relates to a method for assisting the steering of a motor vehicle to keep it in the center of its lane, comprising steps of: - acquisition of values ​​of parameters relating to the dynamics of the motor vehicle and its position in its lane, a first of said parameters being an integral function, and - determination of a steering angle setpoint for the motor vehicle by means of a controller, based on the acquired values ​​and nominal reference values ​​of said parameters.

[0004] It also relates to a motor vehicle adapted to implement such a control method. State of the art

[0005] In an effort to make motor vehicles safer, they are currently being equipped with driving assistance systems and even highly automated driving systems.

[0006] Among these systems, we find in particular the lane centering systems (better known by the English acronym LCA for “Lane Centering Assist”).

[0007] To implement such an “LCA system”, the motor vehicle is equipped with a series of sensors for acquiring data characterizing the state of the motor vehicle and its environment, and software for analyzing this data in order to generate commands to steer the motor vehicle in order to keep it in the center of its traffic lane.

[0008] The software is based on a regulator which takes the form of a status feedback, for example. For example, it is possible to use a double regulation loop which includes: - an open loop term which allows the curvature of the road to be taken into account, by calculating the steering angle required to follow this curvature, and - a closed-loop term (such as a "state feedback") that calculates the steering wheel angle required to maintain or align the vehicle relative to the center of its lane considering that it is a straight line.

[0009] The closed loop term uses a state vector that includes the values ​​of several parameters, one of which is an integral calculated based on previous states.

[0010] LCA systems are intended to be activated in particular in the event of heavy traffic on the road (as part of driving aids in traffic). They are then designed in particular to be used as part of level 2 driving aids (in the sense of the standard defined by the SAE - Society of American Automotive Engineers), that is to say aids requiring the driver to keep their hands on the steering wheel.

[0011] It is therefore understood that the driver must be able to easily regain control of the vehicle at any time. Therefore, the solution generally used consists of measuring the torque applied by the driver to the steering wheel, then, as soon as this torque exceeds a threshold, deactivating this LCA system. The rest of the time, the torque exerted on the steering wheel is considered as a simple disturbance.

[0012] It is therefore understood that, as soon as he exerts a significant torque on the steering wheel, the driver is then forced to manually reactivate the LCA function. To avoid this when conditions allow (typically when the driver exerts a moderate effort on the steering wheel in order to slightly and temporarily correct the trajectory of the vehicle), it is desired to allow the LCA system not to be completely inactivated, but rather to be interrupted momentarily.

[0013] The difficulty then is that at the moment when the LCA system reactivates automatically, the calculated steering instruction is such that it can generate a strong jolt on the steering wheel.

[0014] The problem is in fact that the integral term of the state vector considered in the closed loop continued to be integrated so that it could drift significantly and no longer correspond to the situation.

[0015] A solution to reduce this problem could be to freeze its value, but here again, this value would generally no longer correspond to the situation at the time of reactivation of the LCA system, which would still generate an uncomfortable jolt for the vehicle passengers (and would slow down the return of the vehicle to the center of its traffic lane). Presentation of the invention

[0016] In order to overcome the aforementioned drawback of the state of the art, the present invention proposes a solution to enable, at the moment when the LCA system is automatically reactivated, comfortable and efficient steering of the vehicle towards the center of its lane to be guaranteed.

[0017] More particularly, according to the invention, a control method is proposed such that defined in the introduction, in which, when the implementation of the piloting process has been suspended and then resumes: - the steering angle is acquired (preferably measured) and - the reference value of said first parameter (the one which is an integral function) is modified so as to minimize the difference between the acquired steering angle and the steering angle setpoint.

[0018] Thus, thanks to the invention, at the time of resuming the LCA method, the integral term (which includes time t as an integration variable) is calculated not as a function of the previous states of the system, but in such a way that the steering angle setpoint is equal to the instantaneous steering angle of the vehicle, which guarantees the absence of steering wheel jerks.

[0019] Thus, the driving of the motor vehicle at the time of reactivation of the LCA system can be both smooth and efficient.

[0020] Preferably, the reference values ​​of one or more other parameters are modified to correspond to the instantaneous values ​​(measured or acquired) of these parameters. Thus, the regulation will not seek to directly bring the motor vehicle back to the center of its traffic lane but first to stabilize it on its current trajectory. By gradually returning the reference value(s) to its nominal value(s) (which correspond to the lane center), it is then possible to gradually bring the vehicle back to the center of its traffic lane.

[0021] Other advantageous and non-limiting characteristics of the * according to the invention, taken individually or in all technically possible combinations, are the following:

[0022] - at least a second of said parameters relates to the position of the vehicle at car in its lane;

[0023] - when the implementation of the control method resumes, the value of said at least a second parameter is acquired and is used as a reference value of said at least one second parameter, then, at subsequent times, the reference value of said at least one second parameter is modified so as to gradually return to its nominal reference value;

[0024] - when the implementation of the control method resumes, the values ​​of two first parameters are acquired and are used as reference values ​​of said at least one second parameter, then these reference values ​​are modified so as to gradually return to their nominal reference values;

[0025] - said second parameter is a heading angle of the motor vehicle relative to its traffic lane;

[0026] - said second parameter is a lateral gap between the motor vehicle and the center of its traffic lane;

[0027] - to gradually return to its nominal reference value, the value of reference of said at least one second parameter is calculated by means of a filtering function, preferably a low-pass filtering function;

[0028] - the first parameter is an integral function of a position data of the motor vehicle in its lane, and preferably an integral function of a lateral gap between the motor vehicle and the center of its lane;

[0029] - the values ​​of the parameters are acquired by means of a state observer;

[0030] - the steering angle setpoint of the motor vehicle is equal to the sum of a first component from said controller and a second component depending on the curvature of the traffic lane;

[0031] - it is planned to suspend the implementation of the piloting method until a The driver of the motor vehicle exerts a torque on a steering wheel greater than a predetermined threshold.

[0032] The invention also proposes a motor vehicle comprising a power steering actuator and a computer adapted to control the power steering actuator, programmed to implement a control method as mentioned above.

[0033] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0034] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0035] In the attached drawings:

[0036] [Fig-1] is a schematic top view of a motor vehicle traveling on a road ;

[0037] [Fig.2] represents a functional diagram of the calculations for implementing a method for controlling the motor vehicle of [Fig.l];

[0038] [Fig.3] is a graph illustrating the variations over time of a nominal reference value, a modified reference value, and an actual value of the lateral deviation between the motor vehicle and the center of its traffic lane;

[0039] [Fig.4] illustrates the variations over time of four trajectory tracking parameters, in a particular situation.

[0040] In [Fig.l], a motor vehicle 10 is shown, conventionally comprising a chassis, two front steerable wheels 11, and two rear non-steerable wheels 12. In alternatively, these two rear wheels could also be steered with an adaptation of the control law.

[0041] This motor vehicle 10 comprises a conventional steering system making it possible to act on the orientation of the steered wheels so as to be able to turn the vehicle. This conventional steering system notably comprises a steering wheel connected to connecting rods in order to pivot the steered wheels. In the example considered, it also comprises at least one actuator making it possible to act on the orientation of the steered wheels as a function of the orientation of the steering wheel and / or as a function of a request received from a computer 13. This power steering actuator can, for this purpose, act on the steering column of the vehicle (which is fixed to the steering wheel) or on a rack (which connects the steering column to the steered wheels). Of course, the actuator could be arranged differently.

[0042] The computer 13 is then designed to control the power steering actuator. For this purpose, it comprises at least one processor, at least one memory and various input and output interfaces.

[0043] Thanks to its input interfaces, the computer 13 is adapted to receive input signals coming from different sensors.

[0044] Among these sensors, for example, a front camera is provided, making it possible to locate the position of the vehicle in relation to its traffic lane.

[0045] An angle sensor is also provided for measuring the steering angle of the steered wheels.

[0046] Thanks to its output interfaces, the computer 13 is adapted to transmit an instruction to the power steering actuator.

[0047] Thanks to its memory, the computer 13 stores data used in the context of the method described below. In particular, it stores a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the computer to implement the method described below.

[0048] This method allows the motor vehicle 10 to follow a reference trajectory corresponding to the central line T0 of its traffic lane 30 (which is here defined between a road edge and a discontinuous ground marking line).

[0049] Before describing in more detail the method according to the invention, we can introduce the different variables which will be used, some of which are illustrated in [Fig.l].

[0050] The total mass of the motor vehicle will be noted “m” and will be expressed in kg.

[0051] The center of gravity of the vehicle will be noted “CG”.

[0052] The mass of the vehicle which is exerted on the front wheel set will be noted “Mf” and will be expressed in kg.

[0053] The mass of the vehicle which is exerted on the rear wheel set will be noted “Mr” and will be expressed in kg.

[0054] The wheelbase of the vehicle, that is to say the distance between the axes of these two wheel sets, will be noted “L” and will be expressed in meters.

[0055] The pneumatic rigidity of the rear wheels will be noted Cr and will be expressed in Newton / rad.

[0056] The pneumatic rigidity of the front wheels will be noted Cf and will be expressed in Newton / rad.

[0057] We can consider an orthogonal reference frame (CG, X, Y, Z) attached to the vehicle. Its origin is the same as the center of gravity CG. The X axis corresponds to the longitudinal axis of the vehicle facing the front of the vehicle. The Y axis corresponds to the lateral axis facing the left of the vehicle. When the vehicle is traveling on a horizontal road, the Z axis corresponds to the vertical axis. More generally, this Z axis is the axis normal to the road.

[0058] The steering angle that the front steered wheels make with the longitudinal axis X of the motor vehicle 10 will be noted “ô” and will be expressed in rad.

[0059] It will be noted that the steering wheel angle and the steering angle δ are directly linked, with a gear ratio or even first or second order dynamics. In the following, only the steering angle δ at the wheels will be considered.

[0060] The steering speed of the front wheels will be noted “dô / dt”.

[0061] The longitudinal speed of the vehicle, along the X axis, will be noted v and will be expressed in m / s.

[0062] The relative heading angle between the X axis and the tangent to the center line T0 at the center of gravity CG will be noted “W” and will be expressed in rad.

[0063] The yaw rate of vehicle 1, i.e. its rotation speed around the Z axis, will be noted “drp / dt”.

[0064] The lateral position error, also called lateral deviation, between the center of gravity CG of the vehicle and the center line T0 will be noted y.

[0065] The lateral speed of the vehicle will be noted “dy / dt”.

[0066] At this stage, we can also introduce a notion of “position error integral”, which corresponds to the time integral of the lateral deviations y with respect to the central line T0. This error integral will be noted “Jy.dt”.

[0067] The curvature of the center line T0 of the traffic lane is noted p (in m1). This is the inverse of its radius of curvature, either at the level of the vehicle or at a distance from the latter.

[0068] The method for controlling the motor vehicle 10 is designed to enable this vehicle to follow the central line T0 of its traffic lane, in autonomous mode (without driver intervention).

[0069] This method is implemented when the system for keeping the vehicle in the center of its traffic lane (hereinafter called the LCA system) is activated.

[0070] The way to activate this system and detect the center line T0 of the circum- culture will not be described here.

[0071] On the other hand, it will be possible to briefly describe how the vehicle is kept in the center of its lane when the LCA system is activated and operating nominally. It will then be described how it operates when it has been temporarily deactivated and then reactivates automatically.

[0072] Thus, a distinction will be made between a nominal operation of this system and a particular operation during its reactivation.

[0073] To establish the vehicle control law and thus regulate the steering angle δ of the motor vehicle 10 so that the latter remains in the center of its traffic lane, this vehicle was modeled using a bicycle model.

[0074] In such a model, the two wheels of the front axle are considered to be merged, and the same applies to the two rear wheels. The chassis of the vehicle is modeled by a body which connects the two wheel models.

[0075] The dynamics of the motor vehicle 10 can then be represented by a state vector X, which is expressed here in the form:

[0076] [Math.l] idip / dh dy / dt y dô / dt ô J [-yJr /

[0077] We observe here that one of the terms of this state vector is an integral function depending on the previous states of the motor vehicle 10. This term corresponds here more precisely to the error integral introduced above.

[0078] According to the “bicycle” model used, the equation of this system is written in the following form:

[0079] [Math.2] X — AX + BfrôpBK + Bp.p Y = CX

[0080] In this equation, the term ôFBk is a first component of the steering angle setpoint ô which will be transmitted to the power steering actuator. As will become more clear below, this component makes it possible to keep the vehicle in the center of the traffic lane, considering that the latter is straight.

[0081] A, C, Bô and Bp are determined matrices and vectors.

[0082] The first of the Math2 equations then introduces two terms, including an open loop term Bp.p and a closed loop term Bô.ôFBk- The open loop term is intended to compensate for the steering angle ô by taking into account the curvature of the center line T0. The closed loop term allows the steering angle to be calculated considering that the traffic lane is straight.

[0083] Y represents the measurement vector, and it therefore depends on the state X.

[0084] Matrix A is expressed in the following form:

[0085] il Lf L « X hv ' L.; vuu ï, u 1 ô 0 0 0 Ô 0 CArf-CLL -i Cf ,, 0 Q mv 0 'fn. 0 T o 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 \ 0 0 0 1 0 0 0 /

[0086] The matrix C is expressed in the following form:

[0087] / 1 0 0 0 ( ) 0 0 \ 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 () \ 0 0 0 0 0 0 1 /

[0088] The Bô matrix is ​​expressed in the following form:

[0089] z .. x

[0090] The matrix Bp is expressed in the following form:

[0091] / nx / 0 \

[0092] With reference to [Fig.2], the topology of an example of an LCA system is schematically represented by a block diagram.

[0093] This block diagram comprises a closed loop 25 and an open loop 21.

[0094] The open loop 21a has the function of taking into account the curvature of the road and to compensate for the effect of the turn on the states and the command.

[0095] The closed loop 25 has the function of keeping the vehicle in the center of its traffic lane while the latter is considered straight, that is to say rectilinear.

[0096] We therefore find the two terms introduced above.

[0097] The terms resulting from these two loops, namely the components ôFBK and ôFFD, are added together by means of an adder 27.

[0098] The steering angle ô to be transmitted to the front wheel so that the vehicle 1 moves in a bend having a known curvature p thus depends on the two previous components, so that we can write:

[0099] [Math.3] 5req = ÔFBK + ÔFFD

[0100] In [Fig.2], the state of vehicle 1 is represented by element 22. This element therefore represents the vehicle, with its sensors, its actuators, etc. A set of measured data emerges from this element 22.

[0101] The open loop 21 comprises an anticipatory element 24. This anticipatory element 24 takes into account the curvature p of the traffic lane (calculated for example from the images obtained by the camera) in order to evaluate the component ôFFD of the steering angle ô. This open loop is generally known by the Anglo-Saxon term “feed forward”.

[0102] Considering the bicycle model in steady state (with dX / dt = 0), and assuming the vehicle is in the center of its lane (dy / dt = 0 and y=0) and in an established turn (dô / dt=0), we can then write:

[0103] [Math.4] ^FFD - p( L+ SVV~)

[0104] In this equation, Vsv is the vehicle's own understeer gradient, which is classically defined by the following expression:

[0105] [Math.5] _ Mf Mr v sv- Cf - Cr

[0106] In other words, the component ôFFD of the steering angle ô has a term pL which is determined as a function of the curvature of the turn and the architecture of the vehicle, and a term which makes it possible to take into account the drift of the vehicle when turning.

[0107] The closed loop 25 comprises an observer element 26 which makes it possible to observe the state Xobs of the motor vehicle 10.

[0108]

[0109]

[0110] [YES]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] It also includes a comparator 28 to differentiate between a reference state Xref and this observed state Xobs. This difference forms an error XeiT. It finally comprises a controller 20 which collects the signal delivered by the comparator 28 and generates the component ôFBK of the steering angle ô. This controller 20 in practice comprises a gain Ks in the form of a vector which, once multiplied by the error Xeir, makes it possible to calculate the component ôFBK. The state observer 26 collects a measurement vector Ymes (comprising measured values, such as the steering angle in particular) and delivers the observed state Xobs. The state representation implemented by state observer 26 is based on the bicycle model of the vehicle. This state observer 26 is used to estimate unmeasured values ​​of model parameters. These unmeasured values ​​are for example dy / dt and dô / dt. It should be noted here that, as a variant, this observer could be dispensed with if all values ​​were measured. Denoting x as the estimate of the state vector X, the observer equation can be written as: [Math.6] X = (A-LpC}X+Bôôfbk + LpY with LP a gain value associated with observer element 26. Typically, the control implemented by the closed loop 25 aims to minimize the state vector X around a zero reference state Xref corresponding to a straight line. In other words, the nominal reference values ​​(under nominal driving conditions) are such that we can write: [Math.7] ldvrefldt

[0120]

[0121] In summary, when the LCA system is activated and operating in nominal mode, it is intended to measure the variables of the measurement vector Ymes and the curvature p of the taxiway. This curvature allows the calculation of the ôFFD component.

[0122] The measured variables make it possible, thanks to the state observer 26, to determine the values ​​Xobs>i of the parameters of the state vector X (also called state variables and noted: rp, drp / dt, y, dy / dt, ô, dô / dt, fy .dt).

[0123] The vector XeiT making the difference between these observed values ​​Xobs>i and the corresponding nominal reference values ​​Xref>i then makes it possible to determine the component ôFbk, and therefore to deduce the steering angle setpoint ô.

[0124] There are situations in which regulation in nominal mode must be temporarily interrupted.

[0125] This is for example the case when the driver exerts for a limited duration a torque on the steering wheel which is greater than a simple disturbance but less than a threshold beyond which the LCA system deactivates entirely.

[0126] Typically, this duration is 50ms and this threshold is 4Nm of torque at the steering wheel.

[0127] This is also the case in sharp turns, when the steering angle or lateral deviation exceeds a threshold.

[0128] This is also the case when the longitudinal speed of the vehicle becomes lower than a threshold (2 km / h for example).

[0129] Other situations could also be considered.

[0130] When the LCA system reactivates automatically (i.e. when the situation considered ceases), the error integral Jy.dt is not usable (the cumulative value in the integral is generally not the correct one).

[0131] When the LCA system reactivates automatically (hereinafter referred to as the reactivation moment) and in the seconds that follow (hereinafter referred to as the reactivation phase), the invention proposes to modify the algorithm presented above so that this resumption takes place without generating any jolts to the steering wheel. The nominal operation described above is intended to resume thereafter.

[0132] The idea is, during the reactivation phase, to modify the reference vector Xref in order to take this particular situation into account.

[0133] Thus, at the instant of reactivation, the reference vector Xref is modified to have at least two unharmed terms.

[0134] These terms are preferably the heading angle W and the lateral deviation y. Note that the objective remains that the error integral Jy.dt tends towards 0.

[0135] Here, the two terms corresponding to the heading angle W and the lateral deviation y are considered unaffected.

[0136] We can therefore write, at the time of reactivation:

[0137] [Math. 8] \Xref^d^ref / dt\ Xref^dyrefldt ^refA “ yref ^■ref^ ~ dÔref} dt ^reffi “ ^ref ,dt I fcjsJ j . rej !

[0138]

[0139]

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150] With Wref and yref unharmed. First, we can explain what values ​​are assigned to the terms and Xrefj4. At the instant of reactivation, these two terms are chosen equal to their real (or estimated) values. These values ​​are then, for example, measured on the images acquired by the front camera of the motor vehicle. Alternatively, they could be estimated otherwise. The idea here is not to force the motor vehicle to return abruptly to the center line T0, but to make it return gradually to this line. Then, during the entire reactivation phase, the values ​​of these terms will gradually tend towards zero. The reactivation phase preferably has a duration greater than one second, during which these two terms will remain unaffected. The variation of these two terms will be continuous, which will allow a significant improvement in the control (less oscillations, no overshoot, smoother regulation, etc.). To vary these terms Xrefj2 and Xref>4, any suitable continuous function can be used. Here, it is chosen to vary these two terms according to their values ​​measured at the current time step t, and according to their values ​​calculated at the previous time step t-1. This achieves a sort of smoothing by low-pass filtering. More precisely, this is smoothing by “exponential moving average”. We can therefore write: [Math.9] . y'„f= In each of these equations, the constant w is the weight given to each of the two terms of the equation. It is identical here in both equations but could differ.

[0151] It is preferably greater than 0.99. It is for example chosen to be equal to 0.9975. This weight thus makes it possible to have a reactivation phase of reasonable convergence duration.

[0152] In [Fig.3], the curve Cl represents the nominal reference value Xref>2, that is, the reference value of the lateral deviation y in nominal operating mode. We observe that this value remains zero.

[0153] Curve C3 corresponds to the actual (measured) value of the lateral deviation y. We observe in this [Fig.3] that at 42 seconds on the abscissa scale, the actual lateral deviation y increases. This is due to a steering of the wheels imposed by the driver.

[0154] Curve C2 represents the reference value Xref>2 taken during the reactivation phase. We observe that this value takes at the instant of reactivation (at 60 seconds) a non-zero value equal to the real value, then that it returns to zero in a continuous and continuously derivable manner. The reactivation phase then lasts 20 seconds here.

[0155] For information, we note in this [Fig.3] that at 72 seconds on the abscissa scale, the actual lateral deviation y diverges momentarily. This is due to the fact that the vehicle is arriving on a bend and that it deviates slightly from the center of the traffic lane at the start of this bend.

[0156] At this stage, we can now describe how the term Xref>7, which corresponds to the reference value of the error integral Jy.dt, is calculated.

[0157] Here, the objective of this calculation is to ensure that this term catches up with any steering angle errors that might be made in order to avoid generating any jerks in the steering wheel at the instant of reactivation.

[0158] To do this, the value ôMeasured of the steering angle is measured, then the reference value Xref>7 is calculated so as to minimize the difference between this measured value ô Measured and the steering angle setpoint ô (calculated at the previous time step).

[0159] Here, it will be noted that the measured value comes from a measurement of a steering wheel angle which, taking into account a gear ratio, makes it possible to obtain a steering angle of the wheels. Alternatively, this value could be obtained by calculation, for example by means of another observer.

[0160] Thus, we can write:

[0161] [Math. 10] / -y .dt^Ks^- dMeasured- - 5ffd

[0162] With

[0163] [Math. 11] = Ks{ A Xj + Ks2 A X2+ ... + Ks6 A X6

[0164] Where

[0165] [Math. 12] A i — obs.i " Xrefj

[0166] In these equations, the values ​​Ks; correspond to the terms of the vector forming the gain Ks of the corrector.

[0167] Therefore, the initial value of the error integral is determined via the equation:

[0168] [Math. 13] J value mit y = ----------

[0169] It should be noted here that this calculation can be simplified.

[0170] Indeed, we can consider that the terms AX2 and AX4 are null.

[0171] In [Fig.4], to clearly illustrate the operation of the invention, the variations of four parameters in a particular situation, which is the following, are shown.

[0172] The motor vehicle enters a bend at time t1. At time t2, the driver takes control again so that the LCA system is deactivated. At time t3, the driver hands control back, so that the LCA system is automatically reactivated. Finally, at approximately time t4, the vehicle exits the bend.

[0173] The curve CIO represents the variation of the steering angle when it is calculated using the method according to the invention. The curve Cil represents this same parameter when it is calculated according to a method different from the invention, namely in the event that during reactivation, the reference vector Xref remained zero and where, during the duration of the deactivation, the value of the integral term Xobs>7 of the observed state was fixed. It is noted that thanks to the invention, at time t3, no sudden variation of the steering angle is expected.

[0174] Curve C12 represents the variation of the value of the integral term Xobs>7 when it is determined using the method according to the invention. Curve C13 represents this same parameter when it is determined according to the different method of the invention (when its value is frozen during the interruption of the LCA system).

[0175] Curve C14 represents the variation of the actual value of the lateral deviation y when it is determined using the method according to the invention. Curve C15 represents this same parameter when it is determined according to the different method of the invention. Here again, it is observed that at time t3, the invention makes it possible to avoid any divergence of this lateral deviation y, but on the contrary a smooth and progressive convergence towards 0.

[0176] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

[0177] By way of example, in the embodiment described above, the parameter of the state vector which is an integral function Jy.dt and which is calculated as a function of the preceding states corresponds to the integral of the lateral deviation y between the motor vehicle and the center of its traffic lane. Alternatively, the integral function could be relative to another parameter, typically the relative heading angle between the vehicle and the traffic lane. More generally, the parameters of the state vector could be different from those presented above.

Claims

Claims

1. Method for assisting the steering of a motor vehicle (10) to keep it in the center of its traffic lane (30), comprising steps of: - acquiring values ​​(Xobs>i) of parameters (ip, drp / dt, y, dy / dt, ô, dô / dt, Jy.dt) relating to the dynamics of the motor vehicle (10) and to its position in its traffic lane (30), a first of said parameters (Jy.dl) being an integral function, at least a second of said parameters (y, rp) relating to the position of the motor vehicle (10) in its traffic lane (30), - determining a steering angle setpoint (ô) of the motor vehicle (10) by means of a controller (20), as a function of the values ​​(X obs>i) acquired and of nominal reference values ​​(Xref>i) of said parameters (rp, drp / dt, y, dy / dt, ô, dô / dt, Jy.dt), characterized in that, when the implementation of the piloting method has been suspended and then resumes: - the steering angle (ôMeasured) is acquired and the reference value (Xrefj7) of said first parameter (Jy.dt) is modified so as to minimize the difference between the steering angle (ôMeasured) acquired and the steering angle setpoint (ô), - the value of said at least one second parameter (y, rp) is acquired and is used as the reference value (Xref>2, Xref>4) of said at least one second parameter (y, rp), then, at subsequent times, - the reference value (Xref>2, Xref>4) of said at least one second parameter (y, rp) is modified so as to gradually return to its nominal reference value.

2. Control method according to claim 1, in which, when the implementation of the control method resumes, the values ​​of two first parameters (y, rp) are acquired and are used as reference values ​​(Xref>2, Xref>4) of said at least one second parameter (y, rp), then these reference values ​​(Xref>2, Xref>4) are modified so as to gradually return to their nominal reference values.

3. Piloting method according to one of claims 1 and 2, in which said second parameter is a heading angle (rp) of the motor vehicle (10) relative to its traffic lane (30).

4. Steering method according to one of claims 1 to 3, in which said second parameter is a lateral deviation (y) between the motor vehicle (10) and the center of its traffic lane (30).

5. Control method according to one of claims 1 to 4, in which, to gradually return to its nominal reference value, the reference value (Xrefj2, Xrefj4) of said at least one second parameter (y, ip) is calculated by means of a filtering function, preferably a low-pass filtering function.

6. Control method according to one of claims 1 to 5, in which the first parameter (Jy.dt) is an integral function of a position datum of the motor vehicle (10) in its traffic lane (30), and preferably an integral function of a lateral deviation (y) between the motor vehicle (10) and the center of its traffic lane (30).

7. Control method according to one of claims 1 to 6, in which the values ​​(Xobs>i) of the parameters (rp, drp / dt, y, dy / dt, ô, dô / dt, Jy.dt) are acquired by means of a state observer (26).

8. Control method according to one of claims 1 to 7, in which the steering angle setpoint (ô) of the motor vehicle (10) is equal to the sum of a first component (ôFBk) from said controller (20) and a second component (ôFFD) depending on the curvature (p) of the traffic lane (30).

9. Steering method according to one of claims 1 to 8, in which it is provided to suspend the implementation of the steering method as long as a driver of the motor vehicle (10) exerts on a steering wheel a torque greater than a predetermined threshold.

10. Motor vehicle (10) comprising a power steering actuator and a computer adapted to control the power steering actuator, characterized in that the actuator is programmed to implement a control method according to one of claims 1 to 9.

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