A method for estimating the value of frictional force acting on a part of a power steering system using a mathematical model

Abstract

By considering many physical phenomena, we obtain a method for estimating the value of friction force that does not require long learning times. [Solution] The present invention relates to a method for estimating the value of a friction force applied to a part of a power steering system (1) of a vehicle (2), the part of the power steering system (1) including at least one motor (12) applying a motor torque (T12), the value of the friction force making it possible to modify the motor torque (T12) by means of a mathematical model.

Description

[Technical field]

[0001] The present invention relates to the field of power steering systems for vehicles, and more particularly to a method for calculating the value of the frictional force acting on a part of the power steering system. [Background technology]

[0002] A vehicle steering system is intended to allow a driver to control the trajectory of the vehicle by modifying the steering angle of the vehicle's wheels by means of a steering wheel. The steering angle of the wheels is in particular linked to the angle of the steering wheel. The driver changes the angle of the steering wheel by applying a force to the steering wheel (hereinafter referred to as "steering wheel torque").

[0003] In general, a steering system includes several elements, including the steering wheel, a rack, and two wheels connected to each tie rod. The rack is the part that allows the wheels to change their orientation, i.e., steer, via the tie rod. The rack converts the angle of the steering wheel into the turning of the vehicle's wheels.

[0004] Power steering systems include a computer that determines the control motor torque as a function of the steering wheel torque, thus allowing the driver to turn the steering wheel more or less easily.

[0005] A control motor torque is exerted by the control motor.

[0006] In a mechanical power steering system, there is a mechanical link between the steering wheel and the rack, typically created by a steering column. The steering column is engaged by a steering pinion on the rack. A control motor then applies a control motor torque to the rack or steering column, thereby indirectly applying a control motor torque to the steering wheel.

[0007] In a "by-wire" type power steering system, the steering wheel angle is measured or calculated such that a steering motor exerts a steering motor torque to change the orientation of the vehicle's wheels by means of a rack, and a control motor then exerts a control motor torque directly on the steering wheel to specifically perceive a force on the rack to the driver.

[0008] The components of the power steering system are adjusted to come into contact with each other, but the tolerances during vehicle production and, more generally, any variations inherent in the manufacturing method, such as roughness variations or dimensional variations, result in variations in the values ​​of the friction forces acting on the power steering system between two vehicles of the same series, i.e. between two vehicles with similar characteristics.

[0009] Furthermore, the value of the friction force changes due to wear of the parts, so it also changes over time.

[0010] For mechanical power steering systems, differences in the amount of friction acting on the power steering system can result in differences in driver feel between two vehicles in the same series, but automakers want to keep the difference in feel between two vehicles in the same series under the same conditions as low as possible.

[0011] In the case of "by-wire" type power steering systems, variations in the values ​​of friction forces acting on the top part of the steering system, i.e. the part consisting of the steering wheel and the control motor, can lead to differences in the feeling between two vehicles of the same series, whereas variations in the values ​​of friction forces acting on the bottom part of the steering system, i.e. the part consisting of the rack and the steering motor, can lead to differences in the response to the trajectory of two vehicles of the same series. Variations in the values ​​of friction forces acting on the bottom part of the steering system, i.e. the part consisting of the steering motor and the rack, can lead to differences in the response dynamics at the same load of the steering motor between two vehicles of the same series.

[0012] Thus, in either a mechanical or "by-wire" steering system, the amount of frictional force acting on the vehicle's power steering system, or a portion of the power steering system, throughout the vehicle's operating time is reduced in order to compensate for this by increasing the control motor torque or steering motor torque. value needs to be estimated.

[0013] There is a known solution (patent document 1) that makes it possible to estimate the value of the friction force exerted on the power steering system of a vehicle by, on the one hand, performing a step of obtaining a series of characterization points corresponding to measured values ​​of the friction force related to the values ​​of the measured auxiliary force, and, on the other hand, performing a step of constructing an empirical friction model in which a law of correlation between the characterization points is established. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2015 / 140447 Summary of the Invention [Problem to be solved by the invention]

[0015] The drawback posed by this solution is that it determines the value of the friction force by a large number of characterization points, and therefore this solution requires a long learning time.

[0016] Furthermore, this solution 、 It is independent of the sliding speed and is dynamic, i.e. it only determines values ​​when the contacting elements are in motion.

[0017] The present invention proposes an estimate of the instantaneous friction force value, multiple The present invention aims to overcome all or part of the above-mentioned disadvantages by taking into account the above physical phenomena. [Means for solving the problem]

[0018] The invention relates to a method for estimating a value of a friction force acting on a part of a power steering system of a vehicle, the part of the power steering system comprising at least one motor exerting a motor torque, the value of said friction force making it possible to modify said motor torque, determining a model of a portion of the power steering system corresponding to a mathematical model that virtually represents a portion of the power steering system; measuring a value of at least one input variable on a portion of the power steering system; Calculating at least one output parameter by means of said mathematical model and said at least one input variable; measuring, on a portion of the power steering system, a value of at least one output variable representative of a physical quantity similar to the at least one output parameter; At least one correlation between the at least one output parameter and the at least one output variable. Misalignment Calculate The above Misalignment and the internal coefficient function and correcting the value of at least one internal parameter of the mathematical model as follows: determining a value of the friction force from the at least one corrected intrinsic parameter.

[0019] The method for estimating a friction force value of the present invention is applied to a mechanical power steering system, the part of the power steering system corresponds to the entire power steering system and the motor is a control motor.

[0020] The method for estimating the value of friction force according to the present invention is as follows: By-wire " type steering system. The part of the power steering system then corresponds to the top of the power steering system, the motor being the control motor, or corresponds to the bottom of the power steering system, the motor being the steering motor.

[0021] The terms "motor" and "motor torque" will therefore hereinafter denote either the control motor and the control motor torque, or the steering motor and the steering motor torque, depending on the part of the steering system considered.

[0022] Determining the value of the friction force is Desire Friction of power In other words, the motor torque can be modified to reach a value Fixes By doing so, it is possible to more or less compensate the values ​​of the friction forces so that two vehicles of the same series have equivalent behavior.

[0023] Thereafter, for ease of understanding, the part of the power steering system for which the value of the friction force is estimated will be designated only by the term "steering system".

[0024] The method according to the invention determines a mathematical model which represents in a simplified way the considered steering system. In other words, the mathematical model is a simplified virtual representation of the studied real steering system. In the following, the simplified representation of the considered steering system will be called model power steering system. This mathematical model comprises at least one input parameter, at least one output parameter, at least one internal coefficient and at least one internal parameter, one of which is the value of the friction force exerted on the virtual representation.

[0025] More specifically, the input and output parameters correspond to variables of the physical system that can be measured on the physical system, and the internal parameters correspond to variables of the physical system that cannot be measured. The internal coefficients allow for correction of the internal parameters so as to drive their values ​​towards the values ​​of the corresponding variables of the physical system.

[0026] This method is intended to estimate internal parameters that correspond to values ​​of friction forces acting on a real steering system.

[0027] For this purpose, at least one input variable is measured in the real steering system, which at least one input variable represents the same physical quantity, i.e. physical property, as at least one input parameter of the mathematical model.

[0028] Using the input parameters, at least one output parameter of the mathematical model is calculated in response to the input variables.

[0029] Next, at least one output variable is measured on the actual steering system, the output variable representing the same physical quantity as at least one output parameter of the mathematical model.

[0030] Next, the prediction error is calculated based on the relationship between the output parameters and the output variables. Misalignment is calculated.

[0031] The more representative the mathematical model of the actual steering system, the smaller the prediction error will be: if the mathematical model is perfect, the prediction error will be zero, i.e. the measured output variables and output parameters are equal.

[0032] Therefore, in order to make the mathematical model more representative of the actual steering system, at least one internal parameter of the mathematical model is adjusted to the prediction error. function and through the application of internal coefficients, are modified, i.e., corrected. In the absence of information about the actual steering system, these internal parameters are predefined and therefore poorly representative of the physical quantities to which they correspond in the actual steering system. function Correction of these internal parameters as makes it possible to orient their values ​​towards the values ​​of the immeasurable physical quantities they represent, which therefore makes it possible to obtain estimates of these immeasurable physical quantities.

[0033] However, the value of the friction force acting on the virtual representation is part of the internal parameters of the mathematical model.

[0034] Finally, the value of the friction force acting on the real steering system is set equal to the value of the friction force acting on the virtual representation when the mathematical model is modified.

[0035] The method according to the invention estimates a value of a friction force of the real steering system for each measurement of at least one input variable and at least one output variable on the real steering system. By means of at least two measurements on the steering system at a given point in time, the method estimates a value of a friction force acting on the steering system at a given point in time. The estimation of the value of the friction force is practically instantaneous compared to the calculation time. In other words, it is not necessary to perform measurements on the steering system at different times in order to obtain the desired estimate.

[0036] Furthermore, the method according to the invention allows the analysis of different types of friction, such as the phenomenon of lubrication related to the Stribeck curvature, the phenomenon of viscosity and the phenomenon of bond stiffness, i.e. the stiffness determined by a model in which two solid bodies are in contact with each other through a flexible thin plate. multiple This method thus gives a very accurate estimation of the value of the friction force.

[0037] According to an aspect of the invention, the method measures values ​​of a plurality of input variables on a portion of the power steering system.

[0038] According to a feature of the invention, the method comprises: , out Calculate the force parameters.

[0039] According to an aspect of the invention, the method includes: detecting a plurality of physical quantities in a portion of a power steering system, the physical quantities being similar to a plurality of output parameters; Sude The value of the force variable is measured.

[0040] According to a feature of the invention, the method comprises: , out Force parameters And Multiple between the force variables Misalignment Measure.

[0041] According to a feature of the invention, the method further comprises: calculating values ​​of a plurality of internal coefficients of the mathematical model by at least one Misalignment of function Correct as follows.

[0042] According to a feature of the invention, the mathematical model is a first order mathematical model including a model mass equivalent to a collection of inertias of a portion of the model power steering system subjected to at least one force acting on the portion of the model power steering system.

[0043] The first-order mathematical model corresponds to a reduction in the complexity of a real steering system, consisting of several solid bodies in relative motion, so as to represent this system by only one single mass.

[0044] Therefore, the mathematical model is simple, which allows for a simple software implementation and reduced consumption of computer resources.

[0045] At least one force acting on a part of the model power steering system must be determined on the actual steering system, at least the friction force. correspondence do.

[0046] According to a feature of the present invention, the friction force of the mathematical model is determined by the Lugre model.

[0047] The friction force is modeled by the Lugre model according to the following equation: [Formula 1] JPEG0007655858000001.jpg672[Formula 2] JPEG0007655858000002.jpg1139[Formula 3] JPEG0007655858000003.jpg1169[Formula 4] JPEG0007655858000004.jpg1030 Here, JPEG0007655858000005.jpg517: Internal parameters of the mathematical model that represent the joint stiffness, internal damping, and viscous friction coefficient according to the Lugre model JPEG0007655858000006.jpg43: Internal state of the Lugre model JPEG0007655858000007.jpg33: Motor rotation speed corresponding to the speed of the model mass JPEG0007655858000008.jpg44: The parameter of the Lueglé model that controls the "Stribeck velocity", i.e. the shape of the Stribeck curve that describes the transition between static and kinetic friction JPEG0007655858000009.jpg45: Internal parameters of the Lugrav model JPEG0007655858000010.jpg44: motion Friction Level JPEG0007655858000011.jpg44: Static friction level.

[0048] According to a feature of the invention, the at least one internal coefficient enabling the correction of the at least one internal parameter is determined by application of the Lyapunov theorem.

[0049] The Lyapunov theorem is a positive law called value This is made possible by proving the existence of a function, On the one hand, there is the estimation error between the output parameters of the mathematical model and the output variables of the physical system, known as the prediction error; On the other hand, it depends on the estimation error between the internal parameters of the mathematical model and the values ​​of the corresponding physical quantities of the real system, whose derivatives are negative semidefinite and the estimation error is bounded, proving that the system is stable.

[0050] Furthermore, if the derivative of the Lyapunov function is defined to be negative when the prediction errors are non-zero, it can be shown that these prediction errors converge towards zero.

[0051] The representation of the function thus defined makes it possible to determine in a mathematical manner the representation of at least one internal coefficient of the model and to ensure that the behavior of this model converges towards the zero of the real system it represents.

[0052] According to a feature of the invention, the at least one input variable is selected from the motor torque, the steering torque, the lateral acceleration of the vehicle, or the force on the tie rod.

[0053] Thus, the method uses variables that are commonly measured in steering systems.

[0054] The input variables depend on the steering system considered and the mathematical model selected.

[0055] For a mechanical steering system, at least one input variable is the motor torque, handle Preferably, the three input variables are selected from the motor torque, the steering torque and the lateral acceleration of the vehicle.

[0056] According to a feature of the invention, the output parameter and the output variable correspond to the rotational speed of the motor.

[0057] The rotational speed of the motor, on the one hand, ensures a better response of the dynamic behavior of the steering system than the position of the motor, and, on the other hand, allows easier measurement than the acceleration of the motor.

[0058] The invention will be better understood from the following description of embodiments according to the invention, given as non-limiting examples and illustrated with reference to the accompanying schematic drawings, in which: [Brief description of the drawings]

[0059] [Figure 1] 1 is a schematic diagram of a mechanical power steering system for a vehicle. [Diagram 2]FIG. 2 is a schematic diagram of the power steering system of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] The invention relates to a method for estimating a value of a friction force acting on at least one part of a power steering system 1 of a vehicle 2, and more particularly of an automated vehicle 2 intended for transporting passengers.

[0061] The power steering system 1 described below is of a mechanical type.

[0062] In a manner known per se, as shown in FIG. 1, the power steering system 1 includes a steering wheel 3 which enables the driver to steer the power steering system 1 by applying to the steering wheel 3 a force called the "steering wheel torque" T3.

[0063] The steering wheel 3 is preferably attached to a steering column 4, guided in rotation by the vehicle 2 and meshed by a steering pinion 5, itself on a rack 6 guided in translation by a steering case 7 fastened to the vehicle 2.

[0064] Preferably, each end of the rack 6 is connected to a steering tie rod 8, 9 attached to the steering knuckles of wheels 10, 11 (left wheel 10 and right wheel 11 respectively), thereby allowing longitudinal translation of the rack 6 to modify the rotation angle (yaw angle) of the steering wheel.

[0065] Furthermore, the steering wheels 10, 11 may preferably be driving wheels.

[0066] The power steering system 1 also includes a control motor 12 configured to output a control torque T12 that assists the steering.

[0067] The control motor 12 is preferably an electric motor having two directions of operation and is preferably a brushless type rotary electric motor.

[0068] The control motor 12 can, if desired, be engaged via a reducer in the steering column 4 itself, forming a so-called "single pinion" mechanism, or it can be engaged directly to the rack 6, for example by means of a second pinion 13 separate from the steering pinion 5 which enables the steering column 4 to mesh with the rack 6, forming a so-called "double pinion" mechanism, as shown in FIG. 1, or it can be engaged by a ball screw spaced from the steering pinion 5 and cooperating with a corresponding thread on the rack 6.

[0069] The method for estimating a frictional force value according to the present invention acts on a part of the power steering system 1. In the case described below, the part of the power steering system is the power steering system 1 as shown in FIG. In , downstream of the torque sensor 23 that measures the handle torque T3, that is, from the rack 6 to the torque sensor 23. correspondence do.

[0070] The method includes determining a portion of a model power steering system 1' that corresponds to a mathematical model representing the power steering system 1. The portion of the model power steering system 1' used in the present invention is a simplified version of the power steering system 1, as shown in Figure 2, and in the example shown in Figures 1 and 2, the portion of the model power steering system 1' will be referred to as the model power steering system 1'.

[0071] In order to simplify the software implementation and reduce the computational resource consumption of the power steering system 1, the power steering system 1 is represented in the method according to the invention by a mathematical model which is a simplified virtual representation of the actually studied steering system 1. The mathematical model is a first-order system.

[0072] More specifically, the mathematical model corresponding to the model power steering system 1' includes a model rack 6' exerted by a model steering pinion 5', and a model controlled motor 12' engaging the model rack 6' by means of a second model pinion 13'.

[0073] The mathematical model includes one single model mass M corresponding to a set of inertias of the model power steering system 1'.

[0074] The model mass M is written according to the following formula: [Formula 5] JPEG0007655858000012.jpg559 Here, JPEG0007655858000013.jpg48: Mass of Model Rack 6' JPEG0007655858000014.jpg47: Model control motor 12' inertia JPEG0007655858000015.jpg48: Inertia of model steering pinion 5' JPEG0007655858000016.jpg45: Reducer + 2nd Model Pinion 13' set reduction ratio JPEG0007655858000017.jpg45: Reduction ratio of model steering pinion 5'.

[0075] The model mass M is set to be subjected to at least one force acting on the model power steering system 1'. In this example, the model mass M is subjected to the following four forces:

[0076] The control torque T12 of the control motor 12 in the actual power steering system 1 is correspondence Model motor force T MO Friction at the height of the steering column 4 of power The steering torque T3 measured by the torque sensor 23 in the actual power steering system 1 is calculated by excluding the value. correspondence Model driver force T TB The force applied to the rack 6 by the steering tie rods 8, 9 correspondence Model tie rod force F TR-RA where this force is not measured directly but is estimated from the vehicle's lateral acceleration γ according to the following linear relationship: [Formula 6] JPEG0007655858000018.jpg531, where JPEG0007655858000019.jpg43 is an internal parameter that represents the proportionality coefficient between the lateral force and the lateral acceleration of the vehicle in the region of linear behavior of the tire. Friction force F acting on the actual power steering system 1 Friction is equal to Model friction force JPEG0007655858000020.jpg515.

[0077] Also, the model friction force JPEG0007655858000021.jpg515 is determined to be modeled by the Lugre model according to the following equation: [Formula 7] JPEG0007655858000022.jpg672[Formula 8] JPEG0007655858000023.jpg1139[Formula 9] JPEG0007655858000024.jpg1169[Formula 10] JPEG0007655858000025.jpg1030 Here, JPEG0007655858000026.jpg517: Internal parameters of the mathematical model that represent the joint stiffness, internal damping, and viscous friction coefficient according to the Lugre model JPEG0007655858000027.jpg43: Internal state of the Lugre model JPEG0007655858000028.jpg33: Rotational speed of the control motor 12 corresponding to the speed of the model mass M JPEG0007655858000029.jpg44: The parameter of the Lueglé model that controls the "Stribeck velocity", i.e. the shape of the Stribeck curve that describes the transition between static and kinetic friction JPEG0007655858000030.jpg45: Internal parameters of the Lugrav model JPEG0007655858000031.jpg44: motion Friction Level JPEG0007655858000032.jpg44: Static friction level.

[0078] When the Luegl model is applied to the considered model power steering system, the result is as follows. [Formula 11] JPEG0007655858000033.jpg1066[Formula 12] JPEG0007655858000034.jpg1139[Formula 13] JPEG0007655858000035.jpg13105 Here, JPEG0007655858000036.jpg43: Model The acceleration of mass M, RFE: Model motor power T MO and model driver force T TB The sum of these is expressed as a rack 6 standard. JPEG0007655858000037.jpg44: internal parameters corresponding to possible certain errors in the measurements, such as the presence of an offset in the measurements of the steering torque T3 or the lateral acceleration γ of the vehicle JPEG0007655858000038.jpg43: Let be the differential of the internal state of the Luglet model.

[0079] To create a mathematical model representative of the real steering system 1, only the model mass M may be assumed to be known. Other internal parameters JPEG0007655858000039.jpg530 is too variable to be accurately estimated in advance.

[0080] The method also includes a step of measuring the value of at least one input variable on the power steering system 1. In the example of Figures 1 and 2, the input variables are the control torque T12 of the control motor 12, the steering torque T3, and the lateral acceleration γ of the vehicle.

[0081] The method then comprises: Out Calculating a force parameter is included.

[0082] Out The step of calculating the force parameters comprises: function The rotation speed of the motor 12 is controlled as Velocity of model mass M corresponding to JPEG0007655858000040.jpg33 More specifically, the input variables are integrated in the above mentioned mathematical model, which allows the velocity of the model mass M to be determined. It is then possible to infer JPEG0007655858000042.jpg43.

[0083] The method then includes: , out Force parameters handle Represents physical quantities Sude Measuring the value of the force variable.

[0084] Out During the step of measuring the value of the force variable, the rotational speed of the control motor 12 is measured in the power steering system 1. , out Force parameters And Between the force variables Misalignment The step of calculating e.

[0085] In other words, Misalignment e is , out Force variable? From Equal to minus the force parameter.

[0086] In this case, Misalignment e is the velocity of the model mass M JPEG0007655858000043.jpg43 Control motor 12 rotation speed Equal to the speed minus JPEG0007655858000044.jpg33. [Formula 14] JPEG0007655858000045.jpg419

[0087] Also called prediction error Misalignment e symbolically represents the imperfections in the mathematical model. In other words, if the mathematical model were perfect, Misalignment e is zero.

[0088] This method reduces the prediction error function The method includes the step of correcting a value of at least one internal parameter of the mathematical model as follows:

[0089] In this way, the mathematical model is modified to be more representative of the power steering system 1. To modify the mathematical model, the internal parameters The value of JPEG0007655858000046.jpg530 is corrected.

[0090] Internal parameters JPEG0007655858000047.jpg530 value Fixes To do this, it is necessary to solve equations that are not reproduced here, which reveal nonlinear terms.

[0091] To solve this problem, it is known to separate the nonlinear terms using a structure that contains two estimates of the internal state z. Then, after applying the Lyapunov theorem, the equations for the internal coefficients are determined.

[0092] The method includes determining a value of the friction force from the at least one corrected intrinsic parameter.

[0093] Finally, the friction force acting on the actual power steering system 1 Model friction force corresponding to JPEG0007655858000048.jpg515 JPEG0007655858000049.jpg615 can be determined according to the following formula: [Formula 15] JPEG0007655858000050.jpg1290 Here, JPEG0007655858000051.jpg517: Internal parameters of the mathematical model representing the joint stiffness, internal damping, and viscous friction coefficient according to the Lugre model; JPEG0007655858000052.jpg43: Internal state of the Lugre model JPEG0007655858000053.jpg33: The rotational speed of the control motor 12 corresponding to the speed of the model mass M.

[0094] Determining the value of the friction force is Desire Friction of power In other words, it is possible to modify the value of the control torque T12 so that the control torque T12 reaches a value of Fixes By doing so, it is possible to more or less compensate the values ​​of the friction forces so that two vehicles of the same series have equivalent behavior.

[0095] Of course, the invention is not limited to the embodiments described and represented in the attached drawings: modifications are still possible, in particular with regard to the configuration of the various elements or by the substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

1. 1. A method for estimating a value of a friction force exerted on a part of a power steering system (1) of a vehicle (2), the part comprising a motor (12) exerting a motor torque (T12), the value of the friction force exerted on the part of the power steering system (1) making it possible to modify the motor torque (T12), comprising the steps of: The power steering system (1) is mechanical, and the motor (12) is a controlled motor that applies torque to a rack or steering column; determining a part of a model power steering system (1') corresponding to a mathematical model virtually representing a part of the power steering system (1), the mathematical model including a model of friction forces; measuring the value of at least one input variable (T12, T3, γ) in a portion of the power steering system (1); The mathematical model and the at least one input variable (T12, T3, γ) are used to calculate an output parameter ( ) and In a part of the power steering system (1), the output parameter ( ) measuring the value of an output variable (v) representing a physical quantity corresponding to the The output parameters ( ) and the output variable (v); At least one internal parameter of the mathematical model as a function of the deviation (e) and an internal coefficient ( ) value is corrected, At least one corrected intrinsic parameter ( ) to the friction force (F Friction ) values.

2. A method for estimating a value of a friction force exerted on a part of a power steering system (1) of a vehicle (2), the part including a motor (12) exerting a motor torque (T12), the value of the friction force exerted on the part of the power steering system (1) making it possible to modify the motor torque (T12), comprising: The power steering system (1) is of the by-wire type, and the motor (12) is a steering motor and a control motor, The steering motor applies torque to the rack and the control motor applies torque to the handle; determining a part of a model power steering system (1') corresponding to a mathematical model virtually representing a part of the power steering system (1), the mathematical model including a model of friction forces; measuring the value of at least one input variable (T12, T3, γ) in a part of the power steering system (1); The mathematical model and the at least one input variable (T12, T3, γ) are used to calculate an output parameter ( ) and In a part of the power steering system (1), the output parameter ( ) measuring the value of an output variable (v) representing a physical quantity corresponding to the The output parameters ( ) and the output variable (v); At least one internal parameter of the mathematical model as a function of the deviation (e) and an internal coefficient ( ) value is corrected, At least one corrected intrinsic parameter ( ) to determine the value of the friction force (F Friction ); A part of the power steering system (1) includes: the steering motor and the rack at the bottom of the power steering system (1), or The estimation method is characterized in that the control motor and steering wheel are at the top of the power steering system (1).

3. The mathematical model calculates at least one force (T MO , T TB , F TR-RA , 3. The method according to claim 1 or 2, wherein the model power steering system (1') is a first-order mathematical model including a model mass (M) equal to the set of inertias of a part of the model power steering system (1') subjected to

4. The friction force ( 3. The method of claim 1, wherein the σ is determined by the Lugret model.

5. The at least one internal parameter ( 3. The method according to claim 1, wherein the at least one internal coefficient enabling the correction of (x,y) is determined by applying Lyapunov's theorem.

6. 6. The method according to claim 1, wherein the at least one input variable is selected from the motor torque (T12), the steering torque (T3), the lateral acceleration (γ) of the vehicle (2), or the force on a tie rod.

7. The output parameters ( 7. The method according to claim 1, wherein the output variable (v) corresponds to a rotational speed of the motor (12).

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