FR2821042A1 - Power steering for motor vehicle has control of power steering motor dependent on braking parameters - Google Patents

Abstract

The power steering for a motor vehicle has a control circuit for selective brake operation. The power steering drive has a motor driving the steering rack (8) under a control using operating parameters (P1-4, P5.1,P5.2) of the steering column (4). the control circuit has a first computer (41) to compare an actual torque signal to a theoretical value. It has a second computer (42) to provide a compensation signal (Sc) dependent on the torque of the second parameters (P4,P5.1,P5.2,P5.3,P5.4) including braking parameters. Claims include method for operating the power steering.

Description

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 The invention relates to a steering assembly of a motor vehicle comprising an electric assistance device.

 It relates more specifically to an electric power steering assembly of a motor vehicle, said assembly comprising a rotary steering shaft integral with a steering wheel and cooperating with a steering rack of the steering wheels of the vehicle, an electric motor whose output shaft meshes with the rack or the steering shaft, and a control device providing said electric motor with a control signal adapted to vary the output torque of the electric motor according to operating parameters of the steering shaft and more generally of the vehicle, said control device comprising a first calculation element adapted to develop a significant assist torque signal of a theoretical assist torque value, from a first set of parameters among said operating parameters.

 In known electrical power steering systems, an electric motor drives, via a gearbox, a pinion meshing with the steering rack or the steering shaft, so as to transmit to the rack an assistance effort . The electric motor is controlled by a computer that applies preprogrammed control laws to take into account the evolution of vehicle operating parameters and direction, such as the speed of the vehicle, the torque applied to the steering wheel and the shaft direction by the driver, and the speed of rotation of the steering wheel.

 The preprogrammed control laws are usually in the form of maps. The computer delivers to the electric motor, based on these operating parameters and preprogrammed control laws, a

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 torque control signal corresponding to the output engine torque to be delivered to exert on the rack the desired assistance effort.

 In general, there is no provision for a control loop for correcting the control signal transmitted to the motor based on measured quantities, significant torque or assistance effort actually delivered by the engine.

 An assistance device of this type does not give complete satisfaction, because the parameters to which the control laws are applied do not allow access in a simple and precise manner to an assistance effort adapted to the sensations of the user. .

 In addition, certain vehicles are equipped with electronic global chassis control systems, commonly known as CGC, whose function is to keep the vehicle on an ideal trajectory during a turn, by actions on the acceleration of the vehicle. vehicle and individual braking actions on each of the wheels. These actions are controlled according to a measured yaw rate, and as a function of the position of this measured value with respect to a theoretical value curve. It is known that curved braking generates a steering resistance of the wheels in the form of a relatively large overtorque on the steering wheel (which can be of the order of 20% compared to similar trajectory and speed conditions, in the absence of braking), and known electrical power steering systems do not compensate for such an over torque.

 As a result, such power steering produces, under these braking conditions in curves, a pair of assistance that is unsuitable for matching the torque.

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 steering wheel actually exerted by the driver with a desired torque.

 In the case of the presence on the vehicle of a global chassis control system, it is important to solve this drawback of electric power steering systems of the state of the art.

 The invention therefore aims more precisely at an electric power steering assembly fitted to a vehicle which comprises a global chassis control system, adapted to control the selective braking of one or more wheels by means of individual braking signals which are significant braking parameters. .

 A main object of the invention is to overcome the aforementioned drawbacks and to provide an electric power steering capable of compensating for the effects on the steering wheel torque sensations perceived by the driver, a braking curve due to an electronic system of global chassis control.

 For this purpose, the control device comprises a second calculation element adapted to produce a significant compensation torque signal of a compensation torque value, from a second set of parameters among said operating parameters, said second set of parameters set being different from the first and comprising at least one of said braking parameters, and the control signal results from the sum of the assist torque signal and the compensation torque signal.

 According to other characteristics: said brake parameter of the second set is a braking parameter of a respective rear wheel of the vehicle; said braking parameter is proportional to a braking torque exerted on the associated wheel;

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 the assembly comprises means for measuring the torque exerted by the driver on the steering wheel, adapted to transmit to the control device a signal that is significant for the measured flywheel value, and the control signal is developed as a function of said measured lift value; the assembly comprises means for measuring the speed of the vehicle and means for measuring the speed of rotation of the steering wheel, and the first set of parameters comprises the speed of the vehicle and the speed of rotation of the steering wheel thus measured; the first set consists of the measured vehicle speed, the measured steering wheel rotation speed, and the measured flywheel torque; the assembly comprises means for measuring the angular position of the flywheel relative to the zero neutral steering position, and the second set of parameters comprises the angular position of the flywheel thus measured; said means for measuring the angular position of the steering wheel are adapted to determine, with respect to the zero neutral steering position, a direction of steering of the steering wheel; the second set consists of the angular position of the measured flywheel and two braking parameters respectively corresponding to each of two rear wheels; and the first computing device is a map.

 The invention also relates to a method of controlling, by a torque control signal, the electric motor of an electric power steering assembly of a motor vehicle equipped with a global chassis control system, said global control system. of a chassis being adapted to control the selective braking of one or more wheels by means of individual braking signals

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 significant braking parameters, said assembly comprising a rotary steering shaft integral with a steering wheel and driving a steering rack of the steering wheels of the vehicle, an electric motor whose output shaft meshes with the rack or the shaft of direction, and a controller providing said electric motor with a torque control signal adapted to vary the output torque of the electric motor.

 According to the method of the invention, the torque control signal is developed in the following way: a theoretical assist torque value is determined from pre-recorded data, as a function of a first set of operating parameters. measures ; a compensation torque value is determined from pre-recorded data, as a function of a second set of operating parameters comprising at least one of said braking parameters; the sum of said values of theoretical assist torque and compensation torque thus determined is calculated in order to obtain a torque control value; the torque control signal corresponding to said torque control value is developed.

 In addition: - the value of the speed of the vehicle is measured; the value of the rotational speed of the steering wheel is measured; the value of the torque applied to the flywheel by the driver is measured, and the first set of operating parameters from which the theoretical assist torque value is determined consists of the values thus measured.

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 According to another characteristic of the method, the angular position of the flywheel is measured with respect to a zero steering neutral position, and the second set of operating parameters from which a compensation torque value is determined consists of said position value. angular and at least two braking parameters corresponding to two wheels of the vehicle.

 Advantageously, said at least two braking parameters are the braking parameters respectively corresponding to two rear wheels of the vehicle, respectively a right rear wheel and a left rear wheel.

 Advantageously, the compensation torque value is determined as a function of only one of said braking parameters, chosen as a function of the angular position value of the steering wheel.

s arrière gauche ; - si la valeur du paramètre de freinage choisi est, en valeur absolue, inférieure à une valeur de seuil prédéterminée, le couple de compensation est nul ; - si la valeur du paramètre de freinage choisi est, en valeur absolue, supérieure à ladite valeur de seuil prédéterminée, on réalise les opérations suivantes à partir dudit paramètre de freinage choisi : According to still further features of the method according to the invention: if the angular position value of the steering wheel corresponds to a left turn, the braking parameter chosen is the braking parameter corresponding to the right rear wheel; if the angular position value of the steering wheel corresponds to a right turn, the braking parameter chosen is the braking parameter corresponding to the wheel

s left back; if the value of the braking parameter chosen is, in absolute value, less than a predetermined threshold value, the compensation torque is zero; if the value of the braking parameter chosen is, in absolute value, greater than the said predetermined threshold value, the following operations are carried out starting from the said selected braking parameter:

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1 fonction de transfert de la forme F, (p) =---- ; Ap+B

. on calcule la valeur de couple de compensation à partir de cette variable intermédiaire. . a first intermediate variable is calculated by applying to the selected braking parameter a first

1 transfer function of the form F, (p) = ----; Ap + B

. the compensation torque value is calculated from this intermediate variable.

deuxième fonction de transfert de la forme

a. p '+/. p+ < y

Le procédé comporte en outre l'étape suivante : on calcule une troisième variable intermédiaire à partir de ladite deuxième variable intermédiaire en appliquant à ladite deuxième variable une fonction de retard temporel dont la constante de temps dépend de la valeur absolue de la première variable intermédiaire, calculée au même instant. The method further comprises the following step: a second intermediate variable is calculated by applying to the first intermediate variable a

second form transfer function

at. p '+ /. p + <y

The method further comprises the step of: calculating a third intermediate variable from said second intermediate variable by applying to said second variable a time delay function whose time constant depends on the absolute value of the first intermediate variable, calculated at the same time.

 The method further comprises the following step: the compensation torque value is calculated at each instant by applying to the third intermediate variable a gain dependent on the absolute value of the first intermediate variable, calculated at the same time.

 The invention finally relates to a motor vehicle comprising a power steering assembly as described above or operating according to the method described above.

 Other features and advantages of the invention will become apparent from the following description given by way of nonlimiting example with reference to the accompanying drawings, in which: - Figure 1 is a schematic view of a power steering assembly according to the invention; and

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- la Figure 2 est un schéma représentant le dispositif de commande de l'ensemble de direction assistée de la Figure 1.

- Figure 2 is a diagram showing the control device of the power steering assembly of Figure 1.

 FIG. 1 shows a steering assembly 1 of an electrically assisted motor vehicle, which comprises a steering wheel 2 integral with a first section 3 of a steering shaft 4, connected to a second section 5 of this steering shaft. 4, via a universal joint 6. The steering shaft 4 is here composed of two articulated sections 3.5, but could consist of a part. The steering shaft 4 transmits the torque applied to the steering wheel 2 by the driver of the vehicle to a transmission gear 7, which meshes with a steering rack 8 disposed transversely to the axis of the vehicle between two steered wheels 9A. The steering wheels 9A consist of the front wheels, the two rear wheels being designated by the reference 9B.

 The transmission gear 7 could be replaced by any other suitable transmission member, such as for example a worm. Each guide wheel 9A is pivotable about a vertical pivot axis ZZ under the effect of a linear displacement of the rack 8, said control wheel 9A being actuated by an orientation mechanism comprising a rod 10 connected to a end 11 of the rack 8.

 In Figure 1, there is shown the longitudinal axis X-X of the vehicle, oriented in the direction of travel, and its transverse axis Y-Y.

fonction de six paramètres Pl, P2, P3, P4, P5, 1, Ps. 2 de The steering assembly 1 also comprises an assistance device 12 intended to exert on the rack 8 a force in the same direction as the force exerted by the transmission gear 7, so as to facilitate the actuation of the steering wheel 2 by the driver of the vehicle,

function of six parameters P1, P2, P3, P4, P5, 1, Ps. 2 of

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 operation of the vehicle and operation of the steering.

 The first parameter P1 is constituted by the speed value of the vehicle along the longitudinal axis XX, determined by a conventional speed sensor 21 usually present on the vehicles.

 The second parameter P2 is constituted by the rotational speed of the flywheel 2, measured by an angular speed sensor or, as shown, by an angular position sensor 24 associated with a differentiator 22.

 The third parameter P3 represents the torque applied to the flywheel 2, estimated by means of a torque sensor 23 mounted on the second section 5 of the steering shaft 4, in a region close to the transmission pinion 7.

 The fourth parameter P4 is a significant value of the angular position of the flywheel 2 relative to the zero neutral steering position, this value being provided by the sensor 24.

 The vehicle is also equipped with an electronic system of overall chassis control 25 (which will be called later C.CG for convenience). This system operates according to a known principle consisting in acting in real time on, on the one hand, the power supply of the vehicle engine, and on the other hand on the individual braking of the wheels of the vehicle, in order to correct the trajectory of the vehicle by curve. For this, the CGC system essentially comprises an electronic module, which will subsequently be assimilated, this module receiving at each moment the measured parameters, such as the steering angle of the steering wheels 9A and the steering angle of the steering wheel 2 , given by the angular position sensor 24. The CGC 25 determines, for these measured turning conditions, the theoretical yaw rate profile that the vehicle must follow during

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 the progression of the turn. The yaw rating of the vehicle is also measured at each moment and provided to the CGC.

The latter compares the actual profile with the theoretical profile and accordingly issues corrective instructions adapted to modify the acceleration control of the vehicle (given by the driver by means of the accelerator pedal), and to the vehicle braking system. .

 Only the corrective braking instructions are taken into consideration in the device which is the subject of the invention.

The CGC 25 calculates at each instant the braking torque to be applied to each of the wheels 9A, 9B of the vehicle to match the actual profile of the yaw rate of the vehicle with the theoretical profile. The CGC 25 controls individual braking of each wheel 9A, 9B of the vehicle by delivering a respective braking signal Si, S2, S3, S4 significant of a corresponding braking parameter Ps, l, PS, 2, PS, 3, PS , 4 '
The fifth and sixth parameters Ps. I, Ps, 2 used by the assistance device 12 are the braking parameters, given by the CGC 25, respectively corresponding to the right rear wheel and the left rear wheel of the vehicle.

 It will be understood that the CGC, which operates at all times, delivers corrective braking and acceleration signals only from the moment when vehicle turning conditions are detected.

 The assistance device 12 comprises an electric motor 30 whose output torque Cs is controlled by an electronic control device 33, which delivers to the motor 30 a torque control signal S. The output torque Cs of the electric motor 30 is transmitted to a gearbox 32 via the output shaft 34 of the motor 30, and to an assist pinion 36 meshing with the

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 rack 8. Naturally, the assist pinion 36 could be provided to cooperate directly or indirectly with the steering shaft 4 so as to produce an assist action, not on the rack 8, but upstream.

 Each of the sensors 21,22,23,24 and the CGC 25 are connected to the control device 33 so as to transmit in real time the values of the respective parameters PI, P2, P3, P4, Ps, P5,2 , measured at each moment t.

 Referring now to FIG. 2, the electronic control device 33, which receives as input the six parameters P1, P2, P3, P4, P5, i, P5, 2 in the form of transmitted signals, will be more precisely described. by the sensors 21,22, 23,24, and the CGC 25, and outputs the torque control signal S.

 The electronic device 33 comprises a first computing unit 41 consisting of a map, and a second computing unit 42 constituting a CGC compensator.

premier ensemble de paramètres parmi les paramètres Pl, P2, P3, P4, Ps, iy Ps, 2 précités. Ce premier ensemble de paramètres est constitué de la vitesse du véhicule P1, P2 et du couple volant mesuré P3. The first computing device 41 is a known type of mapping used for the control of the electric power steering of certain existing vehicles, which determines a theoretical assistance torque CAT from a

first set of parameters among the above parameters P1, P2, P3, P4, Ps, iy Ps, 2. This first set of parameters consists of the vehicle speed P1, P2 and the measured flying torque P3.

 The compensator 42 then emits a compensation signal Sc corresponding to a compensation torque Cc calculated from a second set of parameters among the aforementioned parameters P1, P2, P3, P4, P5, I, P5, 2. This second set parameter consists of the angular position P4 of the flywheel 2, the braking parameter Ps, the

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roue arrière droite 9B et du paramètre de freinage Ps. 2 de la roue arrière gauche 9B.

rear right wheel 9B and the braking parameter Ps. 2 of the rear left wheel 9B.

The compensation torque Cc represents an injected torque to compensate for the resistant over-torque felt by the driver, due to the additional braking of the wheels provided by the C.G. C. 25.

 The electronic device 53 furthermore includes an adder 45 which provides the sum of the theoretical assistance signal SAT and the compensation signal Sc (or equivalent of the theoretical assistance torque CAT and the compensation torque CAT) to obtain the signal torque control S (or equivalently the control torque C).

The compensator 42 uses the parameters? 4, Ps, i, P5, 2, which it receives as input, as follows:
The angular position parameter P4 of the steering wheel 2 is used to determine the steering direction of the steering wheel, that is to say left turn or right turn.

In the following process of processing the input parameters of the compensator 42, only the braking parameter P5, 1, PS, 2 corresponding to the rear outer wheel at the turn, ie the braking parameter Ps, i, will be used. the right rear wheel if it is a left turn, or the braking parameter Pos, 2 of the left rear wheel if it is a right turn.

du paramètre de freinage ainsi déterminé ? 1, P5, 2t à une valeur de seuil positive SF préenregistrée. The compensator 42 then compares the absolute value

the braking parameter thus determined? 1, P5, 2t to a prerecorded positive threshold value SF.

If the absolute value thus calculated is less than said threshold value SF, which means that the braking imposed by the CGC on the rear wheel outside the turn is insufficient to justify the injection of a compensating torque, then the torque of compensation Cc calculated at the output of the compensator 42 is zero.

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- On applique au paramètre de freinage P5, 1, P5, 2 de la roue extérieure au virage une première fonction de

transfert de la forme F, (p) =, dans laquelle A et B 4p+

sont des constantes prédéterminées, la variable de fréquence p correspondant au paramètre de freinage Ps, i, Ps. z lequel est une fonction du temps t. Cette première fonction de transfert Fl (p) se comporte comme un filtre passe-bas du premier ordre, dont les constantes sont choisies de manière à filtrer les fréquences supérieures à 15 Hz environ. Une première variable intermédiaire Vl, fonction du temps, est ainsi obtenue.

If this absolute value is greater than the threshold value SF, which corresponds to sufficiently large braking conditions to generate a resistive torque on the driver-responsive steering shaft, then the calculation of the compensation torque Cc is calculated by the following operations:

The braking parameter P5, 1, P5, 2 of the outer wheel at the turn is applied to a first function of

transfer of the form F, (p) =, in which A and B 4p +

are predetermined constants, the variable of frequency p corresponding to the braking parameter Ps, i, Ps. z which is a function of time t. This first transfer function F1 (p) behaves as a first-order low-pass filter whose constants are chosen so as to filter the frequencies greater than about 15 Hz. A first intermediate variable Vl, a function of time, is thus obtained.

F2 (p) = 2 aop, dans laquelle a, A, ss, 6 sont des ss. p +r. p+t5

constantes prédéterminées, pour obtenir une deuxième variable intermédiaire V2, fonction du temps t. This first intermediate variable Vl is applied to a second transfer function

F2 (p) = 2 aop, where a, A, ss, 6 are ss. p + r. p + t5

predetermined constants, to obtain a second intermediate variable V2, a function of time t.

 The second transfer function F2 (p) is equivalent to a derivation operator.

première variable intermédiaire Vl, calculée au même instant t. On obtient ainsi une troisième variable intermédiaire V3, fonction du temps t. The second intermediate variable V2 thus obtained is then applied to a delay function whose time constant depends on the absolute value of the

first intermediate variable Vl, calculated at the same time t. We thus obtain a third intermediate variable V3, a function of time t.

 This third intermediate variable V3 is then applied to a gain that can take two values

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différentes selon la valeur absolue de la première variable intermédiaire Vl, calculée au même instant t.

different according to the absolute value of the first intermediate variable Vl, calculated at the same time t.

A compensation torque value C'c is thus obtained which is multiplied by a start / stop value of 0 or 1 which depends on the state of the compensator 42, which can be neutralized under various conditions, in particular operating conditions. CGC 25 itself.

 By means of the device and the method which have just been described, a reliable compensation is obtained, with an optimum reaction time, for the resistant over-torque produced on the steering shaft by additional braking in curvature due to the CGC. This compensation has the important advantage of maintaining the feeling of effort of the driver to a desired level, undisturbed by the operation of a safety device acting on the braking of the vehicle.

 The invention makes it possible, thanks to the addition of an electronic compensation module in a power steering assembly of a type already used on existing vehicles, to erase the negative effects of a security system, such as the CGC, on the driving sensations of the user.

Claims (21)

 An electric power steering assembly of a motor vehicle equipped with a global chassis control system (25), said global chassis control system being adapted to control the selective braking of one or more wheels by means of signals individual braking

 (S1, S3, S4) significant braking parameters (PS, PS, 2 'PS, 3' PS, 4), said assembly comprising a rotary steering shaft (4) integral with a steering wheel (2 ) and cooperating with a rack (8) for orienting the steering wheels (9A) of the vehicle, an electric motor (30) whose output shaft (34) meshes with the rack (8) or the steering shaft ( 4), and a control device (33) providing said electric motor (30) with a control signal (S) adapted to vary the output torque (Cs) of the electric motor (30) according to operating parameters (Pi , P2, P3, P4, P5, I, Ps, 2) of the steering shaft (4) and more generally of the vehicle, said control device (33) comprising a first computing unit (41) adapted to develop a assist torque signal (SAT) indicative of a theoretical assist torque value (CAT), at

 from a first set of parameters (P1, P2, P3) among said operating parameters, characterized in that the control device (33) comprises a second computing element (42) adapted to produce a torque signal of

 significant compensation (Sc) of a compensation torque value (Cc), from a second set of parameters (P4, P5, 1 / P5, 2) among said operating parameters, said second set (P4, PS , l, Ps, 2) being different from the first (P1, P2, P3) and comprising at least one of said braking parameters (PS, PS, 2) 'and the control signal (S) results from the sum of assist torque signal (SAT) and compensation torque signal (Sc). <Desc / Clms Page number 16>

2. Electrical power steering assembly according to claim 1, characterized in that said braking parameter (? 5, i, Ps) of the second set (P4, PS ,, P5, 2) is a braking parameter of a wheel rear (9B) of the vehicle.  3. Electric power steering assembly according to claim 1 or 2, characterized in that said braking parameter (P5, 1, P5, 2) is proportional to a braking torque exerted on the associated wheel (9B).  4. Electric power steering assembly according to any one of claims 1 to 3, characterized in that it comprises means (23) for measuring the torque exerted by the driver on the steering wheel (2), adapted to transmit to the control device (33) a significant signal of the flywheel torque value (P3) thus measured, and the control signal (S) is produced according to said measured flywheel torque value (P3).  5. Electric power steering assembly according to any one of claims 2 to 4, characterized in that it comprises means (21) for measuring the speed of the vehicle and means (22) for measuring the speed of rotation. of the steering wheel (2), and the first set of parameters (Pi, P2, P3) comprises the vehicle speed (P1) and the rotation speed of the steering wheel (P2) thus measured.  Electric power steering assembly according to claims 4 and 5 taken together, characterized in that

 that the first set (P1, P2, P3) consists of the measured vehicle speed (P1), the measured steering wheel rotation speed (P2), and the measured steering wheel torque (P3).  7. Electric power steering assembly according to any one of claims 1 to 6, characterized in that it comprises means (24) for measuring the angular position of the flywheel relative to the zero neutral steering position, and the second set of parameters (P4, P5,1, <Desc / Clms Page number 17>  PS, 2) comprises the angular position of the wheel (P4) thus measured.

 8. Electric power steering assembly according to claim 7, characterized in that said means (24) for measuring the angular position of the steering wheel are adapted to determine, with respect to the zero neutral steering position, a steering direction of the steering wheel. .  9. Electric power steering assembly according to claims 2 and 8 taken together, characterized in that the second assembly (P4, PS, I, Ps) consists of the angular position of the wheel (P4) measured and two braking parameters (P5,1, P5,2) respectively corresponding to each of two rear wheels (9B).  10. Electrical power steering assembly according to any one of claims 1 to 9, characterized in that the first computing member (41) is a map.  A method of controlling, by a torque control signal, the electric motor (30) of an electric power steering assembly of a motor vehicle equipped with a global chassis control system (25), said global chassis control being adapted to control the selective braking of one or more wheels by means of individual braking signals (S1, S2, 83, S) significant of braking parameters (Ps, i, P2, P5, 3, Pos , 4), said assembly comprising a rotary steering shaft (4) integral with a steering wheel (2) and driving a rack (8) for orienting the steering wheels (9A) of the vehicle, an electric motor (30) whose the output shaft (34) meshes with the rack (8) or the steering shaft (4), and a control device (33) providing said electric motor (30) with a torque control signal (S) adapted to vary the output torque (Cs) of the motor <Desc / Clms Page number 18>  function of a first set of measured operating parameters (P1, P2, P3); a compensation torque value (Cc) is determined from pre-recorded data, as a function of a second set of operating parameters (? 4, Pg, i, Pa, 2) comprising at least one of said parameters of braking (P5, 1, P5, 2); the sum of said theoretical assistance torque (CAT) and compensating torque values (Cc) thus determined is calculated so as to obtain a torque control value (C); the torque control signal (S) corresponding to said torque control value (C) is developed.

 electrical device (30), characterized in that the torque control signal (S) is developed in the following manner: - a theoretical assist torque value (CAT) is determined from pre-recorded data, in  12. Control method according to claim 11, characterized in that it further comprises the steps

 following: the value of the speed (P1) of the vehicle is measured; the value of the rotational speed (P2) of the steering wheel is measured; the value of the torque (P3) applied to the flywheel (2) by the driver is measured, and in that the first set of operating parameters (Pi, P2, P3) from which the torque value of Theoretical assistance (CAT) consists of the values thus measured.  13. A control method according to claim 11 or 12, characterized in that it comprises the following step: - the angular position (P4) of the flywheel is measured with respect to a neutral position of zero steering, <Desc / Clms Page number 19>  and in that the second set of operating parameters from which a compensation torque value (Cc) is determined consists of said angular position value (P4) and at least two braking parameters (Ps, i, Ps, 2) corresponding to two wheels of the vehicle.

 14. Control method according to claim 13, characterized in that the said at least two braking parameters (PS, the PS, 2) are the braking parameters.

 respectively corresponding to two rear wheels (9B) of the vehicle, respectively a right rear wheel and a rear left wheel. 15. Control method according to claim 14, characterized in that the compensation torque value (Cc) is determined as a function of only one of said braking parameters (P5,1, P5,2), selected as a function of the value (P4) of the angular position of the steering wheel.  16. Control method according to claim 15, characterized in that: - if the angular position value (P4) of the steering wheel

 corresponds to a left turn, the braking parameter chosen is the braking parameter (PS, l) corresponding to the right rear wheel; if the angular position value (P4) of the steering wheel corresponds to a right turn, the braking parameter chosen is the braking parameter (? 52) corresponding to the left rear wheel.  17. Control method according to claim 16, characterized in that: - if the value of the selected braking parameter (Psi, Pos, 2) is, in absolute value, less than a predetermined threshold value (SF), the torque compensation (Cc) is zero; if the value of the selected braking parameter (P5, 1, P5,2) is, in absolute value, greater than said value of <Desc / Clms Page number 20>  the compensation torque value is calculated from this intermediate variable (Vl).

 form F, (p) = ----; Ap + B

 P5, 2) a first transfer function of the

 predetermined threshold (SF), the following operations are carried out from said selected braking parameter (Ps, i, PS, 2): cm calculates a first intermediate variable (Vl) by applying to the selected braking parameter (Ps i,  18. Control method according to claim 17, characterized in that it further comprises the following step: a second intermediate variable (V2) is calculated by applying to the first intermediate variable (Vi)

 a second function of transfer of the form

 at. p F2 (p) +. p +

 19. Control method according to claim 18, characterized in that it further comprises the following step: a third intermediate variable (V3) is calculated from said second intermediate variable (V2) by applying to said second variable (V2) a time delay function whose time constant depends on the absolute value of the first intermediate variable (Vi), calculated at the same time.  20. Control method according to claim 19, characterized in that it further comprises the following step: the compensation torque value (Cc) is calculated at each instant by applying to the third intermediate variable (V3) a gain dependent on the absolute value of the first intermediate variable (Vl), calculated at the same time.  21. A motor vehicle having a power steering assembly according to any one of <Desc / Clms Page number 21>  claims 1 to 10 or comprising a power steering assembly operating according to a method according to any one of claims 11 to 20.