METHOD FOR PILOTING A MOTOR BY A PROPORTIONAL-DERIVATIVE REGULATOR TAKING INTO ACCOUNT THE STIFFNESS OF A POWER STEERING SYSTEM

Abstract

A method for piloting a motor of a power steering system of a vehicle, the power steering system having at least one steering wheel and one rack, the motor being piloted by a closed-loop proportional-derivative regulator (R.sub.θ) receiving as input an angular position (θm) of the motor and a setpoint angle (θ.sub.c), the regulator (R.sub.θ) determining a setpoint motor torque (C.sub.c). The method

includes the steps of determining a stiffness compensation, and

modifying the angular position (θ.sub.m) of the motor.

Claims

1. A method for piloting a motor of a power steering system of a vehicle, said power steering system comprising at least one steering wheel and one rack, said motor being piloted by means of a closed-loop proportional-derivative regulator (R.sub.θ) receiving as input an angular position (θ.sub.m) of said motor and a setpoint angle (θ.sub.c), said regulator (R.sub.θ) determining a setpoint motor torque (C.sub.c), wherein the method includes the following steps: determining a stiffness compensation by a stiffness compensation computer (C.sub.comp) determining a correction signal (S.sub.θ, S.sub.c) from an exerted motor torque (Cex) on the power steering system and a stiffness (K.sub.tot) of the power steering system linked to the motor, and modifying the angular position (θ.sub.m) of the motor as a function of the correction signal (S.sub.θ, S.sub.c).

2. The piloting method according to claim 1, wherein the motor applies the exerted motor torque (C.sub.ex) on the rack, and in which the stiffness (K.sub.tot) of the power steering system linked to the motor comprises a mechanical stiffness component (K.sub.m) comprised between the motor and the rack and/or a virtual stiffness component (K.sub.v) comprised between the motor and the at least one steering wheel.

3. The piloting method according to claim 2, wherein when the stiffness (K.sub.tot) of the power steering system linked to the motor comprises the component of mechanical stiffness (K.sub.m) and the component of virtual stiffness (K.sub.v), the stiffness (K.sub.tot) of the power steering system linked to the motor is determined by taking into account a term calculated according to the following formula: $\begin{array}{cc}\frac{1}{K_{\mathrm{tot}}}=\frac{1}{K_v}+\frac{1}{K_m}& \left[\mathrm{math}11\right]\end{array}$ With: K.sub.tot: the stiffness of the power steering system linked to the motor K.sub.v: the virtual stiffness between the motor and the steering wheel K.sub.m: the mechanical stiffness between the motor and the rack.

4. The piloting method according to claim 3, wherein the correction signal (S.sub.θ, S.sub.c) is an angle correction signal (S.sub.θ) modifying the setpoint angle (θ.sub.c) so as to form a corrected setpoint angle (θ.sub.cc) entering the regulator (R.sub.θ).

5. The piloting method according to claim 4, wherein the angle correction signal (S.sub.θ) is added to the setpoint angle (θ.sub.c).

6. The piloting method according to claim 5, wherein the angle correction signal (S.sub.θ) is determined by taking into account a term calculated according to the following formula: $\begin{array}{cc}{S}_{\theta }=\frac{C_{\mathrm{ex}}}{K_{\mathrm{tot}}}& \left[\mathrm{math}12\right]\end{array}$ With: S.sub.θ: the angle correction signal C.sub.ex: the exerted motor torque K.sub.tot: the stiffness of the power steering system linked to the motor.

7. The piloting method according to claim 3, wherein the correction signal (S.sub.θ, S.sub.c) is a torque correction signal (S.sub.c) modifying the setpoint motor torque (C.sub.c) so as to form a corrected setpoint motor torque (C.sub.cc) entering the motor.

8. The piloting method according to claim 7, wherein the torque correction signal (S.sub.c) is added to the setpoint motor torque (C.sub.c).

9. The piloting method according to claim 8, wherein the torque correction signal (S.sub.c) is determined by taking into account a term calculated according to the following formula: $\begin{array}{cc}{S}_C=\frac{C_{\mathrm{ex}}.K_v}{K_{\mathrm{tot}}}& \left[\mathrm{math}13\right]\end{array}$ With: S.sub.c: the torque correction signal C.sub.ex: the exerted motor torque K.sub.tot: the stiffness of the power steering system linked to the motor K.sub.v: the virtual stiffness between the motor and the steering wheel.

10. A vehicle comprising a piloting method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The disclosure will be better understood, thanks to the description below, which relates to several embodiments according to the present disclosure, given by way of non-limiting examples and explained with reference to the appended schematic drawings, in which:

[0061] FIG. 1 is a schematic representation of a first embodiment of the piloting method according to the disclosure;

[0062] FIG. 2 is a schematic representation of a second embodiment of the piloting method according to the disclosure;

[0063] FIG. 3 is a representation of a setpoint angle, an angular position of a motor and an angular position of a rack without implementing the disclosure;

[0064] FIG. 4 is a representation of the setpoint angle, of the angular position of the motor and of the angular position of the rack with implementation of the disclosure in which a stiffness corresponds to a virtual stiffness between the motor and a steering wheel; and

[0065] FIG. 5 is a representation of the setpoint angle, of the angular position of the motor and of the angular position of the rack with implementation of the disclosure in which the stiffness corresponds to the virtual stiffness and to a mechanical stiffness comprised between the motor and the rack.

DETAILED DESCRIPTION OF THE DRAWINGS

[0066] Only the elements necessary for understanding the disclosure have been represented. To facilitate reading of the drawings, the same elements have the same references from one figure to another.

[0067] The disclosure concerns a method 100, 101 for piloting a motor 1 of a power steering system for a vehicle, and more particularly for a motor vehicle intended for the transport of persons.

[0068] The method 100, 101 according to the disclosure is applied, under certain conditions, to a power steering system of the traditional type in which there is a mechanical link, generally produced by a steering column, between a steering wheel and a rack 2. The steering wheel allows a driver to maneuver said power steering device by exerting a force on said steering wheel.

[0069] The steering wheel is preferably mounted on the steering column, guided in rotation on the vehicle, and which meshes, by means of a steering pinion, on the rack 2, which is itself guided in translation in a steering casing attached to said vehicle.

[0070] Preferably, the ends of said rack 2 are each connected to a steering tie-rod connected to the steering knuckle of a steered wheel 3, such that a longitudinal displacement in translation of the rack 2 makes it possible to modify a steering angle (yaw angle) of the steered wheels 3.

[0071] The steered wheels 3 can preferably moreover also be driving wheels.

[0072] The traditional power steering device also comprises a regulator R.sub.θ which pilots a motor 1. The motor 1 can come into engagement, where appropriate via a reducer of the gear reducer type, either on the steering column itself, to form a so-called «single pinion» mechanism, or directly on the rack 2, by means for example of a second pinion separate from the steering pinion which allows the steering column to mesh with the rack 2, to so as to form a so-called «double pinion» mechanism, or even by means of a ball screw which cooperates with a corresponding thread of said rack 2, at a distance from said steering pinion.

[0073] The motor 1 will preferably be an electric motor, with two directions of operation, and preferably a rotary electric motor, of the brushless type.

[0074] When applying a driving assistance function, such as parking assistance, or traffic lane keeping assistance, in a traditional power steering system, the regulator R.sub.θ servo-controls an angular position θ.sub.m of a motor 1 at a setpoint angle θ.sub.c by piloting the motor torque C.sub.ex exerted by the motor 1 on the rack 2. An angular position θ.sub.m of the motor 1 corresponds to an angular position θ.sub.2 of the rack 2 modified by a value of a mechanical stiffness K.sub.m comprised between the control motor 1 and the rack 2.

[0075] The method 100, 101 according to the disclosure is also applied to a «steer-by-wire» type power steering system in which the steering wheel is mechanically detached from the rack 2. In this case, the steering system comprises a steering wheel unit mechanically independent of a rack unit.

[0076] The steering wheel unit comprises the steering wheel.

[0077] In the rack unit, a regulator R.sub.θ pilots a motor 1 which exerts a motor torque C.sub.ex on the rack 2. More precisely, the steering wheel angle is measured or calculated so as to determine a setpoint angle θ.sub.c to be reached by the angular position 62 of the rack 2. The regulator R.sub.θ servo-controls an angular position θ.sub.m of the maneuver motor 1 to the setpoint angle θ.sub.c by piloting a motor torque C.sub.ex exerted by the motor 1 on the rack 2. The angular position θ.sub.m of the maneuver motor 1 corresponds to the angular position θ.sub.2 of the rack 2 modified by a value of a mechanical stiffness K.sub.m comprised between the motor 1 and the rack 2, and by a virtual stiffness K.sub.v programmed in the regulator R.sub.θ and representing a stiffness comprised between the motor 1 and the steering wheel.

[0078] The disclosure relates to a method 100, 101 for piloting the motor 1 of the power steering system in which the regulator R.sub.θ of the motor 1 is a closed-loop proportional-derivative regulator, receiving as input an angular position θ.sub.m of said motor 1 and a setpoint angle θ.sub.c. The regulator R.sub.θ is therefore an angle regulator.

[0079] The method 100, 101 also comprises a step of determining a stiffness compensation by a stiffness compensation computer C.sub.comp determining a correction signal S.sub.θ, S.sub.c from the motor torque C.sub.ex exerted on the rack 2 by the motor 1 and a stiffness of the power steering system linked to the motor 1. The correction signal S.sub.θ, S.sub.c modifies the angular position θ.sub.m of the motor 1 as a function of the stiffness of the power steering system linked to the motor 1.

[0080] A first embodiment of the method 100 according to the disclosure is shown schematically in FIG. 1.

[0081] In this embodiment, the correction signal is an angle correction signal S.sub.θ which is added to the setpoint angle θ.sub.c so as to form a corrected setpoint angle θ.sub.cc entering the regulator R.sub.θ. The regulator R.sub.θ also receives as input the angular position θ.sub.m of the motor 1. The regulator R.sub.θ then determines a setpoint motor torque θ.sub.cc which is transmitted to the motor 1. From this setpoint motor torque, the motor 1 exerts a motor torque C.sub.ex exerted on the rack 2.

[0082] The exerted motor torque C.sub.ex is measured or calculated, then is transmitted to the stiffness compensation computer C.sub.comp so that the latter determines the angle correction signal S.sub.θ. More precisely, the angle correction signal S.sub.θ is calculated according to the formula:

[00005]$\begin{array}{cc}{S}_{\theta }=\frac{C_{\mathrm{ex}}}{K_{\mathrm{tot}}}& \left[\mathrm{math}5\right]\end{array}$

[0083] With:

[0084] S.sub.θ: the angle correction signal

[0085] C.sub.ex: the exerted motor torque

[0086] K.sub.tot: the stiffness of the power steering system linked to the motor

[0087] The stiffness of the power steering system linked to the motor comprising a mechanical stiffness component K.sub.m and a virtual stiffness component K.sub.v, is calculated according to the formula below:

[00006]$\begin{array}{cc}\frac{1}{K_{\mathrm{tot}}}=\frac{1}{K_v}+\frac{1}{K_m}& \left[\mathrm{math}6\right]\end{array}$

[0088] With:

[0089] K.sub.tot: the stiffness of the power steering system linked to the motor

[0090] K.sub.v: the virtual stiffness between the motor and the steering wheel

[0091] K.sub.m: the mechanical stiffness between the motor and the rack

[0092] Alternatively, the stiffness of the power steering system linked to the motor comprising a component of mechanical stiffness K.sub.m, a component of virtual stiffness K.sub.v, and a stiffness of a front axle is calculated according to the formula below:

[00007]$\begin{array}{cc}\frac{1}{K_{\mathrm{tot}}}=\frac{1}{K_v}+\frac{1}{K_m}+\frac{1}{K_{\mathrm{fa}}}& \left[\mathrm{math}7\right]\end{array}$

[0093] With:

[0094] K.sub.tot: the stiffness of the power steering system linked to the motor

[0095] K.sub.v: the virtual stiffness between the motor and the steering wheel

[0096] K.sub.m: the mechanical stiffness between the motor and the rack

[0097] K.sub.fa: the stiffness of the front axle between the rack and a wheel of the vehicle

[0098] A second embodiment of the method 101 according to the disclosure is shown schematically in FIG. 2.

[0099] In this embodiment, the regulator R.sub.θ receives as input the angular position θ.sub.m of the motor 1 and the setpoint angle θ.sub.c. The regulator R.sub.θ then determines the setpoint motortorque C.sub.c. The correction signal S is a torque correction signal S.sub.c which is added to the setpoint motor torque C.sub.c so as to form a corrected setpoint motor torque C.sub.cc piloting the motor 1. From this corrected setpoint motor torque C.sub.cc, the motor 1 exerts a motor torque C.sub.ex exerted on the rack 2.

[0100] The exerted motor torque C.sub.ex is measured or calculated, then is transmitted to the stiffness compensation computer C.sub.comp so that the latter determines the torque correction signal S.sub.c. More precisely, the torque correction signal S.sub.c is calculated according to the formula:

[00008]$\begin{array}{cc}{S}_C=\frac{C_{\mathrm{ex}}.K_v}{K_{\mathrm{tot}}}& \left[\mathrm{math}8\right]\end{array}$

[0101] With:

[0102] S.sub.c: the torque correction signal

[0103] C.sub.ex: the exerted motor torque

[0104] K.sub.tot: the stiffness of the power steering system linked to the motor

[0105] K.sub.v: the virtual stiffness between the motor and the steering wheel

[0106] The stiffness of the power steering system linked to the motor comprising a mechanical stiffness component K.sub.m and a virtual stiffness component K.sub.v, is calculated according to the formula below:

[00009]$\begin{array}{cc}\frac{1}{K_{\mathrm{tot}}}=\frac{1}{K_v}+\frac{1}{K_m}& \left[\mathrm{math}9\right]\end{array}$

[0107] With:

[0108] K.sub.tot: the stiffness of the power steering system linked to the motor

[0109] K.sub.v: the virtual stiffness between the motor and the steering wheel

[0110] K.sub.m: the mechanical stiffness between the motor and the rack

[0111] Alternatively, the stiffness of the power steering system linked to the motor comprising a component of mechanical stiffness K.sub.m, a component of virtual stiffness K.sub.v, and a stiffness of a front axle is calculated according to the formula below:

[00010]$\begin{array}{cc}\frac{1}{K_{\mathrm{tot}}}=\frac{1}{K_v}+\frac{1}{K_m}+\frac{1}{K_{\mathrm{fa}}}& \left[\mathrm{math}10\right]\end{array}$

[0112] With:

[0113] K.sub.tot: the stiffness of the power steering system linked to the motor

[0114] K.sub.v: the virtual stiffness between the motor and the steering wheel

[0115] K.sub.m: the mechanical stiffness between the motor and the rack

[0116] K.sub.fa: the stiffness of the front axle between the rack and a wheel of the vehicle

[0117] FIGS. 3, 4, and 5 illustrate a representation of the setpoint angle θ.sub.c, of the angular position θ.sub.m of the motor 1 and of the angular position θ.sub.2 of the rack 2 respectively without implementation of the disclosure, with implementation of the disclosure in which the stiffness corresponds only to the virtual stiffness K and with implementation of the disclosure in which the stiffness corresponds to the virtual stiffness K and to the mechanical stiffness K.sub.m between the motor 1 and the rack 2, in a «steer-by-wire» steering system.

[0118] In FIG. 3, the regulator R.sub.θ is a closed-loop proportional-derivative regulator, receiving as input an angular position θ.sub.m of said motor 1 and a setpoint angle θ.sub.c, without implementing a stiffness compensation calculator C.sub.comp according to the disclosure. The curves of the angular position θ.sub.m of the motor 1 and of the angular position θ.sub.2 of the rack 2 are close but not superimposed. They are separated by an angle of 0.8°. In other words, the angular position θ.sub.m of the motor 1 and the angular position θ.sub.2 of the rack 2 have a difference of 0.8°. The difference between the angular position of the rack 82 and the setpoint curve θ.sub.c is approximately 10°.

[0119] In FIG. 4, the stiffness of the power steering system linked to the motor 1 is taken equal to the virtual stiffness K.sub.v. The curves of the angular position θ.sub.m of the motor 1 and the curve of the setpoint angle θ.sub.c are close. In other words, the disclosure has reduced the deviation associated with the virtual stiffness K of the power steering system. However, the angular position θ.sub.m of the motor and the angular position θ.sub.2 of the rack 2 still have a difference of 0.8° corresponding to the mechanical stiffness K.sub.m of the power steering system.

[0120] In FIG. 5, the stiffness of the power steering system linked to the motor 1 is taken equal to the virtual stiffness K and to the mechanical stiffness K.sub.m. Thus, the curve of the angular position θ.sub.m of the motor is greater than the curve of the setpoint angle θ.sub.c. In this way, the curve of the angular position θ.sub.2 of the rack 2 is close to the curve of the setpoint angle θ.sub.c, which is the aim of the disclosure. In other words, the disclosure has reduced the deviation associated with the virtual stiffness K.sub.v and the mechanical stiffness K.sub.m of the power steering system.

[0121] FIG. 5 illustrates that the disclosure makes it possible to maintain the angular position θ.sub.2 of the rack 2 substantially equal to the setpoint angle θ.sub.c during external stresses or disturbances F.sub.ext on the rack 2, such as for example a deformation of the road.

[0122] Of course, the disclosure is not limited to the embodiments described and shown in the appended figures. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the disclosure.