Method of managing assisted steering with indirect reconstruction of the steering wheel torque information

Patent metadata

Field	Value
Publication number	US-10486738-B2
Application number	US-201716087980-A
Country	US
Kind code	B2
Filing date	Mar 23, 2017
Priority date	Mar 24, 2016
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

The invention relates to a method for managing an assisted steering device ( 1 ) for a vehicle ( 2 ) comprising a steering wheel ( 3 ) on which the driver exerts a manoeuvring effort, termed the “steering wheel torque” (T 3 ), as well as an assistance motor ( 12 ) intended to provide an assistance effort (T 12 ), said method comprising a steering wheel torque reconstruction step (a) in the course of which the steering wheel torque (T 3 ) is evaluated, such as is actually exerted by the driver on the steering wheel ( 3 ), without calling upon a steering wheel torque sensor ( 14 ) specifically dedicated to the measurement of said steering wheel torque, but by reconstructing an information item representative of said steering wheel torque (T 3 ), termed the “estimated steering wheel torque” (T 3 _estim), on the basis of data termed “external data” ( 83, 812, 8′3, 8′12 ) that is gathered outside a specific steering wheel torque sensor ( 14 ) such as this and which include the angular position of the steering wheel ( 83 ), the angular position ( 812 ) of the shaft of the assistance motor ( 12 ), and the time derivatives ( 8′3, 8′12 ) of these angular positions.

First claim

The invention claimed is:

1. A method of managing a power steering device for a vehicle, said power steering device comprising a steering wheel which allows a driver to maneuver said power steering device by exerting a force, called «steering wheel torque», on said steering wheel, as well as an assist motor intended to provide an assist force to assist the maneuver of said power steering device, said method being characterized in that it comprises a step (a) of reconstructing a steering wheel torque during which the steering wheel torque is evaluated, as it is actually exerted by the driver on the steering wheel, by reconstructing a representative information of said steering wheel torque, called «estimated steering wheel torque», from data called «external data» which are collected within the power steering device or within the vehicle, but excluding a steering wheel torque sensor specifically dedicated to measuring of said steering wheel torque, said external data comprising a value called «steering wheel angle» representative of the angular position of the steering wheel, a value called «motor angle» representative of the angular position of the shaft of the assist motor, as well as the time derivatives of said steering wheel angle and said motor angle and in that, at step (a) of reconstructing a steering wheel torque, on the one hand, a value called «steering wheel angle» representative of the angular position of the steering wheel, and on the other hand, a value called «motor angle» representative of the angular position of the shaft of the assist motor are collected as external data, the difference, called «relative displacement», between the steering wheel angle and the motor angle is calculated, then the relative displacement is multiplied by a predetermined stiffness coefficient, so as to obtain a first component of the estimated steering wheel angle, called «stiffness term».

2. The method according to claim 1 , wherein at the steering wheel torque reconstruction step (a), the time derivative of the steering wheel angle is calculated to estimate the rotational angular speed of the steering wheel, called «steering wheel speed», the time derivative of the motor angle is calculated to estimate the rotational angular speed of the shaft of the assist motor, called «motor speed», the difference, called «relative speed», between the steering wheel speed and the motor speed is calculated, then the relative speed is multiplied by a predetermined viscosity coefficient, so as to obtain a second component of the estimated steering wheel angle, called «dissipation term», which is added to the stiffness term in order to obtain the estimated steering wheel torque.

3. The method according to claim 1 , wherein the stiffness term, and/or respectively the dissipation term, are filtered by means of low-pass filters, whose cut-off frequency is adjusted according to the longitudinal speed of the vehicle (Vvehic).

4. The method according to claim 1 , wherein the stiffness coefficient, and/or respectively the viscosity coefficient, are adjusted depending on to the longitudinal speed of the vehicle.

5. The method according to claim 4 , wherein the stiffness coefficient follows an evolution law depending on the speed of the vehicle, called «stiffness law», according to which the stiffness coefficient first decreases, relative to its initial value associated to a zero speed, before reaching a minimum associated to a speed called «inversion speed», and then gradually increases again with the speed, so as to reach again and then exceed the initial value from and beyond a speed called «threshold speed», which marks the boundary between a first speed interval, called «low-speed range», and a second speed interval, called «high-speed range».

6. The method according to claim 4 , wherein the viscosity coefficient follows an evolution law, called «viscosity law», decreasing depending on the speed of the vehicle.

7. The method according to claim 1 , wherein after the torque reconstruction step (a), a step (b) of open-loop regulation of the assist motor, during which a motor torque setpoint which is applied to the assist motor is determined, said motor torque setpoint comprising, on the one hand, a base setpoint, which is determined from the estimated steering wheel torque, according to predefined assist laws, and on the other hand, a damping setpoint, which is calculated depending on the rotational angular speed of the shaft of the assist motor, called «motor speed», and which serves to adjust the base setpoint.

8. The method according to claim 7 , wherein the damping setpoint is calculated proportionally to the motor speed, by applying a damping gain to said motor speed.

9. The method according to claim 7 , wherein the damping setpoint is weighted by at least one first weighting coefficient which depends on the value of the estimated steering wheel torque.

10. The method according to claim 1 , wherein the steering wheel angle is measured by means of a steering wheel angular position sensor associated to the steering wheel.

11. The method according to claim 1 , wherein the motor angle is measured by means of a motor angular position sensor, for example of the resolver type, which is integrated into the assist motor.

12. The method according to claim 1 , wherein it manages a power steering device within which the steering wheel is mounted on a steering column which meshes with a steering rack, and within which the assist motor is engaged on said steering column or on said steering rack, in that said power steering device includes a specific steering wheel torque sensor, mounted on the steering column and arranged to provide, in normal operation, a direct measurement of the steering wheel torque, and in that the steering wheel torque reconstruction step (a) automatically intervenes in case of failure of the specific steering wheel torque sensor to substitute an estimated steering wheel torque value with the direct measurement of the steering wheel torque.

13. The method according to claim 1 , wherein it manages a power steering device within which the steering wheel is mounted on a steering column which meshes with a steering rack, and within which the assist motor is engaged on said steering column or on said steering rack, in that the steering column is devoid of a specific steering wheel torque sensor, and more particularly devoid of a torsion bar intended to measure the steering wheel torque, and in that the steering wheel torque reconstruction step (a) is used in normal operation to provide the steering wheel torque value necessary for the management of the power steering device.

Assignees

• Jtekt Europe Sas

Inventors

• Moulaire Pascal
• Baudin Yoann
• Gaudin Serge
• Taofifenua Ofaina
• Yamamoto Kazusa

Classifications

• B62D5/0463 Primary

  calculating assisting torque from the motor based on driver input · CPC title

• B62D5/049

  detecting sensor failures · CPC title

• B62D5/0484

  for reaction to failures, e.g. limp home · CPC title