Method For Correcting Measurements Of The Torque Exerted On A Steering Wheel Of An Automobile Vehicle Electric Power-Assisted Steering

Abstract

The method consists in the following when the instantaneous speed of the vehicle is greater than a pre-determined threshold speed: identifying that the vehicle travels in a straight line during a minimum pre-determined period without torque exerted on the steering wheel by the driver of the vehicle; if the prior condition is met, an average residual torque (t m ) is determined for the steering wheel, particularly by calculating a sliding scale of measures of torque on the steering wheel; if the average residual torque (t m ) on the steering wheel is greater than a pre-determined minimum torque, a correction, which is particularly proportional to the average residual torque (t m ), e.g. a linear correction, to be applied to the torque measures on the steering wheel is determined by means of calculation; effective correction (t o ) limited in terms of the speed of variation and amplitude in relation to the correction determined by calculation is applied to the measures of torque on the steering wheel, said corrected measures being subsequently treated by the electronic calculator in order to control the electronic booster motor.

1 . A method for correcting the measurements of the torque exerted on a steering wheel of an automobile vehicle electric power-assisted steering, carried out, when the vehicle is being driven, by a torque sensor disposed on the steering column, the steering system comprising an assistance electric motor controlled by an on-board electronic processor, notably using the measurements of the torque on the steering wheel carried out by the torque sensory, wherein it consists, when the instantaneous speed of the vehicle is higher than a predetermined threshold speed: 
 in identifying that, during a predetermined minimum period of time, the vehicle is being driven in a straight line, without torque exerted on the steering wheel by the driver of the vehicle;    if the preceding condition is met, in determining a mean residual torque on the steering wheel, notably by the calculation of a moving average of the measurements of the torque on the steering wheel;    if the mean residual torque on the steering wheel is higher than a predetermined minimum residual torque, in determining by calculation a correction, in particular proportional to this mean residual torque, for example a linear correction, to be applied to the measurements of the torque on the steering wheels;    in applying an effective correction, limited notably in speed of variation and in amplitudes with respect to the correction determined by calculation, to the measurements of the torque on the steering wheel, the corrected measurements then being processed by the electronic processor in order to control the assistance electric motor.    
   
   
       2 . The correction method as claimed in  claim 1 , wherein the vehicle is identified as being driven in a straight line, without torque exerted on the steering wheel by the driver of the vehicle, if the angular speed of the assistance electric motor is lower than a pre-determined limiting speed, and/or if the rotation speed of the steering wheel is lower than a pre-determined limiting angular speed, and/or if the corrected measurements of the torque on the steering wheel are lower than a predetermined limiting torque.  
   
   
       3 . The correction method as claimed in  claim 1 , wherein the moving average of the measurements of the torque on the steering wheel is reset to the value “zero” whenever the vehicle is started.  
   
   
       4 . The correction method as claimed in  claim 2 , wherein the moving average of the measurements of the torque on the steering wheel is reset to the value “zero” whenever the vehicle is started.