Method for friction compensation in a power steering system and associated estimation method

Patent metadata

Field	Value
Publication number	US-11656137-B2
Application number	US-201816763905-A
Country	US
Kind code	B2
Filing date	Oct 23, 2018
Priority date	Nov 13, 2017
Publication date	May 23, 2023
Grant date	May 23, 2023

Abstract

A method in which a continuous estimation of the intermediate friction rate is carried out, allowing the integration of the method into a general friction compensation method so as to continuously improve the feel on the steering wheel, particularly for speeds below a determined threshold. Also, a method for friction compensation in an electrical power steering system, characterised in that the compensation method takes into account a continuous estimation of the intermediate friction rate obtained by the estimation method.

First claim

The invention claimed is:

1. A method for compensating for friction of an electric power steering of a vehicle, the method comprising:
measuring a first speed by a speed sensor configured to measure a speed of an electric motor of the electric power steering,
determining a second speed by
measuring, by a torque sensor, a steering wheel torque between a steering wheel and a rack of the electric power steering,
time deriving the torque measurement to obtain a torque derivative, and
computing the second speed by applying the torque derivative to a stiffness,

computing a steering wheel speed by summing the first speed and the second speed,
inputting the steering wheel speed to a LuGre model to obtain a continuous estimation of a friction coefficient,
computing a continuous estimation of an intermediate friction rate by dividing the continuous estimation of the friction coefficient by a dynamic friction coefficient of the power steering, measured on a test bench, and
compensating for friction of the electric power system using the continuous estimation of the intermediate friction rate.

2. The method according to claim 1 , further comprising:
obtaining at least one estimated dynamic friction amplitude, and modulating the estimated dynamic friction amplitude by the continuous estimation of the intermediate friction rate,
obtaining a desired dynamic friction τ FRC target amplitude of the electric power steering,
computing a difference between the estimated dynamic friction amplitude and the desired dynamic friction amplitude,
computing a product of the difference with the continuous estimation of the intermediate friction rate to obtain an amount of friction to be compensated,
computing a difference between the amount of friction to be compensated and an estimation of a set of forces opposing a movement of the steering wheel,
compensating for the power steering by monitoring the driver torque by a control unit depending on a target driver torque and the measured steering wheel torque.

3. The method according to claim 2 , wherein computing the difference between the estimated dynamic friction amplitude and the desired dynamic friction amplitude is performed by using a chart or a pre-established database or a data input.

4. The method according to claim 2 , wherein the monitoring of the driver torque is carried out in a closed loop.

5. The method according to claim 3 , wherein the monitoring of the driver torque is carried out in a closed loop.

6. The method according to claim 1 , wherein the continuous estimation of the friction coefficient is computed using the following equation:
μ= sat α* (σ 0 ( V,T ) z+σ 1 ( V,T ) ż )

where:
μ is the continuous estimation of the friction coefficient,
a* is the dynamic friction coefficient of the electric power steering,
V is a speed of the vehicle,
T is a steering temperature,
σ 0 is a stiffness,
σ 1 is a micro-damping, and
z is a state of an internal friction.

Assignees

• Jtekt Europe Sas

Inventors

• Guilemond Alain
• Bourdrez Sébastien
• Slama Tahar
• Moulaire Pascal
• Baudouin Nicolas

Classifications

• B62D5/0481

  monitoring the steering system, e.g. failures · CPC title

• G01L5/221 Primary

  to steering wheels, e.g. for power assisted steering · CPC title

• B62D6/008

  Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications · CPC title