ELECTROMECHANICAL POWER STEERING SYSTEM CONTROL USING ONLY MEASURED OR ESTIMATED STEERING TORQUE SIGNAL

Abstract

A disclosed method can control an electric motor for an electromechanical power steering mechanism for assisting steering for a motor vehicle. The electromechanical power steering mechanism may include a steering column with an upper steering shaft linked to a lower steering shaft by a torsion bar. A torsion angle between the upper steering shaft and the lower steering shaft is configured to be measured or estimated, and an electric motor is configured to apply an assistance torque. The method may involve calculating a desired rotor position with an assist algorithm based on the torsion angle and calculating a PWM pattern by a PWM control unit such that the calculated PWM pattern adjusts a rotor of an electric motor angle such that the torsion angle is decreased.

Claims

1.-8. (canceled)

9. A method for assist control of an electromechanical power steering mechanism for a motor vehicle, wherein the electromechanical power steering mechanism comprises a steering column with an upper steering shaft linked to a lower steering shaft by a torsion bar, wherein a torsion angle between the upper and lower steering shafts is configured to be measured or estimated, wherein an electric motor is configured to apply an assistance torque, the method comprising: calculating a desired rotor position by an assist algorithm based on the torsion angle; and calculating a PWM pattern with a PWM control unit such that the calculated PWM pattern adjusts a rotor of an electric motor angle such that the torsion angle is decreased.

10. The method of claim 9 comprising measuring the torsion angle in a torque sensor unit, which measures a relative shift angle between the upper steering shaft and the lower steering shaft.

11. The method of claim 9 comprising estimating the torsion angle based on vehicle information with at least one of a steering wheel angle sensor or a steering wheel angle speed sensor.

12. The method of claim 9 wherein calculating the desired rotor position by the assist algorithm depends on a speed of the motor vehicle.

13. The method of claim 9 wherein control of the electric motor depends only on the torsion angle and the calculated desired rotor position.

14. The method of claim 9 wherein control of the electric motor is independent of a rotor position sensor of the electric motor.

15. The method of claim 9 wherein control of the electric motor is independent of a current sensor measuring current flowing through motor phases.

16. The method of claim 9 wherein the electric motor is a permanent magnet synchronous motor with at least three phases.

Description

[0012] FIG. 1 shows a schematic illustration of an electromechanical motor vehicle power steering mechanism 1 with illustrated control cycle of an electric motor 2. Arrows with dashed lines mark electrical signals and software variables. Arrows with solid lines mark mechanical couplings.

[0013] The electric motor 2 is a permanent magnet synchronous motor with at least three phases. A steering wheel 3 is fixed to an upper steering shaft 4 of a steering column 5, the steering movement of the driver is transmitted via a torsion bar (not shown) to a lower steering shaft 6. The lower steering shaft 6 is coupled to a rack 7 via a rack-and-pinion mechanism 8. Rotation of the upper and lower steering shaft 4,6 accompanying a steering operation is converted into a reciprocating linear motion of the toothed rack 7 by the rack-and-pinion mechanism 8. A torque sensor unit (TSU) 9 measures the relative shift angle 10 between the upper steering shaft 4 and the lower steering shaft 6. This measured torsion angle 10 is the angle difference between the steering wheel angle and the rack/rotor position. The torque is proportional to the position difference at the both ends of the torsion bar. The torsion angle 10 is fed to an assist algorithm 11 of the electronic control unit of the electric power assisted steering system to determine the desired rotor position 12. Based on the desired rotor position 12 the motor currents are calculated via a PWM (pulse-width modulation) control unit 13. The assist is provided such a way, that the measured torsion angle 10 is decreased. For that a PWM pattern 13 is calculated in the PWM control unit 13 which adjusts the rotor position 14 such that the rack position 15 and accordingly the pinion angle 16 are changed and the torsion angle 10 on the TSU torsion bar is decreased. Provided assist can depend on the motor vehicle speed. The assist control does only depend on the torsion angle and the calculated desired rotor position. The method does therefore not depend on position, speed or current sensors of the electric motor.

[0014] In another embodiment the desired rotor position 12 is defined by a steering wheel angle sensor and/or steering wheel angle speed sensor and other vehicle information e.g. vehicle speed, lateral acceleration and/or yaw rate. From these measurements the torsion of the column can be estimate. Based on this estimation the previously described method can be carried out to provide assist.