Method and system for combined hydraulic and electric power assisted steering

A method for controlling a feedback torque actuator with a motor with an Electric Control Unit (ECU) for giving feedback to a driver, a steering wheel to which the driver applies a driver torque (TD) in a steering system comprising a steering assistance actuator with a torsion bar, wherein the method incorporates the following steps for feedback torque control:

• measuring a steering angle using a steering angle sensing means,
• measuring a torsion-bar torque with the use of a torsion-bar torque sensor of the assistance actuator,
• measuring a current in the motor of said feedback torque actuator,
• transforming the current to an estimated feedback torque by the use of a current-to-torque characteristics of the motor,
• calculating the driver torque by adding the sensed torsion-bar torque and the estimated feedback torque,
• calculating a target feedback torque actuator state from either said calculated driver torque or from said measured steering angle, and
• controlling the mentioned feedback torque actuator via a closed loop current control to achieve said target feedback torque actuator state, so that a desired steering feel is achieved.

A system for controlling a feedback torque actuator with a motor with an Electric Control Unit (ECU) for giving feedback to a driver, a steering wheel to which the driver applies a driver torque (TD) in a steering system comprising a steering assistance actuator with a torsion bar, wherein the system comprises:

• means for measurement of a steering angle,
• a torsion bar torque sensor for measurement of the torque of the torsion bar, the ECU comprising:
• means for measurement of a current in the motor of said feedback torque actuator,
• means for transformation of the above-mentioned current to an estimated feedback torque by the use of a current-to-torque characteristics of the motor,
• means for calculation of the before-mentioned driver torque by adding the sensed torsion-bar torque and the estimated feedback torque,
• means for calculation of a target feedback torque actuator state from either said calculated driver torque or said measured steering angle, and
• means for control of the mentioned feedback torque actuator via a closed loop current control to achieve said target feedback torque actuator state, so that a desired steering feel is achieved.