Steer-by-wire road wheel actuator dither to improve rack force estimation

1 . A method for controlling a motor of a road wheel actuator (RWA) in a steer-by-wire (SbW) steering system of a vehicle, the method comprising, using one or more processing devices:

determining a static friction associated with the SbW steering system;

determining a frequency and an amplitude of a dithering signal based on the determined static friction;

providing a motor torque command signal to the motor;

providing the dithering signal to the motor, wherein the dithering signal is applied to the motor torque command signal, and wherein the dithering signal is configured to allow road disturbances to cause movement of a rack bar of the SbW steering system;

sensing, using one or more sensors associated with the vehicle, the road disturbances; and

generating an emulation signal based on the sensed road disturbances.

2 . The method of claim 1 , further comprising providing the emulation signal to a motor of a handwheel actuator (HWA).

3 . The method of claim 2 , wherein the emulation signal is generated to cause the HWA to move a handwheel of the vehicle in accordance with the sensed road disturbances.

4 . The method of claim 1 , further comprising adjusting the motor torque command signal based on the sensed road disturbances.

5 . The method of claim 1 , further comprising determining the frequency and the amplitude such that the frequency does not cause audible noise and the amplitude does not cause motion of the rack bar.

6 . The method of claim 1 , further comprising providing a second dithering signal to a motor of a handwheel actuator.

7 . The method of claim 1 , wherein the dithering signal includes at least one of a periodic waveform, a square wave, a triangle wave, and a sine wave.

8 . The method of claim 1 , wherein the dithering signal is configured to minimize static friction associated with the SbW steering system without causing audible noise or causing motion of the rack bar.

9 . A system for controlling a motor of a road wheel actuator (RWA) in a steer-by-wire (SbW) steering system of a vehicle, the system comprising:

sensors configured to sense a plurality of values corresponding to operation of the SbW steering system; and

a steering system controller configured to, based on the sensed plurality of values,

determine a static friction associated with the SbW steering system,

determine a frequency and an amplitude of a dithering signal based on the determined static friction,

provide a motor torque command signal to the motor,

provide a dithering signal to the motor, wherein the dithering signal is applied to the motor torque command signal, and wherein the dithering signal is configured to allow road disturbances to cause movement of a rack bar of the SbW steering system,

sense the road disturbances, and

generate an emulation signal based on the sensed road disturbances.

10 . The system of claim 9 , wherein the steering system controller is further configured to provide the emulation signal to a motor of a handwheel actuator (HWA).

11 . The system of claim 10 , wherein the emulation signal is configured to cause the HWA to move a handwheel of the vehicle in accordance with the sensed road disturbances.

12 . The system of claim 9 , wherein the steering system controller is further configured to adjust the motor torque command signal based on the sensed road disturbances.

13 . The system of claim 9 , wherein the steering system controller is further configured to determine the frequency and the amplitude such that the frequency does not cause audible noise and the amplitude does not cause motion of the rack bar.

14 . The system of claim 9 , wherein the steering system controller is further configured to provide a second dithering signal to a motor of a handwheel actuator.

15 . The system of claim 9 , wherein the dithering signal includes at least one of a periodic waveform, a square wave, a triangle wave, and a sine wave.

16 . A processor configured to execute instructions stored in memory, wherein executing the instructions causes the processor to control a motor of a road wheel actuator (RWA) in a steer-by-wire (SbW) steering system of a vehicle, the instructions comprising:

determining a static friction associated with the SbW steering system;

determining a frequency and an amplitude of a dithering signal based on the determined static friction;

providing a motor torque command signal to the motor;

providing a dithering signal to the motor, wherein the dithering signal is applied to the motor torque command signal, and wherein the dithering signal is configured to allow road disturbances to cause movement of a rack bar of the SbW steering system;

sensing the road disturbances; and

generating an emulation signal based on the sensed road disturbances.

17 . The processor of claim 16 , the instructions further comprising providing the emulation signal to a motor of a handwheel actuator (HWA), wherein the emulation signal is generated to cause the HWA to move a handwheel of the vehicle in accordance with the sensed road disturbances.

18 . The processor of claim 16 , the instructions further comprising adjusting the motor torque command signal based on the sensed road disturbances.