Design of an Electric Power Steering System Using a Model Reference Approach and Additional Column or Rack Actuators

Alex Beckerman

Electric power steering (EPS) systems have been adopted by the automotive industry principally because of potential fuel savings over the more conventional hydraulic power steering. EPS lends itself to improvements in automobile steering feel and vehicle response as well as ultimately leading to steer-by-wire systems. This thesis proposes two adaptations of the standard column mounted electric power steering (C-EPS) system. In the first new configuration, an additional motor is placed between the C-EPS motor and the steering wheel for independent control of steering feel. In the second new configuration, an additional motor is placed between the rack and right tie rod for independent control of vehicle response. These new motors, combined with a model reference approach utilizing Proportional-Integral-Derivative (PID) control and linear quadratic regulator (LQR) control, allow for the independent tuning of desired steering feel and vehicle response, leading to new or improved functionality when compared to more traditional EPS systems: disturbance rejection, yaw damping, variable steering ratio, and increased linear tire behavior. Without additional motors, it can still be shown that the model reference approach is advantageous for various traditional EPS functions: assist, return to center, and inertia compensation. These new or improved functions are tested under various conditions with various inputs and compared to a more traditional EPS system.

Comments are closed.