Vehicle having electric power steering with active damping

In a vehicle with an electric power steering system having a steering shaft coupled to a vehicle wheel, an electric motor coupled to the steering shaft, means for determining a driver assist torque, means for determining a return to center torque and means for summing the driver assist torque and the return to center torque to provide a motor command signal to the electric motor, the steering shaft having a resonant frequency of rotational oscillation in free control mode, the improvement comprising:

• means for generating a steering shaft position signal;
• means for filtering the steering shaft position signal, the filtering means having amplitude and phase characteristics of a differentiator from zero Hertz through the resonant frequency of rotational oscillation in free control mode with amplitude and phase lead decreasing relative to those of a differentiator at rotational oscillation frequencies greater than the resonant frequency of rotational oscillation in free control mode;
• means for multiplying the filtered steering shaft position signal by a vehicle velocity factor derived from sensed vehicle velocity to provide an active damping torque;
• the means for summing the driver assist torque and the return to center torque being further effective to sum the active damping torque therewith in providing the motor command signal to the electric motor.