Soft-disable damping for electric power steering

A method for controlling a motor in an electrical power steering system, comprising:

• providing an assist torque with said motor;
• recognizing a critical fault related to said provision of assist torque;
• disabling said assist torque in response to said fault recognition;
• determining the rotational velocity of said motor;
• providing a limited damping torque in response to said disabling of assist torque;
• timing the duration of said provision of limited damping torque;
• and
• commanding said limited damping torque in response to at least one of said timing and said determining.

An electric power steering system for a vehicle comprising a steering input member, an electric motor coupled to the input member, and an electronic controller in signal communication with the motor;

• the electronic controller comprising:
• means for providing an assist torque;
• means for disabling said assist torque;
• means for entering a soft-disable state;
• means for timing the duration of said soft-disable state;
• means for determining a rotational velocity of said motor;
• means for calculating a motor damping in correspondence with said determined velocity;
• means for scaling the calculated motor damping in correspondence with said timing;
• means for limiting the scaled motor damping to provide a command signal;
• and
• means for controlling said motor in correspondence with said command signal.