Electric assist steering system having an improved motor current controller with gain scheduler

An electric assist steering system comprising:

• a torque sensor for sensing applied steering torque and providing a signal having a value indicative of the applied steering torque;
• an electric assist motor drivingly connected to a steering member so that when said electric assist motor is energized, it provides steering assist;
• a motor controller for providing a current command signal having a value functionally related to the sensed applied steering torque;
• sensor means for sensing at least one dynamic operating characteristic of said motor and for providing a signal indicative of the at least one sensed dynamic motor operating characteristic;
• variable gain regulator for receiving said current command signal having a value and for providing a motor current control signal having a value functionally related to the value of said received current command signal and a gain control value;
• gain scheduler operatively coupled to said variable gain regulator and to said sensing means for providing said gain control value to said variable gain regulator in response to said sensed at least one dynamic motor operating characteristic to thereby control the amount of gain of said variable gain regulator;
• and
• drive circuit operatively connected to the variable gain regulator and said motor for energizing said motor in response to said motor current control signal.

A method for controlling the operation of an electric motor, said method comprising the steps of:

• sensing at least one dynamic operating characteristic of the motor and providing a signal indicative of the at least one sensed dynamic motor operating characteristic;
• providing a variable gain regulator for receiving a current command request signal having a value and for providing a motor current control signal having a value functionally related to the value of said received current command request signal and a gain control value;
• providing the gain control value to the variable gain regulator in response to the sensed at least one dynamic motor operating characteristic to thereby control the amount of gain of the variable gain regulator;
• and
• energizing said motor in response to the motor current control signal.