Method and apparatus for controlling an electric assist steering system by linearizing system input-output torque gain

Claim 1

An apparatus for controlling a steering assist system, said steering assist system providing steering assist in response to a steering control signal, said steering assist system including a variable reluctance motor, said apparatus comprising: motor position sensing means for sensing the relative position between the motor's rotor and stator; torque sensing means operatively connected to a vehicle hand wheel for sensing applied steering torque; motor torque assist determining means for determining a desired motor torque assist value in response to the sensed applied steering torque; modifying means for modifying said desired torque assist value to linearize the gain between said desired torque assist value and motor torque output; a plurality of motor torque look=up tables, each of said motor torque look-up tables having a plurality of motor current values that vary as a function of motor position; control means operatively connected to said modifying means and to said motor position sensing means, said control means (i) selecting a first and second torque look-up table from said plurality of look-up tables wherein said first look-up table corresponds to a torque value less than the modified motor torque assist value and said second look-up table corresponds to a torque value greater than the modified motor torque assist value, (ii) determining a first motor current value by interpolating between two current values associated with the two motor positions stored in the first look-up table closest to the sensed motor position, (iii) determining a second motor current value by interpolating between two current values associated with the two motor positions stored in the second look-up table closest to the sensed motor position, and (iv) determining a final motor current value by interpolating between the first and second determined motor current values; and providing a motor control signal in response to said determined final motor current value.

Claim 4

A method for controlling a steering assist system, said steering assist system providing steering assist in response to a steering control signal, said steering assist system including a variable reluctance motor, said method comprising the steps of: sensing motor position by sensing the relative position between the motor's rotor and stator; sensing applied steering torque; determining a desired motor torque assist value in response to the sensed applied steering torque; modifying said desired torque assist value to linearize the gain between said desired torque assist value and motor torque output; providing a plurality of motor torque look-up tables, each of said motor torque look-up tables having a plurality of motor current values that vary as a function of motor position; selecting a first and second torque look-up table from said plurality of look-up tables wherein said first look-up table corresponds to a torque value less than the modified motor torque assist value and said second look-up table corresponds to a torque value greater than the modified motor torque assist value; determining a first motor current value by interpolating between two current values corresponding with two motor positions stored in the first look-up table closest to the sensed motor position; determining a second motor current value by interpolating between two current values corresponding with two motor positions stored in the second look-up table closest to the sensed motor position; determining a final motor current value by interpolating between the first and second determined motor current values; and providing a motor control signal in response to said determined final motor current value.

Claim 6

An apparatus for controlling a steering assist system, said steering assist system providing steering assist in response to a steering control signal, said steering assist system including s variable reluctance motor, said apparatus comprising: motor position sensing means for sensing the relative position between the motor's rotor and stator; torque sensing means operatively connected to a vehicle hand wheel for sensing applied steering torque; motor torque assist determining means for determining a desired motor torque assist value in response to the sensed applied steering torque; modifying means for modifying said desired torque assist value; and a plurality of motor torque look-up tables; control means operatively connected to said modifying means and to said motor position sensing means.