Method and apparatus for controlling an electric assist steering system using two-dimensional interpolation for current commands

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;
• 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 motor torque assist determining 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 desired motor torque assist value and said second look-up table corresponds to a torque value greater than the desired 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.

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;
• providing first and second torque look-up tables, each of said first and second torque look-up tables having a plurality of motor current values that vary as a function of motor position;
• determining a first motor current value by interpolating between two current values corresponding to the two motor positions stored in the first look-up table closest to said sensed motor position;
• determining a second motor current value by interpolating between two current values corresponding to the two motor positions stored in the second look-up table closest to said 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.

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;
• 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 determined desired motor torque assist value and said second look-up table corresponds to a torque value greater than the determined desired 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.