Method and system for fault isolation in an electric power steering system

A method of isolating a fault in an electric power steering system of a vehicle, the method comprising:

• calculating a value for each of a plurality of fault signature components with a vehicle controller;
• comparing each of the calculated values of the plurality of fault signature components to a respective threshold value for each fault signature component, with the vehicle controller, to determine if each of the calculated values of the plurality of fault signature components exceeds its respective threshold value or does not exceed its respective threshold value;
• automatically executing a control action, with the vehicle controller, to indicate a detected fault in the electric power steering system when at least one of the calculated values of the plurality of fault signature components exceeds its respective threshold value;
• and
• comparing a result of the comparison, of each of the calculated values of the plurality of fault signature components to their respective threshold value, with the vehicle controller, to a fault table that relates the results of the comparison to pre-identified faults, to determine if the results of the comparison correspond to a pre-identified fault, when at least one of the calculated values of the plurality of fault signature components exceeds its respective threshold value;
• wherein automatically executing a control action to indicate a detected fault in the electric power steering system when at least one of the calculated values of the plurality of fault signature components exceeds its respective threshold value includes identifying a pre-identified fault when the results of the comparison, of each of the calculated values of the plurality of fault signature components to their respective threshold value, to the fault table correlates to a pre-identified fault.

An electric power steering system for a vehicle, the electric power steering system comprising:

• a steering wheel configured to receive a set of driver steering inputs, including a steering torque and a steering angle;
• a torque sensor configured to measure the steering torque;
• an angle sensor configured to measure the steering angle;
• a steering assembly;
• a steering motor operable for passing a variable motor assist torque to the steering assembly at a torque level which depends in part on the steering angle and the steering torque;
• and
• a controller having tangible, non-transitory memory and operable to execute a set of instructions to:
• calculate a value for each of a plurality of fault signature components, wherein the plurality of fault signature components includes:
• a residual value from a motor circuit equation, the absolute value of the difference between a first self aligning torque value calculated from a tire dynamics model, and a second self aligning torque value calculated from an extended state observer and nominal parameters for the electric power steering system, a variance in the difference between the first self aligning torque value and the second self aligning torque value, an estimated motor resistance in the electric power steering system, an estimated back Electro-Magnetic Force (EMF) constant in the electric power steering system, and a residual value from a vehicle dynamics equation;
• compare each of the calculated values of the plurality of fault signature components to a respective threshold value for each fault signature component, to determine if each of the calculated values of the plurality of fault signature components exceeds its respective threshold value, or does not exceed its respective threshold value;
• compare the calculated values of the estimated motor resistance and the estimated motor back EMF constant to a respective nominal value for each to determine if both the calculated motor resistance value and the calculated motor back EMF constant value deviate from their respective nominal value, or at least one does not deviate from their respective nominal value;
• and
• automatically execute a control action to indicate a detected fault in the electric power steering system when at least one of the calculated values of the plurality of fault signature components exceeds its respective threshold value.