Fault tolerant control for an electric power steering system

Electric power steering (EPS) systems are rapidly replacing existing traditional hydraulic power steering systems due to fuel and cost savings. Methods to improve the reliability of a column mounted EPS are presented. This is accomplished by introducing a fault tolerant scheme for a torque sensor failure; that is, if the sensor signal is lost, this information can still be obtained and used to maintain the power steering assist function. A motor model based observer is used to estimate the total torque on the motor shaft, combined with an independent estimate of the road reaction torque, in order to calculate the torque sensor output. Hardware-in-the-loop (HIL) results are presented to validate the method under more realistic operating conditions.