Passive starting of a torque-ripple-free electric power steering system

Abstract

A method for passively starting an electric power steering (“EPS”) system includes disabling assist torque upon power-up, detecting an index pulse upon a movement of a steering column across one of a plurality of reference positions, enabling assist torque for the EPS system upon detecting the index pulse, receiving a variable input torque command indicative of an external steering input, and ramping a variable assist motor torque towards the variable input torque command after enabling assist torque for the EPS system until the variable assist torque is substantially equal to the variable input torque command; wherein an EPS system apparatus includes a steering wheel for receiving operator inputs coupled to a steering column, a motor coupled to the steering column for applying torque assist to the column, an encoder coupled to the motor for determining the angular displacement of the steering column where the encoder comprises at least one track and a set of sensors for sensing the at least one track to generate a set of signals, a controller connected in signal communication between the encoder and the motor for receiving the set of signals from the encoder and controlling the motor in correspondence with a method for passively starting the electric power steering system, the controller comprising an index pulse detector, an enabler responsive to the index pulse detector for enabling an amplifier, and an amplifier for ramping the variable assist torque in correspondence with a variable input torque command.