Abstract
This paper present a new control strategy of an electric power steering system with variable-gear-ratio mechanism, sometime referred to as active steering. Since this system has two functions, i. e. power-assist and variable-gear-ratio, the control input should be carefully designed taking account of those functions simultaneously. A model following sliding mode controller with a disturbance observer is proposed, where the reference model is designed based on a physical system with a desired fixed gear-ratio. The proposed strategy makes it easy to design a controller corresponding to the desired performances.
