Modeling and compensating friction in power steering

Achieving steering feel that is independent from the inherent mechanical friction is a requirement that prevails in modern electric power steering (EPS) development. Friction affects both the vehicle performance (objective) and the steering feel (subjective). The motivations in reducing and ultimately canceling friction are a simpler development and tuning of the EPS control. This paper proposes a control strategy for the compensation of the friction in a column-assist EPS (C-EPS). It is based on a model of the column, which includes the slip and load dependent friction of the reduction gear. Experimental results on a mass-produced C-EPS validate that the closed-loop performance is similar to that of a linear, frictionless system.