Hydraulic power steering in passenger cars : analysis, modeling and new functionality

Abstract: THIS THESIS COVERS various aspects of hydraulic power assisted steering, HPAS, systems in road vehicles. Power steering is viewed as a dynamic system and is investigated with linear and non-linear modeling techniques.With the help of the linear model, relevant transfer functions and the underlying control structure of the conventional power steering system have been derived and analyzed. The non-linear model has been used in concept validation of a new feature that can be added to traditional power steering units in order to increase functionality. This model also has the capability of co-simulation with a vehicle model in order to create realistic tie-rod loads to the power steering model.This thesis treats energy aspects of power steering systems. In order to point out solutions to energy problems, different methods of reducing energy consumption are discussed.The interest for including more functions in power steering systems in road vehicles has increased with the development of new active safety features such as Lane Keep Assist, LKA. The traditional HPAS system cannot meet these new demands, due to the control units pure hydro-mechanical solution. The Active Pinion concept is presented in this thesis, which is a novel concept for controlling the steering wheel torque for future active safety applications. The concept introduces an additional degree of freedom in the control unit. Active safety features are going to play an increasingly important roll in future safety strategies; therefore, it is essential that sub systems, such as power steering systems, in road vehicles are adjusted to meet new demands.