| Electric power assisted steering (EPAS) is the future of power steering technology. EPAS has the advantage of smaller volume, lighter weight, simpler structure, easier installation and maintenance, lower consumption, better environmental protection. Additionally, it possesses high-level performance such as ensuring different steering feel owing to adjusting steering assisting force according to vehicle speed, which enables it fit for many kinds of vehicle such as car, truck etc. A lot of external famous automobile companies have adopted this kind of steering system and it is necessary for automobile industry of our country to master this high-tech as soon as possible. Therefore, it is of great importance to study and develop this kind of steering system.This dissertation aims to study the modeling, dynamic analysis, control of EPAS and the rules of vehicle handling dynamics, to make a theoretical basis for the design and development of EPAS, to reduce the gap between our country and the developed countries and promote the internal research level on EPAS. This dissertation makes some advance on these following aspects:After a kinematical and dynamical analysis and comparison between two assisting mechanism schemes——worm gear mechanism and planetary gear mechanism schemes, their effects on steering performance such as steering response and steering feel were investigated and their difference were compared using an example. Then some conclusions were drawn, which are useful for application of EPAS to different kinds of vehicles.By the analysis of formation principal of steering torque and the factors affecting it, combining with a vehicle handling dynamic model, a steering dynamic model and an experiential model of tire cornering characteristics, a relative perfect dynamic steering torque model was built. The influence of several factors such as vehicle speed, difference of two front wheel steering angle and tangent force of front wheel on steering torque was investigated by some computation examples, which made a theoretical fundamentals for steering assist curve's design and control method's research.By the dynamic analysis of each part of EPAS including assisting motor, torque sensor and PWM (Pulse Width Modulate) module, a dynamic model of EPAS was built and further transformed to a state-space model which is more fit for control.Several indices such as steering sensitivity and steering feel to evaluate the handling performance of the combination system including EPAS system and vehicle handling system were put forward and their expressions were deduced after the integral analysis of vehicle's handling dynamics and EPAS' dynamics. Having investigated the effects of several factors such as gear ratio of the assisting mechanisms and moment of inertia of the motor etc. on these indices, a stability criterion was built. Finally, based on the restrictions of stability criterion and maximize the object function of steering feel, an optimization model of EPAS system was built and an example was presented.After a principal of steering assist curve design were proposed, a design method, considering steering feel and vehicle handling stability, was put forward and were applied to design of two kinds of steering assist curve—linear and nonlinear assist curve. And the steering feel's expressions for these two kinds of assist curve were deduced and the restriction on the steering feel was proposed, which made the EPAS' applications more practical.After consideration of the difficult problems in design EPAS controller such as the uncertainty of the control object, noise of the torque sensor and disturbance from road, a design method based on Multi-sensitivity method in H-infinity control theory was put forward and the controller was designed. Then the validity of this controller was evaluated by comparison with an ordinary Lead-Lag controller.A simulation software base on MATLAB/Simulink to analyze the performance of the integral system of EPAS system and vehicle system was independently developed, which...
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