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Steering wheel might not be able to return to the center position due to friction torque in the steering mechanism. A return control strategy for the electric power steering using sliding mode approach is proposed in this paper. The sliding mode controller (SMC) is designed based on the rotational dynamics of the steering column. The uncertainties of the system parameters and friction torque are included in the control discontinuity. A trigger rule is also proposed to switch between assist and return controls. Preliminary simulation results show that the proposed algorithm can not only improve the returnability, but also provide the damping compensation.

Electronic Control has been widely used in automotive systems, such as Vehicle Dynamics Control, Anti-Lock Braking Systems, Active Suspension and Steering System control, etc. The rapid prototyping development of an embedded controller for an electronic power assisted steering system (EPAS) will be presented in this paper. A steering model is established in MATLAB/SIMULINK to verify the proposed EPAS in this paper. This model includes the effects of kingpin inclination, caster, camber and lateral offset to calculate the total steering torque. The EPAS control strategy has considered the driver commands and vehicle speed to provide multiple stages of steering torque assistance. TMS320F240 DSP is used as the embedded controller of EPAS. EPAS Control algorithms have been designed using MATLAB/SIMULINK/Real-Time Workshop and Input/Output of Blocksets of TMS320F240 DSP have been developed in SIMULINK.