The Study On The Control Strategy Of Electric Power Steering

EPS is a complex multi-input multi-output control system. Present, there aremany aspects need to improve in the assist characteristic and control strategy. Mainly,the EPS can’t provide reasonable assist steering torque in the full speed range, becauseof the blind spot of linear dynamical characteristic curve. The road factors are rarelyconsidered in the research of control strategy. When the road adhesion coefficient isreduced, there will be an accident, if the EPS provide assist steering torque according tothe original assist characteristic curve.For the above two problems, Based on the actual vehicle test data linearcharacteristic curve was established in this thesis according to the relationshipbetween the steering resistance torque, assistant torque, and an ideal steering wheeltorque. We obtained dynamical characteristic curve for full speed range by linearfitting of gain coefficient and vehicle speed, effectively eliminating the blind spot oflinear dynamical characteristic curve. What’s more, we designed a power controlstrategy with self-adjustment. When the road adhesion coefficient is reduced, roadaffect is reduced through real-time adjustment of the assist characteristic curve.Main works are as follows:1) The dynamic mathematical model of each part of the EPS is established in thisthesis depending on the analysis of the structure and parts of EPS.2) Through research of automotive steering torque, we accordingly determine themethod of determining EPS dynamical characteristic curve. We obtained dynamicalcharacteristic curve for full speed range by linear fitting of gain coefficient andvehicle speed, effectively eliminating the blind spot of linear dynamical characteristiccurve. We accordingly obtained more reasonable assist characteristic.3) For the interference of the performance of the EPS steering which is from theroad, we designed a power control strategy with self-adjustment to reduce the roadaffect.4) The EPS control mode judgment is determined according to comparativeanalysis of power control and back control. Then multi-modal control strategy whichconsist of power control and back control is designed.5) Research and analysis of System-related technology was carried out in thisthesis, such as PID control technology, fuzzy adaptive PID control technology, PWM drive technology, Matlab/Simulink, Matlab/FIS and so on6) Exhaustive simulation research on the assist characteristicand control strategydesigned previously was carried out to prove their correctness and effectiveness. Theevaluation indexes were the sensitivity of steering and the road sense.