Research On Control Mechanism Of Active Steering And Steering Feeling Of EPS System With The Interference Of Active Steering

As a driver-vehicle interface, steering system is a key subsystem of vehicle, which directlyinfluences vehicle handing stability, comfort and driving active stability. On the base of existingElectric Power Steering (EPS) system, researches on the realization, control mechanism, and steeringfeeling of active steering not only can give full play to assist performance of EPS, but also canimprove the deficiency of stability control of EPS system by active steering control. Then, goodsteering characteristics can be obtained and driving active stability can be improved. Thus, thesestudies have important theoretical significance and engineering value. The detail research works arelisted as follows:(1) At the beginning of the dissertation, a review of different power steering systems integratedwith active steering was presented. Recent developments of key technologies for active steeringcontrol, estimation algorithms of vehicle yaw rate and side slip angle, as well as steering feeling ofEPS system were described. Problems of existing research at home and abroad were found out, andsolutions were put forward to solve these problems.(2) An electro-mechanical structure of EPS system integrated with active steering was proposed,and mathematical model of electro-mechanical coupling for steering system and vehicle was built.According to the dynamic analysis of double planetary gear train, as well as performance analysis ofthe steering system such as steering feeling, steering sensitivity, and stability, the problem whetherneed to change installation position of torque sensor or add an additional torque sensor was solved intheory. From the view of the road information feedback, steering feeling affected by theelectro-mechanical parameters of active steering actuator, and the interference conducted by activesteering were analyzed. A basis for the study of steering feeling for the EPS system with theinterference of active steering was provided.(3) Dynamic model for EPS system with no interference of active steering was built, and transferfunction from steering resistant torque to the output of torque sensor was derived. Furthermore, theeffect of assist ratio on steering feeling was qualitatively analyzed. According to the frequencycharacteristic of EPS system, two weighting functions were chosen. Based on H∞control arithmeticand Linear Matrix Inequality (LMI) approach, different feedback controllers were designed with theeffect of two types of combination for weighting functions, and the effects of different weightingstrategies on steering feeling were analyzed. Simuliation results indicate that perfect steering feelling can be obtained by interaction of the two weighting functions.(4) In view of the effects of character speed on vehicle stability, and demand of steering wheelangle for maneuverability, two control programs of varied steering ratio were proposed to keepsteering gain constant. To investigate the different control programs of varied steering ratio,driver-vehicle-road closed-loop system was built. Based on Linear Matrix Inequality approach, arobust PID controller of angular position tracking was designed for Brushless DC Motor (BLDCM).Then, simulation testes of single lane change maneuver were carried out, comparative analyses of thetwo control programs of varied steering ratio were conducted in two aspects, steering wheel angle andpath tracking. Simulation results show that the second control program has better integralperformance than the first one.(5) Coordination strategy for varied steering ratio control and yaw rate control was presented,and yaw rate control was investigated with the reactive of varied steering ratio control. Based onLinear Quadratic Regulator (LQR) optimal control theory, yaw rate controller was designed.Simulation testes in limiting conditions were conducted to verify the effectiveness of the proposedcoordination strategy and the yaw rate controller.(6) Transfer characteristics of angular displacement transmission is changed with the interferenceof active steering, which gives rise to the problem that internal corresponding relations betweenvehicle state and steering wheel angle are also affected. Then, a research scheme that vehicle yaw rateand side slip angle are considered as nonlinear mapping of time series of pinion angle and lateralacceleration was put forward. An estimation algorithm based on Adaptive Neuro-Fuzzy InferenceSystem (ANFIS) was proposed to estimate vehicle yaw rate and side slip angle. To verify theestimation accuracy and generalization of the proposed estimation algorithm based on ANFIS,simulation and actual vehicle test data were used, as well as comparative analyses were conductedbetween the performance of the estimation algorithms based on ANFIS and Radial Basis Function(RBF) neural network respectively. Results indicate that the proposed research scheme is effective,and the generalization of the estimation algorithm based on ANFIS is better than that based on RBFneural network.(7) To solve mutations of steering wheel torque with the interference of active steering, twofeed-forward assistant torque correction strategies for assist motor were presented, which can be usedto carry out feed-forward assistant torque correction control for assist motor of EPS system in thewhole speed range, and not limited to the assist ratio takes value in zero when vehicle speed exceedsthe assist speed region. Meanwhile, in view of the evaluation methods of transient characteristics for step response, two evaluation indexes were put forward to make quantitative comparison of the twofeed-forward assistant torque correction strategies. Results indicate that the correction controlprogram based on the output of torque sensor can achieve better control performance than that basedon vehicle model, and has better adaptability of vehicle speed.(8) Based on virtual experiment technology, three-dimensional model of the EPS systemintegrated with active steering was built by the CAD module of UG software. To verify the transfercharacteristics of torque and angular displacement for the proposed EPS system, as well as theeffectiveness of the assistant torque correction strategies, analyses on kinematics and dynamics of thesteering system were conducted by using CAE module of UG software. To validate the effectivenessof the proposed coordination strategy and the yaw rate controller, virtual testes in limiting conditionswere conducted based on CarSim software.