Research On Automotive EPS Hybrid Control System And Its Theory, Design And Realization

Compared with the traditional hydraulic power steering device, Electric Power Steering(Abbr.EPS) has the advantages of safety,energy saving,environmental protection and so on.It has become the mainstream of power steering technology for passenger cars because of the important role of improvement of portability and the enhancement of handling stability and safety.Assist motor,torque sensor and Electronic Control Unit (Abbr.ECU) are the three key components.The core of the controller is control strategy which not only reflects the EPS control functional requirements,the level of adaptive capacity and intelligence as well as the key bottleneck and technology of independent research and development.EPS system is a complex non-linear dynamics containing discrete events and continuous dynamics.The requirements of vehicle steering are high and involve many factors so that has the typical characteristics of hybrid system.It's difficult to adopt a single control strategy to coordinate the conflicts between the performance requirements under different conditions.In this paper,hybrid control theory was applied to the design of EPS control strategy so as to explore the new theories and new technologies to improve the performance of EPS control system.The main research works are as follows:1.Research on the model structure of EPS hybrid control systemThe dynamic model,control structure and hybrid properties of EPS system was analyzed,then the function model structure and realization model structure were established to provide a prerequisite and basis for the dynamic behavior research,design and realization of EPS hybrid system.2.Research on the design theory and method of EPS hybrid control systemThe dynamic behavior of EPS hybrid control system was analyzed and the switched-controller-based hybrid controller was constructed.According to different working conditions,it is divided into assist control model, return-to-center control model and damping control model,and corresponding flexible PID control algorithm,Fuzzy-PID control algorithm, Bang-Bang-PID control algorithm,as well as switching supervisor and stability supervisor were designed.3.Research on the realization technology of EPS hybrid control systemThe implementation program of measure and test of EPS hybrid control system was analyzed,then the reliable matching method and process of EPS motor was proposed.The H-bridge drive device was designed and the realization of control algorithm under any conditions and the switched-controller-based hybrid controller were developed.4.Research on the measures and tests of EPS hybrid control systemThe measure test platform and full-car test platform of EPS hybrid control system were designed,the measures on the motor's operating characteristics and the EPS controller and the full-car tests of EPS hybrid control system were made.The static and dynamic performance and control functions were then analyzed.The results show the advanced nature,superiority and feasibility of the theoretical analysis and engineering application of EPS hybrid control system.In different discrete-driven events,the switching and function of switched controller were effective and could meet the real-time control demand under different working conditions.Compared with the original controller,under the assist control model and flexible PID control algorithm,the improvement of peak and standard deviation of torque was 5.82%and 9.21%respectively in situ steering test,8.50%and 4.52% respectively in lemniscate test,between 4.04%and 5.19%in slalom test, the steering portability was improved and the driver's fatigue was reduced effectively.Under the return-to-center control model and Fuzzy-PID control algorithm,the improvement of final residual angle and stabilization time were 40%and 13.3%respectively in the 30km/h speed,and the head-sway phenomenon was markedly suppressed in the 60 km/h speed. The steering wheel could be close to the center faster and improve the phenomenon of less than or overshoot.Under the damping control model and Bang-Bang-PID control algorithm,the holding steering torque amplitude was improved 7.69%which not only eliminated the steering wheel jitter caused by the motor torque ripple but also improved the straight-line driving stability and rapid convergence.EPS hybrid control system deals with the non-linear,uncertainty operation into a switched controller structure,which reduces the difficulty and enhances the adaptive capacity and intelligent level of EPS system.