Study On Assisted Torque And Control Method Of EPS For Coach

Electric power steering (EPS) is a new power steering device developed rapidly in recentyears and is definitely the developing tendency of modem vehicle steering system.Foragreeing with three themes of vehicle:safety,and environment protection recourses saving,the research and development of EPS have some practical and long-term significance.However,the available EPS technologies are not applicable completely to commercialvehicles,especially to the coach and the truck.The EPS's application on large and mediumvehicles is rarely reported in documents and literatures,and currently there are severalscholars home and abroad begin their exploring in this fields.In order to enhance marketcompetitiveness and to adapt to the advancement of the times,research and development tosome key technologies of EPS on large and middle commercial vehicles are worth to be done.So researches on some key technologies of EPS for the coach are done in this paper,which issupported by Traffic Science and Technology Research Fund of Shaanxi Province(07-21K)-"The Research and Development of Electric Power Steering (EPS) System forCommercial Vehicles".These researches included the study on models used to compute powerassisted torque and lateral force of front wheels based on control theory more accurately,andthe quantitative revelation and study on change law of power assisted moment,and the studyon the selection methods and control strategies of motor.1.The total steering torque is obtained by reference models of steering torque about EPS,rather than torque sensor used in current technology.A binary quadratic model about tirecornering stiffness is presented and some vehicle handling and stability models as a part ofreference models are constructed respectively based on systems identification,processidentification and neural network.Using these models the needed total steering can be getduring steering under different condition.In the course of modeling,an evaluation way ofnetwork model precision that used prediction results of models is presented.Then testvalidations are conducted on those models and ways.The results indicate simulation valueand test value have higher consistent degree,and these three models have high simulationprecision,so these presented ways are feasible. 2.A way to determine the relation between hand wheel torque and power assisted torquewith some rates is presented.Using a T-S model and fuzzy inference,these rates differentlyunder different speed and loading condition of vehicle are integrated and a 3d surface whichrepresented the relation between rates and different conditions is obtained.According to therelation between hand wheel torque and power assisted torque,different assist characteristiccurve in different conditions can be gained.Using some rates and their corresponding speedand loading of coach and so on several conditions,some simulations are done.The simulationresults show that the better road feel,portability and good tracing property could be obtainedwhile steering was steady during steering,and that the slope of assist characteristic curveaccompany with hand wheel torque is increased.So the assist characteristic and the proposedmethod are relatively ideal.3.A three-phase asynchronous motor with strongly nonlinear and strong couplingcharacteristics is used to provide assisted torque and an adaptive control method for motor ispresented,which is different greatly from DC motor used in current EPS.The adaptive controlmethod is to divide motor operating range into 20 minimal intervals firstly,and then to designdifferent H_∞robust controller for every intervals,and to integrate the 20 controllers into anadaptive controller using a T-S model finally.In state equations of controller,the total 12elements of coefficient matrix,control matrix and output matrix are represented by 12 3dsurfaces differently,and can be represented by 12 query tables.According to the differentmotor condition,these matrix elements can find out the most suitable parameter in theirrelated 3d surface or query tables and can make control effect of controller to realize optimum.The control performance of controller is verified by simulation.The results indicate that theerrors between electromagnetic torque of motor and loading are that less than 0.5Nm underwithout loading mutation,and less than 2Nm without motor parameters perturbation while themax error is less than 4Nm with 30% motor mostly parameters perturbation under loadingmutation.Also the error can always close to zero in 0.02 second after loading mutation.It is tosay that the adaptive controller has favorable control performance and robustness,and it canrestrain loading and the change of motor parameters to make great effect on EPS.So,EPSwould feature stable and reliable performance-and can provide favorable assisted torque during life limit.Also the proposed control method is better.4.An observation model of rotor flux of asynchronous motor is represented based on aT-S model and fuzzy inference.So the current model more accurate in low motor speed andthe voltage model more accurate in high motor speed can be transit smoothly.