Research On Tracking Performance And Torque Distribution Of Virtual Orbit Tramcar

With the rapid development of China’s economy,the urban transportation unfolds multiple development trends.A new way of urban transportation which takes consideration of energy,resource and traffic convenience is presented on the basis of automobiles and subway.The new mode of urban transportation is called the tramcar on the basis of rubber wheels and virtual orbit technology.The tramcar belongs to a kind of unmanned intelligent vehicle driven by four wheel hub motors,which is large capacity like rail transits and maneuverability like automobiles.Autonomous tracking and drive control are the key technologies of the virtual orbit tramcar,the study on the virtual orbit tramcar includes the following contents:Firstly,a two-dimensional mechanical model of maneuvering stability and seven-degree freedom vehicle model are established,and the vehicle dynamic performance and handling characteristics were studied.What’s more,the force analysis of "magic formula" tire model in different work conditions was made.Secondly,a control model which considers the influence of road geometric characteristics on tracking effect is built.The road geometric characteristics are described by geodetic coordinates,road curvatures and road widths of driver’s desired path,which are showed in a way of discrete numerical tables.According to highway route design theory,a model which is about the influence of road curvatures and road widths on ideal longitudinal speed is established.On the basis of that,preview follow theory is used to track the arbitrary path.Thirdly,a computing method about tracking error of arbitrary path is presented to describe the actual track capacity,and the tracking error which is statistical optimizing parameter is as the evaluation index of tracking.According to the large tracking error phenomenon in the working conditions of large curvature road sections,the optimality criteria of vehicles tracking error is presented to optimize the route tracking effect.The ideal longitudinal velocity is modified according to tracking evaluation index,and the revised steering wheel angle is calculated.The correction factors in different ranges of velocity are obtained from optimality criteria of tracking error,and it can be applied to optimize tracking effect on the working conditions of large curvature routes.Finally,a torque distribution algorithm of all wheel drive on the basis of path tracking is established.The kinematics and dynamics parameters of vehicle is obtained from the good working conditions of tracking,and the torque distribution algorithm is set up on basis of the optimal problem which is focus on adhesion coefficient of tire.The method can calculate the transient force values of four tires.The reverse tire model which takes consideration of"magic formula" tire model is applied,and the calculated transient force values can calculate the slip rates and slip angles by the reverse tire model,which can decide the four wheel steering angles and drive torques instruction.In conclusion,the research on the tracking performance and torque distribution algorithm of virtual orbit tramcar can provide theoretical foundation and technical support to manufacture of virtual orbit tramcar.