Study On Control Of The Nextrac Inter-Axle Coupling For On-Demand All-Wheel-Drive Vehicles

Electric controlled on-demand all-wheel-drive(AWD)system has been more and more popular in city SUVs because of its good performance,simple structure and favorable economy.The control strategy of the on-demand AWD system has a direct impact on the vehicle performance.As the key actuator,the Nextrac inter-axle coupling is the foundation of the control strategy.In this paper,the actuator characteristics and the control strategy of the on-demand AWD system were mainly studied.Firstly,the influence on the power performance and maneuverability for the inter-axle torque distribution were analyzed based on the tire properties and vehicle dynamics.The results showed that,the inter-axle torque distribution could improve the power performance and maneuverability significantly on certain conditions with limits.Then,the characteristics of the Nextrac inter-axle coupling were analyzed.The kinetic model of the inter-axle coupling and the powertrain system in a certain on-demand AWD vehicle were built.The characteristic curve between the control current and the transferred torque of the model was basically identical to the actual curve.An on-line calculated thermal model was built by Matlab based on the theory of heat-transfer.The simulation results of this model were similar to that from Ansys.A simulation platform was built by the Carsim and Matlab,which built a foundation for the development of control strategies.A framwork of control strategy with multiple levels,multiple loading conditions and multiple zones was designed based on the optimum torque distribution and kinematics characteristics.A unified form of the target control torque was proposed.The rules of switching between conditions were designed.Specific control strategies under the straight condition,the steering condition and the getting out condition were designed,with parameters corrected by different control sections.The control strategy was simplified according to the real signal configuration to imporve the feasibility of the control strategy.Finally,the control strategy was verified through the model-in-loop(MIL)simulation,the software-in-loop(SIL)simulation and the hardware-in-loop(HIL)simulation.Then the control software was finally tested on the real vehicle.The results from simulations and experiments were show that,the control strategy of the on-demand 4WD system had an obvious promotion on the vehicle power performance and maneuverability.