Study On Integrated Vehicle Dynamics And Energy-saving Optimal Control Of An Eight In-wheel Motored Vehicle

As the “more lighter,more maneuverable,more flexible” becoming the main thought of army and concept of “All-Electric Combat Vehicle”(AECV)putting forward,wheeled armored vehicle driven by in-wheel motors becomes the hot issue of military vehicles.Taking a “Twelfth five-year” national defense pre-research project as background,an eight in-wheel motors driven electric vehicle is chosen as the research object.Because of a significant increase in the number of electronic control subsystems in this vehicle,the integrated control of these active control subsystems to achieve better performances is becoming an urgent research topic.Besides,integrated vehicle dynamics and energy-saving optimal control are also becoming the key research points of vehicle dynamics control and energy optimal control in recent year.Based on the vehicle dynamics theory,this paper established a hierarchical and coordinated vehicle dynamics integrated control strategy to control an eight wheel independent drive/brake/steer electric vehicle.Combining the reconfigurable design of control allocation,a hierarchical integrated vehicle dynamics and energy-saving control strategy is proposed.Evaluation of the overall system is accomplished by off-line and real-time simulation testing under various adverse driving conditions.A full nonlinear vehicle model with 22 degrees of freedom(DOF)is established for the research of stability control strategy.Comparing with the real vehicle testing results,the broad fidelity of the Simulink model is confirmed.Based on the Freescale MC9S12DP256 B hardware platform and dSPACE AutoBox real-time simulator,a controller hardware in the loop(HIL)simulation test platform is built.Besides,a 2DOF linear model of an four-axle vehicle is established,and based on which,the static-state and transient response characteristics is analyzed.These laid the foundation for the study of the integrated vehicle dynamics and energy-saving control.To deal with the characteristics of the over-actuated,underdetermined and actuation constraints of the eight in-wheel motors driven electric vehicle,this paper adopts top-down modular control structure to fully consider driving,braking and steering control subsystem.Based on the structure,a coordinated vehicle dynamics control(CVDC)strategy is proposed,in which tire nolinear saturation characteristics and actuator constraints can be directly taken into consideration in the control allocation.According to the CVDC system and reconfigurable design of control allocation,a hierarchical integrated vehicle dynamics and energy-saving control strategy is presented,in order to improve the vehicle stability and,meanwhile,to reduce the energy consumption.Besides,a drive mode selection subsystem is established,in which the special cases including the failure of some in-wheel motors and different tire-road friction coefficient of each tire are given fully consideration.In terms of the overall integrated and coordinated control system,firstly,based on G-G diagram,a moderated particle reference(MPR)model and an adaptive ? moderator,which can be used in linear and nonlinear area of vehicle,is used to provide vehicle reference states based on driver commands.Secondly,the nonlinear sliding mode control method with strong robustness is adopted to establish the high-level vehicle motion controller,in order to provide generalized control forces/moment.Thirdly,the force allocation subsystem using control allocation optimally distributes the vehicle-level forces and moments to each tire with the consideration of tire friction limits and other constraints.And fixed-point method and active-set method is used to resolve the optimization based control allocation progrmming with actuation redundancy and constraints.This is the key part of the CVDC system.Finally the low-level actuator regulators are used to track the desired slip values.The resulting vehicle states are then fed back to the high-level controller to close the loop.Based on the HIL simulation test platform,the feasibility and robustness of the overall system is verified.The results of HIL test shows that the CVDC control system combining with MPR model and adaptive ? moderator can expand the vehicle driving region to nonlinear friction limits,and can effectively guarantee the vehicle stability and active safety particularly under friction limits.And it also verified the reconfigurable design of CVDC system.In addition,the hierarchical integrated vehicle dynamics and energy-saving control strategy is able to meet the real-time computation requirement in the real controller,and can achieve better energy-saving performance on the premise of vehicle handling stability.