Integrated Longitudinal And Lateral Control Of Four-whell-independent-driving Electric Vehicle During Cornering Brake

In recent years,energy crisis and environmental pollution that traditional fuel vehicles brought about are increasingly serious.Electric vehicle have attracted much attention because of energy-saving and environment-friendly.The four-wheel-independent-driving electric vehicle(FWIDEV),which adopts in-wheel/wheel-side motor driving type and simplifies the structure,can adjust the motor torque and the hydraulic braking torque of each wheel to realize the vehicle motion control.It has the obvious over-actuated characteristic and can pursue higher design target,which can improve vehicle energy optimization,driving safety,and control performance.This dissertation studies integrated longitudinal and lateral control of four-wheel-independent-dring electric vehicle during cornering brake from model and system sturcture,wheel torque distribution and upper level's regulation and control.Firstly,this paper analyses the vehicle structure and characteristic.Based on the software ve DYNA,it indicates different torque distribution can influence the vehicle energy optimization and driving safety.Besides,braking control and torque-vectoring control can apparently improve vehicle connering performance.Based on the analysis of control system,hierarchical control structure is designed by introducing longitudinal force and yaw moment as virtual control.The upper level is regulation and control of virtual control,and the lower level is control allocation of wheel torque.The wheel torque distribution is the basis of the whole control system.In order to realize the integrated longitudinal and lateral control,and to deal with the targets of energy efficiency,handling and stability,a two-step optimization based control allocation method is proposed in the lower control level.Considering the energy efficiency requirement,a static optimization method is used for pre-allocation.On account of non-convex characteristic existing in the motor efficiency MAP,pre-allocation accomplishes via offline optimization,which applies to stable driving condition.Considering the slip constraint and wheel dynamic,dynamic re-allocation is used for considering the handling and safety objectives.For the constrained multi-objective optimization,fuzzy control is adopted to computes the weight coefficient,and model predictive control method is used for optimization.This method can avoid complex online optimization and is easy to apply to meet the main control objectives under various conditions.Cosidering simple longitudinal or lateral control can't meet control requirement under special conditions,a integrated longitudinal and lateral control method is proposed.First,the control admissible region and desired dynamics is regulated.Based on the steering constraint and side slip constraint,control admissible region is built to research the relationship between speed and maximum curvature and regulate desired speed.Then,considering the coupling relationship between longitudinal and lateral motion,a sliding mode controller is proposed to compute longitudinal force and yaw moment.Combined with the wheel torque optimization control allocation,it can effectively improve driving safety under extreme conditions.Lastly,Hardware-in-the-Loop simulation is used to verify the control performance combined with different conditions.Simulation results shows the method proposed in this paper can efficiently improve stability and handling performance under steering and braking operation.