Research On The Rollover Stability Mechanism Analysis And Control Strategies Of Vehicles With Mechanical Elastic Wheel

It is well known that automobile rollover is basically typical traffic safety problems and the rollover safety has raised more concerns as the increasing number of fatal rollover accidents.It is necessary to develop the vehicle rollover prediction system and anti-rollover control system to improve the roll stability and avoid rollover accidents,which has been an area of active research in recent years.However,the traditional pneumatic tire exist some defects of instability of pressure,puncture and burst,which are easy to cause rollover accidents in high speed.An innovative non-pneumatic tire called mechanical elastic wheel(MEW)was introduced and have good characteristics of puncture resistance and damage prevention.Aiming at the issue of yaw and rollover stability for off-road vehicles with MEW,several key problems of rollover stability of vehicle with MEW were studied by the combination of theory,simulation and experiment in this paper,which can provide the basis for the tire selection in the vehicle developing phase and the design of active safety system.The main research contents include the following aspects:1.The nonlinear vehicle modeling with MEW was studied.The structural characteristics and working principle of the MEW was analyzed.By simplifying the structure of the MEW,a corrected steady-state combined longitudinal-slip and cornering brush models of MEW is set up.The flat-bed test rig of tire mechanical properties is used to conduct the steady-state longitudinal-slip and cornering characteristics experiment of the MEW,and the mechanical properties of MEW are analyzed based on the experiment results.The evaluation indexes of the wheel cornering characteristics were extracted from the cornering characteristic curve.According to the theoretical and simulation results,the specific impact of structure parameters on cornering characteristics of MEW was analyzed.Finally,a nonlinear off-road vehicle simulation model with MEW is established and the comprehensive performance of MEW was evaluated by matching the whole vehicle.2.The rollover stability of an off-road vehicle with MEW was studied.The cornering properties of MEW to yaw and rollover stability are analyzed based on phase-plane which utilizes yaw rate and predictive load transfer ratio(PLTR)as the yaw and rollover index respectively.To analyze the relationship between MEW cornering properties and vehicle stability,Based on the genetic algorithm optimized BP neural network(GANN),the inverse dynamics model was built,which used the vehicle stability evaluation parameter as the input and the matched tire performance as the output.The results show that as peak value of lateral force increase and lateral stiffness decrease properly,the vehicle can IV achieve a better stability of yaw and rollover.The test sample results show that the forecasting ability of GANN model for wheel cornering characteristics is satisfied,which will be useful for the improvement of cornering performance of MEW and reduce accidents of rollover caused by the improper matching of wheel and vehicle.3.The rollover evaluation index for rollover warning system was studied.A preview point following algorithm by lateral acceleration feedback for arbitrary path is proposed.To achieve a proper preview time for the driver model,a comprehensive evaluation formula that considers the trajectory deviation,the steering wheel rotation speed and lateral acceleration is used.A novel method is proposed to estimate road friction coefficient based on vehicl braking dynamic modele.and sliding mode control technique is used to build the ideal braking torque controller.The vehicle rollover prediction system is achieved through the preview driver model and the rollover prediction index using an improved predictive load transfer ratio(IPLTR).The new IPLTR index can provide a time-advanced measure of rollover propensity and its effectiveness is verified by virtual tests and experimental test data.To enhance noise robustness of the prediction system,the radial basis function neural network(RBF-NN)model is established,which provides a better noise robustness for rollover warning.4.The problems of obstacle avoidance under emergency in path planning and tracking for vehicle rollover safety were studied.An improved ant colony algorithm considering vehicle parameters is introduced for path planning with obstacle avoidance environment.The PID method is improved for vehicle path tracking by introducing motion control containing steering control and speed control.And for the decoupling of the vehicle steering and speed control,the gain of vehicle lateral acceleration for steer angle is updated according to the vehicle speed.The driving speed and steering properties of driver-vehicle model to rollover stability are analyzed.Moreover,some cooperative braking control strategies based on fuzzy PID are added into the motion control to enhance path tracking and handing performance under emergency obstacle avoidance,which utilizes a predictive load transfer ratio(PLTR)as the rollover index and the rollover controller activates only when the potential for rollover is significant.Simulation results show that the proposed control strategy has good accuracy in both path and speed following and has a better stability of rollover under emergency situation.5.An integrated control algorithm of the differential braking and the active suspension to improve yaw and rollover stability of an off-road vehicle with MEW is developed.First,integrated control algorithm based on differential braking is developed.The fuzzy proportional-integralderivative(PID)methodology is adopted by simultaneous control of the yaw and roll moment,and the wheel slip regulator is designed with sliding mode control technique to prevent the wheels from locking.Second,an active suspension control system based on rollover prediction and fuzzy PID is designed for rollover prevention,which utilizes a PLTR as the rollover index and the fuzzy PID controller activates only when the potential for rollover is significant as measured by the PLTR.Finally,an integrated controller with a rollover stability controller(RSC)by differential braking and active suspension and a yaw stability controller(YSC)by differential braking to improve yaw and rollover stability is developed.The proposed controller,based on the idea that makes YSC and RSC work independently first,then unifies by way of weight according to fuzz control.Simulation results show that the integrated control system could could improve the vehicle yaw and roll stability,and prevent rollover happening.