Optimal Desigh Of Monocoques And Research On Handling Dynamics For Electric Racing Cars

With the development of electric vehicles,electric racing has become a sport that grows faster and faster.For the automobile industry,the electric racing competition is not only a speed competition,but also a platform for technical verification.To give full play to the extreme performance of cars,it is necessary to be as light as possible while have excellent handling characteristics.The smallscale electric racing car is a low speed electric car,which is purely driven by electric power.This paper mainly focuses on the lightweight design of the smallscale electric racing car structure and a series of research on its dynamic performance in the driving process.To ensure the performance of car body structure to meet the required strength and stiffness and ensure the lightweight of the car body,this paper proposed and designed a carbon fiber monocoque body for small racing cars.The car body used carbon fiber/aluminum honeycomb sandwich plate structure with pre-embedded block.Based on the theory of strength stiffness of laminates,the equivalent models of carbon fiber sandwich laminate were investigated.The finite element modeling method of carbon fiber sandwich plate was validated by the structural strength and rigidity experiment.The bonding strength between carbon fiber panel and aluminum honeycomb sandwich was analyzed by stripping experiments.To meet the rigidity and strength of sandwich panel,the blocks were pre-embedded into it,which was verified by experiments.In view of the influence of body quality on the dynamic performance of the car such as acceleration,optimization study was carried out on the monocoque body.The torsion stiffness of the car body was first determined as one of the constraints of the optimal design.Then,the minimum quality of car body was set as the optimization goal.The constraint functions include the torsional rigidity and body deformations under such conditions as high speed turning,large angle of attack,braking,and linear acceleration.Based on the approximate models,the car body was optimized with the layer thickness of carbon fiber and the thickness of aluminum honeycomb as the optimization variables.Genetic algorithm and simulated annealing algorithm were used for optimization,respectively.And their optimization precisions were compared with each other.Finally,the simulations of torsional rigidity and modal analysis of the car body were carried out based on ANSYS.To explore the influence of external environment on car's dynamic characteristics,the aerodynamic force acting on racing car and the ground force acting on tire were studied.The strain balance of the airfoil with three-component bar was first designed.The aerodynamic characteristics of the airfoil were verified by wind tunnel experiments based on the computational fluid mechanics,and the simulation model of flow field of the vehicle was then established.The influences of vehicle speed and sideslip angle on the aerodynamic characteristics were simulated.The relationship between the six-component force coefficient and the sideslip angle of the transient flow field was studied.Secondly,based on the full understanding of magic formula and tire data,a piecewise fitting method was put forward which is suitable for dimensionless magic formula.The fitting results under different conditions and the fit coefficient of magic formula 2002 under part conditions were offered.Finally,the dynamic performance of the vehicle was analyzed by the established nine-degree of freedom model.To analyze the influence of the driver's control behavior on the dynamic characteristics of the car,the integrated control model of driver on direction and speed under any path and the time optimal control model of driver were established.Firstly,the driver's control behavior was analyzed.The driver's direction control model applicable to the racing car was established according to the “preview-follower” theory and the improvement of the search algorithm of preview.The longitudinal velocity control model of the driver was also established through feed-forward-PID feedback.Then,based on both the direction and longitudinal velocity control model of the driver and their uncoupling,the integrated control model under any path was established.According to the characteristics of the racing car,the time-optimal control model of the driver was developed.Finally,to analyze the handling dynamics performance of the car under extreme operating conditions,a closed-loop simulation model of driver-race-road was established based on Simulink-CarSim.The improved preview point searching algorithm,the integrated control model,and the time-optimal control model were verified through the simulation analysis under both typical and complex working conditions,which provides a good theoretical basis for future car design and test.To investigate the influence of the previous research on the handling dynamics performance,a complete electric racing car was developed and acceleration and steering stability tests under simple working conditions were also carried out.The research in this paper provides a new idea for lightweight design of racing cars and automobiles.The research of drivers and vehicle models oriented to the vehicle handling dynamics provides a theoretical basis for both the design and calibration of racing cars and autonomous driving.