Research On The Lateral Dynamic Stability Of FSAE Racecar Based On The Nonlinear Dynamics

The FSAE Racecar is required to have good lateral dynamic stability to turn a corner oravoid an obstacle as quickly as possible. Under these extreme conditions, the car showsnonlinear characteristics that can’t be analyzed using the classic2-wheel-2-DOF vehiclemodel based on the linear tire force. Therefore, the nonlinear tire force and roll motionshould be introduced to study the lateral dynamic stability of FSAE Racecar in thenon-linear domain. The thesis mainly consists of the following parts:(1) The4-wheel-3-DOF vehicle lateral dynamic model including roll motion isestablished based on the classic2-wheel-2-DOF vehicle model. By comparing the phaseplane portrait and the equilibrium-point bifurcation diagram of the new model with theclassic2-wheel-2-DOF and4-wheel-2-DOF vehicle model，it has been demonstrated thatthe roll motion would lead to the decrease of the stable region on the phase plane, whichmeans the car is more easy to be destabilized.(2) The parameters of the FSAE Racecar are identified through multiple methods. Anew self-adaptable differential evolution algorithm is presented to identify the parameters ofMagic Formula2002tire model, which helps to improve the accuracy and efficiency of theidentification. Besides, the inertial parameters of the suspended part, the unsuspended partof the racecar and the driver are determined through the combination of experiments andcalculation. And to get the whole inertial parameters of the racecar (including the driver),the three parts of parameters are integrated.(3) The lateral dynamic phase plane portrait and the equilibrium-point bifurcationdiagram of the4-wheel-3-DOF FSAE racecar model are plotted to determine the steadystate of the racecar under different inputs. The results show two new equilibrium points onthe phase plane, and the reason for their existence is that the parameter of the systemcharacteristic equation, p, is less than zero, and this is caused by the tire cornering stiffnessthat decrease to zero or negative value under extreme conditions. The model is also used tosimulate one of the dynamic events, the skid-pad, to find the extreme performance of the racecar while it is doing steady circling motion at constant radius. And the racecar withfront tires of10psi (68.94kpa) and rear tires of8psi (55.15kpa) is proved to have the bestlateral dynamic stability. This tire pressure setting make its lap times reduce by5.7%comparing to the original setting and improve the lateral extreme performance.(4) The result of the real test shows that the response curve of the motion-stateparameters from the test is consistent with the curve from the simulation while the racecar isdoing circling motion under a certain input of front-wheel-turning angle and vehiclevelocity, which demonstrates the correctness of the newly-established vehicle model.