Study On Prediction Method Of Wheel Dynamic Load During Concept Development Stage

In traditional vehicle development and design philosophy, during the synchronousdevelopment process of vehicle manufacturers and parts suppliers, the performance ofvehicle and component is considered during concept development stage, while the durabilityand reliability are protected during design validation stage. Energy-saving proposes newrequirements of lightweight, which is one of the most important goals of currentautomobile design and development. To achieve this goal, the performance、durability andreliability must be considered at the same time.According to our survey, the main problem that supplier cannot consider durability andperformance simultaneously is that dynamic load of the system boundaries and componentssurrounding cannot be accurately predicted during the concept development stage. The mainreason of the problem is that vehicle dynamic model based on characteristic lack the keyaspects of dynamic load model.In this paper, the wheel dynamic load which is the most urgent need is discussed. Onthe basis of investigation of the status of the relevant models affecting the accuracy of wheeldynamic load, we focus on exploring the modeling approach of wheel dynamic load invehicle dynamic model based on characteristic and studying how to improve the accuracy ofwheel dynamic load during concept development stage. The main contents of this paperconsist of the following five areas.First，the study and improvement of vehicle dynamic model based on dynamic loads.The movement of sprung mass is the basis of the movement of vehicle, and the movement ofother parts is almost described relative to sprung mass. The sprung mass characteristics model is established to lay the foundation for the movement of other parts. Rotating aroundkingpin will make the position and attitude of the spindle change in steering system. For therack and pinion steering system, the characteristics model of rack and pinion steering systemis established. According to theory of roll center, suspension guiding-mechanism model isestablished to accurately calculate the forces and moments transferred to sprung masssystem.Second, pneumatic tire model considered nonlinear characteristic of carcass. Tire ismade from natural rubber、synthetic rubber、fiber、carbon black and so on, plus the combinedeffect of the gas inside, the characteristic of tire carcass is very complicated, which is thewheel model lack of currently. The nonlinear characteristic pneumatic tire model of completefreedom in six directions which can characterize the properties of asymmetry、nonlinearityand hysteresis is established. For the nonlinear carcass model established, the experiment ofsteady-state and dynamic characteristic of pneumatic tire is designed by KC suspension testrig. Assuming vehicle is connected with wheel and suspension in series, the nonlinearcharacteristics of carcass in six directions are isolated according to the deformation of theground and the center of spindle. According to the experimental data, the acquisition methodof the model parameter is researched, and the validity of identification method is confirmedthrough simulation and experimental comparison.Third, suspension bearing characteristic transient model is established. Suspensionbearing characteristic is the characteristic of the suspension as a whole subject shown whensuffered vertical excitation. Traditional suspension bearing characteristic model applied tohandling stability and ride comfort does not consider the friction characteristic of thesuspension or just consider the steady-state friction envelope model only associated with thevertical displacement. Adopting the idea of separation of static and dynamic friction, thesuspension bearing transient characteristic model is established and suspension loads arecalculated by differential equations in real time. For the model established, the static anddynamic parameter identification experiment of the suspension is designed through uniaxialsuspension comprehensive test bench, and the acquisition method of the model parameter is researched.Fourth, hysteresis characteristic suspension KC correction model is established.Suspension rod of different length determines the variation of the suspension kinematics; dueto extensive use of rubber bushing, when subjected to external force, suspension rod willproduce elastic deformation which called compliance. The traditional KC correction modeluse linear or non-linear centerline to describe the deformation caused by kinematics andcompliance. In this paper, Borrowing Fancher formula, hysteresis characteristic suspensionKC correction model is established. To obtain the parameters of the Fancher model with thestep method and experiments often leads to large randomness in the engineering praxis. Aone-time non-linear fitting method to obtain all parameters without estimation is proposed toreduce the calculation error, and the validity of identification method is confirmed throughsimulation and experimental comparison.Last, the research on simulation of wheel dynamic load during concept developmentstage. The correctness of each assembly system is verified by using assembly bench testresults. By the comparison with the results of the actual vehicle handling and stability test,the consistency of the model is verified on the steady-state performance. In other models areguaranteed the same circumstances, the characteristic of key model is changed to comparethe wheel dynamic load, the simulation results show that the key characteristics of the modelaffect the wheel dynamic load significantly, verifying the validity of the model.