Key Characteristics Modeling And Performance Optimization Of Composite Leaf Spring For A Light Bus

With the increasing shortage of energy and environmental pollution,lightweight has become the trend of automobile development.The research enthusiasm of lightweight has also been increasing with the rise of new energy vehicles in the international community in recent years.Leaf spring is a key component of the suspension system.Its function is to connect the vehicle-bridge or the wheel to the body,and to attenuate the vibration transmitted to the body and transfer the load and guide,accounting for 10%-20% of the unsprung mass.As an effective lightweight method for leaf springs,composite leaf springs can not only replace leaf springs without losing bearing capacity,but also have significantly higher fatigue life,vibration reduction capability and safety fracture than leaf springs.Moreover,composite leaf springs can reduce the dynamic load of unsprung mass,reduce the damage to the road surface while the vehicle is in motion,and improve the economy,power performance and safety of the vehicle.It has a promising market and the research heat is also getting higher and higher in recent years.At present,scholars are accustomed to using finite element calculation or experimental methods to study composite leaf springs,lacking in-depth theoretical research on various characteristics of composite leaf springs,resulting a long time-consuming prediction of the composite leaf spring characteristics,which hinders subsequent iterative optimization design work,resulting in the design of composite leaf spring difficult to take into account its various performance indexes,limiting the level of design and development of composite leaf springs.In response to this problem,this paper started from composite mechanics,parametric theoretical models for the key static and dynamic characteristics of composite leaf springs such as stiffness,strength,and modality were established,and the damping characteristic was in-depth studied,and then genetic algorithm was used to optimize the design parameters,thus a set of efficient and reliable composite leaf spring design and development methods was established,which shortens the forward design cycle of composite leaf springs and improves the level of forward design.The specific research work includes the following aspects:(1)Type selection design of composite leaf spring.Under the premise of fully considering the loading condition of composite leaf spring,the methods of improving the reliability of composite leaf spring are studied from aspects of forming process,material selection and structural design to ensure that the original leaf spring is reliably " equivalent substitution".(2)Key static and dynamic characteristics modeling.Parameterized theoretical models were established between material parameters,ply parameters,and macroscopic structural parameters and key static and dynamic characteristics such as composite leaf spring stiffness,strength,and modality.The correctness of the models was verified by bench tests,then the sensitivity between the key design parameters and the static and dynamic characteristics was analyzed.Compared with the traditional finite element method,the established parametric theoretical models can greatly reduce the calculation time while ensuring the accuracy,shorten the forward design and development cycle of the composite leaf spring,and facilitate the subsequent optimization;Based on the Ni-Adams model and the bench test,the damping characteristic of the composite leaf spring was studied.The research method of the damping of the composite leaf spring was put forward to provide reference for the damping research of the composite plate.(3)Comprehensive optimization of composite leaf spring performance.Due to the variety of design variables of the composite leaf spring,the scale of the optimization design problem is huge,which leads to the dramatic increase of the optimization problem solving time.In order to solve the problem of inefficiency of large-scale optimization of static and dynamic characteristics of composite leaf spring,this paper,based on the established theoretical models of static and dynamic characteristics of composite leaf spring,used genetic algorithm firstly to optimize the ply angle and the length of the plies to find the spring body configuration parameters that maximizes the strength and minimizes the mass.Then the key static and dynamic characteristics such as stiffness,strength and modality were optimized to optimize the configuration parameters of the spring body,and the configuration parameters were mapped to the parameters of the ply scheme,which greatly reduced the number of optimization variables and improved optimization efficiency,and an efficient optimization design method for composite leaf springs that fully considers various design parameters and each performance index had been established,and the key design parameters of composite leaf springs had been optimized to achieve the best overall performance.(4)Fatigue performance optimization design of composite leaf spring.Firstly,based on the fatigue failure law of composite materials,the derivation of fatigue failure of composite leaf springs was proposed and verified by bench test.Then several concepts of ply scheme structure,such as sandwich unit,ply capacity,capacity offspring and barrier distance,were put forward.Based on genetic algorithm,the ply sequence of composite leaf spring was optimized,and the fatigue life of the composite leaf spring was greatly improved.Based on the fatigue failure law of composite joints,and combined with the characteristics of composite leaf springs,the fatigue performance of the joint structure of composite leaf springs was designed,and the joint fatigue bench verification test was adopted.(5)Composite leaf spring on board test verification.The possible changes in the performance of the vehicle after replacing the steel leaf spring with the composite leaf spring were analyzed.Combined with the on board test,the results showed that under the premise of the same rigidity,the handling stability and ride comfort of the vehicle after loading the composite leaf spring were changed little,while fuel consumption was reduced;The reliability of the composite leaf spring was tested by road test.The results showed that the designed composite leaf spring has excellent performance and meets the requirements of loading reliability.