Study On The Vehicle Dynamic Performance Based On The System Of The Front/Rear Suspensions For Rhombic Vehicle

With the development of automobile industry, our country has become a bigcountry of automobile in the world, but China is far from being a power country ofautomobile due to the lack of independent research and development capabilities. Atthe same time, its negative influence has been highlighted following the cars’squantity increasing, and the problems of traffic congestion, traffic accidentsincreasing, fuel shortage and environmental pollution are attentioned more and more.As a new car, the chassis layout of the rhombic vehicle is different fromtraditional rectangular layout. Its four wheels is rhombic arrangement, and the frontwheel and the rear wheel are a single wheel with linkage steering function, the middlewheels are driving wheels, which determines the rhombic car may be difference fromthe traditional form in the design of the general arrangement, suspensions, steeringand brake system. The rhombic vehicle not only has complete independent intellectualproperty rights, but also has the advantage of oneself in remission, improving trafficsafety, saving fuel and reducing the environmental pollution. However, the directreference theory and literature data are comparatively few due to rhombic vehicleunique chassis layout and some structural innovation design. There are a lot ofresearch work to do for achieving the production and marketization. The ride comfort,handling stability, design of the suspensions’ parameters and design of suspension andwheel’s structure are studied in this paper, and the main contents include:The basic structure of the rhombic vehicle suspensions and the system of frontand rear wheels are determinded. According to the particularity of the rhombic chassislayout, the double trailing arm independent suspension is selected as the front and rearsuspensions, and the double wishbone independent suspension is selected as middlesuspensions through comparing the traditional suspensions. The double trailing armindependent suspension is not only applicable to the steering wheel, but also is infavor of reducing vehicle centroid. It can meet the basic requirements of the front andrear suspensions, and the structure of the front/rear suspension and wheels aredeterminded to be useful to the performance analysis and optimization work of therhombic vehicle.The model with fifteen degrees of freedom of the rhombic vehicle ride comfort isestablished, and the influence law to the ride comfort is revealed to analysing the design variables on the random road and pulse road respectively. Based on therhombic chassis layout, the dynamics equations of the ride comfort are deduced indetail and the root-mean-square value of vertical weighted acceleration and maximumvertical acceleration of the driver and left rear passenger through solving theequations are used to evaluate the ride comfort of the rhombic vehicle. The model ofthe ride comfort is a theoretical basis to study the vehicle performance, and theinfluence law of the design variables will provide theory reference to the generalarrangement of the rhombic vehicle.The model with two DOF and three DOF of the handling are built, and theinfluence law is revealed by analysing the design variables. At the same time, thedifference between the models with two DOF and three DOF is discovered throughcomparement and analysis. The model of two degree of freedom mainly considers thelateral and yaw motion, and the model of three degree of freedom considers not onlythe lateral and yaw motion, but also the roll motion. The influence law is analysedthrough the simulation of steady static circular test procedure, steering wheel anglestep input test and steering wheel angle pulse input test. The law will not only providetheory reference to the general arrangement and selecting the suspension parameter,but also lay the foundation to study the handling stability in deeply.The parameters of suspension are designed by the collabrative optimizationtechnology. There is the contradictoriness with the influence to the ride comfort andhandling and stability due to the parameter change of the suspensions. Beforeoptimization, the model of ride comfort and handling with three degrees of freedommust be verificated by the test of the real vehicle. The optimization model of thesuspension parameters is built according to the collabrative optimization afterverification, and the vehicle performance is improved synthetically to a certain extentthrough the optimization. The optimized suspension parameters will guide thesuspension structure design, and provide theoretical reference.The optimization design of the beam is done in structure by using theapproximation modeling. According to the features of the rhombic vehicle, the basicstructure of the beam is determined, and the key design size of the beam is determinedthrough sensitivity analysis. The samples of the beam are built by using the Latinhypercube method. Based on the quality and fatigue life of the samples, theapproximate models of the quality and fatigue life are built by Kriging approximationmodeling method, and the key size is optimization designed with the beam fatigue lifeas constraint condition, the beam quality is minimized as the goal. The design method can greatly shorten the design time and save the design cost for the beam of therhombic vehicle.The study in this paper will provide a theoretical basis to selecting the designparameter selection and designing the structure of the front/rear suspensions andfront/rear wheels, which not only has practical significance to prototype production ofthe rhombic car, but also lays theoretical foundation to the production andmarketization in the future. The study has the big significance to the project.