Research Of Suspension K&C Character And Its Influence On Full Vehicle Based On VPT

VPT (Virtual prototype technology) has already became the important tool using in automobile product development. It is the main methods to shorten the duration of R&D , reduce the cost of development, enhance the quality of product. Through using VPT in automobile product development, especially preliminary pre-development, may understand the product performance in advance, avoid developing risk. Virtual prototype technology bases on the multi-body system dynamics, including computer graphics, control and optimal theory etc. Virtual prototype technology has been commercially developed abroad for many years and several products such as ADAMS have been introduced to engineers.Based on the project:"Car Chassis Integrated Development Platform and Research on Its Key Technology", the dissertation conducted quite comprehensive and thorough research on suspension K&C as well as full vehicle performance using VPT, parametric modeling technology,FEA method, sensitivity analysis method and experiment optimization techniques.1. Parametric modeling of suspension and its K&C characterParametric modeling of suspension may construct specific parameter suspension virtual prototype conveniently. It provided a contrast analyze platform for different structural style suspension, as well as identical structural style and different parameter suspension.The dissertation studied the second development process in the platform of UG by using UG/OPEN API language and parametric modeling of suspension was done by UG/OPEN API and C, C + + language. By parametric modeling ,it can be finished to carry out the fast parametric design for main components of typical suspensions, which include double wishbone suspension, Mcpherson suspension, five-link suspension. Based on this work,a primary platform has been built up for car suspension system CAD modules, on which it can be put up to improve the original suspension system and design a new suspension.Expatiated the definition and research contents of suspension K&C character. Analyzed the mechanism of suspension K&C influence on full vehicle character.Comprehensively analyzed the loading method for the research on suspension K&C.Based on these, introduced simulation methods for the research on suspension K&C character. These methods including: parallel wheel travel simulation,reverse wheel travel simulation, single wheel travel simulation, roll simulation and load simulation. Finally,summarized suspension parameters to evaluate kinematics and compliance character.2. Suspension orientation machine influence on suspension character and optimizationIn structure design of suspension ,hardpoint position of the virtual prototype ofen be modified repeatedly by manpower .Then carry on simulation analysis.But, this way should do much repeated work, and the conclusion is not always best.Using DOE function of ADAMS/Insight and sensitivity analysis method can greatly improve the optimization efficiency.First,based on the developed car suspension system CAD modules, the dissertation constructed a double wishbone suspension virtual prototype. Carried on parallel wheel travel simulation to the virtual prototype and finded out the most sensitive coordinate of the hardpoints that affect the suspension character. Took coordinate of the hardpoints as design parameters which will be used in the following optimization design.Camber,toe,kingpin inclination,caster,wheel track were as optimization aim.Constructed optimization aim and constraint function of each suspension K&C character .Then,done optimization design of single objective to make each suspension K&C character meet to the design requirement.Second ,according to sensitivity analysis results,chosen design parameters of multiple objective optimization design.Each design parameter took different discrete values and done design of experiment, then, the design spaces were done automatically by ADAMS/Insight and begin the simulation calculation.Finally, the calculating results were optimized by filtering the design spaces.Third,in order to illustrate suspension and full vehicle parameters which affect anti-dive angle, established vehicle longitudinal stability model when brake and the ideal anti-dive angle was infered. Introduced reasonably choose principle and method of anti-dive angle.Then,utilized the suspension virtual model , studied influence on vehicle longitudinal stability impacted by position of the suspension arms axis.3. Rubber bushing modeling and suspension compliant movementBecause of the large usage of rubber bushing and the increasing of the vehicle speed, influence of suspension compliant movement on full vehicle steering character becomes very important. And rubber bushing modeling is the most important and difficult problem in the research of suspension compliant movement. The dissertation applied systematical research on the problem of rubber bushing modeling.Analyzed the features of some typical bushing models based rate character, pointed out their disadvantages, such as difficulty of solving rate coupling issue, unable to be used to study the influence on suspension compliant movement by the shape, material and install direction of the rubber bushing, plenty of test will be done for modeling.First,Ran the parallel wheel travel simulation to the virtual prototype respectively when bushing stiffness was different numerical value.The results of simulation test were compared.Analyzed the influence on wheel alignment parameters, wheel track,wheel rate owing to changing bushing stiffness.The results showed that the variational rules of wheel alignment parameters, wheel track ,wheel rate along with the changing of bushing stiffness.Increasing the bushing tran-stiffness values, the suspension kinematics characters have a little change; Decreasing the bushing tran-stiffness values ,the suspension kinematics characters have more change; Increasing the bushing rot-stiffness, wheel rate have distinct change.Studied sensitivity of influence on suspension K character impacted by bushing main directional stiffness.Based on sensitivity values, the bushing direction which have bigger influence can be finded out quickly.At the same time,summarized the variational rules of sensitivity values along with bushing stiffness,and point out increasing the bushing tran-stiffness,sensitivity value of bushing tran-stiffness vs. suspension K character become bigger;Decreasing the bushing tran-stiffness,sensitivity value of bushing tran-stiffness vs. suspension K character become smaller;Increasing the bushing rot-stiffness, sensitivity value of bushing rot-stiffness vs.wheel rate become bigger.Second ,proposed the idea of flex-body rubber bushing model and introduced the features of the flex-body rubber model fitful to research on suspension compliant movement: 1 The model can be easily used for research on suspension C character and full vehicle performance impacted by material, shape and install direction of the rubber.2 Modeling needs only material and shape of the rubber, and leaves out the plenty of tests.3 The model includes all directional rate character, and has a high precision.Next, explained the basic theory for flex-body modeling.After a detailed analysis on the constraints surface of bushing metal, interface nodes, modal extraction and other key issues,a flex-body rubber bushing model was established which is suited for suspension compliant movement simulation and analyzed its modal shapes.Then, carried on simulation analysis to the main directional stiffness character of the rubber bushing by single direction loading in ADAMS/view ,and the stiffness character of simulation and test was compared. The results showed that the flex-body model well expresses the deformation of the rubber, and have a satisfactory accuracy. Finally, studied C character of suspension rigid-flex coupling model due to the lateral force.4. Suspension K&C character influence on full vehicle handling stability and ride comfortFirst,stablished full vehicle rigid-flex coupling virtual prototype model including flex-body rubber bushing model, steering system, power transmission, tire and body etc.Next,introduced the definition and evaluation parameters of steady circular response.Elaborated the system and parameters which influence steady circular response. Discovered the factors which influence steady circular response embarking from steady circular response inherent laws.Analyzed influence on steady circular response with emphasis impacted by suspension and new distribution of vertical load on left and right wheel. Through establishing four wheelers mathematical model, analyzed vehicle parameter which influence distribution of vertical load on left and right wheel.Pointed out that changing front and rear suspension roll rate will affect distribution of vertical load on left and right wheel,and steady-state characteristic will be changed.Then,carried on simulation analysis to the full vehicle model. Studied influence of front and rear suspension roll rate on steady circular response.At the same time,steering wheel angle step input test,low speed returnability test ,high speed returnability test were done.Second,explicitly explain the mathematical principle of influence on vehicle steering character impacted by suspension compliant movement by the vehicle double-track movement model with toe angle variety.Discussed the influence on the suspension compliant movement and the vehicle steering character by changing the material of front and rear suspension rubber bushings. Carried on simulation analysis to the full vehicle model.The result showed that:Decreasing the material Young Module of rubber bushings in the front suspension will change the C character of the front wheel toe angle due to the lateral force, and can increase the under steering character of the vehicle;Decreasing the material Young Module of rubber bushings in the rear suspension will change the C character of the rear wheel toe angle due to the lateral force, and can decreas the under steering character of the vehicle.Third,introduced the generation of random roads. The full vehicle model simulated on the random road and pulse road. Established a set of virtual test platform for suspension nature frequency test, and carried on corresponding virtual experiment to the full vehicle model using the virtual test platform. Researched on the full vehicle transfer characteristic. The factors of influencing vertical vibration were analysed, including suspension stiffness, damping and so on.On the analysis of pitch motion, studied influence on pitch motion with emphasis impacted by vehicle speeds, total base,and the analysis were made on the factors of influencing pitch motion, including undamped natural frequency and damping of suspension.