Research Of Hybrid Transfer Path Analysis Method On Vehicle Ride Performance

With the rapid development of the national economy and the people's living standards,while automotive safety, energy saving and environment protection are pursued constantly,the requirements on the vehicle driving performance are also getting higher, vehicle drivingperformance has become an important indicator of the advantages of local brands cars inthe market competition. During the new model development and the driving performanceimprovement of the vehicles which is already in mass production, the identification, analysisand evaluation of the main transfer path which affect the car's driving performance shouldbe accomplished, and accordingly the effective vibration reduction measures can beproposed to improve driving performance and meet the design requirements, that's one of thekey factors to improve the vehicle capability for market competition. However, the testing oftransfer path analysis has long cycles and high costs, and only after the prototype car isavailable, the tests can be performed. Therefore, how to analyze and exactly identify themain transfer path which affects the driving performance during the vehicle design stage,and then the driving performance can be predicted, to shorten the optimization duration andreduce development cost, it has become an important key to succeed on the market for eachOEMs.This research is completed based on"The research and development of vehicle drivingcomfort in low frequency", which is a project of industry-university joint research. Thepaper aims to analyze the method of transfer pass analysis on vehicle driving performancesystematically and deeply, and then the vibration reduction performances of the maintransfer path are optimized to ameliorate vehicle's driving comfort.According to characteristics of the car analyzed in this paper, all TPA models of wholecar, from powertrain, front suspension and rear suspension to driver's floor are built. Thevehicle test on B lever road is performed to study the car's driving performance. The results show that, with the speed increase, the three dimensional and overall weighted accelerationRMS values of the driver's floor increased gradually. Take speeds of50km/h,80km/h and120km/h for examples, the methods of test transfer paths analysis (test TPA) on drivingperformance is researched. Under three typical conditions, TPA calculation that based onpeaks frequency of the spectrum of driver's floor is finished and each total contributionwhich originated from all transfer paths to target is obtained. A comprehensive method,considering both the amplitude and phase, is proposed for evaluating path contribution. Theresults show that, under the condition of these three typical speeds, the Z-direction andX-direction vibrations of the powertrain right mount has the greatest contribution to thez-direction vibration of the driver's floor in all of the transfer paths, followed by theZ-direction vibration of the front point of the front suspension lower control arm, theZ-direction and Y-direction vibrations of the rear suspension lower control arm.Based on the following issues, the virtual transfer path analysis (Virtual TPA) method ofdriving comfort is presented to overcome these issues: firstly, heavy testing workload of thetest TPA; secondly, it is hard to get frequency response functions of some individual pathsdue to structural constraints which is difficult to knock and excitation; third, the transfer pathanalysis cannot be developed in the product development stage. To utilize finite elementmethod and virtual prototype technology, the rigid-flexible coupling model is set up. Thendriving comfort simulation on B-lever road is analyzed, and compared with the results of thetesting, to verify the correctness of the vehicle virtual prototype model. Using the sameanalysis method with test TPA, the virtual TPA is completed,and considering both theamplitude and phase, the main transfer paths which impact driving performance areidentified. According to the total path contribution and transfer path recognition results,results of test TPA and virtual TPA are compared. The results show that, consequences ofdriving performance transfer path analysis result obtained by these two analysis methods isthe same, and the maximum relative error of peak frequency and amplitude, which is aboutthe total contribution of the powertrain, front and rear suspension, is less than13%Then,the validity of the virtual TPA method is verified. So in order to solve the problems of transfer path lost caused by testing conditionlimitations and vehicle structure limitations, and to avoid some complex test work likedisassemble engine,a new hybrid transfer path analysis method is presented. Using the dataobtained from the virtual prototype analysis, the data of missed transfer path is supplied, andthe complete vehicle model of hybrid transfer path analysis is established, furthermore,results of test TPA and hybrid TPA are compared according the results of transfer pathidentification. Except for the transfer path, front suspension up control arm Z-direction,which didn't get in test TPA due to the structure limitation, it has a lager contribution totarget; meanwhile, other main transfer paths are the same by means of these two methods.So as to eliminate the coherent effects between front and rear suspension because ofroad random vibration, the hybrid TPA result of suspension is calculated after principalcomponents analysis. The results of suspension assembly, which is from the method ofhybrid TPA and test TPA, are compared. It explains that the recognition result of maintransfer path is consistent, and the result shows again that the importance of the path, frontsuspension up control arm Z direction can not be ignored.According to problem paths obtained from hybrid TPA, characteristics of enginemountings and suspension bushings were analyzed. The results show that, to improve thedriving perferfomance, some measures should be implemented. First one is, the vibrationisolation ratio of powertrain right mount is bad and its characteristic should be making better.Second one, the frequency response functions, which are between the target and frontsuspension spring Z-direction, rear suspension trailing arm Z-direction, have influences totarget, so the structure of body should be optimized. Last is, the vibration of target is causedby the operation force of the rear point of front suspension upper control arm Z-direction, thefront point of front suspension lower control arm Z-direction, and the rear suspension lateralZ-direction, so the suspension bushing characteristic should be meliorate.For vehicle dynamic parameters of the vibration damping components, which areidentified in transfer path analysis, the optimization analysis of driving performance basedon TPA method is processed. Taking the driver's floor vertical vibration acceleration minimum as optimization objective, and the stiffness of mount and bushing as designvariables, the optimization analysis of transfer path based on vehicle is processed. Finally,using the optimized stiffness of mount and bushing, the driving performance simulation testsare verified. The results show that, with the improved parameters, this vehicle's drivingperformance is significantly improved, and the optimization results are also verified.