Research on Vibration Control of Light Bus Based on Improved Operational-X Transfer Path Analysis
|Keywords||OPAX Transfer path analysis Light bus Vibration control FEM|
NVH (Vibration、Noise and Harshness) is the comprehensive problem to measurevehicle comfort, which is closely related to customer impression and assessment for vehicle.With the living standard improving, NVH performance standard is rising. TPA-Transfer PathAnalysis, as a research method for NVH, has been widely applied to noise source andvibration source positioning for 20 years, being widely accepted abroad, but uncommon inchina.TPA has derived a lot of methods in practical application. Among them conventionalTPA is generally acknowledged as the most precise one and others are developing based on it.However, the disadvantage of long modeling period and hard test workload restrict its wideapplication. OPA is proposed to improve modeling efficiency. The measure has theadvantage of short modeling period but it’s easy to lose path or make erroneous judgment ofpath contribution amount. To overcome the defects, OPAX is proposed. The method isderived on the base of the TPA and it includes the advantage of OPA. It’s a method with themodeling precise of TPA and modeling efficiency of OPA. At present, the research on OPAXis pretty limited and its engineering application is rather rare at home and abroad.Further research on Operational-X TPA is the goal of this work that was relied on thecooperative project“A light bus NVH performance improving”of Jilin University and anenterprise. In the paper, the advantages of Operational-X TPA over conventional TPA andOperational TPA have been proved from the theory and test, and the theory of conditionnumber and coefficient of determination was introduced to Operational-X TPA to improvequality criteria. On this basis, the OPAX empirical formula was put forward through a lot oftests and applied to a light bus to study on contribution of transfer path. Improvementmeasures were implemented and the results prove that vibration was attenuated and theempirical formula is effectively for NVH problem. The main contents of the paper are as followed:1. The research status of the TPA is summarized in the paper and the basic theory ofTPA, the frequency response function theory and the coherence function theory areintroduced. The theoretical basis of the TPA, OPA and OPAX is detailedly exposited and theadvantage and disadvantage of the methods are introduced. For instance, TPA has highprecise but long modeling period and OPA has high modeling efficiency but poor precisionwhile OPAX is a method with precision and efficiency. The modeling process，parametricworking load model and scalability of the POAX are introduced. The theory of conditionnumber and coefficient of determination, being used as the indirect and direct quality criteriais introduced and the theory proof is given.2. For further illustrating the advantages of OPAX, the conventional TPA model、Operational TPA model and OPAX model of engine mount and exhaust suspension werebuilt and the identification precision of FRF、operational loads and contribution of transferpath and the time consuming of three models were contrasted. The results show that OPAXhas great precision and efficiency and can be applied to NVH problem preferably.3. Based on the above work foundation, the paper makes patulous research on OPAX.The OPAX could not only make quick judgment with less parameters but also could improvethe structure precision by using the complex model in the practical application which isknown as scalability. However, the problem of how to build OPAX model using lessparameters by the premise of guarantee of getting high result precision always puzzles theresearchers. To solve the problem, a lot of tests of four parameters related to the OPAX resultprecision have been conducted. The condition number and coefficient of determination asindirect and direct quality criteria is introduced in the paper and OPAX modelingexperiential formula which could guild the engineering is summarized. The workload ofOPAX modeling is decreased by the premise of guarantee of getting high result precision.4. For illustrating the correctness and applicability of the OPAX empirical formula, theOPAX model was built and the analysis on contribution of transfer path was carriedaccording to a light bus vibration problem in speed of 90km/h-110km/h. The results confirmed that the transfer path of rear suspension--car body has the most contribution. Tounderstand characteristics of the transfer path, the modal simulation and experiment wereconducted and first three orders modal was confirmed as the reason of bad characteristics ofthe transfer path. To understand characteristics of the operational loads, the rear suspensionexperiment was conducted and the coupling between tire rolling excitation and the rearsuspension offset frequency was confirmed as the reason of bad characteristics of theoperational loads. Finally, the coupling of tire rolling excitation、the rear suspension offsetfrequency and the first three orders modal of body was confirmed as the reason of the lightbus vibration problem. The research results of this paper show that the OPAX empiricalformula is correct and can be applied to NVH problem preferably.5. The improved scheme is made based on the analysis results of the OPAX. First,changing a new tire tread pattern and making the radial runout test and dynamic balance testmake it satisfy the technical requirements and reduce the input of the excitation energy. Then,combine the FEM analysis results with improved measures made by manufactures, and theimproved method is verified in FEM model and verified by modal test in the vehicle whichwas installed with a sample piece. At last, the sample vehicle is made by using all theimproved measures. The test of the original and improved vehicle is made respectively andthe improved measures are improved effective.In this paper, the OPAX has been researched deeply and applied to a light bus vibrationproblem for the first time. A complete theory and procedure of OPAX application in NVHproblem was proposed. The results of this paper have great practical value and referencesignificance to similar problems.