Method development for half shaft joint characterization to predict and evaluate its influence on low idle vibration in vehicle. 2019-01-1558
Method development for half shaft joint characterization to predict and evaluate its influence on low idle vibration in vehicle.
Prasad Vesikar, Saeed Siavoshani, Siemens PLM
Yuan Wei, FCA LLC
In conventional IC engine powered vehicles, engine low idle vibrations of vehicle between 20 to 50Hz range is very common NVH issue. Engine excitations pass through mounts and half shafts to body structure. Half shaft designs are observed to be major influencing factor in managing these low idle vehicle vibrations. Half shaft’s dynamic characteristics are mainly dependent upon the universal joints design in the shaft. To evaluate the half shaft designs for its influence on the low idle vibration in early phase of vehicle program, predictive model of shaft is required to be generated. The shafts at low idle engine running condition are at specific pre load and shafts needs to be characterized under that preload to use in the full vehicle predictive modeling.
Half shaft manufacturers are generally only characterize shaft joints for its frictional behavior however for predictive modeling the stiffness and damping behavior needs to be identified either from measured frequency response functions under or direct stiffness measurements preload conditions. Test bench based characterization of shaft demonstrated many practical difficulties due to boundary condition simulation and FRF measurements. So a vehicle level based in situ measurements where shafts are mounted in appropriate boundary conditions is proposed in the expectations that when this demonstration show high fidelity modeling technique where vehicle level operational data is available for model validation then more efforts will be invested in test bench design for
This work proposed a pragmatic approach to derive shaft joint stiffness in three translational directions in-situ in vehicle. Then build a Frequency based sub structuring (FBS) model of full vehicle with LH and RH half shafts as two sub structure and remaining vehicle without shafts is third sub structure. Vehicle level operational response at seat track as touch point is measured for multiple half shaft designs. Subjective and objective rankings are observed for touch point response. Using transfer path analysis methodology operational loads are computed at transmission bearing to shaft interfaces and shaft to knuckle interfaces. Using the computed loads performed forced response analysis on full vehicle FBS model. The predicted and measured response at seat track was correlated for different shaft designs.
This approach provided a practical method to compute shaft joint translational stiffness in instu condition using FRF and operational acceleration transmissibility. As the shaft and vehicle hardware is available in this exercise the vehicle level model validation was possible. The next step study is underway where using the similar approach on test bench shaft joint stiffness will be computed and used in vehicle level FBS model which will provide ability to evaluate shaft design in early program stage for its influence on low idle vibration in vehicle.