A model for predicting transmissibility in driveshafts

Noise Vibration and Harshness (NVH) performance is an important indicator used in the “Customer Satisfaction” category in the automotive industry. The powertrain, that is usually composed of the engine and the transmission, driveline, axle and exhaust subsystem, is one of the major sources of excitation in the vehicle, because it transmits vibration energy to the passenger compartment through structure-borne and air-borne paths. A V-model, that is cascading the overall performance of the vehicle down to the components, has been developed to break down the NVH performance. The aim of the analysis is to identify the components that have the dominant contribution regarding transferring noise and vibration in the passenger cavity. Therefore, a Transfer Path Analysis (TPA) is carried out in order to decompose the vibration or noise measured into different transfer systems representing different components. Hence, the measured vibration is the sum of the contributions from the different transfer path. This work of thesis takes place after the identification of the driveshaft as the most dominant contributor for the booming noise. To address this topic, the driveshaft has been introduced and the definition of the transmissibility and the booming noise have been provided. Subsequently, the basic concepts of metrology have been illustrated as the theoretical base for the experimental activity. Two existing models for predicting the transmissibility have been explained and tested experimentally revealing their limitations. On the basis of these findings, a new model has been developed to overcome the issues and the limits.