Investigation of gearbox noise and comparison of varying transfer path analysis methods

Structure borne noises can be transmitted to interior cabin via physical connections by gearbox as well as other active components. Gearbox is connected to body through engine torque rod mount, gearbox mount and engine mount. But also, there are three connections which are chassis cable, clutch pipe and shift cable. Chassis cable is a cable and connected on the body under the battery. Clutch pipe is a pipe which is connected to body through firewall. Shift cable is connected to body through tunnel area where is one of the weak zone of the vehicle for NVH. Experimental Transfer Path Analysis (TPA) Methods are utilized to investigate main paths of vibrations which are eventually perceived as noise components inside the cabin. For identifying the structure and air borne noise transfer paths in a system, Matrix Inversion (MI), Mount Stiffness (MS), Operational Transfer Path Analysis (OTPA) and Operational Path Analysis with Exogenous Inputs (OPAX) Methods exist. In this study, contribution ranking of transmission paths from active system components through the physical connections into the interior cabin are investigated by MI and OPAX Methods. In Matrix Inversion Method, ranking is made by using operational data at passive side, vibration transfer functions from passive side to target and indicators and acoustic transfer functions from passive side to target. To load calculation, operational data and vibration transfer functions are producted. Calculated load at the passive side and acoustic transfer functions are producted to get the contribution of that point to the target. On the other hand, in Operational Path Analysis with Exogenous Method, to calculate the contribution of the points and ranke them, operational data at active and passive side, vibration transfer functions between passive side and target and acoustic transfer functions are needed. Acoustic transfer functions are measured by reciprocally by active the source in the target and measuring the responses at the accelerometers. With using OPAX method, measurement time of transfer functions is decreased. And finally, a comparison of them is presented based on the accuracy of obtained results. The modifications are applied on dominant transfer paths which are determined by the mentioned methods above, respectively. Thus, the accuracy of these two methods are investigated on vehicle level NVH tests while observing the variations in the interior cabin noise level.