Acoustic end-of-line testing of gearboxes and its correlation to the human acoustic perception of gearbox noise in vehicles

Like many other components in the automobile industry, transmissions have to pass an end-of-line (EOL) testing prior to their delivery and installation in vehicles. Originally, the EOL-testing was designed to discover mechanical assembly errors of the gearbox components itself or to identify defects on single gears. However, the EOL-test is nowadays also used for the prediction of acoustic comfort in vehicles. Gearboxes with high acceleration levels on the test rig are assumed to cause high airborne gear harmonics in the passenger compartment. Due to the focus on functionality, the EOL-test usually does not always cover all vehicle-sensitive parameters like rpm range or load. Audible gearbox harmonics may occur in vehicles, whereas the gearboxes themselves were unremarkable on the EOL test rig. To ensure the acoustic comfort of vehicles, different measurements on EOL test stands and in vehicles were undertaken as base for further correlation analysis. The achieved data is recalculated in form of single value correlation coefficients between vehicle and test rig at same operating conditions and between different sensor positions during one measurement.