Acoustic emission of gearboxes at end-of-line testing and in vehicles
Akustische Emissionen von Getrieben auf end-of-line-Prüfständen und in Fahrzeugen
Prior to their delivery, gearboxes are checked at End-Of-Line (EOL) test rigs. These tests mainly focus on the correct function of the drivetrain itself, where there is also paid some attention on the acoustic emission behavior. Due to the very complex vibrational behavior of a vehicle transmission, the EOL test can only give evidence for crucial acoustic failures, e. g. defects on single gears or malfunctions during the shifting process. After a gearbox passes the EOL test, it is no longer assumed to cause any remarkable air-borne gear mesh harmonics in the vehicle. However, there are some transmissions, which are fairly louder in the vehicle compared to the statistical average. The effect of dominant gear mesh harmonics in a vehicle can be induced by many influence parameters (different working conditions compared to the EOL test rig, vehicle transfer path variations), which nowadays cannot be perfectly predicted by the acoustic EOL test. To overcome the problems of not always perfect correlation between EOL and vehicle acoustics, different measurements on EOL test rigs and in vehicles were undertaken as base for further correlation and statistical analysis. Single value correlation coefficients between vehicle and test rig acoustic behavior are the base to expose their acoustic relation. In a second step, the air-borne gearbox noise inside the passenger compartment has been tried to predict by several acceleration signals on the gearbox surface and of the car body at dominant transfer paths. Furthermore, the subjective acoustic performance (acoustic grade) in the vehicle is connected to characteristic numbers, which were calculated from sound pressure levels in the passenger compartment.