NVH improvement of the BEV transmission by altering bearing mounting arrangement.

As per metaphor, “The squeaky wheel gets the grease” the transmission of battery electric vehicle (BEVs) gets topmost attention in terms of NVH improvement. While the engine is getting replaced with an almost silent electric motor, the transmission noise appears persistent and demands more silent transmission. This has raised demand for improvement in design as well as manufacturing quality. Various innovations are being done to drive an improvement in the NVH. Following paper will discuss the improvement in NVH achieved through a design innovation in the way bearings are installed and demonstrated a significant amount of improvement. We have used SMT MASTA used as a simulation tool to predict the expected results and a Transmission Dyno test bench in an anechoic chamber to test the NVH performance on physical sample. The innovation was done on a small single speed two stage reduction gearbox coupled with a 100 NM, 14000 RPM battery electric motor. Though the bearings have comparatively lesser contribution in the overall NVH performance, it plays a significant role in reducing the magnitude of gear noise by altering the way it transmits the reaction forces to the housing. The impact of this can be observed in advanced gear simulation tool using MASTA in terms of reduced transmission error (TE), reduced gear misalignment and vibrations. Actual testing of the prototype sample in anechoic chamber demonstrated the expected improvement of reduced NVH in terms of 2 to 6 dB(A). Additionally, this arrangement of bearing also helped in balancing the wear of both bearings on a shaft and overall increase in the duty cycle. Axial and radial forces distribution over the bearings were altered, it showing overall 25% less damage for a given duty cycle, or same amount of extended life maintaining at the previous damage level.