Experimental design for characterization of force transmissibility through roller bearings in electric machines and transmissions

With the increasing stringent emissions legislation on internal combustion engines, alongside requirements for enhanced fuel efficiency as key driving factors for many OEMs, there are many research activities supported by the automotive industry that focus on the development of hybrid and pure Electric Vehicles. This change in direction from engine downsizing to the use of electric motors presents many new challenges concerning NVH performance, durability and component life. This paper provides an experimental investigation into the measurement of NVH characteristics in these new powertrains, thus characterising the structure borne noise transmissibility through the shaft and the bearing to the housing. A feasibility study and design of a new system level test rig have been conducted to allow for sinusoidal radial loading of the shaft, which is synchronised with the shaft’s rotary frequency under high-speed transient conditions in order to evaluate the phenomena in the system. In the present work, simulations of the rig were conducted using the commercial multi-body dynamics software, AVL EXCITE Power Unit, providing insight to the systems response to different types of bearings such as deep groove ball bearings, tapered roller bearings and the cylindrical roller bearings. Moreover, influence factors such as bearing clearance and the amount of axial bearing preload are investigated. The test rig has multiple novel elements compared to those previously developed. In particular, the rotational speed of the shaft, which significantly exceeds that of previously reported rigs, and the excitation frequency ramp up at the same rate as the frequency of the shaft enabling the phenomena found in Hybrid and Electric Vehicles. The sinusoidal radial load is supplied using a loading device featuring a single load point to minimize undesired excitation effects. With respect to structure borne noise the system response is captured through the vibrational displacement of the shaft and bearing housing.