Estimation of blocked forces from a rear drive unit (RDU) in a test rig fixture

Abstract: In the modern world, vehicle manufacturers are not the sole producer of every component in a vehicle but instead assign different subsystems to various OEMs (Original Equipment Manufacturer). Subsystems such as Rear Drive Units (RDU), Power Transfer Units (PTU), E-drives etc. are developed separately and then integrated into the main vehicle. Integration of such subsystems with the main vehicle requires to be tested each time in order to measure its effects on the overall vehicle. This process highly inhibits the development of such individual subsystems. Hence, in order to reduce testing time while maximizing development time, the component-based TPA (Transfer Path Analysis) is used to predict the effects of each subsystem on the overall vehicle without actual assembly. This method makes use of the “transfer path” which is the path along which a source excites a receiver. In this experiment, the source (active component) is a Rear Drive Unit (RDU) while the receiver (passive component) is a subframe. In this case, the forces exerted by the RDU to the subframe at the contact points are calculated using the FRF of the combined source-receiver system with the measured responses on the subframe. Furthermore, these calculated forces are purely a characteristic of the source (RDU) and entirely independent of what receiver the source may be attached to. These forces are then used to predict the responses on any receiving structure attached to the same source. These characteristic forces calculated from the RDU are called blocked forces. These forces do not require any previous knowledge of the receiving structure. Hence, the primary aim of this report is to estimate and use blocked forces exerted by the RDU to predict responses on the subframe. An additional task was the comparison of predicted responses and measured responses on the subframe.