A robust Transfer Path Analysis method for steering gear vibrations on a test bench

This paper presents a Transfer Path Analysis (TPA) method to predict the transmission of steering gear vibrations of BMW vehicles in a multi-kHz range. The blocked-force TPA concept is used, allowing the active steering system to be measured separately from the vehicle. Compared to classical TPA methods, the blocked-force approach offers possibilities for component-wise optimisation and rapid evaluation of design changes. Crucial for the blocked-force TPA method is the correct determination of the dynamic forces and moments at the interface between the steering gear in operation and the test bench. Using a Dynamic Substructuring approach, various procedures are derived that theoretically lead to the same interface loads. The first procedure relies on direct force measurement corrected for test bench flexibility; the second on a matrix-inverse procedure on an assembly level. By comparing their results before proceeding with the TPA, one is able to make a robust estimation with a good grip on the uncertainty. The operations to obtain the required dynamics of the active component, the test bench and its assembly are reported in a step-by-step way. Quality indicators are introduced for each step in the analysis. The presented methods are validated by means of a comparison with the acoustic levels that were measured directly in the car under the same operational conditions.