Enhancing End-of-Line Defect Classifications and Evaluating Early Testability for Inline Test Stands Using NVH Measurements

Production lines for electric drives consist of successive assembly steps. The highly integrated topology of the unit can lead to complex faults caused by poor components or incorrect assembly. To minimize the added value of a bad motor, a noise-vibration-harshness (NVH) measurement is performed on an in-line test bench (IL). Following the IL, other components (gearbox, inverter, …) are assembled, resulting in a finished electric drive unit. The final state is again tested by a NVH measurement on an end-of-line (EOL) test bench. A novel approach is presented that combines the results of both test benches into an overall picture, thus creating a contextual environment for the EOL. Depending on the interaction of the two test benches, different implications are derived. An identified defect on the EOL can be further classified by deviations already present in the IL test. Deviations that are not present on the IL also indicate processes between the two test stands and thus increase the ability to correctly classify defects on the EOL. If deviations are present on the IL, an indicator of significant testability is derived. This can be further used to accurately detect defects that were previously only detected on the EOL.