Stiffness Injection: A Tool for Vehicle NVH Performance Optimization

Vehicle Acoustic Prototyping in the low to mid frequency range commonly relies on the knowledge of the excitation forces generated by the vibration sources like tires and powertrain. It is current practice to measure the excitation as blocked forces either on a component test bench or using an inverse method on the vehicle itself. In both cases, the measurements are performed with (pre)selected bushings. Since the bushing stiffness results of a trade-off with other performances, like handling and durability, it is most likely that the final bushing stiffness will differ in a later or final design from those used during source excitation testing. As a result, estimating the impact of bushing stiffness changes on the vehicle’s acoustic performance becomes a major challenge in the NVH design process. It is the aim of the presented Stiffness Injection method to provide the sensitivity of the bushings stiffness to the responses at the driver’s ears. This is achieved by introducing extra (virtual) spring / damper elements between the connection points at both the active and passive side of the bushing using the Virtual Point Transformation and experimental Substructuring technique. Overall this results in a cost-effective way to optimize the bushings for NVH purposes. After an academic experimental validation, the limits of the approach are discussed from a theoretical and robust system design point of view. Finally, an industrial application will be presented.