CAE Cooling Module Noise and Vibration Prediction Methodology and Challenges

In the NVH domain, the cooling module is an important subsystem in ground vehicles. Recently, with the development of small high output turbocharged internal combustion (IC) engines, cooling module noise and vibration has become more challenging. Furthermore, with plug-in hybrid electric vehicle (PHEV), in some cases the cooling fan could be operational while the IC engine is not running. This poses a significant challenge for cabin noise enhancement. Small turbocharged IC engines typically require higher cooling capacity resulting in larger fan size designs with higher speed. Accurate prediction of the unbalance loads generated by cooling fan and loads transferred to the body are critical for the Noise Vibration and Harshness (NVH) performance of the vehicle. If the NVH risk of cooling module operation is not well quantified and addressed early in the program, attempts to find solutions in post launch stage could be very expensive and not as effective. In this paper the static unbalance of the fan and motor assembly was studied and the influence of the coupled unbalance was investigated. The results of static unbalance loading, coupled unbalance loading and the combination of both unbalance loadings were compared to measurement data. Furthermore, the bushings of the cooling module, which are typically made of hyper-elastic materials, have a stiffness which is frequency dependent. The influence of modeling the bushings with a constant stiffness value was studied in great details and in contrast, frequency dependent rates for the bushings were used in modeling to quantify the effect of two different models. The noise and vibration CAE results were compared to measurement data and conclusions and recommendations were made based on the best correlation.