Dynamics of high-speed cooling systems in clean energy vehicle under rigid-flexible coupling: combined modeling, vibration analysis, and experimental validation

Cooling system is a core component for vehicle's powertrains to output smoothly and maintain a satisfying noise, vibration, and harshness (NVH) performance. However, advances in clean energy vehicle brings a high requirement for its cooling systems design due to new issues such as the increased heat load, dynamic variations, high-speed vibrations. In this paper, by thoroughly checking the effect of rigid-flexible coupling, we examine the vibration problem in the cooling fans under various external excitations. First, an analytical model is established featuring the structural characteristics of the fixing frame and the fan blades. Then, modal transition is applied reducing the complex kinetic expression, and a time-invariant system model is derived with multi-blade coordinate transformation. Stability and bifurcation analysis are performed regarding different excitation couplings from the rotor, powertrain, and road. The results of the simulation and experiment illustrate that all degrees of freedom (DOFs) are divided into two groups including symmetrical and asymmetrical types and the amplitude is dependent on the coupling natural frequency closest to the excitation frequency. The results also imply the great potential on the optimization and control of the high-speed fan's vibration for the clean energy car.