A Theory on the Relationship Between Drive Train Vibration and Belt-Driven Engine Cooling Fan Fatigue Failures

Fatigue failures observed in a belt-driven engine cooling fan indicated the presence of significant vibration activity. A testing and analysis program was undertaken in an effort to measure the fan vibration characteristics in a vehicle environment, and relate these characteristics to some known source of excitation. The classical vibration analysis of a fan and fan pulley coupled to a crankshaft pulley by a drive belt commonly predicts the fan to be effectively isolated from crankshaft vibration. The results of this testing program, however, indicated the presence of significant torsional and linear vibration at frequencies that corresponded to crankshaft torsional vibration orders, and thus indicated a complex mechanism of energy transfer through the belt system.