Belt Wet Friction and Noise Study

Serpentine belt system has been widely used to drive automotive accessories like power steering pump, alternator, and A/C compressor from a crankshaft pulley. Overload under severe conditions can lead to excessive slippage in the belt pulley interface in poorly designed accessory systems. This can lead to undesirable noise that increases warranty cost substantially. The mechanisms and data of these tribology performance, noise features and system response are of utmost interest to the accessory drive designers. As accessories belt systems are usually used in ambient condition, the presence of water on belt is unavoidable under the raining weather conditions. The presence of water in interface induces larger slippage as the water film in interface changes the friction mechanisms in rubber belt-pulley interface from coulomb friction to friction with mixed lubrication that has negative slope of coefficient of friction (cof) - velocity. The wet friction with negative cof-velocity slope can lead to self-excited vibrations and squeal noise. Conventionally the wet frictions of belts have been characterized by using the test procedure defined in SAE J2432 . Some published literatures presented the noise and tribology properties of wet belt based on the testing on SAE test rig. In this study, a theoretical friction model for wet belt-pulley interface is presented. Based on fundamental tribological principle, the friction model is established by incorporating surface parameters of components of belt and accessory pulley with specific operational conditions according to SAE specification. Good correlation of this friction model with published experimental results is illustrated. The sensitivity analysis of the effects of system parameters including wrap angle and tensions on wet belt friction are presented. The wet slip noise test is conducted on a vehicle and the result is used to identify the spectrum pattern, which is correlated with the published results based on test rig. The investigation is expected to give some insight on how to shift the occurrence condition of the slippage and noise out of the operating range of an engine system.

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See papers presented at Powertrains, Fuels and Lubricants Meeting, June 2009, Florence, ITALY, Session: NVH

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