Influence of water evaporation on the power loss behavior of cylindrical gears lubricated by aqueous polyalkylene glycols

Abstract Aqueous polyalkylene glycols have demonstrated superlubricity in model and gear tests. One challenge for its application in gearboxes is water evaporation and absorption. This study investigated the influence of water evaporation and absorption of aqueous polyalkylene glycols on the power loss behavior of cylindrical gears. To this end, a back-to-back gear efficiency test rig was used. Two aqueous polyalkylene glycols with water contents of 20 and 40 wt% and ISO viscosity grade 22 were considered. The results show that the power losses increase with increasing evaporated water, depending on the circumferential speed. The sensitivity of the power loss to water evaporation is greater at higher initial water contents. Even though the sensitivity of the load-dependent power loss factor is a maximum of +0.060 1/wt%, the load-dependent power loss remains low compared to conventional lubricants. The increase in power loss due to water evaporation is reversible by adding the evaporated water. Monitoring and control of the water content is favorable, especially for water contents which differ significantly from the hygroscopic equilibrium. The accumulated energy dissipation is strongly influenced by the no-load power loss. In order to exploit the superefficiency potential of aqueous polyalkylene glycols, the no-load accumulated energy dissipation has to be reduced.