Optimization and Enhancement of Oil Supply for Hydrodynamic Slider Bearing through Tailored Surface Effects

Description

The oversupply of lubricant to machine elements is quite common in practice because individualsusually err on the side of caution since an undersupply may result in catastrophic failure of anengine or a machine. However, oversupplying lubricant, particularly to small-scale devices e.g.micro-electro-mechanical systems (MEMS), is more than an issue of wastage because the resistancegenerated by an excessive amount of lubricant may interrupt the running. This study addresses thisimportant issue in two aspects: first, to fundamentally understand the correlation betweenquantity of lubricant supply and the effective hydrodynamic lubrication of slider bearingcontact; and second, to enhance the supply of oil to the bearing contact through tailoredsurface effects, such that the total required volume of lubricant can be optimized.What would happen if only limited lubricant is supplied to the bearing contact? Studies onelastohydrodynamic lubrication (EHL) under limited lubricant supply (usually referred to as“starvation”) conditions show that starved EHL leads to a reduction in overall lubricating filmthickness, which is substantially affected by the lubricant replenishment. The lubricant would flowback to the bearing track while waiting for the next bearing roll- or slide-over. Apart from beingdragged into the bearing contact from the inlet, lubricant can also be locally replenished from thevicinity of the contact by surface effects. Therefore, the use of supplied lubricant can only beoptimized if the lubricating film building and fundamental knowledge therein are understood.Furthermore, our recent studies confirmed that the wettability or spreading capability of oil on asolid surface depends on surface or interfacial properties. Thus, tailored surface effectsgenerated through appropriate bearing surface design may increase the entrainment oflubricant into the contact and reduce side-leakage by improving confinement of thelubricant.The scope of this study is confined to hydrodynamic lubricated flat-on-flat sliding contacts. Theexperiment will be conducted using an optical slider bearing tester. Flat-on-flat conformal contact iscommon in practical engineering and particularly in micro- and meso-scale devices, in whichsurface effects can be dominating due to their high surface-to-volume ratio and any excessivelubricant can be detrimental or even fatal. The study aims to facilitate effective thin filmhydrodynamic lubrication under limited lubricant supply conditions through experimentaland theoretical studies.The most original aspect of this proposed work is the experimental approach to the studyof the tailored surface application in hydrodynamically lubricated bearings under limitedamount of lubricant.When the project is completed, we can clarify the relationship between film building capacityand quantity of lubricant supply, as well as enable desirable lubrication through appropriateinterface design. The knowledge and insight acquired in the project are certainly valuable to thelubrication design of advanced miniature devices and MEMS, which are multi-billion dollarindustries and expected to continue to grow.