*2.2. Load*

Viscosity does play a critical role in determining load-carrying capacity in fluid film hydrodynamic bearings. Load-carrying capacity is directly proportional to viscosity and operating speed and inversely proportional to the square of film thickness.

For EHL (ElastoHydrodynamic Lubrication) conditions, due to the nature of the contact of the roller elements and the race—Hertzian by nature—the elastic deflection of mating surfaces significantly influences the load being driven by the material properties of the bearing vs. the viscous-elastic properties of the oil phase in grease. For a Newtonian oil, the following equations govern the film thickness [12,13]:

$$\text{LINE CONNTACT: (h\textsubscript{o}/R)} = \text{(2.65 G}^{0.54} \text{U}^{0.7}\text{)/W}^{0.13} \text{ (Downson, 1970)}\tag{1}$$

$$\text{POINT CONATACT: (h}\_{\text{o}}/\text{R}\_{\text{x}}) = 3.63 \text{ U}^{0.68} \text{ G}^{0.49} \text{ W}^{-0.073} \text{ (1 - e }^{-0.68k}\text{)}\tag{2}$$

where viscosity is contained within the Speed Parameter (U) and load is contained within the Load Parameter (W). In EHL conditions, the film thickness is minimally affected by the load, as seen by the magnitude of the powers for each W shown in the equations.
