Hydrodynamic lubrication

Hydrodynamic lubrication is the lubrication that is achieved by the movement of the oil. The rotation of the crankshaft forces the lubricant to move into the loaded zone of the bearing/crankshaft. As the oil is forced to move into this loaded zone, the pressure increases and it is this hydrodynamic pressure that supports the crankshaft load. As the load increases the oil film thickness is reduced while increasing the hydrodynamic pressure increases the oil film thickness. Hydrodynamic lubrication is present when two components (crankshaft/connecting rods and bearings) are moving at high RPM. The only property of a lubricant that is important in hydrodynamic lubrication is its viscosity. However, viscosity can vary due to the operating parameters of an engine such as pressure/load, temperature and shear forces.