Mechanical Drive Components Bearings Lubrication Gears and Gear Trains Chain and Belt Drives MAE 156A

2 Bearings Ball bearings are appropriate for applications that require smaller sizes and lighter loads; roller bearings are typically used in larger sizes and for heavier loads. Roller bearings are better suited for shock and impact loading conditions. As you might expect, bearings have very low friction coefficients. Bearing TypeCoefficient of Friction Single-Row Ball Spherical or Tapered Roller0.0018

MAE 156A 3 Bearing Reliability The reliability function for bearings (ball and roller) is reasonably modeled using a Weibull probability distribution.

MAE 156A 4 Examples of Bearing Reliability Ball Bearings (SKF Industries) Tapered Roller Bearings (Timken) Normalized Life (L/L 10 ) Reliability Rating Basis

MAE 156A 5 Lubrication Low viscosity lubricants provide better heat transfer and lower viscous friction in applications where the relative speed is high and loads are low. If the loads are high, low viscosity lubricants may be expelled from the contact surfaces. Thick-film or Hydrodynamic lubrication (no surface contact) Boundary lubrication (surface contact) Mixed lubrication Desired operating point

MAE 156A 6 Gear Forces and Torque The tangential force component (W t ) is called the transmitted load.

MAE 156A 7 Simple Gear Train The angular velocities of a pair of gears are inversely proportional to their respective number of teeth. Gears 3 and 4 are idler gears

MAE 156A 8 Chain Drives The 1880's “safety bicycle” has its pedals postioned closer to the ground than the penny-farthing (direct drive) bicycle that it eventually replaced. Recommended Not Recommended Probably not a safety bicycle...

MAE 156A 9 Belt Drive Length

MAE 156A 10 Chain Drive Length The length of a chain used in a chain drive must result in an integer number of links. ceil => round up to nearest integer

MAE 156A 11 Further Reading Shigley, J.E., Mischke, C.R., and Brown, T.H. (eds), Standard Handbook of Machine Design, McGraw-Hill, Lingaiah, K., Machine Design Databook, McGraw-Hill, Rothbart, H.A., Mechanical Design Handbook, McGraw-Hill,