Minimizing Frictional Losses in Crankshaft Bearings of Automobile Powertrain by Diamond-like Carbon Coatings under Elasto-hydrodynamic Lubrication

An efficient powertrain technology contributes to sustainable lowering of greenhouse gas emissions in terms of reducing mechanical losses and saving fossil fuels. Minimization of frictional losses of highly loaded components in automobile powertrain as crankshaft plain bearings and gears offers massive potential for target achievement. Application-related investigations of diamond-like carbon (DLC) coatings ZrCg (a:C-H/ZrCg) and nanocomposite (nc)-ZrC (a‑C:H/ZrC) in lubricated rolling-sliding contacts in twin-disc and gear efficiency test-rig revealed great potential of ZrCg for efficiency improvement in automobile gearboxes by reducing mechanical losses up to 39 % under elasto-hydrodynamic lubrication (EHL) compared to uncoated gears. With regard to plain bearings, ZrCg and nc-ZrC coated modified prototype bearings exhibited a friction advantage of up to 36 % in EHL compared to standard bearings in an engine test bench. This yet largely unknown favorable effect of DLC coatings under rolling-sliding conditions in EHL opening doors to new possibilities in tribology and efficiency improvement was attributed to the thermophysical properties of DLC coatings and was confirmed by simulations of rolling-sliding contacts.