4TH International Congress on Technology - Engineering & SCIENCE - Kuala Lumpur - Malaysia (2017-08-05)

Effect Of Lubricant Formulations On The Friction Performance Of Diamond-like Carbon (DLC) Coated Direct-acting Valve Train Components
Nowadays, government legislators and environmental authorities are demanding automotive manufacturers to produce tribologically-advanced and environment-friendly vehicles. These demands can be met to an appreciable extent by using bio-based lubricants in combination with diamond-like carbon (DLC) coatings. Chemically-modified vegetable oils such as palm trimethylolpropane ester (TMP) are one of the potential candidates to substitute conventional lubricant base oils. In this study, tribological compatibility of conventional lubricant additives [glycerol mono-oleate (GMO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP)] with TMP and tungsten-doped DLC coating (a-C:H:W) has been investigated for cam/tappet interface of direct-acting valve train system of commercial passenger car diesel engine. For reference, polyalphaolefin (PAO) was used as conventional base oil in both additive-free and formulated state (PAO+GMO+MoDTC+ZDDP). Cylinder head test was carried out for 2 hours at camshaft speed of 1200 RPM whereas lubricant temperature and pressure were maintained at 90ºC and 2 bars respectively. Engine head was instrumented with strain gauges and giant-magneto resistive sensor to measure frictional torque and rotational speed of the tappets respectively. Above-mentioned key tribological performance parameters of uncoated cam-tappet pair were measured in the original environment of the engine and values were compared with those of a-C:H:W-coated cam/tappet interface. High rotational speeds of tappets were observed when a-C:H:W-coated components were used irrespective of lubricant formulation. Delamination of coating was observed when a-C:H:W-coated tappets and cam-lobes were used in combination with additive-free base oils.
Rehan Zahid, Masjuki Haji Hassan, Riaz Mufti, Abul Kalam, Mahendra Varman,