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The Effects of Engine Oil Rheology on the Oil Film Thickness and Wear Between a Cam and Rocker Follower
ISSN: 0148-7191, e-ISSN: 2688-3627
Published October 01, 1996 by SAE International in United States
Annotation ability available
Continued interest in energy conservation and carbon dioxide emissions has resulted in enhanced opportunities for development of fuel efficient lubricants. This fuel efficiency has been achieved to a large extent by reducing viscosity as far as volatility and lubrication requirements allow. There has been much industry activity to assess fuel efficient lubricants without compromising engine durability. One area of potential durability concern is that of the overhead camshaft (OHC) rocker follower configuration widely used in modern passenger car engines. A motored cylinder head from an industry standard wear test having an OHC rocker follower configuration has been instrumented to measure oil film thickness (OFT) in an exhaust valve contact by means of an electrical capacitance technique. OFT measurements over the whole of the active part of the cam cycle are presented using both single and multigrade oils based on a variety of commercially available viscosity index improvers at an operating temperature of 100°C. Using single grade oils the measured OFT over the cam nose region was only slightly dependent on the lubricant viscosity for all test conditions. Under steady state motored conditions metallic asperity contact was absent and the surfaces were separated by an electrically insulating film which was present at all times. These observations would suggest that the dominant contribution to measured OFT is due not to viscosity but to the presence of anti-wear films on the metallic surfaces. The effect of adding VIIs to single grade base oils is to enhance the OFT in the predominantly elastohydrodynamic lubrication regimes in the cam flank regions of the cam cycle. However, little OFT enhancement could be found in the heavily loaded regions outside the cam flank regions when using multigrade oils. There is evidence that at higher camshaft speeds the measured film is composed of a surface film augmented by a small hydrodynamic contribution, however it would appear that the surface films laid down under lower speed conditions are more tenacious than those deposited under thicker film operation. Observed wear maxima on the cam follower surface occurred as predicted at positions associated with extended durations of contact with the cam. An apparent thinning of the film occurs (below that observed with single grade oils) when using lower viscosity multigrade oils, around the same positions in the contact cycle.
CitationWilliamson, B. and Bell, J., "The Effects of Engine Oil Rheology on the Oil Film Thickness and Wear Between a Cam and Rocker Follower," SAE Technical Paper 962031, 1996, https://doi.org/10.4271/962031.
SAE 1996 Transactions - Journal of Fuels and Lubricants
Number: V105-4 ; Published: 1997-09-15
Number: V105-4 ; Published: 1997-09-15
- Dyson A, “Kinematics and Geometry of Cam and Finger Follower System”, Tribology Int, V13, N3, pp121 - 132, June 1980
- Colgan T A. and Bell J C, “A Predictive Model for Wear of Valve Train Systems”, SAE Paper No 892145
- Williamson B P, Galliard I R and Benwell S, “Measurement of Oil Film Thickness in the Elastohydrodynamic Contact Between a Cam and Bucket Follower in a Motored Cylinder Head Part 1 Newtonian Oils”, SAE Paper 892150
- Williamson B P and Perkins H N, “The effects of Engine Oil Rheology on the Oil Film Thickness Between a Cam and Rocker Follower” SAE Paper No 922346
- Heemskerk R.S, Vermeiren K N and Dolfsma H, “Measurement of Lubrication Condition in Rolling Element Bearings” ASLE Trans, Vol 25, No 4, 1982, pp 519 - 527
- Hertz H, J reine angew Math, 1886, 92, 156 See also Cameron, A, “Principles of Lubrication” Longmans Green & Co Publication, 1966
- Galvin G D Naylor H and Wilson A R, “The Effect of Pressure and Temperature on Some Properties of Fluids of Importance in Elastohydrodynamic Lubrication”, Proc Instn. Mech Engrs, Vol 178 Pt 3N, 1963-64, pp283-290
- Kreidl N J and Weyl W A, “Phosphates in Ceramic Ware IV, Phosphate Glasses”, Journal of the American Ceramics Society, Vol 24, no 11, 1941 373-378
- Dowson D, “Elastohydrodynamics”, Proc Instn. Mech. Engrs, Vol 182, Pt 3A, 1968, pp151-159
- Bell J C, “Reproducing the kinematic conditions for automotive valve train wear in a laboratory test machine”, J Engg Tribology, Proc Instn. Mech Engre, Vol 210, 1996, pp 135-444
- Bell J C, Delargy K.M and Seeney A.M “The Removal of Substrate Material through Thick Zinc Dithiophosphate Anti-Wear Films”, Proc 18th Leeds-Lyon Symp on Tribology, 1991, pp 387-396 (Elsevier)
- Bell J C and Delargy K M, “The Composition and Structure of Model Zinc Dialkyldithiophosphate Anti-Wear Films”, Proc 6th International Congress on Tribology, 1993, 2, pp 328-332
- Willermet P A, Dailey D P Carter R.O III Schmitz P J, Zhu W, Bell J C and Park D, “The composition and structure of lubricant-derived surface layers formed in a lubricated cam/tappet contact II Effects of adding overbased detergent and dispersant to a simple ZDTP solution”, Tribology Int., Vol 28, No 3, 1995, pp 163-175