Metal transfer, film formation and surface temperatures on a cam in an automotiye engine

• Autorzy: Furey M. , Reinholtz Ch. , Vick B.

Warianty tytułu

PL

Przenoszenie metalu, generowanie warstwy smarowej i temperatura powierzchni krzywki silnika samochodowego

• Języki publikacji: EN

Abstrakty

EN

In an attempt to better understand the mechanisms of valve train wear and lubrication, a study was made to connect two earlier observations with a recent theoretical treatment of tribological processes occurring in the highly-loaded cam/valve lifter assembly of an automotive engine. In previous valve train wear studies conducted by one of the authors (MJF), neutron-activated valve lifters were installed in a V-8 engine connected to a dynamometer for basic research and continuous wear measurements. One important discovery was that metal transfer occurred from the radioactive valve lifters to the cam in a narrow strip at the cam nose. This is where calculations of oil film thickness would predict the thinnest film. In a follow-up study using the identical engine but with non-radioactive valve lifters, tests were carried out with P-32-tagged zinc di(C6)alkyl dithiophosphate (ZDDP) under conditions in which this additive reduced valve lifter wear by 90%. After disassembly of the engine, autoradiographs were made of the cams and valve lifter faces. The results were striking, showing significant film formation localized in the region of the cam nose and encompassing the previously-found narrow strip of metal transfer. Zn, Fe, and Ni di(C6)alkyl dithiophosphates-all thermally decomposing completely at around 205-210°C-were equally effective in reducing valve lifter wear in engine tests while more thermally stable Zn dithiophosphates (C13 and aryl derivatives) had no effect whatsoever on valve lifter wear. Since the cam nose represents not only the region of highest load but also of highest sliding velocity, this would correspond to that of highest expected surface temperature in the absence of an EHL or oil film. But the duration of contact at the peak temperature at the cam nose is short. Is there enough time for a protective film-forming reaction to occur? To examine this and other questions, a general theoretical model developed by Vick was applied to a model cam/valve lifter system with varying load, speed, contact geometry, deformation, and presence of an oil film. Specific conditions were selected to correspond to previous engine studies and to illustrate the theoretical distribution of surface temperatures over the entire rotating cam, including time and decay effects. This information was then compared to the two experimental observations. It is suggested that these studies may add to our understanding not only of the wear mechanisms involved but also of tribochemical reactions, including tribopolymerization as an antiwear mechanism, e.g., the "in situ" surface polymerization of condensation-type monomers.

PL

W obszarze wierzchołka krzywki rozrządu silnika samochodowego występują nie tylko najwyższe obciążenia, ale także największe prędkości poślizgu, co prowadzi do najwyższych spodziewanych temperatur powierzchni w przypadku braku elastohydrodynamicznej warstwy smarowej. Jednak czas występowania szczytowej temperatury w okolicy wierzchołka krzywki jest bardzo krótki. Powstaje więc pytanie czy wystarczy czasu dla wystąpienia reakcji tworzącej warstwę ochronną. W celu rozstrzygnięcia tej i innych kwestii ogólny model teoretyczny opracowany przez Vicka został zastosowany do modelowania systemu krzywka-popychacz ze zmiennym obciążeniem, prędkością, geometrią styku, odkształceniem i występującą warstwą smarową. Wybrano dane wyjściowe odpowiadające zrealizowanym wcześniej przez Fureya badaniom eksperymentalnym silników. Określono rozkłady temperatury na całej powierzchni krzywki. Uwzględniając efekty czasowe i zanikania. Porównano wyniki teoretyczne z rezultatami dwu serii badań eksperymentalnych. Zrealizowane studium może uzupełnić naszą wiedzę nie tylko o mechanizmach zużywania, lecz także o reakcjach tribochemicznych - z uwzględnieniem tribopolimeryzacji jako mechanizmu przeciwzużyciowego np. polimeryzacji monomerów typu kondensacyjnego "in situ" na powierzchni tarcia.

Słowa kluczowe

EN

automotive engine; valve train wear; cams; cam wear; valve lifters; radioactive valve lifters; radioactively-tagged zinc dialkyl dithiophosphate; oil film thickness; surface temperature

PL

silnik samochodowy; zużycie mechanizmu rozrządu; krzywka; zużycie krzywki; popychacz radioaktywny; znakowany radioaktywnie ZDDP; grubość warstwy smarowej; temperatura powierzchni

• Wydawca: Stowarzyszenie Inżynierów i Techników Mechaników Polskich
• Czasopismo: Tribologia
• Rocznik: 2007
• Tom: nr 6
• Strony: 87--117
• Opis fizyczny: Bibliogr. 16 poz., rys., tab.

Twórcy

autor

Furey M.

autor

Reinholtz Ch.

autor

Vick B.

• Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061-0238, U. S. A.

Bibliografia

• 1. Furey, M.J., Kunc, J.F.: "A Radiotracer Approach to the Study of Engine Valve Train Lubrication", Lubrication Engineering, Journal of the American Society of Lubrication Engineers, July 1958, pp. 302-309.
• 2. Furey, M.J.: "Film Formation by and Antiwear Additive in an Automotive Engine", American Society of Lubrication Engineers paper No. 58-LC-12, Proceedings, Lubrication Conference, Los Angeles, CA, Oct. 13-15, 1958, pp. 1-9.
• 3. Furey, M.J., Kunc, J.F.: "Radioisotopes in Fuel and Lubricant Research", Paper 6, Section X, 1959 Fifth World Petroleum Congress, New York, pp. 1-14.
• 4. Rothbart, Harold A.: Cams: Design, Dynamics, and Accuracy, New York, Wiley, 1956, Call no. TJ206 .R82, page 147.
• 5. Sandor, G. N., A. G. Erdman, E. Raghavacharyulu, C. F. Reinholtz: "On the Equivalence of Higher and Lower Pair Planar Mechanisms," Proceedings of the Sixth World Congress of the International Federation for the Theory of Machines and Mechanisms, New Delhi, India, 1983. Reinholtz, C. F., S. G. Dhande, G. N. Sandor, "Kinematic Analysis of Planar Higher-Pair Mechanisms," Mechanism and Machine Theory, Vol. 13, No. 6, 1978, pp. 619-629
• 6. Cameron, A.: Basic Lubrication Theory, 3rd edition, Ellis Horwood Series in Engineering Science, Chichester, West Sussex, England, 1981.
• 7. Vick, B., Furey, M.: "Thermal Analysis of Sliding Contact in Systems With Rotary Motion," Proceedings of WTC2005, World Tribology Conference III, Sept. 12-16, 2005, Washington D.C.
• 8. Wolfram, S.: A New Kind of Science, Wolfram Media, 2002.
• 9. Vick, B.: "Multi-Physics Modeling of Tribological Processes Using Cellular Automata," Proceedings of WTC2005, World Tribology Conference III, Sept. 12-16, 2005, Washington D.C.
• 10. Vick, B.: "Multi-Physics Modeling Using Cellular Automata," NKS2006 Conference, Washington DC, June 15-18, 2006. (also submitted for publication in Complex Systems).
• 11. Barwell, F. T., Roylance, R. J.: "Tribological Considerations in the Design and Operation of Cams-A Review of the Situation", in Cams and Mechanisms, edited by J. Rees Jones, published by Mechanical Engineering Publications for the Institution of Mechanical Engineers, London, 1978, pp. 99-109.
• 12. Vichard, J. P., Godet, M. R.: "Simultaneous Measurement of Load, Friction, and Film Thickness in a Cam-and-Tappet System", Report 21, Experimental Methods in Tribology, The Institution of Mechanical Engineers, London, Proceedings 1967 - 68, Vol. 182, Part 3G, pp. 109-113.
• 13. Furey, M. J., Appledoorn, J. K.: "The Effect of Lubricant Viscosity on Metallic Contact and Friction in a Sliding System", Transactions of the American Society of Lubrication Engineers, Vol. 5, 1962, pp. 149-159.
• 14. Furey, M. J.: "Tribology", Encyclopedia of Materials Science and Engineering, Pergamon Press, Oxford, 1986, pp. 5145-5158.
• 15. Furey, M. J., Kajdas, C.: "Tribopolymerization as a Mechanism of Boundary Lubrication", Chap. 7, pp. 165-201 in Surface Modification and Mechanisms: Fricton Stress, and Reaction Engineering, edited by George E. Totten and Hong Liang, Marcel Dekker Inc., New York, Basel, 2004.
• 16. Furey, M. J., Kajdas, C., Kempinski, R., Molina, G. J., Vick, B.: Tribopolymerization, Molecular Design and Further Questions of Interest", Invited Lecture, Proc. of the 4th International Conference on Tribochemistry, Cracow, Poland, Oct. 3-5, 2005.