A model was developed to study the elastohydrodynamics and contact mechanics of toroidal Continuously Variable Transmission (CVT) type contacts. The aim is to predict the fatigue life, traction and efficiency of such contacts with the intention of making optimizations based on design criteria and constraints. A generalized Reynolds equation was developed for isothermal, transient lubrication of elliptical rough contacts with mixed rolling, two-dimensional sliding, and spinning conditions, incorporating any non-Newtonian model, roughness asperity isothermal elastoplastic interactions, and a three-dimensional subsurface stress analysis. The output is in the form of film thickness and traction maps, including contact efficiency, three-dimensional stress fields, and, finally, the predicted fatigue lives of CVT contacts, based on the Ioannides-Harris life model. A parametric study reveals the effect of surface roughness, lubricant bulk temperature, contact ellipticity ratio, slide-roll ratio, and contact load on the fatigue life, traction and contact efficiency of CVTs, and allows for design optimizations based on a compromise between life, traction and efficiency.

Issue Section:
Technical Papers
Keywords:
mechanical engineering, automobiles, mechanical contact, modelling, fatigue, lubrication, surface topography, rough surfaces
Topics:
Fatigue life, Film thickness, Fluids, Rollers, Shear stress, Stress, Surface roughness, Traction, Disks, Pressure, Rheology, Spin (Aerodynamics), Temperature, Fatigue, Lubrication, Stress analysis (Engineering), Modeling
1.
Patterson, M., 1991, “Traction Drive Contact Optimization,” Proc. 17th Leeds-Lyon Symposium on Tribology, Tribology Series, 18, Elsevier, pp. 295–300.
2.
Ehret, P., Chevalier, F., Dowson, D., Taylor, C. M., Okamura, H., and Sano, T., 2000, “Traction in EHL Elliptical Contacts With Spin Conditions,” Proc. 26th Leeds-Lyon Symposium on Tribology, Tribology Series, 38, Elsevier, pp. 71–83.
3.
Zou
,
Q.
,
Huang
,
C.
, and
Wen
,
S.
,
1999
, “
Elastohydrodynamic Film Thickness in Elliptical Contacts With Spinning and Rolling
,”
ASME J. Tribol.
,
121
, pp.
686
–
692
.
4.
Dowson, D., and Higginson, G. R., 1966, Elasto-Hydrodynamic Lubrication, The Fundamentals of Roller and Gear Lubrication, Pergamon Press, Oxford.
5.
Elsharkawy
,
A. A.
, and
Hamrock
,
B. J.
,
1991
, “
Subsurface Stresses in Micro-EHL Line Contacts
,”
ASME J. Tribol.
,
113
, pp.
645
–
656
.
6.
Bair
,
S.
, and
Winer
,
W. O.
,
1979
, “
A Rheological Model for Elastohydrodynamic Contacts Based in Primary Laboratory Data
,”
ASME J. Lubr. Technol.
,
101
, pp.
258
–
265
.
7.
Gecim
,
B.
, and
Winer
,
W. O.
,
1980
, “
Lubricant Limiting Shear Stress Effect on EHD Film Thickness
,”
ASME J. Lubr. Technol.
,
102
, pp.
213
–
220
.
8.
Johnson, K. L., 1985, Contact Mechanics, (reprint 1994), Cambridge University Press, London.
9.
Sayles
,
R. S.
,
1996
, “
Basic Principles of Rough Surface Contact Analysis Using Numerical Methods
,”
Tribol. Int.
,
29
, pp.
639
–
650
.
10.
Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P., 1992, Numerical Recipes in FORTRAN, 2nd ed., Cambridge University Press, New York.
11.
Nikas, G. K., 1999, “Theoretical Modelling of the Entrainment and Thermomechanical Effects of Contamination Particles in Elastohydrodynamic Contacts,” Ph.D. thesis, in the Imperial College & Science Museum library and in the Mech. Eng. Dept. Library, Imperial College, London, UK.
12.
Ioannides
,
E.
, and
Harris
,
T. A.
,
1985
, “
A New Fatigue Life Model for Rolling Bearings
,”
ASME J. Tribol.
,
107
, pp.
367
–
377
.
13.
Lubrecht, A. A., Jacobson, B. O., and Ioannides, E., 1990, “Lundberg Palmgren Revisited,” Rolling Element Bearings—Towards the 21st Century, seminar organized by the Institution of Mechanical Engineers (UK), November 16, 1990, pp. 17–20.
14.
Tripp, J. H., and Ioannides, E., 1990, “Effects of Surface Roughness on Rolling Bearing Life,” Proc. Japan International Tribology Conference, Nagoya, Japan, pp. 797–802.
15.
Nikas, G. K., 1999, “Development of a Contact Fatigue Model For Continuously Variable Transmissions,” Technical Report TOR-12/99 (Torotrak Project), Imperial College of Science, Technology and Medicine, Mech. Eng. Dept., Tribology Section, London, UK.
16.
Hamrock, B. J., 1994, Fundamentals of Fluid Film Lubrication, McGraw-Hill.
17.
Newall, J. P., Nicolson, D. M., Lee, A. P., and Evans, S. P., 2002, “Development and Assessment of Traction Fluids for Use in Toroidal (IVT) Transmissions,” SAE 2002 World Congress, March 2002, Detroit, MI, USA, Session: Transmission & Driveline Systems Symposium (Part A)-IVT/CVT, Paper No. 02AC-82.
18.
Anghel, V., 2002, private communication with the author about the results of the Mini Traction Machine (MTM rig) for the traction performance of Santotrac 50, Tribology Section, Mech. Eng. Dept., Imperial College, London, UK.
19.
Chang
,
L.
,
1992
, “
Traction in Thermal Elastohydrodynamic Lubrication of Rough Surfaces
,”
ASME J. Tribol.
,
114
, pp.
186
–
191
.
20.
Evans, C. R., and Johnson, K. L., 1987, “The Influence of Surface Roughness on Elastohydrodynamic Traction,” Proc. of the Institution of Mechanical Engineers (IMechE-England), 201, pp. 145–150.
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