Pitting behaviour of different gear oils by using a rolling four ball test configuration Jens Johansson a* Mark T. Devlin b Jeffrey M. Guevremont b Braham Prakash a a Luleå University of Technology, Sweden b Afton Chemical Corporation, Richmond, USA 10 th November 2011 Outline • Motivation for this work • Experimental • Results – Effects of oil properties and additive chemistry on pitting life – Pitting mechanisms in rolling four ball tests – Pit formation vs oil parameters • Conclusion • Future Work
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Pitting behaviour of different gear oils by using a rolling four ball test configuration
Jens Johansson a*
Mark T. Devlin b
Jeffrey M. Guevremont b
Braham Prakash a
a Luleå University of Technology, Sweden
b Afton Chemical Corporation, Richmond, USA
10th November 2011
Outline
• Motivation for this work
• Experimental
• Results– Effects of oil properties and additive chemistry on pitting life– Pitting mechanisms in rolling four ball tests– Pit formation vs oil parameters
• Conclusion
• Future Work
Engine output
Motivation – Energy Losses
Accessories(10%)
Transmission (6%)
Axle(6%)
Braking(14%)
Coast and Idle(16%)
At Wheels(48%)
Possible optimization, without sacrificing durability?
Data taken from:W.J. Bartz, Gear oil influences on efficiency of gear and fuel economy of cars, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. 214 (2000) 189-196.
Motivation – Energy Losses
Possible optimization, without sacrificing durability?
Effects of oil properties and additive chemistry on pitting life
Pitting mechanisms in rolling four ball tests
Gear oil samples and their salient properties
Oil Kinematic Viscosity @100C
(cSt)
High Shear
Viscosity @125C (mPa*s)
Boundary Friction
Coef@130C on
steel
EHD Friction Coef @125C,
1m/s 50N, 4%SR
EHD Film Thickness
@100C & 1 m/s (nm)
R 14.42 6,28 0.110 0.030 106
S 14.36 6,65 0.111 0.013 85
T 13.94 6,47 0.158 0.029 105
U 13.88 6,52 0.158 0.013 89
V 9.53 4,55 0.112 0.027 78
W 9.56 4,61 0.113 0.012 63
X 9.37 4,60 0.162 0.027 76
Y 9.43 4,62 0.148 0.012 66
API GL-5
• Ranking of pitting life
• Fundamental mechanisms• Test parameters:
– 4.3 kN (5.1 Gpa)
– 4000 rpm
9000 stress cycles per minute
– 12.7 mm, AISI 52100 bearing steel
– 120 °C bulk oil temperature
– 15 tests/oil– Additional stopped test
Rolling four ball test machine
Test parameters from:H. Hamaguchi, H. Tanaka, T. Bartels, Test Method for Evaluating Gear Fatigue Life of 4-Stroke motorcycle engine oils, SETC2009, Meeting
Name: Small Engine Technology Conference and Exhibition Penang, Malaysia, 2009.
Pitting results from rolling four ball tests
Oil
Kinematic Viscosity
High Shear
Viscosity
Boundary
Friction Coef
EHD Friction
Coef
EHD Film Thickness
R 14.42 6,28 0.110 0.030 106
S 14.36 6,65 0.111 0.013 85
T 13.94 6,47 0.158 0.029 105
U 13.88 6,52 0.158 0.013 89
V 9.53 4,55 0.112 0.027 78
W 9.56 4,61 0.113 0.012 63
X 9.37 4,60 0.162 0.027 76
Y 9.43 4,62 0.148 0.012 66
Multiple linear regression
Statistical analysis
Multiple linear regression
• Model for pitting life:
• Test variables coded between -1 and 1 through
• Significance level of regression coefficients, found by partial F-tests*
• Low significance due to scatter
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* D.C. Montgomery, Design and Analysis of Experiments, 7th ed., Wiley, Hoboken, N.J, 2009.
“Each stress cycle lowers the activation energy for thermally activated processes”*
*H. Swahn, P. G. Becker, and O. Vingsbo, ”MARTENSITE DECAY DURING ROLLING CONTACT FATIGUE IN BALL BEARINGS.”, Metall Trans A, vol. 7, num. 8, ss. 1099-1110, 1976.