Minimizing Churning losses for enhancing the Energy efficiency of Gear Lubricants
Rahul Meshram, Sanker Bhadhavath, Anil Bhardwaj, A K Harinarain, S K Mazumdar
Indian Oil Corporation Limited, R&D Centre, Sector 13, Faridabad-121007, (India)
ABSTRACT
Gear drives are extensively used for speed optimization and power transmission in Industrial
equipments in steel, cement, power, plants, windmills, automobiles, mining etc. These drives
are generally lubricated using a large sump of oil, therefore a significant amount of energy is
consumed not only in overcoming the metallic friction, but also in pumping, agitation and
overcoming the viscous drag (churning losses) experienced in the contact zone. This viscous
drag or churning is primarily dependent on viscosity as well as base oil types and properties. A
systematic study has been conducted to understand the factors influencing these churning
losses in oils so that these can be optimized by formulation of the oils. This study encompassed
the use of screening techniques such as film thickness, traction coefficient and churning loss
study in a modified FZG Gear Test rig under low load conditions at different speeds, and
validated using a study in actual gear efficiency test. The study covers various types of gear oils
of different viscosities and chemistries to assess the contribution of churning towards energy
efficiency of the oils to be able to optimize the formulation of the oils that work in a zone offering
the highest efficiencies.
Keywords: Energy Efficiency, Churning, Pumping, Agitation, Film thickness, Traction
coefficient, VI improvers, Viscosity etc.
INTRODUCTION
A gearbox is used to transmit power from rotating power source to other device through speed
and torque conversions. It is used in variety of applications across industrial and transportation
sectors. Due to increase in energy costs as well environmental concerns, the focus has shifted
towards improving efficiency of a gearbox by analyzing factors which directly impact efficiency
of a gearbox. Literature reports that a major portion of energy is lost in the gearbox itself. These
power losses are load dependent as well as load independent. The load dependent power
losses are frictional losses in gear mesh, bearings, seals and through leakages, while load
independent power losses mainly comprises of windage and churning losses (1,2) .
A lubricant plays an important role in overcoming these power losses. A carefully formulated
lubricant with friction modifiers helps in reducing frictional and churning losses in mixed,
elastohydrodynamic and boundary lubrication regime (3). These energy losses depend on oil
viscosity and its chemical composition. Viscosity shear thinning and pressure thickening effects
are dependent on base oil and its viscosity index. By improving upon both these factors in
energy efficient industrial lubricants, it is possible to achieve significant energy savings (4).
EXPERIMENTAL STUDY
This study was conducted on gear oils of different viscosity grades. The study comprised of two
parts.
PART I
Screening of the properties of oils that affect the churning losses: This was conducted using the
following test rigs.
(1) EHD Film thickness test rig: The EHD Film thickness rig was used to measure the
physical separation achieved with different oils between a simulated gear contact.
(2) Mini Traction machine: The mini-traction machine was used to characterize the Traction
coefficient, which is a measure of the friction due to viscosity effect under full film or
mixed lubrication regime under simulated gear contacts under different slide roll ratios.
(3) Modified FZG Gear test rig: The churning losses were studied using a modified FZG
Gear Test rig which was run at no load, while monitoring the temperature rise and the
energy consumed during the test.
PART II:
(1) FZG Gear Energy Efficiency Test : To validate the effect of churning losses on overall
energy efficiency, a set of experiments had been performed on a FZG test rig operated
under various load speed combination to assess the difference in energy efficiency.
An attempt was made to validate the experimental results with the theoretical models reported
in literature.
CONCLUSIONS
1. Film thickness and traction coefficient data shows good correlation with churning losses.
2. Both speed and Base oil properties affect the churning losses in gear oils.
3. Modified FZG machine can be used to estimate churning losses in terms of power
consumption and temperature rise.
4. Churning losses form a major component in influencing the overall energy efficiency of
the gear oils, so oils can be reformulated to optimize the viscosity and film thickness
considering the operating conditions prevalent in the gear contacts.
REFERENCES
1. T.T. Petry-Johnson, A. Kahraman, N.E. Anderson and D.R. Chase.,“Experimental
Investigation of Spur Gear Efficiency”, ASME 2007 International Design Engineering
Technical Conferences & Computers and Information in Engineering Conference.
2. Hachiro Mizutani, Yuuichi Isikawa and Dennis P. Townsend., “Effects of Lubrication on
the
Performance of High Speed Spur Gears” NASA TM-101969, 1989, Fifth
International Power Transmission and Gearing Conference.
3. Lev A. Bronshteyn, Jesa H. Kreiner., “Energy Efficiency of Industrial Oils” Tribology
Transactions, 1999, Vol. 42, 4, pp 771-776.
4. Gauthier LePrince , Christophe Changenet , Fabrice Ville , Philippe Velex, Christophe
Dufau and Frédéric Jarnias “Influence of Aerated Lubricants on Gear Churning Losses–
An Engineering Model”, Tribology Transactions, 2011, Vol. 54, pp 929-938