Tribological Properties of Fuel Economy Gearbox Oils Norbert Bader, Eike C. Wittek, Prof. Gerhard Poll Institute of machine design and tribology IMKT Leibniz University Hannover Germany slide 1
Situation Reduce churning / splashing and shear losses in vehicle transmissions with minimal design changes possible solution: utilise fuel economy oils Fuel economy oils are oils with a low base oil viscosity In order to achieve sufficient viscosity at all operating temperatures VI-improvers are added As mixed lubrication can not be fully avoided, wear has to be prevented by special additive packages Suitability for gear lubrication could be proven Open question: How do these oils affect rolling element bearing performance? slide 2
Research objective Behaviour of fuel economy oils in rolling bearings? fatigue tests Wear & Roughness Boundary layer formation Frictional torque Contact simulation Film thickness slide 3
Lubricants Transmission oils from two applications Manual transmission (MT) double clutch transmission (DCT) Three variants of each application Lubricant already in use (series) Reference lubricant (Ref) contains identical vi-improver as the series lubricant Candidate lubricant (CAND) reduced viscosity, high-shear resistant vi-improver Two reference oils with known behaviour included (not fuel economy) Low and high reference oil slide 4
Lubricants MT Series MT Ref MT Cand DCT Series DCT Ref DCT Cand High Ref Low Ref Base oil Density at 15 C in g/ml Kinematic viscosity at 100 C in mm²/s Kinematic viscosity at 40 C in mm²/s Mineral PAO/ Ester PAO / Ester HC / PAO PAO PAO Mineral Partly synthetic 0,876 0,847 0,843 0,842 0,839 0,824 0,885 0,883 6,57 6,47 4,53 7,0 7,0 5,04 10 9,5 35,3 29,5 19,7 34,7 35,2 20,12 90 64 Viscosity index 143 182 150 168 165 194 89 124 VI improver Series Series high-shear resistant Series Series highshear resistant - - slide 5
Fatigue tests: Test specifications springs test bearings chuck cone Test conducted on FE8 test rig Measurement of housing raceway temperatures Vibration monitoring to detect pittings Oil supply with filtered oil at 1,2 l/min support bearings slide 6
Fatigue tests: Test specifications Cylindrical roller thrust bearing 81212 TBA roller number reduced to 15 Axial force 60 kn 24 h run in at 250 min -1 176 h or until failure at 750 min -1 Temperature at housing raceway: 100 Resulting contact pressure 1900 MPa Total running time: until failure or suspended after 200 h 2 tests per lubricant Temperature control via ventilator cooling to 100 slide 7
Fatigue tests Viscosity relation viscosity at operating temperature reference viscosity at which full separation occurs Kappa 0,5 0,4 0,3 0,2 0,1 0 0,45 0,48 0,33 0,33 0,24 0,31 0,31 0,22 Two reference oils lead to similar viscosity relations Series and reference oils of both applications are similar Candidate oils feature lower viscosity relation All tests are conducted in the regime of mixed lubrication slide 8
Fatigue tests: Stationary frictional torque and viscosity at 100 16 14 14 stationary frictional torque in Nm viscosity at 100 C 12 10 8 6 4 11 9,5 10,0 7,3 6,6 6,5 7,0 7,0 5,0 7 6,6 5,6 6,5 4,7 4,5 2 0 Low ref High ref DCT series DCT ref DCT cand MTF series MTF ref MTF cand (90 C) slide 9
Fatigue tests: Running times running time in h 250 200 150 100 50 Pitting WK Pitting WS Pitting GS Pitting GS Pitting WS 0 WEC No WEC slide 10
Fatigue tests: Roughness changes 0,25 arithmetic average roughness Ra in µm 0,2 0,15 0,1 0,05 0 slide 11
0,5 0,4 0,3 0,2 0,1 0 slide 12 Lager 022 Lager 023 Lager 040 Lager 042 Lager 028 Lager 029 Lager 030 Lager 031 Lager 018 Lager 019 Lager 020 Lager 021 Lager 024 Lager 025 Lager 026 Lager 027 Lager 036 Lager 037 Lager 038 Lager 039 Lager 033 Lager 034 Lager 035 Lager 044 Lager 045 Lager 049 Lager 051 Lager 032 Fatigue tests: Wear WS GS WK Low Ref High Ref DCT Serie DCT Ref DCT Kand MT Ref Rotating raceway Stationary raceway Rollerset MT Kand 90 C MT Kand 100 C wear in g
Fatigue tests: Comparison of oil viscosity before and after test New Frischöl oil Gebrauchtöl Oil after test 10 kinematic viscosity at 100 C in cst 8 6 4 2-2,3% -2,1% -5,7% -0,4% -0,9% 0 DCT Serie DCT Ref DCT Kand MTF Ref MTF Kand 90 slide 13
Torque measurements with TRB and DGBB: Test rig I. Thermostat II. Test head III. Torque meter IV. Flexible coupling V. Intermediate shaft VI. Belt drive VII. Volume and temperature control VIII.Oil supply slide 14
Torque measurements with TRB and DGBB : Test rig with DGBB Tests run conducted at 73 Instead of DGBB TRBs were also used slide 15
Torque measurements with TRB and DGBB : Contact pressure max. Hertzian pressure in MPa 2500 2000 1500 1000 500 1451 2220 944 fatigue tests FE-8 1904 0 536 500 N 6008 2500 N 500 N 32008 2500 N 60000 N 81212 slide 16
Torque measurements with TRB and DGBB DCT + Deep groove roller bearing 6008-500N 200 180 160 Torque in Nmm 140 120 100 80 60 40 20 Series with oil supply Series without oil supply Ref with oil supply Ref without oil supply Cand with oil supply Cand without oil supply 0 0 1000 2000 3000 4000 5000 6000 Revolutions in min -1 slide 17
Torque measurements with TRB and DGBB 400 DCT + Tapered roller bearing 32008-500N 350 Torque in Nmm 300 250 200 150 100 Series with oil supply Series without oil supply Ref with oil supply Ref without oil supply Cand with oil supply Cand without oil supply 50 0 0 1000 2000 3000 4000 5000 6000 Revolutions in min -1 slide 18
Lubricant film thickness: Capacitance measurements slide 19
Lubricant film thickness : Capacitance measurements Bear slide 20
Torque measurements: Capacitance measurements slide 21
Lubricant film thickness : Capacitance measurements voltage at condensator in V U 0 time in ms slide 22
Lubricant film thickness : Capacitance measurements 100 min -1 U 0 voltage in V time in ms slide 23
Lubricant film thickness : Capacitance measurements 1000 min -1 U 0 voltage in V time in ms slide 24
Lubricant film thickness : Capacitance measurements 6000 min -1 U 0 voltage in V time in ms slide 25
Lubricant film thickness : Voltage reached Voltage reached as measure of breakdown voltage (charging with U 0 = 0,15 V) voltage reached in V 0,1 0,09 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 6000 4000 2000 1000 500 100 slide 26
Summary All candidate oils reduce churning losses and total bearing friction even though they extend operation under mixed lubrication, except for taper roller bearings at very low speeds An even more pronounced bearing friction torque reduction may be obtained by minimizing the amount of lubricant Early fatigue occurs only with the MTF candidate oil in the cylindrical thrust bearing test at 100, not at 90 In contrast to the low reference oil the early failures with the MTF candidate oil are not related to White Etching Cracks (WEA) Measurable wear of the raceways is observed for the MTF candidate oil as well, to a larger extent at 90 and less prominent at 100. With the other oils, wear is negligible after running-in, in despite of mixed lubrication In summary, a substantial reduction of friction is possible with the investigated fuel economy oils without creating wear or early fatigue problems, with the exception of the MTF candidate oil. slide 27
Acknowledgements German research foundation for drive train technologies (FVA) FVA 619: Tribologisches Verhalten neuartiger Fuel Economy Öle in Wälzlagern Association of industrial research foundations (AiF) "Otto von Guericke" e.v. slide 28
Thank you for your kind attention slide 29