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Experimental Validation of Full Toroidal Fatigue Life

Experimental Validation of Full Toroidal Fatigue Life. Dr. Adrian Lee Torotrak (Development) Ltd. Variator Durability. Objectives Confirm current design S-N curve Assess influence of surface roughness/finish Investigate material importance (KUJ7/Ovako)

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Experimental Validation of Full Toroidal Fatigue Life

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  1. Experimental Validation of Full Toroidal Fatigue Life Dr. Adrian Lee Torotrak (Development) Ltd.

  2. Variator Durability Objectives • Confirm current design S-N curve • Assess influence of surface roughness/finish • Investigate material importance (KUJ7/Ovako) • Understand influence of different traction fluids • Variables Investigated • Surface finish • Contact stress (mean) • Variator speed (mainshaft rpm) • Shot peening • Roller temperature (degC) • Through hardened Material • Fluids • Over 120 variator module tests undertaken CVT-21

  3. Control System Valve Cooler Block Hydraulic Power Pack Gearbox Motor Variator Drive Base Frame Research 100mm Variator Test Rig Variator Test Rigs CVT-21

  4. 100mm Variator Test Module disk Centre rear disk Centre front Rear disk Front disk R2 roller F2 roller pressure Endload direction Rotational F1 F3 R1 R3 To motor Hy-vo chain CVT-21

  5. Contact track Contact track Contact track Smooth disc (Ra<0.1) after 553 hrs Rough disc (Ra>0.13) after 264 hrs Smooth roller (Ra<0.1) after 553 hrs Rough roller (Ra>0.13) after 264 hrs Durability Testing Influence of Surface Roughness CVT-21

  6. Variator Durability TestsInfluence of Surface Finish Torotrak Durability Data 100mm Research Variator Rig 3.5 3 Model - 9th power law 2.5 Mean Hz contact Stress (GPa) 2 1.5 1 1.00 10.00 100.00 1000.00 Stress Cycles (Disc) to failure (million) Model Koyo smooth surface Koyo rough surface Non brg man. Rough surface CVT-21

  7. Before Test After Test Importance of Manufacturing CVT-21

  8. Variator Durability TestsWear Volume Ra = 0.07, Rsk = -1.67 Roller smooth before test Roller smooth after 634hrs running Ra = 0.08, Rsk = -1.67 • Specific film thickness () = hmin / * where *2 = Rq12 + Rq22 • 1<<3 some asperity contact, termed partial or mixed regime. • Tests with type A material & HT (k~ 2×10-9) indicate mixed / full-film EHL • Tests with type B material & HT (k ~ 2×10-11) indicates full-film EHL CVT-21

  9. Failed parts - Smooth parts tests Failed parts - Rough parts tests 100mm Variator Test Rig 100mm Variator Test Rig Front disk/Cracked Centre front disk/spall spline Roller F2/spall 13% 12% 13% Front disk/spall Roller R2/spall 13% 13% 6% Roller R2/spall Centre rear disk/spall 30% 13% 13% 74% Rear disk/spall Variator/Micro-pitting Roller F2/spall Variator Durability TestsFailure Type & Position CVT-21

  10. Variator Durability TestsRoller vs Disc Failure - Uneven Loading CVT-21

  11. Torotrak Durability Data 100mm Research Variator Rig Surface Crack Model - 9th power law Mean Hz contact Stress (GPa) 2002 Design Model Current Traction Fluid HTHL Disc/Rollers Sub-Surface Fatigue 1.00 10.00 100.00 1000.00 Stress Cycles (Disc) to failure (million) Previous Durability Results CVT-21

  12. Variator Durability TestsSurface Initiated Fatigue Failure Cracks Number of cracks and Mean Hz Contact pressure Contact track 100mm Research Variator Rig 10000 1000 100 Number of cracks in one variator No cracks on rollers 10 Cracks 1 1.6 1.8 2 2.2 2.4 2.6 2.8 Mean Hz contact stress (GPa) R19 smooth R19 rough R19 smooth, high speed & temp R19 smooth, high speed R15 smooth R12 smooth R12 rough R12 no S1 heat treatment rollers R12 normal SP rollers R12 carbonitrided rollers R12 smooth, high speed R25 smooth R25 rough R12 deep SP rollers CVT-21

  13. Influence of Fluid on Durability 1000 750 Stress Cycles (millions) 500 250 0 A B C D E F G H I1 I2 Baseline Fluid Type CVT-21

  14. 2.90E+09 2.70E+09 2004 2.50E+09 Mean Hz Contact Stress (Pa) 2.30E+09 2.10E+09 Target Life 9th Power 2004 1.90E+09 9th Power 2002 Completed Tests 7 to 9 times improvement 1.70E+09 Suspended Tests 1.50E+09 1 10 100 1000 10000 Stress Cycles (million) Radical Fatigue Life Improvements 2002 CVT-21

  15. 2.90E+09 Test Suspended 2.70E+09 2.50E+09 Mean Hz Contact Stress (Pa) 2.30E+09 2.10E+09 Target Life 1.90E+09 Completed Tests (75kW typically) Suspended Tests (75kW typically) 1.70E+09 High Power (210kW typically) 1.50E+09 1 10 100 1000 10000 Stress Cycles (million) Excellent High Power Durability CVT-21

  16. Variator Sizing CVT-21

  17. Variator Durability Results • Applying Series 3 SUV duty cycle, base durability curve equivalent to circa 50 % life fraction or circa 340,000 miles life • Durability extended - 9 times improvement to only 5% life used • Outcome - durability exceeds requirements hence downsize CVT-21

  18. Conclusions • IVT size envelope same or smaller than 6AT • Fatigue tests at high power and stress confirm traditional fatigue analysis applicable to the IVT • Interaction between fluid and material has a significant influence on life • SDT design tool enables rapid optimisation of the IVT layout CVT-21

  19. IVT fully competitive with 6AT 6-AT IVT CVT-21

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