Experimental Validation of Full
Toroidal Fatigue Life
Dr. Adrian Lee
Torotrak (Development) Ltd.
Variator Durability
Objectives
Variables Investigated

Confirm current design S-N curve

Surface finish

Assess influence of surface

Contact stress (mean)

Variator speed (mainshaft rpm)

Shot peening

Roller temperature (degC)

Through hardened Material

Fluids

Over 120 variator module tests
roughness/finish

Investigate material importance
(KUJ7/Ovako)

Understand influence of different
traction fluids
undertaken
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Variator Test Rigs
Control System
Cooler
Hydraulic
Power Pack
Valve
Block
Variator
Gearbox
Motor
Drive
Base Frame
Research 100mm Variator Test Rig
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100mm Variator Test Module
disk
Front disk Centre front
Centre rear
disk
Rear disk
R2 roller
pressure
F2 roller
Endload
direction
Rotational
F1 F3
R1 R3
To motor
Hy-vo chain
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Durability Testing
Influence of Surface Roughness
Contact track
Contact track
Contact track
Smoothroller
Rough
roller(Ra>0.13)
(Ra<0.1) after 553
264 hrs
Smoothdisc
Rough
disc(Ra>0.13)
(Ra<0.1) after 553
264 hrs
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Variator Durability Tests
Influence of Surface Finish
Torotrak Durability Data
100mm Research Variator Rig
3
Model - 9th power law
2.5
(GPa)
Mean Hz contact Stress
3.5
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
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Importance of Manufacturing
Before Test
After Test
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Variator Durability Tests
Wear Volume
Roller smooth before test
Roller smooth
after 634hrs running
Ra = 0.07, Rsk = -1.67
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
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Variator Durability Tests
Failure Type & Position
Failed parts - Smooth parts tests
Failed parts - Rough parts tests
100mm Variator Test Rig
Front disk/Cracked
spline
13%
100mm Variator Test Rig
Roller F2/spall
Centre front disk/spall
13%
12%
Roller R2/spall
Front disk/spall
13%
13%
Roller R2/spall
6%
30%
Centre rear disk/spall
13%
74%
13%
Rear disk/spall
Variator/Micro-pitting
Roller F2/spall
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Variator Durability Tests
Roller vs Disc Failure - Uneven Loading
Variator life in terms of disk revolution based on 9th power model
100mm Research Variator Rig
3.0
Mean Hz contact stress (GPa)
12mm r ol l er and di sk
15mm r ol l er and di sk
2.5
19mm r ol l er and di sk
2.0
25mm r ol l er and di sk
1.5
0.1
1
10
Disk revolution to failure (million)
100
1000
Disk in front cavity
Disk in rear cavity
F1 load percentage
F2 load percentage
F3 load percentage
R1 load percentage
R2 load percentage
R3 load percentage
Disk model
Roller model
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Previous Durability Results
Torotrak Durability Data
100mm Research Variator Rig
Mean Hz contact Stress (GPa)
Surface Crack
Model - 9th power law
2002 Design Model
Current Traction Fluid
HTHL Disc/Rollers
1.00
Sub-Surface
Fatigue
10.00
100.00
1000.00
Stress Cycles (Disc) to failure (million)
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Variator Durability Tests
Surface Initiated Fatigue Failure Cracks
Number of cracks and Mean Hz Contact pressure
Contact track
100mm Research Variator Rig
Cracks
Number of cracks in one variator
10000
1000
100
No cracks
on rollers
10
1
1.6
1.8
2
2.2
2.4
2.6
Mean Hz contact stress (GPa)
R19 smooth
R19 smooth, high speed & temp
R15 smooth
R12 rough
R12 normal SP rollers
R12 smooth, high speed
R25 rough
R19 rough
R19 smooth, high speed
R12 smooth
R12 no S1 heat treatment rollers
R12 carbonitrided rollers
R25 smooth
R12 deep SP rollers
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2.8
Influence of Fluid on Durability
Stress Cycles (millions)
1000
750
500
250
0
A
B
C
D
E
F
G
H
I1
I2
Baseline
Fluid Type
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Radical Fatigue Life Improvements
Mean Hz Contact Stress (Pa)
2.90E+09
2.70E+09
2.50E+09
2004
2.30E+09
2002
2.10E+09
Target Life
9th Power 2004
1.90E+09
9th Power 2002
Completed Tests
1.70E+09
Suspended Tests
7 to 9 times improvement
1.50E+09
1
10
100
1000
10000
Stress Cycles (million)
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Excellent High Power Durability
Mean Hz Contact Stress (Pa)
2.90E+09
Test Suspended
2.70E+09
2.50E+09
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)
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Variator Sizing
Start
Manuf. Duty
Cycle
Driveline Power
FDR and Tx
efficiency
Engine Power
Engine Speed
Engine
Control Line
Shunt
Architecture
Overall Tx Ratio
Variator Ratio
Variator Speed &
Torque
Variator
Design
th
Contact Mean Hz
Stress
TDL 9 Power
Law
Contact Life
Fraction
Miners’ Law
Contact Total Life
Fraction
Finish
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Variator Durability Results
100 mm roller, New Fluid
roller life fraction (%)
x 10
-3
V a ria to r R a tio B a n d
4
-0 .4 5 -0 .5 9 -0 .7 2 -0 .8 6 -1 .0 0 -1 .3 1 -1 .6 2 -1 .9 3
to to to to to to to to 0 .5 9 0 .7 2 0 .8 6 1 .0 0 1 .3 1 1 .6 2 1 .9 3 2 .2 4
3
2
1 2 0 m m In p u t D isc
1 0 0 m m In p u t D isc
4 9 .3
2 9 .4
1 5 .2
6 .6
6 .2
1 .7
5 .1
1 .7
1 5 .6
4 .4
4 .6
2 .3
0
0
0
0
1 2 0 m m O u tp u t D isc
1 0 0 m m O u tp u t D isc
3 .5
1
2 .7
0 .8
2 .7
0 .6
3 .6
1 .1
3 1 .3
1 1 .1
1 8 .1
1 2 .6
0 .3
0 .1
0 .6
0 .1
1 2 0 m m R o lle r
1 0 0 m m R o lle r
13
7 .7
5 .5
2 .2
3 .1
0 .8
3 .2
1
1 6 .6
5 .4
7 .5
4 .8
0 .1
0
0 .2
0
1
0
2000
600
0
400
200
TrqTxOut (Nm)
-2000 0
T o ta l
SpdTxOut (rad/s)
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
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5 0 .1
22
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
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IVT fully competitive with 6AT
6-AT
IVT
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