Experimental Validation of Full Experimental Validation of Full Toroidal Fatigue LifeToroidal Fatigue Life

Dr. Adrian Lee

Torotrak (Development) Ltd.

Variator DurabilityVariator Durability

CVT-21

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

Variator Test RigsVariator Test Rigs

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Base Frame

Hydraulic Power Pack Variator Gearbox Motor

Drive

Cooler ValveBlock

Control System

Research 100mm Variator Test Rig

100mm Variator Test Module100mm Variator Test Module

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F1 F3

F2 roller R2 roller

R1 R3

To motor

Rotational

direction

Front disk Centre frontdisk Centre rear

disk Rear disk

Hy-vo chain

Endload

pressure

Durability Testing Durability Testing Influence of Surface RoughnessInfluence of Surface Roughness

Smooth roller (Ra<0.1) after 553 hrs Smooth disc (Ra<0.1) after 553 hrs

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Contact track

Contact track

Contact track

Rough roller (Ra>0.13) after 264 hrs Rough disc (Ra>0.13) after 264 hrs

Variator Durability TestsVariator Durability TestsInfluence of Surface FinishInfluence of Surface Finish

Torotrak Durability Data100mm Research Variator Rig

1

1.5

2

2.5

3

3.5

1.00 10.00 100.00 1000.00

Stress Cycles (Disc) to failure (million)

Me

an

Hz

co

nta

ct

Str

es

s

(GP

a)

Model Koyo smooth surface Koyo rough surface Non brg man. Rough surface

Model - 9th power law

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Importance of ManufacturingImportance of Manufacturing

Before Test After Test

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Variator Durability TestsVariator Durability TestsWear VolumeWear 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 + Rq2

2

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 TestsVariator Durability TestsFailure Type & PositionFailure Type & Position

Failed parts - Smooth parts tests

100mm Variator Test Rig

Front disk/spall

13%

Centre rear disk/spall6%

Rear disk/spall

13%

Roller R2/spall 30%

Centre front disk/spall

12%

Front disk/Cracked spline

13%

Roller F2/spall

13%

Failed parts - Rough parts tests

100mm Variator Test Rig

Roller R2/spall

13%

Variator/Micro-pitting

74%

Roller F2/spall

13%

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Variator Variator DurabilityDurability Tests TestsRoller vs Disc Failure - Uneven LoadingRoller vs Disc Failure - Uneven Loading

Variator life in terms of disk revolution based on 9th power model100mm Research Variator Rig

1.5

2.0

2.5

3.0

0.1 1 10 100 1000

Disk revolution to failure (million)

Me

an

Hz

co

nta

ct

str

es

s (

GP

a)

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

12mm rol l er and di sk

15mm rol l er and di sk

19mm rol l er and di sk

25mm rol l er and di sk

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Previous Durability Results Previous Durability Results

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Torotrak Durability Data100mm Research Variator Rig

1.00 10.00 100.00 1000.00

Stress Cycles (Disc) to failure (million)

Mea

n H

z co

nta

ct S

tres

s (G

Pa)

2002 Design Model

Current Traction FluidHTHL Disc/Rollers

Model - 9th power law

Surface Crack

Sub-SurfaceFatigue

Variator Durability TestsVariator Durability TestsSurface Initiated Fatigue Failure CracksSurface Initiated Fatigue Failure Cracks

Contact track

Cracks

Number of cracks and Mean Hz Contact pressure100mm Research Variator Rig

1

10

100

1000

10000

1.6 1.8 2 2.2 2.4 2.6 2.8

Mean Hz contact stress (GPa)

Nu

mb

er o

f cr

acks

in

on

e va

riat

or

R19 smooth R19 roughR19 smooth, high speed & temp R19 smooth, high speedR15 smooth R12 smoothR12 rough R12 no S1 heat treatment rollersR12 normal SP rollers R12 carbonitrided rollersR12 smooth, high speed R25 smoothR25 rough R12 deep SP rollers

No crackson rollers

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Influence of Fluid on DurabilityInfluence of Fluid on Durability

0

250

500

750

1000S

tre

ss

Cy

cle

s (

mill

ion

s)

A B C D E F G H I1 I2 Baseline

Fluid Type

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1.50E+09

1.70E+09

1.90E+09

2.10E+09

2.30E+09

2.50E+09

2.70E+09

2.90E+09

1 10 100 1000 10000

Stress Cycles (million)

Mea

n H

z C

on

tact

Str

ess

(Pa)

Radical Fatigue Life ImprovementsRadical Fatigue Life Improvements

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2002Target Life

9th Power 2004

9th Power 2002

Completed Tests

Suspended Tests7 to 9 times improvement

2004

1.50E+09

1.70E+09

1.90E+09

2.10E+09

2.30E+09

2.50E+09

2.70E+09

2.90E+09

1 10 100 1000 10000

Stress Cycles (million)

Mea

n H

z C

on

tact

Str

ess

(Pa)

Excellent High Power DurabilityExcellent High Power Durability

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Target Life

Completed Tests (75kW typically)

Suspended Tests (75kW typically)

High Power (210kW typically)

Test Suspended

Variator SizingVariator Sizing

Start

Driveline Power

Engine Power

Engine Speed

Variator Ratio

Contact Mean HzStress

Contact LifeFraction

Variator Speed &Torque

Overall Tx Ratio

Finish

Contact Total LifeFraction

Manuf. DutyCycle

FDR and Txefficiency

EngineControl Line

ShuntArchitecture

VariatorDesign

TDL 9th PowerLaw

Miners’ Law

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Variator Durability ResultsVariator Durability Results

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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

0200

400600

-2000

0

20000

1

2

3

4x 10

-3

SpdTxOut (rad/s)

100 mm roller, New Fluid

TrqTxOut (Nm)

roll

er

life

fra

cti

on

(%

) Variator Ratio Band-0.45to -0.59

-0.59to -0.72

-0.72to -0.86

-0.86to -1.00

-1.00to -1.31

-1.31to -1.62

-1.62to -1.93

-1.93to -2.24

120mm Input Disc 49.3 15.2 6.2 5.1 15.6 4.6 0 0100mm Input Disc 29.4 6.6 1.7 1.7 4.4 2.3 0 0

120mm Output Disc 3.5 2.7 2.7 3.6 31.3 18.1 0.3 0.6100mm Output Disc 1 0.8 0.6 1.1 11.1 12.6 0.1 0.1

Total120mm Roller 13 5.5 3.1 3.2 16.6 7.5 0.1 0.2 50.1100mm Roller 7.7 2.2 0.8 1 5.4 4.8 0 0 22

ConclusionsConclusions

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• 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

IVT fully competitive with 6ATIVT fully competitive with 6AT

IVT6-AT

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