Tribology of a CVT traction drive - Homepage van de … of a CVT traction drive Supervisor:...

Tribology of a CVT traction drive

Supervisor: prof.dr.ir. M. Steinbuch

Coaches: dr.ir. Roëll van Druten

dr.ir. Bas Vroemen

ir. Irmak Aladagli

dr. ir. Theo Hofman

Jeroen van den Brand Lichao Pan

Structure

• Background

• Introduction

• Traction drive modeling

• NuVinci analysis with model

/ name of department PAGE 1 23-5-2013

Aim: predict efficiency of NuVinci transmission, which works as a traction drive

Background: CVT types


Friction

drive

Traction

drive

Manuel E. Joaquim. Ehls: The secret behind cvts. Technical

report, Findett Corporation.

Introduction: traction drive fluid


The mountains flowed

before the Lord

Deborah (1200BC – 1124 BC):

a prophetess of the God of the Israelites

c

p

Det

t

relaxation time

Observation time

Traction fluid behaves in a solid like manner under

high contact stress

(order of 1 [GPa], 10,000 times atmospheric pressure)

LTD Nissan Motor Co. Extroid cvt: for application to rear-wheel-drive cars

powered by large engines.

Modeling


Johnson-Tevaarwerk model

gives good predictions at large

Deborah number:

•Large contact pressure

•Short transit time

Modeling: Johnson-Tevaarwerk model


• Developed in 1978

• Based on limited shear stress theory

• Describing the elastic and plastic behavior in traction drive

• Two key parameters:

elastic shear modulus

average limiting shear strength

Modeling: Johnson-Tevaarwerk model


1JU

CU

2JV

CU

3s b

CU

Ja

4x x

c

F F

NJ

ab

5

y

c

yF F

NJ

ab

6sT

bJ

N a

Losses

3

8c c

G ab

hC

mk

Loewenthal and Rohn investigated

334 traction drives experimental

results, a regression model was

given based on Santotrac 50.

Dimensionless parameters o Dimensionless slip in rolling direction:

o Dimensionless slip in transverse direction:

o Dimensionless spin:

o Dimensionless traction force in rolling direction:

o Dimensionless traction force in transverse direction:

o Dimensionless torque perpendicular to contact area:

Slip loss:

Spin loss:

Transferred power:

Model parameter: Spin, critical factor


a

b

θ

ωA,t

ωA

ωA,n

ωB,n

ωB,t

ωB

ωB

ωA

γ-θ

θ

Body B

Body A

γ-θ

-ωs,A

VA

VB

θ

γ-θ

Spin contact pattern on roller A Contact geometry for spin calculations Angular velocity diagram

γ

Spin:

“a difference in the angular velocity

vector between the bodies in the

direction normal to the contact”

Model parameter: contact size and stress


0.67 0.53 0.067 0.732.69 (1 0.61 )k

c U G WH e

ka

b

Hertzian contact Film thickness

Modeling: film thickness and surface roughness


10-2

10-1

100

101

101

102

103

Rolling speed, [m/s]

Centr

al film

thic

kness,

[nm

]

MTM: Santotrac 50, P = 0.5059 [GPa], T = 40 [ C]

Theory

Experiment 2 2

c

A B

h

NuVinci analysis: Introduction


Batavus’ bike catalog 2012: Vivente NuVinci

The NuVinci hub is a new concept introduced in 2007:

• Simple

• Compact

• Continuous shifting

• Non-hydraulic

NuVinci analysis: geometry and force


Connected to frame

Input

Output

Tilting Ball

Sun disc

Thrust Needle Bearing

Input Deep Groove Ball Bearing

Output Deep Groove Ball Bearing

ɣ αRi

Ro

A

O

C

D

B

Rs α

Rp

ball axle

X

K

Fcl,i

ɣ

Fax,i

Frad,i

Fn,i

ɣ

Frad,o

Fn,o

Fax,o

α

Ri

Ro

Fs

Fcl,o

C D

NuVinci analysis: ratio and tilting angle


NuVinci analysis: contact stress and size


0.54 0.59 0.65 0.71 0.77 0.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.7

1.4

1.6

1.8

2

2.2

Ratio [-]

Conta

ct

str

ess [

GP

a]

Power =80[W], Crank speed = 70 [rpm], Chain ratio = 2 [-]

input/output

sun

0.54 0.59 0.65 0.71 0.77 0.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.70.2

0.25

0.3

0.35

0.4

0.45

Ratio [-]

Conta

ct

dim

ensio

ns [

mm

]

asun

bsun

ainput/output

binput/output

NuVinci analysis: Spin and slip


αγ

γ

γ+α

α

γ-α

γ

ωi

ωi,nωi,t

ωm

ωm

ωm ωo

ωo,nωo,n

ωm,n1

ωm,n2ωm,t1

ωm,t2

ωs

ωm,n3

ωm,t3

K

X 0.54 0.59 0.65 0.71 0.77 0.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.7-100

-50

0

50

Ratio [-]

Spin

[ra

d/s

]


spin,i

spin,o

spin,s

0.54 0.59 0.65 0.71 0.77 0.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.70

0.01

0.02

0.03

0.04

0.05

Ratio [-]

Conta

ct

Spin

[-]

input

output

sun

0.54 0.59 0.65 0.71 0.77 0.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.70

0.02

0.04

0.06

0.08

Ratio [-]

Actu

al slip,

[-]


input

output

sun

, non-dimensional

NuVinci analysis: system efficiency


0.54 0.59 0.65 0.710.770.83 0.91 1 1.1 1.2 1.3 1.4 1.55 1.7 1.850.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Ratio [-]

Eff

icie

ncy,

[-]

Southwest research institute

Experiment

Current prediction

NuVinci analysis: system efficiency


0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

2

4

6

8

10

12

14

Ratio [-]

Pow

er

Loss [

%]

System loss @ Power =80[W], Crank speed=70 [rpm], des

=0.07[-]

Slipi

Spini

Slipo

Spino

Slips

Spions

Rollingi

Rollingo

Rollings

Hysteresisi

Hysteresiso

Hysteresiss

Bearing

NuVinci analysis: Conclusion


• Slip losses are the main source of system losses;

• However, they are very sensitive to contact spin level;

Thus eliminating the spin on contact interface is the key

point to improve a traction drive efficiency.

Questions?


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