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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
/ name of department PAGE 2 23-5-2013
Friction
drive
Traction
drive
Manuel E. Joaquim. Ehls: The secret behind cvts. Technical
report, Findett Corporation.
Introduction: traction drive fluid
/ name of department PAGE 3 23-5-2013
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
/ name of department PAGE 4 23-5-2013
Johnson-Tevaarwerk model
gives good predictions at large
Deborah number:
•Large contact pressure
•Short transit time
Modeling: Johnson-Tevaarwerk model
/ name of department PAGE 5 23-5-2013
• 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
/ name of department PAGE 6 23-5-2013
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
/ name of department PAGE 7 23-5-2013
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
/ name of department PAGE 8 23-5-2013
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
/ name of department PAGE 9 23-5-2013
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
/ name of department PAGE 10 23-5-2013
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
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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
/ name of department PAGE 12 23-5-2013
NuVinci analysis: contact stress and size
/ name of department PAGE 13 23-5-2013
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
/ name of department PAGE 14 23-5-2013
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
]
Power =80[W], Crank speed = 70 [rpm], Chain ratio = 2 [-]
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,
[-]
Power =80[W], Crank speed = 70 [rpm], Chain ratio = 2 [-]
input
output
sun
, non-dimensional
NuVinci analysis: system efficiency
/ name of department PAGE 15 23-5-2013
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
/ name of department PAGE 16 23-5-2013
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
/ name of department PAGE 17 23-5-2013
• 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?
/ name of department PAGE 18 23-5-2013