![Page 1: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/1.jpg)
An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission
Peter WattersonCSIRO Materials Science and Engineering, Australia ICEMS 2008, 19 October 2008, Wuhan, China
![Page 2: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/2.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Objectives
• Provide electric assistance to a bicycle • human – electric hybrid with roughly equal power inputs
• low CO2 transportation
• ... but some exercise
• An automatic transmission – no gear changing
• Fixed ratio chain (or belt) drive from crank to rear wheel• Hence chain drive can be shrouded and kept clean
• Minimum weight
• Maximum efficiency
![Page 3: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/3.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
A Prius in a Bicycle!
![Page 4: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/4.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Electric Continuously Variable Transmission,e-CVT
human input MG1
MG2
output
Ring gear
planet gears
planet CarrierSun gear
S
C
R
Planetary 1
![Page 5: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/5.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Planetary gear speed relationship
• For planetary gear constant
• Speeds obey:
s
r
N
Nk
0)1( crs kk
Ring gear number of teeth
Sun gear number of teeth
![Page 6: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/6.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Planetary gear torque relationship
• From force and torque balance on planet gears
• External torques on the gears obey:
scr TkTTk
k)( 1
1
FF/2
F/2
![Page 7: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/7.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Two hub topology
Planetary 1
spoke rims
shaft (fixed to bike forks)
MG1
chain
Planetary 2
spoke rims
shaft (fixed to bike forks)
MG2
rear hub front hub
![Page 8: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/8.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
One hub topology, axial field MGs
Axial magnetic field MGs can share same stack:
Planetary 2
Planetary 1
spoke rims
shaft (fixed to bike forks)
MG2
MG1
chain
leads
![Page 9: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/9.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
One hub topology, direct drive MG2
Planetary 1
spoke rims
shaft (fixed to bike forks)
MG2
MG1
chain
leads
![Page 10: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/10.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
One hub topology, geared MG2
Planetary 2
Planetary 1
spoke rims
shaft (fixed to bike forks)
MG2
MG1
chain
leads
Ratio of volumes within airgaps = 3
![Page 11: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/11.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
A possible specification
Maximum continuous total electric power 200 W
Maximum continuous rider power 200 W
Predominant rider cadence 75 rpm
Range of rider cadence 60 – 90 rpm
Range of bicycle speeds 15 – 36 km/h
Associated (700 mm diameter) wheel speeds 110 – 270 rpm
Maximum regenerative braking power 400 W
![Page 12: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/12.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
MG ratings for draft rear hub design
• Gear ratios: Planetary 1, 7.24; Planetary 2, 5.32.• Chain ratio 2.33 gives equal Torque/Volume for MG1 and MG2
at their most demanding operating points. Ignoring all losses:
Crank speed (rpm)
Wheel speed (rpm)
MG1 MG2
speed (rpm)
torque (Nm)
power (W)
speed (rpm)
torque (Nm)
power (W)
Low cadence, high speed 60 270 -801 -1.66 139 -1437 -0.41 61
High cadence, low speed 90 110 934 -1.10 -108 -586 -5.02 308
Regenerative braking 400 W,
high speed 0 270 -1955 0.49 -100 -1437 1.99 -300
![Page 13: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/13.jpg)
CSIRO. An Electric Assist Bicycle Drive with Automatic CVT
Conclusions
• Trial rear hub e-CVT design • 200 W human power and 200 W electrical power
• MGs with 19 kN/m2 tangential force at air-gap – realistic.
• Higher power design (e.g. for the US market)• Two hub topology may be needed for extra volume
• Automatic control• No gear changing
• Can base desired speed on pedalling torque and/or cadence
• Can allow rider to vary level of assistance
• Other applications – petrol/electric vehicles including scooters
![Page 14: An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS](https://reader035.vdocuments.mx/reader035/viewer/2022081518/551448df550346414e8b4d2f/html5/thumbnails/14.jpg)
Contact UsPhone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Thank you
CSIRO Materials Science and EngineeringPeter WattersonPrincipal Research Scientist
Phone: 61-2-94137529Email: Peter [email protected]: www.csiro.au/science/ElectricMachines.html