An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS 2008, 19 October 2008, Wuhan, China

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 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

A Prius in a Bicycle! CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

Electric Continuously Variable Transmission, e-CVT Planetary 1 output Ring gear R MG2 planet Carrier Sun gear C human input S MG1 planet gears CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

Planetary gear speed relationship For planetary gear constant Speeds obey: Ring gear number of teeth Sun gear number of teeth 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: -F/2 F -F/2 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

Two hub topology rear hub front hub CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

One hub topology, axial field MGs Axial magnetic field MGs can share same stack: CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

One hub topology, direct drive MG2 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

One hub topology, geared MG2 Ratio of volumes within airgaps = 3 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

A possible specification Maximum continuous total electric power 200 W Maximum continuous rider power 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 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) 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 -1955 0.49 -100 1.99 -300 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 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT

Thank you CSIRO Materials Science and Engineering Peter Watterson Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au CSIRO Materials Science and Engineering Peter Watterson Principal Research Scientist Phone: 61-2-94137529 Email: Peter Watterson@csiro.au Web: www.csiro.au/science/ElectricMachines.html Thank you