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An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS.

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Presentation on theme: "An Electric Assist Bicycle Drive with Automatic Continuously Variable Transmission Peter Watterson CSIRO Materials Science and Engineering, Australia ICEMS."— Presentation transcript:

1 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

2 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 CO 2 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

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

4 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 Carrier Sun gear S C R Planetary 1

5 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

6 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 F/2

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

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

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

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

11 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT A possible specification Maximum continuous total electric power200 W Maximum continuous rider power200 W Predominant rider cadence75 rpm Range of rider cadence60 – 90 rpm Range of bicycle speeds15 – 36 km/h Associated (700 mm diameter) wheel speeds110 – 270 rpm Maximum regenerative braking power400 W

12 CSIRO. An Electric Assist Bicycle Drive with Automatic CVT MG ratings for draft rear hub design Gear ratios: Planetary 1, 7.24; Planetary 2, 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) MG1MG2 speed (rpm) torque (Nm) power (W) speed (rpm) torque (Nm) power (W) Low cadence, high speed High cadence, low speed Regenerative braking 400 W, high speed

13 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/m 2 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

14 Contact Us Phone: or Web: Thank you CSIRO Materials Science and Engineering Peter Watterson Principal Research Scientist Phone: Peter Web:


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