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Interesting power split e-bike transmission

Discussion in 'Fred's House of Pancakes' started by bhtooefr, Aug 2, 2016.

  1. bhtooefr

    bhtooefr Senior Member

    Joined:
    Apr 4, 2016
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    Location:
    Newark, OH, USA
    Vehicle:
    2016 Prius
    Model:
    Three
    Looks like someone (NexxtDrive) actually took the ideas behind the Prius gearbox, and made a power split hybrid based on them: Nexxt Drive Ltd - Gemini - eBike transmission I've been wondering if that was feasible for a few months now...

    US20150291256A1 - Hubs incorporating a variable ratio transmission system - Google Patents appears to be the patent for it, and looking through it, it looks like it's the same basic configuration as a Gen 1/2 Prius - MG1 on the sun gear, rider pedal input on the planet carrier, MG2 not having a reduction gear. The first clever bit is that MG1 fits fully inside of MG2, to reduce width of the assembly. The second clever bit is the one-way clutch that they designed in, to take care of situations where MG1 can't react quickly enough to the rider's torque input (remember, in a Prius, the electronics tell the engine what to do, whereas in a bicycle application, the rider controls everything) - essentially, if the rider applies too much torque too quickly and ends up slipping MG1 for whatever reason - especially when starting out - the clutch will connect the rider's input directly to the hub shell, which honestly, is fine for the Prius-like configuration at lower speeds (where it's most likely to happen), especially because MG2 will kick in quickly and help propel the vehicle too. (Edit: Actually, reading back over the patent, it's mainly enforcing direct drive for the rider until the hub (wheel) RPM exceeds the input RPM. But, if you overwhelm MG1, you may get your pedals engaged into the hub shell.)

    It'll be interesting to see if it ever comes to production - looks like a couple e-bike sites have ridden this design (Electric Bike Report and ExtraEnergy), and they're also working on a lighter weight mid-drive (sits at the pedals, rather than in the rear wheel) version (allowing higher-speed, lower-torque motors to be used, and then gear reduction to the rear wheel, rather than low-speed, high-torque motors that are receiving gear-reduced rider input). Looks like the hard part, according to them, has been the software, to handle the rider's fluctuating torque smoothly...
     
    #1 bhtooefr, Aug 2, 2016
    Last edited: Aug 3, 2016