Cush drive system for use with CVP hub

Discussion in '4-Stroke Engines' started by Marple200, Aug 16, 2011.

  1. Marple200

    Marple200 New Member

    I would like to use the Nuvinci CVP hub with autoshifting function in conjunction with a gas-powered motor.

    The literature says to utilize
    "...a cush drive system must be installed between the
    engine and the CVP to dampen out power pulses from piston acceleration..."

    Does anyone know what would constitute a cush drive system?

  2. loquin

    loquin Active Member

    Cush Drive System. Here are some images of various Cush Drives. Essentially, it's a sort of flexible coupler - placing shock absorbing 'cushions' between the drive and driven elements of a power transmission system. Here are some images of Cush drives in motorcycles. In motorcycles, it's generally between the rear sprocket and the wheel. I would think that you could use a flexible coupler, shown below, (as used with hydraulic pumps, often called a spider coupling) between your gearbox and the Nuvinci, you should be able to work it in.

    Ref Burden's surplus sales for reasonable cost for these type of couplings.

    I don't believe that Staton uses a flexible coupling on his Nuvinci (manual ratio adjust) units, but he also uses a freewheel at the rear sprocket, so there is no 'back torque' applied from CVT to gearbox... I think that it would be more important if you are using an engine whose output approaches the upper limits of the nuvinci hub, but, our small engines (50cc and less) generally don't come come close. I seem to recall that the HP limit for the standard bicycle CVT is 7.5 HP... The Honda 50cc engine is rated at 2.5 HP (or, about 1/3 the CVT limit.)

    Attached Files:

    Last edited: Aug 16, 2011
  3. Marple200

    Marple200 New Member

    That's some very good information.

    They say the operating limits of the hub are:
    Maximum Sustained (Pulse-free) Input Torque 65 Nm (48 lb-ft)
    Maximum Instantaneous (Spike) Input Torque 130 Nm (96 lb-ft)
    Maximum Sustained Input Power 5 kW (7 hp)
    Maximum CVP Speeds Input: 1000 RPM / Output: 1000 RPM

    With the following disclaimer:
    Operation at these limits is not recommended for extended durations, and durability is highly dependent on duty cycle. Higher torque and power configurations can be designed for production applications. Power rating is for electric motors, which deliver pulse-free torque. If an internal combustion engine of any type is used, a cush drive system must be installed between the engine and the CVP to dampen out power pulses from piston acceleration, otherwise internal components can fail prematurely.

    If any 50cc motor is well below these limits, do you think I am safe without the cush system?