Re: CVT interest



jobst.brandt@xxxxxxxxxxxxxxxxxx wrote:

I can't imagine how you can design a CVT for bicycling, because torque
is much higher than that of a small car, there being a trade-off
between rotational speed and torque. Humans operate at about 50 to
100 rpm, 20 times slower than a motor vehicle engine. Beyond that,
most vehicle transmissions are step-down gears that reduce rpm rather
than a step-up transmission as on a bicycle which runs as much as 1:5
ratio. Beside that, mechanical CVT's work on friction, making this
even more difficult.

http://www.sheldonbrown.com/brandt/continuous.html

Jobst Brandt

I agree that a good bicycle CVT will probably not happen in our life time. However, I don't agree with your arguments:

1) A 250 lb. rider standing on a 7.5 in. crank arm generates 156 lb-ft of torque. The Audi A4 has a CVT with a V6 engine with 207 lb-ft of torque.

2) Stepping up speed should be no less efficient than stepping it down.

3) I agree that current CVT's are less efficient than conventional bike chain drives. However, because some CVTs "work on friction" doesn't mean that they are grossly inefficient. Your tires "work on friction" too but that type of friction does not soak up energy because there is no relative sliding motion between the friction surfaces.

The major drawbacks of a bicycle CVT using existing technology are cost, size, and weight.
.

Relevant Pages

  • Re: how much can you torque a bolt
    ... affect the tensile diameter, after all the pitch is what decides how ... The pitch decides how tightening torque converts to stress, ... Friction is in that sense helpful. ... the bolt shears in torsion before its tensile ...
    (sci.engr.mech)
  • Re: Controllable torque electric motor questions
    ... efficiency loss is almost entirely due to frictional losses, which you need to take into account going from the torque at the motor to the torque at the shaft. ... but if your mechanism is designed to not move you need neither motor nor gearbox. ... As soon as things start moving the gearing efficiency _does_ matter a _lot_. ... because Colombic friction is not a viscous drag that is somehow proportional to velocity, it is a constant torque that must be overcome. ...
    (rec.crafts.metalworking)
  • Re: Swing and momentum
    ... Friction in the bearing allows it to transmit a small torque to the ... torque overcomes the friction and the turntable begins to rotate. ... The child can make the turntable rotate even assuming a frictionless ...
    (sci.physics)
  • Re: Swing and momentum
    ... Friction in the bearing allows it to transmit a small torque to the ... torque overcomes the friction and the turntable begins to rotate. ...
    (sci.physics)
Loading