How does an IGH work (broadly)?
 

Hello,

I have zero knowledge about mechanics and would like to understand how an IGH work.

I read several articles* and watched some videos (mostly those from Dan Burkhart, especially the one of the Sturmey Archer 3 speed AW) and would like to check that I basically got it right:

1. The chain or belt-drive is connected to the sprocket
2. The sprocket is connected to the gears in the hub
3. The axle is fixed; To make sure it doesn't move, its ends are semi-flat so they don't rotate in the drop outs; As extra protection, non-turn washers are added; The axle has a fixed gear in the middle ("sun gear"); The axle nuts must be screwed at around 35-40 N.m
4. Other gears, called "planetary gears", revolve around the sun gear to provide different speeds; They are changed by pulling/releasing the speed cable
5. The planetary gears are connected to the gear hub
6. The gear hub is connected to the wheel through the spokes.

In short: pedals → chain → sprocket → gears → hub → spokes → wheel

Is that correct?

There are also springs and prawls in the equation, but I don't know how they fit.

Thank you.

* The articles:
Internal-Gear Hubs
Internal Gear Hub Theory
Gear train - Wikipedia, the free encyclopedia
Hub gear - Wikipedia, the free encyclopedia
Epicyclic gearing - Wikipedia, the free encyclopedia
File:Bicycle hub gear.png - Wikipedia, the free encyclopedia

The internal gears allow the <hub shell-spokes-and-rim> to turn at a different rate or faster or slower than the gear sprocket turning it.

If there is a pawl to have it pushed out to engage the hubshell and drive it, it needs a return spring to push it out.

like a freewheel/freehub when you apply power the pawls , pushed out by the springs engage ..
when you coast the pawls ride over the ramps and you hear clicking.


Herr Schlumpf's 2 speed crank the pedals turn at a different rate than the chainrings ,

reduction gear cranks turn faster than the chainring , overdrive the chainring turns faster than the cranks.

There are also pawls and springs to allow the coasting operation, not germane to the shifting/gearing functions.

There are stages each having a set of pawls . in high an AW3 klicks as the hub is tuning faster than the low gear pawl set .
so it 'freewheels' over the lower gear Pawl/set.

Hence the "clicking" even when pedaling in certain gears..........

Unless you're using a NuVinci hub. Then the gear ratios come from a pair of disks with a third disk between them. As the central disk touches one (the drive disk) at it's outer edge the central disk angles so that the driven disk is contacting the central disk at the inner point. This is one type of traction transmission. Andy.

Puzzled over their diagrams @ fallbrook tech.

Thought it was a few Big Balls in there .. Have some of those hubs, in bikes in the shop.

I try to explain those referring to the circumnavigation closer to the Poles being a shorter distance than at the equator
so the distance shorter takes less time to go around
Relative input and output distances result in the ratio differences

having a town on a River with fishermen they understand navigation better than those inland where things look so Flat,

Along the lines of the variable snowmobile or golf cart transmission, but with a disc rather than a drive belt.

Some useful animations.

basic 3spd hub:
2.972 How a Three Speed Hub Works

Rohloff stepped gear:
Striptease: www.rohloff.de

A more direct answer to you question is IGH hubs have epicycle gearing. That means diferent gears are achieved by using gears that consist of a ring gear with planet gears and a sun gear. Epicycle gears are used in automatic trannies in cars.