Bevel friction wheel 2 transmits rotation to bevel friction wheel 1 which rotates together with shaft 5. The required normal pressure between wheels 1 and 2 is developed by spring3. At normal load, nut 4, spring 3 and wheel 1 all rotate together with shaft 5. When the load is increased, shaft 5 is slowed down with respect to wheel 1 and nut 4, which slides in wheel 1 along a feather key, so that nut 4 moves downward along thread a of shaft 5, increasing the compression of spring 3 and the normal pressure between the friction wheels. The opposite occurs when the load is reduced.
$3371$SmF,ML$