ETA AUTOMATIC WINDING
The automatic winding system first developed by Eterna (which joined ETA in 1932) is certainly the most widely used bidirectional system in the world. With the possible exception of the Jaeger Le Coultre switching-rocker system
(which does not rely on click wheels) it is perhaps also among the most reliable. With reference to the illustration above the power flow from rotor to mainspring (yellow arrow) is illustrated for clockwise rotation of the winding rotor (green hub, with a large lighter green area indicating the rotor mass). Both click wheels are turned by the rotor, but the click between upper and lower wheel is engaged only on the left click wheel (upper and lower are not engaged on the right). Power is thus transmitted from (1) the rotor to (2) the upper left wheel, to (3) the lower left wheel, to (4) the lower right wheel, to (5) the first reduction gear, to (6) the second reduction wheel, and to (7) the mainspring barrel itself. The reduction wheels are necessary to reduce the fast, low torque movement of the rotor into slower, higher-torque movement adequate to wind the mainspring.
With counter-clockwise rotation of the rotor (illustrated below), the upper and lower right click wheels are engaged, while the upper and lower left wheels are disengaged. Thus power flow is transmitted from (1) the rotor to
(2) the upper right wheel, to (3) the lower right wheel, to (4) the first reduction gear, to (5) the second reduction wheel, and to (6) the mainspring barrel itself.
Because the rotor gear and both upper click wheels are constantly engaged, it can be seen that clockwise rotor motion produces unproductive “idling” rotation of the upper right click wheel during winding. With counter-clockwise rotation of the rotor, idling rotation of both the upper and lower left click wheels occurs. (The JLC switching rocker also eliminates this action).