The new IWC automatic winding system

Il nuovo sistema di carica automatica IWC

In issue no. 159 of L'Orologio, currently on newsstands, we continue our analysis of the new IWC 89360 chronograph calibre with a description of the new automatic winding system, which uses a ratchet reverser based on the same principle as the Pellaton system developed by IWC between 1944 and 1952. The working principle of this mechanism is based on an intuition of the Swiss watchmaker Louis Recordon, who in 1780 patented an idea for an automatic winding system in England (we speak only of an idea and not of a design, because the drawings in this patent are little more than sketches), which allowed the watch to be wound in both directions of rotation of the winding rotor, by means of a saw-tooth wheel and two pushing levers.

It was from this idea that Albert Pellaton derived the first version of the IWC automatic winding mechanism, equipped with an oscillating weight (rotor) with limited rotation (at an angle of less than 360°). The first lever-operated inverting device, characteristic of Pellaton's automatic winding, worked with two pushing levers, just as in Luis Recordon's idea, but was later replaced in the final version of 1952 (with a freely rotating rotor, as on all modern automatic calibres) by a similar ratchet device, i.e. with two pulling levers.

The system is still used today on IWC calibres in the 5000 family, which began in 2000 with the launch of the new Portuguese automatic.

For the new chronograph movement, however, the company developed an evolution of the Pellaton system, along the lines of those already used by Seiko and Jaeger-LeCoultre in the late 1960s, but with an important modification.

How it works.

The gear wheel integral with the rotor transmits motion to the first reversing wheel, on which two superimposed eccentrics are fixed. The two eccentrics are in essence two small cylinders whose centres do not coincide with the axis of the reversing wheel, nor with each other. On each of the two eccentrics is pivoted a pair of ratchets, the arms of which overlap two by two and embrace a saw-tooth wheel. The function of the eccentrics is the same as that of a heart cam in the Pellaton system: when the first reversing wheel rotates, through the action of the winding rotor, the two eccentrics cause the ratchets to oscillate.

The doubling of the ratchets (two on one side and two on the other of the saw-tooth wheel) increases the efficiency of the system, as it halves the dead points of the system, i.e. when the ratchets are positioned in such a way that they can neither engage nor push the teeth (e.g. ridge against ridge), thus taking part of the rotor's rotation before becoming active. This is an improvement over both the Pellaton system and the Seiko and Jaeger-LeCoultre systems, whose construction is similar to that of the reverser just seen, but with only one pair of ratchets.

Another obvious advantage of the new invertor system is its simpler construction compared to the Pellaton, with fewer components and their easier positioning, which has a significant impact on assembly time and thus labour costs.