The Calibre 8541 watches from IWC.

The history of the development of the mechanical automatic movement. From 1944 to the present day. It all began in 1944 when Albert Pellaton from Le Locle was appointed head of technology at IWC. As descendant of a famous watchmaking family he set to work immediately on the development of the mechanical automatic wristwatch. The first design was patented in Switzerland on June 14, 1946, under number 254 578. The model was of the type with limited rotor movement, although it contained all the important elements that were subsequently incorporated in series production. The fact that a winding rotor with unlimited movement would offer considerable advantages started a boom among potential manufacturers of such timepieces. Just how lively were the efforts to find the solution can be seen from the number of registered patents and in the diversity and originality of designs. The aim was to solve the problem by means of differently shaped cams. Some watchmakers believed that these should be rotated by the winding rotor and that their edge should always force the levers and forks to the desired reciprocal movement. Others believed that a crank pinion or a few cams would suffice All these systems had inventive defects of one kind or another. Either the power ratio of the mechanism was not sufficient for the maximum exploitation of energy, or there would be too much friction and attrition, or the production costs would be too high, or assembly on the movement would be time-consuming and difficult. It was again left to the creative researchers of IWC to find the decisive design. And it was the only automatic movement design that, instead of causing criticism, led to a celebration. On June 7, 1950 it was registered for patent. We should now like to present you with the technical refinements of this revolutionary design:

The reciprocating motion transmitted to the ratchet support by the cam 1 had a dual function: it enabled the winding rotor mounted on the pivot 2 to rotate freely, and it also activated the shock absorber 3 which cushioned the rotor, the cam and the entire mounting from knocks in any direction. The heart-shaped cam (which had long been in use as a means of returning chronograph hands to the zero position) enabled a maximum exploitation of energy, while both discs 4 on the prongs of the ratchet support, which rotated against the contact surface of the cam, considerably reduced the energy loss through friction. The rotary movement of the ratchet wheel 5 was transferred direct via its pinion 6 to the winding wheels 7 and 8 without the need for an intermediate geared coupling. Besides keeping the movement extremely slim, this also reduced production costs and, not least, eliminated a source of potential malfunction.

Two further IWC innovations were also protected by Swiss patent. Firstly, the combined automatic winding mechanism and movement and, secondly. the winding rotor mounting. One of the most outstanding external features of the IWC automatic wristwatch movement is the case with which it can be serviced: the winding rotor can be removed from its pivot 11 simply by loosening a single screw and pulling back the retaining fork 10.

The rotor mounting is likewise secured by one screw for easy removal, while the other two main elements in the automatic winding mechanism, the ratchet mounting with the fork and the ratchet itself, are both mounted under a single bridge, which is held in position by two screws. When the watch was being designed very special care was taken to ensure unimpeded access to the barrel. This can be detached easily, with no need for prior removal of other parts of the movement, once the two screws retaining the barrel bridge have been loosened. The efficiency of the winding rotor's shock absorbing system has made it possible to fit the bearing with two sensitive rubies 12 and 13. These jewels, together with the slim, highly polished steel pinion 11, have helped to make the automatic winding mechanism highly efficient. And this all contributed to making the IWC watches with Calibre 8541 watchmaking masterpieces.

From the IWC catalogue A01686/01.91  October 1989


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