Since more than one decade, Greubel Forsey is investing in research aimed at developing a mechanical watch movement with 180 days of power reserve. For this aim, the brand set up the EWT (Experimental Watch Technology) Laboratory and implemented the Mechanical Nano project to address the two major constraints that need to be mastered: energy and space.

Today, Greubel Forsey presented Episode 2 as a major breakthrough of the Mechanical Nano project (I wrote about this before, click here ), the Nano Foudroyante EWT, a concept study that for the first time test ever, produced results obtained from a practical watch:



For introduction, a Foudroyante (or flying seconds) mechanism is a jumping seconds indicator which divides a second in several equal partitions, usually four, five, even eight times to indicate quarters, fifths or eighths of a second.

Greubel Forsey started from scratch with a complete rethink of the mechanism so that it effectively only consists of three sections.





This new construction consists, first of all, of a mobile with a double conical-toothed wheel (a) with a very low moment of inertia, which takes its information directly from the escape wheel (b). This principle means that a full gear train is no longer needed to ensure the sub-division of seconds (c):





The last aspect becomes immediately clear if one compares the construction (bottom) to a classical Foudroyante train (top):





By making use of novel state-of-the-art production techniques and a new conceptual approach to the mechanism, both complexity but also size could be tremendously reduced:





It comes as no surprise, really, that the current implementation has one drawback: it is extremely small, too small to read. The Foudroyante hand, for example is only 1.4mm long.

Greubel Forsey thus embedded a 23x loupe on the side of the case to allow appreciating it...easier:





I put together a small video showing the Foudryante hand in action:



So, what are the results of this experimental watch? Quite significant, I might say, after reading through the study* published:

As mentioned above, the currently implementation focuses on the reduction of inertia of the Foudroyante mechanism by simplifying and miniaturising the mechanism.

As the latter is directly coupled to the escape wheel, the additional inertia is easily calculated:

• (a) inertia of a classical escape wheel train
• (b) inertia after addition of the double conical-toothed wheel
• (c) inertia of the foudroyante display (arbor, pinion, hand)
• (d) inertia of the total system as experienced by the escape wheel (r=gear ratio between conical wheel and conical pinion; r=5)
• (e) relative inertia between a classical gear train and the Nano Foudroyante-added geartrain

As you can see, the differences are minimal and thus only claim a marginal cost in terms of energy usage. Just to give you an idea, the relative variation of torque on the mainspring barrel is directly dependent on the  differences in inertia:


(a=0.1025; c=1; both experimental values determined by EWT Lab)

In other words, to maintain a constant amplitude of the balance, only little additional torque is needed. If calculated further, the total loss of amplitude caused by addition of the Nano Foudroyante EWT is only 6°, while the total additonal energy consumed by the system is just 16 nanojules (nJ) per jump.

By way of comparison, a classical foudroyant seconds system consumes 30 microjoules (μJ) per jump.

In other words, the Nano Foudroyante EWT requires 1800x less energy and 96% less space!



But this does not stop here: Greubel Forsey's EWT lab is currently working on an improved version which:

(i) displays the Foudroyante seconds on the dial plane and

(ii) further reduces energy needs down to 5 nJ per vibration, resulting in only 1.2° reduction in amplitude!

For this, the patented GF Diamond Pivot system (US 2011/0044141 A1) will be implemented.

Of course, Greubel Forsey did not set out to produce a high-efficiency Foudroyante system. The overall goal is to revolutionise energy usage and space requirements of a movement, eventually enabling a wristwatch with half-a-year autonomy. The Foudroyante is just an intermediary step to prove their results in a practical application.

Impressive, impressive! Greubel Forsey is on an exciting path, and I am happy to be in-the-loop, as the progress unfolds.

Stay tuned!

Cheers,
Magnus
_____
*)

See: C Zwahlen, F Corneille, F Deschanel: Mechanical Nano. Bulletin Société Suisse de Chronométrie No. 84 (December 2017), p.23ff