Girard Perregaux is one of those brands that tend to fly under our radars. They make some breathtaking watches and even supply their manufacture movements to countless, yet for some reason they remain a “humble” brand; often lacking the recognition they deserve. That is, until the Constant Escapement came along.
For the past 5 years, the folks at Girard Perregaux in La Chaux-de-Fonds have plodded away at bringing their revolutionary Constant Escapement concept first showed to the press in 2008 to fruition. At Baselworld 2013, Girard Perregaux took the watch world by storm with their Constant Escapement LM; the first-ever true constant force watch. After receiving the Aiguille d’Or prize at the GPHG 2013, we thought the groundbreaking watch deserved a closer look.
But what exactly is “constant force” in a horological context?
Well, in your average mechanical watch movement with a standard Swiss lever escapement, the balance wheel oscillates with higher amplitude when fully wound, then gradually diminishes as the mainspring uncoils and the power reserve dwindles. This means that the energy provided to the balance wheel varies throughout the watch’s winding cycle, resulting in inaccurate timekeeping
Several watch manufactures have come up with partial solutions to this, most notably the fusée and chain system first seen on 15th century clocks that you can find in a handful of watches today like the Breguet La Tradition Tourbillon or the Zenith Academy Christophe Colomb Hurricane. There’s even the GPHG 2013 “Men’s Complications” prize winner, Romain Gauthier’s Logical One which sees a new take on the fusée and chain. While these do provide a more consistent force to the escapement, it’s not exactly constant force as the energy transferred to the balance wheel throughout the wind cycle is still variable.
And that’s precisely what makes the Girard Perregaux Constant Escapement so darn special. Unlike the fusée and chain system where the force is regulated via the barrels and mainspring, Girard Perregaux’s Constant Escapement, as the name would imply, is a constant force system applied right into the watch’s regulatory organ, which is exactly where you want it to be if perfect chronometry is the aim of the game.
What Girard Perregaux have done, and it really is quite radical, is come up with an escapement system consisting of two escape wheels with an intermediary device between them and the balance wheel. The intermediary device is that purple-blue silicon component you see, with a14-micron thin (that’s 6x thinner than a human hair) silicon blade in the horizontal center. This system uses a “buckling” action that acts as an energy storage unit, compensating for the variable output of energy from the mainspring by giving constant impulses to the balance wheel.
The easiest way to understand how this works would be to do exactly what its inventor Nicolas Dehon did when he first got the idea: take a train ticket or playing card between your thumb and forefinger and bend it to form a “C” then, then push in the arch. You would feel some resistance until it eventually fails and snaps to the opposite side in an exact mirrored position; releasing force as it does so.
On the Constant Escapement, this happens non-stop with the silicon blade pushing the balance wheel forward and compensating for the variable energy of the barrel, while at the same time liberating that exact amount of energy before the process starts again. This means that regardless of the power reserve, the watch will run at a constant rate. Two escape wheels of 3 teeth each running at 3Hz work in tandem to make this happen.
And as if the escapement wasn’t enough, Girard Perragux have also included a patented new barrel system, where the cover and ratchet wheel are made of a single component. The double twin barrels (that’s 4 barrels in total) provide a power reserve of approximately 7 days when fully wound.
With the Constant Escapement, Girard Perregaux have accomplished what so many watchmakers could only dream of, a true constant force escapement that guarantees uniform chronometry regardless of the power reserve. While this first Constant Escapement timepiece is definitely intended as a high-end collectible (notice the Triple Bridges?), it will be interesting to see how Girard Perregaux further develop and implement this technical marvel on other watches in the future…
Words and images by Amr “The Horophile” Sindi