Girard-Perregaux Constant Escapement Watch Features

Girard-Perregaux unveiled a new invention: a constant force escapement incorporating a thin blade that flexes back and forth. This year, the brand unveiled a watch containing the de- vice. Those who have been waiting for the watch were not disappointed: the consensus among the watch cognoscenti was that it was a highlight of the show.

At the heart of every mechanical watch there is a regulating organ, typically a balance wheel and hairspring, which manages the rate at which the energy from the barrel is released. The more accurately the regulating organ releases the energy, the more accurately the watch keeps time.

The lever escapement, which transmits the mainspring’s energy to the balance wheel, is an engineering marvel, but it has an Achilles’ heel: it can only send the balance wheel the energy it receives, and that energy diminishes as the mainspring winds down, which affects timekeeping accuracy. In a typical wristwatch, the bal- ance wheel’s amplitude can vary by up to 60 degrees as the energy it receives declines.

Some watchmakers seek to improve accuracy by stopping the movement when the power reserve nears its end. A few  have incorporated a remontoir d’egalité – an ancient invention in which a spring is periodically armed or charged with the goal of delivering regular or constant force (impulses) to the balance, regardless of how much energy the spring receives.

That the spring remontoir dates from John Harrison’s work on the marine chronometer H2 in 1739 illustrates both how important constant force is to timekeeping accuracy and how long horologists have been employing springs to achieve it. Earlier remontoir systems date to the 1500s.

G-P’s escapement takes a new approach – one that depends on watchmaking’s wonder material, silicon. Like earlier constructions, G-P’s adds an intermediate spring that stores and releases energy; however, the spring’s form is entirely new. The spring is a 14-micron-thick silicon blade – that’s one-sixth the diameter of a human hair. The blade is formed in one piece with, and at- tached at each end to, a butterfly-shaped silicon frame.

G-P’s watchmakers worked with physicists at the Centre Suisse d'Electronique et de Microtechnique (CSEM) in Neuchâtel to calculate the ideal blade characteristics. In the center of the blade, and integral with it, is an arming lever through which energy is delivered to the blade. Twin escape wheels, each with three smooth “teeth” that look more like modified snail cams than the typical jagged-edge disks, give impulses to jewels on the arming lever. The blade changes shape as it absorbs the energy, then snaps back, delivering a consis- tent impulse to the balance wheel.

The watch itself, called the Constant Escapement, is 48 mm in diameter. The balance wheel and escapement occupy most of the lower half of the face under- neath three small bridges with distinctive Girard-Perregaux arrow-shaped ends. The case is white gold. Price: $123,500