Girard-Perregaux Neo Constant Escapement (Part One) in-depth review
The Girard-Perregaux Neo Constant Escapement is the latest expression of Haute Horlogerie to emanate from the prestigious Manufacture based in La Chaux-de-Fonds. In a series of three articles, Angus Davies looks at constant force and how it confers rate stability. In addition, he provides an insight into this latest creation from the Swiss marque, pointing out the model’s numerous details and the various benefits these confer.
This specific part looks at how a watch works, the problem with fluctuating force within a timepiece and the various historical techniques used to serve the regulating organ with a constant force.
Image – Girard-Perregaux Neo Constant Escapement
How does a ‘regular’ watch work?
Most mechanical watches on the market today are, as you may already know, equipped with a Swiss lever escapement. However, while this latter term is frequently bandied around, many people do not fully understand the workings of a watch equipped with a Swiss lever escapement.
The crown is connected to the winding stem and together with a myriad of tiny components, forms the keyless works. This mechanism features a clutch, allowing the wearer to switch between two modes, depending on whether the crown is in position ‘0’ or position ‘1’. Usually, by pulling out the crown to position ‘1’, the wearer can turn the winding stem to adjust the time indications, including the date (where appropriate). Again, ‘usually’ when the crown is in position ‘0’, the wearer is able to manually tension the mainspring (I will return to this shortly). I’ve used the term ‘usually’ on a couple of occasions as not all watches are the same. Indeed, with some watches the crown may have additional positions and may adjust additional functions; however, for simplicity let’s stick to position ‘0’ and position ‘1’.
When the winding stem is rotated (position ‘0’), kinetic energy is transferred via the transmission wheel to the ratchet wheel. The barrel sits beneath the ratchet wheel and contains a coiled spring termed the ‘mainspring’ (not to be confused with the balance spring). When the ratchet wheel turns, it tensions the mainspring stored within the barrel, causing it to accumulate energy.
Image – Girard-Perregaux Neo Constant Escapement
The amount of energy or force stored within the barrel is significant. If this force were released without any form of control, it could potentially damage some movement components and the energy would disappear within the blink of an eye, meaning the watch would promptly come to a halt.
For a watch to convey accurate information and work reliably, the energy held within the barrel has to be dosed. By sending the energy via a series of gears (the gear train), the magnitude of the energy can be reduced. In effect, the gear train acts a little bit like an electrical transformer, stepping-down the voltage to the desired level.
Once the energy has been stepped-down via the gear train, it reaches the escapement and regulating organ. If we take the Swiss lever escapement as an example, the fourth wheel drives the escape wheel which engages with a pallet lever, serving an impulse to the regulating organ. This in turn allows the escape wheel to unlock, causing the hands to move a defined amount before locking again. It is this repeated locking and unlocking process that controls the ‘flow of time’ ie the watch displays the correct time. However, as I will show later, there are other forms of escapement, albeit they all serve the same purpose.
The problem with force within a watch
Initially, when the mainspring is fully wound, there is an abundance of energy. In some cases, this can actually be excessive with the escapement receiving too much energy, a scenario that may cause ‘rebanking’ or ‘knocking’. This is where the amplitude of the balance wheel is so great that the impulse pin knocks against the outside of the pallet fork, impairing precision. Moreover, the excess force can also damage delicate movement components.
Conversely, as the energy within the barrel diminishes, prior to the watch stopping, the regulating organ will receive insufficient force, leading to a drop in amplitude which, once again, will have an adverse effect on precision.
The relationship between the changing tension of the mainspring and the force serving the escapement can be shown graphically. The force appears as a diagonal line and diminishes in magnitude over time. Ideally, the force reaching the regulating organ should be linear, appearing as a continuous flat/horizontal line on a graph. If the force within a movement is not controlled, the time it actually delivers optimum precision is relatively short.
Historical methods of controlling force
For many years, watchmakers, aware of the problem of waning energy, have sought solutions to ameliorate the issue. Indeed, they have conceived various mechanisms such as the fusée and chain, Geneva stop work and remontoir d’égalité, all of which are separate from the escapement. Allow me to elaborate.
Image – Girard-Perregaux Neo Constant Escapement
Fusée and chain
The fusée and chain consists of a cone-shaped pulley connected to the mainspring barrel by a chain. The chain is wound from the barrel onto the fusée (cone). Where the radius of the cone is smallest, it requires more energy or force to rotate it. As the force within the barrel depletes, the ever-increasing radius of the fusée requires less force to rotate. The shape of the cone ie the degree of slope will influence the behaviour and effectiveness of the system. The fusée and chain mechanism is tried and trusted and works well; however, it is bulky, a factor that will ultimately influence the external dimensions of a watch.
Geneva stop work
The Geneva stop work comprises a finger and a star wheel equipped with a series of arms. The fingerpiece is connected to the mainspring arbor and rotates as the watch is wound, while the star wheel has cut-out sections to form a series of arms. Most of the arms feature concave recesses, save for one arm that has a convex face used to block the star wheel, preventing the arbor from turning. This system ensures that only the flat part shown on the aforementioned graph, the ‘mainspring power curve’, is used and the areas near full wind and zero wind are left unused.
Image – Girard-Perregaux Neo Constant Escapement
Remontoir d’égalité
Lastly, another popular approach to flattening the power curve is to use a remontoir d’égalité. This system involves using an additional wheel, positioned between the fourth wheel of the gear train and the escape wheel. The intermediate wheel employs a short-duration spring to pulse the escapement with a uniform pulse of power. Unlike a mainspring which is designed to harness lots of power that will drive the movement for several hours, the short-duration spring releases a small amount of energy over a few seconds. Again, this form of constant device delivers a relatively flat, horizontal line for several hours with the force diminishing just before the energy barrel becomes totally depleted.
By serving the regulating organ with a constant force, the rate of the watch will remain stable. Returning to the aforementioned graph showing the mainspring power curve, the period the plotted line is horizontal will be much longer, irrespective of the energy held within the barrel. Rate stability is not the same as precision, it’s arguably more important. Indeed, once the movement is regulated, a constant force mechanism will ensure the rate does not fluctuate, conferring superior chronometric performance. This leads me to the Girard-Perregaux Constant Escapement (2013).
Girard-Perregaux Constant Escapement
In 2013, Girard-Perregaux released a timepiece equipped with the ‘Constant Escapement’. Packed with ingenuity and protected by several patents, the innovative mechanism delivered a new means of achieving rate stability. The watch, Constant Escapement L.M, a remarkable exemplar of Haute Horlogerie scooped the GPHG ‘Aiguille D’Or’ in the same year. Unlike the aforementioned systems, the constant force system is not separate from the escapement but an integral part of the escapement.
In part two of my horological trilogy, I will look at the various historical escapements and their relative advantages and disadvantages. In addition, I will return to the Girard-Perregaux Constant Escapement and discuss how it differs from other methods of controlling the flow of time.
Image – Girard-Perregaux Constant Escapement L.M.
Coming next
In the next part, Angus looks at different types of escapement, explaining their characteristics as well as their advantages and disadvantages. Thereafter, he looks at Girard-Perregaux’s pursuit of chronometry including the release of Constant Escapement L.M. in 2013 and the making of its unique silicium escapement spring and buckling blade.
Image – Girard-Perregaux Neo Constant Escapement