Energy Saving energy: the ultimate quest in movement design
The energy from the mainspring barrel is never fully delivered to the balance-wheel and a significant amount of energy is lost along the transmission chain. How can this be prevented?
Ecology and horology share a common concern of saving energy, rightly regarded as a rare resource. When it comes to timepieces, many different forms of progress have been made on the escapement and on materials. Nonetheless, there is one fatal flaw that must be dealt with: some of this precious energy is inevitably lost between its starting point in the barrel and its arrival at the balance-wheel. ‘Some’ can in fact mean a substantial amount!
Disappearing into thin air
The losses measured in this field are definitely pretty awe-inspiring: almost two-thirds of the energy produced by the barrel goes up in smoke. This steep rate stems from two main factors: friction between components and air friction. It is indeed this issue that Cartier sought to address with its ID Two introduced in 2012 – a concept watch that involves fitting the movement in a vacuum-sealed case and thus eliminating at least one of the friction factors.
Without going to such extremes, the air present inside a case remains a largely unknown enemy and its main victim is the balance-wheel. It is important that this organ has the same volumes of air around its circumference along the path of its oscillations. If one side of the balance happened to be too close to a bridge for example, this sudden proximity would result in an excessive air/balance-wheel friction coefficient. The balance-wheel must have room to breathe!
Staring down the barrel
Attentive scrutiny of the transmission chain as a whole reveals that one of the main spots where energy is lost is the barrel itself. “Around 15 to 20%,” according to Eterna’s Vice-President Samir Merdanovic. That is what led this particular manufacturer to take a closer look at this part of the engine. Between 2007 and 2009, Eterna became the first to create a ballbearing-mounted barrel, christened the Spherodrive. This energy-saving advantage right from the barrel was implemented in the 3510 calibre powering the Madison watch, which has an eight-day power reserve.
The subsequent element in the transmission chain is the gear-train, where a substantial amount of energy is also lost. Where exactly? On the wheels themselves, because of their shape or their material.
As far as the shape is concerned, modifying the profile of the teeth makes only a very small difference, but in this frantic rush to improve efficiency, every little counts. Priority is thus given to cutting the teeth profiles so as to ensure a minimum of contact between them.
Meanwhile, materials can reduce friction and thus the loss of energy. Silicon is currently all the rage but is still confined to the regulating organ and there are as yet no silicon gear trains. For the time being there are only two materials boasting high energy efficiency: brass and CuBe, an acronym of the copper-beryllium alloy.
Cartier is a notable exception. “We have already made silicon gear trains and it is definitely possible,” says Carole Forestier-Kasapi, Director of movement development for the Fine Watchmaking division. “It nonetheless remains a very tricky exercise. To enhance their hardness, we also know how to apply a diamond coating on our parts. All these developments are helping us build bridges towards the future of horology.”
“It’s an interesting approach but still hard to industrialise,” points out Salvador Arbona, who creates Richard Mille movements. “That being said, we have a similar approach to the importance of surface treatments; for Richard Mille, all our wheels are cut after rhodium plating so as to avoid any subsequent dispersion of matter”.
Christophe Claret brings things back to basics and issues a stern warning: “In a gear train, what really counts is accuracy. This means that burnishing is of crucial importance, as is the calculation of clearances. Tolerances are extremely tight and there is no room for rough estimates – not now and not ever, because any lack of precision today will generate a set of problems in the future that will only worsen as time goes by”.
The balance-wheel, an energy sinkhole
Finally, at the end of the chain we find the Swiss lever escapement and the figures are eloquent, showing an almost 35% loss of energy. Many in the industry regard improving the gear trains, the barrel and lubricants as mere cosmetic enhancements that are in fact tantamount to filling a leaking bucket.
From this standpoint, the real transition would involve devising a new and more efficient type of balance-wheel. Carole Forestier-Kasapi is working towards this, while not neglecting potential ways of optimising the Swiss lever escapement: “we have to deal with friction of the pivots, of the materials in contact with each other and with air. 30 to 35% of the energy is still being lost at the balance-wheel, but there is still room for optimisation”. Christophe Claret specifies his own view: “Above and beyond issues with materials, correct adjustment of the escapement is also key. A well-regulated escapement is accurate and limits pointless losses of energy. This is an operation requiring both time and competence, but for us there is no question of stinting on this area.”
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