A Closer Look Into Watches With Dual-impulse Escapements
We delve into the other types of dual impulse escapements that have shown great promise in modern watches.
The lever escapement was invented by Thomas Mudge in 1854 in a bid to provide timekeeping capabilities superior to those of other portable timekeepers. How well this goal has been achieved is attested by the accuracy of modern wristwatches, albeit through an evolution of more than 250 years.
As a recap, the success of the lever escapement is attributable to the solidity of its construction, and in contrast to the detent escapement which only impulses the balance in one direction, it provides an impulse to the balance at each vibration, or twice per oscillation, making it is more resistant to shock and importantly, enabling it to be self-starting. However, the lever escapement is far from perfect, particularly with the effects of sliding friction at its impulse surfaces.
This principal weakness was further amplified as beat frequencies began to increase in the 1960s from 2.5Hz or 3Hz to 4Hz and 5Hz (El Primero), leading to numerous attempts at improving its efficiency, primarily reducing the source of friction with new materials and geometries, while others have refocused their efforts on developing alternatives.
A look into natural escapement
Chief among them was George Daniels (1926-2011) who embarked on what was perhaps the most sustained escapement research project since the 19th century. In his book Watchmaking, Daniels expressed that “While it is not suggested that the [lever] escapement cannot be improved, it is probable that the limit of efficiency in the interrelated action of its components has been reached.” Despite its excellent performance in the short term, the problem of frictional changes at its pallets still persists, which led Daniels’ on a decades-long journey in search for an oil-free alternative that culminated in the Co-Axial.
However, prior to that, he invented another escapement that was theoretically superior to the Co-Axial in that both impulses provided to the balance wheel are direct – the independent double-wheel escapement. However, the basic principles of its system proved limiting to the design of the movement as a whole. In addition, the complexity of its construction made it unsuitable for mass production, which only adds to its charm.
Introduced in 1976, the independent double-wheel escapement was in turn founded on the principles of Abraham Louis Breguet’s natural escapement. Having recognised the drawbacks of the then-newly invented lever escapement, primarily its need for lubrication, Breguet sought to design a superior escapement that combined the dual-impulse, self-starting capability of the lever and the direct-impulse, frictionless operation of the detent escapement while eliminating their weaknesses. Characterised by two counter-rotating wheels, the natural escapement was so-called because the impulses given are direct at each vibration, eliminating the need for lubrication.
Breguet experimented with various configurations of this escapement, beginning with having the twin escape wheels mounted on two additional gears, which were directly driven by the gear train. He eventually eliminated the two gears entirely to reduce inertia. In this design, the first escape wheel drives a second escape wheel directly while a set of vertical pins served to lock and unlock the detent. However, due to the manufacturing tolerances of his time, he never fully overcame the issue of play between the geared escape wheels and abandoned the idea to focus on improving the lever.
Breguet’s idea has since inspired three distinct trajectories of development in modern watchmaking. The first branch has greatly benefitted from modern materials such as silicon and nickel phosphorous, which can be fabricated with extreme precision, thereby managing to achieve a construction that is faithful to Breguet’s most effective design, eliminating the issue of backlash caused by play in the coupling of the escape wheels. Some examples include the Ulysse Nardin Dual Direct Escapement as well as the Laurent Ferrier Natural Escapement.
The second adopts Breguet’s earlier design by utilising a pair of auxiliary wheels below to drive the escape wheels above. Modern computer numerical control (CNC) machines, which allow for the fabrication of parts to precise tolerances, has made this configuration viable. However, it still results in a high-inertia construction that totals four wheels being driven by a single gear train. Notable examples that employ this configuration are the F.P. Journe Bi-Axial High-Performance Escapement as well as the Voutilainen Double Direct Impulse Escapement.
The third and most concrete solution, as developed by Daniels, was to allow each escape wheel to be driven by its own gear train and mainspring, eliminating the geared connection in the previous two approaches. Because each mainspring powers only one escape wheel, as with a standard movement, transmission efficiency is significantly higher.
Although Daniels was captivated by the seductive qualities of the double-wheel escapement, incorporating it in a total of six watches including the pair of Space Traveller watches, he had identified several inherent disadvantages. In his book Watchmaking, he noted that the double unlocking at each vibration consumes balance energy and above all, he believed that its complex construction could not be sufficiently miniaturised in a wristwatch.
However, since then, two watchmakers — Charles Frodsham and Bernhard Lederer — have accomplished this, albeit in fairly large cases due to the nature of the movement. Though both have increased the beat frequency to 3Hz, Frodsham’s execution was closer to Daniels’ original design while Lederer’s version represents an evolution.
In an approach that is as obsessive as it is impressive, Lederer altered the geometry of the escapement, primarily the principal locking pallet, to eliminate recoil as well as to prevent the escape wheel from whizzing past the impulse pallet at low amplitude.
Secondly, each gear train is equipped with a remontoir — a mechanism that, while birthed to address the fundamental problem of unequal torque in a movement as the mainspring unwinds, is particularly beneficial for an escapement that is reliant on the parity of two separate gear trains. And lastly, because the remontoir releases fixed, small doses of torque each time, the escapement was fashioned from titanium to ensure the lowest inertia.
These successful attempts at implementing the double-wheel escapement in a wristwatch have in turn evinced what appears to be a greater disadvantage limiting its potential. Because each escape wheel was powered by its own gear train, the escapement could not be conveniently implemented in a tourbillon watch. English watchmaker Derek Pratt had indeed created a tourbillon watch with a double-wheel escapement, but it was not without significant modifications to the entire construction of the movement.
While Daniels’ is not the only one to have developed an alternative escapement in the last 50 years, he proved that the only way to make a meaningful, long-term contribution to precision watchmaking was to ensure its maturity and adaptability to large-scale industrial production.
Conceived in 1975, the Co-Axial was designed with the same goal in mind to realise the merits of both lever and detent escapements without either of their shortcomings. In Omega’s movements, the implementation of the Co-Axial typically necessitates four major components after the fourth wheel of the movement: an intermediary wheel (because the co-axial escape wheel has fewer teeth and spins faster than a regular escape wheel), a pair of coaxial escape wheels, a lever with three ruby pallet stones, and a roller carrying a ruby impulse stone and a ruby impulse pin.
Though it provides the balance with two impulses per cycle, one of these is indirect. The teeth of the large escape wheel impulse the balance directly in a clockwise direction while the teeth of the smaller escape wheel give an indirect impulse to the balance via a lever in a counterclockwise direction. As such, the two impulses could potentially vary in force, though in practice this issue is more abstract than practical, and the advantages that the escapement has over the Swiss lever greatly outweighs it.
The key advantage lies in its high transmission efficiency. Because the transmission of force is tangential, there is little to no friction between the contact points. In other words, the escapement does not require lubrication. However, Omega still lubricates them to ensure longevity.
Roger Smith, the spiritual heir to Daniels, has since designed a single-wheeled version to reduce inertia. Today, the Co-Axial remains the only alternative to the Swiss lever that has been successfully implemented on an industrial scale.
Grand Seiko dual impulse
Last year Grand Seiko debuted a promising new dual-impulse escapement that is presumably slated for mass production, beginning with the new high-beat calibre 9SA5. The new escapement bears similar characteristics to both the Swiss lever as well as the Co-Axial and can effectively be seen as an intermediate design in the evolutionary ladder.
It shares the same basic principles as the Co-Axial in that one of its impulses is transmitted indirectly. The escape wheel impulses the balance directly in one direction and indirectly via a lever in the other. However, while the Co-Axial utilises radial friction, the new escapement relies on a sliding action to deliver impulse to the lever like a traditional Swiss lever escapement, albeit halved.
In other words, it differs from the Co-Axial as the angled pallet reintroduces the need for lubrication. Overall, it still offers superior efficiency compared with the Swiss lever while being simpler and less finicky than the Co-Axial, requiring just one escape wheel.
Apart from doubling down on mainspring torque to power a high-frequency balance wheel, the escapement was also designed to operate with low inertia. The pallet fork and lever are produced using a lithography technique known as MEMS resulting in its exotic, skeletonised parts that are lighter to ensure the quickest rotational acceleration. As such, the calibre 9SA5 accomplishes the rare feat of having both a long power reserve of 80 hours as well as a high beat rate of 5Hz.
With modern manufacturing techniques and materials, the traditional Swiss lever escapement has no doubt seen a remarkable evolution, with prime examples being the Rolex Chronergy and the Patek Philippe Pulsomax. However, the inherent challenges in attempting to design a practical watch escapement, let alone one that can eclipse and supplant the lever, have made these highly sophisticated alternatives a standalone complication in their own right – and thankfully without the associated premium.
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To read the other parts of this series:
- Part 1: Sprung Up – A Deep Dive into Watch Escapements Part 1; Sprung Up – A Deep Dive into Watch Escapements Part 2
- Part 2: Balancing Time – We Cast Our Eyes on the Balance Wheel
- Part 3: Examining the Escape Wheel and Pallet Fork
- Part 4: Deep Dive Into Natural and Detent Escapements of Watches
- Part 5: A Look Into a Watch’s Direct Dual Impulse System