Oscillating Pinion: The Unsung Chronograph Coupling SolutionBy Cheryl Chia
There are various configurations in which a chronograph can be mechanically executed, both as to how the chronograph is actuated via the pusher and how the wheel train of the movement and that of the chronograph are coupled – each no doubt an extensive topic in itself. This article, however, focuses on a specific, alternate configuration of the latter – the poor relative of the horizontal coupling system. For a thorough explanation of the two different actuators, click here.
Coupling systems are typically divided into horizontal clutches as found in many historical or traditionally constructed chronographs such as the Omega 861, the Patek ref. 5070, ref. 5170, the Datograph and the Cornes des Vache just to name a few, and the more modern vertical clutches which, thanks to their compact design, is often found in automatic chronographs such as the Breitling B01 and the Rolex Daytona with the Calibre 4130.
The third and most cost-effective coupling system is the use of an oscillating pinion also known as a rocking pinion that was invented and patented by Edouard Heuer in 1887.
In a traditional horizontal clutch system, a wheel that is mounted on the pivot of the fourth wheel drives an intermediate clutch wheel. When the chronograph is engaged, an intermediate lever shifts the clutch wheel horizontally until it meshes with the chronograph seconds wheel, causing the seconds counter to start ticking. And because the wheels mate horizontally, it is thus called a horizontal or lateral clutch.
The oscillating pinion is a form of horizontal clutch that not only greatly simplified but also improved the engagement of the chronograph. In fact, it is, to date, the simplest, most practical way to couple the going train, which lies on the main plate of the movement, to the chronograph mechanism on top. It is made up of an arbor with a pinion on each end. One pinion meshes with the fourth wheel of the movement and the other, when the chronograph is actuated, pivots to engage with the chronograph wheel. When the chronograph is switched off, the pinion moves away from the chronograph seconds wheel, and the elapsed time hand comes to a halt.
Pros and Cons
The key advantage of the oscillating pinion is that it results in a less visible jump of the seconds hand when the chronograph is activated. While engaging a standard, horizontally coupled chronograph can cause a temporary loss in amplitude as well as the stuttering of the seconds hand as the teeth of the wheels fight to connect, the gear of the oscillating pinion is much smaller, enabling a more orderly, tidier engagement and therefore ensuring minimal impact on the going train. Engagement is also more direct as it does away with the drive wheel as well as clutch wheel, which reduces the load on the gear train. And because of its simple and compact construction, movements can be made smaller, and it can furthermore be combined with an automatic winding system without space concerns.
However, as with horizontal clutches, the teeth profile of the pinion and the chronograph seconds wheel are typically slightly different from the gear teeth in the rest of the movement. Essentially, this fine, pointed teeth, visible in the image above, is not designed for optimal power transmission, but rather to ensure that the wheels don’t collide when they mesh. Thus, like horizontal clutches, the gears would wear out faster if the chronograph is left running over extended periods of time. Hence, a vertical clutch is still superior in this regard as it is driven by friction and does away completely with any toothed engagement that would cause stress.
Admittedly, the main drawback of chronographs that run on an oscillating pinion is more superficial – less parts, hence easier to construct and produce on a large scale, and consequently less desirable – than practical. And the activation of the chronograph is, no doubt, visually less interesting than having a proper horizontal clutch. For these reasons, the oscillating-pinion coupling system is rarely found in high-end chronographs. It is, in essence, designed as an obviously cost-effective, but still impressively reliable and robust piece of engineering.
This is evidenced by its presence in one of the most ubiquitous chronograph movements in watchmaking – the Valjoux 7750 and its various iterations – which power everything from Sinn to Breitling, and thanks to a high-torque mainspring, can often be used reliably as the basis of some highly ingenious watches such as the IWC Doppelchronograph and perpetual calendar.
Introduced in 1974, the Valjoux 7750 was among the earliest automatic chronographs along with the 1969 release of the Heuer-Breitling-Buren caliber 11, the Seiko caliber 6139 and the Zenith El Primero. It dispensed with the column wheel in favour of a layered switching cam for coordinating the start, stop, and reset functions. Crucially, unlike the column wheel, the cam system could be flat stamped and produced in numbers. In the same vein, its simple construction meant that it is less expensive to manufacture while simultaneously being more reliable.
The use of an oscillating pinion allowed the movement to do away with the more conventional driving wheel, intermediate wheel and the arm that carries it. The lower pinion is continuously engaged with the fourth wheel of the movement and when the chronograph is engaged, the cam acts on the pinion arm to bring the upper pinion into engagement with the chronograph seconds wheel.
As mentioned previously, the oscillating pinion system is rarely found outside of Valjoux 7750-derived movements, let alone in high-end chronographs. But, intriguingly, in recent times, there have been a handful of chronographs across various price points north of a Valjoux that have adopted this coupling solution, which, when viewed from the context of each of their unique movement designs, make for extremely compelling watches, nonetheless.
IWC Portugieser Monopusher Chronograph
Though IWC has conceived many ingenious 7750-based movements in the past, one of the most distinctive and unique chronograph movements of recent times is the Portugieser Monopusher Chronograph. Due to the nature of the movement, essentially the brand’s superb 8-day cal. 59000 movement with a chronograph mechanism built on top, the most practical way to couple the chronograph mechanism with the seconds wheel of the base movement was with an oscillating pinion. When the chronograph is activated, the lever supporting the upper pivot of the oscillating pinion is tilted towards the chronograph wheel, engaging it.
As it is a monopusher, the column wheel features three times the number of ratchet teeth to the number of pillars to control the three states: start, stop and reset. The top lever is the reset hammer, which strikes the heart cams of the chronograph second and minutes to reset the respective counters. A brass lever acts as the chronograph brake to ensure that chronograph seconds hand is held firmly in place when the chronograph is stopped. And finally, a third lever at the bottom acts as the clutch lever that tilts the oscillating pinion towards or away from the chronograph seconds wheel to engage or disengage the chronograph respectively.
In terms of performance, apart from having an impressive 8-day power reserve, the movement also features a free-sprung balance wheel.
TAG Heuer Carrera Heuer-01
Unlike the Heuer 02 Chronograph movement which utilises a vertical clutch, the Heuer 01 relies on an oscillating pinion. The movement is based on the Calibre 1887, named for the year Edouard Heuer invented the oscillating pinion. Though made in-house by TAG Heuer, the Calibre 1887 is in turn based on the construction of the Seiko chronograph cal. 6S37, which TAG Heuer had licensed.
The movement is straightforward but no doubt a step up from the standard Valjoux 7750. It is column-wheel controlled, runs at 4Hz and has a 50-hour power reserve.
Admittedly, the appeal of the watch lies more so in the strength of its package. When the Carrera Heuer-01 was launched back in 2015, it was among the first chronograph watches executed in such an ultra-contemporary style at an affordable price with an in-house movement to boot.
F.P. Journe Line Sport Chronographe Monopoussoir Rattrapante
The most surprising candidate on this list to use an oscillating pinion is the F.P. Journe Line Sport Chronographe Monopoussoir Rattrapante as it speaks of a practicality that is rather unusual at this level and sector of watchmaking.
However, François-Paul Journe has long been a champion of this coupling system as some would recall the monopusher chronograph movement developed in the 90s by the group Techniques Horlogères Appliqueés (THA), which consisted of Vianney Halter, Denis Flageollet and Journe himself. The hand-wound movement, which ultilised a column wheel and an oscillating pinion, was first used in the Cartier Monopoussoir CPCP and subsequently in the De Bethune Monopusher DB1.
With the use of this clutch system, the Line Sport Chronographe Monopoussoir Rattrapante was able to be priced extremely attractively, starting from 58,000 Swiss francs for the titanium version and 78,000 Swiss francs for the red gold model – a tiny fraction of the selling price of the 2017 Only Watch version which utilised a proper horizontal clutch.
Due to the compact size of the oscillating pinion, the movement, unsurprisingly, appears slightly empty as compared to traditional, horizontally coupled chronographs with its associated wheels and levers. But naturally, Journe’s use of red gold movement bridges and plates makes up for this in spades. It provides a high contrast to the grey, straight-grained steel springs and levers above.
As with many F.P. Journe watches, the movement is impressively slim, helped in part by the wide and flat levers. It is, in fact, among the slimmest split-seconds chronographs on the market at 12mm high. And in terms of performance, the movement is designed with an impressive 80-hour power reserve, made possible by its sheer diameter.
Bulgari Octo Finissimo Tourbillon Chronograph Skeleton Automatic
The Bulgari Octo Finissimo Tourbillon Chronograph Skeleton Automatic is a startling accomplishment with an ingeniously constructed movement incorporating many interesting ultra-thin solutions in terms of the tourbillon, the chronograph, and the automatic winding mechanism respectively that it is better served in a separate article.
To reduce the height of the movement, the balance wheel, for instance, is free-sprung while the tourbillon is driven by a gear on its periphery rather than the conventional pinion beneath the cage. This reduces the overall height of the tourbillon while also ensuring that it allows space for the chronograph mechanism on the same layer.
Typically, a chronograph mechanism is built on top of the tourbillon, which lies on the main plate. To put things into perspective, consider that a Valjoux 7750 was built with a main plate, a chronograph top plate as well as an upper bridge on top of the chronograph top plate for the automatic winding system.
Additionally, and most strikingly, the Octo Finissimo Tourbillon Chronograph features a chronograph clutch lever that sits flush with the lower tourbillon bridge and connects the column wheel to an oscillating pinion. When the chronograph is actuated, the lever tilts the oscillating pinion towards chronograph seconds wheel, thereby engaging it. In other words, due to space constraints, it is the tourbillon cage that drives the chronograph instead of the fourth wheel. Presently, it is the only chronograph tourbillon movement with such a set-up, and its performance remains to be seen. The mechanism also utilises a one-piece, laterally-sliding reset hammer which simplifies construction and ensures uniform reset of the counters.
The movement boasts a respectable 52-hour power reserve, made possible by a balance wheel that is unusually small for a beat rate of 3Hz.
Richard Mille RM 72-01 ‘Lifestyle’ Flyback Chronograph
Last but by no means least is the RM 72-01 ‘Lifestyle’ Flyback Chronograph which introduces a novel double-pinion system that is said to improve performance of the traditional horizontal clutch or single oscillating-pinion system on a fundamental level.
In a standard Valjoux 7750, the barrel has a pinion in the center that drives the hour recorder directly with a friction clutch. The barrel also drives the motion works for the main hour and minute hands, all of which of course, takes place on the dial side.
The chronograph minutes, on the other hand, is driven by the chronograph seconds, which draws power from the fourth wheel of the movement when engaged. And because the fourth wheel is the fastest spinning wheel in the going train yet also the wheel furthest from the mainspring, there is a necessary loss in amplitude that occurs when the power flow is divided during engagement.
In the RM 72-01, the going train of the movement powers the chronograph seconds but the chronograph minutes is driven by a separate train (a reduction gear) on the dial side, powered directly by the barrel. This essentially isolates the chronograph minutes from the primary going train, which would help reduce the aggressiveness of the impact when the chronograph is engaged.
This is a rather straightforward yet clever solution that is extremely compact. The watch measures just 11.68mm high, and is naturally, considerably thinner than the RM 11, which used a Dubois-Depraz module with a vertical clutch.