Following the deaths of George Daniels (last year) and Derek Pratt (in 2009), François-Paul Journe is perhaps the only living follower of the great 18/19th century French horologist Abraham Louis Breguet that is able to match him in both craft skills and inventiveness.
And it is immediately clear that the Chronomètre Optimum follows Journe's interpretation of the Breguet tradition; the time dial is placed eccentrically on the face of the watch, but the hands are a design Journe has made his own. There is a continuous seconds dial at 9 o'clock and power reserve at 6, but below this the inscription: "Remontoir d'Egalité avec Échappement BHP" indicates, perhaps more importantly, that Journe is also following Breguet's example of continuing horological innovation, addressing two classic problems in mechanical timekeeping. There is also a very French 'peep-show' to be had through the little window at 11 o'clock - it is part of the remontoire; but more of that anon.
The rear view of the watch shows the flawless frosted striping of the 18ct rose-gold watch plate, an anti-clockwise jump-second hand, the 3Hz balance and, below this, the twin escape-wheels of Journe's new version of Breguet's Échappement Naturel, his BHP: High Performance Bi-Axial escapement.
To understand the remontoire and the escapement, we must have a
closer look at the layout of the movement of this fascinating
watch, starting with a few basics. A mechanical watch consists of a
source of power - the mainspring - linked by a train of gears to
the escapement, which is regulated by the oscillations of the
balance wheel. Each gear in the train consists of a 'wheel' with a
large number of teeth and a 'pinion' with a small number of
'leaves', rotating on an arbor.
Looking at the drawing of the movement on the left, enthusiasts may want to follow the gear train, it contains a number of surprises. There is a lot going on, but let's dispose of the peripherals first.
The crown deals with winding and hand setting. Note the twin spring barrels and, on the near one, a train of gears that turn the hand, which shows the power reserve. The sequence of train wheels is numbered, starting from the twin spring barrels. From opposite sides, the barrel teeth engage the pinion of wheel 2 (partly obscured). Conventionally the gearing of the train is calculated so that this wheel turns twice a day - its arbor carrying the hour hand.
We can see that wheel 2 engages the pinion of wheel 3 and that it, in turn, drives the pinion of wheel 4. As wheels have considerably more teeth than pinions, those with mechanical acumen will have realised that the wheels turn faster and faster as we move down the train. Wheel 4 in fact turns once a minute and its arbor carries the jump seconds hand seen on the back of the watch (we'll have more to say about that later).
Normally the 4th wheel would drive the escape-wheel and that would be that. But in Journe's new watch something unusual happens: the pinion of wheel 4 drives an extra wheel, 5, which engages the pinion of wheel 6, which again turns once a minute, in this case carrying the continuous seconds hand seen on the front of the watch. As the watch has a 3Hz balance, this hand will make six jumps a second. Wheel 6 drives 7, which in turn drives the pinion of the first escape-wheel, where a co-axial wheel, 8, meshes with a similar wheel, 9, on the second escape-wheel arbor.
To examine the Remontoir d'Egalité we must return to wheel 5 and discuss remontoires. For good timekeeping there must be a steady supply of energy to the escapement. Classically, due to the way in which steel was produced, mainsprings had very irregular properties, moreover, before the days of precision engineering tooth forms on gears could be uneven and power transmission irregular. Even when these problems were overcome, when a longer running time was required, as in the Chronomètre Optimum, which runs for 70 hours, the initial power of the fully wound spring may overwhelm the escapement. The remontoire is a relatively weak short duration spring, operating between the barrel and the escapement, which is rewound by the mainspring. It is intermittently locked and released to pass its small but, nevertheless, constant power down to the escapement.
The lower part of the train as viewed from the back of the watch.
All the 'normal' wheels in the train are mounted on the watch plate, but not wheel 5. This is mounted on a separate assembly, the remontoire carriage (shaded in yellow on our drawing), which can oscillate on a bearing centred on wheel 6. Note the ratchet-toothed remontoire wheel peeping out from below the dial plate at the top of the picture. The remontoire carriage carries a pallet that locks this wheel. The remontoire spring (shaded blue) pushes this pallet away from the wheel.
The action becomes clearer if we look at the second drawing, showing the lower part of the train as viewed from the back of the watch. We see that wheel 4 drives the remontoire wheel R and, as we have said, carries the jump-second hand. When R is locked, wheel 4 is also locked. The remontoire spring keeps pinion 6 turning by pushing the rim of wheel 5 across it. This movement eventually unlocks the remontoire and wheel 4 leaps anti-clockwise under the power of the mainspring, pulling wheel 5 back to its previous position, tensioning the remontoire spring and relocking the remontoire wheel ready for the cycle to begin again.
Wheel R carries a vertical blade to act as an air brake so that the carriage has time to change position and lock on the next tooth. This fan can be seen in the dial aperture. Journe's remontoire performs the double function of regulating the power of the train and providing entertaining features.
The second drawing also enables us to understand the new BHP escapement. Although the English/Swiss Lever Escapement has been the most successful ever produced, because the pallets impulse the balance indirectly, friction is introduced, lubrication is needed and service intervals are shortened. An escape-wheel can impulse a balance directly, but only in one direction. Clearly to give a direct impulse in both directions, a pair of counter-rotating escape-wheels is required. In the Daniels double wheel escapement such wheels are driven by separate trains.
In Breguet's Échappement Naturel, counter-rotation was achieved by having one wheel driving the other, but the requirements for this arrangement to operate reliably were beyond 18th-century materials and methods. Most of the wheels in the Chronomètre Optimum are made of 18ct gold but those in the escapement assembly are in lightweight titanium, reducing inertia. Swiss precision takes care of the other problems. With the BHP Journe has achieved Breguet's objective.
In the Chronomètre Optimum, Journe combines a number of features to optimise performance: twin barrels deliver power to the 2nd wheel symmetrically and evenly, the remontoire ensures a steady delivery of power to the balance; maintaining a consistent balance amplitude, and the high performance bi-axial escapement does not require lubrication. This watch will probably be another prizewinner for Françoise-Paul Journe.
Further information: www.fpjourne.com