Putting the power reserve display on the back of the watch is nothing new. Incorporating the display into the movement has also been done. Incorporating the power reserve display onto the winding rotor, on the other hand, is a patented world first. Let’s see how Blancpain’s newest L-Evolution Tourbillon makes this technical leap.
Blancpain’s newest L-evolution model is equipped with a tourbillon and a large date display, but the most interesting bit is the power-reserve indication on a subdial directly integrated onto the oscillating weight. This new complication has been achieved by an original and complex construction. Within this solution, the oscillating weight both provides energy and transmits information.
Power-reserve indications are provided by a planetary or differential gearing that correlates the winding rate of the ratchet with the unwinding rate of the barrel. The hand showing the power reserve is usually connected to the output of the differential. In developing its new approach, Blancpain first had to figure out how to put the power-reserve indicator on the axis of the rotor. As illustrated below, the staff of the differential (a) protrudes on the bridge side of the movement. A transmission wheel (b) takes its rotation over the winding-train bridge to the central axis of the rotor (c). A second wheel coaxial with the rotor, which is normally part of the self-winding system, transmits the rotation to the wheel carrying the power reserve hand through a pinion (e), which reverses the direction of rotation.
Another problem Blancpain faced was to make the power-reserve indication easy to read. The problem is solved by adding a fixed wheel (f) on top of the coaxial transmission wheel. A pinion (g) reverses the direction of rotation and a supplementary wheel (h) carrying the dial is placed coaxially with the power-reserve hand. In this way the system cancels out the rotation of the dial due to the winding rotor.
The final challenge was to secure the power-reserve indication when the barrel is fully wound. In this case, friction disconnects the gearing. The hand comes up against the applied buffer (i) allowing the dial to rotate. In this way the hand shows that the mainspring is fully wound, while eliminating any possibility of damaging the mechanism.
In a final touch, the appliqué (i) is fixed on the dial so that it hides the screw securing the rotor to its axle. This creates the illusion of the rotor floating beneath the sapphire-crystal caseback.
This original device is incorporated within the manufacture Blancpain 4225G calibre, as shown below (images may be enlarged with a click).