COUPLING

Coupling is a temporary mechanical connection device that allows two elements of a transmission chain to be joined or separated at will, transmitting the Movement when engaged and interrupting it, without stopping the Motor organ (power source), when disengaged. A watch movement may include several couplings depending on the functions performed: coupling of the Chronograph, which connects the Train (wheel train) of the base to the counting mechanism upon release; time-setting coupling, disconnecting the motion work when the Crown ; or coupling of the automatic winding system. In classic chronographs, the horizontal coupling relies on a mobile wheel that meshes laterally with the chronograph wheel on the driving wheel; simpler and more robust, it can cause a slight jump of the hand at start-up. The vertical coupling, used in more modern calibers, superimposes two coaxial friction discs whose engagement smoothly transmits the movement, without hand jump or noticeable amplitude loss. The quality of a coupling is judged by the smoothness of its engagement, the absence of parasitic play and its long-term reliability: it is a key organ of complicated watches.