Timepiece transmission mechanism with reduced coupling force

A timepiece transmission mechanism, arranged to be integrated in a timepiece movement and comprising at least one differential mechanism including at least one planet wheel set mounted for free rotation and at least three main wheel sets forming the inputs or outputs of said differential mechanism, which three main wheel sets are formed by a frame, a first wheel set arranged to cooperate with a first train, and a second wheel set arranged to cooperate with a second train, only one of said three main wheel sets carrying at least one said planet wheel set permanently meshing with the other two main wheel sets, either directly or through at least one intermediate wheel set which permanently meshes with one of said other two main wheel sets or which is integral in rotation with one of said other two main wheel sets, said differential mechanism being able to kinematically connect said first wheel set and said second wheel set in a coupling position, and to separate them kinematically in an uncoupling position, said transmission mechanism further comprising control means arranged to lock only one of said three main wheel sets in order to couple said differential mechanism, or to completely release said frame and said first wheel set and said second wheel set in order to uncouple said differential mechanism, depending on the position given to said control means by a selector comprised in said transmission mechanism and which is arranged to cooperate with an actuator comprised in said timepiece movement, and/or to be operated by a user, and wherein said control means are returned to a locking wheel set which is whichever of said three main wheel sets on which said differential mechanism is locked in the coupling position, by elastic return means, arranged to exert on said locking wheel set an engaging or friction torque, which is calibrated to allow a safety uncoupling function when the torque transmitted from one to the other of the other main wheel sets distinct from said locking wheel set is higher than said engaging or friction torque, wherein said locking wheel set includes an external toothing with wolf teeth, to allow a safety uncoupling function in one direction of rotation.