Chronograph mechanism for a horological movement and timepiece comprising such a mechanism

A chronograph mechanism for a horological movement comprising:

• a chronograph counter with a shaft and a hand that rotates as one with the shaft,
• a zero-reset mechanism for resetting said chronograph counter to zero, comprising a zero-reset member integral with the shaft and a hammer shaped to cooperate with the zero-reset member and to generate a driving torque under the action of a zero-reset control until the zero-reset member is positioned in a reference position by rotation in the direction of travel of the chronograph counter;
• wherein the zero-reset member is a snail cam having a cam track extending spirally around said shaft of the chronograph counter from a proximal end defining a zone of minimum radius with respect to the shaft to a distal end defining a zone of maximum radius with respect to the shaft;
• wherein said hammer can be displaced by the zero-reset control between a rest position in which the hammer is not in contact with the cam path and a zero-reset position in which the hammer is in contact with the cam path and holds the zero-reset member in said reference position, the hammer generating a driving torque on the zero-reset member between the rest position and the zero-reset position;
• wherein the hammer cooperates with guide members shaped to guide an outward movement of the hammer along a first path between the rest position and the zero-reset position and to guide a return movement of the hammer along a second path between the zero-reset position and the rest position, the first path and the second path of the hammer being non-coincident.