Actuator for a bicycle gear-shift

Actuator device for a bicycle gear-shift, comprising:

• an articulated quadrilateral with four connecting rods hinged together according to four pin axes by four pin elements, in which the first connecting rod is intended to be integrally fixed to the bicycle frame, the second connecting rod is opposite to the first connecting rod in the articulated quadrilateral and is intended to be fixed to a support for a gear-shift derailleur, in which the connecting rods have a substantial width in the direction of the pin axes, with such a width defining an internal space in the articulated quadrilateral, wherein the motor member is arranged inside such an internal space, in which the second pin element also comprises two opposite pins, each inserted in hinging holes formed in the connecting rods converging in the second pin element and in the pin portions of the nut screw;
• a motor member, having a variable length according to a drive axis and active between two opposite pin elements to move them towards and away from each other deforming the articulated quadrilateral, in which the motor member comprises an electric motor housed on a support mounted on a first of the pin elements, a screw arranged axially along the drive axis and put into rotation by the electric motor, a nut screw engaged with the screw and fixed to a second of the pin elements opposite the first, wherein the drive axis perfectly intersects the axis of the second pin element, in which the nut screw comprises two pin portions opposite each other and perpendicular to the nut screw;
• wherein the drive axis substantially intersects the pin axis of both the two pin elements between which the motor member is active, in which the drive axis perfectly intersects at least one of the pin axes of the two pin elements between which the motor member is active.