Device for synchronization of a reverse gear for a motor-vehicle gearbox

A device for synchronization of a reverse gear for a motor-vehicle gearbox comprising:

• a support shaft, fixed in rotation;
• an idle gear wheel configured for constant engagement with a first reverse gear wheel on a primary shaft of the motor-vehicle gearbox and with a second reverse gear wheel on a secondary shaft of the motor-vehicle gearbox, said idle gear wheel being mounted freely rotatable and axially slidable on said support shaft and having a hub that includes a first friction surface;
• a synchronizer ring, which is mounted movable on said support shaft along an axial travel and is axially countered by an elastic element along said axial travel, said synchronizer ring having a second friction surface configured for engagement with said first friction surface, said synchronizer ring being constrained angularly with respect to the support shaft in a way that varies according to a position thereof along the axial travel;
• wherein the idle gear wheel includes a first operating position along said support shaft associated to a condition of disengagement of the reverse gear and a second operating position along said support shaft associated to a condition of engagement of the reverse gear
• wherein:
• during operation, when a reverse gear engagement manoeuvre is carried out, said idle gear wheel can be moved axially along said support shaft from the first operating position to the second operating position with axial drawing of said synchronizer ring along said axial travel, said axial drawing including engagement of said first friction surface and said second friction surface;
• and
• during the axial drawing, and before the second operating position of said idle gear wheel is reached, said synchronizer ring is configured for braking a rotary movement of said idle gear wheel by engagement of said first friction surface and said second friction surface.