A device is described for the engagement and the disengagement of a power take-off in a vehicle (1) with a trailer (2), operatively connected thereto through a cardan (3), comprising a detection device of the angle on the cardan (3) and comparison means of the angle (ε) between one cardan arm (5) and the projection of the other arm (4) of the cardan (3) beyond the cardan (3) itself and one or more preset threshold angles (S, S'), apt to disengage the power take-off when said angle (ε) between one cardan arm (5) and the projection of the other arm (4) of the cardan (3) beyond the cardan (3) itself is greater than a threshold angle (S) and to engage it again when said angle (ε) between one cardan arm (5) and the projection of the other arm (4) of the cardan (3) beyond the cardan (3) itself is smaller than another threshold angle (S') (equal to or different from the first one). Said detection device consists of a pair of position determining systems, arranged one in the area of the vehicle and the other in the area of the trailer. Moreover, the angle to be compared with the threshold angles is calculated with the formula: ε = 180° - arcos [1/2(N/M + M/N - L2/MN)] (14) where: M is the distance between one position determining system and the cardan joint, N is the distance between the other position determining system and the cardan joint L is the distance between the two position determining systems ε is the angle between the cardan arm and the projection of the other arm of the cardan beyond the cardan itself.L'invention concerne un dispositif pour l'embrayage et le débrayage d'une prise de force dans un véhicule (1) avec une remorque (2) reliée fonctionnellement à celui-ci par le biais d'un cardan (3), comprenant un dispositif de détection de l'angle sur le cardan (3) et des moyens de comparaison de l'angle (ε) entre un bras de cardan (5) et la projection de l'autre bras (4) du cardan (3) au-delà du cardan (3) lui-même et un ou plusieurs angles de seuil (S, S') prédéf
