Boîte de vitesse à changement de vitesse de rapport sous charge

The invention relates to a gearbox switchable under load, which has an input shaft coupled to at least one further shaft, which extends parallel to the input shaft, via pairs of gearwheels to achieve different gear stages. One gearwheel of each pair of gearwheels is rotatively fixedly connected to one of the two shafts and the other gearwheel of each pair of gearwheels is optionally rotatively fixedly connectable to the other of the two shafts by a respective friction coupling. Also, in the gearbox, the input shaft is rotatively fixedly connected to an engine shaft; mechanism to reverse the direction of rotation is provided in the torque flow from the input shaft to the output pinion; and mechanism for approximately simultaneously loading the friction couplings of the two lowest gear stages is provided and for starting purposes when driving forward and reversing, the torque flow through both friction couplings is maintained, at most, until an identical speed has been reached between the elements of the friction coupling of the lowest gear stage.