Unity consisting of an electromagnetic retarder and its electric supply

This assembly comprises a stator (3) coaxial with a motor shaft (1) of a vehicle and a rotor (2) integral in rotation with this shaft so as to present an air gap (E), the rotor (2) comprising an inductor, with at least one electromagnet winding (6), capable of generating, under the effect of a current supplied by electrical supply means (G), a magnetic field in an annular ferromagnetic piece (7) of the stator (3) constituting the armature of the retarder, the electrical supply means (G) comprising an alternator whose armature, with polyphase winding (11), forms part of the rotor (2), and whose inductor forms part of the stator (3) and surrounds with a small clearance the rotary armature of this alternator. First switching means (Kr1, Kr2, Kr3) electrically couple the retarder (R) to the alternator (G) and second switching means (Ks1, Ks2, Ks3) which are intended to electrically couple the alternator (G) to the vehicle's on-board network, said first and second switching means being controlled together in two first corresponding positions, for which the alternator operates as a synchronous electrical power supply source of the retarder through its rotary inductor, or else in two second corresponding positions, for which the alternator operates as an asynchronous electrical power supply source of the vehicle's on-board network through its stator armature.