Cooling device and speed change drive unit

A cooling structure intended to cool a rotating electrical machine (ME) and a set of at least one electronic power module of an electronic variable speed drive making it possible to vary an electrical power supply signal of the rotating electrical machine (ME) so as to vary a rotation speed of a shaft (A) driven by the electrical machine (ME) and/or a torque supplied by the electrical machine (ME), the electronic power module comprising a power component, the cooling structure comprising a solid metal body (CM) having an overall tubular form delimited radially by a first contact surface intended to completely radially surround the electrical machine and to be in physical contact with the electrical machine and by a second contact surface completely radially surrounding the first contact surface and intended to be in physical contact with a first power module of the set of at least one power module so as to be able to cool the electrical machine and the power module, the cooling structure comprising a set of at least one cooling channel (CR1, CR2, CR3, CR4) formed in the solid metal body (CM), at a distance from the first contact surface and from the second contact surface, in which a coolant is intended to circulate, the metal box (CM) being of a single piece.