Hybrid propulsion system for a motor vehicle

The propulsion system comprises an internal combustion engine, an electric machine (80; 180) and a double-clutch transmission with a clutch unit and a mechanical gearbox (10; 110). The gearbox (10; 110) comprises two coaxial primary shafts (12, 14; 112, 114) intended to be torsionally connected each to a shaft of the internal combustion engine of the motor vehicle by means of a respective friction clutch of the clutch unit, as well as a secondary shaft (16; 116) and a lay shaft (18; 118) arranged parallel to the two primary shafts (12, 14; 112, 114). The electric machine (80; 180) is permanently cinematically connected to either (14; 114) of the two primary shafts (12, 14; 112, 114) via a first gear train (84, 86, 30; 184, 186, 130) including a pinion (84; 184) carried by an output shaft (82; 182) of the electric machine (80; 180), an intermediate gearwheel (86; 186) carried by an intermediate shaft (88; 188) and a gearwheel (30; 130) carried by said primary shaft (14; 114) and acting as driving gearwheel of a second gear train (30, 42; 130, 142) of the gearbox (10; 110) associated to one of the gears, in particular to the second forward gear. The gearbox (10; 110) further comprises a case and the electric machine (80; 180) is inserted and fixed into a seat (102) formed by that case.