Hybrid powertrain unit for motor-vehicles

A hybrid powertrain unit comprises an internal-combustion engine (E), and a gearbox device (C) with a primary shaft (3) that can be connected to the shaft (5) of the internal-combustion engine (E) via a clutch device (6). The gearbox device (C) comprises a secondary shaft (7) with an output pinion (9) meshing with a first crown wheel (10) of a differential (D), the casing (11) of which is rigidly connected to the casing (2) of the gearbox device (C). The unit further comprises an electrical machine (M) designed to function both as electric motor and as electric generator, having a shaft (16) connected by means of a transmission to a second crown wheel (19) of the differential (D). In the transmission for connection, set between the shaft (16) of the electrical machine (M) and the second crown wheel (19) of the differential (D) is an engagement device (25) that can be driven via an electronic control actuator. The electrical machine (M) can be set coaxially to the output shafts (12, 13) of the differential (D) or parallel thereto. In either case, a variant is envisaged, in which the shaft (16) of the electrical machine (M) is connected to the shaft (5) of the internal-combustion engine (E) by means of a belt transmission (19) and an engagement device (34).