An automotive air blower, in particular a supercharger, includes an air pump, such as an air impeller connected to the output shaft of a transmission system, the input shaft of which is connected, in use, to the engine of a motor vehicle. The input and output shafts are connected to respective branches of a three-branch epicyclic differential gearset. The third branch of the gearset and the input shaft are connected to the rotor of respective electrical machines, the electrical connections of the stators of which machines are connected together via a controller arranged to control the flow of electric power between them.