Alternator rotor, particularly for motor vehicles

The rotor comprises a shaft from which two facing pole plates extend radially, each having a plurality of radial pole fingers whose ends are bent towards the other pole plate and each of which extends between two adjacent fingers of the other pole plate. An excitation winding is situated between the plates coaxial with the shaft. At least one axial ventilation duct is formed in the shaft from which branch radial ducts in correspondence with the pole plates, the ducts communicating with the corresponding ventilation passages provided in each pole plate, which open into recesses defined between pairs of adjacent pole fingers.

BACKGROUND OF THE INVENTION 
The present invention relates to an alternator rotor, particularly for use 
in motor vehicles. 
More specifically, the subject of the invention is a rotor comprising a 
shaft from which two facing pole plates extend radially, each of these 
having a plurality of radial pole fingers whose ends are bent towards the 
other pole plate and each of which extends between two adjacent fingers of 
the other pole plate; at least one excitation winding being situated 
between the plates, coaxial with the shaft. 
The temperature of the rotor of an alternator tends to increase in 
operation, causing a corresponding increase in the resistance of the 
excitation winding. The excitation current is reduced correspondingly. 
SUMMARY OF THE INVENTION 
The object of the present invention is to produce an alternator rotor whose 
characteristics enable its operating temperature to be reduced and, in 
particular, enable the temperature and the increase in the resistance of 
the excitation winding to be limited so as to enable a higher current to 
flow in the winding for a given excitation voltage, with an increase in 
the efficiency of the alternator. 
This object is achieved according to the invention by means of a rotor of 
the type specified above, whose main characteristic lies in the fact that 
at least one axial ventilation duct is formed in the shaft from which 
branch radial ducts in correspondence with the pole plates, the ducts 
communicating with corresponding ventilation passages provided in each 
pole plate, which open into recesses defined between pairs of adjacent 
pole fingers.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to the drawings, an alternator rotor according to the 
present invention comprises a shaft 1 onto which two axially-spaced facing 
pole plates 2 are keyed in known manner. A plurality of radial pole 
fingers 3 extend from each of the plates and are bent towards the other 
pole plate, each extending between two adjacent fingers 3 of the other 
pole plate. 
An annular core, for example of soft iron, is indicated 4 and is arranged 
around the shaft 1 between the pole plates 2 (FIG. 3). An excitation 
winding 5, for example of copper wire, is arranged around the core. 
The shaft 1 is hollow, an axial ventilation duct 6 being formed within it. 
Radial ducts 7 (FIGS. 2 and 3) branch from the axial ventilation duct 6 of 
the shaft 1 in correspondence with the pole plates 2 and communicate with 
corresponding radial ventilation passages 8 provided in each pole plate 2, 
these passages opening through apertures 9 into recesses 10 defined 
between pairs of adjacent pole fingers 3. 
As can be seen from FIG. 3, the radial ducts 7 of the shaft 1 associated 
with each pole plate and the radial ventilation passages 8 of each pole 
plate are formed in axially staggered positions. 
The system formed by the axial ventilation duct 6 and radial ventilation 
ducts 7 of the shaft 1 and by the radial ventilation passages 8 enables an 
air flow to be induced radially through the pole plates in order to reduce 
their temperature in operation. 
A vaned rotor or fan, such as that illustrated in broken outline in FIG. 1, 
may be coupled, in known manner, to the shaft 1 as a result of which, 
during rotation of the rotor, an air flow is drawn through the axial 
ventilation duct 6 in the direction of the arrow F of FIG. 3 and then 
radially outwardly through the radial ventilation passages 8 in the pole 
plates, as indicated by the arrows of FIG. 2. 
The efficient ventilation of the rotor enables the increase in temperature 
of the excitation winding 5 to be limited and the efficiency of the 
alternator thus to be improved.