Forced-fluid flow ventilating system for rotating electrical machines and rotating electrical machine comprising same

1. A ventilation system for a rotary electrical machine for a motor vehicle, comprising a rotor mounted so as to rotate in a stator carried by a casing; the ventilation system provided for cooling the rotary electric machine by forced flow of a cooling fluid; the ventilation system comprising:

first and second rotor fans fixed to opposite first and second axial ends of the rotor, respectively, and driven by the rotor; and

an independent fan spaced apart from the first and second rotor fans and driven independently from the rotor fans for cooling the rotary electric machine at relatively low speeds of rotation of the rotor;

the second rotor fan and the independent fan disposed on the same side of the rotor;

the second rotor fan having a reduced size compared to the first rotor fan so that an air flow output produced by the first rotor fan being substantially equal to the total air flow output produced by the independent fan and the second rotor fan;

the ratio between the outside diameter of the second rotor fan and the outside diameter of the rotor is less than 90%.

2. The ventilation system according to claim 1 , wherein the rotor fans are of the helico-centrifugal or axial type.

3. The ventilation system according to claim 1 , wherein the ratio between the outside diameter of second rotor fan and the outside diameter of the rotor is between 84% and 68%.

4. The ventilation system according to claim 3 , wherein the rotor is an annular claw rotor having two series of teeth roughly of axial orientation, each series of teeth being connected at its base to the external periphery with a given diameter of a flange roughly of transverse orientation and in that the outside diameter of the second rotor fan is equal to the outside diameter of the rotor flange.

5. The ventilation system according to claim 1 , wherein second rotor fan fixed to the rotor is of the centrifugal type.

6. The ventilation system according to 1 , wherein the second rotor fan fixed to the rotor is of the centripetal type.

7. The ventilation system according to claim 1 , wherein the independent fan is able to function at a constant speed of rotation.

8. The ventilation system according to claim 1 , wherein the independent fan is a fan whose speed of rotation is variable in steps.

9. The ventilation system according to claim 1 , wherein the speed of rotation of the independent fan is controlled according to the functioning of the rotary electrical machine by a voltage regulator of the rotary electrical machine.

10. The ventilation system according to claim 1 , wherein the independent fan is rotatably driven by an independent electric motor.

11. The ventilation system according to claim 1 , wherein the independent fan is mounted in a support fixed to a cover of the rotary electrical machine.

12. The ventilation system according to claim 1 , wherein the independent fan is an axial-ventilation fan.

13. A rotary electrical machine comprising:

a casing;

a stator carried internally by the casing;

a rotor rotatably mounted in the stator; and

a ventilation system for cooling the rotary electrical machine by forced flow of air;

the ventilation system including:

first and second rotor fans fixed to opposite front and rear axial ends of the rotor and driven by the rotor, and an independent fan spaced apart from the first and second rotor fans and driven independently from the rotor fans for cooling the rotary electric machine at relatively low speeds of rotation of the rotor;

the second rotor fan and the independent fan disposed on the same side of the rotor;

the second rotor fan having a reduced size compared to the first rotor fan so that an air flow output produced by the first rotor fan being substantially equal to the total air flow output produced by the independent fan and the second rotor fan;

the ratio between the outside diameter of the second rotor fan and the outside diameter of the rotor is less than 90%;

the casing comprising a front bearing, a rear bearing and a cover fixed to the rear bearing;

the front and rear bearings provided with air passages and carrying a brush holder housed in the cover.

14. The rotary electrical machine according to claim 13 , wherein the independent fan is mounted in a support fixed to the cover secured to the rear bearing.