Method and arrangement for cooling claw-pole electric machines

1. A method of cooling an electric machine using a stream of air flowing through the electric machine, the electric machine having a claw-pole rotor arrangement with an active airgap defined between the claw-pole rotor arrangement and a stator core, the claw-pole rotor arrangement including an open claw-pole segment and a closed claw-pole segment, the method comprising:

rotating the claw-pole rotor arrangement in a direction of angular rotation about an axis of rotation;

receiving a stream of air into a first end of the electric machine such that the stream of air flows over an exterior surface of the claw pole rotor arrangement;

causing the stream of air to flow over an indentation on a trailing edge of a proximal end of a finger of the claw-pole rotor arrangement, the indentation not extending to a distal end of the finger or a leading side of the finger, the finger being asymmetrical in shape relative to a plane extending through an axial centerline of the finger and through the axis of rotation, and wherein most of the indentation does not face the active airgap; and

causing the stream of air to flow between fingers on opposing segments of the claw-pole rotor arrangement and over a field winding positioned on the interior of the claw-pole arrangement.

2. The method of claim 1 further comprising causing the stream of air to exit the electric machine at a second end of the electric machine.

3. The method of claim 2 wherein causing the stream of air to flow over the indentation, causing the stream of air to flow between the fingers, and causing the stream of air to exit the electric machine are all accomplished using a fan positioned on the second end of the electric machine.

4. The method of claim 3 wherein the indentation is a chamfer positioned adjacent to a web portion extending between adjacent fingers of the claw-pole arrangement, and wherein the chamfer is elongated in shape having a substantially longer dimension in an axial direction than in a circumferential direction.

5. A method of cooling an electric machine comprising a rotor and a stator core, the rotor separated from the stator core by an airgap in an active airgap region of the rotor, the method comprising:

rotating the rotor about an axis of rotation in a direction of angular rotation, the rotor including a first claw-pole segment and an opposing second claw-pole segment, the first claw-pole segment including a plurality of fingers extending in an axial direction from an end ring, each finger including (i) a distal end and a proximal end with the proximal end fixed to the end ring, (ii) an interior side and an exterior side, the exterior side facing the stator, and (iii) a leading side and a trailing side defined by the direction of angular rotation, and (iv) an indentation on the exterior trailing side of the finger at the proximal end of the finger and substantially outside of the active airgap region of the rotor, the exterior leading side of the finger void of an additional chamfer that is symmetric to the chamfer formed on the exterior trailing side of the finger, and the indentation on the exterior trailing side of the finger not extending to the exterior leading side of the finger; and

receiving a stream of air into a first end of the electric machine such that the stream of air flows over an exterior surface of the end ring of the first claw pole segment, over the indentation on the exterior trailing side of each finger, between alternating fingers on the first claw claw-pole segment and the second claw-pole segment, and over a field winding positioned on the interior of the first claw-pole segment and the second claw-pole segment.

6. The method of claim 5 wherein each finger is asymmetrical in shape relative to a plane of symmetry extending through an axial centerline of the finger and through the axis of rotation of the rotor, wherein the asymmetrical shape of the finger results from the indentation such that the finger is substantially symmetrical except for the indentation.

7. The method of claim 5 wherein a knuckle portion is positioned at the proximal end of the finger with the indentation on the finger extending from the end ring to the knuckle portion.

8. The method of claim 5 wherein the first claw pole segment further includes a web portion extending between adjacent fingers at the proximal ends of the fingers.

9. The method of claim 8 wherein the indentation on the trailing edge of each finger is provided as a surface adjacent to the web portion.

10. The method of claim 9 wherein the surface adjacent to the web portion is a chamfered surface that extends the substantial length of the web portion on the exterior trailing side of the finger.

11. The method of claim 5 wherein the indentation is elongated in shape with a largest indentation dimension extending in a substantially axial direction.

12. The method of claim 5 wherein the indentation is provided as a chamfered surface that is less than forty-five degrees relative to a tangency line on the trailing edge of the finger.

13. The method of claim 12 wherein the chamfered surface is less than thirty degrees relative to the tangency line on the trailing edge of the finger.

14. The method of claim 5 wherein the first claw pole segment and the second claw pole segment are connected by an interior ring.

15. The method of claim 14 wherein the rotor includes a rotor core connected to a shaft, and wherein the second claw pole segment is connected to the shaft and the rotor core.

16. The method of claim 5 wherein the field winding is positioned on a spool located inside of the first claw pole segment and the second claw pole segment.

17. The method of claim 5 wherein the first claw-pole segment is an open claw-pole segment and the second claw-pole segment is a closed claw-pole segment.

18. The method of claim 5 wherein the electric machine is an alternator used in association with a vehicle.