Impeller and cooling fan incorporating the same

1. An impeller comprising:

a hub; and

a plurality of blades radially and outwardly extending from the hub, each of the plurality of blades comprising a windward surface and a leeward surface;

wherein a groove is defined in at least one of the plurality of blades for guiding airflow from the windward surface to the leeward surface; and

wherein a blade vertex is defined at a tip of a front blade, and a projective point is defined on a rear blade via a projection of the blade vertex of the front blade on the rear blade, the groove being defined at the projective point.

2. The impeller as claimed in claim 1 , wherein the groove is defined inclinedly with respect to the windward surface and the leeward surface.

3. The impeller as claimed in claim 1 , wherein the groove has a width greater than 0 mm and not greater than 5 mm.

4. The impeller as claimed in claim 3 , wherein the groove has a width in the range of from 0.5 mm to 1 mm.

5. The impeller as claimed in claim 1 , wherein a height of the groove is smaller than a height of the blade where the groove is defined.

6. The impeller as claimed in claim 1 , wherein a height of the groove is greater than a half of a height of the blade where the groove is defined.

7. The impeller as claimed in claim 6 , wherein the groove passes through the blade along an axial direction of the impeller.

8. The impeller as claimed in claim 1 , wherein the groove divides the blade into a primary blade portion adjacent to the hub and a secondary blade portion apart from the hub.

9. The impeller as claimed in claim 8 , wherein the secondary blade portion is on an extended line of the primary blade portion.

10. The impeller as claimed in claim 8 , wherein an overlapping area is formed between the primary blade portion and the secondary blade portion, the secondary blade portion offsetting outwardly relative to the primary blade portion.

11. The impeller as claimed in claim 8 , wherein a connecting blade portion is located under the groove and interconnects the primary blade portion with the secondary blade portion.

12. The impeller as claimed in claim 8 , wherein a height of the groove equals a height of the blade, and the primary blade portion and the secondary blade portion are connected together via a ring attached to the blades.

13. The impeller as claimed in claim 1 , wherein a ring having an annular shape is fixed at a position of the blade where the groove is defined.

14. The impeller as claimed in claim 1 , wherein the groove is defined in each of the blades.

15. The impeller as claimed in claim 1 , wherein the groove is defined in an outer half of the blade.

16. A cooling fan comprising:

an impeller,

wherein the impeller comprises a hub and a plurality of blades radially and outwardly extending from the hub, each of the plurality of blades comprising a windward surface and a leeward surface, a groove being defined in at least one of the plurality of blades for guiding airflow from the windward surface to the leeward surface; and

wherein a blade vertex is defined at a tip of a front blade, and a projective point is defined on a rear blade via a projection of the blade vertex of the front blade on the rear blade, the groove being defined at the projective point.

17. The cooling fan as claimed in claim 16 , wherein the groove divides the blade into a primary blade portion adjacent to the hub and a secondary blade portion apart from the hub.

18. The cooling fan as claimed in claim 16 , wherein a height of the groove is greater than a half of a height of the blade.