Impeller and cooling fan including the impeller

1. A impeller comprising:

a hub;

a plurality of blades provided around an outer periphery of the hub, wherein each of the plurality of blades has a top edge and a bottom edge opposite to the top edge, wherein each of the plurality of blades includes a rear curving section and a front curving section, wherein the rear curving section is more adjacent to the hub than the front curving section is, wherein each of the plurality of blades further includes an intermediate section connected between the rear curving section and the front curving section; and

at least two connecting rings connected to the plurality of blades, wherein one or more of the at least two connecting rings is disposed between but not connected to the top edges and the bottom edges of the plurality of blades, wherein one of the at least two connecting rings is disposed on the intermediate section.

2. The impeller as claimed in claim 1 , wherein the at least two connecting rings are at a same level.

3. The impeller as claimed in claim 2 , wherein the at least two connecting rings are disposed in a middle between the top edges and the bottom edges of the plurality of blades.

4. The impeller as claimed in claim 1 , wherein the hub has an annular wall connected to a first end of each of the plurality of blades, and wherein one of the at least two connecting rings is connected to a second end of each of the plurality of blades.

5. The impeller as claimed in claim 4 , wherein the annular wall includes an extension portion extending outwards radially and connecting to the first ends of the plurality of blades.

6. The impeller as claimed in claim 1 , wherein each of the plurality of blades has a length between a first end and a second end thereof, and wherein each of the at least two connecting rings is connected to each of the plurality of blades at any position from the second end to where it is at one-third of the length from an annular wall.

7. The impeller as claimed in claim 1 , wherein each of the plurality of blades has a first end and a second end higher than the first end, and wherein the first end is more adjacent to the hub than the second end is.

8. The impeller as claimed in claim 7 , wherein a distance between the top edge and the bottom edge of the blade gradually increases from the first end to the second end of the blade.

9. The impeller as claimed in claim 1 , wherein the at least two connecting rings include two connecting rings, wherein one of the two connecting rings is disposed between but not connected to the top edges and the bottom edges of the plurality of blades, and wherein another of the two connecting rings is connected to the plurality of blades above or below the top edges of the plurality of blades or above or below the bottom edges of the plurality of blades.

10. The impeller as claimed in claim 1 , wherein the hub includes an annular wall connected to an edge of a plate, wherein the plate has a central hole, and wherein the hub includes a reinforcing portion around the central hole of the plate.

11. The impeller as claimed in claim 10 , wherein the reinforcing portion includes a plurality of protruding ribs extending from the central hole towards the annular wall of the hub.

12. The impeller as claimed in claim 10 , wherein the reinforcing portion includes an annular rib around the central hole of the hub.

13. The impeller as claimed in claim 12 , wherein the reinforcing portion further includes a plurality of protruding ribs extending from the annular rib towards the annular wall of the hub.

14. The impeller as claimed in claim 1 , wherein the at least two connecting rings include three connecting rings, wherein one of the three connecting rings is disposed between but not connected to the top edges and the bottom edges of the plurality of blades, and wherein another two of the three connecting rings are connected to the top edges and the bottom edges of the plurality of blades, respectively.

15. The impeller as claimed in claim 14 , wherein the one of the three connecting rings is more adjacent to the hub than the other two of the three connecting rings are.

16. The impeller as claimed in claim 1 , wherein each of the plurality of blades has a thickness of 0.02 to 0.5 mm.

17. The impeller as claimed in claim 16 , wherein each of the plurality of blades has a thickness smaller than 0.1 mm.

18. The impeller as claimed in claim 1 , wherein a quantity of the plurality of blades is 70 to 134.

19. The impeller as claimed in claim 18 , wherein a quantity of the plurality of blades is 91 to 134.

20. The impeller as claimed in claim 1 , wherein an outer diameter of the impeller is larger than or equal to 40 mm.

21. The impeller as claimed in claim 1 , wherein the plurality of blades and the at least two connecting rings are made of polymer.

22. The impeller as claimed in claim 21 , wherein the polymer is a mixture of liquid crystal polymer and carbon fiber.

23. The impeller as claimed in claim 21 , wherein the polymer is a mixture of liquid crystal polymer and mineral fiber.

24. The impeller as claimed in claim 21 , wherein the polymer is a mixture of liquid crystal polymer, glass fiber and mineral fiber.

25. The impeller as claimed in claim 1 , wherein the plurality of blades does not extend beyond a top face of the hub.

26. The impeller as claimed in claim 1 , wherein each of the at least two connecting rings has a thickness larger than or equal to a maximum thickness of each of the plurality of blades.

27. The impeller as claimed in claim 1 , wherein each of the at least two connecting rings has a radial width larger than or equal to a maximum thickness of each of the plurality of blades.

28. A cooling fan comprising:

a fan frame including a base, wherein the base includes a shaft tube;

a stator mounted around an outer periphery of the shaft tube; and

the impeller as claimed in claim 1 , wherein the impeller is rotatably coupled with the shaft tube.