US20140072434A1

US20140072434A1 - Fan impeller structure of centrifugal fan

Info

Publication number: US20140072434A1
Application number: US13/612,885
Authority: US
Inventors: Chun-Ming Wu
Original assignee: Asia Vital Components Co Ltd
Current assignee: Asia Vital Components Co Ltd
Priority date: 2012-09-13
Filing date: 2012-09-13
Publication date: 2014-03-13

Abstract

A fan impeller structure of centrifugal fan includes a hub, a first blade body set and a second blade body set. The hub has an extension section having a first side and a second side. The first blade body set is disposed on the first side, while the second blade body set is disposed on the second side. The first blade body set defines multiple first air inlets and multiple first air outlets. The second blade body set defines multiple second air inlets and multiple second air outlets. The first air outlets of the first blade body set or the second air outlets of the second blade body set are selectively arranged at unequal intervals so as to effectively reduce noise.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to a fan impeller structure of a centrifugal fan, and more particularly to a double-layer fan impeller structure of a centrifugal fan in which at least one layer of blades of the upper and lower layers is selectively arranged at unequal intervals so as to lower the single tone of the blade passing frequency (BPF) and greatly reduce noise.
2. Description of the Related Art
Along with the rapid development of electronic industries, the performance of the electronic components has been more and more enhanced. The electronic components have operated at higher and higher speed. In the meantime, the heat generated by the electronic components has become higher and higher. In case the heat is not dissipated in time, the operation performance of the electronic components will be deteriorated. In some more serious cases, the electronic components may even burn out. In order to dissipate the heat, a miniaturized centrifugal fan is installed in a limited space of the system for carrying away the heat. The centrifugal fan includes a frame body, a fan hub and multiple blade bodies annularly disposed around outer circumference of the fan hub. Each of upper and lower sides of the frame body is formed with an air inlet. A lateral side of the frame body is formed with an air outlet. In operation, the blade bodies rotate to drive the ambient air to flow. The axial airflow going into the frame body from the air inlet is turned to radial airflow, which is exhausted from the air outlet.
When the centrifugal fan operates, the non-uniform wake flowing out from the fan impeller will interact with the tongue to make noise. In the case that the gap between the fan impeller and the tongue is relatively narrow, the noise will be affected by the tongue oscillation caused by the impact of the non-uniform wake onto the tongue and the pressure difference around the tongue. In the case that the gap is 20% the radius of the fan impeller, only the non-uniform wake will affect the major noise source and the non-uniform wake only has little affection on the major noise source. In addition, the wake strength can be lowered by means of adding short vanes between the blades. This can minimize the affection of the non-uniform wake on the pressure turbulence and the noise. According to the above, the conventional technique has the following shortcomings:

1. The structural design is limited.
2. The ratio of upper incoming air volume to lower incoming air volume cannot be flexibly designed according to the characteristics.
3. The noise is loud.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide a fan impeller structure of centrifugal fan, which can effectively reduce noise.
To achieve the above and other objects, the fan impeller structure of centrifugal fan of the present invention includes a hub, a first blade body set and a second blade body set.
The hub has an extension section. The extension section has a first side and a second side. The first blade body set is disposed on the first side. The first blade body set includes multiple first blade bodies. The first blade bodies define therebetween multiple first air inlets and multiple first air outlets. The first air outlets are arranged at unequal intervals. The second blade body set is disposed on the second side. The second blade body set includes multiple second blade bodies. The second blade bodies define therebetween multiple second air inlets and multiple second air outlets. The second air outlets are arranged at equal intervals.
Still to achieve the above and other objects, the fan impeller structure of centrifugal fan of the present invention includes a hub, a first blade body set and a second blade body set.
The hub has an extension section. The extension section has a first side and a second side. The first blade body set is disposed on the first side. The first blade body set includes multiple first blade bodies. The first blade bodies define therebetween multiple first air inlets and multiple first air outlets. The first air outlets are arranged at unequal intervals. The second blade body set is disposed on the second side. The second blade body set includes multiple second blade bodies. The second blade bodies define therebetween multiple second air inlets and multiple second air outlets. The second air outlets are arranged at unequal intervals.
Still to achieve the above and other objects, the fan impeller structure of centrifugal fan of the present invention includes a hub, a first blade body set and a second blade body set.
The hub has an extension section. The extension section has a first side and a second side. The first blade body set is disposed on the first side. The first blade body set includes multiple first blade bodies. The first blade bodies define therebetween multiple first air inlets and multiple first air outlets. The first air outlets are arranged at equal intervals. The second blade body set is disposed on the second side. The second blade body set includes multiple second blade bodies. The second blade bodies define therebetween multiple second air inlets and multiple second air outlets. The second air outlets are arranged at unequal intervals.
The first air outlets of the first blade body set or the second air outlets of the second blade body set are selectively arranged at unequal intervals. This can lower the single tone of the blade passing frequency (BPF). Moreover, the double-layer fan impeller structure can increase the blade passing frequency (BPF) and lower sound pressure weighting so as to greatly reduce noise. In addition, the upper and lower blades can be more flexibly designed according to the boundary condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a first embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 2 is a top view of the first embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 2 a is an enlarged view of circled area 2 a of FIG. 2;

FIG. 3 is a bottom view of the first embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 3 a is an enlarged view of circled area 3 a of FIG. 3.

FIG. 4 is a top view of a second embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 5 is a bottom view of the second embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 6 is a top view of a third embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 7 is a bottom view of the third embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 8 is a top view of a fourth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 9 is a bottom view of the fourth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 10 is a side view of a fifth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 11 is a side view of a sixth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 12 is a top view of a seventh embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 13 is a top view of an eighth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 14 is a top view of a ninth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 15 is a top view of a tenth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 16 is a top view of an eleventh embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 17 is a top view of a twelfth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 18 is a top view of a thirteenth embodiment of the fan impeller structure of centrifugal fan of the present invention;

FIG. 19 is a top view of a fourteenth embodiment of the fan impeller structure of centrifugal fan of the present invention; and

FIG. 20 is a top view of a fifteenth embodiment of the fan impeller structure of centrifugal fan of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIGS. 1, 2, 2 a, 3 and 3 a. FIG. 1 is a perspective view of a first embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 2 is a top view of the first embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 2 a is an enlarged view of circled area 2 a of FIG. 2. FIG. 3 is a bottom view of the first embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 3 a is an enlarged view of circled area 3 a of FIG. 3. According to the first embodiment, the fan impeller structure 1 of centrifugal fan of the present invention includes a hub 11, a first blade body set 12 and a second blade body set 13.
The hub 11 has an extension section 111 having a first side 1111 and a second side 1112. The extension section 111 extends from the circumference of the hub 11 in a direction away from the hub 11.
The first blade body set 12 is disposed on the first side 1111. The first blade body set 12 includes multiple first blade bodies 121. The first blade bodies 121 define therebetween multiple first air inlets 122 and multiple first air outlets 123. The first air outlets 123 are arranged at unequal intervals.
The second blade body set 13 is disposed on the second side 1112. The second blade body set 13 includes multiple second blade bodies 131. The second blade bodies 131 define therebetween multiple second air inlets 132 and multiple second air outlets 133. The second air outlets 133 are arranged at equal intervals.
The first blade body set 12 extends from the first side 1111 of the extension section 111 in a direction away from the hub 11. Each first blade body 121 has a first end 1211 and a second end 1212. The first air inlet 122 is defined between the first ends 1211 of each two adjacent first blade bodies 121. The first air outlet 123 is defined between the second ends 1212 of each two adjacent first blade bodies 121. The second blade body set 13 extends from the second side 1112 of the extension section 111 in a direction away from the hub 11. Each second blade body 131 has a third end 1311 and a fourth end 1312. The second air inlet 132 is defined between the third ends 1311 of each two adjacent second blade bodies 131. The second air outlet 133 is defined between the fourth ends 1312 of each two adjacent second blade bodies 131.
The first ends 1211 together define a first pitch circle 124. A tangent of the first pitch circle 124 at the first end 1211 is defined as a first tangent 125. The first blade body 121 has a first blade body central line 1213. A tangent of the first blade body central line 1213 at the first end 1211 is defined as a second tangent 126. The second tangent 126 intersects the first tangent 125 to contain a first air incoming angle 12 a. The second ends 1212 together define a second pitch circle 127. A tangent of the second pitch circle 127 at the second end 1212 is defined as a third tangent 128. A tangent of the first blade body central line 1213 at the second end 1212 is defined as a fourth tangent 129. The third tangent 128 and the fourth tangent 129 contain a first air outgoing angle 12 b. The third ends 1311 together define a third pitch circle 134. A tangent of the third pitch circle 134 at the third end 1311 is defined as a fifth tangent 135. The second blade body 131 has a second blade body central line 1313. A tangent of the second blade body central line 1313 at the third end 1311 is defined as a sixth tangent 136. The fifth tangent 135 intersects the sixth tangent 136 to contain a second air incoming angle 13 a. The fourth ends 1312 together define a fourth pitch circle 137. A tangent of the fourth pitch circle 137 at the fourth end 1312 is defined as a seventh tangent 138. A tangent of the second blade body central line 1313 at the fourth end 1312 is defined as an eighth tangent 139. The seventh tangent 138 and the eighth tangent 139 contain a second air outgoing angle 13 b. In this embodiment, the first air incoming angle 12 a is larger than or equal to the second air incoming angle 13 a.
The first blade body central line 1213 extends along the first blade body 121 and has a curvature equal to that of the first blade body 121. The second blade body central line 1313 extends along the second blade body 131 and has a curvature equal to that of the second blade body 131. The first blade body central line 1213 is a longitudinal central line of the thickness of the first blade body 121. That is, on the basis of the first blade body central line 1213, the widths extend from the first blade body central line 1213 to two sides of the first blade body 121 are equal to each other. Similarly, the second blade body central line 1313 is a longitudinal central line of the thickness of the second blade body 131. That is, on the basis of the second blade body central line 1313, the widths extend from the second blade body central line 1313 to two sides of the second blade body 131 are equal to each other.
Please now refer to FIGS. 4 and 5. FIG. 4 is a top view of a second embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 5 is a bottom view of the second embodiment of the fan impeller structure of centrifugal fan of the present invention. The second embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The second embodiment is different from the first embodiment in that the first air outgoing angle 12 b is smaller than or equal to the second air outgoing angle 13 b.
Please now refer to FIGS. 6 and 7. FIG. 6 is a top view of a third embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 7 is a bottom view of the third embodiment of the fan impeller structure of centrifugal fan of the present invention. The third embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The third embodiment is different from the first embodiment in that the first air incoming angle 12 a is smaller than or equal to the second air incoming angle 13 a.
Please now refer to FIGS. 8 and 9. FIG. 8 is a top view of a fourth embodiment of the fan impeller structure of centrifugal fan of the present invention. FIG. 9 is a bottom view of the fourth embodiment of the fan impeller structure of centrifugal fan of the present invention. The fourth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The fourth embodiment is different from the first embodiment in that the first air outgoing angle 12 b is larger than or equal to the second air outgoing angle 13 b.
Please now refer to FIG. 10. FIG. 10 is a side view of a fifth embodiment of the fan impeller structure of centrifugal fan of the present invention. The fifth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The fifth embodiment is different from the first embodiment in that the second end 1212 has a height larger than that of the fourth end 1312.
Please now refer to FIG. 11. FIG. 11 is a side view of a sixth embodiment of the fan impeller structure of centrifugal fan of the present invention. The sixth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The sixth embodiment is different from the first embodiment in that the fourth end 1312 has a height larger than that of the second end 1212.
Please now refer to FIG. 12. FIG. 12 is a top view of a seventh embodiment of the fan impeller structure of centrifugal fan of the present invention. The seventh embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The seventh embodiment is different from the first embodiment in that the first blade body 121 has a length larger than that of the second blade body 131.
Please now refer to FIG. 13. FIG. 13 is a top view of an eighth embodiment of the fan impeller structure of centrifugal fan of the present invention. The eighth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The eighth embodiment is different from the first embodiment in that the second blade body 131 has a length larger than that of the first blade body 121.
Please now refer to FIG. 14. FIG. 14 is a top view of a ninth embodiment of the fan impeller structure of centrifugal fan of the present invention. The ninth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The ninth embodiment is different from the first embodiment in that the first end 1211 is aligned with the third end 1311, while the first and second air outlets 123, 133 are not aligned with each other.
Please now refer to FIG. 15. FIG. 14 is a top view of a tenth embodiment of the fan impeller structure of centrifugal fan of the present invention. The tenth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The tenth embodiment is different from the first embodiment in that the first end 1211 is not aligned with the third end 1311 and the first and second air inlets 122, 132 are not aligned with each other.
Please now refer to FIG. 16. FIG. 16 is a top view of an eleventh embodiment of the fan impeller structure of centrifugal fan of the present invention. The eleventh embodiment is partially identical to the tenth embodiment in structure and thus will not be repeatedly described hereinafter. The eleventh embodiment is different from the tenth embodiment in that the first end 1211 is not aligned with the third end 1311 and the first and second air inlets 122, 132 are not aligned with each other.
Please now refer to FIG. 17. FIG. 17 is a top view of a twelfth embodiment of the fan impeller structure of centrifugal fan of the present invention. The twelfth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The twelfth embodiment is different from the first embodiment in that the number of the first blade bodies 121 is more than the number of the second blade bodies 131.
Please now refer to FIG. 18. FIG. 18 is a top view of a thirteenth embodiment of the fan impeller structure of centrifugal fan of the present invention. The thirteenth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The thirteenth embodiment is different from the first embodiment in that the number of the second blade bodies 131 is more than the number of the first blade bodies 121.
Please now refer to FIG. 19. FIG. 19 is a top view of a fourteenth embodiment of the fan impeller structure of centrifugal fan of the present invention. The fourteenth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The fourteenth embodiment is different from the first embodiment in that the first air outlets 123 are arranged at equal intervals, while the second air outlets 133 are arranged at unequal intervals. The characteristic of this embodiment can be combined with the characteristics of the second to thirteenth embodiments to achieve other aspects of the fan impeller structure.
Please now refer to FIG. 20. FIG. 20 is a top view of a fifteenth embodiment of the fan impeller structure of centrifugal fan of the present invention. The fifteenth embodiment is partially identical to the first embodiment in structure and thus will not be repeatedly described hereinafter. The fifteenth embodiment is different from the first embodiment in that the first air outlets 123 are arranged at unequal intervals and the second air outlets 133 are also arranged at unequal intervals. The characteristic of this embodiment can be combined with the characteristics of the second to thirteenth embodiments to achieve other aspects of the fan impeller structure.
The present invention has been described with the above embodiments thereof and it is understood that many changes and modifications in the above embodiments can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.

Claims

What is claimed is:

1. A fan impeller structure of centrifugal fan, comprising:

a hub having an extension section, the extension section having a first side and a second side;

a first blade body set disposed on the first side, the first blade body set including multiple first blade bodies, the first blade bodies defining therebetween multiple first air inlets and multiple first air outlets, the first air outlets being arranged at unequal intervals; and

a second blade body set disposed on the second side, the second blade body set including multiple second blade bodies, the second blade bodies defining therebetween multiple second air inlets and multiple second air outlets.

2. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the first blade body set extends from the first side of the extension section in a direction away from the hub, each first blade body having a first end and a second end, the first air inlet being defined between the first ends of each two adjacent first blade bodies, the first air outlet being defined between the second ends of each two adjacent first blade bodies, the second blade body set extending from the second side of the extension section in a direction away from the hub, each second blade body having a third end and a fourth end, the second air inlet being defined between the third ends of each two adjacent second blade bodies, the second air outlet being defined between the fourth ends of each two adjacent second blade bodies.

3. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the first ends together define a first pitch circle, a tangent of the first pitch circle at the first end being defined as a first tangent, the first blade body having a first blade body central line, a tangent of the first blade body central line at the first end being defined as a second tangent, the second tangent intersecting the first tangent to contain a first air incoming angle, the second ends together defining a second pitch circle, a tangent of the second pitch circle at the second end being defined as a third tangent, a tangent of the first blade body central line at the second end being defined as a fourth tangent, the third tangent and the fourth tangent containing a first air outgoing angle, the third ends together defining a third pitch circle, a tangent of the third pitch circle at the third end being defined as a fifth tangent, the second blade body having a second blade body central line, a tangent of the second blade body central line at the third end being defined as a sixth tangent, the fifth tangent intersecting the sixth tangent to contain a second air incoming angle, the fourth ends together defining a fourth pitch circle, a tangent of the fourth pitch circle at the fourth end being defined as a seventh tangent, a tangent of the second blade body central line at the fourth end being defined as an eighth tangent, the seventh tangent and the eighth tangent containing a second air outgoing angle.

4. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air incoming angle is larger than or equal to the second air incoming angle.

5. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air outgoing angle is larger than or equal to the second air outgoing angle.

6. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air incoming angle is smaller than or equal to the second air incoming angle.

7. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air outgoing angle is smaller than or equal to the second air outgoing angle.

8. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the second end has a height larger than that of the fourth end.

9. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the fourth end has a height larger than that of the second end.

10. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the first blade body has a length larger than that of the second blade body.

11. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the second blade body has a length larger than that of the first blade body.

12. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the first end is aligned with the third end.

13. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first end is not aligned with the third end and the first and second air inlets are not aligned with each other.

14. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the number of the first blade bodies is more than the number of the second blade bodies.

15. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the number of the second blade bodies is more than the number of the first blade bodies.

16. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the second blade bodies of the second blade body set are arranged at equal intervals or unequal intervals.

17. A fan impeller structure of centrifugal fan, comprising:

a first blade body set disposed on the first side, the first blade body set including multiple first blade bodies, the first blade bodies defining therebetween multiple first air inlets and multiple first air outlets, the first air outlets being arranged at equal intervals; and

a second blade body set disposed on the second side, the second blade body set including multiple second blade bodies, the second blade bodies defining therebetween multiple second air inlets and multiple second air outlets, the second air outlets being arranged at unequal intervals.

18. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the first blade body set extends from the first side of the extension section in a direction away from the hub, each first blade body having a first end and a second end, the first air inlet being defined between the first ends of each two adjacent first blade bodies, the first air outlet being defined between the second ends of each two adjacent first blade bodies, the second blade body set extending from the second side of the extension section in a direction away from the hub, each second blade body having a third end and a fourth end, the second air inlet being defined between the third ends of each two adjacent second blade bodies, the second air outlet being defined between the fourth ends of each two adjacent second blade bodies.

19. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the first ends together define a first pitch circle, a tangent of the first pitch circle at the first end being defined as a first tangent, the first blade body having a first blade body central line, a tangent of the first blade body central line at the first end being defined as a second tangent, the second tangent intersecting the first tangent to contain a first air incoming angle, the second ends together defining a second pitch circle, a tangent of the second pitch circle at the second end being defined as a third tangent, a tangent of the first blade body central line at the second end being defined as a fourth tangent, the third tangent and the fourth tangent containing a first air outgoing angle, the third ends together defining a third pitch circle, a tangent of the third pitch circle at the third end being defined as a fifth tangent, the second blade body having a second blade body central line, a tangent of the second blade body central line at the third end being defined as a sixth tangent, the fifth tangent intersecting the sixth tangent to contain a second air incoming angle, the fourth ends together defining a fourth pitch circle, a tangent of the fourth pitch circle at the fourth end being defined as a seventh tangent, a tangent of the second blade body central line at the fourth end being defined as an eighth tangent, the seventh tangent and the eighth tangent containing a second air outgoing angle.

20. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air incoming angle is larger than or equal to the second air incoming angle.

21. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air outgoing angle is larger than or equal to the second air outgoing angle.

22. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air incoming angle is smaller than or equal to the second air incoming angle.

23. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air outgoing angle is smaller than or equal to the second air outgoing angle.

24. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the second end has a height larger than that of the fourth end.

25. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the fourth end has a height larger than that of the second end.

26. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the first blade body has a length larger than that of the second blade body.

27. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the second blade body has a length larger than that of the first blade body.

28. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the first end is aligned with the third end.

29. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first end is not aligned with the third end and the first and second air inlets are not aligned with each other.

30. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the number of the first blade bodies is more than the number of the second blade bodies.

31. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the number of the second blade bodies is more than the number of the first blade bodies.