WO2007097802A2

WO2007097802A2 - Cooling fan with integral housing and impeller

Info

Publication number: WO2007097802A2
Application number: PCT/US2006/048565
Authority: WO
Inventors: Yousef Jarrah; John Herzberger
Original assignee: Minebea Co., Ltd.
Priority date: 2005-12-29
Filing date: 2006-12-18
Publication date: 2007-08-30
Also published as: JP2009522490A; DE112006003159T5; US20070154309A1; WO2007097802A3; TW200730732A

Abstract

A cooling fan is disclosed. The cooling fan comprises fan blades having a primary blade component and a secondary blade component. The primary blade component produces an axial airflow. The secondary blades produce a radial airflow. The axial airflow and the radial airflow, respectively created by the primary blades and the secondary blades, combine to provide an increase axial outflow. The primary and secondary blades combine the axial and radial flows respectively created by the blades to produce an increased outflow. The design has been observed to reduce tonal noise as well.

Description

COOLING FAN WITH INTEGRAL HOUSING AND IMPELLER

CROSS-REFERENCES TO RELATED APPLICATIONS

[01] The present application claims priority from U.S. Provisional Application No. 60/755,303, filed December 29, 2005, and is fully incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

[02] The present invention relates generally to cooling fans and in particular to an impeller design to improve airflow and noise performance in axial fan designs.

[03] Prior art fans (e.g., Fig. 6) comprise a separate housing and fan assembly. The fan assembly fits into an air passage region provided in the housing. The circumference of the air passage must be larger than the circumference of volume of space defined by the rotating blades. Consequently, there is a gap between the tips of the fan blades and the housing wall which defines the air passage region. This gap can be large and accordingly reduce the performance of the air mover device.

BREBF SUMMARY OF THE INVENTION [04] A cooling fan according to the present invention comprises fan blades having a primary blade component and a secondary blade (may also be referred to as the tip blade) component. The primary blade component produces an axial airflow. The secondary blades produce a radial airflow. The axial airflow and the radial airflow, respectively created by the primary blades and the secondary blades, combine to provide an increase axial outflow, thus enabling a greater movement of air to increase the cooling effect of the fan. The resulting device improves aerodynamic efficiency. Tests have also shown reductiond in tonal noise as compared to conventional blade designs which do not incorporate a tip blade. BRIEF DESCRIPTION OF THE DRAWINGS

[05] Fig. 1 shows a side view and a top view of a cooling fan according to an embodiment of the present invention.

[06] Figs. 2A and 2B are schematic illustrations of fan blades according to the present invention.

[07] Fig. 3A illustrates axis of rotation. [08] Fig. 3B illustrates radial direction.

[09] Fig. 4 illustrates the air flows produced by a fan in accordance with the present invention. [10] Figs. 5 A and 5B illustrate variations of wire-frame housings in accordance with the present invention.

[11] Fig. 6 shows a conventional fan with a housing.

DETAILED DESCRIPTION OF THE INVENTION [12] Fig. 1 shows side view and top view images of a prototype for a cooling fan 100 according to an embodiment of the present invention. The images show an impeller unit 104 comprising a motor 124 and fan blades 126. The fan blades 126 are connected to a hub 122, which in turn is fixedly coupled to a rotor portion 128 of the motor 124. The impeller unit 104 is mounted to a fan housing 102. In the embodiment shown in Fig. 1 the fan housing consists only of a base portion 112 onto which the motor is mounted. The images of Fig. 1 also show wires for electrical connection to the motor 124.

[13] In accordance with the present invention, the illustrative embodiment of Fig. 1 shows that the fan blades 126 comprise a primary blade 132 and a secondary blade 136. In the illustrative embodiment of Fig. 1, the secondary blade 134 is disposed at the tip of the primary blade 132.

[14] Further in accordance with an aspect of the present invention as shown in the embodiment of Fig. 1, the fan housing 102 comprises only the base portion 112, and is absent the conventional casing enclosure that encloses the fan blades in the radial direction. See, for example, Fig. 6 which shows a conventional cooling fan design. The conventional fan housing includes a base portion and a fan blade enclosure (casing) that encloses the fan blades along a radial direction, but is open in the axial direction to provide an axial air passage.

[IS] Figs. 2 A and 2B are illustrations showing configurations of a fan blade 226 in accordance with the present invention. Fig. 2A shows a primary blade 232 having a root end 242 that connects to the hub 222. The other end of the primary blade is referred to as the blade tip 244, or simply tip. In accordance with the present invention, a secondary blade 234 is disposed proximate the blade tip 244. As shown in Fig. 1 and illustrated in Fig. 2A, the secondary blade 234 is formed substantially at the tip 244 of the primary blade 232. Fig. 2B illustrates that the secondary blade 234 does not have to be formed at the tip 244, and that some portion of the tip of the primary blade 232 may extend beyond the outer surface of the secondary blade. It is only necessary that the secondary blade 234 be disposed near the tip of the primary blade 232.

[16] Fig. 2 A further illustrates that the secondary blade 234 is disposed roughly in perpendicular relation to the primary blade 232. It will be appreciated that the secondary blade 234 can be provided at an angle θ other than 90°. It will be further appreciated that the secondary blade 234, not unlike the primary blade 232, can be designed to have any suitable combination of parameters used in blade design, e.g., chord length, camber, and so on. In fact, the secondary blades 134 are characterized much in the same way as the primary blades 132. This is illustrated in Fig. 1, where the top view image assumes a direction of fan rotation as shown. For example, the primary blades 132 each has a leading edge 152 and a trailing edge 154. Similarly, the secondary blades 134 each has a leading edge 142 and a trailing edge 144.

[17] hi operation, a cooling fan configured in accordance with the invention will create a radial inflow of air in addition to the normal axial inflow. The resulting axially-directed outflow of air is thus increased because of the additional radial inflow. Referring to Figs. 1 and 4, a cooling fan according to the present invention is absent the conventional enclosure that houses the fan. The absence of the housing opens up the sides, allowing the secondary blades 134 to capture air from the radially-directed periphery of the fan blades 126.

[18] Fig. 4 shows various inflows that are produced by a cooling fan of the present invention. First, there is the conventional axial inflow of air that is produced by the turning of the primary bladesl32. The axial airflow is the flow of air that is substantially parallel to the axis of rotation (Fig. 3A) of the blades. (19] Fig. 4 also shows a radial inflow of air entering along the radial direction. As understood by one of ordinary skill, the radial direction is the direction along which the primary blades extend from the hub toward the tip, as illustrated in Fig. 3B. The radial inflow results from a scooping action of air in the radial direction when the air is captured by the secondary blades 134 as the fan blades 126 turn. This scooping of air along the radial direction is facilitated by not enclosing the impeller 104 in an enclosure, thus eliminating the side walls. The additional radial inflow air stream contributes to the resulting axially-directed outflow stream of air, thus significantly increasing the outflow.

[20] The air that is captured by the secondary blades 134 in the radial direction is forced in the axial direction and combines with the axial inflow to produce the axial outflow as illustrated in Fig. 4. As will be appreciated, the capture of air and subsequent redirection and combination with the axial inflow are controlled by design of the primary blades 132 and secondary blades 134. Parameters including camber angle, stagger angle, chord length, and number of blades are principal design parameters that control the capture effect of the secondary blades. For example, the secondary blades 134 can be designed to produce an amount of radial air flow that is 10% of the axial air flow created by the primary blades 132. Such a design would result in roughly an increase in outgoing airflow by 10%.

[21] The embodiment illustrated in Fig. 1 shows that a secondary blade 134 is provided for each primary blade 132. However, alternate possible embodiments include providing secondary blades for only some of the primary blades. For example, every n'^h primary blade can be configured with a secondary blade proximate its tip. The number for n will depend on the total number of primary blades. The secondary blades should be evenly distributed among the primary blades to ensure the impeller 104 is balanced in order to avoid wobble during operation. Also, symmetrical distribution of the secondary blades in the circumferential direction (or azimuthal direction) ensures a proper scooping action. For example, in one configuration, the impeller can comprise a secondary blade for every other primary blade. In another configuration, the impeller can comprise every third primary blade provided with a secondary blade.

[22] The embodiment illustrated in Fig. 1 shows that the fan housing 102comprises only a base portion 112. There is no casing or enclosure within which the impeller unit 104 is housed. The embodiment of Fig. 1 is simple and cost-effective to build. However, it may be desirable to provide some kind of open-spaced enclosure to house the impeller 104 unit. This aspect of the present invention will now be discussed in connection with Figs. 5A and 5B.

[23] Figs. 5 A and 5B show alternative embodiments to illustrate a further aspect of the present invention. Fig. 5A shows an embodiment in which a wire-frame cage 502 (represented by dashed lines) can be provided as an enclosure. For example, the wire-frame members 512 can be solid members, tubular, have a circular cross-section, and so on. Note that the cage structure does not contain side walls in order to reduce obstructions to the flow of air in the radial directed during fan operation.

[24] Fig. 5B shows a variation where the cage 502 includes strut members 514 to add mechanical strength to the cage. Though the strut members 514 are provided on the sides of the cage, it is noted that they do not substantially occlude radially directed airflow. Based on the examples of cage construction shown in Figs. 5A and 5B, it can be appreciated that any suitable enclosure can be provided so long as the sides of such enclosure are sufficiently open to allow for adequate radially directed airflow. In this way, when an impeller of the present invention is operated within such an open-sided enclosure design, the secondary blades 136 can create a radially-directed inflow of air.

[25] The foregoing embodiment exemplars of the present invention show a fan housing that is substantially absent the enclosure. As noted above, the reason for this is to reduce obstructions to the flow air in the of radial direction to facilitate the capture of air by the secondary blades 134. However, while a fan housing that is absent the conventional enclosure may be a suitable embodiment for some uses, the present invention does not require the complete absence of an enclosure. The wire-frames of Figs. 5A and 5B are an example of such an enclosure. In another example, an enclosure (not shown) that is more that the wire cages of Figs. 5A and 5B can be provided with openings on its sides to allow for a radially-directed inflow of air (Fig. 6 shows what is meant by sides of the enclosure, in the context of this discussion). An enclosure having openings on its sides may be desirable in order to protect a user from the spinning fan blades, while at the same time improving the axial outflow provided by the present invention. The openings can be appropriately designed so that a sufficient amount of air can pass through, allowing the secondary blades 136 to create an adequate radial inflow and direct that flow into the axial outflow stream. The openings can be varied in terms of numbers, sizing, shapes (e.g., slotted, circular, etc), orientation (e.g., diagonal, horizontal, etc), and so on. [26] It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A cooling fan comprising: an impeller having a hub and first fan blades, each first fan blade mounted about the hub in a radial direction, the first blades configured to produce an airflow directed along an path that is parallel to an axis of rotation of the impeller, the impeller further having second fan blades configured to produce a flow of air directed radially relative to the axis of rotation of the impeller and inwardly toward the axis of rotation; a motor operatively coupled to rotate the impeller; and a base to which the motor is fixedly attached.

2. The cooling fan of claim 1 wherein each second fan blade is coupled to a first fan blade.

3. The cooling fan of claim 2 wherein each second fan blade is coupled proximate the tip of a first fan blade.

4. The cooling fan of claim 1 wherein each second fan blade is coupled to a first fan blade, wherein the number of second fan blades equals the number of first fan blades.

5. The cooling fan of claim 1 wherein each second fan blade is coupled to a first fan blade, wherein the number of second fan blades is less than the number of first fan blades.

6. The cooling fan of claim 1 further comprising an enclosure connected to the base and including therein the impeller, the enclosure having openings on its sides.

7. The cooling fan of claim 6 wherein the enclosure is a wire-frame enclosure.

8. A cooling fan comprising: an impeller comprising a motor and a hub operatively coupled to the motor, the hub having a plurality of primary blades connected thereto, each primary blade having a root that connects to the hub and a tip, at least some of the primary blades each further having a secondary blade connected proximate its tip; and a fan housing, the fan housing having a base to which the motor is coupled, the fan housing configured so that there is substantially no impediment to a flow of air into the impeller in the radial direction.

9. The cooling fan of claim 8 wherein the fan housing further has a wire- frame cage connected to the base.

10. The cooling fan of claim 9 wherein the wire-frame cage includes one or more strut members.

11. The cooling fan of claim 8 wherein each primary blade has a secondary blade.

12. The cooling fan of claim 8 wherein the number of secondary blades is less than the number of primary blades.

13. A cooling fan comprising: an impeller unit comprising first fan blades and second fan blades; and a fan housing having a base unit and a substantially unobstructed radially directed path for a radial flow of air toward the fan housing, the impeller unit disposed in the fan housing upon the base unit wherein the second fan blades lie along the radially directed path, the first fan blades producing an axial flow or air toward the fan housing when the first fan blades are turned by a motor, the second fan blades producing a radial flow of air towards the fan housing along the radially directed path.

14. The cooling fan of claim 13 wherein the second blades are connected to the first blades.

15. The cooling fan of claim 13 wherein the second blades are connected to the first blades proximate the tips of the first blades.

16. The cooling fan of claim 13 wherein the number of second blades is less than the number of first blades.

17. The cooling fan of claim 13 wherein the fan housing further comprises a wire-frame cage attached to the base unit.

18. The cooling fan of claim 13 wherein the fan housing further comprises an enclosure to receive the impeller, wherein the enclosure has side openings.