Impeller blade for axial flow fan having counter-rotating impellers

#The present invention relates to an axial flow fan, and more particularly to a multiple impeller arrangement with coaxial impellers that rotate in opposite directions. The multiple impeller counter-rotating axial flow fan of the present invention is especially suitable for use in cooling electronic components.

#A conventional axial flow fan is generally composed of a driving motor, a cylindrical central hub section mounted on a motor shaft attached to the driving motor, a plurality of blades affixed to the hub, and a housing for encasing the fan or impeller, used herein as equivalent terms. Each of the blades extends radially outward from the central hub section of the fan. The motor shaft is attached to the hub section at a central aperture and thus the hub section may be rotated by the driving motor via the motor shaft. In such an arrangement, the hub section together with the blades are rotated by the motor about an axis of the outer casing in order to force air flow from an inlet area to an outlet area of the fan. The blades of the fan are air foils configured so as to make the blades generate a force in the opposite direction of the blade's direction of rotation and an air flow that is perpendicular to the blade's direction of rotation.

#Axial flow fans such as Model No. 5920 produced by IMC Magnetics Corporation, the assignee of the present application, are known which utilize a unipolar winding employing a four pole motor where only two of the windings are ON at a time. These fans employ circuitry including circuit elements of a substantial size, such as an inductor to reduce the starting current, transistors large enough to handle the power levels, and large clamping diodes needed to protect the transistors. Such axial flow fans cannot handle input voltages in the range of 57V-64V, are limited to a maximum input voltage of about 56V, and are more typically operated at an input voltage of about 48V.

#The present invention will be more easily understood with reference to the following drawings.

#FIG. 1 is an exploded perspective view of a single impeller axial flow fan.

#FIG. 2 is a cross-sectional assembled view thereof.

#General Structure of the Axial Flow Fan

#A description of a preferred embodiment of the present invention will now be given. Referring now to the drawings, and in particular to FIGS. 1 and 2, wherein illustrated is an axial flow fan 100, comprising an impeller 10, for generating air flow when rotated, a yoke 20 mounted in impeller 10, a shaft 30 coupled to yoke 20, a permanent magnet 40 mounted in yoke 20, a stator assembly 50, a fan housing 70, an insulation sheet 60 for electrically insulating the base within stator assembly 50 from fan housing 70, and bearings and mounting hardware 80 which serve to secure the shaft 30 to housing 70 while allowing yoke 20 and magnet 40 to freely rotate, thereby rotating impeller 10. The impeller 10 comprises a plurality of blades 11 equally spaced and circumferentially mounted on circular band 12. The permanent magnet 40 mounted in yoke 20, when combined with stator assembly 50, forms an electrical motor which turns impeller 10 when a voltage is applied to an exciting circuit on the printed circuit board within stator assembly 50. The construction of stator assembly 50 is fully described in co-pending and co-owned patent application Ser. No. 09/119,221 entitled “Stator Mounting Method and Apparatus for a Motor,” which was filed on Jul. 20, 1998, and which is incorporated herein by reference.

#As shown in FIG. 7(d), the counter rotating fan of the preferred embodiment is comprised of a first single impeller axial flow fan as described in the preceding paragraph and a second single impeller axial flow fan contained within a single housing. The input of the second single impeller axial flow fan is connected to the output of the first single impeller axial flow fan. In addition, the second single impeller axial flow fan has an impeller that rotates in the reverse direction compared to the direction of rotation of the impeller contained in the first single impeller axial flow fan and the second single impeller axial flow fan has blades that are oppositely pitched as compared to the blades of the first single impeller axial flow fan.