Contra-rotating axial flow fan unit

1. Field of the Invention

The present invention relates to a contra-rotating axial flow fan unit.

2. Description of the Related Art

Conventionally, a cooling fan is installed in electronic devices such as a personal computer, a server and the like to cool electronic parts enclosed within a casing thereof. The electronic parts are densely arranged within the casing and, consequently, the heat emitted from the electronic parts tends to stay within the casing. This requires improvement in the performance of the cooling fan. In particular, a cooling fan capable of delivering an air under a high static pressure and with an increased volume is required in a large-sized electronic device such as a server or the like.

As a cooling fan for increasing the static pressure of the discharged air, there is known a serially arranged axial flow fan unit in which two axial flow fans are connected in series. In the serially arranged axial flow fan unit, an air stream discharged from an upstream fan is introduced into a downstream fan. Due to this construction, the serially arranged axial flow fan unit is capable of efficiently delivering air under a high static pressure and with an increased volume.

In the serially arranged axial flow fan unit, however, the volume and the static pressure of the discharged air are not increased by merely connecting two axial flow fans in series. Since the number of fans is increased in the serially arranged axial flow fan unit, the amount of the electric current needed to rotate the impellers is also increased as compared to a unitary axial flow fan. For that reason, there is a need to efficiently rotate the impellers of the serially arranged axial flow fan unit, thereby reducing the amount of the supplied current.

In order to overcome the problems described above, a preferred embodiment of the present invention includes a contra-rotating axial flow fan unit having an intake side axial flow fan and an exhaust side axial flow fan. The intake side axial flow fan includes an intake side impeller having intake side blades rotatable about a central rotation axis, an intake side motor arranged to rotate the intake side impeller, and an intake side housing having an inner circumferential surface that surrounds the intake side impeller. The exhaust side axial flow fan includes an exhaust side impeller having exhaust side blades rotatable about the central rotation axis, an exhaust side motor arranged to rotate the exhaust side impeller, and an exhaust side housing having an inner circumferential surface that surrounds the exhaust side impeller. Further, at least one intermediate axial flow fan is arranged between the intake side axial flow fan and the exhaust side axial flow fan. There may be a plurality (two or more) intermediate axial flow fans.

The intermediate axial flow fan includes an intermediate impeller having intermediate blades rotatable about the central rotation axis, an intermediate motor arranged to rotate the intermediate impeller, and an intermediate housing having an inner circumferential surface that surrounds the intermediate impeller. A rotational direction of the intermediate impeller is different from that of the impellers adjacent thereto. Therefore, air is drawn into the contra-rotating axial flow fan unit through the intake side axial flow fan and is discharged to the outside through the exhaust side axial flow fan. This makes it possible to increase the volume and the static pressure of the air drawn therein and discharged therefrom.

The intake side axial flow fan may include intake side support ribs arranged to interconnect the intake side motor and the intake side housing, the exhaust side axial flow fan may include a plurality of exhaust side support ribs arranged to interconnect the exhaust side motor and the exhaust side housing, and the intermediate axial flow fan may include intermediate support ribs arranged to interconnect the intermediate motor and the intermediate housing. Due to this feature, a portion of the swirling-direction velocity component of an air stream impinges against the respective support ribs and is changed to an axial velocity component. This increases the static pressure of the air.

It is preferable that the intake side support ribs are arranged between the intake side impeller and the intermediate impeller, the intermediate support ribs are arranged between the intermediate impeller and another intermediate impeller or between the intermediate impeller and the exhaust side impeller, and the exhaust side support ribs are opposite to the intermediate support ribs with the intermediate impeller lying therebetween.

In the above construction, it is preferable that the number of the respective blades differs from the number of the respective support ribs within a respective axial fan. Due to this feature, the frequency of a wind noise generated by the rotation of the respective impellers becomes different from the frequency of an interfering noise generated when the air stream impinges against the respective support ribs, thereby preventing sympathetic vibration of the wind noise and the interfering noise. As a result, it is possible to reduce the noise generated in the contra-rotating axial flow fan unit.

In a preferred embodiment of the present invention, the intermediate housing may be axially opposite to the intake side housing, the exhaust side housing, or another intermediate housing. The respective housings may make contact with one another or may be opposite to one another via gaps therebetween. The respective axial flow fans may be fixed to one another by screws, engaging structures or other suitable fixing mechanisms or materials.

It is preferable that the intake side support ribs, the exhaust side support ribs, and the intermediate support ribs are substantially flat. Each of the intake side support ribs, the exhaust side support ribs, and the intermediate support ribs may have an upper edge and a lower edge. Each of the intake side support ribs, the exhaust side support ribs, and the intermediate support ribs may have an air receiving surface defined between the upper edge and the lower edge to confront an air stream flowing from the intake side impeller toward the exhaust side impeller. It is preferable that the air receiving surface is inclined with respect to the central rotation axis to axially face toward an exhaust side.

It is preferable that the inclination of each of the blades relative to the central rotation axis is substantially the same as the inclination of each of the support ribs with respect to the central rotation axis. This ensures that the air drawn into the contra-rotating axial flow fan unit can smoothly flow through the vicinity of the respective blades and the respective support ribs.

In the respective support ribs of the axial flow fans, it is preferred that the upper edge of each of the support ribs is positioned upstream of the lower edge thereof with reference to the rotational direction of the respective impellers. This allows the air stream to smoothly flow through the vicinity of the respective support ribs with a minimal loss of energy of the air stream.

The respective support ribs may be positioned in an intake side of each of the housings. This ensures that a straightened air stream is smoothly drawn into the contra-rotating axial flow fan unit thereby reducing the noise generated in the contra-rotating axial flow fan unit.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

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