Compact axial fan

An axial fan has an inner-rotor motor which includes a drive end, a non-drive end and a shaft which extends axially from the drive end; and an impeller which includes a cylindrical impeller cup and a number of impeller blades that extend radially from the impeller cup. The impeller cup has an open upstream end and a closed downstream end which is connected to the shaft. In operation, the motor spins the impeller to generate an airflow in a direction from the non-drive end of the motor to the drive end of the motor. The impeller cup is configured to receive the motor therein and surround the drive end of the motor but not the non-drive end of the motor. As a result, the non-drive end of the motor is exposed to the airflow during operation of the fan.

BACKGROUND OF THE INVENTION

The present invention relates generally to axial fans. In particular, the invention relates to an axial fan which includes an inner-rotor motor and a deep-cup rotor which is mounted over the drive end of the motor to thereby substantially reduce the axial length of the fan.

Prior art axial fans typically use specially designed outer-rotor motors to achieve a compact axial length. Two examples of such prior art fans are shown inFIGS.1and2. In these fans the impeller is attached directly to a radially outer portion of the motor which rotates in operation. The motor is attached to a stationary support structure located upstream or downstream of the impeller by detachable struts which mount directly to an outer portion of the motor that remains stationary during operation. This type of motor is produced in a limited range of sizes by specialty fan manufacturers, but it is not mass-produced by the major electric motor suppliers because of its limited use in non-fan applications and because it typically has a lower efficiency than an inner-rotor motor.

For newer compact fan applications, a suitable outer-rotor motor design may not be commercially available. A custom design and development effort requires a significant amount of time and expense which may not be acceptable to today's manufacturers, especially for low to moderate volume applications. Use of a pre-existing, mass produced inner-rotor motor avoids the development time and expense of a custom designed motor and also takes advantage of economies of scale to minimize unit costs.

Fans with inner-rotor motors do exist in the prior art, but they typically are not axially compact. An example of such a fan is depicted inFIGS.3and4. Typically, the motor is supported by a frame or fan housing with struts that attach to the mounting feet of the motor. This fan has a significant axial length which is defined by the combined lengths of the motor, the overhung shaft, the impeller, and an inlet bellmouth. As one can readily see, this prior art inner-rotor motor fan is not axially compact.

Applicant's own prior art Tornado™ fan, which is depicted inFIGS.5and6, is an axially compact fan which incorporates an overhung impeller that includes two small drain holes which allow for fluid communication between the upstream and downstream sides of the impeller cup. These drain holes are provided to prevent pooling of liquids or condensates inside the impeller cup and are not intended to provide reverse flow cooling for the motor. This fan uses a custom inner-rotor motor which is connected to the fan shroud by support struts that are integral to the motor housing and fan shroud. Consequently, the motor cannot be readily removed and replaced.

A prior art fan design which employs reverse flow cooling for a fan motor is described in applicant's U.S. Pat. No. 7,819,641. In the embodiment shown inFIG.6of this patent (which is reproduced in the drawings hereof asFIG.7), a reverse flow cooling arrangement is provided for the downstream impeller414of a counter-rotating fan410. In this fan embodiment, a pressure difference between the upstream and downstream ends of the impeller414induces a portion of the airflow (which is sometimes referred to as a bleed stream and is depicted by the broken-line arrows) to flow upstream through a number of inlet openings454in the downstream end of the impeller cup, through the motor440and back into the main flowpath F through an annular gap456located adjacent the upstream end of the impeller. However, since the impeller414is driven by an outer-rotor motor440, the cooling flow passes through the motor rather than around the outside of the motor. In addition, since no means are provided adjacent the gap456to direct the bleed stream back downstream, in some applications the bleed stream may adversely impact the main flow stream in the flowpath F.

SUMMARY OF THE INVENTION

In accordance with the present invention, an axial fan is provided which comprises an inner-rotor motor which includes a drive end, a non-drive end and a shaft which extends axially from the drive end; and an impeller which includes a cylindrical impeller cup and a number of impeller blades that extend radially from the impeller cup. The impeller cup comprises an open upstream end and a closed downstream end which is connected to the shaft. In operation the motor spins the impeller to generate an airflow in a direction from the non-drive end of the motor to the drive end of the motor. The impeller cup is configured to receive the motor therein and surround the drive end of the motor but not the non-drive end of the motor. As a result, the non-drive end of the motor is exposed to the airflow during operation of the fan.

In accordance with one embodiment of the invention, the fan may comprise a support structure; a shroud which surrounds the impeller blades; and a number of struts which connect the drive end of the motor to at least one of the support structure and the shroud. In this manner, the motor is supported from said at least one of the support structure and the shroud by the struts. In this embodiment, each strut may include a first leg which extends generally perpendicularly to a rotational axis of the fan and a second leg which extends generally perpendicularly from the first leg along an outer surface of the motor. In addition, each first leg may comprise a distal end which is connected to said at least one of the support structure and the shroud and the second leg may comprise a distal end which is connected to the drive end of the motor. Also, the struts may be detachably connected to the drive end of the motor and said at least one of the support structure and the shroud.

In accordance with another embodiment of the invention, the fan may include a support structure; a shroud which surrounds the impeller blades; and a number of struts which connect the motor to at least one of the support structure and the shroud. Thus, the motor is supported from said at least one of the support structure and the shroud by the struts. In this embodiment, each strut may include a first leg which extends generally perpendicularly to a rotational axis of the fan and a second leg which extends generally perpendicularly from the first leg along an outer surface of the motor. Also, each first leg may comprise a distal end which is connected to said at least one of the support structure and the shroud and the second leg may comprise a distal end which is connected to the motor. Furthermore, the struts may be detachably connected to the motor and said at least one of the support structure and the shroud.

In accordance with yet another embodiment of the invention, the fan may include means for deflecting the airflow over the upstream end of the impeller cup. Such means may comprise, for example, a hub deflector which is secured to one of the motor or a support frame for the motor. The hub deflector may comprise a conical ring having an upstream end which is secured to said one of the motor or a support frame for the motor and a downstream end which diverges radially outwardly from the upstream end.

In accordance with a further embodiment of the invention, the downstream end of the impeller cup may include a number of through holes which extend axially therethrough. In this embodiment, the impeller cup may be configured such that a pressure difference between the upstream and downstream ends of the impeller will induce a portion of the airflow to flow into the through holes, through an annulus between the motor and the impeller cup, and back into the airflow at a location upstream of the impeller cup to thereby cool the drive end of the motor.

In accordance with yet another embodiment of the invention, the shroud may comprise a total axial length which is approximately the same as an axial length of the motor. The shroud may comprise an inlet bellmouth and an exit diffuser, in which event the total axial length of the shroud is approximately the same as the axial length of the motor.

In another embodiment of the invention, the impeller cup may comprise an axial cup length which is approximately 2.3 times an axial blade length of the impeller blades. Also, the shroud may comprise an exit diffuser, in which event both the impeller blades and the exit diffuser are incorporated within the axial space claim of the motor. In an alternative embodiment, the impeller cup may comprise an axial cup length which is approximately 1.7 times an axial blade length of the impeller blades. In this embodiment, the shroud does not comprise an exit diffuser, and both the impeller blades and the shroud are incorporated within the space claim of the motor.

Thus, it may be seen that the invention is directed to a compact axial fan which incorporates an integrated inner-rotor motor. Features of the invention include an overhung impeller with an axially deep cup that surrounds the drive end of an inner-rotor motor, detachable support struts that mount to the drive end of the motor, a motor non-drive end which is exposed to the main airflow, and an optional stationary hub deflector which is attached to the motor support frame located between the support struts and the impeller. The impeller cup may include through-holes that allow reverse flow cooling to ventilate the cavity between the impeller cup and drive end of the motor. The hub deflector guides both the mainstream flow and the reverse cooling flow into the impeller main passage. The fan shroud may incorporate an inlet bellmouth and an exit diffuser while remaining axially shorter than the axial length of the motor. The resulting fan provides an axially compact design with good thermal characteristics suitable for use with an inner-rotor motor.

These and other objects and advantages of the present invention will be made apparent from the following detailed description with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar components in the various embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is applicable to a variety of air movers. For purposes of brevity, however, it will be described in the context of an exemplary axial cooling fan. Nevertheless, a person of ordinary skill in the art will readily appreciate how the teachings of the present invention can be applied to other types of air movers. Therefore, the following description should not be construed to limit the scope of the present invention in any manner.

To provide context for the present invention, an exemplary prior art vane-axial cooling fan will first be described with reference toFIG.8. This prior art cooling fan, which is indicated generally by reference number10, is shown to comprise a tubular fan housing12, a motor14which is supported in the fan housing, an impeller16which is driven by the motor, and an outlet guide vane assembly18which extends radially between the motor14and the fan housing12. The fan housing12includes a shroud20which surrounds the impeller16, an inlet bellmouth22which is formed at the upstream end of the shroud, and an exit diffuser section24which is connected to the downstream end of the shroud proximate the outlet guide vane assembly18.

The motor14includes a motor housing26, a stator28which is mounted in the motor housing, a rotor30which is positioned within the stator, and a rotor shaft32which is connected to the rotor. The rotor shaft32is rotatably supported in a front bearing34which is mounted in an upstream end of the motor housing26and a rear bearing36which is mounted in a tail cone38that in turn is mounted to the downstream end of the motor housing. The impeller16includes an impeller cup40and a number of impeller blades42which extend radially outwardly from the impeller cup. The impeller cup40may also include a removable nose cone44to facilitate mounting the impeller16to the rotor shaft32. The outlet guide vane assembly18includes an inner ring46which is attached to or formed integrally with the motor housing28, an outer ring48which is connected to or formed integrally with the fan housing12and a plurality of guide vanes50which extend radially between the inner and outer rings. Thus, in addition to its normal function of straightening the air stream generated by the impeller16, the outlet guide vane assembly18serves to connect the motor14to the fan housing12.

As may be seen fromFIG.8, since the impeller16mounts to the upstream end of the motor14and the diffuser section24extends past the downstream end of the motor, the total axial length of the fan10is determined by the combined lengths of the inlet bellmouth22, the impeller, the motor and the exit diffuser section and/or tail cone38. In certain applications which afford limited space for the cooling fan, the fan depicted inFIG.8may not be appropriate due to its total axial length.

In accordance with the present invention, the total axial length of an axial fan is reduced by providing the fan with an inner-rotor motor and an overhung impeller having an axially deep cup that surrounds the drive end of the motor. Such a fan is shown conceptually inFIG.9. The fan of this embodiment, which is indicated generally by reference number100, includes an impeller102having an axially deep cup104which is mounted to the shaft106of an inner-rotor motor108. The impeller cup104is configured to surround the drive end110of the motor108, leaving only the non-drive end112of the motor exposed to the airflow (which is depicted by the two wide arrows). The fan100includes a shroud114which functions to define a path for the airflow and to provide support for the motor108; however, inFIG.9the structure for mounting the motor108to the shroud has been omitted for clarity. Thus it may be seen that the total axial length of the fan100is basically equal to the length of the motor108. By selecting an appropriate motor, therefore, the fan100may be used in applications affording only limited space for this portion of the cooling arrangement.

Another embodiment of a compact axial fan in accordance with the present invention is shown inFIGS.10and11. Similar to the fan100described above, the fan of this embodiment, which is indicated generally by reference number200, includes an impeller202having an axially deep cup204which is connected by conventional means to the shaft206of an inner-rotor motor208. The impeller cup204is configured to surround the drive end210of the motor208, leaving only the non-drive end212of the motor exposed to the airflow. In the present embodiment, the fan200includes a shroud214which may be connected to a support structure for the fan, such as a support plate216.

The motor208may be connected to the shroud214and/or the support plate216by a number of preferably detachable struts218. As shown inFIGS.10and11, e.g., each strut218includes a first leg220which extends generally perpendicularly to the axis of the fan and a second leg222which extends generally perpendicularly from the first leg along the outer surface of the motor208. In the exemplary embodiment of the invention shown inFIGS.10and11, each first leg220has a distal end224which is connected to or formed integrally with a mounting pad226that in turn is attached to the support plate216. In addition, each second leg222has a distal end228which is connected to the drive end of the motor208. In this manner, the struts218are attached to the drive end of the motor208to thereby provide secure and stable support for the motor within the shroud214. In addition, since the struts218are releasably fastened to both the support plate216and the motor208, removal and replacement of the motor is quick and simple.

In accordance with another aspect of the invention, the downstream end of the impeller cup204may include a number of through holes232to facilitate reverse flow cooling of the drive end210of the motor208. In particular, a pressure difference between the upstream and downstream ends of the impeller202will induce a portion of the airflow (depicted inFIG.11by broken-line arrows) to flow into the through holes232, through the annulus between the outer surface of the motor208and the inner surface of the impeller cup204, and back into the main airflow at a location upstream of the impeller cup204. In this manner, the reverse flow will cool the drive end210of the motor208and lead to improved fan reliability.

In accordance with yet another aspect of the invention, the fan200may include means for deflecting the main airflow around the upstream end of the impeller cup204. Such means may comprise, for example, a hub deflector234which is attached to a motor support frame located between the support struts and the impeller. In the exemplary embodiment of the invention shown inFIGS.10and11, the hub deflector234comprises a conical ring having an upstream end which is secured to the motor support frame and a downstream end which diverges radially outwardly from the upstream end. As shown inFIG.11, the hub deflector234deflects the main airflow (depicted inFIG.11by solid-line arrows) over the upstream edge of the impeller cup204. In this manner, the hub deflector234creates a smooth flowpath transition for the main airflow between the motor208and the impeller cup204. As shown by the broken-line arrows inFIG.11, the hub deflector234also guides the reverse cooling flow back into the main airflow.

As shown inFIG.11, another feature of the present invention is that the shroud214may incorporate an inlet bellmouth236and an exit diffuser238within the axial space claim of the motor208. The resulting fan is an axially compact design with good thermal characteristics suitable for use with an inner-rotor motor.

Referring also toFIG.12, the inventors have found that when the cup length C (i.e., the axial length of the impeller cup204) is approximately 2.3 times the blade length B (i.e., the axial length of the impeller blades240), both the impeller blades and the exit diffuser238may be incorporated within the axial space claim of the motor208. While the exit diffuser238improves fan efficiency, in an alternative embodiment of the invention the exit diffuser can be eliminated while still maintaining the same axial length of the shroud214. In this case, the cup length C may be reduced to approximately 1.7 times the blade length B.

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. For example various features of the different embodiments may be combined in a manner not described herein. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.