Abstract:
A low-noise air moving motor assembly includes a motor assembly having a rotatable shaft, a fan assembly coupled to the rotatable shaft which generates an airflow that passes over at least a portion of the motor assembly. A self-extinguishing flame and noise suppression sleeve is at least partially disposed around the motor assembly. Ideally, the sleeve is a 94 V-0 rated foam material. The fan assembly includes a fan secured to the shaft, a diffuser/bracket assembly coupled to the motor assembly which rotatably receives the shaft. A fan shroud is secured to the diffuser/bracket assembly, wherein rotation of the fan draws air in through the fan shroud and out the diffuser/bracket assembly, the diffuser/bracket assembly having at least one foam piece coupled to curvilinear vanes reduce the noise of air flowing therethrough.

Description:
[0001]     The present invention generally relates to electric motors or generators, and, more particularly, relates to a motor-fan unit employing heat stable, noise-absorbing foam, in proximity to moving parts or surrounding moving parts thereof, to absorb noise generated by the unit.  
       BACKGROUND ART  
       [0002]     Electric motors and generators are well known in the art and have been put to use in a variety of applications. One application is the handling of air. In these circumstances an electric motor is coupled with a fan to generate an air flow or vacuum as necessary. Often, the fan is used to provide cooling air to the motor. In these instances, a fan mounted on a shaft driven by the motor draws air into a fan shroud to compress or pressurize the air. The pressurized air is released into the motor housing via one or more ports which direct the air across the motor windings to draw heat into the flow and exhaust it from the motor housing. Alternatively, the shroud may have exhaust ports so that the air-flow bypasses the motor windings.  
         [0003]     Known motor assemblies have a propensity for generating noise. The fan includes vanes that typically have sharp edges. As air flow is generated over these edges and transitions to another guiding surface noise is generated. In addition to the noise being an undesirable feature, it introduces inefficiencies into the flow of air which decrease motor performance.  
         [0004]     While it has been known to supply foam for purposes of muffling noise generated by various devices, including motors, the foam is always placed in spaced relation to heat generating elements in order to avoid thermally degrading the foam. This makes the positioning of the foam difficult and may require the construction of additional support structures within the devices. Use of foam for noise suppression properties in motors has also been problematic in that the foam, once ignited, continues to burn, rendering the motor and associated equipment inoperable. In order to ensure that the motor temperature does not reach the ignition temperature of the foam, it is required to attach a costly current and/or temperature sensor to the assembly. Once the sensor detects excessive heat or current, the motor is shut down to prevent igniting of the foam. Thus, there is a need in the art for low noise generating motor-fan units that do not suffer from these deficits.  
       SUMMARY OF THE INVENTION  
       [0005]     The disclosure herein provides a low noise air moving motor-fan unit comprising a motor assembly having a rotatable shaft; a fan assembly coupled to said rotatable shaft to rotate therewith and generate an airflow that passes over at least a portion of said motor assembly; and a noise suppression sleeve at least partially disposed around said motor assembly.  
         [0006]     It is another aspect of the invention to provide a motor-fan unit comprising a motor assembly having a rotatable shaft; and a fan assembly coupled to the motor assembly, the fan assembly including a fan secured to the shaft, a fan end bracket for carrying the motor assembly, the fan end bracket having bracket openings therethrough, and a diffuser coupled to the fan end bracket, the diffuser having peripheral openings therethrough, wherein rotation of the fan generates an airflow that passes through the bracket openings and the peripheral openings, the fan assembly carrying at least one foam piece to absorb noise generated by the fan. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     For a complete understanding of the objects, techniques and structure of the invention, reference should be made to the following detailed description and accompanying drawings, wherein:  
         [0008]      FIG. 1  is a partially sectioned front elevational view of a motor-fan unit according to the present invention showing details thereof;  
         [0009]      FIG. 2  is a plan view of an end plate according to the present invention depicting details of a diffuser side of a fan end bracket;  
         [0010]      FIG. 3  is a perspective view of a radial diffuser according to the present invention;  
         [0011]      FIG. 4  is a perspective view of a ported diffuser according to this invention;  
         [0012]      FIG. 5  is a top plan view of a peripheral bypass motor-fan unit in accordance with this invention; and  
         [0013]      FIG. 6  is a top plan view of a tangential bypass motor-fan unit in accordance with this invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 1  shows a motor-fan unit generally indicated by the numeral  10  and which generally includes a motor assembly  15  and a fan assembly  25 . The motor assembly  15  includes an electric motor  16  with an armature or windings  17 , a commutator  18 , and brushes (not shown) which provide a connection from the power source to the commutator  18  and the windings  17 . A shaft  20  is supported on suitable bearings such that it is freely rotatable and is connected to the commutator  18  so as to rotate therewith.  
         [0015]     As shown in  FIG. 1 , the motor assembly is configured with the commutator  18  closest to the fan assembly  25 . The fan assembly  25  of motor-fan unit  10  includes a fan  26  coupled to one end  27  of shaft  20 , as by a nut, such that it rotates therewith. The fan assembly  25  further includes a shroud  30  that surrounds the fan  26 . As is known in the art, the shroud  30  is provided with an axial aperture through which outside air is drawn by the fan  26 . In the embodiment shown, shroud  30  includes a centrally located inlet port  31  formed in a cover portion  32  of shroud  30  coaxially located with the axis A of shaft  20 . The air is exhausted by the fan  26  which is received by a diffuser  80  (to be described more particularly which distributes the air as needed by the end use. A more detailed disclosure of the components of a motor-fan unit  10  is found in U.S. Pat. No. 6,703,754, incorporated herein by reference, and the present application focuses upon the advances to more specific elements of the motor-fan unit  10 .  
         [0016]     With reference to  FIGS. 1 and 2 , motor assembly  15  is provided with a fan end bracket or bracket assembly, generally indicated by the numeral  35 . The fan end bracket  35  generally includes a planar plate portion  36 , which may be annular as shown, and, bracket openings  75  adjacent motor bracket portions  37  extending from the plate portion toward the motor  16 . Motor bracket portions  37  are adapted to support the motor assembly  15 , and is herein adapted to decrease the noise generated by the motor-fan unit  10  through the provision of foam F on the inner surfaces thereof, adjacent said bracket openings  75 . The foam F decreases vibration noise by absorbing waves generated by the movement of the fan vanes through the air and by easing the generated air flow from one direction to another. In other words, as air flow is driven by the fan vanes it is routed by the plate portion  36  through the openings  75  and against the bracket portions  37 . The foam F which is adhered or otherwise fastened to the portions  37  absorbs airflow generated noise and prohibits further generation of noise by providing an absorptive air-flow transition surface.  
         [0017]     The foam F is preferably a V-0 rated foam. Such foam is characterized by properties determined in accordance with UL 94 standards. The foam is heat resistant and has self-extinguishing flame properties, meaning, if the foam encounters sufficient heat for combustion, any flame initiated will not be able to continue burning through the combustion of the foam upon removal of the ignition source. An exemplary foam has a flash point at least greater then 400° C. and an auto-ignition temperature at least greater than 580° C. A particularly preferred foam is melamine foam, and, in a particularly preferred embodiment, Polydamp™ Melamine Foam (PMF; Polymer Technologies, Inc.) is employed. PMF exhibits exceptional resistance to heat and low flammability levels. It does not drip when ignited, and stops burning upon removal of the ignition source. And PMF produces minimal flame and smoke. Indeed, it has been found that use of such a foam precludes the need for costly temperature or current sensors to maintain the motor at a limited temperature that would otherwise ignite the foam.  
         [0018]     The motor-fan unit  10  herein further benefits from the provision of noise suppression sleeve  200 , which is at least partially, and preferably completely, disposed around at least a portion of said motor assembly  15 , as shown in  FIG. 1 . This sleeve  200  is made from V-O rated foam, preferably melamine foam. The sleeve  200  surrounds a majority of the motor  16  and absorbs and muffles noise generated by motor assembly  15  and fan assembly  25 . Indeed, it is believed that the cellular construction assists in diffusing the noise frequencies generated by the fan assembly and further that the foam deflects the noise frequencies in a labyrinth manner so that by the time the air flow exits the motor assembly, the associated noise frequencies are significantly reduced. The sleeve  200  attaches to the fan assembly  25  at a shroud end  204  of the sleeve  200 , and a sleeve cover  202  may cap the noise suppression sleeve  200  at distal end  206 , opposite shroud end  204 . Sleeve cover  202  may include a cover hole  208 , and, in the embodiment shown, a portion of the motor assembly may extend through the cover hole  208 . If desired, the sleeve may be sized longer than the extending length of the motor assembly as shown by the sleeve  200 ′. The sleeve may be attached by fasteners, clips, adhesives, a friction fit or any way in which the sleeve can be held in close proximity to the unit  10 . Distal end  206  may curve inwardly to form a sleeve opening  210 , foregoing the use of a specific cover element like cover  202 . It will be further appreciated that use of the cover  202  is optional. The V-0 rating ensures that the foam F will not be damaged by the heat generated by the operation of motor  16 . Preferably, the sleeve  200  is sized with a diameter that is not greater than the outer diameter of the shroud  30 , as shown, and, it is also preferred that the sleeve cover  202  or sleeve opening  210  be in close proximity or touching contact with the motor assembly  15 . And it has been found that due to the use of a V-0 rated foam that placing the foam in touching contact or in very close proximity to the motor assembly, as evidenced by the sleeve  200 ′, provides the best noise reduction properties while still maintaining the unit&#39;s operating efficiency.  
         [0019]     This foam sleeve concept can also be applied to through flow motor-fan units and to tangential bypass motor-fan units. In  FIG. 5 , a bypass motor-fan unit  300  has the shroud  302  of its fan assembly  303  covered with noise suppression sleeve  304 , made of V-0 Foam. Sleeve cover  306  is open at  308 , and sleeve cover  306  preferably abuts shroud  302 , as at  310 . The shroud  302  includes a plurality of peripheral exhaust ports  311  for venting the air flow generated by the fan within the fan assembly  303 . As noted previously, any conventional means may be used to secure the sleeve to the unit. The sidewall  312  of sleeve of  304  is preferably spaced a small distance from shroud  302  although it could be in touching contact.  
         [0020]     In  FIG. 6 , a tangential bypass motor-fan unit  400  has a tangential exhaust port  402  extending from the fan assembly  403  which is covered with noise suppression sleeve  404 , made of the V-0 Foam. Sleeve  304  does not provide a sleeve cover, but rather is open at end  406 . Sidewall  408  preferably abuts the outer surface of exhaust port  40 , as generally shown. Extending from an interior surface of the sleeve may be internal flanges  408  that form a labyrinth flow path  410 . The path  410  re-directs the air flow and the flanges effectively “scramble” or muffle the noise generated by the unit  400 .  
         [0021]     Additional benefits are realized by employing V-0 rated foam on other elements of a motor-fan unit  10 , particularly diffuser assembly elements, which are disclosed below, with reference to  FIGS. 3 and 4 . A diffuser  80  interacts with fan end bracket  35  to distribute airflow generated by fan  26 , and this combination is referred to as a diffuser/bracket assembly. The diffuser/bracket assembly ( 80 / 35 ) is coupled to the motor assembly  15  and rotatably receives the shaft  20 . A radial-type diffuser assembly is shown in  FIG. 3  and designated generally by the numeral  80 A, and a ported-type diffuser assembly is shown in  FIG. 4  and designated generally by the numeral  80 B and both interact with a fan end bracket  35 , wherein the fan  26  draws air in through fan shroud  30  and forces air out of the air diffuser/bracket assembly. Air from the fan assembly  25  is distributed by these diffuser assemblies  80 A,  80 B. For general reference, the diffuser assemblies, whether radial or ported-type, will be referred to by the numeral  80 . Specific components of these diffusers will include an A or B suffix.  
         [0022]     The radial diffuser  80 A ( FIG. 3 ) includes a planar base member  81 , which may be made annular to define a bore  82 . A plurality of circumferential blades  86 A surround the fan  26  and serve to guide air outwardly from the fan side  85 , wherein a portion may be directed externally of shroud  30  through a plurality of ports  34  provided in the shroud  30  ( FIG. 1 ). A second set of blades  87 A formed on the motor-side  84  of the radial diffuser  80 A channels a remaining portion of the air radially inwardly toward the center of the diffuser  80 A. The blades  87 A may be configured in any pattern, as required by the particular application, including the spiral or pinwheel pattern shown. In contrast to the radial diffuser  80 A, a ported diffuser  80 B, as in  FIG. 4 , has circumferential blades  86 B, at fan side  105 , and enclosed channels  87 B, extending from planar portion  104  and formed in similar patterns to the blades  86 A,  87 A of the radial-type diffuser  80 A, to channel all the incoming and outgoing air as described above. The shroud for a ported diffuser  80 B is completely enclosed.  
         [0023]     Diffuser assemblies  80 , whether of ported-type or radial-type, are provided with a pair of brush cap assemblies  95  that coact with brush retainers  120  which are generally shown in  FIG. 2 . In the embodiments shown in diffusers  80 A,  80 B, channels  93  are formed between a pair of upstanding brush cap members  96 ,  97  formed on the motor side ( 84  of diffuser  80 A and side  105  of diffuser  80 B). Members  96 ,  97  are generally located adjacent the central opening  82  and may radially project to an extent into the opening  82 . The brush cap assemblies  95  of the ported-type diffuser are distinguished in that they are surrounded by channels  87 B as opposed to blades  87 A.  
         [0024]     Herein, the diffuser assemblies  80  are taught to include V-0 foam F on certain elements. Particularly, V-0 foam F is provided on surfaces upon which the airflow impinges as the motor fan unit  10  is operated. More particularly Foam F is provided on blades  87 A (radial diffuser) or enclosed channels  87 B (ported diffuser). It is appreciated that these spiral/pinwheel patterned elements efficiently re-direct the airflow, and, therefore, are generally major contributors to the noise generated by the motor-fan unit  10  which they are selectively employed. Notably, the surfaces of the blades  87 A and enclosed channels  87 B that curve in the direction of the rotation of the diffuser assembly  80  are the surfaces that are covered with Foam F.  
         [0025]     It should now be understood that a new and useful motor-fan unit has been disclosed in accordance with the patent laws. It will further be understood that various modifications and substitutions may be made in the described invention without the departing from the spirit thereof, and, to appreciate the scope of the invention, reference should be made to the following claims.