Patent Application
20090324418
Not Applicable.
Not Applicable.
A typical fan includes a cylindrical hub body with a rotatable blade assembly coupled thereto. The rotatable blade assembly includes a spider with a plurality of arms extending outwardly from a cylindrical central portion connected to the hub body and a plurality of rotatable blades attached to the spider arms. One end of a cylindrical rod, or driveshaft, is disposed within an axial bore through the hub and coupled to the hub body using a set screw or other connection device. A drive unit, such as an electric motor, is coupled to the other end of the driveshaft and operates to transfer power to the hub body in the form of torque by rotating the driveshaft. Due to the coupling of the driveshaft to the hub, and the hub to the blade assembly, rotation of the driveshaft imparts rotation to the hub body and the blades.
Fans are employed in a wide variety of applications and industries, but common design criteria related to fan efficiency and noise requirements, for example, may be employed in many such applications.
A structural and acoustical vibration dampener for a rotatable blade is disclosed. In an example embodiment, a structural/acoustical vibration dampener for a rotatable blade is disclosed with a layer of structural/acoustic damping material coupled to at least a portion of the blade.
In a second example embodiment, a fan blade is disclosed with a structural layer, and a layer of damping material coupled to at least a portion of the structural layer.
In a third example embodiment, a method of applying a structural/acoustical vibration dampener to a fan blade is disclosed. The method identifies a region on the fan blade, and secures the structural/acoustical vibration dampener to the fan blade over at least a portion of the region.
Thus, the structural/acoustical vibration dampener and associated methods comprise a number of features. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments of the disclosure, and by referring to the accompanying drawings.
For a more detailed description of the various embodiments of the structural and acoustical vibration dampener for a rotatable blade, reference will now be made to the accompanying drawings, wherein:
Dynamic systems comprise at least three basic characteristics: mass, stiffness and damping. Real structures have distributed mass, stiffness and damping. Hence, real structures have multiple degrees of freedom. When real structures are attached to rotating machinery, such as an electric motor, for example, their vibration and acoustic response will depend on the distribution of their dynamic characteristics and how they interface with the excitation force exerted by the rotating machinery. Without sufficient damping, such an excitation force may cause cyclic deformation of the attached real structure.
During operation of a fan assembly, for example, the rotating drive unit vibrates, in part due to external loads and any imbalances in the motor itself, and this vibration is transferred via an excitation force to the blades through the driveshaft, hub and other components of the fan assembly. This excitation force may cause the blades to vibrate, and any imbalances in the blade assembly may also contribute to blade vibration. Over time, such vibration and the resulting cyclic deformation may shorten the blade life due to the effects of fatigue. Moreover, vibration of the blade assembly and motor may result in acoustic or sound radiation, producing undesirable audible noise that exceeds acceptable levels.
As the frequency of the excitation force approaches any of the natural or resonance frequencies of the blades, vibration of the blades may be amplified, even though the magnitude of the excitation force may not have changed. When the frequency of the excitation force coincides with a natural frequency of the blades, vibration of the blades is maximized. Thus, the blades experience maximum deformation and produce the highest level of acoustic or sound radiation, often resulting in undesirable levels of audible noise. The deformed shape of a blade responding to application of an excitation force at a frequency equal to a natural frequency of the blade is often referred to as its mode shape. When a blade deforms to one of its mode shapes, the blade may experience complete structural failure.
Some methods of reducing vibration, and the associated fatigue and noise, in a fan assembly are to equip the electric motor with a vibration dampener and/or eliminate imbalances in the motor through maintenance and/or offset imbalances in the blade assembly by coupling small weights to one or more of the blades, as is often done to balance residential ceiling fans. Alternatively, the blade structure may be modified to cause a shift in the natural frequencies of the blades away from the frequency of the motor excitation force, such as by viscous dampening, which involves changing the weight or stiffness of the blade. However, these methods may not adequately dampen or reduce fan vibration, and the associated noise, in certain circumstances.
For example, if a drive unit is a variable speed motor without a vibration dampener, then more than one of its variable speeds may produce an excitation force having a frequency equal to a natural frequency of the blades. Such speeds are referred to as critical speeds, and a variable speed motor in a fan assembly may have multiple critical speeds. Thus, it may not be possible to modify the blade structures by viscous dampening so as to shift their natural frequencies sufficiently away from the excitation frequencies of the motor for all of the critical speeds.
The present disclosure relates generally to apparatus and methods for damping vibration of a rotatable blade. More particularly, the present disclosure relates to a structural and acoustical vibration dampener for a rotatable blade, which is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of a structural/acoustical vibration dampener for a rotatable blade and associated methods with the understanding that the disclosure is to be considered representative only and is not intended to limit the apparatus and methods to that illustrated and described herein. In particular, various embodiments of the structural/acoustical vibration dampener are described in the context of a fan blade. However, these components may be used in any application where it is desired to reduce vibration of a rotating blade and the associated audible noise. Thus, a structural/acoustical vibration dampener for a rotatable blade may be utilized in, for example, a turbine or an airboat, as well as a fan. It is to be fully recognized that the different teachings of the embodiments disclosed herein may be employed separately or in any suitable combination to produce desired results.
As illustrated by
Structural/acoustical vibration dampener 150 may optionally further comprise a protective layer 220 of material, such as foil or other suitable material, that overlies the structural/acoustic damping material 205. In some embodiments where the protective layer 220 comprises foil, the foil is aluminum. If the structural/acoustic damping material 205 has a pressure sensitive, adhesive property, protective layer 220 may adhere directly to structural/acoustic damping material 205 without the need for glue or another similar bonding material. In an embodiment, the structural/acoustic vibration dampener 150 is a specially formulated pressure sensitive, adhesive (PSA) foil-tape consisting of a structural/acoustic damping material 205 overlaid by a foil protective layer 220. One suitable PSA foil tape is Avery Denison FT0816, and suitable PSA tapes are also available from 3M and other suppliers.
The size and positioning of each structural/acoustical vibration dampener 150 on a blade 115 is dictated by the degree of damping needed, or desired, during operation of fan 100. Notably, a suitable, but coarse, damping technique is to extend structural/acoustical vibration dampener 150 the full length and width of blade 115. However, to determine more particularly the degree of damping needed, the natural or resonance frequencies and their corresponding mode shapes for blade 115, in the absence of any structural/acoustical vibration dampener 150, are first identified, either through testing or through experimental or analytical modal analysis. A mode shape, also known as a deflection shape, is the deformed shape of blade 115 resulting from the application of an excitation force, such as that provided by motor vibration, at a frequency equal to a corresponding natural frequency. Blade 115 may have one or more natural frequencies and a mode shape corresponding to each. By identifying and examining each mode shape of blade 115, the location(s) of maximum vibration, or maximum deflection, for blade 115 may be identified. In the locations of maximum vibration, a portion of blade 115 deflects in a first direction and an adjacent portion of blade 115 approximately simultaneously deflects in a second direction that is opposite and out of phase with the first direction. For example, in one representative location of maximum deflection, a portion of blade 115 may deflect upwardly while an adjacent portion of blade 115 approximately simultaneously deflects downwardly relative to a horizontal plane.
Once identified, a structural/acoustical vibration dampener 150 may be positioned at each of these maximum deflection locations to overlap adjacent portions of the blade 115 that vibrate or deform out of phase with one another. In other words, each structural/acoustical vibration dampener 150 so positioned couples a region of high blade vibration in a first direction to a region of high blade vibration in a second direction that is out of phase with the first direction, thereby providing damping to the region. By positioning structural/acoustical vibration damnpener(s) 150 in this manner, maximum blade vibration, and thus deformation, is reduced by the energy-absorbing ability of structural/acoustic damping material 205. Hence, during operation of fan 100, the magnitude of vibrations experienced by blade 115 is reduced. Accordingly, the magnitude of sound pressure waves produced by the blade vibrations is also reduced, yielding a reduction in the level of noise generated by the vibration of blade 115, and therefore fan 100.
At block 520, glue, tape or other bonding material 435 may be applied to the location identified in block 510 if the structural/acoustical vibration dampener comprises a structural acoustic damping material that does not have an adhesive property, such as structural/acoustical vibration dampener 450. Next, at block 530, a layer of structural/acoustic damping material 205 or 405 is applied to the location identified in block 510 or to the bonding material 435 of block 520, respectively, by application of pressure. Once applied, structural/acoustic damping material 205 or 405 ties or couples adjacent portions of the blade 115 that vibrate or deform out of phase with one another. If necessary, glue, tape or other bonding material 435 is applied to structural/acoustic damping material 405 of structural/acoustical vibration dampener 450 at block 540. A protective layer 220 of foil or other suitable material may optionally be overlaid onto structural/acoustic damping material 205 or bonding material 435 covering structural/acoustic damping material 405 by application of pressure at block 550. Lastly, a layer of laminating material 330 may be optionally applied over protective layer 220 and structural/acoustic damping material 205 or 405. The method is repeated as necessary to achieve the desired degree of damping for blade 115.
A structural/acoustical vibration dampener in accordance with the principles disclosed herein should diminish the magnitude of vibrations that a fan blade would otherwise experience in the absence of the structural/acoustical vibration dampener. As a result, the magnitude of sound pressure waves produced by the blade vibrations should also be reduced, which would thereby reduce the level of noise produced by the blades. In addition to noise reduction, the effects of fatigue to the blade would also be reduced, providing a longer service life for the fan.
While various embodiments of a structural/acoustical vibration dampener and methods of constructing a rotatable blade with a structural/acoustical vibration dampener have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this disclosure. The embodiments described herein are representative only and are not limiting. Many variations and modifications of the apparatus and methods are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.
