Abstract:
A hub assembly for a fan reduces transmission of vibrations between the fan motor and the fan blades. The hub assembly comprises a motor assembly, a hub, and a plurality of resilient members. The motor assembly includes a motor and a motor housing surrounding the motor, and the motor is configured to rotate the motor housing during operation. The hub is supported on the motor housing by a plurality of fasteners. The resilient members are at least partially interposed between the hub and the motor housing, and each resilient member of the plurality of resilient members surrounds a portion of a corresponding fastener of the plurality of fasteners.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 62/117,210 entitled “Vibration Isolation System for a Fan Motor,” filed Feb. 17, 2015, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to fans, and, more particularly, to external rotor ceiling fans. 
       BACKGROUND 
       [0003]    Ceiling fans are fans mounted from the ceiling of a room in a building or from the roof of a covered patio, or the like, and have a housing generally supported from a pipe or pole attached to the ceiling. Ceiling fans typically include a motor coupled to a plurality of fan blades to rotate the fan blades. The rotating fan blades provide airflow, enabling the ceiling fan to provide an energy efficient means of cooling or ventilating an area. 
         [0004]    Conventional ceiling fans typically include one of two different types of motors. The first, known in the art as an internal rotor motor is configured such that the rotor is arranged inside the stator and the fan housing and is connected to a shaft extending outside the housing. The shaft is connected to the fan blades, typically through a flywheel and fan blade holders. 
         [0005]    The second type of ceiling fan motor is known as an external rotor motor. In an external rotor ceiling fan, the external housing of the motor is the rotor or is directly attached to the rotor so that the external housing of the fan rotates with the rotor. The external housing spins around the stator, and fan blades attached to the rotor, generally by fan blade holders, rotate to generate airflow. 
         [0006]    During operation of a fan, vibrations are produced by the rotating fan blades and by the motor. These vibrations are transferred between the blades and the motor through the connection therebetween. In some instances, the vibrations can become significant, resulting in additional noise and, in extreme cases, damage to the fan or motor. 
         [0007]    One solution to reduce vibrations is to provide a rubber pad between the rotor and the fan blades or the fan blade holders. This rubber pad, however, provides only minimal reduction in the vibrations since the pad is connected directly to both the fan blade holders and the motor. Additionally, the screws connecting the motor housing to the fan blade holders are directly connected to the motor housing and the fan blade holders, and therefore vibrations are transferred between the motor and fan blades through the screws. 
         [0008]    It would thus be desirable to provide a system to reduce vibrations in external rotor ceiling fans. 
       SUMMARY 
       [0009]    In one embodiment, a hub assembly for a fan reduces transmission of vibrations between the fan motor and the fan blades. The hub assembly comprises a motor assembly, a hub, and a plurality of resilient members. The motor assembly includes a motor and a motor housing surrounding the motor, and the motor is configured to rotate the motor housing during operation. The hub is supported on the motor housing by a plurality of fasteners. The resilient members are at least partially interposed between the hub and the motor housing, and each resilient member of the plurality of resilient members surrounds a portion of a corresponding fastener of the plurality of fasteners. 
         [0010]    In some embodiments, each of the plurality of fasteners includes a head portion and a shaft portion and the hub includes a first side facing said motor housing and a second side facing away from said motor housing. Each resilient member includes (i) a first portion interposed between the motor housing and the first side of the hub and surrounding the shaft portion of the corresponding fastener, and (ii) a second portion interposed between the head portion of the corresponding fastener and the second side of the hub. 
         [0011]    In another embodiment of the hub assembly, the second side of the hub defines a plurality of recesses and the hub defines a plurality of openings. Each of the plurality of openings extends from a corresponding recess of the plurality of recesses to the first side of the hub. Each of the plurality of recesses receives the second portion of one of the plurality of resilient members and the head portion of one of the plurality of fasteners. 
         [0012]    In a further embodiment of the hub assembly, each resilient member includes a third portion connecting the first portion and the second portion, and the third portion is located in a corresponding opening of the plurality of openings. 
         [0013]    In yet another embodiment of the hub assembly, each of the plurality of fasteners includes a head portion and a shaft portion, and the hub includes a first side facing said motor housing and a second side facing away from said motor housing. The hub assembly further comprises a plurality of resilient spacers, and each resilient spacer is interposed between the head portion of a respective fastener and the second side of the hub. 
         [0014]    In some embodiments, the second side of the hub defines a plurality of recesses and the hub defines a plurality of openings, with each opening of the plurality of openings extending from a corresponding recess of the plurality of recesses to the first side of the hub. Each of the plurality of recesses receives one of the plurality of resilient spacers and the head portion of one of the plurality of fasteners. 
         [0015]    In one embodiment, each of the plurality of resilient spacers includes a first annular portion and a second annular portion, the first annular portion having a greater outer diameter than the second annular portion. 
         [0016]    In a further embodiment, the second annular portion of each resilient spacer is positioned in a corresponding opening of the plurality of openings. 
         [0017]    In yet another embodiment of the hub assembly, the plurality of resilient members are formed of an elastomeric material. 
         [0018]    In some embodiments of the hub assembly, the hub defines a plurality of threaded openings configured for mounting a plurality of fan blades to the hub such that each of the plurality of fan blades is mounted to two of the plurality of threaded openings that are adjacent and on opposite sides of the resilient members. 
         [0019]    In another embodiment, a vibration isolation system for a ceiling fan includes a hub and a plurality of resilient members. The hub is hub configured to be supported on a motor housing of a motor assembly by a plurality of fasteners. The resilient members are at least partially interposed between the hub and the motor housing, and each resilient member of the plurality of resilient members surrounds a portion of a corresponding fastener of the plurality of fasteners. 
         [0020]    In one embodiment of the vibration isolation system, each of the plurality of fasteners includes a head portion and a shaft portion and the hub includes a first side facing said motor housing and a second side facing away from said motor housing. Each resilient member includes (i) a first portion interposed between the motor housing and the first side of the hub and surrounding the shaft portion of the corresponding fastener, and (ii) a second portion interposed between the head portion of the corresponding fastener and the second side of the hub. 
         [0021]    In a further embodiment of the vibration isolation system, the second side of the hub defines a plurality of recesses and the hub defines a plurality of openings, each of the plurality of openings extending from a corresponding recess of the plurality of recesses to the first side of the hub. Each of the plurality of recesses receives the second portion of one of the plurality of resilient members and the head portion of one of the plurality of fasteners. 
         [0022]    In another embodiment, each resilient member includes a third portion connecting the first portion and the second portion, the third portion being located in a corresponding opening of the plurality of openings. 
         [0023]    In yet another embodiment of the vibration isolation system, each of the plurality of fasteners includes a head portion and a shaft portion and the hub includes a first side facing the motor housing and a second side facing away from the motor housing. The vibration isolation system further comprises a plurality of resilient spacers, and each resilient spacer is interposed between the head portion of a respective fastener and the second side of the hub. 
         [0024]    In some embodiments of the vibration isolation system, the second side of the hub defines a plurality of recesses and the hub defines a plurality of openings. Each opening of the plurality of openings extends from a corresponding recess of the plurality of recesses to the first side of the hub. Each of the plurality of recesses receives one of the plurality of resilient spacers and the head portion of one of the plurality of fasteners. 
         [0025]    In another embodiment, each of the plurality of resilient spacers includes a first annular portion and a second annular portion, the first annular portion having a greater outer diameter than the second annular portion. 
         [0026]    In a further embodiment according to the disclosure, a fan comprises a motor assembly, a hub, a plurality of resilient members, and a plurality of fan blades supported by the hub. The motor assembly includes a motor and a motor housing surrounding the motor, and the motor is configured to rotate the motor housing during operation. The hub is supported on the motor housing by a plurality of fasteners. The plurality of resilient members are at least partially interposed between the hub and the motor housing, and each resilient member of the plurality of resilient members surrounds a portion of a corresponding fastener of the plurality of fasteners. 
         [0027]    In some embodiments of the fan, each of the plurality of fasteners includes a head portion and a shaft portion and the hub includes a first side facing said motor housing and a second side facing away from said motor housing. Each resilient member includes (i) a first portion interposed between the motor housing and the first side of the hub and surrounding the shaft portion of the corresponding fastener, and (ii) a second portion interposed between the head portion of the corresponding fastener and the second side of the hub. 
         [0028]    In yet another embodiment of the fan, each of the plurality of fasteners includes a head portion and a shaft portion and the hub includes a first side facing said motor housing and a second side facing away from said motor housing. The fan assembly further comprises a plurality of resilient spacers, with each resilient spacer being interposed between the head portion of a respective fastener and the second side of the hub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a bottom view of a ceiling fan having a hub assembly with a vibration isolation system according. 
           [0030]      FIG. 2  is an exploded perspective view of a ceiling fan motor and the vibration isolation system of the ceiling fan of  FIG. 1 . 
           [0031]      FIG. 3  is a side view of the ceiling fan motor and vibration isolation system of  FIG. 2 . 
           [0032]      FIG. 4  is an exploded perspective view of a ceiling fan motor having another vibration isolation system. 
           [0033]      FIG. 5  is a cross-sectional detail view of a grommet, a fastener, and a hub of the vibration isolation system of  FIG. 4 . 
           [0034]      FIG. 6  is a side view of the ceiling fan motor and vibration isolation system of  FIG. 4 . 
           [0035]      FIG. 7  is an exploded perspective view of a ceiling fan motor and another embodiment of a vibration isolation system. 
           [0036]      FIG. 8  is a top perspective view of a hub of the vibration isolation system of  FIG. 7 . 
           [0037]      FIG. 9  is a top view of the hub of the vibration isolation system of  FIG. 7 . 
           [0038]      FIG. 10  is a bottom perspective view of the hub of the vibration isolation system of  FIG. 7 . 
           [0039]      FIG. 11  is a bottom view of the hub of the vibration isolation system of  FIG. 7 . 
           [0040]      FIG. 12  is a cross-sectional detail view of a grommet, a fastener, and a hub of the vibration isolation system of  FIG. 7 . 
           [0041]      FIG. 13  is a side perspective view of the ceiling fan motor and vibration isolation system of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    For the purposes of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. No limitation to the scope of the subject matter is intended by the references. This disclosure also includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the described embodiments as would normally occur to one skilled in the art to which this document pertains. 
         [0043]      FIG. 1  illustrates a bottom view of a ceiling fan  80  having a hub assembly  100  according to the disclosure. The ceiling fan includes a plurality of blades  84 , each of which is attached to a corresponding blade mount  88 . The blade mounts  88  are attached to a hub plate  132 , described in detail below, of the hub assembly  100  using two fasteners  92 . 
         [0044]      FIG. 2  illustrates an exploded view of the hub assembly  100 , which includes a ceiling fan motor  104  and a vibration isolation system  108 . The ceiling fan motor  104  includes an external housing  112 , out of which a mounting shaft  116  extends upwardly and a stationary shaft  120  extends downwardly. In some embodiments, the mounting shaft  116  and the stationary shaft  120  are formed integrally as a single shaft extending through the motor housing  112 . The mounting shaft  116  is configured to be attached to a mounting structure (not shown), for example a ceiling, to mount the fan  80  to the mounting structure. 
         [0045]    The stationary shaft  120  extends downwardly from the housing  112  and is configured to receive stationary components, for example a light, a control switch, and/or an ornamental structure. The motor  104  has a stator (not shown) positioned within the housing  112 , while the housing  112  is configured to act as the rotor for the motor  104 , such that the entire housing  112  rotates when the stator is activated. The housing  112  includes a bottom surface  124  having a plurality of threaded bores  128 . 
         [0046]    The vibration isolation system  108  includes a hub plate  132 , a plurality of resilient upper spacers  136 , a plurality of resilient lower spacers  140 , and a plurality of fasteners  144 . The upper spacers  136  are substantially annular in shape. The lower spacers  140  have an annular lower section  141  and an annular upper section  142 . The outer diameter of the lower section  141  is greater than the outer diameter of the upper section  142 . Each of the upper and lower spacers  136 ,  140  has a central opening  145 ,  146 , respectively, sized to enable a corresponding fastener  144  to extend through the central opening  145  of each of upper spacer  136  and the central opening  146  of each associated lower spacer  140 . In one embodiment, the resilient spacers  136 ,  140  are formed of an elastomeric material, for example rubber. In other embodiments, other desired resilient materials are used for the spacers  136 ,  140 . 
         [0047]    The hub plate  132  is substantially annular, and is formed of a rigid material, for example steel. In some embodiments, the hub plate  132  is formed of other metals, for example aluminum, brass, or iron, while in other embodiments the hub plate  132  is formed of a plastic or a hardened rubber material. In one embodiment, the hub is not formed as a plate, but is instead a toroidal bar or another desired shape. 
         [0048]    The hub plate  132  has an upper surface  148  and a lower surface  152 . The lower surface  152  defines a plurality of recesses  154  and a plurality of openings  156  ( FIG. 3 ) extending through the hub plate  132  from the recesses  154  to the upper surface  148 . The recesses  154  have a shape that corresponds to the shape of the lower section  141  of the lower spacer  140 , and the openings  156  have a shape that corresponds to the upper section of the lower spacer  140 . As a consequence, the recesses  154  and openings  156  each accommodate and fit the respective portions  141 ,  142  of the lower spacers  140  with little or no play therebetween. Each of the openings  156  is configured to align with one of the plurality of threaded bores  128  in the lower surface  124  of the motor housing  112 . 
         [0049]    The lower surface  152  of the hub plate  132  further includes a plurality of threaded holes  160 . The threaded holes  160  are arrayed around the hub plate  132  and are configured to receive blade fasteners  92  ( FIG. 1 ), which fasten the fan blades  84 , or, in the embodiment illustrated in  FIG. 1 , the blade mounting brackets  88  to which the fan blades  84  are connected, to the hub plate  132 . As shown in  FIG. 1 , each blade mounting bracket  88  is configured to attach to two fasteners  92  and the corresponding threaded holes  160  that are on opposite sides of a corresponding one of the recesses  154 . In various embodiments, the threaded holes  160  ( FIG. 3 ) can be arranged in any desired pattern so that a suitable number of fan blades  84  or blade mounting brackets  88  can be attached to the hub plate  132 . 
         [0050]    In some embodiments, the hub plate  132  is substantially hollow, and may not include a uniform upper surface. In such an embodiment, the openings and the threaded holes are surrounded by a thin sleeve, and the hub may include, for example, ribs between the sleeves to provide structural support for the hub plate  132 . 
         [0051]      FIG. 2  illustrates the hub assembly  100  with the motor  104  and vibration isolation system  108  in an assembled state. The lower spacers  140  fit within the recesses  154  and openings  156  of the hub plate  132 . The upper spacers  136  are positioned between the upper surface  148  of the hub plate  132  and the lower surface  124  of the motor housing  112  so that each upper spacer  136  aligns with one of the openings  156  of the hub plate  132 . The fasteners  144  extend through the central openings of the upper and lower spacers  136 ,  140  and engage the threaded bores  128  in the motor housing  112  to secure the hub plate  132  to the motor housing  112 . 
         [0052]    During operation of the fan  100  of  FIG. 1 , the stator (not shown) of the motor  104  is energized, resulting in rotation of the motor housing  112  and the hub plate  132  about the central axis of the motor housing  112  and hub plate  132 . The fan blades  84  spin about the central axis of the fan  100  along with the motor housing  112  and hub plate  132 , producing a flow of air. 
         [0053]    As the fan blades  84  rotate, oscillating vibrations are produced in the blades  84  and transferred via the blade mounting brackets  88  to the hub plate  132 . Additionally, operation of the motor  104  introduces vibrations in the motor housing  112 . The transfer of vibrations between the motor housing  112  and the hub plate  132  is damped in the radial direction (horizontal in the view of  FIG. 3 ) by the resilient lower spacers  140 , which elastically deform within the recesses  154  and openings  156  to isolate the hub plate  132  from the fasteners  144 . 
         [0054]    In the axial direction (vertical in the view of  FIG. 3 ), the resilient upper spacers  136  elastically deform to dampen vibrations and movement between the upper surface  148  of the hub plate  132  and the lower surface  124  of the motor housing  112 , while the lower section  141  of the lower spacer  140  deforms elastically to dampen axial vibrations between the fastener  144  and the hub plate  132 . As a result, the transfer of vibrations and movement between the motor  104  and the fan blades  84  is greatly reduced. 
         [0055]      FIG. 4  illustrates an exploded view of another embodiment of a hub assembly  200  configured to be used in the ceiling fan  80  in place of the hub assembly  100  described above. The hub assembly  200  includes a ceiling fan motor  204  and a vibration isolation system  208 . The ceiling fan motor  204  includes an external housing  212 , out of which a mounting shaft  216  extends upwardly and a stationary shaft  220  extends downwardly. Similarly to the hub assembly  100 , the mounting shaft  216  and the stationary shaft  220  may be formed integrally as a single shaft extending through the motor housing  212 . In any event, the mounting shaft  216  is configured to be attached to a mounting structure (not shown), for example a ceiling, to mount the ceiling fan  80 . 
         [0056]    The stationary shaft  220  extends downwardly from the housing  212  and is configured to receive stationary components, for example a light, a control switch, and/or an ornamental structure. The motor  204  has a stator (not shown) positioned within the housing  212 , while the housing  212  is configured to act as the rotor for the motor  204 , such that the entire housing  212  rotates when the stator is activated. The housing  212  further includes a bottom surface  224  having a plurality of threaded bores  228 . 
         [0057]    The vibration isolation system  208  includes a hub plate  232 , a plurality of resilient grommets  236  and a plurality of fasteners  244 . The hub plate  232  is an annular substantially flat plate, and is formed of a rigid material, for example steel. In some embodiments, the hub plate  232  is formed of other metals, for example aluminum, brass, or iron, while in other embodiments the hub plate  232  is formed of a hardened plastic or rubber material. The hub plate  232  has an upper surface  248  and a lower surface  252 . A plurality of projections  256  extend upwardly from the upper surface  248 , each of which defines an opening  260 . The projections  256  are cylindrical and define an interior that receives at least a portion of the grommet  236 . Further detail regarding the interaction between the projection  256  and the grommets  236  is presented below in connection with the description of  FIG. 5 . Each of the openings  260  is configured to align with one of the plurality of threaded bores  228  in the lower surface  224  of the motor housing  212 . 
         [0058]    The lower surface  252  of the hub plate  232  further includes a plurality of threaded holes  262 . The threaded holes  262  are arrayed around the hub plate  232  and are configured to receive blade fasteners  92 , which fasten blade mounting brackets  88 , to which fan blades  84  are connected, to the hub plate  232 . The threaded holes  262  can be arranged in any desired pattern so that a suitable number of fan blades  84  or blade brackets  88  can be attached to the hub plate  232 . 
         [0059]    As shown more clearly in the detail view of  FIG. 5 , the grommets  236  have an upper region  264 , a lower region  268 , a middle region  272 , and a central opening  276 . The central opening  276  is sized to allow the fastener  244  to fit into the central opening  276  of the grommet  236 . The middle region  272  of the grommet  234  has an outer circumference that is substantially the same size as the inner circumference of the opening  260  in the projection  256 . The upper and lower regions  264 ,  268  are wider than the middle region  272  so that a portion of the upper and lower regions  264 ,  268  cover the surfaces of the projection  256  around the opening  260 . In one embodiment, the grommets  236  are formed of an elastomeric material, for example rubber, though other desired resilient materials are used in other embodiments. 
         [0060]    In the embodiment described, the upper and lower regions  264 ,  268  have an outer diameter that is between approximately 1.5 and 3 times the outer diameter of the middle region  272 . Additionally, the upper and lower regions  264 ,  268  have an axial thickness than is between 2 and 3 times the axial thickness of the middle region  272 . In the illustrated embodiment, the grommet  234  forms a round resilient member with an annular channel defined between the upper and lower regions  264 ,  268  such that the annular channel circumferentially surrounds the middle region  272 . 
         [0061]      FIGS. 5 and 6  illustrate hub assembly  200  with the motor  204  and vibration isolation system  208  in an assembled state. The lower region  268  of the grommets  236  fit in a cavity defined within the projections  256  of the hub plate  232 . The upper region  264  is positioned between the upper surface of the projection  232  and the lower surface  224  of the motor housing  212  in such a way that the central opening of each grommet  236  aligns with one of the openings  228  of the motor housing  212 . The fasteners  244  extend through the central openings  276  of the grommets  236  and engage the threaded bores  228  in the motor housing  212  to secure the hub plate  232  to the motor housing  212 . 
         [0062]    During operation of the fan  80  of  FIG. 1  with the hub assembly  100  installed, the stator (not shown) of the motor  204  is energized, resulting in the motor housing  212  and the hub plate  232  rotating. The fan blades  84  attached to the threaded holes  262  of the hub plate  232  via the blade mounting brackets  88  and the blade fasteners  92  spin with the motor housing  212  and hub plate  232 , producing a flow of air. 
         [0063]    As the fan blades  84  rotate, oscillating vibrations are produced in the fan blades  84  and transferred to the hub plate  232 . Additionally, the operation of the motor  204  introduces vibrations in the motor housing  212 . The vibrations are damped in the radial direction (horizontal in the views of  FIGS. 5 and 6 ) primarily by the middle regions  272  of the grommets  236 , which elastically deform within the openings  260  to dampen the transfer of radial vibrations between the fasteners  244  and the hub plate  232 . In the axial direction (vertical in the views of  FIGS. 5 and 6 ), the upper and lower regions  264 ,  268  of the grommets  236  elastically deform to dampen axial vibrations and movement between the hub plate  232  and the motor housing  212  and between the hub plate  232  and the fasteners  244 . As a result, the transfer of vibrations and movement between the motor  204  and the fan blades  84  is greatly reduced. 
         [0064]      FIG. 7  illustrates an exploded view of another embodiment of a hub assembly  300  that may be used in the ceiling fan  80  of  FIG. 1  in place of the hub assembly  100 . The hub assembly  300  includes a ceiling fan motor  304  and a vibration isolation system  308 . The ceiling fan motor  304  includes an external housing  312 , out of which a mounting shaft  316  extends upwardly and a stationary shaft  320  extends downwardly. The mounting shaft  316  is configured to be attached to a mounting structure (not shown), for example a ceiling  318 , to mount the ceiling fan  80 . The stationary shaft  320  extends downwardly from the housing  312  and is configured to receive stationary components, for example a light, a control switch, and/or an ornamental structure. The motor  304  has a stator (not shown) positioned within the housing  312 , while the housing  312  is configured to act as the rotor for the motor  304 , such that the entire housing  312  rotates when the stator is activated. The housing  312  further includes a bottom surface  324  having a plurality of threaded bores  328 . 
         [0065]    The vibration isolation system  308  includes a hub plate  332 , a plurality of resilient grommets  336  and a plurality of fasteners  344 . As illustrated in the views of  FIGS. 8-11 , the hub plate  332  is an annular plate, and is formed of a rigid material, for example steel, aluminum, brass, iron, hardened plastic, or rubber material. The hub plate  332  has an upper surface  346  and a lower surface  348 . An inner wall  350  and an outer wall  352  extend upwardly from the inner edge and the outer edge, respectively, of the hub plate  332 . 
         [0066]    A plurality of projections  356  extend upwardly from the upper surface  346 , each of which includes an opening  360 . Each of the projections  356  is generally cylindrical and is sized to receive at least a portion of the corresponding grommet  336 . Further detail regarding the interaction of the grommets  336  and the corresponding projections  356  is provided further below in connection with the description of  FIG. 12 . 
         [0067]    As shown in  FIGS. 8-11 , the lower surface  348  includes a beveled portion  358  at the periphery of each of the projections  356 . The beveled portion  358  provides additional clearance between the head of the fasteners  344  and the hub plate  332 . Thus, as the fasteners  344  and/or the hub plate  332  vibrates, the likelihood of the head of the fasteners  344  contacting the hub plate  332  is reduced. Each of the openings  360  is configured to align with one of the plurality of threaded bores  328  in the lower surface  324  of the motor housing  312 . 
         [0068]    The hub plate  332  further includes a plurality of cylindrical projections  363  arrayed around the hub plate  332  extending upwardly from the upper surface  346 . Each cylindrical projection  363  includes a threaded hole  362  opening to the lower surface  348 . The threaded holes  362  are configured to receive blade fasteners such as the blade fasteners  92  of  FIG. 1  to fasten the blade mounting brackets  88  and the fan blades  84  to the hub plate  332 . The threaded holes  362  can be arranged in any desired pattern so that a suitable number of fan blades  84  and/or blade mounting brackets  88  can be attached to the hub plate  332 . 
         [0069]    As shown more clearly in the detail view of  FIG. 12 , the grommets  336  have an upper region  364 , a lower region  368 , a middle region  372 , and a central opening  376 . The central opening  376  is sized to allow the fastener  344  to fit into the central opening  376  of the grommet  336 . The middle region  372  of the grommet  334  has an outer circumference that is substantially the same size as the inner circumference of the opening  360  in the projection  356 . The upper and lower regions  364 ,  368  are wider than the middle region  372  so that a portion of the upper and lower regions  364 ,  368  cover the surfaces of the projection  356  around the opening  360 . In one embodiment, the grommets  336  are formed of an elastomeric material, for example rubber, though other desired resilient materials are used in other embodiments. 
         [0070]    In the embodiment described, the upper and lower regions  364 ,  368  have an outer diameter that is between approximately 1.5 and 3 times the outer diameter of the middle region  372 . Additionally, the upper and lower regions  364 ,  368  have an axial thickness than is between 2 and 3 times the axial thickness of the middle region  372 . In the illustrated embodiment, the grommet  334  forms a round resilient member with an annular channel defined between the upper and lower regions  364 ,  368  such that the annular channel circumferentially surrounds the middle region  372 . 
         [0071]      FIGS. 12 and 13  illustrate the hub assembly  300  with the motor  304  and vibration isolation system  308  in an assembled state. The lower region  368  of each of the grommets  336  fits in a corresponding cavity defined within one of the projections  356  of the hub plate  332 . The upper region  364  is positioned between the upper surface of the projection  332  and the lower surface  324  of the motor housing  312  in such a way that the central opening  376  of each grommet  336  aligns with a corresponding one of the openings  328  of the motor housing  312 . A fastener  344  extends through the central opening  376  of each grommet  336  and engages the corresponding threaded bore  328  in the motor housing  312  to secure the hub plate  332  to the motor housing  312 . 
         [0072]    During operation of the fan  80  of  FIG. 1  with the hub assembly  300  installed, the stator (not shown) of the motor  304  is energized, resulting in the motor housing  312  and the hub plate  332  rotating. The fan blades  84  attached to the threaded holes  362  of the hub plate  332  spin with the motor housing  312  and hub plate  332 , producing a flow of air. As the fan blades  84  rotate, oscillating vibrations are produced in the fan blades  84  and transferred to the hub plate  332 . Additionally, operation of the motor  304  introduces vibrations in the motor housing  312 . The vibrations are damped in the radial direction (horizontal in the views of  FIGS. 12 and 13 ) primarily by the middle regions  372  of the grommets  336 , which elastically deform within the openings  360  to dampen the transfer of radial vibrations between the fasteners  344  and the hub plate  332 . 
         [0073]    In the axial direction (vertical in the views of  FIGS. 12 and 13 ), the upper and lower regions  364 ,  368  of the grommets  336  elastically deform to dampen axial vibrations and movement between the hub plate  332  and the motor housing  312  and between the hub plate  332  and the fasteners  344 , particularly the head of each fastener  344 . As a result, the transfer of vibrations and movement between the motor  304  and the fan blades  84  is greatly reduced. 
         [0074]    It will be appreciated that variants of the above-described and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the disclosure.