Abstract:
The ventilation fan with automatic blade closure mechanism can include pivotable fan blades extending radially from a central hub. The fan blades pivot on their spars to allow the blades to assume positive pitch angles during operation. The fan blades are urged to a flat, substantially coplanar configuration when the fan is not in operation. A mechanism drives a motor shaft, the fan hub, and the blades axially outward for operation, and retracts the shaft, hub, and blades when the fan is not in operation. The tips of the blades seat in a groove of the surrounding rim when the fan is not in operation, with the outer surfaces of the blades, hub, and surrounding rim forming a substantially flat, continuous surface. This surface can be embellished with a decorative display, providing the fan with an attractive appearance when the fan is not in operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to ventilation devices and systems, and particularly to a ventilation fan with an automatic blade closure mechanism. The mechanism adjusts the blades to a substantially planar configuration when the fan is not in operation, thereby closing off airflow through the ventilation duct and permitting a decorative display to be applied to the essentially continuous surface of the coplanar blades. 
     2. Description of the Related Art 
     Built-in ventilation fans in bathrooms, kitchens, and other areas of homes and other structures are well known. Many such fans include some form of closure for the ventilation duct, to prevent relatively warmer or cooler air from flowing into or from the structure when the fan is not operating. These closure devices comprise various forms, e.g., louvers, single hinged panels, etc. These devices are nearly universally installed upon the exterior of the structure, with the blades and other components of the fan being clearly visible in the interior of the structure. At best, some form of grille or guard may be installed across the ventilation duct, primarily to prevent inadvertent contact with the fan while it is in operation. 
     All of these various fan configurations result in the ventilation duct and its fan, or at least some form of grille or guard, being visible from within the room where the system has been installed. While such a fan having a grille or guard thereover may not be particularly unsightly, it is nevertheless obtrusive and does not blend well with the interior décor of the typical home, office, or other non-industrial building structure. 
     Thus, a ventilation fan with automatic blade closure mechanism solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The ventilation fan with automatic blade closure mechanism can be installed on or within a wall or other panel of a building structure. The fan includes various mechanisms for directing the blades to a positive pitch angle during operation to draw air through the fan, and for moving the blades to a flat pitch angle to form a substantially flat and continuous disc when the fan is not in operation. One of the mechanisms retracts the fan motor shaft, fan hub, and fan blades axially, seating the outer tips of the blades in a groove formed in a surrounding rim when the fan is not in operation. This mechanism also extends the fan motor shaft, fan hub, and fan blades axially to unseat the blade tips from the outer rim during fan operation, which axial adjustment also allows the fan blades to automatically adjust to a positive pitch angle when clear of the surrounding rim. 
     As the blades adjust to their flat pitch setting when the fan is inoperative, all of the blades lie in substantially the same plane, with the chords of the blades also lying in a single plane. The blades retract axially due to the retraction of the fan motor shaft and hub when the fan is not in operation, with the outer surfaces of the blades disposed substantially coplanar with the outer surface of the surrounding rim. This uniform surface permits the application of a decorative display over the fan blades, the hub, and the outer rim, if so desired, thereby providing an attractive display when the fan is not in operation. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a front elevation view of a ventilation fan with automatic blade closure mechanism according to the present invention, showing the blades in their closed configuration. 
         FIG. 1B  is a front elevation view of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the blades in their open configuration. 
         FIG. 1C  is a front elevation view of an alternative embodiment of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the blades in their closed configuration with a decorative pattern applied to the closed blades. 
         FIG. 2A  is a detailed perspective view of a single fan blade of the ventilation fan with automatic blade closure mechanism according to the present invention, illustrating the automatic blade pitch adjustment mechanism. 
         FIG. 2B  is a detailed top plan view of a single fan blade of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the blade in its flat or closed orientation as when the fan is inoperative. 
         FIG. 2C  is a detailed top plan view of a single fan blade of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the blade in its positive pitch or open orientation as when the fan is operating. 
         FIG. 3A  is a side elevation view of the motor, fan, and shaft control mechanism of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the fan blades adjusted to their flat pitch or closed orientation by the mechanism and seated in the surrounding outer rim. 
         FIG. 3B  is a side elevation view of the motor, fan, and shaft control mechanism of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the flat fan blades adjusted by the mechanism to clear the surrounding outer rim or frame. 
         FIG. 3C  is a side elevation view of the motor, fan, and shaft control mechanism of the ventilation fan with automatic blade closure mechanism according to the present invention, showing the blades in their fully deployed, positive or open pitch orientation as when the fan is operating. 
         FIG. 4A  is a detailed side elevation view of the shaft control mechanism of the ventilation fan with automatic blade control mechanism according to the present invention, showing the mechanism in the configuration of  FIG. 3A . 
         FIG. 4B  is a detailed side elevation view of the shaft control mechanism of the ventilation fan with automatic blade control mechanism according to the present invention, showing the mechanism in the configuration of  FIG. 3B . 
         FIG. 4C  is a detailed side elevation view of the shaft control mechanism of the ventilation fan with automatic blade control mechanism according to the present invention, showing the mechanism in the configuration of  FIG. 3C . 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The ventilation fan with automatic blade closure mechanism provides for the substantially complete closure of the surrounding ventilation duct opening when the fan is not in operation, thereby substantially preventing the flow of air through the duct. The closed blades form a substantially flat, continuous surface when the fan is not in operation, with this surface providing for the application of a decorative coating or display thereon. 
       FIGS. 1A, 1B, and 1C  provide front elevation views of the ventilation fan with blade closure mechanism  10 , or ventilation fan or fan  10 . The ventilation fan  10  includes a plurality of fan blades or blades  12 , extending radially from a central hub  14 . More specifically, a plurality of fan blade spars  16  extend radially from the hub  14 , with each blade being attached to a corresponding spar  16 . The spars  16  are pivotally attached in the hub  14 , thus allowing the blades  12  to adjust in pitch within limits, described further below. 
     Each blade  12  has a blade tip  18 . The blades  12  are surrounded by a stationary rim  22  defining a vent opening  24  ( FIG. 1B ) having a diameter substantially equal to a fan diameter  20 . As the blades  12  move to a flat pitch and collectively lie in a single plane when the fan  10  is inoperative, they and the hub  14  form a substantially continuous surface to close the vent opening  24  when the fan  10  is not operating. This substantially flat and continuous surface lends itself well to the application of a decorative unified display or pattern  26  thereon, e.g., the pictorial representation of the earth as seen from space, as shown in  FIG. 1C . While the decorative pattern  26  need not be circular and congruent with the fan and vent opening diameter  20 , such circular patterns or displays are well suited to the circular area subtended by the fan blades  12 . Other round or non-round displays may be applied to the blades  12 , hub  14 , and the surrounding stationary field or background  28 . Further embellishment may be provided for the display  26  by installing a decorative frame  30  or the like as a border or periphery for the stationary background  28 , thus forming an effect closely resembling a fine work of art when the fan blades  12  are closed, as shown in  FIG. 1A  and particularly in  FIG. 1C . 
       FIGS. 2A, 2B, and 2C  illustrate the automatic pitch changing operation of the fan blades  12 , with a single exemplary blade  12  being shown in  FIG. 2A . Each fan blade spar  16  has a root or base that is pivotally secured in the hub  14 , allowing the spar  16  and its blade  12  to pivot about the elongate axis of the spar and blade assembly as shown by the pitch change arrows P in  FIGS. 2A and 2C . Each spar  16  includes a spar extension  32  extending radially therefrom, adjacent to the hub  14 . Spring attachment blocks  34  are installed on the hub  14 , with one such block  34  for each blade  12 . A tensile spring  36  is disposed between each block  34  and its spar extension  32 , with this assembly urging the blade  12  to its fully closed, flat pitch orientation as shown in  FIG. 2B . 
     If the blade  12  is formed to have some positive camber, as shown in  FIG. 2A , the center of aerodynamic pressure CP (i.e., the “lift” or thrust developed by the blade) is forward of the geometric center GC of the blade during fan operation, thus urging the blade  12  to a positive angle of attack or open position, as shown in  FIG. 2C , against the force of the tensile spring  36 . (The blade  12  is shown as a flat, non-cambered surface in  FIGS. 2B and 2C , as may be desirable for displaying a decorative pattern thereon.) The pivotal centers SC of the spars  16  may be located rearward of the blade geometric centers BC, i.e., the aerodynamic centers for flat, non-cambered blades, in order to enhance this positive pitch tendency, as shown in  FIGS. 2B and 2C . Pitch limiting stop blocks  38  are provided on the hub  14 , to limit the maximum pitch of the blades  12 . The stop blocks  38  may be located to limit the maximum blade pitch to any desired angle, e.g., 40 degrees, or other maximum pitch angle as desired. Thus, the blades  12  will tend to form a flat, substantially continuous surface due to the force of the tensile springs  36  when the fan  10  is not in operation, but will automatically deploy to a positive pitch due to their forwardly disposed aerodynamic centers when the fan is in operation. 
       FIGS. 3A, 3B, and 3C  provide elevation views in section of the entire ventilation fan  10 , with  FIGS. 4A, 4B, and 4C  providing more detailed views of the fan hub  14 , motor and shaft, and actuating mechanism. The fan  10  is driven by a motor having a central rotor  40  that is surrounded by and rotates within a stationary stator  42 . The rotor  40  is rotationally affixed to a shaft  44  that passes axially and concentrically therethrough, i.e., the shaft  44  rotates with the rotor  40 . The shaft  44  includes a first end  44   a  to which the hub  14  is affixed, and an opposite second end  44   b  having a flange  46  affixed thereto. 
     A motor control switch  48  includes a spring biased, normally on or closed pushbutton or axial shaft  50  (shown more clearly in  FIGS. 4A through 4C ) that bears axially against the flange  46 . This switch  48  is open, i.e., no electrical current flows therethrough, when the button or switch shaft  50  is retracted, as shown in  FIGS. 4A and 4B . If additional clearance is provided between the switch  48  and the flange  46 , the button or shaft  50  is extended ( FIGS. 3C and 4C ) and closes the switch  48  to operate the motor, the rotor  40  and stator  42 , via conventional wiring (not shown). Thus, fan actuation is dependent upon axial movement of the shaft  44  relative to the motor control switch  48 . 
     The axial movement of the shaft  44 , and thus the stator  40 , hub  14 , and fan blades  12 , is controlled by an actuator  52 . The actuator  52  is most preferably a wax actuator type, having a wax core that is selectively heated by a conventional electrical circuit (not shown). An example of such a wax actuator is the Xpelair No. 40984SK, but other equivalent actuators may be used. Wax actuators operate on the principle of the application of heat to the wax core, which causes the wax to expand over a period of time. The expansion of the wax pushes an internal plunger or the like outward, thus extending its actuating shaft  54 . In the case of the ventilation fan  10 , the actuating shaft  54  is connected to a pivotally mounted shaft control link  56  that communicates with the flange  46  of the second end  44   b  of the shaft  44 , via a pair of fingers  56   a  and  56   b  that extend to each side of the flange  46 . 
       FIGS. 3A through 3C , and  FIGS. 4A through 4C , provide progressive views showing the operation of the ventilation fan  10  from its inoperative state through its fully operative state.  FIGS. 3A and 4A  show the mechanism in its inoperative state, i.e., with no electrical power being applied to the apparatus. In this situation the wax actuator  52  is in its cold state, with the actuator rod or shaft  54  being fully retracted. This pivots the shaft control link  56  somewhat to the right, i.e., clockwise, resulting in the second finger  56   b  of the link  56  pushing or urging the flange  46  correspondingly to the right as shown in  FIG. 3A . This draws the motor shaft  44 , and attached rotor  40 , hub  14 , and blades  12  to the right as well, i.e., retracting the blades  12  so their tips  18  seat within a mating groove  58  within the frame  30  or the stationary surrounding field  28  of the fan  10 . The result is that the chords of the blades  12  across their entire tips  18  are drawn flush within the groove  58 , which along with the force of the tensile springs ( FIGS. 2 a    through  2 C) causes the blades  12  to assume a flat, zero pitch state as shown in  FIGS. 1A, 1C, 2B, and 3A . 
     When electrical power is applied to the mechanism, the wax within the wax actuator  52  begins to expand. Electrical power is also applied to the motor control switch  48 , but the switch  48  is held in its open or off position due to the shaft control link  56  until the wax expands sufficiently within the wax actuator  52 . As the wax expands, the actuating shaft  54  of the actuator  52  extends, thereby causing the first finger  56   a  of the link  56  to push the flange  46  to the left as shown in  FIGS. 3A through 3B , thus extending its shaft  44 , rotor  40 , hub  14 , and fan blades  12  axially in the direction of the first end  44   a  of the shaft  44  to unseat the blade tips  18  from the surrounding groove  58 . This intermediate step in the operation of the ventilation fan  10  is shown in  FIGS. 3B and 4B . However, it will be noted in  FIGS. 3B and 4B  that the pushbutton shaft  50  of the motor control switch  48  is not fully extended, i.e., the end of the shaft  50  is still in contact with the flange  46 . Thus, the motor control switch  48  remains open, and no power is being applied to the fan motor. 
     Finally, as the actuator  52  extends its actuating shaft  54  to its fullest extent, the shall control link  56  is pivoted further counterclockwise, causing the first finger  56   a  to push the shaft flange  46  further to the left, as viewed in  FIGS. 3C and 4C . This allows the pushbutton contact  50  of the motor control switch  48  to extend to its fullest extent, allowing the switch  48  to close, thereby supplying electrical power to the fan motor. As the fan blades  12  begin to rotate, they overcome the forces of the tensile springs  36  ( FIGS. 2A through 2C ) and assume a positive pitch angle due to the aerodynamic forces acting upon them, as described further above. This opens the blades  12  to draw air therethrough for normal fan operation. 
     When fan operation is no longer desired, electrical power is removed from the motor control switch  48  and actuator  52 . This may be accomplished conventionally by an automatically controlled thermostatic switch or the like, or by a conventional manually actuated switch. When power is removed from the fan motor and wax actuator  52 , the fan stops rotating within a very short time. This results in the tensile springs  36  drawing the blades  12  to their flattened, zero pitch state, as shown in  FIGS. 3B and 4B . However, the expanded wax within the actuator  52  continues to hold its shaft  54 , and thus the flange  46  and its attached components, in an extended state in the direction of the first end  44   a  of the motor shaft  44  until the wax cools and contracts to some extent. 
     Finally, when the wax actuator  52  has cooled completely, its actuator shaft  54  is completely retracted into the actuator body, as shown in  FIGS. 3A and 4A . This rotates the shaft control link to the right, or clockwise, from its orientation shown in  FIGS. 3B and 4B  to the orientation shown in  FIGS. 3A and 4A . The motor shaft flange  46  is drawn to the right accordingly, with the rotor  40  of the fan motor, the motor shaft  44 , hub  14 , and fan blades  12  all being drawn to the right as viewed in  FIGS. 3A through 4C . This results in the tips  18  of the fan blades  12  again seating within the surrounding groove or channel  58  of the stationary surrounding field  28  or frame  30  of the assembly, thereby completely closing off the air duct or vent opening  24  of the ventilation fan  10 . The resulting closure of the fan blades  12  provides for the application of a unified pattern or display thereon, as exemplified by the decorative unified pattern or display  26  in  FIG. 1C . Thus, the ventilation fan with blade closure mechanism  10  provides an attractive and unobtrusive appearance when not in operation. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.