Abstract:
A food cabinet includes a container holding a refrigerated food product, and the cabinet further includes a cooling device to refrigerate the food product. A fan for the cooling device includes an impeller mounted to a stationary shaft and a motor with a rotor. The impeller is exposed to fluids, but the motor and rotor are opposite a sealed surface and not exposed to the fluids. The impeller is coupled to the rotor by means of complementary sets of magnets mounted on each, such that rotation of the rotor similarly rotates the impeller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Application No. 60/984,222, filed Oct. 31, 2007, and herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates to a food refrigeration system, more specifically to a system for cooling food containers associated with commercial food cabinets. 
       BACKGROUND 
       [0003]    Commercial food cabinets are often equipped with removable food pans allowing for ready access to food that needs to be kept cool. In order to keep the food pans cool, fans are placed below the pans to circulate air and otherwise reduce the temperature of the pan environment. Liquids from the food pans can spill down into the fan area. If the liquids contact the motor, this can impact motor performance and negatively interfere with the operation of the cooling system. Similarly, washing of the upper area of the cabinet can be made more difficult if special care must be taken to avoid contacting the fan motor with wash liquid. 
         [0004]    Traditionally, both area shielding and shaft seals have been used to limit the contamination. However, neither of these methods can form a complete seal against contact with liquids because of the necessary operation of the fan rotor and impeller. 
         [0005]    It would be desirable to provide a refrigeration system wherein the fan motor is completely isolated from the food environment by a fully waterproof barrier. 
       SUMMARY 
       [0006]    A fan is part of a cooling system to cool the removable pans of a food cabinet such as a presentation cabinet or preparation table. The fan impeller is mounted on a stationary shaft in the same environment as the food pans, while the electric motor that powers the fan is mounted outside of the operative environment, separated from the fan impeller and the food pans by a sealed, water-tight barrier. The motor is coupled with the impeller by means of magnets mounted on one or both of the fan and the rotor of the motor. Because there is no direct mechanical connection between the motor and the impeller, the need for some type of moving seal through an opening of the internal housing wall is eliminated. The risk of a liquid contacting the motor from a food spill or during washing is greatly reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIGS. 1A and 1B  show two examples of food cabinets with removable pans. 
           [0008]      FIG. 2  shows a pan cooling system for a food cabinet. 
           [0009]      FIGS. 3A and 3B  show two views of an impeller for a cooling system fan assembly. 
           [0010]      FIGS. 4A and 4B  show two views of a drive motor for a cooling system fan assembly. 
           [0011]      FIG. 5  shows a cooling system fan assembly. 
           [0012]      FIG. 6  shows an exploded view of a cooling system fan assembly. 
           [0013]      FIG. 7  shows the assembly of  FIG. 6  mounted to a sealed surface. 
           [0014]      FIG. 8  shows a cross-section view of a self-sealing screw mounting a shaft to a sealed surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1A  shows a food preparation table  70   a  including condiment pans  50   a.  The table  70   a  provides ready access to a user, which may be an employee or a customer at a food establishment. The food preparation table  70   a  allows for quick access to small quantities of condiment  52   a  for preparing individual servings of food. In typical use, the cabinet  70   a  may be present in a room temperature environment for several hours. The condiment pan  50   a  stores a condiment  52   a,  which needs to be kept at a temperature substantially below room temperature in order to stay fresh. 
         [0016]      FIG. 1B  shows a food presentation station  70   b  including removable pans  50   b.  The station  70   b  displays fresh seafood  52   b  which must also be kept at a low temperature in order to stay fresh. Because the presentation station  70   b  displays fresh seafood  52   b  to customers, it must be washed frequently to avoid the possibility of developing an unpleasant odor. 
         [0017]      FIG. 2  shows an embodiment of a cooling system appropriate to a food cabinet  70 , of which both the food preparation table  70   a  and the food presentation station  70   b  are embodiments. A food pan  50  sits within a cooling frame  60 , which itself sits within the insulated cabinet  70 . As shown, the food pan  50  is easily removable, and several identically shaped food pans may be provided for easy replacement. This configuration divides the cooling environment  4  into an open environment  7  above the food pan  50 , an inner ventilation chamber  8  between the food pan  50  and the cooling frame  60 , and an outer ventilation chamber  9  between the cooling frame  60  and the cabinet  70 . 
         [0018]    The cooling frame  60  includes a set of vertical air grills  62 ,  63 , and  64 . The cooling frame  60  also includes a horizontal air grill  65 . As shown in  FIG. 2 , the cooling frame  60  comprises separate sections  60   a  and  60   b,  the upper section  60   a  primarily vertical in construction and including the vertical air grills  62 ,  63 , and  64  while the bottom section  60   b  is primarily horizontal and includes the horizontal air grill  65 . The bottom section  60   b  may be independently removable from the cabinet  70  (such as for accessing the fan impeller  10 ) while leaving the upper section  60   a  in place. In other embodiments, the cooling frame  60  may be a single unified component including both vertical and horizontal grill sections. 
         [0019]    A fan impeller  10  draws air from the inner ventilation chamber  8  into the outer ventilation chamber  9  and impels the air toward the evaporator coil  72  which is located in a vertical section of the outer ventilation chamber  9 . Air passes the evaporator coil  72  and exits the outer ventilation chamber  9  through one of the vertical air grills  62 ,  63 , and  64 . One of these air grills  62  leads to the open environment  7  above the food pan  50 ; the other two air grills  63  and  64  lead to the inner ventilation chamber  8  directly below the food pan  50 . Passing over the evaporator coil  72  cools the air which subsequently passes through the vertical grills, so that when this air comes in contact with the food pan  50  it acts to reduce the temperature of the food pan  50 . 
         [0020]    Liquids may enter the outer ventilation chamber  9 , either from food spills or during a washing procedure. The impeller  10  and stationary shaft  20  are not vulnerable to damage from casual contact with liquids, and the impeller  10  may be easily removed during washing of the upper area of the cabinet. However, contact with liquids may damage the electric drive motor  30  that drives the impeller  10  if the liquids are able to reach those components. Fortunately, the surface  2  separating the rotor  40  from the impeller  10  also works to isolate the motor  30  from the cooling environment  4  without blocking the magnetic coupling between the rotor  40  and impeller  10 . Thus, food falling proximate to the impeller  10  during operation does not contact the motor  30 , and wash liquid directed to washing the cabinet  70  also does not contact the motor  30 . 
         [0021]      FIG. 3  shows the fan impeller  10 . Four fan blades  12  are evenly positioned about the central body  14 . In the center of the body  14  is a hole  16  to receive the stationary fan shaft  20  (shown in  FIG. 5 ). Positioned within the radius of the body  14  are four magnets  18 . The magnets  18  are positioned a similar distance from the center of the body  14  and are spaced evenly. 
         [0022]    The number of magnets  18  may vary. In one embodiment, an even number of magnets  18  are used. If an even number of magnets  18  are mounted on the central body  14 , the magnets  18  may be aligned in an alternating fashion such that the poles of adjacent magnets are opposite each other, thus reducing a potential source of error in manufacturing. If the four magnets  18  are accidentally placed backwards into the impeller  10 , there is no practical effect, as the same number and relative position of the magnets  18  is preserved. It has also been found that the magnetic coupling between the impeller  10  and the rotor  30  is stronger in the case of alternating opposite poles than if all the poles of the magnets  18  are facing the same direction. 
         [0023]      FIG. 4  shows an electric drive motor  30 , which includes a rotor  40 . The rotor contains magnets  48 , which are spaced evenly in a circular configuration identical to that of the impeller magnets  18 . The rotor magnets  48  should be configured in both spacing and polarity to couple with the impeller magnets  18 . As shown in  FIGS. 3 and 4 , if the impeller magnets  18  are alternating in polarity, the rotor magnets  48  should do likewise. 
         [0024]    As shown in  FIG. 5 , when the fan is assembled, the fan impeller  10  is mounted on the stationary fan shaft  20 . The fan impeller  10  is configured to rotate freely when mounted on the shaft  20 . The stationary fan shaft  20  is secured to the sealed surface  2 , which separates the cooling environment  4  from the motor environment  6 . The surface  2  may be made up of multiple contiguous surfaces or may be a single unbroken surface, but the surface  2  is sealed such that likely contaminants (e.g., fluids) which exist within the cooling environment  4  cannot pass the surface  2  into the motor environment  6 . The sealed surface  2  could be made of any material that will not interfere with the magnetic coupling of the fan assembly—for example, a nonmagnetic metal, or a nonmetal such as plastic or glass. In one embodiment, the sealed surface is made of stainless steel. 
         [0025]    The stationary fan shaft  20  may be attached to the sealed surface by mechanical means. In one embodiment, the fan shaft  20  may protrude through the sealed surface  2 . Because the fan shaft  20  is stationary and does not have to mechanically impart rotation from the motor  30 , an effective seal can still be produced at the surface  2  even if the shaft  20  extends completely through the surface  2  as shown in  FIG. 5 . In the configuration shown in  FIG. 5 , the fan assembly including the impeller  10 , shaft  20 , and motor  30  with rotor  40 , are all physically connected to the surface  2  through the use of an attachment plate  22 . In other configurations, the shaft  20  may be bolted to the surface independently of the motor  40 , may be glued or otherwise directly attached to the surface  2 , or may be built integrally with the surface  2 . The shaft  20  may be secured to the surface  2  by any method that allows the surface  2  to maintain its seal. 
         [0026]    The drive motor  30  is positioned on the other side of the sealed surface  2  in the motor environment  6 , where it is not subject to contact with contaminants from the cooling environment  4 . The drive motor  30  is positioned as shown such that the rotor  40  is aligned with the central body  14  of the impeller  10 . The magnets  18  of the impeller  10  are aligned with the magnets  48  of the rotor  40  such that the rotor  40  and central body  14  are magnetically coupled. When the motor  30  is activated to rotate the rotor  40 , the magnetically coupled impeller  10  also rotates, including the fan blades  12 . Rotation of the fan impeller  10  acts to circulate air within the cooling environment  4 . 
         [0027]    Another embodiment of a cooling assembly is shown in an exploded view as  FIG. 6 . Here, the impeller  10 ′ is securely attached to a hub  14 ′ which includes four magnets  18 ′. The hub  14 ′ is mounted on a stationary shaft  20 ′. The stationary shaft  20 ′ includes a wide base that abuts the sealed surface  2  (shown in  FIG. 7 ) to provide additional stability for the fan assembly. 
         [0028]    The shaft  20 ′ is secured to the sealed surface  2  by means of a screw member  24 . In one embodiment, the screw member  24  is a self-sealing screw, such as a screw with a silicon o-ring under the screw head available from McMaster-Carr. The screw member  24  fastens the shaft  20 ′ tightly to the sealed surface  2 . The screw  24  and shaft  20 ′ are stationary relative to the sealed surface  2 , which allows the sealed surface  2  to maintain an effective seal around the shaft  20 ′. 
         [0029]    In the embodiment of  FIG. 6 , the motor  30 ′ with the rotor  40 ′ is attached to the sealed surface independently of the impeller  10 ′ and hub  14 ′ on the shaft  20 ′. The motor  30 ′ is connected to a motor mount plate  80 . A set of four hex standoffs  82  attach the plate  80  to the sealed surface. Both the motor  30 ′ and standoffs  82  are fastened to the motor mount plate  80  using nuts  84 . The standoffs  82  are attached to the sealed surface by means of screws  26 , which may be self-sealing screws substantially identical to the screw member  24  described above. The motor  30 ′ drives the rotor  40 ′, which is positioned close to the sealed surface and is magnetically coupled by interaction of the rotor magnets  48 ′ and the hub magnets  18 ′. 
         [0030]    The top surface of the rotor  40 ′ includes a central recess of sufficient depth such that the rotor  40 ′, which rotates rapidly during operation of the cooling system, does not come into physical contact with the head of the screw member  24 , which remains stationary during cooling. 
         [0031]      FIG. 7  shows an elevation view of the cooling system as shown in  FIG. 6 , assembled and mounted upon the sealed surface  2 . The shaft  20 ′, the central hub  14 ′, and the impeller  10 ′ are above the surface  2  within the cooling environment  4 . The motor  30 ′, rotor  40 ′, and motor mount plate  80  with standoffs  82  are below the surface  2  within the motor environment  6 . These two part groups do not form a mechanical connection; most notably the head of the screw member  24  does not contact the rotor  40 ′ but rather is located within the recess in the rotor  40 ′. During operation, the motor mount plate  80  attached to the motor  40 ′ does not rotate, and the shaft  20 ′ also does not rotate. The rotor  30 ′, central hub  14 ′, and impeller  10 ′ rotate together due to the magnetic coupling. 
         [0032]      FIG. 8  is a cross-section view of the stationary shaft  20 ′ and self-sealing screw member  24 , which includes an o-ring  25 . When the screw is attached to the sealed surface  2  as shown, the o-ring  25  presses upward tightly to maintain a seal and prevent fluids in the cooling environment  4  from entering the motor environment  6 . 
         [0033]    The embodiments described above are shown by way of illustration and are not limiting on the scope of the invention. Variations, such as in the configuration of the coupled magnets, the fan blades, the motor, or the air circulation within the cooling cabinet, are possible.