MAGNETICALLY COUPLED FAN BLADE AND MOTOR FOR A FOOD CABINET
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.
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This application claims the benefit of U.S. Application No. 60/984,222, filed Oct. 31, 2007, and herein incorporated by reference.
TECHNICAL FIELDThe application relates to a food refrigeration system, more specifically to a system for cooling food containers associated with commercial food cabinets.
BACKGROUNDCommercial 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.
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.
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.
SUMMARYA 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.
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
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.
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.
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.
As shown in
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
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.
Another embodiment of a cooling assembly is shown in an exploded view as
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′.
In the embodiment of
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.
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.
Claims
1. A food product refrigeration system, comprising:
- a container for holding a refrigerated food product;
- a cooling frame substantially around and below the container, the cooling frame including openings designed for allowing the passage of air therethrough;
- a ventilation chamber defined by the cooling frame and an insulated wall substantially around and below the cooling frame, the ventilation chamber containing a fan impeller and an evaporator coil; and
- a motor controlling a rotor, the rotor magnetically coupled to the impeller such that rotation of the rotor by the motor results in operation of the impeller, the motor and rotor separated from the ventilation chamber by a sealed surface;
- wherein the impeller operates to draw air into the ventilation chamber, past the evaporator coil, and out of the ventilation chamber into contact with the container.
2. The refrigeration system of claim 1, wherein
- the ventilation chamber is an outer ventilation chamber;
- an inner ventilation chamber is formed between the container and the cooling frame;
- the cooling frame includes an outlet that opens into the inner ventilation chamber and an outlet that opens into the air above the container; and wherein
- the fan impeller operates to draw air from the inner ventilation chamber into the outer ventilation chamber, past the evaporator coil, and through the outlets of the outer ventilation chamber into both the inner ventilation chamber and the air above the container.
3. The refrigeration system of claim 1, wherein the rotor contains a set of magnets spaced therein, and wherein the impeller contains a set of magnets spaced such that the magnets of the impeller and the magnets of the rotor form individual pairs for magnetic coupling of the rotor and impeller.
4. The refrigeration system of claim 3, wherein each individual pair of coupled magnets is positioned such that the magnets are proximate the sealed surface and on opposite sides of the sealed surface, such that the magnets communicate magnetically across the sealed surface.
5. The refrigeration system of claim 3, wherein the set of impeller magnets are spaced evenly and at a common distance from the center of the impeller, and wherein each magnet is oriented such that its polarity is opposite from the polarity of both of the two magnets adjacent to it.
6. The refrigeration system of claim 1, wherein the container is a condiment pan.
7. The refrigeration system of claim 1, wherein the sealed surface is made of a nonmagnetic material.
8. The refrigeration system of claim 7, wherein the nonmagnetic material is stainless steel.
9. The refrigeration system of claim 1 wherein the impeller is mounted on a stationary shaft that extends upward through the sealed surface, the stationary shaft having an associated stationary seal member.
10. A food cooling system, comprising:
- a food holding area;
- a fan impeller mounted for rotation below the food holding area;
- a motor including a rotor magnetically coupled to drive the fan impeller without mechanical contact between the rotor and the fan impeller; and
- a sealed surface separating the motor from the impeller.
11. The food cooling system of claim 10, wherein the rotor contains a set of magnets spaced therein, and wherein the impeller contains a set of magnets spaced such that the magnets of the impeller and the magnets of the rotor form individual pairs for magnetic coupling of the rotor and impeller.
12. The refrigeration system of claim 1, wherein the set of impeller magnets are spaced evenly and at a common distance from the center of the impeller, and wherein each magnet is oriented such that its polarity is opposite from the polarity of both of the two magnets adjacent to it.
13. The food cooling system of claim 10, wherein the sealed surface is made of a nonmagnetic material.
14. The food cooling system of claim 13, wherein the nonmagnetic material is stainless steel.
15. The food cooling system of claim 10 wherein the impeller is mounted on a stationary shaft that extends upward through the sealed surface, the stationary shaft having an associated stationary seal member.
16. A food preparation cabinet including the food cooling system of claim 10, wherein:
- the food holding area includes a condiment pan holding a condiment;
- the fan impeller located below the condiment pan and exposed to potential contact with condiment that falls from the condiment pan;
- the sealed surface preventing the motor from being contacted by condiment.
17. A food presentation station including the food cooling system of claim 10, wherein:
- the food holding area includes a display area with a removable food tray displaying food product;
- the fan impeller located below the food tray and within the display area;
- the sealed surface preventing the motor from being contacted by wash liquid during cleaning of the display area.
Type: Application
Filed: Sep 2, 2008
Publication Date: Apr 30, 2009
Applicant: Premark FEG L.L.C. (Wilmington, DE)
Inventors: Joseph F. Sanders (North Richland Hills, TX), David L. Whiting (Fort Worth, TX)
Application Number: 12/202,756
International Classification: F25D 17/00 (20060101);