Abstract:
An energy saving, readily removable, portable electric blower for retrofit to conventional 230 volt electric ovens is placed on the oven floor between the heat elements to circulate air through the oven in various directions. One wire of the 115 volt blower motor is coupled by a wire protecting spring metal clip to an element opening in the oven wall for its neutral electrical connection, the second motor wire is coupled to an element conductor so that the blower motor is energized by an oven selector switch. The use of this convection blower can be shown to annually save an average of 350 kwh per household.

Description:
BRIEF SUMMARY OF THE INVENTION 
     This invention relates to energy saving electric oven appliances and particularly to a novel blower for converting a conventional electric oven into a more energy efficient convection oven. 
     It is well known that convection ovens which circulate very hot air throughout an oven cavity are much more efficient than the conventional radiating oven because the heat is evenly distributed in the oven cavity, a lower oven temperature may often be used, and food is cooked faster. For example, it can be shown that a conventional electrical kitchen oven which will roast a chicken in 87 minutes at a temperature of 375° F. will roast an identical chicken in 45 minutes at an oven temperature of 350° using the convection blower to be described, for a net energy savings of 55%. Similar tests using other food products show a net savings of about 57% for baked yeast breads, 42% for baked potatoes, 28% savings for a beef roast, 22% for baked ham. It can be shown that an average annual energy savings of 350 kilowatt-hours per household may be achieved by retrofitting a standard electric oven with the convection blower to be described. 
     The blower to be described employs a short, fractional horsepower motor manufactured by The General Electric Company to withstand oven temperatures to about 560° F. The motor operates on 110-120 volts, obtained within the conventional 220-240 volt oven circuitry. 
     Briefly described the convection blower includes the short motor housed for short profile, vertical shaft operation within a porcelain housing that is placed on the floor of the oven cavity between the conventional oven heating elements. The shaft extends from the top of the porcelain motor housing and supports a blower rotor which is housed within a low, larger diameter cylindrical blower housing having peripheral windows with air diverting sides which are non-radially angled with respect to a tangent to the surface of the housing to exhaust air at various directions into the oven cavity. The exhausted air is drawn in from a plurality of intake ports in the floor of the blower housing. 
     A novel feature of the blower system is that it takes its 110 volt power from the 220 volt oven circuitry. Insulated heat resistant wires extend from the blower motor through a guard spring to a porcelain male connector removably connected to a female connector. The female connector and one of the wires are coupled to an elongated conductive strip having an end clip which is physically attached to the grounded metal housing of the oven. The wire attached to the conductive strip is thus grounded while the second or &#34;hot&#34; wire is attached to one of the switched legs of the oven element so that the convection blower is energized along with the oven element and receives only the 115 volts existing between the one oven leg and grounded oven housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the preferred embodiment of the invention: 
     FIG. 1 is a side elevational view of the convection blower; 
     FIG. 2 is a sectional plan view taken along the lines 2--2 of FIG. 1; 
     FIG. 3 is a sectional elevational view taken along the lines 3--3 of FIG. 2; 
     FIG. 4 is a bottom plan view taken along the lines 4--4 of FIG. 3; 
     FIG. 5 is a schematic drawing of typical oven circuitry and illustrates the circuitry between the blower motor and oven; and 
     FIG. 6 is a detailed view of the oven grounding clip illustrated in FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is an elevational view of the convection blower and illustrates a circular motor housing 10 having a small circular opening 12 that reveals the two terminals 14 of a vertically mounted fractional horsepower motor. In the preferred embodiment, the motor housing 10 is made of glazed porcelain for easy cleaning. The lower end of the housing 10 is flat so that it may rest on the flat floor of a conventional electric oven and, in the preferred embodiment, the lower portion of the housing has an overall diameter of about four inches so that it may be positioned between the curved sections of the lower or baking element of the oven. 
     As best illustrated in the sectional elevational view of FIG. 3, the sides of the housing 10 extend vertically upward approximately 1.2 inches to a horizontal circular plate 16 having an outside diameter of about 7.5 inches. An upper section 18 of the motor housing extends up from the vertical portion of the housing 10 to substantially enclose the motor 20 to protect it from dirt and grease vapors that may be circulated by the blower. The rotatable motor shaft 22 extends through an axial hole through the top end surface of the upper section 18 and is attached to the center of a centrifugal vane blower 24, illustrated in detail in the plan view of FIG. 3. 
     As shown in FIGS. 2 and 3, the blower 24 comprises a flat circular disc divided into approximately twelve peripheral sectors, the end portions of which bend downward to form vanes 26. The vane portion of the blower disc are formed so that their inner edges are slightly spaced from the outer surface of the upper motor housing 18, and the outer edges of the vanes are similarly spaced from the inner surface of a blower housing 28. The blower housing 28 may also be formed of glazed porcelain and is generally cylindrical with an enclosed top 30. The lower peripheral edge of the cylindrical blower housing 28 meshes with the upper peripheral edge of the motor housing plate 16 to form an enclosed blower cage, and is readily removable from the motor housing for ease in cleaning. 
     The side walls of the cylindrical blower housing 28 contain a plurality of windows 32 which, because of the relative thickness of the porcelain walls, are preferably slanted at various angles as shown in the sectional plan view of FIG. 3 to direct the hot air being exhausted into various non-radial directions. As shown in FIG. 1, one or more windows, such as window 34, may have a slanted sill to direct the air into an upward direction. 
     The floor of the blower housing is the horizontal portion of the motor housing upper plate 16 and is formed with a plurality of holes 36 as shown in the bottom plan view of FIG. 4. Thus, when the motor rotates the blower, the vanes draw hot air in through the holes 36 and exhaust it in various directions through the blower housing windows 32. 
     As previously mentioned, the motor 20 and associated circuitry can operate at oven temperatures up to about 560° F. and must be removed from self-cleaning ovens before being subjected to those elevated temperatures. However, the conductive strip clipped to the oven and its attached female connector and wires coupled into the oven circuitry can withstand temperatures up to about 1100° and should not be removed. Before self-cleaning, the blower unit may be easily removed by disconnecting the male wire connector 40 illustrated in FIG. 5 as will subsequently be described. While so removed from the oven, the convection blower assembly may be easily disassembled and, after removal of the motor, may be placed in a conventional dishwasher for cleaning. 
     To dismantle the assembly, the blower housing 28 is lifted from its floor, the vane blower is removed from the motor shaft by removing the nut 38 and removing the blower from the motor shaft, the upper motor housing 18 is then lifted from the lower housing 10, and the motor is then removed together with electrical wire, the wire guard spring 44, and the porcelain wire connector 40. All elements are immersible for cleaning except the motor which, during operation, is contained within the lower housing 10 and upper housing 18 and not within the normal flow of oven dirt and greases. 
     The schematic drawing of FIG. 5 illustrates a typical 230 volt residential oven circuit and the connection thereto of the 110 volt convection blower. Illustrated in section FIG. 5 is a portion of the lower motor housing 10 having therein the round electrical connector hole 12 shown in FIG. 1, and a wire pair 42 leading from the motor power terminals 14 to the male connector 40. For physical protection of the wire pair 42, a wire guard spring 44 with a large diameter end 46 looped behind the connector hole 12 interconnects the motor housing 10 with an annular groove 48 in the connector 40. The pins in the male wire connector 40 engage corresponding terminals in a porcelain female connector 50. One of the terminals in the connector is connected directly to a resilient electrically conductive strip 52, the edge of which is illustrated in FIG. 5 and which is shown in the plan view of FIG. 6. An insulated wire 54 is connected to the second terminal in the connector 50 and exits through a small hole in the connectors side wall and into a raised wire retaining &#34;tunnel&#34; extending lengthwise through the strip 52 and to a point at which the resilient strip is curved around in a reverse direction to form an oven wall retaining clip 55. 
     To install the electrical power to the convection blower, the clip 55 on the conductive strip 50 is inserted into one of heating element terminal passage holes 56 in the oven rear wall 58 and then drawn back so that the clip 55 engages the metallic wall which, together with all exposed metal parts of an oven, is at electrical ground or neutral. To insure proper electrical contact between the clip 55 and an oven wall that may have a baked enamel surface, the clip is provided with a plurality of sharp points 59 through its conductive metal for piercing any coating in the rear wall. The points 59 should be positioned and properly aligned to permit easy installation of the clip and resist removal from the oven wall 58. 
     Illustrated in FIG. 5 is a diagram of a typical electrical oven circuit 62. A thermostat circuit 64 normally operates at 110-120 volts and includes a thermostat control potentiometer or switch 66 for selecting a desired oven temperature. The thermostat employs a temperature measuring thermocouple within the oven and closes a relay to energize a heating element whenever the measured oven temperature falls below the selected temperature. The thermostat relay is connected between a first leg 67 of a 230 volt power source and one end of the oven bake element 72 and broil element 78. The second end of the bake element is connected through an oven selector switch 70 to the second leg 69 of the 230 volt source. Similarly the second end of the broil element 78 is coupled through the oven selector switch 74 to the second leg 69 of the 230 volt source. The two selector switches are usually included in a single manual rotary control which may further include a &#34;pre-heat&#34; position that closes both selector switches 70, 74 to energize both the bake and broil elements. A potential of 115 volts is between the ground or neutral conductor 68 and either of the legs 67, 69. 
     The end of the insulated wire 54 to the convection blower is preferably provided with a conventional spade connector 60 which may be coupled to a divider or Y-spade connector to be installed between one of the spade connector ends of an oven element and its lead-in wire equipped with a female spade connector or screw fastener. Thus, the connector is inserted between one leg of a 230 volt source at an oven element and the neutral or grounded oven wall, so that the convection blower has only 115 volts applied thereto. The spade connector 60 may be connected to either side of either oven element to pick up the 115 volt power. However, it is generally preferable that the current to the convection blower be switched concurrently with the oven bake element without having to pass through an oven element or a thermostat relay. Therefore, the spade connector 60 should be attached to the end of the bake element 72 at the position 80 in the oven circuitry. If the bake element is not readily available, attachment may be made in the broil circuit by attaching the spade connector 60 and a Y-connector at the point 82.