Food oven
BACKGROUND OF THE INVENTION 
     1. FIELD OF THE INVENTION 
     This invention pertains to a conveyor type oven having an insulated shell and a fan for moving a flow of cooling air between the insulation and the exterior shell; the invention also pertains to an inlet door, outlet door and single drive motor for both the fan and a conveyor within the oven. 
     2. PRIOR ART 
     The prior art ovens are typically operable in a temperature range of 225° to 500° F. When and if these ovens are operated at higher temperatures, critical external areas of the oven become too hot to touch. Examples of these critical areas are the access doors. A human can touch 140° F. without being burned or scalded, but anything over that temperature will at least be objectionally uncomfortable and probably of a temperature which can cause injury. 
     Another disadvantage of the prior oven is that it typically has an insulated access door. This access door usually has an inner shell, an outer shell and a layer of insulation between the shells. The periphery of the outer shell gets objectionably hot and when the access door is open, the very hot inner door is presented to the oven operator who will be burned if he or she touches the door inner shell. 
     The prior conveyor oven uses one motor to power the conveyor and if cooling is required by the oven, a complete additional cooling device must be installed. All conveyor mechanisms are believed to be subject to jamming, even if they are of a perfectly 100% reliable design, because an operator using the conveyor may place something upon the conveyor that will not work and if the conveyor jams, provision must be made to prevent structural damage to the conveyor. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an oven which can be heated to a high temperature while having an exterior shell which is cool to the human touch. 
     It is an object of the present invention to provide an oven which does not present a hot surface to a user. 
     It is a further object of the present invention to provide an oven which has minimal heat loss. 
     It is yet a further object of the present invention to provide an economical high temperature commercial food oven usable in a restaurant. 
     Another object of the present invention is to provide an oven having a loader for a conveyor. 
     Yet another object of the present invention is to provide a conveyor type oven having a single electric motor driving both a conveyor and a cooling device. 
     Many other advantages, features and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, an oven is provided having an insulated oven chamber, an exterior cabinet, a conveyor within the oven chamber, and a fan for moving a flow of cooling air between the oven chamber and the exterior cabinet; the oven also has an inlet with interconnected inner and outer doors, an insulated outlet, and a single electric motor connected to both the conveyor and the fan, as distinct aspects of the invention. 
    
    
     ON THE DRAWINGS 
     FIG. 1 is a sectional elevational view of the preferred embodiment of an oven provided in accordance with the principles of the present invention; 
     FIG. 2 is a top view of the fan and conveyor drive taken aong lines II--II of FIG. 1; and 
     FIG. 3 is a sectional top view of the inlet along lines III--III of FIG. 1. 
    
    
     AS SHOWN ON THE DRAWINGS 
     The principles of the present invention are particularly useful when embodied in an oven of the type illustrated in FIG. 1 and generally indicated by the numeral 10. The oven 10 includes a cabinet 11 having an inlet 12 and an outlet 13, a conveyor 14, a friction drive 15 connected to the conveyor 14, a fan 16 and an electric motor 17 connected to both the fan 16 and the conveyor drive 15. 
     The cabinet 11 includes an inner shell 18 formed of sheet metal, an exterior shell 19 formed of sheet metal and a base 20 also formed of sheet metal. The inner shell 18 forms a heatable oven chamber 21 which has therein electric heater elements 22. The inner shell 18 has a bottom 23, sides 24 and a top 25. The exterior shell 19 has sides 26 and a top 27. The inner shell sides 24 and 25 and exterior shell 19 are spaced from each other and held together by rigid insulators 28, which may be ceramic, and by screws 29 fastened through the sides 24, 26 into the insulators 28. There is a layer of thermal insulation 30 wrapped around the inner shell sides 24 and top 25. This insulation 30 is covered by a thin layer of an airtight foil 31, the preferred foil being aluminum. The exterior shell sides 26 and top 27 are spaced outwardly from the insulation 30 and there is a passageway 32 between the insulation 30 and exterior sides 26 and top 27 through which cool air can be moved. The exterior top 27 has an air outlet 33 for exhaust of a flow of cooling air. The inner shell bottom 23 also has a layer of foil covered insulation 34. The bottom 23 is spaced upward from and fastened to the base 20 by insulators 35, which may also be ceramic. The base 20 has a top panel 36 which is underneath the bottom 23. Between the top panel 36 and the bottom 23, there is a plenum chamber 37 for flow of cooling air. The plenum chamber 37 is actually part of the air passageway 32 and the path for cooling air flow extends around the bottom 23 and then upward between the inner and outer sides 24, 26. The fan 16 is continually operated and moves a flow of ambient air through an inlet 38, into and through the plenum 37 and through the passageway 32 and out of the outlet 33. The bottom edge of the exterior side 26 has a flange 39 which slips over and forms an airtight seal against the base 20. The cover assembly having sides 24, 26 and tops 25, 27, which are connected together and nest upon and are supported by the base 20 and bottom 23, is removable from the base 20 by grasping the exterior sides 26 and lifting the entire cover assembly upward and off of the base 20 for service access to the conveyor 14. 
     The conveyor 14 can be one of any well known types which can move an item through an oven. The conveyor 14 shown is of the rotary helical track type and as a trackway 40 extending from the inlet 12 to the outlet 13 and there is a rotatable reel 41 for engaging and advancing an item 42 around the trackway 40 from inlet 12 to outlet 13. When the item 42 is on the trackway 40, it is exposed to heat from the heater elements 22. 
     An important and distinct feature of the present invention is the structure of the inlet 12 in the oven 10. The inlet 12 has an outer door 43 movably mounted on the exerior shell 19, an inner door 44 movably mounted on the inner shell 18 and a connecting rod 45 which opens the inner door 44 where outer door 43 is opened. 
     The outer door 43 is mounted in a pair of upright slides 46, as shown in FIG. 3 and slides upwardly to expose an opening 47 in the exterior side 26. The inner door 44 is rotatably mounted on a hinge shaft 48 which is journalled in a door frame 49 mounted to the inner shell 18. The inner door 44 is closely fitted to the door frame 49 to prevent air flow past the inner door 44. The frame 49 is surrounded by the insulation 30 and does not extend entirely between the inner and outer exterior shells 18, 19. The passageway 32 extends between the inner and outer doors 43, 44 and a flow of cooling air can pass between the inner and outer doors 43, 44 and a flow of cooling air can pass between the doors 43, 44 and maintain the outer door 43 cool. The inner door 44 rotates within the frame 49 and although it may extend into the passageway 32 when opened, the inner door 44 will never protrude out of the outer door opening 47 and in use, or when opened, the inner door 44 is out of reach or touch. The frame 49 has a lower shelf 50 which extends into the oven chamber 21, over the top of the conveyor track 40. The inner door 44 also protrudes into the oven chamber 21 and over the top of the conveyor track 40. The inner door 44 has a pusher surface 51, which projects over the top of the conveyor track 40. As previously mentioned, the oven 10 includes a fan for moving air through the passageway 32 and between the inner and outer doors 43, 44. The flow of cooling air tends to blow the inner door 44 into the oven chamber 21 and there is a counterweight 52 mounted on the inner door 44. The counterweight 52 biases the inner door 44 outward toward the outer door 43 as well as against the air flow. The counterweight 52 also assists in closing the inner door 44 under force of gravity. The outer door 43 is a relatively heavy door and closes under the force of gravity and while closing, also closes the inner door 44 through the action of the connecting rod 45. The entire inlet 12 is removable from the oven with the top cover assembly, which is removable as previously explained. 
     In use and operation of the oven inlet 12, the outer door 43 is lifted and opened and when the outer door 43 goes up, the connecting rod 45 is pulled up and the inner door 44 is pulled open. An item, such as 42, is inserted through the exterior cabinet opening 47 and placed on the frame shelf 50. The outer door 43 is then lowered and the weight and force of the closing outer door 43 is applied to the inner door 44 through the connecting rod 45. The pusher surface 51 of the inner door makes contact against the item 42 and as the inner door 44 is closed, the pusher surface 51 pushes the item off the frame shelf 50 and into the trackway 40 of conveyor 14. One of the important features of this inlet 12 is that if the outer door 43 is not completely closed, the inner door 44 can push the connecting rod 45 out and open the outer door 43. This is of great advantage if the reel 41 is not in the correct position to accept the item 42. Were item 42 placed in the inlet 12 and the outer door 43 released to close when the reel 41 will not accept the item 42, the item 42 will be pushed back into the inlet 12, the inner door 44 will be re-opened by the item 42 and the connecting rod 45 will force the outer door open. When the reel 41 then moves to a position where it will accept the item 42, the outer door will automatically, and without assistance, close and force the inner door 44 closed and the pusher 51 will place the item 42 upon the trackway 40. 
     When the doors 43 and 44 are closed, the fan 16 will move a flow of cooling air through passageway 32 between the doors 43 and 44 and the counterweight 52 will help keep the inner door 44 closed against any pressure of the flowing air. 
     With this construction of inlet 12, the outer door 43 is always cool and the hot inner door 44 is never directly exposed to where it can be easily or accidentally touched. This inlet 12 is especially well suited to a high temperature oven in which the oven chamber 21 is maintained near 600° F. for use with frozen foods. 
     Another important and distinct feature of the oven 10 of this invention is the outlet 13 which has a discharge chute 53 directed out towards a separate outlet frame 54, and a wrap 55 of insulation connecting and adjoining the chute 53 and frame 54. 
     The discharge chute 53 is connected to and extends downward from the bottom 23 of the oven inner shell 18. The chute 53 has a pair of sides 56, one of which is shown and there is a horizontal shaft 57 mounted in the sides 56 and extending across the chute 53. There is an outlet door 58 mounted on the shaft 57. The outlet door 58 spans the width of the chute 53 between the sides 56. The outlet door 58 is a thin piece of sheet metal formed into an inverted &#34;J&#34; shape. The closed end of the inverted &#34;J&#34; shaped outlet door 58 has a spacer welded in for supporting the top of the outlet door 58 above the shaft 52 a distance which exceeds the thickness of the sheet metal forming the outlet door. The discharge chute has a bottom 59 which is not insulated and extends downward past the outlet door 58. The chute bottom 59 extends through the passageway 32 and is exposed to the flow of cooling air through the passageway 32. The outlet frame 54 is mounted to the base 20 and is separate from and spaced from the discharge chute 53. The insulation wrap 55 is a &#34;C&#34; shaped piece of rigid insulation, such as rigid asbestos, and the insulation wrap includes a flange 60 extending downward along and to the outside of each chute side 56 and the outlet frame 54. The outlet door shaft 57 extends through the insulation wrap flanges 60 and retains the wrap 55 to the outlet 13. The oven chamber inner shell 18 and the insulation 30 have a notch to fit around and against the outlet 13, as does the exterior shell 19. 
     In operation of the oven outlet 13, the outlet door 58 is normally closed and there is a flow of air against the chute bottom 59 which helps keep the outlet cool. The outlet frame 54 is not in direct thermal contact with the oven chamber 21, but is adjoined to the discharge chute by the insulation wrap 55. When the conveyor 14 discharges an item 42, the item 42 falls into the chute 53 and goes downward on the bottom 59. The item 42 makes contact with and opens the outlet door 58 and after the item 42 passes under the outlet door 58 the force of gravity automatically closes the outlet door 58. The outlet door 58 operates only as required, is completely independent of the inlet 12, and has a very fast closing action. The outlet door 58 is very easily removed for cleaning by opening the door 58 to the open position shown in dotted line and pushing the door 58 inward towards the oven chamber 21 until the door 58 falls off of the shaft 57. The door 58 will then slide down and out between the sides 56 of the chute 53. The door 58 is easily reinstalled by inserting it into the outlet 13, and sliding it outward over the top of the shaft 57 until it swings downward into the normal closed position. This construction of outlet 13 is very economical, meets sanitation codes and presents no hot surfaces for touch nor does it require any labor for operation. 
     A further distinct and most important feature of the oven 10 of this invention is the single electric motor 17 connected to drive both the fan 16 and the friction drive 15 to the conveyor 14. It will be appreciated that in a commercial food oven that the oven is pre-heated and maintained in a heated state over the operating hours of the business in which the oven 10 is used. As the oven 10 is heated constantly, the fan 16 will be continually operated. For quickness of service, which is important in the food business, the conveyor 14 will also continually be operated. The conveyor 14 in the present oven 10 is a very slow speed device, and surprising as it may seem, when a single electric motor 17 drives both the fan 16 and the conveyor 14, ninety percent (90%) of the motor 17 output power is consumed by the fan 16 and only ten percent (10%) of the power is required by the conveyor 14. 
     It is an accepted expectation that any conveyor 14 can be jammed, even if only once every few years. With the single motor drive of the present invention, if and when, and hopefully it is a seldom if ever occurrence, that the conveyor 14 jams, it will follow that the electric motor 17 will slow down and stall out and the fan 16 will almost or completely cease to operate. When this happens, the entirety of the motor 17 output will be directed into the driving of the conveyor 14. A typical electric motor has a stall torque of about twice its running torque and as a result, the motor 17 will direct into the conveyor 14 upwards of 20 times the normal operating torque required or used by the conveyor 14. With an economical and lightweight design of conveyor 14, such a torque is sufficient to destroy the entire conveyor 14 and turn it right off of the oven base 20 and completely destroy the oven 10. However, the economy of the single motor makes its use enticing and to make it useful, a friction drive 15 is provided between the electric motor 17 and the conveyor 14. The friction drive 15 will handle a torque of a reasonable multiple of the torque required to operate the conveyor 14 but will slip at a torque below that which would structurally damage a jammed conveyor 14. 
     The electric motor 17 includes a reduction gearbox 61 having an output shaft 62. There is a pulley 63 removably mounted on the output shaft 62 and retaind by a set screw as shown. There is a rotatable input shaft 64 connected to the conveyor 14 and having a pulley 65 removably secured by a set screw as shown. There is a friction drive belt 66 connecting the pulleys 63, 65 and providing the friction drive and friction release in the event of jamming of conveyor 14. 
     The motor 17 has a second and full speed output shaft 67 upon which the fan 16 is directly mounted. The fan 16 is a centrifugal blower which rotates co-axially with the armature of motor 20 at about 3200 r.p.m. whereas the first output shaft rotates only at about 1 r.p.m. The motor 17 together with its gearbox 61 is mounted to a motor chassis 68 by a fastener 69 which is positioned co-axially with the fan output shaft 67 and the fan 16. The motor 17 and gearbox 61, and radially spaced first output shaft 62 are rotatable about the fastener 69 and the axis of the fan 16 for tensioning the drive belt 66. In order to maintain tension on the drive belt 66, there is a tightener 70 for securing and maintaining the motor 17 in a position which keeps the drive belt 66 tensioned as desired. The axis of both the conveyor input shaft 64 and the fan 16 are fixed with respect to each other and with respect to the motor chassis 68. 
     The conveyor input shaft 64 is mounted in the motor chassis 68 by a pair of bearings 71. The input shaft 64 freely floats up and down in the bearings 71 and is axially positioned by the tensioned drive belt 66 which lines up the pulleys 63 and 65 with each other. The pulleys 63 and 65 are of different diameters, the large pulley is shown on the conveyor input shaft 64 and the small pulley is shown on the motor output shaft 62. The pulleys 63, 65 are interchangeably mountable on either of the shafts 62 or 64 and are reversible where the large pulley may be mounted on the output shaft 62 and the small pulley may be mounted on the conveyor inut shaft 64 for changing the speed of the conveyor 14, as is shown in dotted line in FIG. 2. 
     The motor chassis 68 and the components mounted thereon, namely the motor 17, fan 16 and friction drive 15, are removable as a unit from the oven 10. The base 20 has a pair of mounts 72 removably fastening the motor chassis 68 to the oven 10. The conveyor input shaft 64 extends upward from the motor chassis 68 and projects through the cabinet 11 and into the oven chamber 21 and the conveyor input shaft 64 can be withdrawn vertically downward and out of the oven 10 together with the motor chassis 68. The base top panel 36 has a fan access 73 through which the fan 16 may be either installed in or removed from the air plenum 37. The air inlet 38 is in an aperture plate 74 which is mounted to the motor chassis 68 and positioned between the fan 16 and motor 17. The aperture plate 74 seals against the base top panel 36, and the air inlet 38 in the aperture plate 74 provides the source of air for the centrifugal fan 16. The bottom of the base 20 has a screen 75 forming and covering an inlet to the fan air inlet 38. The screen 75 has an opening in through which the motor 17, fan 16 and friction drive 15 are installable or removable and the motor chassis 68 fits against the screen 75. In operation the use of the oven 10, the fan 16 and conveyor 14 are continually operating. Ninety percent (90%) of the power from the motor 17 goes to drive the fan 16 and ten percent (10%) goes to drive the conveyor 14. The fan 16 draws in air through the screen 75 and the inlet 38 and moves the air through the passageway 32 and then out of the outlet 33 keeping the exterior shell 19, the outlet 13, and the inlet outer door 43 cool. If and when the conveyor 14 begins to jam, the motor 17 will slow down under the load and the torque to the conveyor input shaft 64 will be increased. The friction drive 15 will drive at and up to about twice the normal maximum required torque but beyond that begins to slip and disconnect the motor 17 from the conveyor 14. With this structure, extra power is available to try and overcome a jam but yet a clutch is provided to release the conveyor 14 if it is badly jammed and therefor structural damage is prevented. When the motor chassis 68 is removed from the oven 10, the speed of the conveyor 14 can be easily changed. The temperature of the oven chamber 21 is constant at about 600° F. for pizza. Therefore the cooling load to keep the cabinet exterior shell 19 cool is constant and the fan 16 should turn at a constant speed. In a food operation using the present oven 10, frozen pizzas take about three and one-half minutes to cook and refrigerated thawed pizzas take about two and one-half minutes to cook. It is at the discretion of the retailer to select his preferred mode of operation. By providing one of the pulleys 63 or 65 about 40% larger than the other pulley, the conveyor cycles of either 21/2 or 31/2 minutes can be obtained by the user of oven 10 by merely removing the motor chassis 68 and reversing the pulleys 63 and 65. With either ratio, the fan 16 speed remains constant and the oven exterior shell 19 remains at the same temperature. This oven 10 may operate at between 500° and 900° F. and even at these temperatures it does not present a single hot edge or surface that will burn a user. When the oven 10 is being used, none of the access doors open up past the exterior shell 19 and no additional counter space need be provided. 
     Although various minor modifications may be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranteed hereon, all such embodiments as reasonably and properly come within the scope of our contribution to the art.