Abstract:
An oven drive system for use with commercial bakery ovens comprises a speed reducer and motor external to the bakery oven, a drive shaft extending from within the oven and operatively coupled to the speed reducer and the motor, and conveyor chain driving caterpillar located within the oven and operatively coupled to the draft shaft. The drive shaft is configured for minimal heat transfer to components external to the oven.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Applicant claims priority based on provisional patent application Ser. No. 60/975,642 filed Sep. 27, 2007, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to drive systems for bakery ovens and more particularly to oven drive assemblies operable inside a commercial bakery oven. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    Modern commercial bakeries of the type utilized in the manufacture of bread, rolls, and similar bakery products employ a large oven enclosure and a conveyor system extending therethrough. Uncooked dough is deposited into bakery pans which are transported by the conveyor through the oven. The speed of operation of the conveyor is coordinated with the length of the conveyor such that the dough is fully baked when a single pass through the oven has been completed. 
         [0004]    Heretofore it has not been practical to position conveyor drive assemblies inside the oven because the elevated temperature within the oven would cause the component parts of the conveyor drive assembly to fail. Prior to the present invention oven conveyor chains have been driven by a single conveyor drive assembly located outside of the oven which overcomes the problem of excessive heat but is unsatisfactory because the entire length of the conveyor is pulled through the oven from a single location. This causes excessive load and chain pull on the conveyor chain as well as more stress on the chain bearings. Also, if the single conveyor drive assembly goes down the entire system is down. 
         [0005]    The present invention comprises an oven drive system which overcomes the foregoing difficulties which have long since characterized the prior art. In accordance with the broader aspects of the invention oven drive assemblies for a bakery oven comprise a drive motor and a speed reducer located outside of the bakery oven, a drive shaft extending into the oven, and a conveyor chain drive caterpillar located inside the oven. The drive shaft preferably configured for minimal heat transfer through the drive shaft to the components of the oven drive assembly located external to the oven. 
         [0006]    All of the components of the conveyor chain drive caterpillar and the drive shaft comprise materials having similar coefficients of thermal expansion such that the components can withstand high temperatures within the oven while minimizing induced thermal stress caused by fluctuation in oven temperature. This facilitates the positioning of oven drive assemblies comprising the invention at substantially equally spaced intervals along the conveyor chain thereby reducing stress on the conveyor chain and maximizing conveyor chain life. Also, failure of one of the oven drive assemblies does not result in the entire system going down as has been the case previously. Rather, the remaining oven drive assemblies compensate for the increased load by operating at elevated stress levels until the failed oven drive assembly can be repaired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A more complete understanding of the present invention may be had by reference to the following Detailed Description when taken in connection with the accompanying Drawings, wherein: 
           [0008]      FIG. 1  is a sectional view of an oven drive assembly comprising one embodiment of the present invention; 
           [0009]      FIG. 1A  is sectional view of one component of the oven drive assembly shown in  FIG. 1 ; 
           [0010]      FIG. 2  is a side view of the oven drive assembly shown in  FIG. 1 ; 
           [0011]      FIG. 3  is a top view of a component of the oven drive assembly shown in  FIG. 1 ; 
           [0012]      FIG. 4  is a perspective view of the component of the oven drive assembly shown in  FIG. 3 ; 
           [0013]      FIG. 5  is side sectional view of an oven drive assembly comprising another embodiment of the present invention; 
           [0014]      FIG. 6  is a side sectional view of an oven drive assembly comprising yet another embodiment of the present invention; and 
           [0015]      FIG. 7  is a plan view of a bakery oven incorporating the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring now to  FIG. 1 , there is shown an oven drive assembly  10  comprising the present invention. The oven drive assembly  10  comprises a drive shaft  16  coupled to a conveyor chain drive caterpillar  18  which drives a conveyor chain inside the oven  14 . The drive shaft  16  includes a first segment  22  coupled at one end thereof to the caterpillar  18  and extending therefrom upwardly through an insulated exterior wall  24  of the oven  14 . 
         [0017]    Outside the oven  14  the first segment  22  of the drive shaft  16  is coupled to a second segment  26  by a heat dissipating coupler  28 . The first segment  22  of the drive shaft  16  may be provided with high thermal conductivity tinned heat exchangers, and forced connective cooling across the shaft can be provided by means of a fan or by means of a temperature controlled enclosure. The second segment  26  is operatively connected to a motor  30  and speed reducer  32  by a drive chain  34  and sprockets  36 . The upper end of the second segment  26  and therefore the entire drive shaft  16  is supported by bearings  37   a  and  37   b.  Bearing  37   a  is a tapered roller bearing or equivalent which supports the weight of the drive shaft  16 . The bearing  37   b  allows for expansion of the second segment  26 . 
         [0018]    During operation of the oven  14  the first segment  22  of the drive shaft  16  is at or near the operating temperature of the oven  14  while the second segment  26  is at or near ambient temperature of the bakery. All components of the drive plate assembly  18  and drive shaft  16  comprise materials having similar coefficients of thermal expansion such that the components can withstand high temperatures within the oven  14  while minimizing induced thermal stress caused by temperature fluctuations. 
         [0019]      FIG. 1A  comprises a sectional view of the coupler  28  which connects the first segment  22  with the second segment  26 . Each coupler  28  may be enclosed in an insulated enclosure  38  and may comprise a disk  40  having an upper surface and a lower surface. The lower surface is slotted and secured with hexagonal setscrews thereby enabling expansion and contraction of the first segment as temperatures within the oven  14  fluctuate. Alternatively, the coupler  28  may comprise a bellows-type coupling, a gear coupling, or other coupling types known in the art for minimizing heat transfer. 
         [0020]    Referring again to  FIG. 1 , sealing gaskets  44  are supported above and below the exterior wall  24  of the oven  14  to minimize volatile organic compounds (VOC), heat loss, product of combustion, and gas leaks from within the oven  14 . Seated above the upper sealing gasket  44  and positioned about the first segment of the drive shaft is one of two or more mechanical shaft coolers  46  comprising the drive shaft  16 . The oven drive assembly  10  is supported by a support and stabilization structure  48  comprising a frame  50 , a tension wire  52  and a tension spring  54  mounted above the oven  14 . 
         [0021]      FIG. 2  is a side view of the oven drive assembly  10  shown in  FIG. 1 . The caterpillar  18  is supported within the oven  14  by a support tower  60 . The location of caterpillar(s)  18  within the oven  14  may vary and is determined according to load analysis of the conveyor in order to achieve an optimal location between all load points of the conveyor. Located above the support tower  60  is an expansion bearing  62  supported by a frame  64 . The expansion bearing  62  surrounds the first segment  22  and accordingly allows movement thereabout as the first segment  22  of the drive shaft  16  expands due to increased oven temperature. The frame components located inside the oven  14  are thermally decoupled from the frame components located outside the oven by ceramic insert pads  65 . 
         [0022]      FIGS. 3 and 4  comprise top and perspective views of the caterpillar  18 , respectively. The caterpillar  18  comprises a chain  66  having conveyor engaging teeth  68  mounted thereon at equally spaced intervals. The chain  66  may be provided with an automatic lubrication system, if desired. The chain  66  is supported on and rotates about a plurality of bearings  70  and sprockets  72 . A tensioner  76  maintains proper tension in the chain  66  for constant engagement between the teeth  68  and conveyor chain C even as the chain  66  expands and contracts due to temperature fluctuation within the oven  14 . Although a particular type of tensioner  16  is shown in the drawings, those skilled in the art will know and understand that other types of tensioners can be used in the making of the invention. 
         [0023]    The expansion bearing  62  and bearings  70  of the caterpillar  18  may comprise sealed hybrid bearings, all steel bearings, or all ceramic bearings capable of withstanding substantially high temperatures and comprising lubricants and other components known in the art to be capable of withstanding substantially high temperatures. The component parts of the oven drive assembly  10  that are located inside the oven  14  are preferably selected from among the materials described in U.S. Pat. No. 6,968,943 and U.S. Pat. No. 7,086,525 the entire contents of which are incorporated herein by reference as if fully set forth herein. 
         [0024]    Referring now to  FIG. 5  there is shown an oven drive system  80  comprising an alternative embodiment of a self-cooling drive shaft  82 . The drive shaft  82  comprises one continuous cylinder  84  coupled at one end to the caterpillar  18  and at an opposite end to the speed reducer  32  and the motor  30 . The drive shaft  82  preferably comprises a material known in the art as capable of tolerating high temperatures such as those generated in the oven  14  while not transferring heat to the components external to the oven  14 . For example, the drive shaft  82  may comprise a ceramic material or other material known for its low thermal conductivity characteristics. The drive shaft  82  can also be hollow and constructed as a heat pipe or as a conduit which circulates coolant in a closed loop system. 
         [0025]    Referring now to  FIG. 6  there is shown an oven drive system  90  comprising a self-cooling drive shaft  92 . The drive shaft comprises one continuous cylinder  94  coupled at one end with the caterpillar  18  and at an opposite end with the speed reducer  32  and motor  30 . Positioned between the shaft coolers  46  are a fluid intake collar  96  and a fluid drain  98  and exhaust  100 . Cooling fluid is inserted into receiving orifices  102  in the cylinder  94  and runs down through the cylinder  94  thereby cooling the drive shaft  92 . The cooling fluid is discharged through venting orifices  104  in the cylinder  94  and fluid drain  98  and exhaust  100 . Alternatively, the drive shaft  92  can be vacuum sealed and provided with a small amount of fluid to act as a heat pipe. 
         [0026]      FIG. 7  comprises a plan view of a commercial bakery oven  110  incorporating the present invention. The oven  110  includes two oven drive assemblies  112  and  114  each comprising the present invention. 
         [0027]    Although preferred embodiments of the invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention.