Oil burner ignition and control package
This invention relates to oil burner ignition and control apparatus and particularly to the combining of the high voltage transformer for the ignition system of an oil burner and the control system for the oil burner in a single package of novel design. 
     Such elements are conventionally packaged separately because combined packages have heretofore been too bulky and unwieldy. The transformers for such systems, which commonly employ cores of bilaterally symmetric U-I configuration, have generally been required to be potted in order to meet stringent Underwriters Laboratories requirements with respect to spacing of high voltage leads. Potting contributes greatly to bulk, weight and manufacturing cost. It has also been common practice to provide a primary winding or coil at one end of the core where a single coil can be positioned while maintaining bilateral symmetry of coil arrangement. This has further contributed to bulkiness of prior art transformers and to the impracticality of a combined package. 
     By departing from these practices of the prior art, the present invention provides a combined package for the transformer for high voltage oil burner ignition and the control system for the oil burner. The transformer is not potted, the core ends are free of coils, and one core end overlaps a circuit board for the control system on both sides of which circuit elements are supported. Although the transfomer is not potted, tight constraints against shorting of the high voltage secondary leads are maintained by provision of insulator bushing means which are positioned in apposition to the transformer secondary coils by means of a bracket which also serves as a mounting for the transformer core. The high voltage leads are drawn through the insulator bushing means and are secured at terminal contacts at the lower end of the bushing means. The entire package is hinged for movement into and out of working association with the ignition leads of the oil burner. 
     Regardless of the specific location of particular coils on the core, prior art ignition transformers have generally provided a bilaterally symmetric arrangement of the coils on the bilaterally symmetric core in order to avoid the magnetic flux aberrations and attendant heating associated with asymmetric arrangements of coils on the symmetric core. According to the present invention, further economy can be realized by arranging a single primary coil on the core in an asymmetric manner, with provision for discontinuous duty cycle operation of the transformer 
     The result of the foregoing departures from the prior art are economical and convenient combined ignition transformer and control systems which can be provided as single units which oil furnace manufacturers can include as OEM equipment with their product. The manufacturer, the installer, the consumer, and the servicer are offered the advantages of reduced manufacturing cost, reduced overall weight and size, greater ease of assembly and increased modularity. 
    
    
     In the drawings, 
     FIG. 1 is a side view of a transformer-control package embodying the invention mounted on an oil burner schematically represented with portions cut away. 
     FIG. 2 is a top view of FIG. 1 with the transformer-control package removed. 
     FIG. 3 is an isometric view taken from above of the transformer-control package. 
     FIG. 4 is an isometric view of the same package taken from below. 
     FIG. 5 is an isometric view taken from above of the transformer-control package with its cover shown in phontom. 
     FIG. 6 is an end view of the preassembled high voltage transformer and tap means illustrated in FIG. 5 with portions cut away. 
     FIG. 7 is an isometric view of the transformer mounting bracket and an insulator tie-down pin. 
     FIG. 8 is an exploded elevation view of the voltage tap means of the present invention. 
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     An oil burner ignition and control package 10 in accordance with the present invention is mounted on an oil burner 15 as illustrated by FIG. 1. Referring to FIGS. 1 and 2, the oil burner includes a combustion chamber 16 defined by walls 17, one of the walls 17 supporting a high voltage box 18 exterior to the combustion chamber 16. 
     Extending from the interior of the high voltage box 18 to a spark gap area 22 within the combustion chamber 16, are an oil nozzle assembly 20 and an adjacent pair of electrically insulated high voltage electrodes 21. 
     Atomized fuel oil or the like provided at the spark gap 22 via an oil nozzle 19 is initially ignited by a high voltage arc generated across the spark gap area 22 by electrically uninsulated distal ends 24 of the electrodes 21. A thermal protection sleeve 23 extends about portions of the fuel nozzle assembly 20 and electrodes 21 within the combustion chamber 16. 
     Under operating conditions, the ignition and control package 10 rests against an upper support flange 26 perimetrically extending about an open top 27 of the high voltage box 18. 
     The package 10 is fastened to the high voltage box by two double leaf hinges 28 which provide limited counterclockwise rotation of the package 10 about the axis of rotation a--a&#39; so as to permit ready access to the high voltage box interior for maintenance purposes. 
     Electrically uninsulated ends 25 of the high voltage electrodes are electrically connected to the control package 10 via a pair of spring-like contacts 30 (FIG. 4) extending between the control package 10 and the electrodes 21 as illustrated in FIG. 1. The spring-like contacts 30 are sized so as to be partially compressed between the electrodes ends 25 and the control package 10 so as to ensure good electrical continuity. 
     Mounted to the underside of the ignition and control package 10 is a flame detector 35 (FIG.4) of, for example, the cadmium sulphide type well known in the art. The flame detector 35 is arranged so as to look between the spring-like contacts 30 into the combustion chamber 16 via an aperture 36 (FIG. 2) provided in a front wall 19 of the high voltage box 18 as indicated by arrow 37. The front wall 19 supports the high voltage electrodes 21 and a conduit portion 29 of the fuel nozzle assembly 20. A side wall 31 of the high voltage box 18 supports a fuel oil intake coupling 32 which is connected to a source (not shown) of fuel oil or the like. 
     The oil burner 15 and the arrangement of the ignition and control package 10 relative to the oil burner are well known in the art. 
     Turning to FIGS. 3 and 4, the ignition and control package 10 includes a housing 40 having a sheet metal cover 41 and a base or mounting plate 42 having an upper surface 48 and a lower surface 49. The sheet metal cover has a top 38, two sides 39, and an end 44. All electrical components of the ignition and control package are advantageously contained within the housing 40 except an external circuit board terminal strip 45, a low voltage control transformer 46, and a circuit breaker reset button 47. 
     Extending from the undersurface 49 of the base plate 42 is a high voltage insulator 50 which extends from the interior of the housing 40 to a point below the base plate 42 via a first window-like aperture defined by a perimetric edge 51, the aperture having dimensions accommodating the insertion from above of the high voltage insulator 50, including the flange 54 thereof. The high voltage insulator 50, preferably in the form of a unitary glass-ceramic molding, includes a pair of terminal contacts 52 having threaded ends 55 to which are secured the pair of spring-like contacts 30 with suitable nuts 56. 
     Turning to FIG. 5, the interior of the housing 40 contains an unpotted high voltage ignition transformer 60 and a control circuit board 70 with an associated circuit breaker 75. 
     The control circuit board 70, circuit breaker 75, flame detector 35, low voltage control transformer 46 and associated wiring and a power semiconductor component (not shown) comprise an interrupted ignition burner control system of the type disclosed by U.S. Pat. No. 3,947,219, assigned to the assignee of the present invention. Such a control system is termed interrupted in that a high voltage ignition transformer, such as the transformer 60, associated with the burner control system, operates on a limited duty cycle wherein energization of the transformer is terminated when combustion within the chamber 16 is sensed by an associated flame detector, such as the flame detector 35. The control system interrupts the operation of the transformer 60 in intervals between ignitions of its associated oil burner 15. 
     The interior of the housing is defined by the upper surface of the base plate 48, the cover 41 and an L-shaped support wall 43 to which is mounted the control transformer 46 and a high-power semiconductor component (not shown) which utilizes the wall 43 as a heat sink. One end of the housing interior is associated with the end wall 44 (FIG. 3) of the cover 41, while the other end of the housing is defined by a leg 57 of the L-shaped support wall 43. 
     The transformer 60 includes a magnetic core of bilaterally symmetric U-I configuration formed of stacked laminations 61 of magnetic steel. Stacked U-shaped laminations form one end 62 of the core and two legs 65 thereof, the central portion of only one of the legs 65 being visible in FIG. 5, while stacked I-shaped laminations constitute the other end 63 of the core and close the open end of the U-shaped lamination stack. The laminations forming the core are fixed relative to each other in a conventional manner by suitable lamination fasteners 64 and connecting outer laminations 59 which extend the length of the core. The ends 62 and 63 of the transformer core are free of transformer coils. The legs 65 of the core are wrapped with transformer coils including a primary coil 66 and two high voltage secondary coils 67, 68. The secondary coils 67, 68 are side-by-side. The single primary coil extends along only a portion of one core leg 65 and is axially aligned with only one of the secondary coils with which it shares one of the core legs 65. While two side-by-side primary coils can be provided if desired, the illustrated and described bilaterally asymmetric primary coil arrangement, resulting from the provision of a primary coil on only one of the side legs 65, can be used with the interrupted ignition burner control system without undue heating due to magnetic flux aberrations. The added degree of heat associated with the asymmetry is dissipated during interruptions of transformer operations, and overall there is a net power savings compared with continuously operating systems, and a substantial manufacturing savings in the use of a single primary coil. 
     The transformer 60 is supported by an understraddling bracket 80 and fastened to it by means of the lamination fasteners 64, which are received in the openings 69 (FIG. 7) which are formed on bracket flanges 72. The flanges 72 directly support the lowermost of the laminations 61 at either end of the core. A cut-out 74 on one side of the bracket accommodates the primary coil 66. The bracket 80 is supported by the base plate 42 to which it is fastened with appropriate screws (not shown) which may be punch-point screws or which may be received in holes 77 (FIG. 7) in the mounting bracket 80. 
     The control circuit board 70 (FIG. 5) has an upper circuit board surface 78 and a lower circuit board surface 79, both of which serve as mounting means for circuit elements 75. The lower circuit board surface 79 is spaced above the upper surface 48 of the support plate 42 by means of a spacer wall 71 extending circumferentially about and in contact with the edge of the circuit board. 
     The circuit board 70 and the transformer 60 extend from respective ends of the housing, associated with the support wall leg 57 and the cover end wall 44, to an intermediate housing location wherein one end 62 of the transformer core is spaced above and overlaps an end portion of the circuit board 70 to advantageously provide compactness which could not be achieved if the transformer were potted or if there were coils on the ends of the transformer core. 
     FIG. 6 illustrates a transformer preassembly 95 prior to its installation on the base plate 42. The preassembly includes the transformer 60 (shown with the primary coil removed) and combined mounting and high voltage tap means including the mounting bracket 80 and the high voltage insulator 50. 
     The secondary coils 67, 68 each have a high voltage terminal leads wire 81 extending from the undersides 82 of the secondary coils 67, 68. These terminal wires 81 extend from the undersides 82 of the secondary coils at terminal points axially and transversely centered. Such locations are illustrated by the &#34;X&#34; marks 83 (FIG. 5) on the top sides of the secondary coils 67, 68, the terminal wires 81 extending from corresponding locations on the undersides 82 of the secondary coils 67, 68. 
     Due to high voltages maintained on the terminal wires 81 during energization of the unpotted transformer 60, strict spacing requirements must be met in order to reduce the risk of short circuiting to an acceptable extremely low level. Such spacing requirements are met by the provision of the high voltage insulator 50 which includes a pair of spaced bushings 53 each having a centered bore or aperture 58 arranged in apposition to its respective terminal point on the underside of the secondary coils, the apertures 58 receiving terminal contacts 52 therethrough. The terminal wires 81 extend through the bushing apertures 58 and are held in place against the side walls of the apertures 58 by terminal contacts 52. The terminal wires 81 are further held in place by the clamping action of terminal contact heads 90 and mounted ends 92 of the spring contacts 30, the tightening of nuts 56 onto threaded end 52 serving as clamping forces. Before such clamping forces are applied, terminal wires 81 are pulled taut such that their exposed portions which bridge the narrow gap represented by length &#34;b&#34; (FIG. 6) are minimal. 
     FIG. 8 represents the prealignment of the transformer secondary windings 67, 68 the mounting bracket 80 and the insulator 50 with terminal wire 81 extending through the bushings 53. The elements shown in FIG. 8 are mated to one another to form the preassembly shown in FIG. 6 whereupon the excess lengths of the terminal wires 81 are trimmed. During this mating, the insulator 50 is inserted upwardly through a window-like aperture 84 (FIG. 7) in the base face 83 of the mounting bracket 80. The flange 54 serves as a detent and abuts the base face 83 of the bracket 80. A tie down peg or pin 85 (FIG. 7) is inserted through an aperture 94 in a bracket side wall 88 and a centered transverse insulator aperture 54 (FIG. 6), until the inserted end 86 of the tie down pin abuts an opposing side wall 87 of the mounting bracket 80. 
     The ignition transformer and control package of the present invention advantageously provides combined mounting and high voltage tap means associated with a high voltage ignition transformer, the tap means and transformer together providing a unitary non-potted assembly mountable as a unit on a windowed mounting base with high voltage terminal contacts projecting below the window of the base (window 51) for contact with ignition electrodes powered by the transformer. 
     The risk of high voltage short circuiting is minimized without potting by the provision of a unitary molding providing a pair of side by side insulator bushings extending from below the housing base plate and directly unwardly into apposition with high voltage transformer terminal points. Associated terminal wires are each drawn through the center of a respective one of the insulator bushings downwardly into anchoring contact with associated terminal contacts extending to points exterior of the housing base plate. 
     The scope of the invention is not necessarily limited to the specific details of the illustrated embodiment, but is defined by the following claims.