Abstract:
A radiant electric heater comprises at least first and second adjacent heating zones ( 8, 12 ), the first heating zone ( 8 ) including a first heating element ( 6 ) and the second heating zone ( 12 ) including a second heating element ( 10 ). The heating elements are supported relative to a base ( 4 ) of thermal and electrical insulation material. Terminal means ( 30 ) is provided at a periphery of the heater for connecting the first and second heating elements ( 6, 10 ) to a source of electrical energy. The heating elements ( 6, 10 ) are formed from a single elongate electrically conductive material, the heating elements having a conjoined first terminal region ( 20 ) connected to a first electrical connector ( 32 ) at the terminal means ( 30 ), having a free second terminal region ( 18 ) connected to a second electrical connector ( 34 ) at the terminal means ( 30 ), and having a free third terminal region ( 16 ) connected to a third electrical connector ( 36 ) at the terminal means ( 30 ). At least one of the first, second and third terminal regions ( 20, 16, 18 ) traverses the second heating zone ( 12 ) for connection to the respective electrical connector ( 32, 34, 36 ).

Description:
[0001]     This invention relates to a radiant electric heater and in particular relates to a radiant electric heater, for example for a glass-ceramic cooking appliance, comprising at least first and second adjacent heating zones.  
       DESCRIPTION OF PRIOR ART  
       [0002]     It is known to manufacture radiant electric heaters for glass-ceramic top cooking appliances which are provided with two heating zones in the form of an inner, circular, heating zone and an outer, annular, heating zone extending around the inner zone. The inner and outer heating zones may, or may not, be separated by a dividing wall of thermal insulating material so as to define, if desired, separate and distinct heating zones on the glass-ceramic cooking surface. The inner and outer heating zones are each constituted by a heating element in the form of a ribbon or coil material which is configured to occupy the space allotted to the heating zone concerned and which is supported on a base of thermal insulation material provided in a dish-like support. Thus, a first heating element is provided in the inner heating zone and a second heating element is provided in the outer heating zone. A probe-type temperature sensor, or other suitable type of temperature sensor, extends over the outer and inner heating zones and is adapted to be responsive in particular to the temperature of the glass-ceramic cooking surface in the region of the inner heating zone. The heating elements are connected to the temperature sensor and to a source of electrical power by way of a terminal block provided at a peripheral wall of the supporting dish. The terminal block is provided adjacent to the temperature sensor and is formed with three electrical connectors, a first connector adjacent to the temperature sensor, a second connector remote from the temperature sensor and a third connector intermediate the first and second connectors. It is common practice in such heaters to connect the first connector externally of the supporting dish directly to an electrical connector of the temperature sensor, for example by means of welding, and internally of the dish to one end of each of the first and second heating elements. It is also common practice to connect the other end of the second heating element to the second connector within the dish and to connect the other end of the first heating element to the third connector within the dish, the connection between the end of the first heating element and the third connector being by way of a link which is secured at one end of the first heating element, passes over the end of the second heating element, and is connected to, or integral with, the third connector.  
         [0003]     Disadvantages of such known radiant electric heaters are that the presence of two separate heating elements and the manner in which the heating elements are secured to the electrical connectors, particularly involving one or more separate links, render the insertion of the heating elements into their positions on the base of insulating material in the supporting dish unsuitable for automatic production methods.  
       OBJECT OF THE INVENTION  
       [0004]     It is an object of the present invention to overcome or minimise the above problems.  
       SUMMARY OF THE INVENTION  
       [0005]     According to the present invention there is provided a radiant electric heater comprising at least first and second adjacent heating zones, the first heating zone including a first heating element and the second heating zone including a second heating element, the heating elements being supported relative to a base of thermal and electrical insulation material, and terminal means provided at a periphery of the heater for connecting the first and second heating elements to a source of electrical energy, wherein the heating elements are formed from a single elongate electrically conductive member, the heating elements having a conjoined first terminal region connected to a first electrical connector at the terminal means, having a free second terminal region connected to a second electrical connector at the terminal means, and having a free third terminal region connected to a third electrical connector at the terminal means, wherein at least one of the first, second and third terminal regions traverses the second heating zone for connection to the respective electrical connector.  
         [0006]     The heating elements may be in the form of a ribbon secured upright into the base of thermal and electrical insulation material.  
         [0007]     The first heating zone may be circular, with the second heating zone being at least part-circular and at least partially surrounding the first heating zone. The conjoined terminal regions of the heating elements may comprise a looped distal region of the second heating element welded to a portion of the first heating element.  
         [0008]     A peripheral wall may be provided around the external periphery of the heater.  
         [0009]     A dividing wall may be provided between the adjacent heating zones.  
         [0010]     A temperature-responsive device may be provided for sensing the temperature in the region of at least the first heating zone.  
         [0011]     The at least one of the first, second and third terminal regions traversing the second heating zone may comprise a plurality of portions of the elongate electrically conductive member electrically connected in parallel.  
         [0012]     The plurality of portions of the elongate electrically conductive member electrically connected in parallel may comprise a plurality of elongate close meanders of the elongate electrically conductive member traversing the second heating zone and electrically interconnected thereacross at least at opposite ends thereof, such as by welding, folding or crimping.  
         [0013]     The meanders may comprise elongate substantially straight sections interconnected by one or more looped ends and may have one or more looped ends thereof which has or have been severed subsequent to electrical interconnection of the meanders in parallel.  
         [0014]     One or more of cuts and welds may be provided at one or more portions of the electrically conductive member, in particular to respectively disconnect and reconnect one or more portions of the elongate electrically conductive member, particularly at the terminal regions thereof.  
         [0015]     The at least one of the terminal regions of the elongate electrically conductive member may traverse the second heating zone such as to overlie or underlie the second heating element and spaced therefrom.  
         [0016]     The at least one of the terminal regions of the elongate electrically conductive member may be provided in one or more recesses or grooves formed in the base of thermal and electrical insulation material underlying the second heating element.  
         [0017]     The free first terminal region may be provided in the second heating zone at an end of the second heating element remote from the conjoined terminal region, with the free second terminal region being provided at an end of the first heating element remote from the conjoined terminal region, the conjoined terminal region and the free first terminal region traversing the second heating zone.  
         [0018]     The at least one of the terminal regions traversing the second heating zone may be substantially non-visibly radiating, or of reduced visible radiance relative to the remainder of the heating elements, when the heater is energised.  
         [0019]     The third electrical connector may be positioned intermediate the first and second electrical connectors.  
         [0020]     The terminal regions of the heating elements may be connected to the respective first, second and third electrical connectors by welding.  
         [0021]     The terminal means may comprise at least one terminal block supported at the periphery of the heater and accommodating the first, second and third electrical connectors.  
         [0022]     The elongate electrically conductive member forming the first and second heating elements with their conjoined and free terminal regions may be provided as a pre-formed component for supporting relative to the base of thermal and electrical insulation material.  
         [0023]     A dish-like support, such as of metal, may be provided, receiving the base of thermal and electrical insulation material. The terminal means may be supported at a peripheral rim of the dish-like support.  
         [0024]     By means of the present invention, a cost-effective radiant electric heater is provided having at least two heating zones and in which at least two heating elements and their associated terminal regions are integrally provided for assembly onto a base of thermal and electrical insulation material, to form the heater. An assembly of the heating elements and their associated terminal regions is readily provided by automated techniques, suitably comprising the use of a jig means into which the integral heating elements are wound, and their terminal regions formed. The assembly is then readily transferred from the jig to the base of insulation material and into the surface of which it is suitably impressed and secured.  
         [0025]     For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a plan view of an embodiment of a radiant electric heater according to the present invention;  
         [0027]      FIG. 2  is a perspective view of a portion of ribbon form heating element material as used in the heater of  FIG. 1 ;  
         [0028]      FIG. 3  is a perspective view of part of a jig in which is formed the integral heating elements and terminal regions thereof of the heater of  FIG. 1 ; and  
         [0029]      FIG. 4  is a plan view of another embodiment of a radiant electric heater according to the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]     Referring to  FIG. 1 , a radiant electric heater comprises a dish-like support  2 , for example of metal, containing a base  4  of thermal and electrical insulation material, for example compressed microporous thermal and electrical insulation material. Secured to the base  4  is a first heating element  6  of ribbon form material inserted upright into the base, the first heating element  6  occupying a substantially circular inner first heating zone  8  in the central region of the heater. Also secured to the base  4  is a second heating element  10  of ribbon form material inserted upright into the base, the second heating element  10  occupying a substantially annular outer second heating zone  12  around the peripheral region of the heater. The first and second heating elements  6 ,  10  are integral, formed of a single elongate electrically conductive member in the form of a length of the ribbon form heating element material. The integral ribbon form heating elements  6 ,  10  may be of corrugated from, such as shown in  FIG. 2  and may be provided with legs  14 , integral therewith or secured thereto, for insertion into the base  4  of insulation material.  
         [0031]     As will be described in detail hereinafter, the first heating element  6  has a free terminal region  16  and the second heating element  10  has a free terminal region  18 . The first and second heating elements  6 ,  10  also have a conjoined terminal region  20 .  
         [0032]     In practice, the first heating element  6  is arranged to be energised whenever the heater is energised, irrespective of the size of a cooking utensil placed on a cooking surface (not shown) below which the heater is arranged, while the second heating element  10  is only energised in conjunction with the first heating element  6 , and only when a relatively large cooking utensil is used such that the cooking utensil overlies both the first and second heating elements  6 ,  10 .  
         [0033]     A peripheral wall  22  of thermal insulation material extends around the periphery of the heater between the outer second heating zone  12  and an upstanding rim of the dish-like support  2 .  
         [0034]     A dividing wall  24  of thermal insulation material may optionally be provided between the first  8  and second  12  heating zones.  
         [0035]     A probe-type temperature-responsive device  26  extends from a periphery of the heater, a temperature-sensing portion  28  of the device  26  extending substantially over the first heating element  6  in the inner first heating zone  8 .  
         [0036]     A terminal block  30  is mounted on the upstanding peripheral rim of the dish-like support  2  adjacent to the temperature-responsive device  26  and is provided with a first electrical connector  32  adjacent to the temperature-responsive device  26 , a second electrical connector  34  remote from the temperature-responsive device and with a third electrical connector  36  intermediate the first and second electrical connectors.  
         [0037]     Externally of the dish-like support  2 , the first electrical connector  32  may be connected directly, for example by welding, to an electrical connector of the temperature-responsive device  26 .  
         [0038]     The conjoined terminal region  20  of the first and second heating elements  6 ,  10  comprises meanders of the ribbon form heating element material traversing the second heating zone  12  and consisting of two elongate substantially straight sections  38 ,  40  interconnected by a loop  42 . Such two elongate substantially straight sections  38 ,  40  may traverse the second heating zone  12  such that they overlie or underlie and are spaced from the second heating element  10 . They are preferably arranged to underlie the second heating element  10  and are provided in one or more recesses or grooves pressed into the base  4  of insulation material underneath the second heating element  10 . The two elongate substantially straight sections  38 ,  40  are electrically connected in parallel by welding them together at regions  44  and  46  at opposite ends thereof. They are also welded to the first electrical connector  32  inside the heater. The loop  42  is effectively redundant and is removed by severing, suitably prior to locating the integral heating elements  6 ,  10  on the base  4 .  
         [0039]     The free terminal region  16  of the first heating element  6  likewise comprises meanders of the ribbon form heating element material traversing the second heating zone  12  and consisting of two elongate substantially straight sections  48 ,  50 , interconnected by a loop  52 . Section  48  is open-ended. The sections  48 ,  50  traverse the second heating zone  12 , preferably underlying and spaced from the second heating element  10  in the same way as described for the sections  38 ,  40  of the conjoined terminal region  20 . The two elongate substantially straight sections  48 ,  50  are electrically connected in parallel by welding them together at regions  54 ,  56  at opposite ends thereof. They are also welded to the third electrical connector  36  inside the heater. The loop  52  is effectively redundant and is removed by severing in the same way as the loop  42 .  
         [0040]     The free terminal region  18  of the second heating element  10  in the outer second heating zone  12  is electrically connected by welding to the second electrical connector  34 .  
         [0041]     The heater is operated either by electrically connecting a power supply (not shown) to the electrical connectors  32  and  36  to energise only the first heating element  6 , or by electrically connecting the power supply to the electrical connectors  34  and  36  to energise both the first heating element  6  and the second heating element  10  in parallel.  
         [0042]     Because the terminal regions  16  and  20  comprise two sections of ribbon form material connected in parallel, they emit substantially no visible radiation, or less visible radiation than the remainder of the heating elements  6 ,  10  when energised, thereby eliminating any requirement for providing shielding or screening of these terminal regions.  
         [0043]     The integral first and second heating elements  6 ,  10  with their terminal regions  16 ,  18  and  20  are advantageously produced as a pre-formed component for securing into the base  4  of insulation material. Such a pre-formed component is suitably prepared by winding the integral first and second heating elements  6 ,  10 , with their terminal regions  16 ,  18 ,  20 , into a jig and then transferring the resulting pre-formed component from the jig to the base  4  of insulation material by appropriate pressing. Part of such a jig is shown in  FIG. 3 . The jig  58  has grooves  60  into which the second heating element  10  is first wound. This is followed by winding in of the first heating element  6  and the conjoined terminal regions  20  and the free terminal region  16 .  
         [0044]     Only the conjoined terminal regions  20  are shown in  FIG. 3 , the free terminal region  16  being similarly arranged. As shown in  FIG. 3 , the two elongate substantially straight sections  38 ,  40  of the conjoined terminal regions  20  are located in grooves  62  in the jig  58 , overlying the outer heating element  10 . The welds  44  and  46  are formed by means of welding heads  64 ,  66  and the loop  42  is then removed by suitable cutting means  67 .  
         [0045]     The jig  58  is then located with the face  68  thereof in contact with the base  4  of insulation material in the dish-like support  2  of the heater and pressure is applied to transfer the pre-formed assembly of the heating elements  6 ,  10 , together with their terminal regions  16 ,  18 ,  20 , to the base  4  and to secure the assembly to the base  4 , with the terminal regions  16 ,  20  deeply recessed into the base  4  and with the outer heating element  10  overlying and spaced from the terminal regions  16 ,  20 .  
         [0046]     Another embodiment of a radiant electric heater according to the present invention, with an alternative arrangement of the terminal regions, is illustrated in  FIG. 4 . Here, as in  FIG. 1 , a dish-like support  2  is provided, with a base  4  of thermal and electrical insulation material, a peripheral wall  22 , and an optional dividing wall  24 . First and second heating elements  6  and  10  are integrally provided in an inner first heating zone  8  and an outer second heating zone  12  respectively. Conjoined terminal regions  20  are provided for the heating elements  6 ,  10  and free terminal regions  16  and  18  are provided for the first  6  and second  10  heating elements respectively.  
         [0047]     The terminal regions  16  and  20  comprise meanders of the ribbon form heating element material traversing the second heating zone  12 , one consisting of three elongate substantially straight sections  70 , extending at one end region of the first heating element  6 , interconnected by loops  72 ,  74 , the other consisting of three elongate substantially straight sections  76 , extending at the other end region of the first heating element  6 , and interconnected by loops  78 ,  80 . The terminal regions  16 ,  20  traverse the second heating zone  12  in the same way as previously described with reference to  FIG. 1 .  
         [0048]     The elongate substantially straight sections  70  of the conjoined terminal regions  20  are electrically connected in parallel by welding them together at regions  82 ,  84  at opposite ends thereof. A looped distal region  86  of the second heating element  10  is also electrically connected by the weld  84  to one of the end regions of the first heating element  6  to form the conjoined terminal regions  20 . The elongate substantially straight sections  76  of terminal region  16  are also electrically connected in parallel by welding them together at regions  88 ,  90  at opposite ends thereof. The loops  72 ,  74 ,  78 ,  80  are effectively redundant and may be removed by cutting, if required.  
         [0049]     The conjoined terminal region  20  is welded to electrical connector  32  of the terminal block  30 , inside the heater and the terminal region  16  is welded to electrical connector  36  of the terminal block  30 , inside the heater. A free end terminal region  18  of the second heating element  10  is welded to electrical connector  34  of the terminal block  30 , inside the heater.  
         [0050]     As a consequence of the arrangement of the first and second heating elements  6 ,  10  in the heater of  FIG. 4  and the provision of the heating elements and the terminal regions  16 ,  18 ,  20  thereof as an integral component, it is necessary to cut the ribbon form heating element material at region  92  and to weld a resulting free end portion  94  to the free end terminal region  18  of the second heating element  10  at a weld region  96 .  
         [0051]     The radiant electric heater shown in  FIGS. 1 and 4  can be modified in a number of respects. For example, the radiant electric heater need not be circular, but could be, for example, oval in configuration with the first heating element  6  occupying a substantially circular heating zone  8  and the second heating element  10  occupying a part-circular (or crescent shaped) heating zone  12  adjacent to the circular heating zone  8 . Furthermore, a heater could be provided having more than two, for example three, heating zones, such as in concentric arrangement.  
         [0052]     Instead of welding being used to electrically connect in parallel the sections of the terminal regions  16  and  20  traversing the second heating zone  12 , other techniques, such as crimping or folding could be used.