Abstract:
A home appliance having an improved gas igniter (or ignitor) including an appliance body, at least one burner assembly supported in the appliance body to provide a heat source for cooking, with the burner assembly including a gas pipe, an igniter in operational communication with the gas pipe, the igniter including a heater element and a shroud covering a portion of the heater element, the shroud including a shroud body defining a chamber having the heater element therein, an inlet opening facing the gas pipe, an outlet opening facing away from the gas pipe, and a constriction intermediate the inlet opening and the outlet opening, thereby defining a fluid flow path through the chamber whereby a fluid stream is directed from the inlet opening, across the heater element, through the constriction to the outlet opening.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention is related broadly to home appliances that employ a heat-generating apparatus and, more particularly, to home appliances that use gas burners as a controlled heat source. 
         [0002]    Home appliances such as ranges and cooktops may use gas burners as a source of heat for cooking. Cooking appliances that may employ gas burners include freestanding ranges that include an oven and a cooktop as well as built-in, stand-alone, wall-mounted ovens. With respect to the present invention, references herein to ranges and built-in ovens may be used interchangablely and both may act as a platform for gas burner use. In addition, while the present application focuses on ranges and ovens, the invention described herein may have applicability with other appliances employing heat such as laundry dryers and the like. 
         [0003]    Gas burners utilize a gas supply such as natural gas or propane mixed with air to provide a combustible gas/air mixture for ignition by a resistive heater element. A user-controlled valve throttles the amount of gas available for the burner to thereby control the amount of heat energy applied by the burner flame to an oven cavity to raise the temperature within the cavity to a predetermined level for cooking. 
         [0004]    In general, a gas-fired oven burner operates when a user first starts the oven or when a hot oven drops below a predetermined temperature. There, a user control or a thermostat switches power to an igniter and a gas valve circuit which are connected in series. It should be noted that the term “igniter” may also be presented as “ignitor”. Both spellings are valid and describe the same structure. As power flows through the igniter the current draw causes the igniter to produce heat. The igniter includes a resistive heater element joined to a base, usually ceramic, for mounting and connection to a power source. A heat shield or shroud keeps wiring and other undesirable matter away from the heater element. 
         [0005]    Once the igniter draws a specific amount of current or achieves a pre-determined temperature; a gas valve opens to allow gas flow to the oven burner where the glowing hot igniter ignites the gas. Once the set temperature is achieved, the control stops all power to the ignition circuit which causes the igniter to dim and the oven gas valve to close thereby cutting off the burner flame. Cycling on and off continues in order to maintain the desired cooking temperature within the oven cavity. 
         [0006]    Once the igniter is activated, it rapidly heats to glowing and the gas should light off quickly. However, with conventional shrouds such is not always the case. 
         [0007]    As seen in  FIGS. 7A and 8A , a prior shroud  100  includes a shroud body  102  that conforms generally to the base of the igniter and partially surrounds the heater element. The body  102  includes vented walls  104  having openings  106  formed therein to allow heat to escape from the igniter while still providing igniter protection. With reference to  FIG. 8A , the heater element  110  is located generally centrally within the shroud  100  and partially surrounded by the vented walls  104 . The entire assembly  100  is in operational communication with a gas pipe  32  to produce a flame F. It should be noted that a flame F is shown in  FIG. 8A  and  FIG. 8B  for clarity. It will be understood that gas is emitted from the pipe prior to ignition. 
         [0008]    As the heater element  110  is heated, convection heat is emitted, as illustrated in  FIG. 8A  by rings C. Given the configuration of the shroud  100 , air is effectively pushed away from the heater element  110  by convection action as the heat from the heater element  110  causes a general airflow away from the heater element  110 . This convection flow can also cause the gas from the gas pipe  32  to be blown away from the heater element  110  thereby directing the gas into a region of the temperature field created by the heating element  110  that is at a lower temperature than areas closer to the heater element  110 , and tending to disburse the gas, causing a lean gas/air mixture. Accordingly, lighting gas ignition for flame F production is delayed until the outer reaches of the temperature field created by the heating element  110  are hot enough to ignite the gas. This time can vary among individual igniters, but has taken as long as eight (8) seconds. 
         [0009]    It is generally desirable to expect gas ignition within four (4) seconds or less after initiation of the ignition process. In addition, the Canadian Standards Association requires ignition within four (4) seconds or less before an appliance can be listed for sale in Canada. Prompt ignition is required to prevent accumulation of gas within the oven cavity which could prove dangerous. In addition to the initial heating of the oven, an unduly long wait for gas ignition can affect oven temperature stability and control, which can have a detrimental effect on appliance efficiency. 
         [0010]    Accordingly, there exists a need for a gas igniter to counter the tendency of convection heat to move gas away from the igniter. There also exists a need to incorporate such structure into the existing structure of the burner assembly and more particularly, in an igniter shroud. 
       SUMMARY OF THE INVENTION 
       [0011]    It is accordingly the intention of the present invention to provide a home appliance with an improved igniter, and an improved igniter that will ignite a cooking flame in a short amount of time, preferably within four seconds or less after gas becomes available. 
         [0012]    It is another object of the present invention to provide a home appliance with an improved igniter, and an improved igniter that will draw gas toward the heater element of the igniter to enhance the ability of the heater to rapidly ignite a cooking flame. 
         [0013]    To those ends, the present invention is directed to a home appliance having an improved gas igniter. The home appliance includes an appliance body and at least one burner assembly supported in the appliance body to provide a heat source for cooking. The burner assembly includes a gas pipe and an igniter in operational communication with the gas pipe. The igniter includes a heater element and a shroud covering a portion of the heater element. The shroud includes a shroud body defining a chamber having the heater element therein, an inlet opening facing the gas pipe, an outlet opening facing away from the gas pipe, and a constriction intermediate the inlet opening and the outlet opening, thereby defining a fluid flow path through the chamber whereby a fluid stream is directed from the inlet opening, across the heater element, through the constriction to the outlet opening. 
         [0014]    Preferably, the shroud body has two converging walls extending toward the constriction and two outlet walls extending away from the constriction. It is further preferred that the two outlet walls diverge to form a flared passageway defining a flue along the fluid flow path. 
         [0015]    Preferentially, the igniter includes a base portion and the shroud body has an elongate generally rectangular portion with the converging walls extending along a long axis of the shroud body. 
         [0016]    It is preferred that the constriction is in a corner of the elongate generally rectangular portion of the shroud body and the outlet walls extend from end portions of the converging walls. 
         [0017]    A home appliance according to claim  1  wherein a portion of the shroud body is preferably juxtaposed with a base portion of the igniter. 
         [0018]    The constriction preferably forms throat of a nozzle and the shroud body preferably has two converging walls extending toward the constriction and two outlet walls extending away from the constriction, whereby the shroud body forms a convergent/divergent nozzle. 
         [0019]    It is further preferred that the constriction is intermediate joined portions of the converging walls. 
         [0020]    The present invention can also be in the form of a gas igniter for a home appliance having least one burner assembly supported in the appliance body to provide a heat source for cooking. There, the gas igniter includes a heater element in operational communication with a gas pipe and a shroud covering a portion of the heater element. The shroud includes a shroud body defining a chamber having the heater element therein, an inlet opening facing the gas pipe, an outlet opening facing away from the gas pipe, and a constriction intermediate the inlet opening and the outlet opening, thereby defining a fluid flow path through the chamber whereby a fluid stream is directed from the inlet opening, across the heater element, through the constriction to the outlet opening. 
         [0021]    Preferably, the shroud body has two converging walls extending toward the constriction and two outlet walls extending away from the constriction. The two outlet walls preferably diverge to form a flared passageway defining a flue along the fluid flow path. 
         [0022]    It is further preferred that the igniter includes a base portion and the shroud body has a elongate generally rectangular portion with the converging walls extending along a long axis of the shroud body. 
         [0023]    Preferentially, the constriction is in a corner of the elongate generally rectangular portion of the shroud body and the outlet walls extend from end portions of the converging walls. 
         [0024]    Preferably, a portion of the shroud body is juxtaposed with a base portion of the igniter. 
         [0025]    It is preferred that the constriction forms a throat of a nozzle and the shroud body has two converging walls extending toward the constriction and two outlet walls extending away from the constriction, whereby the shroud body forms a convergent/divergent nozzle. 
         [0026]    Preferably, the constriction is intermediate joined portions of the converging walls. 
         [0027]    By the above, the present invention provides a straightforward device that can be economically manufactured. Further, the present invention enhances safety during gas ignition and provides improved oven temperature stability and control. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a side view of a home appliance in the form of a range according to the preferred embodiment of the present invention; 
           [0029]      FIG. 2  is a perspective view of the oven cavity illustrating the location of the gas burner assembly; 
           [0030]      FIG. 3  is a perspective view of the oven cavity illustrating the location of the gas pipe and igniter; 
           [0031]      FIG. 4  is a perspective view of the gas pipe and igniter illustrated in  FIG. 4 ; 
           [0032]      FIG. 5  is an exploded view of the gas pipe and igniter assembly; 
           [0033]      FIG. 6  is a perspective view of an igniter according to the preferred embodiment of the present invention; 
           [0034]      FIG. 7A  is a perspective view of a prior art igniter shroud; 
           [0035]      FIG. 7B  is a perspective view of an igniter shroud according to the present invention; 
           [0036]      FIG. 8A  is a diagrammatic end view of a prior art igniter and shroud; 
           [0037]      FIG. 8B  is a diagrammatic end view of an igniter and shroud according to the preferred embodiment of the present invention; and 
           [0038]      FIG. 9  is a perspective view of an igniter shroud according a second preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0039]    Turning now to the drawings and, more particularly to  FIG. 1 , a home appliance in the form of a range is illustrated generally at  10  and includes a generally rectangular, floor-standing range body  12  housing an oven  14  and a cooktop  20 . The oven  14  defines an internal oven cavity  16  for cooking covered by an access door  18 . The cooktop  20  is above the oven and provides a generally horizontal cooking surface. A vertically oriented backsplash  22  extends upwardly from the rear portion of the cooktop  20  and a first control panel  24  with an oven control  26  is mounted to the backsplash  22 . A second control panel  28  extends downwardly from the front portion of the cooktop  20  toward the oven  14 . A series of control knobs  30  is arranged linearly across the second control panel  28  and is provided for cooktop burner control. 
         [0040]      FIG. 1  is shown broken open to illustrate the general location of the present invention within the oven cavity  16 . There, the burner assembly  30  is located near the base of the oven and is in fact underneath a panel that forms the bottom wall of the oven cavity  16 . The burner includes an elongate gas pipe  32  that is perforated with gas distribution holes  34 . A generally planar heat distributor  36  is disposed above the gas pipe  32  to receive heat from flames emitted from the gas pipe  32  and to distribute the heat within the oven cavity  16  for cooking purposes. An igniter  40  is shown in block form attached to an end portion of the gas pipe  32 , as will be seen in greater detail hereinafter, and is in electrical communication with the range power supply using electrical wiring  42 . 
         [0041]    Turning now to  FIG. 2 , the oven cavity  16  includes a well in which the burner assembly  30  resides. The well is illustrated uncovered in  FIG. 2  to display the burner assembly  30 . During oven use, the well is covered with a generally planar panel (not shown) to separate the burner assembly  30  from the interior of the oven cavity  16 . The gas pipe  32  extends from back to front with respect to the oven cavity  16 . The heat distributor  36  is centered over the gas pipe and is formed in a shallow V-shape for proper heat distribution. 
         [0042]      FIG. 3  illustrates the gas burner assembly  30  with the heat distributor  36  removed. Accordingly, the relationship between the igniter  40  and the gas pipe  32  is displayed, with the igniter  40  extending in a generally parallel manner with the gas pipe  32 . The igniter  40  includes a shroud  50  according to the preferred embodiment of the present invention. The structure of the present igniter shroud  50  will be discussed in greater detail hereinafter. 
         [0043]    Turning now to  FIG. 4 , the igniter  40  includes a shroud  50  according to the present invention and is mounted adjacent or directly to the gas pipe  32  across from the gas delivery openings  34 . The igniter  40  may be mounted to the gas pipe  32  in one of several different ways using the shroud  50 .  FIG. 4  shows a bracket  41  that wraps around the pipe  32  and connects to the shroud  50 . Another bracket  43  may provide a different mounting location. Due to the relationship between the igniter  40  and the gas pipe  32 , gas from the gas pipe  32  is directed toward the igniter  40 . 
         [0044]      FIG. 5  illustrates of the gas burner assembly  30  exploded to show the basic burner parts in their entirety. These parts include the L-shaped gas pipe  32  along with the igniter  40  including the shroud  50  and electrical wiring  42 . Proceeding inwardly from the gas pipe  32 , a vertical bracket  38  is provided to mount the gas burner assembly  30  to the walls within the oven cavity (not shown in  FIG. 5 ). Finally, the heat distributor  36  is positionable over the gas pipe to evenly distribute the heat produced by the flame within the oven cavity, as described above. 
         [0045]    Turning now to  FIG. 6 , the igniter  40  includes a resistive heater element  46  formed in a serpentine manner and inserted in a ceramic base  44 . The base  44  is generally rectangular. Power is supplied to the resistive heater element  46  through electrical wiring  42 . The shroud  50  forms a cavity  54  that is configured for telescopic receipt of the base  44  with the elongated shroud body extending far enough away from the base to contain the heating element  46 . 
         [0046]    The shroud  50  defines a working area for the resistive heating element  46 , and, as will be discussed in greater detail hereinafter, a fluid flow path  80  across the heater element  46 . The shroud  50  is configured and positioned to receive sufficient gas from the gas pipe  32  (not shown in  FIG. 6 ) so that the resistive heater element  46  can ignite the gas being emitted from the gas pipe  32  to produce a flame for heat distribution by the heat distributor  36  and ultimate heating of the oven. 
         [0047]    Continuing with reference to  FIG. 6 , the shroud  50  has a generally rectangular shroud body  52  that includes a planar back wall  56  extending the length of the shroud body  52 . The back wall  56  forms a first converging wall that converges toward an imaginary junction with a second converging wall  58 , wherein both the back wall  56  and the second converging wall  58  are terminated before they meet. At the other end of the second converging wall  56 , a flange  60  projects approximately 90 degrees away therefrom and partially overrides the base  44  of the igniter  40 . A side wall  62  projects upwardly approximately 90 degrees away from the back wall  56  and parallels the second converging wall  58 , terminating in a flange  64 . The flange  64  projects away from the side wall  62  at approximately a 90 degree angle and partially overrides the base  44  of the igniter  40  at a position oppositely from the other flange  60 . An inlet opening  74  is defined between the edges of the flanges  60 ,  64  for entry of air and gas into the cavity  54 . 
         [0048]    An end wall  72  is formed from the material of the back wall and  56  and projects away therefrom at approximately 90 degrees. Optionally, a mounting bracket  43  may be formed from material of the side wall  62  and bent to extend away from the side wall  62  in a manner planar with the back wall  56 . 
         [0049]    A first outlet wall  68  extends outwardly from the back wall  56  in a manner that is not coplanar therewith. Similarly, a second outlet wall  70  extends away from the second converging wall  58  at an angle that is not coplanar therewith. A passageway for fluid flow is thereby formed between the first outlet wall  58  and the second outlet wall  70 . The terminus of the outlet walls  68 ,  70  forms the outlet opening  76  for the shroud  50  at the end of the fluid flow path defined by the shroud  50 . The outlet walls,  68 ,  70  preferably diverge, but may also extend in a parallel manner. Together, the outlet walls  68 ,  70  form a flue. 
         [0050]    The back wall  56  and the converging wall  58  extend along planes that are approximately 90 degrees to one another yet never meet. The gap between the back wall  56  and the converging wall  58  forms a constriction  78  in the fluid flow path  80 . 
         [0051]    The shroud  50  thereby defines the fluid flow path  80  extending from the inlet opening  74  across the resistive heater element  46 , through the constriction  78 , away from the constriction  78  intermediate the outlet walls  68  and  70  and, finally, out through the outlet opening  76 . Further, the back wall  56 , acting as a first converging wall, the second converging wall  58 , the constriction  78  and the two outlet walls  68 ,  70  together form a converging/diverging nozzle with the constriction  78  acting as a throat. 
         [0052]    Turning now to  FIG. 7B , the fluid flow path through the shroud  50  is illustrated by arrows  80 . The generally rectangular shape of the shroud  50  allows flanges  60 ,  64  to project away from the second converging wall  58  and the sidewall  62  to thereby define the inlet opening  74 . The heating element, illustrated in phantom at  46 , extends into the cavity  16  from the open end  48  of the shroud  50  and sits adjacent the inlet opening  74 . The fluid flow path  80  is defined by the back wall  56  and the second converging wall  58 , the constriction  78  located at one corner of the generally rectangular shroud  50 , and the outlet walls  68 ,  70  projecting away from the back wall  56  and the second converging wall  58  at the constriction  78 , terminating at the outlet  76 . Accordingly, the gas/air mixture enters the inlet opening  74  to start along the fluid flow path  80 . From the inlet opening  74  the gas/air mixture flows across the heater element  46 . The gas/air mixture is guided toward the constriction  78  by the converging walls  56 ,  58  and exits the chamber  16  through the constriction  78 . From there, the gas/air mixture flows outwardly toward the outlet opening  76  along a path between the outlet walls  68 ,  70  until ignition. 
         [0053]    In operation, and with reference to  FIG. 8B , the heater element  46  is activated and heats the air within the chamber  16 . As the air turns hotter closer to the heater element  46 , convection, illustrated by convection lines C, causes airflow away from the heater element  46 . Heated air at the constriction  78  creates a low pressure region and air is thereby drawn from the inlet opening  74  along with gas being emitted from the gas pipe  32 , thereby forming the gas/air mixture for ignition and combustion. 
         [0054]    Convection-driven fluid flow is then established wherein gas and air are drawn through the inlet  74 , across the heater element  46 , outwardly through the passageway or flue intermediate the outlet walls  68 ,  70  and ultimately through the outlet opening  76 . Accordingly, the gas/air mixture is drawn into a region of higher temperature closer to the heater element  46  and therefore, ignition occurs sooner than it would occur in a prior appliance as hereinbefore discussed with reference to  FIG. 8A . 
         [0055]    Accordingly, the present igniter can ignite the gas in less than four (4) seconds which the current igniter as illustrated in  FIG. 8A  cannot light the gas in less than four (4) seconds. Therefore, the present home appliance with the improved igniter can operate more efficiently by using less gas and bringing the oven to temperature sooner than with prior igniters. Further, safety is enhanced since the chance of unburned gas collecting within the oven cavity is reduced. 
         [0056]    The shroud  50  may be constructed from two or more separate pieces, each with its own mounting arrangement, or it can be formed from a single sheet blank. In either case, the preferred material is some form of metal. As seen in  FIG. 9 , formation of the shroud  50  from a single sheet blank results in outer walls  68 ,  70  that extend outwardly a distance equal to one-half the width of the constriction  78  and do not extend longitudinally the full length of the shroud body  52 . Accordingly, the back wall  56  and the second converging wall  58  are joined by junction portions  82  at either end of the shroud  50 . Optionally, such joined portions  82  could be placed anywhere along the shroud body  52  with multiple outlet walls projecting away from the respective back wall  56  and converging wall  58 . For maximum nozzle effect, it is preferable that the constriction  78  extend at least the length of the heater element  46  at a position adjacent to heater element  46 . Optionally, a number of small flues may be formed by a number of outlet walls with multiple individual constrictions and multiple joined portions of the converging walls. Finally, using multiple components, virtually any shape can be applied to the shroud between the inlet opening and outlet opening, provided the characteristics of a converging/diverging nozzle are achieved. 
         [0057]    It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of a broad utility and application. While the present invention is described in all currently foreseeable embodiments, there may be other, unforeseeable embodiments and adaptations of the present invention, as well as variations, modifications and equivalent arrangements, that do not depart from the substance or scope of the present invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.