Title:
Heat activated air shutter for fireplace
Kind Code:
A1


Abstract:
The present invention is directed to a heating unit, such as a fireplace, including an interior housing forming a combustion chamber. The housing includes a top wall, a rear wall and sidewalls defining an exterior housing about the combustion chamber. A burner assembly is positioned to provide combustion to the combustion chamber and a heat-activated shutter is provided in communication with the burner assembly for controlling flow of air into the burner assembly.



Inventors:
Almasri, Rashed (Ft. Wayne, IN, US)
Beal, Thomas J. (Ossian, IN, US)
Application Number:
11/489742
Publication Date:
07/26/2007
Filing Date:
07/19/2006
Primary Class:
International Classes:
F24B1/18
View Patent Images:
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Primary Examiner:
PRICE, CARL D
Attorney, Agent or Firm:
MCDONNELL BOEHNEN HULBERT & BERGHOFF LLP (CHICAGO, IL, US)
Claims:
We claim:

1. A gas heating unit, comprising: a combustion chamber; and a burner housing assembly positioned to provide combustion to said combustion chamber, wherein said burner housing assembly includes a burner housing and a gas and air mixing assembly in communication with said burner housing, said gas and air mixing assembly functioning to mix gas and air to provide a yellow appearing flame instantaneously after initiation of combustion.

2. The gas heating unit of claim 1, wherein said gas and air mixing assembly is automatically responsive to changes in temperature to maintain said yellow appearing flame over time.

3. A gas heating unit, comprising: a combustion chamber; and a burner housing assembly positioned to provide combustion to said combustion chamber, wherein said burner housing assembly includes a burner housing and a gas and air mixing assembly in communication with said burner housing; said gas and air mixing assembly including a mixing tube assembly, said the mixing tube assembly including a mixing tube having at least one air opening formed at an outer end thereof and a shutter collar assembly sized, shaped and positioned to seal with said at least one air opening of said mixing tube, said shutter collar assembly being attached to a bi-metal coil spring, said bi-metal coil spring being responsive to changes in temperature to withdraw said shutter collar assembly from said at least one air opening in response to an increase of temperature from an ambient temperature and permitting air to enter said at least one air opening.

4. The gas heating unit of claim 3, wherein said burner housing includes a burner housing opening sized and shaped to receive said mixing tube.

5. The gas heating unit of claim 3, wherein said at least one air opening includes an upper air opening and a lower air opening.

6. The gas heating unit of claim 5, wherein said shutter collar assembly includes a first shutter collar having a first shutter collar inside surface and a first shutter gasket attached to said first shutter collar inside surface.

7. The gas heating unit of claim 6, wherein said shutter collar assembly includes a second shutter collar having a second shutter collar inside surface and a second shutter gasket attached to said second shutter collar inside surface.

8. The gas heating unit of claim 7, wherein said upper air opening includes a first shutter collar subassembly and said lower air opening includes a second shutter collar subassembly.

9. The gas heating unit of claim 8, wherein said first shutter collar subassembly is attached to an upper bi-metal coil spring and said second shutter collar subassembly is attached to a lower bi-metal coil spring.

10. A burner housing assembly for use in a heating unit, comprising: a burner housing and a gas and air mixing assembly in communication with said burner housing; said gas and air mixing assembly including a mixing tube assembly, said the mixing tube assembly including a mixing tube having at least one air opening formed at an outer end thereof and a shutter collar assembly sized, shaped and positioned to seal with said at least one air opening of said mixing tube, said shutter collar assembly being attached to a bi-metal coil spring, said bi-metal coil spring being responsive to changes in temperature to withdraw said shutter collar assembly from said at least one air opening in response to an increase of temperature from an ambient temperature and permitting air to enter said at least one air opening.

11. The burner housing assembly of claim 10, wherein said burner housing includes a burner housing opening sized and shaped to receive said mixing tube.

12. The burner housing assembly of claim 10, wherein said at least one air opening includes an upper air opening and a lower air opening.

13. The burner housing assembly of claim 12, wherein said shutter collar assembly includes a first shutter collar having a first shutter collar inside surface and a first shutter gasket attached to said first shutter collar inside surface.

14. The burner housing assembly of claim 13, wherein said shutter collar assembly includes a second shutter collar having a second shutter collar inside surface and a second shutter gasket attached to said second shutter collar inside surface.

15. The burner housing assembly of claim 14, wherein said upper air opening includes a first shutter collar subassembly and said lower air opening includes a second shutter collar subassembly.

16. The burner housing assembly of claim 15, wherein said first shutter collar subassembly is attached to an upper bi-metal coil spring and said second shutter collar subassembly is attached to a lower bi-metal coil spring.

17. The burner housing assembly of claim 16, further including a spring plate connected to said mixing tube, said spring plate having a pair of spring tabs extending therefrom, each of said pair of spring tabs positioned adjacent a respective one of said upper air opening and said lower air opening.

18. The burner housing assembly of claim 17, wherein said upper bi-metal coil spring is attached to an upper of said pair of spring tabs at a mounting portion thereof and said lower bi-metal coil spring is attached to a lower of said pair of spring tabs at a mounting portion thereof.

19. The burner housing assembly of claim 18, when said upper bi-metal coil spring is attached to a first shutter collar subassembly at an attachment portion thereof and said lower bi-metal coil spring is attached to a lower shutter collar subassembly at an attachment portion thereof.

Description:

This application claims benefit from U.S. Provisional Application No. 60/700,639, filed Jul. 19, 2005.

FIELD OF THE INVENTION

The present invention relates generally to fireplaces and similar devices. In particular, the present invention relates to an apparatus for a fireplace unit or the like that regulates primary airflow to a burner of a fireplace. More particularly, the present invention includes an air shutter assembly automatically responsive to heat for controlling airflow to a main burner and/or a secondary burner to a gas fireplace or similar heating/lighting unit.

BACKGROUND OF THE INVENTION

Fireplaces are desirable features in the home. However, devices that burn non-solid materials, such as gas, or that produce heat electrically have gradually replaced traditional wood or other solid fuel-burning fireplaces. Like, wood, the combustion of gas does provide real flames and heat, but requires a careful mixing of gas and air for optimal performance and a realistic flame. This aspect of the gas fireplace, and similar appliances, typically involves the delivery of air for combustion to an arrangement or device where the air is mixed with gaseous fuel, e.g., natural gas and propane (“gas”). Clearly, it is advantageous that the air and gas are mixed at a ratio for proper combustion. Then, the mixed air and gas are delivered to a burner, and ultimately provided to a combustion chamber of the fireplace. In some instances, the mixing of air and gas is accomplished in the actual burner itself.

Multiple such arrangements have been created that are passive in nature, such as manifolds of a given size and shape with orifices designed to deliver a fixed ratio of air and gas for combustion. This ratio is typically optimized at a steady state, heated operating condition. It is well known that steady state operation of a gas fireplace typically takes 30 minutes or more. Some manifolds, ducts, inlet passages, air passages and the like are routed through the fireplace to preheat the combustion air and increase the efficiency of the fireplace. One example of such a device is illustrated in U.S. Pat. No. 6,295,981, which is incorporated in its entirety by reference.

As a fireplace or similar type of unit transitions from a cold start to a steady state of combustion it has been observed that the change in efficiency of the combustion and increase in heat causes an change in the properties of the flames produced. Namely, the flames tend to be blue at the onset of combustion when the unit components and intake gases are at room temperature. The flames gradually transition to a more desirable yellow color as combustion becomes more complete. Since the air/gas ratio of the unit is typically preset for correct burning at a heated, steady state condition in conventional gas fireplace units; a unit may operate under less than ideal combustion conditions at an initial cold start condition creating a condition for a long initial period of time where very little yellow flame is observable.

This start up condition, i.e., with the unit generating a predominantly blue flame, can cause disadvantages, both in a sales environment, where it is desirable to demonstrate a fireplace with yellow flames to a potential buyer and installed where the unit takes a relatively long period of time to reach a condition where the flames have an aesthetically pleasing appearance. The first disadvantage occurs where a salesperson wishes to demonstrate an attractive appearing fireplace without the cost of keeping fireplaces in a steady state, heated condition. The second problem is related to consumer satisfaction of a pleasant appearing fireplace without the long wait for the unit to develop to a steady state condition.

Whereas many gas/air mixing schemes are simply designed and set for a steady state condition, i.e., at operating temperature at equilibrium, some fireplaces provide a mechanism for adjusting the air/gas mixture. However, if improperly adjusted or malfunctioning, these types of schemes can be unreliable, can produce improper air/gas mixtures, and can cause a buildup of soot or unburned carbon deposits or a dangerous condition.

There is a demand therefore, for a simple, reliable, and cost-effective way of producing desirable combustion and aesthetic flame conditions of a fireplace unit or the like in an instantaneous manner from an initial cold start condition through a fully steady state condition. The present invention satisfies that demand.

SUMMARY OF THE INVENTION

The present invention has an objective of providing a desirable mixture of combustion air to a fireplace as the fireplace transitions from a cold start condition to a steady state, heated condition. One example of a fireplace that would be a suitable candidate for the invention is a model “DV360” fireplace manufactured by CFM Corporation. It will be understood that the invention contemplates any suitable gas fireplace or like device. More specifically, the invention is directed to an automatic, heat activated air shutter assembly for moderating the amount of air entering a burner assembly of a fireplace. The air shutter collar assembly is opened and closed by a bi-metal coil or a plurality of bi-metal coils attached to the shutter in such a fashion so that an increasing amount of air is permitted to enter the burner assembly as heat acting on the coil(s) increases.

The fireplace may include a housing, which may take any suitable form as needed or desired and may be in the form of an enclosure or framework, sized and shaped according to a number of considerations. Examples of these considerations include budget, space, aesthetic, mechanical, safety, and other design and operating considerations. Generally, the housing is an enclosure or structure in which or to which mechanisms and components are enclosed or attached. The housing is also that which is attached at an installation location. The housing or box may be manufactured from a wide variety of materials, including plastic resin suitable for the application, sheet metal, burner tube material or any other material known to those skilled in the art.

One embodiment of the housing includes a top panel, a bottom panel, a back panel and opposing side panels. The two opposing side panels are further optional depending on the application. The housing of this embodiment is sized and shaped to accommodate a fire display box positioned therein. The fire display box is designed to present to a viewer the impression of a working, more traditional fireplace. The fire display box may be open to the front for viewing purposes and may optionally be provided with a fixed or movable front panel or panels, which may be at least in part transparent, translucent or opaque. For purposes of this application, the front of the fireplace unit is that side of the unit through which the interior of the unit is at least partially viewable. It should be understood that the exemplary unit used to describe the invention herein will be similar to a conventional fireplace with a single front panel, through which the interior of the fireplace may be viewed. However, the invention also contemplates a “dual-front” or “see-through” unit or other suitable units in which it is desirable to automatically control the flame appearance.

A fire display box is positioned in the housing. For purposes of this application, the term “fire display box” will broadly signify the area similar to the portion or area found in a fuel-burning fireplace in which combustion takes place and from which the fire that is produced thereby may be viewed. Traditionally, this area is known as a “firebox,” “box,” or “fireplace.” Combustion takes place in or near the firebox by way of a burner, which is supplied with air and gas and preferably some form of pilot light or ignition device with which to ignite the air and gas mixture. A shutter is attached on or near the burner or in the intake air pathway to control the flow of intake air into the burner. The shutter includes one or more bi-metal coils attached thereto. When the burner is first lit, the burner assembly, shutter and coils are at ambient temperature and the shutter is in a closed condition. This condition permits a reduced amount of intake air to enter the burner housing. The burner, shutter and coils gradually warm to a heated condition and, in response, the coils function to open the shutter to provide an increased amount of intake air over the time the burner transitions from an initial ambient temperature to a steady state heated condition.

It has been found that the desired, yellow appearance of the flame may be achieved in an instantaneous fashion by use of the bi-metal coil and shutter assembly according to embodiments of the invention. “Instantaneous,” for purposes of this invention is considered about 1-5 minutes, which is a significant improvement over the prior art.

These and other advantages, as well as the invention itself, will become apparent in the details of construction and operation as more fully described and claimed below. Moreover, it should be appreciated that several aspects of the invention can be used in other applications where aesthetically pleasing flames would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a gas fireplace suitable for use with the burner assembly of the invention;

FIG. 2 shows a perspective view of an assembled burner housing assembly made in accordance with one embodiment of the present invention;

FIG. 3 shows an expanded perspective view of the burner housing assembly of FIG. 2;

FIG. 4 shows an exploded view of a dual spring assembly, shutter collar assembly and mixing tube assembly according to an embodiment of the invention;

FIG. 5 shows a perspective view of the assembly of FIG. 4 assembled;

FIG. 6 shows a partial top view of the assembly of FIG. 5;

FIG. 7 shows an end view of the assembly of FIG. 4;

FIG. 8 shows a side view of the mixing tube assembly in an assembled condition;

FIG. 9 shows a perspective view of a mixing tube assembly in an expanded condition;

FIG. 10 shows a perspective view of a mixing tube;

FIG. 11 shows an end view of mixing tube;

FIG. 12 shows a first side view of a mixing tube;

FIG. 13 shows a second side view of a mixing tube rotated 90 degrees;

FIG. 14 shows an end view of a spring plate;

FIG. 15 shows a perspective view of a spring plate;

FIG. 16 shows a side view of a spring plate;

FIG. 17 shows a side view of a tube cap;

FIG. 18 shows the tube cap of FIG. 17 in an end view;

FIG. 19 shows an expanded perspective view of another embodiment of a mixing tube assembly and bimetal coil spring assembly;

FIG. 20 shows a side view of a spring bar;

FIG. 21 shows an end view of a spring bar;

FIG. 22 shows a perspective view of a spring bar;

FIG. 23 shows a top view of bimetal coil spring;

FIG. 24 shows a side view of the bimetal coil spring of FIG. 23; and

FIG. 25 shows an expanded view of the shutter collar assembly.

DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT

The present invention will now be described in detail with reference to certain embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention and how it may be applied to a gas fireplace. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail to prevent unnecessarily obscuring the present invention.

FIG. 1 illustrates a gas-fueled heating unit, which in a preferred embodiment is a fireplace in accordance with one embodiment of the present invention. Referring to FIG. 1, a gas heating unit 60 includes a combustion chamber 61 with sidewalls (not shown), a rear wall 66 and top and bottom walls 63 and 65. Simulated logs, e.g., ceramic gas logs 68 are arranged in a conventional manner over a burner housing assembly 100 according to an embodiment of the invention. A glass front door (not shown) closes the combustion chamber 61 and provides visual access thereto.

Surrounding the combustion chamber 61 is a unit housing or fireplace housing 67. Air circulation pathways are formed within the fireplace housing 67 in a conventional manner. One such pathway allows room air to be brought in from the bottom front of the fireplace housing and beneath the combustion chamber 61 (arrows 72). The room air is then directed along the rear of the combustion chamber 61 (arrows 73). Finally, the room air is directed along the top of the combustion chamber 61 (arrows 74) and back into the room. At this point, the room air has been heated due to the placement of the pathway air proximate to the heated combustion chamber 61.

In another pathway, combustion air (i.e., air entering the combustion chamber 61) is brought in from the exterior of the building through a concentric flue pipe assembly common to this type of fireplace. As will be described below, the combustion air can enter from one of two available ports. Once within the fireplace housing 67, the combustion air travels a pathway immediately outboard of the room air pathways. That is, the inboard side of the combustion air pathway includes the wall structure forming the outboard side of the room air pathway. This placement also aids in the heating of the room air contained within the room air pathways. Combustion air travels downward through the rear of the heating unit 60 (arrows 75), then into the combustion chamber 61 (arrow 76) through combustion chamber air inlets 78 formed in a bottom portion of the rear wall 66. The fireplace housing 67 has exterior sidewalls (not shown), top wall 82, a bottom wall 83 and a rear wall 84.

Disposed within the combustion chamber 61 is a burner housing assembly 100 according to an embodiment of the invention. The burner housing assembly 100 includes a heat-activated mechanism 102 according to an embodiment of the invention. The heat-activated mechanism 102 regulates the mixing of gas and air entering the burner housing assembly 100 in response to changes in temperature by changing the mixture of gas and air in a manner that will be described in greater detail below.

Ignition of the gas and air mixed by the heat-activated mechanism 102 produces a yellow flame or flames 200 in an instantaneous fashion (i.e., in about 1-5 minutes after initial ignition) relative to the prior art, which may typically take 30 or more minutes to achieve. The mechanism 102 maintains the appearance of the flames 200 from a start up condition of the unit through a steady state condition.

Described herein is a fireplace assembly with a heat-activated mechanism, which provides for a predetermined ratio of air and gas at a cold start up condition and transitions to a heated and steady state condition in response to changes in temperature, experienced by the mechanism. While the above-described assembly is intended to be used with a fireplace, it is to be realized that the described arrangement according to the embodiments of the invention could be incorporated in other types of units, such as for example, direct vent, natural vent and vent-less fireplace systems and even gas operated units which are not fireplaces.

FIG. 2 shows an assembled burner housing assembly 100 according to an embodiment of the invention that includes a burner housing 101 and an assembled gas and air mixing assembly 102. The burner housing assembly 100 includes a number of associated or attached components, the details of which are provided in FIG. 3 and the following drawings. Generally, the burner housing assembly 100 includes a burner housing 101, which has a rectangular shape, within which gaseous fuel and air are mixed at least in part through the functioning of the gas and air mixing assembly 102. The burner housing 101 may be fastened together by welding, for example. Other suitable shapes of the housing are contemplated.

Turning to FIG. 3, the burner housing 101 is provided with a port loading channel 104, which fits atop the burner housing and closes the burner housing. Preferably, the port loading channel 104 is provided with a sealant, (not shown) to effect a seal with burner housing 101. Port loading channel 104 includes a plurality of port loading channel openings 106 formed therethrough for gas and air to leave the burner housing in a pattern which may be designed and intended to produce desired flame patterns.

A port loading channel gasket 108 is positioned atop port loading channel 104. One or more ceramic tile 110 is positioned adjacent or atop the port loading channel gasket 108 at least in part to protect the burner housing assembly 100 from direct exposure to heat from flames. The one or more ceramic tile 110 is flanked by one or more burner tile gasket 112. The one or more ceramic tile 110 is held in place by first and second ceramic tile mounting angles 114, which fasten to the burner housing 101 by conventional fasteners 116, such as screws. A securing bracket 118 attaches to the burner housing 101 and includes a pair of log spacer brackets 120, which log spacer brackets overlay ceramic tiles 110 when fastened to the securing bracket.

The burner housing assembly 100 may include other devices for supporting an artificial log set (not shown) above the burner housing assembly. For example, a front log support bracket 122 may be mounted to the burner housing 101 over the ceramic tile mounting angles 114.

The burner housing 101 includes a burner housing opening 126. The gas and air mixing assembly 102 is disposed in the burner housing opening 126. A spring plate gasket 128 is interposed between the burner housing 101 and gas and air mixing assembly 102 to create a seal with the burner housing opening 126. Details of each of the above assemblies and elements of the burner housing assembly 100 are provided hereinbelow.

FIGS. 4-7 show the air and gas mixing assembly 102 in detail. The air and gas mixing assembly 102 includes a mixing tube assembly 130, which is further detailed in FIGS. 8 and 9. The mixing tube assembly 130 includes mixing tube 132, which is an elongated cylinder shape. Upper and lower air openings 134, 136 are formed at an outer end 138 of the mixing tube 132. An annular or washer shaped tube cap 140 is positioned at the outer end 138 of the mixing tube 132.

A shutter collar assembly 142 is positioned over the upper and lower air openings 134, 136 in the size and shaped to closely the over the upper and lower air openings 134, 136. At ambient air temperatures the shutter collar assembly 142 is held closely against the mixing tube 132 so as to close off the upper and lower air openings 134, 136. The shutter collar assembly 142 is held in the closed condition at ambient temperatures by respective upper and lower bi-metal coil springs 144, 146, which are configured to bias the shutter collar assembly 142 in the depicted position. The shutter collar assembly 142, which is disposed on the upper air opening 134, may be considered a first shutter collar subassembly 142a and the shutter collar assembly, which is disposed over the lower air opening 136, may be considered a second shutter collar subassembly 142b.

Each of the upper and lower bi-metal coil springs 144, 146 are fastened to a spring bar 148, which in turn is fastened to a spring plate 150. Spring plate 150 has an opening 152 which is sized and shaped to receive the mixing tube 132.

It can be seen, especially in FIG. 7, that the bi-metal springs on 144, 146 hold the shutter collar assembly closely around the periphery of the mixing tube 132 at the outer end 138 thereof (see FIG. 4). In this way, air is not drawn into the mixing tube 132 during operation because the shutter collar assembly 142 closes over the upper air are opening 134 and the lower air openings 136. The bi-metal coil springs 144, 146 are constructed and oriented in such a fashion to uncoil and pull the shutter collar assembly 142 away from the mixing tube 132 thus exposing the upper air opening 134 and the lower air opening 136, which permits air to enter interior of the mixing tube 132, mix with gaseous fuel and enter the burner housing 101 (see FIG. 3, for example). The embodiment of the gas and air mixing assembly 102 shown in FIGS. 4-7 is intended for use with natural gas, but may be adapted for use with LP gas, as in known in the art and is also shown below with reference to FIG. 19.

FIGS. 8 and 9 show the mixing tube assembly 130. The mixing tube assembly 130 includes a cylindrical mixing tube 132. The mixing tube 132 is also shown in FIGS. 10-13. Referring then to FIGS. 8-13, at the outer end 138 of the mixing tube 132 are formed a pair of cutaway sections, which when tube cap 140 is attached to the outer end of the mixing tube cause the formation of openings 134, 136. The tube cap 140 has a washer or annular shape with a cap opening 141 centrally located therethrough. Spring plate 150 is generally and L-shaped bracket having a plate opening 152, which is sized to receive the mixing tube 132. A spring plate 150 is positioned close to the outer and 138 of the mixing tube 132. Welding, for example, may be used to assemble the mixing tube assembly 132. Any other suitable fastening method may be used.

FIGS. 14-16 show spring plate 150 in detail. Spring plate 150 has a spring plate tube section 158 that includes plate opening 152. A spring plate bend 156 separates the spring plate tube section 158 from a spring plate spring section 160 at an angle of about 90 degrees. The spring plate spring section 160 includes a pair of spaced spring receiving tabs 154.

FIG. 17 and FIG. 18 show tube cap 140, which has a flat washer shape and a centrally located cap opening 141. Tube cap 140 is attached to the outer end 138 of mixing tube 132 (see FIG. 8, for example). The attachment may be accomplished in any suitable fashion, for example by welding.

FIG. 19 shows an embodiment of a mixing tube assembly and a partial shutter collar assembly in detail and usable with LP gas (propane). The mixing tube assembly 230 includes mixing tube 132, which is an elongated cylinder shape. Upper and lower air openings 134,136 are formed at an outer end 138 of the mixing tube 132. An annular or washer shaped tube cap 240 is positioned at the outer end 138 of the mixing tube 132. A manually adjustable choke sleeve 162 is provided on the mixing tube 132 and has the general shape of a flattened ring with a pair of cutouts 164 corresponding in shape and size to the upper and lower air openings 134, 136. The choke sleeve 162 is slidably and rotatably positioned on the mixing tube 132 and over the upper and lower air openings 134, 136 and when rotated can be used to cover or uncover the upper and lower air openings and thus adjust how much of the openings are exposed. A set screw 166 is provided in a slot 168 of the choke sleeve 162 to fix the choke sleeve in place, preferably after adjustment for a desired air/fuel ratio.

Each of the upper and lower bi-metal coil springs 144, 146 are fastened to a spring bar 148, which in turn is fastened to a spring plate 150. Spring plate 150 has an opening 152 which is sized and shaped to receive the mixing tube 132. The free ends 180 of the bi-metal coil springs 144, 146 occlude the upper and lower air openings 134, 136 when in an initial start-up condition (i.e., ambient temperature). As the temperature increases, the bi-metal coil springs 144, 146 unwind and draw away from the upper and lower air-openings 134, 136 to permit entry of an increased volume of air to enter the mixing tube 132.

FIGS. 20-22 show various views of spring bar 148. Spring bar 148 is an “L” shaped bracket having a spring bar hole 170 for fastening the spring bar to a spring plate (see 150 in FIG. 19, for example).

FIGS. 23 and 24 show a bi-metal coil spring 144 according to an embodiment of the invention. It should be noted that upper and lower bi-metal springs 144, 146 (See FIG. 4, for example) are identical in material composition and geometric configuration in this example. For the fireplace used in the above example, it is desired to construct the bi-metal coil springs 144, 146 from a material that withstands 1000 degrees F. maximum temperature and about 800 degrees nominal temperature. The spring type is an ASTM-TM-1, available from Atlanta Alloy Inc., and of a composite construction consisting of two or more materials with different thermal expansion coefficients, and which unwinds when heated. Other bi-metal springs or the equivalent may be used. It should be understood that the amount of movement of the spring and, in some embodiments, the attached shutter assembly, will correspond to the bi-metal materials used, the construction of the spring, and the temperature range experienced by the spring. In other words, a spring used in the mechanism of the invention may be lighter in construction or more sensitive to temperature changes when a relatively lower range of temperature is experienced and a heavier or less sensitive spring will be used when relatively higher range of temperature change is experienced by the spring. In this manner, a properly controlled airflow and mixing ratio is maintained when applying the principles described herein to different unit conditions.

The coil springs 144, 146 are provided in the coiled configuration, in part to be compact and usable in a small space, and in part to provide a large amount of movement, or deflection for the temperature changes experienced by the springs. Each of the bi-metal coil springs 144 include a mounting portion 178 for attaching to the spring receiving tab 154 of a spring plate 150 (see FIG. 15, for example) and spring bar 148. The attachment method is preferably welding to provide the correct positional relationship for proper sealing of the shutter collar assembly 142 to a respective upper and lower air opening 134, 136 (FIG. 4, for example). Other attachment methods may be employed, such as fasteners, screws, rivets and so on. At an end opposite the mounting portion 178 is an attachment portion 180 for attaching the bi-metal coil spring 144 to a shutter collar assembly 142 (see FIG. 4, for example and FIG. 25).

FIG. 25 shows an expanded view of one half of a shutter collar assembly 142. The assembly 142 shown includes a shutter collar 172, which is a curved metallic semi-circular member. Attached to an inside surface 174 of the shutter collar is a shutter gasket 176. The shutter gasket 176 is preferably a closed cell silicone sponge gasket of medium density.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicants claim protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. While the apparatus and method herein disclosed forms a preferred embodiment of this invention, this invention is not limited to that specific apparatus and method, and changes can be made therein without departing from the scope of this invention, which is defined in the appended claims.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.