Patent Description:
Portable wood burning stoves are used in camping, and make use of twigs and sticks as fuel for heat and cooking. Similarly, large portable firepits are used for example in residential back yards for recreation, to provide outdoor heat, and to support limited cooking such as marshmallow roasting.

However, large firepits are generally fueled by piles of heavy logs rather than small twigs, which places significantly greater structural demands on the firepit materials. When experiencing repeated cycles of cold (during disuse) and high heat (during use), fire grates for large firepits are subject to bowing or sagging that may be aesthetically displeasing, may cause a poor fit with other components of the firepit, and may cause unwanted contact with other components of the firepit, or with the ground, thus presenting a potential fire risk.

Large fire grates are also subject to oxidation, and to other deformation that may limit their service life and may, in some circumstances, cause dangerous structural failure with additional attendant fire risk. Conventional fire grates are subject to deformation or may have insufficient air flow, which in turn may lead to inadequate combustion of fuel, inadequate heat production, and excessive generation of smoke. Such heavily built structures are also heavier (and therefore less portable), they require more material to construct, and they may also require more complex (and therefore more expensive) manufacturing steps.

XP55970754A1 discloses a bottom grate: the plate on the lower level where you put charcoal or wood.

<CIT> discloses a meat plate which prevents the oil from falling off in the heat source and causes the flame to escape from the gas fire or charcoal fire by the hot aisle, and to cook the meat with the fire.

<CIT> discloses a meat grill, which grills meat in an open state in which heat is supplied from a heat source such as a gas range or a gas burner, and steam generated by heating a water container filled with water located below the grill.

<CIT> discloses a device for cooking and/or grilling any type of food. In general, the invention deals with a device for cooking and/or grilling, which is particularly suitable for use on the table due to its special construction and equipment.

<CIT> discloses tables and accessories and, more particularly, relates to accessories that can be used on tables with fire pits and/or openings.

<CIT> discloses charcoal grills, and more specifically a new design having a cool base.

It is therefore to be appreciated that such commonly used fire grates have numerous drawbacks, including one or more of high cost, large weight, low portability, poor performance, short service life, smoke generation, fire risk, aesthetic degradation, among others. Accordingly, long-felt needs exist for fire grates that address the forgoing and other concerns.

The invention is directed to a fire grate for a wood burning stove, namely a dome-shaped fire grate formed by being stamped from a sheet metal blank including: a center forming a high-point of the fire grate; a circular perimeter surrounding and spaced from the center, the center being higher than the perimeter; a plurality of radial stiffening ribs formed by bends in the sheet metal and extending from the perimeter and toward the center; at least one circumferential stiffening ring formed by bends in the sheet metal extending at least partially about the center; and a plurality of ventilation holes between the center and the perimeter.

Implementations may include one or more of the following features. The dome-shaped fire grate where the dome-shaped fire grate is a spherical section with a radius of curvature larger than one-half of a width of the fire grate. The dome-shaped fire grate where the center includes a central hub. The dome-shaped fire grate where the fire grate further includes a downward-facing lip around the perimeter. The dome-shaped fire grate where the plurality of radial stiffening ribs include ribs of at least two different lengths. The dome-shaped fire grate where a portion of the dome-shaped fire grate includes an outer stiffening ring that includes no ventilation holes.

The fire grate disclosed herein has particular, but not exclusive, utility for portable back yard firepits.

This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. A more extensive presentation of features, details, utilities, and advantages of the fire grate, as defined in the claims, is provided in the following written description of various embodiments of the disclosure and illustrated in the accompanying drawings.

Illustrative embodiments of the present invention will be described with reference to the accompanying drawings, of which:.

For the purposes of promoting an understanding of the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same.

In accordance with at least one embodiment of the present invention, a fire grate for a wood burning stove is provided which includes novel structural features to prevent significant bending, bowing, sagging, or other deformation under the heat loads expected during normal use cases and plausible exceptional use cases. These features provide the necessary structural performance to support heavy fuel loads at high temperature, while permitting a relatively low weight for the fire grate itself. The disclosed fire grate also includes air flow features conducive to thorough combustion of fuel, which leads to greater heat generation and substantially reduced smoke. The design is readily manufactured as a single namely by being stamped from a sheet metal blank, which permits it to be lighter and less expensive than a multipart assembly of comparable strength.

These descriptions are provided for exemplary purposes only, and should not be considered to limit the scope of the fire grate. Certain features may be added, removed, or modified without departing from the scope of the claimed subject matter.

<FIG> is a cross-sectional view of an example combustion stove, such as a wood burning stove <NUM> including a fire grate <NUM> in accordance with at least one embodiment of the present invention.

The fire grate <NUM> sits within the stove or fire pit <NUM> and supports the weight of fuel <NUM> (e.g., wooden logs and sticks) while permitting air flow through the fire grate <NUM> and stove or fire pit <NUM> to facilitate combustion of the fuel <NUM>. The fire grate <NUM> is strong and stiff to bear the weight of firewood and other fuel <NUM>, both at ambient temperatures and at operating temperatures, and may resist substantial warping or other substantial deformation despite prolonged and repeated exposure to the heat of combustion. The fire grate <NUM> may also be lighter and have greater airflow than other fire grates of comparable size.

In the example embodiment of <FIG>, the combustion stove <NUM> includes a top portion <NUM>, a bottom portion <NUM>, and a middle portion <NUM>. The firepit <NUM> further includes an inner wall or inner body <NUM>, an outer wall or outer body <NUM>, a connecting ring <NUM> located in the top portion <NUM> of the stove <NUM> and attached to or formed as a single piece with the inner body <NUM> and the outer body <NUM>, and a cavity <NUM> defined by the inner body <NUM>, within which the fire grate <NUM> is positioned. The stove <NUM> further includes a top lip <NUM> attached to or formed as a single piece with either of the inner body <NUM> and outer body <NUM>. The stove <NUM> further includes a plurality of outer ventilation holes <NUM> located in the bottom portion <NUM> of the outer body <NUM>, and a plurality of inner ventilation holes <NUM> located in the top portion <NUM> of the inner body <NUM>. In the middle portion <NUM> of the stove <NUM>, the inner body <NUM> terminates in an upward-facing support lip or rollover <NUM> into which the fire grate <NUM> fits, or upon which the fire grate <NUM> rests.

The stove <NUM> further includes a base plate <NUM> attached to the outer body <NUM>, a bracing tray <NUM> supported by stands projecting upward from the base plate, and a catch tray <NUM> supported by stands projecting upward from the bracing tray <NUM> such that the bracing tray is separated from the outer body by an air gap <NUM>, the catch tray <NUM> is separated from the outer body <NUM> by an air gap <NUM>, and the inner body is separated from the outer body by an air gap <NUM>. In an example, air gaps <NUM> and <NUM> are both about <NUM>, while air gap <NUM> is about <NUM>, although other air gaps may be employed that have the disclosed, advantageous effect.

The cavity <NUM> is in fluid communication with the air gap <NUM> via the inner ventilation holes <NUM>, and with air gaps <NUM> and <NUM> via the fire grate <NUM>. The air gaps <NUM> and <NUM> are in fluid communication with ambient air via the outer ventilation holes <NUM>, such that ambient air may be drawn in through the outer ventilation holes <NUM>, heated by combustion of the fuel <NUM>, and expelled through the cavity <NUM> and inner ventilation holes <NUM> to produce advantageous combustion of the fuel <NUM>.

In an example, both the fire grate <NUM> and the stove or firepit <NUM> are made of stainless steel plates having a thickness within a range of between about. <NUM> and about <NUM> thick. Some examples of the fire grate <NUM> and the stove or firepit <NUM> are formed of <NUM> to <NUM> thick, and one example is about <NUM> thick stainless steel. Both thicker and thinner materials are contemplated. In an example, the fire grate <NUM> weighs approximately <NUM>,<NUM> (<NUM> lb), although weights of between about <NUM>,<NUM> (<NUM> oz) and about <NUM>,<NUM> (<NUM> lb) may be provided. In an example, during normal operation the fire grate <NUM> supports a nominal weight of <NUM>,<NUM> (<NUM> lb) (although nominal capacities of between about <NUM>,<NUM> (<NUM> lb) and about <NUM>,<NUM> (<NUM> lb) may be provided), while the fire grate <NUM>, or portions thereof, are heated to between about about <NUM> (<NUM> °F) and about <NUM> (<NUM> °F) by the combustion of the fuel <NUM>, for a time period of between <NUM> and <NUM> hours, and also at ambient temperatures as low as -<NUM> (-<NUM> °F). In an example, during normal operation over a period of years, with repeated cycling (e.g., one hundred cycles) between ambient and operational temperatures, the fire grate <NUM> exhibits little or no warping that would detrimentally affect its aesthetic appearance, its performance, or its fit within the stove or firepit <NUM>.

The primary load carried by the fire grate <NUM> is applied downward, in a direction parallel to axis <NUM>, by the weight of the fuel <NUM> piled on the fire grate <NUM>, which is supported by the upward-facing lip or rollover <NUM> of the inner body <NUM>.

<FIG> is an exemplary representation of a fire grate <NUM> for a wood burning stove in accordance with at least one embodiment of the present invention. In the example shown in the figure, the fire grate is a circular, convex, dome-shaped structure that includes an outer rim <NUM> with a downward-facing lip or rollover <NUM> that provides stiffness, that fits into the upward facing lip or rollover <NUM> of the inner body <NUM> of the stove or firepit <NUM>, and makes it more difficult for the outer rim <NUM> of the fire grate <NUM> to dent, warp, or otherwise deform. The outer rim <NUM> may define the axis <NUM>. In this example, the fire grate <NUM> further includes a central hub <NUM> that is raised above the outer rim <NUM>, a stiff outer ring <NUM>, and a ventilated inner ring <NUM> that reaches from the inner edge <NUM> of the stiff outer ring <NUM> to the outer edge <NUM> of the central hub <NUM> (see <FIG>). The ventilated inner ring <NUM> includes a plurality of ventilation holes <NUM>.

In an example having an outer diameter <NUM> (see <FIG>), the ventilated inner ring <NUM> includes <NUM> circular ventilation holes, each with a diameter of about <NUM>. Other numbers and sizes of holes could be used (e.g., <NUM> - <NUM> holes, each with a diameter of between <NUM> and <NUM>), although while more holes and/or larger holes would mean better overall ventilation, it may mean less structural material and thus a weaker structure for both the ventilated inner ring <NUM> and the fire grate <NUM> overall. Because better ventilation may result in higher fire temperatures, the structure may weaken further due to a combination of heat softening and heat expansion. A weaker structure may have a reduced ability to support the weight of firewood or other fuel piled on top of it (see <FIG>), and may be more prone to collapse or warping. Conversely, fewer holes and/or smaller holes may result in a stronger overall structure and better support for firewood or other fuel, it may also result in worse ventilation and thus a lower combustion temperature, less head output, and increased generation of smoke.

In the implementation in <FIG>, the stiff outer ring <NUM> includes a plurality of short radial stiffening ribs <NUM> that reach from the outer rim <NUM> to the outer edge <NUM> of the ventilated inner ring <NUM>. In some examples, the ventilated inner ring <NUM> of the fire grate <NUM> includes twenty-four short radial stiffening ribs <NUM>, although other examples may include a different number of short radial stiffening ribs <NUM> so long as they achieve the advantageous effects. In an example, the short radial stiffening ribs <NUM> reach a short distance (e.g., <NUM>) into the ventilated inner ring, such that the ends <NUM> of the short radial stiffening ribs <NUM> may be at the same radial distance from the center of the hub <NUM> as the centers of the outermost ventilation holes <NUM>. Other lengths are possible for the short radial stiffening ribs <NUM>, although shorter ribs <NUM> would provide less structural support and stiffening, and longer ribs <NUM> may displace, cover, or otherwise interfere with some of the ventilation holes <NUM>.

The fire grate <NUM> in the example shown in <FIG> may further include a plurality of long radial stiffening ribs <NUM> and <NUM> that reach from the outer rim <NUM> to, or nearly to, the central hub <NUM>. In the example shown in <FIG>, six long stiffening ribs <NUM> reach all the way to the central hub <NUM>, while six interleaved long stiffening ribs <NUM> approach but do not reach with central hub <NUM>. In some examples, the interleaved long stiffening ribs <NUM> reach within about <NUM> of the hub. In some implementations, the interleaved long stiffening ribs <NUM> extend all the way to the central hub <NUM>. Such implementations however would result in a majority of the circumference of the central hub <NUM> comprising interfaces between ribs and the hub itself, which may result in a weaker overall structure. In other implementations, the long stiffening ribs <NUM> may be shortened such that they do not reach all the way to, or do not intersect the central hub <NUM>. In some implementations, the stiffening ribs <NUM> may be shortened even further, so that their distance from the central hub <NUM> is in a range of about <NUM>-<NUM>, for example. However, increasing the distance from the central hub <NUM> or intersecting the central hub <NUM> with the interleaved long stiffening ribs <NUM> may result in less stiffening and thus a weaker structure overall. Depending on the implementation, other numbers of long stiffening ribs <NUM> and <NUM> could be used, although more long radial stiffening ribs <NUM> or <NUM> may mean fewer ventilation holes, and fewer long radial stiffening ribs <NUM> or <NUM> may mean a weaker, less stiff, structure that is more prone to crushing and/or warping.

In addition to the plurality of ventilation holes <NUM>, the ventilated inner ring <NUM> includes an outer concentric stiffening ring <NUM> and an inner concentric stiffening ring <NUM> that provide additional strength, stiffness, and stability to the structure of the fire grate <NUM>, both at ambient temperature and at operating temperatures when a fire is burning in the fire pit <NUM> that includes the fire grate (see <FIG>). In other embodiments, the fire grate <NUM> could include more than two stiffening rings. For example, some embodiments include between <NUM> and <NUM> stiffening rings. Even greater numbers of stiffening rings are contemplated. However, increasing the number of stiffening rings may reduce the number or size of the holes <NUM>, with effects as described above, or else decrease the spacing between the holes <NUM>, which may weaken the structure of the fire grate <NUM>. In still other embodiments, the fire grate <NUM> may include fewer than two stiffening rings, which may result in a weaker, less stiff structure with more space available for ventilation holes.

In the example shown in <FIG>, the central hub <NUM> having a central ventilation hole <NUM>. In other embodiments, the central hub <NUM> is not present or does not include a central hole <NUM>.

In an example, the hub <NUM>, short stiffening ribs <NUM>, long stiffening ribs <NUM> and <NUM>, stiffening rings <NUM> and <NUM> are stamped or otherwise embossed into the material of the fire grate (e.g., stainless steel), although other fabrication methods may be employed. In an example, the fire grate is a spherical section which is formed from a flat, circular blank by the stamping process. In an example, the holes <NUM> and <NUM> are also formed by the stamping process, although they may alternatively be produced by drilling, laser cutting, or other methods.

In some embodiments, one or more of the holes <NUM> may overlap with one or more of the stiffening ribs <NUM>, <NUM>, or <NUM>, or stiffening rings <NUM> and <NUM>. However, in other embodiments the hole pattern, rib pattern, and ring pattern have been selected such that no holes <NUM> overlap with any of the ribs <NUM>, <NUM>, or <NUM>, or rings <NUM> and <NUM>.

<FIG> is an exemplary representation of a fire grate <NUM> for a wood burning stove in accordance with at least one embodiment of the present invention.

The fire grate <NUM> has a diameter <NUM>, and includes the inner ventilated ring <NUM> with an outer diameter <NUM>, the outer stiffening ring with a diameter <NUM>, and the inner stiffening ring with a diameter <NUM>. In an example, diameter <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided), diameter <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided), diameter <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided), and diameter <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided). Other diameters could be used, making the fire grate larger or smaller for different applications.

The fire grate <NUM> also includes the plurality of short radial stiffening ribs <NUM>, each separated from its nearest neighboring short radial stiffening rib <NUM> by an angle <NUM>. The fire grate <NUM> includes a plurality of long radial stiffening ribs <NUM> interleaved with slightly longer radial stiffening ribs <NUM>. Each long radial stiffening rib <NUM> or <NUM> is separated from its nearest neighboring long radial stiffening rib <NUM> or <NUM> by an angle <NUM>, and from its nearest neighboring short radial stiffening rib by an angle <NUM>. In an example, angle <NUM> is <NUM> degrees, while angles <NUM> and <NUM> are both <NUM> degrees. However, other angle spacing is contemplated.

The length of the short radial ribs <NUM> is roughly equal to one half the difference between diameter <NUM> and diameter <NUM>. In an example, this number is equal to <NUM>, and the short radial ribs <NUM> are each about five millimeters longer than that, although other lengths may be employed. In an example, the length of the long radial stiffening ribs <NUM> is about <NUM>, and the length of the long radial stiffening ribs <NUM> is about <NUM>, although other lengths could be employed.

The fire grate <NUM> has a height <NUM> and a radius of curvature <NUM>. The lip <NUM> has a height <NUM>. In an example, height <NUM> is about <NUM> (although heights of between about <NUM> and about <NUM> may be provided, including for larger or smaller fire grates), radius of curvature <NUM> is about <NUM> (although radii of between about <NUM> and about <NUM> may be provided, including for larger or smaller fire grates), and height <NUM> is about <NUM> (although heights of between about <NUM> and about <NUM> may be provided, including for larger or smaller fire grates). Other heights and radii of curvature could be used, but may affect the strength, stiffness, heat softening, and heat expansion properties of the fire grate <NUM>.

<FIG> is an exemplary representation of a fire grate <NUM> for a wood burning stove <NUM> in accordance with at least one embodiment of the present invention.

In the example shown in the figure, the hub <NUM> has a diameter <NUM>, the long radial stiffening ribs <NUM> and <NUM> have a width <NUM>, and the long radial stiffening ribs <NUM> have a separation <NUM> from outer edge of the hub. In an example, diameter <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided), width <NUM> is about <NUM> (although values between about <NUM> and about <NUM> may be provided), and separation <NUM> is about <NUM> (although values between <NUM> and about <NUM> may be provided in some implementations). Still other values are contemplated that create the disclosed, advantageous effect. In an example, the short radial stiffening ribs <NUM> have the same width as the long stiffening ribs <NUM> and <NUM>, although other widths could be employed that had the disclosed effect.

<FIG> is cross-sectional representation of an example stiffening rib <NUM>, <NUM>, or <NUM> or stiffening ring <NUM> or <NUM> of an example fire grate <NUM> for a wood burning stove or firepit <NUM> in accordance with at least one embodiment of the present invention.

The fire grate <NUM> has a material thickness <NUM>, which has been stamped or otherwise embossed with a linear feature <NUM> (i.e., a stiffening rib or ring) represented here in cross section. The linear feature <NUM> has an inner radius of curvature <NUM>, an outer radius of curvature <NUM>, and a height <NUM> above the surface of the fire grate <NUM>. In an example, thickness <NUM> is about <NUM>, inner radius <NUM> is about <NUM>, outer radius <NUM> is about <NUM>, and height <NUM> is about <NUM>. Other values could be employed that had the disclosed advantageous effects.

The example of <FIG> shows a closer view of the downward-facing lip or rollover <NUM>, which is part of the outer rim <NUM> of the fire grate <NUM>. In an example the lip or rollover <NUM> has a height <NUM> of about <NUM> and a thickness <NUM> of about <NUM>. In some embodiments, the outer rim <NUM> of the fire grate <NUM> is circular. In other embodiments, the outer rim <NUM> may be a regular polygon such as a hexagon, octagon, or approximately circular polygon with a plurality of sides. In still other embodiments, the outer rim <NUM> may be oval shaped.

The fire grate <NUM> is made strong and stiff for load bearing of firewood and other fuel, both at ambient temperatures and at operating temperatures, by a balanced combination of a domed shape, a vertically folded outer lip <NUM>, stiff outer ring <NUM>, short radial stiffening ribs <NUM>, long radial stiffening ribs <NUM> and <NUM>, a central hub, and stiffening rings <NUM> and <NUM>. At the same time, the fire grate <NUM> is ventilated by a ventilated inner ring <NUM> that includes a plurality of ventilation holes <NUM>, and by a single ventilation hole <NUM> at the center of the central hub <NUM>. The ventilation provided by these features is sufficient to provide high air circulation through the stove or firepit <NUM> to yield a high heat output and low smoke output relative to existing stoves and firepits.

Accordingly, it can be seen that the fire grate <NUM> fills a long-standing need in the art, by providing a low-cost, lightweight, stampable, high-strength, high-stiffness, high-airflow structure that resists denting, warping, and other deformation while carrying heavy fuel loads at operating temperatures as high as about <NUM> (<NUM> °F), and while cycling repeatedly between ambient temperature and operating temperature.

A number of variations are possible on the examples and embodiments described hereinabove. For example, the fire grate could be made of heavier-gauge material in order to support more weight, or of lighter gauge material in order to become lighter and more portable. The fire grate could be made in different sizes and/or with different degrees of curvature. The relative lengths, widths, and radii of different components could be different than presented herein.

The technology described herein may be used to burn firewood, wood chips or pellets, scrap lumber, paper, cardboard, coal, and other combustible materials. It may be employed for example in lamps, stoves, firepits, fireplaces, furnaces, forges, and boilers, and other combustion heaters. In some implementations, more than one fire grate may be used, or the fire grate may comprise several pieces that collectively form a structure like that described herein.

The logical operations making up the embodiments of the technology described herein are referred to variously as operations, steps, objects, elements, components, or modules. Furthermore, it should be understood that these may be performed in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language.

All directional references e.g., upper, lower, inner, outer, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise, proximal, and distal are only used for identification purposes to aid the reader's understanding of the claimed subject matter, and do not create limitations, particularly as to the position, orientation, or use of the fire grate. Connection references, e.g., attached, coupled, connected, and joined are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily imply that two elements are directly connected and in fixed relation to each other. The term "or" shall be interpreted to mean "and/or" rather than "exclusive or. " Unless otherwise noted in the claims, stated values shall be interpreted as illustrative only and shall not be taken to be limiting.

Claim 1:
A fire grate (<NUM>) formed by being stamped from a sheet metal blank comprising:
a center forming a high-point of the fire grate (<NUM>);
a circular perimeter surrounding and spaced from the center, the center being higher than the perimeter;
at least one circumferential stiffening ring formed by bends in the sheet metal and extending at least partially about the center; and
a plurality of ventilation holes (<NUM>) between the center and the perimeter,
characterized in that
the fire grate is dome-shaped, and in that
the fire grate further comprises a plurality of radial stiffening ribs (<NUM>) formed by bends in the sheet metal and extending from the perimeter and toward the center.