Abstract
The invention relates to an oven comprising an oven cavity (10) with a closable opening (12) for receiving food to be cooked or baked, an evaporation cavity (26) in a bottom wall (24) of the oven cavity (10) and an evaporation heating element (28) being arranged for heating the evaporation cavity (26). According to the invention the evaporation cavity (26) is formed as an embossment in the bottom wall (24) of the oven cavity (10) and the heating power of the evaporation heating element (28) is adapted to evaporate a volume of water to be evaporated that corresponds to the volume of such an embossment.
Claims
1. An oven comprising: an oven cavity with a closable opening for receiving food to be cooked or baked, an evaporation cavity arranged in a bottom wall of the oven cavity as an embossment having a volume formed in the bottom wall of the oven cavity, and an evaporation heating element arranged for heating the evaporation cavity.
2. The oven according to claim 1, wherein the evaporation heating element has a maximum heating power that is specific to heat a volume of water to be evaporated that corresponds to the volume of said evaporation cavity.
3. The oven according to claim 1, wherein the evaporation cavity is integrally formed as an embossment in a sheet of metal forming the bottom wall of the oven cavity.
4. The oven according to claim 1, wherein the evaporation heating element is provided in an area underneath the evaporation cavity, without a direct mechanical contact to the evaporation cavity.
5. The oven according to claim 4, further comprising a bottom heating element comprising a primary heater loop, wherein the primary heater loop is arranged underneath the oven cavity in an area that at least partially surrounds the area underneath the evaporation cavity, and wherein the primary heater loop also at least partially surrounds the evaporation heating element.
6. The oven according to claim 5, wherein the primary heater loop and the evaporation heating element are arranged between the bottom wall of the oven cavity and a cover plate covering the primary heater loop and the evaporation heating element.
7. The oven according to claim 5, wherein the primary heater loop and the evaporation heating element are arranged in two different, essentially parallel planes, such that the primary heater loop and the evaporation heating element maintain essentially the same distance from the bottom wall of the oven cavity, respectively in the area surrounding the area underneath the evaporation cavity and in the area underneath the evaporation cavity.
8. The oven according to claim 1 further comprising: a primary heater loop arranged adjacent to the evaporation heating element; and a controller that is operable to independently operate the primary heater loop at full power in either (i) a heat only mode, in which the evaporation heating element is inactive, or (ii) in a heat and steam operational mode in which the evaporation heating element is operated at full power together with the primary heater loop during cooking operations.
9. The oven according to claim 8, wherein the primary heater loop and the evaporation heating element are controllable to allow contemporaneous activation of the primary heater loop and the evaporation heating element as part of the heat and steam mode, and the controller operates the primary heater loop during the heat and steam mode at a fraction, but less than full power of the primary heater loop when the primary heater loop is operated alone during a heat only mode of operation, said fraction of the full power being from ½ to 1/10.
10. The oven according to claim 1 further comprising: a primary heater loop; and a controller configured to concurrently operate the primary heater loop and the evaporation heating element by switching the primary heater loop and the evaporation heating element into a series electrical connection.
11. The oven according to claim 1, wherein an area of the bottom wall adjacent to the evaporation cavity has a down-grade towards the evaporation cavity in order to direct a condensate on the area of the bottom wall towards and into the evaporation cavity and to provide a stiffening effect to the bottom wall.
12. The oven according to claim 1, wherein the embossment defines the evaporation cavity by means of two consecutive bends leading to a downwardly orientated step in the bottom wall of the oven cavity.
13. The oven according to claim 1, wherein a bottom of the evaporation cavity has a down-grade towards a center of the bottom of the evaporation cavity.
14. The oven according to claim 1, wherein the evaporation cavity or a bottom of the evaporation cavity is concave when seen from an inner side of the oven cavity.
15. The oven according to claim 1 further comprising: a temperature sensor arranged to measure a temperature adjacent to the evaporation cavity and to emit a temperature signal indicative of the temperature measured; and a controller that receives the temperature signal and, based on the temperature signal, controls an electrical power supplied to the evaporation heating element.
16. The oven according to claim 1, wherein the bottom wall of the oven cavity and the evaporation cavity are enameled at least on a side facing an interior of the oven cavity.
17. The oven according to claim 1, wherein the evaporation cavity is provided with a dirt cover, permeable to steam and shaped to allow water and condensate flow from the cavity walls and bottom into the evaporation cavity.
18. An oven comprising: an oven cavity with a closable opening for receiving food to be cooked or baked, an evaporation cavity defined by a deep-drawn embossment integrally formed in a bottom wall of the oven cavity, said evaporation cavity having a volume of 10 to 300 mL, wherein a region of said bottom wall adjacent the evaporation cavity has a down-grade toward the evaporation cavity effective to direct condensate toward and into the evaporation cavity, a layer of enamel applied over an inner surface of said bottom wall of the oven cavity including over an inner surface of said evaporation cavity therein, a primary heater loop arranged underneath the oven cavity and at least partially surrounding the evaporation cavity, a secondary heater loop effective to provide a heating power of between 300 and 800 watts arranged underneath, but not in contact with, the evaporation cavity for evaporating water within the evaporation cavity, said secondary heater loop being at least partially surrounded by said primary heater loop, and a temperature sensor for detecting an overheated condition of the evaporation cavity, said primary and secondary heater loops being arranged on two different, essentially parallel planes, such that they both maintain essentially the same distance from the bottom wall of the oven cavity, said primary and secondary heater loops being operably connected to a controller such that, in a first mode the controller can activate the primary heater loop without activating the secondary heater loop in order to supply cooking power without steam generation, and in a second mode the controller can activate both the primary and secondary heater loops to supply both cooking power and steam generation, wherein activation of the secondary heater loop for sustained periods is prohibited while the primary heater loop is inactive.
19. The oven according to claim 18, said controller being adapted to connect the primary and secondary heater loops in series during said second mode, such that in the second mode said primary heater loop delivers a lower power output than in said first mode.
20. The oven according to claim 18, further comprising a dirt cover positionable over the evaporation cavity from inside the oven cavity, said dirt cover being permeable to steam and shaped to allow water and condensate to flow from the oven cavity into the evaporation cavity, but to prevent food debris from contacting the evaporation cavity.
Description
[0032] An example of an oven according to the present invention is described below by reference to the accompanying schematic drawings in which:
[0033] FIG. 1 shows a cross-sectional side view of an oven according to the present invention, and
[0034] FIG. 2 shows a cross-sectional view from below,
[0035] FIG. 3 shows a view from below onto a bottom heating element,
[0036] FIG. 4 shows a side view of the bottom heating element of FIG. 3, arranged upside down such that a secondary heater loop, which is to be installed to be arranged at an elevation that is lower than an elevation of a primary heating loop, appears above the primary heating loop,
[0037] FIG. 5 shows a cavity bottom wall, heater loops and a cover plate in an exploded view,
[0038] FIG. 6 shows a circuit diagram of an evaporation heating element and a bottom heating element where both heating elements are activated,
[0039] FIG. 7 shows the heating element of FIG. 3 in a switching state where only the bottom heating element is activated,
[0040] FIG. 8 shows an partially cutaway view of a bottom wall provided with an evaporation cavity arranged adjacent to a heating element assembly that includes a primary heater loop and a secondary heater loop equally spaced apart from a surrounding region of the bottom wall and a bottom of the evaporation cavity, respectively;
[0041] FIG. 9 shows a sectional view of an enamel coated bottom wall provided with an evaporation cavity arranged adjacent to primary and secondary heater loops taken along line 9-9 in FIG. 2, in an operational state where a secondary heater loop is active; and
[0042] FIG. 10 shows a sectional view of an enamel coated bottom wall provided with an evaporation cavity arranged adjacent to primary and secondary heater loops taken along line 9-9 in FIG. 2, in an operational state where both the primary and the secondary heater loops are connected in series and active.
[0043] FIG. 1 shows an oven comprising a cavity 10 with a closable opening 12 for receiving food to be cooked or baked within the oven cavity 10. The opening 12 can be closed by means of a front door 14. The oven cavity 10 is defined by sidewalls 16, a rear wall 18, a top wall 20 and a bottom wall 24. A top heating or grill element 22 is mounted in the upper region of the oven cavity 10. The bottom wall 24 comprises an evaporation cavity 26 which is a deep drawn embossment. The embossment defining the evaporation cavity 26 is worked into a steel sheet constituting the bottom wall 24 during a shaping operation where the bottom wall 24 of the oven cavity 10 is defined. Like the bottom wall 24 also sidewalls 16, rear wall 18 and top wall 20 are made of steel sheets and are enameled. An evaporation heating element 28 is provided for heating the evaporation cavity 26 in an area 29 underneath the evaporation cavity 26. The heating power of the evaporation heating element 28 is adapted to evaporate a volume of water to be evaporated that corresponds to the volume of the evaporation cavity 26. The evaporation cavity 26 together with the evaporation heating element 28 act as a steam generation system. Water can be conveyed into the evaporation cavity 26 either by direct pouring or by means of a pipe or a channel. By activation of the evaporation heating element 28 the water is evaporated. The evaporation heating element 28 is arranged in an area 29 underneath the evaporation cavity 26 and can be a second branch of an also provided standard bottom heating element with independent control. This will be explained in more detail in connection with the following Figures. The evaporation heating 28 element is self-supporting and not in direct contact with the bottom wall 24 and the embossment defining the evaporation cavity 26. As an alternative, such an evaporating heating element can be a heating device directly fixed onto the external surface of the embossment defining the evaporation cavity 26 (e.g. a standard heater, a thick film heater, welded, glued or fixed by other means directly onto the external surface of the evaporation cavity 26). A thermostat or temperature sensor 30 is applied to the external surface of the evaporation cavity 26 to prevent overheating (e.g. upon run-out of water) or to control the power delivery and hence the evaporation. The oven can also comprise a steam inlet 32 which is connected to an (not shown) external steam generator so that the evaporation cavity 26 together with the evaporation heating element 26 acts as auxiliary generator or condensation re-evaporator collecting condensate and re-evaporating it. But of course the evaporation cavity 26 and the evaporation heating element 28 can also be used as the only source of steam and/or humidity without an additional steam generator. The evaporation cavity 26 can be protected by a cover, shaped to fit onto it in order to prevent food debris to get in contact with the hot evaporation cavity 26 which would lead to cleanability issues. Since the evaporation cavity 26 is preferably designed to receive a volume of water between 10 and 300 ml, more preferably between 50 to 100 ml, the evaporation heating element 28 preferably provides a heating power between 300 and 800 W so as to be adapted to evaporate an according volume of water during a typical cooking or baking time. A user interface 38 is provided for controlling the oven.
[0044] FIG. 2 shows the oven of FIG. 1 in a sectional view from below. A cover plate which normally covers heater loops, is removed. As can be seen from FIG. 2, the oven comprises an electrical bottom heating element 27 which in turn comprises a primary heater loop 40 for providing bottom heat to the oven cavity 10. This primary heater loop 40 is surrounded by a secondary electrical heater loop 42 which relates to the evaporation heating element 28. The secondary heater loop 42 is provided in an area 29 underneath the evaporation cavity 26 whereas the primary heater loop 40 is arranged in an area 31 that excludes the area 29 underneath the evaporation cavity 26. Primary heater loop 40 is arranged underneath the oven cavity 10 too.
[0045] FIGS. 3 and 4 show a primary heater loop 40 and a secondary heater loop 42 which are arranged in two different, essentially parallel planes 40b and 42b, respectively. These heater loops 40 and 42 can be installed in the oven according to FIGS. 1 and 2 (where the corresponding loops 40 and 42 are shown more schematically). Thus, the assembly including the primary and secondary heater loops 40, 42 is shown in FIG. 4 upside down. Properly installed in the present oven as shown in FIG. 8, however, the secondary heater loop 42 is arranged at an elevation that is lower than an elevation of a primary heating loop 40 by the distance D. However, since the assembly is inverted in FIG. 4, the secondary heater loop 42 appears vertically above the primary heater loop 40. Both planes 40b and 42b are arranged in a distance D to each other wherein the plane 42b comprising the secondary heater loop 42 is above the plane 40b of the primary heater loop 40, wherein “above” refers to an assembled condition of the oven. The distance D between both planes 40b and 42b is such that both heater loops 40 and 42 maintain essentially the same distance from the bottom wall 24 of the oven cavity, respectively in the area 31 surrounding the area 29 underneath the evaporation cavity 26 and in the area 29 under the evaporation cavity 26. For example, in the enlarged, sectional view shown in FIG. 8, the separation S1 between the bottom of the area 31 surrounding the evaporation cavity 26 and the primary heater loop 40, and the separation S2 between the bottom of the evaporation cavity 26 and the secondary heater loop 42 is approximately the same.
[0046] FIG. 5 shows the cavity bottom wall 24 with the evaporation cavity 26 the heater loops comprising the primary heater loop 40 and the secondary heater loop 42 and a cover plate 50 in an exploded view. The cover plate 50 is designed for protecting the primary heater loop 40 and the secondary heater loop 42. In addition to the evaporation cavity 26 also additional reinforcing structures 36 are embossed or deep drawn into the bottom wall 24. A heat insulating layer e.g. of a fibrous material will be arranged below the cover plate 50.
[0047] FIGS. 6 and 7 show a schematic connection diagram comprising the primary heater loop 40 and a secondary heater loop 42 of FIGS. 2 and 5 that are controllable by a controller 67. The controller 67 includes suitable electronic components and is otherwise adapted to issue control signals for establishing the operational modes of the oven described herein. According to FIG. 6, in response to a user-input command received by the controller 67 identifying a desired cooking mode, a first end 42a of secondary heater loop 42 is electrically connected to electrical ground 64 pursuant to an instruction from the controller 67. A second end 42b of secondary heater loop 42 is connected to a first end 40a of primary heater loop 40 which in turn is also connected via a breaker 62 to electrical ground 66. A second end 40b of primary heater loop 40 is connected via breaker 68 to a source of electrical power 70. When, as shown in FIG. 6, breaker 68 is closed (conducting) and breaker 62 is open, both heater loops 40 and 42 are switched into a series electrical connection and are activated by a current running from the source of electrical power 70 to electrical ground 64 to establish an operational mode of heat and steam.
[0048] In the configuration of FIG. 7 where both breakers 62 and 68 are closed by the controller 67 the circuit is configured such that electrical current is running from the source of electrical power 70 through the primary heater loop 40 and through the closed breaker 62 to electrical ground 66 (due to the low resistance of breaker 62 in comparison to secondary heater loop 42). In this case only primary heater loop 40 is activated (heated) whereas secondary heater loop 42 is basically switched off so that the evaporation cavity 26 is not heated directly. Therefore, the second configuration of FIG. 5 relates to the case where the oven is used with bottom heating only and without steam generation. Accordingly, the controller 67 can be configured to operate the primary heater loop 40, without the secondary heater loop 42, and optionally in combination with another heater loop (e.g., convection heating element, broil heating element, etc. . . .), or to operate both the primary heater loop 40 in combination (e.g., in series) with the secondary heater loop 42. The controller 67 can thus optionally prevent sustained operation of the secondary heater loop 42 without also requiring activation of the primary heater loop 40.
[0049] By preventing sustained operation of the secondary heater loop 42 while the primary heater loop 40 is off, thermal stresses on the enamel coating resulting from the different coefficients of thermal expansion of the enamel and the metal from which the bottom wall 24 is formed can be minimized To illustrate this concept, FIG. 9 shows a schematic sectional view of the bottom wall 24 provided with an evaporation cavity and an enamel coating 25 arranged adjacent to the primary and secondary heater loops 40, 42 taken along line 9-9 in FIG. 2. Points where the local temperatures discussed below are present are identified by temperatures T1, T2, T3 and T4. T1 represents the temperature of the enamel coating 25 adjacent to a central region at the bottom of the evaporation cavity 26. T2 represents the temperature of the metal material from which the bottom wall 24 was formed adjacent to a central region at the bottom of the evaporation cavity 26, opposite the location of the temperature T1. T3 represents the temperature of the metal material of the bottom wall 24 along an angled region between bends in the material to form the evaporation chamber 26. And T4 represents the temperature of the metal material of the bottom wall 24 in a surrounding region of the bottom wall 24 that is substantially horizontal and located radially outward from the central region of the evaporation cavity 26, beyond the exterior periphery of the evaporation cavity 26.
[0050] The oven in FIG. 9 is in the operational state prevented by the controller 67, where only the secondary heater loop 42 is active. The active, or operational heater loops are represented in FIGS. 9 and 10 by the solid-filled circles representing the cross section of the heater loops 40, 42, and the off heater loops are represented by open, or unfilled circles. Prolonged operation of the oven in the operational state represented in FIG. 9 can result in the following approximate, steady-state temperatures T1-T4 being established:
TABLE-US-00001 TABLE 1 Temperature Gradients with Oven in Prevented Operational Mode T1 ~100° C. T2 120-140° C. T3 130-160° C. T4 Room Temperature-40° C.
[0051] As can be seen from Table 1, the differences in temperature of the metal material forming the bottom wall 24 at T2, T3 and T4 can cause the metal material to expand to a different extent at each location. Such differences in expansion can exert significant stress on the enamel coating 25, thereby promoting the formation of cracks in, or otherwise damaging that enamel coating 25.
[0052] In an effort to combat damage to the enamel coating 25 as a result of different rates of expansion between T4 and T2 and T3, the controller 67 is adapted to connect the primary and secondary heater loops 40, 42 in series during an operational mode of the oven that generates steam from the water in the evaporation cavity 26. In this operational mode, the primary heater loop 40 is operational (i.e., on), but at a lower power output than a power output at which the primary heater loop 40 is operated when the oven is in a standard bake operational mode (when the primary heater loop 40 is operational but the secondary heater loop 42 is off, and steam is not being generated). Such an operational mode is represented schematically in FIG. 10. Prolonged operation of the oven in the operational state represented in FIG. 10 can result in the following approximate, steady-state temperatures T1-T4 being established:
TABLE-US-00002 TABLE 2 Temperature Gradients with Oven in Enamel-Preserving Operational Mode T1 ~100° C. T2 120-140° C. T3 130-160° C. T4 100-130° C.
[0053] As shown in Table 2, the differences in temperature gradients that exist between T4 and T2 and T3 are much smaller than the corresponding temperature gradients present when the oven is operated in the operational mode represented in FIG. 9. In fact, the temperature ranges for T2, T3 and T4 can optionally overlap. The smaller temperature gradients promote similar thermal expansion of the metal forming the bottom wall 24, thereby exerting less stress on the enamel coating 25.
