GB2486802A

GB2486802A - Induction hob with a spring and bracket

Info

Publication number: GB2486802A
Application number: GB1121834.4A
Authority: GB
Inventors: Neil Volrath
Original assignee: AGA Rangemaster Ltd
Current assignee: AGA Rangemaster Ltd
Priority date: 2010-12-21
Filing date: 2011-12-19
Publication date: 2012-06-27
Anticipated expiration: 2031-12-19
Also published as: GB201021606D0; GB201121834D0; GB2486802B

Abstract

A hob assembly has a housing with a non-conductive ceramic cooking surface 2 fixed to a perimeter frame 1, and a lower support frame (5, fig 2) which presses an induction heater (6, fig 2) in contact with the underside of the cooking surface 2 by a fixing assembly which comprises a bracket having a base part 9 fixed to the housing and a tab which protrudes downwards from the base part through a slotted opening (22, fig 8) in the lower support frame, the tab having a coil spring 15 which is located in a loop-shaped opening so that the spring acts on the underside of the lower frame. The bracket is riveted to the perimeter frame 1, and the spring 15 has a small diameter end (16, fig 5) with a bolt or screw (18, fig 6) that engages a tang (13, fig 4c) of the bracket. During assembly the spring is compressed and slid into the opening.

Description

A CERAMIC HOB ASSEMBLY

This invention relates to improvements in hob assemblies, in particular inductive hob S assemblies which include a non-conductive, e.g. glass ceramic, cooking surface.

It is known to provide hob assemblies for use when cooking in domestic or commercial kitchens. The hob assembly comprises a cooking surface supported by a perimeter support frame within a housing. At spaced locations within the boundaries of the surface one or more heating zones are defined on which pots and pans can be placed, the heating zones being controllable to heat the pots and pans.

Traditionally the heating zones have been defined by resistive electric elements or gas burners. These have the disadvantage that they remain hot long after they have been switched off They are also difficult to keep clean. Recently it has been known to provide a hob which comprises a cooking surface, such as a ceramic sheet, and in which the heating zones are defined by one or more inductive heating devices located underneath the surface. These work by creating a magnetic field using in an inductive coil, which passes through the ceramic cooking surface to any ferromagnetic cooking pots on the top of the surface. Eddy currents induced in the bases of the cooking pots by this magnetic field generate heat. This type of hob is easy to keep clean, and cools rapidly when the coils are de-energised.

Hobs, and cookers which include hobs, are available in a variety of widths and depths, with the most common being either 60cm or 90cm in width and approx 60 cm in depth to coordinate with standard size kitchen units and worktops. Wider cookers, often with two or more ovens located side by side, are also available, so called range cookers.

According to a first aspect the invention provides a hob assembly comprising: a housing including a perimeter support frame and a non-conductive cooking surface fixed to the support frame, and a lower support frame which supports an induction heating assembly which includes at least one inductive heating device, the lower support frame being located underneath the cooking surface such that the at least one heating device is in contact with the underside of the cooking surface, in which the lower support frame is secured to the housing by at least one fixing assembly, in which the fixing assembly comprises: a bracket having a base part which is fixed to the housing and a tab which protrudes downwards from the base part through an opening in the lower support frame, the tab S defining an at least partially closed space on the opposite side of the lower frame to the cooking surface, and a coil spring which is located at least partially within the space, one end of the coil spring acting upon a portion of the tab that is spaced away from the lower support frame and the other end of the spring acting upon the underside of the lower frame adjacent the base part of the bracket, the spring at least partially holding the lower frame up to press the at least one induction heating device into engagement with the underside of the ceramic cooking surface.

By fixing the cooking surface to the support frame using a fixing bracket and a spring ensures that some movement is possible, resisted by the spring, as differential heating of the hotplate and support frame occurs during the use of the assembly. If a rigid fixing is provided the applicant has appreciated that over time the fixing may either fail or the hotplate may crack due to the stresses that arise.

A secondary advantage of the present invention is that the fixing assembly can also readily be assembly by pressing the hotplate into position under the support frame, and then by hand compressing the coil spring and then inserting it into the spaced defined by the tab of the bracket.

A further advantage is that the springs will absorb shock loads on the ceramic surface which may occur during transit of the hob assembly, either due to direct impact on the ceramic surface or if the hob is dropped. The shock absorption may reduce the risk of the hob being damaged.

The spring preferably comprises a coil spring.

The fixing assembly may be arranged so that it can be moved from a dis-asscmblcd state in which the lower support frame is free of the housing and an assembled position in which it fixes the lower support frame to the housing without the usc of any tools, e.g. suitable for hand assembly.

The induction healing module may comprise at least one inductive healing coil which contacts the underside of the ceramic cooking surface. This may be supported by the lower frame between the frame and the cooking surface. The support plate may also support an electronic module for driving and controlling the inductive healing device.

This may be located on the opposite side of the lower frame to the inductive healing coil, and may be connected to it through conductive wires.

The lower support frame may be free to move horizontally and vertically relative to the housing with this movement being constrained within a predefined range solely by the at least one fixing assembly. For instance, the engagement of the coil spring with the hotplate and tab may be the limiting constraint on the amount of movement possible.

The ceramic plate may also be free to move horizontally by a limited amount within the perimeter support frame of the housing.

The perimeter frame of the housing may comprise a large pressing. It may be pressed as a single part from a sheet of stock material. It may form the outer edge of the hob assembly. It may include one a plurality of cooling slots along one edge.

To facilitate this movement of the lower support frame relative to the housing, the tab of the bracket may pass through an oversized slot in the support frame such that the tab does not touch the sides of the opening in the support frame. The relative sizes of the slot and the tab define the amount of allowable movement of the support frame relative to the housing.

The amount of horizontal movement possible may be dependent upon the size of the cut-out in the tab, the thickness of the ceramic plate in the region where the tab passes through it, and the length of the coil spring when fully compressed.

The coil spring may engage the tab directly, but most advantageously it engages the tab indirectly through a locating spacer.

The locating spacer may comprise a head and a shaft that extends away form the head, in which the diameter of the head is greater than the diameter of the end of the coil.

The tab may include a protruding portion, or tang, which extends into the space and extends into a depression in the head of the spacer, with the coil spring surrounding the shaft such that the end of the coil spring engages the underside of the head of the locating spacer.

The locating spacer may, conveniently, comprise a bolt or screw or part of a bolt or screw. The depression may then be formed by the drive slot of the bolt or screw.

The bracket may include a secondary protrusion, or tang, nearest the base portion of the bracket which extends into the space and locates the end of the coil spring that engages the underside of the lower support frame.

The bracket may be an inverted L-shaped, with the base of the L shape comprising a flat plate which forms the base part of the bracket and which is secured to the lower support frame and the stem of the L shape comprising a plate which defines the tab.

The space defined by the tab may comprise a central opening in the tab which may provided with a continuous perimeter so that the tab forms a loop which carries the protrusion that engages the bolt or screw head. This gives the tab the appearance of a small square or circular (or other shaped) closed frame, the spring and optional locating spacer being located within the open centre of the frame.

Alternatively the tab may comprise a hook shape, perhaps of C-shape, with the space being defined as that space which is partly surrounded by the material of the tab and the base.

The base of the bracket may be fixed to the support frame by rivets or welds.

The use of a bolt or screw as part of the fixing assembly reduces the cost of producing the assembly. Only the bracket is needs to be bespoke, with the coil spring and suitable bolts or screws readily available off the shelf There may be at least four fixing assemblies, with one provided towards each corner of the lower support frame.

The coils spring may be a conical coil spring, such that the diameter of the end of the coil which contacts the underside of the ceramic hotplate is larger than the diameter of the end of the coil which engages the underside of the bolt or screw. This spreads the load of the hotplate onto the coil, yet allows a relatively small bolt of screw to be used. This shape of spring also makes hand assembly of the fixing assembly relatively simple without tools.

One or more spacers may be located between the spring and the support plate, the spring and the underside of the bolt or screw and/or between one or more coils of the spring. This allows the amount of compression applied by the coil spring to be varied very easily, by altering the location and thickness of spacers used.

The housing may form part of the outer housing of a hob assembly suitable for inserting into an opening in a preparation surface. It may form a top for a cooker such as a range cooker.

According to a second aspect the invention provides a fixing assembly for use in securing a lower support plate to a housing of a hob according to the first aspect of the invention.

The fixing assembly may include any of the features described hereinbefore.

There will now be described, by way of example only, one embodiment of the present invention with reference to and as illustrated in the accompanying drawings of which: Figure 1 is a view from above of an embodiment of a hob assembly in accordance with the first aspect of the invention; Figure 2 is a cross sectional view of the hob assembly of Figure 1 taken along the section line A-A as marked in Figure 1; Figure 3 is an enlarged view in cross section of the part of the hob assembly enclosed by the dotted circular line marked B in Figure 2; Figure 4(a) is a plan view, (b) a view in cross section and (c) a perspective view of a bracket forming a first part of a fixing assembly used in the hob assembly of Figure 1; Figure 5 is a perspective view of a coil spring which forms a second part of the fixing assembly; Figure 6 is a cross sectional view of a cut-down bolt or screw which forms a third part of the fixing assembly; Figure 7 is a view in perspective showing how the three parts of the fixing assembly co-operate when assembled; and Figure 8 is a view in elevation of the fixing assembly as used to secure the lower support frame of the hob assembly to the housing.

The hob assembly shown in Figure 1 comprises a housing which comprises a large steel pressing which forms a rectangular perimeter frame 1. Located within the frame is a sheet 2 of electrically insulating material, in this case a ceramic, i.e. glass sheet, that forms a flat continuous cooking surface. It is secured to the frame 1 by a bead of suitable resilient adhesive material 3 around its outer edge. The frame 1 extends around all sides of the ceramic sheet 2 and supports the weight of the sheet 2 and any cooking utensils placed on the upper surface of the sheet 2. One long edge of the frame 1 is provided with a set of cooling slots 4 which allow hot air to pass through the frame.

Below the surface of the ceramic sheet 2, and secured to the steel pressing of the housing 1, is a lower support frame 5. This can be seen in Figure 2 and in part in Figure 3 of the drawings. This lower support frame 5 comprises a generally rectangular steel plate, slightly larger in width and length than the ceramic sheet 2 but smaller in width and length than the outer edge of the housing 1. The lower support plate S supports five inductive heating elements 6 on its upper face, which are in contact with the underside of the ceramic plate. Of course, there may be more heating elements or less heating elements in other embodiments whilst still remaining within the scope of the present invention. The inductive heating elements each define four discrete heating zones.

The lower support plate 5 also supports an electronic drive and control circuit 7 which powers the inductive heating elements 6. This can be seen in Figure 2 of the drawings.

The heating elements 6 and electronic drive and control circuit 7 as such are well S known in the art and will not be described in detail here. In brief, each heating element comprises at least one inductive coil, and the electronic circuit includes one or more switches that supply a suitable alternating drive current for the coils. A magnetic sensor is also associated with each coil that turns off the current to the coil if it does not detect the presence of a ferrous object close to it.

As known in the art, to use the hob assembly a pan must be placed on the surface of the ceramic which consists of a ferromagnetic material at least in its base. The electronic drive and control circuit applies an alternating current to the coil of the inductive heating clement which generates a high frequency electromagnetic filed.

This penetrates the non-conductive ceramic sheet and penetrates the base of the pan, setting circulating eddy currents. These currents cause the pan to heat up, which in turn heats the contents of the pan. When the pan is removed the current to the coil is automatically cut-off by the electronic circuit in response to the output from the sensor.

The lower support frame S is fixed to the perimeter frame of the housing such that the coils are pressed into intimate contact with the underside of the ceramic plate using a set of eight fixing assemblies 8. One fixing assembly 8 is shown in Figure 7 and Figure 8. Three are located at spaced locations along the long edges of the lower support frame and one additional one is located at the centre of each of the short edges.

Each fixing assembly 8 comprises a bracket as shown in Figures 4(a) to (c). The bracket has a base portion 9 which includes two holes that enable it to be riveted to the underside of the perimeter frame of the housing 1. A tab 10 extends orthogonally away from one edge of the base portion 9 so that the bracket is L-shaped in cross section. In use the L-shapc will be inverted. The tab 10 comprises a closed loop with a generally square outer perimeter, the outer corners of which are rounded off so that they are not sharp. The inside of the loop is formed by a cut-out and defines a large opening 12. Two tangs 13, 14 extend inwardly towards the centre of the opening 12. A first one 13 is located along the edge of the cut-out furthest from the base, and a second one 14 is located along the edge of the cut-out nearest the base.

Each fixing assembly 8 also comprises a coil spring 15 as shown in Figure 5 of the S drawings. This is smaller in diameter at one end 16 than at the other end 17. The length of the coil spring when unloaded is greater than the spacing between the tips of the tangs 13 and 14.

Finally, the fixing assembly 8 also includes a small bolt or screw 18, having a shank 19 and a head 20. A suitable screw is shown in Figure 6 of the drawings. The head of the bolt or screw 18 is larger in diameter than the diameter of the smaller end 16 of the coil spring 15. The head is slotted to receive a Philips type screw driver, and the first tang 13 of the bracket is sized to fit snugly within the slot 21. Other shape slots could be used of course, as long as they can receive the tip of the tang.

In use the brackets are fixed to the underside of the housing 1 by rivets so that the tabs extend vertically downwards. The tab 10 of the bracket extends through an oversized slot 22 in the lower support frame 5 SO that the cut-out part of the tab 10 and the two tangs 13, 14 extend beyond the underside of the support frame. This can be seen in Figure 8 of the drawings. The coil spring iSis located within the cut-out so that the tang 14 closest the base part of the bracket is located inside the wider end of the coil spring. The bolt 18 is located with the bolt shank 19 inside the coil spring 15 so that the narrow end 16 of the coil spring 15 abuts the underside of the bolt head 20. The tang 13 ncarest the free end of the tab 10 is then located within the slot in the head of the bolt. The spring 15 is held in compression and urges the lower support plate S upwards towards the underside of the ceramic cooking surface 2. This forces the induction device to contact the ceramic sheet 2.

The bracket can be made by stamping and pressing or folding a sheet of metal such as steel. This makes it inexpensive to produce. The bolt can be selected from a wide range of bolts, or even screws. If required, the shaft of the bolt could be but down a little in length.

To assemble the hob assembly, the perimeter housing 1 may first be fitted with the ceramic sheet 2 and then placed upside down on a work surface. The tabs are then fitted, if not already in place, with the tabs of the brackets facing upwards. In a next step the lower support plate iS s lowered into position with the tabs protruding through the slots 22 in the plate. A spring 15 is then selected, and the wider end of the spring is placed on the underside of the support plate S (which is facing upwards) S adjacent the tab. A bolt 1 8 is then placed in the upper free end of the spring (if it has not already been placed there) so that it is supported on the underside of the head 20 by the end of the spring 15. The spring 15 is then compressed by hand and the spring and bolt slid across underneath the tang 13 in the tab. The spring 15 is then released and the protrusion on the end of the tab slots into the slot in the upper face of the head to securely locate the spring in place.

This is repeated for each fixing assembly, and finally the whole assembly is turned over so that it can be secured to the top of a cooker body if required, or to go onto final packaging if not.

Claims

CLAIMS1. A hob assembly comprising: a housing including a perimeter support frame and a non-conductive cooking surface fixed to the support frame, and a lower support frame which supports an induction heating assembly which includes at least one inductive heating device, the lower support frame being located underneath the cooking surface such that the at least one heating device is in contact with the underside of the cooking surface, in which the lower support frame is secured to the housing by at least one fixing assembly, in which the fixing assembly comprises: a bracket having a base part which is fixed to the housing and a tab which protrudes downwards from the base part through an opening in the lower support frame, the tab defining an at least partially closed space on the opposite side of the lower frame to the cooking surface, and a spring which is located at least partially within the space, one end of the spring acting upon a portion of the tab that is spaced away from the lower support frame and the other end of the spring acting upon the underside of the lower frame adjacent the base part of the bracket, the spring at least partially holding the lower frame up to press the at least one induction healing device into engagement with the underside of the ceramic cooking surface.
2. A hob assembly according to claim 1 in which the spring comprises a coil spring and engages the tab indirectly through a locating spacer, in which the locating spacer comprises a head and a shaft that extends away form the head, in which the diameter of the head is greater than the diameter of the end of the coil, and in which the tab includes a protruding portion, or tang, which extends into the space and extends into a depression in the head of the spacer, with the coil spring surrounding the shaft such that the end of the coil spring engages the underside of the head of the locating spacer.
3. A hob assembly according to claim 2 in which the locating spacer comprises a boll or screw or part of a boll or screw.
4. A hob assembly according to claim 2 or 3 in which the bracket includes a secondary protrusion, or tang, nearest the base portion of the bracket which extends into the space and locates the end of the coil spring that engages the underside of the lower support frame.
5. A hob assembly according to any one of claims 2 to 4 in which the space defined by the tab comprises a central opening in the tab provided with a continuous perimeter so that the tab forms a loop which carries the protrusion that engages the bolt or screw head.
6. A hob assembly according to any preceding claim in which the spring is a conical coil spring, such that the diameter of the end of the coil which contacts the underside of the ceramic hotplate is larger than the diameter of the end of the coil which engages the underside of the bolt or screw.
7. A bob assembly according to any preceding claim in which the fixing assembly is arranged so that it can be moved from a dis-assembled state in which the lower support frame is free of the housing and an assembled position in which it fixes the lower support frame to the housing without the use of any tools.
8. A hob assembly substantially as described herein with reference to and as illustrated in the accompanying drawings.