GB2230926A - Microwave oven with improved cooling of the magnetron - Google Patents

Abstract

A combined oven with the thermal and microwave modes of operation comprising a cooking chamber above which is disposed a magnetron 3, a control zone 7 which is disposed above the cooking chamber, a fan 2 for cooling the magnetron and a first conduit 5 which connects the fan to the magnetron and the magnetron to the cooling air outlet, wherein the fan is arranged to feed in parallel with the first conduit 5 a second conduit 4 which is separated from the first conduit 5, said second conduit 4 being of substantially lower height than the first conduit and extending in a position substantially adjacent to the surface 1 which acts as a roof for the oven. <IMAGE>

Description

MICROWAVE OVEN WITH IMPROVED COOLING OF THE MAGNETRON The present invention concerns a microwave oven, in particular a microwave oven which also operates in accordance with conventional thermal procedures, provided with a particular arrangement for cooling of the magnetron.

It is known that there is a particular category of ovens, referred to as combined ovens, which simultaneously offer a conventional mode of operation, that is to say involving the generation of heat by means of electrical resistors or by means of the combustion of a gas, together with a microwave mode of operation.

As is known, microwaves are generated by an emitting valve referred to as a magnetron which transforms electrical energy (raised from the mains voltage to about 4000 volts by means of a high voltage transformer and a multiplier diode) into electromagnetic energy. That is in turn directed by means of the antenna of the magnetron into the cooking chamber into which the food to be dealt with (defrosted, cooked, heated) has been previously introduced.

When the radiation which is generated in that way meets the food, it gives rise to the well known and desired heating effect which is due to the conversion of the electromagnetic energy into thermal energy.

The procedure thus completes the cycle of conversion of energy, from electrical energy to electromagnetic energy and from the latter to thermal energy.

While however the conversion of electromagnetic energy into thermal energy takes place with practically 100% efficiency, that is not the case when converting electrical energy into electromagnetic energy. In that case in fact part of the electrical energy which is expended in the conversion operation (approximately 50%) is directly transformed into thermal energy which is generated within the magnetron and other operating components such as the high voltage transformer.

For that reason all those components and primarily the magnetron tend to undergo a rapid rise in temperature and since the mass of the latter is modest, that rise in temperature could rapidly cause damage thereto unless a cooling system were systematically adopted. In ovens for domestic use, the cooling system is of the forced air type in which, by passing air over suitable cooling vanes provided on the body of the magnetron itself, the temperature thereof is kept within acceptable limits.

However in what are known as combined ovens, when the microwave mode of operation is superimposed on the conventional heating mode, it can happen that the zone (outside the cooking chamber) in which said operating components are accommodated is subjected to a double heating action. That is due a) to the magnetron and b) to the dissipation of heat from the walls of the oven. This can therefore give rise to a critical thermal situation in regard to the components which are disposed around the cooking chamber.

Various processes and apparatuses have been studied and applied for remedying the above serious problem, for the purposes of effectively cooling both the magnetron and the external zone, in particular the upper zone of the cooking chamber.

However, those processes and arrangement in turn suffer from disadvantages, in particular in regard to cost and size, which will now be illustrated.

One of those solutions provides for using a fan with suitable conduits appropriately dedicated to cooling the magnetron, and a second fan with corresponding separate ducts for cooling the external zone of the cooking chamber.

That arrangement provides the desired result but it suffers from the disadvantages of involving a complicated and expensive construction in regard to the oven and a reduction in the usable volume of the oven, because of the volume of space occupied by the fan and the air ducts (with the oven being of the same outside dimensions).

A second type of solution involves placing the magnetron in such a way that it is virtually completely immersed in the forced air duct which coos the oven, in particular at the roof of the oven. That construction assists in reducing the level of costs and in part also the amount of space occupied but it gives rise to the danger that, when the oven is very hot, the cooling air is raised to a high temperature level before passing over the magnetron, so that the latter can no longer be effectively cooled.

Another disadvantage of the above type of construction is that the various operating components of the oven are generally disposed either in the area of the controls or around the cooking chamber1 that is to say it is not possible to separate or construct separately the controls area and the cooking chamber or oven in a true sense.

It would be desirable, and this is the aim of the present invention, to be able.to provide a multi-functional oven designed in such a way as to overcome the above discussed disadvantages, by providing a structure for the cooling system which is as described in the accompanying claims.

According to the present invention, there is provided a combined oven with the thermal and microwave modes of operation comprising a cooking chamber above which is disposed a magnetron, a control zone which is disposed above the cooking chamber, a fan for cooling the magnetron and a first conduit which connects the fan to the magnetron and the magnetron to the cooling air outlet, wherein the fan is arranged to feed in parallel with the first conduit a second conduit which is separated from the first conduit, said second conduit being of substantially lower vertical height than the corresponding height of the first conduit and extending in a position substantially adjacent to the surface which acts as a roof for the oven.

As will become apparent from the following description, the illustrated embodiment of the invention can provide an oven in which all the operating components are contained in a box or module which can be preassembled and pretested for approval, therefore to permit production of the cooking chamber and the associated structure by some manufacturers and construction of the module with the operating components by another manufacturer, thereby permitting the assembly of a single type of module with the operating components on structurally different ovens.

The invention will be better appreciated from the following description which is given solely by way of nonlimiting example with reference to the accompanying drawings in which: Figure 1 is a view from above of the upper zone of the oven according to the invention; and Figure 2 is a side view in section through the centre of the upper zone of the oven according to the invention The following components can be seen in figure 1: the roof of the oven 1, the fan 2, the magnetron 3, the horizontal flat conduit 4 of effectively constant section along its length for cooling the oven, the flat horizontal conduit 5 of variable section, of flared configuration, for cooling the magnetron, and the handles 6 of the door of the oven.

Referring to figure 2, shown thereon is the magnetron 3, the flat horizontal conduit 4 for cooling the oven, the conduit 5 for cooling the magnetron, the fan 2, the roof of the oven 1, the handles 6 of the door of the oven, the zone 7 between the cooking chamber of the oven and the external casing in which all the components for microwave operation of the oven are accommodated, primarily the magnetron 3.

The mode of operation of that oven will now be clear.

The fan 2 draws in air from the control panel (from the side and through the holes for the knobs 8 of the control members 9 of the oven) and directs it, by blowing same, into both the conduits 4 and 5 which do not have any connection between themselves except obviously the intake and outlet openings thereof which are adjacent.

The air which is thus guided within the lower conduit 4 is directed towards the outlet at the level of the handle 6.

The lower conduit 4 is designed in accordance with a geometry of trapezoidal shape, as can be clearly seen from figure 1. It is interrupted approximately in its central region by a vertical 'chimney' which is used for accommodating the magnetron 3. The chimney is completely separated from the conduit 4 by partitioning walls in such a way that the air which flows within the conduit 4 does not have any effect whatever on the magnetron.

The air which is guided within the upper conduit 5 is however blown directly between the cooling vanes on the magnetron 3.

It is essential, for the purposes of improving the efficiency of the magnetron cooling action, that the greatest possible amount of fresh air is blown towards the magnetron by the fan, as it is also desirable that the duct for discharge of the cooling air is as low as possible for reasons of space in the control zone 7 and because the front outlet slots are limited in height by the thickness of the handle of the door.

The conduit 5 is thus of a double-taper configuration, as can be clearly seen from figure 2.

The first part of the conduit 5 in fact connects the fan 2 to the magnetron 3. That first part of the conduit is tapered since it is required to match the width of the fan outlet to the small dimensions of the magnetron.

The second part of the conduit carries the hot air coming from the magnetron towards the front outlet, which is also at the level of the handle 6.

The second part of the conduit 5 is of a flared configuration since it is required to adapt the dimensions of the magnetron to the width of the outlet opening.

Looking therefore at the particular overall geometry of the conduit 5, it will immediately be seen that, in order to prevent throttling effects in regard to the air flow section, it is essential for the area of the air flow section of the conduit to be maintained at as constant a value as possible.

Since therefore the conduit is of a restricted configuration, that means that it is necessary for it to be increased in height as the width thereof decreases in such a way as to keep the overall sectional area thereof unchanged, when the geometry thereof varies.

As can be seen from figure 2, the conduit 5 is of a height which increases from'the inlet opening as far as the magnetron, and a corresponding height which decreases from the magnetron to the outlet opening.

Claims (5)

1. A combined oven with the thermal and microwave modes of operation comprising a cooking chamber above which is disposed a magnetron, a control zone which is disposed above the cooking chamber, a fan for cooling the magnetron and a first conduit which connects the fan to the magnetron and the magnetron to the cooling air outlet, wherein the fan is arranged to feed in parallel with the first conduit a second conduit which is separated from the first conduit, said second conduit being of substantially lower vertical height than the corresponding height of the first conduit and extending in a position substantially adjacent to the surface which acts as a roof for the oven.

2. An oven according to claim 1 wherein the conduit intercepts in its central zone a vertical chimney which is separated from said conduit by partitioning walls, said chimney being arranged to accommodate the magnetron.

3. An oven according to claim 2 wherein the second conduit is of a section whose area is substantially constant along its length.

4. An oven according to claim 3 wherein the magnetron, the fan, the two conduits, the controls with the associated panel and the operating components associated with the controls are contained in a single removable and operationally autonomous assembly.

5. A microwave oven constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.