GB2291496A - Electric cooker ovens - Google Patents

Abstract

An electric cooker oven has a hydraulic bulb sensor (9) which may extend from one oven liner (4) to the other oven liner (5). The oven liners support shelves and the heating elements (6, 7) are located between the liners and the oven wall. Previously a short bulb, typically extending between lines 12 and 13 was used, but this found was not to be so responsive to average oven temperature as the longer bulb. <IMAGE>

Description

ELECTRIC COOKER OVENS This invention relates to electric cooker ovens.

Such ovens typically consist of an oven cavity, a pair of oven liners adjacent opposed sides of the oven cavity, the liners being arranged to provide support for shelves, and electric heating elements interposed between the liners and adjacent sides of the oven cavity.

Heating of the food to be cooked takes place via some direct radiation but mostly via convection air currents. A thermostat, usually of the remote-acting hydraulic type, controls the oven air temperature according to the setting of a thermostat adjuster knob. The thermostat sensing bulb, constructed at the end of a hydraulic capillary tube, is usually conveniently sited towards the top of the rear panel of the oven, where it will not interfere with cooking operations. The bulb is relatively short and centrally mounted with respect to the sides of the oven.

Sometimes, the oven is fitted with an electric motor-driven fan in order to mix thoroughly the oven circulating air. In this type of oven there is no difficulty in accurately sensing the true air temperature of the oven air and good cooking control is relatively easily obtainable.

In ovens not fitted with circulating fans, there is sometimes difficulty in obtaining good correlation between average oven air temperature and that obtaining at the sensing bulb of the control thermostat, with the result that the cyclic temperature of the control thermostat is enlarged in terms of cyclic variation of the average oven air temperature. Thus, while the control thermostat will switch off the electric heating elements when it reaches a predetermined upper temperature controlled by the thermostat adjuster knob, and will switch them back on when it falls below a predetermined lower temperature limit 5-10"C below the upper temperature limit, the oven temperature might cycle between maximum and minimum temperatures 25-30"C apart.

It might be thought that this problem could be overcome by reducing the differential of the cyclic variation of the thermostat, but this could firstly entail difficulties in manufacturing the thermostat and, more importantly, the thermal inertia of the oven and its contents could prevent it accurately following short bursts of input heat and hunting could occur, possibly leading to an undesirable build-up of oven temperature.

The invention provides an electric cooker oven comprising an oven cavity, a pair of oven liners adjacent opposed sides of the oven cavity, the liners being arranged to provide support for shelves, electric heating elements interposed between the liners and adjacent sides of the oven cavity, and a hydraulic oven temperature sensor arranged in the vicinity of the top of the oven cavity, the sensor extending in a direction from side to side of the oven cavity to such an extent that at least one end of the sensor lies in the vicinity of a position above an oven liner.

By arranging that at least one end of the sensor is in the vicinity of a position above an oven liner, and hence more strongly influenced by convection heating from the element between the liner and the adjacent side of the oven cavity than was the short centrally placed sensor which was used hitherto, the temperature of the sensor more accurately reflects the average oven air temperature and the sensor can thus control the average oven air temperature within closer limits.

Advantageously both ends of the sensor lie in the vicinity of positions above the oven liners on respective sides of the oven.

An electric cooker oven constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, which is a schematic view of the electric cooker oven.

The oven may form part of a freestanding cooker, or may be a built-in oven. The door of the oven is not shown. The oven consists of a cavity indicated generally by the reference numeral 1 having opposed side walls 2, 3. Liners 4, 5 are mounted inside the oven walls, and are provided with recesses such as 4a, Sa for supporting shelves. Between each liner 4, 5 and its respective side 2, 3 of the oven cavity are positioned electric heating elements 6, 7 which are energised via a control knob 8, which is mounted in a suitable position on the appliance, although it is shown for convenience separated from the appliance.

Rotation of the knob 8 alters the temperature at which hydraulic sensor 9 operates contacts (not shown) in the switch head 10 to cease the supply of electric current to the electric heating elements 6, 7. The contacts are controlled by a bellows (not shown) which is linked by means of a capillary tube 11 to the hydraulic sensor 9. Expansion of a fluid in the hydraulic sensor due to heating in the oven causes expansion of bellows and consequent opening of contacts.

It was customary to provide a hydraulic sensor hitherto in the illustrated position adjacent the roof of the oven, but the sensor typically only extended between the lines 12, 13.

A problem arose with such an existing sensor with ovens which were not fitted with fans to circulate the air. The control knob 8 could have been set to, say, 200"C, and the electric elements would have been switched off when the sensor reached that temperature. When the sensor cooled by, say, 10"C (depending on the cyclic variation of the thermostat), the elements would have been switched back on. However, in reheating the oven to raise the bulb temperature by 10 C, the actual heat input would be such that the average oven temperature rose by more than this value. Equally, by the time the temperature of the bulb had fallen by 10 C to switch the elements back on, the actual average oven temperature would have fallen by more.It was found that the cycling of the bulb was exaggerated by a factor of two to three times in terms of average oven temperature.

In accordance with the invention, the thermostat bulb is lengthened so that it extends from a position above one liner right across to a position above the other liner. The bulb is still supported centrally as before.

Now the convection currents from the heating elements affect the bulb far more directly than before, with the result that the bulb is far more representative of average oven temperature. The temperature of the bulb is accelerated in both heating and cooling cycles by the direct effect of the relatively low thermal inertia of the heating elements, the net effect of which is a better correlation between the average oven and sensor temperatures.

It follows that the bulb is able to control average oven temperature to within much closer limits than hitherto.

Of course, variations may be made without departing from the scope of the invention.

Thus, for example, the ends of the sensor bulb need not lie precisely at a position above the respective oven liners. For example, it may extend to positions short of the respective oven liners or beyond the respective oven liners.

Claims (3)

1. An electric cooker oven comprising an oven cavity, a pair of oven liners adjacent opposed sides of the oven cavity, the liners being arranged to provide support for shelves, electric heating elements interposed between the liners and adjacent sides of the oven cavity, and a hydraulic oven temperature sensor arranged in the vicinity of the top of the oven cavity, the sensor extending in a direction from side to side of the oven cavity to such an extent that at least one end of the sensor lies in the vicinity of a position above an oven liner.

2. An electric cooker oven as claimed in claim 1, in which both ends of the sensor lie in the vicinity of positions above oven liners at respective sides of the oven.

3. An electric cooker oven substantially as herein described with reference to the accompanying drawings.