GB2348747A - Electric hob control with plate warming mode - Google Patents

Abstract

A cooking hob includes a heater 16 operable to heat a heated zone and a control circuit 10, 12, 14 operative to control a supply of electricity to the heater. The control circuit is operable by way of a select switch 12 in a first mode in which the supply of electricity, by way of an energy regulator 10, is sufficient to heat the heated zone to a temperature suitable for cooking and a second mode in which the supply of electricity, by way of a warming pulse timer 14, is restricted to heat the heated zone to a temperature suitable for warming an item on it e.g. a dish or plate. The warming pulse timer operates to reduce the frequency of pulses applied to the heater circuit from energy regulator 10.

Description

COOKING HOBS The present invention relates to cooking hobs. More particularly, the invention relates to a system which enables a heated zone of a cooking hob to be used both for cooking and as a warming zone.

A typical electric cooking hob includes a plurality of heaters positioned to direct heat onto heated zones of the hob. The heaters may have a single circuit, or they may have multiple circuits, to give different heat levels or different heated areas depending on the control means.

Heat output of each heater is normally controlled by an energy controller which controls the rate at which electrical energy is supplied to the heater. The energy controller may include an energy regulator which operates cyclically to energise and de-energise the heater. Power input to the heater (and therefore the temperature of the heater) is controlled by modifying the ratio between the length of time that the heater is energised and deenergised. In the case of dual-or multi-circuit heaters, an alternative energy controller may be used which incorporates a switch to selectively connect different heater circuits. This can either be used directly to give different heat levels depending on the circuits connected or in conjunction with energy regulator control of the heat output to select different parts of the heater.

While an energy regulator, at its minimum setting, can have an average power output of as low as about 7 percent of the maximum power output, an energy regulator typically has an ON time of about 6 seconds followed by an OFF time of up to about 85 seconds. The relatively long ON period results in the heater becoming too hot for use as a warming zone.

That is the heater may well glow red hot and could cause plates to crack.

As is well-known, there are various types of hob construction, including glass ceramic construction, and alternatives which, for example, include sealed plate heaters mounted in a metal or toughened glass subframe.

This invention has applicability to a wide range of electric hob constructions.

It is normal to provide user controls which allow a user to adjust the power that the energy controllers supply to the heaters, and thereby control the temperature of the heated zones. However, the range of temperatures that a user can obtain is limited on the assumption that the heated zone will be used for cooking. Typically, the highest temperature is intended for rapid boiling or hot frying, while the lowest temperature is intended for slow simmering.

There is generally limited useable space available on a cooking hob and a dedicated warming zone uses hob area which could otherwise be used for cooking. With smaller, generally four heater, hobs it is not practicable to provide a dedicated warming zone and dedicated warming zones are therefore only provided on larger hobs.

Consequently, there is a demand for a cooking hob in which at least one of the zones can function both as a heated zone for cooking purposes and as a warming zone.

According to the present invention there is provided a cooking hob having a heater operable to heat a heated zone and a control circuit operative to control a supply of electricity to the heater, in which the control circuit is operable in a first mode in which the supply of electricity is sufficient to heat the heated zone to a temperature suitable for cooking and a second mode in which the supply of electricity is restricted to heat the heated zone to a temperature suitable for warming an item placed on it.

The heated zone can be used safely to warm an item, thereby achieving the function of a dedicated warming zone. As compared with a conventional cooking hob, a hob embodying the invention requires only the provision of a modified control circuit.

The control circuit typically comprises a first power control stage which operates to control the supply of power to the heater when the circuit is operating in its first mode.

In embodiments according to the last-preceding paragraph, the circuit may further include a power reduction stage operative, when the circuit is operating in the second mode, to receive power supplied from the first power control stage and to supply a lesser power to the heater circuit.

In many embodiments, the first power control stage includes an energy regulator operative to generate pulses of electricity on a switched live output. Most typically, these pulses can be varied in duration and/or frequency by a user control in order that the temperature of the heated zone can be adjusted.

In embodiments according to the last-preceding paragraph, the power reduction stage typically operates to reduce the duration of or the frequency of the pulses applied to the heater circuit.

In an alternative configuration, the control circuit typically comprises a first power control stage which operates to control the supply of power to the heater when the circuit is operating in its first mode and a second power control stage which operates to control the supply of power to the heater when the circuit is operating in its second mode. In such embodiments, the second power control stage typically operates independently of the first power control stage.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figures 1 to 7 show circuit configurations of alternative embodiments of the invention.

Each embodiment comprises a hob having a plurality of heated zones. Associated with each heated zone is a heater having one or more heater circuits. When energised, the or each heater circuit generates heat which causes heating of the heated zone.

Power is supplied to each of the heater circuits by a control circuit. At least one control circuit is suitably constructed to implement the invention. The control circuits of various embodiments will now be described in detail.

The First Embodiment : Figure 1 The first embodiment implements the invention in a singlecircuit heater and provides controlled cooking and warming temperatures.

A control circuit includes an energy regulator 10, a select switch 12, and a warming pulse timer 14 to supply power in a controlled manner to a heater circuit 16. The control circuit is connected to live and neutral lines of a mains supply at L and N.

The energy regulator 10 operates to provide an output on a switched-live line 20. In this embodiment, the energy regulator is of a type which incorporates an electricallyheated bimetallic strip to control a microswitch. A user control, typically a rotary knob, allows a user to control the power supplied to the heater circuit 16. Construction and operation of the energy regulator 10 are conventional and will not be described in further detail here.

The select switch 12 in this embodiment is configured as a single-pole one-way switch. The select switch 12 is connected between the switched-live line 20 and an input line 22 of the heater circuit 16. The heater circuit 16 also has a line connected to the neutral mains supply line N. The warming pulse timer 14 has first and second lines connected across the select switch 12, and a third connection to the neutral mains supply line N.

The energy regulator 10 provides on its output continuous mains-voltage electricity at its maximum power setting and a sequence of on-off periods of mains-voltage electricity at lower power settings. The output of the energy regulator is applied to the switched-live line 20. When the select switch 12 is closed, the mains voltage is fed through the select switch 12 to the heater circuit 16. In this first mode of operation of the control circuit, the power supply to the heater circuit 16 is controlled by the energy regulator 10 alone, and the heated zone is therefore heated to a temperature suitable for cooking.

If the select switch 12 is opened, the mains voltage cannot pass directly to the heater circuit 16. Instead, in a second mode of operation, the mains voltage is received by the warming pulse timer 14. At the start of each period of mains voltage, the warming pulse timer 14 internally interconnects its first and second lines to reset the timer with the result that electricity passes through the warming pulse timer to the heater circuit 16. After a first predetermined interval, the warming pulse timer 14 breaks the connection between its first and second lines with the result that the supply of electricity to the heater circuit 16 ceases and after a second predetermined interval the warming pulse timer 14 re-establishes the connection so as to generate a series of pulses until such time as the energy regulator interrupts the supply of mains voltage.

The first predetermined interval is considerably shorter than the period of the mains voltage received from the energy regulator 10, with the result that the total power supplied to the heater circuit 16 is reduced. Consequently, the temperature of the heated zone is also reduced.

The appropriate pulse length will depend on many factors, including the power rating of the heater and the desired temperature of the heated zone. However, a first predetermined interval of about 2 seconds with a second predetermined interval of 10-15 seconds may be appropriate.

An optimum pulse length for any specific installation can readily be determined by straightforward experiment.

However, as compared with a conventional energy regulator the ON time is relatively short giving the heater insufficient time to heat up to an excessive temperature for warming purposes. Thus, while the glass ceramic cooking surface in a cooking hob can reach temperatures of typically 550 C during cooking, in warming mode the temperature will be significantly lower, such as in the range from 100 to 125 C.

As will be understood, the warming pulse timer 14 supplies pulses of power up to a predetermined pulse rate, with a pulse being initiated for each period of supply of mains voltage by the energy regulator 10. As the periods of mains voltage supplied by the energy regulator become increasingly spaced, so the initiation of pulses of power by the warming pulse timer also become increasingly spaced.

A user can therefore adjust the temperature of the heated zone up to a predetermined maximum while the circuit is operating in the second mode by adjusting the temperature setting of the energy regulator 10.

The Second Embodiment: Figure 2 The second embodiment implements the invention in a dualcircuit heater and provides controlled cooking and warming temperatures.

In the second embodiment, a control circuit includes an energy regulator 110, a select switch 112, and a warming pulse timer 114 to supply power in a controlled manner to first and second heater circuits 116 and 118. The control circuit is connected to live and neutral lines of a mains supply at L and N.

The energy regulator 110 operates to provide an output on a switched-live line 120 and to selectively connect a switched-neutral line 122 to the neutral supply line N.

In this embodiment, the energy regulator 110 is of a dualcircuit type which incorporates an electrically-heated bimetallic strip to control microswitches. A user control, typically a rotary knob, allows a user to control the power supplied to the heater circuits 116,118, and to select whether one or both of the heater circuits are to be energised. If the user chooses that both heater circuits 116,118 are to be ~energised, the energy regulator 110 causes the switched neutral line 122 to become connected to the neutral supply line N. Otherwise, the switched neutral line 122 is open-circuit.

The select switch 112 in this embodiment is configured as a single-pole one-way switch. The select switch 112 is connected between the switched-live line 120 and an input line 124 of the heater circuits 116,118. The first heater circuit 116 is also connected to the neutral mains supply line N, and the second heater circuit is also connected to the switched neutral line 122. The warming pulse timer 114 has first and second lines connected across the select switch 112, and a third connection to the neutral mains supply line N.

The energy regulator 110 provides on its output continuous mains-voltage electricity at its maximum setting and a sequence of on-off periods of mains-voltage electricity at lower power settings. The output of the energy regulator 110 is applied to the switched-live line 120. When the select switch 112 is closed, the mains voltage is fed through the select switch 112 to the heater circuit 116 to the neutral supply line N. If the energy regulator 110 is set for dual circuit operation, the mains voltage will also be fed through the second heater circuit 118 and through the switched neutral line 122 to the neutral supply line N. In this first mode of operation of the circuit, the power supply to the heater circuits 116,118 is controlled by the energy regulator 110 alone, and the heated zone is therefore heated to a temperature suitable for cooking.

If the select switch 112 is opened, the mains voltage cannot pass directly to the heater circuits 118. Instead, in a second mode of operation, the mains voltage is received by the warming pulse timer 114. At the start of each period of mains voltage, the warming pulse timer 114 internally interconnects its first and second lines to reset the timer with the result that electricity passes through the warming pulse timer to the heater circuits 116, 118. After a first predetermined interval, the warming pulse timer 114 breaks the connection between its first and second lines with the result that the supply of electricity to the heater circuits 116,118 ceases and after a second predetermined interval the warming pulse timer 114 reestablishes the connection so as to generate a series of pulses until such time as the energy regulator interrupts the supply of mains voltage. The first predetermined interval and the second predetermined interval are selected as described with reference to the first embodiment.

As in the case of the first embodiment, the warming pulse timer 114 supplies pulses of power up to a predetermined pulse rate, with a pulse being initiated for each period of supply of mains voltage by the energy regulator. As the periods of mains voltage supply become increasingly spaced, so the initiation of pulses of power by the warming pulse timer also become increasingly spaced. A user can therefore control the temperature in the second mode by adjusting the user control of the energy regulator 110.

Moreover, by appropriate setting of the user control, the user can select whether just one or both of the heater circuits 116,118 are to be energised when the circuit is operating in the second mode.

The Third Embodiment: Figure 3 In each of the above embodiments, the warming pulse timer 14,114 is energised whenever the heated zone is in use.

In many cases, this will pose no problem. However, there may also be occasions in which the warming pulse timer is to be energised only when the control circuit is operating in the second mode. The third embodiment implements the invention in a single-circuit heater and provides a controlled cooking temperature and a fixed warming temperature and ensures that the warming temperature is energised only while it is in use.

In this embodiment, the select switch 212 is a single-pole two-way switch. The common terminal of the select switch 212 is connected to the live supply line L and its first and second outputs are connected respectively to input lines of the energy regulator 210 and the warming pulse timer 214.

The energy regulator 210 is connected in a conventional configuration with its switched-live output 220 connected to the heater circuit 216. With the select switch 212 in a first position, the common terminal of the switch 212 is connected to its first output to energise the energy regulator 210. The control circuit then operates in a first mode such that"the energy regulator 210 supplies mains-voltage electricity to the heater circuit 216 in periods of sufficient duration to heat the heated zone to a temperature suitable for cooking. In this mode, there is no supply of power to the warming pulse timer 214.

The warming pulse timer 214 has first and second lines connected respectively to the second output of the select switch 212, and to the heater circuit 216 and a third connection to the neutral mains supply line N. In this embodiment, the warming pulse timer 214 operates such that a mains voltage appearing on its first line will cause the warming pulse timer 214 to interconnect its first and second lines for a predetermined time periodically, such that mains voltage pulses appear on its second line.

With the select switch 212 in a second position its common terminal is connected to its second output to energise the warming pulse timer 214 through its first line. The control circuit then operates in a second mode. In turn, mains voltage pulses are applied through the second line to the heater circuit 216. The length of and interval between the pulses is selected such that the heater circuit 216 causes the heated zone to reach a temperature suitable for warming items.

In this embodiment, the length of pulse and interval between pulses is selected in a manner similar to that described with reference to the first embodiment. The length and number of the pulses applied to the heater circuit 216 are determined solely by the warming pulse timer 214 and cannot be adjusted by the energy regulator 210. Therefore, it must be borne in mind that the temperature achieved must be satisfactory for a wide range of applications since the user will not be able to adjust it.

The Fourth Embodiment: Figure 4 The fourth embodiment is similar to the third embodiment, but includes a dual-circuit heater.

In the fourth embodiment, the select switch 312 is a single-pole two-way switch. The common terminal of the select switch 312 is connected to the live supply line L and its first and second outputs are connected respectively to input lines of the energy regulator 310 and the warming pulse timer 314.

With the select switch 312 in a first position, the common terminal of the select switch 312 is connected to its first output to energise the energy regulator 310. The energy regulator 310 is connected in a conventional configuration with its switched-live output 320 connected to the heater circuits 316,318 such that a user can control the amount of energy supplied to the heater circuits 316,318 and can choose to operate one or both circuits 316,318.

The warming pulse timer 314 is connected and operates substantially as described with respect to the second embodiment. In this embodiment, the warming pulse timer 314 applies pulses to one side of both of the heater circuits 316,318. The energy regulator 310 cannot control the length or frequency of the pulses. However, the energy regulator does control whether one or both of the heater circuits 316,318 are connected to the neutral line, and it therefore controls whether one or both heater circuit 316,318 is active in the second mode.

The Fifth Embodiment: Figure 5 The feature of the fourth embodiment described in the lastpreceding sentence allows a user some control over the amount of heat produced in the second mode. However, it may also be that this could confuse a user. The fifth embodiment is configured such that a user has full control over the temperature and the number of heater circuits operational in the first mode, while in the second mode, both circuits are always operational.

In the fifth embodiment, the select switch 412 is a twopole two-way switch. The energy regulator 410 and the warming pulse timer 414 are connected to a first pole of the select switch 412 in an arrangement which is electrically equivalent to the circuit of the fourth embodiment.

In addition, a second pole of the select switch 412 has its common terminal connected to the neutral supply line and its second output connected by a connection line 422 to the second heater circuit 418. The first output of the second pole of the select switch 412 is unconnected.

Operation of the control circuit of this embodiment in its first mode is substantially identical to the operation of the control circuit of the fourth embodiment in its first mode.

In the second mode, the second pole of the select switch 412 connects the second heater circuit 418 to the neutral supply line irrespective of the setting of the energy regulator 410. (The first heater circuit 416 is permanently connected to the neutral supply line at all times.) Thus, in the second mode of operation of the control circuit, both heater circuits 416,418 are always operational, being heated by pulses of electricity applied to it by the warming pulse timer 414.

The Sixth Embodiment : Figure 6 All of the above embodiments make use of a select switch to change operation of the control circuit between its first and second mode of operation. The sixth embodiment implements the invention without using a separate select switch.

The sixth embodiment has a control circuit which includes a dual-circuit energy regulator 510. The energy regulator generates a first output on a switched line 520. The switched line 520 is connected to one side of a heater circuit 516. The other side of the heater circuit 516 is connected to the live supply line L through a warming pulse timer 514. In addition, the other side of the heater circuit 516 is further connected to the live supply line L through a second heater circuit control microswitch of the energy regulator 510 by way of interconnecting lines 524,526.

The control circuit can be operated in a first mode by a user setting the energy regulator 510 to a setting that would, in the normal application of the energy regulator 510, operate both circuits of a dual-circuit heater. Mains voltage is supplied to the heater through lines 526 and 524 through the energy regulator 510, by-passing the warming pulse timer 514. The energy regulator 510 then controls the heater 516 through the neutral connection 520 either continuously or as a sequence of on-off periods.

Thus, power is supplied to the heater circuit 516 such that it heats the heated zone to a temperature suitable for cooking.

The control circuit can be operated in a second mode by a user setting the energy regulator 510 to a setting that would, in the normal application of the energy regulator 510, operate just one circuit of a dual-circuit heater.

In this mode, the second heater circuit control microswitch of the energy regulator 510 remains open, so that the heater circuit 516 is not connected to the live supply line L through the energy regulator 510 but is instead connected to the live supply line L through the warming pulse timer 514.

In this embodiment, the warning pulse timer 514 operates to detect current passing through the heater circuit 516.

On the detection of a current, the warming pulse timer connects the heater circuit 516 to the live supply line for a first predetermined interval, thereby permitting heating current to flow in the heater circuit 516, and disconnects for a second predetermined interval. As will be understood from the foregoing the first and second predetermined intervals are selected to ensure that power is supplied to the heater circuit 516 such that it heats the heated zone to a temperature suitable for warming items. It will also be understood that the temperature which the heated zone attains is controllable by a user by adjusting the setting of the energy regulator 510.

The Seventh Embodiment: Figure 7 In this embodiment, the control circuit can operate a dual circuit heater with a variable temperature being attainable in both first and second modes of operation.

The select switch 612 is, in this embodiment, a two-pole two-way switch. The warming pulse timer 614 operates in a manner similar to that of the first, second and sixth embodiments.

The switched live line 620 is connected to the common terminal of one pole of the select switch 612. The common terminal of the other pole of the select switch 612 is connected through an interconnecting line 622 to the heater circuits 616,618. First terminals of each of the two poles of the select switch 612 are directly interconnected.

Second terminals of each of the two poles of the select switch 612 are interconnected through the warming pulse timer 614.

With the select switch 612 in a first position (as shown in Figure 7) mains-voltage electricity from the energy regulator 610 is fed to the heater circuits 616,618 through the select switch 612 by way of its interconnected first terminals, such that the control circuit operates in a first mode to supply power to the heater circuits 616, 618 such that they heat the heated zone to a temperature suitable for cooking. In this mode, no power is fed to the warming pulse timer 614.

If the select switch 612 is moved to a second position, opposite to that shown in Figure 6, the pulses generated by the energy regulator 610 are instead fed through the warming pulse timer 614. As has been well described before, the warming pulse timer operates to generate short pulses which are conveyed to the heater circuits 616,618 to heat the heated zone to a temperature suitable for warming items. It will also be understood that the temperature which the heated zone attains, and whether one or both heating circuits 616,618 are operational, can be controlled by a user by adjusting the setting of the energy regulator 610. o-O-o Those skilled in this technical field will recognise that many alternative embodiments of the present invention can readily be constructed. In particular, the invention is not restricted to hobs which use an energy regulator as a first power control stage to control the supply of power to the heater circuit in the first mode of operation.

Furthermore, the construction of a suitable warming pulse timer will be a matter of routine to a skilled person. The warming pulse timer may be implemented as an electromechanical device (for example, having a construction similar to an energy regulator). Alternatively, the warming pulse timer might be implemented as a semiconductor device.

As a further alternative the energy regulator may have a preset warming setting in which its output is a sequence of on-off periods of mains voltage that are short relative to conventional energy regulator settings, such as an on period of about 2 seconds followed by an off period of about 10 to 15 seconds.

Claims (9)

1. CLAIMS 1. A cooking hob having a heater operable to heat a heated zone and a control circuit operative to control a supply of electricity to the heater, in which the control circuit is operable in a first mode in which the supply of electricity is sufficient to heat the heated zone to a temperature suitable for cooking and a second mode in which the supply of electricity is restricted to heat the heated zone to a temperature suitable for warming an item placed on it.
2. 2. A cooking hob as claimed in claim 1, wherein the control circuit comprises a first power control stage which operates to control the supply of power to the heater when the circuit is operating in its first mode.
3. 3. A cooking hob as claimed in claim 2, wherein the circuit further includes a power reduction stage operative, when the circuit is operating in the second mode, to receive power supplied from the first power control stage and to supply a lesser power to the heater circuit.
4. 4. A cooking hob as claimed in any preceding claim, wherein the first power control stage includes an energy regulator operative to generate pulses of electricity on a switched live output.
5. 5. A cooking hob as claimed in claim 4, wherein the pulses can be varied in duration and/or frequency by a user control in order that the temperature of the heated zone can be adjusted.
6. 6. A cooking hob as claimed in claim 5, wherein the power reduction stage operates to reduce the duration of or the frequency of the pulses applied to the heater circuit.
7. 7. A cooking hob as claimed in claim 1 or 2, wherein the control circuit comprises a first power control stage which operates to control the supply of power to the heater when the circuit is operating in its first mode and a second power control stage which operates to control the supply of power to the heater when the circuit is operating in its second mode.
8. 8. A cooking hob as claimed in claim 7, wherein the second power control stage operates independently of the first power control stage.
9. 9. A cooking hob substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.