GB2177271A

GB2177271A - Control means for electrical heating means of a cooker

Info

Publication number: GB2177271A
Application number: GB08614918A
Authority: GB
Inventors: Helmut Waigand; Gunther Wittauer
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-24
Filing date: 1986-06-19
Publication date: 1987-01-14
Also published as: SE8602735L; SE8602735D0; IT8622324V0; IT8620839A1; GB8614918D0; GB2177271B; IT8620839A0; DE3522546A1; IT1189576B; FR2583947B1; FR2583947A1; DE3522546C2

Abstract

The heat output of a cooker heater RH is controlled by adjusting the ON/OFF ratio of a bimetallic cycling switch SE which is maintained closed for an initial maximum power heating phase by means of a timer AS. Switch SE is heated by a heater RS, the current through heater RS passing through the switch SE and through a bimetal switch SZ of timer AS. The duration of the initial heating phase can be adjusted by means of a variable resistor RV in series with a heating resistor RZ of timer AS and gauged with means RE for adjusting the ON/OFF ratio of switch SE. A PTC resistor RT acts to reduce the power consumption of timer AS after switch SZ has opened. <IMAGE>

Description

SPECIFICATION Control means for electrical heating means of a cooker The present invention relates to control means for electrical heating means of a cooker.

For the driving of electrically operated heating zones, in particular cooker plates, it is known to use energy regulators which effect a keying of the heating current with a currentpause ratio, which is variable according to the setting of a setting element, for heat energy dimensioning. In this connection, it is known from DE-OS 32 04 599 to provide measures in which energy-regulated heating zones are, for an initial phase, subject to an initial power loading. The initial power is usually the maximum power available at the heating zone. The control devices for energy regulation and for initial cooking power usually operate in parallel. It would be desirable, however, for the driving power, which by contrast to the heating power represents a loss power, to be reduced as far as possible.

According to the present invention there is provided control means for electrical heating means of a cooker, the control means being operable to set the value of the heat output of such heating means by influencing the supply of operating current to the heating means and comprising first circuit means controllable to cause such heat output to have a maximum value during an initial heating phase by the heating means and second circuit means controllable to cause such heat output to have a selected value during a subsequent heating phase by the heating means, the first and second circuit means being so arranged that the operating current for the heating means is conducted exclusively by way of a switching path of the second circuit means and a control current for the second circuit means is conducted by way of a switching path of the first circuit means.

In a prefered embodiment, control means for heating power control of an electrically operated heating zone operates to set the heating power through a switching-on and heating power control device to a given value through keying of the heating current for a continuous heating phase and to the maximum attainable value for an initial cooking phase. The control current for heating resistors of the heating zone is conducted exclusively by way of a switching path of a control device for the continuous heating phase and a control current for a continuous heating phase control device is conducted by way of the switching path of the initial cooking phase control device.

This provides the advantage that the switching stage for the regulation of the control current for the heating resistors of the heating zone for the control stage, which fixes the initial cooking phase, serves as an amplifier stage. As a result, the control powers for the initial cooking phase controls and thereby their loss powers can be reduced correspondingly.

If the heating current for the heating resistors is conducted directly by way of the continuous heating phase control device, then a power-intensive switching element is needed merely in this region.

Frequently, bimetallic regulating devices are used for the keying of the heating current for energy regulation. These are particularly simple in construction and thereby favourable in price. In this connection, preferably the initial cooking phase control device is formed of a bimetallic time generator unit heatable by current.

If such a unit is acted on by a constant current, then a fixed time span results for the initial cooking phase. For preference, however, the control current for the initial cooking phase control device is conducted by way of a settable resistance element. By this means, the control current for the initial cooking phase control device is adjustable and thus the initial cooking time span variable. The setting of the resistance element to a certain value can be carried out together with the setting of an associated energy regulator.

Expediently, the control current for the initial cooking phase control device is conducted by way of a cold conductor resistor, the resistance-temperature characteristic of which is such that a high resistivity is reached afer the switching-on of the switching path of the initial cooking control device. The aim of this measure is, after the response time, to feed to the initial cooking phase control device just sufficient current for the heating element for the bimetallic switch to retain enough heat to hold the bimetallic switch in its switch position. This minimises energy consumption and avoids unnecessary heat development. In any case, it is desirable to ensure that external heating does not adversely influence the functional capability of the switching system.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of control means embodying the invention; and Fig. 2 is a diagram of a switch arrangement for a variable resistor of the control means of Fig. 1.

Referring now to the drawings, there is shown in Fig. 1 control means for controlling the ioading of a heating resistor RH of a cooking zone of an electric cooker. Mains supply voltage is present at lines L1 and L2. For placing the heating zone into operation, the mains switch combination S1 and S2 is closed. At the same time, an associated energy regulating switch SE is closed by way of an energy regulator RE. Thus, full mains voltage is present at the heating resistor RH and full heat development takes place. The switch SE is constructed as a bimetallic switch, which in the case of current supply to heat a resistor RS, can be opened-and , in the absence of this supply , closed again. Since the current in the case of this heating resistor RS is conducted by way of the switch SE, the heating current is keyed in known manner.

This keying is, however, inhibited during an initial time phase by an initial cooking phase control device AS. In this time phase, a switch SZ, which is also constructed as a bimetallic switch, is opened. Current flows through a resistance path RV, RZ and RT and through heat delivery at the resistor RZ influences the switch SZ so that this is closed after a corresponding time span, namely the initial cooking phase. Only after that can the resistor RS, which in turn heats the switch SE, be acted on by current. From there on, energy regulation takes place through keying until the termination of the cooking process, at which the mains switch combination SI and S2 is opened. Until then, the switch SZ remains closed.

A variable resistor RV serves for selectable dimensioning of the heating current for the resistor RZ and is correspondingly settable with the setting of the energy regulator RE. From this results the heating time of the resistor RZ and of the switch SZ and in consequence thereof the time span until closing of the switch SZ. The resistor RT has a cold conductor characteristic. This means that the resistor RT has good conductivity in an initial phase in which it is still cold and that the conductivity reduces on warming up. The resistance-temperature characteristic of the resistor RT is chosen so that the increased resistance value in the resistor RT is reached through heat development of the resistor RZ only after response of the switch SZ. The purpose of this measure is to limit the current in this phase in such a manner that the heating power through the resistor RZ is sufficient to keep the switch RZ in the closed setting, but that no unnecessary heat beyond that is produced.

The Fig. 2 shows a switch arrangement for the input resistor RV, which in the illustrated example is divided into three regions RV1, RV2 and RV3. The contact places are arranged according to the setting stages of the energy regulator and are contacted in known manner by way of wiping contacts.

Claims

1. Control means for electrical heating means of a cooker, the control means being operable to set the value of the heat output of such heating means by influencing the supply of operating current to the heating means and comprising first circuit means controllable to cause such heat output to have a maximum value during an initial heating phase by the heating means and second circuit means controllable to cause such heat output to have a selected value during a subsequent heating phase by the heating means, the first and second circuit means being so arranged that the operating current for the heating means is conducted exclusively by way of a switching path of the second circuit means and a control current for the second circuit means is conducted by way of a switching path of the first circuit means.

2. Control means as claimed in claim 1, the first circuit means comprises a bimetallic timing device heatable by a further control current.

3. Control means as claimed in claim 2, the first circuit means comprising a settable resistance element to influence the value of the further control current.

4. Control means as claimed in either claim 2 or claim 3, the first circuit means comprising a cold conductor resistor to conduct the further control current.

5. Control means for electric heating means of a cooker, the control means being substantially as hereinbefore described with reference to the accompanying drawings.

6. A cooker comprising electric heating means and control means as claimed in any one of the preceding claims.