1. Field of Application and Prior Art
The invention relates to an appliance for switching on and off several heating devices of a cooker, as well as a cooker having such an appliance.
Radiant heaters with a diameter which can exceed 230 mm exist for hobs with glass ceramic plates, for example. They in part suffer from the problem that an energy or power supply through so-called energy or power control devices on the one hand and an excess temperature protection for the glass ceramic plate over the radiant heater through so-called temperature limiters on the other are limited by the maximum power levels which can be applied and by a so-called flicker standard. The flicker standard indicates how frequently in a specific time period a specific power may be switched on and off for a cooker and is intended to prevent significant supply network reactive effects in line with the power supply companies. The switching capacity of both the power control devices and the temperature limiters, which operate with so-called snap-action switches and such as are for example described in U.S. Pat. Nos. 6,064,045 and 4,633,238, is generally limited. In the USA this is 12 or 13 Ampere, for example, and consequently 100,000 switching cycles must be attainable.
Thus, with the normally predetermined mains voltage, it is not possible to further increase the power of a radiant heater.
2. Problem and Solution
The problem of the invention is to provide the aforementioned appliance and aforementioned cooker enabling the prior art problems to be avoided and which in particular enables the maximum power to be increased, particularly for a hotplate with radiant heating.
This problem is solved by an appliance having the features of claim 1 and a cooker having the features of claim 11. Advantageous and preferred developments of the invention form the subject matter of the further claims and are explained in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description. In line with the present application “have” means that this feature can be inter alia provided, independently of further features.
According to the invention, the appliance has a temperature detection device or in certain circumstances forms the latter and has a temperature-dependent, thermomechanical release or tripping movement as the operating principle. The temperature detection device has a first switching device or is connected thereto and can be directly operated at an adjustable tripping point by a tripping movement in order to switch on and off the first switching device. A second switching device is provided for switching on and off the second heating device. Said second switching device is also activatable by the tripping movement. Both the first and second switching devices are designed for switching the heating power of the particular heating device, that means as so-called power switches, relays, for example. They are so constructed that they achieve the necessary number of switching cycles. For the second switching device or the tripping thereof, it can be directly or indirectly activated by the tripping movement. In the case of a direct activation the switching contacts are directly moved by the tripping movement. With indirect activation in the sense of the present application the tripping of the first switching device is activated by the tripping movement and the signal caused by the same or a switched voltage activates the second switching device. Thus, here activation does not take place in direct mechanical manner via the tripping movement.
Thus, it is possible as a result of the invention to create a temperature detection device which, in place of a conventional temperature limiter, such as can be gathered from U.S. Pat. No. 4,633,238, for example, can be used for monitoring the glass ceramic plate of a hob with radiant heater with respect to excess temperatures. The two heating devices belong to a single hotplate, that means at least on occasions are operated jointly. In particular there is a two or multiple circuit hotplate. Thus, the temperature detection device trips the first and second switching devices and each switching device switches on or off the particular associated heating device. Thus, in the case of an excess temperature, the total power of the hotplate no longer has to be switched by a single switching device of the temperature detection device, so that the total power of the heating devices or hotplate can be increased.
Preferably, when using relays as switching devices, they are so designed that when a current is not flowing through them, that means in the deactivated or uncontrolled state, they are opened. The heating devices connected thereto are then switched off.
According to a first possibility provided by the invention, the second switching device can be directly activated by the first switching device. This can for example take place in that with the first switching device closed for switching on the first heating device the second switching device receives a corresponding electric signal so as to then activate or switch on the second heating device. Alternatively and as a result of the connection of the first heating device to a supply voltage, the second switching device can be supplied with energy for activation. Thus, in this embodiment, the second switching device is not directly activated by the tripping movement and is instead indirectly activated, in that it is controlled by the first switching device activated by the tripping movement.
In another possibility provided by the invention, it is possible to provide a third switching device, which is connected or coupled to the temperature detection device and at an adjustable tripping point can be directly operated by the tripping movement. An operation advantageously takes place simultaneously with the first switching device, that means at the same tripping point. Such a third switching device can directly activate or supply energy to the second switching device, so that it correspondingly switches on or off the second heating device. Thus, here the second switching device is activated by the third switching device, unlike in the previous embodiment where this takes place through the first switching device. This offers the advantage that in this case no further functions or connections have to be provided for the first switching device, but it is necessary to provide the third switching device. However, it is also possible to use a switching device for this purpose which is already present in conventional temperature limiters, such as for example according to U.S. Pat. No. 4,633,238, for indicating a temperature of above 100° C., for example, so as to constitute a hot indicator.
According to another possibility of the invention it is also possible to incorporate the second switching device into the temperature detection device in the same way as the first switching device and in particular with the same construction. In this case increased constructional demands are made, particularly with respect to insulation resistances and gaps.
The third switching device for controlling the second switching device can either operate with a lower voltage than the mains voltage or can be designed for significantly lower currents. Its function is merely to switch the activation current for the second switching device. In the case of power relays and in certain circumstances electronic switches this is relatively low, so that no increased mechanical or contact-specific demands have to be made on the third switching device.
The temperature detection device can advantageously have an expansion device, which expands or brings about a mechanical tripping movement as a function of the detected temperature. It can be a temperature limiter according to U.S. Pat. No. 4,633,238, to which express reference is made. Such a temperature limiter can have two elongated, parallel longitudinal elements, which are coupled at one end and have different temperature expansion coefficients. At a predetermined or detected temperature they expand to a varying degree and this relative movement leads to the tripping movement, because the relative movement between them occurs at the uncoupled end. For this purpose one of the elements can be fixed to the temperature detection device. The other moves relative thereto and gives rise to a force which, together with the tripping movement, can for example operate a switching device or the like.
According to a further development the appliance can have a control for the heating devices or can be connected thereto, for example in the form of a so-called timing or cyclic energy control device. As a result thereof radiant heaters, for example, can be operated cyclically, which means that they are either switched off or switched on at full power. Therefore the level of the energy generation at the heating devices can be predetermined over several cycles or over and beyond a specific time. This is described in U.S. Pat. No. 6,064,045 to which express reference is made. When the control is switched off none of the aforementioned switching devices is activated or activatable. This ensures that the level of the energy generation or the nature of the timing is predetermined by the control or the energy control device. The temperature detection device advantageously merely provides an overheating protection of a glass ceramic plate, for example, against excessive heating by the heating devices.
A cooker according to the invention can contain an aforementioned appliance for at least two independently controllable heating devices. These two heating devices form a hotplate or are very closely juxtaposed, so that in some modes they can be operated jointly for heating a single correspondingly large, stood-on cooking vessel. The first heating device is the main heating device, whereas the second heating device is an additional heating device. The second device can either be connected laterally and roughly over roughly a half to the first heating device and can optionally even completely surround the same. For smaller cooking vessels, they are heated solely by the first heating device. With larger cooking vessels covering the entire surface area of the first and second heating devices, both heating devices are used jointly. With such a joint use, it is naturally advantageous if the temperature detection device in the case of an excess temperature in an area, particularly of the first heating device, not only switches off the latter, but in fact both heating devices. Otherwise and in particular when using radiant heaters, an unaccustomed picture would arise for the user.
Advantageously the power of the first heating device is significantly higher than that of the second heating device and is roughly twice as high, for example.
For the second heating device it is possible to provide a maximum continuous power output corresponding to a power density of max. approximately 2.5 W/cmý. Such a value has the advantage that when using radiant heaters and a glass ceramic plate as the hob, such a power density can be operated so-to-speak in unprotected form, that is without any temperature monitoring for the glass ceramic. Dangerous temperatures of approximately 550° C. and higher cannot be obtained. Such power densities cannot lead to an overheating of the glass ceramic. The power density can also be selected above 2.5 W/cmý if the glass ceramic manufacture's specifications or tests reveal or allow this.
This makes it possible for the temperature device in its function as an overheating protection to only have to monitor the first heating device, but not the second heating device. It can for example cover the first heating device, but not the second heating device. It can alternatively be deactivated in the area of the second heating device. For this purpose it is possible, for example in the case of a rod control unit in the area to be deactivated of one of the two longitudinal elements to be partly replaced by another partial longitudinal element, which has the same temperature expansion as the other longitudinal element. Thus, by heating in the area to be deactivated, there is no relative movement or no contribution to a relative movement.
The cooker can advantageously have a timing or cyclic energy control device, as described hereinbefore and as can for example be gathered from U.S. Pat. No. 6,064,045. This energy control device is constructed for at least for activating the first heating device. Due to the fact that the second heating device is controlled or activated by means of the aforementioned appliance or temperature detection device and the power level of the heating devices is determined by the energy control device, this predetermines the on and off times both for the first heating device and consequently the second heating device.
According to a further development a fourth switching device can be provided and which, independently of the second or third switching device, activates or deactivates the second heating device for synchronous operation with the heating device. This fourth switching device can for example make it possible for a user, as a function of the size of the stood-on cooking vessel, to activate or not activate the additional heater. It can for example be formed by a power switch looped into the supply voltage and in particular a relay, with a corresponding control for a user, for example a contact switch. The second switching device can be provided separately from the energy control device on the cooker. In the manner described hereinbefore, it can be a separate power switch, particularly a relay.
These and further features can be gathered from the claims, the description and the drawings and the individual features, both singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way limit the general validity of the statements made thereunder.