EP0114307B1 - Temperature-regulating device for a heating apparatus - Google Patents

Abstract

1. Temperature regulating and control device for a heating apparatus with a temperature sensor, whose heat transfer element (16) extends between a radiant heater (12) and a glass ceramic cooking surface (11) over part of the radiant heater (12) and which is exposed to the heat generated by the latter, and at one end of the heat transfer member (16), its temperature switch (21) thermally coupled thereto is located outside the heated zone for reducing the heat emission of the heating apparatus, charaterized in that the heat transfer member (16) is constructed in rod-like manner and is formed from a tube (17) of scalefree material, particularly high-grade steel, and an inner rod (31) arranged therein made from good heat conducting material, preferably copper, that the temperature switch is a bimetal switch (21) and that the rod-like heat transfer member (16) is guided essentially diagonally over the radiant heater (12).

Description

The invention relates to a temperature regulating or control device for a heating device with an elongated, in particular rod-shaped or tubular, temperature sensor exposed to heat with a control device arranged at its end for reducing the heat output of the heating device, in particular with a between a radiant heater and a glass ceramic. Cooking surface arranged rod-shaped temperature sensor and a switch actuated by this.

It is already known (DE-OS 3097037) to use a temperature sensor for a temperature limiting device which consists of a sleeve made of quartz glass and a metallic rod of greater thermal expansion arranged inside the sleeve. One end of this rod acts on a snap switch, so that the snap switch is actuated when a certain temperature is reached. The snap switch or another switch sits e.g. in an insulated housing made of steatite, in which the power transmission elements are accommodated between the metal rod and the adjustable snap switch with its electrical leads.

Such controller constructions are relatively expensive, due to the quartz tube and its mechanical storage, but also because of the Geiekekuerung between the sensor rod and the controller head.

It is also known (DE-OS 3108025) to guide a rod-shaped temperature sensor approximately diagonally over the heating unit of a glass ceramic cooktop. This rod-shaped temperature sensor consists of an expansion sleeve made of metal and a rod made of ceramic material, which has a lower thermal expansion. This temperature sensor also acts on a control head located outside the heating area.

The reason that such expansion sensors are used, which act on switches outside the heating area, is that temperatures on the underside of the glass ceramic are in the order of magnitude of around 700 ° C, and that known bimetallic switches cannot withstand these temperatures.

Attempts have also already been made (DE-GM 8109131) to thermally couple a temperature sensor outside the heated area with the aid of a coupling plate to a hotplate made of glass ceramic. However, this is a sensor socket filled with expansion fluid, in which the restrictions on temperature that exist with bimetal switches do not occur. In addition, in this case, coupling is only possible at the edge of the hotplate.

It has also already been proposed (DE-OS 2 943 922) to arrange a bimetallic switch housed in a housing on the edge of a support shell receiving the glass ceramic heater. However, auxiliary heating is required for the bimetal switch so that it receives the correct temperature when the heater is switched on.

Also known is a temperature control device of the type mentioned at the beginning (US-A 3710076), in which a temperature-sensitive element, preferably with a temperature-variable electrical resistance, rests on the underside of a glass ceramic cooking surface.

Furthermore, it is known (DE-A 2045001) to use a copper pin in a mass hotplate from the underside of the hotplate through the hotplate body up to approximately the top thereof. A bimetal switch is located below the hotplate in the heated area. This arrangement is not suitable for higher temperatures.

The invention has for its object to provide a temperature control or control device of the type mentioned, which is easy and inexpensive to manufacture and yet has an accurate temperature behavior, with commercially available bimetal switches can be used.

To achieve this object, it is provided according to the invention that the temperature sensor is designed as a heat transfer element, which is formed by a tube made of scale-free material, in particular stainless steel, with an inner rod arranged therein, preferably made of copper, and is thermally coupled to at least one temperature switch which is outside the heated area.

Thus, while in the prior art the heat sensor acts on a switch due to different expansion or different electrical resistance, according to the measures of the invention the heat sensor is used to conduct the heat to the switch, this switch then being a commercially available bimetal switch can. The scale-free stainless steel is able to withstand the high temperatures even under continuous use, while the material arranged inside is used due to its good thermal conductivity.

The temperature sensor, which in particular can also be rod-shaped, can be guided over the radiant heater, for example, along a diameter, it is of course also possible to use it in curved shapes. The temperature switch is located outside the heated area, in particular in the area of one end of the heat transfer element. Of course, it is possible to attach a switch to both ends of the heat transfer element if, for example, different temperatures are to be sensed. For example, it can be provided that the temperature switch is a commercially available switch, in particular with a bimetal spring washer. This bime

tall switches are available at very low prices so that the entire control device can be manufactured cheaply.

The invention proposes in a further development that the tube is closely connected to the inner rod by pressing, in particular in the form of a prism. This has the advantage that there is a tight connection between the inside of the tube and the inner rod, so that not only is there a good heat transfer, but above all there is even heat transfer at all points of the temperature sensor.

It is particularly favorable if the tube and / or the copper wire is pressed with a cable lug to which the temperature switch is attached, in particular screwed on. The crimping with the cable lug can be carried out simultaneously with the crimping of the tube and inner rod, so that only a single operation is required. The cable lug is preferably also made of copper, preferably with a temperature-resistant surface, which can in particular be a nickel plating.

In a further development, it is provided that the tube has an at least one-sided flattened, in particular triangular cross-section, which may arise when pressing with the inner rod. This design makes it possible to allow the tube to rest directly on the underside of a glass ceramic cooktop, advantageously with the flattened side. This in turn leads to good heat transfer from the surface whose heat is to be monitored to the rod. Instead of the triangular cross section, for example, a semicircular cross section can also be used.

The invention further proposes that the dimensions and / or the shape and / or the thermal conductivity of the tube and / or the inner rod are selected such that the permissible permanent temperature of the temperature switch is not exceeded. For example, the wall thickness of the tube must be selected so that there is good transmission to the inner rod. If necessary, the temperature sensor can also be guided in an arch form over the area to be monitored.

It has been found that the measures according to the invention have surprisingly achieved extremely favorable results. Despite the large difference between the temperature to be controlled and the response temperature of the bimetal temperature controller, surprisingly good cooking and roasting results are achieved in practice. The natural dead time of the system results in a rather large amplitude, but this does not interfere in practical use. There is a very low switching frequency of the temperature controller and a certain overshoot when heating up for the first time, which leads to a desirable reduction in the heating-up times.

• Fig. 1 einen Querschnitt durch einen Strahlheizkörper mit einer Glaskeramik-Kochfläche;
• Fig. 2 eine Aufsicht auf den Strahlheizkörper;
• Fig. 3 eine vergrösserte Seitenansicht der Anordnung des Bimetall-Schalters;
• Fig. 4 einen Querschnitt längs Linie IV-IV in Fig.1.

Further features, details and advantages of the invention will become apparent from the following description of a preferred embodiment and from the drawing. Here show:

• 1 shows a cross section through a radiant heater with a glass ceramic cooktop.
• Figure 2 is a plan view of the radiant heater.
• 3 is an enlarged side view of the arrangement of the bimetal switch;
• Fig. 4 shows a cross section along line IV-IV in Fig.1.

1 shows a cross section through a glass ceramic cooktop 11 and a radiant heater arranged below it. The radiant heater contains a radiant heater 12. The radiant heater 12 is arranged within a molded body 13, which represents a boundary to the outside and to the bottom. An insulating layer 14 is attached below the molded body 13, the entire radiant heater being surrounded by a sheet metal plate 15. A heat transfer element 16 in the form of a straight tube 17 runs transversely to the heating, see also FIG. 2. The heat transfer element 16 is bent down slightly on the right-hand side in FIG. 1, so that its right end 18 passes through an opening in the sheet metal rim 19 can be put through.

On its left side in FIG. 1, the heat transfer element 16 is thermally connected to a bimetal temperature controller 21 via a type of cable lug 20.

2 shows the position of the tube 17 of the heat transfer element and the bimetal temperature controller 21 in detail. It can be seen that the right end extends through the sheet metal rim 19, while the entire tube 17 of the heat transfer element 16 along a diameter over the Radiant heater 12 runs.

The bimetallic temperature controller 21, which can contain a bimetallic spring washer, not shown, is provided with two connecting lines 22, 23, one of which leads to a plug pin 24 of a connecting piece 25, while the other is connected to one end of the radiant heater 12. Since the tube 17 of the heat transfer element 16 is exposed to the heat of the glass ceramic cooktop 11 over practically its entire length, it takes on its temperature and dissipates it to both sides, the heat dissipated to the left being directly via the cable lug 20 is transmitted to the bimetal controller 21. Therefore, the temperature that the bimetal controller assumes is a measure of the temperature of the glass ceramic cooking surface 11, even if its temperature is significantly lower.

The arrangement of the bimetal controller 21 is shown in detail in FIG. 3. The bimetal controller 21 has a housing in which a bimetal spring washer is arranged in a heat-conducting manner. The housing 26 of the bimetal controller 21 has a screw 27 on its right side, onto which the lower leg 28 of the cable lug 20, which is provided with a hole, is attached and screwed tight with the aid of a nut 29. This creates a thermally good connection between the cable lug and the housing 26 of the temperature controller 21.

The upper leg 30 of the cable lug 20 is pressed tightly with the inner rod 31, so that a good heat-conducting connection is also established here.

4 shows the cross section of an embodiment of a heat transfer element 16. It can be seen that it consists of an outer tube 17 with a triangular cross section, in the interior of which a good heat-conducting material is introduced, for example a copper rod 31. The heat transfer element 16 becomes attached such that its upper flat side comes to rest directly on the underside of the glass ceramic cooking surface 11. Due to the relatively low height of the tube 17, the device also requires little space. The wall thickness of the tube 17 can be, for example, about 0.3 mm. The outer tube 17 and the copper rod 31 are brought into good heat-conducting connection by reducing, but preferably by prism-like pressing. During the pressing process, the cable lug 20 is pressed with the copper wire 31 at one end. The cable lug 20, which like the copper rod 31 can consist of electrolytically pure copper, expediently has a temperature-resistant surface, for example a nickel plating.

The heat transfer element 16 is attached on the right-hand side by inserting it into the opening 18, while on the left-hand side a holding hammer 32, for example welded to the tube 17, is simply inserted over the edge 19 of the plate plate 15.

Because of the material used for the heat transfer element 16, it can even be bent slightly, so that other shapes could also be used. The low cross-section of the tube 17, see FIG. 4, enables a very flat construction of the radiant heater, due to which one can either achieve lower plate temperatures at a given height or the overall height of the radiator can be made lower at previous plate temperatures. The heat transfer element 16 is completely insensitive to shock and impact, so that it poses no problems in this respect during installation.

The arrangement of the heat transfer element directly on the underside of the glass ceramic surface has the advantage that the sensor senses influences, such as an offset pot, pot quality, idling, quantity, etc., and can react accordingly. The control behavior is improved on this point.

Another advantage arises within the manufacturing process. A mechanical adjustment of the temperature switching values is no longer necessary. The adjustment is determined by the design of the sensor. The thermal design of the sensor is adjusted to the switching temperature standardized by the bimetal manufacturer by dimensioning the masses and surfaces of the outer jacket (preferably poor heat conductor) and the inner rod (preferably very good heat conductor).

When using a bimetal switch version for all hotplate diameters, the respective sensor rod can be matched to the heating in terms of its thermal data. For example, a stainless steel tube with the dimensions 0 2x0.16 mm is used as the outer jacket for the hotplate heating with a nominal diameter of 145 mm and a copper conductor 0 1.6 mm as the inner rod (hob 180 mm: 0 1.3 mm).

The increase in the mass of the outer jacket increases the dead time (transient response and control amplitude). A change in the copper mass influences the switching temperature measured on the glass ceramic surface due to the change in the amount of heat that can be transported. A further adjustment can be achieved via the position of the sensor and its shape (heat exposure). For example, the pot sensitivity when using a triangular cross section with a narrow side facing the plate is not as pronounced as with a wider side. An angle of 110 ° between the other sides is preferred.

Claims (10)

1. Temperature regulating and control device for a heating apparatus with a temperature sensor, whose heat transfer element (16) extends between a radiant heater (12) and a glass ceramic cooking surface (11) over part of the radiant heater (12) and which is exposed to the heat generated by the latter, and at one end of the heat transfer member (16), its temperature switch (21) thermally coupled thereto is located outside the heated zone for reducing the heat emission of the heating apparatus, characterized in that the heat transfer member (16) is constructed in rod-like manner and is formed from a tube (17) of scale- free material, particularly high-grade steel, and an inner rod (31) arranged therein made from good heat conducting material, preferably copper, that the temperature switch is a bimetal switch (21) and that the rod-like heat transfer member (16) is guided essentially diagonally over the radiant heater (12).

2. Device according to one of the preceding claims, characterized in that the temperature switch (21) is a commercially available bimetal switch, particularly with a bimetal jump disk.

3. Device according to one of the preceding claims, characterized in that the tube (17) is closely connected to the inner rod (31) by moulding, particularly in prismatic shape.

4. Device according to one of the preceding claims, characterized in that tube (17) and/or inner rod (31) is moulded with a type of cable shoe

(20), to which the temperature switch (21) is fixed, particularly screwed.

5. Device according to claim 4, characterized in that the cable shoe (20) is made from copper with a preferably thermally stable surface and which is in particular nickel-coated.

6. Device according to one of the preceding claims, characterized in that the heat transfer member (16) has an at least one-sided flattened, particularly triangular cross-section, which is optionally obtained on moulding tube (17) with inner rod (31 ).

7. Device according to one of the preceding claims, characterized in that the in the case of a glass ceramic cooking surface, the heat transfer member (16) engages directly with the underside thereof.

8. Device according to one of the preceding claims, characterized in that the shape and/or dimensions and/or thermal conductivity of the heat transfer member (16), particularly the tube (17) and/or inner rod (31) are chosen in such a way that the permitted permanent temperature of the temperature switch (21) is not exceeded.

9. Device according to one of the the preceding claims, characterized in that the temperature switch (21) is arranged in the vicinity of a connecting piece (25) provided for the radiant heater.

Images