EP0248285A1 - Electrical heating element - Google Patents

Abstract

In the production of electrical heating elements with PTC elements, it is intended to improve the achievable thermal power. This is achieved by the PTC elements being provided with heat dissipating elements (10, 10') which are shaped such that the heat emitting surface (11) of the PTC elements is arranged at right angles to the heat emitting surface (12) of the heat dissipating elements. <IMAGE>

Description

The invention relates to an electric radiator according to the preamble of claim 1.

PTC thermistors are components whose resistance, starting from the room temperature, drops to a temperature value defined by the structure of the element and then increases suddenly. Therefore, if one supplies such an element with a constant voltage, it automatically regulates its current or power consumption so that the temperature remains in the region of the sudden increase. Due to this characteristic one can use such heating elements for the construction of electric radiators, which regulate their temperature automatically without that separate thermal switches or the like would be necessary for this.

When designing such electric radiators, however, some properties inherent in the PTC elements (PTC = positive temperature coefficient) must be taken into account. On the one hand, the PTC elements are manufactured as thin rods or disks as possible, so that the most homogeneous possible temperature curve inside the element is guaranteed. Secondly, the PTC elements may only be exposed to relatively low surface pressures, since they are very brittle. Furthermore, care must be taken to ensure that the heat is dissipated as uniformly as possible from the surface of the elements, with the current also being supplied via the two surfaces of the elements.

A large number of designs are now known for how PTC elements can be arranged in electric radiators. For heating cartridges, for example, it is proposed (DE-PS 26 l4 433, DE-OS 29 O2 9O9, DE-Gm 8l l4 42O) to arrange several PTC elements in a row, namely between two contact strips, which simultaneously ensure the dissipation of the heat. The entire arrangement is then introduced into a tube and in such a way that the contact surfaces or heat and current dissipation or supply elements are pressed firmly onto the surfaces of the PTC elements. If you now want to distribute the heat over a larger area, it is known (DE-OS 29 O2 9O9) to insert such a heating cartridge into a larger piece of metal, which then carries the heating plate or heat sink or the like. In this arrangement, however, a very high temperature gradient occurs between the actual radiator, namely the overall heat sink and the PTC elements, ie the outside temperature of the radiator is significantly lower than the temperature of the PTC elements. This has several disadvantages. To the one can namely only reach relatively low maximum temperatures of the radiator, since the transition temperatures of PTC elements only reach up to about 300 ° C. Furthermore, the control behavior of such arrangements is relatively poor, since the high heat transfer resistances between the PTC elements and the actual heat-emitting surfaces of the radiator are very high, but the heat capacity of the overall arrangement is also very high. Finally, the power that can be extracted from the PTC elements is significantly lower than the theoretically possible maximum power of the elements. This fact results from the fact that the extractable power is proportional to the temperature difference between the PTC element surface and the ambient temperature divided by the thermal resistance. For this, reference is made to the publication Siemens Components l9 (l98l), volume 2, pages 56 to 59.

In order to be able to extract the highest possible performance from the PTC elements, one generally starts from constructions such as those in DE-OS 28 45 894, DE-PS 3O 46 995, DE-OS 32 O8 8O2, DE-AS 27 43 88O or in DE-OS 3O 22 O34 are shown. All of these documents show constructions in which heat dissipation elements are provided which are connected to the flat sides of the PTC elements on a connecting surface. The heat-emitting surfaces are arranged parallel to the connection surfaces. In principle, the PTC elements are placed between two bands. In any case, these radiators now have the disadvantage that if the heat dissipation elements are coupled with only one surface to an object to be heated, for example to the bottom of a water pot, the second surface of the PTC element cannot serve for heat dissipation. Accordingly, the removable power decreases (or the heat transfer resistance increases). Another problem arises from the fact that with such a construct tion very easily too high surface pressure forces are applied to the PTC elements, since one wants to create the lowest possible heat transfer resistance between the PTC element and heat dissipation element. This leads to the breakage and thus the unusability of the PTC elements. A further difficulty arises in the known arrangements in that all PTC elements are in direct thermal coupling with one another. However, this results in an inexact control behavior, since not every PTC element only monitors its own heat generation, but also that of the other PTC elements. Finally, these known constructions are only suitable for connecting a relatively small number of PTC elements in parallel, since differences in thickness are unavoidable due to mechanical manufacturing tolerances. However, these differences in thickness mean that the thicker PTC elements are pressed too tightly, or the thinner PTC elements have no contact with the heat-dissipating elements at all. If there is (inevitable) heating and thus thermal expansion of both the PTC elements and the heat dissipation elements, the above-mentioned effect is further intensified.

Starting from the above-mentioned prior art, it is an object of the present invention to further develop an electric radiator arrangement of the type mentioned at the outset such that high heating outputs can be achieved with a mechanically simple and insensitive structure.

This object is achieved in that the heat-emitting surfaces are arranged essentially perpendicular to the connecting surfaces. So, so to speak, the heat is conducted around the corner, so that there are completely different (defined and lower) forces between the heat dissipation elements can act that press on the PTC element, as between the heat dissipation elements and the heat consumer, such as a heating plate.

The heat-emitting surface of each heat dissipation element is preferably selected to be many times larger than the connection surface to the PTC element. In this way, a safe dissipation of the heat output generated by the PTC element is guaranteed.

Each PTC element is preferably assigned two heat dissipation elements. The heat is therefore dissipated from both sides by the PTC element, so that the heat transfer resistance can be reduced considerably, and the heating power of a PTC element thus increases significantly.

In order to achieve greater heating capacities, the electric radiator is preferably provided with a plurality of PTC elements which, with the heat dissipation elements interposed, are arranged in a substantially continuous force train - that is to say in series - in such a way that the contact pressures between all PTC element flat sides and the associated ones Connection surfaces of the heat dissipation elements are substantially the same. This arrangement is only possible through the arrangement according to the invention (heat-emitting surfaces essentially perpendicular to the connecting surfaces), since in the usual design a series connection in terms of force leads to a columnar arrangement, with no heat being able to be dissipated in the interior of the column. By means of the embodiment according to the invention, however, all PTC elements can be clamped together (with one force being the same for all), the thickness arrangement of the PTC elements no longer playing a role due to the serial arrangement. The coupling to the heat consumer is completely independent of the coupling of the PTC elements the heat dissipation elements, so that it can be pressed firmly to keep the heat transfer resistance as low as possible. In order to eliminate the thermal expansion and the resulting excessive pressure forces on the PTC elements, it is advantageous to provide a single spring element for all groups of PTC elements in series connection (together with the heat dissipation elements), which absorbs the thermal stresses and defines one Preload easily adjustable.

The PTC elements are preferably connected electrically in parallel, which is particularly advantageous with regard to their control behavior (each PTC element controls independently of the other PTC elements).

In all of the exemplary embodiments, it is advantageous if the heat dissipation elements for each PTC element are thermally decoupled from the heat dissipation elements of the other PTC elements. The advantage of this measure was described at the beginning. You can work in different zones with different energy density and temperature.
The heat dissipation elements preferably serve at the same time as current supply electrodes.

A common housing for several PTC elements is preferably provided together with their heat dissipation elements, so that an extremely compact object is produced. In particular, it is advantageous if the housing comprises a tub element in which the PTC elements are braced against one another (that is, in terms of force in series) with the heat dissipation elements interposed, the tub bottom being arranged parallel to the heat-emitting surfaces. Such a simple arrangement can be designed as a large-area heating element, wherein the area can actually be chosen to be as large as desired by simply adding any number of PTC elements with heat-conducting elements in the manner described arranges together in a common tub.

The construction becomes particularly compact if the housing comprises a cover element, which is preferably held by crimping the rim of the tub in the tub element by pressing against the heat-emitting surfaces. Pressing by crimping has so far not been possible, since very high forces that are difficult to control were applied to the PTC elements. For this purpose, spring elements were used, which were arranged between the tub rim or lid and the PTC element, but on the other hand, as a result, the heat transfer resistance (at least on this side of the PTC element) increased significantly. With the present invention, however, it is possible to use only a very thin electrical insulating film with low thermal resistance, and to carry out the crimping as tightly as possible, since the forces act exclusively on the heat dissipation elements, while the PTC elements by the defined force of the contact pressure (eg the spring element). The tub element can be designed as a recess in a body to be heated, which means e.g. in the construction of a boiler or the like, a particularly low heat transfer resistance is achieved and at the same time the component costs can be reduced considerably.

In a particularly preferred embodiment of the invention, the heat dissipation elements have at least one surface section that runs perpendicular to the heat-emitting surface, but at an acute angle to the connecting surface, with the PTC element. You can then namely several groups, consisting of PTC element and two heat dissipation elements, so that the heat dissipation elements "wedge" in a channel, that is to say they are arranged in a fixed manner, the PTC elements being connected in series and only one spring element Tightening the arrangement is enough.

• Fig. l eine erste bevorzugte Ausführungsform der Erfindung mit Gehäuse,
• Fig. 2 eine Ansicht auf die Ausführungsform nach Fig. l entlang der Linie II-II,
• Fig. 3 bis 6 weitere Konfigurationen,
• Fig. 7 eine weitere bevorzugte Ausführungsform in Draufsicht,
• Fig. 8 einen Schnitt durch die Ausführungsform nach Fig. 7 entlang der Linie VIII-VIII,
• Fig. 8 und lO Ausschnittsdarstellungen des in Fig. 8 mit mit IX/X gezeigten Bereiches,
• Fig. ll eine weitere bevorzugte Ausführungsform der Erfindung, ähnlich der nach Fig. 7,
• Fig. l2 einen Schnitt entlang der Linie XII-XII aus Fig. ll,
• Fig. l3/l3a Ausschnittsvergrößerungen der in Fig. l2 gezeigten Bereiche,
• Fig. l4 einen Schnitt entlang der Linie XIV-XIV aus Fig. l5, einer weiteren Anordnung,
• Fig. l5 eine Draufsicht auf die Anordnung nach Fig. l4,
• Fig. l6 eine weitere bevorzugte Ausführungsform der Erfindung, wobei der Heizkörper an einem Wasserbad befestigt ist, und
• Fig. l7 bis l9 weitere bevorzugte Konfigurationen mit Kreisflächenhälften-Wärmeableitelementen.

Further features essential to the invention can be found in the following exemplary embodiments of the invention, which are explained with reference to figures. Here shows:

• 1 shows a first preferred embodiment of the invention with housing,
• 2 is a view of the embodiment of FIG. 1 along the line II-II,
• 3 to 6 further configurations,
• 7 shows a further preferred embodiment in plan view,
• 8 shows a section through the embodiment according to FIG. 7 along the line VIII-VIII,
• 8 and 10 cutouts of the area shown in FIG. 8 with IX / X,
• FIG. 11 shows a further preferred embodiment of the invention, similar to that according to FIG. 7,
• FIG. 12 shows a section along the line XII-XII from FIG. 11,
• L3 / l3a detail enlargements of the areas shown in FIG. L2,
• L4 shows a section along the line XIV-XIV from FIG. L5, a further arrangement,
• L5 is a plan view of the arrangement of FIG. L4,
• Fig. 16 shows a further preferred embodiment of the invention, wherein the radiator is attached to a water bath, and
• Fig. 17 to l9 further preferred configurations with circular surface halves heat dissipation elements.

The embodiment shown in FIGS. 1 and 2 is a panel radiator that is completely installed in a housing 30. The housing 3O comprises a housing trough 3l, which is open at the top. The interior of the tub 3l is lined with a layer 23 of insulating film. At the edges of the tub rails 2l and 22 are introduced over the entire length. Between the busbars are several groups of heat dissipation elements 10, 10, which have an essentially isosceles, right-angled outline. One catheter surface of the heat dissipation elements 10, 10 l is connected to one of the busbars 2l / 22, while the hypotenuse surfaces of the heat dissipation elements 10, 10 l are opposite. PTC elements l are arranged between the hypotenuse surfaces of the heat dissipation elements 10, 10. The overall grouping, consisting of two heat dissipation elements 10, 10 and the PTC element 1 in between, has essentially a cuboid shape.

A plurality of such “cuboid elements” are arranged in the housing 3O, an insulating layer 23 being seated between two cuboid elements. The insulating layer 23 is made of electrically and thermally poorly conductive material.

The tub 3l has fixed at its upper end (Fig. L) put on lugs 24 which fix a final insulating plate 23 in the longitudinal direction of the tub 3l. On the lower side (FIG. 1), the trough is also closed off by an insulating plate 23, which strikes against fixing lugs 24.

The busbars 2l and 22 are bent inwards at this lower end of the trough 3l and led outwards via connecting wires l6 / l7.

On the inwardly bent sections of the busbars 21, 22 there is a further insulating disk 23 on which an elastic spring element 20 is seated. The elastic spring element is thus supported on the (indirectly) attached to the tub 3l insulating washer 23 and presses against the lowest heat dissipation element 10 in FIG. The uppermost heat dissipation element 10 in FIG. 1 is fixed on the housing 3l via the insulating disk 23, so that the force applied by the spring element 20 is guided through the entire arrangement as a continuous force train through the PTC elements 1. In this way, the same force acts on all PTC elements 1 or - since the PTC elements 1 are of identical design - the same surface pressure.

Due to the triangular arrangement of the heat dissipation elements lO, lOʹ not only the PTC elements l are fixed, but the heat dissipation elements lO, lO gleichzeitig are simultaneously pressed against the edge 35 of the tub 3l. So there is a "wedging" in such a way that you only have to insert the parts (possibly slightly fixed) into the tub 3l with the interposition of the insulating layer 23 when the radiator is being installed, when the overall arrangement with compression of the spring element 2O mechanical attachment of the locking lugs 24 is closed, all individual parts are adjusted and fixed to one another with exactly the same forces will. From this it can be seen that the extremely critical assembly of PTC elements by the arrangement according to the invention can achieve a very considerable advantage in terms of production costs.

Because the individual "heating element cuboids" lO-l-lOʹ are separated from one another by insulating disks 23, each "cuboid" is to be regarded as a detail body thermally decoupled from the other elements. The control behavior is accordingly good. It is also possible to use different PTC elements or those with different transition temperatures, so that a radiator is obtained which has a specific, desired temperature profile over the surface.

The heat dissipation of the radiator to an object to be heated takes place via the heat dissipation surface 11 (see FIG. 2). To accomplish this, the entire radiator is pressed onto the object to be heated with the interposition of a very thin, electrically insulating film. The fact that the heat dissipation elements 10 have very large heat dissipation surfaces 11 - measured at the connecting surfaces between PTC elements 1 and heat dissipation elements 10, 10 - the thermal resistance through the insulating film hardly plays a role. If the heat dissipation elements lO, lOʹ are made of a thermally very good conductive material, e.g. made of aluminum, you get an extremely low thermal resistance between PTC elements 1 and the body to be heated, so that the achievable heat output is extremely high. Furthermore, this arrangement can essentially be enlarged in size as desired, which was previously not possible. Finally, it should be pointed out that the electrical contacting is particularly simple and involves little loss.

3 shows a configuration in which the Electrical insulation between the superimposed heat dissipation elements lO or lOʹ can be dispensed with, since the PTC elements l or the hypotenuse surfaces of the heat dissipation elements lO, lOʹ run in a zigzag between the busbars 2l and 22. This arrangement is even more favorable in terms of component costs. If, in the arrangement shown in FIG. 3, the catheter surfaces of the heat dissipation elements 10, 10 are not grinded flat, but instead are provided, for example, with feet at the triangular corners, so that only the feet of adjacent heat dissipation elements 10, 10 are seated one on the other, then the thermal Reduce the coupling between the heat dissipation elements lO, lOʹ.

FIG. 4 again serves to explain the arrangement shown with reference to FIGS. 1 and 2.

In the arrangement shown in Fig. 5, a very thick insulating washer 23 is arranged between adjacent heat dissipation elements 10, 10, whereby the decoupling is even better. Such an arrangement is particularly advantageous if the object to be heated has a very low thermal resistance in the surface direction (to which the radiator is applied). The correspondingly wide spacing between two heat dissipation elements lO, lOʹ then ensures that no thermal short circuit occurs through the body to be heated.

The arrangement shown in FIG. 6 is a rectangular arrangement which is advantageous in many forms of use. With such an arrangement, for example, the heat dissipation elements 10, 10 ′ can be provided with bores perpendicular to the heat dissipation surfaces 11 (perpendicular to the direction of the drawing), and the arrangement can be used as a heater for flowing air.

The arrangement shown in FIG. 8 is a heater with a circular cross section. Here only two heat dissipation elements lO, lOʹ are provided, which simultaneously serve for the electrical contacting of two PTC elements l. For this purpose, grooves are milled into the heat dissipation elements lO, lOʹ, into which connecting wires l6 and l7 are inserted, which can then be fixed by simply clamping them in (flanging the groove edges). The two heat dissipation elements lO, lOʹ are clamped together via a tension ring l8, wherein between the tension ring l8 and the heat dissipation elements lO, lOelementen the spring element 2O is arranged, which also serves for insulation (if the tension ring l8 is electrically conductive).

9 and 10, two preferred embodiments are explained, FIG. 9 showing a clamping ring 18, which is encased by the spring element 20, while in FIG. 10 the spring element 20 is merely a band. In both cases, grooves are made on the outer edge (with a semicircular cross section) of the heat dissipation elements 10, 10 in which the clamping ring l8 is fixed together with the spring element 20.

The radiator shown here is particularly easy to manufacture and therefore very inexpensive.

The arrangement shown in FIGS. 11 to 13 is again a radiator with a circular outline, in which case the arrangement sits in a housing 30. The housing 3O has a trough element 3l, on the bottom of which an insulating film 23 is seated. On its upper side, the housing 30 is covered by a cover element 33. The cover element 33 is held over flanges 34 of the edge 35 of the tub element 3l. The two heat dissipation elements sit between the cover element 33 and the bottom 32 of the tub element 3l mente lO, lOʹ, between which - as in the previously shown embodiment - the PTC elements l are arranged. The electrical contacting is carried out as shown previously (see Fig. L3a). The cover element 33, like the tub base 32, is electrically insulated from the heat dissipation elements 10, 10 by an insulating layer 23. Of course, in both cases (cover and base), the insulating layer 23 can be replaced, for example, by an oxide layer of the housing material, which is relatively easy, in particular when aluminum is used as the housing material. Although this ensures that the necessary electrical resistance of the insulating layer is ensured, the low necessary layer thickness also ensures a low heat transfer resistance between housing 3O and heat dissipation elements 10, 10.

The embodiment shown in Figs. Ll to l3 has a special feature in that the spring element and the part necessary for clamping is secured by the flange 34, which is opposed to an inclined surface in the heat dissipation elements lO, lOʹ (see Fig. L2 and l3 ). If one attaches the conveyor 34, then not only acts a force perpendicular to the trough bottom 32, but also a force parallel to the trough bottom on the heat dissipation elements 10, 10, so that these are moved or pressed towards one another, in which case the PTC -Elements l are set.

A further advantage in the arrangement shown in FIG. 11 is ensured by a circular recess in the interior of the element, or by semicircular recesses on both heat dissipation elements 10, 10. This recess namely achieves a certain thermal decoupling between the two PTC elements 1.

Furthermore, the assembly of the arrangement can be facilitated by - as shown in Fig. L3 - arranging an insulating strip in the gap between the two heat dissipation elements lO, lOʹ on which the PTC elements l are placed before the cover 33 is placed (see Fig. L3a).

Of course, it is also possible to work with only a single PTC element 1, as is shown schematically in FIGS. 14 and 15.

The arrangement shown in FIG. L6 differs from that according to FIG. L2 in that the tub element 3l is an integral part of the body 4O to be heated. The fixing of the cover 33 and the clamping of the two heat dissipation elements 10, 10 ′ takes place in the same way as explained with reference to FIG. 13 above.

With reference to FIGS. L7 and l9 it should be clarified that individual elements, as shown in FIGS. L4 and l5, can also be combined very well into groups. This arrangement has the particular advantage that there is sufficient electrical contact between the heat dissipation elements lO, lOʹ, but on the other hand a very low thermal coupling is to be expected due to the linear contact, which in turn improves the control behavior of the arrangements. In the arrangements shown in FIGS. L7 and l8, the heat dissipation elements 10, 10 ′ also serve again for electrical contacting, the (circular) busbars 2 1 and 2 10 ′ serving as spring elements 2O in the interior of the arrangements according to FIGS. 17 and 18 . The disk elements according to FIGS. 14 and 15 can also be set up in linear arrangements, as shown in FIG. 19. Here, too, the advantage of sufficient thermal decoupling arises, this arrangement being particularly lightly designed over a large area can be, because you can put any number of individual "heating discs" in a grid of busbars 2l-22-2l ...

When using the heating disc according to FIGS. L4 and l5, it is advantageous if these are manufactured as prefabricated individual parts by fixing the PTC elements l between two heat dissipation elements 10, 10 ′ by an (electrically conductive) adhesive. You can then also electrically isolate these elements on their heat-emitting surfaces 11 (above and below) by means of a lacquer or in another manner known per se, but the edge of the elements must remain electrically conductive.

The exemplary embodiments shown above, or the ideas that can be gathered from them, are to be considered individually and in combination as essential to the invention. In particular, the concept of the invention can also be applied to other heating or cooling elements. In the case of Peltier elements, the heat dissipation elements 10 would then be used (with a slightly modified spatial arrangement, possibly with the interposition of thermal insulators) as the "hot side", the heat dissipation elements 10 as the "cold side".

If necessary, the entire arrangement can be cast.

Reference symbol list:

• l PTC element
• lO / lOʹ heat dissipation element
• ll heat emission surface
• l2 Connection area to the PTC element
• l3 catheter surface
• l4 catheter surface
• l6 connecting wire
• l7 connecting wire
• l8 tension ring
• 2O spring element
• 2l track
• 22 track
• 23 insulation
• 24 locking nose
• 3O housing
• 3l bath element
• 32 tray floor
• 33 cover element
• 34 crimping
• 35 tub rim
• 4O body to be heated

Claims (14)

1. Electric radiator with at least one PTC heating element (l) or PTC element, with heat dissipation elements (lO, lOʹ), which are connected to the flat sides of the PTC element (l) at a connecting surface (l2) and at least one heat dissipation surface (ll) have
characterized,
that the heat emission surfaces (ll) are arranged substantially perpendicular to the connecting surfaces (l2). 2. Radiator according to claim l,
characterized,
that the heat release surfaces (ll) are many times larger than the connecting surfaces (l2). 3. Heating element according to one of the preceding claims,
characterized,
that each PTC element (l) two heat dissipation elements (lO, lOʹ) are assigned. 4. Radiator according to one of the preceding claims,
characterized,
that several PTC elements (l) are provided, which are arranged in series with the interposition of the heat dissipation elements (lO, lOʹ) in a substantially continuous force train such that the contact pressures between all PTC element flat sides and the associated connecting surfaces (l2) are essentially the same are. 5. Radiator according to claim 4,
characterized,
that a single spring element (2O) is provided for all groups of PTC elements (l) with heat dissipation elements (lO, lOʹ). 6. Radiator according to one of the preceding claims,
characterized,
that the PTC elements (l) are electrically connected in parallel. 7. Radiator according to one of the preceding claims,
characterized,
that the heat dissipation elements (lO, lOʹ) of a PTC element (l) are thermally decoupled from those of (or all) other PTC elements (l). 8. Radiator according to one of the preceding claims,
characterized,
that the heat dissipation elements (lO, lOʹ) form the power supply electrodes. 9. Radiator according to one of the preceding claims,
characterized,
that a common housing (3O) for several PTC elements (l) with heat dissipation elements (lO, lOʹ) is provided. lO. Radiator according to claim 9,
characterized,
that the housing (3O) comprises a trough element (3l) in which the PTC elements (l) with the interposition of the heat dissipation elements (lO, lOʹ) are braced against each other (force series), the trough bottom (32) parallel to the heat-emitting surfaces (ll) lies. 11. Radiator according to claim 10,
characterized,
that the housing (30) comprises a cover element (33), which is preferably held by means of a crimp (34) of the tub edge (35) in the tub element (3l) while being pressed against the heat-emitting surfaces (11). 12. Radiator according to claim ll,
characterized,
that the tub element (3l) is designed as a recess of a body to be heated (40). 13. tub element according to claim 4,
characterized,
that the heat dissipation elements (lO, lOʹ) have at least one surface section (l3, l4, l5) which runs perpendicular to the heat emission surface (ll) and at an acute angle (α) to the connecting surface (l2). 14. Radiator according to claim l3,
characterized,
that the angle (α) is 45 ° and the heat emission Surface (ll) essentially has the outline of an isosceles right-angled triangle.

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