EP0248285B1 - Electrical heating element - Google Patents

Description

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

When designing electric radiators with PTC elements, some properties inherent in these elements must be taken into account. On the one hand, the PCT elements are manufactured as thin rods or slices 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.

From DE-U-85 07 557 a heating element is known in which PTC elements, each with a flat side, are placed on a flat side of a heat dissipation element, the heat emission surfaces of which are arranged essentially perpendicular to the PTC element. The other flat side of the PTC element is acted upon by a separate contact and pressure element. The problem with this configuration is that only one of the flat sides of the PTC element is able to give off heat, so that the heat output of each individual PTC element is relatively low. In addition, a temperature gradient is formed over the thickness of the PTC element, which adversely affects the control behavior of the PTC element.

From DE-OS 34 25 208 a radiator according to the preamble of the main claim is known, which is also cylindrical. In this radiator, each heat dissipation element is separately connected to power supplies. According to the above-mentioned publication, it is particularly advantageous if the central perpendiculars of the PTC elements lie on a straight line, that is to say the entire arrangement forms a cylindrical stack. With this arrangement, too, it is not possible for the reasons mentioned above to adapt the shape of the heating element to the intended use and to achieve greater heating outputs.

Starting from the above-mentioned prior art, it is an object of the present invention to develop an electric radiator according to the preamble of claim 1 to the effect that essentially any shapes and sizes of the heat dissipation surface can be assembled from basic elements.

This object is achieved by the features specified in the characterizing part of the main claim. Due to the special shape, distribution takes place in such a way that the force train is divided when the arrangement is clamped, which on the one hand ensures the power connections and on the other hand the heat dissipation from the PTC elements. With a flat design of the heat dissipation elements, defined and low forces can be applied between the heat dissipation elements, which press on the PTC element, while very high forces can be applied between the heat dissipation elements and the heat consumer (e.g. a heating plate) in order to achieve a low heat transfer resistance.

The arrangement can be used not only with PTC elements to produce a radiator, but also with other heating or cooling elements. If Peltier elements were used instead of PTC elements, then one would use one heat dissipation element as the "hot side" and another heat dissipation element as the "cold side" (with a slightly different spatial arrangement, possibly with the interposition of thermal insulators).

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 significantly, and the heating power of a PTC element thus increases significantly.

In order to achieve higher heating outputs, the electric radiator is preferably provided with several PTC elements, which are arranged with the interposition of the heat dissipation elements in a substantially continuous force train - that is to say in terms of force - in such a way that the contact pressures between all PTC element flat sides and the associated connecting surfaces of the heat dissipation elements are essentially the same. This arrangement is only possible through the arrangement according to the invention, 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 takes place completely independently of the coupling of the PTC elements to the heat dissipation elements, so that any pressure can be pressed 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.

If each PTC element is assigned two heat dissipation elements and several such "groups" are combined to form a larger area, 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. Of course, the surface on which the heat dissipation elements conduct the generated heat must be designed so that the thermal decoupling is maintained. Such a thermal decoupling can on the one hand prevent the effects of step temperature tolerances between the individual PTC elements, and on the other hand it is possible, for example over a longer period Heating section to build up a temperature gradient using PTC elements of different transition temperatures.

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, the area actually being able to be chosen as large as desired by simply arranging any number of PTC elements with heat-conducting elements together in a common trough in the manner described.

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). You can do that Form the tub element in one piece with a body to be heated, as a result of which, for example 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 considerably reduced.

Fig. 1

eine erste bevorzugte Ausführungsform der Erfindung mit Gehäuse,

Fig. 2

eine Ansicht auf die Ausführungsform nach Fig. 1 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 10

Ausschnittsdarstellungen des in Fig. 8 mit mit IX/X gezeigten Bereiches,

Fig. 11

eine weitere bevorzugte Ausführungsform der Erfindung, ähnlich der nach Fig. 7,

Fig. 12

einen Schnitt entlang der Linie XII-XII aus Fig. 11,

Fig. 13/13a

Ausschnittsvergrößerungen der in Fig. 12 gezeigten Bereiche,

Fig. 14

einen Schnitt entlang der Linie XIV-XIV aus Fig. 15, einer weiteren Anordnung,

Fig. 15

eine Draufsicht auf die Anordnung nach Fig. 14,

Fig. 16

eine weitere bevorzugte Ausführungsform der Erfindung, wobei der Heizkörper an einem Wasserbad befestigt ist, und

Fig. 17 bis 19

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 the aid of figures. Here shows:

Fig. 1

a first preferred embodiment of the invention with housing,

Fig. 2

2 shows a view of the embodiment according to FIG. 1 along the line II-II,

3 to 6

other configurations,

Fig. 7

another preferred embodiment in plan view,

Fig. 8

7 shows a section through the embodiment according to FIG. 7 along the line VIII-VIII,

8 and 10

Detail representations of the area shown with IX / X in FIG. 8,

Fig. 11

another preferred embodiment of the invention, similar to that of FIG. 7,

Fig. 12

11 shows a section along the line XII-XII from FIG. 11,

Fig. 13 / 13a

Enlarged sections of the areas shown in FIG. 12,

Fig. 14

15 shows a section along the line XIV-XIV from FIG. 15, a further arrangement,

Fig. 15

14 shows a plan view of the arrangement according to FIG. 14,

Fig. 16

a further preferred embodiment of the invention, wherein the radiator is attached to a water bath, and

17 to 19

further preferred configurations with circular surface half 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 30 comprises a housing trough 31 which is open at the top. The interior of the tub 31 is lined with a layer 23 of insulating film. At the edges of the tub, rails 21 and 22 are introduced over the entire length. Between the busbars there are several groups of heat dissipation elements 10, 10 'which have an essentially isosceles, right-angled outline. In each case one catheter surface of the heat dissipation elements 10, 10 'is connected to one of the busbars 21/22, while the hypotenuse surfaces of the heat dissipation elements 10, 10' lie opposite one another. PTC elements 1 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 a PTC element 1 in between, has essentially a cuboid shape.

A plurality of such “cuboid elements” are arranged in the housing 30, with an insulating layer 23 each sitting between two cuboid elements. The insulating layer 23 is made of electrically and thermally poorly conductive material.

The tub 31 has at its upper end (Fig. 1) locking lugs 24, which fix a final insulating plate 23 in the longitudinal direction of the tub 31. On the lower side (FIG. 1), the tub is also closed off by an insulating plate 23, which strikes fixing lugs 24.

The busbars 21 and 22 are bent inwards at this lower end of the trough 31 and guided outwards via connecting wires 16/17.

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 trough 31 insulating plate 23 and presses against the lowest heat dissipation element 10 'in FIG. 1. The uppermost heat dissipation element 10 in FIG. 1 is fixed on the housing 31 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 identical - the same surface pressure.

Due to the triangular arrangement of the heat dissipation elements 10, 10 ', not only are the PTC elements 1 fixed, but the heat dissipation elements 10, 10' are also pressed against the edge 35 of the tub 31 at the same time. So there is a "wedging" in such a way that you only have to insert (if necessary slightly fixed) the parts into the tub 31 with the interposition of the insulating layer 23 when installing the radiator, when the overall arrangement with compression of the spring element 20 by 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" 10-1-10 '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. Furthermore, it is 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. Characterized in 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 10, 10 'are made of a thermally highly 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 heat dissipation elements 10 and 10 'lying on top of one another can be dispensed with, since the PTC elements 1 and the hypotenuse surfaces of the heat dissipation elements 10, 10' run in a zigzag fashion between the busbars 21 and 22. This arrangement is even more favorable in terms of the number of components. If, in the arrangement shown in FIG. 3, the catheter surfaces of the heat dissipation elements 10, 10 'are not ground 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' sit on one another, then one can reduce the thermal coupling between the heat dissipation elements 10, 10 '.

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 disk 23 is arranged between adjacent heat dissipation elements 10, 10 ', as a result of which the decoupling becomes 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 10, 10 '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. Only two heat dissipation elements 10, 10 ′ are provided here, which simultaneously serve for the electrical contacting of two PTC elements 1. For this purpose, grooves are milled into the heat dissipation elements 10, 10 ', into which connecting wires 16 and 17 are inserted, which can then be fixed by simply clamping (flanging the edges of the grooves). The two heat dissipation elements 10, 10 'are clamped together via a tension ring 18, wherein between the tension ring 18 and the heat dissipation elements 10, 10' the spring element 20 is arranged, which also serves for insulation (if the tension ring 18 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 18 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 30 has a trough element 31, 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 trough element 31. The two sit between the cover element 33 and the bottom 32 of the tub element 31 Heat dissipation elements 10, 10 ', between which - as in the previously shown embodiment - the PTC elements 1 are arranged. The electrical contact is made as shown previously (see Fig. 13a). The cover element 33, like the trough 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 required layer thickness also ensures a low heat transfer resistance between housing 30 and heat dissipation elements 10, 10 '.

The embodiment shown in FIGS. 11 to 13 has a special feature in that the spring element and the part necessary for clamping are secured by the flange 34, which is opposed to an inclined surface in the heat dissipation elements 10, 10 '(see FIGS. 12 and 13). If one attaches the conveyor 34, not only does a force acting perpendicular to the trough bottom 32, but also a force parallel to the trough bottom act on the heat dissipation elements 10, 10 ', so that these are moved or pressed towards one another, in which case the PTC elements 1 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 semi-circular 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. 13 - arranging an insulating strip in the gap between the two heat dissipation elements 10, 10 'onto which the PTC elements 1 are placed before the cover 33 is put on ( see Fig. 13a).

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. 16 differs from that according to FIG. 12 in that the tub element 31 is an integral part of the body 40 to be heated. The cover 33 is fixed and the two heat dissipation elements 10, 10 'are clamped together, as also explained with reference to FIG. 13 above.

17 and 19 are intended to clarify that individual elements, as shown in FIGS. 14 and 15, 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 10, 10 ', but on the other hand a very slight 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. 17 and 18, the heat dissipation elements 10, 10 'also serve again for electrical contacting, the (circular) busbars 21 and 21' being simultaneously used as spring elements 20 in the interior of the arrangements according to FIGS. 17 and 18 can serve. 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 21-22-21 ...

When using the heating discs according to FIGS. 14 and 15, it is advantageous if they are manufactured as prefabricated individual parts by fixing the PTC elements 1 between two heat dissipation elements 10, 10 'by means of an (electrically conductive) adhesive. These elements can then also be electrically insulated on their heat-emitting surfaces 11 (top and bottom) by 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, one would then use the heat dissipation elements 10 as the “hot side” and the heat dissipation elements 10 ′ as the “cold side” (with a slightly modified spatial arrangement, possibly with the interposition of thermal insulators).

If necessary, the entire arrangement can be cast.

Reference symbol list:

1

 PTC element

10/10 '

 Heat dissipation element

11

 Heat emission surface

12

 Connection surface to the PTC element

13

 Catheter surface

14

 Catheter surface

16

Connecting wire

17th

 Connecting wire

18th

 Tension ring

20th

 Spring element

21

 Track

22

Track

23

 insulation

24th

Locking nose

30th

casing

31

 Tub element

32

 Tub floor

33

 Cover element

34

 Crimping

35

 Tub rim

40

body to be heated

Claims (10)

1. An electrical heating unit comprising at least one PTC element (1) and associated heat dissipation elements (10, 10') which at a connecting surface (12) are connected to the plane surfaces of said PTC element (1) and have heat emitting surfaces (11) disposed substantially perpendicularly to said connecting surfaces (12) and forming the current supply electrodes,
   characterized in
   that said heat dissipation elements (10, 10') have at least one surface portion (13, 14) which extends perpendicularly to said heat emitting surface (11) and at an acute angle (∝) to said connecting surface (12).
2. A heating unit as claimed in claim 1,
   characterized in
   that the area of said heat emitting surfaces (11) is a multiple of the area of said connecting surfaces (12).
3. A heating unit as claimed in any one of the preceding claims,
   characterized in
   that each of said PTC elements (1) cooperates with two heat dissipation elements (10, 10').
4. A heating unit as claimed in any one of the preceding claims,
   characterized in
   that a plurality of PTC elements (1) is provided, with said heat dissipation elements (10, 10') interposed therebetween, in serial arrangement in a substantially continuous power train so that the contact pressures between all plane surfaces of said PTC elements and the associated connecting surfaces (12) are substantially the same.
5. A heating unit as claimed in claim 4,
   characterized in
   that a single spring element (20) is provided for all groups of PTC elements (1) including heat dissipation elements (10, 10').
6. A heating unit as claimed in any one of the preceding claims,
   characterized in
   that said heat dissipation elements (10, 10') of a PTC element (1) are thermally decoupled from those of another (or all other) PTC elements (1).
7. A heating unit as claimed in any one of the preceding claims,
   characterized in
   that a common housing (30) comprises a trough element (31) in which said PTC elements (1), with said heat dissipation elements (10, 10') interposed therebetween, are mutually braced (in serial power arrangement), the trough bottom (32) being disposed in parallel to said heat emitting surfaces (11).
8. A heating unit as claimed in claim 7,
   characterized in
   that said housing (30) comprises a cover element (33) which is preferably retained in said trough element (31) by means of a curling (34) of the trough edge (35) by pressing said cover element (33) against said heat emitting surfaces (11).
9. A heating unit as claimed in claim 7 or claim 8,
   characterized in
   that said trough element (31) is integral with the member (40) to be heated.
10. A heating unit as claimed in any one of the preceding claims 3 to 9,
    characterized in
    that said heat dissipating elements (10, 10') together with the centrally disposed PTC element (1) form a circular area.

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