EP1915034B1 - PTC heating element - Google Patents

Description

The present invention relates to a PTC heating element having at least one PTC resistor element which is arranged between two printed circuit boards in a housing opening of a housing and is biased under the interposition of at least one of the printed circuit boards against a heat-emitting element, which is held by the housing.

Such a PTC heating element is, for example, from the date of the Applicant EP 0 350 528 known. In this prior art, several PTC heating elements in several levels with the interposition of heat-emitting elements in the form of meandering bent metal strip in a frame are arranged. Within the frame is a spring, which presses the two externally applied to the PTC heating circuit boards for good thermal and electrical contact with the PTC element and the heat-emitting elements for good heat transfer of the heat generated by the PTC resistor element against the adjacent Printed circuit board. In the cited prior art, the PTC heating element is used for air heating. However, other embodiments are known in which the PTC resistor element heats a heating plate. Such embodiments are known in particular for heating or keeping food warm, for example baby food.

The present invention is based on the problem to provide a generic heating element, which can be easily and thus inexpensively.

To solve this problem, the present invention provides a PTC heating element having the features of claim 1. This differs from the generic state of the art by a housing opening, which is surmounted by fastening edges arranged at the edge of the housing opening, wherein the heat-releasing element has pin recesses which are engaged behind by the pins in the case of a heat-emitting element mounted on the housing.

By this engaging behind the heat-emitting element is easily connected to the housing, for example, locked. Alternatively, the pins may also have at their free end, a peg opening engaging behind, formed by melting of the respective pin thickening. Such thickened pins are achieved for example by hot stamping.

However, the pins are not only the attachment of the heat-emitting element relative to the housing. Rather, the pins surround the housing opening and extend beyond the housing opening on the outside. As a result, the pins form a guide formed by the housing in the insertion direction of the printed circuit boards and the at least one PTC resistor element, by means of which the assembly is simplified. The pins may additionally be funnel-shaped at the upper free end for facilitating the easy insertion of the two strip conductors with the at least one PTC resistor element arranged therebetween.

The pin of the PTC heating element according to the invention then comes to a double function. On the one hand, due to their arrangement relative to the housing opening, they permit a simple guided introduction of the printed circuit boards together with the at least one PTC resistance element. In addition, they ensure a secure fixation of the heat-emitting element after the final assembly.

According to a preferred embodiment of the present invention, the pin project beyond an upper, formed by the housing bearing surface for the heat-emitting element having a height which is dimensioned such that lifted by the bias before applying the heat element on the contact surface with respect to this raised PCB not higher than the top of the pin reaches. This creates the possibility to fix the heat-releasing and recorded in the housing opening layer structure during assembly. Preferably, the pins are approximately sized so that the raised over the contact surface upper circuit board is approximately equal in height to the upper end of the pin. With regard to the most gentle possible use of material for the formation of the housing and the pin these should only slightly protrude the upper circuit board in the raised position.

For further simplification of the PTC heating element, it is proposed according to a preferred embodiment of the present invention, the printed circuit board opposite the heat-emitting element, i. the printed circuit board which is provided with respect to the PTC resistor element on the other side than the heat-emitting element, to be provided with at least one spring element which is integrally formed thereon by punching and bending the sheet material forming the printed circuit board and on the housing supported. The spring element is preferably cut out of the sheet metal material forming the printed circuit board in such a way that it first projects on the outside of the contact surface of the at least one PTC resistor element on the corresponding printed circuit board. The projecting portion is then preferably bent on the back of the contact surface under the circuit board and can be supported with this spring leg on the housing, which is preferably closed on its underside opposite the housing opening. In this case, a housing opening in the sense of the present invention is understood as meaning, in particular, a recess which opens to the contact surface for the heat-releasing element and whose size corresponds approximately to the dimensions of the PTC resistance elements accommodated in the housing. In other words, the housing opening has in plan view approximately the contour of the PTC or resistance elements of the PTC heating element.

With regard to a secure and simple determination of connected with cables for electrical connection of the PTC heating element to an electrical power source plug sockets is proposed according to a further preferred embodiment of the present invention to provide the housing with two connector receptacles, each having a detent opening for engaging a formed on the plug sleeve locking tongue, wherein a contact formed by punching and bending the printed circuit board contact tongue arranged in the connector receptacle and thus in a simple manner and permanently electrically connected to the captive secured by the locking connection in the housing connector sleeve.

For easy securing of the two circuit boards in the housing, it has proven advantageous to guide the contact tongue to the respective circuit board in each case by a recessed outside the housing opening on the underside Kontaktzungenausnehmung in a direction perpendicular to the plane of the circuit board out of the housing and by deflecting into the connector receptacle to bring in an orientation in which the contact tongue extends substantially parallel to the circuit board and is inserted into the connector receptacle. In this development is to be understood as a housing opening only that recess in the housing, which serves to receive the PTC or the resistance elements. For example, a housing opening formed with the base area of a single PTC resistance element can be recessed on the housing. The printed circuit boards have an abutting on the PTC resistor element abutment portion, which is surmounted on its outer peripheral surface by a free-punched connection portion. This connection portion is initially in the plane of the circuit board forming sheet metal strip. A partial region of the connection section, ie the front end of the connection section forming the contact tongue, is then bent over by 90 °, so that the contact tongue protrudes substantially at a right angle from the plane of the sheet material. In this state, the circuit board is introduced with its contact portion in the opening of the housing. The contact tongue passes through the recessed on the underside of the housing Kontaktzungenausnehmung and extends beyond the housing on the outside. Thereafter, the projecting portion is formed, for example, by a slider and introduced into the contact tongue receptacle, which extends substantially parallel to the contact surface of the abutment portion, ie parallel to the support surface for the heat-emitting element. After this forming step, the respective conductor track is securely received in the housing. For this purpose, the connection section of the printed circuit board is preferably surrounded relatively tightly by walls of the housing and thus held fixed in position in the housing.

Fig. 1

eine Draufsicht auf die Oberseite eines Ausführungsbeispiels eines PTC-Heizelementes bei abgenommener Heizplatte;

Fig. 2

eine perspektivische Draufsicht auf die Unterseite des in Fig. 1 dargestellten Ausführungsbeispiels,

Fig. 3

eine Längsschnittansicht entlang der Linie III-III gemäß der Darstellung in Fig. 1 bei aufgelegter Heizplatte und

Fig. 4

eine Längsschnittansicht entlang der Linie IV-IV gemäß der Darstellung in Fig. 1 bei aufgelegter Heizplatte.

Further advantages and details of the present invention will become apparent from the following description taken in conjunction with the drawings. In this show:

Fig. 1

a plan view of the top of an embodiment of a PTC heating element with removed heating plate;

Fig. 2

a perspective top view of the underside of in Fig. 1 illustrated embodiment,

Fig. 3

a longitudinal sectional view along the line III-III as shown in FIG Fig. 1 with the heating plate and

Fig. 4

a longitudinal sectional view along the line IV-IV as shown in FIG Fig. 1 with the heating plate on.

The embodiment shown in the drawing is a PTC heating element for heating or keeping warm baby food and is housed within an injection-molded, not shown housing, which forms the holder for the baby food containing vessel (bottle, glass). In the bottom of this injection-molded housing is the PTC heating element shown in the drawing. This forms with its heating plate 2, the support for the baby food receiving vessel, which is directly on the heating plate 2.

The embodiment shown in the drawing has a housing 4, which consists essentially of three separate segments. Thus, the housing has a receiving portion 6 for receiving a heat-generating layer structure, comprising a lower printed circuit board 8, an interposed PTC heating element 10 having a substantially circular shape and an upper printed circuit board 12 (see. Fig. 3 ). To accommodate this layer structure of the receiving portion 6 has a substantially round opening 14, which is only slightly larger than the layer structure. In this case, the lower printed circuit board 8 and the upper printed circuit board 12 each have a circular abutment portion 16 corresponding to the contour of the round PTC element.

On opposite sides of the opening 14 from the opening 14 outgoing, opening to the opening 14 printed circuit board chambers 18, 20 are provided by the housing 4, the bottom of which may be slightly raised relative to the bottom of the opening 14.

The housing 4 forms next to the receiving portion 6, two plug receptacles 22, 24. These plug receptacles 22, 24 are opposite to in Fig. 1 shown top of the PTC heating element by a cover 26 which is located below a formed by the top of the housing 4 contact surface 28 for the heating plate 2. Corresponding to this, the plug receptacles 22 and 24 each have a latching opening 36 which is recessed in the embodiment shown on the inside of the cover 24 and 26, respectively, without enforcing the respective cover 24, 26.

Like the sectional view according to Fig. 3 shows the outer bottom 40 of the circuit board chambers 18, 20 equal in height to the bottom 42 of the housing 4. In extension of the edges of the connector receptacle 22, 24 form contact webs 43 bottom 42 of the housing 2. Between the bottom 40 and the underside of the cover 24, 26, the housing 4 forms a stop 44 for the plug sleeve 30. Below this stop 44, the recess formed by the plug receptacle 22, 24 is pulled through on the underside of the housing 2 to the rear end of the same. In other words, the plug receptacle 22 or 24 continues over the recess 46 to the rear end of the housing 4. To the recess 46 opens a reed 48, which connects as a slot downwardly exposed bottom 40 of the housing with the inside of the receiving portion 40 and which is provided outside the opening 14 and in extension of the plug receptacles 22, 24.

The plug receptacles 22, 24 are bounded on the underside by a web 50 which is provided in the insertion direction of the plug sleeve 30 in the front region of the plug receptacle 22 and 24 and the two contact webs 43 of the respective plug receptacles 22, 24 connects. In the insertion direction behind the plug receptacles 22, 24 each have a Kontaktzungeneinführöffnung 52, which is formed for reasons of injection molding production of the housing 4 with the width of the plug receptacle 22 and 24 (see. Fig. 2 ).

Again Fig. 1 can be seen, the contact surface 28 is surmounted by three pins 54 which are provided at the edge of the circular inner peripheral surface of the opening 14. The pins 54 may be integrally provided on the housing 4 by means of injection molding. alternative can be recessed in the injection molding production of the housing 4 pin recesses into which the pins 54 are inserted. In this embodiment, it is possible, for example, to form the pins at their lower end with spring projections, which are supported on the inside of the bottom of the housing opening 14 and press against the lower printed circuit board 8 to these together with the PTC resistor element 10 and the upper after assembly Printed circuit board 12 to press against the heating plate 2.

In an alternative embodiment, which is realized in the embodiment shown, the lower circuit board 8 integrally formed thereon spring projections 56 (see.
Fig. 4 ). These spring projections 56 are first formed by free cutting of the lower printed circuit board 8 forming sheet material and in a subsequent manufacturing step below the bottom of the lower circuit board 8, so that formed on the inside of the bottom 40, integrally provided with the lower circuit board 8 spring projections 56 are formed are. Preferably, a plurality of spring projections 56 are provided on the circumference of the circular contact portion 16 and guided from there under the lower circuit board 8.

The pins 54 project beyond the contact surface 28 at a height that depends on two factors: on the one hand, the pins serve to hold the pre-assembled layer structure. Due to the force of the spring projections 56, the layer structure for good heat transfer to the heating plate 2 is pressed against the inside of the heating plate 2 after assembly. This means that before the finished assembly, i. before the attachment of the heating plate 2 to the housing 4 of the layer structure, the contact surface 28 surmounted. The distributed around the circumference of the opening 14 pins 54 ensure that even in this raised position, the upper circuit board 12 within the peripheral surface of the opening 14 remains.

In addition, the heating plate 2 has corresponding to the pin 54 recessed pin recesses 58, which are engaged behind after the laying of the heating plate 2 on the contact surface 28 of the pin 54. For this purpose, the pins 54 may have the pin recesses 58 engaging behind latching projections. In the embodiment shown, the pins 54 are formed by hot stamping with a thickening 60 after mounting the heating plate 2, which projects beyond the pin recess 58. The reed base 64 lies within the board chambers 18 and 20, respectively; the contact tongue 66 is electrically connected to the plug sleeve 30.

For assembly, the contact tongue 66 is first bent at the transition to the contact tongue base 64 by 90 ° from the plane of the sheet material out. A bent edge 68 formed in this way is dimensioned such that, when the printed circuit board 8, 12 is inserted into the opening 14, it lies in an extension of the slot-shaped contact tongue receptacle 48. During assembly, ie when inserting the layer structure in the opening 14, the contact tongues 66 are accordingly passed through the Reeds 48 recordings. Thereafter, the length 40 of the protruding longitudinal portion of the contact tongues 66 is deflected by a slider 90 ° in the direction of the respective connector receptacle 22 and 24, so that the front end of the contact tongue 66 is pivoted through the Kontaktzungeneinführöffnung 52 into the connector receptacle 20, 24 , This forming step is usually carried out after the heating plate 2 is fixed to the housing 4 and thus the layer structure is set in terms of height due to the bias of the spring projections 56 in the opening 14. In this case, the contact tongue 66 between the contact tongue receptacle 48 and the stop 44 can be applied substantially against the bottom 40, without any fear that the desired good heat transfer by area concerns of upper circuit board 12 and bottom of the heating plate 2 is lost. After bending over the contact tongue 66, this now extends substantially parallel to the top or bottom 42 of the housing 4, is substantially fixed in height by the bottom 40 and fixed in the width direction within certain limits due to the leadership within the reeds 48 receiving record and so secured in that the plug sleeve 20 can be pushed onto the contact tongue 66 and thus electrically contacted without the contact tongue 66 being able to avoid the frictional forces acting in this case.

LIST OF REFERENCE NUMBERS

2

heating plate

4

casing

6

receiving portion

8th

Lower circuit board

10

PTC resistive element

12

Upper circuit board

14

opening

16

contact section

18

Board chamber

20

Board chamber

22

plug receptacle

24

plug receptacle

26

cover

28

contact surface

30

plug sleeve

32

top

33

bottom

34

catch tongue

36

latching opening

40

ground

42

bottom

43

mooring facilities

44

attack

46

recess

48

Contact tongue receiving

50

web

52

Kontaktzungeneinführöffnung

54

spigot

56

key projection

58

pin recess

60

thickening

62

connecting section

64

Contact tongue base

66

contact tongue

68

fold

Claims (9)

1. PTC heating element with at least one PTC resistance element (10) that is arranged between two electrically conductive plates (8, 12) in a housing opening (14) of a housing (4) and that lies with initial tension against a heat-emitting element (2) with at least one of the electrically conductive plates (12) as an intermediate layer, wherein said heat-emitting element (2) is held at the housing (4), characterised in that attachment tabs (54) arranged on the edge of the housing opening (14) protrude beyond the housing opening (14) and in that the heat-emitting element (2) has tab cuts (58), with the tabs (54) engaging behind them.
2. PTC heating element according to Claim 1, characterised in that the tabs (54) project beyond an upper contact surface (28) for the heat-emitting element (2) at a height that is dimensioned in such a way that the electrically conductive plate (12) that is raised above the contact surface (28) by the initial tension before the placement of the heat-emitting element (2) on to the contact surface (28) does not extend higher than the upper end of the tabs (54).
3. PTC heating element according to Claim 1 or 2, characterised in that the tabs (54) have snap-in pins (34) on the ends that engage with the assigned tab cut (58).
4. PTC heating element according to Claim 1 or 2, characterised in that the free end of the tabs (54) has a thickening (60) on the end that engages behind the tab cut (58), wherein this thickening (60) is formed by means of surface-fusing the tab (54).
5. PTC heating element according to one of the preceding claims, characterised in that the electrically conductive plate (8) lying opposite the heat-emitting element (2) has at least one spring element (56) formed as a single piece on it by means of stamping processing and bending, and that this spring element (56) is supported on the housing (4).
6. PTC heating element according to one of the preceding claims, characterised in that the housing opening (14) is closed on the underside (42) lying opposite the heat-emitting element (2).
7. PTC heating element according to one of the preceding claims, characterised in that the housing (4) forms two plug holders (22, 24), each of which has a locking opening (36) for
   engaging with a snap-in pin (34) formed from a plug socket (30) and in that a contact stud (66) formed by stamping processing and bending of the electrically conductive plate is arranged in the plug holder (22, 24).
8. PTC heating element according to Claim 7, characterised in that the contact stud (66) is guided out of the housing (4) through a contact stud holder (48) cut on the underside outside the housing opening (14) in a direction essentially at right angles to the plane of the electrically conductive plate (8, 12) and is introduced into the plug holder (22, 24) by means of being deviated into the plug holder (22, 24) in a direction running essentially parallel to the plane of the electrically conductive plate (8, 12).
9. PTC heating element according to Claim 8, characterised in that the housing (4) has an opening (46, 52) in extension of the contact stud holder (48), which opening (46, 52) projects into the interior of the housing (4), wherein the contact stud (66) lies exposed towards the underside (42) of the housing (4) in this opening (46, 52).

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