PTC heating element and electric heating device with such a PTC heating element

Abstract

A PTC heating element (2) with at least one PTC element and two conductor tracks assigned to different polarities, which are electrically connected to the PTC element and provided with connection elements (4) for the electrical connection of the PTC element, characterized by an electromagnetic shield (6) formed from a fluid-permeable metal structure (8), which surrounds the PTC element and the conductor tracks and is provided at least partially to a heat-emitting surface that is thermally connected to the PTC element in such a way that a flow gap is formed between the heat-emitting surface and the shield (6), which is formed by a distance between the shield (6) and the heat-emitting surface of between 1.0 and 4.0 mm to generate a turbulence of a fluid to be heated on the heat-emitting surface, resulting in improved heat transfer on the heat-emitting surface.

Description

[0001] The present invention relates to a PTC heating element with at least one PTC element and two conductor tracks assigned to different polarities, which are electrically connected to the PTC element and are provided with connection elements for the electrical connection of the PTC element.

[0002] A PTC heating element according to the preamble features of claim 1 is known from DE 10 2016 224 296 A1 or DE 10 2012 013 770 A1.

[0003] The previously mentioned PTC heating element comprises two sheet-metal shell elements bent and connected to each other, which surround the PTC heating element on the outside. These two shell elements provide shielding against EMC radiation. This prevents the electromagnetic radiation emitted by the PTC heating element from escaping to the outside.

[0004] The previously discussed state of development still leaves room for improvement. The present invention aims to provide a PTC heating element with improved heat dissipation.

[0005] To solve this problem, the present invention proposes a PTC heating element with the features of claim 1. This PTC heating element has a fluid-permeable, preferably water-permeable, metal structure that defines an electromagnetic shield around the PTC element and the conductor tracks. The fluid-permeable metal structure allows the fluid to be heated to pass directly to the heat-emitting surface of the PTC heating element. Thus, in contrast to the prior art according to DE 10 2012 013 770 A1, the heat generated by the PTC element does not first have to pass through a closed shielding shell to be transferred to the medium. Preferably, the metal structure surrounds the PTC heating element and the conductor tracks as a cage. The metal structure is at ground potential, whereas the two conductor tracks are at the potential of the power current.

[0006] US 2019 / 0110339A1 discloses a sauna heater with a resistance heating element and adjacent conductive traces of differing polarities. This heating element is mounted on a housing that holds the heating element at a distance from frame elements on both sides, which support an outwardly convexly curved shield made of wire mesh.

[0007] The PTC heating element according to the invention can be used for heating with air or a liquid heat transfer medium, for example, water. The PTC element can be installed in an air heater so that a layer of corrugated fins, which transfers heat to the air, can be placed directly against the metal structure. Any electrical insulation between the electrically conductive components of the PTC heating element, namely the PTC element and the two conductor tracks, can be provided within the shielding. This insulation prevents the medium to be heated from coming into direct contact with the electrically conductive components of the PTC heating element that carry the power current.

[0008] The PTC heating element according to the invention is typically used in a water heater, which, as an embodiment of an electric heating device, has a circulation chamber. This chamber is usually connected to a pipe system via inlet and outlet ports and is sealed against a connection chamber, so that the connection chamber for the electrical connection of the at least one PTC heating element does not come into contact with the liquid medium to be heated. Moisture or the heat exchanger fluid cannot reach the connection chamber. For this purpose, a partition is provided between the circulation chamber and the connection chamber. This partition is typically penetrated by the connection elements. The connection elements are usually sealed within the connection chamber and pass through it.As already known from DE 10 2016 224 296 A1, a heating element housing can provide a seal against the partition. The circulation chamber of a specific embodiment of an electric heating device of the present invention designed in this way is fluid-tight except for the inlet and outlet openings, so that the liquid medium to be heated is enclosed in the circulation chamber and can flow through it.

[0009] In such a circulation chamber, the PTC heating elements of the present invention are exposed, similar to heating fins. The fluid-permeable metal structure surrounds the heat-emitting surface of the PTC heating element at a close distance, creating a flow gap between the shield and the heat-emitting surface. This flow gap exhibits improved heat transfer compared to previously known solutions, as the fluid flow is swirled by the metal structure, leading to improved heat transfer at the interface, i.e., the heat-emitting surface, of the heat-generating PTC heating element. According to the invention, the shield is, at least in sections, exposed to the heat-emitting surface, which is thermally connected to the PTC element. The distance is typically between 1.0 and 4.0 millimeters.Such a distance allows the flow in the gap to be adjusted in the best possible way with regard to the desired intensive heat transfer between the heat-emitting surface and the medium to be acquired.

[0010] Various metal structures are suitable for achieving the aforementioned effect of turbulence in the fluid being heated, such as metal mesh, metal woven fabric, or expanded metal sheets. Textile structures containing wholly or partially metallic threads, or even incorporating or being formed by textile threads, are also conceivable. The mesh size between individual metallic elements of the fluid-permeable metal structure is determined by the desired shielding effect. However, the mesh size should not be smaller than 1.0 millimeter. While the individual elements of the metal structure can be placed as close together as desired for the required shielding effect, even tightly woven metal structures are fundamentally fluid-permeable. To ensure effective convective heat dissipation, a minimum mesh size should not be undercut.The minimum distance between adjacent fiber or thread elements or expanded metal structures of the metal frame should not be less than 1.0 millimeter. The optimum for achieving good turbulence to generate turbulent flows at the heat-emitting surface of the PTC element, on the one hand, and good flowability for convective heat dissipation, on the other, is achievable with a mesh size between 1.5 and 2.0 millimeters, preferably between 3 and 10 millimeters. Considering stability and, in particular, processability, as well as the desired mesh size, the wire diameter should be between 0.2 and 0.5 millimeters. Such wire diameters are readily woven and available as standard products. In the wavy area, the wire diameter should be selected to be between 0.4 and 1 millimeter.

[0011] Particularly with a view to facilitating easy connection of the PTC heating elements in an electric heating device, the electrical connection lugs associated with the conductor tracks are preferably provided on the same sides of the PTC heating element. These connection lugs extend parallel to each other, so that both connection lugs can be electrically connected in a plug connector with a single plugging motion. The electrical connection lugs are preferably formed integrally with contact plates that form the two conductor tracks. The conductor tracks, in turn, rest against the PTC element. They can be in electrically conductive contact with a main side surface of the PTC element. They can also be in contact with an end face of the PTC element, as taught in DE 10 2016 224 296 A1. The PTC heating element according to the invention can also have the plastic frame disclosed in that aforementioned publication as a heating element housing.The fluid-permeable metal structure can be connected to this plastic frame. The heating element housing can be made of plastic, but this is not mandatory. The heating element housing can also be made of a ceramic material, for example, two corresponding ceramic shells or one ceramic shell and a ceramic cover, which together form a fluid-tight seal between the PTC element and the two conductor tracks. Such a heating element housing is preferably surrounded externally by a cage made of the fluid-permeable metal structure.

[0012] With a view to facilitating easy and simple connection of the shielding, a preferred embodiment of the present invention proposes providing an electrically conductive shielding connection lug on the side of the PTC heating element that is also overlaid by the electrical connection lugs. The shielding connection lug preferably extends parallel to the electrical connection lugs and overlays the shielding. The shielding connection lug can be formed from the fluid-permeable metal material. If this is formed from expanded metal, stamping and stretching in the area of ​​the connection lug can be omitted, so that the shielding connection lug is formed integrally from the expanded metal as a continuous sheet metal segment. The shielding can then be connected via a plug connector.

[0013] The fluid-permeable metal structure can be connected to the heating element housing, for example, by overmolding the plastic material that forms the housing. Typically, the metal structure is connected to a retaining frame that surrounds it externally. This retaining frame can be attached to the metal structure by injection molding, for example. Other methods of attachment, such as gluing, soldering, or welding, are also possible. This retaining frame is usually placed in an injection mold in which the heating element housing is injection molded. The retaining frame seals the metal structure, which is located inside the heating element housing, from the injection mold. During this overmolding process, the metal structure is usually positioned at a certain distance from the heat-extracting surface of the PTC heating element, so that after demolding the heating element housing, the PTC heating element is produced directly from the mold.

[0014] In the electrical heating device proposed by the subordinate aspect of the present invention, the previously mentioned partition wall is also penetrated by the shielding connection lug, which is electrically connected to the shielding, so that the electrical connection of the shielding also takes place in the connection chamber.

[0015] Preferably, a circuit board can be provided in the connection chamber, which has plug-in element receptacles for the plug-in connection of the terminals on the one hand and the at least one shield terminal on the other. Preferably, the electrical heating device has several PTC heating elements of the aforementioned type. In this case, the circuit board connects the terminals of these multiple PTC heating elements. The circuit board can be a connection board that is not equipped with electrical components, but merely has contact tongue receptacles for the electrical contacting of the various electrical terminals and the shield terminals. Such a circuit board serves only to group several PTC heating elements in order to combine them in a single heating circuit. The corresponding circuit board can, of course, group different heating circuits with varying numbers of PTC elements.In any case, the electrical connection for both the power supply and the shielding is preferably made solely via said circuit board. This significantly reduces the wiring effort within the electrical heating device according to the invention.

[0016] According to a further development of the present invention, several PTC heating elements can also be accommodated in a single shielding cage. This creates a uniform shield for the multiple PTC heating elements. The shielding cage can be designed to largely follow the contours of the individual PTC heating elements, so that, even in this preferred development, the effect of turbulence at the interface can be utilized over a large area to improve heat transfer. The shielding cage can consist of two shell segments, one of which, for example, can form receptacles for the respective PTC heating elements. During assembly, these elements can be inserted into the corresponding receptacles before the other element of the shielding cage is placed onto the PTC heating elements to enclose the shielding cage as completely as possible.

[0017] The electromagnetic shielding surrounding the PTC element and its conductor tracks is typically provided all around the electrically conductive and energized components of the PTC heating element. The underside of the PTC heating element, opposite the connection side with its terminals and optionally the shielding tab, can also be enclosed by the fluid-permeable metal structure. Regarding the details of the shielding, only the desired effect of achieving effective EMC protection is of importance.

[0018] In the case of multiple PTC heating elements as part of an electric heating device, the shield connection lug can be formed by a conductor rail that electrically connects the shields of the multiple PTC heating elements. In this case, each individual shield of the PTC heating element typically does not have a connection lug. Rather, the electrically conductive connection of the shield is made solely via the conductor rail and the shield connection lug, which is usually formed as a single unit by the rail.

[0019] Further details and advantages of the present invention will become apparent from the following description of exemplary embodiments in conjunction with the drawing. The drawing shows: Fig. 1 a perspective side view of an embodiment of a PTC heating element; Fig. 2 essential components of an electric heating device using the PTC heating element according to Fig. 1; Fig. 3 a variant of the embodiment according to Fig. 2; Fig. 4 a perspective, partially cut-away side view of a third embodiment of a PTC heating element; Fig. 5 the detail V according to Fig. 4 in enlarged view and Fig. 6 a sectional view along line VI-VI according to Fig. 4.

[0020] The Fig. Figure 1 shows a side view of a PTC heating element 2 with opposing connection elements 4 in the form of metallic connection tabs, which are formed by cutting away sheet metal elements (not shown in detail) and which act as conductor tracks on opposite sides of the PTC element to supply it with current. For details of such a connection of a PTC element, reference is made, for example, to DE 10 2016 224 296 A1. In contrast to the disclosure therein, the PTC element can also be contacted and energized via a main side surface. It is understood that the PTC element is provided with a vapor-deposited or sputtered metallization opposite the contact surface of the conductor track. The PTC element can be energized with different polarities via the two connection elements 4.

[0021] Reference numeral 6 designates a cage made of a fluid-permeable metal structure 8, which in this case completely surrounds the PTC element and the conductor tracks. The metal structure 8 is formed by a metal grid. Behind the metal structure 8, a heating element housing 12 is visible, which seals the conductor tracks and the PTC element in a fluid-tight manner. The heating element housing 12 can be formed by a plastic housing frame that seals ceramic plates on opposing main side surfaces, the plates of which accommodate the at least one PTC element between them, as is known from DE 10 2016 224 296 A1. The heating element housing can be a plastic housing. It can be made partly of ceramic and partly of plastic. Alternatively, the heating element housing 12 can be formed from two or more ceramic components that are fluid-tightly connected to one another, enclosing the PTC element and the two conductor tracks.

[0022] How Fig. As shown in Figure 1, the cage 6 extends completely around the heating element housing 12 in a top view of the embodiment (view parallel to the longitudinal extent of the connection elements 4). The opposite upper and lower surfaces of the heating element housing 12 are also surrounded by the metal structure 8. On the upper surface, the metal structure 8 is projected by shielding connection lugs 14, which extend parallel to the connection elements 4. All connection elements 4 and 14 project beyond the metal structure 8 on the same upper surface and extend parallel to each other.

[0023] How Fig. 2, this design allows each individual PTC heating element to be plugged into electrically conductive traces on a printed circuit board marked with reference numeral 16. This allows both the conductors of different polarities and the shielding tabs 14 to be easily electrically connected. The in Fig. The sketched circuit board 16 is not populated with electronic components. It only has elastic clamping elements that are connected to conductive traces on the circuit board and are designed to allow the individual connection elements 4, 14 to be inserted. Thus, electrical contact can be easily established by inserting the connection elements 4, 14. The circuit board 16 groups individual PTC heating elements 2 into a heating circuit.

[0024] The circuit board 16 can be provided in a connection chamber of an electrical heating device (not shown in detail). Details of such a design can be found, for example, in DE 10 2016 224 296 A1. In addition to this connection circuit board 16, another populated circuit board can be provided in the connection chamber to individually control the individual heating circuits or PTC heating elements 2.

[0025] The aforementioned connecting chamber is Fig. 2 is indicated by reference numeral 18. Below it is a circulation chamber 20 through which the liquid medium to be heated flows. This flowing medium is assumed to be water. The water flowing through the circulation chamber is swirled by the partially permeable metal structure 8 near the heat-emitting outer surface of the heating element housing 12, so that the heat transferred there can be absorbed and dissipated more effectively by the water. Thus, the electromagnetic shielding in the form of the fluid-permeable metal structure 8 also results in better heat transfer and therefore a higher efficiency of the PTC heating element within the electric heating device.

[0026] An alternative connection scheme for the shielding is shown in Fig. Figure 3 shows that in this embodiment, a conductor rail designated by reference numeral 22 forms U-shaped receptacles 24, each of which individually receives the free ends of the cage 6 from the metal structure 8. The U-shaped receptacles 24 have legs extending parallel to the main side surfaces of the PTC heating element, forming a convexly inwardly pre-bent contact section 26 that rests against the outside of the cage with a certain elastic preload. This ensures reliable electrical contact between the conductor rail 22 and the metal structure 8.

[0027] The conductor rail 22 forms a shielding connection lug marked with reference numeral 28. This shielding connection lug 28 is formed integrally with the sheet metal material of the conductor rail 22 and, in this case, is electrically contacted by being inserted through the circuit board 16. However, such contact can also be omitted if the shielding connection lug is inserted into the connection chamber and, for example, plugged into a female connector there.

[0028] The in the Fig. 4 to Fig. The embodiment shown in Figure 5 has a frame-shaped heating element housing 12, which also forms a sealing collar 30 integrally molded onto it. This collar can be inserted into a heater housing in a sealing manner as described in DE 10 2016 224 296 A3. As can be seen, the plastic material defining the outer surfaces of the heating element housing is injection-molded around a retaining frame 32 during the injection molding of the heating element housing 12. This retaining frame 32 surrounds the edge of the flat metal structure 8. The retaining frame 32 is first connected to the metal structure 8 and placed as an insert in the injection mold. The retaining frame 32 forms the inner circumference of the cavity for the formation of the heating element housing 12.

[0029] The connection elements 4 are formed in this case by elongated contact plates 34, which bear against the end face of the PTC element 2 and are energized. A main side surface of the PTC element 2, marked with reference numeral 36 and capable of dissipating heat, is covered on its outer surface with an insulating layer 38, which is sealed at its edges into the material of the heating element housing 12.

[0030] The sealing collar 30 is penetrated by a contact element 40, which is made of sheet metal by stamping and bending and forms a contact section 42 projecting on both sides towards the metal structure 8, which is electrically connected to the metal structure 8. By connecting the shielding terminals 14 formed by the contact element 40, it is possible to electrically connect the metal structure 8, provided on a main side surface 36, to a shielding pole.

[0031] The in the Fig. 4, Fig. 5 to Fig. The embodiment of the contact element shown in Figure 6 has two identically designed contact sections 42, each of which is connected to the respective metal structure 8 provided there as a flat metal mesh on the opposite main side surfaces 36, and of which only the upper contact section 42 is shown. Reference symbol list 2 PTC heating elements 4 Connection element 6 cage 8 Metal structure 12 heating element housings 14 Shielding connection tab 16 circuit board 18 Connection chamber 20 Circulation chamber 22 conductor rail 24 U-shaped recording 26 Contact section 28 Shielding connection tab 30 sealing collars 32 mounting frames 34 contact plates 36 main page areas 38 Insulation layer 40 contact elements 42 Contact section

Claims

[1] PTC heating element (2) with at least one PTC element and two conductor tracks assigned to different polarities, which are electrically connected to the PTC element and are provided with connection elements (4) for the electrical connection of the PTC element, characterized by an electromagnetic shield (6) formed from a fluid-permeable metal structure (8), which surrounds the PTC element and the conductor tracks and is provided, at least in sections, to a heat-emitting surface that is thermally connected to the PTC element in such a way that a flow gap is formed between the heat-emitting surface and the shield (6), which is formed by a distance between the shield (6) and the heat-emitting surface of between 1.0 and 4.0 mm in order to generate a turbulence of a fluid to be heated on the heat-emitting surface, resulting in improved heat transfer on the heat-emitting surface. [2] PTC heating element according to claim 1, characterized by, that the PTC element and the conductor tracks are fluid-tightly enclosed in a heating element housing (12) [3] PTC heating element according to claim 1 or 2, characterized by , that the electrical connection tabs (4) assigned to the conductor tracks extend beyond the shielding (6) on the same sides in a parallel orientation to each other. [4] PTC heating element according to one of the preceding claims, characterized by at least one shield connection tab (14) electrically connected to the shield (6), which extends parallel to the connection tabs (4) and projects above the shield (6). [5] PTC heating element according to any of the preceding claims, characterized by , that the heat-emitting surface is an outer surface of a heating element housing (12) which fluid-tightly accommodates the PTC element and the conductor tracks. [6] PTC heating element according to one of the preceding claims, characterized by, that the electromagnetic shielding (6) is accommodated in a retaining frame (32) which was initially manufactured separately and connected to the electromagnetic shielding (6) and is integrated into the heating element housing (12). [7] PTC heating element according to claim 6, characterized by , that the retaining frame (32) is connected to the heating element housing (12) by means of injection molding. [8] Electric heating device with a heater housing forming a circulation chamber (20) and a connection chamber (18) which is fluid-tight sealed against the circulation chamber by means of a partition, and at least one PTC heating element (2) with at least one PTC element and conductor tracks assigned to two different polarities, which are electrically connected to the PTC element and provided with connection elements (4) which extend through the partition, characterized by, that the PTC element and the conductor tracks are surrounded by an electromagnetic shield (6) formed from a fluid-permeable metal structure (8) and that the partition is penetrated by a shield connection tab (14; 28) which is electrically connected to the shield. [9] Electric heating device according to claim 8 with multiple PTC heating elements according to claim 4, characterized by , that the shielding connection tab (14) is formed by a conductor rail (22) which electrically connects the shielding of the several heating elements (2) to each other. [10] Electric heating device according to claim 9, characterized by , that the conductor rail (22) forms a U-shaped recess (24) in which the shielding (6) is electrically conductively received. [11] Electric heating device according to any one of claims 8 to 10, characterized by, in the connection chamber (18) a circuit board (16) is provided which electrically connects the connection lugs (4) of several PTC heating elements (2) to each other. [12] Electric heating device according to any one of claims 8 to 11, characterized by , in the connection chamber (18) a circuit board (16) is provided which electrically connects the shielding connection tab (14) of several PTC heating elements (2) to each other. [13] Electric heating device according to any one of claims 8 to 11, characterized by that several PTC heating elements are enclosed in a shielding cage formed from the fluid-permeable metal structure.

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