Heat generating element and electric heating device containing such a

Abstract

A heat-generating element for an electric heating device in a motor vehicle, comprising a heating element housing (21) comprising a housing element (22) made of a ceramic and a housing counter-element (24) made of a ceramic, wherein the two housing elements (22, 24) bear against one another in a sealing manner and enclose, between them, a PTC element (40) and conductor tracks (32, 46) which bear electrically conductively against the PTC element (40) and are assigned different polarities for energizing the PTC element (40), wherein the heating element housing (21) carries contact tongues (34) which are electrically conductively connected to the assigned conductor tracks (32, 46), characterized in that at least one of the conductor tracks (32, 46) is formed by an electrically conductive element (30) provided with perforations, which has discrete support points in the vertical direction of the conductor track (32, 46),which bear against the PTC element (40) and one of the housing element (22) and the housing counter element (24).

Description

[0001] The present invention relates to a heat generating element and an electric heating device.

[0002] The present invention relates in particular to a heat-generating element for an electric heating device which is used in a motor vehicle and which must therefore meet different requirements.

[0003] A heat-generating element with the preamble features of claim 1 is known from DE 10 2017 209 990 A1.

[0004] In this prior art, the heating element housing consists of two housing elements that are sealed together. A PTC element is arranged within the heating element housing. The heating element housing also includes conductor tracks assigned to different polarities, which are usually located on opposite sides of the PTC element. These conductor tracks are electrically connected to contact tabs that extend beyond one end of the heating element housing and serve to electrically connect the conductor tracks, and thus the heat-generating element, to a power source.

[0005] Due to the self-regulating properties of PTC elements, a heat-generating element containing such a PTC element should meet certain requirements. For example, the heat should be dissipated from both main side surfaces of the PTC element. The main side surfaces of the PTC element are the largest surfaces of the PTC element. They are usually parallel to each other and connected by edge surfaces, which either connect the main side surfaces as a circumferential surface, as is the case with round or oval PTC elements, or by end surfaces with a straight extension, as is the case with cuboid PTC elements.

[0006] Furthermore, there should be the best possible heat conduction path between the outer surface that emits the heat from the heat-generating element and the PTC element.

[0007] Particularly in high-voltage applications in an electrically powered motor vehicle, it is also necessary to electrically insulate the electrically conductive components of the heat-generating element inside the housing element from the outer surface.

[0008] The corresponding heating cell is usually formed by at least one PTC element and the conductor tracks that can be energized with different polarities and, if necessary, connections to the conductor tracks of the contact tongues that project beyond the outside of the heating element housing.

[0009] EP 1 916 873 A1 discloses a heat-generating element in which the conductor tracks in the form of contact plates are covered on the outside with an insulating layer formed by a ceramic plate. The ceramic plate is sealed into the heating element housing by overmolding with a plastic frame. Thus, the heat-generating element designed in this way can be inserted directly into the flow of the fluid to be heated. It is particularly suitable as a heating element in a water heater.

[0010] EP 1 768 457 A1 and EP 2 873 296 A2 disclose solutions in which the electrical insulation is glued in the form of a multi-layer insulation onto a contact plate forming the conductor track.

[0011] The aforementioned designs do offer the advantage that the contact plate, as a conductor track, is joined together with the insulation to form a single unit, and only this unit needs to be handled and installed in a positioning frame. However, this results in a multi-layer structure from the PTC element to the outer surface that dissipates the heat. Each individual layer must be penetrated by the heat to be dissipated to the outside. At the phase boundaries, impaired heat transfer can occur, which reduces the efficiency of the PTC element. Due to its self-regulating properties, the PTC element can no longer absorb power current if there is no or insufficient heat dissipation. The efficiency of the PTC element is then reduced.

[0012] The present invention is based on the problem of providing a PTC element with improved efficiency.

[0013] To solve this problem, the present invention provides a heat-generating element having the features of claim 1.

[0014] The heat-generating element according to the invention is a heat-generating element for an electric heating device in a motor vehicle. The heat-generating element can then be arranged in a circulation chamber through which the medium to be heated flows. The heat can be extracted from the heat-generating element directly via the outer surface of the heating element housing, which lies as an open surface in the fluid flow. In such a configuration, for example, the heat-generating element is exposed as a type of heating fin in a circulation chamber of an electric heating device, which is only open via hose connection pieces for the fluid to be heated. The connection pieces allow pipes or hoses to be connected to the circulation chamber.Alternatively, the heat-emitting outer surface of the heat-generating element can also be in contact with a radiator element, whose heating fins typically extend essentially at right angles to the heat-emitting outer surface of the heat-generating element and preferably lie directly against it. Thus, the heat generated by the PTC element is predominantly dissipated by conduction into the heating fins. In the former case of a fluid heater with a connecting piece, heat dissipation occurs solely by convection on the outer surfaces of the heating element housing.

[0015] The heating element housing according to the invention comprises a housing element and a housing counter-element. Typically, the heating element housing is formed solely from these two housing elements. A sealing means is typically provided between the two housing elements, sealingly pressing the two housing elements against each other and / or connecting them to each other. The sealing means can be a weld seam, a solder strip, or an adhesive strip. The sealing means is preferably a liquid adhesive introduced into a groove. This adhesive cures, preferably cross-links under the influence of heat, but is then permanently elastic. Silicone, for example, is a suitable sealing means.

[0016] The sealing groove is typically recessed in one of the housing elements, with another of the housing elements having a sealing ridge that engages the sealing groove and dips into the sealing compound filled into the sealing groove. This creates a reliable seal for the interior of the heating element housing.

[0017] Preferably, the housing element and the housing counter-element are made of identical material. This eliminates any relative offset upon heating due to the operation of the heat-generating element and different thermal expansion coefficients between the housing element and the housing counter-element. The two housing elements are preferably made of a ceramic, for example, aluminum oxide. They are typically manufactured to their final contours by sintering.

[0018] The sealing groove is typically designed to extend circumferentially around the PTC element, creating a complete seal for the PTC element. Of course, the sealing ridge is also preferably designed to extend circumferentially and, with uninterrupted circumferential sealing, protrudes into the sealing groove and is immersed in the sealing agent.

[0019] For ease of assembly, it is preferable to design one of the housing element and the housing counter element in a shell-like manner. During assembly of the heat-generating element, the components of the heating cell are first inserted and joined into this housing element, before the other housing element, which is usually designed as a cover element, is placed onto the other housing element to complete the heat-generating element.

[0020] In the heat-generating element according to the invention, at least one of the conductor tracks, usually both conductor tracks, is formed by an electrically conductive element provided with perforations. This electrically conductive element provided with perforations usually has contact points over its entire base area, which contact the PTC element or the housing element. The support points are usually provided offset in a projection surface on a main side surface of the PTC element. In the projection direction, at a specific point, at most, a rather point-like contact occurs on a surface of the PTC element or a surface of the housing element. The corresponding discrete support points improve the introduction of the power current to the surface of the PTC element, whereby this surface is usually the main side surface of the PTC element.

[0021] The electrically conductive element with perforations can be a knitted fabric, a braid, or a woven fabric, each of which consists of or at least comprises electrically conductive threads or fibers. With a view to extending the current conduction path in the vertical direction of the PTC element, electrically non-conductive threads can also be incorporated in addition to such electrically conductive threads or fibers, for example in a braid or woven fabric. These threads can be made of polyamide or silicone, for example. The material forming the electrically conductive threads or fibers can also be a plastic that is electrically conductive. Alternatively, the electrically conductive element with perforations can be expanded metal. Expanded metal also has singular contact points on the outer surface of the expanded metal sheet in the vertical direction, which can lie directly against the PTC element or the housing element.

[0022] The vertical direction is understood to be the direction perpendicular to the planar extension of the conductor tracks. The support points therefore protrude toward the PTC element or the housing element from the plane that essentially contains or defines the conductor tracks. The openings are usually continuous in the vertical direction in the conductor track. A fabric is therefore a fabric that is transparent in the projection direction and has a relatively wide mesh, so that the support points are spaced apart at a certain distance. The spacing should be between 3 and 15 mm, preferably 5 and 10 mm.

[0023] To ensure good thermal conductivity between the main side surface of the PTC element and the outer surface of the heating element housing, which dissipates heat to the outside, any gaps within the perforated, electrically conductive element are filled with a thermally conductive compound, such as an adhesive compound. The adhesive compound can be filled with highly thermally conductive particles to increase thermal conductivity. In any case, it should be avoided that any air remains between the inner surface of the heating element housing and the main side surface of the PTC element. This ensures that the discrete support points of the perforated, electrically conductive element are also circumferentially surrounded by the adhesive compound, essentially at the same level as the surface of the heating element housing or PTC element.Furthermore, to ensure heat dissipation, the adhesive mass should also surround the end faces of the PTC element at the edge surfaces of the heating element housing and fill a gap between these end faces and the opposite inner surfaces of the heating element housing. This allows heat to be dissipated from the heating element housing in all directions, not just perpendicular to the main side surface of the PTC element.

[0024] According to a preferred embodiment of the present invention, the conductor track is extended at the edges beyond the main side surfaces of the PTC element. To compensate for manufacturing tolerances, the conductor track preferably extends beyond the entire contour of the PTC element.

[0025] The conductor track and the contact tongue associated with the conductor track are preferably formed by a single, perforated, electrically conductive element. Thus, to form the contact tongue and the associated conductor track, only this single perforated electrically conductive element needs to be cut to size to provide a contact surface for the PTC element and a contact on the outside of the heating element housing. The contact tongue is formed by a flat piece that forms the male contact element of a plug connection.

[0026] If the heating element housing is made of ceramic, it usually has through-openings on a frame member, via which the heat-generating element is sealingly inserted into a partition wall which is formed as part of a heater housing which defines the circulation chamber and on the side of the partition wall opposite the circulation chamber a connection chamber is formed in which the contact tongues of the heat-generating element are electrically connected.

[0027] To allow the contact reeds to pass through, one of the housing elements is preferably provided with a flange, which usually forms the two through-holes for the contact reeds. A flange is primarily understood to be a thickened portion of the frame beam in the vertical direction of the PTC element. This flange is usually formed by the shell-shaped housing element.

[0028] Further details and advantages of the present invention will become apparent from the following description of an embodiment in conjunction with the drawings, in which: Fig. 1 a perspective exploded view of an embodiment of the heat-generating element according to the invention Fig. 2 a sectional view of the Fig. 1 shown embodiment and Fig. 3 is a perspective, partially sectioned view of an electric heating device incorporating several embodiments of the heat-generating element.

[0029] The Fig. 1 shows all components of the embodiment of a heat-generating element, which are prepared with a fixed geometry and design for producing the heat-generating element.

[0030] The Fig. The heat-generating element, designated by reference numeral 20 in FIG. 2, has a heating element housing 21, which is formed by a shell-shaped housing element 22 and a flat housing counter-element 24 designed in the manner of a cover. The shell-shaped housing element 22 has a base 26 (cf. Fig. 1), which is flat and, with its outer surface 28, defines a heat-emitting outer surface of the heating element housing, which runs plane-parallel to the inside of the base 26. A metal mesh, designated by reference numeral 30, is placed on this base 26 as an exemplary embodiment of an electrically conductive element provided with perforations. This metal mesh 30 forms, as a unitary component, a conductor track 32 and a flat, planar contact tongue 34 associated with the conductor track 32. The conductor track 32 rests on the base 26 of the housing element 22. The conductor track 32 extends through a through-opening 36, which is recessed in a flange 38 of the housing element 22.

[0031] Reference numeral 40 designates a cuboid-shaped PTC element whose main side surfaces 42, 44 are in contact with associated metal meshes 30. A conductor track, designated by reference numeral 46, is identical to the previously described conductor track 32, but is applied inverted to the PTC element 40, so that its contact tongue 34 extends through the flange 38 in the longitudinal direction of the flange 38, offset from the other contact tongue 34. The flange 38 also forms a through-opening 48 for this purpose. The corresponding arrangement of the contact tongues 34 increases the clearance and creepage distance between the two polarities assigned to the conductor tracks 32, 46 inside and outside the heating element housing 22, 24.

[0032] The shell-shaped housing element 22 has a circumferential sealing groove designated by reference numeral 50. As the detail of the sectional view according to Fig. As illustrated in Figure 2, a sealing ridge 52 engages in this sealing groove 50. The sealing ridge 52 is immersed in a permanently elastic adhesive 54, so that a circumferential seal is created around the interior of the heating element housing 42, 24, which accommodates the PTC element 40 and the conductor track 32.

[0033] The two housing elements 22, 24 are made of aluminum oxide. They are sintered parts manufactured to their final contours.

[0034] As can be seen, the two housing elements 22, 24 are shaped such that the outer surfaces 28, 56 formed by these housing elements 22, 24 have a projection surface to the main side surface 44 or 42 of the PTC element 40, which is plane-parallel to these main side surfaces 42, 44. Thus, heat dissipation from the heating element housing 22, 24 can occur directly adjacent to the main side surface 42 or 44 of the PTC element. The heat dissipated by the main side surfaces 42, 44 of the PTC element 40 therefore only penetrates thin, flat layers up to the outer surface 56 in a direction perpendicular to the main side surfaces 42, 44.

[0035] The contact segment 58 of the housing element 24, which is adapted to the contour of the flange 38, lies beyond a projection surface onto the PTC element 40. In other words, when viewed from above onto the outer surface 56 or 58, the PTC element 40 lies laterally next to the flange or the flange 38 or the contact segment 58.

[0036] To produce the illustrated embodiment, the two housing elements 22, 24 are first manufactured as sintered parts. First, the shell-shaped housing element 22 is provided with the metal mesh 30. Its contact tongue 34 is passed through the through-opening 36. Before the metal mesh 30 is applied, a predetermined amount of an adhesive material is typically first applied flatly to the base 36 of the housing element 22. After the metal mesh 30 is inserted into the housing element 22, the PTC element 40 is inserted. The PTC element is pressed against the metal mesh 30 so that the discrete support points formed by the metal mesh 30 are applied in an electrically conductive manner against the surface of the PTC element 40. In a corresponding manner, the support points are applied directly against the base 26 in a thermally conductive manner. This displaces the adhesive.It fills a gap between the peripheral surface of the PTC element 30 and the edge surrounding the base 24 and formed by the housing element 22.

[0037] Adhesive is then applied to the exposed upper side of the PTC element 40. Here, too, the adhesive is applied as evenly as possible. The contact tongue 34 of the further metal mesh 30 is then pushed into the provided through-opening 48. The further conductor track 46 is also pressed against the main side surface 44 of the PTC element in order to make direct electrical contact with the PTC element, thereby displacing the adhesive. When applying the adhesive to the PTC element 40, it can also be introduced into the sealing groove 50. The adhesive used inside the heating element housing 22, 24 can be identical to the adhesive that connects the two housing elements 22, 24 to one another and seals them against one another. By introducing the adhesive between the metal mesh 30 and the two housing elements 22, 24, a firm connection is created between the housing elements 22, 24 anda holding function between them by introducing the adhesive into the sealing groove 50.

[0038] Finally, the housing element 24 is placed on top, with the sealing ridge 52 being inserted into the sealing groove 50. This results in a circumferential seal for the PTC element 40.

[0039] Thereafter, the adhesive is usually pressed from the outside against the outer surface 28 or 56 of the housing elements 22, 24 to ensure that the conductor tracks 32, 46 directly contact the associated inner surfaces of the housing elements 22, 24 and the main side surfaces 42, 44 of the PTC element 40 when the adhesive hardens.

[0040] Curing occurs under this external pressure at an elevated temperature, allowing the adhesive to crosslink more quickly. To achieve this, the heat-generating element can be electrified and thus heated.

[0041] The inclusion of the with reference to the Fig. 1 and Fig. 2 discussed embodiment of the heat-generating element in an electric heating device of a motor vehicle is shown in Fig. 3 illustrates this.

[0042] The electric heating device has a heater housing 1 made of plastic, designated by reference numeral 1. The housing 1 forms inlet and outlet nozzles 2, which each define inlet and outlet openings 3, respectively, leading to a circulation chamber 4, which is fluid-tightly separated from a connection chamber designated by reference numeral 6 by a connection chamber 5 and forms receptacles 7, which are designed as female plug elements of a fluid-tight plug connection, which is created by inserting a sealing collar 8 into the receptacle 7. The sealing collar 8 is formed circumferentially around the flange 38 and the contact segment 58. The sealing collar 8 is usually made of a soft-elastic plastic, in particular silicone. The sealing collar 8 can be formed by overmolding the heat-generating element 20.The flange 38 and the contact segment 58 can have adapted designs that lead to improved sealing and / or holding of the sealing collar 8 on the heat-generating element 20.

[0043] In the Fig.3, the contact tongues 34 protrude with their free ends into the connection chamber 6 and can be electrically connected there, as is basically described, for example, in EP 3 334 244 A1. In the exemplary embodiment shown here, the cover 5 forms the partition wall which seals the circulation chamber 4 in a fluid-tight manner with respect to the connection chamber 6 and forms the receptacles 7. In the exemplary embodiment shown, the cover 5 is inserted into the heater housing as a separate plastic component. Other designs are also conceivable, in which, for example, a base of the heater housing 1 is designed as a separate cover element and the cover 5 is designed in one piece together with the walls of the heater housing 1 which define the connection chamber 6 or the circulation chamber 4 and extend essentially at right angles to the base. List of reference symbols 1 heater housing 2 inlet and outlet ports 3 Inlet or outlet opening 4 Circulation chamber 5 Cover plate 6 Connection chamber 7 Recording 8 sealing collars 20 heat-generating element 21 Heating element housing 22 shell-shaped housing elements 24 Housing counter element 26 Floor 28 exterior area 30 metal mesh 32 tracks, first polarity 34 contact tongues 36 Feed-through opening 38 flange 40 PTC element 42 main side area 44 Main side area 46 Conductor track, second polarity 48 through opening 50 sealing groove 52 Sealing bar 54 glue 56 exterior area 58 Investment segment

Claims

[1] Heat-generating element for an electric heating device in a motor vehicle, comprising a heating element housing (21) comprising a housing element (22) made of a ceramic and a housing counter-element (24) made of a ceramic, wherein the two housing elements (22, 24) bear against one another in a sealing manner and enclose a PTC element (40) and conductor tracks (32, 46) between them, which electrically conductively bear against the PTC element (40) and are assigned different polarities for energizing the PTC element (40), wherein the heating element housing (21) carries contact tongues (34) electrically conductively connected to the assigned conductor tracks (32, 46), characterized bythat at least one of the conductor tracks (32, 46) is formed by an electrically conductive element (30) provided with perforations, which has discrete support points in the vertical direction of the conductor track (32, 46) which bear against the PTC element (40) and one of the housing element (22) and the housing counter element (24). [2] Heat-generating element according to claim 1, characterized by that the electrically conductive element is a braid, a knitted fabric, or a woven fabric (30), each comprising or consisting of electrically conductive threads or fibers, or an expanded metal. [3] Heat-generating element according to claim 1 or 2, characterized by that the openings are filled with an adhesive mass. [4] Heat-generating element according to one of the preceding claims, characterized by that at least one of the housing elements (22, 24) is shell-shaped. [5] Heat-generating element according to one of the preceding claims, characterized bythat one of the housing element (22) and the housing counter-element (24) has a circumferential sealing groove (50) and that the other of the housing element (22) and the housing counter-element (24) has a sealing web (52) engaging in the sealing groove (50), wherein the sealing web (52) is immersed in a sealing agent (54) filled into the sealing groove (50). [6] Heat-generating element according to one of the preceding claims, characterized by that the conductor track (32, 46) and the associated contact tongue (34) are formed by a uniform, electrically conductive element provided with perforations. [7] Heat-generating element according to one of the preceding claims, characterized by that one of the housing elements (22) forms a flange (38) through which the contact tongues (34) extend. [8] Heat-generating element according to one of the preceding claims, characterized bythat the projection surface of one of the main side surfaces (42, 44) of the PTC element (40) onto the outer surfaces (28, 56) of the housing element (20) runs plane-parallel to the main side surface (42, 44) of the PTC element (40). [9] Electric heating device with at least one heater housing (1) with a heat-generating element (20) arranged in a circulation chamber (4), with a heating element housing (21) which joins at least one PTC element (40) and the PTC element (40) and contact tongues (34) as a structural unit, and is projected over by the contact tongues (34) electrically connected to the PTC element (40), and with a partition wall (5) which separates the circulation chamber (4) from a connection chamber (6) of the heater housing (1), in which the contact tongues (16) of the PTC heating element (2) projecting through the partition wall (5) are exposed and electrically connected, characterized by that the heat-generating element is designed according to one of claims 1 to 8. [10] Electric heating device according to claim 9, characterized by that the heat-generating element (20) is sealingly inserted into the partition wall (5).

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