Electric heating device and method for its manufacture

Abstract

Electric heating device including: a housing (100) with a partition (112) that separates a connection chamber (114) from a heating chamber (106) for heat dissipation and from which at least one receiving pocket (116) projects into the heating chamber (106) as a heating fin (110), in which a wedge-shaped pressure element (2) is received, which connects a PTC heating element (20) with at least one PTC element (22) and conductive traces (24) for supplying current to the PTC element (22) with different polarity, which are electrically connected in the connection chamber (114), at least partially surrounds and holds the PTC element (22) in the receiving pocket (116), characterized by the fact that, the PTC heating element (22) is positively engaged in the pressure element (2).

Description

[0001] The present invention relates to an electric heating device with a housing comprising a partition wall that divides a connection chamber from a heating chamber for heat emission. At least one receiving pocket, projecting into the heating chamber as a heating fin, extends from the partition wall. A PTC heating element is provided in this pocket. Furthermore, a pressure element is received in the pocket, which holds the PTC element between opposing inner surfaces of the receiving pocket.

[0002] The PTC heating element has at least one PTC element and conductive traces attached to it. These traces are electrically connected to the PTC element. This connection can be a form-fit, force-fit, and / or material-fit connection.

[0003] The aforementioned general features of the electric heating device apply to the prior art according to EP 1 872 986 A1. They also apply to the implementation of the invention.

[0004] The earlier proposals EP 2 637 474 A1 and EP 2 337 425 A1, both originating from the applicant, each disclose PTC heating elements that are placed in a previously mentioned receiving pocket.

[0005] EP 2 337 425 A1 discloses a solution in which a conductor track adjacent to a main side surface of the PTC element is provided as a sheet metal piece with contact projections bent out of the plane of the sheet metal piece. The contact projections serve solely to improve the electrical contact of the PTC element.

[0006] In the previously described, known solutions, the receiving pocket tapers towards its lower, closed end. Accordingly, the insertion opening, which opens towards the connection chamber, is wider than the lower, closed end of the receiving pocket. The PTC elements and the contact plates on both sides of them are typically clamped in place with a wedge-shaped pressure element, with at least one insulating layer between the conductor tracks and opposing inner surfaces of the receiving pocket. This wedge element ensures that the layers of the layer structure are clamped against each other. These layers consist of at least the PTC elements and the conductor tracks extending perpendicular to the direction of force exerted by the wedge element (usually contact plates), as well as at least one insulating layer.

[0007] Despite the downwardly tapered cross-sectional shape of the receiving pocket, necessitated by manufacturing processes, the wedge element is designed to facilitate efficient heat transfer, preferably between the two opposing heat dissipation surfaces of the PTC element and their respective corresponding inner surfaces of the receiving pocket, with the pressure element interposed. The pressure generated there also presses the opposing heat dissipation surface of the PTC element directly against the opposite inner surface of the receiving pocket, either directly or via an insulating layer.

[0008] CN 109028554 A discloses an electric heating device with the features of claim 1. In this prior art, the PTC heating element is received in a pocket-shaped pressure element, which has opposing side sections connected to each other via a bottom section. The pocket-shaped pressure element accordingly forms a receptacle for the PTC heating element. The pocket-shaped pressure element has a wedge-shaped cross-section to enable uniform heat-conducting contact of the pressure element with the inner surfaces of a receiving pocket that tapers towards its lower end, the end facing away from the connection chamber.

[0009] EP 3 101 365 A1 and US 4 626 666 A each disclose electrical heating devices with a wedge for clamping the PTC element.

[0010] The previously presented prior art solutions all ensure good heat dissipation. However, the problem is that the mounting pocket does not always correspond to the intended shape due to manufacturing tolerances. This is because the PTC elements are subject to considerable dimensional variations due to the manufacturing process. Furthermore, it is not always guaranteed that the heat dissipation surfaces of the PTC element are perfectly straight and flat.

[0011] Pressing in a wedge as a pressure element can lead to stress peaks that can cause the PTC element or a ceramic insulating layer within the mounting pocket to break. Depending on tolerances, the wedge element used as a pressure element in the prior art may not be thick enough in the specific application, so that it essentially sits ineffectively at the lower end of the mounting pocket. Conversely, if the clearance remaining before inserting the wedge element is too small, there is insufficient coverage of the heat dissipation surface of the PTC element in the vertical direction of the mounting pocket, i.e., between the lower end and the insertion opening. As a result, the PTC element overheats and prevents further power current absorption. Consequently, the efficiency of the PTC element is poor.

[0012] It is also possible that layers of the PTC heating element and / or the pressure element 1, or the PTC heating element as a whole, may be pushed out of the receiving tab or migrate out due to vibration.

[0013] The present invention aims to at least partially solve the aforementioned problems.

[0014] The present invention proposes an electric heating device having the features of claim 1 and / or having the features of claim 2.

[0015] According to the solution of claim 1, the PTC heating element is positively engaged in the pocket-shaped pressure element. The pocket-shaped pressure element not only wedges the PTC heating element in the receptacle formed by the pressure element, resulting in a force-fit connection, but also holds and secures the PTC heating element within the pocket-shaped pressure element by at least one positive locking element formed by the pressure element. This not only facilitates the installation of the pocket-shaped pressure element, but also prevents the PTC heating element from unintentionally migrating out, for example, due to vibrations in a motor vehicle, since the solution according to the invention is, in particular, an electric heating device for a motor vehicle.

[0016] According to the alternative embodiment specified in claim 2, the pressure element has a ridge that interacts with the inner surface in a form-fit or force-fit manner to permanently secure and hold the PTC heating element in the receiving pocket. The ridge thus ensures positional stability through form-fit and / or force-fit interaction directly or indirectly with the pressure element. In the installed state, the ridge typically bridges a gap or space and partially keeps it clear. This gap or space extends between the outer end of the ridge, usually the free end, and its mounting end.

[0017] This mounting end can protrude from a sheet metal element that is connected to a base body forming the recess for the pressure element. In this case, the pocket-shaped pressure element is made up of multiple parts.

[0018] Preferably, however, the bridge is formed in one piece on a uniformly designed pressure element.

[0019] As is known in the prior art, the printing element can have a wedge-shaped cross-sectional form. This cross-sectional form is obtained, for example, by connecting the outermost contour points of the printing element. The wedge shape is formed in particular by the free ends of the webs that project from one, preferably both, side wall sections of the printing element towards the associated inner surfaces of the receiving pocket.

[0020] Preferably, several webs project from each of the aforementioned side sections. The wedge shape mentioned above can be created by ensuring that, when designing a base body with essentially constant wall thicknesses, the webs provided at the upper end of the receiving pocket, near the connection chamber, are longer than the webs provided at the lower end of the receiving pocket.

[0021] The webs are elastically deformed in their installed state. The deformability of the webs is preferably selected such that they can absorb and store local stress peaks caused by an uneven contact surface within the receiving pocket, for example, an uneven inner surface. Typically, several webs are arranged across the surface of the heat dissipation area. This creates a uniform elastic preload force, which presses the individual contact surfaces between the layers held in the receiving pocket against each other. In this way, the webs maintain the clamping force exerted by the pressure element and store the clamping force elastically, similar to spring segments. The uniform distribution of the webs applies this elastic preload force evenly to the heat dissipation surfaces of the PTC element, thus ensuring good and lasting heat dissipation.

[0022] The struts are generally designed discretely. Individual struts are spaced apart and preferably distributed across the heat dissipation surface. This discrete arrangement allows each strut to deform locally depending on the contour and unevenness of its corresponding inner surface within the pocket. This ensures that stress concentrations are absorbed locally as effectively as possible.

[0023] The ridges preferably create a gap that can be between 0.1 and 4 millimeters wide. This gap can be filled by a thermally conductive material that incorporates the ridges, in order to ensure optimal heat transfer from the heat dissipation surface of the PTC element to the corresponding inner surface of the receiving pocket.

[0024] With a view to simplifying the pre-tensioning of the ribs when inserting the pressure element into the receiving pocket, it is preferable to shape the rib at an angle towards the inlet opening of the receiving pocket, relative to the heat dissipation surface and the connection chamber. This design facilitates the insertion of the ribs, since each rib pivots about its attachment-side end upon contact with the inner surface during insertion into the receiving pocket, so that the free end is elastically pressed against the inner surface of the receiving pocket.

[0025] Although elastic preload forces are already very effective for securing the position of the pressure element in the receiving pocket, a preferred embodiment of the invention proposes to design the bridge with a tip that engages with the inner surface of the receiving pocket, thus providing a positive locking mechanism. This tip locks into the inner surface. It acts like a barb, preventing the layers provided in the receiving chamber from being pushed out of the receiving pocket against their insertion direction or from migrating out due to vehicle vibrations.

[0026] According to a preferred embodiment of the present invention, the bridge is attached to the pressure element, particularly preferably integrally formed therein. This makes it possible to insert the bridge together with the pressure element into the receiving pocket, so that the tension caused by the pressure element is simultaneously stored as an elastic clamp in the bridge. Furthermore, by pre-connecting the bridge and the pressure element, the number of parts to be handled during the assembly of the electric heating device is reduced, thus simplifying the assembly process.

[0027] One way to positively secure the PTC heating element in the housing is by means of a locking rib that projects beyond the upper end of the PTC heating element. This upper end is located near the connection chamber. The locking rib typically projects over a flat, shallow boundary surface formed by the pressure element, which usually extends parallel to the heat dissipation surface.

[0028] A single retaining rib projecting from one of the side wall sections is sufficient to achieve the positive-locking fit of the PTC heating element in the pressure element. Preferably, retaining ribs are provided on opposite side wall sections. The retaining ribs are typically located at the free end of the side wall sections.

[0029] The pressure element, together with the at least one web, preferably with the at least one retaining web, is preferably formed in a single piece using an extruded profile. This extruded profile is initially produced as a strand and cut to length such that the pressure element completely or at least predominantly covers the heat dissipation area of ​​the PTC element. This does not necessarily mean that the pressure element is in direct contact with the heat dissipation area. Rather, an insulating layer, substantially covering the heat dissipation area of ​​the PTC element, can be provided between the pressure element and the associated heat dissipation area in a manner known per se. The insulating layer accordingly isolates – usually electrically – the pressure element from the conductor forming the conductive track.

[0030] The contact plate typically forms contact tongues in one piece, which are exposed in the connection chamber for the electrical connection of the PTC heating element. Preferably, insulating layers are provided between the contact plates, which usually rest against the heat dissipation surfaces, and the parallel surfaces of the pressure element's receptacle. However, one of these insulating layers can also be omitted to connect the PTC element to ground via the pressure element and the inner surface of the receptacle. In this case, the housing of the electrical heating device forms the ground terminal.

[0031] In a cross-sectional view of the layered receiving pocket, a straight line approximating the free ends of the webs is visible, extending obliquely to the associated heat dissipation surface. This line can form an angle of less than 10° with the heat dissipation surface. The angle is typically between 2° and 8°. Thus, elements of the PTC heating element with plane-parallel main side surfaces, i.e., at least the PTC element and the adjacent conductor tracks, can be used, since adaptation to the possible conical cross-sectional shape of the receiving pocket is achieved through the individual design of the deformation projections, which follow the contour and orientation of the inner surface and are preferably pre-tensioned with approximately the same elastic force in the vertical direction of the pocket.

[0032] The partition wall of the electric heating device according to the present invention can be formed integrally with the receiving pocket. This configuration is suitable for an electric heating device in which a lower housing part defines a circulation chamber into which the receiving pocket projects like a heating fin and forms the inlet and outlet openings for the flow of a medium to be heated in the heating chamber, wherein the corresponding housing part is manufactured by extrusion or aluminum die casting. In this respect, the preferred embodiment of the electric heating device according to the invention corresponds to the embodiment described in EP 1 872 986 A1.The same applies to the electrical connection of the conductor tracks in the connection chamber, which is provided on the side of the partition opposite the circulation chamber and typically connects several PTC heating elements electrically via a circuit board and / or allows control of individual or all PTC heating elements of the electric heating device via a control unit provided in the connection chamber. For this purpose, the conductor tracks typically have connection tabs on their free portion projecting beyond the receiving pocket, which are exposed in the connection chamber. The contact plates that preferably form the conductor tracks can preferably form these connection tabs in one piece at their free end.

[0033] The pressure element itself can be made of a spring-like material, whereby a material with good thermal conductivity should be selected. Thus, spring-hard aluminum, copper, or brass are preferable to sheet steel due to their improved thermal conductivity.

[0034] According to a preferred embodiment of the present invention, a heater housing made of an insulating material is provided, which integrates the PTC element, the conductive traces, and at least one optional insulating layer into a single unit. Such a heater housing typically consists of an insulating material, such as plastic or ceramic, and is accommodated within the recess of the pressure element. The heater housing can be bonded to one or both conductive traces. Alternatively, the conductive traces can be overmolded with the PTC element(s) during the injection molding process of the heater housing. This creates a single unit. The aforementioned thermally conductive material is preferably a material with high thermal conductivity. The thermal conductivity should be at least 3 W / (m K).The material should be applied after the PTC heating element has been inserted into the receiving pocket and after the pressure element has been moved vertically relative to the layers of the layer structure and their tension within the receiving pocket, while the PTC heating element is positioned relative to the pocket. In other words, the loaded pressure element is first inserted into the receiving pocket. The ribs can each be designed so that their contact points or surfaces create a flat contact surface, or they can abut a contoured or arbitrarily inclined surface and trace its contour via the contact points or surfaces formed by the individual ribs.

[0035] After the assembled pressure element has been clamped in the receiving pocket, the compound is poured into the pocket. This compound preferably fills all free spaces in the pocket, ensuring good heat transfer from the PTC element to all internal surfaces of the pocket, including its end faces. The mechanical clamping force is maintained by the spring segments of the pressure element. The compound is preferably a permanently elastic compound, allowing it to exhibit a certain degree of flexibility so that the spring segments can accommodate compensating movements during operation, such as those resulting from the thermal expansion of the individual layers of the structure. A suitable compound is, for example, a two-component silicone, which can be filled with ceramic particles to improve thermal conductivity.

[0036] Further details and advantages of the present invention will become apparent from the following description of an exemplary embodiment in conjunction with the drawing. The drawing shows: Fig. 1 a side view of an embodiment of a printing element for realizing the present invention; Fig. 2 a top view of the in Fig. 1 of the printed element shown; Fig. 3 a perspective side view of the in the Fig. 1 and Fig. 2 shown embodiment of a pressure element after forming; Fig. 4. A cross-sectional view of the printing element according to the Fig. 1 to 3 together with the PTC element included therein Fig. 5 A perspective front view of an embodiment of an electric heating device; with the pressure element partially removed; Fig. 6 a cross-sectional view of the in Fig. 5 shown embodiment and Fig. 7 the detail after Fig. 6 in enlarged view.

[0037] The Fig. Figure 1 shows a side view of a printing element 2, which in this case is designed as an extruded profile made of a metal and in the top view according to Fig. 2 has a basically rectangular base. From opposite end faces of this rectangular base, safety struts 4 project, which - like Fig. 1 illustrates - each protrudes from the same surface of the profile, which is a boundary surface 6 of a recording marked with reference sign 8 (cf. Fig. 3) The side view further illustrates that the profile forms a bottom section 10 and two essentially identical side sections 12. Film hinges 14 are formed between the respective sections 10 and 12 by reducing the material thickness of the profile.

[0038] Each of the side sections 12 has a wedge-shaped cross-section. A multitude of webs 16, formed integrally with the profile, project from an outer surface. How Fig. As illustrated in Figure 3, the webs 16 are designed as ribs extending across the width of the extruded profile. The webs 16 taper to a point at their free end, which is marked with reference numeral 18.

[0039] To produce the exemplary embodiment, the extruded profile is first prepared according to the Fig. 1 and Fig. 2 pressed out. Then length pieces are cut according to the illustration. Fig. 2 cut off. The side sections 12 are bent relative to the bottom section 10 around the film hinges 14. This creates the recess 8 for a PTC heating element 20, which is in Fig. Figure 4 shows the PTC element 22 and the contact plates 24 abutting it on opposite main side surfaces. The main side surface of the PTC element 22 is formed by the largest side surface of this PTC element 22. The main side surface corresponds to the heat extraction surface, which is marked with reference numeral 26. On the side of the contact plate 24 opposite the heat extraction surface 26, there is an insulating layer 28. The PTC heating element 20 according to Fig. Accordingly, the pressure element 2 is electrically separated from the pressure element 2 by the insulating layers 28. Each individual contact plate 24 forms a connecting lug 30 for the electrical connection of the PTC heating element 20. The locking lugs 4 clearly project beyond the upper PTC element 22. The locking lugs 4 can be designed as latching elements that secure the side sections 12 against each other when the pressure element 2 is fitted with the PTC heating element 20. More importantly, the locking lugs 4 prevent the PTC heating element 10 from moving out of the receptacle 8 of the pressure element 2 after it has been installed in a receiving pocket.

[0040] Said and in the Fig. The following receiving pocket, discussed in detail below, can taper conically towards its lower, closed end. The printing element has an outer contour adapted to this cross-sectional shape, which in this case is defined by a connecting line L that joins the free, tapered ends 18 together and into the Fig. 1 and Fig. 4 is marked with reference numeral L. The two in Fig. The four marked connecting lines L enclose an angle α of approximately 10°. The base body of the printing element 2, from which the webs 16 project, already has a slightly wedge-shaped basic form. The webs 16 projecting at a lower end 32 of the printing element 2 are shorter than the webs 16 projecting at an upper end 34 of the printing element. This further reinforces the wedge shape defined by the base body.

[0041] In the assembled state, the boundary surfaces 6 extend parallel to each other and lie flush against the insulating layers.

[0042] The assembly of the pressure element 2 is described below with reference to the Fig. 5 and Fig. Figure 6 explains. These figures show an embodiment of an electric heating device with a housing 100, a housing base 102, and a housing cover 104. The housing base 102 has a circulation chamber 106, which is connected via terminals, of which only one terminal 108 is in Fig. As shown in section 5, the device is connected to a line for a liquid fluid to be heated. The electric heating device is, in particular, a heating device in a motor vehicle.

[0043] The housing base 102 forms a partition 112 that separates the circulation chamber 106 from a connection chamber 114.

[0044] The circulation chamber 106 is penetrated by several heating fins 110 extending longitudinally along the housing base 102. These fins have a substantially U-shaped cross-sectional form in a cross-sectional view and are completely enclosed within the circulation chamber 106. These heating fins 110 form a receiving pocket 116.

[0045] In the illustrated embodiment, the electric heating device has pockets arranged side by side, extending essentially over the entire length of the housing base 102. The receiving pockets 116 are significantly longer than the pressure elements 2. Several pressure elements 2 fit one after the other into the receiving pocket 116 in the longitudinal direction (see figure). Fig. 5) The receiving pockets 116 form opposing inner surfaces 118 on their long sides.

[0046] The connection lugs 30 are exposed in the connection chamber and are electrically conductively connected to the contact plates 116, in this case forming them integrally. In the illustrated embodiment according to the Fig. 5 and Fig. 6. Two connection lugs 32 are provided for each PTC heating element 10 to supply current to the PTC elements 18 with different polarities.

[0047] For assembly, the pressure element 2 is first fitted with the insulating layers 22, the contact plates 24, and the PTC elements 22. These layers are placed into the not yet fully closed housing, approximately as shown in the diagram. Fig. Figure 3 shows the pre-shaped, funnel-shaped opening of the receptacle 8 being inserted. Then the locking tabs 4 are engaged, closing the pressure element 2. The pre-assembled unit is inserted into the receptacle 116. During this process, the tabs 16 deform. Their tapered ends 18 interlock with the inner surface 118 of the receptacle 116 in the installed position, thus permanently and securely holding the pressure element 2, together with the PTC heating element 20, in the installed position within the receptacle 116.

[0048] The Fig. Figure 7 illustrates how the ribs 16 interlock with the inner surface 118 of the receiving pocket 116. This results in a positive-locking connection between the pressure element 2 and the metallic housing 100. Consequently, the pressure element 2 is optionally connected to a ground terminal, which can be formed by the housing 100. A ground monitor can thus detect any failure of the insulating layer 28, which can be significant in high-voltage applications of the invention, e.g., in the field of electromobility.

[0049] Especially the Fig. 6 and Fig.Figure 7 illustrates that the webs 16 provided at one lower end of the receiving pocket 116 are shorter than the webs provided at the opposite end, which opens towards the connection chamber 114. Corresponding to the wedge shape of the receiving pocket 116, the pressure element 2 assumes a wedge shape with its outer contour, whereas the layers of the PTC heating element are aligned parallel to each other and to the boundary surfaces 6 of the pressure element 2. The webs 16 are inclined towards the upper end of the receiving pocket and, accordingly, towards the inlet opening provided there, which leads into the connection chamber 114. This results in a positive-locking connection between the frontally tapered webs 16 and the inner surface 118. Thus, the pressure element holds the heat dissipation surfaces 26 of the PTC element 22 against the inner surface 118 of the receiving pocket 116, with the associated contact plate 24 and the associated insulating layer 28 interposed. Reference symbol list 2 pressure element 4 safety bridge 6 Boundary area 8 shots 10 floor section Section 12 14 film hinge 16 Bridge 18 free ending 20 PTC heating elements 22 PTC elements 24 contact plates / conductor tracks 26 Heat extraction area 28 upper end of the printing element 2 30 connecting flag 32 lower end of the printing element 2 34 Insulation layer 100 cases 102 Case base 104 Case covers 106 Circulation chamber / Heating chamber 108 connection 110 heating fins 112 Partition wall 114 Connection chamber 116 Recording bag 118 interior surface area 120 lower end of the recording pocket

Claims

[1] Electric heating device comprising: a housing (100) with a partition (112) that separates a connection chamber (114) from a heating chamber (106) for heat dissipation and from which at least one receiving pocket (116) projects into the heating chamber (106) as a heating fin (110), in which a wedge-shaped pressure element (2) is received, which connects a PTC heating element (20) with at least one PTC element (22) and conductive traces (24) for supplying current to the PTC element (22) with different polarity, which are electrically connected in the connection chamber (114), at least partially surrounds and holds the PTC element (22) in the receiving pocket (116), characterized by , that, the PTC heating element (22) is positively engaged in the pressure element (2). [2] Electric heating device comprising: a housing (100) with a partition (112) that divides a connection chamber (114) from a heating chamber (106) for heat dissipation and from which at least one receiving pocket (116) projects into the heating chamber (106) as a heating fin (110), in which a wedge-shaped pressure element (2) is received, which connects a PTC heating element (20) with at least one PTC element (22) and conductor tracks (24) electrically connected to the PTC element (22) with different polarities for energizing it. which are electrically connected in the connection chamber (114), at least partially surrounds and holds the PTC element (22) in the receiving pocket (116), characterized by , that, the pressure element (2) at least one form-fit and / or force-fit connection with the inner surface (118) Bridge (16) has. [3] Electric heating device according to any one of the preceding claims, characterized by, that the pressure element (2) has at least one side section (12) which is provided between one of the heat dissipation surfaces (26) and the associated inner surface (118) and from which a plurality of webs (16) project. [4] Electric heating device according to claim 3, characterized by , that the webs (16) provided at an upper end (120) of the receiving pocket (116) near the connection chamber (114) are longer than the webs (16) provided at the lower end of the receiving pocket (118). [5] Electric heating device according to one of claims 3 and 4, characterized by , that the webs (16) are clamped under preload in the receiving pocket (116) between the inner surface (118) of the receiving pocket (116) and the associated heat dissipation surface (26). [6] Electric heating device according to any one of claims 3 to 5, characterized by, that the webs (16) are inclined at an angle to the heat extraction surface (26) and towards the connection chamber (114). [7] Electric heating device according to any one of claims 3 to 6, characterized by , that the bridges (6) have a tip that interlocks with the inner surface (118) of the receiving pocket (116). [8] Electric heating device according to any one of the preceding claims 4 to 7, characterized by that the webs (16) are attached to the pressure element (2), preferably formed in one piece on it. [9] Electric heating device according to any one of the preceding claims, characterized by , that the pressure element (2) is an extruded profile through which opposing side sections (12) and a bottom section (10) connecting them are formed in one piece.

Images