TANK HEATING

Abstract

Tank heating with a PTC heater which includes a PTC heating resistor (1) and a contact element (2), a housing part (6) made of metal, a spring element (5) made of metal that generates a spring force which presses the PTC heater against a heat transfer surface (66) of the housing part (6), and a plastic sheath (7) that surrounds the housing part (6), the spring element (5) and the PTC heater, wherein the spring element (5) is latched or riveted to the housing part (6), characterized in that the spring element (5) is an extruded profile.

Description

[0001] A tank heater with the features specified in the preamble of claim 1 is known from DE 10 2014 212 544 A1.

[0002] Tank heaters for heating liquids in motor vehicles, such as urea solution or water, have a metal housing in which a PTC heater with a PTC heating element and a contact element is arranged, and a plastic jacket that protects the metal housing from contact with the liquid. Extruded profiles, as in the tank heater known from DE 11 2006 001 103 B4, or castings, as in the tank heaters known from DE 10 2014 212 544 A1 and EP 2 506 661 A1, can be used for the metal housing.

[0003] Extruded profiles enable very good thermal coupling of the PTC heating element to the metal housing using simple means, by pressing the extruded profile after inserting the PTC heater.

[0004] However, the possible shapes of the metal housing are limited, which is why castings are increasingly used for the metal housings of tank heaters. Castings also allow the use of more cost-effective alloys, but make it more difficult to achieve good thermal coupling between the PTC heater and the metal housing, especially since channels or pockets cannot be produced with inexpensive alloys to accommodate the PTC heater and then be pressed shut.

[0005] In the tank heater known from DE 10 2014 212 544 A1, a steel spring plate is used, which is fixed to retaining ribs of the housing part. After fixing, the retaining ribs are compressed to press the PTC heater with sufficient pressure against a heat transfer surface of a housing part, thus establishing sufficient thermal contact between the PTC heater and the metal housing. Spring elements made of aluminum-based alloys are known from DE 10 2014 210 799 A1.

[0006] The object of the present invention is to show a way in which the heat coupling of the PTC heater can be improved in a tank heater whose metal housing is a casting.

[0007] This problem is solved by a tank heater with the features specified in claim 1. Advantageous embodiments of the invention are the subject of dependent claims.

[0008] To improve heat transfer, a spring element is attached to the housing component before the casing is encased. This spring element generates a spring force that presses the PTC heater against the heat transfer surface. The spring element is preferably made of an aluminum-based alloy. Aluminum alloys have good thermal conductivity, so the heat generated by the PTC heater can also be dissipated advantageously via the spring element.

[0009] According to the invention, the spring element is snapped or riveted to the housing part. For example, the spring element can be attached to the housing part by clipping it onto the housing part. This advantageously allows for simple manufacturing. Furthermore, snapping or riveting the spring element to the housing part reduces the risk of metal shavings forming, which can cause electrical problems, compared to the conventional method of inserting a spring plate into a groove.

[0010] A further advantageous embodiment of the invention provides that the housing part has walls on opposite sides of the heat transfer surface, which have an undercut with which the spring element is engaged. The spring element can, for example, have two strips with locking hooks, between which a resilient cover surface extends. In this way, the spring element can thus form part of the housing and enable easy assembly of the housing.

[0011] According to the invention, the spring element is an extruded profile. This allows for cost-effective manufacturing. Advantageously, an extruded profile can also be easily rounded before assembly, so that no sharp edges remain after overmolding with plastic.

[0012] During the manufacturing of the tank heater, the casting can be machined before being connected to the PTC heater by flattening the heat transfer surface of the housing part, which is where the heat generated by the PTC heating element is transferred. Preferably, the housing part is flattened by plastic deformation, for example, by pressing a die against it. However, flattening with a rolling tool is also possible. Another option is flattening via machining processes such as milling or grinding.

[0013] The casting can be produced, for example, by die casting, perhaps from an aluminum-based alloy. The surfaces of a casting are generally not as flat or smooth as those of an extruded profile. Therefore, machining the casting can achieve improved thermal contact between the PTC heater and the housing. The preferred method according to the invention, leveling the thermal contact surface by pressing a punch, can be carried out with minimal effort; optionally, the punch acting on the thermal contact surface can be supplemented by a lower punch shaped to match the opposite surface of the housing.

[0014] The PTC heater can contain one or more PTC heating elements and one or more contact elements. In the simplest case, the metal housing is used for the electrical contact of the PTC heating element(s), so a single contact element, such as a contact plate, is sufficient. If the metal housing is electrically insulated from the PTC heating element(s), two contact elements are required. The PTC heating element(s) and contact element(s) can be held by a plastic frame, which can also carry an insulator that electrically isolates the contact element(s) from the metallic housing part. The insulator can be, for example, a ceramic plate, such as one made of aluminum oxide, or a plastic film. It is also possible to use two electrically insulated housing parts for the electrical contact of the PTC heating element(s).

[0015] The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combination specified in each case, but also in other combinations or on their own, without leaving the scope of the invention.

[0016] Further details and advantages are explained using exemplary embodiments of the invention with reference to the accompanying drawings. Identical and corresponding components are identified by matching reference numerals. The drawings show: Fig. 1 a sectional view of a tank heater; Fig. 2 the tank heater of Fig. 1 without plastic casing and spring element; Fig. 3 the spring element of the in Fig. 1 tank heater shown; Fig. 4. a perspective longitudinal section along line A - A through the casting of the in Fig. 1 tank heater shown; Fig. 5 a sectional view of another embodiment of a tank heater; Fig. 6 a sectional view of another embodiment of a tank heater; Fig. 7 an embodiment of a housing part for riveting with a spring element and Fig. 8 Another embodiment of a tank heater without the plastic casing.

[0017] The Fig. 1 Tank heater, shown in a sectional view, contains a PTC heater, which includes at least one PTC heating element 1 and may additionally have, for example, a contact element 2, an insulator 3, and a plastic frame 4 that holds the various components of the PTC heater. The PTC heater is pressed against a heat transfer surface 66 of the housing part 6 by a spring element 5, via which heat generated by the PTC heating element 1 is transferred to the housing part 6.

[0018] In the illustrated embodiment, the PTC resistor 1 rests flat against the heat transfer surface 66 of the housing part, since the PTC resistor 1 is electrically contacted via the housing part 6. In another embodiment, for example, if the PTC heating resistor is electrically insulated from the housing on both sides and is electrically contacted by two contact elements, another component of the PTC heater can also rest flat against the heat transfer surface 66, such as a ceramic plate or other insulator.

[0019] The housing part 6 is a cast part, manufactured, for example, by die casting. Before the PTC heater is connected to the housing part 6, the heat transfer surface 66 of the housing part 6 is flattened by plastic deformation, for example, by pressing a punch against it. This improves the heat coupling of the PTC heater to the housing part 6.

[0020] After leveling the heat transfer surface 66 of the housing part 6 by pressing on a plunger, the PTC heater is placed onto the heat transfer surface 66 and the spring element 5 is clipped onto the housing part 6. Then, the housing part 6, the spring element 5, and the PTC heater positioned between them are overmolded with plastic, so that they are then protected by a plastic sheath 7 from contact with the liquid to be heated.

[0021] The housing part 6 has walls 61 on opposite sides of the heat transfer surface 66, which have an undercut with which the spring element 5 is engaged. The undercut can be formed, for example, by a groove 62 in the respective side wall 61. An upper boundary surface 64 of the groove 62, forming the undercut, runs parallel to the heat transfer surface 66, and a lower boundary surface 65 of the groove 62 runs obliquely to the upper boundary surface of the groove 62. In other words, the groove 62 widens in its longitudinal direction. In this way, the housing part 6 can be more easily demolded from its mold. Fig. Figure 4 shows the hidden cutting edges of a longitudinal section through the housing part 2 in a sectional view, indicated by dashed lines.

[0022] The Fig. The spring element 5, shown in isolation, is latched to the housing part 6. The corresponding positive locking action is perpendicular to the heat transfer surface of the housing part 6. The spring element 5 can have two ribs 51 with locking hooks 52, which engage with the undercut of the opposing side walls 61 of the housing part 6. Advantageously, the limiting surface 64 and / or the contact surface 54 of the locking hooks 52, which engages with the limiting surface, is inclined towards the heat transfer surface 66 so that the spring element 5 can remain securely latched. A resilient top wall 53 extends between the ribs 51 and presses against the PTC heater, for example, against an insulator 3, such as a ceramic plate or plastic. The spring element 5 thus has a U-shaped configuration.Advantageously, the inner surface of the ceiling 55 has a contour curved towards the center of the PTC heater, at least before it is attached, so that after hooking it on, at least the central area of ​​the PTC heater is reliably thermally connected to the heat transfer surface 66 and the spring element 5.

[0023] Both the spring element 5 and the housing part 6 can be made from an aluminum-based alloy. While a cost-effective standard casting alloy can preferably be used for the casting, the spring element 5 is preferably made from a spring-hard alloy such as an AlMgSi alloy. The spring element 5 can be manufactured by extrusion, i.e., it can be an extruded profile. In contrast to a thin steel spring sheet, where sharp edges are difficult to avoid, a spring element made from an aluminum-based alloy can easily have rounded edges. If the spring element is manufactured as an extruded part, for example, the edges can be further processed after cutting to length, e.g., by sandblasting, so that they are subsequently rounded. This significantly reduces the risk of the plastic sheath in contact with the edges tearing at these edges.

[0024] The housing part 6 can have additional walls, for example, a rear wall 63 that runs transversely to the opposing side walls 61, which have the undercut. This provides sufficient protection for the PTC heater from three sides against the overmolding material impacting it at high pressure. The remaining open front is largely covered by the front wall of the plastic frame 4, so that the PTC heater is also adequately protected here. Otherwise, the pressure during overmolding could counteract the spring force of the spring element 5.

[0025] Fig. Figure 5 shows a sectional view of another embodiment of a tank heater, which differs from the embodiment discussed above essentially in the orientation of the locking hooks 52 of the spring element 5. Whereas in the embodiment of Fig. 1 to 4 the locking hooks 52 of the spring element 5 are directed inwards and towards each other, the locking hooks in the exemplary embodiment of the Fig. 5 facing outwards and away from each other. In order to still be able to tightly enclose the PTC heater with side walls 61 and a rear wall, the undercuts are not located on the side walls 61, but on additional side walls 67 further outwards.

[0026] Fig. Figure 6 shows a sectional view of another embodiment of a tank heater. This embodiment differs from the embodiments described above essentially in that the spring element 5 is attached to the housing part 6 by crimping. In the embodiment shown, the housing part 6 has protruding pins 8, preferably on the end face of the walls 61. The pins 8 extend through openings in the spring element 5 and are crimped under preload on the upper side using a tool such that a positive fit is created. Fig. Only one pin 8 is visible on each end face of the housing part 6. However, multiple pins 8 on each side are also possible. The pins 8 can be formed integrally with the housing part 6 or manufactured separately. It is particularly preferred that the pins 8 are arranged laterally offset.

[0027] In Fig. Figure 7 shows an alternative design in which a single, elongated pin 8 with slightly beveled side surfaces extends through an elongated opening in the spring element on each side. However, a variant according to [reference missing] is also possible. Fig. 8, in which the spring element 5 is inserted between rails 9 projecting beyond the spring element 5 and the rails 9 are riveted in certain areas at the edge in such a way that the riveted areas 10 overlap the spring element 5 under preload at the edge and thereby fix it. List of reference symbols 1 PTC heating element 2 Contact element 3 Insulator 4 plastic frames 5 spring element 6 Housing part 7 plastic coating 8 pen 9 rail 10 crimped area 51 bar 52 locking hooks 53 Ceiling wall 54 Contact area 55 Ceiling interior area 61 Side wall 62 Nut 63 Back panel 64 upper boundary surface 65 lower boundary surface 66 Heat transfer surface 67 additional side wall

Claims

[1] Tank heating with a PTC heater containing a PTC heating resistor (1) and a contact element (2), a housing part (6) made of metal, a spring element (5) made of metal, which generates a spring force that presses the PTC heater against a heat transfer surface (66) of the housing part (6), and a plastic casing (7) surrounding the housing part (6), the spring element (5) and the PTC heater, wherein the spring element (5) is locked or caulked to the housing part (6), characterized by , that the spring element (5) is an extruded profile. [2] Tank heater according to claim 1, characterized by that the housing part (6) has side walls (61) on opposite sides of the heat transfer surface (66) which have an undercut with which the spring element (5) is hooked. [3] Tank heating according to claim 2, characterized bythat the undercut in each of the opposite side walls (61) is formed by a groove (62), wherein an upper boundary surface (64) of the groove (62) forming the undercut runs parallel to the heat transfer surface and a lower boundary surface (65) of the groove (62) runs obliquely to the upper boundary surface of the groove (62). [4] Tank heater according to one of the preceding claims, characterized by that the PTC heater has a plastic frame (4) which holds the PTC heating element (1), the contact element (2) and an insulator (3) arranged on the side of the contact element (2) facing away from the PTC heating element (1). [5] Tank heating according to claim 4, characterized by that the spring element (5) rests against the insulator (3). [6] Tank heater according to one of the preceding claims, characterized by that the spring element (5) has two strips (51) with locking hooks (52), between which a resilient ceiling wall surface (53) extends. [7] Tank heater according to one of the preceding claims, characterized by that the spring element (5) is made of an aluminum-based alloy.

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