Method for producing a tank heater and tank heater

Abstract

Method for producing a tank heater, wherein a PTC heater containing a PTC heating resistor (1) is connected to a housing part (6), which is a cast metal part, and then the housing part (6) and PTC heater are encased in plastic, characterized in that the housing part (6) is machined before the PTC heater is connected to the housing part (6) by leveling a heat transfer surface (66) of the housing part (6), via which heat generated by the PTC heating resistor (1) is transferred to the housing part (6), before the plastic coating, a spring element (5) is attached to the housing part (6), which generates a spring force that presses the PTC heater against the heat transfer surface (66), and the housing part (6) has projecting pins (8) which pass through openings in the spring element (5) and are caulked under prestress on the upper side of the spring element (5) facing away from the housing part.

Description

[0001] A tank heater and a method for producing a tank heater with the features specified in the preamble of claim 1 are 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 resistor and a contact element is arranged, and a plastic casing that protects the metal housing from contact with liquid. Extruded profiles, such as in the tank heater known from DE 11 2006 001 103 B4, or cast parts, such 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 a simple, very good thermal coupling of the PTC heating resistor to the metal housing by pressing the extruded profile after the PTC heater has been inserted. However, the possible shapes of the metal housing are limited, which is why cast parts are increasingly being used for metal housings for tank heaters. Cast parts also allow the use of more cost-effective alloys, but they make it more difficult to achieve a good thermal coupling of the PTC heater to the metal housing, particularly since inexpensive alloys cannot be used to create channels or pockets that accommodate PTC heaters and can then be pressed into place.

[0004] In the tank heater known from DE 10 2014 212 544 A1, a steel spring plate is therefore used which is fixed to holding ribs of the housing part, wherein the holding ribs are compressed after fixing in order to press the PTC heater with sufficient pressure against a heat transfer surface of a housing part and thus to establish sufficient thermal contact between the PTC heater and the metal housing.

[0005] The object of the present invention is to show a way how the heat coupling of the PTC heater can be improved in a tank heater whose metal housing is a cast part.

[0006] This object is achieved by a method having the features specified in claim 1 and by a tank heater according to claim 5. Advantageous developments of the invention are the subject of subclaims.

[0007] According to the invention, during the manufacture of the tank heater, the cast part is machined before being connected to the PTC heater by leveling the heat transfer surface of the housing part, through which heat generated by the PTC heating resistor is transferred to the housing part. The housing part is preferably leveled by plastic deformation, for example, by pressing a stamp onto it using a rolling tool. The housing part of the tank heater therefore preferably has a heat transfer surface leveled by plastic deformation. Another possibility is leveling by machining, such as milling or grinding.

[0008] The cast part can be manufactured, for example, by die casting, e.g., from an aluminum-based alloy. The surfaces of a cast part are generally not as flat or smooth as those of an extruded profile. Therefore, by machining the cast part, improved thermal contact between the PTC heater and the housing part can be achieved. The leveling of the thermal contact surface by pressing a stamp, as preferred according to the invention, can be carried out with little effort; if necessary, the stamp acting on the thermal contact surface can be supplemented by a lower stamp shaped to match the opposite surface of the housing part.

[0009] 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 to electrically contact the PTC heating element(s), so that a single contact element, e.g., 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 insulates the contact element(s) from the metallic housing part. The insulator can be, for example, a ceramic plate, such as aluminum oxide, or a plastic film. However, it is also possible to use two electrically insulated housing parts to electrically contact the PTC heating element(s).

[0010] To further improve thermal coupling, according to the invention, a spring element is attached to the housing part before the encasing, generating 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 a good thermal conductivity, so that heat generated by the PTC heater can then also be advantageously dissipated via the spring element.

[0011] According to the invention, the spring element is caulked to the housing part.

[0012] This makes it advantageous to realize simple production.

[0013] A further advantageous development of the invention provides that the housing part has walls on opposite sides of the heat transfer surface, which walls have an undercut to which the spring element is hooked. 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 form part of the housing and enable easy assembly of the housing.

[0014] A further advantageous development of the invention provides for the spring element to be an extruded profile. This allows for cost-effective production. Advantageously, an extruded profile can also be easily rounded before assembly, so that no sharp edges remain when overmolding with plastic.

[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 description of the figures and / or shown alone in the figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from 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 provided with identical reference numerals. They show: Fig. 1 a sectional view of a tank heater; Fig. 2 the tank heating of Fig. 1 without plastic casing and spring element; Fig. 3 the spring element of the Fig. 1 shown tank heater; Fig. 4 a perspective longitudinal section along the line A - A through the casting of the Fig. 1 shown tank heater; 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 caulking with a spring element; and Fig. 8 another embodiment of a tank heater without the plastic jacket.

[0017] The Fig. The tank heater shown in a sectional view in Figure 1 contains a PTC heater that includes at least one PTC heating resistor 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 by a spring element 5 against a heat transfer surface 66 of the housing part 6, via which the heat generated by the PTC heating resistor 1 is transferred to the housing part 6.

[0018] In the illustrated embodiment, the PTC resistor 1 lies 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 lie flat against the heat transfer surface 66, such as a ceramic plate or other insulator.

[0019] The housing part 6 is a cast part, produced, 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 stamp. This improves the thermal coupling of the PTC heater to the housing part 6.

[0020] After leveling the heat transfer surface 66 of the housing part 6, the PTC heater is placed on the heat transfer surface 66 and the spring element 5 is clipped onto the housing part 6. The housing part 6 and the spring element 5, as well as the PTC heater arranged between them, are then overmolded with plastic, so that they are then protected by a plastic jacket 7 from contact with a 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 to which the spring element 5 is hooked. 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 removed from its mold. Fig. 4, in a sectional view of the housing part 2, the hidden cutting edges of a longitudinal section through the housing part 2 are shown by dashed lines to clarify this.

[0022] The Fig. The spring element 5, shown in isolation in Figure 3, is locked to the housing part 6. The corresponding positive connection acts perpendicular to the heat transfer surface of the housing part 6. For this purpose, the spring element 5 can have two strips 51 with locking hooks 52, which hook into the undercut of the opposite side walls 61 of the housing part 6. For this purpose, the boundary surface 64 and / or the contact surface 54 of the locking hooks 52 engaging with the boundary surface are advantageously designed at an angle to the heat transfer surface 66 so that the spring element 5 can remain securely locked in place. Extending between the strips 51 is a resilient top wall 53, which 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 basically U-shaped configuration.Advantageously, the inner surface 55 of the cover has, at least before fastening, a contour curved towards the center of the PTC heater, whereby after hooking, at least the central region of the PTC heater is securely connected to the heat transfer surface 66 and the spring element 5 in a heat-conducting manner.

[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 cast part, 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 reworked after cutting to length, e.g., by sandblasting, so that the edges 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 high-pressure impact of the overmolding material. The remaining open front side 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 a further 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 and the cooperating undercut of the side walls 62. While in the embodiment of the Fig. 1 to 4 the locking hooks 52 of the spring element 5 are directed inwards and facing each other, the locking hooks in the embodiment of the Fig. 5 facing outwards and facing 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 attached to the side walls 61, but rather to additional side walls 67 located further outwards.

[0026] Fig. Figure 6 shows a sectional view of another embodiment of a tank heater. This embodiment differs from the previously described embodiments essentially in that the spring element 5 is secured to the housing part 6 by caulking. 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 caulked on the upper side under prestress with a tool in such a way that a positive connection is created. Fig. 6, only one pin 8 is visible on each end face. 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 be arranged laterally offset.

[0027] In Fig. 7 shows an alternative design in which a single, elongated pin 8 with slightly beveled sides extends through an elongated opening in the spring element on each side. However, a variant according to Fig. 8, in which the spring element 5 is inserted between rails 9 projecting beyond the spring element 5 and the rails 9 are caulked in regions at the edge in such a way that the caulked regions 10 overlap the spring element 5 under pretension at the edge and thereby fix it. List of reference symbols 1 PTC heating resistor 2 contact element 3 Insulator 4 plastic frames 5 spring element 6 Housing part 7 plastic sheath 8 pin 9 Rail 10 caulked area 51 bar 52 locking hooks 53 Ceiling wall 54 contact surface 55 interior ceiling surface 61 side wall 62 grooves 63 Rear wall 64 upper boundary surface 65 lower boundary surface 66 heat transfer surface 67 additional side wall

Claims

[1] Method for producing a tank heater, wherein a PTC heater containing a PTC heating resistor (1) is connected to a housing part (6), which is a cast metal part, and then the housing part (6) and PTC heater are encased in plastic, characterized by , that the housing part (6) is machined before the PTC heater is connected to the housing part (6) by leveling a heat transfer surface (66) of the housing part (6), via which heat generated by the PTC heating resistor (1) is transferred to the housing part (6), before the plastic coating, a spring element (5) is attached to the housing part (6), which generates a spring force that presses the PTC heater against the heat transfer surface (66), and the housing part (6) has projecting pins (8) which pass through openings in the spring element (5) and are caulked under prestress on the upper side of the spring element (5) facing away from the housing part. [2] Method according to claim 1, characterized by that the heat transfer surface (66) is leveled by plastic deformation, preferably by pressing a stamp or by a rolling tool. [3] Method according to one of the preceding claims, characterized by that the spring element (5) is manufactured by extrusion. [4] Method 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 (55) extends. [5] 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), and a plastic casing (7) surrounding the housing part (6), the spring element (5) and the PTC heater, characterized by , that the housing part (6) has a heat transfer surface (66) levelled by plastic deformation or by a machining process, via which heat generated by the PTC heating resistor (1) is transferred to the housing part (6) and against which a spring force generated by the spring element (5) presses the PTC heater, and the housing part (6) has protruding pins which pass through openings in the spring element (5) and which are caulked under prestress on the upper side of the spring element (5) facing away from the housing part. [6] Tank heater according to claim 5, characterized by that the PTC heater has a plastic frame (4) which holds the PTC heating element (1), a contact element (2) and an insulator (3) arranged on the side of the contact element (2) facing away from the PTC heating element (1). [7] Tank heater according to claim 5 or 6, characterized by that the spring element (5) rests against the insulator (3).

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