Container heating

Abstract

Container heating with a heater assembly (1) containing a ceramic PTC heating resistor (11), a plastic housing (3) surrounding an interior space in which the PTC heating resistor (11) is arranged and forming a housing (33) of an electrical connector having contact tongues (4a, 5a) for connecting the heater assembly (1) to a power source, wherein the housing (33) of the electrical connector has a base (34) which separates the interior of the plastic housing (3) from an exterior space, characterized in that each of the contact tongues (4a, 5a) is made of electrically highly conductive metal and is welded to a sheet metal strip (4b, 5b) made of a corrosion-resistant, other metal, which is arranged in the interior of the plastic housing (3).

Description

The invention is based on a container heater having the features specified in the preamble of claim 1, as is known, for example, from DE 10 2018 105 222 A1 and DE 10 2011 056 144 A1.Container heaters are needed in motor vehicles for, among other things, tanks containing corrosive liquids such as urea solution. Corresponding tank heaters have a plastic housing which protects a heater assembly from contact with corrosive liquid and forms a housing of an electrical plug connector via which the heater assembly can be connected to a power source.It is an object of the present invention to provide a way in which the efficiency and safety of such a container heating for urea solution and other corrosive substances can be improved even further.This object is achieved by a container heater having the features specified in claim 1. Advantageous refinements of the invention are the subject matter of dependent claims.In a container heater according to the invention, contact tongues of the plug connector are made of a material with good electrical conductivity, for example a copper alloy, and are electrically conductively connected to a sheet metal strip made of a corrosion-resistant material, for example stainless steel, which is arranged in the interior of the plastic housing.In this way, the contact tongues can enable a very good electrical contact to a power supply with an advantageously low contact resistance, so that only little waste heat falls in the plug housing and damage due to poor contacting can be reliably avoided. In the interior enclosed by the plastic housing, however, a material such as copper would be problematic in the event of a leak, since this could lead to an uncontrolled chemical reaction. According to the invention, corrosion-resistant metal such as stainless steel is used in the interior of the plastic housing, for example V4A steel.The metal strips made of corrosion-resistant metal can protrude from the base of the plug connector. The connecting point between the contact tongues and the sheet metal strips is then located in the exterior of the container heating system. The connection point between contact tongues and corrosion-resistant sheet metal strips in the base of the plug connector housing is preferred, for example by injection molding the connection point with plastic during the production of the plug connector housing.According to the invention, it is provided that the contact tongues are welded to the sheet metal strips. Preferably, each of the contact tongues is welded to an end face of the sheet metal strips. Alternatively, however, an end section of the contact tongues can also overlap with the sheet metal strips.The highly conductive metal from which the contact studs are made preferably has a conductivity of at least 7 MS / m. Suitable materials are, for example, alloys based on copper, in particular bronze alloys, but also aluminum alloys or highly conductive steel. The contact studs can be provided with a metallic coating, for example silver plated, nickel plated, tin plated or gold plated. The contact resistance of the plug connector can thus advantageously be reduced.In a preferred embodiment, the sheet metal strips in the interior bear with a front side in each case on a contact sheet which electrically contacts a first part of PTC resistors, and with a rear side in each case on a contact sheet which electrically contacts a second part of PTC resistors. The PTC heating resistors are thus divided into two groups, each of which contains at least one PTC heating resistor. Each of these two groups is electrically contacted by two contact plates between which PTC heating resistors are held.The number of PTC heating resistors required for a required heating power can be distributed arbitrarily here between these two groups and the location at which the contact plates electrically contact the two sheet metal strips can thus be selected to match a desired position of the plug connector on the plastic housing of the container heater. An unnecessary length of the sheet metal strips which lead to the contact tongues can thus be avoided.An advantageous further development of the invention provides that the sheet metal strips are each welded to the contact sheet metal adjoining its front side and to the contact sheet metal adjoining its rear side. In this way, a reliable electrical contact can be ensured and, in addition, a unit that is easy to handle can be preassembled.The contact plates are preferably bent in an L-shape and each rest with a first leg against one of the sheet metal strips and with a second leg against PTC heating resistors. In this way, it can be achieved that the PTC heating resistors are all arranged in the same geometric plane, which facilitates efficient removal of the heat generated by them. Furthermore, the PTCs can also be arranged closely next to one another, since in the preferred embodiment little space is required in the PTC plane for the connection technology.A further advantageous refinement of the invention provides that the first part of the PTC heating resistors is held in a first plastic frame and the second part of the PTC heating resistors is held in a second plastic frame. In this way, the preassembly to form an easily manageable assembly can be facilitated, in particular if the sheet metal strips are welded to the contact plates abutting them. However, it is also possible to keep all PTC heating resistors in a single plastic frame.Preferably, at least one of the two contact plates is latched to a plastic frame, for example, in that the contact plate has angled tabs with openings in which latching projections of the plastic frame engage. It is also possible for both contact plates bearing against a PTC to be latched to a plastic frame.Further details and advantages of the invention are explained on an exemplary embodiment with reference to the attached drawings. The following are shown: FIG. 1 shows an exemplary embodiment of a container heater according to the invention; FIG. 2 is a sectional view of FIG. 1 ; FIG. 3 shows the heater assembly of the container heater with contact tabs of the plug connector; FIG. 4 shows the heater assembly of the container heater without a plastic frame; and FIG. 5 shows the heater assembly with heat exchanger.The container heater shown in FIGS. 1 and 2 is designed as a tank heater and contains a heater assembly 1 shown in FIG. 3 which bears against a heat exchanger 2 made of metal, as shown in FIG. 5. The heat exchanger 2 can be formed in one piece or consist of several separate parts. In the exemplary embodiment shown, the heat exchanger 2 is formed from three individual, identical extruded parts 2 a, 2 b, 2 c, which each form a passage 7 in which the heater assembly 1 engages. For this purpose, the separate heat exchanger parts 2 a, 2 b, 2 care each pushed with their passage 7 from two end sides onto the heater assembly 1. If a plurality of heat exchanger parts, here the two parts 2 band 2 c, are pushed on from one side, they are preferably pushed on at a distance. After the pushing on, the heater assembly 1 is pressed into the passages 7 of the heat exchanger parts 2 a, 2 b, 2 c.Heater assembly 1 and heat exchanger 2 are surrounded by a plastic housing 3, which in the exemplary embodiment shown is composed of a plurality of parts, for example a lower part 31, an upper part 32 and a housing 33 of an electrical plug connector. The various parts of the plastic housing 3 can be welded to one another, for example the lower part 31 can be connected to the upper part 32 or can be connected to one another in a fluid-tight manner in another way. For example, an O-ring 8 is arranged between the housing 33 of the electrical plug connector and the upper part 32 for sealing purposes.The housing 33 of the electrical plug connector has a base 34, from which contact tongues 4 a, 5 aprotrude, via which the container heater can be connected to a power source. In the housing 33 of the plug connector, the base 34 thus separates an interior space of the container heater, in which the heat exchanger 2 and the heater assembly 1 are arranged, from an exterior space.The contact tongues 4 a, 5 aof electrically highly conductive metal, e.g. copper, are each electrically connected to a sheet metal strip 4 b, 5 bof a corrosion-resistant metal, which is arranged in the interior of the plastic housing 3. In the exemplary embodiment shown, the contact tongues 4 a, 5 atogether with the sheet metal strips 4 b, 5 bform in each case a composite sheet metal strip 4, 5 which projects through the base 34 of the plug connector housing 33. The contact tongues 4a, 5a each form a front end section of this composite sheet metal strip 4, 5, while a rear end section 4b, 5b made of corrosion-resistant metal is arranged in the interior of the container heater.The contact studs 4 a, 5 aare made of highly electrically conductive metal having an electrical conductivity of at least 7 MS / m, for example of a copper-based alloy, while the rear end section 4 b, 5 bof the composite sheet metal strips 4, 5 is made of corrosion-resistant metal, for example of stainless steel. The composite sheet metal strips 4, 5 are produced by welding a sheet metal strip of metal with good electrical conductivity to a sheet metal strip of corrosion-resistant metal, in particular by welding at the respective end sides.The weld 6 - or in another connection more generally the joint - between the contact studs 4a, 5a and the respective end portion 4b, 5b of corrosion-resistant metal is not located in the sealed interior space of the plastic housing 3, but is embedded in the bottom 34 of the connector housing 33 or lies together with the contact studs 4a, 5a in the exterior space. During the production of the plug connector housing 33, the composite sheet metal strips 4, 5 are encapsulated by plastic by injection molding. In this case, in particular, the weld seam 6 between the contact tongues 4 a, 5 aand the rear section 4 b, 5 bof the composite sheet metal strips 4, 5 can also be injection-molded, such that the weld seam 6 is then located in the base 34.The contact studs 4 a, 5 amay be provided with a metallic coating in order to minimize contact resistance of the plug connector. For example, the contact studs 4a, 5a may be silvered.The heater assembly 1 contains a plurality of ceramic PTC heating resistors 11 which are arranged between contact plates 12, 13 and 15, 16, respectively, which can be electrically insulated from the heat exchanger 2 aand 2 b, 2 c, respectively, by an insulator layer 14, for example made of ceramic, in particular aluminum oxide. In low-voltage applications, one of the two contact plates may be grounded together with the heat exchanger 1 and then need not be electrically insulated from it.A part of the PTC heating resistors 11 is held by a first plastic frame 20 and a second part by a second plastic frame 21. Each plastic frame 20, 21 thus holds at least one PTC heating resistor 11. Each of the two plastic frames 20, 21 carries two contact plates 12, 13 and 14, 15, respectively, between which the PTC heating resistors 11 held by the respective plastic frame lie. FIG. 4 shows the heater assembly 1 without the plastic frames 20, 21 for better understanding.As FIG. 3 shows, the composite sheet metal strips 4, 5 extend through between the two plastic frames 20, 21 and are electrically contacted on their front side and on their rear side by contact plates 12, 13 and 15, 16, respectively, which abut against them there. The contact plates 12, 13 and 15, 16 can advantageously be welded to the section 4 band 5 b, respectively, of the sheet metal strip 4 and 5, respectively, lying therebetween.The contact plates 12, 13, 15, 16 are each bent in an L-shaped manner. One of its legs abuts the sheet metal strip 4 or 5, and its other leg abuts the PTC heating resistor or resistors 11 electrically contacted by them. The current direction is exactly the opposite in the PTC heating resistor or resistors 11 held by the first plastic frame 20 to that in the PTC heating resistor or resistors 11 held by the second plastic frame 21.In the exemplary embodiment shown, one of the two contact plates 13, 16 of each plastic frame 20, 21 is latched to the plastic frame 20, 21, for example in that the contact plates 13, 16 have angled brackets 22 with openings in which latching projections of the plastic frames 20, 21 engage. It is also possible for both contact plates 12, 16 and 13, 15 to be latched to the respective plastic frame 20, 21.List of reference characters1 Heater assembly 2 Heat exchanger 2 a Part 2 b Wärmeübertrager part 2 c Wärmeübertrager part 3 Plastic housing 4 Composite sheet metal strips 4 a Kontakt 4 b Blechstreifen 5 Composite sheet metal strips 5 a 5 b Blechstreifen 6 Weld 7 Passage 8 O-ring 11 PTC heating resistor 12 Kontakt 13 14 Insulator layer 15 Kontakt 16 20 Plastic frame 21 Plastic frame 22 Tab 31 Bottom part 32 Top part 33 Plug connector housing 34 Bottom

Claims

Container heater comprising a heater assembly (1) containing a ceramic PTC heating resistor (11), a plastic housing (3) surrounding an interior space in which the PTC heating resistor (11) is arranged and forming a housing (33) of an electrical plug connector, which housing has contact tongues (4a, 5a) for connecting the heater assembly (1) to a power source, wherein the housing (33) of the electrical plug connector has a base (34) which separates the interior space of the plastic housing (3) from an exterior space, characterized in that each of the contact tongues (4a, 5a) is made of metal with good electrical conductivity and is welded in each case to a sheet metal strip (4b, 5b) made of a corrosion-resistant, different metal which is arranged in the interior space of the plastic housing (3).Container heater according to claim 1, characterised in that each of the contact tongues (4a, 5a) electrically contacts one of the sheet metal strips (4b, 5b) at its end face.Container heater according to one of the preceding claims, characterized in that the contact tongues (4a, 5a) and the sheet metal strips (4b, 5b) are connected at a location which lies in the base (34) of the plug connector.Container heater according to one of the preceding claims, characterized in that the contact tongues (4a, 5a) are provided with a metallic coating.Container heater according to claim 4, characterised in that the metallic coating is silver-based.Container heater according to one of the preceding claims, characterized in that the metal with good electrical conductivity has an electrical conductivity of at least 7 MS / m.Container heater according to one of the preceding claims, characterized in that the metal with good electrical conductivity is a copper-based alloy, in particular a bronze.Container heater according to one of the preceding claims, characterized in that the corrosion-resistant metal is stainless steel.Container heater according to one of the preceding claims, characterized in that none of the contact tongues (4a, 5a) projects into the interior of the plastic housing (3).

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