Magnetic core for a filter choke

Abstract

A magnetic core for a filter choke, comprising an outer body closed around a vertical axis and at least one first center leg arranged between two opposite inner sides of the outer body in a direction perpendicular to the vertical axis, is characterized according to the invention in that the center leg consists of at least two leg elements which are positioned in close contact with one another with their mutually facing surfaces, and in that the mutually contacting surfaces of the leg elements are inclined relative to a plane perpendicular to the longitudinal direction of the center leg.

Description

[0001] KOSTAL Automobil Elektrik GmbH & Co. KG

[0002] 1

[0003] Magnetic core for a filter choke

[0004] The invention relates to a magnetic core for a filter choke with an outer body enclosed around a vertical axis and at least a first central web arranged between two opposing inner surfaces of the outer body in a direction perpendicular to the vertical axis, and to a filter choke with such a magnetic core.

[0005] The power electronics of electric vehicles have seen numerous developments and evolutions over the years. Particularly in the area of ​​on-board chargers, the charging devices installed in the vehicle to charge the electric car's battery, there are constant innovations. Besides new switches and circuit board designs, there are also "passive components" such as PFC chokes or filter chokes. A persistent goal in the development of these components is to utilize the available installation space as efficiently as possible and to minimize costs.

[0006] Due to frequent switching operations at high voltages, on-board chargers generate interference emissions. These are divided into differential-mode and common-mode interference, referred to below as DM and CM interference. To prevent this interference from interfering with other electronic devices, such as radios or pacemakers, and impairing their function, filters are incorporated into the electronic circuits to suppress or attenuate this interference. A combination of various components, usually two filter chokes, capacitors, and resistors is used. Specifically, it is common for one choke to attenuate DM interference and a separate one to attenuate CM interference. KOSTAL Automobil Elektrik GmbH & Co. KG

[0007] 2

[0008] Furthermore, a distinction is made between single-phase systems, as are mostly used in China, two-phase systems, as are mostly used in North America, and three-phase systems, as are mostly used in Europe. The number of phases used depends on the characteristics of the power grids in the respective regions.

[0009] For the design of AC filters in on-board chargers, a combined filter is usually used that can handle single-phase, two-phase, or three-phase systems. This requires filter chokes wound with three or four separate windings each. The problem with this winding arrangement is that the direct current (DM) inductance is usually low, resulting in insufficient attenuation of the DM range. Therefore, current technology often involves connecting additional chokes in series for DM attenuation. However, this results in disadvantages such as reduced installation space and increased costs.

[0010] Various publications have shown that the direct magnet (DM) inductance can be increased by extending a central core, typically used as a magnetic core and essentially ring-shaped, with a central rib, which can also be wound. However, these studies considered either single-phase or three-phase systems. Furthermore, these publications consistently referred to laboratory prototypes, where production tolerances typical of mass production are not taken into account. Therefore, these laboratory prototypes are not applicable to mass production, as the air gaps between the outer core (usually round and nanocrystalline) and the additional ferrite core significantly influence the DM inductance, and the maximum benefit is only achieved with minimal air gaps. KOSTAL Automobil Elektrik GmbH & Co. KG

[0011] 3

[0012] Typical mass-produced nanocrystalline magnetic cores exhibit relatively large tolerances in their internal dimensions. Tolerances of + / -1 mm are common, but these pose a problem for the resulting air gap, because if this gap becomes too large, the magnetic core inductance decreases.

[0013] The challenge here was therefore to compensate for the unavoidable manufacturing tolerances in such a way that the air gaps could be reduced to a minimum in order to exploit the maximum advantage of a central web in DM damping.

[0014] This problem is solved according to the invention by the fact that the central web consists of at least two web elements which are positioned close together with their surfaces facing each other, and that the adjacent surfaces of the web elements are inclined relative to a plane perpendicular to the longitudinal direction of the central web.

[0015] The inclination of the adjacent surfaces relative to the plane perpendicular to the longitudinal direction of the central web is preferably between 5° and 15°.

[0016] In a preferred embodiment of the invention, the central web consists of three adjacent web elements, wherein the central web element is wedge-shaped.

[0017] In an advantageous further development of this embodiment of the invention, a second central web is arranged perpendicular to the first central web. The central web element is truncated pyramid-shaped and is a common component of the first and second central webs. The two outer web elements of at least one of the central webs can also be arranged laterally offset from each other. KOSTAL Automobil Elektrik GmbH & Co. KG

[0018] 4

[0019] Further advantageous embodiments and developments will become apparent from the further dependent claims and from the description of an exemplary embodiment of the invention.

[0020] An embodiment of the invention is illustrated and explained below with reference to the drawing. The drawing shows...

[0021] Fig. 1 : a filter choke with a magnetic core designed according to the invention with two central struts,

[0022] Fig. 2: The filter throttle from Fig. 1 in a top view

[0023] Fig. 3: The filter throttle from Fig. 1 in longitudinal section

[0024] Fig. 4: a magnetic core designed according to the invention with two central struts

[0025] As can be seen from the drawing, a magnetic core designed according to the invention comprises an outer body 1 closed around a vertical axis and two central webs 2, 4 arranged between two opposing inner surfaces of the outer body 1 in a direction perpendicular to the vertical axis. This arrangement includes a novel configuration of several web elements 2', 2", 3, 4' 4", which allows adaptation to a wide variety of tolerances. These web elements 2', 2", 3, 4' 4" are typically ferrite cores. The central element is a central web element 3, which essentially corresponds in shape to a truncated pyramid and whose angled surfaces are preferably ground.Around this central web element 3, outer web elements 2', 2", 4' 4" are arranged, which also have ground contact surfaces and which can move longitudinally in guides of a plastic carrier not shown in order to make contact with the central web element 3 and simultaneously with the surrounding outer body 1, preferably made of nanocrystalline core material. KOSTAL Automobil Elektrik GmbH & Co. KG.

[0026] 5

[0027] to ensure this. The outer body 1 must be electrically insulated from a surrounding winding 5 and is therefore usually coated with an approximately 0.5 mm thick epoxy layer T. With ideal tolerance compensation, the thickness of the air gap between the outer web elements 2', 2", 4' 4" and the outer body 1 is thus limited to the thickness of the epoxy layer T, which simultaneously defines the minimum technically feasible air gap.

[0028] For manufacturing reasons, ring-shaped or toroidal cores are generally not used, as these require a very precise curvature (or a ground curvature) at least in the outer area of ​​the contact surface of the outer body 1 on the epoxy layer T in order to ensure a uniform and ideally plane-parallel air gap between the inserted web elements 2', 2", 4' 4" and the outer body 1. Therefore, the outer body 1 of the filter choke described in this invention is preferably rectangular in shape to provide flat contact surfaces between the rounded corners resulting from the manufacturing process, allowing the ground contact surfaces of the web elements 2', 2", 4' 4" to make contact with the greatest possible planarity. Nevertheless, the invention presented here is also applicable with differently shaped outer bodies 1, such as toroids.

[0029] According to the geometric arrangement, the middle web element 3 slides deeper into the structure when the outer body 1 is at the upper end of its dimensional tolerances and protrudes further when the outer core 1 is closer to the lower end of its dimensional tolerance range.

[0030] To adjust the DM inductance, the outer web elements 2', 2", 4' 4" can also be wound with at least one winding 6, 7 each. The more turns applied per winding 6, 7, the higher the DM inductance. It is important that the same number of turns is applied to all outer web elements 2', 2", 4' 4", and that these generate a magnetic field inside the magnetic core, which is directed towards the center. KOSTAL Automobil Elektrik GmbH & Co. KG

[0031] 6

[0032] Bridge element 3 flows. Limits are set by the construction space.

[0033] The modular design is advantageous here, because the bridge elements 2', 2", 4' 4" do not need to be wrapped before assembly like the outer body 1. Instead, for example, 8 pre-wound windings 6, 7 can be used on a circuit board, through which the bridge elements 2', 2", 4' 4" are inserted. The individual parts are then held in position by a plastic carrier (not shown) until they are soldered and, if necessary, potted with potting compound.

[0034] If potting compound is omitted for fixing and thermal coupling, a spring element is provided above the central web element 3, so that this is pushed downwards in the direction of the vertical axis and the outer web elements 2', 2", 4' 4" are pushed outwards. Such an element can be, for example, a metallic spring or a Gappad with a large working range.

[0035] The exact angle of inclination of the adjacent surfaces relative to the plane perpendicular to the longitudinal direction of the respective central web 2, 4 depends on the expected production tolerances and is determined mathematically or experimentally. An angle of 10° to the perpendicular is used as a starting point.

[0036] With this design, tolerances are completely absorbed in one direction and largely absorbed in the other. This is sufficient for most applications. Should it be necessary to completely compensate for tolerances in all directions, it is recommended to increase the height of one of the outer web elements 2', 2", 4' 4" and divide it by an angled cut to achieve further tolerance compensation via sliding wedges. KOSTAL Automobil Elektrik GmbH & Co. KG

[0037] 7

[0038] Alternatively, a spring element, perhaps as part of the plastic carrier (not shown), can be attached under one or more of the web elements 2', 2", 4', 4", which pushes the respective web element 2', 2", 4', 4" upwards in the direction of the vertical axis until all ground contact surfaces of the web elements 2', 2", 4', 4" are in contact. This allows the web elements 2', 2", 4', 4" to be positioned slightly higher or lower relative to the surrounding outer body 1, but the air gaps are reduced to a minimum.

Claims

KOSTAL Automobil Elektrik GmbH & Co. KG 8 Patent claims 1. Magnetic core for a filter choke with an outer body (1) enclosed around a vertical axis and at least a first central web (2) arranged between two opposing inner surfaces of the outer body in a direction perpendicular to the vertical axis, characterized in that the central web (2) consists of at least two web elements (2', 2", 3) which are positioned close together with their surfaces facing each other, and that the adjacent surfaces of the web elements (2', 2", 3) are inclined relative to a plane perpendicular to the longitudinal direction of the central web (2).

2. Magnetic core according to claim 1, characterized in that the inclination of the adjacent surfaces of the web elements (2', 2", 3) relative to the plane perpendicular to the longitudinal direction of the central web (2) is between 5° and 15°.

3. Magnetic core according to claim 1 or 2, characterized in that the central web (2) consists of three adjacent web elements (2', 2", 3) and that the central web element (3) is wedge-shaped.

4. Magnetic core according to claim 3, characterized in that a second central web (4) is arranged perpendicular to the first central web (2), and that the central web element (3) is truncated pyramidal in shape and is a common component of the first central web (2) and the second central web (4). KOSTAL Automobil Elektrik GmbH & Co. KG 9 5. Magnetic core according to claim 4, characterized in that the two outer web elements (2', 2", 4', 4") are arranged laterally offset from each other at least one of the two middle webs (2, 4).

6. Magnetic core according to one of claims 3 to 5, characterized in that the middle web element (3) is subjected to a force in the direction of the vertical axis by a spring element, by which the outer web elements (2', 2", 4' 4") are pushed outwards.

7. Filter choke with a magnetic core according to one of claims 1 to 6, characterized in that it is mounted on a printed circuit board (8) and that windings (6, 7) for the outer web elements (2', 2", 4' 4") are prefabricated on the printed circuit board (8).

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