Device comprising a housing for a C-shaped magnetic core and a cover

Abstract

The invention relates to a device comprising a magnetic core C (5), a conductive bar (1), the magnetic core C (5) being installed around said conductive bar (1). The device comprises a housing (7) having a base (8) and a side wall (9) defining a receiving volume (10) in which the magnetic core C (5) is received, a resin (11) or an adhesive being in the housing (7). The magnetic core C (5) is at least partially contained therein. A cover (12) closes an open face of the housing (7) opposite the base (8), the cover (12) having a closing plate having an inner face facing the housing (7), and an outer face, the closing plate having an elongated orifice through which the conductive bar (1) passes.The cover is fixed by adhesion with resin or glue and it has at least two pins (16) projecting from the inner face of the closing plate, which extend between the magnetic core in C (5) and the side wall of the housing (7), and which are at least partially embedded in the resin (11) or glue. See Figure 5 for the abbreviated version.

Description

Title of the invention: Device comprising a housing for a C-shaped magnetic core and a cover TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of electrical connection between an inverter and an electrical machine whose operation is controlled by this inverter.

[0002] It relates more particularly to solutions enabling the placement of a magnetic core in C around such an electrical link, in order to allow a measurement of the current in this link.

[0003] The invention is described below in the context of an inverter powering and controlling an electric traction motor in a motor vehicle, which is the preferred application of the invention. The present invention is nevertheless applicable to any assembly comprising an inverter and an electrical machine powered by that inverter. STATE OF THE ART

[0004] Electric or hybrid vehicles are generally equipped with one or more inverters which allow, in particular, the generation of alternating voltages adapted to the operation of an electric traction motor, synchronous or asynchronous, from a direct voltage source, such as an electric battery.

[0005] An inverter comprises power modules, forming a "power stage", and comprising electronic switches whose openings and closings are appropriately controlled by a control module, in order to supply the phases (for example the three phases) of an electrical machine.

[0006] The electrical connection between an inverter and an electric motor, allowing an electrical connection to be established between the power stage of the inverter and the phases of the electric motor, is generally made using conductive bars, generally referred to by the English term "busbars" or by the expression "bus bar".

[0007] These busbars, which are thick conductors, generally made of copper, used to transmit electrical power with low resistance and minimal losses, are hereafter referred to as "conducting bars".

[0008] It is important to be able to measure the current flowing in these conductive bars.

[0009] Current measurements can be used, in particular, to provide feedback to the inverter, allowing for precise adjustment of the power outputs and more effective control of the speed and torque of the electric machine. Furthermore, the current measurements provided are important for monitoring and protecting the system. They allow, for example, the detection of overload situations or possible malfunctions of the electrical machine.

[0010] It is known to perform a measurement of the current in a conductive bar using an assembly comprising a magnetic core in C and a Hall effect sensor.

[0011] The expression "C-shaped magnetic core" refers to a component made of a material A magnetic core with a "C"-shaped geometry is also more simply called a "C-core" or, more commonly, a "C-core," according to the English terminology used in the field. In the remainder of this document, these terms are synonymous.

[0012] Thus, to measure the current in a conductive bar, a C-core is used in conjunction with a current sensor, in this case a Hall effect sensor. The C-core serves to concentrate the magnetic field created by the current flowing through the conductive bar, thereby improving the accuracy of the measurement. Thanks to the open shape of the magnetic C-core, the current sensor can be installed in the air gap (the open part of the C-core). The C-core protects the sensor against external magnetic interference, improving the reliability and accuracy of the measurements.

[0013] Various types of C-shaped magnetic cores are available on the market, differing in the material used in their construction or their manufacturing process. In particular, a C-shaped magnetic core can be laminated or wound. A laminated C-shaped magnetic core consists of multiple layers of an insulated magnetic material stacked to form the C-shape of the core, while a wound C-shaped magnetic core is made from a single strip of magnetic material to create a continuous magnetic core that is more efficient at high frequencies.

[0014] When the magnetic core in C is of the laminated type, it is possible to hold the layers together mechanically, for example with punches, and / or to apply a surface treatment. When it is of the wound type, it cannot be coated or overmolded, and therefore cannot be protected against corrosion. However, a wound and untreated magnetic core in C provides the best magnetic characteristics. But these cores, generally made of iron-silicon, are very susceptible to corrosion.

[0015] Regardless of the magnetic core technology in C considered, there is generally a need to ensure its mechanical strength, its protection, and its positioning as precisely as possible when it is in place around a conductive bar.

[0016] Thus, it is known to dispose the magnetic core in C in a housing which can be formed in various ways around a conducting bar.

[0017] The magnetic core in C can be held in position in different ways: it can be glued with a resin, held by an overmolding, or held by a mechanical fixing (clip, screw, etc.).

[0018] While a resin can provide mechanical protection for the magnetic core, it can also tend to retain particles that come into contact with it, particularly metallic particles that could disrupt the operation of the magnetic core. Such particles can be generated, for example, when the conductive bar is welded to another conductive bar in close proximity to the magnetic core. Therefore, the use of a cover to protect the magnetic core and, more generally, the interior of the housing in which it is installed is recommended.

[0019] Document EP2546660 discloses a current sensor system for a three-phase assembly. The system is arranged in a housing closed by a lid. The housing and the lid thus contain three magnetic cores.

[0020] Document EP3086130 relates to an electric current sensor, which includes a magnetic core positioned in a housing covered by a cover portion. The cover portion is attached to the housing by snap-fitting, welding, or gluing.

[0021] Nevertheless, known systems can be improved, particularly with regard to the reliability of their fastening and their ease of implementation. In particular, the installation and fastening of the cover should advantageously be automated. Description of the invention

[0022] The present invention is thus developed in the above context and tends to improve the assembly of a system comprising a magnetic core in C and a conducting bar, in order to carry out a measurement of the current in the conducting bar.

[0023] To this end, the invention relates to a device comprising a magnetic core in C, a conductive bar, the magnetic core in C being installed around said conductive bar, and a housing having a base and a side wall defining a receiving volume in which the magnetic core in C is received. A resin or an adhesive is in the housing and the magnetic core in C is at least partially embedded therein. A cover closes an open face of the housing opposite the base, the cover having a closing plate having an inner face facing the housing, and an outer face, the closing plate having an elongated orifice through which the conductive bar passes.The cover is fixed by adhesion with resin or glue and it has at least two protruding pins on the inner face of the closing plate, which extend between the magnetic core in C and the side wall of the housing, and which are at least partially embedded in the resin or glue.

[0024] The device thus proposed allows for a simple and reliable attachment of a cover to a magnetic core housing in C, when the core is included, in whole or in part, in a resin or adhesive. Since the resin provides the fixing, only precise placement and pressing of the cover onto the open face of the housing are required to close the housing, a process that can be automated. The pins located on the inner face of the cover ensure reliable fixing of the cover by embedding it in the resin. Furthermore, because these pins are interposed between the magnetic core and the side wall of the housing, they can contribute to centering the magnetic core within the housing, or at least ensure that the magnetic core is correctly centered. As the resin is generally not transparent, visual verification of the core's centering is no longer possible once it is embedded (fully encased) in the resin. These mechanically precise centering features are therefore important, as the position of the magnetic core cannot be visually checked after it has been resin-encapsulated.

[0025] The hood may include at least one hole, separate from said elongated orifice, formed through the closing plate and allowing a passage of air.

[0026] The hood may have on its inner face a rib opposite or in contact with a surface of the magnetic core at C.

[0027] The hood rib can be in the resin.

[0028] The inner face may have a higher average roughness than the outer face.

[0029] The hood may include at least one ear extending beyond the side wall of the housing.

[0030] The hood may include, for example, one or two axes of symmetry.

[0031] Each pin can have a height, measured perpendicular to the inner face, greater than 3mm, for example 4mm.

[0032] Each pawn can have a cross-section in the shape of a cross.

[0033] Each pawl can have a shape of revolution and a cross-section of which the diameter is greater than or equal to 1.5 mm over the entire height of the pawn.

[0034] The hood can be made of plastic material.

[0035] The hood may include a metal sheet covered with an insulating coating.

[0036] The invention also relates to an assembly comprising three devices as described above, the three housings of which are formed from a single piece.

[0037] In such an assembly, the cover can be configured to close off the three housings.

[0038] The invention also relates to a system comprising an inverter, a motor electrical, and an assembly such as described above, in which each conductive bar connects a power module of the inverter to a phase of the electric motor.

[0039] The invention finally relates to a motor vehicle comprising such a system and in which the electric motor is configured to provide all or part of the traction of the vehicle. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other advantages, purposes and particular features of the present invention will become apparent from the following non-limiting description of at least one particular embodiment of the devices and methods of the present invention, with reference to the accompanying drawings, in which: • [Fig.1] is a schematic perspective view of an assembly conforming to an embodiment of the invention; • [Fig.2] is a schematic view of a hood that can be used in one embodiment of the invention; • Fig. 3 is a schematic three-dimensional view of the hood of Fig. 2; • Fig. 4 is a side view of the hood of figures 2 and 3; • [Fig.5] illustrates, according to a schematic cross-sectional view, a device conforming to an embodiment of the invention; • [Fig.6] illustrates, according to a schematic three-dimensional view, a system conforming to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present description is given as a non-limiting example of an embodiment.

[0042] Figure 1 represents an assembly according to an embodiment of the invention, within the framework of a set of conductive bars intended to connect an inverter to an electrical machine. In this case, the assembly comprises three conductive bars 1. Each conductive bar 1 has a first end 2 intended to be connected, for example by welding, to an output conductive bar of a power module of an inverter. Each conductive bar 1 also has a second end 3, intended to be connected, for example by a screw, to a phase of an electric motor.

[0043] In the example shown here, an overmolding 4 is formed around the conductive bars 1, notably to hold them in position, protect them, and insulate them. The overmolding 4 can be made of various plastics. For example, it can be made of polyphenylene sulfide, also known by the acronym PPS (from the English "polyphenylene sulfide").

[0044] This material allows the formation of complex shapes, with very thin thicknesses.

[0045] Alternatively, the hood 12 can be formed from a sheet of metal; for example a A steel sheet with an insulating coating (e.g., plastic). This embodiment provides magnetic shielding, which can ensure reliable current measurement.

[0046] It is important to be able to determine the current flowing in each phase of the motor, therefore in each of the conductive bars 1. The current measurement is implemented as follows. A magnetic core in the shape of a C, referenced as 5 (and more clearly visible in [Fig. 3]), also called the C-core 5, is positioned around the conductive bar 1. The C-core 5 concentrates the magnetic field created by the current flowing through the conductive bar. A sensor, usually a Hall effect sensor, is used to measure the current.

[0047] The C-core and the sensor are advantageously positioned at the output of the inverter, that is to say near the first end 2 of the conductive bar.

[0048] According to the present invention, each C-core is installed in a housing 7. The housing 7 is, in the example shown, formed in one piece with the overmolding 4. The housing 7 is intended to accommodate the C-core 5 and forms a well 6 for receiving the current sensor.

[0049] The housing 7 comprises a base 8 (see [Fig.5]) and a side wall 9. The side wall 9 is substantially perpendicular to the base 8. A receiving volume 10 is thus formed for the C-Core 5, which is surrounded by the side wall 9.

[0050] The C-Core 5 is embedded, at least partially, in a resin 11. The resin generally corresponds to the material commonly referred to by the English term "potting," which may be a polyurethane, epoxy, or silicone resin. This is also referred to as encapsulation or resin coating. Alternatively, the C-Core 5 may be at least partially embedded in an adhesive, for example, a silicone or acrylate adhesive. In the remainder of this description, it is assumed that the C-Core 5 is embedded, in whole or in part, in a resin, but the description applies, mutatis mutandis, to an adhesive.

[0051] The resin is introduced into the housing 7 in liquid or paste form, then polymerizes around the magnetic core in C.

[0052] A device according to the present invention comprises a cover 12, which closes the open face of the housing 7 that is opposite the bottom 8. The cover 12 is shown in [Fig. 1] detached from the rest of the device,

[0053] The hood 12 includes a closing plate 13, which is a substantially flat element that is dimensioned to allow the housing 7 to be closed.

[0054] The cover 12 (in particular the closing plate 13) has an outer face 14 and an inner face 15. The terms "outer" and "inner" refer to the position relative to the housing 7, once the cover 12 is in position to close the housing. In other words, the inner face 15 faces the bottom 8 of the housing 7.

[0055] From a structural point of view, and as can be seen in particular in figures 2, 3 and 4, the hood has the following characteristics, in the embodiment shown.

[0056] The hood has pins 16, here two of them, which protrude from the inner face 15. As can be seen in [Fig.5], the pins 16 are included in the resin 11. This inclusion, total or partial, of the pins 16, creates a solid fixing of the cap 12 in the resin 11, and therefore a solid fixing of the cap 12 vis-à-vis the housing 7. In addition, the pins taking up a certain space in the housing 7, the quantity of resin required to completely fill the receiving volume 10 is reduced, which reduces the amount of resin to be polymerized and therefore the polymerization time.

[0057] The pins 16 advantageously have a height (measured perpendicular to the outer face 14) greater than or equal to 3mm, for example of the order of 4mm.

[0058] When the pins 16 have a shape of revolution, the smallest diameter of the cross-section of the pin is advantageously greater than or equal to 1.5 mm, for example on the order of 2 mm. The smallest diameter of the pin may in particular be on the order of the thickness of the closing plate 13.

[0059] The pins 16 can have various shapes, and be for example cylindrical or truncated conical. They can have a cross-section in the shape of a cross, which increases the contact surface with the resin.

[0060] The pins 16 can be solid or hollow, and may have, for example, an annular cross-section.

[0061] The housing 13 may, by way of example, have a depth of between 7 and 14 mm, for example, approximately 11 mm. The cover 12 is placed on the open face of the housing 7 while the housing 7 is filled with liquid resin 11. To prevent air bubbles from being trapped in the housing, particularly between the surface of the resin 11 and the cover 12, during the installation of the cover, the latter has at least one hole 17 allowing the passage of air (in addition to an elongated orifice 18 through which the conductive bar 1 passes). The hole(s) 17, by allowing the passage of air, promote the polymerization of the resin. The cover advantageously has several holes 17, for example, six holes as in the example shown, which are distributed over the surface of the closure plate 13.The holes 17 are small in size, in order to allow air to pass easily without creating a large opening for the passage of resin or particles into the resin. Circular holes 17 with a diameter between 1mm and 3mm can be used, for example.

[0062] The cover 12 further comprises on its inner face 15 at least one rib 19. The rib 19 is a protrusion on the inner face 15 which, once the cover is in position on the open face of the housing 7, is opposite or even in contact with a flat surface of the C-core 5. This rib 19 (or these ribs) may partially follow the geometry of the C-core, and ensures that the C-core 5 is correctly inserted into the housing 7. If the C-core were, for example, to lift during the introduction of the resin 11 in liquid form into the housing 7, then the rib 19 would correct the insertion of the C-core 5 when the cover 12 is put into position, to bring the C-core 5 back into the correct position.

[0063] In addition, the pins 16 are positioned between the C-core 5 and the side wall 9 when the cover 5 is put in place. This can ensure correct centering of the C-core. This centering function generally complements other centering elements in order to correct any excessive off-centering of the C-core 5 when the cover 12 is put in place.

[0064] Generally, the cover 12 is fixed solely by the resin 11. As explained above, the pins 16 play an important role in this fixing, being embedded in the resin 11. Furthermore, the rib 19 can also be embedded in the resin and contribute to fixing the cover 12. Finally, in some embodiments, the resin can be in contact with the inner face 15, to which it adheres. In this case, the inner face 15 can have a coarse roughness that aids adhesion, i.e., bonding, of the resin. Typically, the average roughness Ra can be on the order of Ra = 3. The inner face may have been treated by plasma treatment. The purpose of the plasma treatment is to obtain a high surface tension, which ensures good adhesion of the resin. A surface tension of around 50mN / m can thus be obtained, compared to 32mN / m with a PPS type plastic cover in the absence of this treatment.

[0065] The cover 12 may also include one or more lugs 20. A lug 20 is an outgrowth which extends laterally from the general contour of the closing plate 13, so as to extend laterally from the side wall 9. The lug or lugs 20, which in the example shown are four in number, provide a grip allowing the correct fixing of the cover 12 to be checked by carrying out a pull-out test, by pulling on the level of a lug 20.

[0066] The hood 12 advantageously comprises one axis of symmetry, or even two axes of symmetry. In the example shown, the hood 12 comprises a first axis of symmetry A, along its length, and a second axis of symmetry B, perpendicular to axis A.

[0067] A symmetrical part, particularly one with two axes of symmetry, is simpler to use with an automated system for positioning. Indeed, it can be installed without regard to its orientation. More precisely, as long as the inner face 15 is correctly positioned towards the inside of the housing 7, and the cover 12 is correctly centered and aligned, it can be positioned in either of the two possible orientations. Furthermore, the centering and alignment of the cover 12 can be achieved by inserting the conductive bar into the elongated opening 18. For this purpose, the elongated opening 18 has a shape that corresponds, within a functional clearance, to the cross-section of the conductive bar 1.

[0068] Figure 6 shows a system according to one embodiment of the invention. This system comprises an inverter 21, and each conductive bar 1 of the device is connected to one phase of an electric motor. An output conductive bar 22 of a Power module 23 of inverter 21 is connected to the first end 2 of the conductor bar 1.

[0069] The connection to be made is thus in the immediate vicinity of the magnetic core C present in the housing 7. This connection can advantageously be made by a weld 24. During welding, a very high temperature is generated at the weld. In addition, small metallic particles can be projected, particularly towards the housing 7. During storage and transport of the parts, they can also come into contact with dust and various particles. This is also the case, more generally, throughout the entire lifespan (from production to the end of use) of the device. The cover 12 provides effective protection for the contents of the housing 7, i.e., the resin and the magnetic core C, against these phenomena.

[0070] The present invention thus proposes a device enabling effective protection of a C-core, and ultimately greater reliability of current measurements performed using this core and adapted sensor. The cover used to seal the housing is attached very simply by the resin in which the C-core magnetic element is at least partially embedded. To do this, the cover is placed on the open face of the housing while the liquid resin has just been introduced. The attachment is ensured by embedding pins on the cover in the resin and, if necessary, by adhesion to other parts of the cover. This simple attachment process can be automated. The configuration of the cover allows for very simple installation.

[0071] The invention finds a preferential application in the connection between an inverter and an electric traction motor of a motor vehicle.

[0072] Nomenclature: • 1: Conductive bar • 2: First end of a conductive bar • 3: Second end of a conductive bar • 4: Overmolding • 5: Magnetic C-core • 6: Well • 7: Accommodation • 8: Background • 9: Side wall • 10: Reception volume • 11: Resin • 12: Hood • 13: Closing plate • 14: Outer face Inner face : Pawn : Hole Elongated orifice : Rib : Ear Inverter : Output conductor bar Power module : Welding

Claims

Demands

1. A device comprising a magnetic core C (5), a conductive bar (1), the magnetic core C (5) being installed around said conductive bar (1), a housing (7) having a base (8) and a side wall (9) defining a receiving volume (10) in which the magnetic core C (5) is received, a resin (11) or an adhesive in the housing (7) and in which the magnetic core C (5) is at least partially included, and a cover (12) closing an open face of the housing (7) opposite the base (8), the cover (12) having a closing plate (13) having an inner face (15) opposite the housing (7), and an outer face (14), the closing plate (13) having an elongated orifice (18) through which the conductive bar (1) passes,the device being characterized in that the cover (12) is fixed by adhesion with the resin (11) or the glue and in that it comprises at least two pins (16) projecting from the inner face (15) of the closure plate (13), which extend between the magnetic core in C (5) and the side wall (9) of the housing (7), and which are at least partly included in the resin (11) or the glue.

2. Device according to claim 1, wherein the hood (12) has at least one hole (17), separate from said elongated orifice (18), formed through the closing plate (13) and allowing a passage of air.

3. Device according to claim 1 or claim 2, wherein the hood (12) has on its inner face (15) a rib (19) opposite or in contact with a surface of the magnetic core in C (5).

4. Device according to claim 3, wherein the rib (19) is in the resin (11).

5. Device according to any one of the preceding claims, wherein the inner face (15) has a roughness greater than that of the outer face (14).

6. Device according to any one of the preceding claims, wherein the hood (12) has at least one ear (20) extending beyond the side wall (9) of the housing (7).

7. Device according to any one of the preceding claims, wherein the hood (12) has one or two axes of symmetry.

8. Device according to any one of the preceding claims, in which Each pawn has a height, measured perpendicular to the inner face, greater than 3mm, for example 4mm.

9. Device according to claim 8, wherein each pin has a cross-section in the shape of a cross.

10. Device according to claim 8, wherein each pin has a shape of revolution and a cross-section having a diameter greater than or equal to 1.5 mm over the entire height of the pin.

11. Device according to any one of the preceding claims, wherein the hood (12) is made of plastic material.

12. Device according to any one of claims 1 to 9, wherein the hood (12) comprises a metal sheet covered with an insulating coating.

13. Assembly comprising three devices according to any one of the preceding claims, wherein the three housings (7) are formed of a single piece and wherein the cover (12) is configured to close the three housings (7).

14. System comprising an inverter (21), an electric motor, and an assembly according to claim 13, wherein each conductive bar (1) connects a power module (23) of the inverter (21) to a phase of the electric motor.

15. Motor vehicle comprising a system according to claim 14, wherein the electric motor is configured to provide all or part of the vehicle's traction.

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