Electric motor comprising a power electronics-carrying circuit board and a cooling plate

Abstract

The invention relates to an electric motor comprising a stator (11) having a plurality of field conductors (12) in the form of bars, and a plurality of power electronics components for controlling the field conductors (12). These power electronics components are arranged on a plurality of printed circuit boards (15). At least one printed circuit board (15) is arranged on at least one cooling plate (16), and the cooling plate (16) is arranged in such a way that the field conductors (12) are mechanically and electrically operatively connected to the cooling plate (16) via the current conductors (18) electrically connected to the field conductors (12). In addition, the cooling plate (16) is segmented into at least two sub-segments (16-1), (16-2) which are electrically insulated from one another, and a separating surface (20) formed from insulation (30) comprises at least two sub-segments (16-1, 16-2) which represent less than 20% of a cooling surface (22). The circuit boards (15) are electrically contacted with the sub-segments (16-1, 16-2) of the cooling plate (16) in order to supply power.

Description

[0001] Description

[0002] ELECTRIC MOTOR WITH A PRINTED CIRCUIT BOARD CARRYING POWER ELECTRONICS AND A COOLING PLATE

[0003] The invention relates to an electric motor with a stator-side bar winding.

[0004] Electric motors can have a bar winding on the stator side. The stator has a series of bars as field conductors instead of wound wire conductors. These bars have a low inductance compared to conventional windings. Therefore, a comparatively high current flow is required to generate a given magnetic field. A motor of this type is described in EP19167289 A1.

[0005] However, due to the low resistance of the rods, this high current flow requires only a comparatively low voltage, for example, 12 V. The low voltage makes it possible to arrange the inverter components used to control the rods at close distances from one another. This allows the power electronics components to be arranged, for example, on one or more printed circuit boards (PCBs) that are positioned close to the electric motor (preferably in the housing of the motor). The rods can be used as mechanical supports for the circuit boards, either directly or via electrically conductive rod-like connecting elements.

[0006] The circuit boards are mounted on cooling plates and contacted individually via electrical busbars. The busbars lie on the circuit boards and are contacted to them via screw connections. The screw connections are also fastened in the cooling plates (mechanically decoupled from them) to ensure secure contact. This gives rise to the problem of insulation between the screw connection and the cooling plate, which must be solved for each individual screw connection using a suitable sleeve. Particularly when a circuit board has to be replaced due to defective individual components, the busbars - usually two - which clamp up to 150 circuit boards and supply them with power have to be unscrewed and then fully insulated and screwed back on.

[0007] The invention is based on the object of providing an electric motor with a stator-side bar winding and integrated power electronics, which requires lower repair costs when replacing circuit boards of the power electronics compared to the prior art.

[0008] The solution to the problem consists in an electric motor with the features of patent claim 1.

[0009] This electric motor includes

[0010] - a stator with a plurality of field conductors designed as bars,

[0011] - a plurality of power electronic components for controlling the field conductors, wherein

[0012] - the power electronic components are arranged on one or more printed circuit boards, and

[0013] - at least one printed circuit board arranged on at least one cooling plate,

[0014] - the cooling plate is arranged in such a way that the field conductors, with current conductors that are electrically connected to the field conductors, are in mechanical operative connection with the cooling plate. (This can be achieved by means of through-holes through the cooling plate. However, the mechanical operative connection can also be made indirectly to the cooling plate, for example via holes in the circuit boards, with the circuit boards partially projecting over the edge of the cooling plate at these holes). The current conductors therefore form current-conducting connecting elements between the field conductors and the circuit boards and ultimately to the power electronics components (including semiconductor switches). Due to the mechanical operative connection, these also have a load-bearing property for the cooling plate, and are electrically insulated from it.

[0015] - The invention is characterized in that

[0016] - the cooling plate is segmented into at least two sub-segments 16-1, 16-2 which are electrically insulated from each other,

[0017] - wherein a separation surface 20 between the sub-segments 16-1, 16-2 is less than 20% of a cooling surface 22 and

[0018] - the circuit boards 15 for the power supply are electrically contacted with the sub-segments 16-1, 16-2 of the cooling plate 16.

[0019] The power supply of the electric motor is therefore initially via the sub-segments of the cooling plate(s) to the circuit boards and the power electronics components arranged thereon and from there via the current conductors to the field conductors of the stator.

[0020] The electric motor described differs from conventional electric motors in that the stator features a series of bars as field conductors instead of wound wire conductors. These bars have a low inductance compared to conventional windings. Therefore, a comparatively high current flow is required to generate a given magnetic field.

[0021] The design of the bar winding results in fundamental advantages in machine operation: Due to the segment-by-segment controllability of the magnetic flux between any two field conductors, far more flexible forms of magnetic fields can be impressed into the machine than would be possible with a distributed winding and its inherent superposition effects. This results in many (control-related) advantages with regard to the running characteristics of the machine. Furthermore, the failure of one phase ((of the control) of a field conductor) has far less severe consequences than would be the case, for example, with a double-three-phase or even a normal three-phase machine. Since these effects can also be very well compensated for by the neighboring phases, with appropriate control the drive power drops almost exclusively by only a small fraction with each phase failure, without significantly affecting the remaining characteristics.

[0022] The advantage of the electric motor described over the state of the art for motors of this type is that the busbars are not arranged on the circuit boards, but rather the cooling plate itself ensures the power supply to the circuit boards. In this way, each circuit board can be removed and replaced individually by loosening the screw connection, which usually also forms the contact with the busbars. This means that repairs do not require the removal of large sections or even the entire assembly of circuit boards. This means that when repairing power electronics, this saves a lot of labor and is therefore cost-effective. Repair costs are significantly reduced.

[0023] Furthermore, this structural design, which consists of dividing the cooling plate into at least two segmented sections and using them for contacting and thus for supplying power, ensures that the assembly of the circuit boards is not hindered, but at the same time the entire contact surface of the circuit boards on the cooling plate can be used as a cooling surface. A larger electrical contact surface to the DC supply (instead of a smaller contact surface to corresponding DC busbars) is also advantageous. Although a metallic busbar sunk into a cooling plate would in principle also be thermally conductive, it does not have a cooling effect because it is electrically and therefore largely thermally insulated from the cooling plate (this insulation is also usually omitted, which is an advantage).This means that once the busbar has heated up, no significant heat is dissipated from it, and it therefore does not function as a cooling plate. The term cooling surface is defined as the surface on which the circuit board rests, at least indirectly, over a large area. In some cases, it may be advisable for technical reasons, e.g. for additional electrical insulation or mechanical damping, to place an intermediate layer or film between the circuit board and the cooling plate. In this context, this is also regarded as the circuit board resting flat on the cooling surface, since the cooling surface is there to absorb heat from the circuit board. The separating surface is the surface which, when viewed perpendicular to the cooling plate, is located between the sub-segments of the cooling plate, and which serves to provide electrical insulation between the sub-segments of the cooling plate.

[0024] It should be noted that, in general, it is not necessary to use exactly two current-supplying potentials for the motor described. It is also advantageous to use duplicated potentials or, for example, three potentials with an intermediate circuit center or double (redundant) intermediate circuits, which require more than two current conductors.

[0025] In one embodiment of the invention, the circuit board is contacted at contact points by means of a fastening means on the cooling plate. The fastening means can preferably be a screw connection. By contacting using a fastening means, two necessary requirements, namely the contacting and the fastening between the cooling plate and the circuit board, can be met with one device, which saves additional technical effort. In addition to a screw connection for contacting, click locks or clamping connections would also be suitable.

[0026] Furthermore, it is advantageous if the cooling plate 16 is thermally connected to a heat sink 38. This allows the heat that is conducted from the components via the circuit boards into the cooling plate to be easily dissipated. The heat sink is particularly preferably designed in the form of a cooling line, which in turn preferably runs through the cooling plate in a horizontal plane relative to the cooling surface.

[0027] Furthermore, the subsegments of the cooling plate are preferably designed in a ring-shaped or ring-sector-shaped manner. This allows for a good combination of good contactability of the circuit boards and good heat dissipation. It is also advantageous if the cooling plate is made of aluminum or copper or an alloy of these metals.

[0028] The printed circuit boards can be circular or ring-sector shaped. Printed circuit boards with this shape can be assembled into a circle or ring and thus arranged at one axial end of the machine, optimally adapted to the shape of the electrical machine, while simultaneously achieving a high degree of modularity.

[0029] The terms "axial", "radial" and "tangential" refer to the axis of the rotor and thus to the corresponding axis of symmetry of the stator. "Axial" describes a direction parallel to this axis, "radial" describes a direction orthogonal to the axis, towards it or away from it, and "tangential" is a direction that is directed in a circle around the axis at a constant radial distance from the axis and at a constant axial position. The expression "in the circumferential direction" is synonymous with "tangential".

[0030] When the terms "axial", "radial" and "tangential" are used in relation to a surface, e.g. a cross-sectional surface, the terms describe the orientation of the normal vector of the surface, i.e. the vector that is perpendicular to the surface in question.

[0031] Further embodiments of the invention and further features are explained in more detail with reference to the following figures. These are purely schematic embodiments that do not represent a limitation of the scope of protection. They show:

[0032] Figure 1 shows an electric motor with cooling plates for cooling circuit boards in side view,

[0033] Figure 2 the electric motor in front view,

[0034] Figure 3 is an enlarged view of Figure 1 in the section of the cooling plates in side view with busbars according to the state of the art,

[0035] Figure 4 shows the same section as in Figure 3 with modified arrangement of the power supply,

[0036] Figure 5 shows a three-dimensional cross-section and section of a cooling plate with indicated circuit board,

[0037] Figure 6 , a plan view of a cooling plate with indicated circuit board,

[0038] Figure 7 , a cross section through a cooling plate through a screw connection,

[0039] Figure 8 shows a cross section through a cooling plate with surface cooling lines,

[0040] Figure 9 shows a cross section through a cooling plate with centrally arranged cooling lines and

[0041] Figure 10 is a three-dimensional representation of a cooling plate with ring-segment-shaped sub-segments.

[0042] Figure 1 shows an isometric view of an electric motor 10 which is an embodiment of the invention.

[0043] The electric motor 10 comprises a stator 11 and a rotor arranged essentially within the stator 11, which is not visible in Figure 1. The rotor is connected in a rotationally fixed manner to a shaft, which is also not shown in Figure 1. The rotor is set in rotation about an axis 9 by electromagnetic interaction between the rotor and an energized stator 11. The rotor is separated from the stator 11 by an air gap.

[0044] In other embodiments, the electric motor 10 can also be an external rotor motor or a bell-shaped armature motor.

[0045] The stator 11 comprises a plurality of rigid and straight conductor bars 12 as field conductors. These conductor bars 12 are connected to one another on the end face 13 facing away in Figure 1 via a short-circuit ring. On the rear side 14 of the electric motor 10, the conductor bars 12 are individually fed by respective inverter modules. Since the electric motor 10 is operated at low voltages due to the conductor bars 12, the inverter modules can be arranged relatively close together on printed circuit boards 15 together with other electronic components (DC-DC converter, rectifier). In this example, the printed circuit boards 15 are ring-sector-shaped and many individual circuit boards 15 together form a ring-shaped circuit board structure. The rigid conductor bars can be made from a metallic rod, for example a copper rod, or from a solid multi-filament conductor.

[0046] While the examples assume that the printed circuit boards (PCBs) carry 15 inverter modules, it is also possible that some of the PCBs carry 15 rectifiers and DC / DC converters.

[0047] Figure 2 shows a plan view of such a circuit board structure. The number of circuit boards 15 shown in Figure 2 is reduced compared to the illustration in Figure 1 and is shown in a greatly simplified manner for better clarity. The actual number of such circuit boards 15 depends on the specific design of the electric motor 10, in particular the number of conductor bars 12. Each of the circuit boards 15 comprises a plurality of power electronics components, in particular semiconductor switches 26.

[0048] Furthermore, some or all of the circuit boards 15 can comprise driver circuits and other electronic components such as capacitors (not shown in the figures). The semiconductor switches 26 are power semiconductors such as IGBTs, MOSFETs or JFETs and, depending on the wiring, can additionally comprise diodes (not shown). The semiconductor switches 26 are wired as half-bridges, for example. A capacitor (not shown) can represent an intermediate circuit capacitor of the half-bridges, for example. The semiconductor switches 26 of a circuit board 15 can be assigned to a single phase or to multiple phases.

[0049] Since the electric motor 10 requires relatively high currents in the conductor bars compared to conventional motors with windings, several inverters are preferably connected in parallel to supply power to them. This can be achieved, for example, by the six circuit board structures shown in Figure 1 on three cooling plates 16 all being connected in the same way to the conductor bars 12 and thus being electrically connected in parallel. This takes advantage of the fact that the conductor bars 12 or connecting elements 18 to the conductor bars 12 penetrate the cooling plates 16 and thus also the circuit boards 15 in the same way at the contact points or, in the case of the outermost cooling plate 16, at least make contact.

[0050] Figure 3 shows a sectional view of the electric motor 10 in an oblique view. Here it can be seen that the connecting elements 18 mechanically support and penetrate the three cooling plates 16. This can also be done indirectly by the circuit boards 15 projecting radially beyond the cooling plates 16 and the connecting elements penetrating the circuit boards in the projecting areas. The connecting elements 18 are connected to the conductor bars 12 via shoes 17. The inverters, which are located on the circuit boards 15 in the areas in which one of the connecting elements 18 penetrates a cooling plate 16, are connected in parallel and together provide the current for the conductor bar 12.

[0051] Figure 3 also shows busbars 32 in the design according to the prior art. These are screwed onto the circuit boards 15 and thus fasten them to the cooling plate 16. If a circuit board 15 is defective and has to be replaced, the busbars 32 have to be removed with all the individual screw connections to the circuit boards 15. This means that if there are, for example, one hundred circuit boards 15 with three screw connections each, three hundred screw connections have to be loosened. This effort is reduced by the design according to Figure 4, and further shown schematically and enlarged in Figures 5 to 10.

[0052] Figure 4 shows the same arrangement as Figure 3 with regard to the arrangement of the cooling plates 16 with respect to the electric motor 10 and the motor axis 9, but the contacting of the printed circuit boards 15 is effected by partial segments 16-1 and 16-2 of the cooling plate 16.

[0053] Figure 5 shows a cross-section and a section of a cooling plate 16, as shown in Figure 4, for example. This cooling plate 16 is divided into two sub-segments, a first sub-segment 16-1 and a second sub-segment 16-2. The two sub-segments 16-1 and 16-2 are electrically insulated from one another by an insulation 30. If the cooling plate 16 is viewed perpendicular to the motor axis 9, the sub-segments 16-1 and 16-2 as well as the insulation 30 form a flat surface. The surfaces of the sub-segments 16-1 and 16-2 form a cooling surface 22. In plan view, this cooling surface 22 is divided by a separating surface 20, which is formed by the insulation 30. For advantageous heat dissipation of the amount of heat that is introduced from the printed circuit boards 15, it is expedient if the area of ​​the separation surface 20 is as small as possible; it should amount to at most 20% of the area of ​​the cooling surface 22.Particularly advantageously, the separation area 20 should be less than 10%, particularly advantageously less than 5% of the cooling area 22.

[0054] In Figures 5 and 6, the positioning of a printed circuit board 15 is indicated by a dashed line. Contact points 24 are also shown, via which electrical contact is established between the current-carrying cooling plate 16 and the printed circuit board 15, as well as the power electronics components arranged thereon.

[0055] 5 and 6, the sub-segments 16-1 and 16-2 are designed in the form of two concentric rings. It should be noted that other possible segmentations on the cooling plate 16 may also be expedient, for example as shown in Figure 10. In Figure 10, the sub-segments 16-1, 16-2, 16-3 are divided into ring-segment-shaped units. They have a similar geometric design to that of the printed circuit boards 15 usually and advantageously. It may be expedient for the printed circuit boards 15 to each overlap two sub-segments 16-1 to 16-2 in such a way that, as indicated in Figure 10, contact is made with a respective sub-segment having a different electrical potential.It should be noted that, depending on the electrical wiring, several current-conducting contacts with different potentials may be useful and / or necessary, even when the circuit boards are supplied with direct current.

[0056] The cooling plate 16, which is segmented into its sub-segments 16-1, 16-2 and / or 16-3, is preferably made of aluminum or an aluminum alloy or of copper or a copper alloy. These metals are easy to manufacture, conduct electricity very well and have high thermal conductivity. The cooling plate can therefore perform its function both as a current conductor and as a heat sink. The insulation 30, on the other hand, is preferably made of an insulating plastic. The insulation 30 can also be designed at least partially as an empty space, with air acting as the insulating medium.

[0057] 7 to 9 show cross-sectional views through the cooling plate 16, as shown in Figure 6 and Figure 5, where they are marked with the sections VI I, VI II and IX. In Figure 7, in addition to the sections through the sub-segments 16-1 and 16-2, which are separated from one another by the insulation 30 and which together form the cooling plate 16, the fastening of the printed circuit board 15 on the cooling plate 16 is shown schematically. A fastening means 34, which is designed in the form of a screw connection 36, is provided at a contact point 24. The screw connection 36 is a fastening means 34 which ensures good contact between the current-carrying cooling plate 16 and the printed circuit board 15. In principle, riveted connections can also be expedient, but these make the printed circuit boards 15 difficult to detach in the event of damage.However, snap connections similar to a quick release on a bicycle saddle can also provide a practical way of fastening the circuit board to the cooling plate with good contact.

[0058] In Figures 7 to 9, cross-sectional areas of equal size are shown for the sub-segments 16-1 and 16-2. However, this is not absolutely necessary. It is advantageous if both sub-segments 16-1 and 16-2 are connected to a heat sink 38. In Figures 8 and 9, the heat sink 38 is designed in the form of cooling lines 40. However, a heat sink can also be physical contact with another good heat conductor which conducts the heat away from the cooling plate 16 and out of the motor 10. A heat sink 38 can also be a sufficient distance between the cooling plates 16, through which a fluid, in particular air, flows. Figures 8 and 9 show possible designs for the arrangement of cooling lines 40 through the cooling plate 16. In Figure 8, the cooling line 40 is embedded in grooves in the cooling surface 22. The cooling lines 40 have, as shown in Figure 8, a rectangular cross-section.

[0059] In Figure 9, cooling lines 40 are also introduced into the cooling plate 16, but they are located in the center of the cooling plate 16. Such cooling lines 40 can be produced either by a sand casting process with a lost core, in particular as an aluminum sand casting. Alternatively, the cooling plate can also be divided in a horizontal plane 42, so that the cooling lines are also cut out there in the form of grooves, which result in a closed cooling line 40 when the horizontally divided cooling plate 16 is joined together. The horizontally divided cooling plates can then be joined together during production by means of a soldering process or sealed by circumferential seals. The second alternative would make it possible to create further sub-segments (not shown) which could provide a further independent, current-carrying potential.

[0060] The advantage of the described electric motor 10 and the described arrangement of the power electronics on cooling plates 16 and printed circuit boards 15 is that the cooling plate 16, which also serves to dissipate heat from the power electronic components in the prior art, is simultaneously used to make electrical contact with them. This has the advantage that no additional components in the form of power conduction rails are required, and that these rails do not have to be arranged in a complex manner so as to be electrically insulated from cooling lines. In addition, these power conduction rails do not lie above the printed circuit boards 15 (seen from the direction of view of the cooling plate 16), so that if one printed circuit board 15 is defective, all the contacts on the other printed circuit boards 15 do not have to be removed.The described arrangement therefore requires less assembly effort and fewer parts both during the initial assembly of the electric motor 10 and during a possible repair.

[0061] Reference symbol

[0062] 8 Stator / rotor block

[0063] 9 Motor axle

[0064] 10 Electric motor

[0065] 11 Stator

[0066] 12 conductor bars

[0067] 13 Front side

[0068] 14 Back

[0069] 15 circuit boards

[0070] 16 Cooling plate

[0071] 16- 1 first sub-segment cooling plate

[0072] 16-2 second sub-segment cooling plate

[0073] 17 shoe

[0074] 18 Connecting element

[0075] 20 Separation area

[0076] 22 Cooling surface

[0077] 24 contact points

[0078] 26 semiconductor switches

[0079] 28 screw connection

[0080] 30 I insulation

[0081] 32 Busbar State of the Art

[0082] 34 fasteners

[0083] 36 screw connection

[0084] 38 heat sink

[0085] 40 cooling line

[0086] 42 horizontal plane

Claims

Patent claims 1. Electric motor (10) with: - a stator (11) with a plurality of field conductors (12) designed as bars, - a plurality of power electronic components for controlling the field conductors (12), wherein - the power electronic components are arranged on one or more printed circuit boards (15), - at least one circuit board (15) is arranged on at least one cooling plate (16), - the cooling plate (16) is arranged so that the field conductors (12) current conductors (18) electrically connected to the field conductors (12) are in mechanical operative connection with the cooling plate (16), characterized in that - the cooling plate (16) is segmented into at least two sub-segments (16-1), (16-2) which are electrically insulated from each other, - wherein a separation surface (20) between the sub-segments (16-1), (16-2) is less than 20% of a cooling surface (22) and - the circuit boards (15) for the power supply are electrically contacted with the sub-segments (16-1), (16-2) of the cooling plate (16).

2. Electric motor according to claim 1, characterized in that the contacting of the printed circuit board (15) at contact points (24) by means of a fastening means (34) on the cooling plate (16).

3. Electric motor according to claim 2, characterized in that the fastening means (34) is designed in the form of a screw connection (36).

4. Electric motor according to one of the preceding claims, characterized in that the cooling plate (16) is in thermal connection with a heat sink (38).

5. Electric motor according to claim 4, characterized in that the heat sink (38) is designed in the form of a cooling line (40).

6. Electric motor according to claim 5, characterized in that the cooling line (40) passes through the cooling plate (16) in a horizontal plane (42).

7. Electric motor according to one of the preceding claims, characterized in that the sub-segments (16-1), (16-2) are ring-shaped or ring-sector-shaped.

8. Electric motor according to one of the preceding claims, characterized in that the cooling plate (16) is made of aluminum or copper or of an alloy of these metals.

9. Electric motor according to one of the preceding claims, characterized in that the printed circuit boards (15) are designed in the shape of a circle or ring sector.

10. Electric motor according to one of the preceding claims, characterized in that the cooling plate (16) is arranged perpendicular to the axis (9) of the electric motor (10).

11. Electric motor according to one of the preceding claims, designed to control each of the field conductors (12) with a separate phase.

12. Electric motor according to one of the preceding claims, in which the inverters are designed to generate an alternating voltage with an amplitude of 200 V or less, in particular 150 V or less, in particular 50 V or less.

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