Electric motor

Abstract

An electric motor with stator-side field conductors in the form of bars comprises a number of inverters for controlling the bars, wherein: the power components of the inverters are mounted on one or more circuit boards; the circuit boards are mounted on at least one cooling plate; and the cooling plates are attached directly to the bars or to bar-shaped current conductors attached to the bars. The bars have inner cooling channels or heating tubes in order to carry off heat so that heat is extracted from the bars in the region of the cooling plates.

Description

[0001] Description

[0002] electric motor

[0003] The invention relates to an electric motor with field conductors designed as bars on the stator side.

[0004] Electric motors can be designed so that the stator has a series of bars as field conductors instead of wound wire conductors. The bars have a low inductance compared to conventional windings. Therefore, a comparatively high current flow is required to generate a given magnetic field.

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

[0006] In addition to the high heat loss of the electrical and electronic components caused by the high currents, an electric motor designed in this way also features a high packing density of the electrical and electronic components. Their direct connection to the stator / rotor block via the rods causes further heat input from the stator / rotor block. This disadvantageously results in considerable cooling effort for the electrical and electronic components on the circuit boards.

[0007] The object of the invention is to provide an electric motor that mitigates the aforementioned disadvantage. This object is achieved by an electric motor having the features specified in claim 1.

[0008] The electric motor according to the invention comprises a stator with a plurality of field conductors designed as a bar and an inverter with one or more parallel power units for each of the field conductors for controlling them, wherein the inverter comprises a controller for generating control signals for the power units.

[0009] The output stages of the inverter are arranged on a plurality of printed circuit boards and the printed circuit boards are arranged on at least one cooling plate, wherein the cooling plate is arranged in such a way that the field conductors or current conductors arranged on the field conductors and extending them axially are in mechanical operative connection with the cooling plate.

[0010] Finally, at least one cooling device is provided which comprises a fluid line which is guided at least in sections within one of the field conductors and / or current conductors.

[0011] The electric motor according to the invention advantageously features improved heat dissipation for the field conductors thanks to the cooling device. As a result, a lower heat flow reaches the cooling plates and the electronics arranged on the cooling plates, in particular the inverters. This, in turn, allows for a reduction in the cooling effort in the area of ​​the cooling plates and the electronics.

[0012] The field conductors or current conductors preferably act as mechanical supports for the cooling plates and are therefore in mechanical connection with them. It is possible for the field conductors or current conductors to penetrate the cooling plate and the circuit board. Advantageous embodiments of the electric motor according to the invention emerge from the dependent claims. The embodiment of the independent claims can be combined with the features of one of the subclaims or, preferably, with those of several subclaims. Accordingly, the following additional features can be provided:

[0013] The fluid lines can be water lines. Water is a standard coolant and can be supplied from outside the electric motor, for example, in a factory, so lines suitable for water are appropriate.

[0014] The electric motor can be designed to use an electrically conductive fluid as a coolant, wherein the specific conductivity is at least IO -2 S / m, in particular at least 1 S / m. If the cooling fluid is electrically conductive, this provides an additional current path in the fluid line that would otherwise not be available. As a result, for a given current flow through the field conductor or current conductor, the cross-section of metallic conductor, for example copper, that must be provided for the current is reduced, thus saving material and weight.

[0015] The electric motor can be designed to use air as the cooling fluid. Compared to other media, air has the advantage of requiring minimal structural requirements, since it is not enclosed and sealed off from the components to be cooled. Instead, air can be routed through open cooling channels and is freely available.

[0016] The electric motor can have a pump for a cooling fluid. If the cooling fluid is not supplied from outside, it is advantageous if the electric motor is designed in such a way that a fluid circulation can be generated which ensures heat dissipation through material movement. If the motor has a large number of field conductors, for example more than 50 or even more than 100 field conductors, several pumps can also be present. The electric motor can be designed in such a way that a fluid line is provided for each of the field conductors and / or current conductors and is routed at least sectionally within the field conductor and / or current conductor. It is expedient to provide heat dissipation for each of the field conductors or current conductors because, when the electric motor is in operation, the field conductors or current conductors are evenly exposed to heat and thus each of the field conductors or current conductors contributes more or less equally to the heat transport to the cooling plates.

[0017] It is advisable to locate an area in which the fluid line is routed in the field conductor and / or current conductor axially between a cooling plate and the axial beginning of the rotor. Furthermore, it is advisable to dissipate heat in this area in order to reduce the heat input from the rotor area, i.e., the drive system, into the electronics, i.e., the area of ​​the cooling plates and circuit boards.

[0018] If current conductors are present, they are conveniently connected to the field conductors by means of a shoe, whereby the fluid line can also be routed within the shoe. The shoe serves as a permanent connection between the field conductors and the current conductors. The field conductors belong to the drive side of the electric motor, and the current conductors contact the electronics on the circuit boards and support the cooling plates and circuit boards.

[0019] The electric motor can have a short-circuit ring for electrically connecting the field conductors. The fluid lines for at least two of the field conductors can be connected to one another in the short-circuit ring. This advantageously results in the fluid lines being connected in series on one side of the electric motor, so that the inflow and outflow are on one side of the electric motor. It is expedient to connect the fluid lines together in pairs in the short-circuit ring. If the fluid lines on the front side of the electric motor are connected together in pairs in the short-circuit ring, it can be advantageous to also connect some of the fluid lines together on the back of the electric motor. The fluid lines are expediently connected in blocks of at least two fluid lines in such a way that the resulting connected fluid lines run in a meandering shape through the stator.This reduces the number of inlets and outlets, thus simplifying the design of the electric motor. In principle, the number of inlets and outlets can be reduced to one by connecting all fluid lines in series. In certain motor designs, it may be expedient to use more than one inlet and outlet, i.e., to connect the fluid lines in series only in blocks.

[0020] It is possible for combined fluid lines to be spaced from one another in such a way that they do not belong to adjacent conductor bars. For example, the fluid line of every nth conductor bar can be connected in series, where n is at least two. In the case of n = 2, a fluid line of a first conductor bar is therefore connected to that of the next but one (third) conductor bar. There can then, for example, be n separate fluid channel paths made up of combined fluid lines. This advantageously ensures that if one of the fluid channel paths fails, the lack of cooling does not affect a contiguous block of conductor bars, but is distributed evenly over the circumference of the electric motor.

[0021] The fluid line can be formed at least partially by a cavity or bore in the field conductor and / or power line. In this case, the fluid line essentially has no material of its own, as it is not a separate component. Alternatively, the fluid line can be a separate component. In this case, the fluid line can be made of a metallic material, in particular metallic. This advantageously allows the fluid line itself, and possibly also the cooling fluid, to serve as an electrical conductor.

[0022] The fluid line can also comprise a ceramic material, in particular be made of a ceramic material. Ceramic materials are heat-resistant, chemically resistant, and electrically insulating, making them advantageous in certain electric motor designs.

[0023] The fluid line can be a heat pipe or thermosiphon. It is then preferably arranged completely within one of the field conductors and / or current conductors. The extremely high thermal conductivity of a heat pipe results in strong heat dissipation of the field conductor or current conductor in the area of ​​the evaporator side of the heat pipe. The evaporator side of the heat pipe is preferably arranged in the area of ​​the cooling plates and circuit boards or between these and the stator / rotor block. This primarily prevents or reduces waste heat from the stator / rotor block from additionally heating the cooling plates and circuit boards via the field conductors. The condenser side of the heat pipes can be arranged away from the stator / rotor block and beyond the cooling plates. Alternatively, the condenser end can also be arranged in the area of ​​a short-circuit ring of the electric motor. The heat pipe can also extend into the short-circuit ring.

[0024] In the area of ​​the condenser end of the heat pipe, it is expedient to enable good heat dissipation, for example by providing cooling fins. If the condenser end of the heat pipe is located in the area of ​​the short-circuit ring, the short-circuit ring can, for example, be made of laminated metal, with the individual laminates being able to be spaced apart. This gives the short-circuit ring a large surface area and thus enables efficient heat dissipation. This can be supported by forced air movement, for example by an internal or external fan. The electric motor can have a plurality of printed circuit boards. In particular, a plurality of separate printed circuit boards can be mounted on a cooling plate. The power electronics used can be modularized by distributing them across a plurality of printed circuit boards.Thus, a large number of converters can be provided using a variety of similar printed circuit boards, thereby improving manufacturing in terms of scrap.

[0025] The circuit boards can be circular or ring-sector shaped. The circuit boards can therefore be arranged in a circle or ring that encloses the axis of the electric motor. Circuit boards with this shape can be assembled to form a circle or ring and thus arranged at one axial end of the machine in an optimal way to match the shape of the electrical machine, while at the same time achieving a high level of modularity. The circuit boards can therefore be arranged axially offset to the stator and rotor to save space and form an integral part of the electric motor. In this way, it is also possible to arrange several cooling plates with circuit boards axially offset to one another and thus, for example, to connect inverters arranged at the same azimuthal location in parallel.

[0026] The cooling plate is preferably arranged perpendicular to the axis of the electric motor. In this way, the cooling plate with the circuit boards can be arranged at an axial end of the electric machine in a space-saving manner. A plurality of cooling plates can also be arranged axially offset and close to one another. Furthermore, with such an arrangement, a uniform distance is maintained between the cooling plate and the power electronics and the rods that form the field conductors, thereby simplifying the contacting of the rods.

[0027] It is particularly advantageous if each field conductor is controlled by its own phase. A phase is defined as an AC voltage supply that is phase-shifted by an angle other than zero relative to all other phases used in the electric motor. In this case, a separate inverter is advantageously provided for each field conductor, which controls only this field conductor.

[0028] The inverters can be 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. The voltage generated in this way is the voltage applied to the field conductors, i.e. the stator bars. This comparatively low voltage makes it possible for the components of the inverter to be arranged very close to one another. Distances of around 2 mm can be used between the components such as the power semiconductor switches, which results in a high packing density of the electronic components and the possibility of arranging a large number of inverters in a comparatively small space. This in turn makes it possible to use a large number of phases with little space required, in particular a number of phases that corresponds to the number of stator bars.With a correspondingly high number of stator bars, 48, 72 or even 120 phases can be used.

[0029] The terms "axial", "radial" and "azimuthal" 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 "azimuthal" 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.

[0030] If 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. The electric motor can be advantageously used in applications where a high output of 10 kW or more, in particular 100 kW or more, in special designs 1 MW or more, is required, which can be controlled over a wide torque and power range. The electric motor is also advantageous where a compact design is required. Examples of advantageous areas of application are ship propulsion from small boats to large ships, motor vehicles, pumps, fans, centrifuges in the industrial sector, transport and the food industry.

[0031] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show schematically:

[0032] Figure 1 shows an electric motor with power components arranged on circuit boards supported by cooling plates in an oblique view,

[0033] Figure 2: Front view of circuit boards arranged on a cooling plate,

[0034] Figure 3 shows a section of the electric motor in an oblique view with cooling plates with printed circuit boards,

[0035] Figure 4 a sectional view of a conductor bar with a cooling plate pushed on and with a fluid channel and hose connection,

[0036] Figure 5 is a sectional view of a conductor bar with three cooling plates pushed on and with fluid channel and hose connection,

[0037] Figure 6 shows the routing of fluid channels on the front and back of the electric motor, Figure 7 shows a sectional view of the electric motor with heat pipes as fluid channels,

[0038] Figure 8 shows a section of the front side of the electric motor with a laminated short-circuit ring.

[0039] Figure 1 shows an isometric view of an electric motor 10 which is an exemplary embodiment of the invention. The electric motor 10 comprises a stator 11 and a rotor which is essentially arranged in the stator 11 and 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 of the rotor with an energized stator 11. The rotor is separated from the stator 11 by an air gap. In other embodiments, the electric motor 10 can also be an external rotor motor or a bell-shaped armature motor.

[0040] 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 38. On the rear side 14 of the electric motor 10, the conductor bars 12 are individually fed by associated 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 printed circuit boards 15 together form a ring-shaped circuit board structure.

[0041] While it is assumed in the examples that the circuit boards 15 carry at least the power components of inverters, it is also possible for some of the circuit boards 15 to carry rectifiers and DC / DC converters. Figure 2 shows a plan view of such a circuit board structure. The number of circuit boards 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 actual design of the electric motor 10, in particular the number of conductor bars 12. Each of the circuit boards 15 comprises a plurality of semiconductor switches 422. The semiconductor switches 422 together form power components of inverters which provide an AC voltage for the conductor bars 12.

[0042] 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 422 are power semiconductors, such as IGBTs, MOSFETs or JFETs, and can additionally comprise diodes not shown, depending on the wiring. The semiconductor switches 422 are wired as half-bridges, for example. A capacitor not shown can represent, for example, an intermediate circuit capacitor of the half-bridges. The semiconductor switches 422 of a circuit board 15 can be assigned to a single phase. In an electric motor 10 with a large number of field conductors 12 and a corresponding number of phases, it is advantageous if one circuit board 15 carries the power components for several phases.

[0043] The printed circuit boards 15 further comprise contact points 421 to which the conductor bars 12 are connected. The printed circuit boards 15 are supported by disc-shaped cooling plates 16, wherein the cooling plates 16 can be covered with printed circuit boards 15 on both sides for better space utilization.

[0044] Since relatively high currents are required in the conductor bars of the electric motor 10, several power units 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 printed circuit boards 15 in the same way at the contact points or, in the case of the outermost cooling plate 16, at least contact them.

[0045] 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. The connecting elements 18 are connected to the conductor bars 12 via shoes 17. The output stages, 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. In the structure shown in Figure 3 it can be seen that two of the connecting elements 18 each pass through a circuit board 15. Thus each of the boards carries the output stages for two phases of the electric motor 10. In other variants for the electric motor 10, a single circuit board 15 can also carry just one phase or three or more phases, with the same number of connecting elements 18 passing through the circuit board 15.

[0046] The stator / rotor block 8 of the electric motor 10 and the electronics on the printed circuit boards 15 generate heat. The conductor bars 12 and the connecting elements 18 not only conduct electricity but also act as a thermal bridge between the two components. However, it is particularly important on the electronics side that the additional heat input is not too great, as the electronic components must not exceed a temperature of approximately 80°C for long. However, increased cooling in the area of ​​the printed circuit boards is complex. Figure 4 shows a sectional view of a section of the electric motor 10. The sectional view shows two printed circuit boards 15 which are arranged on both sides on a cooling plate 16. The arrangement in Figure 4 corresponds to that in Figures 1 to 3. The sectional view in Figure 4 therefore only shows two of the circuit boards 15 in the ring structure formed by the printed circuit boards 15.The cooling plate 16 is slid onto a conductor bar 12 and is supported by the conductor bars 12. To facilitate its sliding onto the conductor bar 12, the bar is tapered towards the end. A metallic sleeve 25 creates an enlarged conductor cross-section between the circuit boards 15, i.e., the front and back of the cooling plate 16, in the region of the taper. The cooling plate and the circuit boards 15 can be secured, for example, by means of a nut 26. For this purpose, it is expedient if the conductor bar 12 has an external thread in the end region.

[0047] The conductor bars 12 each comprise a fluid channel 20, for example in the form of a bore. The fluid channel 20 is continuous and ends at the outer end of the conductor bar 12. A hose connection 23 can be attached there, which establishes a connection to a hose 24. The hose 24 and the fluid channel 20 allow a cooling fluid, for example air or water, to flow through the conductor bars 12 and thus dissipate heat. It is possible to lead the fluid channel 20 out of the conductor bar 12 at a different point in order to create a second connection, i.e. a drain.

[0048] The structure shown in Figure 4 can be extended in order to connect more than one cooling plate 16. A corresponding structure is shown in Figure 5. In this embodiment, the end of the conductor bar 12 has a recess 26 towards the end which, in this example, has a larger diameter than the fluid channel 20. The recess 26 is provided with an internal thread. A threaded rod 27 is screwed into the recess 26. The threaded rod 27, in turn, has a fluid channel 20 which, when screwed in, continues the fluid channel 20 of the conductor bar 12. In the example in Figure 5, a series of three cooling plates 16 with the respective circuit boards 15 is then pushed onto the threaded rod 27. In order to ensure current conduction at the correct distances between the circuit boards 15 under the pressure required for contacting and also electrical conduction, sleeves 25, 28 are inserted.At the end of the threaded rod 27, as in the embodiment according to Figure 4, a hose connection 23 is arranged, which connects the fluid channel 20 to a hose 24.

[0049] An advantageous embodiment for creating a return channel for the flow of the cooling fluid is shown in Figure 6. Figure 6 shows, in a highly simplified form and omitting the cooling plates 16 and circuit boards 15, the electric motor 10 with the stator / rotor block 8 penetrated by the conductor bars 12 of the stator 11. The conductor bars 12 open at one end into a short-circuit ring 38 connecting them. The short-circuit ring 38 is designed such that it, in turn, has fluid channels 20 which are designed such that each of them connects the fluid channels 20 of two - in the simplest case, adjacent - conductor bars 12 to one another. In this way, a flow is realized in which a first conductor bar 12 represents an inflow, into which the cooling fluid enters on the back 14 of the electric motor 10, and an adjacent conductor bar 12 represents the outflow, from which the cooling fluid also exits on the back of the electric motor 10.The hoses 23 at the inlet and outlet can be brought together at another point to create a cooling circuit. At this point, the heat can be dissipated to the environment via a heat exchanger or heat sink. It is possible for the aforementioned elements to be designed as part of the electric motor 10. Alternatively, it is also possible for the cooling circuit to already be present at the installation location of the electric motor 10, independently of the electric motor 10, and for the electric motor 10 to be connected to it together with other devices. Since all conductor bars 12 are heated equally from the side of the stator / rotor block 8 and are equally connected to the circuit boards 15, it is expedient to provide a fluid channel 20 for each of the conductor bars 12. However, in certain embodiments of the electric motor 10, the number of conductor bars 12 is high, for example 48, 72, or even 120.In the latter case, there are thus 60 outflows and 60 inflows that must be connected or merged elsewhere and reached for water flow, for example by a pumping system. Therefore, for certain embodiments of the electric motor 10, it is advantageous to partially connect the fluid channels on the rear side 14 as well, as indicated in Figure 6. For this purpose, the connected hose 24 is led directly to another conductor bar 12 and also connected there. In this case, it is expedient to connect different pairs of conductor bars than is the case in the short-circuit ring 38 in order to achieve a meandering guidance of the cooling fluid. In this way, the cooling fluid can be guided through 4, 6, 8 or more of the conductor bars 12 with a single inflow and a single outflow, thereby simplifying the structure.Depending on the cooling requirements, all conductor bars can be combined into a single cooling fluid path, or half, one third or a division into any other desired fractions.

[0050] It is particularly advantageous if a cooling fluid path formed by several series-connected fluid channels comprises the fluid channels of conductor bars that are separated in the azimuthal sequence by one, two, or more intermediate conductor bars. If the conductor bars are consecutively numbered azimuthally, then, for example, a first cooling fluid path can comprise the fluid channels of conductor bars 1, 5, 9, 13, 17..., while a second cooling fluid path can comprise the fluid channels of conductor bars 2, 6, 10, 14, 18..., a third cooling fluid path can comprise those of conductor bars 3, 7, 11, 15, 19..., and a fourth cooling fluid path can comprise those of conductor bars 4, 8, 12, 16, 20.... With these four cooling fluid paths, all fluid channels are part of one cooling fluid path. In other words, the cooling fluid paths are intertwined.If such a cooling fluid path fails due to a technical defect, it does not affect a contiguous block of conductor bars; instead, the cooling loss is advantageously distributed evenly across the conductor bars. The symmetry of the cooling is thus maintained.

[0051] In the examples described so far, the fluid channels are always designed as bores or cavities in the respective elements. Alternatively, it is also possible to form the fluid channels as separate components and to incorporate them, for example, into the conductor bars. Such fluid channels therefore represent separate components. They can, for example, be ceramic, which enables electrical insulation from the conductor bar 12. In alternative embodiments, the fluid channel can also be made of other materials, including metallic materials, for example. In this case, electrical conduction from the conductor bar 12 to other elements must be prevented, for example by using plastic hoses for water guidance.

[0052] As an alternative to open fluid channels 20 through which a cooling fluid flows in one direction, the fluid channels 20 within the conductor bars 12 can also be closed off and designed as heat pipes 30. Such a design is illustrated in Figure 7. Figure 7 shows the electric motor 10 in side view with the stator / rotor block 8 and the conductor bars 12. Furthermore, two cooling plates 16 with printed circuit boards applied on both sides are arranged on the conductor bars 12 on the rear side 14 of the electric motor.

[0053] The heat pipes 30, 31 essentially run along the entire length of the conductor bars. They are arranged such that their evaporator-side ends 31 lie in the area between the stator / rotor block 8 and the cooling plate(s) 16. As a result, the heat is mainly removed from this area, i.e., the waste heat from the output stages of the inverter is dissipated, and waste heat from the stator / rotor block 8 is prevented from contributing to the heating of the output stages on the circuit boards 15. The heat pipes 30 can, for example, be copper-water heat pipes.

[0054] The condenser-side end 32 of the heat pipes 30 can, on the one hand, be located on the rear side 14 of the electric motor 10 at an end of the conductor bars 12 facing away from the stator / rotor block 8. On the other hand, the condenser-side end of the heat pipes 30 can also be located in the region of the short-circuit ring 38. In both cases, recooling of the heat pipes 30 is supported at their condenser-side end, for example, by cooling fins as an air heat exchanger or another type of heat exchanger. A corresponding embodiment is shown in Figure 8.

[0055] Figure 8 shows a section of the end face 13 of the electric motor 10. Part of the stator / rotor block 8 is shown, as well as the conductor bars 12 protruding from it, which terminate in the short-circuit ring 38. The conductor bars 12 contain heat pipes 30, the capacitor-side end of which lies in the region of the short-circuit ring 38. The short-circuit ring 38 itself is formed by spaced-apart individual sheets 39 in the embodiment of Figure 9.

[0056] In alternative embodiments not shown in Figure 9, the short-circuit ring 38 can also be formed from axially assembled individual laminations or simply be a solid ring. It is preferably bonded to the conductor bars by the same high-pressure process used to fix the waveguides in the stator core.

[0057] In an embodiment with spaced-apart individual sheets 39, as shown in Figure 8, the short-circuit ring 38 has a significantly larger surface area compared to a solid short-circuit ring. This surface serves as a heat sink for the heat pipes 30 in the conductor bars 12. Furthermore, this embodiment can also be advantageous for avoiding eddy currents. A fan 41 arranged radially inside this short-circuit ring 38 of the stator 11 on the motor shaft 7 generates a radial cooling air flow. This flow passes through the spaces between the individual sheets 39 and ensures improved heat dissipation from the short-circuit ring 38.

[0058] The cooling of the short-circuit ring 38 can be open (heat exchange with the ambient air, for example, via air slots in the stator) or as a closed cooling circuit with a secondary cooling device. For this purpose, air-to-air cooling units via tube or plate coolers, or air-to-liquid cooling units via jacket or top-mounted coolers, can be used, for example.

[0059] Reference symbol list

[0060] 7 Motor shaft

[0061] 8 Stator / Rotor Block

[0062] 9 Motor axle

[0063] 10 Electric motor

[0064] 11 Stator

[0065] 12 ladder rod

[0066] 13 Front side

[0067] 14 Back

[0068] 15 circuit board

[0069] 16 Cooling plate

[0070] 17 shoe

[0071] 18 Connecting element

[0072] 20 fluid channel

[0073] 23 Hose connection

[0074] 24 hose

[0075] 25 , 28 sleeve

[0076] 26 recess

[0077] 27 threaded rod

[0078] 38 Short final ring

[0079] 30 heat pipe

[0080] 31 evaporator-side end

[0081] 32 capacitor side end

[0082] 39 sheet metal

[0083] 41 fans

[0084] 421 contact points

[0085] 422 Haiblei ter schal ter

Claims

Patent claims 1. Electric motor (10) with: - a stator (11) with a plurality of field conductors (12) designed as a bar, - an inverter with one or more parallel power units for each of the field conductors (12) for controlling them, wherein the inverter comprises a controller for generating control signals for the power units, wherein - the output stages of the inverter are arranged on a plurality of printed circuit boards (15), - the circuit boards (15) are arranged on at least one cooling plate (16), - the cooling plate (16) is arranged in such a way that the field conductors (12) or current conductors (18) arranged on the field conductors (12) and extending them axially are in mechanical operative connection with the cooling plate, - at least one cooling device is provided which comprises a fluid line (20) which is guided at least in sections within one of the field conductors (12) and / or current conductors (18).

2. Electric motor (10) according to claim 1, wherein a fluid line (20) is provided for each of the field conductors (12) and / or current conductors (18) and is guided at least in sections within the field conductor (12) and / or current conductor (18).

3. Electric motor (10) according to one of the preceding claims, in which a region (19) in which the fluid line (20) is guided in the field conductor (12) and / or current conductor (18) lies axially between a cooling plate (16) and an axial beginning of the stator / rotor block (8).

4. Electric motor (10) according to one of the preceding claims, which has a short-circuit ring (38) on the side of the electric motor (10) facing away from the cooling plates (16) for electrically connecting the field conductors (12) and in which the Fluid lines (20) for at least two of the field conductors (12) are connected to one another in the short-circuit ring.

5. Electric motor (10) according to claim 4, wherein the fluid lines (20) for at least two of the field conductors (12) are connected to one another on a side of the electric motor facing away from the short-circuit ring (38).

6. Electric motor (10) according to one of the preceding claims, wherein the fluid line (20) is partially formed by a threaded rod (27) which is screwed into one end of a field conductor (12), the fluid line (20) being continued in the field conductor (12).

7. Electric motor (10) according to claim 6, in which one or more cooling plates (16) are pushed onto the threaded rod (27) alternately with elements for axial positioning, in particular spacer sleeves (25, 28).

8. Electric motor (10) according to one of the preceding claims, wherein the fluid line (20) comprises a metallic material, in particular consists of a metallic material.

9. Electric motor (10) according to one of the preceding claims, wherein the fluid line (20) is formed by a cavity or bore in the field conductor (12) and / or current conductor (18).

10. Electric motor (10) according to one of the preceding claims, wherein the fluid line (20) is a heat pipe (30) and is arranged entirely within one of the field conductors (12) and / or current conductors (18) and / or a short-circuit ring (38) adjoining the field conductor (12).

11. Electric motor (10) according to claim 10, wherein a capacitor-side end of the heat pipe (30) is arranged in the short-circuit ring (38) and the short-circuit ring (38) is formed from spaced-apart sheets.

12. Electric motor (10) according to one of the preceding claims, in which the circuit boards (15) are circular or ring-sector shaped.

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

14. Electric motor (10) according to one of the preceding claims, designed to control each of the field conductors (12) with a separate phase.

15. Electric motor (10) according to one of the preceding claims, wherein 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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