Electric machine

Abstract

An electric machine comprising an internal rotor (2) rotatable about an axis of rotation and a radially external stator (4) with windings (6) guided in axially extending slots (5), and a housing (8) liquid-tightly enclosing the rotor (2) and the stator (4) with a cooling channel (13) radially enclosing the stator (4) at least over part of its axial length and rotating 360°, containing a cooling fluid flowing through it, characterized in that the cooling channel (13) is connected to the slots (5) via a channel connection (16), so that the cooling fluid can be guided from the cooling channel (13) via the channel connection (16) into the slots (5), flowing axially through them, wherein the cooling fluid collecting in a lower region of the housing (8) can be supplied to the cooling channel (13) via a pump (20) provided in the housing (8).and wherein several radially outwardly projecting cooling elements (11) are provided on the outside of the housing (8).

Description

[0001] The invention relates to an electric machine comprising an internal rotor rotatable about an axis of rotation and a radially external stator with windings guided in axially extending slots, as well as a housing that liquid-tightly encloses the rotor and the stator and contains a cooling channel circumferentially rotating around the stator at least over part of its axial length in a radially clasped manner and containing a cooling liquid flowing through it.

[0002] Electric machines are increasingly used in the automotive sector, for example as drive units. An example of this can be found in DE 10 2016 202 886 A1, which shows a machine of the type described above. An inner rotor and an outer stator are provided in a housing, both enclosed within the housing. The housing is equipped with a cooling channel that circulates around the outer stator in a jacket-like fashion. A coolant is contained in the cooling channel and is supplied via an external cooling circuit of the vehicle, or circulates within this circuit. Appropriate connections must be provided on the housing for this purpose, and lines for supplying and removing the coolant must be installed and connected. Additionally, liquid cooling is provided in the interior where the rotor and stator are housed.Inside the machine, there is an additional coolant that is circulated by impellers, which can be set in motion by the rotor. This allows for the wetting and thus cooling of the rotor, and possibly also the stator, by this additional coolant, for example, an oil. The design of this known machine is very complex, as it incorporates two separate cooling methods: external cooling via the cooling jacket and internal cooling.

[0003] Space for integrating such an electric motor is limited in a motor vehicle. Therefore, there is a need for motors that are as compact as possible.

[0004] The invention is therefore based on the problem of providing an improved electrical machine.

[0005] To solve this problem, in an electric machine of the type mentioned at the outset, the invention provides that the cooling channel is connected to the grooves via a channel connection, so that the cooling fluid can be guided from the cooling channel via the channel connection into the grooves, flowing axially through them, wherein the cooling fluid collecting in a lower area of ​​the housing can be supplied to the cooling channel via a pump provided in the housing, and wherein several cooling elements projecting radially outwards are provided on the outside of the housing.

[0006] The electric machine according to the invention operates completely autonomously with regard to its cooling, meaning that it is neither integrated into an external coolant circuit, for example that of a motor vehicle, nor does it require separate, external coolants. This is because the machine is characterized by an internal coolant circuit, meaning that the coolant circulates exclusively within the housing. This internal circulation, in conjunction with the integration of a heat exchanger directly on the outside of the housing in the form of radially outward-projecting cooling elements, is sufficient for machine cooling.

[0007] The design includes a cooling channel, formed within the housing or the cylindrical part of the housing that surrounds the stator externally. This channel, shaped like a jacket, encircles the stator and rotates 360° around it, effectively creating an external cooling jacket containing a coolant. This cooling jacket is part of an internal cooling circuit within the housing, where the coolant is circulated by a pump also integrated into the housing. The external cooling channel is connected to the stator slots, in which the stator windings are guided, via a channel connection. This allows the coolant in the jacketed cooling channel to flow through this connection into the slots and axially through them. In other words, direct slot cooling occurs as the coolant is pumped into the external cooling channel, flows through the connection into the slots, passes through them, and exits axially.Direct slot cooling, or rather the direct cooling of the windings running longitudinally in the slots, is extremely efficient. The exiting coolant, which upon exiting can also wet and cool the axially end winding heads, can partially wet the rotor as well. In any case, it flows into a lower housing area and collects there, from where it is pumped onward by the integrated pump and finally reaches the external cooling channel. As it flows through the cooling channel, the coolant transfers heat to the housing, which is then dissipated to the environment via the external, protruding cooling elements, which act as heat exchangers. These cooling elements can also be convectively cooled, for example, by an external airflow, such as the airflow from the vehicle.

[0008] The electric machine according to the invention is characterized by its compactness and self-contained cooling mechanism, as cooling is achieved exclusively internally via the internal coolant circuit, in conjunction with the heat exchanger arranged on the outside of the housing. No connection to an external coolant circuit, which would require corresponding piping for an inlet and outlet in conjunction with appropriate seals, etc., is necessary, thus simplifying the machine's design and its integration into a small installation space.Furthermore, the machine's design allows for its integration into a 2:1 or 3:1 axle of a motor vehicle. In a 2:1 axle configuration, the power electronics are additionally connected to the electric motor and may also be cooled via the housing. In a 3:1 axle configuration, the electric motor is also directly connected to a gearbox. The stator windings can be of any type, such as hairpin windings, wave windings, or concentrated windings.

[0009] A key feature is the fluidic connection between the outer, jacket-shaped cooling channel and the slots, which allows the coolant, for example, an oil, to flow from the outer cooling channel into and through the slots. According to a first alternative of the invention, this channel connection can be achieved via a radially open, 360° circumferential channel slot formed in the stator, open to both the cooling channel and the slots. This radial channel slot connects the quasi-cylindrical, circumferential cooling channel to the radially outwardly open slots extending axially along the stator, allowing the coolant, supplied from the radial outside via the cooling channel, to flow through the radially extending channel slot into the radially inner slots of the stator. Such a channel slot can be realized, for example, via appropriately shaped stator laminations, from which the stator, designed as a laminated core, is formed.

[0010] According to a second alternative, it is also conceivable that the channel connection is formed via several openings in the stator, open radially to the cooling channel and the slots. The stator is thus provided with a number of openings that is at least equal to the number of slots, with the openings extending radially and communicating at their outer end with the outer cooling channel and at their inner end with a slot in the stator. The openings can, for example, be formed by appropriately shaped laminations of the stator core, which therefore have corresponding recesses for forming the openings. In this case, the openings are, for example, rectangular in cross-section. However, they can also be implemented as bores that are subsequently machined into the stator.

[0011] Preferably, the channel groove or the openings are located axially centrally with respect to the length of the stator. This means that the coolant supplied to the outer cooling channel exits the cooling channel almost centrally with respect to the stator length and flows centrally into the grooves, where it then spreads out to both sides, i.e., in both axial directions, and flows through the grooves. This design with the axially central coolant distribution is advantageous with regard to reducing the pressure loss across the flow path. In this case, the coolant also exits at both axial groove ends and can therefore wet and cool the winding heads on both axial sides of the stator.

[0012] As described, the coolant is pumped from a reservoir located in a lower housing section by an integrated pump and fed to the outer, jacket-like cooling channel. To enable this, a suitable fluid connection to the outer cooling channel must be provided. For this purpose, one or more supply channels can be provided on one or both axial sides of the housing, through which the coolant collecting in a lower housing section can be pumped into the cooling channel. The coolant, which has collected in the reservoir, is thus supplied via one or both housing covers that axially close the housing and form the axial sides of the housing.On one or both housing covers, corresponding supply structures in the form of channels are provided into which the coolant is pumped. These channels communicate with the outer cooling channel, supplying it with coolant via the supply channels. Preferably, corresponding supply channels are provided on both axial sides, i.e., on both housing covers, each communicating with an axial end of the cooling channel. This ensures that the coolant is supplied to the cooling channel from both axial sides. If, as described above, the channel groove or the openings are located axially centrally, the coolant supplied from both sides flows through the cooling jacket only over half its length and then flows through the channel groove or the openings into the grooves, which it also flows through on both sides only over half their length. This is advantageous for reducing any pressure losses.Furthermore, this allows for a correspondingly large coolant volume to be circulated, ensuring very efficient cooling. If a supply channel is provided on only one axial side and the coolant is supplied only on one side of the cooling channel, the coolant flows through the cooling channel almost along its entire length and is then guided via the channel connection into the grooves, which it also flows through along almost its entire length. In this case, there is a kind of meandering fluid flow that extends over the entire axial length, whereas if the supply channels are designed with a central channel groove or bore on both axial sides, there are two such meandering fluid flows, each extending over half the axial length.

[0013] As described, the coolant is preferably supplied to the outer jacket-shaped cooling channel at one or both axial ends, i.e., the supply channel(s) provided on the axial sides connect with their radial ends to the axial ends of the cooling channel.

[0014] A key feature of the invention is the integral integration of a heat exchanger into the housing in the form of radially projecting cooling elements arranged on the outer surface of the housing. These elements significantly increase the outer housing surface area, enabling very efficient heat dissipation to the environment. Preferably, these cooling elements are designed as axially extending cooling fins, i.e., correspondingly narrow, elongated, and somewhat plate-shaped cooling elements of a certain height, which can be arranged in a sufficiently large number at equidistant intervals around the circumference. This allows for an extremely large surface area to be achieved.

[0015] According to a further development, the housing can be designed with two nested cylindrical elements, with the cooling channel formed between the cylindrical elements and the cooling elements arranged on the outer cylindrical element. This two-part housing design simplifies the formation of the jacket-shaped cooling channel, as the corresponding channel geometry can be formed in one or both cylindrical segments. The cylindrical segments are, of course, firmly connected to each other, for example, via an appropriate press fit, and form a liquid-tight housing structure.

[0016] It is particularly advantageous if the outer cylinder element is made of a material with a higher thermal conductivity than the material of the inner cylinder element. As described, heat is dissipated to the environment via the outer surface of the housing, i.e., via the outer cylinder element in conjunction with the cooling elements or fins provided on it, which are particularly those made of a single material or as a single piece. If this outer cylinder element is made of a material with high thermal conductivity, the heat transfer within the material is particularly efficient; that is, the heat transferred from the coolant to the outer cylinder element as it flows through the cooling channel is transported very quickly to the outside through the material of the outer cylinder element. Aluminum is one such material or metal with high thermal conductivity.In contrast, the inner cylindrical element, which supports the stator and must therefore be correspondingly robust, can be made of steel, for example. As described, the coolant is circulated within the internal cooling circuit by an integrated pump. This can be a mechanical pump driven by the rotor. This means that the rotor itself or the rotor shaft may have appropriate blade structures or other pumping mechanisms that allow the mechanical pump to move the coolant from the reservoir into the outer, jacket-shaped cooling channel. Alternatively, an electric pump can be used, which is readily feasible since the electric machine is already connected to a power supply.

[0017] The invention is explained below with reference to an exemplary embodiment and the accompanying drawing. The drawing is a schematic representation.

[0018] The figure shows, purely as a schematic representation, an electric machine 1 comprising a rotor 2 with a rotor axis 3 that rotates about a rotation axis. The rotor is located inside and is surrounded externally by a stator 4. The stator 4 has a number of slots 5 distributed equidistantly around its circumference, in which windings 6, for example hairpin or wave windings, are inserted. These windings extend axially and project axially beyond the stator 5 with corresponding winding heads 7. The stator is fixed in position.

[0019] Furthermore, a housing 8 is provided, which completely encloses the rotor 2 and the stator 4, with the rotor shaft 3 rotatably mounted in the housing via bearing means not shown. The housing consists of a cylindrical, central housing section 9 and two covers 10 forming the axial sides of the housing 8, which are rigidly and liquid-tightly connected to the housing section 9. Distributed around the outer circumference of the housing section 9 are a plurality of radially projecting, axially extending cooling elements 11 in the form of flat, plate-shaped cooling fins, which function as heat exchangers.

[0020] The housing 8 is provided with a 360° circumferential, jacket-like cooling channel 13, which is formed in housing section 9. For this purpose, housing section 9 consists, for example, of an inner cylindrical element 14 and an outer cylindrical element 15, which are nested within each other and firmly connected, for example, by an interference fit. This two-part housing design allows the jacket-like cooling channel 13 to be easily formed between the two cylindrical elements 14 and 15. The outer cylindrical element 15 is made of a material, for example, aluminum, that has a higher thermal conductivity than the material of the inner cylindrical element 14, for example, steel.

[0021] The cylindrical cooling channel 13, extending circumferentially and axially, is connected to each of the slots 5 via a channel connection 16 arranged axially centrally. This means that pressurized coolant present in the cooling channel 13 can flow into each of the slots 5 via this channel connection 16. The channel connection 16 is preferably designed as a channel groove 17, open radially to the cooling channel 13 and the slots 5, and extending 360° around the entire circumference. This groove is formed in the stator, which is also received in the housing 8, for example, via an interference fit. Naturally, the housing section 9 also has a corresponding groove-like opening that leads into the annular groove 17, thus allowing coolant to flow through. As the figure shows, the channel connection 16 is also located axially centrally on the stator 4, so that the coolant can flow out of the cooling channel 13 at a central position and into the slots 5 at a central position.

[0022] To supply the annular cooling channel 13 with coolant, corresponding supply channels 18 are formed on both covers 10 in the example shown, opening at the two axial ends of the cooling channel 13, as shown in the figure. The covers 10 are connected to the housing section 9 in a liquid-tight manner, so that the coolant flows from the supply channels 18 into the cooling channel 13 without loss, as is the case with the entire coolant circuit, which is, of course, completely liquid-tight.

[0023] The supply channels 18 are in turn connected to the interior 19 of the housing 8, where a mechanical pump 20 is provided, which has corresponding conveying elements on both axial sides and is coupled, for example, to the rotor shaft 3, or to the rotor 2. The pump 20 conveys coolant accumulating in the interior 19, which collects in a lower housing area, into the coolant circuit, i.e., into the supply channels 18 and from there into the cooling channel 13, where it then enters the grooves 5.

[0024] For cooling, as described, coolant, for example oil, which accumulates in a reservoir in the lower part of the housing 8, is first drawn in by the pump 20 and, as shown by the flow arrows, conveyed via a connection into the two supply channels 18 on the cover side. The pressurized coolant initially flows radially outwards in the supply channels 18 and then enters the cooling channel 13 at both axial ends, flowing axially through it for half its length.Since the coolant has already absorbed heat from the system at this point, it now transfers this heat to the housing 8 or the housing section 9 and there in particular to the outer cylinder element 15, which, as described, is very good at conducting heat, so that the heat is quickly transported to the outside, where it is very quickly released to the environment via the outside of the housing and in particular the cooling fins 12, which define a very large surface area, by means of air cooling, for example, by the airflow while driving.

[0025] The coolant flows to the channel connection 16, i.e., to the channel groove 17, and enters it. It enters the grooves 5 axially in the center, where it flows to both sides, so that the coolant only flows halfway through each groove. As the flow arrows indicate, the coolant then exits at both ends of the grooves and can wet the winding heads 7. During its flow through the grooves 5, the coolant absorbs heat, thus cooling the stator 4. As it flows downwards, the coolant can also wet and cool the rotor 2. In the lower stator area, the coolant flows directly to the side and downwards. As described, it collects in the lower reservoir of the housing, from where it is then pumped out again by the pump 20 and returned to the circuit.

[0026] The electric machine according to the invention has a highly efficient, self-contained cooling system that operates exclusively within the housing; that is, the coolant circulates exclusively within the housing and is not supplied and removed via an external cooling device, such as a vehicle's coolant circuit. Consequently, the electric machine is not integrated into an external coolant circuit. Furthermore, the integration of the heat exchanger in the form of the cooling fins 12 achieves highly efficient heat transfer and dissipation in conjunction with the outer cooling jacket. The connection, according to the invention, of the outer jacket-shaped cooling channel 13 with the slots 5 and the direct slot cooling also results in highly efficient cooling of the electrical system.

[0027] The electric machine 1 can be connected to power electronics located on the housing 8, which can also be cooled via the housing. The electric machine can also be directly connected to a gearbox, which it drives. List of reference symbols 1 electric machine 2 Rotor 3 Rotor shaft 4 Stator 5 grooves 6 windings 7 winding heads 8 cases 9 Housing section 10 lids 11 cooling elements 12 cooling fins 13 Cooling channel 14 Cylinder element 15 Cylinder element 16-channel connection 17 Channel groove 18 feed channels 19 Inner 20 pump QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 202 886 A1

[0002]

Claims

[1] Electrical machine, comprising an inner rotor (2) rotatable about an axis of rotation and a radially outer stator (4) with windings (6) guided in axially extending slots (5), as well as a housing (8) enclosing the rotor (2) and the stator (4) in a liquid-tight manner, with a cooling channel (13) enclosing the stator (4) at least over part of its axial length in the form of a jacket and circulating by 360°, containing a cooling liquid flowing through it, characterized byin that the cooling channel (13) is connected to the grooves (5) via a channel connection (16), so that the cooling liquid can be guided from the cooling channel (13) via the channel connection (16) into the grooves (5), flowing axially through them, wherein the cooling liquid collecting in a lower region of the housing (8) can be fed to the cooling channel (13) via a pump (20) provided in the housing (8), and wherein a plurality of radially outwardly projecting cooling elements (11) are provided on the outside of the housing (8). [2] Electrical machine according to claim 1, characterized by that the channel connection (16) is a channel groove (17) which is open radially to the cooling channel (13) and to the grooves (5) and which extends 360° around the channel groove, which is formed in the stator (4). [3] Electrical machine according to claim 1, characterized by that the channel connection (16) is formed by a plurality of openings formed in the stator (4) which are open radially to the cooling channel (13) and the grooves (5). [4] Electrical machine according to claim 2 or 3, characterized by e, that the channel groove (17) or the openings are provided axially centrally with respect to the length of the stator (4). [5] Electrical machine according to one of the preceding claims, characterized by that on one or both axial sides of the housing (8) one or more supply channels (18) are provided, via which the cooling liquid collecting in the lower region of the housing (8) can be conveyed into the cooling channel (13) by means of the pump (20). [6] Electrical machine according to claim 5, characterized by that the supply channel(s) (18) open at one or both axial ends of the cooling channel (13). [7] Electrical machine according to one of the preceding claims, characterized by that the cooling elements (11) are axially extending cooling fins (12). [8] Electrical machine according to one of the preceding claims, characterized bythat the housing (8) has two cylinder elements (14, 15) arranged one inside the other, wherein the cooling channel (13) is formed between the cylinder elements (14, 15) and the cooling elements (11) are arranged on the outer cylinder element (15). [9] Electrical machine according to claim 8, characterized by that the outer cylinder element (15) is made of a material with a higher thermal conductivity, in particular aluminum, than the material of the inner cylinder element (14). [10] Electrical machine according to one of the preceding claims, characterized by that the pump (20) is a mechanical pump driven by the rotating rotor (2) or an electric pump.

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