Electric motor having efficiency-optimized winding head

Abstract

In order to provide an electric motor designed for operation with winding head cooling, which is optimized with respect to the frictional power loss caused by a cooling fluid entering the air gap between the rotor and the stator, an electric motor is proposed, comprising a rotor and a stator (10), the stator (10) comprising coil windings (12) made of electrical conductors, the coil windings (12) each form a winding head (14a, 14b) at an axial end (13) of the stator (10), the winding head (14a, 14b) comprising at least one first radially innermost layer of conductor sections (16a, 16b), the conductor sections (16a, 16b) of the first layer, in particular all, of each winding head (14a, 14b) having at least one bend in the same circumferential direction, and the first layer, in particular all of the conductor sections (16a, 16b) of each winding head (14a, 14b) having at least one second radially innermost layer of the conductor sections (16a, 16b). The conductor sections (16a, 16b) of the first layer are arranged such that the conductor sections (16a, 16b) have an inclined course with respect to the circumferential direction of the stator (10), the electric motor has a predetermined direction of rotation (R) for driving a shaft connected to the rotor, and wherein the direction of bending of the conductor sections (16a, 16b) of the first layer at the two axial ends (13) of the stator (10) coincides with the direction of rotation (R) of the electric motor.

Description

[0001] The present invention relates to an electric motor, a method for operating such an electric motor and a vehicle comprising such an electric motor.

[0002] A particular aspect in the use of electric motors in optimal operation is their cooling. Electric motors with a high power density are usually provided with fluid cooling with a closed cooling circuit, for example in a water / glycol cooling jacket. The heat generated during operation is thus transmitted via the stator lamination stack connected in the cooling jacket to the cooling fluid through the stator winding of the electric motor.

[0003] Furthermore, in order to optimally cool electric motors with a higher power density, in addition to cooling the stator lamination stack, active winding head cooling is often used by means of oil injection from the rotor and / or by means of oil from winding head oil distributors integrated in the stator or the motor housing. However, when using a liquid coolant such as oil in the stator space, it proves problematic if the coolant enters the air gap between the rotor and the stator. This can have adverse effects, in particular in terms of the efficiency of the electric motor. Specifically, by active winding head cooling, the cooling oil is thrown radially outward onto the winding head of the stator due to the rotation of the rotor of the electric motor for cooling. Due to the unfavorable geometry, the oil can enter the narrow air gap between the rotor and the stator. This leads to considerable frictional power losses in the electric motor.

[0004] Different winding head designs are known from the prior art.

[0005] EP 2 696 476 A1 discloses a stator and a method for manufacturing the same and, in particular, a technique for an improved method of winding coils to shorten the axial height of the coil end portions of a stator used in electrical machines. The publication "Overview of the Rectangular Wire Windings AC Electrical Machine" by Yu Thao et al. (CES Transaction On Electrical Machines And Systems, Vol. 3, No. 2, June 2019) discloses an overview of rectangular wire windings in AC electrical machines, in which different types of rectangular wire windings, different insertion directions of the rectangular wire windings and insulation structures are compared and analyzed.

[0006] Furthermore, a compact rotary electric machine with high output power is known from US 10,164,491 B2, which optimizes the cooling of the stator winding by adjusting the coil shape of the stator winding with distributed windings to be produced, so that the liquid coolant flows more easily in the circumferential direction of the coil end portion.

[0007] From KR 2022 0096306 A a cooling oil injection structure for an electric machine having a stator core and a coil is known, which coil is wound on the stator core and is formed obliquely with respect to an axial direction of the stator core.

[0008] DE 102010 036428 A1 discloses a stator for a rotary electric machine comprising a hollow cylindrical stator core and stator coils. The stator core has a longitudinal axis or longitudinal axis and a plurality of slots formed in a radially inner surface of the stator core and spaced apart from each other in a circumferential direction of the stator core. The stator coils are composed of a plurality of electric wires mounted on or over the stator core. Each electric wire has at least a first slot section, a second slot section, and a third slot section, and a first turning section and a second turning section. The first, second, and third slot sections are accommodated in three different slots of the stator core, respectively.

[0009] The task on which the invention is based is to provide an electric motor designed for operation by winding head cooling, which is optimized in terms of frictional power losses caused by cooling fluid entering the air gap between rotor and stator.

[0010] The task is solved by an electric motor comprising a stator, which stator comprises coil windings made of electric conductors, which coil windings form winding heads at axial end portions of the stator, which winding heads comprise at least one first radially innermost layer of conductor sections, each first layer of conductor sections of the winding heads, in particular all of them, has at least one bend in the same circumferential direction, so that the conductor sections have an oblique course with respect to the circumferential direction of the stator, wherein the electric motor has a predetermined direction of rotation of a rotor connected to a shaft of the rotor, and wherein the direction of the bends of the conductor sections of the first layer at both axial end portions of the stator coincides with the direction of rotation of the electric motor.

[0011] The radially innermost first layer of conductor sections in the respective winding head is in particular the layer of conductor sections of the stator that is closest to the rotor.

[0012] The bend of the conductor sections occurs in particular at a kink or bend point, which is arranged at the end of the conductor section on the stator side. This is in particular the case when the conductor section emerges from the stator. Opposite the stator-side end is the axially outer end of the winding head. Here, the conductor section is bent again to form the coil winding. This bend of the conductor section forming the oblique course occurs in particular in the process of twisting the winding head. The oblique course is also referred to in particular as crimping.

[0013] The inclined course of the conductor sections ensures that the conductor sections on both winding heads have an inclined forward and outwardly directed course from the point of view of the rotation direction, starting from the point of bending, due to the bending in the same direction, in particular in the direction of rotation of the rotor of the electric motor. This advantageously leads to the cooling fluid, which is thrown outwards by the rotation of the rotor from the region of the rotor, being discharged in a controlled manner outwards by the inclined outwardly extending structure, which is formed by the large number of adjacent conductor sections of the winding head, so that penetration of the cooling fluid into the air gap between the rotor and the stator is advantageously avoided.

[0014] If the conductor sections extend inclined backwards from the point of bending, as is the case with electric motors known from the prior art, the structure formed by the structure of the adjacent conductor sections would hinder the discharge of the cooling fluid to the outside, which would promote the penetration of the cooling fluid into the air gap.

[0015] The direction of rotation of the rotor for driving, in particular the direction of rotation of the rotor for driving components connected to the rotor, for example a shaft in a vehicle for driving the vehicle, is in particular in the forward direction or forward travel.

[0016] Preferably, the winding heads each comprise at least one second radial layer of conductor sections, which are arranged radially outside the conductor sections of the first layer, in particular all conductor sections of the second layer have at least one bend in the circumferential direction of the stator, the conductor sections of the second layer being bent in the opposite direction to the direction of the bend of the conductor sections of the first layer.

[0017] Preferably, a further third radial layer of conductor sections can be provided, which is again designed analogously to the first radial layer.

[0018] The coil winding preferably comprises hairpin plug-in coils, each conductor section corresponding to a bent section of the hairpin plug-in coils. Each conductor section that is inclined in the direction of rotation of the rotor here in particular corresponds to those regions of the bent section of the hairpin plug-in coils that protrude from the stator.

[0019] The shoulder of the hairpin plug-in coil is preferably straight, concave or convex when viewed in the axial direction. The shoulder of the hairpin forms those sections which run away from the hairpin end and face the central curved tip of the hairpin. The shoulder of the hairpin plug-in coil adjoins the conductor sections of the closed winding side that are bent in the direction of rotation, in particular on both sides of the central curved tip.

[0020] The electric motor preferably has a coolant system for supplying coolant to the winding heads of the stator, each winding head being assigned at least one coolant outlet of the coolant system. The coolant outlet is preferably arranged in the rotor such that coolant flowing out of the coolant outlet can be thrown radially outwards onto the winding head during operation of the electric motor.

[0021] The object according to the application is also achieved by a method for operating an electric motor having the aforementioned features, wherein the electric motor is operated in such a way that the rotor is operated in a direction which corresponds to the direction of the bend of the conductor sections of the first layer.

[0022] Preferably, the method comprises the step of supplying coolant of a coolant system of the electric motor into the winding head, wherein a coolant outlet of the coolant system is arranged in the rotor in such a way that the coolant flowing out of the coolant outlet is thrown radially outwards onto the winding head during operation of the electric motor.

[0023] Furthermore, the object according to the application is achieved by a vehicle having an electric motor with the aforementioned features.

[0024] Preferably, the direction of rotation of the rotor is the direction of rotation of the rotor which can be used to drive the vehicle to move forwards.

[0025] The application is explained in more detail below using exemplary embodiments. It is shown in purely diagrammatic form:

[0026] Figure 1 is a sectional view of a stator with stator windings of the prior art,

[0027] Figure 2 is a sectional view of a stator with stator windings according to the application,

[0028] Figure 3 is another sectional view of a stator according to the application,

[0029] Figure 4 a) to Figure 4 b) are schematic sectional views of different winding head configurations, and

[0030] Figure 5 are various embodiments of hairpin plug-in coils.

[0031] Figure 1 A stator 10 of the prior art is shown. The stator 10 comprises a stator body which is designed as a stator lamination stack 11. The stator 10 further comprises stator windings 12. At axial end portions 13 of the stator 10, the stator windings 12 each form a winding head 14a, 14b at the axial end portion 13, comprising a closed winding head 14a and an open winding head 14b. Connection means 17 for electrically connecting the stator windings 12 are provided on the open winding head 14b.

[0032] The winding heads 14a, 14b each have a first layer 20 of conductor sections 15a, 15b. The conductor sections 15a, 15b each form an end region of the stator winding 12 and are those sections which extend out of the stator lamination stack 11. The conductor sections 15a, 15b are formed in particular by hairpin plug-in coils 18, which will be referred to in more detail below with reference toFigure 5 More in detail, the conductor sections 15a, 15b form part of two parallel sections of the hairpin insert coil 18, which adjoin the shoulder 18a, 18b, 18c of the hairpin insert coil 18 at the closed winding head 14b and adjoin the bent end piece of the hairpin insert coil 18 at the open winding head 14a. Each hairpin insert coil 18 has two conductor sections on each winding head, one conductor section being arranged on the inner side and one conductor section being arranged on the outer side. The conductor sections 15a, 15b are assigned to the radially inner first layer of conductor sections.

[0033] In the stator winding 12 known from the prior art as shown in Figure 1 , the conductor sections 15a, 15b have a slanted course starting from the bend point 21. The slant is chosen here such that, viewed in the direction of rotation R of a rotor arranged in the stator 10, the conductor section 15a of one winding head 14a, 14b, in this case the open winding head 14a, is bent against the direction of rotation R and the conductor section 15b of the other winding head 14a, 14b, in this case the open winding head 14b, is bent in the direction of rotation R of the rotor. Figure 1

[0034] As can be seen from Figure 1 , the two conductor sections 15a, 15b are thus arranged offset parallel to one another. During rotation of the rotor and injection of coolant from the rotor region into the winding heads 14a, 14b, the coolant can enter the air gap between the stator 10 and the rotor as a result of the orientation of the conductor sections 15a, 15b. This is caused in particular by the conductor section 15a, which is bent against the direction of rotation R.

[0035] In order to prevent this, an optimized stator winding 12 is provided according to the application as shown in Figure 2 . In Figure 2 , components which essentially correspond to those in Figure 1 have the same reference numerals. Furthermore, Figure 2 shows a sectional view, i.e. a sectional view through the radially inner layer of conductor sections, which is analogous to Figure 1 . Figure 2 The stator winding 12 shown in Figure 1 differs from the stator winding 12 shown in Figure 1 in the arrangement of the conductor sections. In contrast to the stator 10 in Figure 2 , the conductor winding 16a, 16b in Figure 2 is oriented in such a way that the conductor sections start from the bend point 21 at the two axial ends 13 of the stator, i.e. in both winding heads 14a, 14b, are bent in the direction of rotation R of a rotor arranged in the stator and have a corresponding offset in the direction of rotation R.

[0036] Accordingly, the two conductor sections 16a, 16b are arranged axially staggered to each other obliquely. This forms a structure consisting of recesses or channels between the respective conductor sections 16a, 16b of the winding head, which lead obliquely outward in the direction of rotation R and in which the coolant can drain to the outside, so that a penetration of the coolant into the air gap between the rotor and the stator 10 can be effectively prevented.

[0037] Figure 3 A further view of the stator 10 according to the application is shown. In particular, it can be seen here how the first radially inner layer of conductor sections has a stagger according to the application in the direction of rotation R of the rotor. Further radially outer layers of conductor sections can also be provided. They either have the stagger of the conductor sections 16a, 16b of the first layer or an opposite stagger, i.e. opposite to the direction of rotation R of the rotor.

[0038] Figure 4 a) shows a schematic axial sectional view through one of the stator laminations 11 and the winding head 14a. The course of the conductor sections 16a from the bending point 21 towards the respective end of the hairpin insert coil is shown. This surface corresponds to an envelope surface or outer boundary line of the winding head profile. Figure 4 b) shows the position of the section of the winding head profile in a). Figure 4 a). The winding head profile corresponds to a cutting plane along the axis of half of the stator 10. The winding head profile can be designed differently, as shown in the different embodiments A, B and C in a). Figure 4 a). According to embodiment A, the profile is designed to be constricted, that is to say the conductor sections 16a taper on both sides towards the stator laminations 11. According to embodiment B, the profile is designed to be constant, that is to say the conductor sections 16a taper only on one side towards the stator laminations 11 and extend straight on the other side. According to embodiment C, the profile is designed to be expanded, that is to say the conductor sections 16a taper only on one side towards the stator laminations 11 and widen on the other side.

[0039] Figure 5 Various embodiments of the hairpin insert coil 18 are shown. The above Figure 5 An embodiment of the hairpin insert coil with a convexly curved shoulder 18a is shown. Figure 5 In the middle, a further embodiment of the hairpin insert coil 18 is shown, which has a concavely curved shoulder 18b. In the lower part, Figure 5 An embodiment of the hairpin insert coil 18 is shown, in which the shoulder 18c is designed straight or linear. A plurality of the respective hairpin insert coils 18 form the stator winding 12. The hairpin insert coils 18 each have two hairpin ends 19, which form the open ends of the open winding head 14b.

[0040] List of reference signs

[0041] 10 stator

[0042] 11 stator lamination stack

[0043] 12 stator winding

[0044] 13 stator axial end

[0045] 14a, 14b winding head

[0046] 15a, 15b, 16a, 16b obliquely extending conductor sections

[0047] 17 connection device

[0048] 18 hairpin insert coil

[0049] 18a convex shoulder

[0050] 18b concave shoulder

[0051] 18c linear shoulder

[0052] 19 hairpin end

[0053] 20 first layer

[0054] 21 bending point

[0055] A axial direction

[0056] R direction of rotation of the rotor

Claims

1. An electric motor comprising a rotor and a stator (10), wherein, The stator (10) comprises a coil winding (12) composed of electrical conductors, wherein the coil winding (12) respectively forms a winding head (14a, 14b) on an axial end (13) of the stator (10), wherein the winding head (14a, 14b) comprises at least one first radially innermost layer of conductor sections (16a, 16b), wherein the conductor sections (16a, 16b) of the first layer, in particular all of them, of each winding head (14a, 14b) have at least one bend in the same circumferential direction, so that the conductor sections (16a, 16b) have a course inclined with respect to the circumferential direction of the stator (10), characterized in that the electric motor has a predetermined direction of rotation (R) for driving a shaft connected with the rotor, and wherein the direction of bending of the conductor sections (16a, 16b) of the first layer at both axial ends (13) of the stator (10) coincides with the direction of rotation (R) of the electric motor.

2. The electric motor of claim 1, wherein, The winding head (14a, 14b) respectively comprises at least one second layer of conductor sections, which are arranged radially outside the first layer of conductor sections (16a, 16b), wherein the conductor sections of the second layer have at least one bend in the circumferential direction of the stator (10), wherein all conductor sections of the second layer are bent in a direction opposite to the direction of bending of the conductor sections (16a, 16b) of the first layer.

3. The electric motor of any of the preceding claims, wherein, The coil winding comprises hairpin insert coils (18), and wherein the conductor sections (16a, 16b) respectively correspond to the bent sections of the hairpin insert coils (18).

4. The electric motor of claim 3, wherein, The shoulders (18a, 18b, 18c) of the hairpin insert coils (18) are straight, concave or convex in an axial view (A).

5. Electric motor according to any of the preceding claims, having a coolant system for supplying coolant to the winding heads (13) of the stator (10), each of the winding heads (13) being assigned at least one coolant outlet of the coolant system.

6. The electric motor of claim 5, wherein, The coolant outlet is arranged in the rotor such that coolant flowing out of the coolant outlet can be thrown radially outward onto the winding head (13) during operation of the electric motor.

7. A method for operating an electric motor according to any one of claims 1 to 6, wherein, The electric motor is operated such that the rotor rotates in a direction (R) which corresponds to the direction of bending of the conductor sections (16a, 16b) of the first layer.

8. The method according to claim 7, comprising the step of feeding the coolant of the coolant system of the electric motor into the winding head (13), wherein, The coolant outlet of the coolant system is arranged in the rotor such that coolant flowing out of the coolant outlet can be thrown radially outward onto the winding head (13) during operation of the electric motor.

9. A vehicle having an electric motor according to any of claims 5 to 6.

10. The vehicle of claim 9, wherein, The direction of rotation (R) of the rotor is the direction of rotation of the rotor which is suitable for driving the vehicle to travel forward. The direction of rotation (R) of the rotor is the direction of rotation of the rotor which is suitable for driving the vehicle to travel forward.

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