Electric motor with efficiency-optimized winding head
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-30
- Publication Date
- 2026-03-18
AI Technical Summary
Existing electric motors with high power densities face significant frictional power losses due to cooling fluid entering the air gap between the rotor and stator, particularly during active winding end cooling, which affects efficiency.
The electric motor design features a stator with coil windings that have obliquely bent conductor sections at the winding heads, aligned with the rotor's direction of rotation, to direct cooling fluid outward and prevent its entry into the air gap, utilizing a coolant system with outlets that throw coolant radially onto the winding heads.
This design effectively prevents cooling fluid from entering the air gap, reducing frictional power losses and enhancing the motor's efficiency by ensuring controlled discharge of coolant outside the rotor-stator interface.
Smart Images
Figure EP2024061845_21112024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] Electric motor with efficiency-optimized winding head
[0003] The invention relates to an electric motor, a method for operating such an electric motor and a vehicle comprising such an electric motor.
[0004] A key aspect of ensuring optimal operation of an electric motor is its cooling. For electric motors with high power densities, fluid cooling with a closed cooling circuit, such as a water / glycol cooling jacket, is often used. This transports the heat generated during operation via the electric motor's stator winding and the stator laminations joined in the cooling jacket into the cooling fluid.
[0005] In addition to cooling the stator core, active winding head cooling is often used for optimal cooling of an electric motor with even higher power densities. This can be problematic if the coolant gets into the air gap between the rotor and stator, in addition to cooling the stator core. When using a liquid coolant such as oil in the stator chamber, it can be problematic if the coolant gets into the air gap between the rotor and stator. This can have undesirable effects, particularly with regard to the efficiency of the electric motor. In particular, with active winding head cooling, the cooling oil is thrown radially outwards to cool the stator winding heads due to the rotation of the electric motor rotor. Due to unfavorable geometric conditions, the oil can get into the narrow air gap between the rotor and stator. This leads to considerable frictional losses in the electric motor.
[0006] Different winding head designs are known from the state of the art.
[0007] EP 2 696476 A1 discloses a stator and a method for manufacturing the stator, and more particularly, a technique of an improved coil winding method for shortening the axial height of a coil end of a stator to be used in a motor. 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, comparing and analyzing the various types of rectangular wire windings, the various insertion directions of the rectangular wire windings, and the insulation structure.
[0008] Furthermore, from US 10,164,491 B2, a compact rotating electrical machine with high output power is known, with optimized cooling of a stator winding by adapting a coil shape of a stator winding to be manufactured with distributed windings, so that it is easier for a liquid coolant to flow in a circumferential direction from coil ends.
[0009] From KR 2022 0096306 A, a cooling oil injection structure for a motor with a stator core and a coil wound on the stator core and formed obliquely from the stator core with respect to the axial direction of the stator core is known.
[0010] DE 102010 036428 A1 discloses a stator for rotating electrical machines, which includes a hollow cylindrical stator core and a stator coil. The stator core has a longitudinal axis and a plurality of slots formed in the radial inner surface of the stator core and spaced apart from one another in the circumferential direction of the stator core. The stator coil consists of a plurality of electrical conductor wires mounted on the stator core. Each of the electrical conductor wires has at least first, second, and third slot portions and first and second turn portions. The first, second, and third slot portions are received, respectively, in three different slots of the stator core.
[0011] The invention is based on the object of providing an electric motor designed for operation with a winding head cooling, wherein the electric motor is optimized with regard to frictional power losses caused by cooling fluid which enters the air gap between the rotor and the stator.
[0012] This object is achieved by an electric motor comprising a stator, wherein the stator comprises coil windings made of an electrical conductor, wherein the coil windings each form winding heads at axial ends of the stator, wherein the winding heads comprise at least a first radially innermost layer of conductor sections, wherein, in particular, all of the conductor sections of the first layer of each winding head have at least one bend in the same circumferential direction, so that the conductor sections have an oblique course relative to the circumferential direction of the stator, wherein the electric motor has a predetermined direction of rotation of the rotor for driving a shaft connected to the rotor, and wherein the direction of the bend of the conductor sections of the first layer at both axial ends of the stator coincides with the direction of rotation of the electric motor.
[0013] The radially innermost first layer of conductor sections in the respective winding heads is in particular that layer of conductor sections from a plurality of layers of conductor sections of the stator which is closest to the rotor.
[0014] The bending of the conductor sections occurs particularly at a kink or bending point located at a stator-side end of the conductor section. This is particularly where the conductor sections emerge from the stator. Opposite the stator-side end is an axially outer end of the winding head. Here, the conductor sections are again bent to form the coil winding. This bending to form the diagonally running conductor section occurs particularly during a twisting process of the winding head. This diagonal course is also referred to as twisting.
[0015] The oblique course of the conductor sections due to bending in the same direction, particularly in the direction of rotation of an electric motor rotor, ensures that the conductor sections on both winding heads have a course that is directed obliquely forward and outward from the bending point, viewed in the direction of rotation. This advantageously ensures that cooling fluid, which is thrown outward from one region of the rotor onto the stator or the winding head due to its rotation, is discharged to the outside in a controlled manner through the obliquely outwardly extending structure formed by the multitude of adjacent conductor sections of the winding head, thus advantageously preventing the cooling fluid from penetrating the air gap between the rotor and stator.
[0016] If the conductor sections were to run obliquely backwards starting from the bending point, as is usually 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.
[0017] The direction of rotation of the rotor for driving is in particular the direction of rotation of the rotor which is used to drive a component connected to the rotor, for example a shaft in a vehicle for driving the vehicle, in particular in the forward direction or for forward travel.
[0018] Preferably, the winding heads each comprise at least one second radial layer of conductor sections, which is arranged radially outside the first layer of the conductor sections, wherein, in particular, all of the conductor sections of the second layer have at least one bend in the circumferential direction of the stator, wherein the conductor sections of the second layer are bent in a direction opposite to the bending direction of the conductor sections of the first layer.
[0019] Preferably, a further, third radial layer can be provided on conductor sections, which in turn is designed analogously to the first radial layer.
[0020] The coil windings preferably comprise hairpin plug-in coils, with the conductor sections each corresponding to a bent section of the hairpin plug-in coil. The conductor sections, which are bent obliquely in the direction of rotation of the rotor, correspond in particular to those areas of the bent sections of the hairpin plug-in coils that protrude from the stator.
[0021] Preferably, the shoulders of the hairpin plug-in coils are straight, concave, or convex when viewed axially. The shoulders of the hairpin form those sections facing away from the hairpin ends and toward a central bending point of the hairpin. The shoulders of the hairpin plug-in coils adjoin the conductor sections of the closed winding side, which are bent in the direction of rotation, particularly on both sides of the central bending point.
[0022] The electric motor preferably has a coolant system for supplying a coolant to the winding heads of the stator, with each of the winding heads being assigned at least one coolant outlet of the coolant system. Coolant outlets are preferably arranged in the rotor such that coolant emerging from the coolant outlets can be projected radially outward onto the winding heads during operation of the electric motor.
[0023] The object of the invention is further achieved by a method for operating an electric motor having the aforementioned features, wherein the electric motor is operated such that the rotor rotates in a direction which corresponds to the direction of the bending of the conductor sections of the first layer.
[0024] Preferably, the method comprises the step of supplying a coolant of a coolant system of the electric motor into the winding heads, wherein coolant outlets of the coolant system are arranged in the rotor such that coolant emerging from the coolant outlets is thrown radially outward onto the winding heads during operation of the electric motor.
[0025] Furthermore, the object of the invention is achieved by a vehicle having an electric motor with the aforementioned features.
[0026] Preferably, the direction of rotation of the rotor is the direction of rotation of the rotor which is applicable for driving the vehicle for forward travel.
[0027] The invention is explained in more detail below using exemplary embodiments. They show, in purely schematic form:
[0028] Fig. 1 a sectional view of a stator with stator windings from the prior art
[0029] Fig. 2 is a sectional view of a stator with stator windings according to the invention,
[0030] Fig. 3 is a further sectional view of a stator according to the invention,
[0031] Fig. 4 a)-b) schematic sectional views of different winding head configurations, and
[0032] Fig. 5 shows various embodiments of hairpin plug-in coils. Figure 1 shows a stator 10 from the prior art. The stator 10 comprises a stator body, which is designed as a stator core 11. The stator 10 further comprises stator windings 12. At the axial ends 13 of the stator 10, the stator windings 12 each form a winding head 14a, 14b, comprising a closed winding head 14a and an open winding head 14b. A connection device 17 for electrically connecting the stator windings 12 is provided on the open winding head 14b.
[0033] The winding overhangs 14a, 14b each have a first layer 20 of conductor sections 15a, 15b. The conductor sections 15a, 15b each form end regions of the stator winding 12 and are the sections that extend out of the stator laminated core 11. The conductor sections 15a, 15b are formed in particular by hairpin plug-in coils 18, which will be described in more detail with reference to Figure 5. The conductor sections 15a, 15b form part of the two parallel sections of the hairpin plug-in coil 18, which adjoin a shoulder 18a, 18b, 18c of the hairpin plug-in coil 18 at the closed winding overhang 14b and adjoin a bent end piece of the hairpin plug-in coil 18 at the open winding overhang 14a. Each hairpin plug-in coil 18 has two conductor sections on each winding head, with one conductor section being arranged inside and one conductor section being arranged outside.The conductor sections 15a, 15b are assigned to a radially inner first layer of conductor sections.
[0034] In stator windings 12 known from the prior art, such as the one shown in Figure 1, the conductor sections 15a, 15b have an oblique course starting from a bending point 21. The obliqueness is selected such that, viewed in the direction of rotation R of a rotor arranged in the stator 10, the conductor section 15a of one winding overhang 14a, 14b, in Figure 1 the open winding overhang 14a, is bent counter to the direction of rotation R and the conductor section 15b of the other winding overhang 14a, 14b, in particular the open winding overhang 14b, is bent in the direction of rotation R of the rotor.
[0035] As can be seen in Figure 1, the two conductor sections 15a, 15b are arranged offset parallel to each other. During rotor rotation and the injection of coolant from the rotor area into the winding heads 14a, 14b, the orientation of the conductor sections 15a, 15b can cause coolant to enter an air gap between the stator 10 and the rotor. This is caused in particular by the conductor section 15a being bent counter to the direction of rotation R.
[0036] To prevent this, an optimized stator winding 12, as shown in Figure 2, is provided according to the invention. In Figure 2, components which essentially correspond to those in Figure 1 are provided with the same reference numerals. Furthermore, Figure 2 shows a sectional view analogous to Figure 1, i.e. through the radially inner conductor section layer. The stator winding 12 shown in Figure 2 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 1, the conductor windings 16a, 16b in Figure 2 are oriented such that the conductor sections, starting from the bending points 21 at both axial ends 13 of the stator, i.e. in both winding overhangs 14a, 14b, are bent in the direction of rotation R of a rotor arranged in the stator and have a corresponding twist in the direction of rotation R.
[0037] Accordingly, the two conductor sections 16a, 16b are arranged axially offset and inclined relative to each other. This creates a structure of recesses or channels between the respective conductor sections 16a, 16b of a winding head, which extend obliquely outward in the direction of rotation R and through which the coolant can be discharged to the outside, effectively preventing coolant from penetrating the air gap between the rotor and stator 10.
[0038] Figure 3 shows a further view of a stator 10 according to the invention. Here, it can be seen in particular how the first, radially innermost layer of the conductor sections exhibits the inventive twist in the direction of rotation R of the rotor. Further, radially further outward layers of conductor sections can also be provided. These either exhibit the twist of the conductor sections 16a, 16b of the first layer or an opposite twist, i.e., opposite the direction of rotation R of the rotor.
[0039] Figure 4 a) shows a schematic axial sectional view through the stator laminated core 11 and one of the winding heads 14a. It shows the course of the conductor sections 16a, starting from the bending point 21 to the respective ends of the hairpin plug-in coils. The area corresponds to the envelope surface or outer border line of the winding head profile. Figure 4 b) shows the position of the section of the winding head profiles from Figure 4 a). The winding head profiles correspond to a sectional plane along the axis for one half of the stator 10. The winding head profile can be designed in different ways, as illustrated by the various embodiments A, B and C in Figure 4 a). According to embodiment A, the profile is designed to be shrinking, i.e., the conductor sections 16a taper on both sides towards the stator laminated core 11. According to embodiment B, the profile is designed to be constant, i.e.The conductor sections 16a taper towards the stator core 11 on only one side and are straight on the other side. According to embodiment C, the profile is designed to be expanded, i.e., the conductor sections 16a taper towards the stator core 11 on only one side and widen on the other side.
[0040] Figure 5 shows various embodiments of the hairpin plug-in coils 18. The top of Figure 5 shows a design of a hairpin plug-in coil with convexly curved shoulders 18a. The middle of Figure 5 shows another design of a hairpin plug-in coil 18, which has a concave curvature of the shoulders 18b. The bottom of Figure 5 shows a design of a hairpin plug-in coil 18, wherein the shoulders 18c are straight or linear. Several of the respective hairpin plug-in coils 18 form the stator winding 12. The hairpin plug-in coils 18 each have two hairpin ends 19, which form the open ends of the open winding overhang 14b.
[0041] List of reference symbols
[0042] 10 Stator
[0043] 11 Stator laminated core
[0044] 12 stator windings
[0045] 13 axial ends of the stator
[0046] 14a, 14b Winding heads
[0047] 15a, 15b, 16a, 16b diagonal conductor sections 17 connection device
[0048] 18 Hairpin plug-in coil 18a convex shoulder 18b concave shoulder
[0049] 18c linear shoulder
[0050] 19 hairpin ends
[0051] 20 first layer
[0052] 21 bending points
[0053] A axial direction
[0054] R Direction of rotation of the rotor
Claims
Patent claims 1. An electric motor comprising a rotor and a stator (10), wherein the stator (10) comprises coil windings (12) made of an electrical conductor, wherein the coil windings (12) each form winding heads (14a, 14b) at axial ends (13) of the stator (10), wherein the winding heads (14a, 14b) comprise at least a first radially innermost layer of conductor sections (16a, 16b), wherein, in particular, all conductor sections (16a, 16b) of the first layer of each winding head (14a, 14b) have at least one bend in the same circumferential direction, so that the conductor sections (16a, 16b) have an oblique course relative to the circumferential direction of the stator (10), characterized in that the electric motor has a predetermined direction of rotation (R) of the rotor for driving a shaft connected to the rotor, and wherein the direction of the bend 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. Electric motor according to claim 1, wherein the winding heads (14a, 14b) each comprise at least a second layer of conductor sections which is 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 bending direction of the conductor sections (16a, 16b) of the first layer.
3. Electric motor according to one of the preceding claims, wherein the coil windings comprise hairpin plug-in coils (18), and wherein the conductor sections (16a, 16b) each correspond to a bending section of the hairpin plug-in coil (18).
4. Electric motor according to claim 3, wherein shoulders (18a, 18b, 18c) of the hairpin plug-in coils (18) are straight, concave or convex in an axial view (A).
5. Electric motor according to one of the preceding claims, comprising a coolant system for supplying a coolant to the winding heads (13) of the stator (10), wherein each the winding heads (13) are assigned at least one coolant outlet of the coolant system.
6. Electric motor according to claim 5, wherein the coolant outlets are arranged in the rotor such that coolant emerging from the coolant outlets can be thrown radially outward onto the winding heads (13) during operation of the electric motor.
7. A method for operating an electric motor according to one of claims 1 to 6, wherein the electric motor is operated such that the rotor rotates in a direction ® which corresponds to the direction of bending of the conductor sections (16a, 16b) of the first layer.
8. A method according to claim 7, comprising the step of supplying a coolant of a Coolant system of the electric motor into the winding heads (13), wherein coolant outlets of the coolant system are arranged in the rotor such that coolant emerging from the coolant outlets is thrown radially outwards onto the winding heads (13) during operation of the electric motor.
9. Vehicle comprising an electric motor according to one of claims 5 to 6.
10. A vehicle according to claim 9, wherein the direction of rotation (R) of the rotor is the direction of rotation of the rotor which is applicable for propelling the vehicle for forward travel.