Electric machine and motor vehicle with an electric machine

Abstract

The invention relates to an electric machine (100) with a stator (11) which extends along a longitudinal axis (A L) extends and has winding heads (14) connected to an AC power source (15) for generating a stator current, and a rotor (12) comprising a rotor lamination stack (16) and a rotatably mounted rotor shaft (17), wherein a passive oil cooling system with an oil guide (24) having outlet openings (26) is provided within the rotor (12), the outlet openings (26) being configured and oriented to supply the winding heads (14) with oil. The oil guide (24) has a valve (27) with a variable opening cross-section, the valve (27) being connected to an actuator (28) configured without a control module, in particular without a computer-controlled control module, to adjust the opening cross-section of the valve (27) depending on the stator current. Furthermore, the invention relates to a motor vehicle (200) with an electric machine (100) which is part of an electric drive module of the motor vehicle (100).

Description

[0001] The invention relates to an electric machine with a stator extending along a longitudinal axis and having winding heads connected to an alternating current source for generating a stator current, and a rotor comprising a rotor lamination stack and a rotatably mounted rotor shaft, wherein a passive oil cooling system with an oil guide and outlet openings is provided within the rotor, the outlet openings being arranged and aligned to supply the winding heads with oil.

[0002] In addition, the invention relates to a motor vehicle with such an electric machine which is part of an electric drive module of the motor vehicle.

[0003] Electric machines and motor vehicles with such electric machines are known according to the prior art. In particular, electric machines are installed in electric vehicles and hybrid vehicles. Electric machines convert electrical energy into kinetic energy, which initially exists in the form of rotor rotation and can be converted into vehicle motion via a transmission. During operation, high electrical currents are induced, which generate heat due to electrical losses within the electric machine, especially at the stator. The generated heat must be dissipated effectively to maintain continuous and trouble-free operation of the electric machine. For this purpose, the stator winding ends are cooled with oil as a cooling fluid, as described, so that the heat is effectively dissipated from the electric machine. A distinction must be made between active and passive oil cooling systems.

[0004] In an active oil cooling system, oil is actively pumped into the oil channel by means of a pump, with the amount of oil delivered per unit of time being adjustable via a control unit. Active oil cooling is disadvantageously expensive due to the need to maintain and operate the pump and its control via a suitably configured control unit.

[0005] In contrast, passive oil cooling systems maintain oil flow within the oil channels due to centrifugal forces generated in the rotor during the rotating operation of the electric machine. The continuous oil supply in passive oil cooling systems, particularly during towed operation without decoupling, results in significant losses due to oil friction in the rotor shaft, the rotor lamination stack, and / or the air gap between the rotor lamination stack and the stator. During towed operation, the axle is not actively driven. In an all-wheel-drive system, the front axle rotates passively in such a driving situation, meaning that while the wheels turn the axle or gears, the axle is not subjected to any torque by the machine.

[0006] US Patent 2018 / 0241288 A1 discloses an electric machine with active oil cooling. It proposes an electric rotary machine cooling structure in which a coolant is supplied by a pump to the stator and rotor of an electric rotary machine, thereby cooling the stator and rotor. The electric rotary machine cooling structure comprises a first channel that supplies the coolant from the pump to the stator and a second channel that supplies the coolant from the pump to the rotor. A valve regulates the flow of coolant from the first channel and the flow of coolant from the second channel, controlling the cooling state of the stator and the cooling state of the rotor. A computer control system is provided for controlling the valve.

[0007] US Patent 9,331,543 B2 also discloses a comparable electric machine whose valve for regulating coolant flow is controlled by a computer. Specifically, an electric machine module is proposed, with • a housing that at least partially defines a machine cavity; • a coolant jacket that is at least partially defined by the housing; • several coolant openings arranged through sections of the housing to fluidly connect the coolant jacket and the machine cavity; and • one or more solenoid assemblies, which are at least partially carried through the housing and which are positioned substantially adjacent to at least some of the multiple coolant openings, wherein the solenoid assemblies are designed and arranged to control the flow of at least some part of a coolant from the coolant jacket into the machine cavity.

[0008] Furthermore, US Patent 2023 / 0344313 A1 discloses a comparable electric machine whose valve for regulating coolant flow is controlled by a computer. In particular, a motor system is described that consists of a motor with a motor housing, a stator core, a stator winding, and a rotor core, wherein the stator core is mounted in the motor housing, the stator winding is wound around the stator core, and the rotor core is rotatably arranged relative to the stator core. The motor housing has a rotor flow path that is formed at least in the rotor core, wherein the rotor flow path is configured to transport coolant to the stator winding. A valve is provided that is configured to control the flow of the rotor flow path.

[0009] A non-standard electrical machine is described in DE 10 2018 121 348 A1. Specifically, an electric motor for an electric or hybrid vehicle drive is disclosed. The electric machine has a stator, a coolant, and a rotor with an axis of rotation, at least one cooling channel, wherein the cooling channel directs the coolant from the rotor towards the stator, and a first control element, which is movable relative to the axis of rotation between a first position of the first control element and a second position radially outer from the first position with respect to the axis of rotation, and which can be driven by means of a centrifugal force acting on the first control element in the direction of the second position to control a mass flow of the coolant through the cooling channel.

[0010] Starting from this premise, the object of the present invention is to provide an electric machine with passive oil cooling and a motor vehicle with such an electric machine, thereby eliminating the disadvantages of the prior art. In particular, losses due to disproportionately high oil friction within the electric machine are to be avoided.

[0011] This problem is solved by the electric machine according to claim 1 and by the motor vehicle according to claim 10. According to the invention, the oil guide has a valve with a variable opening cross-section, wherein the valve is connected to an actuator which is configured to be free of a control module, in particular free of a computer-controlled control module, in order to adjust the opening cross-section of the valve as a function of the stator current.

[0012] The valve is specifically designed as a flow control valve or throttle valve, which adjusts the amount of oil delivered to the winding heads per unit of time depending on the stator current. This means that less oil is supplied when lower drive power is drawn from the electric machine, and more oil is supplied when higher drive power is drawn. The oil flow is adjusted without active computer control, eliminating the need for software or a control module that requires maintenance. Nevertheless, the reduced oil supply, particularly at lower power outputs, advantageously minimizes losses due to disproportionately high oil friction within the electric machine.

[0013] Advantageous embodiments of the present invention are specified below and in the dependent claims.

[0014] According to an advantageous embodiment of the invention, the actuator comprises an electrical coil, a slide, and a spring, wherein the slide is mounted at least partially within the coil, is displaceable against the force of the spring, and is connected to the valve in such a way that the valve is closed when the spring is unloaded or under the minimum possible load. The actuator preferably has a housing that is attached, at least indirectly, to a housing of the electric machine via a mounting plate and that accommodates the coil, the slide, and the spring. The spring can, in particular, be designed as a helical spring.

[0015] Preferably, the slider consists at least partially of ferromagnetic material or incorporates ferromagnetic material, wherein the spatial distribution of the ferromagnetic material is asymmetrical with respect to the center of the coil when the spring is unloaded. Iron or a suitable ferromagnetic iron alloy, for example, can be used as the ferromagnetic material. Alternatively, the slider is designed at least partially as a permanent magnet, wherein the magnetic axis of the permanent magnet is preferably aligned parallel to the coil axis.

[0016] The electrical coil is preferably connected to the AC power source via a rectifier, allowing the coil to be supplied with a direct current and inducing a magnetic field with a current-dependent strength within the coil. The rectifier can be, for example, a half-wave rectifier or a bridge rectifier. The induced magnetic field exerts a force on the slider, oriented along the coil axis, causing the slider to move against the spring force. The coil's magnetic field is preferably oriented such that the slider is increasingly moved against the spring force as the stator current increases.This means that the valve's opening cross-section is proportional to the stator current, and the amount of oil delivered per unit time by the passive oil cooling system is indirectly dependent on the stator current and thus on the power currently being drawn from the electric motor. If the power demand is low, a small stator current flows through the stator windings and the actuator's electrical coil. Consequently, the magnetic force acting on the valve is low, and the valve has a small opening cross-section, allowing only a small amount of oil to be discharged per unit of time. Conversely, if the power demand is high, a high stator current flows through the stator coil and the actuator's electrical coil. This results in a high magnetic force acting on the valve, and the valve has a large opening cross-section, allowing a large amount of oil to be discharged per unit of time.

[0017] In a further advantageous embodiment, the AC source is designed as a three-phase AC source. Preferably, the coil is electrically connected to the neutral point or to one of the phases of the three-phase AC source.

[0018] The electrical machine can be designed in particular as a Permanent Magnet Excited Synchronous Machine (PMSM), Asynchronous Machine (ASM) or Electrically Excited Synchronous Machine (EESM).

[0019] A specific embodiment of the invention is explained below with reference to the figures. These show: Fig. 1a-d an electric machine; Fig. 2a a first actuator; Fig. 2b a second actuator; Fig. 3 a diagram; Fig. 4 a motor vehicle.

[0020] The Fig. Figures 1a-c each show an electric machine 100 with a housing 10 that accommodates a stator 11 and a rotor 12. The stator 11 has a stator lamination stack 13 and winding ends 14 and extends along a longitudinal axis A. L The winding heads 14, or the windings of the winding heads 14, are connected to an alternating current source 15, which in the illustrated embodiment is designed as a three-phase current source 151, so that the winding heads 14, or the windings of the winding heads 14, are supplied with a stator current in the form of a three-phase current. The rotor 12 has a rotor lamination stack 16 and a rotatably mounted rotor shaft 17, wherein the rotor axis A R the rotor shaft 17 coaxial to the longitudinal axis A LThe stator 11 is supported. An air gap 18 is formed between the rotor 12 and the stator 11. Upon response to a stator current in the form of a three-phase current, the rotor 12 is set into rotation, and drive power can be drawn from the rotor shaft 17 via a gearbox 19 with several gears 20.

[0021] The induced currents generate a high level of heat, particularly in the stator 11. This heat is dissipated by means of passive oil cooling 21, for which the electric machine 100 has an oil circuit. Oil is transported from an oil sump 22 to an oil reservoir 23 in a suitable manner. An oil guide 24 with several oil guide channels 25 is formed within the rotor 12. These channels are connected on one side to the oil reservoir 23 and on the other side to outlet openings 26, which are positioned and oriented differently to fling oil onto the winding heads 14 of the stator 11 when the rotor 12 is rotating. There, the oil absorbs heat and flows back into the oil sump 22 by gravity, where it can release the absorbed heat.

[0022] Fig. Figure 1a shows a first embodiment of the oil guide 24. According to this, an oil guide channel 25 extends along the rotor axis A. Rthe rotor shaft 17 and opens via short radial oil guide channels 25 of the rotor shaft 17 and obliquely oriented oil guide channels 25 of the rotor lamination stack 16 into outlet openings 26, which are arranged on both sides of the end faces of the rotor lamination stack 16. There, the outlet openings 26 are oriented such that the oil is flung off at an oblique angle towards the winding heads 14.

[0023] Fig. Figure 1b shows a second embodiment of the oil guide 24. According to this embodiment, an oil guide channel 25 extends along the rotor axis A. R the rotor shaft 17 and opens via short radial oil guide channels 25 of the rotor shaft 17 into outlet openings 26, which are arranged on the outer surface of the rotor shaft 17. There, the outlet openings 26 are oriented such that the oil is flung off radially in the direction of the winding heads 14.

[0024] Fig. Figure 1c shows a third embodiment of the oil guide 24, which is a combination of the two embodiments according to the Fig. 1a, b is.

[0025] Fig. Figure 1d shows a fourth embodiment of the oil guide 24. According to this embodiment, an oil guide channel 25 extends along the rotor axis A. R the rotor shaft 17 and opens via short radial oil guide channels 25 of the rotor shaft 17 and coaxially aligned oil guide channels 25 of the rotor lamination stack 16 into a discharge surface 38, which is arranged on both sides of the end faces of short-circuit rings 39 of the rotor lamination stack 16. There, the discharge surfaces 38 are oriented such that the oil is flung off at an oblique angle towards the winding heads 14.

[0026] Regardless of the specific design of the oil guide 24, a valve 27 with a variable opening cross-section is provided, wherein the valve 27 is connected to an actuator 28, which is configured to adjust the opening cross-section of the valve 27 depending on the stator current. For this purpose, the valve 27 is designed as a flow control valve 271 or throttle valve.

[0027] The Fig. Figures 2a and 2b each show a detailed view of an actuator 28 in combination with the AC power source 15, which in the illustrated embodiment is designed as a three-phase power source 151. The actuator 28 has a housing 29 that can be connected to the housing 10 of the electric machine via a mounting plate 30. The housing 29 of the actuator 28 accommodates an electrical coil 31, a slide 32, and a spring 33, which in the illustrated embodiment is designed as a helical spring 331. The slide 32 is mounted coaxially and sectionally within the electrical coil 31 and is displaceable against the force of the spring 33. The slide 32 is connected to the valve 27 such that the valve 27 is closed when the spring 33 is unloaded, or in the state of minimum possible load.

[0028] The slide 32 of the in Fig. In the embodiment shown in 2a, the spring 33 is made of ferromagnetic material, and the distribution of the ferromagnetic material is asymmetrical with respect to the center point of the electrical coil 31 when the spring 33 is unloaded. In contrast, the slider 32 of the spring 33 shown in the illustration is asymmetrical. Fig. In the embodiment shown in 2b, the permanent magnet 34 is designed, wherein the magnetic axis of the permanent magnet 34 is parallel to the coil axis A. S is aligned. In both cases, the electrical coil 31 of the actuator 28 is connected to the neutral point 37 of the three-phase power source 151 via an electrical resistor 35 and a rectifier 36. During operation of the electric machine 100, a direct current flows through the electrical coil 31, thereby inducing a magnetic field B. This causes the ferromagnetic slider 32 to Fig. 2a magnetizes and aligns itself with the induced magnetic field B, thereby exerting a force on the slider 32 that opposes the force of the spring 33. The permanent magnet slider 32 according to Fig. 2b also aligns itself with the magnetic field B, thereby exerting a force on the slide 32 that counteracts the force of the spring 33. As the stator current increases, the slide 32 is increasingly displaced against the force of the spring 33, thus increasing the opening cross-section of the valve 27. This results in a demand- and power-dependent supply of oil to the winding heads 14, thereby avoiding losses due to disproportionately high oil supply. A pump and a suitably configured control unit are therefore unnecessary.

[0029] Fig. Figure 3 shows the following losses V in the form of a diagram. SThe performance of the electric machine 100 as a function of the rotational speed N of the electric machine 100 is shown for two different cases, namely with valve 27 open (curve K1) and with valve 27 closed (curve K2). With valve 27 open, the amount of oil delivered by the oil cooling 21 increases with increasing rotational speed N of the rotor 12. At high rotational speeds N, however, the advantages of effective cooling outweigh the high drag losses V. S . Although relatively low drag losses occur even at high engine speeds N when valve 27 is closed. S However, the disadvantages due to the lack of oil cooling outweigh the advantages there. 21. In this respect, the advantages of the low drag losses are diminished. S The electric motor's maximum output (N) is only utilized at low speeds. The drag losses (V) SThe values ​​of the present electric machine 100 approach curve K2 asymptotically in the range of low rotational speeds and curve K1 asymptotically in the range of high rotational speeds.

[0030] Fig. Figure 4 shows a motor vehicle 200 with an electric motor 100, as previously described by the Fig. 1a,b and the Fig. 2a,b was described and is part of an electric drive module of the motor vehicle 200. Reference symbol list 100 electric machine 200 motor vehicles 10 cases 11 Stator 12 Rotor 13 Stator lamination stack 14 winding heads 15 AC power source 151 Three-phase power source 16 Rotor lamination package 17 Rotor shaft 18 air gap 19 gearboxes 20 gear 21 Oil cooling 22 Oil pan 23 Oil reservoir 24 Oil guide 25 Oil guide channel 26 Outlet opening 27 valve 271 Flow valve 28 actuators 29 cases 30 Mounting plate 31 electrical coil 32 sliders 33 spring 331 Coil spring 34 permanent magnet 35 electrical resistance 36 rectifiers 37 Star point 38 Drop surface 39 Short-circuit ring A L Longitudinal axis A R Rotor axis A S Coil shaft B Magnetic field K 1,2 curve V S Trailing losses N speed 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] US 2018 / 0241288 A1

[0006] US 9,331,543 B2

[0007] US 2023 / 0344313 A1

[0008] DE 10 2018 121 348 A1

[0009]

Claims

[1] Electric machine (100) with a stator (11) extending along a longitudinal axis (A L ) extends and has winding heads (14) connected to an alternating current source (15) for generating a stator current, and a rotor (12) comprising a rotor lamination stack (16) and a rotatably mounted rotor shaft (17), wherein a passive oil cooling system with an oil guide (24) with outlet openings (26) is provided within the rotor (12), wherein the outlet openings (26) are arranged and aligned to supply the winding heads (14) with oil, characterized by , that the oil guide (24) has a valve (27) with a variable opening cross-section, wherein the valve (27) is connected to an actuator (28) which is set up free of a control module, in particular free of a computer-controlled control module, to adjust the opening cross-section of the valve (27) depending on the stator current. [2] Electric machine (100) according to claim 1, characterized by , that the actuator (28) has an electrical coil (31), a slide (32) and a spring (33), wherein the slide (32) is mounted at least partially inside the coil (31), is displaceable against the force of the spring (33) and is connected to the valve (27) in such a way that the valve (27) is closed in the unloaded state of the spring (33) or in the state of the least possible load on the spring (33). [3] Electric machine (100) according to claim 2, characterized by , that the slide (32) is at least partially made of ferromagnetic material or has ferromagnetic material. [4] Electric machine (100) according to claim 3, characterized by , that the distribution of the ferromagnetic material in the unloaded state of the spring (33) is asymmetric with respect to the center of the coil (31). [5] Electric machine (100) according to claim 2, characterized by, that the slider (32) is at least partially designed as a permanent magnet (34), wherein the magnetic axis of the permanent magnet (34) is preferably parallel to the coil axis (A S ) is aligned. [6] Electric machine (100) according to any one of claims 3 to 5, characterized by , that the coil (31) is connected to the alternating current source (15) via a rectifier (36) so that the coil (31) can be supplied with a direct current and a magnetic field (B) with a current-dependent magnetic field strength can be induced inside the coil (31). [7] Electric machine (100) according to any one of claims 3 to 6, characterized by , that the magnetic field (B) of the coil (31) is oriented such that the slider (32) is increasingly displaced against the force of the spring (33) as the stator current increases. [8] Electric machine (100) according to any one of claims 1 to 7, characterized by, that the alternating current source (15) is designed as a three-phase alternating current source (151). [9] Electric machine (100) according to claim 8, characterized by , that the coil (31) is electrically connected to the star point (37) or to one of the phases of the three-phase power source (151). [10] Motor vehicle (200) with an electric machine (100) which is part of an electric drive module of the motor vehicle (100), characterized by , that the electric machine (100) is designed according to one of claims 1 to 9.

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