RADIAL FLOW ELECTRIC MOTOR

Abstract

A radial-flow electric motor comprises a stator with a radially inner stator surface and a rotor mounted inside the stator. The rotor defines an axis of rotation and has axially opposite rotor ends and a radially outer rotor surface located near the radially inner stator surface, creating an air gap between them. The rotor also includes a fluid circulation arrangement with at least one fluid channel extending through the rotor to the radially outer rotor surface and configured to receive a liquid via a first pass and a gas via at least a second pass.The fluid circulation arrangement is also configured to direct the liquid and gas into the air gap via centrifugal force when the rotor inside the stator rotates sufficiently to discharge the liquid and gas from the air gap at the axially opposite ends of the rotor, thereby cooling the electric motor.

Description

[0001] The description refers to a radial flux electric motor with air gap cooling.

[0002] An electric motor is a machine that converts electrical energy into mechanical energy. Electric motors can be designed as alternating current (AC) or direct current (DC). The operation of an electric motor is based on the electromagnetic interaction between permanent magnets and the magnetic field generated by the machine's selectively excited coils. Electric motors are divided into two categories based on the direction of the magnetic field: axial flux motors and radial flux motors.

[0003] As a byproduct of the torque generated, electric motors generate heat energy, which can affect motor performance and reliability. Cooling an electric motor can therefore reduce thermal stress on the motor poles or windings and extend the motor's lifespan at or near peak load. In addition, cooling electric motors in general can make motor operation quieter, improve motor operation at higher speeds, and enable a reduction in motor inertia and housing wear.

[0004] DE 10 2021 200 283 A1 describes an electrical machine with a housing, a stator arranged stationary in the housing, a rotor with a rotor shaft, an air gap formed between the rotor and stator, and a cooling device for liquid cooling the electrical machine, wherein the rotor shaft has an axial bore in the axial direction that extends at least partially into a region of the rotor; the rotor has a radially extending air duct that extends from an inner side contacting the rotor shaft to an outer side facing the air gap; and the rotor shaft has a bore that is aligned with the air duct such that air can flow from the rotor shaft into the air gap. Furthermore, a method for generating an air flow in an air gap between the stator and rotor of an electrical machine is described.

[0005] DE 10 2015 223 073 A1 describes an electric motor comprising a stator and a rotor mounted on a rotor shaft for rotation about a rotor axis. The rotor shaft has a hollow section through which a cooling fluid flows and has at least one opening on its outer surface for the passage of the fluid. The at least one opening is designed to direct the cooling fluid directly onto an end face of the rotor and / or onto a winding head of the stator.

[0006] DE 10 2016 210 930 A1 describes a rotor lamination stack for an electrical machine, wherein the rotor lamination stack comprises a plurality of laminations stacked in a stacking direction. The laminations each have at least one inner opening and at least one outer opening, which connect the end faces of the respective lamination to one another and are arranged on two radially spaced-apart concentric circles. The inner openings of laminations offset in the stacking direction are arranged offset from one another in a circumferential direction of the laminations such that at least one inner cooling channel running through the rotor lamination stack is formed. The outer openings of laminations offset in the stacking direction are arranged offset from one another in a circumferential direction of the laminations such that at least one outer cooling channel running through the rotor lamination stack is formed.Furthermore, the at least one inner cooling channel and the at least one outer cooling channel are oriented in different directions. Furthermore, at least one of the two cooling channels (the at least one inner cooling channel and the at least one outer cooling channel) has a screw-spindle shape. Furthermore, an electrical machine with a rotor core as described above and a method for producing the rotor core are described.

[0007] US 2023 / 0 170 762 A1 describes a rotor cooling structure comprising a turbine fan structure provided on the first and second sides of a rotor for an induction motor; a coolant channel having a plurality of coolant channel inlet openings provided on a bottom side of the turbine fan structure and a plurality of coolant channel outlet openings provided at an axial center of the rotor, fluidly communicating with the coolant channel inlet openings and the coolant channel outlet openings, and provided along conductor bars of the rotor; and a plurality of microgroove patterns that hold the coolant channel outlet openings and are provided on both axial sides of the rotor on an outer periphery of the rotor. It can be considered an object to provide an improved radial-flow electric motor, in particular to achieve improved cooling of the electric motor.

[0008] The object is achieved by a radial flux electric motor according to the invention according to claim 1. Furthermore, an exemplary motor vehicle is described which can be operated with the radial flux electric motor according to the invention.

[0009] The radial flux electric motor according to the invention comprises a stator with a radially inner stator surface and a rotor mounted inside the stator. The rotor defines an axis of rotation and has axially opposed rotor ends and a radially outer rotor surface disposed proximate the radially inner stator surface, forming an air gap therebetween. The rotor further comprises a fluid circulation arrangement having at least one fluid channel extending through the rotor to the radially outer rotor surface and configured to receive a liquid, which is pressurized oil, via a first passage and a gas, which is air, via at least a second passage.The fluid circulation assembly is also configured to direct the liquid and gas into the air gap via centrifugal force when the rotor rotates sufficiently inside the stator to discharge the liquid and gas from the air gap at the axially opposite ends of the rotor, thereby cooling the electric motor.The rotor is further configured to suck the gas from an environment of the radial flow electric motor into the second passage by rotating the rotor, in that a negative pressure is generated in the second passage by rotating the rotor, wherein the liquid and the gas are combined in the at least one fluid channel, thereby forming a two-phase mixture which is subsequently injected into the air gap, wherein the two-phase mixture is formed by the liquid mixing with the gas from the at least one second passage as it flows out of the first passage and passes through the at least one second passage.

[0010] In one embodiment, the fluid circulation assembly additionally comprises a rotor shaft disposed coaxially with and secured to the rotor and defining the first passage configured to receive the fluid.

[0011] In one embodiment, the rotor shaft further defines the at least one second passage configured to receive the gas.

[0012] In one embodiment, the rotor defines the at least one second passage.

[0013] In one embodiment, the fluid circulation arrangement comprises a plurality of fluid channels. Each of these fluid channels extends through the rotor to the radially outer rotor surface.

[0014] In one embodiment, the fluid circulation assembly additionally comprises a rotor impeller defining the plurality of fluid channels. The radially outer rotor surface defines circumferentially distributed openings in fluid communication with the respective plurality of fluid channels.

[0015] In one embodiment, the rotor impeller is arranged centrally in the rotor, perpendicular to the axis of rotation.

[0016] In one embodiment, the rotor has a three-part structure including a first lateral rotor part and a second lateral rotor part sandwiching the rotor impeller.

[0017] In one embodiment, the rotor impeller has a laminated impeller structure comprising a first impeller layer and a second impeller layer sandwiching a third impeller layer. The first and second impeller layers, together with the first and second lateral rotor sections, define each of the fluid channels. The third impeller layer and the first and second lateral rotor sections together form a first portion of each fluid channel when the third impeller layer is sandwiched between the first and second impeller layers. The first and second impeller layers together form a second portion of each fluid channel when the third impeller layer is sandwiched therebetween.

[0018] Furthermore, a motor vehicle with a radial flux electric motor according to the invention is described by way of example. Fig. 1 is a schematic diagram of an exemplary motor vehicle having a powertrain that utilizes a radial flux electric motor generator for propulsion. Fig. 2 is a schematic side view of the Fig. 1, in close-up, showing a stator, an internally disposed coaxial rotor, and a fluid circulation arrangement having one or more fluid channels extending radially outwardly over the rotor. Fig. 3 is a schematic perspective partial sectional view of the Fig. 2, comprising an embodiment of a rotor impeller having fluid channels in communication with liquid and gas passages. Fig. 4 is a schematic perspective view of an embodiment of the Fig. 3, showing a laminated impeller structure of the rotor impeller comprising a first impeller lamination and a second impeller lamination sandwiching a third impeller lamination. Fig. Figure 5 is a schematic cross-sectional side view of the Fig. 3-4, showing the first and second impeller laminates together with the first and second lateral rotor sections defining the fluid channels of the fluid circulation arrangement.

[0019] In Fig. 1, an exemplary motor vehicle 10 having a powertrain 12 is depicted. The motor vehicle 10 may be, but is not limited to, a commercial vehicle, an industrial vehicle, a passenger vehicle, an aircraft, a watercraft, a train, or the like. It is also contemplated that the motor vehicle 10 may be a mobile platform, such as an aircraft, an all-terrain vehicle (ATV), a boat, a personal mobility device, a robot, and the like, to fulfill the purposes of this disclosure. The powertrain 12 includes a first power source 14, depicted as an electric motor-generator, configured to generate a first torque of the power source T1 (in Fig. 1) for propelling the motor vehicle 10 via driven wheels 16 relative to a road surface. The motor-generator 14 may be configured as a radial flux electric motor, in which the magnetic flux is generated perpendicular to the motor's rotational axis and the air gap between the rotor and stator of the machine is arranged concentrically with the rotational axis.

[0020] As in Fig. 1, the powertrain 12 may also include a second power source 20, such as an internal combustion engine, configured to produce a second power source torque T2. The power sources 14 and 20 may cooperate to propel the motor vehicle 10 and are operatively connected to a transmission assembly 22. The transmission assembly 22 may be configured to transmit the first and / or second torques T1, T2 to an axle drive unit 24, which in turn may be connected to the driven wheels 16. The first power source 14, hereinafter referred to as a motor-generator, may be attached, for example, to the second power source 20, to (or integrated with) the transmission assembly 22, to the axle drive unit 24, or as a standalone assembly to the structure of the vehicle 10.As shown, the motor vehicle 10 additionally includes a programmable electronic control unit 26 configured to communicate via a high-voltage bus 27 and to control the powertrain 12 to produce a predetermined torque from the power source (the sum of T1 and T2), as well as various other vehicle systems. The motor vehicle 10 additionally includes an energy storage system 28, such as one or more batteries configured to generate and store electrical energy for powering the power sources 14 and 20.

[0021] Fig. 2 shows a general cross-section of the radial flux motor generator 14. As in Fig. 3, the motor-generator 14 includes a non-rotatable stator 30 having a generally cylindrical core 32 and winding slots 34. As also shown in Fig. 3, the stator core 32 also has a radially inner stator core surface 32A. The motor-generator 14 also includes a rotor 36 defining a rotational axis X and rotatably mounted within the stator 30. The stator 30 may include multi-phase AC windings 34A disposed within the winding slots 34, with the windings receiving multi-phase AC power from an inverter to establish a rotating magnetic field that applies torque to the rotor 36. The stator windings 34A are generally located within the winding slots 34, with the end turns of the windings at axially opposite stator ends—a first end 32-1 and a second end 32-2—extending beyond the boundaries of the cylindrical core 32.

[0022] As in Fig. 3, the rotor 36 has a ferromagnetic rotor core 38. The rotor core 38 has axially opposed rotor core ends—a first end 38-1 and a second end 38-2. The rotor core 38 may be made of a relatively soft magnetic material, such as laminated silicon steel. In a permanent magnet machine, the stacked rotor laminations may include cavities forming internal pockets for receiving permanent magnets. In an induction machine, the stacked laminations may have peripheral slots for receiving conducting bars. Alternative rotor designs are also used in the industry and may include, for example, surface-mounted permanent magnet and wire-wound rotors. The rotor core 38 has a radially outer rotor surface 38A disposed proximate the radially inner stator core surface 32A, creating an air gap 40 therebetween (shown in the Fig. ). The air gap 40 extends between the axially opposite first end 38-1 and the second end 38-2 of the rotor core.

[0023] As in the Fig. 2 and Fig. 3, the rotor 36 also includes a fluid circulation assembly 42 having one or more fluid channels 44, each extending radially through the rotor to the radially outer rotor surface 38A. The fluid circulation assembly 42 is configured to receive a liquid 46 via a first passage 50-1 and a gas 48 via one or more second passages 50-2 along the rotational axis X. In particular, the liquid 46 may be pressurized oil and the gas 48 may be air. The fluid circulation assembly 42 is further configured to direct the liquid and gas 46, 48 into the air gap 40 via centrifugal force when the rotor 36 rotates within the stator 30 sufficiently to discharge the liquid and gas from the air gap at the axially opposite ends 38-1, 38-2 of the rotor 36. The fluid circulation arrangement 42 is thus configured to cool the motor-generator 14.

[0024] With further reference to the Fig. 2 and Fig. 3, the fluid circulation assembly 42 may additionally include a rotor shaft 52 arranged coaxially with the rotor 36. The rotor shaft 52 may be attached to the rotor 36 and define the first passage 50-1 for supplying the liquid 46 to the fluid channel(s) 44. In particular, the first passage 50-1 may be arranged along the rotation axis X and configured to receive pressurized liquid 46 from one end of the rotor shaft 52. From the first passage 50-1, the liquid 46 may flow into the internal rotor fluid channels 44 through liquid inlets, which may be configured as one or more third passages 50-3. As shown in the Fig. 2, Fig. 3 and Fig. 5, the third passage(s) 50-3 may be transverse bores arranged substantially perpendicular to the first passage 50-1. When the radial flux motor generator 14 generates the first torque T1, the rotor shaft 52 rotates together with the rotor 36 about the rotational axis X. The rotor shaft 52 may be rotatably supported at both ends of the rotor core 38 (the first end 38-1 and the second end 38-2) by bearings (not shown) and may transmit the first power source torque T1 generated by the rotor 36 through the gear assembly 22 (in Fig. 1) to the driven wheels 16.

[0025] As in Fig. 3, the rotor shaft 52 may further form the second passage 50-2 for supplying the gas 48 to the fluid channel(s) 44. Alternatively, the rotor 36 may form the second passage(s) 50-2 (not shown). Fig. 3, the second passage(s) 50-2 may be arranged substantially parallel to the rotational axis X. The gas 48 may be drawn into the second passage 50-2 by the rotation of the rotor 36, wherein a vacuum is created in the second passage resulting from the connection of the second passage with the radially arranged fluid channel(s) 44. As shown in Fig. 3, the first and second passages 50-1, 50-2 are in fluid communication with each of the fluid channels 44 in the fluid circulation assembly 42. The liquid and gaseous fluids 46, 48 can therefore be combined in the fluid channel(s) 44, forming a two-phase mixture which is subsequently injected into the air gap 40.

[0026] With reference to the Fig. 2-5, the fluid circulation assembly 42 may additionally include a rotor impeller 54 defining a plurality of fluid channels 44. The rotor impeller 54 may be arranged perpendicular to the rotational axis X and mounted centrally in the rotor 36. As shown in Fig. 3, the plurality of channels 44 may define a radially arranged channel pattern defined by the rotor impeller 54. As shown in Fig. 3, the channels 44 extend through the rotor impeller 54 to the radially outer rotor surface 38A. In such an embodiment, the radially outer rotor surface 38A defines circumferentially distributed openings 55 (shown in Fig. 5) that are in fluid communication with the respective plurality of fluid channels 44. As such, the rotor 36 may have a three-part structure (shown in Fig. 3 and Fig. 5), including a first lateral rotor part 36-1 and a second lateral rotor part 36-2 enclosing the rotor impeller 54.

[0027] As in Fig. 4, the rotor impeller 54 may include a laminated impeller structure 56. The laminated impeller structure 56 may include a first impeller layer 56-1 and a second impeller layer 56-2, with a third impeller layer 56-3 sandwiched between them. In other words, the first and second impeller laminations 56-1, 56-2 are disposed on opposite sides of the third impeller lamination 56-3. Although the first and second impeller layers 56-1, 56-2 may have an identical shape and structure, the third impeller layer 56-3 is specifically shaped to create voids in certain areas between the first and second impeller layers when the three laminations are stacked together. Such an arrangement of the three laminations 56-1, 56-2, 56-3 makes it possible to create a continuous path for the fluid channels 44 between them.

[0028] As in Fig. 3, the first, second, and third impeller layers 56-1, 56-2, 56-3 create the fluid channels 44 when installed between the first and second lateral rotor portions 36-1, 36-2. Accordingly, the first, second, and third impeller coatings 56-1, 56-2, 56-3, together with the first and second lateral rotor portions 36-1, 36-2, can define each of the fluid channels 44 in the rotor impeller 54. As shown in Fig. 5, the third impeller layer 56-3 and the first and second lateral rotor sections 36-1, 36-2 together define a first portion 44-1 of each fluid channel when the third impeller layer is interposed between the first and second impeller layers 56-1, 56-2. When the third impeller layer 56-3 is sandwiched between the first and second impeller layers 56-1, 56-2, the first and second impeller layers together form a second portion 44-2 of each fluid channel 44. Thus, the first portion 44-1 of the channel 44 is formed closest to the rotor shaft 52 around the third impeller layer 56-3. The second portion 44-2 of the channel 44 is then formed radially further outward between the first and second vanes 56-1, 56-2. The first and second parts 44-1, 44-2 of the channel are therefore in constant fluid communication and guide the liquid 46 and the gas 48 into the air gap 40 during operation of the radial flux motor generator 14.

[0029] As in Fig.2, the radial flow motor generator 14 also includes a motor housing 58 defining a liquid sump 60. The first passage 50-1 may be formed by a stationary tube 61 attached to the motor housing 58 and extending through the center of the rotor shaft 52, thereby introducing the liquid 46 along the rotational axis X generally parallel to the gas stream 48. The liquid sump 60 is configured to collect the liquid 46 after the liquid has exited the air gap 40 and been returned within the housing 58 or through it to the liquid sump by gravity. Both the liquid sump 60 and the first liquid passage 50-1 in the rotor shaft 52 are in fluid communication with a liquid pump 62. The liquid pump 62 is controlled by the electronic control unit 26 and is configured to pressurize and circulate the liquid 46, iewhich pumps fluid from the fluid sump 60 into the first fluid passage 50-1. The fluid pump 62 may be part of an electric engine cooling system 64 operated by the electronic control unit 26.

[0030] The electronic control unit 26 may be programmed with an algorithm 66 to control the fluid pump 62 based on variables sensed, e.g., via appropriate sensors (generally indicated by the numeral 68), or calculated. Such variables may include, for example, the motor phase current, the motor speed, the temperature of the stator 30 and / or the temperature of the rotor 36, and a flow rate of the fluid 46 in the radial-flow electric motor 14. The temperature of the stator 30 and / or the rotor 36 may be either sensed, otherwise determined, or estimated using the recent history of other sensor readings, including fluid temperature, and an engine operating map 70 programmed into the control unit 26.The electric motor cooling system 64 can therefore be configured to eliminate thermal stresses and, among many other advantages, enable longer life of the radial flux electric motor 14 at higher speeds or near peak load, such as when powering the motor vehicle 10.

Claims

[1] Radial flux electric motor (14), comprising: a stator (30) having a radially inner stator surface (32A) and a rotor (36) mounted within the stator (30), defining an axis of rotation (X) and axially opposite rotor ends (38-1, 38-2) and a radially outer rotor surface (38A) disposed proximate the radially inner stator surface (32A), thereby forming an air gap (40) therebetween; wherein the rotor (36) has a fluid circulation arrangement (42) with at least one fluid channel (44) extending through the rotor (36) to the radially outer rotor surface (38A) and is configured to receive a liquid (46), which is pressurized oil, via a first passage (50-1) and a gas (48), which is air, via at least a second passage (50-2) and to direct the liquid (46) and the gas (48) into the air gap (40) via centrifugal force when the rotor (36) rotates sufficiently within the stator (30) to discharge the liquid (46) and the gas (48) from the air gap (40) at the axially opposite rotor ends (38-1, 38-2) and thereby cool the electric motor (14); wherein the rotor (36) is designed to suck the gas (48) from an environment of the radial flow electric motor (14) into the second passage (50-2) by rotation of the rotor (36), by generating a negative pressure in the second passage (50-2) by the rotation of the rotor (36); wherein the liquid (46) and the gas (48) are combined in the at least one fluid channel (44) to form a two-phase mixture which is then injected into the air gap (40); wherein the two-phase mixture is formed by the liquid (46) mixing with the gas (48) from the at least one second passage (50-2) as it flows out of the first passage (50-1) and passes through the at least one second passage (50-2). [2] The radial flux electric motor (14) of claim 1, wherein the fluid circulation assembly (42) further comprises a rotor shaft (52) disposed coaxially with and fixed to the rotor (36) and defining the first passage (50-1). [3] The radial flux electric motor (14) of claim 2, wherein the rotor shaft (52) defines the at least one second passage (50-2). [4] The radial flux electric motor (14) of claim 2, wherein the rotor (36) defines the at least one second passage (50-2). [5] The radial flux electric motor (14) of claim 1, wherein the fluid circulation assembly (42) includes a plurality of fluid channels (44), and wherein each fluid channel (44) extends through the rotor (36) to the radially outer rotor surface (38A). [6] The radial flux electric motor (14) of claim 5, wherein the fluid circulation assembly (42) further comprises a rotor impeller (54) defining the plurality of fluid channels (44), and wherein the radially outer rotor surface (38A) defines circumferentially distributed openings (55) in fluid communication with the respective plurality of fluid channels (44). [7] Radial flux electric motor (14) according to claim 6, wherein the rotor impeller (54) is arranged centrally in the rotor (36) perpendicular to the axis of rotation (X). [8] The radial flux electric motor (14) of claim 7, wherein the rotor (36) has a three-part structure including a first lateral rotor part (36-1) and a second lateral rotor part (36-2) sandwiching the rotor impeller (54). [9] Radial flux electric motor (14) according to claim 8, wherein: the rotor impeller (54) has a laminated impeller structure (56) comprising a first impeller layer (56-1) and a second impeller layer (56-2) sandwiching a third impeller layer (56-3), and together with the first and second lateral rotor sections (36-1, 36-2) defines each of the fluid channels (44).

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