NL2025893B1 - Electric motor with improved cooling - Google Patents

Abstract

Electric motor with improved cooling The invention relates to an electric motor (100) comprising a stator (102) and a rotor (104A, 1048) enclosing said stator. The stator comprises electromagnets (114) which produce as a by-product heat. For cooling the invention uses a (centrifugal) fan (118), that has two configurations: a first configuration in which the fan is mechanically driven by the rotor and a second configuration in which the fan is idling. This is achieved by, for example, frictional coupling between fan and rotor in the first configuration. Several options to achieve this coupling are provided. Decoupling the fan in the second configuration minimizes energy consumption when cooling is not needed. Preferable the switching from the first to the second configuration and vice versa is performed by thermal elements comprising bi-metallic strips (302, 304), memory metal (306), or a bellows (310) pressing at least a part of the fan against the rotor. Another possibility is for example the use of a movable part sticking out of the stator pressing against the rotor thereby frictionally coupling the fan and the rotor.

Description

Electric motor with improved cooling Technical field of the invention.

[0001] The invention relates to an electric motor comprising a stator and a rotor, the rotor rotatable around an axis, the stator comprising electromagnets, the electromagnets located in a hermetically sealed inner volume, the electromagnets in working generating a rotating magnetic field, the electromagnets as a byproduct generating heat, the motor comprising a mechanical fan for causing an air flow for cooling, the fan comprising a multitude of blades rotatably mounted around an axis, the rotation of the blades caused by the rotor.

Acknowledgement.

[0002] The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No.

848620. Background of the invention.

[0003] Such a method is known from Chinese patent publication CN106357051A. This publication describes an in-wheel electric motor with a stator and a rotor. A rim and tire are mounted on the rotor. The rotor shows vent holes for air entering the motor. An axial fan (denoted as item 18) is mounted in the motor while a centrifugal fan, (denoted as item 4-1) with a centrifugal fan blade (denoted as item 5) is mounted on a sidewall of the rotor. The axial fan, being an integral part of the rotor, always rotates together with the rotor, and in one embodiment the centrifugal fan is made to rotate with the rotor as well.

[0004] A disadvantage of the disclosed motor is that the inside of the motor is exposed to the air from environment. Thereby moisture and dirt can enter the motor. Closing the vent holes is no solution, as then the cooling of the fans stops.

[0005] Another disadvantage is that cooling of the stator only takes place by air expelled by the centrifugal fan blown between the outside of the stator and the rim of the wheel.

[0006] Yet another disadvantage is that the drag caused by the two fans is, for a given rotational speed of the rotor, always identical, independent of the actual cooling need. In general a higher cooling efficiency is associated with a higher drag, and thus a lower overall efficiency of the motor. The cooling is designed to be sufficient for the most demanding use cases (e.g.: high ambient temperature, steep hill climb, etc) and will be overdone for normal use cases {e.g.: normal ambient temperature, no hill climb). Therefore also the energy efficiency of the motor will, due to the drag of the fan, in most cases be less than necessary.

[0007] The invention intends to solve the before mentioned disadvantages, or at least some of them, or offer an alternate solution.. Summary of the invention.

[0008] To that end the motor according to the invention is characterized in that the fan is positioned in the sealed inner volume (110) and the fan has at least two configurations, a first configuration showing a larger air displacement and a higher drag than a second configuration.

[0009] By placing the fan in the sealed inner volume no debris or moisture can enter the sealed inner volume. Cooling is achieved by passing air over the walls forming the sealed inner volume. By having a fan with two configurations, one configuration showing a larger air displacement and a larger drag (thus: energy use) than in the second configuration, the fan need not use more energy than necessary. Preferably the rotor coaxially encloses the stator.

[0010] In an embodiment the rotor coaxially surrounds the stator, the stator located in the sealed inner volume.

[0011] Here the rotor completely surrounds the stator, and thus encloses the sealed inner volume. As the person skilled in the art will recognize this implies that the rotor comprises atleast two parts, as otherwise entrance to the inner parts of the motor (for repair, maintenance etc.) would not be possible.

[0012] In another embodiment the motor is an in-wheel electric motor.

[0013] Especially in an in-wheel motor this cooling arrangement is beneficial.

[0014] In another embodiment the fan is a centrifugal fan.

[0015] The air near the axis is not moving radially. The impeller of a centrifugal fan will fling the air outward. Due to its relative thin construction, a centrifugal fan is most suited to be integrated in an in-wheel motor, as can be seen in the figures part of this document. [tis noted that there are several types of centrifugal fans: forward curved (having straight or curved blades), backward curved (having straight or curved blades) and radial fans (having straight blades extending in the radial direction)

[0016] In yet another embodiment the blades are mounted on a ring, the ring perpendicular to and rotatable around the axis, the blades in the first configuration mechanically coupled to the rotor, the blades in the second configuration mechanically decoupled from the rotor and the blades in the second configuration freely rotatable with respect to the rotor.

[0017] Here the blades, mounted on a ring, are rotatable around the axis, for example by mounting the ring with blades on a roller bearing. It is possible to couple the ring and rotor using, for example, a pin, but preferably a frictional coupling is used.

In the first configuration the ring is pressed against a part that rotates with the rotor (or against the rotor itself) and, due to friction, the blades are forced to rotate together with the rotor. If the ring, and thus the blades, are not pressed against the rotor, or a part that rotates with the rotor, the blades can “idle” and the fan will in this second configuration consume less energy than in the first configuration. The ring is then frictionally decoupled from the rotor.

[0018] In still another embodiment the change in configuration comprising a change in orientation of the blades.

[0019] The fan is typically mounted on or near a part of the rotor that is perpendicular to the axis. In the first configuration the blades typically have a length going radially outward and a width parallel to the axis. By re-orienting them such, that the width is perpendicular to the axis (flush against the rotor surface) the air displacement is minimal, as is the drag. As an alternative the blades can be turned such that instead of going outward, they are oriented approximately coaxially around the axis, air displacement and drag are minimized as well. Situations in between these two extremes lead to an air displacement and drag in between these extremes.

Preferably this is achieved by blades made of or comprising bi-metallic strips or made of or comprising memory metal. Also forming the blades as bellows filled with a fluid can induce such changes. Also an element that change form due to a temperature change, the elements comprising bi-metallic strips, memory metal or a bellows filled with a fluid can be used to change the orientation of the blades.

It is noted that this embodiment is easiest implemented using straight blades.

[0020] In yet another embodiment the change in configuration comprises a change in form of the blades.

[0021] By changing the pitch of the blades the air displacement and drag can be changed. Preferably this is achieved by blades made of or comprising bi-metallic strips, or made of or comprising memory metal. Also forming the blades as bellows filled with a fluid can induce such changes. Also an element that change form due to a temperature change, the elements comprising bi-metallic strips, memory metal or a bellows filled with a fluid can be used to change the form of the blades.

[0022] In still another embodiment the configuration is changed using a moving part of the stator.

[0023] A construction alike to the swashplates of a helicopter can be used to transfer an axial movement on the stator to an axial movement on the (rotatable) fan. As an alternative the ring on which the blades are mounted can have a hat on the center, and a hard ball on the axis can push in an axial direction against the ring.

[0024] In a further embodiment the moving part of the stator is moved using an electric motor.

[9025] Using an electric motor on the stator is not only a simple solution, but also enables to bring the fan in the first condition when a high heat dissipation is expected, thereby anticipating instead of only reactively turning the fan on or off.

[0026] In still another embodiment electric power is transferred from the stator to the rotor to bring the fan from the first to the second configuration or vice versa.

[0027] When electric power is transferred form the stator to the rotor, for example by inductive coupling, electric power for a motor mounted on the stator can be generated, the electric power only used for changing the orientation or form of the blades of the fan, or the coupling between fan blades and rotor, can be changed,

[0028] In yet another embodiment the motor comprises a magnetic gap between the rotor and the electromagnets, the motor comprising a fan mounted at a first side of the stator, the stator comprising one or more holes located at a radius smaller than or equal to the intake of the fan to pass air from one side of the stator to the other, as a result of which the fan generates an airflow flowing radially outward at the first side of the motor through the magnetic gap radially inward to the gaps.

[0029] This describes a preferred path for the air flow in the inner volume.

[0030] In still another embodiment the switching from the first configuration to the second configuration is accomplished by a mechanical form change of an element, the element comprising a bi-metal or a memory metal, or a bellows filled with a fluid.

[0031] By using an element that changes form due to change in temperature, for example the earlier mentioned friction coupling takes place when the element's temperature is above a certain temperature and the frictional decoupling takes place when the element’s temperature is below a certain temperature. Although solids expand when heated, this expansion is often insufficient to achieve a result as intended here. However, bi-metal strips, memory metal are known to give sufficiently large displacements and also a bellows filled with a fluid can give a sufficiently large displacement, especially if a phase transition is involved.

[0032] In yet another embodiment parts of the motor show dimples and/or extrusions 5 and/or fins to improve heat transfer.

[0033] To improve the heat transfer the fan blows air through the inner volume, transporting heat from the electromagnet on the stator to a rotor that is exposed to the environment. To further improve the heat transfer dimples and extrusions and/or fins are formed on the rotor and/or the stator.

Inthe case of the rotor the dimples, extrusions and/or fins can be placed on surfaces exposed to the inner volume, but also on surfaces exposed to the environment.

[0034] In still another embodiment the fan comprises means to increase the rotational speed of the fan above the rotational speed of the rotor

[0035] Such means may comprise for example a gear box comprising gear wheels or a belt. Brief description of the drawings.

[0036] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end: Figure 1 schematically shows an in-wheel motor according to the invention, Figure 2 schematically shows a fan for use in the in-wheel motor of figure 1, Figure 3 schematically shows an element comprising a bi-metallic strip, Figure 4 schematically shows an element using memory metal, and Figure 5 schematically shows an element comprising a fluid filled bellows. Detailed description of the invention.

[0037] Figure 1 schematically shows an in-wheel motor according to the invention,

[0038] An in-wheel motor 100 has a stator 102 and a (two-part) rotor 104A, 104B coaxially surrounding the stator. The rotor is made of (at least) two parts that are demountable with respect to each other to enable access to the enclosed volume 106 when needed (during manufacturing, service and repair). The stator is fixedly connected to an main axle 108. The rotor is via bearings 110 rotatably mounted on the main axle. In this particular embodiment the main axle is hollow and electric cables 112 are fed from the electronics outside the in-wheel motor to electromagnets 114 mounted on the stator through the main axle. Permanent magnets 116 mounted on the rotor closely surround the electromagnets and the magnetic field of these permanent magnets interacts with the rotating magnetic field generated by the electromagnets, thereby inducing a torque on the rotor. A fan 118 is mounted on the rotor, the fan having an inlet 120 near the axis and an outlet 122 near the circumference of the fan.

To the rotor a rim 124 and a tire 126 are connected. Also a brake disk 128 of a disk brake is mounted on the rotor.

[0039] Heat is generated due to eddy currents induced in the magnetic material and due to ohmic losses. This heat is removed using fan 118 that forces air around the electromagnets and through the gap between electromagnets and permanents magnets, brings the thus heated air in contact with the rotor part 104A, that in turn is cooled by ambient air. The air is then passed through the stator by holes 130 to the inlet of the fan.

[0040] There will likely be some spillage from air going from the fan outlet to the fan inlet without going to the other side of the stator. This is minimized by making the space between fan and stator sufficiently small or even closing the gap by a seal between fan and stator.

[0041] It is noted that here the housing of the fan is shown to be connected to the rotor. The skilled person will recognize that as an alternative the housing of the fan may be connected to the stator, and in working only the blades to the rotor. An advantage of mounting the fan on the stator is that the before mentioned air spillage now passes over the rotor and is thereby cooled. A disadvantage is that to drive the impeller of the fan a rotating part must go from the rotor to the impeller.

[0042] It is further noted that the fan need not have a housing if closely positioned between rotor and stator, as these walls then act as housing.

[0043] Figure 2 schematically shows a fan for use in the in-wheel motor of figure 1,

[0044] A fan 118 has a housing 202, 204. The housing further shows a perforated inlet 120 and a perforated outlet 122. In the housing a ring 208 is rotatably mounted on fan bearing 208, that is rotatably mounted on main axle 208 via a fan bearing 210. On the ring a multitude of blades 212 are mounted. An element 214 changes form when the temperature changes.

[0045] The fan can be connected to the stator (via housing element 202) or to the rotor (via housing element 204). The element 214 can in the first configuration contact the rotor and thereby make a frictional connection to the rotor. As a result of that frictional contact the ring with the blades (the impeller) of the fan will rotate. However, when the element does not contact the rotor (in the second configuration), the fan will idle. This means that in the first configuration air is circulated, at the cost of drag, while in the second configuration no air is circulated, and no drag is caused by the fan. it is noted that hysteresis can be built into the element, for example using a magnet, to attach to the rotor. It is further noted that, to avoid wear when switching from the first to the second configuration, an element with a bi-stable form can be used.

[0048] Figure 3 schematically shows an element comprising a bi-metallic strip 302, 304.

[0047] A bi-metallic strip, or a multitude of such strips, can be used for the element. A strip 302 with a high thermal expansion coefficient is connected to a strip 304 with a low thermal expansion coefficient. As a result of the different thermal expansion coefficients the strip will deform when heated, for example from a strip form to a curved form.

[0048] Figure 4 schematically shows an element using memory metal 306, {also known as shape-memory alloy, memory alloy, smart metal, smart alloy, or muscle wire).

[0049] Memory metal can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. A strip 306 of memory metal is attached (welded, glued, soldered) to, for example the rotor. In “cold” condition (when the memory metal can be deformed) a spring 308 pulls a strip 308, towards the rotor, but when the strip of memory metal 306 overcomes the force of spring 308 and pushes against the (ring of the) impeller 204.

[0050] Figure 5 schematically shows an element comprising a fluid filled bellows 310,

[0051] Here a fluid filled bellows expands when the temperature rises, and frictionally connects the rotor and the ring of the impeller. It is noted that the fluid can be a combination of materials, for example a mixture of oil and propanol, thus building up a limited pressure over a small temperature range when the propanol evaporates.

[0052] It is noted that the stator may comprise a moving part that is moved using an auxiliary motor. Such a moving part, for example an extendable axle or spindle extending in line with the main axle, has two positions, a first position in which it pushes the fan against the rotor and a second position where it is free from the fan. In the first position of the extendable axle the fan is in the first configuration, and in the second position of the extendable axle the fan is in the second configuration. Such an extendable spindle is best equipped with a thrust bearing ending in a ball on the axis of the motor, or as an alternative with an axial ball bearing.

[0053] The spindle can be moved by an auxiliary motor, that only moves when going from the first to the second position and vice versa. Thereby energy consumption of such a motor is minimal, and lifetime is long.

[0054] It is further noted that in many embodiments there is a demand to switch from the first to the second position and vice versa quickly to avoid wear. For this a bi-stable element or switch can be used, for example an element that “snaps through” from one position to another.

[0055] The person skilled in the art will, with these pointers, come up with many more solutions. It is expressly noted that the invention is not limited to the examples shown in figure 3 or described elsewhere in this application.

Claims (17)

Conclusions. 1. An electric motor (100) with a stator (102) and a rotor (104A, 104B), the rotor rotatable about an axis (106), the stator with electromagnets (108), the electromagnets in a closed inner volume (110), the electromagnets while generating a rotating magnetic field, the electromagnets generating heat as a by-product, the electric motor comprising a mechanical fan (112, 200) for causing an airflow for cooling, the fan comprising a plurality of blades (214) which are rotatable are mounted about the shaft (106), the rotation of the blades caused by the rotor (104B), characterized in that the fan is positioned in the enclosed inner volume (110) and the fan has at least two configurations, a first configuration being exhibits greater air displacement and higher air resistance than a second configuration. The electric motor of claim 1 wherein the rotor (104A, 104B) coaxially surrounds the stator (102), the stator being contained within the sealed inner volume (110). The electric motor according to any one of the preceding claims, wherein the electric motor is an in-wheel motor. The electric motor of any preceding claim wherein the fan is a centrifugal fan. The electric motor of any preceding claim, wherein the blades are mounted on a ring (212), the ring perpendicular to and rotatable about the axis (106), the blades in the first configuration mechanically coupled to the rotor, the blades in the second configuration mechanically disengaged from the rotor and in the second configuration freely rotatable relative to the rotor. The electric motor of claim 5 wherein the mechanical clutch is a friction clutch and the mechanical clutch is a friction clutch. The electric motor of any preceding claim wherein the change in configuration comprises a change in orientation of the blades. The electric motor of any preceding claim wherein the change in configuration includes a change in the shape of the blades. The electric motor of any preceding claim wherein the switching from the first configuration to the second configuration is accomplished by a mechanical deformation of an element (216), the element comprising a bimetal or a shape memory metal, or a bellows filled with a liquid . The electric motor of any one of claims 8-9 wherein the change in shape or orientation is caused at least in part by a bimetal or a memory metal. The electric motor according to any one of claims 8-10, wherein the blades comprise a bimetal or a memory metal or a bellows filled with a liquid. The electric motor of any preceding claim wherein the configuration is changed using a moving part of the stator. The electric motor of claim 12 wherein the moving part of the stator is moved by an auxiliary electric motor on the stator. The electric motor of any preceding claim wherein electrical power is transferred from the stator to the rotor to move the fan from the first to the second configuration or vice versa. The electric motor of any preceding claim wherein the electric motor motor comprises a magnetic gap between the rotor and the electromagnets, the electric motor motor comprising a fan mounted on a first side of the stator, the stator being one or more within a radius less than or equal to includes holes located flush with the inlet of the fan to allow air to pass from one side of the stator to the other side of the stator, causing the fan to generate an airflow that flows radially outwardly on the first side of the motor through the magnetic opening radially inward and back through the holes. The electric motor according to any one of the preceding claims, wherein parts of the motor have dimples and/or extrusions and/or fins to improve heat transfer. The electric motor according to any one of the preceding claims, wherein the motor comprises means for increasing the speed of the fan above the speed of the rotor.