WO2013170350A1

WO2013170350A1 - Liquid cooling arrangement for external rotor electric machine

Info

Publication number: WO2013170350A1
Application number: PCT/CA2013/000458
Authority: WO
Inventors: Stephen Fleming
Original assignee: Tm4 Inc.
Priority date: 2012-05-14
Filing date: 2013-05-09
Publication date: 2013-11-21

Abstract

A liquid cooling arrangement for electric machines uses a continuous cooling tube associated with a heat-storing element. The cooling tube has a serpentine configuration and the heat-storing element includes longitudinal slots starting from both longitudinal ends of the heat-storing element. Notches are aligned with the longitudinal slots and are provided on opposite longitudinal ends. Accordingly, it is possible to slightly deform the heat-storing element to properly position it into the internal stator of an electric machine. An internal biasing assembly may be used to force the external surface of the heat-storing element to the internal surface of the stator.

Description

TITLE

LIQUID COOLING ARRANGEMENT FOR EXTERNAL ROTOR ELECTRIC MACHINE

FIELD

[0001] The present invention relates to electric machines. More specifically, the present invention is concerned with a liquid cooling arrangement for electric machines and with electric machines provided with such a liquid cooling arrangement.

BACKGROUND

[0002] Electric machines, motors or generators, are well known in the art. It is also widely known that electric machines generate heat as a byproduct and that this heat must be somehow extracted from the machine to improve the performance of the machine and/or prevent early degradation or failure thereof.

[0003] Electric machines are often air-cooled. This is easily done by providing apertures in the body of the machine to force air therethrough. The efficiency of such a cooling arrangement is often poor since air is a generally low efficiency cooling fluid. Furthermore, some electric machines operate in such adverse environments that it is not possible to provide an electric machine with apertures to allow air therein. Accordingly, fluid cooling arrangements for electric machines have also been designed.

[0004] Some permanent magnet electric machines are provided with an internal stator and an external rotor generally enclosing the stator. When this is the case, the stator has a generally cylindrical body and coils are so mounted to the cylindrical body as to outwardly produce a magnetic field that interacts with the externally provided rotor. Since the heat is generally generated in the stator that is somewhat enclosed by the rotor, it may be difficult to install a fluid cooling arrangement inside an enclosed stator of such an external rotor electric machine.

BRIEF DESCRIPTION OF THE DRAWINGS [0005] In the appended drawings:

[0006] Figure 1 is a perspective view of a liquid cooling arrangement according to a first illustrative embodiment;

[0007] Figure 2 is a sectional side elevation view of an electric machine provided with the liquid cooling arrangement of Figure 1 ;

[0008] Figure 3 is a perspective view of the stator of the electric machine of Figure 2;

[0009] Figure 4 is a sectional view taken along line 4-4 of Figure 3;

[0010] Figure 5 is a perspective view of a liquid cooling arrangement according to a second illustrative embodiment;

[0011] Figure 6 is a perspective view of a liquid cooling arrangement according to a third illustrative embodiment; and [0012] Figure 7 is a sectional view similar to Figure 4 but illustrating a fourth illustrative embodiment of a liquid cooling arrangement.

DETAILED DESCRIPTION

[0013] An object is generally to provide an improved liquid cooling arrangement for electric machines.

[0014] More specifically, in accordance with an illustrative embodiment, there is provided a liquid cooling arrangement to be inserted in the internal stator of an electric machine, the internal stator being provided with an internal surface, the liquid cooling arrangement comprising:

a tubular body provided first and second longitudinal ends and an external surface so configured and sized as to be applied to the internal surface of the internal stator; the first and second longitudinal ends include expansion slots and notches so configured as to allow the deformation of the tubular body; the tubular body also includes a cooling path provided with a fluid inlet and a fluid outlet;

a biasing assembly so configured and sized as to bias the external surface of the tubular body against the internal surface of the internal stator.

[0015] According to another aspect, there is provided an electric machine comprising:

an internal stator provided with an internal surface;

an external rotor coaxially mounted about the internal stator; and a liquid cooling arrangement inserted in the internal stator, the liquid cooling arrangement comprising:

a tubular body provided first and second longitudinal ends and an external surface so configured and sized as to be applied to the internal surface of the internal stator; the first and second longitudinal ends include expansion slots and notches allowing deformation of the tubular body; the tubular body also includes a cooling path provided with a fluid inlet and a fluid outlet; and

[0016] The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one", but it is also consistent with the meaning of "one or more", "at least one", and "one or more than one". Similarly, the word "another" may mean at least a second or more.

[0017] As used in this specification and claim(s), the words

"comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "include" and "includes") or "containing" (and any form of containing, such as "contain" and "contains"), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. [0018] The term "about" is used to indicate that a value includes an inherent variation of error for the device or the method being employed to determine the value.

[0019] The expression "connected" should be construed herein and in the appended claims broadly so as to include any cooperative or passive association between mechanical parts or components. For example, such parts may be assembled together by direct coupling, or indirectly coupled using further parts. The coupling can also be remote, using for example a magnetic field or else.

[0020] It is to be noted that the expression "electric machine" is to be construed herein as encompassing both electric motors and electric generators disregarding the technology used in these machines.

[0021] Other objects, advantages and features will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings.

[0022] Generally stated, cooling arrangements according to illustrative embodiments use a cooling tube associated with a heat-storing element. The cooling tube has a serpentine configuration and the generally cylindrical heat-storing element includes longitudinal slots starting from both longitudinal ends of the heat-storing element. Notches are aligned with the longitudinal slots and are provided on opposite longitudinal ends. Accordingly, it is possible to slightly deform the heat-storing element to properly position it into the internal stator of an electric machine. Furthermore, the longitudinal slots and the notches allow the material of the heat-storing element to contract and expand at a different rate than the material forming the stator of the electric machine without undue deformation of the stator and without contact loss occurring between these elements. An adequate heat transfer between the heat-storing element and the stator is therefore possible while allowing the use of different materials forming these elements. A biasing assembly may be used to force the external surface of the heat-storing element against the internal surface of the stator.

[0023] Turning now to Figures 1 to 4, a liquid cooling arrangement

10 according to a first illustrative embodiment will be described.

[0024] The liquid cooling arrangement 10 includes a heat-storing element in the form of a tubular body 12 and a cooling path in the form of a continuous serpentine cooling tube 14 embedded in the tubular body 12.

[0025] The tubular body 12 includes an external surface 16 and first and second longitudinal ends 18 and 20. Eight expansion slots 22 are provided from the first longitudinal end 18 and eight expansion slots 24 are provided from the second longitudinal end 20. The expansion slots 22 are open to the first longitudinal end 18 but do not reach the second longitudinal end 20. The slots 22 end in a generally cylindrical transverse aperture 23. Conversely, the expansion slots 24 are open to the second longitudinal end 20 but do not reach the first longitudinal end 18. The slots 24 end in a cylindrical transverse aperture 25.

[0026] The first longitudinal end 18 also includes eight notches 27 generally aligned with the slots 24 while the second longitudinal end 20 also includes eight notches 29 generally aligned with the slots 22. This is more clearly illustrated in Figure 4. [0027] The combination of the slots from one longitudinal end and the aligned notch provided in the other longitudinal end make it easier to deform the tubular body 10 for insertion into a stator as will be described hereinbelow. Furthermore, the transverse apertures 23 and 25 also decrease the force required to deform the tubular body 10.

[0028] One skilled in the art will understand that the size of the aperture 23 could be varied.

[0029] The serpentine cooling tube 14, shown in dashed lines in

Figure 1 , includes a fluid inlet 26 and a fluid outlet 28.

[0030] As can be seen from Figure 1 , the expansion slots 22 and 24 are provided in U-shaped portions of the serpentine cooling tube 14 to allow a continuous cooling tube 14 while providing expansion slots open to either longitudinal end of the body 12.

[0031] Figure 2 schematically illustrates portions of an electric machine 50 provided with the liquid cooling arrangement 10. The electric machine 50 includes a stator 52 provided with coils 54 and a rotor 56 provided with permanent magnets 58.

[0032] The stator 52 includes a generally cylindrical inner surface 60 against which a portion of the outer surface 16 of the cooling arrangement 10 is applied. A bottom shoulder 62 of the stator 52 and a top shoulder 64 of the body 12 ensure a proper insertion of the cooling arrangement 10 in the stator 52. Of course, the shoulders 62 and 64 could be different than those illustrated herein. [0033] As can be seen on the sectional Figure 2, the internal surface

66 of the body 12 includes a central constriction 68 defined by two angled wall portions 70 and 72.

[0034] Figure 2 also illustrates an internal biasing assembly 74 used to bias the external surface 16 of the tubular body 12 against the internal surface 60 of a stator 52. The biasing assembly 74 is provided with first and second rings 76, 78 and a plurality of fasteners 80 (two shown in Figure 2) interconnecting the first ring 76 to the second 78. The outside peripheral walls 82 of the rings 76 and 78 are so angled as to generally correspond to the angle wall portions 70 and 72.

[0035] Accordingly, once the cooling arrangement 10 is slightly deformed to be inserted in the stator 12, thanks to the expansion slots 22 and 24 and the notches 27 and 29, the fasteners 80 can be tightened causing the rings 76 and 78 to be pulled towards one another (see arrows 86). The interaction of the angled walls 82, 70 and 72 deforms the body 12 so as to push the outer wall 16 of the body 12 onto the inner surface 60 of the stator 52 (see arrows 88). Accordingly, an adequate heat transfer is achieved between the stator 52 and cooling arrangement 10.

[0036] The expansions slots 22 and 24 and the notches 27 and 29 allow the stator 52 and the cooling arrangement 10, made of dissimilar materials, to thermally expand and/or contract at different rates without causing non-elastic deformation of these elements and while keeping an adequate contact therebetween to allow for an adequate heat transfer. [0037] The rings 76 and 78 can be made of the same material as the stator 52, typically steel, to thermally expand and contract at the same rate thereof.

[0038] Of course, other fastening arrangements could be used. For example, the fasteners 80 of Figure 2 could be replaced by rivets (not shown), provided that compressing means (not shown) are used to temporarily maintain the rings 76 and 78 towards one another while the rivets are installed.

[0039] As will easily be understood by one skilled in the art, other mechanisms mounted inside the tubular body and designed to provide an outwardly directed radial force could be used to bias the external surface of the tubular body against the internal surface of the stator.

[0040] For example, a biasing assembly described in US Patent

6,960,851 entitled "Cooling device including a biasing element" and naming Poulin et al. as inventors could be used but would required slight modifications to the tubular body 10. This document is incorporated by reference herein in its entirety.

[0041] Figure 3 illustrates, in a perspective view, the stator 52 in which the cooling assembly 10 has been inserted. It is to be noted that the internal biasing assembly is not shown for clarity purpose.

[0042] Finally, Figure 4, which is a sectional view taken along line 4-

4 of Figure 3 illustrates the relationship between the slot, notches and cooling tube of the illustrative embodiment. [0043] It will easily be understood by those skilled in the art that both the cooling tube 14 and the body 12 can be made of many adequate heat transfer material. For example, the cooling tube 14 could be made of stainless steel while the body 12 could be made of aluminum. Of course, other materials such as, for example, copper for the tube and cast iron, plastic, zinc or magnesium for the body could be used. One skilled in the art will be in a position to select compatible materials for the tube and body.

[0044] Turning now to Figure 5 of the appended drawings, a liquid cooling arrangement 100 according to a second illustrative embodiment will be described. It is to be noted that the liquid cooling arrangement 100 is similar to the liquid cooling arrangement 10 illustrated in Figures 1 to 4. Accordingly, only the differences therebetween will be described hereinbelow, for concision purpose.

[0045] The cooling path of the liquid cooling arrangement 100 is defined by a cooling tube 102 that is not embedded in the tubular body 104 but is inserted and deformed in a serpentine channel 106 provided on the external surface 108 of the tubular body 104. The serpentine channel 106 has a generally C-shaped cross-section.

[0046] The continuous cooling tube 102 is therefore in physical contact with both the body 104 and the stator (not shown), when the liquid cooling arrangement 100 is inserted in a stator.

[0047] The expansion slots 1 10 are provided between the longitudinal portions of the cooling tube 102 to prevent interference therebetween. The notches 1 1 1 are aligned with the slots 1 10, as described above. [0048] Such a cooling tube configuration described in US Patent

6,992,41 1 , entitled "Liquid cooling arrangement for electric machines" and naming Houle et al. as inventors. This document is incorporated by reference herein in its entirety.

[0049] Turning now to Figure 6 of the appended drawings, a liquid cooling arrangement 200 according to a third illustrative embodiment will be described. Again, since the liquid cooling arrangement 200 is similar to the liquid cooling arrangement 10 illustrated in Figures 1 to 4, only the differences therebetween will be described hereinbelow.

[0050] The cooling path of the liquid cooling arrangement 200 includes eight U-shaped cooling tubes 202 each including a fluid inlet 204 and a fluid outlet 206. Expansion slots 208 are provided either between the U- shaped cooling tubes 202 or between the longitudinal legs thereof so as to not interfere with the operation of the cooling tubes 202. The notches 209 are aligned with the slots 208, as discussed hereinabove.

[0051] The cooling path also includes a manifold 210 provided with a fluid inlet 212 and a fluid outlet 214 and mounted to the inlets 204 and outlets 206 of the cooling tubes 202 to provide a single inlet and outlet for the liquid cooling arrangement 200. It is to be noted that the manifold 210 is schematically illustrated in Figure 10.

[0052] Of course, one skilled in the art will understand that the number of U-shaped cooling tubes 202 can be changed.

[0053] Finally turning to Figure 7 of the appended drawings, a liquid cooling arrangement 300 according to a fourth illustrative embodiment will be described. The liquid cooling arrangement 300 is very similar to the liquid cooling arrangement 10 of Figure 4, accordingly, for concision purpose, only the differences between these cooling arrangements will be described hereinbelow.

[0054] Generally stated, the main difference between the cooling arrangements 300 and 10 concerns the shape and size of the notches 302 and 304. Indeed, while the notches 27 and 29 of Figure 4 are generally narrow and shallow, the notches 302 and 304 of the liquid cooling arrangement 300 are wider and deeper. One skilled in the art will understand that the shape and size of the notches are dependent on the required flexibility of the arrangement.

[0055] It is to be noted that while the external surfaces of the cooling arrangement bodies is shown herein as having shoulders defining different body diameters, straight cylindrical outside surfaces could be used. As will be easily understood by one skilled in the art the external surface of the body of the cooling arrangement generally corresponds to the internal surface of the stator of the electric machine to provide an adequate contact therebetween.

[0056] It is also to be noted that heat transfer materials such as adhesive, thermal grease or thermal pads could be provided between the external surface of the body and the internal surface of the stator to improve the heat transfer from the stator to the liquid cooling arrangement.

[0057] It is to be understood that the liquid cooling arrangement is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The liquid cooling arrangement is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the liquid cooling arrangement has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature of the subject liquid cooling arrangement as defined in the appended claims.

Claims

What is claimed is:

1. A liquid cooling arrangement to be inserted in the internal stator of an electric machine, the internal stator being provided with an internal surface, the liquid cooling arrangement comprising:

2. A liquid cooling arrangement as recited in claim 1 , wherein each expansion slow provided on the first longitudinal end is aligned with a corresponding notch on the second longitudinal end and wherein each expansion slow provided on the second longitudinal end is aligned with a corresponding notch on the first longitudinal end.

3. A liquid cooling arrangement as recited in claim 1 , wherein each expansion slot ends in a generally cylindrical transverse aperture.

4. A liquid cooling arrangement as recited in claim 1 , wherein the cooling path is defined by a cooling tube embedded in the tubular body.

5. A liquid cooling arrangement as recited in claim 4, wherein the embedded cooling tube is a continuous serpentine cooling tube.

6. A liquid cooling arrangement as recited in claim 1 , wherein the external surface of the tubular body includes a serpentine channel and wherein the cooling path is defined by a cooling tube inserted in the serpentine channel.

7. A liquid cooling arrangement as recited in claim 6, wherein the serpentine channel has a generally C-shaped cross-section.

8. A liquid cooling arrangement as recited in claim 1 , wherein the cooling path is defined by at least two generally U-shaped cooling tubes interconnected by a manifold providing the fluid inlet and the fluid outlet of the cooling path.

9. A liquid cooling arrangement as recited in claim 8, wherein the at least two generally U-shaped cooling tubes are defined by two longitudinal legs interconnected by an integral elbow; the expansion slots of the first longitudinal end of the tubular body are provided between the longitudinal legs while the expansion slots of the second longitudinal end of the tubular body are provided between adjacent generally U-shaped cooling tubes.

10. A liquid cooling arrangement as recited in claim 1 , wherein the tubular body includes an internal surface and wherein the biasing assembly is an internal biasing assembly mounted to the internal surface of the tubular body and configured and sized to provide an outwardly directed biasing force to apply the external surface of the tubular body against the internal surface of the stator.

1 1. A liquid cooling arrangement as recited in claim 10, wherein the internal surface provided with a constriction defined by first and second angled wall portions; the internal biasing assembly includes first and second rings each provided with an angled peripheral wall configured and sized to contact a respective angled wall portion of the tubular body, and with at least two fasteners interconnecting the first and second rings; wherein the at least two fasteners are so mounted to the first and second rings that rotation of the fasteners forces the second ring towards the first ring thereby applying an outwardly directed biasing force to apply the external surface of the tubular body against the internal surface of the stator.

12. A liquid cooling arrangement as recited in claim 1 1 , wherein the first and second rings are made of the same material as the stator to thereby thermally expand and contract at about the same rate.

13. A liquid cooling arrangement as recited in claim 1 1 , wherein the first ring includes apertures configured to allow the fasteners therethrough and wherein the second ring includes threaded apertures configured and sized to receive a threaded portion of the fasteners.

14. An electric machine comprising:

an internal stator provided with an internal surface;

an external rotor coaxially mounted about the internal stator; and

a liquid cooling arrangement inserted in the internal stator, the liquid cooling arrangement comprising: