Liquid cooling arrangement for electric machines

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 casing of the machine to force air therethrough. The efficiency of such a cooling arrangement is generally poor since air is a generally low efficiency cooling fluid. Furthermore, some electric machines operate in environments that are such that it is not possible to provide 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 an exploded view of the liquid cooling arrangement of Figure 1 ,

[0008] Figure 3 is a sectional view of the liquid cooling arrangement of Figure 1 mounted in an external rotor electric machine;

[0009] Figure 4 is a sectional view taken along line 4-4 of Figure 1 ;

[0010] Figure 5 is a sectional view similar to Figure 4 illustrating a liquid cooling arrangement according to a second illustrative embodiment; and

[0011] Figure 6 is a sectional view similar to Figure 4 illustrating a liquid cooling arrangement according to a third illustrative embodiment. DETAILED DESCRIPTION

[0012] In accordance with an illustrative embodiment, there is provided a liquid cooling arrangement to be inserted in an internal stator of an electric machine. The liquid cooling arrangement comprises a tubular body provided with 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 tubular body includes longitudinal cooling channels, a fluid inlet and a fluid outlet both in fluid communication with a respective one of the longitudinal cooling channels; the first and second longitudinal ends include recesses open to adjacent longitudinal cooling channels. The liquid cooling arrangement also includes covers that are insertable into the recesses to complete a cooling path between the fluid inlet and the fluid outlet.

[0013] 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 comprises a tubular body provided with 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 tubular body includes longitudinal cooling channels, a fluid inlet and a fluid outlet both in fluid communication with a respective one of the longitudinal cooling channels; the first and second longitudinal ends include recesses open to adjacent longitudinal cooling channels. The liquid cooling arrangement also includes covers that are insertable into the recesses to complete a cooling path between the fluid inlet and the fluid outlet. [0014] 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.

[0015] 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.

[0016] In the present specification and in the appended claims, various terminology which is directional, geometrical and/or spatial in nature such as "longitudinal", "horizontal", "front", rear", "upwardly", "downwardly", etc. is used. It is to be understood that such terminology is used for ease of description and in a relative sense only and is not to be taken in any way as a limitation upon the scope of the present disclosure.

[0017] Further, in this specification, the terms "axial direction",

"axially", "axial", and the like, refer to the direction of the rotation axis of the rotor, the direction of the central axis of the cylindrical stator, and the directions corresponding to them, the terms "radial direction", "radially", "radial", and the like, refer to the directions perpendicular to such axial directions, and the terms "circumferential direction", "circumferentially", "circumferential", and the like, refer to each direction along the circumference of a circle drawn about a given point of the rotation axis on a plane perpendicular to the rotation axis. [0018] 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 connection, or indirectly connected using further parts therebetween. The connection can also be remote, using for example a magnetic field or else.

[0019] 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.

[0020] 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.

[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 include an extruded tubular body provided with longitudinal conduits formed therein at generally regular intervals. To form a serpentine cooling channel, adjacent longitudinal conduits are interconnected by separate covers mounted to the body. An inlet and outlet for the cooling fluid are also provided. The tubular body includes longitudinal slots starting from both longitudinal ends thereof. Accordingly, it is possible to slightly deform the heat-storing element to properly position it into the internal stator of an electric machine and to provide proper contact therebetween. Furthermore, the longitudinal slots 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 decrease the risks of 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 which is generally C-shaped, thanks to a full length longitudinal slot 14. The liquid cooling arrangement 10 includes an external surface 16 and first and second longitudinal ends 18 and 20. Expansion slots 22 are provided from the first longitudinal end 18 while 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. Conversely, the expansion slots 24 are open to the second longitudinal end 20 but do not reach the first longitudinal end 18.

[0025] The body 12 is provided with integrally formed longitudinal cooling channels 26 shown in dashed lines in Figure 1 . These cooling channels 26 alternate with the slots 22 and 24. The two cooling channels 26 that are adjacent to the slot 14 (only one shown in Figure 1 ) define a fluid inlet and a fluid outlet and are respectively provided with connectors 28 and 30 as will be further described hereinbelow. [0026] The longitudinal end 20 of the body 12 includes three (3) recesses 32 (shown in dashed lines) configured and sized to receive path- forming covers 34 configured to interconnect two adjacent cooling channels 26. Similarly, The longitudinal end 18 of the body 12 includes four (4) recesses 36 configured and sized to receive path-forming covers 34 (not shown in Figure 1 ) also configured to interconnect two adjacent cooling channels 26. Indeed, as can be seen from this figure, the size, shape and position of the recesses 32 and 36 are such that each recess is in line with two adjacent longitudinal cooling channels 26.

[0027] Accordingly, when the covers 34 are in place in the recesses

32 and 34, a fluid tight cooling path is formed between the inlet and the outlet.

[0028] Figure 2 of the appended drawings illustrates a partially exploded view of the liquid cooling arrangement 10. As can be seen from this Figure, the covers 34 associated with the longitudinal ends 18 and 20 are identical and each include two (2) peripheral grooves 38 and 40 configured and sized to respectively receive O-rings 42 and 44. These O-rings 42 and 44 define sealing means to ensure that the cooling path thus created between the inlet and the outlet is fluid tight.

[0029] One skilled in the art will understand that there are many possible methods to ensure that the covers 34 stay in the recesses 32 or 36. For example, heat-resistant adhesive can be used, the covers 34 may be welded in place or a portion of the interface between the cover and the surrounding longitudinal end (18 or 20) can be locally deformed.

[0030] The connector 28 defining the inlet of the cooling arrangement 10 is also exploded in Figure 2. The three-part connector 28 includes an insertion element 46 an elbow 48 and a threaded connection element 50. The insertion element 46 includes two grooves 52, 54 configured and sized to respectively receive an O-ring 56, 58 for fluid tightness purposes.

[0031] Or course, the structure of the connector 30 is identical to the above-described structure of the connector 28.

[0032] One skilled in the art will understand that the elbow 48 and threaded connection element 50 are shown for illustration only since they could be replaced by other connection elements.

[0033] Figure 3 illustrates a sectional view of an electric machine

100 provided with a liquid cooling arrangement 10 as illustrated in Figures 1 and 2. The electric machine 100 is of the external rotor type and therefore includes an external rotor 102 provided with permanent magnets 104 on an inner surface thereof. The stator 106 includes a stack of laminations 107 provided with external facing slots (not shown) in which coils 108 are mounted. The central aperture of the stator 106 is slightly larger than the cooling arrangement 10 to allow the insertion of the cooling arrangement 10 therein.

[0034] The stator 106 includes a generally cylindrical inner surface

1 10 against which a portion of the outer surface 16 of the cooling arrangement 10 is applied.

[0035] The internal surface 1 12 of the body 14 includes a central constriction 1 14 defined by two angled wall portions 1 16 and 1 18. [0036] Figure 3 also illustrates an internal biasing assembly 120 used to bias the external surface 16 of the tubular body 14 against the internal surface 1 10 of a stator 106. The biasing assembly 120 is provided with first and second rings 122, 124 and a plurality of fasteners 126 (two shown in Figure 3) interconnecting the first ring 122 to the second 124. The outside peripheral walls 128, 129 of the rings 122 and 124 are so angled as to generally correspond to the angled wall portions 1 16 and 1 18.

[0037] Accordingly, once the cooling arrangement 10 is slightly deformed to be inserted in the stator 106, thanks to the expansion slots 22 and 24 and the slot 14, the fasteners 126 can be tightened causing the rings 122 and 124 to be pulled towards one another. The interaction of the angled walls 1 16, 1 18, 128 and 129 deforms the body 12 so as to push the outer wall 16 of the body 12 onto the inner surface 1 10 of the stator 106. Accordingly, an adequate heat transfer is realized between the stator 106 and cooling arrangement 10.

[0038] The expansions slots 22 and 24 allow the stator 106 and the cooling arrangement 10, often 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 thereby allow for an adequate heat transfer.

[0039] The rings 122 and 124 can be made of the same material as the laminations of the stator 106, typically steel, to thermally expand and contract at the same rate thereof.

[0040] Of course, other fastening arrangements could be used. For example, the fasteners 126 of Figure 3 could be replaced by rivets (not shown), provided that compressing means (not shown) are used to temporarily maintain the rings 122 and 124 towards one another while the rivets are installed.

[0041] 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.

[0042] One skilled in the art will understand that the electric machine

100 is schematically illustrated in Figure 3 and that other elements such as an enclosure and bearings, are required for the machine to operate properly.

[0043] Turning now to Figure 4 of the appended drawings, which is a sectional view taken along line 4-4 of Figure 1 , the cover 34 will be further described.

[0044] As can be seen from this figure, the cover 34 includes a curved surface 60 interconnects the two adjacent cooling channels 26. Accordingly, the head loss is minimal.

[0045] Figure 4 also illustrated the shoulder 62 provided at the bottom of the recess 36 to properly position the cover 34 therein.

[0046] One skilled in the art will understand that mechanical or chemical means can be used to ensure that the covers 34 stay in place in the recess 36. [0047] Figure 5 is a sectional view similar to Figure 4 illustrating a second illustrative embodiment. As can be seen from this figure, the cover 34' does not have a curved surface but is simply a rectangular section block of material that can be inserted in the recess 36'. The embodiment of Figure 5 is slightly less expensive to manufacture but accounts for a greater head loss.

[0048] Finally Figure 6, also a sectional view similar to Figure 4, illustrates a third illustrative embodiment. As can be seen from this Figure, the cover 34" is made of plastic material so that it may be inexpensively manufactured by molding. Of course, one skilled in the art will be in a position to select plastic material that can withstand the maximal temperature of the stator. The cover 34" is maintained in the recess 36 by a plate 64 that is held in place by local deformation of the edge of the recess 36 (see numeral 66).

[0049] One skilled in the art will understand that the body 12 of the liquid cooling arrangement could be provided without the slot 14 to yield a non- C-shaped body.

[0050] Similarly, while the body 12 is shown and described as having expansion slots, these slots could be omitted and the body could be press-fitted into the stator.

[0051] One skilled in the art will understand that the body 12 can be manufactured by an extrusion process followed by simple machining steps to cut the various slots 14, 22 and 24 and to machine the recess 32 and 36 receiving the path forming covers 34. [0052] While the cooling channels 26 are shown herein as axial voids in the body 12, these cooling channels could be defined by hollow tubes (not shown) present in the body 12 during its fabrication.

[0053] While cylindrical shaped cooling arrangements have been described above, other shapes, such as polygons, could be used for the outer surface of the cooling arrangement and for the inner surface of the stator. Of course, the shape of these surfaces must correspond and be designed to provide an adequate contact and hence an adequate heat transfer.

[0054] 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.

[0055] The liquid cooling arrangements of the illustrative embodiments are made of a thermally conductive material, such as aluminum, copper, or stainless steel, but may alternatively be made of a polymer, ceramic, or any combination thereof. The liquid cooling arrangements may be cast, machined or manufactured using any suitable method.

[0056] As will easily be understood by one skilled in the art, other sealing means could be applied between the covers and the cavities.

[0057] It is to be understood that the invention is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The invention 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 present invention 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 invention as defined in the appended claims.