WO2012139210A1

WO2012139210A1 - Oil cooled electric machine with reservoir

Info

Publication number: WO2012139210A1
Application number: PCT/CA2012/000365
Authority: WO
Inventors: George Bursuc; Martin Houle; Marc Lupien
Original assignee: Tm4 Inc.
Priority date: 2011-04-11
Filing date: 2012-04-11
Publication date: 2012-10-18

Abstract

An electric machine which is oil-cooled and which includes an oil reservoir is described herein. The oil enters the reservoir via the rotation of the rotor and exits the reservoir via a relatively small outlet.

Description

TITLE

Oil cooled electric machine with reservoir.

FIELD

[0001] The present invention relates to electric machines. More specifically, the present invention is concerned with an oil cooled outer rotor electric machine.

BACKGROUND

[0002] Electric machines are well known in the art. Heat generated in these machines has to be dissipated so as to prevent premature failure of the machine.

[0003] Air and liquids have been used to cool electric machines. The efficiency of air-cooling is generally poor and care must be taken when cooling machines with liquids that could cause electrical failure of the machines.

[0004] Oil is generally an interesting liquid to cool electric machines, in part since it may also lubricate various parts of the machine. However, the relatively high viscosity of oil often lowers the efficiency of an electric machine when it is totally or partially immerged in a bath of oil since the rotor has to overcome the friction against the oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] In the appended drawings:

[0006] Figure 1 is a sectional schematic view of an electric machine provided with an oil reservoir according to an illustrative embodiment; the electric machine being shown rotating at low speed;

[0007] Figure 2 is a sectional schematic view similar to Figure 1 illustrating the electric machine rotating at medium speed;

[0008] Figure 3 is a sectional schematic view similar to Figure 1 illustrating the electric machine rotating at high speed; and

[0009] Figure 4 is a sectional schematic view similar to Figure 1 illustrating the electric machine rotating at its maximal speed.

DETAILED DESCRIPTION

[0010] In accordance with an illustrative embodiment, there is provided an oil-cooled electric machine including:

an inner stator defining a longitudinal axis;

an outer rotor so mounted around the stator as to rotate about the longitudinal axis;

an enclosure surrounding the rotor; and a side reservoir having a top fluid inlet and a bottom fluid outlet; the top fluid inlet being larger than the bottom fluid outlet; both the fluid inlet and the fluid outlet being in a fluid communication with the enclosure;

wherein a) oil present in the enclosure is transferred to the reservoir via the rotation of the outer rotor projecting oil in the top fluid inlet of the side reservoir and b) cooled oil present in the side reservoir is transferred by gravity to the enclosure via the bottom fluid outlet.

[0011] 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.

[0012] 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.

[0013] In the present specification 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. [0014] Other objects, advantages and features of the oil cooled electric machine 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.

[0015] Figure 1 of the appended drawings illustrates, in a schematic sectional view, an electric machine 10 provided with an internal stator 12 defining a longitudinal axis 13 and an outer rotor 14. The electric machine 10 is mounted in an enclosure 16 that is designed to contain oil therein. The enclosure 16 is associated with a side reservoir 18 that has a large upper oil inlet 20 and a relatively small lower oil outlet 22, both the inlet and outlet 20 and 22 are in fluid communication with the enclosure 16.

[0016] The side reservoir 18 includes a cooled wall 24 provided with embedded cooling tubes 26 connected to a cooling fluid inlet 28 and a cooling fluid outlet 30. Cooling fluid may thus be circulated in the cooling tubes 26 via a fluid pump (not shown) to evacuate heat present in the reservoir 18 and thereby to cool the oil present in the reservoir 18. It is to be noted that cooling fins (not shown) or other elements (also not shown) used to increase the contact surface between the cooling tubes 26 and the oil contained in the side reservoir 18 could be used.

[0017] The oil outlet 22 is provided with an oil filter 32 filtering impurities present in the oil. A conduit 23 fluidly connects the oil outlet 22 to the enclosure 16.

[0018] One skilled in the art will easily understand that the oil 34 present in the enclosure 16 is transferred to the reservoir 18 via the rotation of the outer rotor 14 projecting oil in the top fluid inlet 20 of the side reservoir 18 and that the cooled oil 36 present in the side reservoir 18 is transferred by gravity to the enclosure 16 via the bottom fluid outlet 22.

[0019] Figure 1 shows the electric machine 10 when the rotor 14 is not rotating or is rotating very slowly. As can be seen from this figure, the level of oil 34 in the enclosure 6 is the same as the level of cooled oil 36 in the side reservoir 18.

[0020] Figure 2 shows the electric machine 10 having its rotor 14 rotating at a medium speed as indicated by arrow 38. When this is the case, rotation of the rotor 14 forces some of the oil 34 present in the enclosure 16 to be transferred to the cooled side reservoir 18 through the large inlet 20 (see arrows 40). Indeed, the rotational motion of the rotor 14 imparts some energy to a portion of the oil that is transported to the reservoir 18. Since the outlet 22 is much smaller than the inlet 20, there is a restriction in the return of the cooled cooling oil to the enclosure 16. Accordingly, the level of oil 34 in the enclosure 16 is lowered and the level of oil 36 in the reservoir 18 is raised since the quantity of cooled oil transferred to the enclosure 16 via the outlet 20 by gravity is lower than the quantity of oil transferred to the reservoir 18 by the rotation of the rotor 14. Therefore, less friction between the rotor 14 and the oil 34 exists.

[0021] Figure 3 shows the electric machine 10 having its rotor 14 rotating at a high speed as indicated by arrow 42. When this is the case, rotation of the rotor 14 forces the major portion of the oil 34 present in the enclosure 16 to be transferred to the cooled reservoir 18 through the large inlet 20 (see arrows 44). Again, since the outlet 22 is much smaller than the inlet 20, there is a restriction in the return of the cooled cooling oil to the enclosure 16. Accordingly, the level of oil 34 in the enclosure 16 is greatly lowered and the level of oil 36 in the reservoir 18 is raised. Therefore, less friction between the rotor 14 and the oil 34 exists.

[0022] Finally, Figure 4 shows the electric machine 10 having its rotor

14 rotating at its maximal speed as indicated by arrow 46. When this is the case, rotation of the rotor 14 forces almost all of the oil 34 present in the enclosure 16 to be transferred to the cooled reservoir 18 through the large inlet 20 (see arrows 48). Again, since the outlet 22 is much smaller than the inlet 20, there is a restriction in the return of the cooled cooling oil to the enclosure 16. Accordingly, the level of oil 34 in the enclosure 16 is greatly lowered and the level of oil 36 in the reservoir 18 is raised. Therefore, minimal friction between the rotor 14 and the oil 34 exists. It is to be noted that the oil reservoir 18 is so configured and sized that when the rotor 14 rotates at its maximal speed, the overflow of cooling oil cascades onto the rotating rotor to ensure a minimal amount of oil 34 in the enclosure 16 to adequately cool the machine 10.

[0023] It is to be noted that this sizing of the reservoir 18 so that it overflows onto the rotating rotor 14 is optional.

[0024] It is also to be noted that the level of oil in the enclosure 16 and reservoir 18 are shown herein for illustration purpose and that the shape and capacity of these elements are schematic.

[0025] As will be understood by one skilled in the art, the system described hereinabove is so designed that there is a maximum level of cooling oil in the reservoir 16 when the electric machine 10 is stopped, blocked or operating at low speeds. When this is the case, the machine 10 has thermal inertia provided by the large amount of cooling oil surrounding it. On the other hand, when the electric machine 10 rotates its rotor 14 at nominal and higher speeds, the amount of oil present in the reservoir 16 is minimal to reduce the friction created between the rotor 14 and the oil to thereby minimize the effects of the oil bath on the overall efficiency of the electric machine.

It is also to be noted that the effective size of the oil outlet 22 or of the conduit 23 could be modified by an active mechanism (not shown) depending on the rotational speed of the rotor 14 to achieve the adequate amount of cooling oil in the enclosure 16. In other words, it would be possible to provide means to vary the diameter of the outlet or of the conduit to thereby modify the rate at which cooled oil is transferred from the side reservoir to the enclosure.

[0026] It is believed that one skilled in the art will be in a position to determine the size of the oil outlet 22 so as to yield a system that has a predetermined amount of oil 34 in the enclosure when the machine 10 is operating at nominal speeds.

[0027] One skilled in the art will understand that while the oil reservoir

18 was shown provided with an active cooling system, other portions of the electric machine or of the enclosure 16 could have an active or passive cooling system. Similarly, other cooling systems, either active or passive, could be used to cool the oil present in the enclosure 16 and/or the side reservoir 18. As non-limiting examples, cooling tubes could be present in the side reservoir 18 or fins could be installed on the outside surface of the enclosure 16 and reservoir 18 to cool the oil by convection. [0028] It is to be noted that while only one reservoir 18 has been illustrated herein, a second reservoir (not shown) could be positions on the other side of the electric machine 10 to play the same role when the rotation direction of the machine is reversed with respect to the clockwise rotation direction illustrated herein.

[0029] One skilled in the art will understand that the oil filter 32 could be positioned elsewhere in the system.

[0030] It is to be noted that the outer surface of the rotor could include elements to improve the transport of oil from the enclosure 16 to the reservoir 18. For example, the outside surface of the stator could be partially or totally covered with micro-vanes (not shown).

[0031] It is to be understood that the oil cooled electric machine is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The oil cooled electric machine 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 oil cooled electric machine 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.

Claims

WHAT IS CLAIMED IS:

1. An oil-cooled electric machine including:

an inner stator defining a longitudinal axis;

an enclosure surrounding the rotor; and

a side reservoir having a top fluid inlet and a bottom fluid outlet; the top fluid inlet being larger than the bottom fluid outlet; both the fluid inlet and the fluid outlet being in a fluid communication with the enclosure;

2. The oil-cooled electric machine of claim 1 , wherein the side reservoir includes a cooling system.

3. The oil-cooled electric machine of claim 2, wherein the cooling system is an active cooling system provided with a cooling tube provided with a cooling fluid inlet and a cooling fluid outlet.

4. The oil-cooled electric machine of claim 3, wherein the cooling tube is associated with a wall of the side reservoir.

5. The oil-cooled electric machine of claim 1 , further including an oil filter so configured as to filter impurities of the cooling oil.

6. The oil-cooled electric machine of claim 1 , wherein the side reservoir is so configured and sized that overflowing oil cascades onto the rotor.

7. The oil-cooled electric machine of claim 1 , wherein the bottom fluid outlet includes a conduit interconnecting the bottom of the side reservoir to the enclosure.

8. The oil-cooled electric machine of claim 7, further including means to vary the diameter of either the fluid outlet and the conduit to thereby modify the rate at which oil is transferred from the side reservoir to the enclosure.

9. The oil-cooled electric machine of claim 7, further comprising an oil filter associated with the conduit to filter the oil as it is transferred from the side reservoir to the enclosure.

10. The oil-cooled electric machine of claim 1 , wherein the rotor has an outer surface provided with oil transporting elements.

11. The oil-cooled electric machine of claim 10, wherein the oil transporting elements include miniature vanes.