WO2006007709A1

WO2006007709A1 - Air cooled internal stator electric machine

Info

Publication number: WO2006007709A1
Application number: PCT/CA2005/001127
Authority: WO
Inventors: Stéphane POULIN; Louis-Philippe Bibeau; Jean-François LAVIGNE
Original assignee: Tm4 Inc.
Priority date: 2004-07-20
Filing date: 2005-07-18
Publication date: 2006-01-26

Abstract

An electric machine of the internal stator type includes a cooling assembly to cool the machine via a flow of air. The internal stator includes a generally cylindrical body having a central aperture. The cooling assembly is mounted inside the central aperture of the stator and includes a fresh air inlet, a heated air outlet, an intermediate wall provided between the fresh air inlet the heated air outlet, fins in contact with the internal surface of the stator and a fan drawing air from the fresh air inlet and expelling air from the heated air outlet.

Description

TITLE OF THE INVENTION

Air Cooled Internal Stator Electric Machine

FIELD OF THE INVENTION

[0001] The present invention generally relates to electric machines provided with an internal stator and an external rotor. More specifically, the present invention is concerned with such an electric machine where the internal stator is air- cooled.

BACKGROUND OF THE INVENTION

[0002] Electric machines having internal stators and external rotors are known in the art. For example United States Patent no. 5,327,034 issued on July 5, 1994, entitled "Electrically motorized wheel assembly" and naming Couture et al. as inventors describes a motor-wheel having an internal stator and an external rotor.

[0003] Cooling of such electric machines is generally more complicated than cooling more conventional external stator machines since one cannot rely on convection alone since the external rotor prevents direct contact between ambient air and the stator. Indeed, heat is mostly generated in stators of electric machines and access to internal stators is more problematic than access to external stators.

OBJECTS OF THE INVENTION

[0004] An object of the present invention is therefore to provide an air- cooled electric machine provided with an internal stator.

[0005] It is to be noted that the expression "electric machine" is to be construed herein as meaning an electric motor and/or an electric generator. [0006] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0000] In the appended drawings:

[0000] Figure 1 is a top plan view of a cooling insert according to a first embodiment of the present invention;

[0000] Figure 2 is a schematic sectional view of an electric machine provided with the cooling insert of Figure 1 ; the sectional view relates to line 2-2 of Figure 1 ;

[0000] Figure 3 is a schematic sectional view similar to Figure 2 but illustrating the flow of air when the cooling fan rotates in a direction opposite the rotation direction of Figure 2;

[0000] Figure 4 is a is a top plan view of a cooling insert according to a second embodiment of the present invention;

[0000] Figure 5 is a schematic sectional view of an electric machine provided with the cooling insert of Figure 4; the sectional view relates to line 5-5 of Figure 4; and

[0000] Figure 6 is a top plan view of a cooling insert according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0001] Generally stated, the present invention is concerned with the air cooling of an internal stator type electric machine where the internal stator includes a generally tubular body having a central aperture. An air-cooling assembly is mounted inside the central aperture of the stator. An embodiment of the cooling assembly includes a central fresh air inlet, a peripheral heated air outlet, an intermediate wall provided between the fresh air inlet the heated air outlet, fins directly or indirectly in contact with the internal surface of the central aperture of the stator and a fan drawing air from the fresh air inlet and expelling air through the heated air outlet.

[0002] Turning to Figures 1 and 2 of the appended drawings, a cooling assembly according to a first embodiment of the present invention will be described. More specifically, Figure 1 illustrates a cooling insert 10 and Figure 2 schematically illustrates the cooling assembly mounted inside the internal stator 12 of an electric machine 14. The electric machine 14 also includes an external rotor 16, a casing 18 and an output shaft 20.

[0003] The cooling assembly includes the cooling insert 10, a fan 22 mounted inside the stator 12 and an air diverting plate 24 provided with a central aperture 26.

[0004] The cooling insert 10, better seen in Figure 1 , includes a central aperture 28 defined by and intermediate wall 29, internal cooling fins 30 and external S-shaped cooling fins 32. The S-shaped cooling fins 32 are each provided with contacting surfaces 34 configured and sized to contact the internal surface 36 of the stator 12. [0005] It is to be noted that the generally S-shape of the fins 32 allow an adequate deformation of the fins 32 for the insertion of the insert 10 inside the stator 12. More specifically, the insert 10 may be inserted inside the stator 12 via a counterclockwise rotation (with respect to Figure 1 ) associated with a pressure along the entry direction. The biasing force of the fins 32 trying to regain their original shape shown in Figure 1 maintain the insert inside the stator 12 while providing an adequate contact between the contact surface 34 and the internal surface 36 of the stator 12 to allow heat to be transferred from the stator 12 to the insert 10.

[0006] The insert 10 may be made of heat conducting material, such as, for example aluminum or aluminum alloys, according to conventional extrusion processes.

[0007] The fan 22 is mounted at the bottom wall 38 of the stator 12 and is so configured and sized to draw air from the central aperture 28 of the insert 10 and to expel air from the peripheral portion of the insert 10, i.e. through the S-shaped fins 32. It is to be noted that the fan 22 is very schematically illustrated in the appended figures. The fan 22 may for example be a squirrel cage electric fan.

[0008] The air diverting plate 24, provided with a central aperture 26, is so mounted to the casing 18 as to leave a gap 40 between itself and the casing 18. The air diverting plate 24 is mounted to the casing via six discrete spacers 42 (only two shown) and fasteners (not shown). As seen in Figure 2, the air diverting plate 24 abuts the insert 10 that extends beyond the casing 18.

[0009] In operation, the fan 22 axially draws air from the air inlet of the cooling assembly, i.e. the central aperture 26 of the diverting plate 24 (see arrow 44). The drawn air passes through the central aperture 28 of the cooling insert 10 (see arrows 46). The drawn air is thus heated by the internal fins 30 carrying heat from the external fins 32 in contact with the stator 12. The partially heated air then passes through the fan blade (see arrow 48) to be pushed between the external fins 32 (see arrows 50). The pushed air thereby directly contacts the external fins 32 and the internal surface 36 of the stator 12. Accordingly, the air draws more heat from the cooling insert 10 to thereby cool the stator 12. When it reaches the diverting plate 24, the pushed air is diverted (see arrow 52) so as to pass between the plate 24 and the end of the casing 18, i.e. the heated air outlet, to exit the electric machine 14 in a radial direction.

[0010] One skilled in the art will understand that by making the warmed air exit the electric machine 14 in a direction away from the inlet, the drawn air is not warmed by the exiting air, thereby improving the cooling effect.

[0011] Figure 2 illustrates optional end fins 54 mounted to the end of the casing 18 to further improve the cooling effect of the radially exiting air.

[0012] It is to be noted that the fan 22 can be continuously operated or may be controlled by an optional temperature sensor (not shown) that start the fan 22 when the electric machine reaches a predetermined temperature.

[0013] Alternatively, the fan 22 can be a simple fan blade directly or indirectly connected to the shaft 20 of the rotor 16 to thereby draw cooling air only when the machine 14 is in operation.

[0014] Turning now briefly to Figure 3 of the appended drawings, the electric machine 14 is shown with the fan 22 rotating in the opposite direction of the direction shown in Figure 2. In this case, the fresh air enters radially and exits axially. More specifically, the air enters from the space between the plate 24 and the end of the casing 18 (see arrow 53), is drawn between the external fins 32 (see arrow 51 ), passes through the fan blades (see arrow 49) and is pushed through the insert 10 (see arrow 47) and exits through the central aperture 26 of the plate 24. [0015] It is to be noted that while the cooling insert 10, is described hereinabove as being a one-piece element, it could be formed of a stack on thinner elements having the cross-section illustrated in Figure 1. This facilitates the insertion of the separate elements inside the stator. For example, it has been found that one centimeter thick elements were adequate.

[0016] Turning now to Figures 4 and 5 of the appended drawings, a cooling assembly according to a second embodiment of the present invention will be described. It is to be noted that since the cooling assembly of these figures is very similar to the cooling assembly illustrated in Figures 1 to 2 and described hereinabove, only the differences between these cooling assemblies will be described hereinbelow.

[0017] Figure 4 illustrates a cooling insert 100 to be inserted inside the stator 12. The insert 100 has a generally C-shaped cross-section and includes a wall 101 having an outer surface 102 configured and sized to be in contact with the inner surface 36 of the stator 12 and internal fins 104. The fins 104 are therefore in contact with the inner surface 36.

[0018] To be inserted inside the stator 12, free ends 106 and 108 are brought closer together via a pair of tongs (not shown) configured and sized as to enter the apertures 110. Once inserted, the pressure is released from the tongs and the outer surface 102 properly contacts the inner surface 36 to thereby allow heat to be transferred from the stator 12 to the insert 100.

[0019] A tubular air guide 112 provided with a central aperture 113 and an integral air deflecting plate 114 is mounted to the end of the casing 18 via six spacers 116 (only two shown) and fasteners (not shown). [0020] It is to be noted that since the cooling insert 100 includes a continuous outer wall, the insert 100 does not abut the deflecting plate 114 since it would prevent air from exiting the insert 100.

[0021] The operation of the cooling assembly of Figures 4 and 5 is very similar to the operation of the cooling assembly of Figures 1 and 2. A notable difference is that the axially drawn air (see arrows 118) will not be heated before it reaches the fan 22 since the tubular air guide 112 is not in direct contact with the cooling insert 100.

[0022] One skilled in the art will understand that the flow of cooling air may be reverse (not shown) with respect to Figure 5, by reversing the direction of rotation of the fan 22.

[0023] Turning now briefly to Figure 6 of the appended drawings, a cooling insert 200 according to a third embodiment of the present invention will be described. Since the insert 200 is very similar to the insert 100 of Figure 4, only the differences between these inserts will be described hereinbelow.

[0024] Mainly, the difference between the insert 200 and the insert 100 concern the method of maintaining the insert inside the central aperture of the stator. While the insert 100 relies on the biasing force caused by the insert trying to regain its original shape after it has been deformed to be inserted in the stator 12, the insert 200 includes a separate biasing assembly 202.

[0025] The biasing assembly 202 includes first and second wedging devices 204 and 206 maintained together by fastening assemblies 208. The biasing assembly 202 is to be mounted to the insert 200 via opposite surfaces 210, 212.

[0026] In the specific example illustrated in Figure 6, the first and second opposite surfaces 210 and 212 are convex. The first and second wedging devices 204 and 206 each have a trapezoidal cross-section and have a longitudinal dimension substantially equal to a longitudinal dimension of the insert 200.

[0027] Each of the first and second wedging devices 204 and 206 includes fastening apertures (not shown) to accept a part of the fastening assembly. Furthermore, the wedging device 204 includes shoulder portions (not shown) to accept the head of a fastener.

[0028] Each fastening assembly 208 includes a bolt 214 inserted through the shoulder portion and the matched fastening apertures (not shown) of the first and second wedging devices 204 and 206. A deformable portion in the form of a disc springs 216 is inserted onto each bolt 214 between the second wedging device 206 and a respective first nut 218. The disc springs 216 includes, for example, one or more Belleville spring washers mounted in series. However, many other types of disc springs could be used. In addition, a second nut 220 is threaded onto each bolt 214 to positively lock the nuts onto the bolt.

[0029] To mount the cooling insert 200 in the stator, the cooling insert 200 without the biasing assembly 202, or with the biasing assembly 202 in a non-biasing position, is inserted inside the central aperture of the stator. The nuts 218 of the fastening assemblies 218 are then tightened until a good contact exists between the external surface 222 of the insert 200 and the internal surface of the stator. Indeed, by tightening the fastener assemblies 202, the wedging devices 204 and 206 are pulled towards one another. The corresponding trapezoidal shape of the wedging devices 204 and 206 and of the first and second opposite surfaces 210 and 212 force the opposed surfaces apart from one another, thereby forcing the external surface 222 onto the internal surface of the stator.

[0030] Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An electric machine comprising: an internal stator having a generally cylindrical body provided with a central aperture defining an internal surface; an external rotor coaxial with said internal stator; a cooling assembly mounted inside said central aperture of said stator; said cooling assembly including:

- a fresh air inlet;

- a heated air outlet;

- an intermediate wall provided between said fresh air inlet and said heated air outlet;

- fins in contact with said internal surface;

- air moving means drawing air from said fresh air inlet and expelling air from said heated air outlet.

2. The electric machine recited in claim 1 , wherein said cooling assembly further comprises an air deflecting plate at said heated air outlet to deflect heated air away from said fresh air inlet.

3. The electric machine recited in claim 1 , wherein said fresh air inlet, said heated air outlet, said intermediate wall and said fins are defined by an integral cooling insert.

4. The electric machine recited in claim 1 , wherein said fins are defined by a cooling insert and wherein said fresh air inlet, said heated air outlet and said intermediate wall are defined by a separate tubular air guide mountable inside said cooling insert.

5. The electric machine recited in claim 1 , wherein said cooling fins are generally S-shaped and provided with a contact surface so configured as to be brought in contact with said internal surface of said stator.

6. The electric machine recited in claim 1 , wherein said air moving means include a fan.

7. The electric machine recited in claim 6, wherein said fan is so associated with said rotor as to rotate therewith.

8. The electric machine recited in claim 1 , wherein said fresh air inlet is centrally located with respect to said heated air outlet.

9. A cooling assembly for an electric machine including an internal stator having a generally cylindrical body provided with a central aperture defining an internal surface and an external rotor coaxial with said internal stator; said cooling assembly comprising: a fresh air inlet; a heated air outlet; an intermediate wall provided between said fresh air inlet and said heated air outlet; fins configured and sized as to contact the internal surface of the stator; and air moving means drawing air from said fresh air inlet and expelling air from said heated air outlet.

10. The cooling assembly recited in claim 9, further comprising an air deflecting plate at said heated air outlet to deflect heated air away from said fresh air inlet.

11. The cooling assembly recited in claim 9, wherein said fresh air inlet, said heated air outlet, said intermediate wall and said fins are defined by an integral cooling insert.

12. The cooling assembly recited in claim 9, wherein said fins are defined by a cooling insert and wherein said fresh air inlet, said heated air outlet and said intermediate wall are defined by a separate tubular air guide mountable inside said cooling insert.

13. The cooling assembly recited in claim 9, wherein said cooling fins are generally S-shaped and provided with a contact surface so configured as to be brought in contact with the internal surface of the stator.

14. The cooling assembly recited in claim 9, wherein said air moving means include a fan.

15. The cooling assembly recited in claim 14, wherein said fan is so associated with said rotor as to rotate therewith.

16. The cooling assembly recited in claim 9, wherein said fresh air inlet is centrally located with respect to said heated air outlet.