WO2004112222A1

WO2004112222A1 - Electrical machine having a cooling system

Info

Publication number: WO2004112222A1
Application number: PCT/US2004/017868
Authority: WO
Inventors: John Fiorenza; David Martin Rose; Tim J. Vetta; Felix Belkin
Original assignee: Briggs & Stratton Corporation
Priority date: 2003-06-10
Filing date: 2004-06-07
Publication date: 2004-12-23

Abstract

An electrical machine (10) including a stator (35), a rotor (40), a blower (30) coupled by a shaft (55) to the rotor (40), a first housing portion (20), and a second housing portion (25). The first housing portion (20) includes a first plurality of openings (70), and the second housing portion (25) includes a second plurality of openings (90). The blower (30) is disposed adjacent to the second housing portion (25) and extends radially beyond the second plurality of openings (90). Rotation of the rotor (40) drives the blower (30) relative to the stator (35).

Description

ELECTRICAL MACHINE HAVING A COOLING SYSTEM

FIELD OF THE INVENTION

The present invention relates to a system of and method for cooling an

electrical machine.

BACKGROUND

An electrical machine (e.g., a brushless DC motor, AC motor, or generator) generally includes a stator having stator windings in magnetic interaction with a rotor. When energized with electrical current, the stator windings generate heat, which can reduce motor efficiency, cause breakdowns, and create hot surfaces. Manufacturers seek an electrical machine that increases fluid movement past the stator windings to cool the electrical machine without significant additional cost.

SUMMARY

In one embodiment, the invention provides an electrical machine (e.g., a motor or generator) including a stator, a shaft having a rotational axis, and a rotor supported by the shaft where the rotor rotates with the shaft relative to the stator. The electrical machine further includes first and second housing portions fixed relative to the stator. The first housing portion has a first plurality of openings and the second housing portion has a second plurality of openings. The electrical machine also includes a blower coupled to the shaft. The blower is disposed adjacent to the second housing portion and extends radially beyond the second plurality of openings. The invention increases fluid movement past the stator windings, thereby reducing the heat generated by the stator windings.

In one construction, the electrical machine is a brushless direct current (DC), axial air-gap motor and the blower includes a cage blower having a plurality of vanes. The vanes are disposed outside of the second plurality of openings in a radial direction with respect to a rotational axis of the rotor. The cage blower draws fluid through the openings in the first housing portion, through a passage past the outer winding turns of the stator, through a passage over the top of the stator, out the openings in the second housing portion, and discharges the fluid in the radial direction with respect to the rotational axis of the shaft. The second housing portion can include one or more ribs to guide the fluid over the top of the stator. In another construction, the electrical machine is a multi-pole generator.

Other features and aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is perspective view of one construction of an electrical machine embodying the invention.

Fig. 2 is a cross-sectional view of the electrical machine of Fig. 1.

Fig. 3 is a partial perspective view of an endbell to the electrical machine shown in Fig. 1. Fig. 4 is a perspective view of a first side of an endcap to the electrical

machine shown in Fig. 1.

Fig. 5 is a perspective view of a second side of the endcap shown in Fig. 1.

Fig. 6 is a perspective view of the blower shown in Fig. 1.

Fig. 7 is a cross-sectional view of the electrical machine of Fig. 1, which includes a rotor of a generator.

Fig. 8 is a cross-sectional view of the electrical machine of Fig. 1, which includes a stator of a generator.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of

"including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of the terms "connected," "coupled," and "mounted" and variations thereof herein are used broadly and encompass both direct and indirect connections, couplings, and mountings. In addition, the terms "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

Fig. 1 shows a perspective view of one construction of an electrical machine embodying the invention. For the description below, it will be assumed, unless stated otherwise, that the electrical machine shown in Figs. 1-5 is an electric motor 10. The electric motor 10 includes a housing 15 having an endbell 20 (also referred to as a "first housing portion") and an endcap 25 (also referred to as a "second housing portion"). A blower 30 is disposed adjacent to the endcap 25 to move a fluid (e.g., air) through the housing 15. As discussed further below, the invention is applicable to other electrical machines (e.g., generators) .

Fig. 2 shows a cross-sectional view of the electric motor 10 of Fig. 1. The electric motor 10 includes a stator 35 separated by an air-gap 37 from a rotor 40. The stator 35 includes a core 45 and a plurality of stator windings 50. The rotor 40 includes a plurality of permanent magnets having magnetic poles and is coupled to a shaft 55. The rotor 40 and attached shaft 55 have a rotational axis 60. When energized with electrical current, the stator windings 50 create magnetic fields that magnetically interact with the magnetic poles of the permanent magnets to drive rotation of the rotor 40 and shaft 55. While the motor 10 shown in Fig. 2 is a brushless direct current (DC), axial air-gap motor, the invention is capable of being used with other motors including AC synchronous motors, brush motors, induction motors, etc.

Referring to Fig. 2, the stator windings 50 are equipped to receive (m) phase current(s) in accordance to the design of the motor 10, where (m) is an integer greater than or equal to one. One construction of the stator 35 includes a circular-shaped core 45 having a plurality of stator teeth disposed along the circumference of the stator core 45. The stator windings 50 are disposed on the stator teeth. The stator core 45 includes an inner radial section 47. The inner radial section 47 is discussed below in relation to the location of openings 90. The stator core 45 further includes a central opening that receives the shaft 55 of the rotor 40. The stator 35 mounts to the endcap 25 of the housing 15 using a fastener (e.g., threaded bolt, press fit hub, etc.). Other various constructions of the stator 35 and ways of coupling the stator 35 to the electrical machine can be used. The windings 50 shown in Fig. 2 are wire wound, but can be of other various types (e.g., wave wound, lap wound, concentric wound, stamped, printed on a circuit board, etc.).

Fig. 2 shows the rotor 40 attached to the shaft 55 and separated by the air-gap 37 from the stator 35. One construction of the rotor 40 includes permanent magnets positioned along a circular-ring adjacent to the stator 35. In another construction, the rotor 40 can include a ring of magnetic material to interact with the stator 35. Of course, the rotor can be constructed differently for other types of electric motors and electrical machines.

Fig. 3 shows one construction of the endbell 20 including a plurality of openings 70 or apertures that draws or discharges fluid into or out of the housing 15 (Fig. 1). The openings 70 are disposed along a periphery 75. The endbell 20 includes a sidewall 80 and an end plate 85, that is, for the construction shown, integral with the sidewall 80. The position of the openings 70, where the sidewall 80 meets the end plate 85, allows for the ingress or egress of fluid into or out of the motor 10. As discussed further below, the fluid (typically air) flows past the outer portions of the stator windings 50. The location of the openings 70 along the periphery 75 or the end plate 85 can vary. Various methods (e.g., drilling, stamping, cast, etc.) known to those in the art can be used to form the openings 70. In addition, the openings 70 can include various shapes (e.g., square, oval, etc.).

Another construction of the housing 15 can include one or more intermediate portions 87 separating the endbell 20 and the endcap 25. The intermediate portions 87 can include the plurality of openings 70 or an additional plurality of openings. Additionally, the terms "endbell" and "endcap" are not meant to limit the endbell 20 or the endcap 25. That is, the endbell 20 can also be referred to as an "endcap" and endcap 25 can also be referred to as an "endbell."

Fig. 4 shows one construction of the endcap 25 including a plurality of ingress/egress openings 90. Various sizes and shapes (e.g., oval, rectangular, triangular, etc.) of the openings 90 can be used to provide a sufficient flow of fluid through the endcap 25. At least a portion of the openings 90 are disposed within the inner radial section 47 (see Fig. 2) of the stator core 45. Disposing at least a portion the openings 90 within the inner radial section 47 of the stator core 45 provides a flow of fluid over the top of the stator windings 50 and reduces the required size of the blower 30 (discussed further below). Yet, the disposition of the openings 90 can range radially outward to the outer periphery of the stator core or the periphery of the outer turns of the stator windings 50 (see Fig. 2). Similar to the openings 70 described above, various methods (e.g., drilling, stamping, casting, etc.) can be used to form the openings 90. The endcap 25 also includes wire openings 92 to receive wire that provides electrical power to the stator windings 50. Opening 95 receives the shaft 55 attached to the rotor 40. The endcap 25 also includes a mounting boss 97 to receive a fastener to couple the endcap 25 to the endbell 20. The mounting boss 97 can be of the type (e.g., interior threaded) and size compatible to receive various fasteners (e.g., bolts, screws, etc.) and is not limiting on the invention.

Fig. 5 shows one construction of the endcap 25 including an end plate 195 having a plurality of thickened portions or ribs 100 positioned between the openings 90. Each of the ribs 100 includes an opening 105 to receive the fastener for coupling the stator 35 to the endcap 25. The ribs 100 provide additional strength to the endcap 25, and a passage 110 (see Fig. 2) between adjacent ribs 100 provides a fluid pathway. The pathway allows the fluid to flow over one side of the stator 35. The shape, thickness, and number of the ribs 100 can vary to provide the desired flow of fluid past the windings 50. In another construction, the endcap 25 can include additional intermediate ribs between adjacent ribs. In yet another embodiment, the passages 110 can be formed by indentations in the thickness of the endcap 25 rather than defined by the ribs 100.

Fig. 2 shows one path of flow of the fluid through the housing 15. Fig. 2 includes arrows to show the path of cooling fluid through the openings 70, through a passage 112 past the outer turns of the stator windings 50, through a passage 110, out through the openings 90 (which are outlet openings for this construction), and out through the blower 30. Fig. 2 shows a blower 30 positioned axially over the openings 90 outside of the motor 10. The blower 30 couples to the shaft 55 of the rotor 40 such that rotation of the rotor 40 and shaft 55 drives the blower 30. For the construction shown, the blower 30 draws fluid into the motor 10 through the openings 70. For another construction, the blower 30 pushes the fluid into the motor 10 through the openings 90. That is, the blower 30 can be of a type and at a position to force fluid into the openings 90 of the housing 15 and discharge the fluid out the openings 70. In yet another construction, the blower 30 can be positioned adjacent to the openings 70 to draw fluid through the openings 90 into the housing 15, past the stator windings 50, and discharge out the openings 70. hi the construction shown in Fig. 2, the blower 30 includes a cage blower 115 positioned over the openings 90. Other types (e.g., axial) and/or sizes of the blower 30 can be used.

Fig. 6 shows a perspective view of the cage blower 115. The shaft 55 drives the rotation of the cage blower 115 to force the fluid through the housing 15. The construction of the cage blower 115 allows fluid to discharge in a broad radial area, reduces pressure losses into or from the housing 15, and allows simple assembly. One construction of the cage blower 115 includes a circular-shaped cover 120, a bottom ring 125, and a plurality of vanes 130 disposed at a radial distance from the shaft 55 (Fig. 2). The cover 120 includes a hub 135 to receive the shaft 55. The vanes 130 are supported and coupled (e.g., rivets, weld, adhesive, mechanically interconnected, etc.) between the cover 120 and the bottom ring 125. The vanes 130 extend radially outward of the openings 90 of the endcap 25 with respect to the shaft 55. Accordingly, for the construction shown, the location of the openings 90 near the shaft 55 reduces the size of the cage blower 115. In other constructions, the radial disposition of the openings 90 from shaft 55 and the respective size of the cage blower 115 can vary. The cage blower 115 may be made from various materials (e.g., sheet metal, steel, iron, etc.) and can be formed using various methods (e.g., cast, machined, welded, etc.).

In one construction, the vanes 130 are at an angle to a line through shaft 55 to force the discharge of fluid in a radially outward direction with respect to the shaft 55. The discharge of fluid in a radially outward direction expands the heat exchange area and reduces resistance of the fluid flow discharged from the housing 15. In another construction, a box fan coupled to the shaft 55 can push fluid in an axial direction with respect to the shaft 55, and discharge the fluid in a direction along the longitudinal axis of the shaft 55 into openings 90. The length, angle, and depth of the vanes 130 can vary.

In another construction, the blower 30 can be disposed inside the housing 15 between the stator 35 and the endcap 25. In yet another construction, the blower 30 can be directly coupled to the rotor 40. In yet another construction of the invention, one or more additional blowers can be coupled to the shaft 55 and disposed at the various locations described above for the blower 30. The additional blowers can be designed to push/draw the fluid through the housing 15 in combination with the operation of the blower 30.

In operation, electrical power is provided to the stator windings 50 to generate magnetic fields. The magnetic fields produced by the stator windings 50 interact with the magnetic fields of the rotor 40. This results in the rotation of the rotor 40, shaft

55, and cage blower 115. The electrical power through the windings 50 also generates heat, which reduces the efficiency of the machine. As shown by the arrows in Fig. 2, the cage blower 115 draws fluid into the motor 10 through the openings 70, upward through a passage 112, past the outer turns of the stator windings 50, through a passage 110 over the top of the stator windings 50, and discharges the fluid out the openings 90. Based on principles of thermodynamics, the stator windings 50 exchange heat with the cooling fluid, and the cooling fluid carries the excess heat away from the electrical machine.

Another embodiment of the invention is shown in Figs. 7 and 8. For Figs. 7 and 8 the electrical machine of Fig. 1 is a generator and, specifically, a two-pole, axial air gap generator 700. However, the invention is not limited to the generator shown in Figs. 7 and 8. For example, the generator can include more than two poles.

With reference to Fig. 7, the rotor 705 includes a first plurality of magnets 710 providing a first pole (e.g., a north pole), and a second plurality of magnets 715 providing a second pole (e.g., a south pole). The rotor 705 is fixedly coupled to a rotating shaft 720, which rotates the rotor 705 when a mechanical energy is applied to the shaft 720. The rotating rotor 705 produces a rotating magnetic field that interacts with the stator.

With reference to Fig. 8, the stator 725 includes a stator core 730 having a plurality of teeth 735. The stator 725 also includes windings 740 placed (e.g., wound) around the plurality of teeth 735. For the construction shown, the windings 740 are wound in a concentric winding arrangement. However, other winding arrangements are possible, including a lap winding arrangement. As is well known, the coil spans in a concentric winding arrangement differ in turn length; while the coil spans in a lap winding arrangement have the same turn length.

One problem typically associated with a generator is voltage droop. A first potential cause of voltage droop is an increase in resistance of the windings 740 under load due to heat. A second potential cause of voltage droop is that the flux of the magnets 710 and 715 decreases when hot. One solution to help reduce voltage droop is to implement the inventive cooling scheme with the generator 700. That is, the generator 700 can be constructed similar to the multiple constructions described above in connection with the motor 10 of Figs. 1-5. However, rather than running the electrical machine as a motor, it is run as a generator. Allowing the fluid to flow across the stator 725, as described earlier, cools the stator (and the windings 740), thereby reducing voltage droop.

In another construction of the electrical machine, the rotor (40 in Fig. 2) defines an outer periphery and the apertures 70 can be disposed within the outer periphery of the rotor 40. The location of the apertures 70 within the outer periphery of the rotor 40 allows the fluid to flow past the rotor 40, thereby cooling the rotor 40. Therefore, if the electrical machine is the generator 700, the cooling of the rotor helps to reduce voltage droop for the generator 700.

Thus, the invention provides, among other things, an exemplary electrical machine having a cooling system. Various features and advantages of the invention are set forth in the following claims.

Claims

CLAIMSWhat is claimed is:

1. An electrical machine comprising:

a shaft having a rotational axis;

a rotor connected to the shaft and rotating with the shaft;

a stator having a plurality of stator windings, the stator windings in magnetic interaction with the rotor;

a stationary first housing portion having a first plurality of openings;

a stationary second housing portion having a second plurality of openings and a plurality of axially extending ribs to receive the stator, the ribs defining fluid pathways to the second plurality of openings;

a blower coupled to the shaft, the blower being disposed adjacent to the second housing portion and extending radially outward of the second plurality of openings with respect to the shaft;

wherein, when the rotor rotates, the blower draws a fluid through the first plurality of openings, in an axial direction along the outer turns of the stator windings, in a radially inward direction toward the rotational axis of the shaft between the ribs, and axially through the second plurality of openings; and

wherein the blower discharges the fluid in a radially outward direction with respect to the rotational axis of the shaft.

2. The electrical machine of claim 1 , wherein the blower includes a cage fan.

3. The electrical machine of claim 1 , wherein the first plurality of openings are located along a periphery of the first housing portion.

4. The electrical machine of claim 1 , wherein the second plurality of openings are located adjacent to the rotational axis.

5. The electrical machine of claim 1, wherein the second housing portion includes a generally planar wall and the second plurality of openings is disposed in the planar wall between the periphery and the shaft.

6. The electrical machine of claim 1, wherein the rotor includes at least one circular ring having a plurality of alternating magnetic poles separated by an air-gap from the stator.

7. The electrical machine of claim 1, further including at least one intermediate portion between the first housing portion and the second housing portion.

8. The electrical machine of claim 7, wherein the at least one intermediate portion includes a third plurality of openings to receive fluid into the housing.

9. The electrical machine of claim 1 , wherein at least a portion of the rotor is disposed in an axial direction from at least a portion of the stator, the rotor and stator being separated by a gap.

10. The electrical machine of claim 9, wherein the rotor includes at least one magnet disposed in an axial direction from the stator, the at least one magnet magnetically interacting with the stator via the gap.

11. The electrical machine of claim 1, wherein the ribs are wedge shaped.

12. The electrical machine of claim I₅ wherein the stator is affixed to the ribs.

13. An electrical machine comprising:

a stator;

a shaft having a rotational axis;

a rotor supported by the shaft and rotating with the shaft;

a stationary first housing portion having a first plurality of openings;

a stationary second housing portion having a second plurality of openings; and

a blower coupled to the shaft, the blower being disposed adjacent to the second housing portion and extending radially outward of the second plurality of openings with respect to the shaft.

14. The electrical machine of claim 13, wherein the blower draws a fluid through the first plurality of openings into the electrical machine.

15. The electrical machine of claim 13, wherein the blower draws a fluid through the second plurality of openings and pushes the fluid out of the electrical machine through the first plurality of openings.

16. The electrical machine of claim 13 , wherein the blower pushes a fluid through the second plurality of openings and out of the electrical machine through the first plurality of openings.

17. The electrical machine of claim 13, wherein the blower includes a cage blower, and wherein the cage blower receives a fluid via the second plurality of openings and forces the fluid in a radially outward direction with respect to the shaft.

18. The electrical machine of claim 13 , wherein the blower forces a fluid through the second plurality of openings and into the electrical machine.

19. The electrical machine of claim 13, wherein the blower includes a cage blower having a plurality of vanes, and wherein the plurality of vanes are disposed outside of the second plurality of openings in a radial direction with respect to the shaft.

20. The electrical machine of claim 13, wherein the second housing portion includes one or more ribs to guide a fluid between the first plurality of openings and the second plurality of openings.

21. The electrical machine of claim 20, wherein the ribs are wedge shaped.

22. The electrical machine of claim 20, wherein the stator is affixed to the ribs.

23. The electrical machine of claim 13, wherein the second housing portion includes a generally planar wall, and wherein the second plurality of openings is disposed in the generally planar wall.

24. The electrical machine of claim 13, wherein the stator has an outer radial periphery, and wherein the second plurality of openings is disposed within the outer radial periphery of the stator.

25. The electrical machine of claim 13, wherein the stator includes a stator core, wherein the stator core has an outer radial periphery, and wherein the second plurality of openings is disposed within the outer radial periphery.

26. The electrical machine of claim 13, wherein the stator core includes a plurality of teeth, wherein the stator teeth have a radially inward section, and wherein at least a portion of the second plurality of openings is disposed within the radially inward section.

27. The electrical machine of claim 26, wherein the second plurality of openings is disposed within the radially inward section of the stator core.

28. The electrical machine of claim 13, wherein the stator includes stator windings, wherein the blower draws fluid into the housing through the first plurality of openings, past the outer turns of the stator windings, and through the second plurality of openings, and wherein the blower discharges the fluid in a radial outward direction from the motor axis.

29. The electrical machine of claim 13, wherein the first housing portion includes a generally cylindrical wall, and wherein the first plurality of openings are disposed at least in part in the generally cylindrical wall.

30. The electrical machine of claim 13 , wherein the first housing portion includes a generally planar wall, and wherein the first plurality of openings are disposed at least in part in the generally planar wall.

31. The electrical machine of claim 13, wherein the first housing portion includes a generally planar wall and a generally cylindrical wall, and wherein the first plurality of openings are disposed in the generally planar wall and the generally cylindrical wall.

32. An electrical machine of claim 13 , further including a third housing portion

fixed relative to the stator.

33. An electrical machine of claim 32, wherein the third housing portion is generally between the first and second housing portions in an axial direction.

34. An electrical machine of claim 13, wherein the electrical machine is a motor.

35. An electrical machine of claim 13, wherein the electrical machine is a generator.

36. An electrical machine of claim 13, wherein the rotor defines a periphery, and wherein at least a portion of the first plurality of openings is disposed within the periphery.

37. The electrical machine of claim 13, wherein at least a portion of the rotor is disposed in an axial direction from at least a portion of the stator, the rotor and stator being separated by a gap.

38. The electrical machine of claim 37, wherein the rotor includes at least one magnet disposed in an axial direction from the stator, the at least one magnet magnetically interacting with the stator via the gap.