WO2012028183A1

WO2012028183A1 - A rotating electric machine

Info

Publication number: WO2012028183A1
Application number: PCT/EP2010/062800
Authority: WO
Inventors: Peter Isberg; Per-Olof Lindberg; Nassar Abu-Sitta
Original assignee: Abb Ab
Priority date: 2010-09-01
Filing date: 2010-09-01
Publication date: 2012-03-08

Abstract

A rotating electric machine comprises a housing 2 having an envelope surface and an end plate supporting a shaft 29 at each opposite end of the envelope surface. At least one gas shield 10a, 10b divides an interior of the housing 2 into a closed partition and an open partition. The closed partition defines a closed volume within which an inner cooling flow 2 circulates, and the open partition comprises outer cooling ducts 8 through which an outer cooling flow 14 flows. The outer cooling ducts 8 are positioned between the envelope surface and the closed partition.

Description

A rotating electric machine TECHNICAL FIELD

The present invention relates generally to rotating electric machines, such as motors and generators, and more

particularly to cooling of rotating electric machines.

BACKGROUND ART

Traction motors are electric motors used for propulsion of vehicles, e.g. rail vehicles such as trains, underground trains, trams and/or road vehicles such as cars and trucks. During operation of a traction motor, heat is generated, whereby cooling of the traction motors is an important aspect to consider. It is known to cool motors with open self ventilated air, open forced ventilated air, closed self ventilated air and water cooling. The environment in which traction motors operate is often full of polluting particles and/or gases such as dust, sand, pollution, etc. Such particles can have a detrimental effect on key components of the motor, whereby a closed ventilation system is preferred in such conditions providing better protection of the winding and lower the maintenance need.

GB 927,390 presents an electric motor assembly comprising a rotor and a stator mounted within a casing, ducting

extending from outside said casing through said stator, a fan secured to said rotor shaft within said casing and formed with a first set of blades adapted to pass a first cooling gas from outside said casing through said ducting and a second set of blades extending adjacent to said first set of blades and adapted to circulate a second cooling gas within said casing and over the external surface of said ducting within said casing, and means for keeping said two cooling gases substantially separate. While such a solution prevents ambient gas from reaching the inner parts of the motor, the cooling of the presented motor assembly can be improved further. SUMMARY OF THE INVENTION

An object of the present invention is to improve cooling of a rotating electric machine.

According to a first aspect of the invention, there is provided a rotating electric machine comprising: a stator, a rotor and a shaft; a housing having an envelope surface and an end plate supporting the shaft at each opposite end of the envelope surface; and at least one gas shield dividing an interior of the housing into a closed partition and an open partition. The closed partition defines a substantially closed volume within which an inner cooling flow is

configured to circulate. The open partition comprises outer cooling ducts through which an outer cooling flow is configured to flow. The outer cooling ducts are positioned between the envelope surface and the closed partition.

Through this positioning of the outer cooling ducts even an existing electric machine can be easily modified to comprise a closed and an open partition according to the invention.

The outer cooling ducts may be an integral part of the housing . The rotating electric machine may further comprise a first air circulating means configured to generate the inner cooling flow, and a second air circulating means configured to generate the outer cooling flow.

The second air circulating means may be arranged inside of the housing. The first air circulating means and the second air

circulating means may comprise at least one fan. A fan is a simple means for providing an air circulation.

The fan may comprise an inner set of blades for the inner cooling flow and an outer set of blades for the outer cooling flow.

The fan may be cast in one piece which reduces the risk of failure of the fan by reducing the number of moving

components . The fan can be made of material with thermal conductivity more than 50 W/(m-K), such as more than 100 W/(m-K), 150 W/(m-K) or 200 W/(m-K). Choosing an appropriate material, such as aluminium, increases the heat conduction from the inner cooling flow to the outer cooling flow, the fan acting effectively as a heat exchanger.

The fan may be thermally connected to a shaft of the

rotating electric machine.

The rotating electric machine may further comprise a

labyrinth seal between the fan and the at least one gas shield. The labyrinth seal allows for free rotation while still substantially separating the gases in the inner cooling flow and the outer cooling flow.

A gas shield part of the labyrinth seal may be provided with a groove on its radially outward surface. The groove can collect at least part of any liquid or heavier particles that would otherwise enter the labyrinth seal.

The at least one gas shield may be made of material with thermal conductivity more than 50 W/(m-K), such as more than 100 W/(m-K), 150 W/(m-K) or 200 W/(m-K) . The gas shield comprising aluminium also increases the heat conduction from the inner cooling flow to the outer cooling flow. The at least one gas shield may comprise axially extending fins . The fins increase the heat exchange area and thereby increase the heat transfer between the inner cooling flow and the outer cooling flow. At least one gas shield may be connected to the stator using a seal of a resilient material.

The stator may comprise stator cooling ducts extending essentially axially, and a rotor may comprise rotor cooling ducts extending essentially axially. By moving air through the axial cooling ducts in the inner cooling flow, cooling is significantly improved compared to cooling only by moving air along an outer end surface of the rotor and/or stator.

The rotating electric machine may comprise two gas shields axially positioned on either side of the stator. Generally, all terms used in the claims are to be

interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus,

component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Fig 1 is a schematic sectional view of a rotating electric machine according to an embodiment of the present invention, Fig 2 is a schematic detail sectional view of the labyrinth seal of Fig 1, and Fig 3 is a schematic sectional view of the rotating electric machine of Fig 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig 1 is a schematic sectional view of a rotating electric machine 1 according to an embodiment of the present

invention. The view is a sectional view through the middle of the machine 1, as illustrated by the line C-C in Fig 3. The rotating electric machine can for example be a traction motor for vehicle propulsion. The rotating electric machine can be a motor or a generator, or both. The machine 1 comprises a stator 3 with windings 18 and a rotor 5. The rotating electric machine 1 can for example be an induction motor. A housing 2 protects the interior of the machine 1 from the environment in which it is installed. In Fig 1 the housing 2 is shown to surround the stator 3, but in some embodiments of the invention the stator 3 can also be an integral part of the housing 2 constituting a major portion of the envelope surface of the same . The rotor 5 is connected to a shaft 29 whereby the machine 1 is mechanically connected to external components.

Furthermore, the machine 1 comprises connectors (not shown) to electrically connect the machine 1 to receive, in the case of a motor, or provide, in the case of a generator, electric energy.

During use, the machine 1 will generate heat. In order to prevent damage to components of the machine 1, cooling is provided, in this case using a system for closed self ventilated cooling. This means that ambient air (or other ambient gas) is used for cooling, but the ambient air is not in direct contact with the innermost parts of the machine 1. A fan 9 is thus provided to move air, or any other suitable gas, through the machine 1 to remove heat from the machine.

In the present embodiment, the cooling is based on two cooling flows, an inner cooling flow 12 and an outer cooling flow 14. The fan 9 comprises an inner set of blades 22 for the inner cooling flow 12 and an outer set of blades 23 for the outer cooling flow 14. Each set of blades comprise an appropriate number of blades, e.g. between 10 and 20 blades. The number of inner blades 22 can be less, more, or the same as the number of outer blades 23. Optionally, the fan 9 is made in one piece, reducing a risk of failure compared to a multi piece fan. Alternatively, two separate fans may be provided to generate the inner cooling flow 12 and the outer cooling flow 14.

The rotor 5 comprises rotor cooling ducts 6 that extend substantially axially, i.e. along the major axis 28 of the machine 1. The rotor cooling ducts 6 can be provided

straight through the rotor 5, i.e. parallel to the major axis 28, or the rotor cooling ducts 6 can rotate about the axis, e.g. the shaft 29, in their extension through the rotor 5. In fact, the rotor cooling ducts 6 can assume any suitable shape as long as the ducts have an opening on either side of the rotor 5 along the major axis 28 of the machine . Analogously, the stator 3 comprises stator cooling ducts 4 that extend substantially axially, i.e. along the major axis 28 of the machine 1. The stator cooling ducts 4 can be provided straight through the stator 3, i.e. parallel to the major axis 28, or the stator cooling ducts 4 can rotate about the axis, e.g. the shaft 29, in their extension through the stator 3. In fact, the stator cooling ducts 4 can assume any suitable shape as long as the ducts have an opening on either side of the stator 29 along the major axis 28 of the machine.

The fan 9 is attached to the shaft 29 of the machine, allowing the fan 9 to rotate when the shaft 29 rotates. The inner set of blades 22 thus moves the air of the inner cooling flow 12. Since there are axial cooling ducts 4 in the stator 3 and axial cooling ducts 6 in the rotor, the air is circulated axially in the inner cooling flow 12 through both the stator 3 and the rotor 5. The air may be moved to the right through the stator cooling ducts 4 and back to the left through the rotor cooling ducts 6 as indicated in Fig 1, or in an opposite direction, as long as there is an axially circulating flow through both the rotor 5 and the stator 3. By moving air through the cooling ducts in the inner cooling flow 12, cooling is significantly improved compared to cooling only by moving air along an outer surface of the rotor 5 and/or stator 3. In addition a temperature rise in the motor will be better distributed in the axial direction of the structure.

Optionally, a winding shield 27 is provided around the windings 18. The winding shield can for example be a film of suitable material, e.g. heat resistant polymers. The winding shield reduces turbulence and recirculation which can occur due to the geometric design of the windings 18. The winding shield can fully or partially cover the coil end. The shield can also be provided with holes to improve the cooling of the end winding. The outer set of blades 23 of the fan also rotate with the shaft 29, moving air in the outer cooling flow 14. The outer cooling flow 14 moves relatively cool air from outside the housing 2 through an input aperture 21 in the housing, through outer cooling ducts 8 and out from the machine 1 through a second, output aperture 24.

The outer cooling ducts 8 are provided radially outside of the stator cooling ducts 4. The outer cooling ducts 8 also extend substantially axially, i.e. along the major axis 28 of the machine 1. The outer cooling ducts 8 can be provided in the housing 2, between the housing 2 and the stator 3 or in a position of the stator 3 radially outside of the stator cooling ducts 4. The outer cooling ducts 8 can be straight, i.e. parallel to the major axis 28, or the outer cooling ducts 8 can rotate about the axis, e.g. the shaft 29, in their extension. In fact, also the outer cooling ducts 8 can assume any suitable shape as long as the ducts have an opening on either side of the machine 1 to allow air to flow through the machine 1, from the input aperture 21 to the output aperture 24.

To separate the inner cooling flow 12 and the outer cooling flow 14, a first gas shield 10a and a second gas shield 10b are provided. The gas shields lOa-b can be rotationally symmetrical and they at least wrap around the shaft 29 and abut the stator 3, directly or indirectly, all around the shaft 29.

The first gas shield 10a connects to the stator 3 on one side and is part of a labyrinth seal 16 with the fan 9 on the other side. The labyrinth seal 16 prevents substantial amounts of gas to flow between the inner cooling flow 12 and the outer cooling flow 14. This is beneficial since the outer cooling flow can contain contaminants such as water, dust or other particles which could be detrimental if large amounts are transferred to the inner cooling flow 12. The second gas shield 10b connects to the stator 3 on one side and the housing 2 on the other side. Optionally, a seal 30 of a resilient material, e.g. rubber, is provided between the second gas shield 10b and the stator. For example, the seal 30 can be an o-ring.

Optionally, one or both gas shields lOa-b are provided with axially extending fins 42a-b. The fins increase the heat transfer area between the inner cooling flow and the outer cooling flow. The inventors have realised that, since the gas shields 10a- b are not a mechanically bearing construction, these can be made of aluminium, e.g. cast aluminium. Aluminium has the advantage of being a great heat conductor, e.g. compared to iron. When the gas shields lOa-b are provided in aluminium, or other suitable heat conducting material, heat of the inner cooling flow 12 is transferred by the gas shields lOa-b and is further conducted to the air of the outer cooling flow 14. The gas shields lOa-b thus operate as heat conductors between the inner cooling flow 12 and the outer cooling flow 14.

Optionally, the fan 9 can also be made of aluminium, or other suitable heat conducting material, to increase the heat conducting effect from the inner cooling flow 12 to the outer cooling flow 14. Furthermore, by increasing the heat conducting capability of the fan, heat from the shaft 29 is led away, leading to a cooling effect on the shaft 29, which can reduce thermal stress on bearings or other components thermally connected to the shaft 29. Furthermore, the inner flow by the second gas shield 10b increases cooling in that section of the machine 1, which can reduce thermal stress on components in that area, such as bearings.

Fig 2 is a schematic detail sectional view of the labyrinth seal 16 of Fig 1. The labyrinth seal 16 comprises matching recesses and protruding members, whereby the fan 9 can still rotate freely around the fixed first gas shield 10a. The number of such recesses and protruding members can vary and is not limited to the illustration of Fig 2. In one

embodiment, the gas shield part 25 of the labyrinth seal 16 comprises a groove 26, positioned axially in a position which corresponds to the end of an outer part of the fan part 40 of the labyrinth seal 16. In other words, the groove 26 is provided on the radially outward surface of gas shield part 25 on the inside of the end of the fan part 40. In this way, if there is any liquid, e.g. water, in the outer cooling flow 14, and the liquid comes in contact with the labyrinth seal, the groove 26 can collect the liquid, whereby gravity will pull the liquid to the bottom part of the groove 26, where the liquid falls down and can be drained through the housing 2. This reduces the risk even more of any liquid passing through the labyrinth seal 16 from the outer to the inner side of the gas shield lOa-b. The groove also will function in equal way for heaver particles such as sand.

Fig 3 is a schematic sectional view of the rotating electric machine 1 of Fig 1. The view is a sectional view through a line A-A in Fig 1. The windings have been omitted in Fig 3 in order not to obscure the illustration. Here the stator 3 and the rotor 5 can be seen with stator cooling ducts 4 and rotor cooling ducts 6, respectively. The housing 2 is provided with outer cooling ducts 8.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

A rotating electric machine (1) comprising:

a stator (3), a rotor (5) and a shaft (29);

a housing (2) having an envelope surface and an end plate supporting the shaft (29) at each opposite end of the envelope surface;

and at least one gas shield (10a, 10b) dividing an interior of the housing (2) into a closed partition and an open partition, the closed partition defining a substantially closed volume within which an inner cooling flow (12) is configured to circulate, and the open partition comprising outer cooling ducts (8) through which an outer cooling flow (14) is configured to flow;

characterized in that the outer cooling ducts (8) are positioned between the envelope surface and the closed partition .

The rotating electric machine (1) according to claim 1, wherein the outer cooling ducts (8) are an integral part of the housing (2) .

The rotating electric machine (1) according to any one of the preceding claims, further comprising a first air circulating means configured to generate the inner cooling flow (12), and a second air circulating means configured to generate the outer cooling flow (14) .

The rotating electric machine (1) according to claim 3, wherein the second air circulating means is arranged inside of the housing (2) .

The rotating electric machine (1) according to any of claims 3 and 4, wherein the first air circulating means and the second air circulating means comprise at least one fan ( 9 ) .

6. The rotating electric machine (1) according to claim 5, wherein the fan (9) comprises an inner set of blades (22) for the inner cooling flow (12) and an outer set of blades (23) for the outer cooling flow (14) . 7. The rotating electric machine (1) according to any of claims 5-6, wherein the fan (9) is cast in one piece.

8. The rotating electric machine (1) according to any of claims 5-7, wherein the fan (9) is made of material with thermal conductivity more than 50 W /(m - K) , such as more than 100 W l(m - K) , 150 W /(m - K) or 200 W /(m - K) .

9. The rotating electric machine (1) according to claim 8, wherein the fan (9) comprises aluminium.

10. The rotating electric machine (1) according to any of claims 5-9, wherein the fan (9) is thermally connected to the shaft (29) of the rotating electric machine (1) .

11. The rotating electric machine (1) according to any of claims 5-10, further comprising a labyrinth seal (16) between the fan (9) and the at least one gas shield (10a, 10b) . 12. The rotating electric machine (1) according to claim 11, wherein a gas shield part (25) of the labyrinth seal (16) is provided with a groove (26) on its radially outward surface.

13. The rotating electric machine (1) according to any one of the preceding claims, wherein the at least one gas shield (10a, 10b) is made of material with thermal conductivity more than 50 W /(m - K) , such as more than 100 W /(m - K) , 150 W /(m - K) or 200 W /(m - K) .

14. The rotating electric machine (1) according to claim 13, wherein the at least one gas shield (10a, 10b) comprises aluminium .

15. The rotating electric machine (1) according to any one of the preceding claims, wherein the at least one gas shield (10a, 10b) comprises axially extending fins (42a, 42b) .

16. The rotating electric machine (1) according to any one of the preceding claims, wherein at least one gas shield (10a, 10b) is connected to the stator (3) using a seal (30) of a resilient material.

17. The rotating electric machine (1) according to any one of the preceding claims, wherein the stator (3)

comprises stator cooling ducts (4) extending essentially axially, and a rotor (5) comprises rotor cooling ducts (6) extending essentially axially.

18. The rotating electric machine (1) according to any one of the preceding claims, comprising two gas shields (10a, 10b), one at each opposite end of the stator (3).