SE1551021A1

SE1551021A1 - An electric machine

Info

Publication number: SE1551021A1
Application number: SE1551021A
Authority: SE
Inventors: Fröling Claes; Bergman Erik
Original assignee: Bombardier Transp Gmbh
Priority date: 2015-07-13
Filing date: 2015-07-13
Publication date: 2017-01-14
Also published as: WO2017009001A1; EP3323193A1; CN107836073A; SE539576C2

Abstract

13 ABSTRACT An electric machine comprises a stator (1) and a rotor (5)rotatably disposed within the stator. At least the rotor andwindings (3) of the stator are sealingly enclosed by an end shield(12) arranged at each axial end of the machine in a space (16)filled with gas. Wafters (18) are arranged on the rotor for mixinggas trapped in said space. A member (30) is arranged in saidspace (16) for directing gas moved by the wafters (18) at leastpartially radially towards the radial periphery of the space formixing this gas with gas in a peripheral portion of said space. (Pig. 4).

Description

An electric machine TECHNICAL FIELD OF THE INVENTION AND BACKGROUNDART The present invention relates to an electric machine comprising astator having a stator body with a stator winding configured toelectrically create a plurality of stator poles disposed around theinner periphery of the stator body, a rotor rotatably disposed within said stator and having a rotorbody, means configured to sealingly enclose at least said rotor and thestator winding comprising an end shield arranged at each axialend of the machine and at each said end enclosing a space filledwith gas, delimited by the end shield and an axial end of said rotorbody and surrounding a respective axial end portion of the statorwinding, and wafters arranged on each axial end of the rotor body for mixinggas trapped in the respective said space upon rotation of the rotorbody.

Such an electric machine may operate as motor and/or generator,although this disclosure will focus mainly on the operation thereofas a motor.

The present invention is particularly applicable to electricmachines in the form of motors of the type defined in theintroduction for creating a traction force of a track-bound vehicle,especially a rail vehicle, and this application of such an electricmachine will mainly be discussed below without for that sakerestricting the invention thereto. Such a motor may of coursefunction as a generator when braking the vehicle.

Such an electric machine is totally enclosed, which means thatthe internal gas, normally air although other gases are possible, but air will hereinafter be considered as said gas, is “trapped”inside the electric machine and will theoretically never escapesaid space unless the machine is disassembled (in practise it mayleak out very slowly and finally be replaced by new air, but thatwill take a very long time compared to for an open machine). Thereason for enclosing the rotor and the stator windings of theelectric machine in this way is to protect these parts against dirtand contaminations when the machine is used in an environmentin which the machine is exerted thereto, such as in anunderground train. However, during operation of the electricmachine heat is created by losses mainly in the stator body, therotor body and the stator windings resulting in a temperatureincrease of the air trapped in said space. The temperature is theparameter restricting the maximum power of operation of anelectric machine of this type when it functions as a motor and themaximum power which may be delivered thereby in the case ofgenerator function, in which the insulation layers of the statorwindings and the bearings for the shaft of the electric machineare the components most sensitive to high temperatures. Theinsulation layers of the stator windings will be degraded orpartially destroyed above a certain temperature and lubricants ofsaid bearings will run dry at an excess temperature, which meansthat the bearings will not get any lubrification and may seize. Thelife time of these components is then of course also dependentupon which temperature they are exposed to during the operationof the electric machine, so that a reduction of this temperaturemeans that the maintenance intervals may be prolonged. Thismeans that the efficiency of the cooling of such an electricmachine is very important, and that is the reason for thearrangement of said wafters for mixing air trapped in said spaceinside the electric machine for increasing the heat transport to theexterior of the machine and attempting to avoid the creation ofhot spots at critical locations inside said space.

SUMMERY OF THE INVENTION The object of the present invention is to provide an electricmachine of the type defined in the introduction being improved inat least some aspect with respect to such electric machinesalready known.

This object is according to the invention obtained by providingsuch an electric machine with the features listed in thecharacterizing part of appended claim 1.

By introducing a said member in each of the spaces in which gasis trapped the gas moved by the wafters through rotation of therotor body will take a long way inside said space before circulatingback to the wafters. This means that colder gas closer to theperiphery of the space will be mixed with a warmer gas and thetemperatures will even out. The inventor has found out that inabsence of such a member in said space the wafters on the rotorbody will rotating the gas around in tangential direction and alsopushing the gas in radial direction, but since there is a lowpressure region radially internally of the wafters gas needs to flowback into this region and the same gas is then rotating backaround the wafters preventing the gas from reaching furtherradially for being mixed with cooler gas. Thus, the arrangementof said member means that less heat is transferred to the bearingthrough the end shield and more heat will be transferred throughthe radially peripheral walls of the end shield. This means that itwill be possible for a certain power of operation of the electricmachine to lower the temperature of the bearings and also of theinsulation layers of the stator winding for prolonging the life timethereof and the maintenance intervals for lubrification of thebearings, or expressed in another way, a higher maximum powerof operation of the electric machine is obtained.

According to an embodiment of the invention each said memberextends in said space from the region of said wafters, which is located radially internally of an axial end portion of the statorwinding, radially outwardly towards and at least to the region ofthe axial end of said winding so as to guide gas moved by saidwafters along the member from said region of said wafters and atleast to the axial end of the winding. This results in a bettercooling of said stator winding than compared to no such memberspresent in said space.

According to another embodiment of the invention each saidmember extends past the axial end of the stator winding andfurther around the axial end portion of the stator winding and inthe direction of the opposite axial end of the machine into anannual portion of said space peripherally surrounding the axialend portion of the winding. By guiding the gas moved by saidwafters along a member with this extension hotter gas willefficiently be mixed with colder gas and the temperatures will beefficiently evened out inside said space resulting in an increasedtransfer of heat energy through peripheral walls of the end shieldand a lowering of the temperature of said bearings and also thestator windings.

According to another embodiment of the invention said memberis configured to guide gas moved by said wafters upon rotation ofthe rotor body from the region of said wafters along an axial endportion of the stator winding and back to said region while flowingradially along internal axial end walls of said end shield. Thismeans that warmer gas will be moved along said stator windingand further to the region of colder gas and transfer heat throughperipheral and axial end walls of the end shield before arriving tosaid region of the wafters again.

According to another embodiment of the invention said membercomprises a portion forming an obstacle preventing gasinfluenced by said wafters upon rotation of the rotor body to carryout a movement in a circular path to circulate back to said waftersand instead guide this gas further away from the wafters towards the radial periphery of said space. Such an obstacle will assist inobtaining the movement of the gas inside said space desired.

According to another embodiment of the invention each saidmember is made of a shaped plate, which may according toanother embodiment of the invention be made of steel.

According to another embodiment of the invention the electricmachine comprises an impeller with blades arranged on one endof the rotor body to conduct air in a path externally of said statorbody and peripheral parts of said end shields delimiting anannular portion of each said space surrounding an axial endportion of said winding for external cooling of the stator body andparts of said end shields upon rotation of said rotor body. Thisincreases the advantages of guiding the gas moved by the waftersto said annular space, since the external cooling of the wallsdelimiting this space there will enhance a transfer of heat throughthe end shield wall and lower the temperature of the gas movingback to the region of said wafters and then also coming close tothe bearings considerably.

According to another embodiment of the invention said impelleris arranged on the non-driven end of a shaft of the machine towhich said rotor body is secured.

According to another embodiment of the invention the electricmachine is a permanent magnet machine and said rotor body isprovided with a plurality of permanent magnets, and as analternative the electric machine may be an asynchronous electricmachine.

The invention also relates to a track-bound vehicle electricmachine having the features of the electric machine according tothe present invention as defined above. The advantages of sucha track-bound vehicle electric machine appear clearly from theabove discussion.

The invention also relates to a driving arrangement for a track-bound vehicle comprising an electric machine according to theinvention, use of an electric machine according to the inventionin a driving arrangement for generating a traction force of a track-bound vehicle as well as a track-bound vehicle having a drivingarrangement for generating a traction force of the vehicleincluding at least one electric machine according to the presentinvention. Also the advantageous features and the advantages ofsuch a driving arrangement, use and vehicle appear clearly fromthe above discussion of the different embodiments of an electricmachine according to the present invention.

Further advantages as well as advantageous features of theinvention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGSWith reference to the appended drawings below follows a specificdescription of an embodiment of the invention cited as an example. ln the drawings: Fig.1 shows an electric machine of the type to which thepresent invention belongs in a longitudinal cross-sectionview, Fig. 2 is a perspective view of the electric machine shown inFig. 1, Fig. 3 is an enlarged cross-section view of a part of an axial end of an electric machine of the type shown in Fig. 1and 2 according to the prior art, and Fig. 4 is a view corresponding to Fig. 3 for an electric machine according to an embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THEINVENTION A track-bound vehicle electric machine of the type to which thepresent invention relates is shown in Figs. 1 and 2. The electricmachine has a stator1 with a stator body 2 with a stator winding3 received in stator ducts not shown in the figure in the internalwall of the stator body and having axial end portions 4 of the coilforming the stator winding extending axially out of the stator body2 on the both sides thereof.

A rotor 5 with a rotor body 6 is rotatably disposed within the statorby being secured to a shaft 7 extending axially through theelectric machine and having a non-driven end 8 and a driven end9, which may be connected to a gearbox of the vehicle V. Theshaft 7 is received in bearings 10, 11 in an end shield 12, 13arranged at each axial end of the machine, and this end shieldhas an end wall 14 and a lateral peripheral wall 15 fixed tightly toan axial end of the stator body 2 so as to enclose a space 16, 17filled with air surrounding a respective axial end portion 4 of thestator winding.

Wafters 18 are arranged on each axial end 19 of the rotor bodyfor mixing air trapped in the respective space 16, 17 upon rotationof the rotor body.

An impeller 20 with blades (not shown) is arranged on the non-driven end 8 of the rotor body to rotate upon rotation of the rotorbody and by that conduct air from the exterior through a centralopening 21 of an end flange 22 of the machine in a path externallyof the stator body and the lateral peripheral walls of the endshields as indicated by arrows A in Fig. 1 (see also Fig. 3 and 4).

This results in an external cooling of the stator body 2 and partsof the end shields upon rotation of the rotor body.

Fig. 3 is an enlarged cross-section view of a part of an axial endof the electric machine shown in Fig 1. A wafter 18 secured to anaxial end of the rotor body 6 in the form of a short-circuit ring isindicated by a dashed line. lt is shown how a space 16 in whichair is trapped is delimited by an end wall 14 and a lateralperipheral wall 15 of the end shield 12, an axial end 27 of thestator body 2 and the axial end 23 of the rotor body. This space16 has an annular portion 24 surrounding the axial end portion 4of the stator winding and located directly internally of the endshield wall 15 being externally cooled by rotation of the impeller20 as indicated by the arrow A. lt is shown through the ring 25how air is moved by the wafters 18 upon rotation of the rotor bodyand the wafters are rotating the air around in tangentials directionand is also pushing the air in radial direction. However, sincethere is a low pressure region below, i.e. centrally with respect tothe wafters, air needs to flow back into this region and the sameair is then rotating back around the wafters as indicated by thering 25. This means that heat produced by the stator winding andin the rotor heating the air in the region 26 of the wafters will notreach the colder air further radially, especially in said annularportion 24 of the space.

Fig. 4 is a view similar to that of Fig. 3 of an electric machineaccording to an embodiment of the invention, in which a member30 is arranged in each space 16 and configured to direct airmoved by the wafters 18 upon rotation of the rotor body radiallytowards the radial periphery of the space for mixing this air withair in a peripheral portion of the space. The member is here madeby a shaped steel plate having at one end a portion 31 formingan obstacle preventing air influenced by the wafters upon rotationof the rotor body to carry out a movement in a circular path, asshown in Fig. 3, to circulate back to the wafters and instead guidethis air further away from the wafters towards the radial periphery of the space 16. The member 30 extends past the axial end 32 ofthe stator winding and further around the axial end portion 4 ofthe stator winding and in the direction of the opposite axial end ofthe machine into said annular portion 24 of the space peripherallysurrounding the axial end portion of the winding. The member 30is configured to guide air moved by the wafters along and aroundit as shown through the path B with arrows. This means that theair is forced to take a long way around the plate 30 beforecirculating back to the wafter, so that colder air in said annularportion 24 of the space will be mixed with warmer air and thetemperatures will even out. This means that the heat flow throughthe peripheral wall 15 of the end shield will increase, whereas theheat flow through the end wall 14 of the end shield towards thebearing will be reduced. This will result in a reduction of thetemperature of the bearing as well as the temperature of thehottest part of the stator winding, i. e. the central part thereofclosest to the wafter region.

A reduction of the temperature of these parts of the stator windingby about 10 K may double the life time of the stator windings,whereas the maintenance intervals of the bearings forlubrification thereof may be prolonged substantially by a similarreduction of the temperature of the bearings during operation ofthe electric machine.

The invention is of course not in any way restricted to theembodiment described above, but many possibilities tomodifications thereof will be apparent to a person with ordinaryskill in the art without departing from the scope of the inventionas defined in the appended claims.

Claims

1. Claims 1 _

2. An electric machine comprising: o a stator (1) having a stator body (2) with a statorwinding (3) configured to electrically create a pluralityof stator poles disposed around the inner periphery ofthe stator body, o a rotor (5) rotatably disposed within said stator andhaving a rotor body (6), o means configured to sealingly enclose at least saidrotor (5) and the stator winding (3) comprising an endshield (12, 13) arranged at each axial end of themachine and at each said end enclosing a space (16,17) filled with gas, delimited by the end shield (12, 13)and an axial end of said rotor body (6) and surroundinga respective axial end portion (4) of the stator winding,and o wafters (18) arranged on each axial end of the rotorbody (6) for mixing gas trapped in the respective saidspace upon rotation of the rotor body, characterized in that it comprises in each said space (16,17) a member (30) configured to direct gas moved by saidwafters (18) upon rotation of the rotor body at least partiallyradially towards the radial periphery of said space for mixingthis gas with gas in a peripheral portion (24) of said space.

3. An electric machine according to claim 1, characterized inthat each said member (30) extends in said space (16, 17)from the region (26) of said wafters (18), which is locatedradially internally of an axial end portion (4) of the statorwinding, radially outwardly towards and at least to the regionof the axial end (32) of said winding so as to guide gas movedby said wafters along the member from said region of saidwafters and at least to the axial end of the winding. 11

4. An electric machine according to claim 2, characterized inthat each said member (30) extends past the axial end (32)of the stator winding (3) and further around the axial endportion (4) of the stator winding and in the direction of theopposite axial end of the machine into an annular portion (24)of said space peripherally surrounding the axial end portionof the winding.

5. An electric machine according to any of the preceding claims,characterized in that said member (30) is configured toguide gas moved by said wafters (18) upon rotation of therotor body (16) from the region (26) of said wafters along anaxial end portion (4) of the stator winding and back to saidregion while flowing radially along internal axial end walls ofsaid end shield.

6. An electric machine according to any of the preceding claims,characterized in that said member comprises a portion (31)forming an obstacle preventing gas influenced by saidwafters (18) upon rotation of the rotor body (6) to carry out amovement in a circular path to circulate back to said waftersand instead guide this gas further away from the wafterstowards the radial periphery of said space (16, 17).

7. An electric machine according to any of the preceding claims,characterized in that each said member (30) is made of ashaped plate.

8. An electric machine according to claim 6, characterized inthat each said member (30) is made of a steel plate.

9. An electric machine according to any of the preceding claims,characterized in that it comprises an impeller (20) withblades arranged on one end of the rotor body (6) to conductair in a path externally of said stator body (2) and peripheralparts of said end shields (12, 13) delimiting an annular

10.

11.

12.

13.

14.

15. 12 portion (24) of each said space surrounding an axial endportion (4) of said winding for external cooling of the statorbody and parts of said end shields upon rotation of said rotorbody. An electric machine according to claim 8, characterized inthat said impeller (20) is arranged on the non-driven end (8)of a shaft (7) of the machine to which said rotor body (6) issecured. An electric machine according to any of the preceding claims,characterized in that it is a permanent magnet machine andsaid rotor body is provided with a plurality of permanentmagnets. An electric machine according to any of claims 1-9,characterized in that it is an asynchronous electric machine. A track-bound vehicle electric machine, characterized in thatit is an electric machine according to any of claims 1-11. A driving arrangement for a track-bound vehicle,characterized in that it comprises an electric machineaccording to claim 12. Use of an electric machine according to any of claims 1-11 ina driving arrangement for generating a traction force of atrack-bound vehicle (V). A track-bound vehicle having a driving arrangement forgenerating a traction force of the vehicle including at leastone electric machine according to any of claims 1-11.