SE539576C2

SE539576C2 - An electric machine

Info

Publication number: SE539576C2
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: 2017-10-17
Also published as: WO2017009001A1; EP3323193A1; CN107836073A; SE1551021A1

Description

An electric machine TECHNICAL FIELD OF THE INVENTION AND BACKGROUND ART The present invention relates to an electric machine comprising a stator having a stator body with a stator winding configured to electrically create a plurality of stator poles disposed around the inner periphery of the stator body, a rotor rotatably disposed within said stator and having a rotor body, means configured to sealingly enclose at least said rotor and the stator winding comprising an end shield arranged at each axial end of the machine and at each said end enclosing a space filled with gas, delimited by the end shield and an axial end of said rotor body and surrounding a respective axial end portion of the stator winding, and wafters arranged on each axial end of the rotor body for mixing gas trapped in the respective said space upon rotation of the rotor body.

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

The present invention is particularly applicable to electric machines in the form of motors of the type defined in the introduction for creating a traction force of a track-bound vehicle, especially a rail vehicle, and this application of such an electric machine will mainly be discussed below without for that sake restricting the invention thereto. Such a motor may of course function as a generator when braking the vehicle.

Such an electric machine is totally enclosed, which means that the 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 escape said space unless the machine is disassembled (in practise it may leak out very slowly and finally be replaced by new air, but that will take a very long time compared to for an open machine). The reason for enclosing the rotor and the stator windings of the electric machine in this way is to protect these parts against dirt and contaminations when the machine is used in an environment in which the machine is exerted thereto, such as in an underground train. However, during operation of the electric machine heat is created by losses mainly in the stator body, the rotor body and the stator windings resulting in a temperature increase of the air trapped in said space. The temperature is the parameter restricting the maximum power of operation of an electric machine of this type when it functions as a motor and the maximum power which may be delivered thereby in the case of generator function, in which the insulation layers of the stator windings and the bearings for the shaft of the electric machine are the components most sensitive to high temperatures. The insulation layers of the stator windings will be degraded or partially destroyed above a certain temperature and lubricants of said bearings will run dry at an excess temperature, which means that the bearings will not get any lubrification and may seize. The life time of these components is then of course also dependent upon which temperature they are exposed to during the operation of the electric machine, so that a reduction of this temperature means that the maintenance intervals may be prolonged. This means that the efficiency of the cooling of such an electric machine is very important, and that is the reason for the arrangement of said wafters for mixing air trapped in said space inside the electric machine for increasing the heat transport to the exterior of the machine and attempting to avoid the creation of hot spots at critical locations inside said space.

SUMMERY OFTHEINVENTION The object of the present invention is to provide an electric machine of the type defined in the introduction being improved in at least some aspect with respect to such electric machines already known.

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

By introducing a said member in each of the spaces in which gas is trapped the gas moved by the wafters through rotation of the rotor body will take a long way inside said space before circulating back to the wafters. This means that colder gas closer to the periphery of the space will be mixed with a warmer gas and the temperatures will even out. The inventor has found out that in absence of such a member in said space the wafters on the rotor body will rotating the gas around in tangential direction and also pushing the gas in radial direction, but since there is a low pressure region radially internally of the wafters gas needs to flow back into this region and the same gas is then rotating back around the wafters preventing the gas from reaching further radially for being mixed with cooler gas. Thus, the arrangement of said member means that less heat is transferred to the bearing through the end shield and more heat will be transferred through the radially peripheral walls of the end shield. This means that it will be possible for a certain power of operation of the electric machine to lower the temperature of the bearings and also of the insulation layers of the stator winding for prolonging the life time thereof and the maintenance intervals for lubrification of the bearings, or expressed in another way, a higher maximum power of operation of the electric machine is obtained.

According to an embodiment of the invention each said member extends in said space from the region of said wafters, which is located radially internally of an axial end portion of the stator winding, radially outwardly towards and at least to the region of the axial end of said winding so as to guide gas moved by said wafters along the member from said region of said wafters and at least to the axial end of the winding. This results in a better cooling of said stator winding than compared to no such members present in said space.

According to another embodiment of the invention each said member extends past the axial end of the stator winding and further around the axial end portion of the stator winding and in the direction of the opposite axial end of the machine into an annual portion of said space peripherally surrounding the axial end portion of the winding. By guiding the gas moved by said wafters along a member with this extension hotter gas will efficiently be mixed with colder gas and the temperatures will be efficiently evened out inside said space resulting in an increased transfer of heat energy through peripheral walls of the end shield and a lowering of the temperature of said bearings and also the stator windings.

According to another embodiment of the invention said member is configured to guide gas moved by said wafters upon rotation of the rotor body from the region of said wafters along an axial end portion of the stator winding and back to said region while flowing radially along internal axial end walls of said end shield. This means that warmer gas will be moved along said stator winding and further to the region of colder gas and transfer heat through peripheral and axial end walls of the end shield before arriving to said region of the wafters again.

According to another embodiment of the invention said member comprises a portion forming an obstacle preventing gas influenced by said wafters upon rotation of the rotor body to carry out a movement in a circular path to circulate back to said wafters and instead guide this gas further away from the wafters towards the radial periphery of said space. Such an obstacle will assist in obtaining the movement of the gas inside said space desired.

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

According to another embodiment of the invention the electric machine comprises an impeller with blades arranged on one end of the rotor body to conduct air in a path externally of said stator body and peripheral parts of said end shields delimiting an annular portion of each said space surrounding an axial end portion of said winding for external cooling of the stator body and parts of said end shields upon rotation of said rotor body. This increases the advantages of guiding the gas moved by the wafters to said annular space, since the external cooling of the walls delimiting this space there will enhance a transfer of heat through the end shield wall and lower the temperature of the gas moving back to the region of said wafters and then also coming close to the bearings considerably.

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

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

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

The invention also relates to a driving arrangement for a track-bound vehicle comprising an electric machine according to the invention, use of an electric machine according to the invention in a driving arrangement for generating a traction force of a track-bound vehicle as well as a track-bound vehicle having a driving arrangement for generating a traction force of the vehicle including at least one electric machine according to the present invention. Also the advantageous features and the advantages of such a driving arrangement, use and vehicle appear clearly from the above discussion of the different embodiments of an electric machine according to the present invention.

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

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings below follows a specific description of an embodiment of the invention cited as an example.

In the drawings: Fig. 1 shows an electric machine of the type to which the present invention belongs in a longitudinal cross-section view, Fig. 2 is a perspective view of the electric machine shown in Fig. 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. 1 and 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 THE INVENTION A track-bound vehicle electric machine of the type to which the present invention relates is shown in Figs. 1 and 2. The electric machine has a stator 1 with a stator body 2 with a stator winding 3 received in stator ducts not shown in the figure in the internal wall of the stator body and having axial end portions 4 of the coil forming the stator winding extending axially out of the stator body 2 on the both sides thereof.

A rotor 5 with a rotor body 6 is rotatably disposed within the stator by being secured to a shaft 7 extending axially through the electric machine and having a non-driven end 8 and a driven end 9, which may be connected to a gearbox of the vehicle V. The shaft 7 is received in bearings 10, 11 in an end shield 12, 13 arranged at each axial end of the machine, and this end shield has an end wall 14 and a lateral peripheral wall 15 fixed tightly to an axial end of the stator body 2 so as to enclose a space 16, 17 filled with air surrounding a respective axial end portion 4 of the stator winding.

Wafters 18 are arranged on each axial end 19 of the rotor body for mixing air trapped in the respective space 16,17 upon rotation of 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 rotor body and by that conduct air from the exterior through a central opening 21 of an end flange 22 of the machine in a path externally of the stator body and the lateral peripheral walls of the end shields 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 parts of the end shields upon rotation of the rotor body. Fig. 3 is an enlarged cross-section view of a part of an axial end of the electric machine shown in Fig 1. A wafter 18 secured to an axial end of the rotor body 6 in the form of a short-circuit ring is indicated by a dashed line. It is shown how a space 16 in which air is trapped is delimited by an end wall 14 and a lateral peripheral wall 15 of the end shield 12, an axial end 27 of the stator body 2 and the axial end 23 of the rotor body. This space 16 has an annular portion 24 surrounding the axial end portion 4 of the stator winding and located directly internally of the end shield wall 15 being externally cooled by rotation of the impeller 20 as indicated by the arrow A. It is shown through the ring 25 how air is moved by the wafters 18 upon rotation of the rotor body and the wafters are rotating the air around in tangentials direction and is also pushing the air in radial direction. However, since there is a low pressure region below, i.e. centrally with respect to the wafters, air needs to flow back into this region and the same air is then rotating back around the wafters as indicated by the ring 25. This means that heat produced by the stator winding and in the rotor heating the air in the region 26 of the wafters will not reach the colder air further radially, especially in said annular portion 24 of the space. Fig. 4 is a view similar to that of Fig. 3 of an electric machine according to an embodiment of the invention, in which a member 30 is arranged in each space 16 and configured to direct air moved by the wafters 18 upon rotation of the rotor body radially towards the radial periphery of the space for mixing this air with air in a peripheral portion of the space. The member is here made by a shaped steel plate having at one end a portion 31 forming an obstacle preventing air influenced by the wafters upon rotation of the rotor body to carry out a movement in a circular path, as shown in Fig. 3, to circulate back to the wafters and instead guide this air further away from the wafters towards the radial periphery of the space 16. The member 30 extends past the axial end 32 of the stator winding and further around the axial end portion 4 of the stator winding and in the direction of the opposite axial end of the machine into said annular portion 24 of the space peripherally surrounding the axial end portion of the winding. The member 30 is configured to guide air moved by the wafters along and around it as shown through the path B with arrows. This means that the air is forced to take a long way around the plate 30 before circulating back to the wafter, so that colder air in said annular portion 24 of the space will be mixed with warmer air and the temperatures will even out. This means that the heat flow through the peripheral wall 15 of the end shield will increase, whereas the heat flow through the end wall 14 of the end shield towards the bearing will be reduced. This will result in a reduction of the temperature of the bearing as well as the temperature of the hottest part of the stator winding, i. e. the central part thereof closest to the wafter region.

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

The invention is of course not in any way restricted to the embodiment described above, but many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the scope of the invention as defined in the appended claims.

Claims

1. An electric machine comprising: • a stator (1) having a stator body (2) with a stator winding (3) configured to electrically create a plurality of stator poles disposed around the inner periphery of the stator body, • a rotor (5) rotatably disposed within said stator and having a rotor body (6), • means configured to sealingly enclose at least said rotor (5) and the stator winding (3) comprising an end shield (12, 13) arranged at each axial end of the machine 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 surrounding a respective axial end portion (4) of the stator winding, and • wafters (18) arranged on each axial end of the rotor body (6) for mixing gas trapped in the respective said space upon rotation of the rotor body, the electric machine comprising in each said space (16, 17) a member (30) configured to direct gas moved by said wafters (18) upon rotation of the rotor body at least partially radially towards the radial periphery of said space for mixing this gas with gas in a peripheral portion (24) of said space,characterizedin that said member comprises a portion (31) forming an obstacle preventing gas influenced by said wafters (18) upon rotation of the rotor body (6) to carry out a movement in a circular path to circulate back to said wafters and instead guide this gas further away from the wafters towards the radial periphery of said space (16, 17).

2. An electric machine according to claim 1,characterizedin that each said member (30) extends in said space (16, 17) from the region (26) of said wafters (18), which is located radially internally of an axial end portion (4) of the stator winding, radially outwardly towards and at least to the region of the axial end (32) of said winding so as to guide gas moved by said wafters along the member from said region of said wafters and at least to the axial end of the winding.

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

4. An electric machine according to any of the preceding claims,characterizedin that said member (30) is configured to guide gas moved by said wafters (18) upon rotation of the rotor body (16) from the region (26) of said wafters along an axial end portion (4) of the stator winding and back to said region while flowing radially along internal axial end walls of said end shield.

5. An electric machine according to any of the preceding claims,characterizedin that each said member (30) is made of a shaped plate.

6. An electric machine according to claim 5,characterizedin that each said member (30) is made of a steel plate.

7. An electric machine according to any of the preceding claims,characterizedin that it comprises an impeller (20) with blades arranged on one end of the rotor body (6) to conduct air in a path externally of said stator body (2) and peripheral parts of said end shields (12, 13) delimiting an annular portion (24) of each said space surrounding an axial end portion (4) of said winding for external cooling of the stator body and parts of said end shields upon rotation of said rotor body.

8. An electric machine according to claim 7,characterizedin that said impeller (20) is arranged on the non-driven end (8) of a shaft (7) of the machine to which said rotor body (6) is secured.

9. An electric machine according to any of the preceding claims,characterizedin that it is a permanent magnet machine and said rotor body is provided with a plurality of permanent magnets.

10. An electric machine according to any of claims 1-8,characterizedin that it is an asynchronous electric machine.

11. A track-bound vehicle electric machine,characterizedin that it is an electric machine according to any of claims 1-10.

12. A driving arrangement for a track-bound vehicle,characterizedin that it comprises an electric machine according to claim 11.

13. Use of an electric machine according to any of claims 1-10 in a driving arrangement for generating a traction force of a track-bound vehicle (V).

14. A track-bound vehicle having a driving arrangement for generating a traction force of the vehicle including at least one electric machine according to any of claims 1-10.