Permanent-Magnet Synchronous Machine with Automatic Rotor Decoupling in the Winding Short Circuit

A permanent-magnet synchronous machine includes a stator in which a stator winding is arranged, a rotor which can rotate about a rotation axis and in which permanent magnets are arranged, wherein the rotor is connected to a motor shaft via a connecting device which is formed such that it initially connects the rotor to the motor shaft in a rotationally fixed manner, such that a torque which is generated by the interaction of stator winding and permanent magnet is transmitted to the motor shaft, where the connecting device is further configured automatically break the rotationally fixed connection of the rotor in the event of a short circuit of the stator winding, such that a torque that acts on the motor shaft is no longer transmitted to the rotor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a permanent-magnet synchronous machine, where the synchronous machine has a stator, in which a stator winding is arranged, a rotor that is rotatable about an axis of rotation, in which permanent magnets are arranged and that is connected to a motor shaft via a connecting device, and where the connecting device is configured to connect the rotor to the motor shaft in a torsion-proof manner, such that torque generated by the interaction of stator winding and the permanent magnets is transmitted to the motor shaft.

The present invention also relates to a land vehicle, where the land vehicle has a number of propulsion drives, which each have a synchronous machine and which each drive one wheel of the land vehicle via the synchronous machine.

2. Description of the Related Art

With land vehicles (this particularly applies rail vehicles, but is not necessarily restricted to rail vehicles however), there are often many converters and electric motors present, which each drive one wheel of a wheel set. If an individual converter or electric motor fails, then the land vehicle continues to operate without the failed converter or the failed electric motor. If the electric motor is a permanent-magnet synchronous motor and an electric motor of this type fails with a winding short circuit, i.e., a short circuit occurs in the stator winding, in the prior art the associated converter is switched off and is disconnected for the electric motor. After the converter has been switched off, an external voltage is no longer supplied to the failed electric motor. However, the rotation is still imparted to the rotor by the moving vehicle via the wheel-to-rail contact or via the wheel-to-ground contact. The permanent magnets arranged in the rotor therefore induce voltage in the stator winding. The induced voltage drives a fault current via the fault point at which the short circuit has occurred. This often causes arcs and/or high thermal losses to occur. As a consequence, the insulation of the stator winding can overheat and burn. Also the copper of the stator winding can also start to melt under some circumstances. Over and above these effects, already seen as negative per se, noise (actually harmless in itself) can also be generated which, for example, can cause considerable annoyance to passengers in a rail vehicle.

It is therefore of advantage, in the event of a winding short circuit, to disconnect the rotor (more precisely, the active part of the rotor) from the rotating wheel, so that the active part no longer rotates. Then, as a result of the absence of rotation in the stator winding, voltage is also no longer induced, such that consequential damage no longer occurs beyond the winding short circuit.

Safety couplings to decouple the driving motor from the drive train in the event of a fault are known. These are mostly switched separately (actively), however.

DE 10 2013 104 558 A1 discloses a drive train for a rail vehicle, which comprises a wheel set shaft and a large wheel to transmit a torque from a drive unit to the wheel set shaft. In this drive train, an overload coupling is connected to the wheel set shaft in a torsion-proof manner. The overload coupling couples the large wheel in a torsion-proof manner to the wheel set shaft. The overload coupling has a predetermined switching torque. If this switching torque is exceeded, then the overload coupling releases the large wheel in relation to the wheel set shaft. As taught in DE 10 2013 104 558 A1, the wheel set shaft is therefore released from the drive if a mechanically effective torque is exceeded. This embodiment is not suitable for a disconnection in the event of a winding short circuit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a permanent-magnet synchronous machine configured such that, in the event of a winding short circuit, torque transmission from the motor shaft to the rotor of the permanent-magnet synchronous machine can be suppressed in a simple and reliable way.

This and other objects and advantages are achieved in accordance with the invention by a permanent-magnet synchronous machine in which a connecting device is configured such that it initially only connects a rotor to a motor shaft in a torsion-proof manner, such that torque generated by the interaction of a stator winding and permanent magnets is transmitted to the motor shaft, and the connecting device is configured such that, in the event of a short circuit of the stator winding, it automatically releases the torsion-proof connection of the rotor, such that torque acting on the motor shaft is no longer transmitted to the rotor.

As a result of this embodiment, in the event of a winding short circuit, and automatic release of the torsion-proof connection of the rotor to the motor shaft occurs. The disadvantages stated above are therefore avoided.

The motor shaft can be identical to the rotor shaft, i.e., that shaft on which the rotor is arranged. As an alternative, the shaft can involve another shaft. In any event, however, the motor shaft is that shaft via which a torque is output by the permanent-magnet synchronous machine.

In a possible embodiment of the synchronous machine, a rotor is arranged in a torsion-proof manner on a rotor shaft different from the motor shaft, the motor shaft including a hub enclosing the rotor shaft, a bearing is arranged between the rotor shaft and the hub, the connecting device comprises a retaining element, via which the hub is initially pressed radially onto the rotor shaft, such that, as a result of the pressing, the torque generated by the interaction of stator winding and permanent magnets is transmitted to the motor shaft, and the retaining element consists at least partly of a material of which the strength and/or cohesion is reduced such that, in the event of a short circuit of the stator winding resulting from an overheating of the stator winding that occurs and/or arcs occurring, the pressing of the hub onto the rotor shaft is reversed.

The advantage of this embodiment is that the rotor, as is also usual, can be arranged in a torsion-proof manner on the rotor shaft.

In this embodiment, the retaining element can be formed as the bandage surrounding the hub radially externally. A possible material of the bandage is a glass fiber mat or carbon fiber mat impregnated with a hardener. A melting temperature of the hardener in this case should lie between around 200° C. and around 300° C., in particular between around 250° C. and around 280° C. These types of hardeners are known to persons skilled in the art. An example of suitable hardener is especially a hardener of which the “glass temperature” lies in this range. Thermoplastics can be chosen as these types of hardeners.

The bearing between the rotor shaft and the hub makes it possible for no damage to occur during continuation of the journey of the land vehicle and thus in particular on continuation of the rotation of the motor shaft, in particular for a free rotation of the motor shaft relative to the rotor shaft to be possible. Preferably, the bearing is configured as an emergency bearing. Because of its configuration as an emergency bearing the bearing between the motor shaft and the rotor shaft can be formed simply and at very low cost. The emergency bearing, on the other hand, does not have to be able to guarantee continuous operation over days, weeks and months. It is sufficient to be able to continue the journey of the land vehicle, for example, to the next repair facility.

In a further possible embodiment of the synchronous machine, the rotor is supported rotatably on the motor shaft, the connecting device, comprise a ring, which is connected to the rotor in a torsion-proof manner at an axial end of the rotor, the connecting device comprises at least one bolt, which is arranged partly in a recess of the ring and partly in a recess of the motor shaft, such that the torque generated by the interaction of the stator winding and permanent magnet is transferred via the bolt to the motor shaft, the connecting device comprises a retaining element, via which a radial displacement of the bolt from the recess of the motor shaft is initially prevented, and the retaining element consists at least partly of a material of which the strength and/or cohesion is reduced far such that, in the event of a short circuit of the stator winding due to an overheating of the stator winding that occurs and/or an occurrence of arcs, the bolt is displaced out of the recess of the motor shaft.

The advantage of this embodiment is that the torque applied by the synchronous machine during normal operation (i.e., when the torsion-proof connection exists between rotor and motor shaft) is transferred via the bolts. On the other hand, only the forces exerted by the bolts on the retaining element and centrifugal forces act on the retaining element. These forces are very small, however.

The retaining element can be formed in this case, for example, as the bandage surrounding the ring radially externally. The possible materials of the bandage have already been mentioned above.

Preferably, the connecting device has at least one compression spring, via which a force directed radially outwards is exerted on the bolt. The effect of this is that, when the strength and/or the cohesion of the retaining element is reduced, the bolt is actively pressed radially outwards by the compression spring. The compression spring can be formed, for example,—via a suitable configuration or by a stop, such that, after the bolt has been pushed out of the motor shaft, it does not project into the ring itself. As an alternative, the compression spring can be dimensioned such that, although it pushes the bolt out of the motor shaft, and thereafter projects into the ring itself, it cannot transfer any appreciable torque however, but is sheared off itself beforehand for example.

It is currently especially preferred to embody the synchronous machine such that the rotor is rotatably supported on the motor shaft, the connecting device comprises a first coupling part, which is arranged on the motor shaft in a torsion-proof manner, the connecting device comprises a second coupling part, which is connected to the rotor in a torsion-proof manner, the connecting device comprises a retaining element penetrating the first and the second coupling part axially, via which the first coupling part is initially pushed axially against the second coupling part, such that the torque generated by the interaction of the stator winding and permanent magnets is transmitted to the motor shaft by the first and second coupling part, and the retaining element consists at least partly of a material, of which the strength and/or cohesion, in the event of a short circuit of the stator winding, is reduced far enough by an overheating of the stator winding that occurs and/or by the occurrence of arcs, for a pressure exerted by the retaining element on the first and the second coupling element to be reduced far enough for it to make possible a displacement of the first and the second coupling element away from each other.

This embodiment has the advantage in particular that the release of the connecting element, i.e., the removal of the torsion-proof connection of the rotor to the motor shaft, can be initiated reliably, where the initiation is independent of the axial position at which the winding short circuit has occurred and at which consequently the greatest amount of heat develops. Experience shows, in particular that, when the winding short circuit occurs, this generally occurs in one of the two winding heads.

The retaining element can be formed as a number of bandages. The possible materials of the bandages have already been explained above.

As an alternative it is possible, for the retaining element to be formed as a number of bolts, which are secured at the two axial ends by fixing elements, and for the fixing elements to consist of a material of which the strength and/or cohesion is reduced in the event of a short circuit of the stator winding through the occurrence of overheating of the stator winding and/or the occurrence of arcs.

The fixing elements can be formed as fuses, for example. The fuses can consist of a soft solder that has a suitable solidus temperature, for example. The various soft solders are known to persons skilled in the art, where the solders have solidus temperatures of between 138° C. and 308° C. Within the framework of the current invention, soft solders with a solidus temperature of between 200° C. and 300° C., in particular of between 250° C. and 280° C., are suitable. For example, a eutectic mixture of 99.3% tin and 0.7% copper has a melting point of 227° C. The same applies for a eutectic mixture of 99.0% tin, 0.3% silver and 0.7% copper. Pure tin has a melting point of 232° C., a mixture of 89% tin, 10.5% antimony and 0.5% copper has a solidus temperature of 242° C. Each of these soft solders can be used as the material for a fuse. Other soft solders with a higher or a lower solidus temperature can also be used, as required. Likewise suitable plastics can be used, such as PEEK.

Preferably, at least one compression spring is arranged between the first and the second coupling part, via which a force driving the first and the second coupling part apart from one another is exerted on the first and the second coupling part. The effect of this is that when the strength and/or the cohesion of the retaining element is reduced, the coupling parts are actively pushed away from one another by the compression spring.

The bearing via which the rotor is supported on the motor shaft is preferably formed as an emergency bearing. As a result of the embodiment as an emergency bearing, the support of the rotor on the motor shaft can be formed simply and at very low cost. The emergency bearing, on the other hand, does not have to guarantee continuous operation over days, weeks and months. It is sufficient to be able to continue the current journey of the land vehicle for a period of time.

It is also an object of the invention to provide a land vehicle of the type stated at the outset which is configured with the drives having an inventive synchronous machine.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In accordance withFIG. 1, a land vehicle1has a number of propulsion drives2. The propulsion drives2each drive at least one wheel3of the land vehicle1. The propulsion drives2, in order to drive the respective wheel3, each have a synchronous machine4. As a rule, respective synchronous machine4is fed via a respective converter. The converters are also not shown in the figure.

As depicted in the diagram inFIG. 1, the land vehicle1comprises a rail vehicle. This embodiment, within the framework of the present invention for a land vehicle, represents the normal case. The present invention, however, can also be used when the land vehicle1is not rail-bound, such as when the land vehicle1comprises an electric automobile and each wheel of the electric automobile has its own drive.

In accordance withFIG. 2the synchronous machine4has a stator5. Arranged in the stator5is a stator winding6. The stator winding6has a central part6′ and also two winding heads6″. The central part6′ of the stator winding6is that part of the stator winding6that is located in the stator5itself. The winding heads6″ are those parts of the stator winding6that project axially beyond the stator5.

The synchronous machine4further has a rotor7. The rotor7is arranged on a shaft8. The shaft8and with it the rotor7are rotatable about an axis of rotation9. In many embodiments of the present invention, which will be explained in conjunction with the further figures, the shaft8involves the motor shaft10of the synchronous machine4. In other embodiments, a separate shaft different from the motor shaft10is involved. In this case, the shaft8is flush with the motor shaft10, meaning that the axis of rotation9of the shaft8is identical to the axis of rotation of the motor shaft10. Arranged in the rotor7are permanent magnets11. The synchronous machine4is therefore formed as a permanent-magnet synchronous machine. The permanent magnets11or their magnetic field and a rotating field generated by applying power to the stator winding6act together in the operation of the synchronous machine4to create a torque.

The terms “axial”, “radial” and “tangential” are always related to the axis of rotation9. “Axial” is a direction parallel to the axis of rotation9. “Radial” is a direction orthogonal to the axis of rotation9on the axis of rotation9towards it or away from it. “Tangential” is a direction which runs both orthogonally to the axial direction and also orthogonally to the radial direction. Thus “tangential” means a direction that, with a constant axial position and with a constant radial distance, is directed in a circular shape about the axis of rotation9.

Within the framework of the embodiment in accordance withFIG. 3, the shaft8is a separate shaft, i.e., a different shaft from the motor shaft10. Within the framework of the embodiment in accordance withFIG. 3, the shaft8will be referred to below as the rotor shaft. The rotor7is arranged in a torsion-proof manner on the rotor shaft8. The motor shaft10has a hub12. The hub12encloses the rotor shaft8. Arranged between the rotor shaft8and the hub12is a bearing13. In principle, the rotor shaft8is therefore rotatable relative to the hub12. The bearing13can be formed in particular as an emergency bearing.

The rotor7is connected (indirectly via the rotor shaft8) to the motor shaft10via a connecting device14. The connecting device14, within the framework of the embodiment in accordance withFIG. 3, initially comprises the hub12. Furthermore, the connecting device14comprises a retaining element15. The hub12is pressed radially onto the rotor shaft8via the retaining element15. As a result of the pressing, it is possible to transmit the torque, which is generated by the interaction of stator winding6and permanent magnets11, onto the motor shaft10. The connecting device is thus configured such that it (initially) connects the rotor7to the motor shaft10in a torsion-proof manner. The retaining element15generally brings about a friction-fit connection, in some cases a form-fit connection, of the rotor shaft8to the motor shaft10.

The retaining element15, however, consists at least partly (preferably completely) of a material of which the strength and/or cohesion is reduced such that, in the event of a short circuit of the stator winding6due to an overheating of the stator winding6that occurs and/or an occurrence of arcs, the pressing of the hub on the rotor shaft is reversed. For example, the retaining element15can be formed as a bandage made of a type of material that surrounds the outside of the hub12radially. If the bandage heats up as a result of a winding short circuit and the fault currents occurring as a result, the bandage loses its strength.

The pressing is removed such that the rotor shaft8becomes rotatable relative to the motor shaft10via the bearing13. With subsequent cooling of the bandage, although this hardens again, the previous torsion-proof connection between motor shaft10and rotor shaft8(and via the rotor shaft8further to the rotor7) will not be re-established, however. Instead, the connection remains removed. The connecting device14is thus configured such that, in the event of a short circuit of the stator winding6, it automatically releases the torsion-proof connection of the rotor7, such that torque acting on the motor shaft10is no longer transmitted to the rotor7.

Further possible embodiments of the synchronous machine4will be explained below in conjunction withFIGS. 4 and 5. In these embodiments the rotor is supported directly on the motor shaft10to allow it to rotate. In these embodiments, however, the rotor7is also connected to the motor shaft10via the connecting device14. The connecting device14, like the embodiment in accordance withFIG. 3, is configured such that it (initially) connects the rotor7to the motor shaft10in a torsion-proof manner. In this state, it is thus possible for a torque that is generated by the interaction of stator winding6and permanent magnets11to be transmitted to the motor shaft10. The connecting device14is, however, both in the embodiment in accordance withFIG. 4and in the embodiment in accordance withFIG. 5, configured such that, in the event of a short circuit of the stator winding6, the connecting device14automatically releases the torsion-proof connection of the rotor7. Torque acting on the motor shaft10is then no longer transmitted to the rotor7. With these embodiments, after the torsion-proof connection has been released, the connection also stays released.

In the embodiment in accordance withFIG. 4, the connecting device14comprises a ring16, which is connected to the rotor7in a torsion-proof manner at an axial end of the rotor7. The ring16has at least one recess. Two recesses of this kind are shown inFIG. 4. Mostly three or four recesses are present. Furthermore, the motor shaft10has a corresponding recess in each case for each recess of the ring16.

A single recess of the ring16and the corresponding recess of the motor shaft10will always be referred to below. The corresponding information also applies even if the ring16and the motor shaft10each have a number of recesses.

Both the recess of the ring16and the recess of the motor shaft10run radially. A bolt17is introduced into the recess of the ring16. The bolt17extends through the recess of the ring16into the corresponding recess of the motor shaft10. The bolt17is thus arranged partly in the recess of the ring16and partly in the recess of the motor shaft10. The bolt causes a form-fit connection of the rotor7and the motor shaft10. The torque generated by the interaction of stator winding6and permanent magnets11can thus be transferred via the bolt17to the motor shaft10.

The transmission of the torque is of course only possible for as long as the bolt17is arranged in both recesses (i.e., both in the recess of the ring16and in the recess of the motor shaft10). Furthermore, centrifugal forces act on the bolt17during rotation of the motor shaft10. The connecting device14therefore comprises a retaining element18, via which a radial displacement of the bolt17out of the recess of the motor shaft10is (initially) prevented. The retaining element18can be formed, as depicted inFIG. 4, as a bandage, which surrounds the outside of the ring16radially. In a similar way to the embodiment in accordance withFIG. 3, the retaining element18consists at least partly (preferably even completely) of a material of which the strength and/or cohesion is reduced in the event of a short circuit of the stator winding6due to an overheating of the stator winding6that occurs and/or an occurrence of arcs. The above information about the retaining element15of the embodiment ofFIG. 3is usable in a similar way.

In the event of a short circuit of the stator winding6, the retaining element18thus loses its capability to hold back the bolt17. This enables the bolt17to move out of the recess of the motor shaft10. In a later cooling down of the bandage, the bandage does re-harden. However, the bolt17is not pushed back into the recess of the motor shaft10. The bold17can actually, under some circumstances, fall back into the recess as a result of centrifugal forces. At the latest, with a new rotation of the motor shaft10, it will be moved out of the recess of the motor shaft10again by the centrifugal forces occurring. If necessary (this is not also shown inFIG. 4), the connecting device can furthermore have a compression spring, via which a force directed radially outwards is exerted. The compression spring is arranged in this case within the motor shaft10.

FIG. 5shows a further embodiment of the rotor arrangement of the synchronous machine4. This embodiment is currently especially preferred. In the embodiment in accordance withFIG. 5, the connecting device14comprises a first coupling part19and a second coupling part20. The first coupling part is arranged on the motor shaft10in a torsion-proof manner. The second coupling part20is connected to the rotor7in a torsion-proof manner. The connecting device14furthermore comprises a retaining element21. The retaining element21penetrates both the rotor7and the first coupling part19and also the second coupling part20axially. A pressure ring22is mostly arranged on the other side of the rotor7facing away from the coupling parts19,20, which is also penetrated axially by the retaining element21. The retaining element21is under compressive tension. With the retaining element21, the first coupling element19is therefore (initially) pressed against (tensioned on) the second coupling element20. The fact that the retaining element21presses the coupling elements19,20against one another means that it is possible to transmit the torque generated by the interaction of stator winding6and permanent magnets11to the motor shaft10. The torque is thus transmitted by the interaction of first and second coupling part19,20. As a rule, a friction-fit connection, in some cases a form-fit connection, of the rotor7to the motor shaft exists via the coupling parts19,20.

As in the embodiments ofFIGS. 3 and 4, in the embodiment ofFIG. 5, the retaining element also consists of a material of which the strength and/or cohesion, in the event of a short of the stator winding6, is reduced such that, by the overheating of the stator winding6that occurs and/or an occurrence of arcs, a pressure exerted by the retaining element21on the first and the second coupling part19,20is reduced. The pressure is in particular reduced far enough for the retaining element to make possible an axial displacement of the first and second coupling part19,20away from one another. The coupling parts19,20are thereby no longer connected to one another in a torsion-proof manner, such that a rotation of the motor shaft is decoupled from a rotation of the rotor7. The retaining element21(depending on its embodiment) can, for example, move out of the coupling parts19,20, release itself or shear off.

In the embodiment in accordance withFIG. 5, the retaining element21can be formed as a number of bandages23. This is shown for a single bandage23in the upper part ofFIG. 5. What has been stated above in conjunction withFIG. 3andFIG. 4applies analogously for the embodiment of the bandages23as such.

As an alternative, the retaining element21can be formed as a number of bolts24that are secured at both axial ends by fixing elements25. This is shown in the lower part ofFIG. 5. The bolts24consist of steel or another suitable material. The strength and the cohesion of the bolts24is maintained even in the event of a short circuit of the stator winding6. The fixing elements25, however, consist of a material of which the strength and/or cohesion is reduced in the event of a short circuit of the stator winding6due to the overheating of the stator winding6that occurs and/or by the occurrence of arcs. In particular, the fixing elements25can comprise fuse links.

Preferably, in accordance with the embodiment shown inFIG. 5, compression springs26are arranged between the first and the second coupling part19,20. With the compression springs26, a force driving the first and the second coupling part19,20away from one another can be exerted on the first and second coupling parts19,20. This enables it to be insured that the coupling formed by the coupling parts19,20opens immediately when the fixing elements25on the one side or on the other side of the rotor7lose their strength or their cohesion.

Within the framework of the embodiments ofFIG. 4andFIG. 5, the rotor7is supported on the motor shaft10via a bearing27. The bearing27is preferably formed as an emergency bearing.

In summary the present invention thus relates to a permanent-magnet synchronous machine4having a stator5, in which a stator winding6is arranged. The synchronous machine4has a rotor7that is rotatable about an axis of rotation9, in which permanent magnets11are arranged. The rotor7is connected to a motor shaft10via a connecting device14. The connecting device14is configured such that it initially connects the rotor7to the motor shaft10in a torsion-proof manner, such that torque generated by the interaction of stator winding6and permanent magnets11is transferred to the motor shaft10. The connecting device14is furthermore configured such that, in the event of a short circuit of the stator winding6, the connecting device14automatically releases the torsion-proof connection of the rotor7, such that a torque acting on the motor shaft10is no longer transmitted to the rotor7.

The present invention has many advantages. In particular, it is simple to implement. Furthermore, in the event of a winding short circuit, the torsion-proof connection of the rotor7to the motor shaft10can be removed in a simple and reliable way.

Although the invention has been illustrated and described in greater detail by the preferred exemplary embodiments, the invention is not restricted solely to the disclosed examples and other variations can be derived therefrom by the person skilled in the art, without departing from the scope of protection of the invention.