Electric machine

An electric machine includes a housing which accommodates a stator and a rotor rotationally supported about an axis of rotation, and has a front/rear air inlet opening on a top face and an air outlet opening therebetween. A front/rear air conveying element draws into the air inlet openings air which is discharged from the air outlet opening during operation. A cooler is mounted on the top face of the housing, covering the air inlet openings and the air outlet opening in a hood-like manner, such that discharged air is fed back to the air inlet openings. The cooler has a front/rear partition arranged between the air outlet opening and the corresponding air inlet opening and extending upward from the top face. Air guiding elements are arranged in the housing and/or in the cooler for feeding discharged air at least partially to the respective other air inlet opening.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2012/054391, filed Mar. 13, 2012, which designated the United States and has been published as International Publication No. WO 2012/136453 and which claims the priority of German Patent Application, Serial No. 10 2011 006 844.9, filed Apr. 6, 2011, pursuant to 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The present invention relates to an electric machine,wherein the electric machine comprises a housing in which a stator is arranged and in which a rotor is rotationally supported about an axis of rotation,wherein the housing extends from a front end to a rear end when viewed in the direction of the axis of rotation,wherein on a top face the housing comprises a front air inlet opening in the vicinity of the front end, a rear air inlet opening in the vicinity of the rear end, and an air outlet opening therebetween,wherein the electric machine comprises a front and a rear air conveying element by means of which air is drawn in at the front and the rear air inlet openings and discharged at the air outlet opening during operation of the electric machine,wherein an auxiliary cooler is mounted on the top face of the housing, which auxiliary cooler covers the front and the rear air inlet openings and the air outlet opening with side walls and a top cover in a hood-like manner, such that the air discharged at the air outlet opening is fed back to the front and the rear air inlet openings,wherein the auxiliary cooler comprises a front and a rear auxiliary partition,wherein the front and the rear auxiliary partitions are arranged between the air outlet opening and the front and the rear air inlet openings and extend upward from the top face of the housing.

Such electric machines are generally known.

Electric machines having an auxiliary cooler are known in various embodiments. They are on the one hand divided into single-flow and double-flow machines in respect of the path of the primary air which flows through the electric machine. Single-flow electric machines have one air inlet opening in the vicinity of the front end and one air outlet opening in the vicinity of the rear end. Double-flow electric machines have—as explained above—an air inlet opening in the vicinity of each of the front end and of the rear end and an air outlet opening therebetween. Electric machines having an auxiliary cooler are furthermore subdivided in respect of the cooling of the primary air in the auxiliary cooler into electric machines in which the primary air is cooled by water and into electric machines in which the primary air is cooled by secondary air. The present invention relates to electric machines having an auxiliary cooler, in which machines the primary air is cooled by secondary air.

With regard to such electric machines, many tubes running parallel to the axis of rotation are present in the auxiliary cooler. The tubes are open to the outside. The air (primary air) discharged from the electric machine at the air outlet opening circulates around the tubes and as a result the tubes absorb the heat contained in the circulating primary air. This means that the tubes cool the primary air before the primary air is fed back to the electric machine. The secondary air flows through the tubes, thereby cooling the tubes, and the secondary air is thus heated.

The direction of flow of the secondary air is parallel to the axis of rotation, namely from the rear end toward the front end of the electric machine. Due to this circumstance the cooling capacity is greatest at the rear end of the auxiliary cooler, at which the secondary air is introduced into the tubes. The cooling effect at the front end is however smallest. According to the prior art the primary air fed to the front air inlet opening is therefore warmer than the primary air fed to the rear air inlet opening. Temperature differences of approximately 20 Kelvin result in practice.

The temperature differences occurring with regard to the primary air fed to the electric machine by way of the front and rear air inlet openings result in the electric machine being cooled less well in the front region than in the rear region. Due to this circumstance a performance level of the electric machine determined by its construction can often not be fully utilized. Furthermore, this results in a reduced service life for the electric machine. As a rule of thumb, an increase in temperature of 10 Kelvin results in a 50% reduction in the service life of the electric machine.

SUMMARY OF THE INVENTION

The object of the present invention consists in creating an electric machine in which the temperature differences between the air fed to the front air inlet opening and the air fed to the rear air inlet opening are at least reduced, as far as possible even completely compensated for.

The object is achieved by an electric machine having a housing in which a stator is arranged and in which a rotor is rotationally supported about an axis of rotation, wherein the housing extends from a front end to a rear end when viewed in the direction of the axis of rotation, wherein on a top face the housing comprises a front air inlet opening in the vicinity of the front end, a rear air inlet opening in the vicinity of the rear end, and an air outlet opening therebetween, wherein the electric machine comprises a front and a rear air conveying element by which air is drawn in at the front and the rear air inlet openings and discharged at the air outlet opening during operation of the electric machine, wherein an auxiliary cooler is mounted on the top face of the housing, which auxiliary cooler covers the front and the rear air inlet openings and the air outlet opening with side walls and a top cover in a hood-like manner, such that the air discharged at the air outlet opening is fed back to the front and the rear air inlet openings, wherein the auxiliary cooler includes a front and a rear auxiliary partition, wherein the front and the rear auxiliary partitions are arranged between the air outlet opening and the front and the rear air inlet openings and extend upward from the top face of the housing, wherein air guiding elements are arranged in the housing and/or in the auxiliary cooler, by the air discharged at the region of the air outlet opening facing the front air inlet opening is fed at least partially to the rear air inlet opening and the air discharged at the region of the air outlet opening facing the rear air inlet opening is fed at least partially to the front air inlet opening.

Advantageous embodiments of the electric machine according to the invention are set down in the dependent claims.

According to the invention, provision is made in the case of an electric machine of the type mentioned in the introduction that air guiding elements are arranged in the housing and/or in the auxiliary cooler, by means of which the air discharged at the region of the air outlet opening facing the front air inlet opening is fed at least partially to the rear air inlet opening and the air discharged at the region of the air outlet opening facing the rear air inlet opening is fed at least partially to the front air inlet opening.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance withFIGS. 1 to 3an electric machine has a housing1. A stator2is arranged in the housing1. A rotor3is furthermore mounted in the housing1. The rotor3is capable of rotation about an axis of rotation4.

The housing1extends from a front end5to a rear end6when viewed in the direction of the axis of rotation4. According to the illustration shown inFIG. 1, the front end5of the housing1is the drive-side end of the electric machine while the rear end6is the operator-side end of the electric machine. This is however not relevant to the invention. The reverse could equally apply.

The housing1comprises on a top face a front air inlet opening7, a rear air inlet opening8and an air outlet opening9. The front air inlet opening is arranged in the vicinity of the front end5, the rear air inlet opening8in the vicinity of the rear end6. The air outlet opening9is arranged between the two air inlet openings7,8.

The electric machine comprises a front air conveying element10and a rear air conveying element11. By means of the front air conveying element10air is drawn in at the front air inlet opening8during operation of the electric machine, blown through the electric machine and discharged at the air outlet opening9. In similar fashion, by means of the rear air conveying element11air is drawn in at the rear air inlet opening8and discharged at the air outlet opening9during operation of the electric machine. The air conveying elements10,11are as a general rule designed as fans which are likewise arranged in rotatably fixed fashion on a rotor shaft12on which the rotor3is arranged in rotatably fixed fashion. Alternatively, the air conveying elements10,11can be implemented by the rotor3itself.

An auxiliary cooler13is mounted on the top face of the housing1. The auxiliary cooler13comprises side walls14and a top cover15in accordance withFIGS. 1 and 3. The auxiliary cooler13covers the front and the rear air inlet openings7,8and the air outlet opening9in a hood-like manner. The air discharged at the air outlet opening9is therefore fed back to the front and the rear air inlet openings7,8.

The auxiliary cooler13comprises—see particularly clearlyFIG. 1—a front and a rear auxiliary partition16,17. The auxiliary partitions16,17are arranged according toFIGS. 1 and 3between the air outlet opening9and the front air inlet opening7on the one hand and the air outlet opening9and the rear air inlet opening8on the other hand.

They extend upward from the top face of the housing1. The air discharged from the air outlet opening9must therefore firstly rise upward between the two auxiliary partitions16,17before it can flow across the auxiliary partitions16,17downward again to the air inlet openings7,8.

There are furthermore tubes18running in the auxiliary cooler13. Secondary air is directed through the tubes18, as indicated inFIG. 1by arrows A. For example, a corresponding fan element19can be present for this purpose.

Due to the direction of flow of the secondary air—which in the present case is directed from the rear end to the front end6,5—the cooling effect of the secondary air in the vicinity of the rear end6is greater than in the vicinity of the front end5. In the prior art, this results in temperature differences of approximately 20 Kelvin between the primary air fed to the electric machine by way of the front air inlet opening7and the primary air fed to the electric machine by way of the rear air inlet opening8. In order to reduce and where possible completely compensate for said temperature differences, according to the invention air guiding elements are arranged in the housing1and/or in the auxiliary cooler13. By means of the air guiding elements—see the corresponding dashed arrows B inFIG. 1—a crossing of the air flows is effected. The air which is discharged at the region of the air outlet opening9facing the front air inlet opening7is therefore fed at least partially to the rear air inlet opening8. In similar fashion, the air which is discharged at the region of the air outlet opening9facing the rear air inlet opening8is fed at least partially to the front air inlet opening7. How this is achieved and how the corresponding air guiding elements can be embodied will be described in detail in the following in conjunction withFIGS. 4 to 11in which the tubes18are either entirely or partially omitted from the illustration in order to give a better overview.

According toFIG. 4, when viewed at right angles to the axis of rotation4the front and the rear auxiliary partitions16,17each have at least one first region20and at least one second region21. The first regions20are distanced further away than the second regions21from the top cover15of the auxiliary cooler13. In particular, the second regions21can extend up to the top cover15of the auxiliary cooler13while the first regions20are distanced away from the top cover15of the auxiliary cooler13.

According toFIG. 4, when viewed in the direction of the axis of rotation4the first regions20of both auxiliary partitions16,17are situated opposite the second regions21of the respective other auxiliary partition17,16. In some cases this embodiment can itself be sufficient in order to effect the air guidance according to the invention. As a general rule, however, air delivery elements22are arranged in the region of the upper ends of the second regions21. By means of the air delivery elements22, which are arranged at the second regions21of the front auxiliary partition16, one part of the air discharged in the region of the air outlet opening9facing the front air inlet opening7is deflected in the direction of the first region20of the rear auxiliary partition17situated opposite when viewed in the direction of the axis of rotation4. In similar fashion, by means of the air delivery elements22, which are arranged in the region of the upper end of the second region21of the rear auxiliary partition17, one part of the air discharged in the region of the air outlet opening9facing the rear air inlet opening8is deflected in the direction of the first region20of the front auxiliary partition16situated opposite when viewed in the direction of the axis of rotation4.

In the case that the second regions21do not extend up to the top cover15of the auxiliary cooler13, it is preferred that the air delivery elements22arranged there extend up to the top cover15of the auxiliary cooler13. Alternatively, however, a clearance may also remain here.

It is possible that the air delivery elements22deflect the air flowing to them directly by 90°. Alternatively, a deflection by a smaller angle is possible, for example by approximately 45 to 70°. A gradual deflection is also possible.

Alternatively or in addition to the embodiment according toFIG. 4it is possible that the air guiding elements according toFIG. 5comprise a number of axial partitions23which are arranged in the auxiliary cooler13. The axial partitions23in this case each run according toFIG. 5from the front to the rear auxiliary partition16,17.

In a further embodiment the air guiding elements according toFIG. 6comprise a housing partition24. The housing partition24is, as the name suggests, arranged in the housing1of the electric machine. Said embodiment can be implemented as required in isolation or in combination with the embodiments ofFIGS. 4 and/or 5.

The housing partition24is arranged in such a manner that it divides the air outlet opening9into a first and a second cross-sectional region25,26. The air drawn in by way of the front air inlet opening7is discharged in the first cross-sectional region25from the air outlet opening9. In similar fashion, the air drawn in by way of the rear air inlet opening8is discharged in the second cross-sectional region26from the air outlet opening9.

With regard to the embodiment according toFIG. 6, in the region of the air outlet opening9the housing partition24runs essentially at right angles to the axis of rotation4. The first cross-sectional region25is therefore arranged completely in the region of the air outlet opening9facing the front air inlet opening7. In similar fashion, with regard to the embodiment fromFIG. 6, the second cross-sectional region26is arranged completely in the region of the air outlet opening9facing the rear air inlet opening8. The embodiment according toFIG. 6is in particular expedient in the situation when on the one hand the auxiliary partitions16,17are divided into the first and second regions20,21, the air delivery elements22are present at the second regions21and the axial partitions23are arranged in each case in the transitional region from first to second region20,21of the auxiliary partitions16,17.

FIGS. 7 to 9show a further possible embodiment of the auxiliary cooler13. According toFIGS. 7 to 9the air guiding elements27to29are designed in such a manner that together with the auxiliary partitions16,17they form two flow channels which are separate from one another. The air which is fed to the electric machine by way of the front air inlet opening7is discharged from the air outlet opening9in the region25of the air outlet opening9facing the front air inlet opening7. The air which is fed to the electric machine by way of the rear air inlet opening8is discharged from the air outlet opening9in the region26of the air outlet opening9facing the rear air inlet opening8. This applies especially if the housing partition24is present in the housing1in accordance with the illustration inFIG. 7.

The air discharged from the air outlet opening9in the respective region25,26is in each case blown into one of the flow channels according toFIGS. 7 to 9. The air blown into the flow channels—shown inFIGS. 7 to 9by corresponding, partially dashed arrows—is fed by means of the respective flow channel to the respective other air inlet opening8,7.

In order to be able to feed the air to the respective other air inlet opening8,7the flow channels must cross. The height at which the flow channels cross is in principle freely selectable. The flow channels preferably cross in the auxiliary cooler13beneath the tubes18. In order to illustrate this the lowermost row of tubes18is included in the drawing inFIG. 8. This embodiment in particular has the advantage that the air crossing can be produced by means of a separate component which is arranged between the electric machine and the auxiliary cooler13.

In order to implement the flow channels the air guiding elements27to29can comprise a transverse partition27and two separating elements28,29.

The transverse partition27runs at right angles to the axis of rotation4. It separates the region25of the air outlet opening9facing the front air inlet opening7and the region26of the air outlet opening9facing the rear air inlet opening8from one another, in that case that the housing partition24is present in the housing1of the electric machine and runs at right angles to the axis of rotation4, the line of the transverse partition27corresponds to the line of the housing partition24. A possible distance of the transverse partition27from the housing partition24should be as small as possible (or 0).

The separating element28(front separating element28) is arranged between the front auxiliary partition16and the transverse partition27. The separating element29(rear separating element29) is arranged between the rear auxiliary partition17and the transverse partition27. When viewed in the direction of the axis of rotation4, the separating elements28,29extend from the respective auxiliary partition16,17to the transverse partition27. Possible distances of the separating elements28,29to the auxiliary partitions16,17and to the transverse partition27should be as small as possible (or 0). When viewed at right angles to the axis of rotation4, the separating elements28,29extend from side wall14to side wall14of the auxiliary cooler13. Possible distances of the separating elements28,29to the side walls14of the auxiliary cooler13should be as small as possible (or 0).

When viewed at right angles to the axis of rotation4, according toFIGS. 8 and 9the separating elements28,29are ramped in opposite directions from bottom to top. Alternatively, the separating elements28,29could be stepped—seeFIG. 10—or mixed stepped and ramped—seeFIG. 11.

When viewed in the vertical direction the transverse partition27is self-contained in the regions in which it runs both above the front separating element28and also above the rear separating element29. Similarly, when viewed in the vertical direction the transverse partition27is self-contained in the regions in which it runs both below the front separating element28and also below the rear separating element29. In the region which when viewed in the vertical direction lies between the two separating elements28,29the transverse partition27is interrupted. This means that the air which exits from the regions25,26from the air outlet opening9can switch to the respective other side in this height region.

The present invention has many advantages. In particular, with a relatively simple structure a significant reduction is achieved in the temperature differences between the front and the rear end5,6of the electric machine, in some cases even an almost complete elimination thereof.

The above description serves only to illustrate the present invention. The scope of protection of the present invention is however to be determined solely by the appended claims.