METHOD FOR THE PRODUCTION OF A BUSH

Abstract

A method for producing a bush and a bush for a rotor shaft are disclosed. The method includes: providing a flat metal strip; introducing at least one of (i) a surface structure onto one side of the flat metal strip for at least one of enlarging a heat-transferring area and directing a coolant, and (ii) at least one hole into the flat metal strip; and rolling up the flat metal strip to form the bush. The surface structure, if provided, lies on an inner surface area of the bush.

Claims

1. A method for producing a bush for arranging in a cavity of a rotor shaft, comprising providing a flat metal strip, introducing at least one of (i) a surface structure onto one side of the flat metal strip for at least one of enlarging a heat-transferring area and directing a coolant, and (ii) at least one hole into the flat metal strip, rolling up the flat metal strip to form the bush, wherein the surface structure if provided lies on an inner surface area of the bush.

2. The method according to claim 1, further comprising post-processing an outer surface area of the bush.

3. The method according to claim 1, wherein at least one of: the surface structure is introduced by embossing, lasering, water-jetting, milling, a machining method, rolling or bending, and the at least one hole is introduced by stamping or drilling.

4. A bush for a rotor shaft, comprising: a flat metal strip rolled up to provide a circumferentially extending inner surface area and a circumferentially extending outer surface area; at least one of (i) a surface structure provided on the inner surface area for at least one of enlarging a heat-transferring area and directing a coolant, and (ii) at least one hole penetrating through the flat metal strip.

5. The bush according to claim 4, wherein the surface structure has peaks and troughs, wherein a height difference H between a peak and a trough is 0.20 mm≤H≤4.0 mm.

6. The bush according to claim 4, wherein the at least one hole has a circular, oval or angled shape.

7. The bush according to claim 4, wherein the surface structure defines a thread.

8. The bush according to claim 4, wherein the flat metal strip is slitted, wherein a slit has a ratio of a difference of a bush outside diameter in untensioned state to a shaft inside diameter relative to a width of the occurring slit in an inserted state of ≤0.318±0.01.

9. The bush according to claim 4, wherein two circumferential ends of the flat metal strip are connected to one another via a form-fitting connection.

10. The bush according to claim 4, wherein the flat metal strip is formed in one piece.

11. The bush according to claim 4, wherein the flat metal strip has at least one layer of zinc, aluminium or a tin alloy or a layer of copper or a copper alloy or an aluminium alloy.

12. The bush according to claim 4, wherein the flat metal strip is composed of a carrier material of steel, aluminium or an aluminium alloy.

13. A rotor for an electric motor, comprising: a rotor shaft with a cavity, a bush arranged in the cavity, the bush including: a flat metal strip rolled up to provide a circumferentially extending inner surface area and a circumferentially extending outer surface area; at least one of (i) a surface structure provided on the inner surface area for at least one of enlarging a heat-transferring area and directing a coolant, and (ii) at least one hole penetrating through the flat metal strip.

14. An electric motor comprising the rotor according to claim 13.

15. The rotor according to claim 13, wherein the surface structure is provided, the surface structure including peaks and troughs, and wherein a heat difference H between a peak and a trough is 0.20 mm≤H≤4.0 mm.

16. The rotor according to claim 13, wherein the at least one hole is provided, the at least one hole having a circular, oval, or angled shape.

17. The rotor according to claim 13, wherein the bush is slitted, wherein a slit has a ratio of a difference of a bush outside diameter in untensioned state to a shaft inside diameter relative to a width of the occurring slit in an inserted state of ≤0.318±0.01.

18. The rotor according to claim 13, wherein two circumferential ends of the bush are connected to one another via a form-fitted connection.

19. The rotor according to claim 13, wherein the bush has a layer of copper, copper alloy, or aluminium alloy disposed on the inner surface area.

20. The rotor according to claim 13, wherein the bush has at least one layer of zinc, aluminium, or a tin alloy disposed on an outer surface area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] There are shown here, respectively schematically:

[0026] FIG. 1 a sectional illustration through an electric motor according to the invention, with a rotor with a rotor shaft, in the cavity of which a bush, produced by a method according to the invention and likewise according to the invention, is arranged,

[0027] FIG. 2 a detail illustration from FIG. 1,

[0028] FIG. 3 a view onto a bush according to the invention,

[0029] FIG. 4 a detail illustration of a possible embodiment of a bush according to the invention, with an undercut connection,

[0030] FIG. 5 an embodiment of a slitted bush according to the invention, with holes.

DETAILED DESCRIPTION

[0031] According to FIG. 1, an electric motor 1 according to the invention, which can be installed for example in a motor vehicle which is at least partially electrically driven, has a rotor 2 with a rotor shaft 3 and a cavity 4, wherein a bush 5 according to the invention is arranged, in particular plugged in or jammed in, in the cavity 4. Sheet packages 6 are arranged on the rotor shaft 3.

[0032] In order to now be able to achieve as high a performance of the electric motor 1 as possible, its rotor 2 is internally cooled, i.e. a coolant 10 flows through the cavity 4, in the present case through the bush 5. For the further increase of performance of the electric motor 1, the bush 5 has on an inner surface area a surface structure 7 with peaks 8 and troughs 9. Through the surface structure 7, a coolant 10 flowing in the bush 5 in operation, is eddied and thereby homogenised, whereby an improved cooling effect can be achieved. Furthermore, the surface structure 7 brings about an enlargement of the surface which is available for the heat transfer, and thereby improves the cooling capacity.

[0033] A height difference H (cf. FIG. 2) between one of the peaks 8 and one of the troughs 9 can be between 0.2 mm and 4.0 mm here, wherein of course the peak tops or respectively troughs can be configured to be pointed or rounded or also plateau-shaped. Purely theoretically of course also not only are uniform peaks 8 or respectively troughs 9 provided, but also distributed as desired.

[0034] Observing the surface structure 7 in the case of the bush 5 according to FIGS. 1 and 2, it can be seen that the surface structure 7 forms a thread there. A pitch of such a thread can be between 0.4 mm and 4 mm, whereby depending on the pitch of the thread a faster or slower conveying of the coolant 10 takes place through the bush 5. Purely theoretically, however, the pitch of the thread can also be zero, whereby a longer dwelling of the coolant 10 in the bush 5 can be achieved.

[0035] Additionally or alternatively to the surface structure 7, the bush 5 can also have holes 11, as is illustrated according to FIG. 5, wherein the holes 11 completely penetrate the bush 5. Alternatively again such holes can also be formed with a thin base, i.e. only as a depression. Irrespective of the embodiment, such depressions or respectively holes 11 present an enlargement of the surface which is available for heat transfer and thereby enable an improved cooling performance.

[0036] Observing the bush 5 of FIG. 5 further, it can be seen that it has a slit 12 which in particular simplifies an introducing and fixing of the bush 5 in the cavity 4 of the rotor shaft 3, as for the mounting of the bush 5 in the cavity 4, it only has to be slightly compressed and can then be inserted into the cavity 4. When the bush 5 is then released, it tensions elastically against the inner surface area of the cavity 4 autonomously, whereby for example a further fixing can be omitted. A width B of the slit 12 occurring in the inserted state of the bush 5 between the ends lying opposite one another in diameter is defined from the ratio of the difference of the diameters “bush 5 untensioned to shaft inside diameter” relative to the width B of the slit 12 of the bush 5 occurring in the inserted state under specification of a ratio value of 0.318±0.01. Depending on the shaft inside diameter, a small width B of the slit 12 denotes an only very small reduction of the bush diameter and consequently an extremely small joint gap. Depending on the outside diameter of the bush 5 in the untensioned state, a larger width B of the slit 12 is required, in order to be able to join the bush 5 at all. The following applies here:

[0037] A bush diameter +0.1 mm with respect to the shaft inside diameter of 30-50 mm entails ca. 0.35 mm width B of the slit 12, whereas a bush diameter +0.2 mm with respect to the shaft inside diameter of 30-50 mm requires ca. 0.65 mm width B of the slit 12. With a bush diameter +0.3 mm with respect to the shaft inside diameter of 30-50 mm, this requires ca. 0.95 mm width B of the slit 12. A relationship results herefrom.

[00001]$\frac{\left(\mathrm{outside}\varnothing \mathrm{of}\mathrm{the}\mathrm{bush}5\mathrm{untensioned}-\mathrm{shaft}\mathrm{inside}\varnothing \right)}{\mathrm{width}B\mathrm{of}\mathrm{the}\mathrm{slit}12}\le 0.318\pm 0.01$

[0038] In the bushes 5 illustrated according to FIGS. 3 and 4, it can be seen that two circumferential ends 13, 13′ are connected to one another via a form-fitting connection 14. According to FIG. 3, the form-fitting connection 14 is configured here as a so-called male/female connection, whereas according to FIG. 4 this is configured in the manner of a puzzle connection and can form for example an undercut connection. Hereby it is possible to fix the two circumferential ends 13, 13′ of the bush 5 according to the invention securely to one another and for example to close a slit 12 lying therebetween.

[0039] The bush 5 can be formed here in one piece, wherein purely theoretically it is also conceivable that this is formed in a multi-layered manner, so that the bush 5 has at least one, in particular outer, layer 15 of zinc, aluminium or a tin alloy and/or an, in particular inner, layer 16 of for example copper or brass or aluminium. The base material of the bush 5 is usually formed from steel and the layers 15, 16 are thinner than the base material. In order to be able to achieve as high a heat transfer as possible to the coolant 10 flowing in the bush 5, it is advantageous to form the inner layer 16 of the bush 5 from a material with good thermal conductivity, i.e. for example copper or brass. A forming of the outer layer 15 from zinc or respectively aluminium or from a tin alloy offers the advantage furthermore that hereby good sliding characteristics are to be achieved, whereby an inserting of the bush 5 into the cavity 4 of the rotor shaft 3 is simplified. Of course, a completely one-piece configuration of the bush 5 and also a single-layer configuration of the bush 5 is also conceivable, for example from copper, as is illustrated according to FIG. 5.

[0040] In order to now be able to produce the rotor 2 as economically as possible, a method according to the invention is proposed, in which firstly the bush 5 is prefabricated separately and is only subsequently inserted into the cavity 4 of the rotor shaft 3. Hereby, a laborious processing of an internal surface area of the cavity 4, taking place from the interior, can be dispensed with. The bush 5 according to the invention is produced here in accordance with the method according to the invention as follows:

[0041] Firstly, a flat metal strip is produced, in particular cut to size or stamped, wherein subsequently on one side of the flat metal strip the surface structure 7 is introduced for enlarging the heat-transferring area and/or for directing the coolant 10. Additionally or alternatively, further also at least one hole 11 can be introduced into the flat metal strip. Subsequently, this flat metal strip is rolled up to form the bush 5, wherein the surface structure 7, which is present if applicable, lies on an inner surface area (cf. FIGS. 1 and 2).

[0042] The outer surface area of the bush 5 can be subsequently further post-processed, for example ground, in order to balance out dimension- and position tolerances. The surface structure 7 can be introduced for example by embossing, lasering, water-jetting, milling, grinding, a machining method, rolling or bending. The at least one hole 11 can be introduced for example by stamping or drilling. Of course, it is also conceivable here that the surface structure 7 is provided cumulatively with at least one hole 11, or that the hole 11 forms a component part of the surface structure 7.

[0043] Through the separation of the production of the surface structure 7 from the actual producing of the rotor 2, the surface structure 7 can be produced extremely economically and nevertheless in a high-quality manner. Surface structures 7 can also be created which would not be able to be thus produced with a processing of an inner surface area of the cavity 4 of the rotor shaft 3.

[0044] With the method according to the invention for the production of the bush 5 and for the production of the rotor 2, thus also an electric motor 1 can be produced with such a rotor 2 more economically, but nevertheless having high performance.