SHAFT ASSEMBLY

Abstract

A shaft assembly comprises: a hollow shaft with an axis of rotation, and a hub body connected to the hub body in a force-locking manner, wherein the hollow shaft comprises, viewed in cross-section, a circumferentially closed wall with a plurality of circumferentially distributed support portions in abutting contact with the hub body and with spring portions spaced from an inner circumferential face of the hub body, wherein inner surface regions of the spring portions lie on a smaller radius around the axis of rotation than inner face regions of the support portions, wherein the wall comprises a varying thickness over the circumference, wherein the thickness in the support portions is smaller than in the spring portions.

Claims

1.-15. (canceled)

16. A rotor shaft assembly for an electric motor, comprising: a hollow motor shaft with a shaft tube, a first journal element connected to a first end of the shaft tube by welding and a second journal element connected to a second end of the shaft tube by welding, wherein the first journal element and the second journal element each comprise a bearing portion, and the hollow motor shaft comprises an axis of rotation; wherein the shaft tube includes at least three support portions and at least three spring portions arranged alternately around the circumference, wherein viewed in a cross-section an imaginary outer circular line is defined by a radius around the axis of rotation extending to an outer face of the support portions, wherein the spring portions are formed radially inwardly such that outer surface regions of the spring portions starting from a respective circumferentially adjacent support portion have a continuously increasing radial distance to the imaginary outer circular line, and such that inner surface regions of the spring portions have a smaller distance from the axis of rotation than inner surface regions of the support portions; wherein at least one of the first journal element and the second journal element comprises a sleeve-shaped connecting portion with an annular connecting face, wherein the annular connecting face is welded in butt joint to an end face of the shaft tube, wherein an outer face of the connecting portion continuously merges into an outer face of the shaft tube at least in circumferential sections of the support portions; a rotor laminate stack connected to the hollow motor shaft with radial pretension in a force locking manner, with the rotor laminate stack including a plurality of rotor laminates, wherein viewed in cross-section the three circumferentially distributed support portions are in frictional contact with the rotor laminate stack, and with three spring portions spaced from an inner circumferential face of the rotor laminate stack.

17. The rotor shaft assembly according to claim 16, wherein the connecting portion of the journal element is connected to the shaft tube without axial overlap, and wherein at least in circumferential sections of the support portions a stepless outer surface is formed in the connecting region of the journal element and the shaft tube to facilitate axial mounting of the rotor laminate stack onto the hollow motor shaft.

18. The rotor shaft assembly according to claim 16, wherein the outer face and/or an inner face of the contact portion of the journal element is circular in a cross-sectional view.

19. The rotor shaft assembly according to claim 16, wherein the hollow motor shaft includes an end portion with a conical outer face designed to facilitate pressing the rotor laminate stack axially onto the hollow motor shaft, wherein the conical outer face is formed in at least one of the connecting portion of the journal element and the end portion of the shaft tube.

20. The rotor shaft assembly according to claim 16, wherein both, the first journal element and the second journal element are welded in butt joint to a respective end face of the shaft tube along the entire circumference.

21. The rotor shaft assembly according to claim 16, wherein one of the first journal element and the second journal element is provided with shaft splines for connecting a torque transmitting element, wherein the other one of the first journal element and the second journal element has no shaft splines.

22. The rotor shaft assembly according to claim 16, wherein the support portions, viewed in cross section, respectively extend over a larger angular range than the spring portions, with the angular range of the support portions being at least 60? and at most 90?, and the angular range of the spring portions being at least 30? and at most 60?.

23. The rotor shaft assembly according to claim 16, wherein at least one of the hollow motor shaft and the rotor laminate stack has a surface roughness of at least 0.1 Rz.

24. The rotor shaft assembly according to claim 16, wherein the shaft tube includes exactly three support portions and exactly three spring portions arranged alternately around the circumference.

25. The rotor shaft assembly according to claim 16, wherein the support portions comprise an outer contour adapted to the inner contour of the rotor laminate stack, with the inner contour of the rotor laminate stack being circular in a cross-sectional view.

26. The rotor shaft assembly according to claim 16, wherein the spring portions are configured such that they are substantially subject to compressive stresses in a mounted condition.

27. The rotor shaft assembly according to claim 16, wherein the shaft tube is a drawn part.

28. A method comprising: drawing a hollow input tube through a drawing die to form a shaft tube with a non-circular cross-section including at least three support portions and at least three spring portions arranged alternatingly about the circumference, with the support portions forming radial maxima and the spring portions forming radial minima of the shaft tube viewed in a cross-section, wherein viewed in a cross-section an imaginary outer circular line is defined by a radius around an axis of rotation extending to an outer face of the support portions, wherein the spring portions are formed radially inwardly such that outer surface regions of the spring portions starting from a respective circumferentially adjacent support portion have a continuously increasing radial distance to the imaginary outer circular line, and such that inner surface regions of the spring portions have a smaller distance from the axis of rotation than inner surface regions of the support portions; providing a first journal element and a second journal element, wherein the first journal element and the second journal element each comprise a bearing portion; butt-welding a first connecting portion of the first journal element to a first end face of the shaft tube, and butt-welding a second connecting portion of the second journal end to a second end face of the shaft tube, with the shaft tube, the first journal element and the second journal element connected therewith forming a hollow motor shaft with the axis of rotation; and providing a plurality of rotor laminates as a hub body, and connecting the rotor laminates onto the hollow motor shaft with an interference fit, with the plurality of support portions of the hollow motor shaft coming into frictional contact with in inner circumferential face of the rotor laminates and the plurality of spring portions spaced from the inner circumferential face, wherein the spring portions have a continuous shape in the circumferential direction between two circumferentially adjacent support portions, such that the plurality of rotor laminates are connected to the hollow motor shaft with radial pretension in a force locking manner.

29. The method according to claim 28, further comprising: producing the hollow motor shaft to have an end portion with a conical outer face for facilitating mounting the rotor laminate stack axially onto the hollow motor shaft.

30. The method according to claim 28, wherein the drawing step produces the hollow shaft tube with a surface roughness of more than 1.0 Rz, and wherein the rotor laminates have a circular inner contour in a cross-sectional view and have a surface roughness of more than 1.0 Rz at the inner circumferential surface coming into contact with the supporting faces of the hollow shaft tube.

31. The method according to claim 28, wherein the hollow shaft tube is formed such that, in a cross-sectional view, the spring portions are radially closer to the axis of rotation than the support portions and are at least one of undercut-free or stepless in circumferential direction starting from a respective support portion adjoining in the circumferential direction.

32. The method according to claim 28, wherein the shaft tube is produced by drawing such that in an unassembled state the outer contour of the shaft tube viewed in cross-section comprises absolute maxima within a circumferential extension of the support portions, wherein in the mounting process the support portions, starting from a respective one of the absolute maxima, come into surface contact in both circumferential directions with the inner contour of the rotor laminates.

33. The method according to claim 28, wherein the hollow input tube is a circular input tube having a constant wall thickness; and the drawing die forms the cross-sectional contour of the shaft tube with the spring portions and the support portions.

34. The method according to claim 28, wherein the shaft tube is made from a hardenable metal material, wherein the shaft tube remains non-hardened after connecting the first journal element and second journal element thereto.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0033] Examples are explained below with reference to the drawing figures, which are as follows.

[0034] FIG. 1A shows a three-dimensional view of a shaft assembly according to a first example;

[0035] FIG. 1B shows a cross-section of the shaft assembly of FIG. 1A;

[0036] FIG. 1C shows the hollow shaft of the shaft assembly of FIG. 1A as a detail in cross-section;

[0037] FIG. 1 Dshows a three-dimensional view of the hollow shaft shown in FIGS. 1A and 1C;

[0038] FIG. 1E shows an exploded perspective view of the hollow shaft shown in FIG. 1D;

[0039] FIG. 1F shows a perspective view of the shaft assembly shown in FIG. 1D during assembly;

[0040] FIG. 2 shows a graphical representation of the transmittable maximum torque over the speed of a shaft assembly with variable wall thickness over the circumference, compared with a shaft assembly according to the state of the art, with constant wall thickness over the circumference;

[0041] FIG. 3A shows a cross-section of a shaft assembly in a slightly modified example;

[0042] FIG. 3B shows an enlarged view of the hollow shaft of the shaft assembly in FIG. 3A with further details;

[0043] FIG. 4A shows a cross-section of a shaft assembly in a further example;

[0044] FIG. 4B shows a perspective view of the hollow shaft of the shaft assembly of FIG. 4A;

[0045] FIG. 4C shows an exploded perspective view of the hollow shaft shown in FIG. 4A;

[0046] FIG. 4D shows a perspective view of the rotor body of FIG. 4A.

[0047] FIG. 5 shows a shaft assembly in a further example in cross-section;

[0048] FIG. 6 shows a shaft assembly in a further example in cross-section;

[0049] FIG. 7 shows a shaft assembly in a further example in cross-section; and

[0050] FIG. 8 shows a shaft assembly in a further example in cross-section.

DETAILED DESCRIPTION

[0051] FIGS. 1A to 1E, which are described together below, show a shaft assembly 2 in a first example. The shaft assembly 2 comprises a hollow shaft 3 and a hub body 4, which are frictionally connected to each other. The frictional connection of the two components (3, 4) is made in particular by means of an interference fit, wherein a longitudinal interference fit or transverse interference fit can be used.

[0052] Viewed in cross section, the hollow shaft 3 has a circumferentially closed wall 5 with a plurality of support portions 6 distributed over the circumference and spring portions 7 alternating therewith in the circumferential direction. In the assembled state of the hub body 4, the spring portions 7 are elastically pre-stressed so that they load the support portions 6 located therebetween in the circumferential direction and in the radial direction. As a result, the support portions 6 are in frictional contact with the hub body 4 under radial pre-tensioning force, so that a torque can be transmitted between the shaft and the hub.

[0053] The spring portions 7 and the support portions 6 can be configured in the same manner respectively among each other, and in particular symmetrical. Starting from a central region located centrally between two support portions 6 adjacent in the circumferential direction, the spring portions 7 form in each circumferential direction respectively a bending beam loaded with an individual load. By appropriate configuring the geometrical proportions of the spring portions 7, such as thickness, curvature and/or circumferential length, the spring behavior and thus the press fit between shaft 3 and hub 4 can be set according to the technical requirements in terms of speed and torque.

[0054] The wall 5 of the hollow shaft is configured in particular such that the inner circumferential face 10 of the hollow shaft 3, viewed in cross section, has a maximum distance from the axis of rotation B in a circumferential region of the support portions 6, and has a minimum distance from the axis of rotation B in a circumferential region of the spring portions 7. A smallest inner radius r6 of the support portions 6 can be larger than a smallest inner radius r7 of the spring portions 7. That is, the support portions 6 form absolute maxima of the wall 5, while the intermediate spring portions 7 form absolute minima.

[0055] Viewed in cross-section, the support portions 6 are in contact with a support face 8 over a certain circumferential extent with the inner face 9 of the hub body 4. It generally applies that the number and the extension of the support portions 6 and the spring portions 7, respectively, influence the springing behavior and thus the pre-tensioning force of the press-fit assembly between the shaft 3 and the hub 4. The support portions 6 have an outer contour 8 adapted to the inner contour 9 of the hub body 4, wherein the inner contour 9 of the hub body 4 is circular cylindrical.

[0056] The hollow shaft 3 is configured such that the support portions 6 in the unassembled state of the arrangement have a maximum outer radius R6max which is greater than the inner radius r4 of the hub 4. The maximum outer radius R6max is to be understood as the radius which extends from the axis of rotation B to a point on the surface of the support portions 6 at a maximum radial distance therefrom. The maximum outer radius of the shaft 3 formed by the maximum outer radius R6max of the support portions 6 is designated R3max. The outer contour of the support portions 6 can have an outer radius R8 deviating from the maximum radius R6max, which in the unassembled state of the hub can in particular also be slightly smaller than the inner radius r4 of the hub 4. The spring portions 7 can have, starting from the support portions 6 adjacent thereto in the circumferential direction, respectively a continuously increasing radial distance to an imaginary circular line K with radius R6max through the maximum of the support portions, respectively to the circular cylindrical inner face 9 with inner radius r4 of the hub 4.

[0057] It can be seen, in particular in FIGS. 1B and 1C, that the hollow shaft 3 in the present example has three support portions 6 and three spring portions 7, which are distributed alternately and regularly around the circumference. This results in good centering and mutual support of the shaft and hub. The design with three support portions and three spring portions results in a respective pitch of 120? about the axis of rotation B. Viewed in cross section, the support portions 6 extend respectively over an angular range ?6 of, in particular, about 60? to 90? about the axis of rotation, and/or are in contact with the inner face 9 of the hub 4 over said angular range. Accordingly, the spring portions 7, which are contactless with respect to the hub 4 in the assembled state thereof, each extend over an angular range ?7 of approximately 30? to 60? in the circumferential direction, viewed in cross-section. However, it is understood that the shaft 3 can also have a different number than three of contact and spring portions 6, 7, with which correspondingly different circumferential lengths are possible.

[0058] It can be seen in particular in FIG. 1C that the wall 5 of the hollow shaft 3 has a thickness d5 varying over the circumference. In this case, a mean and/or smallest wall thickness d6 in the support portions 6 is smaller than a mean and/or smallest wall thickness d7 in the spring portions 7. In the present example, the wall thickness d7 of the spring portions 7 is substantially constant in the circumferential direction, although a varying course is also possible. The wall thickness d6 of the support portions 6 is also substantially constant in the circumferential direction. A transition section 18 with a wall thickness that varies in the circumferential direction is respectively formed between the support portions 6 and the spring portions 7, wherein the wall thickness changes in particular continuously in this transition section 18. The largest and/or average wall thickness d7 of the spring portions 7 can be at least 1.5 times the smallest wall thickness d6 of the support portions 6.

[0059] As can be seen in particular from FIG. 1E, the hollow shaft 3 comprises a shaft tube 11 and two journal elements 13, 13 connected thereto at the ends 12, 12. The journal elements 13, 13 each have a connecting portion 14, 14 whose outer contour is adapted to the inner contour 15 of the shaft tube 11. The journal elements 13, 13 are pressed into the ends of the shaft tube 11 and form-locking and force-locking connection therewith, although other types of connection, such as a material connection (welding), are also possible. The shaft tube 11 can be produced with the spring portions 7 provided therein, for example, by drawing, hydroforming or radial hammering or rotary swaging. In the drawing process, a round input tube with constant wall thickness is drawn through a drawing die which forms the cross-sectional contour of the shaft 3 and, where applicable, sets a wall thickness which varies over the circumference. By specifically configuring the drawing and annealing process, the strength of the shaft 3 can be set such that hardening is not necessary afterwards.

[0060] The surface roughness of the hollow shaft before assembly can be between 0.1 Rz and 1000 Rz, in particular between 1.0 Rz and 100 Rz. The same applies to the surface roughness of the hub body.

[0061] The hollow shaft can be configured such that its radial travel s3 is greater than:

[00003]$\frac{R_{p0,2}*A}{E*?*D_{3a}}*\left(1-\frac{?*D_{3a}^2}{2*A}-?\right)$

and/or that its spring rate k3 is less than:

[00004]$?*l_{34}*E*{\left(1-\frac{?*D_{3a}^2}{2*A}-?\right)}^{-1}$

[0062] It applies that a possible geometry compensation between shaft 3 and hub 4 increases with increasing spring travel s3 and that the loads in the contact area between shaft and hub decrease accordingly with decreasing spring rate k3.

[0063] FIG. 2 shows in graphic form the maximum torque over speed (line L2) that can be transmitted by the shaft assembly 2, compared with a shaft assembly 202 with a round hollow shaft with constant wall thickness (line L202), and a shaft assembly 102 with a polygonal hollow shaft with constant wall thickness (line L102), respectively.

[0064] It can be seen that for a shaft assembly 202 with a round hollow shaft with constant wall thickness, the maximum transmissible torque Mmax decreases sharply with increasing speed n (curve 202). Compared with this, the curve L102 for the maximum transmissible torque Mmax falls flatter for a shaft assembly 102 with a polygonal hollow shaft with constant wall thickness. This means that high torques can still be transmitted even at higher speeds. The best results are achieved by the shaft assembly 2, whose hollow shaft has a variable wall thickness over the circumference. It can be seen from the associated characteristic curve L2 that this slopes much flatter towards higher speeds n. This results in an advantageous torque transmission. Advantageously, this results in an even higher speed capacity for transmitting the required high torques. This is achieved by the circumferentially distributed spring portions 7 exerting spring forces on the respective intermediate support portions 6, which are thus pressed against the contact face of the hub body 4. The wall thickness of the shaft, which varies over the circumference, supports a homogeneous stress distribution, resulting in a particularly strong radial spring effect. This results in a particularly large geometry compensation for dimensional and positional deviations as well as thermal and centrifugal force-induced deformations between the shaft 3 and hub 4, so that a secure frictional connection between the components (3, 4) is maintained even at high speeds.

[0065] FIGS. 3A and 3B, which are jointly described below, show a shaft assembly 2 in a slightly modified example. This largely corresponds to the example according to FIGS. 1 and 2, so that reference is made to the above description with regard to the common features. The same and/or corresponding details are provided with the same reference signs as in FIG. 1.

[0066] A difference lies in the shape of the spring portions 7, which have a somewhat smaller circumferential extension ?7 and are less inwardly deformed. Accordingly, the support portions 6 have a somewhat larger circumferential extension ?6 than in the above example. This results in greater rigidity of the hollow shaft 3, which leads to correspondingly greater forces in the interference fit between the shaft 3 and the hub body 4.

[0067] FIGS. 4A to 4D, which are described together below, show a shaft assembly 2 in a further example. This corresponds largely to the examples according to FIGS. 1 to 3, so that reference is made to the above description with regard to the common features. The same and/or corresponding details are provided with the same reference signs as in FIGS. 1 to 3.

[0068] In the present example according to FIG. 4, the wall 5 of the hollow shaft 3 has a thickness d5 that varies over the circumference. A mean and/or smallest wall thickness d6 in the support portions 6 is smaller than a mean and/or smallest wall thickness d7 in the spring portions 7. In the present example, the spring portions 7 are straight. The wall thickness of the spring portions 7 is substantially constant in the circumferential direction, although a variable course is also possible. In the end regions adjoining the spring portions 7, the wall thickness of the support portions 6 is variable in the circumferential direction, in particular with continuous transitions. In this case, viewed in cross-section, the wall thickness d6 in a central region of the respective support portion 6 is thinner than in the end regions of the support portion (in each circumferential direction) which merge into the respective adjacent spring portion 7. The largest and/or average wall thickness d7 of the spring portions 7 is at least 1.5 times the smallest wall thickness d6 of the support portions 6. The circumferential extent of the spring portions 7, which are non-contacting with respect to the hub 4 in the assembled state thereof, can be between 30? and 60? in this example. The circumferential extent of the support portions 6, which are in contact with the hub 4 in the assembled state, is correspondingly between 60? and 90?.

[0069] As shown in particular in FIG. 4C, the hollow shaft 3 comprises a shaft tube 11 and two journal elements 13, 13 connected thereto at the ends 12, 12. The journal elements 13, 13 each have a connecting portion 14, 14 for connection to the shaft tube 11 and a bearing section 19, 19 for rotatably supporting the shaft in a stationary component. The connecting portions 14, 14 are formed in a flange-like manner and are placed frontally on an associated end face of the shaft tube 11 and firmly connected thereto. The connection can be made, in particular, in a material-locking manner by welding. One of the journal elements 13 has shaft splines for being connected in a rotationally fixed manner to a connecting component (not shown), wherein it is understood that, depending on the application, the other journal element 13 can also be configured accordingly with shaft splines. A further feature of the present example is that the hollow shaft 3 has an end portion with a conical outer face 21. The conical outer face 21 enables simple assembly of the hub body 4, which is pressed axially onto the hollow shaft 3 for connection.

[0070] FIG. 5 shows a further example of a shaft assembly 2. This largely corresponds to the example shown in FIG. 4, the description of which it is thus referred. Identical and/or corresponding details are provided with the same reference signs.

[0071] In the present example according to FIG. 5, the spring portions 7 are designed with a concave inner face 25, and/or are curved concavely overall between the transition portions 18 adjoining in the circumferential direction. Accordingly, the outer face is convex. Furthermore, in the present example, the spring portions 7 are formed longer in the circumferential direction than the support portions 6, without being limited thereto, and in particular have respectively a circumferential extent ?7 of more than 60?. Correspondingly, the circumferential extent ?6 of the support portions 8 is smaller and is less than 60? respectively, in an example with three support and spring portions in each case.

[0072] FIG. 6 shows a further example of a shaft assembly 2. This largely corresponds to the example shown in FIG. 4 or FIG. 5, the description of which is thus referred to. The same and/or corresponding details are provided with the same reference signs.

[0073] In the present example according to FIG. 6, the spring portions 7 are designed with a convex inner face 25, and/or are curved convexly overall between the transition portions 18 adjoining them on both sides in the circumferential direction. Accordingly, the outer faces of the spring portions 7 are concave. Furthermore, in the present example, the spring portions 7 are formed shorter in the circumferential direction than the support portions 6, without being limited thereto, and in particular have respectively a circumferential extent ?7 of less than 60?. Accordingly, the circumferential extent 6 of the support portions 8 is greater than 60?, in an example with three support and spring portions each.

[0074] FIG. 7 shows a further example of a shaft assembly 2. This largely corresponds to the example according to FIG. 1, the description of which is thus referred to. The same details are provided with the same reference signs.

[0075] In the present example according to FIG. 7, the spring portions 7 are relatively short in the circumferential direction and respectively have a circumferential extent ?7 of in particular less than 20?. A tubular component 20 is further provided, which is inserted into the shaft tube 11 and causes elastic or elastic-plastic deformation of the spring portions 7 by relative twisting. The component 20 remains in the shaft tube 11 after the deformation of the spring portions 7 and, as the case may be, can be used for a coolant guiding feature. It is understood that the shaft assemblies 2 according to FIGS. 1 to 4 can also be designed with such a tubular component 20 or one adapted in shape, respectively.

[0076] FIG. 8 shows a further example of a shaft assembly 2. This largely corresponds to the example shown in FIG. 7, the description of which it is thus referred to. The same details are provided with the same reference signs.

[0077] In the present example according to FIG. 8, the spring portions 7 are radially plastically deformed by means of a suitable expanding tool 30 after the shaft tube 11 and hub body 4 have been assembled. This causes the connecting faces of the components 3, 4 to bear against each other with sufficient contact force. It is understood that such an expanding tool can also be used for the shaft assemblies shown in FIGS. 1 to 6.

[0078] As an alternative to the examples according to FIGS. 7 and 8, an example is also conceivable in which the spring portions 7 are radially plastically deformed by internal high-pressure forming after the shaft tube 11 and hub body 4 have been assembled.

LIST OF REFERENCE SIGNS

[0079] 2 shaft assembly [0080] 3 hollow shaft [0081] 4 hub body [0082] 5 wall [0083] 6 support portion [0084] 7 spring portion [0085] 8 support face [0086] 9 inner face [0087] 10 inner circumferential face [0088] 11 shaft tube [0089] 12, 12 end [0090] 13, 13 journal element [0091] 14, 14 connecting portion [0092] 15 inner contour [0093] 16, 16 arm [0094] 17 reverse portion [0095] 18 transition portion [0096] 19, 19 bearing portion [0097] 20 component [0098] 21 outer face [0099] 25 inner face of spring portion [0100] 30 expanding tool [0101] ? circumferential angle [0102] A cross-sectional face [0103] B longitudinal axis [0104] d wall thickness [0105] D diameter [0106] E E-modulus [0107] k spring rate [0108] L characteristic line [0109] M torque [0110] n speed [0111] ? transverse contraction coefficient [0112] r inner radius [0113] R outer radius [0114] S spring travel