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 shaft assembly, comprising: a hollow shaft with an axis of rotation; and a hub body which is connected to the hollow shaft in a force locking manner; wherein the hollow shaft, viewed in cross-section, includes a circumferentially closed wall with a plurality of circumferentially distributed support portions that are 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 surface regions of the support portions; and wherein the wall has a varying thickness along the circumference, with a thickness in the support portions being less than in the spring portions.

17. The shaft assembly according to claim 16, wherein a smallest inner radius of the support portions is larger than a smallest inner radius of the spring portions.

18. The shaft assembly according to claim 16, wherein the support portions, viewed in cross section, respectively extend over an angular range of at least 5° and at most 115°.

19. The shaft assembly according to claim 16, wherein the spring portions, viewed in cross section, respectively extend over an angular range of at least 5° and at most 115°.

20. The shaft assembly according to claim 16, wherein the wall has a varying thickness in the circumferential direction within each of the support portions.

21. The shaft assembly according to claim 16, wherein a maximum thickness of the spring portions is at least 1.1 times as large as a minimum thickness of the support portions.

22. The shaft assembly according to claim 16, wherein the hollow shaft includes at least three support portions and at least three spring portions arranged alternately along the circumference.

23. The shaft assembly according to claim 16, wherein the support portions comprise an outer contour adapted to the inner contour of the hub body.

24. The shaft assembly according to claim 16, wherein, starting from the support portions respectively adjoining in circumferential direction, the spring portions have a continuously increasing radial distance from an imaginary circular line with radius of an outer circumferential face of the support portions.

25. The shaft assembly according to claim 16, wherein the spring portions are configured such that they are substantially subject to compressive stresses in an assembled state of the hub body.

26. The shaft assembly according to claim 16, wherein the hollow shaft is configured as a motor shaft for an electric motor and has a shaft tube and two journal elements connected to opposite ends of the shaft tube, and wherein the hub body has a rotor laminate stack comprising a plurality of rotor laminates.

27. The shaft assembly according to claim 26, wherein at least one of the journal elements comprises a connecting portion connected to an end portion of the shaft tube, with a circumferential contour of the connecting portion being adapted to a mating contour of the shaft tube, so that the journal element and the shaft tube engage into each other in a form-locking manner.

28. The shaft assembly according to claim 16, wherein at least one of the hollow shaft and the hub body has a surface roughness of at least 0.1 Rz.

29. The shaft assembly according to claim 16, wherein the hollow shaft is configured so as to have a radial spring travel for which the following applies: $s3=\left(R3\max -R3\min \right)>\frac{R_{p0,2}*A}{E*\pi *D_{3a}}*\left(1-\frac{\pi *D_{3a}^2}{2*A}-\mu \right)$ wherein: R3max is a maximum radius of the shaft in unmounted condition, R3min is a maximum radius of the shaft in maximum radial-elastic deflected state, D3a is twice a maximum radius of the shaft in unmounted condition, E is a modulus of elasticity of the shaft, A is a cross-sectional area of the shaft, μ is a transverse contraction coefficient of the shaft, and Rp0.2 is a yield strength of the shaft material.

30. The shaft assembly according to claim 16, wherein the hollow shaft is configured so as to have a spring rate for which the following applies: $k3=\frac{F_{\mathrm{rad}}}{U_{34}}<\pi *l_{34}*E*{\left(1-\frac{\pi *D_{3a}^2}{2*A}-\mu \right)}^{-1}$ wherein: Frad are effective radial forces between the shaft and the hub body in assembled condition, U34 is an effective interference between a largest outside diameter of the shaft and a smallest inner diameter of the hub body in unmounted condition, E is a modulus of elasticity of the shaft, l.sub.34 is a length of a mating surface between the shaft and the hub body, D3a is twice a maximum radius of the shaft in unmounted condition, and μ is a transverse contraction coefficient of the shaft.

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. 1D shows 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. 5 shows a shaft assembly in a further example in cross-section;

[0047] FIG. 6 shows a shaft assembly in a further example in cross-section;

[0048] FIG. 7 shows a shaft assembly in a further example in cross-section; and

[0049] FIG. 8 shows a shaft assembly in a further example in cross-section.

DETAILED DESCRIPTION

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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 a6 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 a7 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] The hollow shaft can be configured such that its radial travel s3 is greater than:

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

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

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

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] A difference lies in the shape of the spring portions 7, which have a somewhat smaller circumferential extension a7 and are less inwardly deformed. Accordingly, the support portions 6 have a somewhat larger circumferential extension a6 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.

[0066] FIGS. 4A to 4C, 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.

[0067] 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°.

[0068] 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.

[0069] 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.

[0070] In the present example according to FIG. 5, the spring portions 7 are designed with a concave inner face 11, 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 α7 of more than 60°. Correspondingly, the circumferential extent α6 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.

[0071] 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.

[0072] In the present example according to FIG. 6, the spring portions 7 are designed with a convex inner face 11, 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 α7 of less than 60°. Accordingly, the circumferential extent α6 of the support portions 8 is greater than 60°, in an example with three support and spring portions each.

[0073] 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.

[0074] 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 α7 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.

[0075] 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.

[0076] 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.

[0077] 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

[0078] 2 shaft assembly [0079] 3 hollow shaft [0080] 4 hub body [0081] 5 wall [0082] 6 support portion [0083] 7 spring portion [0084] 8 support face [0085] 9 inner face [0086] 10 inner circumferential face [0087] 11 shaft tube [0088] 12, 12′ end [0089] 13, 13′ journal element [0090] 14, 14′ connecting portion [0091] 15 inner contour [0092] 16, 16′ arm [0093] 17 reverse portion [0094] 18 transition portion [0095] 19, 19′ bearing portion [0096] 20 component [0097] 21 outer face [0098] 30 expanding tool [0099] α circumferential angle [0100] A cross-sectional face [0101] B longitudinal axis [0102] d wall thickness [0103] D diameter [0104] E E-modulus [0105] k spring rate [0106] L characteristic line [0107] M torque [0108] n speed [0109] μ transverse contraction coefficient [0110] r inner radius [0111] R outer radius [0112] s spring travel