Assembled Shaft and Method for Manufacturing an Assembled Shaft

Abstract

The invention discloses a method of manufacturing an assembled shaft, comprising the following steps: at least one of a step of expanding the inner diameter of at least a joining portion of a first shaft element and a step of reducing the outer diameter of at least a joining portion of a second shaft element; positioning the joining portion of the first shaft element around the joining portion of the second shaft element; welding the first shaft element and the second shaft element by forcing a current flow through the first shaft element and the second shaft element; and at least one of a step of reducing the inner diameter of at least the joining portion of the first shaft element and a step of increasing the outer diameter of at least the joining portion of the second shaft element.

Claims

1. A method of manufacturing an assembled shaft, comprising the following steps: at least one of a step of expanding the inner diameter of at least a joining portion of a first shaft element and a step of reducing the outer diameter of at least a joining portion of a second shaft element; positioning the joining portion of the first shaft element around the joining portion of the second shaft element; welding the first shaft element and the second shaft element by forcing a current flow through the first shaft element and the second shaft element; and at least one of a step of reducing the inner diameter of at least the joining portion of the first shaft element and a step of increasing the outer diameter of at least the joining portion of the second shaft element.

2. Method according to claim 1, further comprising the step of arranging a flexible element between the joining portion of the first shaft element and the joining portion of the second shaft element.

3. The method according to claim 2, further comprising the steps of forming a circumferential recess in the second shaft element; and positioning the flexible element in the circumferential recess.

4. The method according to claim 1, further comprising at least one of the following two steps: forming a protrusion on the first shaft element that is directed to the second shaft element; forming a protrusion on the second shaft element that is directed to the first shaft element; and further comprising the following step: welding the first shaft element and the second shaft element by melting the protrusion by the current flow.

5. The method according to claim 4, further comprising the step of forming the protrusion in the axial direction from the axial end face of the second shaft element toward the axial end face of the first shaft element.

6. The method according to claim 4, wherein the step of forming a protrusion on first shaft element that is directed to the second shaft element and/or forming a protrusion on second shaft element that is directed to the first shaft element comprises the step of forming a cone shaped protrusion.

7. The method according to claim 1, further comprising the steps of forming an essentially cylindrical opening in the end face of the first shaft element extending in the axial direction of the first shaft element, wherein the essentially cylindrical opening in the end face of the first shaft element forms the joining portion of the first shaft element; and positioning the joining portion of the second shaft element in the essentially cylindrical opening in the end face of the first shaft element.

8. The method according to claim 1, wherein the step of expanding the inner diameter of at least the joining portion of the first shaft element comprises the step of heating at least the joining portion of the first shaft element; and the step of reducing the inner diameter of at least the joining portion of the first shaft element comprises the step of cooling at least the joining portion of the first shaft element.

9. The method according to claim 1, wherein at least one of the first shaft element and second shaft element is a hollow shaft.

10. The method according to claim 1, further comprising the step of arranging a rotor of an electric motor on at least one of the first shaft element and the second shaft element.

11. The method according to claim 1, wherein the step of welding the first shaft element and second the second shaft element by forcing a current flow through the first shaft element and the second shaft element comprises a capacitor discharge welding.

12. An assembled shaft, comprising: a first shaft element having a joining portion having an inner diameter; a second shaft element having a joining portion having an outer diameter, wherein the joining portion of the first shaft element is arranged around the joining portion of the second shaft element by press fit; characterized in that the front face of the joining portion of the second shaft element is welded to the first shaft element.

13. The assembled shaft according to claim 12, wherein a flexible element is arranged between the joining portion of the first shaft element and the joining portion of the second shaft element.

14. An electric motor, comprising the assembled shaft manufactured according the method steps according to claim 1, wherein a rotor is arranged on at least one of the first shaft element and second shaft element.

15. A vehicle having the assembled shaft according to claim 12.

16. An electric motor, comprising the assembled shaft according to claim 12, wherein a rotor is arranged on at least one of the first shaft element and second shaft element.

17. A vehicle having the electric motor according to claim 14.

Description

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

[0050] The invention is now explained in further detail with reference to the enclosed drawings depicting non-limiting and exemplary embodiments of the present invention, wherein:

[0051] FIG. 1 shows a sectional view of a joint of a first shaft member and a second shaft member;

[0052] FIG. 2 shows a magnified portion of FIG. 1, which is of particular interest;

[0053] FIG. 3a shows an assembled shaft manufactured from three shaft elements;

[0054] FIG. 3b shows an assembled shaft manufactured from three shaft elements;

[0055] FIG. 4 shows a portion of the second shaft element, in which recess are formed for accommodating an elastic element;

[0056] FIG. 5 shows the first shaft element and the second shaft element before welding; and

[0057] FIG. 6 shows the first shaft element and the second shaft element after welding and pressing the first shaft element on the second shaft element in a sectional and partially cut away view.

DETAILED DESCRIPTION OF THE INVENTION

[0058] A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.”

[0059] FIG. 1 shows a sectional view of a portion of an assembled shaft 100 comprising a first shaft element 102 and a second shaft element 104. The first shaft element 102 and the second shaft element 104 are essentially cylindrical. A joining portion 118 of the second shaft element 104 is positioned in a cylindrical opening 108 formed in the first shaft element 102. The cylindrical opening 108 extends essentially in the axial direction. A joining portion 106 of the first shaft member 102 extends along the opening 108 in the first shaft element 102 in axial direction and fixes the joining portion 118 of the second shaft element 104 in radial and axial direction. In other words, the joining portion 120 of the first shaft element 102 and the j oining portion 118 of the second shaft element 104 extend in axial direction.

[0060] FIG. 2 shows portion 114 of FIG. 1 in a magnified view. On the second shaft element 104 a protrusion, a cone 116 or the like is formed. In FIG. 2 the cone 116 is schematically shown to extend into the first shaft element. This is not the case after welding the first shaft element and the second shaft element 104. Before inserting the joining portion 118 of the second shaft element 104 into the axial opening 108 and the joining portion 120 of the first shaft element, the j oining portion 120 of the first shaft element is heated, such that the inner diameter of the j oining portion 120 of the first shaft element 102 is increased. The second shaft element 104 is moved into the axial opening 108 until the cone 116 touches the axial end face 122 of the first shaft element 102. Thus, an axial end face 124 of the second shaft element 104 is spaced apart from the axial end face 122 of the first shaft element 102.

[0061] Thereafter, the first shaft element 102 and the second shaft element 104 are pressed towards each other in the axial direction, and the current flow is forced through the first shaft element 102 and the second shaft element 104. The current flow can be generated by capacitor discharging. The current flows through the cone 116 and melts the cone 116 such that the melted material of the cone 116 seals the end face 122 of the first shaft element 102 and the end face 124 of the second shaft element 104 and fixes the end face 122 of the first shaft element 102 to the end face 124 of the second shaft element 104. Thereafter, the temperature of the joining portion 120 of the first shaft element 102 is reduced. Since the j oining portion 120 and the end face 122 of the first shaft element 102 have been heated before welding formation of cracks can be reduced significantly if not eliminated. After cooling the j oining portion 120 of the first shaft element the first shaft element 102 and the second shaft element 104 are fixed by welding at their respective end faces 122 and 124 as well as by a press fit generated by a protrusion 106 extending from the end face 122 in axial direction of the first shaft element 102 against the j oining portion 118 of the second shaft member 104. Capacitor discharge welding is known to the person skilled in the art and does not have to be explained in further detail herein.

[0062] Reference is made to FIG. 3a showing an assembled shaft 200 having three shaft elements 202, 204 and 206. The shaft elements are fixed to each other as described herein by pressing and welding. The first shaft element 202 is a hollow shaft. The second shaft element 204 and the third shaft element 206 are partially hollow. On the first shaft element 202 the rotor 208 of an electric motor can be fixed. The second shaft element 204 and the third shaft element 206 may act as a hub.

[0063] FIG. 3b shows another embodiment of an assembled shaft 300 comprising three shaft elements 302, 304 and 306. On the first shaft element 300 to a rotor 308 of an electric motor may be arranged. The first shaft element 302 is hollow. The second shaft element 304 is partially hollow. The third shaft element 306 is solid. The first shaft element 302, the second shaft element 304 and the third shaft element 306 may be fixed as described herein by pressing and welding. The second shaft element 304 and the third shaft element 306 may act as a hub. The shaft elements may be made of steel. Shaft elements that face a high load may be made of high-alloy steel, tempered steel or hardened steel, and shaft elements that face a lower load may be made of low-allow steel.

[0064] FIG. 4 shows the j oining portion 118 of the second shaft element 104 in a partially cut away view. In the second shaft element a circumferential recess 110 is formed. The circumferential recess 110 extends in the radial direction of the second shaft element 104 and extends around the perimeter of the second shaft element 104. Within the recess 110 an elastic element 112 is positioned.

[0065] Reference is made to FIG. 5 showing a sectional and partially cut away view of the first shaft element 102 and the second shaft element 104 during the process of joining the first shaft element 102 and the second shaft element 104. The protrusion 106 of the j oining portion 120 of the first shaft element is partially moved on the j oining portion 118 of the first shaft element, such that the elastic element 112b is compressed and the elastic element 112a is not compressed. Since the protrusion 106 comprises a larger diameter than the j oining portion 118 of the first shaft element 104, since the j oining portion 120 of the first shaft element 102 has been heated, the joining portion 120 of the first shaft element 102 is slightly spaced apart from the joining portion 104 of the first shaft element 118. The elastic elements 112a, 112b act to center and/or align the first shaft element 102 with respect to the second shaft element 104.

[0066] FIG. 6 shows a sectional and partially cut away view of the first shaft element 102 and the second shaft element 104 after cooling the protrusion 106 of the j oining portion 120 of the first shaft element. As shown in FIG. 6 the j oining portion 106 of the first shaft element and the j oining portion 110 of the second shaft element 104 abut each other to form a press fit and compresses the flexible elements 112a and 112b.

[0067] The elastic element 112a, 112b may be made of plastics, a peek polymer, polyethylene, rubber like material, non-ferreous metal, low-allow metals or the like.

[0068] The inventors of the present invention have recognized that by the pressing and the welding technology described herein high load requirements at low cost may be met. The welded joint of the shaft members is preferably made by capacitor discharge welding as a low-cost, high-quality welded joint and is overlaid with a press fit such that it is capable of absorbing high torsional forces of a static and dynamic nature and capable of absorbing static and dynamic alternating bending stresses as well as bending circumferential stresses via the press fit. This represents a significant cost reduction compared with the laser welding processes commonly used today, which are very cost-intensive and do not exhibit the same behavior under continuous load.

[0069] Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. It is understood that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. The operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. It is intended that the claims and claim elements recited below do not invoke 35 U.S.C. §112(f) unless the words “means for” or “step for” are explicitly used in the particular claim. The above-described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.