Method for manufacturing a hollow rotor shaft

Abstract

The present invention relates to a method for manufacturing a rotor hollow shaft (R).

Description

[0001] The invention relates to a method for producing a hollow rotor shaft.

[0002] Due to the increasing demands on electric motors in cars - higher performance with the same or smaller installation space - effective cooling of the system is playing an increasingly important role.

[0003] If heat dissipation is insufficient, efficiency decreases, wear on individual components increases, and the increasing linear expansion of components made of different materials becomes problematic. For this reason, effective heat dissipation from electric motors is a particular challenge.

[0004] JP 2003-235210 A and JP 2020-162198 A describe a hollow shaft with an inner contour designed as a double cone to achieve optimized cooling. DE 10 2020 007 864 A1 also discloses a hollow shaft with an inner contour designed as a double cone to prevent expansion of the hollow shaft due to centrifugal forces. Further approaches are described in EP 2 127 775 A1, EP 1 025 923 A1, and DE 197 22 359 A1.

[0005] These hollow shafts are manufactured using processes such as radial forging, forging, hammering, rotary swaging, and mostly as at least two-part solutions that are joined together using friction welding or an orbital thermal joining process.

[0006] The disadvantage of these processes is that only one outer diameter can be machined, so that changes in the cross-section require the corresponding tools to be advanced or a re-clamping process to be performed. Due to undercuts in the area of ​​the double cone, a continuous inner mandrel would also be impossible to achieve during production. The cited publications are silent on process design.

[0007] The aim of this invention is to demonstrate a method by which a hollow rotor shaft can be manufactured cost-effectively.

[0008] This object is achieved by a method having the features of patent claim 1. Further advantageous embodiments are described in the subclaims.

[0009] The teaching of the invention relates to a method for producing a hollow rotor shaft, comprising the following steps: - Providing a pipe; - placing the pipe with its first pipe end on an inner mandrel with a conical outer base contour in its extension; - Inserting a pre-setter with a conical outer base contour on the side opposite the inner mandrel into the second pipe end; - setting the tube, the inner mandrel and the pre-setter in rotation, whereby at least one spinning roller acts on the tube from the outside in such a way that the outer basic contour of the inner mandrel and the pre-setter is impressed into the inner contour of the spin-formed base body of the hollow rotor shaft, so that the base body forms an increasing wall thickness with a double cone and thus starting from the tube ends in the longitudinal extension towards the center of the base body; - Forming at least one pipe end into a functional section of the hollow rotor shaft.

[0010] The inventor has discovered a cost-effective way to manufacture a hollow rotor shaft by eliminating expensive, complex manufacturing processes such as radial forging, forging, hammering, rotary swaging, and, for the most part, a solution consisting of at least two parts joined together by friction welding or an orbital thermal joining process. Thus, according to the invention, the hollow rotor shaft, with a preferably split double cone in the interior of the base body and a particularly formed or shaped tube end to form a functional section, can be produced cost-effectively and easily in one clamping operation using flow-forming.

[0011] The functional section can, in particular, have a bearing seat, a seal, and / or a toothing. This can, for example, be machined and / or heat-treated if necessary.

[0012] The provided tube can have an initial thickness between 4.0 and 12.0 mm. The initial wall thickness can be at least 5.0 mm, preferably at least 6.0 mm, and in particular a maximum of 10.0 mm, preferably a maximum of 8.0 mm, depending on the dimensions of the hollow rotor shaft to be produced. The tube can be drawn, welded from a sheet metal blank, or a forged preform can be used.

[0013] According to the invention, the pre-setter has a hollow projection and the inner mandrel has a recess, wherein the projection is inserted when the pre-setter is inserted into the second pipe end until the projection engages in the recess, whereby the inner mandrel and the pre-setter come into contact and remain in contact during the action of the flow-forming roller. Due to the engagement of the projection in the recess and the resulting contact between the inner mandrel and pre-setter, they are locked against one another and thus produce sufficient accuracy and rigidity for the flow-forming process. The pipe material can be pressed against the outer base contours of the inner mandrel and pre-setter via the flow-forming roller, thus reliably and accurately creating a cavity in the base body of the hollow rotor shaft with a double cone and thus creating an increasing wall thickness starting from the pipe ends in the longitudinal extension towards the center of the base body.

[0014] According to one embodiment, the inner mandrel can have a central through-hole through which an ejector is guided. After the flow-forming of the base body, the ejector is moved into position for the forming or machining of the second tube end, particularly synchronously with the pre-setter. The ejector serves in particular to stabilize the inner mandrel and can thus hold the inner mandrel in position to create the dimensionally accurate cavity in the base body of the hollow rotor shaft.

[0015] Preferably, the ejector engages the projection of the pre-setter, with the outer contour of the ejector essentially corresponding to the inner contour of the hollow projection. This allows for continuous stabilization and dimensionally accurate creation of the desired base body with the double cone.

[0016] Furthermore, according to the invention, after the base body has been flow-formed, the pre-setter is raised to a working position in order to form the second tube end of the hollow rotor shaft using a flow-forming roller. This allows at least one tube end to be efficiently formed in one piece from the provided tube into a functional section, for example, a future bearing seat, seal, and / or gearing for power transmission.

[0017] Preferably, the second pipe end can be pressed against the projection of the pre-setter in order to reshape the functional section, wherein the inner contour of the functional section substantially corresponds to the outer contour of the projection.

[0018] According to one embodiment, the first pipe end can be formed into a functional section by means of flow forming in a further process.

[0019] According to one embodiment, the inner mandrel can have additional ribs in longitudinal extension distributed over the circumference in addition to the conical outer base contour.

[0020] According to one embodiment, the pre-setter can have additional ribs in longitudinal extension distributed over the circumference in addition to the conical outer base contour.

[0021] By means of the ribs on the conical outer base contour of the inner mandrel and / or the pre-setter, corresponding ribs are formed along the inner contour of the hollow body, which lead to an enlargement of the surface in the double cone of the base body and thus the cooling performance can be increased, whereby a cooling fluid can be passed through the cavity of the hollow rotor shaft for heat dissipation.

[0022] According to one embodiment, the inner mandrel and the pre-setter can be placed and / or inserted into the pipe ends along their longitudinal extension in such a way that the double cone is flow-formed asymmetrically. Alternatively, a symmetrical inner contour can also be created on the base body of the hollow rotor shaft.

[0023] The invention is explained in more detail using the following embodiments in conjunction with the drawing.

[0024] The drawing shows Fig. 1 to 4) a schematic sectional view of a sequence at different times in the process of the method according to the invention for producing a hollow rotor shaft and Fig. 5 and Fig. 6) two embodiments of hollow rotor shafts in schematic sectional representation produced according to the method according to the invention.

[0025] The invention proposes a method for producing a hollow rotor shaft (R), cf. Fig. 5 and Fig. 6. First, a tube (1) is provided, which can have an initial wall thickness between 4.0 and 12.0 mm and can be drawn, welded from a sheet metal blank to form a tube, or consist of a forged preform.

[0026] The pipe (1) is placed in a device not shown, preferably in a flow-forming device, with its first pipe end (1.1) on an inner mandrel (2), see Fig. 1. The inner mandrel (2) has a conical outer base contour (2.1) along its extension. This means that the circumference of the inner mandrel (2) in the area of ​​the first pipe end (1.1) is essentially the same as, or slightly smaller than, the inner circumference of the first pipe end (1.1) and tapers towards the pipe center.

[0027] The inner mandrel (2) has a central through-opening (2.3) through which an ejector (5) is guided or in which an ejector (5) is positioned.

[0028] A pre-setter (3) with a conical outer contour (3.1) is inserted into the second pipe end (1.2) on the side opposite the inner mandrel (2). The pre-setter (3) has a hollow projection (3.2). The inner mandrel (2) has a recess (2.2) which, together with the ejector (5) positioned centrally in the central through-opening (2.3) of the inner mandrel (2), forms a concentric recess such that the projection (3.2) of the pre-setter (3) can be completely accommodated therein.

[0029] When inserting the pre-setter (3) into the second pipe end (1.2), the projection (3.2) is inserted until it engages, preferably completely, in the recess (2.2), thereby bringing the inner mandrel (2) and the pre-setter (3) into contact. The outer contour (5.1) of the ejector (5) essentially corresponds to the inner contour (3.21) of the hollow projection (3.2).

[0030] The tube (1), the inner mandrel (2), the ejector (5) and the pre-setter (3) are set in rotation, symbolised by a rotating arrow, either directly or by frictional engagement, whereby at least one spinning roller (4) acts on the tube (1) from the outside in such a way that the outer basic contour (2.1, 3.1) of the inner mandrel (2) and the pre-setter (3) is impressed / shaped into the inner contour (1.1) of the spin-formed base body (1*) of the hollow rotor shaft (R), see Fig. 2.

[0031] In this case, the at least one pressure roller (4) travels along the length of the pipe (1), which is supported by the inner mandrel (2) and the pre-setter (3) in contact therewith, in order to produce a double cone in the base body (1*) and thus an increasing wall thickness (1.4) starting from the pipe ends (1.1, 1.2) in the longitudinal extension towards the center of the base body (1*).

[0032] After the flow-forming of the double cone, the pre-setter (3) is moved out of the produced base body (1*), whereby the ejector (5) moves synchronously with the pre-setter (3) into position, in particular to the next working position, in order to provide the projection (3.2) with sufficient stability for the forming of the second pipe end (1.2), see Fig. 3.

[0033] The forming of the at least one pipe end (1.1, 1.2) into a functional section (L) of the hollow rotor shaft (R), which can later have, for example, a bearing seat, a seal and / or a toothing after further optional processing, in particular a machining operation, is preferably carried out in the same device by raising the pre-setter (3) to a working position after the flow-forming of the base body (1*) in order to form the second pipe end (1.2) into a functional section (L) of the hollow rotor shaft (R) by means of a flow-forming roller (4), see Fig. 4. In this case, the second tube end (1.2) is preferably pressed against the projection (3.2) of the pre-setter (3) to reshape the functional section (L), wherein the inner contour (L2) of the functional section (L) essentially corresponds to the outer contour (3.22) of the projection (3.2). The ejector (5) preferably remains in the projection (3.2), in particular as a support and centering aid.

[0034] The pre-setter (3) is removed and the ejector (5) is retracted / retracted into the central through-opening (2.3) of the inner mandrel (2) so that the hollow rotor shaft (R) with at least one formed functional section (L) can be removed from the device.

[0035] Not shown, the first pipe end (1.1) can be formed into a functional section (L) by means of flow-forming in a further process, preferably in a separate device not shown.

[0036] Fig. 5 shows an embodiment of a hollow rotor shaft (R) in a schematic sectional view produced according to the method according to the invention.

[0037] Fig. 6 shows a further embodiment of a hollow rotor shaft (R) in a schematic sectional view produced according to the method according to the invention, wherein in comparison to the embodiment in Fig.6 additional ribs are embossed / molded into the double cone to increase cooling performance. This can be achieved by providing the inner mandrel (2) and / or the adapter (3) with additional ribs distributed longitudinally around the circumference in addition to the conical outer base contour (2.1, 3.1) (not shown).

[0038] Both embodiments show a symmetrical double cone, whereby it is also conceivable and not shown here that the inner mandrel (2) and the pre-setter (3) are placed and / or inserted into the pipe ends (1.1, 1.2) in their longitudinal extension in such a way that the double cone can be flow-formed asymmetrically.

[0039] The features described can all be combined with each other, as far as technically possible.

Claims

[1] Method for producing a hollow rotor shaft (R) comprising the following steps: - Providing a pipe (1); - placing the pipe (1) with its first pipe end (1.1) on an inner mandrel (2) with a conical outer base contour (2.1) in its extension; - inserting a pre-setter (3) with a conical outer base contour (3.1) on the side opposite the inner mandrel (2) into the second pipe end (1.2); - setting the tube (1), the inner mandrel (2) and the pre-setter (3) in rotation, wherein at least one pressure roller (4) acts on the tube (1) from the outside in such a way that the outer basic contour (2.1, 3.1) of the inner mandrel (2) and the pre-setter (3) is impressed into the inner contour (1.1) of the pressure-formed base body (1*) of the hollow rotor shaft (R), so that the base body (1*) forms an increasing wall thickness (1.4) with a double cone and thus starting from the tube ends (1.1, 1.2) in the longitudinal extension towards the center of the base body (1*); - forming at least one tube end (1.2) into a functional section (L) of the hollow rotor shaft (R), characterized byin that the pre-setter (3) has a hollow projection (3.2) and the inner mandrel (2) has a recess (2.2), wherein the projection (3.2) is inserted into the second pipe end (1.2) when the pre-setter (3) is inserted until the projection (3.2) engages in the recess (2.2), as a result of which the inner mandrel (2) and the pre-setter (3) come into contact and remain in contact during the action of the spinning roller (4), wherein the pre-setter (3) is raised to a working position after the spinning roller has been used to form the second pipe end (1.2) into a functional section (L) of the hollow rotor shaft (R) by means of the spinning roller (4). [2] Method according to claim 1, wherein the inner mandrel (2) has a central through-opening (2.3) through which an ejector (5) is guided, wherein the ejector (5) is moved synchronously with the pre-setter (3) into position for the forming of the second pipe end (1.2) after the flow-forming of the base body (1*). [3] Method according to claim 2, wherein the outer contour (5.1) of the ejector (5) corresponds to the inner contour (3.21) of the hollow projection (3.2). [4] Method according to claim 1, wherein the second pipe end (1.2) is pressed against the projection (3.2) of the pre-setter (3) in order to reshape the functional section (L), wherein the inner contour (L2) of the functional section (L) corresponds to the outer contour (3.22) of the projection (3.2). [5] Method according to one of the preceding claims, wherein the first pipe end (1.1) is formed into a functional section (L) by means of flow-forming in a further process. [6] Method according to one of the preceding claims, wherein the inner mandrel (2) has additional ribs in longitudinal extension distributed over the circumference in addition to the conical outer base contour (2.1). [7] Method according to one of the preceding claims, wherein the pre-setter (3) has additional ribs in longitudinal extension distributed over the circumference in addition to the conical outer base contour (3.1). [8] Method according to one of the preceding claims, wherein the inner mandrel (2) and the pre-setter (3) are placed and / or inserted in their longitudinal extent into the pipe ends (1.1, 1.2) in such a way that the double cone is asymmetrically flow-formed.

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