Method for manufacturing a load-transmitting shaft

Abstract

Method for manufacturing a load-transmitting shaft (24) for a drive train of a motor vehicle, comprising the steps Providing a circuit board (10) made from a sheet of metal and Producing a hollow shaft (18) by tensile-compressive forming from the blank (10), characterized in that After the provision of the metal sheet and before the production of the hollow shaft (18), a blank part (16) is produced by punching and pressing, wherein the blank part (16) has a circular outer contour (12), a central through-hole (14) and an elongation in the longitudinal direction and the load-transmitting shaft (24) consists of at least two hollow shafts (18; 26, 28) connected to each other in the longitudinal direction.

Description

[0001] The invention relates to a method for manufacturing a load-transmitting shaft, and to a shaft manufactured by the method which can be used in a drive train of a motor vehicle for transmitting drive power.

[0002] It is known to produce a thick-walled pipe from a hollow block using the so-called "Mannesmann process" by skew rolling, which is then further processed in a subsequent rolling process to reduce the wall thickness as much as possible. Due to the thin wall thickness, the pipe can be manufactured economically and easily bent to create any desired path for the fluids conveyed through it. These thin-walled seamless pipes are not designed to transmit torque loads.

[0003] It is known that in the drivetrain of a motor vehicle, load-transmitting shafts are used between a power source, in particular an internal combustion engine and / or an electric traction motor, and the driven drive wheels, via which drive power generated in the power source is transmitted. The load-transmitting shaft is, for example, a rotor shaft of the electric traction motor, an output shaft of an internal combustion engine, a transmission shaft of a gearbox for converting torque and speed into the transmitted power, a drive shaft leading to a differential gear, or a wheel shaft leading from a differential gear to the respective drive wheel. Load-transmitting shafts are generally designed as solid shafts, although in some cases a load-transmitting solid shaft may be bored or machined to create a hollow shaft.For example, one of the two coaxial transmission shafts of a dual-clutch transmission is designed as a thick-walled hollow shaft.

[0004] From DE 197 22 359 A1 a spinning machine for the production of internally toothed hollow gears is known.

[0005] From DE 43 06 372 C1 it is known to form a sheet metal blank into a hood and subsequently to form the hood into a gear part with hub by pressing.

[0006] From DE 196 20 812 A1 it is known to produce a rotationally symmetric body from a pipe section by pressure forming, wherein the rotationally symmetric body can be designed as an internally and / or externally toothed lamellar body for the automotive industry.

[0007] From DE 14 52 610 A a method for forming a hollow metal object from a workpiece blank is known, in which a mandrel is inserted into a through-opening of the workpiece blank.

[0008] From DE 10 2020 106 612 A1 it is known to press an insert element into a hollow shaft in order to transmit torque with virtually no loss.

[0009] From Lange, Kurt [ed.]: Forming Technology: Handbook for Industry and Science. Vol. 3. Sheet Metal Working. 2nd, completely revised and expanded edition. Berlin Heidelberg: Springer-Verlag, 1990. 470-475. - ISBN 978-3-662-10686-0, it is known that larger diameter reductions can be achieved in several forming stages during synchronous drawing.

[0010] There is a constant need to manufacture load-transmitting shafts in a motor vehicle's drivetrain cost-effectively.

[0011] The object of the invention is to demonstrate measures that enable the cost-effective production of load-transmitting shafts for a drive train of a motor vehicle.

[0012] The problem is solved by a method with the features of claim 1, a shaft with the features of claim 6, a shaft with the features of claim 7, and a use with the features of claim 8. Preferred embodiments are specified in the dependent claims and the following description, each of which, individually or in combination, may represent an aspect of the invention, the scope of protection being determined by the claims. When a feature is presented in combination with another feature, this serves only to simplify the presentation of the invention and is in no way intended to imply that this feature cannot also constitute a further development of the invention without the other feature.

[0013] One embodiment of the invention relates to a method for manufacturing a load-transmitting shaft for a motor vehicle's drivetrain, comprising the steps of providing a blank made from a sheet metal blank and producing a hollow shaft from the blank by tensile-compressive forming, wherein, after providing the sheet metal blank and before producing the hollow shaft, a blank is produced by punching and pressing, the blank having a circular outer contour, a central through-opening, and a longitudinal elongation, and the load-transmitting shaft consisting of at least two hollow shafts connected longitudinally one behind the other. In particular, the hollow shaft and / or the resulting shaft are subsequently used as a load-transmitting shaft and / or as part of a load-transmitting shaft in the motor vehicle's drivetrain.

[0014] For the production of the hollow shaft, a blank is used instead of a solid metal block or a hollow metal block. The blank can already be part of a sheet of metal, which is readily available as a standard, often standardized, semi-finished product at low cost. Customizing the geometry of a solid or hollow metal block to fit the load-bearing shaft to be produced is unnecessary. Instead, the blank can be cut to length and / or stamped from the cost-effective sheet metal according to the desired geometry of the hollow shaft.

[0015] The blank derived from the sheet metal is therefore already a rolled product, having undergone plastic deformation during the rolling process of the sheet metal production. This results in the metal grains in the blank being elongated transversely to one thickness direction, and the elongation of the blank in the thickness direction during tensile-compressive forming leads to particularly high strength in the hollow shaft. It is assumed that the plastic deformation of the grains elongated transversely to the thickness direction during tensile-compressive forming blocks and tilts otherwise present sliding planes, thus preventing dislocations within the microstructure of the formed hollow shaft under load. With the same amount of material, the hollow shaft produced in this way can transmit a higher maximum torque than a solid shaft.

[0016] Since the hollow shaft contains material in the particularly stressed outer radius areas, while the less stressed inner radius areas are devoid of material, a high maximum transmission power can be achieved cost-effectively with less material. The hollow shaft used for the load-transmitting shaft in the drive train can thus utilize the material provided by the circuit board in those radius areas that enable high power density and high maximum transmissible torque with a small installation space and minimal material usage. Despite the hollow shaft's smaller cross-section compared to a solid shaft, it maintains high strength, which ensures the high power density and high maximum transmissible torque.

[0017] Tensile-compressive forming eliminates the need for machining, thus preventing material loss in the form of chips. Instead, virtually all the material provided by the blank can be cost-effectively formed into the hollow shaft. By tensile-compressive forming the rolled blank, a hollow shaft with high strength can be produced cost-effectively for the load-bearing shaft, enabling the cost-effective manufacturing of load-bearing shafts for a motor vehicle's powertrain.

[0018] The production of the blank from the sheet metal can be carried out by either punching or pressing, preferably simultaneously. For example, the punching tool can also be a pressing tool, which, with a defined contour outside of the cutting dies, presses against the blank to be produced, thereby pressing the blank against a counter contour. The flat blank, which is only conceptually present in the sheet metal and identifiable via the cutting dies of the punching tool, can exist after punching and pressing as a three-dimensionally formed blank, which may still be recognizable as a flat disc in at least some areas, but in particular already exhibits an axial extension that facilitates the subsequent tensile-compressive forming.

[0019] Since the load-transmitting shaft consists of at least two hollow shafts connected longitudinally one behind the other, no further components are required to manufacture it, thus keeping production costs low. Particularly when the load-transmitting shaft is very long and / or geometrically complex, it can be advantageous to assemble it section by section using several hollow shafts. The connection of longitudinally connected hollow shafts can be achieved primarily by material bonding, for example, by welding, laser welding, or brazing. However, it is also possible to connect the hollow shafts by friction and / or using intermediate connecting elements, such as clamps, screws, or hooks.

[0020] The hollow shaft has a greater axial extent than its maximum outer diameter. Preferably, the axial extent of the hollow shaft is at least 1.5 times, more preferably at least 2.5 times, and most preferably at least 3.5 times greater than the maximum outer diameter.

[0021] In particular, the blank has a circular outer contour, preferably produced by stamping from the metal sheet. The circular outer contour of the blank allows the radially outer surface of the hollow shaft to be defined during tensile-compressive forming. This circular outer contour automatically results in a rotationally symmetrical outer surface of the hollow shaft without the need for machining. In particular, it is possible for the rotationally symmetrical outer surface of the hollow shaft to be present directly after tensile-compressive forming and to require essentially no further machining.

[0022] Preferably, the blank has a through-hole, particularly a central one, wherein a tool for applying a radially outward-directed compressive force is inserted in the through-hole, and the through-hole is widened at least in an axial portion. The through-hole can be produced, in particular, simultaneously with punching the blank from the sheet metal. Preferably, exactly one punching tool can be used for this purpose. With the aid of the through-hole, the tool inserted into the through-hole can process and / or shape the radially inner area of ​​the blank during tensile-compressive forming. Preferably, the tool can drive material from the blank from the radial inside to the radial outside, thereby causing additional work hardening, particularly in the radially outer edge regions of the hollow shaft.Furthermore, it is possible to drive so much material radially outwards that the outer diameter can increase. It is even possible that after the plastic expansion of the through-hole, the hollow shaft produced in this way will have a larger outer diameter in at least one axial region than the blank before tensile-compressive forming.

[0023] In particular, tensile-compressive forming is repeatedly applied to produce different outer diameters and / or wall thicknesses along the longitudinal direction of the hollow shaft. If the geometry of the hollow shaft to be produced is to change along the longitudinal direction with respect to its inner diameter, outer diameter, and / or wall thickness, this can be achieved by producing the respective different axial areas along the longitudinal direction in stages. If necessary, the machine tool used for tensile-compressive forming can be retooled. Preferably, however, only the relevant manufacturing parameters of the machine tool are changed and gradually increased during operation for the various tensile-compressive forming processes to be applied.

[0024] Particularly preferably, a first hollow shaft is manufactured from a first blank and a second hollow shaft from a second blank, wherein the first and second blanks have end faces of different sizes and the first and second hollow shafts have different outer diameters, and in particular, the first hollow shaft is partially pressed into the second hollow shaft. If the load-transmitting shaft is very long and / or geometrically very complex, it can be advantageous to assemble the load-transmitting shaft section by section from several hollow shafts that are inserted one behind the other in the longitudinal direction. For this purpose, an axial shaft section can easily be provided during the tensile-compression forming of the respective blank, which, when inserted together, result in a sufficiently rotationally stable, preferably conical, press fit.This can eliminate the need for a material-bonded connection or the use of intermediate connecting elements, or at most only provide a supporting effect.

[0025] The invention further relates to a shaft for a motor vehicle drivetrain, wherein the shaft is manufactured according to the method, which can be further developed and refined as described above, and is designed for transmitting a torque of at least 50 Nm, preferably at least 80 Nm, and particularly preferably at least 120 Nm. The shaft is, for example, a transmission shaft of a gearbox for converting torque and speed into the transmitted power, a drive shaft leading to a differential gear, or a wheel shaft leading from a differential gear to the respective drive wheel.By tensile-compression forming of the rolled blank, the hollow shaft can be produced cost-effectively with sufficient strength for the load-transmitting shaft to transmit the torque of the intended drive power, thus enabling cost-effective production of load-transmitting shafts for a motor vehicle drive train.

[0026] The invention further relates to a shaft for a rotor of an electric machine for the electric drive of a motor vehicle, wherein the shaft is manufactured according to the method, which can be further developed and refined as described above, and is designed for transmitting a torque of at least 10 Nm, preferably at least 20 Nm, and particularly preferably at least 30 Nm. The load-transmitting shaft can be configured as the rotor shaft of an electric traction machine for the purely electric drive of the motor vehicle. By compressive tensile forming of the rolled blank, the hollow shaft with sufficient strength for transmitting the torque of the intended drive power can be produced cost-effectively, thus enabling the cost-effective manufacture of load-transmitting shafts for a motor vehicle drivetrain.

[0027] The invention further relates to the use of the at least one hollow shaft produced according to the method, which can be further developed and refined as described above, as a load-transmitting shaft and / or part of a load-transmitting shaft in a motor vehicle drivetrain for the purpose of transmitting drive torque. By tensile-compression forming of the rolled blank, the hollow shaft with high strength can be produced cost-effectively for the load-transmitting shaft, thus enabling the cost-effective production of load-transmitting shafts for a motor vehicle drivetrain.

[0028] The invention is explained below by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention, either individually or in combination. The drawings show: Fig. 1: A schematic perspective view of a circuit board at an initial stage of a manufacturing process, Fig. 2: a schematic perspective view of the circuit board formed into a raw part made of Fig. 1 at a subsequent second point in time of the manufacturing process, Fig. 3: a schematic perspective view of the raw part formed into a hollow shaft made of Fig. 2 at a subsequent third point in the manufacturing process and Fig. 4: A schematic perspective view of a hollow wave made up of two hollow waves. Fig. 3 composite load-transmitting shaft 2 at a subsequent fourth point in time of the manufacturing process.

[0029] With the in Fig. 1 to Fig. According to the manufacturing process described in section 3, a load-transmitting shaft 24 for a motor vehicle drivetrain can be produced, the strength of which is sufficient to transmit a torque generated by an internal combustion engine and / or an electric motor from the motor vehicle's drive power. For this purpose, the shaft can be machined from a provided sheet of metal. Fig. The circuit board shown in section 10 is to be punched out. The circuit board has in the Fig. In the embodiment shown in Figure 1, a circular outer contour 12 and a central through-opening 14 are present. Since the circuit board 10 is stamped from a rolled metal sheet, elongated grains oriented perpendicular to the thickness direction of the circuit board are present in the microstructure of the circuit board 10.

[0030] As in Fig. As shown in Figure 2, the blank 10 can be formed into a blank 16 by pressing. Compared to a flat sheet, the blank 16 has a significant extension in the axial direction of the blank 10. In particular, it is possible to simultaneously perform the punching of the blank 10 and the forming of the blank 10 into the blank 16 by pressing. In the Fig. In the embodiment shown in Figure 2, the circular outer contour 12 of the circuit board is made of Fig. 1 essentially retained its original shape, with only a radially inner area of ​​the circuit board 10 being elongated in the axial direction. In particular, the through-opening 14 can be widened or created for the first time during pressing.

[0031] If the in Fig. 1. The circuit board shown, 10, or the one in Fig. 2. If the raw part 16 shown is formed by, in particular repeatedly, tensile-compressive forming, the resulting shape can change. Fig. The hollow shaft 18 shown in Figure 3 is produced. By appropriately adjusting the process parameters, slightly different axial sections 20 with different outer diameters and / or different inner diameters and / or different wall thicknesses can be formed, which are preferably connected to each other via rounded and / or chamfered axial transition areas 22. The hollow shaft 18 or several hollow shafts 18 connected one behind the other in the axial direction can be used as the load-transmitting shaft for the drive train of the motor vehicle.

[0032] As in Fig. As shown in Figure 4, the load-bearing shaft 24 can be composed of two or more hollow shafts 18. In the figure shown in Fig.In the embodiment shown in Figure 4, a first hollow shaft 26 and a second hollow shaft 28 are connected to each other by a weld 30. The first hollow shaft 26 and the second hollow shaft 28 have the same outer diameter at the weld 30 and preferably also the same inner diameter and wall thickness. However, a deliberate radial offset can also be provided on the facing sides of the first hollow shaft 26 and the second hollow shaft 28, so that the weld 30 can be a fillet weld. Particularly preferably, the first hollow shaft 26 and the second hollow shaft 28 are centered relative to each other at their respective inner diameters using an inserted tool, while the weld 30 is produced from the radial outside to create the metallurgical connection. Reference symbol list 10 circuit boards 12 Outer contour 14 Passage opening 16 Raw part 18 Hollow shaft 20 Axial section 22 Transition area 24 load-bearing shaft 26 first hollow shaft 28 second hollow shaft 30 weld seam

Claims

[1] Method for manufacturing a load-transmitting shaft (24) for a drive train of a motor vehicle, comprising the steps Providing a circuit board (10) made from a sheet of metal and Producing a hollow shaft (18) by tensile-compressive forming from the blank (10), characterized by , that After the provision of the metal sheet and before the production of the hollow shaft (18), a blank part (16) is produced by punching and pressing, wherein the blank part (16) has a circular outer contour (12), a central through-hole (14) and an elongation in the longitudinal direction and the load-transmitting shaft (24) consists of at least two hollow shafts (18; 26, 28) connected to each other in the longitudinal direction. [2] Method according to claim 1, wherein the circuit board (10) has a circular outer contour (12), the outer contour (12) being produced by punching from the metal sheet. [3] Method according to claim 1 or 2, wherein the circuit board (10) has a through-opening (14), wherein a tool for imprinting a radially outward directed pressure force is used in the through-opening (14) and at least in an axial partial area the through-opening (14) is widened. [4] Method according to any one of claims 1 to 3, wherein tensile-compressive forming is repeatedly applied to produce different outer diameters and / or different wall thicknesses along a longitudinal direction of the hollow shaft (18). [5] Method according to any one of claims 1 to 4, wherein a first hollow shaft (26) is made from a first blank and a second hollow shaft (28) is made from a second blank, wherein the first blank and the second blank have end faces of different sizes and the first hollow shaft (26) and the second hollow shaft (28) have different outer diameters, wherein the first hollow shaft (26) is partially pressed into the second hollow shaft (28). [6] Shaft (24) for a drive train of a motor vehicle, wherein the shaft (24) is manufactured according to the method according to one of claims 1 to 5 and is designed for the transmission of a torque of at least 50 Nm, preferably at least 80 Nm and particularly preferably at least 120 Nm. [7] Shaft (24) for a rotor of an electric machine for the electric propulsion of a motor vehicle, wherein the shaft (24) is manufactured according to the method according to one of claims 1 to 5 and is designed for the transmission of a torque of at least 10 Nm, preferably at least 20 Nm and particularly preferably at least 30 Nm. [8] Use of the at least one hollow shaft (18) produced according to the method of any one of claims 1 to 5 as a load-transmitting shaft (24) and / or part of a load-transmitting shaft (24) in a drive train of a motor vehicle for the purpose of transmitting a drive torque.

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