Method for producing a drive component for a vehicle, and drive component produced by means of said method
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2024-06-26
- Publication Date
- 2026-05-20
AI Technical Summary
The existing methods for producing drive components with differentials and differential wheels are complex and costly, particularly in automated systems, due to the need for screwing a fastening flange onto an inner wheel body, which can lead to eccentricity and requires additional processing steps and materials.
A method involving capacitor discharge welding to directly connect the fastening flange of the differential housing to the inner wheel body, eliminating the need for screws and allowing for simultaneous centering and mechanical fastening, thereby reducing production complexity and costs.
This method simplifies the production process, reduces material usage and weight, minimizes the risk of material defects, and ensures precise concentric alignment, enabling efficient torque transmission while avoiding the need for additional heat treatment or extensive material melting.
Smart Images
Figure EP2024067885_16012025_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] Method for producing a drive component for a vehicle, and drive component produced by this method
[0004] State of the art
[0005] Drive arrangements are known in the prior art that transmit the output torque of, for example, an electric motor to the output side of a vehicle. One such drive arrangement, which may also include a clutch device for interrupting the power transmission to the output side, is shown, for example, in DE 10 2021 210 796 A1. Such drive arrangements have a drive component with a differential and a differential gear on the output side. The differential gear is mechanically fixed to a differential housing of the differential.
[0006] To manufacture the drive component consisting of a differential and differential gear, it is known to insert the differential housing into an inner recess of an inner gear body of the differential gear and to screw a circumferential mounting flange of the differential housing to the inner gear body, as described, for example, in DE 32 15 430 A1. When inserting the differential housing into the differential gear, a centering surface on the differential gear serves, in the prior art, to radially align or center the differential gear relative to the differential housing, which is necessary to prevent eccentricity between the differential gear and the differential housing. The screwing process, which may also involve securing devices to prevent accidental loosening of the screws, is complex and represents a significant cost factor in an automated production facility. Disclosure of the Invention
[0007] The invention relates to a method for producing a drive component for a vehicle, wherein the drive component comprises at least one differential and one differential gear, comprising the steps:
[0008] - Providing a differential gear with a rotational axis, an external toothing and an internal gear body extending from the external toothing in the direction of the rotational axis, which internal gear body has an internal recess,
[0009] - Providing a differential with a differential housing, wherein the differential housing has a circumferential mounting flange,
[0010] - Inserting the differential housing into the inner recess of the inner wheel body and
[0011] - Establishing a mechanical connection between the mounting flange of the differential housing and the inner gear body of the differential gear. According to the invention, the mounting flange is welded directly to the inner gear body in a capacitor discharge welding step. Furthermore, the invention relates to a drive component manufactured using this method.
[0012] In the context of the present application, a rotational axis of the differential gear is understood to be a concentric axis through the center of the differential gear, around which axis the differential gear rotates during rotation. This is therefore the rotational axis of the differential gear. The differential gear can have external teeth on its outer circumference, for example, in the form of helical gearing. Starting from the external teeth, an internal gear body of the differential gear extends in the direction of the rotational axis. The internal gear body can be designed in different ways. Many embodiments are possible here. For example, but not necessarily, the internal gear body can be designed as a wheel disc. The internal gear body has an internal recess with a preferably circular cross-section. In the context of the present application, the rotational axis of the differential gear defines an axial direction.Each direction perpendicular to this forms a radial direction. A differential is understood to be a transfer case which has at least one differential housing. The differential housing can be designed as a differential cage or differential carrier. The differential housing can have shaft hubs at opposite ends, in the bores of which a drive shaft is each mounted. The drive shafts can, as is common in the art, be rotationally fixedly coupled to bevel gears in the differential housing, wherein the bevel gears mesh with differential gears rotatably mounted on a differential pin anchored to the differential housing. The drive shafts can rotate about a common axis, which axis also represents the axis of rotation of the differential housing.The differential housing must be connected to the differential gear in such a way that the axes of rotation of both joining partners are concentrically aligned with each other or coincide within a tolerance.
[0013] A fastening flange is understood to mean a circumferential projection which projects from the differential housing in the radial direction and has, for example, a cylindrical shape, which can in particular be formed integrally on the differential housing.
[0014] Capacitor discharge welding is a special type of resistance welding process in which the energy required for welding is drawn from a capacitor bank serving as an intermediate storage device. This capacitor bank is discharged, for example, via a pulse transformer, creating a pulsed direct current with a high amperage value that welds the joining parts together in a weld zone. Capacitor discharge welding, as it is known, is also referred to as KE welding.
[0015] Direct welding of the mounting flange to the inner wheel body means that a surface section of the mounting flange is brought into direct contact with a surface section of the inner wheel body through the welding process, and a material bond is created between these surface sections through the capacitor discharge welding step. Advantages of the invention
[0016] The process presented here avoids the disadvantages inherent in the prior art. Advantageously, the complex bolting of the mounting flange of the differential housing to the inner gear body of the differential gear is eliminated. This also eliminates the process steps and materials required to secure the bolts. The number of processing stations and the throughput time in the production facility can be advantageously reduced. Furthermore, the weight of the drive component can be slightly reduced. After welding, accidental loosening of the joining parts is impossible.
[0017] Another advantage is that, unlike other welding methods such as laser beam welding and electrode steel welding, there is no extensive melting of the material. This minimizes the risk of cracking or pore formation in the materials of the joining partners, which is particularly important for a drive component on the output side of a vehicle with regard to mechanical stability when transmitting high torques. In addition, fewer welding gases, smoke, and dirt emissions are produced during welding. Welding is advantageously carried out simultaneously along the circumferential weld seam, so that there is no overlap area between the start and end points of the weld seam, as is the case with laser beam welding. This means that the weld seam has the same consistency at all points in the circumferential direction. No further heat treatment is necessary after the welding process.
[0018] Furthermore, the capacitor discharge welding step particularly advantageously allows the centering of the differential housing and differential gear to be performed in a single process step, simultaneously with the formation of the mechanical fastening. The tolerance dimensions at the joints of the differential gear and the differential housing can therefore be designed to be tight. The welded connection between the differential housing and the differential gear thus advantageously fulfills two functions. On the one hand, it ensures that a sufficiently large torque can be transmitted from the differential gear to the differential, and on the other hand, the necessary tolerances with regard to the concentricity of the differential gear and differential housing and the specifications for radial runout deviations can be better maintained.
[0019] Advantageous embodiments and further developments of the invention are made possible by the features contained in the dependent claims.
[0020] Preferably, the mounting flange is welded to the inner gear body along at least one circumferential weld seam. The circumferential weld seam has sufficient strength to ensure the transmission of high torques between the differential gear and the differential housing. Furthermore, the weld seam secures the relative radial position of the differential gear and the differential housing. However, the method is not limited to the production of a single circumferential weld seam. It is also possible to weld the differential gear to the differential housing along two or more circumferential weld seams during the capacitor discharge welding step.
[0021] Advantageously, the inner recess of the inner gear body has a first inner wall section surrounding the rotation axis, having a first inner diameter, and the mounting flange has at least one first outer wall section with an outer diameter. Before the capacitor discharge welding is performed, the outer diameter is larger than the first inner diameter. During the capacitor discharge welding step, the components can be displaced in the axial direction despite the diameter differences. Different embodiments exist, as will be explained below.
[0022] To limit the relative axial position of the differential gear and differential housing, it is advantageous if the inner recess of the differential gear has at least one projection extending inward from the first inner wall section, wherein the projection has an axial stop surface and a circumferential second inner wall section, wherein the second inner wall section has a smaller inner diameter than the first inner wall section. The inner wall sections are preferably cylindrical in shape. This embodiment is advantageous because the axial stop surface is clearly formed directly by the projection of the differential gear, against whose stop surface the differential housing comes into contact during the welding process. This reliably secures the axial end position of both joining partners.Deviating from this embodiment, it is also possible for the axial position of the two joining partners to be aligned by placing the differential gear and differential housing on a common reference surface of the tool in the welding station.
[0023] In an advantageous embodiment, prior to the capacitor discharge welding step, the fastening flange has at least one circumferential rib on an outer circumferential surface facing the inner wheel body, which rib projects radially toward the inner wheel body and forms the outer wall section. This rib is welded to the first inner wall section of the inner recess during capacitor discharge welding. In another embodiment, it is also possible to weld a partial section of the cylindrical outer wall of the fastening flange to an inner wall section of the inner wheel body in a narrow overlap area.
[0024] In both cases, simultaneously with the capacitor discharge welding step, a relative movement between the differential housing and the differential gear can take place in an axial direction parallel to the axis of rotation until the differential housing reaches its end position on the differential gear, wherein the end position is achieved in particular by the fastening flange being in contact with the axial stop surface.
[0025] Particularly in connection with the embodiment with the circumferential rib, it can be advantageous to press the differential housing with the mounting flange into the inner recess during capacitor discharge welding by applying a pressing force acting in the axial direction. Since the outer diameter of the rib is larger than the corresponding inner diameter of the inner wall section of the inner recess of the differential gear, the rib can thus be initially heated by the heat associated with the welding process. The applied pressing force then presses the rib, softened by the heat, into the inner recess. In this embodiment, welding and pressing of the rib into the first inner wall section occur simultaneously.In another embodiment, it may be sufficient to press the two joining partners together with a slight force, especially if the overlap area between the inner wall section and the outer peripheral wall is quite narrow. The narrow overlapping surfaces on the outer peripheral wall of the mounting flange and the inner wall section of the inner gear body, heated by capacitor discharge welding, then allow the two joining partners to be displaced in the axial direction until the axial end position is reached, without the mounting flange having to be pressed into the inner recess with great force. In this case, the mounting flange is subjected to a force but not pressed in.
[0026] In all embodiments, the differential gear can have at least one first centering surface, and the differential housing can have at least one second centering surface. Advantageously, a centering holding device engaging the first centering surface and the second centering surface can ensure a predetermined radial distance between the first centering surface and the second centering surface until the end of the welding process, at least during the capacitor discharge welding step. The first centering surface can be provided, for example, on the outer wall of a shaft hub of the differential housing, while the second centering surface is arranged, for example, on an inner side of the differential gear facing the differential housing.The centering fixture can fix both joining partners to the centering surfaces, keeping them in a predetermined radial position relative to each other, in which the predetermined rotation axes of both parts are concentric. During welding, the radial position is maintained until the end of the welding process, so that the joining partners are only moved axially relative to each other.
[0027] Short description of the drawings
[0028] Possible embodiments of the invention are explained below with reference to the accompanying figures. The drawing shows: Figure 1 shows a first embodiment of a cross-section through a drive component manufactured according to the method according to the invention,
[0029] Figure 2 shows an enlarged section II from Figure 1,
[0030] Figure 3 shows a second embodiment of a cross-section through a drive component manufactured according to the method according to the invention,
[0031] Figure 4 shows an enlarged section III of Figure 3,
[0032] Figure 5 shows a greatly enlarged detail IV from Figure 4,
[0033] Figure 6 shows a third embodiment in a schematic detailed representation with a similar structure to the embodiment of Figure 4,
[0034] Figure 7 shows a fourth embodiment with two circumferential weld seams,
[0035] Figure 8 shows a drive component according to the state of the art.
[0036] Embodiments of the invention
[0037] Figure 8 shows the basic structure of a drive component 1, which is known from the prior art. The drive component 1 comprises at least one differential 2 and one differential gear 3. The drive component 1 can be part of a drive arrangement, as known, for example, from DE 10 2021 210 796 A1. The drive arrangement can, for example, transmit the drive torque generated by an electric machine via a gear stage to the differential gear 3 (so-called E-axis). The differential gear 3 has an axis of rotation 31 and an external toothing 33 facing away from the axis of rotation, which meshes with a driving gear (not shown) in the drive arrangement. The differential gear 3 is designed to transmit a torque absorbed via the external toothing 33 to the differential 2.For this purpose, the differential gear 3 has an inner gear body 32 extending from the external toothing 33 in the direction of the rotation axis 31, which is provided with an internal recess 34. The differential 2 has a rotatable differential housing 21, which is provided at opposite ends with two shaft hubs 6a, 6b, in whose bores 9a, 9b a drive shaft (not shown in Figure 8) is mounted. The differential housing 21 can be rotatably mounted about the rotation axis 31 via rolling bearings 10 in a drive arrangement. The drive shafts (not shown) can be non-rotatably coupled in the differential housing 21 to bevel gears 4a, 4b, wherein the bevel gears 4a, 4b mesh with differential gears 5a, 5b. The differential gears 5a, 5b are rotatably mounted on a differential pin 5 which is anchored to the differential housing 21.The drive shafts rotate around a common axis, which axis is also the rotational axis of the differential housing 21. The differential housing is connected to the differential gear in such a way that the rotational axes of both joining partners are concentrically aligned with each other, or coincide in the rotational axis 31. As can also be seen in Figure 8, the differential housing 21 has a circumferential mounting flange 22, which protrudes radially from the differential housing 21.
[0038] The drive component 1 shown in Figure 8 is manufactured as follows. The differential housing 21 is inserted into the inner recess 34 of the differential gear 3, with the outer wall of the mounting flange 2 and the inner wall of the inner recess 34 serving as centering surfaces to radially align the differential housing 21 relative to the differential gear 3. The axial end position is achieved by the mounting flange 22 being in contact with the inner gear body 32. The screws 60 are screwed through the disc-shaped inner gear body 32 into the mounting flange 22 and secured.
[0039] Figure 1 shows a first embodiment of a cross-section through a drive component 1 manufactured according to the method according to the invention. Identical parts are provided with the same reference numerals, so that the individual components of the differential 2 are not repeated here and only the differences are discussed. In contrast to the illustration in Figure 8, in Figure 1 the differential gear 3 has an inner gear body 32 which is, for example, beveled downwards. The differential gear 3 is preferably made of steel. The side surfaces of the inner gear body 32 are, for example, conical. The inner gear body 32 has a circular inner recess 34 which concentrically surrounds the axis of rotation 31. According to the invention, the differential housing 2 with the fastening flange 22 in Figure 1 is inserted from above into the inner recess 34 of the differential gear 3.How this is done exactly will be explained below using the enlarged section II in Figure 1, which is shown in Figure 2.
[0040] As can be seen in Figure 2, the continuous inner recess 34 of the inner gear body 32 has a preferably cylindrical, first inner wall section 34a, which surrounds the rotation axis 31 and has a first inner diameter D1. Furthermore, in this exemplary embodiment, the inner recess 34 has a projection 35 extending inward from the first inner wall section 34a. The projection 35 forms a circumferential step which has an axial stop surface 35a and a circumferential second inner wall section 34b. The second inner wall section 34b has a smaller inner diameter D3 than the first inner wall section 34a.
[0041] The differential housing 21 is preferably manufactured as a cast part made of cast steel. The mounting flange 22 is formed integrally with the differential housing 21 and has, for example, a largely cylindrical outer peripheral surface 24, which, however, in this exemplary embodiment is provided with an outer wall section 23 that projects radially from the outer peripheral surface 24 toward the inner gear body 32. The projecting outer wall section 23 forms a circumferential rib and has an outer diameter D2 that is slightly larger than the inner diameter D1 before the capacitor discharge welding is performed.
[0042] Before performing the capacitor discharge welding, it is recommended to remove at least the outer wall section 23 and / or the first inner wall section 34a from a carbon layer, for example by mechanical grinding, in order to enable better weldability of the material in the capacitor discharge welding.
[0043] Furthermore, the differential gear 3, as best seen in Figure 1, has a first centering surface 42. The first centering surface 42 can be formed, for example, by a cylindrical inner wall surface bordering the inner gear body 32 at the lower edge of the differential gear 3, which extends parallel to the rotation axis 31. As indicated in Figure 2, the first centering surface 41 can alternatively also be formed on the upper section of the differential gear 3. As further shown in Figure 1, the differential housing 22 has at least one second centering surface 43, which is formed, for example, by an outer surface of the shaft hubs 6a; 6b running parallel to the rotation axis 31.
[0044] To carry out the method, a centering holding device 90 aligns the differential housing 21 with the second centering surface 43 and the differential gear 3 with the first centering surface 42 such that, by means of the centering holding device 90, a predetermined radial distance R is set between the first centering surface 42 and the second centering surface 43, which is selected such that the axes of rotation of the differential housing 21 and the differential gear 3 are concentric with one another and therefore coincide with the axis of rotation 31 in Figure 1. While maintaining this radial centering (by fixing the radial position), the differential housing 21 can now be lowered in the axial direction in Figure 1 until the radially projecting outer wall section 23 touches the inner gear body 32.Although the outer wall 24 in Figure 2 is spaced apart from the first inner wall surface 34a, the outer wall section 23 protrudes slightly beyond the inner diameter D1 of the first inner wall section 34a due to the larger outer diameter D2. The overlap can be, for example, 0.3 mm.
[0045] The differential housing 21 is now subjected to a pressing force F1 in the axial direction in the direction of the arrow in Figure 1, and simultaneously the capacitor discharge welding is initiated. The press-in process presses the fastening flange 22 into the first inner wall section 34a until the fastening flange 22 comes into contact with the contact surface 35a. This position of the two joining partners is shown in Figures 1 and 2. Through the simultaneous welding process, the outer wall section 23 is heated and, at the same time, welded to the inner wall section 34a for the press-in process and pressed into it. During the capacitor discharge welding step, the centering holding device 90 ensures the predetermined radial distance R between the first centering surface 42 and the second centering surface 43 until the end of the welding process.The fastening flange 22 is now welded to the inner wheel body 32 along a circumferential weld seam 80.
[0046] An advantageous second embodiment of the method is illustrated in Figures 3 to 5. Figure 3 shows the drive component 1 during production. Figure 4 shows the enlarged section III from Figure 3, and Figure 5 shows a further enlarged detail section IV from Figure 4.
[0047] The following will focus on the differences from the first embodiment. Figure 3 shows that the inner wheel body 32 in this embodiment is not chamfered and has a disc-like structure.
[0048] Figure 4 shows that in this embodiment, too, the inner recess 34 can be provided with a step or projection 35, similar to the first embodiment. Therefore, similar to the first embodiment, the inner recess 34 has a cylindrical first inner wall section 34a surrounding the rotation axis 31 and having a first inner diameter D1, as well as an axial stop surface 35a and a circumferential second inner wall section 34b, which has a smaller inner diameter than the first inner wall section 34a. In contrast to the first embodiment, the outer wall surface 24 of the fastening flange 22 has a continuous cylindrical surface and no rib.The first outer wall section 23 of the outer wall surface 24 intended for welding is therefore formed in Figures 4 and 5 by that part of the outer wall surface 24 which is inserted into the first inner wall section 34b. As can best be seen in Figure 5, in this exemplary embodiment too, the outer diameter D2 of the first outer wall section 23 is initially approximately larger than the inner diameter D1 of the first inner wall section 34a before the welding process. Furthermore, the inner wall section 34a can additionally be provided with a small chamfer 26 at its lower end in Figures 4 and 5, which facilitates the insertion of the fastening flange 22. At the end of the first inner wall section 34a opposite the chamfer in the axial direction, a countersink 27 is provided, which can, for example, accommodate welding material.
[0049] When establishing the connection between the fastening flange 22 and the inner gear body 32, the differential housing 21 is moved upward in Figure 3, or the differential gear 3 is moved downward. By initiating capacitor discharge welding, the material in the region of the first inner wall section 34a and the first outer wall section 23 is heated. With a force F2 that is significantly lower than the force F1 for press-fitting in the first exemplary embodiment, the fastening flange 22 can now be brought into contact with the stop surface 35a, wherein at the same time a welded connection is produced in the narrow overlap area created by the axial displacement between the heated first inner wall section 34a and the heated first outer wall section 23. In this exemplary embodiment, too, a circumferential welded connection is created, but without a press-fitting process.
[0050] Figure 6 shows a third embodiment in a schematic detailed representation with a similar structure to the second embodiment of Figure 4. In contrast to the embodiment of Figure 4, in this embodiment, the inner gear body 32 forms a wheel disc at the lower end of the differential gear 3, projecting inward toward the rotational axis 31. The inner recess 34 is multiply stepped in this embodiment.
[0051] Figure 7 shows a fourth embodiment of the invention. Here, too, the inner recess 34 of the inner gear body 32 is stepped several times. The fastening flange 22 is also provided with a step. This makes it possible to weld, in the same capacitor discharge welding step, both a first outer wall region of the fastening flange 22 with a larger outer diameter to a first inner wall section of the inner recess 34 in the region of the weld seam 82 in Figure 7, and simultaneously weld a second outer wall region of the fastening flange 22 with a smaller outer diameter to a second inner wall section in the region of the weld seam 81. The end result is two weld seams 81, 82 with different diameters, which are arranged staggered in different planes and extend around the rotation axis 31.Of course, more than two circumferential welds can also be considered.
[0052] It is understood that, within the scope of the present invention, further embodiments of the method according to the invention are possible, which result partially or entirely from combinations of the exemplary embodiments described in Figures 1 to 7. For example, it is possible to dispense with the projection 35 and the stop surface 35a in Figure 2 and to ensure the axial end position of the differential housing 21 relative to the differential gear 3 by having both joining partners rest on a common reference surface in the tool, for example, the centering holding device.
Claims
Claims 1. A method for producing a drive component (1) for a vehicle, wherein the drive component (1) comprises at least one differential (2) and one differential gear (3), comprising the steps: Providing a differential gear (3) with a rotational axis (31), an external toothing (33) and an internal gear body (32) extending from the external toothing (33) in the direction of the rotational axis (31) and having an internal recess (34), Providing a differential (2) with a differential housing (21), wherein the differential housing (21) has a circumferential fastening flange (22), Inserting the differential housing (21) into the inner recess (34) of the inner wheel body (32) and Producing a mechanical connection between the fastening flange (33) of the differential housing (21) and the inner gear body (32) of the differential gear (33), characterized in that the fastening flange (22) is welded directly to the inner gear body (32) in a capacitor discharge welding step.
2. Method according to claim 1, characterized in that the fastening flange (22) is welded to the inner wheel body (32) along at least one circumferential weld seam (80).
3. Method according to claim 1 or 2, characterized in that the inner recess (34) has a first inner wall section (34a) surrounding the rotation axis (31) and having a first inner diameter (D1), and the fastening flange (22) has at least a first outer wall section (23) having an outer diameter (D2), wherein the outer diameter (D2) is larger than the first inner diameter (D1) before the capacitor discharge welding is carried out.
4. Method according to claim 3, characterized in that the inner recess (34) has at least one projection (35) extending inwards from the first inner wall section (34a). wherein the projection (35) has an axial stop surface (35a) and a circumferential second inner wall section (34b), wherein the second inner wall section (34b) has a smaller inner diameter (D3) than the first inner wall section (34a).
5. Method according to one of the preceding claims, characterized in that the fastening flange (22) has, before the step of capacitor discharge welding, on an outer circumferential surface (24) facing the inner wheel body (32), at least one circumferential rib which projects radially towards the inner wheel body (32) and forms the outer wall section (23), which is welded to the first inner wall section (34a) of the inner recess (34) during capacitor discharge welding.
6. Method according to one of the preceding claims, characterized in that simultaneously with the step of capacitor discharge welding, a relative movement takes place between the differential housing (21) and the differential gear (3) in an axial direction parallel to the axis of rotation (31) until the differential housing (21) reaches its end position on the differential gear (3).
7. Method according to claim 3 and claim 6, characterized in that the end position is reached by the fastening flange (22) being in contact with the axial stop surface (35a).
8. Method according to one of claims 6 or 7, characterized in that the differential housing (21) with the fastening flange (22) is pressed into the inner recess (24) during the capacitor discharge welding by applying a pressing force (F1) acting in the axial direction.
9. Method according to one of the preceding claims, characterized in that the differential gear (3) has at least one first centering surface (41; 42) and the differential housing (22) has at least one second centering surface (43), and that by means of a centering holding device (90) acting on the first centering surface (41; 42) and the second centering surface (43), at least during the capacitor discharge welding step, a predetermined radial distance (R) between the first centering surface (41; 42) and the second centner surface (43) is ensured until the end of the welding process.
10. Drive component (1) for a vehicle with at least one differential (2) and one differential gear (3), characterized in that a mechanical connection between a fastening flange (22) of a differential housing (21) of the differential (2) and an inner gear body (32) of the differential (3) is produced according to the method according to claims 1 to 9.