Vibration decoupling of highly stressed gear components of a vehicle

Abstract

The invention relates to a drive unit for a motor vehicle, comprising a housing (1) with a support ring (3) with internal teeth arranged in the interior of the housing (1) and comprising a carrier (5) with external teeth, wherein the internal teeth of the support ring (3) and the external teeth of the carrier (5) engage with each other and form a splined connection, wherein the external teeth are conically rolled and a first polymer coating (7) is applied to an outwardly facing cylindrical surface of the external teeth.

Description

[0001] The invention relates to a drive unit for a motor vehicle, and to a method for manufacturing such a drive unit for a motor vehicle.

[0002] Electric drive units (EDUs) for electric vehicles, especially in high-end and luxury vehicles, should be particularly quiet. However, increasingly higher power outputs are expected of EDUs, which place greater stresses on the drivetrain and consequently result in higher levels of NVH (noise, vibration, and harshness). These disadvantages typically arise particularly with new multi-gear systems where torque is supported via a housing. These systems often employ splined connections.

[0003] Since the housings are typically made of die-cast aluminum, and torque-transmitting components are usually made of steel due to load requirements, their differing thermal expansion rates negatively affect gear backlash during operation. This backlash becomes noticeable, for example, through noise, especially during load changes. Due to the die-casting process of an aluminum housing as described above, the internal gearing of the housing typically has chamfers, so that an internal cylindrical component with teeth (usually a sheet steel part) often only has line contact in the tooth flanks at the lowest insertion point, which is disadvantageous.

[0004] In this context, CN 221683535 U relates to a drive assembly with the following characteristics: An output shaft of a drive element is provided with a first transmission element. The gearbox is provided with an input shaft, the input shaft is equipped with a second transmission element, and the first and second transmission elements are engaged; a protective film is clamped between the first and second transmission elements and is arranged on the surface of at least one of the first and second transmission elements.

[0005] DE 102023 003 284 B3 discloses an electric drive device comprising an electric machine, a gearbox housing, a planetary gear set which has a ring gear and is arranged in the gearbox housing, on which an internal toothing is provided as a first toothing, into which a corresponding external toothing provided on the ring gear engages as a second toothing, whereby the ring gear is rotationally fixed to the gearbox housing, and a plastic element arranged between the toothings, by means of which the toothings are supported against each other, wherein the plastic element has wall areas directed inwards in the radial direction of the ring gear, which are spaced apart from each other in the axial direction of the ring gear to form a receiving area in which the ring gear is arranged, the axial end faces of which bear axially against the wall areas.

[0006] DE 872 140 B discloses a gear with a non-metallic running surface, characterized in that the gear consists of a metallic base body containing the teeth in correspondingly reduced dimensions, which is provided with a covering of plastic, rubber or a similar material to form the running surface.

[0007] The object of the invention is to reduce backlash in a drive unit with a plug-in gear connection.

[0008] The invention is defined by the features of the independent claims. Advantageous further developments and embodiments are the subject of the dependent claims.

[0009] A first aspect of the invention relates to a drive unit for a motor vehicle, comprising a housing with a support ring with internal teeth arranged in the interior of the housing and comprising a carrier with external teeth, wherein the internal teeth of the support ring and the external teeth of the carrier engage with each other and form a splined connection, characterized in that the external teeth are conically rolled and a first polymer coating is applied to an outwardly facing cylindrical surface of the external teeth, wherein the first polymer coating only partially covers the external teeth axially.

[0010] Preferably, the housing is made of die-cast aluminum, while the support is preferably made of steel. The drive unit is intended in particular for a battery-electric vehicle.

[0011] To distribute the surface pressure evenly over the length of the gear teeth in a component coupling of internal and external gear teeth as described above, the external gear teeth are rolled conically according to the invention, such that initial contact occurs at the center of the gear teeth and, under torque load, the surface contact spreads from there along the flank length, particularly elastically. This results in a flank combination similar to a cambered flank.

[0012] Centering of the internal and external gearing is advantageously achieved via the root circle of the internal gearing and the tip circle of the external gearing, as this can be advantageously machined. The remaining internal gearing of the housing part remains in its cast state (with disadvantageously large manufacturing tolerances), so that there are disadvantageously tapered gaps or gaps between the root circle of the external gearing and the tip circle of this internal gearing, as well as on the flanks towards the end of the gearing.

[0013] To achieve an additional damping effect, a first polymer coating is selectively applied as a molded covering to fill these gaps. This is particularly advantageous for bridging manufacturing-related tolerances. This bridging is advantageously achieved by designing the overlap so that no backlash occurs between the internal and external gear teeth.

[0014] The following are the beneficial effects of this approach and this design of the drive unit: - Precise centering and alignment of the support ring and the carrier relative to each other is possible via the root circle of the internal gearing to the tip circle of the external gearing. This offers particular advantages with regard to manufacturing quality and during operation of the drive unit with respect to vibrations and noise. - A fit and reversal clearance, especially in the radial direction, can be eliminated by the first polymer coating in gear clearances: This in turn offers advantages with regard to vibrations and noise (so-called NVH system), especially during load changes, reversal of direction of rotation and a partial load range in which the drive unit is operated. It is also possible to reduce axial play, particularly by compressing the first polymer sleeve during pressing into the housing. This, in turn, also reduces the occurrence of vibrations and noise. - The reduced vibrations offer advantages for the service life of the splined connection. Furthermore, a functional advantage is achieved through a firm bond between the internal splines and the first polymer shell (which is preferably vulcanized), as it can partially absorb shear forces that arise, among other things, from the chamfers of the outer housing splines on the flanks or from displacement mechanisms of the elastic polymer material under surface pressure. This results in a cost advantage in the assembly process, since the carrier with the external teeth, onto which the first polymer coating is applied, is a ready-to-install part. - The first polymer coating offers a functional advantage through reduced abrasion in the splined connection, as its plastic surface adheres to the tooth gaps of the die-cast surface of the housing toothing.

[0015] According to an advantageous embodiment, the carrier is a sheet steel hollow gear carrier for receiving a hollow gear.

[0016] According to another advantageous embodiment, the support is a sliding sleeve support for receiving a sliding sleeve.

[0017] According to a further advantageous embodiment, a second polymer layer is applied to an inwardly facing surface of the carrier. This second polymer layer is made possible, in particular, by an additional internal polymer injection molding to further decouple an internal component, e.g., a ring gear.

[0018] According to another advantageous embodiment, the first polymer sheath has an increase in thickness in the axial direction of the carrier.

[0019] According to a further advantageous embodiment, the external toothing has outwardly open radial perforations into which projections of the first polymer sheath are inserted.

[0020] Secondary features such as the aforementioned perforations offer a functional advantage by increasing the tolerable shear forces. These secondary features are geometric design elements, such as the perforations, which are preferably punched into the carrier or its external teeth, particularly to create openings. During injection molding to produce the first polymer layer, these openings fill with polymer material, thus preventing displacement and detachment of the first polymer layer.

[0021] Advantageously, if these perforations completely penetrate the outer teeth, a plastic layer for producing the second polymer shell can also be molded onto the inner side of the outer teeth in the same injection molding process, so that another, internally centered component (for example, a ring gear) is also damped by the polymer material.

[0022] According to a further advantageous embodiment, the internal toothing of the support ring and the external toothing of the carrier are centered relative to each other via a base circle of the internal toothing and a head circle of the external toothing.

[0023] According to the invention, the first polymer coating only partially covers the external teeth axially.

[0024] The partial application of the first polymer coating offers the advantage of higher torque transmission between the internal and external gear teeth. This is made possible in particular by partial direct contact between these gear teeth, while the polymer nevertheless reduces backlash.

[0025] Another aspect of the invention relates to a method for manufacturing a drive unit for a motor vehicle, wherein an external toothing of a carrier is tapered and a first polymer coating is applied to a cylindrical surface of the external toothing by an injection molding and vulcanizing process, and wherein an internal toothing of a support ring of a housing and an external toothing of the carrier are brought into engagement with each other to form a splined connection, wherein the first polymer coating only partially covers the external toothing axially.

[0026] A composite component is manufactured using an injection molding and vulcanization process, comprising the toothed metallic carrier and the first polymer coating on the toothing. This polymer damping is particularly effective at low torque loads (or lower rotational speeds).

[0027] Advantageously, this achieves increased layer adhesion through surface activation, preferably also through phosphating, a bonding layer before the application of the first polymer coating by injection molding and vulcanization.

[0028] According to a further advantageous embodiment, radial holes are introduced into the external teeth, which are then injected with polymer from the first polymer sheath.

[0029] Advantages and preferred further developments of the proposed method result from an analogous and substantive transfer of the above statements made in connection with the proposed drive unit.

[0030] Further advantages, features and details will become apparent from the following description, in which - possibly with reference to the drawing - at least one embodiment is described in detail.

[0031] They show: Fig. 1: A first assembly of a drive unit according to an embodiment of the invention. Fig. 2: A second assembly of a drive unit according to a further embodiment of the invention. Fig. 3: A carrier with its external teeth according to an embodiment of the invention. Fig. 4: A carrier with its external teeth according to a further embodiment of the invention. Fig. 5: Perforations in the external teeth according to an embodiment of the invention. Fig. 6: A first polymer coating that is only partially applied according to a further embodiment of the invention. Fig. 7: A second polymer sheath opposite the external toothing according to a further embodiment of the invention. Fig. 8: A method for manufacturing a drive unit for a motor vehicle according to an embodiment of the invention

[0032] The representations in the figures are schematic and not to scale.

[0033] Fig. Figure 1 shows a cross-sectional view of a drive unit for a motor vehicle. A support ring 3 with internal teeth is arranged in a housing 1. External teeth on a carrier 5 engage with these internal teeth. The carrier 5 is designed as a sheet steel ring gear carrier 9 for receiving a ring gear 11.

[0034] Fig. Figure 2 shows a cross-sectional view of an alternative drive unit for a motor vehicle. A support ring 3 with internal teeth is arranged in a housing 1. External teeth on a carrier 5 engage with these internal teeth. The carrier 5 is designed as a sliding sleeve carrier 13 for receiving a sliding sleeve 15.

[0035] In both cases, the one that Fig. 1 and the one Fig. 2 The internal teeth of the support ring 3 and the external teeth of the carrier 5 engage with each other and form a splined connection.

[0036] Fig. Figure 3 shows the external toothing of the carrier 5 in a manufacturing phase still without the first polymer coating 7. In the state of Fig. 4 the carrier 5 has the first polymer sheath 7 on the radial outside, i.e. the outwardly facing sheath surface of the external toothing.

[0037] From above, the Fig. Figure 5 shows that the external toothing is tapered on one side of the carrier 5 and therefore, together with the first polymer layer 7, has an axial slope. This is shown in particular by the dashed guidelines, which illustrate the resulting angle of the outer surface of the external toothing due to the change in radius along an axial coordinate. The external toothing also has outwardly directed radial perforations 19 into which projections of the first polymer layer 7 are inserted, so that the first polymer layer 7 adheres better to the surface of the outer surface of the external toothing.

[0038] Fig. Figure 6 shows a partial axial covering of the external teeth by the first polymer layer 7 for transmitting very high torques. As an example, the first polymer layer 7 extends along an axial direction over half the width of the external teeth.

[0039] Fig. Figure 7 shows, in addition to the first polymer coating 7, a second polymer coating 17 applied to an inwardly facing surface of the external toothing.

[0040] Fig. Figure 8 shows a method for manufacturing a drive unit for a motor vehicle, wherein an external toothing of a carrier 5 is tapered S1 and a first polymer coating 7 is applied to a cylindrical surface of the external toothing by an injection molding and vulcanizing process S2, and wherein an internal toothing of a support ring 3 of a housing 1 is brought into engagement with the external toothing of the carrier 5 S3 to form a splined connection.

[0041] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without leaving the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description. Reference symbol list 1 case 3 support ring 5 carriers 7 first polymer coating 9 steel sheet hollow wheel carriers 11 Ring gear 13 sliding sleeve carriers 15 sliding sleeve 17 second polymer coating 19 holes

Claims

[1] Drive unit for a motor vehicle, comprising a housing (1) with a support ring (3) with internal teeth arranged inside the housing (1) and comprising a carrier (5) with external teeth, wherein the internal teeth of the support ring (3) and the external teeth of the carrier (5) engage with each other and form a splined connection, characterized by , that the external toothing is conically rolled and a first polymer coating (7) is applied to an outwardly facing surface of the external toothing, wherein the first polymer coating (7) only partially covers the external toothing axially. [2] Drive unit according to claim 1, wherein the carrier (5) is a sheet steel ring gear carrier (9) for receiving a ring gear (11). [3] Drive unit according to claim 1, wherein the carrier (5) is a sliding sleeve carrier (13) for receiving a sliding sleeve (15). [4] Drive unit according to one of the preceding claims, wherein a second polymer sheath (17) is applied to an inwardly facing outer surface of the external toothing. [5] Drive unit according to one of the preceding claims, wherein the first polymer sheath (7) has a thickness increase in the axial direction of the carrier (5). [6] Drive unit according to one of the preceding claims, wherein the external toothing has outwardly open radial perforations (19) into which projections of the first polymer sheath (7) are inserted. [7] Drive unit according to one of the preceding claims, wherein the internal toothing of the support ring (3) and the external toothing of the carrier (5) are centered relative to each other via a root circle of the internal toothing and a tip circle of the external toothing. [8] Method for manufacturing a drive unit for a motor vehicle, wherein an external toothing of a carrier (5) is tapered (S1) and a first polymer shell (7) is applied to a cylindrical surface of the external toothing by an injection molding and vulcanizing process (S2), and wherein an internal toothing of a support ring (3) of a housing (1) and an external toothing of the carrier (5) are brought into engagement with each other (S3) to form a splined connection, wherein the first polymer shell (7) only partially covers the external toothing axially. [9] Method according to claim 8, wherein radial holes (19) are introduced into the external toothing, which are injected with polymer of the first polymer shell (7).

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