Electronic limited slip differential; electric drive system

Abstract

The invention relates to a differential (1) for an electric drive system, comprising a differential cage (2), a friction clutch (3) having an inner disk carrier (4) with disks (5) attached thereto for conjoint rotation, wherein the inner disk carrier (4) has a collection edge (6) for conducting oil (7) and passing it through the inner disk carrier (4) to the disks (5), wherein a nozzle (8) is provided for supplying the oil (7) in the direction of the collection edge (6), wherein the nozzle (8) is oriented in such a way that an oil flow (7) emerging from the nozzle (8) is oriented obliquely to the axis of rotation (9) of the friction clutch (3). The invention also relates to an electric drive system for an electric vehicle having a differential (1).

Description

[0001] P240707

[0002] - 1 - eLSD differential; electric drive system

[0003] The invention relates to a differential for an electric drive system with a friction clutch, comprising an inner plate carrier with plates attached thereto in a rotationally fixed manner, wherein the inner plate carrier has a catching edge for guiding oil and passing it through the inner plate carrier to the plates.

[0004] Specifically, the invention relates to an electric differential, i.e., a rear axle limited-slip differential, also known as an active differential or electronic limited-slip differential (eLSD). As is known, eLSDs enable the transmission of torque from the drive shaft to the output shafts in a motor vehicle and simultaneously allow the output shafts to rotate at different speeds as required.

[0005] In electronic differentials, mechanical components are replaced by electric actuators and sensors. Compared to mechanical differentials, electronic limited-slip differentials offer better control over torque distribution. This adaptability improves traction, stability, and overall handling.

[0006] As with all power components, and especially electrical power components, functionality and power efficiency are largely determined by heat dissipation. Against this background, both active and passive cooling strategies are established. In particular, cooling strategies using fluids such as oil, implemented as wet cooling strategies, enable advantageously efficient heat dissipation. Active cooling strategies, through the feasible use of pumps, allow for a further improvement in cooling performance with regard to heat dissipation.

[0007] The potential of a wet and active cooling strategy is not yet being used advantageously and efficiently for eLSDs in the current state of the art. For example, no state-of-the-art technology with active lubrication of an eLSD from the outside via P240707 exists.

[0008] - 2 - a nozzle is known. It is only known that oil is used for passive lubrication in mass-produced motor vehicles.

[0009] Initial designs for cooling concepts related to the inventor's eLSD envisioned a single nozzle positioned outside the differential housing. However, with this nozzle orientation, virtually no oil reaches the friction clutch, as it is positioned circumferentially offset from the oil jet in the prior art. The oil jet cannot simply be shifted axially towards the friction clutch, because this would result in insufficient oil supply to the bevel gears and, furthermore, the limited number of bores would make it difficult for the oil to penetrate the multi-plate clutch from the outside. This is particularly true at higher speeds during operation of the electric drive system's differential.

[0010] The present invention aims to achieve an improvement over the prior art. Known disadvantages are to be eliminated or at least mitigated. This particularly concerns increasing the cooling resource efficiency of differentials for electric drive systems by improving the lubrication of the friction clutch. The eLSD is to be improved.

[0011] In a differential as presented above, this is achieved according to the invention by providing a nozzle for supplying the oil in the direction of the catching edge, wherein the nozzle is oriented such that an oil flow through it is oriented obliquely to the axis of rotation of the friction clutch.

[0012] In other words, the invention relates to an improved lubrication system for a differential with an integrated eLSD clutch. Specifically, an improvement in the lubrication of the clutch is achieved. The clutch is preferably designed as a disengaging clutch and, even more preferably, as a friction clutch.

[0013] To improve lubrication, the nozzle is beveled / tilted in the direction of the electric drive system's axis of rotation and positioned outside the differential housing. The angle is determined by the positions of P240707.

[0014] - 3 -

[0015] The nozzles, the friction clutch, and the bevel gear set of the eLSD are determined. Due to the angled arrangement of the nozzle, the oil is injected into the differential basket at an angle.

[0016] This means that the injection is not horizontal and thus parallel to the direction of the axis of rotation, but at a predetermined angle to a transverse plane to the axis of rotation (radially and circumferentially). Therefore, the nozzle for active lubrication is no longer arranged at a 90° angle to the differential's axis of rotation, as is established in the prior art, or in other words, at a rotation angle of 0° around the x-axis of the vehicle's coordinate system. The angled shape of the oil jet ensures lubrication of both the differential components (bevel gears, plain bearings, splines) and the multi-plate clutch.

[0017] Advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0018] In the context of the explanation of the embodiments, the directional specifications refer to the differential and thus to the electric drive system. The axial direction corresponds to the longitudinal axis of the electric drive system, i.e., the axis of rotation. The radial direction is defined at the height of the differential. That is, the radial direction is perpendicular to the axis of rotation. The circumferential direction is defined in the third dimension of a Cartesian coordinate system.

[0019] It has proven advantageous if the nozzle is aligned on an end face of the inner lamella carrier or on an area radially below the capture edge.

[0020] This means that the nozzle's design ensures direct lubrication of central components of a disconnect clutch, preferably a friction clutch, of the differential according to the invention via the oil flow exiting the nozzle. This direct lubrication of the friction clutch results in improved convective heat transfer from the clutch surface. The improved convective heat transfer from the P240707

[0021] - 4 -

[0022] The friction clutch's connection to the oil flow results in improved heat dissipation from the clutch surface. This technical effect significantly increases the clutch's performance and service life. This is particularly advantageous given the friction clutch's central function: heat transfer as a link for torque transmission in the electric drive system.

[0023] This further means that preferably two areas of oil flow determination are advantageous in the sense of two embodiments. In the sense of a first embodiment, the nozzle is preferably aligned with the end face of the inner fin carrier, or in the sense of a second embodiment, with the area radially below the catch edge of the inner fin carrier. With the first embodiment, heat transfer is achieved from a large and easily accessible surface. The size of the surface preferably correlates with a large amount of heat-carrying surface.

[0024] This means that, by means of the nozzle on the catch edge of the inner lamella carrier, as a second embodiment of the oil flow control area, the oil is collected in the catch edge, thus localizing the oil at a central point. The further technical effect of this oil accumulation will be described later in the discussion of the differential according to the invention.

[0025] The two embodiments of the oil flow determination areas shown above are advantageous with regard to waste heat management and friction clutch efficiency, and thus with regard to heat transfer.

[0026] Furthermore, it is advantageous if the nozzle is aligned at an angle of attack α of 30° to 45°, in particular 37.5°, to the axis of rotation of the friction clutch.

[0027] This means that the nozzle orientation is preferably predetermined using methods of computational fluid dynamics (e.g., CFD). This further means that it is preferably predetermined taking into account the fluidic flow behavior and phenomena. P240707

[0028] - 5 -

[0029] Furthermore, in an advantageous embodiment, the angle of attack α is set within a range of 30° to 45°. This range of values ​​for the angle of attack α allows for targeted oil flow, preferably to the previously described components of the differential according to the invention. The components are accessible to the oil flow via this angle of attack. This is advantageous with regard to direct oil application, meaning that heat management is favorably influenced.

[0030] Furthermore, it is advantageous if a differential basket is provided with at least one cutout that is prepared to allow the oil flow from outside the differential basket into an interior of the differential basket.

[0031] The design of the differential housing, featuring at least one cutout, allows oil to be supplied from outside the housing into its interior. This is particularly advantageous given the limited space inside the differential housing, as the nozzle is positioned outside this space.

[0032] To allow the oil jet / flow to penetrate to the edge of the inner clutch carrier, the cutouts in the differential housing must be large enough to allow oil to pass through the nozzle. This means that the dimensions of at least one cutout in the tangential, and therefore circumferential, direction are preferably made large enough. For this reason, a 3-pinion differential design is more advantageous than a 4-pinion differential design.

[0033] It has proven advantageous to have a spherical support ring recessed to allow the oil flow to be guided to the catching edge of the inner lamellar carrier.

[0034] This means that, via the recess of components of the differential according to the invention, which are arranged in the interior of the differential basket, the technical effect is achieved that oil flows through the at least one recess to the or P240707

[0035] - 6 - is supplied to the area(s) of purpose explained above.

[0036] The recesses are preferably provided on components that are arranged axially between the local recess and the friction clutch inside the differential carrier. Furthermore, the components are preferably arranged axially between the recess of the differential carrier and the inner plate carrier. Additionally, a spherical support ring is preferably included among these components and thus designed with a recess.

[0037] The technical effect of this preferred embodiment described above corresponds to the previously described technical effect. An advantage is that the geometry of the recess is preferably designed to correspond to and reflect the angle of attack of the nozzle. Furthermore, the recess is locally limited. This local limitation is designed in both the radial and circumferential directions such that the oil jet / flow is guided through the local recess depending on the angle of attack.

[0038] This embodiment advantageously facilitates the simple, flow-through of the oil stream from the nozzle without flow losses or changes in the flow angle. This is advantageously achieved with regard to targeted, angle-accurate oil flow guidance and the avoidance of losses in flow velocity and / or oil volume. The advantages are reflected in improved oil resource efficiency.

[0039] Furthermore, it is advantageous if the nozzle is designed to allow a jet flow velocity sufficient to guide the oil from an inlet area into the differential basket to the friction clutch.

[0040] It is advantageous that the oil exits at a speed that is preferably predetermined depending on the viscosity of the oil. Furthermore, it is advantageous that the oil exits along a flow path outside the P240707, depending on the flow path to be traversed up to the previously described target areas.

[0041] - 7 - and within the interior of the differential basket, at a predetermined speed. Furthermore, it is advantageous that the speed of the oil discharge is predetermined depending on air resistance. The preferred embodiment of the flow velocity ensures a defined supply of oil.

[0042] It is further advantageous that the defined oil supply preferably includes the supply as intended, without oil dripping down the flow path due to insufficient velocity. Furthermore, it also preferably includes the supply as intended, without excessive oil splashing from the impact surface due to excessive velocity.

[0043] Furthermore, it is advantageous if the differential is designed to be actively cooled with oil for heat dissipation, for example using a pump.

[0044] This means that, by using the embodiment of the differential according to the invention as an actively cooled differential, the utilization of existing active cooling circuits of the preferably electric drive system is advantageously simple. This implies advantages with regard to the integration of the differential according to the invention into the existing drive system of electric motor vehicles.

[0045] These advantages relate particularly to assembly, design, and thus costs, but also to the utilization of existing drive system structures in terms of cooling circuits and oil pumps. Furthermore, advantages arise from the larger oil volumes that can be supplied to the friction clutch via an active oil supply design compared to a passive one. This is particularly beneficial for improved cooling during high-speed maneuvers.

[0046] Furthermore, it is advantageous if the angle of attack of the nozzle depends on the arrangement of the nozzle to the differential basket and the position and geometry of the friction clutch and the bevel gear set.

[0047] This means that the angle of attack depends on the arrangement of the nozzle to the differential basket as well as the position and geometry of the friction clutch and P240707

[0048] - 8 - of the bevel gear set is variable. By varying the angle depending on the embodiment of the differential, i.e., the arrangement of the components of the differential, an advantageous variability of the lubrication solution of the differential according to the invention is achieved.

[0049] It is also advantageous if the nozzle is prepared to perform spraying of a circumferential catching edge of the inner lamella carrier.

[0050] This means that by spraying the circumferential catch edge, the oil, preferably cooling oil, is applied to the catch edge in this embodiment. Due to the rotational forces occurring in the differential according to the invention for an electric drive system, the catch edge acts similarly to an oil pump, so that the oil is collected externally, and thus in the preferably circumferential catch edge, as a result of inertia. The collection of the oil therefore preferably corresponds to a collection of the oil in the catch edge.

[0051] With regard to the oil transport from the circumferential retaining edge into the interior of the inner vane carrier, that is, preferably the oil passage to the steel vanes of the inner vane carrier, its embodiment with at least one geometric recess is advantageous. An alternative embodiment to the at least one recess is an inclined bore. Furthermore, the embodiment of the at least one recess as an end-face bore is advantageous. In this embodiment, the oil is transported through the at least one bore into the inner vane carrier to the individual vanes during operation of the electric drive system, that is, under rotational speed.

[0052] The differential according to the invention preferably provides lubrication of the friction clutch in the opposite direction of travel.

[0053] Also presented is an electric drive system for an electric vehicle with a differential according to one of the preceding claims. P240707

[0054] - 9 -

[0055] Due to the embodiment of the electric drive system with a differential according to the invention, the advantages shown for the differential are also valid for the electric drive system.

[0056] The invention is explained in more detail below with the aid of a drawing. An embodiment of the differential according to the invention is shown. It illustrates:

[0057] Fig. 1 shows a schematic representation of a section of a first embodiment of a differential according to the invention in a cross-sectional view and

[0058] Fig. 2 shows a real component representation of an eLSD according to the state of the art in a partially cutaway view.

[0059] The drawings are purely schematic and serve only to illustrate the invention. The same elements are identified by the same reference numerals. The features of the individual embodiments may be mutually complementary or interchangeable.

[0060] Fig. 1 shows a schematic cross-sectional view of a section of a first embodiment of a differential 1 according to the invention. The differential 1 according to the invention (in this embodiment as an electronic limited-slip differential, eLSD) is equipped with a differential carrier 2 and is designed for an electric drive system with an integrated disconnect clutch in the embodiment of a friction clutch 3. The friction clutch 3 has an inner plate carrier 4 with plates 5 attached thereto in a rotationally fixed manner.

[0061] The lamellae 5 are preferably made of steel. The inner lamella carrier 4 has a preferably circumferential retaining edge 6 for guiding an oil flow 7 and conducting the oil flow 7 through the inner lamella carrier 4 to the lamellae 5. Furthermore, the differential 1 according to the invention has a schematically depicted nozzle 8 for supplying the oil flow 7 in the direction of the retaining edge 6. The nozzle 8 is oriented such that a P240707

[0062] - 10 - outgoing oil flow 7, that is, flow of oil / generated jet, is oriented obliquely to the axis of rotation 9 of the friction clutch 3.

[0063] The nozzle 8 is aligned with an end face 10 of the inner lamella carrier 4 or with a radial area 11 below the catch edge 6. The nozzle 8 is preferably aligned at an angle of attack α 12 of 30° to 45° relative to the axis of rotation 9 of the friction clutch 3. The nozzle 8 is further designed to allow a flow velocity of the oil / oil jet / oil stream 7 sufficient to guide the oil stream 7 within the interior 13 of the differential carrier 2, despite any components such as spherical support rings 14, from an inlet area 15 into the differential carrier 2 to the friction clutch 3.

[0064] For example, the spherical support ring 14 has a recess 16 to guide the oil flow 7 to the catch edge 6 of the inner plate carrier 4. The angle of attack α 12 of the nozzle 8 also depends on the arrangement of the nozzle 8 in the differential carrier 2 and the position and geometry of the friction clutch 3 and the bevel gear set 17.

[0065] Fig. 2 shows a real component representation of an eLSD in a partially cutaway view according to the prior art. Shown are the differential housing / differential basket 2, the axis of rotation 9 of the drive or transmission shaft (not shown), bearings 18 in the form of plain bearings for supporting and bearing the drive or transmission shaft, a bevel gear set 17 in axial and end-face arrangement, and an inner plate carrier 4 comprising a plate pack with plates 5 made of steel. The differential 1 extends in radial 11, tangential 19, and axial 20 directions. P240707 DE

[0066] - 11 -

[0067] List of reference signs

[0068] 1 Differential I Electronic locking differential I eLSD I Guided transverse lock

[0069] 2 Differential basket I Differential housing

[0070] 3 Friction clutch / separating clutch

[0071] 4 inner slat carriers

[0072] 5 slats

[0073] 6 catch edge

[0074] 7 Oil flow / oil jet / oil

[0075] 8 nozzle

[0076] 9. Axis of rotation

[0077] 10 Front surface

[0078] 11 radial

[0079] 12 Angle of attack a

[0080] 13 Interior

[0081] 14 Spherical support ring

[0082] 15 Entrance area

[0083] 16 recess

[0084] 17 bevel gear set

[0085] 18 warehouses

[0086] 19 tangential

[0087] 20 axial

Claims

P240707 DE - 12 - Patent claims 1. Differential (1) for an electric drive system, comprising a differential carrier (2), a friction clutch (3), having an inner plate carrier (4) with plates (5) attached thereto in a rotationally fixed manner, wherein the inner plate carrier (4) has a retaining edge (6) for guiding oil (7) and passing it through the inner plate carrier (4) to the plates (5), characterized in that a nozzle (8) is provided for supplying the oil (7) in the direction of the retaining edge (6), wherein the nozzle (8) is oriented such that an oil flow (7) emanating from the nozzle (8) is directed obliquely to the axis of rotation (9) of the friction clutch (3).

2. Differential (1 ) according to claim 1 , characterized in that the nozzle (8) is aligned on an end face (10) of the inner lamella carrier (4) or on a region radially (11 ) below the catching edge (6).

3. Differential (1 ) according to one of claims 1 or 2, characterized in that the nozzle (8) is aligned at an angle of attack α (12) of 30° to 45°, in particular 37.5°, to the axis of rotation (9) of the friction clutch (3).

4. Differential (1 ) according to one of claims 1 to 3, characterized in that the differential basket (2) is provided with at least one cutout which is prepared to allow the oil flow (7) from outside the differential basket (2) into an interior (13) of the differential basket (2).

5. Differential (1 ) according to one of claims 1 to 4, characterized in that a spherical support ring (14) is recessed to allow the oil flow (7) to be guided to the catching edge (6) of the inner lamella carrier (4). P240707 DE - 13 - 6. Differential (1 ) according to one of claims 1 to 5, characterized in that the nozzle (8) is designed to enable such a flow velocity of the oil flow (7) that is sufficient to guide the oil flow (7) from an inlet area (15) the differential basket (2) to the friction clutch (3).

7. Differential (1 ) according to one of claims 1 to 6, characterized in that the differential (1 ) is arranged to be actively cooled, for example by using a pump, with oil for heat dissipation.

8. Differential (1 ) according to one of claims 4 to 7, characterized in that the angle of attack a (12) of the nozzle (8) depends on the arrangement of the nozzle (8) in the differential basket (2) and the position and geometry of the friction clutch (3) and the bevel gear set (17).

9. Differential (1 ) according to one of claims 1 to 8, characterized in that the nozzle (8) is prepared to perform a spraying of a circumferential catching edge (6) of the inner lamella carrier (4).

10. Electric drive system for an electric vehicle with a differential (1 ) according to one of the preceding claims.

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