Bearing concept for an electric torque vectoring system

Abstract

Proposed is an electrically actuated torque vectoring unit (1) with an input gear stage (2) and two planetary gear stages (3, 4) as a superimposed gear unit (16), each of which has an output shaft (5, 6) and the two planetary gear stages (3, 4) are torque-transmitting coupled to the input gear stage (2), wherein the input gear stage (2) is driven by an electric motor (7), wherein the output shaft (17) of the input gear stage (2) has two spaced-apart rolling bearings (8, 9) which support the output shaft (17) to the housing (10) and thus the input gear unit (18), wherein each rolling bearing ring (11, 12, 13, 14) bears against its peripheral component at one axial end and has no contact with its peripheral component at its other axial end.

Description

[0001] DE 10 2015 223 131 A1 discloses a drive device for a motor vehicle, comprising a differential gear and a torque vectoring unit with an electric machine, wherein the differential gear has a first and a second planetary gear set rotatably mounted on a common web, wherein the first planetary gear set meshes with at least a first sun gear, the second planetary gear set meshes with at least a second sun gear, and the two planetary gear sets mesh with each other at least in pairs, and wherein at least the second sun gear is connected to the torque vectoring unit for redistributing the torque between the first and second sun gear.

[0002] DE 10 2014 103 485 B4 discloses an axle assembly comprising a motor, a differential assembly, a housing, a gearbox, and a reduction gear set. The gearbox includes a first and a second planetary gear set, which comprise associated (i.e., first and second) ring gears, planet carriers, and sun gears. The first planet carrier is coupled to a differential carrier of the differential assembly for common rotation. The second ring gear is rotationally fixed to the housing. The second planet carrier is coupled to the second differential output for common rotation. The second sun gear is coupled to the first sun gear for common rotation.The reduction gear set is arranged between an output shaft of the motor and the first ring gear and comprises a first gear coupled to the output shaft for common rotation and a second gear coupled to the first ring gear for common rotation.

[0003] US 7 311 631 B2 shows a torque vectoring unit for a motor vehicle powertrain.

[0004] DE 10 2021 126 647 B3 discloses a drive unit for a motor vehicle, comprising a differential gear which has a drive element, a first output shaft and a second output shaft, a traction motor which is connected to the drive element of the differential gear in a torque-transmitting manner, and a torque-vectoring unit for actively generating a differential torque between the two output shafts, wherein the torque-vectoring unit comprises an electric motor, a superimposed gear and a control unit for controlling the electric motor by means of a control signal to generate a differential torque between the two output shafts.

[0005] WO 2015 / 1 69 837 A1 shows a torque vectoring or torque distribution device for a vehicle.

[0006] The state of the art, published by experts, is also accessible in the publication STEINHILPER W., SAUER B.: Konstruktionselemente des Maschinenbaus. 2. 6th edition. Berlin / Heidelberg : Springer, 2008. Pages 2-4, 136-138, 155-158. - ISBN 978-3-540-76653-7.

[0007] The task is to provide improved bearing arrangement in a torque vectoring unit, which is achieved with the features of claim 1.

[0008] The torque vectoring unit has an input gear stage which has its own output shaft, which also serves as the drive shaft for transmitting torque from the input gear stage to the superimposed gear of the torque vectoring unit. That is to say, the torque vectoring unit according to the invention has an electric motor, an input gear stage, and a superimposed gear.

[0009] A differential gear is not included in the torque vectoring unit. The difference between the superimposed transmission according to the invention and a differential gear lies in the fact that the superimposed transmission of a torque vectoring unit acts on a drive shaft with the applied torque of the electric motor in such a way that the rotational speed of the wheel on the drive shaft is increased relative to the rotational speed of the wheel opposite it along the wheel axis. In a differential gear, the drive torque is usually introduced to the planetary carrier and distributed equally to the left and right wheels, assuming the same road friction coefficients on both wheels. If there are different road friction coefficients on the two wheels of an axle with an intermediate differential gear, the wheel with the higher road friction coefficient will "brake" due to the higher friction.The corresponding differential gear (in a bevel gear differential) or sun gear (in a spur gear differential) then rotates at a different speed than the respective gear assigned to the other wheel. The differential gear, a planetary gear with one input and two outputs, is able to convert these speed differences, ensuring that the wheel with the lower coefficient of friction does not receive a disproportionate amount of drive torque and thus avoid slippage (wheel spinning).

[0010] The superimposed transmission according to the invention is provided with two planetary gears, wherein, in contrast to the conventional differential transmission, the torque is introduced via the sun gear of one of the planetary gears (first sun gear), transmitted via a common ring gear to the other (second) planetary gear, and both (first and second) planetary gears have an interface to a (first and second) shaft via their (first and second) planet carrier.

[0011] The electromechanical axle drive train typically includes an electric motor designed to propel the vehicle (electric drive machine). This motor is usually connected to the planetary carrier of a differential gear, so that the torque from the electric motor (possibly via a reduction gear to convert the high speed of the electric motor into a lower speed for the differential gear, thus converting the low torque from the electric motor into a higher torque for the differential gear) is transmitted to the differential gear to drive two wheels of an axle.

[0012] The first and second shafts of the superimposed transmission are operatively connected in the drive train so that the torque vectoring unit can contribute its function to the driving behavior and superimpose the drive torque path with the torque supplied by the electric motor of the torque vectoring unit (superimposed transmission).

[0013] The superimposed transmission according to the invention is implemented in the drive train as follows. The electric motor of the torque vectoring unit is not energized.

[0014] The first planet carrier of the first planetary gear set of the superimposed transmission is connected to the planet carrier of the differential gear set via a first shaft in a torque-resistant manner. This allows the torque applied by the electric drive motor to the differential gear set to be simultaneously transmitted via the first shaft, through the first planet carrier of the first planetary gear set of the superimposed transmission set, into the second planetary gear set of the superimposed transmission set. The second planet carrier of the second planetary gear set then transmits the torque from the superimposed transmission set to the first output shaft leading to the first wheel. The unpowered electric motor of the torque vectoring unit does not "manipulate" the first output shaft of the differential gear set.

[0015] When the electric motor of the torque vectoring unit is energized, it transmits a direction-dependent torque through the input gear of the input stage, via the output shaft of the input stage, to the (first) sun gear of the first planetary gear of the superimposed gear unit – this output shaft of the input gear also serves as the drive sun shaft for the superimposed gear unit. Thus, the first planetary gear unit receives two input torques: one from the electric drive motor to the first planet carrier of the first planetary gear unit, and one from the electric motor of the torque vectoring unit to the (first) sun gear of the first planetary gear unit. The torque, which is then reduced / overdriven, is transferred from the first planetary gear unit to the second planetary gear unit via the ring gear common to the second planetary gear unit.Since the (second) sun gear of the second planetary gear set is fixed to the frame, meaning it is rigidly supported against a housing component, the only remaining output for the second planetary gear set is the torque at its second planet carrier, which is rigidly connected to the first output shaft of the differential. Consequently, the additional torque input from the superimposed gear set accelerates or decelerates the first wheel relative to the second output shaft of the differential and thus also relative to the second wheel. Advantageously, the control system is designed to detect cornering and thus energize the electric motor of the torque vectoring unit in such a way that the first wheel should rotate faster or slower relative to the second wheel.

[0016] The steering angle during cornering can be used as a control variable, allowing the electric motor of the torque-vectoring unit to be energized in the desired direction of rotation. This ensures that either the output of the first planetary gear overtakes the output of the second planetary gear, or vice versa. This results in a torque-vectoring function that allows the outer wheel to rotate faster, reducing slippage and instability when cornering at high speeds and improving driving dynamics.

[0017] This clearly distinguishes between a differential gear and the torque vectoring unit according to the invention with its superimposed gear.

[0018] The superimposed gearbox has two planetary gear sets coupled to each other via a common ring gear. Each planetary gear set has a shaft that is rotationally fixed to its planet carrier.

[0019] One shaft is provided for each driven wheel of the vehicle. Within the scope of this invention, one shaft is the output shaft from the differential gear, and the other shaft is a shaft non-rotatably coupled to a planet carrier. Thus, a drive torque variation can be applied to the two wheels of an axle of the vehicle via the operation of the electric motor, which rotates the input gear stage.

[0020] The drive sun shaft is mounted in a floating configuration, meaning that no locking elements are provided for the axial fixation of the rolling bearings, so that each rolling bearing has no degree of freedom in either axial direction. According to the invention, each ring of each rolling bearing is restricted in only one axial direction. The rolling bearings of the drive sun shaft support each other axially. Forces in the axial direction are transmitted from one rolling bearing ring through the rolling elements to the other rolling bearing ring of that bearing. Furthermore, the outer rings of the rolling bearings are axially supported by two interlocking housing halves as peripheral components, thus determining the absolute position of the drive sun shaft's mounting. To achieve preload in the drive sun shaft's mounting, the rolling bearings used for the mounting can be preloaded against each other using shims.

[0021] Advantageously, the torque vectoring unit can be equipped with an electric motor to drive it.

[0022] The torque vectoring unit according to the invention can advantageously also feature improved bearing arrangements for its superimposed gear unit. The superimposed gear unit comprises two planetary gear units (first and second) coupled to each other via a common ring gear. To achieve good load distribution within the system, each planet carrier is provided without its own radial bearing in the form of an additional rolling bearing. The radial positioning of the two shafts, which are rotationally fixed to the planet carriers, is achieved via the planetary gear sets and the common ring gear. Since the second sun gear is rotationally fixed relative to the housing, and the first sun gear is torque-transmittingly connected to the input gear unit, and the ring gear is a common component of both planetary gear units of the superimposed gear unit, the first and second planet carriers can be radially freed without an additional rolling bearing.The two shafts, each connected to the first and second planet carriers in a torque-resistant manner, are radially oriented to the respective first and second sun gears.

[0023] The axial support of the two planet carriers of the superimposed gear unit is provided by three thrust bearings. A first thrust bearing is located between the first planet carrier and the common ring gear that fits over it. A second thrust bearing is located between the two planet carriers, and a third thrust bearing is located between the second planet carrier and the common ring gear that fits over it. All three thrust bearings have sheet metal raceways and are designed as needle roller bearings.

[0024] In particular, at least two of the three axial rolling bearings are designed as identical parts, meaning that they have at least the same shape and number of needles as rolling elements, although the raceway discs may vary due to the connection to the peripheral components.

[0025] The common ring gear advantageously has a uniform tooth pattern for both planetary gear sets. Furthermore, the axial ends of the common ring gear are closed with cover rings, so that the shaft can protrude through its respective cover.

[0026] The common ring gear is mounted opposite the housing by a fixed bearing designed as a rolling bearing.

[0027] An advantageous embodiment of the invention is shown in the figure. Fig.Figure 1 shows a torque vectoring unit 1 with an input gear stage 2 designed as an input gear 18 and a superposition gear 16. The superposition gear 16 has two first and second planetary gear stages 3 and 4 connected to each other via a common ring gear 15, which respectively include the first and second planetary gear of the preceding general description.

[0028] The input gear stage 2 has two axially parallel spur gears that mesh with each other. The torque from the electric motor 7 of the torque vectoring unit 1 is applied to a double gear shaft 24 via a first gear 22 of the spur gear chain and transmitted via a pinion 23 mounted on this double gear shaft 24 to the second gear 25 of the spur gear chain. This sets the output shaft 17 of the input gear stage 2 in rotation. The output shaft 17 of the input gear stage 2 is also the drive sun shaft 26. The first and second rolling bearings 8 and 9 support the drive sun shaft 26 relative to the housing 10. The rolling bearings 8 and 9 are axially positioned on the drive sun shaft 26 such that they flank the input gear 18.The inner rings 11 and 12 of the rolling bearings 8 and 9 are mounted on the drive sun shaft 26 and each bears only one side against a diameter shoulder formed by the drive sun shaft 26. The diameter shoulder is located axially between the two rolling bearings 8 and 9. The outer rings 13 and 14 of the rolling bearings 8 and 9 are inserted into housing 10 and each bear only one side against a diameter shoulder of the bearing housing for the rolling bearing 8 and 9. This contact is located on the axially opposite side of the bearing housing on the diameter shoulder of the respective rolling bearing 8 and 9.

[0029] Apart from the area of ​​the rolling bearings with bearings 8 and 9, the sun gear of the first planetary gear stage 3 is located on the drive sun shaft 26 and is formed integrally with it. The first planetary gear stage 3 also has a planet carrier and planet gears. The planet carrier of the first planetary gear stage 3 is integrally connected to the shaft 27 driven by the drive motor 20, which also drives the differential gear 19 via its planet carrier. The differential gear 19 has two output shafts, 5 and 6, with the second output shaft 6 passing through this shaft 27 and extending through the superimposed gear 16 to transmit the drive torque from the drive motor 20 to one of the wheels. The second output shaft 6 is non-rotatably connected to the planet carrier of the second planetary gear stage 4 via a non-rotatable connection 21 (indicated here by a splined connection).The schematically indicated sun gear 28 of the second planetary gear stage 4 is fixed to the frame. Thus, when the electric motor 7, with the superimposed gear 16, drives the second output shaft 6, the drive for propelling the vehicle is transmitted from the drive electric motor 20 to both the left and right wheels (not shown here) at the ends of the first and second output shafts 5, 6.

[0030] When the electric motor 7 is energized and its torque is transmitted via the input gear stage 2 to the superimposed gear 16 and then to the second output shaft 6, a torque difference can be introduced between the first and second output shafts 5, 6. This process is called torque vectoring, as one of the two wheels on an axle is driven more than the other, thus increasing the vehicle's stability when cornering. Reference symbol list 1 Torque Vectoring Unit 2nd input gear stage 3 first planetary gear stage 4 second planetary gear stage 5 first output shaft 6 second output shaft 7 Electric motor 8 first rolling bearing 9 second rolling bearing 10 housings 11 first inner ring 12 second inner ring 13 first outer ring 14 second outer ring 15 common ring gear 16 superimposed gear units 17 Output shaft (input gear stage) 18 Input gearbox 19 Differential gears 20 Drive electric motor 21 rotationally fixed connection 22 first gear 23 sprockets 24 Double gear shaft 25 second gear 26 Drive sunshaft 27th wave 28 sun wheel

Claims

[1] Electrically operated torque vectoring unit (1) with an input gear stage (2), which has an output shaft (17) and two planetary gear stages (3, 4) as superposition gears (16), and the two planetary gear stages (3, 4) are coupled to the input gear stage (2) in a torque-transmitting manner, wherein the input gear stage (2) is driven by an electric motor (7), wherein the output shaft (17) of the input gear stage (2) has two spaced-apart rolling bearings (8, 9) which support the output shaft (17) to the housing (10) and thus the input gear (18) in a flanking manner, wherein each rolling bearing ring (11, 12, 13, 14) bears at one axial end against its peripheral component and has no bearing at its other axial end against its peripheral component, wherein the bearing of the roller bearing ring designed as the output shaft (17) of the input gear stage (2) Drive sun shaft (26) is floating, characterized bythat the output shaft (17) of the input gear stage (2) has the first sun gear of the first planetary gear stage (3) of the superposition gear (16) formed in one piece as a drive sun shaft. [2] Torque vectoring unit (1) according to claim 1, characterized by that the two planetary gear stages (3, 4) are coupled via a common ring gear (15). [3] Torque vectoring unit (1) according to one of the preceding claims, characterized by that the inner rings (11, 12) each bear on one side against a separate diameter shoulder of the output shaft (17) and have no contact on their axially opposite side. [4] Torque vectoring unit (1) according to one of the preceding claims, characterized by that each outer ring (13, 14) bears on one side against a shoulder of its receptacle in the housing (10), the opposite side of this outer ring (13, 14) having no contact. [5] Torque vectoring unit (1) according to one of the preceding claims, characterized by that the two rolling bearings (8, 9) flank the input gear stage (2) so that the radial forces of the input gear (18) are transmitted axially between the two rolling bearings (8, 9) to the output shaft (17).

Images