DE102021123307B4 - Electric axle drive train - Google Patents

Abstract

The invention relates to an electric axle drive train (1) for an electrically driven motor vehicle (2), comprising an electric machine (3) with a rotor (5) which is rotatably mounted relative to a stator (4) and has a rotor shaft (15), and a gear arrangement (7) which is acted upon by a hydraulic fluid (13), which can be coupled to the rotor (5) of the electric machine (3) in a torque-transmitting manner, and the electric machine (3) and the gear arrangement (7) form a structural unit (6), and the rotor shaft (15) engages axially in a differential gear (70) of the gear arrangement (7), wherein the differential gear (70) has a differential sun gear (71) which is arranged coaxially to the rotor shaft (15) and which is connected to a first output shaft (72) of the electric axle drive train (1) in a torque-transmitting manner, wherein a rotor disk (8) is operatively connected to the rotor shaft (15) in a torque-transmitting manner and is designed in such a way that that the rotor disk (8) and the differential sun gear (71) form a labyrinth seal (11) with a sealing gap (12) which separates a wet space (19) of the differential gear (70) acted upon by hydraulic fluid (13) from a dry space (14) of the electrical machine (3), and the rotor disk (8) is configured such that when the rotor shaft (15) and/or the differential sun gear (71) rotate in the sealing gap (12), a centrifugal force-induced spinning effect oriented in the direction of the wet space (19) is brought about on the hydraulic fluid (13).

Description

The present invention relates to an electric axle drive train for an electrically driven motor vehicle, comprising an electric machine with a rotor rotatably mounted relative to a stator with a rotor shaft, and a gear arrangement acted upon by a hydraulic fluid, which can be coupled to the rotor of the electric machine in a torque-transmitting manner and the electric machine and the gear arrangement form a structural unit, and the rotor shaft engages axially in a differential gear of the gear arrangement, wherein the differential gear has a differential sun gear arranged coaxially to the rotor shaft, which is connected to a first output shaft of the electric axle drive train in a torque-transmitting manner.

Electric motors are increasingly being used to power motor vehicles in order to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the suitability of electric drives for everyday use and to offer users the same driving comfort they are used to.

A detailed description of an electric drive can be found in an article in the magazine ATZ 113th year, 05/2011, pages 360-365 by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold with the title: Highly integrated and flexible electric drive unit for electric vehicles, which probably represents the closest state of the art. This article describes a drive unit for an axle of a vehicle, which includes an electric motor that is arranged concentrically and coaxially to a bevel gear differential, with a switchable 2-speed planetary gear set arranged in the power train between the electric motor and the bevel gear differential, which is also positioned coaxially to the electric motor or the bevel gear differential or spur gear differential. The drive unit is very compact and, thanks to the switchable 2-speed planetary gear set, allows a good compromise between climbing ability, acceleration and energy consumption. Such drive units are also referred to as e-axles or electrically operated drive trains.

As a rule, with such electric axles it is necessary to seal the gear chamber, which is supplied with hydraulic fluid, from the air gap, which is designed as a dry space, between the stator and rotor of the electric machine of the electric axle. Due to the comparatively high number of revolutions of the rotor, this sealing point places high demands on a low-friction design of the corresponding seal, which cannot always be met by sliding seals with low contact pressure.

The EN 10 2013 225 519 A1 shows a planetary gear, in particular for a motor vehicle, with an input shaft forming a sun gear, with a planet carrier which carries a first set of planet gears and a second set of planet gears, with a first ring gear which is assigned to the first set of planet gears, with a second ring gear which is assigned to the second set of planet gears, with a first locking means by means of which the first ring gear can be locked, and with a second locking means by means of which the second ring gear can be locked.

The DE 91 15 647 U1 shows a drive motor, the shaft of which is supported at the drive-side end by means of a bearing and is hollow, wherein a pinion provided with an axle shoulder is connected to the shaft in a rotationally fixed manner by means of the axle shoulder inserted into the hollow shaft end, wherein the bearing is arranged on the side of the pinion facing away from the hollow shaft end on a shaft stub connected to the latter and is inserted into the bearing bore of a bearing shield connected to the motor housing via an end shield.

The US 2019/ 0 337 505 A1 shows an electric drive for powering a motor vehicle.

The EN 10 2011 076 527 A1 shows an electric drive for a vehicle with an electric machine which is coupled to an output via an intermediate gear, wherein a drive housing is provided which accommodates the electric machine and the intermediate gear and in which a common, passively operated oil circuit is provided for lubrication and/or cooling.

It is therefore the object of the invention to provide an electric axle drive train for an electrically driven motor vehicle that reduces or completely eliminates the problems known from the prior art and enables particularly low-friction operation.

This object is achieved by an electric axle drive train for an electrically driven motor vehicle, comprising an electric machine, with a rotor rotatably mounted relative to a stator with a rotor shaft, and a gear arrangement acted upon by a hydraulic fluid, which can be coupled to the rotor of the electric machine in a torque-transmitting manner and the electric machine and the gear arrangement form a structural unit, and the rotor shaft engages axially in a differential gear of the gear arrangement, wherein the differential gear has a has a differential sun gear arranged coaxially to the rotor shaft, which is connected to a first output shaft of the electric axle drive train in a torque-transmitting manner, wherein a rotor disk is operatively connected to the rotor shaft in a torque-transmitting manner and is designed such that the rotor disk and the differential sun gear form a labyrinth seal with a sealing gap, which separates a wet space of the differential gear acted upon by hydraulic fluid from a dry space of the electric machine, and the rotor disk is configured such that when the rotor shaft and/or the differential sun gear rotates in the sealing gap, a centrifugal force-induced centrifugal effect oriented in the direction of the wet space is caused on the hydraulic fluid.

Advantageous embodiments are specified in the subclaims.

This provides the advantage that a contactless seal with a high sealing effect can be provided from a combination of centrifugal disc (rotor disc) and labyrinth seal.

First, the individual elements of the claimed subject matter of the invention are explained in the order in which they appear in the set of claims, and particularly preferred embodiments of the subject matter of the invention are described below.

An electric axle drive train of a motor vehicle can comprise at least one electric machine and at least one transmission arrangement, wherein the electric machine and the transmission arrangement preferably each form a structural unit. The electric axle drive train preferably has a first electric machine with a first transmission arrangement and a second electric machine with a second transmission arrangement.

In particular, it can be provided that an electric machine and a transmission arrangement are arranged in a common drive train housing. Alternatively, it would of course also be possible for the electric machine to have a motor housing and the transmission to have a transmission housing, with the structural unit then being able to be achieved by fixing the transmission arrangement relative to the electric machine. This structural unit is sometimes also referred to as an electric axle.

The electric machines and the gear arrangements can also be accommodated individually or together in a drive train housing. The drive train housing is provided at least to accommodate the electric machine and the gear arrangement. The drive train housing is preferably formed from a metallic material, particularly preferably from aluminum, gray cast iron or cast steel, in particular by means of a primary forming process such as casting or die casting. In principle, however, it would also be possible to form the drive train housing from a plastic.

The drive train housing can particularly preferably have a pot-like basic shape, so that the electric machine and the transmission can be inserted into the drive train housing via the open front side of the housing.

An electrical machine is used to convert electrical energy into mechanical energy and/or vice versa, and usually comprises a stationary part known as a stator, stand or armature, and a part known as a rotor or runner which is arranged to be movable relative to the stationary part.

In connection with the invention, the electrical machine can be designed as a radial or axial flux machine. In order to form an axle drive train that is particularly compact in terms of axial flow, axial flux machines are preferred.

The electric machine is intended in particular for use within an electrically operated drive train of a motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds of greater than 50 km/h, preferably greater than 80 km/h and in particular greater than 100 km/h can be achieved. The electric motor particularly preferably has an output of greater than 30 kW, preferably greater than 50 kW and in particular greater than 70 kW. It is further preferred that the electric machine provides speeds of greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, very particularly preferably greater than 12,500 rpm.

The transmission arrangement of the electric axle drive train can be coupled in particular to the electric machine, which is designed to generate a drive torque for the motor vehicle. The drive torque is particularly preferably a main drive torque, so that the motor vehicle is driven exclusively by the drive torque.

The gear arrangement can include a differential gear. A differential gear is a planetary gear with one input and two outputs. It usually has the function of driving two to drive the wheels of a motor vehicle in such a way that they can rotate at different speeds in curves, but with the same propulsive force.

According to an advantageous embodiment of the invention, the rotor disk can be designed in the shape of a truncated cone. The advantage of this embodiment is that this results in a particularly long sealing gap and the truncated cone design of the disks enables a high degree of dimensional stability to be achieved, particularly at high speeds. Furthermore, the truncated cone design of the rotor disk allows an axial force component caused by centrifugal force to be applied to the hydraulic fluid, so that the hydraulic fluid is always guided in the direction of the wet space when it comes into contact with the rotor disk and/or in the sealing gap, which further improves the sealing effect.

According to a further preferred development of the invention, it can also be provided that the rotor disk is formed from a metallic sheet, whereby the disk can be manufactured particularly cost-effectively.

Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the rotor disk is formed by means of a deep-drawing process, which also contributes to a cost-effective production of the disk.

According to another particularly preferred embodiment of the invention, it can be provided that the rotor disk is arranged in a rotationally fixed manner on a sun gear of a planetary gear that is connected to the rotor shaft in a torque-transmitting manner. This also makes it possible to achieve the effect that the rotor disk can be manufactured and assembled in a cost-effective manner. Furthermore, the invention can also be further developed in such a way that the rotor disk is arranged in a rotationally fixed manner on a sun gear of a planetary gear that is connected to the rotor shaft in a torque-transmitting manner.

In a likewise preferred embodiment variant of the invention, it can also be provided that the differential sun gear has, at its distal end directed towards the rotor shaft, a first frustoconical ring-shaped section with a first angle between a surface line and a frustoconical axis of the first frustoconical ring-shaped section and a second frustoconical ring-shaped section adjoining the first section with a second angle between a surface line and a frustoconical axis of the second frustoconical ring-shaped section, wherein the first angle is larger than the second angle. This can further improve the labyrinth seal.

It may also be advantageous to further develop the invention in such a way that the rotor disk has a first frustoconical ring-shaped section with a first angle between a surface line and a frustoconical axis of the first frustoconical ring-shaped section and a second frustoconical ring-shaped section adjoining the first section with a second angle between a surface line and a frustoconical axis of the second frustoconical ring-shaped section, wherein the first angle is greater than the second angle, which can also contribute to a further optimization of the labyrinth seal.

According to a further preferred embodiment of the subject matter of the invention, it can be provided that the differential sun gear has a contour adapted to the rotor disk, so that the sealing gap has a substantially constant gap height over the extent of the sealing gap. This can also improve the sealing effect of the labyrinth seal.

Finally, the invention can also be advantageously designed such that the rotor shaft and/or the sun gear of the planetary gear have/have a conical contour opening towards the differential sun gear on their respective distal end directed towards the differential sun gear on their inner surface. The advantage that this results in is in particular that lubrication is applied. In the embodiment shown, the hydraulic fluid 13 is a gear oil. The gear arrangement 7 can be coupled to the rotor 5 of the electric machine 3 in a torque-transmitting manner.

The rotor shaft 15 engages axially in a differential gear 70 of the gear arrangement 7, which is particularly good in the 3 can be recognized.

In the embodiment of the 3 the rotor shaft 15 comprises a sun gear 20 which engages in the planetary gear 21. The sun gear 20 can be formed or connected to the rotor shaft 15 in one piece or in multiple pieces. The sun gear 20 is therefore a part of the rotor shaft 15 in the sense of this application.

The differential gear 70 has a differential sun gear 71 arranged coaxially to the rotor shaft 15, which is connected in a torque-transmitting manner to a first output shaft 72 of the electric axle drive train 1, which is designed as a hollow shaft.

As can be seen from the detailed view of the 4 As can be seen, a rotor disk 8 is operatively connected to the rotor shaft 15 or the sun gear 20 in a torque-transmitting manner and is designed such that the rotor disk 8 and the differential sun gear 71 form a labyrinth seal 11 with a sealing gap 12 which separates a wet space 19 of the differential gear 70, which is acted upon by hydraulic fluid 13, from a dry space 14 of the electric machine 3. The rotor disk 8 is configured such that when the rotor shaft 15 and/or the differential sun gear 71 rotates in the sealing gap 12, a centrifugal force-induced centrifugal effect oriented in the direction of the wet space 19 is brought about on the hydraulic fluid 13.

This is shown in the detailed view in the 5 explained further. Firstly, it can be seen that the rotor disk 8 is formed in the shape of a truncated cone.

In the embodiment shown, the rotor disk 8 is formed from a metal sheet using a deep-drawing process. The rotor disk 8 is fixed to the rotor shaft 15 or the sun gear 20 in a rotationally fixed manner using a press fit. For this purpose, the rotor disk 8 has a substantially axially extending ring section 9 which rests against the rotor shaft 15 or the sun gear 20.

The differential sun gear 71 has, at its distal end 26 directed toward the rotor shaft 15, a first frustoconical ring-shaped section 22 with a first angle 23 between a surface line and a frustoconical axis of the first frustoconical ring-shaped section 22 and a second frustoconical ring-shaped section 24 adjoining the first section 22 with a second angle 25 between a surface line and a frustoconical axis of the second frustoconical ring-shaped section 24. It can be clearly seen that the first angle 23 is larger than the second angle 25.

Analogously, the rotor disk 8 has a first frustoconical ring-shaped section 27 with a first angle 28 between a surface line and a frustoconical axis of the first frustoconical ring-shaped section 27 and a second frustoconical ring-shaped section 29 adjoining the first section 27 with a second angle 30 between a surface line and a frustoconical axis of the second frustoconical ring-shaped section 29, wherein here too the first angle 28 is greater than the second angle 30.

The differential sun gear 71 thus has a contour adapted to the rotor disk 8, so that the sealing gap 12 has a substantially constant gap height over the extent of the sealing gap 12.

The rotor shaft 15 and/or the sun gear 20 of the planetary gear 21 also has, on its respective distal end 31 directed toward the differential sun gear 71, a conical contour 33 on its inner surface 32 that opens toward the differential sun gear 71, so that during operation of the axle drive train 1, an axial force is applied to the hydraulic fluid 13 by centrifugal force should it enter the dry space 14. This assists in leading the hydraulic fluid 13 out of the dry space 14.

The invention is not limited to the embodiments shown in the figures. The above description is therefore not to be regarded as restrictive, but as explanatory. The following patent claims are to be understood in such a way that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the patent claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a ranking.

List of reference symbols

1

Axle drive train

2

Motor vehicle

3

electric machine

4

stator

5

rotor

6

structural unit

7

Gear arrangement

8th

Rotor disc

9

Ring section

11

Labyrinth seal

12

Sealing gap

13

Hydraulic fluid

14

Drying room

15

Rotor shaft

18

roller bearing

19

Wet room

20

Sun gear

21

Planetary gear

22

Section

23

angle

24

Section

25

angle

26

End

27

Section

28

angle

29

Section

30

angle

31

End

32

Shell surface

33

Contour

70

Differential gear

71

first differential sun gear

72

Output shaft

73

second differential sun gear

Claims (10)

Electric axle drive train (1) for an electrically driven motor vehicle (2), comprising an electric machine (3) with a rotor (5) which is rotatably mounted relative to a stator (4) and has a rotor shaft (15), and a gear arrangement (7) which is acted upon by a hydraulic fluid (13), which can be coupled to the rotor (5) of the electric machine (3) in a torque-transmitting manner, and the electric machine (3) and the gear arrangement (7) form a structural unit (6), and the rotor shaft (15) engages axially in a differential gear (70) of the gear arrangement (7), wherein the differential gear (70) has a differential sun gear (71) which is arranged coaxially to the rotor shaft (15) and which is connected to a first output shaft (72) of the electric axle drive train (1) in a torque-transmitting manner, characterized in that a rotor disk (8) is operatively connected to the rotor shaft (15) in a torque-transmitting manner and is designed in such a way is that the rotor disk (8) and the differential sun gear (71) form a labyrinth seal (11) with a sealing gap (12) which separates a wet space (19) of the differential gear (70) acted upon by hydraulic fluid (13) from a dry space (14) of the electric machine (3), and the rotor disk (8) is configured such that when the rotor shaft (15) and/or the differential sun gear (71) rotate in the sealing gap (12), a centrifugal force-induced spinning effect oriented in the direction of the wet space (19) is brought about on the hydraulic fluid (13). Electric axle drive train (1) according to Claim 1 , characterized in that the rotor disk (8) is designed in the shape of a truncated cone. Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor disk (8) is formed from a metallic sheet Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor disk (8) is formed by means of a deep-drawing process. Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor disk (8) is fixed to the rotor shaft (15) by means of a press fit. Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor disk (8) is arranged in a rotationally fixed manner on a sun gear (20) of a planetary gear (21) which is connected to the rotor shaft (15) in a torque-transmitting manner. Electric axle drive train (1) according to one of the preceding claims, characterized in that the differential sun gear (71) has, at its distal end (26) directed towards the rotor shaft (15), a first frustoconical ring-shaped section (22) with a first angle (23) between a surface line and a frustoconical axis of the first frustoconical ring-shaped section (22) and a second frustoconical ring-shaped section (24) adjoining the first section (22) with a second angle (25) between a surface line and a frustoconical axis of the second frustoconical ring-shaped section (24), wherein the first angle (23) is greater than the second angle (25). Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor disk (8) has a first frustoconical ring-shaped section (27) with a first angle (28) between a surface line and a frustoconical axis of the first frustoconical ring-shaped section (27) and a second frustoconical ring-shaped section (29) adjoining the first section (27) with a second angle (30) between a surface line and a frustoconical axis of the second frustoconical ring-shaped section (29), wherein the first angle (28) is greater than the second angle (30). Electric axle drive train (1) according to one of the preceding claims, characterized in that the differential sun gear (71) has a contour adapted to the rotor disk (8), so that the sealing gap (12) has a substantially constant gap height over the extent of the sealing gap (12). Electric axle drive train (1) according to one of the preceding claims, characterized in that the rotor shaft (15) and/or the sun gear (20) of the planetary gear (21) have/has, at their respective distal end (31) directed towards the differential sun gear (71), a conical contour (33) opening towards the differential sun gear (71) on their inner circumferential surface (32).

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