WO2021115690A1

WO2021115690A1 - Electric drive

Info

Publication number: WO2021115690A1
Application number: PCT/EP2020/081118
Authority: WO
Inventors: Tobias SCHLITTENBAUER; Timo Kiekbusch
Original assignee: Robert Bosch Gmbh
Priority date: 2019-12-10
Filing date: 2020-11-05
Publication date: 2021-06-17
Also published as: DE102019219218A1

Abstract

The invention relates to an electric drive (10), comprising an electric machine (14), a rotor shaft (18) and a transmission (16), which comprises a transmission input shaft (34). The transmission input shaft is connected to the rotor shaft (18) by means of a shaft-shaft connection (62). The rotor shaft (18) is supported in a first bearing (20), and the transmission input shaft (34) coupled to the rotor shaft by means of the shaft-shaft connection (62) is held in a second bearing (30) as a fixed bearing and in a third bearing (32) as a floating bearing. The invention further relates to the use of the electric drive (10) in the context of an electric axle module (12) of an electrically driven vehicle.

Description

Electric drive

Technical area

The invention relates to an electric drive with an electric machine with a rotor shaft and a transmission which comprises a transmission input shaft which is connected to the rotor shaft via a shaft-shaft connection. The invention also relates to the use of the electric drive in an e-axle module of an electrically powered vehicle.

State of the art

DE 102017010371 A1 discloses a geared motor which comprises a rotor shaft. A first floating bearing and a fixed bearing are provided to support the rotor shaft. One end of the rotor shaft, which goes beyond the floating bearing, is connected to one end of an adapter shaft via a spline, with another end of the adapter shaft being non-rotatably connected to a sun gear of a planetary gear. According to this solution, a second floating bearing is provided for the adapter shaft.

DE 102016223 694 A1 describes a motor vehicle transmission device with a transmission and an electrical machine, the rotor of which is connected to the transmission via a transmission input shaft. A one-piece shaft is provided which forms both the rotor shaft of the electrical machine and the transmission input shaft of the transmission. To support the one-piece shaft, three roller bearings are provided, with a first gear on the one-piece shaft between a first roller bearing and a second roller bearing is arranged, while a rotor packet is arranged on the one-piece shaft between the second roller bearing and a third roller bearing.

DE 102012 205 707 A1 discloses a transmission. The transmission has a drive shaft which forms a rotor shaft of an electrical machine. A drive pinion designed as a worm and a rotor of the electrical machine are arranged on the drive shaft. A floating bearing is provided between the drive pinion and the rotor. To support the drive shaft, two further bearings are provided, each of which is arranged at one end of the drive shaft. The drive pinion is located between the floating bearing and one of the two bearings on the drive shaft, while the rotor is arranged between the floating bearing and the other of the two bearings on the drive shaft.

Presentation of the invention

According to the invention, an electric drive is proposed with an electric machine with a rotor shaft and a transmission which comprises a transmission input shaft which is connected to the rotor shaft via a shaft-shaft connection. The rotor shaft is mounted in a first bearing and the transmission input shaft coupled to it via the shaft-shaft connection is received in a second bearing as a fixed bearing and a third bearing as a floating bearing.

The storage arrangement proposed according to the invention for the electric drive is in particular independent of different temperature expansions, in particular in comparison to an adjusted storage.

In a further development of the solution proposed according to the invention, the shaft-shaft connection comprises a form-fitting connection, for example a spline. Advantageously, a positive connection, for example a spline or a wedge / multi-wedge connection, can be installed very easily and represents a robust torque transmission option. The shaft-shaft connection comprises a radial support surface on which the rotor shaft is supported on the transmission input shaft. With this solution, a considerable improvement in the smoothness of the running of the rotor shaft and transmission input shaft coupled to one another via the shaft-shaft connection and thus of the electrical drive proposed according to the invention can be achieved in an advantageous manner.

In an advantageous further development of the solution proposed according to the invention, the radial support surface is represented by a lateral surface of a shaft journal which is formed on the transmission input shaft. As a result, a radial support surface for the rotor shaft that is particularly simple in terms of production technology can be achieved in an advantageous manner.

In an advantageous further development of the electrical drive proposed according to the invention, the shaft-shaft connection made up of the rotor shaft and the transmission input shaft includes an axial support on which the rotor shaft is fixed in the axial direction on the transmission input shaft. Since this is mounted in a second and a third bearing, the bearing designed as a fixed bearing is able to absorb the axial load.

In addition, the shaft-shaft connection is designed in such a way that a positive connection comprises, for example, a spline or a wedge / multi-wedge connection in a clearance fit and a radial support surface in a minimal fit. The shaft-shaft connection is located between the rotor shaft and the transmission input shaft. The minimum clearance fit is designed in such a way that, taking into account the tolerance chain of the entire system, a minimum clearance of 1 pm is maintained. Advantageously, the play on the radial support surface is made as small as possible and the play within the spline is selected accordingly, so that the components connected to one another by the shaft-shaft connection do not become tensioned.

In a further development of the solution proposed according to the invention, the splines on the electric drive as part of the shaft-shaft connection are supplied with lubricant by grease lubrication or oil lubrication in order to reduce the mechanical loads and thus increase the service life of the electric drive. In the case of the electric drive proposed according to the invention, the first bearing of the rotor shaft of the electric machine can also be preloaded in the axial direction via at least one spring element. In the case of the spring element, a spring element that can be fixed to the gear housing in the form of a disk spring or a disk spring assembly can be used in an advantageous manner.

The present invention also relates to the use of the electric drive in an e-axle module of an electrically powered vehicle.

Advantages of the invention

The solution proposed according to the invention can advantageously save a fourth bearing on an electric drive. As a result, mechanical wear can be reduced, particularly on the spline, as part of the shaft-shaft connection. In addition, the 3-bearing concept proposed according to the invention leads to a reduction in the tolerance-related stresses in the shaft-shaft connection between the rotor shaft on the one hand and the transmission input shaft on the other.

By designing the clearance fit on the spline and providing the radial support surface, self-centering of the shaft-shaft connection between the rotor shaft and the transmission input shaft can be ensured with a low torque.

The solution proposed according to the invention advantageously enables the shaft-shaft connection to be lubricated, be it through a separate supply of a lubricating grease or a transport of lubricating medium from the transmission to the shaft-shaft connection.

As a result, the service life of the electric drive proposed according to the invention can be extended considerably. Due to the weight savings that can be achieved, an increase in the power density can be achieved, which is achieved in particular by the functional separation of the bearings with regard to an axial and Radial force absorption is achieved. A possible design of the floating bearing as a roller bearing, roller sleeve or roller ring can significantly increase the load-bearing capacity of the bearing.

The 3-bearing concept proposed according to the invention for a fixed-loose bearing of the shaft assembly made up of the input shaft and rotor shaft enables a considerable improvement in smoothness to run compared to, for example, an employed bearing, regardless of different temperature-related expansions, for example between shaft and housing. A reduction in the power loss can be achieved due to a lack of preload, which leads to a more efficient drive. In the case of the electrical drive proposed according to the invention, axial forces are only transmitted via a bearing, which enables a simpler housing design. Furthermore, a considerable simplification of the assembly can be achieved.

Brief description of the drawings

Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

It shows:

FIG. 1 shows a longitudinal section through the electric drive proposed according to the invention.

Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, a repeated description of these elements being dispensed with in individual cases. The figures represent the subject matter of the invention only schematically.

The illustration according to FIG. 1 shows a longitudinal section through an electric drive 10, which is not described here as an e-axis module 12 shown electric vehicle is used. The electrically driven vehicle can be, for example, a passenger car, a utility vehicle or a truck.

According to the sectional illustration in FIG. 1, the electric drive 10 is provided by an electric machine 14 and a transmission 16 coupled to it. The electrical machine 14 comprises a rotor shaft 18. The rotor, which is schematically indicated here in block form and rotates within a housing 28, is received on this. The rotor shaft 18 is received at one end in a first bearing 20. The first bearing 20 is, for example, a roller bearing with an inner ring 22 and an outer ring 24 surrounding it. Between the inner ring 22 and the outer ring 24, rolling elements 26 are arranged, which in this case are designed as balls. Instead of this type of bearing as the first bearing 20, cylindrical roller bearings, tapered roller bearings, deep groove ball bearings or the like could also be used as the first bearing 20. In FIG. 1 it is indicated schematically that the first bearing 20 is arranged in the housing 28 of the electrical machine 14. The first bearing 20 can, for example, be preloaded in the axial direction via a spring element indicated here, for example a plate spring 74. Instead of a spring element in the form of a disk spring 74, a disk spring pack or a corrugated spring can also be used in order to preload the first bearing 20 in the axial direction.

As can also be seen from the illustration according to FIG. 1, the rotor shaft 18 is provided with a cavity 52 into which a shaft journal 76 of a transmission input shaft 34 is inserted.

A shaft-shaft connection 62 between the rotor shaft 18 on the one hand and the transmission input shaft 34 on the other hand is provided by a spline 48.

The spline 48 encompasses torque transmission surfaces 56 extending in the axial direction, parallel to the axis of symmetry 64 of the shaft journal 76 or the transmission input shaft 34. A clearance fit 50 is implemented between these and the inner circumference of the rotor shaft 18 in the area of the cavity 52 of the rotor shaft 18. These allows the greatest possible degree of self-centering within the framework of the shaft-shaft connection 62 between the rotor shaft 18 on the one hand and the transmission input shaft 34 on the other hand.

As can also be seen from FIG. 1, the transmission input shaft 34 has two bearings. On the one hand in a second bearing 30, which is also a roller bearing, which is mounted in the housing 28, and on the other hand in a third bearing 32 which is designed as a floating bearing. An axial movement 66 of the third bearing 32 is indicated by the double arrow 66 shown in FIG. The positions of the second bearing 30 and the third bearing 32 can also be interchanged.

The shaft assembly of the rotor shaft 18 and the transmission input shaft 34, which is supported by the shaft-shaft connection 62 in the first bearing 20, in the second bearing 30 serving as a fixed bearing, and in the third bearing 32 serving as a floating bearing, is connected to one another via the splines 48. FIG. 1 shows that a radial support surface 58 is formed as part of the shaft-shaft connection 62 by the circumferential or lateral surface of the shaft journal 76 of the transmission input shaft 34. FIG. 1 also shows that a shaft collar 78 is implemented on the rotor shaft 18. The shaft collar 78 is located at the end of the rotor shaft 18 opposite the first bearing 20. The shaft collar 78 extends inward in the radial direction and engages, for example, in a circumferential groove or an undercut 44 that is formed on the circumference of the transmission input shaft 34, and fixes the Rotor shaft 18 in the axial direction. In addition, the shaft collar 78 on the end of the rotor shaft 18 opposite the first bearing 20 serves to support it on the inner ring 22 of the second bearing 30, which serves as a fixed bearing, and which thus absorbs the axial forces of the rotor shaft 18. Alternatively, there is the possibility of supporting the rotor shaft 18 on a shaft collar 78 of the transmission input shaft 34.

The second bearing 30, which serves as a fixed bearing for the transmission input shaft 34, is designed, for example, as a ball bearing according to FIG. 1 and comprises an inner ring 22 and an outer ring 24, the outer ring 24 being mounted in the housing 28 of the transmission 16. Similarly, the third bearing 32, which serves as a floating bearing, also includes an inner ring 22 in the illustration according to FIG. 1 and an outer ring 24, the rolling elements 26 of the third bearing 32 being given by cylindrical rollers 27.

FIG. 1 also shows that a pinion 36 is formed on the transmission input shaft 34. The pinion 36 meshes with a gear 40, which in turn is mounted on the circumference of an intermediate shaft 38. The gearwheel 40 is mounted on its seat 42 on the intermediate shaft 38, for example shrunk onto its circumference, connected to it via a shaft-hub connection or joined with a material fit, for example welded. In the area of the seat 42 there is an undercut 44 and a collar 46 of the intermediate shaft 38 on which the gear 40 rests. The intermediate shaft 38 is supported, for example, at a first bearing point 68 and a second bearing point 70 in the housing 28 of the transmission 16 of the electric drive 10. The bearing points 68, 70 of the intermediate shaft 38 can be designed, for example, as roller bearings.

FIG. 1 also shows that a radial shaft sealing ring 54 is arranged on the circumference of the rotor shaft 18 of the electrical machine 14. This has the task of sealing the transmission 16 from the cavity 52 of the electrical machine 14, in which the rotor rotates. The radial shaft sealing ring 54 indicated in FIG. 1 separates the oil volume within the transmission 16 from the dry interior of the electrical machine 14 of the electrical drive 10. As shown in FIG Disk springs 74 can be acted upon in the axial direction, indicated by a setting direction 72 of the first bearing 20 in the sectional illustration according to FIG. 1. In the case of a wet electrical machine 14, a seal is unnecessary.

The shaft-shaft connection 62 between the rotor shaft 18 and the transmission input shaft 34 is designed symmetrically to the axis of symmetry 64. To reduce mechanical wear, either separate grease lubrication can be provided through which grease can be transported to the spline 48. Alternatively, there is the possibility of supplying the spline 48 via a lubricating medium, such as the oil stored in the gearbox 16, for example. The supply of the lubricating medium can take place via a targeted supply, so that a continuous supply of lubricating medium is ensured through the spline 48 and the mechanical wear can be minimized. The electrical machine 14 is sealed against the lubricating medium by a radial shaft sealing ring 54.

The positive connection in the form of the spline 48 can also be implemented without lubrication.

Instead of the arrangement shown in Figure 1, in which the shaft journal 76 is formed at one end of the transmission input shaft 34 and protrudes into the cavity 52 of the rotor shaft 18, a reverse design can also take place, in which the shaft journal 76 is part of the rotor shaft 18 and this protrudes into a cavity which is formed in the interior of the transmission input shaft 34.

Both versions are possible. With the support of the shaft assembly of the transmission input shaft 34 and rotor shaft 18 shown in longitudinal section in FIG. 1, a 3-bearing concept for electrical drives 10 is proposed, whereby tolerance-related tensions within the shaft-shaft connection 62 can be reduced. The design of the clearance fit 50 on the spline 48 and the radial support surface 58 designed with a minimum clearance fit ensure self-centering of the transmission input shaft 34 and the rotor shaft 18 coupled to it at low torque, so that even at high speeds, the electrical machine 14 and the motor run smoothly Transmission input shaft 34 can be shown. In the solution proposed according to the invention in the form of the electric drive 10, there is a considerably improved accessibility for lubricant in relation to the accessibility of the spline 48 and the radial support surface 58 with minimal clearance fit, so that the service life of the electric drive 10 shown in longitudinal section in FIG. 1 is considerably improved can be. Due to the weight saving associated with the proposed solution, an increase in the power density can be achieved.

It should also be emphasized that the 3-bearing concept proposed according to the invention, consisting of the first bearing 20, the second bearing 30 serving as a fixed bearing and the third bearing 32 serving as a floating bearing, is able to compensate significantly better for temperature-related expansions compared to an adjusted bearing . Due to the lack of bias, the power loss of the electric drive 10 proposed according to the invention can be reduced, so that its efficiency is increased. Occurring Axial forces are only transmitted via one bearing, that is to say the second bearing 30, which serves as a fixed bearing, as a result of which the design of the housing 28 can be considerably simplified. The invention is not restricted to the exemplary embodiments described here and the aspects emphasized therein. Rather, a large number of modifications are possible within the range specified by the claims, which are within the scope of expert action.

Claims

Expectations

1. Electric drive (10) with an electric machine (14) with a rotor shaft (18) and a gear (16) which comprises a gear input shaft (34) which is connected to the rotor shaft (62) via a shaft-shaft connection (62). 18) is connected, characterized in that the rotor shaft (18) is mounted in a first bearing (20) and the transmission input shaft (34) coupled to this via the shaft-shaft connection (62) in a second bearing (30) as Fixed bearing and in a third bearing (32) is added as a floating bearing.

2. Electric drive (10) according to claim 1, characterized in that the shaft-shaft connection (62) comprises a form-fitting connection, in particular a spline (48) or a wedge or multi-wedge connection.

3. Electric drive (10) according to claims 1 and 2, characterized in that the shaft-shaft connection (62) comprises a radial support surface (58) on which the rotor shaft (18) is supported on the transmission input shaft (34) .

4. Electric drive (10) according to claim 3, characterized in that the radial support surface (58) is formed by a lateral surface of a shaft journal (76) of the transmission input shaft (34).

5. Electric drive (10) according to claims 1 to 4, characterized in that the shaft-shaft connection (62) comprises an axial support (60) on which the rotor shaft (18) in the axial direction on the transmission input shaft (34 ) is set.

6. Electric drive (10) according to claims 1 to 5, characterized in that the rotor shaft (18) has a shaft collar (78) with which it is axially or on a shaft shoulder of the transmission input shaft (34) on the second bearing (30) supports.

7. Electric drive (10) according to claim 2, characterized in that the spline (48) is designed in a clearance fit (50) between the rotor shaft (18) and the transmission input shaft (34).

8. Electric drive (10) according to claim 2, characterized in that the spline (48) has axially extending torque transmission surfaces (56) or convex torque transmission surfaces.

9. Electric drive (10) according to claim 2, characterized in that the positive connection in the form of the spline (48) has a grease lubrication or an oil lubrication.

10. Electric drive (10) according to claims 1 to 9, characterized in that the first bearing (20) of the rotor shaft (18) of the electrical machine (14) is preloaded in the axial direction via at least one spring element (74).

11. Electric drive (10) according to claims 1 to 9, characterized in that the first bearing (20) of the rotor shaft (18) is designed as an employed bearing.

12. Use of the electric drive (10) in an e-axle module (12) of an electrically powered vehicle.