DE102021000484A1 - Vehicle transmission for an electrically driven vehicle - Google Patents

Abstract

The invention relates to a vehicle transmission (5) for an electrically driven vehicle, having at least one switchable spur gear stage (20), which is formed by at least one fixed wheel (22, 23) and at least one idler wheel (24, 25), the idler wheel (24, 25) is mounted on a transmission shaft (6) and a plain bearing bush (30) made of plastic is provided for the mounting of the idler wheel (24, 25), which extends essentially completely over an axial width (26) of the idler wheel (24, 25), bearing play being provided between a sliding surface (32) of the plain bearing bush (30) and the transmission shaft (6) and the sliding surface (32) having transverse lubrication grooves (34).

Description

The invention relates to a vehicle transmission for an electrically driven vehicle.

Transmissions of high-speed electrical machines pose challenges for the bearings of idler gears due to the high differential speeds and centrifugal forces that occur.

Planetary gears for wind turbines to generate electricity are, for example, from the DE 102 60 132 AI known. Usually in such planetary gears, as is also in the DE 102 60 132 AI is described, roller bearings used as bearing elements for the planetary gears. However, the prior art also describes plain bearings as bearing elements, for example the EP 1 544 504 A2 or the AT 509 624 A1 . Plain bearing bushes are usually used as plain bearings, which are shrunk onto the axle or pressed into the planet wheel. Replacing such plain bearings in the event of maintenance or in the event of wear is complex and therefore expensive.

the WO 2019/178630 A1 discloses a wind turbine gearbox, in particular a planetary gearbox, with at least one gear wheel which is mounted on an axle, with a sliding surface being arranged between the gear wheel and the axle or between the axle and an axle mount. The sliding surface is arranged on at least one layer of hardfacing material made from a plain bearing material. The overlay welded sliding layer is intended to simplify maintenance of the plain bearing in that the plain bearing becomes accessible by removing the axle.

An object of the invention is to create a vehicle transmission for an electrically driven vehicle with a longer service life.

The aforementioned object is achieved with the features of the independent claim.

Favorable configurations and advantages of the invention result from the further claims, the description and the drawing.

According to one aspect of the invention, a vehicle transmission for an electrically driven vehicle is proposed, with at least one shiftable spur gear stage, which is formed by at least one fixed wheel and at least one idler wheel, with the idler wheel being mounted on a transmission shaft and one for mounting the idler wheel Plain bearing bush made of plastic is provided, which extends substantially completely over an axial width of the loose wheel. A bearing clearance is provided between a sliding surface of the plain bearing bush and the transmission shaft. The sliding surface has transverse lubrication grooves.

By using a plain bearing bush made of plastic, in particular made of a high-performance plastic, an improved service life of the vehicle transmission can be advantageously achieved.

A normal plain bearing has a bush that is located between two friction partners. There are always two friction surfaces that need to be lubricated. The gliding process is divided into two areas.

The plastic bushing can be arranged in one of the friction partners. The sliding bearing bush can advantageously be integrated into the at least one loose wheel. This reduces a friction surface, meaning that only one friction surface then has to be lubricated. In an alternative exemplary embodiment, however, the plain bearing bush can also be arranged on the transmission shaft.

The bearings of idler gears thus retain their performance even at the relatively high speeds of electrical machines in drive systems of electrically powered vehicles. Because cross-lubrication grooves are provided in the sliding surface of the plain bearing bush, permanent lubrication of the sliding surface can be achieved. A possible total failure of the vehicle transmission due to the otherwise threatening tearing of the hydrodynamic oil lubricating film due to the high temperatures of the oil used for lubrication can thus be avoided.

With the plain bearing made of a high-performance plastic, tearing off the oil lubricating film is not critical, since the plastic has emergency running properties even without an oil lubricating film.

As is usual in the prior art, the bearing play can typically be between 50 μm and 100 μm.

The early degradation of commonly used needle bearings due to the high differential speeds and centrifugal forces in the vehicle transmission can be avoided with the use of plain bearing bushes made of plastic.

According to an advantageous embodiment of the vehicle transmission, the plain bearing bush can be formed from a polyamideimide, in particular from an amorphous, thermoplastically processable polyamideimide.

Such a polyamideimide, abbreviated PAI, is known under the brand name Torion from Solvay SA. Torion is an amorphous, thermoplastically processable polyimide that obtains its thermoplastic properties through the incorporation of aromatic amide groups.

A plain bearing bush made of polyamide-imide has sufficient emergency running properties even if the lubricating oil film breaks off, so that the vehicle transmission can continue to be operated at least for a limited time.

According to an advantageous embodiment of the vehicle transmission, the transverse lubricating grooves can be arranged to run obliquely to an axis of rotation of the loose wheel. In this way, a reliable supply of lubricating oil to the sliding surface of the plain bearing bush can be achieved. The risk of the lubricating oil film tearing off at very high speeds of the vehicle transmission can thus advantageously be avoided.

According to an advantageous embodiment of the vehicle transmission, the plain bearing bush can be formed from at least two axially consecutive sliding rings, which are separated by radially circumferential circumferential lubricating grooves. As a result, a reliable, uniform distribution of the lubricating oil on the sliding surface of the plain bearing bush can be achieved. The risk of the lubricating oil film tearing off at very high speeds of the vehicle transmission can thus advantageously be avoided.

According to an advantageous embodiment of the vehicle transmission, the slide rings can have transverse lubrication grooves offset radially with respect to one another. In this way, it is possible to supply the surface of the slide bearing with lubricating oil over a large area.

The transverse lubricating grooves can advantageously be arranged in such a way that the oil can escape to the right and left from the middle of the raceway of the sliding surface, and the areas to the right and left of the middle can thus be lubricated favorably.

The transverse lubrication grooves can be distributed evenly over the circumference of the sliding surface. Depending on the size of the bore of the plain bearing bush, a number of at least six transverse lubricating grooves, for example, can advantageously be distributed over the circumference.

However, depending on the friction partners and the speeds of the vehicle transmission, the number of transverse lubrication grooves can be adjusted. A depth of the transverse lubricating grooves can also be increased in order to achieve better distribution of the lubricating oil.

According to an advantageous embodiment of the vehicle transmission, the peripheral lubricating grooves can have a groove depth that varies along an inner circumference of the sliding ring bush. In particular, the circumferential lubricating grooves can have a groove depth that varies elliptically along the inner circumference of the sliding ring bush. In this way, an even better distribution of the lubricating oil on the surface of the plain bearing can be achieved. This enables the sliding surface to be oiled evenly.

According to an advantageous embodiment of the vehicle transmission, the plain bearing bush can have two slide rings, which are spaced apart axially and distributed over the axial width of the idler wheel.

According to an advantageous embodiment of the vehicle transmission, the plain bearing bush can be pressed into a bore of the loose wheel. Favorably, the plain bearing bushing can be pressed into the bore of the loose wheel, so that a relative speed only occurs between the plain bearing and the transmission shaft.

In an alternative embodiment, it is also possible for the plastic bushing to be provided as a coating for the bore of the loose wheel. In this way, an advantageous connection of the plastic bushing to the bore of the loose wheel can be achieved.

According to an alternative advantageous embodiment of the vehicle transmission, a bearing clearance can be provided between an inside of the bore and the plain bearing bush. In this way, the plain bearing bush can have bearing play both on the radial inside and on the radial outside and can therefore rotate at a speed relative to the transmission shaft and the idler gear that is not precisely defined.

According to an advantageous embodiment, the vehicle transmission can have two gears, which are formed by two spur gear stages each having a switchable idler wheel, the vehicle transmission being provided for driving wheels of an electric vehicle or a fuel cell vehicle and with at least one idler wheel supporting the plain bearings -Jack has.

In particular, the above-mentioned vehicle transmission can be provided for heavy commercial vehicles with an electric drive or a fuel cell drive. Such a vehicle transmission with loose wheels, which Having plain bearing bushes made of high-performance plastic can have an advantageously increased service life compared to a vehicle transmission according to the prior art with idler wheels usually mounted.

Further advantages result from the following description of the drawing. In the drawings an embodiment of the invention is shown. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into further meaningful combinations.

• 1 eine Draufsicht auf ein Losrad eines Fahrzeuggetriebes nach einem Ausführungsbeispiel der Erfindung;
• 2 eine Abwicklung der Gleitlager-Buchse des Losrads nach 1 entlang ihres Umfangs;
• 3 eine schematische Ansicht eines Antriebssystems eines elektrisch antreibbaren Fahrzeugs mit einem Fahrzeuggetriebe nach einem Ausführungsbeispiel der Erfindung;

show:

• 1 a plan view of a loose wheel of a vehicle transmission according to an embodiment of the invention;
• 2 a development of the plain bearing bush of the loose wheel 1 along its perimeter;
• 3 a schematic view of a drive system of an electrically driven vehicle with a vehicle transmission according to an embodiment of the invention;

In the figures, the same or similar components are denoted by the same reference symbols. The figures only show examples and are not to be understood as limiting.

1 shows a plan view of a loose wheel 24 of a vehicle transmission 5 according to an embodiment of the invention. 2 shows a development of the plain bearing bushing 30 of the loose wheel 24 along its circumference 44.

The idler wheel 24 can be provided for a vehicle transmission 5 of an electrically driven vehicle with at least one switchable spur gear stage 20, which is formed by at least one fixed wheel 22, 23 and at least one idler wheel 24, 25. Such vehicle transmissions are in the 3 until 5 shown as an example.

The loose wheel 24 is on a gear shaft 6 (see 3 ) mounted with an axis of rotation 42. A plain bearing bushing 30 made of plastic, in particular a high-performance plastic, is provided for mounting the idler wheel 24 and extends essentially completely over an axial width 26 of the idler wheel 24 , 25 . A bearing clearance is provided between a sliding surface 32 of the plain bearing bush 30 and the transmission shaft 6 . The sliding surface 32 has transverse lubricating grooves 34 for evenly distributing an oil lubricating film over the sliding surface 32 .

The plain bearing bush 30 is expediently pressed into the bore 40 of the loose wheel 24 in order to achieve a firm connection between the plain bearing bush 30 and the transmission shaft 6 .

In an alternative embodiment, however, a bearing clearance can also be provided between an inside of the bore 40 and the plain bearing bush 30 so that the plain bearing bush 30 could also rotate at a speed relative to the transmission shaft 6 and to the loose wheel 24 .

The plain bearing bushing 30 can advantageously be formed from a polyamideimide, in particular from an amorphous, thermoplastically processable polyamideimide. Such a polyamideimide, abbreviated PAI, is available under the brand name Torion from Solvay S.A. known. Torion is an amorphous, thermoplastically processable polyimide that obtains its thermoplastic properties through the incorporation of aromatic amide groups.

Such a high-performance plastic can advantageously be used for the proposed plain bearing bush 30, since the plain bearing bush 30 has adequate emergency running properties even if the lubricating oil film with the plastic breaks off. In addition, a plain bearing bushing 30 made of Torion has an advantageously long service life.

As in 2 As can be seen, the plain bearing bush 30 is formed from four axially consecutive sliding rings 38 which are separated by radially circumferential circumferential lubrication grooves 36 . The sliding rings 38 have transverse lubrication grooves 34 offset radially with respect to one another.

The transverse lubricating grooves 34 are arranged to run obliquely to the axis of rotation 42 of the loose wheel 24 in order to achieve an even distribution of the lubricating oil film over the sliding surface 32 .

The peripheral lubricating grooves 36 have a groove depth that varies along the inner circumference 44 of the slide ring bushing 30 in order to achieve a good supply of the sliding surface 32 with lubricating oil. In particular, the circumferential lubricating grooves 36 can have a groove depth that varies elliptically along the inner circumference 44 of the sliding ring bushing 30 , which enables even better oil distribution on the sliding surface 32 .

In an alternative exemplary embodiment, the slide bearing bushing 30 can also have only two sliding rings 38 which are distributed over the axial width 26 of the loose wheel 24, 25 at an axial distance from one another. In this case, for example, the sliding rings 38 of the plain bearing bush 30 that are inner in the axial direction 42 can be omitted, so that only one slide ring 38 is arranged in the axial direction 42 on an outside of the plain bearing bush 30 . With this, too, a favorable sliding behavior of the plain bearing bush 30 with sufficient emergency running properties can advantageously be achieved.

3 shows a schematic view of a drive system 1 of an electrically driven vehicle with a vehicle transmission 5 according to an exemplary embodiment of the invention.

The vehicle transmission 5 comprises two gear stages, which are formed by two spur gear stages 20 each having a switchable loose wheel 24, 25. The loose wheels 24, 25 each have the slide bearing bushing 30.

The loose wheels 24, 25, which in the 1 and 2 correspond to the illustrated embodiment are mounted on a transmission shaft 6 with an axis of rotation 42 . A plain bearing bushing 30 made of plastic, in particular a high-performance plastic, is provided for mounting the idler gears 24, 25 and extends essentially completely over an axial width 26 of the idler gear 24, 25. A bearing clearance is provided between a sliding surface 32 of the plain bearing bush 30 and the transmission shaft 6 . The sliding surface 32 has transverse lubricating grooves 34 for evenly distributing an oil lubricating film over the sliding surface 32 .

The vehicle transmission 5 is provided for driving wheels of an electric vehicle or a fuel cell vehicle. In particular, the vehicle transmission 5 can be provided for heavy commercial vehicles with an electric drive or fuel cell drive. Such a vehicle transmission 5 with idler wheels 24, 25, which have plain bearing bushes 30 made of high-performance plastic, can have an advantageously increased service life compared to a vehicle transmission according to the prior art with idler wheels usually mounted.

The drive system 1 in 3 comprises a first electrical machine 2 and a second electrical machine 3, which in turn each comprise a stator 2.1, 2.3 and a rotor 3.2, 3.3. These are preferably mechanically coupled to a transmission housing 4 shown with a dot-dash line. The vehicle transmission 5 is arranged in the transmission housing 4 as a change-speed transmission 5 which comprises the transmission shaft 6 as the input shaft 6 and an intermediate shaft 7 arranged parallel thereto.

The two switchable loose wheels 24 , 25 which mesh with the fixed wheels 22 , 23 of the intermediate shaft 7 are arranged on the transmission shaft 6 . The combinations of idler wheel 24 with fixed wheel 22 and idler wheel 25 with fixed wheel 23 represent the two gear stages of vehicle transmission 5.

The intermediate shaft 7 has a driven gear 8 which drives a differential gear 9 (only indicated schematically) in that the driven gear 8 meshes with a differential gear 10 . The differential gear 9, which can optionally be designed to be locked, then drives over in the representation 3 by the two arrows 11 symbolized cardan shafts wheels of the vehicle.

The vehicle transmission 5 is extremely simple and efficient and includes exactly two switchable spur gear stages 20, which are indicated in the form of two switching elements 12 accordingly. The output gear 8 is arranged in the axial direction of the parallel axis of rotation 42 of the input shaft 6 and an axis of rotation 43 of the intermediate shaft 7 between these two spur gear stages.

Furthermore, the vehicle transmission 5 can drive a power take-off 14 accordingly via a further transmission element, here via a further gear pair 13 indicated, to which, for example, a retarder, which is shown in FIG 3 is not shown, can be connected. All in all, this results in an extraordinarily compact structure, which can be driven by the two electrical machines 2, 3 at different power levels as required. For example, if the electric drive system is used in a commercial vehicle, with different power for different loads of the commercial vehicle. Nevertheless, the individual electrical machines 2, 3 remain compact and are positioned together with the transmission housing 4 in the vehicle, not shown here, and are connected to the vehicle frame of the vehicle via the transmission housing 4. The relatively sensitive electrical components of the electrical drive system, of which only the electrical machines 2, 3 are shown here, are therefore positioned inside the vehicle and are sprung together with the vehicle opposite the driven wheels, so are the components and in particular the lines connecting them to protect against unnecessary movements while driving the vehicle.

Reference List

1

drive system

2

electric machine

2.1

stator

2.2

stator

3

electric machine

3.1

rotor

3.2

rotor

4

gear case

5

gearbox

6

input shaft

7

intermediate shaft

8th

output gear

9

differential gear

10

differential wheel

11

Arrow

12

switching element

13

pair of gears

20

spur gear stage

22

fixed wheel

23

fixed wheel

24

loose wheel

25

loose wheel

26

Broad

30

plain bearing bush

32

sliding surface

34

cross lubrication groove

36

Circumferential lubrication groove

38

sliding ring

40

drilling

42

axis of rotation

43

axis of rotation

44

Scope

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 10260132 [0003]
• EP 1544504 A2 [0003]
• AT 509624 A1 [0003]
• WO 2019/178630 A1 [0004]

Claims (10)

Vehicle transmission (5) for an electrically driven vehicle, with at least one shiftable spur gear stage (20), which is formed by at least one fixed wheel (22, 23) and at least one idler wheel (24, 25), the idler wheel (24, 25 ) is mounted on a transmission shaft (6) and a plain bearing bush (30) made of plastic is provided for mounting the idler wheel (24, 25), which extends essentially completely over an axial width (26) of the idler wheel (24, 25 ) extends, wherein a bearing clearance is provided between a sliding surface (32) of the plain bearing bush (30) and the gear shaft (6) and wherein the sliding surface (32) has transverse lubricating grooves (34). vehicle transmission claim 1 , wherein the plain bearing bush (30) is formed from a polyamideimide, in particular from an amorphous, thermoplastically processable polyamideimide. vehicle transmission claim 1 or 2 , wherein the transverse lubrication grooves (34) are arranged to run obliquely to an axis of rotation (42) of the loose wheel (24, 25). Vehicle transmission according to one of the preceding claims, in which the plain bearing bush (30) is formed from at least two axially consecutive sliding rings (38) which are separated by radially running peripheral lubrication grooves (36). vehicle transmission claim 4 , wherein the slide rings (38) have transverse lubrication grooves (34) offset radially with respect to one another. vehicle transmission claim 3 or 4 , wherein the circumferential lubricating grooves (36) have a groove depth that varies along an inner circumference (44) of the slide ring bush (30), in particular wherein the circumferential lubricating grooves (36) have an elliptically varying depth along the inner circumference (44) of the slide ring bush (30). have groove depth. Vehicle transmission according to one of the preceding claims, wherein the sliding bearing bush (30) has two slip rings (38) which are arranged at a distance from one another and distributed over the axial width (26) of the idler wheel (24, 25). Vehicle transmission according to one of the preceding claims, wherein the plain bearing bush (30) is pressed into a bore (40) of the loose wheel (24, 25). Vehicle transmission according to one of Claims 1 until 7 , wherein a bearing clearance is provided between an inside of the bore (40) and the plain bearing bush (30). Vehicle transmission according to one of the preceding claims, comprising two gear stages, which are formed by two spur gear stages (20), each having a switchable idler wheel (24, 25), the vehicle transmission (5) for driving wheels of an electric vehicle or a fuel cell -Vehicle is provided and wherein at least one loose wheel (24, 25) has the plain bearing bush (30).

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