DE102023111698B4 - Electric axle drive train - Google Patents

Abstract

The invention relates to an electric axle drive train (1) for a motor vehicle (2), with an electric traction machine (3) which is drivingly connected to at least one wheel (4) of the motor vehicle (1) via a transmission (5), wherein the transmission (5) and the electric traction machine (3) are integrated into a hydraulic system (30) at least for cooling and/or lubrication (40), which comprises a pump arrangement (6) which is driven by an electric pump drive (7) which is supplied with electrical power from an electrical on-board network (8) of the motor vehicle (1).
In order to improve the functional safety of the electric axle drive train (1), the electric pump drive (7) is connected to the electric traction machine (3) in an emergency drive manner such that the pump arrangement (6) is driven by the electric traction machine (3) in an emergency operation even if the electric pump drive (7) is not or only insufficiently supplied with electrical power from the electrical on-board network (8) of the motor vehicle (1).

Description

The invention relates to an electric axle drive train for a motor vehicle, with an electric traction machine which is drivingly connected to at least one wheel of the motor vehicle via a transmission, wherein the transmission and the electric traction machine are integrated into a hydraulic system at least for cooling and/or lubrication, which comprises a pump arrangement which is driven by an electric pump drive which is supplied with electric current from an electrical on-board network of the motor vehicle.

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 everyday suitability of electric drives and to offer users the driving comfort they are used to.

A detailed description of an electric drive can be found in an article by 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 This article describes a drive unit for an axle of a vehicle, which comprises an electric motor that is arranged concentrically and coaxially to a bevel gear differential, with a switchable 2-speed planetary gear set being 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 axle drive trains.

From the DE 10 2010 048 837 A1 Such a drive device is known with at least one electric motor and at least one planetary differential that can be driven by a rotor of the electric motor, the planetary differential having at least one planet carrier that is operatively connected to a rotor of the electric motor, first planetary gears and second planetary gears that are rotatably mounted on the planet carrier, and a first sun gear and a second sun gear, each of which is operatively connected to an output shaft of the planetary differential. The first planetary gears mesh with the first sun gear and each of the second planetary gears meshes with the second sun gear and with one of the first planetary gears. Furthermore, the sun gears are arranged coaxially with a rotation axis of the rotor.

From the publications DE 10 2004 061 034 A1 , DE 42 36 124 A1 , DE 10 2016 107 452 B4 , DE 11 2014 001 249 B4 , US 5 769 182 A , DE 10 2010 043 251 A1 and DE 10 2018 206 287 A1 Various oil supply systems with pumps for transmissions have already become known.

When developing the electrical machines and transmissions intended for electric axles, there is a continuing need to increase their power density, so that the cooling required for this, especially of the electrical machines and transmissions, is becoming increasingly important. Due to the necessary cooling performance, hydraulic fluids such as cooling oils have become the standard in most concepts for removing heat from the thermally stressed areas of an electrical machine and/or transmission.

The gears usually provided in the designated electric axles are generally lubricated with a gear oil, which is often also used as cooling oil for the electric machine. In order to reliably deliver the lubricant or cooling oil to the various lubrication or cooling points, it is known to create a corresponding hydraulic fluid circuit in the corresponding electric axles.

It is therefore quite common to create an oil sump within an electric axle to store the amount of oil required for lubrication and cooling, from which the above-mentioned hydraulic fluid circuit is fed with oil.

However, the volume required for an oil sump is limited by two essential factors: firstly, by the available installation space in the electric axle drive train and, secondly, by the maximum permissible filling level in the transmission to achieve the efficiency specifications, in particular by avoiding splashing losses of rotating gear components.

The American disclosure document US 2021/0355941 A1 discloses a fluid pumping system for a vehicle having an internal combustion engine, the fluid pumping system comprising: a housing; an electric motor; a rotatable first input adapted to be driven by the internal combustion engine; a rotatable second input driven by the electric motor and a pump having a pump rotor selectively rotated by the other of the first input and the second input, the fluid pumping system further comprising a one-way clutch restricting rotation of the second input to a single direction of rotation.

The German disclosure document DE 199 23 154 A1 discloses a hydraulic actuation system, in particular for an automated transmission, such as an automatic transmission system, or an automated clutch of a motor vehicle with a drive motor, with pumping means, such as a pump, wherein said pumping means is designed such that it is connected in a power-transmitting manner to a drive motor or a transmission of the vehicle via a mechanical drive and via a freewheel mechanism, wherein the pumping means can additionally be connected in a power-transmitting manner to an electric motor, wherein the motor or the transmission system and the electric motor are connected to the pump via a drive connection, through which the two power sources are added together.

The object of the invention is to improve the functional safety in the operation of an electric axle drive train according to the preamble of patent claim 1.

The object is achieved in an electric axle drive train for a motor vehicle, with an electric traction machine that is connected to at least one wheel of the motor vehicle via a transmission, wherein the transmission and the electric traction machine are integrated into a hydraulic system at least for cooling and/or lubrication, which comprises a pump arrangement that is driven by an electric pump drive that is supplied with electric current from an electrical on-board network of the motor vehicle, in that the electric pump drive is connected to the electric traction machine for emergency drive in such a way that the pump arrangement is driven by the electric traction machine in an emergency operation even if the electric pump drive is not supplied with electric current from the electrical on-board network of the motor vehicle or is only supplied with insufficient electric current. In this way, a minimum cooling of the electric traction machine is ensured when the motor vehicle is in operation. The hydraulic system advantageously comprises a hydraulic circuit with a hydraulic reservoir in which a suitable hydraulic fluid, such as hydraulic oil, is provided, which is suitable both for cooling and for lubrication in the electric drive train components. The electrical system of the motor vehicle is preferably a twelve-volt electrical system. The pump arrangement can provide a sufficient cooling oil volume flow for the electric traction machine during operation of the motor vehicle even if the electrical system fails. In addition, the pump arrangement can regulate the cooling oil volume flow as required during normal operation of the motor vehicle. The electric axle drive train in question is intrinsically safe. In this context, intrinsically safe means that the electric axle drive train is safe in itself without any requirements for its environment. Overheating of the electric traction machine is safely avoided even if the electrical system is not functioning or is only functioning to a limited extent. The pump arrangement can comprise two separate hydraulic pumps, both of which are driven by the electric pump drive. The two pumps can be combined in a single pump, which is also referred to as a tandem pump. The pump arrangement comprises a main pump that pumps hydraulic fluid from a hydraulic fluid reservoir to the electric traction machine. In the electric traction machine, the hydraulic fluid is preferably used for cooling. It is particularly advantageous to arrange a heat exchanger in a hydraulic line that connects the main pump to the electric traction machine. This allows the cooling function to be further improved. The pump arrangement also includes a dry sump pump that pumps hydraulic fluid from a transmission sump into the hydraulic fluid reservoir. Hydraulic fluid collects in the transmission sump when the electric axle drive train is in operation. This is hydraulic fluid that is supplied to the transmission for cooling and/or lubrication. In addition, the hydraulic fluid that is or was used to cool the electric traction machine collects in the transmission sump. The dry sump pump ensures that an undesirable amount of hydraulic fluid does not collect in the transmission sump, which is also known as the dry sump.

A preferred embodiment of the electric axle drive train is characterized in that a pump drive shaft of the pump arrangement is connected to a transmission shaft via an emergency drive connection. The connection between the pump drive shaft and the transmission shaft is made, for example, via an additional drive gear. The pump drive shaft can be connected to an existing gear in the transmission or to an additional gear via this drive gear.

A further preferred embodiment of the electric axle drive train is characterized in that the emergency drive connection is assigned to a transmission output. The emergency drive connection on a wheel side or differential side of the transmission is advantageous because the transmission output has speeds of the same order of magnitude as the typical pump speeds. This means that the required gear ratio is lower and is therefore easier to implement in terms of design and production. A connection via a belt drive or chain drive, possibly also via several gear stages, is also possible. A typical pump speed is up to five thousand revolutions per minute, for example. A typical wheel speed is up to two thousand five hundred revolutions per minute, for example. In comparison, the speed of the electric traction machine is more than ten thousand revolutions per minute, for example.

Another preferred embodiment of the electric axle drive train is characterized in that the emergency drive connection includes a freewheel. The freewheel ensures that the electric pump drive can always increase the volume flow delivered as needed during normal operation. Here, the electric pump drive takes on the entire load. In the event of a fault, the drive comes from the gearbox in order to maintain the emergency cooling oil supply to the electric traction machine. If the speed from the gearbox is sufficient for normal operation, the electric drive of the pump arrangement is advantageously set to a relevant speed without torque. In the event of a fault, i.e. if the electric drive fails or if the power supply fails, the electric pump drive is dragged along by the electric traction machine via the emergency drive connection. If this results in impermissible loads on the control electronics of the electric pump drive, a second freewheel can be inserted between the electric pump drive and the pump arrangement.

Another preferred embodiment of the electric axle drive train is characterized in that the emergency drive connection comprises a summing gear. The summing gear is, for example, a planetary gear or a epicyclic gear. The summing gear makes it possible to increase a basic speed provided by the electric traction machine via the emergency drive connection via the electric pump drive, in particular when the direction of rotation is the same, or to reduce it, in particular when the drives rotate in opposite directions. Here, the two drives always share the load during normal operation of the motor vehicle. In the event of a fault, a sufficient cogging torque of the electric pump drive must be used to ensure that this part of the summing gear maintains a speed of zero.

Another preferred embodiment of the electric axle drive train is characterized in that the emergency drive connection is arranged at one end of the pump drive shaft of the pump arrangement. Depending on the application, the pump drive shaft can be extended accordingly. When using the freewheel as described above, it is preferably arranged at an end of the pump drive shaft of the pump arrangement facing away from the electric pump drive. In the solution with the summing gear described above, this is also arranged at the end of the pump drive shaft, but preferably axially between the pump arrangement with the pump drive shaft and the electric pump drive.

A further preferred embodiment of the electric axle drive train is characterized in that a pressure relief valve is arranged in the hydraulic system upstream of the electric traction machine. The pressure relief valve serves in particular to protect the electric traction machine from high oil pressures at low temperatures. In such cases, at least part of the hydraulic fluid can be discharged via a suitable bypass line before it reaches the electric traction machine.

A further preferred embodiment of the electric axle drive train is characterized in that the main pump and the dry sump pump are combined in a tandem pump. This has proven to be advantageous with regard to the available installation space.

The invention may also relate to a separately tradable component or a separately tradable individual part for an electric axle drive train described above.

The invention also relates to a method for operating an electric axle drive train as described above. The electric axle drive train is also referred to as an e-axle.

The electrical machine serves to convert electrical energy into mechanical energy and/or vice versa, and it generally comprises a stationary part known as a stator, stand or armature and a part known as a rotor or runner which is movable, in particular rotatable, relative to the stationary part.

The electric machine of the axle drive train according to the invention is preferably designed as an axial flux machine. The magnetic flux in an electric axial flux machine (AFM) is directed axially in the air gap between the stator and rotor to a direction of rotation of the rotor of the axial flux machine. There are different types of axial flux machines. A known type is a so-called I-arrangement, in which the rotor is arranged axially next to a stator or between two stators.

Another known type is a so-called H-arrangement, in which two rotors are arranged on opposite axial sides of a stator. In principle, it is also possible for a plurality of rotor-stator configurations as I-type and/or H-type to be arranged axially next to one another. In this context, it would also be possible to arrange one or more rotor-stator configurations of the I-type and one or more rotor-stator configurations of the H-type next to one another in the axial direction. In particular, it is also preferable for the rotor-stator configurations of the H-type and/or the I-type to be essentially identical, so that they can be combined in a modular manner to form an overall configuration. Such rotor-stator configurations can in particular be arranged coaxially to one another and connected to a common rotor shaft or to several rotor shafts.

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

For the purposes of this application, motor vehicles are considered to be land vehicles that are moved by mechanical power without being tied to railway tracks. A motor vehicle can, for example, be selected from the group of passenger cars (PCs), lorries (HGVs), mopeds, light motor vehicles, motorcycles, buses (KOM) or tractors.

The gear arrangement 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 is preferably designed as a planetary gear, very particularly preferably as a switchable, in particular two-speed planetary gear.

• 1 eine schematische Darstellung eines elektrischen Achsantriebsstrangs mit einer elektrischen Traktionsmaschine, einem Getriebe und einer Pumpenanordnung, die zusätzlich zu einem elektrischen Pumpenantrieb über eine Notantriebsverbindung von der elektrischen Traktionsmaschine antreibbar ist, gemäß einem ersten Ausführungsbeispiel mit einem Freilauf; und
• 2 eine ähnliche Darstellung wie in 1 gemäß einem zweiten Ausführungsbeispiel mit einem Summiergetriebe.

Further advantages, features and details of the invention emerge from the following description, in which various embodiments are described in detail with reference to the drawing. They show:

• 1 a schematic representation of an electric axle drive train with an electric traction machine, a transmission and a pump arrangement, which can be driven by the electric traction machine via an emergency drive connection in addition to an electric pump drive, according to a first embodiment with a freewheel; and
• 2 a similar representation as in 1 according to a second embodiment with a summing gear.

In the 1 and 2 an electric axle drive train 1 for a motor vehicle indicated only by a reference number 2 is shown schematically in two exemplary embodiments. The electric axle drive train 1 comprises an electric traction machine 3, which is connected in terms of drive to at least one wheel 4 of the motor vehicle 2 with the interposition of a transmission 5.

In the 1 and 2 The same reference symbols are used for identical or similar parts. First, the similarities between the two are explained in the 1 and 2 The embodiments shown are described below. The differences between the two embodiments are then discussed.

In the motor vehicle 2, a hydraulic system 30 is used for cooling and/or lubrication, in particular for cooling the electric traction machine 3 and for cooling and/or lubricating the transmission 5. A suitable hydraulic fluid, such as hydraulic oil, which is also referred to as oil for short, is provided in a hydraulic fluid reservoir 33.

A pump arrangement 6 serves to convey the hydraulic medium. The pump arrangement 6 comprises a single electric pump drive 7. The electric pump drive 7 comprises a pump motor 9, which is supplied with electrical power from an on-board electrical network 8. The pump motor 9 is preferably designed as a BLDC Electric motor. The letters BLDC stand for English terms that in German mean a brushless direct current motor.

The pump arrangement 6 comprises a main pump 34 and a dry sump pump 35. The main pump 34 conveys hydraulic medium via a suction line 31 with a filter 32 and conveys it to the electric traction machine 3 via a heat exchanger 36. Between the heat exchanger 36 and the electric traction machine 3, the hydraulic system 30 comprises a pressure relief valve 45 to which a bypass line 46 is connected. The bypass line 46 opens into a dry sump 41 in the transmission 5. The dry sump 41 in the transmission 5 is also referred to as the transmission sump.

Two pump symbols are used to represent the main pump 34 and the dry sump pump 35. The two pumps 34 and 35 can be combined in a tandem pump. Both pumps or pump sumps 34 and 35 are driven via a common pump drive shaft 11; 21.

A main delivery line 44, in which the heat exchanger 36 is arranged, extends from the main pump 34. The main delivery line 44 is hydraulically connected to the electric traction machine 3 at a hydraulic connection point 37. In the electric traction machine 3, the hydraulic fluid provided via the main delivery line 44 with the heat exchanger 36 is used for cooling.

The hydraulic fluid is discharged at a hydraulic connection point 38. The hydraulic fluid discharged from the electric traction machine 3 is fed to a cooling and/or lubrication system 40 of the transmission 5 via a hydraulic line 39. The cooling and/or lubrication system 40 is in the 1 and 2 only indicated by a symbol. The hydraulic fluid used in the transmission 5 for cooling and/or lubrication 40 is collected in the dry sump 41 or transmission sump in the transmission 5.

The hydraulic fluid collected in the transmission 5 is sucked out of the transmission sump or dry sump 41 via a hydraulic line 42 with the aid of the dry sump pump 35. The sucked-out hydraulic fluid is returned to the hydraulic fluid reservoir 33 via a hydraulic line 43 with the dry sump pump 35.

In 1 the pump drive shaft 11 of the pump arrangement 6 is mechanically connected via an emergency drive connection 12, for example to a transmission shaft 18 at a transmission output 13 of the transmission 5. The mechanical connection can be made via a pump drive gear 14, which is connected to the transmission shaft 18 in an emergency drive manner via at least one further transmission gear.

The emergency drive connection 12 in 1 further comprises a freewheel 15 which is connected between the pump drive shaft 11 and the pump drive gear 14. A further freewheel 16 is connected between the pump motor 9 and the main pump 34 of the pump arrangement 6. The further freewheel 16 is optional.

The freewheels 15 and 16 are designed and arranged in such a way that in the event of a fault, the drive maintains an emergency cooling oil supply from the gearbox 5. In normal operation, the electric pump drive 7 can drive the two pumps 34 and 35 faster than would be possible from the gearbox 5.

In 2 the pump drive shaft 21 of the pump arrangement 6 is connected to a transmission shaft 28 via an emergency drive connection 22. The transmission shaft 28 is, for example, a transmission input shaft of the transmission 5. A pump drive gear 24 is connected in a rotationally fixed manner to the transmission shaft 28.

The pump drive gear 24 is connected to the pump drive shaft 21 via a summing gear 25. The summing gear 25 is, as can be seen in 2 sees, arranged axially between the pump drive shaft 21 and the electric pump drive 7.

The pump motor 9 of the electric pump drive 7 drives a sun gear of the summing gear 25. A planet carrier is connected in a rotationally fixed manner to the pump drive shaft 21. A ring gear of the summing gear 25 is connected to the pump drive gear 24.

list of reference symbols

1

electric axle drive train

2

motor vehicle

3

electric traction machine

4

wheel

5

transmission

6

pump arrangement

7

electric pump drive

8

electrical system

9

pump motor

11

pump drive shaft

12

emergency drive connection

13

transmission output

14

pump drive gear

15

freewheel

16

further freewheel

18

transmission shaft

21

pump drive shaft

22

emergency drive connection

24

pump drive gear

25

summing gear

28

transmission shaft

30

hydraulic system

31

suction line

32

filter

33

hydraulic fluid reservoir

34

main pump

35

dry sump pump

36

heat exchanger

37

hydraulic connection point

38

hydraulic connection point

39

hydraulic line

40

cooling and/or lubrication

41

transmission sump

42

hydraulic line

43

hydraulic line

44

main conveyor line

45

pressure relief valve

46

bypass line

Claims (8)

Electric axle drive train (1) for a motor vehicle (2), with an electric traction machine (3) which is connected to at least one wheel (4) of the motor vehicle (2) via a transmission (5), wherein the transmission (5) and the electric traction machine (3) are integrated into a hydraulic system (30) at least for cooling and/or lubrication (40), which comprises a pump arrangement (6) which is driven by an electric pump drive (7) which is supplied with electric current from an electrical on-board network (8) of the motor vehicle (2), wherein the electric pump drive (7) is connected to the electric traction machine (3) for emergency drive in such a way that the pump arrangement (6) is driven by the electric traction machine (3) in an emergency operation even when the electric pump drive (7) is not supplied with electric current from the electrical on-board network (8) of the motor vehicle (2) or is only supplied with insufficient electric current, wherein the pump arrangement (6) comprises a main pump (34) which is supplied with electric current from a Hydraulic fluid reservoir (33) delivers hydraulic fluid to the electric traction machine (3), characterized in that the pump arrangement (6) comprises a dry sump pump (35) which delivers hydraulic fluid from a transmission sump (41) into the hydraulic fluid reservoir (33). Electric axle drive train according to claim 1 , characterized in that a pump drive shaft (11; 21) of the pump arrangement (6) is connected to a transmission shaft (18; 28) via an emergency drive connection (12; 22). Electric axle drive train according to claim 2 , characterized in that the emergency drive connection (12) is assigned to a transmission output (13). Electric axle drive train according to claim 2 or 3 , characterized in that the emergency drive connection (12) comprises a freewheel (15). Electric axle drive train according to claim 2 or 3 , characterized in that the emergency drive connection (22) comprises a summing gear (25). Electric axle drive train according to one of the Claims 2 until 5 , characterized in that the emergency drive connection (22) is arranged at one end of the pump drive shaft (21) of the pump arrangement (6). Electric axle drive train according to one of the preceding claims, characterized in that a pressure relief valve (45) is arranged in the hydraulic system (30) in front of the electric traction machine (3). Electric axle drive train according to one of the preceding claims, characterized in that the main pump (34) and the dry sump pump (35) are combined in a tandem pump.

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