Description

The invention relates to an electric drive for driving a motor vehicle. An electric drive can serve as the sole drive for the motor vehicle or can be provided in addition to an internal combustion engine, whereby the electric drive and the internal combustion en gine can each drive the motor vehicle separately or jointly superimposed.

US 10 272 767 B1 discloses an electric drivetrain system, comprising an electric drivetrain of an electric vehicle, comprising an inverter component, a gearbox compo nent and a motor component. A first cooling system uses ethylene glycol and water based coolant (EGW). The first cooling system comprises an EGW coolant loop to distribute the coolant through at least one of the inverter component, a housing of the gearbox component, and a housing of the motor component to remove heat from the inverter component, the housing of the gearbox component, and the housing of the motor component. A second cooling system uses oil based coolant. The second cool ing system comprises an oil coolant loop to distribute the oil based coolant through at least one of internal components of the gearbox component and internal components of the motor component to remove heat from at least the internal components of the gearbox component, and from at least the internal components of the motor compo nent. An oil coolant pump controls a flow of the oil based coolant through the oil coolant loop and a heat exchanger transfers heat from the oil coolant loop to the EGW coolant loop, away from the electric drivetrain, to a vehicle cooling system having a radiator.

EP 3517335 A1 discloses an electric vehicle including a power control unit, a driving motor, a first cooling channel fitted with a first pump that causes a first cooling liquid cooled in a first heat exchanger to flow through the power control unit and a second heat exchanger in this order and return to the first heat exchanger, and a second cool ing channel fitted with a second pump that causes a second cooling liquid cooled by the first cooling liquid in the second heat exchanger to flow through the driving motor and return to the second heat exchanger. The second pump starts or stops circulation of the second cooling liquid, or increases or reduces a circulation volume of the second cooling liquid, based on one or both of the temperature of the power control unit and the temperature of the first cooling liquid.

From WO 2020/069744 A1 an electric drive for driving a motor vehicle is known with a housing arrangement, an electric machine, a planetary unit and a power transmission unit. The housing arrangement has a first housing part on the motor side, a second housing part on the transmission side, and an intermediate housing part which sepa rates a motor space and a transmission space from each other. The intermediate hous ing member has a motor-side casing portion extending axially into the outer casing portion of the first housing member, and a transmission-side casing portion extending axially into the second housing member. A sealed cavity for a coolant to flow through is formed between the outer surface of the motor-side casing portion and the inner surface of the first housing part.

Document WO 2015/058788 A1 discloses a drive assembly for a motor vehicle with a first gear and a second gear, wherein the first gear and the second gear are drivingly connected to one another, and a lubricant filling which, in a static built-in condition of the drive assembly, defines a lubricant level. A first reservoir is arranged above the lubricant level which can be filled with lubricant as a result of the rotation of the first gear. A second reservoir is arranged above the lubricant level which can be filled with lubricant as a result of the rotation of the second gear. The first reservoir serves to lubricate a first bearing region, whereas the second reservoir serves to lubricate a sec ond bearing region of the drive assembly.

A key issue in connection with electric drives is thermal behavior. Both the electric machine and the transmission generate heat that must be dissipated to avoid imper missibly high temperatures and thus ensure a long service life. It is an object to propose an electric drive with electric machine and transmission, which ensures reliable cooling and lubrication of rotating drive parts and thus has a long ser vice life.

The object is met by an electric drive according to claim 1. Embodiments are described in the dependent claims.

According to an aspect of the disclosure the electric drive for a motor vehicle comprises

- a housing assembly with an inner casing portion and an outer casing portion forming a casing cooling structure through which a water based coolant is made to flow;

- an electric machine with a stator connected to the inner casing portion of the housing assembly and a rotor with a rotor shaft rotatably supported in the hous ing assembly;

- a transmission to transmit a rotary movement from the rotor shaft to drive a driveline of the motor vehicle;

- an oil sump with an oil provided to cool and lubricate the rotor and transmission; and

- a housing shield arranged radially outside of the outer casing portion and at least partially below the rotary axis of the rotor, thereby forming a shield cooling structure through which oil can flow towards the oil sump, wherein the casing cooling structure including the coolant is hydraulically separated from the shield cooling structure for the oil, thereby forming a heat exchanger.

The shield cooling structure arranged radially outside from the casing cooling structure, and at least partially encasing it, advantageously allows a heat exchange between the water based coolant flowing through the casing cooling structure and the oil flowing through the shield cooling structure. A separate heat exchanger for cooling the oil can thus be omitted, resulting in a more simple and lightweight electric machine. The shield cooling structure being arranged below the rotary axis of the rotor allows to gather the oil used for cooling the rotor with winding heads which significantly improves the per formance of the electric machine. The expression below is to be understood with ref erence to the direction of gravity force with the electrical drive being in ready-to-operate installation. Accordingly the housing shield can be arranged radially between the outer casing portion and the oil sump. The housing shield covers, for example a sector of at least 45° in circumferential direction of the rotary axis of the rotor.

According to an embodiment, the housing shield overlaps with the outer casing portion in axial direction along at least one half of an axial length of the outer casing portion. The farther the housing shield overlaps with the outer casing portion, the more effective the formed heat-exchanger works. For example, the housing shield overlaps with the outer casing portion along the full axial length of the outer casing portion. To further enhance the heat exchange, the shield cooling structure can comprise channels run ning generally in parallel in axial direction. The channels advantageously provide a greater surface and thus improved heat transfer from the oil to the shield cooling struc ture. Further, channels allow to use both axial flow directions. Generally, the shield cooling structure may have a downward slope to provide an oil flow due to gravity force, the oil flowing for example towards an outlet passage from the shield cooling structure into the oil sump. Each channel may as well have the downward slope. Further, one or more first channels can have the downward slope to provide an oil flow towards a first axial end of the shield cooling structure with a first outlet passage from the shield cool ing structure into the oil sump, and one or more second channels can have the down ward slope to provide an oil flow towards a second axial end of the shield cooling structure with a second outlet passage from the shield cooling structure into the oil sump.

According to a further embodiment, the shield cooling structure comprises fins con nected to the outer cooling casing and/or the housing shield. The fins also provide a greater surface and thus improved heat transfer from the oil to the shield cooling struc ture.

According to a further embodiment, the shield cooling structure comprises an inlet pas sage to receive oil from the rotor inside the inner casing portion, wherein the outlet passage and the inlet passage are arranged in axial direction at opposite ends of the shield cooling structure. Alternatively, the shield cooling structure may comprise two or more such inlet passages, for example one at each end of the shield cooling structure.

According to a further embodiment, the rotor shaft is hollow and an oil supply duct is connected to an inner diameter of the rotor shaft. The oil supply duct may comprise at least two oil flow paths, a first flow path to the inner diameter of the rotor shaft and a second flow path to rotating parts, bearing members and/or sealing members of the transmission. The rotor shaft can comprise radial bores to convey oil from the inner diameter of the rotor shaft to the rotor and or to the stator. The oil can be centrifuged along the rotor toward end-windings of the stator, which are advantageously cooled by the oil. The end-windings may also be referred to as winding heads. At least a portion of the radial bores can be arranged at axial positions along the rotor shaft, which cor respond to axial positions of the end-windings of the stator.

According to a further embodiment, the oil supply duct is connected to an oil reservoir arranged radially above the rotor shaft, the oil reservoir gathering oil conveyed from the oil sump upwards by rotation of gears of the transmission. The embodiment is ad vantageously simple in construction as no active pump is necessary for the circulation of the oil.

According to an alternative embodiment, a pump is provided for conveying oil from the oil sump to the oil supply duct, which advantageously provides enhanced control of the oil circulation. A filter can be provided in oil flow direction before the pump.

Exemplary embodiments and further advantages of the electric drive for a motor vehi cle will be illustrated as follows with reference to the accompanying drawings, wherein

Figure 1 shows a longitudinal section of a first exemplary embodiment of the electric drive;

Figure 2 shows a schematic representation of the longitudinal section of the embodi ment of Figure 1 ; Figure 3 shows a schematic representation of a cross section of the embodiment of Figure 1 ; and

Figure 4 shows a longitudinal section of a second exemplary embodiment of the elec tric drive in a schematic representation. In Figure 1 , an electric drive for a motor vehicle with a housing assembly 1 , an electric machine 2, a transmission 3, an oil sump 4 and a housing shield 5 is depicted in a longitudinal cut along a rotary axis A of a rotor 10 of the electric machine 2. Figure 2 shows the same section as a schematic representation and in Figure 3, a further sche matic representation is depicted illustrating the housing assembly 1 and the housing shield 5 in a cross section rectangular to the rotary axis A. A first exemplary embodi ment will be described with regard to Figures 1 , 2 and 3 jointly.

The housing assembly 1 comprises an inner casing portion 6 and an outer casing por tion 7 forming a casing cooling structure 8 through which a water based coolant is made to flow. The casing cooling structure 8 forms a cooling jacket around the electric machine 2. The water based coolant can be made to flow in a coolant circuit by a coolant pump (not depicted). The electric machine 2 comprises a stator 9 connected to the inner casing portion 6 of the housing assembly 1. A rotor 10 of the electric ma chine 2 with a hollow rotor shaft 11 is rotatably supported in the housing assembly 1 by bearing means 26.

The transmission 3 is provided to transmit a rotary movement from the rotor shaft 11 to drive a driveline of the motor vehicle comprising, for example, a reduction gear 30, a differential drive 31 and a coupling, wherein the coupling may be arranged at any suitable position of the transmission 3. The reduction gear 30 comprises a first pair of gears with a first gear 23 meshing with a second gear 27, a second pair of gears being formed by a third gear 28 meshing with a fourth gear 29, so that a rotational movement introduced by the rotor shaft 11 is translated from a high speed to a low speed. The driving first gear 23 is connected coaxially to the rotor shaft 11 in a rotationally fixed way and can be supported in the housing assembly 1 by bearing means 32. The re duction gear 30 can comprise an intermediate shaft 33, which is rotatably supported via bearing means 34, rotating around an axis B extending parallel to the rotational axis A of the rotor 10. The second gear 27 can be connected to the intermediate shaft 33 in a rotationally fixed way. Further, the intermediate shaft 33 comprises the third gear 28 formed as a pinion, which is integrally connected with the intermediate shaft 33. The third gear engages the fourth gear 29, which drives the differential drive 31 around a differential axis C. The driving first gear 23 comprises a smaller diameter and a smaller number of teeth than the diameter and, respectively, the number of teeth of the second gear 27. Also, the third gear 28 comprises a smaller diameter and a smaller number of teeth than the fourth gear 29, thus a reduction towards a lower rotational speed is achieved. The fourth gear 29 is fixedly connected to differential housing 35 of the differential drive 31. The differential housing 35 is rotatably supported in the hous ing assembly 1 around the differential axis C by bearing means 36. The differential housing 35 comprises a radial bore into which a journal 37 is inserted. Two differential gears 38 are rotatably supported on the journal 37 around a journal axis. The two dif ferential gears 38 engage two sideshaft gears 39, which are arranged coaxially relative to the differential axis C. The two sideshaft gears 39 each comprise means to achieve a rotationally fixed connection with associated sideshafts (not depicted), for example splines, so that torque can be transmitted to the vehicle wheels. The two sideshaft gears 39 are axially supported relative to the differential housing 35 by friction reducing sliding discs.

The oil sump 4 forms a lower closure of the housing assembly 1 for collecting oil drip ping downwards through gravitational force from the electrical machine 2 and the trans mission 3. The oil flow from the transmission 3 to the oil sump 4 is illustrated by an arrow P. The oil level in the oil sump 4 can be identical with the oil level in the trans mission 3 through communicating chambers. The oil is provided to cool and lubricate the rotor 10 and the transmission 3. The housing shield 5 is arranged radially outside of the outer casing portion 7 and at least partially below the rotary axis A of the rotor 10, thereby forming a shield cooling structure 12 through which oil can flow towards the oil sump 4, wherein the casing cooling structure 8 including the coolant is hydrau lically separated from the shield cooling structure 12 for the oil, thereby forming a heat exchanger 14. The housing shield 5 is arranged below the electric machine 2 to collect oil dripping off the stator 9 and the rotor 10 and flowing downwards inside the inner casing portion 6 through gravitational force. Accordingly, inlet channels 16 connecting an inner space of the inner casing portion 6 with the shield cooling structure 12 are provided, the oil flow through the inlet channels 16 being illustrated by arrows P. The shield cooling structure is formed by the space between the outer casing portion 7 and the housing shield 5, which is arranged radially between the outer casing portion 7 and the oil sump 4. The housing shield 5 can overlap with the outer casing portion 7 in axial direction along at least one half of an axial length of the outer casing portion 7 to pro vide sufficient heat exchange between the water based coolant flowing through casing cooling structure 8 and the oil in the shield cooling structure 12. In the depicted em bodiment, the housing shield 5 overlaps with the outer casing portion 7 in axial direction along essentially the full axial length of the outer casing portion 7. The housing shield 5 may cover a sector of at least 45° in circumferential direction of the rotary axis A of the rotor 10, thus providing sufficient space inside the integrated heat exchanger 14 to effectively cool the oil by the water based coolant. The oil flow through the shield cool ing structure 12 is illustrated by an arrow P. The water based coolant in the casing cooling structure 8 may flow through circumferential channels formed in the inner cas ing portion 6, thus forming a cross-flow heat exchanger 14.

The shield cooling structure 12 can comprise first and second channels 40, 41 (Figure 3) running generally in parallel in axial direction. The first channel 40 can be separated from the second channel 41 by a wall 42, so that the oil can flow in the first channel 40 in opposite axial direction compared to the oil flow in the second channel 41. Further, the shield cooling structure 12 comprises fins 43 connected to the outer casing portion 7, which can be connected to the housing shield 5 as well or instead. The shield cooling structure 12 has a downward slope to provide an oil flow towards an outlet passage 15 to the oil sump 4. The oil flow into the oil sump 4 through the outlet passage 15 is illustrated by an arrow P. The shield cooling structure 12 further comprises at least one of the inlet passages 16 to receive oil from the rotor 10 inside the inner casing portion 6, wherein the outlet passage 15 and the inlet passage 16 are arranged in axial direc tion at opposite ends of the shield cooling structure 12. There can be two inlet pas sages 16 arranged at opposite ends of the shield cooling structure 12, the oil flowing either through the first or the second channel 40, 41. Alternatively, the oil may flow from a first end of the shield cooling structure 12 to a second end through the first channel 40 and back through the second channel 41 to the first end, which advanta geously provides a longer retention time for the oil in the heat exchanger 14.

The rotor shaft 11 of the electric machine 2 is hollow and an oil supply duct 17 is con nected to an inner diameter 18 of the rotor shaft 11 , to supply oil as coolant and lubri cant through the rotor shaft 11. Further, the rotor shaft 11 comprises radial bores 21 to convey oil from the inner diameter 18 of the rotor shaft 11 to the rotor 10 of the electric machine 2 for cooling purposes. The electric machine 2 comprises the stator 9 and the rotor 10 that is rotatable relative to the stator 9 and that drives the rotor shaft 11 con nected thereto when the electric machine 2 is energized. The rotor 10 may be config ured, for example, as a stack of rotor laminations mounted on the rotor shaft 11. The electric machine 2 can be configured as a synchronous or asynchronous machine. The sleeve-like casing cooling structure 8 is connected to the stator 9. The electric machine 2 may serve as a drive source for a driveline of a motor vehicle, and may be controlled by means of power electronics, such as a pulse inverter with an integrated electronic control unit (ECU, not depicted). The electric machine 2 can be supplied from a current controlling source (not depicted) and can operate in a motor mode, wherein electrical energy is converted into mechanical energy to drive the rotor shaft 11 and the compo nents drivingly connected thereto, or in a generator mode, wherein, conversely, me chanical energy is converted into electrical energy, which can then be stored in a bat tery. In the present disclosure the electric machine is also referred to as electric motor. The stator 9 includes an electrical winding forming a first end-winding 44 at a first side of the stator 9 and a second end-winding 45 at the opposite second side of the stator 9. The oil leaking from the rotor shaft 11 through the radial bores 21 is centrifuged further along the rotor 10 towards the stator windings, in particular the first and second end-windings 44, 45. The radial bores 21 may be arranged at axial positions corre- sponding to the axial positions of the first and second end-windings 44, 45.

The oil supply duct 17 comprises two oil flow paths, a first flow path 19 to the inner diameter 18 of the rotor shaft 11 and a second flow path 20 to rotating parts, including the gears and shafts of the reduction gear 30 and the differential drive 31 , to bearing members 32, 3436 and to sealing members of the transmission 3. The oil flow through the oil supply duct 17 and branching into the first and second flow paths 19, 20 is illustrated by arrow P. The bearing means 26 are lubricated via the first flow path through the rotor shaft 11. The depicted embodiment comprises an oil reservoir 22 arranged radially above the rotor shaft 11 , the oil supply duct 17 being connected to said oil reservoir 22, which is adapted to gather oil conveyed upwards from the oil sump 4 by rotation of the gears 23, 27, 28, 29 of the transmission 3. It is an advantage that the oil flow via the first and second flow paths 19, 20 can be provided from the reservoir 22 through gravity force, which renders any active circulation pump obsolete for the oil cooling and lubricating circuit in this embodiment. Further, as a fraction of the oil is retained in the reservoir 22, the lower oil level in the oil sump 4 can advanta geously keep churning losses in the transmission 3 low.

A second exemplary embodiment is described with regard to Figure 4, wherein the electric drive for a motor vehicle is depicted schematically in a longitudinal cut along the rotary axis A of the rotor 10 of the electric machine 2. This second embodiment largely corresponds to the first embodiment shown in Figures 1 to 3, thus reference is made to the above description. Identical or corresponding details have been denoted with identical reference signs as in Figures 1 to 3 above.

A special feature of the embodiment according to Figure 10 is that the oil circuit com prises a pump 24 for conveying oil from the oil sump 4 to the oil supply duct 17. The oil is conveyed from the oil sump 4 to the pump 24 via a suction duct 47. The pump 24 can be driven by a supporting electric motor 46. The pump 24 allows a more purposeful distribution of the oil for the internal cooling of the electric machine 2. The oil supply duct 17 branches into the first flow path 19 to the inner diameter 18 of the rotor shaft 11 and into the second flow path 20 to the transmission 3. An oil reservoir above the rotor shaft 11 can be omitted in this embodiment. A filter 25 can be provided in oil flow direction before the pump 2, i.e. between the oil sump 4 and the pump 24.

Reference numerals

1 Housing assembly

2 Electric machine

3 Transmission

4 Oil sump

5 Housing shield

6 Inner casing portion

7 Outer casing portion

8 Casing cooling structure

9 Stator

10 Rotor 11 Rotor shaft 12 Shield cooling structure

14 Heat exchanger

15 Outlet passage

16 Inlet passage

17 Oil supply duct

18 Inner diameter oft he rotor shaft

19 First flow path

20 Second flow path 21 Radial bore 22 Reservoir

23 First gear

24 Pump

25 Filter

26 Bearing means

27 Second gear

28 Third gear 29 Fourth gear 30 Reduction gear

31 Differential drive

32 Bearing means

33 Intermediate shaft

34 Bearing means

35 Differential housing

36 Bearing means

37 Journal

38 Differential gears

39 Sideshaft gears

40 First channel

41 Second channel

42 Wall

43 Fins

44 First end-windings

45 Second end-windings

46 Supporting electric motor

47 Suction duct

A Rotary axis

B Intermediate shaft axis

C Differential axis

P Arrow