Description

The invention relates to an electric drive arrangement for a vehicle with a housing, an electric machine, a transmission and a hydraulic circuit for circulating a fluid to cool and lubricate the electric machine and the transmission.

From US 2019/0229582 A1 , a vehicle drive device is known with a lubricating path including a first oil pump to pump up an oil stored in the casing by the first oil pump and to supply the oil to the power transmission mechanism for lubricating the power transmission mechanism, and a cooling path that is separated from the lubricating cir cuit and provided for the rotating electric machine, the cooling path including a second oil pump to pump up the oil stored in the casing by the second oil pump to supply the oil exclusively to the rotating electric machine for cooling the rotating electric machine, the second oil pump is an electric oil pump, and the cooling path is provided with an oil cooler cooling the oil to be supplied to the rotating electric machine.

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.

US 2018/241288A1 discloses a rotating electrical machine cooling structure such that a cooling medium is supplied by a pump to a stator and rotor of a rotating electrical machine, thereby cooling the stator and rotor, the rotating electrical machine cooling structure comprising a first passage that supplies the cooling medium from the pump to the stator; a second passage that supplies the cooling medium from the pump to the rotor; and a valve that regulates a flow of the cooling medium of the first passage and a flow of the cooling medium of the second passage, wherein a cooling state of the stator and a cooling state of the rotor are controlled by the valve.

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.

The electric machine and the transmission of an electric drive for a vehicle have differ ent cooling and lubrication requirements, which depend on operation conditions. A per formance of the electric machine is thermally limited in operation. Inherent losses may occur in the copper, iron and magnets of electric motors, where material properties limit the temperatures of the respective components and structures. Effective cooling is necessary to achieve adequate torque performance. A passive splash lubrication of the transmission results in churning losses under high-speed operation. The combina tion of cooling and lubrication for both the electric machine and the transmission is a compromise with regard to efficiency.

It is therefore an object to propose an electric drive for a vehicle with a hydraulic circuit for circulating a fluid for efficient cooling and lubrication of the electric machine and the transmission.

The object is solved by an electric drive arrangement for a vehicle, comprising:

- a housing;

- an electric machine with a stator connected to the housing and including stator end-windings, and a rotor with a rotor shaft rotatably supported in the housing;

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

- a hydraulic circuit for circulating a fluid to cool and lubricate the electric machine and the transmission, comprising - an oil sump formed in a lower portion of the housing,

- a reservoir arranged above the oil sump, wherein the reservoir is configured to temporarily store and feed oil to rotating parts of the transmission, and

- a bi-directional pump which is hydraulically connected to the oil sump on a suc tion side, which is further hydraulically connected to the reservoir on a first pres sure side and which is hydraulically connected to cooling nozzles of the electric machine on a second pressure side.

When the bi-directional pump is operated in a first direction of rotation, fluid is supplied to the reservoir, and when the bi-directional pump is operated in a second direction of rotation, fluid is supplied to the cooling nozzles for cooling the stator end-windings.

An advantage of the electric drive arrangement is that the bi-directional pump of the hydraulic circuit can be operated to optimize the cooling and lubrication of the electric machine and the transmission, depending on the actual cooling and lubrication require ments, by switching between the first and second direction of rotation. The first direc tion of rotation can advantageously be applied for high speed operation of the vehicle and accordingly high rotation speed of the rotor and the transmission parts. In high speed operation, the torque requirements of the electric machine are lower, so that spray cooling of the winding heads via the cooling nozzles is not required. Instead, lubrication of the transmission components running at high speed can advantageously be achieved by fluid supplied to the reservoir. A final drive of the transmission, for example, may still be passively splash lubricated. Due to the reduced oil level in the oil sump, churning losses are advantageously reduced.

The second direction of rotation can advantageously be applied for low speed opera tion of the vehicle and accordingly lower rotation speed of the rotor and the transmis sion parts, compared to the high speed mode. In low speed operation, high torque requirements are common, the high currents resulting in copper losses, so that the fluid supplied to the cooling nozzles can advantageously cool the stator end-windings, thus reducing the losses. A high-pressure spray cooling of the winding heads is possible when the bi-directional pump is operated in the second direction of rotation, while the lubrication of the transmission in the low speed mode does not require active fluid sup ply. The passive splash lubrication of the transmission is effective under low speed conditions as churning losses are lower due to low rotation speeds.

The fluid circulated in the hydraulic circuit is a cooling and lubricating fluid, like e.g. an oil. The oil sump is arranged to gather fluid, which drips of the electric machine and the transmission due to gravitational force, which fluid despite the expression oil sump is not limited to oil-based cooling and lubricating fluids.

According to an embodiment, the bi-directional pump is hydraulically connected via the reservoir to an inner diameter of the driveshaft and/or to the transmission, wherein, when the bi-directional pump is operated in the first direction of rotation, fluid is sup plied to the inner diameter of the driveshaft and/or to the transmission. The active lu brication of the transmission does not require high-pressure fluid supply under high speed conditions and the electric machine can advantageously be supplied with low- pressure coolant fluid via the driveshaft, for example via radial bores of the driveshaft connecting the inner diameter with the rotor. The rotor is cooled and the fluid is further centrifuged toward the stator and the stator end-windings are thus also cooled.

According to a further embodiment, the bi-directional pump is hydraulically connected to a heat exchanger on the first pressure side and/or on the second pressure side to cool the fluid. The heat exchanger is for example a fluid/water heat exchanger. The first and second pressure sides can be hydraulically separated, each being connected to a heat exchanger. The two heat exchangers may still be arranged as one integral part.

Alternatively, the first and second pressure sides can be hydraulically connected in a pressure side junction upstream of a single heat exchanger. A backflow of fluid be tween the first and second pressure sides is avoided by check valves arranged be tween the bi-directional pump and the pressure side junction. According to a further embodiment, the hydraulic circuit comprises a mode control valve hydraulically con nected to the bi-directional pump on the first pressure side and on the second pressure side, a hydraulic stator path connecting the mode control valve with the cooling noz zles, and a hydraulic transmission path connecting the mode control valve with the reservoir. Thus, the bi-directional pump is hydraulically connected on the first pressure side via the mode control valve to the reservoir, whereas the bi-directional pump is hydraulically connected on the second pressure side via the mode control valve to the cooling nozzles.

According to a further embodiment, the mode control valve is a three-way two-position directional valve, which can be hydraulically actuated via a pressure line, which is hy draulically connected to the bi-directional pump on the first pressure side. When the bi-directional pump is operated in the first direction of rotation, the first pressure side is pressurized to a first pressure level, which actuates the mode control valve such that the bi-directional pump is hydraulically connected on the first pressure side to the res ervoir. A pressure control valve is arranged downstream of the hydraulic pressure line branch-off, which provides that the mode control valve is actuated by the built-up pres sure, before opening and allowing the fluid to flow from the first pressure side to the mode control valve. When the bi-directional pump is operated in the second direction of rotation, the second pressure side is pressurized to a second pressure level and the former first pressure side becomes the suctions side of the bi-directional pump. The pressure in the pressure line drops and the valve returns to its unactuated position, which can be achieved by a bias spring, such that the bi-directional pump is hydrau lically connected on the second pressure side to the cooling nozzles.

When the bi-directional pump is operated in the first direction of rotation, the first pres sure side is pressurized to the first pressure level to supply fluid for active cooling of the rotor and active lubrication of the transmission, wherein a fluid level in the oil sump is advantageously reduced by supplying fluid to the reservoir. When the bi-directional pump is operated in the second direction of rotation, the second pressure side is pres surized to the second pressure level, which is higher than the first pressure level, to supply fluid to the cooling nozzles, while a fluid level in the oil sump is increased. Ac cording to a further embodiment, the reservoir is hydraulically connected to the oil sump and when the bi-directional pump is operated in the second direction of rotation, fluid flows back from the reservoir to the oil sump.

According to a further embodiment, the reservoir is arranged inside the housing. Ac cording to an alternative embodiment, the reservoir is arranged external to the housing. The reservoir can at least partially be arranged radially above the rotor shaft. According to a further embodiment, the electric drive arrangement may comprise a cooling arrangement to cool the fluid, which is hydraulically connected to a suction side of the bi-directional pump. As the suction side is the respective non-active first or sec ond pressure side of the bi-directional pump, the first and second pressure sides are connected in a suctions side junction upstream of the bi-directional pump, which may be connected to the cooling arrangement. To prevent backflow from the respective active first or second pressure sides to the suction side, check valves are arranged between the bi-directional pump and the junction. The cooling arrangement includes:

- an inner casing portion and an outer casing portion of the housing, the inner casing portion and an outer casing portion forming a casing cooling structure through which a water based coolant is made to flow,

- a housing shield arranged radially outside of the outer casing portion and at least partially below a rotary axis of the rotor, thereby forming a shield cooling structure through which fluid can flow towards the oil sump.

The casing cooling structure including the coolant is hydraulically separated from the shield cooling structure for the fluid, thereby providing a heat exchange between the coolant and the fluid.

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 fluid flowing through the shield cooling structure. An additional suction side heat exchanger for cool ing the fluid is thus provided, resulting in a more effective cooling of the fluid. The shield cooling structure being arranged below the rotary axis of the rotor allows to gather the fluid used for cooling the rotor and the winding heads. The expression below is to be understood with reference to the direction of gravity force with the electrical drive being in ready-to-operate installation. Accordingly the housing shield can be arranged radi ally 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.

To further enhance the heat exchange of the cooling arrangement, the shield cooling structure can comprise channels running generally in parallel in axial direction. The channels advantageously provide a greater surface and thus improved heat transfer from the fluid to the shield cooling structure. Further, channels allow to use both axial flow directions. Generally, the shield cooling structure may have a downward slope to provide a fluid flow due to gravity force, the fluid 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. The shield cooling structure may further comprise 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 fluid to the shield cooling structure.

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

Figure 1 shows an exemplary embodiment of the electric drive arrangement in a sche matic illustration;

Figure 2 shows the embodiment of Figure 1 , illustrating an operation of the bi-direc tional pump in a first direction of rotation;

Figure 3 shows the embodiment of Figure 1 , illustrating an operation of the bi-direc tional pump in a second direction of rotation;

Figure 4 shows a further exemplary embodiment of the electric drive arrangement in a schematic illustration;

Figure 5 shows a further exemplary embodiment of the electric drive arrangement in a schematic illustration;

Figure 6 shows the embodiment of Figure 5 in a schematic cross-sectional view.

In Figure 1 , an electric drive arrangement for a vehicle is depicted, wherein a housing 1 , an electric machine 2, a transmission 3, an oil sump 4 and a reservoir 5 are shown as a schematic representation of a longitudinal cut along a rotary axis A of a rotor 10 of the electric machine 2. The electric machine 2 has a stator 9 connected to the hous ing 1 and including stator end-windings 31 , the rotor 10 being rotatable relative to the stator 9. A driveshaft 11 is connected to the rotor 10 and rotatably supported in the housing 1 about the axis of rotation A. The transmission 3 is adapted to transmit a rotary movement from the driveshaft 11 to drive a driveline of the vehicle, which is not depicted. The transmission 3 may comprise, for example, a reduction gear, a differen tial drive and a coupling, which are not depicted. A hydraulic circuit 7 for circulating a fluid to cool and lubricate the electric machine 2 and the transmission 3 is in part sche matically depicted. The hydraulic circuit 7 comprises the oil sump 4 formed in a lower portion of the housing 1 , the reservoir 5 arranged above the oil sump 4, wherein the reservoir 5 is configured to temporarily store and feed fluid to rotating parts of the transmission 3 and a bi-directional pump 24 which is hydraulically connected to the oil sump 4 on a suction side via a fluid supply line 20. The bi-directional pump 24 is further hydraulically connected to the reservoir 5 on a first pressure side 22 and to the cooling nozzles 33 of the electric machine 2 on a second pressure side26. When the bi-direc tional pump 24 is operated in a first direction of rotation, fluid is supplied to the reservoir 5, and when the bi-directional pump 24 is operated in a second direction of rotation, fluid is supplied to the cooling nozzles 33 for cooling the stator end-windings 31. The bi-directional pump 24 is further hydraulically connected via the reservoir 5 to an inner diameter 18 of the driveshaft 11 and to the transmission 3. When the bi-directional pump 24 is operated in the first direction of rotation, fluid is further supplied to the inner diameter 18 of the driveshaft 11 and to the transmission 3. In the depicted embodiment, the reservoir 5, which is arranged inside the housing 1 on the transmission side, com prises outlets 8 to supply fluid to bearings and gears of the transmission 3 and to the rotor 9 via the inner diameter 18 of the driveshaft 11. The fluid is administered via radial bores 21 of the driveshaft 11 connecting the inner diameter 18 with the rotor 10. The fluid is centrifuged along the rotor 10 towards the stator 9, and flows back into the oil sump 4 due to gravitational force, shown by arrows F.

The housing 1 includes an intermediate wall 16 separating the oil sump 4 on a motor- side of the housing 1 from a transmission sump 6 on a transmission-side of the housing 1. A passage 37 in the intermediate wall 16 allows fluid dripping off the transmission 3 to flow into the machine-side reservoir 5, as shown by arrow F. The fluid level in the transmission sump 6 can be higher during low speed operation to provide adequate splash lubrication, whereas during high speed operation, the fluid level in the transmis sion sump 6 is reduced to keep churning losses low.

A mode control valve 12 is hydraulically connected to both the first and second pres sure sides 22, 26 of the bi-directional pump 24, which unite at a junction 28 down stream of the bi-directional pump 24. A check valve arrangement 29 prevents fluid flow from the respective active one of the first and second pressure sides 22, 26 to the non active one. The mode control valve 12 is hydraulically actuated via a pressure line 30, which in this embodiment is hydraulically connected to the bi-directional pump 24 on the first pressure side 22. Thus, depending on the direction of rotation of the bidirec tional pump 24 the mode control valve 12 is actuated between its two positions. When the bi-directional pump 24 is operated in the first direction of rotation, the mode control valve 12 is actuated by the pressure in the pressure line 30 into a first position. The downstream check valve of the check valve arrangement 29 on the first pressure side 22 is biased towards its closed position by a check valve spring 39, which is adapted to keep the check valve closed to allow the pressure to build up in the pressure line 30 when the first pressure side 22 becomes the active one. In the first position, a hydraulic transmission path 15 connecting the mode control valve 12 with the reservoir 5 is hy draulically connected to the bi-directional pump 24 on the first pressure side 22. When the bi-directional pump 24 is operated in the second direction of rotation, the mode control valve 12 is not pressurized and thus actuated into a second position by a return spring 32. In the second position, a hydraulic stator path 14 connecting the mode con trol valve 12 to the cooling nozzles 33 is hydraulically connected to the bi-directional pump 24 on the second pressure side 26.

The two directions of rotation of the bi-directional pump 24 provide two modes of the hydraulic circuit 7 for optimized cooling and lubrication of the electric machine 2 and the transmission 3, depending on the operating conditions of the electric drive. The bi directional pump 24 is driven by an electric motor 34. In the fluid supply line 20 up stream of the bi-directional pump 24, a suction filter 25 is arranged. Downstream of the suction filter 25, the fluid supply line 20 is split at a suction side junction 27 into two branches, which are connected to the first and second pressure sides 22, 26 of the bi directional pump 24, respectively. As the suction side of the bi-directional pump 24 is the respective non-active first or second pressure side 22, 26 of the bi-directional pump 24, a backflow of fluid from the respective active first or second pressure sides 22, 26 to the suction side is avoided by the check valves 29 arranged between the bi-direc tional pump 24 and the suction side junction 27. On the first and second pressure sides 22, 26 of the bi-directional pump 24, the fluid is cooled in a heat exchanger 35 arranged upstream of the mode control valve 12.

The embodiment of the electric drive arrangement is now further illustrated with regard to Figure 2, which shows the electric drive arrangement of Figure 1 with the bi-direc tional pump 24 being operated in the first direction of rotation. By reversing the pump ing direction of the bidirectional pump 24 to the first direction of rotation, the the hy draulic circuit 7 provides lubrication and cooling fluid optimized for high speed opera tion of the electric machine 2. The downstream check valve 29 on the first pressure side 22 is biased towards its closed position by a check valve spring 39, which is adapted to keep the check valve 29 closed at the moment when the pumping direction is reversed, to build up a pressure in the pressure line 30. By pressurizing the first pressure side 22, the mode control valve 12 is actuated via the pressure line 30 against the biasing force of the return spring 32. The mode control valve 12 directs the fluid flow to the hydraulic transmission path 15. The check valves 29 establish a fluid flow from the supply line 20 through the bi-directional pump 24 towards the first pressure side 22 into the hydraulic transmission path 15, which flow is shown by full lines, whereas the dotted lines show inactive lines. Generally, crossing lines are not con nected, unless otherwise stated or depicted by a dot. The first pressure side 22 is pressurized to a first pressure level to supply fluid for active cooling of the rotor 10 and active lubrication of the transmission 3. By supplying fluid to the reservoir 5, depicted by a high fluid level 38 in the reservoir 5, whereas a fluid level 36 in the transmission sump 6 is reduced.

The embodiment of the electric drive arrangement is now further illustrated with regard to Figure 3, which shows the electric drive arrangement of Figure 1 with the bi-direc tional pump 24 being operated in the second direction of rotation. The second pressure side 26 is pressurized to a second pressure level, which is higher than the first pressure level to supply fluid to the cooling nozzles 33, while a fluid level 36 in the transmission sump 6 is increased, e.g. to the fluid level in the in the oil sump 4. The reservoir 5 is hydraulically connected to the oil sump 4 to allow fluid to flow back from the reservoir 5 to the oil sump 4, resulting in a corresponding fluid level 38 in the reservoir 5. The hydraulic pressure line 30 is not pressurized by the bi-directional pump 24, as the first pressure side 22 now forms the suction side of the bi-directional pump 24. Thus the mode control valve 12 is actuated towards its second position by the return spring 32. The check valves 29 establish a fluid flow from the supply line 20 through the bi-direc tional pump 24 towards the second pressure side 26 and into the hydraulic stator path 14. The fluid is supplied to the cooling nozzles 33, which spray the fluid onto the wind ing heads 31 of the stator 9. From the stator 9 the fluid runs down by gravitational force towards the oil sump 4 as shown by arrows F. The hydraulic transmission path 15 is not pressurized and no fluid is actively transported to the transmission 3, which is splash lubricated from the transmission sump 6, which is sufficient for low speed oper ation of the vehicle and accordingly lower rotation speed of the rotor 10 and rotating parts of the transmission 3.

In Figure 4, a further exemplary embodiment of the electric drive arrangement is shown in a similar schematic illustration as the embodiment of Figure 1. Identical parts are denoted with the same reference numerals. The electric drive arrangement according to this embodiment comprises the housing 1 , the electric machine 2, the transmission 3 and the oil sump 4, which are not described in detail again. Reference is made to the description above.

The reservoir 5, however, is arranged outside the housing 1. The hydraulic circuit 7 for circulating the fluid to cool and lubricate the electric machine 2 and the transmission 3 comprises the oil sump 4 formed in a lower portion of the housing 1 , the external res ervoir 5 arranged above the oil sump 4, wherein the external reservoir 5 is configured to temporarily store and feed fluid to rotating parts of the transmission 3. The bi-direc tional pump 24 is hydraulically connected to the oil sump 4 on the suction side via the fluid supply line 20. The bi-directional pump 24 is further hydraulically connected to the external reservoir 5 on the first pressure side 22 and to the cooling nozzles 33 of the electric machine 2 on a second pressure side 26. When the bi-directional pump 24 is operated in the first direction of rotation, fluid is supplied to the external reservoir 5, and when the bi-directional pump 24 is operated in the second direction of rotation, fluid is supplied to the cooling nozzles 33 for cooling the stator end-windings 31. The bi-directional pump 24 is further hydraulically connected via the external reservoir 5 and conduits 17 to the inner diameter 18 of the driveshaft 11 and to the transmission 3. In the depicted embodiment, the fluid is supplied through the conduits 17 from the external reservoir 5 to the bearings and gears of the transmission 3 and to the rotor 9 via the inner diameter 18 of the driveshaft 11. The fluid level 36 in the oil-sump 4 is depicted by two broken lines, wherein the lower fluid level 36 appears when the bi directional pump 24 is operated in the first direction of rotation and the higher fluid level 36 appears when the bi-directional pump 24 is operated in the second direction of rotation.

In Figure 5, a further exemplary embodiment of the electric drive arrangement is shown in a similar schematic illustration as the embodiment of Figure 4. In Figure 6, the em bodiment of Figure 5 is shown in a schematic cross section through housing 1 at an axial position of the electric machine 2, wherein parts of the electric machine 2 are not depicted. Figures 5 and 6 are described together. Identical parts are denoted with the same reference numerals. The electric drive arrangement according to this embodi ment comprises the housing 1 , the electric machine 2, the transmission 3, the oil sump 4 and the external reservoir 5, which are not described in detail again. Reference is made to the description above.

The hydraulic circuit 7 for circulating a fluid to cool and lubricate the electric machine 2 and the transmission 3 comprises the oil sump 4 formed in a lower portion of the housing 1 , the external reservoir 5 configured to temporarily store and feed fluid to rotating parts of the transmission 3 and the bi-directional pump 24 which is hydraulically connected to the oil sump 4 on a suction side via a fluid supply line 20. In this embod iment, the bi-directional pump 24 is directly hydraulically connected to the reservoir 5 on the first pressure side 22 and to the cooling nozzles 33 of the electric machine 2 on the second pressure side 26. Thus, no mode control valve is necessary to connect the first or second pressure side 22, 26 to the hydraulic transmission path 15 and the hy draulic stator path 14, respectively. A pressure side cooling of the fluid may be provided for one or both of the hydraulic transmission path 15 and the hydraulic stator path 14 by arranging one or two heat exchangers.

In the depicted embodiment, however, the electric drive arrangement comprises an alternative cooling arrangement 19 to cool the fluid, which is arranged at a suction side of the bi-directional pump 24. As the suction side is the respective non-active first or second pressure side 22, 26 of the bi-directional pump 24, the first and second pres sure sides 22, 26 are connected at the suction side junction 27 upstream of the bi directional pump 24, which is connected to the cooling arrangement 19. To prevent a fluid backflow from the respective active first or second pressure sides 22, 26 to the suction side, check valves 29 are arranged between the bi-directional pump 24 and the suction side junction 27. The cooling arrangement 19 includes an inner casing por tion 41 and an outer casing portion 42 of the housing 1 , the inner casing portion 41 and an outer casing portion 42 forming a casing cooling structure 43 through which a water based coolant is made to flow. A housing shield 40 is arranged radially outside of the outer casing portion 42 and at least partially below the rotary axis A of the rotor 10, thereby forming a shield cooling structure 44 through which fluid can flow towards the oil sump 4. The casing cooling structure 43 may similarly be arranged in the hous ings 1 of the earlier described embodiments. The casing cooling structure 43 including the coolant is hydraulically separated from the shield cooling structure 44 for the fluid, thereby providing a heat exchange between the coolant and the fluid. Advantageously, a suction side heat exchanger for cooling the fluid is thus provided, resulting in a less complicated hydraulic circuit 7, in which the heat exchanger on the pressure side and the mode control valve are omitted.

The shield cooling structure 44 arranged below the rotary axis A of the rotor 10 gathers fluid for cooling the rotor 10 and the winding heads 31. To further enhance the heat exchange of the cooling arrangement 19, the shield cooling structure 44 can comprise channels 45, 47 running generally in parallel in axial direction. The channels 45, 47 advantageously provide a greater surface and thus improved heat transfer from the fluid to the shield cooling structure 44. Further, the channels 45, 47 allow to use both axial flow directions. Generally, the shield cooling structure 44 may have a downward slope to provide a fluid flow due to gravity force, the fluid flowing for example towards at least one outlet passage 46 from the shield cooling structure 44 into the oil sump 4, which is depicted by arrows F. Each channel 45, 47 may as well have the downward slope. The shield cooling structure 44 may further comprise fins 48 connected to the outer cooling casing portion 42 and/or the housing shield 40. The fins 48 also provide a greater surface and thus improved heat transfer from the fluid to the shield cooling structure 44. The oil flow through the shield cooling structure 44 is illustrated by arrows F. The water based coolant in the casing cooling structure 43 may flow through cir cumferential channels (not depicted) formed in the inner casing portion 41 , thus form ing a cross-flow heat exchanger. The shield cooling structure 44 can comprise first and second channels 45, 47 running generally in parallel in axial direction. The first channel 45 can be separated from the second channel 47 by a wall 49, so that the oil can flow in the first channel 45 in opposite axial direction compared to the oil flow in the second channel 47. The shield cooling structure 44 further comprises at least one inlet pas sage 50 to receive fluid from the rotor 10 inside the inner casing portion 41, wherein the outlet passage 46 and the inlet passage 50 are arranged in axial direction at oppo- site ends of the shield cooling structure 44. There can be two inlet passages 50 ar ranged at opposite ends of the shield cooling structure 44, the fluid flowing either through the first or the second channel 45, 47.

The fluid level 36 in the oil-sump 4 is depicted by two broken lines, wherein the lower fluid level 36 appears when the bi-directional pump 24 is operated in the first direction of rotation and the higher fluid level 36 appears when the bi-directional pump 24 is operated in the second direction of rotation.

The depicted parts and features of all the exemplary embodiments of the electric drive are schematic representations, which may deviate from engineering drawing stand ards. Regarding the function and technical details of the parts and features, the de scription takes precedence over the drawings.

Reference Numerals

1 Housing

2 Electric machine

3 Transmission

4 Oil sump

5 Reservoir

6 Transmission sump

7 Hydraulic circuit

8 Outlet

9 Stator

10 Rotor 11 Driveshaft 12 Mode control valve

14 Hydraulic stator path

15 Hydraulic transmission path

16 Intermediate wall

17 Conduits

18 Inner diameter oft he rotor shaft

19 Cooling arrangement

20 Fluid supply line 21 Radial bore 22 First pressure side

24 Bi-directional pump

25 Filter

26 Second pressure side

27 Suction side junction

28 Pressure side junction

29 Check valve arrangement

30 Pressure line

31 Stator end windings

32 Spring

33 Cooling nozzles

34 Electric motor 35 Heat exchanger

36 Fluid level

37 Passage

38 Fluid level

39 Check valve spring

40 Housing shield

41 Inner casing portion

42 Outer casing portion

43 Casing cooling structure

44 Shield cooling structure

45 First channels

46 Outlet passage

47 Second channels

48 Fins

49 Wall

50 Inlet passage A Rotary axis F Arrows