DE102021202421A1 - Cooling of rotor shafts - Google Patents

Abstract

An arrangement (10) for cooling a hollow shaft (20), in particular a rotor shaft of an electric drive (100), having a hollow shaft (20) which is open on a first side (21) in the axial direction (A) and on a second side (22) opposite the first side (21) has at least one outlet opening (23) introduced in the axial direction (A), which is cost-effective and enables improved cooling, it is proposed that on the second side (22) of the hollow shaft (20) to arrange at least one guide section (30) which encompasses the at least one outlet opening (23) on the circumference at least in regions and projects beyond at least one stator end winding (200) axially at the end.

Description

The invention relates to an arrangement for cooling a hollow shaft, in particular a rotor shaft of an electric drive, having a hollow shaft, wherein the hollow shaft is open on a first side in the axial direction, and on a second side, opposite the first side, at least one side is introduced in the axial direction Has outlet opening, wherein the hollow shaft in the region of the first side opens into an intermediate space, wherein the intermediate space has at least one inlet opening for receiving a coolant. Furthermore, the invention relates to an electric drive and a motor vehicle.

In the operation of electric motors, a particularly high thermal load occurs in the area of the stator windings. In particular, edge sections of the stator windings or the so-called end windings can overheat and impair the durability of the electric motor. Coolant ducts integrated in the stator are known for dissipating the excess heat of the stator windings, which increase the space requirement and the construction complexity of the stator.

With an increasing market share of electric vehicles, the need for cost-effective and at the same time more efficient electric drives or hybrid transmissions is increasing. Since drives of this type make up a significant proportion of the overall costs of an electric vehicle, the drive must be precisely designed to meet the vehicle requirements. Based on a specific performance, an optimally cooled electric drive can be built smaller or with less material than an electric drive with insufficient cooling. An optimally cooled electric drive can thus be manufactured more cost-effectively and operated with higher efficiency due to lower operating temperatures.

Concepts for cooling electric drives are already known, in which different components are successively cooled by an oil. In this case, stator end windings and hollow shafts of rotors are usually cooled in series or one after the other. This means that the oil, which has already absorbed thermal energy from the rotor, reaches the stator end windings, which impairs the cooling effect there.

The object of the invention is to create an arrangement for cost-efficient and improved cooling of electric drives. This object is achieved by the features specified in claim 1. Further advantageous configurations of the invention are described in the dependent claims.

According to one aspect of the invention, an arrangement for cooling a hollow shaft, in particular a rotor shaft of an electric drive, is provided. The arrangement has a hollow shaft, the hollow shaft being open on a first side in the axial direction and having at least one outlet opening made in the axial direction on a second side opposite the first side. The first side serves as an inlet opening for the coolant into an inner volume or cavity of the hollow shaft. The coolant can preferably be in the form of an oil or an oil mixture. The coolant can flow out of the cavity of the hollow shaft on the second side of the hollow shaft.

In the region of the first side, the hollow shaft opens into an intermediate space, the intermediate space having at least one inlet opening for accommodating a coolant. The coolant can be conducted from a coolant channel into the intermediate space through the inlet opening. The intermediate space can preferably be formed by a housing.

According to the invention, at least one guide section is arranged on the second side of the hollow shaft. The at least one guide section surrounds the at least one outlet opening on the circumference at least in regions and protrudes axially at the end beyond at least one stator end winding of a stator winding, which surrounds the rotor radially at least in regions.

Preferably, the guide section can guide the coolant that emerges from the at least one outlet opening axially beyond the hollow shaft or parallel to the hollow shaft. This increases the retention time of the coolant on the hollow shaft. The guide section can deflect the coolant axially in such a way that one or more end windings are no longer acted upon by the coolant. As a result of this measure, the end windings of the stator are no longer heated by the coolant that has already been heated. For this purpose, coolant can be sprayed onto the end windings of the stator parallel to the introduction into the intermediate space, in order to achieve a separate cooling effect. The coolant is thus not repeatedly used to absorb heat, which improves the cooling effect.

The at least one guide section can be designed, for example, in the form of a collar, which prevents the heated coolant from coming into contact with the end windings of the stator when it exits the hollow shaft.

The coolant conducted into the intermediate space via the at least one inlet opening can initially collect in the gap. Even with a low pressure of the coolant, a necessary coolant level is reached in order to convey the coolant into the rotor shaft, which is designed as a hollow shaft. The hollow shaft preferably has a maximum speed of more than 10,000 rpm. Due to the resulting centrifugal forces, the coolant flowing in is pressed against an inner wall within the cavity of the hollow shaft. Thus, the coolant flowing in can spread axially along the inner wall of the cavity or inner volume.

The at least one outlet opening, which opens into the intermediate space, can preferably be connected to a coolant channel in a fluid-carrying manner. The coolant channel can have further outlet openings or coolant nozzles parallel to the outlet opening. The coolant channel is used to transport cooled coolant, which is fed into the hollow shaft in parallel and applied to the end windings within the electric drive. This results in two thermally decoupled coolant flows that can reconnect after heating and behind the second side of the hollow shaft.

The heated coolant can be guided along an outer wall of a housing for the purpose of cooling or through an external cooler or heat exchanger. The cooled coolant can then be supplied again via the at least one coolant channel to absorb heat.

In principle, the arrangement can be used in all electric drives with an oil pump and oil cooling. For example, the arrangement can be used in a hybrid transmission, in an electric front axle or rear axle, in an electric auxiliary drive, in a transmission and the like. The arrangement can be used in particular in mobile or stationary applications. For example, the arrangement can be used in commercial vehicles, passenger cars, agricultural or forestry vehicles, construction machinery, rail vehicles, drive units, conveyor systems and the like for efficient cooling of components inside the housing.

With such an arrangement, an internal rotor cooling concept can be provided which functions independently and is efficient. No additional components are required to achieve an increase in efficiency, which is particularly advantageous in the case of highly loaded electric machines in tight installation spaces.

In one exemplary embodiment, the rotor shaft is designed as a hollow shaft and is surrounded radially at least in regions by a stator with stator windings. The stator windings end axially in end windings, which are subject to greater thermal stress. Preferably, the at least one guide section has an axial extent that protrudes beyond the stator windings and also the end windings on the axial end.

The emerging coolant for the internal rotor cooling system no longer reaches the end windings of the stator with thermal energy that has already been absorbed, as was previously the case. The coolant emerging from the hollow shaft is directed past the end windings, which means that the end winding cooling itself is also more efficient. In particular, the end windings are not heated by the coolant which is heated and emerges from the hollow shaft. In addition, the cooling capacity can be positively influenced by the design of the interior of the hollow shaft.

For example, the inner wall of the hollow shaft can have a contour that promotes a more even distribution of the coolant and/or controls a propagation speed of the coolant within the hollow shaft.

On the basis of simulations or tests, an optimal angle or conicity of the inner wall of the hollow shaft can also be found and varied for the respective application in order to enable an additional increase in the efficiency of the internal rotor cooling.

The rotor shaft can be cooled independently of other components of the electric drive if the at least one inlet opening opening into the intermediate space is connected to a coolant channel in a fluid-conducting manner, with the coolant channel having at least one coolant nozzle, in particular for cooling stator windings, on a side opposite the inlet opening. In other words, provision is made for the coolant to be split into two independent paths. The resulting partial flows absorb different amounts of heat and form a quasi-parallel circuit.

Through an inlet in the housing, the coolant can be supplied to the coolant channel at a low pressure level for cooling. One side of the coolant channel is directed towards the end windings of the stator or is connected to an end winding cooling system. An opposite side of the coolant channel can have the at least one inlet opening, which opens into the intermediate space. The inlet opening preferably points in the direction of a rotor shaft center point.

When the coolant has finally passed the entire axial length of the laminated rotor core or the hollow shaft, it can flow out again via outlet openings. For this purpose, the hollow shaft can taper on the second side. In a corresponding tapered section of the hollow shaft, axial bores can be introduced, which act as outlet openings.

The outlet openings can touch at least one point on their circumference with a largest inner diameter of the hollow shaft. In this way, the coolant can flow out particularly easily, since the outlet openings are arranged flush with the inner wall of the hollow shaft. In contrast to the known solutions, the coolant is not flung against the winding overhangs when it exits the hollow shaft, but is guided axially past the winding overhangs through the guide section so as not to reduce the cooling effect of the winding overhang cooling provided specifically for this purpose. For this purpose, the guide section is provided on the stub shaft or on the second side of the hollow shaft, radially on the outside of the outlet bores or outlet openings. This guide section encompasses the outlet openings on the peripheral side and ensures that the coolant is redirected axially. The coolant is thus transported further and only thrown into the housing of the electric drive after the end windings.

The winding overhang cooling can preferably have at least one coolant nozzle, which is directed at the winding overhangs in such a way that local cooling of the winding overhangs is realized. Areas that are thermally overstressed can be specifically cooled and the durability of the stator can be increased.

Instead of a separate, tubular coolant duct, the coolant duct is designed to be particularly compact and technically simple in a housing section in the interaction between a guide element and a recess made in the housing. As a result, minimum distances to the winding overhangs to be cooled and to other components within the housing volume can be reduced.

According to one embodiment, the at least one coolant nozzle is introduced into a guide element or formed at the edge between the guide element and a housing section. The guide element preferably closes off a groove or recess made in a housing section at least on one side and forms a coolant channel, with the inlet opening extending through the housing section.

In particular, at least one coolant nozzle can be formed in the guide element in the form of through-openings or, for example, as a gap between the guide element and at least one housing section. A coolant, in particular in the form of an oil, can be fed through the inlet into the coolant channel formed and sprayed onto at least one end winding or transported into the hollow shaft via the at least one coolant nozzle or the inlet opening from the coolant channel. The coolant that has come out of the coolant channel can then absorb the heat from the end windings and the hollow shaft and transport it away from the housing volume in such a way that the coolant is conducted through a heat exchanger, for example.

According to a further exemplary embodiment, the at least one inlet opening has an orifice plate or a valve for adjusting a coolant flow. This measure allows the inflow of the coolant into the intermediate space to be controlled particularly precisely. In this way, in particular, the coolant that is supplied via the coolant channel can be adjusted with regard to its proportions between the internal rotor cooling and the winding overhang cooling. Thus, depending on the cooling requirement, a larger or smaller proportion of volume flow can be supplied to the hollow shaft. This results in an inversely proportional volume flow component, which is available for winding overhang cooling. In this way, the ratio between the end winding cooling and the internal rotor cooling can be controlled or regulated, for example by a control device or a bimetal.

In this case, the volume flow in the direction of the intermediate space can be reduced and the pressure of the coolant can be increased by reducing the orifice or the orifice opening or a valve opening of the valve.

The flow rate of the coolant within the hollow shaft can be influenced by a speed of the hollow shaft.

According to a further embodiment, the hollow shaft has a cylindrical or conical cavity, the conically shaped cavity tapering in the direction of the first side. A cylindrically shaped cavity can be produced technically in a particularly simple manner. A driving pressure for the coolant can be additionally increased by a conical contouring of the inner wall of the cavity, so that a larger amount of the coolant can flow through the hollow shaft per unit of time. In this case, the conically shaped cavity can have a diameter which increases in the direction of the second side.

Alternatively or additionally, further contouring of the inner wall of the cavity, for example helical, may be provided to cause further interaction of the inner wall with the coolant. The residence time of the coolant in the hollow shaft can be reduced or increased, as a result of which the amount of heat that the coolant absorbs is controlled.

The hollow shaft can be of particularly simple technical design if the at least one guide section is integrally connected to the hollow shaft. Alternatively or additionally, the at least one guide section can be connected to the hollow shaft by fastening means, a form fit, a force fit or a friction fit. In a two-part configuration, the hollow shaft and the guide section are components that are independent of one another and can be connected to one another. Fastening means such as screws or rivets, adhesive connections, welded connections, soldered connections, pinched or clamped connections and the like can be used to connect the guide section to the hollow shaft on the second side.

In the case of an integral configuration of the hollow shaft and the guide section, both components are preferably made of an identical material. In a two-part configuration, the guide section can have a material composition that differs from that of the hollow shaft.

According to a further exemplary embodiment, the intermediate space is delimited at least on one side by a fluid-tight housing cover, the intermediate space on the first side of the hollow shaft being fluid-tightly connected to a cavity of the hollow shaft by a bearing of the hollow shaft. The exiting coolant can preferably reach the intermediate space in the direction of the center of the shaft via the inlet opening. The intermediate space can preferably be formed between a housing section or a housing cover and a bearing of the hollow shaft in the area of the first side.

Depending on the configuration of the housing cover, it can be glued, welded or provided with a seal in order to ensure a fluid-tight closure of the intermediate space. The bearing of the hollow shaft can be configured as a ball bearing or as a roller bearing, for example. The bearing is sealed in the direction of the intermediate space in order to prevent the coolant from escaping through the bearing.

A seal between the bearing of the hollow shaft and the intermediate space can be designed in the form of a labyrinth seal, for example.

According to a further aspect of the invention, an electric drive with an arrangement according to the invention is provided. By using the arrangement, the efficiency of the cooling and the performance of the electric drive can be increased.

In principle, the electric drive can be used in all mobile or stationary units. The arrangement can be used in any electric motors or rotor shafts to be cooled. The electric drive can be designed, for example, as an MEB axle drive, an electric auxiliary drive, a hybrid transmission, an mHEV drive and the like.

• 1 eine schematische Schnittdarstellung eines elektrischen Antriebs mit einer Anordnung gemäß einer ersten Ausführungsform, und
• 2 eine schematische Schnittdarstellung eines elektrischen Antriebs mit einer Anordnung gemäß einer zweiten Ausführungsform.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Show it:

• 1 a schematic sectional view of an electric drive with an arrangement according to a first embodiment, and
• 2 a schematic sectional view of an electric drive with an arrangement according to a second embodiment.

In the figures, the same structural elements each have the same reference numbers.

the 1 shows a schematic sectional illustration of an electric drive 100 with an arrangement 10 according to a first specific embodiment. The electric drive 100 is configured as an electric motor, for example.

The arrangement 10 has a rotor shaft which is designed as a hollow shaft 20 . The hollow shaft 20 is designed to be open on a first side 21 in the axial direction A and has at least one outlet opening 23 introduced in the axial direction A on a second side 22 opposite the first side 21 . The first side 21 serves as a feed 24 for a coolant into a cavity 25 of the hollow shaft 20.

The coolant can preferably be in the form of an oil or an oil mixture. The coolant can flow out of the cavity 25 of the hollow shaft 20 on the second side 22 of the hollow shaft 20 . The hollow shaft 20 tapers on the second side 22, a plurality of outlet openings 23 being provided in the area of the tapering second side 22.

The outlet openings 23 can at least one point of their circumference with a Touch the largest inner diameter D of the hollow shaft 20. In this way, the coolant can flow out particularly easily, since the outlet openings 23 are arranged flush with the inner wall 26 of the hollow shaft 20 .

At least one guide section 30 is arranged on the second side 22 of the hollow shaft 20 . In the exemplary embodiment shown, the guide section 30 forms a peripheral collar which at least partially encompasses the outlet openings 23 on the peripheral side and extends in the axial direction A from the hollow shaft 20 or parallel to the hollow shaft 20 . For example, the guide section 30 is designed integrally with the hollow shaft 20 .

In the exemplary embodiment shown, the hollow shaft 20 has a cylindrically shaped cavity 25 .

The hollow shaft 20 is part of a rotor R of the electric drive 100 and is surrounded by a stator S radially on the outside. The stator S has stator end windings 200 which are cooled parallel to the hollow shaft 20 by the coolant.

By using the guide section 30 , the coolant thrown out of the outlet openings 23 is axially guided or diverted during operation of the electric drive 100 in such a way that the stator end windings 200 are no longer hit by the coolant exiting from the hollow shaft 20 . As a result, the coolant heated in the hollow shaft 20 can no longer thermally impair or heat up the stator end windings 200 . The arrows illustrate the flow of the coolant through the hollow shaft 20 .

The coolant is introduced into a guide element 40 which closes off a groove or recess 41 introduced into a housing section 50 at least on one side and forms a coolant channel 42 . The coolant is conducted through an inlet opening 43 into an intermediate space 51 . The inlet opening 43 extends through the housing section 50 and opens into the intermediate space 51 . The guide element 40 is coupled to the housing section 50 in a fluid-tight manner via sealing rings 44 .

The intermediate space 51 is located in the area of the first side 21 of the hollow shaft 20 and is connected to the supply 24 of the hollow shaft 20 in a fluid-conducting manner. The intermediate space 51 is delimited axially at the end by a housing cover 52 . The housing cover 52 is connected to the housing section 50 in a fluid-tight manner. Furthermore, the intermediate space 51 is sealed in the area of a bearing 53 of the hollow shaft 20 . For this purpose, the bearing 53 designed as a ball bearing is sealed on one side.

The inflow of the coolant into the intermediate space 51 is controlled by an orifice 60 which is arranged in the at least one inlet opening 43 . Alternatively, the coolant flow can be adjusted by a valve, not shown, which can be positioned in the inlet opening 43 .

The at least one inlet opening 43 opening into the intermediate space 51 is connected to the coolant channel 42 in a fluid-conducting manner. The coolant channel 42 has at least one coolant nozzle 45 on a side opposite the inlet opening 43 . The coolant nozzle 45 serves to cool the stator windings 201 and in particular the stator end windings 200. A plurality of coolant nozzles 45 can be distributed over the circumference of the stator S. The coolant channel 42 can extend, for example, over an entire circumference or over part of the circumference of the housing section 50 .

the 2 shows a schematic sectional illustration of an electric drive 100 with an arrangement 10 according to a second embodiment. In contrast to the in 1 The exemplary embodiment shown has the electric drive 100 on an arrangement 10 with a hollow shaft 20 which has a conically shaped cavity 25 . The hollow space 25 tapers in the direction of the first side 21. The hollow shaft 20 thus has the largest inner diameter D in the area of the second side 22.

Reference List

100

electric drive

200

stator end winding

201

stator windings

10

arrangement

20

hollow shaft

21

first page

22

second page

23

exit port

24

supply

25

cavity of the hollow shaft

26

wall of the hollow shaft

30

guide section

40

guiding element

41

recess

42

coolant channel

43

intake port

44

sealing rings

45

coolant nozzle

50

housing section

51

space

52

housing cover

53

bearing of the hollow shaft

60

cover

A

axial direction

D

largest inner diameter of the hollow shaft

R

rotor

S

stator

Claims (10)

Arrangement (10) for cooling a hollow shaft (20), in particular a rotor shaft of an electric drive (100), having a hollow shaft (20), the hollow shaft (20) being open on a first side (21) in the axial direction (A). and on a second side (22) opposite the first side (21) has at least one outlet opening (23) introduced in the axial direction (A), wherein the hollow shaft (20) in the region of the first side (21) in an intermediate space (51 ) opens out, the intermediate space (51) having at least one inlet opening (43) for receiving a coolant, characterized in that at least one guide section (30) is arranged on the second side (22) of the hollow shaft (20), the at least one Guide section (30) which encompasses at least one outlet opening (23) on the circumference at least in regions and projects beyond at least one stator end winding (200) axially at the end. arrangement according to claim 1 , wherein the hollow shaft (20) is designed as a rotor shaft and is surrounded radially at least in regions by a stator (S) with stator windings (201), wherein the at least one guide section (30) has an axial extent which extends the stator windings (201, 200 ), in particular at least one stator end winding (200), protrudes axially at the end. arrangement according to claim 1 or 2 , wherein the at least one inlet opening (43) opening into the intermediate space (51) is connected to a coolant channel (42) in a fluid-conducting manner, the coolant channel (42) having at least one coolant nozzle (45) on a side opposite the inlet opening (43), in particular for cooling of stator windings (201). arrangement according to claim 3 , wherein the at least one coolant nozzle (45) is introduced into a guide element (40), wherein the guide element (40) closes off a groove or recess (41) made in a housing section (50) at least on one side and forms a coolant channel (42), wherein the inlet opening (43) extends through the housing section (50). Arrangement according to one of Claims 1 until 4 , wherein the at least one inlet opening (43) has an orifice (60) or a valve for adjusting a coolant flow. Arrangement according to one of Claims 1 until 5 , wherein the hollow shaft (20) has a cylindrical or conical cavity (25), wherein the conically shaped cavity (25) tapers towards the first side (21). Arrangement according to one of Claims 1 until 6 , wherein the at least one guide section (30) is integrally connected to the hollow shaft (20), or wherein the at least one guide section (30) can be connected to the hollow shaft (20) by fastening means, a form fit, a force fit or a friction fit. Arrangement according to one of Claims 1 until 7 , the intermediate space (51) being delimited on at least one side by a fluid-tight housing cover (52), the intermediate space (51) being delimited on the first side (21) of the hollow shaft (20) by a sealed bearing (53) and the intermediate space ( 51) is connected to a cavity (25) of the hollow shaft (20). Electric drive (100) having an arrangement (10) according to one of the preceding claims. Motor vehicle, having at least one electric drive (100) each with an arrangement (10) according to one of Claims 1 until 8th .

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