EP4097828A1

EP4097828A1 - Cooling of an electric drive in an electrically driven vehicle

Info

Publication number: EP4097828A1
Application number: EP20839318.1A
Authority: EP
Inventors: Peter Zweigle; Martin Kuehnemund; Marie-Luies Schoeneck; Julius Georgemannan; Anton Schuelin
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-01-30
Filing date: 2020-12-23
Publication date: 2022-12-07
Also published as: DE102020201127A1; US20230106304A1; CN115004518A; WO2021151599A1

Abstract

The invention relates to an electric drive (10) of an electrically driven vehicle. The electric drive (10) comprises a rotor (22) and a stator (24) which is enclosed by a housing (25). The housing (25) is formed by an outer part (48) and an inner part (50), each of which has an axial ribbing (62, 64) extending in an axial direction (78) of the housing (25).

Description

COOLING AN ELECTRIC DRIVE IN AN ELECTRIC DRIVEN VEHICLE

Technical area

The invention relates to an electric drive for an electrically driven vehicle with a rotor and a stator which is enclosed by a housing. The invention also relates to the use of the electric drive in an e-axle module of an electrically powered vehicle.

State of the art

DE 10 2018 200365 A1 discloses a cooling unit for cooling an electrical machine. The cooling unit has a hollow cylindrical cooling jacket and a cooling channel formed on the cooling jacket. The cooling channel is implemented on a radially outer surface of the cooling jacket with respect to a central axis of the cooling unit.

DE 10 2012 008 209 A1 relates to an electrical machine with a housing and a casing concentrically surrounding the housing. An annular, liquid-tight closed cooling jacket through which a coolant can flow extends between the housing and the jacket. The cooling jacket has a plurality of coolant channels arranged next to one another in the axial direction and extending in the circumferential direction of the housing, which coolant channels extend between ribs which are arranged on the outer circumference of the housing.

DE 10 2010 029 986 A1 relates to an electrical machine with a housing in which a stator and a rotor are arranged. The housing has a Outer jacket and an inner jacket that is partially spaced from it and faces the stator. A cooling jacket is implemented between the outer jacket and the inner jacket. The cooling jacket comprises a plurality of channels running around an axis of rotation of the electrical machine for the passage of the cooling medium.

In the case of electrical machines that are used in electric drive axles of electric vehicles, their stator is usually cooled with liquid. For this purpose, the stator is built into an aluminum housing manufactured using an extrusion process. The housing is usually double-walled and has webs between the two walls that extend in the longitudinal direction of the housing. The separating webs create cooling water channels running parallel to one another. In each of the two end shields of the electrical machine there are deflection pockets which deflect the liquid emerging from a longitudinal channel by 180 ° and divert it into the adjacent channel. As a result, the electrical machine flows around the entire circumference of the housing jacket in a meandering manner and is thus cooled.

It is also known that a cooling water guide is formed in a cost-effective way by lengthening a front bearing plate and by lengthening a rear bearing plate. As a result, an outer wall and an inner wall of the cooling housing can be formed. The housing itself is saved in this way. With this option, a first end shield is designed as a die-cast part, while a second end shield is generally designed as an extruded part.

Disclosure of the invention

According to the invention, an electric drive for an electrically driven vehicle is proposed, the electric drive comprising an electric machine with a rotor and a stator and the rotor being enclosed by a housing. The housing comprises an outer part and an inner part, each of which has an axial ribbing extending in the axial direction of the housing. By dividing the housing of the electrical machine into an inner part and an outer part, on the one hand the diverting pockets previously required can be saved from a manufacturing point of view. Furthermore, the solution proposed according to the invention can prevent cooling fluid from flowing over from a cooling channel into a cooling channel adjacent to it, so that overall, the cooling power that is available to dissipate heat from an electrical machine can be kept essentially constant.

In a further development of the solution proposed according to the invention, the electric drive is designed so that the axial ribs in the joined state of the outer part or the inner part of the housing form an intermediate space through which the cooling medium flows exclusively in the tangential direction. The meandering portion of the cooling medium flow present in previous solutions can be significantly reduced and ideally completely avoided by the solution proposed according to the invention, so that an exclusively tangential flow of the cooling medium is established.

In a further advantageous embodiment of the solution proposed according to the invention, there is an inlet and an outlet for the cooling medium on the outer part, which are arranged at an axial distance from one another. Due to the distance between inlet and outlet that can be achieved due to the axial distance, flow short-circuits of the cooling medium can be avoided, so that this is rather impressed with a flow through the respective cooling channels extending in the axial direction, which is associated with constant heat dissipation.

In an advantageous further development of the solution proposed according to the invention, the inlet and the outlet on the outer part of the housing are advantageously arranged at an offset of, for example, 180 ° with respect to one another. In this way it can be achieved that the inlet and outlet for the cooling medium are opposite one another and a flow path extending exclusively in the tangential direction is impressed on the cooling medium, assisted by gravity. Offset angles other than 180 ° are also possible. In an advantageous embodiment of the solution proposed according to the invention, the inlet for the cooling medium lies in a first axial plane, while the outlet of the cooling medium preferably lies in a second axial plane which is spaced apart from this, as seen in the axial direction; the inlet and the outlet can also be arranged in the same axial plane.

Such an arrangement of the inlet and outlet of the cooling medium makes it possible to optimize the only tangential flow path of the cooling medium, so that a maximum of heat loss can be dissipated from the electrical machine.

The electric drive proposed according to the invention also includes axial ribs that are implemented on draft angles of the outer part and the inner part of the housing. The formation of draft bevels on the outer and inner parts of the housing, which form the coolant channels in the joined state and extend in the axial direction, enable a housing of the electrical machine that includes an inner and outer part to be manufactured by die-casting processes.

Advantageously, in the solution proposed according to the invention, the outer part and inner part of the housing can each be designed with a conicity, which also contributes to easier removal of the outer part and inner part of the housing if they are manufactured by means of die-casting processes.

In the solution proposed according to the invention, the axial ribbing is carried out in an inner circumferential surface of the outer part within a machined area, the axial ribbing of the outer part on the inner circumferential surface of the outer part in particular comprising a cylindrical overturning. In contrast, the axial ribbing on an outer circumferential surface of the inner part of the housing within a machined area is designed in such a way that in particular a conical overturning is formed there. Due to the subsequent, in particular machining, machining of the inner part and outer part in the area of the axial ribbing within the draft angles, the geometry of the cooling channels extending essentially in the axial direction can be kept particularly flat, which ensures optimal heat dissipation of waste heat from the electrical Machine on the one hand and on the other hand a particularly space-saving design for coolant channels with it.

In the solution proposed according to the invention, the electric drive is designed in such a way that the conicity is determined by a first diameter and a second diameter, for example of the inner part of the housing. The corresponding conicity of the outer part of the housing is complementary to this.

The electric drive is advantageously designed in such a way that the stator of the electric machine is fixed in the inner part of the housing in particular by a shrink connection, in particular is shrunk into it. This allows a particularly simple assembly of the stator of the electrical machine in the inner part of the housing without the need for fastening elements or the like.

In an advantageous variant of the electrical drive proposed according to the invention, the axial ribbing of the inner part of the housing is provided with interruptions. As a result, a turbulent flow condition is impressed on a flow of the cooling medium, by means of which a significant improvement in the dissipation of heat from the electrical machine can be achieved.

The invention also relates to the use of the electric drive in an e-axle module of a drive train of an electrically driven vehicle.

Advantages of the invention

In an advantageous manner, the rib-shaped design of both the outer part and the inner part of the housing of the electrical machine achieves a very large surface, which leads to optimal heat transfer to the cooling medium, for example cooling water. Furthermore, it should be emphasized as very advantageous that the flow assumes a turbulent state due to the flow around the axial ribs, which are provided on the outer part and the inner part, seen in the axial direction of the housing is associated with a considerable improvement in the heat transfer that can be achieved. Since the cooling channels in the solution proposed according to the invention are not shown as a cavity in a part, for example in a cast core, they can be made very flat due to the dimensional coordination of the outer part and the inner part. As a result of the flat cooling channels, the largest possible amount of the flowing cooling medium is connected to the surface on which the heat is to be dissipated, so that the heat can be optimally absorbed by the cooling medium or transferred to it. Due to the very flat design of the channels shown for the flow of the cooling medium as spaces or flat gaps between the axial ribs on the inner and outer parts of the housing, a very high flow speed of the cooling medium can be achieved.

In the solution proposed according to the invention, the cooling is designed in such a way that, in the case of a tolerance-related smallest cross-section, the permissible flow resistance is not exceeded on the one hand and, on the other hand, sufficient cooling capacity is ensured with the largest cross-section.

In the solution proposed according to the invention, the cooling water flow is optimized in that the cooling water flows in at the inlet and emerges again from the cooling channel geometry at an outlet connection opposite it which is offset by 180 °. In this way, half of the cooling water is routed around both sides of the electrical machine in a tangential manner. The interlocking axial ribs on the inner part and outer part of the housing ensure the necessary flow influencing of the cooling medium as well as the optimization of the achievable cooling effect. Since the inlet and outlet of the cooling medium are as far apart as possible in the axial direction, an essentially complete flow around the two-part housing, including the inner and outer parts, is achieved. In principle, the two connections, i. H. the inlet and the outlet for the cooling medium can also be arranged on one and the same axial plane.

The outer part of the housing can be made, for example, as a cast part and provided with draft angles. The inner part of the housing is cylindrical due to the manufacturing process. To the channel cross-section, ie the In order not to let the space in which the cooling medium flows become too large, the raised protruding parts of the axial ribs in the inner and outer parts are completely or partially machined so that, for example, with regard to the axial ribs, they can be machined to the effect that these are either designed to be conically turned or cylindrically turned. In both cases, the presence of the draft angles on the inner and outer parts can advantageously be used to optimize the geometry of the cooling channels, ie the spaces in the form of a gap between the inner part and the outer part of the housing.

Brief description of the drawings

Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

Show it:

Figure 1 is a perspective view of an electric drive with a laterally flanged gear,

Figure 2 is a partial sectional view of the electric drive according to Figure 1,

FIG. 3 shows a cooling medium flow on a housing proposed according to the invention with an outer part and an inner part,

FIG. 4 shows a plan view of an inner part pushed into an outer part of the housing with a shrunk-in stator,

Figure 5 is a perspective view of the outer part of the housing,

Figure 6 shows a first variant of an inner part with external axial ribs and FIG. 7 shows a second embodiment variant of the inner part with interruptions in the axial ribbing.

FIG. 1 shows a perspective view of an electric drive 10 which has a first end plate 12 and a second end plate 16. Between the first end shield 12 and the second end shield 16, a motor housing 14 with a laterally flanged transmission 18 is arranged. An electrical machine, not shown in detail, of the electrical drive 10 is accommodated in the motor housing 14.

FIG. 2 shows a partial sectional illustration of the electric drive 10 according to the perspective view in FIG. 1.

FIG. 2 shows that a rotor shaft 20, on which a rotor 22 of an electrical machine is received, is rotatably supported in a first bearing 26 and a second bearing 28. The rotor shaft 20 of the electric machine rotates relative to a stator 24 of an electric machine that is fixedly mounted on a housing. The first bearing 26 is received in the first end shield 12. The second bearing 28 is mounted in the laterally flanged gear 18. The transmission 18 comprises an intermediate shaft 30 on which a gear is received, which meshes with a drive pinion of the rotor shaft 20. Cooling channels 32 run in the motor housing 14. The individual cooling channels 32 are formed by separating webs 34 in the longitudinal direction. Each of the cooling channels 32 opens into a first deflecting pocket 36 or into a second deflecting pocket 38, which are either incorporated into the first end shield 12 or into the material of the second end shield 16.

Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, a repeated description of these elements being dispensed with in individual cases. The figures represent the subject matter of the invention only schematically. FIG. 3 shows a schematic representation of a flow 46 of the cooling medium through a housing 25. The cooling medium enters a cooling system of the housing 25 via an inlet 42 and leaves it at an outlet 44 25 formed by an outer part 48 and an inner part 50. In the joined state, the outer part 48 and the inner part 50 define a channel geometry, as will be described in more detail below. It can be seen from FIG. 3 that the inlet 42 and the outlet 44 can be oriented at an offset 52 of, for example, 180 ° to one another. Offset angles other than 180 ° are also possible. Furthermore, the illustration according to FIG. 3 shows that there is an axial distance 54 between the inlet 42 and the outlet 44 for the cooling medium. While the inlet 42 for the cooling medium lies in a first axial plane 56, the outlet 44 for the cooling medium is located in a second axial plane 58 further spaced apart from this first axial plane 56 in the axial direction A particularly long flow path can be impressed on the cooling medium so that the cooling medium can transport a maximum of heat away from the electric drive 10. Alternatively, there is also the possibility of arranging the inlet 42 and the outlet 44 in one and the same axial plane.

It can also be seen from the illustration according to FIG. 3 that a flow 46 of the cooling medium takes place essentially in the tangential direction and splits behind the inlet 42. Since the inlet 42 and the outlet 44 for the cooling medium are far apart as seen in the axial direction 78, a practically complete flow around the housing 25 of the electric drive 10 is achieved. In principle, the inlet 42 and the outlet 44 could also be arranged on one and the same axial plane.

FIG. 4 shows that the inner part 50 is pushed into the outer part 48 of the housing 25 of the electric drive 10. Between the outer part 48 on the one hand and the inner part 50 on the other hand, an annular gap-shaped intermediate space 60 is created. The geometry of the annular gap-shaped intermediate space 60 is essentially flat, so that there is a large contact surface between the cooling medium and the surface to be cooled and optimal heat transfer to the cooling medium takes place can. As FIG. 4 shows, the individual segments of the annular gap-shaped intermediate space 60 are on the one hand due to the axial ribbing 62 of the inner part 50 and, on the other hand, formed by the axial ribbing 64 of the outer part 48. FIG. 4 also shows that the stator 24 of the electrical machine is shrunk into the inner part 50 by a shrink connection 66 and is thus fixed without further fastening elements being required.

FIG. 4 also shows that the stator 24 of the electrical machine surrounds the rotor 22 of the electrical machine, which is received on the rotor shaft 20.

FIG. 5 shows a perspective illustration of the outer part 48 of the housing 25. The perspective illustration according to FIG. 5 shows that the outer part 48 of the housing 25 can be manufactured, for example, as a cast part, for example as an aluminum die-cast part. For this purpose, the outer part 48 has draft angles 68. Due to the draft bevels 68, an easier removal of the finished cast blank of the outer part 48 from a casting mold or a casting tool is possible. As FIG. 5 further shows, the outer part 48 comprises an axial ribbing 64 on its inner circumferential surface, which consists of individual axial ribs which are spaced apart from one another in the circumferential direction and which each comprise a base 72.

Furthermore, FIG. 5 shows that the individual ribs of the axial ribbing 64 of the outer part 48 have a cylindrical overturn 71 within a machined area 74. Such a machining of the respective upper sides of the individual ribs of the axial ribbing 64 on the inner circumference of the outer part 48 defines the annular gap-shaped intermediate space 60 in relation to the outer part 48.

Analogously to the illustration according to FIG. 5, the inner part 50 of the housing 25 shown in the illustration according to FIG. 6 has the axial ribbing 62 on its outer jacket surface. The individual ribs of the axial ribbing 62 on the outer circumference of the inner part 50 run essentially parallel to one another. As can also be seen from the illustration according to FIG. 6, the inner part 50 of the housing 25 is designed with a conicity 82 as seen in the axial direction 78. This means that the inner part 50 as shown in FIG. 6, viewed in the axial direction 78, is provided with a variable diameter which varies from a first diameter 84 to a second diameter 86 tapering stretches. As FIG. 6 also shows, the stator 24 is attached to an inner circumferential surface of the inner part 50, for example via the shrink connection 66 shown in FIG. 4 between the stator 24 of the electrical machine and the inner part 50 of the housing 25.

FIG. 6 also shows that the axial ribbing 62 of the inner part 50 of the housing 25 also has a machined area 74. The machined area 74 of the axial ribbing 62 of the inner part 50 is provided with a conical overturn 70. Within the conical overturning 70, the upper edges of the individual ribs of the axial ribbing 62 are machined, i. H. worn away.

When the inner part 50 is joined to the outer part 48 of the housing 25 shown in FIG. 5, the annular gap-shaped intermediate space 60 shown in FIG. 4 is created, within which the cooling medium flows tangentially (cf. position 46 in the illustration according to FIG. 3).

FIG. 7 shows an alternative design option for the inner part 50 of the housing 25. According to the illustration in FIG. 7, the inner part 50 includes an end face 80. The individual ribs of the axial ribbing 62 of the inner part 50 have individual interruptions 76. The individual interruptions 76 of a single rib of the axial ribbing 62 of the inner part 50 according to the illustration in Figure 7 are aligned with the interruptions 76 of adjacent individual ribs of the axial ribbing 62. This creates grooves 88 that extend in the circumferential direction of the inner part 50 and the cooling medium as it flows through an arrangement impose a turbulent flow condition from outer part 48 and inner part 50. The turbulent flow state of the cooling medium, which flows through the annular gap-shaped intermediate space 60 according to the flow 46 according to FIG. 3, improves heat dissipation from the housing 25 of the electric drive 10 proposed according to the invention.

The design variant of the inner part 50 according to FIG. 7 results in a significant increase in the surface and an impression of a turbulent flow state in relation to the cooling medium which the annular gap-shaped intermediate space 60 between the outer part 48 on the one hand and the inner part 50 of the housing 25 on the other hand.

The invention is not restricted to the exemplary embodiments described here and the aspects emphasized therein. Rather, it is within the by the

Claims specified range, a variety of modifications possible, which are within the scope of professional action.

Claims

Expectations

1. Electric drive (10) of an electrically powered vehicle with a rotor (22) and a stator (24) which is enclosed by a housing (25), characterized in that the housing (25) has an outer part (48) and a Inner part (50) each having an axial ribbing (62, 64) extending in the axial direction (78) of the housing (25).

2. Electric drive (10) according to claim 1, characterized in that the axial ribbing (62, 64) in the joined state of the outer part (48) and the inner part (50) form an intermediate space (60) which is essentially in flows through tangential direction.

3. Electric drive (10) according to claims 1 and 2, characterized in that the outer part (48) has an inlet (42) and an outlet (44) for a cooling medium, which are positioned at an axial distance (54) from one another.

4. Electric drive (10) according to claims 1 to 3, characterized in that the inlet (42) and the outlet (44) have an offset (52) with respect to one another.

5. Electric drive (10) according to claims 1 to 4, characterized in that the inlet (42) in a first axial plane (56) and the outlet (44) in a second axial plane (58) spaced apart therefrom in the axial direction (78) ) lies.

6. Electric drive (10) according to claims 1 to 5, characterized in that the axial ribs (62, 64) are carried out on draft bevels (68) of the outer part (48) and the inner part (50) of the housing.

7. Electric drive (10) according to claims 1 to 6, characterized in that the outer part (48) and the inner part (50) of the housing (25) are each designed with a conicity (82).

8. Electric drive (10) according to claims 1 to 7, characterized in that the axial ribbing (64) on an inner circumferential surface of the outer part (48) has a machined area (74) which is made in particular as a cylindrical overturning (71).

9. Electric drive (10) according to claims 1 to 7, characterized in that the axial ribbing (62) on a first outer peripheral surface of the inner part (50) has a machined area (74), which is designed in particular as a conical overturning (70) .

10. Electric drive (10) according to claims 1 to 9, characterized in that the conicity (82) is determined by a first diameter (84) and a second diameter (86) of the inner part (50) of the housing (25).

11. Electric drive (10) according to claims 1 to 10, characterized in that the stator (24) of the electric machine is fixed by a shrink connection (66) in the inner part (50) of the housing (25).

12. Electric drive (10) according to claims 1 to 11, characterized in that the axial ribbing (62) of the inner part (50) of the housing (25) has interruptions (76) which give the flow (46) of the cooling medium a turbulent state imprint.

13. Use of the electric drive (10) according to one of the preceding claims in an e-axle module of an electrically powered vehicle.