WO2023186399A1

WO2023186399A1 - Improved metal stator housing of an electric machine and manufacturing method for the same

Info

Publication number: WO2023186399A1
Application number: PCT/EP2023/053909
Authority: WO
Inventors: Saparivel PALANISAMY; Venkatesan KUPPUSAMY; Hari Krishnan
Original assignee: Valeo Eautomotive Germany Gmbh
Priority date: 2022-03-31
Filing date: 2023-02-16
Publication date: 2023-10-05

Abstract

A metal stator housing (7a, 7b) of an electric machine (1) and a manufacturing method for the same is disclosed. The metal stator housing (7a, 7b) comprises a cooling channel (9) and is manufactured by use of investment casting, particularly in one piece. In addition, an electric machine (1) with such a metal stator housing (7a, 7b) and an electric vehicle (18) with such an electric machine (1) is disclosed.

Description

Improved metal stator housing of an electric machine and manufacturing method for the same

TECHNICAL FIELD

The invention relates to a metal stator housing of an electric machine, wherein the stator housing comprises a cooling channel, and to a method of manufacturing the same. Moreover, the invention relates to an electric machine, which comprises a metal stator housing of the above kind, a stator, which is arranged in the metal stator housing, and a rotor, which is rotatably arranged in the stator. Finally, the invention relates to an electric vehicle with a drivetrain comprising an electric machine as defined above, which is provided to propel the electric vehicle.

BACKGROUND ART

A metal stator housing of an electric machine and a manufacturing method for the same as well as an electric machine and an electric vehicle of the above kind are generally known. A liquid (e.g. water or oil) can pass (e. g. under pressure) through the cooling channel of the housing to cool the electric machine. For this reason, the cooling channel may hydraulically be connected to a pump and a cooler. To form the cooling channel, the stator housing commonly is made of an inner stator housing part and an outer stator housing part with the cooling channel in-between. Because the liquid is under pressure, when it flows through the cooling channel, a proper sealing is necessary according to prior art to avoid that the cooling fluid drains out of a gap between the inner stator housing part and the outer stator housing part. For this reason, usually sealings like O-rings are used to seal the cooling channel on both sides of the same. However, attaching O-rings is time consuming and checking a proper seat of the same in the mounted condition of the housing is problematic. Moreover, sealings may degrade over time what increases the risk of a leakage. DISCLOSURE OF INVENTION

An object of the invention is to provide an improved metal stator housing of an electric machine, an improved electric machine, an improved electric vehicle and an improved method of manufacturing such a metal stator housing. In particular, a solution shall be proposed, which reduces the number of parts and if possible avoids the use of sealings without compromising the liquid-tightness of the cooling channel.

The object of the invention is solved by a method of manufacturing a metal stator housing as disclosed in the opening paragraph, wherein the stator housing (including the cooling channel) is manufactured by use of investment casting.

In particular, the method can comprise the steps of manufacturing a plastic or wax model of the stator housing, surrounding the plastic or wax model with ceramic slurry and filling ceramic slurry into a cavity of the plastic or wax model, wherein the cavity corresponds to the cooling channel, forming a mold by curing the ceramic slurry and melting and removing the plastic or wax model by application of heat, filling molten metal into the mold and removing the mold after the metal has been solidified.

Alternatively, the method can comprise the steps of manufacturing a plastic or wax model of the stator housing (only) in an area surrounding the cooling channel, filling ceramic slurry into a cavity of the plastic or wax model, wherein the cavity corresponds to the cooling channel, forming a core by curing the ceramic slurry and melting and removing the plastic or wax model by application of heat, forming a mold by inserting the core into an outer mold, the shape of which corresponds to the metal stator housing except of the core (i.e. the outer mold corresponds to the outer contour of the metal stator housing), filling molten metal into the mold and removing the mold including the core after the metal has been solidified.

In the first preferred embodiment, the mold is one-piece and includes the core for the cooling channel. Accordingly, the plastic or wax model of the stator housing in this embodiment includes a cavity corresponding to the cooling channel. In the second embodiment, the core for the cooling channel is a separate piece, which is put into an outer mold, the shape of which corresponds to the metal stator housing except of the core. The outer mold and the core form the mold for the casting process. In both cases, the mold comprises the core for the cooling channel.

In general, the investment casting process comprises the manufacturing of a plastic or wax model, the surface of which (including interior surfaces) is covered by ceramic slurry. Then, the ceramic slurry is cured, and the plastic or wax of the model is melted and removed by application of heat. In particular, said curing and melting/removing can be done in a single process step. However, it is also possible to cure the ceramic slurry first so that a mold or core is formed and to subsequently melt and remove the plastic or wax. Finally, molten metal is filled into the mold, which forms the stator housing. Once the metal has solidified, the mold can be removed (e.g. by application of vibration) so that the metal stator housing results in the end. In the second embodiment, the outer mold can be made by use of investment casting, too, but can also be made by use of another casting technique.

The object of the invention is also solved by a metal stator housing as defined in the opening paragraph, wherein the metal stator housing is manufactured in one piece by use of investment casting. In particular, the metal stator housing can be manufactured according to the above method and its preferred variants. In addition, the object of the invention is solved by an electric machine, which comprises a metal stator housing of the above kind.

Finally, the object of the invention is solved by an electric vehicle with a drivetrain comprising an electric machine as defined above, which is provided to propel the electric vehicle.

By use of the proposed measures, sealings for a cooling channel can be saved what on the one hand reduces the bill of materials and on the other hand reduces the risk of leakage because of a damaged or degraded sealing. Hence, the cooling channel of the proposed stator housing is liquid-tight over a long time and usually for the whole lifetime of the electric machine. Accordingly, the electric machine in this respect does not need much maintenance or does not need maintenance at all.

Further advantageous embodiments are disclosed in the claims and in the description as well as in the figures.

In an advantageous embodiment, the plastic or wax model is manufactured by use of a 3D printer. Hence, complex shapes of the plastic or wax model and in turn of the metal stator housing can easily be produced.

Beneficially, after solidification of the molten metal, the cured ceramic slurry is removed from the cooling channel by application of vibration. Vibration assists removing the ceramic slurry from the metal stator housing, in particular also within the cooling channel. By these measures, the cooling channel can be cleaned well what reduces the risk that residues of the ceramic slurry get into a cooling circuit later on when the electric machine is in operation.

It is particularly advantageous if after removing the cured ceramic slurry from the cooling channel, residues are washed out by a liquid (in particular by water) flowing through the cooling channel or are blown out by applying forced air through the cooling channel. By these measures, the cooling channel can be cleaned even better what reduces the aforementioned risk further.

BRIEF DESCRIPTION OF DRAWINGS

The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

Fig. 1 shows a sectional view of an exemplary electric machine;

Fig. 2 shows a stator housing in perspective view;

Fig. 3 shows the stator housing of Fig. 2 in front view;

Fig. 4 shows a plastic or wax model of the stator housing of Fig. 2 in cross sectional view;

Fig. 5 shows ceramic slurry surrounding and flowing into the plastic or wax model of Fig. 4;

Fig. 6 shows a mold for the stator housing of Fig. 2 which is based on the plastic or wax model of Fig. 4 and which is ready for casting;

Fig. 7 shows molten metal in the mold of Fig. 6;

Fig. 8 shows the stator housing of Fig. 2 after removal of the mold in cross sectional view;

Fig. 9 shows a plastic or wax model for the cooling channel of the stator housing of Fig. 2 in cross sectional view;

Fig. 10 shows ceramic slurry flowing into the plastic or wax model of Fig. 9; Fig. 11 shows a core for the cooling channel after removal of the plastic or wax model of Fig. 9 in perspective view;

Fig. 12 shows an outer mold for the outer contour of the stator housing of Fig. 2 and

Fig. 13 shows a schematic view of an electric vehicle.

DETAILED DESCRIPTION

Generally, same parts or similar parts are denoted with the same/similar names and reference signs. The features disclosed in the description apply to parts with the same/similar names respectively reference signs. Indicating the orientation and relative position is related to the associated figure.

Fig. 1 shows a half section through a schematically drawn electric machine 1 . The electric machine 1 comprises a rotor shaft 2 with a rotor 3 mounted thereon, wherein the rotor shaft 2 is rotatably supported around a rotor axis A and relative to a stator 5 by means of (rolling) bearings 4a, 4b. The rotor 3 has a rotor lamination pack and rotor magnets mounted therein which are not explicitly shown in Fig. 1 . Moreover, the stator 5 has a stator lamination pack with stator windings arranged therein which are not explicitly shown in Fig. 1 either.

Moreover, the electric machine 1 comprises a housing 6 with stator housing 7a and a bearing plate 8. The stator housing 7a comprises a cooling channel 9, through which a (liquid) heat carrier can flow to cool the electric machine 1 .

Fig. 2 shows a perspective view of a further example of a stator housing 7b. In particular, Fig. 2 shows cooling channel connectors 10a, 10b of the stator housing 7b which are hydraulically connected to the cooling channel 9 and which are provided to connect the electric machine 1 (strictly speaking its cooling channel 9) to a cooling circuit. Fig. 3 additionally shows a front view of the stator housing 7b of Fig. 2.

Figs. 4 to 8 now illustrate process steps of a first embodiment of a method for manufacturing the metal stator housing 7a, 7b. In detail, Fig. 4 shows a plastic or wax model 11a of the stator housing 7b in axial section. For example, the plastic or wax model 11 a can be manufactured by use of a 3D printer what allows producing complex shapes. However, other methods for making the plastic or wax model 11a are applicable as well. In particular, the plastic or wax model 11a comprises a cavity 12, which corresponds to the cooling channel 9.

Fig. 5 shows a second process step where the plastic or wax model 11a is surrounded with ceramic slurry 13 and where ceramic slurry 13 is filled into a cavity 12.

Fig. 6 illustrates a further process step where a mold 14 is formed by curing the ceramic slurry 13 and by melting and removing the plastic or wax model 11a by application of heat. The mold 14 is one-piece and comprises an outer mold 15a (strictly speaking an outer mold section) and a core 16a (strictly speaking a core section), wherein the core 16a corresponds to the later cooling channel 9. So basically, a shape remains which encloses a virtual metal stator housing 7b (of course under consideration of shrinkage of the metal used for the stator housing 7b).

Fig. 7 illustrates a process step where molten metal 17 is filled into the mold 14. Note that Figs. 4 to 8 do not explicitly shows a casting channel, but in reality one or more of these channels are provided to allow the metal flow into the mold 14).

Fig. 8 finally shows the metal stator housing 7b after the metal 17 has been solidified and after the mold 14 has been removed (e.g. by subjecting the metal stator housing 7b to vibration). So, concluding, a first embodiment of a method of manufacturing the metal stator housing 7a, 7b can comprise the steps of: manufacturing a plastic or wax model 11 a of the stator housing 7a, 7b, surrounding the plastic or wax model 11 a with ceramic slurry 13 and filling ceramic slurry 13 into a cavity 12 of the plastic or wax model 11a, wherein the cavity 12 corresponds to the cooling channel 9, forming a mold 14 by curing the ceramic slurry 13 and melting and removing the plastic or wax model 11 a by application of heat, filling molten metal 17 into the mold 14 and removing the mold 14 after the metal 17 has been solidified.

However, this is not the only possibility to fabricate a metal stator housing 7a, 7b, and Figs. 9 to 12 illustrate a second embodiment of a method for manufacturing the metal stator housing 7a, 7b.

Fig. 9 in detail shows a plastic or wax model 11 b of the stator housing 7b in an area surrounding the cooling channel 9. It is to be noted that the plastic or wax model 11 b of Fig. 9 is not a mold 14 for the whole stator housing 7b, but just for a core 16b for the cooling channel 9. Again, the plastic or wax model 11 b may be made by use of a 3D printer of by any other applicable method.

Fig. 10 shows a process step where ceramic slurry 13 is filled into a cavity 12 of the plastic or wax model 11 b, which cavity 12 corresponds to the cooling channel 9. In a further process step, the core 16b is formed by curing the ceramic slurry 13 and by melting and removing the plastic or wax model 11b by application of heat. Fig. 11 shows the resulting core 16b with the plastic or wax removed in perspective view.

Fig. 12 shows an outer mold 15b, the shape of which corresponds to the metal stator housing 7b except of the core 16b or in other words which corresponds to the outer contour of the metal stator housing 7b. The outer mold 15b can be made by use of investment casting as well but can also be made by use of another casting technique. In a next process step, a mold 14 is formed by inserting the core 16b into the outer mold 15b. So again, a shape results which encloses a virtual metal stator housing 7b (of course again under consideration of shrinkage of the metal used for the stator housing 7b). The shape of the mold 14 corresponds to the shape of the mold 14 shown in Fig. 6. Moreover, the subsequent process steps of the second embodiment equal to or are at least similar to the process steps illustrated by Figs. 6 to 8. That is why reference is also made to Figs. 6 to 8 and their description in view of the further process steps of the second embodiment.

Concluding, a second embodiment of a method of manufacturing the metal stator housing 7a, 7b can comprise the steps of: manufacturing a plastic or wax model 11 b of the stator housing 7a, 7b in an area surrounding the cooling channel 9, filling ceramic slurry 13 into a cavity 12 of the plastic or wax model 11 b, wherein the cavity 12 corresponds to the cooling channel 9, forming a core 16b by curing the ceramic slurry 13 and melting and removing the plastic or wax model 11 b by application of heat, forming a mold 14 by inserting the core 16b into an outer mold 15b, the shape of which corresponds to the metal stator housing 7a, 7b except of the core 16b, filling molten metal 17 into the mold 14 and removing the mold 14 including the core 16b after the metal 17 has been solidified.

Both the first and the second embodiment of the manufacturing method are examples of an investment casting process. These embodiments are advantageous but nevertheless the stator housing 7a, 7b can also be manufactured by a different type of investment casting.

Beneficially, the outcome of such an investment casting process can be a one- piece stator housing 7a, 7b with a cooling channel 9 inside. So, there is no need for sealing the cooling channel 9 against drainage by use of separate sealings like O-rings etc. Instead, sealings for a cooling channel 9 can be saved what on the one hand reduces the bill of materials and on the other hand reduces the risk of leakage because of a damaged or degraded sealing. Hence, the cooling channel 9 of the proposed stator housing 7a, 7b is liquid-tight over a long time and usually for the whole lifetime of the electric machine 1 . Accordingly, the electric machine 1 in this respect does not need much maintenance or does not need maintenance at all.

Generally, after solidification of the molten metal, the core 16a, 16b can be removed from the cooling channel 9 by application of vibration. Vibration causes or at least assists removing the core 16a, 16b from the metal stator housing 7a, 7b. By these measures, the cooling channel 9 can be cleaned well what reduces the risk that residues of the core 16a, 16b get into a cooling circuit later on when the electric machine 1 is in operation. To get the cooling channel 9 even cleaner and to reduce the aforementioned risk even further, residues of the core 16a, 16b can be washed out by a liquid (in particular by water) flowing through the cooling channel 9 or blown out by applying forced air through the cooling channel.

Fig. 13 finally shows an electric vehicle 18 with a drivetrain comprising an electric machine 1 as defined hereinbefore, which is provided to propel the electric vehicle 18. In detail, the electric machine 1 is coupled to gearbox 19, side shafts 20 and finally to the wheels 21 . The electric machine 1 may be provided for powering the electric vehicle 18 permanently in a pure electric car or intermittently, e.g. in combination with a combustion engine in a hybrid car. In addition, the electric vehicle of Fig. 13 comprises a cooling circuit with the electric machine 1 , a pump 22 and a cooler 23, wherein the electric machine 1 is connected to tubes of the cooling circuit via its cooling channel connectors 10a, 10b.

It is noted that the invention is not limited to the embodiments disclosed hereinbefore, but combinations of the different variants are possible. In reality, the stator housing 7a, 7b, the mold 14, the electric machine 1 and the electric vehicle 18 may have more or less parts than shown in the figures. It is also noted, that the stator housing 7a, 7b, the mold 14, the electric machine 1 and the electric vehicle 18 or parts thereof are not necessarily drawn to scale in the Figs.

Moreover, the description may comprise subject matter of further independent inventions.

It should also be noted that the term "comprising" does not exclude other elements and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

List of Reference Numerals

1 electric machine

2 rotor shaft

3 rotor

4a, 4b bearing

5 stator

6 housing

7a, 7b stator housing

8 bearing plate

9 cooling channel

10a, 10b cooling channel connector

11a, 11 b plastic or wax model

12 cavity

13 ceramic slurry

14 mold

15a, 15b outer mold

16a, 16b core

17 molten metal

18 electric vehicle

19 gearbox

20 side shaft

21 wheel

22 pump

23 cooler

A rotor axis

Claims

1 . Method of manufacturing a metal stator housing (7a, 7b) of an electric machine (1 ), wherein the stator housing (7a, 7b) comprises a cooling channel (9), characterized in that the stator housing (7a, 7b) is manufactured by use of investment casting.

2. Method as claimed in claim 1 , characterized by the steps of manufacturing a plastic or wax model (1 1 a) of the stator housing (7a, 7b), surrounding the plastic or wax model (1 1 a) with ceramic slurry (13) and filling ceramic slurry (13) into a cavity (12) of the plastic or wax model (11 a), wherein the cavity (12) corresponds to the cooling channel (9), forming a mold (14) by curing the ceramic slurry (13) and melting and removing the plastic or wax model (11 a) by application of heat, filling molten metal (17) into the mold (14) and removing the mold (14) after the metal (17) has been solidified.

3. Method as claimed in claim 1 , characterized by the steps of manufacturing a plastic or wax model (1 1 b) of the stator housing (7a, 7b) in an area surrounding the cooling channel (9), filling ceramic slurry (13) into a cavity (12) of the plastic or wax model (11 b), wherein the cavity (12) corresponds to the cooling channel (9), forming a core (16b) by curing the ceramic slurry (13) and melting and removing the plastic or wax model (11 b) by application of heat, forming a mold (14) by inserting the core (16b) into an outer mold (15b), the shape of which corresponds to the metal stator housing (7a, 7b) except of the core (16b), filling molten metal (17) into the mold (14) and removing the mold (14) including the core (16b) after the metal (17) has been solidified.

4. Method as claimed in claim 2 or 3, characterized in that the plastic or wax model (11a, 11 b) is manufactured by use of a 3D printer.

5. Method as claimed in any one of claims 2 to 4, characterized in that after solidification of the molten metal (17), the cured ceramic slurry (13) is removed from the cooling channel (9) by application of vibration.

6. Method as claimed in claim 5, characterized in that after removing the cured ceramic slurry (13) from the cooling channel (9), residues are washed out by a liquid flowing through the cooling channel (9) or are blown out by applying forced air through the cooling channel.

7. Metal stator housing (7a, 7b) of an electric machine (1), wherein the metal stator housing (7a, 7b) comprises a cooling channel (9), characterized in that the metal stator housing (7a, 7b) is manufactured in one piece by use of investment casting.

8. Electric machine (1), comprising a metal stator housing (7a, 7b) as claimed in claim 7, a stator (5), which is arranged in the metal stator housing (7a, 7b) and a rotor (3), which is rotatably arranged in the stator (5).

9. Electric vehicle (18) with a drivetrain comprising an electric machine (1 ) as claimed in claim 8, which is provided to propel the electric vehicle (18).