Electric machine with improved cooling bores and method of making the same

Abstract

An electric machine (1) with a stator (7), a rotor (10) and a cooling system (15) for cooling the electric machine (1) by means of a liquid coolant is disclosed, wherein the cooling system (15) comprises a plurality of bores (22a, 22b, 23a, 23b) for spraying the coolant into an interior (E) of the electric machine (1). At least some of the bores (22a, 22b, 23a, 23b) each comprise a first bore section (B1), which is distant from said interior (E) and which has a first diameter (d1), and a second bore section (B2), which opens into said interior (E) and which has a second diameter (d2), wherein the first bore section (B1) and the second bore section (B2) are hydraulically interconnected and wherein the first diameter (d1) is larger than the second diameter (d2). Moreover, a vehicle (26) with such an electric machine (1) and methods for manufacturing the bores (22a, 22b, 23a, 23b) of the cooling system (15) of an electric machine (1) are disclosed.

Description

[0001] Electric machine with improved cooling bores and method of making the same

[0002] TECHNICAL FIELD

[0003] The invention relates to an electric machine with a stator, a rotor and a cooling system for cooling the electric machine by means of a liquid coolant, wherein the cooling system comprises a plurality of bores for spraying the coolant into an interior of the electric machine. Moreover, the invention relates to a vehicle with such an electric machine, wherein the electric machine is provided to propel the vehicle, and to methods of manufacturing the bores of the cooling system of such an electric machine.

[0004] BACKGROUND ART

[0005] An electric machine, a vehicle and methods of the above kinds are each generally known. Bores may be used to spray a coolant into the interior of an electric machine for cooling parts of the electric machine there, for example, a stator and / or a rotor of the electric machine. One drawback is that common designs do not provide for concentrating a cooling effect on hot spots effectively. Moreover, a varying wall thickness in a part of the electric machine, in which the bores are arranged, may lead to different flow resistances of the bores and hence to an inhomogeneous cooling effect.

[0006] DISCLOSURE OF INVENTION

[0007] Accordingly, an object of the invention is to provide an improved electric machine, an improved vehicle and improved methods of manufacturing cooling bores. In particular, a possibility for effective concentration of a cooling effect on hot spots of the electric machine and for compensating a varying wall thickness in a part of the electric machine, in which the bores are arranged, shall be proposed.

[0008] The object of the invention is solved by an electric machine as disclosed in the opening paragraph, wherein at least some of the bores each comprise a first bore section, which is distant from said interior and which has a first diameter, and a second bore section, which opens into said interior and which has a second diameter, wherein the first bore section and the second bore section are hydraulically interconnected and wherein the first diameter is larger than the second diameter. In particular, the first diameter can be at least two times the second diameter.

[0009] Moreover, the object of the invention is solved by a vehicle as disclosed in the opening paragraph, wherein the vehicle comprises an electric machine of said kind and wherein the electric machine is provided to propel the vehicle.

[0010] The object of the invention is also solved by a method as disclosed in the opening paragraph, wherein the first bore section is drilled with a first drill and subsequently the second bore section is drilled with a second drill. In particular, the second drill may have a thickened drill shaft so that the second drill is less prone to breakage.

[0011] Finally, the object of the invention is solved by an alternative method as disclosed in the opening paragraph, wherein the first bore section and the second bore section are drilled with a single stepped drill. In this way, the bore can be manufactured in a single process step.

[0012] By use of the proposed measures, a laminar flow of the coolant can be obtained or improved. Moreover, a minimum outlet velocity can be ensured. Accordingly, the cooling effect can be concentrated on hot spots more effectively. In addition, a flow resistance of the bores can easily be set, in detail by the lengths of the first and second bore section. In this way, a varying wall thickness in a part of the electric machine, in which the bores are arranged, can easily be compensated. Such a part may be a housing of the electric machine. For example, the second bore sections (with the smaller diameter) of at least two of the bores can have the same length, whereas the first bore sections (with the larger diameter) of the at least two bores have different length. In other words, a flow resistance can be set or a varying wall thickness can be compensated by varying the lengths of the first bore sections. In particular, the second bore sections of all bores can have the same length, whereas the first bore sections of at least two of the bores have different length.

[0013] For example, the bores can be directed to a stator winding head of the stator or to a rotor winding head of the rotor. Accordingly, hot spots of the electric machine can effectively be cooled. Further on, it is beneficial if the first bore section and the second bore section are coaxial.

[0014] In this way, manufacturing the bores is eased

[0015] In one embodiment, the cooling system can comprise a stator channel, which is arranged in a stator housing of the electric machine and comprises an annular section, wherein the first bore section opens from the annular section. In this way, the coolant can be supplied to a plurality of bores by the annular section.

[0016] In one further embodiment, the cooling system can comprise a helical section hydraulically connected to the annular section. The helical section can be provided for cooling a stator housing part, which the stator is built into. In this way, the stator can be cooled at its cylindrical outer surface (strictly speaking at its cylindrical jacket).

[0017] In an advantageous embodiment, the stator cooling system can comprise a helical section, which is hydraulically separated from the annular section, the annular section can be provided to be flown through by a first liquid coolant and the helical section can be provided to be flown through by a second liquid coolant, which is different from the first coolant.

[0018] Accordingly, two different coolants can be used for the annular section, where the bores are located, and the helical section, which is used for cooling the stator at its cylindrical outer surface. Because the first coolant is sprayed into an interior of the electric machine, it can be used there for lubrication of parts of the electric machine if the first coolant has a lubrication function. Parts to be lubricated, for example, can be bearings of the electric machine. In contrast, the second lubricant can be water based without a prominent lubrication function but with superior cooling characteristics. So, well chosen coolants can be used for different functions by the proposed measures.

[0019] For example, a transition from the first bore section to the second bore section can be conical, step shaped or rounded. Conical and step shaped transitions are easy to manufacture, whereas rounded transitions usually are better in view of the coolant flow and cause less turbulences. In yet another embodiment, the bores can be orientated angularly in view of a rotor axis. In this way, the coolant can also be sprayed onto an inner or outer surface of stator winding head or rotor winding head and not only on their front faces.

[0020] BRIEF DESCRIPTION OF DRAWINGS

[0021] The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

[0022] Fig. 1 shows a half sectional view of an exemplary electric machine;

[0023] Fig. 2 shows an oblique view of an exemplary inner stator housing with an annular and a helical cooling section;

[0024] Fig. 3 shows a cross sectional view of the inner stator housing of Fig. 2 viewed at a slight angle from the side;

[0025] Fig. 4 shows a detailed cross sectional view of the inner stator housing of Fig. 3 and

[0026] Fig. 5 shows a schematic view of an electric vehicle.

[0027] DETAILED DESCRIPTION

[0028] 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.

[0029] Fig. 1 shows a half sectional view of an exemplary electric machine 1. The electric machine 1 comprises a machine housing 2 with a stator housing 3, wherein the stator housing 3 comprises an inner stator housing 4 and an outer stator housing 5 radially arranged out of the inner stator housing 4. Moreover, the machine housing 2 comprises a bearing shield 6. In addition, the electric machine 1 comprises a stator 7 with a stator lamination stack 8 and stator windings arranged in the stator lamination stack 8, from which only the stator winding heads 9 are visible in Fig. 1. Further on, the electric machine 1 comprises a rotor 10 with a rotor shaft 1 1 and a rotor lamination stack 12 mounted to the rotor shaft 1 1 . In addition, the rotor 10 comprises rotor windings arranged in the rotor lamination stack 12, from which only the rotor winding heads 13 are visible in Fig. 1 . Moreover, the electric machine 1 comprises a first (roller) bearing 14a in the inner stator housing 4 and a second (roller) bearing 14b in the bearing shield 6 for rotatably supporting the rotor 10 around a rotor axis RA.

[0030] Further on, the electric machine 1 comprises a cooling system 15 with a stator cooling system 16 and a rotor cooling system 17. The stator cooling system 16 comprises a stator channel 18 in the machine hosing 2 (in detail in the stator housing 3), and the rotor cooling system 17 comprises rotor channels 19a, 19b in the machine hosing 2. Moreover, the cooling system 15 comprises connecting channels 20a, 20b, which connect the stator channel 18 and the rotor channels 19a, 19b, and connectors 21 a, 21 b, wherein the connector 21 a forms a coolant inlet and the connector 21 b forms a coolant outlet as it is illustrated in Fig. 1 by the coolant flow F. Further on, the cooling system 15 (in detail the stator cooling system 16) comprises stator nozzle or bores 22a, 22b, which are directed onto the stator winding heads 9 so that a coolant is sprayed onto the stator winding heads 9 for cooling the same. In addition, the cooling system 15 (in detail the rotor cooling system 17) comprises rotor nozzle or bores 23a, 23b, which are directed onto the rotor winding heads 13 so that a coolant is sprayed onto the rotor winding heads 13 for cooling the same. The coolant may have a lubrication function and may be used for lubrication of parts in the interior E of the electric machine 1 , for example for lubrication of the bearings 14a, 14b.

[0031] In the example of Fig. 1 the (stator) bores 22a, 22b are oriented perpendicularly in view of the rotor axis RA, and the (rotor) bores 23a, 23c are oriented parallel to the rotor axis RA. However, alternatively, the bores 22a, 22b, 23a, 23c can also be orientated angularly in view of a rotor axis RA. In this way, the coolant can also be sprayed on different surfaces of stator winding head 9 or rotor winding head 13 and not only on the surfaces indicated in Fig. 1.

[0032] In general, at least some of the bores 22a, 22b, 23a, 23b each comprise a first bore section B1 , which is distant from said interior E and which has a first diameter d1 , and a second bore section B2, which opens into said interior E and which has a second diameter d2, wherein the first bore section B1 and the second bore section B2 are hydraulically interconnected and wherein the first diameter d1 is larger than the second diameter d2. This feature is not visible in Fig. 1 but depicted in Fig. 4 in detail.

[0033] Figs. 2 to 4 now show an example of an inner stator housing 4a. Fig. 2 shows an oblique view of the inner stator housing 4a, Fig. 3 shows a cross sectional view of the inner stator housing 4a viewed at a slight angle from the side, and Fig. 4 shows a detailed cross sectional view of the inner stator housing 4a.

[0034] The inner stator housing 4a comprises a stator channel 18 with an annular section S1 , from where the first bore section B1 opens, and a helical section S2. In one embodiment, the helical section S2 can be hydraulically connected to the annular section S1 . Accordingly, the helical section S2 and the annular section S1 are flown through by a common coolant, and a cooling circuit can be kept relatively simple. In an alternative embodiment, the helical section S2 can be hydraulically separated from the annular section S1. In that case, the annular section S1 can be flown through by a first liquid coolant and the helical section S2 can be flown through by a second liquid coolant, which is different from the first coolant. In this embodiment, the first coolant is the one, which is sprayed into the interior E of the electric machine 1 . Accordingly, if the first coolant has a lubrication function, it can be used for lubrication of parts of the electric machine 1 , for example, the bearings 14a, 14b. In contrast, the second lubricant can be water based without a prominent lubrication function but with superior cooling characteristics. So, well chosen coolants can be used for different functions by the proposed measures.

[0035] To balance a flow F between the stator channel 18 and a rotor channel 19’, which is embodied as a pipe here, balancing means 24 can be provided between the stator channel 18 and a rotor channel 19’. In this example, in detail, the balancing means 24 comprise two narrowings 25a, 25b, and in detail the coolant flows from the stator channel 18 (in detail from its annular section S1 ) into the connecting channel 20’ and from there into the rotor channel 19’. It should be noted that the rotor channel 19’ seems to hover in Fig. 2. However, in reality, the rotor channel 19’ can be fixed to the machine housing 2, for example. Fig. 4 shows that the first bore section B1 and the second bore section B2 are coaxial. In this way, the bores 22a are easy to manufacture. For example, the first bore section B1 can be drilled with a first drill and subsequently the second bore section B2 can be drilled with a second drill. In particular, the second drill can have a thickened drill shaft so that it is less prone to breakage. In an alternative embodiment, the first bore section B1 and the second bore section B2 can be drilled with a single stepped drill. In this way, the bores 22a can be made very fast. Preferably, the first diameter d1 can be at least two times the second diameter d2.

[0036] A transition C from the first bore section B1 to the second bore section B2 can be conical, step shaped or rounded. Conical and step shaped transitions C are easy to manufacture, whereas rounded transitions C usually are better in view of the coolant flow and cause less turbulences.

[0037] Generally, the proposed measures provide for a laminar flow of the coolant and ensure a minimum outlet velocity by choosing a suitable second diameter d2. Accordingly, the cooling effect can be concentrated on hot spots of the electric machine 1 more effectively. In addition, a flow resistance of the bores 22a, 22b, 23a, 23c can easily be set, in detail by the lengths 11 , 12 of the first and second bore section B1 and B2. In this way, a varying wall thickness in a part of the electric machine 1 , in which the bores 22a, 22b, 23a, 23c are arranged, can easily be compensated. Such a part may be the machine housing 2 like it is the case in the depicted examples. As is depicted in the Figs., a plurality of (stator) bores 22a, 22b and (rotor) bores 23a, 23c can be provided, and for said compensation, the second bore sections B2 of at least two of the bores 22a, 22b, 23a, 23c can have the same length I2, whereas the first bore sections B1 of the at least two bores 22a, 22b or 23a, 23c can have different length 11 , for example. In particular, the second bore sections B2 of all bores 22a, 22b or 23a, 23c can have the same length I2, whereas the first bore sections B1 of at least two of the bores 22a, 22b or 23a, 23c have different length 11 . In other words, a flow resistance can be set or a varying wall thickness can be compensated in particular by varying the lengths 11 of the first bore sections B1 .

[0038] It should be noted at this point that the technical teaching, although it partly was disclosed only in the context of the stator cooling system 16 and the (stator) bores 22a, 22b, equally applies to the rotor cooling system 15 and the (rotor) bores 23a, 23c. Fig. 5 finally shows an electric vehicle 26 with an electric machine 1 as defined hereinbefore, which is provided to propel the electric vehicle 26. In detail, the electric machine 1 is coupled to an optional gearbox 27, side shafts 28 and finally to the wheels 29. The electric machine 1 may be provided for powering the electric vehicle 26 permanently in a pure electric car or intermittently, e.g. in combination with a combustion engine in a hybrid car. The electric vehicle 26 additionally comprises a coolant pump 30 and cooler or heat exchanger 31 , which together with the cooling system 15 of the electric machine 1 form a cooling circuit.

[0039] 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 electric machine 1 and the electric vehicle 26 may have more or less parts than shown in the figures. It is also noted that the electric machine 1 and the electric vehicle 26 or parts thereof are not necessarily drawn to scale in the Figs. Moreover, the description may comprise subject matter of further independent inventions.

[0040] 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.

[0041] List of References

[0042] 1 electric machine

[0043] 2 machine housing

[0044] 3 stator housing

[0045] 4, 4a inner stator housing

[0046] 5 outer stator housing

[0047] 6 bearing shield

[0048] 7 stator

[0049] 8 stator lamination stack

[0050] 9 stator winding head

[0051] 10 rotor

[0052] 11 rotor shaft

[0053] 12 rotor lamination stack

[0054] 13 rotor winding head

[0055] 14a, 14b bearing

[0056] 15 cooling system

[0057] 16 stator cooling system

[0058] 17 rotor cooling system

[0059] 18 stator channel

[0060] 19a, 19b, 19’ rotor channel

[0061] 20a, 20b, 20’ connecting channel

[0062] 21 a, 21 b connector (coolant inlet or coolant outlet)

[0063] 22a, 22b stator nozzle or bore

[0064] 23a, 23b rotor nozzle or bore

[0065] 24 balancing means

[0066] 25a, 25b narrowing 26 vehicle

[0067] 27 gear

[0068] 28 side shaft

[0069] 29 wheel

[0070] 30 coolant pump

[0071] 31 cooler / heat exchanger d1 first diameter d2 second diameter

[0072] 11 first length

[0073] 12 second length

[0074] B1 first bore section

[0075] B2 second bore section

[0076] C transition

[0077] E interior of electric machine

[0078] F coolant flow

[0079] RA stator axis / rotor axis

[0080] 51 annular section

[0081] 52 helical section

Claims

Claims1. Electric machine (1 ) with a stator (7), a rotor (10) and a cooling system (15) for cooling the electric machine (1 ) by means of a liquid coolant, wherein the cooling system (15) comprises a plurality of bores (22a, 22b, 23a, 23b) for spraying the coolant into an interior (E) of the electric machine (1 ). wherein at least some of the bores (22a, 22b, 23a, 23b) each comprise a first bore section (B1 ), which is distant from said interior (E) and which has a first diameter (d1 ), and a second bore section (B2), which opens into said interior (E) and which has a second diameter (d2), wherein the first bore section (B1 ) and the second bore section (B2) are hydraulically interconnected and wherein the first diameter (d1 ) is larger than the second diameter (d2).

2. Electric machine (1 ) as claimed in claim 1 , wherein the first bore section (B1 ) and the second bore section (B2) are coaxial.

3. Electric machine (1 ) as claimed in claim 1 or 2, wherein the stator cooling system (16) comprises a stator channel (18), which is arranged in a stator housing (3) of the electric machine (1 ) and comprises an annular section (S1 ), wherein the first bore section (B1 ) opens from the annular section (S1 ).

4. Electric machine (1 ) according to claim 3, wherein the stator channel (18) comprises a helical section (S2) hydraulically connected to the annular section (S1 ).

5. Electric machine (1 ) according to claim 3, wherein the stator cooling system (16) comprises a helical section (S2), which is hydraulically separated from the annular section (S1 ), the annular section (S1 ) is provided to be flown through by a first liquid coolant and the helical section (S2) is provided to be flown through by a second liquid coolant, which is different from the first coolant.

6. Electric machine (1 ) according to any one of the claims 1 to 5, wherein a transition (C) from the first bore section (B1 ) to the second bore section (B2) is conical, step shaped or rounded.

7. Electric machine (1) according to any one of the claims 1 to 7, wherein the bores (22a, 22b, 23a, 23b) are orientated angularly in view of a rotor axis (RA).

8. Electric machine (1) according to any one of the claims 1 to 8, wherein the bores (22a, 22b, 23a, 23b) are directed to a stator winding head (9) of the stator (7) or to a rotor winding head (13) of the rotor (10).

9. Electric machine (1) according to any one of the claims 1 to 9, wherein the second bore sections (B2) of at least two of the bores (22a, 22b, 23a, 23b) have the same length (I2), whereas the first bore sections (B1 ) of the at least two bores (22a, 22b, 23a, 23b) have different length (11 ).

10. Electric machine (1 ) according to claim 9, wherein the second bore sections (B2) of all bores (22a, 22b, 23a, 23b) have the same length (I2), whereas the first bore sections (B1 ) of at least two of the bores (22a, 22b, 23a, 23b) have different length (11).11 . Vehicle (26) with an electric machine (1 ) according to any one of the claims 1 to 10, wherein the electric machine (1 ) is provided to propel the vehicle (26).

12. Method of manufacturing the bores (22a, 22b, 23a, 23b) of the cooling system (15) of an electric machine (1) according to any one of the claims 1 to 10, wherein the first bore section (B1 ) is drilled with a first drill and subsequently the second bore section (B2) is drilled with a second drill.

13. Method as claimed in claim 12, wherein the second drill has a thickened drill shaft.

14. Method of manufacturing the bores (22a, 22b, 23a, 23b) of the cooling system (15) of an electric machine (1) according to any one of the claims 1 to 10, wherein the first bore section (B1 ) and the second bore section (B2) are drilled with a single stepped drill.

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