Electric machine with balancing a coolant flow between a stator cooling system and a rotor

Abstract

An electric machine (1) with a stator (7), a rotor (10) and a cooling system (15), which is based on a liquid coolant, is disclosed. The cooling system (15) comprises a stator cooling system (16) for cooling the stator (7) and a rotor cooling system (17) for cooling the rotor (10), wherein the rotor cooling system (17) is hydraulically connected to the stator cooling system (16). Moreover, the cooling system (15) comprises balancing means (24), which are designed for balancing a coolant flow (F) of the liquid coolant between the stator cooling system (16) and the rotor cooling system (17). Moreover, a vehicle (26) with such an electric machine (1) is disclosed.

Description

[0001] Electric machine with balancing a coolant flow between a stator cooling system and a rotor cooling system and vehicle thereto

[0002] TECHNICAL FIELD

[0003] The invention relates to an electric machine with a stator, a rotor and a cooling system, which is based on a liquid coolant. The cooling system comprises a stator cooling system for cooling the stator and a rotor cooling system for cooling the rotor, wherein the rotor cooling system is hydraulically connected to the stator cooling system. Moreover, the invention relates to a vehicle with such an electric machine, wherein the electric machine is provided to propel the vehicle.

[0004] BACKGROUND ART

[0005] An electric machine and a vehicle of the above kinds are each generally known. Using a common coolant for both the stator cooling system and the rotor cooling system at first sight eases cooling of an electric machine. However, the rather complex hydraulic system within an electric machine, which involves a variety of flow resistances of the separate branches, lead to unforeseen problems in terms of an effective use of the cooling power. In detail this means that it is complicated to effectively cool hot spots of the electric machine, whereas excessive flow rates on parts of the electric machine, which do not produce too much heat, are avoided.

[0006] DISCLOSURE OF INVENTION

[0007] Accordingly, an object of the invention is to provide an improved electric machine and an improved vehicle. In particular, the cooling power shall effectively be used in interconnected stator and rotor cooling systems.

[0008] The object of the invention is solved by an electric machine as disclosed in the opening paragraph, wherein the cooling system comprises balancing means, which are designed for balancing a coolant flow of the liquid coolant between the stator cooling system and the rotor cooling system. 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.

[0009] By use of the proposed measures, a coolant flow between the stator cooling system and the rotor cooling system can be balanced what provides the possibility of effectively using a cooling power in interconnected stator and rotor cooling systems. In detail this means that, on the one hand, hot spots of the electric machine are effectively cooled, whereas on the other hand, excessive flow rates on parts of the electric machine, which do not produce too much heat, are avoided. For example, the balancing means can be embodied as one or more narrowings in the cooling system or in other words as flow orifices. In this context, one should note that the term “flow orifice” may synonymously used instead of “narrowing” in this disclosure.

[0010] In one embodiment, the cooling system for the coolant flow can comprise a stator channel of the stator cooling system, a rotor channel of the rotor cooling system, a connecting channel, which connects the stator channel and the rotor channel, and a connector forming a coolant inlet or coolant outlet, wherein the stator channel is arranged in a stator housing of the electric machine and is annular or at least comprises an annular section and wherein the connector is arranged in the annular section.

[0011] In this way, the stator housing provides a double function and it not only houses the stator but is also used for cooling the stator at its cylindrical outer surface. Moreover, the cooling system of the electric machine by use of the connector can easily be connected to a superordinate cooling circuit, for example to a cooling circuit of a vehicle, which the electric machine is built into.

[0012] In the above context, advantageously a) the balancing means can comprise narrowings in or of the stator channel on both sides of the connector, wherein the connecting channel connects to the stator channel between the narrowings and / or b) the balancing means can comprise a narrowing in or of the connecting channel.

[0013] In case a) the balancing means control the coolant flow from the connector to the stator channel, whereas in case b) the balancing means control the coolant flow in the connecting channel. Cases a) and b) may be combined, what is particularly useful if there is a (non- specified) third cooling system, which is hydraulically connected to the stator and rotor cooling system.

[0014] Beneficially, the connecting channel can connect to the stator channel vis-a-vis of the connector. In this way, in particular in case a), the narrowings in the or of the stator channel can be arranged close to each other.

[0015] In one further embodiment, the stator channel 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).

[0016] In a further 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.

[0017] Accordingly, two different coolants can be used for the annular section and the helical section, which is used for cooling the stator at its cylindrical outer surface. In case that 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.

[0018] For spraying out the coolant, the stator channel can comprise stator nozzles or bores. In particular, the stator nozzles or bores can be arranged in the annular section of the stator channel.

[0019] In another beneficial embodiment, the rotor channel can run around the rotor shaft and can comprise rotor nozzles or bores for spraying out the coolant. In this way, a complicated rotor cooling via a hollow rotor shaft can be avoided. Instead, the rotor channel is fixed in relation to the machine housing and preferably has no moving parts. The rotor channel in particular can be annular and moreover can be formed by a pipe. In case of two different coolants in the stator cooling system, the first coolant is sprayed out.

[0020] Generally, the connecting channel can be arranged in the stator housing of the electric machine, can be formed by a pipe running out of the or within the stator housing or partially can be arranged in the stator housing of the electric machine and partially can be formed by the pipe running out of the or within the stator housing.

[0021] If the connecting channel is arranged in the stator housing, installing the cooling system is comparably easy. However, if the connecting channel is formed by a pipe, then manufacturing the machine housing is eased and installation of the connecting channel is more flexible so that it can easily be adapted to different machine types

[0022] BRIEF DESCRIPTION OF DRAWINGS

[0023] The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

[0024] Fig. 1 shows a half sectional view of an exemplary electric machine;

[0025] Fig. 2 shows an oblique view of an exemplary inner stator housing with an annular and a helical cooling section;

[0026] Fig. 3 shows an oblique view of the inner stator housing of Fig. 2 more from the top side;

[0027] Fig. 4 shows a cross sectional view of the inner stator housing of Fig. 2 viewed at a slight angle from the side;

[0028] Fig. 5 shows a detailed cross sectional view of the inner stator housing of Fig. 2 and

[0029] Fig. 6 shows a schematic view of an electric vehicle.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Further on, the electric machine 1 comprises a cooling system 15, which is based on a liquid coolant, wherein the cooling system 15 comprises a stator cooling system 16 for cooling the stator 7 and a rotor cooling system 17 for cooling the rotor 10. The stator cooling system 16 comprises a stator channel 18 in the machine housing 2 (in detail in the stator housing 3), and the rotor cooling system 17 comprises rotor channels 19a, 19b in the machine housing 2. Moreover, the cooling system 15 comprises connecting channels 20a, 20b, by which the rotor cooling system 17 is hydraulically connected to the stator cooling system 16. In detail, the connecting channels 20a, 20b connect the stator channel 18 and the rotor channels 19a, 19b. Moreover the cooling system 15 comprises 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. In the example of Fig.1 , the connecting channels 20a, 20b are arranged in the stator housing 3 of the electric machine 1 .

[0034] Further on, the cooling system 15 (in detail the stator cooling system 16) comprises stator nozzles 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 nozzles 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. In detail, the rotor channels 19a, 19b, in which the rotor nozzles or bores 23a, 23b are arranged, can run around the rotor shaft 1 1 . 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.

[0035] In the example of Fig. 1 the stator nozzles or bores 22a, 22b are oriented perpendicularly in view of the rotor axis RA, and the rotor nozzles or 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 .

[0036] Figs. 2 to 5 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 an oblique view of the inner stator housing 4a more from a top side, Fig. 4 shows a cross sectional view of the inner stator housing 4a viewed at a slight angle from the side, and Fig. 5 shows a detailed cross sectional view of the inner stator housing 4a.

[0037] Generally, the cooling system 15 comprises balancing means 24, which are designed for balancing a coolant flow F of the liquid coolant between the stator cooling system 16 and the rotor cooling system 17. In the given example, the balancing means 24 comprise narrowings 25a, 25b in or of the stator channel 18 on both sides of the connector 21 a. The connector 21 a is not visible in Figs. 2 and 3, but it is arranged radially out of the stator channel 18 between the narrowings 25a, 25b (see also Figs. 4 and 5 in this context). The connecting channel 20a, 20’ partially is arranged in the stator housing 3a of the electric machine 1 and partially is formed by a pipe running within and also out of the stator housing 3a. Concretely, there is a first section of the connecting channel 20a, which is arranged in the stator housing 3a, and a second section of the connecting channel 20’, which is embodied as a pipe. In this example, the connecting channel 20a connects to the stator channel 18 between the narrowings 25a, 25b, in detail vis-a-vis of the connector 21 a. In addition, the balancing means 24 comprise a narrowing 25c in or of the connecting channel 20a. It should be noted at this point that the narrowings 25a, 25b can also be used without the narrowing 25c and the narrowing 25c can be used without the narrowings 25a, 25b.

[0038] The coolant enters the cooling system 15 via the connector 21 a and flows into the stator channel 18 and the connecting channel 20a, 20’ and from there into the rotor channel 19’. Because the connecting channel 20a connects to the stator channel 18 vis-a-vis of the connector 21 a, the narrowings 25a, 25b can be arranged close to each other, and a very compact design of the balancing means 24 can be provided.

[0039] Again, the rotor channel 19’ runs around the rotor shaft 11 and comprises rotor nozzles or bores 23a for spraying out the coolant. However, in this embodiment the rotor channel 19’ does not run within the machine housing 2 but is formed by a pipe mounted to the machine housing 2. In the Figs. 2 to 5, the rotor shaft 11 is not shown, however, in reality it extends along the rotor axis RA and is radially arranged within the rotor channel 19’ at the axial position of the rotor channel 19’.

[0040] In this example, the stator channel 18 is arranged in the inner stator housing 4a and comprises an annular section S1 , in which the connector 21 a, the narrowings 25a, 25b and the stator nozzles or bores 22a are arranged, 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 then, 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 such an 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.

[0041] By use of the proposed measures, a coolant flow F between the stator cooling system 16 and the rotor cooling system 17 can be balanced what provides the possibility of effectively using a cooling power. So, hot spots of the electric machine 1 can effectively be cooled without having excessive flow rates on parts of the electric machine 1 , which do not generate much heat.

[0042] Fig. 6 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 a cooler or heat exchanger 31 , which together with the cooling system 15 of the electric machine 1 form a cooling circuit.

[0043] 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.

[0044] 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.

[0045] List of References electric machine

[0046] 2 machine housing

[0047] 3, 3a stator housing

[0048] 4, 4a inner stator housing

[0049] 5, 5a outer stator housing

[0050] 6 bearing shield

[0051] 7 stator

[0052] 8 stator lamination stack

[0053] 9 stator winding head

[0054] 10 rotor

[0055] 11 rotor shaft

[0056] 12 rotor lamination stack

[0057] 13 rotor winding head

[0058] 14a, 14b bearing

[0059] 15 cooling system

[0060] 16 stator cooling system

[0061] 17 rotor cooling system

[0062] 18 stator channel

[0063] 19a, 19b, 19’ rotor channel

[0064] 20a, 20b, 20’ connecting channel

[0065] 21 a, 21 b connector (coolant inlet or coolant outlet)

[0066] 22a, 22b stator nozzle or bore

[0067] 23a, 23b rotor nozzle or bore

[0068] 24 balancing means

[0069] 25a..25c narrowing 26 vehicle

[0070] 27 gear

[0071] 28 side shaft

[0072] 29 wheel 30 coolant pump

[0073] 31 cooler / heat exchanger

[0074] E interior of electric machine

[0075] F coolant flow RA stator axis / rotor axis

[0076] S1 annular section

[0077] S2 helical section

Claims

Claims1. Electric machine (1 ) with a stator (7), a rotor (10) and a cooling system (15), which is based on a liquid coolant, wherein the cooling system (15) comprises a stator cooling system (16) for cooling the stator (7) and a rotor cooling system (17) for cooling the rotor (10), wherein the rotor cooling system (17) is hydraulically connected to the stator cooling system (16), wherein the cooling system (15) comprises balancing means (24), which are designed for balancing a coolant flow (F) of the liquid coolant between the stator cooling system (16) and the rotor cooling system (17).

2. Electric machine (1 ) as claimed in claim 1 , wherein the cooling system (15) for the coolant flow (F) comprises a stator channel (18) of the stator cooling system (16), a rotor channel (19a, 19b, 19’) of the rotor cooling system (17), a connecting channel (20a, 20b, 20’), which connects the stator channel (18) and the rotor channel (19a, 19b, 19’), and a connector (21 a, 21 b) forming a coolant inlet or coolant outlet, wherein the stator channel (18) is arranged in a stator housing (3, 3a) of the electric machine (1 ) and is annular or at least comprises an annular section (S1 ) and wherein the connector (21 a, 21 b) is arranged in the annular section (S1 ).

3. Electric machine (1 ) as claimed in claim 2, wherein a) the balancing means (24) comprise narrowings (25a, 25b) in or of the stator channel (18) on both sides of the connector (21 a, 21 b) and wherein the connecting channel (20a, 20b, 20’) connects to the stator channel (18) between the narrowings (25a, 25b) and / or b) the balancing means (24) comprise a narrowing (25c) in or of the connecting channel (20a, 20b, 20’).

4. Electric machine (1 ) according to claim 2 or 3, wherein the connecting channel (20a, 20b, 20’) connects to the stator channel (18) vis-a-vis of the connector (21 a, 21 b).

5. Electric machine (1 ) according to any one of the claims 1 to 4, wherein the stator channel (18) comprises a helical section (S2) hydraulically connected to the annular section (S1).

6. Electric machine (1 ) according to any one of the claims 1 to 4, 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.

7. Electric machine (1 ) according to any one of the claims 2 to 6, wherein the stator channel (18) comprises stator nozzles or bores (22a, 22b) for spraying out the coolant.

8. Electric machine (1 ) according to claim 7, wherein the stator nozzles or bores (22a, 22b) are arranged in the annular section (S1 ) of the stator channel (18).

9. Electric machine (1 ) according to any one of the claims 2 to 8, wherein the rotor channel (19a, 19b, 19’) runs around the rotor shaft (1 1 ) and comprises rotor nozzles or bores (23a, 23b) for spraying out the coolant.

10. Electric machine (1 ) according to any one of the claims 1 to 9, wherein the connecting channel (20a, 20b, 20’) is arranged in the stator housing (3, 3a) of the electric machine (1 ), is formed by a pipe running out of the or within stator housing (3, 3a) or partially is arranged in the stator housing (3, 3a) of the electric machine (1 ) and partially is formed by the pipe running out of the or within stator housing (3, 3a).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).

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