OIL-COOLED ELECTRIC MACHINE WITH OIL DIFFUSER

Abstract

An electrical machine intended to move a motor vehicle, with a rotor and comprising a casing (4) housing a stator, the stator comprising a ferromagnetic subassembly (3) comprising a stack of magnetic metal sheets, and electrical conductors extending along a winding path, with first coils (5) arranged annularly around the axis at a first axial end (E1) of the stator and second coils (6) arranged annularly around the axis at a second axial end (E2) of the stator, the electrical machine being cooled by an oil circulation circuit, the electrical machine comprising at its first axial end an oil distribution ring (1) delimiting a first oil chamber (Ch1), and at its second axial end an oil distribution shell (2), which delimits a second oil chamber (Ch2), the oil distribution shell being integrated into the ferromagnetic subassembly.Abstract figure: Fig. 5.

Description

Title of the invention: OIL-COOLED ELECTRIC MACHINE WITH OIL DIFFUSER

[0001] The invention relates to an electrical machine comprising a stator and a rotor, the stator comprising a path of electrical conductors, the electrical machine being equipped with an oil cooling system.

[0002] The stator comprises a stack of magnetic metal sheets with notches intended to house the conductor windings. The path of the conductors comprises return loops at the axial ends of the housings formed by the notches, these return loops are called 'buns' in the language of those skilled in the art.

[0003] The cooling system comprises an oil circuit which bathes said buns.

[0004] In these configurations, annular oil chambers are provided to convey pressurized oil near the buns and cause spraying of the buns.

[0005] An example of such a configuration is described in document FR3049127.

[0006] Regarding the cooling of the buns by means of oil, specific rings are provided which make it possible to generate an oil spray via nozzles from pressurized oil supply chambers.

[0007] Furthermore, such an electric machine is generally assembled by shrink fitting, by inserting the stator into a casing previously expanded by heating. After cooling, the outer cylindrical wall of the stator is clamped in the casing with residual stress, hence the name shrink fitting. The assembly process generates requirements on the dimensions of the parts and on the assembly order of the parts intended to constitute the electric machine.

[0008] It is noted that the electric machine can be a simple motor, but most often the machine is reversible and can be selectively used as a motor or as a generator depending on the phases of use of the vehicle.

[0009] In electric or hybrid vehicles, engineers seek to increase the specific power of electric machines to be able to produce very high torque in a limited space.

[0010] It is therefore increasingly important to design a high-performance cooling system to support the integration of the electric machine, i.e. the traction motor, into the vehicle.

[0011] It should be noted that the present invention is applicable to any machine electric, even outside the context of an electric traction / propulsion vehicle.

[0012] The inventors sought to propose a new cooling solution for electrical machines which combines easy assembly and good performance of spraying the winding coils.

[0013] For this purpose, the present invention provides an electrical machine intended to move a motor vehicle, the electrical machine comprising a rotor mounted for rotation about a machine axis and comprising a casing housing a stator, the stator comprising a ferromagnetic subassembly comprising a stack of magnetic metal sheets extending transversely to the axis, and electrical conductors extending along a winding path, with first coils arranged in an annular manner around the axis at a first axial end of the stator and second coils arranged in an annular manner around the axis at a second axial end of the stator, the electrical machine being configured to be cooled by an oil circulation circuit, the electrical machine comprising at the first axial end an oil distribution ring delimiting a first oil chamber,and comprising at the second axial end an oil distribution ferrule, the oil distribution ferrule delimiting a second oil chamber, characterized in that the oil distribution ferrule is integrated into the ferromagnetic subassembly.

[0014] Thanks to the provisions promoted above, the ferromagnetic subassembly with the integrated oil distribution ferrule is prepared before assembly.

[0015] The stator comprises phase connectors which occupy a fairly large space, in particular in the radial direction, which makes it difficult to design, in the known art, an oil distribution shell which can be assembled after the stator has been inserted into the casing.

[0016] Integrating the oil distribution ferrule into the ferromagnetic subassembly advantageously eliminates this difficulty.

[0017] It is noted that the oil circulation circuit comprises a pump which sends oil under pressure, typically between 2 and 5 bars, into the first oil chamber and into the second oil chamber. A system for distributing or spraying oil from said chambers towards the buns is provided, which will be discussed below. A return flow of oil to the oil reservoir is provided.

[0018] It is noted that the oil also allows the bearings of the rotor shaft bearings to be lubricated.

[0019] In practice, the oil chambers are annular in shape and are located radially outside the buns.

[0020] According to one embodiment, axial channels are provided for communicating fluid the first oil chamber and the second oil chamber. As a result, only one pressurized oil inlet point is needed to supply the entire stator cooling system.

[0021] According to one embodiment, the channels are formed as internal channels arranged in the ferromagnetic subassembly. Thus, it is not necessary to provide a channel in the thickness of the wall of the casing or outside the casing. The overall size of the electrical machine is not increased by the presence of the stator oil cooling circuit.

[0022] According to one embodiment, the oil distribution ring comprises first radial holes for spraying oil towards the first buns, and the oil distribution ferrule comprises second radial holes for spraying oil towards the second buns. All regions of the buns are bathed in oil. The radial holes are small holes regularly distributed and around the circumference and adapted to generate droplets, or even an oil mist, directed towards the buns.

[0023] According to one embodiment, the oil distribution ferrule forms an insertion stop when mounting the ferromagnetic subassembly, intended to come into contact with a shoulder of the casing.

[0024] For this purpose, the casing comprises an annular shoulder, directed towards the second axial end. Advantageously, this shoulder is located in the mouth area of ​​the casing, i.e. the second end area, and proves to be relatively easy to produce by machining, unlike a shoulder to be produced at the bottom of the casing as is known in the prior art.

[0025] According to one embodiment, the oil distribution ferrule comprises an annular plate and an annular rim extending from the annular plate axially opposite the first axial end and radially outward. The annular rim comprises a frustoconical portion and a curved edge directed towards the first axial end.

[0026] Whereby, the oil distribution ferrule forms on the one hand the end magnetic annular plate of the ferromagnetic stack, and on the other hand the wall delimiting the second chamber. The annular rim belongs to the same part while being integral with said annular plate. The oil distribution ferrule can be formed in two parts made integral by welding or structural bonding.

[0027] According to one embodiment, the oil distribution ferrule is made of ferromagnetic material as a single piece. In other words, the oil distribution ferrule is formed integrally in a single piece, for example by cutting and forming from a starting blank.

[0028] According to one embodiment, a sealing joint is provided between an edge of the rim curved annular rim and annular shoulder. This prevents pressurized oil from entering peripheral portions external to the stator.

[0029] The invention further relates to a method of assembling an electrical machine intended to move a motor vehicle, the electrical machine as assembled comprising a rotor mounted for rotation about a machine axis and comprising a casing housing a stator, the electrical machine being configured to be cooled by an oil circulation circuit, the method comprising: - provide a motor housing forming a housing with a bottom at a first axial end and a mouth at a second axial end, - heat the crankcase to a predefined temperature, - insert into the crankcase an oil distribution ring intended to delimit a first oil chamber, - inserting into the casing a stator comprising a ferromagnetic subassembly comprising a stack of magnetic metal sheets extending transversely to the axis, and electrical conductors extending along a winding path, with first coils arranged annularly around the axis at a first axial end of the stator and second coils arranged annularly around the axis at a second axial end of the stator, characterized in that the ferromagnetic subassembly comprises an oil distribution shell, the oil distribution shell delimiting with the casing a second oil chamber, the oil distribution shell being integrated into the ferromagnetic subassembly.

[0030] According to one embodiment, the insertion movement is stopped by contact of the oil distribution ferrule on a shoulder of the casing.

[0031] The invention further relates to an electromotive group comprising an electric machine as described above.

[0032] The invention further relates to a vehicle comprising an electric machine as described above or an electromotive group as described above.

[0033] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: [Fig.l] is a schematic representation of an electromotive group intended to move a motor vehicle, illustrating an electric machine, a reducer, a differential and wheel shafts, according to an exemplary embodiment of the present invention; [Fig.2] illustrates in sectional view and in perspective, an example of an electromotive group; [Fig.3] is a schematic representation illustrating the assembly process of various elements making up the electrical machine; [Fig.4] illustrates in sectional view and in perspective, the second end zone with the oil distribution ferrule; [Fig.5] is a schematic representation of an axial section of the stator; [Fig.6] is a partial schematic representation of a cross-section of the ferromagnetic subassembly of the stator; [Fig.7] illustrates in perspective view an example of the construction of an oil distribution ferrule.

[0034] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not necessarily shown to scale. This applies in particular to the clearance gaps and to the thickness of the magnetic sheets, the thicknesses of which have been exaggerated in order to facilitate understanding of the description.

[0035] We are interested here in an electric or hybrid motor vehicle, namely a vehicle equipped with an electric powertrain.

[0036] In practice, the electric or hybrid vehicle comprises an electromotive group. The electromotive group comprises an electric machine 10, used as a motor or as an alternator / generator depending on the driving circumstances, and a transmission usually equipped with a speed reducer. The electromotive group can be arranged on the rear axle or the front axle of the vehicle. There can be one or more electromotive groups in an electric or hybrid vehicle.

[0037] With reference to [Fig.l], in addition to the aforementioned electric machine 10, the electromotive group comprises a reducer 83, a differential 84 and wheel shafts 85, which are elements considered known per se, therefore not described here in detail.

[0038] The large pinion 86 of the reducer as well as the wheel shafts 85 rotate around the axis marked B.

[0039] The electrical machine 10 comprises a first static part called stator 1ST and a second rotating part called rotor 1RT, the rotor being mounted to rotate around an axis denoted A also called machine axis. Thus, the electrical machine 10 has a main axis of rotation A.

[0040] In this document, reference is made to a cylindrical type spatial reference based on the main axis A. A so-called axial direction is parallel or coincident with the main axis A. The adverb axially characterizes an axial direction.

[0041] A so-called radial direction noted R is defined by a direction perpendicular to the axis A and which intersects the axis A. The adverb radially characterizes an axial direction, qualified as "internal" if it is directed towards the axis and qualified as "external" if it is directed away from the axis. A so-called tangential direction is defined by a direction perpendicular to the axis and perpendicular to the local radial direction at the point of interest.

[0042] The rotor 1RT is mounted on a shaft 68. The shaft 68 is mounted on bearings via roller bearings (only one of which is shown in [Fig.2]) as known per se.

[0043] The electrical machine generally extends between a first axial end E1 located on the output pinion side and a second axial end E2 where the electrical power supply connections arrive.

[0044] The electric machine 10 is here a radial flux machine. The main magnetic field lines in the air gap are directed radially.

[0045] The stator 1ST is arranged around the rotor. The stator 1ST is mounted in a stationary manner, i.e. it does not rotate around the axis A (note that the motor as a whole moves when it is mounted in a vehicle).

[0046] As visible in figures 3 and 5, the stator 1ST comprises a stack of magnetic metal sheets 32, this stack forms the main part of what is called ferromagnetic subassembly 3.

[0047] Each magnetic metal sheet 32 ​​is obtained by cutting a blank of magnetizable metal material into the desired shape. The thickness of the blank and of the metal sheet resulting from the cutting is for example in practice between 0.3 mm and 0.8 mm. Each magnetic metal sheet 32 ​​may be coated with an electrically insulating varnish. The varnish prevents the passage of current between sheets and greatly reduces eddy current losses.

[0048] Each magnetic metal sheet is made of mild silicon steel, preferably grain oriented. The magnetic metal sheets are assembled together by structural welding and bonding.

[0049] With reference to [Fig.6], each magnetic metal sheet comprises an annular outer portion 30 and teeth 31 extending in the direction of the axis A. Depending on the architecture and the power of the machine, the number of magnetic metal sheets can range from 25 to 200, without these numbers being limiting.

[0050] The free end of the teeth comprises in the example illustrated a flattened or flared shape 33 which makes it possible to retain the conductive wires or conductive rods once these are mounted in the groove formed by the interval between the different aligned teeth.

[0051] The teeth 31 project radially in the direction towards the axis A. Two neighboring teeth together delimit a notch 44 for housing electrical winding conductors.

[0052] In addition to the ferromagnetic subassembly, the stator comprises electrical conductors 8 extending along a winding path. The winding path comprises first buns 5 arranged in an annular manner around the axis A at the first axial end E1 of the stator 1ST. The winding path comprises second buns 6 arranged in an annular manner around the axis A at the second axial end E2 of the stator.

[0053] The electrical conductors 8 may be conventional electrical wires. The electrical conductors may also be metal rods or strips.

[0054] As known per se, at each end of the grooves formed by the notches, an electrical conductor makes a 180° turn to continue its path in another groove of notches, this is a half-turn loop or a return loop. Adjacent return loops together form a 'bun' so called by similarity to a hair bun.

[0055] The electric machine is equipped with a cooling system 9 based on oil circulation. The cooling system comprises an oil circuit which bathes said coils of the windings.

[0056] The oil used in the cooling system 9 is an essentially dielectric liquid; the oil does not conduct electricity. If stray currents arise inside the oil, they remain negligible and marginal compared to the currents which pass in the phases of the stator. The oil used for cooling also serves the lubrication function, in particular of the bearings and rollers.

[0057] The cooling system 9 comprises a pump 91 arranged in a lower portion 90 of the reducer, forming a reservoir and filled with oil.

[0058] The oil circulation circuit of the cooling system comprises an oil supply channel 92 which supplies pressurized oil to the electric machine. In the generic example illustrated in [Fig.l], the pressurized oil enters a first oil chamber Chl in the electric machine, this first oil chamber being on the side of the first axial end EL

[0059] The first oil chamber Chl has an annular shape. From the first oil chamber, the pressurized oil then joins a second oil chamber Ch2, arranged at the second axial end E2 and also having an annular shape.

[0060] The first oil chamber Chl is delimited by an oil distribution ring marked 1.

[0061] The second oil chamber Ch2 is delimited by an oil distribution ferrule marked 2 and which is of particular interest in the context of the present invention.

[0062] Advantageously, axial channels denoted 12 are provided to put the first oil chamber Chl and the second oil chamber Ch2 into fluid communication. In the example illustrated, said axial channels 12 are made inside the ferromagnetic subassembly 3. As a variant, passages could be provided in the body of the casing 4 to fluidly connect the second oil chamber to the first oil chamber.

[0063] To return to the illustrated example, each of the magnetic metal plates 32 comprises a series of orifices 120 as visible in [Fig.6], the orifices 120 being distributed all around the circumference close to the outer peripheral radial zone of the stator.

[0064] The oil distribution ring comprises first radial bores 11 for spraying oil towards the first buns 5. The oil distribution ferrule comprises second radial bores 26 for spraying oil towards the second buns 6. When the first and second oil distribution chambers are under pressure, said radial bores are adapted to generate oil droplets directed towards the buns which cool the conductors 8.

[0065] The sprayed oil is recovered by gravity in the bottom of the stator and the oil joins by channeled paths 93,95 a return channel 94 directed towards the reservoir 90 by gravity.

[0066] Upstream of the radial spray holes 11, 26, the oil pressure prevailing in particular in the first and second oil chambers Chl, Ch2 can be between 2 bars and 5 bars. Downstream of the radial spray holes 11, 26, the oil is at ambient pressure (1 bar) and drips under the effect of gravity to join the return channel 94.

[0067] Advantageously according to the present invention, the oil distribution ferrule 2 is integrated into the ferromagnetic subassembly 3 and delimits the second oil chamber Ch2.

[0068] The oil distribution ferrule 2 comprises an annular plate 20 and an annular rim 22. The annular plate 20 is similar to the other magnetic metal plates 32 already described.

[0069] As can be seen in particular in Figures 4 and 5, the annular rim 22 extends from the annular plate 20 on the one hand axially opposite the first axial end and on the other hand radially outwards.

[0070] The annular rim 22 comprises a frustoconical portion and a curved edge 24 directed towards the first axial end EL

[0071] The oil distribution ferrule 2 may be manufactured from ferromagnetic material as a single piece. Alternatively, the oil distribution ferrule 2 may be manufactured in the form of two pieces assembled together, namely the flat annular plate 20 on the one hand and the annular rim 22 of truncated cone shape on the other hand.

[0072] In the example illustrated, a seal 74 is mounted on the curved edge 24 of the annular rim 22. The seal 74 mounted on the curved edge of the annular rim bears on an annular shoulder 42 of the casing 4. Said annular shoulder 42 is provided at the mouth of the casing, i.e. in the second end zone E2.

[0073] The annular plate 20, the annular rim 22 and the bore wall 47 together delimit the second oil chamber Ch2.

[0074] [Fig.3] illustrates the assembly process of the electric machine. We place everything first the casing 4 in a vertical position, namely the bottom facing downwards and the mouth facing upwards. The casing is heated to a predetermined temperature, for example at least 150°C or even 200°C. The casing is then in an expanded configuration under the effect of the coefficient of thermal expansion, in particular expanded radially outwards.

[0075] Then, the oil distribution ring 1 is inserted into the bottom of the casing 4. There remains a sufficient radial gap and this presents no difficulty. The distribution ring is equipped with seals, for example lip seals, one of the seals comes into contact with the bottom of the casing and the other will be approached by the ferromagnetic subassembly. The distribution ring, the casing and the ferromagnetic subassembly delimit the first oil chamber.

[0076] Then the ferromagnetic subassembly 3 is inserted, which is inserted precisely into the general cylindrical bore 47 of the casing. It is the temperature differential that leaves a small gap suitable for insertion from top to bottom. It is noted that the oil distribution ferrule comes with the ferromagnetic subassembly and it is the oil distribution ferrule that stops the downward movement when its peripheral rim comes into contact with the shoulder 42 at the mouth of the casing, i.e. in the second end zone E2.

[0077] The insertion movement is stopped by contact of the curved edge 24 of the oil distribution ferrule 2 on the shoulder 42 of the casing 4.

[0078] After having installed a bearing 71 (shown in [Fig.2]) as well as the elements necessary for the electrical connection of the three phases (not shown), a closing plate 7 is inserted. The closing plate 7 forms the support for the bearing as well as the external electrical connections.

[0079] After assembly, the progressive cooling of the casing causes a radial retraction which cancels the gap between the ferromagnetic subassembly and the casing and even causes an intentional tightening of the ferromagnetic subassembly.

[0080] In [Fig.5], it is noted that the inner radius of the stator is marked RI, the axial channels are at a radius R2 relative to the axis A, the outer peripheral surface of the ferromagnetic subassembly 3 is at a distance from the axis marked R3 and the mouth of the housing housing has a general radius R4.

[0081] Between the second buns 6 and the closing plate 7, the electrical elements are arranged which allow the conductors of each of the phases to be connected to connection terminals and to external wiring 72.

[0082] An O-ring 75 is provided for sealing between the closing plate and the casing 4.

[0083] As visible in [Fig.7], the oil distribution ferrule also comprises projections 23 projecting inwards which geometrically correspond to the teeth 31 of the magnetic metal plates 32.

Claims

Claims

1. An electrical machine (10) for moving a motor vehicle, the electrical machine comprising a rotor (1RT) mounted to rotate about a machine axis (A) and comprising a casing (4) housing a stator (1ST), the stator comprising a ferromagnetic subassembly (3) comprising a stack of magnetic metal sheets extending transversely to the axis, and electrical conductors (8) extending along a winding path, with first coils (5) arranged annularly around the axis at a first axial end (El) of the stator and second coils (6) arranged annularly around the axis at a second axial end (E2) of the stator, the electrical machine being configured to be cooled by an oil circulation circuit, the electrical machine comprising at the first axial end an oil distribution ring (1) delimiting a first oil chamber (Chl),and comprising at the second axial end an oil distribution ferrule (2), the oil distribution ferrule delimiting a second oil chamber (Ch2), characterized in that the oil distribution ferrule is integrated into the ferromagnetic subassembly.,

2. Electrical machine according to claim 1, characterized in that axial channels (7) are provided for fluidly connecting the first oil chamber (Chl) and the second oil chamber (Ch2), preferably the channels are formed as internal channels arranged in the ferromagnetic subassembly.

3. Electrical machine according to any one of claims 1 to 2, characterized in that the oil distribution ring comprises first radial bores (11) for spraying oil towards the first buns, and the oil distribution ferrule comprises second radial bores (22) for spraying oil towards the second buns (6).

4. Electrical machine according to any one of claims 1 to 3, characterized in that the oil distribution ferrule forms an insertion stop when mounting the ferromagnetic subassembly, intended to come into abutment against a shoulder (42) of the casing.

5. An electrical machine according to any one of claims 1 to 4, characterized in that the oil distribution ferrule comprises an annular plate and an annular rim (22) extending from the annular plate axially opposite the first axial end and radially outward.

6. An electrical machine according to any one of claims 1 to 5, characterized in that the oil distribution ferrule (2) is made of ferromagnetic material as a single piece.

7. An electrical machine according to claim 4, characterized in that a seal is provided between an edge of a curved flange (24) of the annular rim and the annular shoulder.

8. A method of assembling an electrical machine (10) intended to move a motor vehicle, the electrical machine as assembled comprising a rotor (1RT) mounted for rotation about a machine axis (A) and comprising a casing (4) housing a stator (1ST), the electrical machine being configured to be cooled by an oil circulation circuit, the method comprising: - providing a motor casing forming a housing with a bottom at a first axial end (El) and a mouth at a second axial end (E2), - heating the casing to a predefined temperature, - inserting into the casing an oil distribution ring (1) intended to delimit a first oil chamber (Chl) - inserting into the casing a stator comprising a ferromagnetic subassembly (3) comprising a stack of magnetic metal sheets extending transversely to the axis, and electrical conductors (8) extending along a path of winding,with first buns (5) arranged in an annular manner around the axis at a first axial end (El) of the stator and second buns (6) arranged in an annular manner around the axis at a second axial end (E2) of the stator, characterized in that the ferromagnetic subassembly comprises an oil distribution shell (2), the oil distribution shell delimiting with the casing a second oil chamber (Ch2), the oil distribution shell being integrated into the ferromagnetic subassembly.,

9. Assembly method according to claim 8, characterized in that the insertion movement is stopped by contact of the oil distribution ferrule on a shoulder of the casing.

10. An electric motor vehicle comprising an electric machine according to any one of claims 1 to 7.

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