ELECTRIC MACHINE WITH SELF-CONNECTING WATER JACKET AXIALLY COMPRESSED

Abstract

The invention relates to an electrical machine comprising a housing (2), a sleeve (1) mounted inside the housing and including passages for the circulation of cooling fluid, a stator (3) mounted inside the sleeve, a rotor mounted inside the stator and pivotally mounted relative to the housing about a machine axis, a closing cover (4) arranged opposite a housing bottom, characterized in that the sleeve is formed of steel, and the closing cover (4) exerts axial compression on the sleeve so as to generate expansion of the sleeve in a radial direction perpendicular to the axis. Figure 3

Description

Title of the invention: ELECTRIC MACHINE WITH AXIALLY COMPRESSED SELF-CONNECTING WATER JACKET

[0001] The invention relates to an electrical machine with a water jacket, allowing circulation of cooling fluid suitable for cooling said electrical machine.

[0002] In an electric traction or propulsion vehicle, there is provided an electric machine of generally substantial power which operates as a motor for traction phases and which operates as a generator during energy recovery phases (braking, deceleration, downhill driving).

[0003] In many cases, said electrical machine must be cooled efficiently and air cooling is not sufficient; it is necessary to use circulating cooling of a coolant.

[0004] We are particularly interested here in cooling by a water-based liquid circulating in a jacket interposed / intercalated between the stator and the machine casing. This can be referred to as peripheral cooling to distinguish these solutions from cooling by dielectric oil circulating within the machine itself.

[0005] In the vast majority of known designs, the water jacket is made of aluminum alloy. The casing is made of aluminum alloy.

[0006] In other known embodiments, passages are provided for the circulation of cooling fluid in the casting of the crankcase without the interposition of a separate water jacket.

[0007] In electrical machines, the torque generated at the core of the machine induces a reaction torque in the stator which must be transferred to the casing. This requirement applies in particular to peripheral water-cooling configurations, especially to a configuration with an interposed water jacket.

[0008] To meet this requirement, a shrink-fit assembly is performed, firstly of the sleeve in the housing and secondly of the stator in the sleeve. To perform this shrink-fit assembly, the outer part is heated, expanding due to the temperature increase. The inner part is then inserted, and the outer part is allowed to cool. The minimal insertion clearance is eliminated by the cooling process, resulting in a significant clamping force, sufficient to withstand the machine torque described above.

[0009] The shrink-fit assembly process requires specific manufacturing means and a significant processing time.

[0010] The inventors therefore sought to propose new solutions for designing and implementing a water jacket without the need to use a process assembly by shrink fitting.

[0011] To this end, the present invention proposes an electric machine comprising a casing, a sleeve mounted inside the casing and including passages for a circulation of cooling fluid, a stator mounted inside the sleeve, a rotor mounted inside the stator and pivotally mounted relative to the casing around a machine axis, a closing cover arranged opposite a bottom of the casing, characterized in that the sleeve is formed of steel, and the closing cover exerts an axial compression on the sleeve so as to generate an expansion of at least a part of the sleeve in a radial direction perpendicular to the axis.

[0012] The radial expansion thus produced creates a radial stress, that is to say, a clamping force capable of absorbing the machine torque. It is noted that the radial expansion occurs both radially inwards and radially outwards.

[0013] Advantageously, a clamping exists at the interface between the stator and the sleeve and a clamping exists at the interface between the sleeve and the housing.

[0014] The choice of steel makes it possible to take advantage of the large elastic range available for steels, axial compression resulting in deformation in the elastic range, which is conducive to the establishment of residual stresses that will persist throughout the life of the assembled electrical machine.

[0015] Thanks to the provisions described above, an assembly equivalent to shrink-fit assemblies can be achieved, but without using a heating machine and more quickly. In particular, the present invention eliminates the need for a shrink-fit operation between the sleeve and the stator.

[0016] It is noted that the cooling fluid circulates outside the jacket wall.

[0017] It is noted that the shirt has a general cylindrical shape.

[0018] It should be noted that the diametral dimensions of the machine are smaller than with known configurations for a given stator diameter; indeed, the radial thickness of the sleeve is particularly small. Thus, the compactness of the machine is improved, as well as its ease of integration into the vehicle architecture.

[0019] According to one embodiment, the shirt comprises: - a central portion forming a site for heat exchange with the stator via the cooling fluid, - a first end portion intended to be fitted into the bottom of the casing, and - a second end portion intended to be fitted into a portion of the casing's mouth.

[0020] According to an advantageous embodiment, the closing cover closes the opening of the housing. According to an advantageous embodiment, the closing cover carries a bearing of rotor bearing.

[0021] According to one embodiment, the central portion of the sleeve comprises, in axial section, base areas intended to come into contact with the outer peripheral wall of the stator, and apex areas intended to come into contact with the inner wall of the housing.

[0022] According to one embodiment, the central portion forms annular water passage channels and the central portion of the jacket includes annular dikes, each pair of adjacent annular dikes delimiting an annular water passage channel.

[0023] The annular water passage channels are delimited on the inner radial side by the base zones constrained to the stator body. The annular dike apex zones are constrained to the casing.

[0024] This arrangement allows for the management of the cooling fluid circulation and, at the same time, the transfer of torque experienced by the stator to the crankcase, thus achieving the necessary torque transfer. It should be noted that this torque transfer occurs through the cylinder liner.

[0025] According to one embodiment, there is no direct contact between the stator and the housing, the sleeve forms the entire mechanical interface between the stator and the housing.

[0026] According to one embodiment, the first end portion and the second end portion have longitudinal ribs. As a result, the first end portion and the second end portion undergo virtually no reduction in length, because they have an axial stiffness much greater than the axial stiffness of the central portion, said central portion functioning like an accordion, and having a lower equivalent Young's modulus in the axial direction than the end portions.

[0027] According to one embodiment, at least one radially internal indexing boss is provided, configured to cooperate with a groove formed in the stator.

[0028] According to one embodiment, each annular dike includes at least one depression in a summit area, set back inside a circumscribed circle delimiting the annular dike.

[0029] According to one embodiment, the shirt is obtained by a hydroforming process.

[0030] According to one embodiment, the sleeve has a wall thickness between 0.5 mm and 1.5 mm.

[0031] According to one embodiment, the radial clearance of the sleeve is between 3 mm and 6 mm.

[0032] One can choose stainless steel or standard steel to manufacture the liner.

[0033] According to one embodiment, the first end portion includes a shoulder forming a stop for the axial positioning of the stator. The first end portion acts as a spacer.

[0034] The sleeve includes a free front edge abutting the bottom of the housing.

[0035] The sleeve includes a rear free edge placed under axial pressure by the rim of the closing lid.

[0036] The invention further relates to a vehicle comprising an electric machine as described above.

[0037] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: [Fig.1] is an exploded perspective view representation of an example of an embodiment of the invention on an electrical machine; [Fig.2] is a perspective view representation of an example embodiment of a water jacket according to the present invention; [Fig.3] illustrates in partial axial section view the arrangement of the different parts involved; [Fig.4] illustrates an example of the path of cooling fluid in the jacket; [Fig.5] schematically illustrates in detailed axial section the effects of axial compression on the central portion of the liner; [Fig.6] illustrates in partial perspective view an indexing function with respect to the stator; [Fig.7] schematically illustrates in cross-section the depressions forming passages between the annular canals; [Fig. 8] schematically illustrates an example of a sequence of assembly operations.

[0038] In the various figures, the same reference numerals designate identical or similar elements. For clarity, some elements are not necessarily shown to scale. This applies in particular to the assembly clearance of the liner (inner and outer) before it is subjected to axial compression.

[0039] We are interested here in an electric machine. Of particular interest here are electric machines for electric or hybrid motor vehicles, namely vehicles equipped with an electric powertrain.

[0040] In practice, the electric or hybrid vehicle includes at least one electromotor unit with an electric machine, arranged on the front axle and / or the rear axle.

[0041] Depending on the driving circumstances, the electric machine is used as a motor or as a generator.

[0042] We are interested here in an electrical machine of the radial flux type.

[0043] Carter

[0044] The electric machine ME comprises a housing 2. The housing 2 contains the internal components of the electric machine. In addition, the housing 2 can contain all or part of the transmission, in particular, for example, a speed reduction stage.

[0045] The casing 2 is made of aluminum alloy. More precisely, it is a part obtained from aluminum casting with further machining, in particular it has a main machined bore intended to receive the water jacket, as will be described in more detail later.

[0046] As known ensoi, the housing 2 is provided with reinforcing ribs and various fixing elements to allow the housing to be fixed in the electromotor unit, which itself can be mounted elastically relative to the vehicle body.

[0047] The housing 2 includes a housing base marked 2B on the output shaft side and a housing mouth marked 2C through which the components, namely the sleeve, the stator and the rotor, are inserted.

[0048] The bottom of the housing can be formed as a separate part from the cylindrical body. In the illustrated example, the bottom of the housing is formed integrally with the body.

[0049] Shirt

[0050] The ME electric machine includes a sleeve 1 mounted inside the housing 2. The sleeve includes passages for the circulation of cooling fluid. These passages take the form of annular channels 7.

[0051] The sleeve 1 is formed from steel.

[0052] Steel exhibits a wide range of elastic behavior which will be exploited as discussed below.

[0053] The sleeve 1 has a general cylindrical shape centered on the machine axis noted A.

[0054] Advantageously, the liner 1 is obtained by a hydroforming process. The liner is manufactured from a cylindrical section of raw steel, which in the illustrated example is then deformed by a hydroforming press. This makes it possible to obtain pronounced deformations without the risk of initiating cracks. The various shapes obtained are discussed below.

[0055] The sleeve 1 has a wall thickness of between 0.5 mm and 1.5 mm. Preferably, the sleeve 1 may have a wall thickness of between 0.7 mm and 0.9 mm.

[0056] As illustrated in Figures 1, 2 and 8, the sleeve 1 comprises, with reference to the axial direction A: - a central AI portion forming a heat exchange site with the stator via the cooling fluid, - a first end portion IB intended to be fitted into the bottom of the housing 2B, and - a second end portion IC intended to be arranged in the mouth of the housing 2C.

[0057] The length of the central portion IA along axis A is greater than the length of the end portions 1B,1C which are of similar length.

[0058] According to a non-limiting example, the length of the central portion IA can be between 10 cm and 50 cm, the length of the end portions can be between 4 cm and 10 cm, these dimensions being to be adapted to the configuration of the machine.

[0059] In the non-limiting example illustrated in [Fig.4], the cooling fluid enters the machine at the location of the first end portion IB (path PF1), then flows through the annular channels 7 (path PF2), then exits the machine at the location of the second end portion IC (path PF3).

[0060] The first end portion 1B and the second end portion IC have longitudinal ribs 16, which greatly reduce the length reduction of these end portions under axial compression.

[0061] The first end portion IB includes a shoulder 17 forming a stop for the axial positioning of the stator. In other words, the first end portion IB acts as a spacer between the bottom of the housing 2B and the central portion IA.

[0062] The central portion 1A of the sleeve comprises, in axial section, as particularly visible in Figures 3 and 5, base areas 10 intended to come into contact with the outer peripheral wall of the stator, and apex areas 11 intended to come into contact with the inner wall of the housing.

[0063] The central portion IA forms annular water passage channels identified as 7. In addition, the central portion IA of the jacket includes annular dikes 11. Each pair of adjacent annular dikes delimits an annular channel 7.

[0064] As illustrated in [Fig.7], each annular dike 11 includes at least one depression 12 in a summit area, set back inside a circumscribed circle CC which delimits the periphery of the annular dike.

[0065] In the illustrated example, there are 6 depressions evenly distributed around the circumference. According to alternative solutions, one, two, or more depressions may be provided.

[0066] The radius RI coinciding with the outer cylindrical surface of the stator can be between 15 cm and 25 cm.

[0067] The radius R2 coinciding with the inner cylindrical surface of the housing can be between 15 cm and 25 cm.

[0068] The gap between RI and R2 corresponds to the radial footprint of the sleeve. According to a non-limiting example, this radial footprint of the sleeve is between 3 mm and 6 mm, which is thinner than the known art and which makes it possible to make the architecture of the machine radially compact.

[0069] The sleeve 1 includes a free front edge 18 abutting the bottom of the housing. This free front edge forms a collar which extends in a plane perpendicular to the axis.

[0070] The sleeve 1 includes a rear free edge 19 placed under axial pressure by the rim of the closing cover. This rear free edge 19 forms a collar which extends in a plane perpendicular to the axis.

[0071] In the illustrated example there are seven annular canals and eight dikes, but the number of annular canals and dikes can of course be any number.

[0072] Stator / Rotor

[0073] The electric machine ME includes a stator 3 mounted inside the casing. The electric machine includes a rotor 5 mounted inside the stator. The rotor 5 is pivotally mounted relative to the housing about a machine axis. A roller bearing is provided on the bottom side of the housing and a roller bearing is provided at the opening of the housing.

[0074] The rotor 5 can be of the permanent magnet type or of the wound type; it is not described in further detail here, as this is known per se. The rotor 5 rotates about the axis A.

[0075] The stator 3 comprises a stack of ferromagnetic laminations and windings of electrical conductors. The stator is not described in further detail here, as it is known per se.

[0076] Longitudinal grooves 33 are observed in the stator.

[0077] The sleeve provides at least one radially internal indexing boss 31, configured to cooperate with (be received in) a groove 33 formed in the stator.

[0078] Cover / Compression / Self-tightening

[0079] The ME electric machine includes a closing cover 4 arranged in the mouth area of ​​the housing.

[0080] The closing cover 4 includes a bearing surface for receiving a rotor bearing.

[0081] The closing cover 4 closes and delimits an internal electromagnetic zone of the machine so as not to allow any foreign body or fluid element to enter, in particular in the air gap zone.

[0082] The closing cover 4 is fixed by fastening means, for example screws, which push the cover towards the bottom of the housing.

[0083] The dimensional chain is such that, as a result, the closing cover 4 pushes the rear free edge 19 of the liner 1 towards the bottom of the crankcase. More specifically, the closing cover 4 includes a rim, denoted 41, which bears circumferentially on the flange of the rear edge 19 to push the liner 1 towards the bottom of the crankcase.

[0084] The sleeve 1 thus undergoes axial compression. As already mentioned, the first end portion 1B and the second end portion IC are provided with axial ribs and have an equivalent Young's modulus in the axial direction much greater than the Young's modulus of the central portion IA. It is therefore the central portion that undergoes the reduction in length.

[0085] The length of the shirt can be reduced by a few tenths of a millimeter or even by a few millimeters; it is the central portion that sees the reduction in length occur, by a few percent in relative decrease.

[0086] Figure 5 illustrates the phenomenon of radial expansion under the effect of axial compression. The unhatched contour marked PI corresponds to the position of the base zones 10 and the apex zones 11 before the cover is fitted, i.e. in the absence of axial compression exerted on the sleeve.

[0087] The hatched contour marked P2 corresponds to the position of the base zones 10 and the apex zones 11 after the cover has been put in place, i.e. in the presence of the axial compression exerted on the sleeve.

[0088] The central portion functions in the manner of an accordion.

[0089] The base zones 10 are displaced radially inwards and exert pressure against the cylindrical outer surface 30 of the stator. Simultaneously, the apex zones 11 are displaced radially outwards and exert pressure against the cylindrical inner surface 20 of the housing.

[0090] Depending on the position of each dike 11, there may be a displacement of the summit crest in the axial direction.

[0091] As compression occurs, the clearances (external J1 and internal J2) required for assembly are eliminated, and furthermore, a radial stress is generated. This radial stress allows the transmission of a torque, in particular the machine torque mentioned at the beginning of this description.

[0092] It is noted that the sum of the sets, J1 + J2, can generally be between 50 hundredths and a few tenths of a millimeter.

[0093] Assembly

[0094] As illustrated in [Fig. 8], during an operation labeled OP01, the sleeve 1 is inserted into the housing 2, along the axial direction and towards the bottom of the housing. Next, the stator 3 of the machine is inserted in the same direction, during an operation labeled OP02. Then, the rotor 5 of the machine is inserted in the same direction, during an operation labeled OP03. Finally, the closing cover 4 is inserted, during an operation labeled OP04.

[0095] According to a variant of the assembly method, the stator 3 can be pre-assembled in the sleeve 1 as a macro-component.

[0096] Screwing the closing cover 4 causes axial compression of the sleeve described above and radial expansion of the sleeve described above.

Claims

Demands

1. Electric machine (EM) comprising: a housing (2), a sleeve (1) mounted inside the housing and including passages for the circulation of cooling fluid, a stator (3) mounted inside the sleeve, a rotor (5) mounted inside the stator and pivotally mounted relative to the housing about a machine axis (A), a closing cover (4) arranged opposite a housing bottom, characterized in that the sleeve is formed of steel, and the closing cover exerts axial compression on the sleeve so as to generate an expansion of at least a portion of the sleeve in a radial direction perpendicular to the axis.

2. Electric machine according to claim 1, characterized in that the jacket comprises: - a central portion (IA) forming a heat exchange site with the stator via the cooling fluid, - a first end portion (IB) intended to be arranged in the bottom of the casing, and - a second end portion (IC) intended to be arranged in a mouth portion of the casing.

3. Electric machine according to claim 2, characterized in that the central portion of the sleeve comprises, in axial section, base areas (10) intended to come into contact with the outer peripheral wall of the stator, and apex areas (11) intended to come into contact with the inner wall of the housing.

4. Electric machine according to claim 2, characterized in that the central portion forms annular water passage channels and the central portion of the jacket comprises annular dikes, each pair of adjacent annular dikes delimiting an annular water passage channel.

5. Electric machine according to any one of claims 2 to 4, characterized in that the first end portion (IB) and the second end portion (IC) have longitudinal ribs (16).

6. An electric machine according to any one of claims 1 to 5, characterized in that it provides at least one indexing boss (31), radially internal, configured to cooperate with a groove (33) space provided in the stator.

7. An electrical machine according to any one of claims 1 to 6, characterized in that each annular dam comprises at least one depression (12) in a crest area, set back inward from a circumscribed circle (CC) delimiting the annular dam.

8. Electric machine according to any one of claims 1 to 7, characterized in that the sleeve (1) is obtained by a hydroforming process.

9. Electric machine according to any one of claims 1 to 8, characterized in that the first end portion (IB) comprises a shoulder (17) forming a stop for axial positioning of the stator.

10. Electric motor vehicle comprising an electric machine according to any one of claims 1 to 9.

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