METHOD FOR MANUFACTURING A SHORT-CIRCUIT RING OF AN ELECTRIC MOTOR

Description

[0001] The present invention relates to a method of manufacturing a short-circuit ring for an electric motor.

[0002] Electromagnetic induction motors, and in particular squirrel-cage asynchronous motors, essentially consist of a static element or stator, and a rotating element, i.e. a rotor which is mounted inside the stator on a rotating motor shaft.

[0003] In more detail, the rotor normally comprises a plurality of longitudinal bars, made from an electrically conductive material, and a stack of magnetic sheets, made for example from rolled steel, which are assembled on the rotating shaft and have a plurality of longitudinal grooves; the conductive bars of the rotor are housed in the grooves and are coupled at their ends to two short-circuit rings in a squirrel cage configuration.

[0004] The solutions currently used to couple short-circuit rings to the conductive bars have drawbacks and are open to improvement.

[0005] In particular, according to a first solution, the end of each rotor bar is housed in a circular groove machined in the short-circuit ring, and its end surface bears against the face of the groove; the two parts are then brazed, using a filler material which is inserted into the groove opposite the junction zone.

[0006] Solder fills the gap between two adjacent bars, but this arrangement requires a large volume of solder to fill the open volume.

[0007] Another solution known in the state of the art uses shims which are placed in the groove of the short-circuit ring and are interposed between two adjacent bars.

[0008] This solution allows for a reduction in the volume of solder required to make the connection, but it requires additional precautions for the positioning of the shims during soldering. Imperfect positioning of the shims can lead to quality problems, leading, for example, to cracking of the connection between the bar and the ring and then to failure of the connection in service.

[0009] Furthermore, current construction provisions for the assembly of short-circuit rings with rotor bars impose a limit in terms of peripheral linear speed of the rotor, for example of the order of 100m / s.

[0010] Document DE 10 2013 202557 A1 discloses a squirrel cage for a rotor, comprising a plurality of bars extending in an axial direction. Two squirrel cage rings are arranged at opposite ends of the plurality of bars. Each ring comprises a connecting disc and a short-circuit disc. The connecting disc has a plurality of recesses, in each of which a cage bar is arranged, such that the plurality of cage bars is mechanically fixed relative to the connecting disc. The short-circuit disc rests directly against the connecting disc in the axial direction.

[0011] Document US 2013 / 127291 A1 discloses a method for forming a rotor that comprises a plurality of conductive bars connected to two short-circuit rings that extend around a longitudinal axis. Each short-circuit ring has a coupling face that extends transversely to the longitudinal axis and has a plurality of cavities. The ends of each bar are housed in two corresponding cavities, and each cavity has a closed bottom wall transverse to the longitudinal axis so as to house, in a non-through manner, one end of a bar. Filling elements each extend projecting between two adjacent cavities.

[0012] US 2021 / 083561 A1 discloses a squirrel cage of a dynamoelectric rotating machine, which comprises two short-circuit rings assembled with a rotor having a plurality of conductive bars. Each ring has a plurality of niches. A protrusion is provided in each niche. During assembly, the ends of each bar are inserted into two corresponding niches, then each bar is compressed by a compressive force applied to the short-circuit ring, and each protrusion pierces into one end of the cage bar.

[0013] US 2014 / 339950 A1 discloses a rotor assembly having a central body and a plurality of conductive bars. At each end of the central assembly is a corresponding end disc. Each disc includes a plurality of slots or cavities. During assembly, the ends of each bar are press-fitted into two slots and then the bars are welded to the discs.

[0014] Therefore, a main aim of the present invention is to provide a solution offering improvements over the known state of the art, and especially to produce short-circuit rings which make the junction with the rotor bars more reliable and simpler to produce, with a superior mechanical capacity for taking up centrifugal forces allowing higher peripheral linear speeds for the motors.

[0015] This object is achieved by a method of manufacturing a short-circuit ring for an electric motor which comprises a rotor including a plurality of rotor bars, the manufacturing method comprising at least the following steps: (a): producing a body of substantially annular shape in a single piece of electrically conductive material, which develops around a reference axis and comprises a coupling face with the rotor bars which develops transversely with respect to the longitudinal reference axis; (b): producing, on the coupling face of the annular body, a plurality of housing niches which are spaced at regular distances from each other in a circumferential direction along the coupling face, each housing niche extending in a direction substantially parallel to the longitudinal reference axis and having a closed bottom wall transverse to the longitudinal reference axis so as to house, in a non-through manner, an end portion of a rotor bar, and a plurality of filling elements, each filling element extending between two adjacent housing niches,projecting from the corresponding closed bottom walls and being configured to fill, at least partially, a space between the end portions of two adjacent rotor bars once the rotor bars are housed in the corresponding housing niches, the manufacturing method being characterized in that the step of producing the plurality of filling elements and the plurality of housing niches comprises the following substeps: (c) milling the annular body by forming the housing niches hollowed out in the annular body at regular distances from each other and extending from the coupling face towards the inside of the annular body in a direction substantially parallel to the reference axis, the solid or unmilled portions of the coupling face between each pair of adjacent housing niches forming the plurality of filling elements; producing,in a circumferential direction along an inner edge and an outer edge of the coupling face a first groove and a corresponding second groove; radially milling, at predefined positions, portions of the coupling face between the first groove and the second groove, in order to form the plurality of housing niches alternating in sequence with solid or unmilled portions of the coupling face, each solid or unmilled portion between each pair of adjacent housing niches forming a corresponding filling element.

[0016] Other aspects and advantages of the invention will appear on reading the following description, given solely by way of example and with reference to the appended drawings, among which: [ FIG. 1 ] there Figure 1 is a longitudinal section schematically illustrating an example of an asynchronous electric railway traction motor equipped with two short-circuit rings; [ FIG. 2 ] there Figure 2 schematically illustrates a portion of a short-circuit ring according to a possible embodiment; [ FIG. 3 ] there Figure 3 is a front view schematically illustrating the short-circuit ring of the figure 2 coupled to the electric motor's conductive bars figure 1 , seen from the side of the conductive bars; [ FIG. 4 ] there Figure 4 schematically illustrates a portion of a short-circuit ring according to another possible embodiment; [ FIG. 5 ] there Figure 5 is a front view schematically illustrating the short-circuit ring of the figure 4 coupled to the electric motor's conductive bars figure 1 , seen from the side of the conductive bars; [ FIG. 6 ] there Figure 6 is a sectional view along plane AA schematically illustrating a rectified portion of a short-circuit ring illustrated in the figure 2 or on the figure 4 ; [ FIG. 7 ] there Figure 7 is a block diagram schematically representing a method of manufacturing a short-circuit ring for an electric motor, according to the invention; [ FIG. 8 ] there Figure 8 is a block diagram schematically representing a method of assembling a short-circuit ring to a rotor of an electric motor having a plurality of rotor bars, which is not covered by the attached claim.

[0017] It should be noted that in the following detailed description, components that are identical or similar, from a structural and / or functional point of view, bear the same numerical references, whether or not they are shown in different embodiments of the present description.

[0018] It should also be noted that, in order to clearly and concisely describe the present invention, the drawings are not necessarily to scale and certain features may be shown in schematic form.

[0019] Furthermore, when the term "adapted" or "arranged" or "configured" or a similar term is used herein in reference to any component as a whole, or any part of a component, or a combination of components, it is to be understood to mean and encompass the structure and / or configuration and / or shape and / or positioning of the component or part to which such term refers.

[0020] Furthermore, when the terms "substantially" or "substantially" are used herein, they are to be understood as encompassing a possible variation of plus or minus 5% from an indicated reference value or position; further, when the terms transverse or transversely are used herein, they are to be understood as encompassing a direction not parallel to the reference part(s) or direction(s) / axis(s) to which they refer, and perpendicularity is to be considered a specific case of transverse direction.

[0021] There figure 1 schematically illustrates an example of an electric motor, in particular an asynchronous railway traction motor, designated by the reference number 1.

[0022] According to possible embodiments well known to those skilled in the art and for this reason not illustrated below in detail, the motor 1 comprises a frame 30 inside which are assembled a stator 20, and a rotor 2 comprising a stack of magnetic laminations 3 and a plurality of conductive bars 4, made for example of copper or aluminum, which are inserted into the magnetic laminations 3 of the rotor 2.

[0023] As a whole, the rotor 2 is mounted on a rotating shaft 5 rotating about a longitudinal reference axis X, with the rotor bars 4 arranged longitudinally, at a distance from each other, about this longitudinal reference axis X.

[0024] As schematically illustrated in the figure 1 , the motor 1 further comprises a first flange 6, arranged on the control side of the motor 1, a second flange 7 opposite the control side, a first bearing 8 arranged on the control side, and a second bearing 9 arranged on the side opposite the control side.

[0025] The conductive bars 4 are connected to each other by two short-circuit rings 10 in order to form a squirrel cage configuration.

[0026] In particular, the figure 2 And 4 schematically illustrate possible embodiments of a short-circuit ring designated by the reference number 10.

[0027] The short-circuit ring 10 comprises a body of substantially annular shape which is made of a single piece of electrically conductive material, for example copper or aluminum, and develops around a longitudinal reference axis X10, that is to say a longitudinal axis substantially coinciding with the axis of rotation X of the rotary shaft 5 in the mounted configuration of the motor 1.

[0028] Furthermore, the annular body comprises a coupling face 12 with the rotor bars 4 which develops transversely with respect to the longitudinal reference axis X, and in particular along a plane substantially perpendicular to the longitudinal reference axis X, and comprises a plurality of housing niches 13 and a plurality of filling elements 14 provided in an alternating sequence on the same coupling face 12.

[0029] In particular, as illustrated in the figures 2 à 6 , the housing niches 13 are spaced at regular distances from each other along the coupling face 12 and along a circumferential path, indicated on the figures 3 And 5 by arrow C.

[0030] According to a possible embodiment of the short-circuit ring 10, each housing niche 13 extends in a direction substantially parallel to the longitudinal reference axis X10 and comprises a bottom wall 16 closed and transverse to the longitudinal reference axis X10.

[0031] In this way, each housing niche 13 delimits a space closed at the bottom and intended to house, in a non-through manner, an end portion 4a of a corresponding rotor bar 4.

[0032] Furthermore, each filling element 14 extends between two adjacent housing niches 13, projecting relative to the corresponding closed bottom walls 16 in a direction substantially parallel to the longitudinal reference axis X and towards the rotor 2 in the mounted configuration of the engine 1. In particular, each filling element 14 is configured to fill, at least partially, a space 17 between the end portions 4a of each pair of adjacent rotor bars, once the rotor bars 4 are housed in the corresponding housing niches 13.

[0033] According to a possible embodiment, each housing niche 13 is hollowed out in the annular body and extends from the upper surface of the coupling face 12 towards the interior of the annular body, to the corresponding closed bottom wall 16, in a direction substantially parallel to the longitudinal reference axis X10.

[0034] In this possible embodiment, each filling element 14 is formed by a solid portion of the coupling face between two adjacent housing niches 13.

[0035] According to an embodiment illustrated in the figures 4 And 5 , the housing niches 13, viewed in a plane substantially perpendicular to the longitudinal reference axis X, are configured in a bone shape. By "bone shape" is meant that the silhouette of the housing niches 13 has two lobes and a narrowed portion between these lobes, generally with the external shape of an 8.

[0036] According to a possible embodiment illustrated in the figure 6 , the coupling face 12, seen along a median and circumferential section of the annular body, that is to say along the circular cut-off line AA indicated on the figures 2 And 4 , has a substantially rectangular sawtooth-shaped profile.

[0037] There figure 7 schematically illustrates a method of manufacturing a short-circuit ring 10 according to the invention, this method being identified by the overall reference number 100 and comprising at least the following steps: 110: producing a body of substantially annular shape in a single piece of electrically conductive material, which develops around a longitudinal reference axis, i.e. the longitudinal reference axis X10, and comprises a coupling face 12 with the rotor bars 4 of a motor 1, the coupling face 12 developing transversely with respect to the longitudinal reference axis X10; 120: producing, on the coupling face 12 of the annular body, a plurality of housing niches 13 and a plurality of filling elements 14, in which the housing niches 13 are spaced at regular distances from each other in a circumferential direction C along the coupling face 12, and each housing niche 13 extends in a direction substantially parallel to the longitudinal reference axis X10 and comprises a closed bottom wall 16, transverse to the longitudinal reference axis X10 so as to house, in a non-through manner,an end portion 4a of a rotor bar 4, and wherein each filling element 14 extends between two adjacent housing niches 13, projecting relative to the corresponding closed bottom walls 16 and is configured to fill, at least partially, a space 17 between the end portions 4a of two adjacent rotor bars 4, once the rotor bars 4 are housed in the corresponding housing niches 13.

[0038] According to a possible embodiment of the manufacturing method 100, the step 120 of producing the plurality of filling elements 14 and the plurality of housing niches 13 comprises at least the following sub-step: 122: milling the annular body by forming the housing niches 13 hollowed out at regular distances from each other and extending from the coupling face 12 towards the inside of the annular body in a direction substantially parallel to the reference axis X10, the portions of the coupling face 12 solid or not milled between each pair of adjacent housing niches 13 forming the plurality of filling elements 14.

[0039] In particular, according to a possible embodiment, the sub-step 122 consisting of milling the annular body by forming the housing niches 13, comprises the fact of producing a plurality of housing niches 13 in the shape of bones.

[0040] According to another possible embodiment, step 120 of producing the plurality of filling elements 14 and the plurality of housing niches 13 comprises at least the following sub-steps: 124: produce, along an internal edge 12a and an external edge 12b of the coupling face 12 and in a circumferential direction, indicated on the figures 2 And 4 by the circular arrow C, a first groove 12c and a corresponding second groove 12d. The grooves 12c and 12d can be made by milling; 126: radially milling, at predefined positions, portions of the coupling face 12 between the first groove 12c and the second groove 12d, in order to form the plurality of housing niches 13 alternating in sequence with the plurality of filling elements 14, each filling element 14 being formed by a corresponding portion of the coupling face 12, solid or not milled, between each pair of adjacent housing niches 13.

[0041] The radial direction of the millings is indicated on the figures 3 And 5by the reference arrow Y which is located in a plane transverse to the longitudinal reference axis X10.

[0042] There figure 8 schematically illustrates a method 200 for assembling a rotor 2 of an electric motor 1, and in particular rotor bars 4 of the rotor 2 to a short-circuit ring 10, comprising at least the following steps: 210: coupling a short-circuit ring 10 illustrated above, to the plurality of rotor bars 4 of the rotor 2 by housing an end portion 4a of each rotor bar 4 in a corresponding housing niche 13 of the short-circuit ring 10, with each filling element 14 which fills, at least partially, a space 17 between the end portions 4a of two adjacent rotor bars 4; 220: irreversibly securing the short-circuit ring 10 to the end portion 4a of each rotor bar 4.

[0043] In particular, step 220 consisting of securing the short-circuit ring 10 to each rotor bar comprises at least the following sub-steps: 222: insert electrically conductive filler material 18 into each housing niche 13; and 224: braise the filler material by irreversibly securing the short-circuit ring 10 to the end portion 4a of each rotor bar 4.

[0044] The definition of "irreversibly" must be interpreted here as referring to the creation of a mechanical connection between two parts which can be separated after their joining only by means of a process involving the at least partial destruction of one or both coupled parts.

[0045] Clearly, a second short-circuit ring 10 can be secured with the same methods to the opposite end portion 4b of each rotor bar 4.

[0046] In this way, an electric motor 1 is produced, and in particular an asynchronous motor for railway traction, in which each rotor bar 4 has an end portion, and not only the head surface of this end portion, which is easily housed in a corresponding housing niche 13 and irreversibly secured there with the short-circuit ring 10, by means of the electrically conductive filler material 18 inserted in each housing niche 13.

[0047] Furthermore, the filling elements 14 in practice form bosses structurally integrated into the annular body and, as illustrated for example in the figure 4 , each filling element fills the space 17 which forms between the end portions of two adjacent rotor bars once the bars 4 are housed in the corresponding housing niches 14.

[0048] In this way, the assembly of the rotor bars 4 with the ring 10 is more precise, and the space 17 to be filled with the filler material 18 is significantly reduced compared to the solutions of the known art.

[0049] It is clear from the above description that the manufacturing method 100 according to the invention makes it possible to achieve the aim underlying the present invention.

[0050] Indeed, the structure of the short-circuit ring 10 makes it possible to create a simpler and more precise mechanical connection with the conductive bars 4, inducing a mechanical capacity for taking up centrifugal forces which advantageously allows higher peripheral linear speeds compared to the solutions of the known art.

[0051] The short-circuit ring 10, the electric motor 1, the manufacturing method 100 and the assembly method 200 thus designed are susceptible to modifications and variations. For example, the shape of the housing niches 13 or of the filling elements 14 can be configured differently; the annular body 12 can be produced using any possible machining or joining method; certain steps or sub-steps of the method 100 or of the method 200 can be carried out in a different sequence compared to that described below and illustrated in the figures 7 And 8 .

[0052] All fittings can also be replaced by technically equivalent elements.

Claims

1. A method for manufacturing (100) a short-circuit ring (10) for an electric motor (1) comprising a rotor (2) including a plurality of rotor bars (4), the manufacturing method (100) comprising at least the following steps: - (110): producing a body of substantially annular shape in a single piece of electrically conductive material, which develops around a reference axis (X10) and comprises a coupling face (12) with the rotor bars (4) which develops transversely with respect to the longitudinal reference axis (X10); - (120): producing, on the coupling face (12) of the annular body, a plurality of housing recesses (13) which are spaced at regular distances from one another in a circumferential direction (C) along the coupling face (12), each housing recess (13) extending in a direction substantially parallel to the longitudinal reference axis (X10) and having a closed bottom wall (16) transverse to the longitudinal reference axis (X10) so as to house, in a non-through manner, an end portion (4a) of a rotor bar (4), and a plurality of filler elements (14), each filler element (14) extending between two adjacent housing recesses (13), projecting with respect to the corresponding closed bottom walls (16) and being configured to fill, at least partially, a space (17) between the end portions (4a) of two adjacent rotor bars (4) once the rotor bars (4) are housed in the corresponding housing recesses (13), the manufacturing method (100) being characterized in that the step (120) consisting in producing the plurality of filler elements (14) and the plurality of housing recesses (13) comprises the following sub-steps: - (122) milling the annular body (12) by forming the housing recesses (13) hollowed out in the annular body at regular distances from one another and extending from the coupling face (12) toward the inside of the annular body in a direction substantially parallel to the reference axis (X10), the solid or unmilled portions of the coupling face (12) between each pair of adjacent housing recesses (13) forming the plurality of filler elements (14); - (124) producing, in a circumferential direction along an inner edge (12a) and an outer edge (12b) of the coupling face (12), a corresponding first groove (12c) and second groove (12d); - (126) radially milling, at predefined positions, portions of the coupling face (12) between the first groove (12c) and the second groove (12d), in order to form the plurality of alternating housing recesses (13) in sequence with solid or unmilled portions of the coupling face (12), each solid or unmilled portion between each pair of adjacent housing recesses (13) forming a corresponding filler element (14).