Rotor for an electric motor provided with end flanges incorporating plastic magnets

Abstract

The invention relates to a rotor (10) for an electric motor (30), comprising: - a rotor shaft (12) rotatably mounted about an axis (X); - a stack of laminations (14) mounted coaxially on the rotor shaft (12), the stack of laminations (14) comprising a plurality of internal cavities (15); - a plurality of permanent magnets (16) housed inside the internal cavities (15) of the stack of laminations (14); - a front flange (17) and a rear flange (19) mounted coaxially on the rotor shaft (12) and arranged axially on either side of the stack of laminations (14); characterised in that each of the front and rear flanges (17, 19) comprises an outer part (172, 192) which is arranged facing the stack of laminations (14) and which comprises a plurality of plastic magnets (23) formed from a matrix made from plastic material incorporating particles having magnetic properties.

Description

[0001] Rotor for electric motor equipped with end flanges incorporating plasto-magnets

[0002] The invention relates to a rotor for an electric motor. The invention also relates to an electric motor comprising such a rotor.

[0003] In general, modern electric motors consist of a rotor attached to a shaft and a stator surrounding the rotor. The stator is mounted in a housing containing bearings for the shaft's rotation. The rotor has a body formed by a stack of laminations or claw poles held together by a suitable fastening system. The rotor body has internal cavities housing permanent magnets. The stator has a body made of a stack of laminations forming a ring, the inner face of which has teeth that define pairs of slots opening inwards towards the stator body. These slots receive phase windings. These phase windings pass through the slots in the stator body and form coils that protrude from either side of the stator body.Phase windings can, for example, consist of a plurality of U-shaped conductor segments, with the free ends of two adjacent segments joined together by welding.

[0004] In the rotor, the lamination stack is axially clamped between a front flange and a rear flange mounted coaxially to the shaft. Each flange is generally disc-shaped, extending in a radial plane perpendicular to the shaft axis. Each flange has a central hole for coaxial mounting on the shaft and several through holes for mounting screws that pass axially through the entire lamination stack. These screws are secured to the flanges with nuts. The front and rear flanges are typically made of a non-magnetic, heat-conducting material, such as a metal.

[0005] In a conventional electromagnet, as illustrated in Figure 1, the magnetic flux generated by the permanent magnets radiates 360° along the direction of magnetization, forming curved field lines that loop between the two poles of the magnet. However, some of these LC field lines follow divergent paths, which can lead to flux losses. This results in suboptimal torque generation by this type of rotor.

[0006] One of the aims of the invention is therefore to provide a solution to the problem of magnetic flux losses within an electric motor rotor as mentioned above. To this end, according to a first aspect, the invention relates to an electric motor rotor comprising:

[0007] - a rotor shaft mounted to rotate around an axis;

[0008] - a sheet metal package mounted coaxially on the rotor shaft, said sheet metal package comprising a plurality of internal cavities separated by intermediate portions, so that the sheet metal package presents an alternation of internal cavities and intermediate portions when following a circumference of the rotor;

[0009] - a plurality of permanent magnets housed inside the internal cavities of the sheet metal bundle;

[0010] - a front flange and a rear flange mounted coaxially on the rotor shaft and arranged axially on either side of the lamination pack; wherein the permanent magnets are orthoradially magnetized, such that each has two adjacent end faces in the orthoradial direction of opposite polarity, the permanent magnets located in two internal cavities adjacent in the circumferential direction being of alternating polarities, and wherein each of the front and rear flanges comprises an external portion which is disposed opposite the lamination pack and which comprises a plurality of plastic magnets formed from a plastic matrix incorporating particles possessing magnetic properties, each plastic magnet being axially aligned with one of the intermediate portions of the lamination pack and having two polar faces, flat and perpendicular to the axis of the shaft,namely a first polar face oriented towards the stack of laminations and a second polar face oriented towards the outside of the rotor, the first polar face having a polarity opposite to that of the second polar face and the same polarity as the end faces of the permanent magnets adjoining said intermediate portion.

[0011] In this configuration, the rotor of the invention will create a magnetic repulsion force between the plasto-magnets and the permanent magnets, which will tend to redirect the magnetic field lines generated by the permanent magnets, at the axial ends of the rotor, towards the stator. This will therefore reduce flux losses.

[0012] According to other characteristics, the rotor of the invention comprises one or more of the following optional characteristics considered alone or in all possible combinations:

[0013] - the particles possessing magnetic properties are made of a material chosen from ferrites or rare earths. - each of the front and rear flanges includes an external part oriented towards the outside of the rotor, said external part being made of a material chosen from polyamide (PA) 6, polyamide (PA) 12, polyphenylene sulfide (PPS) or aluminium.

[0014] - each plastic magnet has an annular sector shape.

[0015] - each intermediate portion, surrounded by the end faces of the two permanent magnets contiguous to it, is inscribed in a cylindrical crown sector extending over an arc of a circle which is substantially equal to the arc of a circle defined by the annular sector formed by the plasto-magnet which faces axially this intermediate portion.

[0016] According to another aspect, the invention also relates to an electric motor comprising a rotor as defined above.

[0017] The invention will be better understood upon reading the following non-limiting description, made with reference to the figures attached hereto.

[0018] [Fig. 1] is a schematic view illustrating the magnetic field lines generated by a conventional electromagnet.

[0019] [Fig. 2] is a view of an electric motor equipped with a permanent magnet rotor according to the invention, the motor being seen from its front side.

[0020] [Fig. 3] is a longitudinal sectional view of the engine in Figure 2 along section plane P.

[0021] [Fig. 4] is a perspective view of the permanent magnet rotor equipping the motor in Figure 2.

[0022] [Fig. 5] is a cross-sectional view of the rotor in Figure 4.

[0023] [Fig. 6] is a perspective view of the end flanges equipping the rotor in Figure 4.

[0024] [Fig. 7] is an axial view of one of the end flanges shown in Figure 6.

[0025] Throughout this description and in the claims, the terms "axial" and "radial" and their derivatives are defined with respect to the rotor's axis of rotation. Thus, an axial orientation refers to an orientation parallel to the rotor's axis of rotation, and a radial orientation refers to an orientation perpendicular to the rotor's axis of rotation. An orthoradial orientation refers to an orientation perpendicular to a radial orientation in a plane perpendicular to the rotor's axis of rotation. Furthermore, by convention, the terms "front" and "rear" refer to separate positions along the rotor's axis of rotation. In particular, the "front" end of the rotor shaft corresponds to the end of the shaft on which a pulley, pinion, or spline can be mounted for transmitting the rotor's rotational motion to any other similar motion transmission device.

[0026] With reference to Figures 2 and 3, an electric motor 30 is shown, employing a rotor 10 according to the invention. This electric motor 30 includes, in particular, a two-part housing containing the rotor 10, which is rotationally fixed to the shaft 12, and an annular stator 36 that surrounds the rotor 10 coaxially with the shaft 12. The housing consists, in particular, of a front bearing 32 in the shape of a ring and a rear bearing 34 in the shape of a bell partially covering the front bearing 32, the front and rear bearings 32, 34 being fixed together, for example by means of screws. Bearings 32, 34 each centrally carry a ball bearing 33 and 35 respectively for the rotational mounting of the shaft 12. As illustrated in Figure 3, bungs 37 project axially on either side of the stator body 36 and are housed in the intermediate space separating the stator 36 from the respective bearings 32, 34.In the configuration shown, the motor 30 is configured to allow the circulation of a cooling fluid in an internal fluid circulation channel 31 formed between the front and rear bearings. This cooling fluid can enter the motor 30 via a fluid inlet nozzle 38 extending from the outer periphery of the rear bearing 34 and opening into the internal channel 31; the cooling fluid can exit the motor 30 via a fluid outlet nozzle 39.

[0027] Figures 4 and 5 represent a rotor 10 according to the invention, the rotor 10 comprising a body formed by a stack of laminations 14 made of a ferromagnetic material, in particular steel, and a plurality of permanent magnets 16 intended to be housed in a plurality of internal cavities 15 formed inside the stack of laminations 14, each internal cavity 15 housing a permanent magnet 16. The stack of laminations 14 is mounted coaxially on a shaft 12 mounted to rotate about an axis X. The shaft 12 may be press-fitted into a central opening in the stack of laminations 14 so as to rotationally link the rotor body with the shaft 12.

[0028] The sheet metal pack 14 is formed from an axial stack of sheets which extend in a radial plane perpendicular to the X axis of the shaft 12. A plurality of fixing holes 11 are made in the sheet metal pack 14 to allow the passage of fixing bolts 13 of the sheets of the pack. These mounting holes 11 are through holes, allowing a bolt 13 to pass through each hole. As shown in Figure 3, one end of the bolts 13 bears against the outer face of a front end flange 17, while the other end of the bolts 13 bears against the outer face of a rear end flange 19. Thus, the stack of laminations 14 is axially clamped between the front end flange 17 and the rear end flange 19. These flanges 17 and 19 ensure the balancing of the rotor 10 while also providing secure retention of the magnets 16 within their cavity 15.Balancing can be achieved by adding or removing material from the flanges. Material removal can be achieved by machining, while material addition can be achieved by inserting elements into openings provided for this purpose and distributed along the circumference of the flange 17, 19.

[0029] As illustrated in Figure 5, the cavities 15 extend radially with respect to the X-axis and are axially through-holes. They have an inner portion 151, with a substantially triangular cross-section, and an outer portion 152, with a rectangular cross-section, and are uniformly distributed around the X-axis. Two directly adjacent cavities 15 are separated by an intermediate portion 141 or 142 of the lamination stack 14, so that the rotor body consists of alternating cavities 15 and intermediate portions 141, 142 when following a circumference of the rotor 10. Each intermediate portion 141, 142 preferably has a general T-shape. Each cavity 15 houses a single magnet 16, the magnet 16 being configured to fill the inner portion 151 of said cavity 15.The permanent magnets 16 are orthoradially magnetized, meaning that the two end faces 16a, 16b of each magnet 16, which are adjacent to each other in the orthoradial direction, are magnetized so as to generate a magnetic flux in an orthoradial orientation with respect to the X axis. Among these end faces 16a, 16b, a distinction must be made between face 16a, corresponding to the South pole of the magnet 16, represented by the letter S in Figure 5, and face 16b, corresponding to the North pole of the magnet 16, represented by the letter N in Figure 5. The magnets 16 located in two consecutive cavities 15 have alternating polarities. Thus, the intermediate portions 141 of the sheet metal bundle 14 adjoin the faces 16a of two consecutive magnets 16 and the intermediate portions 142 of the sheet metal bundle adjoin the faces 16b of two consecutive magnets 16.As arranged, the magnets 16 generate in the sheet metal bundle 14 a radially oriented magnetic flux directed towards the outer periphery of the rotor body.

[0030] With reference to Figure 6, each of the end flanges 17 and 19 of the rotor 10 is shown. Each flange 17, 19 is disc-shaped, extending in a radial plane perpendicular to the X-axis of the shaft 12. The flange 17, and 19 respectively, have a central opening 21, and 22 respectively, for coaxial mounting on the shaft 12, and several through holes 24 for receiving the mounting bolts 13, which pass axially through the entire stack of laminations 14. The flanges 17 and 19 are formed by molding a plastic material. The plastic material may advantageously be chosen from polyamide (PA) 6, polyamide (PA) 12, and polyphenylene sulfide (PPS). The flange 17, respectively 19, is formed of a first outer half-disc 171, respectively 191, oriented towards the outside of the rotor 10, and a second outer half-disc 172, respectively 192, oriented towards the sheet metal pack 14.The first outer half-disk 171, respectively 191, is made of plastic or aluminum, and the second outer half-disk 172, respectively 192, comprises a plurality of annular sector-shaped plastic magnets 23, formed from a plastic matrix incorporating particles possessing magnetic properties. The matrix material may advantageously be chosen from polyamide (PA) 6, polyamide (PA) 12, and polyphenylene sulfide (PPS), and the particles possessing magnetic properties may advantageously be made of a material chosen from ferrites or rare earths.

[0031] Each plastic magnet 23 has axial magnetization, so that it has two end faces 231 and 232, which are flat and perpendicular to the X-axis, called polar faces. Among these polar faces 231 and 232, a distinction must be made between face 231, corresponding to the South pole of the plastic magnet 23, and face 232, corresponding to the North pole of the plastic magnet 23. Two adjacent plastic magnets 23 have alternating polarities. Thus, as shown in Figure 7, the outer half-disk 192 of the flange 19 which faces the stack of sheets 14 is formed of an alternation of polar faces 231, 232 when following a circumference of the rotor 10. Similarly, the outer half-disk 172 of the flange 17 which faces the stack of sheets 14 is formed of an alternation of polar faces 231, 232 when following a circumference of the rotor 10.

[0032] As shown in dashed lines in Figure 5, each plastic magnet 23 is axially aligned with one of the intermediate portions 141, 142 of the sheet metal stack 14 such that its polar face 231 or 232, which is oriented towards the sheet metal stack 14, has the same polarity as the end faces 16a or 16b of the permanent magnets 16 that adjoin said intermediate portion. Thus, each of the intermediate portions 141 faces axially, on each side, the polar face 231 of one of the plastic magnets 23 of the flange 17 and the flange 19, and each of the intermediate portions 142 faces axially, on each side, the polar face 232 of another of the plastic magnets 23 of the flange 17 and the flange 19.In addition, preferably, each intermediate portion 141, respectively 142, surrounded by the two end faces 16a, respectively 16b, is inscribed in a cylindrical crown sector extending over an arc of a circle that is substantially equal to that defined by the annular sector formed by the polar face 231, respectively 232, of the plastic magnet 23 which faces it axially, so that each plastic magnet 23 has two end zones partially facing axially the permanent magnets 16 surrounding said intermediate portion 141, respectively 142. In particular, each of said end zones is aligned axially with the end face 16a or 16b of one of said permanent magnets 16 which has the same polarity as the polar face of the plastic magnet 23 which faces the stack of sheets 14.

[0033] Thus configured, the end flanges 17 and 19 will redirect the magnetic field lines generated by the permanent magnets 16 of the rotor 10 towards the stator 36 due to the axial alignment of the pole faces 231, which have an S polarity, with the intermediate portions 141 and the end faces 16a, which also have an S polarity, and due to the axial alignment of the pole faces 232, which have an N polarity, with the intermediate portions 142 and the end faces 16b, which also have an N polarity. This axial alignment will create a magnetic repulsion effect that will tend to deflect the field lines oriented axially at the ends of the rotor so that they are ultimately directed towards the stator 36.

[0034] Thus configured, the rotor 10 of the invention makes it possible to greatly reduce flux losses at the axial ends of the rotor by redirecting the field lines from the ends towards the stator.

[0035] The invention is obviously not limited to the configuration of the invention as described above.

Claims

DEMANDS 1. Rotor (10) for electric motor (30) comprising: - a rotor shaft (12) mounted to rotate around an axis (X); - a sheet metal pack (14) mounted coaxially on the rotor shaft (12), said sheet metal pack (14) comprising a plurality of internal cavities (15) separated by intermediate portions (141, 142), so that the sheet metal pack (14) presents an alternation of internal cavities (15) and intermediate portions (141, 142) when following a circumference of the rotor (10); - a plurality of permanent magnets (16) housed inside the internal cavities (15) of the sheet metal bundle (14); - a front flange (17) and a rear flange (19) mounted coaxially on the rotor shaft (12) and arranged axially on either side of the sheet metal bundle (14); in which the permanent magnets (16) are orthoradially magnetized, such that each has two end faces (16a, 16b) adjacent in the orthoradial direction of opposite polarity, the permanent magnets (16) located in two internal cavities (15) adjacent in the circumferential direction being of alternating polarities, characterized in that each of the front and rear flanges (17, 19) comprises an external part (172, 192) which is disposed opposite the sheet bundle (14) and which comprises a plurality of plastic magnets (23) formed of a plastic matrix incorporating particles having magnetic properties, each plastic magnet (23) being axially aligned with one of the intermediate portions (141, 142) of the sheet bundle (14) and having two polar faces (231, 232),planar and perpendicular to the axis of the shaft, namely a first polar face oriented towards the stack of laminations (14) and a second polar face oriented towards the outside of the rotor (10), the first polar face having a polarity opposite to that of the second polar face and the same polarity as the end faces (16a, 16b) of the permanent magnets (16) which adjoin said intermediate portion (141, 142).

2. Rotor (10) according to claim 1, characterized in that the particles possessing magnetic properties are made of a material selected from ferrites or rare earths.

3. Rotor (10) according to claim 1 or 2, characterized in that each of the front and rear flanges (17, 19) comprises an external part (171, 191) oriented towards the outside of the rotor (10), said external part (171, 191) being made of a material selected from polyamide (PA) 6, polyamide (PA) 12, polyphenylene sulfide (PPS) or aluminum.

4. Rotor (10) according to any one of the preceding claims, characterized in that each plasto-magnet (23) has an annular sector shape.

5. Rotor (10) according to claim 4, characterized in that each intermediate portion (141, 142), surrounded by the end faces (16a, 16b) of the two adjacent permanent magnets (16), is inscribed within a cylindrical ring sector extending over an arc of a circle that is substantially equal to the arc of a circle defined by the annular sector formed by the plasto-magnet (23) which faces axially this intermediate portion (141, 142).

6. Electric motor (30) comprising a rotor (10) according to any one of the preceding claims.

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