WO2020083511A1 - Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness - Google Patents

Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness Download PDF

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Publication number
WO2020083511A1
WO2020083511A1 PCT/EP2018/079452 EP2018079452W WO2020083511A1 WO 2020083511 A1 WO2020083511 A1 WO 2020083511A1 EP 2018079452 W EP2018079452 W EP 2018079452W WO 2020083511 A1 WO2020083511 A1 WO 2020083511A1
Authority
WO
WIPO (PCT)
Prior art keywords
stator
magnetic
yoke
permanent magnet
electric machine
Prior art date
Application number
PCT/EP2018/079452
Other languages
French (fr)
Inventor
Masahiro Kayano
Yoji Hashimoto
Ren ISHIDA
Nicolas Labbe
Jean-Sébastien Metral
Original Assignee
Aichi Steel Corporation
Valeo Equipements Electriques Moteur Sas
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aichi Steel Corporation, Valeo Equipements Electriques Moteur Sas filed Critical Aichi Steel Corporation
Priority to PCT/EP2018/079452 priority Critical patent/WO2020083511A1/en
Publication of WO2020083511A1 publication Critical patent/WO2020083511A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/17—Stator cores with permanent magnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K23/00—DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors
    • H02K23/02—DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors characterised by arrangement for exciting
    • H02K23/04—DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors characterised by arrangement for exciting having permanent magnet excitation

Definitions

  • Stator for a rotating electric machine comprising at least one permanent magnet with a variable radial thickness
  • the invention relates to a stator of a rotating electric machine, provided with at least one permanent magnet with a variable radial thickness.
  • the invention has particularly advantageous applications in the fields of motor vehicle starters, electric powertrain systems, and permanent magnet DC motors.
  • the invention applies to vehicles with 12 V to 48 V on-board voltage.
  • the invention applies to rotating electric machines having a rotation speed of 2000 to 5000 rpm.
  • the invention applies to an electric motor of a starter, having a rotation speed of 2000 rpm to 5000 rpm, the starter having thus an output torque of 50 N.m to 10 N.m and a mechanical power of 1 kW to 3 kW available on the output shaft.
  • Motor vehicle starters which implement rotary electrical machines provided with a stator, or inductor, comprising several permanent magnets and a rotor, or armature, having a body of cylindrical shape, and a winding formed from conducting wires.
  • the rotor body consists of a stack of plates having longitudinal slots in which the wires of the winding are inserted, consisting for example of pin- shaped conductors.
  • the rotor is in addition provided with a collector comprising a plurality of contact pieces connected electrically to the wires of the winding.
  • the inductor comprises a metal yoke, the inner face of which supports a plurality of permanent magnets intended to produce an induction field.
  • the permanent magnets are configured as cylindrical segments, with angular distribution at regular intervals inside the yoke, and separated uniformly from the armature by a radial air gap.
  • the permanent magnets are generally fixed on the inner face of the yoke by means of clamps extending in the longitudinal direction in the spaces provided between the permanent magnets.
  • the patent application WO2016162636A1 describes a starter comprising a rotating electric machine provided with a stator, said stator comprising a set of magnetic poles, characterized in that a permanent magnet forms at least two poles of the set of said magnetic poles.
  • the application describes a permanent magnet forming all of said magnetic poles, the permanent magnet being one single piece and having a cylindrical shape.
  • this solution has the disadvantage to require large amounts of magnetic material and therefore rare earths.
  • rare earths which are popular for their exceptional magnetic properties, are problematic mainly for two reasons. Firstly, the rare earths market is changeable and the price of rare earths elements involved in the manufacturing of permanent magnets is high. Secondly, when mining and refining rare earths, poisonous chemicals are released into the environment. This is why industries today desire to reduce rare earths amounts so as to save money and reduce their environmental impact.
  • stator for a rotating electric machine comprising:
  • a magnetic sector forming one pole of said assembly of magnetic poles, characterized in that a radial thickness of the magnetic sector varies between two straight lines perpendicular to a central axis of the yoke, each one of these straight lines intersecting the central axis and forming between them an angle of at least 5°, and in that the yoke has a complementary shape to a shape of the magnetic sector, in such a way that a radial thickness of the stator is almost constant.
  • Magnetic pole means usually a point where the magnetic field lines converge. With the cylindrical geometry of a rotating electric machine, a magnetic pole is a portion of a line, oriented radially, where the magnetic field lines converge. In practice, it is not strictly a portion of a line, it has a thickness according to the orthoradial direction.
  • Ring means a direction according to a radius of the stator.
  • Orthoradial or “tangential” means a direction according to a direction perpendicular to a radius of the stator.
  • Magnetic sector means an angular portion of a permanent magnet comprising a magnetic pole. This portion is not necessarily detached physically, in other words, a magnetic sector is a geometric sector which does not correspond necessarily to an independent magnet.
  • the radial thickness of the stator is equal to the radial thickness of the magnetic sector and the yoke. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator. Even if the stator further comprises other elements like electronic components or mechanical elements, the thickness of the stator should be understood as the sum of the thicknesses of the magnetic sector and the yoke.
  • the invention makes it possible to produce smaller magnets compared to those of prior art, while keeping today’s starters performances.
  • This is possible thanks to the optimization of the shape of the magnets and the geometry of the yoke, which has a complementary shape to the shape of the magnetic sectors.
  • the optimized shape allows to spare raw material while being sufficient to produce the magnetic field necessary to the performances of the starter.
  • the complementary shape of the yoke allows to concentrate the magnetic flux between the magnetic poles, so as to minimize magnetic losses. This results in substantial savings of rare earths, leading to costs savings and simultaneously to a reduction of environmental impact. This results as well in a substantial reduction of the stator weight, which is very positive when designing a rotating electric machine.
  • the magnets can be directly overmoulded in the yoke, which has a complementary shape to the shape of the magnets. It is thus possible to get away from clamps.
  • the geometry of the magnets and the shape of the magnets being complementary to the shape of the yoke, allows also to improve the support of the magnets in the orthoradial direction.
  • the invention allows to reduce the noise of a rotating electric machine comprising such a stator.
  • an external surface of the magnetic sector, facing the yoke has a radius of curvature smaller than a radius of curvature of an external surface of the yoke.
  • the external surface of the magnetic sector, facing the yoke has a convex shape. That is to say that, viewed from the exterior of the stator, the external surface of the magnetic sector, facing the yoke, exhibits a convex shape.
  • the assembly of magnetic poles of the stator is formed by a plurality of magnetic sectors whose external surface facing the yoke has at least one concave shape.
  • at least one magnetic sector has a convex external surface facing the yoke.
  • all magnetic sectors have a convex external surface facing the yoke.
  • the concave shape that exhibits the profile of the plurality of magnetic sectors allows to spare raw material.
  • the plurality of magnetic sectors form the inner peripheral surface of the stator, which is cylindrical.
  • two adjacent magnetic sectors are in contact according to a portion of a radial plane of the yoke.
  • the thickness of the contact portion is smaller than the maximum radial thickness of a magnetic sector.
  • two adjacent magnetic sectors are in contact according to a single point.
  • the thickness of the contact portion is non- existent and at this radial position, the thickness of the stator is equal to the thickness of the yoke.
  • the plurality of magnetic sectors has a flower shape, the magnetic sectors forming petals of the flower.
  • a radial thickness of said stator is almost constant on at least 90 % of the circumference of said stator.
  • the radial thickness of the stator is equal to the radial thickness of the magnetic sector and the yoke. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator.
  • the yoke comprises an outer portion and an inner portion, said inner portion having an outer peripheral surface pressed against an inner peripheral surface of the outer portion, and said inner portion having an inner peripheral surface fitting the shape of at least one magnetic sector.
  • the outer portion and inner portion of the yoke form one single block of steel.
  • the outer portion and inner portion of the yoke are in steel.
  • the outer portion of the yoke is in steel and the inner portion is made of a laminated core. According to one embodiment, the outer portion of the yoke is made of a laminated core and the inner portion is in steel.
  • the outer portion and inner portion of the yoke are formed with a single laminated core.
  • the core is made of laminated metal sheets.
  • the core is made of thin metal sheets.
  • the yoke exhibits a large radial thickness compared to a yoke of prior art.
  • the thickness of the yoke can reach about 4 mm locally, compared to about 2 mm for a yoke of prior art.
  • This large radial thickness combined with a core made of thin metal sheets, allows to absorb the vibrations of the stator, and thus to reduce the noise of a rotating electric machine comprising such a stator.
  • the thin metal sheets allow to dissipate energy by friction between sheets.
  • the laminated metal sheets are in steel.
  • the laminated metal sheets are buttoned up, welded together, bonded or tightened with bars.
  • the inner portion of the yoke is inserted into the outer portion of the yoke.
  • the inner portion and the outer portion of the yoke are joined together by any mean such as gluing, nailing, crimping, welding, soldering, screwing, or with a clip.
  • the yoke being in steel and thus comprising large amounts of iron, exhibits magnetic properties. These magnetic properties, associated to the complementary shape of the yoke, allow to close the magnetic circuit and avoid losses. So the yoke plays a mechanical support role, but also acoustic and magnetic roles.
  • the contact surface between the inner portion of the yoke and the outer portion of the yoke is almost cylindrical. “Almost” shall mean that some fixing means may be provided on the inner surface of the outer portion of the yoke, and on the outer surface of the inner portion of the yoke.
  • the peripheral outer surface of the inner portion of the yoke is provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion of the yoke.
  • the contact surface between the inner portion of the yoke and the outer portion of the yoke come up to or reach at least one extremity of a magnetic sector.
  • the contact surface between the inner portion of the yoke and the outer portion of the yoke come up to or reach all the extremities of all magnetic sectors.
  • the ratio between the volume occupied by the plurality of magnetic sectors and the volume occupied by the magnetic sectors and the inner portion of the yoke is greater or equal to 50 %.
  • the plurality of magnetic sectors forming the magnetic poles has a cylindrical inner surface with a radius named the first radius and an outer surface having at least one concave shape, said outer surface being inscribed in a cylinder with a radius named the second radius, the plurality of magnetic sectors occupying at least 50 % of the volume of a ring with an inner radius the first radius and an outer radius the second radius.
  • the invention thus allows to spare about 40 % of magnetic material compared to the magnets of prior art, while keeping the same performances.
  • the stator comprises at least one permanent magnet, said permanent magnet forming at least one magnetic sector.
  • the permanent magnet forms two magnetic sectors.
  • the permanent magnet forms three magnetic sectors, or more.
  • the stator comprises a plurality of permanent magnets, each permanent magnet forming one single magnetic sector.
  • the plurality of permanent magnets has a flower shape, the permanent magnets forming petals of the flower.
  • the inner surface of the stator is cylindrical and is formed by the inner surfaces of the permanent magnets.
  • the stator comprises one single permanent magnet forming the plurality of magnetic sectors.
  • the permanent magnet has a flower shape, the magnetic sectors forming petals of the flower.
  • the inner surface of the stator is cylindrical and is formed by the inner surface of the permanent magnet.
  • One permanent magnet means a single solid component that may comprise several directions of magnetization. In other words a magnet may not comprise several magnets (several pieces of magnets) joined together and forming a block.
  • the petal shape of the magnetic sectors facilitates the support of the at least one magnet in the orthoradial direction. Indeed, the curved shapes of the magnetic sectors allow to oppose to attractive magnetic forces, which act mainly towards the orthoradial direction, when the motor is operating.
  • the at least one permanent magnet is inserted into the yoke.
  • the at least one permanent magnet is stapled or stuck on the yoke.
  • the at least one permanent magnet is overmoulded in the yoke.
  • the overmoulding allows to oppose to mechanical forces such as vibrations and shocks. It is thus possible to get away from any fixing mean, such as clamps.
  • the inner portion of the yoke and the at least one permanent magnet overmoulded in the inner portion of the yoke are inserted together in the outer portion of the yoke.
  • the at least one permanent magnet is in ferromagnetic material.
  • the at least one permanent magnet is a moulded magnet based on magnetic particles embedded in a binder made of a non-magnetic material.
  • the magnetic particles are anisotropic rare earth magnetic particles.
  • the magnetic particles measure several micrometers to several hundreds of micrometers.
  • a magnetic particle comprises an easy axis of magnetization.
  • the at least one magnet already has magnetic particles that are aligned during moulding and therefore prior to assembly thereof in the motor. This has the advantage that it is possible to assemble the already oriented magnet in the motor.
  • said binder has a melting point lower than the Curie point of said magnetic particles.
  • the magnetic particles are for example made of neodymium-iron- boron or of samarium-iron-nitrogen.
  • the binder is for example made of a plastic material.
  • the magnetic material used preferably has a remanence in the order of 0.6 Tesla. The method of measurement of the remanence of the material is that described in the standard NFEN60404-5.
  • the magnetic particles are magnetized in such a way that a magnetic field in the air gap varies sinusoidally along a circumference of said air gap.
  • the at least one permanent magnet is a polar anisotropically aligned magnet.
  • the direction of magnetization of the easy axes of the magnetic particles varies progressively along a circumference of said stator:
  • the easy axes of magnetization of the magnetic particles are arranged so that the magnetization vector gradually inclines in the direction of the change in mechanical angle; - furthermore, when the mechanical angle is between the two consecutive magnetic sectors, the easy axes of magnetization of the magnetic particles are arranged so that the magnetization vector is oriented in the circumferential direction;
  • the easy axes of magnetization of the magnetic particles are aligned so that the magnetization vector gradually inclines in the direction of the center of the stator;
  • magnetic flux lines are formed along the magnetization vector, between the inner surface of the magnetic sector and the outer surface of the magnetic sector. According to one embodiment, about half of the magnetic flux lines of one magnetic sector are connected to half of the magnetic flux lines of a consecutive magnetic sector through magnetic flux lines that are in the yoke.
  • magnetic flux lines that are in the yoke extend from the outer surface of a magnetic sector to the outer surface of a consecutive magnetic sector along an orthorad ial direction. Thanks to a thicker yoke between two consecutive magnetic sectors, it is possible to prevent the saturation of the magnetic flux in the yoke, from adjacent magnetic sectors.
  • the direction of the magnetic field varies following a curved direction.
  • the field lines of the magnetic field form a convex shape, viewed from the exterior of the stator. The field lines impinge on the yoke since the yoke allows to close the magnetic circuit.
  • the plastic-bonded magnets are anisotropic, that is to say the magnetic particles are aligned during moulding in order to obtain a polar anisotropically aligned magnet.
  • the plurality of magnetic sectors is magnetized according to a configuration of the Halbach type.
  • the plastic-bonded magnets are anisotropic, that is to say the magnetic particles are aligned during moulding in order to obtain the Halbach structure.
  • the starter has a Halbach orientation that provides magnetic flux only towards the armature. In fact, this makes it possible to improve the efficiency of the starter owing to the very high level of the field H of reaction of the armature.
  • the assembly of magnetic poles can have up to 36 poles.
  • the invention also relates to a rotating electric machine, for instance for a starter or a starter-alternator, comprising a stator as previously defined.
  • the rotating electric machine has a rotation speed of 2000 rpm to 5000 rpm. According to one embodiment, the rotating electric machine is put in a vehicle with 12 V to 48 V on-board voltage.
  • the rotating electric machine comprises a rotor separated from said stator by an air gap almost constant on at least 90 % of the circumference of said air gap. « Almost » shall mean a variation of 2 to 3 % of the air gap.
  • the invention also relates to a starter comprising a rotating electric machine as previously defined.
  • the starter has an output torque of 50 N.m to 10 N.m.
  • the starter has an output mechanical power of 1 kW to 3 kW .
  • the starter is put in a vehicle with 12 V to 48 V on- board voltage.
  • the invention also relates to a powertrain system comprising a rotating electric machine as previously defined.
  • the powertrain system is put in a vehicle with 12 V to 48 V on-board voltage.
  • FIG. 1 is a schematic side view of a starter according to the present invention
  • Fig. 2 is a schematic cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 ;
  • Fig. 3a and 3b are schematic cross-sectional views of the rotor and stator, according to two different embodiments of the invention, of the electrical machine that is part of the starter in Fig. 1 ;
  • Fig. 4 shows the device for producing a single-piece permanent magnet of the stator according to the present invention;
  • Fig. 5 is a partial cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 showing the magnetic vector distribution inside the magnetic sectors;
  • Fig. 6 is a partial cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 , showing the magnetic field lines inside the stator composed of magnetic sectors and the yoke.
  • Fig. 1 shows, schematically, a starter 1 for an internal-combustion engine of a motor vehicle.
  • This direct-current starter 1 comprises, on the one hand, a rotor 2, also called armature, which is able to rotate about an axis X, and on the other hand, a stator 3, also called inductor, positioned around the rotor 2.
  • the rotor 2 is separated from the stator 3 by an air gap 6.
  • the rotating electrical machine formed by the stator 3 and the rotor 2 is of the six-pole type. As a variant, the machine could be of the four-pole type.
  • This stator 3 comprises a yoke 4 bearing a permanent magnet 5 forming a set of poles.
  • the rotor 2 comprises a rotor body 7 and a winding 8 wound in slots in the rotor body 7.
  • the rotor body 7 consists of a stack of plates having longitudinal slots.
  • pin-shaped conducting wires 11 are threaded inside the slots 16 generally on two separate layers.
  • the winding 8 forms buns 9 on either side of the rotor body 7.
  • the rotor 2 is provided, at the back, with a collector 12 comprising a plurality of contact pieces connected electrically to the conducting elements, consisting here of the pins 11 of the winding 8.
  • a group of brushes 13 and 14 is provided for electrical supply to the winding 8, one of the brushes 13 being earthed on the starter 1 and the other brush 14 being connected to a terminal 15 of a contactor 17.
  • the brushes are for example four in number.
  • the brushes 13 and 14 will rub against the collector 12 when the rotor 2 is rotating, which makes it possible to supply the rotor 2 by commutation of the electric current in sections of the rotor 2.
  • the contactor 17 comprises, besides the terminal 15 connected to the brush 14, a terminal 29 connected, via an electrical connection element, to an electrical supply of the vehicle, notably a battery.
  • the starter 1 further comprises a starter drive assembly 19 mounted sliding on a drive shaft 18 and can be made to rotate about the axis X by the rotor 2.
  • a speed reducing assembly 20 is interposed between a shaft of the rotor 2 and the drive shaft 18.
  • the starter drive assembly 19 comprises a drive element formed by a pinion 21 that is intended to engage with a drive member of the heat engine, such as a starter ring gear.
  • a drive member of the heat engine such as a starter ring gear.
  • the starter drive assembly 19 further comprises a free wheel 22 and a pulley washer 23, together defining a groove 24 for receiving the end 25 of a fork 27.
  • the fork 27 is actuated by the contactor 17 to displace the starter drive assembly 19 relative to the drive shaft 18, along the axis X, between a first position in which the starter drive assembly 19 drives the heat engine via the drive pinion 21 , and a second position in which the starter drive assembly 19 is disengaged from the starter ring gear of the heat engine.
  • an internal contact plate (not shown) makes it possible to establish a connection between the terminals 15 and 29 in order to supply power to the electric motor. This connection will be cut on deactivation of the contactor 17.
  • Fig. 2 shows a stator 3 of a rotary electric machine. This stator, for example for a starter 1 of a combustion engine, comprises:
  • a radial thickness of the magnetic sector 52 varies between two straight lines perpendicular to a central axis of the yoke 4, each one of these straight lines intersecting the central axis and forming between them an angle of at least 5°, and in that the yoke 4 has a complementary shape to a shape of the magnetic sector 52, in such a way that a radial thickness of the stator 3 is almost constant.
  • « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator 3.
  • the rotor 2 is separated by the stator 3 by an air gap 6.
  • the air gap 6 is almost constant on at least 90 % of the circumference of said air gap 6. « Almost » shall mean a variation of 2 to 3 % of the air gap.
  • the stator 3 comprises a yoke 4 and magnetic poles, whose positions are identified by the labels P1 , P2, P3, P4, P5 and P6.
  • the magnetic poles are formed by a plurality 5’ of magnetic sectors 52, which are separated from each other by dotted lines 54.
  • An external surface 521 of a magnetic sector 52, facing the yoke 4, has a radius of curvature smaller than a radius of curvature of an external surface 44 of the yoke 4.
  • An external surface 56 of the plurality 5’ of the six magnetic sectors 52, formed by the external surfaces 521 of each magnetic sector 52, has six concave shapes 53 facing the yoke 4.
  • Two adjacent magnetic sectors 52 are in contact according to a portion 541 of a radial plane of the yoke 4.
  • the thickness of the contact portion 541 is smaller than the maximum radial thickness 522 of a magnetic sector. But other situations could be considered, for instance two adjacent magnetic sectors can be in contact according to a single point. In this case, the thickness of the contact portion 541 is non-existent and at this radial position, the thickness of the stator is equal to the thickness of the yoke.
  • the plurality 5’ of magnetic sectors 52 has a flower shape, the magnetic sectors 52 forming petals of the flower.
  • the stator 3 has a radial thickness almost constant on at least 90 % of the circumference of said stator 3. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator 3. Indeed, the presence of chamfers on the magnetic sectors 52, or of magnetic shunts on the yoke 4, may generate a small local change in the radial thickness of the stator.
  • the yoke 4 comprises an outer portion 42 and an inner portion 43, said inner portion 43 having an outer peripheral surface pressed against an inner peripheral surface of the outer portion 42, and said inner portion 43 having an inner peripheral surface 41 fitting the shape of the plurality 5’ of magnetic sectors 52.
  • the magnetic sectors 52 lodge into the concavities of the yoke 4.
  • the contact surface 45 between the inner portion 43 and the outer portion 42 is showed with a dotted line, and is almost cylindrical.“Almost” shall mean that some fixing means may be provided on the inner surface of the outer portion of the yoke, and on the outer surface of the inner portion of the yoke.
  • the peripheral outer surface of the inner portion 43 of the yoke could be provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion 42 of the yoke 4.
  • the contact surface 45 between the inner portion 43 of the yoke and the outer portion 42 of the yoke come up to the extremities of the magnetic sectors 52.
  • the outer portion 42 and inner portion 43 of the yoke form one single block of steel.
  • the outer portion 42 and inner portion 43 of the yoke 4 are formed with a single laminated core. In these two embodiments, the boundary between the inner portion 43 and the outer portion 42 is simply fictive.
  • the outer portion 42 and inner portion 43 of the yoke are in steel.
  • the outer portion 42 of the yoke 4 is in steel and the inner portion 43 is made of a laminated core.
  • the outer portion 42 of the yoke 4 is made of a laminated core and the inner portion 43 is in steel.
  • the outer portion 42 and inner portion 43 are distinct.
  • the inner portion 43 of the yoke 4 is inserted into the outer portion 42 of the yoke.
  • the inner portion 43 and the outer portion 42 of the yoke 4 are joined together by any mean such as gluing, nailing, crimping, welding, soldering, screwing, or with a clip.
  • the core is made of laminated metal sheets, the laminated metal sheets being in steel.
  • the core is made of thin laminated metal sheets.
  • the laminated metal sheets are buttoned up, welded together, bonded or tightened with bars.
  • the yoke 4 exhibits a large radial thickness compared to a yoke of prior art.
  • the thickness of the yoke 4 can reach about 4 mm locally, compared to about 2 mm for a yoke of prior art.
  • This large radial thickness combined with a core made of thin metal sheets, allows to absorb the vibrations of the stator, and thus to reduce the noise of a rotating electric machine comprising such a stator.
  • the thin metal sheets allow to dissipate energy by friction between sheets.
  • the plurality 5’ of magnetic sectors 52 is supported by the internal surface 41 of the yoke 4. But the yoke 4 does not only play a mechanical support role.
  • the yoke 4 being in steel and thus comprising large amounts of iron, exhibits magnetic properties. These magnetic properties, associated to the complementary shape of the yoke, allow to close the magnetic circuit and avoid losses. So the yoke 4 plays a mechanical support role, but also acoustic and magnetic roles.
  • the plurality 5’ of magnetic sectors 52 forming the magnetic poles has a cylindrical inner surface 55, made of the six inner surfaces 523 of each magnetic sector 52, with a radius named the first radius R1 and an outer surface 56 having six concave shapes 53, said outer surface 56 being inscribed in a cylinder with a radius named the second radius R2, the plurality 5’ of magnetic sectors 52 occupying at least 50 % of the volume of a ring with an inner radius the first radius R1 and an outer radius the second radius R2.
  • the ratio between the volume occupied by the plurality 5’ of magnetic sectors 52 and the volume occupied by the magnetic sectors 52 and the inner portion 43 of the yoke is greater or equal to 50 %.
  • the presence of the six concave shapes 53, facing the yoke 4 allows to spare about 40 % of magnetic material compared to the cylindrical permanent magnet of prior art, while keeping the same performances (cf. WO2016162636A1 ).
  • Fig. 3a and b show two embodiments of the invention.
  • the stator 3 comprises a plurality 5 of six permanent magnets 51 , each permanent magnet 51 forming one single magnetic sector 52.
  • the inner surface of the stator is cylindrical and is formed by the inner surfaces of the permanent magnets.
  • the stator 3 comprises one single permanent magnet 51 forming the plurality 5’ of magnetic sectors 52.
  • the inner surface of the stator is cylindrical and is formed by the inner surface of the permanent magnet.
  • One permanent magnet means a single solid component that may comprise several directions of magnetization. In other words a magnet may not comprise several magnets (several pieces of magnets) joined together and forming a block.
  • the magnetic sectors 52 are in ferromagnetic material.
  • Fig. 4 illustrates the case of a single permanent magnet 51 which is a moulded magnet based on anisotropic rare earth magnetic particles 31 embedded in a binder 32 made of a non-magnetic material.
  • the binder 32 is placed in a mould 34 of flower shape that surrounds a core made up of a set of permanent magnets 35, the number of which corresponds to the number of poles of the stator 3, here six.
  • Each of the magnets 35 is magnetically oriented radially. Two consecutive magnets 35 have magnetic field orientations B1 , B2 that are opposite to one another.
  • the binder 32 is heated to its melting point, which is lower than the Curie point of the magnetic particles 31. It may be mentioned here that the Curie point is the temperature at which the magnetic particles 31 are demagnetized.
  • the magnetic particles 31 initially demagnetized, are put inside the mould 34 and are magnetized following the configuration of the magnetic flux generated by the magnets 35 while the temperature inside the mould 34 decreases, which causes gradual hardening of the binder 32. At the end of the process, the magnetized particles 31 are trapped by the binder 32 while having been magnetized in such a way that between two consecutive poles P1 -P6, the direction of the magnetic field generated by the magnet 5 gradually varies along a circumference of the stator 3.
  • the binder 32 consists of a plastic, and the magnetic particles 31 can be made of neodymium-iron-boron or of samarium-iron-nitrogen.
  • the material used preferably has a remanence in the order of 0.6 tesla.
  • the method of measurement of the remanence of the material is that described in the standard NFEN60404-5.
  • the magnetic particles 31 and the binder 32 can be made of any other material suitable for the application.
  • the value of the remanence can also be adapted as a function of the magnetic power required from the electrical machine.
  • the permanent magnet 51 already has magnetic particles that are aligned during moulding and therefore prior to assembly thereof in the motor. This has the advantage that it is possible to assemble the already oriented magnet 51 in the motor.
  • the permanent magnet 51 is inserted into the yoke 4.
  • the permanent magnet 51 is stapled or stuck on the yoke 4, or by any suitable fixing mean.
  • a permanent magnet 51 is directly overmolded in the yoke 4, since the yoke 4 has the benefit to be complementary in shape to a permanent magnet 51. It is thus possible to get away from any fixing mean, such as clamps.
  • the overmoulding combined to the petal shapes of the magnetic sectors, allow to get a good mechanical support for a magnet 51. Indeed, on one side the overmoulding allows to oppose to mechanical forces (vibrations, shocks). On the other side, the curved shapes of the magnetic sectors allow to oppose to attractive magnetic forces, which act mainly towards the orthoradial direction, when the motor is operating.
  • the inner portion 43 of the yoke 4 and the at least one permanent magnet 51 overmolded in the inner portion 43 of the yoke 4 are for example inserted together in the outer portion 42 of the yoke 4.
  • the peripheral outer surface of the inner portion 43 of the yoke 4 is provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion 42 of the yoke 4.
  • the magnetic particles are magnetized in such a way that a magnetic field in the air gap varies sinusoidally along a circumference of said air gap.
  • the stator 3 comprises one single permanent magnet 51 .
  • the single permanent magnet 51 comprises six magnetic sectors 52 and thus comprises six magnetic poles.
  • the positions of the poles P1 and P2 are illustrated with dotted lines, in the middle of each magnetic sector 52.
  • the magnetic flux lines 37 generated by the permanent magnet 51 are illustrated in Fig. 6. More precisely, as can be seen in Fig.
  • the direction of the magnetization vector 36 varies between a substantially radial orientation D1 in a first direction, for example from the air gap 6 to the yoke 4, to reach a substantially orthoradial orientation D2 in the middle of a zone delimited by the two consecutive poles P1 and P2 and continues to vary gradually, reaching a substantially radial orientation D3 in a second direction opposite to the first direction, for example from the yoke 4 to the air gap 6 of the machine.
  • the evolution of the direction of the magnetization vector 36 is of course the opposite when starting from a radial orientation D3 (from the yoke 4 to the air gap 6).
  • magnetic flux lines 371 are formed along the magnetization vector 36, between the inner surface 523 of the magnetic sector and the outer surface 521 of the magnetic sector 52.
  • About half of the magnetic flux lines 371 of one magnetic sector 52 are connected to half of the magnetic flux lines 371 of a consecutive magnetic sector 52 through magnetic flux lines 372 that are in the yoke.
  • the magnetic flux lines 372 that are in the yoke extend from the outer surface 523 of a magnetic sector to the outer surface 523 of a consecutive magnetic sector 52 along an orthoradial direction.
  • the field lines of the magnetic field form a convex shape, viewed from the exterior of the stator 3. The field lines impinge on the yoke 4 since the yoke 4 allows to close the magnetic circuit.
  • the radial component of the magnetic field in the air gap 6 varies sinusoidally along the circumference of the air gap 6 of the electrical machine.

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Abstract

Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness Stator (3) for a rotating electric machine, comprising : - a yoke (4), - an assembly of magnetic poles (P1, P2, …) comprising at least two pairs of poles, - a magnetic sector (52) forming one pole of said assembly of magnetic poles, characterized in that a radial thickness of the magnetic sector (52) varies between two straight lines perpendicular to a central axis (X) of the yoke (4), each one of these straight lines intersecting the central axis (X) and forming between them an angle of at least 5°, and in that the yoke (4) has a complementary shape to a shape of the magnetic sector (52), in such a way that a radial thickness of the stator (3) is almost constant.

Description

Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness
The invention relates to a stator of a rotating electric machine, provided with at least one permanent magnet with a variable radial thickness. The invention has particularly advantageous applications in the fields of motor vehicle starters, electric powertrain systems, and permanent magnet DC motors.
In particular, the invention applies to vehicles with 12 V to 48 V on-board voltage.
For example, the invention applies to rotating electric machines having a rotation speed of 2000 to 5000 rpm. In particular, the invention applies to an electric motor of a starter, having a rotation speed of 2000 rpm to 5000 rpm, the starter having thus an output torque of 50 N.m to 10 N.m and a mechanical power of 1 kW to 3 kW available on the output shaft.
Motor vehicle starters are known which implement rotary electrical machines provided with a stator, or inductor, comprising several permanent magnets and a rotor, or armature, having a body of cylindrical shape, and a winding formed from conducting wires.
As is known per se, the rotor body consists of a stack of plates having longitudinal slots in which the wires of the winding are inserted, consisting for example of pin- shaped conductors. The rotor is in addition provided with a collector comprising a plurality of contact pieces connected electrically to the wires of the winding.
Moreover, the inductor comprises a metal yoke, the inner face of which supports a plurality of permanent magnets intended to produce an induction field. The permanent magnets are configured as cylindrical segments, with angular distribution at regular intervals inside the yoke, and separated uniformly from the armature by a radial air gap. The permanent magnets are generally fixed on the inner face of the yoke by means of clamps extending in the longitudinal direction in the spaces provided between the permanent magnets. In order to limit the number of magnets used in the stator, which limits the number of assembly operations to be carried out on the assembly line during manufacture of the starter, the patent application WO2016162636A1 describes a starter comprising a rotating electric machine provided with a stator, said stator comprising a set of magnetic poles, characterized in that a permanent magnet forms at least two poles of the set of said magnetic poles. In particular, the application describes a permanent magnet forming all of said magnetic poles, the permanent magnet being one single piece and having a cylindrical shape.
However, like previous solutions mentioned above, this solution has the disadvantage to require large amounts of magnetic material and therefore rare earths. But rare earths, which are popular for their exceptional magnetic properties, are problematic mainly for two reasons. Firstly, the rare earths market is changeable and the price of rare earths elements involved in the manufacturing of permanent magnets is high. Secondly, when mining and refining rare earths, poisonous chemicals are released into the environment. This is why industries today desire to reduce rare earths amounts so as to save money and reduce their environmental impact.
The problem is thus to find a solution which allows to save magnetic material while keeping today’s starters performances. In order to fulfill these requirements, the invention proposes a stator for a rotating electric machine, comprising:
• a yoke,
• an assembly of magnetic poles comprising at least two pairs of poles,
• a magnetic sector forming one pole of said assembly of magnetic poles, characterized in that a radial thickness of the magnetic sector varies between two straight lines perpendicular to a central axis of the yoke, each one of these straight lines intersecting the central axis and forming between them an angle of at least 5°, and in that the yoke has a complementary shape to a shape of the magnetic sector, in such a way that a radial thickness of the stator is almost constant.
“Magnetic pole” means usually a point where the magnetic field lines converge. With the cylindrical geometry of a rotating electric machine, a magnetic pole is a portion of a line, oriented radially, where the magnetic field lines converge. In practice, it is not strictly a portion of a line, it has a thickness according to the orthoradial direction.
“Radial” means a direction according to a radius of the stator. “Orthoradial” or “tangential” means a direction according to a direction perpendicular to a radius of the stator.
“Magnetic sector” means an angular portion of a permanent magnet comprising a magnetic pole. This portion is not necessarily detached physically, in other words, a magnetic sector is a geometric sector which does not correspond necessarily to an independent magnet.
The radial thickness of the stator is equal to the radial thickness of the magnetic sector and the yoke. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator. Even if the stator further comprises other elements like electronic components or mechanical elements, the thickness of the stator should be understood as the sum of the thicknesses of the magnetic sector and the yoke.
Thus, the invention makes it possible to produce smaller magnets compared to those of prior art, while keeping today’s starters performances. This is possible thanks to the optimization of the shape of the magnets and the geometry of the yoke, which has a complementary shape to the shape of the magnetic sectors. On one side, the optimized shape allows to spare raw material while being sufficient to produce the magnetic field necessary to the performances of the starter. On the other side, the complementary shape of the yoke allows to concentrate the magnetic flux between the magnetic poles, so as to minimize magnetic losses. This results in substantial savings of rare earths, leading to costs savings and simultaneously to a reduction of environmental impact. This results as well in a substantial reduction of the stator weight, which is very positive when designing a rotating electric machine. In addition, the magnets can be directly overmoulded in the yoke, which has a complementary shape to the shape of the magnets. It is thus possible to get away from clamps. The geometry of the magnets and the shape of the magnets being complementary to the shape of the yoke, allows also to improve the support of the magnets in the orthoradial direction. Eventually, thanks to the structure of the yoke which has a large radial thickness of material allowing to absorb the vibrations of the stator, the invention allows to reduce the noise of a rotating electric machine comprising such a stator. According to one embodiment, an external surface of the magnetic sector, facing the yoke, has a radius of curvature smaller than a radius of curvature of an external surface of the yoke. In other words, the external surface of the magnetic sector, facing the yoke, has a convex shape. That is to say that, viewed from the exterior of the stator, the external surface of the magnetic sector, facing the yoke, exhibits a convex shape.
According to one embodiment, the assembly of magnetic poles of the stator is formed by a plurality of magnetic sectors whose external surface facing the yoke has at least one concave shape. In other words, at least one magnetic sector has a convex external surface facing the yoke. For example, all magnetic sectors have a convex external surface facing the yoke. The concave shape that exhibits the profile of the plurality of magnetic sectors allows to spare raw material.
According to one embodiment, the plurality of magnetic sectors form the inner peripheral surface of the stator, which is cylindrical.
According to one embodiment, two adjacent magnetic sectors are in contact according to a portion of a radial plane of the yoke. The thickness of the contact portion is smaller than the maximum radial thickness of a magnetic sector.
According to one embodiment, two adjacent magnetic sectors are in contact according to a single point. In this case, the thickness of the contact portion is non- existent and at this radial position, the thickness of the stator is equal to the thickness of the yoke.
In other words, the plurality of magnetic sectors has a flower shape, the magnetic sectors forming petals of the flower. According to one embodiment, a radial thickness of said stator is almost constant on at least 90 % of the circumference of said stator. The radial thickness of the stator is equal to the radial thickness of the magnetic sector and the yoke. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator.
According to one embodiment, the yoke comprises an outer portion and an inner portion, said inner portion having an outer peripheral surface pressed against an inner peripheral surface of the outer portion, and said inner portion having an inner peripheral surface fitting the shape of at least one magnetic sector.
According to one embodiment, the outer portion and inner portion of the yoke form one single block of steel.
According to one embodiment, the outer portion and inner portion of the yoke are in steel.
According to one embodiment, the outer portion of the yoke is in steel and the inner portion is made of a laminated core. According to one embodiment, the outer portion of the yoke is made of a laminated core and the inner portion is in steel.
According to one embodiment, the outer portion and inner portion of the yoke are formed with a single laminated core.
For example, the core is made of laminated metal sheets.
For example, the core is made of thin metal sheets. At some angular positions, regularly spaced, the yoke exhibits a large radial thickness compared to a yoke of prior art. For example, the thickness of the yoke can reach about 4 mm locally, compared to about 2 mm for a yoke of prior art. This large radial thickness, combined with a core made of thin metal sheets, allows to absorb the vibrations of the stator, and thus to reduce the noise of a rotating electric machine comprising such a stator. Indeed, the thin metal sheets allow to dissipate energy by friction between sheets. For example, the laminated metal sheets are in steel. For example, the laminated metal sheets are buttoned up, welded together, bonded or tightened with bars. According to one embodiment, the inner portion of the yoke is inserted into the outer portion of the yoke.
According to one embodiment, the inner portion and the outer portion of the yoke are joined together by any mean such as gluing, nailing, crimping, welding, soldering, screwing, or with a clip.
The yoke, being in steel and thus comprising large amounts of iron, exhibits magnetic properties. These magnetic properties, associated to the complementary shape of the yoke, allow to close the magnetic circuit and avoid losses. So the yoke plays a mechanical support role, but also acoustic and magnetic roles.
According to one embodiment, the contact surface between the inner portion of the yoke and the outer portion of the yoke is almost cylindrical. “Almost” shall mean that some fixing means may be provided on the inner surface of the outer portion of the yoke, and on the outer surface of the inner portion of the yoke.
According to one embodiment, the peripheral outer surface of the inner portion of the yoke is provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion of the yoke.
According to one embodiment, the contact surface between the inner portion of the yoke and the outer portion of the yoke come up to or reach at least one extremity of a magnetic sector.
According to one embodiment, the contact surface between the inner portion of the yoke and the outer portion of the yoke come up to or reach all the extremities of all magnetic sectors. According to one embodiment, the ratio between the volume occupied by the plurality of magnetic sectors and the volume occupied by the magnetic sectors and the inner portion of the yoke is greater or equal to 50 %.
According to one embodiment, the plurality of magnetic sectors forming the magnetic poles has a cylindrical inner surface with a radius named the first radius and an outer surface having at least one concave shape, said outer surface being inscribed in a cylinder with a radius named the second radius, the plurality of magnetic sectors occupying at least 50 % of the volume of a ring with an inner radius the first radius and an outer radius the second radius.
The invention thus allows to spare about 40 % of magnetic material compared to the magnets of prior art, while keeping the same performances.
According to one embodiment, the stator comprises at least one permanent magnet, said permanent magnet forming at least one magnetic sector. For example, the permanent magnet forms two magnetic sectors. In another example, the permanent magnet forms three magnetic sectors, or more.
According to one embodiment, the stator comprises a plurality of permanent magnets, each permanent magnet forming one single magnetic sector. In other words, the plurality of permanent magnets has a flower shape, the permanent magnets forming petals of the flower.
According to one embodiment, the inner surface of the stator is cylindrical and is formed by the inner surfaces of the permanent magnets.
According to one embodiment, the stator comprises one single permanent magnet forming the plurality of magnetic sectors. In other words, the permanent magnet has a flower shape, the magnetic sectors forming petals of the flower.
According to one embodiment, the inner surface of the stator is cylindrical and is formed by the inner surface of the permanent magnet. "One permanent magnet" means a single solid component that may comprise several directions of magnetization. In other words a magnet may not comprise several magnets (several pieces of magnets) joined together and forming a block.
The petal shape of the magnetic sectors facilitates the support of the at least one magnet in the orthoradial direction. Indeed, the curved shapes of the magnetic sectors allow to oppose to attractive magnetic forces, which act mainly towards the orthoradial direction, when the motor is operating.
According to one embodiment, the at least one permanent magnet is inserted into the yoke.
According to one embodiment, the at least one permanent magnet is stapled or stuck on the yoke.
According to one embodiment, the at least one permanent magnet is overmoulded in the yoke. The overmoulding allows to oppose to mechanical forces such as vibrations and shocks. It is thus possible to get away from any fixing mean, such as clamps.
According to one embodiment, the inner portion of the yoke and the at least one permanent magnet overmoulded in the inner portion of the yoke are inserted together in the outer portion of the yoke.
According to one embodiment, the at least one permanent magnet is in ferromagnetic material.
According to one embodiment, the at least one permanent magnet is a moulded magnet based on magnetic particles embedded in a binder made of a non-magnetic material. According to one embodiment, the magnetic particles are anisotropic rare earth magnetic particles. For example, the magnetic particles measure several micrometers to several hundreds of micrometers. According to one embodiment, a magnetic particle comprises an easy axis of magnetization.
Thus, the at least one magnet already has magnetic particles that are aligned during moulding and therefore prior to assembly thereof in the motor. This has the advantage that it is possible to assemble the already oriented magnet in the motor.
For example, said binder has a melting point lower than the Curie point of said magnetic particles. The magnetic particles are for example made of neodymium-iron- boron or of samarium-iron-nitrogen. The binder is for example made of a plastic material. According to one embodiment, the magnetic material used preferably has a remanence in the order of 0.6 Tesla. The method of measurement of the remanence of the material is that described in the standard NFEN60404-5.
According to one embodiment, the magnetic particles are magnetized in such a way that a magnetic field in the air gap varies sinusoidally along a circumference of said air gap.
According to one embodiment, the at least one permanent magnet is a polar anisotropically aligned magnet. In other words, between two consecutive poles, the direction of magnetization of the easy axes of the magnetic particles varies progressively along a circumference of said stator:
- when a mechanical angle is at the center of a magnetic sector, that is to say at the position of a magnetic pole, the easy axes of magnetization of the magnetic particles are arranged so that a resulting magnetization vector faces outward in the radial direction;
- next, as the mechanical angle moves toward the adjacent magnetic sector, the easy axes of magnetization of the magnetic particles are arranged so that the magnetization vector gradually inclines in the direction of the change in mechanical angle; - furthermore, when the mechanical angle is between the two consecutive magnetic sectors, the easy axes of magnetization of the magnetic particles are arranged so that the magnetization vector is oriented in the circumferential direction;
- next, as the mechanical angle moves toward the center of the adjacent magnetic sector, the easy axes of magnetization of the magnetic particles are aligned so that the magnetization vector gradually inclines in the direction of the center of the stator;
- finally, when the mechanical angle is at the center of the adjacent magnetic sector, that is to say at the position of the consecutive magnetic pole, the easy axes of magnetization of the magnetic particles are arranged so that the magnetization vector faces inward in the radial direction.
These steps, repeated in the circumferential direction, build a polar anisotropic alignment pattern.
With this arrangement, a magnetic field is supplied only to the inner circumferential surface side of the stator, so that an ideal alignment pattern can be obtained. This ideal alignment pattern allows to prevent magnetic flux leakage, which would occur on the outer circumferential surface of a stator of prior art.
According to one embodiment, inside each magnetic sector, magnetic flux lines are formed along the magnetization vector, between the inner surface of the magnetic sector and the outer surface of the magnetic sector. According to one embodiment, about half of the magnetic flux lines of one magnetic sector are connected to half of the magnetic flux lines of a consecutive magnetic sector through magnetic flux lines that are in the yoke.
According to one embodiment, magnetic flux lines that are in the yoke extend from the outer surface of a magnetic sector to the outer surface of a consecutive magnetic sector along an orthorad ial direction. Thanks to a thicker yoke between two consecutive magnetic sectors, it is possible to prevent the saturation of the magnetic flux in the yoke, from adjacent magnetic sectors. In other words, between two consecutive poles, the direction of the magnetic field varies following a curved direction. In particular, between two consecutive poles, the field lines of the magnetic field form a convex shape, viewed from the exterior of the stator. The field lines impinge on the yoke since the yoke allows to close the magnetic circuit.
In this case, the plastic-bonded magnets are anisotropic, that is to say the magnetic particles are aligned during moulding in order to obtain a polar anisotropically aligned magnet. According to one embodiment, the plurality of magnetic sectors is magnetized according to a configuration of the Halbach type.
In this case, the plastic-bonded magnets are anisotropic, that is to say the magnetic particles are aligned during moulding in order to obtain the Halbach structure.
Thus, the starter has a Halbach orientation that provides magnetic flux only towards the armature. In fact, this makes it possible to improve the efficiency of the starter owing to the very high level of the field H of reaction of the armature. According to one embodiment, the assembly of magnetic poles can have up to 36 poles.
The invention also relates to a rotating electric machine, for instance for a starter or a starter-alternator, comprising a stator as previously defined.
According to one embodiment, the rotating electric machine has a rotation speed of 2000 rpm to 5000 rpm. According to one embodiment, the rotating electric machine is put in a vehicle with 12 V to 48 V on-board voltage.
According to one embodiment, the rotating electric machine comprises a rotor separated from said stator by an air gap almost constant on at least 90 % of the circumference of said air gap. « Almost » shall mean a variation of 2 to 3 % of the air gap.
The invention also relates to a starter comprising a rotating electric machine as previously defined.
According to one embodiment, the starter has an output torque of 50 N.m to 10 N.m.
According to one embodiment, the starter has an output mechanical power of 1 kW to 3 kW .
According to one embodiment, the starter is put in a vehicle with 12 V to 48 V on- board voltage. The invention also relates to a powertrain system comprising a rotating electric machine as previously defined.
According to one embodiment, the powertrain system is put in a vehicle with 12 V to 48 V on-board voltage.
The invention will be better understood on reading the description given hereunder and on examining the accompanying figures. These figures are only given for purposes of illustration and do not limit the invention in any way. Fig. 1 is a schematic side view of a starter according to the present invention;
Fig. 2 is a schematic cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 ; Fig. 3a and 3b are schematic cross-sectional views of the rotor and stator, according to two different embodiments of the invention, of the electrical machine that is part of the starter in Fig. 1 ; Fig. 4 shows the device for producing a single-piece permanent magnet of the stator according to the present invention;
Fig. 5 is a partial cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 showing the magnetic vector distribution inside the magnetic sectors;
Fig. 6 is a partial cross-sectional view of the rotor and stator of the electrical machine that is part of the starter in Fig. 1 , showing the magnetic field lines inside the stator composed of magnetic sectors and the yoke.
Elements that are identical, similar or analogous keep the same references from one figure to another.
Fig. 1 shows, schematically, a starter 1 for an internal-combustion engine of a motor vehicle. This direct-current starter 1 comprises, on the one hand, a rotor 2, also called armature, which is able to rotate about an axis X, and on the other hand, a stator 3, also called inductor, positioned around the rotor 2. The rotor 2 is separated from the stator 3 by an air gap 6. In the example illustrated, the rotating electrical machine formed by the stator 3 and the rotor 2 is of the six-pole type. As a variant, the machine could be of the four-pole type.
This stator 3, described in more detail below, comprises a yoke 4 bearing a permanent magnet 5 forming a set of poles. The rotor 2 comprises a rotor body 7 and a winding 8 wound in slots in the rotor body 7. The rotor body 7 consists of a stack of plates having longitudinal slots. To form the winding 8, pin-shaped conducting wires 11 (more easily seen in Fig. 2) are threaded inside the slots 16 generally on two separate layers. The winding 8 forms buns 9 on either side of the rotor body 7. The rotor 2 is provided, at the back, with a collector 12 comprising a plurality of contact pieces connected electrically to the conducting elements, consisting here of the pins 11 of the winding 8.
A group of brushes 13 and 14 is provided for electrical supply to the winding 8, one of the brushes 13 being earthed on the starter 1 and the other brush 14 being connected to a terminal 15 of a contactor 17. The brushes are for example four in number.
The brushes 13 and 14 will rub against the collector 12 when the rotor 2 is rotating, which makes it possible to supply the rotor 2 by commutation of the electric current in sections of the rotor 2. The contactor 17 comprises, besides the terminal 15 connected to the brush 14, a terminal 29 connected, via an electrical connection element, to an electrical supply of the vehicle, notably a battery.
The starter 1 further comprises a starter drive assembly 19 mounted sliding on a drive shaft 18 and can be made to rotate about the axis X by the rotor 2.
A speed reducing assembly 20 is interposed between a shaft of the rotor 2 and the drive shaft 18. The starter drive assembly 19 comprises a drive element formed by a pinion 21 that is intended to engage with a drive member of the heat engine, such as a starter ring gear. As a variant, it would be possible to use a pulley system.
The starter drive assembly 19 further comprises a free wheel 22 and a pulley washer 23, together defining a groove 24 for receiving the end 25 of a fork 27. The fork 27 is actuated by the contactor 17 to displace the starter drive assembly 19 relative to the drive shaft 18, along the axis X, between a first position in which the starter drive assembly 19 drives the heat engine via the drive pinion 21 , and a second position in which the starter drive assembly 19 is disengaged from the starter ring gear of the heat engine. On activation of the contactor 17, an internal contact plate (not shown) makes it possible to establish a connection between the terminals 15 and 29 in order to supply power to the electric motor. This connection will be cut on deactivation of the contactor 17. Fig. 2 shows a stator 3 of a rotary electric machine. This stator, for example for a starter 1 of a combustion engine, comprises:
• a yoke 4,
• an assembly of magnetic poles P1 , P2, ... comprising at least two pairs of poles,
· a magnetic sector 52 comprising one pole of said assembly of magnetic poles,
characterised in that a radial thickness of the magnetic sector 52 varies between two straight lines perpendicular to a central axis of the yoke 4, each one of these straight lines intersecting the central axis and forming between them an angle of at least 5°, and in that the yoke 4 has a complementary shape to a shape of the magnetic sector 52, in such a way that a radial thickness of the stator 3 is almost constant. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator 3.
In this example of an electric machine with six poles, as illustrated in Fig. 2, the rotor 2 is separated by the stator 3 by an air gap 6. The air gap 6 is almost constant on at least 90 % of the circumference of said air gap 6. « Almost » shall mean a variation of 2 to 3 % of the air gap. The stator 3 comprises a yoke 4 and magnetic poles, whose positions are identified by the labels P1 , P2, P3, P4, P5 and P6. The magnetic poles are formed by a plurality 5’ of magnetic sectors 52, which are separated from each other by dotted lines 54.
An external surface 521 of a magnetic sector 52, facing the yoke 4, has a radius of curvature smaller than a radius of curvature of an external surface 44 of the yoke 4. An external surface 56 of the plurality 5’ of the six magnetic sectors 52, formed by the external surfaces 521 of each magnetic sector 52, has six concave shapes 53 facing the yoke 4.
Two adjacent magnetic sectors 52 are in contact according to a portion 541 of a radial plane of the yoke 4. The thickness of the contact portion 541 is smaller than the maximum radial thickness 522 of a magnetic sector. But other situations could be considered, for instance two adjacent magnetic sectors can be in contact according to a single point. In this case, the thickness of the contact portion 541 is non-existent and at this radial position, the thickness of the stator is equal to the thickness of the yoke.
The plurality 5’ of magnetic sectors 52 has a flower shape, the magnetic sectors 52 forming petals of the flower. The stator 3 has a radial thickness almost constant on at least 90 % of the circumference of said stator 3. « Almost » shall mean a variation of 2 to 3 % of the radial thickness of the stator 3. Indeed, the presence of chamfers on the magnetic sectors 52, or of magnetic shunts on the yoke 4, may generate a small local change in the radial thickness of the stator.
The yoke 4 comprises an outer portion 42 and an inner portion 43, said inner portion 43 having an outer peripheral surface pressed against an inner peripheral surface of the outer portion 42, and said inner portion 43 having an inner peripheral surface 41 fitting the shape of the plurality 5’ of magnetic sectors 52. Thus, the magnetic sectors 52 lodge into the concavities of the yoke 4.
The contact surface 45 between the inner portion 43 and the outer portion 42 is showed with a dotted line, and is almost cylindrical.“Almost” shall mean that some fixing means may be provided on the inner surface of the outer portion of the yoke, and on the outer surface of the inner portion of the yoke. For example, the peripheral outer surface of the inner portion 43 of the yoke could be provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion 42 of the yoke 4. As illustrated in Fig. 2, the contact surface 45 between the inner portion 43 of the yoke and the outer portion 42 of the yoke come up to the extremities of the magnetic sectors 52.
Several embodiments can be considered. For example, the outer portion 42 and inner portion 43 of the yoke form one single block of steel. As a variant, the outer portion 42 and inner portion 43 of the yoke 4 are formed with a single laminated core. In these two embodiments, the boundary between the inner portion 43 and the outer portion 42 is simply fictive.
According to another embodiment, the outer portion 42 and inner portion 43 of the yoke are in steel. According to another embodiment, the outer portion 42 of the yoke 4 is in steel and the inner portion 43 is made of a laminated core. According to another embodiment, the outer portion 42 of the yoke 4 is made of a laminated core and the inner portion 43 is in steel. In these three embodiments, the outer portion 42 and inner portion 43 are distinct. The inner portion 43 of the yoke 4 is inserted into the outer portion 42 of the yoke. The inner portion 43 and the outer portion 42 of the yoke 4 are joined together by any mean such as gluing, nailing, crimping, welding, soldering, screwing, or with a clip.
The core is made of laminated metal sheets, the laminated metal sheets being in steel. Preferably, the core is made of thin laminated metal sheets. The laminated metal sheets are buttoned up, welded together, bonded or tightened with bars.
At some angular positions, regularly spaced, the yoke 4 exhibits a large radial thickness compared to a yoke of prior art. For example, the thickness of the yoke 4 can reach about 4 mm locally, compared to about 2 mm for a yoke of prior art. This large radial thickness, combined with a core made of thin metal sheets, allows to absorb the vibrations of the stator, and thus to reduce the noise of a rotating electric machine comprising such a stator. Indeed, the thin metal sheets allow to dissipate energy by friction between sheets.
The plurality 5’ of magnetic sectors 52 is supported by the internal surface 41 of the yoke 4. But the yoke 4 does not only play a mechanical support role. The yoke 4, being in steel and thus comprising large amounts of iron, exhibits magnetic properties. These magnetic properties, associated to the complementary shape of the yoke, allow to close the magnetic circuit and avoid losses. So the yoke 4 plays a mechanical support role, but also acoustic and magnetic roles.
As illustrated in Fig. 2, the plurality 5’ of magnetic sectors 52 forming the magnetic poles has a cylindrical inner surface 55, made of the six inner surfaces 523 of each magnetic sector 52, with a radius named the first radius R1 and an outer surface 56 having six concave shapes 53, said outer surface 56 being inscribed in a cylinder with a radius named the second radius R2, the plurality 5’ of magnetic sectors 52 occupying at least 50 % of the volume of a ring with an inner radius the first radius R1 and an outer radius the second radius R2. In other words, the ratio between the volume occupied by the plurality 5’ of magnetic sectors 52 and the volume occupied by the magnetic sectors 52 and the inner portion 43 of the yoke is greater or equal to 50 %. The presence of the six concave shapes 53, facing the yoke 4, allows to spare about 40 % of magnetic material compared to the cylindrical permanent magnet of prior art, while keeping the same performances (cf. WO2016162636A1 ).
Fig. 3a and b show two embodiments of the invention. In Fig. 3a, the stator 3 comprises a plurality 5 of six permanent magnets 51 , each permanent magnet 51 forming one single magnetic sector 52. The inner surface of the stator is cylindrical and is formed by the inner surfaces of the permanent magnets.
In Fig. 3b, the stator 3 comprises one single permanent magnet 51 forming the plurality 5’ of magnetic sectors 52. The inner surface of the stator is cylindrical and is formed by the inner surface of the permanent magnet.
Other embodiments can be considered, one permanent magnet 51 forming two magnetic sectors 52, or three magnetic sectors, or more.
"One permanent magnet" means a single solid component that may comprise several directions of magnetization. In other words a magnet may not comprise several magnets (several pieces of magnets) joined together and forming a block. The magnetic sectors 52 are in ferromagnetic material. Fig. 4 illustrates the case of a single permanent magnet 51 which is a moulded magnet based on anisotropic rare earth magnetic particles 31 embedded in a binder 32 made of a non-magnetic material. The binder 32 is placed in a mould 34 of flower shape that surrounds a core made up of a set of permanent magnets 35, the number of which corresponds to the number of poles of the stator 3, here six. Each of the magnets 35 is magnetically oriented radially. Two consecutive magnets 35 have magnetic field orientations B1 , B2 that are opposite to one another.
For this purpose, the binder 32 is heated to its melting point, which is lower than the Curie point of the magnetic particles 31. It may be mentioned here that the Curie point is the temperature at which the magnetic particles 31 are demagnetized.
The magnetic particles 31 , initially demagnetized, are put inside the mould 34 and are magnetized following the configuration of the magnetic flux generated by the magnets 35 while the temperature inside the mould 34 decreases, which causes gradual hardening of the binder 32. At the end of the process, the magnetized particles 31 are trapped by the binder 32 while having been magnetized in such a way that between two consecutive poles P1 -P6, the direction of the magnetic field generated by the magnet 5 gradually varies along a circumference of the stator 3.
In one embodiment example, the binder 32 consists of a plastic, and the magnetic particles 31 can be made of neodymium-iron-boron or of samarium-iron-nitrogen. The material used preferably has a remanence in the order of 0.6 tesla. The method of measurement of the remanence of the material is that described in the standard NFEN60404-5. As a variant, the magnetic particles 31 and the binder 32 can be made of any other material suitable for the application. The value of the remanence can also be adapted as a function of the magnetic power required from the electrical machine.
Thus, the permanent magnet 51 already has magnetic particles that are aligned during moulding and therefore prior to assembly thereof in the motor. This has the advantage that it is possible to assemble the already oriented magnet 51 in the motor. The permanent magnet 51 is inserted into the yoke 4.
The permanent magnet 51 is stapled or stuck on the yoke 4, or by any suitable fixing mean. In a preferred embodiment, a permanent magnet 51 is directly overmolded in the yoke 4, since the yoke 4 has the benefit to be complementary in shape to a permanent magnet 51. It is thus possible to get away from any fixing mean, such as clamps. Moreover, the overmoulding, combined to the petal shapes of the magnetic sectors, allow to get a good mechanical support for a magnet 51. Indeed, on one side the overmoulding allows to oppose to mechanical forces (vibrations, shocks). On the other side, the curved shapes of the magnetic sectors allow to oppose to attractive magnetic forces, which act mainly towards the orthoradial direction, when the motor is operating.
The inner portion 43 of the yoke 4 and the at least one permanent magnet 51 overmolded in the inner portion 43 of the yoke 4 are for example inserted together in the outer portion 42 of the yoke 4.
The peripheral outer surface of the inner portion 43 of the yoke 4 is provided with notches, said notches fitting into grooves put in on the peripheral inner surface of the outer portion 42 of the yoke 4. According to one embodiment, the magnetic particles are magnetized in such a way that a magnetic field in the air gap varies sinusoidally along a circumference of said air gap.
In an example illustrated in the Fig. 5 and 6, the stator 3 comprises one single permanent magnet 51 . In this non-limiting example, the single permanent magnet 51 comprises six magnetic sectors 52 and thus comprises six magnetic poles. In the Fig. 5, the positions of the poles P1 and P2 are illustrated with dotted lines, in the middle of each magnetic sector 52. The magnetic flux lines 37 generated by the permanent magnet 51 are illustrated in Fig. 6. More precisely, as can be seen in Fig. 5, between two consecutive poles P1 and P2, the direction of the magnetization vector 36 varies between a substantially radial orientation D1 in a first direction, for example from the air gap 6 to the yoke 4, to reach a substantially orthoradial orientation D2 in the middle of a zone delimited by the two consecutive poles P1 and P2 and continues to vary gradually, reaching a substantially radial orientation D3 in a second direction opposite to the first direction, for example from the yoke 4 to the air gap 6 of the machine. The evolution of the direction of the magnetization vector 36 is of course the opposite when starting from a radial orientation D3 (from the yoke 4 to the air gap 6). These steps, repeated in the circumferential direction, build a polar anisotropic alignment pattern.
In other words, inside each magnetic sector 52, magnetic flux lines 371 are formed along the magnetization vector 36, between the inner surface 523 of the magnetic sector and the outer surface 521 of the magnetic sector 52. About half of the magnetic flux lines 371 of one magnetic sector 52 are connected to half of the magnetic flux lines 371 of a consecutive magnetic sector 52 through magnetic flux lines 372 that are in the yoke. The magnetic flux lines 372 that are in the yoke extend from the outer surface 523 of a magnetic sector to the outer surface 523 of a consecutive magnetic sector 52 along an orthoradial direction.
Thanks to a thicker yoke 4 between two consecutive magnetic sectors 52, it is possible to prevent the saturation of the magnetic flux in the yoke, from adjacent magnetic sectors 52. In other words, between two consecutive poles 52, the direction of the magnetic field varies following a curved direction. In particular, between two consecutive poles P1 , P2, ... the field lines of the magnetic field form a convex shape, viewed from the exterior of the stator 3. The field lines impinge on the yoke 4 since the yoke 4 allows to close the magnetic circuit.
In such a configuration, the radial component of the magnetic field in the air gap 6 varies sinusoidally along the circumference of the air gap 6 of the electrical machine.
All the features described here for « one single permanent magnet 51 » or « the plurality 5 of permanent magnets 51 » do apply to each other, and in the same way.
Of course, the foregoing description is given purely as an example and does not limit the scope of the invention, which would not be left if the various elements are replaced with any others that are equivalent.

Claims

Claims
1. Stator (3) for a rotating electric machine, comprising :
• a yoke (4),
• an assembly of magnetic poles (P1 , P2, ...) comprising at least two pairs of poles,
• a magnetic sector (52) forming one pole of said assembly of magnetic poles,
characterized in that a radial thickness of the magnetic sector (52) varies between two straight lines perpendicular to a central axis (X) of the yoke (4), each one of these straight lines intersecting the central axis (X) and forming between them an angle of at least 5°, and in that the yoke (4) has a complementary shape to a shape of the magnetic sector (52), in such a way that a radial thickness of the stator (3) is almost constant.
2. Stator (3) according to claim 1 , characterized in that an external surface (521 ) of the magnetic sector (52), facing the yoke (4), has a radius of curvature smaller than a radius of curvature of an external surface (44) of the yoke (4).
3. Stator (3) according to any of claims 1 and 2, characterized in that the assembly of magnetic poles of the stator is formed by a plurality (5’) of magnetic sectors
(52) whose external surface facing the yoke (4) has at least one concave shape
(53).
4. Stator (3) according to any of the preceding claims, characterized in that a radial thickness of said stator (3) is almost constant on at least 90 % of the circumference of said stator (3).
5. Stator (3) according to any of the preceding claims, characterized in that the yoke (4) comprises an outer portion (42) and an inner portion (43), said inner portion (43) having an outer peripheral surface pressed against an inner peripheral surface of the outer portion (42), and said inner portion (43) having an inner peripheral surface (41 ) fitting the shape of at least one magnetic sector (52).
6. Stator (3) according to the preceding claim, characterized in that the contact surface between the inner portion (43) of the yoke and the outer portion (42) of the yoke is almost cylindrical.
7. Stator (3) according to any of claims 5 and 6, characterized in that the ratio between the volume occupied by the plurality (5’) of magnetic sectors (52) and the volume occupied by the magnetic sectors and the inner portion (43) of the yoke is greater or equal to 50 %.
8. Stator (3) according to any of the preceding claims, characterized in that it comprises a plurality (5) of permanent magnets (51 ), each permanent magnet
(51 ) forming one single magnetic sector (52).
9. Stator (3) according to any of the claims 1 to 7, characterized in that it comprises one single permanent magnet (51 ) forming the plurality (5’) of magnetic sectors
(52).
10. Stator (3) according to any of the preceding claims, characterized in that the at least one permanent magnet (51 ) is a moulded magnet based on magnetic particles (31 ) embedded in a binder (32) made of non-magnetic material.
11. Stator (3) according to the preceding claim, characterized in that the magnetic particles (31 ) are anisotropic rare earth magnetic particles.
12. Stator (3) according to any of the claims 10 and 11 when dependent of claim 3, characterized in that the at least one permanent magnet (51 ) is a polar anisotropically aligned magnet.
13. Stator (3) according to any of the claims 3 to 11 when dependent of claim 3, characterized in that the plurality (5’) of magnetic sectors (52) is magnetized according to a configuration of the Halbach type.
14. Rotating electric machine, for instance for a starter (1 ) or a starter-alternator, comprising a stator (3) according to any one of the preceding claims.
15. Rotating electric machine according to the preceding claim, characterized in that it comprises a rotor (2) separated from the stator (3) by an air gap (6) almost constant on at least 90 % of the circumference of said air-gap.
16. Starter (1 ) comprising a rotating electric machine according to claim 14 or 15.
17. Powertrain system comprising a rotating electric machine according to claim 14 or 15.
PCT/EP2018/079452 2018-10-26 2018-10-26 Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness WO2020083511A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2018/079452 WO2020083511A1 (en) 2018-10-26 2018-10-26 Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2018/079452 WO2020083511A1 (en) 2018-10-26 2018-10-26 Stator for a rotating electric machine, comprising at least one permanent magnet with a variable radial thickness

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WO2020083511A1 true WO2020083511A1 (en) 2020-04-30

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1206514B (en) * 1961-03-10 1965-12-09 Litton Industries Inc DC motor
US4777717A (en) * 1986-03-24 1988-10-18 Mitsubishi Denki Kabushiki Kaisha Method for manufacturing a magnet-type motor yoke assembly
JP2010288337A (en) * 2009-06-10 2010-12-24 Minebea Co Ltd Motor
DE102009046902A1 (en) * 2009-11-20 2011-05-26 Robert Bosch Gmbh Stator for use in permanently excited direct current motor utilized in auxiliary device in motor vehicle, has hollow cylindrical stator part for receiving rotating armature, where stator part and magnet exhibit varying wall thickness
WO2016162636A1 (en) 2015-04-07 2016-10-13 Valeo Equipements Electriques Moteur Starter stator for a motor vehicle, provided with a permanent magnet forming a plurality of poles
DE102016219395A1 (en) * 2016-10-06 2018-04-12 Brose Fahrzeugteile GmbH & Co. Kommanditgesellschaft, Würzburg Segment magnet and permanent magnet motor with segment magnets
WO2018199271A1 (en) * 2017-04-28 2018-11-01 愛知製鋼株式会社 Permanent-magnet-field dc motor as well as stator therefor and rare earth anisotropic bond magnet therefor

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1206514B (en) * 1961-03-10 1965-12-09 Litton Industries Inc DC motor
US4777717A (en) * 1986-03-24 1988-10-18 Mitsubishi Denki Kabushiki Kaisha Method for manufacturing a magnet-type motor yoke assembly
JP2010288337A (en) * 2009-06-10 2010-12-24 Minebea Co Ltd Motor
DE102009046902A1 (en) * 2009-11-20 2011-05-26 Robert Bosch Gmbh Stator for use in permanently excited direct current motor utilized in auxiliary device in motor vehicle, has hollow cylindrical stator part for receiving rotating armature, where stator part and magnet exhibit varying wall thickness
WO2016162636A1 (en) 2015-04-07 2016-10-13 Valeo Equipements Electriques Moteur Starter stator for a motor vehicle, provided with a permanent magnet forming a plurality of poles
DE102016219395A1 (en) * 2016-10-06 2018-04-12 Brose Fahrzeugteile GmbH & Co. Kommanditgesellschaft, Würzburg Segment magnet and permanent magnet motor with segment magnets
WO2018199271A1 (en) * 2017-04-28 2018-11-01 愛知製鋼株式会社 Permanent-magnet-field dc motor as well as stator therefor and rare earth anisotropic bond magnet therefor

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