JP2004336880A - Magnetic flux amount variable magnet-type rotor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic flux amount variable magnet-type rotor which enables demagnetization at high-speed revolution. <P>SOLUTION: This rotor is provided with permanent magnet direct-acting mechanisms (10, 11, and 13) which pull out permanent magnets 4 of an IPM in the axial direction at its high-speed revolution. The permanent magnet 4 engages with a guide incline 15 of a weight 11 through a retainer bar 10, and the weight 11 shifts in the radial direction by an own centrifugal force which is retained by a guide cover 13, whereby the permanent magnet 4 shifts in the axial direction and deviates from an iron core 3 of a rotor, thus enabling demagnetization at high speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic flux variable magnet type rotor.
[0002]
Problems to be solved by the prior art and the invention
Permanent magnet type synchronous machines are more suitable for rotary electric machines for vehicles that require higher reliability and smaller and lighter weight because they can realize higher output, more compact and simpler configuration than other types of synchronous machines. Since the rotating electrical machine for vehicles has a wide rotation speed range, if a sufficiently large magnet magnetic field is secured to secure low-speed torque, an excessive armature winding induced voltage is generated during high-speed rotation, so the magnet magnetic field during high-speed rotation is reduced. It has been proposed to provide a demagnetizing mechanism for performing the operation.
[0003]
Patent Document 1 discloses that a permanent magnet of a magnet type rotor core is housed together with a spring in a sliding hole formed in the rotor core in a radial direction, and when a centrifugal force acting on the permanent magnet increases, the permanent magnet resists the elastic biasing force of the spring. A structure has been proposed in which a magnet comes out of the sliding hole, thereby reducing the amount of magnetic flux applied to the rotor core by the permanent magnet.
[0004]
However, in this technique, since the magnetic poles of the magnet are formed on two side surfaces facing in the circumferential direction, the magnetic poles are extended substantially in the circumferential direction, which is currently the mainstream, and the magnetic poles are formed on both main surfaces. It cannot be applied to a magnet-type rotor core using a thin plate-shaped magnet. In addition, a ceramic magnet having excellent properties as a permanent magnet is fragile and may be damaged by such a magnet motion.
[0005]
Patent Document 2 discloses that a soft magnetic flux passage member (magnetic flux short-circuit member) is radially inserted in a magnetic flux short-circuit reduction slit provided between two adjacent magnets in a circumferential direction in a rotor core of the IPM. A coil spring and a ring that is axially urged by the coil spring are provided on both sides of the rotor core in the axial direction so as to be movable, and both ends of the magnetic flux path member in the axial direction are connected to the ring by a link mechanism. Has proposed a structure in which a magnetic flux path member is urged radially inward through a ring and a link mechanism.
[0006]
In this structure, when a centrifugal force acts on the magnetic flux path member, the magnetic flux path member moves radially outward in the slit against the urging force of the coil spring, and short-circuits the permanent magnet magnetic flux to perform demagnetization.
[0007]
However, this technology requires a coil spring, a ring, and a link mechanism on both sides of the rotor core, so the size is large, the noise of the link mechanism that rotates at high speed is noisy, and it is not easy to install a cooling fan on the end face of the rotor core. However, it has been difficult to put the conventional air-cooled motor into practical use.
[0008]
The present invention has been made in view of the above problems, and has as its object to provide a magnetic flux variable magnet type rotor capable of realizing demagnetization during high-speed rotation.
[0009]
[Patent Document 1] JP-A-7-288940 [Patent Document 2] JP-A-11-275787
[Means for Solving the Problems]
The magnetic flux amount variable magnet rotor according to the first invention has an even number of permanent magnets and an even number of magnet insertion grooves which are provided in the axial direction at predetermined intervals in the circumferential direction and accommodate the permanent magnets so as to be movable in the axial direction. A variable magnetic flux type rotor having a rotor core having a rotating shaft fixed to the rotor core, wherein the permanent magnet is disposed close to the end face of the rotor core and partially rotates the permanent magnet axially outward from the magnet insertion groove during high-speed rotation. It is characterized by having a permanent magnet linear motion mechanism that deviates from
That is, according to the present invention, since the permanent magnet linear motion mechanism causes the permanent magnet to partially deviate from the rotor core in the axial direction at the time of high-speed rotation, the variable magnetic flux amount magnet for IPM having a demagnetizing effect at the time of high-speed rotation. Can be realized. According to the present invention, it is possible to use a thin plate-shaped magnet that extends substantially in the circumferential direction and has magnetic poles formed on both main surfaces thereof. Can be significantly increased. Further, since a link mechanism for converting the axial movement of the drive unit into the radial movement as in Patent Literature 2 can be dispensed with, the movement mechanism can be simplified.
[0011]
In a preferred aspect, the apparatus has a thin sleeve inserted in the magnet insertion groove to accommodate the permanent magnet so as to be movable in the axial direction. With this configuration, since the permanent magnet does not slide in the magnet insertion hole having fine irregularities provided through the rotor core made of the laminated electromagnetic steel sheet, the permanent magnet can be moved smoothly and reliably. . Further, although an exciting force or a bending stress is applied to the permanent magnet through the rotor core, the sleeve receives the brittle magnet instead of the brittle magnet, so that damage to the magnet can be prevented.
[0012]
In a preferred aspect, the permanent magnet linear motion mechanism includes a guide member fixed to the rotating shaft and extending substantially in a radial direction, and a guide slope that is separated from the rotor core as going radially outward. The weight includes a weight held movably in the axial direction, and a guide member having one end in contact with the permanent magnet in the magnet insertion hole and the other end in contact with the guide slope of the weight.
[0013]
Thus, at low speed rotation, the weight is pressed radially inward by the urging force (magnetic attraction force) generated by the permanent magnet being magnetically attracted into the rotor core, and the permanent magnet is accommodated in the rotor core, and the weight of the rotor core is reduced. The amount of magnet magnetic flux can be increased. During high-speed rotation, the centrifugal force acting on the weight increases, and the weight moves radially outward, whereby the weight causes the permanent magnet to deviate axially from the rotor core via the guide member against the magnetic attraction force. And reduces the amount of magnetic flux in the rotor core. That is, the permanent magnet shifts to an axial position where the centrifugal force of the weight and the magnetic attraction force acting on the permanent magnet balance in a vector manner. As a result, an IPM exhibiting a demagnetization function during high-speed rotation can be realized. Note that a spring may be added.
[0014]
In a preferred aspect, the permanent magnet linear motion mechanism is fixed to the rotating shaft and displaces the permanent magnet in the axial direction, and the electromagnetic linear motion mechanism has a positive correlation in accordance with the number of rotations. And a power supply unit for applying a rotation speed correlation voltage that causes the permanent magnet to partially deviate from the magnet insertion hole during high-speed rotation by applying a changing voltage. The electromagnetic linear motion mechanism may be an electromagnetic linear solenoid or a motor having a spiral mechanism for converting a rotary operation into a linear motion.
[0015]
As a result, the permanent magnet is shifted to an axial position where the electromagnetic biasing force of the electromagnetic linear motion mechanism and the magnetic attraction force acting on the permanent magnet are balanced. As a result, an IPM exhibiting a demagnetization function during high-speed rotation can be realized. Also in this case, a spring may be added.
[0016]
In a preferred aspect, the power supply unit includes a generator having a rotor fixed to a rotating shaft of a rotor core. With this configuration, it is possible to easily generate the voltage applied to the electromagnetic linear motion mechanism that is substantially proportional to the rotation speed. Note that this generator can easily be an AC generator having a coil that links with the magnet magnetic flux, and the electromagnetic linear motion mechanism can easily be an AC solenoid. As the magnetic flux of the generator, for example, the magnetic flux of a permanent magnet housed in a rotor core can be used.
[0017]
A magnetic flux variable magnet type rotor according to a second aspect of the present invention has an even number of permanent magnets, a rotor core having an even number of magnet insertion holes that are provided in the axial direction at predetermined intervals in the circumferential direction and accommodate the permanent magnets, A variable magnetic flux type rotor having a rotating shaft that supports a rotor core, characterized in that it has a relative linear motion mechanism that moves the rotor core in the axial direction relative to the stator during high-speed rotation.
[0018]
That is, the present invention achieves demagnetization by axially displacing the rotor core with respect to the stator during high-speed rotation. For example, the rotor core supported by the rotating shaft so as to be axially displaceable and relatively non-rotatable may be displaced in the axial direction during high-speed rotation, and conversely, the stator may be displaced in the axial direction. In this way, the overall mechanism can be simplified, and the impact on the permanent magnet can be reduced to improve reliability. As the relative linear motion mechanism, the above-described weight centrifugal force mechanism or linear solenoid mechanism can be adopted, but there is no need to move a large number of permanent magnets in the axial direction, and only one moving object is required.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that these examples show embodiments, and it is naturally possible to replace constituent elements with known alternative elements.
(Example 1)
(Description of overall configuration)
FIG. 1 is a schematic axial cross-sectional view of an IPM that employs the variable magnetic flux type rotor of the first embodiment. However, cross-sectional hatching is omitted. In the following embodiments, the magnet magnetic flux amount control during the electric operation will be described, but the magnet magnetic flux amount control during the power generation operation is also essentially possible by reversing the circumferential movement direction of the weight.
[0020]
1 is a motor frame, 2 is a rotor (rotor), 3 is a rotor core (rotor core) made of laminated magnetic steel sheets, 4 is a permanent magnet, 5 is a stator (stator), 6 is a stator coil (stator coil), 7 is a rotating shaft, 8 is a bearing, 9 is a magnet cover, 10 is a retainer bar (guide member), 11 is a weight, 12 is a magnet cover, and 13 is a guide bar (guide member).
[0021]
The stator core of the stator 5 is fixed to the inner peripheral surface of the peripheral wall of the motor frame 1, and the stator coil 6 is wound around the stator core. Inside the stator 5 in the radial direction, a rotor 2 composed of a rotating shaft 7, a rotor core 3, a permanent magnet 4, and a permanent magnet linear motion mechanism described later is rotatably accommodated.
[0022]
The rotating shaft 7 is rotatably supported by the motor frame 1 via a bearing 8, and is inserted into a rotating shaft insertion hole of the rotor core 3 and fixed to the rotor core 3. A total of four magnet insertion holes are provided in the rotor core 3 at 90 degrees apart from each other in the axial direction. Each magnet insertion hole accommodates a permanent magnet 4 made of a rectangular ceramic thin plate, and two permanent magnets 4 adjacent in the circumferential direction have opposite polarities. The radially outer main surface and the radially inner main surface of the permanent magnet 4 are magnetic pole surfaces. The IPM itself has a general structure except for a magnet cover and a demagnetizing mechanism which will be described later, and further description will be omitted.
[0023]
(Description of permanent magnet linear motion mechanism)
Next, a permanent magnet linear motion mechanism which is a feature of this embodiment will be described below with reference to FIGS. FIG. 2 is a schematic cross-sectional view as viewed from the line AA in FIG. 1 toward the rotor core.
[0024]
The permanent magnet linear motion mechanism includes a retainer bar (guide member) 10, a weight 11, and a guide bar (guide member) 13. Although not shown in FIG. 1, a metal sleeve is press-fitted into the magnet insertion hole of the rotor core 3, and a long and thin plate-shaped permanent magnet 4 is axially movable in the sleeve. Is contained. Of course, the long and thin plate-shaped permanent magnet 4 may be wrapped in a resin or metal sleeve and housed in the sleeve.
[0025]
One end of the retainer bar 10 is fixed to one end of the permanent magnet 4 held movably in the axial direction within the sleeve, and the other end is movably engaged with the weight 11 in the axial direction along a later-described guide slope 15. It is a guide member.
[0026]
The weight 11 is a heavy metal trapezoidal block having a guide slope 15 moving away from the rotor core 3 toward the outside in the radial direction, and has a through hole through which a guide bar 13 described later penetrates in the radial direction. It can be moved in any direction.
[0027]
The guide bar 13 is formed of four long rods fixed to the rotating shaft 7 and extending substantially in the radial direction in proximity to the front end face of the rotor core 3, and guide members for holding the weight 11 movably in the radial direction. It is. The guide bar 13 does not have to be in the shape of a long bar as long as it can hold the weight 11 movably in the radial direction.
[0028]
(Operation explanation)
The permanent magnet linear motion mechanism of this embodiment will be described below.
[0029]
During low-speed rotation, the permanent magnet 4 is housed in the magnet insertion hole (more precisely, in the sleeve) of the rotor core 3 by magnetic attraction. As a result, the permanent magnet 4 urges the weight 11 radially inward through the retainer bar 10, and the weight 11 is pressed radially inward. Thereby, the amount of magnet magnetic flux of the rotor core 3 can be increased.
[0030]
During high-speed rotation, the centrifugal force acting on the weight 11 increases and moves outward in the radial direction. As a result, the guide slope 15 of the weight 11 causes the permanent magnet 4 to deviate from the rotor core 3 to the rear side in the axial direction via the retainer bar 10 against the axial magnetic attraction of the permanent magnet 4, and the rotor core 3 Decrease magnet flux.
[0031]
That is, the permanent magnet 4 shifts to an axial position where the centrifugal force of the weight 11 and the magnetic attraction force acting on the permanent magnet 4 balance vectorwise. As a result, an IPM exhibiting a demagnetization function during high-speed rotation can be realized. FIG. 3 shows the relationship between the rotor speed and the back electromotive voltage (magnet electromotive force) of the stator coil according to this embodiment. In this embodiment, the counter-electromotive voltage can be substantially saturated during high-speed rotation by the relative rotation.
[0032]
(Modification)
In the above embodiment, the inclined end surface of the retainer bar 10 only abuts on the guide inclined surface 15 of the weight 11, but may be more firmly connected as shown in FIG.
[0033]
In FIG. 4, a front end portion 101 of the retainer bar 10 is formed to be wider in a circumferential direction than a main portion of the retainer bar 10, and the front end portion 101 of the retainer bar 10 is formed on a guide slope 15 of a weight 11 and has a diameter. It is accommodated in a long groove 110 extending in the axial direction. The opening 111 of the long groove 110 is narrowed from both sides in the circumferential direction, and is smaller than the front end 101 of the retainer bar 10. This prevents the retainer bar 10 from engaging with the weight 11 not only when the weight 11 pushes the retainer bar 10 but also when it is pulled.
[0034]
(Modification)
In the above-described embodiment, the guide slope 15 of the weight 11 is formed at an angle away from the rotor core 3 toward the outside in the radial direction, but may be formed at an angle approaching the rotor core 3 toward the outside in the radial direction. Good.
(Example 2)
An IPM employing the magnetic flux variable magnet type rotor of the present invention will be described below with reference to FIG. FIG. 5 is a schematic axial sectional view of the IPM. 5 and 6 have no relation to the reference numerals in FIGS. 1 to 4 for describing the first embodiment.
[0035]
1 is a motor frame, 2 is a rotor (rotor), 3 is a rotor core (rotor core) made of laminated magnetic steel sheets, 4 is a permanent magnet, 5 is a stator (stator), 6 is a stator coil (stator coil), Reference numeral 7 denotes a rotating shaft, 8 denotes a bearing, 10 denotes a retainer bar, 11 denotes an electromagnetic linear solenoid, and 13 denotes a small generator. The linear solenoid 11 and the generator 13 constitute a permanent magnet linear motion mechanism referred to in the present invention.
[0036]
The stator core of the stator 5 is fixed to the inner peripheral surface of the peripheral wall of the motor frame 1, and the stator coil 6 is wound around the stator core. Inside the stator 5 in the radial direction, a rotor 2 composed of a rotor shaft 7, a rotor core 3, a permanent magnet 4, and a permanent magnet linear motion mechanism described later is rotatably accommodated.
[0037]
The rotating shaft 7 is rotatably supported by the motor frame 1 via a bearing 8, and is inserted into a rotating shaft insertion hole of the rotor core 3 and fixed to the rotor core 3. A total of four magnet insertion holes are provided in the rotor core 3 at 90 degrees apart from each other in the axial direction. Each magnet insertion hole accommodates a permanent magnet 4 made of a rectangular ceramic thin plate, and two permanent magnets 4 adjacent in the circumferential direction have opposite polarities. The radially outer main surface and the radially inner main surface of the permanent magnet 4 are magnetic pole surfaces. The IPM itself has a general structure except for a magnet cover and a demagnetizing mechanism which will be described later, and further description will be omitted.
[0038]
(Description of permanent magnet linear motion mechanism)
Next, a permanent magnet linear motion mechanism which is a feature of this embodiment will be described below with reference to FIGS. FIG. 6 is a schematic cross-sectional view as viewed from the line AA of FIG. 5 toward the front side. This permanent magnet linear motion mechanism has the linear solenoid 11 and the small generator 13 as described above.
[0039]
The retainer bar 10 made of a non-magnetic material is a rod-shaped member that connects a rear end of a plunger 12, which is a movable member of a linear solenoid 11 described later, and a front end of the permanent magnet 4.
[0040]
The linear solenoid 11 is a cylindrical electromagnet that is fixed to the inner peripheral surface of the peripheral wall of the motor frame 1 around the rotating shaft 7, and is formed by winding a coil around a yoke 17. In this embodiment, the linear solenoid 11 has a simple electromagnet structure for the sake of simplicity, but various known electromagnetic linear actuators can be employed. A soft magnetic plunger 12, which is a movable member of the linear solenoid 11, is housed in the linear solenoid 11, and the plunger 12 is fixed to the rotating shaft 7 so as to be movable in the axial direction and not to rotate in the circumferential direction. Since this kind of electromagnetic linear solenoid itself is well known, further description is omitted.
[0041]
The small generator 13 is a magnet type three-phase AC generator, and includes a generator rotor (rotor) 19 fixed to the rotating shaft 7 and a generator fixed surrounding the outer peripheral surface of the rotor with a small electromagnetic gap. And a child (stator) 14.
[0042]
The stator includes a cylindrical case 17 fixed to the front end wall of the motor frame 1, a generator stator core 23 fixed to the inner peripheral surface of the case 17 to form a cylindrical yoke, and a slot provided therein. And a wound stator coil 22.
[0043]
A generator rotor (rotor) 19 is fitted and fixed to the rotating shaft 7 and fixed to an outer peripheral portion of the generator rotor core 18 made of laminated electromagnetic steel sheets forming a yoke and forming a yoke. And a permanent magnet 15. The permanent magnets 15 are magnetized alternately in polarity at a predetermined pitch in the circumferential direction, and magnetic poles are formed on the outer peripheral surface of the permanent magnet 15 at predetermined pitches in the circumferential direction and alternately in polarity. Since this kind of small generator is well known, further description is omitted.
[0044]
The three-phase output terminal of the stator coil 22 is sent to a rectifier circuit 16 through a three-phase line 20 which is an output line, and the rectifier circuit 16 rectifies the rectified circuit to apply a DC voltage to a coil of the linear solenoid 11 through a two-phase line 21. Output. The small generator 13 may be a single-phase AC generator in addition to the above-described three-phase AC generator, and the single-phase generated voltage may be supplied to the AC voltage driven linear solenoid 11 via a rectifier circuit. It may be applied without.
[0045]
(Operation explanation)
The permanent magnet linear motion mechanism of this embodiment will be described below.
[0046]
The rotor 2 rotates in synchronization with a rotating magnetic field formed by the stator 5. When the rotor 2 rotates, the generator rotor 19 fixed to the rotating shaft 7 also rotates. Then, since the magnetic flux of the permanent magnet 15 alternately interlinks with the stator coil 22 of the generator stator 14, the stator coil 22 generates a three-phase AC voltage. The three-phase AC voltage is rectified into a DC voltage by the rectifier circuit 16 and applied to a coil wound around the yoke 17 of the linear solenoid 11, and the magnetic field generated by this coil causes the plunger 12 to be sucked toward the front side in the axial direction. .
[0047]
It is to be noted that the state where the permanent magnet 4 is entirely inserted into the rotor core 3 is most stable. That is, the permanent magnet 4 has a magnetic attraction toward the inside of the rotor core 3. Therefore, at the start of rotation, the permanent magnet 4, the retainer bar 10, and the plunger 12 are at the positions indicated by broken lines. However, when the rotation speed increases and the power generation voltage of the small generator 13 increases, the yoke 17 moves the plunger 12 to the yoke 17 Since the electromagnetic attraction force drawn into the magnet increases, the permanent magnet 4 is pulled out to the axial position where the electromagnetic attraction force and the magnetic attraction force acting on the permanent magnet 4 are balanced, thereby realizing demagnetization during high-speed rotation. Can be.
(Example 3)
In the first and second embodiments, the permanent magnet 4 is deviated from the rotor core 3 in the axial direction during the high-speed rotation. Instead, the rotor is rotated in the high-speed rotation according to the same principle as the first and second embodiments. 2 may be displaced in the axial direction relatively to the stator 5.
[0048]
For example, the rotor core 3 is fitted to the rotating shaft 7 so as to be movable in the axial direction and non-rotatable relative to each other. May be drawn out in the axial direction. Instead, the stator 5 is fitted to the motor frame 1 so as to be movable in the axial direction, and the stator 5 is rotated at high speed by centrifugal force of the weight or by electromagnetic force as in the first and second embodiments. 5 may be pulled out in the axial direction.
[Brief description of the drawings]
FIG. 1 is a schematic axial cross-sectional view of an IPM employing a variable magnetic flux amount magnet type rotor according to a first embodiment.
FIG. 2 is a schematic cross-sectional view taken along line AA of FIG. 1 and viewed from a rotor core side.
FIG. 3 is a characteristic diagram showing a back electromotive force characteristic when the magnetic flux variable magnet type rotor according to the first embodiment is used.
FIG. 4 is a partially enlarged cross-sectional view showing a modification of the permanent magnet linear motion mechanism of FIG.
FIG. 5 is a schematic axial cross-sectional view of an IPM employing the variable magnetic flux amount type magnet rotor of the second embodiment.
FIG. 6 is a schematic cross-sectional view taken along line AA of FIG. 5 in a direction opposite to the rotor core side.
[Explanation of symbols]
1 motor frame 2 rotor (magnetic flux variable magnet type rotor)
3 Rotor core 4 Permanent magnet 5 Stator 6 Stator coil 7 Rotating shaft 10 Retainer bar (permanent magnet linear motion mechanism)
11 weight (permanent magnet linear motion mechanism)
13 Guide bar (permanent magnet linear motion mechanism)

Claims (6)

A rotor core having an even number of permanent magnets, an even number of magnet insertion holes which are provided in the axial direction at predetermined intervals in the circumferential direction and accommodate the permanent magnets so as to be movable in the axial direction, and a rotating shaft fixed to the rotor core In the variable magnetic flux amount magnet type rotor having
A magnetic flux variable magnet type rotor having a permanent magnet linear motion mechanism disposed close to an end face of the rotor core to partially deviate the permanent magnet from the magnet insertion hole outward in the axial direction during high-speed rotation. The variable magnetic flux type magnet rotor according to claim 1,
A magnetic flux variable magnet type rotor having a thin-walled sleeve inserted into the magnet insertion hole and accommodating the permanent magnet so as to be movable in the axial direction. The variable magnetic flux type magnet rotor according to claim 1,
The permanent magnet linear motion mechanism,
A guide member fixed to the rotating shaft and extending in a substantially radial direction;
A weight that has a guide slope that moves away from the rotor core as going radially outward, and that is held movably in the radial direction by the guide member;
A guide member having one end in contact with the permanent magnet in the magnet insertion hole and the other end in contact with the guide slope of the weight;
A variable magnetic flux type magnet rotor comprising: The variable magnetic flux type magnet rotor according to claim 1,
The permanent magnet linear motion mechanism,
An electromagnetic linear motion mechanism fixed to the rotating shaft and displacing the permanent magnet in the axial direction,
A power supply unit that applies a rotation speed correlation voltage that causes the permanent magnet to partially deviate from the magnet insertion hole during high-speed rotation by applying a voltage that changes according to the rotation speed to the linear solenoid;
A variable magnetic flux type magnet type rotor characterized by having: The variable magnetic flux type magnet rotor according to claim 1,
The magnetic flux variable magnet rotor, wherein the power supply unit comprises a generator having a rotor mounted on the rotating shaft. A variable magnetic flux amount having an even number of permanent magnets, a rotor core having an even number of magnet insertion holes that are provided in the axial direction at predetermined intervals in the circumferential direction and that accommodates the permanent magnets, and a rotating shaft that supports the rotor core. In a magnet type rotor,
A magnetic flux variable magnet type rotor having a relative linear motion mechanism for moving the rotor core axially relative to the stator during high-speed rotation.

Images