DE102012021209A1 - Stator assembly for electric machine e.g. spindle motor having fluid dynamic bearing system, has a pole tooth having windings which are arranged with winding wires that are arranged in vibration-damped manner on the pole teeth - Google Patents

Abstract

The stator assembly (34) comprises several pole teeth comprising a stator core (36), in which each pole tooth has windings (38) which are arranged with the winding wires. The winding wires of the windings are arranged in vibration-damped manner on the pole teeth. A viscoelastic material such as rubber or natural rubber is arranged between the pole teeth and the winding wires of the windings. The pole teeth are coated with the viscoelastic material in the region of the windings.

Description

Field of the invention

The invention relates to a stator assembly for an electric machine, in particular a stator assembly for a spindle motor with fluid dynamic bearing system, as it can be used for example for driving hard disk drives.

State of the art

In electrical machines with electric motors, such. B. spindle motors for driving hard disk drives, the stator assembly consists of a stator core with a plurality of pole teeth, wherein each of the pole teeth coils of a winding consisting of a plurality of turns of a winding wire are arranged.

The stator core of the stator assembly is typically a laminated stack of stator laminations, for example, a number of 0.2 mm thick laminations.

Hard disk drives comprise a read / write device with which the data to be stored on the hard disk is written to or read from the disk. The read-write device is driven by a servo system which positions the magnetic heads of the read-write device at the respective positions of the storage disk.

A hard disk drive is a complex, oscillatory system consisting of various assemblies. The electromagnetic drive in the hard disk drive generates a broadband excitation and can, under certain conditions, resonate natural frequencies of the servo system of the read / write heads. In this case we speak of resonance. At resonance, excitation frequencies, in this case especially of the stator arrangement, are close to a natural frequency of the servo system.

This servo system is a mechanical assembly and has several specific natural frequencies, it has been found that these natural frequencies can be excited by the spindle motor, in particular by lying at about 10 to 60 kHz resonances of the stator assembly to vibrate.

The winding wires of the stator windings are moved in the electrical operation of the motor by magnetic forces, and the stator core of the stator assembly is thereby excited to oscillate, which then transferred via the hard disk housing to the servo system and stimulate this to resonate.

This means that under certain operating conditions, the frequencies generated by the stator assembly, and in particular the harmonic frequencies, fall within the range of the natural frequencies of the servo system and thereby stimulate the servo system to vibrate and interfere with operation. The types of vibration are bending vibrations, torsional vibrations and shearing vibrations.

Disclosure of the invention

If a design were to resonate, there are various technical possibilities to avoid this or to reduce the resonance amplitude. Changes in the mechanical design of the components of the stator assembly, structural stiffness, tensile stiffness, bending stiffness, torsional stiffness (depending on geometry and material) can change natural frequencies and natural vibration. In addition, one can reduce the amplitudes in the case of resonance by various types of damping.

• – Die Eigenfrequenzen des Bauteils oder der Baugruppe.
• – Die Eigenschwingform des Bauteils oder der Baugruppe.
• – Die Dämpfungswerte sowie der Dämpfmechanismus.

The following parameters are of interest in experimental and numerical modal analysis:

• - The natural frequencies of the component or assembly.
• - The natural vibration of the component or assembly.
• - The damping values and the damping mechanism.

It is therefore an object of the invention to design a stator assembly of an electric machine so that sharp resonance amplitudes are prevented or shifted to frequency ranges in which they do not interfere with the servo system of the read-write device or other components of the hard disk drive.

This object is achieved by a stator assembly with the features of claim 1.

Preferred embodiments of the invention and further advantageous features are indicated in the dependent claims.

The stator assembly comprises a stator core having a plurality of pole teeth, each pole tooth being wound with a winding of winding wire. The winding wire preferably has a circular cross section and is made of electro copper. For electrical insulation, it is provided on its surface with an insulating varnish.

According to the winding wires of the windings are arranged vibration damped on the pole teeth.

Due to the vibration-damped, ie soft and thus somewhat movable arrangement of the winding wires on the pole teeth, in particular the higher resonance frequencies or harmonic frequencies of the stator arrangement are damped or shifted in their frequency range. Depending on the design of the stator, the shift of the frequencies can be made to higher or lower frequencies.

For the vibration damped arrangement of the winding wires on the pole teeth, a viscoelastic material may be used, which is arranged between the pole teeth and the winding wire, so that the winding wires do not rest directly on the metal of the pole teeth. This allows for movement of the winding on the order of microns.

This viscoelastic material may preferably comprise rubber or a material based on natural rubber, since these materials have a very good damping, especially at high frequencies.

According to a first embodiment of the invention, the pole teeth may be coated at least in the region of the windings with the viscoelastic material, d. H. the viscoelastic material is applied directly to the surface of the pole teeth, and then the winding wire is wound on the viscoelastic material.

In another embodiment of the invention, the viscoelastic material may be formed as a film or tape, which is applied to the pole teeth in the region of the windings. The pole teeth are first wound with a band of viscoelastic material and then wound with the winding wire.

In another embodiment of the invention, the winding wire itself may be coated with the viscoelastic material. This results in the advantage that not only a good damping against the stator core and the pole teeth is given, but the viscoelastic material at the same time takes over the electrical insulation of the winding wires.

The provision of a viscoelastic material between the winding wires and the stator core prevents vibrations generated by the windings from being transmitted to the stator core without being damped and causing it to resonate. The viscoelastic material dampens the vibration generated by the winding wire and in particular the resonance amplitudes at higher frequencies.

This results in lower amplitudes in the case of resonance and the resonance frequency is shifted in total to uncritical frequency ranges, where they do not stimulate the resonant frequency of the servo system of the read-write heads of the hard disk drive to vibrate.

The winding wires of the stator windings are excited in the electrical operation of the electric motor by magnetic forces to vibrate. Mechanical isolation of the winding wires from the stator core by the viscoelastic material can reduce and damp propagation of the vibrations on the stator assembly.

According to the invention, other possibilities are provided to reduce the oscillation amplitudes of the stator arrangement or to shift the natural frequencies into higher or lower frequency ranges.

A first possibility is to increase the number of windings of the windings at the same wire diameter, which leads to an increase of the winding mass, so that overall the resonance frequencies (and harmonics) are shifted downwards in the direction of the lower frequencies. Accordingly, a reduction in the number of turns of the windings shifts the resonant frequencies of the stator assembly upwardly toward the higher frequencies.

Another possibility is to move the center of gravity of the entire winding of a pole tooth as far as possible radially outward in the direction of the ends of the teeth, so that certain natural frequencies of the stator reduce. Conversely, a shift of the center of gravity of the winding, ie the center of gravity, radially inwardly, causes an increase in certain natural frequencies.

It is also an effective possibility to design the pole teeth slightly differently in their geometry so that each pole tooth has a slightly different natural frequency. In this way, the formation of a sharp resonance amplitude with high quality is avoided.

In this case, in particular, the length of a pole tooth or a plurality of pole teeth can be slightly different or the width of a pole tooth or a plurality of pole teeth can be slightly different. The width of a Polzahns may be variable in the radial direction or in the axial direction of the stator core, the changes also affect the design of the individual stator laminations to each other.

The connection points of a stator plate to an adjacent plate in the axial direction can be slightly different for the different pole teeth in shape and relative position. This results in a slightly different behavior of the other pole teeth for a pole tooth to be wound in relation to the position of the resonance amplitudes and their height, which leads to a deviating behavior of the stator arrangement.

The contact surface of the stator laminations to one another can be processed in order to increase the friction between the individual stator laminations and thereby to achieve a slightly different behavior with respect to the position of the resonant amplitudes and their height, which leads to an altogether deviant behavior of the stator arrangement.

In a preferred embodiment of the invention, the stator core of the stator assembly consists of a plurality of stacked stator laminations. In order to prevent a self-resonance with high quality, it is also provided according to the invention to form the stator laminations of different thickness, for example, two different thickness stator laminations are used in different stacking for the entire stack. It can also be used more than two different thickness stator laminations.

The stator core usually comprises a closed return, on which the pole teeth are arranged. By appropriate choice of the inner radius or outer radius of the return path, the resonant frequency of the stator assembly can also be influenced.

Preferably, the inner radius of the conclusion of the stator core is at least 60% of the total radius of the stator core. Preferably, the outer radius of the conclusion of the stator core is at least 70% of the total radius of the stator core.

Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. This results in further features and advantages of the invention.

Brief description of the drawings

1A shows a section through a fluid dynamic bearing system of a spindle motor with a first embodiment of a stator according to the invention.

1B shows a section through a fluid dynamic bearing system of a spindle motor with a further embodiment of a stator according to the invention.

2 shows a cross section through an engine according to the 1A or 1B ,

3 shows an enlarged section through a stator assembly according to the invention.

3 shows an enlarged section through a further embodiment of a stator according to the invention.

Description of preferred embodiments of the invention

The 1A and 1B each show a section through a fluid dynamic bearing system for a spindle motor and are drawn to scale with a given scale.

The 1A and 1B differ only by the configuration of the stator core of the stator, so that initially both figures are described together.

The spindle motor comprises a base plate 10 , which has a central opening for receiving a bearing bush 12 having. A wave 14 is in a bore of the bearing bush 12 rotatably received, the shaft 14 at her from the bushing 12 protruding end of a rotor component 22 wearing. The rotor component 22 includes a flat bottom, the one end face of the bearing bush 12 opposite and from this by a filled with bearing fluid bearing gap 20 is disconnected. A lower bearing surface of the rotor component 22 forms together with a front side of the bearing bush 12 a thrust bearing 28 out, while facing bearing surfaces of shaft 14 and bearing bush 12 preferably two radial bearings 24 . 26 form. The two, arranged at an axial distance from each other, radial bearings 24 . 26 and the thrust bearing 28 are characterized by bearing structures disposed on one or both opposing bearing surfaces. The bearing gap 20 extends between the bearing bush 12 and the wave 14 and further between the end face of the bearing bush 12 and the bottom of the rotor 22 , At the outer diameter of the thrust bearing 28 the storage gap goes 20 in a gap with a larger gap distance over, which as a sealing gap 30 acts. This sealing gap 30 sits over the outer circumference of the bearing bush 12 continues and widens conically outward in the form of a conical capillary seal.

At the bottom is the shaft 14 widened and has a stopper ring 16 on that in the example shown in one piece with the shaft 14 is formed, but also as a separate component with the shaft 14 can be connected. The stopper ring 16 has a larger outer diameter than the shaft 14 and is in a recess of the bearing bush 12 arranged and filled with a bearing fluid gap 20 surround. The stopper ring 16 has the task of securing against falling out of the shaft 14 from the bushing 12 , The lower end of the bearing bush 12 is through a cover plate 18 locked.

It can be a recirculation channel 32 be present, the one to the thrust bearing 28 adjacent section of the storage gap 20 with one to the stopper ring 16 connecting adjacent section of the storage gap with each other. As a result, the bearing fluid in the bearing can circulate in a closed circuit. Furthermore, there is a pressure equalization between the through the recirculation channel 32 connected sections of the warehouse.

The spindle motor includes an electromagnetic drive system that consists of one on the base plate 10 arranged stator assembly 34 respectively. 34 ' and one on the rotor component 22 arranged rotor magnet 40 consists. By appropriate energization of the windings of the stator assembly 34 respectively. 34 ' results in an electromagnetic rotating field, which on the rotor magnet 40 acts and the rotor component 22 set in rotation.

As an abutment to the thrust bearing 28 it may be provided a magnetic bearing, which consists of the rotor magnet 40 and a rotor magnet axially opposite ferromagnetic ring 42 and / or from an axial offset between the rotor magnet 40 and the stator assembly 34 (so-called magnetic offset) can exist.

The stator arrangement 36 respectively. 36 ' consists of a stator core in the form of a stator core 36 respectively. 36 ' and a winding arranged on the stator core 38 respectively. 38 ' ,

How to get out 1A can take the stator core 36 the stator assembly 34 consist of several stacked stator laminations, wherein in the embodiment according to 1A several thin stator laminations 36b stacked on top of each other and on the bottom and top each much thicker stator laminations 36a be used as a conclusion. Typical thicknesses of the stator are z. B. 0.15 mm, 0.2 mm and 0.35 mm.

Out 1B it turns out that the stator core 36 ' consists of several stator laminations, wherein the stator laminations are all formed differently thick or at least two different thickness stator laminations 36a ' respectively. 36b ' be used in any order.

Due to the different thickness stator laminations results in a different vibration behavior of the stator compared to an equal stator with stator of the same thickness, d. H. the excitation frequency is shifted, which can reduce the risk of excitation of the natural frequencies of the servo system of the hard disk drive.

The connection points of a stator plate to an adjacent plate in the axial direction can be slightly different for the different pole teeth in shape and relative position. This results in a slightly different behavior of the other pole teeth for a pole tooth to be wound in relation to the position of the resonance amplitudes and their height, which leads to a deviating behavior of the stator arrangement.

The contact surface of the stator laminations to one another can be processed in order to increase the friction between the individual stator laminations and thereby to achieve a slightly different behavior with respect to the position of the resonant amplitudes and their height, which leads to an altogether deviant behavior of the stator arrangement.

2 shows a section through the stator according to 1A , You can see the stator core 36 , which in the region of the inner diameter approximately annular as a stator conclusion 37a is formed, wherein distributed on the circumference of the ring, a number of radially outwardly projecting pole teeth 37 are arranged. The pole teeth are each with a pole piece 37b Mistake.

It is an external rotor motor. In an internal rotor motor, the pole teeth on the inner circumference of the stator yoke would be directed radially inwards in the direction of the axis of rotation.

The stator arrangement 34 is from a rotor component 22 surrounded, on whose inner peripheral surface of the rotor magnet 40 is arranged, which consists of a plurality of alternately arranged magnetic poles.

The rotor magnet is through an air gap from the outer periphery of the stator assembly 34 separated.

On every pole tooth 37 is a coil of a winding 38 arranged, consisting of several turns of a winding wire 39 consists. The conclusion of the stator core 36 has an inner radius R _i and an outer radius R _a . The length of each Polzahns is L _z ( 3 ). The width of the pole tooth is B _z . The total radius of the stator core is R _s .

Preferably, the inner radius R _{i of} the conclusion of the stator core is at least 60% of the total radius R _{s of} the stator core. Preferably, the outer radius R _{a of} the conclusion of the stator core is at least 70% of the total radius R _{s of} the stator core.

3 shows an enlarged view of two adjacent pole teeth 37 of the stator core 36 ,

According to the invention, the winding 38 or are the winding wires 39 not directly on the stator core of the pole tooth 37 but in between is a layer or layer of a viscoelastic material 46 arranged.

For example, the viscoelastic material may be formed as a foil or tape that surrounds the pole tooth 37 is wound. The electrical winding 38 is then on the viscoelastic material 46 wound. Alternatively, the pole tooth 37 also with the viscoelastic material 46 be coated. The viscoelastic material may include rubber or a natural rubber-based material because these materials have very good cushioning, especially at high frequencies. In another variation (not shown), a layer of viscoelastic material may additionally be applied between some or all of the stator laminations for vibration damping. The layer thickness of this viscoelastic material can be from a few micrometers to several millimeters. This wide scope results from the large number of possible designs of the hard disk motor. The viscoelastic material may be added as a separate, solid component, or may be applied as a liquid to the surface of one or more stator laminations and solidified after application.

The contact surface of the stator laminations to one another can be provided with a viscoelastic material in order to increase the friction and damping between the individual stator laminations and thereby to achieve a slightly different behavior with respect to the position of the resonant amplitudes and their height, which leads to a deviating behavior of the overall Stator arrangement leads.

An influence on the behavior of the stator arrangement also has the geometry of the pole teeth as well as the design and arrangement deviating shaped pole teeth. In this case, in particular, the lengths of a pole tooth and / or a plurality of pole teeth may be slightly different and / or the width of a pole tooth or a plurality of pole teeth may be slightly different.

The width of a Polzahns may be variable in the radial direction or in the axial direction of the stator core, the changes may also affect the design of the individual stator laminations to each other.

For example, you can change a single pole tooth of a single stator or more pole teeth of a stator or the pole teeth of several stator plates in their geometry (length, width, diameter), so that natural frequencies and natural modes of the stator assembly (stator core with winding) are changed. In this way, no dominant resonance amplitude of high quality arises. In 3 the width of the pole tooth on the stator yoke is denoted by B _zi and the width of the pole tooth on the pole shoe is B _za . If B _zi and B _za are chosen to be the same width, this corresponds to the width B _z in 2 , If B _zi and B _za are chosen to be of different widths, the result is a pole tooth with a radial conical shape whose width either increases or decreases relative to the outer diameter of the stator core. In this case, the length Lz can be varied. The current manufacturing tolerance for such a stamped part in mass production is in the range of 0.01 millimeters to about 0.05 millimeters. The geometric differences from one pole tooth to another pole tooth are therefore greater in length and width than the current manufacturing tolerance of a stator lamination, they are about 0.2 millimeters to several millimeters. The size changes in the geometry are proportional to the changes in the natural frequency, small changes usually only minor changes in certain natural frequencies result.

The modification of width and length of the pole tooth influences / changes z. B. the flexural rigidity and the torsional rigidity of the stator assembly. This changes the dynamic behavior, eg. B. certain natural frequencies, the stator assembly, because it has changed the stiffness and mass of the stator at the same mass of the winding.

The arrangement of geometrically modified pole teeth in the stator in the axial direction or in the circumferential direction can be ordered or disordered.

This means that, for example, the changed pole teeth in the laminated stack (stator packet) are aligned axially one above the other or have a certain offset in the circumferential direction, eg. B. offset by one or more pole teeth. There are a large number of possibilities for positioning the pole teeth of individual stator laminations in the stator packet relative to one another. It also depends on how many pole teeth in the complete stator package in their geometry / Dimension and how many stator laminations were changed.

4 shows a modified embodiment of the invention, wherein the stator core 36 or the pole teeth with a winding 38 ' or a winding wire 39 ' wound, the insulation or coating with a viscoelastic material 39a ' includes.

The metal of the winding wire 39 ' is with a viscoelastic material 39a ' surrounded, which is the direct contact of the winding wire 39 ' to the stator core 36 or the pole tooth 37 prevents and the winding wire 39 ' vibration-dampened and thus somewhat flexible on the pole tooth 37 holds.

5 Fig. 12 schematically shows a diagram showing the frequency response of a base plate in the vicinity of the stator assembly without the use of viscoelastic material and with the use of viscoelastic material between the turns of the winding wire and the stator core.

The curve 48 shows a frequency response using a conventional stator assembly without damping with viscoelastic material. In particular, one can see fairly high resonance amplitudes 48a . 48b . 48c , which can stimulate the servo system of the read / write head of the hard disk drive to unwanted resonances.

The curve 50 shows a frequency response using a stator assembly with a viscoelastic material 46 between the winding 38 and the stator core 36 , The viscoelastic material in this example has an initial thickness of 45 μm.

It can be seen that in particular the resonance amplitudes of the frequency response are substantially attenuated. Furthermore, it can be seen that the individual natural frequencies are shifted into higher frequency ranges, which can also make a positive contribution to reducing a self-oscillation of the servo system.

An influence on the behavior of the stator arrangement also has the position of the center of gravity of the winding of a pole tooth with respect to the pole tooth. With uniform winding along the length L _{z of} the pole tooth, the center of gravity of the winding is in the middle of the illustrated length L _z . Now, if a turn from the radial inner position moved to the radially outer position with a number of turns of 45 turns, so can the resonance frequency z. B. change by 200 Hz. If sufficient winding space is present, then the behavior of the stator arrangement can be adapted with respect to the resonance amplitudes by means of an aligned winding. A displacement of the center of mass of the entire winding of a pole tooth as far as possible radially outwards in the direction of the ends of the teeth causes the resonant frequency of the stator arrangement to be reduced. Conversely, a shift of the center of gravity of the winding, ie the center of gravity, radially inwardly, causes an increase in the resonance frequency.

In 1A It is shown that the stator core at its inner diameter radially to the base plate 10 is guided. This guide is preferably carried out by a press fit along the entire axial guide length. If the stator core is guided only partially along its axial height, the resonance behavior of the stator arrangement also changes.

The problem described above of the transmission of vibrations from a drive motor to other components of a module and the resulting excitation of natural frequencies also applies to a fan motor, which is used in many applications for cooling. Therefore, the above-described embodiments also lead to an improvement of an electric motor for a fan.

LIST OF REFERENCE NUMBERS

10

baseplate

12

bearing bush

14

wave

16

stopper ring

18

cover

20

bearing gap

22

rotor component

24

radial bearings

26

radial bearings

28

thrust

30

seal gap

32

recirculation

34, 34 '

stator

36, 36 '

stator core

36a, 36a '

stator lamination

36b, 36b '

stator lamination

37

pole tooth

37a

Stator yoke

37b

pole

38, 38 '

winding

39, 39 '

winding wire

39a '

coating

40

rotor magnet

42

ferromagnetic ring

44

axis of rotation

46

Viscoelastic material

48

Frequency response without viscoelastic material

48a

resonance amplitude

48b

resonance amplitude

48c

resonance amplitude

50

Frequency response with visoelastic material

R _a

outer radius

R _i

inner radius

R _s

total radius

L _z

length

B _z

width

B _zi

width

B _za

width

Claims (14)

Stator arrangement for an electric machine, having a plurality of pole teeth ( 37 ) comprehensive stator core ( 36 . 36 ' ), whereby on each pole tooth ( 37 ) a winding ( 38 . 38 ' ) of winding wire ( 39 . 39 ' ), characterized in that the winding wires ( 39 . 39 ' ) of the windings vibration damped on the pole teeth ( 37 ) are arranged. Stator arrangement according to claim 1, characterized in that between the pole teeth ( 37 ) and the winding wire ( 39 . 39 ' ) of the windings a viscoelastic material ( 46 ) is arranged. Stator arrangement according to claim 1 or 2, characterized in that the pole teeth ( 37 ) at least in the region of the windings with the viscoelastic material ( 46 ) are coated. Stator arrangement according to one of claims 1 to 3, characterized in that the stator core ( 36 . 38 ' ) of several stator laminations ( 36a . 36a ' . 36b . 36b ' ) and the stator laminations ( 36a . 36a ' . 36b . 36b ' ) in the contact region to each other at least partially with the viscoelastic material ( 46 ) are coated. Stator arrangement according to claim 1 or 2, characterized in that the viscoelastic material ( 46 ) is formed as a film and in the region of the windings on the pole teeth ( 37 ) is applied. Stator arrangement according to claim 1 or 2, characterized in that the winding wire ( 39 ' ) with the viscoelastic material ( 39a ' ) is coated. Stator arrangement according to one of claims 1 to 6, characterized in that the viscoelastic material ( 46 . 39a ' ) Rubber or natural rubber. Stator arrangement according to one of claims 1 to 7, characterized in that the individual pole teeth ( 37 ) differ in their geometry. Stator assembly of one of claims 1 to 8, characterized in that the stator core ( 36 . 36 ' ) of several stator laminations ( 36a . 36b . 36a ' . 36b ' ), wherein stator laminations are used with at least two different thicknesses. Stator arrangement according to one of claims 1 to 9, characterized in that the stator core ( 36 . 36 ' ) includes a conclusion on which the pole teeth ( 37 ), wherein the inner radius of the return path is at least 60% of the total radius of the stator core. Stator arrangement according to one of claims 1 to 10, characterized in that the stator core ( 36 . 36 ' ) includes a conclusion on which the pole teeth ( 37 ), wherein the outer radius of the return path is at least 70% of the outer radius of the stator core. Electric motor with a stator arrangement according to one of claims 1 to 11. Hard disk drive with an electric motor according to claim 12. Fan with an electric motor according to claim 12.

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