CN1727709A - Gas hydrodynamic bearing, motor having the same and disk driver - Google Patents

Abstract

The present invention relates to a gas hydrodynamic bearing. It includes shaft and shaft sleeve, its internal circumferential surface is directed against the external circumferential surface of the shaft by means of microfine gap, and includes a basically-cylindrical hub, it can apply surface pressure to the outside of the described shaft sleeve and is assembled on the described shaft sleeve, on the external circumferential surface of the described shaft and internal circumferential surface of the described shaft sleeve at least more than one hydrodynamic pressure generation groove can be formed. If the linear expansion coefficients of the described shaft, shaft sleeve and hub are respectively defined as alpha 0, alpha 1 and alpha 2, so that it can meet the relationship formula alpha 1 less than alpha 0 less than alpha 2.

Description

Aero dynamic bearing, motor and disk drive with this aero dynamic bearing

Technical field

The disk drive that the present invention relates to aero dynamic bearing, has the motor of this aero dynamic bearing and have this motor.The present invention is applied in such motor, that is, this motor can make disk (for example hard disk and DVD), disc apparatus and have the laser printer rotation of this motor.

Background technique

The motor of disk (for example hard disk) rotation need rotated at a high speed and under the highi degree of accuracy.As the bearing device of the motor that makes the disk rotation, the hydrodynamic pressure bearing that can stablize rotation is universal just day by day.Usually, hydrodynamic pressure bearing comprises two members: first and second members.First member is a columnar shaft, and one or two plate-like thrust plate is located on this one or both ends.Second member faces toward the outer peripheral surface of described axle by radial clearance, and faces toward one or two plane of thrust plate by the thrust gap.On member, have dynamic pressure and generate groove facing at least one (described surface and described dwell set are hereinafter referred to as " bearing surface ") in two surfaces in these gaps, this groove has man type or spiral-shaped, and lubricating fluid (for example air or oil) is present in these gaps.If in first and second members one with respect to another rotation, the lubricating fluid pumping effect that generates groove by dynamic pressure increases the hydrodynamic pressure in radial clearance and the thrust gap so.Like this, the rotary side of first and second members is upwards floated with respect to its fixed side, and has during rotation kept the contactless state between first and second members.

In aero dynamic bearing, gas is used as lubricating fluid.With oil is different as the hydrodynamic bearing of lubricating fluid, there is not the lubricating fluid leakage problem in aero dynamic bearing.Yet, very little with the viscous resistance value of oil phase comparison gas.Therefore, compare with the oil dynamic bearing, this aero dynamic bearing has adopted such structure,, has increased the speed of rotary side in bearing surface that is, and establishes supported clearance less than the supported clearance of oil dynamic bearing.By such structure, in gas bearing, produced enough swivel bearing power.Usually, in the oil dynamic bearing, supported clearance is 2 to 5 μ m, but supported clearance is 2 μ m or littler in aero dynamic bearing.Under the situation of aero dynamic bearing, because supported clearance is less, 1) when supported clearance narrows down owing to temperature raises, promptly, when the thermal expansion coefficient of described axle during greater than the thermal expansion coefficient of axle sleeve, bearing surface contacts thereby supported clearance disappears, and produces the state that can not rotate that is called lock state.In addition, 2) when supported clearance broadens owing to temperature raises, that is, when the thermal expansion coefficient of described axle during less than the thermal expansion coefficient of axle sleeve, it is not enough that swivel bearing power becomes, and the running accuracy variation.Existing multiple prior art is used for preventing the variation of supported clearance.According to one of prior art, with the material of Cuprum alloy as axle sleeve, with the material of Austenitic Stainless Steel as axle, and two kinds of material coefficient of thermal expansion coefficient values are equal to each other substantially.According to another prior art, make by the material that differs from one another facing to the bearing surface in thrust gap.When a kind of material was the rustless metal, another kind of material was pottery, for example zirconium oxide.By this prior art, select for use a kind of material to make it have the Coefficient of Thermal Expansion value that equates substantially with another kind of material, and reduce the wear extent that produces owing to the friction between axle or thrust plate and the axle sleeve.

Summary of the invention

Yet the material of fixed side and rotary side is elected as mutually the same substantially in arbitrary relevant prior art.Because material must select from this scope, therefore consider other aspects, for example workability, price and slickness, the combination of material can not be optimized.

The objective of the invention is to widen range of choice to fixed side and rotary side material.

The present invention also can reduce the variation of the gap size that causes owing to variation of temperature.

According to an example of aero dynamic bearing of the present invention, this bearing comprises: axle; Axle sleeve, its inner peripheral surface is by the outer peripheral surface of micro-gap facing to described axle; And the hub of substantially cylindrical, it applies surface pressure to the outside of described axle sleeve, and is assembled on the described axle sleeve; Dynamic pressure generates at least one of inner peripheral surface that groove is formed on the outer peripheral surface of axle and axle sleeve, and if the coefficient of linear expansion of axle, axle sleeve and hub is defined as α respectively ₀, α ₁, α ₂, satisfy relation α so ₁＜α ₀＜α ₂

In this aero dynamic bearing, when temperature is 20 ℃, axle sleeve is assembled on the hub, and axle sleeve is pressed to internal side diameter fixes.If temperature raises, the radial clearance between axle and the axle sleeve is because relation α so ₁＜α ₀And be tending towards narrowing down.The variable quantity in this gap is defined as A.Fastening width between axle sleeve and the hub (fastening width) is because relation α ₁＜α ₂And diminish, therefore relaxed the surface pressure between axle sleeve and the hub, and axle sleeve is tending towards radially expanding.This expansion makes the radial clearance between axle and the axle sleeve broaden.This swell increment is defined as B.As a result, swell increment B and gap variable quantity A cancel each other out, thereby reduce or suppressed because the actual change of the radial clearance that the temperature rising causes.In addition, owing to satisfied above-mentioned inequality, therefore can the material of optimum can be applied in the various members according to workability, price and lubricity.

Preferably, if axle sleeve during with 20 ℃ and the fastening width between the hub are defined as δ, the assembling diameter between axle sleeve and the hub is defined as 2R ₂, and the difference between maximum serviceability temperature and 20 ℃ being defined as Δ T, the relation (1) below satisfying so is and if be defined as t with the thickness of axle sleeve ₁, hub thickness be defined as t ₂, the relation (2) below satisfying so:

2R ₂ΔT(α ₂-α ₁)≤δ …(1)

t ₂/t ₁≥0.25 …(2)。

If satisfied relation (1), just can fix fastening width, in the serviceability temperature scope of aero dynamic bearing although axle sleeve expands.Yet in this case,, when fixing hub, have only hub to be out of shape so, and do not apply predetermined surface pressure to axle sleeve along expansion direction by shrink fit or press fit if compare the thickness of hub with axle sleeve extremely thin.Here it is is provided with the reason of relation (2).Like this, when axle sleeve and hub being assembled each other, between them, applied predetermined surface pressure by the fastening width that satisfies relation (1).As a result, reduce the variation of radial clearance, and prevented the loosening of assembled portion.

When axle, axle sleeve and hub are made by the material that satisfies above-mentioned condition, can obtain the variable quantity of radial clearance by equation:

At first, the assembling diameter between internal diameter, axle sleeve and the hub of the external diameter of axle, axle sleeve and the external diameter of hub are defined as 2R respectively ₀, 2R ₁, 2R ₂And 2R ₃The longitudinal modulus of elasticity of material, axle sleeve and hub material is defined as E ₁And E ₂, the Poisson's ratio of material, axle sleeve and hub material is defined as ν ₁And ν ₂By press fit or shrink fit and the surface pressure Pm that on the fastening surface between hub and the axle sleeve, produces can represent by following formula (3):

$\mathrm{Pm}=\mathrm{\&delta;}/\left\{2R_2(\frac{R_2^2+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^2}{E_1(R_2^2-{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^2)}+\frac{R_3^2+R_2^2}{E_2(R_3^2-R_2^2)}-\frac{v_1}{{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">E</figure-callout>}}_1}+\frac{v_2}{E_2})\right\}---\left(3\right)$

The internal diameter of axle sleeve has dwindled u, and u is represented by following formula (4) by Pm:

$u=-\frac{2R_1^2{R}_2^2\mathrm{Pm}}{E_1(R_2^2-R_1^2)R_1}---\left(4\right)$

Therefore, radial clearance Cr becomes when normal temperature

Cr＝R ₁-R ₀-u …(5)

Then, if temperature rising Δ T, the reduction volume of surface pressure Pm and sleeve diameter can be obtained by following formula (6) to (8) so:

$P{m}^{\&prime;}={\mathrm{\&delta;}}^{\&prime;}/\left\{2R_2^{\&prime;}(\frac{R_2^{\&prime;2}+R_1^{\&prime;2}}{E_1(R_2^{\&prime;2}-R_1^{\&prime;2})}+\frac{R_3^{\&prime;2}+R_2^{\&prime;2}}{E_2(R_3^{\&prime;2}-R_2^{\&prime;2})}-\frac{v_1}{{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">E</figure-callout>}}_1}+\frac{v_2}{E_2})\right\}---\left(6\right)$

$\left.\begin{array}{c}{R}_0^{\&prime;}=R_0(1+{\mathrm{\&alpha;}}_0\mathrm{\&Delta;T})\\ {\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}=R_1(1+{\mathrm{\&alpha;}}_1\mathrm{\&Delta;T})\\ R_2^{\&prime;}=R_2(1+{\mathrm{\&alpha;}}_1\mathrm{\&Delta;T})\\ R_3^{\&prime;}=R_3(1+{\mathrm{\&alpha;}}_2\mathrm{\&Delta;T})\\ {\mathrm{\&delta;}}^{\&prime;}=2R_2({\mathrm{\&alpha;}}_1-{\mathrm{\&alpha;}}_2)\mathrm{\&Delta;T}+\mathrm{\&delta;}\end{array}\right\}...\left(7\right)$

$u^{\&prime;}=-\frac{2{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;2}{R}_2^{\&prime;2}P{m}^{\&prime;}}{E_1(R_2^{\&prime;2}-R_1^{\&prime;2}){\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20041005466600121.png,A20041005466600131.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}}---\left(8\right)$

Radial clearance Cr ' can be expressed as following formula (9) after temperature raises:

Cr′＝R ₁′-R ₀′-u′

＝(R ₁α ₁-R ₀α ₀)ΔT-u′ …(9)

Therefore, the radial clearance variable quantity can be expressed as following formula:

Cr-Cr′＝R ₁-R ₀-u-(R ₁α ₁-R ₀α ₀)ΔT+u′ …(10)

Wherein, u ' is by formula (7) being brought into the value that obtains in formula (6) and the formula (8).

Because aero dynamic bearing of the present invention has above-mentioned effect, therefore the motor that includes following member can stably be worked, thus it comprise described aero dynamic bearing, be used for fixing axle bearing, be installed on the bearing stator be installed in hub on the magnet relative with stator.

According to the present invention, have only coefficient of linear expansion to be made as predetermined inequality relation with near the member the bearing surface, just can reduce the variable quantity of radial clearance.Owing to can guarantee the surface pressure of the assembled portion between axle sleeve and the hub, so the range of choice of member has broadened.This helps the various devices of using gases hydraulic bearing.

Description of drawings

Fig. 1 is a schematic cross sectional views of cuing open the hard disk drive of getting according to embodiment along axial rotary; And

Fig. 2 is used for the motor of hard disk drive along axial sectional view.

Embodiment

Explain embodiments of the invention below with reference to accompanying drawing.Fig. 1 is a schematic cross sectional views of cuing open the hard disk drive of getting according to embodiment along axial rotary (hereinafter referred to as axially).Hard disk drive 10 comprises: housing 11, and its inside keeps clean; Dynamic pressure bearing motor (hereinafter referred to as motor) 1 is located in the housing 11; With actuator 12.A plurality of (being four in the drawings) disk 6 is installed on the motor 1 vertically.If drive motor 1, disk 6 is just along predetermined direction rotation so.Arm 14 with magnetic head 13 is installed on the actuator 12 with respect to disk 6, thereby arm 14 is along radially extending.When not using hard disk drive 10, magnetic head 13 is fallen back on position away from disk 6 with arm 14, if motor 1 is driven, magnetic head 13 is owing to the operation of actuator 12 is rotated so, thus magnetic head 13 near disk 6 with read.

Fig. 2 show be used for hard disk drive 10 motor 1 along axial sectional view.Fig. 2 cuts open the partial elevation view of getting along cat line X-X.Motor 1 comprises: fixed component 2, and it is fixed on the internal surface of housing 11; Rotating member 3, thus can be by the aero dynamic bearing supporting rotating member of describing after a while 3 with respect to fixed component 2 rotations; Stator 4 and magnet 5.

Fixed component 2 comprises basic recessed plate-like bearing 21, interior axle 22, outer shaft 23, goes up thrust plate 24 and lower thrust plate 25.Central part office at bearing 21 is formed with the through hole (not shown), and the periphery of this through hole is thicker in to form convex portion (boss) 21a.The periphery of bearing 21 is provided with cylindrical wall 21b.Stator 4 is installed on the internal surface of wall 21b.Electric current is supplied with the coil of stator 4 from the flexible circuit board (not shown) of the reservations office of external power supply by being located at bearing 21.In axle 22 have the column profile, and its lower end is assembled in the through hole and by convex portion 21a and supports.Outer shaft 23 has cylindrical shape.On the excircle that axle 22 exposed from convex portion 21a in outer shaft 23 was assemblied in.Lower thrust plate 25 extends vertically from outer shaft 23.In fitting into, lower thrust plate 25 make lower thrust plate 25 be clipped between the lower end surface and convex portion 21a of outer shaft 23 in the axle 22.Last thrust plate 24 also from outer shaft 23 along radially extending, in the upper-end surface of outer shaft 23 contact and fits into 22.

Rotating member 3 comprises the hub 31 of substantially cylindrical.The upper end of hub 31 surrounds through hole 31b.Rotating member 3 also comprises cylinder-shaped sleeve 32, and axle sleeve 32 shrink fit are advanced in the inner peripheral surface of hub 31.Rotating member 3 also comprises retaining member 33a and a plurality of (among the figure being four) dividing plate 33.The upper and lower end face of axle sleeve 32 is clipped between upper and lower thrust plate 24 and 25 by micro-gap (hereinafter referred to as the thrust gap) 32a and 32c, thereby upper and lower end face is respectively facing to upper and lower thrust plate 24 and 25.The inner peripheral surface of axle sleeve 32 is by the outer peripheral surface of micro-gap (hereinafter referred to as radial clearance) 32b facing to outer shaft 23.The inner peripheral surface of the hub 31 that exposes from the upper and lower end of axle sleeve 32 surrounds upper and lower thrust plate 24 and 25 and convex portion 21a.Has flange 31a near the lower end on the outer peripheral surface of hub 31.The outer peripheral surface that hub 31 is lower than flange 31a keeps magnet 5.The part that hub 31 is higher than flange 31a has uniform external diameter.The upper end of interior axle 22 is passed through hole 31b and is exposed to the outside of hub 31.Magnet 5 is facing to stator 4.Dividing plate 33 stretches to higher outer peripheral surface from the flange 31a of hub 31, to determine between the disk 6 along axial distance.Retaining member 33a is a fixing device, is used for a plurality of (figure is four) disks 6 and dividing plate 33 are fixed to hub 31.

The upper surface of the lower surface of last thrust plate 24 and lower thrust plate 25 is formed with many groove 24a and 25a, groove 24a and 25a with arc internally to outer bend.Groove 24a and 25a have the degree of depth of several microns (μ m), and arrange with the distance that is equal to each other diametrically.When rotating member 3 rotations, groove 24a and 25a produce pumping effect, that is, the air that will be present among the 32a of thrust gap is inwardly carried.Like this, generated the dynamic pressure of thrust gap 32a and 32c, and kept between fixed component 2 and the rotating member 3 along axial contactless state.Last half-sum lower half portion of the outer peripheral surface of outer shaft 23 is formed with many L shaped groove 23a and 23b, and groove 23a and 23b have the degree of depth of several microns (μ m).Groove 23a and 23b are along radially arranging with the distance that is equal to each other.Groove 23a and 23b produce pumping effect when rotating member 3 rotation, will be present in air among the radial clearance 32b towards the conveying of turning back of each groove.Like this, generated the dynamic pressure of radial clearance 32b, and kept between fixed component 2 and the rotating member 3 along contactless state radially.As mentioned above, constitute the part of thrust gap 32a and 32c and radial clearance 32b as hydrodynamic gas-lubricated bearing.

Then, will the action of motor 1 be described.

If with the coil of electric current supply stator 4, will between stator 4 and magnet 5, produce magnetic force so, hub 31 begins rotation with axle sleeve 32 by this magnetic force.Then, in above-mentioned thrust gap 32a and 32c and radial clearance 32b, produce dynamic pressure, and rotating member 3 has kept the contactless state with respect to fixed component 2 when continuing rotation.

When rotating member 3 rotation, fixed component 2 and rotating member 3 are because the heat from coil is tending towards expanding according to its thermal expansion coefficient, and the heat of coil is by powering and the rising of ambient temperature causes.In this embodiment, outer shaft 23 is by having thermal expansion coefficient (α ₀=6.2 * 10 ^-6/ ℃) Al ₂O ₃-TiC (aluminum oxide-titanium carbide-titanium) pottery is made.Axle sleeve 32 is by having thermal expansion coefficient (α ₁=5.1 * 10 ^-6/ ℃) Al ₂O ₃Make.Hub 31 is by having thermal expansion coefficient (α ₂=10.1 * 10 ^-6/ ℃) the plain stainless steel of iron make.With the external diameter 2R of outer shaft 23 facing to the part of axle sleeve 32 ₀Be made as 9.994mm, the internal diameter 2R of axle sleeve 32 ₁Be made as 10mm, and with the assembling diameter 2R between axle sleeve 32 and the hub 31 ₂Be made as 17.5mm.Hub 31 is higher than the external diameter 2R of the part of flange 31a ₃Be made as 20mm, and the fastening width δ of the assembled portion between hub 31 and the axle sleeve 32 is made as 10 μ m.Under these conditions, can according to following formula (10) obtain when temperature be 20 ℃ of radial clearances when being 80 ℃ variation radially with temperature, its result is 0.02 μ m or littler.Can obtain the value in formula (1) left side, its result is 5.25 μ m.The thickness t of hub 31 ₂Thickness t with axle sleeve 32 ₁Ratio t ₂/ t ₁Be 0.33, this has satisfied formula (1) and (2), and the surface pressure of necessity is applied to assembled portion.

Compare, if identical materials is used for axle sleeve 32 and outer shaft 23, radial clearance variable quantity radially is 0.3 μ m so.

Although the of the present invention single embodiment with various sizes, performance, hydraulic bearing, motor and hard disk drive has been described in the front, the present invention is not limited to these embodiments.Without departing from the scope of the invention, can make variations and modifications.

Claims (6)

1. aero dynamic bearing comprises:

Axle;

Axle sleeve, its inner peripheral surface is by the outer peripheral surface of micro-gap facing to described axle; And

The hub of substantially cylindrical, it applies surface pressure to the outside of described axle sleeve, and is assembled on the described axle sleeve, wherein

On at least one of the inner peripheral surface of the outer peripheral surface of described axle and described axle sleeve, be formed with dynamic pressure and generate groove, wherein

If the coefficient of linear expansion of described axle, axle sleeve and hub is defined as α respectively ₀, α ₁, α ₂, satisfy relation α so ₁＜α ₀＜α ₂

2. aero dynamic bearing as claimed in claim 1 is characterized in that,

If described axle sleeve during with 20 ℃ and the fastening width between the described hub are defined as δ, the assembling diameter between axle sleeve and the hub is defined as 2R ₂, and the difference between maximum serviceability temperature and 20 ℃ is defined as Δ T, relation (1) below satisfying so, and

If the thickness of axle sleeve is defined as t ₁, hub thickness be defined as t ₂, relation (2) below satisfying so:

2R ₂ΔT(α ₂-α ₁)≤δ …(1)

t ₂/t ₁≥0.25 …(2)。

3. motor with aero dynamic bearing comprises:

Axle;

Axle sleeve, its inner peripheral surface is by the outer peripheral surface of micro-gap facing to described axle; And

The hub of substantially cylindrical, it applies surface pressure to the outside of described axle sleeve, and is assembled on the described axle sleeve, wherein

On at least one of the inner peripheral surface of the outer peripheral surface of described axle and described axle sleeve, be formed with dynamic pressure and generate groove, wherein

If the coefficient of linear expansion of described axle, axle sleeve and hub is defined as α respectively ₀, α ₁, α ₂, satisfy relation α so ₁＜α ₀＜α ₂, and

Described motor also comprises the bearing that is used for fixing described axle, is installed in stator and magnet on this bearing, thereby this magnet is installed on the described hub facing to described stator.

4. motor as claimed in claim 3 is characterized in that,

In described aero dynamic bearing,

If described axle sleeve during with 20 ℃ and the fastening width between the described hub are defined as δ, the assembling diameter between axle sleeve and the hub is defined as 2R ₂, and the difference between maximum serviceability temperature and 20 ℃ is defined as Δ T, relation (1) below satisfying so, and

If the thickness of axle sleeve is defined as t ₁, hub thickness be defined as t ₂, relation (2) below satisfying so:

2R ₂ΔT(α ₂-α ₁)≤δ …(1)

t ₂/t ₁≥0.25 …(2)。

But 5. disk unit that the disk storage medium of stored information is installed on it, this disk unit comprises:

Housing;

Motor is used for rotating recording disc and is fixed on described housing;

And data access arrangement, be used for the data of read/write on described recording disc, wherein

Described motor comprises: axle; Axle sleeve, its inner peripheral surface is by the outer peripheral surface of micro-gap facing to described axle; And the hub of substantially cylindrical, it is installed as to the outside of described axle sleeve and applies surface pressure,

Described motor also comprises aero dynamic bearing, wherein at least one of the inner peripheral surface of the outer peripheral surface of described axle and described axle sleeve, is formed with dynamic pressure and generates groove,

If the coefficient of linear expansion of described axle, axle sleeve and hub is defined as α respectively ₀, α ₁, α ₂, satisfy relation α so ₁＜α ₀＜α ₂,

Described motor also comprises the bearing that is used for fixing described axle, is installed in stator and magnet on this bearing, thereby this magnet is installed in the described hub facing to described stator.

6. hard disk drive as claimed in claim 5 is characterized in that,

In described aero dynamic bearing,

If the fastening width between described axle sleeve and the described hub is defined as δ, the assembling diameter between axle sleeve and the hub is defined as 2R ₂, and the difference between maximum serviceability temperature and 20 ℃ is defined as Δ T, relation (1) below satisfying so, and

If the thickness of axle sleeve is defined as t ₁, hub thickness be defined as t ₂, relation (2) below satisfying so:

2R ₂ΔT(α ₂-α ₁)≤δ …(1)

t ₂/t ₁≥0.25 …(2)。

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