JPH11514779A - Spindle motor for disk drive with hydrodynamic bearing containing viscosity-optimized lubricant - Google Patents

Abstract

The disk drive 10 includes a housing 12, a center axis 80, a fixed member 34 fixed with respect to the housing and coaxial with the center axis, and a rotatable member rotatable about the center axis with respect to the fixed member. 36. A stator 38 is fixed with respect to this housing. A rotor 70 is supported by the rotatable member and is magnetically coupled to the stator. At least one data storage disk 16 is mounted coaxially with the rotatable member. A fluid bearing 37 interconnects the fixed and rotatable members and includes a base fluid formulation 84. The base fluids are selected such that one viscosity is greater than the desired viscosity of the drive, the other is less than the desired viscosity, and the viscosity of the formulation is within a selected range of the desired viscosity.

Description

DETAILED DESCRIPTION OF THE INVENTION               Has a hydrodynamic bearing containing a viscosity-optimized lubricant                   Spindle motor for disk drive                                Background of the Invention   The present invention relates to a spindle motor for a disk drive / data storage device, and For details, refer to the lubricating fluid optimized for hydrodynamic bearings in this spindle motor. You.   Disk drives known as “Winchester” type disk drives Data storage devices are well known in the art. Winchester Disc The drive uses digital data in a thin layer of magnetizable material on the surface of a rotating disk. Read and write data. Reading and writing operations are performed via the transducer carried by the slider body. Do. The slider and transducer are sometimes collectively referred to as a head, and typically include A single head is associated with the disk surface. These heads are operated under the control of electronic circuits. A plurality of circular and concentric data tracks on this disk surface are Selectively moved to one of the Each slider body has an automatic air bearing surface Including. As the disk rotates, it draws air under the air bearing surface, It lifts the slider 100 to 150 microns above the disk surface and floats it Generates a rising force.   The most commonly used type of actuator in modern disk drive products is , A rotary movable coil actuator. The disc itself is typically a brush It is mounted "stacked" on the hub structure of a DC spindle motor. spindle The rotation speed of the motor is determined by the timing of the commutation signal to the stator winding It is controlled accurately by a motor drive circuit device that controls both power and power. Typical The spindle motor speed was in the range of 3600 rpm. The current technology is Increase the speed of the pindle motor to 7200 rpm, 10,000 rpm and more Increased.   One of the main sources of noise in disk drives and data storage devices is the spindle motor. It is. Disk drive manufacturers have recently introduced spindle motors with traditional ball bearings. Replace roller bearings with "fluid" bearings, such as hydrodynamic or hydrostatic bearings. And began to pay attention. Fluid bearings rely on a fluid film separating the bearing surfaces, and Are much quieter and generally have less vibration. Dynamic pressure bearings A self-pumping bearing that internally generates pressure to maintain separation. Static pressure Bearings require an external source of pressurized fluid to maintain fluid film separation. For fluid bearings The relative motion between the bearing surfaces at this point occurs completely within the fluid film so that the bearing surfaces do not come into contact. Shear element.   The situation is that the solid bearing surfaces often come into contact with each other and the upright stresses Typical boundary lubrication or elastic flow, such as occurring, roller bearings, ball bearings and plain bearings It is different from the use of body lubrication. In these boundary lubrication applications, the main purpose of the lubricant is Modifying the interface to reduce wear and friction. The chemical properties of the lubricant interface Most important.   In hydrodynamic bearing applications, completely different fluid properties are important for the function of this bearing It is. Boundary properties are only important when starting and stopping disk rotation. Normal In operation, the most important property is the bulk property. Use for disk drive applications Fluid bearings intended for this purpose have low power loss and can be used with limited oil supply. Small units that need to be suitable for a long life without escaping It is. Commercially available lubricants are mostly used for small hydrodynamic bearing applications in disk drives. It is inappropriate in some way.   Lubricant properties that must be controlled and the degree of control that must be achieved The degree is specific to small fluid bearings for disk drives. These characteristics include electrical Power loss, viscosity and its temperature dependence, surface migration, vapor pressure and evaporation rate, oxidation resistance Resistance and corrosion resistance, rheology, boundary properties and system compatibility. The viscosity is Determines power loss and bearing stiffness, and is relatively constant over various operating conditions Should. Lubricants should have small surface movement to prevent crawling out of the bearing is there. Lubricants should have high oxidation and reaction resistance and extend bearing life It is. Rheology is a deformation and flow response to shear.   The lubricant should also be compatible with the other materials of the disk drive. For example, lubrication The surface movement or outgassing of the agent increases the adhesion friction between the head and the disc, Interaction between the head and the disc by reducing the structure or operation of the head Should not spoil. Therefore, the formulation of a fluid with appropriate hydrodynamic bearing properties is Different considerations are needed for fluids intended for lubricants. Other disadvantages of commercially available lubricants are: Manufacturers often do not provide the exact composition of their lubricants, making disk drive It is possible that some additives may be included that are not compatible with the sensible operation.                                Summary of the Invention   The disk drive data storage system of the present invention comprises a housing, a central axis, A fixing member fixed with respect to the housing and coaxial with the central axis, and A rotatable member rotatable about the central axis with respect to the fixed member is included. Stator Are fixed with respect to this housing. The rotor is It is supported and magnetically coupled to this stator. At least one data entry A storage disk is mounted coaxially with the rotatable member. Fluid bearing Interconnecting a fixed member and a rotatable member of a base fluid formulation, the viscosity of which is The base fluid formulation gives the hydrodynamic bearing the desired power consumption and stiffness. Thus, the desired viscosity is within the selected range. This formulation of the base fluid will provide the desired viscosity. A first base fluid having a first viscosity greater than a second viscosity and a second A second base fluid having a viscosity of   In a preferred embodiment, the desired viscosity is between 4 and 10 centipoise (cP) at 70 ° C. The exact absolute viscosity is between. The base fluid is blended to make the total viscosity 10% of the desired viscosity. %, Most preferably within 2-5%. Besides, this basic fluid Has a viscosity index of at least 110 and an evaporation range of volume to surface area ratio ( V / A) Based on about 1.9 to 2.0 mm, 1.0 × 10^-3mg / d-mm^TwoLess than It is.   Suitable base fluids include perfluoropolyethers, esters, synthetic hydrocarbons and And highly refined mineral hydrocarbons. The most preferred base fluids are diesters , Polyol esters and polyalphaolefins. These basic fluids Can be mixed in various combinations, for example, a combination of only esters, Combination of only alpha olefins or at least one ester and With It can be a combination of only one polyalphaolefin.   These most preferred base fluids are petroleum-based coals, which are conventional standard fluid lubricants. It offers several advantages in disk drive applications over hydrogenated, such as viscosity Improved temperature relationship, low evaporation, low vapor pressure, low surface movement, oxidation resistance Performance is improved and boundary performance is similar, but can be easily improved with additives All are compatible with the other materials in Eve and have a pure chemical composition. It has been found that the characteristics of this can be well controlled.                             BRIEF DESCRIPTION OF THE FIGURES   FIG. 1 is a plan view of a disk drive data storage device according to the present invention.   FIG. 2 is a sectional view of a dynamic pressure spindle motor according to the present invention.   FIG. 3 shows, for clarity, one of the hydrodynamic spindle motors according to line 3-3 in FIG. It is the schematic sectional drawing which removed a part.                          Detailed Description of the Preferred Embodiment   The present invention provides a dynamic pressure optimized lubricating fluid composition for disk drive specific requirements. Disk drive and data storage device with bearing or hydrostatic bearing spindle motor It is a place. FIG. 1 is a plan view of a typical disk drive 10 in which the present invention is useful. FIG. The disk drive 10 includes a housing base 12 and an upper cover 1. There are four. The housing base 12 forms a sealed environment in combination with the upper cover 14. Makes and protects internal components from contamination by elements from this sealed environment.   The disk drive 10 is further provided with a spindle by a disk clamp 18. There is a disk pack 16 mounted for rotation on a motor (not shown) . The disc pack 16 is mounted so as to rotate together about a central axis. There are several individual disks. Each disk has an associated head 20, the The head is mounted on the disk drive 10 in communication with the disk surface. ing. In the example shown in FIG. 1, the head 20 is supported by the bent portion 22 and then the head 20 is It is mounted on the head mounting arm 24 of the actuator body 26. As shown in FIG. Actuators are of the type known as rotary moving coil actuators , A voice coil motor (VCM), generally designated 28. Voice coil motor 28 pivots the actuator body 26 together with the head 20 attached thereto. G Rotating about axis 30 moves head 20 along arcuate path 32 to the desired data track. Place it on the rack. FIG. 1 shows a rotary actuator. Also available for disk drives with other types of actuators, such as tutors It is for.   FIG. 2 is a sectional view of the hydrodynamic bearing spindle motor 32 according to the present invention. spin The dollar motor 32 includes a fixing member 34, a hub 36, and a stator 38. FIG. In the embodiment shown in FIG. 1, the fixing member is fixed to the base 1 by the nut 40 and the washer 42. 2 is a shaft fixed and attached. The hub 36 is connected to the shaft 3 via a dynamic pressure bearing 37. Interconnected with the shaft 34 so as to rotate about 4. The bearing 37 has a radial There are facing working surfaces 44 and 46, and axial working surfaces 48 and 50. On axis 34 Has fluid ports 54, 56 and 58, which supply a lubricating fluid 60, It assists in circulating fluid along the working surface of the bearing. The lubricating fluid 60 is provided in a known manner. Is supplied to the shaft 34 by a fluid source (not shown) coupled to the interior of the shaft 34 at.   The spindle motor 32 further includes axial working surfaces 48 and 5 of the dynamic pressure bearing 37. There is a thrust bearing 45 forming zero. The counter plate 62 presses the operating surface 48 Immediately, this dynamic pressure bearing is stabilized in the axial direction, and the hub 36 is To place. An O-ring 64 is provided between the counter plate 62 and the hub 36 And seals the dynamic pressure bearing. In this seal, the dynamic pressure fluid 60 The escape from between the seat 62 and the hub 36 is prevented.   The hub 36 includes a central core 65 and a disk pack 16 (shown in FIG. 1). There is a disk carrying member 66 that supports it for rotation about. Disk drive The disc 16 is supported by a disc clamp 18 (also shown in FIG. 1). It is held on a member 66. A permanent magnet 70 is mounted on the outer diameter of the hub 36. Thus, it acts as a rotor of the spindle motor 32. The core material 65 is a magnetic material And act as a back iron for the magnet 70. The rotor magnet 70 is an integral ring. Or a plurality of individual magnets spaced around the hub 36. Can also be made. The rotor magnet 70 magnetizes to create one or more magnetic poles.   The stator 38 is attached to the base 12 and includes a stator stack 72 and a stator Includes winding 74. Stator winding 74 is attached to stator stack 72. The stator winding 74 is configured such that the rotor magnet 70 and the hub 36 rotate about a central axis 80. To be radially spaced from the rotor magnet 70. The stator 38 Already, such as several C clamps 76 secured to base 12 by bolts 78 It is attached to the base 12 in a known manner.   The commutation pulse applied to the stator winding 74 generates a rotating magnetic field, which is In communication with 70, the hub 36 is rotated about a central axis 80 of the bearing 37. Commutation path The DC current pulse for which the polarization has been selected The rotor magnet is driven toward the motor winding and its speed is controlled.   In the embodiment shown in FIG. 2, the spindle motor 32 is a "bottom of the hub" type motor, The axial position of the motor 38 is below the hub 36. The radial position of the stator 38 is also The stator windings 74 are secured to the inner diameter surface 82 of the stack 72. Substitute In an embodiment, the stator is located within the hub rather than under the hub. Stator half The radial position may be inside or outside the hub. In addition, the spindle motor is It can have a fixed axis as shown, or have a rotating axis. Axis of rotation In a spindle motor, the bearing has a rotating shaft and an outer fixed sleeve coaxial with the rotating shaft. between.   FIG. 3 shows, for clarity, the dynamic spindle motor 32 according to line 3-3 in FIG. FIG. 3 is a schematic sectional view partially removed from FIG. The stator 38 includes a laminate 72 and a stator It includes windings 74, which are coaxial with the rotor magnet 70 and the central core 65. S The data winding 74 is composed of phase windings W1, V1, U1, W wound around the teeth of the laminate 72. 2, V2 and U2. These phase windings intersect perpendicularly with the central axis 80. It is made of a coil having a coil axis. For example, the phase winding W1 is It has a coil axis 83 perpendicular to 80. A radial working surface 44 of the hydrodynamic bearing 37; 46 is formed by the outer diameter surface of the shaft 34 and the inner diameter surface of the central core 65. Radial working surface 4 4 and 46 are separated by a lubricating fluid 84 that maintains gap C during normal operation. Have been.                          1.Optimization of lubricant viscosity   According to one aspect of the present invention, the lubricating fluid is capable of accurately defining fluid viscosity. Therefore, the power loss and bearing load capacity for a specific design hydrodynamic bearing that uses the fluid (Ie, bearing stiffness) with a base fluid formulation selected to optimize.   Power consumption (P) and bearing stiffness (K) are proportional to fluid viscosity according to the following relationship: , Where μ_BIs the absolute viscosity of the fluid formulation, ω is the rotation speed of the hub, and C is the radial operation The gap between surfaces 44 and 46 (or at axial working surfaces 48 and 50) or The clearance, and R, is the characteristic length of the radial and / or axial working surface.   In disk drive applications with small hydrodynamic bearings, power capacity and load capacity are important. It is important. Therefore, specify the exact viscosity at any particular temperature for the lubricating fluid. It is desirable that the desired viscosity be obtained so that the size and structure of the spindle motor It fluctuates. Lubricants of any viscosity value are not commercially available. The lubricating fluid of the present invention, Each includes a blend of base fluids of similar chemical composition but different viscosities. These groups The basic fluid is accurately compounded to reduce the overall viscosity to the desired viscosity, preferably within 10%, Is also preferably within 2 to 5%. Formulate the basic fluid according to the following relationship, However, μ_B   = Temperature T of the formulation of the base fluid_cAbsolute viscosity at T_c   = Temperature at the desired viscosity; ν_n   = Kinematic viscosity of the base fluid n; n = 1 an integer greater than 1; ρ_n   = Density of the base fluid n; χ_n   = Weight ratio of base fluid n; and χ₁  + Χ_Two  … +… Χ_n  = 1_o   For example, if n = 2 and the desired kinematic viscosity of the formulation is ν, then ν₁> Ν> ν_TwoAnd ν₁ And ν_TwoBy properly selecting, a lubricating fluid having a desired viscosity can be obtained.   Suitable base fluids include perfluoropolyethers, synthetic hydrocarbons and highly There are refined (highly purified) mineral hydrocarbons. The most preferred base fluids include Diester, polyol ester and polyalphaolefin (PAO) You. These base fluids can be formulated in various combinations, however, Steal-only combinations, polyalphaolefin-only combinations, and at least Contains a combination of only one ester and at least one polyalphaolefin Is preferred. A single ester or polyalphaolefin has the desired viscosity. However, it can be used in alternative embodiments of the invention if other desired properties are satisfied. Wear.   These most preferred base fluids are petroleum-based coals, which are conventional standard fluid lubricants. It has been found that there are several advantages in disk drive applications over hydrogen hydride. These base fluids have very low temperature-dependent viscosity, low evaporation and low vapor pressure. With low surface migration, improved oxidation resistance, and similar boundary performance, Easy to upgrade, compatible with other materials in the disk drive, and pure Because the chemical composition is known, all properties can be well controlled. Therefore, these fluids Minimizes head and disk interface degradation and reduces bearing and disk drive Make the life longer.   In a preferred embodiment, these base fluids are formulated to provide a volume to surface area ratio (V / A) of about Accurate 4-10 centipoise (cP) at 70 ° C. based on 1.9-2.0 mm Absolute viscosity, viscosity index of at least 110, and 1.0 × 10^-3mg / d-mm^Two Evaporations in the range of less than are obtained.   In addition, these base fluids are due to outgassing of this fluid from the bearings to the disc. The contribution to the adhesion friction (“stiction”) between the head and the disc Existing under various conditions such as hot or humid conditions It is preferably selected to be less than or equal to the contribution of the chemical or lubricant. These chemicals or lubricants include, for example, grease and ferrofluid seals. is there.                2.Incorporating selected additives into the lubricating fluid   In another aspect of the invention, the lubricating fluid is a high viscosity index base fluid (or base fluid). Compound) and the contact between the head and disc It contains a mixture of additives selected to be effective to resist.   The viscosity of the lubricating fluid of the hydrodynamic bearing decreases with increasing temperature. This is the power loss And lower the bearing load capacity for a given thickness of fluid. Small dynamic bearings Power loss and large fluctuations in bearing load capacity are I can't do it.   Viscosity index (VI) is any method that represents the sensitivity of a lubricant to viscosity-temperature, Often interpreted as the temperature dependence of viscosity. Viscosity finger of a fluid with a given viscosity A higher number indicates that the viscosity of the fluid does not change much with temperature. Power consumption Is an important parameter for small dynamic bearings in disk drives. The VI index is desirable. Typical viscosity indices for several classes of fluids are Shown in Table 1:   An ester fluid contains oxygen, as well as hydrogen and carbon, and is an ester Fluids are unique compared to natural and synthetic hydrocarbon fluids for disk drive applications Show the benefits. These benefits include high viscosity index, high oxidation resistance, improved boundary moisture It has lubricating properties, low surface mobility compared to synthetic hydrocarbons, and low evaporation.   For example, commercially available diester fluids have a high VI index and good oxidation resistance, Poor contact resistance to metal contact. This converts the commercially available diester fluid into Is used in small dynamic pressure bearings that have very little Restrict things to do.   Commercial fluids contain sufficient metal deactivating additive to last for the life of the bearing. Not in. In addition, most commercially available fluids do not fit at the head-disk interface. Contains a lot of ingredients. Often, manufacturers control the exact composition of commercially available fluids. Not in. Use of these fluids unintentionally degrades the performance of the disk drive May be.   The lubricating fluid of the present invention may comprise a diester fluid or polyalphaolefin. Formulation of a base fluid with high VI index and anti-oxidation, corrosion resistance and metal Giving the deactivation properties that this fluid conforms to the head-disk interface, Significantly higher contact degradation resistance than commercial ester and / or synthetic hydrocarbon formulations And combinations of additives selected to show   Suitable types of antioxidants include amines (arylamines), phenols or There are nitrogen and oxygen containing inhibitors, such as mixtures of both. Most preferred type of acid Antioxidants include butylhydroxytoluene (liquid hindered phenol), alcohol Kildiphenylamine, phenyl alpha naphthylamine, or a combination thereof There are two or more combinations of antioxidants. Of these additives in the basic lubricating fluid Preferred treatment levels are between 0.25% and 3% by weight.   Suitable types of rust and corrosion inhibitors or metal passivators include metal sulfones Of acid salts, long-chain amines, carboxylic acid derivatives, thiadiazoles and triazoles There are conductors, as well as amine phosphates. The most preferred types are synthetic or petroleum sulfones Calcium, synthetic or petroleum barium sulfonate, alkenyl succinic acid derivatives and And triazole derivatives. Preferred treatment of these additives in the basic lubricating fluid The processing level is 0.02% to 0.5% by mass.   The lubricating fluid of the present invention further improves wear resistance, high pressure metal contact characteristics and friction characteristics. Contains additives to improve. Preferred additives of this type include dialkyldithiophosphates , Alkyl and allyl disulfides and polysulfides, dithiocarba Neutral phosphorus such as mate, alkyl phosphate, molybdenum complex, triphenyl phosphate Acid esters (triallyl and trialkyl) or two of these additives There are combinations of the above. The most preferred antiwear additives include dialkyldithiophosphorous acid Lead, molybdenum disulfide, liquid amine phosphate, and propylated and butyl Triphenyl phosphate. Preferred treatment of these additives in basic lubricating fluids The level is between 0.1% and 4% by mass.   Fats and / or synthetic hydrocarbons based on high VI index diesters and the above Additive formulation, more resistant to contact degradation than commercially available ester or synthetic hydrocarbon formulations , A dynamic pressure fluid is obtained. Various formulations were tested and the head and disc It was found to fit the interface. These formulations are applied between the head and the disc. Does not significantly increase friction and causes other interference at the head-disk interface Was. These blends can be used at high loads and high temperatures against refined paraffinic petroleum. It was also found to be excellent in power consumption and lifetime.                3.Application of improved fluid with high shear strength viscosity index   In another aspect of the invention, the lubricating fluid is combined with a base fluid and a highly shear resistant viscosity modifier (" VI improvers "). VI improvers reduce the temperature dependence of the viscosity of the base fluid. cut back. The temperature dependence of viscosity is very important, and the high temperature dependence It is not desirable for the function of small bearings for dollar motors. To minimize this effect, The selected commercially available polymer is blended with the base fluid according to the present invention to form a spindle motor. The improvement was actually measured by the temperature / power consumption curve. Power consumption is less dependent on temperature And observed.   In the preferred embodiment of the present invention, the temperature and viscosity behavior is unsuitable, but otherwise Given a suitable base fluid, the high molecular weight soluble polymer is 5 to 5 wt. Add to the base fluid at a concentration of 50%. The molecular weight of this polymer is 10,000 ~ 1,000,000 daltons is preferred. Suitable polymer VI improvers include Include, but are not limited to, acrylates, polyisoprenes, and polystyrene. Not.   Under the conditions encountered in the small hydrodynamic bearing according to the invention, the shear rate is higher than 106 per second. is there. The shear rate is determined by the bearing working surface with respect to the width of the bearing gap (gap C shown in FIG. 3). Is defined as the rate of change in speed. Shear conditions between bearing surfaces can destroy polymer Limits the life of the VI improver. The VI effect, among other factors, Because of the mer chain length, the effectiveness of the VI enhancer is reduced by shear failure.   In a further preferred embodiment of the present invention, the selected polymer VI improver is a solid polymer Has a tensile strength of at least 700 kg / cm^Two(10,000 psi) and heat resistant A class of high shear failure resistant poly with a degradability of at least 250 ° F (121 ° C) Belongs to Ma. The polymer thus has a shear strength. Polymers of this class Include polyphenylene sulfide, polyetheretherketone, and polyetherether. There are, but are not limited to, soluble forms of materials such as ruimide.   In an even more preferred embodiment, the solid polymer has a tensile strength of at least 984 kg. / Cm^Two(14,000 psi), with heat degradation resistance of 260 ° C (500 ° F) or more It is. This class of polymers includes polyamide-imides, polyimides, But not limited to nzoimidazole, and liquid crystal polymer. That In an even more preferred embodiment, the solid polymer has a tensile strength of at least 1,400 k g / cm^Two(20,000 psi) with a heat aging resistance of at least 371 ° C (70 ° C). 0 ° F). This class of polymer includes back tubes and other back But not limited to carbon monsterfullerene.   In a most preferred embodiment, the polymer VI enhancer has the properties of the preceding group, and Which provide this fluid with antioxidant and metal deactivation protection, as discussed above. Functional or chemically modified.   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize the spirit and scope of this invention. It can be seen that changes can be made in form and detail without departing from the scope. Would.

────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventors Reutold, Hans             United States 95060 California             Santa Cruz, Gurkey Street             849 (72) Inventor Jennings, David, Jay.             United States 95060 California             Santa Cruz, Novel Number 2 Be             660 (72) Inventor Ladd, Gregory, Eye.             United States 95003 California             Aptos, Dolphin Drive 1496 (72) Inventor Heine, Gunter, Kay.             United States 95003 California             Aptos, Driftwood Court 143

Claims (1)

[Claims] 1. A disk drive data storage system comprising: a housing; a central axis; a fixed member fixed with respect to the housing and coaxial with the central axis; a stator fixed with respect to the housing; and rotatable about the central axis with respect to the fixed member. A rotatable member; a rotor supported by the rotatable member and magnetically coupled to the stator; at least one data storage disk coaxially mounted to the rotatable member; a head attached to the data storage disk. An actuator for supporting in close communication therewith; and a fluid bearing interconnecting the fixed member and the rotatable member, comprising a composition of a base fluid, wherein the base fluid in the composition is replaced by the base fluid. One of the viscosities for this disk drive data storage system Bearings selected such that the viscosity of the other base fluids is less than the desired viscosity and the viscosity of the formulation of these base fluids is within a selected range of the desired viscosity. system. 2. The disk drive / data storage system of claim 1, wherein said selected range is effective to provide said hydrodynamic bearing with a desired power consumption and stiffness. 3. The disk drive data storage system of claim 1, wherein the viscosity of the base fluid formulation is within 10% of the desired viscosity. 4. 2. The disk drive data storage system of claim 1, wherein the viscosity of the base fluid formulation is within 2-5% of the desired viscosity. 5. 2. The disk drive data storage system of claim 1, wherein the viscosity of the base fluid formulation is 4 to 10 centipoise (cP) absolute at 70C. 6. The disk drive data storage system of claim 1, wherein the formulation of the base fluid has a viscosity index of at least 110. 7. 3. The disk drive data storage system of claim 1 wherein the range of evaporation of the base fluid formulation is 1.0.times. Based on a volume to surface area ratio (V / A) of about 1.9 to 2.0 mm. A system that is less than 10 ⁻³ mg / d · mm ² . 8. The disk drive data storage system of claim 1, wherein the formulation of the base fluid comprises a base fluid selected from the group consisting of perfluoropolyethers, esters, synthetic hydrocarbons, and mineral hydrocarbons. 9. 9. The disk drive data storage system of claim 8, wherein the formulation of the base fluid comprises a base fluid selected from the group consisting of diesters, polyol esters and polyalphaolefins. 10. 3. The disk drive data storage system of claim 1, wherein the formulation of the base fluid comprises a formulation of at least two esters with different kinematic viscosities. 11. 2. The disk drive data storage system of claim 1, wherein the formulation of the base fluid comprises a formulation of at least two polyalphaolefins with different kinematic viscosities. 12. The disk drive data storage system of claim 1, wherein the formulation of the base fluid comprises a formulation of at least one ester and at least one polyalphaolefin having different kinematic viscosities. 13. The disk drive data storage system of claim 1, further comprising: an actuator; and a head supported by the actuator for communicating with and in close proximity to the data storage disk, wherein the head and the disk are bounded by A system having a surface, wherein the formulation of the fluid conforms to this interface. 14． A disk drive comprising: a housing; a central axis; a fixed member fixed with respect to the housing and coaxial with the central axis; a stator fixed with respect to the housing; a rotatable member rotatable about the central axis with respect to the fixed member; A rotor supported by the rotatable member and magnetically coupled to the stator; at least one data storage disk coaxially mounted to the rotatable member; and a head proximate to and adjacent to the data storage disk. actuator supported to contact; with well fluid bearing interconnecting the rotatable member and the fixing member, comprises a blend of n basic flow body, the absolute viscosity mu _B is selected for the disk drive desired Within a selected range of viscosities, where n is an integer greater than 1. These basic fluids are formulated according to the following relationship, Where T is the temperature, _Tc is the temperature at the desired viscosity, ν _n is the kinematic viscosity of the base fluid n, ρ _n is the density of the base fluid n, χ _n is the weight ratio of the base fluid n, χ ₁ + Χ ₂ ... +... Χ _n = 1 and a bearing where ν ₁ >ν> ν ₂ where the kinematic viscosity of the formulation of the base fluid is ν. 15. 15. The disk drive of claim 14, wherein the selected range is effective to provide the hydrodynamic bearing with desired power consumption and stiffness. 16. 15. The disk drive of claim 14, wherein the absolute viscosity [mu] _B of the base fluid formulation is within 10% of the desired viscosity. 17． 15. The disk drive of claim 14, wherein the absolute viscosity [mu] _B of the base fluid formulation is within 2-5% of the desired viscosity. 18. 15. The disk drive of claim 14, wherein the formulation of the base fluid has an absolute viscosity [mu] _B of 4-10 centipoise (cP) at 70 [deg.] C. 19. 15. The disk drive of claim 14, wherein the formulation of the base fluid has a viscosity index of at least 110. 20. 15. The disk drive of claim 14, wherein the range of evaporation of the basic fluid formulation is 1.0 x ^10-3 mg based on a volume to surface area ratio (V / A) of about 1.9 to 2.0 mm. / D · mm ² disk drive. 21. 15. The disk drive of claim 14, wherein the base fluid formulation comprises a base fluid selected from the group consisting of perfluoropolyethers, esters, synthetic hydrocarbons, and mineral hydrocarbons. 22. 22. The disk drive of claim 21, wherein the base fluid formulation comprises a base fluid selected from the group consisting of diesters, polyol esters, and polyalphaolefins. 23. 15. The disk drive of claim 14, wherein the base fluid formulation comprises at least two ester-only formulations having different kinematic viscosities. 24. 15. The disk drive of claim 14, wherein the base fluid formulation comprises at least two ester-only formulations having different kinematic viscosities. 25. 15. The disk drive of claim 14, wherein the formulation of the base fluid comprises a combination of at least one ester and at least one polyalphaolefin having different kinematic viscosities. 26. A fluid bearing disk drive lubricating fluid for lubricating a fluid bearing in a disk drive having a viscosity that is within 2-5% of a desired viscosity to provide the desired power consumption and stiffness to the fluid bearing. And a formulation of the base fluid; and wherein the formulation of the base fluid has a first base fluid having a first viscosity greater than the desired viscosity and a second base fluid having a second viscosity less than the desired viscosity. 2. Lubricating fluid including basic fluid.