Fluid bearing with a variable depth groove

A fluid bearing that utilizes a variable depth groove is described. The fluid bearing includes two surfaces that are rotatable relative to one another, with a groove on at least one of the surfaces. The floor of the groove is non-constant in depth.

TECHNICAL FIELD

The present invention relates to hard disk drives, and in particular to fluid bearings used in hard disk drives.

BACKGROUND ART

Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.

The basic hard disk drive model was established approximately 50 years ago and resembles a phonograph. That is, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm with a suspended slider is utilized to reach out over the disk. The arm carries a head assembly that has a magnetic read/write transducer or head for writing or reading information to or from a location on the disk. The complete head assembly, e.g., the suspension and head, is called a head gimbal assembly (HGA).

In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.

The spindle assembly includes bearing components—specifically, fluid dynamic bearings—that support rotation of the disk. These fluid dynamic bearings create fluid pressure between the stationary and rotating sections of the spindle assembly. Current fluid dynamic bearing geometries have tradeoffs with respect to performance metrics such as stiffness, damping, stability (the propensity to ingest air), and running torque (power consumption).

SUMMARY

A fluid bearing that utilizes a variable depth groove is described. The fluid bearing includes two surfaces that are rotatable relative to one another, with a groove on at least one of the surfaces. The floor of the groove has a non-constant depth measured from the groove borders.

BEST MODES FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the alternative embodiments of the present invention; a fluid bearing that utilizes variable depth grooves. While the invention will be described in conjunction with the alternative embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

The discussion will begin with an overview of a fluid bearing in conjunction with its operation within a hard disk drive spindle motor and components connected therewith. The discussion will then focus on embodiments of a fluid bearing with variable depth grooves.

FIG. 1shows a disk drive spindle motor in which fluid bearing designs of the present invention are useful; however, the present invention is not so limited. That is, the fluid bearings to be described below may be useful in other applications.

FIG. 1is a vertical sectional view of a shaft100rotating within a sleeve102and supporting a hub104for rotation with the shaft. The hub104supports one or more disks for rotation within the disk drive. To provide a stable support between the sleeve102and shaft100, fluid dynamic journal bearings108and110are provided in the gap112between the inner surface of sleeve102and the outer surface of shaft100. An exemplary groove pattern115is shown in the two groove bearing regions108and110. The grooves115generate hydrodynamic pressure to maintain space between the outer surface of the shaft100and the inner surface of the sleeve102. The grooves115may be formed on either or both of the inner and outer surfaces.

In the example ofFIG. 1, the grooves are slanted upward and downward relative to the direction of rotation120, their outer ends are directed forward, and their inner ends are directed rearward relative to the direction of rotation, in order to drive the fluid toward the apex of each of the grooves115. Dynamic pressure is generated in the gap between the surface of the shaft100and the surface of the sleeve102due to the relative rotary motion of the shaft and sleeve. As the shaft or sleeve moves in the direction of arrow120, fluid between the shaft and sleeve flows along each groove. Thus, the grooves115both accumulate and retain fluid in the gap between the shaft100and the sleeve102, and pressurize the fluid to increase the bearing load.

The embodiment ofFIG. 1also utilizes a thrust bearing138between the plate140on the end of shaft100or end of shaft142and the facing surface144of counterplate146. Grooves may be formed on either surface of the thrust bearing, pumping fluid along the grooves toward the center axis101. The rotational action of the grooves both accumulates fluid in the grooves and maintains fluid in the gap, and generates the necessary pressure to boost the shaft and surface142above the facing surface of the counterplate to allow for free relative rotation without frictional contact.

The grooves on the thrust bearing138can also be shaped in accordance with the principals of the present invention in order to enhance the stiffness, damping and stability characteristics of the bearing while not increasing running torque.

The groove shapes of the present invention may be advantageously employed on the bearing surfaces of fluid bearings shown in the following figures; however, the invention is not limited to these motor designs. In a journal bearing, grooves may be formed on the outer surface of the shaft, the inner surface of the sleeve or part of each surface. Grooves also may be used on thrust bearing surfaces, either on the thrust plate or counter plate; or on either surface of a conical or spherical bearing. The figures that follow illustrate a number of exemplary groove shapes according to embodiments of the present invention.

With reference toFIG. 2, a view of a fluid bearing300with an exemplary groove303is illustrated.FIG. 2illustrates a single groove; however, there may be more than one groove. In the present embodiment, the groove borders301and302can be represented as linear, continuous line segments that separate the groove303from the land of the bearing surface.

With reference toFIG. 3, a cross-sectional view of an exemplary variable depth groove330with a floor336that is linear and continuous is illustrated. In the present embodiment, the groove floor336can be represented as a linear, continuous line between each of the groove walls333and334. The depth of the groove330is non-constant. In other words, the groove walls333and334are not of the same length.

With reference toFIG. 4, a cross-sectional view of an exemplary variable depth groove340with a floor345,346,347that is linear and discontinuous is illustrated. In the present embodiment, the groove floor345,346and347between each of the groove walls343and344consists of a number of linear segments that in totality are discontinuous. The depth of the groove340is non-constant. In other words, the groove walls333and334are not of the same length.

With reference toFIG. 5, a cross-sectional view of an exemplary variable depth groove350with a floor355that is non-linear and continuous is illustrated. In the present embodiment, the groove floor355is a non-linear, continuous line between each of the groove walls353and354. The depth of the groove350is non-constant. In other words, the groove walls353and354are not of the same length.

With reference toFIG. 6, a cross-sectional view of an exemplary variable depth groove360with a floor that is non-linear and discontinuous is illustrated. In the present embodiment, the groove floor includes a linear segment366and non-linear segments365and367. The depth of the groove360is non-constant. In other words, the groove walls363and364are not of the same length.

While the embodiments illustrated inFIGS. 2-6show specific instances of groove shapes, the present invention is suitable to alternative shapes. Likewise, different combinations of shapes can be used depending upon the application. That is, for example, a fluid bearing may incorporate grooves all of the same shape, or some combination of the various general shapes described above.

Modeling simulation results based on the use of fluid bearings according to the embodiments of the present invention demonstrate that changing groove shape to change performance characteristics such as stiffness, damping, and stability does not proportionally change running torque. In other words, stiffness, damping and stability metrics can be positively changed without a commensurate negative effect on running torque. More specifically, a groove shape can be selected that increases stiffness and damping, for example, but decreases torque (and thus decreases power consumption).

Furthermore, the different groove shapes may affect the aforementioned performance characteristics by different amounts. Thus, as mentioned above, a groove shape can be selected depending upon the specific requirements of the intended application. In other words, a groove shape can be selected that provides a desired balance between the various performance characteristics.

Embodiments of the present invention, a fluid bearing that utilizes a variable depth groove to increase design flexibility of performance characteristics, are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.