Patent Application
20070013240
1. Field
Various aspects of the present invention relate generally to spindle motors, and in particular, to Fluid Dynamic Bearing (FDB) motors for use in disc drives.
2. Related Art
Magnetic disc drives are well known for magnetically storing information. Broadly speaking, a magnetic disc drive includes a magnetic disc that rotates at high speed as a transducing head “flies” over a surface of the disc. The transducing head records information on the disc surface by impressing a magnetic field on the disc. Information is read back using the transducing head by detecting magnetization of the disc surface. The transducing head is moved radially across the surface of the disc so that different data tracks can be read back.
Over the years, storage density has tended to increase and the size of the storage system has tended to decrease. This trend has led to greater precision and lower tolerance in the manufacturing and operating of magnetic storage discs. For example, to achieve increased storage densities, the transducer head is placed increasingly close to the surface of the storage disc to track ever more densely positioned data tracks.
Additionally, as the storage system size has tended to decrease, the available space for the motor, including the stator and windings used to drive the motor, have decreased accordingly. For example, rotation of a motor may be achieved through a stator that, when energized, communicates with a magnet associated with a rotatable hub, which supports one or more magnetic discs, to induce rotation of the hub and the one or more magnetic discs. The stator generally includes a plurality of “teeth” formed of a magnetic material, where each of the teeth is wound with a winding or wire that when energized creates a torque between the stator and the rotor portion of the motor. The power or torque of the motor depends, at least in part, on the stator size, magnet size, and the number of windings of the wire.
As the available space for the stator and windings decreases with system size, the use of increasingly fine gage wire is generally used to fit an adequate number of winding turns around the stator teeth to produce a desired torque. Increasingly fine gage wire, however, increases the winding resistance, which in turn results in high copper losses (generally equal to the current squared times resistance of the wire). Increased copper losses draw more power and may drain device battery life in an unacceptable amount of time, especially in relatively cold conditions in which the motor current is generally higher due to viscous losses in the motor's fluid dynamic bearing systems(s).
Accordingly, systems and methods for providing a spindle motor, and in particular, an FDB spindle motor, with improved operating characteristics are desired.
According to one aspect, a motor including a fluid bearing system is provided. In one example, a motor includes a first stationary motor member and a second motor member disposed for relative rotation and having a fluid bearing region disposed between opposing surfaces of the first and second motor members. A stator is disposed with the first motor member and includes a plurality of stator teeth, each of the stator teeth including a coil of wire wound thereon. A heat transfer device is further included, wherein the heat transfer device is operable to transfer heat away from the stator coils toward the fluid bearing during relative rotation of the first motor member and second motor member. The transfer of heat from the coils toward the first motor member or the second motor member may result in heating the bearing fluid of the motor, thereby reducing the viscosity of the bearing fluid.
In one example, the heat transfer device includes one or more air vanes to direct air through, over, or adjacent the stator to transfer heat via convection. In other examples, thermally conductive materials or elements may be placed adjacent the stator to transfer heat via conduction. Additionally, the heat transfer device may be incorporated into a flux shield disposed axially adjacent the stator.
According to another aspect, a method for transferring heat within a fluid bearing motor is provided. In one example, the method includes activating a stator to cause relative rotation of the stator and a rotor, the stator including stator teeth wrapped with coils of wire. Heat is transferred from the coils of the stator toward a rotor member, thereby heating bearing fluid associated with a fluid bearing of the motor.
Various aspects and examples are better understood upon consideration of the detailed description below in conjunction with the accompanying drawings and claims.
For a fuller understanding of examples used herein, reference is made to the accompanying drawings in the following detailed description.
The following description is presented to enable a person of ordinary skill in the art to make and use various aspects of the inventions. Descriptions of specific materials, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the inventions. For example, aspects and examples may be employed in a variety of motors, including motors for use in disc storage drives. Motors for disc storage drives may be designed and may operate in a number of ways. The exemplary motors and other exemplary subject matter provided herein are for illustrating various aspects and are not intended to limit the range of motors and devices in which such examples and aspects may be applied.
In one aspect and one example described herein, an exemplary method and system are provided for transferring heat from the stator to the rotor, whereby the temperature of bearing fluid of the motor is increased. In one example, air (or gas) is directed to, over, or adjacent to coils of the motor stator and toward members of the motor, such as the shaft or sleeve, which may include surfaces defining one or more bearing regions (including, e.g., Fluid Dynamic Bearing (FDB) regions) of the motor. In other examples, thermally conductive materials are positioned between stator coils to transfer or communicate heat from the coils to members of the motor. Transferring heat to bearing fluid (or lubricating liquid) of the bearing regions or to members of the motor that include, or are in thermal communication with the bearing fluid, raises the temperature and lowers the viscosity of the bearing fluid. Lowering the viscosity of the bearing fluid generally reduces the power required for a given torque and rotational speed of the motor.
Exemplary FDB motor systems may benefit, for example, from improved thermal compensation of overall motor power losses at relatively cold temperatures and a shortened duration of higher initial power draw from a power source (e.g., a battery). The power dissipated in the winding coils due to copper losses manifests as heat generated, and this heat may be transferred to the rotor by convection and/or conduction where it serves to warm the rotor, thus lowering the viscosity of the bearing fluid and corresponding viscous losses. The lower viscous losses may result in lower running current, which in turn lowers the I2R copper losses and improves device battery life (where I is electrical current in the coils and R is the resistance of the coils).
The general configuration and arrangement of storage system 10 shown in
An inner radial surface of sleeve 205 and outer radial surface of shaft 220 form a gap therebetween, which includes a lubricating liquid or bearing fluid during operation. One or both of the radial surfaces may include circumferentially disposed groove regions 225 and 226 where groove region 225 and/or groove region 226 may be asymmetrical and may function to circulate lubricating liquid through portions of motor 200, e.g., recirculation channel 207. A groove region 228 may further be formed between and end surface of sleeve 205 and hub 202 to form a thrust bearing, for example. Various other groove regions may be formed between opposing motor members as will be recognized by those of ordinary skill in the art.
Mounted with sleeve 205 and base 204 is a stator 212 that, when energized, communicates with a magnet 213 associated with hub 202 and induces rotation of hub 202 and stationary shaft 220 relative to sleeve 205. Stator 212 includes plurality of “teeth” (see, e.g., teeth 313 as shown in
Additionally, motor 200 includes stator heat transfer device 250. In this example, stator heat transfer device 250 is incorporated with a flux shield (not separately indicated) of motor 200, which is disposed adjacent stator 212. In other examples, motor 200 may include a conventional flux shield in addition to a heat transfer device 250. Further, stator heat transfer device 250 is shown disposed axially between stator 212 and a relatively rotational portion of motor 200, e.g., hub 202 and/or magnetic disc 216 disposed with hub 202, and is operable to transfer heat inward toward an inner radius of stator 212.
Heat transfer device 250 operates through conduction and/or convection to transfer heat from coils 216 of stator 212 toward motor members associated with bearing regions of motor 200, e.g., toward sleeve 205, hub 202, shaft 220, and the like. The transfer of heat may be directed to various members of motor 200 to raise the temperature of bearing fluid as it resides in any of a number of locations, for example, bearing regions 225, 226, or 228, recirculation channel 207, fluid reservoirs or capillary seals (not indicated in
The transfer of heat from coils 216 to the bearing fluid acts to reduce viscosity of the bearing fluid. Accordingly, power losses associated with high viscosity of the bearing fluid may be reduced. This feature may be particularly advantageous during spin-up or start-up of motor 200 or when operating in relatively cool temperature environments (e.g., below room temperature, approximately 22 degrees Celsius). For example, in applications associated with hard disc drive spindle motors, which may include an ester based bearing fluid in the bearing regions, it may be desirable to transfer heat as described to the bearing region and bearing fluid. The viscosity of exemplary ester based bearing fluids may be substantially reduced by warming the bearing fluid, e.g., from a start-up temperature in the range of −15 to 5° C., to a greater temperature.
In some examples, heat transfer device 250 may include vanes, baffles, openings, or other features or characteristics which operate to direct or allow a flow of air to pass over, by, or through elements of or associated with stator 212 (e.g., coils 216). The flow of air may further be directed toward one or more motor members, thereby transferring heat to motor members via convection. In other examples, heat transfer device 250 may include thermally conductive material or materials (e.g., having a high thermal conductivity similar to or greater than that of copper, aluminum, and the like, compared with low thermal conductivity materials such as air, ceramics, plastics, and the like) to conduct heat away from stator 212 and coils 216 toward motor members, thereby transferring heat via conduction. For example, a structure of one or more conductive elements may be disposed between adjacent teeth of stator 212 and coils 216 and fixed in place, e.g., potted with a thermally conductive adhesive or the like, to conduct heat away from coils 212. Additionally, the heat transfer device may include multiple devices for transferring heat both by convection and conduction, e.g., with conductive elements placed between stator coils as well as a structure for directing airflow between stator coils and/or adjacent the conductive elements and toward motor members.
Additionally, heat transfer device 250 may be separate from and placed adjacent to a flux shield. In one example, a multilayer structure, including a first layer suitable for flux shield purposes (such as magnetic steel or the like) may be disposed adjacent to or bonded to a high thermally conductive material layer (such as copper, aluminum, or the like).
Ribs 315 may also be shaped or disposed in various ways to direct the airflow down through the gaps of ribs 315 and/or inward toward the rotor generally disposed within the inner diameter of stator 312 during operation (see, e.g., the airflow directions shown in
Additionally, ribs 315 could be positioned below or extend from below stator 312. For example, ribs 315 may be attached to or formed integral with a base (see, e.g., base 204 of
Heat transfer device 350 and flux shield 314 may include various thermally conductive materials, including but not limited to metal such as copper, aluminum, or the like. Additionally, flux shield 314, including ribs 315, could be potted or attached directly to stator 312 or stator teeth 313 with an adhesive, e.g., a thermally conductive adhesive such as a zinc oxide filled adhesive or the like. Alternatively, ribs 315 or conductive fins could be potted or attached in place as shown in
As previously described, during relative movement of motor members, circumferential airflow is induced by the shearing effect of opposing surfaces. An exemplary direction of airflow is shown generally in
Additionally, various combinations of elements described with respect to heat transfer device 350 shown in
This description is exemplary and will be apparent to those of ordinary skill in the art that numerous modifications and variations are possible. For example, various exemplary methods and systems described herein may be used alone or in combination with various FDB systems and methods. Additionally, particular examples have been discussed and how these examples are thought to address certain disadvantages in related art. This discussion is not meant, however, to restrict the various examples to methods and/or systems that actually address or solve the disadvantages.
