Low power spindle motor with a stepped shaft

A spindle motor for use in a disk drive, the spindle motor including a shaft having a larger diameter section and a smaller diameter section with a step formed therebetween. The spindle motor also includes a bearing sleeve having a central cylindrical opening, the shaft is inserted into the central cylindrical opening. A bearing gap is formed between the shaft and the bearing sleeve, the bearing gap being filled with lubricating fluid. A thrust plate is fixedly mounted on the shaft in the area of the step such that an upper side of the thrust plate is placed adjacently to the larger diameter section and a lower side of the thrust plate is placed adjacently to the smaller diameter section of the shaft.

FIELD OF THE INVENTION

The following invention relates to brushless direct current spindle motors of the type used in disk drives and in particular relates to improvements in hydrodynamic bearings for such motors.

BACKGROUND OF THE INVENTION

Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, the information being accessed by means of transducers located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable.

Electric spindle motors of the type used in disk drives conventionally rely on ball bearings to support a rotary member, such as a rotating hub, on a stationary member, such as a shaft. Ball bearings are known to wear parts, and in time increased friction will cause failure of the motor. In addition, ball bearings create debris in the form of dust or fine particles that can find their way into “clean” chambers housing the rotary magnetic disks which are driven by the motor. The mechanical friction inherent in ball bearings also generates heat, noise and vibration, all of which are undesirable in a disk drive motor.

Fluid bearings represent a considerable improvement over conventional ball bearings in spindle drive motors. In these types of systems, lubricating fluid, either gas or liquid, functions as the actual bearing surface between a stationary base or housing in the rotating spindle or rotating hub of the motor. Liquid lubricants, for example, oil, complex ferro-magnetic fluids or even air, have been utilized in hydrodynamic bearing systems. As compared with ball bearings, fluid dynamic bearings have improved running accuracy, greater impact strength and lower noise generation.

One example of a spindle motor utilizing a prior art fluid dynamic bearing is disclosed in U.S. Pat. No. 5,658,080. The '080 patent shows a spindle motor including a shaft retained in a shaft retainer and a thrust plate provided to the shaft. A thrust dynamic pressure fluid bearing is provided between the thrust plate and the shaft retainer. A radial dynamic pressure fluid bearing is provided between the shaft retainer and the shaft. A ring-shaped space formed between the outer circumferential surface of the thrust plate and the inner circumferential surface of the shaft retainer is partially filled with oil. Ring-shaped projections are provided on the outer circumferential surface of the thrust plate. When the motor is running at a high-speed, oil in the ring-shaped space is retained on the shaft retainer and through this oil, oil in the thrust dynamic pressure fluid bearings at the upper and lower surface sides are communicated with each other.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spindle motor with a stepped shaft which saves run-current and, therefore, reduces power consumption of the spindle motor.

Present invention provides a spindle motor for use in a disk drive, the spindle motor including a shaft having a larger diameter section and a smaller diameter section with a step formed therebetween. The spindle motor also includes a bearing sleeve having a central cylindrical opening, the shaft is inserted into the central cylindrical opening. A bearing gap is formed between the shaft and the bearing sleeve, the bearing gap being filled with lubricating fluid. A thrust plate is fixedly mounted on the shaft in the area of the step such that an upper side of the thrust plate is placed adjacently to the larger diameter section and a lower side of the thrust plate is placed adjacently to the smaller diameter section of the shaft.

The above and other objects, aspects, features and advantages of the invention will be more readily apparent from the description of the preferred embodiments thereof taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND THE DRAWINGS

As shown inFIG. 1, a compact electronic spindle motor10preferably includes a central rotatable shaft12supporting for rotation a rotor14having a hub16. When the motor10is used in a disc drive, the hub16will support and carry a magnetic disc (not shown) during rotation. The rotor14comprises an annular vertical rotor support wall24, which supports rotor magnets26. A stator18preferably includes an annular vertical stator support wall20, which supports a plurality of stator windings22such that the stator windings are located in opposing relationship with rotor magnets26. The stator support wall20defines an inner cylindrical hole28. A bearing sleeve30is inserted into the inner cylindrical hole28and is fixedly mounted therein. The bearing sleeve30may be glued to the inner wall of the hole28.

In the preferred embodiment, the shaft12preferably has a first cylindrical portion38having an outer diameter D1, a second cylindrical portion48having an outer diameter D2and a third cylindrical portion58having an outer diameter D3. The outer diameter D1of the first cylindrical portion38is greater than the outer diameter D2of the second cylindrical portion48. A step42is formed between the first and the second cylindrical portions of the shaft. The hub16is mounted for rotation on the third cylindrical portion58of the shaft12. The outer diameter D3of the third cylindrical portion may be different from the outer diameter D1of the first cylindrical portion. A thrust-washer36is fixedly mounted on the second cylindrical portion48of the shaft12adjacently to the step42. The thrust-washer36has an outer diameter D4.

In the preferred embodiment, the bearing sleeve30has an inner void32with substantially cylindrical walls and at least three chambers of various inner diameters. A first sleeve chamber34has an inner diameter d1, a second sleeve chamber44has an inner diameter d2and a third sleeve chamber54has an inner diameter d3. The inner diameter d3of the third sleeve chamber54is slightly greater than the outer diameter D2of the second cylindrical shaft portion48. The inner diameter d2of the second sleeve chamber44is slightly greater than the outer diameter D4of the thrust-washer36.

The central shaft12is preferably inserted into the inner void32such that the second cylindrical shaft portion48is located within the third sleeve chamber54and the thrust-washer36is located within the second sleeve chamber44. The shaft12is secured from falling out from the void32by a counter-plate46, which is placed into the first sleeve chamber34. The counter-plate46is fixed with respect to the bearing sleeve30. The counter-plate46has a central cylindrical bore52having an inner diameter d4. The inner diameter d4of the bore52is slightly greater than the outer diameter D1of the first cylindrical shaft portion38and is smaller than the outer diameter D4of the thrust-washer36. Thus, the portion of the counter-plate46adjacent to the thrust-washer36secures the thrust-washer within the second sleeve chamber44and prevents the shaft12from falling out of the void32.

As mentioned above, the inner diameter d4of the bore52is slightly greater than the outer diameter D1of the first cylindrical shaft portion38. Therefore, a gap40is formed between an outer surface of the shaft12and an inner surface of the bore52. The gap40is filled with an appropriate lubricating fluid. The bore52preferably has a tapered portion56the tapering slope of which is preferably calculated such that there is an adequate surface tension between lubricating fluid within the bearing and the walls of the bore52and the shaft12. During rotation, the lubricating fluid is kept inside the bearing structure by a capillary seal formed by the fluid within the tapered portion56. The tapered portion56also provides a reservoir for the lubricating fluid.

At least one radial bearing50is provided between opposing side walls of the first cylindrical shaft portion38and the bore52. In the preferred embodiment, radial hydrodynamic bearings50are provided in the area of the first cylindrical shaft portion38and the second cylindrical shaft portion48. Dynamic pressure generating grooves60may be formed on either the outer surface of the shaft12, as shown inFIG. 4, or the inner surface of the bore52. A top thrust bearing62is provided between opposing sides of the counter-plate46and the thrust-washer36by forming herringbone or spiral grooves on either of these opposing sides. A bottom thrust-bearing64is preferably provided between opposing sides of the thrust-washer36and the second sleeve chamber44by forming herringbone or spiral grooves on either of these opposing sides. Thus, as shown inFIG. 1, at least one thrust bearing is formed on the lower side of the thrust-washer adjacent to the smaller diameter portion of the shaft12. The two thrust bearings in combination with the stepped shaft provide an adequate support for the shaft12in the axial direction and a proper alignment of the thrust-washer.

In a typical spindle motor utilizing hydrodynamic thrust bearings, such bearings have to have very high stiffness characteristics. In contrast with currently available designs, the described embodiment of the present invention, where at least one thrust bearing is located on the side of the thrust-washer adjacent to the smaller diameter portion of the shaft, results in a good motor performance wherein only the top thrust bearing62is characterized by high stiffness. The lower thrust bearing64, however, has a low stiffness. The reduced stiffness of the lower thrust bearing results in a lower power consumption of the provided spindle motor.

A second embodiment of the spindle motor is shown in FIG.2. In accordance with the second embodiment, a compact electronic spindle motor110preferably includes a rotatable sleeve130supporting for rotation a rotor114having a hub116. The bearing sleeve130may be glued to the hub116. When the motor110is used in a disc drive, the hub116will support and carry a magnetic disc (not shown) during rotation. The rotor114comprises an annular vertical rotor support wall124, which supports rotor magnets126. A stator118preferably includes an annular vertical stator support wall120, which supports a plurality of stator windings122such that the stator windings are located in opposing relationship with rotor magnets126. The stator support wall120defines an inner cylindrical cup-shaped opening128. A central fixed stepped shaft112is inserted into the bottom wall of the cylindrical cup-shaped opening128and is fixedly mounted therein.

In the second preferred embodiment, the shaft112preferably has a first cylindrical portion138having an outer diameter D11, a second cylindrical portion148having an outer diameter D12and a conical portion158having an outer diameter varying from D12(along the connection with the second cylindrical portion148) to D13(along the connection with the bottom wall of the cup-shaped opening128). The outer diameter D11of the first cylindrical portion138is greater than the outer diameter D12of the second cylindrical portion148. A step142is formed between the first and the second cylindrical portions of the shaft. The outer diameter D13of the conical portion158is preferably smaller than the outer diameter D12of the same shaft portion. A thrust-washer136is fixedly mounted on the second cylindrical portion148of the shaft112adjacently to the step142. The thrust-washer136has an outer diameter D14.

In the second preferred embodiment, the bearing sleeve130has an inner void132with substantially cylindrical walls and at least three chambers of various inner diameters. A first sleeve chamber134has an inner diameter d11, a second sleeve chamber144has an inner diameter d12and a third sleeve chamber154has an inner diameter d13. The inner diameter d13of the third sleeve chamber154is slightly greater than the outer diameter D11of the first cylindrical shaft portion138. The inner diameter d12of the second sleeve chamber144is slightly greater than the outer diameter D14of the thrust-washer136.

The central shaft112is preferably inserted into the inner void132such that the first cylindrical shaft portion138is located within the third sleeve chamber154and the thrust-washer136is located within the second sleeve chamber144. The shaft112is secured from falling out from the void132by a counter-plate146, which is placed into the first sleeve chamber134. The counter-plate146is fixed with respect to the bearing sleeve130. The counter-plate146has a central cylindrical bore152having an inner diameter d14. The inner diameter d14of the bore152is slightly greater than the outer diameter D12of the second cylindrical shaft portion148and the conical shaft portion158and is smaller than the outer diameter D14of the thrust-washer136. Thus, the portion of the counter-plate146adjacent to the thrust-washer136secures the thrust-washer within the second sleeve chamber144and prevents the shaft112from falling out of the void132.

As mentioned above, the inner diameter d14of the bore152is slightly greater than the outer diameter D12of the second cylindrical shaft portion148. Therefore, a gap140is formed between an outer surface of the shaft112and an inner surface of the bore152. The gap140is filled with an appropriate lubricating fluid. The conical shaft portion158forms a tapered portion156the tapering slope of which is preferably calculated such that there is an adequate surface tension between lubricating fluid and the walls of the bore152and the shaft112. During rotation, the lubricating fluid is kept inside the bearing structure by a capillary seal formed by the fluid within the tapered portion156. The tapered portion156also provides a reservoir for the lubricating fluid.

At least one radial bearing150is provided between opposing side walls of the first cylindrical shaft portion138and the third sleeve chamber154. In the preferred embodiment, radial hydrodynamic bearings150are provided in the area of the first cylindrical shaft portion138and the second cylindrical shaft portion148. Dynamic pressure generating herringbone grooves may be formed on either the outer surface of the shaft112or the inner surface of the third sleeve chamber154. A bottom thrust bearing162is provided between opposing sides of the counter-plate146and the thrust-washer136by forming herringbone or spiral grooves on either one of these opposing sides. A top thrust-bearing164ais preferably provided between opposing sides of the thrust-washer136and the second sleeve chamber144by forming herringbone or spiral grooves on either one of these opposing sides. Alternatively, the top thrust bearing164bmay be provided between the top side166of the shaft112and the opposing side of the sleeve chamber154. Thus, as shown inFIG. 2, at least one thrust bearing is formed on the lower side of the thrust-washer adjacent to the smaller diameter portion of the shaft112. The two thrust bearings in combination with the stepped shaft provide an adequate support for the shaft112in the axial direction and a proper alignment of the thrust-washer.

Similarly to the first embodiment, the described second embodiment of the spindle motor having at least one thrust bearing located on the side of the thrust-washer adjacent to the smaller diameter portion of the shaft, results in a good motor performance wherein only the top thrust bearing164aor164bis characterized by high stiffness. The lower thrust bearing162, however, has a low stiffness. The reduced stiffness of the lower thrust bearing results in a lower power consumption of the provided spindle motor.

A third embodiment of the spindle motor is shown in FIG.3. In accordance with the third preferred embodiment, a compact electronic spindle motor210preferably includes a rotatable sleeve230supporting for rotation a rotor214having a hub216. The bearing sleeve230may be glued to the hub216. When the motor210is used in a disc drive, the hub216will support and carry a magnetic disc (not shown) during rotation. The rotor214comprises an annular vertical rotor support wall224, which supports rotor magnets226. A stator218preferably includes an annular vertical stator support wall220, which supports a plurality of stator windings222such that the stator windings are located in opposing relationship with rotor magnets226. The stator support wall220defines an inner cylindrical cup-shaped opening228. A central fixed stepped shaft212is inserted into the bottom wall of the cylindrical cup-shaped opening228and is fixedly mounted therein. The central shaft212may be press-fit into the bottom wall of the cup-shaped opening and may be further secured in a top cover (not shown) of the provided disc drive. Although this top-cover attachment of the shaft is not currently utilized with 2.5″ disc drives, it may be utilized with the presently provided motor because of the motor's low power consumption.

In the third preferred embodiment, the shaft212preferably has a first cylindrical portion238having an outer diameter D21, a second cylindrical portion248having an outer diameter D22, a first conical portion258having an outer diameter varying from D22(along the connection with the second cylindrical portion248) to D13(along the connection with the bottom wall of the cup-shaped opening228) and a second conical portion268having an outer diameter varying from D21(along the connection with the first cylindrical portion238) to D25(adjacent to the hub216). The outer diameter D21of the first cylindrical portion238is greater than the outer diameter D22of the second cylindrical portion248. A step242is formed between the first and the second cylindrical portions of the shaft. The outer diameter D23of the first conical portion258is preferably smaller than the outer diameter D22of the same shaft portion. The outer diameter D25of the second conical portion268is preferably smaller than the outer diameter D21of the same shaft portion. A thrust-washer236is fixedly mounted on the second cylindrical portion248of the shaft212adjacently to the step242. The thrust-washer236has an outer diameter D24.

In the third preferred embodiment, the bearing sleeve230has an inner void232with substantially cylindrical walls and at least three chambers of various inner diameters. A first sleeve chamber234has an inner diameter d21, a second sleeve chamber244has an inner diameter d22and a third sleeve chamber254has an inner diameter d23. The inner diameter d23of the third sleeve chamber254is slightly greater than the outer diameter D21of the first cylindrical shaft portion238. The inner diameter d22of the second sleeve chamber244is slightly greater than the outer diameter D24of the thrust-washer236.

The central shaft212is preferably inserted into the inner void232such that the first cylindrical shaft portion238and the second conical shaft portion268are located within the third sleeve chamber254and the thrust-washer236is located within the second sleeve chamber244. The shaft212is secured from falling out from the void232by a counter-plate246, which is placed into the first sleeve chamber234. The counter-plate246is fixed with respect to the bearing sleeve230. The counter-plate246has a central cylindrical bore252having an inner diameter d24. The inner diameter d24of the bore252is slightly greater than the outer diameter D22of the second cylindrical shaft portion248and the first conical shaft portion258and is smaller than the outer diameter D24of the thrust-washer236. Thus, the portion of the counter-plate246adjacent to the thrust-washer236secures the thrust-washer within the second sleeve chamber244and prevents the shaft212from falling out of the void232.

As mentioned above, the inner diameter d24of the bore252is slightly greater than the outer diameter D22of the second cylindrical shaft portion248. Similarly, the inner diameter d23of the third sleeve chamber254is slightly greater than the outer diameter D21of the first cylindrical shaft portion238. Therefore, a gap240is formed between an outer surface of the shaft212and inner surfaces of the bore252and the sleeve230. The gap240is filled with an appropriate lubricating fluid. The conical shaft portions258and268form tapered portions256at the top of the sleeve230and the bottom of the bore252. The tapering slope of portions256is preferably calculated such that there is an adequate surface tension between lubricating fluid and the walls of portions256. During rotation, the lubricating fluid is kept inside the bearing structure by a capillary seal formed by the fluid within the tapered portion256. The tapered portion256also provides a reservoir for the lubricating fluid.

At least one radial bearing250is provided between opposing side walls of the first cylindrical shaft portion238and the third sleeve chamber254. In the preferred embodiment, radial hydrodynamic bearings250are provided in the area of the first cylindrical shaft portion238and the second cylindrical shaft portion248. Dynamic pressure generating herringbone grooves may be formed on either the outer surface of the shaft212or the inner surface of the third sleeve chamber254. A bottom thrust bearing262is provided between opposing sides of the counter-plate246and the thrust-washer236by forming herringbone or spiral grooves on either one of these opposing surfaces. A top thrust-bearing264is preferably provided between an upper surface of the thrust-washer236and the opposing surface of the second sleeve chamber144by forming herringbone or spiral grooves on either one of these opposing surfaces. Thus, as shown inFIG. 3, at least one thrust bearing is formed on the lower side of the thrust-washer adjacent to the smaller diameter portion of the shaft212. The two thrust bearings in combination with the stepped shaft provide an adequate support for the shaft212in the axial direction and a proper alignment of the thrust-washer.

Similarly to the first and second embodiments, the described third embodiment of the spindle motor having at least one thrust bearing located on the side of the thrust-washer adjacent to the smaller diameter portion of the shaft, results in a good motor performance wherein only the top thrust bearing264is characterized by high stiffness. The lower thrust bearing262, however, has a low stiffness. The reduced stiffness of the lower thrust bearing results in a lower power consumption of the provided spindle motor.

The disclosed invention is particularly useful if utilized in connection with a 2.5″ disc drive. However, the invention may be used with other spindle motors as well.

For the convenience of the reader, the above description has focused on a representative sample of all possible embodiments, a sample that teaches the principles of the invention and conveys the best mode contemplated for carrying it out. The description has not attempted to exhaustively enumerate all possible variations. Other undescribed variations or modifications may be possible. For example, where multiple alternative embodiments are described, in many cases it will be possible to combine elements of different embodiments, or to combine elements of the embodiments described here with other modifications or variations that are not expressly described. Many of those undescribed variations, modifications and variations are within the literal scope of the following claims, and others are equivalent.