Abstract:
A fluid dynamic bearing includes a bearing member ( 30 ) axially defining an inner bearing hole therein, and a spindle shaft ( 20 ) rotatably received in the bearing hole with a bearing clearance formed between an inner periphery of the bearing member and an outer periphery of the spindle shaft. Lubricant is filled in the bearing clearance. One of the inner periphery and the outer periphery comprises a bearing surface ( 10 ) with channels formed therein. The channels form a plurality of outer communication ends ( 1316   b ) at opposite sides of the bearing surface in the axial direction of the bearing member.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to bearings, and more particularly to a fluid dynamic bearing.  
       BACKGROUND  
       [0002]     Due to request for low abrasion on rotational elements to achieve an extended life and for low extent of noise, fluid dynamic bearings (FDB) have been used in conventional fan motors and hard disk drive motors.  
         [0003]     In a typical FDB, a shaft is pivotably inserted into a bearing sleeve with a bearing clearance formed therebetween. Pressure-generating grooves are formed on either the outer peripheral surface of the shaft or the inner peripheral surface of the bearing sleeve. The bearing clearance is filled with lubricant oil that provides a medium through which a dynamic fluid pressure field is generated upon relative rotation between the bearing sleeve and the shaft. During normal operation, the spinning of the shaft sets up a steady pressure field around the bearing clearance that separates the shaft and the bearing sleeve and thus prevents metal-to-metal contact.  
         [0004]      FIG. 4  shows a dynamic pressure-generating groove pattern of a so called “herringbone” type. Each groove is V-shaped and has two branches  87   a ,  87   b  having a common intercrossing area  88 . Suppose a top side of the groove pattern faces outside, so the lubricant oil in the groove at the top side exposes to atmosphere. Sealing measures must be taken to prevent leakage of the lubricant oil at the top side. When the shaft rotates, the lubricating oil is driven from ends of the branches  87   a ,  87   b  to the intercrossing area  88  to generate a high pressure. At the same time, because a part of the lubricating oil is moved to the intercrossing area  88 , the lubricating oil remaining near the ends of the branches  87   a ,  87   b  generates a very low pressure. This low pressure is required to be even lower than the outside atmosphere pressure so that the lubricant oil at the top edge does not flow outside. However, if the lower pressure generated by the lubricating oil at the top edge is very close to the outside atmosphere pressure, the lubricating oil is still possible to leakage, when the motor is subject to vibration during use or the motor is used in a location where the outside atmosphere pressure is lowered. Therefore, the lower pressure generated by the lubricating oil at the top edge is desired to be low enough.  
         [0005]     For the foregoing reasons, there is a need for a fluid bearing having an improved capability to prevent leakage of lubricating oil.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a fluid dynamic bearing which has an improved capability to prevent oil leakage.  
         [0007]     A fluid dynamic bearing in accordance with the present invention comprises a bearing member axially defining an inner bearing hole therein, and a spindle shaft rotatably received in the bearing hole with a bearing clearance formed between an inner periphery of the bearing member and an outer periphery of the spindle shaft. Lubricant is filled in the bearing clearance. One of the inner periphery and the outer periphery comprises a bearing surface with channels formed therein. The channels form a plurality of outer communication ends at opposite sides of the bearing surface in the axial direction of the bearing member.  
         [0008]     Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which:  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a cross sectional view of a fluid dynamic bearing according to a preferred embodiment of the present invention;  
         [0010]      FIG. 2  is an enlarged, unfurled view of the radial bearing surface of the fluid dynamic bearing of  FIG. 1 ;  
         [0011]      FIG. 3  is a plan view of fluid dynamic bearing of a thrust type according to an alternative embodiment of the present invention; and  
         [0012]      FIG. 4  is an enlarged, unfurled view of a radial bearing surface of a conventional fluid dynamic bearing. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0013]      FIG. 1  shows by way of example an embodiment of a fluid dynamic bearing. This fluid dynamic bearing is used, for example, in connection with a hard disk drive motor, a fan motor and a scanner motor or the like. The fluid dynamic bearing comprises a bearing sleeve  30 , and a spindle shaft  20  rotatably received in the bearing sleeve  30 .  
         [0014]     The inner peripheral surface of the bearing sleeve  30  is formed with at least one bearing surface  10 . The bearing surface  10  of the bearing sleeve  30  is opposed to an outer peripheral surface of the spindle shaft  20 , with a bearing clearance defined therebetween. The bearing clearance is filled with fluids like lubricating oil that provides a medium through which a dynamic fluid pressure field is generated upon relative rotation at high speed between the bearing sleeve  30  and the spindle shaft  20 . Thus, the bearing sleeve  30  can radially support the spindle shaft  20  in a non-contact manner.  
         [0015]     Referring also to  FIG. 2 , the bearing surface  10  is shown in an unfurled view. The bearing surface  10  comprises axially continuous first and second regions m 1 , m 2  with a boundary line  18 . It should be understood that the first and second regions m 1 , m 2  are in fact cylindrical in a real bearing product.  
         [0016]     In the first region m 1 , a set of parallel first channels  13   a  and a set of parallel second channels  16   a  are formed in an alternating manner along extension of the bearing surface  10 . The first and second channels  13   a ,  16   a  are inclined with respect to an axis of the fluid dynamic bearing. The first and second channels  13   a ,  16   a  deviate from the axis of the fluid dynamic bearing with different angles so that any two neighboring first and second channels  13   a ,  16   a  either intercross at an upper edge (a top side of the bearing surface  10 ) of the first region m 1  to form an outer communication end  1316   b  thereat, or intercross at an lower edge (immediately above boundary line  18 ) of the first region m 1 .  
         [0017]     In the second region m 2 , third and fourth channels  13   b ,  16   b  are formed in an alternating manner along extension of the bearing surface  10 , being symmetrical with the first and second channels  13   a ,  16   a  respectively with respect to the boundary line  18 . Thus, any two neighboring third and fourth channels  13   b ,  16   b  either intercross at an upper edge (immediately below boundary line  18 ) of the second region m 2 , or intercross at a lower edge (a bottom side of the bearing surface  10 ) of the second region m 2  to form the outer communication end  1316   b.    
         [0018]     Since the first and second regions m 1 , m 2  of the bearing surface  10  are axially continuous, the first, second, third and fourth channels  13   a ,  16   a ,  13   b ,  16   b  collectively communicate with each other at the boundary line  18  to form a plurality of inner communication ends  1316   a  thereat. As a result, every two symmetrical channels form a V-shaped groove. Specifically, the first channels  13   a  in the first region m 1  and corresponding third channels  13   b  in the second region m 2  form a plurality of first V-shaped grooves  13 , and the second channels  16   a  in the first region m 1  and corresponding fourth channels  16   b  in the second region m 2  form a plurality of second V-shaped grooves  16 . The first grooves  13  and the second grooves  16  are alternatingly arranged along extension of the bearing surface  10 .  
         [0019]     When the rotary shaft  20  rotates, the lubricating oil at the outer communication ends  1316   b  is driven to the inner communication ends  1316   a  of the first and second grooves  13 ,  16  under a centrifugal pumping force caused by rotation of the rotary shaft  20 . A large amount of lubricating oil at the inner communication ends  1316   a  then establishes a high fluid pressure to separate the rotary shaft  20  and the bearing sleeve  30  in radial direction.  
         [0020]     In the present invention, the first and third channels  13   a ,  13   b  of each first grooves  13  are in communication with the second and fourth channels  16   a ,  16   b  of one neighboring second groove  16  at the opposite top and bottom sides of the bearing surface  10  in the axis of the bearing sleeve  30 , thereby forming the outer communication ends  1316   b  thereat respectively. The lubricating oil at each outer communication end  1316   b  is thus driven to a center area of the bearing surface  10  along two separate paths, i.e., the first and second channels  13   a ,  16   a , or  13   b ,  16   b . Therefore, it is easy for more lubricating oil to move to the center area of the bearing surface  10 . In other words, the lubricating oil remaining at the outer communication end  1316   b  becomes less in comparison with the conventional fluid bearing in which only one lubricating oil flow path is arranged. As a result, the pressure generated by the lubricating oil at the opposite sides of the bearing surface  10  becomes further lower than that of the conventional fluid bearing. Suppose the top side of the bearing surface  10  faces an outside of the bearing sleeve  30 , this further lower pressure provides an enhanced capability to prevent leakage of lubricating oil at the top side of the bearing surface  10 .  
         [0021]     In the above-mentioned fluid dynamic bearing, the second region m 2  is continuous to the first region m 1 . Alternatively, the second region m 2  is axially spaced from the first region m 1 . Thus, the first, second, third and fourth channels  13   a ,  16   a ,  13   b ,  16   b  do not communicate directly with each other at the center area of the bearing surface  10 . In stead, an annular recessed region may be formed between the first and second regions m 1 , m 2 . The first, second, third and fourth channels  13   a ,  16   a ,  13   b ,  16   b  all communicate with the recessed region, whereby the lubricating oil can be collected to the recessed region to establish a high fluid pressure field thereat.  
         [0022]     In addition, the first and second channels  13   a ,  16   a  are not necessary to intercross with each other at the lower edge of the first region m 1  of the bearing surface  10 , and the third and fourth channels  13   b ,  16   b  are not necessary to intercross with each other at the upper edge of the second region m 2  of the bearing surface  10 .  
         [0023]      FIG. 3  illustrates by way of example a bearing surface  10 ′ of a thrust fluid dynamic bearing according to an alternative embodiment of the present invention. The bearing surface  10 ′ comprises first and second annular regions n 1 , n 2  with a boundary line  18 ′. In the first region n 1 , a plurality of first and second channels  13   a ′,  16   a ′ is formed, intercrossing at an outer edge of the bearing surface  10 ′. In the second region n 2 , a plurality of third and fourth channels  13   b ′,  16   b ′ is formed, intercrossing at an inner edge of the bearing surface  10 . The first channels  13   a ′ and corresponding third channels  13   b ′ intercross at a center area of the bearing surface  10  around the boundary line  18 ′ to form a plurality of first generally V-shaped grooves  13 ′, and the second channels  16   a ′ and corresponding fourth channels  16   b ′ intercross at the center area of the bearing surface  10 ′ around the boundary line  18 ′ to form a plurality of second generally V-shaped grooves  16 .  
         [0024]     In the preferred embodiment of the present invention, the bearing surface  10  is formed on the inner periphery of the bearing sleeve  30 . Alternatively, the bearing surface may be formed on the outer periphery of the spindle shaft  20 .  
         [0025]     It is understood that the invention may be embodied in other forms without departing from the spirit thereof. The above-described examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given above.