Patent Publication Number: US-2007110348-A1

Title: Fluid dynamic bearing unit

Description:
BACKGROUND OF THE INVENTION  
      1. Field Of The Invention  
      The present invention relates to a fluid dynamic bearing unit for both radial and axial bearing loads. In particular, the present invention relates to a standardized fluid dynamic bearing unit made from modularized components and unitized completed components. The bearing unit being suitable for use in, for example, hard disk drives (HDD&#39;s) or Digital Versatile disc drives (DVD&#39;s).  
      2. Description of Related Art  
      In recent years, spindle motors have been used as driving devices or components for the rotational parts in office automation equipment such as computers and hard disk drives. These devices, over time, have continuously increased capacity and have been miniaturized. For spindle motors used in these devices, high reliabilities for motor fluctuation accuracy (NRRO (asynchronous fluctuation)), noise, sound duration, rigidity, and the like are strongly desirable.  
      In the past, for the axle bearing of the rotating axis of this type of spindle motor, a compound ball bearing device, which is made by combining a plurality of a ball bearing, was widely used. Incidentally, recently, for hard disk drives, there has been an even stronger demand for an increase in recording capacity, an improvement in impact load carrying capacity, low noise and an acceleration of data access speed. To respond to these demands, there is an attempt to improve materials and the engineering precision of the inner and outer rings and rotating body of the ball bearing. However, these measures alone are not sufficient, and the limitations of roller bearings themselves have come to be recognized. In order to respond to these limitations, the use of fluid dynamic bearings has been implemented.  
       FIG. 11  shows an axle rotating spindle motor using a fluid dynamic bearing. This spindle motor  00  comprises a base  02 , a rotor hub  03  supported by the base  02 , and a fluid dynamic bearing device  01  placed between the base  02  and the rotor hub  03 .  
      A sleeve  010  of the fluid dynamic bearing device  01  is fitted into and fixed to an inner circumferential surface of a cylindrical wall  07  of the central part of the base  02 , and a rotating axle  030 , which is perpendicular to the rotor hub  03 , is fitted into this sleeve  010 . A minute gap between the sleeve  010  and the rotating axle  030  is filled with lubricating oil, and pressure is generated in the lubricating oil by both the rotation of the rotating axle  030 , and the action of dynamic pressure grooves (for example, herringbone type grooves)  051  and  052 , which were formed on the inner circumferential surface of the sleeve  010 . The dynamic pressure caused by action of the dynamic pressure grooves  051  and  052  freely supports the rotation of the rotating axle  030  in the radial direction while the rotating axle  030  does not contact the inner circumferential surface of the sleeve  010 . The dynamic pressures grooves  051  and  052  are formed at the upper and lower inner circumferential surface of the sleeve  010 . Instead, these dynamic pressure grooves can be formed on the outer circumferential surface of the rotating axle  030 .  
      The details are not shown in  FIG. 11 , but a dynamic pressure grooves (for example, herringbone type grooves) are formed on a upper surface of a counter plate  020  and a lower end surface of the sleeve  010 , both of which respectively face a lower end surface and a upper end surface of a thrust ring  060 , which is fitted into a lower end part of the rotating axle  030 . A minute gap is formed between the opposing surfaces adjacent each dynamic pressure groove. Lubricating oil is filled in each gap, and pressure is generated in the lubricating oil by the rotation of the rotating axle  030 . The dynamic pressure caused by action of these dynamic pressure grooves, freely supports rotation of the thrust ring  060  in the axial direction while the thrust ring  060  does not contact with the upper surface of the counter plate  020  or the lower end surface of the sleeve  010 . These dynamic pressure grooves can be formed on the lower end surface and the upper end surface of the thrust ring  060 .  
      Consequently, the base  02  freely supports the rotation of the rotating axle  030  of the rotor hub  03 , by means of the fluid dynamic bearing device  01 . In addition, the structure of the motor, which includes a stator  05 , a permanent magnet  06 , etc., is no different from a spindle motor that uses conventional compound ball bearings.  
      In the past, since the component parts such as the sleeve  010 , the rotating axle  030 , the counter plates  020 , and the like were not modularized, when fluid dynamic bearing devices as component parts of driving devices were required, each of these fluid dynamic bearing devices  01  had to be individually manufactured by each manufacturer conforming to the structure and performance required for each equipment or device. Thus, it was not easy to quickly manufacture a large quantity of fluid dynamic bearing devices with high performance and high reliability.  
      In the meantime, a number of proposals at the level of the spindle motor for this problem have been made. By modularizing as many components of a spindle motor as possible, and by making components that contain fluid dynamic bearing devices the common components, entirety of completed components are unitized so that the common components can be used as-is even when component&#39;s specifications and equipment types are diversified. By enabling the exchange of only the relevant components, when some components become defective, good components are re-utilized, and the cost is reduced. (see References: Unexamined Patent Application 2000-175405 Official Gazette (Kokai 2000-175405), Examined Utility Model Application S56-157427 Official Gazette (Examined S56-157427), Examined Utility Model Application S56-133121 Official Gazette (Examined S56-133121)) Furthermore, “components” as referred here include not only “a component of the smallest unit” but also “assembled components” that are made by combining a plurality of “a component of the smallest unit”.  
      However, the structures and dimensions of these modularized components are specified, first and foremost, for adapting to these spindle motors and are not standardized for various equipment and devices to be commonly used. Thus, it is desirable to have standardized fluid dynamic bearings made from modularized components that are suitable for use in various type of machine or device.  
     SUMMARY OF THE INVENTION  
      The invention of this application solves the above-mentioned problems of the existing conventional fluid dynamic bearing devices by modularizing the fluid dynamic bearing device and using the “completed product” (assembled component). The fluid dynamic bearing of this invention is easy to manufacture and is standardized so that it is possible to use it in various type of machine or device including a hard disk drive. These fluid dynamic bearing units provide appropriate assembly, the desired structure and functionality, and provide the structure in concert with unitization, and especially, show bearing functionality corresponding to load in both radial and axial directions.  
      A fluid dynamic bearing unit of one embodiment of the present invention is composed of a combination of a plurality of modularized elements, having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a flange-attached shaft element having a flange part at one end. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element closinging a lower end of the case element, an outer ring element fitted into the case element; and a flange-attached shaft element inserted into the outer ring element so that the flange part thereof is located between a lower end surface of the outer ring element and an upper surface of the end plate element. A first dynamic pressure groove is formed on an inner circumferential surface of the outer ring element or an outer circumferential surface of the main body of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the radial direction between both of these facing surfaces, i.e., the inner circumferential surface and the outer circumferential surface. A second dynamic pressure groove is formed on a lower end surface of the outer ring element or an upper surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure, which receives the load in the axial direction. A third dynamic pressure groove is formed on an upper surface of the end plate element or a lower surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove, the second dynamic pressure groove, as well as the third dynamic pressure groove.  
      A fluid dynamic bearing unit of another embodiment of the present invention is composed of a combination of a plurality of modularized elements, having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a straight shaft element. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface and an outer ring element fitted into the tubular case element. A shaft element is inserted into the outer ring element. A first dynamic pressure groove is formed on an inner circumferential surface of the outer ring element or an outer circumferential surface of the shaft element to cause the generation of dynamic pressure which receives the load in the radial direction. A second dynamic pressure groove is formed on an upper surface of the end plate element or a lower surface of the shaft element to cause the generation of dynamic pressure, which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove as well as the second dynamic pressure groove.  
      A fluid dynamic bearing unit of another embodiment of the present invention is composed of a combination of a plurality of modularized elements, having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a flange-attached shaft element having a flange part at one end. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element closing the lower end part of the case element, an outer ring element fitted into the case element and an inner ring element inserted into the outer ring element. A flange-attached shaft element is fitted into the inner ring element in such a way that the flange part thereof is located between a lower end surface of the outer ring element as well as a lower end surface of the inner ring element and an upper surface of the end plate element. A first dynamic pressure groove is formed on an inner circumferential surface of the outer ring element or an outer circumferential surface of the inner ring element to cause the generation of dynamic pressure which receives the load in the radial direction. A second dynamic pressure groove is formed on a lower end surface of the outer ring element or an upper surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure, which receives the load in the axial direction. A third dynamic pressure groove is formed on an upper surface of the end plate element or a lower surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove, the second dynamic pressure groove, and the third dynamic pressure groove.  
      A fluid dynamic bearing unit of another embodiment of the present invention is composed of a combination of a plurality of modularized elements having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a straight shaft element. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element closing the lower end part of the case element, an outer ring element fitted into the case element, a flange-attached inner ring element having a flange part at one end inserted into the outer ring element in such a way that the flange part of the flange-attached inner ring element is located between a lower end surface of the outer ring element and an upper surface of the end plate element. A shaft element is fitted into the flange-attached inner ring element. A first dynamic pressure groove is formed on an inner circumferential surface of the outer ring element or an outer circumferential surface of the main body of the flange-attached inner ring element to cause the generation of dynamic pressure which receives the load in the radial direction. A second dynamic pressure groove is formed on a lower end surface of the outer ring element or an upper surface of the flange part of the flange-attached inner ring element to cause the generation of dynamic pressure, which receives the load in the axial direction. A third dynamic pressure groove is formed on an upper surface of the end plate element or a lower surface of the flange part of the flange-attached inner ring element to cause the generation of dynamic pressure which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove, the second dynamic pressure groove, as well as the third dynamic pressure groove.  
      A fluid dynamic bearing unit of another embodiment of the present invention is composed of a combination of a plurality of modularized elements, having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a flange-attached shaft element having a shaft part in a middle section. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element closing the lower end part of the case element, a first outer ring element as well as a second outer ring element both fitted into the case element and a flange-attached shaft element inserted into the first outer ring element as well as the second outer ring element in such a way that the flange part thereof is located between a lower end surface of the first outer ring element and an upper surface of the second outer ring element. A first dynamic pressure groove is formed on an inner circumferential surface of the first outer ring element or an outer circumferential surface of the main body of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the radial direction. A second dynamic pressure groove is formed on an inner circumferential surface of the second outer ring element or an outer circumferential surface of the main body of the flange-attached shaft element to cause the generation of dynamic pressure, which receives the load in the radial direction. A third dynamic pressure groove is formed on a lower surface of the first outer ring element or an upper surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. A fourth dynamic pressure groove is formed on an upper surface of the second outer ring element or a lower surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove, the second dynamic pressure groove, the third dynamic pressure groove, as well as the fourth dynamic pressure groove.  
      A fluid dynamic bearing unit of another embodiment of the present invention is composed of a combination of a plurality of a modularized element, having a plurality of dynamic pressure generation mechanism parts, and freely supporting relative rotation of a flange-attached shaft element having a flange part at one end. The fluid dynamic bearing comprises a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element closing the lower end part of the case element, a first outer ring element as well as a second outer ring element both fitted into the case element, a flange-attached shaft element inserted into the first outer ring element as well as the second outer ring element in such a way that the flange part thereof is located between a lower end surface of the second outer ring element and an upper surface of the end plate element. A spacer element surrounds the flange part of the flange-attached shaft element and positions the second outer ring element relative to the end plate element. A first dynamic pressure groove is formed on an inner circumferential surface of the first outer ring element or an outer circumferential surface of the main body of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the radial direction. A second dynamic pressure groove is formed on an inner circumferential surface of the second outer ring element or an outer circumferential surface of the main body of the flange-attached shaft element to cause the generation of dynamic pressure, which receives the load in the radial direction. A third dynamic pressure groove is formed on a lower surface of the second outer ring element or an upper surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. A fourth dynamic pressure groove is formed on an upper surface of the end plate element or a lower surface of the flange part of the flange-attached shaft element to cause the generation of dynamic pressure which receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces corresponding to the first dynamic pressure groove, the second dynamic pressure groove, the third dynamic pressure groove, as well as the fourth dynamic pressure groove.  
      Another embodiment of a fluid dynamic bearing unit freely supports the relative rotation of a straight shaft element having multiple dynamic pressure generation mechanism parts. The fluid dynamic bearing unit is composed of a combination of multiple modularized elements, and includes a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element that closes the lower end part of the above-mentioned case element, a first outer ring element as well as a second outer ring element fit into the above-mentioned case element, and a first inner ring element inserted into the above-mentioned first outer ring element. A second flange-attached inner ring element having a flange part at one end is inserted into the above-mentioned second outer ring element so that the flange part thereof is sandwiched between the lower end surface of the second outer ring element and the upper surface of the end plate. A shaft element is fit into the first inner ring element and the second flange-attached inner ring element. A first dynamic pressure groove is formed on the inner circumferential surface of the first outer ring element or the outer circumferential surface of the first inner ring element for generation of dynamic pressure that receives the load in the radial direction. A second dynamic pressure groove is formed in the inner circumferential surface of the second outer ring element or the inner circumferential surface of the second flange-attached inner ring element to cause the generation of dynamic pressure that receives the load in the radial direction. A third dynamic pressure groove is formed on the lower end surface of the second outer ring element or on the upper surface of the flange part of the second flange-attached inner ring element to cause the generation of dynamic pressure that receives the load of the axial direction. A fourth dynamic pressure groove is formed on the upper surface of the end plate element or on the lower surface of the flange part of the second flange-attached inner ring element to cause the generation of dynamic pressure that receives the load in the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces of the first dynamic pressure groove, the second dynamic pressure groove, the third dynamic pressure groove and the fourth dynamic pressure groove.  
      Another embodiment of a fluid dynamic bearing unit freely supports the relative rotation of a stepped shaft element having a large diameter part and a small diameter part, and has multiple sets of dynamic pressure generation grooves. The fluid dynamic bearing unit is composed of a combination of multiple modularized elements, and is characterized by a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element that closes the lower end part of the tubular case element and fits into the tubular case element, a first outer ring element having a cylindrical shaped inner circumferential surface of a large diameter and a second outer ring element having a cylindrical shaped inner circumferential surface of a small diameter. A stepped shaft element is inserted into the first outer ring element and the second outer ring element so that large diameter part thereof is inserted into the first outer ring element, and the small diameter part thereof is inserted into the second outer ring element. A first dynamic pressure groove is formed on the inner circumferential surface of the first outer ring element or the outer circumferential surface of the large diameter part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the radial direction. A second dynamic pressure groove is formed in the inner circumferential surface of the second outer ring element or the outer circumferential surface of the small diameter part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the radial direction. A third dynamic pressure groove is formed on the upper end surface of the second outer ring element or on the surface of the step part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces of the first dynamic pressure groove, the second dynamic pressure groove and the third dynamic pressure groove.  
      Another embodiment of a fluid dynamic bearing unit freely supports the relative rotation of a stepped shaft element having a small diameter part and a large diameter part and having multiple sets of dynamic pressure generation grooves. The fluid dynamic bearing is composed of a combination of multiple modularized elements and is characterized by a tubular case element having a cylindrical shaped inner circumferential surface, an end plate element that closes the lower end part of the above-mentioned case element and fit into the above-mentioned case element, a first outer ring element having a small diameter cylindrical inner circumferential surface as well as a second outer ring element having a large diameter cylindrical inner circumferential surface. A stepped shaft element is inserted into the first outer ring element as well as the second outer ring element so that the small diameter part thereof is inserted into the first outer ring element and the large diameter part thereof is inserted into the second outer ring element. A first dynamic pressure groove is formed on the inner circumferential surface of the first outer ring element or the outer circumferential surface of the small diameter part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the radial direction. A second dynamic pressure groove is formed in the inner circumferential surface of the second outer ring element or the outer circumferential surface of the large diameter part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the radial direction. A third dynamic pressure groove is formed on the lower end surface of the first outer ring element or on the surface of the step part of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the axial direction. A fourth dynamic pressure groove is formed on the upper surface of the end plate element or on the lower end surface of the stepped shaft element to cause the generation of dynamic pressure that receives the load of the axial direction. Lubricating oil is filled in the minute gap between each of the facing surfaces of the first dynamic pressure groove, the second dynamic pressure groove, the third dynamic pressure groove and the fourth dynamic pressure groove.  
      In the above embodiments of the fluid dynamic bearing, the elements on which the dynamic pressure grooves are formed are made of steel that can be hardened or stainless steel that can be hardened. The dynamic pressure grooves are formed on these elements, after the elements are heat treated and ground, by means of electrochemical machining.  
      Furthermore, in the above embodiments of the fluid dynamic bearing, a step part is formed in the lower end part of the case element, the end plate element is fit together with said step part, and the lower end part of the case element is made so as to be closed. Exceptional accuracy is obtained due to the fact that grinding of the inner circumferential surface of the case element and the step part can be done at the same time in one setting. The right angle between the upper surface of the end plate and the shaft center of the case element becomes easy to produce, the assembly accuracy of each element that forms the fluid dynamic bearing unit is improved, and high relative rotational accuracy of the shaft element is obtained.  
      Further features and advantages will appear more clearly on a reading of the detailed description, which is given below by way of example only and with reference to the accompanying drawings wherein corresponding reference characters on different drawings indicate corresponding parts.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 1.  
       FIG. 2  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 2.  
       FIG. 3  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 3.  
       FIG. 4  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 4.  
       FIG. 5  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 5.  
       FIG. 6  is a cross-sectional view of a variation example of the fluid dynamic bearing unit of embodiment 5.  
       FIG. 7  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 6.  
       FIG. 8  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 7.  
       FIG. 9  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 8.  
       FIG. 10  is a cross-sectional view of the fluid dynamic bearing unit of embodiment 9.  
       FIG. 11  is a cross-sectional view of a spindle motor used by a conventional fluid dynamic bearing device.  
    
    
     DETAILED DESCRIPTION  
      Formerly, fluid dynamic bearings, due to various obstacles (such as the supply system of the constituent parts, the assembly system of the bearings) were only used in limited technical areas and applications. The present invention, by making the constituent parts modularized and the completed product unitized, achieves standardization. Thus, easily supplying and making it possible to use the fluid dynamic bearings of various types and various specifications desired by engineers engaged in the development of products such as machines and devices including hard disk drives(HDD&#39;s) and digital versatile disk drives (DVD&#39;s).  
      According to the present invention, fluid dynamic bearing units of various standardized specifications, which can be used in various machines and devices, become easy to manufacture. Regardless of the kind of machine and device, the manufacturer of these machine and device will be able to immediately procure various elements of the fluid dynamic bearing units or the constituent parts thereof, when necessary, to assemble the fluid dynamic bearing units with the desired structure and dynamic pressure bearing function (including bearing rigidity with respect to the both the radial and axial direction loads). Selecting the optimum design from the viewpoint of the use of the bearing device and the desired structure becomes easy.  
      A fluid dynamic bearing unit according to the present invention freely supports the relative rotation of shaft elements of various shapes such as a flange-attached shaft element having a flange part at one end, a straight shaft element, a flange-attached shaft element having a flange part in the middle part and a stepped shaft element having a large diameter part and a small diameter part. The fluid dynamic bearing unit is broken down into multiple elements that are easy to modularize such as a case element, an end plate element, an outer ring element, a first outer ring element, a second outer ring element, an inner ring element, a flange-attached inner ring element, a first inner ring element, a second inner ring element, a second flange-attached inner ring element, a spacer element, and a shaft element. The inside of a bearing container is formed by one end part of a case element closed by the end plate element and other parts of various specifications from the parts listed above appropriately mutually assembled, collected and fixed. A dynamic pressure groove for the purpose of generating a dynamic pressure that receives the load in the radial direction or the axial direction on the prescribed surface of a prescribed element is formed. In the minute gaps between the opposing surfaces, one of which surface is the dynamic pressure groove, lubricating oil is filled in. And, at least, the elements in which a dynamic pressure groove is formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after the heat treatment has been performed and the grinding has been finished, the dynamic pressure groove is formed by means of electrochemical machining.  
      Done in this way, a fluid dynamic bearing unit provided with the desired structure and dynamic pressure bearing function (including bearing rigidity with respect to the load of the radial and axial directions) is obtained. The following embodiments are some examples of the standardized modular fluid dynamic bearings of the present invention.  
     Embodiment 1  
      Next, embodiment 1 of the invention of this application will be explained.  
       FIG. 1  is a cross-sectional view of embodiment 1 of a fluid dynamic bearing unit  1 . The fluid dynamic bearing unit  1  freely supports relative rotation of a flange-attached shaft element  40  having a flange part  42  on one end (the lower edge in  FIG. 1 ). The flange-attached shaft element  40  has a main part  41  having an outer circumferential surface  43 . The flange part  42  has an upper surface  44  and a lower surface  45 . The fluid dynamic bearing unit  1  has a tubular case element  10  having a cylindrical shaped inner circumferential surface  11 , and a disc shaped end plate element  20  that closes the lower end part of the case element  10 . A cylindrical shaped outer ring element  30  fits into the case element  10 . The flange part  42  is arranged so as to be sandwiched between a lower end surface  32  of the outer ring element  30  and an upper surface  21  of the end plate element  20 . The flange-attached shaft element  40  is inserted into the outer ring element  30 . The end of the flange-attached shaft element  40  that is away from the end having the flange part  42  protrudes from the topside of the case element  10 .  
      In the fluid dynamic bearing unit  1 , generally, the flange-attached shaft element  40  rotates, but an integrated assembly body composed of the case element  10 , the end plate element  20  and the outer ring element  30 , may be made the rotating side. The fluid dynamic bearing unit  1  may be used with the illustrated up-down position reversed.  
      First dynamic pressure grooves, for example, grooves  51 - 1 ,  51 - 2 , are formed on the inner circumferential surface  31  of the outer ring element  30 . The first dynamic pressure grooves generate dynamic pressure between the outer circumferential surface  43  and the opposing inner circumferential surface  31 . The dynamic pressure receives (i.e. supports) the load in the radial direction. A second dynamic pressure groove  52  is formed on the lower end surface  32 . The Dynamic pressure generated between the upper surface  44  and the lower end surface  32  receives the axial direction load. A third dynamic pressure groove  53  is formed on the upper surface  21  of the end plate element  20 . The first, second and third dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  are collectively referred to as dynamic pressure grooves  51 ,  52  and  53  hereafter. The dynamic pressure generated between the upper surface  21  and the lower surface  45  receives the axial direction load. These dynamic pressure grooves  51 ,  52  and  53 , are formed in a herring bone shape, but the shape is not restricted at all, and being formed in a spiral shape, a circular arc shape, a straight line shape and the like is also acceptable.  
      The first dynamic pressure grooves  51 - 1  and  51 - 2 , are formed in two places and are separated in the axial direction. This way the shaft element  40  obtains a high bearing rigidity, since the shaft element  40  is supported at two places in the axial direction. This is particularly advantageous when the axial direction dimension of the fluid dynamic bearing unit  1  is large. The first dynamic pressure grooves may be formed at only one place if the axial dimension of the case element  10  needs to be reduced.  
      A minute gaps is formed between each of the dynamic pressure grooves  51 ,  52  and  53  and a respective facing surface. Lubricating oil is filled in each of the gaps. The lubricating oil is filled from a lubricating oil seal mechanism part  60 . This lubricating oil seal mechanism part  60  is a gap formed by the space between the outer circumferential surface  43  and the open end side of the outer ring element  30  having slightly widened diameter.  
      This gap of the lubricating oil seal mechanism part  60  has a bigger width than the width of the minute gap formed between each of the dynamic pressure grooves  51 ,  52  and  53  and the facing surface. Since the capillary force in the gap of this widened seal mechanism part  60  works as the holding force of the lubricating oil, the oil doesn&#39;t leak out via the gap of the seal mechanism part  60 .  
      The elements on which the dynamic pressure grooves  51 ,  52  and  53  are formed, i.e., the outer ring element  30  and the end plate element  20 , are manufactured from steel that can be hardened or stainless steel that can be hardened. The ring element  30  and the end plate element  20  are heat treated and ground. Because of the hardening, the dynamic pressure grooves  51 ,  52  and  53  are difficult to damage and their high dimensional accuracy can be maintained not only at the time of the assembly and at the time of handling of a single element, but also when the operation of a fluid dynamic bearing unit is suspended and at the time of rotation activation. Since the shape of the dynamic pressure grooves  51 ,  52  and  53  is maintained, the dynamic pressure bearing function as designed is exhibited. The dynamic pressure grooves  51 ,  52  and  53  are formed by means of electrochemical finishing to obtain fine surface roughness. In addition, by use of electrochemical machining, the machining time for the purpose of dynamic pressure groove formation can be shortened. After heat treatment, the inner circumferential surface  11 , the outer circumferential surface and the surface of both ends of the case element  10  are finished by grinding. After the heat treatment the upper surface  21  and the outer circumference of the end plate  20  are finished by grinding. Furthermore, it is acceptable to manufacture the flange-attached shaft element  40  with the same kind of material, heat treat similarly, and finish by grinding. It is also acceptable to manufacture the end plate element  20  with normal stainless steel and carry out a coating of DLC (Diamond-Like Carbon) to raise the hardness of the surface.  
      The flange part  42  of the flange-attached shaft element  40  may be formed integral with the main body  41 , or may be formed as a separate body and attached to the shaft element  40  by assembling by means of pressing in, bonding, caulking, welding and the like methods or using more than one of these methods at same time.  
      A step part  12  is formed in the lower end part of the case element  10 . The outer circumferential edge part of the end plate element  20  is fit in the step part  12 . The lower end part of the case element  10  is closed by the end plate element  20 .  
      Since simultaneously grinding of the surfaces of the step part  12  that faces upper surface  21  and the inner circumferential surface  11  is possible, exceptional accuracy can be obtained. The accuracy makes perpendicularity of the upper surface  21  and the shaft center of the case element  10  easier to produce, improves the assembly accuracy of each element constituting the fluid dynamic bearing unit  1 , and allows high relative rotation accuracy of the shaft element  40  to be obtained.  
      The assembly formed by the case element  10  closed by the end plate element  20  is called a bearing container. It is also possible to form this bearing container in one piece. A one piece bearing container also allows modularization. By making bearing container one piece, the number of elements is reduced by one, the work of fitting the end plate element  20  into the lower end part of the case element  10  is eliminated, and the structure and the assembly work of the fluid dynamic bearing unit  1  is simplified.  
      The outer ring element  30  is fitted into the case element  10  by means of shrink fitting, caulking, bonding or like methods. The assembly of the outer ring element  30  and the case element  10  rotates as a unit.  
      To maintain the dimensional relationships and the position relationships that exist at the time of assembly in all kinds of use environment temperatures, as far as possible, materials with small differences in the coefficient of linear expansion are selected. For same reasons, the planning and improvement of machining and assembly accuracy related to roundness, cylindricity, surface roughness, flatness, parallelism and the like are also important.  
      Furthermore, to manufacture standardized fluid dynamic bearing  1  that can be used in various kinds of machines and devices, the accuracy of the external shape, dimensions, surface properties of the case element  10  and the end plate element  20 , the external diameter dimensions, surface properties and the like of the shaft element  40  also must be sufficiently paid attention to so that highly accurate fitting and attaching with the various kinds of machines and devices can be achieved. For same reasons finishing the roundness, cylindricity or cylindricality, surface roughness and the like to a high precision is necessary. Furthermore, the unevenness of the diameter of the elements and the width dimensions of these is reduced as far as possible.  
      In the fluid dynamic bearing  1 , constituted as mentioned above, modularization of each element is easy and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      When the flange-attached shaft element  40  is constantly being pressed in an axial direction towards the endplate element  20  by means of a bias effect such as a magnetic force that works between a rotating side element and a fixed side element, appropriate clearance between the flange-attached shaft element  40  and adjacent surfaces during rotation of the flange-attached shaft element  40  and stability and improved rotation accuracy of the flange-attached shaft element  40  is obtained. Even in the absence of such bias effect, the dynamic pressure that is generated in the minute gap formed at the second dynamic pressure groove  52  and the third dynamic pressure groove  53  holds appropriate clearance between the flange-attached shaft element  40  and adjacent surfaces during rotation of the flange-attached shaft element  40 , and stabilizes and improves the rotation accuracy of the flange-attached shaft element  40 .  
      The dynamic pressure grooves  51 ,  52  and  53  are respectively formed in the inner circumferential surface  31 , the lower end part  32  and the upper surface  21 , but are not limited to these. Instead the dynamic pressure grooves  51 ,  52  and  53  may be formed on the complimentary surfaces, i.e., outer circumferential surface  43 , the upper surface  44 , and the lower surface  45  of the flange-attached shaft element  40 . In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves are formed by electrochemical machining. Even when the location of the dynamic pressure grooves  51 ,  52  and  53  is changed, the same effects as mentioned above can be produced.  
     Embodiment 2  
      Next, embodiment 2 of the invention of this application will be explained.  
       FIG. 2  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 2. The fluid dynamic bearing unit  1  freely supports relative rotation of a shaft element  40 . The shaft element  40  has a main part  41  having an outer circumferential surface  43 . The fluid dynamic bearing unit  1  has a tubular case element  10  having a cylindrical shaped inner circumferential surface  11 , and a disc shaped end plate element  20  that closes the lower end part of the case element  10 . A cylindrical shaped outer ring element  30  fits into the case element  10 . The shaft element  40  is inserted into the outer ring element  30 .  
      First dynamic pressure grooves, for example grooves  51 - 1 ,  51 - 2 , are formed on the inner circumferential surface  31  of the outer ring element  30 . The first dynamic pressure grooves generate dynamic pressure between the outer circumferential surface  43  and an opposing inner circumferential surface  31  of the outer ring element  30 . The dynamic pressure receives (i.e. supports) the load in the radial direction. A second dynamic pressure groove  52  is formed on an upper surface  21  of the end plate element  20 . The Dynamic pressure generated between the upper surface  21  and a lower end part  46  of the shaft element  40  receives the axial direction load. Lubricating oil is filled in the minute gap formed between the first dynamic pressure grooves  51 - 1 ,  51 - 2 , the second dynamic pressure groove  52  and the respective opposing surfaces.  
      The elements on which the dynamic pressure grooves are formed, i.e., the outer ring element  30  and end plate element  20 , are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat treated and ground, a first dynamic pressure groove  51 - 1 ,  51 - 2  and a second dynamic pressure groove  52  are formed by means of electrochemical machining.  
      Since the rest of the constitution does not differ from that of embodiment 1 a detailed explanation has been omitted.  
      In the fluid dynamic bearing  1  of the second embodiment, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the outer ring element  30  and the straight shaft element  40  is easy and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      Furthermore, the outer ring element  30  and the end plate element  20  are manufactured from steel that can be hardened or stainless steel that can be hardened. The dynamic pressure grooves  51 - 1 ,  51 - 2 , and  52  are formed on these elements in same manner as described in the context of the first embodiment and they exhibit same properties and advantages as described previously.  
      Furthermore, the fluid dynamic bearing unit  1  of this embodiment 2 is of simple constitution compared to that of embodiment 1, and is a suitable for use when it is not necessary to generate dynamic pressure in the axial direction in order to cause the shaft element to float to the extent required for the fluid dynamic bearing unit  1  of embodiment 1, and when the bias effect of a magnetic force and the like that works between the rotating side element and the fixed side element that always presses the shaft element  40  towards the end plate element  20  is expected. In addition, the same kind of effects as in embodiment 1 can be produced.  
      Furthermore, as in embodiment 1, first and second dynamic pressure grooves  51 - 1 ,  51 - 2  and  52  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves are formed by electrochemical machining. Even when the location of the dynamic pressure grooves  51 - 1 ,  51 - 2  and  52  is changed, the same effects as mentioned above can be produced.  
     Embodiment 3  
      Next, embodiment 3 of the invention of this application will be explained.  
       FIG. 3  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 3. The fluid dynamic bearing unit  1  of embodiment 3 differs from the fluid dynamic bearing unit  1  ( FIG. 1 ) of embodiment 1 in that an outer ring element  30  of the third embodiment is thinner, and an inner ring element  70  is placed in the resulting space between a flange-attached shaft element  40  and the outer ring element  30 . The inner ring element  70  rotates relative to the outer ring element  30 . The flange-attached shaft element  40  is fit into the inner ring element  70  to form one unit therewith and rotates therewith. The inner ring element  70  and the outer ring element  30  form a bearing in the radial direction. The lower end of the inner ring element  70  contacts an upper surface  44  of a flange part  42  of the flange-attached shaft element  40 .  
      First dynamic pressure grooves comprised of an upper dynamic pressure groove  51 - 1  and a lower dynamic pressure groove  51 - 2 , the same as embodiment 1, are formed on an inner circumferential surface  31  of the outer ring element  30 . A minute gap is formed between the dynamic pressure grooves  51 - 1 ,  51 - 2  and an outer circumferential surface  73  of the inner ring element  70 . The second dynamic pressure groove  52  and the third dynamic pressure groove  53  are formed in same places as embodiment 1. Lubricating oil is filled into the minute gaps corresponding to the first dynamic pressure groove  51 - 1 ,  51 - 2 , the second dynamic pressure groove  52  and the third dynamic pressure groove  53 .  
      The dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  and the elements in which the dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  are formed are manufactured as previously disclosed in the context of first embodiment, and have the same properties and advantages.  
      The lubricating oil seal mechanism part  60  is a gap formed by the space between the outer circumferential surface  73  and the outer ring element  30  by means of the fact that the diameter of the open end side of the outer ring element  30  is slightly widened.  
      Since the rest of the constitution does not differ from that of embodiment 1, a detailed explanation has been omitted.  
      In the fluid dynamic bearing  1  of the third embodiment, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the outer ring element  30 , the inner ring element  70  and the straight shaft element  40  is easy and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      Furthermore, while using the same flange-attached shaft element  40 , by changing the radial distance of the gap formed between the outer ring element  30  and the inner ring element  70 , the dynamic pressure generated in this gap can be adjusted to suit the desired use conditions, i.e., the desired load in the radial direction. In addition, effects the same as those of embodiment 1 can be produced.  
      Furthermore, as in embodiment 3, first, second and third dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  are changed, the same effects as mentioned above can be produced.  
     Embodiment 4  
      Next, embodiment 4 of the invention of this application will be explained.  
       FIG. 4  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 4. The parts that correspond to embodiment 2 arid embodiment 3 have the same reference numerals.  
      As illustrated in  FIG. 4 , the fluid dynamic bearing unit  1  of this embodiment 4, when compared to the fluid dynamic bearing unit  1  ( FIG. 2 ) of embodiment 2, differs in that an outer ring element  30  is thinner, and a flange-attached inner ring element  70  is placed in the resulting space between a straight shaft element  40  and the outer ring element  30 . The flange-attached inner ring element  70  rotates relative to the outer ring element  30 . The shaft element  40  is fit into the inner ring element  70  to form one unit therewith and rotates therewith. The flange-attached inner ring element  70  and the outer ring element  30  form a bearing in the radial direction.  
      Furthermore, when compared to the fluid dynamic bearing unit  1  ( FIG. 3 ) of embodiment 3, embodiment 4 differs in that instead of the flange-attached shaft element  40  of the fluid dynamic bearing unit  1  of embodiment 3, the straight shaft element  40  is used. Also, in place of the straight inner ring element  70 , the flange-attached inner ring element  70  is used. A flange part  72  of the flange-attached inner ring element  70  is sandwiched between a lower end surface  32  of the outer ring element  30  and an upper surface  21  of an end plate element  20 , and relative rotation with respect to these surfaces is possible.  
      A second dynamic pressure groove  52 , similar to that in embodiment 3, is formed in the lower end surface  32  and faces an upper surface  74  of the flange part  72 . Furthermore, a third dynamic pressure groove  53 , similar to that in embodiment 3, is formed in the upper surface  21  of the end plate element  20  and faces a lower surface  75  of the flange part  72 . The place where first dynamic pressure grooves  51 - 1 ,  51 - 2  are formed does not differ from embodiment 3. A minute gap is formed between each of the first, second and third dynamic pressure groove  51 - 1 ,  51 - 2 ,  52 ,  53  and the facing surfaces. Lubricating oil is filled into the minute gaps.  
      The dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  and the elements in which the dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  are formed are manufactured as previously disclosed in the context of first embodiment, and have the same properties and advantages. The flange-attached inner ring element  70  and the shaft element  40  also, can be manufactured from steel or stainless steel that can be heat treated, heat treated and ground.  
      Since the rest of the constitution does not differ from that of embodiment 3, a detailed explanation has been omitted.  
      In the fluid dynamic bearing  1  of the fourth embodiment, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the outer ring element  30 , the flange-attached inner ring element  70  and the straight shaft element  40  is easy and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      Furthermore, while using the same straight shaft element  40 , by changing the radial distance of the gap formed between the outer ring element  30  and the inner ring element  70 , the dynamic pressure generated in this gap can be adjusted to suit the desired use conditions, i.e., the desired load in the radial direction. In addition, effects the same as those of embodiment 3 can be produced.  
      Furthermore, as in embodiment 1, first, second and third dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  51 - 1 ,  51 - 2 ,  52  and  53  are changed, the same effects as mentioned above can be produced.  
     Embodiment 5  
      Next, embodiment 5 of the invention of this application will be explained.  
       FIG. 5  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 5. As illustrated in the figure, the fluid dynamic bearing unit  1  of embodiment 5, when compared to the fluid dynamic bearing unit  1  ( FIG. 1 ) of embodiment 1, differs in that a flange part  42  of a flange-attached shaft element  40  in the fluid dynamic bearing unit  1  of embodiment 5 is shifted to the middle part in the axis direction of the shaft element  40 . The outer ring element  30  has been divided in two and positioned so that the flange part  42  is sandwiched from above and below.  
      Accordingly, in the embodiment 5, the two outer ring elements that sandwich the flange part  42  from above and below are a first outer ring element  30 , and a second outer ring element  80 . Reference numerals  81 ,  82 ,  83  refer to an inner circumferential surface, a lower end surface and an upper end surface of the second outer ring element  80 , respectively. Reference numerals  43 - 1 ,  43 - 2 , respectively, refer to a upper outer circumferential surface positioned in the upper part, and to a lower outer circumferential surface positioned in the lower part, of the flange part  42 . Reference numeral  47  refers to a lower end part of the shaft element  40 . New reference numerals  91 ,  92 ,  93  and  94  respectively refer to first, second, third and fourth dynamic pressure grooves. The same reference numerals are affixed to the other parts that correspond to embodiment 1.  
      The fluid dynamic bearing unit  1  of embodiment 5 freely supports relative rotation of the flange-attached shaft element  40  having the flange part  42  in the middle. The fluid dynamic bearing unit  1  includes a tubular case element  10  having a cylindrical inner circumferential surface  11 , and a disc shaped end plate element  20  that closes the lower end part of the case element  10 . The short cylindrical first outer ring element  30  and the second outer ring element  80  fit into the case element  10 . The flange part  42  is sandwiched between a lower end surface  32  of the first outer ring element  30  and the upper end surface  83  of the second outer ring element  80 . The flange-attached shaft element  40  is inserted into the first outer ring element  30  and the second outer ring element  80 . The lower end surface  82  of the second outer ring element  80  contacts the upper surface  21  of the end plate element  20 , but the lower end surface  47  of the flange-attached shaft element  40  slightly floats from the upper surface  21  of the end plate element  20 .  
      The dynamic pressure groove  91  is formed on an inner circumferential surface  31  of the first outer ring element  30 . The dynamic pressure groove  91  generates dynamic pressure between the upper outer circumferential surface  43 - 1  and the inner circumferential surface  31 . This dynamic pressure receives the load in the radial direction. The dynamic pressure groove  92  is formed on the inner circumferential surface  81  of the second outer ring element  80 . The dynamic pressure groove  92  generates dynamic pressure between the lower outer circumferential surface  43 - 2  and the inner circumferential surface  3   1 . This dynamic pressure also receives the load in the radial direction. The dynamic pressure groove  93  is formed on the lower end surface  32  of the first outer ring element  30 . The dynamic pressure groove  93  generates dynamic pressure between an upper surface  44  of flange part  42  and the lower end surface  32 . This dynamic pressure receives the load in the axial direction. The dynamic pressure groove  94  is formed on the upper end surface  83  of the second outer ring element  80 . The dynamic pressure groove  93  generates dynamic pressure between a lower surface  45  of flange part  42  and the upper end surface  83 . This dynamic pressure receives the load in the axial direction. Lubricating oil is filled into each of the minute gap formed between each of the dynamic pressure groove  91 ,  92 ,  93  and  94  and respective opposing surface.  
      The dynamic pressure grooves  91 ,  92 ,  93  and  94  and the elements in which the dynamic pressure grooves  91 ,  92 ,  93  and  94  are formed, in embodiment 5, are manufactured as previously disclosed in the context of first embodiment, and have the same properties and advantages. Furthermore, manufacturing the flange-attached shaft element  40  with the same material as these elements, carrying out heat treatment in the same way, and grinding is also acceptable.  
      The flange part  42 , formed in the middle, is integrated with the main body  41 , but it is also possible to assemble flange part  42  on the flange-attached shaft element  40  by means of pressing in, bonding, caulking, welding and the like methods or using those methods at the same time.  
      The rest of the constitution does not differ from embodiment 1 and so a detailed explanation is omitted.  
      In the fluid dynamic bearing  1  of the fifth embodiment, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the outer ring element  30 , the second outer ring element  80 , and the flange-attached shaft element  40  is easy and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      Furthermore, by changing the radial distance of the gap formed between the outer ring element  30  and the flange-attached shaft element  40 , the dynamic pressure generated in this gap can be adjusted. Additionally, by changing the radial distance of the gap formed between the outer ring element  80  and the flange-attached shaft element  40 , the dynamic pressure generated in this gap can be adjusted. Thus, the dynamic pressure generated in these two gaps can be adjusted to suit the desired use conditions, i.e., the desired load in the radial direction.  
      Furthermore, in a fluid dynamic bearing unit  1  of the same height, by variously changing the ratio of the axial direction dimension of the upper part and the axial direction dimension of the lower part of the main body  41  of the flange-attached shaft element  40 , and in proportion thereto variously changing and combining the axial direction height W 1  of the outer ring element  30  and the axial direction height W 2  of the outer ring element  80 , it is possible to adjust the dynamic pressure that receives the load in the radial direction to suit a desired use condition.  
      Furthermore, by variously changing the axial direction height W 1 , the axial direction height W 2  and correspondingly changing the axial direction position of the flange part  42  the dynamic pressure generation position that receives the load of the axial direction can be adjusted to suit the axial direction center of gravity position of all the rotating bodies including the rotating side elements. This reduces the movement that knocks down the flange-attached shaft element  40  and the whirling vibration attributable to the gyroscopic movement of the flange-attached shaft element  40 . The rotation of the flange-attached shaft element  40  can be stabilized, and the rotation accuracy can be improved.  
      Furthermore, if the dynamic pressure generated is equal to the load in the axial direction, a more effective reduction of the whirling vibration attributable to the gyroscopic movement of the flange-attached shaft element  40  becomes possible. Furthermore, when the reduction effect equal to that whirling vibration is desired, it can be achieved by the generation of a smaller dynamic pressure by means of adjusting, as described above, the dynamic pressure generation position that receives the axial direction load. By means of this, power consumption can be reduced.  
      When the shaft element  40  is not constantly being pressed in an axial direction by means of a bias effect such as a magnetic force between a rotating side element and a fixed side element, the dynamic pressure that is generated in the minute gap corresponding to dynamic pressure grooves  93  and  94  holds appropriate clearance between the flange-attached shaft element  40  and the adjacent surfaces and stabilizes and improves the rotation accuracy of the flange-attached shaft element  40 . In addition, the same effects as in embodiment 1 can be produced.  
      Furthermore, as in embodiment 1, the dynamic pressure grooves  91 ,  92 ,  93  and  94  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  91 ,  92 ,  93  and  94  are changed, the same effects as mentioned above can be produced.  
      Next, examples of variations of embodiment 5 will be explained.  
      In this embodiment 5, as illustrated in  FIG. 6 , the diameter D 1  of one half (upper half in the figure) bordered by the flange part  42  and diameter D 2  of the other half (lower half in the figure) can be varied so as to be different. In the example shown in  FIG. 6  D 1 &gt;D 2 , but is not limited thereto. The degree of freedom for adjustment of the pressure that receives the load in the radial direction can be further increased as illustrated in the example of  FIG. 6 .  
      Furthermore, in the dynamic pressure generation part formed in the gap in the radial direction formed by the second outer ring element  80  and the small diameter main body  41  (small diameter radial pressure bearing part), since the small diameter can reduce the friction loss, bearing failure torque is reduced and power consumption can be reduced (converted to low power consumption).  
      In addition, due to the fact that friction loss is reduced in the radial pressure bearing part of the small diameter, the movement that acts in the direction that knocks down the flange-attached shaft element  40  is reduced. Thus, the whirling vibration due to the gyroscopic movement of the flange-attached shaft element  40  is reduced, the relative rotation thereof is stabilized and an improvement of rotational stability is provided for.  
     Embodiment 6  
      Next, embodiment 6 of the invention of this application will be explained.  
       FIG. 7  is a cross-sectional view of a fluid dynamic bearing unit of embodiment 6. The same reference numerals are affixed to the parts that correspond to embodiment 5 and embodiment 1.  
      As illustrated in  FIG. 7 , the fluid dynamic bearing unit  1  of embodiment 6, when compared to the fluid dynamic bearing unit  1  of embodiment 5 ( FIG. 5 ), differs in that a flange part  42  of a flange-attached shaft element  40  of the fluid dynamic bearing unit  1  of embodiment 6 has been shifted to one end part (lower end part) of the flange-attached shaft element  40 , and in order to position a second outer ring element  80  with respect to an end plate element  20 , a ring shaped spacer element  100  is provided. This ring shaped spacer element  100  is disposed so as to surround the flange part  42  of the flange-attached shaft element  40 .  
      Consequently, the fluid dynamic bearing unit  1  of embodiment 6 freely supports the relative rotation of a flange-attached shaft element  40  having the flange part  42  on one end. A case element  10  of the fluid dynamic bearing unit I has the end plate element  20 , a first outer ring element  30  and the second outer ring element  80  fit into the case element  10 . The flange-attached shaft element  40  is inserted into the first outer ring element  30  and the second outer ring element  80  with the flange part  42  thereof sandwiched between the lower end surface  82  of the second outer ring element  80  and an upper surface  21  of the end plate element  20 . A ring shaped spacer element  100  is provided so as to surround the flange part  42  of the flange-attached shaft element  40 .  
      A dynamic pressure groove  91  is formed on the inner circumferential surface  31  of the first outer ring element  30 . The dynamic pressure groove  91  generates dynamic pressure between the outer circumferential surface  43  and the inner circumferential surface  31 . This dynamic pressure receives the load in the radial direction. The dynamic pressure groove  92  is formed on the inner circumferential surface  81  of the second outer ring element  80 . The dynamic pressure groove  92  generates dynamic pressure between the outer circumferential surface  43  and the inner circumferential surface  81 . This dynamic pressure also receives the load in the radial direction. The dynamic pressure groove  93  is formed on the lower end surface  82  of the second outer ring element  80 . The dynamic pressure groove  93  generates dynamic pressure between an upper surface  44  of the flange part  42  and the lower end surface  82 . This dynamic pressure receives the load in the axial direction. The dynamic pressure groove  94  is formed on the upper surface  21  of the end plate element  20 . The dynamic pressure groove  94  generates dynamic pressure between a lower surface  45  of flange part  42  and the upper surface  21 . This dynamic pressure receives the load in the axial direction. Lubricating oil is filled into each of the minute gap formed between each of the dynamic pressure groove  91 ,  92 ,  93  and  94  and respective opposing surface.  
      The elements in which the dynamic pressure grooves  91 , 92 , 93  and  94  are formed, the first outer ring element  30 , the second outer ring element  80  and the end plate element  20 , are made from steel that can be hardened or stainless steel that can be hardened. The elements are heat treated and ground and then, by means of electrochemical machining the first dynamic pressure groove  91 , the second dynamic pressure groove  92 , the third dynamic pressure groove  93 , and the fourth dynamic pressure groove  94  are formed in the elements.  
      Since the rest of the constitution does not differ from that of embodiment 5, a detailed explanation is omitted.  
      In the fluid dynamic bearing unit  1  of embodiment 6, constituted as mentioned above, the modularization of each element that constitutes it, namely, the case element  10 , the end plate element  20 , the first outer ring element  30 , the second outer ring element  80 , the flange-attached shaft element  40 , and the spacer element  100  is easy, and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit  1  is easily manufactured.  
      Furthermore, by changing the radial distance of the gap formed between the outer ring element  30  and the main body  41 of the flange-attached shaft element  40 , the dynamic pressure generated in this gap can be adjusted. Additionally, by changing the radial distance of the gap formed between the outer ring element  80  and the main body  41  of the flange-attached shaft element  40 , the dynamic pressure generated in this gap can be adjusted. Thus, the dynamic pressure generated in these two gaps can be adjusted to suit the desired use conditions, i.e., the desired load in the radial direction.  
      Furthermore, in a fluid dynamic bearing unit  1  of the same height, by variously changing the axial direction height W 1  of the first outer ring element  30  and the axial direction height W 2  of the second outer ring element  80 , the dynamic pressure that receives the load in the radial direction can be adjusted to suit a desired use condition. Also, by changing the radial distance of the gap formed by the first outer ring element  30  and the main body  41 as well as the gap formed by the second outer ring element  80  and the main body  41 , the dynamic pressure generated in these gaps can be adjusted to suit a desired use condition becomes possible. These two methods of adjusting dynamic pressure may be combined to suit a desired use condition.  
      Furthermore, by means of the spacer element  100 , even when the flange part  42  is of differing thickness&#39;, the axial direction position of the first outer ring element  30  and the second outer ring element  80  can be accurately adjusted and set with respect to the end plate element  20 .  
      Furthermore, the first outer ring element  30 , the second outer ring element  80  and the end plate element  20  in which dynamic pressure grooves  91 ,  92 ,  93  and  94  are formed, are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, dynamic pressure grooves are formed by electrochemical machining. Thus, these elements can be obtained with high hardness and high dimensional accuracy. Particularly, since dynamic pressure grooves of fine surface roughness can be obtained and the shape thereof is maintained, the dynamic pressure bearing function as designed can be exhibited. In addition, by means of electrochemical machining, the machining time for the purpose of dynamic pressure groove formation can be shortened. Besides, effects the same as in embodiment 5 can be produced.  
      Furthermore, in embodiment 6, the dynamic pressure grooves  91 ,  92 ,  93  and  94  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  91 ,  92 ,  93  and  94  are changed, the same effects as mentioned above can be produced.  
     Embodiment 7  
      Next, embodiment 7 of the invention of this application will be explained.  
       FIG. 8  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 7. As illustrated in the figure, the fluid dynamic bearing unit  1  of the seventh embodiment, when compared to the fluid dynamic bearing unit  1  ( FIG. 4 ) of embodiment 4, differs in that an outer ring element  30  and a flange-attached outer ring element  70  in the fluid dynamic bearing unit  1  of embodiment 7 are divided in two parts.  
      Accordingly, the upper part of the outer ring element  30  is still called the first outer ring element  30 , and an inner circumferential surface and a lower end surface thereof is still referred to with reference numerals  31  and  32 . The lower part of the outer ring is newly regarded as a second outer ring element  80 , and to an inner circumferential surface, a lower end surface and an upper end surface thereof, are referred to with numerals (reference numerals the same as embodiment 6 ( FIG. 7 ))  81 ,  82 , and  83 . The upper part of the flange-attached outer ring element  70  is still called a first inner ring element  70 , and to an outer circumferential surface thereof, the same as in embodiment 4, reference numeral  73  is affixed. The lower end surface of first inner ring element  70  is referred to with reference numeral  76 . The lower part is newly regarded as a second flange-attached outer ring element  110 , and to a main part, a flange part, a outer circumferential surface, a upper surface of the flange part, a lower surface of the flange part, and a upper end part new reference numerals  111 ,  112 ,  113 ,  114 ,  115 ,  116  are, respectively, affixed. The other parts that correspond to embodiment 4 and have the same reference numerals are affixed to them.  
      The fluid dynamic bearing unit  1  of the seventh embodiment freely supports the relative rotation of a straight shaft element  40 , and is provided with a case element  10 , and an end plate element  20 . The first outer ring element  30  and the second outer ring element  80  fit into the case element  10 , and the first inner ring element  70  fit into the first outer ring element  30 . The second flange-attached inner ring element  110 , having a flange part  112 , is sandwiched between the lower end surface  82  of the second outer ring element  80  and an upper surface  21  of the end plate element  20 . The second flange-attached inner ring element  110  is inserted into the second outer ring element  80 . The shaft element  40  is fit into the first outer ring element  70  and the second flange-attached inner ring element  110 .  
      The dynamic pressure groove  91  is formed on the inner circumferential surface  31  of the first outer ring element  30 . The dynamic pressure groove  91  generates dynamic pressure between the outer circumferential surface  73  and the inner circumferential surface  31 . This dynamic pressure receives the load in the radial direction. The dynamic pressure groove  92  is formed on the inner circumferential surface  81  of the second outer ring element  80 . The dynamic pressure groove  92  generates dynamic pressure between the outer circumferential surface  113  and the inner circumferential surface  81 . This dynamic pressure also receives the load in the radial direction. The dynamic pressure groove  93  is formed on the lower end surface  82  of the second outer ring element  80 . The dynamic pressure groove  93  generates dynamic pressure between an upper surface  114  of flange part  112  and the lower end surface  82 . This dynamic pressure receives the load in the axial direction. The dynamic pressure groove  94  is formed on the upper surface  21  of the end plate element  20 . The dynamic pressure groove  94  generates dynamic pressure between a lower surface  115  of flange part  112  and the upper surface  21 . This dynamic pressure receives the load in the axial direction. Lubricating oil is filled into each of the minute gap formed between each of the dynamic pressure groove  91 ,  92 ,  93  and  94  and respective opposing surface.  
      The lower end surface  32  of the first outer ring element  30  and the upper end surface  83  of the second outer ring element  80  make contact, and the lower end surface  76  of the first inner ring element  70  contacts the upper end surface  116  of the second flange-attached inner ring element  110 . The lower end surface  46  of the shaft element  40  slightly floats from the upper surface  21  of the end plate element  20 .  
      The elements in which the dynamic pressure grooves are formed, in this embodiment 7, the first outer ring element  30 , the second outer ring element  80  and the end plate element  20 , are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, by means of electrochemical machining, the first dynamic pressure groove  91 , the second dynamic pressure groove  92 , the third dynamic pressure groove  93  and the fourth dynamic pressure groove  94  are, respectively, formed. Furthermore, the first inner ring element  70  and the second flange-attached inner ring element  110  also can be manufactured from the same material.  
      Since the rest of the constitution does not differ from embodiment 4, a detailed explanation has been omitted.  
      In the fluid dynamic bearing  1  of the seventh embodiment, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the fist outer ring element  30 , the second outer ring element  80 , the first inner ring element  70 , the second flange-attached inner ring element  110 , and the shaft element  40  is easy, and by means of each element being modularized in this way, a standardized fluid dynamic bearing unit is easily manufactured.  
      Furthermore, by changing the radial distance of the gap formed by the first outer ring element  30  and the first inner ring element  70 , and the gap formed by the second outer ring element  80  and the main body  111  of the second flange-attached inner ring element  110  to different dimensions, the dynamic pressure subject to the load in the radial direction can be adjusted to suit the desired use conditions  
      Furthermore, in a fluid dynamic bearing unit  1  of the same height, by variously changing the axial direction height W 1  of the first outer ring element  30  and the axial direction height W 2  of the second outer ring element  80 , and correspondingly variously changing the axial direction height of the first inner ring element  70  and the axial direction height of the second flange-attached inner ring element  110 , and combining these change in axial dimensions with the adjusting of the dynamic pressure as described above, both the dynamic pressure generation position and the dynamic pressure can be adjusted to suit desired use conditions.  
      When the dynamic pressure and the dynamic pressure generation position are adjusted in this way, i.e., by having the gap radius formed by the first outer ring element  30  and the first inner ring element  70  (radius of a virtual cylindrical film which the gap center forms), and the gap radius formed by the second outer ring element  80  and the main body  111  of the second flange-attached inner ring element  110  differ, the degree of freedom of the adjustment of the above-mentioned dynamic pressure can be further widened. Furthermore, the inner diameter of the first inner ring element  70  and the inner diameter of the second flange-attached inner ring element can differ, and in line with this, the shaft element  40  can be have a stepped construction having a large diameter part and a small diameter part (refer to embodiments 8 and 9 described below). The shaft element with multiple steps can also be considered. By such diverse combinations diverse adjustment of the dynamic pressure and the dynamic pressure generation position is possible. Due to this, prompt response to the design requirements of the bearing that is optimum for diverse load states becomes possible.  
      The dynamic pressure grooves  91 ,  92 ,  93  and  94  and the elements in which the dynamic pressure grooves  91 ,  92 ,  93  and  94  are formed, in embodiment 7, are manufactured as previously disclosed in the context of first embodiment, and have the same properties and advantages. In addition, effects the same as embodiment 4 can be produced.  
      Furthermore, as in embodiment 4, the dynamic pressure grooves  91 ,  92 ,  93  and  94  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  91 ,  92 ,  93  and  94  are changed, the same effects as mentioned above can be produced  
     Embodiment 8  
      Next, embodiment 8 of the invention of this application will be explained.  
       FIG. 9  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 8. The fluid dynamic bearing unit  1  of embodiment 8 can be thought of as the fluid dynamic bearing unit  1  of embodiment 5 ( FIG. 6 ) in which the flange part  42  of the flange-attached shaft element  40  has been cut out. Accordingly, the same reference numeral  40  is affixed to the new stepped shaft element formed with the flange part  42  cut out. The upper half (large diameter part), the lower half (small diameter part), the downward facing surface of the step part thereof, are referred to with the new reference numerals  41 - 1 ,  41 - 2 ,  48  respectively. To the other parts that correspond to the embodiment 5 ( FIG. 6 ) the same reference numerals are affixed.  
      The fluid dynamic bearing unit  1  of embodiment 8 freely supports the relative rotation of a stepped shaft element  40  having an upper half large diameter part  41 - 1  and a lower half small diameter part  41 - 2 . The fluid dynamic bearing unit  1  is provided with a tubular case element  10  having a cylindrical shaped inner circumferential surface  11 , and an end plate element  20  that closes the lower end part of the case element  10 . The fluid dynamic bearing also includes the first outer ring element  30  having a cylindrical shaped inner circumferential surface  31  of a large diameter and a second outer ring element  80  having a cylindrical shaped inner circumferential surface  81  of a small diameter, and the stepped shaft element  40  is inserted into a first outer ring element  30  and a second outer ring element  80  so that the large diameter part  41 - 1  thereof inserted into the first outer ring element  30  and the small diameter part thereof  41 - 2  inserted into the second outer ring element  80 .  
      The dynamic pressure groove  91  is formed on the inner circumferential surface  31  of the first outer ring element  30 . The dynamic pressure groove  91  generates dynamic pressure between the outer circumferential surface  43 - 1  of the large diameter part  41 - 1  of the stepped shaft element  40  and the inner circumferential surface  31 . This dynamic pressure receives the load in the radial direction. The dynamic pressure groove  92  is formed on the inner circumferential surface  81  of the second outer ring element  80 . The dynamic pressure groove  92  generates dynamic pressure between the opposing outer circumferential surface  43 - 2  of the small diameter part  41 - 2  of the stepped shaft element  40  and the inner circumferential surface  81 . This dynamic pressure also receives the load in the radial direction. The dynamic pressure groove  93  is formed on the upper end surface  83  of the second outer ring element  80 . The dynamic pressure groove  93  generates dynamic pressure between the opposing surface of the step part  42  of the stepped shaft element  40  and the lower end surface  82 . This dynamic pressure receives the load in the axial direction. Lubricating oil is filled into each of the minute gap formed between each of the dynamic pressure groove  91 ,  92 , and  93  and respective opposing surface.  
      The lower end surface  32  of the first outer ring element  30  and the upper end surface  83  of the second outer ring element  80  (the part further to the outside from the part which the third dynamic pressure groove  93  forms) are in contact, and the lower end surface  82  of the second outer ring element  80  and the upper surface  21  of the end plate element  20  are in contact. The lower end surface  47  of the stepped shaft element  40  is floated slightly from the upper surface  21  of the end plate element  20 .  
      The elements in which the dynamic pressure grooves are formed in embodiment 8, the first outer ring element  30  and the second outer ring element  80 , are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, by means of electrochemical machining, the first dynamic pressure groove  91 , the second dynamic pressure groove  92  and the third dynamic pressure groove  93  are, respectively, formed. Furthermore, it is also acceptable to manufacture the stepped shaft element  40  from the same material, carry out heat treatment in the same way, and finish with grinding.  
      Since the rest of the constitution does not differ from the variation example ( FIG. 6 ) of embodiment 5, a detailed explanation is omitted.  
      In the fluid dynamic bearing unit  1  of the eighth embodiment, constituted as mentioned above, modularization of each element that constitutes it, namely, the case element  10 , the end plate element  20 , the first outer ring element  30 , the second outer ring element  80 , and the stepped shaft element  40 , is easy. With each element modularized in this way a standardized fluid dynamic bearing unit  1  can be easily manufactured.  
      Furthermore, by changing the outer diameter dimension D 1  of the large diameter part  41 - 1  and the outer diameter dimension D 2  of the small diameter part  41 - 2  of the stepped shaft  40  and correspondingly changing the inside diameter of the first outer ring element  30  and the second outer ring element  80  it is possible to adjust the dynamic pressure subject to the load in the radial direction to suit the desired use conditions.  
      Furthermore, in a fluid dynamic bearing unit  1  of the same height, by variously changing the ratio of the axial direction dimension of the large diameter part  41 - 1 , and the axial direction dimension of the small diameter part  41 - 2 , of the stepped shaft element  40 , and in response thereto variously changing and combining the axial direction height W 1  of the first outer ring element  30  and the axial direction height W 2  of the second outer ring element  80 , it is possible to adjust the dynamic pressure that receives the load of the radial direction and the dynamic pressure generation position to suit a desired use condition.  
      Furthermore, since the axial direction height W 2  of the second outer ring element  80  and the axial position of the step part of the stepped shaft element  40  can be adjusted, the position of a dynamic pressure generation part formed in the minute gap between the facing surface of stepped shaft  40  and outer ring element  80  can be adjusted to suit the center of gravity of the entire rotating body in the axial direction. Thereby, the movement that acts in the direction that knocks down the stepped shaft element can be reduced and the whirling vibration attributable to the gyroscopic movement of the stepped shaft element  40  is lowered. The relative rotation of the stepped shaft  40  is stabilized causing the improvement of rotational accuracy.  
      Furthermore, due to the fact that the outer end part of the stepped shaft element  40  is connected to the load member of the rotor hub and the like, a comparatively high bearing rigidity is necessary. On the large diameter part  41 - 1  side of the stepped shaft element  40  positioned on the opposite side of the side which the case element  10  has closed by the end plate element  20 , the radial dynamic pressure bearing part of the large diameter having comparatively low bearing rigidity is set. The small diameter part  41 - 2  side of the stepped shaft element  40  is positioned on the side on which the case element  10  has been closed by the end plate element  20 . Since friction loss is proportional to the third power of the bearing diameter, the radial dynamic pressure bearing part having this small diameter can reduce friction loss and so, when viewed as a whole, by means of a simple constitution, while ensuring the necessary bearing rigidity, bearing failure torque is reduced as much as possible and power consumption is also reduced.  
      In addition, due to the fact that friction loss can be reduced in the small diameter radial dynamic pressure bearing part, the movement that acts in the direction that knocks down the stepped shaft element  40  can be reduced. Because of this aspect also, the whirling vibration attributable to the gyroscopic movement of the stepped shaft element is reduced, the relative rotation thereof is stabilized, and the rotational accuracy is improved.  
      Furthermore, the first outer ring element  30  and the second outer ring element  80  that are the elements in which dynamic pressure grooves  91 ,  92  and  93  are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, by means of electrochemical machining, these dynamic pressure grooves  91 ,  92  and  93  are finished, and so, these elements can be obtained with high hardness and high dimensional accuracy. They are difficult to damage and a high dimensional accuracy can be maintained. Particularly, since dynamic pressure grooves of fine surface roughness can be obtained and the shape thereof is maintained, the dynamic pressure bearing function as designed can be exhibited. In addition, by means of electrochemical machining, the machining time for the purpose of dynamic pressure groove formation can be shortened.  
      In addition, this embodiment 8 can produce the same effects as the variation example ( FIG. 6 ) of embodiment 5. However, the fluid dynamic bearing unit  1  of embodiment 8 is suitable for use when the action that constantly presses the shaft element  40  towards the end plate element  20  due to the bias effect of magnetic force and the like that works between a rotating side element and a stationary side element is present. On this point the action and effect of the eighth embodiment are different from that of the fifth embodiment ( FIG. 6 ).  
      Furthermore, as in embodiment 1, the dynamic pressure grooves  91 ,  92  and  93  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  91 ,  92  and  93  are changed, the same effects as mentioned above can be produced.  
     Embodiment 9  
      Next, embodiment 9 of the invention of this application will be explained  
       FIG. 10  is a cross-sectional view of a fluid dynamic bearing unit  1  of embodiment 9. In the fluid dynamic bearing unit  1  of embodiment 9 the large and small diameter of the upper half part and the lower half part of the stepped shaft  40  of the eighth embodiment are reversed. Consequently, in embodiment 9, a small diameter part  41 - 1  forms the upper half and a large diameter part  41 - 2  forms the lower half. Furthermore, in line with this, the inner circumferential surface diameter of a first outer ring element  30  is small and each the inner circumferential surface diameter of and a second outer ring element  80  is large. A step surface  49  is formed at the step part of a stepped shaft element  40  and is facing upwards. The same reference numerals are affixed to the other parts that correspond to embodiment 8.  
      The fluid dynamic bearing unit  1  of embodiment 9 freely supports the rotation of the stepped shaft element  40  having the small diameter  41 - 1  upper half and the large diameter  41 - 2  lower half. The fluid dynamic bearing unit  1  of embodiment 9 includes a tubular case element  10  having a cylindrical shaped inner circumferential surface  11 , and an end plate element  20  that closes the lower end part of the case element  10 . The fluid dynamic bearing unit  1  also includes the first outer ring element  30  having a cylindrical shaped inner circumferential surface  31  of a small diameter and the second outer ring element  80  having a cylindrical shaped inner circumferential surface  81  of a large diameter fit into a case element  10 . The stepped shaft element  40  is inserted into the first outer ring element  30  and the second outer ring element  80 . The small diameter part  41 - 1  of the shaft element  40  is inserted into the first outer ring element  30  and the large diameter part  41 - 2  thereof is inserted into the second outer ring element  80 .  
      A dynamic pressure groove  91  is formed on the inner circumferential surface  31  of the first outer ring element  30 . The dynamic pressure groove  91  generates dynamic pressure between the outer circumferential surface  43 - 1  of the small diameter part  41 - 1  of the stepped shaft element  40  and the inner circumferential surface  31 . This dynamic pressure receives the load in the radial direction. A dynamic pressure groove  92  is formed on the inner circumferential surface  81  of the second outer ring element  80 . The dynamic pressure groove  92  generates dynamic pressure between the opposing outer circumferential surface  43 - 2  of the large diameter part  41 - 2  of the stepped shaft element  40  and the inner circumferential surface  81 . This dynamic pressure also receives the load in the radial direction. A dynamic pressure groove  93  is formed on a lower end surface  32  of the first outer ring element  30 . The dynamic pressure groove  93  generates dynamic pressure between the opposing surface of the step part  42  of the stepped shaft element  40  and the lower end surface  32 . The dynamic pressure groove  94  is formed on an upper surface  21  of the end plate element  20 . A dynamic pressure groove  94  generates dynamic pressure between an opposing lower end surface  47  of the stepped shaft element  40  and the upper surface  21 . This dynamic pressure receives the load in the axial direction. Lubricating oil is filled into each of the minute gap formed between each of the dynamic pressure groove  91 ,  92 ,  93  and  94  and respective opposing surface.  
      The lower end surface  32  of the first outer ring element  30  and an upper end surface  83  of the second outer ring element  80  make contact, and a lower end surface  82  of the outer ring element  80  and the upper surface  21  of the end plate element  20  make contact.  
      The elements in which the dynamic pressure grooves are formed, the first outer ring element  30 , the second outer ring element  80  and the end plate element  20 , are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, by means of electrochemical machining, the first dynamic pressure groove  91 , the second dynamic pressure groove  92 , the third dynamic pressure groove  93  and the fourth dynamic pressure groove  94  are formed. Furthermore, manufacturing the stepped shaft element  40  from the same material, performing the same heat treatment and the grinding is also acceptable.  
      Since the rest of the constitution does not differ from embodiment 8, a detailed explanation has been omitted.  
      In the fluid dynamic bearing unit  1  of embodiment 9, constituted as mentioned above, modularization of each element such as the case element  10 , the end plate element  20 , the first outer ring element  30 , the second outer ring element  80  and the stepped shaft element  40  is easy, and with each element modularized in this way, standardized fluid dynamic bearing unit  1  is easily manufactured.  
      Furthermore, by changing the outer diameter dimension D 1  of the small diameter part  41 - 1  and the outer diameter dimension D 2  of the large diameter part  41 - 2  of the stepped shaft element  40  and correspondingly changing the inside diameter of the first outer ring element  30  and the second outer ring element  80  it is possible to adjust the dynamic pressure subject to the load in the radial direction to suit the desired use conditions.  
      Furthermore, in a fluid dynamic bearing unit  1  of the same height, by variously changing the ratio of the axial direction dimension of the small diameter part  41 - 1 , and the axial direction dimension of the large diameter part  41 - 2 , of the stepped shaft element  40 , and in response thereto variously changing and combining the axial direction height W 1  of the first outer ring element  30  and the axial direction height W 2  of the second outer ring element  80 , it is possible to adjust the dynamic pressure that receives the load of the radial direction and the dynamic pressure generation position to suit a desired use condition.  
      Furthermore, since the axial direction height W 1  of the axial direction height of the first outer ring element  30  and the axial position of the step part of the stepped shaft element  40  can be adjusted, the position of a dynamic pressure generation part formed in the minute gap between the facing surface of stepped shaft  40  and first outer ring element  30  can be adjusted to suit the center of gravity of the entire rotating body in the axial direction Thereby, the movement that acts in the direction that knocks down the stepped shaft element can be reduced and the whirling vibration attributable to the gyroscopic :movement of the stepped shaft element  40  is lowered. The relative rotation of the stepped shaft  40  is stabilized causing the improvement of rotational accuracy.  
      Furthermore, the small diameter of the radial dynamic pressure bearing part reduces friction loss, which in turn reduces bearing failure torque, which in turn can reduce power consumption.  
      In addition, due to the fact that friction loss can be reduced in the small diameter radial dynamic pressure bearing part, the movement that acts in the direction that knocks down the stepped shaft element  40  can be reduced. Because of this aspect, the whirling vibration attributable to the gyroscopic movement of the stepped shaft element is reduced, the relative rotation thereof is stabilized, and the rotational accuracy is improved.  
      Furthermore, the first outer ring element  30  and the second outer ring element  80  and the end plate element  20  that are the elements in which dynamic pressure grooves  91 ,  92 ,  93  and  94  are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, heat treated and ground. Then, by means of electrochemical machining, these dynamic pressure grooves  91 ,  92 ,  93  and  94  are finished, and so, these elements can be obtained with high hardness and high dimensional accuracy. They are difficult to damage and a high dimensional accuracy can be maintained. Particularly, since dynamic pressure grooves of fine surface roughness can be obtained and the shape thereof is maintained, the dynamic pressure bearing function as designed can be exhibited. In addition, by means of electrochemical machining, the machining time for the purpose of dynamic pressure groove formation can be shortened.  
      The dynamic pressure that is generated in the third dynamic pressure groove  93  and the fourth dynamic pressure groove  94  maintains the appropriate clearance between the opposing surface of the step part  42  of the stepped shaft element  40  and the lower end surface  32 , and between the opposing lower end surface  47  of the stepped shaft element  40  and the upper surface  21 . This effect of the dynamic pressure is similar to an action in which the stepped shaft element  40  is constantly being pressed in an axial direction towards an endplate element  20  by means of a bias effect such as a magnetic force that works between a rotating side element and a fixed side element. The effect of the dynamic pressure is to stabilize the relative rotation of the stepped shaft element  40  and improve rotation accuracy. In addition, the same effects as in embodiment 8 can be produced.  
      Furthermore, as in embodiment 1, the dynamic pressure grooves  91 ,  92 ,  93  and  94  can be formed on the complimentary surface. In this case also, elements in which dynamic pressure grooves are formed are manufactured from steel that can be hardened or stainless steel that can be hardened, and after being heat-treated and ground, the dynamic pressure grooves thereof are formed by electrochemical machining. Even when the locations of the dynamic pressure grooves  91 ,  92 ,  93  and  94  are changed, the same effects as mentioned above can be produced.  
      The invention of this application is not limited to the working examples above. In a range in which the essentials there do not change, various variations are possible. For example, in embodiments 8 and 9 the step part (the part that shifts from a large diameter part to a small diameter part) of the stepped shaft element  40  can also be made a tapered shape. While preferred embodiments of the invention has been described, various modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.