Patent Publication Number: US-2005139444-A1

Title: Bicycle hub

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to Japanese Patent Application No. 2003-430236. The entire disclosure of Japanese Patent Application No. 2003-430236 is hereby incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to a bicycle hub and more specifically to a bicycle rear hub that is arranged in the center portion of a wheel, mounted to the frame of the bicycle, and configured such that a sprocket can be mounted thereto.  
      2. Background Information  
      A bicycle wheel typically includes a centrally located hub, a plurality of spoke extending outwardly from the hub and a rim coupled to the outer ends of the spokes. The hub typically includes a spindle or hub shaft mounted in a detachable and non-rotatable manner to the frame of the bicycle, a hub body mounted in a freely rotatable manner to the hub shaft, and a pair of bearings configured to support the hub body in such a manner that it can rotate freely with respect to the hub shaft. In the case of a rear hub (free hub) mounted to the rear wheel of a bicycle, the hub is further provided with a drive body mounted in a freely rotatable manner to the hub shaft and a one-way clutch configured and arranged to transfer rotation from the drive body to the hub body in only one direction (the direction corresponding to forward travel of the bicycle). One known example of this type of rear bicycle hub is disclosed in U.S. Pat. No. 6,260,681, which shows a bicycle hub having a pair of rolling bearings installed between the drive body and the hub shaft and arranged so as to be spaced apart from each other. The inner ring of the rolling bearing located farther toward the outside in the axial direction of the hub shaft is pressed by a pressing member that is screwed onto the hub shaft. The rolling bearing located farther toward the inside in the axial direction of the hub shaft is arranged so as to touch against the hub shaft and the drive body. A cylindrical spacer is installed between the inner rings of the two rolling bearings. Thus, the drive body is pressed by the pressing member through the bearings and thereby positioned with respect to the hub body.  
      In the conventional bicycle hub the above described United States Patent, the outer rings of the rolling bearings are fitted tightly to the inner circumference of the drive body and the inner rings of the rolling bearings are fitted tightly to the outside circumferential surface of the hub shaft. When these kinds of bearings are installed between the drive body and the hub shaft, the innermost one of the bearings is first press fitted into the drive body and then the hub shaft is press fitted into the innermost one of the bearings. Next, the spacer is inserted and the outermost one of bearings is press fitted into position. Finally, the pressing member is installed so as to press against the inner ring of the outermost bearing and position the drive body with respect to the hub body.  
      In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved rear bicycle hub. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.  
     SUMMARY OF THE INVENTION  
      With the conventional bicycle hub described above, the inner ring and outer ring of the outer rolling bearing tend to become displaced relative to each other when the inner ring thereof is pressed with the pressing member. Depending on the amount of the displacement, there is the possibility that variation will occur in the torque of the drive body when the drive body is rotated relative to the hub shaft. If the torque of the drive body varies, the drive body will not rotate smoothly relatively to the hub shaft and the hub will not feel well made when one holds it in one&#39;s hand and rotates the hub shaft or the drive body. Thus, it is difficult provide such a hub with a high quality feel.  
      The object of the present invention is to reduce the variation of the torque of the drive body.  
      In view of the above mentioned problems and object, a bicycle hub is provided in accordance with a first aspect of the present invention that is configured with a hub shaft, a tubular hub body, a first rolling bearing, a second rolling bearing, a tubular drive body, a one-way clutch, a third rolling bearing, a fourth rolling bearing, a tubular spacer, and a pressing member. The hub shaft is configured to be mounted to a bicycle frame and form a center axis of rotation of the bicycle hub. The tubular hub body is arranged on the hub shaft to rotate about the center axis of the hub shaft. The first rolling bearing is arranged between the hub body and the hub shaft at a first end of the hub body. The second rolling bearing is arranged between the hub body and the hub shaft at a second end of the hub body and spaced apart from the first rolling bearing in an axial direction of the hub shaft. The tubular drive body is arranged on the hub shaft in a rotatable manner and configured such that at least one sprocket can be mounted to an outside circumference thereof. The one-way clutch is configured and arranged to transfer rotation from the drive body to the hub body in only one direction. The third rolling bearing is arranged in a gap between the drive body and the hub shaft. The third rolling bearing has an outer ring abutting and an inner ring. The outer ring of the third rolling bearing abuts against the drive body and fits loosely inside the drive body to have a clearance with respect to an inside circumference of the drive body. The inner ring of the third rolling bearing abuts against the hub shaft and fits tightly onto the hub shaft. The fourth rolling bearing is arranged to an outwardly of the third rolling bearing in the axial direction of the hub shaft. The fourth rolling bearing has an outer ring fitting and an inner ring. The outer ring of the fourth rolling bearing abuts the hub shaft and fits loosely inside the drive body to have a clearance with respect to the inside circumference of the drive body. The inner ring of the fourth rolling bearing abuts the hub shaft and fitting tightly onto the hub shaft. The tubular spacer is arranged on the hub shaft in such a manner as to be pinched between the inner rings of the third and fourth rolling bearings. The pressing member is configured to be fastened onto the hub shaft to press against the inner ring of the fourth rolling bearing and position the drive body relative to the hub body.  
      With this bicycle hub, when the pedals are rotated in the direction corresponding to forward travel of the bicycle and the rotation of the pedals is transmitted to the sprocket, the drive body rotates in the same direction. The rotation of the drive body is transferred to the hub body by means of the one-way clutch and the wheel rotates. When this hub is assembled, first the hub body is mounted to the hub shaft using the first and second bearings and then the component parts of the one-way clutch are mounted to the hub body and drive body. Next, the third bearing is installed into the drive body. Since the outer ring of the third bearing fits loosely in the drive body with a certain degree of clearance there-between, it can be installed smoothly into the drive body. Next, the inner ring of the third bearing is press fitted onto the hub shaft so that the drive body is mounted to the hub shaft. Then, the spacer is mounted to the hub shaft in such a manner as to abut against the third bearing and the fourth bearing is installed onto the hub shaft using the pressing member such that the inner ring of the fourth bearing is press fitted onto the hub shaft and the drive body is positioned with respect to the hub body. Hear again, the fourth bearing can be inserted smoothly into the drive body because the outer ring of the fourth bearing fits loosely in the drive body with a certain degree of clearance. As a result, the outer ring and the inner ring do not readily become displaced from each other in the axial direction of the hub shaft during press fitting. Since the outer rings of the third and fourth bearings are fitted loosely into the drive body, the outer rings move smoothly together with the inner rings when the third and fourth bearings are press fitted onto the hub shaft and it is difficult for the outer rings to become axially displaced relative to the inner rings. Consequently, variation does not readily occur in the torque of the drive body.  
      According to a second aspect of the present invention, the bicycle hub of the first aspect of the present invention is further provided with a seal member disposed between the outer ring of the fourth rolling bearing and the drive body. Since the fourth bearing is located toward the outside of the hub, there is the potential for liquids and other contaminants to penetrate the inside of the hub through the gap (loose fit) between the outer ring of the fourth bearing and the inner circumference of the drive body. The seal member seals the gap between the outer ring and the inner circumference of the drive body to make it difficult for contaminants to enter the hub.  
      According to a third aspect of the present invention, the bicycle hub of the first or second aspect of the present invention is configured with the internal surface of the drive body having an annular groove for installing the seal member is provided in the internal surface of the drive body. Since the seal member is installed into a groove provided in the drive body, it is not necessary to make a groove in the rolling bearing and a commercially available rolling bearing can be used.  
      According to a fourth aspect of the present invention, the bicycle hub of anyone of the first to third aspects of the present invention is configured such that the first and second rolling bearings are angular ball bearings and the third and fourth rolling bearings are ball bearings. Angular ball bearings having a high thrust load strength are used for the hub body because thrust forces tend to act on the hub body. Meanwhile, ball bearings are used for the drive body because the thrust forces that act on the drive body are weaker than those acting on the hub body.  
      According to a fifth aspect of the present invention, the bicycle hub of anyone of the first to fourth aspects of the present invention is configured such that the drive body includes a first or inner cylindrical body configured to have at least one sprocket mounted to the outside circumference thereof, and a second or outer cylindrical body configured to mate in a non-rotatable manner with an inner circumferential part of the first cylindrical body, be arranged generally inside the hub body, and have the one-way clutch mounted thereto. Since the drive member is made up of two cylindrical bodies and the second cylindrical body fits inside the first cylindrical body, the water resistance performance of the hub can be improved and the work required to assemble the hub is simplified.  
      According to a sixth aspect of the present invention, the bicycle hub of anyone of the first to fifth aspects of the present invention is configured such that the one-way clutch includes at least one clutch pawl, a force applying member and a plurality of ratchet teeth. The at least one clutch pawl is movably mounted to the drive body between an extended position and a retracted position. The force applying member is configured and arranged to apply a force against the at least one clutch pawl to urge the at least one clutch pawl toward the extended position. The ratchet teeth are provided on the hub body, are configured to selectively mate with the at least one clutch pawl when the drive body rotates in one direction such that the rotation of the drive body is transferred from the at least one clutch pawl to the ratchet teeth on the drive body, and are configured to retract the at least one clutch pawl to the retracted position when the drive body rotates in the other direction. Thus, the drive body is able to transfer rotation to the hub body in only one direction by means of the engagement and disengagement of the clutch pawls and ratchet teeth.  
      According to a seventh aspect of the present invention, the bicycle hub of the sixth aspect of the present invention is configured such that the ratchet teeth are formed on the internal surface of a cylindrical member that is fixed to the internal surface of the hub body. The ratchet teeth require a higher strength than the hub body as a whole and this arrangement allows the ratchet teeth to be provided on a member that is separate from the hub body. As a result, the weight of the hub can be reduced while maintaining the strength of the one-way clutch.  
      With the present invention, the outer rings of the third and fourth bearings move smoothly together with the inner rings when the third and fourth bearings are press fitted onto the hub shaft because the outer rings of the third and fourth bearings are fitted loosely into the drive body. As a result, the outer and inner rings do not easily become displaced with respect to each other in the axial direction of the hub shaft and variation is less likely to occur in the torque of the drive body.  
      These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Referring now to the attached drawings which form a part of this original disclosure:  
       FIG. 1  is a side elevational view of a bicycle equipped a rear hub in accordance with a first embodiment of the present invention;  
       FIG. 2  is a partial cross sectional view of the rear hub in accordance with the first embodiment of the present invention;  
       FIG. 3  is an enlarged cross sectional view of the drive body mounting section of the rear hub shown in  FIG. 2 ; and  
       FIG. 4  is an enlarged cross sectional view, corresponding to  FIG. 3 , of the drive body mounting section of a rear hub in accordance with a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.  
      Referring initially to  FIG. 1 , a bicycle  100  is illustrated that is equipped with a rear hub  1  in accordance with a first embodiment of the present invention. The bicycle  100  is an off-road bicycle, i.e., an all terrain bicycle (ATB) or a mountain bike (MTB). The bicycle  100  includes a front fork  101  and a frame body  102  that form a frame  103 . In the preferred embodiment, the front fork  101  is equipped with suspension and the frame body  102  is configured to support the front fork  101  in a freely rotatable manner at a front portion thereof. The bicycle  100  further includes a handlebar unit  104  fastened to the front fork  101 , a drive unit  105 , a front wheel  107  having spokes  106  mounted to the front fork  101  and a rear wheel  108  having spokes  106  and mounted to a rear portion of the frame body  102 .  
      The drive unit  105  includes a front sprocket cluster  109  and a rear sprocket cluster  110 , a front derailleur  111 , and a rear derailleur  112  that form front and rear gear changing devices  113  and  114 . The drive unit  105  includes a chain  115  that is operatively disposed on the front and rear sprocket clusters  109  and  110 . The drive unit  105  has front crank arms with pedals that the rider pushes to operate the drive unit  105  in a conventional manner.  
      The rear hub  1  in accordance with the embodiment of the present invention will now be described. In the following explanations, the terms “left” and “right” will be used from the perspective of viewing the bicycle from the rear. Moreover, as used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a bicycle equipped with the rear hub  1  of the present invention. Accordingly, these terms, as utilized to describe the rear hub  1  of the present invention should be interpreted relative to a bicycle equipped with the rear hub  1  of the present invention.  
      As shown in  FIG. 2 , the two ends of the rear hub  1  are fastened to a rear part of the frame  103  along with the rear derailleur  112 . The rear hub  1  basically includes a hub shaft or spindle  5 , a generally cylindrical or tubular hub body  6  and a drive body  7 . The hub shaft  5  is fastened to a rear part of the frame  103 , while the hub body  6  is arranged over the outside circumference of the hub shaft  5  with clearance there-between so as to rotate around the hub shaft  5 . The drive body  7  is arranged on the right side of the hub body  6  in such a manner as to be coaxial with the hub body  6  and to partially overlap with the inside of the hub body  6 . The rear hub  1  further includes a one-way clutch  8 , a pair of hub rolling bearings  10  and  11 , a pair of freewheel rolling bearings  12  and  13 , a generally cylindrical or tubular spacer  14  and a pressing member  15 . The one-way clutch  8  is configured and arranged to transfer rotation from the drive body  7  to the hub body  6  only in the direction corresponding to forward travel of the bicycle  100 . The hub rolling bearings  10  and  11  are arranged between the hub body  6  and the hub shaft  5  so as to form first and second rolling bearings that supports the hub body  6  on the hub shaft  5  in a rotatable manner. The freewheel rolling bearings  12  and  13  (a left and right pair) are arranged in the gap between the drive body  7  and the hub shaft  5  and spaced apart from each other in the axial direction of the hub shaft  5 . The freewheel rolling bearings  12  and  13  form third and fourth rolling bearings that supports the drive body  7  on the hub shaft  5  in a rotatable manner. The spacer  14  is a tubular member arranged in such a manner as to be pinched between the inner rings of the freewheel rolling bearings  12  and  13 . The pressing member  15  that is screwed onto the hub shaft  5  so as to press against the fourth freewheel rolling bearing  13  and position the drive body  7  relative to the hub body  6 .  
      The hub shaft  5  basically includes a generally cylindrical or tubular main shaft body  20 , a generally cylindrical or tubular threaded shaft  21  and a flange member  22 . The main shaft body  20  supports the four rolling bearings  10  to  13 . The threaded shaft  21  passes through the main shaft body  20 . The flange member  22  is inserted into the left end of the main shaft body  20 . The main shaft body  20  includes a large-diameter cylindrical section  20   a , a small-diameter cylindrical section  20   b , a pair of (first and second) externally threaded sections  20   c  and  20   d , a flange section  20   e , and a step section  20   f . The large-diameter cylindrical section  20   a  is positioned on the inside of the hub body  6 . The small-diameter cylindrical section  20   b  is positioned inside the drive body  7 . The first and second externally threaded sections  20   c  and  20   d  are formed on the outside surface of both ends of the shaft main body  20 . The flange section  20   e  has a larger diameter than the large-diameter cylindrical section  20   a , and is formed between the large-diameter cylindrical section  20   a  and the small-diameter cylindrical section  20   b . The step section  20   f  is formed on the small-diameter cylindrical section  20   b . Additionally, as shown in  FIG. 3 , the small-diameter cylindrical section  20   b  is provided with bearing mounting surfaces  20   g  and  20   h  having larger diameters than the other portions of the small-diameter cylindrical section  20   b.    
      The threaded shaft  21  has a large-diameter head section  21   a  formed on the left end thereof, a shaft section  21   b  that passes through the main shaft body  20 , and a third externally threaded section  21   c  formed on the right end of the shaft section  21   b . A contact member  25  is mounted in a freely rotatable manner to the head section  21   a  and serves to pinch the frame  103  between itself and the flange member  22 . An O-ring serving to prevent the contact member  25  from falling off is installed between the head section  21   a  and the contact member  25 . The flange member  22  is inserted into the left end of main shaft body  20  and is prevented from falling out by an O-ring  24  installed in the gap between the flange member  22  and the internal surface of the main shaft body  20 . A flanged nut  112   a  provided on the derailleur  112  is screwed onto the third threaded section  21   c  of the threaded shaft  21  so as to pinch the rear derailleur  112  and the forked rear portion of the frame  103  between itself and the head section  21  a, thereby fastening the hub shaft  5  to the frame  103  in a non-rotatable manner.  
      The hub body  6  is made of, for example, a lightweight aluminum alloy and its external circumferential surface is provided with first and second hub flanges  31  and  32  (left and right pair) that are spaced apart from each other. A brake mounting section  33  configured such that the rotor  120  of a disk brake can be mounted thereto is provided on the internal and external surfaces of the left end of the hub body  6 . A one-way clutch mounting section  34  configured such that the one-way clutch  8  can be mounted thereto is provided on the internal surface of the right end of the hub body  6 . Bearing mounting sections  35  and  36  for mounting the bearings  10  and  11  are provided on the internal surface of the hub body  6  at positions axially inward of the brake mounting section  33  and axially inward of the one-way clutch mounting section  34 . The hub body  6  is supported by the first and second bearings  10  and  11  in such a manner that it can rotate freely with respect to the hub shaft  5 . The spokes  106  ( FIG. 1 ) hook onto the first and second hub flanges  31  and  32  and serve to link the wheel rim  121  ( FIG. 1 ) to the hub body  6 .  
      The first and second bearings  10  and  11  are angular ball bearings in which the balls are supported by, for example, opposing slanted surfaces and seals are provided on the axially outward facing sides thereof. The first bearing  10  has an outer ring or cone  10   a  that is screwed into the bearing mounting section  35 , an inner ring or cone  10   b  mounted to the external surface of the main shaft body  20  of the hub shaft  5 , and a plurality of balls  10   c  arranged between and in contact with the outer and inner rings  10   a  and  10   b . The second bearing  11  has an outer ring or cone  11   a  that is screwed into the bearing mounting section  36 , an inner ring or cone  11   b  mounted to the external surface of the main shaft body  20  of the hub shaft  5 , and a plurality of balls  11   c  arranged between and in contact with the outer and inner rings  11   a  and  11   b . The inner ring  10   b  is screwed onto the first threaded section  20   c  provided on the external surface of the main shaft body  20 , while the inner ring  11   b  is press fitted onto the external surface of the main shaft body  20  in such a manner as to abut against the flange section  20   e . The inner ring  10   b  is positioned and locked (prevented from turning) by a lock nut  58  that is screwed onto the first threaded section  20   c.    
      The drive body  7  is a generally cylindrical body made of, for example, steel and is configured such that a sprocket cluster  110  having a plurality of sprockets can be mounted thereto in a non-rotatable manner. As shown in  FIG. 3 , the external surface of the drive body  7  is provided with a sprocket mounting section  40  on which the sprocket cluster  110  is mounted in a non-rotational manner. The sprocket mounting section  40  comprises, for example, splines. A nut installing section  41  comprising internal threads is provided on the internal surface of the right-hand end of the drive body  7  so that a fastening nut (not shown) can be installed for the purpose of fastening the sprocket cluster  110 . A circular arc shaped clutch pawl support section  42  is provided on the external surface of the left-hand end of the drive body  7  and serves to support the clutch pawls  50  (discussed later) of the one-way clutch  8  in such a manner that the clutch pawls  50  can stand up (extended position) and lie down (retracted position) freely. Bearing mounting surfaces  43  and  44  are provided on the internal surface of the drive body  7  and have slightly smaller inside diameters than the rest of the internal surface of the drive body  7 . The outer rings  12   a  and  13   a  of the third and fourth rolling bearings  12  and  13  are installed into these bearing mounting surfaces  43  and  44 . A first annular groove  45  is formed closely adjacent to the bearing mounting surface  43  and a second annular groove  46  is formed closely adjacent to the bearing mounting surface  44 . A step section  47  is formed to the left of the bearing mounting surface  43 .  
      In this example, the third and fourth rolling bearings  12  and  13  are sealed ball bearings that are sealed on both sides with the bearing surfaces being formed by races having primarily circumferentially supporting bearing surfaces (called herein “circumferential ball bearings”). The third rolling bearing  12  has an outer ring or race  12   a  installed into the respective bearing mounting surface  43  of the drive body  7 , an inner ring or race  12   b  mounted onto the respective bearing mounting surface  20   g  of the hub shaft  5 , and a plurality of balls  12   c  arranged between and in contact with the outer and inner rings  12   a  and  12   b . The fourth rolling bearing  13  has an outer ring or race  13   a  installed into the respective bearing mounting surface  44  of the drive body  7 , an inner ring or race  13   b  mounted onto the respective bearing mounting surface  20   h  of the hub shaft  5 , and plurality of balls  13   c  arranged between and in contact with the outer and inner rings  13   a  and  13   b . The outer rings  12   a  and  13   a  and the bearing mounting surfaces  43   44  are loosely fitted together such that they having a degree of clearance between the outer ring and the bearing mounting surface, while the inner rings  12   b  and  13   b  and the bearing mounting surfaces  20   g  and  20   h  are tightly fitted together. Consequently, the outer rings  12   a  and  13   a  can be installed smoothly into the bearing mounting surfaces  43  and  44  of the drive body  7 . Meanwhile, the inner rings  12   b  and  13   b  can be press fitted onto the hub shaft  5  in such a manner that they are held securely in place.  
      A flexible retaining ring  48  is installed into the first annular groove  45  and the outer ring  12   a  is positioned by being sandwiched between the step section  47  and the retaining ring  48  such that it cannot move in the axial direction. The inner ring  12   b  is positioned by being abutted against the step section  20   f  of the hub shaft  5 . A seal member  49 , e.g., an O-ring, is installed into the second annular grove  46 . The seal member  49  serves to seal the gap between the outer ring  13   a  and the mounting surface of the drive body  7  (which are loosely fitted) and prevent liquids and other contaminants from entering the hub.  
      The spacer  14  is installed such that the ends thereof touch against the inner ring  12   b  and the inner ring  13   b  and serves to position the first and fourth rolling bearings  12  and  13  such that a prescribed spacing is maintained there-between.  
      The pressing member  15  is screwed onto the second externally threaded section  20   d  of the hub  5 . The pressing member  15  serves to press the inner ring  13   b  and position the drive body  7  with respect to the hub body  6 . When the pressing member  15  is screw-tightened, the inner ring  13   b , the spacer  14 , and the inner ring  12   b  are pressed against the step section  20   f  of the hub shaft  5  and the drive body  7  is thereby installed onto the hub shaft  5  in such a manner as to have a prescribed position with respect to the hub body  6 . Meanwhile, the rear hub  1  is fastened to the frame  103  by means of the frame  103  being pinched between the pressing member  15  and the rear derailleur  112 .  
      The one-way clutch  8  has a plurality of equally spaced apart clutch pawls  50 , a plurality of saw-tooth-shaped ratchet teeth  51  forming a ratchet part  52 , and a ring-shaped spring member  53 . The clutch pawls  50  are moveably mounted on the clutch pawl support section  42  of the drive body  7  in such a manner that they can stand up (extended position) and lie down freely (retracted position). The ratchet part  52  is serration-fitted into the one-way clutch mounting section  34  of the hub body  6  in a non-rotatable manner with the saw-tooth-shaped ratchet teeth  51  on the internal surface thereof. The ring-shaped spring member  53  applies a force against the clutch pawls  50  in such a manner as to urge the clutch pawls  50  toward a standing posture (extended position). The ratchet part  52  is prevented from coming out of place by the retaining ring  57 . When the drive body  7  rotates in the direction corresponding to forward motion of the bicycle, the clutch pawls  50  of the one-way clutch  8  engage with the ratchet teeth  51  and the rotation is transferred to the hub body  6 . Conversely, when the hub body  6  rotates in the direction corresponding to forward motion of the bicycle, such as during downhill travel, or when the drive body  7  is rotated in the direction opposite the direction corresponding to forward motion of the bicycle, the clutch pawls  50  are pressed by the ratchet teeth  51  in opposition to the spring force of the spring member  53  such that they lie down and rotation is not transferred between the hub body  6  and the drive body  7 .  
      The gap between the outer ring  10   a  and inner ring  10   b  of the first rolling bearing  10  and the gap between the right-hand end of the hub body  6  and the drive body  7  are sealed with dust seals  55  and  56 , respectively.  
      When a rear hub  1  constituted as described heretofore is assembled, first the hub body  6  is mounted to the hub shaft  5 . This is accomplished by first screwing the outer rings  10   a  and  11   a  of the first and second rolling bearings  10  and  11  (it is assumed the bearings are already assembled) into the internal surface of the hub body  6  such that the outer rings  10   a  and  11   a  are securely fastened therein and also screwing the ratchet part  52  of the one-way clutch  8  into the internal surface of the hub body  6  such that it is securely fastened therein. The main shaft body  20  of the hub shaft  5  is then inserted into the hub body  6  from the right side (i.e., the right side from the perspective of  FIG. 2 ) and the inner ring  10   b  of the first bearing  10  is screwed onto the first externally threaded section  20   c . In this way, the compression of the balls of the first and second rolling bearings  10  and  11  is adjusted while mounting the hub body  6  to the hub shaft  5  in a freely rotatable manner.  
      Next, the drive body  7  is mounted onto the hub shaft  5 . Before this is done, the clutch pawls  50  are mounted to the clutch pawl support section  42  of the drive body  7  and the spring member  53  is mounted to the clutch pawls  50 . Then the third rolling bearing  12  is installed into the bearing mounting surface  43  of the drive body  7  and the retaining ring  48  is installed into the first annular groove  45 , the outer ring  12   a  being positioned by the retaining ring  48 . The third rolling bearing  12  is then oriented toward and press fitted onto the bearing mounting surface  20   g  of the hub shaft  5 , thereby mounting the drive body  7  onto the hub shaft  5 . From this state, the spacer  14  is installed over the hub shaft  5 , the seal member  49  is installed into the second annular groove  46 , and then the fourth rolling bearing  13  is installed onto the bearing mounting surface  20   h . The fourth rolling bearing  13  is installed by screwing the pressing member  15  onto the second externally threaded section  20   d  such that it presses against the inner ring  13   b  of the fourth rolling bearing  13  and causes the inner ring  13   b  to be press fitted onto the bearing mounting surface  20   h . During the press fitting, the outer ring  13   a  moves smoothly in the axially inward direction (leftward in  FIG. 3 ) in accordance with the movement of the inner ring  13   b  because the outer ring  13   a  is loosely fitted into the bearing mounting surface  44  of the drive body  7 . As a result, the inner ring  13   b  and the outer ring  13   a  do not easily become displaced relative to each other in the axial direction and variation does not readily occur in the torque of the drive body  7 . Finally, after fully tightening the pressing member  15 , the assembly of the rear hub  1  is completed by installing the dust seals  55  and  56 .  
     Second Embodiment  
      Referring now to  FIG. 4 , a rear hub  60  in accordance with a second embodiment will now be explained. In view of the similarity between the first and second embodiments, the parts of the second embodiment that are identical to the parts of the first embodiment will be given the same reference numerals as the parts of the first embodiment. Moreover, the descriptions of the parts of the second embodiment that are identical to the parts of the first embodiment may be omitted for the sake of brevity. Although the previous embodiment presents a case in which the rear hub  1  is mounted to the frame  103  using a threaded shaft, the present invention is not limited to such an arrangement.  FIG. 4  shows the rear hub  60  that is configured to be mounted to the frame  103  of the bicycle  100  in a freely detachable manner using a well-known quick release configuration (not shown). This rear hub  60  is intended for use with road bikes (or “road racers”) and is lighter in weight than the rear hub  1  of the previously described embodiment.  
      The rear hub  60  comprises a hub shaft  65 , a hub body  66 , and a drive body  67 . The rear hub  60  is further provided with a one-way clutch  68 , a first rolling bearing (not shown), a second rolling bearing  71 , third and fourth rolling bearings  72  and  73 , a generally cylindrical or tubular spacer  74 , and a pressing member  75 . The one-way clutch  68  is configured and arranged to transfer rotation from the drive body  67  to the hub body  66  only in the direction corresponding to forward travel of the bicycle. The first rolling bearing (not shown) and the second rolling bearing  71  are arranged between the hub body  66  and the hub shaft  65 . The third and fourth rolling bearings  72  and  73  are arranged in the gap between the drive body  67  and the hub shaft  65  and spaced apart from each other. The tubular spacer  74  is arranged in such a manner as to be pinched between the inner rings  72   b  and  73   b  of the third and fourth rolling bearings  72  and  73 . The pressing member  75  screws onto the hub shaft  65 , and presses against the fourth rolling bearing  73  to position the drive body  67  with respect to the hub body  66 .  
      The hub shaft  65  is a generally cylindrical member having a well-known quick release shaft passing through the inside thereof. The hub shaft  65  is provided with two step sections  65   a  and  65   b  located on both sides of the section where the one-way clutch  68  is mounted. A first externally threaded section (not shown) and a second externally threaded section  65   d  are formed on both ends of the hub shaft  65 . A cylindrical bearing seat  80  is mounted to the hub shaft  65  at a position axially inward of the second externally threaded section  65   d . The bearing seat  80  is loosely fitted onto the external surface of the hub shaft  65  with a degree of clearance and is positioned along the hub shaft  65  by the step section  65   b . A step section  80   a  is provided on the left end of the bearing seat  80  for the purpose of positioning the third bearing  72 . The bearing seat  80  is provided on the hub shaft  65  so that the drive body  67  and the bearing seat  80  can be changed (replaced) together with ease.  
      The hub body  66  is supported in a freely rotatable manner on the hub shaft  65  by means of the first bearing and second bearing  71  mounted inside the hub body  66 . A one-way clutch mounting section  66   a  is provided on the internal surface of the right-hand end of the hub body  66  and the ratchet part  91  of the one-way clutch  68  is installed in a non-rotatable but freely removable manner in the clutch mounting section  66   a . The internal face of the ratchet part  91  is provided with ratchet teeth  90 .  
      In this embodiment, the drive body  67  comprises a first cylindrical body  82  that is made of, for example, an aluminum alloy and has a sprocket cluster mounted to the outside circumference thereof and a second cylindrical body  83  that is made of, for example, a steel material, has the one-way clutch  68  mounted thereon, is arranged generally inside the hub body  66 , and mates in a non-rotatable manner with an inner circumferential part of the first cylindrical body  82 . The second cylindrical body  83  is fastened to the first cylindrical body  82  by being screwed into the first cylindrical body  82 . The clutch pawls  89  of the one-way clutch  68  are mounted to the external circumferential surface of the second cylindrical body  83  in such a manner that they can stand up and lie down freely. The clutch pawls  89  are spring-loaded in a standing posture by a spring member  92 .  
      Two bearing mounting surfaces  84  and  85  are provided on the internal surface of the first cylindrical body  82  and have smaller inside diameters than the rest of the internal surface of the first cylindrical body  82 . Also provided in the internal surface of the first cylindrical body  82  are a first annular groove  86  formed adjacent to the bearing mounting surface  84  and a second annular groove  87  formed in the bearing mounting surface  85 . A retaining ring  95  is installed into the first annular groove  86  and an O-ring  96  having, for example, a rectangular cross sectional shape is installed into the second annular groove  87 .  
      The third and fourth rolling bearings  72  and  73  have the same constituent features as in the previously described embodiment. The rolling bearing  72  is provided with an outer ring  72   a , an inner ring  72   b  and a plurality of balls  72   c . The rolling bearing  73  is provided with an outer ring  73   a , an inner ring  73   b , and a plurality of balls  73   c . The fits between the inner rings  72   b  and  73   b  and the bearing seats  80  are tight fits, while the fits between the outer rings  72   a  and  73   a  and the bearing mounting surfaces  84  and  85  of the first cylindrical body  82  are loose fits with clearance.  
      The spacer  74  is arranged so as to abut against both the inner ring  72   b  of the third rolling bearing  72  and the inner ring  73   b  of the fourth rolling bearing  73 . The pressing member  75  is screwed onto the second externally threaded section  65   d  so as to press against the inner ring  73   b  of the fourth rolling bearing  73  through the dust seal  97 .  
      In the case of a rear hub  60  configured as described heretofore, when the pressing member  75  is pressed against the inner ring  73   b  of the fourth rolling bearing  73  during installation of the drive body  67  onto the hub shaft  65 , the outer ring  73   a  of the fourth rolling bearing  73  moves smoothly in the axial direction along with the inner ring  73   b  because the outer ring  73   a  fitted loosely into the first cylindrical member  82  of the drive body  67 .  
      Although in the previous embodiments ball bearings are used for the third and fourth bearings, the present invention is not limited to ball bearings. It is also acceptable to use roller bearings or any other type of bearing that is a rolling bearing.  
      Although in the previous embodiments the rear hub is mounted to the frame together with the rear derailleur, the present invention is not limited to the mounting arrangements presented in the previous embodiments. For example, it is also acceptable for the rear hub to be mounted using nuts on both ends of the rear hub.  
      Although in the previous embodiments the pressing member  15  or  75  is screwed onto the hub shaft, it is also acceptable for the pressing member to be press fitted. In such a case, it is good to press fit the bearing  13  or  73  together with the pressing member  15  or  75 . It is also acceptable to use an O-ring or the like to prevent the pressing member  15  or  75  from coming out of position, similarly to the contact member  22 . In such a case, the pressing member  15  or  75  should be installed after press fitting the bearing  13  or  73  with a separate member.  
      In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Finally, terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.  
      While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.