Compound bearing apparatus

A compound bearing apparatus of the present invention comprising a shaft, a sleeve outer ring surrounding the shaft, two rows of rotating bodies disposed between the shaft and the sleeve including a first row of the rotating bodies interposed between an outer rolling contact recess formed directly on the outer periphery of the shaft and a first inner rolling contact recess formed on the inner peripheral surface of the sleeve outer ring, and a second row of the rotating bodies interposed between an outer rolling contact recess formed on the outer periphery of an inner ring fitted onto the shaft and a second inner rolling contact recess formed on the inner peripheral surface of the sleeve, and a pair of inner and outer sealing plates having a through hole at the central portion thereof; wherein at the one side of the apparatus where the first row of the rotating bodies is provided, the sealing plates are mounted between the sleeve outer ring and the shaft with leaving between the plates and the sleeve outer ring or the shaft a slight clearance sufficient to provide a labyrinth seal function, and at the other side of the apparatus where the second row of the rotating bodies is provided, the sealing plates are mounted between the sleeve outer ring and the inner ring with leaving between the plates and the sleeve outer ring or the inner ring a slight clearance sufficient to provide a labyrinth seal function.

BACKGROUND OF THE INVENTION 
TECHNICAL FIELD 
The present invention relates to a compound bearing apparatus including two 
rows of rotating bodies, in particular to a compound bearing apparatus 
including on both ends thereof a pair of sealing plates of non-contacting 
type especially suitable for the spindle motor to be used in the hard disk 
drive means. 
DESCRIPTION OF THE PRIOR ART 
In the art, some bearing apparatus includes an annular sealing plate or 
plates mounted between the inner and outer rings or between the shaft and 
the outer ring so as to prevent the lubricant from splashing out of the 
apparatus or to prevent dust or dirt from entering into the apparatus. In 
the prior art, the sealing plates of non-contacting type may be employed 
in these bearing apparatus. 
In the case of bearing apparatus including inner and outer rings, the 
sealing structure of non-contacting type including a sealing plate is 
secured at its outer peripheral portion by means of adhesive to the end 
face of the outer ring with leaving a slight clearance between the inner 
peripheral portion thereof and the inner ring to avoid the contacting of 
the sealing plate with the inner ring. 
Upon rotating the inner or outer ring, there is still a problem of flowing 
the lubricant enclosed within the apparatus out through the clearance 
defined at the non-contacting portion. In particular, in the case of the 
bearing apparatus employed in the spindle motor of the hard disk drive 
means, the lubricant will be splashed and dispersed out through the slight 
clearance defined between the sealing plate and the inner ring during the 
rotation of the motor in high speed. Thus produced finely dispersed 
lubricant or oil mist is apt to get into the disk enclosure of the hard 
disk drive means and adhered to the magnetic disk or magnetic head to 
cause the crushing accident of the disk and the head. 
One of the countermeasures having been taken for preventing the 
above-mentioned accident is to contact the inner peripheral portion of the 
sealing plate with the inner ring. The outer peripheral portion thereof is 
secured to the outer ring. However, such structure can not be adopted 
under the following reasons; 
the heat or the torque due to friction can be produced; 
the leakage of the lubricant will be caused by the wear of the sealing 
plate; and 
wear particles can be produced. 
Presently, under the reasons mentioned above, there is also the bearing 
apparatus including the sealing structure of the non-contacting type at 
the equipment side and an additional labyrinth seal mechanism or a 
magnetic fluid seal mechanism at the opposite side. In the case that the 
additional labyrinth seal mechanism is included, there is a tendency to 
increase the manufacturing cost because of its complicated structure. In 
the case that the magnetic fluid seal mechanism is included, there is a 
tendency to spread the magnetic fluid out under the effect of centrifugal 
force, and sometimes the magnetic fluid will be dispersed under the effect 
of local difference of pressure. In conclusion, both mechanism 
mentioned-above are also not suitable for utilizing in the spindle motor 
for the hard disk drive means. 
Accordingly, the object of the present invention is to provide a compound 
bearing apparatus suitable for the spindle motor of the hard disk drive 
means. In such a compound bearing apparatus, the labyrinth seal mechanism 
or mechanisms which was provided in the prior art additionally is 
incorporated thereinto so as to increase the sealing function of the 
sealing structure of the non-contacting type to the level in which 
sufficient effect can be obtained. 
SUMMARY OF THE INVENTION 
This object is achieved by a compound bearing apparatus comprising a shaft, 
a sleeve outer ring surrounding the shaft, two rows of rotating bodies 
disposed between the shaft and the sleeve including a first row of the 
rotating bodies interposed between an outer rolling contact recess formed 
directly on the outer periphery of the shaft and a first inner rolling 
contact recess formed on the inner peripheral surface of the sleeve outer 
ring and a second row of the rotating bodies interposed between an outer 
rolling contact recess formed on the outer periphery of an inner ring 
fitted onto the shaft and a second inner rolling contact recess formed on 
the inner peripheral surface of the sleeve, and a pair of inner and outer 
sealing plates having a through hole at the central portion thereof; 
wherein at the one side of the apparatus where the first row of the 
rotating bodies is provided, the sealing plates are mounted between the 
sleeve outer ring and the shaft with leaving between the plates and the 
sleeve outer ring or the shaft a slight clearance sufficient to provide a 
labyrinth seal function, and at the other side of the apparatus where the 
second row of the rotating bodies is provided, the sealing plates are 
mounted between the sleeve outer ring and the inner ring with leaving 
between the plates and the sleeve outer ring or the inner ring a slight 
clearance sufficient to provide a labyrinth seal function. 
Alternatively, a compound bearing apparatus comprising a two-stepped shaft 
including an enlarged diameter shaft portion and a reduced diameter shaft 
portion, a sleeve outer ring surrounding the stepped shaft, two rows of 
rotating bodies disposed between the shaft and the sleeve including a 
first row of the rotating bodies interposed between an outer rolling 
contact recess formed directly on the outer periphery of the enlarged 
diameter shaft portion of the two-stepped shaft and a first inner rolling 
contact recess formed on the inner peripheral surface of the sleeve outer 
ring and a second row of the rotating bodies interposed between an outer 
rolling contact recess formed on the outer periphery of an inner ring 
fitted onto the reduced diameter shaft portion of the two-stepped shaft 
and a second inner rolling contact recess formed on the inner peripheral 
surface of the sleeve, and a pair of inner and outer sealing plates having 
a through hole at the central portion thereof; wherein at the one side of 
the apparatus where the first row of the rotating bodies is provided, the 
sealing plates are mounted between the sleeve outer ring and the enlarged 
diameter shaft portion with leaving between the plates and the sleeve 
outer ring or the enlarged diameter shaft portion a slight clearance 
sufficient to provide a labyrinth seal function, and at the other side of 
the apparatus where the second row of the rotating bodies is provided, the 
sealing plates are mounted between the sleeve outer ring and the inner 
ring with leaving between the plates and the sleeve outer ring or the 
inner ring a slight clearance sufficient to provide a labyrinth seal 
function.