Endless belt power transmission systems or components – Friction drive pulley or guide roll – With stationary support for pulley or guide roll
Reexamination Certificate
2001-12-14
2004-02-17
Charles, Marcus (Department: 3682)
Endless belt power transmission systems or components
Friction drive pulley or guide roll
With stationary support for pulley or guide roll
C474S135000
Reexamination Certificate
active
06692393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pulley ball bearing and a pulley, for instance, a pulley that is a component of a wrapping connector transmission device installed in an engine for an automobile.
2. Description of the Related Art
As it is well known, engines for automobiles are equipped with a wrapping connector transmission device for driving a component of the engine such as cam shaft as well as various auxiliary equipment such as an alternator, a water pump, an oil pump, and an air conditioner by utilizing the revolution of the engine output shaft. This wrapping connector transmission device is equipped with an idler pulley and a tension pulley as floating pulleys for increasing the contact angle of the wound belt or for adding the required tension to the belt as well as a pulley for driving auxiliary equipment to which the belt is wound.
In the case of this kind of floating pulley, the pulley circumferential surface that comes into contact with the belt must have an idling structure against the irrotational shafts such as the fixed shaft. As an example, forming the pulley circumferential surface directly on the outside diameter of the outer ring of ball bearings (bevel type outer ring) is known. On the other hand, a structure in which the pulley main body possessing pulley circumferential surface integrally inter-fitted with ball bearings, is widely used.
As shown in
FIG. 6
, ball bearings used in the latter pulley are equipped with an outer ring
30
fitted into the inner diameter portion of the pulley main body (not illustrated), an inner ring
31
fitted into an irrotational shaft, a plurality of balls
32
assembled between both ball grooves
30
a
and
31
a
of the outer ring
30
and the inner ring
31
, a retainer
33
to retain the balls
32
at required intervals in the circumferential direction, and a pair of seals
34
for sealing grease filled between the outer ring 30 and the inner ring
31
. In the case of this kind of pulley, it is composed so that the outer ring
30
revolves together with the pulley main body when the pulley main body receives the revolving drive from the belt and revolves.
As for the conventional structure of the ball bearings for such a pulley, the pitch circle diameter (PCD) of ball
32
normally lies roughly in the middle of the outside diameter of the outer ring
30
and the inside diameter of the inner ring
31
. The ball groove depth (shoulder height)
30
t
of the outer ring
30
and the ball groove depth
31
t
of the inner ring
31
are set so that they fall within about 20% of the ball diameters.
In making such a setting, in a state of general usage including usage to other objects, disadvantages should not occur to the ball bearings. Concretely speaking, this is based on the fact that consideration is given so that extreme drop in rigidity caused by the formation of ball grooves
30
a
,
31
a
do not occur, or drop in bearing performance caused by radial load and thrust load do not occur.
On the other hand, since high load or offset load (moment load) hardly acts on this kind of pulley, load will not have great influence on the life of the ball bearings. However, in case where the grease deteriorates and its life is shortened, it results in shortening the life of the ball bearings. In other words, in cases such as the usage mode, during high speed revolution of the outer ring
30
, if the addition of load is small, slippage occurs between the balls
32
and the inner and outer rings
30
,
31
, the grease temperature rises because of friction heat, causing early deterioration of grease, and as a result, there is concern that it may shorten the life of the ball bearings.
Such a problem can be solved by increasing the amount of grease that is filled between the outer ring
30
and the inner ring
31
, but as mentioned above, if the amount of grease is merely increased under the setting conditions of each portion of the ball bearings, the sealing ratio of the amount of grease versus the space volume between the outer ring
30
and inner ring
31
becomes excessively larger than the optimum value, so it brings forth temperature rise of grease caused by agitation heat build-up and grease leakage. As a result, on the contrary, it becomes a factor for shortening the life of the grease.
In comparison with this, if the depth of the ball groove
30
a
of the outer ring
30
and the depth of the ball groove
31
a
of the inner ring
31
are made shallow, the space volume between both rings
30
and
31
can be made larger. However, if the depths of the ball grooves
30
a
and
31
a
of both rings
30
and
31
are merely made shallow, in case where thrust load (axial load) acts upon them, the so called shoulder stranded state where the ball
32
becomes stranded on the shoulders
31
a
1
and
30
a
1
of the inner ring
31
or outer ring
30
occurs, and roughness or separation occurs on the surface of the ball
32
or ball grooves
30
a
and
31
a
, and there is concern of the life of the ball bearings being shortened.
On the other hand, as for the retainer
33
of the ball bearings, the snap-on type made of synthetic resin is broadly used, and the cross section is designed so that the inner diameter side and the outer diameter side has identical dimensions versus the pitch circle diameter (PCD) of the ball
32
.
However, if the revolution speed of the outer ring
30
becomes high, and for instance, the dn value (inside diameter d X number of revolutions n) becomes around 250,000, the retainer
33
is influenced by the centrifugal force, and expand as well as deform. As a result, the guide surface edge of the claws for the deformed retainer
33
comes into close contact with the ball
32
, causing abnormal friction and heat build-up, or the retainer
33
is pushed out in the axial direction by the ball
32
, and there is fear of causing interference with the seal
34
. This may lead to concerns such as the shortening of the retainer life, and in turn, the shortening of the ball bearing life.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the aforementioned circumstances, and it is a technical object of the present invention to prolong the life of pulley ball bearings, and in turn, the life of the pulleys by increasing the sealed amount of grease at the optimum ratio by sufficiently securing the space volume between inner and outer rings while effectively solving the problems of shoulder stranded balls, and at the same time by reducing the expansion and deformation caused by large centrifugal forces at the time the outer ring revolves at high speed as much as possible by increasing the rigidity of the retainer is heightened.
In order to achieve the above-mentioned technical object, in a ball bearing for a pulley that is inter-fitted to a pulley main body having pulley circumferential surface coming into contact with a belt, the present invention is characterized by setting ball groove depths formed in an inner ring and an outer ring of the ball bearings so that a risk rate of shoulder stranded balls is approximately equal between the inner ring and the outer ring under pure thrust load.
In other words, the present invention has been devised by paying our attention to the point that the risk rate of the shoulder stranded contact ellipse based on contact of the ball at the time pure thrust load (pure axial load) acts, varies between the inner ring and the outer ring, in case where the depths of ball grooves of the inner ring and the outer ring are both made the same as in the conventional ones. In other words, this is based on paying attention to the point that in case where the depths of the ball grooves for the inner ring and the outer ring are made equal to each other, the permissible thrust load of the inner ring side that becomes the judgment standard of whether the ball becomes stranded on the shoulder of the inner ring or not, and the permissible thrust load of the outer ring side that becomes the judgment standard of whether the ball becomes strande
Fukuwaka Masao
Inoue Seiya
Kanamoto Takahiro
Kawamura Hiroshi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Charles Marcus
NTN Corporation
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