Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-08-31
2002-05-21
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S450000
Reexamination Certificate
active
06390685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roller bearing which uses cylindrical-shaped, conical-shaped or spherical-shaped rollers as its rolling elements.
2. Description of the Related Art
Now,
FIG. 16
shows a state of contact between two cylindrical-shaped elements. Conventionally, there are known various kinds of mechanical elements using this state of rolling contact, such as a roller bearing. On the other hand, this state of rolling contact raises a possibility that, in two end portions of the contact portion in an X-axis direction between the two cylindrical-shaped elements, there can be generated an excessively large contact stress, that is, a so-called edge load. It is also known that such edge load gives rise to the shortened lives of the mechanical elements. In view of this, in a roller bearing, as shown in
FIG. 17
, a rolling element or a rolling surface is subjected to a crowning so as to gradually reduce the contact stress at the two end portions of the contact portion.
The crowning itself is a known technique. For example, as disclosed in Japanese Utility Model Unexamined Publication No. Hei. 05-89943, there is known an invention which relates to a crowning. Also, referring to the profile of the crowning, there is well known a so called logarithmic crowning which can be expressed by the following equation (1) (A paper titled “Roller bearings under radial and eccentric loads” written by P. M. Johns and R. Gohar, published by TRIBOLOGY International, Vol. 14, 1981, pages 131-136).
δ
=
-
w
π
L
e
(
1
-
v
1
2
E
1
+
1
-
v
2
2
E
2
)
In
(
1
-
(
1
-
0.3033
2
b
L
e
)
(
2
x
L
e
)
2
)
(
1
)
where,
&dgr;: sum of crowning quantities of two contact elements (a roller and a raceway surface of an inner race)
w: contact load
L
e
: effective contact length in a bus extending direction between two contact elements
E
1
, E
2
: Young's modulus of two contact elements (the roller and the inner race)
&ngr;
1
, &ngr;
2
: Poisson's ratios of two contact elements (the roller and the inner race), and
b: ½ of Hertz contact width.
In fact, it is difficult to apply this logarithmic crowning. Therefore, there is a crowning technique which, as disclosed in Japanese Utility Model Unexamined Publication No. Hei. 03-12015, uses a combination of two or more arcs. Also there are proposed crowning techniques which are composed of a single arc, and a combination of a straight line and an arcs. Further, there is known a so-called partial crowning technique in which crownings are subjected only onto the two end portions of the contact surface of a roller or a rolling surface.
According to the above-mentioned crowning techniques, as shown by a two-dot chained line in
FIG. 18
, preferably, with respect to the effective contact length L
e
in the bus extending direction, a contact stress may be large in the central portion of the contact portion and gradually decrease in the two end portions of the contact portion. On the other hand, of course, it is not desirable that there is produced an edge load due to the excessively small crowning as shown by line A in FIG.
18
. Further, it is not desirable that in case where the crowning reduction quantity is increased excessively due to the excessively large crowning as shown by line B in
FIG. 18
, the actual contact length of the bus runs short, which gives rise to the shortened life of the roller bearing.
In the above-mentioned logarithmic crowning according to the equation (1), by assuming a contact load w, the crowning profile can be determined. In case where the assumed contact load w is coincident with a load in an actual operation time, the long life of the roller bearing can be expected. However, in case where the two loads are not coincident with other, the long life cannot be expected. Also, for mechanical elements in practical use, it is rare that a load to be applied to the mechanical elements is constant. Inmost cases, various levels of loads are actually applied to the mechanical elements during operation. Further, in a bearing which is used practically, there is a case where a misalignment can occur when assembling the bearing, that is, the misalignment can occur between a center line of a rolling element and a center line of a raceway of an inner race. In that case, the rolling element and the raceway of the inner race are contacted with each other in an inclined manner. Therefore, even in case where the above-mentioned logarithmic crowning has been subjected to the roller or rolling surface, there is still raised a possibility that an edge load can occur on one side end face of the roller or rolling surface to thereby give rise to the shortened life of the bearing. This shows that the above-mentioned logarithmic crowning according to the equation (1) cannot always attain the extended life of the roller bearing.
On the other hand, in the crowning profiles according to the above-mentioned crowning techniques respectively using a single arc, a combination of two or more arcs, and a combination of a straight line and arcs, there have not yet been made the concrete and clear numerical values that can contribute toward extending the life of the roller bearing.
SUMMARY OF THE INVENTION
The present invention aims at eliminating the above-mentioned drawbacks found in the conventional roller bearing. Accordingly, it is an object of the invention to provide a roller bearing in which the numerical values of crowning profiles respectively according to concrete combinations of arcs and the numerical values of a partial crowning profile can be made clear to thereby be able to extend the life of the roller bearing.
The object can be achieved by a roller bearing which comprises: a first race having a first raceway; a second race having a second raceway; and a rolling element provided rotatably between the first raceway and the second raceway. In the roller bearing, the sum &dgr; of a crowning quantity of the rolling element and at least a crowning quantity of a first raceway surface of the first raceway, at a first point X
1
and a second point X
2
, wherein the first point X
1
is positioned apart from a center of the rolling element or the first raceway in a bus extending direction of a bus of the rolling element by 0.425 L
e
, and the second point X
2
is positioned apart from the center in the bus extending direction by 0.5 L
e
, where L
e
denotes an effective contact length in the bus extending direction between the first raceway surface of the first raceway and the rolling surface of the rolling element, satisfies follow equations (1) and (2):
at the first point X
1
-
3.264
C
π
·
L
e
·
E
′
·
Z
·
cos
α
In
(
0.2775
+
1.583
×
R
·
C
π
·
E
′
·
L
e
3
·
Z
·
cos
α
)
≤
δ
≤
-
4.896
C
π
·
L
e
·
E
′
·
Z
·
cos
α
In
(
0.2775
+
1.939
×
R
·
C
π
·
E
′
·
L
e
3
·
Z
·
cos
α
)
(2-1)
and, at the second point X
2
-
3.264
C
π
·
L
e
·
E
′
·
Z
·
cos
α
In
(
2.192
×
R
·
C
π
·
E
′
·
L
e
3
·
Z
·
cos
α
)
≤
δ
≤
-
4.896
C
π
·
L
e
·
E
′
·
Z
·
cos
α
In
(
2.684
×
R
·
C
π
·
E
′
·
L
e
3
·
Z
·
cos
α
)
(2-2)
where,
E′: equivalent modulus of elasticity;
2/E′=(1−&ngr;
1
2
)/E
1
+(1−&ngr;
1
2
)/E
2
E
1
, E
2
: Young's modulus of the rolling element and the first race,
&ngr;
1
, &ngr;
2
: Poisson
Natsumeda Shinichi
Shimomura Yuuji
Hannon Thomas R.
NSK Ltd.
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