Roller bearing

Details Roller bearing Roller bearing

1999-12-07

2001-07-03

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S565000, C384S569000, C384S571000

Reexamination Certificate

active

06254277

ABSTRACT:

TECHNICAL FIELD
The present invention relates to cylindrical roller bearings or tapered roller bearings and, more specifically, to a roller bearing suitable for use under heavy load or high moment load.
BACKGROUND ART
Conventionally, as this type of roller bearing, there has been provided one in which tapered rollers are placed between inner and outer rings, both end portions of an outer circumferential surface of each tapered roller being subjected to trapezoidal crowning so as to reduce edge loads that act on both end portions of the tapered roller.
However, even a conventional tapered roller bearing in which trapezoidal crowning has been applied to both end portions of an outer circumferential surface of each tapered roller as mentioned above has a problem that contact stress becomes extremely high locally at some places as shown in FIG.
5
(B).
In FIG.
5
(A), the abscissa shows the distance of the raceway surface of the inner ring from the raceway center of the inner ring along a generatrix, i.e., inner-ring generatrix position, while the ordinate shows the crowning depth that is a clearance between the tapered roller and raceway surface. Also, in FIG.
5
(B), the abscissa shows the inner-ring generatrix position, while the ordinate shows contact stress produced between roller and inner-ring raceway surface. As can be seen from FIGS.
5
(A) and
5
(B), in this tapered roller bearing, contact stresses are produced, concentrated at places where the crowning starts.
FIGS.
5
(A) and
5
(B) assume a state in which a moment load is applied to the bearing, where the inclination angle between inner and outer rings of the bearing is set at 0°6′. In this case, since contact stresses are concentrated particularly on a one-side start place of the crowning, the bearing is further shortened in life.
Because of the occurrence of stress concentration at places where the crowning starts as shown above, the conventional tapered roller bearing has a problem that its life becomes shorter when subjected to heavy load or high moment load.
It is therefore an object of the present invention to provide a roller bearing in which contact stress between rollers and raceway is uniformized by optimizing the configuration of a clearance between the rollers and the raceway.
DISCLOSURE OF THE INVENTION
In order to attain the above object, the present invention provides a roller bearing having an inner ring, an outer ring and a plurality of rollers, characterized in that:
in a state in which an outer circumferential surface of each of the rollers and a raceway surface of the inner ring or a raceway surface of the outer ring have been brought into contact with each other under no load so that a roller profile which is a line of intersection between a plane passing through an axis of the roller and the outer circumferential surface of the roller and an outer-ring profile which is a line of intersection between the raceway surface of the outer ring and a plane passing through an axis of the outer ring, or the roller profile and an inner-ring profile which is a line of intersection between the raceway surface of the inner ring and a plane passing through an axis of the inner ring, are in contact with each other under no load, if a magnitude of a clearance between the roller profile and the outer-ring profile or the inner-ring profile is represented by Y(x) and if such a magnitude of a clearance between the roller profile and the inner-ring profile or the outer-ring profile as can make uniform stress applied to between contact surfaces of the outer circumferential surface of the roller and the raceway surface of the outer ring or the raceway surface of the inner ring based on an elastic contact theory is represented by Yp(x), then the following equation holds:
Y
(
x
)
=kYp
(
x
)
where x is a distance from an axial center of the roller along a tangent line common to the two profiles that are in contact with each other under no load, and k is a positive constant.
According to the roller bearing of the present invention, the magnitude Y(x) of the clearance between the roller profile and the outer-ring profile or the inner-ring profile is a value which results from multiplying, by k (a positive number), such a magnitude Yp(x) of the clearance between the roller profile and the inner-ring profile or the outer-ring profile as can make uniform stress applied to between contact surfaces of the outer circumferential surface of the roller and the raceway surface of the outer ring or the raceway surface of the inner ring based on the elastic contact theory. This elastic contact theory is based on the assumption of an infinite length and not applicable to actual rollers of finite lengths. Therefore, providing the clearance of Y(x)=kYp(x), which results from merely multiplying the Yp(x) by k (a positive number), allows edge loads to be relaxed so that relatively uniform load is applied to the rollers and the raceway surfaces in rollers of finite lengths. Accordingly, the tapered roller bearing of the invention is capable of enduring heavy loads and high moment loads, thus being prolonged in life.
Also, in the roller bearing of one embodiment, the Yp(x) is a logarithmic curve shown by an equation:
Yp
(
x
)={(1−&ngr;
1
2
)/
E
1
+(1−&ngr;
2
2
)/
E
2
}Qd×
log{1−2
x/la
)
2
}
−1
/(&pgr;·
la
)
where E
1
is a Young's modulus of the roller, E
2
is a Young's modulus of the inner and outer rings, &ngr;
1
is a Poisson's ratio of the roller, &ngr;
2
is a Poisson's ratio of the inner and outer rings, Qd is a load of the roller, and la is an effective length of the roller profile.
In this roller bearing, because the Yp(x) is the logarithmic curve as shown above, the contact stress between roller and raceway surface is greatly uniformized so that breakage due to repetition fatigue is unlikely to occur, the roller bearing being prolonged in life.
Further, in the roller bearing of one embodiment, a value of k is within a range of 1.5 to 10.
It was found out by an experiment that edge loads become larger with the value of k less than 1.5, and that an axial central load of the outer circumferential surface becomes larger with the value of k more than 10. With the value of k falling within a range of 1.5 to 10, improvement in durability was recognized as compared with the prior art.


REFERENCES:
patent: 4877340 (1989-10-01), Hoeprich
patent: 0 347 247 (1989-12-01), None
patent: 2-107810 (1990-04-01), None

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