Roller bearing

Details Roller bearing Roller bearing

2000-01-06

2001-05-08

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S568000

Reexamination Certificate

active

06227711

ABSTRACT:

The present invention relates to a roller bearing with symmetrical barrel shaped rollers comprising an inner race, an cuter race and rollers, each of which having at least one rounded end, and of the type where rollers and race tracks have longitudinal section profiles with substantially the same radius of curvature and which is bigger than the distance between the outer race track and the axis of the bearing, measured perpendicularly to the race track, whereby the rollers during normal operating conditions are axially moveable between the race tracks without hindrance from axial confinements at the race tracks for allowing relative misalignment and axial displaceability of the race tracks.
BACKGROUND OF THE INVENTION
The end of rollers in such a bearing normally consist of a chamfered section. There is normally a relatively sharp edge between the chamfered section and the rest of the roller. At roller bearings of this type with symmetrical, barrel shaped rollers and especially when used on a substantially vertical axis, as shown in
FIG. 1
, a roller in the unloaded zone might move outwards to an extent permitted by the internal radial clearance. The relatively sharp edge between the chamfered section and the rest of the roller is thus in contact with the raceways. As the rotation continues the roller is forced to regain its normal position, i.e. it is caused to move towards the centre. This causes problems relating to stresses, service life and lubricant film thickness. These problems can be solved in the way that the relatively sharp edge between the chamfered section and the rest of the roller is rounded according to certain criteria.
SE-C 8404813-1 shows a bearing of the type where rollers and race tracks have longitudinal section profiles with substantially the same radius of curvature and which radius is bigger than the distance between the outer race track and the axis of the bearing, measured perpendicularly to the race track, whereby the rollers during normal operating conditions are axially moveable between the race tracks without hindrance from axial confinements at the race tracks for allowing relative misalignment and axial displaceability of the race tracks. Such a bearing is especially susceptible to the problems referred to hereabove.
U.S. Pat. No. 4,802,775, discloses a roller bearing having rollers with rounded end portions. It comprises an inner race, an outer race and rollers arranged between these races. The roller has a predetermined relationship between a maximum diameter of each roller, length of each roller, and radius of curvature of a contact portion between a rolling surface of the roller and a chamfer portion of the roller. The predetermined relationship is presented below.
0.04(Dalr)≦Rk≦0.20(Dalr), where
Rk, Da and lr denotes curvature radius, maximum diameter of the roller and length of the roller, respectively. In this bearing there will be a radius of curvature which is not big enough for ascertaining that the stresses will be so small that the problems mentioned above are avoided.
PURPOSE AND MOST ESSENTIAL FEATURES OF THE INVENTION
The purpose of the invention is to prevent operational problems relating to stresses, service life and lubricant film thickness in a roller bearing with symmetrical, barrel shaped rollers, and of the type referred to in the introduction of the description, particularly, but not only, when used on a substantially vertical axis. The rollers are provided with end drop zones, i.e. end portions in which the roller has a much smaller longitudinal curvature radius than the radius of curvature of the barrel shaped roller itself. This arrangement results in tangential contact, i.e. the roller is supported by the raceway along a line segment, which results in prevention of operational problems which occur if the contact between rollers and raceways is based on a single point instead of a line segment.
In order to achieve the purpose of the invention, the following characterising criteria for the rounded portion of the end of the roller to be used in a roller bearing of the kind referred to are given below.
1) The minimum radius of the rounded end portion, also known as minimum end drop radius, is also important since if it is too small then the contact stresses will be too high. Also, the lubricant film thickness should be of at least half the magnitude of the film thickness at the center of the roller.
2) The maximum length of the rounded end portion of the rollers, also known as maximum end drop length, is also important since unnecessary reduction of load carrying contact will be the result if this length is too long.
3) The minimum length of the rounded end portion of the rollers, also known as minimum end drop length, is of great importance since if this length is too short then the operational problems presented above will still be present due to too short tangential contact.
4) The end drop radius does not have to be constant.


REFERENCES:
patent: 3910656 (1975-10-01), Price et al.
patent: 4802775 (1989-02-01), Takata
patent: 5752775 (1998-05-01), Tsutsui et al.
patent: 2129066 (1984-05-01), None

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