Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2002-05-29
2004-08-03
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S513000, C384S540000
Reexamination Certificate
active
06769809
ABSTRACT:
The invention relates to a double row angular contact ball bearing, the special structure of which is particularly well suited to the mounting of gears to rotate with respect to supports, particularly gearboxes and transmission gearboxes and especially helicopter auxiliary or main transmission gearboxes.
The invention also relates to a cantilever mounting of gears on a special-purpose bearing according to the invention, particularly for mounting helicopter main or auxiliary transmission gearbox gears, and the invention finally relates to a modular assembly comprising at least one gear, a specialized purpose bearing according to the invention, and a device for preloading the bearing, on which the gear is cantilever mounted, according to the special-purpose mounting according to the present invention.
In helicopter transmission gearboxes, whether these be main transmission gearboxes inserted between the propulsion units, generally turbo engine units, and the main rotors, and arranged as at least one step-down stage, for reducing the rotational speed of the output shaft or shafts of the propulsion units to a nominal speed at which the main rotors are rotated, or whether these be auxiliary transmission gearboxes inserted between rear transmission shafts connected to take-offs or auxiliary outputs from main transmission gearboxes, and tail or anti-torque rotors for driving the latter in rotation, the gears of such transmission gearboxes are generally supported by at least two rolling bearings, the rolling bodies of which may be balls or rollers, generally cylindrical or conical ones.
One of the bearings may be mounted at the “nose” of the gear (on the opposite side to the side via which the gear is driven in rotation), while the other bearing is mounted at the “tail” of the gear (on the side via which the gear is driven in rotation), but the gear may also be mounted on the same side of at least two rolling bearings which, irrespective of the mounting, reacts the radial loads while just one of the bearings reacts the axial load.
When the mounting of a gear entails precise axial positioning, as may be the case with a spiral bevel gear, the meshing conditions of which may entail either a minimum clearance or no axial clearance, particularly when the level of dynamic loadings on the gear is high, bearings are combined in what are known as “O” or “X” configurations, preloaded by adjustment with angular contact ball bearings or taper roller bearings.
Whether the rolling bodies in the bearings are tapered rollers or balls, it is known that “O” bearings are combinations of at least two bearings such that, if the normals to the points of contact between the rolling bodies and the raceways of the corresponding races are considered, the intersections of these normals with the axis of the bearings delimit an axial segment of a length that exceeds the axial distance joining the extreme points of contact (axially farthest apart) of the rolling bodies, so that the said normals to the points of contact delimit, about the axis of the associated bearings, a pseudo “O”.
In the case of an “X” configuration of bearings, the said normals to the points of contact between the rolling bodies and the races of the bearings diverge and are directed radially and axially towards the outside of the bearings, so as to delimit, on the common axis of the bearings, a segment of a length shorter than the axial distance joining the extreme points of contact (in reverse set-up by comparison with an “O” configuration of bearings).
The preloading of two associated bearings, for example two angular contact ball bearings mounted in opposition (“O” configuration), is achieved after shims or spacers of variable and adjustable axial thickness have been arranged between the inner races and the outer races of the two bearings, so that, in the presence of such suitable shims or spacers, the axial clamping of the inner race of a bearing against the corresponding shims and towards the inner race of the other bearing, bearing against a shoulder, imposes a “no load” pressure on the two bearings. Under these conditions of mounting of this arrangement, the application of external forces to the bearings leads to a reduction in the axial preload, which means that the bearings can run with a small or practically zero clearance, corresponding to the required conditions. This preload entails that the axial dimensions of the spacers or shims fitted, for example peel shims, are determined after a succession of mountings and measurements. This results in lengthy and tricky adjustment of the preload, this drawback adding to the one ensuing from the need to fit the said spacers or shims in order to control the preload.
In order to dispense with the need to adjust the preload, it is known practice for the two bearings, which are matched and the internal geometry of which is defined to obtain the desired preload by construction, to be mounted back to back and for the shims or spacers and adjustments thus to be eliminated. However, the two bearings are then likely to be too heavily loaded, and it is known practice for this drawback to be remedied by fitting a third bearing, generally a cylindrical roller bearing, on the line of shafts, to provide additional support and thus avoid cantilever mounting.
To react the axial loads exerted on gears while at the same time mounting them for rotation, it has also already been envisaged for use to be made of other types of bearing, particularly ball bearing variants of the “deep groove” type with three or four points of contact (of the balls with the races), of which one of the two races, generally the inner race, is split into two half-races.
In a deep groove bearing it is known that the raceway of each race, inner or outer, has just one curvature, which is not necessarily the same for both races. Because of this or these curvatures, one consequence of the radial clearance, needed for such a bearing to run correctly, is that such a bearing has fairly large axial clearances which do not allow sufficiently precise mounting, particularly of gears in the axial direction.
To avoid these disadvantages, it has been proposed for use to be made of bearings of the “three-point contact” type, in which one of the races, generally the inner race, is made in two parts so that the centres of curvature of the two raceway grooves formed respectively in the two parts of the split race are offset by an axial distance which corresponds to a saving in axial clearance, or alternatively “four-point contact” bearings, similar to “three-point contact” bearings as regards the race which is split into two parts, whereas in the other race, which is of one piece, the raceway groove is machined with an ogee-shaped cross section having two radii of curvature with centres which are axially offset, each with respect to the other and both with respect to the centre of the balls.
This results in bearings which are more precise and have a smaller axial clearance than conventional deep groove bearings.
However, among the various solutions known in the prior art for reacting the axial loads exerted on gears, the first solution, which consists in using ball bearings of the three-point or four-point contact type, has the drawback of leaving degrees of freedom in the axial direction.
A second solution, which consists in using a preloaded mounting of two associated bearings, which are tapered roller bearings or angular contact ball bearings, to cancel these degrees of freedom in the axial direction, does, on the other hand, have the drawback of entailing adjustment of the preload by insertion of shims of variable and adjustable axial thickness. Furthermore, in the case of mounting “O” configured or “X” configured bearings, it is necessary to adjust the preload while at the same time making sure that the gear is positioned precisely in the axial direction, this making mounting operations more complicated and increasing the costs of assembly in production and of maintenance.
Note that the use of two bearings, one of which is mounted at the “nose” of
Eurocopter
Hannon Thomas R.
Sturm & Fix LLP
LandOfFree
Asymmetric double row angular contact ball bearing, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Asymmetric double row angular contact ball bearing, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Asymmetric double row angular contact ball bearing, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3358887