Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2003-01-08
2004-03-02
Lavinder, Jack (Department: 3683)
Bearings
Rotary bearing
Antifriction bearing
C384S510000, C029S898062
Reexamination Certificate
active
06698936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improvements made in the field of composite bearings with double ball bearings for the rotary support of a rotating shaft of a very high precision device, wherein these bearings with double ball bearings are constituted by the juxtaposition of two bearings with single ball bearings having two respective corresponding races, interior or exterior, fitting tightly axially one against the other with predetermined pre-stress.
DESCRIPTION OF THE PRIOR ART
In some very high precision devices (for example, in inertial navigation centers), it is necessary and indispensable that a rotating shaft is mounted and supported in a bore with very great precision of coaxiality without any play, in order to obtain high performances. Such a requirement necessitates that the balls of the ball bearings remain permanently in the contact of their path in order to avoid the consequences inherent in “take-offs” of the balls (generation of shocks, wear and tear, appearance of plays), which are eventually reflected by a loss of precision of the device. In order to clarify ideas, it will be noted that in the case of the appearance of a vibratory operating regime, it is an effort which can for example reach 900 N which can be exerted on a ball bearing race having a diameter of the order of 35 mm and a thickness of around 3 mm.
In order to be able to meet practical requirements, one thus resorts to bearings equipped not with single ball bearings, but with double ball bearings.
The easiest solution, which would consist in using a single bearing equipped with double juxtaposed ball bearings, however, cannot be used. This is because, even if very high precision machinery were used, the double ball bearings have dimensional differences (distance between axes, diameters of the balls, diameter of the receptacles, etc.), which are too great for the rotating shaft to be able to be supported in the bore with all the required precision and absence of play.
Thus it is known that one can resort to two bearings with single ball bearings, which are paired and which are then implemented under axial pre-stress of their respective corresponding races, either interior or exterior, in such a way that they thus behave like a single bearing with double ball bearings. In this case, as opposed to the single bearing with double ball bearings, each bearing can be manufactured with all the desired precision. The respective co-operating faces of the two races, interior or exterior, of the two bearings can be rectified in order to be in perfect contact one against the other. Also, the rigidity conferred by the pre-stressing finally leads to a bearing (hereinafter referred to as “composite bearing” because it is constituted by the reunion of two bearings with mono-ball bearings), which can satisfy practical requirements with regard to precision and the absence of play of the assembly of the rotating shaft in the support bore.
Even if the results obtained with this type of composite bearing satisfy practical requirements, on the other hand the assembly processes of such a composite bearing are complex and present many problems.
A usual assembly process takes place as follows. After pairing of the composing pieces (and in particular of the two races to be placed side by side under pre-stress), the two bearings are dismounted, then a first race is implemented in support against an axial capacity; for example in the case of an interior race, it is mounted on the shaft just to the point of abutment against a radial, annular retaining wall provided on the shaft.
The second race is then pre-positioned in immediate proximity to the first race, but without being in contact with it; in the example considered of interior races, the second race is mounted in turn on the shaft in immediate proximity of the first race.
One thus brings an axial pressure tool against the second race and, with the assistance of this tool, one displaces the second race axially towards the first race just to the point of physical contact with it, then one continues to exert a force on the second race until the support pre-stress of the second race on the first reaches a predetermined value. Still within the scope of the considered example of interior races, the tightening tool can consist in a nut which is screwed on the end of the shaft, which is threaded to this effect. This nut, which is moreover appropriately suited to be in perfect axial support against the second race, is suitable, in the course of its rotation, for displacing the second race to first of all take it against the first race, then for putting the two races under axial pre-stress at a pre-determined value.
The drawbacks of this existing process consist in that it is necessary on the one hand to specifically adjust (threading for the tightening nut) the support element of the races under pre-stress (the support bore for exterior races, the shaft for interior races) and on the other hand it is necessary to maintain in permanence the elements necessary for the assembly (threading and nut), since the pre-stress of the races is only due to the presence of the tightening tool (nut screwed on the threading for example). This results in an increase in weight of the unit and, in the case of interior races, an inertial modification of the mobile gear. These constraints may not be accepted, in particular when it is a matter of reducing as far as possible the dimensions of the device thus equipped and reducing the weight thereof, as well as when it is a matter of increasing the response rapidity performances by reducing in a maximum way the inertias of the mobile parts.
In order to attempt to overcome said drawbacks, one has proposed the combining of the second race, in support under pre-determined pre-stress against the first race, by adhering (by a resin film) the second race on its support. In this case, it is admittedly still necessary to resort to a tightening tool to place the second race and the first side by side and to exert the pre-stress until the adhering of the second race on its support is mechanically effective. However, the tightening tool can then be withdrawn, and it is no longer present in the completed device which is ready to function.
However, this process itself also has drawbacks. Firstly, even if the tightening tool is admittedly not maintained in the device, certain adjustments necessary to its use remain in place: thus, in the case of a nut suitable for pushing the second race, the threading realized either in the bore (for exterior races) or on the end of the shaft (for interior races) remains on the bore or on the shaft. Practice may not accept the presence of this adjustment, which is not necessary to the functioning of the device.
In particular, the adhering film for combining the second race, which is relatively thin (for example typically 1.5 &mgr;m), is not very resistant to thermal shocks (for example typically variation of 3 to 4° C. per second in an ambiance of around 70° C.). The adhering film fractures and the races are no longer maintained under pre-stress (even becoming unstuck from their support), in such a way that the shaft is no longer supported with the required precision and the device loses its precision, or is even no longer in a state of being able to function.
In order to attempt to overcome these drawbacks, it has been proposed to increase the thickness of the layer of glue, which thus becomes able to withstand severe thermal conditions without deterioration. However, due to the very reason of the thickness of the layer of glue, the rigorous coaxiality of the races and of the support can no longer be assured when the races are put in place on the support. It is thus necessary to conserve axial positioning zones (without glue), which are suitable for assuring the mutual axial maintenance of the races and of the support and of the axial zones of different diameter (with glue), which are suitable for making the races solid with the support.
Such an assembly process necessitates manufacturing processes and prov
Augot Michel
Dardelet Hervé
Jenger Marc
Larson & Taylor PLC
Pezzlo Benjamin A
Sagem SA
LandOfFree
Tool for constructing a pair of races of a bearing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tool for constructing a pair of races of a bearing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tool for constructing a pair of races of a bearing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3188120