Device for manufacturing a groove bearing, and method of manufacturing a groove bearing by means of the device

The invention relates to a device for manufacturing a hydrodynamic groove bearing formed with pumping grooves. The device comprises a hard pin around which, or a hard sleeve in which, a cage is arranged which has one or more annular patterns of holes which are concentric with the pin or sleeve and which are engaged by hard balls which project from both sides of the cage. The pin or sleeve and the cage can be translated and rotated relative to each other, the balls bearing against a bearing surface of the pin or sleeve. The bearing surface is constituted by a groove bottom of a continuous groove which is concentric with the pin or sleeve, the groove bottom extending in longitudinal sectional planes of the pin or sleeve as an arc of a circle whose radius is at least equal to the radius of the balls.

BACKGROUND OF THE INVENTION 
The invention relates to a device for manufacturing a groove bearing having 
a bearing shaft and a bearing bush with cooperating bearing surfaces, of 
which at least one bearing surface is formed with at least one pattern of 
pumping grooves. The device comprises a bearing part and a cage which has 
one or more annular patterns of holes which are concentric with the pin or 
sleeve and which are engaged by hard balls which project from the cage and 
bear against a bearing surface of the bearing part. The bearing part and 
the cage are rotatable relative to each other. The bearing part may be a 
hard pin around which, or a hard pin in which, the cage is arranged. 
The invention further relates to a method of manufacturing a groove 
bearing. 
The device defined above and a method to be carried out by means of the 
device are known from EP-A 0,002,292, herewith incorporated by reference. 
The prior-art device is suitable for carrying out a method of 
manufacturing a hydrodynamic groove bearing comprising a bearing shaft and 
a bearing bush, which form cooperating surfaces, of which at least one 
surface is formed with at least one pattern of shallow lubricant pumping 
grooves. Such a hydrodynamic bearing is described in, for example, GB-A 
1,022,391 and in GB-A 1,163,018, herewith incorporated by reference. 
The prior-art device comprises a hard pin around which, or a hard sleeve in 
which, a cylindrical cage is arranged which has one or more annular 
patterns of holes which are arranged symmetrically about the central axis 
of the cage and which are engaged by hard balls having a diameter larger 
than the wall thickness of the cage. The cage and the pin or sleeve are 
each coupled to a drive arrangement capable of impressing a translation 
and a rotation upon the cage and the pin or sleeve. Thus, in carrying out 
the prior-art method the assembly comprising the pin or sleeve, the cage 
including the balls is translated and rotated relative to a bearing bush 
and a bearing shaft respectively, the balls bearing against the pin or the 
sleeve and being impressed into the softer material of the bearing bush 
and the bearing shaft respectively to form grooves therein. 
It has been found that in carrying out the prior-art method the pin or the 
sleeve of the prior-art device is subjected to substantial wear as a 
result of large Hertzian stresses produced at the contact surfaces between 
the pin or sleeve and the balls. The wear manifests itself particularly as 
deformations of the pin or sleeve surfaces facing the cage, so that the 
contact surface of the pin or the sleeve becomes irregular, resulting in 
an inaccurate groove depth. In addition, this leads to a substantial wear 
of the balls. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve the device defined in the 
opening paragraph so as to minimize said wear. 
To this end the device in accordance with the invention is characterized in 
that the bearing surface of the bearing part, which may be a pin or 
sleeve, is constituted by a groove bottom of a continuous groove which is 
concentric with the central axis of the pin or sleeve, the groove bottom 
extending in a longitudinal sectional plane of the pin or sleeve, which 
plane contains the central axis, as an arc of a circle whose radius is at 
least equal to the radius of the balls. 
In the device in accordance with the invention the surface pressure at the 
contact surfaces of the pin or sleeve and the balls is kept within 
permissible limits, so that the device enables reproducible groove 
bearings with a high long-term accuracy to be manufactured. If required, 
the cage of the device may have several annular patterns of holes. 
An embodiment of the device in accordance with the invention, in which the 
balls can sustain large forces for a long time, is characterized in that 
the balls have been compressed isostatically. 
It is another object of the invention to provide a simple method which can 
be implemented by means of the device in accordance with the invention. 
The method in accordance with the invention, which employs the device in 
accordance with the invention, which device comprises a hard pin around 
which, or a hard sleeve in which, a cage provided with hard balls is 
arranged, is characterized in that exclusively the cage or the pin or 
sleeve is driven to be translated or rotated. This means that if the cage 
is driven the pin or sleeve performs exclusively secondary movements 
derived from the cage movements, and if the pin or sleeve is driven the 
cage performs exclusively secondary movements derived from the movements 
of the pin or sleeve. This method simply ensures a favourable hobbing 
movement of the balls.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 the reference numeral 1 denotes a bearing bush of a hydrodynamic 
bearing, whose inner surface 3 should be formed with a groove pattern 3a. 
The bearing bush 1 is immobilized by means, not shown. An assembly 
comprising a bearing part (hard pin 5), a cylindrical cage 7 and hardened 
isostatically compressed metal balls is arranged in the bearing bush. The 
balls 9 engage in holes 13 formed in the cage 7 in an annular pattern 
which is symmetrical about the central axis 11. The pin 5 has a concentric 
groove 15 whose groove bottom 17 serves as a bearing surface for the balls 
9 and has the shape of an arc of circle viewed in the sectional planes of 
the pin 5 which contain the central axis 11, the plane of the drawing 
being one of these planes. The radius of the circle comprising said arc of 
circle is equal to the radius of the spherical balls 9. The balls 9 have a 
diameter which is so much larger than the maximum clearance g between the 
bearing bush 1 and the bottom 17 of the groove in the pin 5 that the 
desired groove depth in the bearing bush 1 can be obtained. The cage 7 is 
coupled to a drive arrangement, not shown, which is known per se and which 
is capable of impressing a translational movement v.sub.k and a rotational 
movement w.sub.k on the cage 7. Since the balls 9 partly engage in the 
groove 15 axially couple the cage to the pin and movements of the cage 7 
also cause the pin 5 to be moved. Thus, the assembly comprising the pin, 
the cage and the balls is translated and rotated through the bearing bush 
1, the balls rolling along the bottom 17 of the groove in the pin 5 and 
along the inner surface 3 of the bearing bush 1, thereby causing bearing 
grooves to be formed in the softer material of the bearing bush 1. The 
number of helical bearing grooves thus formed corresponds to the number of 
balls used. The pitch of these grooves depends on the ratio between the 
translational velocity v.sub.k and the rotational velocity w.sub.k of the 
cage 7. Thus, by varying this ratio grooves of varying pitch can be 
obtained. In order to form a herringbone pattern the direction of rotation 
should be reversed upon completion of a specific travel. 
In the situation illustrated in FIG. 1 the cage 7 is driven but it is also 
possible to drive the pin 7, the secondary movements being performed by 
the cage 7. 
FIG. 2 shows how bearing grooves 21a can be formed in an outer surface 21 
of a bearing shaft 23. The bearing part of the device is comprised of a 
hardened cylindrical sleeve 25 with a continuous groove 27 whose groove 
bottom serves as a bearing surface for a plurality of balls 33 arranged in 
a cage 31. Similarly to the cage 7 in the above example the cage 31 is 
coupled to a drive arrangement, the secondary movements v.sub.p and 
w.sub.p being performed by the sleeve 25. 
For completeness' sake it is to be noted that the invention is not limited 
to the embodiments disclosed herein. For example, the cage may have 
several annular patterns of holes and the pin or sleeve may have a 
corresponding number of grooves.