[0001] This invention relates to a self-aligning thrust roller bearing incorporating at
least two coaxial race tracks and a number of rollers provided between the race tracks
and in engagement with these, said rollers being arranged in at least two rows beside
each other, the race tracks and the rollers being curved in axial section and the
axes of the rollers being inclined in the same direction relative to the bearing axis.
[0002] Spherical thrust roller bearings are earlier known. These bearings generally have
one row of unsymmetrical rollers, one bearing ring with a spherical race track and
one bearing ring with a roller guiding flange.
[0003] Rings having flanges are expensive to manufacture and bearings having such rings
have a high starting friction. It is thus desirable to avoid the need of the flange.
A possible method for avoiding a flange is to use symmetrical rollers. A roller is
in this respect considered to be symmetrical if it can be divided in two congruent
halves with a cross sectional plane half way between the ends of the roller. Symmetrical
rollers having such a large axial extension and being arranged with such a large angle
between the roller axis and the bearing axis as the rollers appearing in spherical
thrust bearings are however difficult to guide with a desired precision. Furthermore,
the sliding in the contact points between the roller and the race track will be large,
which leads to power losses and a risk for bearing failure due to the generated friction
heat,
[0004] The purpose of the present invention is to provide a bearing of the type defined
in the preamble, wherein a good roller guiding is obtained without a flange on one
of the rings and which has low friction at start and during operation.
[0005] This is achieved according to the invention thereby that the bearing is given the
characteristics defined in the accompanying claim 1.
[0006] Due to the fact that all rollers of the bearing have the same revolution angular
speed about the bearing axis only one cage for the rollers is needed, which saves
space and coat. A good roller guiding can easily be obtained by the rollers being
arranged to contact each other adjacent the inner race ring or by means of a guiding
ring at the outer race ring. Both roller rows are subjected to load when the bearing
takes up axial load, which guarantees a good guiding of all rollers. By using two
rollers instead of one roller with a corresponding axial extension it is possible
to halve the bearing friction losses, since the relative sliding at the contact between
the roller and the race track, i.e. the relation between the sliding speed and the
rolling speed, is about proportional to the length of the roller,
[0007] Hereinafter the invention will be further described with reference to the accompanying
drawing, which shows an axial section through a bearing according to an embodiment
of the invention.
[0008] The bearing has two rings 1 and 2 each having two axial race tracks for a number
of symmetrical rollers 3,4 provided between the rings, which rollers are arranged
in double rows, whereby the rollers in both rows are preferably identical. The roller
rows are situated side by side and the axes 5,6 of the rollers in each roller row
are inclined in the same direction relative to the bearing axis 7. The race track
of the ring 2 has preferably a spherical surface, which means that the ring 1 and
the set of rollers with the rollers 3,4 and roller cage 8 can be freely tilted relative
to the ring 2 without causing a too high contact pressure at the contact between the
roller and the race track. If only a limited self-alignment is aimed at, it is possible
to let the surface of the race track be non-apherioal.
[0009] As both roller rows will take up load when the bearing is subjected to axial load
the load capacity of the bearing is of the same size as the load capacity of a one
row bearing, the rollers of which are twice as long as the rollers 3 and 4 and has
a corresponding contact angle. A. limited length of the rollers 3,4 together with
the fact that both roller rows are exposed to load means that the guiding of the rollers
will not cause any great difficulties. In order to obtain a good roller guiding it
is possible to allow the ends of the rollers of rollers in different rows to contact
each other adjacent the inner race ring 1 such as shown in point 9. Alternatively
it is possible to arrange a guiding ring 10 between the roller rows adjacent the outer
race ring,
[0010] In all roller bearings having curved race track profiles and correspondingly curved
roller profiles a certain sliding will take place at the contact points between the
roller race track and the roller, which will cause friction losses. An estimation
of how large these losses are in a bearing is the size of the relative aliding in
these contact points.. The relative sliding is defined as the ratio between the sliding
speed and the rolling speed in the contact points. It can be shown that in a bearing
having symmetrical rollers and in which a pure rolling takes place in only one rolling
contact point the relative sliding is proportional to the lengeth of the roller. If
the available length of the roller is divided on several rollers, such as in the present
invention, the relative sliding is reduced and thereby also the friction losses as
also the load is divided on several rollers.
[0011] The rollers of the two rows in a beari ag according to the invention always have
the same revolution angular speed relative to the bearing rings, as the bearing rings
rotate relative to each other. A single cage can thus be used for both roller rows
wi thout risking that the rollers of one row will influence the rollers of the other
row through the cage. Besides being space saving the use of one single cage means
that the bearing ; will be more easy to manufacture and to handle as it incorporates
as few separate parts as possible
[0012] Within the scope of the invention it is possible to vary the bearing design within
wide ranges. The mean angle between the bearing axis and the roller axes can for instance
be chosen be tween 20° and 90°. The bearing can also be provided with three or more
rows of rollers if it is desired to produce an extra large load capacity and a low
relative sliding. The race tracks can also be arranged on more than two rings.
1. A self-aligning thrust roller bearing incorporating at least two coaxial race tracks
and a number of rollers provided between the race tracks and in engagement with these,
said rollers being arranged in at least two rows beside each other, the race tracks
and the rollers being curved in axial-section and the axes (5,6) of the rollers being
inclined in the same direction relative to the bearing axis (7), characterized thereby,
that all rollers are symmetrical around central cross-sectional planes through the
respective rollers, the rollers being guided without the aid of any flange engaging
the rollers ends.
2. A self-aligning thrust roller bearing according to claim 1, characterized thereby,
that it has a single roller cage (8).
3. A self-aligning thrust roller bearing according to any one of claims 1 or 2, characterized
thereby, that it incorporates a roller guiding ring (10) provided between the rows
of rollers.
4. A self-aligning thrust roller bearing according to any one of claims 1 or 2, characterized
thereby, that the adjacent ends of rollers in different rows are arranged to engage
each other.
