Bearing for the shaft of a machine element

A bearing having two rows of rolling elements has a flange extending outwardly from its outer ring. The flange is affixed to a facing surface inside of an aluminum housing, with a portion of the outer ring extending, with a play fit, in a bore of the housing.

This invention relates to a bearing for the shaft of a machine element, 
especially a pinion shaft of a drive, comprising a two row, prestressed 
rolling bearing with a radially outwardly directed flange on the outer 
ring for supporting a shaft in a bore of a housing of light metal or the 
like. 
Bearings for shafts having a two row prestressed rolling bearing are 
already known. DE-OS No. 27 53 108 shows a bearing arrangement, especially 
for use in a pinion bearing for rear axle drives. In this arrangement 
there is an outer ring common to both of the bearing rows. One end of the 
outer ring has a radially extending support flange having support holes. 
The bearing also has two separate inner rings, and a spacing ring between 
the inner rings. The axial length of the spacing ring is suitably selected 
for the desired prestress in the bearing. The outer surface of the outer 
ring of this known rolling bearing has, with the exception of annular 
grooves between the rolling body rows, a constant diameter. This known 
rolling bearing is so arranged in the bore of the drive housing, that it 
supports the cylindrical outer surface over its whole length in the 
cylindrical bore of the drive housing, with an interference fit in the 
radial direction. The radial flange of the outer ring abuts, as a rule, 
the outer facing side of the drive housing, and serves thereby solely for 
the axial alignment of the bearing and thereby of the machine par 
extending therethrough. 
There is a trend today, on the basis of cost and weight saving, to employ 
light metal housings, whereby, however, the different material expansion 
of light metal and antifriction bearing steel change in dependence on the 
temperature in the region of the interference fit between the bearing 
layer and housing, thereby resulting in change in the prestress force in 
the bearing. A change in the prestress force can result in large play in 
the bearing that influences the precision of the intermeshing between the 
teeth of the pinion and bevel gears. Increased noise development and 
larger wear follow, and in the extreme case this may lead to tooth 
failure, as well as the early failure of the bearing or even damage to the 
light metal housing. 
The invention is therefore directed to the provision of a bearing of the 
above-described type, which is especially suitable for use with a light 
metal housing, wherein the drive experiences essentially no change of the 
prestress force as well as the geometrical proportions of the parts of the 
bearing as a result of changes of operation dependent characteristics such 
as temperature. 
In accordance with one feature of the invention the bearing, in operation, 
is held in the housing in the axial as well as the radial direction, 
solely by the flange. There are no other holding positions of the bearing 
outer ring in the bore of the light metal housing, except a fitting with 
play. There is also a radial play between these parts. Consequently, the 
temperature influence on the pinion bearing is eliminated, so that in the 
event of increases of temperature there is no influence thereof on the 
prestress force. The large play which occurs in conventional bearings, as 
a result of changes in the prestress, and the resultant undesirable 
disadvantages of such play, are thereby prevented. 
In order to avoid significant changes of the geometrical proportions of the 
machine elements that engage one another, for example, the tooth meshing 
in the gears, in accordance with a further feature of the invention, the 
rolling bearing is so arranged in the housing that the radially outwardly 
directed flange of the outer ring abuts an inner facing surface of the 
housing. The distance between the holding plane (i.e., the plane of this 
facing surface) and the plane in which the force originates on the machine 
elements is thereby as small as possible, and as a result the influence of 
temperature is as small as possible. This means, in a rear axle drive, 
that the influence of temperature on the tooth meshing is practically 
eliminated. 
According to a further feature of the invention one of the radially 
overlying surfaces of the rolling bearing and housing, for example, the 
bore of the housing or the outer surface of the outer ring of the rolling 
bearing, is provided with a radially extending, relatively small centering 
surface, over the bore surface of the housing or outer surface of the 
outer ring. This centering flange serves essentially only to center the 
rolling bearing assembly accurately, before the holding screws of the 
flange are tightened to fasten the rolling bearing against the housing. It 
is thereby insured that the rolling bearing, and thereby also machine 
elements mounted thereon, for example, a pinion gear, are accurately 
centrally aligned in the bore of the housing. The centering surface can 
advantageously be formed as a centering collar arranged on the outer 
surface of the outer ring of the rolling bearing or in the bore of the 
housing. 
Instead of an annular centering band, in accordance with a further feature 
of the invention, several centering projections may be distributed about 
the circumference of the bearing, the centering projections having a minor 
radial dimension and extending from the corresponding surface of the 
bearing. 
According to a still further feature of the invention, the centering 
surface, i.e., the centering band or centering projections are arranged 
adjacent the outer ring. As a result, the rolling bearing cannot be 
installed in a tilted position. 
In a further especially advantageous embodiment of the invention, the 
bearing rollers are formed of either balls or tapered rollers, and the 
contact lines of these elements are inclined to the turning axis of the 
bearing, whereby the rolling bearing on the one hand can withstand greater 
bending movements and on the other hand has a shorter length in the axial 
direction. The arrangement wherein the tapered rollers are provided in the 
bearing row adjacent the flange of the outer ring has the particular 
advantage that the flange is stiffened due to its location adjacent the 
bearing row having the highest force thereon. In order to reduce the 
bending of the shaft to a minimum the distance between the center pressure 
points, i.e., the intersection point of the contact lines of both rolling 
bearing rows with the turning axis of the rolling bearing, is preferably 
from 1.5 to 2.0 times the diameter of the pinion drive shaft.

Referring now to FIG. 1, therein is illustrated a rear axle drive 
consisting of a housing 1 of light metal, for example, an aluminum alloy. 
One end of the housing 1 is covered by a cover 2. A drive shaft 4, having 
a diameter "d", extends through a bore 3 in the other end of the housing 
1. A pinion gear 5 is mounted on the forward end of the shaft 4. A drive 
shaft 6 extends through a bore in the housing at right angles to the drive 
shaft 4, and a bevel gear 7 is mounted on the drive shaft 6. The teeth of 
the bevel gear 7 and pinion gear 5 mesh, so that turning movements of the 
drive shaft 4 are translated into turning movements of the bevel gear. The 
pinion gear 5 is supported in the housing 1 by a two row rolling bearing 
8. This two row bearing 8 is comprised of a common outer ring 9 having 
races 10 and 11 for the rows 12 and 13 respectively of rolling bodies. The 
bearing 8 has two axially separated inner rings 16 and 17, with races 14 
and 15 respectively on their outer surfaces, these races facing the races 
10 and 11 respectively. A spacing ring 18 is positioned axially between 
the inner rings 16 and 17 and abutting these inner rings. The spacer 18 
has an axial length +1" that is selected or prearranged, corresponding to 
the desired preloading of the bearing. The row 12 of rolling bodies is 
comprised of balls 19, of which two diametrically opposite balls are shown 
in FIG. 2. The contact lines 20, 21 of these two balls, i.e., the 
diametrical lines of the balls extending through the contact points of the 
balls with the race 10 of the outer ring 9 and the race 14 of the inner 
ring 16, are inclined to the turning axis 22 of the rolling bearing 8. The 
rolling bodies of the other rolling body row 13 are tapered rollers 23, 
whose turning axes 24 are likewise inclined to the turning axis 22 of the 
bearing 8, so that the contact lines 25, 26 of the two diametrically 
opposite tapered rollers shown intersect the turning axis 22 of the 
rolling bearing 8 likewise at an angle less than 90.degree.. The contact 
lines 20, 21, 25 and 26 form an "O" so that the rolling bearing rows 12 
and 13 may be said to be in an "O-arrangement". In other words, the 
contact lines of each row converge towards the respective axial end of the 
bearing. The intersection points between the contact lines 20, 21 and 25, 
26 with the turning axis 22 of the rolling bearing 8, i.e., the so-called 
center pressure points, lay relatively far from one another, so that a 
wide support base for the drive shaft 4 is obtained. The length "a" of 
this support base, i.e., the distance between the center pressure point is 
advantageously chosen such that depending on the diameter "d" of the drive 
shaft 4, and the force action plane, the sagging or bending of the shaft 
is a minimum. In one example, this result is obtained when the ratio a/d 
equals 1.5 to 2.0. 
The outer ring 9 of the rolling bearing 8 is formed on one end, i.e., the 
end in the region of the row 13 of tapered rollers 23, with an annular 
radially outwardly directed flange 27. Several axially directed bores 28 
are distributed about the circumference of this flange. Studs 29 in 
threaded holes 30 of the housing, extend axially through the holes 28 of 
the flange, with nuts being threaded on the bolts to firmly hold the 
bearing to extend axially in the housing. In this manner the bearing 
arrangement is so arranged that one end of flange 27 lays against the 
inner facing surface 31 of the housing 1, whereby the distance between the 
axis of the drive shaft 6 and the attachment plane of the bearing to the 
pinion gear shaft is very small. Consequently, influences of temperature 
on the meshing of the teeth of the gears is reduced to a minimum. The 
outer surface 32 of the outer ring 9 of the rolling bearing 8 is provided 
in the vicinity of the flange 27, with a relatively small projecting band 
33 with a diameter D.sub.2 slightly greater than the diameter D.sub.1 of 
the surface 32. This centering band 33 is fit in the inner surface of the 
bore 3, such that in the cold condition there is zero or a minimum play. 
The bore 3 has a diameter d.sub.B. Before and during the assembly of the 
rolling bearing 8 in the drive, the diameter D.sub.2 of the centering band 
33 is smaller or the same as the diameter d.sub.B of the bore 3. The 
prestress is thereby not influenced by the necessity of overcoming an 
interference fit during the assembly. 
The centering band 33 thereby serves to straighten out the rolling bearing 
8 in the assembly of the rear axle drive to be actually centered with 
respect to the bore 3, whereby the threaded bolts 29 are held fast and 
firmly hold the rolling bearing 8 in the axial and radial directions. The 
remainder of the outer surface 32 of the outer ring has a greater play 
with respect to the inner surface of the bore 3 (having a diameter 
d.sub.B) due to its lesser diameter D.sub.1 so that the rolling bearing 8 
is supported in the housing solely by the flange. When the rear axle drive 
is heated, the housing 1, of light metal, expands more than the rolling 
bearing 8 of antifriction bearng seal, due to the higher thermal expansion 
coefficient of the light metal. Since the rolling bearing 8 is radially 
supported by the flange 27, and not in the bore 3, the expansion of the 
bore 3 of the housing has substantially no influence on a nonexistent 
interference fit between the outer surface of the outer rings 9 and the 
boring 3 of the housing 1, and thereby also has no effect on the 
preloading in the rolling bearing 8. Since the parts of the rolling 
bearing 8 are prepared from the same material, and consequently have the 
same thermal expansion coefficient, the prestress in the rolling bearing 
does not change, or only changes to an insignificant extent. Consequently, 
the heating of the rear axle drive does not result in temperature 
dependent increase of the bearing play of the pinion bearing, which would 
negatively influence the accuracy of the intermeshing of the gear teeth 
and thereby would lead to greater noise and wear. 
Tests with a structure in accordance with the invention have shown that, in 
such a bearing arrangement in a light metal housing with respect to 
prestress forces and axial stiffness, the bearing of the invention has 
more favorable properties than comparable conventional bearings. In the 
radial direction, with respect to the tooth mesh displacement there is no 
deterioration of bearing characteristics, as opposed to conventional 
bearing structures. The thermally dependent influence on the tooth mesh 
displacement is also much lower. 
It is possible, alternatively to the above-described example of the 
invention, to change the construction of the bearing. Thus, instead of an 
annular centering band 33, the surface 32 of the outer ring may be 
provided with several individual projections distributed about its 
circumference, such projections serving to center the bearing. If a ring 
band is provided, it can be formed as a part of the outer ring itself, but 
it is also possible to employ a separate ring adapted to be assembled on 
the outer surface of the outer ring. In general, the centering surface, 
instead of being on the outer surface of the outer ring, may alternatively 
be provided in the bore of the housing, whereby the centering band, 
individual centering projections, or the like are provided directly in the 
bore or are separately formed and assembled in the bore. 
Instead of the above-disclosed rolling bearing having one row of tapered 
rollers and one row of balls, it is possible, in accordance with the 
invention, to alternatively provide the bearing with two rows of balls or 
two rows of tapered bearings. Further, instead of the above-described 
"O-arrangement", the rolling body rows can obviously be selected to have 
an "X-arrangement". Finally, it is evident that the invention is not 
limited to a bearing for a pinion shaft of a rear axle drive. Thus, the 
invention may be employed for other types of bearings for a shaft of a 
machine element in a housing of light metal or the like.