Steering column bearing

A steering column bearing is comprised of an outer bush and an inner bush held in the outer bush. The outer bush includes: an inner ring having a lip portion and a retaining protrusion formed projectingly along the circumferential direction at a predetermined interval from the lip portion in an axial direction; an outer ring having protrusions; a support leg by which an outer peripheral surface portion of the inner ring not corresponding to a hollow cylindrical recess and an inner peripheral surface portion of the outer ring corresponding to that outer peripheral surface portion are integrally connected to each other in the circumferential direction; and reinforcing ribs each of which extends from an outer peripheral surface portion of the inner ring corresponding to the lip portion to the support leg, and integrally connects the outer peripheral surface of the inner ring, the inner peripheral surface of the outer ring, and the support leg.

The present invention relates to a steering column bearing for supporting a 
steering column shaft in a motor vehicle. 
Conventionally, a ball bearing or a slide bearing formed of a synthetic 
resin is used as a steering column bearing for supporting a steering 
column shaft in a motor vehicle. In general, with respect to the bearing 
for supporting the steering column shaft in a motor vehicle, the load and 
rotating conditions concerning the speed and the like are not so 
stringent, but the stability in friction torque and the vibration 
absorption characteristic for absorbing vibrations acting on the column 
shaft during idling and the like are required. As for the ball bearing, 
its friction torque is stable, but its vibration absorbing characteristic 
is inferior. In addition, since it is necessary to finish with high 
dimensional accuracy the housing to which the ball bearing is fixed, as 
well as the column shaft supported by the ball bearing, there are 
drawbacks in that the bearing itself is expensive, and that the processing 
cost also becomes high. 
As compared to the aforementioned ball bearing, the slide bearing formed of 
a synthetic resin has advantages in that it is inexpensive in cost, and 
that it excels in the vibration absorbing characteristic. However, since 
an appropriate bearing clearance is required between the slide bearing and 
the column shaft, there is a drawback in that colliding sound occurs 
between the column shaft and the bearing due to the vibration occurring in 
the shaft, and is imparted as uncomfortable noise to the driver of the 
vehicle. If the clearance is reduced to suppress the occurrence of the 
colliding sound, the phenomenon of stick slip occurs, thereby giving rise 
to the problem of hampering the stability of the friction torque. 
In view of the above-described problems, a bearing device for a steering 
column has been proposed in Japanese Utility Model Application Laid-Open 
No. 8817/1994 (hereafter referred to as the prior art technique), wherein, 
during the steering (rotating) of the steering wheel, the load acting on 
the column shaft can be supported smoothly by the beating, while in a 
state in which no load is applied to the column shaft during such as 
idling, the vibrations acting on the shaft can be absorbed. 
With the bearing device for a steering column in accordance with this prior 
art technique, the drawbacks of the above-described conventional art are 
overcome, and, during the steering (rotating) of the steering wheel, the 
load acting on the column shaft can be supported smoothly by the bearing, 
while in a state in which no load is applied to the column shaft during 
such as idling, the vibrations acting on the shaft can be absorbed. 
However, in a case where the bearing is firmly pressure-fitted into the 
housing for the purposes of preventing the bearing from coming off axially 
and rotating in the circumferential direction, the bearing is 
pressure-fitted into the housing at the outer peripheral surface of its 
outer ring. However, since the outer ring and the inner ring are connected 
to each other by means of the plurality of support legs extending in their 
axial direction, the pressure-fitting force differs at outer peripheral 
surface portions corresponding to the support leg portions and at outer 
peripheral surface portions not corresponding to the support leg portions. 
Hence, the pressure-fitting force does not act uniformly on the inner bush 
held by the enlarged-diameter hollow cylindrical portion of the inner ring 
supporting the column shaft. As a result, there is a problem in that an 
adverse effect is exerted on the dimensional accuracy of the inside 
diameter (roundness) of the inner bush. 
In addition, in a case where a member (bracket) for fixing the housing onto 
the vehicle body side is attached to the outer peripheral surface of the 
housing by welding, there is a problem in that a welding strain due to the 
welding exerts an adverse effect on the dimensional accuracy of the inside 
diameter (roundness) of the housing, thereby further deteriorating the 
dimensional accuracy of the inside diameter (roundness) of the inner bush 
of the bearing fixed in the housing. If these problems are compounded, the 
dimensional accuracy of the inside diameter (roundness) of the inner bush 
of the bearing is further aggravated. The quality of the dimensional 
accuracy of the inside diameter (roundness) of the inner bush of the 
bearing affects smooth sliding between the inner bush and the column shaft 
supported by the inner bush. The deterioration of these members hampers 
the smooth sliding, and is a problem which should be avoided as 
practically as possible. 
SUMMARY OF THE INVENTION 
The present invention has been devised to overcome the above-described 
problems while making use of the advantages of the above-described prior 
art technique, and it is an object of the present invention to provide a 
steering column bearing which does not affect the dimensional accuracy of 
the inside diameter (roundness) of the inner bush, as well as a bearing 
device using the bearing. 
In accordance with the present invention, the above object is attained by a 
bearing for a steering column comprising: a resilient outer bush and an 
inner bush, wherein the outer bush includes: an inner ring which has a lip 
portion arranged in a circumferential direction thereof in a vicinity of 
one end of a hollow cylindrical inner peripheral surface thereof and 
projecting radially and a retaining protrusion formed projectingly along 
the circumferential direction at a predetermined distance from the lip 
portion in an axial direction thereof so as to define a hollow cylindrical 
recess in association with the lip portion and the hollow cylindrical 
inner peripheral surface; an outer ring which has a plurality of 
protrusions formed on its outer peripheral surface along an axial 
direction thereof and arranged in a circumferential direction thereof; a 
support leg by which an outer peripheral surface portion of the inner ring 
not corresponding to the hollow cylindrical recess and an inner peripheral 
surface portion of the outer ring corresponding to that outer peripheral 
surface portion are integrally connected to each other in the 
circumferential direction; and at least three reinforcing ribs each of 
which extends axially from an outer peripheral surface portion of the 
inner ring corresponding to the lip portion to the support leg, and 
integrally connects an outer peripheral surface portion of the inner ring, 
an inner peripheral surface portion of the outer ring, and the support 
leg, and wherein the inner bush is held in the hollow cylindrical recess 
of the inner ring. 
In addition, in accordance with the present invention, the above object is 
also attained by a bearing device for a steering column wherein the 
bearing is pressure-fitted in a housing at the protrusions on the outer 
peripheral surface of the outer ring, and wherein the column shaft is 
supported in such a manner as to be in sliding contact with the lip 
portion of the inner ring of the outer bush with an interference range and 
to maintain a predetermined bearing clearance with an inner peripheral 
surface of the inner bush. 
In the above-described arrangement, the lip portion and the retaining 
protrusion of the inner ring of the outer bush may be an annular lip 
portion and an annular retaining protrusion which are respectively formed 
in such a manner as to extend continuously along the inner circumferential 
direction of the inner ring, or may be a plurality of lip portions and a 
plurality of retaining protrusions which are respectively arranged on the 
inner peripheral surface of the inner ring at intervals along the 
circumferential direction. In a preferred example, the lip portion is 
formed such that the diameter of a phantom circle formed by the distal end 
of the lip portion (i.e., the inside diameter of the lip portion referred 
to in the present invention) is smaller than the inside diameter of the 
inner bush by 0.02 mm to 0.20 mm or thereabouts. 
As a material of the resilient outer bush, it is possible to cite an 
elastic rubber material or an elastic synthetic resin. As preferred 
examples of the elastic synthetic resin, it is possible to cite those 
which are soft and tough and Generally have a Shore hardness (JIS K 7215, 
ISO 868, ASTM D 2240) of 40 to 60 and an impact resilience value (JIS K 
6301, ISO 1767, ASTM D 2632) of 50 to 80, and in which the behavior of 
rubber-like resilience remains, such as a polyester-ether copolymer, 
polyurethane, and the like. 
As a preferred example of the inner bush, it is possible to cite a wound 
bush in which a strip having a three-layered structure comprising a thin 
steel sheet, a sintered metal layer joined integrally to the surface of 
this thin steel sheet, and a synthetic resin layer impregnating and 
coating the sintered metal layer is wound in a hollow cylindrical shape 
with the synthetic resin layer placed on the inner side thereof. 
With the bearing device for a steering column according to the present 
invention, since the outer peripheral surface portion of the inner ring 
not corresponding to the hollow cylindrical recess and the inner 
peripheral surface portion of the outer ring corresponding to that outer 
peripheral surface portion are integrally connected to each other by the 
support leg in their circumferential direction, the pressure-fitting force 
at the time when the bearing is pressure-fitted and fixed in the housing 
does not directly act on the hollow cylindrical recess of the inner ring. 
Consequently, the dimensional accuracy of the inside diameter (roundness) 
of the inner bush held in the hollow cylindrical recess is not affected. 
In addition, by virtue of the above-described arrangement, even in a case 
where a welding strain due to welding exerts an adverse effect on the 
dimensional accuracy of the inside diameter (roundness) of the housing, 
deviations in the dimensional accuracy of the inside diameter of the 
housing does not directly affect the hollow cylindrical recess of the 
inner ring. Hence, the dimensional accuracy of the inside diameter 
(roundness) of the inner bush held in the hollow cylindrical recess is not 
affected. 
As described above, in accordance with the present invention, since the 
outer peripheral surface portion of the inner ring not corresponding to 
the hollow cylindrical recess and the inner peripheral surface portion of 
the outer ring corresponding to that outer peripheral surface portion are 
integrally connected to each other by the support leg in their 
circumferential direction, the pressure-fitting force at the time when the 
bearing is pressure-fitted and fixed in the housing does not directly act 
on the hollow cylindrical recess of the inner ring. Hence, the dimensional 
accuracy of the inside diameter (roundness) of the inner bush inserted and 
held in the hollow cylindrical recess is not affected. Therefore, it is 
possible to provide a bearing device for a steering column in which an 
appropriate clearance (sliding clearance) is maintained between the inner 
bush and the column shaft supported by the inner bush, so that smooth 
sliding is effected. 
Hereafter, a detailed description will be given of the present invention 
with reference to the drawings, and the above and other objects and 
features of the present invention will become more apparent therefrom. It 
should be noted that the present invention is not limited to the following 
preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
First, a description will be given of the prior art technique with respect 
to the present invention with reference to FIGS. 5 and 6. In FIGS. 5 and 
6, a bearing device 1 for a steering column is comprised of: a bearing 4 
including an outer bush 2 consisting of an elastic rubber material or an 
elastic synthetic resin and an inner bush 3 inserted to an inner surface 
of the outer bush 2; a housing 5 for pressure-fitting and fixing the 
bearing 4 therein; and a column shaft 6 supported by the bearing 4. The 
outer bush 2 includes an outer ring 12 having on its outer peripheral 
surface a plurality of protrusions 11 formed along the axial direction of 
the bush and over the entire circumference thereof, and an inner ring 14 
which is integrally connected to the inner surface of the outer ring 12 by 
means of a plurality of supporting legs 13 extending in the axial 
direction. The inner ring 14 includes an annular lip portion 16 formed in 
the circumferential direction at one end of its inner surface 15 in such a 
manner as to project radially inwardly with a slightly smaller inside 
diameter than the inside diameter of the inner bush 3, an 
enlarged-diameter hollow cylindrical portion 17 continuing from the lip 
portion 16, and a retaining protrusion 18 formed over part or the whole of 
the circumference of the enlarged-diameter hollow cylindrical portion 17 
spaced apart from the lip portion 16 with a predetermined distance in the 
axial direction and having an inside diameter larger than the inside 
diameter of the inner bush 3 and smaller than the outside diameter 
thereof. The inner bush 3 is inserted and held in the enlarged-diameter 
hollow cylindrical portion 17 between the annular lip portion 16 and the 
retaining protrusion 18 on the inner surface of the inner ring 14 of the 
outer bush 2. The outer bush 2 holding the inner bush 3 is pressure-fitted 
and fixed in the housing 5 at the protrusions 11 on the outer peripheral 
surface of its outer ring 12. The column shaft 6 is supported in such a 
manner as to be brought into sliding contact with the annular lip portion 
16 on the inner surface of the inner ring 14 of the outer bush 2 with an 
interference range, while maintaining a predetermined bearing clearance 
with the inner peripheral surface of the inner bush 3. 
With the above-described bearing device 1 for a steering column in 
accordance with this prior art technique, the drawbacks of the 
above-described conventional art are overcome, and, during the steering 
(rotating) of the steering wheel, the load acting on the column shaft 6 
can be supported smoothly by the bearing 4, while in a state in which no 
load is applied to the column shaft 6 during such as idling, the 
vibrations acting on the shaft 6 can be absorbed. However, in a case where 
the bearing 4 is firmly pressure-fitted into the housing 5 for the 
purposes of preventing the bearing 4 from coming off axially and rotating 
in the circumferential direction, the bearing 4 is pressure-fitted into 
the housing 5 at the outer peripheral surface of its outer ring 12. 
However, since the outer ring 12 and the inner ring 14 are connected to 
each other by means of the plurality of support legs 13 extending in their 
axial direction, the pressure-fitting force differs at outer peripheral 
surface portions corresponding to the support leg 13 and at outer 
peripheral surface portions not corresponding to the support leg 13. 
Hence, the pressure-fitting force does not act uniformly on the inner bush 
3 held by the enlarged-diameter hollow cylindrical portion 17 of the inner 
ring 14 supporting the column shaft 6. As a result, there is a problem in 
that an adverse effect is exerted on the dimensional accuracy of the 
inside diameter (roundness) of the inner bush 3. 
In addition, in a case where a member (bracket) for fixing the housing 5 
onto the vehicle body side is attached to the outer peripheral surface of 
the housing 5 by welding, there is a problem in that a welding strain due 
to the welding exerts an adverse effect on the dimensional accuracy of the 
inside diameter (roundness) of the housing 5, thereby further 
deteriorating the dimensional accuracy of the inside diameter (roundness) 
of the inner bush 3 of the bearing 4 fixed in the housing 5. If these 
problems are compounded, the dimensional accuracy of the inside diameter 
(roundness) of the inner bush 3 of the bearing 4 is further aggravated. 
The quality of the dimensional accuracy of the inside diameter (roundness) 
of the inner bush 3 of the bearing 4 affects smooth sliding between the 
inner bush 3 and the column shaft 6 supported by the inner bush 3. The 
deterioration of these members hampers the smooth sliding, and is a 
problem which should be avoided as practically as possible. 
The present invention has been devised to overcome the above-described 
problems while making use of the advantages of the above-described prior 
art technique. 
As shown in FIGS. 1 to 4, a bearing device 20 for a steering column in 
accordance with a preferred embodiment of the present invention is 
comprised of: a bearing 23 including an outer bush 21 formed of an elastic 
rubber material or an elastic synthetic resin and an inner bush 22 
inserted and held in the outer bush 21; a pipe-shaped housing 24 in which 
the bearing 23 is pressure-fitted and fixed; and a column shaft 25 
supported by the inner bush 22. 
The outer bush 21 includes: an inner ring 35 which has a plurality of (in 
this example, six) lip portions 32 arranged in the circumferential 
direction in the vicinity of one end of a hollow cylindrical inner 
peripheral surface 31 and projecting radially inwardly, and a plurality of 
(in this example, six) retaining protrusions 34 formed projectingly along 
the circumferential direction at a predetermined distance from the lip 
portions 32 in the axial direction so as to define a hollow cylindrical 
recess 33 in association with the lip portions 32 and the hollow 
cylindrical inner peripheral surface 31; an outer ring 38 which has a 
plurality of protrusions 36 formed on its outer peripheral surface along 
the axial direction and arranged in the circumferential direction, and an 
annular collar portion 37 extending radially outwardly at one end thereof; 
a support leg 39 by which an outer peripheral surface portion of the inner 
ring 35 not corresponding to the hollow cylindrical recess 33 and an inner 
peripheral surface portion of the outer ring 38 corresponding to that 
outer peripheral surface portion are integrally connected to each other in 
the circumferential direction; and three reinforcing ribs 40 which extend 
from an outer peripheral surface portion of the inner ring 35 
corresponding to the lip portions 32 to the support leg 39, and is 
integrally connected to an outer peripheral surface portion of the inner 
ring 35, an inner peripheral surface portion of the outer ring 38, and the 
support leg 39. 
In the outer bush 21, the annular collar portion 37 formed integrally with 
one end of the outer ring 38 is required when the bearing 23 is secured to 
an end of the housing 24 at the time of the pressure-fitting and fixing of 
the bearing 23 in the housing 24 which will be described later. The 
annular collar portion 37 is not required when the bearing 23 is 
pressure-fitted and fixed at an arbitrary position within the housing 24. 
The reinforcing ribs 40 reinforce the inner ring 35 at the portion where 
the hollow cylindrical recess 33 is formed, and in this example three 
reinforcing ribs 40 are formed at equal intervals in the circumferential 
direction such that they do not correspond to each other in the radial 
direction. The number of the reinforcing ribs 40 is not necessarily be 
limited to three insofar as they can be disposed at equal intervals in the 
circumferential direction such that they do not correspond to each other 
in the radial direction. The reason for disposing the reinforcing ribs 40 
at equal intervals in the circumferential direction such that they do not 
correspond to each other in the radial direction is to ensure that the 
inside dimension of the inner bush 22, which will be described later and 
is inserted and held in the hollow cylindrical recess 33, will not be 
affected by the pressure-fitting force occurring when the bearing 23 is 
pressure-fitted and fixed in the housing 24. 
The inner bush 22 is constituted by a so-called wound bush in which a strip 
having a three-layered structure comprising a thin steel sheet, a sintered 
metal layer joined integrally to the surface of this thin steel sheet, and 
a synthetic resin layer impregnating and coating the sintered metal layer 
is wound in a hollow cylindrical shape with the synthetic resin layer 
placed on the inner side. In FIG. 1, reference numeral 41 denotes a butted 
portion of the wound bush. 
The bearing 23 is formed as the inner bush 22 is inserted and held in the 
hollow cylindrical recess 33 of the inner ring 35 of the outer bush 21. In 
this arrangement, the plurality of lip portions 32 formed on the hollow 
cylindrical inner peripheral surface 31 of the inner ring 35 is formed in 
such a manner as to project radially inwardly with an inside diameter D 
(which refers to the diameter of a phantom circle formed by the distal 
ends of the lip portions 32) slightly smaller than the inside diameter d 
of the inner bush 22. Specifically, the lip portions 32 are formed such 
that the inside diameter of the lip portions 32 is smaller than the inside 
diameter of the inner bush 22 by an amount corresponding to the clearance 
(sliding clearance) between the inner bush 22 and the column shaft 
supported by the inner bush 22, e.g., by 0.02 mm to 0.20 mm. In addition, 
the retaining protrusions 34 are so formed that the inside diameter of the 
protrusions 34 is larger than the inside diameter of the inner bush 22 and 
smaller than the outside diameter of the bush 22. Accordingly, the inner 
bush 22 is prevented from coming off the inner ring 35 as the inner bush 
22 is inserted and held in the hollow cylindrical recess 33 of the inner 
ring 35. 
With the bearing device 20 for a steering column formed as described above, 
since the outer peripheral surface portion of the inner ring 35 not 
corresponding to the hollow cylindrical recess 33 and the inner peripheral 
surface portion of the outer ring 38 corresponding to that outer 
peripheral surface portion are integrally connected to each other by the 
support leg 39 in their circumferential direction, the pressure-fitting 
force at the time when the bearing 23 is pressure-fitted and fixed in the 
housing 24 does not directly act on the hollow cylindrical recess 33 of 
the inner ring 35. Consequently, the dimensional accuracy of the inside 
diameter (roundness) of the inner bush 22 inserted and held in the hollow 
cylindrical recess 33 is not affected. Therefore, an appropriate clearance 
(sliding clearance) is maintained between the inner bush 22 and the column 
shaft 25 supported by the inner bush 22, so that smooth sliding is 
effected without causing malfunctioning such as uneven abutment. 
In addition, the effect of the pressure-fitting force is exerted on not 
only the dimensional accuracy of the inside diameter of the inner bush 22 
but also the lip portions 32 of the inner ring 35. Further, since the 
interference range of the lip portions 32 with respect to the column shaft 
25 is not affected by the pressure-fitting force, the column shaft 25 is 
slidably and resiliently supported on and by the lip portions 32 with a 
predetermined interference range. Accordingly, in the state in which the 
load does not act on the column shaft 25 during such as idling, the column 
shaft 25 is resiliently supported by the lip portions 32. Hence, 
vibrations acting on the column shaft 25 are absorbed, the generation of 
colliding sound between the column shaft 25 and the inner bush 22 is 
prevented, and the load acting on the column shaft 25 during the steering 
of the steering wheel is smoothly supported by the inner bush 22 with the 
above-described appropriate clearance (sliding clearance).