U.S. patent application number 09/727802 was filed with the patent office on 2002-06-06 for housed steering column.
Invention is credited to Beaman, Michael D..
Application Number | 20020067874 09/727802 |
Document ID | / |
Family ID | 24924128 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067874 |
Kind Code |
A1 |
Beaman, Michael D. |
June 6, 2002 |
HOUSED STEERING COLUMN
Abstract
A housing encloses at least a portion of a steering shaft, and a
preloaded ball bearing mounted within the housing supports the
steering shaft. The preloaded ball bearing has loaded balls that
are preloaded and unloaded balls that are free floating, an
unloaded ball being positioned between each loaded ball. A split
raceway provides two angular contact raceways that are preloaded
axially against the loaded balls.
Inventors: |
Beaman, Michael D.;
(Torrington, CT) |
Correspondence
Address: |
John C. Bigler
Michael Best & Friedrich LLP
942 Memorial Parkway
Phillipsburg
NJ
08865
US
|
Family ID: |
24924128 |
Appl. No.: |
09/727802 |
Filed: |
December 1, 2000 |
Current U.S.
Class: |
384/521 |
Current CPC
Class: |
F16C 25/08 20130101;
F16C 19/20 20130101; F16C 2326/24 20130101; B62D 1/16 20130101;
F16C 33/60 20130101; F16C 33/3713 20130101; F16C 19/06
20130101 |
Class at
Publication: |
384/521 |
International
Class: |
F16C 033/37 |
Claims
Having described the invention, what is claimed is:
1. A housed steering column comprising: a steering shaft; a housing
enclosing at least a portion of the steering shaft; and a preloaded
ball bearing mounted within the housing and supporting the steering
shaft, the preloaded ball bearing comprising loaded balls that are
preloaded and unloaded balls that are free floating, an unloaded
ball being positioned between each loaded ball; and a split raceway
providing two angular contact raceways that are preloaded axially
against the loaded balls.
2. The housed steering column according to claim 1, wherein the
preloaded ball bearing has sufficient preload to provide a bearing
stiffness of at least 5000 newtons per millimeter.
3. The housed steering column according to claim 1, wherein the
unloaded balls are smaller in diameter than the loaded balls.
4. The housed steering column according to claim 3, wherein the
unloaded balls are made of steel.
5. The housed steering column according to claim 1, wherein the
unloaded balls are made of a polymer and the loaded balls are made
of steel.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to steering columns for
motor vehicles and, more particularly, to steering columns that
have a steering shaft supported by a bearing within a housing.
[0002] Current automotive steering columns require bearings that
provide high stiffness without high torque, even when operating
with misalignment and variations in press fit of the bearing. A
preferred type of bearing for such applications is a zero clearance
ball bearing. Generally, the bearings that are used have a full
complement of balls because there is inadequate space for a cage or
ball separator. However, when the bearings are under load, the
balls contact each other and bind, causing high torque spikes. This
condition is known as "ball gagging".
[0003] The trend is for automotive manufacturers to increase
steering column natural frequency, requiring higher and higher
bearing stiffness. Current bearing designs can only marginally meet
today's requirements, even with 100 percent inspection by hand and
a significant percentage of bearings being rejected as scrap.
Further increases in bearing preload, as a means to increase
bearing stiffness beyond today's levels, are not possible with the
current bearing designs because of the high torque spikes caused by
ball gagging.
[0004] The foregoing illustrates limitations known to exist in
present devices and methods. Thus, it is apparent that it would be
advantageous to provide an alternative directed to overcoming one
or more of the limitations set forth above. Accordingly, a suitable
alternative is provided including features more fully disclosed
hereinafter.
SUMMARY OF THE INVENTION
[0005] In one aspect of the invention, this is accomplished by
providing a housed steering column comprising a steering shaft, a
housing enclosing at least a portion of the steering shaft, and a
preloaded ball bearing mounted within the housing and supporting
the steering shaft. The preloaded ball bearing has loaded balls
that are preloaded and unloaded balls that are free floating, an
unloaded ball being positioned between each loaded ball. A split
raceway provides two angular contact raceways that are preloaded
axially against the loaded balls.
[0006] The foregoing and other aspects will become apparent from
the following detailed description of the invention when considered
in conjunction with the accompanying drawing figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0007] FIG. 1 is a cross sectional view of a housed steering column
illustrating the present invention;
[0008] FIG. 2 is a cutaway pictorial view of the preloaded ball
bearing of FIG. 1 showing half the bearing removed;
[0009] FIG. 3 is a drawing of bearing raceways and loaded and
unloaded balls of the preloaded ball bearing of FIG. 1; and
[0010] FIG. 4 is a drawing of bearing raceways and loaded balls of
a preloaded ball bearing according to the prior art.
DETAILED DESCRIPTION
[0011] Referring now to the drawings, FIG. 1 illustrates a housed
steering column 10 according to the present invention comprising a
steering shaft 12, a housing 14 enclosing at least a portion of the
steering shaft 12, and a preloaded ball bearing 16.
[0012] The preloaded ball bearing 16 has a machined inner race 18,
and a two-piece outer race 20 that provides two angular contact
raceways that are preloaded by resilient biasing members 22 against
loaded balls 24. A drawn cup 26 encloses the resilient biasing
members 22, compressing them together, and is pressfit into the
housing 14. The machined inner race 18 is pressfit over the
steering shaft 12. As shown in FIG. 2, unloaded balls 28 (indicated
by stippled shading) are also located in the angular contact
raceway provided by the inner and outer races 18 and 20, one
unloaded ball 28 being positioned between each loaded ball 24.
[0013] The unloaded balls 28 may be made slightly undersize, i.e.,
with a diameter slightly less than that of the loaded balls 24, so
that the unloaded balls 28 are free floating and serve to separate
the loaded balls rather than carry load. Alternatively, or in
addition to being slightly undersize, the unloaded balls 28 may be
made of a polymer, such as, for example, acetal, nylon or
polypropylene, or of another type of material with a stiffness less
than the material (typically steel) of the loaded balls 24, so that
unloaded balls are free floating and do not carry load. The free
floating balls effectively separate the loaded balls without the
space requirements of a ball cage or separator.
[0014] FIG. 3 shows the directions of rotation of the loaded and
unloaded balls 24 and 28 as the adjacent inner and outer races 18
and 20 undergo relative rotation, indicated by the arrows 30 and
32. Note that there is minimal scuffing of unloaded balls 28
against loaded balls 24 because there the directions and rotational
speeds of the balls are complementary. There is some scuffing of
the unloaded balls 28 against the races 18 and 20 due to the
generally opposite directions of adjacent surfaces, but such
scuffing does not result in ball gagging because those balls are
undersize or otherwise without load.
[0015] In contrast to the present invention, current zero clearance
ball bearings used in housed steering columns have loaded balls 34
arranged in a full complement such that each loaded ball 34 scuffs
against an adjacent loaded ball 34 with their surfaces moving in
generally opposite directions, as indicated in FIG. 4. As a result
of this scuffing, when the preload of the split outer race is
increased to increase bearing stiffness, ball gagging occurs at the
contact points indicated at numeral 36, in response to relative
rotation of the inner and outer races 38 and 40, indicated by the
arrows 42 and 44.
[0016] Applicant has found that the current zero clearance ball
bearings with full complement loaded balls require 100 percent
inspection and a high (barely acceptable) rate of scrap to meet
automobile manufacturers' current requirements of a bearing
stiffness of 4,000 newtons per millimeter and are unable to meet
new bearing stiffness requirements that may be above 10,000 newtons
per millimeter. However, Applicant has found that, with the present
invention, bearing stiffness requirements of 5,000 and even more
that 10,000 newtons per millimeter can be met without 100 percent
inspection and without high rates of scrap.
* * * * *