Note: Descriptions are shown in the official language in which they were submitted.
` BACXGROUND OF THE INVENTION
This invention re~tes generally to flexible joints and more ~
particularly to a new and improved housing and bearing construction '
for b~lI joints such'as are'used in automo~ive steering linkages
or the like.'
PROBLEMS rN THE ART ~ '
It is presently thè'practice in the art to fabricate ball ~-;
~oints from forged hbusings provided with separate internal spheri~
cal bearing inserts for supporting thè male ball studs. In many
instances the spherical bearing inserts have been formed of
synthetic resinous materials but a probIem has been present in that
such plastic bearing materials have been lacking in longevity -
under high-stress operating conditions, particularly when operated
in high temperature environments. Operation of automotive pivot
joints-in hot environments has only recently been dictated by
the required pollution control devices added within the hood
shells of the engine-compartments.
In an effort to offset the high temperature environment problems
pivot joints have'recently been fabricated with spherical bearings ,-
formed of annular metal inserts which overcome the heat problem
. .
but which require highly accurate machining operations both with
respect to the fabrication-of the metal inserts and the - ,
required annular seat supporting surface which must be accurately
located and formed in the'housing.
SUMMARY OF TH~ rNvENTroN
In general,,the present invention comprises a noveI pivot
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.. . . . . : .
1081~89
-2- joint housing and bearing construction which can be fabricated
at hiyh rates of production with such housings including integrally
formedspherical bearing surfaces which surfaces are located and
shaped simaltaneously with the forging and internal machining of
the housings, and by the formation of a localized annular hardened
zone at the spherical bearing surface.
~ he localized hardened bearing zones a~e formed by an
induction heating step precisely performed on the housing after
the above mentioned forging and machining steps, and by a
-10- subsequent quenching whereby cooling fluid is precisely applied
to the housing so as to maintain localization of the induction
heating to a predetermine~annular zone at the bearing surface.
As a result, the metal in the balance of the housing remains
none-hardened, tough, and fatigue resistant so as to be metallurgi-
cally proper for the main housing material.
As another aspect of the present invention, the novel pivot
joint housing construction includes lubrication grooves in the
spherical bearing surface which form grease reservoirs in the
bearing surface whithout the presence of aberrations in the
-20- finished bearing surface.
As still anothersaspect of the present invention, the above
mentionedlubrication grooves are asymmetrically located with
respect to the spherical bearing surface to prevent machine tool
chatter during the final machining of the surface.
As another aspect of the present invention, the pivot joint
in one of its embodiments includes a novel ball stud construction
wherein the lubrication grooves are formed in the spherical bearing
-30- surface of the ball stud during the forging thereof.
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~ ~081~89
-3- As still another aspect of the invention the pivot joint
on one of its embodiments comprises a novel ball stud construction
which includes a forged head portion that includes a refined spherical
bearing surface devoid of surface film and decarbonization.
It is, therefore, an object of the present invention to
provide an improved pivot joint housing construction which includes
an integral spherical bearing surface surrounded by a localized
hardened zone of high wear resistance, with the metal of the remain-
der of the housing portion being unhardened and metallurgically
-10- proper for a high degree of strength and fatigue resistance.
It is another object of the present invention to provide a
pivot joint housing of the type described adapted for fabrication
at high production rates by an inductor electrode and quenching
apparatus which are repeatedly locateable with respect to precise
portions of the housing workpieces.
It is still another object of the present invention to
provide a novel pivot joint housing construction provided with
integral hardened spherical bearing surfaces that include
-20- lubEication grooves located in the bearing surface without the
presence of spherical aberrations adjacent the grooves.
It is another object of the present invention to provide
a novel pivot joint of the type described that comprises a novel
ball stud that includes lubrication grooves in the spherical bearing
surface thereof, said grooves being integrally formed in the bearing
surface during the forging thereof.
It is still another object of the present invention to
provide a novel pivot joint construction of the type described that
comprises a ball stud that includes a refined sp~erical bearing
-30-
surface that is devoid of surface decarbonization and surface film
normally resulting from the heat treating operation.
- 1081489
-4- Further object and advantages of the present invention will
be apparent from the following description, reference being had to
the accompanying drawings wherein a preferred form of embodiment of
the invention is clearly shown.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side sectional view of a ball joint including
a housing constructed in accordance with the present invention;
Fig, 2 is a partial side elevational view of a workpiece
used in forming the housing of Fig. l;
-10- Figs. 3 through 5 are side elevational views, partially in
section, of the workpiece of Fig. 2 in various steps of formation;
Fig. 6 is a bottom elevational view of the workpiece
corresponding to Fig. 5;
Fig. 7 is an end sectional view of the workpiece of the
preceding figures;
Fig. 8 is a side elevational view showing an induction
heating electrode andan associated fixture for locating the work-
piece of the preceding figures;
Fig. 9 and Fig. 10 are side and end elevational views
-20- of a ball stud constructed in accordance with the present invention; -
and
Fig. 11 and Fig. 12 are side and end elevational views of a
second ball stud constructed in accordance with the presentinvention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring in detail to the drawings, Fig. 1 illustrates a
typical pivot joint including a housing constructed in accordance
with the present invention, with such housing being indicated
generally at 10. The housing includes a cavity 12 that includes
-30- an inner wall suface 14 ans a spherical bearing surface 16.
With continued reference to Fig. 1, a ball stud is indicated
': . ' .,, . : ',, ' . ~ . . . ,~ . : ~. .
, . . . ~ .
-` 1081~8~
-~5- generally at 10. The housing in¢;ludes a cavity 12 that includes
an inner wall surface 14 and a spherical bearing surface 16.
With continued reference to Fig. 1, a ball stud indicated
generally at 18 includes a ball shaped end 20 which is pivotally
supported by bearing surface 16 as well as by a bearing surface
22 formed on a removable bearing insert 24.
Bearing insert 24 is urged inwardly by a compression spring
26 which is interposed between an end closure 28 and the bearing
insert. The housing further includes a shank portion 30 as well
as a top opening 32 which includes a tapered wall 34 the latter
permitting angular movement of the shank 36 upon pivoting thereof.
The assembly of Fig. 1 also includes a dust cover 38, sleeve
40, and nut 42.
Referring next to Fig. 2, the above mentioned housing 10 is
formed from a workpiece W which consists of a rod of carbon steel
with sufficient carbon content to permit subsequent induction
hardening. A suitable steel material is referred to as the middle
carbon type, such as SAE 1040.
After the workpiece W has been sheared to length from bar
stock, it is heated and forged to the shape shown in Fig. 3
wherein the housing 10, with the cavity 12, have been forged to
the shape illustrated.
The workpiece is next subjected to a coining operation to
form the grease grooves 46 with such grooves being eccentrically
located so as not to be directly opposite each other as seen in
Fig. 6.
It is important to mention that during the forging operation,
or when forging and coining operations are performed to include
the grease grooves, then the surface carbon is removed as a result
of the working of the metal during the forging or forging and coin-
ing steps.
It should further be pointed out that such surface decarboni-
zation normally would inherently preclude the subsequent induction
1081~89
-6- hardening of the wall portion of the housing where the spherical
bearing is to be formed.
In accordance with the present invention the workpiece W
is subjected to an internal machining operation using a circular
milling cutter so as to machine away the surface decarbonization
and accurately locate and finally shape and finish the previously
mentioned spherical bearing surface 16. Inner wall portion 14
is also machined at the same time to remove the taper left by the
forging die.
A bottom hole 32 is also formed in the housing as well as a
groove 52 for receiving the end closure 28. Such bottom hole 32
and groove 52 can be cut at the same time the wall surface 14
and bearing surface 16 are machined.
It should further be mentioned that during the internal
machining the grease grooves 46 are cut down in length and
any surface aberrations present in Fig. 3 are machined away such
that the bearing curvature wi~ll be accurately produced. As
still another operation, a radial hole 54 is formed through the
wall of the hbusing for the subsequent mounting of a grease
fitting.
Reference is next made to Fig. 5, which illustrates the
machining of the outwardly tapered surface 34 at the opening 32.
The workpiece of Figs. 5 through 7 is next positioned over an
inductor eIectrode assembI~ indicated generally at 60 which
includes an induction coil 62 and induction connector 64 mounted
on a suitable supp~rting body 66.
The assembly of Fig. 8 further includes a lower positioning
fixture 68 for receiving and positioning the bottom of housing 10
and an upper positioning fixture 70 for engaging and positioning
the top of housing 10. The upper positioning fixture 70 is
provided with extending and retracting mechanism as well as a
spring loaded arrangement, not illustrated.
With continued reference to Fig. 8, the lower fixture is
- ~1)8~48~?
-7- provided with a quenching inlet conduit 72 having radially
extending outlet orifices indicated by dotted deIineation at 74. -
when a coolant fluid is admitted under pressure into quench
conduit 72, it is directed outwardly through the radial orifices
74 and impinges on the bearing surface 16. An alternate way of
quenching can be effected by introducing the coolant through
passage 71 in upper positioning fixture 70.
In operation, having been forged and finished to the
configuration of Fig. 6, housing 10 is placed in the induction
heating apparatus with the top of the supporting body 66 inserted
into the cavity 12 of housing lO.such that the induction coil 62
is precisely positioned in close~proximity to spherical bearing
surface 16. The induction coil 62 is next energized with a
predetermined appropriate Kmount of power to induction harden
spherical bearing surface 16 and to also harden the underlying
zone 80 to the predetermined depth.
It has been found that by using a SAE 1040 hot rolled steel
with the forged area having a Brinell har~ness of 143-229, then
the depth of the hardened:zone 80 shbuld be formed with a zone .
depth of between .010 and .090 of an inch with the preferred .
range being between .020 and .080. This will produce a surface
hardness of between 40 and 70 Rockwell C with the preferred range
being between 50 and:60 Rockwell C. This depth of surface zone
has been found to be ideal for both a wear resistant bearing
surface and tough fatigue resistant housing.
..
1081~89
-8- Reference is next made to 9 and 10 which illustrates a ball stud
constructed in accordance with a modefication of the present inven-
tion, with such stud being indicated generally at 118. In this embodi-
ment the head portion 120 is provided with longitudinally extending
lubrication grooves 124, instead of forming such lubrication grooves
in the spherical bearing surface 16 of the housing portion as was
the case with the previously described embodiment of Figs. 1-6.
Figs, 11 and 12 show a modified ball stud construction
similar to the embodiment of Figs. 9 and 10 except that the lubrica-
-10- tion grooves 134 are of spirally extending configuration.
In both of the ball stud embodiments illustrated the spiral
grooves are positioned so as not to be diametrically opposite one from
another so as to eliminate vibratory machine chatter during a finish
machining operation later to be described.
Reference is next made to Figs. 9 and 10 which illustrate
a ball stud constructed in accordance with a modification of the
present invention and indicated generally at 118. In this embodiment
the lubricating grooves 46 are eliminated from the housing seat 22
and instead are formed in the spherical outer surface of the ball stud.
-20- Ball stud 118 is formed from a carbon steel blank which is
cold headed to form an enlarged head portion on a shank portion 122
with the head portion including a spherical outer surface 120.
A plurality of spaced lubricating grooves 124 are formed
in spherical outer surface 120 during the cold heading operation
which forms the head portion on the ball stud. Such lubricating
grooves 124 serve as cavities for retaining grease that maintains
a film of lubricant at the confronting spherical bearing surfaces
120 on the stud and 22 on the housing.
-30-
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~ ~081489
-9- It has been determined that in the production of certain
designs of pivot joints, which include raised bottom shells, or
webs, in the bottom of the housing forging, it is also possible to
hot forge the flare or tapered wall 34 of the top opening 32 simul-
taneously with the hot forging of the housing portion 10. This
eliminates the need for seperate machining operation to provide the
flare 34 needed for angularity of stud movement. However, in such
pivot joint designs where the flare 34 can be hot forged, it is not
possible to also simultaneously forge the lubricating grooves 46.
-10- Hence, it becomes ecconomically desirable to form the lubricating
grooves 124 in the spherical outer surfàce 120 of the ball stud 118.
In accordance with the present invention, the ball stud 118
of Figs. 9 and 10 can be economically and accurately produced by the
following production steps:
1. A carbon steel blank is upset in a cold heading machine
to form the shank portion 122 and enlarged head portion that includes
the spherical outer surface 120, with the longitudinally extending
lubricating grooves 124 being forged into surface 120 by a suitable
shaped forging die.
-20- 2. The spherical outer surface 120 is next subjected to a
machining operation, such as grinding, to accurately establish the
spherical radius to specified tolerances for the particular job
requirement. For example, with a 1 3/64" diameter ball a typical
tolerance for automotive applications would be .5205 - .5165 spherical
radius after grinding.
3. The workpiece is next heat treated to case harden the
outer surface. A typical heat treatment would be to carbon-nitride
in an atmospheric furnace with a temper at 400 degrees for one hour
minimum at heat after quench. This will result in a case depth of
-30- .006 - .014 with the spherical surface file hard for the typical
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-- 1081~89
-10-1 3/64" diameter ball mentioned above.
4. The spherical outer surface 120 is next refined,
preferably by a vibratory-slurry treatment wherein the heat treated
workpieces are tumbled in a drum type container in the presence of a
slurry of water and ceramic pellets. This polishing operation serves
to refine the spherical surface by removing surface decarbonization
and surface film which resulted from the above described heat treating
operation.
After the finished ball studs 118 have been subjected to
~10- the above mentioned steps they are ready to be assembled into the
pivot joint, as seen in Fig. 1, with the spherical outer surface 120
pivotally supported on the spherical beaiing surface 22 of the hou-
sing portion 10.
Figs. 11 and 12 illustrate a modified ball stud 128 which
is identical to the previously described embodiment of Figs. 9 and 10
except that the lubricating grooves 134 are of spiral configuration
instead of straight as was the case with the prior embodiment.
It will be noted that in the case of both -ball stud con-
structions the lubricating grooves are circumferentially space~at 120
-20- degrees so as to not be located diametrically opposite one another.
It has been determined that this spacing arrangement eliminates the
possibility of vibratory chatter during the machining step.
Further objects and adve~ages of the present invention will
be apparent from the following description, reference is ~eing had
to the accompanying drawings wherein preferred forms of embodiments of
the invention are clearly shown.
-30-
