Ball and socket joints with wear indicator

A wear indicator for knuckle or swivel joints of the ball and socket type wherein the spherical surfaces in swivelling engagement are urged in bearing engagement by a retainer member accomplishing the double function of holding the ball and the socket in assembly and of applying a pre-load force to the ball to prevent vibration and rattle and to compensate for wear of the bearing surfaces. The wear indicator is in the form of an elongate member attached to the pre-load retainer member at a portion thereof which is progressively movable in the direction of wear of the bearing surfaces of the joint for maintaining the pre-load pressure upon the bearing surfaces. The elongate member which, preferably, takes the form of a grease fitting in lubricated joints or the form of a rod in dry or in lubricated-for-life, projects a predetermined distance from an end of the socket when the joint is new, and retracts at least flush or even with a reference plane, such as the plane of the socket end, when the joint has worn to a degree requiring replacement. Alternatively, the tip of the elongate member projects through an aperture in a closure plate mounted at the end of the socket when the joint is new, and retracts with its tip at least flush with the outer surface of the plate when the wear of the joint is such as to require replacement, thus forming a visual and tactile wear indicator.

BACKGROUND OF THE PRESENT INVENTION 
The present invention relates to a bearing assembly for knuckle or swivel 
joints in general, and more particularly to ball and socket joints of very 
simple structure provided with a wear indicator. 
Knuckle or swivel joints of the ball and socket type are commonly used in 
motor vehicle steering tie rod assemblies, in drag links, torque rods and 
like structures, in which there is a requirement for transmitting a force 
from a member to another while permitting one member to swivel or pivot 
relative to the other. 
Knuckle or swivel joints of the ball and socket type consist generally of a 
stud terminating in a full or partial ball disposed within a socket member 
in swivelling slidable engagement with a conforming concave spherical 
segment of the socket member. The engaged bearing surfaces of the ball and 
of the socket are biased, or pre-loaded, towards each other such as to 
provie a relatively tight assembly eliminating play and rattle and 
automatically compensating for wear of the bearing surfaces. 
Ball and socket knuckle or swivel joints are of the dry type, or of the 
prelubricated type without lubricator for replenishing the lubricant, or 
are provided with a grease fitting permitting to occasionally replenish 
the supply of lubricant, for example during normal servicing of a motor 
vehicle. Whatever the type of ball and socket joints installed on a motor 
vehicle, progressive wear and tear of the bearing surfaces in constant 
preloaded swivelling engagement gradually proceed to a state beyond the 
capability of the pre-load structure to compensate for wear, to the point 
where play and rattle begin to appear under excessive loads which are 
beyond the capability of the wear compensation pre-load to accommodate. 
Although such excessive wear, which requires replacement of the joint, may 
be estimated by an experienced mechanic while servicing a motor vehicle, 
through visual inspection of the joints, or by means of appropriate 
gauges, or simply by manually shaking the steering tie rod assembly, for 
example, and approximately judging the amount of play and rattle, and the 
looseness of the joints, it is evident that such a procedure of checking 
for wear leaves much to be desired. 
SUMMARY OF THE INVENTION 
The present invention has for principal object to provide ball and socket 
joints of all types with a wear indicator requiring no special technique 
for checking for wear, such as the gauges used for that purpose, and 
permitting to determine the amount of wear of the joints principally by 
visual inspection, for the purpose of replacing the joint prior to the end 
of its useful life, for example prior to having been subjected to an 
amount of wear which could lead to unsafe conditions such as excessive 
play in a motor vehicle steering mechanism, or actual accidental 
separation of the joint through pulling of the ball member from its 
socket. 
In addition, the present invention contemplates a particular simple 
structure for a ball and socket knuckle or swivel joint with built-in wear 
indicator, and applicable to nonlubricated joints as well as lubricated 
joints provided with a grease fitting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in greater detail, and first to FIGS. 1-3, the 
example of structure shown therein for a knuckle or swivel joint 10 
modified according to the present invention is substantially as disclosed 
in details in application Ser. No. 251,254, and comprises a cold-headed 
ball 12 having a projecting stud 14 integrally formed or welded at one end 
thereof. The ball 12 has a main body portion 15 of relatively large 
diameter proximate its integral junction with the stud 14. The side of the 
ball 12 diametrically opposite to the stud 14 has a hemispherical 
protrusion 16 of substantially smaller diameter than the ball main body 
portion 15, a generally flat annular shoulder 18 surrounding the 
hemispherical protrusion 16. The main portion 15 of the ball 12, between 
the annular shoulder 18 and the stud 14, is formed with a spherical 
surface 19. The ball 12 is disposed in a socket 20 having a bore 22 and an 
integrally formed shank 26 projecting from an outside surface of the 
socket. The bore 22 is formed with a spherical surface 23 to mate with the 
spherical surface 19 on the main portion 15 of the ball 12. The socket 
bore 22 has an open end 24 through which projects the stud 14. 
The bore 22 of the socket 20 terminates at its other end with an annular 
shoulder 36 and an annular lip 38 forming a circular groove 39 receiving a 
disk-like pre-load and retainer cap 40. The retainer cap 40 is preferably 
a stamping of spring steel formed with a centrally disposed threaded neck 
41, a partially spherical recess or cavity 42, and a peripheral flange 44, 
a reverse bend 46 being formed between the recess 42 and the peripheral 
flange 44. The neck 41 threadably receives a grease fitting 48, as shown, 
or other lubricator plug. 
As illustrated at FIG. 1, the socket 20 is originally provided with a 
straight lip flange or rim 38' shown in dashed lines, and the three 
principal parts forming the knuckle or swivel joint 10 are assembled 
together by placing the ball 12 in the bore 22 of the socket 20, disposing 
the retainer cap 40 with its partially spherical recess 42 in engagement 
with the hemispherical protrusion 16 of the ball and, by a swaging 
operation, bending over the socket rim 38' such as to capture the edge of 
the peripheral flange 44 of the retainer cap 40 in the circular groove 39, 
between the socket annular shoulder 36 and the socket bent-over annular 
lip 38. It will be readily appreciated that, during the swaging operation, 
the edge of the peripheral flange 44 is somewhat flattened elastically 
thus resulting in applying a pre-load to the assembled parts that causes 
the partially spherical surface 19 of the ball main portion 15 to firmly 
engage the partially spherical surface 23 of the socket bore 22, and which 
also results in firmly applying the partially spherical surface of the 
recess 42 of the retainer cap 40 firmly in engagement with the 
corresponding surface of the hemispherical protrusion 16 of the ball 12, 
Therefore, in addition to providing for finish assembly of the parts, the 
swaging operation causes a pre-load to be exerted on the bearing surfaces 
in mutual swivelling engagement, which prevents rattles and which 
automatically compensates for play due to normal wear of the joint, in 
operation after installation. 
The center of the spherical surface 19 of the ball main body portion 15 and 
the center of the ball hemispherical protrusion 16 coincide such that the 
knuckle and swivel joint of the invention can be angulated to any extreme 
position, such as illustrated in phantom line at FIG. 1, without any 
binding. 
When the ball and socket joint 10 is new, FIG. 1, the grease fitting 48 
projects a certain distance beyond the plane of the annular lip 38. After 
the knuckle and swivel joint 10 has been in service for a period of time, 
progressive wear of the swivelling bearing surfaces in engagement, 
including more particularly the wear of the spherical peripheral surface 
19 of the ball main body portion 15 and of the corresponding spherical 
surface 23 of the socket bore 22, and relatively less importantly the wear 
of the partially spherical surface of the recess 42 of the pre-load 
retainer cap 40 and of the corresponding spherical surface of the ball 
hemispherical protrusion 16, causes the grease fitting 48 to be 
progressively displaced in the direction of the pre-load force exerted by 
the retainer cap 40, tending to constantly urge in engagement the bearing 
surfaces. 
This results in the neck 41 of the retainer cap 40 to progressively sink 
within the end of the socket bore 22 closed by the retaining cap 40, as 
illustrated at FIG. 2. The amount of wear of the joint bearing surfaces is 
proportionally represented by the position of the grease fitting 48 
relative to the plane of the annular lip 38, such that the position of the 
grease fitting 48 provides an indication of the degree of wear of the 
knuckle or swivel joint 10. Any arbitrary distinct visual reference may be 
used to determine, with a given degree of safety, initial closeness to the 
end of the joint useful life. For example, when the neck 41 of the 
retainer cap 40 in which is threadably fitted the grease fitting 48 is 
flush with or below the plane of the annular lip 38, this may be 
arbitrarily considered to be the indication that the knuckle or swivel 
joint 10 has reached the end of its useful life and needs to be replaced. 
By appropriate dimensioning of the elements of the swivel or knuckle joint 
10, and more particularly by appropriate dimensioning of the length of the 
retainer cap neck 41, a relatively accurate wear gauge is provided which, 
by simple visual inspection, permits to determine the amount of wear of 
the swivel or knuckle joint 10, and to effectuate replacement by a new 
joint assembly prior to the wear reaching a limit beyond the capability of 
the pre-load retainer cap 40 to compensate for, through the pre-load force 
applied by the retainer cap 40 to the swivelling bearing surfaces, and at 
a safe stage prior to reaching excessive wear resulting in a reduction of 
the diameter of the main portion 15 of the ball 12 contemporaneously with 
an increase in diameter of the spherical surface 23 in the socket bore 22 
that may cause the stud 14 and ball 12 assembly to separate from the 
socket member 22 by pulling through the open end 24 of the socket member. 
The reference position for indicating the limit of permissible wear is 
therefore, in the example chosen, the position corresponding to the base, 
FIG. 2, of the grease fitting 48 being flush with the plane of the annular 
lip 38, which may be checked by visual sighting or by way of a ruler 
placed across the lip 38 in close proximity with the grease fitting base. 
Referring now to FIGS. 4-5, the structure of the ball and socket joint 10' 
illustrated therein is identical to that of FIGS. 1-3, except that the 
structure does not include a grease fitting, the grease fitting being 
replaced by a plug 50 fitted in the neck 41 disposed at the center of the 
pre-load retainer cap 40. The ball and socket joint 10' is of the dry 
type, or of the lubricated-for-life type which is provided, during 
assembly with a supply of lubricant which needs not be replenished during 
the useful life of the joint. The ball and socket joint 10' of FIGS. 4-5 
consists of an assembly of the same elements as the joint 10 of FIGS. 1-3, 
with the mentioned exception of the grease fitting being replaced by a 
plug 50, for the purpose of reducing inventory of parts, and for purpose 
of utilizing the neck 41 of the retainer cap 40 as a built-in wear 
indicator. By correct dimensioning of the length of the neck 41, the neck 
41 is transformed into a wear indicator which, when the ball and socket 
joint 10' is new, projects an appropriate distance from the plane of the 
annular lip 38 holding the retainer and pre-load cap 40 in position in the 
groove 36 at the end of the bore 22 in the socket member 20. The wear of 
the joint 10' may be checked visually by sighting the retainer cap neck 41 
with the plane of the annular rim 38 or by using a straight edge such as a 
ruler 54 and displacing the straight edge across the face of the lip 38, 
diametrically. If the retainer cap neck 41 projects beyond the plane of 
the end of the socket 20 as represented by the annular lip 38, it is 
prevented from being displaced diametrically as a result of engagement 
with the neck 41, FIG. 4. However, if the ball and socket joint 10' has 
worn beyond its useful life, the straight edge 54, FIG. 5, can be freely 
displaced across the face of the lip 38 without interference caused by 
engagement with the protruding neck 41 as a result of the wear of the 
bearing surfaces in engagement having been compensated by the elastic 
deformation of the closure cap 40 in a direction applying the pre-load 
force to the bearing surfaces and having retracted the retainer cap neck 
41 beyond the plane of the annular surface of the lip 38. 
The principles of the invention are also applicable to full ball and socket 
knuckle or swivelling joints, an example of which is illustrated at 60 at 
FIGS. 6-7. The structure of the ball and socket joint 60 comprises a full 
ball 12 integrally formed, or welded, on the end of a stud 14. The ball 12 
is spherical and is disposed in a socket 20 having a bore 22 provided with 
a spherical surface portion 23 engaged by the spherical surface 19 of the 
ball 12. The socket 20 has an outwardly diverging frusto-conical open end 
portion 24 through which projects the stud 14. The socket bore 22 has an 
enlarged cylindrical bore portion 25, an annular step surface 27 being 
formed between the spherical portion 23 of the bore 22 and the enlarged 
cylindrical bore portion 25. The surface of the annular step 27 is an 
imaginary plane intersecting the spherical surface 19 of the ball 12 
substantially along a diameter. The pre-load retainer cap 40 is 
structurally identical to the retainer cap 40 of FIGS. 1-3, except that 
its spherical recess 42 is of a size to accommodate the full ball 12. The 
ball 12 may be provided with a flat surface, not shown, disposed such as 
to correspond to the outlet of the grease fitting 48, and resulting in 
providing a space which, after filling with grease, acts as a grease 
reservoir, in addition to the reservoir of lubricant formed in the socket 
enlarged bore portion 25 between the pre-load retainer cap and the annular 
surface 27 in the socket 20. 
The retainer cap neck 41 and the grease fitting 48 of the full ball and 
socket joint 60 together, through proper dimensioning of the elements, act 
as a wear indicator. When the ball and socket joint 60 is new, the 
pre-load retainer cap neck 41 and grease fitting 48 project a certain 
distance from the plane of the annular lip 38, FIG. 6, while, after the 
joint has worn beyond its useful life, the retainer cap neck 41 and the 
grease fitting 48 have become displaced in the direction in which pre-load 
is applied by the retainer cap 40 to the bearing surfaces in engagement to 
a predetermined position easily visually identifiable. Such predetermined 
position is, for example, the base of the hexagonal head of the grease 
fitting 48 being even with the plane of the annular lip 38, indicating 
that the worn ball and socket joint 60 must be replaced by a new one. 
The structure of the full ball and socket joint 60' of FIGS. 8-9 is alike 
that of FIGS. 6-7, except that the pre-load retainer cap neck 41 and the 
grease fitting 48 of the structure of FIGS. 6-7 are omitted. The full ball 
and socket joint 60' of FIGS. 8-9 is of the dry type or of the 
prelubricated type, or lubricated-for-like type. As a result of 
appropriate dimensioning of the elements, including the size of the ball 
12 and the height or thickness of the socket 20, more particularly as to 
the distance separating the annular surface 27 in the socket bore 22 from 
the groove 36 in which is disposed the flange 44 of the pre-load retainer 
cap 40, and the thickness of the spring steel of which the retainer cap 40 
is made, when the full ball and socket joint 60' is new a portion of the 
exterior surface of the retainer cap 40, as shown at 56 at FIG. 8, 
projects beyond the plane of the annular lip 38. A straight edge 54 
displaced across the surface of the annular lip 38 is consequently lifted 
while sliding over the portion 56 of the exterior surface of the retainer 
cap 40 projecting beyond the plane of the lip 38. After the full ball and 
socket joint 60' has reached the end of its useful life, the straight 
edge 54, FIG. 9, may be slipped across the face of the retainer lip 38 
without engaging the farthest projecting portion 56 of the exterior 
surface of the pre-load retainer cap 40, thus indicating that it is time 
to replace the ball and socket joint 60'. 
Referring to FIGS. 10-11, an example of structure for a knuckle or swivel 
joint 70, as disclosed in application Ser. No. 292,634, comprises a stud 
14 provided at one end with an integral cold headed half-ball 12 having a 
peripheral convex surface 19 and a flat end face 18. The half-ball 12 is 
disposed within a socket member 20 provided with a shank 26 fastened to 
the periphery of the socket member 20 by any convenient means, such as by 
friction welding for example. The socket member 20 has a bore 22 from 
which projects, at one end, the stud 14 of the stud and half-ball unit. 
The peripheral convex spherical surface 19 of the half-ball 12 slidingly 
engages an inner concave spherical surface portion 23 formed in the bore 
22 of the socket member 20. The half-ball 12 and its attached stud 14 are 
capable of swivelling relative to the socket member 20. The bore 22 of the 
socket member 20 has an open end 24 through which projects the stud 14. 
A dished retainer cap 40, made of resilient spring metal in the form of a 
disk and having a convex face 57 disposed toward the flat end face 18 of 
the half-ball 12 closes the other end of the socket bore 22. The retainer 
cap 40 is held in position at the other end of the bore 22 of the socket 
20 by an inwardly radially bent lip 38, such that the peripheral flange 44 
of the retainer cap 40 is held in a groove 39 formed between the lip 38 
and an annular shoulder surface 36 in the socket bore 22 proximate its 
other end. The retainer cap 40 has a centrally disposed aperture 58 in 
which is press-fitted or otherwise mounted a grease fitting 48. The grease 
fitting 48 has an enlarged foot 71 having a convex end face 72 and forming 
a bearing button urged against the flat end face 18 of the half-ball 12 as 
a result of elastic deformation and partial flattening of the dished 
retainer cap 40 during formation, by swaging, of the cap retaining lip 38. 
In this manner, a pre-load force is applied by the retainer cap through 
the convex end face 72 of the grease fitting 48 to the spherical bearing 
surfaces 19 and 23. In the structure disclosed, the grease fitting 48 may 
eventually be used to replenish the reserve of lubricant present between 
the retainer cap 40 and the flat end face 18 of the half-ball 12. 
The elements forming the half-ball and socket 70 are so dimensioned, and 
more particularly the length of the grease fitting 48 is so dimensioned, 
that when the half-ball and socket joint 70 is new a straight edge 54 
being slipped across the annular surface of the lip 38 of the socket 20 
encounters the projecting tip of the grease fitting 48. When the bearing 
surfaces in engagement have worn to the point that a straight edge 54 
displaced across the surface of the lip 38 no longer encounters the tip of 
the grease fitting 48, as a result of the tip of the grease fitting 48 
having retracted beyond the plane of the lip 38, FIG. 11, this indicates 
that it is time to replace the worn joint by a new one. 
The structure of FIGS. 10-11 is readily adaptable to knuckle or swivel 
joints of the dry type or of the lubricated-for-life type, simply by 
replacing the grease fitting 48 by a rod, formed integral with the bearing 
button 71 and projecting through the aperture 58 in the pre-load retainer 
cap 40, such as to normally project beyond the plane of the annular lip 38 
when the ball and socket joint is new, and below the surface of the 
annular lip 38 when the half-ball and socket joint 70 has worn beyond its 
useful life term. A similar structure is illustrated at 70' at FIGS. 12 
and 13 wherein the bearing button 71 is provided with a stem 74 passed 
through the aperture 58 in the pre-load retainer cap 40 and which has a 
tip 76 normally projecting through an aperture 77 in a disk plate 78 when 
the half-ball and socket joint 70' is new. The disk plate 78 is mounted at 
its marginal edge in the groove 39 below the lip 38, together with the 
marginal flange 44 of the pre-load retainer cap 40. The length of the stem 
74 is such that when the half-ball and socket joint 70' reaches the end of 
its useful life, the tip 76 of the stem 74 disappears below the outer 
surface of the disk plate 78. The structure of FIGS. 12-13 therefore 
provides a half-ball and socket joint 70' with a wear indicator which can 
be checked by hand feel. As long as the end 76 of the stem 74 projects 
through the aperture 77 in the plate 78, the joint may be left where 
installed, but when checking reveals that the tip 76 of the pin stem 74 no 
longer projects beyond the plate 78, the joint needs replacement. 
Referring now to FIGS. 14-15 illustrating an example of structure for a 
knuckle or swivel joint 80 particularly well adapted to accomplish the 
object of the present invention, the joint 80 comprises a cold-headed 
half-ball 12 having a projecting stud 14 formed integrally at one end 
thereof the half-ball 12 being swivellingly disposed in a socket 20. The 
end of the half-ball 12 has a partially spherical surface portion 19 in 
swivelling engagement with a mating spherical surface 23 formed in the 
bore 22 of the socket 20 proximate the open end 24 thereof through which 
projects the stud 14. A cup-shaped pre-load retainer cap 40 having an 
annular peripheral flange 44 is held at the other end of the bore 22 in 
the socket 20 by a lip 38 formed by bending over the socket rim 38', shown 
in dashed lines, such as to form the lip 38, an elastomeric O-ring 85 
being compressibly held between the lip 38 and the peripheral flange 44 of 
the cup-shaped retainer cap 40. The cup-shaped retainer cap 40 has a flat 
end wall 86 provided with a centrally disposed aperture 87 through which 
is disposed a grease fitting 88 having a stem 89 and an enlarged end or 
foot portion 90 provided with a spherical surface 92 in engagement with 
the concave spherical surface 84 in the conical cavity 82 of the half-ball 
12. The elastic deformation and compression of the elastomeric O-ring 85 
generally combined with a slight elastic deformation of the flange 44 of 
the cup-shaped closure cap 40, biases the end wall 86 of the closure cap 
40 and consequently the spherical surface 92 of the enlarged end or foot 
portion 90 of the grease fitting 88 in firm engagement with the spherical 
portion 84 of the cavity 82 in the half-ball 12, and the peripheral 
spherical surface 19 of the half-ball 12 in engagement with the spherical 
surface 23 of the socket bore 22. A channelway 94 is provided through the 
center of the stem 89 of the grease fitting 88 to supply grease to the 
interior of the socket 20 between the closure cap 40 and the half-ball 12 
to lubricate the bearing surfaces in swivelling engagement, by means of a 
grease gum, not shown, fitting the tip 96 of the stem 89. Preferably, the 
channelway 94 does not have a check valve preventing reverse flow of 
grease therethrough, the engagement of the spherical end face 92 of the 
enlarged portion or foot 90 of the grease fitting 88 in engagement with 
the spherical concave surface 84 in the half-ball cavity 82 normally 
acting as a check valve, with the added feature that when the half-ball 12 
and stud 14 assembly is angulated, as shown at FIG. 14a, excessive grease 
in the space between the half-ball 12 and the retainer cap 40 is 
eliminated without causing hydraulic lock as a result of the pressure 
lifting the spherical surface 92 of the grease fitting foot portion 90 
against the pre-load force exerted by the compression O-ring 85 from the 
concave spherical surface 84, thus allowing surplus grease to reverse flow 
through the channelway 94 and relieving the internal pressure that may 
cause hydraulic lock. 
The length of the stem 89 of the grease fitting 88 is such that the end of 
the tip 96 of the grease fitting projects beyond the plane of the socket 
retaining lip 38, when the joint 80 is new. A straight edge 54 being 
diametrically translated over the end of the socket 20 in sliding 
engagement with the surface of the lip 38 is enabled to slip across 
without interference only after the end of the grease fitting tip 96 is 
flush with, or below, the plane of the surface of the lip 38, FIG. 15. 
When such condition is observed, which indicates wear of the bearing 
surfaces in engagement and more particularly of the ball spherical surface 
19 and socket internal spherical surface 23, beyond an acceptable limit, 
the joint 80 should be replaced. 
The structure of FIGS. 14-15 is readily adaptable to knuckle or swivel 
joints of the dry type and of the lubricated-for-life type such as 
illustrated at 100 at FIGS. 16-17, the grease fitting being replaced by a 
rod 102 substantially shaped like the grease fitting 88 of the structure 
of FIGS. 14-15, but without the grease channelway and the grease gun 
fitting tip. The rod 102 could be made with a length such that its tip 104 
would interfere with a straight edge being passed transversely over the 
surface of the socket lip 38, when the knuckle or swivel joint 100 is new, 
and let the straight edge pass over freely without interference, when the 
knuckle or swivel joint 100 has reached the end of its useful life. 
Preferably however, the joint 100 is provided with a disk plate 106 
installed between the inner face of the socket lip 38 and the elastomeric 
O-ring 85. The disk plate 106 has an aperture 108 at its center through 
which the tip 104 of the rod 102 projects, when the joint is new, FIG. 16, 
and which is retracted at least flush with the outer surface of the disk 
plate 106 when the joint is worn, FIG. 17. Therefore, the condition of the 
joint 100 may be easily checked simply by finger feel, determining whether 
or not the tip 104 of the rod 102 projects beyond the outer surface of the 
disk plate 106. When the rod tip 104 no longer projects, replacement of 
the joint is required. 
It will be readily appreciated that is structures of ball and socket joints 
provided with a grease fitting, the tip of the grease fitting may be 
arranged to project through an aperture in a plate, such as the plate 78, 
FIGS. 12-13, or the plate 106, FIGS. 16-17, a predetermined finite 
distance when the joint is new, and a lesser finitedistance when the joint 
needs replacement such that a grease gun is prevented from fitting over 
the tip through interference with the plate surface.