Ball and socket joint

A ball and socket joint is of the type in which a ball pin is supported by a bearing insert retained within a housing. The bearing insert has axial slots in one end which upon assembly of the joint allow the insert to be deformed in a more consistant manner. An annular groove in one end of the insert defines two thin lips one of which upon assembly is deformed to provide a preload to the joint.

This invention relates to ball and socket joints of a type that is well 
known (UK Pat. No. 1,323,047) in which a bearing member or insert of a 
resilient material such as acetal resin or nylon is held within the cavity 
of a cup shaped socket formed in a housing. The bearing insert in such a 
ball and socket joint forms a part-spherical bearing surface by partially 
enclosing the ball of the ball pin, the ball pin having a shank which 
extends through an aperture in the base of the cup shaped socket. 
One problem with ball joints of this type is that to insert the ball pin 
and bearing sub-assembly into the cavity formed in the bearing housing 
requires the bearing insert to experience a severe deformation. 
To produce this deformation a large assembly force is required, and this 
makes the prediction and control of the bearing preload difficult in a 
production environment. If the preload is too great the bearing friction 
will be too large; if the preload is not enough movement of the ball pin 
relative to the bearing housing may develop very rapidly. 
An object of this invention is to reduce the force required to assemble 
such a ball joint and enable ball joints to be manufactured with a more 
consistant level of preload. 
According to this invention there is provided a ball and socket joint 
comprising a housing having a substantially cup-shaped cavity, a ball pin, 
the shank of which passes through an aperture in the housing and a bearing 
insert of a resilient material retained within the housing and partially 
enclosing the part-spherical head of the ball pin, the bearing insert 
having a thickened end portion which before assembly has an outside 
diameter which is greater than the internal diameter of the co-operating 
portion of the housing and has a cylindrical bore of substantially the 
same diameter as the part-spherical head of the ball pin wherein the 
thickened end portion has axial slots extending from its end face. 
Preferably the axial slots become wider towards the end face of the 
thickened end portion. 
Preferably the thickened end portion has an annular groove in the end face 
defining inner and outer lips. 
Conveniently it is also provided that the bearing insert is retained by a 
bearing end cap secured in the mouth of the housing which abuts a shoulder 
formed in said housing. 
Preferably before insertion of the bearing end cap into the housing the 
outer lip of the thickened end portion protrudes axially beyond the 
shoulder in the housing, the outer lip being compressed by the end cap 
when said cap is secured in place.

The ball and socket joint shown in FIG. 1 comprises a housing 10, a ball 
pin 11, a bearing insert 12, a flexible boot 13 and an end cap 14. The 
housing 10 has a substantially cup shaped cavity 15, said cavity 15 having 
an aperture 16 in its base portion 17 which is of a truncated spherical 
form and two cylindrical portions 18 and 19. Cylindrical portion 19 is in 
the mouth 22 of the cavity 15 and is of a larger diameter than cylindrical 
portion 18. A shoulder 21 separates the cylindrical portions 18 and 19. 
The ball pin 11 has a shank 23 which passes through the aperture 16 in the 
base of the cavity 15 and is sealed to the housing 10 by a flexible boot 
13 to prevent the ingress of debris, and a part-spherical head 24 the 
surface of which co-operates with the inner surface of the bearing insert 
12. The bearing insert 12 is of acetal resin, being a low friction 
abrasion resistant material having sufficient resilience to permit 
assembly as described below. 
FIG. 2 shows the bearing insert 12 before assembly. It is substantially cup 
shaped, having an aperture 25 in a truncated spherical base portion 26 to 
allow the passage of the ball pin shank 23 and a thickened end portion 27. 
The thickened end portion 27 has an end face 28 and a cylindrical bore of 
substantially the same diameter as that of the ball portion 24 of the ball 
pin 11 and a flared outer surface. The flared outer surface of the 
thickened end portion 27 is of substantially the same diameter as that of 
the diameter D2 of the co-operating portion 18 of the housing 10 at its 
equator E--E and increases to a diameter D1 of greater diameter than the 
diameter D2 towards the end face 28. The end face 28 has an annular groove 
29 which defines two lips, an inner lip 30 and an outer lip 31. Six 
tapered axial slots 32 extend from the end face 28 to a position at or 
beyond the equator E--E, the slots 32 becoming wider towards the end face 
28 than at the equator E--E. Alternate slots connect with shallow grease 
grooves 33 in the inner surface of the bearing insert, extending to the 
end of the rim 41 of the base portion 26. 
To assemble the joint the ball portion 24 of the ball pin 11 is placed in 
to the bearing insert 12 to form a bearing sub-assembly. For convenience 
the bearing insert 12 maybe slightly deformed by this operation causing it 
to loosely grip the ball portion 24 of the ball pin 11. This allows the 
bearing sub-assembly to be more easily handled. The bearing sub-assembly 
is then inserted into the housing 10, the bearing insert 12, in particular 
the thickened end portion 27, undergoing deformation resulting in a 
reduction in the diameter of said thickened end portion from D.sub.1 to 
D.sub.2. 
FIG. 3 illustrates the relative positions of the housing 10, the ball pin 
11 and the bearing insert 12 before insertion of the end cap 14. The outer 
lip 31 of the bearing insert 12 protrudes beyond the shoulder 21. The end 
cap 14 is then inserted into the mouth 22 of the housing 10 with 
sufficient force to compress the outer lip 31 of the bearing insert 12 and 
allow the end cap 14 to abut the shoulder 21. In so doing the end cap 14 
provides a further preload to the assembled ball joint. The mouth 22 of 
the housing 10 is then peened inwardly to secure the bearing end cap 14 
and so maintain the bearing preload. 
By increasing the width of the slots 32 towards the end face 28, adequate 
bearing surface area and strength are retained in the portion adjacent to 
the equator E--E. The tapered form of the slots 32 also assists moulding 
and if a linear taper is used as shown this simplifies the tooling of the 
mould. 
The shoulder 21 obviates the need to closely control the force on the end 
cap 14 during assembly and allows the mouth to be peened without altering 
the bearing preload. 
In the second embodiment of the invention shown in FIG. 4 many parts of the 
ball and socket joint are similar or modifications of those described with 
respect to FIGS. 1-3, so that where appropriate the same reference 
numerals are used with the addition of 100 and only the differences and 
modifications will be described. 
The housing 110 has a substantially cup shaped cavity 115 having a 
part-spherical base portion 117 and a cylindrical portion 118. 
In this embodiment the shank 123 of the ball pin 111 passes through the 
aperture formed by the mouth 122 of the cavity 115 and an aperture 150 in 
the end cap 114. 
The bearing insert 112 is substantially identical to the insert 12 
described above except that the base portion 126 is elongated to provide a 
greater bearing area. This form of ball and socket joint is more suitable 
for a motor vehicle suspension application in which a compressive load is 
applied through the ball pin shank 123. 
Compared with known ball and socket joints which do not have the slots 32, 
the force required to produce this deformation is reduced by the presence 
of the axial slots 32. This is helped by the annular groove 29, it being 
easier to deform material of thickness X than material of thickness Y.