Ball joint
Ball joint


In an automobile, ball joints are spherical
bearings that connect the control arms to the steering knuckles. They are used on virtually
every automobile made and work similar to the ball and socket design of the human hip
joint. A ball joint consists of a bearing stud and
socket enclosed in a casing; all these parts are made of steel. The bearing stud is tapered
and threaded, and fits into a tapered hole in the steering knuckle. A protective encasing
prevents dirt from getting into the joint assembly. Usually, this is a rubber-like boot
that allows movement and expansion of lubricant. Motion control ball joints tend to be retained
with an internal spring, which helps to prevent vibration problems in the linkage.
The “Off-Set” ball joint provides means of movement in systems where thermal expansion
and contraction, shock, seismic motion, and torsional motions, and forces are present. Theory A ball joint is used for allowing free movement
in two planes at the same time, including rotating in those planes. Combining two such
joints with control arms enables motion in all three planes, allowing the front end of
an automobile to be steered and a spring and shock suspension to make the ride comfortable.
Unlike a kingpin suspension, this allows for adjusting the camber and caster of the wheel
suspension. Both systems allow adjustment of the toe angle. This ability to fine tune
the suspension allows manufacturers to make the automobile more stable and easier to steer,
compared to the older kingpin style suspension. The smoother ride also increases tire tread
life, since the ball-joint suspension allows the vehicle to be adjusted to track in a level
fashion. Purpose On modern vehicles, ball joints are the pivot
between the wheels and the suspension of an automobile. They are today almost universally
used in the front suspension, having replaced the kingpin/linkpin arrangement, but can also
be found in the rear suspension of a few higher performance autos. Ball joints play a critical
role in the safe operation of an automobile’s steering and suspension.
In automobile suspension, the two ball joints are called the “upper ball joint” and “lower
ball joint”. Lower ball joints are typically larger and wear out faster as the entire front
end weight rests solely upon them. Front wheel drive
Unlike a kingpin, which requires an assembly in the center of the wheel in order to pivot,
joints connect to the upper and lower end of the spindle, to the control arms. This
leaves the center section open to allow the use of front wheel drive. Older kingpin designs
can only be used in a rear wheel drive configuration. Types Sealed ball joints do not require lubrication
as they are “lubed for life”, but most ball joints have grease fitting and are designed
for periodic addition of a lubricant. This is usually a very high viscosity lubricant.
Generally speaking, standard ball joints will outlive sealed ones because eventually the
seal will break, causing the joint to dry out and rust. Additionally, the act of adding
new lubricant pushes out old and dry lubricant, extending the life of the joint.
SRJs are high precision ball joints consisting of a spherical outer and inner race separated
by ball bearings. The ball bearings are housed in a spherical retainer and roll along both
the inner and outer surfaces. This design allows the joint to have very low friction
while maintaining a large range of motion and backlash as low as 1 µm. SRJs are often
used in parallel robotics applications like a Stewart platform, where high rigidity and
low backlash are essential. Failure
While there is no exact lifespan that can be put on sealed ball joints, they can fail
as early as 80,000 miles in modern vehicles, and much sooner in older vehicles. Signs of
a failing ball joint start with a clicking, popping or snapping sound when the wheel is
turned and eventually turn into a squeaking sound at the end of a stop, when the gas pedal
is used and/or also when hitting bumps. Another symptom could be ‘thud’ noises coming from
front suspension when going over bumps. Dry ball joints have dramatically increased friction
and can cause the steering to stick or be more difficult.
If a ball joint fails, the results can be dangerous as the wheel’s angle becomes unconstrained,
causing loss of control. Because the tire will be at an unintended angle, the vehicle
will come to an abrupt halt, damaging the tires. Also, during failure, debris can damage
other parts of the vehicle. Other uses While in automotive parlance the term “ball
joint” usually refers to the primary ball joint connections at the ends of the control
arms, this type of joint is used in other parts as well, including tie rod ends. In
these other applications, they are typically called tie rod ends or when they are an inner
tie rod end on a rack and pinion steering system they are called inner socket assemblies.
These joints are also used in a number of other non-automotive applications, from the
joints of dolls to other mechanical linkages for a variety of devices, or any place where
a degree of rotation in movement is desired. See also
Rod end bearing References External links

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