Understanding Limited Slip Differential

Understanding Limited Slip Differential


Consider a situation,
where a vehicle fitted with the standard differential
move straight and
one drive wheel is on a surface with
good traction
and the other we’ll is on a slippery
track.
In a standard differential the left and
right
axle rotations are completely
independent.
since one wheel is on a slippery track,
the standard differential will make the
wheel spin in excessive speed,
while the good traction wheel will
remain almost dead.
This means high power supply to the
slippery wheel,
and low power flow to the good traction
wheel.
So the vehicle won’t be able to move.
One way to overcome this problem is to
limit the independency or relative motion
between the left and right axles.
‘Limited slip differentials’ are introduced for this purpose.
One of the most commonly used LSD
technology is
Clutch pack based.
First let’s go through it constructional features.
Apart from its basic components a
limited slip differential has got a
series of friction and steel plates
packed between the side gear and the
casing.
Friction discs are locked with the side
gear.
So the friction discs and the side gear
will always move together.
Steel plates have external pads
and are made to fit in the case groove,
so they can rotate with the case.
If any of the clutch pack assembly is
well pressed,
the frictional force within them will make it move
as a single solid unit.
Since the steel plates are locked with the case
and the friction discs with the side gear,
in a well pressed clutch pack,
motion from the casing is directly
passed to the corresponding axle.
Space between the side gears is fitted
with a preload spring
The pre-load spring will always give a thrust force.
and will press clutch pack together.
You can note that spider and side gear are bevel gears.
It has got one speciality.
When torque is transmitted through a bevel
gear system,
axial forces are also induced apart from
the tangential force
The axial force tries to separate out the gears.
You can note that,
side gear and axle are two separate units.
The side gear has got a small allowance
for axial movement.
so during high torque transmission
through spider-side gear arrangement,
a high separating thrust force is also
transmitted to the clutch pack.
This force presses and locks the clutch
pack assembly
against wall the casing.
Now, back to the initial problem.
Since, one wheel is on a high traction surface,
the torque transmitted to it will be
higher.
so the thrust force developed
due to the bevel gear separation action
also will be high at that side.
Thus the clutch pack at high traction wheel side will be pressed firmly,
and the clutch pack will be locked.
So power from the differential casing
will flow directly
to the high traction axle, via the clutch pack
assembly.
On the other hand,
clutch pack on the low traction wheel side is not engaged yet,
so power flow will be limited to that side.
So the vehicle will be able to overcome
the traction difference problem.
However while taking a turn,
the LSD can act like a normal differential.
In this case thrust force developed due
to the bevel gear separation action
won’t be that high,
so the plates in the clutch pack
will easily overcome the frictional
resistance
and will be able to slip against each other.
Thus the right and left wheel can have
different speed,
just like an open differential.
Following are the other commonly used
technologies,
used to overcome the drive wheel
traction difference problem.
Thank you !


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