The differential is an integral part of
all four-wheelers.
wheels receive power from the engine via
a drive shaft
and the main function of the
the differential is to allow these wheels to
turn
at different RPMs while receiving power
from the engine
consider these wheels which are
negotiating a turn
the left wheel has to travel
more distance than the right wheel
which means that the left wheel has to
rotate at a higher speed
if these wheels were connected using a
solid shaft as shown
the wheels would have to slip to
accomplish the turn
this is exactly where a differential
comes in
the ingenious mechanism in a
the differential allows left and right
wheels to turn at different RPMs
while transferring power to both wheels
step by step we will learn how a
differential achieves this feat
using its simplest configuration
power from the engine is transferred to
the ring gear through a pinion gear
the ring gear is connected to a spider
gear which is at the heart of the
differential
the spider gear is free to rotate in two
different ways
one along with the ring gear and two
on its axis
the spider gear meshes with two side
gears
so power from the engine flows from the
pinion to the left and right wheels
as shown
now let's consider different cases when
the vehicle moves straight
the spider gear rotates along with the
ring gear but it does not rotate on its
own axis
the spider gear will push and make both
side gears turn at the same speed
when the vehicle is moving straight the
spider side gear assembly will move as a
single solid unit
consider the case when the vehicle is
taking a right turn
the spider gear plays a pivotal role
here
along with the rotation of the ring gear
the spider gear spins on its axis
the spider gear is forced to do
this second spin
to meet the demands of the right and
left wheels differing speeds
so the spider gear is having a combined
rotation
the effect of combined rotation on the
side gear is interesting
when properly meshed the side gear has
to have the same peripheral velocity
as the spider gear
when the spider gear is spinning and
rotating the peripheral velocity at the
the left side of the spider gear
is the sum of spinning and rotational
velocity
however on the right side, it is the
difference between the two
the left side gear will have higher
speed compared to the right side gear
which is how the differential manages to
turn left and right wheels at different
speeds while taking a left turn
the spider gear will spin in the
opposite direction
to carry load one more spider
gear is usually added
four spider gear arrangements are used
for heavy load vehicles
apart from allowing wheels to rotate at
different RPMs the differential has two
more functions.
the first of these alternate functions
is speed reduction at the pinion
ring gear assembly which will result in
torque multiplication
the other function is to turn the power
flow direction by 90 degrees
the differential we have gone through so
far is known as an open or standard
differential
it is capable of turning wheels at
different RPMs
but it has one major drawback consider a
situation
where one wheel of a vehicle is on a
surface with good traction
and another wheel is on a slippery track
in this case a standard differential
will send the majority of the power to
the slippery wheel
so the vehicle won't be able to move
to overcome this problem limited slip
differentials were introduced.
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