How a Differential works ?

How a Differential works ?


Differential is an integral part of all four wheelers.
Wheels receive power from the engine via a drive shaft.
The main function of the differential
is to allow these wheels to turn at different RPM,
while receiving power from the engine.
Consider these wheels which are negotiating a turn.
differential working animation
It is clear that the left wheel has
to travel more distance compared to the right wheel.
This means 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.
The ingenious mechanism in a differential
allows left and right wheels to turn at different rpm,
while
transferring power to both the wheels.
We will learn how differential achieves this
in a step by step manner,
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.
Spider gear is free to make 2 kinds of rotations,
one along with the ring gear
and second on its own axis.
Spider gear is meshed with 2
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.
The vehicle moves straight.
In this case spider gear rotates along with the ring gear,
but does not rotate on its own axis.
Spider gear will push and make the side gears turn,
and both will turn at the same speed.
Or when the vehicle is moving straight,
Spider- Side gear assembly will move as a single solid unit.
Now 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,
it rotates on its own axis.
So the spider gear is having a combined rotation.
The effect of combined rotation, on the side gear is interesting.
When properly meshed side gear has to have
same peripheral velocity as that of the spider gear.
When the spider gear is spinning as
well as rotating,
peripheral velocity at the left side of spider gear
is sum of spinning and rotational velocity.
But at right side it is difference of the two.
Or left side gear will have higher speed
compared to the right side gear.
This is the way 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.
In order to carry load
one more spider gear is usually added.
4 spider gear arrangement
is also used for heavy load vehicles.
Apart from allowing wheels to rotate at different rpm,
differential has got 2 more functions.
First is speed reduction at pinion ring gear
assembly.
This will result in torque multiplication.
The other function is to turn the power flow
direction by 90 degree.
The differential we have gone through so far
is known as open or standard differential.
It is capable of turning wheels at different
rpm,
but it has got one major drawback.
Consider a situation where one wheel of the vehicle
is in a surface with good traction
and other wheel 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 are introduced.
We will learn more about them in a separate video.
Thank you


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