An open differential is the mechanism that receives the power from the transmission
usually through a driveshaft and splits that power in two and sends it to the left and right of the
driven wheels and allows them to rotate at different speeds.
When the vehicle is cornering the inner wheel rotates slower and offers more resistance, this causes the planet wheels
to rotate on its own axis and it increases the speed of the outer by the same percentage that the inner wheel slows down.
The open differential often referred to as just a differential can also be used to split the power between the front and
rear wheels in an all/four wheel drive vehicles and then two other differentials can further split
the power to the left and right wheels.
The ability to rotate both driven wheels at different speeds is the primary objective of the differential, it separates
the both wheels by allowing them to have their own final shaft instead of one continuous shaft between the both wheels.
If there is a vehicle that is required to only travel in a straight line then a differential would not be required, the
driveshaft could be connected to a single final shaft. The problem with a single shaft is that it does not allow the vehicle to
corner properly. The outer wheels rotate faster than the inner wheels and the lack of a differential does not facilitate this.
A rear wheel drive differential will be used to explain a common configuration of the open differential and how it
The differential mechanism is housed inside of a round-ish metal casing with an opening at the front to connect the
driveshaft to. Inside of this casing is also lubricated as anywhere else where metal rubs on or against metal.
Inside of the case the driveshaft rotates a disc using teeth on the edge of the driveshaft and the disc similar to
gears. This disc can be on the left or the right side on the inside of the casing and whichever side its on it is attached
to one of the sun wheels (similar in shape to the disc but smaller).
The shaft to both wheels has a sun wheel inside of the casing. Both sun wheels are connected to each other by two or more
planet gears and the planet gears rotate from an extension off the main disc. All of these components rotate as the vehicle moves.
Even with all of these components the differential allows the two shafts to each have half of the
torque and horsepower and they rotate equally when moving in a straight line.
A rear wheel drive vehicles will have one differential will have one differential, a front wheel drive vehicle will
also have one differential but it is usually integrated into the transmission. A part time four wheel drive should have two
differentials and a full time four/all wheel drive would have three differentials but the center differential could be integrated
into the transmission.
There have been improvements to the basic or open differential which would be the
limited slip differential and the locking differential.