Differential

A differential is a mechanism that allows the two driven wheels to rotate at different speeds to assist in cornering.

Function

When turning a corner, the outer wheels will follow a path with a greater radius of curvature. This difference in radius means the outside wheels will have to travel a longer distance, and rotate faster than the inside wheels.in a rear wheel drive car, the front two wheels are allowed to rotate at a different rate, so this does not pose a problem. The rear wheels, however, both have to be driven by the engine, and therefore are mechanically connected to each other, so there is no freedom of movement between them inherent in the design.

[need a pic of cornering to demonstrate wheel travel difference]

Types

Open Differential

An open differential is a gear assembly that allows the two rear wheels to spin independently of each other, while maintaining the average rotational speed. If the outside wheel spins faster than it would without the differential, the inside wheel must spin and equivalent amount slower. Similarly, the torque transferred to the ground, but is split in varying amounts between the two rear wheels depending on their relative velocities. The faster spinning wheel will see a proportionally greater amount of torque from the engine.

This torque differential between the two wheels can become problematic in high torque applications where the torque is desired to go to the wheel with the greatest amount of traction, not the greatest rotational velocity, such as corner exit, or corner entry if using an inboard brake. To solve this problem, a differential that can limit the amount of slip is desired.

Limited Slip Differential

A limited slip differential (LSD) allows the two wheels to rotate at different speeds, but is limited to a maximum difference. The maximum limit is the torque bias ratio (TBR) of the LSD.

Spool

not really a kind of differential, just a way to lock the half shafts together

Electronic Differential

It is fairly common to find electric formulas where the battery pack powers more than one motor on each side of the car. These two motors are then controlled individually and behave like if a virtual electronic differential was separating each other.

not sure if anyone uses eLSDs but they're common in industry, dont know if this is the right section or the LSD section is better

Differentials used in Formula

Name	Type	TBR	Comments
Torsen University Special	T-1 or T-2 Torsen LSD	2.6:1	obsolete
TRE mk1			obsolete
TRE mk2
Drexler

Further Reading

• https://www.taylor-race.com/sites/default/files/DIFFERENTIAL%20ESSAY%20W%20PHOTOS2.pdf
• Engineering Explained:Differentials (Youtube Playlist)