The differential is a mechanical device that receives the machine torque from a shaft and allocating on two other, allowing each of them to rotate at different speeds according to the trajectory. It’s a reduction mechanism, before the force of the motor is transferred to the wheels, manages power and rotary speed, allowing the two wheels on the same axle to rotate at different speeds.

The differential in its simplest configuration, is constituted by a planet carrier cage which are bound the two axes, two satellites positioned on the axes, and meshed with two planetary solidarity with the drive shafts.

This epicyclic gear train, on a straight path, transmits the same torque to the wheels, and then the number of turns, cornering, having the outer wheel to travel a greater trajectory, allows it to rotate faster, so as not to lose grip; the difference in speed of rotation between the inner and outer wheel is more evident when the curve to travel is more tighter.

This ingenious mechanism improves the stability of the car when cornering, and has the only downside to distribute most torque to the wheel with less grip;

funzionamento differenziale, Close-Up Engineering

however, this problem is solved with the limited slip differential, which has a sensor that perceiving the torque difference between the two wheels, blocks the satellites, and eliminates thus the use of differential allowing the wheels to rotate at the same speed. The progress of technology has allowed the creation of active differentials, governed by a computer that analyzes the sensor data, calculating steering angle, lateral acceleration and automatically adjusting torque distribution, reducing the hardness of the steering and all other effects negative that occur in the condition of understeer.