While vehicle is moving on straight ahead path ring gear, differential case, differential, pinion gear and two differential side gears all turn as one unit. Two differential pinion gears do not rotate on pinion shaft. Due to which they exert equal force on two differential side gears. As a result of which side gears turn at same speed as ring gear. Which causes both the driving wheels to turn at same speed.
When the car began to move on curved road path the differential pinion gears rotate on pinion shaft. This permits outer wheel to run faster than inner wheel. Suppose that one wheel turns slower than the other as car move on curve path. As the differential case rotates pinion gears must rotate on their shaft. This occurs because pinion gear must walk round slower turning differential side gear. So pinion gear carry additional rotatory motion to faster turning outer wheel on turn. If differential case speed is considered to be 100%. The rotation action of pinion gear carry 90% of this speed to slower rotating inner wheel. It sends 110% of speed faster rotating wheel.
In this way differential allows one drive wheel to turn faster than the other. Thus when-ever vehicle goes round a turn outer wheel travel greater distance than the inner drive wheel. Two pinion gears rotating on their shaft it send more rotating motion to the outer wheel. While vehicle is moving on straight road pinion gears do not rotate on their shaft. It will apply equal torque to the differential side gear. Therefore both drive wheels rotate at same speed.
Differential for front wheel driver and rear wheel drive are similar in construction and working .
