Differential Locks
Since the so-called "free" differentials only allow a certain torque ratio between both driving shafts, the tractive driving force of a vehicle is limited by the road-tire pair with the lowest usable friction. E.g. for a differing road surface contact between the left and right lanes, the wheel with the higher coefficient of friction can only transfer the maximum traction torque of the wheel from the smooth road. If the driving torque exceeds the maximum transferable torque limited by friction (Chapter 4.4), the wheel with the lower friction potentional spins. The same happens in multi-axle drives between the axles. The torque can only be transferred in the determined ratio. In real driving conditions, differing road grip (μ-split) and differing road loads, e.g. in cornering, are reasons for the differing friction potentials.
If the wheels of an axle were rigidly connected with each other, in case of unequal friction between the right and the left lane, the larger adhesion potential could be utilised (when doing so, a moment around the vertical axis of the vehicle which can have a negative effect on driving stability arises). In order to achieve the transmission of a maximum driving torque, also when differentials are employed, differential locks were developed, which according to the design, enable the effect of a differing locking intensity between both output shafts. The achieved locking effect is characterized by the locking value S. It is defined as the ratio between the maximum possible torque difference at both differential outputs and the input moment ME:

Eq. 3-52

When the losses through friction in the differential are ignored, we get:

Eq. 3-53

According to their efficiency, differential locks can be classified into:
Positively-engaged Differential Locks,
Friction-based Differential Locks.