The locking differential locks both the wheels to the same axle. Different from an open differential, which splits the rotational force between the wheels and letting them spin at different speeds, a locking differential does not allow them to spin at differing speeds.
An open differential allows for individual tire spins during turns, or other wise it would result in tire scuffing. But the disadvantage with this is that in off-road situations, the tires would slip, because the differential transfer torque to the wheel that offers less resistance, thereby decreasing torque on wheels which receive good traction.
A locking differential is designed to overcome this. What a locking differential does is that it locks both the differentials on particular conditions, offering the same torque, regardless of the traction the individual wheels are receiving. A locking differential is no use unless there is a significant difference in the spinning speeds of the wheels. And because of that a locking differential is used only in off-road vehicles.
The working of a locking differential is simple. It simply provides a shift between unlocked (open differential) and locked wheels. This locking and unlocking of this facility can either be done manually or automatically. There are two kinds of locking differentials, Selectable locking and Automatic locking.
Selectable locking
This requires the driver to switch between open or closed differential manually. This can be accomplished in many ways. 1) compressed air 2) cable operated mechanism 3) electronic solenoids.
The electronic method is also called the ‘e locker’ and is highly complex and requires some forward thinking for the driver to use it effectively.
Automatic lockers
The automatic lockers do not require the driver to lock the differentials manually. This system ensures that power is transmitted to all the wheels regardless of traction. But it ensures one wheel is slower than the other during a turning. Since at the position of movement, the wheels are locked, the correct term would be ‘automatic un-lockers.’
Advantage
a) Automatic action, no driver decision necessary.
b) Cons: Increased tire wear and noticeable impact on driving behavior. During cornering, the automatic locker is characterized by heavy understeer which gets transferred instantly to power oversteer when traction is exceeded.
Spool
A spool is a device that directly connects the wheels to the ring gear. Since there is no left-right differentiation in speeds, scruffing of tire happens and it becomes unmanageable in wet weather. This mechanism is used only in competition vehicles and not used in normal purpose cars.