PHASE 10

iii. AUTOMATIC LOCKERS:

Transmit power to each wheel through a pair of dog clutches. Differential action, such as when cornering is provided by  automatically disengaging the appropriate clutch when one wheel rotates faster than the other. This results in differential action which occurs in ratcheting stages rather than being smooth and progressive. Power received by the differential is automatically directed to the wheel with greater traction. Therefore, if one wheel is lifted off the ground, the other wheel will receive the total power applied to the differential to maintain vehicle mobility.

Traction is far superior to conventional and limited slip differentials. While automatic locking differential provide excellent performance off road, vehicle handling, particularly on highway, is sacrificed. Unlocking during cornering can be sudden, resulting in a rapid change of direction, particularly in short wheel based vehicles. During sharp cornering an audible ratcheting sound usually occurs as differential action takes place and a loud banging noise may be heard when the unit locks up again.

Tire wear is usually increase. On 4WD vehicles, installation is normally considered for the rear axles only. Front axle installations can cause extreme difficulties in steering.

  

iv. MANUALLY LOCKABLE DIFFERENTIALS

Use a conventional differential in conjunction with a mechanical locking device which can be operated at the driver’s discretion. when locked, both axles will then turn at the same speed irrespective of the road surface. When it is unlocked, the differential functions as a conventional differential giving predictable handling, long service life and no increase in tire wear. It can be installed in both the front and rear axles without compromising on-road performance. Although manually lockable differentials are available in tractors and some military style vehicles, the installation in mass produced recreation type vehicles have been restricted by high cost and complexity of installation  

v. VISCOUS COUPLING:
The viscous coupling is often found in all-wheel-drive vehicles. It is commonly used to link the back wheels to the front wheels so that when one set of wheels starts to slip, torque will be transferred to the other set.

The viscous coupling has two sets of plates inside a sealed housing that is filled with a thick fluid, as shown in below. One set of plates is connected to each output shaft. Under normal conditions, both sets of plates and the viscous fluid spin at the same speed. When one set of wheels tries to spin faster, perhaps because it is slipping, the set of plates corresponding to those wheels spins faster than the other. The viscous fluid, stuck between the plates, tries to catch up with the faster disks, dragging the slower disks along. This transfers more torque to the slower moving wheels -- the wheels that are not slipping.

When a car is turning, the difference in speed between the wheels is not as large as when one wheel is slipping. The faster the plates are spinning relative to each other, the more torque the viscous coupling transfers. The coupling does not interfere with turns because the amount of torque transferred during a turn is so small. However, this also highlights a disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually starts slipping.

A simple experiment with an egg will help explain the behavior of the viscous coupling. If you set an egg on the kitchen table, the shell and the yolk are both stationary. If you suddenly spin the egg, the shell will be moving at a faster speed than the yolk for a second, but the yolk will quickly catch up. To prove that the yolk is spinning, once you have the egg spinning quickly stop it and then let go -- the egg will start to spin again (unless it is hard boiled). In this experiment, we used the friction between the shell and the yolk to apply force to the yolk, speeding it up. When we stopped the shell, that friction -- between the still-moving yolk and the shell -- applied force to the shell, causing it to speed up. In a viscous coupling, the force is applied between the fluid and the sets of plates in the same way as between the yolk and the shell.