An alternative
to an open differential is a limited-slip differential. A limited-slip
diff allows some slippage to occur up to a certain point between the spin
rates of the two wheels before it attempts to direct torque to the wheel
with the greater traction by limiting the slip on the wheel with the least
traction. This solution provides the driver better control of their truck,
especially through quick turns. Limited slip diffs may use only gears
to handle torque transfer or, more commonly, a set of clutch and friction
plates. One notable truck that uses a limited slip differential is Ford's
high performance SVT Lightning.
The last
type is a locking differential. Locking diffs allow very little slippage
to occur between two wheels. When one wheel starts to lose traction the
gears lock together to minimize wheel spinning and ensure power is sent
equally to both wheels at all times. Unless the axle itself starts to
slip, and you don't have a center differential between the front and rear
axles, locking differentials can get you out of most sticky off-road situations.
Locking differentials
come in two flavors: mechanical and electronic.
Mechanical
locking differentials typically engage when some RPM threshold is broken
between two wheels. When slippage occurs, and relative wheel RPM dramatically
changes, it centrifugally trips a flyweight in the locking mechanism,
causing gears in the differential to engage and tying both wheel spin
rates together. As soon as the wheels both have traction the locker disengages.
An electronic
locking differential, or ELocker in Eatonese, engages electronically with the touch
of a button when the driver determines a need for more traction. The button
sends an electromagnetic signal to an armature, engaging a ball bearing
ramp that pushes pins into the back side of the gear and locks the axle.
When the signal is turned off, pressing the button again, the ball ramp
slides back into place disengaging the locking pins. Think about twisting
a dial to lock the axles together and you can picture an ELocker in operation.
Toyota has
also offered its own version of an electric locking rear diff for the
Tacoma pickup for several years now as optional factory equipment.
Now that
you have had a backgrounder in differentials, it's time for the classified
stuff. Consider the following for your eyes only.
We took a
trip out to Eaton's restricted proving grounds to test drive the new ELocker
first hand. Set out in Michigan's rural backcountry near the town of Marshall,
the proving grounds condense every test and torture a differential might
face in the real world into a heavily rutted, wooded and instrumented
640 acre lab facility. If Dante had been an off-roader, Eaton's proving
ground would have been his inspiration for the 10th ring, the ring for
traction control product manufacturers who sell underengineered differentials
as OEM equipment.
