Approach Angle
Starting
from level ground, this is the degree of slope a vehicle can approach
without scraping or hitting the front undercarriage. It's a great
indication of the ability to navigate severe off-road terrain like
boulders and logs. A short front overhang produces high angles of
approach, thus increasing off-road ability.
Articulation
A
Trail Rated® suspension is limber like a gymnast. How exactly?
Flexibility is the key to good articulation. The more a wheel can
travel, or flex, the better it can maintain contact with terra firma and
provide the traction needed to cross an array of obstacles.
Axle
A
rigid piece of metal that connects the front and/or rear wheels
together. The suspension components attach to the axle and to the
vehicle's body frame.
Axle Articulation
The
ability of one axle to move relative to the chassis. It is the measure
of the ease with which tires stay in contact with the ground (and retain
traction) on very uneven terrain.
Axle Differential
An
axle differential is a gear system located in the center housing of an
axle assembly designed to allow the wheels to rotate at different speeds
during cornering.
Brake Traction Control System
Transfers torque from one wheel to another on the same axle when wheel slip conditions are detected.
Breakover Angle
The
degree of slope that defines the largest ramp or hill that a vehicle
can travel over without scraping against the frame or underbody
components.
Center Differential ? Geared
A
gear system located inside the transfer case of full-time 4WD vehicles.
It is used to distribute drive torque to the front and rear driveshafts
and allows the front and rear wheels to rotate at different speeds
during cornering.
Clutch Plates
A
series of alternating steel plates within the transfer case of many
on-demand or automatic 4WD systems. One set of plates is splined to the
clutch assembly hub of the rear driveshaft; the other set is splined to
the clutch drum attached to the front driveshaft. The clutch housing is
usually filled with a viscous, silicone-type fluid that clings to the
discs to help transfer torque to the driveshaft. The engagement of
clutch plates can also be controlled electronically.
Coil Springs
A
coil of flexible metal that can be compressed or stretched along its
centerline axis without permanent deformation. Coil springs support the
weight of the vehicle while allowing the wheels to travel up and down
over bumps.
Continuously Variable Transaxle
A stepless transmission that uses a sheave clutch to transmit engine torque.
Crawl Ratio
Essential
for serious off-road treks involving steep hill climbs and descents,
this is the final drive ratio of a vehicle in low-range. It allows Jeep
vehicles to "creep" along (without depressing the accelerator) at very
low speeds. Essentially, the vehicle does all the work. Crawl ratio is
determined by this formula: first gear ratio x rear axle ratio x
low-range 4WD ratio. The higher the number, the better the off-road
capabilities.
Crow-Hope
Vehicle
shudder and tire scuffing due to a binding condition in the driveline.
Usually caused by operating in basic 4WD or part-time 4WD modes on dry
pavement.
Departure Angle
When
returning to level ground from a descent, this angle indicates the
degree of a slope from which a vehicle can depart without scraping or
hitting the rear undercarriage.
Differential
A
gear system that transmits torque to the drive wheels, while also
allowing the wheels to rotate at different speeds when cornering. 4WD
vehicles have differentials in both the front and rear axles.
Driveshaft
Shaft
connecting the transmission output shaft to the differential drive
pinion shaft. Four-wheel-drive vehicles add a second driveshaft from the
transfer case to the front differential.
Electronically Controlled Coupling
Manages the torque split from front to rear with no driver input needed for smooth and automatic performance.
Fixed Yoke Output Assembly
Effectively handles the extra output from the transfer case and helps to ensure smooth and durable driveline operation.
Four Wheel Drive
A
drivetrain that utilizes a transfer case to distribute engine power
between the front and rear axles in order to drive all four wheels.
Full-time four-wheel-drive systems utilize a center differential, which
enables the front and rear driveshafts to turn at different speeds,
thereby allowing engagement on dry pavement for normal driving
conditions. A part-time system does not employ a center differential
and, during normal driving conditions, must operate only in two-wheel
drive. With a part-time system, the four-wheel-drive mode is to be used
only when off-road or on wet or slippery surfaces.
Front Axle Disconnect
A
mechanical or vacuum-operated component used primarily on
four-wheel-drive models to connect and disconnect drive torque to the
front axle. When shifting from four-wheel drive to two-wheel drive, this
system disengages the front axle from the front driveline, so that the
front wheels aren't turning the front driveline unnecessarily. This
reduces unnecessary front driveline wear, noise and fuel consumption.
Gerotor Coupling
A
speed-sensing component used in four-wheel-drive systems, which
includes a fluid pump, a piston and a set of clutch plates. When a speed
difference occurs between the front and rear driveshafts of the vehicle
(as when a wheel loses traction), the gerotor pump in the transfer case
supplies instantaneous pressure to the clutch plates that transfer
torque to the axle where the wheels have more traction. This coupling is
smaller, lighter and faster acting than conventional four-wheel-drive
power-transferring components.
Ground Clearance
Don't
drag your belly through the mud?just clear nasty logs, rocks, and
uneven ground without sustaining undercarriage damage. Jeep® Trail
Rated® 4x4s feature optimized approach, departure, and breakover angles
to keep you in the clear.
High-Range
A 4WD mode used for on-road or light off-road use.
High Descent Control
This
system uses the ABS braking to control the car's motion downhill. Also
allows a smooth and controlled hill descent in rough terrain without the
driver needing to touch the brake pedal. If the vehicle accelerates
without the driver input, the system will automatically apply the brakes
to slow down to the desired vehicle speed.
Jounce/Rebound
The
motion of a wheel that compresses its suspension. If a wheel is at full
jounce, it is at the upper limits of its travel. The opposite of jounce
is rebound ? or wheel movement that decompresses a vehicle's
suspension.
Limited-Slip Differential
Provides
the same basic functions as an axle differential, but with an added
advantage: when the drive wheel begins spinning as a result of being on a
slippery surface, a limited-slip differential automatically transfers
torque to the opposite wheel to help improve traction.
Locking Differential
Provides
even more traction than a limited-slip differential by "locking" the
axle shafts together when the driver wants to do it. Locking
differentials do not allow for wheel-speed differences and must not be
used on dry, paved roads.
Low Crawl Speed
The
"crawl ratio" is the lowest gear ratio in a vehicle and is determined
by multiplying the first gear ratio times the low-range ratio times the
axle ratio.
Low-Range
A 4WD mode used for severe off-road conditions.
Maneuverability
Athletic.
Agile. Trail Rated®. Jeep® 4x4s have the footwork to navigate narrow
gaps, dodge emergency situations and avoid cosmetic damage to underbody
sills thanks to precision steering and optimized wheelbases. Even
gazelles don't move like this.
Neutral
When
the shifter is in this position, the front and rear axles spin freely.
Sometimes used for towing a Jeep vehicle behind another vehicle (such as
a motor home), so that uncoupling the driveshafts is not required. Also
used in the process of shifting into 4-Low.
Open-Center Differential
Located
in the transfer case on some full-time four-wheel-drive vehicles, this
component works in the same way as an open differential in the axles,
but is of a more compact design. This component employs a planetary
gearset, with planetary gears that revolve around the sun gear and
inside the ring gear.
Power Robbing Friction
Surface resistance to relative motion, as of a body sliding or rolling.
Progressive Axle
Progressive
front and rear axles transfer torque side to side in search of the
wheel with the greater traction. This mechanical (gerotor pump) system
transfers torque relative to differences in wheel speed rather than
torque difference. The end result is a system that can deliver far more
torque to the wheel that needs it than conventional limited-slip
differential systems.
Running Ground Clearance
The distance from the ground to the lowest point between the axles.
Shift-on-the-Fly
The ability to shift from two-wheel drive to four-wheel drive while the vehicle is moving.
Skid Plate
Helps protect the undercarriage from damage when driving off-road.
Solid Axle/Coil Springs
Ideal
off-road equipment. Instead of each wheel on an axle being sprung
separately (like independent suspension designs), a solid axle connects
the suspension of two wheels. Coil springs then support the vehicle's
weight and allow the wheels to travel up and down over terrain.
Suspension Travel
From full jounce to full rebound, this is the amount of vertical wheel movement allowed by the suspension.
Tow Hooks
Heavy-duty
forged steel hooks in the front and rear of a vehicle that provide
attachment points for snatch-em straps and winch cables (see the
Off-Road Driving Tips section) should you get stuck.
Traction
Traction
in 4x4 is equivalent to grip on Asphalt. Trail Rated® traction helps
you stay in control on untamed terrain, slippery (wet, mud, snow)
conditions, and on steep grades.
Transfer Case
Mounted
behind and driven by the vehicle transmission, the transfer case
transmits power to the front and rear driveshafts in 4WD Jeep vehicles
and offers high and low range. For the full line of Jeep transfer cases
see the Get Ready section.
Transmission
A
mechanism that transfers torque into usable driving power through the
use of gearsets. These gearsets multiply engine torque in varying
amounts to meet specific driving demands.
Two Wheel Drive
When
the shifter is in this position, the front axle spins freely while
power is sent to the rear axle and wheels, which then drive the vehicle.
Viscous Coupling
A
speed-sensitive device located in the transfer case that transmits
drive torque between the front and rear driveshafts when wheel-slip
occurs. Viscous couplings are typically used on all-wheel-drive vehicles
and vehicles with automatic and on-demand four-wheel-drive systems.
