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Driving Dynamics
“The dynamics targets for the new Explorer were clear: Make it
ride and handle better than ever before, including being more
stable, safer, easier to drive and more reassuring. In order to
achieve that, we had to start over and design the first
purpose-built chassis for a Ford SUV – an all-new Explorer from the
tires to the roof-rack.”
– Dale Claudepierre,
Compact Sport Utility Vehicle Line Director
- New independent rear suspension with “porthole-in-frame”
design, allowing for an additional third row of seats and
seven-passenger seating, as well as improved ride and handling
- Better off-road capability with increased ground
clearance and better approach and departure angles
- Coil-over-shock and short- and long-arm (SLA) front
suspension
- New AdvanceTrac interactive vehicle dynamics
system, combining the benefits of traction control and electronic
stability (yaw) control (available later in 2001)
- Improved Control-TracTM 4×4 system
- Improved turning radius, and steering column and
steering wheel enhancements
- Standard antilock brakes with electronic brake force
distribution (EBD) and improved brake operation
The 2002 Ford Explorer’s new independent rear suspension is
literally at the base of the vehicle’s most significant innovations
– including its improved ride, handling and package. Added to this
are a stiffer frame, more precise steering, new front suspension,
improved powertrains and several chassis detail changes – all of
which work to fulfill Explorer’s promise of offering a significantly
smoother and more pleasant driving experience.
The dynamics team focused on four key attributes related to the
driving experience: agility, precision, stability and comfort. The
objective was to create the ideal balance between the four without
making compromises.
Independent Rear Suspension
Explorer’s new independent rear suspension (IRS) system replaces
the former solid axle design. IRS offers significantly better
handling over both smooth and rough surfaces. Working with the new
front suspension, IRS reduces rear-end squat during acceleration and
front dive/rear jacking during emergency braking.
IRS offers ride and handling benefits over a solid rear axle
design because each wheel reacts independently to bumps in the road,
moving both up and rearward to absorb the bumps and reduce impact
harshness. The result is improved ride quality.
Because each component performs very specific tasks, the
suspension can be designed to be extremely stiff laterally, while
offering more longitudinal compliance.
These two important functions are more easily separated than in
traditional solid-axle designs, which typically offer high
longitudinal stiffness – because the axles are bolted to long leaf
springs and, thus, offer imprecise lateral control.
The IRS’s ability to soak up longitudinal forces, such as those
imposed by potholes or sharp pavement bumps, translates directly
into a more comfortable ride and reduced harshness. Maintaining
lateral stiffness helps keep the rear of the vehicle from swaying
side-to-side in bumps or maneuvers. Likewise, it reduces
sensitivity to wind gusts. In addition, the suspension’s ability to
maintain optimum contact between the tires and pavement also helps
communicate important feedback – handling “feel” – to the driver
through the steering wheel.
In highway dips, Explorer’s suspension is designed to deliver a ride
that’s plush without wallowing. In abrupt, high-speed lane changes,
Explorer is designed to respond quickly to steering and track
predictably.
Explorer’s new IRS configuration also is designed to drastically
reduce rear-end skate, which is the lateral movement that occurs
when a vehicle with a solid rear axle travels over sharp bumps or
washboard/corrugated road surfaces.
The new suspension has a short- and long-arm (SLA) and
coil-over-shock design. The upper control arm is cast aluminum.
The lower control arm is stamped steel.
The IRS configuration permits the rear floor of the vehicle to be
lowered nearly 7 inches. This lower floor allows the new Explorer
to offer an optional third-row seat with plenty of headroom and
without compromising cargo space or utility. Even with the lower
floor, overall ground clearance was able to be improved an inch –
which strengthens the vehicle’s off-road capabilities.
This innovative packaging of the new IRS system is achieved
through the “porthole-in-frame” design technique. The design is
related to the way the rear half-shafts are packaged – literally via
holes in the frame versus under the frame.
A traditional truck or SUV frame is straight from front to back,
with ladder-like braces across it for strength. The line cannot be
completely straight, however, because it would run into the rear
axle assembly.
That is why nearly every manufacturer puts a large semi-circular
bend in the frame to follow the rear wheel well. The rear axle then
runs beneath it, which limits interior space. For Explorer, using
the traditional wisdom would have meant a narrow third-row seat.
To overcome these obstacles, the Explorer team members had to
think differently.
“After a brainstorming session one day, we asked ourselves why we
were trying to work around the frame. Instead, we decided to put a
porthole in it and work with it,” explains Manfred Rumpel, chassis
integration manager. “We worked out some calculations in basic
frame theory and physics, and we were able to prove that a
porthole-in-frame design would have all the necessary strength and
much better packaging flexibility.”
The circular hole on each side of the rear frame is reinforced
with a steel tubular tunnel that provides exceptional strength and
room for the half-shafts to move.
Rumpel and other team members have applied for five patents on
Explorer, including the “porthole-in-frame” design.
Other rear changes include the shock damping, which has been
increased to reduce suspension bounce and make the vehicle feel more
firmly planted on the ground when traversing rough surfaces and
undulating roads.
A new hollow rear stabilizer bar is used. It is nearly
40-percent lighter than the previous solid bar but provides
comparable performance. Urethane bushings – used previously in
front stabilizer bars only – are now used in the rear. The change
further helps to isolate the driver from road noise.
Front suspension
Explorer’s front suspension also is a short- and long-arm (SLA)
design with significant revisions such as a shorter front-end
overhang that result in a tighter turning circle (36.7 feet versus
the previous 38.4 feet), crisper steering, improved response to
sharp bumps, better cornering capabilities and enhanced
durability.
The front suspension also uses a coil-over-shock design,
replacing the previous torsion bar arrangement. Switching from
torsion bars to coil springs reduces rough-road steering column
shake and ride harshness by allowing suspension components to better
absorb fore-aft impact forces when a wheel hits a sharp bump. Coil
springs also maintain vehicle ride height better than torsion bars –
thus reducing the potential for front-end realignment in older
vehicles.
Shock damping has been increased, as in the rear. Also changed
are all-new upper and lower control arms, bushings, and stabilizer
links and retainers. The stabilizer bar is held in position with
urethane bushings that offer better on-center steering than
traditional rubber bushings.
Also improved is the “scrub radius” – the distance between the
tire centerline and the point at which an imaginary line between the
upper and lower ball joints intersects with the ground. It has been
reduced from 2.5 inches to 0.5 inches. Minimizing the scrub radius
improves tire wear and straight-line tracking by reducing pull when
front braking is uneven.
Driver feedback also benefits from a considerable attention to
detail. Explorer’s brake pedal is designed to be firm and
progressive, allowing the driver to modulate braking force by feel.
Acceleration is strong at tip-in, without excessive whine and roar.
The throttle-cable was tuned to damp vibrations that could travel
via the cable through the accelerator pedal and to the driver’s
foot. The engine is designed to sound reassuringly healthy under
full-throttle runs, but disappear into the background at normal
speeds.
AdvanceTrac Interactive Vehicle Dynamics
Explorer will be available with AdvanceTrac- a computer-driven
interactive vehicle dynamics system – later in 2001. It is Ford’s
first SUV available with such technology. The system enhances
stability in extreme driving conditions when drivers misjudge speed
or road conditions.
Developed in conjunction with Ford’s involvement with Formula One
racing, the optional AdvanceTrac system monitors driver
inputs, such as steering, throttle and brakes, and the corresponding
vehicle response – yaw, lateral acceleration and wheel speed – to
control brake force distribution and vehicle stability.
AdvanceTrac helps maintain vehicle stability at the limits
of tire adhesion via a combination of yaw rate sensors, the antilock
braking system and traction control system.
Data from the yaw rate sensor, a steering-wheel position sensor,
a lateral acceleration sensor and wheel speed sensors are monitored
through the ABS control module.
When required, AdvanceTrac applies the brakes at one or
more wheels to correct excessive yaw. If the vehicle’s yaw rate is
excessive in a turn, brake force on the outside front wheel helps
keep the vehicle on the desired path. If the yaw rate is lower than
that intended by the driver, force is applied to the inside front
brake.
Explorer’s antilock braking system with electronic brake force
distribution will be offered from introduction. The fully
integrated AdvanceTrac system will be introduced later in 2001.
Improved Control TracTM 4×4 Performance
Explorer’s optional Control TracTM four-wheel-drive system has
been refined for 2002 to make it more “transparent” to the driver,
while improving its abilities in limited traction situations. (For
details, see Powertrain/Drivetrain section.)
Steering
All Explorer models are equipped with power rack-and-pinion
steering, in addition to the steering improvements provided by the
revised front suspension geometry – including a 1.7-foot tighter
turning radius. The system has a modified steering linkage that
results in a more precise feel.
A tilt/rake steering column is standard on XLS and XLT models. A
combination tilt/telescoping, rake/reach column is standard on Eddie
Bauer and Limited models. The steering column tilts over an arc
range of 2.8 inches and telescopes over a range of 1.8 inches.
The steering wheel itself also has been redesigned to improve its
feel across a broader range of hand sizes. Key changes include
re-profiled detents on the backside of the wheel.
Brakes
Explorer’s four-wheel disc brakes have been improved for quieter
operation and more responsive pedal effort and consistency.
Explorer’s four-wheel, three-channel antilock braking system
(ABS) with electronic brake force distribution (EBD) is standard.
The ABS controls the front wheels independently and the rear wheels
in tandem during heavy braking – to improve vehicle control.
The ABS with EBD employs dynamic proportioning to achieve shorter
stopping distances. It works by measuring braking force versus
traction and allocating brake force to the wheels that have the best
grip for stopping even before the ABS system kicks in. This helps
reduce the braking distance.
The front discs have: larger rotors (305 millimeters compared
with 286 mm) for reduced operating temperatures; new
low-metallic-content, non-asbestos lining for reduced noise; stiffer
calipers with added lining volume and swept area to provide more
uniform brake pad loading for reduced noise and wear; and an
optimized brake pad insulator for reduced brake noise.
The rear discs increase from 11.2 inches to 11.8 inches (285 mm
to 301 mm).
Tires
Explorer is available in a wide variety of tires and wheels – all
carefully selected to match and enhance the vehicle’s dynamics
capabilities. They include P235/70R16 all-season tires for the XLS
and XLT series. The all-season tires are engineered for improved
ride, steering, noise and fuel economy.
For the Eddie Bauer and Limited models, Explorer is fitted with
P255/70R16 all-terrain tires. They are engineered for improved
ride, fuel economy, noise reduction and all-weather capability.
The tires are mounted on 16- by 7-inch wheel designs – varying
from full-face steel and cast aluminum to cast five-spoke aluminum
and chrome full-face steel, depending on the model.
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