13
Roll Stability Program
Bendix RSP, an element of the overall ESP system,
addresses rollover conditions. In the case of a potential
roll event, the ECU will override the throttle and quickly
apply brake pressure at all wheel ends to slow the vehicle
combination. The level of braking application during an
RSP event will be proportional to roll risk.
See Figure 11
.
Yaw Stability
Yaw stability counteracts the tendency of a vehicle to spin
about its vertical axis. During operation, if the friction
between the road surface and the tires is not sufficient
to oppose lateral (side) forces, one or more of the tires
can slide, causing the truck/tractor to spin. These events
are referred to as either an "under-steer" situation (where
there is a lack of vehicle response to steering input due to
tire slide on the steer axle) or an "over-steer" (where the
tractor's rear end slides out due to tire slide on the rear axle)
situation. Generally, shorter wheelbase vehicles (tractors,
for instance) have less natural yaw stability, while longer
wheelbase vehicles (straight trucks, for instance) have
greater natural yaw stability. Factors that influence yaw
stability are: wheelbase, suspension, steering geometry,
weight distribution front to rear, and vehicle track width.
Yaw Control
Yaw Control responds to a wide range of low- to high-
friction surface scenarios including rollover, jackknife
and loss-of-control. It is the recommended system for all
power vehicles and especially critical for tractors pulling
trailers. In the case of vehicle slide (over-steer or under-
steer situations), the system will reduce the throttle and
then brake one or more of the “four corners” of the vehicle
(in addition to potentially applying the trailer brakes), thus
applying a counter-force to better align the vehicle with an
appropriate path of travel.
For example, in an over-steer situation, the system applies
the “outside” front brake; while in an under-steer condition,
the “inside” rear brake is applied. (See Figure 12)
IMPORTANT SAFETY INFORMATION
ABOUT THE BENDIx
®
ESP
®
STABILITY
SYSTEM
ESP May Reduce The Vehicle Speed
Automatically
ESP can make the vehicle
decelerate automatically .
ESP
can slow the vehicle with or
without the operator applying
the brake,
and
even when the throttle is being applied .
CAUTION
To minimize unexpected deceleration and reduce the risk
of a collision the operator must:
• Avoid aggressive driving maneuvers, such as sharp
turns or abrupt lane changes at high speeds, which
might trigger the stability system.
• Always operate the vehicle safely, drive defensively,
anticipate obstacles and pay attention to road, weather
and traffic conditions. ABS, ATC and ESP stability
systems are no substitute for prudent, careful driving.
Towing Doubles Or Triples May Reduce The
Effectiveness Of Stability Systems
ESP is designed and optimized for trucks and for tractors
that tow single trailers. If a tractor equipped with ESP
is used to power multiple trailer combinations (known
as “doubles” or “triples”)
the effectiveness of the ESP
system may be greatly reduced .
Extremely careful
driving is always required when towing doubles or triples.
Excessive speed and aggressive maneuvers, such as
sharp turns, sudden steering inputs or abrupt lane changes
should be avoided.
Limitations Of Stability Systems
The ESP stability system’s effectiveness may be greatly
reduced if:
• The load shifts due to improper retention, accident
damage or the inherently mobile nature of some loads
(for example, hanging meat, live animals or partially
laden tankers),
• The vehicle has an unusually high or off-set center of
gravity (CG),
• One side of the vehicle drops off the pavement at an
angle that is too large to be counteracted by a reduction
in speed,
• The vehicle is used to haul double or triple trailer
combinations,
• If very rapidly winding steering inputs are inputted at
high speeds,
• There are mechanical problems with suspension
leveling of the tractor or trailer resulting in uneven loads,
• The vehicle is maneuvering on a high banked road
creating either additional side forces due to the weight
(mass) of the vehicle or a deviation between expected
& actual yaw rates,
• Gusty winds are strong enough to cause significant
side forces on the vehicle and any towed vehicles.
To Maximize The Effectiveness Of ESP:
• Loads must be properly secured at all times.
• Drivers need to exercise extreme caution at all times,
and avoid sharp turns, sudden steering inputs or abrupt
lane changes at high speeds, particularly if:
› the vehicle hauls loads that could shift,
› the vehicle or load has a high or off-set center of
gravity (CG) when loaded, or
› the vehicle tows doubles or triples.
