BENDIX MC-12 MODULATOR CONTROLLER ASSY Informations techniques télécharger pdf (Page 10)

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.

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.

FIGURE 12 - YAW CONTROL EXAMPLE

A Real World Example Of How Yaw Control

Operates:

Excessive speed exceeds the threshold, creating a

situation where a vehicle is likely to spin and jackknife.

The Bendix

Yaw Control system reduces engine throttle

and selectively applies brakes to reduce the tendency

to jackknife.

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