BENDIX BW2262 Manuale Utente Scaricare il pdf (Pagina 5)

Speed sensors

monitor wheel

rotation

Speed signal

to ECU

ECU interprets

speed signals

and activates valves

Hold and release solenoids

control air pressure in the

brake chambers

Braking force

remains at

optimum level

Res.

FIGURE 4 - Overview of Trailer ABS Operation

ABS PERFORMANCE CHARACTERISTICS

Routine Braking

During routine braking operations, there is no indication of

excessive wheel slip. The electronic control unit interprets

this condition as normal and ABS remains inactive.

ABS Controlled Braking

The control unit continuously monitors all available wheel

speed sensors. Data from the sensors is used to calculate

values of wheel speed and wheel slip and to make a best

estimate of the true vehicle speed. This data allows the

control unit to detect impending wheel lock and to hold the

wheel slip at an optimum value to maximize braking

effectiveness. The best possible vehicle stability is assured

while stopping distance is minimized.

Control is accomplished by operation of relay based

modulator valves. The control unit makes a new

assessment of conditions and updates the control signal

to the modulator valves at a rate of approximately 100 times

per second.

Under normal (non-ABS) conditions, trailer ABS relay valves

operate exactly like conventional mechanical relay valves.

(Refer to Figures 11 through 14.) During ABS operation,

the control unit operates the valves to override the supply

of air to the chambers. During an ABS release, supply air

is held off while the chambers are vented to the atmosphere.

In hold mode, supply air is blocked and chamber air is held

constant. When required, air is applied to the chamber at

a controlled rate by modulating the hold side of the valve.

The antilock system does not apply additional braking

power. Rather, it controls air pressure to release and hold

brake torque, thereby increasing a vehicle’s capacity for

quick, straight stops. With ABS installed, vehicle operation

is safer, resulting in improved protection of driver, cargo

and equipment.

ABS Component Function

Figure 4 shows an overview of the operation of the Bendix

A-18

™

trailer ABS system.

Speed sensors (1) monitor wheel rotation and provide

information (2) on wheel rotation to the central electronic

control unit.

The Electronic Control Unit (3) receives the sensor signal,

interprets the pulse information, and constantly calculates

the relationship of speed, acceleration, and deceleration.

A control signal (4) is sent to the ABS relay valve (5), which

then controls the pressure to the air chambers.

System Designs

When operating on high traction surfaces with a loaded

vehicle, there is little difference between types of ABS

control. Performance differences appear when vehicles

are lightly loaded and operating on variable and poor traction

surfaces. Examples of poor traction surfaces are ice and

combinations of ice, snow and asphalt. Operating a vehicle

in a curve highlights differences in stability between various

systems.

ABS system designs provide compromises between stability

and stopping distance while addressing cost, complexity

and reliability issues.

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BENDIX BW2262 Manuale Utente Pagina 5

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