BENDIX BW2335 User Manual download pdf (Page 4)

Rapid Exhaust (Figure 7) - The Rapid Exhaust operation

described in the following text occurs when the modulator is

controlling service chamber(s). During a rapid brake release

the quick release modulator will exhaust air differently to a

“slow” brake release.

An example of this would be the case if the driver made a

severe brake application then lifted his foot from the foot

valve. During a rapid brake release, the air previously delivered

to the brake chamber is vented through the M-32

™

modulators as follows:

For the M-32QR

™

Modulator: The bias valve moves to its

closed position, closing the air return route to the brake

valve’s exhaust. Air pressure against the exhaust valve within

the M-32

™

modulator overcomes the spring force and allows

air to exhaust through the M-32QR

™

modulator exhaust port.

Residual air pressure between the bias valve and the brake

pedal flows back to the brake valve exhaust.

For the M-32

™

Modulator: As in the “slow” brake release,

air pressure travels back to the brake valve’s exhaust, but

also the air pressure against the exhaust valve within the

M-32

™

modulator overcomes the spring force and allows air

to exhaust through the M-32

™

modulator exhaust port.

ANTILOCK OPERATION

GENERAL

If a service brake application is made and the antilock system

detects an impending wheel lockup, the antilock controller

will make a controlled brake application using the modulator.

In order to control the brake application, the coils of the two

solenoid valves contained in the modulator are energized or

de-energized in a preprogrammed sequence by the antilock

controller. When a solenoid coil is energized, and depending

whether the exhaust or hold solenoid is energized, it either

opens or closes, thereby causing the exhaust or

reapplication of air pressure to the brake actuator. The

solenoids in the modulator are controlled independently by

the antilock controller (ECU).

An experienced driver (of a vehicle without ABS) who

encounters wheel lock-up may sometimes “pump the brakes”

in order to attempt to prevent wheel lock-up and maintain

vehicle control. In the case of an ABS braking system, the

driver does not need to “pump the brakes” since the antilock

controller is able to apply and release the brakes using the

modulators, with far greater speed and accuracy. Depending

on the number of modulators used, some systems are able

to apply braking power to wheels independently (see page

2).

ANTILOCK EXHAUST (Figure 8)

When wheel lock is detected or imminent, the antilock

controller energizes the supply and exhaust solenoids in

the modulator.

Energizing the supply solenoid allows application air to flow

to the control side of the supply diaphragm. Air pressure

acting on the supply diaphragm, along with the spring force,

enables the diaphragm to prevent further delivery of air to

the brake chamber.

Energizing the exhaust solenoid shuts off the air normally

applied to the control side of the exhaust diaphragm to keep

it closed. Air pressure acting on the exhaust diaphragm,

overcomes the spring force, and allows air to exhaust through

the exhaust port.

ANTILOCK HOLD MODE (Figure 9)

The antilock controller will place the modulator in the Hold

position when it senses that the correct wheel speed (braking

force) has been attained. The antilock controller will also

FIGURE 7: M-32

™

AND M-32QR

™

MODULATORS RAPID NON-ANTILOCK EXHAUST OF SERVICE BRAKES

Supply or Hold

Diaphragm

Open

Spring

Brake

Chamber

Brake

Valve

Exhaust

Diaphragm

Exhaust

Valve

Open

Exhaust

Port

M-32

™

Modulator

M-32QR

™

Modulator

Bias

Valve

Delivery

Port

Supply

Port

Supply or Hold

Diaphragm

Open

Spring

Brake

Chamber

Brake

Valve

Exhaust

Diaphragm

Exhaust

Valve

Open

Exhaust

Port

Delivery

Port

Supply

Port

1 2 3 4 5 6 7 8

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BENDIX BW2335 User Manual Page 4

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