BENDIX BW1664 manual NON-ANTILOCK Exhaust, Antilock Operation

	EXHAUST	EXHAUST
		SOLENOID
	DIAPHRAGM
EXHAUST PORT
		BRAKE VALVE
		SUPPLY
		SOLENOID
BRAKE	SUPPLY	SPRING
		SPRING
CHAMBER	DIAPHRAGM
FIGURE 5 - M-21™, M-22™MODULATOR NON-ANTILOCK EXHAUST OF SERVICE BRAKES (NORMAL)

NON-ANTILOCK EXHAUST

The manner in which air exhausts through the modulator differs, depending upon how rapidly the brake application is released by the driver.

Normal Exhaust (Figure 5) - During a normal, relatively "slow", brake release, air moves back through the modulator in the reverse direction as it flowed during application. The internal components of the modulator will remain in the same position as they assumed during application until air pressure decreases to approximately one half psi, at which time the supply diaphragm will seat on the supply passage. Air will generally not be expelled from the modulator exhaust port during normal brake release.

Rapid Exhaust (Figure 6) - The rapid exhaust operation described in the following text only occurs when the modulator is controlling two type 30 (or larger) service chambers. During a very rapid brake release the modulator will exhaust air in a different manner. 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, air from the exhaust diaphragm flows back through the open exhaust solenoid and to the application device's exhaust. With pressure removed from the control side of the exhaust diaphragm, air, returning to the modulator from the service chambers, lifts the exhaust diaphragm from its seat. Returning air flows past the open

exhaust and out the modulator exhaust port. Air will also flow past the open supply diaphragm and back to the application device's exhaust.

ANTILOCK OPERATION

GENERAL

If a service brake application is made and the antilock system detects an impending wheel lockup, the antilock controller will immediately begin modification of the brake application using the modulator.

In order to modify the brake application, the coils of the two solenoid valves contained in the modulator are energized or de-energized in a pre programmed sequence by the antilock controller. When a solenoid coil is energized, a shuttle within the solenoid moves, and depending upon the function of the specific solenoid, it either opens or closes thereby causing the exhaust or re-application of air pressure to the brake actuator. The solenoids in the modulator are controlled independently by the antilock controller. By opening and closing the solenoid valves in the modulator, the antilock controller is able to simulate what the driver does when he "pumps the brakes". It must be remembered, however, that unlike the driver the antilock controller is able to "pump" each modulator, along with the brakes connected to it, independently and with far greater speed and accuracy.

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