BENDIX BW1664 manual Antilock Exhaust Figure, Antilock Hold

	EXHAUST	EXHAUST
		SOLENOID
	DIAPHRAGM
EXHAUST PORT
		BRAKE VALVE
		SUPPLY
		SOLENOID
BRAKE	SUPPLY	SPRING
		SPRING
CHAMBER	DIAPHRAGM
FIGURE 6 - M-21™, M-22™MODULATOR NON-ANTILOCK EXHAUST OF SERVICE BRAKES (RAPID)

ANTILOCK EXHAUST (FIGURE 7)

When wheel lock is detected, or imminent, the antilock controller simultaneously energizes both the supply and exhaust solenoids in the modulator. Energizing the supply solenoid causes its exhaust to close and inlet to open. With the inlet of the supply solenoid open, application air is permitted to flow to the control side of the supply diaphragm. Air pressure acting on the supply diaphragm causes it to close the supply and prevent further delivery of air to the brake chamber.

Energizing the exhaust solenoid closes its inlet and opens its exhaust. By closing the exhaust solenoid inlet, application air is prevented from flowing to the control side of the exhaust diaphragm. Air pressure, which was present on the control side of the exhaust diaphragm flows out the exhaust port of the modulator. With control air pressure removed from the exhaust diaphragm, brake application air forces the exhaust diaphragm to unseat which allows it to flow out the modulator exhaust port. The modulator will remain in the antilock exhaust mode until the antilock controller senses that wheel speed has increased. The modulator can enter the antilock hold or re-apply mode from the antilock exhaust mode.

ANTILOCK HOLD

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 place the modulator in the hold position, prior to entering the re-apply, when it detects recovery from a locked wheel condition. In this mode of operation the modulator supply solenoid remains energized while the exhaust solenoid is de-energized. De-energizing the exhaust solenoid opens its inlet and closes its exhaust. Opening the exhaust solenoid inlet, allows application air to flow to the control side of the exhaust diaphragm which then seals the exhaust passage. With the exhaust diaphragm seated, further exhaust of brake chamber air pressure is prevented. Because the supply solenoid remains energized the supply diaphragm remains seated, thus preventing application air from flowing to the delivery port and out to the brake chamber. The modulator can enter the antilock exhaust or re-apply mode from the antilock hold mode.

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