BC Transit – Air Brake Course

ABS (Anti Lock Air Brake Systems)
• ABS are typically made up of 3 main sections:
speed sensing, decision-making, and brake releasing or modulation.
• As the wheels rotate, vehicle speed is detected by the sensors which
delivers a pulsating current monitored by an ECU (Electronic Control
Unit).
• With normal braking, the sensors will detect a graduated decrease in
pulsating current, with no change to braking.
• If the ECU detects a sudden change (wheel lockup) in the pulsating
current, the ABS system will activate, thereby signaling a release of
air from the brakes (modulation).
• As the brakes begin to release, the wheels will regain traction, the
pulsating current will be restored, and the ECU will allow the brakes to
re-apply.
• If the lockup re-occurs the apply-and-release cycle will repeat as
often as necessary – most systems are capable of cycling the brakes
up to five times per second.
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