Easy to follow guide on how an automotive anti-lock brake system works, this
information pertains to most vehicles.
The anti-lock brake system (ABS) helps to maintain control and directional stability
of an automobile in case of extreme braking circumstances, this is achieved by controlling
the rotational speed of each wheel by metering the brake line pressure to each individual
(Note: if the ABS light is "ON" while driving the anti-lock portion of the system
is in bypass mode and will not operate.)
The ABS assembly is made up partially of a central electronic unit, control solenoids
and an electrical connector, during an ABS operation event, one or more of the solenoids
help dump brake line pressure to a particular wheel allowing rotation.
ABS Warning Light
The motor and valve is designed to control fluid to each wheel which can either
add or drop pressure.
The system uses a reluctor-wheel to track rotation which is picked up by a sensor.
ABS Motor and Valve
A wheel speed sensor is used to pick up a magnetic pulse wave pattern generated
by the reluctor ring and is feedback to the ABS computer. The location of wheel
speed sensor may vary, on some vehicles the front sensor is made into the steering
knuckle or spindle, near the front wheel hub or outer CV joint.
ABS Wheel Reluctor
Research has shown that an anti-lock brake system can decrease the chance of
a vehicle accident by 18% and was introduced in the late seventies. By using gyroscopic
and steering wheel angle sensors, not only does ABS provide non-skid functionality
but it also supports electronic stability control, brake assist and traction control.
There are several types of ABS systems; some of the more popular systems are
based on the Bosch ABS Actuator (BAA), Nippon-Denso ABS Actuator (NAA) systems.
The basic idea is the same, Nippon-Denso systems has a separate solenoid pack and
ABS computer, where as the Bosch systems both the components are combined.
High quality brake fluid must be used in ABS brake systems due to harsh usage.
When the ABS system detects a problem a fault code is stored in the ABS system control
unit and the warning light illuminated. Most ABS brake systems are "real time",
when a code has triggered, and the repair made, the code should clear itself within
a few yards of driving.
ABS Wheel Speed Sensor
Article first published 2016-02-03