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How Does it Work /
ABS Brakes
How Anti Lock Brakes Work
Anti Lock Brake Operation and Description
The Antilock Brake Skid system or the ABS maintains the control and directional
stability of an automobile in case of extreme braking circumstances. This is
achieved by controlling the rotational speed of every wheel and metering the
brake line pressure at the time of skid braking. The system works on most types of
road surfaces and decreases the risk of an accident and severity of
an impact. Research has shown that a antilock brake system can decrease the chance of
a vehicle accident by 18%.
ABS brake systems were introduced in the late seventies and
have enjoyed great technological advances since that time. Not only does ABS provide
non-skid functionality but it also supports electronic stability control, brake
assist, traction control, etc. Recently, two additional sensors have been added
to the system,
a gyroscopic sensor and a steering wheel angle sensor. Both synchronize to match the
direction of the car with the direction of the steering wheel.
The wheel angle sensor also helps the ABS system control the outer wheels to have a
more positive braking effect when compared to the inner wheels on the curve.
Typical ABS Brake System
The ABS assembly is made up of a central
electronic unit, four solenoid valves and two or more electric hydraulic pumps.
The function of the electric hydraulic pump is to supply brake fluid pressure to the braking
system by forcing hydraulic pressure to a reservoir located in
the accumulator. The four solenoid pressure valves control brake fluid pressure for each individual wheel. During a ABS operation event,
one or more of the solenoid valves dump brake line
pressure to a particular wheel allowing it to start turning.
There are several types of ABS systems, some of the most popular models are based
from the Bosch ABS
Actuator (BAA), Nippondenso ABS Actuator (NAA) systems. The basic design and assembly is
the same,
the Nippondenso system has a separate solenoid relay pack and ABS computer,
where as in the Bosch system both the components are combined. Also, there is an immediate
connection between the wheel speed sensors and the ECU (engine control unit),
these systems are connected by the CAN (Controller Area Network) bus, this system communicates
by sending multiple signals to multiple devices at any given time.
Each wheel has a dedicated speed sensor which sends a electronic signal to the
ABS
controller, by this signal the rotational speed of the wheel can be
determined. The location of wheel speed sensor may vary, on most vehicles the front
sensor is made into the
steering knuckle, near the
front wheel hub or outer CV joint. In the rear of the vehicle the sensor rings
are bolted to the rear driver assembly on the ring gear or attached to the
outer axle
flange on each side.
Common Problems and Fixes
Wheel Speed Sensor (configurations may vary)When the ABS system detects a problem a fault code is stored
in the ABS system
control unit. When an error occurs the ABS warning light located on the dashboard flashes or stays on
steadily. The ABS computer
stores a diagnostic code until the malfunction has been repaired. To retrieve
ABS trouble codes on older vehicles can be tricky because of the variation of
retrieval methods, in this case a
car repair
manual is needed. On newer vehicles a diagnostic information connector is
located under the dash on the drivers side, a trouble code scanner
can be attached to retrieve ABS codes similar to
engine trouble codes. After
the problem has been repaired codes should erase automatically with no
procedure from the scan tool. (real time system) after the
vehicle has been moved about 6 feet and the brake pedal has been pressed for five seconds.
When
repairs have been completed the ABS, MIL (malfunction indicator lamp) should
not be illuminated, if the ABS light remains on there is still a problem,
re-scan the ABS computer for further repairs.
Basic Maintenance
ABS brake systems apply more wear and tear to the brake fluid and can wear brake
fluid down chemically. Be sure to flush your brake system with manufacturer
recommended brake fluid ( DOT 3 or 4) when brake service is performed to ensure proper operation of the ABS brake system in your car.
How Does it Work /
ABS Brakes
Check Manufacturer Specific ABS Brakes
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