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How Does it Work /
ABS Brakes
How the Antilock Brake System Works
Anti Lock Brake Operation and
Description
The antilock brake system or the
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 every wheel by metering the
brake line pressure at
the time of extreme 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 an 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, additional sensors have been added to the
system, gyroscopic sensors and steering wheel angle sensors. 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 an 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), Nippon-Denso ABS
Actuator (NAA) systems. The basic design and assembly is the same, the
Nippon-Denso 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 an electronic signal to the
ABS controller, from 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, some even use the vehicles speedometer (Vehicle Speed Sensor) to read
rear wheel speed.
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 driver's 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
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