Anti Lock Brake ABS Operation and Description
The antilock brake system or
the ABS
control unit 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
wheel 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 sensor VSS (vehicle speed sensor) to read rear wheel speed.
Wheel Speed Sensor (configurations may vary)
Common Problems and Fixes
Today's brake systems are reliable and easy to maintain, most systems are designed
for easy service and brake pad replacement. If the brake pedal becomes hard to push,
there can be a possibility of a broken vacuum supply line or a failed
power brake booster. It is also very important to use the correct type of brake
fluid; otherwise the brake system can malfunction. This can lead to problems such
as spongy feeling pedal and the brake pedal travel becoming excessive. Only the
highest quality brake fluid must be used in a brake system and must never be reused
and must always be discarded immediately after the fluid storage container is opened
to avoid moisture contamination. When adding brake fluid to the master cylinder
care must be taken make sure brake fluid is not spilled on the paint of the car,
brake fluid is very corrosive and will destroy the paint.
Squealing brakes is an indication of a problem with the brake system. Most of
the time a squealing noise can be a warning that the brake pads are worn down and
need to be replaced. Other causes can be overheated brake pads or rotors. Sometimes
rust can get impregnated on the brake lining material and cause grumbling or squeaking
noises. When cleaning brake components prior to service precautions must be taken.
Most brake systems contain microscopic fibers that are extremely hazardous to your
health. While cleaning with brake system cleaner there is an increased chance of
inhaling these fibers that accumulate on the brake components. Cleaning should be
done in a well ventilated area, use an air filter respirator if possible for best
results.
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 in most cases. (Real time system) when the vehicle
has been moved about 6 feet and the brake pedal has been pressed for five seconds
the codes should clear. 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.
If further technical
assistance is needed, our certified car repair technicians are ready to
answer your car questions.
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