Antilock braking system (abs)

ANTILOCK
BRAKING SYSTEM
(ABS)
BY,
ARAVINDKUMAR B

Anti-lockBrakingSystem
 What is an Anti-Lock Braking System (ABS)?
 History of ABS
 Motivation for ABS Development
 Overview
 Principles for ABS Operation
 ABS Components Overview
 ABS Components
 How does ABS work?
 System Diagram
 Anti-Lock Brake Types
 Advantages & Disadvantages
 ABS Problems

Anti-lock braking system (ABS) is an
automobile safety system prevent the
wheels of a vehicle locking as brake
pedal pressure is applied - often
suddenly in an emergency or short
stopping distance. This enables the
driver to have steering control,
preventing skidding and loss of
traction.

ABS is a safety related feature that assists the driver
in deceleration of the vehicle in poor or marginal
braking conditions (e.g., wet or icy roads).
In such conditions, panic braking by the driver (in
non-ABS-equipped cars) results in reduced braking
effectiveness and loss of directional control due to
the tendency of the wheels to lock.
In ABS-equipped cars, the wheel is prevented from
locking by a mechanism that automatically regulates
braking force to an optimum for any given low-
friction condition

• 1929 :- ABS was first developed for aircraft by the
French automobile and aircraft pioneer Gabriel
Voisin, as threshold braking on airplanes is nearly
impossible.
• 1936: German company Bosch is awarded a
patent an “Apparatus for preventing lock-braking
of wheels in a motor vehicle”.
• 1936-: Bosch and Mercedes-Benz partner - R&D
into ABS.
• 1972: WABCO partners with Mercedes-
Benz developing first ABS for trucks.
• 1978: First production-line installation of ABS into
Mercedes and BMW vehicles.
• 1981: 100,000 Bosch ABS installed.
• 1985: First ABS installed on US vehicles.

• 1986: 1M Bosch ABS installed.
• 1987: Traction control - in conjunction with
ABS – used on passenger vehicles.
• 1989: ABS hydraulic unit combined with
standard hydraulic brake unit
• 1995: Electronic Stability - in conjunction with
ABS and TCS - for passenger cars.
• 2000: 6 of 10 new cars on the road are
ABS
equipped.
• Nowadays:- Almost all new cars have ABS.

• Under hard braking, an ideal braking system
should:
Provide the shortest stopping distances
on all surfaces
 Maintain vehicle stability and steer ability.

When the brake pedal is depressed during driving, the
wheel speed decreases and the vehicle speed does as
well. The decrease in the vehicle speed, however, is
not always proportional to the decrease in the wheel
speed. The non-correspondence between the wheel
speed and vehicle speed is called “slip” and the
magnitude of the slip is expressed by the “slip ratio”
which is defined as follows:
Slip ratio = (Vehicle speed – Wheel speed)/Vehicle speed × 100%
When the slip ratio is 0%, the vehicle speed corresponds
exactly to the wheel speed. When it is 100%, the
wheels are completely locking (rotating at a zero
speed) while the vehicle is moving.
See Fig 2.

Figure 2. Illustration of the relationship between
braking coefficient and wheel slip

•The best braking
action occurs at
between 10-20%.
•If vehicle speed and
wheel speed is the
same wheel slippage
is 0%
•A lock-up wheel will
have a wheel slippage
of 100%
(A) Slip ratio
(B) Coefficient of friction between tire
and road surface
(1) Icy road
(2) Asphalt-paved road
(3) Control range by ABS

2 shows the relationship between• Figure
braking
shown that values
co-efficient and wheel slip. It is
for
stopping/traction
higher than
the slide
force are
the slide
proportionately
values for
cornering/steering force. A locked-up wheel
provides low road handling force and minimal
steering force.

Hydraulic unit.
Electronic brake control
module (EBCM).
Two system fuses.
Four wheel speed sensors.
Interconnecting wiring
The ABS indicator
The rear drum brake.

(1)ABS control module and
hydraulic control unit (ABSCM &
H/U).
(2) Two-way connector.
(3) Diagnosis connector.
(4) ABS warning light.
(5) Data link connector (for
SUBARU select monitor).
(6)Transmission controlmodule
(AT models only).
(7) Tone wheels.
(8) ABS wheel speed sensor.
(9) Wheel cylinder.
(10) G sensor.
(11) Stop light switch.
(12) Master cylinder.
(13) Brake & EBD warning light.
(14) Lateral G sensor (STi).

• ABS brake system are
–Integrated
• An integrated system has the master
cylinder and control valve assembly
made together.
–Nonintegrated
• A nonintegrated has the master
cylinder and control valve assembly
made separate.

• ABS systems consist of 4 primary
components:
1ABS Controller; the brains of the
system. ABS Controllers are a computer
that reads the inputs and then controls the
system to keep the wheels from locking up
and skidding.
2ABS Speed Sensors; there are generally
one on each wheel (sometimes they are
located on the differential).
It detects a change in acceleration in the
longitudinal direction of the vehicle and
outputs it to the ABSCM as a voltage signal.

3ABS Modulator/Valves; some system
have separate valves for each wheel with a
modulator to control them. Other systems
they are combined. In either case they
work with the controller and the pump to
add or release pressure from the individual
wheels brakes to control the braking.
4ABS Pumps; since the ABS
modulator/valves can release pressure from
the individual wheels brakes there needs to
be a way to restore the pressure when
required. That is what the ABS pumps job
is. When the pump is cycling, the driver
may experience a slight pedal vibration.
This cycling is happening many times per
second and this slight vibration is natural.

Figure 3. ABS Operating Diagram

We will discuss how one of the simpler system works.
 Sensors at each of the four wheels  sense the rotation of the wheel.
 Too much brake application  wheel stop rotating
 Sensors  ECU  releases brake line pressure  wheel turns
again.
 then ECU applies pressure again  stops the rotation of the wheel
releases it again and so on
NB:
 This releasing and re-application or pulsing of brake pressure
happens 20-30 times per second or more.
 This keeps the wheel just at the limit before locking up and
skidding no matter
 ABS system can maintain extremely high static pressure and must be
disabled before attempting repairs.

During pressure increase
mode of operation fluid is
allowed to flow through
both solenoids to the brake
caliper
Solenoid 1
Pressure increase
Solenoid 2
Pressure decrease/Vent
solenoid
Brake line under pressure
Brake fluid line not under pressure

Solenoid 1
Pressure increase
During Pressure Hold
mode of operation both
solenoids are closed and
no additional fluid is
allowed to flow to brake
calipers.
Solenoid 2

During Pressure Vent mode
the pressure increase solenoid
is closed. The Vent solenoid
opens allowing fluid to vent
into an accumulator chamber
Solenoid 1
Pressure increase
Solenoid 2

• Figure 4. ABS Block Diagram

• Advantages:
1. It allows the driver to maintain directional stability
and control over steering during braking
2. Safe and effective
3. Automatically changes the brake fluid pressure at
each wheel to maintain optimum brake performance.
4. ABS absorbs the unwanted turbulence shock waves
and modulates the pulses thus permitting the wheel
to continue turning under maximum braking pressure

• Disadvantages
1. Stop Times - Anti-lock brakes are made
to provide for surer braking in slippery
conditions. However, some drivers
report that they find the stopping
distances for regular conditions are
lengthened by their ABS system, either
because there may be errors in the
system, or because noise of the ABS
may contribute to the driver not braking
at the same rate.
1. Delicate Systems - It's easy to cause a
problem in an ABS system by messing
with the brakes. Problems
disorientation of the ABS
around
include
system, where a compensating brake
sensor causes the vehicle to shudder,
make loud noise or generally brake
worse.

3. Cost - An ABS can be expensive
to maintain. Expensive sensors on
each wheel can cost hundreds of
dollars to fix if they get out of
calibration or develop other
problems. For some, this is a big
reason to decline an ABS in a
vehicle.
4. System damage - A variety of
factors can cause the system to
be less effective, and can present
with everything from shuddering of
the vehicle to loud noises while
trying to stop

Problems withABS
The sensors on the wheels
contaminated by metallic dust.
might get
When this
condition occurs the sensors become less
efficient in picking up problems. In modern
ABS systems, two more sensors are added
to help:
 wheel angle sensor,
 gyroscopic sensor

The idea
gyroscopic
behind this is that
sensor detects that
when the
the car’s
direction is not the same as what the wheel
sensor reports, the ABS software will cut in to
brake the necessary wheel in order to help
the car go the direction the driver intends.

 Statistics show that approximately 40 % of automobile
accidents are due to skidding.
 Skidding , vehicle instability, steer inability and long
distance stopping, These problems commonly occur
on vehicle with conventional brake system which can
be avoided by adding devices calledABS.
 If there is an ABS failure, the system will revert to
normal brake operation. Normally the ABS warning
light will turn on and let the driver know there is a fault.

Antilock braking system (abs)

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