Dr.

Walid Abdelghaffar
 Safety systems in vehicles

1) Passive safety systems protect the passengers in

case of an accident
 Airbag
 Seat-belt tightener

2) Active safety systems help prevent accidents

 Antilock braking system ABS
 Electronic Stability Program ESP

 Traction control system TCS

 Antilock Braking System
􀂄 Prevents the wheels from locking and thus
allows avoiding obstacles
􀂄 The vehicle remains under control even while
braking on one-sided slippery road
􀂄 The stopping distance is usually shortened
compared to locked wheels
 Purpose of ABS
 Automatic, electronic regulation of brake pressure to prevent the
wheels from locking up during braking.
 Driver maintains the ability to steer vehicle

4 Dr. Walid Abdelghaffar

Typical Layout of System
(with ABS)

6
 ABS

 Modulator
 VSS/
 Vehicle
speed
sensors
 Electronic
Brake
Control
Unit
7
 ABS and Tire Traction.

Maximum braking traction occurs

when tire slip is between 10% and
20%. A rotating tire has 0% slip and a
locked-up wheel has 100% slip.

The brakes slow rotation of the wheels;

friction between tire and road stops the
vehicle and allows it to be steered.
If tire traction is reduced, stopping
distances increase, and directional
stability of the vehicle suffers.

A free-rolling wheel has nearly zero

.tire slip, while a locked wheel has
100% tire slip.
 ABS

Antilock brakes will not provide shortest stops when

braking on loose gravel or dirt, or in deep, fluffy
snow. A locked wheel will stop the vehicle faster
because loose debris builds up and forms a wedge that
helps stop the vehicle.
 ABS
Wheel locks up-
reduces power to that
wheel
Pulsates brakes if sliding
Pulsates brakes on hard
braking
Stops vehicle under
control

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 Fundamental ABS systems
 Antilock Brake Systems address two conditions
related to brake application; wheel lockup and
vehicle directional control.

 ABS helps stop a car in the shortest possible

distance by pressuring at a given wheel up to 15
times per second, The driver can not do this.

 Without ABS when brakes are applied with enough

force to lock the wheels the vehicle slides
uncontrollably and steering control is lost as well.
 ABS OPERATION
All ABS control tire slip by monitoring relative
deceleration rates of the wheels during braking, by
one or more wheel speed sensors.

If one wheel starts to slow at a faster rate than others,

or at a faster rate than programmed in the control
module, it indicates a wheel is starting to slip and is
in danger of losing traction and locking.
 SYSTEM CONFIGURATIONS
All ABS keep track of wheel deceleration rates with
wheel speed sensors. The various ABS use a different
number of sensors, depending on how the system is
configured.
 Four-Channel ABS
On some applications, each wheel is equipped with its
own speed sensor.

This type of arrangement is called a “four-wheel, four-

channel” system since each wheel speed sensor provides
input for a separate hydraulic control circuit or
“channel.”
The term channel always refers to the number of
separate or individually controlled ABS hydraulic
circuits in an ABS,
not the number of wheel speed sensor electrical circuits.
NOTE: For vehicle stability systems to function, there has to be four
wheel speed sensors and four channels so the hydraulic control unit
Continued
can pulse individual wheel brakes to help achieve vehicle stability.
Three-Channel ABS
Some four-wheel ABS have a separate wheel speed
sensor for each front wheel but use a common speed
sensor for both rear wheels.

These are called “three-channel” systems. The rear

wheel speed sensor is mounted in either the differential
or the transmission.

The sensor reads the combined or average speed of both

rear wheels. This type of setup saves the cost for an
additional sensor and reduces the complexity of the
system by allowing both rear wheels to be controlled
simultaneously.
Single-Channel ABS
The single-channel rear-wheel-only ABS is used on many
rear-wheel-drive pickups and vans. Ford’s version is
Rear Antilock Braking System (RABS), while GM and
Chrysler call theirs Rear Wheel Anti-Lock (RWAL).

The front wheels have no speed sensors, and only a single

speed sensor mounted in the differential or transmission
is used for both rear wheels.

Rear-wheel antilock systems are typically used on

applications where vehicle loading can affect rear wheel
traction, which is why it is used on pickup trucks and
vans.
Integral and Non-integral
Another distinction between ABS is whether they are
integral or non-integral ABS.

Integral systems combine the brake master cylinder and

ABS hydraulic modulator, pump, and accumulator into one
assembly.

Integral systems do not have a vacuum booster for power

assist and rely instead on pressure generated by the electric
pump for this purpose.

Most of the older ABS applications are integral systems.

Continued
 System components

 Speed Sensors: monitor wheel speed.

 G Sensor: monitors rate of deceleration.
 ABS ECU: monitors sensor inputs and controls the
Actuator.
 ABS Actuators: control brake system pressure.
 Control Relay: controls the Actuator Pump Motor and
Solenoids.
 ABS Warning Lamp: alerts the driver to system
conditions.
Component Layout
 Basic operation

 Four Wheel ABS Systems use speed sensors .The

speed sensors are monitored by ECU when the wheel
speed sensors detect any sudden changes in wheel
speed. The ABS ECU calculates the rotational speed of
the wheels and the change in their speed, then the ECU
instructs the actuator to provide the optimum braking
pressure to each wheel.
(ABS Not Activated)
PRESSURE HOLDING MODE
Pressure Reduction Mode
Pressure Increase Mode
The actuator consists
of six or eight 2
position solenoid
valves, a pump and
reservoir. Each
hydraulic circuit is
controlled by

a single set of
solenoids:

• pressure holding
solenoid.

• pressure reduction
solenoid.
Pressure Holding Valve
Pressure Reduction Valve
ABS – Hydraulic Components

• Brake calipers
• Lines / hoses
• Hydraulic
control unit
• Master cylinder

37 Dr. Walid Abdelghaffar

ABS - Electronic Components

• Stop lamp switch

• Wheel speed sensors
– Inductive (early vehicles)
– Active (late model vehicles)
– Note: VSS = Vehicle Speed Sensor
• Electronic control unit
• Hydraulic control unit
• Return pump relay
• Malfunction Indicator Lamp

38 Dr. Walid Abdelghaffar

Inductive Wheel Speed Sensor
 When an inductive pickup is
used:
 AC voltage is created when
teeth move through the
Magnetic field surrounding the
sensor

Wheel hub cross section

39 Dr. Walid Abdelghaffar

Active Wheel Speed Sensor
 A newer version
sensor:
 Magnetic field near
sensor alternates N-
S-N… Sensor is a
switch with voltage
supplied to it. A DC
square wave is
created as switch is
turned on and off.
Frequency increases
with wheel speed.

40 Dr. Walid Abdelghaffar

 Effects of Unequal VSS Output

 ABS MIL will illuminate after driving

 Caused by:
 Tire sizes that do not match factory
specifications
 Tire circumferences unequal
Normal braking without ABS intervention is still
possible

41 Dr. Walid Abdelghaffar

 Hydraulic Control Unit

• Electric motor and

pumps
• Solenoid valves
• Pressure sensor
• Electronic control
module

Located in engine compartment

42 Dr. Walid Abdelghaffar

 Electronic Stability Program (ESP)

The Electronic Stability Program’s function is to act on

the transverse movement while the ABS or the TCS
maximize the grip of the tire in the longitudinal
direction preventing skidding and locking of the
wheels.
What is so special about ESP?
􀂄 Surveys the vehicle‘s behavior
(longitudinal and lateral dynamics)
􀂄 Watches the driver‘s commands
(Steering angle, brake pressure, engine torque)
􀂄 Is continuously active
in the background
What is so special about ESP?
􀂄 Recognizes critical situations – in many cases
before the driver does
􀂄 Considers the possible ways of intervening:
- Wheel-individual brake pressure application
- Intervention in the engine management
Why is ESP so important?
* Frequent cause for accidents:
􀂄 The driver loses control of his vehicle.
i.e. through
􀂄 speeding
􀂄 misinterpretation of the course
or the road condition
􀂄 sudden swerving
Why is ESP so important?
* 60% of all accidents with fatal injuries are caused by
side crashes
* These side crashes are mainly caused by skidding
because of excessive speed, driving errors or
excessive steering movements
What are the components of ESP?
What are the components of ESP?
Sensors for monitoring vehicle-state and driver inputs
• 􀂄 ESP-ECU with micro processor
• 􀂄 Hydraulic unit for stabilizing brake-application
 What are the components of ESP?

Wheel sensors
- individually monitors each wheel’s speed without
physical contact
- recognizes wheel speeds from close to zero r.p.m.
- detects the direction of the wheel’s rotation
What are the components of ESP?
􀂄 The gyro meter/accelerometer sensor

 It is located under the rear bench seat in the center of the body.
The yaw rate is the speed of rotation of the vehicle around its
vertical centerline
The lateral acceleration is subjected in a sideway direction (Lateral).
It is both a yaw rate and a lateral acceleration sensor.
What are the components of ESP?
􀂄 THE ADDITIONAL REGULATION UNIT(ARU)

It modulates the braking pressure in the calipers in the

event of ABS, or ESP regulation
What are the components of ESP?
􀂄 The ECU
What are the components of ESP?
􀂄 The ECU
 How does ESP work?
􀂄 ESP analyzes the driver‘s intention

Position of the steering wheel

+ wheel speed
+ position of the accelerator
+ brake pressure
= ECU recognizes
driver’s intention
How does ESP work?
 In what situations is ESP needed?

Examples:

􀂄 Avoiding an obstacle
􀂄 Sudden wrenching of the steering wheel
􀂄 Driving on varying road surfaces
(Longitudinal
and/or lateral changes)
 In what situations is ESP needed?
􀂄 Avoiding an obstacle

1) Hit the brakes, wrench the steering wheel: Vehicle tends to under-steer
2) ESP brakes the left rear wheel, vehicle obeys steering-wheel input
3) Reverse steering input: When the vehicle tends to oversteer, the ESP
brakes the front right wheel
4) Vehicle becomes stable again
 In what situations is ESP needed?
􀂄 When sudden wrenching of the steering wheel

1) Vehicle tends to break away.

Automatic breaking-pressure rise at the front right wheel
2) Vehicle is stable
3) Vehicle tends to break away.
Automatic breaking-pressure rise at the front left wheel
4) Vehicle is stable
In what situations is ESP needed?

􀂄 When driving on varying road surfaces

􀂄 Vehicle tends to break away (understeer):
􀂄 ESP intervenes and brakes the right rear wheel while at the
same time reducing engine torque
Physical Example of ESP Response

􀂄 ESP helps to correct (over

steer) by braking the outside
front wheel.
A Physical Example of ESP Response

􀂄 ESP helps to correct (under

steer) by braking the inside
rear wheel.
 A Physical Example of ESP Response

􀂄 ESP helps to correct 􀂄 ESP helps to correct

(under steer) by braking the inside (over steer) by braking the outside
front wheel. rear wheel.
 TCS
Traction control
system
 Difference between ABS & TCS :

ABS --- slipping during braking.

TCS --- slipping in snowy and icy conditions.

 Traction Control System
􀂄 Fast interventions in engine management and

brakes prevent the driven wheels from spinning

􀂄 Safe drive off is possible even on one-sided slippery road

􀂄 TCS prevents the vehicle from skidding when accelerating

too much in a turn

 TCS on-off

most systems have a button that allows the

driver to deactivate TCS.

 warning light will illuminate to remind the driver

TCS is not available.

Disabling TCS does not affect the operation of

the ABS system.
 Purpose of TCS

prevent wheel spin during slipping. (high slip

ratio)

the TCS reduces engine torque and drive wheel

speed.
 TCS main components

TCS controller (common or separate).

Wheel speed sensors. (slip ratio)

solenoid valves (actuators).

Pump and high pressure accumulator (shared

with ABS).
 How TCS works?

The wheel speed sensors monitor signals from

the four wheels to determine the speed of each
wheel and vehicle speed to determine the slip
ratio .
 Torque limitation
ECU activates the actuator solenoids and pump
to the brakes at the drive wheels.

Control spark timing or disable one or

more of Fuel injectors.
Shifting transmission.
 TCS operation
 TCS is off :
 TCS operation
 TCS is on :
 TCS diagnosis
If a malfunction occurs ,the TCS indicator light
will light and alert the driver that a malfunction
has occurred.

The TCS ECU will also store codes for each of

the malfunctions.
Regenerative Braking
in hybrid cars
 Regenerative Braking

Energy recovery mechanism

 Reduces vehicle speed by converting some of

its kinetic energy into a useful form of energy
instead of dissipating it as heat as in a
conventional friction brake.

 The converted kinetic energy is stored for

future use.
 Hybrid Car Energy Usage

1.Engine adds energy to system

2.Energy is recovered by braking
3.Recovered energy is stored
4.Stored energy is returned to the system.
 Current Models w/ Regen.
Brakes
Toyota Prius
50 MPG

Honda Civic Hybrid

45 MPG

Ford Fusion Hybrid

39 MPG
 Current Problems

 Recent brake feel and application issues

 Inherently Complex Systems
○ Regenerative Braking
○ Conventional Friction Braking
○ Antilock Braking
○ Vehicle Stability Control Functions
 Addressed by software fixes
○ (Reflashing)Reprogramming Control Module’s
Read-Only Memory
○ Replacing Control Module
 Current Problems

 “Different Brake Feel” due to possible

engagement of ABS during transitions in the
ratio of region to hydraulic braking.
 “Inconsistent brake feel” during slow and
steady application of brakes on rough or slick
roads when the ABS is activated.
ABS Malfunction Indicator Lamp (MIL)

Illuminated in key position 2

 Goes out with engine running
Illuminated when a fault is present
Will indicate low available voltage (< 10.5 V)
Flickering off and on while engine is running
indicates a voltage supply problem

125 Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar