Bridgwater College

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Braking Systems
Bridgwater College
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ANTI - LOCK BRAKING and TRACTION CONTROL
SYSTEMS
Bridgwater College Lecturer - Tim Cornish
TMC
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Anti - Lock Braking Systems were first developed
in the aircraft industry to aid and further
improve the landing capabilities of the aircraft.
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Anti - Lock Braking Systems were first developed
in the aircraft industry to aid and further
improve the landing capabilities of the aircraft.

• This improved the following
• the stopping distance of
• the plane.

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Anti - Lock Braking Systems were first developed
in the aircraft industry to aid and further
improve the landing capabilities of the aircraft.

• This improved the following
• the stopping distance of
• the plane.
• control of the plane on
• landing.

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Anti - Lock Braking Systems were first developed
in the aircraft industry to aid and further
improve the landing capabilities of the aircraft.

• This improved the following
• the stopping distance of
• the plane.
• control of the plane on
• landing.
• safety in poor weather
• conditions.

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Anti - Lock Braking Systems were first developed
in the aircraft industry to aid and further
improve the landing capabilities of the aircraft.

• This improved the following
• the stopping distance of
• the plane.
• control of the plane on
• landing.
• safety in poor weather
• conditions.
• directional stability.

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• Anti - lock braking systems on vehicles provide
  the same
• advantages as with aircraft. Any system must
  fulfil the
• following criteria
• maintenance of manoeuvrability (lateral guiding
  of the
• front wheels).

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• Anti - lock braking systems on vehicles, provide
  the same
• advantages as with aircraft. Any system must
  fulfil the
• following criteria
• maintenance of manoeuvrability (lateral guiding
  of the
• front wheels).
• maintenance of directional stability (lateral
  guiding of
• the rear wheels).

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• Anti - lock braking systems on vehicles, provide
  the same
• advantages as with aircraft. Any system must
  fulfil the
• following criteria
• maintenance of manoeuvrability (lateral guiding
  of the
• front wheels).
• maintenance of directional stability (lateral
  guiding of
• the rear wheels).
• reduction in braking distance in comparison with
  a
• conventional system.

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• Anti - lock braking systems on vehicles provide
  the same
• advantages as with aircraft. Any system must
  fulfil the
• following criteria
• maintenance of manoeuvrability (lateral guiding
  of the
• front wheels).
• maintenance of directional stability (lateral
  guiding of
• the rear wheels).
• reduction in braking distance in comparison with
  a
• conventional system.
• Guarantee of low regulation amplitudes (pedal
  reactions
• and comfort).
• OVERALL IMPROVED SAFETY OF THE VEHICLE.

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The need for ABS.
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The need for ABS - directional control
maintained.
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Loss of Adhesion in wet weather conditions -
aquaplaning.
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This diagram shows an INTEGRATED ABS system.
Brake Pressure Unit
Brake Servo
ABS Unit
High Pressure Pump
PUMP UNIT
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This diagram shows an INTEGRATED ABS system.
Brake Pressure Unit
Brake Servo
ABS Unit
High Pressure Pump
This system comprises of - a brake pressure
unit functional INTEGRATION of the master
cylinder and brake servo with the ABS regulation
unit.
PUMP UNIT
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This diagram shows an INTEGRATED ABS system.
Brake Pressure Unit
Brake Servo
ABS Unit
High Pressure Pump
This system comprises of - a brake pressure
unit functional INTEGRATION of the master
cylinder and brake servo with the ABS regulation
unit.
PUMP UNIT
- a pump unit source of high pressure (180
bars) for the hydraulic servo.
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This diagram shows ADDITIONAL ABS system.
ADDITIONAL REGULATION UNIT (ABS)
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This diagram shows ADDITIONAL ABS system.
ADDITIONAL REGULATION UNIT (ABS)
An additional ABS system comprises - a tandem
master cylinder with servo (vacuum or hydraulic)
which produces the brake pressure and distributes
it to the callipers through the brake pipes.
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This diagram shows ADDITIONAL ABS system.
ADDITIONAL REGULATION UNIT (ABS)
An additional ABS system comprises - a tandem
master cylinder with servo (vacuum or hydraulic)
which produces the brake pressure and distributes
it to the callipers through the brake pipes.
- an additional regulation unit, modulating the
brake pressure in each calliper independently of
the effort applied to the brake pedal.
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Schematic Diagram Bosch 2SE system
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Hydraulic Circuit
A
The ABS system contains a - hydraulic
circuit. - electrical circuit.
B
This circuit has 4 callipers (A) connected to the
tandem master cylinder which generates the brake
pressure.
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Hydraulic Circuit
C
A load sensitive compensator (C) modifies the
braking pressure to the rear callipers according
to body movement.
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Hydraulic Circuit
D
The Additional Regulator Unit (D), modifies the
brake pressure in the callipers in such a way as
to prevent the wheel locking.
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Electrical Circuit
This circuit comprises of - 4 wheel speed
sensors (E) which generate electrical impulses
whose frequency depends on the speed of rotation
of the wheel.
E
E
E
E
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Electrical Circuit
F
An electronic control unit (F) which uses the
signals from the wheel sensors and controls the
solenoid valve in the regulation unit.
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H
Electrical Circuit
A warning lamp (G) located in the instrument
panel and a connector (H) enabling fault
diagnosis.
G
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Diagnostic self check.
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Electrical Circuit - The Wheel Sensor
Nearly all modern ABS systems have four channel
operation. That is to say that there is a wheel
sensor fitted on each of the road wheels. The ECU
can monitor up to 8000 sensor signals per second
and can take action within a few milliseconds.
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Electrical Circuit - The Wheel Sensor
Nearly all modern ABS systems have four channel
operation. That is to say that there is a wheel
sensor fitted on each of the road wheels. The ECU
can monitor up to 8000 sensor signals per second
and can take action within a few milliseconds.
PERMANENT MAGNET
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Electrical Circuit - The Wheel Sensor
Nearly all modern ABS systems have four channel
operation. That is to say that there is a wheel
sensor fitted on each of the road wheels. The ECU
can monitor up to 8000 sensor signals per second
and can take action within a few milliseconds.
PERMANENT MAGNET
SOFT IRON CORE
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Electrical Circuit - The Wheel Sensor
Nearly all modern ABS systems have four channel
operation. That is to say that there is a wheel
sensor fitted on each of the road wheels. The ECU
can monitor up to 8000 sensor signals per second
and can take action within a few milliseconds.
PERMANENT MAGNET
SOFT IRON CORE
WINDING
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Electrical Circuit - The Wheel Sensor
The wheel sensor is known as a PASSIVE sensor.
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Electrical Circuit - The Wheel Sensor
Reluctor tooth on driveshaft
Pick up coil in wheel sensor with permanent magnet
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Electrical Circuit - The Wheel Sensor
As the reluctor tooth approaches the pick up coil
tooth, a magnetic field increases in strength,
thus generating a voltage in the pick up coil.
Farad
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Electrical Circuit - The Wheel Sensor
Just before the tooth is in line with the pick up
coil tooth, maximum voltage is generated.
Farad
MAXIMUM VOLTAGE
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Electrical Circuit - The Wheel Sensor
ZERO VOLTAGE
The reluctor tooth is now in line with the pick
up coil tooth, the magnetic field is longer
growing (moving) thus no voltage is generated in
the pick up coil.
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Electrical Circuit - The Wheel Sensor
NEGATIVE VOLTAGE
The reluctor tooth is now moving away from the
pick up coil tooth and the magnetic field is
collapsing (moving in the opposite direction).
The voltage has become negative.
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Electrical Circuit - The Wheel Sensor
The reluctor tooth has moved some distance from
the pick up coil tooth and the voltage generated
voltage has dropped back to ZERO.
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Electrical Circuit - The Wheel Sensor
With an oscilloscope an AC waveform should
be produced with the wheel rotating.
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Electrical Circuit - The Wheel Sensor
Experiment Using the computer program
Crocodile Clips produce a simple ABS layout with
wheel sensors. Use the oscilloscope to test the
wheel sensors. You must carry out the following
tests 1. Set the motor speed to 50 rpm and the
wheel sensor to 1 Hz. 2. Using the
oscilloscope test each wheel sensor for
operation. 3. Does the polarity of the waveform
change. If so why? 4. Set the motor speed
to 100 rpm and the sine wave generator to
3Hz. What do you notice about the waveform
signal? One the next screen is an example.
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Electrical Circuit - The Wheel Sensor
250ohms
Farad
Volt
Amp
Ohm
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Electrical Circuit - The Wheel Sensor
Resistance/continuity check
250ohms
Farad
Volt
Amp
Ohm
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Control System - Modulator.
Over the next few screens you will see the
operation of the hydraulic modulator. The
solenoid drawn only represents 1 of the 4 in
the system. There is 1 solenoid plunger for each
separate wheel. Fluid flow through the solenoid
valve is determined by the solenoid plunger, the
position of which is determined by current
supplied by the ECU to the energising coil. The
3 plunger positions needed to control the system
are obtained in response to ECU outputs of 0A,
2A and 5A.
Solenoid Valve
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The ABS Regulator Unit
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Master Cylinder
Pump OFF
Solenoid Winding
Solenoid Plunger
ABS ECU
0A
Solenoid Current
Brake Calliper
When the output from the ECU is 0A the return
spring holds the plunger into position.
Wheel Sensor
Hydraulic Accumulator
Hydraulic Modulator - Normal operation ABS not
activated.
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Master Cylinder
Pump ON
Solenoid Winding
Solenoid Plunger
ABS ECU
5A
Solenoid Current
Brake Calliper
When 5A is applied from the ECU it is forced to
the upper end of its travel. ABS is in use.
Wheel Sensor
Hydraulic Accumulator
Hydraulic Modulator - Skid Sensed Pressure
Reduction
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Master Cylinder
Pump ON
Solenoid Winding
Solenoid Plunger
ABS ECU
2A
Solenoid Current
Brake Calliper
The weaker magnetic flux produced by 2A holds
the plunger half way. The ECU will increase
pressure again until a skid is detected.
Wheel Sensor
Hydraulic Accumulator
Hydraulic Modulator - Pressure Being Held Steady.
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Hydraulic Modulator
Master Cylinder
Control System (closed loop).
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brake pressure control unit
Hydraulic Modulator
Master Cylinder
Control System (closed loop).
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computes change of speed U
brake pressure control unit
Hydraulic Modulator
Master Cylinder
Control System (closed loop).
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controls pressure
computes change of speed U
C
brake pressure control unit
Hydraulic Modulator
Master Cylinder
Control System (closed loop).
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controls pressure
computes change of speed U
C
brake pressure control unit
Hydraulic Modulator
Master Cylinder
Control System (closed loop).
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ABS SYSTEMS - DELCO VI - GM Latest System
Block Diagram
30
K200
F38
15
F43
30
F20
15 -Ignition ON 30 - Battery Positive 31 -
Ground A 205 - Brake modulation F20 - Fuse F38 -
Fuse F43 - Fuse H5 - Tell brake system H26 - tell
tale ABS K50 - ABS ECU K61 -Engine ECU K200 ABS
relay M205 - ABS motor pack P17 - Wheel sensor
FL P18 - Wheel sensor FR P19 - Wheel sensor
RL P20 - Wheel sensor RR S8 - Brake light
switch WEG -Odometer signal Y205.1 - Solenoid
valve FR Y205.3 - Solenoid valve RL X13 -
Diagnose Y205.2 - Solenoid valve FL Y205.4 -
Solenoid valve RR
P17
K50
Y205.1 Y205.2 Y205.3 Y205.4
P18
P19
A 205
P20
M205
K61
S8
WEG
H5
31
H26
X13
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Traction Control
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TRACTION CONTROL
It has long been known that safety and vehicle
performance is improved if spinning of the road
wheels could be prevented under driving
conditions. When a wheel spins, traction is lost
and vehicle control is jeopardised. This control
problem arises because spinning of a rear wheel
causes the back of the vehicle to move sideways
and loss of adhesion at the front results in loss
of steering control. Since many vehicles are now
fitted with ABS, the speed sensors on each wheel
can also be used to signal when a wheel starts to
spin. The existence on the vehicle of this
sensing equipment means that it is a
comparatively small step to fit a TCS.
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TRACTION CONTROL - TCS

• There are 2 main additional requirements of a
  tractive
• control system
• throttle controller - varies the output of the
  engine.
• ECU - detects spin at any wheel and overcomes
  it by
• applying the brake on that wheel and
  simultaneously
• reduces engine power. Vehicles with an ABS system
  have a
• dual ABS traction control ECU.

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TRACTION CONTROL - TCS
Throttle Controller Engine torque is controlled
either by fitting an additional throttle
(electronically controlled) or using an actuator
on the main throttle. When an electronic
actuator controls the position of the throttle
the traditional mechanical linkage becomes
redundant so a drive by wire system is
employed. Vehicles fitted with this electronic
throttle control have the accelerator pedal
connected to a potentiometer.
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Throttle and Pedal Position Potentiometer
Operation The position sensor contains a
potentiometer or variable resistor. The variable
resistor has a power supply from the ECU (5
volts), connected at one end of the
resistor track, the other end connected to earth
via the ECU.
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Throttle and Pedal Position Potentiometer
Operation The throttle/pedal position sensor
contains a potentiometer or variable resistor.
The variable resistor has a power supply from the
ECU (5 volts), connected at one end of the
resistor track, the other end connected to earth
via the ECU.
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Throttle and Pedal Position Potentiometer
Operation A third terminal on the sensor
connects to wiper contact. The wiper sweeps
backwards and forwards along the resistance
track when the throttle/pedal is opened and
closed.
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Throttle and Pedal Position Potentiometer
Depending on the wiper position the voltage at
the wiper contact will vary. On most systems,
the voltage will rise as the throttle/pedal is
opened.
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Throttle and Pedal Position Potentiometer
Depending on the wiper position the voltage at
the wiper contact will vary. On most systems,
the voltage will rise as the throttle is opened.
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Throttle and Pedal Position Potentiometer
Depending on the wiper position the voltage at
the wiper contact will vary. On most systems,
the voltage will rise as the throttle is opened.
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Throttle and Pedal Position Potentiometer
The ECU monitors the signal voltage from the
third terminal and therefore has an exact
indication of throttle position. The ECU also
requires an indication that the throttle is at
idle. This may be achieved by having a set
voltage range of 0.5 to 0.7 volts when the
throttle is closed.
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Throttle and Pedal Position Potentiometer
Wth the multi plug connected, check the
following - power supply, normally 5 volts.
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Throttle and Pedal Position Potentiometer
Wth the multi plug connected, check the
following - power supply, normally 5 volts. -
zero volts on earth path (accept up to 0.1
volts).
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Throttle and Pedal Position Potentiometer
Wth the multi plug connected, check the
following - power supply, normally 5 volts. -
zero volts on earth path (accept up to 0.1
volts). - check signal voltage at centre
terminal. It should rise smoothly as throttle
is opened.
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Throttle and Pedal Position Potentiometer
If there is no power supply availiable or the
supply voltage is incorrect, then check wiring
from the sensor to the ECU. If the voltage on the
earth circuit is greater than 0.1 v, then check
for a high resistance or poor connection. If the
signal from the centre terminal jumps at all,
suspect a sensor fault and replace potentiometer.
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ROTARY ACTUATOR - Throttle Control
M
ECU controls rotary actuator clockwise /
anti-clockwise to control engine rpm/power.
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ROTARY ACTUATOR - Throttle Control
M
Vehicle near full throttle ECU detects spin and
activates actuator to close throttle.
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ROTARY ACTUATOR - Throttle Control
M
Vehicle near full throttle ECU detects spin and
activates actuator to close throttle and
simultaneously applies the brake/s ant the
spinning wheel.