this a new system in automotive to reduce the stopping distance and to improve the vehicle behavior in braking

1. ABS(Antilock Braking System)ABS(Antilock Braking System)
Prepared by:Prepared by:
Eng. Wael SaberEng. Wael Saber

3. ObjectivesObjectives
At the end of this presentation, you should be able to:At the end of this presentation, you should be able to:
 Explain the function of and purpose for ABS.Explain the function of and purpose for ABS.
 Describe the customer interface with ABS.Describe the customer interface with ABS.
 List the hydraulic and electronic components used for ABS.List the hydraulic and electronic components used for ABS.
 Explain the difference between the two types of wheelExplain the difference between the two types of wheel
speed sensors.speed sensors.
 Describe what happens in the “Pressure Hold” phase ofDescribe what happens in the “Pressure Hold” phase of
ABS control.ABS control.
 Describe what happens in the “Pressure Release” phase ofDescribe what happens in the “Pressure Release” phase of
ABS control.ABS control.
 Locate background and diagnostic information concerningLocate background and diagnostic information concerning
ABS.ABS.

4. A Brief HistoryA Brief History
1952: ABS for aircraft.1952: ABS for aircraft.
1978: ABS for the passenger cars.1978: ABS for the passenger cars.
1981: ABS for commercial vehicles.1981: ABS for commercial vehicles.
Initially ABS was extra equipment in top-endInitially ABS was extra equipment in top-end
vehicles.vehicles.
The immense improvements in driving safety led toThe immense improvements in driving safety led to
ABS becoming standard equipment in practically allABS becoming standard equipment in practically all
classes of vehicle – worldwide.classes of vehicle – worldwide.

5. The world’s first system for closed-loop control ofThe world’s first system for closed-loop control of
vehicle dynamics.vehicle dynamics.

6.  Experts estimate that wheel lock-up is responsibleExperts estimate that wheel lock-up is responsible
for about 10 % of all accidents.for about 10 % of all accidents.
 Up until the seventies, hitting the brakes too hardUp until the seventies, hitting the brakes too hard
could lead to an accident.could lead to an accident.
 The reason:The reason: When the coefficient of slip betweenWhen the coefficient of slip between
tires and road surface is too low, hitting the brakestires and road surface is too low, hitting the brakes
can cause wheel lock-up.can cause wheel lock-up.
 The vehicle is no longer steerable and goes into aThe vehicle is no longer steerable and goes into a
skid.skid.

7. AdvantagesAdvantages
Automatic, electronic regulation of brake pressureAutomatic, electronic regulation of brake pressure
Preventing wheel lock-upPreventing wheel lock-up
 Reduce the total braking distance as far as possible.Reduce the total braking distance as far as possible.
 Ability to steer the vehicle in an emergency braking situation.Ability to steer the vehicle in an emergency braking situation.
 Increase vehicle stability.Increase vehicle stability.
Reducing the danger of accidents when braking.Reducing the danger of accidents when braking.

8. Without ABSWithout ABS
““Hard to Steer”Hard to Steer”
With ABSWith ABS
““Perfect Steering”Perfect Steering”

9. Without ABSWithout ABS
With ABSWith ABS

10. Without ABSWithout ABS
““Instability”Instability”
With ABSWith ABS
““Stable (on-track)”Stable (on-track)”

11. Driving with ABSDriving with ABS
Driver applies brakes:Driver applies brakes:
If wheels do not approach lock-up, then ABS is not activated.If wheels do not approach lock-up, then ABS is not activated.
As vehicle is braked, ABS may be able to prevent wheel lock-As vehicle is braked, ABS may be able to prevent wheel lock-
up by simplyup by simply holding the brake fluid pressureholding the brake fluid pressure from going anyfrom going any
higher.higher.
If driver feels brake pedal pulsate, then ABS isIf driver feels brake pedal pulsate, then ABS is reducingreducing brakebrake
fluid pressure in order to insure that wheels continue rotate.fluid pressure in order to insure that wheels continue rotate.
This action may be accompanied by pump noise.This action may be accompanied by pump noise.

12. ComponentsComponents
Lines/Hoses
(ECU)

14. Electronic ComponentsElectronic Components
 Stop lamp switch (S9/1)Stop lamp switch (S9/1)
 Wheel speed sensors (L1-L4)Wheel speed sensors (L1-L4)
 VSS = Vehicle Speed SensorVSS = Vehicle Speed Sensor
 Electronic control unit (N47)Electronic control unit (N47)
 Hydraulic control unit (A7)Hydraulic control unit (A7)
 Return pump relay (K40)Return pump relay (K40)
 Malfunction Indicator LampMalfunction Indicator Lamp
Hydraulic ComponentsHydraulic Components
Brake calipers.Brake calipers.
Lines / hoses.Lines / hoses.
Hydraulic control unit.Hydraulic control unit.
Master cylinder.Master cylinder.

17.  Wheel speed sensors (L1-L4):Wheel speed sensors (L1-L4):
 Inductive (early vehicles).Inductive (early vehicles).
 Active (late model vehicles).Active (late model vehicles).

18. Inductive Wheel Speed SensorInductive Wheel Speed Sensor
 AC voltage is created when teeth moveAC voltage is created when teeth move
through the Magnetic field surrounding thethrough the Magnetic field surrounding the
sensorsensor

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

24. Normal Braking ModeNormal Braking Mode
 No wheel speed difference. PressureNo wheel speed difference. Pressure
created by driver operation of the mastercreated by driver operation of the master
cylinder.cylinder.

25. ABS Control Mode: “PressureABS Control Mode: “Pressure
Hold”Hold”
(Example shown - RF wheel)(Example shown - RF wheel)
 Vehicle Speed Signal indicates wheel isVehicle Speed Signal indicates wheel is
about to lock.about to lock.
 Pressure still applied, but can’tPressure still applied, but can’t increaseincrease
because ABS control module hasbecause ABS control module has
activated valve y8.activated valve y8.

27. ABS Control Mode: “PressureABS Control Mode: “Pressure
Release”Release”
ToTo reduce pressure atreduce pressure at locking wheel (thelocking wheel (the
wheel that has stopped spinning):wheel that has stopped spinning):
ABS control module:ABS control module:
•• Activates return pumpActivates return pump
•• Activates Valve y8 so no more pressureActivates Valve y8 so no more pressure
can be appliedcan be applied
••Activates valve y9 so pressure at brake canActivates valve y9 so pressure at brake can
be reducedbe reduced

30.  These valves can be pulsed very rapidly.These valves can be pulsed very rapidly.
You can feel this stage of operationYou can feel this stage of operation
through the brake pedal.through the brake pedal.

32. Thank You for listeningThank You for listening
With my best wishesWith my best wishes
 Any Questions?Any Questions?
 With foot on brake pedal, a pulsation willWith foot on brake pedal, a pulsation will
be felt.be felt.
 VSS = Vehicle Speed SensorVSS = Vehicle Speed Sensor