ABS(Antilock Braking ABS(Antilock Braking System) System)

Prepared by:Prepared by:

Eng.\ Wael Eng.\ Wael SaberSaber

ObjectiObjectivesves

At the end of this presentation, you should be able At the end of this presentation, you should be able to: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 List the hydraulic and electronic components used for

ABS.ABS. Explain the difference between the two types of wheel Explain the difference between the two types of wheel

speed sensors.speed sensors. Describe what happens in the “Pressure Hold” phase Describe what happens in the “Pressure Hold” phase

of ABS control.of ABS control. Describe what happens in the “Pressure Release” Describe what happens in the “Pressure Release”

phase of ABS control.phase of ABS control. Locate background and diagnostic information Locate background and diagnostic information

concerning ABS.concerning ABS.

A Brief HistoryA Brief History1952: 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-end Initially ABS was extra equipment in top-end vehicles.vehicles.

The immense improvements in driving safety The immense improvements in driving safety led to ABS becoming standard equipment in led to ABS becoming standard equipment in practically all classes of vehicle – worldwide.practically all classes of vehicle – worldwide.

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

Experts estimate that wheel lock-up is Experts estimate that wheel lock-up is responsible for about 10 % of all accidents.responsible for about 10 % of all accidents.

Up until the seventies, hitting the brakes too Up until the seventies, hitting the brakes too hard could lead to an accident.hard could lead to an accident.

The reason: The reason: When the coefficient of slip When the coefficient of slip between tires and road surface is too low, between tires and road surface is too low, hitting the brakes can cause wheel lock-up.hitting the brakes can cause wheel lock-up.

The vehicle is no longer steerable and goes The vehicle is no longer steerable and goes into a skid.into a skid.

AdvantagesAdvantagesAutomatic, 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 Ability to steer the vehicle in an emergency braking situation.situation.

Increase vehicle stability.Increase vehicle stability.

Reducing the danger of accidents when braking.Reducing the danger of accidents when braking.

Without Without ABSABS

““Hard to Steer”Hard to Steer”With ABSWith ABS

““Perfect Steering”Perfect Steering”

Without Without ABSABS

With ABSWith ABS

Without Without ABSABS

““Instability”Instability”With ABSWith ABS

““Stable (on-track)”Stable (on-track)”

Driving with Driving with ABSABS

Driver applies brakes:Driver applies brakes:

If wheels do not approach lock-up, then ABS is not If wheels do not approach lock-up, then ABS is not activated.activated.

As vehicle is braked, ABS may be able to prevent As vehicle is braked, ABS may be able to prevent wheel lock-up by simply wheel lock-up by simply holding the brake fluid holding the brake fluid pressure pressure from going any higher. from going any higher.

If driver feels brake pedal pulsate, then ABS is If driver feels brake pedal pulsate, then ABS is reducing reducing brake fluid pressure in order to insure that brake fluid pressure in order to insure that wheels continue rotate. This action may be wheels continue rotate. This action may be accompanied by pump noise.accompanied by pump noise.

ComponComponentsents

Lines/Hoses

(ECU)

Electronic Electronic ComponentsComponents

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 Hydraulic ComponentsComponents

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

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

Inductive Wheel Speed Inductive Wheel Speed SensorSensor

AC voltage is created when teeth AC voltage is created when teeth move through the Magnetic field move through the Magnetic field surrounding the sensorsurrounding the sensor

Active Wheel Speed SensorActive Wheel Speed Sensor

A newer version sensor:A newer version sensor: Magnetic field near sensor Magnetic field near sensor alternates N-alternates N-

S-N…S-N… Sensor is a Sensor is a switch with voltage supplied switch with voltage supplied

to it.to it. A DC square wave is created as switch A DC square wave is created as switch

is turned on and off.is turned on and off. Frequency increases with wheel speed.Frequency increases with wheel speed.

Normal Braking ModeNormal Braking Mode

No wheel speed difference. Pressure No wheel speed difference. Pressure created by driver operation of the created by driver operation of the master cylinder.master cylinder.

ABS Control Mode: ABS Control Mode: “Pressure Hold”“Pressure Hold”

(Example shown - RF (Example shown - RF wheel)wheel) Vehicle Speed Signal indicates wheel Vehicle Speed Signal indicates wheel

is about to lock.is about to lock. Pressure still applied, but can’t Pressure still applied, but can’t

increase increase because ABS control module because ABS control module has activated valve y8.has activated valve y8.

ABS Control Mode: ABS Control Mode: “Pressure Release”“Pressure Release”

To To reduce pressure at reduce pressure at locking wheel (the locking 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 Activates valve y9 so pressure at brake can be reducedcan be reduced

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

Thank You for listeningThank You for listeningWith my best wishesWith my best wishes

Any Questions?Any Questions?

With foot on brake pedal, a pulsation With foot on brake pedal, a pulsation will be felt.will be felt.

VSS = Vehicle Speed SensorVSS = Vehicle Speed Sensor