copyright © 2007 by nelson, a division of thomson canada limited. 49-1chapter 49 prepared by martin...

Chapter 49 Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 49-1

Prepared byMartin Restoule

Algonquin College

Antilock Brake, Antilock Brake, Traction Traction Control, and Control, and Stability Control Stability Control SystemsSystems

4949


ObjectivesObjectives

• Explain how antilock brake systems work to bring a vehicle to a controlled stop.

• Describe the differences between an integrated and a non-integrated antilock brake system.

• Briefly describe the major components of a two-wheel antilock brake system.

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• Briefly describe the major components of a four-wheel antilock brake system.

• Describe the operation of the major components of an antilock brake system.

• Describe the operation of the major components of automatic traction and stability control systems.

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• Explain the best procedure for finding ABS faults.

• List the precautions that should be followed whenever working on an antilock brake system.

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ABS FeaturesABS Features

• The ABS system pulses the brakes more rapidly than the driver can (up to 15 times per second).

• Pulsing the brakes prevents wheel lockup.

• Preventing wheel lockup provides for more stable stopping.

• Preventing wheel slip allows the wheels to turn as directed.

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A Common ABS SystemA Common ABS System

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Hydraulic ComponentsHydraulic Components

• Control valve assembly– Controls the release and application of

brake system pressure to the wheel brake assemblies.

• Booster pump– Provides pressurized hydraulic fluid for the

ABS system.

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• Booster/master cylinder assembly– Contains the

valves and pistons used to modulate hydraulic pressure during ABS operation.

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• Fluid accumulator– Stores fluid that is

removed from the wheel circuits during the ABS cycle.

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• Hydraulic control unit– Contains several components in one unit.

• Hydraulic valves– Control and direct hydraulic pressure.

• Solenoid valves• Main valve• Wheel circuit valves

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Electrical/Electronic ComponentsElectrical/Electronic Components

• Control module– Controls ABS

operation and monitors the system.

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• Brake pedal switch– Signals the control module when the brake

is applied.

• Data Link Connector (DLC)– Provides access to and/or control of vehicle

information.

• Lateral position sensor– Is used on some systems to monitor

sideways movement of the vehicle.

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• Pressure switch– Controls pump operation and the low

pressure warning lamp.

• Pressure differential switch– Sends a signal to the control module when

there is an undesirable difference of pressure at the wheel brake units.

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• Wheel speed sensors– Sends wheel speed

information to the ABS module.

– Is usually comprised of a magnet and a coil of wire and produces an AC signal.

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A Typical Four-Wheel ABS SystemA Typical Four-Wheel ABS System

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ABS TypesABS Types

• Integral– Combines the master cylinder, power

booster, and ABS hydraulic circuitry in one unit.

• Non-Integral– Uses a conventional power booster and

master cylinder.

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ABS System ChannelsABS System Channels

• One-channel system– Only modulates both rear brakes at the

same time.

• Three-channel system– Has individual circuits to each front wheel

and one circuit to both rear wheels.

• Four-channel system– Controls each wheel separately.

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ABS Operating ModesABS Operating Modes

• Pressure hold (retaining)– No additional pressure is allowed to reach

the brake.

• Pressure release (decrease)– Pressure is released so the wheel can turn.

• Pressure apply (increase)– Brake pressure is reapplied to the affected

brake.

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A Typical Traction Control SystemA Typical Traction Control System

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A Typical Traction Control SystemA Typical Traction Control System

• The technology and hardware of antilock braking systems is used to control tire traction and vehicle stability.

• Automatic traction control (ATC) system uses the ABS pump to apply the brakes when a drive wheel attempts to spin and lose traction.

• The system works best when only 1 drive wheel has good traction.

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Typical Stability Control SystemTypical Stability Control System

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Stability Control System OperationStability Control System Operation

• Like traction control systems, stability controls are based on and linked to the antilock brake system.

• On some vehicles the stability control system is also linked to the electronic suspension system.

• Stability control systems momentarily apply the brakes at any 1 wheel to correct oversteer or understeer.

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Desired Effects of Stability Control Desired Effects of Stability Control

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Service Safety PrecautionsService Safety Precautions

• Always use lines and hoses designed for ABS vehicles.

• Never use silicone brake fluid in an ABS system (Dot 3 is usually recommended).

• Always follow the proper bleeding procedure.

• Never open a bleeder screw with the system pressurized.

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Service Safety PrecautionsService Safety Precautions

• Never disconnect or reconnect electrical connectors with the ignition switch on.

• Do not install electronic accessories near any control module.

• Keep the wheel speed sensors clean and follow the recommended installation and adjustment procedures.

• Never use a hammer to install speed sensor toothed rings.

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Diagnostic TestsDiagnostic Tests

• Pre-diagnostic inspections and test drive

• Warning light symptom troubleshooting

• On-board ABS control module (trouble code) testing

• Individual trouble code and component testing

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Visual InspectionsVisual Inspections

• Check fluid level.• Inspect hoses,

lines, and fitting for leaks or damage.

• Inspect all brake components.

• Check for loose wheel bearings.

• Check outer CV joint alignment.

• Check tire tread depth.

• Check electrical connections for corrosion and damage.

• Inspect wheel sensors and wiring.

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Typical Wheel Speed Sensor Typical Wheel Speed Sensor WaveformWaveform

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SummarySummary

• DOT 3 is recommended for most antilock brake systems and some power brake systems.

• Modern antilock brake systems provide electronic/hydraulic pumping of the brakes up to 15 times per second.

• ABS systems are classified as integral and non-integral.

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SummarySummary

• Integrated antilock brake systems combine the master cylinder, hydraulic booster, and hydraulic circuitry in a single assembly.

• On a non-integrated ABS, the master cylinder and hydraulic valve unit are separate assemblies, and a vacuum boost is used.

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SummarySummary

• Automatic traction control (ATC) is a system that applies the brakes or cuts back engine power when a drive wheel attempts to spin and lose traction.

• Automatic stability systems correct oversteer and understeer by applying one wheel brake.

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SummarySummary

• A malfunction in the ABS system typically causes the electronic control module to shut off or inhibit the system.

• A loss of hydraulic fluid or power booster pressure will disable the antilock brake system.

copyright © 2007 by nelson, a division of thomson canada limited. 49-1chapter 49 prepared by martin...

Documents

wheel antilock brake

hydraulic valves control

antilock brake systems

wheel brake assemblies

common abs system

traction control

control module

stability control systems