copyright © 2007 by nelson, a division of thomson canada limited. 49-1chapter 49 prepared by martin...
TRANSCRIPT
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
Chapter 49 Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 49-2
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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Chapter 49 Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 49-3
ObjectivesObjectives
• 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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ObjectivesObjectives
• Explain the best procedure for finding ABS faults.
• List the precautions that should be followed whenever working on an antilock brake system.
continued…
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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.
continued…
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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.
continued…
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Hydraulic ComponentsHydraulic Components
• Booster/master cylinder assembly– Contains the
valves and pistons used to modulate hydraulic pressure during ABS operation.
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Hydraulic ComponentsHydraulic Components
• Fluid accumulator– Stores fluid that is
removed from the wheel circuits during the ABS cycle.
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Hydraulic ComponentsHydraulic Components
• 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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Electrical/Electronic ComponentsElectrical/Electronic Components
• 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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Electrical/Electronic ComponentsElectrical/Electronic Components
• 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.
continued…
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Electrical/Electronic ComponentsElectrical/Electronic Components
• 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.
continued…
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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.
continued…
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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.
continued…
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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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Chapter 49 Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 49-31
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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Chapter 49 Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 49-32
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.