Automotive Technology

y Chapter Objectives Explain how antilock brake systems work to bring a vehicle to a controlled stop.Explain how antilock brake systems work to bring a vehicle to a controlled stop. Describe the differences between an integrated and a nonintegrated ABS.Describe the differences between an integrated and a nonintegrated ABS. Briefly describe the major components of a two-wheel antilock brake system.Briefly describe the major components of a two-wheel antilock brake system. Briefly describe the major components of a four-wheel antilock brake system.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 an antilock brake system. Describe the operation of the major components of automatic traction and stability control systems.Describe the operation of the major components of automatic traction and stability control systems. Explain the best procedure for finding ABS faults.Explain the best procedure for finding ABS faults. List the precautions that should be followed whenever working on an ABS.List the precautions that should be followed whenever working on an ABS.

n First introduced on 1954 Lincoln n 1978 Mercedes made first ABS that worked well n Can’t defy the law of nature or physics n Reduces distance to stop n Most effective on dry concrete

n Antilock Brakes

n Normal driving will not notice difference n Anti-lock Event n Unrestricted tire rotation is 0% slip n Tire locked up is 100% slip n When we have 100% slip, the tire loses traction and vehicle motion changes into heat energy. (not very effective!)

Maximum Braking Force Between 10 and 20 Percent Slip WET CONCRETE

n Locked wheels prevent directional control n Wheel lock up can be prevented by limiting brake pressure to a point just short of lockup.

Pressure ModulationPressure Modulation Pedal FeelPedal Feel

n Diagonally Split System Controls Two Hydraulic circuits (2 channel)Controls Two Hydraulic circuits (2 channel) n Front/Rear Split System Controls Three Hydraulic circuit (3 channel)Controls Three Hydraulic circuit (3 channel) n Full Four Wheel System Controls Four Hydraulic Circuits (4 channel) (page 203) Usually intergrated with traction controlControls Four Hydraulic Circuits (4 channel) (page 203) Usually intergrated with traction control Page 228C

n Normal operation when in conventional mode (if warning light, disables ABS) n Heavy braking causes hydraulic pressure modulation (Pedal Feel) n Integrated System (Combined parts)227C n Non-Integrated System (Separate Parts) n ABS operates independently of base system ABS Operation/Modes Description - Page 226C - 227C

ELECTRONIC CONTROL UNIT n Inputs and Outputs (228C) n Some ABS ECU’s have dual boards n Controls HCU n Full Diagnostics n Controls Warning Lights n Can control each wheel brake independently. (four channel) Most are three channel n Mechanical Noises

HYDRAULIC CONTROL UNIT (HCU) Page261C Teves Mk IV

Hydraulic Control Unit (Integral)

Hydraulic Control Unit (Non-Integral)

ACCUMULATOR Stores high pressure brake fluid from Pump Supplies high pressure fluid in ABS mode 2800 to 3400 PSI Must bleed before replacement or service 257C

PUMP AND MOTOR n Motor is 12V Electric (235C) n Works independently of the base brake system n Pressurizes brake fluid up to 2800 psi. n Turns on when ever pressure drops below a predetermined level n Some are replaceable seperately

WHEEL SPEED SENSORS n Detects rotation of wheel n Permanent magnet type n 3 Parts Permanent magnetPermanent magnet CoilCoil YokeYoke n Induces AC voltage varied frequency 229C to 231C

RELUCTOR (Tone Ring)

ELECTRICAL COMPONENTS n HCU SOLENOID RELAY Used on some systemsUsed on some systems n HCU MOTOR RELAY n MAIN POWER RELAY n PRESSURE SWITCHES (430L) Generally will turn on Anti-lock Warning lightGenerally will turn on Anti-lock Warning light Pg 235C

PUMP MOTOR RELAY

B+ Cruise Control TCC Brake Lights CHMSLABS Switch Operation Or Power Relay

SELF DIAGNOSTICS n Each time Ignition is turned on ABS does a self diagnostic check. n Some systems do check while car is moving. n Indicator Lamp Operation

n ABS Components Hydraulic ComponentsHydraulic Components –Accumulator –Valve Block

–Booster pump –Booster/master cylinder assembly Accumulator

n Other Hydraulic Components –Fluid accumulators –Hydraulic control unit –Main valve –Modulator unit –Solenoid valve –Valve block assembly –Wheel circuit valves

n Electrical/Electronic Components –ABS control module –Brake pedal sensor –Data link connector (DLC) –Diagnostic trouble code (DTC) –Indicator lights –Lateral acceleration sensor –Pressure switch –Pressure differential switch –Relays –Wheel speed sensor –Toothed ring

Four-Wheel Systems (Integral)Four-Wheel Systems (Integral) ABS System – No Braking

Four-Wheel Systems (Integral)Four-Wheel Systems (Integral) ABS System – ABS in Operation

GM ABS-VIGM ABS-VI Add on SystemAdd on System ElectromagneticElectromagnetic Fast acting solenoid valvesFast acting solenoid valves Screw PlungersScrew Plungers 4 Channel4 Channel Can cycle 7 times per secondCan cycle 7 times per second 5 Separate Diagnostic modes5 Separate Diagnostic modes

General Motors' Electromagnetic Antilock Brake SystemsGeneral Motors' Electromagnetic Antilock Brake Systems

Automatic Traction ControlAutomatic Traction Control Integration with Traction ControlIntegration with Traction Control

n Automatic Stability Control

n Antilock Brake System Service Safety PrecautionsSafety Precautions Relieving Accumulator PressureRelieving Accumulator Pressure

n Diagnosis and Testing Pre-Diagnostic InspectionPre-Diagnostic Inspection Visual InspectionVisual Inspection Test DriveTest Drive Self-DiagnosisSelf-Diagnosis Testers and Scanning ToolsTesters and Scanning Tools Testing Components with ABS Scan ToolsTesting Components with ABS Scan Tools

Testing Components with a Lab ScopeTesting Components with a Lab Scope

Component ReplacementComponent Replacement –Wheel speed sensor service –Brake system bleeding