Hydraulic ABS (H-ABS) & Hydraulic Power Brake (HPB)

Hydraulic ABS (H-ABS) &Hydraulic Power Brake (HPB)Section 2

HYDRAULICS ABS (H-ABS)OverviewMeritor WABCO Hydraulic Anti‑lock Braking System(ABS) is an electronic wheel speed monitoring andcontrol system used on medium-duty trucks, busesand motor home chassis equipped with a hydraulicbrake system.How Hydraulic ABS WorksABS wheel sensors detect wheel speeds. The sensorsgenerate signals that are transmitted to an ElectronicControl Unit (ECU). If the wheels start to lock, the ECUsignals the modulator assembly, a control valve assembly, to regulate the brake pressure of each lockingwheel.During an ABS stop, a solenoid valve in the modulatorassembly is rapidly pulsed; that is, it opens and closesseveral times to control the brake pressure. When thisoccurs, drivers may notice a pulsating of the brakepedal.XpresswayPlus.ArvinMeritor.com2- An ABS indicator lamp on the vehicle dash alerts thedriver to a possible system fault and provides blinkcode information to diagnose the system.NOTE:If the ABS indicator lamp comes on during normalvehicle operation, drivers may complete their trip, butare instructed to have their vehicles serviced as soonas possible.In the unlikely event of an ABS system malfunction,the ABS in the affected wheel will be disabled and willreturn to normal braking. The other sensed wheels willretain their ABS function.System LayoutA typical Meritor WABCO D version Hydraulic ABSsystem with a Cab-Mounted ECU is illustrated below.Contact Customer Care1-888-725-9355

h-abs System ComponentsELECTRONIC CONTROL UNITS (ECU)C VERSION HABSCAB MOUNTEDNEWSERVICE EXCHANGEPART NO. NO.S446 044 047 0S446 044 061 0S446 044 062 0S446 044 047 7S446 044 061 7S446 044 062 7CORECOREGROUP MD Version ECUsPartSERVICE EXCHANGENumber NO.S446 044 085 0S446 044 085 0S446 044 086 0S446 044 086 0CORECOREGROUP NO.ECU452ECU452XC3103XC3104CAB Mounted ECU 12-Volt4S/4MD Version ECUsPart service exchange core coreNUMBER NO.GROUP NO.S446 109 010 0S446 109 010 7ECU453XC3106Frame Mounted ECU 12-Volt 4S/4MContact Customer Care1-888-725-9355XpresswayPlus.ArvinMeritor.com2-

2h-abs System ComponentsMODULATOR ASSEMBLIES C Version Hydraulic ABS D Version Hydraulic ABSOEM modulator assemblies are sold with dry modulator valves. For aftermarket, Meritor WABCO sells only wet modulator valves (valves prefilled with brake fluid). To help you identify the proper replacement parts, we have included the OEM part numbers. OEM Dry modulator valveassemblies are listed WITHOUT the S suffix.NOTE: If the number of the valve you are replacing is for a dry valve, the ArvinMeritor customer service representative will provide thecorrect WET valve in its place.Replacement PartsC VersionHABS Modulator ValveModulator Assy. ModulatorBracket RemarksS478 407 011 0N/AN/AValve includes bracketS478 407 012 0N/AN/AValve includes bracket—D VERSIONHABS Modulator ValveXpresswayPlus.ArvinMeritor.com2- —Modulator Assy. ModulatorS478 407 353 2Replacement PartsBracket Remarks478 407 014 0S478 407 056 0S478 407 356 4S478 407 015 0S478 407 056 0S478 407 356 4478 407 016 0S478 407 056 0S478 407 358 4S478 407 357 4S478 407 018 0S478 407 060 0S478 901 352 4S478 407 019 0------------------ ------------------ S478 407 027 0S478 407 058 0S478 407 056 4S478 407 028 0------------------ ------------------ Replaced by S478 407 062 0478 407 033 0S478 407 060 0S478 901 352 4For aftermarket repl. assy. order part no.S478 407 018 0478 407 061 0S478 407 058 0S478 407 055 2For aftermarket repl. assy. order part no.S478 407 062 0S478 407 062 0S478 407 058 0S478 407 055 2For aftermarket repl. assy. order part no.S478 407 015 0Two brackets used in this assembly.Replaced by S478 407 062 0Contact Customer Care1-888-725-9355PB-01134 Revised 8-07

HYDRAULIC POWER BRAKE (hpb) Components1 IntroductionOverview1 IntroductionFigure 1.3MASTER CYLINDER ASSEMBLYMeritor WABCO’s Hydraulic Power Brake (HPB) is a braking andvehicle control system for Business Class trucks, Classes 4through 7, and buses that are equipped with hydraulic brakes.The HPB system provides the following functions. Full power brake performance Brake control functions including Anti-Lock Braking System(ABS), Automatic Traction Control (ATC) and Electronic Brakeforce Distribution (EBD) Optional parking brake controlSystem ComponentsThe HPB system consists of two main components — the HydraulicCompact Unit (HCU) and a dual circuit master cylinder. The HPBsystem is also available with an optional parking brake pressuresupply valve. Figure 1.1, Figure 1.2 and Figure 1.3.Figure 1.1HCU WITHOUT OPTIONAL POWERPARKING BRAKE SUPPLY VALVE4004475aFigure 1.3Hydraulic Compact UnitThe HCU consists of an electronic control unit, two independentelectric motors driving two pump systems, two accumulators, a dualcircuit fluid reservoir with integrated filters, pressure relief valves,solenoid valves and a dual circuit relay valve. The HCU is mounted tothe vehicle frame rail with two brackets. Figure 1.4. Two pump motors draw brake fluid from the reservoir topressurize the accumulators. The motors are not serviceable. Two gas-filled hydraulic accumulators store energy supplied bythe pumps. Accumulators are sealed at the factory and arenon-refillable. Accumulators may be replaced without replacingthe entire HCU.4004474bFigure 1.1Figure 1.2HCU WITH OPTIONAL POWER PARKINGBRAKE PRESSURE SUPPLY VALVE The ECU processes sensor signals and generates solenoid valvecommands to reduce, maintain or increase brake pressure forcontrol function. The ECU constantly monitors the pressure in theaccumulators, using one pressure sensor per brake circuit. TheECU may be replaced without replacing the complete HCU. The optional pressure supply valve controls the Spring-Applied/Hydraulic Released (SAHR) parking brake. The pressure supplyvalve is mounted on the HCU behind the accumulator. Thepressure supply valve may be replaced without replacing theentire HCU. The dual circuit HCU reservoir holds the hydraulic brake fluid.The reservoir may be replaced without replacing the entire HCU.4004474cFigure 1.2Meritor WABCO Maintenance Manual MM-0401 (Issued 12-04)Contact Customer -

HYDRAULIC POWER BRAKE (hpb) Components1 IntroductionFigure 1.4Figure 1.5HYDRAULIC COMPACT UNITWITHOUT PRESSURE SUPPLY VALVEMASTER CYLINDER ASSEMBLYMASTERCYLINDERRESERVOIRDUAL CIRCUITHCU RESERVOIRRESERVOIR CAPECUFOOT BRAKESWITCHFLUID LEVELSENSOR SWITCH4004477aFigure 1.5PUMPMOTORS (2)ACCUMULATORSWheel-End Sensors4004476aFigure 1.4Master Cylinder AssemblyThe dual circuit master cylinder with an integrated relay valveprovides the translation of brake pedal force into hydraulic brakingpressure, and sends the driver’s demand signal to the HCU.Figure 1.5.A Meritor WABCO wheel-end sensor is installed at each wheelwhose speed is to be monitored. These sensors generate electronicsignals which are sent to the ECU. A sensor spring clip holds thewheel speed sensor in place. Figure 1.6. The sensor and sensor clipmust be lubricated before installation and whenever wheel-endmaintenance is performed.Figure 1.6SENSORSPRINGCLIP The foot brake switch provides brake status to the ECU andeliminates the need for a brake light switch. The master cylinder reservoir holds the hydraulic brake fluid. The fluid sensor switch monitors fluid level in the master cylinderreservoir. The master cylinder reservoir and both switches may bereplaced without replacing the entire master cylinder. The master cylinder cap provided by Meritor WABCO contains aspecial gore material that allows the reservoir to breathe, andserves as a filter to help prevent contaminants from gettinginto the reservoir. This is the only cap approved for use withMeritor WABCO HPB. Replacement caps may be obtained fromMeritor WABCO.24004479aFigure 1.6Meritor WABCO Maintenance Manual MM-0401 (Issued 12-04)XpresswayPlus.ArvinMeritor.com2- WHEEL-ENDSENSORContact Customer Care1-888-725-9355

HYDRAULIC POWER BRAKE (hpb) Components1 IntroductionTOOLBOX SoftwareLow Pressure HoseTOOLBOX Software is a PC-based diagnostics program requiredto diagnose HPB system faults. For HPB, version 5.0 or higher isrequired. The program runs in Windows 98 or higher. TOOLBOX is available from SPX Service Solutions, 1-800-328-6657.Figure 1.7.This manual contains service information for a low pressure hosewhich is not produced by Meritor WABCO but is an integral part ofthe HPB system.How the HPB System WorksMeritor WABCO’s hydraulic power braking system provides theenergy required to actuate the brakes and control the electronicbrake force distribution (EBD), ABS and ATC functions. The HCU isactivated each time the ignition is turned on or whenever the driversteps on the brake pedal. If the system is equipped with the optionalpower park brake, the HCU also supplies the energy to release andcontrol the service and park brakes.Figure 1.7TOOLBOXSOFTWAREIncludes Spanish and French Versions for ABS and HABSTM MER I OC O R W A B TTOOLBOX ETDYO UN E EK N O WSOFTWARThe Meritor WABCO HPB system for trucks is illustrated inFigure 1.8. A complete HPB system layout, with hydraulic brakelines, appears in the Appendix.TOAWHPC-based diagnostics and troubleshooting for Meritor WABCO: Pneumatic ABS (D and E Versions) Trailer ABS (Easy-StopTMand Enhanced Easy-StopTM with PLC) Hydraulic ABS Hydraulic Power Brake (HPB) Electronic Leveling Valves for Tractors Electronic Leveling Valves for Trailers 1004690cFigure 1.7Figure 1.8HPB SYSTEM LAYOUTHCU RESERVOIRMASTERCYLINDERRESERVOIRHCU DERASSEMBLYACCUMULATORS (2)RELAYVALVESECUWHEEL-ENDSENSORS (4)FRONT AXLEREAR AXLE4004478aFigure 1.8Meritor WABCO Maintenance Manual MM-0401 (Issued 12-04)Contact Customer -

HYDRAULIC POWER BRAKE (hpb) ComponentsHydraulic Compact Unit (HCU) Assembly - with ECUS478 407 924 2 (NEW) S478 407 991 7 (Service Exchange)Hydraulic Compact Unit (HCU) Assembly - without ecus478 407 933 2 (new) s478 407 992 7 (Service Exchange) Replacement parts include the HCU assembly, ECU, reservoir, accumulators, pressure supply valve, parkingbrake switch, relay valve, and appropriate hardware kits. SAHR is not distributed by Meritor WABCO, pleasecontact the OEM for product details.ECU and reservoir may be purchased individually.Mounting bracket is not included with the replacement assembly.ComponentsHCUS478 407 122 0Electronic Control UnitS446 046 009 2HCU ReservoirS451 900 523 2HCU Bracket (front)S478 901 052 2HCU Bracket (rear)S478 901 053 2AccumulatorS458 501 026 1ReservoirS451 900 523 2Relay ValveS478 407 930 2 (no ATC) orRelay ValveS478 407 929 2 (with ATC)PumpS478 905 152 2Electronic Control Unit (ECU)Replacement KitsNEW PARTNO.SERVICEEXCHANGE NO.ECU Replacement KitDESCRIPTIONCOREGROUPCORENO.ECU455XC3123ECU replacement kit ,ABS with ATCECU replacement kit,ABS onlyS446 046 920 2S446 046 990 7Kits contains ECU, 2pressure sensor sealsand 4 screwsServices446 046 009 2ECU Hardware KitKit contains twopressure seals andfour screws.S446 046 921 2XpresswayPlus.ArvinMeritor.com2- Services446 046 009 2Contact Customer Care1-888-725-9355

HYDRAULIC POWER BRAKE (hpb) ComponentsHCU Reservoir Replacement KitsPART NO.HCU Reservoir Replacement KitS451 900 922 2APPLICATION INFORMATIONREMARKSKit contains HCU reservoir, fourscrews, reservoir plug and fourrubber grommets.Services451 900 531 2Rubber Grommet KitS451 900 923 2Kit contains four rubbergrommets.Accumulator Replacement KitsAccumulator Replacement KitPART NO.S458 501 924 2APPLICATION INFORMATIONREMARKSKit contains two accumulatorslabeled with warning statementand two O-rings.Services458 501 019 2Accumulator O-ring KitS458 501 923 2Kit contains twoO-rings.Pressure Supply Valve Replacement KitsPressure Supply Valve Replacement KitPART NO.S476 901 920 2APPLICATION INFORMATIONKit includes solenoid valve with coil, O-ring and nut.Coil Kit for Pressure Supply ValveS472 879 920 2Contact Customer Care1-888-725-9355Kit contains coil, nut and O-ring.XpresswayPlus.ArvinMeritor.com2-