Systems And Components In Commercial Vehicles Edition 1998© Copyright WABCO 1998WABCOFahrzeugbremsenA Division ofWABCO Standard GmbHThe right of amendment is reservedTable of ContentsPage Operation of Air Braking Systems (4)1. MotorVehiclesBraking System (6)Components of the Motor Vehicle’s Braking System (7)2. TrailersBraking System (62)Equipment For Trailer Braking Systems (64)3.Anti-Lock Braking System (ABS) (79)4.Sustained-Action Braking Systems On Motor Vehicles (89)5. EBS - Elektronisch geregeltes Bremssystem (93)6.Air Suspension Systems and ECAS(Electronically Controlled Air Suspension) (105)7.Clutch Servo (117)8.Air Braking Systems InAgricultural Vehicles (121)9.ETS-Elektronic Door Control SystemFor Motor Coaches (131)10.Installation Of Pipes And Screw Unions (139)11.Index (151)Operation of Air Braking Systems1. Compressed Air Supply The compressed air supplied by the com-pressor (1) flows to the air dryer (3) via the unloader (2) which automatically con-trols the pressure within the system with-in a range of between 7.2 and 8.1 bar, for instance. In the air dryer, the water va-pour in the air is extracted and expelled through the air dryer’s vent. The dried air then flows to the quadruple-circuit pro-tection valve (4) which, if one or several circuits are defective, secures the intact circuits against any loss in pressure. Within the service braking circuits I and II, the air supply from the reservoirs (6 and 7) flows to the brake valve (15). In Circuit III the air supply from the reservoir (5) flows through the 2/2-way valve which is integrated in the trailer control valve (17) to the automatic hose coupling (11) and on to the check valve (13), the hand brake valve (16) and the relay valve (20) into the spring-loaded portion of the Tris-top spring brake actuators (19). Circuit IV supplies air to any ancillary consumers, in this case an exhaust brake.The trailer’s braking system receives compressed air through the hose cou-pling (11) with its supply hose connected. This air then passes the line filter (25)and the relay emergency valve (27) be-fore reaching the reservoir (28) and alsoflows to the supply ports of the ABS relayvalves (38).2. Operation:2.1 Service Braking SystemWhen the brake valve (15) is actuated,compressed air flows via the ABS sole-noid control valve (39) into the brakechambers (14) of the front axle and to theload-sensing valve (18). This valve re-verses and the air flows via the ABS so-lenoid control valve (40) into the servicebrake portion (brake chambers) of theTristop spring brake actuators (19). Thepressure in the brake cylinders generat-ing the force required for the wheel brakedepends on the amount of force appliedto the brake valve, and on the load car-ried on the vehicle. This brake pressureis controlled by the load-sensing valve(18) which is connected to the rear axleby means of a linkage. Any change in thedistance between the vehicle’s chassisand its axle caused by loading or unload-ing the vehicle causes the brake pres-sure to be continuously adjusted. At thesame time, via a pilot line, the load-emptyvalve integrated in the brake valve is af-fected by the load-sensing valve. Thusthe brake pressure on the front axle isalso adjusted to the load carried on thevehicle (mostly on lorries).The trailer control valve (17) actuated bythe two service braking circuits pressuriz-es the pilot connection of the relay emer-gency valve (27) after passing the hosecoupling (12) and the connecting “con-trol“ hose. The air supply from the air res-ervoir (28) is thus allowed to passthrough the relay-emergency valve, thetrailer release valve (32), the adaptervalve (33) and on to the load-sensingvalve (34) and the ABS relay valve (37).The relay valve (37) is actuated by theload-sensing valve (34) and the com-pressed air flows to the brake chambers(29) on the front axle. The ABS relayvalves (38) are actuated by the load-sensing valve (35), and the compressedair is allowed to pass to the brake cham-bers (30 and 31). The service pressureon the trailer, which is similar to the out-put pressure from the towing vehicle, isautomatically adjusted by the load-sens-ing valves (34 and 35) for the load carriedon the trailer. In order to prevent overb-raking of the wheel brake on the frontaxle in the partial-braking range, theservice pressure is reduced by the adapt-er valve (33). The ABS relay valves (onthe trailer) and the ABS solenoid control valves (on the towing vehicle) are used to control (pressure increase, pressure hold, pressure release) the brake cylin-ders. If these valves are activated by the ABS ECU (36 or 41), this control process is achieved regardless of the pressure al-lowed to pass by the brake valve or the relay emergency valve.When they are not needed (solenoids are dead), the valves operate as relay valves and achieve a faster increase or de-crease of the pressure for the brake cyl-inders.2.2Parking Braking System When the hand brake valve (16) is actu-ated and locked, the spring-loaded por-tions of the Tristop spring brake actua-tors (19) are exhausted fully. The force needed for the wheel brake is now pro-vided by the heavily preloaded springs of the Tristop spring brake actuators. At the same time, the pressure in the line lead-ing from the hand brake valve (16) to the trailer control valve (17) is reduced. Brak-ing of the trailer commences by the pres-sure increasing in the connecting ‘supply’hose. Since the guideline of the Council of the European Communities (RREG) that a tractor-trailer combination must be held by the motor vehicle alone, the pres-sure in the trailer’s braking system can bereleased by moving the hand brake leverinto its ‘control’ position. This permits theparking braking system to be examinedas to whether it fulfills the provisions ofthe RREG.2.3 Auxiliary Braking SystemDue to sensitive graduation of the handbrake valve (16) the lorry can be brakedby means of the spring-loaded portionseven if the service braking systems I andII have failed. The brake force for thewheel brake is produced by the force ofthe preloaded springs of the Tristopspring brake actuators (19) as describedunder ‘Parking Braking System’ althoughthe spring-loaded portions are not ex-hausted fully but only to the extent re-quired for the braking performance.3. Automatic Braking of theTrailerIn the event of the connecting ‘supply’line breaking, the pressure will drop rap-idly and the relay emergency valve (27)will cause full application of the trailer’sbrakes. In the event of the connecting‘control’ line breaking, the 2/2-way valveintegrated in the trailer control valve (17)will, when the service braking system isactuated, throttle the passage of the sup-ply line leading to the hose coupling (11)to such an extent that the rupture of thesupply line causes a rapid drop in pres-sure in the supply line and the relayemergency valve (27) causes the trailerto be braked automatically within the le-gally stipulated time of no more than 2seconds. The check valve (13) securesthe parking braking system against anyinadvertent actuation if the pressuredrops in the supply line leading to thetrailer.4. ABS ComponentsThe motor vehicle usually has three tell-tale lamps (ASR having one additionallamp) fitted for indicating functions andfor continuously monitoring the system. Italso has a relay, an information moduleand an ABS socket (24).After actuating the driving switch, the yel-low telltale lamp will come on if the trailerhas no ABS or if the connection has notbeen established. The red lamp will go offwhen the vehicle exceeds a speed of ap-prox. 7 k.p.h. and the safety circuit of theABS electronics has not detected an er-ror.Air braking system with ABS/ASR (4S/4M)Legend:Pos.1Compressor2Air dryer with combined unloader3Four circuit protection valve 4Air reservoir 5Clamps6Test coupling 7Drain valve 8Check valve9Brake valve with integralauto load proportioning valve 10Hand control valve with trailer control 11Relay valve 12Piston cylinder 13Brake chamber14ASR-Control cylinder153/2 Solenoid valve 16Tristop-Brake actuator 17Quick release valve 18Load sensing valve 19Knuckle joint20Trailer control valve 21Hose coupling, supply 22Hose coupling, control 23Two-Way valve 24ABS Warning lamp 25ABS Info lamp 26ABS-socket27Sensor extension cable 28Solenoid cable 29Socket30Sensor braket31Sensor with cable 32Pole wheel33ABS-Solenoid valve 34Electronic control unit 35Info module 36Pressure switch 37Proportional valve383/2 Directional control valve12381234,5714379171333282729,3031,3224253435181915626112316212220108361.Components Of The Motor Vehicle’s Braking SystemAir Intake Filters1.Moist Air FilterPurpose:To prevent impurities from the air getting into the compressor (by using suction fil-ters) or into the vents of compressed air equipment (by using vent filters); they also serve to muffle the noise caused by the intake of air or by blowing it off.Operation:Moist air filters (for normal operating con-ditions). The air is taken in through an opening in the cap, flows through the fil-ter medium where it is cleaned and then flows on to the air intake of the compres-sor.Oil Bath Air CleanerOperation:Oil bath air cleaner (for air containing a large mount of dust)The air is taken in through the sieve plate below the cap and the central pipe, and then passed across the surface of the oil where any dust particles can settle. From the surface of the oil, the air is pushed upward, flows through a filter package which retains any impurities which may still be contained in the air and any oil particles carried over before reaching the air intake of the compressor.Moist Air Filter432 600 . . . 0 to 432 607 . . . 0Oil Bath Air Cleaner432 693 . . . 0 to 432 699 . . . 0Purpose:Production of compressed air for road vehicles and static systems. Operation:The pulley on the end of the crankshaft is rotated by a vee-belt driven off the vehi-cle’s engine. This rotation causes the connecting rods to to move the pistons. As the piston travels downwards clean air from either the engine air cleaner or the moist air filter (or alternatively an oil bath air cleaner) is drawn in trough the inlet valve. As the piston moves up-wards, the inlet valve closes, and air is pumped through the delivery valve into the the reservoir.The type of lubrication depends on the construction of the compressor, and can be splash or pressure fed.Single Cylinder Air Compressor 411 1 . . . . . 0 and 911 . . .. . . 0Twin CylinderAir Compressor 411 5 . . . . . 0 and 911 5 . . . . . 0Air Cleaner1.Purpose:To clean the air delivered by the com-pressor and to precipitate the humidity it contains.Operation:The air entering at port 1 flows through annular gap A into Chamber B. As it passes through the gap A, the air cools and some of the water vapour it contains will condensate. The air then flows through the filter (a) to Port 2.At the same time, the pressure in Cham-ber B opens the inlet (3) of the valve body (d) and the condensate runs through the filter (f) into Chamber C. As the pressure in Chamber B falls, the inlet(3) closes and the outlet (b) opens. The condensate is now blown outside by the pressure in Chamber C. When the pres-sures in Chambers B and C are bal-anced, outlet (b) closes.Pin (C) can be used to check whether the automatic drain valve is working proper-ly.Air Cleaner 432 511 . . . 0Air Dryer432 410 . . . 0 and432 420 . . . 0Purpose:Drying of the compressed air supplied by the compressor by extracting the mois-ture present in the air. This is effected by a progress of cold regenerated adsorp-tion drying where the air compressed by the compressor is led through granulates (adsorbens) capable of adsorbing the moisture contained in the air. Operation:Variant 1 (Control Via Separate Un-loader Valve 432 420 ... 0)In the feed phase, the compressed air supplied by the compressor flows via Port 1 into Chamber A. Here the conden-sate caused by the reduction in tempera-ture will collect, reaching Outlet (e) via Duct C.Via Fine Filter (g) integrated in the car-tridge, and via Annulus (h), the air will reach the upper side of Desiccant Car-trige (b), being cooled in the process, and further condensate will precipitate. Moisture is extracted from the air as it passes through Granulate (a) this mois-ture is absorbed by the surface and the fine ducts [diameter: 4 x 106 m = 4Å(Angström)] of the extremely porousgranulate.Since the oil molecules are more than 4Åin size they cannot enter the fine ducts ofthe granulates. This makes the granulaterobust. The steam portion of the oil is notadsorbed. The dried air reaches the airreservoirs via Check Valve (c) and Port21. At the same time, the dried air alsoreaches the re-generation reservoir viathrottling port and Port 22.When cut-out pressure in the system isreached, Chamber B is pressurized fromthe unloader valve via Port 4. Piston (d)moves downwards, opening Outlet (e).The air, the condensate plus any impuri-ties and oil carbon from Chamber A willbe emitted via Duct C and Outlet (e).When cut-in pressure at the unloadervalve is reached, Chamber B is ventedonce again. Outlet (e) closes and the dry-ing process will commence as describedabove.Any malfunction due to icing in extremeconditions in the area of Piston (d) canbe prevented by fitting a Heating Car-tridge (f) which will switch on at tempera-tures below 6°C and switch off againwhen the temperature reaches approx.30°C.Variant 2 (Control Via Integral Unload-er Valve 432 410 ... 0)The process of drying the air is as de-scribed under Variant 1 In this version,however, the cut-out pressure will reachChamber D via Bore (l), acting on Dia-phragm (m). After overcoming the springresistance, Inlet (n) will open, and Piston(d), now pressurized, will open Outlet (e).The air supplied by the compressor willnow be emitted via Chamber A, Duct Cand Vent 3. Piston (d) also acts as apressure relief valve. In the event of anyexcess pressure, Piston (d) will auto-matically open Outlet (e). If, due to airconsumption, the supply pressure in thesystem falls to a value below cut-in pres-sure, Inlet (n) will close and the pressurefrom Chamber B will be reduced via theunloader valve's vent. Outlet (e) willclose and the drying process will com-mence once again.432 420 432 410Air Dryer 1.Air Dryer With Return-Flow Limiting Valve432 413 . . . 0 and432 415 . . . 0The single-chamber air dryers from this series have an integrated return-flow lim-iting valve which permits the required amount of air to be taken from the main reservoir provided the multiple-circuit protection valve permits a return flow. Thus no separate regenerating reservoir is required.Operation:Variant 1 (Control Via Separate Un-loader Valve432 413 ... 0)In the delivery phase the compressed air supplied by the compressor flows through Port 1, opens the check valve (i) and flows into Chamber A. Due to the drop in temperature, condensation water collects there which reaches the outlet (e) through Duct C.The air is dried as described under 432 420. At the same time, dried air also flows into Chamber E, pressurizing dia-phragm (o). This arches towards the right, releasing the passage between Chambers E and G via Throttling Port (s). The air supply also reaches Chamber H via Filter (l), pressurizing Valve (q). Once the force of the pressure spring, preset by means of Screw (r), has been over-come, Valve (q) is lifted. The air supplywill now reach Chamber F, acting on theother side of the diaphragm (o) with aslightly lower pressure in keeping withthe retention of Valve (q).When the cut-off pressure within the sys-tem has been reached, Chamber B ispressurized by the unloader via Port 4.The piston (d) moves downwards andopens the outlet (e). The check valve (i)closes the passage to Port 1 and the airfrom Chamber A flows through Duct Cand is emitted to atmosphere at the outlet(e).Due to the drop in pressure in ChamberG, the check valve (c) closes. The air tobe regenerated is now taken from the airreservoirs, which is why a multiple-circuitprotection valve must permit its returnflow. The air supply at Port 21 flowsthrough Chamber E, the throttling port (s)where it expands, on into Chamber Gand thus to the underside of the granu-late cartridge (b).As it passes through the granulate car-tridge (b) in an upward direction, the hu-midity on the surface of the granulate (a)is taken up by the air and emitted to at-mosphere at Vent 3 after passing Duct Cand the opened outlet (e). The return flowis completed when the pressure on theleft of the diaphragm (q) has been re-duced to a point where it reaches its clos-ing position.When the cut-in pressure at the unloaderis reached, the pressure in Chamber B isreduced once again. The outlet (e) clos-es and the drying process starts again asdescribed above. Outlet 31 also has asafety valve for the pressure side.Variant 2 (Control Via Integral Unload-er Valve 432 415 ... 0)In this variant, the cut-off pressure reach-es Chamber J via the connecting holeinto Chamber J and acts on the dia-phragm (m). After the spring force hasbeen overcome, the inlet (n) opens andthe piston (d) which is now pressurizedopens the outlet (e).The air delivered by the compressor nowflows through Chamber A, Duct C and isemitted to atmosphere at Vent 3. The pis-ton (d) at the same time acts as a popvalve. When the pressure is excessive,the piston (d) automatically opens theoutlet (e).If air consumption causes the supplypressure within the system to fall belowthe cut-in pressure, the inlet (n) closesand the pressure from Chamber B is re-duced through the vent of the unloadervalve. The outlet (e) closes and the dry-ing process begins again.432 413 432 415Twin Chamber Air Dryer 432 431 . . . 0 and432 432 . . . 0Operation:a) Control without Integral Un-loader ValveThe compressed air supplied by the compressor flows to Bore E via Port 1. Due to a reduction in temperature, con-densate may form at Bore E, reaching Idling Control Valve (m) via Bore L. From Bore E, the compressed air will pass Valve (k), enter Chamber B, and reach the upper side of Desiccant Cartridge (c) via Fine Filter (e) integrated into the car-tridge, and via Annulus A.Through Sieve Plate (a), the pre-cleaned compressed air will pass downwards through Granulate (b) sewn into a filter bag in Cartridge (c), reaching Bore G via Sieve Plate (d) and Check Valve (f).As the air passes through Granulate (b), the inherent moisture is retained by the extremely porous granulate. From Bore G, the compressed air reaches the air reservoirs through Check Valve (g) and via Port 2.Through the throttling port of Valves (fand p) designed according to the sweptvolume of the compressor used, part ofthe dried compressed air from Bore Gwill reach the underside of Cartridge (s),passing Granulate (r) in an upward direc-tion (backflush). In this process, themoisture adhering to the fine ducts of theextremely porous Granulate (r) is takenup by the dried air and reaches Vent 3via Annulus K, Chamber H and past theopen rear side of Valve (o).The additional Charging Valve (h) en-sures that Control Valves (k and o) donot switch over when the system is filledinitially. Valve (h) will not open until asupply pressure of > 5 bar has beenreached at Port 2, permitting com-pressed air to reach Chamber C. If thetimeswitch element integrated in the so-lenoid valve then opens the current sup-ply to Trip Coil (j), Armature (i) will be at-tracted. Compressed air from ChamberC will now flow into ChamberD and, viaBore F, into Chamber M, moving the con-trol valves against the spring force intotheir end positions on the left.The passage from Bore E to Chamber Bis closed. The compressed air present inChamber B will now be emitted at Port 3after passing by the open rear side ofControl Valve (k) and going through BoreN. Check Valve (g) will close and thepressure in the system continues to beensured. As a consequence of the pres-sure reduction in Chamber B, CheckValve (f) will also close.The compressed air supplied by thecompressor will now flow from Bore Ethrough Chamber H, Annulus K andthrough Granulate (r) of Cartridge (s).The drying process of the compressedair is as described before. After Valve (p)and Check Valve (g) have opened, thedried air reaches the reservoirs via Port2. Through the throttling port of Valve (f),dried air reaches the underside of Gran-ulate (b), causing a back-flushing proc-ess to take place here, too.After approx. 1 minute, the time-switchelement will break the current supply tothe trip coil. Armature (i) will close thepassage from Chanber C, opening thevent, thus reducing the pressure inChambers D and M. Through the springforce and the pressure in Bore G, thecontrol valves are returned to their endpositions on the right. Control Valve (o)will close the passage to Chamber H,and Control Valve (k) will open the pas-432 431Air Dryer 1.sage to Chamber B. The compressed air supplied by the compressor is now again fed into Granulate (b), and the drying process will commence as described be-fore, with alternating cartridges continu-ing to be used at one-minute intervals. When the unloader valve switches to idling once the input cut-out pressure has been reached, pressure is being fed in at Port 4, pressurizing, and moving down-wards, Piston (m), opening the idling control valve. Any condensate and impu-rities will be emitted together with the air supplied in the idling phase via Vent 3. When the unloader valve switches to load, Port 4 is vented and the idling con-trol valve closes the passage to Vent 3. Any malfunction due to icing in extreme conditions in the area of Piston (m) can be prevented by fitting a Heating Car-tridge (l) which will switch on at tempera-tures below 6°C and switch off again when the temperature reaches approx. 30°C.b) Control Via Integral UnloaderValveThe air is dried as described under a). The pressure building up at Port 2 when the system is being filled is also present in Chamber P, pressurizing the under-side of Diaphragm (t). As soon as theforce resulting therefrom is larger thanthe force of Pressure Spring (n), Dia-phragm (t) will arch, taking with it Piston(q). This opens Inlet (u), and Piston (m),now pressurized, is moved downward,opening the idling control valve. Any con-densate and impurities will be emitted to-gether with the air supplied in the idlingphase via Vent 3. The compressor willcontinue to run idle until the pressurewithin the system has fallen to a valuebelow the unloader valve's cut-in pres-sure. The pressure in Chamber P belowDiaphragm (t) will fall simultaneously.Pressure Spring (n) will move Piston (q)and Diaphragm (t) back to their originalpositions. Outlet (u) will close, and thepressure from Chamber O will be re-duced via the vent of the unloader valve.The idling control valve with Piston (m)will close once again. The compressedair will now again flow into Bore E andreach the air reservoirs via Port 2 afterbeing dried in Desiccant Containers (b orr). The system is subsequently filledonce again up to the cut-out pressure ofthe unloader valve.Application:Depending on the respective application,WABCO provides Single and TwinChamber Air Dryers.The decision of whether to use a Singleor a Twin Chamber Air Dryer will dependon the compressor's swept volume andon its duty cycle.Single Chamber Air Dryerscan normally be used for applications upto a swept volume of ≈ 500 litres/minuteand a duty cycle of up to ≈ 50%. Any de-viations of these standard values shouldbe tested in road-test runs.Twin Chamber Air Drierscover the area > 500 litres/minute and >50% up to 100% duty cycle. Swept vol-umes in excess of 1000 litres/ minuteshould be tested in road-test runs 432 432Purpose:To automatically control the operating pressure in an air braking system and to protect its pipes and valves from contam-ination. Depending on the variant used, it also serves to control a downstream anti-freeze pump or single chamber air dryer. Operation:a)UnloaderThe compressed air supplied by the compressor flows via Port 1 and Filter (g) to Chamber B. When Check Valve (e) has opened, it flows through the line leading from Port 21 to the air reservoirs and to Chamber E. Port 22 is intended for controlling a downstream anti-freeze pump.Pressure builds up in Chamber E, acting the underside of Diaphragm (c). As soon as that pressure is greater than the force of Compression Spring (b), preset by means of Screw (a), diaphragm (c) will arch upward, taking with it Piston (m). Outlet (l) closes and Inlet (d) opens, per-mitting the compressed air to pass from Chamber E to Chamber C, forcing Piston (k) downwards against the force of Com-pression Spring (h). Outlet (i) opens and the compressed air supplied by the com-pressor is released to atmosphere via Exhaust 3. The fall in pressure in Cham-ber B closes Check Valve (e), thus se-curing the pressure in the system.The compressor will now continue to idleuntil the pressure within the system fallsbelow the Unloader’s cut-in pressure.The pressure in Chamber E below Dia-phragm (c) continues to fall. This causesthe force of Compression Spring (b) topush the diaphragm, together with Piston(m), downwards. Inlet (d) closes, Outlet(l) opens and the air from Chamber C isreleased to atmosphere at Exhaust 3 af-ter passing Chamber F and a connectinghole. Compression Spring (h) forces upPiston (k) and outlet (i) is closed. The airsupplied by the compressor now flowsinto Chamber B, passing Filter (g), andopens Check Valve (e). The system isonce again being filled until the Unload-er’s cut-off pressure has been reached.b) Unloader with Pilot Connec-tion 4 and Port 23This type of Unloader differs from thetype described under a) merely in theway the cut-off pressure is controlled.The cut-off pressure is not taken from in-side the unloader but from the supply linedownstream from the air dryer. The pas-sage from Chamber B to Chamber E isclosed, and there is no Check Valve (e).Via Port 4 and Chamber A, the air fromthe reservoir flows to Chamber E, actingon Diaphragm (c). After that it continuesto operate as described under a). Thepassage between Chambers C and D isopen, permitting pilot pressure fromChamber C to be taken at Port 23 to ac-tuate the single chamber air dryer.c) Tyre inflation connectionAfter removing the protective cap, thetyre inflation hose is fastened by meansof a union nut moving Pin (f). The pas-sage between Chamber B and Port 21 isclosed. The air supplied by the compres-sor now flows from Chamber B to the tyreinflation hose, passing Pin (f). In theevent of the pressure in the system ex-ceeding 12+2 bar or 20 bar respective-ly during this process, Piston (k) which isdesigned to act as a safety valve willopen Outlet (i) and the pressure is re-leased to atmosphere via Exhaust 3.Before using the tyre inflation facility, thereservoir pressure must be reduced to avalue below the Unloader’s cut-in pres-sure since no air can be extracted whilstthe compressor is running idle12–Combined Unloader975 303 . . . 0。
