63

Equipment ForTrailer Braking Systems

2.

64

Trailer complying with the ECE Directive

Trailer with twin-line air braking system2.

Council Directive 71/320/EEC of the ”Eu-ropean Communities“ and ECE Regula-tion 13 are contained in the manualentitled ”Legal Requirements“.

This manual is available from our Depart-ment AM-M4, Tel. (511) 922 1688 quot-ing Part Number 815 000 051 3.

651

Legend:1. Hose coupling2. Line filter3. Double release valve with check valve4. Relay emergency valve5. Two-way valve6. Brake Chamber7. Air reservoir8. Drain valve9. Quick release valve10. ABS electronics

11. ABS relay valve12. ABS parking socket13. Dummy coupling with fastening14. Load sensing valve with integral knuckle joint15. Load sensing valve with integral test valve16. Plate, ALV setting17. ABS-Elektrowendel18. Tristop Spring Brake Actuator19. Pressure limiting valve20. Adjusting valve

Semi-trailer with twin-line airbraking system 2.

Semi-trailer complying with the ECE Directive

66 1

Purpose:To protect the air braking system againstdirt.

Operation:The compressed air reaching the line fil-ter via port 1 passes through the filtercartridge in which any particles of dirt areretained; the compressed air is cleanedbefore it reaches any downstream appli-ances from port 2.

If the line filter is blocked, the filter car-tridge is pushed upwards against theforce of the pressure spring and the com-pressed air will pass through the line fil-ter without being cleaned.

If port 1 is exhausted while the filter car-tridge is blocked, the pressure in port 2can push the cartridge downwardsagainst the force of the compressionspring. This permits return flow from port2 to port 1.

Trailer Release Valve963 00. . . . 0

Purpose:To release the braking system for thepurpose of moving a trailer that is discon-nected from the tractor unit. The doublerelease valve has been designed for usein braking systems using Tristop® springbrake actuators.

Operation:When a semitrailer is connected to theprime mover, air from the supply lineflows through port 11 into chamber (B). Ifpiston (a) is still in the release position itis pushed out into the driving position bythe supply pressure. The air from thesupply line then flows through port 2 to

the relay emergency valve and on to thereservoir on the trailer.

When the trailer is uncoupled, port 11and therefore chamber (B) are exhaust-ed causing the relay emergency valve toapply the trailer brakes. To release thebrakes, piston (a) is pushed home man-ually using knob (b). This closes the pas-sage from port 11 to port 2 and aconnection between chamber (A) andport 2 is established.

The reservoir pressure of the semi-trailerat port 12 flows to the relay emergencyvalve via port 2, causing it to reverse.The brake actuators are exhausted andthe trailer brakes released.

Air Line Filter and Trailer Release Valve2.Line Filter432 500 . . . 0

671

Trailer Release Valve 2.

Purpose:Releasing the braking system (for sys-tems with Tristop® cylinders) to moveunhitched trailers.

Operation:While coupling the trailer onto the vehi-cle, make sure that the piston (a) is still inparking position; if yes, push it to thedriving position. When the coupling headis connected, compressed air flowsthrough port 1-1 into chamber A. If thepiston (c) is still in release position, it ispushed out into driving position by thesupply pressure. The air supply thenpasses through port 21 into the relayemergency valve and then into the trail-er's air reservoir.

Compressed air flows through port 1-2into chamber B, opens the check valve(b), passes through chamber C and port22 into the downstream two-way quickrelease valve and pressurises theTristop® cylinder's spring compressionchambers.

Pressure in Port 1-1 and, subsequently,chamber A is reduced in the unhitchedposition. To release the service brakingsystem, use the actuating knob to pushthe piston (c) until stop. This blocks thepassage from port 1-1 to port 21,and aconnection is created between chamberA and port 1-2.

The air supply at port 1-2 flows throughport 21 into the trailer emergency valveand switches it to driving position, there-by reducing the pressure in the brakecylinder.

The piston (a) is pulled out when theparking brake is activated. The com-pressed air in chamber C and at port 22is released into the atmosphere via ex-haust 3. The downstream quick releasevalve reverses and pressure is reducedin the Tristop® cylinder's spring com-pression chambers.

Trailer Release Valve963 001 05 . 0

68 1

Relay Emergency Valves2.

Relay Emergency Valve with adjustable predominance 971 002 150 0 and Trailer Release Valve 963 001 012 0

Purpose:To control the twin-line braking system ofa trailer.

Operation:a) Relay Emergency ValveCompressed air passes from the tractorthrough the supply line hose coupling toport 1, passes grooved ring (c) and con-tinues through port 1-2 to the trailer res-ervoir.

Upon actuation of the tractor brakes,compressed air flows via the hose cou-pling in the control line and port 4 to theupper side of piston (a). The piston isforced down and by seating on valve (f)closes outlet (b) and opens inlet (g). Airfrom the trailer reservoir port 1-2 nowflows via ports 2 to the downstreambrake valves and into chamber (C) viapassage (A). Pressure builds up againstvalve (k).

As soon as the pressure in chamber (C)predominates, valve (k) opens againstthe force of pressure spring (i). The airflows into chamber (D) via passage (B),

acting on the underside of piston (a). Asa result of the compounding of forces inchambers (D) and (E), the pilot pressureacting on the upper side of piston (a) isovercome and piston (a) is forced up.

In the case of partial brake application,valve (f) closes inlet (g) and a neutral po-sition is reached. In the case of full brakeapplication, inlet (g) is kept open by pis-ton (a) over the entire braking process.

A maximum predominancce of 1 bar canbe established between ports 2 and 4 bymeans of adjusting the tension of pres-sure spring (i) using set screw (h).

When the tractor brakes are released,port 4 is vented and the pressure in ports2 forces piston (a) upward to the top of itsstroke. Inlet (g) is closed and outlet (b) isopened. The compressed air at ports 2 isexhausted to atmosphere through valve(f) and exhaust 3. Due to the drop inpressure in chamber (C), the com-pressed air in chamber (D) flows viabores (j) of valve (k) into chamber (C)and on to exhaust 3.

When the trailer is uncoupled or in theevent of a rupture in the supply line, port1 is exhausted and the pressure actingon the upper side of piston (d) is re-duced. The load in pressure spring (e)and the supply pressure at port 1-2 forc-es up piston (d) and valve (f) closes out-

let (b). As piston (d) continues to moveup, it moves away from valve (f) and inlet(g) opens. The supply pressure at port 1-2 flows to the downstream brake valvesvia ports 2 at a 1:1 ratio.

b) Trailer Release ValveIf the relay emergency valve is used incombination with automatic load-sensingbraking or a manually adjustable load ap-portioning valve without a release posi-tion, Trailer Release Valve 963 001 . . . 0permits the trailer being moved when un-coupled. For this purpose, piston (l) ispushed home by hand via push (m). Thiscloses the passage from port 11 of thetrailer release valve to port 1 of the relayemergency valve and a connection be-tween port 1 of the relay emergencyvalve and port 12 of the trailer releasevalve is established. Pressure from thetrailer reservoir at port 12 flows throughport 1 of the relay emergency valve,causing it to reverse into the driving posi-tion. The brake actuators are exhausted.

If piston (l) is not pulled out manually allthe way when the trailer is re-coupled,the supply pressure from the motor vehi-cle will force it out. The release valve isonce more in its normal position in whichport 11 of the release valve and port 1 ofthe relay emergency valve are connect-ed.

69

Relay Emergency Valves 2.

1

Relay Emergency Valve with adjustable predominance 971 002 152 0

Purpose:To control the twin-line braking system ofa trailer when the braking system of theprime mover is actuated. Automaticbraking of the semi-trailer in the event ofpartial or total loss of pressure in the sup-ply line.

This relay emergency valve should beused particularly in long multi-axle semi-trailers.

Operation:a) Service Brake ApplicationCompressed air passes from the primemover through the supply line hose cou-pling to port 1, passes grooved ring (c)and continues through port 1-2 to thesemi-trailer reservoir. At the same time,compressed air from the supply line forc-es down piston (c) and valve (e) againstthe load in pressure spring (d). Outlet (a)opens and ports 2 are connected with ex-haust 3.

Upon actuation of the tractor brakes,compressed air flows via the hose cou-pling in the control line and port 4 to theupper side of piston (k). The piston isforced down and by seating on valve (e)closes outlet (a) and opens inlet (f). Airfrom the semi-trailer reservoir port 1-2now flows via ports 2 to the downstreambrake actuators and into chamber (D) viapassage (B). Pressure builds up againstvalve (i). As soon as the pressure inchamber (C) predominates, valve (i)opens against the force of pressurespring (h). The air flows into chamber (E)via passage (C), acting on the undersideof piston (k). As a result of the com-pounding of forces in chambers (A) and(E), the pilot pressure acting on the up-per side of piston (k) is overcome andpiston (k) is forced up.

In the case of partial brake application,valve (e) closes inlet (f) and a neutral po-sition is reached. In the case of full brakeapplication, inlet (f) is kept open by piston(k) during the entire braking process.

A maximum predominance of 1 bar canbe established between ports 2 and 4 bymeans of adjusting the tension of pres-sure spring (h) using set screw (g).

When the tractor brakes are released,port 4 is vented and the pressure in ports(2) forces piston (k) upward to the top ofits stroke. Inlet (f) remains closed andoutlet (a) is opened. The compressed airat ports 2 is exhausted to atmospherethrough valve (e) and exhaust 3. Due tothe drop in pressure in chamber (A), thecompressed air in chamber (E) flows viabores (j) of valve (i) into chamber (D) andon to exhaust 3.

b) Automatic BrakingWhen the trailer is uncoupled, or in theevent of a rupture in the supply line, port1 is exhausted and the pressure actingon the upper side of piston (c) is reduced.The load in pressure spring (d) and thepressure from the reservoirs at port 1-2force up piston (c), and valve (e) closesoutlet (a). As piston (c) continues tomove up, it moves away from valve (e)and inlet (f) opens. Via ports 2, the reser-voir pressure flows to the brake cham-bers at a 1:1 ratio.

In the case of the control line rupturing,automatic braking takes effect as de-scribed above since the pressure in thesupply line is reduced as soon as thetowing vehicle is braked.

70

Relay Emergency Valves2.

1

Relay Emergency Valve with adjustable predominance 971 002 300 0

Purpose:To control the twin-line braking system ofa trailer.

Operation: The relay emergency valve, passing thegrooved ring (c), to Port 1-2 and on to thetrailer’s air reservoir.

When the motor vehicle’s braking sys-tem is actuated, air flows through the‘control’ hose coupling and Port 4 until itreaches the upper side of piston (a). Thismoves downwards, and as it rests on thevalve (f) it closes the outlet (b) and opensthe inlet (g). The compressed air from thetrailer’s air reservoir (Port 1-2) now flowsthrough Ports 2 to the downstream brakevalves and Duct C into Chamber B,where the pressure begins to rise.

As soon as the force in Chamber B isgreater, the valve (k) is opened againstthe force of the pressure spring (i). Theair now flows through Duct A into Cham-ber D, acting on the underside of piston

(a). Through the compounding of theforces acting in Chambers D and E, thepilot pressure acting on the upper side ofpiston (a) is overcome and that pistonmoves upwards.

Within the range of partial brake applica-tion, the valve (f) following piston (a)closes the inlet (g) and a neutral positionhas been reached. At full brake applica-tion, piston (a) keeps the inlet (g) openfor the whole of the braking process.

By adjusting the initial tension of thepressure spring (i) by turning the setscrew, a pressure predominance of up to1 bar can be set for Ports 2 over Port 4.

When the braking process in the motorvehicle is ended, causing Port 4 to beevacuated, piston (a) is moved to its up-per end position by the air pressure inPorts 2. The compressed air in Ports 2 isevacuated to atmosphere through valve(f) and Vent 3. Due to the fall in pressurein Chamber B, the compressed air inChamber D flows back through the holes(j) in valve (k) into Chamber B and fromthere to Vent 3.

When the trailer is disconnected, or ifthere is a rupture in the supply line, the

pressure in Port 1 is evacuated and thepressure on the upper side of piston (d)is reduced. The force of the pressurespring (e) and the supply pressure atPort 1-2 pushes piston (d) upwards,moving valve (f) and closing the outlet(b). As piston (d) continues to move up-wards, it is raised off valve (f) and the in-let (g) opens. The trailer’s air supply atPort 1-2 flows through Ports 2 to thedownstream brake valves in full.

The relay emergency valve is also avail-able with a release valve 963 001 01. 0,its part number being 971 002 7.. 0. For‘Operation’, please refer to Page 68.

711

Purpose:To limit output pressure to a preset level.

Operation:The air fed into chamber (A) via port 1(high-pressure) flows through inlet (d)into chamber (B) and on to port 2 (low-pressure). At the same time, piston (e) ispressurized but is initially held at the topof its stroke by pressure spring (f).

As soon as the pressure in chamber (B)reaches the level set for the outlet pres-sure, piston (e) overcomes the load inpressure spring (f) and moves down.Valves (a) and (c) close inlets (b) and (d).If the pressure in chamber (B) has in-creased above the preset level, piston(e) will continue its downward motion,thus opening outlet (h). The excess airwill escape to atmosphere through pis-ton (e) and exhaust 3. As the presetpressure level is reached, outlet (h) isclosed once more.

In the event of a leakage in the low-pres-sure line causing a loss in pressure, pis-ton (e) will lift valve (a). Inlet (b) opensand the required quantity of air is fedthrough. In Variant 475 010 3.. 0, piston(e) will raise valve (c), thus closing inlet(d).

When port 1 is exhausted, the higherpressure in chamber (B) lifts valves (c)and (a). Inlet (d) opens and the low-pres-sure line is exhausted via chamber (A)and port 1. In the process, piston (e) isreturned to the end of its stroke by theload in pressure spring (f).

The set pressure limit can be alteredwithin a certain range by changing thecompression of spring (f) by means ofadjusting screw (g).

Pressure Limiting Valves 2.

475 010 0 . . 0

475 010 3 . . 0

Pressure Limiting Valve475 010 . . . 0

72 1

Relay Valves2.

Purpose:To rapidly supply and evacuate com-pressed air from pneumatic equipmentand to reduce response times in pneu-matic braking systems.

Operation:When the braking system is actuated,compressed air flows into chamber (A)via port 4, forcing down piston (a). Outlet(c) is closed and inlet (b) is opened. Thesupply pressure at port 1 now flows intochamber (B) and to the downstreambrake actuators via ports 2.

The pressure buidling up in chamber (B)acts on the underside of piston (a). Assoon as this pressure begins to exceed

the supply pressure in chamber (A), pis-ton (a) is forced up. Inlet (b) closes and aneutral position is reached.

When the pilot pressure is partially re-duced, piston (a) is moved up onceagain. Outlet (c) is opened and the ex-cess pressure at port 2 escapes via ex-haust 3. If the pilot pressure at port 4 failscompletely, the pressure in chamber (B)forces piston (a) to the top of its strokeand outlet (c) opens. The downstreambrake actuators are exhausted fully viaexhaust 3.

973 001 . . . 0 973 011 00 . 0

Relay Valve973 001 . . . 0 and973 011 00. 0

731

Height Limiting Valve andQuick Release Valve

Purpose:Height limitation on vehicles with an airlift device.

Operation:The height limiting valve is mounted onthe chassis of the vehicle using bolt (c).Tappet (b) is connected to the axle via asteel cable. If during a lifting operationusing the raise/lower valve, the distancebetween the chassis and the axle ex-

ceeds the specified limit, tappet (b) ispulled down, followed by valve (a) whichcloses the connection between ports 1and 2. When tappet (b) is pulled out, port2 is exhausted.

After lowering of the chassis, tappet (b)returns to its original position and valve(a) re-opens the connection betweenports 1 and 2.

2.Height Limiting Valve964 001 . . . 0

Quick Release Valve973 500 . . . 0

Purpose:Rapid evacuation of long control or pilotlines, and of brake actuators.

Operation:When there is no air on the valve, theouter edge of diaphragm (a) which isslightly prestressed seats against ex-haust 3, closing the passage from port 1to chamber (A). Compressed air fromport 1 pushes back the outer edge and

reaches the downstream brake actua-tors via ports 2.

When the pressure at port 1 is reduced,the higher pressure in chamber (A) forc-es diaphragm (a) to arch upwards. De-pending on the reduction in pressure, thedownstream brake actuators are nowpartially or completely exhausted via ex-haust 3.

74

Adapter Valve and 3/2 Directional Control Valve2.

Purpose:To reduce the braking force of the axle tobe adapted during partial brake applica-tions and rapid exhausting of brake actu-ators.Trailers being operated inmountainous regions and frequently cov-ering downhill journeys always show in-creased wear on the brake linings of thefront wheels because the arrangement ofthe larger front-wheel brake actuators re-quired for stopping will cause excessbraking on the front axle. By using thisAdapter Valve, the brake force on thefront axle is reduced on the front axle tothe extent that both axles are brakedevenly; this does not, however, in anyway impair the brake force in emergencybraking.

Operation:Piston (b) is held at the top of its strokeby the load in pressure spring (c). Dia-phragm (a) closes the passage from port1 to ports 2. When the brakes are ap-plied, the air flows via port 1 to the upperside of diaphragm (a) where pressurebegins to build up. As soon as this pres-sure exceeds that of pressure spring (c)set by means of screw (d), piston (b) isforced down. The air now flows past theouter edge of diaphragm (a) and viaports 2 to the downstream brake actua-tors.

The pressure building up at ports 2 alsoacts on the underside of diaphragm (a),thus supporting the force of pressure

spring (c). As soon as these forces ex-ceed the pressure acting on the upperside of diaphragm (a), piston (b) is re-turned to the top of its stroke. A neutralposition is reached.

If the pressure at port 1 is increased fur-ther, the load in pressure spring (c) isgradually overcome and the air finallyreaches the brake actuators at a 1:1 ra-tio. After a reduction in pressure at port 1,pressure spring (c) forces piston (b) up tothe top of its stroke. The pressure inchamber (B) forces diaphragm (a) toarch upward. Depending on the reduc-tion in pressure at port 1, the brake actu-ators are exhausted partially orcompletely.

Adapter Valvewith linear characteristic975 001 . . . 0

3/2 Directional Control Valve463 036 . . . 0

Purpose:Alternate connection of the service line(consumer) with the pressure line or theexhaust, the valve locking into either po-sition.

Operation:When turning knob (a) is actuated in arotary direction, piston (b) is moved

downwards via a cam. Outlet (d) closesand inlet (c) opens, and the compressedair at Port 1 flows into the service line viaPort 2. When turning knob (a) is turnedthe other way, piston (b) is returned to itsoriginal position by the force of the com-pression spring. Inlet (c) closes and theservice line is exhausted via outlet (b)and Port 3.

75

Purpose:To pressurize an air line when current issupplied to the solenoid.

Operation:The supply line from the air reservoir isconnected to port 1. The armature (d)which forms the valve core keeps inlet(c) closed by the load in pressure spring(b).

When a current reaches solenoid coil (a),

armature (d) is lifted, outlet (e) is closedand inlet (c) is opened. The compressedair from the supply line will now flow fromport 1 to port 2, pressurizing the workingline.

When the current to solenoid coil (a) isinterrupted, pressure spring (b) will re-turn armature (d) to its original position.Inlet (c) is closed, outlet (e) is openedand the working line is exhausted viachamber (A) and exhaust 3.

Solenoid Valves 2.

1

3

2

4

e

A

d

a

b

c

3/2-Way Solenoid ValveNormally Closed472 1. . . . . 0

Purpose:To vent an air line when current is sup-plied to the solenoid.

Operation:The supply line from the air reservoir isconnected to port 1 and thus air is al-lowed to flow through chamber (A) andport 2 into the working line connected toport 2. The armature (d) which forms thecore of the valve is forced down byspring (b), closing outlet (c).

When a current reaches solenoid coil (a),

the armature (d) is lifted, inlet (e) isclosed and outlet (c) is opened. Thecompressed air from the working line willnow escape to atmosphere via port 3and the downstream operating cylinderis exhausted.

When the current to solenoid coil (a) isinterrupted, pressure spring (b) will re-turn armature (d) to its original position.Outlet (c) is closed and inlet (e) isopened, again allowing air to pass to theworking line via chamber (A) and port 2.

3/2-Way Solenoid ValveNormally Open472 1. . . . . 0

1

3

24

e

A

d

a

b

c

76

Load Sensing Relay Emergency Valve2.

Purpose:Control of the dual-line trailer brakingsystem when the motor vehicle's brakingsystem is operated. Automatic control ofthe braking force as a function of vehicleload by means of the integrated load-sensing valve.Automatically braking the trailer in theevent of partial or complete loss of pres-sure in the supply line.The Load-Sensing Relay EmergencyValve is specifically designed for semi-trailers with several axles.

Operation:The valve is mounted on the vehiclechassis and is attached to a spring armon the axle via a linkage. When the vehi-cle is empty, the distance between theaxle and the valve is greatest and lever(j) is in its lowest position. As the vehicleis loaded, this distance is reduced and le-ver (j) is moved towards its "fully laden"position. The movement of lever (j) caus-es the cam plate to move tappet (l) to aposition corresponding to the vehicleload.

Via the hose coupling of the supply lineand port 1, pressure from the motor vehi-cle passes groove ring (h), port 1-2 andthen reaches the semi-trailer's air reser-voir. At the sime time, piston (k) andvalve (g) are moved downwards by thesupply pressure. Outlet (n) opens andports 2 are connected with exhaust 3.

When the motor vehicle's braking systemis operated, air flows to chamber (A) viathe hose coupling in the control line andport 4, pushing down piston (b) whichcloses outlet (d) and opens inlet (p). Theair from port 4 reaches chamber (C) be-low diaphragm (e), acting on the effectivesurface area of relay piston (f).

At the same time, air flows to chamber(B) via open valve (a) and passage (E),acting on the upper side of diaphragm(e). This initial by-pass pressure elimi-nates any reduction in pilot pressure (upto 1.0 bar max.) in the "partially laden"condition. As the pilot pressure continuesto rise, piston (r) is forced up against theload of spring (s), closing valve (a).

Load Sensing Relay Emergency Valve475 712 . . . 0

77

Load Sensing Relay Emergency Valve 2.Through the pressure building up inchamber (C), relay piston (f) is forceddownwards. Outlet (n) closes and inlet(m) opens. The supply pressure at port1-2 now flows into chamber (D) via inlet(m) and then reaches the downstreambrake actuators via ports 2. At the sametime, pressure builds up in chamber (D),acting on the underside of relay piston(f). As soon as this pressure exceedsthat in chamber (C), relay piston (f)moves upwards, closing inlet (m).

As piston (b) moves downwards, dia-phragm (e) is pushed against vane (o),thus continuously increasing the effec-tive diaphragm surface area. As soon asthe force acting on the underside of thediaphragm in chamber (C) is equal tothat acting on piston (b), the pistonmoves upwards. Inlet (p) is closed, a bal-anced position is reached.

The position of tappet (l), which is de-pendent on the position of lever (j), deter-mines the output braking pressure.Piston (b) with vane (o) needs to cover astroke according to the position of tappet(l) before valve (c) begins to operate.This stroke also changes the effectivesurface area of diaphragm (e). In the "ful-ly laden" position, the input pressure atport 4 flows into chamber (C) at a ratio of1:1. Since relay piston (f) receives fullpressure, it keeps inlet (m) open and theinput braking pressure is not controlled.

When the motor vehicles braking systemis released, port 4 is exhausted and relaypiston (f) is pushed into its upper positionby the pressure in ports 2. Outlets (d)and (n) open and the air in ports 2 andchamber (C) is released to atmospherevia exhaust 3.

Automatic BrakingWhen the supply line is disconnected orbroken, port 1 will be exhausted and thepressure on the upper side of piston (k)is reduced. The pressure from the airreservoirs at port 1-2 pushes piston (k)upwards. Valve (g) closes outlet (n). Aspiston (k) continues to move upward, itwill leave valve (g) and inlet (m) opens.Full reservoir pressure now reaches thebrake actuators via ports 2. In the eventof the control line breaking, automaticbraking will take place as describedabove since the pressure in the supplyline is reduced in connection with thetrailer control valve via the defective lineas soon as the towing vehicle is braked.

78 1

Automatic Load Sensing Valve2.

Automatic Load Sensing Valve 475 713 . . . 0

Purpose:Automatic control of the braking force inpneumatic actuators as a function of thevehicle load.

Operation:The load sensing valve is mounted onthe vehicle chassis and is actuated via aconnecting cable attached to the axle bymeans of a tension spring. When the ve-hicle is empty, the distance between theaxle and the valve is greatest and lever(f) is in its lowest position. As the vehicleis loaded, this distance is reduced and le-ver (f) moves from its ”empty“ position to-wards its ”fully laden“ position. Themovement of lever (f) causes cam plate(g) to move valve tappet (i) to a positioncorresponding to the vehicle load.

Output pressure from the relay emergen-cy valve reaches chamber (A) via port 1,acting on piston (b) which is forced down,closing outlet (c) and opening inlet (k).The air now flows to chamber (E) belowdiaphragm (d) and via ports 2 to thedownstream brake actuators.

At the same time, air flows into chamber(d) via opened valve (a) and channel (B),and acts on the upper side of diaphragm(d). This pressure control provides un-modulated output at low pilot pressures.If the pilot pressure increases further,piston (l) is forced up against the load inpressure spring (m) and valve (a) closes.

The downward motion of piston (b) re-leases diaphragm (d) from its seat in theload sensing valve, pushing it against thefanned out portion of piston (b). The ef-fective surface area of the diaphragm isthus increased continuously until it ex-ceeds the area of the upper side of thepiston. Thus, piston (b) is raised againand inlet (k) closed. A neutral position isreached. (Inlet (k) will remain open onlyin fully laden condition ”1:1“). The pres-sure delivered to the actuators of the fullyladen vehicle corresponds to the pres-sure in the load sensing valve deliveredfrom the relay emergency valve. With apartially laden or unladen vehicle, how-ever, this pressure is reduced according-ly.

When the brake pressure has been re-duced, piston (b) is forced up by the

pressure in chamber (E). Outlet (c)opens, and the air is exhausted to atmos-phere via valve tappet (i) and exhaust 3.

With each brake application, air flowsinto chamber (F) via passage (C), actingon washer (e) which is pushed againstvalve tappet (i). At a brake pressure 0.8bar, a frictional connection is establishedbetween valve tappet (i) and the housing.The load sensing valve's reducing ratio isthus locked and remains so even whenthe distance between the axle and thechassis is changed further. Tensionspring (h) compensates these variationsin travel.

An integral pressure spring in the loadsensing valve moves valve tappet (i) intothe ”fully laden“ position in the event ofthe linkage fracturing.

791

Automatic Load Sensing Valve 2.

Automatic Load Sensing Valve 475 714 . . . 0

Purpose:Automatic regulation of the brake pres-sure in pneumatic brake actuators on air-sprung axles (axle assemblies) as afunction of the pilot pressure of the airbellows.

Operation:The load sensing valve is mounted onthe vehicle chassis with the exhaust 3pointing downwards. Ports 41 and 42 areconnected to the air suspension bellowson both sides of the vehicle by means ofpipes.

The pilot pressure from the bellows actson pistons (m) and (k). Depending on thispressure which varies with the vehicleload, guide sleeve (i) with its attachedcam (h) are moved against spring (z) andthe position is set depending on the vehi-cle load.

When the brakes are applied, com-pressed air from the relay emergencyvalve flows into chamber (A) via port 1,pressurizing piston (d) which is forceddown, closing outlet (e) and opening inlet(c). The air now flows into chamber (B)below diaphragm (f) and to the down-stream actuators via ports 2.

At the same time, air flows into chamber(C) via opened valve (b) and passage(F), acting on the upper side of dia-phragm (f). This pressure control pro-vides unmodulated output at low pilotpressures when the vehicle is partiallyladen. If the pilot pressure increases fur-ther, piston (a) is forced up against theload in pressure spring (s) and valve (b)closes.

The downward motion of piston (d) re-leases diaphragm (f) from its seat in theload sensing valve, pushing it against thefanned-out portion of piston (d). The ef-fective surface area of the underside ofdiaphragm is thus increased continuous-ly until the forces on either side of the pis-ton are the same as on the underside ofdiaphragm (f). Thus, piston (d) is raisedagain and inlet (c) closed. A neutral posi-tion is reached. (Inlet (c) will remain openonly in the fully laden condition). Thepressure in the actuators then corre-sponds to the vehicle load and the outputbrake pressure of the tractor brake valveor the relay emergency valve.

When the brake pressure is reduced (re-lease of the brakes), piston (d) is forcedup by the pressure in chamber (B). Outlet(e) opens and the air is exhausted to at-mosphere via valve tappet (r) and ex-haust 3.

Every brake application forces air intochamber (E) via passage (D), acting onmoulded rubber part (p) which is forcedagainst valve tappet (r). Any brake pres-sure > 0.8 bar establishes a frictionalconnection between valve tappet (r) andthe housing. The load sensing valve's re-duction ratio is blocked and is main-tained even when dynamic axle loadshifting occurs when the brakes are ap-plied. If the bellows load increases with apartially laden vehicle, roller (g) ispushed against spring (o). Tappet (r)does not move from the position it was inwhen the brakes were first applied.

For checking the load sensing valve, atest hose is connected to port 43. As it isscrewed into place, piston (n) is pushedinto the housing, breaking the connec-tion of ports 41 and 42 to pistons (m) and(k). At the same time, a connection is es-tablished from port 43 to pistons (m) and(k). The load sensing valve adjusts to aregulating position corresponding to thepressure in the test hose.

80 1

Load Sensing Relay Emergency Valve2.

Load Sensing Relay Emer-gency Valve 475 715 . . . 0

Purpose:Regulation of the dual-line trailer brakingsystem when the towing vehicle's brak-ing system is actuated.Automatic regulation of the brake forceby means of the integrated load-sensingvalve as a function of the vehicle loadand thus of the actuating pressure of theair bellows.Automatic braking of the trailer in theevent of partial or complete loss of pres-sure in the supply line.

The Load-Sensing Relay EmergencyValve is specifically designed for air-sprung semi-trailers with several axles.

Operation:The valve is mounted on the vehiclechassis with the exhaust 3 pointingdownwards. Ports 41 and 42 are con-nected to the air suspension bellows onboth sides of the vehicle.

The pilot pressure from the air suspen-sion bellows acts on pistons (p) and (o).Depending on this pressure which varieswith the vehicle load, guide sleeve (n)with its attached cam is moved againstspring (m) and the position is set de-pending on the vehicle load.

The air from the motor vehicle reachesthe semi-trailer's air reservoir via the”supply“ hose coupling, port 1, port 1-2and grooved ring (h). At the same time,the supply pressure forces down piston(r) and thus valve (g). Outlet (t) opensand ports 2 are connected with exhaust3.

When the brakes are applied, com-pressed air flows via the hose coupling inthe control line and port 4 to chamber(A), acting on piston (b) which is forceddownwards, closing outlet (d) and open-ing inlet (v). The compressed air fromport 4 reaches chamber (C) below dia-phragm (e), acting on the effective sur-face area of relay piston (f).

At the same time, air flows into chamber(B) via open valve (a) and passage (G),acting on the upper side of diaphragm(e). This pressure control provides un-modulated output at low pilot pressures(up to 1.0 bar) when the vehicle is partial-ly laden. As the pilot pressure increasesfurther, piston (w) is forced up againstthe load in pressure spring (x) and valve(a) closes.

The pressure building up in chamber (C)forces relay piston (f) downwards. Outlet(t) closes and inlet (s) opens. The supplypressure present at port 1-2 now flowsinto chamber (d) and to the downstreembrake actuators via ports 2.

This causes pressure to increase inchamber (D) which acts on the undersideof relay piston (f). As soon as this pres-sure exceeds that in chamber (C), relaypiston (f) moves upwards and inlet (s)closes.

As piston (b) moves downwards, dia-phragm (e) moves against vane (u), thus

811

Load Sensing Relay Emergency Valve 2.continuously increasing the effective sur-face area of the diaphragm. As soon asthe force acting on the underside of thediaphragm in chamber (C) is the sameas that acting on piston (b), the piston ismoved upwards. Inlet (v) is closed and aneutral position is reached.

The position of tappet (i) which dependson the position on guide sleeve (n), de-termines the output pressure. Piston (b)with vane (u) must cover a stroke corre-sponding to the position of tappet (i) be-fore valve (c) begins to operate. Thisstroke changes the effective surfacearea of diaphragm (e). In the ”fully laden“position, the input pressure at port 4flows into chamber (C) at a ratio of 1:1.Since relay piston (f) receives full pres-sure, it keeps inlet (s) open and the inputbraking pressure is not controlled.

When the motor vehicle's braking sys-tem is released, port 4 is exhausted andrelay piston (f) is pushed into its upperposition by the pressure in ports 2. Out-lets (d) and (t) open and the air in ports 2and chamber (C) is released to atmos-phere via exhaust 3.

Every brake application forces air intochamber (E) via passage (F), acting onmoulded rubber part (k) which is forcedagainst valve tappet (i). Any brake pres-sure > 0.8 bar establishes a frictionalconnection between valve tappet (i) andthe housing. The relay emergencyvalve's reduction ratio is blocked and ismaintained even when dynamic axleload shifting occurs when the brakes areapplied. If the bellows load increaseswith a partially laden vehicle, roller (l) ispushed against spring (j). Tappet (i) doesnot move from the position it was in whenthe brakes were first applied.

For checking the load-sensing valve, atest hose is connected to port 43. As it isscrewed into place, piston (q) is pushedinto the housing, breaking the connec-tion of ports 41 and 42 to pistons (p) and(o). At the same time, a connection is es-tablished from port 43 to the pistons. Theload-sensing valve adjusts to a regulat-ing position corresponding to the pres-sure in the test hose.

Automatic Braking:When the supply line is disconnected orbroken, port 1 will be exhausted and thepressure on the upper side of piston (r) isreduced. The pressure from the air res-ervoirs at port 1-2 pushes piston (r) up-wards. Valve (g) closes outlet (t). Aspiston (r) continues to move upward, itwill leave valve (g) and inlet (s) opens.Full reservoir pressure now reaches thebrake actuators via ports 2.

831

3.

Anti-Lock Braking System (ABS)

84 1

Anti-Lock Braking System (ABS)3.Introduction: Anti-Lock Braking Systems (ABS) are

used to prevent locking of a vehicle’swheels as a result of excessive actuationof the service braking system, especiallyon slippery roads. As a consequence,lateral control is maintained on brakedwheels even at full brake application toensure that both the stability and steera-bility of a vehicle are ensured as far asphysically possible. At the same time,the utilization of the available adhesionof the tyre on the road and thus vehicleretardation and stopping distance areoptimized.

Following their introduction by WABCOFahrzeugbremsen, a division of WABCOStandard GmbH, in the early Eighties,Anti-Lock Braking Systems (ABS) arenow being offered by nearly all Europeanmanufacturers of commercial vehicles.

In recent years, WABCO has continu-ously worked on further improving theexcellent quality and performance char-acteristics of ABS.

Key developments have been:

� The introduction of Drive-Slip Controlsystems (ASR) in 1986

� The introduction of the ABS ”VARIO-C“ for trailers in 1989The increasing demand of trailermanufacturer for simple installationand testing whilst maintaining theusual WABCO quality standard hasbeen the reason for WABCO devel-oping its new ABS generation, VarioCompact ABS - VCS. Both modularsystems are based on state-of-the-art electronics technology with high-performance micro computers andhigh-capacity data storage, takingmodern diagnostic principles into ac-count.

� With the ABS/ASR ‘C’ generation formotor vehicles and motor coaches,WABCO has presented a systemwhich offers the following essentialtechnical novelties:

ABS-Functions� Control Performance

By further optimizing the control algo-rithm, the utilization of adhesion andcontrol comfort were improved evenmore.

� Setting ECU ParametersModern memory modules can beused to set customer-specific vehicledata either when the ECU is beingmade or after production of a com-mercial vehicle.

ASR-Functions� Pneumatic Engine Control

IIn combination with a proportionalvalve designed for that purpose anda suitable control cylinder in the actu-ating linkage of the fuel-injectionpump, considerable improvements intraction and in control comfort areachieved.

� Electronic Engine ControlThe ECU has interfaces to commer-cial electrical or electronic enginecontrol systems, and correspondingSAE interfaces.

� Functional DisplayThe driver is informed of any auto-matic actuation of the ASR system,thus indicating to him that the roadmay be slippery.

Special Functions

� Top Speed Control

� ABS/ASR Function Switch

� Diagnostic Interface / Flash Code

WABCO has continuously improved theperformance of this safety system. Theconstantly rising competitive pressure inthe transport trade and falling vehicleprices have not stopped at ABS, either.

The highlights listed below which applyto the 4th generation of ABS/ASR are in-tended to specifically meet these re-quirements.

851

Anti-Lock Braking System (ABS)

ABS/ASR D VersionThe New Generation of ControlUnitsChanged vehicle concepts, the desire forfurther improving functions and continu-ous cost reductions for the system haveculminated in the development of the DVersion of ABS/ASR.

Special Features:� The single plug concept:

This design permits the allocation ofpartial cable harnesses on the vehi-cle to their respective plugs.

� The valve relays previously locatedoutside the control unit have nowbeen integrated.

� The D Version has a databus inter-face for communication with othersystems.

� ABS/ASR systems now only requireone ASR solenoid valve (differentialbrake valve).

3.

4-Channel ABS/ASR (C Version)4-wheel motor lorry with rear-wheel drive

ABS/ASR componentsABS components

1. pole wheel and sensor2. brake chamber (front axle)3. ABS solenoid control valve4. air reservoir5. Tristop spring-brake actuator

(rear axle)6. ABS solenoid control valve7. two-way valve8. differential brake valve9. electronic control unit10. proportional valve12. ASR actuating cylinder13. ASR functional switch14. ABS indicator lamp15. ASR indicator lamp

4- Channel ABS/ASR (D Version)

86

Anti-Lock Braking System (ABS)3.

WABCO’s top speed limiting system withits proportional valve (GBProp) complieswith the latest European legislation forthe equipment of heavy-duty commercialvehicles with cruise control systems andhas been granted EC type approval forthe parts.

Its components include the ABS/ASRECU, a proportional valve and actuatingcylinders which have been used suc-cessfully in recent years in WABCO-ABS/ASR systems for pneumatic enginecontrol. Other components include idle-stop cylinders (only required for single le-ver fuel-injection pumps), a speed set/ASR functional switch and an ASR indi-cator lamp plus a speedograph with C3/B7 output.

The speed limiter begins to operate evenbefore the vehicle has reached the max-imum speed stored in the ECU in a non-volatile EE-PROM memory. Via the pro-portional valve and the actuating cylin-der, the control lever of the fuel-injectionpump is moved so that the vehicle’s per-missible maximum speed cannot be ex-ceeded.

In addition, GBProp allows the driver toset a limiting speed freely selectable an-ywhere between 50 k.p.h. and the presetmaximum speed by actuating the speed-set/ASR functional switch and have thisspeed monitored by the system althoughhe has to continue to push down the ac-celerator pedal (this not being a fully au-tomatic cruise control system).

The top speed stored in the ElectronicControl Unit (ECU) can either be definedby the vehicle manufacturer (at the endof production) or by officially authorizedworkshop personnel at a service stationusing WABCO’s Diagnostic Controller.

The ECU stores any faults which mayoccur by type and frequency and, via theinterface designed to ISO 9141 and bymeans of the Diagnostic Controller, per-mits the error memory to be read out ordeleted, functional testing to be doneand the system’s parameters to be set.

Integrated Speed LimiterGBProp

ABS/ASRGBProp ECU

air reservoir

speed-set/ASR functional switch

speedograph

proportional valve

actuating cylinder

indicator lamps

87

VCS is a ready-to-install ABS system fortrailers meeting all legal requirements ofthe A category.The range of systems extends from a 2S/2M system for semitrailers to a 4S/3Msystem for towbar trailers or, for in-stance, a semitrailer with a steering axle.

In keeping with the specific needs of thetrailer manufacturers, VCS is availableeither as a compact unit or as a modularsystem, i. e. ECU and valves are in-stalled separately.Both ABS relay valves and ABS solenoidvalves can be used. The choice dependson the braking system used, and moreparticularly on time response. It is impor-tant that the appropriate ECU is used.

If the control valves are not electricallyactuated, the ordinary increase or de-crease of brake pressure the driverneeds is not affected. The special func-tion of ”maintaining brake pressure“serves to improve both the control per-formance of the ABS system, and airconsumption.

� one ECU (Electronic Control Unit)with one, two or three control chan-nels, subdivided into the followingfunctional groups:

� input circuit� main circuit� safety circuit� valve actuation

In the input circuit, the signals generatedby the respective inductive sensors arefiltered and converted into digital infor-mation for determining period lengths.

The main circuit consists of a microcom-puter. It contains a complex programmefor the computation and logical operationof the control signals and for outputtingthe actuating variables for the valve con-trol system.

The safety circuit monitors the ABS sys-tem, i. e. the sensors, solenoid controlvalves, ECU and wiring, before the vehi-cle moves off and whilst it is in motion, ir-respective of whether the brakes arebeing actuated or not. It alerts the driverto any errors or defects by means of anindicator lamp and shuts off the whole orpart of the system. Whilst the conven-tional brake remains operational, it isonly the anti-lock system which is deacti-vated wholly or in part.

The valve actuation contains (outputstages) which are actuated by the sig-nals from the main circuit and whichswitch the current for actuating the con-trol valves.

The electronic control unit of the VARIOCompact ABS is a further developmentfrom the established Vario-C ABS, build-ing on its proven principles.

Anti-Lock Braking System (ABS) 3.Vario Compact ABS (VCS)for Trailers

ABS Relay Valve **)

1 st and 2 nd rely valves

3 rd relay valves

Supply ISO 7638

Diagnosis 24N (24S) Supply *)

*) optional **) optionally flanged to compact unit

with retarder control *) integrated speed switch (ISS) *) Sensors (2 or 4)

88

Anti-Lock Braking System (ABS)3.

Purpose:The purpose of the solenoid controlvalve on the trailer is to increase,reduce or hold the pressure in the brakecylinders during a braking processdepending on the control signals, inmilliseconds, received from the ECU.

Operation:a) Pressure IncreaseValve solenoids I and II are not ener-gized, the inlet of valve (i) and the outletof valve (h) are closed. The pilot cham-ber (a) of diaphragm (c) is pressureless.The compressed air at Port 1 flows fromChamber A through the open inlet (b)into Chamber B and from there throughPort 22 to the brake cylinders. At thesame time, the compressed air alsoflows through the hole (d) into the pilotchamber (g) of diaphragm (f), and outlet(e) remains closed.

b) Pressure ReduceWhen the ABS ECU transmits the signalto decrease the pressure, valve solenoidI is energized, valve (i) closes the pas-sage to Vent 3 and the passage to the pi-

lot chamber (a) is opened. Thecompressed air from Chamber A flowsinto the pilot chamber (a) and diaphragm(c) closes inlet (b) leading into ChamberB. At the same time, valve solenoid II re-verses, valve (h) closes the passage ofhole (d), permitting the compressed airfrom pilot chamber (g) to escape throughVent 3. Diaphragm (f) opens outlet (e)and the at Port 2 escapes to atmospherevia Vent 3.

c) Pressure HoldBy receiving a pulse, the passage toVent 3 is closed by valve (h) as valve so-lenoid II reverses. The compressed airfrom Chamber A flows through the hole(d) back into the pilot chamber (g) and di-aphragm (f) closes outlet (e). Thus thepressure in Chamber B and thus thebrake cylinders cannot increase or de-crease.

Solenoid Control Valve472 195 . . . 0

89

ABS Relay Valve472 195 02 . 0

Anti-Lock Braking System (ABS) 3.

Purpose:The purpose of the solenoid controlvalve on the trailer is to increase, re-duce or hold the pressure in the brakecylinders during a braking process de-pending on the control signals, in milli-seconds, received from the ECU.Thisconsists of two subassemblies:The actual relay valve and the electro-magnetic control valve.

Operation:a) Supply pressure present but no:The annular piston (c) is pushed againstthe seat (b) by the pressure spring (d),closing Port 1 against Chamber B (andthus Port 2).As (e. g. 1 bar) is applied at Port 4, thisflows via the solenoids (M1 and M2) intothe upper piston chamber A, forcing pis-ton (a) downwards. A small gap opens atthe seat (b) and air from Port 1 flows intoChamber B. At Outlet 2 and thus in thebrake cylinders, pressure begins to rise.Since the upper and lower sides of piston(a) have identical surfaces, that pistonwill return to its original position as soonas the pressure at 2 is equal to that at 4.The annular piston (c) is again in contactwith the seat (b) and the passage from 1to Chamber B is closed.

When the falls, piston (a) is raised andthe pressure in Port 2 escapes to Vent 3through Chamber B.

b) Operation in ABS control:Pressure Increase:The solenoids (M1 and M2) are deadand there is actuating pressure in Cham-ber A. Piston (a) is in its lower end posi-tion and the air supply flows from Port 1to 2.

Pressure hold:Solenoid M1 is energized and the arma-ture has attracted. This causes the airsupply from Port 4 to Chamber A to beinterrupted (in spite of the rise in actuat-ing pressure).

The pressures in Chamber A and B areequalized. The annular piston againrests on seats (b). The compressed aircannot flow from 1 to 2 or from 2 to 3(outside).

Pressure Reduce:Solenoid M2 is energized, the passageto Chamber A thus being closed. Theraised seal at the foot of M2 opens thepassage to Vent 3 and the pressure fromChamber A escapes to atmospherethrough the inside opening of the annularpiston (a). This causes piston (a) to beraised and the pressure from Port 2 andthe connected brake cylinder escapes toatmosphere through Chamber B andVent 3.

90

Anti-Lock Braking System (ABS)3.

1

ABS Relay Valve472 195 04 . 0(Flat twin valve)

Purpose:ABS relay valve (flat twin valve) consistsof two relay valve parts with commonports for supply pressure and controlpressure. It is used in the air braking system in frontof the brake cylinders to modulate thebraking pressure in the brake cylinders.When the valve is activated by the ABSelectronic control unit, the pressure in thebrake cylinders is modulated (pressureincrease, pressure hold, pressure re-lease) regardless of the pressure al-lowed to pass by the brake valve or theemergency valve. The device has a two-relay-valve function in passive position(i.e. without solenoid activation), and isused to increase and decrease pressurein the brake cylinder through short re-sponse and pressure build-up and re-lease times.

Operation:Pressure build-up without ABS Con-trol:Both valve solenoids (M1 and M2) arede-energized, the annular piston (f) ispressed against the seat (e) by the pres-sure spring (b), and the passage fromport 1 to chamber B is closed.

If control pressure is supplied at port 4, it

flows through the solenoids (M1 and M 2)into the upper piston chamber A, pressesthe piston (c) against the annular piston(f) and opens the narrow gap in the seat(e). The supply pressure at port 1 flowsthrough the filter (a) into chamber B andinto port 23. There is pressure build-upalso in the brake cylinders. The sameprocess also takes place in the oppositerelay valve for ports 22. Since the upperand lower sides of the piston (c) haveequal surfaces, the piston returns to itsoriginal position as soon as the pressureat ports 22 and 23 is equal to the pres-sure at port 4. The annular piston (4) liesclose to the seat (e) again, and the pas-sage from port 1 to chamber B isblocked.

If the control pressure decreases, thepiston (c) is raised and the pressure inports 22 and 23 is released via chamberB to exhaust 3.

Operation with ABS-Control:

a) Pressure build-upThe solenoids (M1 and M2) are de-ener-gized and control pressure builds up inchamber A. The piston (c) is in its leftstop position and air supply flows fromport 1, through ports 22 and 23, into thebrake cylinders.

b) Pressure releaseSolenoid M2 is energized and closes thepassage from port 4 to chamber A. The

raised gasket at the bottom of M2 clearsthe way to exhaust 3 and the excesspressure from chamber A escapes throu-gh the inner opening of the piston (c) toexhaust 3. This raises the piston (c), andthe pressure on the brake cylinder is re-leased accordingly.

c) Pressure holdSolenoid M2 is de-energized again, sole-noid M1 is energized, and the armatureattracted. Thus, (despite the increasingcontrol pressure) air supply from port 4 tochamber 4 is interrupted.There is equal pressure in chambers Aand B, and the annular piston(f) is pres-sed against the seat (e) by the pressurespring (b). Compressed air can neitherflow from 1 to 22 and 23, nor from 22and 23 to 3 (into the atmosphere).

d) Pressure releasePower is supplied to solenoids M1 andM2. The passage from port 4 to chamberA is closed and compressed air fromchamber A escapes via the check valve(d) on port 4, whereas the pressure fromchamber B and from ports 22 and 23 nowescapes through the fully open outlet(the piston (c) is in its right stop position)on the seat (e) and exhaust 3 into the at-mosphere.

91

Anti-Lock Braking System (ABS) 3.

1

ABS Sensor Installation

Clamping Bush899 759 815 4

The clamping bush has 4 spring ele-ments held on one side only which, whenunder stress, generate a force betweensensor and hole causing defined friction-al engagement in the direction of thesensor.This causes the sensor to be hold by theclamping bush in such a way that when itis being fitted it can be pushed againstthe pole wheel and automatically adjuststo a minimum gap when the vehicle is in

motion. This eliminates the process ofhaving to adjust the gap and aligning thesensor (cable exit).

In open arrangements, the clampingbush and the sensor are fitted with atemperature and splash-resistant grease(Staburags or silicone grease - Part No.830 502 06. 4) to protect them from cor-rosion and dirt.

The rotary motion of the wheel is pickedup by means of a pole wheel (1) movingwith the hub and a pulse-generating sen-sor (3) held in the brake spider plate by aclamping bush (2).Pole wheels for medium and heavy-dutycommercial vehicles have 100 teeth.

Because of the diagonal referencespeed forming, the ratio of the number ofteeth and the wheel’s circumferencemust be identical on front and rearwheels, any deviation not exceeding afew percent.

ABS Sensor441 032 . . . 0

The inductive sensor comprise a perma-nent magnet, core and coil. The magnet-ic flux surrounding the coil is cut by the

rotating motion of the toothed wheel in-ducing an A.C. voltage whose frequencyis directly proportional to wheel speed.

92 1

Anti-Lock Braking System (ABS)3.

Purpose:Via the pressure allowed to pass by theactuating cylinder, the proportional valvecontrols the control lever of the fuel-in-jection pump.

The output pressure is directly propor-tionate to the solenoid flux controlled bythe ECU (GBProp) by means of pulse-width modulation (PWM) with which theproportional valve is actuated. The lowhysteresis permits a wide range of cylin-der pressures to achieve both very rapidand virtually stationary adjusting move-ments for the control lever.

Operation:In the basic position (valve solenoid notenergized), the solenoid armature is incontact with the plunger (a) and keepsthe inlet (b) closed.

When current reaches the solenoid, thearmature forces the plunger (a) down-wards, opening the inlet (b). The air sup-ply at Port 1 now flows through Port 2and on to the actuating cylinder. De-pending on the pulse output by the ECU,the pressure in the actuating cylinder iseither held at a constant level (armatureattracts, closing the inlet) or reduced (ar-mature continues to attract, opening theoutlet (c) and the compressed air es-capes to atmosphere through Port 3).

Proportional Solenoid Valve472 250 . . . 0 (GBProp)

931

Anti-Lock Braking System (ABS) 3.

The actuating cylinder is fitted in the ad-justing linkage between the acceleratorand the fuel-injection pump. When actu-ated from the proportional valve, thecompressed air flows through Port andinto Chamber A, moving the piston to-wards the left. The piston rod which isnow being retracted causes the control

lever of the fuel-injection pump to bemoved towards its idling position. De-pending on the space available for instal-lation, either retracting (Fig. 1) orprotruding (Fig. 2) operating cylindersare used.

Operating Cylinder(Idle-Stop Cylinder)421 444 . . . 0 (GBProp)

For single-lever fuel-injection pumps, anidle-stop cylinder is required to preventthe engine being switched off by thespeed limiter if the pump lever can bebrought to the zero-delivery position bythe actuating cylinder.

Operating Cylinder(Actuating Cylinder)421 44. . . . 0 (GBProp)

Fig. 1

Fig. 2

951

4.

Sustained-Action Braking SystemsOn Motor Vehicles

96 1

Sustained-Action Braking Systems On Motor Vehicles4.

Legend:a quadruple system protection

valve

b air reservoir

d operating current relay

e 3/2-way solenoid valve

f operating cylinder for fuel injection pump

g operating cylinder for the exhaust butterfly valve

i towing vehicle foot brake valve with an electrical switch

Fig. 2:Circuit for the electro-pneumatic enginebrake in combination with the servicebraking system operated by compressedair.Upon application of the dual-circuit brakevalve (i), the electrical switch of the brakevalve activates the engine brake via the

operating contact relay (d) and the 3/2-way solenoid valve (e). This means thatit is activated every time the servicebraking system is being used, thus sup-porting the air brake and reducing thewear on the mechanical foundationbrake to the greatest possible extent.

Legend:a quadruple system protection

valve

b air reservoir

c towing vehicle foot brake valve

d operating current relay

f operating cylinder for fuel injection pump

g operating cylinder for the exhaust butterfly valve

h 3/2-way valve

According to Section 41 of the GermanMotor Vehicle Construction and UseRegulation, motor coaches with a per-missible total weight in excess of 5.5 tand other motor vehicles with a permissi-ble total weight in excess of 9 t have tohave an additional sustained-actionbraking system fitted. Sustained-actionbrakes are engine brakes or systemswhich achieve a similar braking perform-ance.The purpose of an engine brake is to

brake the towing vehicle independentlyfrom the service braking system, therebyreducing the wear on the mechanicalfoundation brake to the greatest possibleextent.

Fig. 1:The engine brake is switched on bymeans of a foot-operated three-wayvalve (h) which supplies air pressure forthe operating cylinders for the butterflyvalve and the fuel-injection pump.

Fig. 1

Fig. 2

971

Sustained-Action Braking SystemsOn Motor Vehicles 4.

Purpose:To pressurise and exhaust operating cyl-inder e. g. exhaust braking system.

Operation:The compressed air arriving from the airreservoir flows through Port 1 and reach-es the 3/2-way valve, until it reaches theunderside of the closed inlet valve (e).When the actuating button (a) is pusheddown, the plunger (b) is forced down-wards against the force of the pressurespring (c) until it makes contact with theinlet valve (e), closing the outlet (d) and,as it continues to move downwards,opening the inlet valve (e). The com-

pressed air now flows through Port 2 tothe downstream operating cylinders.

When the actuating button (a) is re-leased, the pressure spring (c) forces theplunger (b) back into its upper end posi-tion. Pushed by the supply pressure andthe pressure spring (f), the inlet valve (e)follows the upward motion of the plunger(b) and closes the passage to Port 1.Through the opening outlet (d) the com-pressed air from Port 2 now flows to Port3 and the operating cylinders are evacu-ated once again.

3/2-Way Valve463 013 . . . 0

98 1

Sustained-Action Braking Systems On Motor Vehicles4.

Air Cylinder421 410 . . . 0 and 421 411 . . . 0

Purpose:Shutting off the fuel injection pump andoperating the butterfly in the exhaustbrake system.

Operation:Air enters the cylinders from either the 3way valve or the 3 way magnet valvethrough port 1. As pressure builds up be-hind piston (a) the push rod (b) movesoutwards against the load of springs (c).

Cylinder 421 410 . . . 0 is connected tothe lever on the fuel injection pump, sothat when operated, the lever movesfrom the ”idle“ position to the ”stop“ posi-

tion. The cylinder is also connected intothe throttle linkage, so that as long as theexhaust brake is in operation, it is impos-sible to depress the accelerator pedal.

Cylinder 421 411 . . . 0 is connected tothe butterfly in the exhaust pipe, so thatwhen operated, the butterfly closes. Theback pressure created in the enginegives a braking effect to the vehicle.

When the cylinders are exhausted, thesprings (c) push the piston (a) back to itsoriginal position.

421 411

412 410

991

Sustained-Action Braking SystemsOn Motor Vehicles 4.

Purpose:To switch on or off electrical units andlamps according to the application.

Operation:Application ”E“ (normally open)On reaching the switch pressure the dia-phragm (d) together with the contactplate (e) is raised and a connection at thepoles (a and b) is made.

With a pressure fall this connection isagain interrupted.

Application ”A“ (normally closed)On reaching the switch pressure the dia-phragm (d) is raised together with thetappet. The tappet (c) lifts the contactplate (e) and the connection at the poles(a and b) is interrupted.

With a pressure fall this connection is re-made.

Purpose:To pressurize an air line when current issupplied to the solenoid.

Operation:The supply line from the air reservoir isconnected to port 1. The armature (b)which forms the valve core keeps inlet(c) closed by the load in pressure spring(d).

When a current reaches solenoid coil (e),armature (b) is lifted, outlet (a) is closed

and inlet (c) is opened. The compressedair from the supply line will now flow fromport 1 to port 2, pressurizing the workingline.

When the current to solenoid coil (e) isinterrupted, pressure spring (d) will re-turn armature (b) to its original position.Inlet (c) is closed, outlet (a) is openedand the working line is exhausted viachamber (A) and exhaust 3.

Pressure Switch441 014 . . . 0

3/2-Way Solenoid ValveNormally Closed472 170 . . . 0

Fig. "E" Fig. "A"