brake system modifications and new features - · pdf filebrake system modifications and new...

Mercedes-Benz Service

Brake SystemModifications and New Features

Model 374, 375, 930 - 934, 940 - 944, 950 - 954, 970 - 976

– This printout will not be recorded by the update service. Status: 07 / 2007 –

Mercedes-Benz Service

Daimler AG · Technische Information und Werkstatteinrichtung (GSP/TI) · D-70546 Stuttgart

Brake SystemModifications and New Features

Model 374, 375, 930 - 934, 940 - 944, 950 - 954, 970 - 976


Information and copyright

Ordering workshop information

You can order all printed workshop information from GSP/TI, such as Intro-duction into Service Manuals, System Descriptions, Function Descriptions, Technology Guides, Technical Data Manuals and adhesive labels, from the following sources:

Within GermanyFrom our GSP/TI Shop on the Internet Link: http://gsp-ti-shop.daimler.com

or alternativelyE-mail: [email protected]:+49-(0)18 05/0 10-79 79Fax: +49-(0)18 05/0 10-79 78

Outside GermanyPlease consult the contact person responsible for your market.

Product portfolio

You can also find comprehensive information on our complete product port-folio in our Internet portal.Link: http://open-after-sales.daimler.com

Questions and Suggestions

If you have any questions or suggestions concerning this product, please write to us.E-mail: [email protected]: +49-(0)18 05/0 10-79 78

or alternativelyAddress: Daimler AG

GSP/TISHPC R822, W002D-70546 Stuttgart

© 2007 by Daimler AG

This document, including all its parts, is protected by copyright.Any further processing or use requires the previous written consent of Daimler AG., department GSP/TIS, HPC R822, W002, D-70546 Stuttgart. This applies in particular to reproduction, distribution, alteration, translation, microfilming and storage and/or processing in electronic systems, including databases and online services.

Picture no. of title image: N00.00-3158-00Order no. of this publication: 6517 1250 02

03/07


Contents

3iBrake System Modifications and New Features

Preface 7

Overview

EPB II 8

Active Brake Assist/Pressure control system 11

Frequent-stop comfort brake/Condensation sensor 12

Twin-diaphragm brake cylinder/Combination brake cylinder 13

Brake control (BS) - EPB II function

Actros

Telligent brake system 14

Rear axle brake application 18

Brake control (BS) 22

Atego, Axor

Front axle brake application 30

Rear axle brake application 36

Trailer control 40

Acceleration skid control 44


Contents

4 i Brake System Modifications and New Features

Active Brake Assist (ABA) function

Actros

Networking 46

Traffic situation evaluation 47

Activation 48

Information collection 49

Warning stages 50

Emergency stop 52

System limits 53

Pressure control system function

Atego, Axor

Compressed air production 62

Component descriptions

Drive axle axle modulator 31.13 64

Pressure ratio valve 68

Central Brake Unit 69

Pressure limiting valve with vent 70

3/2-way valve for auxiliary braking effect 71

Radar sensor controller unit 72

Active Brake Assist control unit 73

Four-circuit protection valve 74

Condensation sensor with drain valve 76


Contents


Repair instructions

Central Brake Unit 78

Active Brake Assist control unit 79

Drive axle axle modulator 31.13 80

Combination brake cylinder 84

Condensation sensor 90

Abbreviations 93

Index 95


6 Brake System Modifications and New Featuresi– This printout will not be recorded by the update service. Status: 07 / 2007 –

Preface


Dear Reader,

This brochure is intended for the use of technical personnel familiar with the service and maintenance of Mercedes-Benz trucks.

This brochure is divided into the following sections:

• Modifications/new features• Function descriptions• Component descriptions• Repair instructions

This brochure summarizes the new and modified func-tion descriptions, component descriptions and repair operations. These will also be made available in WIS. All other documents in WIS retain their validity.

All the information relating to technical data in this brochure was valid as of February 2007 and may therefore differ from the current production configura-tion.

We will publicize further modifications and new features in the relevant WIS documents only. Individual details in this brochure may therefore differ from more up-to-date versions published in WIS.

Daimler AG

After Sales Service Engineering Trucks, GSP/TCST

February 2007


8

Ove

rvie

w

Brake System Modifications and New Featuresi

EPB II

Brake control (BS) - EPB II

A new second generation of the electropneumatic brake, Brake control (BS) - EPB II, was successively introduced as of 2006 for both light and heavy trucks.

Brake control (BS) - EPB II is, like the first generation, designed as a twin-circuit, solely pneumatic basic brake system with an additional electropneumatic circuit.

The previous functions have been optimized and new functions have been added in accordance with the following main development aims:

• Improving system availability and system reliability

• Preventing critical safety-related interventions in the brake control - EPB II system and in other vehicle systems

• Extending the external deceleration functions (such as Active Brake Assist)

Actros system features

New additions to the Actros include a modified brake value sensor, a relay-valve operated axle modulator and a modified rear axle redundancy concept with special pressure ratio valve. The CAN connection and the power supply to the axle modulator have redundant designs to increase system availability.

All other pneumatic and electropneumatic components have been adopted unchanged from the previous brake control (BS) system.

Atego and Axor system features

A completely new component has been added to the Atego and Axor - the Central Brake Unit (CBU) - which is a central controller unit. As with the Actros, a modi-fied rear axle redundancy concept with a new axle modulator and pressure ratio valve has also been introduced. The wear sensors on the rear axle are directly connected to the axle modulator on the Atego and Axor.

A new 3/2-way valve, designed as a combination valve, has also been introduced to provide auxiliary braking effect.

The CAN connection and the power supply to the axle modulator have redundant designs to increase system availability.

Note

• Due to the effect on the front axle pressure control circuit, the new brake control (BS) - EPB II system still cannot be installed with code (B23) Four-wheel parking brake.

• The new brake control (BS) - EPB II system is not installed on any all-wheel drive vehicles or vehicles with front axle disk brakes and rear axle drum brakes.


Ove

rvie

w

9Brake System Modifications and New Features i

EPB II

Brake value sensor

The sensor operates in exactly the same way as the previous brake value sensor.

The following design changes have been made:

• The boot sealing the sensor against the pedal bracket and cab has been replaced by a plastic cover and 2 axial-sealing O-rings.

• The brake value sensor is now sealed against the pedal bracket by a perimeter seal. The seal is positioned in a guide to ensure that it is installed in the correct position and is not lost during transport.

• The brake value sensor has a smaller design, made possible due to a reduction in actuation forces.

Modified rear axle redundancy concept

The previous rear axle redundancy valve is no longer present. The redundant pressure set by the brake value sensor is held back by a 3/2-way valve flange-mounted to the axle modulator when the elec-tropneumatic control circuit is intact.

In the event of electronic failure, the redundant pressure is directed to the two integrated relay valves via the outlet valves in the axle modulator. This means that, even when the system is operating at the redundant level, the relay valves are still used to improve time-related braking characteristics. Previously, an additional relay valve was required in the rear axle redundancy valve.

Axle modulator

The new axle modulator is an improved version of the previous axle modulator and has been introduced with the new brake control (BS) - EPB II system to regulate the rear axle brake pressure. In terms of design, the new axle modulator is different from the previous version in that the two integrated relay valves are now actuated by electrically pulsed 2/2 inlet and outlet valves installed on each side (previously actuation was performed proportionally for each side).

The relay valves, equipped with separate reservoir pressure connections, direct the required brake pres-sure to the brake cylinders.

The new axle modulator has 2 wear sensor inputs which are only used on the Atego and Axor. On the Actros, the wear sensors are read by the rear module, as previously. The control circuit electronics for the trailer control valve are integrated into the axle modu-lator electronics. The trailer control valve is now actu-ated via an additional connector plug on the axle modulator.


10

Ove

rvie

w


EPB II

Central Brake Unit

The Central Brake Unit (CBU) is a completely new component.

It combines the following components in one mecha-tronic unit:

• Brake value sensor• Telligent brake control (BS) control unit• Front axle proportioning valve• Front axle redundancy valve

3/2-way valve for auxiliary braking effect (only Axor)

The 3/2-way valve for auxiliary braking effect is actu-ated electrically by the brake control (BS) control unit, in contrast to the solely pneumatically actuated 3/2-way valve for auxiliary braking effect in the Actros. Compressed air is supplied via the reservoir pressure from circuit 4, as on the Actros.

Pressure ratio valve

The new pressure ratio valve is used on all vehicles with brake control (BS) - EPB II. It is connected solely pneumatically between the brake value sensor (connection 21) and axle modulator (connection 4) and reduces the pressure set by the brake value sensor by a fixed 2:1 ratio. In addition, a special new character-istic improves the brake response time when the elec-tronic control system fails.


Ove

rvie

w


Active Brake Assist/Pressure control system

Active Brake Assist (ABA)

Active Brake Assist (ABA) was introduced as of 08/2006 to further improve the safety of our vehicles. This assistance system is targeted at "rear-end colli-sions with moving objects" with the aim of avoiding as many critical situations as possible and reducing the consequences of an accident without introducing any sort of additional risk to road traffic.

Code (BC7) Active Brake Assist (ABA) can be ordered as special equipment.

Pressure control system, 10 bar

Certain vehicles of the Atego II and Axor II model series are equipped with a 10 bar pressure control system.

Due to the introduction of the 10 bar pressure control system, the following modifications had to be made to the compressed air system:

• Reduction of the pressure control switching range to 9.3 to 10 bar

• Omission of the 12 bar constant pressure reservoir (the condensation sensor is now located on the reservoir of circuit 2)

• New 4-circuit protection valve (omission of 10 bar pressure limiter for brake circuits 1 and 2)

• Adaptation of characteristic of trailer control valve to comply with EC braking ratio range

• Larger brake cylinders on vehicles with antilock brake system (ABS)

• Reduction of design pressure to 8 bar


12

Ove

rvie

w


Frequent-stop comfort brake/Condensation sensor

Frequent-stop comfort brake

The frequent-stop comfort brake is based on the same technology as the previous frequent-stop brake (the rear wheels are braked via rocker switches) but the switch-on condition has been changed so that the frequent-stop brake switch only has to be actuated once. The frequent-stop brake is engaged and released via the accelerator pedal. The brake control (BS) system monitors standstill and idle conditions.

This reduces the stress on the driver because he/she only needs to actuate the frequent-stop brake switch once at the start and once at the end of a trip (e.g. garbage collection operations). In addition, the frequent-stop comfort brake reduces wear on the spring brake cylinder, thus reducing repair and service requirements.

Code (B24) Frequent-stop comfort brake can be ordered as special equipment.

New condensation sensor

Starting in 06/2006, the previous condensation sensor has successively been replaced with a new version in all model series. In addition to a new sensor design, the main feature of the new condensation sensor is an integrated drain valve. When performing a function test on the new condensation sensor, the reaction times for the transition between the various states (wet/dry) must be taken into account.


Ove

rvie

w


Twin-diaphragm brake cylinder/Combination brake cylinder

Twin-diaphragm brake cylinder from Arfesan

Certain Atego models are equipped with a twin-diaphragm brake cylinder from Arfesan. Contrary to the previous combination brake cylinders, the spring accumulator is manually released by means of a release pin attached to the combination brake cylinder.

Combination brake cylinder with internal release bolt

The internal release bolt concept was developed for units with limited installation space. The release bolt remains in the unit during the release process. The release bolt is equipped with an indicator (red indi-cator pin) at the outer end. The length of this indicator pin changes (approx. 4 to 6 mm) to indicate the condi-tions "Operational" and "Not operational":

• Indicator pin retracted and flush with surface:Operational

• Indicator pin extended:Not operational

Combination brake cylinder with internal bleed valve

An external bleed valve can cause excessive amounts of moisture to enter the spring chamber of the spring accumulator. The new combination brake cylinders are therefore equipped with an internal bleed valve.

Note

The indicator (red indicator pin) of the emergency release device only indicates the condition "Not operational". Before removing a combination brake cylinder, it is always necessary to check whether the spring accumulator is fully released.

Note

Due to the design of the system, sometimes a venting noise can be heard at the relay valve when the parking brake is actuated at the same time as partial braking with the service brake at low brake pressures (up to 1.3 bar) and at low pressure gradients (actuation speed < 3 bar/s). The reason is that the internal bleed valve does not close in this condition and a small amount of air can thus flow into the empty spring chamber during partial brake application by the driver. This air then escapes via connection 12 to the relay valve. This is not considered to be a leak because the condi-tion does not occur when the spring accumulator contains air or the pressure in the brake system is increased rapidly.


Telligent brake system

14

Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Vehicles with code (ZX2) EPB II

1 Trailer/semitrailer data interface2 ASIC data bus13.07 Brake value sensor16.07 Proportioning relay valve18.07 Trailer control valve20.02 Single-circuit diaphragm cylinder22.01 Combination brake cylinder24.04 Pressure ratio valve31.13 Drive axle axle modulator33.08 Front axle redundancy valve35.02 Coupling head for supply35.03 Coupling head for brake45.01 ABS solenoid valve

A3 Drive control (FR) control unitA6 Engine control (MR) control unitA7 Base module (GM)A11 Brake control (BS) control unitA28 Drive axle axle modulatorA64 Front module (FM)A65 Rear module (HM)A68 Master switch module 4A77 Dash support switch module 1

Validity

Model 930, 932, 933, 934

B30 Left front axle rpm sensorB31 Right front axle rpm sensorB32 Left 1st rear axle rpm sensorB33 Right 1st rear axle rpm sensorB36 Left 1st front axle

brake wear sensorB37 Right 1st front axle

brake wear sensorB40 Left 1st rear axle

brake wear sensorB41 Right 1st rear axle

brake wear sensorP2 Instrument (INS)S40 ASR cutout buttonS41 Hill holder switch

V1 Reservoir pressure (circuit 1)V2 Reservoir pressure (circuit 2)V3 Reservoir pressure (circuit 3)

CAN 1 Vehicle CANCAN 2 Interior CANCAN 3 Frame CANCAN 4 Engine CANCAN 6 Brakes CAN

E Electric componentP Pneumatic component

a Reservoir pressureb Brake pressurec Redundant brake pressure


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



General

The Telligent brake system is an electronically moni-tored and electrically controlled pneumatic brake system.

The Telligent brake system consists of a purely pneu-matic dual-circuit brake system, which is actuated by the electric brake control.

The electric brake control overlays the conventional, purely pneumatically operating control of the service brake and adds the following functions:

• Antilock brake system (ABS)• Acceleration slip regulation (ASR)• Automatic load-dependent brake pressure control

(ALB)• Hill holder• Brake Assist System

The stability control (SR) function can be integrated in the Telligent brake system as special equipment.

When a trailer or semitrailer is attached, the Telligent brake system is also responsible for controlling the trailer brake system. The pneumatic and electrical control capabilities of the trailer brake mean that trailers or semitrailers with purely pneumatic or elec-tropneumatic brake system can be connected without problem.

The individual regulation of brake pressure for the wheel brakes on the front and rear axles forms the basis for all the functions of the Telligent brake system.

The brake circuits of the front axle, the rear axle and the trailer or semitrailer are each safeguarded by a pneumatic safety circuit referred to as the redundancy circuit.

In the event of partial or total failure of the electric brake control, the wheel brakes are actuated with the relevant redundant brake pressure (c) by purely pneu-matic means.



16

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Electrically regulated brake application

The travel of the brake pedal is registered by 2 sensors in the brake value sensor (13.07) and is converted into electrical values for the brake control (BS) control unit (A11).

The brake control (BS) control unit (A11) uses the values to compute the specified deceleration and the brake pressure (b) required for this. The brake pres-sure (b) necessary for producing the specified deceler-ation is transmitted over the brakes CAN (CAN 6) by control commands from the brake control (BS) control unit (A11) to the drive axle axle modulator (31.13).

The electronics in the brake control (BS) control unit (A11) regulate the brake pressure (b) at the front axle and the electronics in the drive axle axle modulator (31.13) regulate the brake pressure (b) at the rear axle.

The calculated brake pressure (b) is applied at the front axle via the proportioning relay valve (16.07) and at the rear axle direct by the drive axle axle modulator (31.13). The pressure sensors in the proportioning relay valve (16.07) and in the drive axle axle modulator (31.13) monitor the applied brake pressure (b).

The brake control (BS) control unit (A11) uses the signals from the rpm sensors (B30, B31, B32, B33) to calculate the rate of rpm change at the wheels and from this it determines the actual deceleration of the vehicle and the wheel slip.

If there is a difference between the actual deceleration and the specified deceleration, braking is adjusted by an appropriate control command.

Dynamic axle load shift

When the brakes are applied, a dynamic axle load shift occurs, i.e. the load on the rear axle decreases and the load on the front axle increases.

The Telligent brake system counteracts the dynamic axle load shift by distributing the brake pressure (b) to the axles to oppose the dynamic axle load shift.

Because wheel slip occurs when power is transmitted from the tires to the road, the brake control (BS) control unit (A11) regulates the brake pressure (b) while braking to produce equal wheel slip among the regulated axles.


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Differential slip control

The differential slip control replaces the conventional ALB function. Differential slip control starts at moderate wheel speed differences.

ABS control

If one or more wheels shows a tendency to lock up when high rpm differences occur, the brake control (BS) control unit (A11) triggers the familiar ABS control.

ASR control

If one or more of the drive wheels shows a tendency to spin when high rpm differences occur, the brake control (BS) control unit (A11) triggers the familiar ASR control.

Brake wear correction

Brake wear correction occurs only between the wheel brakes on the front and rear axles. Correction between the wheel brakes on one axle is not possible.

The brake wear sensors (B36, B37, B40, B41) at the wheel brakes continuously register the wear of the brake linings on the front and rear axles for the brake control (BS) control unit (A11).

The brake control (BS) control unit (A11) activates the brake wear correction when there is a difference in the amounts of wear between the brake linings on the front and rear axles.

Brake wear correction matches the wear difference of the brake linings on the axles by means of slight alter-ations of the brake pressure (b).

Brake wear correction operates only in the case of slight wheel speed differences in the partial braking range up to a deceleration of 30% of the total braking power.

As 90 % of all brake applications occur in this partial braking range, proper correction of brake wear between the axles is guaranteed within the service life of the brake linings.


Rear axle brake application

18

Brak

e co

ntro

l (BS

) - E

PB II

func

tion




12.08 Rpm sensor13.07 Brake value sensor22.01 Combination brake cylinder24.04 Pressure ratio valve31.13 Drive axle axle modulator33.08 Front axle redundancy valve

A11 Brake control (BS) control unit

FB Parking brake

V1 Reservoir pressure (circuit 1)V2 Reservoir pressure (circuit 2)

a Reservoir pressureb Brake pressurec Redundant brake pressured Control pressure/ventilation

Validity

Model 930, 932, 933, 934


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Prerequisites

• Vehicle moving. • Reservoir pressure (V1, V2) in circuit 1 and circuit

2.• The electric brake control is operational.• No faults are indicated in the driver information

system (FIS) display in the Instrument (INS).

Function sequence

1 The brake pedal is depressed.

2 The sensors in the brake value sensor (13.07) register the pedal travel electrically for the brake control (BS) control unit (A11).

3 The brake control (BS) control unit (A11) uses the pedal travel to compute the specified deceleration of the vehicle.

4 Via connection 21, the pneumatic component of the brake value sensor (13.07) directs a redundant control pressure (c) corresponding to the pedal travel through the pressure ratio valve (24.04) to the closed redundancy valve of the drive axle axle modulator (31.13).

5 The brake control (BS) control unit (A11) uses the calculated specified deceleration to actuate the electronics of the drive axle axle modulator (31.13) via the brakes CAN.

6 The electronics of the drive axle axle modulator (31.13) convert the control command from the brake control (BS) control unit (A11) into electrical control signals for the internal valves and cause them to apply the brake pressure (b).

7 Reservoir pressure (a) is directed from connections 11 and 12 as brake pressure (b) though connections 21 and 22 of the drive axle axle modulator (31.13) into the combination brake cylinders (22.01) of the rear wheel brakes and the wheels are braked.

8 During the entire brake application, the electronics of the drive axle axle modulator (31.13) record the values from the internal pressure sensors and the signals from the rpm sensors (12.08) on the rear wheels and transmits these to the brake control (BS) control unit (A11) via the brakes CAN.

9 The brake control (BS) control unit (A11) evaluates the signals and values of the drive axle axle modulator (31.13) to calculate the actual deceleration and the wheel slip.

If the actual deceleration deviates from the spec-ified deceleration, the brake control (BS) control unit (A11) causes the drive axle axle modulator (31.13) to reduce or increase the brake pressure (b).

10 The driver releases the brake pedal and the brake application is complete. The applied brake pres-sure (b) and the applied redundant brake pressure (c) are released again through connections 3 of the vents.

Note

In the case of ABS control, the internal valves of the drive axle axle modulator (31.13) perform the "pressure build-up", "pressure hold" and "pressure release" functions in the same way as the ABS solenoid valves on the front axle.



20

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake application at rear axle in the event of an electrical fault in the brake system

Validity

Model 930, 932, 933, 934


12.08 Rpm sensor13.07 Brake value sensor22.01 Combination brake cylinder24.04 Pressure ratio valve31.13 Drive axle axle modulator33.08 Front axle redundancy valve

A11 Brake control (BS) control unit

FB Parking brake

V1 Reservoir pressure (circuit 1)V2 Reservoir pressure (circuit 2)

a Reservoir pressureb Brake pressurec Redundant brake pressured Control pressure/ventilation


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Prerequisites

• Vehicle moving. • Reservoir pressure (V1, V2) in circuit 1 and

circuit 2. • The electronic brake control is not operational. The

redundancy valves are de-energized and open.• The driver information system (FIS) display in the

Instrument (INS) indicates a fault in the electric brake control.

Function sequence

1 The brake pedal is depressed.

2 Via connection 21 the pneumatic component of the brake value sensor (13.07) directs a redun-dant brake pressure (c) corresponding to the pedal travel to the closed pressure ratio valve (24.04).There, the redundant brake pressure (c) is reduced in the ratio 2:1.

3 The control valve integrated in the pressure ratio valve (24.04) directs the reduced redundant brake pressure (c) to connection 4 of the drive axle axle modulator (31.13). The integrated de-energized redundancy valve, which is open, directs the reduced redundant brake pressure (c) to the relay valves of the drive axle axle modulator (31.13). The integrated relay valves apply reservoir pres-sure (a) from connections 11 and 12 accordingly. This is directed as brake pressure (b) through connections 21 and 22 into the combination brake cylinders (22.01) of the rear wheel brakes, and the wheels are braked.

The reduction in the redundant brake pressure (c) also reduces the applied brake pressure (b).This reduced brake pressure (b) guarantees a sufficient braking effect.

4 The driver releases the brake pedal and the brake application is complete. The applied brake pressure (b) and the applied redundant brake pressure (c) are released again through connections 3 of the vents.

Note

The brake application occurs with no electronic monitoring or electrical control. There is no over-laid electric brake control. The brake pressure is applied relative to the travel of the brake pedal by purely pneumatic means.


Brake control (BS)

22

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake control (BS)

Shown on 4-channel system

1 Trailer/semitrailer data interface

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 20.02 Single-circuit diaphragm brake cylinder 22.01 Combination brake cylinder 24.04 Pressure ratio valve 28.04 Double check valve 30.03 Pressure limiting valve with vent

(only on model 374.65, 375.40, 944.03/23, 950.62)

31.13 Drive axle axle modulator 33.08a 3/2-way air admission valve33.21 3/2-way valve for auxiliary braking effect

(only on model 374.65, 375.40, 944.03/23, 950.62)

35.02 Coupling head for supply 35.03 Coupling head for brake 45.01 ABS solenoid valve (only on 4-channel system)

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976

A3 Drive control (FR) control unit A6 Engine control (MR) control unit A7 Base module (GM) A110a1 Brake control (BS) control unit P2 Instrument (INS)

S33 Frequent-stop brake switch S40 ASR cutout button S41 Hill holder switch

B Brake value sensor RD Redundancy valve RE Control electronics PV Proportioning valve

NV Reservoir pressure (ancillary consumers) V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3)

CAN 1 Vehicle CAN CAN 4 Engine CAN CAN 6 Brakes CAN

a Reservoir pressure b Brake pressure c Redundant brake pressure


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake control (BS)

General

The brake control (BS) - EPB II system is an electronic/pneumatic brake system based on a purely pneumatic dual-circuit basic brake system and an overlaid elec-tropneumatic brake circuit.

The overlaid electropneumatic brake circuit controls the braking of the vehicle when the brake control (BS) is intact.

The pneumatic dual-circuit basic brake system is divided into the redundant front axle brake circuit, the redundant rear axle brake circuit and the redundant trailer brake circuit.

As long as the electropneumatic brake circuit is oper-ating correctly, the redundancy circuits are kept in reserve, giving priority to the electropneumatic brake control.

If there is a failure of the electronics, the purely pneu-matic dual-circuit basic brake system takes over to brake the vehicle. In the case of redundancy, the Central Brake Unit (CBU) (13.08) modulates a single-circuit pneumatic control pressure from brake circuit 2.

Components

The brake control (BS) - EPB II system consists of the following components:

• Central Brake Unit (CBU) (13.08) • Drive axle axle modulator (31.13) • Trailer control valve (18.07) • Pressure ratio valve (24.04) • Brake wear sensors (12.07) • Rpm sensors (12.08) • ABS solenoid valves (45.01)

(only on 4-channel system) • Double check valves (28.04) • 3/2-way air admission valve (33.08a) • 3/2-way valve for auxiliary braking effect (33.21)

(only on model 374.65, 375.40, 944.03/23, 950.62)


Brake control (BS)

24

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Block diagram

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 31.13 Drive axle axle modulator 33.08a 3/2-way air admission valve 33.21 3/2-way valve for auxiliary braking effect

(only on model 374.65, 375.40, 944.03/23, 950.62)

45.01 ABS solenoid valve

A3 Drive control (FR) control unit A6 Engine control (MR) control unit A7 Base module (GM) P2 Instrument (INS)


Validity

Model 374, 375, 940, 942, 943, 944, 950, 952, 953, 954


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake control (BS)

Block diagram

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 31.13 Drive axle axle modulator 33.08a 3/2-way air admission valve 45.01 ABS solenoid valve (only on 4-channel system)

A3 Drive control (FR) control unit A6 Engine control (MR) control unit A7 Base module (GM) P2 Instrument (INS)


Validity

Model 970, 972, 974, 975, 976


Brake control (BS)

26

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Function

The central control unit of the brake control (BS) - EPB II system is the Central Brake Unit (CBU) (13.08). The CBU (13.08) combines the brake control (BS) control unit (A110a1), the brake value sensor (B), the redun-dancy valve (RD) and the proportioning valve (PV) into a single mechatronic unit. From the signal of the posi-tion sensors in the brake value sensor (B) the software generates the signal for the brake light switch. To avoid any influence of the electropneumatic brake circuit, the front axle redundancy pressure is held back by the closed redundancy valve (RD). The brake pressure necessary at the front axle for the required deceleration is regulated via the proportioning valve (PV) and the integrated pressure sensor.

The open and closed loop control functions for the rear axle are performed by the new drive axle axle modulator (31.13). In relation to the specified pres-sure values transmitted by the brake control (BS) control unit (A110a1), and taking into account the actual pressure values measured by the integrated pressure sensors, the drive axle axle modulator (31.13) regulates the brake pressure at the rear axle.The relay valves integrated in the drive axle axle modulator (31.13) are no longer actuated proportion-ally, but by pulsed actuation of the inlet and outlet valves.

Due to the new redundancy concept, direction switching of the rear axle redundancy circuit is performed via a redundancy valve (RD) flange-mounted to the drive axle axle modulator (31.13), which is also actuated by the drive axle axle modulator (31.13).

The pressure in the rear axle redundancy circuit is limited by a mechanically acting and separately mounted pressure ratio valve (24.04).

To improve system availability, the networking between the drive axle axle modulator (31.13) and the CBU (13.08) with the brakes CAN (CAN 6) is redundant.

Likewise, the trailer control valve (18.07) is actuated electrically via the drive axle axle modulator (31.13) on the basis of the specified values generated in the brake control (BS) control unit (A110a1).

When the electropneumatic control system is intact, the redundancy pressure is held back in the trailer control valve (18.07).If there is a failure of the elec-tronics, the trailer control valve (18.07) is actuated via the redundant pressure set by the brake value sensor (B) of the CBU (13.08).


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake control (BS)

Additional control and adjustment functions

The brake control (BS) is also responsible for the following control and adjustment functions:

• Wheel speed sensing and tire matching • Differential slip control • Antilock brake system (ABS) • Acceleration slip regulation (ASR) • Drag torque control • Stability optimization • Hill holder • Frequent-stop brake (special equipment) • Brake Assist System

Wheel speed sensing and tire matching

Automatic tire matching continuously compensates for differences between the actual tire sizes and thus between the rolling circumferences of the rpm-sensed wheels. The wheel speeds are compared with the cali-brated vehicle speeds from the tachograph.If imper-missible tire pairings are used or if the speed signals vary significantly, an error message is generated.

Differential slip control

During the first brake application, the brake control (BS) control unit (A110a1) calculates the brake pres-sure necessary at each axle to achieve the required deceleration. In the pressure build-up phase the brake control (BS) control unit (A110a1) detects the loads on each axle from the rpm differences at the wheels between the individual axles, and then regulates the brake pressure accordingly. The brake control (BS) control unit (A110a1) corrects the brake pressure so as to minimize slip differences at the wheels between the individual axles.


Brake control (BS)

28

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Antilock brake system (ABS)

ABS regulation prevents the wheels from locking up when the wheel rpm differences are high, i.e. when certain wheels have reached their upper slip limit. Interaxle and interwheel differential locks are deacti-vated if engaged.

Acceleration slip regulation (ASR)

The ASR function detects whether drive wheels are tending to spin.

• Via the drive control (FR), ASR engine intervention decreases the engine torque in order to reduce drive slip.

• Through selective ASR brake intervention, any drive wheel that shows a tendency to spin is braked via the drive axle axle modulator (31.13).

Leading and trailing axles are regulated together with the drive axle brake control, but should not be braked when ASR regulation is active. For this reason, the drive axle axle modulator (31.13) actuates a 3/2-way air admission valve (33.08a), which holds back the ASR brake pressure via double check valves (28.04).

• The ASR shutoff function serves to improve traction, e.g. for off-road operations.


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake control (BS)

Drag torque control

Drag torque control prevents the drive wheels from locking up due to a brief increase engine torque in deceleration mode with poor road contact.

Stability optimization

Solo semitrailer tractors generally exhibit a very low rear axle load as a percentage of the whole. In order to guarantee the stability of the rear end under braking, the deceleration at the front axle is limited by software measures in certain models.

If there is a failure of the electronics (redundancy case), the front axle pressure remains unlimited.

Hill holder

The hill holder helps the driver to keep his vehicle steady while stationary and when moving off, particu-larly on gradients, without having to apply the parking brake. When the hill holder is engaged, the brake pres-sure applied with the service brake is maintained.

Frequent-stop brake

The frequent-stop brake operates in a similar way to the hill holder and is intended for municipal vehicles etc.In contrast to the hill holder, a minimum brake pressure of 3.5 bar is applied at all axles.

Brake Assist System

The Brake Assist System evaluates the actuation speed and travel of the brake pedal. It can thus detect an emergency braking situation at an early stage and increases the brake pressure if necessary.


Front axle brake application

30

Brak

e co

ntro

l (BS

) - E

PB II

func

tion




12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 20.02 Single-circuit diaphragm brake cylinder 30.03 Pressure limiting valve with vent

(only on model 374.65, 375.4, 944.03/23, 950.62)

31.13 Drive axle axle modulator 33.21 3/2-way valve for auxiliary braking effect

(only on model 374.65, 375.4, 944.03/23, 950.62)

45.01 ABS solenoid valve (only on 4-channel system)

A110a1 Brake control (BS) control unit

AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valvePV Proportioning valve RD Redundancy valve RV Relay valve SV Control valve W Travel sensor WV Shuttle valve

NV Reservoir pressure (ancillary consumers) V2 Reservoir pressure (circuit 2)

a Reservoir pressure b Brake pressure c Redundant brake pressure d Control pressure

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Function

When the brake pedal is operated, the position sensors (W) register the pedal travel and report it to the brake control (BS) control unit (A110a1).

So that the electropneumatic brake circuit is not over-laid by redundant brake pressure (c), the redundancy valve (RD) is closed electrically by the brake control (BS) control unit (A110a1).

The proportioning valve (PV) is actuated by the brake control (BS) control unit (A110a1) and forwards the available reservoir pressure (a) to the relay valve (RV) as the control pressure (d) according to the target deceleration calculated by the brake control (BS) control unit (A110a1).

According to the control pressure (d) from the propor-tioning valve (PV), the relay valve (RV) now sends the available reservoir pressure (a) as brake pressure (b) to connections 21 and 22.

The pressure sensor (D) reports the brake pressure (b) set by the relay valve (RV) to the brake control (BS) control unit (A110a1).

The brake pressure (b) applied to connections 21 and 22 then flows via the shuttle valve (WV) in the 3/2-way valve for auxiliary braking effect (33.21) (only on model 374.65, 375.40, 944.03/23, 950.62) and via the ABS solenoid valves (45.01) (only on 4-channel system) to the single-circuit diaphragm brake cylin-ders (20.02) of the front axle.

The rpm sensors (12.08) evaluate any wheel rpm change and provide the brake control (BS) control unit (A110a1) with feedback on the actual deceleration attained and the wheel slip. If the actual deceleration attained deviates from the target deceleration, the brake control (BS) control unit (A110a1) corrects accordingly.

When the brake pedal is released, the applied brake pressure (b) and the control pressure (d) are released via the vent, connection 3.

Note

Model 944.03/23, 950.62

The pressure limiting valve with vent (30.03) and the 3/2-way valve for auxiliary braking effect (33.21) in these vehicles serve to satisfy the legal requirement for auxiliary braking effect in the event of failure of the pneumatic front axle brake circuit. Depending on the location of the defect, the left front wheel is braked with a pressure of 2.5 bar.The pressure is supplied from the reservoir pressure (NV).



32

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Front axle brake application with pneumatic failure of front axle brake circuit

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 20.02 Single-circuit diaphragm brake cylinder 30.03 Pressure limiting valve with vent 31.13 Drive axle axle modulator 33.21 3/2-way valve for auxiliary braking effect 45.01 ABS solenoid valve


AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve PV Proportioning valve RD Redundancy valve RV Relay valve SV Control valve W Travel sensor WV Shuttle valve


a Reservoir pressure b Brake pressure c Redundant brake pressure d Control pressuree Unpressurized

Validity

Model 374.65, 375.4, 944.03/23, 950.62


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



General

Legal requirements stipulate that adequate decelera-tion must be guaranteed in the event of a pneumatic failure of the front axle brake circuit. In this case the left front wheel is braked in order to decelerate the vehicle adequately.

Function

There is no brake pressure present at connection 11 of the 3/2-way valve for auxiliary braking effect (33.21). The reservoir pressure (NV) present at connection 1 is restricted to 2.5 bar via the pressure limiting valve without vent (30.03). Since the pressure sensor (D) does not report any pressure(s) to the brake control (BS) control unit (A110a1), the control unit opens the control valve (SV) in the 3/2-way valve for auxiliary braking effect (33.21). The restricted reservoir pressure (a) now flows through the open control valve (SV) and the shuttle valve (WV) as brake pressure (b) to connection 2 of the 3/2-way valve for auxiliary braking effect (33.21). Via the left ABS sole-noid valve (45.01) the brake pressure (b) travels to the left single-circuit diaphragm brake cylinder (20.02) on the front axle.



34

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake application at front axle in the event of an electrical fault in the brake system


12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 20.02 Single-circuit diaphragm brake cylinder 30.03 Pressure limiting valve with vent

(only on model 374.65, 375.40, 944.03/23, 950.62)

31.13 Drive axle axle modulator 33.21 3/2-way valve for auxiliary braking effect

(only on model 374.65, 375.40, 944.03/23, 950.62)

45.01 ABS solenoid valve (only on 4-channel system)


AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve PV Proportioning valve RD Redundancy valve RV Relay valve SV Control valve W Travel sensor WV Shuttle valve


a Reservoir pressure b Brake pressure c Redundant brake pressure d Vent

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



General

If there is a failure of the electronics, the front axle is braked via the purely pneumatic redundancy circuit.

An error message is output on the driver information system (FIS) display in the Instrument (INS).

Function

When the brake pedal is actuated, the pneumatic component of the brake value sensor (B) directs a reservoir pressure (a) corresponding to the pedal travel from connection 11, 12 as redundant brake pressure (c) through the de-energized open redun-dancy valve (RV) and through the de-energized open proportioning valve (PV) to the relay valve (RV).

According to the redundant brake pressure (c), the relay valve (RV) now sends the available reservoir pressure (a) as brake pressure (b) to connections 21 and 22.

The brake pressure (b) applied to connections 21 and 22 then flows via the shuttle valve (WV) in the 3/2-way valve for auxiliary braking effect (33.21) (only on model 374.65, 375.40, 944.03/23, 950.62) and via the ABS solenoid valves (45.01) (only on 4-channel system) to the single-circuit diaphragm brake cylin-ders (20.02) of the front axle.

When the brake pedal is released, the applied brake pressure (b) and the redundant brake pressure (c) are released via the vent, connection 3.

Note

In semitrailer tractors the brake pressure at the front axle is not limited in the event of an elec-tronics failure because this function is only imple-mented in software.



36

Brak

e co

ntro

l (BS

) - E

PB II

func

tion



12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 20.02 Single-circuit diaphragm brake cylinder 22.01 Combination brake cylinder 24.04 Pressure ratio valve 31.13 Drive axle axle modulator

A110a1 Brake control (BS) control unitCAN 6 Brakes CAN

AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve FB Parking brake PV Proportioning valve RD Redundancy valve RE Control electronics RV Relay valve W Travel sensor

V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2)


Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



Function


The target deceleration calculated by the brake control (BS) control unit (A110a1) is transmitted to the control electronics (RE) in the drive axle axle modu-lator (31.13). The data exchange occurs via the brakes CAN (CAN 6).

So that the electropneumatic brake circuit is not over-laid by redundant brake pressure (c), the redundancy valve (RD) at the drive axle axle modulator (31.13) is closed electrically.

The control electronics (RE) close the outlet valves (AV) and, via the inlet valves (EV), the available reser-voir pressure (a) is forwarded to the relay valves (RV) in the drive axle axle modulator (31.13) as the control pressure (d) according to the target deceleration calculated by the brake control (BS) control unit (A110a1).

According to the control pressure (d) from the inlet vales (EV), the relay valves (RV) in the drive axle axle modulator (31.13) apply the available reservoir pres-sure (a) as brake pressure (b) to connections 21 and 22 and then on to the combination brake cylinders (22.01) of the rear axle.

The pressure sensors (D) in the drive axle axle modu-lator (31.13) report the brake pressures (b) applied by the relay valves (RV) in the drive axle axle modulator (31.13) to the control electronics (RE).

The rpm sensors (12.08) evaluate any wheel rpm change and provide the brake control (BS) control unit (A110a1) with feedback on the actual deceleration attained and the wheel slip. If the actual deceleration deviates from the target deceleration, the brake control (BS) control unit (A110a1) corrects accord-ingly.




38

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Brake application at rear axle in the event of an electrical fault in the brake system

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 20.02 Single-circuit diaphragm brake cylinder 22.01 Combination brake cylinder 24.04 Pressure ratio valve 31.13 Drive axle axle modulator


AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve FB Parking brake PV Proportioning valve RD Redundancy valve RE Control electronics RV Relay valve W Travel sensor

V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2)

a Reservoir pressure b Brake pressure c Redundant brake pressure d Vent

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion



General

If there is a failure of the electronics, the rear axle is braked via the purely pneumatic redundancy circuit.

An error message is output on the driver information system (FIS) display in the Instrument (INS).

Function

The actuation of the brake pedal causes the pneu-matic component of the brake value sensor (B) to send a reservoir pressure (a) proportional to the pedal travel from connection 11 and 12 to connection 23 as a redundant brake pressure (c) and then on to the pressure ratio valve (24.04).

The pressure ratio valve (24.04) reduces the redun-dant brake pressure (c) in the ratio 2:1 and forwards it to the drive axle axle modulator (31.13).

Via the de-energized open redundancy valve (RD) in the drive axle axle modulator (31.13), the redundant brake pressure (c) flows via the outlet valves (AV) to the relay valves (RV) in the drive axle axle modulator (31.13).

Proportional to the redundant brake pressure (c), these relay valves (RV) then direct the available reser-voir pressure (a) as brake pressure (b) to connections 21 and 22 and then on to the combination brake cylin-ders (22.01) of the rear axle.



Trailer control

40

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Trailer control

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 20.02 Single-circuit diaphragm brake cylinder 22.01 Combination brake cylinder 24.04 Pressure ratio valve 31.13 Drive axle axle modulator 35.02 Coupling head for supply 35.03 Coupling head for brake

A110a1 Brake control (BS) control unit CAN 6 Brakes CAN

AS Breakaway coupling AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve FB Parking brake PV Proportioning valve RD Redundancy valve RE Control electronics RV Relay valve W Travel sensor

V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3)


Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Trailer control

Function


The target deceleration calculated by the brake control (BS) control unit (A110a1) is transmitted via the brakes CAN (CAN 6) to the control electronics (RE) of the drive axle axle modulator (31.13).

The proportioning valve (PV) in the trailer control valve (18.07) is actuated by the control electronics (RE) of the drive axle axle modulator (31.13) according to the target deceleration and directs the available reservoir pressure (a) as control pressure (d) to the relay valve (RV) in the trailer control valve (18.07).

The redundant brake pressure (c) and the control pres-sure (d) set by the proportioning valve (PV) in the trailer control valve (18.07) are present at this relay valve (RV) simultaneously at connection 42. The control pressure (d) set by the proportioning valve (PV) is preferred, and the available reservoir pressure (a) flows to the coupling head for brake (35.03) as a brake pressure (b) proportional to the control pressure (d).

The pressure sensor (D) in the trailer control valve (18.07) reports the brake pressure (b) applied by the relay valve (RV) in the trailer control valve (18.07) to the control electronics (RE) of the drive axle axle modulator (31.13).

The rpm sensors (12.08) evaluate any wheel rpm change and provide the control electronics (RE) of the drive axle axle modulator (31.13) with feedback on the actual deceleration attained and the wheel slip. If the actual deceleration deviates from the target decelera-tion, the drive axle axle modulator (31.13) corrects accordingly.



Trailer control

42

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Trailer control in the event of an electrical fault in the brake system

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 18.07 Trailer control valve 20.02 Single-circuit diaphragm brake cylinder 22.01 Combination brake cylinder 24.04 Pressure ratio valve 31.13 Drive axle axle modulator 35.02 Coupling head for supply 35.03 Coupling head for brake


AS Breakaway coupling AV Outlet valve B Brake value sensor D Pressure sensor EV Inlet valve FB Parking brake PV Proportioning valve RD Redundancy valve RE Control electronics RV Relay valve W Travel sensor

V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3)


Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Trailer control

General

If there is a failure of the electronics, the trailer or semitrailer is braked via the purely pneumatic redun-dancy circuit.

An error message is output on the driver information system (FIS) display in the Instrument (INS) (P2).

Function

The actuation of the brake pedal causes the pneu-matic component of the brake value sensor (B) to send a reservoir pressure (a) proportional to the pedal travel via connection 23 to the trailer control valve (18.07) as a redundant brake pressure (c). According to the redundant brake pressure (c), the relay valve (RV) in the trailer control valve (18.07) now sends the available reservoir pressure (a) as brake pressure (b) to the coupling head for brake (35.03).



Acceleration skid control

44

Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Acceleration slip regulation

12.07 Brake wear sensor 12.08 Rpm sensor 13.08 Central Brake Unit (CBU) 22.01 Combination brake cylinder 24.04 Pressure ratio valve 28.04 Double check valve31.13 Drive axle axle modulator 33.08a 3/2-way air admission valve

A110a1 Brake control (BS) control unitA3 Drive control (FR) control unitA6 Engine control (MR) control unit

AV Outlet valve D Pressure sensor EV Inlet valve RD Redundancy valve RE Control electronics RV Relay valve W Travel sensor

V1 Reservoir pressure (circuit 1)

CAN 1 Vehicle CANCAN 4 Engine CANCAN 6 Brakes CAN

a Reservoir pressure b Brake pressure c Redundant brake pressure d Control pressure/ventilation

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Brak

e co

ntro

l (BS

) - E

PB II

func

tion


Acceleration skid control

General

The acceleration slip regulation (ASR) attempts to prevent the drive wheels from spinning when grip is lost. The function of the acceleration slip regulation (ASR) is integrated in the brake control (BS) control unit (A110a1).

ASR engine intervention

From the signals of the rpm sensors (12.08) the drive axle axle modulator (31.13) detects any tendency of the drive wheels to slip and forwards this information to the brake control (BS) control unit (A110a1) for evaluation. In order to reduce the drive slip, the brake control (BS) control unit (A110a1) authorizes a reduc-tion in engine torque via the engine control (MR) control unit (A6).

Selective ASR brake intervention

From the signals of the rpm sensors (12.08) the drive axle axle modulator (31.13) detects any tendency of a drive wheel to slip and forwards this information to the brake control (BS) control unit (A110a1) for evalua-tion.

Via the drive axle axle modulator (31.13) the brake control (BS) control unit (A110a1) authorizes an appropriate brake pressure (b) to be sent to the drive wheel that is tending to slip. The data exchange occurs via the brakes CAN (CAN 6).

ASR shutoff

The acceleration slip regulation (ASR) can be shut off using the ASR cutout button in order to improve trac-tion, e.g. for off-road operations. The ASR indicator lamp in the Instrument (INS) lights up when ASR control is switched off or during ASR intervention.

The function is reactivated automatically when the ignition is switched off and on again.

Note

Leading and trailing axles are regulated together with the drive axle brake control, but should not be braked when ASR regulation is active. For this reason, the drive axle axle modulator (31.13) actu-ates the 3/2-way air admission valve (33.08a), which holds back the brake pressure (b) via double check valves (28.04).


Networking

46

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


Data flow diagram

Input informationa Information

from brake control (BS) control unit (A11): - Average front axle speed- Brake pedal status

b Information from radar sensor controller unit (ART) (A63.1):- Distance to vehicle in front - Relative speed - Relative acceleration

c Information from rear module (HM) (A65):- Driving level status

d Information from drive control (FR) control unit (A3): - Kickdown - Accelerator pedal position

e Information from master switch module 4 (A68):- Active Brake Assist (ABA) status

Output information f Request by Active Brake Assist (ABA) control unit

(A111) for necessary warning

g Request by Active Brake Assist (ABA) control unit (A111) to decelerate vehicle

Validity

Model 930, 932, 934

Integration in overall network

A3 Drive control (FR) control unit A7 Base module (GM) A11 Brake control (BS) control unit A28 Drive axle axle modulator A63.1 Radar sensor controller unit (ART) A65 Rear module (HM) A68 Master switch module 4 A77 Dash support switch module 1 A111 Active Brake Assist (ABA) control unitB1 Foot throttle actuator B28 Center roof speaker B44 Brake value sensor CAN 1 Vehicle CAN CAN 2 Interior CAN CAN 3 frame CAN CAN 6 Brakes CAN P2 Instrument (INS) S195 Active Brake Assist (ABA) button


Traffic situation evaluation

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


General

The ever increasing density of traffic on our roads means that hazardous situations arise more and more frequently. Active Brake Assist (ABA) has been devel-oped to reduce the number of rear-end collisions in particular.

Active Brake Assist (ABA) permanently evaluates the traffic situation in front of the vehicle it is installed in. The vehicle distances and the difference in speed rela-tive to the vehicles ahead are recorded and any changes are evaluated to establish whether there is a risk of a rear-end collision. Evaluation becomes more critical the less time the driver has to react to a hazardous situation.

A vehicles in front is included in the evaluation process if:

• It is detected for at least 1 s• It is at least 7 m away• It is driving at a speed of at least 10 km/h

Active Brake Assist (ABA) is designed to first warn the driver in a critical situation. This gives the driver the opportunity to avoid these critical situations by braking or by taking evasive action.Active Brake Assist (ABA) evaluates all "relevant driver activities" that the driver can undertake to deal with the situation.

This ensures that the driver can keep control of his vehicle at all times. If the system does not detect any reaction by the driver, the vehicle is then decelerated automatically with the assistance of the brake control (BS) system.

Note

Active Brake Assist (ABA) does not protect against inattentiveness or driving mistakes. It is intended solely as an aid to support the driver. The ABA only reacts to vehicles in front which are moving, and not to stationary obstacles on the road (e.g. the end of a traffic jam or a broken-down vehicle). Furthermore, the radar sensor controller unit (ART) (A63.1) must be correctly adjusted, other-wise the system may fail to correctly recognize the traffic situation in front of the vehicle.


Activation

48

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


1 Activation

After the ignition is switched on, the Active Brake Assist (ABA) control unit (A111) starts the initialization and self-test phase.

When Active Brake Assist (ABA) is active, the LED in the Active Brake Assist (ABA) button (S195) in dash support switch module 1 (A77) is switched off. The status of the Active Brake Assist (ABA) system is indi-cated redundantly in the driver information system (FIS) display of the instrument (INS) (P2).

The driver can use the Active Brake Assist (ABA) button (S195) at any time to deactivate or activate Active Brake Assist (ABA), even during intervention by the brake system. However, the visual warning in the driver information system (FIS) display remains active even with the system switched off.

The following conditions must be met for Active Brake Assist (ABA) to operate:

• Vehicle speed 15 km/h • Vehicle at driving level

If the radar sensor controller unit (ART) (A63.1) detects that the vehicle is not at the driving level via the information from the rear module (HM) (A65), meaning that the transmitter/receiver lobes of the radar sensor are not aligned correctly, the radar sensor controller unit (ART) (A63.1) switches off. This deactivates Active Brake Assist (ABA).


Information collection

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


2 Collecting information about the traffic situation

The radar sensor controller unit (ART) (A63.1) records information about the traffic situation up to 150 m in front of the vehicle.

The radar sensor controller unit (ART) (A63.1) trans-mits signals and then receives the signals reflected back off any obstacles. The radar sensor controller unit (ART) (A63.1) operates with 3 transmitter/receiver lobes (A), which each have a read angle of 3.4° and partially overlap each other.

Based on the received signals and the signal travel times, the radar sensor controller unit (ART) (A63.1) continuously measures the distance to the vehicle in front along with its relative speed and relative acceler-ation.

The radar sensor controller unit (ART) (A63.1) trans-mits the distance to the vehicle in front and its relative speed/acceleration over the frame CAN (CAN 3) to the base module (GM) (A7). From there, the informa-tion is sent over the vehicle CAN (CAN 1) to the Active Brake Assist (ABA) control unit (A111), which evalu-ates the current traffic situation based on this informa-tion and information about the vehicle it is installed in.

A Transmitter and receiver lobes


Warning stages

50

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


3 Warning stages

If there is a risk of a rear-end collision with the vehicle in front, the driver is warned of this in two warning stages before the Active Brake Assist (ABA) system automatically initiates an emergency stop.The system always runs through both warning stages before an emergency stop is performed. A distance warning from the adaptive cruise control system (ART) may already have been issued if the adaptive cruise control system (ART) is also active.

ART warnings and ABA warnings are different:

• An ART distance warning is recognizable by a double tone which sounds once. The control logic of the adaptive cruise control system first brakes the vehicle and then warns the driver or, if a critical situation occurs suddenly, brakes the vehicle and warns the driver at the same time. In some cases, the system only brakes the vehicle without issuing a warning (up to 20% of max. deceleration).

• An ABA distance warning is recognizable by a continuously repeating tone or a permanent warning tone. The ABA control system first warns the driver (for at least 1 s) and then brakes the vehicle (30% of max. deceleration).

3.1 ART distance warning

To warn the driver, the drive control (FR) control unit (A3) sends the "Warning ON" and "Warning tone ON" messages to the Instrument (INS) (P2) via the vehicle CAN (CAN 1).

The red warning bar and an appropriate warning symbol is activated in the driver information system (FIS) display (P2p1). In addition, a warning tone is output at the center roof speaker (B28) which is actu-ated directly by the Instrument (INS) (P2).

Note

The duration of the respective warning stage is based on the time available for the driver to react when a rear-end collision is threatening but is always at least 1 s per warning stage.

Note

An ART distance warning can only be issued if adaptive cruise control (ART) is installed and switched on.

Distance warning system indicator

P2 Instrument (INS)P2p1 Driver information display (FIS)


Warning stages

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


3.2 ABA warning stage 1: "Situation critical"

When a critical situation occurs, a warning indicator is activated in the driver information system (FIS) display (P2p1) and a regular intermittent warning tone is output by the center roof speaker (minimum duration 1 s).

At the same time, the radio and hands-free system are muted so that the driver can concentrate fully on the traffic.

3.3 ABA warning stage 2: "Situation very critical"

When a very critical situation occurs, a warning indi-cator is activated in the driver information system (FIS) display (P2p1) and an intermittent warning tone is output by the center roof speaker (minimum duration 1 s).

The radio and hands-free system remain muted.

In addition, the service brake is actuated with up to 30% of the max. deceleration effect and the brake lights are switched on.

During warning stages 1 or 2, intervention by the brake system may be suppressed if the ABA detects one of the following driver activities:

• Actuation of the brake pedal: The driver has recognized the situation and has reacted accordingly.

• Actuation of the turn signal: Actuation of the turn signal(max. 20 s) indicates a lane change; the driver has caused the situation intentionally and has reacted accordingly.

• Heavy acceleration or kickdown: Heavy acceleration or kickdown indicates the driver's wish to accelerate quickly; in this case, it is assumed that the driver is aware of and has caused the situation intentionally (e.g. by overtaking).

• Target loss: Performing an obstacle avoidance maneuver with target loss indicates that the driver has recognized the situation and has reacted accordingly.

• The driver shuts off Active Brake Assist (ABA) by actuating the Active Brake Assist (ABA) button (S195).

Note

The indicators in the driver information system (FIS) display (P2p1) remain active.


Emergency stop

52

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


4 Emergency stop

If no driver activity is detected and there is still the threat of a collision, Active Brake Assist (ABA) initiates an emergency stop (emergency braking).

The messages required for an emergency stop are sent from the Active Brake Assist (ABA) control unit (A111) to the brake control (BS) control unit (A11) via the vehicle CAN (CAN 1).

During the emergency stop (emergency braking) trig-gered by the ABA, the warning indicator lights up in the driver information system (FIS) display (P2p1) and a continuous warning tone is output at the center roof speaker (B28).

An initiated emergency stop (emergency braking) can only be canceled by one of the following driver activi-ties:

• Kickdown • The driver shuts off Active Brake Assist (ABA) with

the Active Brake Assist (ABA) button (S195)

Once initiated, the emergency stop cannot be canceled by any other activities. This prevents unin-tended cancellation of the emergency stop by inad-vertent activation of functions, e.g. turn signal lamp.

Note

After an emergency stop, the vehicle is only braked for a maximum of 5 additional seconds at standstill by the Active Brake Assist (ABA) system.


System limits

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5 System limits

5.1 Limitations of vehicle detection system

5.1.1 Driving offset from vehicles in front

The radar sensor controller unit (ART) (A63.1) deter-mines the distances, the relative speeds and the angles of vehicles which are located inside the detec-tion zone in front of the vehicle.

In order to determine which vehicle of all the vehicles detected is actually the vehicle in front, the detected vehicles are assigned to lanes.

Vehicles in front which have an off-center lane posi-tion may cause detection problems because they may be located outside the detection zone of the radar sensor controller unit (ART) (A63.1). As a result, the distance to the vehicle immediately in front may become too close because the radar sensor controller unit (ART) (A63.1) only detects the distance to the vehicle which is located in the detection zone.

5.1.2 Close lane changes by vehicles in front

Vehicles which change into the lane of the vehicle equipped with ARA without leaving sufficient distance between the vehicles can only be detected once they are in the detection zone of the radar sensor controller unit (ART) (A63.1).

The driver must therefore increase the distance to the vehicle in front by braking.

Vehicles in front

Lane change


System limits

54

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.1.3 Vehicles at side of road

In some cases, vehicles moving along the side of the road (e.g. malfunctioning vehicles) may be unneces-sarily detected by the radar sensor.

5.1.4 Vehicles at on ramps, exit ramps or intersections

The system can have problems detecting the vehicle in front at on ramps, exit ramps or intersections.

• Vehicles entering the road: Target may be detected late meaning that no warning is issued and no braking occurs although the vehicle is already partially in the same lane.

• Vehicles leaving the road: Target may be released late meaning that a brief warning is issued or braking occurs although the vehicle is already on the next lane.

Vehicles at side of road

Vehicles at on ramps, exit ramps or intersections


System limits

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.1.5 Vehicles in front on bends

The vehicle in front is determined on the basis of the angle of the bend calculated by the radar sensor controller unit (ART) (A63.1). Data such as the distance to the detecting vehicle, relative speed (stationary or moving), relative acceleration etc. are essential for the Active Brake Assist (ABA) system to function correctly.

On bends, and when entering/exiting bends, the system may detect vehicles late or briefly detect "vehi-cles in front" in rare cases where the circumstances are unfavorable.

5.1.6 Vehicles on front when bend continues in opposite direction

Depending on the radius of the bend, vehicles in front may be detected by the radar sensor but not assigned to the same lane as the detecting vehicle because the system assumes that the lane of the detecting vehicle (F) continues in the same direction.

As a result, the ART and ABA do not react to these vehicles.

Vehicle in front on bend continuing in opposite direction

F Continuation of lane of detecting vehicle (in theory)

Vehicles in front on bends


System limits

56

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.2 Warnings in particular driving situations

5.2.1 Warnings during overtaking maneuvers

When overtaking, the ABA or the ART may issue a distance warning if the overtaking maneuver is partic-ularly tight. This is caused by the detecting vehicle briefly tailgating the vehicle in front just before or while moving aside.

Warning during overtaking maneuvers


System limits

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


• Visual warningThe ABA only issues a visual warning (no braking) if the turn signal is actuated or the driver applies significant pressure to the foot throttle actuator (B1). The ART only issues a visual warning (no braking) if the driver applies significant pressure to the foot throttle actuator (B1) (the ART does not react to the turn signal).

Even when switched off, the ART and ABA issue visual warnings (no braking) in very critical situations.

• Visual warning with warning tone(no braking)If the turn signal is not actuated and the foot throttle actuator (B1) has not been actuated noticeably, the ABA issues an acoustic and visual warning during tight overtaking maneuvers.

Even when switched off, the ART and ABA issue visual warnings with warning tone (no braking) in very critical situations.

• Visual warning with warning tone and brakingIf the foot throttle actuator (B1) has not been actuated noticeably, the ART may brake the vehicle slightly during very tight overtaking maneuvers and warn the driver about the situation with an acoustic and visual warning. In this type of situation, the ABA generally does not brake the vehicle and only issues a warning because the situation has nearly always eased or the detecting vehicle has moved across during the minimum warning time of the ABA.

• BrakingIf the foot throttle actuator (B1) has not been actuated noticeably, the ART may brake the vehicle slightly during very tight overtaking maneuvers. This is not an ABA brake application.


System limits

58

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.2.2 Warning when vehicles move out to another lane

When the vehicle in front moves out to another lane, the driver often slows down before the vehicle is on the neighboring lane. This reduces the distance between the vehicles and increases the difference in speed. The ART may issue a warning. Since the ART reacts quickly and early by decelerating the vehicle, the situation is eased in good time and the ABA no longer intervenes. This effect can be increased when a vehicle moves out of a lane or drives off the road on a bend. On bends and at the start/end of a bend, a vehicle that have moved across may still be detected by the sensor for a short period, even though the vehicle is already on the next lane over.

Warning when vehicles move out to another lane


System limits

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


• Visual warningA visual warning is only issued if the driver applies significant pressure to the foot throttle actuator (B1) and drives in close to the vehicle in front at the same time. Generally, the warning is issued by the ART but it may also be issued by the ABA in rare, very critical situations.

Even when switched off, the ART and ABA issue visual warnings (no braking) in very critical situations.

• Visual warning with warning tone (no braking)This warning is issued when the ART is switched off, the detecting vehicle moves in very close to the vehicle moving across and the foot throttle actuator (B1) is not actuated or is held in the same position. Generally, the warning is issued by the ART but it may also be issued by the ABA in rare, very critical situations.

Even when switched off, the ART and ABA issue visual warnings with warning tone (no braking) in very critical situations.

• Visual warning with warning tone and brakingIf the foot throttle actuator (B1) has not been actuated noticeably, the ART may brake the vehicle slightly during very tight lane change maneuvers and warn the driver about the situation with an acoustic and visual warning. The ABA does not brake in this type of situation and only issues a warning (visual and acoustic) because the situation has nearly always eased during the minimum warning time of the ABA or the vehicle in front has already completed its lane change maneuver.

• BrakingIf the foot throttle actuator (B1) has not been actuated noticeably, the ART may brake the vehicle slightly during very tight lane changemaneuvers.This is only a brief, slight deceleration of the detecting vehicle and not an ABA brake application.Frequent, long-lasting brake applications may be caused by an incorrectly adjusted (lateral adjustment) radar sensor controller unit (ART) (A63.1).


System limits

60

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.2.3 Warnings when no vehicle is in front

These warnings are issued by the ART, not by the ABA. When activated, the ART also issues warnings about stationary obstacles e.g. vehicles that have broken down. Faulty warnings may be caused by bends (incl. driving on to a bend), posts, guardrails at the outside of the bend, traffic signs projecting out into the road and bridges.

Warning although no vehicle in front

Note

Very frequent brake applications due to stationary obstacles may be caused by an incorrectly adjusted (height adjustment) radar sensor controller unit (ART) (A63.1).


System limits

Act

ive

Brak

e A

ssis

t (A

BA) f

unct

ion


5.2.4 Warning about stopping vehicles

In individual cases, ABA distance warnings may be issued when a vehicle in front is stopping e.g. if the vehicle in front brakes erratically or brakes hard briefly, causing the distance to the vehicle in front (A) to reduce quickly. The driver often does not notice this (e.g. when stopping at traffic lights or at the end of a traffic jam).

Warning about stopping vehicles

A Distance to vehicle in front


Compressed air production

62

Pres

sure

con

trol

sys

tem

func

tion


Function diagram

Vehicles with pressure control system shown with single-cylinder compressor and single-chamber air drier with integrated pressure regulator

1.01 Single cylinder compressor 4.07 4-circuit protection valve

with integrated pressure limiter 5.01 Single-chamber compressed air reservoir 6.12 Single-chamber air drier

with integrated pressure regulator 10.01 Cut-out 12.09 Condensation sensor (B76) 30.01 Safety valve 38.02 Test connection M16X1.5

B71 Brake circuit 1 and 2 reservoir pressure sensor

NV Ancillary consumer distributor

V1 Supply circuit 1 (RA) V2 Supply circuit 2 (FA)V4 Separate compressed-air reservoir

Validity

Model 374, 375, 940, 942, 943, 944, 950, 952, 953, 954, 957, 970, 972, 974, 975, 976 with pressure control system


Pres

sure

con

trol

sys

tem

func

tion


Compressed air production

Function

The compressed-air required for braking is produced by the single-cylinder compressor (1.01) driven by the engine. Afterwards the compressed-air flows from the single-cylinder compressor (1.01) to the single-chamber air drier with integrated pressure regulator (6.12), in which the compressed-air is dried and the pressure in the brake system is limited to the set value by the integrated pressure regulator. If the pressure has reached the set value, the pressure regulator switches off and the air delivered by the single-cylinder compressor (1.01) escapes into the atmo-sphere. If the reservoir pressure in the brake system drops below a certain value, the pressure regulator switches on again and the single-cylinder compressor (1.01) fills the brake system up to the set value again.

The compressed air reaches the 4-circuit protection valve with integral pressure limiter (4.07) from the single-chamber air drier with pressure regulator (6.12).

In the 4-circuit protection valve with integrated pres-sure limiter (4.07) the compressed air is divided up into 4 circuits and the pressure for supply circuit 3 and 4 limited to 8.5 bar. The pressure for supply circuit 1 (V1) and 2 (V2) is not limited, the pressure corre-sponds to the shutoff pressure of the pressure regu-lator in the single-chamber air drier with integrated pressure regulator (6.12).

The compressed air to the reservoirs flows through the outlets on the 4-circuit protection valve with inte-grated pressure limiter (4.07).

The brake circuit 1 and 2 reservoir pressure sensor (B71) is located on the 4-circuit protection valve with integrated pressure limiter (4.07).

The brake circuit 1 and 2 reservoir pressure sensor (B71) records the pressures in brake circuit 1 and 2 which are displayed in the instrument (INS) (P2).

For monitoring air dehumidification, a condensation sensor (12.09) and to protect against overpressure a safety valve (30.01) are installed on the single-chamber compressed-air reservoir (5.01) of brake circuit 2.

Note

As of 31.5.05, the safety valve (30.01) is only fitted on compressed-air reservoirs with a test pressure PS < 15.5 bar.


Drive axle axle modulator 31.13


Com

pone

nt d

escr

ipti

ons

Location

The drive axle axle modulator (31.13) is located in the area above the drive axle on the frame crossmember.

Shown on model 93431.13 Drive axle axle modulator

Validity

Model 930, 932, 933, 934




Com

pone

nt d

escr

ipti

ons

Task

• Data exchange with brake control (BS) control unit (A11) via brakes CAN (CAN 6)

• Brake pressure control of drive axle • Brake pressure control of second rear axle

on 3 or 4-axle vehicles • Separated brake pressure control in the event of

an intervention of the antilock brake system (ABS) or acceleration slip regulation (ASR) for the left or right wheel of the drive axle

• Suppression of the trailing axle or leading axle during the intervention of the acceleration slip regulation (ASR)

• Record the signals from the rpm sensors (12.08) at the wheels of the drive axle

• Retaining the redundancy pressure during an electropneumatic control

• Electrical actuation of the trailer control valve (18.07)

Design

12.08 Rpm sensor31.13 Drive axle axle modulatorAV Outlet valveD Pressure sensorEV Inlet valveRD Redundancy valveRE ElectronicsRV Relay valve

Pneumatic connections3 Vent connection4 Compressed air supply (redundant brake pressure)

11 Brake circuit 1 supply (left side)12 Brake circuit 1 supply (right side)21 Brake circuit release (left side)22 Brake circuit release (right side)




Com

pone

nt d

escr

ipti

ons

Location

The drive axle axle modulator (31.13) is located in the area above the drive axle, in the longitudinal frame member on the right.

Depending on model, the drive axle axle modulator (31.13) can also be mounted on the crossmember above the drive axle.

Illustrated on model 970 31.13 Drive axle axle modulator

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976




Com

pone

nt d

escr

ipti

ons

Task

• Data exchange with brake control (BS) control unit (A110a1) via brakes CAN (CAN 6)

• Brake pressure control of drive axle • Brake pressure control of second rear axle

on 3 or 4-axle vehicles • Separated brake pressure control in the event of

an intervention of the antilock brake system (ABS) or acceleration slip regulation (ASR) for the left or right wheel of the drive axle

• Suppression of the trailing axle or leading axle during the intervention of the acceleration slip regulation (ASR)

• Registering the signals from the brake wear sensors (12.07) and the rpm sensors (12.08) at the wheels on the drive axle.

• Retaining the redundancy pressure during an electropneumatic control

• Electrical actuation of the trailer control valve (18.07)

Design

12.07 Brake wear sensor12.08 Rpm sensor31.13 Drive axle axle modulatorAV Outlet valveD Pressure sensorEV Inlet valveRD Redundancy valveRE ElectronicsRV Relay valve

Pneumatic connections3 Vent connection4 Compressed air supply (redundant brake pressure)

11 Brake circuit 1 supply (left side)12 Brake circuit 1 supply (right side)21 Brake circuit release (left side)22 Brake circuit release (right side)


Pressure ratio valve


Com

pone

nt d

escr

ipti

ons

Illustrated on model 97024.04 Pressure ratio valve

24.04 Pressure ratio valve

DR Pressure regulator valveSV Control valve

Pneumatic connections1/4 Compressed air supply (redundant brake pres

sure)2 Compressed air release (to drive axle axle modula-

tor)3 Vent connection

Shown on model 954.5324.04 Pressure ratio valve

Location

The pressure ratio valve (24.04) is located in the area above the rear axle on the inner side of the right longi-tudinal frame member.

Task

The pressure ratio valve (24.04) pneumatically reduces the redundant brake pressure in the ratio 2:1.

Design

Validity

Model 374.6, 375.4, 930, 932, 933, 934, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Central Brake Unit


Com

pone

nt d

escr

ipti

ons

Location

The Central Brake Unit (CBU) (13.08) is mounted under the maintenance flap on the driver side.

Task

• Control of all central functions of the brake control (BS)

• Perform control operations on the front axle • Registering the signals from the brake wear

sensors (12.07) and the rpm sensors (12.08) at the wheels on the front axle.

• Brake pressure regulation during intervention by the antilock brake system (ABS) for the front axle

• Generate brake light switch signals • Retain the redundancy pressure

during electropneumatic control

Design

13.08 Central Brake Unit (CBU)

13.08 Central Brake Unit (CBU)


B Brake value sensor D Pressure sensor PV Proportioning valve RD Redundancy valve RV Relay valve W Travel sensor

Pneumatic connections3 Vent connection

11 Brake circuit 2 supply 12 Brake circuit 2 supply 21 Brake circuit release (left side) 22 Brake circuit release (right side) 23 Compressed air release (redundant brake

pressure)

Validity

Model 374.6, 375.4, 940, 942, 943, 944, 950.5/6, 952.5/6, 953.6, 954.5, 970, 972, 974, 975, 976


Pressure limiting valve with vent


Com

pone

nt d

escr

ipti

ons

Location

The pressure limiting valve with vent (30.03) is located on a bracket behind the steering gear together with the 3/2-way valve for auxiliary braking effect (33.21).

Task

The pressure limiting valve with vent (30.03) pneumat-ically limits the reservoir pressure coming from the ancillary consumer connection to 2.5 bar.

Design

30.03 Pressure limiting valve with vent33.21 3/2-way valve for auxiliary braking effect

30.03 Pressure limiting valve with vent

Pneumatic connections1 Compressed air supply (brake circuit 4 supply)2 Compressed air release

(to 3/2-way valve for auxiliary braking effect)3 Vent connection

Validity

Model 374.65, 375.4, 944.03/23, 950.62


3/2-way valve for auxiliary braking effect


Com

pone

nt d

escr

ipti

ons

Location

The 3/2 way valve for auxiliary braking effect (33.21) is located on a bracket behind the steering gear together with the pressure limiting valve with vent (30.03).

Task

The 3/2-way valve for auxiliary braking effect (33.21) boosts the braking effect at the rear axle in the event of pneumatic failure of the front axle brake circuit. During a brake application, the 3/2-way valve for auxiliary braking effect (33.21) directs a reduced brake pressure to the left single-circuit diaphragm brake cylinder of the front axle.

Design

Validity

Model 374.65, 375.4, 944.03/23, 950.62

30.03 Pressure limiting valve with vent33.21 3/2-way valve for auxiliary braking effect

33.21 3/2-way valve for auxiliary braking effect

SV Switching valveWV Shuttle valve

Pneumatic connections1 Compressed air supply

(from pressure limiting valve with vent)2 Compressed air release (to brake cylinder)3 Vent connection

11 Compressed air supply (brake pressure from CBU)


Radar sensor controller unit


Com

pone

nt d

escr

ipti

ons

Location

The radar sensor controller unit (ART) (A63.1) is located in the middle of the front bumper.

Task

The radar sensor controller unit (ART) (A63.1) trans-mits radar signals for distance measurement and receives the radar signals reflected off the obstacles. The distance and relative speed of the target object in front are detected based on the signal travel times of the received signals and corresponding messages are transmitted to the drive control (FR) control unit and, on vehicles with code (BC7) Active Brake Assist (ABA), also to the Active Brake Assist (ABA) control unit (A111).

The range is up to to 150 m.

A63.1 Radar sensor controller unit (ART)

Validity

Model 930, 932, 933, 934


Active Brake Assist control unit


Com

pone

nt d

escr

ipti

ons

Location

The Active Brake Assist (ABA) control unit (A111) is located in the electrical compartment on the passenger side, under the dash support. The Active Brake Assist (ABA) control unit (A111) is installed directly under the brake control (BS) control unit (A11).

Task

The Active Brake Assist (ABA) control unit (A111) receives all the necessary data (preconditioned) concerning the vehicle in front from the radar sensor controller unit (ART) (A63.1). From this data, the Active Brake Assist (ABA) control unit (A111) calcu-lates the current traffic situation and the risk of a rear-end collision.

In critical situations, the Active Brake Assist (ABA) control unit (A111) sends appropriate information to warn the driver to the instrument (INS) (P2) and, if necessary, a request to decelerate the vehicle to the brake control (BS) control unit (A11).

A3 Drive control (FR) control unitA11 Brake control (BS) control unitA111 Active Brake Assist (ABA) control unit

Validity

Model 930, 932, 934


Four-circuit protection valve


Com

pone

nt d

escr

ipti

ons

Location on vehicleswith pressure control system

The 4-circuit protection valve with integrated pressure limiter (4.07) is installed in the area of the battery carrier on the outside of the left longitudinal frame member.

Depending on the vehicle model, the 4-circuit protec-tion valve with integrated pressure limiter (4.07) can also be installed on the inside of the left longitudinal frame member.

Task on vehicleswith pressure control system

The task of the 4-circuit protection valve with inte-grated pressure limiter (4.07) is to safeguard the intact compressed air circuits against a possible defective compressed air circuit, to limit compressed air circuits 3 and 4 to the specified operating pres-sures and to hold the reservoir pressures of all brake circuits to the specified level.

Illustrated on model 970 4.07 4-circuit protection valve

with integrated pressure limiter

Note

In the 4-circuit protection valve with integrated pressure limiter (4.07) used for the pressure control system, the 10 bar pressure limitation for brake circuit 1 and 2 is missing. The switch range of the pressure regu-lator in the single-chamber air drier with integrated pressure regulator (6.12) is simultaneously the operating pressure for brake circuits 1 and 2.

Validity

Model 374, 375, 940, 942, 943, 944, 950, 952, 953, 954, 957, 970, 972, 974, 975, 976with pressure control system


Four-circuit protection valve


Com

pone

nt d

escr

ipti

ons

Design on vehicles with pressure control system

4.07 4-circuit protection valve with integrated pressure limiter

A Pressure limiter 8.5 bar with integrated safety valve for brake circuits 3 and 4

B Check valve in connections 25 and 26

C Return flow safeguard to connections 21 and 22

D Protection valve (overflow valves with limited return flow)

B71 Brake circuit 1 and 2 reservoir pressure sensor

Pneumatic connections1 Compressed-air supply (from pressure regulator) 21 Brake circuit 1 supply 22 Brake circuit 2 supply 23 Trailer brake supply, circuit 3 24 Ancillary consumer supply, circuit 4 25 Parking brake supply, circuit 3 26 Automatic door, clutch operation

and gearshift supply, circuit 4 27 Pressure switch 5.5 bar, circuit 3 28 Pressure switch 5.5 bar, circuit 4


Condensation sensor with drain valve


Com

pone

nt d

escr

ipti

ons

Location

Depending on the vehicle equipment, the condensa-tion sensor (B76) is either installed on the single-chamber compressed-air reservoir (5.01), which is used as a constant pressure reservoir, or on the single-chamber compressed-air reservoir (5.01), which is located at the lowest point.

Task

The condensation sensor (B76) records the condensa-tion water yield in the compressed-air system.

B76 Condensation sensor

Validity

Model 374, 375, 930, 932, 933, 934, 940, 942, 943, 944, 950, 952, 953, 954, 957, 970, 972, 974, 975, 976


Condensation sensor with drain valve


Com

pone

nt d

escr

ipti

ons

Design Function

After switching on the ignition, the heating element (3) heats up the brass tip (1).The heating elements (3) needs approx. 75 s to reach operating temperature. During this time, the message "No condensation water" is output in the maintenance system (WS).

The heat of the brass tip (1) located in the air is measured by the temperature sensor (2) and passed on to the maintenance system (WS). If there is too much condensation water in the single-chamber compressed-air reservoir (5.01) and if the measuring tip (1) is surrounded by water, then the heat of the brass tip (1) is dissipated by the water due to the good thermal conductivity of the water and operating temperature drops.

The temperature sensor (2) measures the reduced operating temperature and after a reaction time of approx. 90 s to 120 s passes this on to the mainte-nance system (WS). The message "Condensation water" is displayed in the Instrument (INS). By pressing the key button (6) the drain valve (5) is opened and the condensation water is pushed out of the single-chamber compressed-air reservoir (5.01) due to the excess pressure.

Note

Once the condensation water is drained, the driver can reset the message "Condensation water" in the maintenance system (WS) in the "Mainte-nance" menu using the steering wheel buttons.

1 Brass tip 2 Temperature sensor 3 Heating element 4 Brass housing 5 Drain valve 6 Key button



Central Brake Unit

78

Repa

ir in

stru

ctio

ns


AR42.25>W>3200A Remove/install Central Brake Unit (CBU) 7.9.06

MODEL 970, 972, 974, 975, 976 with CODE (ZX2) EPB II

W42.25>1187>06

1 Pedal bracket

13.08 Central Brake Unit (CBU) (A110)

A110a1 Telligent brake system (BS) control

unit

ed Remove/install

1 Remove/install pedal bracket AR29.10>W>0300BB

2 Detach Central Brake Unit (13.08) from

pedal bracket

iInstallation: Replace self>locking nuts.

n BA42.60>N>1003>03A

3 Install in the reverse order

4 Parameterize brake control control unit

(A110a1) using STAR DIAGNOSIS

i Only if the Central Brake Unit (13.08)

was replaced.

Adjust the parameters manually

(depending on vehicle equipment) in the in

the parameterization submenu of the

brake control menu.

STAR DIAGNOSIS Compact diagnostic

system for commercial vehicles

n Service brake valve / brake value sensor

Number Designation Model

375.1, 970,

972, 974, 975,

976

BA42.60>N>1003>03A Central Brake Unit (CBU) to pedal bracket Nm 22


Active Brake Assist control unit

Repa

ir in

stru

ctio

ns


AR42.32>W>0001A Remove/install Active Brake Assist (ABA) control unit 18.7.06

MODEL 930, 932, 934 with CODE (BC7) Active Brake Assist (ABA)

W42.32>1013>08

A3 Drive control (FR) control unit

A11 Telligent brake system (BS) control

unit

A111 Active Brake Assist (ABA) control

unit

e d Remove/install

1 Remove footwell cover on front passenger

side

AR68.30>W>1300MP

2 Remove lower trim on passenger side

3 Disconnect electrical connector on the

Active Brake Assist (ABA) control unit

(A111)

4 Remove Active Brake Assist (ABA) control

unit (A111)


6 Commission the Active Brake Assist (ABA)

control unit (A111) using STAR DIAGNOSIS

i Only if the Active Brake Assist (ABA)

(A111) control unit has been replaced.

Commissioning takes place in the control

unit exchange selection and is menu>

assisted.

WH58.30>Z>1049>13A

Commercially available tools

Number Designation

WH58.30>Z>1049>13A STAR DIAGNOSIS Compact diagnostic system for commercial vehicles 651 131 10 00



80

Repa

ir in

stru

ctio

ns


AR42.25>W>3104C Remove/install axle modulator 24.10.06

MODEL 930, 932, 933, 934 with CODE (ZX2) EPB II

W42.25>1145>05

1 Rpm sensor electrical connector

2 Brake cylinder compressed air line


4 Redundancy actuation compressed>

air line

5 Electrical connectors (axle

modulator)


7 Supply pressure compressed>air line


9 Electrical connector for redundancy

control

31.13 Drive axle axle modulator

e d Remove/install

i Notes on compressed air connection

systems

AH00.18>N>0001>01A

1 Switch off ignition

2 Secure vehicle against rolling

3 Relieve reservoir pressure of compressed>

air system completely

4 Remove fifth wheel coupling i Only on model 934. AR31.10>W>0001A

5 Separate electrical connectors for rpm

sensor (1, 6) from drive axle axle modulator

(31.13)

i To do this, slide the locks of the

electrical connectors for rpm sensor (1, 6)

upwards.

6 Separate electrical connectors (5) from

drive axle axle modulator (31.13)

i To do this, pull out the side plug

locking devices.

7 Separate electrical connector for

redundancy control (9) from drive axle axle

modulator (31.13)

8 Detach brake cylinder compressed air lines

(2, 3)

AR42.10>W>0900C

9 Detach reservoir pressure compressed air

lines (7, 8)

AR42.10>W>0900C

10 Detach redundancy actuation compressed

air line (4)

AR42.10>W>0900C



Repa

ir in

stru

ctio

ns


11 Remove drive axle axle modulator (31.13). n BA42.25>N>1004>01A


13 Read out and erase fault memory or erase

fault memory bit if necessary

i Only required if the drive axle axle

modulator (31.13) has been replaced.

14 Check compressed air connections on drive

axle axle modulator (31.13) for leaks

i To do this, depress the brake pedal and

spray the compressed air connections with

a commercially available leak detecting

spray or soapy water.

15 Perform function test on brake test stand

n Electropneumatic brake (EPB)

Number Designation Model 930,

932, 933,

934

BA42.25>N>1004>01A Bolt, axle modulator to frame Nm 90



82

Repa

ir in

stru

ctio

ns


AR42.25>W>3104D Remove/install axle modulator 24.10.06

MODEL 970, 972, 974, 975, 976 with CODE (ZX2) EPB II

W42.25>1214>11

1 Electrical connectors (axle modulator)

2 Electrical connector for brake wear sensor




6 Redundancy actuation compressed>air line

7 Electrical connector for redundancy control



10 Electrical connector for brake wear sensor


31.13 Drive axle axle modulator

1 Switch off ignition

2 Secure vehicle against rolling

3 Relieve reservoir pressure of compressed>

air system completely

4 Separate electrical connector for brake

wear sensor (2, 10) and electrical connector

for rpm sensor (3, 11) from drive axle axle

modulator (31.13)

i To do this, push the locks of the

electrical connector for rpm sensor (3, 11)

upwards.

5 Separate electrical connectors (1) from the

drive axle axle modulator (31.13)

i To do this, pull out the side plug

locking devices.

6 Separate electrical connector for

redundancy control (7) from drive axle axle

modulator (31.13)

7 Detach brake cylinder compressed air lines

(4, 9)

AR42.10>W>0900C

8 Detach reservoir pressure compressed air

lines (5, 8)

AR42.10>W>0900C

9 Detach redundancy actuation compressed

air line (6)

AR42.10>W>0900C

10 Remove drive axle axle modulator (31.13). n BA42.25>N>1004>01A


12 Read out and erase fault memory or erase

fault memory bit if necessary

i Only required if the drive axle axle

modulator (31.13) has been replaced.



Repa

ir in

stru

ctio

ns


13 Check compressed air connections on drive

axle axle modulator (31.13) for leaks

i To do this, depress the brake pedal and

spray the compressed air connections with

a commercially available leak detecting

spray or soapy water.

14 Perform function test on brake test stand

n Electropneumatic brake (EPB)

Number Designation Models

375.1, 970,

972, 974,

975, 976

BA42.25>N>1004>01A Bolt, axle modulator to frame Nm 90


Combination brake cylinder

84

Repa

ir in

stru

ctio

ns


AR42.10>W>0030A Releasing combination cylinder mechanically 23.5.06

MODEL 374, 375, 675, 676, 677, 679, 930, 932, 933, 934, 940, 942, 943, 944, 950, 952, 953, 954, 957, 958, 970, 972, 974, 975,976with single diaphragm cylinder

W42.10>1134>11

Combination cylinder with interior release bolt

1 Release bolt

A Spring accumulator mechanically released (the indicator pin

is unscrewed)

B Spring accumulator mechanically tensioned (the indicator

pin is screwed in)

W42.20>1009>11

Combination cylinder with exterior release bolt

1 Release bolt

A Spring accumulator mechanically released (the release bolt is

unscrewed)

B Spring accumulator mechanically tensioned (the release bolt

is screwed in)



Repa

ir in

stru

ctio

ns


Releasing

1 Secure vehicle against rolling i If the compressed air at the spring

actuator fails, the parking brake can be

released mechanically.

2 Unscrew release bolt (1) p Do not use the impact wrench to

unscrew the release bolt (1) as it could tilt

the release bolt (1) and thus cause damage

to the combination cylinder.

n Models 374, 375, 930, 932, 933, 934,

940, 942, 943, 944, 950, 952, 953, 954, 957,

958, 970, 972, 974, 975, 976

BA42.10>N>1006>08A

n Model 675, 676, 677, 679 BA42.10>N>1003>08C

Tensioning

3 Pressurize the compressed>air system up to

cutoff pressure

4 Release parking brake i The thread of the release bolt (1) is

unloaded by pressurizing the spring

actuator.

5 Screw in release bolt (1) p Do not use the impact wrench to screw

in the release bolt (1) as it could tilt the

release bolt (1) and thus cause damage to

the combination cylinder.

n Brake cylinder


374, 940, 942,

943, 944

with drum brake

Model

374, 940, 942,

943, 944

with disk brake

BA42.10>N>1005>08A Spring accumulator release bolt in

driving position

M16¥1.5 Nm 35 35

BA42.10>N>1006>08A Spring actuator release bolt in released

position

M16¥1.5 Nm 70 70

n Brake cylinder

Number Designation Models 375.1,

970, 972, 974,

975, 976 with

drum brake

Model

375.1, 970, 972,

974, 975, 976

with disk brakes


driving position

M16¥1.5 Nm 35 35


position

M16¥1.5 Nm 70 70

n Brake cylinder


375.3, 950, 952,

953, 954 with

drum brake

Model

375.3/4, 950, 952,

953, 954, 957

with disk brake


driving position

M16¥1.5 Nm 35 35


position

M16¥1.5 Nm 70 70



86

Repa

ir in

stru

ctio

ns


n Brake cylinder

Number Designation Models 930, 932,

933, 934 with

drum brake

Model 930, 932,

933, 934 with

disk brake


driving position

M16¥1.5 Nm 35 35


position

M16¥1.5 Nm 70 70

n Brake cylinder


958.0/2/4 with

drum brake

Model

958.2/4 with disk

brakes


driving position

M16¥1.5 Nm 35 35


position

M16¥1.5 Nm 70 70


675, 676, 677, 679

BA42.10>N>1002>08C Spring accumulator release bolt in driving

position

M16¥1.5 Nm 35

n Brake cylinder


675, 676, 677, 679

BA42.10>N>1003>08C Spring actuator release bolt in released

position

M16¥1.5 Nm 70

n Brake cylinder



Repa

ir in

stru

ctio

ns


AR42.10>W>0030B Releasing combination cylinder mechanically 19.4.05

MODELS 970, 972, 974, 975, 976with double diaphragm cylinder

W42.10>1202>12

1 Release pin

2 Holder (for release pin)

3 Washer

4 Nut

5 Plug

W42.10>1201>06

1 Release pin

3 Washer

4 Nut

5 Plug

6 Spring stop

A Release pin engaged



88

Repa

ir in

stru

ctio

ns


7 Release plate

8 Washer

W42.10>1203>03

3 Remove release pin (1) from holder (2) i To do so, release the cotter pin,

unscrew the nut (3) and remove the washer

(5).

4 Remove stop plug (5)

5 Insert release pin (1) into hole of

combination cylinder and turn 90∞

clockwise until release pin (1) is engaged

p Make sure that the release pin (1) is

securely engaged (A) in the spring stop (6),

otherwise it could work loose.

6 Screw nut (4) with washer (3) onto release

pin (1)

7 Mechanically release combination cylinder

by tightening nut (4)

p Tighten the nut (4) to max. 120 Nm

only, otherwise the combination cylinder

will be damaged.

n BA42.10>N>1009>08A

8 Move parking brake lever to full brake

position

i The combination cylinder is purged.

Tensioning

9 Pressurize the compressed>air system up to

cutoff pressure

10 Release parking brake i Air is admitted into the combination

cylinder, thus relieving the load on the

release pin (1).

11 Unscrew nut (4) with washer (3) from

release pin (1)

i Only perform this step with used

combination cylinders.



Repa

ir in

stru

ctio

ns


Unscrewing the nut (4) tensions the

combination cylinder again.

12.1 Remove release pin (1) i Only perform this step with used


Turn release pin (1) 90∞ counterclockwise

and remove.

12.2 Turn release plate (7) with washer (8) 90∞

counterclockwise and remove

i Only perform this step with new


The release plate (7) with the washer (8) is

no longer required after removal.

p The release plate (7) must be removed,

otherwise the spring accumulator part will

not function.

13 Fit release pin (1) in holder (2), screw nut

(4) with washer (3) onto release pin (1) and

secure with new cotter pin

i Only perform this step with used


14 Seal hole on spring accumulator part with

stop plug (5)

n Brake cylinder


375.1, 970, 972,

974, 975, 976

with drum brake

Model

375.1, 970, 972,

974, 975, 976

with disk brakes

BA42.10>N>1009>08A Nut on release pin in release position,

double diaphragm cylinder

Nm 120 120


Condensation sensor

90

Repa

ir in

stru

ctio

ns


AR42.10>W>0050A Remove/install condensation sensor 25.1.07

MODEL 374, 375, 930, 932, 933, 934, 940, 942, 943, 944, 950, 952, 953, 954, 957, 958, 970, 972, 974, 975, 976

W42.10>1206>05

Condensation sensor (B76) without drain

valve

1 Connector

2 Jack

3 O>ring


W42.10>1207>05

Condensation sensor (B76) with drain valve

1 Connector

2 Jack

3 O>ring

4 Button (drain valve)

5 Paint protective cap



Condensation sensor

Repa

ir in

stru

ctio

ns


1 Depressurize compressed>air system

2 Remove paint protective cap (5) i Only for condensation sensor (B76)

with drain valve, if available.

3 Detach connector (1) from jack (2)

4 Unscrew condensation sensor (B76)

g Checking

5 Check condensation sensor (B76) using

multimeter

iOnly in the case of complaint.

Condensation sensor (B76) without drain

valve

AR42.10>W>0050>01A

Condensation sensor (B76) with drain valve AR42.10>W>0050>01B

Condensation sensor status: "Dry" BE42.10>N>1017>10B

Condensation sensor status: "Wet" BE42.10>N>1018>10B

y Test adapter WF58.50>W>4260>04A

d Install

6 Install condensation sensor (B76) i A dropped condensation sensor (B76)

must always be replaced, even if there is no

visible damage.

Inspect O>ring (3), replace if necessary.

n BA42.60>N>1001>02A

7 Fit connector (1) onto jack (2)

8 Fit paint protective cap (5) i Only for condensation sensor (B76)

with drain valve, if available.

9 Read out fault memory in the maintenance

system (WS), if necessary, delete stored

faults

10 Rest maintenance system (WS) using STAR

DIAGNOSIS or over the instrument (INS).

i Only when there was no water in the

compressed air system, the condensation

sensor (B76) did not record the

corresponding status and therefore had to

be replaced.

Test and adjustment values for service brake


375.1/3/4, 944

Model

374, 940 without

code BC3

BE42.10>N>1017>10B Condensation sensor status: "Dry" Volt 1.1 to 2 1.1 to 2

BE42.10>N>1018>10B Condensation sensor status: "Wet" Volt 3.1...4 3.1...4


Condensation sensor

92

Repa

ir in

stru

ctio

ns




374, 940 with

code BC3

Model

930, 932, 933, 934,

950, 952, 953, 954, 957





942, 943

Model

958.0/2/4





970, 972, 974,

975, 976

without code

BC3

Model

970, 972, 974,

975, 976

with code BC3



n Condensation sensor


374, 940, 942,

943, 944

Models 375.1,

970, 972, 974,

975, 976

Model

375.3/4, 950, 952,

953, 954, 957

Model 930, 932,

933, 934

BA42.60>N>1001>02A Condensation sensor in

compressed air reservoir

M22x1.5 Nm 50 50 50 50

n Condensation sensor

Number Designation Type 958

BA42.60>N>1001>02A Condensation sensor in

compressed air reservoir

M22x1.5 Nm 50


93Brake System Modifications and New Features

Abbreviations

i

ABA

Active Brake Assist

ABS

Antilock brake system

ALB

Automatic load-dependent brake force control

ART

Wheel sensor (adaptive cruise control)

AS

Breakaway coupling

ASR

Acceleration slip regulation

AV

Exhaust valve

B

Brake value sensor

BS

Brake control

CAN

Controller Area Network

CBU

Central Brake Unit

D

Pressure sensor

DR

Pressure regulator valve

EPB

Electropneumatic brake

EV

Intake valve

FB

Parking brake

FIS

Driver information system

FM

Front Module

FR

Drive control

GM

Base module

HA

Rear axle

HM

Rear module

INS

Instrument cluster


Abbreviations

94 Brake System Modifications and New Featuresi

MR

Engine control

PV

Proportioning valve

RD

Redundancy valve

right

Control electronics

RV

Relay valve

SR

Stability control

SV

Control valve

AGM

Reservoir pressure

VA

Front axle

W

Position sensor

WIS

Workshop information system

WV

Shuttle valve

WS

Maintenance system


95Brake System Modifications and New Features

Index

i

AABS control . . . . . . . . . . . . . . . . 17

Acceleration skid control . . . . . . . . 28, 44

Activation . . . . . . . . . . . . . . . . . 48

Active Brake Assist . . . . . . . . . . . 11, 46

Active Brake Assist control unit . . . . . 73, 79

Adjustment functions . . . . . . . . . . . . 27

Antilock brake system . . . . . . . . . . . 28

ART distance warning . . . . . . . . . . . . 50

ASRbrake intervention . . . . . . . . . . . . 45control . . . . . . . . . . . . . . . . . 17engine intervention . . . . . . . . . . . . 45shutoff . . . . . . . . . . . . . . . . . 45

Axle load displacement . . . . . . . . . . . 16

Axle modulator . . . . . . . . . . . 9, 64, 80

BBlock diagram . . . . . . . . . . . . . . . 24

Brake applicationFront axle . . . . . . . . . . . . . . . . 30Rear axle . . . . . . . . . . . . . . 18, 36

Brake Assist System . . . . . . . . . . . . 29

Brake control (BS) - EPB II . . . . . . . . . . . 8

Brake value sensor . . . . . . . . . . . . . . 9

Brake wear correction . . . . . . . . . . . 17

CCentral Brake Unit . . . . . . . . . 10, 69, 78

Combination brake cylinder . . . . . . . 13, 84

Compressed air production . . . . . . . . . 62

Condensation sensor . . . . . . . . 12, 76, 90

Control functions . . . . . . . . . . . . . . 27

DData flow diagram . . . . . . . . . . . . . 46

Differential slip control . . . . . . . . . 17, 27

Drag torque control . . . . . . . . . . . . 29

Dynamic axle load shift . . . . . . . . . . . 16

EElectrically regulated brake application . . . . 16

Emergency stop . . . . . . . . . . . . . . 52

FFrequent-stop brake . . . . . . . . . . 12, 29

Frequent-stop comfort brake . . . . . . . . 12

HHill holder . . . . . . . . . . . . . . . . . 29

LLane change . . . . . . . . . . . . . . . . 53

PPressure control system . . . . . . . . . . 11

Pressure limiting valve with vent . . . . . . . 70

Pressure ratio valve . . . . . . . . . . 10, 68

Protection valve . . . . . . . . . . . . . . 74

RRadar sensor controller unit . . . . . . . . . 72

Rear axle redundancy concept . . . . . . . . . 9

Receiver lobes . . . . . . . . . . . . . . . 49

SSingle-chamber air drier with pressure regulator 63

Single-chamber compressed air reservoir . . . 63

Stability optimization . . . . . . . . . . . . 29

System features . . . . . . . . . . . . . . . 8

System limits . . . . . . . . . . . . . . . 53

TTelligent brake system . . . . . . . . . . . 14

Tire matching . . . . . . . . . . . . . . . 27

Traffic situation . . . . . . . . . . . . . . 49

Trailer control . . . . . . . . . . . . . . . 40

Transmitter lobes . . . . . . . . . . . . . 49

Twin-diaphragm brake cylinder . . . . . . . . 13


Index

96 Brake System Modifications and New Featuresi

VVehicle detection . . . . . . . . . . . . . . 53

WWarning stages . . . . . . . . . . . . . . . 50

Warnings . . . . . . . . . . . . . . . . . 56

Way valve for auxiliary braking . . . . . . 10, 71

Wheel speed sensing . . . . . . . . . . . . 27


brake system modifications and new features - · pdf filebrake system modifications and new...

Documents