Mercedes-Benz Service. Brake System Modifications and New Features Model 374, 375, , , ,

Transcription

1 Mercedes-Benz Service Brake System Modifications and New Features Model 374, 375, , , ,

2 Mercedes-Benz Service Brake System Modifications and New Features Model 374, 375, , , , Daimler AG Technische Information und Werkstatteinrichtung (GSP/TI) D Stuttgart

3 Information and copyright Ordering workshop information You can order all printed workshop information from GSP/TI, such as Introduction into Service Manuals, System Descriptions, Function Descriptions, Technology Guides, Technical Data Manuals and adhesive labels, from the following sources: Within Germany From our GSP/TI Shop on the Internet Link: or alternatively Telephone:+49-(0)18 05/ Fax: +49-(0)18 05/ Outside Germany Please consult the contact person responsible for your market. Product portfolio You can also find comprehensive information on our complete product portfolio in our Internet portal. Link: Questions and Suggestions If you have any questions or suggestions concerning this product, please write to us. Fax: +49-(0)18 05/ or alternatively Address: Daimler AG GSP/TIS HPC R822, W002 D 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 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: N Order no. of this publication: /07

4 Contents 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 Brake System Modifications and New Features i 3

5 Contents 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 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 4 i Brake System Modifications and New Features

6 Contents Repair instructions Central Brake Unit 78 Active Brake Assist control unit 79 Drive axle axle modulator Combination brake cylinder 84 Condensation sensor 90 Abbreviations 93 Index 95 Brake System Modifications and New Features i 5

7 6 Brake System Modifications and New Features i

8 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 function 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 configuration. 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-todate versions published in WIS. Daimler AG After Sales Service Engineering Trucks, GSP/TCST February 2007 Brake System Modifications and New Features i 7

9 8Overview 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. i Brake System Modifications and New Features 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 modified 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.

10 Brake value sensor Axle modulator EPB II Overview 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 electropneumatic control circuit is intact. 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 pressure 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 modulator electronics. The trailer control valve is now actuated via an additional connector plug on the axle modulator. 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. Brake System Modifications and New Features i 9

11 Overview EPB II Central Brake Unit The Central Brake Unit (CBU) is a completely new component. It combines the following components in one mechatronic unit: Brake value sensor Telligent brake control (BS) control unit Front axle proportioning valve Front axle redundancy valve 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 characteristic improves the brake response time when the electronic control system fails. 3/2-way valve for auxiliary braking effect (only Axor) The 3/2-way valve for auxiliary braking effect is actuated 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. 10 i Brake System Modifications and New Features

12 Active Brake Assist (ABA) Active Brake Assist/Pressure control system Pressure control system, 10 bar Overview 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 collisions 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. 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 Brake System Modifications and New Features i 11

13 Overview 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. 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. 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. 12 i Brake System Modifications and New Features

14 Twin-diaphragm brake cylinder/combination brake cylinder Twin-diaphragm brake cylinder from Arfesan Combination brake cylinder with internal bleed valve Overview 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. 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. 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 indicator pin) at the outer end. The length of this indicator pin changes (approx. 4 to 6 mm) to indicate the conditions "Operational" and "Not operational": Indicator pin retracted and flush with surface: Operational Indicator pin extended: Not operational 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 condition does not occur when the spring accumulator contains air or the pressure in the brake system is increased rapidly. Brake System Modifications and New Features i 13

15 Brake control (BS) - EPB II function Telligent brake system Telligent brake system Vehicles with code (ZX2) EPB II 1 Trailer/semitrailer data interface 2 ASIC data bus Brake value sensor Proportioning relay valve Trailer control valve Single-circuit diaphragm cylinder Combination brake cylinder Pressure ratio valve Drive axle axle modulator Front axle redundancy valve Coupling head for supply Coupling head for brake ABS solenoid valve A3 Drive control (FR) control unit A6 Engine control (MR) control unit A7 Base module (GM) A11 Brake control (BS) control unit A28 Drive axle axle modulator A64 Front module (FM) A65 Rear module (HM) A68 Master switch module 4 A77 Dash support switch module 1 B30 B31 B32 B33 B36 B37 B40 B41 P2 S40 S41 Left front axle rpm sensor Right front axle rpm sensor Left 1st rear axle rpm sensor Right 1st rear axle rpm sensor Left 1st front axle brake wear sensor Right 1st front axle brake wear sensor Left 1st rear axle brake wear sensor Right 1st rear axle brake wear sensor Instrument (INS) ASR cutout button Hill holder switch V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3) CAN 1 CAN 2 CAN 3 CAN 4 CAN 6 Vehicle CAN Interior CAN Frame CAN Engine CAN Brakes CAN Validity Model 930, 932, 933, 934 E P a b c Electric component Pneumatic component Reservoir pressure Brake pressure Redundant brake pressure 14 i Brake System Modifications and New Features

16 General The Telligent brake system is an electronically monitored and electrically controlled pneumatic brake system. The Telligent brake system consists of a purely pneumatic 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 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 pneumatic means. Brake control (BS) - EPB II function 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 electropneumatic 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. Brake System Modifications and New Features i 15

17 Brake control (BS) - EPB II function Telligent brake system 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 pressure (b) necessary for producing the specified deceleration 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. 16 i Brake System Modifications and New Features

18 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 Telligent brake system 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 alterations 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. Brake control (BS) - EPB II function 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. Brake System Modifications and New Features i 17

19 Brake control (BS) - EPB II function Rear axle brake application Rear axle brake application Vehicles with code (ZX2) EPB II Rpm sensor Brake value sensor Combination brake cylinder Pressure ratio valve Drive axle axle modulator Front axle redundancy valve A11 Brake control (BS) control unit FB Parking brake V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) a b c d Reservoir pressure Brake pressure Redundant brake pressure Control pressure/ventilation Validity Model 930, 932, 933, i Brake System Modifications and New Features

20 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. Rear axle brake application 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. Brake control (BS) - EPB II function 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). If the actual deceleration deviates from the specified deceleration, the brake control (BS) control unit (A11) causes the drive axle axle modulator (31.13) to reduce or increase the brake pressure (b). 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). 10 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 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. Brake System Modifications and New Features i 19

21 Brake control (BS) - EPB II function Rear axle brake application Brake application at rear axle in the event of an electrical fault in the brake system Vehicles with code (ZX2) EPB II Rpm sensor Brake value sensor Combination brake cylinder Pressure ratio valve Drive axle axle modulator Front axle redundancy valve A11 Brake control (BS) control unit FB Parking brake V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) a b c d Reservoir pressure Brake pressure Redundant brake pressure Control pressure/ventilation Validity Model 930, 932, 933, i Brake System Modifications and New Features

22 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. Rear axle brake application Function sequence 1 The brake pedal is depressed. 2 Via connection 21 the pneumatic component of the brake value sensor (13.07) directs a redundant 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 pressure (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. Brake control (BS) - EPB II function 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. Note The brake application occurs with no electronic monitoring or electrical control. There is no overlaid electric brake control. The brake pressure is applied relative to the travel of the brake pedal by purely pneumatic means. 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. Brake System Modifications and New Features i 21

23 Brake control (BS) - EPB II function Brake control (BS) Brake control (BS) Shown on 4-channel system 1 Trailer/semitrailer data interface Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Single-circuit diaphragm brake cylinder Combination brake cylinder Pressure ratio valve Double check valve Pressure limiting valve with vent (only on model , , /23, ) Drive axle axle modulator 33.08a 3/2-way air admission valve /2-way valve for auxiliary braking effect (only on model , , /23, ) Coupling head for supply Coupling head for brake ABS solenoid valve (only on 4-channel system) 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 S40 S41 B RD RE PV Frequent-stop brake switch ASR cutout button Hill holder switch Brake value sensor Redundancy valve Control electronics Proportioning valve NV Reservoir pressure (ancillary consumers) V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3) CAN 1 CAN 4 CAN 6 Vehicle CAN Engine CAN Brakes CAN 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 a b c Reservoir pressure Brake pressure Redundant brake pressure 22 i Brake System Modifications and New Features

24 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 electropneumatic 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 operating correctly, the redundancy circuits are kept in reserve, giving priority to the electropneumatic brake control. Components Brake control (BS) 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 , , /23, ) Brake control (BS) - EPB II function If there is a failure of the electronics, the purely pneumatic 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 singlecircuit pneumatic control pressure from brake circuit 2. Brake System Modifications and New Features i 23

25 Brake control (BS) - EPB II function Brake control (BS) Block diagram Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Drive axle axle modulator 33.08a 3/2-way air admission valve /2-way valve for auxiliary braking effect (only on model , , /23, ) ABS solenoid valve A3 A6 A7 P2 CAN 1 CAN 4 CAN 6 Drive control (FR) control unit Engine control (MR) control unit Base module (GM) Instrument (INS) Vehicle CAN Engine CAN Brakes CAN Validity Model 374, 375, 940, 942, 943, 944, 950, 952, 953, i Brake System Modifications and New Features

26 Block diagram Brake control (BS) Brake control (BS) - EPB II function Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Drive axle axle modulator 33.08a 3/2-way air admission valve ABS solenoid valve (only on 4-channel system) A3 A6 A7 P2 CAN 1 CAN 4 CAN 6 Drive control (FR) control unit Engine control (MR) control unit Base module (GM) Instrument (INS) Vehicle CAN Engine CAN Brakes CAN Validity Model 970, 972, 974, 975, 976 Brake System Modifications and New Features i 25

27 Brake control (BS) - EPB II function Brake control (BS) 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 redundancy valve (RD) and the proportioning valve (PV) into a single mechatronic unit. From the signal of the position 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 pressure 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 proportionally, 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) flangemounted 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 electronics, the trailer control valve (18.07) is actuated via the redundant pressure set by the brake value sensor (B) of the CBU (13.08). 26 i Brake System Modifications and New Features

28 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 Differential slip control Brake control (BS) During the first brake application, the brake control (BS) control unit (A110a1) calculates the brake pressure 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) - EPB II function 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 calibrated vehicle speeds from the tachograph.if impermissible tire pairings are used or if the speed signals vary significantly, an error message is generated. Brake System Modifications and New Features i 27

29 Brake control (BS) - EPB II function Brake control (BS) 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 deactivated 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. 28 i Brake System Modifications and New Features

30 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. Frequent-stop brake Brake control (BS) 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. Brake control (BS) - EPB II function Hill holder The hill holder helps the driver to keep his vehicle steady while stationary and when moving off, particularly on gradients, without having to apply the parking brake. When the hill holder is engaged, the brake pressure applied with the service brake is maintained. Brake System Modifications and New Features i 29

31 Brake control (BS) - EPB II function Front axle brake application Front axle brake application Shown on 4-channel system Brake wear sensor Rpm sensor Central Brake Unit (CBU) Single-circuit diaphragm brake cylinder Pressure limiting valve with vent (only on model , 375.4, /23, ) Drive axle axle modulator /2-way valve for auxiliary braking effect (only on model , 375.4, /23, ) 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 valve PV 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, i Brake System Modifications and New Features

32 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 overlaid 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). Front axle brake application 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. Brake control (BS) - EPB II function According to the control pressure (d) from the proportioning 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 , , /23, ) and via the ABS solenoid valves (45.01) (only on 4-channel system) to the single-circuit diaphragm brake cylinders (20.02) of the front axle. Note Model /23, 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). Brake System Modifications and New Features i 31

33 Brake control (BS) - EPB II function Front axle brake application Front axle brake application with pneumatic failure of front axle brake circuit Brake wear sensor Rpm sensor Central Brake Unit (CBU) Single-circuit diaphragm brake cylinder Pressure limiting valve with vent Drive axle axle modulator /2-way valve for auxiliary braking effect ABS solenoid valve A110a1 Brake control (BS) control unit AV B D EV PV RD RV SV W WV Outlet valve Brake value sensor Pressure sensor Inlet valve Proportioning valve Redundancy valve Relay valve Control valve Travel sensor Shuttle valve NV Reservoir pressure (ancillary consumers) V2 Reservoir pressure (circuit 2) a b c d e Reservoir pressure Brake pressure Redundant brake pressure Control pressure Unpressurized Validity Model , 375.4, /23, i Brake System Modifications and New Features

34 General Legal requirements stipulate that adequate deceleration 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 Front axle brake application 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 solenoid valve (45.01) the brake pressure (b) travels to the left single-circuit diaphragm brake cylinder (20.02) on the front axle. Brake control (BS) - EPB II function Brake System Modifications and New Features i 33

35 Brake control (BS) - EPB II function Front axle brake application Brake application at front axle in the event of an electrical fault in the brake system Shown on 4-channel system Brake wear sensor Rpm sensor Central Brake Unit (CBU) Single-circuit diaphragm brake cylinder Pressure limiting valve with vent (only on model , , /23, ) Drive axle axle modulator /2-way valve for auxiliary braking effect (only on model , , /23, ) 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 valve PV 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 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, i Brake System Modifications and New Features

36 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 Front axle brake application 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 redundancy 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 , , /23, ) and via the ABS solenoid valves (45.01) (only on 4-channel system) to the single-circuit diaphragm brake cylinders (20.02) of the front axle. Brake control (BS) - EPB II function 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 electronics failure because this function is only implemented in software. Brake System Modifications and New Features i 35

37 Brake control (BS) - EPB II function Rear axle brake application Rear axle brake application Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Single-circuit diaphragm brake cylinder Combination brake cylinder Pressure ratio valve Drive axle axle modulator A110a1 Brake control (BS) control unit CAN 6 Brakes CAN AV B D EV FB PV RD RE RV W Outlet valve Brake value sensor Pressure sensor Inlet valve Parking brake Proportioning valve Redundancy valve Control electronics Relay valve Travel sensor V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) a b c d Reservoir pressure Brake pressure Redundant brake pressure 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, i Brake System Modifications and New Features

38 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). The target deceleration calculated by the brake control (BS) control unit (A110a1) is transmitted to the control electronics (RE) in the drive axle axle modulator (31.13). The data exchange occurs via the brakes CAN (CAN 6). So that the electropneumatic brake circuit is not overlaid by redundant brake pressure (c), the redundancy valve (RD) at the drive axle axle modulator (31.13) is closed electrically. Rear axle brake application 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 accordingly. When the brake pedal is released, the applied brake pressure (b) and the control pressure (d) are released via the vent, connection 3. Brake control (BS) - EPB II function The control electronics (RE) close the outlet valves (AV) and, via the inlet valves (EV), the available reservoir 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 pressure (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 modulator (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). Brake System Modifications and New Features i 37

39 Brake control (BS) - EPB II function Rear axle brake application Brake application at rear axle in the event of an electrical fault in the brake system Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Single-circuit diaphragm brake cylinder Combination brake cylinder Pressure ratio valve Drive axle axle modulator A110a1 Brake control (BS) control unit CAN 6 Brakes CAN AV B D EV FB PV RD RE RV W Outlet valve Brake value sensor Pressure sensor Inlet valve Parking brake Proportioning valve Redundancy valve Control electronics Relay valve Travel sensor V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) a b c d Reservoir pressure Brake pressure Redundant brake pressure 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, i Brake System Modifications and New Features

40 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 Rear axle brake application The actuation of the brake pedal causes the pneumatic 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 redundant 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). Brake control (BS) - EPB II function Proportional to the redundant brake pressure (c), these relay valves (RV) then direct the available reservoir pressure (a) as brake pressure (b) to connections 21 and 22 and then on to the combination brake cylinders (22.01) of the rear 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. Brake System Modifications and New Features i 39

41 Brake control (BS) - EPB II function Trailer control Trailer control Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Single-circuit diaphragm brake cylinder Combination brake cylinder Pressure ratio valve Drive axle axle modulator Coupling head for supply Coupling head for brake A110a1 Brake control (BS) control unit CAN 6 Brakes CAN AS AV B D EV FB PV RD RE RV W Breakaway coupling Outlet valve Brake value sensor Pressure sensor Inlet valve Parking brake Proportioning valve Redundancy valve Control electronics Relay valve Travel sensor V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3) a b c d Reservoir pressure Brake pressure Redundant brake pressure 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, i Brake System Modifications and New Features

42 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). 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). Trailer control 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 deceleration, the drive axle axle modulator (31.13) 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. Brake control (BS) - EPB II function The redundant brake pressure (c) and the control pressure (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). Brake System Modifications and New Features i 41

43 Brake control (BS) - EPB II function Trailer control Trailer control in the event of an electrical fault in the brake system Brake wear sensor Rpm sensor Central Brake Unit (CBU) Trailer control valve Single-circuit diaphragm brake cylinder Combination brake cylinder Pressure ratio valve Drive axle axle modulator Coupling head for supply Coupling head for brake A110a1 Brake control (BS) control unit CAN 6 Brakes CAN AS AV B D EV FB PV RD RE RV W Breakaway coupling Outlet valve Brake value sensor Pressure sensor Inlet valve Parking brake Proportioning valve Redundancy valve Control electronics Relay valve Travel sensor V1 Reservoir pressure (circuit 1) V2 Reservoir pressure (circuit 2) V3 Reservoir pressure (circuit 3) a b c d Reservoir pressure Brake pressure Redundant brake pressure 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, i Brake System Modifications and New Features

44 General If there is a failure of the electronics, the trailer or semitrailer is braked via the purely pneumatic redundancy circuit. An error message is output on the driver information system (FIS) display in the Instrument (INS) (P2). Function Trailer control The actuation of the brake pedal causes the pneumatic 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). When the brake pedal is released, the applied brake pressure (b) and the redundant brake pressure (c) are released via the vent, connection 3. Brake control (BS) - EPB II function Brake System Modifications and New Features i 43

45 Brake control (BS) - EPB II function Acceleration skid control Acceleration slip regulation Brake wear sensor Rpm sensor Central Brake Unit (CBU) Combination brake cylinder Pressure ratio valve Double check valve Drive axle axle modulator 33.08a 3/2-way air admission valve A110a1 Brake control (BS) control unit A3 Drive control (FR) control unit A6 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 CAN CAN 4 Engine CAN CAN 6 Brakes CAN a b c d Reservoir pressure Brake pressure Redundant brake pressure 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, i Brake System Modifications and New Features

46 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 reduction in engine torque via the engine control (MR) control unit (A6). ASR shutoff Acceleration skid control The acceleration slip regulation (ASR) can be shut off using the ASR cutout button in order to improve traction, 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. Brake control (BS) - EPB II function 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 evaluation. 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). 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) actuates the 3/2-way air admission valve (33.08a), which holds back the brake pressure (b) via double check valves (28.04). Brake System Modifications and New Features i 45

47 Active Brake Assist (ABA) function Networking Data flow diagram 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 unit B1 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 Input information a Information from brake control (BS) control unit (A11): - Average front axle speed - Brake pedal status b c d Information from radar sensor controller unit (ART) (A63.1): - Distance to vehicle in front - Relative speed - Relative acceleration Information from rear module (HM) (A65): - Driving level status 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 Validity Model 930, 932, 934 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 46 i Brake System Modifications and New Features

48 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 developed 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 relative 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 Traffic situation evaluation 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. Active Brake Assist (ABA) function 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, otherwise the system may fail to correctly recognize the traffic situation in front of the vehicle. Brake System Modifications and New Features i 47

49 Active Brake Assist (ABA) function Activation 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 indicated 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). 48 i Brake System Modifications and New Features

50 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) transmits 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 acceleration. Information collection The radar sensor controller unit (ART) (A63.1) transmits 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 information is sent over the vehicle CAN (CAN 1) to the Active Brake Assist (ABA) control unit (A111), which evaluates the current traffic situation based on this information and information about the vehicle it is installed in. Active Brake Assist (ABA) function A Transmitter and receiver lobes Brake System Modifications and New Features i 49

51 Active Brake Assist (ABA) function Warning stages 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 actuated directly by the Instrument (INS) (P2). Distance warning system indicator P2 Instrument (INS) P2p1 Driver information display (FIS) 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. 50 i Brake System Modifications and New Features

52 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" Warning stages Active Brake Assist (ABA) function When a very critical situation occurs, a warning indicator 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. Brake System Modifications and New Features i 51

53 Active Brake Assist (ABA) function Emergency stop 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) triggered 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 activities: 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 unintended cancellation of the emergency stop by inadvertent 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. 52 i Brake System Modifications and New Features

54 5 System limits 5.1 Limitations of vehicle detection system Driving offset from vehicles in front The radar sensor controller unit (ART) (A63.1) determines the distances, the relative speeds and the angles of vehicles which are located inside the detection 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. System limits Active Brake Assist (ABA) function Vehicles in front which have an off-center lane position 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. Vehicles in front 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. Lane change Brake System Modifications and New Features i 53

55 Active Brake Assist (ABA) function System limits Vehicles at side of road In some cases, vehicles moving along the side of the road (e.g. malfunctioning vehicles) may be unnecessarily detected by the radar sensor Vehicles at on ramps, exit ramps or intersections Vehicles at side of road 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 on ramps, exit ramps or intersections 54 i Brake System Modifications and New Features

56 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 "vehicles in front" in rare cases where the circumstances are unfavorable. Vehicles in front on bends System limits Active Brake Assist (ABA) function 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) Brake System Modifications and New Features i 55

57 Active Brake Assist (ABA) function System limits 5.2 Warnings in particular driving situations Warnings during overtaking maneuvers When overtaking, the ABA or the ART may issue a distance warning if the overtaking maneuver is particularly tight. This is caused by the detecting vehicle briefly tailgating the vehicle in front just before or while moving aside. Warning during overtaking maneuvers 56 i Brake System Modifications and New Features

58 Visual warning The 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. System limits Visual warning with warning tone and braking If 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. Braking If 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. Active Brake Assist (ABA) function Even when switched off, the ART and ABA issue visual warnings with warning tone (no braking) in very critical situations. Brake System Modifications and New Features i 57

59 Active Brake Assist (ABA) function System limits 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 58 i Brake System Modifications and New Features

60 Visual warning A 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. System limits Visual warning with warning tone and braking If 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. Braking If the foot throttle actuator (B1) has not been actuated noticeably, the ART may brake the vehicle slightly during very tight lane change maneuvers.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). Active Brake Assist (ABA) function Brake System Modifications and New Features i 59

61 Active Brake Assist (ABA) function System limits 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). 60 i Brake System Modifications and New Features

62 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). System limits Active Brake Assist (ABA) function Warning about stopping vehicles A Distance to vehicle in front Brake System Modifications and New Features i 61

63 Pressure control system function Compressed air production 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 B71 Brake circuit 1 and 2 reservoir pressure sensor circuit protection valve with integrated pressure limiter NV Ancillary consumer distributor 5.01 Single-chamber compressed air reservoir 6.12 Single-chamber air drier V1 Supply circuit 1 (RA) with integrated pressure regulator V2 Supply circuit 2 (FA) Cut-out V4 Separate compressed-air reservoir Condensation sensor (B76) Safety valve Test connection M16X1.5 Validity Model 374, 375, 940, 942, 943, 944, 950, 952, 953, 954, 957, 970, 972, 974, 975, 976 with pressure control system 62 i Brake System Modifications and New Features

64 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 singlechamber 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 singlecylinder compressor (1.01) escapes into the atmosphere. 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). Compressed air production In the 4-circuit protection valve with integrated pressure 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 corresponds to the shutoff pressure of the pressure regulator 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 integrated 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. Pressure control system function Note As of , the safety valve (30.01) is only fitted on compressed-air reservoirs with a test pressure PS < 15.5 bar. Brake System Modifications and New Features i 63

65 Component descriptions Drive axle axle modulator Location The drive axle axle modulator (31.13) is located in the area above the drive axle on the frame crossmember. Shown on model Drive axle axle modulator Validity Model 930, 932, 933, i Brake System Modifications and New Features

66 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) Drive axle axle modulator Design Component descriptions Rpm sensor Drive axle axle modulator AV Outlet valve D Pressure sensor EV Inlet valve RD Redundancy valve RE Electronics RV Relay valve Pneumatic connections 3 Vent connection 4 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) Brake System Modifications and New Features i 65

67 Component descriptions Drive axle axle modulator 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 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, i Brake System Modifications and New Features

68 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) Drive axle axle modulator Design Component descriptions Brake wear sensor Rpm sensor Drive axle axle modulator AV Outlet valve D Pressure sensor EV Inlet valve RD Redundancy valve RE Electronics RV Relay valve Pneumatic connections 3 Vent connection 4 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) Brake System Modifications and New Features i 67

69 Component descriptions 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 longitudinal frame member. Task The pressure ratio valve (24.04) pneumatically reduces the redundant brake pressure in the ratio 2:1. Design Shown on model Pressure ratio valve Pressure ratio valve DR SV Pressure regulator valve Control valve Illustrated on model Pressure ratio valve Pneumatic connections 1/4 Compressed air supply (redundant brake pres sure) 2 Compressed air release (to drive axle axle modulator) 3 Vent connection 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, i Brake System Modifications and New Features

70 Location The Central Brake Unit (CBU) (13.08) is mounted under the maintenance flap on the driver side. Design Central Brake Unit Component descriptions Central Brake Unit (CBU) 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 Central Brake Unit (CBU) A110a1 Brake control (BS) control unit B D PV RD RV W Brake value sensor Pressure sensor Proportioning valve Redundancy valve Relay valve Travel sensor Pneumatic connections 3 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 Brake System Modifications and New Features i 69

71 Component descriptions Pressure limiting valve with vent 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) pneumatically limits the reservoir pressure coming from the ancillary consumer connection to 2.5 bar. Design Pressure limiting valve with vent /2-way valve for auxiliary braking effect Pressure limiting valve with vent Pneumatic connections 1 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 , 375.4, /23, i Brake System Modifications and New Features

72 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). 3/2-way valve for auxiliary braking effect 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. Component descriptions Design Pressure limiting valve with vent /2-way valve for auxiliary braking effect /2-way valve for auxiliary braking effect SV WV Switching valve Shuttle valve Validity Model , 375.4, /23, Pneumatic connections 1 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) Brake System Modifications and New Features i 71

73 Component descriptions Radar sensor controller unit 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) transmits 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, i Brake System Modifications and New Features

74 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). Active Brake Assist control unit Component descriptions A3 A11 A111 Drive control (FR) control unit Brake control (BS) control unit Active Brake Assist (ABA) control unit 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) calculates the current traffic situation and the risk of a rearend 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). Validity Model 930, 932, 934 Brake System Modifications and New Features i 73

75 Component descriptions Four-circuit protection valve Location on vehicles with 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 protection valve with integrated pressure limiter (4.07) can also be installed on the inside of the left longitudinal frame member. Task on vehicles with pressure control system The task of the 4-circuit protection valve with integrated 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 pressures and to hold the reservoir pressures of all brake circuits to the specified level. Illustrated on model circuit protection valve with integrated pressure limiter Validity Model 374, 375, 940, 942, 943, 944, 950, 952, 953, 954, 957, 970, 972, 974, 975, 976 with pressure control system 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 regulator in the single-chamber air drier with integrated pressure regulator (6.12) is simultaneously the operating pressure for brake circuits 1 and i Brake System Modifications and New Features

76 Design on vehicles with pressure control system Four-circuit protection valve Component descriptions circuit protection valve with integrated pressure limiter A B C D Pressure limiter 8.5 bar with integrated safety valve for brake circuits 3 and 4 Check valve in connections 25 and 26 Return flow safeguard to connections 21 and 22 Protection valve (overflow valves with limited return flow) B71 Brake circuit 1 and 2 reservoir pressure sensor Pneumatic connections 1 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 Brake System Modifications and New Features i 75

77 Component descriptions Condensation sensor with drain valve Location Depending on the vehicle equipment, the condensation sensor (B76) is either installed on the singlechamber 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 condensation 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, i Brake System Modifications and New Features

78 Design 1 Brass tip 2 Temperature sensor 3 Heating element 4 Brass housing 5 Drain valve 6 Key button Condensation sensor with drain valve 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 maintenance 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. Component descriptions B76 Condensation sensor Note Once the condensation water is drained, the driver can reset the message "Condensation water" in the maintenance system (WS) in the "Maintenance" menu using the steering wheel buttons. Brake System Modifications and New Features i 77

79 Repair instructions Central Brake Unit AR42.25>W>3200A Remove/install Central Brake Unit (CBU) MODEL 970, 972, 974, 975, 976 with CODE (ZX2) EPB II 1 Pedal bracket Central Brake Unit (CBU) (A110) A110a1 Telligent brake system (BS) control unit W42.25>1187>06 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 i Brake System Modifications and New Features

80 Active Brake Assist control unit AR42.32>W>0001A Remove/install Active Brake Assist (ABA) control unit MODEL 930, 932, 934 with CODE (BC7) Active Brake Assist (ABA) Repair instructions W42.32>1013>08 A3 A11 A111 Drive control (FR) control unit Telligent brake system (BS) control unit 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) 5 Install in the reverse order 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 Brake System Modifications and New Features i 79

81 Repair instructions Drive axle axle modulator AR42.25>W>3104C Remove/install axle modulator MODEL 930, 932, 933, 934 with CODE (ZX2) EPB II 1 Rpm sensor electrical connector 2 Brake cylinder compressed air line 3 Brake cylinder compressed air line 4 Redundancy actuation compressed> air line 5 Electrical connectors (axle modulator) 6 Rpm sensor electrical connector 7 Supply pressure compressed>air line 8 Supply pressure compressed>air line 9 Electrical connector for redundancy control Drive axle axle modulator W42.25>1145>05 e d i Remove/install 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) 9 Detach reservoir pressure compressed air lines (7, 8) 10 Detach redundancy actuation compressed air line (4) AR42.10>W>0900C AR42.10>W>0900C AR42.10>W>0900C 80 i Brake System Modifications and New Features

82 Drive axle axle modulator Remove drive axle axle modulator (31.13). n BA42.25>N>1004>01A 12 Install in the reverse order 13 Read out and erase fault memory or erase fault memory bit if necessary 14 Check compressed air connections on drive axle axle modulator (31.13) for leaks i Only required if the drive axle axle modulator (31.13) has been replaced. i To do this, depress the brake pedal and spray the compressed air connections with a commercially available leak detecting spray or soapy water. Repair instructions 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 Brake System Modifications and New Features i 81

83 Repair instructions Drive axle axle modulator AR42.25>W>3104D Remove/install axle modulator MODEL 970, 972, 974, 975, 976 with CODE (ZX2) EPB II 1 Electrical connectors (axle modulator) 2 Electrical connector for brake wear sensor 3 Rpm sensor electrical connector 4 Brake cylinder compressed air line 5 Supply pressure compressed>air line 6 Redundancy actuation compressed>air line 7 Electrical connector for redundancy control 8 Supply pressure compressed>air line 9 Brake cylinder compressed air line 10 Electrical connector for brake wear sensor 11 Rpm sensor electrical connector Drive axle axle modulator W42.25>1214>11 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) 8 Detach reservoir pressure compressed air lines (5, 8) 9 Detach redundancy actuation compressed air line (6) AR42.10>W>0900C AR42.10>W>0900C AR42.10>W>0900C 10 Remove drive axle axle modulator (31.13). n BA42.25>N>1004>01A 11 Install in the reverse order 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. 82 i Brake System Modifications and New Features

84 13 Check compressed air connections on drive axle axle modulator (31.13) for leaks 14 Perform function test on brake test stand n Electropneumatic brake (EPB) Number Designation Models 375.1, 970, 972, 974, 975, 976 Drive axle axle modulator i To do this, depress the brake pedal and spray the compressed air connections with a commercially available leak detecting spray or soapy water. Repair instructions BA42.25>N>1004>01A Bolt, axle modulator to frame Nm 90 Brake System Modifications and New Features i 83

85 Repair instructions Combination brake cylinder AR42.10>W>0030A Releasing combination cylinder mechanically 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, 976 with single diaphragm cylinder Combination cylinder with interior release bolt 1 Release bolt A B Spring accumulator mechanically released (the indicator pin is unscrewed) Spring accumulator mechanically tensioned (the indicator pin is screwed in) W42.10>1134>11 Combination cylinder with exterior release bolt 1 Release bolt A B Spring accumulator mechanically released (the release bolt is unscrewed) Spring accumulator mechanically tensioned (the release bolt is screwed in) W42.20>1009>11 84 i Brake System Modifications and New Features

86 Releasing Combination brake cylinder 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. Repair instructions n Models 374, 375, 930, 932, 933, 934, 940, 942, 943, 944, 950, 952, 953, 954, 957, 958, 970, 972, 974, 975, 976 n Model 675, 676, 677, 679 BA42.10>N>1006>08A 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 Number Designation Model 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 M Nm BA42.10>N>1006>08A Spring actuator release bolt in released position M Nm 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 BA42.10>N>1005>08A Spring accumulator release bolt in driving position M Nm BA42.10>N>1006>08A Spring actuator release bolt in released position M Nm n Brake cylinder Number Designation Model 375.3, 950, 952, 953, 954 with drum brake Model 375.3/4, 950, 952, 953, 954, 957 with disk brake BA42.10>N>1005>08A Spring accumulator release bolt in driving position M Nm BA42.10>N>1006>08A Spring actuator release bolt in released position M Nm Brake System Modifications and New Features i 85

87 Repair instructions Combination brake cylinder n Brake cylinder Number Designation Models 930, 932, 933, 934 with drum brake BA42.10>N>1005>08A BA42.10>N>1006>08A Spring accumulator release bolt in driving position Spring actuator release bolt in released position M M Nm Nm Model 930, 932, 933, 934 with disk brake n Brake cylinder Number Designation Model 958.0/2/4 with drum brake Model 958.2/4 with disk brakes BA42.10>N>1005>08A Spring accumulator release bolt in driving position M Nm BA42.10>N>1006>08A Spring actuator release bolt in released position M Nm n Brake cylinder Number Designation Model 675, 676, 677, 679 BA42.10>N>1002>08C Spring accumulator release bolt in driving position M Nm 35 n Brake cylinder Number Designation Model 675, 676, 677, 679 BA42.10>N>1003>08C Spring actuator release bolt in released position M Nm i Brake System Modifications and New Features

88 Combination brake cylinder AR42.10>W>0030B Releasing combination cylinder mechanically MODELS 970, 972, 974, 975, 976 with double diaphragm cylinder 1 Release pin 2 Holder (for release pin) 3 Washer 4 Nut 5 Plug Repair instructions W42.10>1202>12 1 Release pin 3 Washer 4 Nut 5 Plug 6 Spring stop A Release pin engaged W42.10>1201>06 Brake System Modifications and New Features i 87

89 Repair instructions Combination brake cylinder 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. 88 i Brake System Modifications and New Features

90 Combination brake cylinder Unscrewing the nut (4) tensions the combination cylinder again Remove release pin (1) i Only perform this step with used combination cylinders Turn release plate (7) with washer (8) 90 counterclockwise and remove Turn release pin (1) 90 counterclockwise and remove. i Only perform this step with new combination cylinders. The release plate (7) with the washer (8) is no longer required after removal. Repair instructions 13 Fit release pin (1) in holder (2), screw nut (4) with washer (3) onto release pin (1) and secure with new cotter pin 14 Seal hole on spring accumulator part with stop plug (5) p The release plate (7) must be removed, otherwise the spring accumulator part will not function. i Only perform this step with used combination cylinders. n Brake cylinder Number Designation Model 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 Brake System Modifications and New Features i 89

91 Repair instructions Condensation sensor AR42.10>W>0050A Remove/install condensation sensor MODEL 374, 375, 930, 932, 933, 934, 940, 942, 943, 944, 950, 952, 953, 954, 957, 958, 970, 972, 974, 975, 976 Condensation sensor (B76) without drain valve 1 Connector 2 Jack 3 O>ring B76 Condensation sensor W42.10>1206>05 Condensation sensor (B76) with drain valve 1 Connector 2 Jack 3 O>ring 4 Button (drain valve) 5 Paint protective cap B76 Condensation sensor W42.10>1207>05 90 i Brake System Modifications and New Features