Read EBS (EPB) text version

EBS (EPB)Electronically Controlled Braking System

Description of System and Functions

1998 Edition

© Copyright WABCO 1998 WABCO Fahrzeugbremsen A Division of WABCO Standard GmbH The right of amendment is reserved

EBS

Table of Contents

Introduction ............................................................... 3 Benefits of EBS ......................................................... 3 System Design ................................................... 6 / 34 Description of Components..................................... 7 Brake Signal Transmitter ....................................... 7 Central Module ...................................................... 9 Proportional Relay Valve ..................................... 10 Backup Valve....................................................... 12 Axle Modulator..................................................... 14 Trailer Control Valve ............................................16 Other Components .............................................. 17 Description of a 4S/4M System.............................. 18 Function of Electro-Pneumatic Portion of the System....................................................... 18 Electrical/Electronic Circuits ................................ 20 Control Functions................................................. 21 Supporting Functions........................................... 22 Error Detection........................................................ 23 EBS ,,Emergency Operations"............................... 24 Testing the EBS ...................................................... 25 Operation and Dials ................................................ 26 Error Code Description .......................................... 27 Diagnosis................................................................. 28 Diagnostic Controller ........................................... 28 Program Description ............................................29 Using the Diagnostic Controller ........................... 30 Using a PC........................................................... 33 Function scheme ...................................................... 35

2

WABCO

Introduction / Benefits of EBS

EBS

Preface

Comments on the publication "EBS - Electronically controlled Braking System, Description of System and Functions 815 000 262 3". EBS enhances vehicle and road safety by means of reducing the stopping distance, achieving improved braking stability and montitoring the braking system. In addition, EBS considerably improves both economic efficiency and driving comfort. For this reason, EBS will be included in new vehicle series, the pioneer being ACTROS from Daimler-Benz which has an electronically controlled air braking system fitted as standard equipment. This system by name of "Telligent® Braking System" from Daimler-Benz (formerly EPB), is a joint development by Daimler-Benz and WABCO. Please note: The term "Telligent® Braking System" comprises the whole of the braking system, not only its controlling system which we call EPB. The ACTROS "Telligent® Braking System" contains some specific Daimler-Benz features for which WABCO, in applications for vehicles from other manufacturers, has substituted its own solutions. These include the following functions described in the publication in more detail:

Introduction

Increasing competition in the transport trade has also caused the requirements for braking systems to be increased steadily. The introduction of the Electronically controlled Braking System EBS is the logical step to meet this and other requirements. EBS permits perpetual optimized balancing of the braking forces among the individual wheel brakes, and of the towing vehicle and its trailer. The comprehensive diagnostic and monitoring functions of the Electronically controlled Braking System are one of the basic requirements for effective fleet logistics.

Benefits of EBS

EBS Effectively Reduces Maintenance Costs.

n n

EBS combines a large number of functions. The objective is to reduce maintenance costs whilst maximizing braking safety, e.g. by minimizing lining wear of the wheel brakes. Individual control according to the wear criteria on both front and rear axles harmonizes lining wear. By evenly spreading the load across all wheel brakes, total wear is minimized. In addition, maintenance and lining change intervals coincide. Laidup costs are drastically reduced. Depending on the vehicle's service profile and other factors, the vehicle owner achieves considerable savings. A comparison of maintenance costs for the braking system and the foundation brakes for a tractor-trailer combination using EBS versus a combination with a modern conventional braking system shows high savings for the first vehicle owner.

n n n

redundancy valve, rear axle redundancy special control functions in the area of brake force distribution (differential, drive-slip control DSR), lining wear control and trailer control testing and ACTROS. diagnostic methods typical for

n

WABCO

2

3

EBS

Benefits of EBS

EBS Ensures Compatibility Between Tractor and Trailer - At Any Time

The harmonization of the braking processes for the whole of the tractor-trailer combination, especially if combinations are varied frequently, can often not be achieved satisfactorily by conventional means. Improper balancing, e.g. if a trailer is not braked effectively enough, will cause uneven lining wear. EBS will recognize any incompatibility between the towing vehicle and its trailer, harmonizing the braking performance. If the brakes work at their best possible operating point, this not only optimizes maintenance costs for the brakes but also provides a maximum in safety and comfort.

Comprehensive Diagnostic Facilities

One basic requirement for effective fleet logistics are low-maintenance systems. EBS provides the vehicle owner with up-to-date information on the state of his braking system and the foundation brakes. This permits anticipated maintenance scheduling. EBS monitors both all essential components and the braking system's functions. Any defects are recognized by the system and accurately displayed for maintenance. The maintenance specialist can then rectify the error in question.

4

WABCO

Benefits of EBS

EBS

Increasing Braking Safety

When developing EBS, WABCO did not merely take its bearings from the applicable legal requirements. Next to the benefit for the user, it is safety which takes priority. For this reason, a vehicle fitted with EBS is capable of much more than what is legally required.

conventional braking system

EBS

speed

stopping distance

The High Degree Of Safety Through ABS Is Achieved By Several Factors:

n n n

Shorter response and pressure buildup times for the brakes on front and rear axles and trailer axles Improved ABS function Towing vehicle / trailer properly balanced at all times

n n

Constant monitoring of the service brake and its components. In the event of the performance of the wheel brakes being reduced, this will be recognized by the EBS, and the driver is alerted. Integrated ASR function provides optimized vehicle stability and traction when moving off.

WABCO

2

5

EBS

System Design

Modular Design of WABCO EBS

The configuration and the structure of WABCO's EBS permits a high degree of flexibility for the vehicle manufacturer when designing the system. For this reason, the most varied of needs can be met: For meeting the essential requirements of the vehicle owner, WABCO recommends an EBS which comprises individual pressure control on front and rear axles and trailer control, and which provides for pneumatic redundancies in all braking circuits.

n n n n n

partial or full system type of redundancy trailer control strategy elecrical interfaces etc.

2P/1E-EBS

AM TCV BST PRV BV S W = Axle Modulator = Trailer Control Valve = Brake Signal Transmitter = Proportional Relay Valve = Backup Valve = Speed Sensor = Wear Sensor

This EBS consists of a dual circuit and an overriding single-circuit electro-pneumatic circuit. This configuration is described as 2P/1E-EBS. The single circuit electro-pneumatic part of the system consists of one central electronic control unit (central module), the axle modulator with integrated electronics for the rear axle, a brake signal transmitter with parely pneumatical integrated stroke sensors and brake switches, an electro-pneumatic control valve and two ABS valves for the front axle, plus an electro-pneumatic

trailer control valve. An expansion of this configuration by an additional axle modulator for the rear axles would then provide a 6-channel EBS. The structure of the subordinate dual-circuit pneumatic part of the system is basically identical with that of a conventional braking circuit. This part of the system serves as a backup and becomes effective only if the electro-pneumatic circuit fails.

6

WABCO

Description of Components

EBS

Brake Signal Transmitter 480 001 ... 0

The brake signal transmitter is used to generate electrical and pneumatic signals to apply to, or release pressure from, the Electronically controlled Braking System (EBS). This unit is designed for two pneumatic and electrical circuits respectively. Commencement of actuation is electrically recorded. A sensor reads the travel of the actuating pin which is then, after modulation of its pulse width, transmitted as an electrical signal. In addition, there is an output of the pneumatic backup pressures in Circuits 1 and 2. In this process, the pressure of the 2nd circuit is retained slightly. Optional: Via an additional control port, the pneumatic characteristic of the 2nd circuit can be modified.

Position (MB Actros): Driver's cab - front Installation location: similar to previous brake valve

WABCO

2

7

EBS

Description of Components

Brake Signal Transmitter 480 001 ... 0

Function

Central Module Backup Valve

Air Reservoir

Proportional Relay Valve

Air Reservoir

8

WABCO

Description of Components

EBS

Central Module 446 130 ... 0

The central module is used to control and monitor the Electronically controlled Braking System. From the signal received from the brake signal transmitter it determines the vehicle's intended retardation. Together with the wheel speeds measured by the wheel speed sensors, the intended retardation is the input signal for EBS control which uses these readings to establish the index pressure values for the front and rear axles and the trailer control valve. The index pressure for the front axle is compared with the actual value taken, and any differences are balanced by means of the proportional relay valve. Output of the trailer control pressure is achieved in a similar manner. In addition, the wheel speeds are evaluated to commence ABS control by modulating the brake pressures in the brake cylinders in the event of the wheels showing a tendency to lock. The central module exchanges data, via the EBS system bus, with the axle modulator (or axle modulators in 6S/6M systems). Electrical braking systems for trailers are actuated via a data interface to ISO 11992. The central module communicates with other systems of the towing vehicle (engine control, retarder, etc.) via a vehicle data bus.

Installation location (MB Actros): foot space - passenger side

WABCO

9

EBS

Description of Components

Proportional Relay Valve 480 202 ... 0

In the Electronically controlled Braking System, the proportional relay valve is used as an actuator for the output of brake pressures at the front axle. It consists of a proportional solenoid valve, a relay valve and a pressure sensor. Electrical actuation and monitoring are effected by the central module of the hybrid system. The control current determined by the electronics is converted by the proportional relay valve into control pressure for the relay valve. The output pressure of the proportional relay valve is proportional to that pressure. The pneumatic actuation of the relay valve is effected by the redundant pressure of the brake signal transmitter.

Installation location (MB Actros): front shock absorber area - left

10

WABCO

Description of Components

EBS

Proportional Relay Valve 480 202 ... 0

Function

Brake Signal Transmitter

Central Module

Air Reservoir

Air Reservoir

Brake Chamber Front Axle

Rear Axle

WABCO

11

EBS

Backup Valve 480 205 ... 0

Description of Components

The backup valve is used to rapidly increase or decrease the pressure for the brake cylinders on the rear axle in the case of a backup; it consists of several valve units which have to perform the following functions, among others:

n n n n

3/2-way valve to prevent backup operation if the electro-pneumatic braking circuit is not defective relay valve function for improving the time response of the backup pressure retention in order to synchronize the commencement of pressure output on the front and rear axles in the event of a backup pressure reduction to avoid overbraking of the rear axle to the largest possible extent in the case of a backup.

The backup valve used in Actros also has a 2/2-way valve which is energized when ABS is activated, in order to prevent unintentional throughput of the rear axle backup pressure during ABS control cycles.

Installation location (MB Actros): frame inside, near rear axle

12

WABCO

Description of Components

EBS

Backup Valve 480 205 ... 0

Function

Central Module

Axle Modulator

Air Reservoir

WABCO

2

13

EBS

Description of Components

Axle Modulator 480 103 ... 0

The axle modulator controls the brake cylinder pressures on both sides of one or two rear axles. It contains two independent pneumatic pressure control channels (Channels A and B), each containing one inlet and one exhaust valve, plus one pressure sensor, sharing one electronic control unit. The index pressures and external monitoring functions are provided by the central module. In addition, two speed sensors monitor and evaluate the wheel speeds. In the event of a tendency to lock or to spin being detected, the index value provided is adjusted. Two sensors can be connected for monitoring lining wear. The axle modulator has one additional port for connecting a backup pneumatic braking circuit. One double check valve per side transmits the higher of the two pressures (electro-pneumatic or redundant) to the brake cylinder.

Installation location (MB Actros): rear axle

14

WABCO

Description of Components

EBS

Axle Modulator 480 103 ... 0

Function

Central Module

Air Reservoir

Air Reservoir

Tristop® Brake Actuator

Tristop® Brake Actuator

Backup Valve

WABCO

2

15

EBS

Description of Components

Trailer Control Valve 480 204 ... 0

In the Electronically controlled Braking System, the trailer control valve is used as a control element to output the hose coupling pressures. The trailer control valve consists of a proportional solenoid valve, a relay valve, a breakaway emergency valve and a pressure sensor. Electrical actuation and monitoring are effected by the central module. The control current determined by the electronics is converted by the proportional solenoid valve into control pressure for the relay valve. The output pressure of the trailer control valve is proportional to that pressure. The pneumatic actuation of the relay valve is effected by means of the backup pressure from the brake signal transmitter and the output pressure from the hand brake valve.

Installation location (MB Actros): near air reservoirs

16

WABCO

Description of Components

EBS

Trailer Control Valve 480 204 ... 0

Function

Central Module

Air Reservoir

Brake Signal Transmitter

Front Axle

Hand Brake Valve

Other Components

Other components of the electronically controlled braking system: Proportional Relay Valve: 480 202 005 0 (8x4 vehicles) 480 202 004 0 (all other vehicles from 08/97) Backup Valve: 480 205 001 0 Axle Modulator: 480 103 002 0 (4x2 vehicles up to 07/97) 480 103 001 0 (6x2, 6x4, 6x2/4 and 8x4 vehicles up to 07/97) 480 103 004 0 (4x2 vehicles from 08/97) 480 103 005 0 (6x2, 6x4, 6x2/4 and 8x4 vehicles from 08/97) Trailor Control Valve: 480 204 001 0 ABS Solenoid Valve: 472 195 008 0

n n n n

ABS solenoid valves wheel speed sensors brake lining wear sensors ASR solenoid valve for 6x2 and 6x2/4 vehicles which pneumatically disconnects the additional axle from the driving axle during ASR control cycles.

Part Numbers

(for the components in Actros): Central Module: 446 130 000 0 (all vehicle types up to 07/97) 446 130 005 0 (4x2 semitrailer tractors from 08/97) 446 130 004 0 (all other vehicles from 08/97) Brake Signal Transmitter: 480 001 000 0

WABCO

2

17

EBS

Description of a 4S/4M System

Function of Electro-Pneumatic Portion of the System

The electro-pneumatic portion of the tractor system and its signal path operate via

Signal processing and error monitoring for the rear axle are covered by the axle modulator, permitting the sensor values to be made available to the central module via the data bus.

Operation of Pneumatic Backup

The front and rear axle circuits follow different backup procedures: The front axle circuits uses the additional backup principle whilst the rear axle circuit is equipped with a backup which can be actuated via a solenoid valve.

n

Brake signal transmitter Two distance sensors establish the index value which is transmitted after modulation of pulse width; two switches are used to confirm the index value. Central module To establish the index value for the individual axles, and system control Proportional relay valve to control the pressure for the front axle ABS solenoid valves for rapid ABS pressure control cycles at the wheel brakes on both sides of the front axle Backup valve for retaining the backup pressure of the rear axle Axle modulator with integrated control unit to control the brake pressure on both sides of the rear axle(s).

n n n n n

Additional Backup on the Front Axle

The pneumatically operating front axle backup circuit uses a

n n

Brake Signal Transmitter with 2 pneumatic circuits (front and rear axles), and a Proportional Relay Valve relay valve with combined pilot control via the pneumatic front axle circuit and the proportional solenoid valve

to act on the brake cylinders of the front axle. When the brake signal transmitter is actuated, there is output of electro-pneumatic pressure via the proportional valve. As a ratio of the actuating force, the proportional valve is supplied with pressure from the brake signal transmitter, with a delay in pneumatic backup pressure. This pressure is added to the electro-pneumatic output pressure. The output pressure from the proportional valve is adjusted to the given index pressure by adjusting the electro-pneumatic pressure accordingly. In the event of the electro-pneumatic system failing, the pneumatic backup pressure is allowed to pass through. Because of the necessity of holding back the redundant brake pressure of the front axle versus the electropneumatic output pressure (e. g. for optimizing wear or integrating a sustained-action brake), the "electrical brake signal transmitter" has predominance over the pneumatic output pressure of the front axle at the brake signal transmitter (2nd pneumatic circuit of the brake signal transmitter).

EBS can be switched on either via the electrical driving switch (Cl. 15) or by actuating the brake signal transmitter and its integrated brake switch. The brake pedal's travel measured is interpreted as the index retardation and converted by the central module, taking into account a number of criteria, into the index pressures for the front and rear axles. The index value for the axle modulator is transmitted by the central module via a system bus. The axle modululator reads and controls the brake pressures of the wheel brakes on both sides of the rear axle. The brake pressure of the front axle is controlled by the central module via the proportional relay valve with the integrated pressure sensor. The wheel speeds are read by the sensors known from the ABS system and are used, among other things, as the input value for the pressure control and regulating algorithms, and for the ABS and ASR functions. In order to achieve lining wear control, the lining wear, sensors read the degree of wear of the linings in the individual wheel brakes. The sensor signals from the front axle are picked up by the central module, those from the rear axle by the axle modulator.

18

WABCO

Description of a 4S/4M System

EBS

Rear Axle Backup

The pneumatic backup on the rear axle uses a

n n n

Brake Signal Transmitter with 2 pneumatic circuits (front and rear axles), a Backup Valve with a 2/2-way solenoid valve, a 3/2-way valve and a relay valve, and Double Check Valves integrated in the axle modulator for the rear axle

to act on the brake cylinders on the rear axle. With properly operating EBS, i. e. electronic pressure output is possible on the rear axle, the 3/2-way valve is brought into the "suppress backup" position by the electronical output pressure on the left rear wheel.

Operation of Trailer Control

Trailer control is effected via a dual-circuit electropneumatic trailer control valve (one circuit being electropneumatic, the other purely pneumatic). This is actuated by the central module. A proportional valve and a pressure sensor allow electro-pneumatic control of the trailer's actuating pressure. The function of the purely pneumatic part of the trailer control valve is similar to that of a conventional trailer control valve (actuation from port 42 via circuit 1, breakaway safeguard, pressure control through parking braking system). The pneumatic control port is fed by the brake signal transmitter's backup port for the rear axle and will not allow any pressure to pass until the ratio falls to below pel/p42 ~ 0.5. If that ratio is exceeded, the electropneumatically actuated pressure acts on its own.

WABCO

19

EBS

Description of a 4S/4M System

Electrical/Electronic Circuits

The electronically controlled braking system is electrically energized via two non-fused feed lines. Terminal 30a: Voltage supply for brake signal transmitter 1st circuit, proportional relay valve, trailer control valve and the ABS valves. Terminal 30b: Voltage supply for brake signal transmitter 2nd circuit, axle modulator and backup valve. For communicating with other vehicle systems (engine, transmission, retarder), the central module has a bus interface. The axle modulator, the ABS valves, the porportional relay valve for the front axle and the trailer control valve can be separately switched off via a short-circuit proof electronic switch integrated in the central module. The external pressure and wear sensors are earthed in the central module and the axle modulator. Connection to vehicle earth is not permissible. The sensors of the central module are earthed in a neutral point in the vicinity of the central module (l <= 1 m). Another neutral point (l <= 1 m) is used as a connecting point for energy earth (backup valve, brake signal transmitter, axle modulator). The earthing wires of the ABS valves lead back to the central module where they can be separated

by means of an electronic switch in the event of a fault. The connection between the central module and the axle modulator is effected via a separately specified CAN system bus. For actuating, and exchanging data with, electrical braking systems in trailers, the central module has an electrical data interface to ISO 11992. The trailer system does not receive its energy supply from the central module. The data stored to Part 2 of ISO 11992 are processed by the central module according to their relative importance and their function, and exchanged for communication with other bus users depending on the vehicle manufacturer's bus specifications. The brake signal transmitter contains two separate electrical circuits. Via two switches, the actuation process is recognized. These switches perform the following functions:

n n n

perceiving the commencement of the braking process, activating the EBS (when driving switch is in the "off" position), if not activated, the offset values of the index value sensors are calibrated, and monitored.

20

WABCO

Description of a 4S/4M System

EBS

The non-contact distance sensors supply the central module with the electrical index braking value in the form of signals with modulated pulse widths. Both signals from the electrical backup transmitter are evaluated equally. The brake pressures on the front axle and at the "control" hose coupling are controlled by means of proportional relay valves with regulated current. The actual pressure sensors are integrated in valve modules. The actual values are transmitted in the form of analog signals. Reading the axle load is no longer necessary. The differential slip which changes with the vehicle's load is picked up by the wheel speed sensors and evaluated by the central module which also actuates the valves. The central module can display the system status via a yellow EBS info lamp and a red warning lamp. An additional yellow info lamp indicates that ASR is in operation. The functions and colours of the lamps may, however vary with different vehicle manufacturers. Mercedes-Benz, for instance, use a display on the dashboard showing the status of the system. For monitoring brake lining wear, potentiometers (or, as an alternative in the case of drum brakes, limit switches) must be provided for input to the central module from the front axle. The rear axle lining wear sensors provide input to the axle modulator; the readings are transmitted to the central module via the control system bus. For the individual axles, the sensors are separately supplied with short-circuit proof voltage of 5 volts.

Brake Force Distribution

The distribution of the brake forces across the front and rear axles is dependent, among other factors, on the comparison of the actual and index values for vehicle retardation within the program for the process of "retardation control". The controlling variables are the wheel speeds picked up by the speed sensors. The evaluation of the readings from the wheel speed sensors show the differences in the slip of the front and rear axles, i. e. differential slip control. With the best possible brake force distribution, there is ideally no differential slip between the axles of the towing vehicle. The pressure on the front and rear axles is controlled in such a way that the differential slip approximates zero.

Brake Lining Wear Control

In a non-critical braking process the brake force distribution is adjusted according to the wear signals received, i.e. a perceived variance in lining wear. The pressure on the wheel brakes showing more wear is reduced slightly, the pressure on the wheel brakes showing less wear being increased correspondingly, thus ensuring that the total retardation requested by the driver does not change.

Trailer Control

Trailer control is achieved both electrically via the motor vehicle interface (ISO 11992) and pneumatically via the electro-pneumatic trailer control valve. For reasons of economy, no sensors are being provided for coupling forces. The deceleration of the motor vehicle initially lies around the middle of the EC braking band. If the deceleration of the trailer also lies in the middle of the band, no coupling forces occur. If the trailer deviates from the middle band position, the motor vehicle's ECU will perceive this by means of the retardation control portion of the program, and will adjust the trailer's actuating pressure accordingly. Any higher response threshold of the trailer's brakes will be compensated by a corresponding inshot. That inshot of pressure in the trailer's control line (yellow) will be approx. 2 bar when the braking process is commenced. Most problems known today are solved with this approach. WABCO has been instrumental in standardizing the electrical motor vehicle/trailer interface (ISO 11992).

Control Functions

Retardation Control

Retardation control is used to adjust the level of brake pressure to the retardation as desired by the driver (defined as z in %). At equal pedal actuation, the vehicle is always retarded at the same rate, regardless of the load carried at the time. To make the driver subjectively perceive any deterioration caused by a change of the coefficient of friction on a wheel brake (e.g. fading when going downhill), retardation control will end any adaptation process as soon as a given (fixed) maximum value has been reached. Also included in retardation control are an adaptation to the brake hysteresis. Every time the brake is released, the releasing steps are selected in such a way that the brake force is adjusted immediately. This function achieves the earliest possible release of the brake, i.e. a sensation similar to driving a passenger car.

WABCO

21

EBS

Description of a 4S/4M System

EBS integrates the following time-tested functions:

Supporting Functions

Generating The Nominal Brake Value (Index Value)

The brake pedal travel picked up by the sensors in the brake signal transmitter is transmitted to, and "processed" by, the central module. For this purpose, the travel is converted into nominal retardation as shown by the characteristic curve as illustrated below.

Anti-Lock Function (ABS)

The control logic is aware, from the speed behaviour of the wheels, whether one or several wheels are showing a "tendency to lock" and will then decide whether the respective brake pressure is to be lowered, maintained or increased. The wheels of the rear axle are controlled in analogy to this concept within their optimal range (individual control Ø IR). On vehicles with 3 or 4 axles which use 4S/4M systems, the non-sensed wheels are also laterally controlled. On roads with extreme differences in the nearside and offisde coefficients of friction, vehicles are very difficult to control, if at all, when ABS operates, due to the differences in brake pressure buildup (yawing incidence). For this reason the brake pressure on the front axle wheel brakes is not controlled independently, permitting the driver to take steering action (modified individual control Ø MIR). If there is a tendency of the driving wheels to lock on a low friction surface while the sustained-action brake is being used, thereby causing the vehicle to be potentially unstable, the vehicle's CAN bus will switch off the ABS and the sustained-action brake, thus ensuring that stability is maintained.

Determination of nominal brake value

Pressure Control on Front And Rear Axles And Electro-Pneumatic Trailer Actuation

The index pressures computed from the nominal brake value using the overriding control algorithms are output in the pressure control curcuits for the front and rear axles, and for trailer control. To improve the pressure control properties, the magnetic flux is controlled within the solenoid valves.

Drive Slip Control (ASR)

Similar to the ABS function, the control electronics will perceive whether the driving wheels are within the stable range of the µ-slip curve as the vehicle is being accelerated. If the wheels show a "tendency to spin", the CAN bus and the engine control system will adjust the engine's performance and/or brake the wheels of the driving axle via the axle modulator. Activated ASR control is displayed via a control lamp.

Speed Sensors And Tyre Coordination

Reading the wheel speeds is similar to the procedure known from the ABS system. Automatic tyre coordination compensates for any difference in nominal tyre sizes and thus the rolling circumferences among axles. If impermissible pairs of tyres are used, this will be recognized as a defect. If tyre sizes are changed, this requires resetting of the parameters.

22

WABCO

Error Detection

EBS

Error detection measures are used to avoid the effects of system failures and/or to alert the driver to any functional defects. In part the error detection principles are similar to those of a conventional ABS (monitoring of ABS valves, speed sensors, computer hardware). A large part of the monitoring activities, however, relates to specific operational areas of the EBS (EBS sensor systems, EBS solenoid actuation, brake pressure output, data transmission via CAN bus). In addition to the speed sensor signals, EBS evaluates numerous other sensor singals, checking them for accuracy. Nominal Value Sensor Systems (Sensors And Switches) The brake signal transmitter supplies two sensor signals and two switch signals. The sensor signals (modulated for pulse width) are checked for adherence to the permissible range and for mutual deviations. The switch signals (digital) are checked for their proper switching status. Brake Pressure Sensors (Front and Rear Axles, Trailer Control Valve) The signals (analog) of the pressure sensors in the pressure control circuits are checked for adherence to the permissible range. Please note: The wiring of both rear axle pressure sensors is not externally accessible - this is part of the internal wiring of the axle modulator. Wear Sensors (Front and Rear Axles) The signals (analog) of the wear sensors are checked for adherence to the permissible range. EBS monitors the actuation of the dedicated EBS solenoid valves. Front Axle Proportional Relay Valve / Trailer Control Valve The continuous magnets (pressure proportional to the magnetic flux) of the front axle proportional relay valve and the trailer control valve are monitored for their proper actuation status. Inlet and Outlet Solenoid Valves for Rear Axle Modulator The inlet and outlet solenoid valves of the rear axle are located within the axle modulator. The magnet wiring is not accessible. EBS monitors the brake pressure output. Both the electrically controlled brake pressures and the

pneumatic redundant pressures are monitored. Front axle brake pressure insufficient / trailer control valve brake pressure insufficient Checks are made to establish whether there is a minimum brake pressure (at the front axle or at the trailer control valve) at a certain magnetic energy. Excessive rear axle pressure deviation (nearsideoffside) During normal braking operation (neither ABS nor ASR controlled) the brake pressure readings have to be close to identical on both sides of the rear axle. If the brake pressure exceeds a certain tolerance range, the system will identify an error. Failure of rear axle redundancy In certain situations (stationary vehicle, parking brake on) the electrical brake pressure output on the front and rear axles will be prevented. If the driver now depresses the brake pedal, the front and rear axles will be braked by means of pneumatic redundancy. If the front axle brake pressure exceeds a certain value, a certain minimum pressure also has to be present at the rear axle. If this is not the case, the system will identify an error. Rear axle redundancy cannot be switched off The output of pneumatic redundancy pressure at the rear axle is usually prevented by the redundancy valve. If, due to an error, this can no longer be prevented, it may no longer be possible to reduce the rear axle brake pressure when ABS control takes place (because the rear axle redundancy pressure which is not subject to ABS will reach the brake cylinders on the rear axle). In this situation, an error will be recognized. EBS monitors the transmission of data

n n n

between the EBS central module and the axle modulator (system bus) between the EBS and other system control equipment (vehicle bus) between the towing vehicle and its electronically braked trailer.

If no communication is possible, or if communication is suddenly terminated, an error will be recognized.

WABCO

2

23

EBS

EBS ,,Emergency Operations"

Once an error has been detected, certain functional sectors of the EBS will usually be deactivated. Functions which are not impaired by the failure will be maintained. For the operation of EBS with limited functional scope, the term ,,emergency operations" is commonly used. The following functions can be deactivated in the event of a defect: Operation without ABS function The ABS function can be deactivated at one individual wheel, at one axle, or for the whole vehicle. (Possible causes: defective speed sensor signal, ABS valve failure, ...) Operation without ASR function Drive-slip control can be deactivated either partially or completely. If it is shut down completely this means that both brake control and engine control will be shut down. Partial deactivation means that only brake control has been shut down. (Possible causes: defective speed sensor signal, ...)

Pressure control operation / Auxiliary pressure control Control of the brake pressure will usually require the signal from the brake pressure sensor. If this signal is no longer available, it is possible to generate brake pressure electrically by using certain auxiliary quantities. This we call pressure control operation or auxiliary pressure control. The accuracy of the pressure generated is, however, limited compared with proper pressure control. (Possible causes: failure of a pressure sensor signal, ...) Redundancy operation If electrical pressure output is no longer possible, the axle in question is braked by means of the pneumatic redundancy pressure. (Possible causes: defective solenoid or defective solenoid wiring, ...)

24

WABCO

Testing the EBS

EBS

When testing the EBS, the following special features must be taken into account:

n

Testing the Backup Valve: When the vehicle is stationary, with the parking brake on and the brake pedal depressed, the axle modulator is switched off; this allows the backup valve on the rear axle to be checked using a pressure gauge which is connected to the rear axle brake cylinder. Now the failure of the electronic circuit is simulated. In this case the output pressure must be approximately half the supply pressure. Maximum Pressure Output: When the brakes are actuated > 80%, the pressure output must be at its maximum on the front and rear axles, and at the control hose coupling (yellow). Pressure Inshot: By tapping the brake pedal (brake lamp switch closed), the pressure inshot, brief pressure pulse of approx. 2 bar, can be checked at the control hose coupling (yellow) using a pressure gauge. At the same time, the readings for the contact pressures of the brakes on the motor vehicle can be taken.

n

n

Testing on the Roller Dynamometer: For testing a vehicle with an electronic braking system (MB Actros) on a roller dynamometer, the following criteria must be met: The wheels on one axle are inert, the others are turning at a speed < 12 k.p.h. for at least 20 seconds, or the vehicle is stationary, the parking brake is released, the brake pedal is actuated for more than 5 seconds after the ignition has been switched on. Now the maximum EBS brake pressures can be measured. The system is in working order.

n

WABCO

2

25

EBS

Operation and Dials

Dashboard (Type MB Actros)

Position 1: display, red section Position 2: display, green section Position 3: operating keys for vehicle diagnostics

SYSTEM Button This button can be used to display information on the outside temperature, operational, service or diagnostic data: pushed once = operational information pushed twice = service mode pushed three times = diagnostic mode for the first electronics system pushed repeatedly = diagnosis mode for additional electronic systems. QUIT Button This button can be used to n suppress the display of category "0" defects n suppress the display of information in the green section n end the diagnostic mode. RESET + QUIT Buttons These buttons can be used to n delete any defects stored from the error memory (by authorized workshop staff) n and for executing other non-EBS functions which are not covered by this document. INFO Button This button is used to request additional information in the electronics system selected, such as additional data of an operational, service or diagnostic nature, and the location of a defect.

The display consists of a green and a red section. The green section shows operational and control information, and the outside temperature. The red display section is used for displaying warnings and defects. Any defect in an electronic system appears in the red section of the display in the form of an error code, which is then stored and allocated to a group of defects. At the same time, the warning buzzer comes on.

26

WABCO

Error Code Description

EBS

Mercedes-Benz Type Actros

The display of the status of the system and the warning facility for the driver in the event of a defect are achieved via the CAN bus and the display matrix shown below. The diagnostic requirement for as disparate a recognition of all errors as possible for easy location of defects by the service department has been taken into account in the safety concept. If the system detects a defect, this is stored in the central module. This also applies to any errors found in the axle modulators. The central module stores up to 16 system errors for the purpose of diagnosis.

The errors can be deleted only while the vehicle is stationary. For testing, the following are required:

n n

full supply pressure 24 volts operating voltage.

1st example:

1

10

02

1 = defect of intermediate importance 10 = control unit 02 = undervoltage

ON-BOARD Diagnosis: If the red display, for instance, shows the system abbreviation `EPB' with an error code (see top right-hand side of this page), the electro-pneumatic braking system is defective. The first digit beneath the letters `EPB' indicates the significance of the defect. Actros provides for significance ratings 0, 1 and 2. 0: slight defect = display may be suppressed (using QUIT key) cannot be suppressed cannot be suppressed. The photograph shows the red display returning a currently existing defect. 2nd example: 1 22 03

1: intermediate defect = 2: serious defect =

The two digits following indicate the error path, and the last two digits provide information on the type of error or defect. In the event of several errors or defects existing at any one time, only the defect with the greatest significance will be displayed, and its significance may, in individual cases, increase from 1 to 2. If this happens and an error is displayed with a first digit of `2' which is not listed in the error code table below, this may be found under the first digit of `1'. Any error appearing in the green (2) display only currently exists if it is preceded by the letter `a'. Any errors perceived will be stored in the corresponding error memory of the ECU.

1 = defect of intermediate importance 10 = redundancy valve 02 = disconnected feed line OFF-BOARD Diagnosis: The display instrument is also used for OFF-BOARD diagnosis as an intermediary between the control units and external testing equipment such as the Diagnostic Controller, or PC diagnosis. After connection setup, the red display (1) only shows the first digit, i. e. the error significance. When OFF-BOARD diagnosis is used, the SYSTEM, INFO and RESET buttons are deactivated.

WABCO

2

27

EBS

Diagnostic Controller

Diagnosis

Ill. 2: Connection of the Diagnostic Controller

The Diagnostic Controller is a computer which is able to exchange data with control units (which are computers, too). In this context, data shall mean the following:

n n

error messages stored in the ECU commands transmitted from the Controller to the ECU where they trigger certain procedures.

In order to be able to communicate with an ECU, a special program is required. This program is stored on the respective program card. Program card and ECU must be based on the same system! The Diagnostic Controller Set (446 300 331 0) comprises the following:

n n n n n n n n n n

Diagnostic Controller Carrying Case

446 300 320 0 446 300 022 2

Accessories: Program Card Connecting Cable (ACTROS) Multimeter Cable, black Multimeter Cable, red Keyboard 446 300 7xx 0 884 904 933 0 894 604 301 2 894 604 302 2 446 300 328 0 PIN Assignment: Plug PIN 2 PIN 1 PIN 4 Socket PIN 1 PIN 2 PIN 8

+24 volts (red) ground (brown) K-line (yellow)

The following ECUs can be tested: 446 130 000 0 446 130 004 0 446 130 005 0 Ill. 3: Diagnostic Socket

In addition, it is possible that other ECUs can be tested using this program card. Connecting the Diagnostic Controller to the Vehicle's Diagnostic Socket: One end of the connecting cable is plugged into the Diagnostic Controller (Ill. 2), the other to the diagnostic socket in the control box (Ill. 1) of Actros. Ill. 1: Diagnostic Socket

28

WABCO

Diagnosis

EBS

Program Description

1 Diagnosis 1 Error Location 2 Actuation 1 ASR on/off 2 Pressure Output 1 Prop. valve FA 2 Axle modulator RA 3 Axle modulator AA 4 Trailer control valve* 3 Pulse/Test Program 1 Modulator FA left 2 Modulator FA right 3 Axle modulator RA* 4 Axle modulator AA* 5 ASR deactivate AA* 4 Backup System 1 RA backup program 2 FA backup characteristic raise 3 Trailer control valve backup program 5 ABS deactivate trailer* 3 Testing and Measuring Values 1 Speed Sensors 1 Sensor 2 Sensor 3 Sensor 4 Sensor 5 Sensor 6 Sensor FA left FA right RA left RA right AA left* AA right*

2 Pressure Sensors 1 Pressure sensor FA 2 Pressure sensor RA 3 Pressure sensor AA* 4 Pressure sensor trailer control valve* 3 Wear Sensors 4 Brake Signal Transmitter 5 Switch Positions 1 Brake switch 2 Button ASR off-road 3 Button ABS off-road* 6 Voltages 4 Control Unit Data 1 Parameters 1 display / change** 2 transmit 1 ECU - DC 2 DC - ECU 2 WABCO data 2 Commissioning* 3 Multimeter 1 Direct voltage 2 Alternating voltage 3 Resistance 4 Options 1 Help texts 2 Variant 3 ECUs for testing 5 Special Functions

* only if installed on the vehicle ** available only after entering PIN FA = Front Axle RA = Rear Axle AA = Additional Axle

WABCO

2

29

EBS

Diagnosis

Using the Diagnostic Controller

Description of the Menu Items for Program Card 446 300 7xx 0

1. 1.1 Diagnosis Error Location First the error memory of the ECU is read out, and the errors are sorted as they appear in the display. The user then has the option of either repairing the defect or have the next error displayed. Once all errors have been displayed, the error memory can be cleared. During the deletion process, diagnosis is suspended briefly (to give the ECU the opportunity to once again detect any errors or defects, and store them in the error memory). This is followed by the error memory being read in once more, and the findings shown. Actuation "Actuation" is used to actuate certain components within the EBS system to check whether they are in proper working order. For this purpose, various test programs are executed for individual functional groups. Since these programs usually have to be run while the vehicle is on the roller dynamometer, the ASR function is deactivated when tests for the rear axle / additional axle with sensors are selected in order to prevent that axle being braked. Only modules are offered for selection for which the parameters of the control unit show that they have been installed on the vehicle. For details on test procedures, please refer to the instructions for using the program card.

any major leakages within the pneumatic system will be detected. Please note: To make sure that the vehicle cannot "jump" from the roller when tested on the dynamometer, the rear axle is always braked as the front axle is being tested, and when the rear axle / additional axle is tested, the front axle is braked as well. In all test / pulse programs, a maximum braking pressure of 2 bar is output on the axles included. If the PIN code has been entered, a braking pressure can be freely selected between 1 and 10 bar. 1.2.3 Pulse / Test Program Special pulse or test programs can be used to make sure that the wiring and pipes are in order, and that the front axle's ABS valves, the axle modulators for the rear axle and the additional axle, and the ABS cut-off relay for the additional axle are working properly. Here, too, the axle which is not being tested is braked to prevent the vehicle "jumping" from the roller dynamometer when the brake force is excessive. 1.2.4 Backup System In the event of the control unit failing altogether, it must be possible to use the backup system for pneumatic braking of the vehicle. For checking whether that this system is in good working order, three test programs are available which check different parts of the system. It is advisable to check the backup system everytime the vehicle has been serviced or repaired! 1.2.5 Deactivation Trailer ABS The ABS deactivation relay for the trailer is switched on and off once a second for ten seconds. To check that it is working properly, a corresponding test plug with a lamp must be plugged into the trailer socket, or a voltmeter connected. 1.3 Testing and Measuring Values This part of the program can be used to display switch positions and measuring values. If a sensor is not available, or if it supplies an invalid signal, the program will not show the (wrong) measuring value but a number of dashes "----" instead. This always indicates a defective or inactive sensor. This will happen only for sensors which, according to the parameters set, have been installed on the vehicle.

1.2

1.2.1 ASR On/Off Manually switching the ASR function on/off. In addition, the current status of the ASR (on/off) appears on the display. 1.2.1 Pressure Output The various steered axles (FA, RA, AA, trailer control valve) a pressure of 2 bar can be output individually (if PIN has been entered, this is freely selectable). When the test program has been initiated, the pressure picked up by the various pressure sensors before and after output are displayed. The first reading ("pressure reading 1") should be 0 bar since this reading is taken at atmospheric pressur. The second reading ("pressure reading 2") should be approx. 2 bar or the preselected braking pressure (after entering the PIN). With these programs it is possible to verify that the various control valves, together with the pressure sensors, are in proper working order. In addition,

30

WABCO

Diagnosis

EBS

1.3.1 Speed Sensors The output voltage amplitudes of the speed sensors are displayed, together with the measured wheel speeds. In order to be able to detect any wobble of the pole wheel, both the current and the minimum / maximum amplitudes are shown. The display will appear at wheel speeds > 1.8 k.p.h. Since the wheel speed sensors are usually tested on the roller dynamometer, the ASR function is switched off when the values for the rear axle's / additional axle's sensors are selected in order to prevent braking. 1.3.2 Pressure Sensors The readings for the braking pressure on the steered axle, (front axle, rear axle, additional axle, trailer control valve) can be displayed individually. Both the index pressures and the actual pressure readings are shown. 1.3.1 Wear Sensors The brake lining wear is shown [%] for all axles with sensors. 1.3.4 Brake Signal Transmitter In addition to the output signals [ms] of the two circuits of the brake signal transmitter, the braking performance [%] and the index retardation [%] are also displayed. 1.3.5 Switch Positions The status of the following switches can be displayed: n brake switches 1 + 2 (in the brake signal transmitter) n button ASR off-road n button ABS off-road The program cannot perceive which buttons have actually been fitted in the vehicle. For this reason, it will always display all buttons which can be connected to the ECU. 1.3.6 Voltages The following supply voltages are displayed: n Terminal 15 (Pin X1/7) n Terminal 30a (Pin X1/8) n Terminal 30b (Pin X1/9). In addition to the voltage readings, their index voltages are shown. If the actual voltage at Terminal 30b lies above its minimum index voltage, the cause is often a defect in the axle modulator circuit. For this reason, "check AM" will be displayed. 1.4 Control Unit Data This menu item can be used to read out and display the manufacturing data and the 2.

component number from the control unit (menu item: "read WABCO data"). In addition it is possible to display the parameters which apply to the vehicle. After entering the PIN code, which is restricted to authorized workshop staff, the "special functions" menu item can be used to change the parameters and rewrite them into the control unit. Furthermore, the data can be transferred from one control unit to another using the Diagnostic Controller (this also requires entry of the PIN code). If the connected control unit contains a set of parameters unknown to the program, the parameter designations or their contents are not displayed in plain text. In this case, please refer to the documents on the control unit for the corresponding text. After the last of the parameters has been reached, or after "END", the program will inquire whether the changed values are to be stored in the ECU. If this is confirmed, the program will, after a safety inquiry, request entry of the date. This will be stored in the control unit, together with the parameters. Commissioning By means of "Commissioning", the whole of the ABS can be tested, and a test log printed (e. g. after initial installation or comprehensive repairs). Commissioning is divided into two parts:

n n

functional testing printed log

Please note: If functional testing has been commenced, this has to be processed step by step. It is not possible to go back to a previous step, or to skip any steps. If the Diagnostic Controller's voltage supply fails, all data previously measured and stored for the printed log are deleted. This is why it is important that the diagnostic connection is never severed if a printed log is required. The data for the printed log are stored in the Controller the moment its user confirms a measuring process or an inquiry by pushing a button. In some cases the program may decide automatically whether any step within the testing procedure has been properly carried out (e. g. pushing a button, pressure readings). If this does not occur, the user is given a yes/no option (e. g. after pulse programs).

WABCO

31

EBS

Diagnosis

If an error has occurred during a testing procedure, this can be executed once again. In addition, it allows the commissioning process to be aborted prematurely. A test log can, however, still be printed. 2.1 Functional Testing For functional testing, the vehicle must be stationary (wheel speed must be zero on at least one axle), and no errors may have been stored. The vehicle may be moved only if the program expressly requests this. For the program's exact execution sequence, please refer to the operating instructions for the program card. Printing the Test Log After the test, a test log can be printed. As mentioned previously, the Controller must stay connected to its voltage supply. Any disconnection at any time will delete all data. The connection to the printer is established by means of the rear 25-pole socket and a serial printer cable. The cable must have DB 25 plugs (not sockets!) on both ends.

3.

Multimeter The integrated multimeter function can be used to take electrical readings on the vehicle. Only the desired measuring function (direct voltage, alternating voltage or resistance) needs to be selected. The measuring range is set automatically by the unit. Application: direct voltage: alternating voltage: resistances: on-board voltage sensor voltage valve, relays, sensors, line continuity

2.2

PLEASE NOTE: The multimeter is designed only for voltages within the vehicle's range (low potential). 4. 4.1 Options Help Texts With this function, the user can obtain additional operating instructions. When this function has been switched on, more detailed information on the program will appear at the appropriate times between the various steps. Version This function shows the status of the components supplied (Controller and program card). ECUs for Testing Output of WABCO numbers for the control units which are supported by the program. At present this applies to the following control units:

4.2

4.3

n n n

5.

446 130 000 0 446 130 004 0 446 130 005 0

The program works with printers which are EPSON FX compatible, with a serial interface (RS232). The printer's transmission parameters must be set to the following configuration: speed: data bits: stop bit: parity bit: 1200 baud 8 1 X ON / X OFF

Special Functions After entering a Personal Identification Number (PIN code), menu item 1.4 (parameters) can be cleared. The PIN may be issued only to specialized staff specifically authorized by the vehicle manufacturer.

32

WABCO

Diagnosis

EBS

Using a PC

As an alternative to the Diagnostic Controller, a PC can be used for vehicle diagnosis. Hardware Requirements n notebook / laptop wherever possible n recommended PC 486 or higher n 4 MB main memory, colour display 640 x 480 n approx. 3 MB available harddisk space, plus 3½" floppy disk drive n 1 COM interface (9-pin connection) for WABCO Diagnostic Interface 446 301 021 0 n Windows 3.xx, Windows 95

Ill. 2: Connection of Laptop with Diagnostic Connection in Actros

Ill. 1: Hardware Components

In preparation for tests on the vehicle, this Diagnostic Interface (No. 446 301 021 0) must be connected to the PC and the vehicle's diagnostic socket (Ill. 2). When the ignition is switched on, this provides the power supply for the Diagnostic Interface (lamp in the interface is on). Components Program (diskettes) 446 301 5xx 0 Diagnostic Interface Set 446 301 021 0 (consisting of Interface and connecting cable for the PC) Connecting Cable (ACTROS) 884 904 933 0

When the connection has been established as shown above, testing may commence. Now all functions described under "Diagnosis using the Diagnostic Controller" can be done via PC diagnosis.

WABCO

2

33

EBS

System Design

EBS- Brake System for Track 4 x 2

Legende 1. Central Module 2. Brake Signal Transmitter

3. Proportional Relay Valve 4. Solenoid Modulator Valve - ABS

5. Axle Modulator 6. Backup Valve 7. Trailer Control Valve

34

WABCO

Function Scheme

EBS

Legende

1. Brake Signal Transmitter (BWG) 2. Proportional Relay Valve 3. Solenoid Modulator Valve - ABS 4. Speed Sensor 5. Wear Sensor 6. Backup Valve 7. Axle Modulator 8. Trailer Control Valve Load Empty Valve in Brake Signal Transmitter with gearing i = 1 : 1 bei p4 = p 21 (Failure Axle Modulator) i = 2 : 1 bei p4 = p 0 bar Proportional Relay Valve with gearing i=1:1 Backup Valve with gearing, actuating only by ABS-Action at the rearaxle and failured of Axle Modulator i=2:1

WABCO

35

EBS

36

WABCO

Information

EBS (EPB)

36 pages

Find more like this

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

36488


You might also be interested in

BETA
8150101253
815 010 020 3
TEBS E Retrofit Instructions for Semi & Centre Axle Trailers with Air supspension
8150100493.fm