Y096980 1 en 000 EBS5 Introduction

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System introduction EBS5

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SYSTEM DESCRIPTION

Electronic Brake System EBS 5 for commercial vehicle

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Table of contents 0.

Scope of this document.......................................................................2

1.

EBS basic principle ..............................................................................3

2.

EBS-Components .................................................................................4 2.1.

Trailer Control Module (TCM)............................................................................5

2.2.

Pressure control valve (PCV) ............................................................................5

2.3.

Electronic Control Unit (ECU) ...........................................................................5

2.4.

Axle load sensor.................................................................................................5

2.5.

Steering-angle sensor (SAS).............................................................................5

2.6.  Yaw-rate sensor (YRS) .......................................................................................6

3.

EBS architecture...................................................................................6

4.

EBS Functions......................................................................................9

5.

Basic system data ..............................................................................10

0. Scope of this document This document is a general introduction of Electronically controlled Brake System (EBS) for customer information. The target of the document is to get understanding in the basic structure and operation principle of the system and must not  be considered as system specification or system offer from th Knorr-Bremse. The description is based on EBS5 system (5  generation EBS) from Knorr-Bremse.

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1. EBS basic principle The main advantage of the EBS system is the high level functionality and system modularity with relative simple system architecture. Different vehicle variants, different performance requirements can be covered with a few numbers of system components and layouts via EoL programming of the central ECU (Electronic Control Unit). The main tool of EBS to realize this flexibility is the unlimited control over brake pressure. Independently from the brake pedal position, EBS is capable to change the brake pressure, either to increase or decrease through electronic control. However pneumatic control line installed parallel in case of serious failure in the electric system of the vehicle. The principle of the control for one pneumatic channel can be seen in the figure below.

  y    l   p   p   u   s   e   r   u   s   s   e   r    P

Pneumatic mode: Let consider that the electronic is out of order (the EBS is not energized). In this case the brake pressure will be built on the same way as in the conventional pneumatic brake system. The EPM (Electronic Pressure Modulator) contains a relay valve. When the EPM is not energized, the solenoids (back-up valve, inlet valve, outlet valve) are in their default position and the pneumatic control line from the FBM (Foot Brake Module) is directly connected to the control input of the relay valve. FBM contains two-circuit pressure control valve as conventional pneumatic foot brake valve. When the driver activates the brake pedal, it will set a pressure proportional to pedal movement, and it will build the pressure in the brake chamber through the relay valve. This is the way of braking also in case of serious failure in the electronic system (back-up). Electric mode (normal operation): In case of normal operation (EBS is energized) the central Electronic Control Unit (ECU) reads the pedal position from the sensor which is integrated in the FBM. Based on the pedal position (and several other conditions) central ECU calculates the required pressure to each pneumatic channel Copyright 2010 © Knorr-Bremse AG. All rights reserved, including industrial property rights applications. Knorr-Bremse AG retains any power of disposal, such as for copying and transferring Knorr-Bremse Group

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and sends this pressure demand to the EPM (which has also an electronic control unit) via CAN. EPM receives the pressure demand and will close the back-up solenoid to avoid any effect on the relay valve from the pneumatic back-up control line, and it will set the demanded pressure via the activation of inlet and outlet solenoids and using its integrated pressure sensor for control feedback. Wheel speed and lining wear sensors are connected to the EPM. EPM processes the sensor signals and sends the sensor values to the central ECU via CAN.

2. EBS-Components EBS system can be built up of the following components: Foot Brake Module (FBM) There is a displacement sensor integrated in foot brake module of EBS system to measure the brake pedal movement, which will be transferred into driver retardation demand. FBM has also two pneumatic control circuits. In case of serious electrical failure in the system, the vehicle can be braked via the pneumatic back-up line. There are FBM existed for hanging pedal (mainly truck application) or for floor installation (mainly bus application).

Electro-Pneumatic Module (EPM) The EPM is an electro-pneumatic actuator. It comprises a relay-valve, filter, silencer, solenoid-valve for backup circuit, an inlet valve and outlet valve (solenoids), pressure sensor, electronic control unit and pneumatic as well as electric connections. Wheel-speed sensors and lining-wear sensors also can be connected to EPM which will transmit the signal to the EBS-ECU via Brake-CAN. There are 2 different types of EPM are existed: 1C-EPM: it is a single-channel actuator. It can serve one pneumatic channel with two wheels. 2C-EPM: it is a double-channel actuator. It can serve two individual pneumatic channels with four wheels.

5

3

1

6

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2

LWSA,B

1

WSSB

2

1

WSSA

2

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4

2

3

1

4

2

CAN1+U

CAN+U

2

1

WSSA

2

WSSB

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2

LWSA,B

L SW C, D

1

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W SS D

W SS C

P

P

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2

 ALS1,2

P

U

U 4

1

U

2

21

22

2

21

22

1

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4

1

3

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System introduction EBS5

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Trailer Control Module (TCM)

The TCM is an electro-pneumatic actuator designed for trailer pressure control of the towing vehicle. It contains a relay valve, filter, silencer, solenoid-valves for back-up, inlet valve and outlet valve, pressure sensor and pneumatic as well as electric connectors. Furthermore, the brake-pressure may be controlled by the service-brakesystem as well by the parking-brake-system. In addition, a valve provides for the so-called tear-off-function.

2.2.

Pressure control valve (PCV)

This valve is used for ESP and improved ABS function, as the front-axle is equipped with only one EPM. The PCV provides individual-wheel control. The PCV concerned is a series-production ABS-PCV.

2.3.

Electronic Control Unit (ECU)

The main “intelligence” if the EBS is concentrated into the central ECU. It contains the operating system, hardware drivers, brake control algorithms, monitoring and service functions. The software part of the ECU can be divided in two parts, main software and dataset. The main software contains all functions and features which covers the complete vehicle range and application (which are supported by EBS5), and it must be configured with particulars of the vehicle via the dataset.

2.4.

Axle load sensor

External axle load sensor can be used in EBS system in case the axle load information is not available on CAN communication line. There are two analogue sensors can be connected to EBS system in order to measure the axle load. The axle load sensor can be a pressure sensor (vehicle with air suspension) or displacement sensor (leaf suspended vehicles). The sensors have to be connected to 2C-EPM.

2.5.

Steering-angle sensor (SAS)

The Steering-angle sensor (SAS) is a contact-less, analogue angle sensor measuring of the absolute angle position of steering wheel. The output is a digital sensor value via CAN-interface. This sensor is required for EBS with ESP. The sensor is mounted on the steering column in such a way that only the turning angle of the steering wheel is measured without disturbance from any superimposed secondary movements.

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System introduction EBS5

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Yaw-rate sensor (YRS)

The YRS is a combined yaw rate and lateral acceleration sensor. The output is a digital sensor value via CAN-interface. This sensor is needed for EBS with ESP. The mounting location of the YRS is the frame of the vehicle. It is to be chosen in such a way, that only vehicle-dynamic related motions occur at the location. The mounting location should be very stiff, as this leads to a high natural resonance frequency level.

3. EBS architecture The following picture represents a service brake system for a 6x2 tag tractor with ESP:

   S    W    L

   S    W    L

 U

P 

   S    W    L

       P        U        P        U        P        U

   S    W    L

   S    W    L

   S    W    L

The front axle of the vehicle is controlled by a single 1C-EPM. However additional PCV-s are installed between the brake cylinders and 1C-EPM which makes the possibility to control different pressure on left and right side of front axle if any vehicle dynamic function (ABS or ESP) requires it. It means that the front axle has one electronically controlled EBS-channel, but 2 ABS-channels.

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The second axle (driven axle) is controlled by a 2C-EPM for individual side control. The individual control is utilized by ABS, TCS and ESP functions. The third axle (not driven lift axle) is controlled by a single 1C-EPM, meaning one EBS and also one  ABS channel. ABS is realizing select low control on this axle. It is also possible to control this axle as a “slave axle” without this additional 1C-EPM, in this case the control pressure is coming from the driven axle. Such a solution can be applied if the axle load ratio is constant between second and third axle, and direct ABS control is not required on the slaved axle. The layout for a 4x2 city bus (or distribution truck without trailer connection) application without ESP is the following:

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Vehicle layouts Using 1C-EPM and 2C-EPM in the system setup, there are several variants of brake system architecture can be built according to the requirements, for example: 2 axle:

1C-EPM

PCV

2C-EPM

TCM driven axles

s teer ed ax les

lif t axle s

engine

3 axle:

4 axle:

4 axle:

Articulated bus:

CAN architecture The EBS is integrated into the vehicles CAN-Bus structure (CANJ1939). Within the EBS additional 3 different CAN-buses are implemented: • CAN-Brake: to accommodate a maximum of five stations. Its nodal point is located in the ECU. • CAN-Sensor: where the ESP sensors (SAS, YRS) are connected to • CAN-Trailer: the link to the trailer CAN-vehicle

CAN-trailer  

PCV-B

part.: 4 EBS-SG part.: 1

EPM-1

part.: 3 δH

PCV-A U

FA

ωz

U

CAN-sensor 

2 1

EPM-3

EPM-2

RA

EBS with ESP

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4. EBS Functions The functions of EBS5 system are implemented in the central control unit (ECU). Some of the functions are only optional, and can be enabled or disabled by EoL programming. The main EBS functions are the following: Electronic brake force control The driver’s demand for retardation is recorded and converted into braking pressures taking into account the axle load such a way that the demanded retardation versus brake pedal position characteristic is independent from the load condition of the vehicle. The brake pedal characteristic can be adjusted by EoL parameter. ABS function The target of ABS function is to prevent wheel lock up during braking to maintain the steering and stability of the vehicle and to minimize stopping distance. The ABS intervenes during braking whenever the available friction between the road and the tire of a monitored wheel is less than the braking force applied to the wheel causing the wheel to decelerate (impending wheel to lock) quickly. ATC function The target of ATC function (Automatic Traction Control) is to avoid the spinning of the driven wheels in order to keep the vehicle stability during driving and to increase the traction force during acceleration. ATC can be divided in two sub-functions: engine control and brake control. DTC function The target of DTC function (Drag Torque Control) is to avoid the locking tendency of driven wheels caused by engine inertia on low friction surface. If the average speed of driven wheels indicates locking because of the low friction, DTC requests a certain amount of engine torque to get the driven wheels rolling. Brake Assistant Function Based on experiences, the drivers pedal movement is fast enough only in the beginning of an emergency braking and the brakes are not applied fully. The target of this function is to aid the driver in such a situation, saving valuable time in the first, high-speed period of the emergency braking. Based on the drivers brake demand and the speed of the brake pedal actuation, the brake pressure will be increased compared to the original drivers demand. Lining wear display and control Lining wear sensors can be connected directly to the modulators (EPM) close to the axles. EPM reads the sensor value and sends the information to the central ECU. ECU presents the lining wear values on CANJ1939 (to make instrument cluster able to show it for the driver), and also for diagnostic purposes. Additional EBS can take into consideration the measured sensor values in the brake control such a way that it modifies brake force distribution in order to synchronize the wear between the axles. In case of critical pad wear, EBS will warn for pad change. It is possible to use lining wear switch instead of lining wear sensor for pad wear warning, but in this case EBS can not measure the pad wear, and not able to synchronize it between the axles. Retarder integration The task of the function is to reduce the load of friction brakes replacing the braking force with the actuation of auxiliary brakes. The auxiliary brakes (which can be engine controlled endurance brake, and primary or secondary retarder) are activated automatically by the EBS if the brake pedal applied. The retarder integration function does not change the compatibility between the towing and towed vehicle (the retarder contribute the braking of both towing and towed vehicle).

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Coupling Force Control The target of the Coupling Force Control function is the distribution of brake energy between the towing and towed vehicle. The output of the function is a pressure difference which modifies the pressure of the trailer coupling head. Trailer brake function Trailer brake function allows to brake the trailer independently from the towing vehicle. Using a pushbutton on the dashboard, EBS set 4 bar brake pressure to the trailer if the vehicle speed is under a certain limit (nearly standstill). Bus Stop Brake (Door brake) function The Door brake function is developed especially for city bus applications. Target of the function is to provide the driver with a way holding the vehicle at stand still while the engine is still running without using the foot brake or parking brake. Differential lock inhibit The power supply to the differential lock switch has to come from EBS. EBS checks the speed difference between drive wheels and if the speed difference is over a certain limit, EBS prohibits the engagement request to protect the differential lock against damage. Hill Start Aid function The Hill Start Aid function is used to simplify starting on up-hill slopes by holding the service brake pressure or delaying the service brake release in order to give the driver extra time for the manoeuvring of the pedals. The function is not intended to be used as parking brake. Software Anti-compound If the parking brake active signal is available, EBS will limit the pressure on the axle with spring brake chambers if parking brake engaged. ESP function The target of ESP function (Electronic Stability Program) is to keep the driving stability of the vehicle. It can do this only within the limits of the physics! ESP consists of two sub-functions: Yaw Control (YC): handle situations like jack-knifing, under- and over-steering on low and middle- µ conditions. Roll Over Prevention (ROP): reduces the risk of rolling over on high- and middle- µ conditions. Driver information and diagnostic The warning and information displays are different for the different applications; it depends on the vehicle electric system. The main communication interface of EBS5 for display and warnings is the CANJ1939 communication line which also the interface for diagnostic (KWP over CAN). However there is the possibility to control some lamps directly from the EBS ECU.

5. Basic system data • • • • • • •

24 V vehicle system voltage Up to 12.5 bar  supply pressure for service brake Up to 10 bar  brake-cylinder pressure 8.5 bar  trailer supply pressure and trailer brake pressure Only passive WSS Lining/pad wear sensor (analogue) or switch (on/off) can be connected to EPM EBS is suitable for both disc brakes and drum brake

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