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BRAKE-BY-WIRE

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Overview
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General Architecture of EHB System
Working Principle of EHB

Design Methodology
 Desired Attiributes
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Physical Architecture
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Regenerative Braking

Case Study
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Wheel Brake Control Unit
Brake Pedal Feel Emulator and Brake Pedal Interface Unit
Energy Management System
Communications System
Central Control Unit

Mercedes-Benz Sensotronic

Pros
...

Future Aspects

Contents

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Overview

Brake-by-wire technology in
automotive industry
represents the replacement of
traditional components such as
the pumps, hoses, fluids, belts
and vacuum servos and master
cylinders with electronic
sensors and actuators
...


General architecture of
an electromechanical braking
(EMB) system in a drive-bywire car is shown beside
...


General Architecture of an Electromechanical
Braking System

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Once the driver inputs a brake command to the system via a humanmachine interface - HMI (e
...
the brake pedal), four independent
brake commands are generated by the ECU based on high level brake
functions such as anti-lock braking system (ABS) or vehicle stability
control (VSC)
...
As this network might not be
able to properly communicate with the e-calipers due to network
faults, HMI sensory data are also directly transmitted to each e-caliper
via a separate data bus
...
The controller provides drive control
commands for a power control module
...

In addition to tracking its reference brake command, the caliper
controller also controls the position and speed of the brake actuator
...
Because of the safety critical
nature of the application, even missing a limited number of samples
of these sensory data should be compensated for
...
g
...

 Reliability; the reliability of a by-wire system has to be comparable to a
comparable hydraulic/mechanical implementation
...

 Maintainability; the maintainability intervals have to be at least as long
as present systems
...

 Communications; for safety related communication systems, SAE class
C is required
 Costs; have to be equal or less than those of conventional systems
 Package space; small enough to account for easy integration of
components

Desired Attributes

Additionally, the functional
requirements for the BBW
system include:
 Regenerative Braking
...

 Integrated Park Brake
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 ABS
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The performance requirements
for the system were:
 Near zero Drag
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 High score on brake pedal
feel
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 Improved brake response
time
...

 Meet all existing FMVSS135
and ECE13 standards
...


The brake-by-wire system when
integrated into the vehicle
consists of five main sections see
figure beside :
1
...

2
...

3
...

4
...

5
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Physical Architecture

Central to the BBW systems operation
are intelligent actuators
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The actuator consists of:
 Brushless DC motor
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 Integrated park brake
...
(WBCU)

Wheel Brake Control Unit

The BPFE and the BPIU form the
control section part of the driver
interface
...

 Provide the driver with feedback to
the amount of brake requested
...

The BPFE realized these requirements
with a simple variable rate spring and
damper unit with two pressure and
one displacement sensor
...

 Energy Architecture
...

 The WBCUs communicate with each other
on a replicated TDMA (Time Division
Multiple Access) FlexRay bus, also
connected to this bus is the CCU
...

 The BPIU functions as the pedal node
interpreting the drivers brake demand and
provides the WBCUs with three CAN
busses each containing three replicated
drivers brake demand request values
...


Energy Architecture

The requirements for the energy system were identified as:
 To provide electrical energy that can be converted into mechanical
energy for brake force
...
g
...

 Must provide power from 2 independent sources (ECE R13)
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 To reliably report detectable faults and provide fault containment
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 To control energy distribution to the WBCUs and the BPIU
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 To provide power for items that must be always active
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 Provision of warnings of energy level
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 The communication system has to support compos ability, e
...
,
subsystems can be developed independently and integration is
done by simply plugging the subsystems together
...

 The communication system has to support the distribution of the
replicas to avoid common mode failures
...
g
...

 Distributed control loops, e
...
, brakes, have to be synchronized
and therefore require a common global time base in all
participating nodes
...
The CCU’s tasks are:
 Central repository for all diagnostics
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 Regenerative brake interface
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Traction Control
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Smart parking functions like:
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Hill start
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Central Control Unit

Case Study
Mercedes-Benz
Sensotronic Brake Control

Architecture of Sensotronic

Sensotronic Brake Control (SBC) is an electro-hydraulic brake system developed by
Daimler and Bosch
...

 For conventional brake systems, the driver creates brake pressure in the wheels via the
master brake cylinder
...
A piston pump driven by an electric motor
supplies a controlled brake fluid pressure between 140 and 160 Bar in the gas
diaphragm reservoir
...

Because it determines the necessary braking pressure for each of the four wheels
separately and also measures them individually, it can regulate the brake pressure on
the individual wheels via the wheel pressure modulators
...

 By the use of a travel sensor and a pressure sensor it measures how fast and how
strongly the brake is actuated
...
Normally, the master
brake cylinder is detached from the brake circuit
...
If ESP intervenes, the high-pressure reservoir supplies the
required brake pressure quickly and precisely to the wheel brakes, without any driver
involvement
...
& Cons
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In May 2004, Mercedes recalled 680,000 vehicles to fix
the complex brake-by-wire system
...
3 million cars were recalled, partly because of
further unspecified problems with the Sensotronic
Brake Control system
...
"But we cannot get the doubts
out of customers' heads

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