ABSTRACT
Brake performance can be divided into two distinct classes:1) Base brake performance2) Controlled brake performance.A base brake event can be described as a normal or typical stop in which the driver maintains the vehicle in its intended direction at a controlled deceleration level that does not closely approach wheel lock. All other braking events where additional intervention may be necessary, such as wheel brake pressure control to prevent lock-up, application of a wheel brake to transfer torque across an open differential, or application of an induced torque to one or two selected wheels to correct an under- or over steering condition, may be classified as controlled brake performance. Statistics from the field indicate the majority of braking events stem from base brake applications and as such can be classified as the single most important function. From this perspective, it can be of interest to compare modern-day Electro-Hydraulic Brake (EHB) hydraulic systems with a conventional vacuum-boosted brake apply system and note the various design options used to achieve performance and reliability objectives.
INTRODUCTION
What is an EHB System?
The next brake concept. This system is a system which senses the driver?s will of braking through the pedal simulator and controls the braking pressures to each wheels. The system is also a hydraulic Brake by Wire system
Many of the vehicle sub-systems in today?s modern vehicles are being converted into ?by-wire? type systems. This normally implies a function, which in the past was activated directly through a purely mechanical device, is now implemented through electro-mechanical means by way of signal transfer to and from an Electronic Control Unit. Optionally, the ECU may apply additional ?intelligence? based upon input from other sensors outside of the driver?s influence. Electro-Hydraulic Brake is not a true ?by-wire? system with the thought process that the physical wires do not extend all the way to the wheel brakes. However, in the true sense of the definition, any EHB vehicle may be braked with an electrical ?joystick? completely independent of the traditional brake pedal. It just so happens that hydraulic fluid is used to transmit energy from the actuator to the wheel brakes. This configuration offers the distinct advantage that the current production wheel brakes may be maintained while an integral, manually applied, hydraulic failsafe backup system may be directly incorporated in the EHB system. The cost and complexity of this approach typically compares favorably to an Electro-Mechanical Brake (EMB) system, which requires significant investment in vehicle electrical failsafe architecture, with some needing a 42 volt power source. Therefore, EHB may be classified a ?stepping stone? technology to full Electro-Mechanical Brakes.

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Electro-Mechanical Brake

presented by:

SONU KUMAR
ROLL NO.-06/ME/05

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abstract:-

The Electro-Mechanical Braking Systems represents a complete change in requirements from the previous hydraulic and electro-hydraulic braking systems. The EMB processing components must be networked using high-reliability bus protocols that ensure comprehensive fault tolerance as a major aspect of system design. The use of electric brake actuators means additional requirements, including motor control operation within a 42-volt power system and high temperatures, and a high density of electronic components.

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Brake performance can be divided into two distinct classes:
1) Base brake performance
2) Controlled brake performance.
A base brake event can be described as a normal or typical stop in which the
driver maintains the vehicle in its intended direction at a controlled deceleration level
that does not closely approach wheel lock. All other braking events where additional
intervention may be necessary, such as wheel brake pressure control to prevent lockup,
application of a wheel brake to transfer torque across an open differential, or
application of an induced torque to one or two selected wheels to correct an under- or
over steering condition, may be classified as controlled brake performance. Statistics
from the field indicate the majority of braking events stem from base brake
applications and as such can be classified as the single most important function. From
this perspective, it can be of interest to compare modern-day Electro-Hydraulic Brake
(EHB) hydraulic systems with a conventional vacuum-boosted brake apply system
and note the various design options used to achieve performance and reliability
objectives.
The next brake concept. This system is a system which senses the driver's will of
braking through the pedal simulator and controls the braking pressures to each
wheels. The system is also a hydraulic Brake by Wire system.
Many of the vehicle sub-systems in today’s modern vehicles are being converted into
“by-wire” type systems. This normally implies a function, which in the past was
activated directly through a purely mechanical device, is now implemented through
electro-mechanical means by way of signal transfer to and from an Electronic Control
Unit. Optionally, the ECU may apply additional “intelligence” based upon input from
other sensors outside of the driver’s influence. Electro-Hydraulic Brake is not a true
“by-wire” system with the thought process that the physical wires do not extend all
the way to the wheel brakes. However, in the true sense of the definition, any EHB
vehicle may be braked with an electrical “joystick” completely independent of the
traditional brake pedal. It just so happens that hydraulic fluid is used to transmit
energy from the actuator to the wheel brakes. This configuration offers the distinct
advantage that the current production wheel brakes may be maintained while an
integral, manually applied, hydraulic failsafe backup system may be directly
incorporated in the EHB system. The cost and complexity of this approach typically
compares favorably to an Electro-Mechanical Brake (EMB) system, which requires
significant investment in vehicle electrical failsafe architecture, with some needing a
42 volt power source. Therefore, EHB may be classified a “stepping stone”
technology to full Electro-Mechanical Brakes.


FAILSAFE AND SYSTEM COMPLEXITIES
Analogous to a vacuum boosted system in base brake mode, EHB supplies a braking
force proportional to driver input, which reduces braking effort. The boost
characteristics also contribute to the pedal “feel” of the vehicle. If the boost source
fails, the system resorts to manual brakes where brake input energy is supplied in full
by the driver. As would be expected, the pedal forces vs. vehicle deceleration
characteristics are significantly affected.
This is shown by the input pedal force vs. Brake line pressure output in Figure 1 of
a typical vacuum boosted vehicle.