22-02-2013, 02:53 PM
SEMINAR REPORT ON ELECTRO-HYDRAULIC BRAKE
ELECTRO-HYDRAULIC.pdf (Size: 1.28 MB / Downloads: 262)
INTRODUCTION
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 ressures 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.
ELECTRO-HYDRAULIC BRAKE
Electrohydraulic brake systems are the combination of
electronics and hydraulics to create a more versatile brake
system. The electronics provide control flexibility, while
the hydraulics supply the power.
Electrohydraulic braking offers
many advantages over raditional hydraulic braking
systems. These advantages can be exploited to provide
improved system performance and greater comfort for the
operator. Valves can be moved away from the cab and
closer to the brakes, reducing plumbing costs. Remote
operations are easily handled without having to duplicate
the valving. Vehicle controls can be improved by
implementing a variety of control schemes such as
electrohydraulic
brake systems, anti-lock brake systems (ABS), and traction
control systems (TCS). These systems are a result of
hydraulics and electronics combining to create brake
systems that provide value added features for the machine
operator.
WORKING
First, the driver’s input is normally interpreted by up to
three different devices: a brake switch, a travel sensor, and
a pressure sensor while an emulator provides the normal
pedal “feel”. To prevent unwanted brake applications, two
of the three inputs must be detected to initiate base brake
pressure. The backup master cylinder is subsequently
locked out of the main wheel circuit using isolation
solenoid valves,
so all wheel brake pressure must come from a
high-pressure accumulator source. This stored energy is
created by pressurizing brake fluid from the reservoir with
an electrohydraulic pump into a suitable pre-charged
vessel. The accumulator pressure is regulated by a
separate pressure sensor or other device. The “by-wire”
characteristics now come into play as the driver’s braking
intent signals are sent to the ECU. Here an algorithm
translates the dynamically changing voltage input signals
into the corresponding solenoid valve driver output current
waveforms.As the apply and release valves open and close,
a pressure sensor at each wheel continuously “closes the
loop” by feeding back information to the ECU so the next
series of current commands can be given to the solenoid
valves to assure fast and accurate pressure response.
It is obvious the EHB
system is significantly more complex in nature. To address
this concern, numerous steps have been taken to eliminate
the possibility of boost failure due to electronic or
mechanical faults. In the ECU design, component
redundancy is used throughout. This includes multiple wire
feeds, multiple processors and internal circuit isolation for
critical valve drivers. The extra components and the
resulting software to control them, does add a small level
of additional complexity in itself.
MASTER CYLINDER
The master cylinder is a control device that converts
non-hydraulic pressure (commonly from a driver's foot) into hydraulic
pressure, in order to move other device(s) which are located at the
other end of the hydraulic system, such as one or more slave
cylinders. As piston(s) move along the bore of the master cylinder,
this movement is transferred through the hydraulic fluid, to result in
a movement of the slave cylinder(s). The hydraulic pressure created
by moving a piston (inside the bore of the master cylinder) toward
the slave cylinder(s) compresses the fluid evenly, but by varying the
comparative surface-area of the master cylinder and/or each slave
cylinder, one will vary the amount of force and displacement applied
to each slave cylinder