PEPS
AEL2501
Antilock Brake System
L t r delivered
Lecture
d li r d by:
b
Prof. Ashok.C.Meti
Professor & Registrar
A.C.Meti MSRSAS
MSRSAS--Bangalore
MSRSAS
1
M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Session Objectives
j
A.C.Meti MSRSAS
• To understand the concepts of ABS
• To study a typical ABS configuration and
its working
• To understand the underlying principles of
TCS and
d ESP
2
M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Introduction
A.C.Meti MSRSAS
• Moving Vehicles possess Kinetic Energy.
Energy
• Brakes convert the kinetic energy
gy into heat by
y rubbingg a
disk pad against a disk (in a disc brake) or brake shoe
against brake drum (in a drum brake).
• Maximum deceleration is achieved when maximum energy
conversion is taking place in the braking system.
• This conversion is less efficient when a tyre is skidding.
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• When the tires skid:
A.C.Meti MSRSAS
– Braking distance
increases
– Steering control is lost
– Tyre
T
wear will
ill be
b
abnormal
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
Braking sequence w/o ABS AEL2501
A.C.Meti MSRSAS
Stopping
pp g distance
Factors determining the stopping
distance of a vehicle:• The
Th magnitude
i d off the
h force
f
pressing the shoe against a drum
governs the resistance to rotation of
a road wheel.
wheel During this operation
the road surface has to drive the
wheel around.
• The limit of this drivingg force is
reached when the resistance of the
brake equals the maximum
frictional force that is produced by
the tyre and the road
road. (ADHESIVE
FORCE).
• When this limit is reached the
vehicle begins to skid,
skid so any extra
force on the brake shoe will not
produce any increase in the rate of
stopping. (most noticeable on a wet
and slippery surface).
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
• During a skid the stopping distance is
increased because the adhesion
between a skidding wheel and the
road is less than that given by a
wheel that is on the verge of
skidding.
• This is achieved by the use of ABS
(Anti-Lock Braking System), which
pprevent the road wheels lockingg upp
(by sensing a locked wheel, releasing
it momentarily and re-applying it).
• The electronic sensing arrangement
that is used in ABS for the detection
of slip can be further utilized to
control
t l andd limit
li it the
th maximum
i
traction force used to propel the
vehicle. (Traction Control System TCS.)
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• NHTSA defines an ABS as a portion of a service
b k system
brake
t that
th t automatically
t
ti ll controls
t l the
th
degree of rotational wheel slip during braking by:
A.C.Meti MSRSAS
– S
Sensing
i the
h rate off angular
l wheel
h l rotation.
rotation
i
– Transmitting signals regarding the rate of wheel
rotation to one or more de
devices,
ices which
hich interpret these
signals and generate responsive controlling output
signals.
– Transmitting those signals to one or more devices
which adjust
j brakingg forces in response
p
to the signals.
g
National Highway Traffic Safety Administration
http://www.nhtsa.dot.gov/cars/
M.S Ramaiah School of Advanced Studies - Bangalore
7
PEPS
AEL2501
• ABS systems use a combination of electronic and
yd au c syste
systemss to modulate
odu ate the
t e brakes
b a es
hydraulic
individually to prevent them from locking.
• Requirements of ABS:
– Fail safe system
– Maneuverability must be maintained (Good steering and road holding
must be maintained))
– Immediate response (Brakes applied gently or slammed – appropriate response)
– Operational influences (e.g. No reaction on the Pedal, YAW control)
– Controlled
C
ll d Wheel
Wh l (At least one wheel on each side should be controlled on a
separate circuit)
– Speed range of operation ( Must operate all speed conditions)
– Other operating conditions ( Recognize aquaplaning. Operate on an uneven
A.C.Meti MSRSAS
road surface. Slow speed on snow…)
8
M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Components
p
of ABS
• Antilock systems basically consist of:
A.C.Meti MSRSAS
–
–
–
–
Wheel Speed sensors
El t i Control
Electronic
C t l Units
U it
Hydraulic Modulator
Wheel Brakes
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
• The Wheel Sensors
Sensors: The inductive type
wheel sensors detect the speed of rotation /
wheel lock condition and signals the ECU
• The ECU: A vehicle may have 2, 3 and 4
channel ABS installation. The ECU is the
main control unit which co-ordinates
co ordinates the
functioning of ABS
• Hydraulic Modulator:
Modulator Based upon the
signals
i l from
f
the
th ECU,
ECU through
th
h the
th solenoid
l id
valves, controls the wheel-brake pressure
for optimal braking.
• Wheel
Wh l Brakes
B k : At
A the
h wheel
h l bbrakes,
k the
h
braking pressure transferred from the
hydraulic modulator serves to force the
b k li
brake
linings
i
against
i t the
th brake
b k drums,
d
or in
i
the case of disc brakes the brake pads
against the brake discs.
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
4-channel ABS
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
How ABS works?
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
• ABS works in a closed loop with a series of inputs and
outputs
• The most important inputs are from the wheel speed
sensors
• The main output is brake system pressure control by the
ECU commands
• The ECU compares the signals from each of the wheel
sensors and measures the acceleration or deceleration of an
individual wheel.
• From this data and prepre-programmed look
look--up tables
tables, brake
pressure to one or more of the wheels is regulated
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• Through the ECU command, the brake pressure can be– Reduced
– held constant
– allowed to increase.
• In ABS, following variables are sensed, used or controlled:
A.C.Meti MSRSAS
– Pedal Force
Force: determined by the driver
– Brake Pressure:
Pressure Under ABS action, it can be reduced, increased or
regulated
– Controlled variable:
variable Actual changes in brake pressures in other
words, change in the wheel speed which then allows acceleration,
deceleration and slip to be determined
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
A.C.Meti MSRSAS
AEL2501
• Road/vehicle conditions
conditions: From the wheel speed sensor
inputs, the ECU calculates the following:
• Vehicle reference speed
speed: Determined by the combination
of two diagonal wheels. ECU takes this as reference after
the start of the braking
• Wheel acceleration & deceleration
deceleration: It is a real time
measurement which is constantly changing
• Brake slip
slip: Though it can not be directly measured, a value
can be computed from the reference speed. This decides
whether / when ABS should take over the control of the
brake pressure
p
as
• Vehicle deceleration
deceleration: The ECU uses the reference speed
the starting point and decreases it linearly. The rate is
determined by the evaluation of all signals from the wheel
speed sensors.
sensors
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
A.C.Meti MSRSAS
• Driven and non-driven wheels must be treated differently
• A llogical
i l combination
bi i off wheel
h l deceleration
d l i / acceleration
l i
and slip are used as the controlled variable
• The actual control strategy for ABS varies depending upon
the operating conditions.
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Reset
Simplified Antilock Flow Chart
Initialize
Main
Wheel speed,
Vehicle speed
calculations
System & controller
checks
Inhibit
Allow Antilock
Mode
select
Analyze system
for rules
Channell treatment
Ch
t t
t
for ABS shutdown
No
ABS
W
Warranted?
t d?
Yes
A.C.Meti MSRSAS
State space
analysis
Valve actuation
Elect motor actuation
M.S Ramaiah School of Advanced Studies - Bangalore
17
PEPS
AEL2501
ABS Control Strategy
• Start of ABS action – ‘First Control Cycle
S
Smoothing’
thi ’ (Minor changes in wheel speed)
• The threshold of engagement is critical
– Too soon – Distraction to the driver, component wear
– Too late – Steering / stability could be lost on the first control cycle
• Even road surface regulation
A.C.Meti MSRSAS
– Ideal condition – adhesion is almost constant
– Regulation frequency relatively low with small
pressure change
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• Vehicle Yaw
– While braking with different road surfaces with different adhesion
under the left and right front tyre, the vehicle will yaw – (Rotation
about vertical axis)
A.C.Meti MSRSAS
• ABS tends
d to reduce
d
this
hi by
b properly
l adjusting
dj i the
h braking
b ki
pressure to the required wheels.
19
M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Traction Control System
y
- TCS
A.C.Meti MSRSAS
• Traction control works at the opposite end of the scale
from ABS — dealingg with acceleration rather than
deceleration.
• Some vehicles also use a traction control system in
conjunction
j
i with
i h the
h ABS.
ABS
• Traction control helps the ABS improve vehicle traction by
minimizing wheel slip on the drive axle during
acceleration.
p the traction
• If a wheel on the drive axle starts to slip,
control system automatically brakes the wheel slightly,
transferring engine torque to the wheels with better
traction.
traction
• If all the drive wheels start to slip, the traction control
y
may
y also reduce engine
g ppower.
system
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Engine ECU
• Traction control systems
are referred to byy several
different names,
depending on the
manufacturer. These
include:
Wheel Sensors
Control Switch
Ignition
Throttle
ABS
ECU
Hydraulic
Modulator
Brake
B
k
Cylinders
Diagnostics
A.C.Meti MSRSAS
– Automatic Traction
Control (ATC)
– Traction Control (TC)
– Acceleration Slip
Regulation/Anti-Spin
Regulation/ Automatic
Slip regulation (ASR)
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Electronic Stability Control
A.C.Meti MSRSAS
[Programme – ESP]
• The electronic stability program (ESP) is a
further enhancement to the anti-lock
braking system (ABS) and traction control
system (TCS).
• The ESP is designed to detect a difference
between the driver's control inputs and the
actual response of the vehicle.
• When differences are detected, the system
intervenes by providing braking forces to
the appropriate wheels to correct the path
of the vehicle.
g
for
• This automatic reaction is engineered
improved vehicle stability, particularly
during severe cornering and on low-friction
road surfaces
surfaces, by helping to reduce overover
steering and under-steering.
Audi: Electronic Stability Program (ESP).
BMW: Dynamic Stability Control (DSC).
DaimlerChrysler:
i
C
Electronic
l
i Stability
S bili
Program (ESP).
Ford Motor Company: Advance Trac.
General Motors: Active Handling System
((Corvette))
Jaguar: Dynamic Stability Control (DSM).
Lexus: Vehicle Skid Control (VSC)
Porsche: Porsche Stability Management
(PSM).
Volkswagen: Electronic Stability Program
(ESP).
Volvo: Dynamic Stability Traction Control
(DTSC).
M.S Ramaiah School of Advanced Studies - Bangalore
22
PEPS
AEL2501
A.C.Meti MSRSAS
• To implement ESP functionality,
functionality additional sensors must be added to
the ABS system.
• A steering wheel angle sensor is used to detect driver input with a yaw
rate
te sensor
e
andd a low
l -G sensor
lowe
th t measure
that
e
e the vehicle
ehi le response.
e
e
• Some ESP systems include a connection to the EMS controller of the
vehicle to enable reductions in engine torque when required.
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
ESC II - Electronic Stability Control* with steering intervention
A.C.Meti MSRSAS
• As a logical extension of the current ESC, an active
steering control function (ASC).
(ASC)
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• ESC II works on the basis of the sensors already used by
ESC but it offers distinctly more comfort and safety in the
ESC,
proven ABS, EBD, TCS and AYC functions:
A.C.Meti MSRSAS
– Lead steering to improve vehicle responsiveness
– Convenient ESC intervention with steering, brakes and engine
control, as well as optional extension to control active suspension
– Easier
E i to
t control
t l range off vehicle
hi l dynamics
d
i
– Reduced stopping distance and steering effort on roadways with
differing friction levels
– Automatic compensation of load alternations
– Optimized rollover and trailer stability
[ EBD: Electronic Brake Distribution (or Electronic Brake-force Distributor) ]
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
A.C.Meti MSRSAS
AEL2501
*ESC (Electronic Stability Control) = ESP (Electronic Stability Program)
M.S Ramaiah School of Advanced Studies - Bangalore
26
PEPS
AEL2501
A.C.Meti MSRSAS
The Electro-Hydraulic Parking Brake
(
(EHP)
)
• The EHP is a space-saving alternative
to the EPB integrated in the brake
caliper.
• It consists of an Electronic Brake
System (EBS) with the capability of
developing its own pressure and an
electrically operated combined caliper,
caliper
which is hydraulically pretensioned by
the EBS and then locked electromechanically.
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
• Advantages:
– Removal
R
l off all
ll mechanical
h i l transmission
i i units
i
– A low system weight and an optimized packaging
Additional functions
• Optional additional functions can be achieved on the EHP
and
d EPB when
h used
d iin combination
bi ti with
ith the
th electronic
l t i
brake system:
A.C.Meti MSRSAS
–
–
–
–
–
Automatic tightening and loosening
Hill Start Assist
Automatic Vehicle Hold
Parking assistance if combined with a distance sensor system
Vehicle immobilizer
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M.S Ramaiah School of Advanced Studies - Bangalore
PEPS
AEL2501
Summaryy
A.C.Meti MSRSAS
• The ABS concept has been explained
• A typical ABS configuration and working
for an automobile have been studied
• TCS and ESP systems have been discussed
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