UKACC Research Student Presentations, 7 May 2009
1
1
Abstract
—
Over the recent year, a considerable growth
in
the
number of vehicle
s
on the road, has been observed. This
increases importance of vehicle safety a
nd m
inimization of fuel
consumption,
subsequently
prompting manufacturers of cars
to equip their product
s
, with more advanced features such as
Adaptive Cruise Control (ACC), Collision Avoidance and
Collision
W
arning
S
ystem (CWS).
In this PhD project we
c
on
centrate on new methods for ACC,
for optimization of fuel
consumption in urban traffic. T
his work will include:
D
esign of
the simulation model suitable for this application
,
d
esign of
virtual traffic environment
bas
ed on the models
,
i
nvestigation
and
desig
n of suitable
h
ybrid control algorithm,
most likely
using the ideas of non

linear predictive control
,
r
eal

time
im
plementation of the algorithms and
tes
t
s
.
I.
I
NTRODUCTION
daptive cruise control (ACC) is the
extension
of the
Cruise Control system (CC
),
it is
able to vary the
velocity
of the vehicle
depending
o
n
the
behavior
of the
other vehicles moving in front of the vehicle equipped with
ACC by applying the brake and modulating the throttle
to
produce the necessary power
.
This
system uses
the
radar
or
other sensory devices
to measure the
distance
between
vehicles (
the time
takes to
return the beam to
emitter
)
(
figure.
1
)
. [
1
]
The extended version of the ACC is so

called ACC
stop&go
.
In the urban area and traffic jam
situation
where
driver needs freq
uently to apply the accelerator
and
brake
pedal the
stop&go system
make
s
the driving less tire

some
.
Unlike the ACC
normally working
for
high

speed
s
this
system works in the speed range of less than 30km/h and
slowing down to zero.
F
igure.
2
classified the
characteristics
and
maximum braking capacity for ACC and Stop&Go
system.
It is known that ACC is capable of managing
the traffic
flow,
b
y
making platoons of vehicles
it
improve
s
highway
capacity.
Under
this condition a lot of vehicles moving at
highway sp
eed behind other ones
with small inter

distance
can
increase density of the vehicles in the
highway.
I
t also
has
the positive effect on the optimization of fuel
consumption
e
specially for
heavy
vehicle
s this is
due to
significant effect of the
a
erodynamic drag
dependent on the
cross
section
front area
for such vehicle
.
[2
]
Another version of the velocity
controlling syste
m has been
introduced
along with de
veloping the CC and ACC system
which uses the information
about the r
oad ahead
of the
vehicl
e
to meet the aim of the reducing the fuel consumption
which is so

called Look Ahead Cruise
Controller [
3
]
.
I
n
this
case some derivative velocity control
ling system is
introduced
as instance
Predictive Cruise
Control (
PCC)
[
4
],
Expert Cruise Control
(ECC
) [
5
] and Model Predictive
control (
MPC
) [
6
].
Figure.1 Performance of the ACC system
overview
[14
]
Figure.
2
differences
between
ACC and Stop&Go system [15]
Figur.
3
a truck using Look A
head
Cruise
Controller [
3
]
II.
VEHICLE
M
ODEL
To
design
an
ACC
system and
to
carry
out the investigation
on it
,
the
longitudinal
dynamic
model of the vehicle is
essential.
Designing of the Hybrid Adaptive Cruise
Control

Stop&GO
Payman Shakouri
,
Prof. And
rz
ej Ordys,
Dr. Mohamad Askari
Faculty of Engineering

Kingston University
A
UKACC Research Student Presentations, 7 May 2009
2
2
A.
Longitudinal model of the vehicle
Using
the second
Newton’s
law, the
relationship between
resis
ting
force (
Rolling resistance, A
ero
dynamic
drag)
,
brake
torque and wheel t
orque
obtained from figure.
4
and
defined by following equation:
̇
(
)
(1)
Where
is the wheel torque,
is the brake torque,
is related to aerody
namic Force and last terms in
equation.1 defines the
rolling resistance and gravitational
forces respectively.
As Aerodynamic drag force is a function of the square of the
speed thus is the most significant parameter
affecting on the
performance of the vehicle
in velocity of more than 48 km/h
[
7
],
it can
be determined
as following function:
(
)
(
2
)
Where
is the air density
which
equals to
1.225 kg/m
3
, A
is
maximum
vehicle cross area
in [m
2
]. I
n [
7
] an approximated
relationship for this parameter was determined as function
of the car mass
in the range of 800

2000
kg:
(
)
(
3
)
is the drag Coefficient
varying for different body
shape
,
is velocity of the vehicle
(m/s
2
)
and
air veloc
ity
which
could be neglected in the calculations.
The friction coefficient is nonlinear function of the
slip
(=s)
,
(
)
.W
ithout
braking the vehicle
velocity is
almost
the
same as the wheel
velocity (
0
)
.
But in [
8
]
friction coefficient consider as constant and equal to 0.5 in
norma
l road condition.
S
lip
is
determined
as follows
:
slip =1

(4)
: Vehicle linear
velocity
:
Wheel radius
:
wheel angular velocity
B.
Powertrain
Automatic transmission to transfer the torque from engine to
gearbox applies a torque convertor.
The t
orque convertor
consists of three essential parts including impeller, the
turbine and
the reactor. Impeller is connected to crankshaft
which transmits the power t
o
turbine by the hydraulic oil
inside of the torque
convertor.
In turn the
turbine is
connected to the output shaft of the convertor which is
coupled to the input shaft of the gear
box. The torque v
aries
depending upon gear ratio
. Finally the
output
torque from
the gearbox will be transmitted to the wheels after passing
through the final drive
.
The modeling of
the
powertrain
follows the method being
applied in [
9
].
Figure.
4
schematic model of the vehicle showing various
f
orces acting on it during moving on the road
Figure.5
Transmission of the torque and velocity form engine to wheels
The equation
determining the difference between engine
torque and impeller torque
i
s defined: [
9
]
̇
(
5
)
Where;
: Engine speed
(rpm)
: Summation of engine and impeller moment of inertia
(Kg.m
2
)
: Engine torque
(N.m)
: Impeller torque
(N.m)
The schema
tic model of the vehicle
powert
ra
i
n
is depicted
in Figure.
5
.
The parameters pl
aying the important role on the
performance of a torque convertor are expressed as
following [
12
]:
Speed ratio=
=
/
Torque ratio
=
=
/
Efficiency =
Capacity factor or K

factor =
= speed /
√
The capacity factor shows the ability of the convertor to
absorb or
transmit torque [
7
].
F
igure.
6
illustrate
s
the
relationship between the above parameter in which the
torque ratio, efficiency and
input capacity factor are plotted
against the speed ration [
7
].
Input
torqu
e of
the convertor
can be define as follows
:
(
)
(
6
)
UKACC Research Student Presentations, 7 May 2009
3
3
Figure.
6
performance characteristic of a torque convertor [12]
Figure.
7
Capacity factor of an internal combustion engine [
12
]
Where
the impeller torque (
converter input torque
)
and
is the impeller speed (
converter input speed
)
.
The
engine and the convertor should have a similar rang
e
of
capacity factor
s
(
)
to achieve proper matching.
Having the
Engine operating point
,
can be obtained
from figure.
7
.
Interpolating
from
figure.
6
the speed
ratio
will be found.
The
speed
ratio
,
the torque ratio
of the torque
convertor and
can be determined as function of the
.
Because
and
the velocity of the impeller
equals to the engine speed
therefore the torque of the
impeller can be found
. So
that the equation (
6
) can be
modified as following:
(
)
(
7
)
Having the
,
enable us to find the output
characteristic of the torque convertor:
(
8
)
(
9
)
: Turbine torque
N
t :
Turbine angular velocity
(
)
=
(
)
Speed ratio
=
(
)
=
(
)
Knowing that the torque and speed output from the torque
convertor equals to the input characteristic of the gear
box
help us to find the outpu
ts of the gearbox:
Figure.8
Block diagram of the vehicle
(
10
)
(
11
)
Where
are
respectively
transmission input
and
output
torque
,
transmission
output
and
input speed.
is transmission ratio
and
varies
depending on shifting
gear number, in another
wo
rd is
a
function of the gear setting.
Multiplying the transmission output torque by final drive
ratio determines the wheel
torque,
which can be used to
obtain the angular velocity of the wheel.
It is assumed that there is
a single source actuation system
due to the fact that
under normal
operation, the
vehicle
deceleration is in range
of

2m/s
2
,
so
the rear and the front
brakes can be expected to
have same brake
pressure [
12
]
therefore
the total
brake torque can be used
in
calculation. I
n
reality
while braking the load transfers from rear axle to
front axle [
7
] that in turn request the different braking force
and also the
maximum braking force must be introduced for
each axle separately in order to preventing the vehicle from
slipping and guarantee the safety of the vehicle, that is the
reasons of
the
innovation of the ABS (Anti Brake System
).
Las
t
term in equ
ation (1)
is gravitational force
acting
on
vehicle
travelling
uphill
or
downhill and sign of this force
would be negative or positive accordingly.
Consequently
̇
wh
ich is
the
acceleration
of the vehicle is
obtained
.
By integrating
of
this
parameter
the velocity of
the
vehicle
will
be obtained.
Figure.8 depicts the block diagram of the vehicle in
simulation.
III.
CONTROLLER
In designing the controller system the control objectives
should be identified and suitable criteria and constrains on
the base of the specified t
argets is devised.
The typical controller method is
the
PID controller which
has
been affluently used by
the industry. To guarantee the
robustness and reducing disturbances in the
system, the
new
method such as fuzzy logic and Model
Predictive
Control
(
MPC
)
, etc has been introduced.
Linear system can
consistently work with existing control
method
and to deal with any non

linearity
in the system
the
linearization
methods could
be applied to
approximate
th
e
nonlinear system to linear
and then current linear control
techniques could easily be used for such
the
systems
. [
12
]
UKACC Research Student Presentations, 7 May 2009
4
4
Actually the model of ACC
consists
of two control
loops.
Inner

loop
consisting
of CC
and model of the vehicle
works
as tracking velocity and try
ing to reduc
e the q
uantity of the
error (difference between actual velocity and desired
velocity)
so the inner

loop introduced as CC system. Outer
loop
works
as tracking vehicle
system
and calculates the
new desired value of velocity being applied as
reference
value for the
inner

loop. The
outer loop by using the input
data including
the actual velocity of the vehicle, distance
from leading vehicle, desired velocity and desired distance
calculates the new value of the velocity for the CC.
[12]
(figure.8)
IV.
VIRTUAL TRAFFIC ENVI
RONMENT
To guarantee
the functionality of
the ACC simulation model
over the various different traffic situations, the
traffic
model
is needed to
represent
different
traffic
condition
s
.ASM
Traffic
which has been developed by “
dspace
”
[1
3
] provides
us
with
reliable, flexible and time

saving testing facility by
mean
s of creating any kind of
traffic scenario.
Some traffic scenario
s where a
vehicle equip
ped with ACC
could
encounter
in real
ity are as follows:
When the Vehicle equipped with ACC is faster
than t
he leading vehicle;
More than one vehicle drive on the different lane
from the vehicle fitted with ACC
and might one of
them cuts in the following vehicle’s lane;
Leading and following vehicle travel at the same
speed and with constant distance from each
other,
suddenly the leading vehicle leaves the lane.
In oncoming traffic when the
vehicle equipped with
ACC drive at higher speed than vehicle
ahead and
have to reduced the velocity until an oncoming
vehicle has passed to perform a lane change
A
pedestrian cross
es
the road
where
the fully
stop
of
th
e vehicle or swerving by driver is needed.
V.
C
ONCLUSION
S
In this paper w
e explain briefly about Automatic driver
assistance system which
reduce the risk of accident, provide
the
driver with comfort and s
afety and reduce
fuel
consumption. All of these devices uses the same concept but
with different point of view which can be found as their
i
mpact of the safety and comfort. The model of the vehicle
was explained and formulated. The block diagram of the
ACC
was expressed. Finally the brief explanation of the
virtual traffic envir
onment was presented. In the PhD
project
a
preci
se
study and verification will
be
carried out on
all
mentioned
issues
and new method
s
will be
introduced
.
Figure.8
the
block diagram of the ACC (inner

loop & outer

loop)
[
12
]
Figure.9 3

D Visualization of the ASM Traffic in MotionDesk
[dspace]
A
CKNOWLEDGEMENT
I would like to appreciate of my supervisor
y team Pro. A.
Ordys and Dr. M.
Askari for their valuable
help. I’m
also
grateful of my parents who without their support get g
oing
on this way would be impossible.
R
EFERENCES
[1]
H.Winner, K.Winter, B.Lucas et al,
ACC Adaptive Cruise Control
,The Bosch Yellow Jacket,2003
[2]
A.Vahidi, A. Eskandarian, Research Advances in
Intelligent Collision
Avoidance and Adaptive Cruise Control,
IEEE Trans. Intelligent
Transportation system
, vol. 4, September 2003.
[3]
Look

Ahead Control for heavy truck to minimize trip time and fuel
consumption, E.
Hellström,
M.
Iva
rsson, J. Åslund, L. Niel
sen,
ScienceDirect, 2008
[4]
F.
Lattemann. et al,The
Predictive
Cruise Control

A System to reduce
Fuel Consumption of Heavy Duty
Trucks, SAE
paper,2004

01

2616
[5]
A.Wingren,Fordonsreglering med F
ramforhallninn ,MSc Thesis
Linkö
ping University
[6]
D.Axehill
,J.
Sjöberg
,
Adaptive
Cruise Control for Heavy Vehicles
Hybrid Control and MPC
A,Linkopings University,2003
[7]
J. Y. Wang, Theory of Ground Vehicle, third Edition, p.265

268,
2001
[8]
S. C. T. Filho, D. C. Donha, Automobile Stop

AND

Go Cruise
Control System Tuned b
y Genetic Algorithm, University of Sao
Paulo, 2004
[9]
U
sing simulink and Stateflow in Automotive Application
[10]
S. C. T. Filho, D. C. Donha, Automobile Stop

AND

Go Cruise
Control System Tuned by Genetic Algorithm, University of Sao
Paulo, 2004
[11]
D. B. Maciuca, Brake
modeling
and Control, p.409

410, L.Vlacic,
M.Parent, F.Harashima, Intelligent Vehicle Technologies
[12]
P.Riis, Adaptive Cruise Controller Simulation as an Embedded
Distributed
System,
MSc thesis, Linkoping University, 2007
[13]
dspace Gmbh ,
ASM
Traffic
,2008
[14]
www.audiusa.com/.../safety_technology.html
[15]
D.Maurel, AAC System

Overview and examples
, Brake modeling
and Control, p.4
2
9

, L.Vlacic, M.Parent, F.
Harashima, Intelligent
Vehicle Technologies
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