Conference Proceedings of the Academy of Romanian Scientists
PRODUCTICA Scientific Session
ISSN 2067-2160
Volume 7, Number 1/2015
185
CONSIDERATIONS ON VEHICLES STABILITY
IMPROVEMENTS THROUGH MODERN TECHNOLOGIES
AND DEDICATED SOFTWARE
Tiberiu GIURGIU 1,
Miron ZAPCIU2
Rezumat. Scopul lucrării este de a prezenta noi perspective asupra dinamicii
vehiculelor, cu precădere asupra stabilităţii şi mobilităţii acestora. În ultimul timp,
siguranţa în trafic reprezintă o problemă de maximă importanţă, iar creşterea stabilităţii
vehiculelor ar putea fi o soluţie de reducere a numărului de accidente rutiere. Vor fi
prezentate noi tehnologii privind controlul stabilităţii precum şi date statistice referitoare
la eficienţa acestor sisteme. De asemenea este prezentat si un studiu de caz cu privire la
comportamentul unui camion 6x6 în timpul testului de dublă schimbare a direcției de
deplasare (ISO 3888).
Abstract. The purpose of the paper is to present new insights on vehicles dynamics,
especially on stability and mobility. Nowadays, traffic safety is a very important issue and
the growth of stability of a vehicle could be a solution to reduce accidents on public
roads. New technologies in terms of stability control are presented and also statistical
data regarding the effectiveness of these modern devices. Finally, a case study is
presented regarding the behavior of a 6x6 truck when performing a double lane change
maneuver (ISO 3888).
Keywords: stability control, embedded systems, vehicle dynamics, ISO 3888 DLC
1. Introduction
The actual society needs in terms of mobility represent the main reason for traffic
accidents and therefore the engineers from automotive industry are desperately
trying to find solutions to increase road safety in all countries around the world.
Loss of vehicle´s stability is a situation that nobody would like to confront with
especially when driving on crowded roads and/or with high speed. Therefore the
stability control issue is a subject that worth being debated.
First of all, the main causes that could generate the rollover of a vehicle should be
mentioned:

1
inadequate speed related to infrastructure configuration (longitudinal/side
slope, obstacle passing), incoming maneuvers (steering, braking), weather
Eng., PhD student, Machines and Systems Department, Polytechnic University of Bucharest
Romania, (e-mail: [email protected]).
2
Prof., Coordinator, PhD, Production Machines and Systems Department, Polytechnic University
of Bucharest, Romania ([email protected]).
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Ioan-Tiberiu Giurgiu, Miron Zapciu
conditions (snow, ice, wind, wet surface) or vehicle category (car, SUV,
truck, liquid carrier);

technical problems related to tires (eg: explosion of a tire), suspension
(eg: breaking of a spring), direction system (eg: oversteer or understeer
effect) or braking system (eg: blocking of one side braking pads on disc);

a high position of the center of gravity related to vehicle configuration;

driver distraction;

interaction with other objects: vehicles, protection rails, trees, pylons.
Fig. 1. SUV performing an evasive maneuver on track (“Elk test”) [1]
Obviously, all vehicles that are certified to be driven on public roads have to be
rigorously tested in terms of stability, for passenger’s protection. As it can be seen
in Figure 1, during an evasive maneuver (known as “Elk test”) performed in real
track conditions, one or more wheels might lose contact with the running surface.
Therefore, testing engineers are searching safer solutions for evaluating a
vehicle’s stability performances either in real testing phase – by replacing human
driver with steering robots, but especially during virtual prototype phase – by
performing dynamic simulations in dedicated software (MBS – Multi-Body
Simulation) on 3D simplified model of a vehicle (see Figure 2).
Fig. 2. Evasive maneuver simulated in ADAMS performed on 3D model of a SUV [2]
Considerations on vehicles stability improvements through modern technologies and dedicated software 187
2. Embedded systems in vehicle stability control
It also has to be mentioned that important improvements in stability control have
been realized during the last decades. New technologies were developed,
electronic field is more and more exploited and embedded systems are very
common lately in this area of interest.
As presented in [3], the innovation element brought by embedded systems
consists in connecting vehicle components like electronic control units (ECU),
engine components, wheel sensors, steering angle sensors or lateral acceleration
sensors, to a high speed network. The principle of functioning of ESP (Electronic
Stability Program) consists in permanently comparing the actual state of the
vehicle with the desired one, given by the driver’s input through the steering
wheel [5].
1
Fig. 3. Main sensors used by ESP (Electronic Stability Program): 1. hydraulic modulator with addon ECU, 2. wheel speed sensor, 3. steering angle sensor, 4. yaw-rate sensor. [3]
Beside the sensors presented in Figure 3, the vehicle stability system also uses
lateral acceleration sensors and brake pressure sensors.
In Figure 4 is presented an overview of the ESP network and the positioning of
different sensors on a passenger car.
Fig. 4. ESP network of a passenger car [3]
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Ioan-Tiberiu Giurgiu, Miron Zapciu
3. Chassis control system
Another field of interest, when talking about vehicle safety, is represented by
chassis control technology. If during the 80’s the main development area in terms
of vehicles dynamic performances was related to mechanical progress, nowadays
the accent is focused on chassis control technology [4].
As it can be seen in Figure 5, the development of chassis control was divided in 3
generations. The beginnings of this technology promoted the 4WS system which
consisted in transmitting the angle of the front wheels to the rear ones,
mechanically through the shaft. The benefits brought by this system were a good
stability of the vehicle at high speed (at small steering angles) and a very small
turning radius at low speeds.
Fig. 5. Chassis control system timeline [4]
Afterwards, the first generation was marked by the development of DYC – Direct
Yaw Control that used a new concept at that time: independent control of traction
and braking forces on left-right sides of the vehicle, which enabled yaw moment
to be used for controlling vehicle behavior.
The second generation began to bring this domain of chassis control in the main
area of interest for vehicle engineers, and VGS technology (Variable Gear ratio
Steering system) represented the innovation. Moreover, the ultimate main control
system at that time was steer-by wire (SBW) technology, which gave more
flexibility to interior designers, as steering wheel was no more needed, due to lack
of any mechanical connection between driver and wheels. Anyway, it takes time
to develop such a technology as the system is not yet available on common
passenger cars.
Since 2000, third generation highlights the concept of cooperative system
(similar-embedded system) in order to increase dynamic performances beyond the
Considerations on vehicles stability improvements through modern technologies and dedicated software 189
level of those assured by conventional systems. The requirements to increase
braking and turning performances to the limit are related to SBW technology,
active suspension, camber control and special tires.
Fig. 6. Concept of future integrated Chassis control [4]
As it is presented in Figure 6, we can notice that the integrated chassis control
technology involves the use of many sensors in order to obtain information from
the main subsystems of the vehicle: steering, suspension, traction and braking,
reasoning the importance of electronic development in automotive.
4. Nowadays technologies in terms of stability control
Nowadays, the automotive world has developed on a large scale, and vehicles
producers are more and more interested in designing more sophisticated cars, that
offer a high level of comfort for passengers but for the driver himself. Stability
control systems are mandatory in Europe since 2012 for all new cars, but as it can
be seen in Table 1, there are many types of such technologies.
Table 1. Worldwide types of ESC systems for passenger cars
No.
Type of stability control system
Users
Hyundai, Kia, Mercedes Benz,
Jeep, Renault, Saab, Chrysler,
Citroen, Peugeot, Dodge, Skoda
Suzuki, Toyota
Ford, BMW, Mazda, Land
Rover, Jaguar
Nissan, Subaru, Alfa Romeo
1.
ESP - Electronic Stability Program
2.
VSC - Vehicle Stability Control
3.
DSC - Dynamic Stability Control
4.
VDC - Vehicle Dynamic Control
5.
ESP - Electronic Stabilisation Program
6.
DSTC - Dynamic Stability And Traction Control
Volvo
7.
VSA - Vehicle Stability Assist
Honda
8.
ASC - Active Stability Control
Mitsubishi
Audi, Volkswagen
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Ioan-Tiberiu Giurgiu, Miron Zapciu
9.
PSM - Porsche Stability Management
Porsche
10.
STC - Stability and Traction Control
Fiat
11.
MSP - Maserati Stability Program
Maserati
As it concerns trucks developers, stability issue is even more debated, and we can
mention some of the most commonly used control systems:

ESC - Electronic Stability Control - Bendix Commercial Vehicle Systems;

VEST - Volvo Enhanced Stability Technology;

RSA - Mack Road Stability Advantage;

RSC - Roll Stability Control - for trucks and tractors, from Meritor
Wabco;

TRS - Trailer Roll Stability - from Haldex Commercial Vehicle Systems.
5. Case study – stability analysis of a 6x6 truck
The case study analysis regards a 6x6 truck designed for materials transportation
in different types of superstructures: ISO containers, open or semi-open platform.
The vehicle has no electronic control of stability or other similar technologies, but
it has servo direction and anti-lock braking system.
5.1. Static analysis
When talking about stability of trucks, the most important aspect is the position of
center of mass, especially in vertical direction. The factor that predicts the
capability of a truck to perform different types of maneuvers at different speeds is
given by equation 1:
SRT 
T

2H
(1)
where:
 SRT is the Static Roll Threshold;
 T is the track width;
 H is the height of the center of mass;

 is the roll angle (due to tyres suspension and other vehicle elements
compliance).
In the literature [6], we can find the fleet rollover rate based on SRT values and
crash rates.
Considerations on vehicles stability improvements through modern technologies and dedicated software 191
Analyzing figure 7, it can be noticed that the greater the SRT value, the lower the
crash rate becomes, in other words – the vehicle is more stable. Anyway, SRT
value is determined by the track width which is limited by the public
transportation regulation.
Fig. 7. Fleet
Rollover Rate [6]
In our case, SRT is given by the following estimated values:
 T = 2000 mm;
 H = 1500 mm;
  = 0.25 deg.
so,
SRT 
2000
 0.25  0.66  0.25  0.41 g
2  1500
(2)
According to literature and nowadays regulation, a minimum value of 0.35 for
SRT is required for trucks that travel on public roads. As it results from equation
2, the studied truck complies with this requirement.
5.2. Dynamic analysis
One of the most relevant parameters that determine the stability of a vehicle,
measured in dynamic tests, is the lateral acceleration. This parameter has a great
importance during different types of maneuvers at different speeds: double lane
change, cornering, braking and so on.
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Performing an evasive maneuver is one of the most common stability test not only
for passenger cars but for trucks and buses also, given the fact that such a situation
is quite often met on nowadays chaotic traffic.
Fig. 8. Double lane change results at 40 km/h
During the ISO 3888 “Double lane change” maneuver performed with the studied
truck we obtained a maximum value of lateral acceleration of 0.272 g at an
average speed of 40 km/h (see figure 8). Afterwards, by increasing the speed at 50
km/h, the lateral acceleration value has grown until 0.360 g (see figure 9).
Fig. 9. Double lane change results at 50 km/h
The track was configured in accordance with existing regulation and the test was
repeated 2 times in each direction for the speed of 50 km/h. First test, at 40 km/h
was performed in order to observe the behavior of the truck and to assure drivers
Considerations on vehicles stability improvements through modern technologies and dedicated software 193
accommodation with the track. During the tests, no wheel lost the contact with the
ground and no marking cone has been touched by the truck.
Table 2. ISO 3888 Double lane change test results.
Test
number
1
2
3
4
5
6
First
steering
maneuver
left
right
left
right
left
right
Instantaneous
speed (km/h)
40.16
41.9
52.88
50.65
49.85
49.61
Average
values of
speed (km/h)
41
50.75
Maximum
lateral
acceleration (g)
0227
0.272
0.360
0.322
0.351
0.335
Average values of
lateral
acceleration (g)
0.25
0.34
Comparing the obtained results (see table 2) with the specialty literature [7], we
can say that the tested truck has a good behavior when performing this kind of
maneuvers at such a high position of center of mass. Though, because of the lack
of outriggers and other safety reasons increasing speed at 60 km/h would have
been risky for the integrity of the truck and its occupants.
Having the above values of the lateral acceleration, we suppose that at 60 km/h
the 0.5 g limit could have been reached and the rollover might occur. Therefore,
simulations could be useful for a better prediction of such phenomena or at least
to determine the maximum entry speed that keeps the truck on track.
6. Conclusions and future work
The paper gives some insights on vehicles dynamic performances, in terms of
mobility and stability, through the perspective of increasing traffic safety by
preventing or at least reducing vehicles rollover.
It is presented a short description of embedded systems from their beginnings to
present and the variety of stability control systems that can be found in the
automotive industry during the last decades. It can be obviously noticed that the
progress of electronic devices and the integration of embedded systems on
passenger cars, trucks and buses brought an important increase of safety on public
roads.
Finally, a case study on the behavior of a 6x6 truck without ESC during ISO 3888
double lane change test on track. The obtained results shall be compared with
others resulting from testing a similar truck equipped with ESC other stability
control technology. Moreover, simulations will be performed in dedicated
software in order to predict the boundary entry speed on the double lane change
maneuver that keeps the vehicle with all tires on track.
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Ioan-Tiberiu Giurgiu, Miron Zapciu
7. Acknowledgements
This work has been funded by the Sectorial Operational Programme Human
Resources Development 2007-2013 of the Ministry of European Funds through
the Financial Agreement POSDRU/159/1.5/S/138963.
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